Effective Extraction of Cr(VI) from Hazardous Gypsum Sludge via Controlling the Phase Transformation and Chromium Species

In-situ passivation of Cr/Cr (VI) in the co-combustion ash of dyeing sludge and biomass via controlling the phase transformation of sulfate

The existence of sulfur fixation products in co-combustion ash of dyeing sludge and biomass influenced the leaching behavior of Cr/Cr (VI), however, the underlying mechanisms remained unclear. In this paper, we attempted to investigate the interaction between sulfur fixation product and leaching behavior of Cr/Cr (VI) and reveal the passivation mechanism of sulfur fixation products on Cr/Cr (VI). Results shows that 8 % CaSO4 inhibited the leaching of Cr and Cr (VI) in dyeing sludge ash, with inhibition ratios of 32.12 % and 61.94 %, respectively. Following Cr invasion, lattice expansion and crystal defects were observed on CaSO4·2 H2O (002) crystal plane in simulated ash, namely, isomorphous substitution and defect adsorption among CaSO4·2 H2O (002) played dominant roles in Cr immobilization. The binding energy of CaSO4·2 H2O (002) to CrO42- was as low as -205.51 kJ/mol, further confirming the chemical action to Cr (VI). Detailly, active Ca atoms on CaSO4·2 H2O (002) and bound water initially bonded to O atoms of CrO42-. And then the formation of covalent bond (Ca-OCr) stretched Ca-Os in CaSO4·2 H2O (002) from 2.169 / 2.170 Å to 2.304 / 2.314 Å, leading to the formation of the SO42- vacancy. The substitution of CrO42- for SO42- vacancy was spontaneous and tendentious, with -1076.58 kJ/mol energy change. This work revealed a hidden passivation "passageway" to Cr via the regulation of sulfur fixation products in co-combustion ash of dyeing sludge and biomass, offering a potential possibility for in-situ passivation to Cr/Cr (VI). SYNOPSIS: This work proposes a practicable method to adjust the interaction between by-products (sulfate and chromium) to in-situ solve the Cr/Cr (VI) leaching "puzzle" from silico-aluminous co-combustion ash of dyeing sludge and biomass.

Insights into biostimulation-enhanced microbial detoxification of chromium ore processing residue-contaminated soil: The critical role of Cr(VI) key host-phase transformation and soil microbiota shifts

The continuous and slow release of Cr(VI) from chromium ore processing residue contaminated soil (COPR-soil) poses a substantial threat to soil and groundwater. Despite microbial reduction is considered as an effective approach for the remediation of Cr(VI)-contaminated soil, the efficiency and rate of Cr(VI) reduction in COPR-soil, especially Cr(VI) embedded in minerals (e.g., vaterite, Ca/Al-Cr layered double hydroxide (Ca/Al-Cr LDH)) remain low. Here, a biostimulation-enhanced microbial detoxification strategy was developed, utilizing the strong electron transfer properties of FeSx. The removal efficiency of Cr(VI) from COPR-soil reached 99.9 %, with a 9-fold increase in the reduction rate of dissolved Cr(VI) compared to microbial remediation. FeSx semiconductor nanoparticles adhered tightly to the surface of the electroactive bacterium Pannonibacter phragmitetus BB (BB), facilitating mineral-microbial interactions that increased protein concentration by 35.8 % and Cr(VI) tolerance by 23.0 %. Biostimulation with FeSx significantly enhanced the biochemical dissolution capacity and electron shuttle potential of BB, accelerating the transformation of Cr(VI) host-phases. Vaterite was completely converted to calcite with a 22 % increase in transformation degree, while the interlayer nanoconfined Ca-Cr coordination in Ca/Al-Cr LDH shifted to a more accessible outer nonconfined structure. This transformation reduced the Cr(VI) binding capacity by 68.6 % and 79.4 %, respectively, effectively releasing Cr(VI) from mineral. Soluble Fe(III) emerged as a critical electron shuttle, enabling indirect electron transfer from BB to Cr(VI) via the Fe(III)/Fe(II) redox cycle. Additionally, biostimulation enhanced soil fertility and stability, fostering microbial consortia with improved resistance to environmental stresses through Cr(VI) efflux and intracellular translocation of Fe-Fe carrier complexes. This study provides a promising strategy to promote effective microbial remediation of COPR-soil.

Electricity-powered cryptic CO2 fixation pathway in heterotrophic Shewanella oneidensis for acetate synthesis

Microbial electrosynthesis of CO2 is a sustainable carbon neutral technology. Although known for its diverse and efficient extracellular electron transfer (EET) characteristics, the bacteria of Shewanella genus have never been reported for use in electrosynthesis of multi-carbon chemicals. Herein, the electricity-powered conversion of CO2 to acetate was achieved under ammonium regulation for the first time in the model strain (Shewanella oneidensis MR-1), due to the activation of its intrinsic reductive glycine pathway. A high electron flux from cathode into MR-1 was achieved through the unique electron uptake pathway mediated by endogenous iron release, biomineralization of iron oxide, and inherent EET pathways. Consequently, MR-1 delivered an acetate production rate of 78.6 ± 4.2mmol m-2 d-1, significantly surpassing those of previously reported electro-autotrophic acetogens under similar operating conditions. Our findings not only provide a novel platform for one-carbon biorefinery, but also prompt recognition to the complexity of EET and CO2 fixation.

Oxide Heterostructure Engineering Drives Stable Lattice Oxygen Evolution for Highly Efficient and Robust Water Electrolysis

Achieving a highly active and stable oxygen evolution reaction (OER) is critical for the implementation of water electrolysis in green hydrogen production but remains challenging. Steering the OER pathway from an adsorbate evolution mechanism (AEM), where a metal site serves as the active site, to the lattice oxygen mechanism (LOM) has been found to enhance OER activity; however, it suffers from low stability. In this work, we propose to construct CuOx/Co3O4 heterointerface, which enables the realization of a stable LOM pathway. The lattice oxygen characteristics are modulated near the heterointerface, resulting in a shift in the reaction pathway from AEM to LOM. In situ X-ray Absorption Fine Structure results further reveal that the valence state of cobalt is stabilized during the OER process, which alleviates corrosion of cobalt and maintains LOM stability. Consequently, the obtained CuOx/Co3O4 exhibits outstanding activity and stability for overall water electrolysis in freshwater, natural seawater, and high-salt wastewater, with a low overpotential of 308 mV at 100 mA cm-2 and stable overall water electrolysis at 500 mA cm-2 for 100 h. Our work demonstrates interface engineering as an effective strategy to activate and stabilize lattice oxygen, advancing the design of high-performance electrocatalysts for energy and environmental applications.

A novel graphene oxide functionalized hydrocalumite/cellulose composite for the selective and simultaneous removal of tetracycline and Cr(VI)

Tetracycline antibiotic and hexavalent chromium removal from the wastewater is crucial for preventing future environmental trouble. This study aimed to develop an eco-friendly biocomposite made from an enhanced graphene oxide-functionalized hydrocalumite/cellulose composite for co-adsorbative removal of TC antibiotic and toxic Cr(VI). The synthesized GO@CellHC composite was characterized using various microscopic techniques. The GO@CellHC composite possessed the superior removal for TC and Cr(VI), achieving 27.4 and 42.6 mg/g in single systems, and 24.8 and 39.6 mg/g in binary systems, all within 40 min. In pH results, the maximum removal was observed at an acidic pH of 3 for Cr(VI) and 5 for TC, respectively. The co-ions results demonstrated that the composite efficiently removed both pollutants, except in the presence of PO43- and CO32-. The Langmuir isotherm indicated the strongest adsorption capacity and favored both systems. Thermodynamic studies revealed that the adsorption of both systems onto the GO@CellHC composite removes TC and Cr(VI) by endothermic and spontaneous system. Kinetic results demonstrated that TC adsorption showed a higher rate constant k2 (single: 0.01676 min-1 and binary: 0.0138 min-1) compared to Cr(VI) adsorption (single: 0.01478 min-1 and binary: 0.01007 min-1). The GO@CellHC composite retained more than 80 % after three cycles, and field results suggesting that the biocomposite can be utilized for the removal of binary water pollutants.

Phase transformation of calcium sulfate at mineral-solution interface: An overlooked pathway for selective enrichment of cadmium

The reactions at the mineral-solution interface govern whether heavy metals (HMs) ions are retained within minerals or migrate with the solution, thus influencing their cycling and fate. However, the mechanisms driving this differential behavior of HMs at the interface remain poorly understood. In this study, we present a novel paradigm for the selective retention of HMs ions at the mineral-solution interface. By confining the solution on the mineral surface to a defined volume, specifically thinning it down to a thickness of 50 nm, selective retention of Cd ions in the presence of coexisting Cu and Zn ions was achieved. The distribution coefficient of Cd in the mineral reaches as high as 41.44, significantly exceeding that of Cu at 0.13 and Zn at 0.07. Combined with DFT calculations, the results reveal that this selectivity arises from the regulation of the ion desolvation free energy by the solution nanofilm, precisely compensating the energy cost for Cd incorporation as an impurity into the mineral lattice. This work not only enriches the understanding of ion separation behavior at natural mineral-solution interfaces but also offers a new strategy for heavy metal separation and enrichment in industrial applications.

