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Remediating hexavalent chromium [Cr(VI)] from contaminated water systems is a significant concern due to its harmful effects on human health, aquatic life, and plants. To tackle this issue, scientists have created a chitosan cross-linked hydrous ceria incorporated cupric oxide bio-polymeric composite (CHCCO) by combining chitosan biopolymer with corresponding metal ions using glutaraldehyde as a cross-linker. The composite was characterized using advanced analytical instruments such as FTIR, p-XRD, SEM, XPS, etc. The synthesized composite (CHCCO) was then tested for its efficiency in removing Cr(VI) from synthetic Cr(VI) aqueous samples. The parameters examined included pH, material dose, contact time, concentration, temperature, and co-existing ions. The experimental data showed that the kinetics and equilibrium data fit well with the pseudo-second-order and the Freundlich isotherm models, respectively. Thermodynamic analysis demonstrated that the investigated surface adsorption process is spontaneous and endothermic. Except for the SO 4 2- ion, no other species imparts adverse influence significantly on the reaction. The CHCCO bio-composite surfaces were refreshed using a dilute NaOH (1.0 M) solution and effectively recycled five times for Cr(VI) adsorption, indicating no significant surface activity deterioration. This study highlights the high effectiveness of CHCCO bio-polymeric composites in Cr(VI) remediation and the potential for this technology as an easy-to-use technique for environmental restoration., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

To address the increasing demand for sensitive and selective sample preparation methods for metal analysis; preconcentration of intended analyte from complex sample matrices before analysis is required to improve the performance of analysis instruments. In this study, we have engineered a sustainable and portable syringe-based hand-operable three-dimensionally (3D) printed sample pretreatment apparatus equipped with a replaceable bio-based thin- film metal sorbent. This device effectively addresses the challenges of sample matrix interference in metal analysis. A metal sorbent film composed of chitosan (CS) and polydopamine (PDA) leveraged the diverse functional groups in the CS/PDA matrix to significantly enhance the extraction efficiency for various metals. Our approach demonstrated excellent analytical performance, with coefficients of determination (R 2 ) of 0.9982 for copper (Cu) and 0.996 for chromium (Cr). The method achieved low limits of detection (LOD) of 0.3 μg L -1 for Cr and 0.7 μg L -1 for Cu. Precision and practicality assessments using actual urine samples yielded satisfactory relative standard deviations (RSD%) ranging from of 1.6 %-8.5 % for both metals, indicating minimal interference from the sample matrix. Moreover, our approach exhibited robust performance even after seven consecutive extraction and desorption cycles, highlighting its sustainability and practical applicability for laboratory and on-site sample pretreatment., Competing Interests: Declaration of competing interest The authors declare that they have no competing interests., (Copyright © 2024 Elsevier B.V. All rights reserved.)

The increasing use of hexavalent chromium (Cr(VI)) has exposed large populations to this environmental and occupational carcinogenic agent. Therefore, researchers have been interested in removing this substance through adsorbents. This study aimed to investigate the efficiency of natural zeolite in the direct adsorption of Cr(VI) from airflow and its adsorption modeling. In this study, a nebulizer device produced the Cr(VI) mist. The efficiency of natural zeolite in Cr(VI) adsorption from airflow, modeling of fixed column adsorption, and the effective parameters on adsorption efficiency including the initial concentration of chromium, airflow rate, and adsorption bed depth were studied. To facilitate the prediction of the performance of natural zeolite's adsorption column, Yoon-Nelson, Thomas, BDST, and Buhart-Adams models were used. The results showed that the adsorption capacity diminished with increased airflow rate and initial concentration, while it increased with elevated height of the adsorption bed. Yoon-Nelson, Thomas, and BDST models corresponded to experimental data with a correlation coefficient of 0.9933, but the information of the Buhart-Adams model had a lower correlation coefficient (around 0.6677). In conclusion, natural zeolite can be used as an efficient low-cost adsorbent for directly Cr(VI) removing from the airflow in a fixed bed column., (© 2024. The Author(s).)

Industrial wastewater containing heavy metal Cr(VI) seriously affects the health of organisms and may even lead to cancer. Developing efficient adsorbents that can quickly separate heavy metals is crucial for treating wastewater. In this study, magnetic multiwalled carbon nanotubes (MMWCNTs) with moderate particle size and abundant surface active sites were prepared by coating multiwalled carbon nanotubes with magnetic nanoparticles. The results of FTIR, XRD, TG, VSM, BET, and EDS showed MWCNTs completely encapsulated on the surface of the magnetic nanoparticles, with a particle size of approximately 30 nm. Oxygenated groups provided abundant surface active sites and formed numerous mesopores. The response surface methodology was used to optimize the adsorbent dose, adsorption contact time and adsorption temperature, and the removal rate of Cr(VI) was more than 95%. The quasi-second order kinetics and Freundlich adsorption isotherm model explained the adsorption process to Cr(VI). MMWCNTs interacted with Cr(VI) through electrostatic attraction, reduction reactions, complexation, and other means. The extensive hydrogen bonding of the green solvent deep eutectic solvent (DES) was employed to desorb the MMWCNTs and desorption rate exceed 90%. Even after five adsorption-regeneration cycles, the adsorbent maintained a high capacity. In conclusion, these novel MMWCNTs, as efficient adsorbents paired with DES desorption, hold broad potential for application in the treatment of Cr(VI)-contaminated wastewater., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

This study addresses the limited understanding of chromium-microbial mat interactions in estuarine tidal flats. The aims were to evaluate (1) the efficiency of the microbial consortium in Cr(III) removal from seawater; (2) the elemental and mineralogical composition of the microbial mat as a natural system in the Cr removal, (3) the effects of metal on microphytobenthos, and (4) possible interactions of Cr with other metals present in the consortium. Microbial mats were exposed to Cr(III) solutions at different concentrations (2-30 mg Cr/L). Analysis such as metal concentration, organic matter content, chlorophyll a and phaeopigment concentrations, abundance of diatoms and cyanobacteria, SEM-EDS, and XRD were performed. Most of the Cr(III) was deposited, as chromium oxide/hydroxide, on the surface of all microbial mat components. The complete microbial mat, comprising sediments, detritus, EPS, and diverse microorganism communities, exhibited a remarkable capacity to accumulate Cr(III), retaining over 87% in the solution., (© 2024. The Author(s), under exclusive licence to Springer Nature B.V.)

Developing cost-effective and efficient adsorbents for heavy metals in multicomponent systems is a challenge that needs to be resolved to meet the challenges of wastewater treatment technology. Two adsorbents were synthesized, characterized, and investigated for the removal of Cd 2+ and Cr 3+ as model heavy metals in their single and binary solutions. The first adsorbent (ACZ) was a nanocomposite formed of O-Carboxymethyl chitosan, sodium alginate, and zeolite. While, the other (ACL) contained ZnFe layered double hydroxides instead of the zeolite phase. Adsorbents were characterized using XRD, FTIR, SEM, and swelling degree analysis. For single heavy metal adsorption isotherms, data for both adsorbents was best fitted and indicated a multilayer adsorption nature. For binary adsorption, Langmuir model with interacting parameters showed the best results compared to other models for both pollutants. For single system, Avrami model was found to be the best model representing the adsorption kinetics data, which indicates that the mechanism of adsorption follows multiple kinetic orders that may change during duration of adsorption process. Numerous interaction mechanisms can occur between the heavy metals and functional groups in the synthesized hydrogels such as NH 2 , COOH, and OH groups leading to efficient adsorption of metal ions., Competing Interests: Declaration of competing interest All authors declare no competing interests., (Copyright © 2024 Elsevier B.V. All rights reserved.)

