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.

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.

A hybrid advanced oxidation process combining sonochemistry (US) and electrochemistry (EC) for the batch scale degradation of ibuprofen was developed. The performance of this hybrid reactor system was evaluated by quantifying on the degradation of ibuprofen under the variation in electrolytes, frequency, applied voltage, ultrasonic power density and temperature in aqueous solutions with a platinum electrode. Among the methods examined (US, EC and US/EC), the hybrid method US/EC resulted 89.32%, 81.85% and 88.7% degradations while using NaOH, H2SO4 and deionized water (DI), respectively, with a constant electrical voltages of 30V, an ultrasound frequency of 1000kHz, and a power density of 100WL(-1) at 298K in 1h. The degradation was established to follow pseudo first order kinetics. In addition, energy consumption and energy efficiencies were also calculated. The probable mechanism for the anodic oxidation of ibuprofen at a platinum electrode was also postulated.

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.