Search Results (77)

In this study, the in situ solvothermal synthesis of a copper-based metal–organic framework (Cu-BTC MOF) into two porous ceramic substrates with a 10 cm diameter and 2 cm thickness was reported. X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, diffuse reflectance spectroscopy (DRS), Tauc plot analysis, optical microscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were the techniques that were utilized to verify the formation and incorporation of the MOF into ceramics (two samples, with different SiO₂ particles; 500 µm (Ceramic 1), and 150 µm (Ceramic 2)). The synthesized Cu-MOF exhibited a crystalline structure. Both the composites and the Cu-MOF exhibited visible-light absorption, with optical band gaps of 2.5 eV and 2.4 eV, respectively, as determined by DRS. TEM images demonstrated that crystalline MOF domains were successfully included inside the ceramics. Methyl orange (MO), Congo red (CR), and methylene blue (MB) were used to assess the composites’ ability to remove dyes. Catalytic hydrogenation, powered by in situ hydrogen production from NaBH₄ hydrolysis, demonstrated high removal efficiencies of 91–97% after 60 min. Adsorption, on the other hand, was ineffective. Despite undergoing four consecutive cycles without performance degradation, the materials demonstrated remarkable recyclability. Cu-MOF@ceramic composites are effective, durable, and practically applicable for improved wastewater treatment. Full article

The development of non-noble metal catalysts provides a cost-effective and sustainable route for glucose oxidation to gluconic acid. In this study, a series of catalysts based on inexpensive transition metals (Cr, Cu, Ni, Fe) and/or Au were synthesized using siliceous supports (SiO₂ and MCM-41) and systematically evaluated. The aim was to partially or fully replace noble metals with lower-cost alternatives, while maintaining high catalytic performance. Comprehensive characterization—including ICP-AES for composition, N₂ adsorption–desorption for porosity, XRD for structure, H₂-TPR for reducibility, and NH₃-TPD for acidity—was conducted to establish structure–property relationships. Among the tested catalysts, Ni- and Fe-based systems exhibited superior stability, with NiO/SiO₂ achieving gluconic acid yields comparable to Au. The bimetallic Au–Ni/SiO₂ catalyst displayed enhanced metal–support interactions and minimal leaching (<2%), while Au–Fe/SiO₂ improved selectivity, yielding up to 23% gluconic acid, surpassing 5Fe/SiO₂ (18%) and 0.3Au/SiO₂ (15%), albeit with lower stability. These results highlight the potential of low-cost transition-metal and bimetallic catalysts as efficient and economically viable systems for selective glucose oxidation, providing insights for rational catalyst design in sustainable carbohydrate valorization. Full article

Layered compounds containing the T₂O plane (T = transition metal), which is the anti-type of the CuO₂ plane in cuprate superconductors, have been explored widely because of their diverse physical properties. Among them, KV₂Se₂O has attracted much attention due to its interesting physical properties, especially the magnetic order. In this work, we report a new isostructural chromium oxyselenide, RbCr₂Se₂O. It was synthesized using a solid-state method using Rb₂CO₃ as the source of Rb and O for the title compound, with the assistance of Ba. The compound crystallizes in the space group P4/mmm with lattice parameters a = 4.01123(8) Å and c = 7.49357(18) Å. Magnetic susceptibility measurements indicate an antiferromagnetic transition at 345 K for RbCr₂Se₂O and also above room temperature, as the Néel temperature is T_N ≈ 400 K for KV₂Se₂O. The analysis of variable temperature XRD data reveals the anisotropic thermal expansion of the RbCr₂Se₂O lattice. The almost unchanged lattice parameter a near the transition temperature and the broad peak with an onset temperature of ~360 K in the differential scanning calorimetry data may have a relationship with the magnetic ordering. The measurement of electrical resistivity demonstrates the semiconducting behavior of RbCr₂Se₂O. The thermal activation model and variable-range hopping model are proposed to describe the conduction mechanism in the high- and low-temperature ranges, respectively. Full article

