In the current work, three adsorbent materials were developed; biochar derived from date palm fiber (C), date palm fiber biochar/chitosan nanoparticles (CCS), and biochar/chitosan nanoparticles composite supplemented with glutamine (CCSG). These compounds were used as solid adsorbents to remove As5+ from polluted water. Several characterization approaches were used to investigate all the synthesized solid adsorbents, including TGA, N2 adsorption/desorption isotherm, SEM, TEM, ATR-FTIR, and zeta potential. CCSG demonstrated good thermal stability, with a maximum specific surface area of 518.69 m2/g, a microporous radius of 0.97 nm, total pore volume of 0.25 cm3/g, an average particle size of 38 nm, and pHpzc of 6.9. To optimize the reaction conditions, various sorption factors were examined, including contact time, pH, initial As5+ concentration, adsorbent dosage, temperature, and ionic strength. The study found that the modified samples were able to remove more As5+ (CCS; 256.0 mg/g and CCSG; 376.0 mg/g) than unmodified ones (C; 150.5 mg/g). The As5+ removal procedure corresponded well with Langmuir isotherm model. Thermodynamic and kinetic experiments show that the Elovich, PFO, and Van't Hoff plot with endothermic, spontaneous, and physisorption nature are the best fitted models. EDTA has the highest desorption efficiency percentage (98.8%). CCSG demonstrated enhanced reusability after six application cycles of As5+ adsorption/desorption, with only a 4% decrease in the efficiency of adsorption. This study demonstrates that CCSG effectively remove As5+ in wastewater and use agricultural solid waste residues (date palm fiber; DPF) for environmental remediation purposes.
Research Article
Effective removal of As5+ from aqueous medium using date palm fiber biochar/chitosan/glutamine nanocomposite: kinetic and thermodynamic studies
https://doi.org/10.21203/rs.3.rs-5256147/v1
This work is licensed under a CC BY 4.0 License
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Date palm
biochar
chitosan
nanocomposite
adsorption
arsenic
The fast rise of urbanization and industrialization has led to significant heavy metal contamination of the aquatic environment. Heavy metals in wastewater, including arsenic, copper, chromium, cadmium, zinc, cobalt, nickel, manganese, iron, mercury, and lead, pose a significant threat to human health and environmental safety due to their toxicity and bioaccumulation (Mehmood et al. 2022). Contamination of water with arsenic (As5+) is considered as a class 1 human carcinogen as classified by the International Agency for Research on Cancer (IARC(, is a growing global concern [2, 3]. Arsenic contamination can come from natural processes like rock weathering and mineral dissolution, as well as human activity like fossil fuel burning, mining, and pesticide use. Long-term usage of As5+-polluted water can cause several types of cancer, including lung, skin, hyperpigmentation, bladder, and hyperkeratosis (Yao et al. 2024). Numerous chemical, physical, and biological procedures have been used to treat As5+-contaminated water, such as precipitation, ion exchange, flocculation, membrane separation, reverse osmosis, solvent extraction, and biological membranes (Amen et al. 2020). These procedures have some limitations such as high operational costs, partial metal removal, high energy requirements, and formation of poisonous residual metal sludge. Among all the procedures, the adsorption is recognized as ideal technology for wastewater treatment technique due to its simplicity of operation, accessibility of different solid adsorbents, there is no need for a large application area, inexpensive due to the ability of solid adsorbent reusability, high efficiency, fast, and ecologically friendly as there is no toxic byproducts (Wang et al. 2024). Relevant research investigations have been conducted on the adsorption of As5+, including: Hossain et al. prepared magnetic graphene oxide for removing As5+, revealing a small amount of solid adsorbent, 0.14 g/L, effectively removed 98% of As5+ in 20 min (Hossain et al. 2024). Furthermore, Zouli et al. fabricated an iron-titanium/carbon composite detecting a maximum adsorption capacity (Xmax) of 86 mg/g at pH 6 (Zouli 2024). In addition, Sugita et al. used Mg-based adsorbents to remove As5+ from contaminated water samples and As5+ had removal performance in the order MgCO3 < Mg(OH)2<MgO (Sugita et al. 2024).In another investigation, Hussain et al. employed a hydrothermal approach to generate sulphur-doped copper ferrite, which effectively removed dissolved arsenic. The results indicated that one gram of S-CuFe2O4 is sufficient to provide 275 gallons of arsenic-free water (Hussain et al. 2024). However, we believe that they are unsafe chemical substances and so unfriendly to the environment, so biomaterials should be used instead. In recent researches, various bioadsorbents have been employed for As5+ decontamination. Hshakoor et. al. studied the removal of the As5+ from aqueous solutions using six types of various biosorbents (water chestnut shell, egg shell, corn cob, java plum seed, pomegranate peel, and tea waste) (HShakoor et al. 2019). Nguyen et al. assessed the removal performance of luffa fiber as an effective bioadsorbent on the purification of water polluted by As5+ (Nguyen et al. 2020). Recently, on sugarcane bagasse biochar modified with thiol and biochar based on rice husk have also been used to remove As5+ from polluted water (Masood ul hasan et al. 2024). Biochar is substance rich with carbon made from various organic wastes, including municipal sewage sludge and wastes from agricultural works (Murtaza et al. 2024). Biochar garnered great interest due to its distinctive properties such as large specific surface area, stability, high cation exchange capacity, and carbon content (Sun et al. 2022). However, there are obstacles in recycling material, separating it from water, and regeneration. Chitosan is a cationic natural biopolymer material formed by the deacetylation of chitin via alkaline circumstances. It exhibits diverse features such as biocompatibility, biodegradability, hydrophilicity, non-toxic characteristics, and adsorption properties. The cationic heavy metals may be actively adsorbed onto chitosan by its functional groups, which include hydroxyl and amino groups. The lack of surface chemical functional active sites groups on the biochar/chitosan composite surface has limited its adsorption capacity. However, adding functional group-rich material can boost the adsorption capability of the composite. By changing surface characteristics such as specific area and surface functional groups, electron transfer capacity, zeta potential, element distribution, and cation exchange capacity, chemical modification can increase the adsorption capacity of biochar. (Enaime et al. 2020). These changes impact porosity and enrich the biochar surface with oxygen-containing surface functional groups, particularly carboxyl groups. Moreover, it is a technique to give certain chemical modifications like etherification, grafting, or cross-linking actions for further endowing chitosan with superior adsorption qualities (Pillai et al. 2009). Many studies have focused on using raw and processed biochar to remove contaminants from water systems. Glutamine is a non-toxic amino acid, having hydrophilic functional groups including carboxylic acids and amides, with a molecular formula C5H10N2O3 (Kolangare et al. 2019). The addition of negatively charged carboxyl groups and hydrophilic to the biochar/chitosan composite surface contributes to improved adsorption characteristics and performance. In recent years, amino acids have been used as As5+ adsorbents due to their carboxyl (-COOH) and amino (-NH2) molecular structures, which allow for heavy metal ion coordination and chelation. While hydrophilic amino acids like lysine, glycine, and cysteine are commonly employed for As5+ removal [18, 19]. However, as far as we are aware, there is no research on biochar based on date palm fiber modified with glutamine amino acid in this field was studied up to now.
