Hydrogenated Bismuth Molybdate Nanoframe for Efficient Sunlight-Driven Nitrogen Fixation from Air

Light-Driven Nitrogen Fixation to Ammonia over Aqueous-Dispersed Mo-Doped TiO2 Colloidal Nanocrystals

Photocatalytic nitrogen fixation to ammonia and nitrates holds great promise as a sustainable route powered by solar energy and fed with renewable energy resources (N2 and H2O). This technology is currently under deep investigation to overcome the limited efficiency of the process. The rational design of efficient and robust photocatalysts is crucial to boost the photocatalytic performance. Widely used bulk materials generally suffer from charge recombination due to poor interfacial charge transfer and difficult surface diffusion. To overcome this limitation, this work explores the use of aqueous-dispersed colloidal semiconductor nanocrystals (NCs) with precise morphological control, better carrier mobility, and stronger redox ability. Here, the TiO2 framework has been modified via aliovalent molybdenum doping, and resulting Mo-TiO2 NCs have been functionalized with charged terminating hydroxyl groups (OH-) for the simultaneous production of ammonia, nitrites, and nitrates via photocatalytic nitrogen reduction in water, which has not been previously found in the literature. Our results demonstrate the positive effect of Mo-doping and nanostructuration on the overall N2 fixation performance. Ammonia production rates are found to be dependent on the Mo-doping loading. 5Mo-TiO2 delivers the highest NH4+ yield rate (ca. 105.3 μmol g-1 L-1 h-1) with an outstanding 90% selectivity, which is almost four times higher than that obtained over bare TiO2. The wide range of advance characterization techniques used in this work reveals that Mo-doping enhances charge-transfer processes and carriers lifetime as a consequence of the creation of new intra band gap states in Mo-doped TiO2 NCs.

Research Progress in Composite Materials for Photocatalytic Nitrogen Fixation

Ammonia is an essential component of modern chemical products and the building unit of natural life molecules. The Haber-Bosch (H-B) process is mainly used in the ammonia synthesis process in the industry. In this process, nitrogen and hydrogen react to produce ammonia with metal catalysts under high temperatures and pressure. However, the H-B process consumes a lot of energy and simultaneously emits greenhouse gases. In the "double carbon" effect, to promote the combination of photocatalytic technology and artificial nitrogen fixation, the development of green synthetic reactions has been widely discussed. Using an inexhaustible supply of sunlight as a power source, researchers have used photocatalysts to reduce nitrogen to ammonia, which is energy-dense and easy to store and transport. This process completes the conversion from light energy to chemical energy. At the same time, it achieves zero carbon emissions, reducing energy consumption and environmental pollution in industrial ammonia synthesis from the source. The application of photocatalytic technology in the nitrogen cycle has become one of the research hotspots in the new energy field. This article provides a classification of and an introduction to nitrogen-fixing photocatalysts reported in recent years and prospects the future development trends in this field.

Photocatalytic Synthesis of Ammonia from Pinecone Graphite-Phase Carbon Nitride Loaded with MoS2 Nanosheets as Co-catalysts

Photocatalytic nitrogen fixation is a promising alternative to the Haber-Bosch process to alleviate the energy and environmental crises. Here, we designed a pinecone-shaped graphite-phase carbon nitride (PCN) catalyst supported with MoS₂ nanosheets by a supramolecular self-assembly method. The catalyst shows an excellent photocatalytic nitrogen reduction reaction (PNRR) due to the larger specific surface area and the enhancement of visible light owing to the reduced band gap. Under simulated sunlight, the sample of PCN loaded with 5 wt % MoS₂ nanosheets (MS5%/PCN) shows a PNRR efficiency of 279.41 μmol g^-1 h^-1, which is 14.9 times that of bulk graphite-phase carbon nitride (g-C₃N₄), 4.6 times that of PCN, and 5.4 times that of MoS₂, respectively. The unique pinecone-like structure of MS5%/PCN not only improves the ability of light absorption but also assists in the uniform loading of MoS₂ nanosheets. Likewise, the existence of MoS₂ nanosheets improves the light absorption ability of the catalyst and reduces the impedance of the catalyst. Furthermore, as a co-catalyst, MoS₂ nanosheets can efficiently adsorb nitrogen (N₂) and serve as active N₂ reduction sites. From the perspective of structural design, this work can offer novel solutions for the creation of effective N₂-fixing photocatalysts.

