Facile One-Pot Synthesis of Sustainable Carboxymethyl Chitosan - Sewage Sludge Biochar for Effective Heavy Metal Chelation and Regeneration

Modified chitosan: Insight on biomedical and industrial applications

Chitosan (CS), a by -product of chitin deacetylation can be useful in a broad range of purposes, to mention agriculture, pharmaceuticals, material science, food and nutrition, biotechnology and of recent, in gene therapy. Chitosan is a highly desired biomolecule due to the existence of many sensitive functional groups inside the molecule and also because of its net cationicity. The latter provides flexibility for creating a wide range of derivatives for particular end users across various industries. This overview aims to compile some of the most recent research on the bio-related applications that chitosan and its derivatives can be used for. However, chitosan's reactive functional groups are amendable to chemical reaction. Modifying the material to show enhanced solubility, a greater range of application options and pH-sensitive targeting and others have been a major focus of chitosan research. This review describes the modifications of chitosan that have been made to improve its water solubility, pH sensitivity, and capacity to target chitosan derivatives. Applying the by-products of chitosan as antibacterial, in targeting, extended release and as delivery systems is also covered. The by-products of chitosan will be important and potentially useful in developing new biomedical drugs in time to come.

Fabrication of engineered biochar for remediation of toxic contaminants in soil matrices and soil valorization

Biochar has emerged as an efficacious green material for remediation of a wide spectrum of environmental pollutants. Biochar has excellent characteristics and can be used to reduce the bioavailability and leachability of emerging pollutants in soil through adsorption and other physico-chemical reactions. This paper systematically reviewed previous researches on application of biochar/engineered biochar for removal of soil contaminants, and underlying adsorption mechanism. Engineered biochar are derivatives of pristine biochar that are modified by various physico-chemical and biological procedures to improve their adsorption capacities for contaminants. This review will promote the possibility to expand the application of biochar for restoration of degraded lands in the industrial area or saline soil, and further increase the useable area. This review shows that application of biochar is a win-win strategy for recycling and utilization of waste biomass and environmental remediation. Application of biochar for remediation of contaminated soils may provide a new solution to the problem of soil pollution. However, these studies were performed mainly in a laboratory or a small scale, hence, further investigations are required to fill the research gaps and to check real-time applicability of engineered biochar on the industrial contaminated sites for its large-scale application.

Functionalization of Shorea faguetiana biochar using Fe2O3 nanoparticles and MXene for rapid removal of methyl blue and lead from both single and binary systems

The synthesis of polymeric magnetic composites is a promising strategy for the rapid and efficient treatment of wastewater. Lead and methyl blue are extremely hazardous to living organisms. The sorption of Pb2+ and the dye methyl blue (MB) by biochar is an ecologically sustainable method to remediate this type of water pollution. We functionalized Shorea faguetiana biochar with Fe2O3 and MXene, resulting in Fe2O3/BC/MXene composites with an efficient, rapid, and selective adsorption performance. Based on X-ray photoelectron and Fourier transform infrared spectrometry, we found that the Fe2O3/BC/MXene composites had an increased number of surface functional groups (F-, C[double bond, length as m-dash]O, CN, NH, and OH-) compared with the original biochar. The batch sorption findings showed that the maximum sorption capacities for Pb2+ and MB at 293 K were 882.76 and 758.03 mg g-1, respectively. The sorption phenomena obeyed a pseudo-second-order (R2 = 1) model and the Langmuir isotherm. There was no competition between MB and Pb2+ in binary solutions, indicating that MB and Pb2+ did not influence each other as a result of their different adsorption mechanisms (electrostatic interaction for Pb2+ and hydrogen bonding for MB). This illustrates monolayer sorption on the Fe2O3/BC/MXene composite governed by chemical adsorption. Thermodynamic investigations indicated that the sorption process was spontaneous and exothermic at 293-313 K, suggesting that it is feasible for practical applications. Fe2O3/BC/MXene can selectively adsorb Pb2+ ions and MB from wastewater containing multiple interfering metal ions. The sorption capacities were still high after five reusability experiments. This work provides a novel Fe2O3/BC/MXene composite for the rapid and efficient removal of Pb2+ and MB.

Highly effective removal of multi-heavy metals from simulated industrial effluent through an adsorption process employing carboxymethyl-chitosan composites

Monochloroacetic acid precursor-based carboxymethyl chitosan resins were prepared using the chitosan with variant molecular weight. The carboxymethylation assured enhanced active sites on the resin surface, acidic media stability, and henceforth its appropriate constitution to facilitate enhanced multi-heavy metal adsorption-desorption and subsequent regeneration potential. Zn, Pb, and Fe multimetal adsorption properties were investigated. Thereby, kinetic and equilibrium models were sought for their fitness to represent heavy metal sorption data with the preferred complex adsorbate system. The adsorbate system complexity and its constituent co-existing cations significantly influence the sorption characteristics of the mentioned multi-heavy metal ions. The optimal adsorption capabilities for Zn, Pb, and Fe were 238.10 mg g-1, 4.78 mg g-1, and 147.06 mg g-1, respectively. Low-cost acid-base solutions were also considered for the effective regeneration of the resin even after three adsorption-desorption cycles. Prominent findings of the work assured excellent functionality of the carboxymethyl-chitosan resin for the simultaneous lead, iron, and zinc ion elimination from mimicking real-world effluent systems.

DOTA functionalized adsorbent DOTA@Sludge@Chitosan derived from recycled shrimp shells and sludge and its application for lead and chromium removal from water

DOTA@Sludge@Chitosan was synthesized by a facile treatment using DOTA (1,4,7,10-tetraazacyclododecane-N,N',N,N'-tetraacetic acid) to modify dry sludge and chitosan in an acidic solution. The performance of developed DOTA@Sludge@Chitosan was investigated for the adsorptive removal of Cr6+ and Pb2+ from water. Characterization studies showed that the materials possess a large surface area (52.009 m2/g), pore volume (0.069 cm3/g), and abundant functional groups of amino and hydroxyl. The prepared material showed a synergetic effect due to carboxylic acid and sludge, effectively removing Cr6+ and Pb2+. It reached 329.4 mg/g (Pb2+) and 273.3 mg/g (Cr6+) at 20 °C, much higher than commercial activated carbon. The regeneration of the adsorbent was tested for six adsorption and desorption cycles. The results demonstrate that the DOTA@Sludge@Chitosan adsorbent well-maintained high adsorption capacity attributed to its stability, making it a promising adsorbent for heavy metals removal from industrial effluent.