The fundamental purpose of the research is to identify an operative and environmentally safe adsorbent for removing As5+ from the aquatic system. We used agricultural solid waste residues (date palm fiber; DPF) to produce biochar (C) and created biochar/chitosan as biocomposites nanoparticles (CCS), which was subsequently modified with glutamine (CCSG). We studied many parameters that impact the adsorption performance of As5+, such as pH, contact time, applied temperature, initial concentration, adsorbent dose, and ionic strength. Date palm pits extract (DPE) was performed as caping agent for the conversion of the fabricated solid materials into stable nanoparticles under ultrasonic grinding conditions. Several physicochemical techniques were investigated, including ATR-FTIR, TGA, SEM, TEM, point of zero charge, and N2 adsorption/desorption. This study sheds light on the use of functionalized solid adsorbents to eliminate heavy metals cations from polluted water, paving the way for their practical implementation in wastewater treatment. Solid adsorbents reusability and sustainability was studied after several adsorption and desorption cycles.
2.1 Materials
Date palm pits and date palm fiber were obtained from Al-Wishayl special garden, Al-Rustaq, Sultanate of Oman. Sodium arsenate heptahydrate (> 98%), chitosan, sodium chloride (> 99.0%), sodium hydroxide (≥ 98%), hydrochloric acid (37%), acetic acid (96%), nitric acid (69%), ethylenediaminetetraacetic acid (99.5%), cysteine (≥ 95%), ethylene diamine (99.5%), trimethyl chloro-silane (C11H17ClO2SSi, > 99.5%), bis(trimethylsilyl)trifluoroacetamide (C8H18F3NOSi2, > 99.0%), diethyl ether ((CH3CH2)2O, > 99.8%), pyridine (C5H5N, > 99.8%), chloroform (CHCl3, > 99.5%), and, ethyl acetate (CH3COOC2H5, > 99.7%). were supplied by Sigma-Aldrich Co., USA. Stock solution of each compound was prepared using deionized water.
2.2 Date palm pits extract preparation (DPE)
Date palm pits were gathered and washed manually by distilled water to remove any residual impurities. After drying, they were ground by using Retsch ZM200 titanium mill, Germany.
Date palm pits extract was created as follows; 20 g of crushed date palm pits powder were added to 500 mL of distilled water and stirred continuously for 18 h using a magnetic stirrer followed by filtration. The remaining dried powder weighed 14.5 g, implying that the produced extract comprised approximately 5.5 g of the dissolved date palm pit components. The solution containing DPE was stored in clean glass bottles at 5 oC for successive uses.
2.3 Fabrication of solid adsorbents
2.3.1 Preparation of date palm fiber biochar (C)
Date palm fiber was chopped into small pieces, washed with pure water to remove associated pollutants and dust, dried at 120 oC, and crushed into powder. The biochar was produced using a slow pyrolysis technique involving the powder of date palm fiber (DPF) in a muffle furnace. The temperature gradually rose to 300°C with a heating rate of 15 oC/min and kept for 1 h before being elevated to 550°C and held for 2 h. The increased temperature accelerates the pyrolysis process and improves the biochar's properties. After this duration, the system was cooled to the ambient temperature.
2.3.2 Preparation of date palm fiber biochar/chitosan nanoparticles (CCS)
The chitosan-modified date palm fiber biochar was prepared by combining 1.0 g of chitosan with 2%, 100 mL of acetic acid. The solution was stirred for 6 h before adding 1.0 g of the created biochar to the chitosan solution. The previous mixture was agitated with a stirrer for 2 h to achieve a uniform suspension. The produced homogeneous solution was dropped using microsyringe into 1.0 mol/L, 200 mL of sodium hydroxide solution. The produced beads were filtered and washed numerous times with ultra-pure water until a neutral washing solution. The washed beads were dried for 24 h at 90 oC, and grinded in Retsch ZM200 titanium mill. The obtained fine powder of biochar/chitosan (0.5 g) was transferred into nanoparticles by sonication (Probe Sonicator IG-96A), for 15 min in the presence of 150 mL of the pre-prepared DPE solution which acts as a caping agent for the formed nanoparticles. Filtered via centrifugation and dried at 120 oC for 10 h [20, 21].
2.3.3 Preparation of d biochar/chitosan nanoparticles supplemented with glutamine (CCSG)
It is prepared in the same manner as before (sec.2.3.2), except for adding 0.1 g of glutamine to the previously prepared chitosan solution.
2.4 Characterization and analysis
Numerous organic natural chemicals found in the recovered DPE operate as environmentally acceptable anticoagulant capping agents for nanoparticles. The 0.5 g of powdered date palm was acidified with HCl, allowed to cool, and then diethyl ether and ethyl acetate were used to extract the extract. The extracted solution was then evaporated under vacuum at 45°C. The extracted sample was resuspended in 60 µL of BSTFA (bis(trimethylsilyl)trifluoroacetamide) + TMCS (trimethylchloro-silane) 99:1 silylation reagent and 50 µL of pyridine to convert functional groups to trimethylsilyl groups (abbreviated TMS) before GC analysis. The GC-MS technique (Agilent Technologies) was set with gas chromatograph (7890B) and detector of mass spectrometer (5977A) The GC was operational with DB-5MS column (internal diameter of 30 m x 0.25 mm and 0.25 µm as a film thickness). Analyses were carried out using H2 as the carrier gas at 1.0 ml/min as flow rate of at a splitless, injection volume of 1 µL. The temperature program fwas adjusted to be: 60°C for 1 min; increasing to 10°C /min up to 320°C and for 10 min. At 300°C, 320°C, the injector and detector were held. Mass spectra were obtained by electron ionization (EI) at 80 eV: using a spectral range of m/z 50–800 and solvent delay 4.2 min. The mass temperature was 230°C and Quad 150°C. By comparing the spectrum fragmentation pattern with those found in Wiley and NIST Mass Spectral Library data, many natural materials might be recognized.
The thermal behavior of DPF, C, CCS, and CCSG was determined using a thermoanalyzer (SDT Q600 V20.9 Build 20, UK) at a nitrogen flow rate of 20 mL/min and a heating rate of 15 oC/min up to 900 oC.
