Cerium-Doped CuFe-Layered Catalyst for the Enhanced Oxidation of o-Xylene and N,N-Dimethylacetamide: Insights into the Effects of Temperature and Space Velocity.

Volatile organic compounds (VOCs) are among the most potential pollutant groups that cause air quality degradation because of their toxic effects on human health. Although catalytic oxidation is an effective method for VOC removal, further studies are required to develop more efficient and affordable catalysts. In this study, cerium (Ce) was doped into a CuFe-layered material (Ce-CuFe) to improve the catalytic oxidation efficiencies of N,N-dimethylacetamide (DMAC) and o-xylene. The synthesized catalyst was characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), energy-dispersive X-ray spectroscopy (EDS), Fourier-transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) analysis. XRD analysis confirmed the successful doping of Ce atoms into the CuFe-layered structure, while in the SEM and TEM images the catalyst appeared as uniformly distributed two-dimensional plate-like particles. The catalytic oxidation performance of the Ce-CuFe was investigated at six temperatures between 200 and 450 °C and three space velocities in the range of 31000-155000 mLh-1g-1 for the oxidation of DMAC and o-xylene, which functioned as polar and nonpolar solvents, respectively. At 200 °C, the Ce-CuFe catalyst performed 50% greater when oxidizing o-xylene while exhibiting a DMAC oxidation efficiency that was 42% greater than that achieved using undoped CuFe. The Ce-CuFe could remove DMAC and o-xylene with an efficiency higher than 95% at 450 °C. Furthermore, Ce-doped CuFe exhibited high resistance against moisture and outstanding reusability performance with only a 5.6% efficiency loss after nine reuse cycles. Overall, the incorporation of Ce into a CuFe-layered material is a promising strategy for the oxidation of various VOCs.

Loose Nanofiltration Membrane Incorporating CeZnFe Layered Double Hydroxide with Enhanced Dye/Salt Separation Performance and Self-Cleaning Ability.

The high-salinity wastewater from the textile industry faces a significant challenge in effectively separating dyes and salts. In this study, a CeZnFe-layered double hydroxide (LDH)-incorporated nanofiltration (LNF) membrane was fabricated using the conventional interfacial polymerization (IP) technique to fractionate dyes and salts within the wastewater. The impact of CeZnFe LDH on various aspects of membrane performance was examined, including water flux, dye removal efficiency, dye/salt separation capability, self-cleaning ability, and membrane integrity. The addition of LDHs resulted in improved membrane surface hydrophilicity, thereby enhancing water flux. The optimized TFN membrane (0.050 wt% LDH in PIP solution) significantly improved pure water flux, exceeding 150%. All TFN membranes exhibited excellent performance in dye and salt fractionation (93% for Congo red, 2.6% for NaCl, and 40.7% for Na2SO4). Also, excellent self-cleaning ability was observed for the optimized membrane, exhibiting a remarkable water flux recovery rate after three operation cycles. Moreover, including CeZnFe LDH in the optimized TFN membrane played a significant role in enhancing membrane integrity. This study provides new inspiration for fabricating self-cleaning loose NF membranes using CeZnFe LDH for effective dye/salt separation.

Enhanced generation of reactive radicals and electrocatalytic oxidation of levofloxacin using a trimetallic CuFeV layered double hydroxide-containing electrode.

In Electro-Fenton (EF) processes, the use of iron as a catalyst under acidic conditions results in increased costs and potential secondary pollution. To address these issues, we developed a CuFeV layered double hydroxide (LDH) coating on graphite felt (GF) (CuFeV LDH@GF) that offers an effective performance across a broad pH range without causing metal pollution. The CuFeV LDH@GF cathode exhibited a good oxygen reduction performance, high stability, and an efficient removal of levofloxacin (LEV) over a wide pH range (pH = 3-10). The simultaneous presence of Cu2+/Cu3+, Fe2+/Fe3+, and V4+/V5+ redox pairs played a crucial role in facilitating interfacial electron transfer, thereby enhancing the production and subsequent activation of H2O2 within the system. The apparent rate constant (kapp) of LEV removal under neutral conditions with the CuFeV LDH@GF electrode was more than twice that of the raw GF electrode. This improvement can be attributed to the CuFeV LDH coating, which increased the generation of hydroxyl radicals (•OH) from 0.64 to 1.27 mM. Importantly, the CuFeV LDH@GF electrode maintained its efficiency and stability even after 10 reuse cycles. Additionally, GC-MS analyses revealed the degradation of intermediate compounds, which included cyclic and aliphatic compounds. This study provides significant insights into the synergistic effects of trimetallic LDHs, contributing to the development of high-performance cathodes.

