Search Results (75)

A polyoxometalate-based metal–organic complex with the ability to treat pollutants in water was obtained under hydrothermal conditions, namely [Ni(H₂L)(HL)₂](PMo₁₂O₄₀)·3H₃O·4H₂O (1) (H₂L = 4,4′-(1H,1′H-[2,2′-biimidazole]-1,1′-diyl)dibenzoicacid). Structural analysis reveals that the [Ni(H₂L)(HL)₂] units are interconnected into a 2D layer via hydrogen bonds between adjacent carboxyl groups and water molecules of crystallization. [PMo₁₂O₄₀]³⁻ anions are embedded within the larger pores of the layer and are connected to the adjacent layers through hydrogen bonds, ultimately expanding the structure into a 3D supramolecular architecture. The intermolecular interactions were studied via Hirshfeld surface (HS) analysis. Electrochemical performance tests reveal that 1 exhibits electrocatalytic activity toward the oxidation and reduction of diverse pollutants in water, including NO₂⁻, Cr(VI), BrO₃⁻, Fe(III), and ascorbic acid (AA). Additionally, it can also serve as an amperometric sensor for the detection of BrO₃⁻ and Cr(VI). Photocatalytic studies reveal that compound 1 functions as a bifunctional photocatalyst, which not only achieves efficient degradation of organic dyes but also demonstrates remarkable reduction efficiency for toxic Cr(VI). Compound 1 demonstrates significant potential for practical water remediation applications. Full article

TiO₂ mesoporous supports were obtained by the sol–gel method from different precursors (titaniumethoxide, isopropoxide, or butoxide) in the presence of nonionic, cationic, and anionic surfactants. Among these samples, those obtained from Ti isopropoxide, Brij58 w/o activated carbon (AC), were selected as supports. Photocatalysts were obtained by modifying these supports with Ag, Fe, and AgFe (each metal around 1% mass). The characterization results showed a stronger influence of titania precursors, surfactants, and AC on the texture and an insignificant effect on the crystalline structure and morphology of the obtained materials. X-ray photoelectron spectroscopy revealed the effects of AC and Fe on the Ag⁰ concentration and of Ag on Fe-reduced species. Based on this information, the results obtained by H₂-TPR, UV–Vis, Raman, and photoluminescence spectroscopy were explained. The performance of the photocatalysts was evaluated in the degradation of Congo Red (CR) and Crystal Violet (CV) dyes under UV and visible light. The Ag-TiO₂ sample exhibited the best activity in degrading CR at acidic pH and in degrading CV under basic conditions. In visible light, we observed the significant effects of the surface plasmon resonance, AC, Ag, and Fe on the activity in CR photodegradation. The proposed kinetics and mechanisms complete the study of the reactions. Full article

Emerging pollutants, such as N-acetyl-para-aminophenol, pose significant challenges to environmental sustainability, and Bi₂Fe₂O₂ (BFO) nanomaterials are an emerging class of piezoelectric materials. This study presents a novel piezoelectric-driven Fenton system based on Bi₂Fe₄O₉ nanosheets for the efficient degradation of organic pollutants. BFO nanosheets with varying thicknesses were synthesized, and their piezoelectric properties were confirmed through piezoresponse force microscopy and heavy metal ion reduction experiments. The piezoelectric electrons generated within the BFO nanosheets facilitate the in situ production of hydrogen peroxide, which in turn drives the Fenton-like reaction. Furthermore, the piezoelectric electrons enhance the redox cycling of iron in the Fenton process, boosting the overall catalytic efficiency. The energy band structure of BFO nanosheets is well-suited for this process, enabling efficient hydrogen peroxide generation and promoting Fe³⁺ reduction. The findings demonstrate that thinner BFO nanosheets exhibit superior piezoelectric activity, leading to enhanced catalytic performance. Additionally, the incorporation of gold nanodots onto BFO nanosheets further boosts their piezocatalytic efficiency, particularly in the reduction of Cr (VI). The system exhibited robust oxidative capacity, stability, and recyclability, with reactive oxygen species (ROS) verified via electron paramagnetic resonance spectroscopy. Overall, BFO nanosheets, with their optimal energy band structure, self-supplied hydrogen peroxide, and enhanced Fe³⁺ reduction, represent a promising, sustainable solution for advanced oxidation processes in wastewater treatment and other applications. Full article