Simultaneous Cr(VI) reduction and Cr(III) sequestration in a wide pH range by using magnetic chitosan-based biopolymer

The simultaneous reduction of Cr(VI) and sequestration of the resulting Cr(III) in one process is highly desirable as a cost-effective and environmental-friendly approach for the decontamination of Cr(VI)-polluted wastewater. However, most of the existing adsorptive materials are only effective in low pH environments (pH = 1-3), severely restricting the adsorption efficiency and cost effectiveness. Herein, we proposed a chitosan-based magnetic porous microsphere (PPy@PMCS) for simultaneous Cr(VI) reduction and Cr(III) sequestration in a wide pH range. Benefiting from its abundant interaction sites, Cr(VI) was effectively adsorbed on the surface and then immediately reduced to Cr(III) with much lower toxicity. Most importantly, the resulting Cr(III) was in-situ sequestrated by the complexation of chitosan matrix. As a result, PPy@PMCS exhibited a maximum Cr(VI) adsorption capacity of 330.42 mg/g at pH 2.0 and an adsorption capacity of 167.82 mg/g even at near neutral pH (6.0), which is superior to most reported adsorbents. Furthermore, the exhausted PPy@PMCS can be rapidly separated from solutions under an external magnetic field and facilely regenerated. The proposed novel biopolymer-based material shows great application potentials in wastewater treatment.

A review on heavy metal biosorption utilizing modified chitosan

Heavy metal pollution in water bodies is a global concern. The prominent source of metal contamination in aqueous streams and groundwater is wastewater containing heavy metal ions. Elevated concentrations of heavy metals in water bodies can have a negative impact on water quality and public health. The most effective way to remove metal contaminants from drinking water is thought to be adsorption. A deacetylated derivative of chitin, chitosan, has a wide range of commercial uses since it is biocompatible, nontoxic, and biodegradable. Due to its exceptional adsorption behavior toward numerous hazardous heavy metals from aqueous solutions, chitosan and its modifications have drawn a lot of interest in recent years. Due to its remarkable adsorption behavior toward a range of dangerous heavy metals, chitosan is a possible agent for eliminating metals from aqueous solutions. The review has focused on the ideas of biosorption, its kinds, architectures, and characteristics, as well as using modified (physically and chemically modified) chitosan, blends, and composites to remove heavy metals from water. The main objective of the review is to describe the most important aspects of chitosan-based adsorbents that might be beneficial for enhancing the adsorption capabilities of modified chitosan and promoting the usage of this material in the removal of heavy metal pollutants.

Hydroxylamine facilitated catalytic degradation of methylene blue in a Fenton-like system for heat-treatment modified drinking water treatment residues

Rational treatment of drinking water treatment residues (WTR) has become an environmental and social issue due to the risk of secondary contamination. WTR has been commonly used to prepare adsorbents because of its clay-like pore structure, but then requires further treatment. In this study, a Fenton-like system of H-WTR/HA/H₂O₂ was constructed to degrade organic pollutants in water. Specifically, WTR was modified by heat treatment to increase its adsorption active site, and to accelerate Fe(III)/Fe(II) cycling on the catalyst surface by the addition of hydroxylamine (HA). Moreover, the effects of pH, HA and H₂O₂ dosage on the degradation were discussed with methylene blue (MB) as the target pollutant. The mechanism of the action of HA was analyzed and the reactive oxygen species in the reaction system were determined. Combined with the reusability and stability experiments, the removal efficiency of MB remained 65.36% after 5 cycles. Consequently, this study may provide new insights into the resource utilization of WTR.

Progress in preparation and properties of chitosan-based hydrogels

Chitosan is a kind of natural polysaccharide biomass with the second highest content in nature after cellulose, which has good biological properties such as biocompatibility, biodegradability, hemostasis, mucosal adsorption, non-toxicity, and antibacterial properties. Therefore, hydrogels prepared from chitosan have the advantages of good hydrophilicity, unique three-dimensional network structure, and good biocompatibility, so they have received extensive attention and research in environmental testing, adsorption, medical materials, and catalytic supports. Compared with traditional polymer hydrogels, biomass chitosan-based hydrogels have advantages such as low toxicity, excellent biocompatibility, outstanding processability, and low cost. This paper reviews the preparation of various chitosan-based hydrogels using chitosan as raw material and their applications in the fields of medical materials, environmental detection, catalytic carriers, and adsorption. Some views and prospects are put forward for the future research and development of chitosan-based hydrogels, and it is believed that chitosan-based hydrogels will be able to obtain more valuable applications.

Adsorptive removal of antibiotic pollutants from wastewater using biomass/biochar-based adsorbents

This study explores adsorptive removal measures to shed light on current water treatment innovations for kinetic/isotherm models and their applications to antibiotic pollutants using a broad range of biomass-based adsorbents. The structure, classifications, sources, distribution, and different techniques for the remediation of antibiotics are discussed. Unlike previous studies, a wide range of adsorbents are covered and adsorption of comprehensive classes of antibiotics onto biomass/biochar-based adsorbents are categorized as β-lactam, fluoroquinolone, sulfonamide, tetracycline, macrolides, chloramphenicol, antiseptic additives, glycosamides, reductase inhibitors, and multiple antibiotic systems. This allows for an assessment of their performance and an understanding of current research breakthroughs in applying various adsorbent materials for antibiotic removal. Distinct from other studies in the field, the theoretical basis of different isotherm and kinetics models and the corresponding experimental insights into their applications to antibiotics are discussed extensively, thereby identifying the associated strengths, limitations, and efficacy of kinetics and isotherms for describing the performances of the adsorbents. In addition, we explore the regeneration of adsorbents and the potential applications of the adsorbents in engineering. Lastly, scholars will be able to grasp the present resources employed and the future necessities for antibiotic wastewater remediation.

Simultaneous Recovery of Nitrogen and Phosphorus from Sewage by Magnesium Ammonium Phosphate Method with Magnesium-Loaded Bentonite

Excessive nitrogen (N) and phosphorus (P) result in serious eutrophication of water. In this study, magnesium modified acid bentonite was prepared by the impregnation method, and nitrogen and phosphorus were simultaneously removed by the magnesium ammonium phosphate method (MAP), which solved the problem of the poor adsorption capacity of bentonite. The morphology and structure of MgO-SBt were characterized by XRD, FT-IR, SEM, EDS, XPS, BET, etc. The results show that the acidified bentonite can increase the distance between bentonite layers, the layer spacing is expanded to 1.560 nm, and the specific surface area is expanded to 95.433 m²/g. After Mg modification, the characteristic peaks of MgO appear at 2θ of 42.95°, 62.31°, and 78.72°, indicating that MgO has been successfully loaded and that MgO bonded to the surface and interior pores of the acidified bentonite, boosting adsorption performance. When the dosage of MgO-SBt is 0.25 g/L, pH = 9, and N/P ratio is 5:1, the maximum adsorption capacity of MgO-SBt for N and P can reach 193.448 mg/g and 322.581 mg/g. In addition, the mechanism of the simultaneous adsorption of nitrogen and phosphorus by MgO-SBt was deeply characterized by the kinetic model, isothermal adsorption model, and thermodynamic model. The results showed that the simultaneous adsorption of nitrogen and phosphorus by MgO-SBt was chemisorption and a spontaneous exothermic process.