Robust ternary system of corncob-derived carbon quantum dots/ ZnFe2O4/graphene oxide for wastewater treatment

Water contamination emerging from urban and industrial waste disposal is posing an alarming threat to human and marine life. Hence, it is imperative to take a crucial approach to lowering the overall cost and time of wastewater treatment. The efficiency of heterogeneous photo Fenton green wastewater treatment processes relies mainly on the morphology and surface interface properties of photocatalysts for harnessing maximum sunlight energy. This research work reports for the first time the hydrothermal synthesis of ternary zinc ferrite coupled with carbon quantum dots derived primarily from corncob biomass and supported over graphene oxide. The physiochemical properties and microstructure of magnetic graphene oxide anchored over carbon quantum dots included Fourier Transform Infrared Spectroscopy, Scanning Electron Microscope/Energy Dispersive X-ray, X-ray photoelectron spectroscopy, X-ray diffraction and Ultraviolet-Visible Spectroscopy. The effect of several factors on the photocatalytic degradation of Rhodamine B (RhB) dye was studied and maximum degradation was attained at optimized conditions of pH = 4, catalyst concentration (20 mg/100 mL), oxidant dose (10 mM) and degradation time (60 min). Response surface methodology was used to determine the optimization of various interacting parameters. The current research focused on the utilization of waste corncob biomass as a potential candidate for the novel ternary nanocomposite for effective treatment dye wastewater and reuse of treated dye water over wheat seeds germination.

Heavy metal mitigation in soil and plants using organic and inorganic amendments alone and in combination

The use of organic and inorganic amendments like stilbite-zeolite (SZ) and nano-biochar (NBC) in phytoremediation holds immense promise, long-term stability, and its effectiveness necessitate comprehensive research. This study aimed to evaluate their potential in mitigating heavy metal contamination in soil and plants. Our results shows that SZ and NBC treatments significantly impacted heavy metal levels, notably reducing arsenic (As), nickel (Ni), lead (Pb), cadmium (Cd), and mercury (Hg) accumulation in plant tissues. The treatments exhibited varying degrees of effectiveness in reducing heavy metal levels. Notably, SZ2 treatment decreased As and Pb levels by 33.33% and 20%, respectively, while NBC3 achieved even greater reductions, lowering As by 53.33% and Pb by 30%. Moreover, SZ2, SZ5, and NBC3 treatments halved Cd levels, showcasing their potential in mitigating heavy metal contamination in rice. However Hg levels remained largely unaffected, except for NBC1, which unexpectedly doubled its concentration. In soil, SZ2 treatment significantly reduced metal concentrations, particularly Cd (66.8% reduction) and Hg (70.7% reduction). Conversely, SZ3 and SZ7 treatments increased metal concentrations, suggesting that certain zeolite applications might enhance metal bioavailability. NBC treatments showed varying effectiveness, with NBC3 being the most effective, substantially reducing As, Pb, and Cd levels.

Kinetic and Isothermal Analysis of the Adsorptive Elimination of Direct Yellow 26 Dye Utilizing Activated Bioadsorbent From Textile Effluent

Due to their widespread usage in recent years, synthetic dyes may be difficult to remove and pose a health concern. Bioadsorbents proved a low-cost and sustainable method for dye removal. In this study, straight yellow 26 is extracted from textile effluent using sugarcane bagasse. Sugarcane bagasse was treated with propionic acid to enhance the adsorption capability and 0.25 mm particle size was used for further studies which was confirmed by BET analysis. Standard solutions of direct yellow 26 dye were prepared from 10 to 100 ppm concentrations and absorbance was recorded with the help of a UV visible spectrophotometer. After optimizing different parameters (concentration of dye and bioadsorbent dose, pH, time, and particle size), the studies explored that the maximum dye removal percentage was 89% obtained at pH 3, contact time 120 min, particle size 0.25 mm, high adsorbent, and low concentration of dye solution. The kinetic studies were also employed to comprehend the adsorption isotherm and Freundlich isotherm that revealed the pseudo-first-order adsorption process.

Comparative analysis of new natural coagulant extracts for turbidity removal in water systems

The ability of two plant materials, lupin beans and rice straw, to serve as sources of coagulation-active components for water treatment was investigated using synthetic turbid water. The functional groups, surficial architecture, and elemental composition of lupin beans and rice straw were determined using FTIR, scanning electron microscope, and X-ray (EDAX). The point of zero charges, zeta potential, and particle size distribution of aqueous extracts were measured. The optimal dosage of 50 mg/L of the lupin bean extract achieved 86.4% turbidity removal at initial turbidity of 500 NTU, pH 7, and 25 °C. Similarly, rice straw extract achieved 63.3% removal under the same conditions. The coagulation efficiency of both extracts improved with higher initial turbidity and temperatures between 20 and 40 °C, and their performance was unaffected by pH variations. Combining natural coagulants with alum reduced alum usage by 25-50%, achieving up to 98.7% turbidity removal. These results suggest that the use of natural coagulants can effectively lower treatment costs and reduce environmental impacts associated with chemical coagulants.

Adsorption of emerging pollutants utilizing chitosan derivatives: Recent advances and future perspective

Globalization resulted in technological advancement, and urban population growth. Consequently, pollution emerged as an imminent risk to the survival of all species on Earth. Consequently, on a worldwide basis, sustainability become a major issue for legislators. Inconsistent impacts on both human and animal growth and wellness triggered health issues associated with water contamination through the chronic toxicants. Micropollutants' pollution prompted severe concerns due to their malignant, indestructible, and accumulative properties. The elimination of these toxins from industrial processes has become one of the most significant ecological challenges. A variety of both organic and simulated sorbents are available, and each of these have unique benefits. In the recent years, chitosan and its composite materials have been attempted and have been proven to be applicable for the resolution of many challenging issues related to water pollution. Among various notable benefits of adsorption processes, economic viability, ease of access, and adherence to environmental regulations are notable. Considering the above-mentioned issues, the article targets the assessment of chitosan and its composite materials for relevant environmental applications. Accordingly, the article aims to examine the performance, advantages, and disadvantages of chitosan as an adsorbent.

Green synthesized MgO combined with dielectric barrier discharge plasma enhanced phosphorus (P) recovery from livestock wastewater: A dual approach for management of wastewater and P resources

Phosphorus (P) recovery from wastewater using integrated techniques i.e., adsorption combined with advanced oxidation technologies is a novel approach for cleaning wastewater and preventing eutrophication. This approach, however, has not been extensively studied, particularly in the context of real wastewater applications. In this study, a green biomass-based sol-gel method was developed using potato starch (PS) and MgCl2·6H2O to synthesize MgO (PS-MgO). The unique synthesis method resulted in PS-MgO composed predominantly of spherical particles with an average size of about 103 nm and exhibited superior P adsorption performance compared to commercial MgO materials (GH-MgO and AD-MgO). The Langmuir maximum P adsorption capacity (mg/g) of the PS-MgO was 429.4, while that of the commercial GH-MgO and AD-MgO was 341.3 and 421.7, respectively, at the solution pH 7.0. The kinetic model fitting demonstrated that the adsorption rate of PS-MgO was faster than the two commercial MgOs. Importantly, PS-MgO can maintain a high P adsorption capacity across a wide pH range (425 mg/g at pH 5.0 and 369 mg/g at pH 11.0), whereas the P adsorption capacities of GH-MgO (153 at pH 5.0 and 297 at pH 11.0) and AD-MgO (422 at pH 5.0 and 200 at pH 11.0) were more pH-dependent. In addition, PS-MgO exhibits high selectivity for P capture in solutions containing coexisting ions, and the P-loaded PS-MgO can efficiently release P through acid or base treatment, highlighting its potential for reuse as a fertilizer. To enhance P recovery from real livestock wastewater, the dielectric barrier discharge (DBD) plasma technology was combined with MgO adsorption. The P recovery capacity of MgOs from livestock wastewater increased 1.4-1.7 times after DBD plasma treatment, attributed to the degradation of aromatic proteins and microbial metabolites. These findings provide new insights into the design of efficient and environmentally friendly materials for P recovery, while also demonstrating the potential of integrating advanced oxidation technologies with adsorption processes.