The efficient removal of dyes and Cr(VI) from wastewater is imperative. Therefore, a mixed metal oxide CuMoV(450) derived from a polyoxometalate-based metal–organic framework (POMOF) [Cu(2,2′-bipy)][Cu(2,2′-bipy)₂]₂[PMo₈V₆O₄₂]•2H₂O (CuMoV) was synthesized by calcination, fully characterized by XRD, XPS, FT-IR, and SEM methods, and explored for the heterogeneous catalytic degradation of methylene blue (MB) dye and the catalytic reduction of Cr(VI) in aqueous media over NaBH₄ under mild conditions. The removal rates for MB and Cr(VI) were 95.9% (30 min) and 96.5% (2.0 min), respectively. The pseudo-first-order rate constants of MB degradation and Cr(VI) reduction were 0.093 min⁻¹ and 1.536 min⁻¹, respectively. The highly catalytic reusability of CuMoV(450) was confirmed by the recycling experiments. Moreover, the possible mechanisms of MB degradation and Cr(VI) reduction were proposed. The catalytic activities of CuMoV(450) were much better than those of its parent compound CuMoV, proving that POMOFs were good candidates for the preparation of mixed metal oxides with excellent catalytic performances. This work not only indicates that CuMoV(450) has the potential to be a satisfied catalyst for wastewater remediation via catalytic degradation and reduction, but also gives a clue to synthesize mixed metal oxides with excellent catalytic properties by the calcination of POMOFs. Full article

Pollution of freshwater by synthetic organic dyes is a major concern due to their high toxicity and mutagenicity. In this study, the degradation of Congo red (CR) and malachite green (MG) dyes was investigated using nanostructured Gd₂O₃. It was prepared using the coprecipitation method, using gadolinium nitrate and concentrated formic acid, with subsequent calcination at 600 °C. Its morphology corresponds to hollow porous microspheres with a size between 0.5 and 7.5 μm. The optical bandgap energy was determined by using the Tauc method, giving 4.8 eV. The degradation of the dyes was evaluated by UV-vis spectroscopy, which revealed that dissociative adsorption (in the dark) played a key role. It is explained by the cleavage and fragmentation of the organic molecules by hydroxyl radicals (^•OH), superoxide radicals (^•${\mathrm{O}}_2^{-}$) and other reactive oxygen species (ROS) produced on the surface of Gd₂O₃. For CR, the degradation percentage was ~56%, through dissociative adsorption, while UV light photocatalysis increased it to ~65%. For MG, these values were ~78% and ~91%, respectively. The difference in degradation percentages is explained in terms of the isoelectric point of solid (IEPS) of Gd₂O₃ and the electrical charge of the dyes. FTIR and XPS spectra provided evidence of the role of ROS in dye degradation. Full article

Toxic metal ions such as cadmium-Cd(II) and chromium-Cr(VI) are toxic, do not degrade easily in nature, and can cause various disorders and diseases in humans. Removing and monitoring Cd(II) and Cr(VI) ions is necessary for improving water quality. This study aimed to produce an adsorbent from activated carbon of Capsicum annuum and assess its ability to adsorb Cd(II) and Cr(VI) ions from water. The results showed that the adsorbent from C. annuum was porous after its conversion to activated carbon. The pH_(PZC) of carbon-based Capsicum annuum was acidic, with a pH of 2.68. The highest capacities for both metal ions were observed at a pH of 1 for Cr(VI) and pH 5 for Cd(II), with capacities of 18.38 and 29.48 mg/g, respectively. The Freundlich sorption model proved to be the most suitable method. The adsorption of Cr(VI) and Cd(II) increased when the initial concentrations were raised from 20 and 60 mg/L; thereafter, a decrease was observed. The data showed that the adsorption of Cd(II) was fast and reached a maximum in 40 min, while Cr(VI) increased with time up to 30 min; thereafter, the rate for Cr(VI) decreased, while equilibrium was reached for Cd(II) ions. The temperature effect showed that the adsorption of Cd(II) and Cr(VI) ions reached a maximum at 55 and 45 °C, respectively. The results of enthalpy change (ΔH°) showed that the uptake process was exothermic, while the change in thermodynamic values of Gibbs energy (ΔG°) indicated that the sorption process was spontaneous and achievable. The greatest adsorption capacities for Cd(II) and Cr(VI) ions were 34.34 and 15.24 mg/g, respectively. The activated carbon from C. annuum proved to be effective for the adsorption of Cd(II) and Cr(VI) from wastewater. Full article

