Heterogeneous sonocatalysis, as an emerging advanced oxidation process (AOP), has shown immense potential in water treatment and been widely demonstrated to remove persistent organic compounds in the past decade. The present article aims to provide a comprehensive review on the development of a heterogeneous catalyst for enhancing the ultrasonic degradation rate of organic pollutants from a viewpoint of sonocatalytic mechanism. The rational design and fundamentals for preparing sonocatalysts are presented in the context of facilitating the heterogeneous nucleation and photo-thermal-catalytic effects as well as considering the mechanical stability and separation capacity of the heterogeneous catalyst. In addition, some new trends, ongoing challenges and possible methods to overcome these challenges are also highlighted and proposed.

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%.

In order to determine the optimal operating conditions of full-scale soil washing processes for the removal of heavy metals, the effect of high-power ultrasound on the conventional mechanical soil washing process was investigated in a large lab-scale 28kHz sonoreactor. The soil samples were obtained from an abandoned railway station site in Seoul, Korea, which was contaminated with Cu (242.7±40.0mg/kg), Pb (441.3±49.8mg/kg), and Zn (358.0±35.7mg/kg). The treated concentrations of three heavy metal species in each process were compared with the regulation levels. It was found that higher performance, satisfying the regulation levels, was obtained in the ultrasonic/mechanical process due to the combined effects of macroscale mixing and microscale sonophysical effects. Moreover ultrasound played a more important role in less favorable conditions for the mechanical washing process (less acidic or less washing liquid conditions). Considering the application of the ultrasonic/mechanical soil washing process in real contaminated sites, the optimal conditions for the reactor with the bottom area of 15×15cm and the input ultrasound power of 250W were determined as follows: (1) the amount of soil per an operation was a 300g; (2) the ratio of soil and liquid was 1:3; (3) the concentration of acidic washing liquid was 0.5M HCl.

Sonoelectrochemical process has emerged as a novel integrated technology for various applications starting from sonoelectroplating till the remediation of a wide range of contaminants. Although a promising new technology, the application of sonoelectrochemical technology for pollutant degradation are mostly on a laboratory scale, utilizing the conventional reactor configuration of the electrolytic vessel and ultrasonic horns dipped in it. This type of configuration has been believed to be responsible for its sluggish evolution with lower reproducibility, scale-up and design aspects. To achieve a major turn with an enhanced synergy, refinements in the form of optimizing the co-ordination of the governing parameters of both the technologies (e.g., power, frequency, liquid height, electrode material, electrode size, electrode gap, applied voltage, current density etc.) have been validated. Besides, in order to supplement knowledge in the already existing pool, rigorous research on the past and present status has been done. Challenges were also identified and to overcome them, critical discussions covering an overview of the progressive developments on combining the two technologies and its major applications on pollutant degradation were conducted.

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.