Enhanced photocatalytic N2 fixation by promoting N2 adsorption with a co-catalyst

Dual-defect semiconductor photocatalysts for solar-to-chemical conversion: advances and challenges

Among the renewable energy technologies to deal with increasing energy crisis and environmental concerns, solar-to-chemical conversion via photocatalysis holds great promise for sustainable energy supply. To date, a variety of modification strategies with different types of semiconducting materials have been proposed to boost photocatalytic efficiency. Recently, dual-defect semiconductor photocatalysts have emerged as an advantageous candidate with superior performance in improving photocatalytic activity compared to their defect-free or single-defect counterparts. In this review, focus is laid on the advances of dual-defect semiconductor photocatalysts for energy photocatalysis. Possible schemes for two different defects within a single semiconductor are firstly sorted based on the types of defects, and synthesis strategies to achieve various defect schemes as well as techniques to characterize different defects are then introduced. In particular, the effect of different defects on photocatalytic performance is emphasized, and the advances in dual-defect semiconductors for solar-to-chemical conversions are summarized based on different defect schemes. Finally, the future challenges and opportunities of dual-defect semiconductors for photocatalysis are discussed. This article is expected to provide an overall insight into existing dual-defect semiconductor photocatalysts and inspire the development of new defect-rich materials for photocatalytic energy production.

Triggering Dual Two-electron Pathway for H2 O2 Generation by Multiple [Bi-O]n Interlayers in Ultrathin Bi12 O17 Cl2 towards Efficient Piezo-self-Fenton Catalysis

Piezo-self-Fenton system (PESF) has been emerging as a promising water treatment technology but suffering from unsatisfied H2 O2 production efficiency. Herein, we rationally design a Bi12 O17 Cl2 piezo-catalyst with multiple [Bi-O]n interlayers towards highly efficient H2 O2 production. The introduction of [Bi3 O4.25 ] layers initiates dual two-electron pathway for H2 O2 generation by altering the interlayer properties. It is found that the additional [Bi3 O4.25 ] layers not only enhance the polarization electric field but also serve as active sites for triggering dual pathways of two-electron O2 reduction and H2 O oxidation reaction for H2 O2 production. Therefore, the Bi12 O17 Cl2 exhibits an ultrahigh rate of H2 O2 generation (7.76 mM h-1  g-1 ) in pure water. Based on the adequate H2 O2 yield, a PESF was constructed for acetaminophen (ACE) degradation with an apparent rate constant of 0.023 min-1 . This work not only presents a potential strategy of tuning the activity of bismuth based piezo-catalysts but also provides a good example on the construction of highly efficient PESF for environmental remediation by using natural mechanical energy.

Nitrogen adsorption on Nb2C6H4+ cations: the important role of benzyne (ortho-C6H4)

N2 adsorption is a prerequisite for activation and transformation. Time-of-flight mass spectrometry experiments show that the Nb2C6H4+ cation, resulting from the gas-phase reaction of Nb2+ with C6H6, is more favorable for N2 adsorption than Nb+ and Nb2+ cations. Density functional theory calculations reveal the effect of the ortho-C6H4 ligand on N2 adsorption. In Nb2C6H4+, interactions between the Nb-4d and C-2p orbitals enable the Nb2+ cation to form coordination bonds with the ortho-C6H4 ligand. Although the ortho-C6H4 ligand in Nb2C6H4+ is not directly involved in the reaction, its presence increases the polarity of the cluster and brings the highest occupied molecular orbital (HOMO) closer to the lowest occupied molecular orbital (LUMO) of N2, thereby increasing the N2 adsorption energy, which effectively facilitates N2 adsorption and activation. This study provides fundamental insights into the mechanisms of N2 adsorption in "transition metal-organic ligand" systems.

