A review on ultrasound assisted synthesis of metal oxide and doped metal oxide nanocatalysts and subsequent application as photocatalyst for dye degradation

Abstract In recent years, research on improving the synthesis of catalysts has been at the forefront because of advancements in nanotechnology and greener conventions. Using ultrasound (US) during nanocatalysts synthesis is one of the green approaches that can yield improved catalyst characteristics under conditions of shorter reaction time and requirement of low temperature and pressure. The current paper aims at giving an insight into US‐assisted synthesis (emphasized on sol‐gel and hydrothermal) of different metal oxide nanocatalysts. It has been elucidated that US‐assisted synthesis gives nanocatalyst with narrower particle size distribution with lower mean size, higher surface area, better morphology with less agglomeration, and higher catalytic activity. Ultrasound has thus been demonstrated to yield improvements in morphological, optical, and electronic properties of the nanocatalysts, however, scalability and industrial application of sonochemical synthesis have not been seen very popular. Some guidelines for future research into the development of novel nanocatalysts and industrial scale‐up studies are also provided. The review also summarizes the application of these metal oxides as photocatalysts for dye degradation or effluent treatment containing dyes, highlighting the fundamentals of photocatalysis as well. A comparative study has been reported for catalysts obtained using the US‐assisted synthesis and conventional synthesis of the photocatalysts in terms of catalytic activity. The benefits of using ultrasound‐assisted synthesis in terms of higher photocatalytic degradation have been clearly demonstrated.