Currently, several organic dyes found in wastewater cause severe contamination problems for flora, fauna, and people in direct contact with them. This research proposes an alternative for the degradation of polluting dyes using ZnO nanoparticles (NPs) synthesized by an ecological route using leaf and root extracts of Ambrosia ambrosioides as a reducing agent (with a weight/volume ratio = 4%). Scanning Electron Microscopy (SEM) was used to determine the morphology, showing an agglomeration of cluster-shaped NPs. Using Transmission Electron Microscopy (TEM), different sizes of NPs ranging from 5 to 56 nm were observed for both synthesized NPs. The composition and structure of the nanomaterial were analyzed by infrared spectroscopy (FT-IR) and X-ray diffraction (XRD), showing as a result that the NPs have a wurtzite-like crystalline structure with crystallite sizes around 32–37 nm for both samples. Additionally, the bandgap of the NPs was calculated using Ultraviolet Visible Spectroscopy (UV–Vis), determining values of 2.82 and 2.70 eV for the NPs synthesized with leaf and root, respectively. Finally, thermogravimetric analysis demonstrated that the nanoparticles contained an organic part after the green synthesis process, with high thermal stability for both samples. Photocatalytic analysis showed that these nanomaterials can degrade four dyes under UV irradiation, reaching 90% degradation for methylene blue (MB), methyl orange (MO) and Congo red (CR) at 60, 100 and 60 min, respectively, while for methyl red (MR) almost 90% degradation was achieved at 140 min of UV irradiation. These results demonstrate that it is effective to use Ambrosia ambrosioides root and leaf extracts as a reducing agent for the formation of ZnO NPs, also evidencing their favorable application in the photocatalytic degradation of these four organic dyes. Full article

The adsorption efficiency of Cr(VI) and anionic textile dyes onto MgAl-layered double hydroxides (LDHs) and MgAl-LDH coated on bio-silica (b-SiO₂) nanoparticles (MgAl-LDH@SiO₂) derived from waste rice husks was studied in this work. The material was characterized using field-emission scanning electron microscopy (FE-SEM/EDS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopic (XPS) techniques. The adsorption capacities of MgAl-LDH@SiO₂ were increased by 12.2%, 11.7%, 10.6%, and 10.0% in the processes of Cr(VI), Acid Blue 225 (AB-225), Acid Violet 109 (AV-109), and Acid Green 40 (AG-40) dye removal versus MgAl-LDH. The obtained results indicated the contribution of b-SiO₂ to the development of active surface functionalities of MgAl-LDH. A kinetic study indicated lower intraparticle diffusional transport resistance. Physisorption is the dominant mechanism for dye removal, while surface complexation dominates in the processes of Cr(VI) removal. The disposal of effluent water after five adsorption/desorption cycles was attained using enzymatic decolorization, photocatalytic degradation of the dyes, and chromate reduction, satisfying the prescribed national legislation. Under optimal conditions and using immobilized horseradish peroxidase (HRP), efficient decolorization of effluent solutions containing AB-225 and AV-109 dyes was achieved. Exhausted MgAl-LDH@SiO₂ was processed by dissolution/precipitation of Mg and Al hydroxides, while residual silica was used as a reinforcing filler in polyester composites. The fire-proofing properties of composites with Mg and Al hydroxides were also improved, which provides a closed loop with zero waste generation. The development of wastewater treatment technologies and the production of potentially marketable composites led to the successful achievement of both low environmental impacts and circular economy implementation. Full article

