The activity and selectivity of catalytic peroxide oxidation of chlorophenols over Cu–Al hydrotalcite/clay composite

Novel VUV/g-C3N4 system with high adaptability to varied environmental conditions and outstanding degradation capacity for chlorophenols

Given the limitations of conventional vacuum ultraviolet (VUV) systems, a novel vacuum ultraviolet/graphite carbon nitride (VUV/g-C₃N₄) system with high adaptability to varying environmental conditions was developed. Compared with conventional VUV and UV/g-C₃N₄ systems, the VUV/g-C₃N₄ system demonstrates a much higher ability for the efficient degradation of chlorophenols (CPs). In particular, the VUV/g-C₃N₄ system exhibits outstanding performance even at low pH and high concentrations of humic acid and SO₄^2-. Alkaline conditions and the presence of HCO₃^- can further promote CP removal. In addition, the feasibility of the VUV/g-C₃N₄ system was verified by its stable operation in both river water and tap water. Unlike conventional photochemical systems relying on •OH, the dominant reactive species for CP degradation by the VUV/g-C₃N₄ system was identified to be •O₂^-. This study conclusively provided a novel system for the efficient photocatalytic treatment of pollutants.

Preparation of Fe-Cu-kaolinite for catalytic wet peroxide oxidation of 4-chlorophenol

Fe-Cu-kaolinites were prepared by co-precipitation and hydrothermal methods, and characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM), where 2 wt.% natural kaolinite was dispersed, and the ratios of (Al + Fe + Cu)/clay = 10 mmol/g and Al/(Fe + Cu) = 5/1 were maintained. The effect of different drying methods (vacuum drying, ethanol exchange drying, freeze-drying, microwave drying, normal oven drying) and different Fe/Cu molar ratio (0/2, 0.4/1.6, 0.8/1.2, 1/1, 1.2/0.8, 1.6/0.4, 2/0) was also assessed. Catalytic wet peroxide oxidation (CWPO) reaction of 4-chlorophenol (4-CP) was used to probe the reactivity and activity of the materials prepared. The results showed that Fe and Cu could be successfully intercalated into the interlayer of kaolinite by hydrothermal method, where specific surface area and pore volume increased by 19 times and 7 times, respectively; the intensity of basal space (001) reflection peak was reduced by 80%, and tip width was doubly increased. The catalyst possessed higher reactivity, with 85.5% of 4-CP conversion being observed, whereas only 15.2% of 4-CP was removed over raw kaolinite. High-power microwave drying (720 W) was the best drying method, because it resulted in greater microstructure and thus higher reactivity (85.3% of 4-CP conversion), with lower active metal (Fe or Cu) leaching (3.96 mg L^-1). Fe/Cu molar ratio of 0.8-1.0/1.2-1.0 was considered as the optimum ratio in pillaring solution, for maintaining higher catalytic activity (85-90% of 4-CP conversion) and lower metal (Fe or Cu) leaching (7-9.3 mg L^-1).

Chloride ions promoted the catalytic wet peroxide oxidation of phenol over clay-based catalysts

Catalytic wet peroxide oxidation (CWPO) of phenol over clay-based catalysts in the presence and absence of NaCl was investigated. Changes in the H2O2, Cl(-), and dissolved metal ion concentration, as well as solution pH during phenol oxidation, were also studied. Additionally, the intermediates formed during phenol oxidation were detected by liquid chromatography-mass spectroscopy and the chemical bonding information of the catalyst surfaces was analyzed by X-ray photoelectron spectroscopy (XPS). The results showed that the presence of Cl(-) increased the oxidation rate of phenol to 155%, and this phenomenon was ubiquitous during the oxidation of phenolic compounds by H2O2 over clay-based catalysts. Cl(-)-assisted oxidation of phenol was evidenced by several analytical techniques such as mass spectroscopy (MS) and XPS, and it was hypothesized that the rate-limiting step was accelerated in the presence of Cl(-). Based on the results of this study, the CWPO technology appears to be promising for applications in actual saline phenolic wastewater treatment.

Catalytic Degradation of Pyrrole in Aqueous Solution by Cu/SBA-15

Present study reports parametric and kinetic study for catalytic per oxidation (CPO) of pyrrole by Cu/SBA-15 catalyst using H2O2 as an oxidant. Brunauer-Emmett-Teller surface area, Fourier transform infra-red spectroscopy and thermo gravimetric-differential thermal analyses were used for the characterization of catalyst. Effects of various operating variables such as initial concentration of pyrrole (Co): 48.3–386.8 mg/L, catalytic dose (Cw): 0.5–2 g/L, stoichiometric ratio of hydrogen peroxide/pyrrole: 1–4, and reaction temperature (T): 50–60°C were studied. More than 85% pyrrole mineralization was observed at the optimum conditions of Cw = 1.5 g/L, stoichiometric ratio of hydrogen peroxide/pyrrole = 3, T = 55°C at pH = 6.1. A two-step pseudo-first-order kinetic model well-described the pyrrole mineralization by the CPO process.

Catalytic Wet Peroxide Oxidation of Chlorophenol Over a Ce0.86Cu0.14–x O2 Catalyst

A Ce0.86Cu0.14–x O2 catalyst was prepared by the citric acid complex method and characterized by X-ray diffraction, scanning electron microscopy, and temperature-programmed reduction, and its activity in the catalytic wet peroxide oxidation of 4-chlorophenol (4-CP) and 2,4-dichlorophenol (2,4-DCP) was investigated. The results showed that the Cu2+ ions dissolved into the CeO2 lattice to form a Ce0.86Cu0.14–x O2 solid solution with a coarse, interconnected, porous, and cotton-like morphology. The metal–oxygen bonds were weakened by solid-solution formation in the Ce0.86Cu0.14–x O2 catalyst. This weakening facilitated H2O2 activation and decomposition to form highly oxidative HO∙ species that can lead to significant chlorophenol mineralization. A total organic carbon removal rate greater than 80% was achieved after 2 h reaction at 50°C and at an initial 4-CP and 2,4-DCP concentration of 50 mg/L. The effects of H2O2 dosage, catalyst dosage, and initial chlorophenol concentration on catalytic efficiency were also determined.