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\DOI{10.5802/crchim.351}
\datereceived{2024-04-11}
\daterevised{2024-07-16}
\datererevised{2024-09-03}
\dateaccepted{2024-10-01}
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%\makeatletter
%\def\TITREspecial{\relax}
%\def\cdr@specialtitle@english{Materials and Energy Valorization of Biomass and Waste : The Path for Sustainability and Circular Economy Promotion}
%\def\cdr@specialtitle@french{Valorisation \'energ\'etique et mati\`ere de la biomasse et des d\'echets : la voie de la durabilit\'e et de la promotion de l'\'economie circulaire}
%\makeatother

\begin{document}

\begin{noXML}

\CDRsetmeta{articletype}{research-article}

\title{Valorization of pinecone as a pyrolysis feedstock:
identification of bio-oil and synthesis of activated biochar for Cr(VI)
elimination from wastewater}

\alttitle{Valorisation de pommes de pin comme mati\`{e}re premi\`{e}re
pour la pyrolyse : identification de la bio-huile et synth\`{e}se de
biochar activ\'{e} pour l'\'{e}limination du Cr(VI) des eaux us\'{e}es}

\author{\firstname{Amenah Adnan} \lastname{Alfares}}
\address{Mosul University, Department of Chemistry, College of Science,
Majmoaa Street, 41002, Mosul, Iraq}
\email[A. A. Alfares]{amenahadnan@uomosul.edu.iq}

\author{\firstname{Afyaa Muayed} \lastname{Younis}}
\addressSameAs{1}{Mosul University, Department of Chemistry, College of
Science, Majmoaa Street, 41002, Mosul, Iraq}
\email[A. M. Younis]{afyaamy2005@uomosul.edu.iq}

\author{\firstname{Lana Abdalhameed} \lastname{Rasheed}}
\addressSameAs{1}{Mosul University, Department of Chemistry, College of
Science, Majmoaa Street, 41002, Mosul, Iraq}
\email[L. A. Rasheed]{lanaabdalhameed@uomosul.edu.iq}

\author{\firstname{Abdelrahman Basil} \lastname{Fadhil}\CDRorcid{0000-0003-1594-4293}\IsCorresp}
\addressSameAs{1}{Mosul University, Department of Chemistry, College of
Science, Majmoaa Street, 41002, Mosul, Iraq}
\email{abdelrahmanbasil@yahoo.com}
\email[A. B. Fadhil]{abdelrahmanbasil@uomosul.edu.iq}

\keywords{\kwd{Pinecone}\kwd{Pyrolysis}\kwd{Bio-oil}\kwd{Activated
biochar}\kwd{Cr(VI) adsorption}}

\altkeywords{\kwd{Pommes de
pin}\kwd{Pyrolyse}\kwd{Bio-huile}\kwd{Biochar
activ\'{e}}\kwd{Adsorption du Cr(VI)}}

\begin{abstract}
The thermal pyrolysis of pinecone (PC) to produce pyrolytic oil (PO)
and solid biochar (BC) in a batch-scale fixed-bed reactor at numerous
temperatures (400--600 \textdegree C) for diverse time intervals
(30--120 min) using different particle sizes (0.26--0.841 mm) and
various rates of heating \mbox{(10--50 \textdegree C/min),} as established in
this work, led to the production of a high yield of the PO (42.12\%) at
\mbox{500 \textdegree C} for 1 h with a 0.40 mm particle size and a heating
rate of 30 \textdegree C/min. The bio-oil (BO) content in the resulting
PO amounted to 10.20\%. The \tsup{1}H NMR and GC-MS spectroscopy,
besides the ultimate analysis of the BO, were identified. The
consequences disclosed that the BO principally consisted of oxygenated
hydrocarbons, which amounted to 54.98\%, besides the N-organic
compounds and hydrocarbons, whose contents were 6.95\% and 2.60\%,
respectively. The BO had a high content of C and H besides its
remarkably high caloric value (26.99 MJ/kg), suggesting its potential
as a high-energy fuel. The K\tsub{2}CO\tsub{3}-activation of the BC
leftover after the pyrolysis of PC produced a microporous activated
biochar (ABC) with a BET surface area of 465.55 m\tsup{2}/g and 1.97 nm
average pore diameter using 2:1 K\tsub{2}CO\tsub{3}:BC impregnation
ratio at  750 \textdegree C for 1 h. The ABC exhibited an adsorptive
elimination of 98.71\% for 100 mL of solution containing 150 ppm of
Cr(VI) from its aqueous phase using \mbox{0.20 g} of ABC at 35 \textdegree C
for 140 min and a pH = 2.0. The Langmuir isotherm and the
psedue-2{nd}-order model of kinetics best described the Cr(VI)
adsorption by the ABC. In conclusion, PC could be used as a pyrolysis
feedstock to produce BO with high-content aromatic oxygenates besides
ABC with a high surface area, a microporous structure and an efficient
ability to eliminate Cr(VI) ions from\break wastewater. 
\end{abstract}

\begin{altabstract}
La pyrolyse de pommes de pin (PC) pour produire de l'huile pyrolytique
(PO) et du biochar (BC) a \'{e}t\'{e} effectu\'{e}e dans un
r\'{e}acteur \`{a} lit fixe \`{a} de nombreuses temp\'{e}ratures
(400--600 \textdegree C), pour divers temps de r\'{e}sidence
(30--120 min) en utilisant diff\'{e}rentes tailles de particules
(0,26--0,841 mm) et vitesses de chauffage (10--50 \textdegree C/min).
Les r\'{e}sultats exp\'{e}rimentaux montrent la production d'un
rendement \'{e}lev\'{e} de PO (42,12 \%) \`{a} 500 \textdegree C pendant
1 h avec une taille de particule de 0,40 mm et une vitesse de chauffage
de 30 \textdegree C/min. La teneur en biohuile (BO) du PO obtenu est de
10,20 \%. Les analyses NMR, GC-MS et ultime r\'{e}v\`{e}lent que la BO
est principalement constitu\'{e}e d'hydrocarbures oxyg\'{e}n\'{e}s
(54,98 \%), ainsi que de compos\'{e}s N-organiques (6,95 \%) et
d'hydrocarbures (2,60 \%). La BO produite poss\`{e}de une teneur
\'{e}lev\'{e}e en C et H en plus de sa valeur calorifique
remarquablement \'{e}lev\'{e}e (26,99 MJ/kg), ce qui sugg\`{e}re son
potentiel d'utilisation en tant que combustible \`{a} haute
\'{e}nergie. L'activation du BC g\'{e}n\'{e}r\'{e} avec du
K\tsub{2}{CO}\tsub{3} (ratio massique de 2:1) \`{a} 750 \textdegree C
pendant 1 h a produit un mat\'{e}riau microporeux (ABC) avec une
surface BET de 465,55 m\tsup{2}/g et un diam\`{e}tre de pore moyen de
1,97 nm. L'ABC a montr\'{e} une \'{e}limination par adsorption de
Cr(VI) de 98,71 \% pour une dose d'ABC de 2 g/L, une temp\'{e}rature de
35 \textdegree C, un temps de contact de 140 min et un pH = 2,0. De
plus, l'isotherme de Langmuir et le mod\`{e}le cin\'{e}tique du
pseudo-second-ordre d\'{e}crivent le mieux l'adsorption du Cr(VI) par
l'ABC. En conclusion, les d\'{e}chets de PC pourraient \^{e}tre
utilis\'{e}s comme mati\`{e}re premi\`{e}re de pyrolyse pour produire
du BO riche en hydrocarbures oxyg\'{e}n\'{e}s et un biochar activ\'{e}
ayant une surface sp\'{e}cifique \'{e}lev\'{e}e, une structure
microporeuse et une importante capacit\'{e} \`{a} \'{e}liminer les ions
Cr(VI) des eaux us\'{e}es.
\end{altabstract}

\shortrunauthors

\maketitle

\pagebreak

\twocolumngrid

\end{noXML}

\section{Introduction}\label{sec1}

Due to the growing awareness of environmental protection and the
diminishing of petroleum reserves, the search for renewable and
eco-friendly resources has gained prominence~\cite{1,2,3,4}. Biomass
(BM) is a significant alternative energy source that can slow down the
fossil fuels depletion. The BM-based precursors are renewable, and
producing biofuel from such sources via thermal pyrolysis is a
promising approach to converting BM into numerous products compared to
other thermochemical conversion processes~\cite{5,6}. In this
technique, the BM precursor is heated in the presence or absence of a
catalyst to create various energy sources (liquid, gas, or solid) in a
temperature range between 450--600~\textdegree C in a limited oxygen
environment~\cite{4}. Fast pyrolysis is the most common method of
converting BM feed into a liquid fuel called PO or BO. Nonetheless, the
latter owns several defects in handling, storage, and transportation
besides having several merits compared with solid sources~\cite{5}. One
of the typical uses of the PO is as an alternative fuel for
furnaces~\cite{6}. However, its usage in engines and turbines requires
some modification, including reducing its elevated content of
O-compounds~\cite{6,7}. The PO can also be employed in synthesizing
bio-chemicals through catalytic pyrolysis~\cite{6,7}.

