Multilayer ultrathin Ag-δ-Bi2O3 with ultrafast charge transformation for enhanced photocatalytic nitrogen fixation

Construction of 2D/2D S-scheme Bi2MoO6/Zn-TCPP heterojunction via in-situ self-assembly growth strategy to enhance interface effect for efficient photocatalytic hydrogen production

Two-dimensional/two-dimensional (2D/2D) heterojunctions are considered to be an effective strategy for forming strong interface effects and facilitating photogenerated carrier separation. However, it is usually limited by the size mismatch of the materials, even at the expense of its redox capability. Herein, 2D/2D S-scheme heterojunction photocatalyst Bi2MoO6/Zn-TCPP (BMO/ZTP) composed of 2D Bi2MoO6 and 2D Zn-TCPP (TCPP: tetrakis (4-carboxyphenyl) porphyrin) (MOFs) was constructed by in-situ self-assembly growth strategy. The size-compatible 2D/2D composites had abundant surface active sites and strong interactions. In addition, band bending and interfacial electric field (IEF) effect based on S-scheme heterojunction could accelerate the separation and migration of photogenerated carriers in BMO/ZTP. The best hydrogen precipitation rate of the BMO/ZTP was 10900.94 umol·g-1·h-1, which was 38.90 and 3.24 times higher than that of Bi2MoO6 (280.26 umol·g-1·h-1) and Zn-TCPP (3360.34 umol·g-1·h-1), respectively. The results indicated that 2D/2D BMO/ZTP S-scheme heterojunction could enhance the interface effect and retain strong reducing electrons to achieve efficient photocatalytic hydrogen production, which was confirmed by ultraviolet photoelectron spectroscopy (UPS), Tafel curve, electron spin resonance (ESR) and time-resolved photoluminescence (TRPL) characterization and density functional theory (DFT) calculations. This work provided a general strategy for constructing 2D Bi2MoO6 and 2D MOFs S-scheme heterojunctions to enhance interface effects for achieving efficient photocatalytic hydrogen production.

Recent advances in photocatalytic nitrogen fixation and beyond

The traditional synthesis of ammonia is an industrial process with high energy consumption that is not environmentally friendly; thus, it is urgent to develop cost-effective approaches to synthesize ammonia under ambient conditions. In recent years, the photochemical synthesis of ammonia has become a hot research frontier. In this mini review, we summarize the recent advances in materials sciences for photocatalytic nitrogen fixation. Beyond nitrogen fixation, we talk about an alternative for artificial ammonia synthesis and coupling reactions with other reactions for the synthesis of other high-value chemicals. The results and findings of this review will help the development of ammonia synthesis and the synthesis of other high-value chemicals.

Polymorphism and Visible-Light-Driven Photocatalysis of Doped Bi2O3:M (M = S, Se, and Re)

δ-Bi₂O₃:M (M = S, Se, and Re) with an oxygen-defective fluorite-type structure is obtained by a coprecipitation method starting from the bismuth oxido cluster [Bi₃₈O₄₅(OMc)₂₄(dmso)₉]·2dmso·7H₂O (A) in the presence of additives such as Na₂SO₄, Na₂SeO₄, NH₄ReO₄, Na₂SeO₃·5H₂O, and Na₂SO₃. The coprecipitation of the starting materials with aqueous NaOH results in the formation of alkaline reaction mixtures, and the cubic bismuth(III)-based oxides Bi₁₄O₂₀(SO₄) (1c), Bi₁₄O₂₀(SeO₄) (2c), Bi₁₄O₂₀(ReO_4.5) (3c), Bi_12.25O_16.625(SeO₃)_1.75 (4c), and Bi_10.51O_14.765(SO₃)_0.49(SO₄)_0.51 (5c) are obtained after microwave-assisted heating; formation of compound 5c is the result of partial oxidation of sulfur. The compounds 1c, 2c, 4c, and 5c absorb UV light only, whereas compound 3c absorbs in the visible-light region of the solar spectrum. Thermal treatment of the as-prepared metastable bismuth(III) oxide chalcogenates 1c and 2c at T = 600 °C provides a monotropic phase transition into their tetragonal polymorphs Bi₁₄O₂₀(SO₄) (1t) and Bi₁₄O₂₀(SeO₄) (2t), while compound 3c is transformed into the tetragonal modification of Bi₁₄O₂₀(ReO_4.5) (3t) after calcination at T = 700 °C. Compounds of the systems Bi₂O₃-SO_x (x = 2 and 3) and Bi₂O₃-Re₂O₇ are thermally stable up to T = 800 °C, whereas compounds of the system Bi₂O₃-SeO₃ completely lose SeO₃. Thermal treatment of 4c and 5c in air results in the oxidation of the tetravalent to hexavalent sulfur and selenium, respectively, upon heating to T = 400-500 °C. The as-prepared cubic bismuth(III)-based oxides 1c-5c were studied with regard to the photocatalytic decomposition of rhodamine B under visible-light irradiation with compound 3c showing the highest turnover and efficiency.