Nitrogen gas adsorption/desorption was used to measure the specific area of surface (SBET, m2/g), pore size( \(\:\stackrel{-}{r}\), nm), and total pore volume (VP, cm3/g) of C, CCS, and CCSG using NOVA 3200e gas sorption analyzer (Quantachrome Corporation, USA). Prior to N2 gas adsorption, the solid samples (50 mg) were degassed for 16 h at 10− 4 Torr and 120°C.
Scanning electron microscopy (JEOL JSM-6510LV model, Japan) was used to investigate the morphology of solid adsorbents (C, CCS, and CCSG). The samples were prepared via deposition on an aluminum holder covered in a carbon grid and then coated with a thin gold layer under high vacuum. The SEM was run at 15 kV as an accelerating voltage.
Transmission electron microscopy employing a JEOL-JEM-2100 model from Japan is also used to study the morphology of produced adsorbent particles (C, CCS, and CCSG). The samples were sonicated for 60 min in ethanol before being transferred to a copper grid.
Surface functional groups for all solid adsorbents were analyzed using Attenuated total reflectance with Fourier transform infrared (ATR -FTIR) spectroscopy at 4000–400 cm− 1, with ten sequential scans at resolution.
Zeta potentials for each adsorbent were measured to evaluate pHPZC in pH range of 2–12. The solid adsorbent material's surface is positively charged for pH values less than pHPZC and negatively charged at pH levels more than pHPZC. The measurement of pHPZC is crucial in understanding how solid adsorbents adsorb heavy metal cations.
2.5 Adsorption experiments
The adsorption of As5+ by all synthesized solid adsorbents (C, CCS, and CCSG) was investigated using a batch adsorption technique that involved shaking 25 mL of As5+ solution with 400 mg/L and 0.025 g of adsorbent mass at pH 6, 27 oC, and for 90 min. The adsorbate solution was shaken before being centrifuged at 3000 rpm for 10 min. Then, the concentration at equilibrium Ce (mg/L) of As5+ was determined by a hydride generation-atomic absorption spectrometer (HG-AAS; AgilentAA240 with VGA–77; Australia). Three sets of measurements were made, and the average values were utilized. The percentage of removal (R%) of As5+ and the equilibrium sorption capacity Xe (mg/g) were calculated using (Eqs. 1, 2, Table 1), respectively. The effects of various application settings, such as adsorbent solid dosage (0.1–2.0 g/L, mass in g/volume in L), pH (1–9), contact shaking time (5–90 min), starting As5+ concentration (50–500 mg/L), temperature (27–47 oC), and initial solution ionic strength (µ, 0.05–0.40 mol/L), were investigated by a series of batch adsorption studies.
|
Model name |
Models |
Symbols significance |
Number |
|---|---|---|---|
|
Removal percentage |
\(\:R\%=\frac{({C}_{i}-{C}_{e})}{{C}_{i}}\times\:100\) |
Ci (initial conc. of As5+, mg/L) Ce (equilibrium conc. of As5+, mg/L) |
1 |
|
Equilibrium adsorption capacity |
\(\:{X}_{e}=\frac{({C}_{i}-{C}_{e})}{m}\times\:V\) |
Xe (equilibrium sorption capacity, mg/g) V (volume of As5+solution, L) m (mass of solid adsorbent, g) |
2 |
|
Kinetic models |
|||
|
Adsorption capacity at certain time |
\(\:{X}_{t}=\frac{({C}_{i}-{C}_{t})}{m}\times\:V\) |
\(\:{X}_{t}\)(adsorption capacity in mg/g at time t, min) |
3 |
|
Pseudo-first order |
\(\:{X}_{t}={X}_{exp}(1-{e}^{-{k}_{1}t})\) |
k1 (PFO rate constant, min− 1) |
4 |
|
Pseudo-second order |
\(\:{X}_{t}=\:\frac{{{X}_{exp}}^{2}{k}_{2}\:t}{1+\:{X}_{exp}\:{k}_{2}\:t}\) |
Xexp (experimental adsorption capacity, mg/g) k2 (PSO rate constant, g/mg.min) |
5 |
|
Elovich |
\(\:{X}_{t}=\frac{1}{\beta\:}Ln(1+\alpha\:\beta\:t)\) |
\(\:\alpha\:\:\)(initial rate of As5+adsorption, mg/g.min) \(\:\beta\:\:\)(extent of surface coverage, g/mg) |
6 |
|
Adsorption isotherm models |
|||
|
Langmuir |
\(\:{X}_{e}=\frac{b{X}_{m}{C}_{e}}{1+b{C}_{e}}\) |
\(\:b\:\)(Langmuir constant, L/mg) Xm (maximum Langmuir adsorption capacity, mg/g) |
7 |
|
Separation factor |
\(\:{R}_{L}=\frac{1}{1+b{C}_{i}}\) |
\(\:{R}_{L}\:\)(separation factor) |
8 |
|
Freundlich |
\(\:{X}_{e}={K}_{F}\:{C}_{e}^{\frac{1}{n}}\) |
n (Freundlich constant related to the adsorption intensity) KF (Freundlich constant related to the extent of adsorption, L1/n. mg1–1/n/g) |
9 |
|
Temkin |
\(\:{X}_{e}\:=\frac{R\:T}{{b}_{T}}\text{ln}{K}_{T}\:{C}_{e}\) |
R (universal gas constant, 8.314 J/mol. K) T (absolute adsorption temperature, K) KT (equilibrium binding constant, L/g) bT (Temkin constant, J/mol) |
10 |
|
Dubinin-Radushkevich |
\(\:{X}_{e}=\:{X}_{DR}\:{e}^{-{K}_{DR\:\:}{\epsilon\:}^{2}}\) |
XDR (D-R adsorption capacity, mg/g) KDR (D-R constant, mol2/kJ− 2) EDR (mean adsorption-free energy, kJ/mol) |
11 |
|
Mean adsorption-free energy |
\(\:{E}_{DR}\:=\:\frac{1}{\sqrt{2{K}_{DR}}}\) |
12 |
|
|
Thermodynamic studies |
|||
|
Distribution constant |
\(\:{K}_{s}=\:\frac{{C}_{s}}{{C}_{e}}\) |
Cs (surface adsorbed As5+, mg/g) |
13 |
|
Van’t Hoff |
\(\:\text{ln}{K}_{s}=\:\frac{\varDelta\:S^\circ\:}{R}\:-\:\frac{\varDelta\:H^\circ\:}{RT}\) |
\(\:\varDelta\:S^\circ\:\:\)(entropy change, kJ/mol. K) \(\:\varDelta\:H^\circ\:\:\)(heat change, kJ/mol) |
14 |
|
Gibbs free energy |
\(\:\varDelta\:G^\circ\:=\varDelta\:H^\circ\:-T\varDelta\:S^\circ\:\) |
\(\:\varDelta\:G^\circ\:\:\)(Free energy change, kJ/mol) |
15 |
The adsorption activity was observed, and the obtained data were analyzed to provide insights into the adsorption mechanisms and the efficiency of solid adsorbent materials for As5+removal. Several adsorption parameters were computed using several kinetics and equilibrium nonlinear adsorption models.