Numerous studies have been announced in the literature on the thermal
pyrolysis of varied biowastes and non-edible seeds to produce multiple
pyrolysis products, including PO and biochar (BC). Table~\ref{tab1} 
offers pyrolysis conditions required to produce the desired products
from multiple BM feeds in the literature. According to
Table~\ref{tab1},  it is notable that the products yield from the
thermal pyrolysis of various BM precursors can be attributed to many
factors, including the chemical composition of the parent feed viz. its
content of cellulose, hemi cellulose and lignin, which their ratios in
the authentic raw material affects greatly its pyrolysis products
output~\cite{20}. 

\begin{figure*}
{\vspace*{-2pt}}
\includegraphics{fig01}
{\vspace*{-2pt}}
\caption{\label{fig1}Images display pinecone.}
\end{figure*}

%tab1
\begin{table*}
\caption{\label{tab1}Precursors are used in the production of PO at
multiple conditions{\vspace*{-2pt}}}
\begin{tabular}{cccc}
\thead
Precursor & Pyrolysis conditions & Yield (\%) of product & Ref. \\ 
\endthead
Orange peels & 650~\textdegree C; 1~h; 10~\textdegree C/min & 32.05\% BC & \cite{8} \\ 
Saga seeds & 571~\textdegree C; 0.50~h; 271 cc/min N\tsub{2}-flow & 5.55\% PO & \cite{9} \\ 
Gold mohar & 600~\textdegree C; 20~\textdegree C/min & 48.0\% PO & \cite{10} \\ 

Manilkara zapota seeds & 
\parbox[t]{15pc}{\centering 500~\textdegree C, 1~h; 80~\textdegree C/min,
1.0~mm particle size; 8:1 catalyst: feed; 100~cc/min N\tsub{2}-flow} &
45.22\% PO & \cite{11} \\ 

Cashew skin & 400~\textdegree C, 10~\textdegree C/min; 50~mL/min N\tsub{2}-flow & 37.10\% PO & \cite{12} \\ 

\parbox[t]{9pc}{\centering Mixed date stones and Pistachio shells}\vspace*{2pt} & 
\parbox[t]{12pc}{\centering 500~\textdegree C, 1.50~h; 20~\textdegree C/min, 50 mesh particle size} & 51.20\% PO & \cite{13} \\

\parbox[t]{10pc}{\centering African star apple defatted seeds cakes}\vspace*{2pt} & 400~\textdegree C, 1~h;
10~\textdegree C/min & 33.10\% PO & \cite{14} \\ 

Chicken waste & 500~\textdegree C, 2~h; 10~\textdegree C/min & 61.60\%
PO & \cite{15} \\ 
Beauty leaf fruit husk & 500~\textdegree C; 3~min and 20~s & 45.0\% PO
& \cite{16} \\ 
Palm kernel cake & 401~\textdegree C, 70~mL/min N\tsub{2}-flow & 63.0\%
PO & \cite{7} \\ 
Ficus nitida wood & 500~\textdegree C; 100\textdegree/min; 100~mL/min
N\tsub{2}-flow & 41.85\% PO & \cite{17} \\ 
Date and cherry seeds & 500~\textdegree C, 1~h; 40~\textdegree C/min,
0.25~mm particle size & 55.55\% PO & \cite{18} \\ 
Date stones & 500~\textdegree C; 10~\textdegree C/min, 1.50~mm particle
size & 36.64\% PO; 16.12\% BC & \cite{6} \\ 
Flaxseed residue & 500~\textdegree C, 60~mL/min N\tsub{2}-flow &
58.30\% PO & \cite{19}
\botline
\end{tabular}
{\vspace*{-2pt}}
\end{table*}

As a member of the \textit{Pinaceae} family, pines are perennial trees
with an average height of 50~m. The pine trees carry dark green needles
bearing cones. The cone is convex with a length of 5--10~cm. As an
outcome of the massive production of cones worldwide, cones are
discarded as solid waste (Figure~\ref{fig1}). Most pine trees are
mostly planted to be involved in the manufacture of paper
pulps~\cite{21}.

Like any BM material, the PC comprises cellulose, lignin, and resins.
When the PC is subjected to thermal destruction, these constituents are
decomposed to evolve multiple gaseous products, leaving behind a solid
residue with a carbonaceous structure that could be a valuable
precursor to synthesize activated carbon (AC)~\cite{22}. Cellulose,
hemicellulose, lignin, and other constituents of PC comprise functional
groups, including the sulfhydryl (thiol), carbonyl (ketone), alcohols,
carboxyl, sulfonate, esters, thioether, and amine. Such functional
groups can be helpful in linking to heavy metals~\cite{22}. According
to the literature, PC was used in multi purposes. For example, Abujazar
et~al.~\cite{23} announced the utilization of PC powder as a cheap and
natural coagulant agent for treating iron and steel factory effluents,
and proved its effectiveness for this purpose. Guo et~al.~\cite{24}
synthesized sulfonated hydrochar to be employed as an effective
catalyst for the dehydration of carbohydrate. Lastly, the integrated
steam gasification process of PC for the production of H\tsub{2} and
biomethanol was declared by Turgut and Dincer~\cite{25}. In addition to
those studied, the utilization of PC as a potential precursor for AC
synthesis was also announced in the literature. In general, the PC was
transformed into BC, and the latter was modified and used as an
adsorbent to eliminate bisphenol-A and a toxic azo dye (SB3) from
aqueous medium with a removal capacity of 38.387~mg/g and 346.856~mg/g,
respectively~\cite{26}. The BC resulting from the thermal destruction
of PC was modified with AlCl\tsub{3}, and the resulting composites were
implemented in extracting F-ions from drinking groundwater with an
elimination capacity of 14.07~mg/g and a removal performance of
87.13\%~\cite{27}. Carbonization of PC to BC, followed by
KOH-activation of the latter to synthesize AC for removing naphthalene
from paraffin oil, was announced in the literature with a removal
capacity of 435~mg/g~\cite{28}. A magnetic hydrochar was produced from
PC and then treated with ammonia to be applied to eradicate Cr(VI) from
the aqueous phase. The magnetic adsorbent exhibited an adsorption
capacity of 154.0~mg/g~\cite{29}. Ma et~al.~\cite{30} investigated the
adsorption elimination of Cr(VI) from wastewater using the nanoscale
zero-valent iron supported on PC-derived BC, which exhibited a removal
performance of 39.05\% at the typical experimental conditions. Saif 
et~al.~\cite{31} reported the creation of AC from PC via carbonization
of PC, followed by H\tsub{3}PO\tsub{4} \mbox{activation} of the resulting BC.
The as-created AC was then implemented to reject various heavy metal
ions, including Cr(VI), from wastewater with an adsorptive capability
of  29.6~mg/g. Stripping Cr(VI) from the aqueous phase over the BC
originating from PC was doped with zinc-doped nickel ferrite and then
employed in extracting Cr(VI) from the aqueous solution with a removal
efficiency of 95.0\%~\cite{32}. Finally, the creation of AC from the
pine needle employing the resultant AC to remove Cr(VI) ions from
\mbox{wastewater} was announced by Ayoub et~al.~\cite{33} who reported an
adsorptive capacity of 65.36~mg/g.   

Investigations relating to the creation of biofuel from PC are limited.
Torrefaction of the North American PC was explored by McNamee 
et~al.~\cite{34}, who concluded that this process enhanced the fuel
features of the PC, as well as raised its HHV and diminished its
volatiles and moisture content. Kang et~al.~\cite{35} used Ca--Fe and
HZSM-5 to catalyze the thermal destruction of PC to create aromatic
\mbox{hydrocarbons} and found that the said catalyst enhanced the
deoxygenation and aromatization of the PC on pyrolysis in addition to
lessening the emissions of PAHs. In another study, Chen et~al.~\cite{36}
\mbox{investigated} pyrolysis-GC/MS experiments of the PC and the treated PC
at 338~\textdegree C and 342~\textdegree C and found that the N content
of the PC was above that of the treated PC. Also, with the increment of
the conversion rate, the activation energies of the PC and the treated
PC initially declined and then raised. Nonetheless, conducting thermal
pyrolysis of PC with optimizing the experimental conditions that will
lead to producing the maximum output of PO, including the temperature
of pyrolysis, pyrolysis period, the particle size of PC, and the rate
of heating, has not been announced yet as far as we know. Additionally,
the complete analysis of the BO fraction separated from the resulting
PO to recognize its chemical composition and its influential functional
groups utilizing diverse techniques, like GC-MS, FTIR and \tsup{1}H NMR
spectroscopy, in addition to its ultimate analysis has not been touched
to the best of the author's knowledge. Moreover, exploiting the BC
resulting from thermal pyrolysis of PC to create a high surface area
microporous activated BC using the K\tsub{2}CO\tsub{3} activation route
with implementing the latter in the efficient elimination of Cr(VI)
ions from wastewater has not been established yet.

\section{Experimental} \label{sec2}
\subsection{Feedstock and chemicals}\label{ssec21}

The fresh precursor, PC, was brought from the forest area in Mosul
city, north of Iraq. The PC was thoroughly washed with DW several
times, followed by sun-drying for 48~h, crushing to a powder form, and
finally sieving to acquire a particle size of 60~mesh. Iodine
(I\tsub{2}, solution, 0.1 N),
Na\tsub{2}S\tsub{2}O\tsub{3}${\cdot}$5H\tsub{2}O,
99.0--100.5\%, K\tsub{2}CO\tsub{3} (99.0\%), and
K\tsub{2}Cr\tsub{2}O\tsub{7} (99.90\%) were of analytical reagent (AR)
grade chemicals and were purchased from Scharlau chemicals, Spain. 