Advances in Semiconductor-Based Nanocomposite Photo(electro)catalysts for Nitrogen Reduction to Ammonia

Photo(electro)catalytic nitrogen fixation technology is a promising ammonia synthesis technology using clean solar and electric energy as the driving energy. Abundant nitrogen and water as raw materials uphold the principle of green and sustainable development. However, the generally low efficiency of the nitrogen reduction reaction has seriously restricted the application and development of this technology. The paper introduces the nitrogen reduction process and discusses the main challenges and differences in the current photo(electro)catalytic nitrogen fixation systems. It focuses on promoting the adsorption and activation of N2 and the resolution and diffusion of NH3 generated. In recent years, reviews of the modification strategies of semiconductor materials in light of the typical cases of nitrogen fixation have been reported in the literature. Finally, the future development trend of this field is analyzed and prospected.

Recent progress of photocatalysts based on tungsten and related metals for nitrogen reduction to ammonia

Photocatalytic nitrogen reduction reaction (NRR) to ammonia holds a great promise for substituting the traditional energy-intensive Haber–Bosch process, which entails sunlight as an inexhaustible resource and water as a hydrogen source under mild conditions. Remarkable progress has been achieved regarding the activation and solar conversion of N₂ to NH₃ with the rapid development of emerging photocatalysts, but it still suffers from low efficiency. A comprehensive review on photocatalysts covering tungsten and related metals as well as their broad ranges of alloys and compounds is lacking. This article aims to summarize recent advances in this regard, focusing on the strategies to enhance the photocatalytic performance of tungsten and related metal semiconductors for the NRR. The fundamentals of solar-to-NH₃ photocatalysis, reaction pathways, and NH₃ quantification methods are presented, and the concomitant challenges are also revealed. Finally, we cast insights into the future development of sustainable NH₃ production, and highlight some potential directions for further research in this vibrant field.

Recent Advances in Application of Graphitic Carbon Nitride-Based Catalysts for Photocatalytic Nitrogen Fixation

Ammonia, the second most-produced chemical, is widely used in agricultural and industrial applications. However, traditional industrial ammonia production dominated by the Haber-Bosch process presents huge resource and environment issues due to the massive energy consumption and CO₂ emission. The newly emerged nitrogen fixation technology, photocatalytic N₂ reduction reaction (p-NRR), uses clean solar energy with zero-emission, holding great prospect to achieve sustainable ammonia synthesis. Although great efforts are made, the p-NRR catalysts still suffer from poor N₂ adsorption and activation, inferior light absorption, and fast recombination of photocarriers. Due to the tunable electronic structure of the metal-free polymeric graphitic carbon nitride (g-C₃ N₄ ), the above-mentioned issues can be significantly alleviated, making it the most promising p-NRR photocatalyst. This review summarizes the recent development of g-C₃ N₄ -based catalysts for p-NRR, including the working principle of p-NRR catalysts, the challenges of developing p-NRR catalysts, and corresponding solutions. Particularly, the roles of defect engineering and heterojunction construction on g-C₃ N₄ to the enhancement of photocatalytic performances are emphasized. In addition, computational studies are introduced to deepen the understanding of reaction pathways. At last, perspectives are provided on the development of p-NRR catalysts.

A minireview on catalysts for photocatalytic N2 fixation to synthesize ammonia

Ammonia (NH3) is an important feedstock in chemical industry. Nowadays NH3 is mainly produced via the industrialized Haber-Bosch process, which requires substantial energy input, since it operates at high temperatures (400-650 °C) and high pressures (20-40 Mpa). From the energy conservation point of view, it is of great significance to explore an alternative avenue to synthesize NH3, which is in line with the concept of sustainable development. Very recently, photocatalytic N2 fixation (PNF) has been discovered as a safe and green approach to synthesize NH3, as it utilizes the inexhaustible solar energy and the abundant N2 in nature to synthesize NH3 under mild conditions. A highly efficient catalyst is the core of PNF. Up to now, extensive studies have been conducted to design efficient catalysts for PNF. Summarizing the catalysts reported for PNF and unraveling their reaction mechanisms could provide guidance for the design of better catalysts. In this review, we will illustrate the development of catalysts for PNF, including semiconductors, plasmonic metal-based catalysts, iron-based catalysts, ruthenium-based catalysts and several other catalysts, point out the remaining challenges and outline the future opportunities, with the aim to contribute to the development of PNF.