This work investigated the effects of gamma irradiation on the adsorption capacities of rice husk (RH) for the removal of Cu²⁺, Cr³⁺, and Zn²⁺ ions from aqueous solutions, with potential applications in wastewater remediation. RH samples were gamma-irradiated at doses up to 40 kGy and characterized using SEM-EDS, XRF, FTIR, XRD, and BET analyses. While morphological and textural changes remained subtle, FTIR and SEM-EDS confirmed the formation and intensification of oxygen-containing functional groups, including –OH, –COOH, and C=O, as well as increased exposure of silica (Si–O) on the surfaces, which substantially enhanced surface reactivity of RH toward metal ions. Batch adsorption experiments revealed that 40-kGy irradiated RH samples (RH-40) exhibited the highest removal efficiencies compared to non-irradiated and lower-dose samples (RH-0, RH-10, RH-20, and RH-30), specifically with improvements of 415% for Cu²⁺, 502% for Cr³⁺, and 663% for Zn²⁺ compared to RH-0, determined at the initial concentration of 10 mg/L. Kinetic studies also showed rapid adsorption within the first 10–15 min, dominated initially by boundary-layer diffusion, followed by chemisorption-driven equilibrium behavior. The pseudo-second-order (PSO) model provided an excellent fit for all metals (R² = 0.999), indicating maximum model-predicted kinetic capacities of 555.56 mg/g (Cu²⁺), 769.23 mg/g (Cr³⁺), and 434.78 mg/g (Zn²⁺). Langmuir isotherms also fitted well (R² = 0.941–0.995), with predicted monolayer capacities of 535.33 mg/g (Cu²⁺), 491.64 mg/g (Cr³⁺), and 318.88 mg/g (Zn²⁺). Freundlich modeling further indicated favorable heterogeneous adsorption, with K_F values of 42.614 (Zn²⁺), 20.443 (Cr³⁺), and 16.524 (Cu²⁺) and heterogeneity factors (n) greater than 1 for all metals. These overall results suggested that gamma irradiation substantially enhanced RH functionality that enabled fast and high-capacity heavy-metal adsorption through surface oxidation and carbon valorization. Gamma-irradiated RH, therefore, represented a promising, low-cost, and environmentally friendly biosorbent for wastewater treatment applications. Full article

The influence of M site substitution in MCr₂O₄ nanoceramics on their properties is examined in this research. This study is an attempt to correlate the structural, morphological, and optical properties of M-site-modified chromites. The MCr₂O₄ nanoceramics-CuCr₂O₄, CoCr₂O₄, and NiCr₂O₄ were synthesized using a wet chemical sol–gel auto-combustion method, and all three samples were annealed for 4 h at 900 °C. X-ray diffraction analysis showed that the XRD patterns of CuCr₂O₄, CoCr₂O₄, and NiCr₂O₄ correspond to single-phase cubic crystal structures with the space group Fd-3m. Using the Scherrer equation, the crystallite sizes were found to be 9.86 nm, 6.73 nm, and 10.73 nm for CuCr₂O₄, CoCr₂O₄, and NiCr₂O₄, respectively. Other parameters, including crystal structure, micro-strain, lattice constant, unit cell volume, X-ray density, packing factor, and the stacking fault of the calcined powder samples, were determined from data acquired from the X-ray diffractometer. Energy dispersive X-ray spectroscopy (EDX) was employed to confirm the appropriate chromite elements in their expected stoichiometric proportions, removed from other impurities. The identification of the functional groups of the samples was performed using Fourier Transform Infrared Spectroscopy (FTIR). The absorption bands characteristic of tetrahedral and octahedral coordination compounds of the spinel structure are found between 450 and 750 cm⁻¹ for all three samples in the spectrum. From the UV-absorption spectra, and using Tauc’s plot, the energy bandgap values for CuCr₂O₄, CoCr₂O₄, and NiCr₂O₄ were measured to be 1.66 eV, 1.82 eV, and 2.01 eV, respectively. The dielectric properties of the chromites were studied using an LCR meter. Frequency-dependent dielectric properties, including Dielectric constant and Tangent loss, were calculated. These findings suggest the feasibility of the use of these synthesized chromites for optical devices and other optoelectronic applications. Full article

In this work, two novel nanoscale zero-valent iron (nZVI) composites (nanoscale zero-valent iron and copper-intercalated montmorillonite (MMT-nFe⁰/Cu⁰) and carbon microsphere-supported sulfurized nanoscale zero-valent iron (CMS@S-nFe⁰)) were used to treat soil contaminated with both Cr(VI) and p-nitrophenol (PNP), and added persulfate (PMS). Experiments found that the pollutant removal effect has a great relationship with the ratio of water to soil, the amount of catalyst, the amount of PMS, and the pH value. When the conditions are adjusted to the best (water–soil = 2:1, catalyst 30 g/kg, PMS 15 g/kg, pH 7–9), both materials fix Cr(VI) well and decompose PNP. The removal rates of Cr(VI) and PNP by the MMT-nFe⁰/Cu⁰ system are 90.4% and 72.6%, respectively, while the CMS@ S-nFe⁰ system is even more severe, reaching 94.8% and 81.3%. Soil column leaching experiments also proved that the fixation effect of Cr can last for a long time and PNP can be effectively decomposed. Through detection methods such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS), we found that Cr(VI) was effectively reduced to Cr(III) by Fe⁰ and Fe²⁺ ions and subsequently transformed into stable FeCr₂O₄ spinel oxides, and the groups produced after the decomposition of PNP could also help fix the metal. This work provides a way to simultaneously treat Cr(VI) and PNP pollution, and also allows the use of multifunctional nZVI composites in complex soil environments. Full article