Constructing ZnO/NiO Nanocomposites as a Photocatalyst and Investigating Photocatalytic Effectiveness for Wastewater Treatment

The goal of the present work is to create ZnO/NiO nanocomposites (NCs) for the photocatalytic destruction of organic contaminants using the co-precipitation technique. To investigate physiochemical characteristics, FT-IR, UV visible spectroscopy, SEM, and XRD were used. The ZnO hexagonal phase and the NiO cubic phase in the ZnO/NiO NCs were verified by the diffraction pattern. NCs were discovered to have larger average crystallite sizes. The bandgap energy calculated from the Tauc plot for the ZnO is 3.02 and 2.74 eV for the ZnO/NiO NC's. SEM analysis revealed the morphological study and particle size was calculated using the histogram technique and found to be 124.5 nm for the ZnO and 49.2 nm for the ZnO/NiO NCs. Photocatalytic degradation in the presence of sunlight showed 72.8% degradation of Methylene blue (MB) for the ZnO and 79.2% for the ZnO/NiO NCs. The increase in the photocatalytic capablity for the NCs is attributed to the synergistic effect between ZnO and NiO which effectively separated charge carriers preventing greater recombination rate. The robustness of ZnO/NiO NCs as a catalyst option was shown by their exceptional performance.

Toxic Dye Degradation Employing Phoenix dactylifera Seed Extract for the Green Synthesis of Silver Nanoparticles: Characterization and Application

This research highlights the facile green synthesis of silver nanoparticles (AgNPs) using Phoenix dactylifera seed extracts and its photocatalytic application for the degradation of toxic dyes. The AgNPs synthesis was confirmed by the appearance of its representative absorption peak at 416 nm in UV-visible absorption spectroscopy. Moreover, the reduction of silver ions to Ag was justified through Fourier transform infrared (FTIR) spectroscopy. X-ray diffraction pattern revealed crystalline AgNPs structure with particle size ranging from 5 to 15 nm calculated using the Debye-Scherrer equation. The rectangular-like structural morphology of synthesized AgNPs was observed in scanning electron micrographs. The as-synthesized AgNPs demonstrated higher photocatalytic activity for the degradation of malachite green (MG) and congo red (CR) followed by methylene blue (MB), and crystal violet (CV) under UV irradiation. In addition, rate constant (k) and percentage degradation were also calculated. The present study presents a facile green synthesis pathway and its potentially successful manipulation in the reduction of toxic dyes under the illumination of UV-light.

Abatement of methylene blue and diazinon pesticide from synthetic solutions using magnetic biochar from pistachio shells modified with MOF-808

This study develops a magnetic composite from pistachio shell biochar (PSBC/CoFe₂O₄) modified with MOF-808 for removing methylene blue (MB) dye and diazinon (DA) pesticide from water. The composite, with a surface area of 151.53 m2/g and magnetic saturation of 19.653 emu/g, allowed easy separation from solutions. Key adsorption factors such as pH, temperature, contact time, adsorbent dosage, and initial pollutant concentration were optimized. Maximum removal efficiencies of 99.32% for MB and 99.14% for DA were achieved at adsorbent dosages of 1 g/L for MB and 1.5 g/L for DA, initial concentrations of 5 mg/L, temperatures of 55 °C, contact times of 60 min for MB and 80 min for DA, and pH levels of 9 for MB and 6 for DA. Thermodynamic analysis confirmed that the adsorption process is spontaneous and endothermic, with enthalpy values of 55.091 kJ/mol for MB and 42.028 kJ/mol for DA, while entropy values indicated increased randomness during adsorption. Kinetic studies revealed that adsorption involved both physical and chemical interactions, with intraparticle diffusion not being the rate-limiting step. The Freundlich isotherm model provided the best fit (R2 = 0.971 for MB and 0.988 for DA), highlighting heterogeneous surface interactions. The composite showed higher adsorption capacities for MB (31.44 mg/g) than for DA (21.49 mg/g) and exhibited excellent regeneration potential, performing better in deionized water due to the inhibitory effects of salts in non-deionized water.

Anodic oxidation using 3D carbon felt/PbO2 anode: a electron transfer-mediated system for degradation of Rhodamine B

This study investigates the use of porous structured carbon felt (CF) as a substrate for the preparation a lead dioxide (CF/PbO2) anode for the electrochemical oxidation of Rhodamine B (RhB). Compared to traditional titanium-based lead dioxide (Ti/PbO2) and graphite sheet-based lead dioxide (GS/PbO2) anodes, the CF/PbO2 anode exhibited superior electrocatalytic activity, achieving a RhB degradation efficiency exceeding 99%. After 10 cycles, the electrocatalytic activity of CF/PbO2 anode remained robust, with a degradation efficiency of over 97%. Fluorescence spectroscopy, quenching experiments, and electrochemical tests indicate that the electrochemical oxidation behaviour on CF/PbO2 and GS/PbO2 anodes was governed by direct electron transfer, while indirect oxidation via •HO radicals was pivotal for the Ti/PbO2 anode. LC-MS analysis identified the intermediates of RhB degradation, contributing to the proposed degradation pathway. This study provides an efficient anode for the electrochemical degradation of organic pollutants in water.

Adsorption of Acid Yellow 36 and direct blue 86 dyes to Delonix regia biochar-sulphur

This study aims to investigate a new approach to removing hazardous dyes like Direct Blue 86 (DB86) and Acid Yellow 36 (AY36) from aqueous environments. Delonix regia biochar-sulphur (DRB-S), made from Delonix regia seed pods (DPSPs), is an inexpensive and environmentally friendly adsorbent. Different characterization investigations using BJH, BET, FTIR, SEM, DSC, TGA, and EDX were utilized in the descriptions of the DRB-S biosorbent. The optimal pH for AY36 dye and DB86 dye adsorption to the DRB-S adsorvbent was at pH 1.5. For the adsorption of AY36 and DB86 to DRB-S, equilibrium was attained at 30 and 90 min of reaction time interaction. The Langmuir model (LGM) and pseudo-second-order-model (PSOM) best describe the biosorption of both dye molecules to the biosorbent owing to the equal and homogeneous spread of the dye molecules over the biosorbent porous surface and a chemisorption process which involved the valency force through the exchange of electrons between the dye molecules and the prepared biosorbent. The determined biosorption capacities for both dyes (AY36 and DB86) were found to be 270.27 mg/g and 36.23 mg/g, respectively. In conclusion, this recently synthesised DRB-S adsorbent exhibited an impressive sorption capacity and successfully removed AY36 and DB86 dyes. This suggests that the biosorbent has potential applications in wastewater treatment and can be recycled without affecting its adsorption effectiveness.

Empowering wastewater treatment with step scheme heterojunction ternary nanocomposites for photocatalytic degradation of nitrophenol

The ongoing challenge of water pollution necessitates innovative approaches to remove organic contaminants from wastewater. In this work, new two-dimensional S-scheme heterojunction photocatalysts Bi2O3/CdS and MoS2/Bi2O3/CdS that are intended for the effective photocatalytic destruction of 4-nitrophenol, a dangerous organic pollutant, are synthesized and characterized. Utilizing a solvothermal method, successfully generated these ternary nanocomposites, which were characterized through various techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), high resolution transmission electronmicroscopy (HRTEM), Brunauer-Emmett-Telle (BET) and diffuse reflectance spectroscopy (DRS). Our results demonstrated that the Bi2O3/CdS heterojunction achieved an 86% degradation rate of 4-nitrophenol, while the MoS2/Bi2O3/CdS composite exhibited exceptional photocatalytic performance, achieving nearly complete degradation (99%) within 120 min under visible light irradiation. Most importantly the improved photocatalytic activity of MoS2/Bi2O3/CdS heterojunction originated from the release of internal electric field in S-scheme heterojunction. This enhanced activity is attributable to the synergistic effects of the heterojunctions that facilitate more effective charge separation and generation with more OP and RP confirmed the composite synthesis using S-scheme. The S-scheme is further confirmed by XPS, DRS, XPS-VB and photocurrent response. These findings highlight the promising application of these advanced photocatalysts in real-world wastewater treatment processes, offering a sustainable solution to combat water pollution.

Insights into the adsorption mechanisms of VOCs molecules on non-oxidized and oxidized SnO2 (110) monolayer: DFT analysis

CONTEXT

Designing efficient sensitive materials for the detection of volatile organic compounds (VOCs) such as ethanol, acetone, and benzene is stringent owing to the significant environmental and health risks induced by these compounds, in addition to their role as biomarkers for chronic diseases and food quality. This study investigates the adsorption mechanisms of VOC molecules (ethanol, acetone, and benzene) on both non-oxidized and oxidized SnO2 (110) monolayers and identifies the most suitable surface for gas sensing applications. For this, we examined structural properties, adsorption energies, density of states, gas responses, and recovery times. Additionally, we identified the most stable adsorption sites for each gas. Our results indicate that the oxidized SnO2 surface exhibits superior adsorption properties, response sensitivity, and recovery times, making it more effective for detecting VOC molecules, with particularly high sensitivity to ethanol. These findings are consistent with reported experimental results.

