Synthesis of triethylenetetramine modified sodium alginate/CuS nanocrystal composite for enhanced Cr(VI) removal: Performance and mechanism

Carboxymethyl cellulose/alginate/chitosan-based polyelectrolyte complex hydrogel with irregularly shaped multi-metallic nanowires for efficient continuous-flow Cr(VI) remediation

The efficient removal of hexavalent chromium (Cr(VI)) from industrial wastewater is a pressing environmental challenge. A natural polyelectrolyte complex (PEC) hydrogel composed of carboxymethyl cellulose, alginate and chitosan, was developed to support Pd/Au/Ag/Pt nanowires for the continuous-flow catalytic reduction of Cr(VI) to the less toxic Cr(III). PEC hydrogels are formed through the association of oppositely charged polyelectrolytes, a process that is primarily driven by entropy gain due to the release of counterions, resulting in highly porous networks with tunable physical and chemical properties. These characteristics make them ideal platforms for nanoparticle stabilization and catalytic applications. Crosslinking with glutaraldehyde, citric acid and calcium ions further improved the stability and porosity of the hydrogels. Pd/Au/Ag/Pt nanowires, synthesised through galvanic replacement and co-reduction of Pd/Au/Ag nanowires formed via an oriented attachment mechanism, exhibit a distinctive, irregular, undulating morphology that enhances their suitability for introduction into hydrogel matrices. These multi-metallic nanowires achieved complete Cr(VI) reduction within 15 min. When incorporated into a nanocomposite hydrogel, the Pd/Au/Ag/Pt nanowires significantly enhanced catalytic activity while maintaining structural integrity and high catalytic efficiency. Notably, the system achieved complete Cr(VI) reduction within 5 h of continuous-flow operation, highlighting its potential as a robust and scalable solution for industrial wastewater remediation.

Synthesis, characterization, and photocatalytic activity of a carboxymethyl cellulose sodium-based hybrid material for efficient degradation of hexavalent chromium

Conventional water treatment technologies often struggle to eliminate Cr(VI) effectively. Consequently, developing efficient and cost-effective photocatalysts for degrading Cr(VI) has emerged as a promising approach to environmental remediation. In this study, two novel cellulose-based photocatalytic hydrogel materials, designated CF and CFS, were synthesized by cross-linking varying concentrations of Fe(III) and Fe(III) + sodium citrate (SC) with sodium carboxymethyl cellulose (CMC), marking their first application in the photocatalytic reduction of Cr(VI) in aquatic environments. Photocatalytic degradation experiments revealed that the Fe(III) concentration was 0.3 M with a Fe(III): SC molar ratio of 2:1, 150 mg/L Cr(VI) could be 100 % degraded within 90 min. The microscopic structure and chemical properties of photocatalysts were thoroughly characterized, and the results confirmed the successful cross-linking of CMC with Fe(III) and Fe(III) + SC. Optical and electrochemical tests indicated that CFS exhibited a broader visible-light absorption range, a narrower band gap, and significantly improved separation and transfer of photogenerated carriers. Furthermore, CFS had a highly photochemically active Fe(III)-SC complex, which established a Fe(III)/Fe(II) cycling process via the metal-ligand-charge transfer (MLCT) pathway, leading to the rapid degradation of Cr(VI). CF and CFS still had good stability and reusability after five cycles. Therefore, this study provides an approach for removing Cr(VI) contaminants.

Enhanced phosphate removal from aqueous environments using three-dimensional La-doped carboxylic carbon nanotubes/alginate: Performance and mechanisms