Hexavalent chromium (Cr (VI)) and para-chlorophenol (4-CP) are prevalent industrial wastewater contaminants that are recalcitrant to natural degradation and prone to migration in aquatic systems, thereby harming biological health and destabilizing ecosystems. Consequently, their removal is imperative. Compared to conventional chemical treatment methods, CW-MFC technology offers broader application potential. Leersia hexandra Swartz can enhance Cr (VI) and 4-CP absorption, thereby improving wastewater purification and electricity generation in CW-MFC systems. In this study, three CW-MFC reactors were designed with L. hexandra Swartz in distinct configurations, namely, stacked, multistage, and modular, to optimize the removal of Cr (VI) and 4-CP. By evaluating wastewater purification, electrochemical performance, and plant growth, the optimal influent hydraulic retention time (HRT) was determined. The results indicated that the modular configuration at an HRT of 5 days achieved superior removal rates and power generation. The modular configuration also supported the best growth of L. hexandra, with optimal photosynthetic parameters, and physiological and biochemical responses. These results underscore the potential of modular CW-MFC technology for effective detoxification of complex wastewater mixtures while concurrently generating electricity. Further research could significantly advance wastewater treatment and sustainable energy production, addressing water pollution, restoring aquatic ecosystems, and mitigating the hazards posed by Cr (VI) and 4-CP to water and human health. Full article

The global serious pollution situation urgently needs green, efficient, and sustainable development methods to achieve heavy metal pollution control. The photocatalytic properties of anatase are sufficient to achieve pollution control by providing photoelectrons to harmful heavy metals. However, since natural anatase particles tend to agglomerate and deactivate in water, most studies have been conducted to prepare TiO₂–biochar nanocomposites using chemical synthesis methods. In the present study, we utilized pyrolytic sintering to load natural anatase onto biochar to obtain natural anatase–biochar (TBC) composites. Characterization tests, such as X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS), showed that anatase was uniformly partitioned into the surface and pores of biochar without destroying the lattice structure. Due to its photocatalytic properties, TBC degraded Cr (VI) by 99.63% under light conditions. This is 1.58 times higher than the dark condition. Zeta potential showed that the surface of the TBC was positively charged under acidic conditions. The charge attraction between TBC and chromium salt was involved in the efficient degradation of Cr (VI). Different sacrificial agents as well as gas purge experiments demonstrated that photoelectrons (e⁻) and superoxide radicals (${\mathrm{O}}_2^{-}$) dominated the degradation of Cr (VI). TBC has the characteristics of high efficiency, stability, and sustainability. This may provide a new idea for the preparation of photocatalytic materials and the realization of environmental protection and sustainable development through heavy metal pollution control. Full article

Electrodeposited chromium plating continues to be widely used in a number of specialized areas, such as weapons, transport, aerospace, etc. However, the formation of texture, hydrogen content and residual stress can degrade the serviceability and lead to material failure. The effect of post heat treatment processes on the relationship of texture, hydrogen content, residual stress and corrosion resistance of hexavalent [Cr(VI)] chromium coatings deposited on Cr–Ni–Mo–V steel substrates was investigated. Macrotexture was measured by XRD. Microtexture, dislocation density and grain size were studied by EBSD. With the increase of the heat treatment temperature, it was found that the fiber texture strength of the (222) plane tended to increase and subsequently decrease. Below 600 °C, the increase in the (222) plane texture carried a decrease in the hydrogen content, residual stress, microhardness and an increase in the corrosion resistance. In addition, crack density and texture strength were less affected by the heat treatment time. Notably, relatively fewer crack densities of 219/cm², a lower corrosion current density of 1.798 × 10⁻⁶ A/dm² and a higher microhardness of 865 HV were found under the preferred heat treatment temperature and time of 380 °C and 4 h, respectively. The hydrogen content and residual stress were 7.63 ppm and 61 MPa, with 86% and 75% reduction rates compared to the as-plated state, respectively. In conclusion, in our future judgement of the influence of heat treatment on coating properties, we can screen or determine to a certain extent whether the heat treatment process is reasonable or not by measuring only the macrotexture. Full article

Cu₂ZnSnSe₄ (CZTSe) nanoparticles (NPs) were successfully synthesized via a solvothermal method. Their structural, compositional, morphological, optoelectronic, and electrochemical properties have been characterized by X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), Field-emission scanning electron microscopy (FE-SEM), transmission electron microscope (TEM), UV–vis absorption spectroscopy, and electrochemical impedance spectroscopy (EIS) techniques. Porosimetry and specific surface area in terms of the Brunauer–Emmett–Teller (BET) technique have also been studied. XRD indicates the formation of a polycrystalline kesterite CZTSe phase. Raman peaks at 173 and 190 cm⁻¹ confirm the formation of a pure phase. TEM micrographs revealed the presence of nanoparticles with average sizes of ~90 nm. A BET surface area of 7 m²/g was determined. The CZTSe NPs showed a bandgap of 1.0 eV and a p-type semiconducting behavior. As a proof of concept, for the first time, the CZTSe NPs have been used as a visible-light-driven photocatalyst to Congo red (CR) azo dye degradation. The nanophotocatalyst material under simulated sunlight results in almost complete degradation (96%) of CR dye after 70 min, following a pseudo-second-order kinetic model (rate constant of 0.334 min⁻¹). The prepared CZTSe was reusable and can be repeatedly used to remove CR dye from aqueous solutions. Full article