Bimetallic atom synergistic covalent organic framework for efficient electrochemical nitrate reduction

Electrochemical reduction has emerged as an effective method to remove nitrate from industrial wastewater. Nevertheless, this method has been largely restricted by the lack of low-cost and efficient electrocatalysts. Here, we demonstrate a porous two-dimensional covalent organic framework (2D COF) material as a promising electrocatalyst, which is obtained via a Schiff base reaction by combining copper phthalocyanine with bipyridine sites for precise copper coordination. The bidentate coordinated COF material has a robust framework and stable chemical property, allowing the isolated Cu sites to be embedded into the regular pores with controlled and uniformly dispersed active centers. The well-defined design of the reaction monomers makes the COF material to trap nitrate ions more easily from aqueous solution. By rationally combining the synergistic effect of 2D COF and Cu active sites, the CuTAPc-CuBPy-COF electrocatalyst shows much higher nitrate reduction efficiency than CuTAPc-BPy-COF under low superpotential and different nitrate concentrations. The high NO3- conversion (90.3 %) and NH3 selectivity (69.6 %) are achieved. To our best acknowledge, this is the first demonstration of bi-copper-based COF material for NO3-RR electrocatalysis, which provides a new direction for the rational design of COFs as significant electrocatalysts for nitrate reduction.

Defects-Induced Single-Atom Anchoring on Metal-Organic Frameworks for High-Efficiency Photocatalytic Nitrogen Reduction

Aiming to improve the photocatalytic activity in N2 fixation to produce ammonia, herein, we proposed a photochemical strategy to fabricate defects, and further deposition of Ru single atoms onto UiO-66 (Zr) framework. Electron-metal-support interactions (EMSI) were built between Ru single atoms and the support via a covalently bonding. EMSI were capable of accelerating charge transfer between Ru SAs and UiO-66, which was favorable for highly-efficiently photocatalytic activity. The photocatalytic production rate of ammonia improved from 4.57 μmol g-1  h-1 to 16.28 μmol g-1  h-1 with the fabrication of defects onto UiO-66, and further to 53.28 μmol g-1  h-1 with Ru-single atoms loading. From the DFT results, it was found that d-orbital electrons of Ru were donated to N2 π✶-antibonding orbital, facilitating the activation of the N≡N triple bond. A distal reaction pathway was probably occurred for the photocatalytic N2 reduction to ammonia on Ru1 /d-UiO-66 (single Ru sites decorated onto the nodes of defective UiO-66), and the first step of hydrogenation of N2 was the reaction determination step. This work shed a light on improving the photocatalytic activity via feasibly anchoring single atoms on MOF, and provided more evidences to understand the reaction mechanism in photocatalytic reduction of N2 .

Nitrogen activation and surface charge regulation for enhancing the visible-light-driven N2 fixation over MoS2/UiO-66(SH)2

A series of dehydrated MoS2/UiO-66(SH)2 (MS/UiS) composites has been prepared as photocatalysts for N2 fixation. Typically, 10% MS/UiS exhibits the best performance with an NH4+ yield rate of 54.08 μmol∙g-1∙h-1. 15N isotope test confirmed that the sample 10% MS/UiS was most effective for reducing N2 to ammonia. Such enhanced activity was due to the presence of abundant unsaturated Zr and Mo sites which would synergistically promote the adsorption and activation of N2. The photogenerated electrons would transfer to the unsaturated Zr-O clusters while part of photogenerated electrons at the interface migrate to MS via MoVI-O interactions between MS and UiS. These two electron transfer pathways effectively promote the separation of photogenerated carriers. The activated N2 is reduced to ammonia by the synergistic effect of protonated hydrogen and photogenerated electrons. Finally, a possible N2 fixation mechanism is proposed which emphasizes the significant roles of nitrogen activation and interface interaction in composites photocatalyst for improving photocatalytic performance.

One-step fabrication of Cu-doped Bi2MoO6 microflower for enhancing performance in photocatalytic nitrogen fixation

This study enhances the photocatalytic N₂ immobilization performance of Bi₂MoO₆ through Cu doping. Cu-doped Bi₂MoO₆ was synthesized via a simple solvothermal method. Various characterizations were implemented to examine the influence of Cu doping on the properties of Bi₂MoO₆. Results indicated that the doped Cu element had a valence state of + 2 and substituted the position of Bi³⁺. Cu doping exerted minimal effect on the morphology of Bi₂MoO₆ but largely influenced the energy band structure. The band gap was slightly narrowed, and the conduction band was raised, such that Cu-doped Bi₂MoO₆ could generate more electrons with stronger reducibility. Moreover, importantly, Cu doping reduced work function and improved charge separation efficiency, which was considered the major cause of enhanced photoactivity. In addition, the Cu-Bi₂MoO₆ catalyst exhibited higher capability in the adsorption and activation of N₂. Under the combined effects of the aforementioned changes, Cu-Bi₂MoO₆ demonstrated considerably higher photocatalytic efficiency than Bi₂MoO₆. The optimized NH₃ generation rate reached 302 μmol/L g^-1h^-1 and 157 μmol/L g^-1h^-1 under simulated solar light and visible light, respectively, both achieving about 2.2 times higher than that of Bi₂MoO₆. This work provides a successful example of improving photocatalytic N₂ fixation, and it may show some light on the design and preparation of heteroatom-doped semiconductor photocatalysts for N₂-to-NH₃ conversion.

