Adsorption of chromium(III) on lignin

Preparation and Characterization of Lignin Nanoparticles from Different Plant Sources

This article presents new research on producing lignin nanoparticles (LNPs) using the antisolvent nanoprecipitation method. Acetone (90%) served as the lignin solvent and water (100%) as the antisolvent, using five types of lignins from various sources. Comprehensive characterization techniques, including NMR, GPC, FTIR, TEM, and DLS, were employed to assess both lignin and LNP properties. The antioxidant activity of the LNPs was evaluated as well. The results demonstrated the successful formation of spherical nanoparticles below 100 nm with initial lignin concentrations of 1 and 2%w/v. The study highlighted the crucial role of lignin purity in LNP formation and colloidal stability, noting that residual carbohydrates adversely affect efficiency. This method offers a straightforward, environmentally friendly approach using cost-effective solvents, applicable to diverse lignin sources. The innovation of this study lies in its demonstration of a cost-effective and eco-friendly method to produce stable, nanometric-sized spherical LNPs. These LNPs have significant potential as reinforcement materials due to their reinforcing capability, hydrophilicity, and UV absorption. This work underscores the importance of starting material purity for optimizing the process and achieving the desired nanometric dimensions, marking a pioneering advancement in lignin-based nanomaterials.

Amino-modified upcycled biochar achieves selective chromium removal in complex aqueous matrices

Chromium pollution of groundwater sources is a growing global issue, which correlates with various anthropogenic activities. Remediation of both the Cr(VI) and Cr(III), via adsorption technologies, has been championed in recent years due to ease of use, minimal energy requirements, and the potential to serve as a highly sustainable remediation technology. In the present study, a biochar sorbent sourced from pineapple skins, allowed for the upcycling of agricultural waste into water purification technology. The biochar material was chemically modified, through a green amination method, to produce an efficient and selective adsorbent for the removal of both Cr(VI) and Cr(III) from complex aqueous matrices. From FTIR analysis it was evident that the chemical modification introduced new C-N and N-H bonds observed in the modified biochar along with a depletion of N-O and C-H bonds found in the pristine biochar. The amino modified biochar was found to spontaneously adsorb both forms of chromium at room temperature, with binding capacities of 46.5 mg/g of Cr(VI) and 27.1 mg/g of Cr(III). Interference studies, conducted in complex matrices, showed no change in adsorption capacity for Cr(VI) in matrices containing up to 3,000× the concentration of interfering ions. Finally, Cr(III) removal was synergized to 100% adsorption at interfering ions concentrations up to 330× of the analyte, which were suppressed at higher interference concentrations. Considering such performance, the amino modified biochar achieved selective removal for both forms of chromium, showing great potential for utilization in complex chromium pollution sources.

The role of glycosylation in non-productive adsorption of cellulase to lignin isolated from pretreated corn stover

Glycosylation, a general post-translational modification for fungal cellulase, has been shown to affect cellulase binding to its substrate. However, the exact impact of glycosylation on cellulase-lignin interaction remain unclear. Here, we demonstrated that the lignin isolated from tetrahydrofuran-pretreated corn stover exhibits strong adsorption capability to cellulase due to its negatively charged and porous structure. For the cellulases with varying glycosylation levels, the less-glycosylated protein showed high adsorption capability to lignin, and that trend was observed for the main cellulase components secreted by Penicillium oxilicum, including endoglucanase PoCel5B, cellobiohydrolase PoCel7A-2, and β-glucosidase PoBgl1. Additionally, N-glycan sites and motifs were examined using mass spectrometry, and protein structures with N-glycans were constructed, where PoBgl1 and PoCel7A-2 contained 13 and 1 glycosylated sites respectively. The results of molecular dynamics simulations indicated that the N-glycans impacted on the solvent-accessible surface area and secondary structure of protein, and the binding conformation of lignin fragment on cellulase, resulting in a decrease in binding energy (14 kcal/mol for PoBgl1 and 13 kcal/mol for PoCel7A-2), particularly for van der Waals and electrostatic interaction. Those findings suggested that glycosylation negatively impacted the lignin-cellulase interaction, providing a theoretical basis for the rational engineering of enzymes to reduce lignin-enzyme interaction.

Design and function of lignin/silk fibroin-based multilayer water purification membranes for dye adsorption

The treatment of dye wastewater poses a significant challenge to the sewage recycling industries. However, the reduction of secondary pollution resulting from the membrane residues, to maintain high performance, remains a considerable obstacle. A novel approach for the fabrication of multilayer nanofiber structures using a layer-by-layer electrostatic spinning technique with biological materials was reported in this study. Incorporating the chemical adsorption advantages of lignin nanofiber and the physical adsorption advantages of silk fibroin (SF) nanofiber enabled the full realization of excellent dye interception performance. A comparative analysis was conducted on the lignin derived from eucalyptus, pine, and straw to determine the most suitable option. Notably, eucalyptus lignin exhibited superior antimicrobial properties. The adsorption of crystal violet by eucalyptus lignin/SF membrane was consistent with the Freundlich isotherm model and the pseudo-second-order kinetic model, revealing a chemisorption mechanism involving Π-Π conjugation, hydrogen bonding, and the binding of anions and cations. The lignin/SF membrane exhibited a retention rate exceeding 99.5 % for crystal violet, methylene blue, and brilliant green dyes. Furthermore, it demonstrated efficacy in retaining heavy metal ions, including cadmium and copper. The original biomass material imparts the property of rapid degradation to a multilayer membrane that can be used as an effective and eco-friendly water purification material.