Single atom catalysis for electrocatalytic ammonia synthesis

This review points out major challenges and outlook of NH3 synthesis via SACs. Summarizing the deficiencies of existing research can help researchers to continuously innovate and improve, and explore new research approaches.

Rational Design of Graphene Derivatives for Electrochemical Reduction of Nitrogen to Ammonia

The conversion of nitrogen to ammonia offers a sustainable and environmentally friendly approach for producing precursors for fertilizers and efficient energy carriers. Owing to the large energy density and significant gravimetric hydrogen content, NH₃ is considered an apt next-generation energy carrier and liquid fuel. However, the low conversion efficiency and slow production of ammonia through the nitrogen reduction reaction (NRR) are currently bottlenecks, making it an unviable alternative to the traditional Haber-Bosch process for ammonia production. The rational design and engineering of catalysts (both photo- and electro-) represent a crucial challenge for improving the efficiency and exploiting the full capability of the NRR. In the present review, we highlight recent progress in the development of graphene-based systems and graphene derivatives as catalysts for the NRR. Initially, the history, fundamental mechanism, and importance of the NRR to produce ammonia are briefly discussed. We also outline how surface functionalization, defects, and hybrid structures (single-atom/multiatom as well as composites) affect the N₂ conversion efficiency. The potential of graphene and graphene derivatives as NRR catalysts is highlighted using pertinent examples from theoretical simulations as well as machine learning based performance predictive methods. The review is concluded by identifying the crucial advantages, drawbacks, and challenges associated with principal scientific and technological breakthroughs in ambient catalytic NRR.

Looking for Options to Sustainably Fixate Nitrogen. Are Molecular Metal Oxides Catalysts a Viable Avenue?

Fast and reliable industrial production of ammonia (NH₃) is fundamentally sustaining modern society. Since the early 20^th Century, NH₃ has been synthesized via the Haber-Bosch process, running at conditions of around 350-500°C and 100-200 times atmospheric pressure (15-20 MPa). Industrial ammonia production is currently the most energy-demanding chemical process worldwide and contributes up to 3% to the global carbon dioxide emissions. Therefore, the development of more energy-efficient pathways for ammonia production is an attractive proposition. Over the past 20 years, scientists have imagined the possibility of developing a milder synthesis of ammonia by mimicking the nitrogenase enzyme, which fixes nitrogen from the air at ambient temperatures and pressures to feed leguminous plants. To do this, we propose the use of highly reconfigurable molecular metal oxides or polyoxometalates (POMs). Our proposal is an informed design of the polyoxometalate after exploring the catabolic pathways that cyanobacteria use to fix N₂ in nature, which are a different route than the one followed by the Haber-Bosch process. Meanwhile, the industrial process is a "brute force" system towards breaking the triple bond N-N, needing high pressure and high temperature to increase the rate of reaction, nature first links the protons to the N₂ to later easier breaking of the triple bond at environmental temperature and pressure. Computational chemistry data on the stability of different polyoxometalates will guide us to decide the best design for a catalyst. Testing different functionalized molecular metal oxides as ammonia catalysts laboratory conditions will allow for a sustainable reactor design of small-scale production.