Assessment of agricultural waste biochars for remediation of degraded water-soil environment: Dissolved organic carbon release and immobilization of impurities in one- or two-adsorbate systems

This paper presents a method of agricultural waste management - the production of two biochars (BC) from potato and raspberry stems. It defines the potential of these materials for remediation of degraded water and soil environments. The performed study included analyses of BC physicochemistry, dissolved organic carbon (DOC) release and ability to immobilize copper (Cu), tetracycline (TC) and carboxin (CB) in one- and two-adsorbate systems. The BCs were obtained with pyrolysis at 600 °C for 30 min in a nitrogen atmosphere. Their DOC was predominantly constituted of substances with large molecular weights and high aromaticity, meaning that both BCs can be safely applied as soil additives. Potato-biochar (P-BC) had a more developed surface than raspberry-biochar (R-BC). The specific surface area (S_BET) of P-BC was 122 m²/g, whilst of R-BC was 87 m²/g. As a result, the efficiency of impurity adsorption in the one-adsorbate systems was higher for P-BC (61.75% for Cu, 73.84% for TC, and 54.43% for CB). In the two-adsorbate systems, organic impurities improved the immobilization of heavy metal ions on BCs. The efficiency of Cu adsorption on P-BC when TC was present was 88.29%. Desorption of Cu from BC was highest using HCl, whilst that of TC and CB was highest using NaOH. Maximum desorption was observed in a two-adsorbate system with TC + CB (up to 63.6% for TC). These results confirmed that potato and raspberry stems can be used to produce highly effective BCs with large application potential, especially for remediation of degraded soils and polluted waters.

Selenium Oxoanions Removal from Wastewater by MoS42− Intercalated FeMgAl LDH: Catalytic Roles of Fe and Mechanism Insights

FeMgAl−MoS4 LDH was successfully synthesized by a one-pot hydrothermal process followed by ion-exchange methods, and this novel adsorbent was first conducted for aqueous selenite and selenate elimination. The Fe as a component for metal cation layers of LDHs could modulate the layer charge density, leading to more functional groups inserted into layers, and more importantly, this heterogeneous Fe can catalyze the surface reactions between Se(IV) or Se(VI) with S(-II) for oxoanions sequestration. The mechanisms are ion exchange between functional groups with HSeO3− and SeO32− for Se(IV) or SeO42− for Se(VI), followed by reduction by S(-II) from MoS42− groups. The existence of Fe in LDH cation layers, obviously enhanced the reactions (almost two times more for Se(IV) and three times more for Se(VI), respectively), resulting in satisfying adsorption capacities of 483.9 mg/g and 167.2 mg/g for Se(IV) and Se(VI), respectively. Mechanisms were further revealed by elementary analysis, XRD, FT−IR, SEM−EDX, and XPS, as well as the quantitative study. For sorption kinetics, the calculated values of capacities from the pseudo-second-order model are much closer to the experimental values. For sorption isotherms, Langmuir is better than the Freundlich isotherms model for closer capacities (505 mg/g for selenite and 172 mg/g for selenate). All these results demonstrated that the presence of heterogeneous Fe could catalyze the reduction of Se (IV/VI) for the aqueous system, and maybe other high oxidative states hazardous ions. So FeMgAl−MoS4 is a kind of novel adsorbent that offers a promising multi-functional and highly efficient solution for water selenium purification.

Efficient adsorption of heavy metals from wastewater on nanocomposite beads prepared by chitosan and paper sludge

Chitosan was commonly used with inorganic salt and organic compounds to prepare adsorption material for water treatment. Different materials were mixed for the preparation, leading to a high cost for water treatment. Sludge from papermaking has abundant fiber and inorganic salt, which can reduce the addition of raw materials in preparing the adsorption material and thus lower the cost. This work used recycled industrial paper sludge to prepare adsorption material to remove heavy metals from wastewater. The adsorption properties of the prepared sludge-chitosan material for Cu²⁺ and Cr³⁺ in wastewater were investigated. The impacts of adsorption time, pH, and initial concentrations of Cu²⁺ and Cr³⁺ on adsorption amount were studied and optimized. The saturated adsorption capacity of sludge-chitosan material for Cu²⁺ and Cr³⁺ can reach 114.6 and 110.3 mg/g. The adsorption kinetics satisfied the pseudo-second-order model, indicating two modes, physical diffusion, and chem-sorption, in the heavy metal adsorption by the sludge-chitosan materials. Physical distribution has little Effect on chemical adsorption. The materials can be applied to treating Cu²⁺ and Cr³⁺ containing wastewater with the proposed cheap and readily available sludge-chitosan material. The results confirmed that sludge-chitosan material possessed good regeneration performance and was an ideal adsorbent.

Adsorption of tetracycline by Nicandra physaloides (L.) Gaertn seed gum and Nicandra physaloides(L.) Gaertn seed gum/Carboxymethyl chitosan aerogel

In this study, novel aerogels of Nicandra physaloides (L.) Gaertn seed gum (NPG) and Nicandra physaloides (L.) Gaertn seed gum/Carboxymethyl chitosan (NPG/CMC) were prepared by freeze-drying method for removing tetracycline (TC) from water. Scanning electron microscope (SEM), X-ray diffraction (XRD),Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and Brunauer-Emmett-Teller (BET) were used to characterize structure and morphology of NPG and NPG/CMC aerogels. The average pore diameter of NPG and NPG/CMC were 3.04 and 1.2 nm, the specific surface areas were 2.67 and 0.73 m²/g, respectively. The maximum adsorption capacity of NPG and NPG/CMC aerogels for TC based on Langmuir isotherm was 266.7 and 332.23 mg/g respectively. Through thermodynamic and kinetic studies, it was found that the adsorption processes of the two adsorbents were spontaneous and followed the pseudo-second-order kinetic model. And the process of NPG adsorption of TC was endothermic, while NPG/CMC was exothermic.

A critical review on utilization of sewage sludge as environmental functional materials

Sewage sludge (SS) is increasingly used as an environment functional material to reduce or control pollution and improve plant growth because of the large amounts of carbon and essential plant nutrients in it. To achieve the best application results, it is essential to comprehensively review recent progress in SS utilization. This review aims to fill the gaps in knowledge by describing the properties of SS, and its usage as adsorbents, catalysts and fertilizers, and certain application mechanisms. Although SS generates several benefits for the environment and humans, many challenges still exist to limit the application, including the risks posed by potentially toxic substances (e.g., heavy metals) in SS. Therefore, future research directions are discussed and how to make SS applications more feasible in terms of technology and economy.

A green approach towards sorption of CO2 on waste derived biochar

Carbon capture technologies have advanced in recent years to meet the ever-increasing quest to minimize excessive anthropogenic CO₂ emissions. The most promising option for CO₂ control has been identified as carbon capture and storage. Among the numerous sorbents, char generated from biomass thermal conversion has shown to be an efficient CO₂ adsorbent. This study examines various characteristics that can be used to increase the yield of biochar suited for carbon sequestration. This review gives recent research progress in the area, stressing the variations and consequences of various preparation processes on textural features such as surface area, pore size and sorption performance with respect to CO₂'s sorption capacity. The adjoining gaps discovered in this field have also been highlighted herewith, which will serve as future work possibility. It aims to analyse and describe the possibilities and potential of employing pristine and modified biochar as a medium of CO₂ capture. It also examines the parameters that influence biochar's CO₂ adsorption ability and pertinent challenges regarding the production of biochar-based CO₂ sorbent materials.