Effective assessment of biopolymer-based multifunctional sorbents for the remediation of environmentally hazardous contaminants from aqueous solutions

Persistent contaminants in wastewater effluent pose a significant threat to aquatic life and are one of the most significant environmental concerns of our time. Although there are a variety of traditional methods available in wastewater treatment, including adsorption, coagulation, flocculation, ion exchange, membrane filtration, co-precipitation and solvent extraction, none of these have been found to be significantly cost-effective in removing toxic pollutants from the water environment. The upfront costs of these treatment methods are extremely high, and they require the use of harmful synthetic chemicals. For this reason, the development of new technologies for the treatment and recycling of wastewater is an absolute necessity. Our way of life can be made more sustainable by the synthesis of adsorbents based on biomass, making the process less harmful to the environment. Biopolymers offer a sustainable alternative to synthetic polymers, which are manufactured by joining monomer units through covalent bonding. This review presents a detailed classification of biopolymers such as pectin, alginate, chitosan, lignin, cellulose, chitin, carrageen, certain proteins, and other microbial biomass compounds and composites, with a focus on their sources, methods of synthesis, and prospective applications in wastewater treatment. A concise summary of the extensive body of knowledge on the fate of biopolymers after adsorption is also provided. Finally, consideration is given to open questions about future developments leading to environmentally friendly and economically beneficial applications of biopolymers.

Influence of structure and functional group of modified kraft lignin on adsorption behavior of dye

Utilization of kraft lignin to produce bio-based adsorptive material for effective dye adsorption from industrial wastewater is essential to fulfilling the significant environmental protection needs. Lignin is the most abundant byproduct material with a chemical structure containing various functional groups. However, the complicated chemical structure makes it somewhat hydrophobic and incompatible, which limits its direct application as an adsorption material. Chemical modification is a common way to enhance lignin properties. In this work, the kraft lignin was modified through direct amination using Mannich reaction and oxidization followed by amination as new route of lignin modification. The prepared lignins, including aminated lignin (AL), oxidized lignin (OL), and aminated-oxidized lignin (AOL), as well as unmodified kraft lignin, were analyzed by Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), elemental analysis and ¹H-nuclear magnetic resonance measurements (¹HNMR). The adsorption behaviors of modified lignins for the malachite green in aqueous solution were investigated well and discussed, as well as the adsorption kinetics and thermodynamic equations. Compared with other aminated lignin (AL), the AOL displayed a high adsorption capacity of 99.1 % dye removal, due to its more effective functional groups. The change in structure and functional groups on the lignin molecules during oxidation and amination had no effect on its adsorption mechanisms. The adsorption process of malachite green on different kinds of lignin belongs to endothermic chemical adsorption, which mainly consists of monolayer adsorption. The modification of lignin through oxidation followed by amination process, afforded kraft lignin a broad potential application in the field of wastewater treatment.

Chitosan-Lignin Carbon Framework Encapsulated Cu Catalyst Facilitates Base-free Hydrogen Evolution from Methanol/Water

Methanol reforming in aqueous solution provides a significantly attractive and promising pathway to release hydrogen with mild H2 release condition and high H2 storage capacity. Exploring non-noble metal-based catalysts with...

Functionalization of Zeolite NaP1 for Simultaneous Acid Red 18 and Cu(II) Removal

The efficiency of azo dye Acid Red 18 (AR18) and Cu(II) ions simultaneous removal from an aqueous solution on NaP1CS and NaP1H was investigated, taking into account the effect of the phase contact time, pH, initial concentration, temperature, and interfering ions presence. Zeolite denoted as NaP1CS was modified by chitosan (CS) and zeolite denoted as NaP1H was modified by hexadecyltrimethylammonium bromide (HDTMA). In order to characterize sorption properties of NaP1CS, the obtained sorbent was characterized using Fourier transform infrared spectroscopy (FTIR) and nitrogen adsorption/desorption (ASAP). The kinetic parameters were determined by means of the pseudo first order (PFO), pseudo second order (PSO), and intraparticle diffusion (IPD) kinetic models. To present the adsorption data, three different isotherm models (Langmuir, Freundlich and Dubinin-Radushkevich) were used. The desorption process was also examined. It was found that for sorbent NaP1CS the pseudo second order (PSO) kinetic model and the Langmuir isotherm fitted best the experimental data. Moreover, it was noted that the acidic pH is appropriate to achieve the best sorption properties of NaP1CS for Cu(II) and NaP1H for AR18 and Cu(II). The thermodynamic parameters indicate an endothermic process. The most effective solution for the desorption process was found to be 1 M HCl. The results indicate that simultaneous removal of dye AR18 and Cu(II) on modified zeolite NaP1CS or NaP1H is possible and proceeds with a very good efficiency. The obtained zeolites could effectively adsorb AR18 an Cu(II) simultaneously, but their adsorption abilities were rather different.

Kinetic description of site ensembles on catalytic surfaces

We demonstrate that the Langmuir-Hinshelwood formalism is an incomplete kinetic description and, in particular, that the Hinshelwood assumption (i.e., that adsorbates are randomly distributed on the surface) is inappropriate even in catalytic reactions as simple as A + A → A₂ The Hinshelwood assumption results in miscounting of site pairs (e.g., A*-A*) and, consequently, in erroneous rates, reaction orders, and identification of rate-determining steps. The clustering and isolation of surface species unnoticed by the Langmuir-Hinshelwood model is rigorously accounted for by derivation of higher-order rate terms containing statistical factors specific to each site ensemble. Ensemble-specific statistical rate terms arise irrespective of and couple with lateral adsorbate interactions, are distinct for each elementary step including surface diffusion events (e.g., A* + * → * + A*), and provide physical insight obscured by the nonanalytical nature of the kinetic Monte Carlo (kMC) method-with which the higher-order formalism quantitatively agrees. The limitations of the Langmuir-Hinshelwood model are attributed to the incorrect assertion that the rate of an elementary step is the same with respect to each site ensemble. In actuality, each elementary step-including adsorbate diffusion-traverses through each ensemble with unique rate, reversibility, and kinetic-relevance to the overall reaction rate. Explicit kinetic description of ensemble-specific paths is key to the improvements of the higher-order formalism; enables quantification of ensemble-specific rate, reversibility, and degree of rate control of surface diffusion; and reveals that a single elementary step can, counter intuitively, be both equilibrated and rate determining.

