The valance state of vanadium-key factor in the flexibility of potassium vanadates structure as cathode materials in Li-ion batteries

Potassium hexavanadate (K₂V₆O₁₆·nH₂O) nanobelts have been synthesized by the LPE-IonEx method, which is dedicated to synthesis of transition metal oxide bronzes with controlled morphology and structure. The electrochemical performance of K₂V₆O₁₆·nH₂O as a cathode material for lithium-ion batteries has been evaluated. The KVO nanobelts demonstrated a high discharge capacity of 260 mAh g⁻¹, and long-term cyclic stability up to 100 cycles at 1 A g⁻¹. The effect of the vanadium valence state and unusual construction of the nanobelts, composed of crystalline and amorphous domains arranged alternately were also discussed in this work. The ex-situ measurements of discharged electrode materials by XRD, MP-AES, XAS and XPS show that during the subsequent charge/discharge cycle the potassium in the K₂V₆O₁₆·nH₂O structure are replacing by lithium. The structural stability of the potassium hexavandate during cycling depends on the initial vanadium valence state on the sample surface and the presence of the “fringe free” domains in the K₂V₆O₁₆·nH₂O nanobelts.

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, K₂V₆O₁₆·nH₂O nanobelts and KV₃O₈ 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 V⁴⁺/V⁵⁺ 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), N₂ adsorption, scanning electron microscopy (SEM), photoluminescence (PL), and UV–vis diffuse reflectance spectroscopy (DRS). Synthesized K₂V₆O₁₆·nH₂O and KV₃O₈ 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 KV₃O₈ 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 V⁴⁺ 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.

Potassium vanadates were synthesized via the facile method based on liquid-phase exfoliation with ion exchange. Different synthesis temperatures (20−80 °C) resulted in various phase compositions, morphologies, and V⁴⁺/V⁵⁺ ratios. The obtained samples were demonstrated as efficient visible-light driven photocatalysts, resulting in more than 90% degradation of methylene blue within the first 30−60 min. The enhanced photoactivity is attributed to the high content of V⁴⁺ species, which are beneficial for the separation of photogenerated electrons and holes and their lifetime.

Controlling the structure and morphology of zinc borate by adjusting the reaction temperature and pH value: formation mechanisms and luminescent properties

Zinc borate micro/nanostructured phosphors with three different compositions and structures have been prepared. When Tb³⁺ ions were doped into the zinc borate matrix, the three phosphors yielded tunable emissions.

Structure characteristics and photoactivity of simultaneous luminescence and photocatalysis in CaV2O6 nanorods synthesized by the sol–gel Pechini method

CaV₂O₆ nanorods show simultaneous luminescent and photocatalytic activities meaning that CaV₂O₆ could be a potential photoactive material with a layered structure constructed by line-arranged VO₅ units.