A sustainable reuse strategy of converting waste activated sludge into biochar for contaminants removal from water: Modifications, applications and perspectives

Conversion of sewage sludge to biochar for contaminants removal from water achieves the dual purpose of solid waste reuse and pollution elimination, in line with the concept of circular economy and carbon neutrality. However, the current understanding of sludge-derived biochar (SDB) for wastewater treatment is still limited, with a lack of summary regarding the effect of modification on the mechanism of SDB adsorption/catalytic removal aqueous contaminants. To advance knowledge in this aspect, this paper systematically reviews the recent studies on the use of (modified) SDB as adsorbents and in persulfate-based advanced oxidation processes (PS-AOPs) as catalysts for the contaminants removal from water over the past five years. Unmodified SDB not only exhibits stronger cation exchange and surface precipitation for heavy metals due to its nitrogen/mineral-rich properties, but also can provide abundant catalytic active sites for PS. An emphatic summary of how certain adsorption removal mechanisms of SDB or its catalytic performance in PS-AOPs can be enhanced by targeted regulation/modification such as increasing the specific surface area, functional groups, graphitization degree, N-doping or transition metal loading is presented. The interference of inorganic ions/natural organic matter is one of the unavoidable challenges that SDB is used for adsorption/catalytic removal of contaminants in real wastewater. Finally, this paper presents the future perspectives of SDB in the field of wastewater treatment. This review can contribute forefront knowledge and new ideas for advancing sludge treatment toward sustainable green circular economy.

Efficient removal of mercury and chromium from wastewater via biochar fabricated with steel slag: Performance and mechanisms

Biochar derived from biomass is regarded as a promising adsorbent for wastewater treatment, but the high cost of modification is still a challenge for its large-scale practical applications. In this study, we employed steel slag as a low-cost fabricant and synthesized hydrothermally carbonized steel slag (HCSS), as a stable environmentally functional material for heavy metal removal. Typically, positively and negatively charged heavy metal contaminants of Hg²⁺ and Cr₂O₇²⁻ were employed to testify the performance of HCSS as an adsorbent, and good capacities [(283.24 mg/g for Hg (II) and 323.16 mg/g for Cr (VI)] were found. The feasibility of HCSS on real wastewater purification was also evaluated, as the removal efficiency was 94.11% and 88.65% for Hg (II) and Cr (VI), respectively. Mechanism studies revealed that the modification of steel slag on bio-adsorbents offered copious active sites for pollutants. As expected, oxygen-containing functional groups in HCSS acted as the main contributor to adsorption capacity. Moreover, some reactive iron species (i.e., Fe²⁺) played an essential role in chemical reduction of Cr (VI). The adsorptive reactions were pH-dependent, owing to other more mechanisms, such as coprecipitation, ion-exchange, and electrostatic attraction. This promising recycling approach of biomass waste and the design of agro-industrial byproducts can be highly suggestive of the issues of resource recovery in the application of solid waste-derived environmentally functional materials for heavy metal remediation.

Progress in Research of Chitosan Chemical Modification Technologies and Their Applications

Chitosan, which is derived from chitin, is the only known natural alkaline cationic polymer. Chitosan is a biological material that can significantly improve the living standard of the country. It has excellent properties such as good biodegradability, biocompatibility, and cell affinity, and has excellent biological activities such as antibacterial, antioxidant, and hemostasis. In recent years, the demand has increased significantly in many fields and has huge application potential. Due to the poor water solubility of chitosan, its wide application is limited. However, chemical modification of the chitosan matrix structure can improve its solubility and biological activity, thereby expanding its application range. The review covers the period from 1996 to 2022 and was elaborated by searching Google Scholar, PubMed, Elsevier, ACS publications, MDPI, Web of Science, Springer, and other databases. The various chemical modification methods of chitosan and its main activities and application research progress were reviewed. In general, the modification of chitosan and the application of its derivatives have had great progress, such as various reactions, optimization of conditions, new synthetic routes, and synthesis of various novel multifunctional chitosan derivatives. The chemical properties of modified chitosan are usually better than those of unmodified chitosan, so chitosan derivatives have been widely used and have more promising prospects. This paper aims to explore the latest progress in chitosan chemical modification technologies and analyze the application of chitosan and its derivatives in various fields, including pharmaceuticals and textiles, thus providing a basis for further development and utilization of chitosan.

Treatment of faecal sludge and sewage effluent by pinewood biochar to reduce wastewater bacteria and inorganic contaminants leaching

Biochar is a valuable treatment option for faecal sludge management (FSM). However, the sanitation application rates of biochar in FSM are not well established. There is also a gap in knowledge about the effect of actual raw sewage effluent and sludge on organic and inorganic contaminants migration of biochar treated soil. This study investigated the concentration and migration rates of N, P, E. coli and faecal coliform bacteria through different soil-bed biochar column treatments leached with raw faecal sludge and sewage effluent. Forty-four soil-bed leaching columns with pinewood biochar rates at 5, 10 and 20 t/ha were set at the Bloemspruit wastewater plant, South Africa. The pinewood biochar used had a pH of 10.21, total C composition of 92%, surface area of 517 m²/g, and a pore size of 1.7 nm. It was found that the 20 t biochar per ha treatment with faecal sludge increased water retention (flows of 33 mm/h. at 0 t/ha compared to 0.8 mm/h. at 20 t/ha) and leachates purification. High detections were observed for faecal coliforms and E.coli above 4331 CFU/100 mL from the effluent and faecal sludge in soils without biochar. Detection of E.coli at 20 t/ha decreased to 1 CFU/100 mL while the faecal coliforms still had counts above 10 CFU/ 100 mL. The results showed a decreasing rate of nitrates, phosphates, zinc and copper with an increasing biochar application rate. Pinewood biochar showed significant removal efficiencies of bacteria (between 89 and 98%) and nitrates and phosphates (between 68 and 98%). Significant differences were seen at P < 0.05 between the means of the treatments with and without biochar. The results from the study show that pinewood biochar applied at rates between 5 and 20 t/ha has a high organic and inorganic contaminants reduction potential for FSM.