Enhanced removal of Cr(VI) via in-situ synergistic reduction and fixation by polypyrrole/sugarcane bagasse composites

Reduction and recycling of Cr(VI) can offer environmental governance and sustainable development. Polypyrrole/sugarcane bagasse composites (PPy/SCB) for efficient adsorption and reduction of Cr(VI) in wastewater were prepared by in-situ polymerization. The effects of the initial pH, Cr concentration, adsorbent dosage, contact time, composition ratio and temperature on adsorption capacity were explored. The optimal Cr(VI) adsorption capacity of PPy/SCB was achieved when the pH value was 2.0. The adsorbents before and after adsorption were characterized, which confirmed that adsorption process affects the morphology, composition and structure of the PPy/SCB surface. The adsorption kinetics data of Cr(VI) were best fitted by the pseudo-second-order model, which indicated that Cr(VI) concentration gradient played a driving role in this process. The adsorption isotherm data were consistent with the Langmuir isotherm model with the adsorption capacity of 156-251 mg/g. Synergic effect of PPy and SCB during the processes of electrostatic adsorption and ion exchange, in-situ reduction of electron donors, and coordination were found to be responsible for the rapid removal and toxicity reduction of total Cr in aqueous solution. Cr(VI) anions can be chelated by oxygen-containing functional groups on SCB surface after reduction to simple cations, which was confirmed by Fourier transform infrared spectrometry and X-ray photoelectron spectroscopy results. This study provides a reasonable scheme for the targeted use of waste biomass for heavy metal pollution control.

Lignin-derived (nano)materials for environmental pollution remediation: Current challenges and future perspectives

The supply of affordable drinking and sufficiently clean water for human consumption is one of the world's foremost environmental problems and a large number of scientific research works are addressing this issue Various hazardous/toxic environmental contaminants in water bodies, both inorganic and organic (specifically heavy metals and dyes), have become a serious global problem. Nowadays, extensive efforts have been made to search for novel, cost effective and practical biosorbents derived from biomass resources with special attention to value added, biomass-based renewable materials. Lignin and (nano)material adorned lignin derived entities can proficiently and cost effectively remove organic/inorganic contaminants from aqueous media. As low cost of preparation is crucial for their wide applications in water/wastewater treatment (particularly industrial water), future investigations must be devoted to refining and processing the economic viability of low cost, green lignin-derived (nano)materials. Production of functionalized lignin, lignin supported metal/metal oxide nanocomposites or hydrogels is one of the effective approaches in (nano)technology. This review outlines recent research progresses, trends/challenges and future prospects about lignin-derived (nano)materials and their sustainable applications in wastewater treatment/purification, specifically focusing on adsorption and/or catalytic reduction/(photo)degradation of a variety of pollutants.

Nano-Structured Lignin as Green Antioxidant and UV Shielding Ingredient for Sunscreen Applications

Green, biocompatible, and biodegradable antioxidants represent a milestone in cosmetic and cosmeceutical applications. Lignin is the most abundant polyphenol in nature, recovered as a low-cost waste from the pulp and paper industry and biorefinery. This polymer is characterized by beneficial physical and chemical properties which are improved at the nanoscale level due to the emergence of antioxidant and UV shielding activities. Here we review the use of lignin nanoparticles in cosmetic and cosmeceutical applications, focusing on sunscreen and antiaging formulations. Advances in the technology for the preparation of lignin nanoparticles are described highlighting structure activity relationships.

Revisiting lignin: a tour through its structural features, characterization methods and applications

A pedagogical overview of the main extraction procedures and structural features, characterization methods and state-of-the-art applications.

Facile synthesis of easily separated and reusable silver nanoparticles/aminated alkaline lignin composite and its catalytic ability

Green synthesis of silver nanoparticles (AgNPs) has received increasing attention. In this study, AgNPs were prepared through in-situ reduction by aminated alkaline lignin (AAL). Compared with alkaline lignin (AL), AAL exhibited stronger reduction capacity (increased by 36%) due to the introduced amine groups and better water solubility. Moreover, the coordination effect of amine groups on AAL improved the binding force between lignin and AgNPs. The content of AgNPs in AgNPs/AAL composite were 2.4 times higher than that in AgNPs/AL, such content could be further increased through increasing the reduction pH or prolonging the heating time. The results of XPS, XRD and TEM showed that the AgNPs were spherical and monodisperse with an average particle size about 17 nm. Additionally, the size of AgNPs was affected by the amination degree of lignin. AgNPs/AAL exhibited good catalytic performance for the reduction of 4-nitrophenol to 4-aminophenol, and this compound could be easily recovered and reused for at least eight cycles.

Inexpensive Organic Materials and Their Applications towards Heavy Metal Attenuation in Waters from Southern Peru

There is interest in using locally available, low cost organic materials to attenuate heavy metals such as Cd, Cr, Cu, Hg, Ni, Pb, and Zn found in surface waters in Peru and other developing regions. Here we mesh Spanish language publications, archived theses, and prior globally available literature to provide a tabulated synthesis of organic materials that hold promise for this application in the developing world. In total, nearly 200 materials were grouped into source categories such as algae and seashells, bacteria and fungi, terrestrial plant-derived materials, and other agricultural and processing materials. This curation was complemented by an assessment of removal potential that can serve as a resource for future studies. We also identified a subset of Peruvian materials that hold particular promise for further investigation, including seashell-based mixed media, fungal blends, lignocellulose-based substrates including sawdust, corn and rice husks, and food residuals including peels from potatoes and avocadoes. Many studies reported percent removal and/or lacked consistent protocols for solid to liquid ratios and defined aqueous concentrations, which limits direct application. However, they hold value as an initial screening methodology informed by local knowledge and insights that could enable adoption for agriculture and other non-potable water reuse applications. While underlying removal mechanisms were presumed to rely on sorptive processes, this should be confirmed in promising materials with subsequent experimentation to quantify active sites and capacities by generating sorption isotherms with a focus on environmental conditions and specific contaminated water properties (pH, temperature, ionic strength, etc.). These organics also hold promise for the pairing of sorption to indirect microbial respiratory processes such as biogenic sulfide complexation. Conversely, there is a need to quantify unwanted contaminant release that could include soluble organic matter and nutrients. In addition to local availability and treatment efficacy, social, technical, economic, and environmental applicability of those materials for large-scale application must be considered to further refine material selection.