\subsection{Proximate, ultimate, and thermogravimetric analyses of
pinecone}\label{ssec22}

Based on the ASTM standard test methods, the PC weight percentages of
moisture, volatile matter (VM), ash, and fixed carbon (FC) were
quantified. The PC was placed in a silica crucible, heated to
110~\textdegree C in a hot air oven for 2~h, cooled to room
temperature, and weighed. The dried sample left previously was
implemented to quantify the VM\% by heating a crucible containing it
after being enclosed with a lid in a muffle furnace at 950 ${\pm}$
20~\textdegree C for 7~min. The remaining solid was cooled inside a
desiccator and weighed~\cite{37}. The weight loss represents the VM,
while the solid residue is the FC. The residual carbon in the crucible
was heated at 700~\textdegree C ${+}$ 50~\textdegree C for 30~min without a
lid. The crucible was preserved inside a desiccator to gain ambient
temperature, and the solid residual solid was considered
ash\%~\cite{37}. The ultimate of the PC (C, H, N, and S) was carried
out using an elemental analyzer (Elementar, Vario EL~III, Germany). By
difference, the O\% was quantified. The analysis was accomplished on a
dry basis. Based on the ultimate analysis results, the HHV of the PC
was calculated as per Dulong's formula, presented in
Equation~(\ref{eq1})~\cite{38}. 
{\begin{equation}\label{eq1}
\text{HHV}~(\mathrm{MJ}/\mathrm{kg}) = 0.3383 \times \text{C} +  1.443
\times \left(\mathrm{H} - \dfrac{\mathrm{O}}{8}\right).
\end{equation}}\unskip
Thermogravimetric analysis (TGA) of the PC was done employing a thermal
analyzer (SDT-Q600 T.A. Simultaneous TGA/DSC, USA) to specify the
thermal breakdown performance of the PC at a heating rate of
10~\textdegree C/min. The sample (${\sim}$5 mg) was placed in a platinum
crucible and heated between 35--1000~\textdegree C under a stream of
N\tsub{2} gas and air. Finally, the PC contents of cellulose,
hemicellulose, and lignin were identified utilizing the method proposed
by Mansor et~al.~\cite{39}. To specify the extractive \% of PC, a known
PC mass (5.000 g) was treated with 60~mL of acetone at 90~\textdegree C
for 2~h, followed by drying at 105~\textdegree C and 100~\textdegree C.
Weight difference before and after extraction represents the extractive
\%. After extraction, 1.000~g of the resulting material was treated
with 150~mL of NaOH at 80~\textdegree C on a hot plate for 3.5~h to fix
the hemicellulose \%. After washing with deionized water, the sample
was dried between 105~\textdegree C and 110~\textdegree C until
attaining a fixed mass. The pre- and post-treatment weight differences
signify the hemicellulose \%. Determining the lignin \% was
accomplished by treating 1,000~g of the material remaining after the
extraction with 30~mL of 98\% H\tsub{2}SO\tsub{4}. After boiling the
mixture at 100~\textdegree C for 1~h, the resulting mixture was
filtered, while the solid residue was washed with 10\% BaCl\tsub{2}
solution before drying at between 105~\textdegree C and 110~\textdegree
C. The mass alteration before and beyond extraction signifies the
lignin \%. The cellulose \% was obtained by subtracting the PC's
initial mass from the previously calculated weights of the other three
constituents.

\subsection{Pyrolysis experiments of the pinecone}\label{ssec23}

{\vspace*{-2pt}}

The pyrolysis trails of PC were carried out in an inert atmosphere
using a semi-batch reactor (Figure~\ref{fig2}).

\begin{figure}
\includegraphics{fig02}
{\vspace*{-2pt}}
\caption{\label{fig2}Pyrolysis reactor used in thermal cracking trails.}
\end{figure}

The pyrolysis reactor was cylindrical. It was built of stainless steel
with a 30~cm length, 5~cm external inner diameter, and 4~cm internal
diameter. The reactor was surrounded by an electrically heated
cylindrical furnace and was provided with a PID controller to adjust
the temperature and heating rate of the process. After feeding the
reactor with the required PC mass (40~g), it was heated from ambient
temperature until reaching the targeted temperature. The reactor was
linked to a condenser to condense the volatile vapors, which were
collected in a glass vessel placed in an ice bath (dry ice ${+}$ acetone
${+}$ salt). The reactor was blushed with N\tsub{2} gas (50~mL/min) for
15~min to expel the atmospheric oxygen before each experiment.
Ultimately, the reactor was left to acquire ambient temperature, and
the produced residue was collected as BC~\cite{40}. Calculating the
yields of PO, BC, and non-condensable gases was completed based on the
following equations~\cite{41,42}:

{{\fontsize{8.7}{10}\selectfont\begin{eqnarray}
&\displaystyle\hspace*{-1pc} \text{Yield of Liquid}~(\%) 
 = \dfrac{\text{Weight of
the PO produced}~(\mathrm{g})}{\text{Total weight of PC used}~(\mathrm{g})} \times 100 \label{eq2} 
\hspace*{-1pc}\nonumber \\\Seqnsplit
&\displaystyle \text{Yield of BC}~(\%) 
 = \dfrac{\text{Weight of BC}~(\mathrm{g})}
{\text{Total weight of PC used}~(\mathrm{g})}\times 100 \label{eq3} \Seqnsplit 
&\displaystyle\hspace*{-1pc} \text{Yield of Gases and loss}~(\%) 
 = 100 - [\%~\text{PO yield} + \%~\text{BC yield}]. \label{eq4}
\hspace*{-1pc}\nonumber \\ 
\end{eqnarray}}\unskip}
The pyrolysis temperature (400--600~\textdegree C), the particle size
of PC (0.26--0.841~mm), duration of pyrolysis (30--150~min), and the
heating rate (10--50~\textdegree C/min) were optimized upon the thermal
decomposition process of PC so as to disclose the typical settings that
will produce the highest yield of the PO. {\vspace*{-2pt}}

\subsection{Identification of pyrolytic oil}\label{ssec24} 

{\vspace*{-2pt}}

The PO produced under typical thermal pyrolysis conditions of PC was
fractionated into two fractions by a separating funnel. These fractions
included the BO fraction (upper phase) and the aqueous fraction (lower
phase). The BO fraction was identified for its functional groups using
Fourier Transform Infrared spectroscopy (FTIR JASCO V-630, USA). The
{attenuated} Total Reflectance (ATR) method was employed to analyze the
BO. For this purpose, a small drop of the BO was placed on the ATR
crystal, and the analysis was carried out in the range of 
400--4000~cm$^{-1}$ wave number at a 40 scanning with a step size of
4~cm$^{-1}$. The chemical composition of the BO was achieved using 1H
NMR and GC-MS spectroscopy. The \tsup{1}H NMR spectra of BO were
acquired on a Bruker 400~MHz NMR spectrometer (Bruker BioSpin, GmbH)
with a 5.0~mm inverse triple resonance (TXI) probe for \tsup{1}H NMR.
At the same time, CDCl\tsub{3} was employed as a solvent, and Tetra
Methyl Silane (TMS) was implemented as the internal standard. The gas
chromatography-mass spectrometry (GC--MS) spectrometry was employed to
determine the composition of BO qualitatively and quantitatively. A
GC--MS analyzer (Agilent 8860-5977B) under a stream of carrier gas (He)
and a flow rate of 1~mL/min. The injector temperature and injection
volume were respectively fixed at 280~\textdegree C and 1~${\upmu}$L.
The oven program was originated at 60~\textdegree C (1~min), then
elevated to 200~\textdegree C at 12~\textdegree C~min$^{-1}$ rate of
heating, and lastly, the temperature was raised to 280~\textdegree C at
a heating rate of 5~\textdegree C~min$^{-1}$, where it was kept for
4~min~\cite{40}.\looseness=-1

\subsection{Biochar activation by K\tsub{2}CO\tsub{3}}\label{ssec25} 

The BC produced upon the thermal degradation of the PC was utilized to
prepare the AC. Firstly, the BC was ground by an electrical grinder,
followed by sieving using a 60-mesh sieve. Synthesis of the ABC from
the resulting BC was carried out through immersing a known mass of the
BC (5.0~g) in solutions containing various impregnation ratios of the
activator (K\tsub{2}CO\tsub{3}) on weight bases. The mixture was
stirred for 5~h and left overnight in a desiccator. After drying at
105~\textdegree C for 5~h, thermal activation of the dried samples was
accomplished in a muffle furnace at a given temperature and duration.
The activated samples were then raised with a solution of 1.0 M HCl and
washed several times until neutral water~\cite{43}. Synthesis of the
ABC from BC was carried out by adjusting the activation conditions,
including the ratio of the activator (0:5:1--3:1 w/w) and activation
duration (30--120~min), as well as the activation temperature
(550--850~\textdegree C). The yield of the AC was calculated based on
Equation~(\ref{eq1})~\cite{44}:
{\begin{equation}\label{eq5}
\text{AC yield}~(\%) = 
\dfrac{\text{Maa of the produced ABC}~(\mathrm{g})}
{\text{Mass of BC used}~(\mathrm{g})}\times 100.
\end{equation}}\unskip

\subsection{Characterization of the activated Biochar}\label{ssec26}

The surface physical morphology of the activated BC was perceived by
the field emission scanning electronic microscope model (TESCAN MIRA
FESEM, Czech Republic). The porosity and structural features of the AC
carbon were examined by the N\tsub{2} adsorption--desorption isotherms
model (A BELSORP MINI II, Japan, surface area and porosimetry
analyzer). The BET method was applied to calculate the specific surface
area of the AC. The GB/T 12496.8--2015 standard methodology was
implemented to determine the iodine number (IN) of the so-produced
AC~\cite{45}. An X-ray diffraction (XRD) model (a Malvern Panalytical
X-ray diffractometer, UK) was employed to identify the crystal
structure.{\vspace*{-4pt}}