Resource utilization of tannery sludge to prepare biochar as persulfate activators for highly efficient degradation of tetracycline

In this work, a low-cost carbon-based catalyst (TSBC) was prepared by the facile one-pot pyrolysis of tannery sludge (TS) and used to activate persulfate (PS) for tetracycline (TC) removal. The results showed that TSBC-500 exhibited optimal physicochemical properties and the best performance for PS activation to remove TC from drinking water. Approximately 99.1% of TC was removed in the TSBC-500/PS system, which was considerably higher than those in the TSBC-500 adsorption and pure PS systems. Radical quenching experiments indicated that •OH and SO₄•^- played major roles in the TC removal in the TSBC-500/PS system. In addition, transition metals, functional groups, and the high degree of carbon structural defects were beneficial for PS activation to degrade TC. This study not only newly contributes to high-value utilization of TS as a PS activator but also offers an efficient method for the removal of organic pollutants.

Simultaneous capturing of mixed contaminants from wastewater using novel one-pot chitosan functionalized with EDTA and graphene oxide adsorbent

The emergence of inorganic and organic contaminants has raised great concerns owing to their adverse impact on human health and ecological security. Herein, first time one-pot process was applied for chitosan (CS) functionalization using graphene oxide (GO) and ethylenediaminetetraacetic acid (EDTA) for simultaneous capturing of toxic inorganic (lead (Pb²⁺) and cadmium (Cd²⁺)) and organic (ciprofloxacin (CIP) and sildenafil (SDF)) contaminants from wastewater. In this approach, we believe that CS would work as a backbone, GO would capture both inorganic and organic contaminants via electrostatic interactions, while EDTA would make complexation with heavy metals. Various parameters including pH, reaction time, concentration, reusability etc. were evaluated to achieve the best experimental result in monocomponent system. The prepared adsorbent displayed an excellent monolayer adsorption capacity of 351.20 and 264.10 mg g^-1 for Pb²⁺ and Cd²⁺, respectively, while a heterogeneous sorption capacity of 75.40 and 40.90 mg g^-1 for CIP and SDF, respectively. The kinetics data fitted well to Pseudo-second order (PSO) kinetics model for both types of contaminants and gave faster interaction towards metal ions (higher k₂) than organic contaminants. Experimental results showed excellent adsorption efficiencies at environmental levels in the capturing of both inorganic and organic contaminants at the same time from polluted water. The capturing mechanism of both types of contaminants was explained by elemental mapping, EDS, and FT-IR spectra. Overall, easy synthesis, excellent capturing capacity, and reusability imply that the prepared adsorbent has a sufficient potential for the treatment of co-existing toxic contaminants in water.

Recovery, regeneration and sustainable management of spent adsorbents from wastewater treatment streams: A review

Adsorption is the most widely adopted, effective, and reliable treatment process for the removal of inorganic and organic contaminants from wastewater. One of the major issues with the adsorption-treatment process for the removal of contaminants from wastewater streams is the recovery and sustainable management of spent adsorbents. This review focuses on the effectiveness of emerging adsorbents and how the spent adsorbents could be recovered, regenerated, and further managed through reuse or safe disposal. The critical analysis of both conventional and emerging adsorbents on organic and inorganic contaminants in wastewater systems are evaluated. The various recovery and regeneration techniques of spent adsorbents including magnetic separation, filtration, thermal desorption and decomposition, chemical desorption, supercritical fluid desorption, advanced oxidation process and microbial assisted adsorbent regeneration are discussed in detail. The current challenges for the recovery and regeneration of adsorbents and the methodologies used for solving those problems are covered. The spent adsorbents are managed through regeneration for reuse (such as soil amendment, capacitor, catalyst/catalyst support) or safe disposal involving incineration and landfilling. Sustainable management of spent adsorbents, including processes involved in the recovery and regeneration of adsorbents for reuse, is examined in the context of resource recovery and circular economy. Finally, the review ends with the current drawbacks in the recovery and management of the spent adsorbents and the future directions for the economic and environmental feasibility of the system for industrial-scale application.

Mechanistic insights of removing pollutant in adsorption and advanced oxidation processes by sludge biochar

With the accelerated industrialization, more and more sewage sludge (SS) needs to be treated properly. The conversion of sludge into harmless biochar material with dual utilization value of adsorption and catalysis by pyrolysis is in line with the concept of sustainable development. However, the reaction mechanisms of pristine sludge biochar (SDBC) and its composites (SDBCs) in adsorption, persulfate (PS), and Fenton-like advanced oxidation processes (AOPs) are very closely related to its adsorption performance and catalytic efficiency. In this paper, from the application mechanisms of SDBC in adsorption and AOPs, we review in detail the common methods for synthesizing SDBC and their characteristics. We discuss the synthesis techniques that affect the structural, chemical, and catalytic properties of SDBC, including gasification, pyrolysis, and hydrothermal carbonation (HTC). The pyrolysis temperature, environmental factors, and sludge characteristics have important effects on the properties of SDBC, leading to different mechanisms in adsorption and catalytic processes. Furthermore, this paper systematically generalizes the mechanisms of SDBCs in adsorption, where π-π interactions and electrostatic attractions are the main adsorption mechanisms. Then, activation mechanisms of SDBCs in PS and Fenton-like AOPs systems are discussed, including free radical pathways and non-free radical pathways. Finally, we present several challenges and perspectives for the application of SDBC and SDBCs in the field of adsorption, PS, and Fenton-like AOPs from the mechanistic point of views.

Chitosan-modified biochar: Preparation, modifications, mechanisms and applications

The chitosan-modified biochar composite, as a carbohydrate polymer, has received increasing attention and becomes a research hotspot. It is a promising impurity adsorption material, which has potential application value in the agricultural environment fields such as soil improvement and sewage purification. The composite can combine the advantages of biochar with chitosan, and the resulting composite usually exhibits a great improvement in its surface functional groups, adsorption sites, stability, and adsorption properties. In addition, compared to other adsorbents, the composite truly achieves the concept of "waste control by waste". In this paper, the preparation method, composite classification, adsorption mechanism, and models of biochar modified by chitosan are introduced, meanwhile, we also review and summarize their effects on the decontamination of wastewater and soil. In addition to common heavy metal ions, we also review the adsorption and removal of some other organic/inorganic pollutants, including (1) drug residues; (2) dyes; (3) phosphates; (4) radionuclides; (5) perfluorochemicals, etc. Moreover, challenges and prospects for the composite are presented and further studies are called for the chitosan-biochar composite. We believe that the composite will lead to further achievements in the field of environmental remediation.

Recent development of magnetic biochar crosslinked chitosan on heavy metal removal from wastewater - Modification, application and mechanism

Heavy metal contamination in water bodies is currently in an area of greater concern due to the adverse effects on human health. Despite the good adsorption performance of biochar, various modifications have been performed on the pristine biochar to further enhance its adsorption capability, at the same time overcome the difficulty of particles separation and mitigate the secondary pollution issues. In this review, the feasibility of chitosan-modified magnetic biochar for heavy metal removal from aqueous solution is evaluated by critically analysing existing research. The effective strategies that applied to introduce chitosan and magnetic substances into the biochar matrix are systematically reviewed. The physicochemical changes of the modified-biochar composite are expounded in terms of surface morphology, pore properties, specific surface area, surface functional groups and electromagnetism. The detailed information regarding the adsorption performances of various modified biochar towards different heavy metals and their respective underlying mechanisms are studied in-depth. The current review also analyses the kinetic and isotherm models that dominated the adsorption process and summarizes the common models that fitted well to most of the experimental adsorption data. Moreover, the operating parameters that affect the adsorption process which include solution pH, temperature, initial metal concentration, adsorbent dosage, contact time and the effect of interfering ions are explored. This review also outlines the stability of modified biochar and their regeneration rate after cycles of heavy metal removal process. Lastly, constructive suggestions on the future trends and directions are provided for better research and development of chitosan-modified magnetic biochar.

