Removal of Pb(II) from contaminated waters using cellulose sulfate/chitosan aerogel: Equilibrium, kinetics, and thermodynamic studies

Fabrication of a novel polyvinylpyrrolidone/chitosan-Schiff base/Fe2O3 nanocomposite for efficient adsorption of Pb(II) and Hg(II) ions from aqueous solution

A novel magnetic polyvinylpyrrolidone/chitosan-Schiff base/Fe2O3 (PVP/CS-SB/Fe2O3) adsorbent was prepared by one-pot facile co-precipitation route for adsorption of Pb(II) and Hg(II) ions from aqueous solution. Fourier transform infrared-spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscope (SEM), vibrating sample magnetometer (VSM) and Brunauer-Emmett-Teller (BET) were used to characterize the synthesized PVP/CS-SB/Fe2O3. The results predicted that the successfully synthesis of magnetic CSSB-PVP@Fe2O3. The effects of important factors such as pH solution, contact time, concentration of metal ions, adsorbent dose and co-existing ions on Pb(II) and Hg(II) adsorption were investigated. The maximum adsorption capacities of Pb(II) and Hg(II) ions at optimal conditions were 120 mg/g and 102.5 mg/g, respectively. The kinetic studies predicted that the adsorption followed the pseudo-second-order (PSO) model as chemisorption using the coordination of active sites of PVP/CS-SB/Fe2O3 with the metal ions and also n-π interactions. Reproducibility results predicted that the excellent regeneration ability after 6 adsorption cycles. According to the results of this work, the PVP/CS-SB/Fe2O3 nanocomposite is promising for Pb(II) and Hg(II) ions adsorption and can be potential as a simple, low-cost, high-efficient adsorbent for decontamination of other heavy metal ions from aqueous solution.

Bio-Based Aerogels for the Removal of Heavy Metal Ions and Oils from Water: Novel Solutions for Environmental Remediation

Contamination of the aqueous environment caused by the presence of heavy metal ions and oils is a growing concern that must be addressed to reduce their detrimental impact on living organisms and safeguard the environment. Recent efficient and environmentally friendly remediation methods for the treatment of water are based on third-generation bioaerogels as emerging applications for the removal of heavy metal ions and oils from aqueous systems. The peculiarities of these materials are various, considering their high specific surface area and low density, together with a highly porous three-dimensional structure and tunable surface chemistry. This review illustrates the recent progress in aerogels developed from cellulose and chitosan as emerging materials in water treatment. The potential of aerogel-based adsorbents for wastewater treatment is reported in terms of adsorption efficacy and reusability. Despite various gaps affecting the manufacturing and production costs of aerogels that actually limit their successful implementation in the market, the research progress suggests that bio-based aerogels are ready to be used in water-treatment applications in the near future.

Chitosan-cellulose nanocomposite: Preparation, characterization, and evaluation as cationic color precipitant in sugar clarification process

The present paper aims to use natural biodegradable polymers of chitosan (CS) and cellulose (CEL) to synthesize green chitosan-cellulose (CS-CEL) nanocomposite as a new clarifying agent. This is the cutting-edge of the sugar industry's clarification process. The CS-CEL nanocomposite showed outstanding results in zeta potential analysis, with a maximum value (+) 57.73 mV, leading to remarkableresults in coloradsorption via electrostatic attraction. It was also observed that CS-CEL has high mechanical stability. When CS and CS-CEL nanocomposite were used in the clarification of sugarcane (MJ), the findings demonstrated an improvement in colorremoval of up to 8.7% using CS and 18.1%using CS-CEL nanocomposite compared to currently phosphotation clarification process. Also, Turbidity decreased using CS-CEL nanocomposite compared to the traditional phosphotation clarification process. Overall, we can conclude that CS-CEL nanocomposite has considerable efficiency in sugarcane juice clarification process as a green biodegradable adsorbent and flocculating material to produce sulfur-free sugar.

