Vacancy Engineering in Semiconductor Photocatalysts: Implications in Hydrogen Evolution and Nitrogen Fixation Applications

A critical review on bismuth oxyhalide based photocatalysis for pharmaceutical active compounds degradation: Modifications, reactive sites, and challenges

Ammonia, one of the most basic substances in modern organic synthesis, is not only of great significance to human society, but also the backbone on which earth's life depends. Photocatalysis potentially provides a sustainable ammonia production technology as an alternative to the traditional Haber–Bosch process, and has been attracting extensive research interest recently. The development of efficient photocatalysts remains one of the fundamental issues for boosting the solar-to-ammonia efficiency. Significant and fruitful research on bismuth-based photocatalysts for nitrogen fixation to ammonia has been reported in recent years. This review summarizes and discusses recent advances in photocatalytic nitrogen fixation to ammonia over bismuth-based semiconductors. The fundamentals of solar-to-ammonia conversion and reported methods for ammonia quantification are introduced, together with a specific focus on strategies to enhance the performances of bismuth-based photocatalysts for nitrogen fixation. Finally, we cast a personal prospect on the future development of this vibrant research area, by which we hope to provide a useful scaffold for future research for the rational design of efficient bismuth-based photocatalysts for sustainable ammonia production.

Artificial nitrogen fixation over bismuth-based photocatalysts: fundamentals and future perspectives

Engineering of defects in semiconductors provides an effective protocol for improving photocatalytic N2 conversion efficiency. This review focuses on the state-of-the-art progress in defect engineering of photocatalysts for the N2 reduction toward ammonia. The basic principles and mechanisms of thermal catalyzed and photon-induced N2 reduction are first concisely recapped, including relevant properties of the N2 molecule, reaction pathways, and NH3 quantification methods. Subsequently, defect classification, synthesis strategies, and identification techniques are compendiously summarized. Advances of in situ characterization techniques for monitoring defect state during the N2 reduction process are also described. Especially, various surface defect strategies and their critical roles in improving the N2 photoreduction performance are highlighted, including surface vacancies (i.e., anionic vacancies and cationic vacancies), heteroatom doping (i.e., metal element doping and nonmetal element doping), and atomically defined surface sites. Finally, future opportunities and challenges as well as perspectives on further development of defect-engineered photocatalysts for the nitrogen reduction to ammonia are presented. It is expected that this review can provide a profound guidance for more specialized design of defect-engineered catalysts with high activity and stability for nitrogen photochemical fixation.

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Photocatalytic nitrogen reduction to ammonia: Insights into the role of defect engineering in photocatalysts

The investigation of the structural and morphological stability of leaf-templated and oxygen vacancy engineered materials is of great importance along with the detailed study of catalytically active sites. In this work, oxygen vacancy engineered leaf-templated CaTiO3 materials have been synthesized by using NaBH4 as a reductant and the formation of oxygen vacancies was confirmed by using different spectroscopic and morphological techniques. Leaf-templated CaTiO3 with the optimum amount of oxygen vacancies showed improved photocatalytic H2 evolution and N2 fixation abilities in comparison to pristine CaTiO3. Density functional theory calculations suggested that the O-vacancies present in the TiO2 plane played a crucial role in enhancing the photocatalytic performance than the O-vacancies present in the CaO plane of CaTiO3. The optimized material showed good structural stability but with a loss in morphological features. It is concluded that the benefits of efficient light absorption by the three-dimensional morphology of leaf-templated semiconductor materials could not be utilized in the studied solid–liquid binary phase reactions. The enhanced photocatalytic performance could solely be attributed to the optimum oxygen vacancy sites, which promote the surface reactions and improve the separation of photogenerated charge carriers. This work is expected to provide a future direction in the smart design of application-oriented three-dimensional photocatalysts and other materials.

Unraveling the structural and morphological stability of oxygen vacancy engineered leaf-templated CaTiO3 towards photocatalytic H2 evolution and N2 fixation reactions

Br doped porous bismuth oxychloride micro-sheets with rich oxygen vacancies and dominating {0 0 1} facets for enhanced nitrogen photo-fixation performances.