Chitosan-assisted MOFs dispersion via covalent bonding interaction toward highly efficient removal of heavy metal ions from wastewater

Metal organic frameworks (MOFs) have been considered to be robust adsorbent for the removing heavy metal ions from wastewater due to their unique properties such as large active sites, high specific surface area and high porosity, etc., however, their practical engineering application faces the problem of serious agglomeration. In this work, a new strategy of chitosan (CS) assisting MOF dispersion was proposed to develop the new generation of MOF-based adsorbents, namely, CS grafted UiO-66-NH₂ composite materials (CGUNCM). The UiO-66-NH₂ was selected and it was grafted onto the main chains of CS through covalent bonding interaction with the aid of glutaraldehyde, which was totally different from the common method that grafting molecular chains on the surface of MOFs resulting in the dramatic reduction of active adsorption sites. The results show that grafting MOFs onto CS main chains not only greatly improves the dispersion of MOFs but also reserves the morphology of MOFs as much as possible. The adsorption performances toward Cu(II) and Pb(II) were intensively studied by varying adsorbate concentration, ionic strength, the contact time, adsorption temperature and pH value of solution. The results show that the composite adsorbent exhibits high adsorption efficiency and the adsorption equilibrium can be reached within 45 min, and the maximum adsorption capacity toward Cu(II) and Pb(II) achieve 364.96 mg/g and 555.56 mg/g, respectively. Furthermore, the composite adsorbent shows good reusability. This work provides a new method of fabricating the MOF-based adsorbent and paves the way for the practical application of such adsorbents in wastewater treatment.

A critical review of biochar-based materials for the remediation of heavy metal contaminated environment: Applications and practical evaluations

The contamination of heavy metals (HMs) in the environment has aroused a global concern. The valid remediation of HM contaminated environment is a highly significant issue. As alternative to carbon materials, biochar has been vastly documented for the remediation of HM contaminated environment. However, there are some possible imperfections to meet the actual remediation tasks as the finite properties of raw biochar, and the remediation process is complex and unexpectedly. This review focuses on the progress made on environmental HM remediation by biochar-based materials within the past six years. The property analysis and key modifications of biochar are summarized inspired by their applicability or necessity for HM decontamination, and the environmental remediation as well as the implicated mechanisms are thoroughly elaborated from multiple pivotal sides. The evaluations of practical application associated with biochar amendment are also presented. Finally, some pertinent improvements and research directions are proposed. To our knowledge, this article is the first time to make a systematic summary on the reliability and practicability of biochar-based materials for environmental HM remediation, and critically pointed out the existing issues to facilitate the judicious design of biochar-based materials and understanding the research trends. It is also aims to provide reference for subsequent research and propel the practical applications.

Optimizing magnetic functionalization conditions for efficient preparation of magnetic biochar and adsorption of Pb(II) from aqueous solution

Recoverable magnetic biochar has great potential for treating wastewater contaminants such as Pb(II). However, whether magnetic modification could enhance metal adsorption efficiency is currently contradictory in the literature mainly due to the differences in selecting various magnetic functionalization conditions. Considering this gap in knowledge, the effects of magnetic functionalization method (impregnation and precipitation), concentration of precursor iron solution (0.01-1 M), and pyrolysis temperature (300-700 °C) on the characteristics and Pb(II) adsorption capacity of biochar were systematically investigated in this paper. Results indicated that Fe₃O₄ was the main product for magnetic biochars synthesized using the impregnation (denoted as FWFe(3)) and precipitation methods (denoted as FWFe(2)). Magnetic functionalization resulted in remarkably increased pH and more negative zeta potential for FWFe(2) samples, whereas FWFe(3) samples showed the opposite trends. The adsorption of Pb(II) on different biochars fitted the pseudo-second order model and the Langmuir model. The maximum adsorption capacity was 817.64 mg/g for FWFe(2)1M700C (precipitation by 1 M of Fe(II)/Fe(III), pyrolysis at 700 °C), outperforming FWFe(3) and pristine biochar samples by around 5-13 times. Mechanism study indicated that the adsorption mainly involved electrostatic attraction, ion exchange, co-precipitation, and complexation. Pb(II) adsorption capacity was strongly dependent on the alkali pH of biochar. However, this efficiency was less affected by biochar surface area and its morphology. The higher pH of FWFe(2) samples not only led to an increased surface charge for stronger electrostatic attraction and ion exchange but also favored the formation of co-precipitates. By contrast, FWFe(3) samples showed a decreased adsorption capacity for Pb(II) with increased concentration of embedded iron. Overall, magnetic biochar, prepared using precipitation followed by high-temperature pyrolysis (such as, FWFe(2)1M700C), can be a promising adsorbent for Pb(II) adsorption from wastewater.

Sewage sludge-derived biochar for the adsorptive removal of wastewater pollutants: A critical review

The production of biochar from sewage sludge pyrolysis is a promising approach to transform the waste resultant from wastewater treatment plants (WWTPs) to a potential adsorbent. The current review provides an up-to-date review regarding important aspects of sewage sludge pyrolysis, highlighting the process that results major solid fraction (biochar), as high-value product. Further, the physio-chemical characteristics of sewage-sludge derived biochar such as the elemental composition, specific surface area, pore size and volume, the functional groups, surface morphology and heavy metal content are discussed. Recent progress on adsorption of metals, emerging pollutants, dyes, nutrients and oil are discussed and the results are examined. The sewage sludge-derived biochar is a promising material that can make significant contributions on pollutants removal from water by adsorption and additional benefit of the management of huge volume of sewage. Considering all these aspects, this field of research still needs more attention from the researchers in the direction of the technological features and sustainability aspects.

Biochar derived from fruit by-products using pyrolysis process for the elimination of Pb(II) ion: An updated review

Water pollution is one of the most concerning global environmental problems in this century with the severity and complexity of the issue increases every day. One of the major contributors to water pollution is the discharge of harmful heavy metal wastes into the rivers and water bodies. Without proper treatment, the release of these harmful inorganic waste would endanger the environment by contaminating the food chains of living organisms, hence, leading to potential health risks to humans. The adsorption method has become one of the cost-effective alternative treatments to eliminate heavy metal ions. Since the type of adsorbent material is the most vital factor that determines the effectiveness of the adsorption, continuous efforts have been made in search of cheap adsorbents derived from a variety of waste materials. Fruit waste can be transformed into valuable products, such as biochar, as they are composed of many functional groups, including carboxylic groups and lignin, which is effective in metal binding. The main objective of this study was to review the potential of various types of fruit wastes as an alternative adsorbent for Pb(II) removal. Following a brief overview of the properties and effects of Pb(II), this study discussed the equilibrium isotherms and adsorption kinetic by various adsorption models. The possible adsorption mechanisms and regeneration study for Pb(II) removal were also elaborated in detail to provide a clear understanding of biochar produced using the pyrolysis technique. The future prospects of fruit waste as an adsorbent for the removal of Pb(II) was also highlighted.