Synthesis and characterization of pendant N,N-dimethylaminobenzaldehyde-functionalized chitosan Schiff base composite (CS@MABA) as a new sorbent for removal of Pb(II) ions from aqueous media

In this work, new pendant N,N-dimethylaminobenzaldehyde-functionalized chitosan Schiff base composite (CS@MABA) was prepared from the simple and convenient condensation reaction between chitosan (CS) and N,N-dimethylaminobenzaldehyde (MABA) in ethanol-glacial acetic acid (1:1 v/v) and characterized by Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), differential scanning calorimetry (DSC) and scanning electron microscope (SEM). The as-prepared composite CS@MABA was applied for the removal of Pb(II) ions, due to the presence of imine, hydroxyl and phenyl groups, and the effects of important parameters such as solution pH, contact time and sorbent dosage on the removal percentage and adsorption capacity were investigated and discussed. The optimum conditions were found to be at pH 5, adsorbent dosage of 0.1 g, Pb(II) concentration of 50 mg/L and contact time of 60 min. The maximum Pb(II) removal percentage was found to be 94.28 % with the high adsorption capacity of 165 mg/g. The adsorption capacity of CS@MABA is remain 87 % after 5 adsorption-desorption cycles. The adsorption kinetic and isotherm studies indicated that the Pb(II) removal by CS@MABA follows a pseudo-first order and Langmuir models, respectively. Compared to similar compounds, the synthesized CS@MABA composite has shown a relatively high yield for removing Pb(II) ions. According to these results, the CS@MABA suggested for the sorption of other heavy metals.

Synthesis of Xanthan Gum Anchored α-Fe2O3 Bionanocomposite Material for Remediation of Pb (II) Contaminated Aquatic System

Increases in community and industrial activities have led to disturbances of the environmental balance and the contamination of water systems through the introduction of organic and inorganic pollutants. Among the various inorganic pollutants, Pb (II) is one of the heavy metals possessing non-biodegradable and the most toxic characteristics towards human health and the environment. The present study is focussed on the synthesis of efficient and eco-friendly adsorbent material that can remove Pb (II) from wastewater. A green functional nanocomposite material based on the immobilization of α-Fe₂O₃ nanoparticles with xanthan gum (XG) biopolymer has been synthesized in this study to be applied as an adsorbent (XGFO) for sequestration of Pb (II). Spectroscopic techniques such as scanning electron microscopy with energy dispersive X-ray (SEM-EDX), Fourier transform infrared (FTIR), transmission electron microscopy (TEM), X-ray diffraction (XRD), ultraviolet visible (UV-Vis) and X-ray photoelectron spectroscopy (XPS) were adopted for characterizing the solid powder material. The synthesized material was found to be rich in key functional groups such as -COOH and -OH playing important roles in binding the adsorbate particles through ligand-to-metal charge transfer (LMCT). Based on the preliminary results, adsorption experiments were conducted, and the data obtained were applied to four different adsorption isotherm models, viz the Langmuir, Temkin, Freundlich and D-R models. Based on the high values of R² and low values of χ², the Langmuir isotherm model was found to be the best model for simulation of data for Pb (II) adsorption by XGFO. The value of maximum monolayer adsorption capacity (Q_m) was found to be 117.45 mg g^-1 at 303 K, 126.23 mg g^-1 at 313 K, 145.12 mg g^-1 at 323 K and 191.27 mg g^-1 at 323 K. The kinetics of the adsorption process of Pb (II) by XGFO was best defined by the pseudo-second-order model. The thermodynamic aspect of the reaction suggested that the reaction is endothermic and spontaneous. The outcomes proved that XGFO can be utilized as an efficient adsorbent material for the treatment of contaminated wastewater.

Application of new chitosan 2,4-dihydroxyacetophenone Schiff base @SrFe12O19 nanocomposite for remove of Pb(II) ion from aqueous solution

A new chitosan 2,4-dihydroxyacetophenone Schiff base @SrFe₁₂O₁₉ (Cs-SB@SrFe₁₂O₁₉) nanocomposite was successfully prepared by one-pot reaction and fully characterized for its functional groups, morphology, elemental analysis and thermal behavior by FT-IR, XRD, VSM, DSC, TGA, zeta potential, FE-SEM and EDS techniques. The VSM result showed that Cs-SB@SrFe₁₂O₁₉ has M_s of 11.81 emu/g and H_c of 5488 Oe, known as hard magnetic material. Finally, the as-prepared sample utilized as a new sorbent for the removal of Pb(II) ions from aqueous solution by using batch adsorption experiments. The adsorption of Pb(II) was carried out at different pH, contact time and initial dose of Cs-SB@SrFe₁₂O₁₉. The maximum adsorption capacity was found to be 132 mg/g (99 %) at pH 5 and the contact time of 120 min. Finally, the kinetic studies reveals that the adsorption process of Cs-SB@SrFe₁₂O₁₉ followed by the pseudo second order kinetics model. Also, the sample showed excellent recyclable efficiency up to 5 cycles.

