A feasible approach for azo-dye methyl orange degradation in siderite/H2O2 assisted by persulfate: Optimization using response surface methodology and pathway.

Siderite was applied to the binary oxidant system of siderite-catalyzed hydrogen peroxide (H2O2) and enhanced with persulfate (PS). In the absence of PS, methyl orange (MO) almost could not be degraded by the siderite/H2O2 process. However, adding PS significantly improved the capacity of MO to oxidize azo-dye. The influence of individual and interaction of reaction factors have been explored with a simple response surface methodology (RSM) based on central composite design (CCD). The quadratic model with low probabilities (<0.0001) at a confidence level of 95% was satisfactory to predict MO degradation in siderite/H2O2/PS system, whose correlation coefficients of R2 and R2-adj were 0.9569 and 0.9264, respectively. Moreover, the optimum operation conditions of 21.20 mM, 2.75 g/L, 3.86 mM, and 4.69 for H2O2, siderite, PS and initial pH, respectively with the response of C/C0 around 0.047. Radical scavenging experiments and electron spin resonance (ESR) determined that ·OH was crucial for MO degradation, while the contribution of SO4·- was minor. The surface morphology and iron content of siderite before and after the oxidation process showed clear differences. Possible intermediates and a degradation pathway were proposed based on the results of UV-Vis spectral and GC-MS analysis. Moreover, the toxicity to Vibrio fischeri bioluminescent bacterium has increased in the earlier degradation stage due to the generated by-products and weaken with the continuous treatment. This study demonstrated that the siderite/H2O2/PS system was effective over a relatively wide pH range without producing secondary pollutants, making it a promising technology and potential environmentally benign approach to azo-dye wastewater treatment.

Structural Modification Strategies, Interfacial Charge-Carrier Dynamics, and Solar Energy Conversion Applications of Organic-Inorganic Halide Perovskite Photocatalysts.

Over the past few decades, organic-inorganic halide perovskites (OIHPs) as novel photocatalyst materials have attracted intensive attention for an impressive variety of photocatalytic applications due to their excellent photophysical (chemical) properties. Regarding practical application and future commercialization, the air-water stability and photocatalytic performance of OIHPs need to be further improved. Accordingly, studying modification strategies and interfacial interaction mechanisms is crucial. In this review, the current progress in the development and photocatalytic fundamentals of OIHPs is summarized. Furthermore, the structural modification strategies of OIHPs, including dimensionality control, heterojunction design, encapsulation techniques, and so on for the enhancement of charge-carrier transfer and the enlargement of long-term stability, are elucidated. Subsequently, the interfacial mechanisms and charge-carrier dynamics of OIHPs during the photocatalytic process are systematically specified and classified via diverse photophysical and electrochemical characterization methods, such as time-resolved photoluminescence measurements, ultrafast transient absorption spectroscopy, electrochemical impedance spectroscopy measurements, transient photocurrent densities, and so forth. Eventually, various photocatalytic applications of OIHPs, including hydrogen evolution, CO2 reduction, pollutant degradation, and photocatalytic conversion of organic matter.

Improved photocatalytic conversion of high-concentration ammonia in water by low-cost Cu/TiO2 and its mechanism study.

Platinized TiO2 (Pt/TiO2) as a benchmark photocatalyst shows superior photocatalytic performance in environmental remediation. In order to reduce the cost of photocatalyst for practical use, a series of cooper loaded TiO2 (Cu/TiO2) photocatalysts were prepared by photoreduction method and compared with pure TiO2 and Pt/TiO2 in terms of overall ammonia conversion efficiency and selective oxidation. The as-prepared Cu/TiO2 samples were characterized and analyzed by physicochemical instrumental measurements. The results show that about 60% Cu2+ ions in suspension can be photodeposited onto the surface of TiO2 under UV light irradiation, and is mainly composed by a mixture of Cu/Cu+. The Cu/P25 (0.3 wt% Cu) sample was screened out as the optimal photocatalyst, via photoilluminance spectra analysis and photocatalytic oxidation of ammonia. It shows even better performance compared to Pt/TiO2 in the oxidation of high concentration of ammonia, due to the strong coordination effect by Cu(NH3)n complex formation. Through Electron Spin Resonance (EPR) analysis, and free radical suppression experiments, the active oxidative species account for ammonia oxidation and selective product generation were analyzed, and the possible reaction mechanisms involving photocatalytic ammonia conversion were proposed. ●OH has been identified as the main oxidant that affects the removal efficiency of ammonia nitrogen, whereas O2●- mainly affects the production of N2 and h+ is mainly responsible for the production of NO3-. These results indicate that Cu/TiO2 could be used as a low-cost and efficient photocatalyst in pretreatment process for conversion of high concentration of ammonia in wastewater.

Degradation of bisphenol A by persulfate coupled with dithionite: Optimization using response surface methodology and pathway.

The degradation efficiency of bisphenol A (BPA) was investigated in the process of persulfate (PS) coupled with dithionite (DTN) as a function of concentration of BPA, PS, DTN and solution pH. A simple response surface methodology (RSM) based on central composite design (CCD) was employed to determine the influence of individual and interaction of above variables and the optimum processing parameters. It is satisfactory of a quadratic model with low probabilities (<0.0001) at a confidence level of 95% to predict the BPA degradation efficiency. The model was well fitted to the actual data and the correlation coefficients of R2 and R2-adj were 0.9270 and 0.8885, respectively. In addition, the obtained optimum conditions for BPA degradation were 1.79 µM, 131.77 µM, 93.64 µM for BPA, PS, DTN and pH = 3.62, respectively. It achieved a degradation efficiency >90% within 150 min. Moreover, the trapping experiment of active species demonstrated that SO4·- and ·OH were the dominant species and natural water matrix showed an obvious inhibition effect on BPA degradation. The BPA degradation pathway was predicted based on GC-MS results in this study.