Zinc oxide incorporated carbon nanotubes or graphene oxide nanohybrids for enhanced sonophotocatalytic degradation of methylene blue dye

Abstract

Zinc oxide (ZnO) nanocrystallites with different weight ratios are incorporated into carbon nanotubes (ZnO/CNTs) or graphene oxide (ZnO/GO) nanohybrids using ultrasonication/hydrothermal approach. The produced nanohybrids were tested in heterogeneous photocatalytic degradation of methylene blue dye (MB) under visible light illumination and in-situ ultrasonication. The zinc oxide incorporated carbon nanotubes nanohybrid having about 70 wt% of ZnO (ZnO(70)/CNT) showed marked visible light photocatalytic activity enhancement for MB degradation (99%, 0.5 g/L catalyst, 0.015 min−1) compared to the rest of the nanohybrids. The performance of MB degradation using ZnO(70)/CNT nanohybrid was even enhanced during employing the dual sonophotocatalysis approach achieving a rate constant of 0.019 min−1. This arises from the structural advantages at the ZnO(70)/CNT interface by which an improvement in electronic conductivity, facile electron transfer, charge carriers separation and increased oxygen vacancies were thoroughly achieved. This was highly ascertained via the catalysts characterization performed via many physiochemical techniques including XRD, TEM-SAED, FTIR, UV–Vis diffuse reflectance, and electrical conductivity, IPCE, PL and EIS. The scavenger studies of the photocatalytic and sonophotocatalytic processes of the MB degradation using ZnO(70)/CNT illustrate the importance of OH (followed by an electron) and holes (followed by OH), respectively proposing the importance of direct and indirect production of OH; as a strong oxidizing moiety.