The kinetics investigation was conducted on As5+ adsorption onto C, CCS, and CCSG using nonlinear expressions of pseudo-first order (PFO, Eq. 4), pseudo-second order (PSO, Eq. 5), and Elovich (Eq. 6). While nonlinear isotherm models, featuring Langmuir (Eq. 7), Freundlich (Eq. 9), Temkin (Eq. 10), and Dubinin-Radushkevich (Eq. 11) were used to analyze equilibrium data of As5+ adsorption on C, CCS, and CCSG as given in Table 1.
Three thermodynamic parameters namely change in enthalpy, (ΔH°, kJ/mol), change in entropy, (ΔS°, kJ/mol.K), and Gibb’s free energy, (ΔG°, kJ/mol) were estimated by Eqs. 14, 15 (Table 1).
Table 1: Applied models depict the adsorption process.
2.6 Desorption and reusability experiment
Desorption of As5+ tests are important for regenerating the three chosen adsorbents (C, CCS, and CCSG). Desorption was studied by adding 0.10 g of solid to 100 mL of 400 mg/L As5+ at pH 6, stirring, and 27°C. After 25 min, the adsorbents were rinsed with 100 mL of 0.1 mol/L desorbing agent (dist. water, HCl, HNO3, ethylene diamine, cysteine, and EDTA). The desorbed concentration of As5+ in solution was assessed using the predefined atomic absorption spectrometer. The desorption percentage was calculated using Eq. 16 to evaluate the solid nanoparticles performance after frequent application.
where Cd is the equilibrium metal ion (As5+) concentration after desorption from adsorbents (mg/L), m is the mass of solid adsorbent (g), V is the desorbing agent volume (L), and Xm is the adsorbent's greatest capacity of adsorption (mg/g).
3.1 Characterization techniques
3.1.2 GC-M examination of date palm pits extract
The chemical content of the extract of date palm pits (DPE) was analyzed using GC-MS (gas chromatography-mass spectrometry) and the obtained data is presented in Table S1. Figure S1 shows a chromatogram of DPE of the most active discovered chemicals. There were twenty chemical compounds found in DPE, with the most common being 9-octadecenoic acid, (E)-, TMS derivative (20.33%), dodecanoic acid, TMS derivative (15.89%), Hydroquinone, 2TMS derivative (12.41%), and palmitic acid, TMS derivative (11.64%). The data in Table S1 revealed that the extract also contained acids, alkanes, alkyl benzenes, aromatic benzene derivatives, alcohols, carboxylic acids, fatty acid derivatives, glycerides, lipids, phytosterols, terpenes, and steroids. DPE has a vital role as anticoagulant capping agent which acts as stabilizer by inhibiting nanoparticles overgrowth and preventing aggregation/coagulation because of the attendance of numerous active chemical mixtures which are rich in hydroxyl groups (Shu et al. 2020). So, causing the creation of nanostructures.
3.1.3. Characterization of solid adsorbents
Figure 1a shows thermal analysis curves for DPF, C, CCS, and CCSG. Weight loss of 0.9, 3.2, and 3.6% was found for C, CCS, and CCSG, respectively at 120 ℃ due to the removal of absorbed water (Gemeay et al. 2021). Biochar with lesser hydrophilic surface functional groups is superior to that treated with chitosan or reinforced with glutamine. The date palm fiber (DPF) mass loss occurred in four stages. The first stage up to 120°C, was due to moisture loss (vaporization), representing 6.3% of the total weight loss. From 260–340 oC, the second stage of mass loss involves the degradation of low molecular weight hemicellulose ([C5(H2O)4]n) with additional mass loss of 30.7%. The third phase of the mass loss at from 320–380°C corresponds to the heat breakdown of cellulose ([C6(H2O)5]n). The final stage is about decomposition of lignin ([C10H12O3]n) ranging from 300–580°C [24, 25]. Biochar solid sample (C) graph shows that weight loss (18.31 wt%) was occurring between 250 and 400°C. Aliphatic structures decomposed at temperatures exceeding 250°C. The discharge of volatile chemical compounds such as CO2 was produced by the breakdown of the date palm biochar's functional groups (carboxylic acid groups and lactones) (Hadj-Otmane et al. 2024). The breakdown of anhydride, carbonyl, and ether operates by releasing CO and CO2 at temperatures ~ 350°C (Wang et al. 2021). Over 400°C, the mass loss is connected with the dissolution of aromatic rings that exist on the surface of biochar, which occurs by liberating volatile chemicals [28, 29]. The thermal degradation for CCS and CCSG started at approximately 160°C, and continued until 450°C, with weight loss of ~ 51.88%. During the temperature between 250 ℃ to 340 ℃ in CCS thermal curve, a significant weight loss was observed due to chitosan chain decomposition and oxidation, sugar ring dehydration, and polymer degradation (Chen et al. 2022). At temperatures above 600 oC, which represents the ash remains, almost no mass loss was found. This result suggests the chitosan was not merely adhered on the date palm fiber biochar surface, but rather complexly linked together.
Textural characterization of solid adsorbent is an important technique to describe the capacity of adsorption and way of pollutant adsorption. Figure 1b shows the porous structure property of the produced adsorbents as measured by the N2 adsorption/desorption isotherms. Porous structure is characterized by the specific surface area (SBET, m2/g), pore volume (VP, cm3/g), and average pore radius (\(\:\stackrel{-}{r}\), nm) which are listed in Table 2. The prepared materials are classified as type II isotherm by the IUPAC (International Union of Pure and Applied Chemistry) with H4 hysteresis loop for C and CCS and H3 hysteresis loop for CCSG [6, 26, 31]. The specific surface area and pore volume for samples were found to be 349.09 m2/g, 0.21 cm3/g for C, 499.51 m2/g, 0.26 cm3/g for CCS, and 518.69 m2/g, 0.25 cm3/g for CCSG. The order of SBET values from the highest is: CCSG, CCS, and C. The pore volume change is comparable to that of the SBET. The results revealed that date palm fiber biochar particles improved significantly after modification in terms of pore volume and surface area. It is obvious that the insertion of biochar in the chitosan matrix followed by modification with glutamine results in a greater surface area, which may be associated to the disruption and solid structure heterogeneity. Furthermore, the average pore size for C (1.22 nm) ˃ CCS (1.05 nm) ˃ CCSG (0.97 nm) which indicates the microporous and mesoporous character of the samples.