Degradation of emerging pollutants on bifunctional ZnFeV LDH@graphite felt cathode through prominent catalytic activity in heterogeneous electrocatalytic processes.

The heterogeneous Electro-Fenton (EF) process is a promising wastewater treatment technology that can generate onsite H2O2, and operate in a wide pH range without generating a metal sludge. However, the heterogeneous EF process needs bifunctional cathode electrodes that can have high activity in 2e- oxygen reduction reaction and H2O2 decomposition. Herein, ZnFeV layered double hydroxide (LDH), as a heterogeneous catalyst, was coated on the graphite felt (ZnFeV LDH@GF) cathode using the electrophoretic deposition method. ZnFeV LDH@GF cathode was able to generate 59.8 ± 5.9 mg L-1 H2O2 in 90 min under a constant supply of O2. EF process with ZnFeV LDH@GF cathode exhibited 89.8 ± 6.8% removal efficiency for pharmaceutical (ciprofloxacin) at neutral pH. Remarkably, the apparent reaction rate constant (kapp) of the ZnFeV LDH@GF-EF was 2.14 times that of the EF process with pristine GF. ZnFeV LDH coating increased the hydroxyl radical (•OH) production of the EF process from 1.74 mM to 3.65 mM. The pathway of •OH production is thought to be a single electron transfer from redox couples of Fe2+/Fe3+ and [Formula: see text] to H2O2. After 10 reuse cycles, the ZnFeV LDH@GF cathode retained 90.2% of its efficiency. Eight intermediate compounds were identified by GC-MS including cyclic compounds and aliphatic compounds.

Peroxydisulfate-assisted sonocatalytic degradation of metribuzin by La-doped ZnFe layered double hydroxide.

Metribuzin is an herbicide that easily contaminates ground and surface water. Herein, La-doped ZnFe layered double hydroxide (LDH) was synthesized for the first time and used for the degradation of metribuzin via ultrasonic (US) assisted peroxydisulfate (PDS) activation. The synthesized LDH had a lamellar structure, an average thickness of 26 nm, and showed mesoporous characteristics, including specific surface area 110.93 m2 g-1, pore volume 0.27 cm3 g-1, and pore diameter 9.67 nm. The degradation efficiency of the US/La-doped ZnFe LDH/PDS process (79.1 %) was much greater than those of the sole processes, and the synergy factor was calculated as 3.73. The impact of the reactive species on the sonocatalytic process was evaluated using different scavengers. After four consecutive cycles, 10.8 % loss occurred in the sonocatalytic activity of the La-doped LDH. Moreover, the efficiency of the US/La-doped LDH/PDS process was studied with respect to the degradation of metribuzin in a wastewater matrix. According to GC-MS analysis, six by-products were detected during the degradation of metribuzin. Our results indicate that the US/La-doped ZnFe LDH/PDS process has great potential for efficient degradation of metribuzin-contaminated water and wastewater.

Synthesis of visible light responsive ZnCoFe layered double hydroxide towards enhanced photocatalytic activity in water treatment.

In this study, a ternary layered double hydroxide containing Zn, Co, and Fe transition metals (ZnCoFe LDH) was developed using a co-precipitation procedure. The as-synthesized photocatalyst was evaluated for its performance in the degradation of methylene blue (MB) under visible light irradiation. The effects of various process conditions including photocatalyst dosage, pollutant concentration, pH, lamp distance, and lamp power were investigated. The ZnCoFe LDH achieved approximately 74% photodegradation efficiency owing to the narrow bandgap of 2.14 eV. The Langmuir-Hinselwood rate constants were calculated as 1.17 min-1 and 3.55 min-1 for photolysis by LED lamp alone and for photocatalysis by LED/ZnCoFe LDH, respectively. The photocatalytic ability of the LDH was attributed to the generation of radical species like •OH and O2•-. The photocatalytic degradation intermediates of MB were determined by GC-MS analysis. The catalyst retained its performance throughout seven reuse cycles with only a 4.17% reduction in removal efficiency. The energy per order EEO of the ZnCoFe/LED process in 180 min treatment time was determined as 5.41 kWh.m-3. order-1. This study shows that ZnCoFe LDH has sufficient activity and photostability for long-term application in photocatalytic water treatment.

Layered double hydroxides for removing and recovering phosphate: Recent advances and future directions.

