Bismuth-based photocatalyst for photocatalytic oxidation of flue gas mercury removal: A review.

Photocatalytic oxidation method is a promising technology for solving flue gas mercury (Hg) pollution from industrial plants. Semiconductor photocatalysts have been widely applied in energy conversion and environmental remediation. However, key issues such as low light absorption capacity, wide energy band gap, and poor physicochemical stability severely limit the application of photocatalysts in practical industrial plants. In recent years, bismuth-based (Bi-based) photocatalysts, including bismuth oxide halide BiOX (X = Cl, Br or I), bismuth salt oxymetal BiVO4, and BiOIO3 etc., have increasingly aroused scientists' attention due to their peculiar crystalline geometric structures, tunable electronic structure and high photocatalytic performance. In present review, we firstly review the photocatalytic reaction mechanism and main photocatalytic oxidation mechanism of mercury. Secondly, the synthetic methods of Bi-based photocatalysts are summarized. Then, according to the mechanism of mercury removal, the experimental modifying approaches including heterojunction making, external atoms doping, defect creating, and crystal face regulating to promote the photocatalytic oxidation of mercury removal are summarized, as well as the determination of the band gap and electronic density of states (DOS) of Bi-based photocatalysts to elucidate the photocatalytic oxidation mechanism via density functional theory (DFT) calculation. Furthermore, constructing electronic transmission channels is an efficient way to improve the photocatalytic activity. Finally, challenges and perspectives of Bi-based photocatalyst for photocatalytic oxidation of mercury removal are presented. In addition, the excellent performance photocatalysts and efficient pollution removal equipment for mercury removal in industrial plants are still required in-depth study.

Guan Y ，Liu Y ，Lv Q ，Wu J ... -  《-》

Bismuth-Based Photocatalysts for Solar Photocatalytic Carbon Dioxide Conversion.

Photocatalytic CO2 conversion into solar fuels is an effective means for simultaneously solving both the greenhouse effect and energy crisis. In the past ten years, bismuth-based photocatalysts for environmental remediation have experienced a golden period of development. However, solar photocatalytic CO2 conversion has only been developed over the past five years and, until now, no reviews have been published on bismuth-based photocatalysts for the photocatalytic conversion of CO2 . For the first time, solar photocatalytic CO2 conversion systems are reviewed herein. Synthetic methods and photocatalytic CO2 performances of bismuth-based photocatalysts, including Sillén-structured BiOX (X=Cl, Br, I); Aurivillius-structured Bi2 MO6 (M=Mo, W); and Scheelite-structured BiVO4 , Bi2 S3 , BiYO3 , and BiOIO3 , are summarized. In addition, activity-enhancing strategies for this photocatalyst family, including oxygen vacancies, bismuth-rich strategy, facet control, conventional type II heterojunction, Z-scheme heterojunction, and cocatalyst deposition, are reviewed. Finally, the main mechanistic research methods, such as in situ FTIR spectroscopy and theoretical calculations, are presented. Challenges and research trends reported in studies of bismuth-based photocatalysts for photocatalytic CO2 conversion are discussed and summarized.

Ye L ，Deng Y ，Wang L ，Xie H ，Su F ... -  《-》

Enhanced photocatalytic Hg(0) oxidation activity of iodine doped bismuth molybdate (Bi(2)MoO(6)) under visible light.

The application of photocatalytic Hg0 oxidation under visible light is an up-and-coming method to solve the problem of energy shortage and environmental pollution. In this work, iodine doped Bi2MoO6 nanomaterials were prepared by one-step solvothermal method. The photocatalytic oxidation efficiency was greatly improved by iodine doping from 35.5% to 95.2% in the N2 + 4% O2 atmosphere under visible light. The main reason was that iodine doping decreased the band gap of the catalyst, expanded the optical response range and intensity, sped up the separation rate of photoinduced carriers and reduced the recombination rate. In addition, the flue gas components of SO2 and NO played a promoting role in mercury removal. Iodine doped Bi2MoO6 had good stability and still maintained high mercury removal efficiency after 5 cycles. Density functional theory (DFT) calculations and experiments demonstrated that iodine doping changed the valence band and conduction band of the catalyst, making superoxide ions, hydroxyl radicals and photoinduced hole become the active species of the catalytic reaction.

Zhang Y ，Zhao Y ，Xiong Z ，Xiao R ，Gao T ，Liu P ，Liu J ，Zhang J ... -  《-》

Typical layered structure bismuth-based photocatalysts for photocatalytic nitrogen oxides oxidation.

Traditional NOx treatment methods require external reducing reagents and harsh reaction conditions, which is not conducive to effectively eliminate NOx at low concentration, especially at ppb levels. Fortunately, low concentration NOx can be removed by photocatalytic oxidation under mild reaction conditions. Bismuth (Bi)-based photocatalysts with the layered structure have obtained considerable concerns of photocatalytic NOx oxidation. This review focused on typical layered Bi-based photocatalysts (Bi2WO6, Bi2O2CO3, BiOY (YCl, Br, and I), BiOIO3, and BiOCOOH) with the structure of [Bi2O2]2+ layer for photocatalytic NOx oxidation. The strategies (morphological control, defect engineering, heterostructure construction, etc.) to improve photocatalytic oxidation activity were summarized. Furthermore, the mechanism involving various free radicals (hydroxyl radical, superoxide radical, etc.) of photocatalytic oxidation of NOx was proposed. In addition, the non-NO2 selectivity was also illuminated. Lastly, the current drawbacks and further research directions for photocatalytic NOx oxidation were elaborated. The development of photocatalysts with high photocatalytic activity, wide light absorption range, and non-NO2 selectivity is the focus of future research. This review aims to provide a pandect and theoretical guidance for the practical application of photocatalytic oxidation of NOx.

Ma C ，Wei J ，Jiang K ，Chen J ，Yang Z ，Yang X ，Yu G ，Zhang C ，Li X ... -  《-》

BiOX (X = Cl, Br, I) photocatalytic nanomaterials: Applications for fuels and environmental management.

Energy and environmental issues are the major concerns in our contemporary "risk society". As a green technique, photocatalysis has been identified as a promising solution for above-mentioned problems. In recent decade, BiOX (X = Cl, Br, I) photocatalytic nanomaterials have sparked numerous interest as economical and efficient photocatalysts for energy conversion and environmental management. The distinctive physicochemical properties of BiOX nanomaterials, especially their energy band structures and levels as well as relaxed layered nanostructures, should be responsible for the visible-light-driven photocatalytic performance improvement, which could be utilized in dealing with the global energy and environmental challenges. In this review, recent advances for the enhancement of BiOX photocatalytic activity are detailedly summarized. Furthermore, the applications of BiOX photocatalysts in water splitting and refractory organic pollutants removal are highlighted to offer guidelines for better development in photocatalysis. Particularly, no relative reports in previous studies were documented in CO2 reduction as well as heavy metals and air pollutants removal, thus this review presented as a considerable research value. Challenges in the construction of high-performance BiOX-based photocatalytic systems are also discussed. With the exponential growth of studies on BiOX photocatalytic nanomaterials, this review provides unique and comprehensive perspectives to design BiOX-based photocatalytic systems with superior visible light photocatalytic activity. The knowledge of both the merits and demerits of BiOX photocatalysts are updated and provided as a reference.

Yang Y ，Zhang C ，Lai C ，Zeng G ，Huang D ，Cheng M ，Wang J ，Chen F ，Zhou C ，Xiong W ... -  《-》