Ultrasound waves at the service of photocatalysis: from sonochemical synthesis to ultrasound-assisted and piezo-enhanced photocatalysis

Sonication induces physical and chemical effects, such as promoting the mass transfer and active radical formation, that can be harnessed for process intensification in numerous fields, including photocatalysis. In this perspective, we discuss recent advances in the main domains where photocatalysis and ultrasound technology overlap, namely ultrasound-assisted synthesis of photocatalysts with controlled structural and morphological features and hybrid technologies combining ultrasound and light irradiation (sonophotocatalysis and piezo-enhanced photocatalysis). The latter, an external field-enhanced photocatalytic technology, is a relatively new approach that promises to boost photocatalytic efficiency (with enhancements up to 400%), even though significant challenges remain to be addressed. Finally, we offer some perspectives on the future of ultrasound-assisted photocatalysis, discussing current gaps in knowledge, economics, and scale-up issues.