Thickness-dependent piezo-photo-responsive behavior of ZnAl-layered double hydroxide for wastewater remediation

Understanding of the structural–performance correlations allow for the rational design of piezo-photocatalytic materials with profound benefits for catalytic activity. In this study, the ZnAl layered double hydroxides (ZnAl-LDHs) with different thickness are applied in the piezo-photocatalytic process for carbamazepine (CBZ) pollutants degradation. The piezo-photocatalytic efficiency of ultra-thin ZnAl-LDHs sheets (ZnAl-U) reaches 95.8 % with the reaction rate constant of 0.148 min-1 for CBZ degradation, being 1.61 and 3.02 times of the thin ZnAl-LDH (ZnAl-T) and bulks ZnAl-LDHs (ZnAl-B), respectively. This result is attributed to that ZnAl-U is more sensitive towards light irradiation and external stress than ZnAl-T and ZnAl-B, thus producing higher current and more reactive oxygen species (O2•−, HO• and 1O2) for piezo-photocatalytic degradation of CBZ. At the same time, the piezo-photocatalytic rate constant of ZnAl-U is 3.36 times of the sum of the individual piezocatalysis and photocatalysis, which is due to that the piezoelectric field boosts the separation of photo-induced electron-hole pairs and modulates the alignment of band energy, resulting in a synergetic enhanced piezo-photocatalytic reaction. This work discloses the significance of structure on the ZnAl-LDHs piezo-photocatalytic performance, and highlights the role of piezoelectric field on the improvement of photocatalytic process.