\subsection{Adsorptive elimination of Cr(VI) by activated
biochar}\label{ssec27}

Following a batch method, the Cr(VI) adsorption tests were completed in
250~mL Erlenmeyer flasks. The batch adsorption studies evaluated the
ABC performance under different pH, various Cr(VI) initial
concentrations, the dosage of the ABC, the \mbox{adsorption} temperature, and
the adsorption duration. To complete the adsorption trials, a mixture
of the ABC and 50~mL of Cr(VI) solution were agitated at room
temperature (25~\textdegree C) for a predetermined time until
equilibrium was reached. The Cr(VI) solution was centrifuged at 5000
rpm for 15~min after adsorption. After separation, the Cr(VI)
concentration in the clear supernatants was measured with an atomic
absorption spectrometer \mbox{(NOVA A350-analyitkjena-Germany).} The
adsorption removal percentage (AR\%) of Cr(VI) was calculated as per
Equation~(\ref{eq2}): 
{\begin{equation}\label{eq6}
\text{AR}~(\%) = \dfrac{({C}_{0} - {C}_{\mathrm{e}})} {{C}_{0}} \times 100, 
\end{equation}}\unskip
where, $C_{0}$ and $C_{\mathrm{e}}$ signify the primary and equilibrium
concentration (mg/L) of the Cr(VI), \mbox{respectively.} The amount of Cr(VI)
adsorbed at equilibrium ($q_{\mathrm{e}}$, mg/g) by the as-synthesized
ABC was calculated using Equation~(\ref{eq3}):
{\begin{equation}\label{eq7}
{q}_{\mathrm{e}} = \dfrac{({C}_{{o}} - {C}_{\mathrm{e}}){V}}{{W}},
\end{equation}}\unskip
where, $V$ is the Cr(VI) solution volume (L), and ``$W$'' is the mass
(g) of the ABC employed in the adsorption experiments, respectively.

\section{Results and discussion}\label{sec3}
\subsection{Characterization of pinecone}\label{ssec31}

The possibility of implementing BM as a pyrolysis feedstock can be
derived from its ultimate and proximate analyses. Table~\ref{tab2}
shows the dry ultimate and proximate analyses of the PC compared with
different lignocellulosic BM sources on a dry basis. From the ultimate
analysis of PC, the latter had a higher C\% than other lignocellulosic
BM sources. Also, the PC exhibited an H\% above that established for
other lignocellulosic BM sources, but it was less than that reported
for \textit{Cascabela Thevetia} seeds~\cite{46}. The N\% and S\% in the
PC were lesser than those established for other BO sources, and in some
cases, the N\% and S\% of the PC were comparable. It was announced that
the low N\% and S\% in a BM feed indicates that it will emit less
SO$_{x}$ and NO$_{x}$ upon combustion~\cite{46}. Besides, the decreased
S levels in a BM feed indicate less corrosion during the combustion or
thermal pyrolysis~\cite{35}. Finally, the O\% in the PC was, in most
cases, below that established for other BM feeds. The low O\% for BM
feed will increase its calorific value besides producing BO with a low
content of the O compounds~\cite{21,46}.

%tab2
\begin{table*}
\caption{\label{tab2}The PC analysis results are compared with other BM
feeds\vspace*{-3pt}}
\begin{tabular}{cccccccc}
\thead
\multicolumn{8}{c}{{Ultimate Analysis (on a dry bases)}} \\ \cline{1-8}
{{Biomass}} & {C} & {{H}} & {{N}} & {{S}} & {{O}} & {H/C} & {O/C} \\ 
\endthead
{{PC}} & 51.06 & {6.26} & {0.60} & {0.06} & {42.02} & 1.47 & 0.61 \\ 
{{Acai seeds}} & 43.29 & {5.98} & {1.29} & {0.10} & {47.59} & 1.65 & 0.82 \\ 
{{\textit{Cascabela Thevetia} seeds$^{\mathrm{b}}$}} & 46.08 & 
{7.20} & {6.43} & {-} & {40.29} & \01.875 & 0.65 
\botline
\end{tabular}
{\vspace*{.45pc}}

\begin{tabular}{cccccc}
\thead
{{Biomass}} & {{Moisture \%}} & {{Ash\%}} & {{V.M.\%}} & {{F.C.\%}} & {{Calorific value (MJ/kg)}} \\ 
\endthead
{{PC}} & {4.55} & {0.92} & {75.30} & {23.78} & {18.72} \\ 
{{\textit{Cascabela Thevetia} seeds$^{\mathrm{b}}$}} & 
{5.10} & {4.20} & {73.81} &{16.20} & {18.71} \\ 
{{Castor seed hulls}} & {4.40} & {6.71} & {72.05} & {16.89} & {13.85} 
\botline
\end{tabular}
{\vspace*{.45pc}}

\begin{tabular}{ccccc}
\thead
{Biomass} & {{Extractive \%}} & {{Cellulose \%}} & {{Hemicellulose \%}} & {{Lignin \%}} \\ 
\endthead
{PC} & {7.0} & {33.50} & {36.60} & {22.90} \\ 
{Neem seeds}$^{\mathrm{d}}$ & {29.24} & {38.04} & {21.94} & {13.58} 
\botline
\end{tabular}
\tabnote{$^{\mathrm{a}}$From Ref.~\cite{5};
$^{\mathrm{b}}$From Ref.~\cite{46};
$^{\mathrm{c}}$From Ref.~\cite{46};
$^{\mathrm{d}}$From Ref.~\cite{46}.}
{\vspace*{-4pt}}
\end{table*}

In comparison with the ultimate analysis of PC samples in the
literature, the C, H, N, S, and O contents of the PC used in the
preparation of chemically AC were respectively 47.71\%, 6.16\%, 0.12\%,
1.21\%, and 44.80\%~\cite{47}. On the other hand, the C, H, N, S, and O
contents of the N-rich PC were respectively 43.99\%, 3.65\%, 1.67\%,
0.51\%, and 47.57\%~\cite{48}. The elemental analysis outcomes of the
PC used in this study were comparable to some of those mentioned above.
Nonetheless, variations in the elemental composition of varied PC
samples worldwide could be ascribed to the type of soil where the PC
trees are planted, besides the soil's chemical composition and the
country's climate. 

The proximate analysis outcome of the PC disclosed that its contents of
moisture, ash, volatile matter, and fixed carbon were 4.55\%, 0.92\%,
75.30\%, and 23.78\%, respectively. For the moisture \% of the PC, it
was below that reported for \textit{Cascabela Thevetia} seeds~\cite{46}
and coaster seed~\cite{46} but comparable to that of the castor seed
hull~\cite{49}. Ahmad et~al.~\cite{50} declared that a 10.0\% moisture
content in the BM feed is recommended as a pyrolysis precursor. The
volatile material \% for the PC was above that reported for the other BD
feeds tabulated in Table~\ref{tab2}. According to Ahmad
et~al.~\cite{50}, the production of gases and liquid products increases
when the BM feed possesses a high volatile matter \%. Also, the produced
fuel will have a higher ignition performance. The PC had a fixed
carbon \% above that \mbox{announced} for \mbox{\textit{Cascabela Thevetia}}
seeds~\cite{46} and castor seed hull~\cite{49}, but it was comparable to
that established for other BM feeds presented in Table~\ref{tab2}. The
fixed carbon \% for the PC suggests its suitability for being utilized
successfully in pyrolysis~\cite{51}. The ash\% of the PC was comparable
to that of the castor seed hull~\cite{49}, but it was below that
established for other BM feeds presented in Table~\ref{tab2}. This
parameter must be as low as possible, as it adds several adverse
effects on the feature of the BM feed, like the low heating value,
formation of slag, and corrosion or blockage of the
equipment~\cite{46}. As per the literature, the FC\%, VM\%, and ash\%
for a sample of PC in the literature were respectively 23.41\%,
73.98\%, and 2.61\%~\cite{47}. These findings are comparable to those
established for the PC sample used in this work. However, the
variations in the FC\%, VM\%, and ash\% for varied PC samples worldwide
may belong to the chemical composition of the PC samples besides the
standard procedures followed upon determining these features.

The extractive \% for the PC was below that announced for other BM
seeds. This outcome is expected as these seeds contain a high
percentage of oil, which raises its extractive \%. The content of lignin
for the PC was above that of neem seeds~\cite{46} and below that of
coaster seeds~\cite{46}. Higher lignin content in the BM feed favors
char formation during pyrolysis~\cite{34}. Finally, the calorific value
of the PC was comparable to that of \textit{Cascabela Thevetia}
seeds~\cite{46} but higher than that reported for the castor seed hull
and coaster seed. As per the properties of the PC, it can be utilized
as a thermal pyrolysis precursor. Moreover, the component analysis of
any BM feed has a potential impact on its thermal pyrolysis behavior as
an outcome of the percentages of the components in the parent feed,
which in turn affects the output of its pyrolysis products. 