A biochar (KBC) enriched with O functional groups was prepared by torrefaction using lignin-rich kiwifruit branches (KBM) as a raw material, which was characterized, and then KBC was used to adsorb hexavalent chromium (Cr 6+ ) from water. The results showed that KBC contained more functional groups compared to KBM. The maximum adsorption of Cr 6+ by KBC could reach 143.64 mg·g -1 and also had better adsorption performance than other adsorbents reported in some other reports. Cr 6+ absorption by KBC was mainly a mechanism of electrostatic interaction and adsorption-reduction coupling. FTIR and XPS revealed that -OH, -COOH, CO and CC on KBC participated in Cr 6+ adsorption and new groups (C=O) were generated during the process of adsorption, which implied that a redox reaction occurred. 2D-COS and DFT calculations showed that the order of functional groups on KBC interacting with Cr 6+ was -OCH 3  > -COOH > -OH > phenolic hydroxyl, and the binding tightness of the different functional groups to Cr 6+ was -OCH 3 (the shortest displacement of both groups after the adsorption) > -COOH > -OH > phenolic hydroxyl. KBC has good regeneration performance, and it is a good adsorbent for Cr 6+ ., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

The development of biocompatible adsorbents is vital for environmental remediation to control and reduce pollution and waste accumulation in ecosystems. Biocompatible hydrogels represent an innovative class of materials that are primarily composed of polymer chain units forming their structural framework. They have a high affinity for water molecules. This research thus aims to incorporate iron oxide particles into the gelatin matrix to produce gelatin hydrogel beads to remove hexavalent chromium from an aqueous solution. The synthesized beads, known for their consistent size, low friction, high specific surface area, mechanical stability, and lightweight characteristics, demonstrated their suitability for various industrial applications. The effectiveness of these hydrogels in removing hexavalent chromium ions was confirmed through a thorough analysis using techniques such as FTIR, TGA, SEM, EDX, VSM, and XPS. Batch experiments revealed that the gelatin-based nanocomposite beads exhibited optimal adsorption efficiency under acidic conditions, lower initial concentrations of chromium ions, extended contact time, and elevated temperature (50-60 °C). The composite achieved a maximum removal efficiency of 99% at pH 1, with an adsorbent dose of 0.5 g at 50 °C, and an initial concentration of 50 mg per liter. The use of 0.7 N NaOH in the regeneration process resulted in a commendable 70.5% desorption efficiency, enabling potential reuse and regeneration. Significantly, the desorption efficiency remained consistently high even after four desorption-readsorption cycles, contributing to the economic and environmental sustainability of chromium removal. Additionally, the study determined that the sorption process was feasible, spontaneous, and endothermic. These collective findings suggest that magnetic gelatin hydrogel beads could serve as a cost-effective alternative adsorbent for the efficient removal of chromium ions from aqueous solutions., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

In this work, polypyrrole (PPy) was synthesized on the surface of waste surgical face masks (SFM) with a novel environmentally-friendly in-situ-surface polymerization approach and used as an adsorbent for removing hexavalent chromium (Cr(VI)). In this method, the SFM surface was activated using KMnO 4 , resulting in the immobilization of porous MnO 2 , on which pyrrole can be polymerized efficiently. The novelty of this method is the presence of the oxidant on the surface before the polymerization step, which results in a better surface modification with polypyrrole. This method provides adsorbents with higher adsorption capacity compared to the conventional polymerization method with ammonium persulfate (APS). The adsorbent prepared at the mass ratios of 1.0 and 2.0; respectively, for KMnO 4 /SFM and pyrrole/SFM showed the highest performance. The adsorbent characterization revealed the successful polymerization of pyrrole on the surface of SFM. Reusability of the KMnO 4 and pyrrole solutions were successful with remarkable results, showing the advantage of this technique compared to the conventional polymerization method with APS. The effect of different factors on the adsorption process was investigated. The removal rate was around 98% under the optimum conditions (pH, 2; adsorbent dosage, 3 g L -1 ; contact time, 60 min). The equilibrium data were well fitted by Langmuir isotherm (R 2  =  0.9999). Kinetic investigations revealed that the adsorption process fitted well with the pseudo-second-order model. The adsorbent was regenerated for up to five cycles. One of the most important advantages of the proposed method compared to other methods is the reduction of wastewater during the synthesis process.

A highly efficient low-cost adsorbent was prepared using raw and chemically modified cellulose isolated from sugarcane bagasse for decontamination of Cr(VI) from wastewater. First, cellulose pulp was isolated from sugarcane bagasse by subjecting it to acid hydrolysis, alkaline hydrolysis and bleaching with sodium chlorate (NaClO 3 ). Then, the bleached cellulose pulp was chemically modified with acrylonitrile monomer in the presence Fenton's reagent (Fe +2 /H 2 O 2 ) to carry out grafting of acrylonitrile onto cellulose by atom transfer radical polymerization. The developed adsorbent (acrylonitrile grafted cellulose) was analyzed by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR). Both raw cellulose and acrylonitrile grafted cellulose were used for chromium removal from wastewater. The effects of metal ion concentration, pH, adsorbent dose and time were studied, and their values were optimized. The optimum conditions for the adsorption of Cr(VI) onto raw and chemically modified cellulose were: metal ion concentration: 50 ppm, adsorbent dose: 1 g, pH: 6, and time: 60 min. The maximum efficiencies of 73% and 94% and adsorption capacities of 125.95 mg/g and 267.93 mg/g were achieved for raw and acrylonitrile grafted cellulose, respectively. High removal efficiency was achieved, owing to high surface area of 79.92 m 2 /g and functional active binding cites on grafted cellulose. Isotherm and kinetics studies show that the experimental data were fully fitted by the Freundlich isotherm model and pseudo first-order model. The adsorbent (acrylonitrile grafted cellulose) was regenerated using three different types of regenerating reagents and reused thirty times, and there was negligible decrease (19%) in removal efficiency after using it for 30 times. Hence, it is anticipated that acrylonitrile could be utilized as potential candidate material for commercial scale Cr(VI) removal from wastewater.