Plasmon-enabled N2 photofixation on partially reduced Ti3C2 MXene

Benefiting from the superior conductivity, rich surface chemistry and tunable bandgap, Ti₃C₂ MXene has become a frontier cocatalyst material for boosting the efficiency of semiconductor photocatalysts. It has been theoretically predicted to be an ideal material for N₂ fixation. However, the realization of N₂ photofixation with Ti₃C₂ as a host photocatalyst has so far remained experimentally challenging. Herein, we report on a sandwich-like plasmon- and an MXene-based photocatalyst made of Au nanospheres and layered Ti₃C₂, and demonstrate its efficient N₂ photofixation in pure water under ambient conditions. The abundant low-valence Ti (Ti^(4-x)+) sites in partially reduced Ti₃C₂ (r-Ti₃C₂) produced by surface engineering through H₂ thermal reduction effectively capture and activate N₂, while Au nanospheres offer plasmonic hot electrons to reduce the activated N₂ into NH₃. The Ti^(4-x)+ active sites and plasmon-generated hot electrons work in tandem to endow r-Ti₃C₂/Au with remarkably enhanced N₂ photofixation activity. Importantly, r-Ti₃C₂/Au exhibits ultrahigh selectivity without the occurrence of competing H₂ evolution. This work opens up a promising route for the rational design of efficient MXene-based photocatalysts.

A Comprehensive Review on the Recent Development of Ammonia as a Renewable Energy Carrier

Global energy sources are being transformed from hydrocarbon-based energy sources to renewable and carbon-free energy sources such as wind, solar and hydrogen. The biggest challenge with hydrogen as a renewable energy carrier is the storage and delivery system’s complexity. Therefore, other media such as ammonia for indirect storage are now being considered. Research has shown that at reasonable pressures, ammonia is easily contained as a liquid. In this form, energy density is approximately half of that of gasoline and ten times more than batteries. Ammonia can provide effective storage of renewable energy through its existing storage and distribution network. In this article, we aimed to analyse the previous studies and the current research on the preparation of ammonia as a next-generation renewable energy carrier. The study focuses on technical advances emerging in ammonia synthesis technologies, such as photocatalysis, electrocatalysis and plasmacatalysis. Ammonia is now also strongly regarded as fuel in the transport, industrial and power sectors and is relatively more versatile in reducing CO2 emissions. Therefore, the utilisation of ammonia as a renewable energy carrier plays a significant role in reducing GHG emissions. Finally, the simplicity of ammonia processing, transport and use makes it an appealing choice for the link between the development of renewable energy and demand.

A review on vertical and lateral heterostructures of semiconducting 2D-MoS2 with other 2D materials: a feasible perspective for energy conversion

Fossil fuels as a double-edged sword are essential to daily life. However, the depletion of fossil fuel reservoirs has increased the search for alternative renewable energy sources to procure a more sustainable society. Accordingly, energy production through water splitting, CO₂ reduction and N₂ reduction via photocatalytic and electrocatalytic pathways is being contemplated as a greener methodology with zero environmental pollution. Owing to their atomic-level thickness, two-dimensional (2D) semiconductor catalysts have triggered the reawakening of interest in the field of energy and environmental applications. Among them, following the unconventional properties of graphene, 2D MoS₂ has been widely investigated due to its outstanding optical and electronic properties. However, the photo/electrocatalytic performance of 2D-MoS₂ is still unsatisfactory due to its low charge carrier density. Recently, the development of 2D/2D heterojunctions has evoked interdisciplinary research fascination in the scientific community, which can mitigate the shortcomings associated with 2D-MoS₂. Following the recent research trends, the present review covers the recent findings and key aspects on the synthetic methods, fundamental properties and practical applications of semiconducting 2D-MoS₂ and its heterostructures with other 2D materials such as g-C₃N₄, graphene, CdS, TiO₂, MXene, black phosphorous, and boron nitride. Besides, this review details the viable application of these materials in the area of hydrogen energy production via the H₂O splitting reaction, N₂ fixation to NH₃ formation and CO₂ reduction to different value-added hydrocarbons and alcohol products through both photocatalysis and electrocatalysis. The crucial role of the interface together with the charge separation principle between two individual 2D structures towards achieving satisfactory activity for various applications is presented. Overall, the current studies provide a snapshot of the recent breakthroughs in the development of various 2D/2D-based catalysts in the field of energy production, delivering opportunities for future research.

