Photocatalytic N2 Fixation Research Articles

Magnetic‐Field‐Stimulated Efficient Photocatalytic N2 Fixation over Defective BaTiO3 Perovskites

AbstractEfficient coupling solar energy conversion and N2 fixation by photocatalysis has been shown promising potentials. However, the unsatisfied yield rate of NH3 curbs its forward application. Defective typical perovskite, BaTiO3, shows remarkable activity under an applied magnetic field for photocatalytic N2 fixation with an NH3 yield rate exceeding 1.93 mg L−1 h−1. Through steered surface spin states and oxygen vacancies, the electromagnetic synergistic effect between the internal electric field and an external magnetic field is stimulated. X‐ray absorption spectroscopy and density functional theory calculations reveal the regulation of electronic and magnetic properties through manipulation of oxygen vacancies and inducement of Lorentz force and spin selectivity effect. The electromagnetic effect suppresses the recombination of photoexcited carriers in semiconducting nanomaterials, which acts synergistically to promote N2 adsorption and activation while facilitating fast charge separation under UV‐vis irradiation.

The metallic 1T-WS2 as cocatalysts for promoting photocatalytic N2 fixation performance of Bi5O7Br nanosheets

Recently, widespread attention has been devoted to the typical layered BiOCl or BiOBr because of the suitable nanostructure and band structure. However, owing to the fast carrier recombination, the photocatalytic performance of BiOX materials is not so satisfactory. Loading 1T phase WS2 nanosheets (NSs) onto Bi5O7Br NSs can improve the photocatalytic N2 fixation activity. Among these, the obtained 1T-WS2@Bi5O7Br composites with optimum 5% 1T-WS2 NSs display a significantly improved photocatalytic N2 fixation rate (8.43mmolL−1h−1g−1), 2.51 times higher than pure Bi5O7Br (3.36mmolL−1h−1g−1). And the outstanding stability of 1T-WS2@Bi5O7Br-5 composites is also achieved. Exactly, the photoexcited electrons from Bi5O7Br NSs are quickly transferred to conductive 1T phase WS2 as electron acceptors, which can promote the separation of carriers. In addition, 1T-WS2 NSs can provide abundant active sites on the basal and edge planes, which can promote the efficiency of photocatalytic N2 fixation. This work offers a novel solution to improve the photocatalytic performance of Bi5O7Br NSs.

Photocatalytic N2 fixation by plasmonic Mo-doped TiO2 semiconductor

Photocatalytic N2 fixation has attracted substantial attention in recent years, as it represents a green and sustainable development route toward efficiently converting N2 to NH3 for industrial applications. How to rationally design catalysts in this regard remains a challenge. Here we propose a strategy that uses plasmonic hot electrons in the highly doped TiO2 to activate the inert N2 molecules. The synthesized semiconductor catalyst Mo-doped TiO2 shows a NH3 production efficiency as high as 134 µmol·g−1·h−1 under ambient conditions, which is comparable to that achieved by the conventional plasmonic gold metal. By means of ultra-fast spectroscopy we reveal that the plasmonic hot electrons in the system are responsible for the activation of N2 molecules, enabling improvement the catalytic activity of TiO2. This work opens a new avenue toward semiconductor plasmon-based photocatalytic N2 fixation.

Quantifying the photocatalytic role and activity at the edge and surface of Pd co-catalysts using N2 fixation as a case

A protocol to quantitatively determine the atom-specific catalytic activities of the edge and surface atoms on metal co-catalysts toward photocatalytic N2 fixation was presented, and the higher catalytic activity of the edge atoms was proved.

Enhanced photocatalytic nitrogen fixation in BiVO4: constructing oxygen vacancies and promoting electron transfer through Ohmic contact

The Ag nanoparticles deposited on the surface of BiVO4 containing oxygen vacancies are employed in photocatalytic N2 fixation. The NH3 generation rate is enhanced by constructing abundant oxygen vacancies and promoting electron transfer by Ohmic contact.