Owing to the powerful affinity of tannin toward heavy metal ions, it is frequently immobilized on adsorbents to enhance their adsorption properties. However, natural adsorbents containing tannin have been overlooked owing to its water solubility. Herein, a novel natural adsorbent based on the immature persimmon residue (IPR) with soluble tannin removed was fabricated to eliminate Pb(II) and Cr(VI) in aquatic environments. The insoluble tannin in IPR endowed it with prosperous properties for eliminating Pb(II) and Cr(VI), and the IPR achieved maximum Pb(II) and Cr(VI) adsorption quantities of 68.79 mg/g and 139.40 mg/g, respectively. Kinetics and isothermal adsorption analysis demonstrated that the removal behavior was controlled by monolayer chemical adsorption. Moreover, the IPR exhibited satisfactory Pb(II) and Cr(VI) removal efficiencies even in the presence of multiple coexisting ions and showed promising regeneration potential after undergoing five consecutive cycles. Additionally, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) analysis unveiled that the elimination mechanisms were primarily electrostatic attraction, chelation and reduction. Overall, the IPR, as a tannin-containing biosorbent, was verified to possess substantial potential for heavy metal removal, which can provide new insights into the development of novel natural adsorbents from the perspective of waste resource utilization., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Carbonized bacterial cellulose embedded with highly dispersed nano zero-valent iron (nZVI), denoted as nZVI@CBC, was prepared through one-step in situ carbothermal treatment of bacterial cellulose adsorbing iron(III) nitrate. The structure characteristics of nZVI@CBC and its performance in removing hexavalent chromium Cr(VI) were investigated. Results showed the formation of nZVI@CBC with a surface area of 409.61 m 2 /g at 800 °C, with nZVI particles of mean size 28.2 nm well distributed within the fibrous network of CBC. The stability of nZVI was enhanced by its carbon coating, despite some inevitable oxidation of exposed nZVI. Batch experiments demonstrated that nZVI@CBC exhibited superior removal efficiency compared to bare nZVI and CBC. Under optimal conditions, nZVI@CBC exhibited a high Cr(VI) adsorption capacity of up to 372.42 mg/g. Therefore, nZVI@CBC shows promise as an effective adsorbent for remediating Cr(VI) pollution in water., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Electrocatalysis offers great promise for water purification but is limited by low active area and high uncontrollability of electrocatalysts. To overcome these constraints, we propose hybrid bulk electrodes by synthesizing and binding a Pd nanocatalyst (nano-Pd) to the electrodes via amyloid fibrils (AFs). The AFs template is effective for controlling the nucleation, growth, and assembly of nano-Pd on the electrode. In addition, the three-dimensional hierarchically porous nanostructure of AFs is beneficial for loading high-density nano-Pd with a large active area. The novel hybrid cathodes exhibit superior electroreduction performance for the detoxification of hexavalent chromium (Cr 6+ ), 4-chlorophenol, and trichloroacetic acid in wastewater and drinking water. This study provides a proof-of-concept design of an AFs-templated nano-Pd-based hybrid electrode, which constitutes a paradigm shift in electrocatalytic water purification, and broadens the horizon of its potential engineered applications., (© 2022 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Because nanocellulose has a large specific surface area and abundant hydroxyl functional groups due to its unique nanomorphology, interest increases as an eco-friendly water treatment material. However, the distinctive properties of nanocellulose, which exists in a dispersion state, strongly hamper its usage in practical water treatment processes. Additionally, nanocellulose shows low performance in removing anionic pollutants because of its anionic characteristics. In an effort to address this challenge, regenerated cellulose (RC) hydrogel was fabricated through cellulose's dissolution and regeneration process using an eco-friendly aqueous solvent system. Subsequently, a crosslinking process was carried out to introduce the cationic functional groups to the RC surface PEI coating (P/RC). As a result, the PEI surface cationization process improved the mechanical rigidity of RC and showed an excellent Cr(VI) removal capacity of 578 mg/g. In addition, the prepared P/RC maintained more than 90% removal efficiency even after seven reuses., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Bioremediation is an essential feature of microorganisms concerning contaminations in soil and water. The use of microorganisms has been proved to be an effective treatment of industrially released effluents comprising of heavy metals, such as chromium (VI). In the current study, seasonal variations were observed in the concentrations of chromium(VI) as the samples from selected locations showed an increase in mean concentration during the summer compared to the low mean during winter, suggesting excessive evaporation in the summer leading to the heavy metal accumulation. Among the 35 isolates obtained from tannery effluent contaminated wastewater sources the 3 unique strains identified as Streptococcus pyogenes strain APRRJVITS10, Pseudomonas putida strain APRRJVITS11, and Bacillus thuringiensis strain APRRJVITS15, showed tolerance toward chromium(VI) and the maximum tolerance for each strain was 1250 ppm. The media optimization through shake flask methods showed chromium(VI) (in 100 ml LB broth) removal of 47.82%, 48.11%, and 49.93% by S. pyogenes , P. putida, and B. thuringiensis respectively. Further, Pseudomonas putida showed chromium(VI) (in 1500 ml LB broth) removal of 50.48% in optimized conditions, proving to be highly potential for treating effluent wastewater for chromium(VI) removal.

A novel composite material was prepared by blending graphene oxide into polyethyleneimine grafted sodium alginate. The synthesized material was investigated as adsorbent and photocatalyst for the removal of hexavalent chromium (Cr (VI)) from aqueous solutions. The composite material has shown remarkable removal efficiency for Cr (VI) in high initial concentration solutions as the removal rate reached 86.16% and 99.92% for adsorption and photoreduction, respectively. We discovered experimentally that the adsorption was dominated via electrostatic interaction while the blending of GO could contribute in stimulating electrons for the photoreduction process. Moreover, the photoreduction can alter the surface charge of chromium species, thus electrostatic repulsion could regenerating the active sites of composite spontaneously. The conduction band energy was calculated as -2.04 eV, which proved that blending GO can narrow the bandgap of the composite material, thus enhance the light response and the photoreduction ability towards Cr (VI)., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Acidic vinegar residue (VR) and toxic hexavalent chromium (Cr(VI)) are unfavorable substances due to their toxicity against the environment. In this study, modified biochar was prepared to investigate the removal mechanisms of Cr(VI). The results showed that ZnCl 2 could yield highly aromatic products with improved pore structures. The adsorption capacity of modified biochar reached the highest efficiency (236.81 mg g -1 ) when the mass ratio of ZnCl 2 /VR was 1, which is higher than the control (9.96 mg g -1 ). In addition, Cr(VI) adsorption coexisted with physical and chemical adsorption. The mechanisms of modified biochar to Cr(VI) removal included electrostatic attraction, pore filing, reduction and surface complexation. Notably, as a fermented product, VR biochar was a nitrogen-rich product; the formation of the amino group could provide a direct solid site for Cr(VI) adsorption. Subsequently, amorphous silica could be converted into silanol to provide additional adsorption sites. This work establishes the theoretical basis for efficient Cr(VI) removal and VR reuse., (Copyright © 2021 Elsevier B.V. All rights reserved.)

A cellulose-g-poly-(acrylamide-co-sulfonic acid) polymeric bio-adsorbent (CASA) was prepared by grafting copolymerization, and used to adsorb Cr(III) from leather wastewater. The SEM, XRD, FTIR, and XPS results showed that CASA contains many spherical particles and functional groups such as NH 2 , CO, and HSO 3 . The adsorption experiments revealed that CASA presented excellent adsorption performance for Cr(III) (274.69 mg/g of max adsorption capacity) from high-salinity wastewater, which was much better than other reported adsorbents with different structures. Meanwhile, adsorption equilibrium could be reached within 10 min due to the introduction of abundant sulfonic acid groups on its surface. In addition, the adsorption process followed the Langmuir adsorption isotherm, and the experimental data conformed to the pseudo-second-order kinetics model. Moreover, the main adsorption mechanisms include chelation, electrostatic interactions, and cation exchange, which provide an important theoretical basis for the removal of toxic inorganic pollutants from leather wastewater., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Chromium is a potentially poisonous and carcinogenic species, which originates from human activities and various industries such as leather, steel, iron, and electroplating industries. Chromium is present in various oxidation states, among which hexavalent chromium (Cr(VI)) is highly toxic as a natural contaminant. Therefore, chromium, particularly Cr(VI), must be eliminated from the environment, soil, and water to overcome significant problems due to its accumulation in the environment. There are different approaches such as adsorption, ion exchange, photocatalytic reduction, etc. for removing Cr(VI) from the environment. By converting Cr(VI) to Cr(III), its toxicity is reduced. Cr(III) is essential for the human diet, even in small amounts. Today, biopolymers such as alginate, cellulose, gum, pectin, starch, chitin, and chitosan have received much attention for the removal of environmental pollutants. Biopolymers, particularly polysaccharides, are very useful compounds due to their OH and NH 2 functional groups and some advantages such as biodegradability, biocompatibility, and accessibility. Therefore, they can be widely applied in catalytic applications and as efficient adsorbents for the removal of toxic compounds from the environment. This review briefly investigates the application of polysaccharide-based (nano)materials for efficient Cr(VI) removal from the environment using adsorption/reduction, photocatalytic, and chemical reduction mechanisms., (Copyright © 2021. Published by Elsevier B.V.)