Sustainable Strategies in the Synthesis of Lignin Nanoparticles for the Release of Active Compounds: A Comparison

The preparation of nanoparticles represents a powerful tool for lignin valorization, as it combines easy methodologies with high application potential. Different synthetic strategies and various lignin sources have been employed in the process. However, the great variability in the lignin structure prevents a direct comparison of the so far reported lignin nanoparticles (LNPs), especially as regards their physicochemical and functional properties. To this purpose, two green protocols, that is, solvent-antisolvent and hydrotropic, were optimized and used to generate LNPs from the same softwood kraft lignin. The nanomaterials were fully characterized to extrapolate structure/property relationships and reveal any differences in the mechanism of self-assembly. Furthermore, tests on methylene blue entrapment capacity and release behavior at two different pH values (2.0 and 7.4) evidenced a clear dependence on the LNPs characteristics and thus on the strategy adopted for their production.

Zno/Carbon nanofibers for efficient adsorption of lead from aqueous solutions

Hybrid nanofibers based on ZnO loaded activated carbon nanofibers (ZnO-ACNFs) are proposed here for the elimination of hazardous lead from aqueous solutions. The prepared ZnO nanoscale material was loaded into the polyacrylonitrile nanofibers (PAN NFs) which were later carbonized by using a novel method named as a plate-sandwich method. The Synthesized nanofibrous composite was characterized by SEM, TEM, EDX, FTIR and XRD techniques to analyze its chemical and morphological properties. Moreover, the nanocomposite was efficaciously applied for the lead (Pb²⁺) ions removal from wastewater and simulated water through continuous filtration and batch filtration. The ZnO-ACNFs membrane showed outstanding results in adsorptive removal, giving adsorption capacity of 92.59 mg/g within the contact time of 45 min. Compared to their counterparts (ZnO and CNFs), the hybrid ZnO-ACNFs showed excellent performance in removing toxic lead.

Characteristics of natural biopolymers and their derivative as sorbents for chromium adsorption: a review

Abstract

Chromium is widely used in industry, and improper disposal of wastewater and industrial residues containing excessive chromium can contaminate water and soil, endangering both environmental and human health. Natural biopolymers and their derivatives have been investigated for removal of chromium (Cr) from wastewater. Cellulose, lignin, tannin, chitin, chitosan, and polypeptides are abundant in nature, and have high potential as adsorbents due to their easy access, low cost, and the recyclability of the captured heavy metals. In order to improve their mechanical strength, recyclability, specific surface area, binding site number, and adsorption rate as adsorbents, native materials have also been modified. This review discusses the source of chromium contamination and the main species of interest, as well as their toxicity. The structures of the aforementioned biopolymers were analyzed, and the adsorption mechanism of chromium and the main influencing factors on this process are discussed. The modification methods of various adsorbents and their adsorption effects on chromium are also detailed, and the developmental direction of research on the use of biopolymer adsorption remediation to control chromium contamination is discussed.

Graphical abstract

Adsorption of Cu (II) and Cd (II) from Wastewater by Sodium Alginate Modified Materials

Natural macromolecule adsorbing materials are alternatives for remediation of heavy metals’ polluted waters. In this study, sodium alginate composite gel (SACL) was synthesized from sodium alginate (SA), polyethylene glycol oxide (PEO), and nanomaterials to remove wastewater Cu (II) and Cd (II). The adsorption efficiency of SACL was analysed in relation to the contact time, initial concentrations of metal ions, temperature, adsorbent dosage, and solution pH. Three models, i.e., kinetic model, isothermal adsorption model, and thermodynamic model, were used to fit the experimental data. Our results showed that the highest removal rates of Cu (II) and Cd (II) from wastewater were 96.8% and 78%, respectively, under the condition of the best liquid-solid ratio of 12.5 ml·g−1, and the contact time of 180 min (25°C). Overall, the SACL adsorption of Cu (II) and Cd (II) was spontaneous. The adsorption kinetics and the isothermal adsorption were fitted well with the pseudo-second-order kinetic equation and Langmuir equation, respectively. Combined with SEM-EDS and FTIR analysis, results suggested that SACL adsorbs wastewater Cu (II) and Cd (II) mainly through chemical reaction on its surface area. Altogether, this work concludes on SACL as an efficient and ecofriendly adsorbent for wastewater Cu (II) and Cd (II).

Elimination of Cr(VI) from chromium slag with poplar lignin by electrochemical treatment in sulfuric acid solution

In this paper, we proposed a novel method to eliminate nocuous Cr(VI) from chromium slag with poplar lignin by electrochemical treatment in sulfuric acid solution. In this electrochemical process, self-made Ti/SnO₂-Sb anode and graphite cathode were applied, and the oxidative degradation of lignin proceeded simultaneously with the reduction of Cr(VI) in one pot. The influences of pivotal factors on electrocatalytic redox efficiency were investigated, such as chromium slag concentration, lignin concentration, current density, sulfuric acid concentration, and reaction time. The results showed that the elimination rate of Cr(VI) in chromium slag was 97.16 ± 1.13% and the total yield of lignin degradation products reached 93.78 g/kg lignin under the optimal conditions. X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDS), and UV-visible spectrophotometer studies confirmed that most of the Cr(VI) ions were reduced to Cr(III) ions with the aid of lignin, and a small amount of Cr(VI) ions were adsorbed by lignin residue. Importantly, this method provides a typical example of "waste control by waste", which is treating waste chromium slag with waste lignin that can be an effective way to eliminate Cr(VI).