This study utilized a straightforward co-precipitation method to successfully synthesize Ce-La-X(Mn/Pr)-O composite materials for treating simulated hexavalent chromium (Cr(VI)) wastewater with distinctively porous and fluffy textures, along with tubular morphologies. Notably, Ce-La-Mn-O demonstrated a remarkable specific surface area of 96.2698 m²/g, mesoporous architecture with a pore diameter of 6.9511 nm, and an impressive adsorption capacity of 88.79 mg/g. Under optimized conditions, specifically an initial Cr(VI) concentration of 20 mg/L, a Ce-La-Mn-O dosage of 0.8 g/L, a reaction temperature of 40 °C, an initial pH of 6, and with the application of simulated daylight, the removal rate of Cr(VI) exceeded 98% within 15 min. Even after three cycles, the removal rate was maintained at above 80%. Based on a comprehensive suite of morphological, structural, and performance characterizations, the introduction of Mn/Pr was found to modify the structure of Ce-La-O and enhance the synergistic interactions among the metals within the Ce-La-O framework. In addition, Ce-La-Mn-O exhibited superior visible light absorption properties and dual functionality for catalytic reduction and adsorption. All three materials were found to form -OH polar bond functional groups, converting it to Cr(III) and subsequently forming Cr(OH)₃. The Ce-La-X(Mn/Pr)-O composite materials provide a robust theoretical foundation for exploring the dual functional synergistic effects in the efficient removal of Cr(VI) from aqueous systems, indicating their vast potential for practical applications. Full article

Chromium (Cr) contamination, widely present in the environment, poses a significant threat to both ecology and human health. Microbial remediation technology has become a hot topic in the field of heavy metal remediation due to its advantages, such as environmental protection, low cost, and high efficiency. This paper focused on using various characterization and analysis methods to investigate the bioreduction effect and mechanism of microorganisms on Cr(VI) under various influencing factors. The main contents and conclusions were as follows: Shewanella oneidensis MR-1 was selected as the target strain for studying its reduction of Cr(VI) at different inoculation amounts, temperatures, pH values, time intervals, etc. The results indicated that S. oneidensis MR-1 exhibited an optimal reduction effect on Cr(VI) at pH 7 and a temperature of 35 °C. Additionally, electron shuttles (ESs), including humic acid (HA) and 9,10-antraquinone-2,6-disulfonate (AQDS), were introduced into the degradation system to improve the reduction efficiency of S. oneidensis MR-1. Upon adding goethite further, S. oneidensis MR-1 significantly enhanced its reducing ability by converting Fe(III) minerals to Fe(II) and reducing Cr(VI) to Cr(III) during electron transfer. Full article

Franklinite-zincochromite-gahnite solid solutions were prepared using ceramic or coprecipitation methods, and their pigmenting capacity as cool ceramic pigments in different glazes (double and single firing frits and porcelain frit) was studied. XRD, UV–Vis–NIR diffuse reflectance, CIEL*a*b* colour analysis, band gap measurements, and the photocatalytic degradation of Orange II were carried out to characterise the samples. The following criteria for high red colouring capacity and high NIR reflectance at the minimum Cr amount were found to be the optimal compositions for an intense reddish cool pigment: Zn(Fe_1.8Cr_0.2), Zn(Al_1.5Cr_0.5) and Zn(Al_1.3Cr_0.5Fe_0.2)O₄. All the powders showed a direct semiconductor behaviour, with a band gap of approximately 2 eV, which fell in the visible range (620 nm); the visible light photocatalysis of Orange II was moderate, but franklinite-zincochromite Zn(Fe_1.8Cr_0.2) stood out compared with silver orthophosphate. Full article