Sonophotocatalysis: synergisms of photocatalysis with cavitation and piezotronic effect

Sonophocatalysis is a hybrid advanced oxidation process that has shown great promise in the degradation of several pollutants and in water disinfection. The combination of photocatalysis and ultrasound irradiation can result in synergistic effects arising from physical (promoted mass transfer) and chemical phenomena (enhanced radical generation). However, reaction conditions and the nature of the pollutant play a key role in determining the extent of synergistic improvements. More recently, a different strategy to promote photocatalytic activity by ultrasound irradiation, based on the piezotronic effect, has been proposed. Piezo-enhanced photocatalysis is an external field-enhanced photocatalytic technology that can boost photocatalytic efficiency up to 400%. In this chapter the mechanisms of enhancement in the two strategies will be presented, discussing as well our current gaps in understanding. The latest and most notable applications of these technologies will be reviewed, and the limitations that hinder their real-life applicability will be critically discussed.