METHODS

The calculations were performed using density functional theory (DFT), implemented in the Quantum ESPRESSO code. The Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional was employed, along with a plane-wave basis set and a cutoff energy of 65 Ry. A comprehensive analysis of various VOC gas interactions with SnO2 surfaces was identified by examining the most stable adsorption sites for each gas.

Tin(IV)Porphyrin-Based Porous Coordination Polymers as Efficient Visible Light Photocatalyst for Wastewater Remediation

Two porphyrin-based polymeric frameworks, SnP-BTC and SnP-BTB, as visible light photocatalysts for wastewater remediation were prepared by the solvothermal reaction of trans-dihydroxo-[5,15,10,20-tetrakis(phenyl)porphyrinato]tin(IV) (SnP) with 1,3,5-benzenetricarboxylic acid (H3BTC) and 1,3,5-tris(4-carboxyphenyl)benzene (H3BTB), respectively. The strong bond between the carboxylic acid group of H3BTC and H3BTB with the axial hydroxyl moiety of SnP leads to the formation of highly stable polymeric architectures. Incorporating the carboxylic acid group onto the surface of SnP changes the conformational frameworks as well as produces rigid structural transformation that includes permanent porosity, good thermodynamic stability, interesting morphology, and excellent photocatalytic degradation activity against AM dye and TC antibiotic under visible light irradiation. The photocatalytic degradation activities of AM dye were found to be 95% by SnP-BTB and 87% by SnP-BTC within 80 min. Within 60 min of visible light exposure, the photocatalytic degradation activities of TC antibiotic were found to be 70% by SnP-BTB and 60% by SnP-BTC. The enhanced catalytic photodegradation performances of SnP-BTB and SnP-BTC were attributed to the synergistic effect between SnP and carboxylic acid groups. The carboxylic acid connectors strongly resist the separation of SnP from the surface of SnP-BTB and SnP-BTC during the photodegradation experiments. Therefore, the high degradation rate and low catalyst loading make SnP-BTB or SnP-BTC more efficient than other reported catalysts. Thus, the present investigations on the porphyrin-based photocatalysts hold great promise in tackling the treatment of dyeing wastewater.

Peroxydisulfate activation by synergized modified AgCuFe2O4@GO nanoparticle electrode with anchored MnO2 in cefixime three-dimensional electrochemical degradation: Optimization and mechanisms

Cefixime (CFX) is a potent antibiotic against gram-positive and gram-negative bacteria that resists degradation and typical removal procedures. This research aimed to synthesize a modified AgCuFe2O4@GO nanoparticle electrode with anchored MnO2 for removing CFX by three-dimensional electrochemical oxidation. The physical and chemical characteristics of the nanocomposite were evaluated using various techniques, including FESEM, XRD, EDS-mapping, FTIR, BET, VSM, and TGA. The analysis found that the AgCuFe2O4@GO with anchored MnO2 nanoparticle electrode has a large specific surface area, acceptable crystal structure, good magnetic characteristics, and a quasi-spherical form. At pH 5, 40 mg/L of CFX concentration, 0.4 g/L of the nanocomposite, 3 cm of electrode interval, 0.12 mM of persulfate electrolyte, and 12.5 mA/cm2 of current density for 40 min, the process reached removal effectiveness of 97.1% for the synthetic sample and 90.7% removal efficiency for the actual sample, while had rate mineralization of 61.8% and 241.1 kWh/g energy consumption. Pseudo-first-order (R2 = 0.997) and Langmuir-Hinshelwood (R2 = 0.769) kinetic experiments provided values of KC = 7.788 mg/L.min and KL-H = 0.011 L/mg, respectively, confirming conformity to these models. The adsorption isotherms demonstrated that the CFX antibiotic complies with the Temkin model with an R2 of 0.959. The particle electrode eliminated 86.1% of the contaminant over five cycles of regeneration and recovery, showcasing outstanding chemical stability. Throughout this process, persulfate functioned as both an oxidizing agent and an electrolyte, so amplifying the production of active radicals that degrade the pollutant and improve removal efficiency. Due to its magnetic properties, chemical stability, reusability, and high efficiency, modified AgCuFe2O4@GO with anchored MnO2 is suggested for purifying industrial and medicinal wastewater.

Smart and advanced nanocomposites of rGO-based Ni-doped Co3O4/TiO2 for next-level photocatalysis and gas sensing application

The rGO-based 5% Ni-doped Co3O4/TiO2 (GNCT) p-n heterojunction nanocomposite was synthesized using hydrothermal method. The resulting nanocomposite's morphology, structure, surface area, elemental composition, electrical and optical properties were thoroughly examined using a variety of techniques. The GNCT nanomaterial achieved an impressive 99.11% degradation within 40 min, while GPCT closely followed with a 96.6% efficiency. Its smart nanomaterial also excels as a n-butanol sensor, with GNCT showing a sensitivity of 91.51%, and GPCT registering 86.51%. This dual-functionality highlights its potential as an advanced material for environmental and sensing applications. Additionally, GNCT exhibited excellent stability across multiple cycles, underscoring its potential for gas sensing and environmental applications. The remarkable performance of GNCT is a result of the synergistic effects of its morphology (nanosheet), surface area (540.215 m2/g), band gap (1.93 eV), and photosensitivity (36.92%), which collectively make it an ideal candidate for the photocatalytic and gas sensing applications.

Robustic and hybrid cobalt doped BaFe12O19 hexaferrites for the photocatalytic degradation of Congo Red for wastewater treatment

The industrial sector faces a significant challenge in finding the highly effective and efficient treatments for harmful dye-based color effluents. In this study, pure and cobalt doped barium hexaferrite of chemical formula, Ba1-xCoxFe12O19 (x = 0-0.06) are made via sol-gel auto-combustion (SC) methodology. These nano hexaferrite based catalysts are employed for the photodegradation of Congo Red (CR) pollutant. X-rays diffraction investigation confirms the creation of pristine M-type with a hexagonal structure for the prepared hexaferrites. Field emission scanning electron microscopy analysis shows the existence of the hexagonal-shaped grains with well-defined grain boundaries. The reduction in the band gap of prepared hexaferrites are observed with the cobalt doping which is helpful in enhancing the photocatalytic performance. The X-ray photoelectron spectroscopy examination verifies the oxidation states of all elements found in the fabricated specimens. From the photocatalytic measurements, it is observed that the CR dye attains the removal percentage of 87.90%, 90.73%, 91.86% and 94.88% for the BaFe12O19 (x = 0.00), Ba0.08Co0.02Fe12O19 (x = 0.02), Ba0.06Co0.04Fe12O19 (x = 0.04), and Ba0.04Co0.06Fe12O19 (x = 0.06) hexaferrites under the natural sunlight of two hours. In addition, the reusability potential of prepared hexaferrites is also studied over the six consecutive experimental cycles. The excellent photodegradation performance of the Co- doped barium M-type hexaferrites for the removal of CR dye makes them highly useful for the wastewater remediation.

Removal of organic pollutants from paper mill effluent using Taro (Colocasia esculenta L. Schott) in an electro-assisted horizontal subsurface flow constructed wetland: Experimental and kinetic studies

In this study, the phytoremediation potential of Taro (Colocasia esculenta L. Schott) plant was examined, utilizing horizontal subsurface flow constructed wetlands with and without an electric current supply for the purpose of removing pollutants from paper mill effluent. For this, different wetlands were set up with varying concentrations of effluent: CW (Control), CW1 (25%), CW2 (50%), CW3 (75%), CW4 (100%). After 45 days, the highest plant height (85.13 ± 4.24 cm), leaf area index( 250.83 ± 10.14), fresh biomass (565.30 ± 6 .10 g), root biomass (392.85 ± 4.34 g), root-to-shoot ratio (2.41 ± 2.10), relative growth rate (0.044 ± 0.002 gg-1d-1), and chlorophyll content (3.29 ± 0.07 mg/g fwt) was observed in CW2 with current supply, along with significant removal of pollutants (pH: 7.13 ± 0.15, EC: 2.33 ± 0.07 dS/m, TDS: 192.52 ± 6.12 mg/L, COD: 490.17 ± 5.01 mg/L, BOD: 206.74 ± 5.92 mg/L, potassium: 73.27 ± 4.11 mg/L, sodium: 46.62 ± 2.27 mg/L, phosphate phosphorus: 34.08 ± 1.43 mg/L, and nitrate nitrogen: 104.85 ± 5.94 mg/L) and highest first-order rate constant (k) values. Furthermore, the microbial community assessment of constructed wetlands using V3-V4 16S rRNA sequence data was prepared on the Illumina MiSeq framework. The major phyla identified were Proteobacteria, Firmicutes, Bacteroidetes, Actinobacteria, Chloroflexi, Acidobacteria, Nitrospirae, Planctomycetes, and others. The findings offer innovative insights for sustainable wastewater treatment strategies through phytoremediation of paper mill effluent using Taro plants in modified constructed wetlands and highlight the role of diverse microbial communities capable of degrading various pollutants in wastewater.