Surface structure-dependent photocatalytic O2 activation for pollutant removal with bismuth oxyhalides

The purification of water and air by semiconductor photocatalysis is a rapidly growing area for academic research and industrial innovation, featured with ambient removal of organic or inorganic pollutants by using solar light as the energy source and atmospheric O₂ as the green oxidant. Both charge transfer and energy transfer from excited photocatalysts can overcome the spin-forbidden nature of O₂. Layered bismuth oxyhalides are a new group of two-dimensional photocatalysts with an appealing geometric and surface structure that allows the dynamic and selective tuning of O₂ activation at the surface molecular level. In this Feature Article, we specifically summarize our recent progress in selective O₂ activation by engineering surface structures of bismuth oxyhalides. Then, we demonstrate selective photocatalytic O₂ activation of bismuth oxyhalides for environmental control, including water decontamination, volatile organic compound oxidation and nitrogen oxide removal, as well as selective catalytic oxidations. Challenges and opportunities regarding the design of photocatalysts with satisfactory performance for potential environmental control applications are also presented.

Efficient Ambient Electrocatalytic Ammonia Synthesis by Nanogold Triggered via Boron Clusters Combined with Carbon Nanotubes

Currently, the development of stable electrochemical nitrogen reduction reaction (ENRR) catalysts with high N₂ conversion activity and low cost to instead of the traditional Haber-Bosch ammonia production process of high-energy consumption remains a great challenge for researchers. Here, we have immobilized reductive closo-[B₁₂H₁₁]^- boron clusters on a carbon nanotubes (CNT) surface and have successfully prepared a novel Au-CNT catalyst with extraordinary ENRR activity after adding HAuCl₄ to the CNT-[B₁₂H₁₁]^- precursor. The excellent properties of ammonia yield (57.7 μg h^-1 cm^-2) and Faradaic efficiency (11.97%) make it possible to achieve using this Au-CNT catalyst in large-scale industrial production of ammonia. Furthermore, its outstanding cyclic stability and long-term tolerability performance make it one of the most cost-effective catalysts to date. Here, by means of density functional theory we disclose the associative mechanism of N₂-to-NH₃ conversion on the Au(111) surface, providing visual theoretical support for the experimental results.

BCN-Encapsulated Nano-nickel Synergistically Promotes Ambient Electrochemical Dinitrogen Reduction

The electricity provided by solar or wind power can drive nitrogen in the atmosphere, combining with ubiquitous water to form ammonia, and distributed production methods can alleviate the irreversible damage to the environment caused by the energy-intensive Haber-Bosch process. Here, we have designed a novel Ni-doped BCN heterojunction (S/M-BOPs-1) as a catalyst for the electrochemical nitrogen reduction reaction (NRR). The ammonia yield rate and Faraday efficiency in NRR driven by S/M-BOPs-1 reach up to 16.72 μg^-1 h^-1 cm^-2 and 13.06%, respectively. Moreover, S/M-BOPs-1 still maintains high NRR activity and excellent stability after recycling for eight times and long-time operation of 12 h. Using density functional theory calculations, we reveal a possible NRR path for N₂ to NH₃ on Ni, BCN, and the S/M-BOPs-1 composite surfaces. The interaction between the BCN matrix and Ni nanoparticles promotes a synergetic effect for the electrochemical NRR efficiency due to the partial electron transfer from the Ni particles to BCN that inhibits hydrogen evolution reaction and decreases the rate-determining step on Ni surfaces toward NRR by ∼1.5 times. Therefore, efficient NRR performance can be achieved by tuning the electronic properties of non-noble metals via the formation of a heterointerface.