Kinetics, isotherms, and mechanism of removing cationic and anionic dyes from aqueous solutions using chitosan/magnetite/silver nanoparticles

Modified magnetite chitosan with silver nanoparticles was synthesized and tested for removing cationic and anionic dyes in aqueous solutions. Initial dye concentration, pH, and contact time were examined. Results showed that pH (4.0) was optimal for removing anionic dyes (methyl orange) and pH 8.0 for removing cationic dyes (methylene blue). According to these results, zeta potentials were found to be 8.43 and - 39.17 mV at pH 4.0 and 8.0, respectively. So, it is attracted to positively charged cationic dyes in an alkaline medium and negatively charged anionic dyes in an acidic medium because of their opposite charges. Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), thermal gravimetric analysis (TGA), and zeta potential measurements were used to characterize the synthesized nanosorbents. A pseudo-second-order kinetic model is fitted with the Langmuir adsorption model, with an adsorption capacity of 417 and 476 mg/g for methyl orange and methylene blue, respectively. For both dyes, modified magnetite chitosan with silver nanoparticles showed high regeneration capability and recovery for up to four cycles without adsorption efficiency loss. Furthermore, modified magnetite chitosan with silver nanoparticles, as prepared in the present study, was demonstrated to be an effective adsorbent for organic pollutants in wastewater.

Chitosan grafted tetracarboxylic functionalized magnetic nanoparticles for removal of Pb(II) from an aqueous environment

In this study, the chitosan-grafted tetracarboxylic functionalized magnetic nanoparticle (Fe₃O₄@TCA@CS) was synthesized via in situ co-precipitation process and amidation reaction to improve efficiency of adsorption process and obtain cost-effective adsorbents for removal of toxic Pb(II) metal from aqueous environment. The Fe₃O₄@TCA@CS nanocomposite was analyzed by FTIR, TEM-EDX, TGA, XRD, BET, and Zeta potential. The performance of Fe₃O₄@TCA@CS for Pb(II) ions adsorption was achieved as a function of pH, dose, contact time, initial Pb(II) concentration, and temperature. The influence of coexisting ions such as Na⁺, Ca²⁺, Mg²⁺, and Cd²⁺on removal efficiency of Pb(II) was also investigated. The results revealed that the coexisting ions had little influence on Pb(II) removal efficiency. The pseudo-first-order and Freundlich models were better to describe the adsorption of Pb(II) onto Fe₃O₄@TCA@CS and the maximum adsorption capacity of Pb(II) was 204.92 mg/g at pH:5.5; adsorbent dose: 0.015 g; and temperature: 298 K. Thermodynamic studies revealed that the Pb(II) adsorption onto Fe₃O₄@TCA@CS was an exothermic process. In conclusion, the study provides a new, simple, low-cost, and effective chitosan-based magnetic nanocomposite as a promising adsorbent with excellent adsorption capacity, magnetic separation, and reusability for Pb(II) removal from an aqueous environment.

How to avoid mistakes in treating adsorption isotherm data (liquid and solid phases): Some comments about correctly using Radke-Prausnitz nonlinear model and Langmuir equilibrium constant