Preparation of NaNbO3 microcube with abundant oxygen vacancies and its high photocatalytic N2 fixation activity in the help of Pt nanoparticles

In this study, the photocatalytic N₂ immobilization performance of NaNbO₃ is enhanced via oxygen vacancy introduction and Pt loading. The designed Pt-loaded NaNbO₃ with rich oxygen defects (Pt/O-NaNbO₃) is synthesized by combining ion-exchange and photodeposition methods. Characterization result indicates that the O-NaNbO₃ has hollow microcube morphology and higher surface area than NaNbO₃. The introduced oxygen defects greatly affect the energy band structure. The band gap is slightly narrowed and the conduction band is raised, allowing O-NaNbO₃ to generate electrons with strong reducibility. Moreover, the oxygen defects reduced the work function of NaNbO₃, leading to increased charge separation in the bulk phase. The loaded Pt nanoparticles can further increase the surface charge separation via the formed Schottky barriers between Pt and O-NaNbO₃, which was thought to be the primary cause of the increased photocatalytic activity. Additionally, the oxygen vacancies and metal Pt also contribute to the adsorption and activation of N₂. Under the combined effect of the above changes, Pt/O-NaNbO₃ presents much higher photoactivity than NaNbO₃. The optimized NH₃ production rate reaches 293.3 μmol/L g^-1h^-1 under simulated solar light, which is approximately 2.2 and 20.2 times higher than that of O-NaNbO₃ and NaNbO₃, respectively. This research offers a successful illustration of how to improve photocatalytic N₂ fixation and may shed some light on how to design and construct efficient photocatalysts by combining several techniques.

First-principles-driven catalyst design protocol of 2D/2D heterostructures for electro- and photocatalytic nitrogen reduction reaction

Ammonia synthesis from nitrogen is a vital process and a necessity in a variety of applications including energy, pharmaceutical, agricultural, and chemical applications. The electro- and photocatalytic nitrogen reduction reactions (NRRs) are promising sustainable processes operated under milder conditions than the conventional Haber-Bosch process. However, the main pain points of these catalytic processes are their low selectivity and low efficiency. This perspective presents the recent status and the design protocols for developing promising 2D/2D heterojunction catalysts for the NRR, using the first-principles approach. The current theoretical studies are briefly discussed, and available methods are suggested for the development and design of new potential 2D/2D heterojunctions as efficient electro- and photo-NRR catalysts.

Understanding Aerobic Nitrogen Photooxidation on Titania through In Situ Time-Resolved Spectroscopy

Nitrate is an important raw material for chemical fertilizers, but it is industrially manufactured in multiple steps at high temperature and pressure, urgently motivating the design of a green and sustainable strategy for nitrate production. We report the photosynthesis of nitrate from N₂ and O₂ on commercial TiO₂ in a flow reactor under ambient conditions. The TiO₂ photocatalyst offered a high nitrate yield of 1.85 μmol h^-1 as well as a solar-to-nitrate energy conversion efficiency up to 0.13 %. We combined reactivity and in situ Fourier transform infrared spectroscopy to elucidate the mechanism of nitrate formation and unveil the special role of O₂ in N≡N bond dissociation. The mechanistic insight into charge-involved N₂ oxidation was further demonstrated by in situ transient absorption spectroscopy and electron paramagnetic resonance. This work exhibits the mechanistic origin of N₂ photooxidation and initiates a potential method for triggering inert catalytic reactions.