Photocatalytic Dinitrogen Fixation with Water on Bismuth Oxychloride in Chloride Solutions for Solar-to-Chemical Energy Conversion

Ammonia is an indispensable chemical. Photocatalytic NH₃ production via dinitrogen fixation using water by sunlight illumination under ambient conditions is a promising strategy, although previously reported catalysts show insufficient activity. Herein, we showed that ultraviolet light irradiation of a semiconductor, bismuth oxychloride with surface oxygen vacancies (BiOCl-OVs), in water containing chloride anions (Cl^-) under N₂ flow efficiently produces NH₃. The surface OVs behave as the N₂ reduction sites by the photoformed conduction band electrons. The valence band holes are consumed by self-oxidation of interlayer Cl^- on the catalyst. The hypochloric acid (HClO) formed absorbs ultraviolet light and undergoes photodecomposition into O₂ and Cl^-. These consecutive photoreactions produce NH₃ with water as the electron donor. The Cl^- in solution compensates for the removed interlayer Cl^- and inhibits catalyst deactivation. Simulated sunlight illumination of the catalyst in seawater stably generates NH₃ with 0.05% solar-to-chemical conversion efficiency, thus exhibiting significant potential of the seawater system for artificial photosynthesis.

Sulfur Vacancy-Rich O-Doped 1T-MoS2 Nanosheets for Exceptional Photocatalytic Nitrogen Fixation over CdS

Here, we reported that sulfur vacancy-rich O-doped 1T-MoS₂ nanosheets (denoted as SV-1T-MoS₂) can surpass the activity of Pt as cocatalysts to assist in the photocatalytic nitrogen fixation of CdS nanorods. SV-1T-MoS₂ cocatalysts exhibit sulfur vacancies, O-doping, more metallic 1T phase, and high electronic conductivity, thus leading to the exposure of more active edge sites, high Brunauer-Emmett-Teller surface area, enhanced visible light absorption, and improved electron separation and transfer, which are beneficial for photocatalytic nitrogen fixation. Consequently, the optimized 30 wt % SV-1T-MoS₂-/CdS composites exhibit an outstanding nitrogen fixation rate of 8220.83 μmol L^-1 h^-1 g^-1 and long-term stability under simulated solar light irradiation, significantly higher than pure CdS nanorods, CdS-Pt (0.1 wt %), and 30 wt % 1T-MoS₂/CdS composites. The catalytic mechanism of photocatalytic nitrogen fixation on SV-1T-MoS₂ is discussed by density functional theory calculations.

Surface-defect-engineered photocatalyst for nitrogen fixation into value-added chemical feedstocks

Surface-defect-engineered photocatalyst for nitrogen fixation.

Ultrathin Nanotubes of Bi5O7I with a Reduced Band Gap as a High-Performance Photocatalyst

Bismuth oxyhalide (Bi-O-X) is a group of layered semiconductors, which are promising candidates for photocatalysis due to their inherent internal electric field and adjustable band gap through composition and morphology control. Bismuth-rich Bi-O-X has improved stability and advantageous band structure compared to those of Bi-O-X and hence has attracted an increasing amount of research interest. In this work, ultrathin nanotubes of Bi₅O₇I with a 5 nm diameter and a 1 nm wall are obtained through a hydrothermal method while the phase and morphology of the products are regulated by the pH values and polyvinylpyrrolidone (PVP) concentration of the reaction system, of which the products can be tuned from BiOI nanosheets to Bi₅O₇I nanobelts and ultrathin Bi₅O₇I nanotubes. PVP and pH control is important to the formation of the nanotubes as formation occurs via a PVP-guided oriented attachment from primary nanoparticles of Bi₅O₇I. The poorly crystalline and porous structure of the resultant bismuth-rich ultrathin nanotubes not only exposes more surface atoms but also exhibits a highly reduced conduction band minimum. The resultant band gap of 2.39 eV (as compared to 3.20 eV for the nanobelts) arises from the undercoordinated bismuth centers brought about by the rich oxygen vacancies in the nanotubes. The largely reduced band gap effectively enhances visible-light absorption, while the short charge-diffusion length of the nanotubes further reduces the charge-carrier loss in recombination.

Efficient Nitrogen Fixation Catalyzed by Gallium Nitride Nanowire Using Nitrogen and Water

Ammonia is one of the most important bulk chemicals in modern society. However, the highly energy-extensive contemporary industrial production of ammonia was developed in the early 20th century and requires extensive heating of highly pressurized flammable hydrogen gas, whose global production still relies heavily on non-sustainable petroleum. The development of "sustainable" nitrogen fixation process represents a grand aspirational chemical pursuit concerning our future human well-being. Herein, we report an ultra-stable nitride-based photosensitizing semiconductor that enables efficient, sustainable, and mild photochemical nitrogen fixation. The catalyst exhibits strong chemisorption of nitrogen and enables immediate electron donation from its surface vacancy to nitrogen. In addition, it was also demonstrated that the nitride-based semiconductor possesses the potential to minimize electron-hole recombination.

