A combined ultrasound (US)/H2O2 process was used to oxidize arsenite to arsenate, yielding a synergistic effect value of 1.26. This showed that the combined process could be an effective method of oxidizing arsenite, instead of using either ultrasonic or H2O2 oxidation processes. This combined process was successfully modeled and optimized using a Box-Behnken design with response surface methodology (RSM). The effects of the US power density, the initial concentration of arsenite, and the H2O2 concentration on the sonochemical oxidation efficiency of arsenite were investigated. Analysis of variance indicated that the proposed quadratic model successfully interpreted the experimental data with coefficients of determination of R 2 = 0.95 and adjusted R 2 = 0.91. Through this model, we can predict and control the oxidation efficiency under different conditions. Furthermore, the optimal conditions for the oxidation of arsenite were found to be a US power density of 233.26 W L−1, an initial arsenite concentration of 0.5 mg L−1, and an H2O2 concentration of 74.29 mg L−1. The predicted oxidation efficiency obtained from the RSM under the optimal conditions was 88.95%. A confirmation test of the optimal conditions verified the validity of the model, yielding an oxidation efficiency of 90.1%.

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The contribution is equal.Uniform core-shell structured magnetic mesoporous TiO 2 (Fe 3 O 4 @SiO 2 @mTiO 2 ) nanospheres have been fabricated via a kinetic-controlled Stöber method. A silica interlayer with a thickness of ~ 25 nm was introduced as a passivation barrier to prevent the photodissociation, as well as increase the thermal stability of the core-shell materials. After being crystallized at 600 °C under nitrogen, the resultant nanospheres (Fe 3 O 4 @SiO 2 @mTiO 2 -600) possess well-defined core-shell structures with a high magnetic susceptibility (~ 17.0 emu g -1 ) and exhibit uniform mesopores (~ 5.2 nm), large BET surface area (~ 216 m 2 g -1 ) and pore volume (~ 0.20 cm 3 g -1 ). More importantly, the magnetic mesoporous TiO 2 has been demonstrated for the first time as a high efficient and stable sonocatalyst for the degradation of bisphenol-A. The pseudo first-orderreaction constant of the magnetic mesoporous TiO 2 is measured to be 0.164 min -1 , which is 1.49 and 2.27 times higher than that of P25 and ultrasound alone, respectively. The remarkable performance is attributed to the fast mass diffusion, large adsorption rate and enhanced hydroxyl-2 radical-production rate. More importantly, the catalysts can be easily recycled within 2 minutes by using an external magnetic field and a constant catalytic activity is retained even after eight cycles. This study paves a promising way for the design and synthesis of magnetic separable sonocatalysts for the degradation of organic pollutants, which is of significant importance for practical applications from both environmental and industrial points of view.

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