Preparation of a highly active MoS2/TiO2 composite for photocatalytic oxidation of nitrite under solar irradiation

Abstract

MoS₂/TiO₂ composite photocatalysts with visible-light activity were in situ fabricated on titanium substrates via a simple two-step hydrothermal synthesis method, using titanium foil as the Ti source. The structure, morphology, composition and optical properties of the as-prepared photocatalysts were characterized by XRD, SEM, TEM, XPS, UV-vis and PL analyses, respectively. TiO₂ exists in the form of nanofibers (NFs), with their length ranging from about 40 nm to 150 nm and a diameter of about 10 nm. MoS₂ microspheres are homogeneously dispersed on the surface of TiO₂ NFs, forming a MoS₂/TiO₂ composite. The photocatalytic oxidation rate of NO₂⁻ under simulated solar irradiation can reach 62% by the MoS₂/TiO₂ composite synthesized in a hydrothermal system with a C₂H₅NS/Na₂MoO₄ molar ratio of 1 : 0.6 under 200 °C for 24 h, which is much higher than that by pristine TiO₂ NFs, P25 and pure MoS₂. The photocatalytic oxidation process of NO₂⁻ obeys the Langmuir–Hinshelwood kinetic model (pseudo-first order reaction), and the reaction rate constant (k) of the as-prepared composite is about 0.19194 h⁻¹. The presence of MoS₂ significantly enhances the visible light absorption of the catalyst, which is conducive to the generation of electrons and holes, thus guaranteeing good photoactivity of the catalyst. The band gap of the composite is about 2.2 eV, indicating the enhanced absorption of visible light. By this simple and low-consumption method, the composite is firmly combined with the titanium substrate, which is convenient for recycling and environmentally friendly implementation.