Eutrophication is a widespread environmental challenge caused by excessive phosphate. Thus, wastewater engineers primarily aim to limit the phosphate concentration in water bodies. Layered double hydroxides (LDHs) are lamellar inorganic materials containing tunable brucite-like structures. This review discusses the fundamental aspects and latest developments in phosphate removal using LDH-based materials. Based on the divalent cations, Ca, Mg, and Zn-containing LDHs are largely used along with trivalent cations such as Al and Fe owing to their limited toxicities. However, classical LDHs are affected by the presence of co-existing anions, have a narrow working pH range, and have moderate adsorption capacities. Binary LDHs have been designed to be selective towards phosphate by the addition of a third metal such as Zr4+. Developing LDH composites with magnetic, polymeric or carbon materials are feasible approaches for increasing adsorption capacity, stability, and reusability of LDHs. Biochar as a carrier material for LDHs achieved remarkable phosphate adsorption performance and improved LDH dispersion, anion exchange capacity, and ease of separation. The use of recovered phosphate as an SRF, which is a type of bioavailable fertilizer, is a promising approach.

Anodic oxidation of bisphenol A by different dimensionally stable electrodes.

Bisphenol A (BPA) is a known endocrine disrupter and was detected in surface waters. We investigated the mineralization of BPA by electrochemical oxidation. Six different types of electrodes, including the boron-doped diamond (BDD), platinum (Pt), and mixed metal oxide (MMO) electrodes; RuO2-IrO2, RuO2-TiO2, IrO2-Ta2O5, and Pt-IrO2, were compared as the anode material. Total organic carbon (TOC) was analyzed to monitor the mineralization efficiency of BPA. BDD achieved 100% BPA mineralization efficiency in 180 min and at a current density of 125 mA/cm2, whereas the TOC removal efficiency of Pt was 60.9% and the efficiency of MMO electrodes ranged between 48 and 54%. BDD exhibited much lower specific energy consumption, which corresponds to a lower energy cost (USD63.4 /kg TOC). The effect of operational parameters showed that the BDD anode was much more affected by the current density, initial BPA concentration, and electrolyte concentration than the other parameters such as the stirring speed and interelectrode distance.

Enhancing the permeability and antifouling properties of cellulose acetate ultrafiltration membrane by incorporation of ZnO@graphitic carbon nitride nanocomposite.

This study reports the modification of cellulose acetate (CA) membrane with zinc oxide (ZnO)@graphitic carbon nitride (g-C3N4) nanocomposite to improve the antifouling and separation performance. Different combinations of the CA-based membranes such as CA/g-C3N4, CA/ZnO, and CA/ZnO@g-C3N4 were fabricated using the non-solvent induced phase separation (NIPS) method. Membranes were analyzed for their morphology (SEM), porosity, pore size, contact angle, permeability, rejection, and antifouling properties. According to the SEM images of CA/ZnO@g-C3N4, the formation of pear-shaped macro voids and finger-like canals originating from the top layer was evident. Nanocomposite blended membrane with 0.25 wt.% ZnO@g-C3N4 achieved the largest pore radius (3.05 nm) and the lowest contact angle (67.7°). With these characteristics, 0.25 wt.% ZnO@g-C3N4 membrane obtained a pure water flux of 51.3 LMH, which is 2.1 times greater than the bare CA and high BSA and dye rejections with 97.20% and 93.7% respectively. Finally, the antifouling resistance of the CA membrane was greatly improved with FRR increasing from 73.7% to 94.8%, which was accompanied by a significant decrease in the fouling resistance parameters.

Degradation of thiocyanate by electrochemical oxidation process in coke oven wastewater: Role of operative parameters and mechanistic study.

This study presents the removal of thiocyanate (SCN-) from coke oven wastewater by the electrooxidation (EO) process. Initially, the performances boron-doped diamond (BDD) and different DSA (Dimensionally stable anode) electrodes including Ti/IrO2, Ti/IrO2-RuO2, and Ti/IrO2-RuO2-TiO2 in SCN- removal were compared. BDD anode outperformed the Ti-based mixed metal oxide (MMO) anodes achieving 96.51% SCN- removal efficiency. The most favorable conditions for the removal of SCN- using BDD anode were determined as follows: pH = 9, current density = 43.10 A m-2, and the electrolyte concentration (Na2SO4) = 2.5 g L-1. The strong role of ⦁OH in the removal of SCN- was confirmed by the addition of radical quenching agents. The evolution of the intermediates as a result of the EO of SCN- was determined. Under the determined conditions, the EO process could remove 84.13% of SCN- and 94.67% of phenol from a real coke oven wastewater, which was comparable to that of the simulated solution. The electrical energy consumption cost of the process to remove 1 kg of SCN- was calculated as 0.208 US $. Overall, the study showed the EO using BDD anode is a cost-effective method for the removal of SCN- from a coke oven wastewater.