The thermal degradation behavior of any BM feed can be estimated by
thermogravimetric analysis (TGA). The TGA examination of the PC
accomplished at a 10~\textdegree C/min heating rate in a temperature
range of 35 to 1000~\textdegree C under a stream of N\tsub{2} gas and
air is presented in Figure~\ref{fig3}, which {confirmed} that, like any
BM feed, the thermal decomposition of PC possessed through three chief
periods, namely drying, devolatilization, and char creation
zone~\cite{52}. The drying zone (1{st} stage) started from ambient
to 150~\textdegree C. This stage mainly excludes unbonded water
molecules and some very lightweight ingredients~\cite{53}. The
devolatilization period (2{nd} stage) is also named the active
pyrolysis step. This stage initiated from 150~\textdegree C to
550~\textdegree C. This stage involves the thermal degradation of the
heavier molecule as an outcome of the larger heat supply. During this
period, the greatest quantities of hot volatiles are generated as a
consequence of the thermal decomposition of the PC components, viz.
hemicellulose, cellulose, and a slight lignin~\cite{54}. The last zone
of thermal destruction is the 3rd stage, also called the char formation
zone. This stage usually occurs at a temperature above 550~\textdegree
C and is primarily ascribed to the thermal degradation of lignin at a
prolonged rate~\cite{55}. The DTG thermograph (Figure~\ref{fig3})
disclosed that nearly 10\% of the PC was decomposed in the 1st
pyrolysis stage, while about 70\% of the decomposition occurred in the
2nd. Moreover, the first peak in the DTG thermogram belongs to the
moisture and mild volatile component elimination at a temperature above
150~\textdegree C. Based on the literature, cellulose and lignin
degrade at temperatures above that of hemicellulose~\cite{56,57}.
Hemicellulose and cellulose decomposition peaks occurred at
temperatures between 200--500~\textdegree C. Lignin degradation starts
at 180~\textdegree C, but its degradation is prolonged and continues at
higher temperatures (${>}$500~\textdegree C). Char generation upon
pyrolysis is influenced by lignin composition. A higher lignin content
in BM leads to increased char production. Additionally, higher energy
is needed to trigger the reaction~\cite{58}. Comparable performance was
also observed in the present study, with~minor differences due to
differences in the composition of the raw BM feed~\cite{58}. Notably,
the thermal decomposition behavior of the PC used in this work was
analogous to that established for other PCs in the
literature~\cite{58,59}. These studies disclosed that the active
devolatilization zone of the PC samples was nearly between
200~\textdegree C and 500~\textdegree C. Nonetheless, the~minor
differences in the percentages of the decomposition stages may be
ascribed to the type of inert gas used upon performing the TGA
measurement besides the heating rate of the decomposition process. 
\looseness=-1

\begin{figure}
\includegraphics{fig03}
{\vspace*{-3pt}}
\caption{\label{fig3}TGA-DTG thermograms of the PC.}
\end{figure}

\subsection{Optimization of thermal pyrolysis parameters}\label{ssec32}

Thermal pyrolysis of the PC in a fixed-bed reactor was accomplished to
analyze the influence of the process parameters, including pyrolysis
temperature, pyrolysis time, particle size of the PC, and heating rate
on the PO, BC, and gas yields, as presented in Figure~\ref{fig4}(a--d).
However, during the optimization of the thermal pyrolysis experiments,
the PO output was adopted as a starting point to transfer from one
variable to the following variable until reaching the typical pyrolysis
variables that will lead to producing the maximum output of the PO.

\begin{figure*}
{\vspace*{-2pt}}
\includegraphics{fig04}
{\vspace*{-3pt}}
\caption{\label{fig4}The pyrolysis parameters influence on the product
yields.}
{\vspace*{-3pt}}
\end{figure*}

It is clear from Figure~\ref{fig4}(a), which examines the influence of
the pyrolysis temperature of the PC on its product yields. The PO yield
was low at 400~\textdegree C because of the incomplete pyrolysis of the
PC. Low pyrolysis temperatures are associated with limited heat and
mass transfer of the BM particle inside the reactor, causing a low PO
output. When the temperature increased above 400~\textdegree C, the PO
yield reached a maximum of 500~\textdegree C. At this temperature, the
heat and mass transfer between the PC particles will be maximum because
of the longer contact time, which permits the complete transformation
of the PC into volatile products~\cite{13,42}. So, the yield of the PO
is \mbox{enhanced.} Beyond 500~\textdegree C, the output of the PO reduced may
be due to the transformation of the PC at higher temperatures into
non-condensable vapors as a consequence of the secondary thermal
destruction reactions, which enhance the PC fragmentation besides the
produced PO into non-condensable \mbox{products} (CO, CO\tsub{2}, CH\tsub{4},
H\tsub{2}, etc.)~\cite{13}. On the other hand, the output of the BC
diminished with increasing thermal pyrolysis temperature while the gas
yield rose. These consequences originated from the secondary thermal
destruction reactions of the feed and BC as an outcome of the quick
endothermic degradation of the produced BC into non-condensable gases.
The production of the highest yield of the PO from the PC at
500~\textdegree C was comparable to the typical temperature for thermal
degradation of various BM sources, like mixed date stones, pistachio
shells stones~\cite{13} and babool seeds~\cite{60}. However, a maximum
pyrolysis temperature of 500~\textdegree C was less than that required
for thermal destruction of Mahua seed (525~\textdegree C)~\cite{61}. 
\looseness=-1

The period at which the precursor spends inside the pyrolysis reactor
is one of the variables determining the pyrolysis product output. It
was reported that the pyrolysis completion is highly connected to the
pyrolysis period since shorter intervals may lead to partial feed
degradation. Furthermore, to undergo thermal cracking, the feed must
remain in the reactor for an extended period upon the cracking so as to
allow heat to spread throughout the entire particle~\cite{61,62}.
Therefore, it is essential to determine the ideal time for the
pyrolysis process. The thermal degradation of the PC was tested over
several intervals (30--150~min) while retaining other variables, as
presented in Figure~\ref{fig4}(b), which showed that the higher liquid
output was obtained by lengthening the pyrolysis period from 30~min to
60~min, the PO output boosted from 37.45\% to 40.80\%. Such an outcome
suggests that a period of 60~min is sufficient to condense all the
volatile vapors produced upon thermal degradation of the parent feed.
Nonetheless, beyond this duration, the PO output declined due to the
continuous thermal degradation of the authentic feed besides the
produced volatiles into non-condensable vapors~\cite{9}. On the other
side, an \mbox{increase} in the gaseous yield and a diminish in the BC yield
were noticed when the duration of pyrolysis increased as a consequence
of the additional gasification of the parent feed, PO, and the produced
BC into non-condensable vapors at the expense of the BC
yield~\cite{9,11,15}. The thermal pyrolysis of mixed date and cherry
seeds~\cite{18} and pistachio shells~\cite{62} resulted in similar
findings.

The mass and heat transfer within the pyrolysis zone is greatly
affected by the feed's particle size, thus affecting the output of the
pyrolysis product. It was reported that large particles prefer char
formation upon thermal pyrolysis while producing gases and liquid
products prefer smaller particles~\cite{40}. Accordingly, thermal
destruction of the PC was carried out employing particles of various
sizes (0.25, 0.297,0.4, 0.595, and 0.841mm), with maintaining
temperature, time, and rate of heating fixed at 500~\textdegree C,
60~min, and 30~\textdegree C/min, respectively. It was found that with
decreasing the particle size, the PO yield rose as a consequence of
increased heat and mass transfer, which offered an entire conversion of
BM feed into products~\cite{18}. The highest yield of the PO was
produced employing particles of 0.40~mm size. Figure~\ref{fig4}(c)
exhibited that particles of the bigger size prefer the production of BC
rather than other products because of the incomplete transformation of
the BM feed. Thus, the heat transfers between the BM feed \mbox{particles}
fall, causing a decline in the yields of the PO and gases. Mishra and
Mohanty announced similar observations on the thermal degradation of
\textit{Samanea saman} seeds~\cite{41}.

Among the experimental variables that have an essential impact on the
product's yield upon the thermal destruction process is the rate of
heating of the feed inside the reactor. Thus, it is necessary to find
out the typical heating rate of the BM feed during the thermal cracking
process. To do so, thermal pyrolysis of the PC was accomplished at
multiple heating rates ranging from 10~\textdegree C/min to
50~\textdegree C/min, preserving other factors at their optimal values.
Based on the findings in Figure~\ref{fig4}(d), the lowest output of PO
and gases and the highest production of BC were obtained at the lowest
heating rate. Such findings could be ascribed to the imperfect thermal
destruction of the authentic PC particles inside the reactor as an
outcome of the insufficient mass and heat transmission among the PC
particles~\cite{40,42}. An improvement in the PO yield from 36.45\% to
42.12\% was noticed as the rate of heating rose from 10~\textdegree
C/min to 30~\textdegree C/min, as a possible increase in the mass heat
and conduction among PC particles. As an outcome of the endothermic
cracking of the PC (rapid fragmentation reactions), heating rates
beyond 30~\textdegree C/min caused a diminish in the PO
yield~\cite{18}. Figure~\ref{fig4}(d) also clarifies that the BC yield
decreased, while increased gaseous product yield was noticed with
increasing heating rate. This outcome suggests the PC's quick
decomposition into non-condensable gases due to the secondary thermal
destruction reactions~\cite{17,18}. Al-Layla et~al.~\cite{40} and Mishra
et~al.~\cite{41} reported similar consequences upon the thermal
decomposition of milk thistle and \textit{Samanea saman} seeds,
respectively. As we stated earlier, determining the typical
experimental conditions of the thermal pyrolysis of PC was based on the
conditions that will lead to produce the highest output of the PO. So,
as per outcomes presented in Figure~\ref{fig4}, the highest yield of
the PO (42.12\%) was produced using 0.40~mm particle size of the PC at
500~\textdegree C for 60~min and 30~\textdegree C/min rate of heating.
\looseness=-1

\subsection{Identification of PC-derived bio-oil}\label{ssec33} 

The PO produced at the typical experimental conditions (500~\textdegree
C, 60~min, 0.40~mm particle size, and 30~\textdegree C/min heating
rate) was fractionated in a \mbox{separating} funnel into the BO and aqueous
phases. The BO yield amounted to 10.20\% of the total weight of the PO.
This BO was identified for its chemical composition and ultimate
analysis.  