High-impressive separation of photoinduced charge carriers on step-scheme ZnO/ZnSnO3/Carbon dots heterojunction with efficient activity in photocatalytic NH3 production

Photocatalytic N2 fixation has been overgrowing since the 20th century because the Haber–Bosch process is more energy-intensive. Therefore other sustainable alternatives are highly needed. A simple procedure for constructing novel ZnO/ZnSnO3/Carbon Dots hybrid nanocomposites was exhibited through the hydrothermal approach. The surface morphology, crystal structure, and phase of the designed nanomaterials were assayed with various analyses. In this research paper, photocatalytic N2 fixation induced by ternary ZnO/ZnSnO3/Carbon Dots system. The results displayed that the ZnO/ZnSnO3/Carbon Dots (0.5 mL) system has remarkable activity in the N2 fixation process compared with the sole ZnO and ZnO/ZnSnO3 (30%), which is 11.5 and 2.1 times, respectively. The durability of the optimum system, as an essential character of the nanocomposite, was assayed in four recycles. Moreover, the effect of solvent, electron scavenger and media pH in the NH4+ generation rate was investigated. At last, a suitable mechanism was offered for the notable N2 photofixation improvement. This novel information could clarify the construction of impressive systems for nitrogen photofixation.

2D g-C3N4 as a bifunctional photocatalyst for co-catalyst and sacrificial agent-free photocatalytic N2 fixation and dye photodegradation

Photocatalytic N2 fixation is an ecofriendly technology to produce ammonia.

A novel Bi2S3/KTa0.75Nb0.25O3nanocomposite with high efficiency for photocatalytic and piezocatalytic N2fixation

A Bi2S3/KTa0.75Nb0.25O3(KTN) nanocomposite was synthesizedviaa two-step hydrothermal method and first applied in piezo-/photocatalytic N2fixation.

Site-exposed Ti3C2 MXene anchored in N-defect g-C3N4 heterostructure nanosheets for efficient photocatalytic N2 fixation

Exposed Ti sites with high activity and selectivity can efficiently accept photoinduced electrons from N-defects in g-C3N4 for photocatalytic N2 fixation.

A new nitrogen fixation strategy: the direct formation of *N2− excited state on metal-free photocatalyst

For photocatalytic N2 fixation, electrons at the valence-band edge of the photocatalyst can be directly excited to π* orbitals, which not only significantly activates N2, but also effectively improves the selectivity.

Novel N-Black In2O3−x/InVO4 heterojunction for efficient photocatalytic fixation: synergistic effect of exposed (321) facet and oxygen vacancy

A novel N-Black In2O3−x/InVO4 catalyst was designed by coupling InVO4 nanosheets into defect-rich N-Black In2O3−x nanorods to construct multiple heterojunctions using the NH2-MIL-68(In) as a template for efficient photocatalytic N2 fixation.

Efficient photocatalytic H2 evolution, CO2 reduction and N2 fixation coupled with organic synthesis by cocatalyst and vacancies engineering

Photocatalytic conversion of solar energy into fine chemicals or renewable fuels is an attractive strategy to achieve sustainable and ecological development. Herein, 2D/2D-3D Ni12P5/ZnIn2S4 (NP/ZIS) heterostructures are prepared via zinc vacancies (VZn) engineering and cocatalyst modification. The NP/ZIS presents efficient reactivity and stability for visible-light-driven photocatalytic splitting of benzyl alcohol into H2 and benzaldehyde at room temperature due to significantly improved charge carrier separation and transportation via the VZn defect level, the downward band bending and the Coulomb attraction. Compared to pure water splitting and individual ZIS, the thermodynamics and kinetics of H2 production over 7% NP/ZIS are enhanced by 15825.6 and 12.2 times, respectively. Notably, NP/ZIS also shows promising capability for photocatalytic CO2 reduction and N2 fixation coupled with organic synthesis. This work offers a practical plane to fabricate efficient photocatalysts and sheds light on promising reaction to simultaneous utilize photoexcited holes and electrons toward solar-to-chemical energy conversion.