Lignin side chain region participates in Cd detoxification related to the cultivar-dependent Cd accumulation in Brassica chinensis L

To investigate the effect of lignin in the cultivar-dependent Cd detoxification of Brassica chinensis L., Cd and lignin contents, lignin composition and laccase genes expressions in low-Cd-accumulating (LAJK) and high-Cd-accumulating (HAJS) cultivars grown under control (CK) and 25 μM Cd-treatment were determined. The results showed that lignin combined about 14 % of total Cd in both LAJK and HAJS. LAC genes were more up-regulated in HAJS than in LAJK, indicating that the LAC genes were involved in the cultivar-dependent lignin functions. Higher β-aryl ether (A) proportion in the lignin side chain region in LAJK than in HAJS were observed, whereas resinol (B) and phenylcoumaran (C) constitute much higher proportions in HAJS than in LAJK. Chemical calculation to estimate Cd affinity associating with lignin side chain region displayed that i) β-aryl ether (A) exhibited major coupling with lignin aromatic region; ii) resinol (B) and phenylcoumaran (C) displayed major participation in complexation with Cd. We therefore conclude that Cd compartmentalization in the secondary cell wall (SCW) by coupling with lignin side chain region is responsible for Cd detoxification related to cultivar-dependent Cd accumulation of Brassica chinensis. This is the first study on lignin composition in relation to Cd retention mechanisms in SCW.

Synthesis of Chitosan-Ignosulfonate Composite as an Adsorbent for Dyes and Metal Ions Removal from Wastewater

Sodium lignosulfonate is a polymer with extensive sources and abundant functional groups. Therefore, it has potential value for research and wide utilization. In this study, the adsorption material was prepared by blending sodium lignosulfonate and chitosan, which could adsorb anionic and cationic dyes and metal ions. The composite was characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and thermogravimetry (TG). The results showed that the composite was cross-linked mainly by the strong electrostatic interaction between the protonated amino group in chitosan and the sulfonate group in sodium lignosulfonate. Moreover, the effects of initial concentration, adsorption time, initial pH, and mass ratio of chitosan to sodium lignosulfonate on the adsorption performance of the composite were investigated. Meanwhile, the adsorption processes were agreed well with the pseudo-second-order kinetic model and Langmuir isotherm model. The adsorption mechanism was that the electrostatic interaction between the protonated amino and hydroxyl groups of the composite with anionic (SO3 -) and HCrO4 - groups of Congo red and Cr(VI), respectively. In addition, the electrostatic interaction between SO3 - of the composite and positively charged group of Rhodamine B played an important role in the adsorption of Rhodamine B.

Cr(III) Adsorption by Cluster Formation on Boehmite Nanoplates in Highly Alkaline Solution

The development of advanced functional nanomaterials for selective adsorption in complex chemical environments requires partner studies of binding mechanisms. Motivated by observations of selective Cr(III) adsorption on boehmite nanoplates (γ-AlOOH) in highly caustic multicomponent solutions of nuclear tank waste, here we unravel the adsorption mechanism in molecular detail. We examined Cr(III) adsorption to synthetic boehmite nanoplates in sodium hydroxide solutions up to 3 M, using a combination of X-ray diffraction (XRD), Raman, X-ray photoelectron spectroscopy (XPS), scanning/transmission electron microscopy (S/TEM), electron energy loss spectroscopy (EELS), high-resolution atomic force microscopy (HR-AFM), time-of-fight secondary ion mass spectrometry (ToF-SIMS), Cr K-edge X-ray absorption near edge structure (XANES)/extended X-ray absorption fine structure (EXAFS), and electron paramagnetic resonance (EPR). Adsorption isotherms and kinetics were successfully fit to Langmuir and pseudo-second-order kinetic models, respectively, consistent with monotonic uptake of Cr(OH)₄^- monomers until saturation coverage of approximately half the aluminum surface site density. High resolution AFM revealed monolayer cluster self-assembly on the (010) basal surfaces with increasing Cr(III) loading, possessing a structural motif similar to guyanaite (β-CrOOH), stabilized by corner-sharing Cr-O-Cr bonds and attached to the surface with edge-sharing Cr-O-Al bonds. The selective uptake appears related to short-range surface templating effects, with bridging metal connections likely enabled by hydroxyl anion ligand exchange reactions at the surface. Such a cluster formation mechanism, which stops short of more laterally extensive heteroepitaxy, could be a metal uptake discrimination mechanism more prevalent than currently recognized.

Fabrication of magnetic lignosulfonate using ultrasonic-assisted in situ synthesis for efficient removal of Cr(Ⅵ) and Rhodamine B from wastewater

A novel and eco-friendly one-step approach has been developed to fabricate magnetic lignosulfonate (MLS) with high performance in wastewater treatment. The obtained MLS was characterized by FTIR, XRD, SEM, TEM, VSM. The results showed that MLS had a good magnetic behavior in an applied magnetic field and its saturation magnetization intensity was up to 43.98 emu/g. Moreover, MLS exhibited excellent adsorption properties for Cr(Ⅵ) (57.14 mg/g) and Rhodamine B (22.47 mg/g). Simultaneously, the adsorption kinetics and adsorption isotherm experiments indicated that the data was agreed well with the pseudo-second-order and Langmuir model, respectively. After five regeneration cycles, the desorption efficiencies of Cr(Ⅵ) and Rhodamine B could reach more than 70% and 85%, respectively. Hence, the magnetic lignosulfonate is a promising material as a highly adsorptive and recyclable adsorbent for removing metal ions and cationic pollutants in wastewater.