The CO₂ hydrogenation process is thought to be one of the feasible methods for producing methanol fuel, which might be used to fulfill future energy demands. Improving the catalytic efficiency and understanding of the process are essential elements for the viability of CO₂ conversion routes. Here, a co-precipitation method was used to synthesize Ni-Cu bimetallic catalysts supported by chromium oxide (Cr₂O₃). To examine nickel (Ni)’s promoting role, the synthesized catalysts were incorporated with different concentrations of Ni. The N₂ adsorption–desorption isotherm exposed the mesoporous nature of Cr₂O₃-based Ni-Cu catalysts. A Fourier Transform Infrared (FTIR) spectroscopy investigation revealed the effective doping of Ni-Cu metal oxides on the surface of Cr₂O₃ by instigating an FTIR absorption band in the region associated with the FTIR absorption of metal oxides. The uniform morphology and homogenous, as well as highly dispersed, form of both Ni and Cu metal were recorded using a Field Emission Scanning Electron Microscope (FESEM) and X-ray Diffraction (XRD) techniques. The surface chemistry, metal–metal, and metal–support interactions of the Ni-Cu/Cr₂O₃ catalysts were disclosed via temperature program reduction (TPR) as well as X-ray photoelectron spectroscopy (XPS). The synergism between the Ni and Cu metals was revealed using both XPS and TPR techniques, which resulted in improving the catalytic profile of Ni-Cu/Cr₂O₃ catalysts. The activity data obtained by applying a slurry reactor demonstrated the active profile of Ni for CO₂ reduction to methanol in terms of the methanol synthesis rate. The promoting role of Ni was established by observing the progressing and linear increase in methanol selectivity by Ni enrichment to the Ni-Cu/Cr₂O₃ catalysts. Structure and activity studies recognized the promoting role of Ni by experiencing metal–metal and metal–support interactions with highly dispersed metal oxides over the Cr₂O₃ support in the current case. Full article

This work aims to study the catalytic properties of Fe, Cr, and Cu catalysts deposited on chitosan–silica (SBA-15) composites in liquid phase oxidation of cyclohexane (CH) with H₂O₂ and photocatalytic hydrogen evolution reaction. The catalysts were obtained by consecutive adsorption of chitosan (CS) and metal ions (Fe³⁺, Cr³⁺, Cu²⁺) on SBA-15 at ambient conditions. Characterization of the catalysts by XRD, IR spectroscopy, XPS, TEM, SEM, etc., showed the CS and metal ion adsorption on the solid support. Modification with CS provided better immobilization of the metal ions on SBA-15. The synthesized catalysts demonstrated different performance in liquid phase oxidation of cyclohexane with H₂O₂ under mild conditions at 40 °C and atmospheric pressure. Cyclohexane conversion on Fe–CS/SBA-15 (18.5%) and Cr–CS/SBA-15 (21.6%) was higher than on Cu–CS/SBA-15 (9.3%). The influence of different conditions of the reaction such as time, temperature, catalyst dosage, substrate and oxidant ratio on cyclohexane conversion in the presence of the most efficient Cr–CS/SBA-15 catalyst was also studied. The optimal reaction conditions were found to be the following: duration of reaction—4 h, temperature of reaction—50 °C, m_cat—0.03 g, a substrate/H₂O₂ ratio of 1:3. In addition, Cr–CS/SBA-15 and Fe–CS/SBA-15 catalysts were studied in a photocatalytic H₂ evolution reaction. The Fe-containing catalyst demonstrated superior efficiency in photocatalytic H₂ evolution. The total volume of hydrogen produced within 3 h was 103 mL/g. Thus, this study demonstrates that chitosan possesses promising potential in the design of the supported catalysts for cyclohexane oxidation and photocatalytic hydrogen evolution reactions. Full article