\subsubsection{\tsup{1}HNMR analysis}\label{sssec331}

Table~\ref{tab3} demonstrates the \% of different kinds of H defined by
the chemical shift results of the BO created through pyrolysis of PC.
At the same time, Figure~1S (supplementary material)
shows the \tsup{1}H NMR spectra of BO. The \tsup{1}H NMR spectrum for
the BO obtained by thermal destruction of PC at 500~\textdegree C
showed that the region between 6.50 ppm and 7.0 ppm suggested that the
as-created BO contains multiple functional groups. The \tsup{1}H NMR
spectra of the as-created BO revealed three key areas: aliphatic,
olefinic, and aromatic~\cite{40,61,62,63}. Nonetheless, the area between
0.50--3.0 exhibited crowded peaks belonging to the aliphatic fraction of
the BO, whereas peaks in the region between 4.5--6.3 ppm express the
olefinic part. Chemical shifts between 6.0 and 9.0 ppm best
characterize the aromatic resonances~\cite{40,61}. Based on the above
findings, the as-synthesized BO was predominantly composed of aliphatic
structural components. Aliphatic hydrocarbons comprised 89.34\% of the
BO, while aromatic hydrocarbons constituted 7.0\%. The \tsup{1}HNMR
measurements of the acquired BO are consistent with those obtained from
other BO samples synthesized from various precursors, like the dried
black liquor solids~\cite{64}, tobacco processing wastes~\cite{65}, and
algal waste~\cite{66}. The BO samples originating from these precursors
disclosed that the major peaks were crowded in the region belonging to
the aliphatic fraction of the BO. So, following the \tsup{1}H NMR
outcomes, it can be concluded that the resulting BO consisted of many H
atoms originating from the aliphatic CH\tsub{3}--, CH\tsub{2}-- and
CH-- groups~\cite{66}. Nevertheless, the difference in the types of H
that occurred among the BO samples in the literature could be ascribed
to many issues, including the chemical composition of the parent BM
feed, the pyrolysis circumstances, and the kind of feedstock employed.

%tab3
\begin{table*}
\caption{\label{tab3}Hydrogen types deduced from \tsup{1}H NMR
spectroscopy}
\begin{tabular}{cccccc}
\thead
Type of H & Chemical shift (ppm) & H\%$^{\mathrm{a}}$ 
& H\%$^{\mathrm{b}}$ & H\%$^{\mathrm{c}}$ & H\%$^{\mathrm{d}}$ \\ 
\endthead
Aromatic, CHO & 6.0--9.50 & \09.69 & \07.53 & 13.09 & 25.45 \\ 
Phenolic (O--H) or olefinic proton & 4.50--6.0 & - & 19.86 & - & \06.64 \\ 
CH\tsub{3}--C${=}$O, CH\tsub{3}--N, --CH\tsub{3}--C & 3.0--4.50 & 18.27 & \07.21 & \01.34 & \05.99 \\ 
Aliphatic and $\upalpha$-hetero atoms & 1.5--3.0 & 38.07 & 19.86 & 54.42 & 29.61 \\ 
CH\tsub{3}, CH\tsub{2} and alkanes & 0.0--1.50 & 45.36 & \07.53 & 31.15 & 32.31
\botline
\end{tabular}
\tabnote{$^{\mathrm{a}}$BO from PC;
$^{\mathrm{b}}$BO from dried black liquor solids~\cite{64};
$^{\mathrm{c}}$BO from tobacco processing wastes~\cite{65};
$^{\mathrm{d}}$BO from algal waste~\cite{66}.}
{\vspace*{4pt}}
\end{table*}

\subsubsection{Ultimate analysis of bio-oil}\label{sssec332}

Table~\ref{tab4} compares the contents of C, H, N, S, and O of the BO
separated from the resulting PO under the optimal experimental
conditions with other BO samples produced from various feedstocks in
the \mbox{literature.} Following the outcomes presented in Table~\ref{tab4},
the C\% of the BO derived from thermal pyrolysis of PC was above the
contents of other elements, and such an outcome is expected, as C is
the main element in any BM feed. It was also noticed that the C\% of
the BO originated from thermal pyrolysis of PC, which was above that
established for BO samples created from various BM feeds in the
literature. It was reported that the high C\% of BO raises its heating
value~\cite{40}. Besides, the H\% of the produced BO was greater than
that established for other BO samples in the literature
(Table~\ref{tab4}).  The H/C molar ratio of the as-produced BO was
1.27, implying that it ranges between light and heavy petroleum
oils~\cite{18}. Furthermore, the H/C molar ratio of the BO produced
from the thermal degradation of PC was above that declared for BO
samples originating from the pyrolysis of \textit{Samanea saman}
seeds~\cite{41}, cotton seed~\cite{14}, and Tung seed
residues~\cite{64}. It was established that the amount of heat produced
upon the combustion of BO is highly related to its H/C~\cite{67}.
Sultana et~al.~\cite{68} announced that the H/C molar ratio affects the
aromatization degree of BO, in addition to other factors, including the
presence of a catalyst, the chemical composition of the BM feed, and
conditions applied to the pyrolysis process. On the other hand, it was
noticed that the BO produced from the PC had a lower O\% than the
pristine PC as an outcome of the transformation of the oxygenated
hydrocarbons in the parent feed into non-condensable gases~\cite{35}.
Besides, the O\% in the as-created BO was below that established from
mixed date stones and pistachio shells~\cite{13}, Samanea saman
seeds~\cite{41}, and Tung seed residues~\cite{67}. It was established
that the BO with a lower O\% will be less corrosive and needs lower
upgrading conditions besides having a higher calorific value~\cite{41}.
It is evident from Table~\ref{tab4} that the N\% and S\% of the
produced BO were \mbox{below} those announced for BO samples from other BM
feeds (Table~\ref{tab4}). Such lower values of O\% and S\% suggest that
the BO emissions of NO$_{x}$ and SO$_{x}$ will be less~\cite{13,41}.
The calorific value (HHV) of the BO resulting from thermal pyrolysis of
the PC was above that announced for BO samples originating by thermal
destruction of various BM feeds (Table~\ref{tab4}). Such an outcome
could be ascribed to many factors, such as the H/C molar ratio of the
parent feed besides the chemical composition (its contents of
cellulose, hemi cellulose, and lignin). 

%tab4
\begin{table*}
\caption{\label{tab4}Ultimate analysis of the PC-derived BO (dry
bases)}
\tabcolsep=4.5pt
\begin{tabular}{cccccccccc}
\thead
BO source & C\% & H\% & N\% & S\% & 
\parbox[t]{4pc}{\centering O\% by difference} & H/C &  O/C
& \parbox[t]{5pc}{\centering Calorific value (MJ/kg)} & Ref. \\ 
\endthead
PC & 65.04 & 6.87 & 0.36 & 0.02 & 27.71 & 1.27 & 0.31 & 26.99 & This
work \\ 
\parbox[t]{7pc}{\centering Mixed date stones and pistachio shells} & 60.50 & 6.84 & 0.30 & - &
32.06 & 1.35 & 0.39 & 24.54 & \cite{13} \\ 
Cotton seed & 62.66 & 2.06 & 3.45 & - & 31.83 & 0.39 & 0.38 &
23.14 & \cite{14} \\ 
\textit{Samanea saman} seed & 61.47 & 4.01 & 3.47 & 1.88 & 29.17 & 0.78 & 0.17 & 21.23 & \cite{41} \\ 
Tung seed residues & 60.63 & 4.56 & 0.43 & 0.06 & 34.52 & 0.91 & 0.43
& 22.89 & \cite{67}
\botline
\end{tabular}
\end{table*}

\subsubsection{GC-MS analysis of bio-oil}\label{sssec333}

The GC-MS analysis can better recognize the variety of components found
in BO. Because of its complex composition, it was declared that BO
comprises more than 300 chemical components~\cite{41}. Aliphatic,
oxygenates, nitrogenates, heterocyclic, monoaromatics, and
polyaromatics were the six primary categories into which these
compounds were sorted~\cite{40}. According to the literature, most BO
samples contain esters, ethers, amines, nitriles, aldehydes, ketones,
and acids~\cite{40,41}. Following the findings presented in
Figure~\ref{fig5}, the BO synthesized from the thermal decomposition of
PC contained different organic compounds, and the O-organic compounds
prevailed. These compounds were composed of phenols (63.55\%), alcohols
(16.57\%), ketones (6.85\%), furans (5.45\%), aromatics (2.92\%), acids
(1.16\%), and hydrocarbons (1.30\%). The resulting BO contained a~minor
ratio of nitrogenate (0.33\%). Acetic acid and furans are the most
common byproducts of woody BM pyrolysis~\cite{7}. The degradation of
lignin in PC also yields other phenolic compounds, including phenol,
methyl phenol, methoxy phenol, methyl methoxy phenol, ethyl methoxy
phenol, vinyl methoxy phenol, eugenol, and propenyl methoxy
phenol~\cite{69}. The GC-MS spectrum is presented in Figure~2S
(supplementary material), while Table~1S lists all chemical compounds
present in the as-produced BO detected by the GC-MS. 

\begin{figure}
\includegraphics{fig05}
\caption{\label{fig5}Types of organic compounds present in the BO.}
\end{figure}

\subsection{Optimization of activated biochar synthesis}\label{ssec34} 

The K\tsub{2}CO\tsub{3} activation method was employed in converting
the BC leftover from the thermal decomposition of the PC. One of the
most effective factors affecting both the yield and surface area of the
ABC production is the molar ratio of the activator. The activator is
the key factor responsible forming the porous structure of the ABC as
an outcome of the chemical reactions occurred as the precursor and the
activator mixture is subjected to heat upon activation, including
dehydration reactions. So, finding the proper molar ration of the
activator must be \mbox{specified.} The effect of activator impregnation ratio
(IR), temperature, and duration on ABC yield and IN were explored to
reach the typical conditions that will lead to the development of the
best ABC sample. It was shown that the ABC production dropped as the
activator's IR increased. This result suggests that tar and other
volatile compounds are released from the BC at higher activator
concentrations, leading to a drop in the ABC yield~\cite{18,44}.
Furthermore, as an additional activator is added, more C atoms in the
feed skeleton will break down due to their reaction with the activator,
besides further burning off the sample, thus lowering the ABC
output~\cite{44}. Similar findings were established upon
K\tsub{2}CO\tsub{3}-activation of the BC resulting from co-pyrolysis of
mixed date and cheery seeds~\cite{18}. As the activator quantity rose
from 1:1 to 2:1, as shown in Figure~3S(a), the microporosity of the ABC
pointed out by the IN improved, indicating that the latter IR is
typical to construct a more microporous structure ABC. When BC was
overactivated with excessive activator concentrations (${>}$2:1), the
walls of the adjunct micropores broke down and bigger pores (meso- or
macro-pores), and thus the IN turned down~\cite{70}. 

