Performance study of photocatalytic hydrogen production from ZnO double-walled nanotubes based on density functional theory

Abstract

The exploration of photocatalytic materials can be an effective measure to deal with the energy crisis and environmental pollution. Based on previous studies, we investigated the geometric and electronic structures of optimized single-walled and double-walled ZnO nanotubes using the hybrid function B3LYP based on density functional theory and calculated the stability and band edge positions of the nanotubes in detail. The calculations show that the band gaps of monolayer, single-walled nanotube (SWNT), and double-walled nanotube (DWNT) are 3.726 eV, 3.722 eV, 3.447 eV, respectively, and it can be seen that the DWNT present the lowest band gap values. At the same time, the bond lengths of ZnO SWNTs and DWNTs are the same as those of ZnO monolayer, and the formation and strain energies of nanotubes decrease with the increase of nanotubes' diameter. The comparison of band edge position and hydrolytic redox potential of ZnO SWNT and DWNT shows that they both have hydrogen production ability. And combined with the smaller band gap value of DWNTs indicating its ability to absorb a broader solar spectrum, we suggest that ZnO DWNTs may exhibit higher catalytic activity than monolayer and SWNTs in photocatalytic hydrogen production.