This study prepared epoxy–clay nanocomposites (ECNs) by incorporating organophilic clays modified with either non-redox cetyltrimethylammonium bromide (CTAB) or redox-active aniline pentamer (AP), then compared their anticorrosion performance on metal substrates in saline environments. The test solution contained 2 wt% alkaline copper quaternary (ACQ) wood preservatives. Cold-rolled steel (CRS) panels coated with the ECNs were evaluated via electrochemical impedance spectroscopy (EIS) in saline media both with and without ACQ. For CRS coated with unmodified epoxy, the Nyquist plot showed impedance dropping from 255 kΩ to 121 kΩ upon adding 2 wt% ACQ—indicating that Cu²⁺ ions accelerate iron oxidation. Introducing 1 wt% CTAB–clay into the epoxy increased impedance from 121 kΩ to 271 kΩ, while 1 wt% AP–clay raised it to 702 kΩ. This improvement arises because the organophilic clay platelets create a more tortuous path for Cu²⁺ and O₂ diffusion, as confirmed by ICP–MS measurements of Cu²⁺ after EIS and oxygen permeability tests (GPA), thereby slowing iron oxidation. Moreover, ECN coatings containing AP–clay outperformed those with CTAB–clay in corrosion resistance, suggesting that AP not only enhances platelet dispersion but also promotes formation of a dense, passive metal oxide layer at the coating–metal interface, as shown by TEM, GPA, and XRD analyses. Finally, accelerated salt-spray exposure following ASTM B-117 yielded corrosion behavior consistent with the EIS results. Full article

A variety of variables, such as organic matter input, redox conditions, depositional rates, and terrigenous input, affect the deposition of black shale. Furthermore, because of the significant regional variations in paleodepositional environments, these factors have a complex role in organic matter enrichment. Global geological events influenced sedimentary conditions, organic enrichment, and the development of organic-enriched shales during the Late Ordovician to Early Silurian. The Wufeng–Longmaxi Formation black shales in Southeastern Chongqing were analyzed for X-ray diffraction (XRD), major and trace element geochemistry, and total organic carbon (TOC) data; this led to further analysis of the relationship between the depositional environment and organic matter aggregation and rock type evolution. The primary minerals found in the Wufeng–Longmaxi shale are quartz, feldspar, carbonatite (calcite and dolomite), and clay. The high index of compositional variability (ICV) values (>1) and the comparatively low chemical index of alteration (CIA) values (52.6–72.8) suggest that the sediment source rocks are juvenile and are probably experiencing weak to moderate chemical weathering. The selected samples all show negative Eu anomalies, flat heavy rare earth elements, and mildly enriched light rare earth elements. The ratios of La/Th, La/Sc, Th/Sc, ΣREE-La/Yb, TiO₂-Ni, and La/Th-Hf suggest that acidic igneous rocks were the main source of sediment, with minor inputs from ancient sedimentary rocks. The correlations of paleoclimate proxies (Sr/Cu, CIA), redox proxies (V/Cr, V/Ni, V/(V + Ni), Ni/Co, U/Th), paleoproductivity proxies (Ba_xs, Cu_EF, Ni_EF), and water mass restriction proxies (Mo/TOC, U_EF, Mo_EF) suggest a humid–semiarid, anoxic, moderate–high paleoproductivity, and moderate–strongly restricted environment. On the basis of the aforementioned interpretations, the paleoenvironment of the Wufeng–Longmaxi Formations was established, with paleoredox conditions and restricted water masses likely being the primary factors contributing to organic matter enrichment. Full article

To understand the characteristics of the pollution risk of potentially toxic elements (PTEs) at a rare and precious metal mining site in Guangxi and to provide scientific evidence for the comprehensive evaluation and soil remediation of PTE pollution at the site, the Cd, As, Co, Cu, Cr, Ni, Pb, and Zn contents of five areas were determined. Laboratory testing was conducted on five soil plots in the selected five suspected contaminated areas (electroplating workshop, sewage treatment area, and boiler room). Correlation analysis, infrared spectroscopy (FTIR), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) were used to evaluate and analyze PTE pollution. The average contents of Cd, Co, As, Pb, Zn, and Cu at the site were higher than the background values in the Guangxi soil. The Probability Mass Function (PMF) model was used to perform a source apportionment of the PTEs and determine the main pollution sources and their contribution rates. The results of the single factor pollution of the PTEs showed that Cd, Ar, and Cr were heavy pollutants, and Co was a light pollutant. The Nemerow comprehensive pollution index analysis showed that the study area was heavily polluted. The Earth accumulation index results show that Cd exhibited a very serious accumulation, Cu and Zn exhibited mild to moderate accumulations, and As and Co exhibited moderate accumulations. The FTIR results showed that C=O in the soil was chelated with PTEs in some samples, which weakened the characteristic peaks of C=O in proteins and polypeptides. The XRD results showed that cadmium hydroxide, lead oxide, and zinc hydroxide were present in the soil samples. The XPS results showed that the production of O²⁻ in the O 1s high-resolution spectra mainly came from the metal oxides produced by the polluting metals. Meanwhile, the microbial results showed that the pollution risk of PTEs affected the soil microbial community structure and diversity to some extent. Full article

