Insight into Potassium Vanadates as Visible-Light-Driven Photocatalysts: Synthesis of V(IV)-Rich Nano/Microstructures for the Photodegradation of Methylene Blue.

Photocatalysis is regarded as a promising tool for wastewater remediation. In recent years, many studies have focused on investigating novel photocatalysts driven by visible light. In this study, K 2 V 6 O 16 · n H 2 O nanobelts and KV 3 O 8 microplatelets were synthesized and investigated as photocatalysts. Samples were obtained via the facile method based on liquid-phase exfoliation with ion exchange. By changing the synthesis temperature (20-80 °C), different compositions, morphologies, and V 4+ /V 5+ ratios were obtained and investigated as photocatalysts for organic dye degradation. Potassium vanadates' structural, morphological, and optical properties were characterized using X-ray diffraction(XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), Physical Property Measurement System (PPMS), thermogravimetric analysis (TGA) with mass spectrometry (MS), N 2 adsorption, scanning electron microscopy (SEM), photoluminescence (PL), and UV-vis diffuse reflectance spectroscopy (DRS). Synthesized K 2 V 6 O 16 · n H 2 O and KV 3 O 8 showed an efficient absorption in the visible wavelength region with a narrow band gap energy of 1.80 and 1.91 eV, respectively. Their photocatalytic activity was evaluated by the degradation of methylene blue (MB) under simulated solar light illumination. The KV 3 O 8 microplatelets exhibited the greatest photocatalytic activity, resulting in more than 90% degradation of the dye within the first 30 min. It is suggested that the observed excellent photocatalytic performance is attributed to the high content of V 4+ species. Furthermore, the influence of active species was investigated, and the mechanism responsible for the photodegradation of the MB dye was discussed for the first time for potassium vanadates.