Wastewaters is generally polluted with various inorganic and organic contaminants which require effective multipurpose purification technology. In this respect, a novel V 2 O 5 @Ch/Cu-TMA nanobiosorbent was constructed via encapsulation of nanoscale metal organic frameworks (Cu-TMA) into vanadium pentoxide-imbedded-chitosan matrix to comprehensively investigate its efficiency in removal of levofloxacin drug (LEVO) (e.g., organic pollutant) and chromium (VI) (e.g., inorganic pollutant) from water. Both LEVO drug and Cr(VI) adsorptions were correlated to pseudo-second order (R 2  = 1) and Langmuir isotherm (R 2  = 0.9924 for LEVO and R 2  = 0.9815 for Cr(VI)). Adsorption of Cr(VI) was confirmed to be spontaneous and endothermic reactions, while LEVO was found to proceed via spontaneous and exothermic reactions based on the thermodynamic parameters. The emerged V 2 O 5 @Ch/Cu-TMA is regarded as an excellent nanobiosorbent for removal of inorganic contaminant as Cr(VI) from all natural water samples (tap, sea and wastewater) with percentages range 92.43%-96.95% and organic contaminant as LEVO drug from tap and wastewater (91.99%-97.20%)., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Montmorillonite K10 (MMT K10) supported copper oxide nanoparticles (CuONPs) were synthesized by incorporating CuONPs onto the surface of MMT K10 by reducing the metal precursor with the help of hydrazine hydrate. Effects of various factors on the efficiency of composite to remove hexavalent chromium were studied to find out the optimum conditions for maximum removal. Under optimum conditions 15 mg of the synthesized nanocomposite was found capable to almost completely remove (99.9 %) hexavalent chromium in 30 min from a 10 ppm aqueous chromium solution and that too in a wide range of pH from 2.88 to 5.56. The synthesized MMT K10 supported CuONPs were characterized by UV, SEM-EDX, FTIR and XRD studies. The average particle size of supported CuONPs was found to be 22.9 nm. Antibacterial potential of the prepared composite was also studied for one Gram-positive bacterium Staphylococcus aureus (ATCC 25323) and one Gram-negative bacterium Pseudomonas aeruginosa (ATCC 27853). The prepared nanocomposite was found to have excellent bactericidal potential and its statistical analysis was performed using t-test which indicates both bacterial strains of Pseudomonas aeruginosa and Staphylococcus aureus show different zone of inhibition for different concentrations.

Metal organic frameworks (MOFs) have become premium candidates for the removal of hazardous contaminants from wastewater. However, MOFs have a vast obstacle which is their poor recyclability. In this study, ZIF-67 was decorated with magnetic Fe 3 O 4 nanoparticles, and then embedded into aminated chitosan (AmCs) matrix to form core-dual shell Fe 3 O 4 /ZIF-67@AmCs composite beads. Diverse analysis tools were utilized to ensure the successful fabrication of the magnetic composite beads. The fabricated magnetic composite beads were examined their adsorptive removal aptitude towards toxic Cr(VI) ions. The gained results refereed that a maximum adsorption capacity of 119.05 mg/g was attained by magnetic Fe 3 O 4 /ZIF-67@AmCs composite beads at 25 °C. The process obeyed both of Langmuir and Freundlich isotherm models, and the pseudo 2nd order was more suitable kinetic model to represent the adsorption process. Besides, Fe 3 O 4 /ZIF-67@AmCs composite showed an excellent recyclability for the removal of Cr(VI) ions from their aqueous solutions for seven consecutive cycles., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Biopolymers are promising materials for water treatment applications due to their abundance, low cost, expandability, and chemical structure. In this work, gelatin hydrogels filled with cellulose in the form of pristine eucalyptus residues (PER) or treated eucalyptus residues (TER) were prepared for adsorption and chromium removal in contaminated water. PER is a lignocellulosic compound, with cellulose, hemicellulose, and lignin, while TER has cellulose as a major component. FT-Raman Spectroscopy and FTIR analysis confirmed the crosslink reaction with glutaraldehyde and indicated that fillers altered the gelatin molecular vibrations and formed new hydrogen bonds, impacting the hydrogels' crystalline structure. The hydrogen bond energy was altered by the cellulosic fillers' addition and resulted in higher thermal stability (~10 °C). Hydrogels presented a Fickian diffusion, where gelatin hydrogel showed the highest swelling ability (466%), and composites showed lower values with the filler content increase. The chromium adsorption capacity presented values between 12 and 13 mg/g, i.e., featuring an excellent removal capacity which is related with hydrogel crosslinked structure and fibers surface hydroxyl groups, highlighting gelatin hydrogel TER 5% with better removal capacity. The developed hydrogels were produced from biomacromolecules with low-cost and potential application in contaminated water., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Amino acid sequences in metal-binding proteins with chelating properties offer exciting applications in biotechnology and medical research. To enhance their application in bioremediation studies, we explicitly aimed to identify specific metal-binding chelating motifs in protein structures for two significant pollutants, such as mercury (Hg 2+ ) and chromium Cr(V1). For this purpose, we have performed an extensive coordination chemistry approach by retrieving Hg 2+ and Cr(V1) binding protein structures from the protein database and validated using the B-factor, a term defining uncertainty of the atoms and with occupancy to obtain the best binding motifs. Our analysis revealed that acidic amino acids like aspartic acid, glutamic acid, and basic amino acids such as cysteine and histidine are predominant in coordinating with these metals. The order of preference in Hg 2+ -bound structures is predicted to be Cys > His > Asp > Glu, and for Cr(V1) is His > Asp > Glu. Examination of the atomic coordinates and their distance from each metal revealed that the sulfur atoms of cysteine showing more preference towards Hg 2+ coordination with an atomic distance ranging from 1.5 to 2.9 Å. Likewise, oxygen atoms of aspartic acid, glutamic acid and nitrogen atoms of histidine are within 2 Å of Cr(V1) coordination. Based on these observations, we obtained C-C-C, C-X(2)-C-C-(X)2-C, H-C-H motifs for Hg 2+ , and D-X(1)-D, H-X(3)-E motif for Cr(V1) to be shared within the coordination space of 3 Å. As a future scope, we propose that the identified metal-binding chelating motifs are oligopeptides and can display on the surface of microorganisms such as Escherichia coli and Saccharomyces cerevisiae for effective removal of natural Hg 2+ and Cr(V1) through biosorption. Hence, our results will provide the basis for futuristic bioremediation.

Background: Porphyra haitanensis now faces serious heavy metal pollution problems. Natural deep eutectic solvents (NADESs) have been recognized as a novel class of sustainable solvents, which can be used for heavy metal removal. In this study, 28 kinds of NADESs were prepared and investigated as eluent in the removal of lead (Pb), cadmium (Cd), chromium (Cr), arsenic (As), and copper (Cu) from P. haitanensis for the first time, and the adsorption mechanism of NADESs was also studied., Results: The removals were greatly improved by NADESs compared with control where the removal rates of Pb, Cd, Cr, As and Cu were 17.4-87.54%, 57.54-100%, 9.8-48.59%, 21.32-78.24% and 11.68-79.73%, respectively. The optimal condition was 10% water content and solid-liquid ratio of 1:20. Moreover, the addition of 20% natural surfactant arabic gum can further increase the heavy metals removal rates of NADESs. The adsorption mechanism experiments showed that the pseudo second-order model and the Freundlich adsorption model can better explain the adsorption mechanism of NADESs on heavy metals removal., Conclusion: Taken together, a green and efficient method for removing heavy metals from P. haitanensis was established. © 2020 Society of Chemical Industry., (© 2020 Society of Chemical Industry.)