Modulation of Bi2 MoO6 -Based Materials for Photocatalytic Water Splitting and Environmental Application: a Critical Review

Highly active photocatalysts driving chemical reactions are of paramount importance toward renewable energy substitutes and environmental protection. As a fascinating Aurivillius phase material, Bi₂ MoO₆ has been the hotspot in photocatalytic applications due to its visible light absorption, nontoxicity, low cost, and high chemical durability. However, pure Bi₂ MoO₆ suffers from low efficiency in separating photogenerated carriers, small surface area, and poor quantum yield, resulting in low photocatalytic activity. Various strategies, such as morphology control, doping/defect-introduction, metal deposition, semiconductor combination, and surface modification with conjugative π structures, have been systematically explored to improve the photocatalytic activity of Bi₂ MoO₆ . To accelerate further developments of Bi₂ MoO₆ in the field of photocatalysis, this comprehensive Review endeavors to summarize recent research progress for the construction of highly efficient Bi₂ MoO₆ -based photocatalysts. Furthermore, benefiting from the enhanced photocatalytic activity of Bi₂ MoO₆ -based materials, various photocatalytic applications including water splitting, pollutant removal, and disinfection of bacteria, were introduced and critically reviewed. Finally, the current challenges and prospects of Bi₂ MoO₆ are pointed out. This comprehensive Review is expected to consolidate the existing fundamental theories of photocatalysis and pave a novel avenue to rationally design highly efficient Bi₂ MoO₆ -based photocatalysts for environmental pollution control and green energy development.

Insights into the Recent Progress and Advanced Materials for Photocatalytic Nitrogen Fixation for Ammonia (NH3) Production

Ammonia (NH3) is one of the key agricultural fertilizers and to date, industries are using the conventional Haber-Bosh process for the synthesis of NH3 which requires high temperature and energy. To overcome such challenges and to find a sustainable alternative process, researchers are focusing on the photocatalytic nitrogen fixation process. Recently, the effective utilization of sunlight has been proposed via photocatalytic water splitting for producing green energy resource, hydrogen. Inspired by this phenomenon, the production of ammonia via nitrogen, water and sunlight has been attracted many efforts. Photocatalytic N2 fixation presents a green and sustainable ammonia synthesis pathway. Currently, the strategies for development of efficient photocatalyst for nitrogen fixation is primarily concentrated on creating active sites or loading transition metal to facilitate the charge separation and weaken the N–N triple bond. In this investigation, we review the literature knowledge about the photocatalysis phenomena and the most recent developments on the semiconductor nanocomposites for nitrogen fixation, following by a detailed discussion of each type of mechanism.

Progress of Metal Oxide (Sulfide)-Based Photocatalytic Materials for Reducing Nitrogen to Ammonia

The Haber–Bosch process has been an important approach to produce ammonia for meeting the food need of increasing population and the worldwide need of nitrogenous fertilizers since 1913. However, the traditional ammonia production process is a high energy-consumption process, which usually produces 1 metric ton ammonia with releasing around 1.9 metric tons CO2. Photocatalytic ammonia synthesis under solar light as energy source, an attractive and promising alternative approach, is a very challenging target of reducing fossil energy consumption and environmental pollution. Therefore, photocatalytic ammonia production process would emerge huge opportunities by directly providing nitrogenous fertilizers in a distributed manner as needed in the agricultural fields. In this article, different metal oxide (sulfide)-based photocatalytic materials for reducing nitrogen to ammonia under ambient conditions are reviewed. This review provides insights into the most recent advancements in understanding the photocatalyst materials which are of fundamental significance to photocatalytic nitrogen reduction, including the state-of-the-art, challenges, and prospects in this research field.