Recyclable polyurethane foam loaded with carboxymethyl chitosan for adsorption of methylene blue

Novel composite foam (CMCTS-PUF-s) was prepared by immobilizing carboxymethyl chitosan (CMCTS) on polyurethane foam (PUF) in which amino groups in CMCTS reacted with isocyanate groups in polyurethane prepolymer. The adsorption capacity of the optimal composite foam (CMCTS-PUF-5) reached to 118.2 mg/g with 5% CMCTS loading. The removal rate to methylene blue (MB) was up to 97.1%, which was obviously higher than 18.9% of PUF. After recycling for five times, the removal rate still reached 83.2%, which strongly proved the excellent reusability of immobilizing CMCTS modified PUF. The characterization results of FTIR and TG showed that CMCTS was well loaded on PUF by covalent bond. The Young's modulus and tensile strength of CMCTS-PUF-5 were increased by 252% and 97% compared with that of PUF. MIP characterization result showed the porosity of CMCTS-PUF-5 was 73.99% and the pore sizes were mainly distributed between 50 and 150 µm, which provide sufficient diffusion channels and active sites for MB dyes. The adsorption kinetics and isotherm proved pseudo-second-order kinetic model and Langmuir isotherm model could well describe the adsorption process of CMCTS-PUF-5. Therefore, CMCTS-PUF-s presents excellent recoverability, high stability and attractive adsorption efficiency, shows the potential application in future treatment of dye wastewater.

Biochars and Engineered Biochars for Water and Soil Remediation: A Review

Biochars (BCs) are considered as ecofriendly and multifunctional materials with significant potential for remediation of contaminated water and soils, while engineered biochars (E-BCs) with enlarged surface areas and abundant surface functional groups can perform even better in environmental remediation. This review systematically summarizes the key physical and chemical properties of BCs that affect their pollutant sorption capacities, major methods employed for modification of E-BCs, the performance of BCs/E-BCs in removing major types of organic (e.g., antibiotics and pesticides) and inorganic pollutants (e.g., heavy metals), and the corresponding removal mechanisms. The physical and chemical properties of BCs—such as ash or mineral contents, aromaticity, surface structures, pH, and surface functional groups (e.g., C=O, -COOH, -OH, and -NH2)—depend primarily on their feedstock sources (i.e., plant, sludge, or fecal) and the pyrolysis temperature. Ion exchange, precipitation, electrostatic attraction, and complexation are the main mechanisms involved in the adsorption of inorganic pollutants on BCs/E-BCs, whereas hydrogen bonding, pore filling, electrostatic attraction, hydrophobic interaction, and van der Waals forces are the major driving forces for the uptake of organic pollutants. Despite their significant promises, more pilot and field scale investigations are necessary to demonstrate the practical applicability and viability of BCs/E-BCs in water and soil remediation.

Carboxymethyl chitosan‒promoted luminescence of lanthanide metallogel and its application in assay of multiple metal ions

In this work, the luminescence of lanthanide supramolecular metallogel formed by the self-assembly of 5,5',5″-(1,3,5-triazine-2,4,6-triyl)tris(azanediyl)triisophthalate (H₆L) and Tb³⁺ was efficiently promoted by carboxymethyl chitosan (CMCS). The total quantum yield of the resultant metallogel (denoted as H₆L/Tb³⁺/CMCS gel) was 9 times higher than the gel without CMCS. The average lifetime of H₆L/Tb³⁺/CMCS gel increased from 0.51 ms to 1.20 ms. More importantly, the aqueous dispersion of H₆L/Tb³⁺/CMCS xerogels showed a stable and pH-dependent luminescence. Based on the selective affinity of CMCS to different metal ions as well as with the aid of principal component analysis, H₆L/Tb³⁺ /CMCS can be used as a sensor array to distinguish 11 metal ions (P < 0.05). This work provides a new strategy for the design and development of bio-based functional luminescent lanthanide supramolecular metallogels.

Lead(II) adsorption on microwave-pyrolyzed biochars and hydrochars depends on feedstock type and production temperature

Adsorption of lead(II) using carbon-rich chars is an environmentally sustainable approach to remediate lead(II) pollution in industrial wastewater. We studied mechanisms for lead(II) adsorption from synthetic wastewater by biochars produced by microwave-assisted pyrolysis and hydrochars by hydrothermal carbonization at three temperatures using four feedstocks. Lead(II) adsorption was highest (165 mg g^-1) for canola straw biochar produced at 500 °C. Except for chars derived from sawdust, biochars outperformed hydrochars for lead(II) adsorption due to changes in solution pH driven by char pH. As char production temperature increased, lead(II) adsorption decreased in hydrochar mainly due to interaction with aromatic carbon but increased in biochar due to precipitation as hydrocerussite and lead oxide phosphate. Lead(II) adsorption also occurred via surface complexation and cation-ᴨ interaction, as the data fitted well to Freundlich, Langmuir and Temkin models, and the pseudo-first and pseudo-second order kinetic models, depending on feedstock type and production temperature. More than 80% of lead(II) adsorption occurred in the first 3 h for both types of chars; with a few exceptions, adsorption continued for almost 24 h. We conclude that production method, production temperature and feedstock type are crucial factors to consider in designing chars as adsorbents for removing lead(II) from wastewater.

Adsorption of metals from oil sands process water (OSPW) under natural pH by sludge-based Biochar/Chitosan composite

Some metals in oil sands process water (OSPW) are potential threats to human health and the environment. Hence, the removal of excess metals from OSPW is of great significance. In this study, anaerobic sludge waste from a wastewater treatment plant, was reused to prepare sludge-based biochar. A Biochar/Chitosan (Biochar/CS) adsorbent with excellent removal efficiency for metals (Cr, Cu, Se and Pb) in real OSPW was prepared through a facile hydrothermal method. The structural properties of the synthesized Biochar/CS composite were characterized via X-ray diffraction (XRD), scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) method. This study reports for the first time the removal of metals from OSPW under natural pH using Biochar/CS adsorbent. The composite exhibited a higher removal efficiency towards Cr (83.9%), Cu (97.5%), Se (87.9%) and Pb (94.3%) when the initial concentrations of Cr, Cu, Se and Pb were 0.02914, 0.06185, 0.00800 and 0.00516 mg/L, respectively, at a dosage of 0.5 g/L, compared with biochar or chitosan alone. The possible adsorption mechanism was proposed, and the enhanced removal ability was due to the improved specific surface area and pore volume, which increased by about 20 and 14 times as compared with chitosan. Functional groups in the composite, such as -NH₂, -OH and some oxygen containing groups, were also responsible for the enhanced removal ability, which also might be the reason for the better performance of the composite than biochar alone due to the lack of functional groups on the biochar. Moreover, the adsorption process was best modelled by the Freundlich model, pseudo second order and intraparticle diffusion kinetic models. The results indicated that chemical adsorption might play the dominant role in the removal process. Overall, the Biochar/CS composite would be a promising and effective adsorbent for metals removal, owing to its advantages of being cost-effective and environmentally friendly.