Microbial bioremediation of heavy metals-polluted industrial effluents has been adopted as one of the most effective eco-friendly tool to cope up with the harmful effects of metals. This study was designed to investigate the biosorption potential of marine actinomycetes isolated from the Alexandrian Mediterranean Seacoast, Egypt, with their potential use in metal remediation of industrial effluents. Among the nine marine actinomycetes isolates, Streptomyces rochei ANH showed the highest versatile metal resistance capability with MIC values of 125 mg/l for Cr 6+ and 60 mg/l for both Cd 2+ and Pb 2+ . Additionally, scanning electron micrographs showed complete disintegration of Cr 6+ -treated biomass compared with the control ones where spores remained intact and connected in long chains. The study also aimed to improve the percentage of Cr 6+ biosorption by S. rochei ANH biomass using the statistical designs of Plackett-Burman and Box-Behnken where up to 85% of Cr 6+ removal was recorded under the following conditions: pH (5), incubation temperature (30 °C), contact time (3 h), agitation speed (90 rpm), initial Cr 6+ concentration (50 mg/l) and living biomass concentration (10 mg/ml). The results also showed that the percentage of Cr 6+ biosorption by S. rochei ANH decreased gradually beyond these values. Moreover, the results revealed that the use of the biomass of S. rochei ANH is an effective biotechnological agent for the biological treatment of heavy metal-contaminated tannery effluent where the percentages of metal removal were in the following order: Ni 2+ (100%) ≥ Cu 2+  ≥ Mn 2+  ≥ Fe 2+  > Pb 2+ (95%) ≥ Cd 2+  > Cr 6+ (86%). Furthermore, the treated effluent exhibited a stimulating effect on the germination process of Lepidium sativum seeds. Therefore, the present study implies that S. rochei ANH can be considered a powerful candidate to mitigate hazardous heavy metals pollution from industrial effluents and improve the water quality for agricultural purposes.

The presence of inorganic pollutants such as Cadmium(II) and Chromium(VI) could destroy our environment and ecosystem. To overcome this problem, much attention was directed to microbial technology, whereas some microorganisms could resist the toxic effects and decrease pollutants concentration while the microbial viability is sustained. Therefore, we built up a complementary strategy to study the biofilm formation of isolated strains under the stress of heavy metals. As target resistive organisms, Rhizobium -MAP7 and Rhodotorula ALT72 were identified. However, Pontoea agglumerans strains were exploited as the susceptible organism to the heavy metal exposure. Among the methods of sensing and analysis, bioelectrochemical measurements showed the most effective tools to study the susceptibility and resistivity to the heavy metals. The tested Rhizobium strain showed higher ability of removal of heavy metals and more resistive to metals ions since its cell viability was not strongly inhibited by the toxic metal ions over various concentrations. On the other hand, electrochemically active biofilm exhibited higher bioelectrochemical signals in presence of heavy metals ions. So by using the two strains, especially Rhizobium -MAP7, the detection and removal of heavy metals Cr(VI) and Cd(II) is highly supported and recommended.

A facile, environmentally benign approach had been developed for the preparation of dual self-healing and adsorption hydrogel through hydroxypropyl chitosan (HPCS), polyacrylamide (PAM) and polyvinyl alcohol (PVA). The self-healing capability of the hydrogels without any external stimulus was ascribed to dynamic Schiff-base bonds, borate bonds and hydrogen bonds, while the adsorption capacity of hydrogels came from the protonated amino group effect at a specific pH. It was demonstrated that the HPP DN hydrogel had a maximum equilibrium swelling ratio of 643% and a maximum compressive strength of 267 kPa. The weight loss of HPP DN hydrogel was 14.26% lower than that of HPCS/PAM single network hydrogel, furthermore, HPP DN hydrogel could achieve self-healing within 10 h. Due to the large number of active groups, the adsorption capacity of Cr 6+ reached 95.31 mg/g. It could adsorb in a wide pH range of 1 to 6, and could describe by pseudo-first-order kinetic model and Langmuir adsorption isotherm model, which would provide a new idea for the adsorption and removal of heavy metal ions. In short, the prepared HPP hydrogel had dual self-healing ability, adsorption capacity and mechanical strength, which would make it a promising candidate for long-life adsorbent., Competing Interests: Declaration of competing interest We declare that there are no commercial interests or related interests that conflict with the submitted work., (Copyright © 2021 Elsevier B.V. All rights reserved.)

It is challenging work to develop a low-cost, efficient, and environmentally friendly Cr(VI) adsorbent for waste water treatment. In this paper, we used hemicelluloses from chemical fiber factory waste as the raw material, and prepared two kinds of carbon materials by the green hydrothermal method as adsorbent for Cr(VI). The results showed that hemicelluloses hydrothermally treated with citric acid (HTC) presented spherical shapes, and hemicelluloses hydrothermally treated with ammonia solution (HTC-NH 2 ) provided spongy structures. The adsorption capacity of the samples can be obtained by the Langmuir model, and the adsorption kinetics could be described by the pseudo-second-order model at pH 1.0. The maximum adsorption capacity of HTC-NH 2 in the Langmuir model is 74.60 mg/g, much higher than that of HTC (61.25 mg/g). The green hydrothermal treatment of biomass with ammonia solution will provide a simple and feasible way to prepare adsorbent for Cr(VI) in waste water treatment.

This study is the first to evaluate the effects of Iron oxides (FeO x ) species and their decoration on graphene oxide/chitosan (GO/CS) composites for Cr(VI) removal and the possibility of Fe secondary pollution. Results show that Fe(III) is a better decoration material than Fe(II) and decoration through immersion-evaporation shows a higher adsorption capacity of Cr(VI) (Q e ) than co-precipitation. Fe 2 O 3 -GO/CS as the only eco-friendly composite for enhanced Cr(VI) removal is further used for batch adsorption experiments, characterization, kinetics, isotherms, and thermodynamic studies. It is found that Cr(VI) removal mainly includes electrostatic attraction between Cr(VI) oxyanions and surface -NH 3 + and -OH 2 + , and the adsorbed Cr(VI) partially reduces to Cr(III). Q e increases with the increasing initial Cr(VI) concentration, contact time, and temperature, while decreases with the increasing pH and mass and volume ratio (m/v). The coexisting ions (Cl - , NO 3 - , SO 4 2- , PO 4 3- , As, Fe, and Pb) can cause an obvious decrease of Q e . The removal efficiency (R e ) and Q e are 94.3% and 83.8 mg/g, respectively under the optimal conditions. After five times of regeneration, R e is still as high as 84% and Q e drops about 2.6%. Cr(VI) adsorption is spontaneous and endothermic, which is best fitted with the Sips model, and the fitted maximum Q e is 131.33 mg/g., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Extensive industrial activities have led to an increase of the content of chromium in the environment, which causes serious pollution to the surrounding water, soil and atmosphere. The enrichment of chromium in the environment through the food chain ultimately affects human health. Therefore, the remediation of chromium pollution is crucial to development of human society. A lot of scholars have paid attention to bioremediation technology owing to its environmentally friendly and low-cost. Previous reviews mostly involved pure culture of microorganisms and rarely discussed the optimization of bioreduction conditions. To make up for these shortcomings, we not only introduced in detail the conditions that affect microbial reduction but also innovatively introduced consortium which may be the cornerstone for future treatment of complex field environments. The aim of this study is to summary chromium toxicity, factors affecting microbial remediation, and methods for enhancing bioremediation. However, the actual application of bioremediation technology is still facing a major challenge. This study also put forward the current research problems and proposed future research directions, providing theoretical guidance and scientific basis for the application of bioremediation technology., (Copyright © 2020 The Authors. Published by Elsevier Inc. All rights reserved.)