Removal of heavy metals from water sources in the developing world using low-cost materials: A review

Heavy metal contamination is a growing concern in the developing world. Inadequate water and wastewater treatment, coupled with increased industrial activity, have led to increased heavy metal contamination in rivers, lakes, and other water sources in developing countries. However, common methods for removing heavy metals from water sources, including membrane filtration, activated carbon adsorption, and electrocoagulation, are not feasible for developing countries. As a result, a significant amount of research has been conducted on low-cost adsorbents to evaluate their ability to remove heavy metals. In this review article, we summarize the current state of research on the removal of heavy metals with an emphasis on low-cost adsorbents that are feasible in the context of the developing world. This review evaluates the use of adsorbents from four major categories: agricultural waste; naturally-occurring soil and mineral deposits; aquatic and terrestrial biomass; and other locally-available waste materials. Along with a summary of the use of these adsorbents in the removal of heavy metals, this article provides a summary of the influence of various water-quality parameters on heavy metals and these adsorbents. The proposed adsorption mechanisms for heavy metal removal are also discussed.

Potential Use of Biochar from Various Waste Biomass as Biosorbent in Co(II) Removal Processes

The removal of Co(II) ions from aqueous media was done using three types of biochars obtained from algae waste biomass, mustard waste biomass, and soy waste biomass. The biochar samples were obtained by pyrolysis of waste biomass resulted from biofules production, at relative low temperature (600–650 °C), and this procedure can be considered a suitable alternative to reduce the volume of such waste. FTIR spectra recorded for each type of biochar reveal the presence of several functional groups that can be used as binding sites for Co(II) retention. The batch biosorption experiments were performed as a function of initial Co(II) ions concentration and contact time, at constant solution pH (5.0), sorbent dose (8.0 g/L), and room temperature (25 ± 1 °C). The sorption experiments showed that the Co(II) ions retention reaches the equilibrium in maximum 60 min, and the maximum sorption capacity follows the order: Mustard biochar (MBC—24.21 mg/g) < soy biochar (SBC—19.61 mg/g) < algae biochar (ABC—11.90 mg/g). The modeling of experimental data proves that the retention of Co(II) ions from aqueous solution occurs through electrostatic interactions, and that the sorption process takes place until a monolayer coverage is formed on the outer surface of the biochar. This information is very useful in the design of a suitable desorption system. The desorption results showed that by treating the biochar samples loaded with Co(II) ions with 0.1 mol/L HNO3 solution, over 92% of Co(II) ions are desorbed and can be recovered, and the biochar samples can be used in at least three sorption/desorption cycles. All the experimental observations sustain the potential use of biochar obtained from different types of waste biomass as a promising alternative sorbent for the removal of Co(II) ions from aqueous media.

Preparation of a Novel Lignin Nanosphere Adsorbent for Enhancing Adsorption of Lead

Carboxymethyl lignin nanospheres (CLNPs) were synthesized by a two-step method using microwave irradiation and antisolvent. The morphology and structure of CLNPs were characterized by ³¹P-NMR, FTIR, and SEM, and the results showed that they had an average diameter of 73.9 nm, a surface area of 8.63 m² or 3.2 times larger than the original lignin, and abundant carboxyl functional groups of 1.8 mmol/g. The influence of dosage, pH, contact time, and concentration on the adsorption of metal ions onto CLNPs were analyzed, and the maximum adsorption capacity of CLNPs for Pb(II) was found to be 333.26 mg/g, which is significantly higher than other lignin-based adsorbents and conventional adsorbents. Adsorption kinetics and isotherms indicated that the adsorption of lead ions in water onto CLNPs followed the pseudo-second-order model based on monolayer chemisorption mechanism. The main chemical interaction between CLNPs and lead ions was chelation. CLNPs also showed an excellent recycling performance, with only 27.0% adsorption capacity loss after 10 consecutive adsorption–desorption cycles.

Preparation of Xylan-g-/P(AA-co-AM)/GO Nanocomposite Hydrogel and its Adsorption for Heavy Metal Ions

Xylan-g-/P(AA-co-AM)/Graphene oxide (GO) hydrogels were prepared and used in the removal of heavy mental ions. Acrylamide (AM), acrylic acid (AA), and xylan were used as the raw materials to prepare the hydrogels with ammonium persulfate (APS) as the initiator. The prepared hydrogels were characterized by Fourier transform infrared (FTIR), thermogravimetric analysis (TGA), and energy dispersive X-ray (EDX). Some important properties of nanocomposite hydrogels such as swelling behavior, mechanical property, and adsorption capacity were also examined as well as the regeneration of the hydrogels. The results showed that the prepared hydrogels reached the equilibrium state of swelling after 12 h, and the compressive strength of the hydrogel with 30 mg of GO could reach up to 203 kPa. Compared with traditional hydrogel, the mechanical properties of the hydrogels with GO were obviously improved. The maximum adsorption capacity of hydrogels for Pb²⁺, Cd²⁺, and Zn²⁺ could reach up to 683 mg/g, 281 mg/g, and 135 mg/g, respectively. After five cycles of adsorption and desorption, the recovery rate of the hydrogels on Pb²⁺, Cd²⁺, and Zn²⁺ was still up to 87%, 80%, and 80%, respectively—all above 80%.

A review on the interactions between engineered nanoparticles with extracellular and intracellular polymeric substances from wastewater treatment aggregates

Engineered nanoparticles (ENPs) will inevitably enter wastewater treatment plants (WWTPs) due to their widespread application; thus, it is necessary to study the migration and transformation of nanoparticles in sewage treatment systems. Extracellular polymeric substances (EPSs) such as polysaccharides, proteins, nucleic acids, humic acids and other polymers are polymers released by microorganisms under certain conditions. Intracellular polymeric substances (IPSs) are microbial substances contained in the body with compositions similar to those of extracellular polymers. In this review, we summarize the characteristics of EPSs and IPSs from sewage-collecting microbial aggregates containing pure bacteria, activated sludge, granular sludge and biofilms. We also further investigate the dissolution, adsorption, aggregation, deposition, oxidation and other chemical transformation processes of nanoparticles, such as metals, metal oxides, and nonmetallic oxides. In particular, the review deeply analyzes the migration and transformation mechanisms of nanoparticles in EPS and IPS matrices, including physical, chemical, biological interactions mechanisms. Moreover, various factors, such as ionic strength, ionic valence, pH, light, oxidation-reduction potential and dissolved oxygen, influencing the interaction mechanisms are discussed. In recent years, studies on the interactions between EPSs/IPSs and nanoparticles have gradually increased, but the mechanisms of these interactions are seldom explored. Therefore, developing a systematic understanding of the migration and transformation mechanisms of ENPs is significant.

