Construction of NiO and Ti3+ self-doped TNTs thin film as a high quantum yield p-n type heterojunction via a novel photoelectrodeposition-assisted anodization method

Abstract

Recently, p-n type heterojunctions have been considered promising photocatalysts for application in energy conversion and storage systems. Therefore, in this study, the photoelectrodeposition-assisted anodization method has been proposed as a novel procedure to construct a p-n type heterojunction hybrid consisting of NiO nanoparticles (with different dosages) and 1D TiO2 nanotube arrays (NiO/TNTs) for wastewater purification. The results revealed that using the photoelectrodeposition-assisted anodization method not only led to the introduction of Ni2+ and Ti 3+ into TiO2 anatase lattice, but also significantly enlarged TNTs’ dimension. Furthermore, incorporating TNTs with NiO had a significant impact on its optical properties, in which doping 4 wt% of Ni2+ (NiO-TNTs (4%)) reduced the band gap energy from 3 to 1.6 eV. Also, by coupling an optimum dosage of NiO, the photocurrent density and photoconversion efficiency of TNTs were remarkably boosted from 0.17 to 0.58 mA.cm−2 and from 0.11% to 0.34%, respectively. Due to the promotion in optical properties and photo-induced charge generation, NiO-TNTs (4%) indicated much better photocatalytic activity than the pure sample. As compared with TNTs, the 2,4-dichlorophenol degradation percentage by NiO-TNTs (4%) increased from 75% to 100% under UV and from 49% to 71% under visible light irradiation. Moreover, the kinetics study confirmed that all photocatalytic reactions followed zero-order kinetics. Based on scavenging reactive species tests, holes (h+) had the main portion (with 43%) in 2,4-dichlorophenol degradation by NiO-TNTs (4%). The rest of the degradation pathways were proceeded with e-, •OH, and •O2– species by accounting for 27%, 21% and 9%, respectively.