The excessive amounts of phosphorus (P) discharged and usage have caused eutrophication and algal blooms, which seriously jeopardize the environment even the human health. In this study, carbon nanotubes (CNTs) served as carriers to develop a lanthanum-based sodium alginate hydrogel (La-CNT-COOH/SA) aimed at efficiently removing phosphate from wastewater. Characterization results confirmed successful deposition of La(OH)3 nanoparticles onto CNT-COOH. The optimal adsorption efficiency of La-CNT-COOH/SA hydrogels occurred at pH 4, with a maximum adsorption capacity of 54.4 mg/g under an initial phosphate concentration of 60 mg/L. Batch experiments demonstrated that La-CNT-COOH/SA performed well across a favorable pH range and exhibited high tolerance to common coexisting ions during phosphate adsorption. Adsorption isotherms indicated a dominance of both physical and chemical mechanisms in phosphate removal by La-CNT-COOH/SA. At elevated phosphate concentrations, the adsorption process followed quasi-second-order kinetics, primarily driven by chemical adsorption. Multi-instrument characterization emphasized that the substantial loading of La(OH)3 on CNT-COOH significantly contributed to adsorption, alongside crosslinked lanthanum ions on sodium alginate and abundant hydroxyl groups. Mechanisms of adsorption by La-CNT-COOH/SA encompassed electrostatic interactions, surface precipitation, and in-sphere complexation (La-O-P). These findings on fabrication, properties, and adsorption mechanisms of the phosphate-removal hydrogel lay a theoretical foundation for applying biomass-based materials in large-scale remediation practices.

Unveiling the biointerfaces characteristics and removal pathways of Cr(Ⅵ) in Bacillus cereus FNXJ1-2-3 for the Cr(Ⅵ)-to-Cr(0) conversion

Although less toxic than hexavalent chromium, Cr (Ⅲ) species still pose a threat to human health. The Cr (Ⅵ) should be converted to Cr (0) instead of Cr (Ⅲ), which is still involved in biological detoxification filed. Herein, for the first time, it was found that Cr(Ⅵ) can be reduced into Cr(0) by Bacillus cereus FNXJ1-2-3, a way to completely harmless treatment of Cr(Ⅵ). The bacterial strain exhibited excellent performance in the reduction, sorption, and accumulation of Cr(Ⅵ) and Cr (Ⅲ). XPS etching characterization inferred that the transformation of Cr(Ⅵ) into Cr(0) followed a reduction pathway of Cr(Ⅵ)→Cr (Ⅲ)→metallic Cr(0), in which at least two secretory chromium reductases (ECrⅥ→Ⅲ and ECrⅢ→0) worked. Under the optimum condition, the yield ratio of Cr(0)/Cr (Ⅲ) reached 33.90%. In addition, the interfacial interactions, ion channels, chromium reductases, and external electron donors also contributed to the Cr(Ⅵ)/Cr(0) transformation. Findings of this study indicate that Bacillus cereus FNXJ1-2-3 is a promising bioremediation agent for Cr(Ⅵ) pollution control.

Photothermal, superhydrophobic, conductive, and anti-UV cotton fabric loaded with polydimethylsiloxane-encapsulated copper sulfide nanoflowers

Multifunctional textiles have attracted widespread attention with the improvement of awareness of health. Especially, the fluorine-free superhydrophobic and conductive cellulose fiber-based fabrics have received intensive interest due to their broad and high-value applications. Herein, the copper sulfide nanoflowers were in-situ deposited on cotton fabric followed by polydimethylsiloxane (PDMS) treatment for encapsulating CuS nanoflowers and obtaining superhydrophobicity, recorded as Cot@PTA@CuS@PDMS. Cot@PTA@CuS@PDMS possesses superhydrophobicity with contact angles of 153.0 ± 0.4°, photothermal effect, excellent UV resistance, good conductivity, and anti-fouling. Interestingly, the resistance of Cot@PTA@CuS@PDMS is significantly reduced from 856.4 to 393.1 Ω under simulated sunlight irradiation with 250 mW/cm2. Notably, the resistance can be slightly recovered after shutting off simulated sunlight. Besides, Cot@PTA@CuS@PDMS has efficient oil-water separation efficiency for corn germ oil and castor oil, respectively. Briefly, this work provides a novel, facile, and promising strategy to fabricate multifunctional fiber-based textiles with the reversible change of resistance under simulated sunlight irradiation, inspiring more scholars to control the resistance change of textiles by light irradiation.