Recent Progress of Metal Sulfide Photocatalysts for Solar Energy Conversion

Artificial photosynthetic solar-to-chemical cycles enable an entire environment to operate in a more complex, yet effective, way to perform natural photosynthesis. However, such artificial systems suffer from a lack of well-established photocatalysts with the ability to harvest the solar spectrum and rich catalytic active-site density. Benefiting from extensive experimental and theoretical investigations, this bottleneck may be overcome by devising a photocatalytic platform based on metal sulfides with predominant electronic, physical, and chemical properties. These tunable properties can endow them with abundant active sites, favorable light utilization, and expedited charge transportation for solar-to-chemical conversion. Here, it is described how some vital lessons extracted from previous investigations are employed to promote the further development of metal sulfides for artificial photosynthesis, including water splitting, CO₂ reduction, N₂ reduction, and pollutant removal. Their functions, properties, synthetic strategies, emerging issues, design principles, and intrinsic functional mechanisms for photocatalytic redox reactions are discussed in detail. Finally, the associated challenges and prospects for the utilization of metal sulfides are highlighted and future development trends in photocatalysis are envisioned.

Chemical looping based ammonia production-A promising pathway for production of the noncarbon fuel

Ammonia, primarily made with Haber-Bosch process developed in 1909 and winning two Nobel prizes, is a promising noncarbon fuel for preventing global warming of 1.5 °C above pre-industrial levels. However, the undesired characteristics of the process, including high carbon footprint, necessitate alternative ammonia synthesis methods, and among them is chemical looping ammonia production (CLAP) that uses nitrogen carrier materials and operates at atmospheric pressure with high product selectivity and energy efficiency. To date, neither a systematic review nor a perspective in nitrogen carriers and CLAP has been reported in the critical area. Thus, this work not only assesses the previous results of CLAP but also provides perspectives towards the future of CLAP. It classifies, characterizes, and holistically analyzes the fundamentally different CLAP pathways and discusses the ways of further improving the CLAP performance with the assistance of plasma technology and artificial intelligence (AI).

Anchoring Black Phosphorus Quantum Dots on Fe-Doped W18 O49 Nanowires for Efficient Photocatalytic Nitrogen Fixation

Herein, we demonstrate that the surface anchoring of black phosphorus quantum dots (BPQDs) and bulk iron-doping in W₁₈ O₄₉ nanowires significantly promotes the photocatalytic activity toward N₂ fixation into NH₃ . More specifically, a NH₃ production rate of up to 187.6 μmol g^-1  h^-1 could be achieved, nearly one order of magnitude higher than that of pristine W₁₈ O₄₉ (18.9 μmol g^-1  h^-1 ). Comprehensive experiments and density-functional theory calculations reveal that Fe-doping could enhance the reducing ability of photo-generated electrons by decreasing the work function and elevating the defect band (d-band) centers. Additionally, the surface BPQDs anchoring could facilitate the N₂ adsorption/activation owing to the increased adsorption energy and advantaged W-P dimer bonding-mode. Therefore, synergizing the surface BPQD anchoring and bulk Fe-doping remarkably enhanced the photocatalytic activity of W₁₈ O₄₉ nanowires for NH₃ production.

The fabrication of graphitic carbon nitride hollow nanocages with semi-metal 1T' phase molybdenum disulfide as co-catalysts for excellent photocatalytic nitrogen fixation

Improving the efficiency of photogenerated carrier separation is essential for photocatalytic N₂ fixation. Herein, the 2D semi-metal 1T'-MoS₂ was uniformly distributed in g-C₃N₄ nanocages (CNNCs) by a hydrothermal method, and the 1T'-MoS₂/CNNC composite was obtained. 1T'-MoS₂ as a co-catalyst can promote the transfer of electrons, improve the separation efficiency of photogenerated carriers, and also increase the number of effective active sites. In addition, the unique nanocage morphology of CNNCs is conducive to the scattering and reflection of incident light and improves the light absorption capacity. Therefore, the optimized 1T'-MoS₂/CNNC composite (5 wt%) shows a significantly improved photocatalytic N₂ fixation rate (9.8 mmol L^-1 h^-1 g^-1) and good stability, which is significantly higher than pure CNNCs (2.9 mmol L^-1 h^-1 g^-1), Pt/CNNC (8.2 mmol L^-1 h^-1 g^-1) and Pt/g-C₃N₄ nanosheet (CNNS, 6.3 mmol L^-1 h^-1 g^-1). This work guides guidance for the design of green and efficient N₂ fixation photocatalysts.