Morphological and physiological responses of Momordica charantia to heavy metals and nutrient toxicity in contaminated water

This study investigates the impact of industrial wastewater from leather, household, and marble sources on the growth, physiological traits, and biochemical responses of Momordica charantia (bitter melon). Industrial activities often lead to the release of contaminated effluents, which can significantly affect plant health and agricultural productivity. Water analysis revealed that leather effluent contained high concentrations of heavy metals, including cadmium (2.67 mg/L), lead (1.95 mg/L), and nickel (1.02 mg/L), all of which exceeded the recommended safety limits for irrigation. Seed germination was significantly reduced, with only 45% germination in seeds irrigated with leather effluent, compared to 90% in the control group. Similarly, in plants treated with leather wastewater, shoot length, and root length were reduced by 38% and 42%. Chlorophyll content showed a marked decline, with chlorophyll "a" reduced by 25% and chlorophyll "b" by 30% in wastewater-treated plants, indicating impaired photosynthetic activity. Antioxidant enzyme activity, including catalase and superoxide dismutase, increased by up to 40%, reflecting a stress response to heavy metal toxicity. These findings highlight that industrial wastewater severely disrupts plant metabolic processes, leading to stunted growth and physiological stress. To safeguard crop productivity and food security, stringent wastewater treatment protocols must be implemented to mitigate environmental contamination. Future research should focus on developing advanced remediation techniques and sustainable wastewater management practices to reduce heavy metal toxicity and enhance soil health.

Concentration of steroid hormones in sediment of surface water resources in China: systematic review and meta-analysis with ecological risk assessment

The risk quotient (RQ) related to Estrone (E1), 17β-E2 (E2), Estriol (E3) and 17α-ethynylestradiol (EE2) in sediment of water resources in China was calculated using Monte Carlo Simulation (MCS) method. Fifty-four papers with 64 data-reports included in our study. The rank order of steroid hormones in sediment based on log-normal distribution in MCS was E1 (3.75 ng/g dw) > E3 (1.53 ng/g dw) > EE2 (1.38 ng/g dw) > E2 (1.17 ng/g dw). According to results, concentration of steroid hormones including E1, E2 and E3 in sediment of Erhai lake, northern Taihu lake and Dianchi river was higher than other locations. The rank order of steroid hormones based on percentage high risk (RQ > 1) was EE2 (87.00%) > E1 (70.00%) > E2 (62.99%) > E3 (11.11%). Hence, contamination control plans for steroid hormones in sediment of water resources in China should be conducted continuously.

Enhanced extraction of heavy metals from gypsum-based hazardous waste by nanoscale sulfuric acid film at ambient conditions

Low-cost, low-energy extraction of heavy metal(loid)s (HMs) from hazardous gypsum cake is the goal of the metallurgical industry to mitigate environmental risks and carbon emissions. However, current extracting routes of hydrometallurgy often suffer from great energy inputs and substantial chemical inputs. Here, we report a novel solid-like approach with low energy consumption and chemical input to extract HMs by thin films under ambient conditions. Through constructing a nanoscale sulfuric acid film (NSF) of ∼50 nm thickness on the surface of arsenic-bearing gypsum (ABG), 99.6% of arsenic can be removed, surpassing the 50.3% removal in bulk solution. In-situ X-ray diffraction, infrared spectral, and ab initio molecular dynamics (AIMD) simulations demonstrate that NSF plays a dual role in promoting the phase transformation from gypsum to anhydrite and in changing the ionic species to prevent re-doping in anhydrite, which is not occurred in bulk solutions. The potential of the NSF is further validated in extracting other heavy metal(loid)s (e.g., Cu, Zn, and Cr) from synthetic and actual gypsum cake. With energy consumption and costs at 1/200 and 1/10 of traditional hydrometallurgy separately, this method offers an efficient and economical pathway for extracting HMs from heavy metal-bearing waste and recycling industrial solid waste.

The Impurity Removal and Comprehensive Utilization of Phosphogypsum: A Review

Phosphogypsum (PG), a byproduct during the phosphoric acid production process, also known as the wet process, contains complex and diverse impurities, resulting in low utilization and considerable accumulation. This leads to a massive waste of land resources and a series of environmental pollution problems. Given the current urgent ecological and environmental situation, developing impurity removal processes with low energy consumption and high efficiency, exploring valuable resource recovery, preparing high value-added PG products, and broadening the comprehensive utilization ways of PG are significant strategies to promote the sustainable consumption of PG and sustainable development of the phosphorus chemical industry. This review comprehensively summarizes the advantages and disadvantages of existing PG impurity removal and utilization technologies and probes into the future development direction, which provides references and ideas for subsequent PG research.

Cr(VI) Reduction and Sequestration by FeS Nanoparticles Formed in situ as Aquifer Material Coating to Create a Regenerable Reactive Zone

Remediation of large and dilute plumes of groundwater contaminated by oxidized pollutants such as chromate is a common and difficult challenge. Herein, we show that in situ formation of FeS nanoparticles (using dissolved Fe(II), S(-II), and natural organic matter as a nucleating template) results in uniform coating of aquifer material to create a regenerable reactive zone that mitigates Cr(VI) migration. Flow-through columns packed with quartz sand are amended first with an Fe2+ solution and then with a HS- solution to form a nano-FeS coating on the sand, which does not hinder permeability. This nano-FeS coating effectively reduces and immobilizes Cr(VI), forming Fe(III)-Cr(III) coprecipitates with negligible detachment from the sand grains. Preconditioning the sand with humic or fulvic acid (used as model natural organic matter (NOM)) further enhances Cr(VI) sequestration, as NOM provides additional binding sites of Fe2+ and mediates both nucleation and growth of FeS nanoparticles, as verified with spectroscopic and microscopic evidence. Reactivity can be easily replenished by repeating the procedures used to form the reactive coating. These findings demonstrate that such enhancement of attenuation capacity can be an effective option to mitigate Cr(VI) plume migration and exposure, particularly when tackling contaminant rebound post source remediation.

Upcycling of Cr-Containing Sulfate Waste into Efficient FeCrO3/Fe2O3 Catalysts for CO2 Hydrogenation Reaction

Upcycling Cr-containing sulfate waste into catalysts for CO2 hydrogenation reaction benefits both pollution mitigation and economic sustainability. In this study, FeCrO3/Fe2O3 catalysts were successfully prepared by a simple hydrothermal method using Cr-containing sodium sulfate (Cr-SS) as a Cr source for efficient conversion and stable treatment of Cr. The removal rate of Cr in Cr-SS can reach 99.9% at the optimized hydrothermal conditions. When the synthesized catalysts were activated and used for the CO2 hydrogenation reaction, a 50% increase in CO2 conversion was achieved compared with the catalyst prepared by impregnation with a comparable amount of Cr. According to the extraction and risk assessment code (RAC) of the Reference Office of the European Community Bureau (BCR), the synthesized FeCrO3/Fe2O3 is risk-free. This work not only realizes the detoxification of the Cr-SS but transfers Cr into stable FeCrO3 for application in a catalytic field, which provides a strategy for the harmless disposal and resource utilization of Cr-containing hazardous waste.

Is Cr(III) re-oxidation occurring in Cr-contaminated soils after remediation: Meta-analysis and machine learning prediction

Whether Cr(III) in Cr(III)-containing sites formed after Cr(VI) reduction and stabilization remediation are re-oxidized and pose toxicity risks again has been a growing concern. In this study, 1030 data were collected to perform a meta-analysis to clarify the effects of various factors (oxidant type, soil and Cr(III) solid compound properties, aging conditions, and testing methods) on Cr(III) oxidation. We observed that the soil properties of clay, pH ≥ 8, the lower CEC capacity, easily reducible Mn content, and Cr(III) content, and the higher Eh value and Fe content can promote the re-oxidation of Cr(III). Publication bias and sensitivity analyses confirmed the stability and reliability of the meta-analysis. Subsequently, we used five machine learning algorithms to construct and optimize the models. The prediction results of the RF model (RMSE <1.36, R2 >0.71) with good algorithm performance showed that after ten years of remediation, the extractable Cr(VI) concentration in the soil was 0.0087 mg/L, indicating a negligible secondary pollution risk of Cr(III) re-oxidation. This study provides theoretical support for subsequent risk management and control after Cr(VI) soil remediation and provides a solution for the quantitative prediction of Cr(III) re-oxidation.