Preparation and characterization of P-type zeolite for adsorption of Cr3+, Ni2+, and Co2

Acid-washed coal fly ash (AW-CFA) was subjected to wet grinding activation followed by hydrothermal crystallization to synthesize P zeolite (FAZ-P). The FAZ-P obtained at 120 °C for 24 h exhibited a maximum relative crystallinity of 93.15% and was employed for the adsorption of Cr3+, Ni2+, and Co2+ from aqueous solutions. The zeolitization of coal fly ash (CFA) leads to an increase in specific surface area to 44.00 m2/g, resulting in the formation of nano-sized P zeolite crystals with uniformly narrow fissures and sizes within the range of 10-30 nm. Adsorption experimental results indicate that FAZ-P exhibits maximum adsorption capacities of 49.03 mg/g for Cr3+, 22.20 mg/g for Ni2+, and 27.25 mg/g for Co2+. The adsorption equilibrium data for both mixed and single-metal ion solutions conform to the Langmuir model, with the affinity sequence for heavy metal ions being Cr3+  > Co2+  > Ni2+. The pseudo-first-order and pseudo-second-order kinetic models effectively described the adsorption behavior of Cr3+, Ni2+, and Co2+. Increasing the initial pH value of the solution significantly enhanced the adsorption capacity of the adsorbent for heavy metal ions. The removal mechanism of metal ions involves both adsorption and ion exchange processes. The thermodynamic parameters indicated that the adsorption process was spontaneous and endothermic.

The regulation of CuSNPs' interface for further enhancing mechanical and photothermal conversion properties of chitosan/@CuSNPs hybrid fibers

Our previous study has demonstrated that the microstructure of copper sulfide nanoparticles (CuSNPs) can be controlled to enhance mechanical and photothermal conversion properties of chitosan (CS)/CuSNPs hybrid fibers. However, achieving optimal dispersion and compatibility of CuSNPs within a CS matrix remains a challenge, this study aims to improve dispersion and compatibility by modifying the CuSNPs' interface, thereby enhancing mechanical and photothermal conversion properties of hybrid fibers. The interfaces of @CuSNPs (CuS@Xylan NPs, CuS@SA NPs, and CuS@PEG NPs) contain hydroxyl groups, facilitating the hydrogen bonds formation with the CS matrix. The dispersibility is further enhanced by the synergistic effect of xylan and SA's anionic charges with cationic chitosan. Notably, the viscosity of the CS/@CuSNPs hybrid spinning solution is significantly enhanced, resulting in improved breaking strength for initial hybrid fibers. Specifically, the breaking strength of CS/CuS@Xylan NPs hybrid fibers reaches 1.4 cN/dtex, exhibiting a 42.86 % and 20.6 % increase over CS and CS/CuSNPs hybrid fibers. Simultaneously, the CS/CuS@Xylan NPs hybrid fibers exhibit exceptional photothermal conversion performance, surpassing that of CS fibers by 5.2 times and CS/CuSNPs hybrid fibers by 1.4 times. The regulation of interface modification is an efficient approach to enhance the tensile strength and photothermal conversion properties of CS/CuSNPs hybrid fibers.

Enhanced Cr(VI) stabilization by terrestrial-derived soil protein: Photoelectrochemical properties and reduction mechanisms

Glomalin-related soil protein (GRSP) is a stable iron-organic carbon mixture that can enhance heavy metal sequestration in soils. However, the roles of GRSP in the transformation and fate of Cr(VI) have been rarely reported. Herein, we investigated the electrochemical and photocatalytic properties of GRSP and its mechanisms in Cr(VI) adsorption and reduction. Results showed that GRSP had a stronger ability for Cr(VI) adsorption and reduction than other biomaterials, with the highest adsorption amount of up to 0.126 mmol/g. The removal efficiency of Cr(VI) by GRSP was enhanced (4-7%) by ultraviolet irradiation due to the hydrated electrons produced by GRSP. Fe(II) ions, persistent free radicals, and oxygen-containing functional groups on the GRSP surface as electron donors participated in the reduction of Cr(VI) under dark condition. Moreover, Cr(III) was mainly adsorbed on the -COOH groups of GRSP via electrostatic interactions. Based on 2D correlation spectroscopy, the preferential adsorption occurred on the GRSP surface for Cr(VI) in the sequential order of CO → COO- → O-H → C-O. This work provides new insights into the Cr(VI) adsorption and reduction mechanism by GRSP. Overall, GRSP can serve as a natural iron-organic carbon for the photo-reduction of Cr(VI) pollution in environments.