A novel Z-scheme Bi-Bi2O3/KTa0.5Nb0.5O3 heterojunction for efficient photocatalytic conversion of N2 to NH3

A novel Z-scheme photocatalyst Bi-Bi2O3/KTa0.5Nb0.5O3 (KTN) composite was prepared by a simple solvothermal method. Compared with KTN, Bi/KTN, and Bi2O3/KTN, Bi-Bi2O3/KTN ternary composite catalyst presented much better photocatalytic ammonia-synthesis efficiency....

Heterojunction photocatalysts for artificial nitrogen fixation: fundamentals, latest advances and future perspectives

As an indispensable energy source, ammonia plays an essential role in agriculture and various industries. Given that the current ammonia production is still dominated by the energy-intensive and high carbon footprint Haber-Bosch process, photocatalytic nitrogen fixation represents a low-energy consuming and sustainable approach to generate ammonia. Heterostructured photocatalysts are hybrid materials composed of semiconductor materials containing interfaces that make full use of the unique superiorities of the constituents and synergistic effects between them. These promising photocatalysts have superior performances and substantial potential in photocatalytic reduction of nitrogen. In this review, a wide spectrum of recently developed heterostructured photocatalysts for nitrogen fixation to ammonia are evaluated. The fundamentals of solar-to-ammonia conversion, basic principles of various heterojunction photocatalysts and modification strategies are systematically reviewed. Finally, a brief summary and perspectives on the ongoing challenges and directions for future development of nitrogen photofixation catalysts are also provided.

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.

Schottky Junctions with Bi Cocatalyst for Taming Aqueous Phase N2 Reduction toward Enhanced Solar Ammonia Production

Solar-powered N2 reduction in aqueous solution is becoming a research hotspot for ammonia production. Schottky junctions at the metal/semiconductor interface have been effective to build up a one-way channel for the delivery of photogenerated electrons toward photoredox reactions. However, their applications for enhancing the aqueous phase reduction of N2 to ammonia have been bottlenecked by the difficulty of N2 activation and the competing H2 evolution reaction (HER) at the metal surface. Herein, the application of Bi with low HER activity as a robust cocatalyst for constructing Schottky-junction photocatalysts toward N2 reduction to ammonia is reported. The introduction of Bi not only boosts the interfacial electron transfer from excited photocatalysts due to the built-in Schottky-junction effect at the Bi/semiconductor interface but also synchronously facilitates the on-site N2 adsorption and activation toward solar ammonia production. The unidirectional charge transfer to the active site of Bi significantly promotes the photocatalytic N2-to-ammonia conversion efficiency by 65 times for BiOBr. In addition, utilizing Bi to enhance the photocatalytic ammonia production can be extended to other semiconductor systems. This work is expected to unlock the promise of engineering Schottky junctions toward high-efficiency solar N2-to-ammonia conversion in aqueous phase.

Photoexcited Electron Dynamics of Nitrogen Fixation Catalyzed by Ruthenium Single-Atom Catalysts

It is still a grand challenge to exploit efficient catalysts to achieve sustainable photocatalytic N₂ reduction under ambient conditions. Here, we developed a ruthenium-based single-atom catalyst anchored on defect-rich TiO₂ nanotubes (denoted Ru-SAs/Def-TNs) as a model system for N₂ fixation. The constructed Ru-SAs/Def-TNs exhibited a catalytic efficiency of 125.2 μmol g^-1 h^-1, roughly 6 and 13 times higher than those of the supported Ru nanoparticles and Def-TNs, respectively. Through ultrafast transient absorption and photoluminescence spectroscopy, we revealed the relationship between catalytic activity and photoexcited electron dynamics in such a model SA catalytic system. The unique ligand-to-metal charge-transfer state formed in Ru-SAs/Def-TNs was found to be responsible for its high catalytic activity because it can greatly promote the transfer of photoelectrons from Def-TNs to the Ru-SAs center and the subsequent capture by Ru-SAs. This work sheds light on the origin of the high performance of SA catalysts from the perspective of photoexcited electron dynamics and hence enriches the mechanistic understanding of SA catalysis.

