Highly effective photocatalytic performance of {001}-TiO2/MoS2/RGO hybrid heterostructures for the reduction of Rh B

Abstract

Effective separation and rapid transfer of photogenerated electron-hole pairs are key features of photocatalytic materials with high catalytic activity, which could be achieved in co-catalysts. It is reported that the two-dimensional (2D) MoS₂ is a promising co-catalyst due to its unique semi-conductive properties and graphene-like layered structure. However, the application of MoS₂ as a co-catalyst is limited by its poor electrical conductivity. On the other hand, it is worth noting that TiO₂ possesses reactive crystal facets, which is one of the dominant mechanisms for the separation of photogenerated electron-hole pairs. In this work, we prepared MoS₂/RGO hybrids as co-catalysts which were doped to TiO₂ with highly reactive {001} planes via the hydrothermal method. It was found that the {001}-TiO₂/MoS₂/RGO photocatalysts with 7 wt% MoS₂/RGO co-catalyst show the highest photodegradation activity for the degradation of Rh B under visible light irradiation (λ > 400 nm), which could result from the synergy of the effective separation of electron-hole pairs by the {001} facets in TiO₂ and the rapid transfer of electron-hole pairs in MoS₂/RGO. The results show that the {001}-TiO₂/MoS₂/RGO hybrid is a low-cost and stable photocatalyst for the effective degradation of Rh B under visible light.

Scheme 1. Synthetic routes for the {001}-TiO₂ nanosheets and the {001}-TiO₂/MoS₂/RGO composites.

Fig. 1. (a) XRD patterns for MoS₂/RGO, {001}-TiO₂ and {001}-TiO₂/MoS₂/RGO, the inset is at 2θ = 5–45°; (b) Raman spectrum for {001}-TiO₂/MoS₂/RGO; (c) XPS survey spectrum for {001}-TiO₂/MoS₂/RGO; high-resolution spectra of {001}-TiO₂/MoS₂/RGO (d) Ti 2p; (e) Mo 3d; (f) S 2p.

Fig. 2. SEM images of MoS₂ (a), MoS₂/RGO (b), TiO₂ (c) and {001}-TiO₂/MoS₂/RGO (d).

Fig. 3. TEM images of RGO (a), MoS₂ (b), MoS₂/RGO (c), {001}-TiO₂ (d), {001}-TiO₂/MoS₂/RGO (e); HRTEM image of {001}-TiO₂/MoS₂/RGO (f).

Fig. 4. Photocatalytic degradation of Rh B under visible light irradiation over (λ > 400 nm) (a) {001}-TiO₂/MoS₂/RGO with different RGO percentages; (b) {001}-TiO₂/MoS₂/RGO with different contents of MoS₂/0.03RGO; (c) blank, {001}-TiO₂, {001}-TiO₂/0.07GO, {001}-TiO₂/0.07MoS₂ and {001}-TiO₂/0.07(MoS₂/0.03RGO). (d) UV-visible spectra of {001}-TiO₂/MoS₂/RGO.

Fig. 5. (a) UV-vis diffusive reflectance spectra of pure {001}-TiO₂ and {001}-TiO₂/MoS₂/RGO; the inset is corresponding plot of the transformed Kubelka–Munk function versus the energy of light; (b) N₂ adsorption/desorption isotherms of pure {001}-TiO₂ and {001}-TiO₂/MoS₂/RGO; (c) PL spectra of pure {001}-TiO₂ and {001}-TiO₂/MoS₂/RGO under 400 nm excitation wavelength; (d) electrochemical impedance spectroscopy (EIS) Nyquist plots of the sample electrodes which are made from the pure {001}-TiO₂ and {001}-TiO₂/MoS₂/RGO treated with visible light (λ > 400 nm) irradiation; (e) schematic diagram for photocatalytic mechanism of {001}-TiO₂/MoS₂/RGO.