In this study, cortical cells resultant from wool fibers were loaded with TiO 2 nanoparticles in a hydrothermal process and were then engineered as organic-nonorganic hybrid composite photocatalysts for both photodegradation of organic dyes and photoreduction of heavy metal ions. The microstructure and photocatalytic properties of TiO 2 modified cortical cells (i.e. both orthocortical and paracortical cells) were systematically characterized using a series of analytical techniques including FESEM, TEM, element analysis, Mott-Schottky curve, BET specific surface area, Zeta potentials, as well as XRD, FTIR, XPS, DRS, PL, UPS, EDS and ESR spectra. Their photocatalytic performance and trapping experiments of the TiO 2 modified cortical cells were measured in the photodegradation of methylene blue (MB) dye and Congo Red (CR) dye as well as the photoreduction of Cr(VI) ions under visible light irradiation. It was found that anatase TiO 2 nanoparticles were chemically grafted on the surface of the two cortical cells via O-Ti 4+ /O-Ti 3+ bonds, and that TiO 2 nanoparticles were formed inside the orthocortical cells in the hydrothermal process. The TiO 2 modified orthocortical and paracortical cells possessed much higher photocatalytic efficiency than the commercially available TiO 2 nanoparticle powder, Degussa P25, in the photodegradation of cationic MB dye and photoreduction of Cr(VI) ions, while their photocatalytic efficiency in the photodegradation of anionic CR dye is smaller because of their greater negative Zeta potentials and photogenerated holes as the main reactive radical species. In comparison with the TiO 2 modified paracortical cells, the higher photocatalytic efficiency of the TiO 2 modified orthocortical cells was demonstrated in the photodegradation of MB dye solution and this might be due to both the S-doped TiO 2 nanoparticles infiltrated into the naturally hydrophilic orthocortical cells and the primary reactive radical species of photogenerated holes being trapped in the cells.

The effect of chitosan and Fe 3 O 4 magnetic nanoparticles on the chromium adsorption property of Moringa oleifera activated carbon (AC) was explored. Various techniques were applied to reveal the properties of adsorbers to absorb chromium ions. A majority of the pollutant was removed at pH2 and 50 min. The kinetic behavior of the chromium uptake process was governed by the pseudo-second-order kinetic model (PSOKM). Based on the thermodynamic investigation, the chromium adsorption using all adsorbers was exothermic and spontaneous. The maximum single-layer adsorption capacity of AC, CS/AC, AC/Fe 3 O 4 , and CS/AC/Fe 3 O 4 adsorbers was 56.78 mg/g, 114.80 mg/g, 121.70 mg/g, and 130.80 mg/g, respectively. The isotherm constants quantity highlighted that the Cr-adsorption process is optimal and physical. The acquired findings revealed that the modification of AC by chitosan and Fe 3 O 4 nanoparticles increased the Cr adsorption. Adsorbers re-used up to 5 stages with a yield >90 %, which indicates that the composites are a promising option for Cr removal., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

In this study, carboxymethyl cellulose (CMC) was employed to stabilize zero-valent iron nanoparticles (CMC-nFe 0 ) to improve their dispersity and antioxidation for enhanced hexavalent chromium (Cr(VI)) removal. Scanning electron microscope (SEM) observation revealed that the nFe 0 agglomerated in clusters, while the CMC-nFe 0 connected as chains and presented higher dispersity. Therefore, compared with 54% of the nFe 0 , the Cr(VI) removal rate of the CMC-nFe 0 increased by 0.8 time, reaching 97%. Besides, the nFe 0 precipitated in 1 d and was obviously oxidized within 7 d under anoxic condition, leading to a rapid decease of Cr(VI) removal efficiency from 54% to 3% in 56 d. In contrast, the CMC-nFe 0 showed no obvious subsidence and oxidized phenomenon within 14 d, which retained a relatively high Cr(VI) removal efficiency of 63% in 56 d, contributing to effective blockage of dissolved oxygen infiltrating from solution to nFe 0 particles in presence of CMC. After reaction, the valence state distribution of Cr between solution and material surface indicated that Cr(VI) reduction was dominant comparing to physical adsorption to particles in the remediation process conducted by CMC-nFe 0 . In addition, lower initial pH and higher iron dosage facilitated Cr(VI) removal. Those results indicated that the dispersive and antioxidative characteristics of CMC-nFe 0 were significantly superior to those of nFe 0 , and CMC stabilization thereafter can be a promising method to promote Cr(VI) elimination by nFe 0 ., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

The objective of the current manuscript is to develop a systematic and simplified expert system for the selection of suitable adsorbent to treat Cr(VI). Selection of adsorbent among the large options available by considering all possible factors and their interaction is required in an easy, organized and rational way. In this study, fuzzy logic is used for the choosing an appropriate adsorbent for the Cr(VI) removal. Multiple attribute decision making (MADM) is utilized to work out the relative weighting values for the chosen sorbent. The preference index is calculated by using the subjective and objective weights. The normalized value associated with each parameter has given on the basis of effect of each parameter on the removal of Cr(VI) and uptake capacity of each material. The associated MADM method results and the barriers of the approach is mentioned to lay the basis for in addition enhancement.

Herein, for the first time, the adsorption mechanism of HCrO 4 - and CrO 4 2- (as models of Cr(VI)) by bacterial cellulose (BC), polyaniline (PANI), and BC/PANI was performed using Density Functional Theory (DFT) in both acidic and neutral pH. For this purpose, three forms of neutral, partially (pp), and fully protonated (fp) were assumed for PANI in neutral and acidic media to elucidate the influence of pH. The results indicated that the formation of hydrogen bonds (H-bond) had the main contribution in the adsorption of CrO 4 2- and HCrO 4 - onto both BC and PANI. Besides, the adsorption energy of PANI was nearly 3 times as much as BC in both acidic and neutral pH. The design of the BC/PANI complex improved the stability of PANI by increasing in HOMO-LUMO energy gap from 1.1 eV to 1.97 eV. The establishment of more H-bonds, and the appearance of two different types of H-bonds, O⋯H and N⋯H, and their smaller distances (average 1.5 Å), were observed in HCrO 4 - /BC-fp-PANI complexes, while one type of hydroxyl H-bond (average 2 Å) was detected in CrO 4 2- /BC-pp-PANI. It proved the adsorption of Cr(VI) is more favorable in acidic pH. The small value of charge transferred (-0.001-0.01) showed that interfacial interaction was governed by physisorption., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