In situ preparation of g-C3N4 nanosheet/FeOCl: Achievement and promoted photocatalytic nitrogen fixation activity

Climate change, global warming, and population growth have led researchers to use eco-sociable procedures for the N₂ reduction reaction. It has discovered that N₂ molecule can be transformed into NH₃ in ambient circumstances with nanocomposites upon visible irradiation. In this research paper, a new visible-light-driven photocatalyst was constructed, with various weight percents of FeOCl particles (10, 20, 30, and 40%) that have adhered on NS-CN. Subsequently, multiple features of the nanocomposites were assayed in detail. The results illustrated that the NS-CN/FeOCl (20%) system has remarkable photoactivity in the NH₄⁺ production reaction in comparison with the NS-CN and CN, which showed 2.5 and 8.6 higher activity, respectively. The durability of NS-CN/FeOCl (20%) system, as a substantial factor, was assayed for 5 recycles. Moreover, the effect of electron quenchers, pH of media, and solvent was studied. At last, a feasible Z-scheme mechanism for the remarkable improvement of N₂ fixation efficiency was offered.

Zeolite-seed-directed Ru nanoparticles highly resistant against sintering for efficient nitrogen activation to ammonia

To stabilize Ru nanoparticles against sintering is an urgent problem in the utilization of Ru-based catalysts for NH₃ synthesis. In the present study, we used Ru-containing ZSM-5 as seeds to crystallize ZSM-5, and the resulted Ru@ZSM-5 catalyst is highly resistant against Ru sintering. According to the results of diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) and transmission electron microscopy (TEM) analyses, the average size of Ru nanoparticles is around 3.6 nm, which is smaller than that of Ru/ZSM-5-IWI prepared by incipient wetness impregnation. In NH₃ synthesis (N₂:H₂ = 1:3) at 400 °C and 1 MPa, Ru@ZSM-5 displays a formation rate of 5.84 mmol_NH3 g_cat^-1 h^-1, which is much higher than that of Ru/ZSM-5-IWI (2.13 mmol_NH3 g_cat^-1 h^-1). According to the results of TEM, N₂-temperature-programmed desorption (N₂-TPD), X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure (XAFS) studies, it is deduced that the superior performance of Ru@ZSM-5 is attributable to the small particle size and the ample existence of metallic Ru⁰ sites. This method of zeolite encapsulation is a feasible way to stabilize Ru nanoparticles for NH₃ synthesis.

Computational Design of Transition Metal Single-Atom Electrocatalysts on PtS2 for Efficient Nitrogen Reduction

Electrocatalytic nitrogen reduction is promising to serve as a sustainable and environmentally friendly strategy to achieve ammonia production. Single-atom catalysts (SACs) hold great promise to convert N₂ into NH₃ because of the unique molecular catalysis property and ultrahigh atomic utilization ratio. Here, we demonstrate a universal computational design principle to assess the N₂ reduction reaction (NRR) performance of SACs anchored on a monolayer PtS₂ substrate (SACs-PtS₂). Our density functional theory simulations unveil that the barriers of the NRR limiting potential step on different SAC centers are observed to be linearly correlated to the integral of unoccupied d states (UDSs) of SACs. As a result, the Ru SAC-PtS₂ catalyst with the largest number of UDSs exhibits a much lower barrier of the limiting step than those of other SACs-PtS₂ catalysts and the Ru(0001) benchmark. Our work bridges the apparent NRR activity and intrinsic electronic structure of SAC centers and offers effective guidance to screen and design efficient SACs for the electrochemical NRR process.

Few-Layer Black Phosphorus Nanosheets: A Metal-Free Cocatalyst for Photocatalytic Nitrogen Fixation

Exploiting an appropriate strategy to prepare fine crystal quality black phosphorus nanosheet (BPNS) catalyst is a major challenge for its practical application in catalysis. Herein, we address this challenge by developing a rapid electrochemical expansion strategy for scale preparation of fine crystal quality BPNSs from bulk black phosphorus, which was demonstrated to be an active cocatalyst for photocatalytic nitrogen fixation in the presence of CdS as a photocatalyst. The transient photocurrent and charge density studies show that the BPNSs can efficiently accelerate charge separation of CdS, leading to the enhanced photocatalytic activities of BPNS/CdS nanocomposites for nitrogen fixation. The 1.5% BPNS/CdS photocatalyst exhibits the highest photocatalytic activity for nitrogen fixation with an NH₃ evolution rate of 57.64 μmol·L^-1·h^-1. This study not only affords a rapid and simple strategy for scale synthesis of fine crystal quality BPNSs but also provides new insights into the design and development of black phosphorus-based materials as low-cost metal-free cocatalysts for photocatalytic nitrogen fixation.