Efficient removal of selenate in water by cationic poly(allyltrimethylammonium) grafted chitosan and biochar composite

The discovery of cheap and eco-friendly functional materials for the removal of anionic heavy metal ions is still challenging in the treatment of heavy metal-contaminated water. Herein, a new poly(allyltrimethylammonium) grafted chitosan and biochar composite (PATMAC-CTS-BC) was introduced for the removal of selenate (SeO₄^2-) in water. Results suggest that the PATMAC-CTS-BC showed a rapid removal of SeO₄^2- with efficiency of >97% within 10 min and it followed a pseudo-second-order model. High capacity of SeO₄^2- adsorption by the composite was achieved, with maximum value of 98.99 mg g^-1 based on Langmuir model, considerably higher than most of reported adsorbents. The thermodynamic results reflected the spontaneous and exothermic nature of SeO₄^2- adsorption onto the composite. The composite could be applied at a wide initial pH range (2-10) with high removal efficiency of SeO₄^2- because of permanent positive charges of quaternary ammonium groups (=N⁺-). The removal mechanisms of SeO₄^2- were mainly attributed to electrostatic interactions with =N⁺- and protonated -NH₃⁺ groups, and redox-complexation interactions with -NH₂, -NH-, and -OH groups. Besides SeO₄^2-, the hexavalent chromium (Cr₂O₇^2-) was considered as example to further demonstrate the anion removal capability of cationic hydrogel-BC composite. The study outcomes open up new opportunities to efficiently remove anionic heavy metal ions (e.g., SeO₄^2- and Cr₂O₇^2-) in water using these materials.

Conversion of sewage sludge into biochar: A potential resource in water and wastewater treatment

Production of biochar from sewage sludge (SS) is consistent with the goal of sustainable resource recovery and promotes a wastewater-based circular economy. Thermochemical conversion of SS to biochar resolves two major issues simultaneously as it minimizes the cost of disposal and acts as a resource to eliminate the toxic contaminants from water and wastewater. The reusability and ready availability of the biochar, irrespective of the season, makes it an economically viable material for wastewater treatment. In this review, explicit insights into the production, modification and usage of SS derived biochar are provided including (i) the production yield, (ii) characteristic features such as physical, chemical, electrochemical and morphological aspects, and (iii) impact on contaminant removal through adsorption, catalytic and electrochemical processes. Particular attention is given to the use of SS derived biochar as an adsorbent for contaminants present in wastewaters, the potential use of biochar as a catalyst and support material in advanced oxidation processes and the use of biochars as an electrode material. The effect of pyrolysis conditions and co-pyrolysis with other materials on biochar properties is explored and insight is provided into the toxicity of biochar components present at different process conditions.

Recent Developments in Chitosan-Based Adsorbents for the Removal of Pollutants from Aqueous Environments

The quality of water is continuously under threat as increasing concentrations of pollutants escape into the aquatic environment. However, these issues can be alleviated by adsorbing pollutants onto adsorbents. Chitosan and its composites are attracting considerable interest as environmentally acceptable adsorbents and have the potential to remove many of these contaminants. In this review the development of chitosan-based adsorbents is described and discussed. Following a short introduction to the extraction of chitin from seafood wastes, followed by its conversion to chitosan, the properties of chitosan are described. Then, the emerging chitosan/carbon-based materials, including magnetic chitosan and chitosan combined with graphene oxide, carbon nanotubes, biochar, and activated carbon and also chitosan-silica composites are introduced. The applications of these materials in the removal of various heavy metal ions, including Cr(VI), Pb(II), Cd(II), Cu(II), and different cationic and anionic dyes, phenol and other organic molecules, such as antibiotics, are reviewed, compared and discussed. Adsorption isotherms and adsorption kinetics are then highlighted and followed by details on the mechanisms of adsorption and the role of the chitosan and the carbon or silica supports. Based on the reviewed papers, it is clear, that while some challenges remain, chitosan-based materials are emerging as promising adsorbents.

Egg shell biochar-based green catalysts for the removal of organic pollutants by activating persulfate

The sulfate radical based advanced oxidation processes (SR-AOPs) has shown great potential in environmental remediation. In recent years, metal-free catalysts have attracted great attention due to their properties of low environmental risk and high catalytic activity. Among them, biochar-based catalysts are widely studied for their low cost by using substance existing in nature as raw material. In this work, egg shell derived biochar (ES-biochar), which was prepared by a simple one-pot pyrolysis method, has been proven to be an effective and innovative catalyst to activate persulfate for aqueous organic pollutant degradation. In addition, ES-biochar showed superior performance in the degradation reaction with removal efficiency of more than 90% in 120 min for 2,4-dichlorophenol (2,4-DCP), which was selected as a representative organic pollutant. Further quenching tests and electron spin resonance spectroscopy demonstrated that both free-radicals and non-radicals pathways were involved in this process, and OH dominated in free-radicals process. More importantly, this work not only proposed a novel biochar material as an efficient persulfate activator, but also provided a value-added reuse approach for egg shell in line with the concept of resource recycling and environmental sustainability.

Unravelling the Environmental Application of Biochar as Low-Cost Biosorbent: A Review

In this age, a key target for enhancing the competitiveness of the chemical, environmental and biotechnology industries is to manufacture high-value products more efficiently and especially with significantly reduced environmental impact. Under this premise, the conversion of biomass waste to a high-value added product, biochar, is an interesting approach under the circular economy principles. Thus, the improvements in the biochar production and its new and innovative uses are hot points of interest, which are the focus of vast efforts of the scientific community. Biochar has been recognized as a material of great potential, and its use as an adsorbent is becoming a reliable strategy for the removal of pollutants of different streams, according to its high adsorption capacity and potential to eliminate recalcitrant compounds. In this review, a succinct overview of current actions developed to improve the adsorption capability of biochar, mainly of heavy metal and organic pollutants (dyes, pharmaceuticals and personal care products), is summarized and discussed, and the principal adsorption mechanisms are described. The feedstock and the production procedure are revealed as key factors that provide the appropriate physicochemical characteristics for the good performance of biochar as an adsorbent. In addition, the modification of the biochar by the different described approaches proved their feasibility and became a good strategy for the design of selective adsorbents. In the last part of this review, the novel prospects in the regeneration of the biochar are presented in order to achieve a clean technology for alleviating the water pollution challenge.