Modification of TiO2 by Er3+ and rGO enhancing visible photocatalytic degradation of arsanilic acid

As a typical wide band gap photocatalyst, titania (TiO₂) cannot use the visible light and has fast recombination rate of photogenerated electron-hole pairs. Simultaneous introduction of erbium ion (Er³⁺) and graphene oxide (rGO) into TiO₂ might overcome these two drawbacks. In this study, Er³⁺ and rGO were co-doped on TiO₂ to synthesize Er³⁺-rGO/TiO₂ photocatalyst through a two-step sol-gel method. Based on the UV-visible diffuse reflectance spectra and photoluminescence spectrum, the introduction of Er³⁺ and rGO increased the visible light absorption efficiency and enhanced the migration of photogenerated electron. Pure TiO₂ has almost no photocatalytic activity for arsanilic acid (p-ASA) degradation under visible light irradiation. However, while doping with 2.0 mol% Er³⁺ and 10.0 mol% rGO, the p-ASA could be completely degraded within 50 min by the Er³⁺-rGO/TiO₂ photocatalyst under visible light irradiation, and most of produced inorganic arsenic was in situ removed by adsorption from the solution. The reactive oxygen species (ROS) reacting with p-ASA was determined and superoxide radical (O₂^•-) and singlet oxygen (¹O₂) were the dominant ROS for the oxidation of p-ASA and arsenite. This work provides an approach of introducing Er³⁺ and rGO to enhance the visible light photocatalytic efficiency of TiO₂.

Extra-modification of zirconium dioxide for potential photocatalytic applications towards environmental remediation: A critical review

Photocatalytic degradation is a valuable direction for eliminating organic pollutants in the environment because of its exceptional catalytic activity and low energy requirements. As one of the prospective photocatalysts, zirconium dioxide (ZrO₂) is a promising candidate for photoactivity due to its favorable redox potential and higher chemical stability. ZrO₂ has a high rate of electron-hole recombination and poor light-harvesting capabilities. Still, modification has demonstrated enhancements, especially extra-modification, and is therefore worthy of investigation. This present review provides a comprehensive overview of the extra-modifications of ZrO₂ for enhanced photocatalytic performance, including coupling with other semiconductors, doping with metal, non-metal, and co-doping with metal and non-metal. The extra-modified ZrO₂ showed superior performance in degrading the organic pollutant, particularly dyes and phenolic compounds. Interestingly, this review also briefly highlighted the probable mechanisms of the extra-modification of ZrO₂ such as p-n heterojunction, type II heterojunction, and Z-scheme heterojunction. The latter heterojunction with excellent electron-hole space separation improved the photoactivity. Extensive research on ZrO₂'s photocatalytic potential is presented, including the removal of heavy metals, the redox of heavy metals and organic pollutants, and the evolution of hydrogen. Modified ZrO₂'s photocatalytic effectiveness depends on its band position, oxygen vacancy concentration, and metal defect sites. The opportunities and future problems of the extra-modified ZrO₂ photocatalyst are also discussed. This review aims to share knowledge regarding extra-modified ZrO₂ photocatalysts and inspire new environmental remediation applications.

Synthesis of ultra-large ZrO2 nanosheets as novel adsorbents for fast and efficient removal of As(III) from aqueous solutions

Consumption of water having excessive arsenic (As) contamination can cause adverse health effects on human beings. In this study, novel ultra-large zirconium oxide (ZrO₂) nanosheets were successfully synthesized using graphene oxide (GO) templates and their adsorption-ability was studied for arsenite (As(III)). Owing to higher values of surface area, numbers of available hydroxyl groups and strong chemisorption binding affinity towards As(III), the synthesized novel ultra-large ZrO₂ nanosheets showed high adsorption-ability for As(III) over a wide pH range. Experimental results demonstrated that the maximum adsorption-ability of the ZrO₂ nanosheets for As(III) reached to 74.9 mg/g at pH 6. BET, zeta potential, effect of initial pH, FTIR and XPS have been used to analyze the As(III) adsorption process on the ZrO₂ nanosheets. The experiments for effects of co-existing ions indicated that ZrO₂ nanosheets possessed good anti-interference ability towards co-existing ions. Furthermore, the ZrO₂ nanosheets demonstrated very fast and excellent treatment of simulated real As(III) polluted water, consequently the effluent concentration met the standard regulated by World Health Organization. This study suggested that the as-prepared ZrO₂ nanosheets could be potentially applied in practical drinking water treatment.

UV Photocatalytic Activity for Water Decomposition of SrxBa1−xNb2O6 Nanocrystals with Different Components and Morphologies

Strontium barium niobate SrxBa1-xNb2O6 (SBN) nanocrystals with different components (x=0.2, 0.4, 0.6, and 0.8) were synthesized by Molten Salt Synthesis (MSS) method at various reaction temperatures (T = 950°C, 1000°C, 1050°C, and 1100°C). The SBN nanocrystals yielded through flux reactions possess different morphologies and sizes with a length of about ~100 nm~7 μm and a diameter of about ~200~500 nm. The Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD) techniques were used to study the compositions, structures, and morphologies of the nanocrystals. The absorption edges of the SBN nanocrystals are at a wavelength region of approximate 390 nm, which corresponds to band-gap energy of ~3.18 eV. The SBN nanocrystals with different sizes display different photocatalytic activity under ultraviolet light in decomposition of water. The SBN60 nanocrystals exhibit stable photocatalytic rates (~100~130 μmol of H2·g−1·h−1) for hydrogen production. The SBN nanocrystals can be a potential material in the application of photocatalysis and micro/nanooptical devices.