Highly efficient recovery of Zn2+/Cu2+ from water by using hydrotalcite as crystal seeds

The efficient and waste-free recovery of heavy metals is critical for heavy metal wastewater treatment. In this work, we explored how heavy metals can be recovered as valuable chemicals in the presence of crystal seeds. Hydrotalcite (one kind of layered double hydroxides (LDHs)) was used as crystal seeds to recover Zn2+ in the presence of Al3+ from water (i.e., seed-Zn2+-Al3+ system), which was compared with the monometallic heterogeneous system (seed-Zn2+) and direct coprecipitation (Zn2+-Al3+) system. Our results demonstrated that the seed-Zn2+-Al3+ system possessed a recovery rate of 2.6-2.8 times and a recovery kinetic rate of 2.7-5.9 times higher than those of the other two systems. Differing from the latter two systems, hydrotalcite seeds could induce Zn2+ and Al3+ to form ZnAl-LDH in seed-Zn2+-Al3+. Interestingly, the ZnAl-LDH presents a compositional divalent/trivalent cation molar ratio of ca. 3, which is comparable with the value in the hydrotalcite. It was demonstrated that the hydrotalcite seeds could act as a template to significantly induce the formation of ZnAl-LDH complying with the seed's structure and compositional ratio. Similar induction effect of seeds as the Zn2+ system was further verified in Cu2+ systems. This work provides a novel strategy for efficient recovery of heavy metals with product selectivity.

Photocatalytic degradation of acid blue 74 by Co: WO3 nanoparticles: Kinetics and response surface methodology studies

Energy-efficient sol-gel synthesis was achieved through the microwave assisted self-combustion route to produce hexagonal Tungsten oxide semiconductor (WO3). The photocatalytic activity was enhanced by doping Cobalt (Co) into the crystalline structure of the nanoparticle, which were subsequently sintered at 400 °C for an hour. The structural and morphological properties of the Co-doped WO3 were revealed using X-ray diffraction (XRD) characterization. The nanoparticles exhibited an amorphous structure before annealing, due to the short heating time during combustion synthesis. Sintering the nanoparticle transformed the nanoparticle from a monoclinic phase to orthorhombic phase structure. Additional analysis techniques, including scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive X-ray spectrum analysis (EDS). To assess the photocatalytic performance of these particles, Acid Blue 74 (AB 74) was employed in photodegradation experiments under UV light irradiation within a semi-continuous reactor. The photodegradation of dye molecules was evaluated utilizing a UV-Vis spectrophotometer, and the mineralization efficiency of the dye was determined through total organic carbon analysis (TOC). The results indicated that the dimension of the synthesized nano catalyst fell within the range of 70-120 nm, and it exhibited the ability to completely degrade a solution with an initial dye concentration of 20 ppm within 60 min. Various parameters affecting the photocatalytic reaction, including the photocatalyst dosage, initial dye concentration, pH and temperature of the dye solution were also investigated. The experiments were designed using Response surface methodology (RSM), through which a mathematical model for the dye removal process was developed.

Synthesis and characterization of titanium dioxide nanoparticles from Bacillus subtilis MTCC 8322 and its application for the removal of methylene blue and orange G dyes under UV light and visible light

Over the last decade there has been a huge increase in the green synthesis of nanoparticles. Moreover, there is a continuous increase in harnessing the potential of microorganisms for the development of efficient and biocompatible nanoparticles around the globe. In the present research work, investigators have synthesized TiO2 NPs by harnessing the potential of Bacillus subtilis MTCC 8322 (Gram-positive) bacteria. The formation and confirmation of the TiO2 NPs synthesized by bacteria were carried out by using UV-Vis spectroscopy, Fourier transforms infrared (FT-IR), X-ray diffraction (XRD), scanning electron microscope (SEM), and energy dispersive X-ray spectroscopy (EDX/EDS). The size of the synthesized TiO2 NPs was 80-120 nm which was spherical to irregular in shape as revealed by SEM. FTIR showed the characteristic bands of Ti-O in the range of 400-550 cm-1 and 924 cm-1 while the band at 2930 cm-1 confirmed the association of bacterial biomolecules with the synthesized TiO2 NPs. XRD showed two major peaks; 27.5° (rutile phase) and 45.6° (anatase phase) for the synthesized TiO2 NPs. Finally, the potential of the synthesized TiO2 NPs was assessed as an antibacterial agent and photocatalyst. The remediation of Methylene blue (MB) and Orange G (OG) dyes was carried out under UV- light and visible light for a contact time of 150-240 min respectively. The removal efficiency for 100 ppm MB dye was 25.75% and for OG dye was 72.24% under UV light, while in visible light, the maximum removal percentage for MB and OG dye was 98.85% and 80.43% respectively at 90 min. Moreover, a kinetic study and adsorption isotherm study were carried out for the removal of both dyes, where the pseudo-first-order for MB dye is 263.269 and 475554.176 mg/g for OG dye. The pseudo-second-order kinetics for MB and OG dye were 188.679 and 1666.667 mg/g respectively. In addition to this, the antibacterial activity of TiO2 NPs was assessed against Bacillus subtilis MTCC 8322 (Gram-positive) and Escherichia coli MTCC 8933 (Gram-negative) where the maximum zone of inhibition in Bacillus subtilis MTCC 8322 was about 12 mm, and for E. coli 16 mm.

Phase transformation of Cr(VI) host-mineral driven by citric acid-aided mechanochemical approach for advanced remediation of chromium ore processing residue-contaminated soil

The slow release of Cr(VI) from chromium ore processing residue-contaminated soil (COPR-soil) poses a significant environmental and health risk, yet advanced remediation techniques are still insufficient. Here, the slow-release behavior of Cr(VI) in COPR-soil is observed and attributed to the embedded Cr(VI) in the lattice of vaterite due to the isomeric substitution of CrO42- for CO32-. A citric acid-aided mechanochemical approach with FeS2/ZVI as reductive material was developed and found to be highly effective in remediating COPR-soil. Almost all Cr(VI) in COPR-soil, including Cr(VI) embedded in the minerals, are reduced with a reduction efficiency of 99.94%. Cr(VI) reduction kinetics indicate that the Cr(VI) reduction rate constant in the presence of citric acid was 4.8 times higher compared to its absence. According to the Raman spectroscopy, X-ray diffraction (XRD), and Electron Probe X-ray Micro-Analyzer (EPMA) analysis, the reduction of Cr(VI) embedded in vaterite was mainly attributed to the citric acid-induced protonation effect. That is, under the protonation effect, the embedded Cr(VI) could be released from vaterite through its phase transformation to calcite, whose affinity to Cr(VI) is low. While the reduction of released Cr(VI) could be promoted due to the complexation of citric acid with disulfide groups on FeS2/ZVI. The results of long-term stability tests demonstrated that the remediated COPR-soil exhibited excellent long-term stability, which may also be associated with improved utilization of available carbon and electron donors by the Cr(VI) reducing bacteria (Proteobacteria)-dominated microbial community in the presence of citric acid, thereby promoting to establish a stable reducing microenvironment. Collectively, these findings will further our understanding of the reduction remediation of COPR-soil, especially in the case of Cr(VI) embedded in minerals.

Mechanistic insights into mitigating Cd stress in plants using typical organic waste fermentation solutions

Finding practical solutions for utilizing agricultural organic wastes has always been a challenge. To address this, our study investigated the effects and mechanisms of different exogenous organic waste fermentation solutions on alleviating Cd stress in plants using hydroponic experiments. Out of the seven fermentation solutions examined, pea fermentation liquid (T3), chicken manure (T5), molasses (T6), and chitosan oligosaccharide broth (T9) exhibited positive effects. They increased shoot fresh weight by 1.17%, 26.83%, 7.94%, and 15.59%, and root fresh weight by 50.00%, 12.21%, 81.19%, and 19.47%, respectively. Conversely, amino acid mother liquid (T7) and potassium polyaspartate liquid (T8) reduced shoot fresh weight by 34.21% and 24.74%, and root fresh weight by 27.06% and 7.10%, respectively. All organic waste liquids reduced Cd concentration in shoots and roots. Corn fermentation liquid (T4) reduced Cd in shoots from 87.91 to 19.20 mg/kg, while molasses (T6) reduced Cd in roots from 980.94 to 260.47 mg/kg. SEM-EDX results revealed that molasses (T6) effectively repaired Cd damage on root surfaces. In addition, several waste liquids mitigated microelement absorption disturbances. All waste liquids reduced MDA, corn fermentation liquid (T4), chicken manure (T5), molasses (T6), potassium polyaspartate liquid (T8), and chitosan oligosaccharide liquid (T9) significantly decreased H2O2 by 21.6-38.3%. Structural equation model (SEM) and correlation analysis highlighted the importance of root Mg, Cu, and Zn content and CAT activity in relieving Cd stress and promoting plant growth. Overall, molasses (T6) and chicken manure (T5) demonstrated the most beneficial combined effects, while amino acid mother liquid (T7) and chitosan oligosaccharide liquid (T9) should be exercised with caution due to their weaker effects.

