ZnO nanoparticles implanted in TiO2 macrochannels as an effective direct Z-scheme heterojunction photocatalyst for degradation of RhB

A ZnO/TiO2 heterojunction photocatalyst based on ZnO nanoparticles embedded in the hierarchically structured TiO2 framework containing parallel macroporous channels and thin mesoporous walls has been synthesized by a common calcination treatment using zinc chloride and tetrabutyl titanate as the raw materials. The materials properties of the ZnO/TiO2 heterojunction photocatalysts have been carefully characterized with SEM/TEM, XRD, FTIR, XPS, BET analyses, UV-Vis absorption and photoluminescence spectroscopy. The photocatalytic performance for decomposition of Rhodamine B (RhB) under UV light irradiation has been systematically investigated in correlation with the materials structures. The apparent RhB degradation rate constant (k) has been determined to be 20.7 x 10(-3) min(-1) for the optimal hybrid photocatalyst with 5 wt% of ZnO loading, significantly higher that of pure TiO2 (12.2 x 10(-3) min(-1)) and pure ZnO nanoparticles (5.7 x 10(-3) min(-1)), respectively. Active species trapping experiments reveal that center dot OH and center dot O2(-) play the major roles in the photocatalytic reactions. The enhanced performance can be ascribed to the formation of a direct Z-scheme heterojunction structure between ZnO and TiO2 in contrast to the usual type-II heterojunction.