The invention discloses a preparation method for a nitrogen and boron co-doped porous carbon material. The preparation method comprises the following steps: uniformly mixing paranitroaniline, boric acid and sulfuric acid, and then heating while reacting, secondarily washing with water and freeze-drying, thereby obtaining a precursor rich in nitrogen and boron; pre-carbonizing the precursor under anitrogen atmosphere; uniformly mixing the obtained pre-carbonizing product with potassium hydroxide and then activating under high temperature under the nitrogen atmosphere; soaking and washing the product with dilute acid, secondarily washing with water and freeze-drying; lastly, graphitizing the obtained sample under high temperature under the nitrogen atmosphere, thereby obtaining the nitrogenand boron co-doped porous carbon material. According to the invention, the technical process is simple and convenient, two elements of nitrogen and boron can be doped into the carbon material in onestep, the cost is low and the preparation method is easy for large-scale production.

Preparation method for nitrogen and boron co-doped porous carbon material

The invention discloses a preparation method of a three-dimensional-structure bismuth oxychloride @ bismuth oxybromide composite ultrathin nanosheet and belongs to the technical field of synthesis ofphotocatalytic materials. The preparation method includes: dissolving bismuth nitrate pentahydrate and sodium dodecyl benzene sulfonate into a mannitol solution, stirring at room temperature till complete dissolution, taking and slowly adding a saturated sodium chloride solution into the above solution, and continuing stirring to obtain a white turbid solution; transferring an obtained solution into a hydrothermal reaction kettle for reaction to obtain a product-an ultrathin bismuth oxychloride nanosheet; taking and dispersing the ultrathin bismuth oxychloride three-dimensional nanosheet intoa saturated potassium bromide solution, and forming the three-dimensional-structure bismuth oxychloride @ bismuth oxybromide composite ultrathin nanosheet through high-temperature ion exchange. The preparation method is simple and easy-to-implement in operation process, and a synthetic bismuth oxychloride/bismuth oxybromide composite material has a three-dimensional structure formed by self-assembly of ultrathin two-dimensional nanosheets and is large in specific surface area and stable in structure.

Preparation method of three-dimensional-structure bismuth oxychloride @ bismuth oxybromide composite ultrathin nanosheet

The invention discloses a preparation method of a bismuth oxychloride@bismuth oxybromide composite ultrathin nanosheet of a three-dimensional structure, and belongs to the technical field of synthesisof photocatalytic materials. The preparation method is characterized by comprising the steps that bismuth nitrate pentahydrate and sodium dodecyl benzene sulfonate are dissolved in a mannitol solution, stirring is conducted at room temperature until bismuth nitrate pentahydrate and sodium dodecyl benzene sulfonate are completely dissolved, a saturated sodium chloride solution is slowly added to the solution above, stirring continues to obtain a white turbid solution, the obtained solution is transferred into a hydrothermal reaction kettle for a reaction to prepare ultrathin bismuth oxychloride nanosheet products, the ultrathin bismuth oxychloride three-dimensional nanosheets are taken and dispersed in a saturated potassium bromide solution, and the bismuth oxychloride/bismuth oxybromide composite ultrathin nanosheet of the three-dimensional structure is formed through high-temperature ion exchange. The preparation method has the advantages that the operation process is simple and easyto implement, and the synthesized oxychloride/bismuth oxybromide composite material has a three-dimensional structure formed by self-assembly of the ultrathin two-dimensional nanosheets and is largein specific surface area and stable in structure.

Preparation method of bismuth oxychloride@bismuth oxybromide composite ultrathin nanosheet of three-dimensional structure

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Br doped porous bismuth oxychloride micro-sheets with rich oxygen vacancies and dominating {0 0 1} facets for enhanced nitrogen photo-fixation performances.

Preparation method for nitrogen and boron co-doped porous carbon material

Preparation method of three-dimensional-structure bismuth oxychloride @ bismuth oxybromide composite ultrathin nanosheet

Preparation method of bismuth oxychloride@bismuth oxybromide composite ultrathin nanosheet of three-dimensional structure