Two flaws in concepts were identified and discussed in the paper ("Removal of Pb(II) from contaminated waters using cellulose sulfate/chitosan aerogel: Equilibrium, kinetics, and thermodynamic studies". J. Environ. Manag. 286, 112167; https://doi.org/10.1016/j.jenvman.2021.112167). In the literature, the Radke-Prausnitz model is expressed in different forms, but some of them are incorrect. The first flaw is related to the nonlinear form of the Radke-Prausnitz model. The nonlinear form of this three parameters model is expressed correctly as [Formula: see text] . The units of two parameters are A_RP (L/kg) and B_RP [(mol/kg)/(mol/L)^β] by considering q_e (mol/kg) and C_e (mol/L). The limitation for its exponent is 0≤ β ≤ 1. This model is developed by two authors (Radke and Prausnitz). The correct paper (DOI: 10.1021/i160044a003) cited as reference of this model is "Radke, C.J., Prausnitz, J.M., 1972. Adsorption of organic solutes from dilute aqueous solution of activated carbon. Ind. Eng. Chem. 11, 445-451". The second is the misconception about the unit of the Langmuir constant (K_L; L/mg). The correct unit of K_L is litre per milligram of adsorbate (i.e., Pb ions), not litre per milligram of adsorbent (the cellulose sulfate/chitosan aerogel material as reported by Najaflou and co-workers. They proposed a new equation [K_L (L/mg) × m/V (mg/L)] to convert the Langmuir constant and then applied it to calculate the thermodynamic parameters of the adsorption process. The m/V is a solid/liquid ratio (g/L or kg/L). However, this conversion and application are mistakes that were thoroughly discussed in this paper. The correction is K_Eq^o=1γ_Adsorbate×K_LLmol×C^omolL, with C° (1 mol/L by definition) being the standard state of solute and γ_Adsorbate (dimensionless) being the activity coefficient of adsorbate in solution. To avoid unexpected mistakes, the present authors suggest that researchers should have a correct citation (citing the original reference instead of using secondary references) and check the consistency of units (i.e., the constants of adsorption models) carefully.

Isotherm models for adsorption of heavy metals from water - A review

Adsorption is a widely used technology for removing and separating heavy metal from water, attributed to its eco-friendly, cost-effective, and high efficiency. Adsorption isotherm modeling has been used for many years to predict the adsorption equilibrium mechanism, adsorption capacity, and the inherent characteristics of the adsorption process, all of which are substantial in evaluating the performance of adsorbents. This review summarizes the development history, fundamental characteristics, and mathematical derivations of various isotherm models, along with their applicable conditions and application scenarios in heavy metal adsorption. The latest progress in applying isotherm models with a one-parameter, two-parameter, and three-parameter in heavy metal adsorption using carbon-based materials, which has gained much attention in recent years as low-cost adsorbents, is critically reviewed and discussed. Several experimental factors affecting the adsorption equilibrium, such as solution pH, temperature, ionic strength, adsorbent dose, and initial heavy metal concentration, are briefly discussed. The criteria for selecting the optimum isotherm for heavy metal adsorption are proposed by comparing various adsorption models and analyzing mathematical error functions. Finally, the relative performance of different isotherm models for heavy metal adsorption is compared, and the future research gaps are identified.

Improper Estimation of Thermodynamic Parameters in Adsorption Studies with Distribution Coefficient KD (qe/Ce) or Freundlich Constant (KF): Considerations from the Derivation of Dimensionless Thermodynamic Equilibrium Constant and Suggestions

Adsorption processes often include three important components: kinetics, isotherm, and thermodynamics. In the study of solid–liquid adsorption, “standard” thermodynamic equilibrium constant $\left(K_{\text{Eq}}^{\text{o}}\right.$ ; dimensionless) plays an essential role in accurately calculating three thermodynamic parameters: the standard Gibbs energy change (∆G°; kJ/mol), the standard change in enthalpy (∆H°; kJ/mol), and the standard change in entropy [∆S°; J/(mol × K)] of an adsorption process. Misconception of the derivation of the $K_{\text{Eq}}^{\text{o}}$ constant that can cause calculative errors in values (magnitude and sign) of the thermodynamic parameters has been intensively reflected through certain kinds of papers (i.e., letters to editor, discussions, short communications, and correspondence like comment/rebuttal). The distribution coefficient (KD) and Freundlich constant (KF) have been intensively applied for calculating the thermodynamic parameters. However, a critical question is whether KD or KF is equal to $K_{\text{Eq}}^{\text{o}}$ . This paper gives (1) thorough discussion on the derivation of thermodynamic equilibrium constant of solid–liquid adsorption process, (2) reasonable explanation on the inconsistency of (direct and indirect) application of KD or KF for calculating the thermodynamic parameters based on the derivation of $K_{\text{Eq}}^{\text{o}}$ , and (3) helpful suggestions for improving the quality of papers published in this field.