| Parameters | C | CCS | CCSG |
|---|---|---|---|
| SBET (m2/g) | 349.09 | 499.51 | 518.69 |
| VP (cm3/g) | 0.21 | 0.26 | 0.25 |
| \(\:\stackrel{-}{\varvec{r}}\) (nm) | 1.22 | 1.05 | 0.97 |
| pHPZC | 6.20 | 6.60 | 6.90 |
Various surface chemical functional groups of the adsorbents (C, CCS, and CCSG) were exposed to ATR-FTIR analysis in the range of 4000–400 cm− 1 as presented in Fig. 1c. The stretching bands at about 1063 (C–O), 1438 (–CH2), 1573 (C = O), 2976 (–CH), and 3373 cm− 1 (–OH) were observed from ATR-FTIR spectra of C [32]. Correspondingly, in the ATR-FTIR spectra of CCS, the chemical functional groups mentioned above were observed around the appropriate wavenumber. However, the peak at 1573 cm− 1 shifted to 1555 cm− 1 for amide I (C = O stretching), and a new peak appeared at 1656 cm− 1 for amide II (bending modes of N-H) indicated that the carboxyl groups reacted with chitosan during composite formation [33]. While CCSG has witnessed structural changes, namely the emergence of –COOH and –CONH–. At 3167, 1500, and 1407 cm− 1, respectively, the stretching vibration peak of -OH, the stretching vibration peak of C = O, and the bending vibration absorption peak of -COOH were identified. The bending vibration peak in -NH and The C = O stretching vibration peak in -CONH- emerged at 1580 and 1675 cm− 1, respectively, confirming the presence of -COOH and -CONH- in CCSG structure [34].
Most adsorption systems rely on electrostatic interactions between adsorbents and adsorbates. Measuring the surface charge of the adsorbent is crucial for confirming the possibility of electrostatic interactions. The zeta potential was used to evaluate the chemical surface charge as elucidated in Fig. 1d and calculate the point of zero charge (pHPZC) as given in Table 2. The PZC was determined to be 6.2, 6.6, and 6.9 for C, CCS, and CCSG. At pH < pHPZC, the surface charge of all synthesized adsorbents is positive while at pH > pHPZC, the surface charge is negative.
Figure 1: TGA curves (a), N2 adsorption (b), ATR-FTIR spectra (c), and pHPZC (d) for C, CCS, and CCSG. In addition to TGA of date palm fiber (DPF).
SEM was used to examine samples (C, CCS, and CCSG) structure and morphology, the magnification pictures given in Figs. 2a–c. The SEM picture Fig. 2a of the C shows stacked rocky layers structure with many pores which is a representative of biochar solid material, irregular, and a rather smooth surface [35, 36]. After modification, the surface of CCS became rough, with tiny particles holding on to the surface Fig. 2b which might be related to the
enhancement of superficial area. These tiny particles were probably chitosan. Furthermore, these microscopic particles remained on the surface of the CCSG as shown in Fig. 2c which in turn proves the distribution of chitosan and glutamine amino acid on the CCSG surface.
Figure 2: SEM (a–c) and TEM (d–f) images for C, CCS, and CCSG, respectively.
Figures 2d–f exhibit TEM micrographs of the manufactured solid adsorbents. Figure 2d shows that C has a layered and porous structure due to the biochar's intrinsic nature [32]. Compared to C in Fig. 2d, the surfaces of CCS and CCSG in Figs. 2e, 2f showed a noticeable sparkle and clusters, indicating that the chitosan and glutamine amino acid had been constructed on the surface. It became apparent that the C, CCS, and CCSG TEM particle sizes were approximately 450, 23, and 38 nm, respectively. The resultant solid particles disperse when biochar is inserted into the biopolymer framework in CCS and CCSG, which has distinct characteristics from the two solids.
Table 2: Characterization parameters for the fabricated solid adsorbents.
3.2 Static adsorption removal of As5+
3.2.1 Impact of solid dose
The study examined the effect of different quantities of solid adsorbents (C, CCS, and CCSG) on adsorption efficiency (R%) as shown in Fig. 3a. While the Removal% of As5+ was computed using Eq. 1. At a pH 6 and 27°C, 0.1 to 2.0 g/L of adsorbent dose was combined with 25 mL of As5+ solution (400 mg/L) and stirred at 3000 rpm for 90 min. The adsorption efficiency increased from 21, 38, and 68% at 0.1 g/L to 43, 65, and 93% at 1.0 g/L for adsorbents (C, CCS, and CCSG), respectively. The increase in the removal percent by nearly 2.1, 1.7, and 1.4 times increase for C, CCS, and CCSG, respectively. The increase in the capacity of adsorption can be connected to the increase in active sites/As5+ ratio. Maximum adsorption occurred at a solid sorbent dosage of 1.0 g/L on CCSG, which may be attributed to the presence of hydrophilic and negatively charged -NH2, -OH, and -COOH groups that provide more binding sites for As5+. In addition, due to the large surface area confirmed by the N2 adsorption/desorption. High adsorbent doses resulted in poor As5+ adsorption, possibly owing to the occurrence of unsaturated binding active sites and the absence of available As5+. However, fixed As5+ concentrations reduce sorption capacity (Niazi et al. 2024)38]. To investigate further adsorption parameters, a dosage of 1.0 g/L of all adsorbents was chosen based on these results.