Lignin materials for adsorption: Current trend, perspectives and opportunities

Lignin is a highly aromatic low value biomass residue, which can be utilized for chemicals, fuels and materials production. In recent years significant attention has focused on adsorbent materials from lignin. However, only 5% of available lignin is exploited worldwide, thus significant opportunities still exist for materials development. This review summarizes recent research advances in lignin-based adsorbents, with a particular emphasis on lignin, its modification and carbon materials derived from this abundant feedstock. Lignin derived activated carbons have been utilized for air pollutant adsorption (e.g. CO₂, SO₂ and H₂S), while modified lignin materials have been developed for the removal of organic dyes and organics (like methylene blue, Procion Blue MX-R and phenols), heavy metals (such as Cu, Zn, Pb and Cd), or recovery of noble metals (e.g., Pd, Au and Pt). Future perspectives highlight how green chemistry approaches for developing lignin adsorbents can generate added value processes.

Isothermal Adsorption Properties for the Adsorption and Removal of Reactive Blue 221 Dye from Aqueous Solutions by Cross-Linked β-Chitosan Glycan as Acid-Resistant Adsorbent

Dye effluent causes serious pollution and damage to the environment and needs a series of treatments before it can be discharged. Among the numerous effluent treatment methods, adsorption is the simplest and does not cause secondary pollution. Bio-adsorbents are especially advantageous in the treatment of low-concentration dye effluent. In this study, the adsorption and removal capacities of unmodified α- and β-chitosan and modified β-chitosan (β-chitosan cross-linked with triethylenetetramine, BCCT) on C.I. Reactive Blue 221 (RB221) dye were compared. The experiments were performed on the adsorption of the RB221 dye by unmodified α- and β-chitosan and cross-linkage⁻modified BCCT at different temperatures and for different durations, which are presented along with the relevant adsorption kinetics calculations. According to the results, as the temperature increased from 303 to 333 K, the initial adsorption rates of the adsorbents, α-chitosan, β-chitosan, and BCCT, for the RB221 dye, changed from 1.01 × 10², 4.74 × 10², and 1.48 × 10⁶ mg/g min to 5.98 × 10⁴, 4.23 × 10⁸, and 1.52 × 1013 mg/g min, respectively. BCCT thus showed the best adsorption for the dye at all temperatures from the Elovich model. These results confirmed the successful introduction of a polyaminated and cross-linked extended structure as a modification for the BCCT adsorbent, which makes it resistant to acid hydrolysis and gives it the functional amine group for dye adsorption, thereby promoting the ability of BCCT to adsorb dyes under strongly acidic conditions. The compound synthesized in this study is expected to be a good choice in the future for purifying strongly acidic effluent containing anionic organic dyes.

High-efficiency extraction of bromocresol purple dye and heavy metals as chromium from industrial effluent by adsorption onto a modified surface of zeolite: Kinetics and equilibrium study

Tannery industrial effluent is rich in heavy metals and basic dyes as bromocresol purple (BCP), poses an economic problem and a serious danger to the environment. This research had evaluated the importance of the adsorption properties of a modified clinoptilolite (CL) (a type of zeolite) for the removal of BCP dye and some heavy metals as total chromium (tCr) in the ammoniac phase. The modified adsorbent was prepared by mixing solid waste (SW) and CL in a ratio 10:1. The CL, SW, and CL-SW materials were characterized and the adsorption behavior of the later to BCP and tCr was completely studied. The batch removal showed the optimal conditions for BCP adsorption: pH (6.5), time (t) (60 min), temperature (T) (303.15 K), sorbent dosage (m) (60.4 mg), and initial concentration (C_o) (11.7 mg/L). Moreover, the optimum conditions for tCr removal were: pH (8.8), t (55 min), T (303.15 K), m (400 mg), and C_o (16.0 mg/L). Cr desorption mechanism was an ion exchange reaction. The experimental data of tCr were best fitted by the Freundlich isotherm and the pseudo-second-order kinetic model. The maximum adsorption capacities of BCP and tCr onto the CL-SW were 175.5 mg/g and 37 mg/g, respectively. Thermodynamic studies revealed that the adsorptions were spontaneous and endothermic with an increase of entropy. The CL modified adsorbent seems to be a good and efficient for the removal of dyes as BCP and such heavy metals including Cr. Surprisingly, this treatment has largely improved the physicochemical properties of the industrial wastewater and proved a new concept "Polluter Cleans Polluters (PoClPos)".

Lignin and Lignin Based Materials for the Removal of Heavy Metals from Waste Water-An Overview

Water Pollution through heavy metals is the concerned issue as many industries like tanning, steel production and electroplating are the major contributors. Various toxic Heavy metals are a matter of concern as they have severe environmental and health effects. Most commonly, conventional methods are using to remove these heavy metals like precipitation, ion exchange, which are not economical and have disposal issues. Adsorption of heavy metals by different low-cost adsorbents seems to be the best option in wastewater treatment. Many agricultural by-products proved to be suitable as low-cost adsorbents for removing heavy metals efficiently in a minimum time. Lignin residues that involves both agricultural and wood residues and sometimes separated out from black liquor through precipitation have adsorption capacity and affinity comparable to other natural adsorbents. However, lignin as bio adsorbents have the advantage of less cost and gives efficient adsorption results. This study is a review of the recent literature on the use of natural lignin residues for heavy metals adsorption under different experimental scenarios.