The temperature of activation offers an immense effect on the yield and
porosity of ABC. As indicated in Figure~3S(b), higher activation
temperatures decreased the ABC yield as a consequence of the thermal
pyrolysis of lignin with the increment of \mbox{temperature} above
600~\textdegree C. Also, chemical activation by K\tsub{2}CO\tsub{3}
initiates between 450~\textdegree C and 500~\textdegree C and involves
two phenomena, pyrolysis and activation of lignin with
K\tsub{2}CO\tsub{3}, leading to the gasification of carbon in the
structure of the feed into CO besides the degradation of
K\tsub{2}CO\tsub{3} into K\tsub{2}O, as follows~\cite{70}:
{\begin{equation}\label{eq8}
\mathrm{K}_{2}\mathrm{CO}_{3} + 2\mathrm{C} \rightarrow 2\mathrm{K} +
3\mathrm{CO}
\end{equation}}\unskip
The K\tsub{2}CO\tsub{3} may also suffer from thermal decomposition into
CO\tsub{2} and K\tsub{2}O, and the occurrence could cause further
activation of the feed, as follows:
{\begin{eqnarray}
\mathrm{C} + \mathrm{CO}_{2} &\rightarrow& 2\mathrm{CO} \label{eq9} \Seqnsplit
2\mathrm{K}_{2}\mathrm{O} + \mathrm{C} &\rightarrow& 4\mathrm{K} + \mathrm{CO}_{2} \label{eq10} 
\end{eqnarray}}\unskip
Such a reaction will cause a diminish in the ABC output. Figure~3S(b)
shows that raising the activation temperature from 550 to
750~\textdegree C produced more micropores in the ABC structure. This
occurs as an outcome of the above chemical reactions, which result in
the gasification of the authentic feed into CO and CO\tsub{2}, leaving
behind an ABC with a well-developed microporous structure and thereby
improving the IN~\cite{18,44,70}. The degradation of the ABC
microporous structure caused a drop in the IN at temperatures beyond
750~\textdegree C~\cite{18,71}, which may be due to harsh degradation
of the feed besides the produced ABC structure into non-condensable
gases, which in turn causes a widening in the microporous~\cite{18}. 

The activation time during the synthesis of ABC needs to be optimized
due to its economic significance. Figure~3S(c) revealed that an
increase in duration resulted in a decline in the ABC yield, which was
caused by the aggressive burn-off of the parent BC as a consequence of
the prolonged activation period at high temperatures~\cite{44}. The IN
increased when the activation time was raised from 30 to 60~min,
according to Figure~3S(c). This outcome suggests that by extending the
activation time at an elevated temperature, the pore created as a
result of the activation will be blocked by the evolved volatile
matter. So, with extending time, these vapors will be expelled out of
the resulting porous structure of the produced ABC. Nonetheless,
activation periods beyond 60~min diminished the IN of the resulting
ABC, as an outcome of the microporous blockage by vapor evolved upon
thermal activation, resulting in a diminish in the IN~\cite{44,71}.

\subsubsection{Identification of K\tsub{2}CO\tsub{3}-activated
biochar}\label{sssec341}

After synthesizing the best ABC sample at the optimal activation
settings (2:1 K\tsub{2}CO\tsub{3}: BC, 750~\textdegree C; 1~h), surface
texture, morphology, and the crystalline structure were identified
using the N\tsub{2}-adosotion--desoprtion isotherms at 77 K, FESEM, and
XRD, as demonstrated in Figure~\ref{fig6}. The FE-SEM specified the
morphology assessment of the ABC surface. Figure~\ref{fig6}(a) shows
that the ABC had a rough, uneven surface with some granules.
Furthermore, fissures, holes, and cavities of different sizes were also
noticed on the ABC surface. Such cracks and cavities, alongside the
pores, will allow the adsorption of various molecules to enter them
more quickly, leading to a high elimination efficacy.
Figure~\ref{fig6}(b) shows the XRD pattern of the ABC, as previously
mentioned. It showed the presence of two immense specific peaks
associated with the (002) and (101) phases of amorphous carbon, located
at $2\rmtheta = 24$\textdegree\ and $2\rmtheta =
44$\textdegree~\cite{72}. In addition to the pore size distribution
curves of the ABC, as constructed, Figure~\ref{fig6}(c) shows the
N\tsub{2} adsorption--desorption isotherms. At low relative pressure
($P/P_{0}<0.05$), the ABC N\tsub{2} uptake curve abruptly increased
before plateauing, indicating that the isotherm represented type I, a
characteristic of microporous materials~\cite{72}. The ABC created
above showed a $\mathrm{SA}_{\mathrm{BET}}$ of 465.55 m\tsup{2}/g and a
mean pore diameter of  1.97~nm, affirming its microporous structure.
The surface area of the ABC developed by the direct chemical activation
of PC by KOH amounted to 478.89 m\tsup{2}/g~\cite{73}. In comparison,
the direct activation of the PC by H\tsub{3}PO\tsub{4} produced an ABC
having a BET surface area of 1597 m\tsup{2}/g~\cite{74}, compared to
1823 m\tsup{2}/g for that developed by the direct activation of PC by
ZnCl\tsub{2}~\cite{74}. Nonetheless, besides the synthesis conditions,
the type of activator used in preparing ABC potentially impacts the
texture of the resulting ABC.\looseness=-1

\begin{figure*}
{\vspace*{-2pt}}
\includegraphics{fig06}
{\vspace*{-3pt}}
\caption{\label{fig6}The FESEM image, XRD patterns, and N\tsub{2}
adsorption--desorption isotherms of the ABC.}
{\vspace*{-3pt}}
\end{figure*}

\subsubsection{Application of ABC in Cr(VI) removal}\label{sssec342} 

The ABC prepared under the typical experimental conditions was tried to
eliminate Cr(VI) ions from its aqueous phase. The investigation was
performed by optimizing the experimental conditions affecting the
process. One of the variables that possesses an energetic influence on
the adsorption of Cr(VI) from solution is the initial pH of the
solution, as this parameter affects the electrostatic combination of
the Cr(VI) species with the surface of the ABC~\cite{75}. So, assessing
the pH effect on the AR of Cr(VI) from solution by the as-developed ABC
was accomplished by conducting the adsorption of Cr(VI) from a solution
having different pH (2, 4, 6, 7, and 8) while keeping other variables
fixed as given in Figure~\ref{fig7}(a). This figure disclosed that
increasing the solution's pH from 2.0 to 8.0 caused a decline in the
AR\% of Cr(VI) from the aqueous phase. The highest AR\% was obtained at
a pH ${=}$\ 2.0, while beyond this value, the AR\% declined
progressively, which is consistent with former studies~\cite{76,77}. In
the acidic environment (pH ${<}$ 6.0), the surface of the resulting ABC
can be positively charged through the interaction with the extra H+,
which in turn augments the adsorption of negatively charged anions of
Cr(VI). As the solution's pH rises, \mbox{competition} between the OH-- and
anionic groups containing Cr(VI) for the active sites will occur,
preventing Cr(VI)\break removal \cite{75,76,77}.

\begin{figure*}
{\vspace*{-4pt}}
\includegraphics{fig07}
{\vspace*{-4pt}}
\caption{\label{fig7}Effect of adsorption variables on the Cr(VI)
adsorption by the PC-derived ABC.}
{\vspace*{-4pt}}
\end{figure*}

The effect of various Cr(VI) ion concentrations in the range of
25--150~mg/L on the AC adsorption performance was evaluated. The setup
in which the trials were conducted is indicated in the legend of
Figure~\ref{fig7}(b). As the concentration of Cr(VI) ions rose from 25
ppm to 150 ppm, the amount of Cr(VI) ions absorbed by the ABC rose from
9.87~mg/g to 57.96~mg/g. This effect results from the high
concentration ascent, which will motivate the species of Cr(VI) ions to
proceed toward the ABC active locations, resulting in better pollutant
adsorption~\cite{75}. Similar findings were declared upon the AR of
Cr(VI) from wastewater over some biowaste-derived
adsorbents~\cite{78,79}.

To analyze the impact of the ABC dose on the AR\% of Cr(VI) ions, a
series of experiments were conducted using varying amounts of the ABC,
ranging from 0.10 g to 0.40 g. Concurrently, other conditions were
established, as illustrated in Figure~\ref{fig7}(c). Trying more ABC
amounts enhances the AR\% of Cr(VI) ions. This is because as the ABC
mass employed in the \mbox{adsorption} process increases, the number of
particles (or active binding sites) responsible for the AR of the
pollutant~\cite{77,78}. When 0.20 g of the ABC was tried, the maximum
AR\% efficiency was reached. Amounts beyond 0.20 go of the ABC lessened
the AR\% of Cr(VI) ions. This finding could be because the additional
doses of ABC may congregate and \mbox{overlap} ABC particles, reducing the
number of active sites available to remove the pollutant and causing a
decline in its AR\%~\cite{74}.