3.2.2 Effect of starting solution pH
The pH has a direct impact on both the adsorbent active sites and the shape of pollutant ions (As5+). To test the effect of pH on solid adsorbents (C, CCS, and CCSG), the solution's pH was adjusted using either 0.1 M NaOH and/or 0.1M HCl from 1 to 9 with 0.025 g solid adsorbents, 25 mL of 400 mg/L As5+ at 27 oC, and 90 min shaking duration as illustrated in Fig. 3b. It is perceived that As5+ adsorption is limited at lower and higher pH values. The highest As5+ adsorption occurs at pH 6. It achieves adsorption capacity of 42, 63, and 92% for C, CCS, and CCSG, respectively. The removal % gradually increased from 1–6 and slightly dropped from 6 to 9. Proton ions (H3O+) is more adsorbed than As5+ at lower pH levels (< pHPZC) due to the more ionic mobility of proton than arsenic ion forms (H2AsO4− and HAsO4 − 2 ) [32, 39]. Figure 1d shows that C, CCS, and CCSG had a point of zero charge (pHpzc) of around 6.2, 6.6, and 6.9, respectively. When pH exceeds pHpzc, the surface of adsorbents acquired negative charges, which may hinder arsenic species (HAsO42–) adsorption owing to the established electrostatic repulsion (Gan et al. 2015). However, when the pH was higher than neutral, the adsorption effectiveness decreased due to polymer chain shrinkage caused by deprotonation of chitosan amino groups (Rahmi 2018). CCSG outperformed C and CCS in terms of As5+ adsorption, suggesting that the addition of chitosan and glutamine was beneficial for As5+ removal. It is possible that protonation of -NH2 and -OH resulted in positively charged molecules that show considerable promise for sequestering As5+ (in the form of AsO4 − 3 and AsO3−) via electrostatic attraction. Consequently, pH6 was nominated as the most suitable pH for As5+ adsorption from aqueous medium onto all the investigated adsorbents.
Figure 3: The impact of adsorbent dose (a) and pH (b) on As5+ adsorption onto C, CCS, and CCSG (Ci = 400 mg/L, T = 27 oC, and t = 90 min).
3.2.3 Kinetic studies and impact of shaking time
The kinetics of As5+ adsorption onto C, CCS, and CCSG samples was studied from 5 to 90 min at pH 6, 25 mL, 400 mg/L As5+, solid dose (1.0 g/L), temperature (27°C) to further determine the adsorption mechanism of the adsorbents. We evaluated the kinetic indicators of three adsorbents using PFO (Eq. 4, Fig. 4a), PSO (Eq. 5, Fig. 4b), and Elovich (Eq. 6, Fig. 4c) nonlinear models. Table 3 shows the model parameters for removing As5+ metal ions on solid samples. At the beginning of adsorption time, the rapid adsorption of As5+ on the adsorbents could be attributed to the abundance of available active sites where the ration of solid active sites/ As5+ is higher. Then, as the adsorption sites were depleted, the adsorption capacity slowly increased until reaching equilibrium after 25 min. The time-dependent adsorption data was successfully fitted by PFO kinetic model based on correlation coefficients R2 (0.9439–0.9730) and reduced chi-squared χ2 (1.8681–3.4750) for all solid samples. Furthermore, the adsorbed amount of As5+ metal ions calculated using PFO model closely corresponded to the experimental one which is derived from the Langmuir Eq. (1.99, 2.38, and 0.74% as differences in the cases of C, CCS, and CCSG, respectively). Despite R2 values for the adsorption of As5+ ions by PSO kinetic model are nearly high (0.8542–0.8984). However, there was a substantial discrepancy between the estimated and observed Langmuir adsorption capacities (17.28, 16.72, and 20.72% for C, CCS, and CCSG, respectively). In addition to the higher calculated reduced chi-squared χ2 (5.1629–14.4098) proves the invalid application of PSO in comparison with PFO nonlinear model. This revealed that PSO model could not best describe the As5+ adsorption, because the investigational adsorption capabilities did not accord with the model's hypothetical prospects. Hence, the PFO model is the beneficial kinetic model, indicating the physical adsorption process [42, 43]. The Elovich model has good applicability for As5+ adsorption (R2 = 0.8926 on average). CCS and CCSG had significantly higher α values than C, indicating an increase in the primary rate of adsorption after modification. The degree of surface coverage (β, g/mg) value, is inversely linked to the correspondence of adsorbate to adsorbent, is significantly lower for CCS and CCSG compared to C demonstrating that the modified ones (CCS and CCSG) exhibit greater affinity to As5+ than C (Nguyen et al. 2020).
| Models | Parameters | C | CCS | CCSG | |
|---|---|---|---|---|---|
| PFO | Xexp (mg/g) | 147.5 | 249.9 | 373.2 | |
| k1 (min− 1) | 0.0840 | 0.0771 | 0.0739 | ||
| R2 | 0.9439 | 0.9688 | 0.9730 | ||
| χ2 | 1.8681 | 3.1290 | 3.4750 | ||
| PSO | Xexp (mg/g) | 176.5 | 298.8 | 453.9 | |
| k2 (g/mg.min)×10− 4 | 4.9953 | 2.5606 | 1.6013 | ||
| R2 | 0.8542 | 0.8984 | 0.8901 | ||
| χ2 | 5.1629 | 6.2058 | 14.4098 | ||
| Elovich | α (mg/g.min) | 19.7859 | 33.1947 | 47.6115 | |
| β (g/mg) | 0.0233 | 0.0129 | 0.0084 | ||
| R2 | 0.8827 | 0.8972 | 0.8979 | ||
| χ2 | 4.7160 | 9.9450 | 22.5613 | ||
| Langmuir | Xm (mg/g) | 150.5 | 256.0 | 376.0 | |
| b (L/mg) | 0.11821 | 0.0759 | 0.1163 | ||
| RL | 0.0207 | 0.0319 | 0.0210 | ||
| R2 | 0.9797 | 0.9820 | 0.9910 | ||
| χ2 | 0.9230 | 3.4948 | 3.3513 | ||
| Freundlich | 1/n | 0.2472 | 0.3477 | 0.2989 | |
| KF (L1/n. mg1 − 1/n/g) | 46.6780 | 48.3148 | 95.9714 | ||
| R2 | 0.7603 | 0.8443 | 0.8292 | ||
| χ2 | 4.3942 | 14.3297 | 19.0735 | ||
| Temkin | bT (J/mol) | 28.6213 | 56.1971 | 77.5609 | |
| KT (L/g) | 1.6615 | 0.6723 | 1.1925 | ||
| R2 | 0.8574 | 0.9348 | 0.9165 | ||
| χ2 | 4.6134 | 5.9995 | 9.3233 | ||
| Dubinin-Radushkevich | XDR (mg/g) | 148.6 | 251.9 | 361.5 | |
| KDR (kJ/mol) | 0.4842 | 0.6264 | 0.4416 | ||
| EDR (kJ/mol) | 1.0162 | 0.8934 | 1.0641 | ||
| R2 | 0.9869 | 0.9942 | 0.9876 | ||
| χ2 | 0.2397 | 0.5329 | 1.3871 | ||
| Thermodynamic parameters | R2 | 0.9186 | 0.9307 | 0.9264 | |
| ΔHo (kJ/mol) | 4.8284 | 4.6216 | 6.4387 | ||
| ΔSo (kJ/mol.K) | 0.0369 | 0.0389 | 0.0320 | ||
| ‒ΔGo (kJ/mol) | 27 ℃ | 6.2464 | 7.0475 | 3.1727 | |
| 34 ℃ | 6.5051 | 7.3198 | 3.3970 | ||
| 40 ℃ | 6.7266 | 7.5531 | 3.5892 | ||
| 45 ℃ | 6.9112 | 7.7476 | 3.7494 |
Figure 4: Nonlinear PFO (a), PSO (b), and Elovich (c) nonlinear kinetic equations for the adsorption of As5+ onto C, CCS, and CCSG (T = 27 oC, Ci = 400 mg/L, dosage 1.0 g/L, pH = 6, t = 5–90 min).
