Unveiling the synergy between efficient charge separation and transport in multiphasic Titania-ZnO heterojunctions for enhanced solar-driven photocatalytic hydrogen evolution

High charge carrier recombination and low charge transport greatly limits the solar photocatalytic performance of titania. Heterojunction based modification strategies have been emerging as a path towards enhanced photocatalytic hydrogen evolution through efficient charge transport dynamics. Herein, multiphasic titania-ZnO nanocomposites have been prepared to study the role of biphasic and triphasic heterojunctions on the charge transfer dynamics and resultant photocatalytic hydrogen generation capability. Biphasic as well as triphasic heterojunctions of titania-ZnO nanocomposites have been prepared with varying phase compositions. The phase ratios of anatase/rutile/ZnO of triphasic heterojunctions was found to affect the charge transfer dynamics as well as their redox capabilities. The triphasic sample with an anatase-rutile ratio of 1.7 formed intimate heterojunctions between its constituent phases as revealed by the HRTEM studies and which led to superior charge transport properties. Its charge transfer resistance was only 0.85 and 0.4 times that of the pristine anatase and ZnO respectively. Further, it displayed the highest electron lifetime and reduction capability. As expected this triphasic sample showed the highest solar photocatalytic hydrogen production capability amongst all the samples with a yield of 7.04mmolg-1 h-1 which was 38% better than pristine anatase. This was further doubled with the integration of thin film strategy along with the triphasic heterojunction. This study reveals that multiphasic composite heterojunctions can be a path towards efficient charge transfer dynamics leading to superior photocatalytic performance.