New opportunities for efficient N2 fixation by nanosheet photocatalysts

Catalytic ammonia synthesis from dinitrogen (N2) under mild conditions has been considered to be the "holy grail" of N2 fixation, which is one of the most important chemical processes in the agriculture, biological and industrial fields. Given that current artificial N2 fixation is still dominated by the energy-intensive Haber-Bosch process, solar N2 fixation represents an encouraging and fascinating route for carbon-free and energy-saving N2 fixation. However, its practical application is seriously hampered by surface sluggish reaction kinetics. In this minireview, we share our perspectives on the use of two-dimensional (2D) nanosheets for the manipulation of photocatalytic N2 fixation. Nanosheet photocatalysts serve as the perfect platform for the engineering of surface active sites, including defects and iron, all of which can not only bolster photon-exciton interaction toward robust charge carriers generation upon light absorption, but also mimic the function schemes of MoFe-cofactor in nitrogenase toward sufficient N2 binding and activation. These merits endowed by nanosheets photocatalysts provide instructive information on exploring the rich nitrogen photochemistry on solid surfaces and offer new opportunities for the design of novel photocatalysts towards efficient N2 fixation.

Defect state of indium-doped bismuth molybdate nanosheets for enhanced photoreduction of chromium(vi) under visible light illumination

The construction of defect states is an effective method for regulating the energy band structure of photocatalytic semiconductor materials.

Efficient solar-driven conversion of nitrogen to ammonia in pure waterviahydrogenated bismuth oxybromide

Solar-driven reduction of dinitrogen to ammonia under mild conditions has attracted widespread interest in recent years. In this study, we first report low-temperature hydrogenated BiOBr for the direct synthesis of ammonia from dinitrogen with high efficiency under solar-light irradiation. In a proof of concept, the hydrogenation treatment can lead to surface disorder due to the strong reducing capacity of hydrogen. Oxygen atoms can be activated, and they can escape from the surface structure to form oxygen vacancies. Then, defect engineering can broaden the photoelectricity absorption window and effectively trigger interfacial electron transfer from the semiconductor to the combined nitrogen. This method exhibits a satisfactory result for photocatalytic nitrogen fixation, yielding about 2.6 times more NH₃ than that obtained from the original sample. The corresponding apparent quantum efficiency can reach a significant value of 2.1% under 380 nm monochromatic light irradiation. These results may pave a new way for the synthesis of highly active photocatalysts for efficient nitrogen fixation under solar light irradiation.

Samples of H-BiOBr use water as reactant which demonstrates efficient nitrogen fixation under sunlight.

Dinitrogen photoactivation: status quo and future perspectives

New perspectives for dinitrogen activation: an overview of photochemical pathways to cleave the strong N–N bond.

Light-Switchable Oxygen Vacancies in Ultrafine Bi5 O7 Br Nanotubes for Boosting Solar-Driven Nitrogen Fixation in Pure Water

Solar-driven reduction of dinitrogen (N₂ ) to ammonia (NH₃ ) is severely hampered by the kinetically complex and energetically challenging multielectron reaction. Oxygen vacancies (OVs) with abundant localized electrons on the surface of bismuth oxybromide-based semiconductors are demonstrated to have the ability to capture and activate N₂ , providing an alternative pathway to overcome such limitations. However, bismuth oxybromide materials are susceptible to photocorrosion, and the surface OVs are easily oxidized and therefore lose their activities. For realistic photocatalytic N₂ fixation, fabricating and enhancing the stability of sustainable OVs on semiconductors is indispensable. This study shows the first synthesis of self-assembled 5 nm diameter Bi₅ O₇ Br nanotubes with strong nanotube structure, suitable absorption edge, and many exposed surface sites, which are favorable for furnishing sufficient visible light-induced OVs to realize excellent and stable photoreduction of atmospheric N₂ into NH₃ in pure water. The NH₃ generation rate is as high as 1.38 mmol h^-1 g^-1 , accompanied by an apparent quantum efficiency over 2.3% at 420 nm. The results presented herein provide new insights into rational design and engineering for the creation of highly active catalysts with light-switchable OVs toward efficient, stable, and sustainable visible light N₂ fixation in mild conditions.