3.2.4 Static adsorption isotherms and effect of initial concentration
Figure 5a–d shows the equilibrium adsorption isotherms as nonlinear Langmuir (Eq. 7, Fig. 5a), Freundlich (Eq. 9, Fig. 5b), Temkin (Eq. 10, Fig. 5c), and Dubinin-Radushkevich (Eq. 11, Fig. 5d) models. While related isotherm parameters are presented in Table 3. These isotherms predict adsorption based on mutual interactions between adsorbate and adsorbent with different principles especially Langmuir and Freundlich with contradictory postulates. The adsorption isothermal experiment was conducted at pH 6, 1.0 g/L solid dosage, temperature (27°C), and starting As5+ concentration (50–500 mg/L). Increasing the initial concentration of As5+ may improve adsorption capacity since a high concentration gradient encourages As5+ ions to diffuse towards adsorption sites of solid adsorbents (C, CCS, and CCSG) (Zhou et al. 2020). However, further increasing starting As5+ concentration could not improve adsorption capability due to restricted adsorption sites in solid adsorbents (Song et al. 2018). The Langmuir, Dubinin-Radushkevich, and Temkin nonlinear models are more accepted than the Freundlich model due to greater coefficients of correlation (R2) and lower reduced chi square (χ2) values as shown in Table 3. All model fits had R2 values more than 0.8574, suggesting strong significance. The prepared adsorbents had Langmuir maximum adsorption capacities follow this sequence CCSG ˃ CCS ˃ C (376.0, 256.0, and 150.5 mg/g, respectively). This could be due to the existence of novel surface chemical functional groups on the composites' surface, in addition to their larger surface areas. The RL estimates (Eq. 8) for all the adsorbents in this investigation are 0 < RL < 1, indicating a good adsorption process. On the other hand, the correlation coefficient values produced for the nonlinear Freundlich model are lower than those calculated for the Langmuir model for all solid samples. The Langmuir model exceeded the Freundlich model in describing As5+ sorption, demonstrating that monolayer sorption was the dominating process on all three sorbent homogenous surfaces. The Freundlich model parameter (sorption intensity, 1/n) determines whether the process of adsorption was chemisorption in nature (for 1/n > 1) or physisorption (for 1/n < 1), based on heterogeneity (Yao et al. 2024). In the current study, 1/n revealed values below one, indicating the physisorption mechanism. CCS and CCSG had higher sorption intensity (1/n) and KF (L1/n/ mg1 − 1/n. g) than C, indicating a stronger capacity to adsorb As5+. The Temkin model effectively applies As5+ adsorption across all samples, as evidenced by high correlation values (0.8574–0.9348). The lower Temkin isotherm constant bT values (bT ˂ 8000 J/mol) (28.6213–77.5609 J/mol) reflect physical adsorption process between the adsorbate and adsorbent (Kamal et al. 2019). bT (J/mol) is inversely associated with the adsorption heat (Ao et al. 2012). The endothermic nature of the adsorption process is suggested by the positive values reported for bT. (Adeogun and Babu 2021). The R2 values found in DR model (Dubinin-Radushkevish) isotherm model for As5+ were among 0.9869 and 0.9942 for all three sorbents. The Dubinin-Radushkevich equation yields almost similar adsorption capacity (XDR) to the Langmuir model. If the EDR value is less than 8 kJ/mol, adsorption is thought to be a physical process with pore-filling as the primary mechanism (Niazi et al. 2018). If the EDR value is between 8.0–16.0 kJ/mol, chemical adsorption and ion exchange yield control of the process. Our data indicates that As5+ rapidly occupies accessible adsorption sites on the solid adsorbents surface, with EDR values ranging from 0.8934 to 1.0641 kJ/mol. This suggests that physical sorption is the major mechanism.
Figure 5: Nonlinear Langmuir (a), Freundlich (b), Temkin (c), and D-R (d) fitting for As5+ adsorption onto C, CCS, and CCSG (T = 27 oC, Ci = up to 500 mg/L, solid dose 1.0 g/L, pH = 6, t = 25 min).
Table 3: Kinetic, isotherm nonlinear, and thermodynamic parameters for the adsorption of As5+ onto C, CCS, and CCSG at 27 oC.
3.2.5 Effect of adsorbate solution ionic strength
Batch tests were assumed to investigate the effect of foreign ions on adsorption system at various concentrations of NaCl to simulate real-world adsorption conditions, and the results are given in Fig. 6a. Each NaCl solution is given at different dosage to achieve a range of ionic strength (µ, 0.05–0.40 mol/L). The As5+ initial concentration was kept at 400 mg/L, and the solution volume was 25 mL with 1.0 g/L of adsorbent dosage (C, CCS, and CCSG) at 27 oC. Obviously, the quantity of As5+ adsorbed decreases as the ionic strength rises from NaCl µ, 0.05–0.40 mol/L. The attachment of As5+ ions to the surface of C, CCS, and CCSG is hampered by the interference of sodium and chloride ions (Makhlouf et al. 2024). Increasing the ionic strength of the adsorption solution from nearly µ ≈ 0.05 to µ ≈ 0.40 reduces As5+ removal from 43 to 26%, 65 to 48%, and 94 to 77% for C, CCS, and CCSG, respectively (with nearly 17% decrease). External ions (Na+ and Cl−) can greatly increase the thickness of the diffuse electric double layer, which protects adsorbents and As5+ in solution. This keeps As5+ and adsorbent particles from coming too close together, lowering their electrostatic attraction and slowing the adsorption process. Higher electrolyte concentrations can cause electrolyte ions to block surface negative charges, reducing the overall quantity of As5+ adsorbed. Although foreign ions have a negative impact on the adsorption efficiency, this percentage indicates that even at elevated concentrations of interferents ions, the prepared samples (C, CCS, and CCSG) exhibit accepted selectivity for the uptake of As5+ ions.