The sorption and short-term immobilization of lead and cadmium by nano-hydroxyapatite/biochar in aqueous solution and soil

In this study, the composite materials using different ratios of biochar (BC) to nano-hydroxyapatite (nHAP) were prepared for the remediation of lead (Pb) and cadmium (Cd) contaminated water and soil. The sorption and the immobilization experiments indicated a higher sorption capacity and immobilization efficiency of Pb compared to those of Cd. The characteristics of XRD, FTIR, SEM, and XPS manifested that dissolution-precipitation, cation exchange, complexation, and cation-π interaction were the main four mechanisms for the sorption of Pb²⁺ and Cd²⁺ using composite material PC1 (nHAP/BC = 1/1). From semi-quantitative analysis, the mineral effect accounted for the majority of the immobilization of Pb and Cd. Due to obvious Pb-precipitates in the sorbed material, dissolution-precipitation primarily affected the sorption of Pb using PC1, while the immobilization of Cd was mainly attributable to cation exchange. Such results corresponded to the stable Pb-precipitates and unstable Cd-compounds in soil, among which the latter was prone to be released into the environment. The sorption capacity in aqueous solutions and the immobilization efficiencies in the soil for both Pb and Cd increased with the addition of nHAP, which were linearly correlated to the nHAP proportion in the composite materials. In future practical applications, the percentages of composite materials can be designed according to the specific pollutant concentration. This study sheds light on the explicit immobilization mechanisms for Pb and Cd in aqueous solutions to better understand their behaviors in the soil remediated by relevant materials.

Chitosan Functionalized with 2-Methylpyridine Cross-Linker Cellulose to Adsorb Pb(II) from Water

In this study, chitosan was chemically modified with 2-methylpyridine. Subsequently, the modified chitosan was cross-linked to cellulose using succinic anhydride. Additionally, the capacity of cellulose derivatives to adsorb Pb(II) ions in an aqueous solution was studied through the determination of Pb(II) ions concentration in water, using microwave plasma atomic emission spectroscopy (MP-AES). A maximum adsorption capacity of 6.62, 43.14, 60.6, and 80.26 mg/g was found for cellulose, cellulose-succinic acid, cellulose-chitosan, and cellulose-chitosan-pyridine, respectively. The kinetic data analysis of the adsorption process showed a pseudo-second-order behavior. The increase in metal removal from water is possibly due to metal chelation with the carbonyl group of succinic acid, and the pyridine groups incorporated into chitosan.

Pectin/Activated Carbon-Based Porous Microsphere for Pb2+ Adsorption: Characterization and Adsorption Behaviour

The development of effective heavy metal adsorbents has always been the goal of environmentalists. Pectin/activated carbon microspheres (P/ACs) were prepared through simple gelation without chemical crosslinking and utilized for adsorption of Pb²⁺. Scanning electron microscopy (SEM) revealed that the addition of activated carbon increased the porosity of the microsphere. Texture profile analysis showed good mechanical strength of P/ACs compared with original pectin microspheres. Kinetic studies found that the adsorption process followed a pseudo-second-order model, and the adsorption rate was controlled by film diffusion. Adsorption isotherms were described well by a Langmuir isotherm model, and the maximum adsorption capacity was estimated to be 279.33 mg/g. The P/ACs with the highest activated carbon (P/AC_2:3) maintained a removal rate over 95.5% after 10 adsorption/desorption cycles. SEM-energy-dispersive X-ray spectrum and XPS analysis suggested a potential mechanism of adsorption are ion exchange between Pb²⁺ and Ca²⁺, electronic adsorption, formation of complexes, and physical adsorption of P/ACs. All the above results indicated the P/ACs may be a good candidate for the adsorption of Pb²⁺.

Porous Aerogels and Adsorption of Pollutants from Water and Air: A Review

Aerogels are open, three-dimensional, porous materials characterized by outstanding properties, such as low density, high porosity, and high surface area. They have been used in various fields as adsorbents, catalysts, materials for thermal insulation, or matrices for drug delivery. Aerogels have been successfully used for environmental applications to eliminate toxic and harmful substances-such as metal ions or organic dyes-contained in wastewater, and pollutants-including aromatic or oxygenated volatile organic compounds (VOCs)-contained in the air. This updated review on the use of different aerogels-for instance, graphene oxide-, cellulose-, chitosan-, and silica-based aerogels-provides information on their various applications in removing pollutants, the results obtained, and potential future developments.