ZnO/Sn3O4 amorphous-crystalline heterojunctions for Cr(VI) visible photocatalysis: Simple synthesis with excellent performance

Abstract

This paper is devoted to the construction of amorphous/crystalline heterojunction by a simple one-step hydrothermal method to realize the effective photocatalytic reduction of high concentration chromium. Taking amorphous ZnO/crystalline Sn3O4 (Z/S) as an example, the precursor of Sn(II) preferentially formed crystalline Sn3O4 based on the difference of complex constant (1010.8vs 104.4). The precursor of Zn(II) is then hydrolyzed and bonded to the surface of Sn3O4 by sn-O-Zn. The capping effect produced by citric acid selective adsorption on crystal surface significantly improves the proportion and stability of amorphous ZnO (aZnO). Interestingly, the introduction of aZnO transformed the surface structure of the Sn3O4 from micropore to hierarchical pore structure, which accelerated the adsorption of pollutants. The typical catalytic and characterization result illustrated that rich interfacial chemical bonds, abundant of oxygen vacancies and high interfacial potential energy difference collectively expedite the photoreduction of Cr(VI) on Z/S heterojunction. Up to 95.6 % (60 min for 0.1 g/L) and 59.1 % (100 min for 0.2 g/L) removal efficiency, importantly, proved that sequential-crystallization-based adsorption inducted design has advantages in the simple construction of high-quality amorphous heterostructures.