Over the past few decades, researchers have focused on developing new compositions and preparation techniques for geopolymers, as multifunctional products, to optimize their characteristics for use in multiple applications. Therefore, this paper investigates metakaolin geopolymer foam and introduces new geopolymer foams based on hybrid metakaolin and wollastonite mineral precursors for water purification. The geopolymer foams were prepared using an alkaline activator, mineral-based powders (wollastonite and metakaolin), a foaming agent (aluminum powder), and a foam stabilizer (olive oil). In addition to mechanical tests and assessments of the adsorption capacity of heavy metal ions, the geopolymer foams were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The geopolymer foams exhibited unique pore structures, containing four classes of pore networks with diameters around 1000 µm, 25 µm, 3 µm, and a well-arranged mesopore network of 50 nm. The utilization of wollastonite (CaSiO₃) alongside metakaolin as a hybrid precursor led to fundamental changes in the composition of the geopolymer binders: a new crystal phase, Ca₅(SiO₄)₂(OH)₂, was formed, and the Si-Al-Na crystal phase disappeared, which led to an increase in the amorphous phase from 87% to 92%. The adsorption rate of heavy metal ions, namely Cr, Co, Cu, Zn, Pd, and As, increased upon introducing wollastonite as a precursor, with absorption rates ranging from 11% to 68%. The findings also revealed that wollastonite significantly increased the geopolymers foams’ compressive strength and elastic modulus from 30 KPa to 67 KPa and from 31 MPa to 126 MPa, respectively. Full article

High-entropy materials, characterized by complex chemical compositions, are difficult to identify and describe structurally. These problems are encountered at the composition design stage when choosing an effective method for predicting the final phase structure of the alloy, which affects its functional properties. In this work, the effects of introducing oxide precipitates into the matrix of a high-entropy TiCoCrFeMn alloy to strengthen ceramic particles were studied. The particles were introduced by the ex situ method, such as TiO₂ in the form of anatase, and by the in situ method, consisting of the reconstruction of CuO into TiO₂. In both cases, it was assumed that after the homogenization process, carried out at 1000 °C, ceramic precipitates in the rutile phase, commonly considered a stable allotropic form of TiO₂, would be obtained. However, the microscopic observations and XRD analyses, supported by EDS chemical composition microanalysis and EBSD backscattered electron diffraction, clearly revealed that, regardless of the method of introducing oxides, the final strengthening phase obtained was a mixture of TiO₂ in the form of anatase with the Magnelli phase of Ti₂O₃. In this work, phase reconstruction in the Ti-O system was analyzed using changes in the Gibbs free energy of the identified oxide phases. 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

The electromagnetic railgun, a novel kinetic energy weapon, has found utility in military operations due to its enhanced safety features and superior precision. This study investigates the enhancement of wear resistance in CuCrZr rails through the plasma cladding of CuCrZr-CeO₂ coatings with a varying Cerium dioxide (CeO₂) content. To enhance the wear resistance of the CuCrZr track, plasma cladding of CuCrZr-CeO₂ coatings with varying CeO₂ content was investigated. The impact of CeO₂ content (0%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%) on the microstructure, phase composition, and mechanical properties of the CuCrZr coating was assessed using scanning electron microscopy (SEM), X-ray diffraction (XRD), EDS (Energy Dispersive Spectrometer) surface scanning, friction and wear tests, and hardness analysis. The findings indicate that a CeO₂ content of 0.15% leads to a transition in the coating’s microstructure from columnar to equiaxed crystals, with the densest grain structure. Beyond 0.15% CeO₂, pore defects in the coating increase, compromising mechanical properties. The coating containing 0.15% CeO₂ exhibits optimal performance, with a hardness of 75.3, representing a 5.31% increase compared to CeO₂-free CuCrZr coatings. Under a 10 N load, the friction coefficient decreases by approximately 17.9% to about 0.64. Moreover, the minimum wear mass is reduced by 44.7% to 3.87 mg. The aforementioned research findings hold immense importance in extending the lifespan of the electromagnetic railgun and improving its operational efficiency. Full article