Production of Flocculants, Adsorbents, and Dispersants from Lignin

Currently, lignin is mainly produced in pulping processes, but it is considered as an under-utilized chemical since it is being mainly used as a fuel source. Lignin contains many hydroxyl groups that can participate in chemical reactions to produce value-added products. Flocculants, adsorbents, and dispersants have a wide range of applications in industry, but they are mainly oil-based chemicals and expensive. This paper reviews the pathways to produce water soluble lignin-based flocculants, adsorbents, and dispersants. It provides information on the recent progress in the possible use of these lignin-based flocculants, adsorbents, and dispersants. It also critically discusses the advantages and disadvantages of various approaches to produce such products. The challenges present in the production of lignin-based flocculants, adsorbents, and dispersants and possible scenarios to overcome these challenges for commercial use of these products in industry are discussed.

Preparation of biochar from Enteromorpha prolifera and its use for the removal of polycyclic aromatic hydrocarbons (PAHs) from aqueous solution

EP-biochar was produced from Enteromorpha prolifera (EP) at temperatures of 200-600°C under limited-oxygen conditions and then activated using HCl and HF. To optimize the sorption of pyrene (PYR) and benzo[a]pyrene (BaP), the effect of the pyrolysis temperature was studied, and the results showed that EP-biochar produced at 500°C gave the highest removal efficiency. The physiochemical properties of EP-biochar pyrolyzed at 500°C were characterized. The examination indicated that the surface area of EP-biochar was 205.32m²/g. The effect of the EP-biochar dosage and initial solution pH on the adsorption were studied in batch adsorption experiments. Kinetic studies indicated that the adsorption processes of PYR and BaP agreed well with a pseudo second-order kinetic model. The sorption equilibrium data were well described by the Langmuir model. Desorption experiments were conducted to test the strength of binding interactions of EP-biochar. The results showed that PYR and BaP were difficult to dissolve in water after adsorption. Regeneration experiments demonstrated that the biochars regenerated at 200°C retained approximately 48% and 40% of their initial PYR and BaP uptake.

Laccase-Catalyzed Synthesis of Low-Molecular-Weight Lignin-Like Oligomers and their Application as UV-Blocking Materials

The laccase-catalyzed oxidative polymerization of monomeric and dimeric lignin model compounds was carried out with oxygen as the oxidant in aqueous medium. The oligomers were characterized by using gel permeation chromatography (GPC) and matrix-assisted laser desorption ionization time-of-flight mass spectroscopy (MALDI-TOF MS) analysis. Oxidative polymerization led to the formation of oligomeric species with a number-average molecular weight (M_n ) that ranged from 700 to 2300 Da with a low polydispersity index. Spectroscopic analysis provided insight into the possible modes of linkages present in the oligomers, and the oligomerization is likely to proceed through the formation of C-C linkages between phenolic aromatic rings. The oligomers were found to show good UV light absorption characteristics with high molar extinction coefficient (5000-38 000 m^-1  cm^-1 ) in the UV spectral region. The oligomers were blended independently with polyvinyl chloride (PVC) by using solution blending to evaluate the compatibility and UV protection ability of the oligomers. The UV/Vis transmittance spectra of the oligomer-embedded PVC films indicated that these lignin-like oligomers possessed a notable ability to block UV light. In particular, oligomers obtained from vanillyl alcohol and the dimeric lignin model were found to show good photostability in accelerated UV weathering experiments. The UV-blocking characteristics and photostability were finally compared with the commercial low-molecular-weight UV stabilizer 2,4-dihydroxybenzophenone.

Adsorption of PtCl62− from Hydrochloric Acid Solution by Chemically Modified Lignin Based on Rice Straw

A novel adsorbent with the properties of selective adsorption based on rice straw was used to adsorb PtCl62− from hydrochloric acid solution by batch sorption. Many influencing factors for PtCl62− adsorption, such as initial concentration of PtCl62−, adsorption time, and concentration of hydrochloric acid, were optimized. The results suggested that the saturation adsorption capacity of PtCl62− was 218.8mgg−1 and the equilibrium adsorption time was 120min. The adsorbent had excellent selectivity on PtCl62− when the concentration of hydrochloric acid was lower than 0.5molL−1. The adsorption fitted well with the Langmuir isotherm model and pseudo-second-order kinetics model. The adsorption mechanism was investigated by FT-IR and X-ray photoelectron spectroscopy analyses and it indicated that PtIV was reduced to PtII by hydroxy groups and then coordinated with N through ion exchange between Cl− and PtCl42−.

Fabrication of mesoporous lignin-based biosorbent from rice straw and its application for heavy-metal-ion removal

Lignocellulosic biomass offers the most abundant renewable resource in replacing traditional fossil resources. However, it is still a major challenge to directly convert the lignin component into value-added materials. The availability of plentiful hydroxyl groups in lignin macromolecules and its unique three-dimensional structure make it an ideal precursor for mesoporous biosorbents. In this work, we reported an environmentally friendly and economically feasible method for the fabrication of mesoporous lignin-based biosorbent (MLBB) from lignocellulosic biomass through a SO₃ micro-thermal-explosion process, as a byproduct of microcrystalline cellulose. BET analysis reveal the average pore-size distribution of 5.50nm, the average pore value of 0.35cm³/g, and the specific surface area of 186m²/g. The physicochemical properties of MLBB were studied by fourier transform infrared spectroscopy (FTIR), attenuated-total-reflection fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), and element analysis. These results showed that there are large amounts of sulfonic functional groups existing on the surface of this biosorbent. Pb(II) was used as a model heavy-metal-ion to demonstrate the technical feasibility for heavy-metal-ion removal. Considering that lignocellulosic biomass is a naturally abundant and renewable resource and SO₃ micro-thermal-explosion is a proven technique, this biosorbent can be easily produced at large scale and become a sustainable and reliable resource for wastewater treatment.

Adsorption of Cu(ii) ions in aqueous solution by aminated lignin from enzymatic hydrolysis residues

Aminated lignin (AL) has been prepared by a Mannich reaction for the removal of Cu(ii) ions from aqueous solution.