%tab5
\begin{table*}
\caption{\label{tab5}Adsorption isotherms values and $Q_{\mathrm{m}}$ value for
the ABC and other adsorbents}
\begin{tabular}{cccccc}
\thead
\multicolumn{6}{c}{{Type of isotherm}} \\ \cline{1-6}
\multicolumn{3}{c}{{Langmuir isotherm}} & 
\multicolumn{3}{c}{{Freundlich isotherm}} \\\cline{1-3}\cline{4-6}
$R^{2}$ & $Q_{\mathrm{m}}$ (mg/g) & $K_{\mathrm{L}}$ (L/mg) & 
$R^{2}$ & {$K_{\mathrm{F}}$ (mg/g)/(mg/L)$^{1/n}$} & $n$ \\ 
\endthead
0.9911 & 62.90 & 0.4300 & 0.9811 & {20.45} & 1.69 
\botline
\end{tabular}
{\vspace*{.5pc}}

\tabcolsep=8pt\begin{tabular}{cccc}
\thead
\multicolumn{4}{c}{Comparison of $Q_{\mathrm{m}}$ for Cr(VI) adsorption by the
ABC compared to other adsorbents}\\ 
{{Adsorbent}} & {$Q_{\mathrm{m}}$ (mg/g)} & Isotherm & {{Ref.}} \\ 
\endthead
{{Magnetic AC}} & {57.80} & Langmuir & {\cite{84}} \\ 
{{Fe\tsub{3}O\tsub{4} NPs}} & {25.06}  & Langmuir & {\cite{85}} \\ 
{{Peach stones-derived AC}} & {14.05}  & Langmuir & {\cite{86}} \\ 
{{Mango kernel-derived AC}} & {\07.10} & Langmuir & {\cite{87}} \\ 
{{Nutshell-derived AC}}     & {46.20}  & Langmuir & {\cite{88}} \\ 
{{ABC}}                     & {62.90}  & Langmuir & {This work}
\botline
\end{tabular}
\end{table*}

The effect of the adsorption temperature on the AR\% of Cr(VI) ions by
the as-created ABC was investigated from 15~\textdegree C to
55~\textdegree C while maintaining other circumstances constant, as
presented in the legend of Figure~\ref{fig7}(d). The AR\% of Cr(VI)
ions enhanced as the temperature rose from 15~\textdegree C to
35~\textdegree C, then decreased. At 35~\textdegree C, the highest AR\%
of Cr(VI) ions was achieved. The solution's viscosity declines as
temperature rises, allowing Cr(VI) ions to diffuse into ABC pores and
improve the AR\%~\cite{73,80}. Moreover, collisions between the ABC
particles with ions of Cr(VI) enhance as the adsorption temperature
rises, causing higher elimination of the Cr(VI) ions from the
solution~\cite{80}. The decrease in AR\% of Cr(VI) ions beyond
35~\textdegree C may be due to the desorption of the pollutant ions
from the ABC surface into the solution~\cite{73}.

It is necessary to examine the point at which a system reaches
equilibrium from an economic perspective. Thus, varied durations
(30--120~min) were examined upon exploring the effect of time on the
AR\% of Cr(VI) ions from its solution while preserving other parameters
at their ideal values. The information provided in Figure~\ref{fig7}(e)
showed that the adsorption duration had a desirable effect on the AR\%
of Cr ions by the ABC. The equilibrium was attained at 150~min, while
the prolonged period had no further impact on the ABC because empty
holes existing for the adsorption no longer occur~\cite{73,80}.

\subsubsection{Adsorption isotherms of Cr(VI) by the activated
biochar}\label{sssec343}

The adsorption isotherms of Cr(VI) adsorption over the as-produced ABC
were analyzed using the Langmuir and Freundlich isotherms, and their
\mbox{non-linear} equations and plots are offered in Table~1S and Figure~4S
(supplementary material).

It was reported that the Langmuir isotherm proposes that the adsorption
of an adsorbate on a given adsorbent is homogenous and
mono-layer~\cite{81}. On the contrary, Freundlich suggests that the
adsorption is heterogeneous and multi-layers~\cite{80}. After analyzing
the adsorption outcomes of Cr(VI) by the as-synthesized ABC, it was
concluded that the adsorption of Cr(BI) by the ABC is possible, as the
value of $R_{\mathrm{L}}$ (separation factor) was above 0.0 and less than 1.0.
Also, the value of n was above 1.0~\cite{81,83}. However, the Langmuir
model best described the adsorption of Cr(VI) by the ABC, as this model
exhibited a higher correlation coefficient ($R^{2}$) compared to the
Freundlich isotherm, demonstrating that the adsorption of the said
pollutant by the ABC was homogenous and mono-layer. Table~\ref{tab5}
displays values of the constants relating to the adsorption isotherms.
It also compares the maximum adsorption capacity ($Q_{\mathrm{m}}$, mg/g) of
Cr(VI) adsorption over the as-produced ABC to other adsorbents in the
literature. It was noticed that the $Q_{\mathrm{m}}$ value for Cr(VI) adsorption
by the as-produced ABC was above that established for other adsorbents.
Nonetheless, the variance in the $Q_{\mathrm{m}}$ values for different
adsorbents could be ascribed to many factors, including the surface
area and mean pore diameter of the adsorbent, the initial concentration
of the pollutant in the examined solution, and amount of the adsorbent
used in the AR process. Accordingly, the ABC developed from the PC has
the potential to be applied on the industrial\break scale.

\subsubsection{Adsorption mechanism}\label{sssec344}

The solute's adsorption mechanism must be explored on the adsorbent
solid surface to remove various pollutants from an aqueous phase.
Mechanism of the pollutant's adsorption from the liquid phase involves
several mechanisms, such as ion exchange, dipole--dipole, chemical
bonding, dipole--induced dipole, and H-bonding~\cite{89,90,82}. However,
the pore-filling mechanism, which significantly depends on the
adsorbent surface area, remains the primary mechanism for eliminating
pollutants from the \mbox{liquid} phase, while another mechanism could be
axillary. So, the above mechanisms could eliminate Cr(VI) from the
liquid phase~\cite{73,82}.

\section{Conclusions}\label{sec4}

Thermal pyrolysis of PC in a fixed-bed reactor showed that the
operation conditions affected the maximum yield of the PO. The highest
yield of the PO amounted to 42.12\% at 500~\textdegree C for 1~h using
0.40~mm particle size with a 30~\textdegree C/min rate of heating.
Moreover, the BO content in the produced PO was 10.20\%. The BO was
mainly composed of oxygenated compounds, which amounted to 54.98\%,
besides the N-organic compounds and hydrocarbons, whose contents were
6.95\% and 2.60\%, respectively. Besides, the BO exhibited a high
content of C and H besides its high caloric value (26.99~MJ/kg).
Activating the BC leftover from the pyrolysis of PC with
K\tsub{2}CO\tsub{3} produced a microporous ABC with 465.55 m\tsup{2}/g
and 1.97 nm average pore diameter using 2:1 K\tsub{2}CO\tsub{3}: char
at 750~\textdegree C for 1~h. This ABC was also implemented in the
adsorptive elimination efficiency of 150 mg/L Cr(VI) solution, which
amounted to 98.71\% utilizing 0.20 g of the ABC at 35~\textdegree C for
150~min and a pH of 2.0. Besides, the adsorption of Cr(VI) by the
as-produced ABC followed the Langmuir adsorption isotherm. In
conclusion, PC could be used as a pyrolysis feedstock for producing
high-content aromatic oxygenates BO, as well as ABC, with a high
surface area and a well-developed microporous structure. 

\section*{List of abbreviations}

{\vspace*{-2pt}}

\begin{inftab}
\begin{tabular}{@{}ll@{}}
\tbody
BM & Biomass \\ 
PC & Pinecone \\ 
PO & Pyrolytic oil \\ 
BC & Bio-char \\ 
BO & Bio-oil \\ 
HHV & Higher heating value \\ 
AC & Activated carbon \\
ABC & Activated bio-char \\ 
TGA & Thermogravimetric analysis \\
GCMS & Gas chromatography-mass spectroscopy \\
\tsup{1}H NMR & Proton magnetic nuclear spectroscopy \\ 
BET & Brunauer--Emmett--Teller \\ 
FESEM & \parbox[t]{12pc}{\raggedright Field emission scanning electron microscope} \\ 
XRD & X-ray diffraction \\ 
AR & Adsorptive removal
\end{tabular}
\end{inftab}

{\vspace*{-2pt}}

\section*{Declaration of interests}

{\vspace*{-2pt}}

The authors do not work for, advise, own shares in, or receive funds
from any organization that could benefit from this article, and have
declared no affiliations other than their research organizations.

{\vspace*{-2pt}}

\section*{Acknowledgements}

{\vspace*{-2pt}}

We thank Mosul University, College of Science, Department of Chemistry
for supporting this research work.

\back{}

{\vspace*{-2pt}}

\section*{Supplementary data}

{\vspace*{-2pt}}

Supporting information for this article is available on the journal's
website under \printDOI\ or from the author.

\CDRsupplementaryTwotypes{supplementary-material}{\cdrattach{crchim-351-suppl.pdf}}

{\vspace*{-2pt}}

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\bibliography{crchim20240274}
\refinput{crchim20240274-reference.tex}

\end{document}