A review on radionuclide pollution in global soils with environmental and health hazards evaluation

Human populations are being exposed to a wide spectrum of radiation from soils as a result of the availability of radiation sources. Assessing the ecological and health effects of radionuclides in soils is crucial to support the optimal soil management practices but large-scale studies are limited. This study compiled data on radionuclides (226Ra, 232Th, 40K, 238U, and 137Cs) in soils located across the world (44 countries and 159 places) between 2008 and 2022 and applied radiological hazards indices and several multivariate statistical approaches. The average activity concentration (Bq/kg) of 226Ra, 232Th, 40K, 238U, and 137Cs were 408.56, 144.80, 508.78, 532.78, and 83.12, respectively, whereas 226Ra, 232Th, 40K, and 238U exceeded the standard limits. The principal component analysis explained more than 91% of variation in soils. Based on the geoaccumulation index, 40K posed moderately to heavy contamination whereas 238U and 226Ra posed moderate contamination in soils. Moreover, the mean values of radiological hazards evaluation such as radium equivalent activity (487.17 Bq/kg), external radiation hazard indices (1.32), internal hazard indices (2.15), absorbed dose rate (247.86 nGyh-1), annual effective dose rate (1.82 mSvy-1), activity utilization index (4.54) and excess lifetime cancer risk (63.84 × 10-4) were higher than recommended limit suggesting significant radiological risks in study region soils. The findings indicated that the study area soils were contaminated by radionuclides and unsafe for hazards in terms of the health risks linked with studied radioactive contents. The study is valuable for mapping radioactivity across the globe to determine the level of radioactivity hazards.

Influence of brassinosteroid and silicon on growth, antioxidant enzymes, and metal uptake of leafy vegetables under wastewater irrigation

Vegetable cultivation under sewage irrigation is a common practice mostly in developing countries due to a lack of freshwater. Long-term usage provokes heavy metals accumulation in soil and ultimately hinders the growth and physiology of crop plants and deteriorates the quality of food. A study was performed to investigate the role of brassinosteroid (BRs) and silicon (Si) on lettuce, spinach, and cabbage under lead (Pb) and cadmium (Cd) contaminated sewage water. The experiment comprises three treatments (control, BRs, and Si) applied under a completely randomized design (CRD) in a growth chamber. BRs and Si application resulted in the highest increase of growth, physiology, and antioxidant enzyme activities when applied under canal water followed by distilled water and sewage water. However, BRs and Si increased the above-determined attributes under the sewage water by reducing the Pb and Cd uptake as compared to the control. It's concluded that sewerage water adversely affected the growth and development of vegetables by increasing Pb and Cd, and foliar spray of Si and BRs could have great potential to mitigate the adverse effects of heavy metals and improve the growth. The long-term alleviating effect of BRs and Si will be evaluated in the field conditions at different ecological zones.

Microbial synthesis of titanium dioxide nanoparticles and their importance in wastewater treatment and antimicrobial activities: a review

Nanotechnology (NT) and nanoparticles (NPs) have left a huge impact on every field of science today, but they have shown tremendous importance in the fields of cosmetics and environmental cleanup. NPs with photocatalytic effects have shown positive responses in wastewater treatment, cosmetics, and the biomedical field. The chemically synthesized TiO2 nanoparticles (TiO2 NPs) utilize hazardous chemicals to obtain the desired-shaped TiO2. So, microbial-based synthesis of TiO2 NPs has gained popularity due to its eco-friendly nature, biocompatibility, etc. Being NPs, TiO2 NPs have a high surface area-to-volume ratio in addition to their photocatalytic degradation nature. In the present review, the authors have emphasized the microbial (algae, bacterial, fungi, and virus-mediated) synthesis of TiO2 NPs. Furthermore, authors have exhibited the importance of TiO2 NPs in the food sector, automobile, aerospace, medical, and environmental cleanup.

Chromium removal from chromium gypsum through microwave hydrothermal crystal phase regulation

Chromium gypsum (CG) is a common hazardous waste formed in chromium salt or electroplating industries. The trapped or lattice-doped CrO42- in gypsum crystals are difficult to be reduced or removed by traditional methods, which will be re-oxidized or slowly released during long-term hypaethral storage. In this study, microwave hydrothermal treatment was applied to remove chromium in CG. Under optimal conditions (solid-liquid ratio of 1:5, 0.1 M sulfuric acid as liquid media, and 110 °C), over 99% of the chromium in CG can be removed within 10 min. XRD spectra indicated that 59.8% gypsum was transformed to from dihydrate gypsum to hemihydrate gypsum. The toxicity leaching test shows that chromium in CG is 377.0 mg/L before detoxification and 0.55 mg/L after detoxification, which proves that chromium in CG lattice can be efficiently removed. This work enables to significantly advance the dehydration phase transformation process of gypsum and release the heavy metal impurities within it more quickly and provides new possibilities to treat similar solid waste containing gypsum or minerals with hydration water.

Z. AL-bonsrulah H. Optimization of oil industry wastewater treatment system and proposing empirical correlations for chemical oxygen demand removal using electrocoagulation and predicting the system's performance by artificial neural network

The alarming pace of environmental degradation necessitates the treatment of wastewater from the oil industry in order to ensure the long-term sustainability of human civilization. Electrocoagulation has emerged as a promising method for optimizing the removal of chemical oxygen demand (COD) from wastewater obtained from oil refineries. Therefore, in this study, electrocoagulation was experimentally investigated, and a single-factorial approach was employed to identify the optimal conditions, taking into account various parameters such as current density, pH, COD concentration, electrode surface area, and NaCl concentration. The experimental findings revealed that the most favorable conditions for COD removal were determined to be 24 mA/cm2 for current density, pH 8, a COD concentration of 500 mg/l, an electrode surface area of 25.26 cm2, and a NaCl concentration of 0.5 g/l. Correlation equations were proposed to describe the relationship between COD removal and the aforementioned parameters, and double-factorial models were examined to analyze the impact of COD removal over time. The most favorable outcomes were observed after a reaction time of 20 min. Furthermore, an artificial neural network model was developed based on the experimental data to predict COD removal from wastewater generated by the oil industry. The model exhibited a mean absolute error (MAE) of 1.12% and a coefficient of determination (R2) of 0.99, indicating its high accuracy. These findings suggest that machine learning-based models have the potential to effectively predict COD removal and may even serve as viable alternatives to traditional experimental and numerical techniques.

UV and solar-based photocatalytic degradation of organic pollutants from ceramics industrial wastewater by Fe-doped ZnS nanoparticles

UV and solar-based photocatalytic degradation of 2,4-dichlorophenol (2,4-DCP) as an organic contaminant in ceramics industry wastewater by ZnS and Fe-doped ZnS NPs was the focus of this research. Nanoparticles were prepared using a chemical precipitation process. The cubic, closed-packed structure of undoped ZnS and Fe-doped ZnS NPs was formed in spherical clusters, according to XRD and SEM investigations. According to optical studies, the optical band gaps of pure ZnS and Fe-doped ZnS nanoparticles are 3.35 and 2.51 eV, respectively, and Fe doping increased the number of carriers with high mobility, improved carrier separation and injection efficiency, and increased photocatalytic activity under UV or visible light. Doping of Fe increased the separation of photogenerated electrons and holes and facilitated charge transfer, according to electrochemical impedance spectroscopy investigations. Photocatalytic degradation studies revealed that in the present pure ZnS and Fe-doped ZnS nanoparticles, 100% treatment of 120 mL of 15 mg/L phenolic compound was obtained after 55- and 45-min UV-irradiation, respectively, and complete treatment was attained after 45 and 35-min solar light irradiation, respectively. Because of the synergistic effects of effective surface area, more effective photo-generated electron and hole separation efficiency, and enhanced electron transfer, Fe-doped ZnS demonstrated high photocatalytic degradation performance. The study of Fe-doped ZnS's practical photocatalytic treatment capability for removing 120 mL of 10 mg/L 2,4-DCP solution made from genuine ceramic industrial wastewater revealed Fe-doped ZnS's excellent photocatalytic destruction of 2,4-DCP from real industrial wastewater.

