Si/SiO2/Al2O3 Supported Growth of CNT Forest for the Production of La/ZnO/CNT Photocatalyst for Hydrogen Production

Abstract

The use of ZnO as a photocatalyst with a reduced recombination rate of charge carriers and maximum visible light harvesting remains a challenge for researchers. Herein, we designed and synthesized a unique La/ZnO/CNTs heterojunction system via a sol–gel method to evaluate its photocatalytic performance for hydrogen evolution. A ferrocene powder catalyst was tested for the production of CNT forests over Si/SiO2/Al2O3 substrate. A chemical vapor deposition (CVD) route was followed for the forest growth of CNTs. The La/ZnO/CNTs composite showed improved photocatalytic efficiency towards hydrogen evolution (184.8 mmol/h) in contrast to 10.2 mmol/h of pristine ZnO. The characterization results show that promoted photocatalytic activity over La/ZnO/NTs is attributed to the spatial separation of the charge carriers and extended optical absorption towards the visible light spectrum. The optimum photocatalyst shows a 16 h cycle performance for hydrogen evolution. The H2 evolution rate under visible light illumination reached 10.2 mmol/h, 145.9 mmol/h and 184.8 mmol/h over ZnO, La/ZnO and La/ZnO/CNTs, respectively. Among the prepared photocatalysts, ZnO showed the lowest H2 evolution rate due to the fast recombination of electron–hole pairs than heterojunction photocatalysts. This research paves the way for the development of ZnO and CNT-based photocatalysts with a wide optical response and reduced charge carrier recombinations.