Modulating oxygen vacancy of ZnO for visible-light driven photocatalytic H2 evolution via facile gas treatment approach

Photocatalytic hydrogen production through water splitting is one of the most promising approaches for sustainable and renewable energy source. In recent years, research on defect rich metal oxide semiconductors has increased tremendously. N-type semiconductor ZnO exhibits a wide direct band gap of 3.3eV, limiting the optical absorption at UV range, hindering the photocatalytic performance of pristine ZnO. Furthermore, short charge carriers life time can also decrease the efficiency for hydrogen evolution. In this report, crystal defect engineering via oxygen vacancy tailoring was conducted, narrowing the bandgap of ZnO, while creating interstitial defects that reduces the recombination rate of electrons and holes. ZnO was synthesized via hydrothermal method using zinc acetate dihydrate and sodium hydroxide as precursors before subjecting for conditional annealing for 30, 60, 90 and 120 min for 200 degrees C, 300 degrees C, 400 degrees C and 500 degrees C. A series of characterization techniques were used to authenticate the effects of oxygen vacancy in ZnO. Experimental studies revealed that ZnO annealed at 400 degrees C for 120 min exhibit the highest amount of hydrogen produced through photochemical reactions. Therefore, the degree of oxygen vacancies in ZnO semiconductor can be regulated through diligent control of annealing parameters. Specifically, finding the optimum annealing temperature and duration were the focus in this study that relates to its photocatalytic hydrogen evolution rate.