A Critical Review of the Enhanced Recovery of Rare Earth Elements from Phosphogypsum

The increasing demand for rare earth elements (REEs), especially from new and innovative technology, has strained their supply, which makes the exploration of new REE sources necessary, for example, the recovery of REEs from phsophogypsum (PG). PG is a byproduct during the wet production of phosphoric acid, which is an attractive secondary resource for REEs due to a large amount of REEs locked in them. In most cases, REEs contained in PG are mainly encapsulated in the gypsum crystal, leading to a low leaching efficiency. Therefore, it is particularly important to use various methods to enhance the leaching of REEs from PG. In this review, we summarized and classified various enhanced leaching methods for the recovery of REEs from PG, and the advantages and disadvantages of different methods were compared. A joint method of recrystallization and RIL may be a promising enhanced leaching approach for the recovery of REEs from PG. Recrystallization could achieve both the complete REE release and simultaneous preparation of industrial materials with high value added, such as high-strength α-hemihydrate gypsum by phase transformation of PG, and the RIL technology could adsorb the releasing REEs and realize their efficient extraction. Such a combination appears to show significant advantages because of high REE recovery, as well as high value-added product preparation at low cost.

The ability of twisted nanographene for removal of Pb2+, Hg2+ and Cd2+ ions from wastewater: Computational study

CONTEXT

Heavy metal ion removal from wastewater has become a global concern due to its extensive negative effects on human health and the environment. The density functional theory is employed to investigate the possibility of removing Pb2+, Hg2+, and Cd2+ ions from wastewater using nano-graphene. Researchers have shown that NG can efficiently remove heavy metals from media. Additionally, it was shown that the adsorption of Pb2+, Hg2+, and Cd2+ ions might reduce the large pristine NG (HOMO-LUMO) gap.

METHODS

HSE06 may accurately represent NG electrical characteristics. The DFT-D3 method was also used to account for Van der Waals interactions in the present study. The results demonstrated that charge transfer and binding energy remained greater in cation-NG systems with greater electron transfer rates. Pb2+, Hg2+, and Cd2+ adsorption results indicated that Egap was significantly reduced by 68%, 15%, and 21%, respectively. The Pb2+@NG complex exhibited the strongest oscillator strength. This may be explained by the enormous occupation number difference between the 2px orbital of the C atoms and the 6 s orbital of the Pb2+ cations. The greater Ebin value of Pb2+@NG is consistent with the increased predicted redshifts (199 nm). DFT (hybrid functional HSE06) studies that rely on time showed that the relevant complexes have "ligand-to-metal charge transfer" excitations. In general, it was found that Pb2+@NG had the greatest k value, binding energy, redshifts, and charge transfer rate among the complexes. The theoretical insights of this study may influence experimental efforts to identify NG-based compounds that are effective and efficient at removing pollutants from wastewater.

Metals (Ga, In) decorated fullerenes as nanosensors for the adsorption of 2,2-dichlorovinyldimethylphosphate agrochemical based pollutant

Owing to the fact that the use of 2,2-dichlorovinyldimethylphosphate (DDVP) as an agrochemical has become a matter of concern due to its persistence and potential harm to the environment and human health. Detecting and addressing DDVP contamination is crucial to protect human health and mitigate ecological impacts. Hence, this study focuses on harnessing the properties of fullerene (C60) carbon materials, known for their biological activities and high importance, to develop an efficient sensor for DDVP. Additionally, the sensor's performance is enhanced by doping it with gallium (Ga) and indium (In) metals to investigate the sensing and trapping capabilities of DDVP molecules. The detection of DDVP is carefully examined using first-principles density functional theory (DFT) at the Def2svp/B3LYP-GD3(BJ) level of theory, specifically analyzing the adsorption of DDVP at the chlorine (Cl) and oxygen (O) sites. The adsorption energies at the Cl site were determined as - 57.894 kJ/mol, - 78.107 kJ/mol, and - 99.901 kJ/mol for Cl_DDVP@C60, Cl_DDVP@Ga@C60, and Cl_DDVP@In@C60 interactions, respectively. At the O site, the adsorption energies were found to be - 54.400 kJ/mol, - 114.060 kJ/mol, and - 114.056 kJ/mol for O_DDVP@C60, O_DDVP@Ga@C60, and O_DDVP@In@C60, respectively. The adsorption energy analysis highlights the chemisorption strength between the surfaces and the DDVP molecule at the Cl and O sites of adsorption, indicating that the O adsorption site exhibits higher adsorption energy, which is more favorable according to the thermodynamics analysis. Thermodynamic parameters (∆H and ∆G) obtained from this adsorption site suggest considerable stability and indicate a spontaneous reaction in the order O_DDVP@Ga@C60 > O_DDVP@In@C60 > O_DDVP@C60. These findings demonstrate that the metal-decorated surfaces adsorbed on the oxygen (O) site of the biomolecule offer high sensitivity for detecting the organophosphate molecule DDVP.

Characterization and synthesis of new adsorbents with some natural waste materials for the purification of aqueous solutions

In this study, hexavalent chromium Removal from aqueous environments was investigated by using polyaniline composites with some natural waste materials. Batch experiments were used, and some parameters such as contact time, pH and adsorption isotherms were determined for the best composite with the highest removal efficiency. Scanning Electron Microscope (SEM), Fourier Transform Infrared (FTIR) spectroscopy, and X-ray Diffraction (XRD) were used to characterize the composites. According to the results, the polyaniline/walnut shell charcoal/PEG composite outperformed other composites and showed the highest chromium removal efficiency of 79.22%. Polyaniline/walnut shell charcoal/PEG has a larger specific surface area of 9.291 (m²/gr) which leads to an increase in its removal efficiency. For this composite, the highest removal efficiency was obtained at the pH = 2 and 30 min contact time. The maximum calculated adsorption capacity was 500 mg/g.

Unveiling the migration of Cr and Cd to biochar from pyrolysis of manure and sludge using machine learning

Heavy metal (HM) in biochar derived from pyrolysis of sludge or manure is the main issue for its large-scale application in soils for carbon sequestration. However, there is a paucity of efficient approaches to predict and comprehend the HM migration during pyrolysis for preparing low HM-contained biochar. Herein, the data on the feedstock information (FI), additive, total concentration of feedstock (FTC) of HM Cr and Cd, and pyrolysis condition, were extracted from the literature, to predict total concentration (TC) and retention rate (RR) of Cr and Cd in sludge/manure biochar using ML for mapping their migration during pyrolysis. Two datasets for Cr and Cd were compiled with 388 and 292 data points from 48 and 37 peer-review papers. The results indicated that the TC and RR of Cr and Cd could be predicted by the Random Forest model with test R² of 0.74-0.98. Their TC and RR in biochar were dominated by the FTC and FI, respectively; while pyrolysis temperature was the most important to Cd RR. Moreover, potassium-based inorganic additives decreased the TC and RR of Cr while increased those of Cd. The predictive models and insights provided by this work could aid the understanding of HM migration during manure and sludge pyrolysis and guide the preparation of low HM-contained biochar.

Water Decontamination from Cr(VI) by Transparent Silica Xerogel Monolith

Cr(VI) is highly soluble and mobile in water solution and extremely toxic. In order to obtain a specific material with adsorption properties towards Cr(VI), and that can be used in environmental remediation of water contaminated with Cr(VI), one-step sol-gel technique, at low temperature (50 °C), has been optimized to prepare transparent silica-based xerogel monolith by using tetraethyl orthosilicate as precursor. The obtained xerogel, with disk shape, was fully characterized by Raman, BET, FE-SEM and XRD analysis. The results indicated that the material showed silica amorphous phase and high porosity. The study of the adsorption properties towards different concentrations of Cr(VI), in the form of HCrO₄^- in acidic condition, showed prominent results. The absorption kinetics were evaluated by studying different models, the final result showing that the absorption of Cr(VI) occurred through intra-particle diffusion process, following two steps, and that the absorption equilibrium is regulated by Freundlich isotherm model. The material can be restored by reducing the hazardous Cr(VI) to Cr(III), a less toxic form of chromium, by 1,5-diphenylcarbazide, and with successive treatment in acidic water.

Progresses in lignin, cellulose, starch, chitosan, chitin, alginate, and gum/carbon nanotube (nano)composites for environmental applications: A review

Water sources are becoming increasingly scarce, and they are contaminated by industrial, residential, and agricultural waste-derived organic and inorganic contaminants. These contaminants may pollute the air, water, and soil in addition to invading the ecosystem. Because carbon nanotubes (CNTs) can undergo surface modification, they can combine with other substances to create nanocomposites (NCs), including biopolymers, metal nanoparticles, proteins, and metal oxides. Furthermore, biopolymers are significant classes of organic materials that are widely used for various applications. They have drawn attention due to their benefits such as environmental friendliness, availability, biocompatibility, safety, etc. As a result, the synthesis of a composite made of CNT and biopolymers can be very effective for a variety of applications, especially those involving the environment. In this review, we reported environmental applications (including removal of dyes, nitro compounds, hazardous materialsو toxic ions, etc.) of composites made of CNT and biopolymers such as lignin, cellulose, starch, chitosan, chitin, alginate, and gum. Also, the effect of different factors such as the medium pH, the pollutant concentration, temperature, and contact time on the adsorption capacity (AC) and the catalytic activity of the composite in the reduction or degradation of various pollutants has been systematically explained.