3.2.6 Influence of adsorption temperature and thermodynamic parameters
It's important to analyze the obtained parameters of thermodynamic (ΔS°, ΔH°, and ΔG°), which indicate changes in entropy, enthalpy, and free energy to realize the energetics of As5+ removal by C, CCS, and CCSG. The parameters (ΔS° and ΔH°) were obtained using the Van’t Hoff equation (Eq. 14, Fig. 6b), whereas ∆G° (free energy change) was calculated using Eq. 15. These values are shown in Table 3. The adsorption followed the temperature coefficient, as seen in Fig. 6b by the strong linear relationship between Ln (KS) and 1/T. The higher correlation coefficients (R2) values for the Van't Hoff plot, which ranged between 0.9186 and 0.9307, demonstrate the model's applicability. It is confirmed that the adsorption process is endothermic in nature requiring additional energy based on the calculated positive value of ΔH°. This is due to the fact that solvated water molecules must be displaced by As5+ ions. (Ananta et al. 2015). The heat values for physical adsorption range from 20–40 kJ/mol and chemisorption from 40–400 kJ/mol. According to our results, the values of ΔH° (4.6216–6.4387 kJ/mol) demonstrated a physical adsorption process. The increase in ΔS° values implies a rise in system entropy due to randomness at the interface between solid surface and liquid phases. This rise in entropy is caused by the displacement of water molecules by As5+ ions to adsorb on the surface of adsorbents. Moreover, the decrease in ΔG° values suggest that As5+ adsorption by all solid adsorbents is thermodynamically viable and spontaneous. As temperature increases, the value of ΔG° lowers, indicating that As5+ adsorption is increasingly practicable (Mahmoud et al. 2020). In general, physical adsorption has a lower ∆G° (-20 to 0 kJ/mol) compared to chemical adsorption (-80 to -400 kJ/mol). As a result, the adsorption of As5+ was classified as physical adsorption based on the negative values of ∆G° (3.1727–7.7476 kJ/mol).
3.3 Desorption and reusability of solid adsorbents
An ideal adsorbent should have elevated adsorption capacity and properties of desorption efficient for purpose of reduction the treatment cost (Moslehi et al. 2024). This study tested the stability and reusability of adsorbents (C, CCS, and CCSG) using 0.1 mol/L desorbing agent (dist. water, HCl, HNO3, ethylene diamine, cysteine, and EDTA) to desorb As5+. Figure 6c displays the efficiency of desorption (D.E%, Eq. 16) of As5+ from the C, CCS, and CCSG surface, with different solutions. EDTA is the most effective solvent for pre-adsorbed As5+.
The removal efficacy of As5+ by C, CCS, and CCSG reduced after the first and sixth cycles, as follows in Fig. 6d: 43–40%, 64–58%, and 94–90% for C, CCS, and CCSG, respectively. After six cycles of sorption and desorption, the As5+ sorption capacity of solid adsorbents reduced slightly. Higher removal rates in the first cycle of applications can be related to the presence of abundant more active sites. After the first sorption-desorption cycle, As5+ sorption decreased slightly during the other regeneration cycles. This could be due to adsorbent binding sites saturation or a partial loss of the adsorbent's uptake sites during the cleaning phase of the adsorption-desorption test (Saning et al. 2024).
Figure 6: Effect of ionic strength (a), Van’t Hoff plot (b), desorption study of As5+ (c), and reusability (d) of C, CCS, and CCSG after six adsorption/desorption cycles (T = 27 oC, Ci = 400 mg/L, dosage 1.0 g/L, pH = 6, t = 25 min).
3.4 Comparing CCSG with other solid adsorbents
The maximum adsorption capacity of various adsorbents in comparison with CCSG are portrayed in Table 4 (Hu et al. 2015; Liu et al. 2017, 2024; Basu et al. 2021; Pervez et al. 2021; Sahu et al. 2022; Din et al. 2024). The outcomes in Table 4 show that CCSG has competitive As5+ ions adsorption capability. The newly synthesized adsorbent (CCSG) is a favorable and exceptional solid adsorbent for removing As5+ ions in a variety of applications.
| Adsorbents | Xm (mg/g) | Ref. |
|---|---|---|
| Magnetic chitosan/biochar composite (MCB) | 17.9 | (Liu et al. 2017) |
| β-FeOOH@GO | 69.0 | (Pervez et al. 2021) |
| FeOx-GOCS-0.08 | 61.9 | (Liu et al. 2024) |
| GO-MnO2-Goe-Ca-Alg beads | 34.2 | (Basu et al. 2021) |
| Eleocharis dulcis biochar loaded with CuO (EDB-CuO) | 26.1 | (Din et al. 2024) |
| Iron-impregnated biochar | 2.2 | (Hu et al. 2015) |
| MPAC-500 and MPAC-600 (magnetic-activated carbons synthesized from the peel of Pisum sativum pea) | 0.4930 and 0.9451 respectively | (Sahu et al. 2022) |
| CCSG | 376.0 | This study |
Using natural solid adsorbents in wastewater treatment procedures is a prospective methodology for removing heavy metals from polluted water. Herein, As5+ removal from aqueous medium was examined by the static batch adsorption procedures employing adsorbents such as date palm fiber biochar (C) and date palm fiber biochar/chitosan nanoparticles (CCS), which were then enhanced with glutamine (CCSG). Inserting chitosan and glutamine into date palm fiber biochar through composite matrix synthesis produced unique surface chemical functional groups on the CCSG surface. This led to increased activity at surface sites and more exterior pores. SEM analysis revealed that the adsorbents had a porous and uneven surface that facilitates As5+ ion adsorption. Adsorption kinetic data followed pseudo-first order equation, with Langmuir isotherm model more compatible with As5+ data. Based on the Langmuir isotherm nonlinear model, the CCSG composite had a maximum capacity of adsorption of 376.0 mg/g, with adsorption equilibrium attained after 25 min. Thermodynamic explorations indicate that the adsorption procedure is both spontaneous and endothermic. According to prior results, the adsorption of As5+ by the produced solid materials exhibited monolayer sorption. Previous research has shown that CCSG has exceptional adsorption and unique properties for wastewater treatment. Authors should pay special attention to biopolymer materials and solid agricultural waste in environmental applications because of their natural abundance, eco friendliness, increased sustainability, and biodegradability.
Author contributions
All authors [Al Isaee Khalifa, Laila M. Alshandoudi, Asaad F. Hassan, and Amany G. Braish] contributed to the study conception and design, materials preparation, data collection and analysis.
Funding: This study was funded by Ministry of Higher Education, Research and Innovation of Sultanate of Oman number BFP/GRG/EBR/2023/158.
Conflict of interest: There are no conflicts to declare.
Ethical approval: Not applied. This study did not involve human participants and/or animals.
Consent to participate: Not applied
Consent for publication: Not applied
Competing interests: The authors declare no competing interests
Availability of data and materials: It is available upon reasonable request.
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