The hydrogels-metal organic frameworks hybrid materials have received increasing attentions in recent years. The pectin hydrogel (PH) was derived from mandarin orange peels by-products and calcium chloride was applied as a cross-linker for incorporation with Fe-TAC metal organic frameworks (MOFs) for the formation of PHM composite on in situ synthesis method. The synthesized PHM composite was characterized by SEM, FT-IR, XRD and N 2 adsorption-desorption and investigated for the adsorption of anionic species, Cr(VI) as well as cationic species, Pb(II) ions from aqueous solution. The adsorption kinetics for Cr(VI)/Pb(II) ions removal followed the pseudo-second order kinetic model and the equilibrium adsorption data were well fitted by Langmuir model. The maximum adsorption capacities of Cr(VI)/Pb(II) ions were 825.97 and 913.88 mg g -1 , respectively. High swelling capacity (1500.0%) was also characterized for PHM composite after only 400 min and excellent stability for eight cycles with respect to regeneration with 0.1 mol L -1 HCl. The validity of PHM composite for simultaneous removal from real water matrices were confirmed as Cr(VI) (99.73, 99.87 and 99.87%) and Pb(II) (99.02, 98.55 and 98.55%) from tap water, sea water and industrial wastewater samples, respectively., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Chromium(VI) contamination of drinking water arises from industrial activity wherever there is a lack of environmental legislation enforcement regarding the removal of such pollutants. Although it is possible to remove such harmful metal ions from drinking water through large-scale facilities, there currently exists no safe and simple way to filter chromium(VI) oxoanions at the point of use (which is potentially safer and necessary in remote locations or humanitarian scenarios). High-surface-area cloth substrates have been functionalized with calixarene molecules for the selective capture of aqueous chromium(VI) oxoanions in the presence of structurally similar anions. This is accomplished by pulsed plasmachemical deposition of a linker layer and subsequent functionalization with dimethylaminomethyl-calixarene (5,11,17,23-tetrakis[(dimethylamino)methyl]-25,26,27,28-tetrahydroxycalix[4]arene). Chromium(VI) oxoanions are captured by simply passing polluted water through the functionalized cloth, while other ions not harmful/beneficial to human health remain in the water. These cloth filters are simple to use, highly selective, and easily recyclable-thus making them attractive for point-of-use application in geographic regions lacking appropriate wastewater treatment plants or flawed environmental monitoring systems. Chromium(VI) pollutants have been successfully removed from real-world contaminated industrial wastewater streams using the dimethylaminomethyl-calixarene functionalized cloths.

Two novel chitosan Schiff bases namely chitosan pyrazolo[3,4-b]quinoxaline Schiff base (Ch-PQ 1 ) and chitosan phenyl-1H-pyrazolo[3,4-b]quinoxaline Schiff base (Ch-PQ 2 ) were synthesized as a modification of chitosan in order to increase its ability in heavy metal removal from wastewater. Their structures were characterized by FT-IR spectroscopy, TGA analysis and X-ray diffraction. They were tested for the removal of hexavalent chromium from synthetic samples. In addition pH conditions, polymer dosage, Cr (VI) initial concentration and contact time were studied as a key factor for the adsorption process. Kinetic studies of the removal process were also clarified. Furthermore, experimental equilibrium data were fitted to Langmuir and Freundlich adsorption isotherms. Both chitosan Schiff bases showed high removal efficiency, the result indicated that Cr (VI) removal using Ch-PQ 1 and Ch-PQ 2 was 96.4% and 98.8% respectively., Competing Interests: Declaration of competing interest the authors declare that there is no conflict of interest., (Copyright © 2020. Published by Elsevier B.V.)

Determination of Cr(VI) in rice is reported using ion chromatography (IC) and dynamic reaction cell inductively coupled plasma mass spectrometry (DRC-ICP-MS). Cr(VI) is separated from other Cr species within 4.5 min using NH 4 NO 3 solution at pH 8.8 as mobile phase. Spectral interferences on 52 Cr + are minimized with NH 3 in DRC. The detection limit of (LOD) Cr(VI) is 0.06 ng mL -1 . This methodology is utilized for the determination of Cr(VI) in different rice samples and can also be applied for screening of rice for toxicity with respect to Cr. The Cr species are leached from rice powder into 5% (v/v) tetramethyl ammonium hydroxide (TMAH) solution in an ultrasonic bath. The extracts are analyzed by IC-DRC-ICP-MS for Cr(VI). Spike recoveries of Cr(VI) are 98-102% and precision between sample replicates is better than 6.3%. No Cr(III) is converted to Cr(VI) during extraction. Cr(VI) is present in all the rice samples analyzed., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Chitosan (CS) is an attractive bio-adsorbent in pollutant removal due to its environment-friendly properties and abundant adsorption sites. However, the weak mechanical properties and strong dissolubility in acidic conditions of CS hinder its wide application. Herein, a facile method was proposed to fabricate polydopamine (PDA) and CS cross-linked graphene oxide (GO) (GO/CS/PDA) composite aerogel for Cr (VI) removal. GO was cross-linked with CS, forming a reinforced and three-dimensional macroporous structure; the introduced PDA was simultaneously cross-linked with CS and GO, providing more abundant nanopores and active sites for Cr(VI) removal. Based on the batch experiment results, GO/CS/PDA exhibited an optimized mass ratio (1:20:2) of GO, CS, and PDA for the most effective Cr(VI) adsorption; the adsorption removal rate of Cr(VI) was pH dependent, with the highest removal rate at pH = 3.0. The pseudo-second-order kinetic and Freundlich models were more suitable for fitting the adsorption kinetics and adsorption isotherms, respectively, and the maximum adsorption capacity for GO/CS/PDA was 312.05 mg/g at 298 K. Thermodynamics parameters indicated that the adsorption was a spontaneous and exothermic process. The excellent mechanical integrity and reusable adsorption performance of GO/CS/PDA promise the adsorbent with satisfactory reusability., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Microbial fuel cells (MFCs) offer a promising solution towards recovery and treatment of heavy metal pollutants. In this study, two-chambered MFCs were employed for recovery of chromium, copper and vanadium (Cr (VI), Cu (II) and V (V)). One g/L concentrations of K2Cr2O7, CuCl2 and NaVO3 served as catholytes, while a mixed culture was used as anolyte. Cr (VI), Cu (II) and V (V) were reduced biologically into less toxic forms of Cr (III), Cu and V (IV) respectively. Power density and cathodic efficiency were calculated for each of the catholytes. Cr (VI) gave the maximum power density and cathodic efficiency due to its high redox potential. Current produced depended on the concentration of the catholyte. Over a period of time, biological reduction of catholytes lead to decrease in the metal concentrations, which demonstrated the application of MFC technology towards heavy metal treatment and recovery in a reasonably cost-effective manner., (© FEMS 2020.)

Immobilised magnetic nanoparticles are extensively used owing to their superparamagnetic nature, surface interaction, and binding specificity with the appropriate portentous substances. The present research focuses on the development of a portentous, robust carrier, which integrates the silica-coated amino-functionalised magnetic nanoparticle (AF-MnP) with the plant extracts of Cynodon dactylon (L1) and Muraya koenigii (L2) for the stable and enhanced removal of hazardous hexavalent chromium pollutant in the wastewater. Vibrating sample magnetometer ( M s - 45 emu/g) determines the superparamagnetic properties; Fourier-transform infrared spectroscopy determines the presence of functional groups such as NH 2 , Si-O-Si, C=C; high-resolution transmission electron microscopy, field emission scanning electron microscope and energy-dispersive X-ray spectroscopy determine the size of the green adsorbents in the range of 20 nm and the presence of elements such as Fe, N, and Si determines the efficacy of the synthesised silica-coated AF-MnP. The AF-MnP-L1 shows the maximum adsorption capacity of 34.7 mg/g of sorbent calculated from the Langmuir isotherm model and the process follows pseudo-second-order kinetics. After treatment, the adsorbents can be easily separated from the solution in the presence of an external magnetic field and are reused for nine cycles after acid treatment with the minimal loss of adsorption efficiency.

