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

A ZnO/TiO 2 heterojunction photocatalyst based on ZnO nanoparticles embedded in the hierarchically structured TiO 2 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/TiO 2 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 × 10 −3  min −1 for the optimal hybrid photocatalyst with 5 wt% of ZnO loading, significantly higher that of pure TiO 2 (12.2 × 10 −3  min −1 ) and pure ZnO nanoparticles (5.7 × 10 −3  min −1 ), respectively. Active species trapping experiments reveal that •OH and •O 2 − 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 TiO 2 in contrast to the usual type-II heterojunction.