Core@shell structured Au@SnO2 nanoparticles with improved N2 adsorption/activation and electrical conductivity for efficient N2 fixation

The design of electrocatalysts with enhanced adsorption and activation of nitrogen (N₂) is critical for boosting the electrochemical N₂ reduction (ENR). Herein, we developed an efficient strategy to facilitate N₂ adsorption and activation for N₂ electroreduction into ammonia (NH₃) by vacancy engineering of core@shell structured Au@SnO₂ nanoparticles (NPs). We found that the ultrathin amorphous SnO₂ shell with enriched oxygen vacancies was conducive to adsorb N₂ as well as promoted the N₂ activation, meanwhile the metallic Au core ensured the good electrical conductivity for accelerating electrons transport during the electrochemical N₂ reduction reaction, synergistically boosting the N₂ electroreduction catalysis. As confirmed by the ¹⁵N-labeling and controlled experiments, the core@shell Au@amorphous SnO₂ NPs with abundant oxygen vacancies show the best performance for N₂ electroreduction with the NH₃ yield rate of 21.9 μg h^-1 mg^-1_cat and faradaic efficiency of 15.2% at -0.2 V_RHE, which surpass the Au@crystalline SnO₂ NPs, individual Au NPs and all reported Au-based catalysts for ENR.

Highly boosted gas diffusion for enhanced electrocatalytic reduction of N2 to NH3 on 3D hollow Co-MoS2 nanostructures

Transition metal chalcogenide MoS₂ catalysts are highly selective for the electrochemical reduction of dinitrogen (N₂) to ammonia (NH₃) in aqueous electrolytes. However, due to the low solubility of N₂ in water, limited N₂ diffusion and mass transport have heavily restricted the yield and the faradaic efficiency (FE). Here, we have demonstrated a highly efficacious assembled gas diffusion cathode with hollow Co-MoS₂/N@C nanostructures to significantly improve the electrochemical reduction of N₂ to NH₃. Our results revealed that the synthesized Co-MoS₂ heterojunctions with abundant graphitic N groups exhibited a superb NH₃ yield of 129.93 μg h^-1 mg_cat^-1 and a high faradaic efficiency of 11.21% at -0.4 V vs. the reversible hydrogen electrode (RHE), as well as excellent selectivity and stability. The strategy described in this study offers new inspiration to design high-performance electrocatalyst assemblies for the sustainable environmental and energy applications.

Polyaniline-TiO2 composite photocatalysts for light-driven hexavalent chromium ions reduction

In order to develop efficient photocatalysts, great efforts have been made to reduce hexavalent chromium to trivalent chromium. The photocatalytic efficiency of this reduction depends largely on the adsorption and diffusion of hexavalent chromium ions on the surface of the photocatalyst. In this paper, polyaniline-TiO₂ composite can effectively improve the photocatalytic reduction performance and stability of hexavalent chromium ion. The effect of polyaniline (PANI) thickness on Cr(VI) activity and stability of photocatalytic reduction was studied by adjusting the content of PANI on Mesoporous TiO₂ (MT) surface. Under the irradiation conditions, the reaction results showed that the reduction rate was 100%, and the maximum reaction rate reached 0.62 min^-1 when the PANI modification was 3.0%. Moreover, the results showed that the reduction performance remained 100% after ten cycles. The main reason is that the PANI modified on the surface of TiO₂ is rich in positively charged amino group, which can efficiently adsorb the reactant Cr(VI), and make the product Cr(III) leave the reaction interface quickly, thus ensuring the performance of photocatalyst.

2D MXene-derived Nb2O5/C/Nb2C/g-C3N4 heterojunctions for efficient nitrogen photofixation

Novel 2D MXene-derived Nb₂O₅/C/Nb₂C/g-C₃N₄ showed a high nitrogen reduction rate in water (0.365 mmol h⁻¹ g_cat⁻¹); the nitrogen reduction efficiency could be further promoted 2.5 times (0.927 mmol h⁻¹ g_cat⁻¹) with the optimized pH of 9.

Copper nanocrystals anchored on an O-rich carbonized corn gel for nitrogen electroreduction to ammonia

Copper nanocrystals anchored on an O-rich carbonized corn gel for electrochemical N₂ fixation to NH₃ with a faradaic efficiency of 25.89% and an NH₃ yield rate of 1514 μg h⁻¹ mg_Cu⁻¹ at −0.3 V versus an RHE in 0.1 M Na₂SO₄.