An environmental friendly and cost effective method was used for the preparation of silver‑iron oxide (α-Fe 2 O 3 -Ag) nanocomposite using guava (Psidium guajava) leaf extract, which can be used as an adsorbent for decontamination of chromium (VI) ions from aqueous media. XRD analysis revealed that both Iron oxide and silver nanoparticles are crystalline in nature with face-centered cubic and rhombohedral geometry respectively. The FESEM micrographs of Fe 2 O 3 -Ag nanocomposite displayed irregular shaped particles with an average size of 50-90 nm. BET surface area analysis suggests that the prepared Fe 2 O 3 -Ag nanocomposites are mesoporous in nature with surface area of 122.72 m 2 /g. The adsorption of Cr(VI) was pH dependent and maximum adsorption occurred at pH = 4 with maximum adsorption capacity of 71.34 mg/g. Thermodynamic parameters reveals that the Cr(VI) adsorption on Fe 2 O 3 -Ag surface is endothermic and spontaneous in nature. The adsorbed Cr(VI) on Fe 2 O 3 -Ag surface was recovered and can be reused up to five cycles., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020. Published by Elsevier B.V.)

The potential of indigenously isolated bacteria from the Estância Velha stream to reduce Cr(VI) was evaluated and also the chromium contamination over the past ten years was verified in one of the most important industrial centers of Brazil, the "Brazilian Capital of Tanneries," Estância Velha municipality in the Rio Grande do Sul State, South Brazil. Samples were collected from the Estância Velha stream at the source (P1), as well as at upstream (P2) and downstream (P3) of the most demographically area. The bacterial strains reduced between 52.5 and 61.6% of 250 mg L -1 Cr(VI) in 48 h. The genus Acinetobacter was the most abundant and could efficiently reduce 500 mg L -1 of Cr(VI); for example, P2.8 and P2.9 strains of Acinetobacter ursingii reduced 21.3 and 24.5% of 500 mg L -1 of Cr(VI), respectively, after 48 h. Moreover, an analysis of Cr levels in the stream sediment reported up to 3594 mg. L -1 of total Cr and up to 138 mg. L -1 of Cr(VI) in 2009. Acinetobacter strains were identified as the most abundant and efficient in reducing Cr(VI), makes them an ideal candidate for cleaning environments contaminated with tannery effluents, an approach that is more cost-effective than the traditional methods.

The sensing of chromium(VI) (Cr(VI)) is highly desired, due to its toxic and carcinogenic effects upon human health. Fluorescent probes, especially carbon nanodots (CNDs), have been widely used for Cr(VI) sensing via the inner filter effect (IFE). However, improving the sensitivity of these probes remains a difficult issue. In this work, CNDs derived from β-Lactoglobulin were applied as an ultrasensitive fluorescent probe for Cr(VI). With 260 nm excitation, the CNDs showed multi-band emission, including an ultraviolet 360 nm peak. The spectral matching of the CNDs with Cr(VI) led to synergistic suppression of both the excitation and emission light in the fluorescent sensing. As a consequence, the CNDs showed high sensitivity toward Cr(VI), the detection limit reaching as low as 20 nM. Moreover, taking advantage of the multi-emissive property of the CNDs, the synergistic effect was proven in an IFE-based sensing system, which might be extended to the design of other kinds of fluorescent probes.

Materials coming from renewable resources have drawn recently an increased attention in various applications as an eco-friendly alternative in the synthesis of novel functional materials. Polysaccharides, with their prominent representative - chitosan (CS), are well-known for their sorption properties, being able to remove metal ions from dilute solutions either by electrostatic interactions or chelation. In this context, we proposed here a comparative study on Cu 2+ , Zn 2+ , Ni 2+ , Fe 3+ , and Cr 3+ metal ions removal from industrial wastewaters by CS-based composite cryogels using batch technique. The composite cryogels consisting of CS embedding a natural zeolite, namely clinoptilolite, were synthesized by cryogelation, and their sorption performance were compared to those of CS cryogels and of acid-activated zeolite. A deeper analysis of thermodynamics and kinetics sorption data was performed to get insights into the sorption mechanism of all metal ions onto sorbents. Based on the optimized sorption conditions, the removal of the above-mentioned ions from aqueous solutions by the composite sorbent using dynamic technique was also evaluated.

Chromium (Cr) poses serious consequences on human and animal health due to its potential carcinogenicity. The present study aims at preparing a novel biochar derived from Chenopodium quinoa crop residues (QBC), its activation with magnetite nanoparticles (QBC/MNPs) and strong acid HNO 3 (QBC/Acid) to evaluate their batch and column scale potential to remove Cr (VI) from polluted water. The QBC, QBC/MNPs and QBC/Acid were characterized with SEM, FTIR, EDX, XRD as well as point of zero charge (PZC) to get an insight into their adsorption mechanism. The impact of different process parameters including dose of the adsorbent (1-4 g/L), contact time (0-180 min), initial concentration of Cr (25-200 mg/L) as well as solution pH (2-8) was evaluated on the Cr (VI) removal from contaminated water. The results revealed that QBC/MNPs proved more effective (73.35-93.62-%) for the Cr (VI) removal with 77.35 mg/g adsorption capacity as compared with QBC/Acid (55.85-79.8%) and QBC (48.85-75.28-%) when Cr concentration was changed from 200 to 25 mg/L. The isothermal experimental results follow the Freundlich adsorption model rather than Langmuir, Temkin and Dubinin-Radushkevich adsorption isotherm models. While kinetic adsorption results were well demonstrated by pseudo second order kinetic model. Column scale experiments conducted at steady state exhibited excellent retention of Cr (VI) by QBC, QBC/MNPs and QBC/Acid at 50 and 100 mg Cr/L. The results showed that this novel biochar (QBC) and its modified forms (QBC/Acid and QBC/MNPs) are applicable with excellent reusability and stability under acidic conditions for the practical treatment of Cr (VI) contaminated water., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Short staple microfibers (SSM) based on chitosan (CS) or silk fibroin (SF) were fabricated via the wet-rotate-spinning technique and employed to adsorb hexavalent chromium from aqueous solution. Adsorption efficiencies, physicochemical and morphological properties of CS and SF-SSM were systematically investigated and evaluated before and after adsorption of Cr(VI) using different techniques like ATR-FTIR, TGA, XRD, XPS, and SEM. CS and SF-SSM showed removal efficiency (>90 %) toward Cr(VI) ions. Pseudo-second order kinetic and Langmuir isotherm models could describe the Cr(VI) ions uptake process. Considering the inexpensive, sustainability and higher adsorption capacity of CS and SF-SSM hold great promising applications as natural adsorbent materials for removing different hazardous metals from aqueous medium., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Nanoscale biomass materials derived from food materials (e.g., polysaccharide, protein, organic acid) have shown great promises with regard to the removal of heavy metal in wastewater treatment. Herein, we have developed the functionalized cellulose nanofibrous mats as an environment-friendly biosorbent via electrospinning of cellulose acetate solution, followed by deacetylation and citric acid modification. The morphology, chemical, and structural characterizations of the cellulose nanofibrous mats were examined by SEM, FTIR, XRD, DSC, and TGA to follow each stage of the preparation process of them. The effect of the incorporation of citric acid in the cellulose molecule on the adsorption performance of the naofibrous mats was then studied by batch adsorption experiments. Consequently, citric acid-modified cellulose nanofibrous mats with reasonably high absorption selectivity for Cr(VI) can be readily prepared. Results from this study may provide a promising food materials-based biosorbent that can be used as an emerging material in wastewater treatment application., Competing Interests: Declaration of competing interest The authors declare that they have no conflict of interests., (Copyright © 2020 Elsevier B.V. All rights reserved.)