Oxygen vacancy induced fast lithium storage and efficient organics photodegradation over ultrathin TiO2 nanolayers grafted graphene sheets

A Comprehensive Review on the Boosted Effects of Anion Vacancy in the Heterogeneous Photocatalytic Degradation, Part II: Focus on Oxygen Vacancy

Environmental problems, including the increasingly polluted water and the energy crisis, have led to a need to propose novel strategies/methodologies to contribute to sustainable progress and enhance human well-being. For these goals, heterogeneous semiconducting-based photocatalysis is introduced as a green, eco-friendly, cost-effective, and effective strategy. The introduction of anion vacancies in semiconductors has been well-known as an effective strategy for considerably enhancing the photocatalytic activity of such photocatalytic systems, giving them the advantages of promoting light harvesting, facilitating photogenerated electron-hole pair separation, optimizing the electronic structure, and enhancing the yield of reactive radicals. This Review will introduce the effects of anion vacancy-dominated photodegradation systems. Then, their mechanism will illustrate how an anion vacancy changes the photodegradation pathway to enhance the degradation efficiency toward pollutants and the overall photocatalytic performance. Specifically, the vacancy defect types and the methods of tailoring vacancies will be briefly illustrated, and this part of the Review will focus on the oxygen vacancy (OV) and its recent advances. The challenges and development issues for engineered vacancy defects in photocatalysts will also be discussed for practical applications and to provide a promising research direction. Finally, some prospects for this emerging field will be proposed and suggested. All permission numbers for adopted figures from the literature are summarized in a separate file for the Editor.

Oxygen vacancies enhance the lithium ion intercalation pseudocapacitive properties of orthorhombic niobium pentoxide

While orthorhombic niobium pentoxide (T-Nb₂O₅) is one of the most promising energy storage material with rapid lithium ion (Li⁺) intercalation pseudocapacitive response, a key challenge remains the achievement of high-rate charge-transfer reaction when fabricated into thick electrodes. Herein, we report a facile method to create intrinsic defects in T-Nb₂O₅ through a hydrogen (H₂) reduction, which is effective to overcome the limitations of electrochemical utilization and rate capability. Due to the high number of active sites introduced, the specific capacity of hydrogenated (H-) Nb₂O₅ with oxygen vacancies reaches 649 C g^-1 at 0.5 A g^-1, greatly exceeding that of T-Nb₂O₅ which is 580 C g^-1. In addition, theformation of oxygen vacancies leads to increased donor density and enhanced electrical conductivity, which accelerates charge storage kinetics and enables excellent long-term cycling stability (86% retention after 2000 cycles). The analysis of electrochemical impedance spectroscopy (EIS) plots and the calculation of Li⁺ diffusion coefficients (D_Li) further explains the high rate-performance of H-Nb₂O₅. When the electrode thickness increased to 150 μm, the H-Nb₂O₅ still delivers excellent electrochemical properties. Therefore, the introduction of oxygen vacancies provides a new method towards the improvement of the electrochemical properties of various transition metal oxides.

Synthesis and characterization of a heterojunction rGO/ZrO2/Ag3PO4 nanocomposite for degradation of organic contaminants

Synergy between surface adsorption and photocatalysis is key for effective contaminant degradation in the liquid phase. Herein, we report a heterojunction photocatalyst of reduced graphene oxide (rGO)/zirconium dioxide (ZrO₂)/silver phosphate (Ag₃PO₄) that incorporates this synergy for 4-nitrophenol (PNP) removal. Compared with other photocatalyst combinations, ZrO₂ and Ag₃PO₄ coupling generates reactive species with greater degradation potential. ZrO₂ and rGO were synthesized by a green approach using a one-step hydrothermal reaction in ethanol-water. The growth of rGO/ZrO₂ and Ag₃PO₄ were accomplished and the functions of each part were well developed together. The rGO/ZrO₂/Ag₃PO₄ composite exhibited enhanced light absorption and a low band gap energy (2.3 eV) owing to rGO and Ag₃PO₄ integration. The composite's photocatalytic activity was much higher than that of ZrO₂, Ag₃PO₄, or ZrO₂/Ag₃PO₄. The maximal adsorption of PNP was 26.88 mg/g, and a pseudo-first-order model described the PNP degradation kinetics (k = 0.034 min^-1). Synergy between the three components resulted in 97% PNP removal in 90 min, and even after five cycles, 94% PNP removal was obtained. The quantum yield of the system (7.31 × 10^-5 molecules/photon) was compared with those in previous reports to assess the photocatalytic performance and energy requirements.