A novel approach to modify Stenotrophomonas sp. D6 by regulating the salt composition in the growth medium: Enhanced removal performance of Cr(VI)

In this study, a novel and effective modified microbial reducing agent was developed to detoxify Cr(VI) from aqueous solutions. This was achieved by carefully controlling specific salt components in the growth medium. Based on the single-salt modification, several effective modified salts were selected and added to the medium for synergistic modification. The results showed that the synergistic modification with NH4Cl and KH2PO4 had the best detoxification effect on Cr(VI), reaching 98.5% at 100 mg/L Cr(VI), which was much higher than the 43.7% of the control (original Luria-Bertani medium). This enhancement was ascribed to the ability of NH4Cl and KH2PO4 to stimulate the growth of Stenotrophomonas sp. D6 promoted chromate reductase secretion. The protein content of the modified medium supernatant was significantly increased by 10.76% compared to that before modification. Based on the micro-characterization, the main process for the elimination of Cr(VI) is microbial reduction rather than biosorption. Most of the reduced Cr was found in the extracellular suspension, thereby suggesting that the primary reduction occurred outside the cells, whereas only a small fraction was detected intracellularly. Overall, this study provides a simple and effective method for microbial treatment of heavy metals in aqueous solutions.

Sodium alginate hydrogel-encapsulated trans-anethole based polymer: Synthesis and applications as an eradicator of metals and dyes from wastewater

Clean and safe water resources are essential for environmental safety and human health. Hydrogels and biomass polymers have attracted considerable attention in recent years, considering their nontoxicity, controllable performance, and high adsorption capacity. The interpenetrating network described here is a combination of a biomass polymer and a hydrogel adsorbent was established, the biomass polymer microspheres were first prepared with the combination of biomass monomer trans-anethole and maleic anhydride copolymer. A simple, environmentally friendly, and facile method of incorporating biomass polymer into sodium alginate biopolymer was developed by introducing the cross-linking agents calcium chloride and glutaraldehyde into the biomass polymer. Furthermore, the biomass polymer sodium alginate hydrogel (BP@SA/H) was characterized by FTIR, XPS, SEM, and XRD. In order to test materials' performance, the removal of pollutants and the adsorption study were also investigated after and before adsorption toward metals and dyes in water. We examined the factors influencing the materials, adsorption capability, such as initial concentration, time, absorbent amount, and pH. Moreover, the maximum adsorption values for Pb+2 and Cd+2 were 734.9 and 722 mg/g. While the adsorption toward RhB dye are 745 mg/g. In addition, the adsorption results were investigated using kinetic and isothermal models, demonstrating that biomass polymer hydrogel adsorption is chemisorption. Therefore, the as-developed biomass polymer sodium alginate hydrogel (BP@SA/H) is an exceptional multifunctional material that can be used to remove hazardous pollutants from wastewater.

Comprehensive removal of various dyes by thiourea modified chitosan/nano ZnS composite via enhanced photocatalysis: Performance and mechanism

Dyeing wastewater is a carcinogenic pollutant, which is widely known for its harmful effects on humans and marine organisms. In this study, a novel composite was prepared by blending thiourea modified chitosan with zinc sulfide nanoparticles (T-CS/ZnS) to comprehensively remove methyl orange (MO), rhodamine B (Rh B), and methylene blue (MB) effectively. Characterization results suggested that the synthesized composite has an irregular and rough surface that provided high specific surface area for adsorption process, while the strong optical response and low bandgap width contributed to the subsequent photocatalytic degradation of adsorbed dye molecules. Under optimum experimental conditions, the removal rates of MO, Rh B, and MB were 99.59 %, 99.49 %, and 91.04 %, respectively. Amino and hydroxyl groups provide electrons in photocatalytic reactions. The reaction process is consistent with the quasi-first-order kinetic model, and the material has good stability and regeneration potential. This study indicated that T-CS/ZnS composite is a highly effective material for the treatment of dyeing wastewaters.