Recent Advances in Plasmonic Photocatalysis Based on TiO2 and Noble Metal Nanoparticles for Energy Conversion, Environmental Remediation, and Organic Synthesis

Plasmonic photocatalysis has emerged as a prominent and growing field. It enables the efficient use of sunlight as an abundant and renewable energy source to drive a myriad of chemical reactions. For instance, plasmonic photocatalysis in materials comprising TiO₂ and plasmonic nanoparticles (NPs) enables effective charge carrier separation and the tuning of optical response to longer wavelength regions (visible and near infrared). In fact, TiO₂ -based materials and plasmonic effects are at the forefront of heterogeneous photocatalysis, having applications in energy conversion, production of liquid fuels, wastewater treatment, nitrogen fixation, and organic synthesis. This review aims to comprehensively summarize the fundamentals and to provide the guidelines for future work in the field of TiO₂ -based plasmonic photocatalysis comprising the above-mentioned applications. The concepts and state-of-the-art description of important parameters including the formation of Schottky junctions, hot electron generation and transfer, near field electromagnetic enhancement, plasmon resonance energy transfer, scattering, and photothermal heating effects have been covered in this review. Synthetic approaches and the effect of various physicochemical parameters in plasmon-mediated TiO₂ -based materials on performances are discussed. It is envisioned that this review may inspire and provide insights into the rational development of the next generation of TiO₂ -based plasmonic photocatalysts with target performances and enhanced selectivities.

Recent advances in photocatalytic nitrogen fixation: from active sites to ammonia quantification methods

Photocatalytic nitrogen fixation has become a hot topic in recent years due to its mild and sustainable advantages. While modifying the photocatalyst to enhance its electron separation, light absorption and nitrogen reduction abilities, the role of the active sites in the catalytic reaction cannot be ignored because the N[triple bond, length as m-dash]N nitrogen bond is too strong to activate. This review summarizes the recent research on nitrogen fixation, focusing on the active sites for N2 on the catalyst surface, classifying common active sites, explaining the main role and additional role of the active sites in catalytic reactions, and discussing the methods to increase the number of active sites and their activation ability. Finally, the outlook for future research is presented. It is hoped this review could help researchers understand more about the activation of the nitrogen molecules and lead more efforts into research on nitrogen fixation photocatalysts.

Hollow porous prismatic graphitic carbon nitride with nitrogen vacancies and oxygen doping: a high-performance visible light-driven catalyst for nitrogen fixation

Hollow porous prismatic graphitic carbon nitride with nitrogen vacancies and oxygen doping was successfully constructed using dicyandiamidine as the only raw material via a facile two-step strategy of a low-temperature hydrothermal method followed by a subsequent calcination process. The as-obtained graphitic carbon nitride showed a hollow prismatic morphology with loose spongy-like walls, a hierarchical pore structure, and a specific surface area of 220.16 m2 g-1. Such graphitic carbon nitride exhibited an ultrahigh nitrogen fixation rate of 118.8 mg L-1 h-1 gcat-1 under visible light irradiation and showed excellent stability during the reactions. A possible mechanism for photocatalytic nitrogen fixation on the catalyst was proposed as follows: under visible-light irradiation, graphitic carbon nitride with nitrogen vacancies and oxygen doping underwent charge separation to generate electron-hole pairs, and then the photogenerated electrons on the conduction band were quickly transferred to the nitrogen vacancy induced mid-gap state; consequently, the trapped electrons reacted with the activated nitrogen on the nitrogen vacancies to produce ammonia. The significant enhancement in the photocatalytic nitrogen fixation performance of graphitic carbon nitride can be attributed to its unique hollow prismatic morphology with a loose porous structure, fully exposed active sites of nitrogen vacancies, more negative conduction band, suitable visible-light response and the efficient separation of photogenerated electron-hole pairs.

Ultrathin nanosheet-anchored hexahedral prismatic Bi2MoO6 arrays: one-step constructed and crystal facet-based homojunctions boosting photocatalytic CO2 reduction and N2 fixation

A fascinating Bi₂MoO₆ homojunction (HJ) array vertically grown on an FTO substrate was built up through a convenient one-step route; the array consisted of ultrathin nanosheet (NS)-anchored hexahedral prismatic nanorods (NR).