Novel MoS2 quantum dots as a highly efficient visible-light driven photocatalyst in water remediation

Abstract

A direct and efficient hydrothermal system has been established for the synthesis of MoS₂ quantum dots (QDs). Novel MoS₂ QDs are an excellent potential photocatalysts to enhance photocatalytic response by charge separation under visible light irradiation. The optimum capability of QDs demonstrated the excellent photocatalytic ability for the degradation of organic pollutants. The microstructural, morphological, and optical properties of the MoS₂ QDs are defined via X-ray diffraction (XRD), SEM, HRTEM, XPS, and UV-Vis absorption spectroscopy techniques. Under visible light irradiation, MoS₂ QDs have great photocatalytic response for the degradation of Rh B that is 20 times higher than those of bulk MoS₂ materials. The QDs possess practically the same catalytic response after 5 recycle runs, which is an evident proof of its stability. This course might pave the route toward creating current visible-light caused QD photocatalyst strategies for the highly valuable degradation of organic pollutants or antibiotics.

Fig. 1. The UV-Vis spectra of the bulk, micro-scale and MoS₂ QDs. The inset shows the corresponding plots of (αhυ)² against photon energy (hυ).

Fig. 2. The XPS spectrum of MoS₂ QDs. (a) Survey spectrum; (b) high resolution of Mo; (c) high resolution of S; (d) high resolution of O; (e) Photoluminescence spectra of prepared the bulk, micro-scale and MoS₂ QDs under 355 nm excitation.

Fig. 3. (a) XRD patterns of the bulk, micro-scale and MoS₂ quantum dots. (b) TEM images of the as-prepared micro-scale MoS₂ (scale bar = 200 nm), (c) high resolution images of MoS₂ QDs (scale bar = 5 nm), the inset shows the SAED of the selected area.

Fig. 4. (a) Photocatalytic degradation of RhB over the bulk, micro-scale and MoS₂ quantum dots under visible light irradiation, (b) comparison of apparent rate constants, (c) the TOC amount of organic pollutants before and after irradiation, (d) recycling performance of MoS₂ QDs for organic pollutants, (d) recycling performance of MoS₂ QDs for organic pollutants, (e) effect of trapping reactive species on the photocatalytic degradation pathway, (f) EPR spectra in the methanol dispersion for DMPO˙O₂⁻, (g) XRD pattern of the QDs before and after the photocatalytic experiment, (h) electrochemical impedance spectra, (i) the photocatalytic reaction mechanism of organic pollutants over QDs.