Defect and Interface Engineering on Two‐Dimensional Nanosheets for the Photocatalytic Nitrogen Reduction Reaction

AbstractReducing dinitrogen (N2) to ammonia (NH3) under mild conditions is a very significant nitrogen cyclic process, which plays a vital role in agricultural, biological and industrial fields. The Haber‐Bosch process as a current mainstream way of N2 fixation has particularly high energy consumption, occupying about 1 % of the world energy production. In contrast, the photocatalytic N2 reduction reaction provides a green route almost without energy consumption and environmental pollution. However, there are many challenges that needs to be solved urgently, such as, for example, low quantum yield, inefficient N2 adsorption and activation and an unclear N2 fixation mechanism. Nowadays, tactics for improving the catalytic performance mainly focus on producing more active sites via defect or interface engineering. Generally, two‐dimensional materials with defect or interface engineering can not only accelerate photon‐exciton interactions, but also enhance sufficient N2 binding, activation and hydrogenation. In this Minireview, we will first summarize the principles of photocatalytic N2 fixation, and then discuss progress in the development two‐dimensional (2D) materials with defect and interface engineering for photocatalytic N2 fixation. Finally, we describe ammonia detection methods and recent important developments and challenges in this field.

Enhanced photocatalytic N2 fixation via defective and fluoride modified TiO2 surface

Photocatalytic N2 fixation (PNF) provides a low-cost route to generate ammonia. The poor conversion efficiency from photon to ammonia seriously hinders the step forward because of the low concentration of N2 molecules. Herein, we demonstrate a photocatalyst with surface oxygen vacancies (Vo) and a F modified surface to facilitate N2 adsorption and activation on the surface of catalysts. The Vo site promotes the chemical adsorption of N2, electron transfer from catalyst to N2. F modification switches the TiO2 surface properties from hydrophilic to aerophilic, thus facilitating the adsorption of N2. Meanwhile, the hydrogen reduction reaction (HER) is suppressed, as protons hard to adsorb on F capped surfaces. The optimal NH3 production rate can reach 206 μmolh−1g−1, which is ∼ 9 times higher than that of pure TiO2 nanoparticles (∼23 μmolh−1g−1). This report provides a potential strategy to overcome mass transfer limitation and achieve a high conversion efficiency in PNF.

Creation of rich oxygen vacancies in bismuth molybdate nanosheets to boost the photocatalytic nitrogen fixation performance under visible light illumination

There is a huge demand for ammonia worldwide due to its extensive utilization in various technical applications. However, its production is still dependent on the traditional Haber-Bosch process under high temperature and pressure, which has enormous pressure on both the world energy supply and global warming issue. In this work, bismuth molybdate nanosheets rich in oxygen vacancies were created via NaOH treatment of bismuth molybdate nanosheets by a simple, robust and cost-effective process of NaOH etching treatment at room temperature to boost the photocatalytic nitrogen fixation to produce ammonia under visible light illumination at room temperature and ambient pressure. It was found that rich oxygen vacancies largely improved both the photogenerated charge carrier separation and N2 adsorption/activation capabilities of bismuth molybdate nanosheets. Thus, an enhanced, stable photocatalytic N2 fixation performance with a superior average ammonia production rate of near 800 μmol·g−1·h−1 was achieved under visible light illumination in repeated uses. Even better photocatalytic N2 fixation performance was observed under simulated solar illumination. The photocatalyst showed good tolerance to oxygen, allowing the use of air rather pure N2 in the reaction. Thus, it is promising for ammonia production from the photocatalytic N2 fixation with solar energy by these bismuth molybdate nanosheets with rich oxygen vacancies, which could provide a greener and more sustainable alternative than the traditional Haber-Bosch process.

Black Phosphorus and Carbon Nitride Hybrid Photocatalysts for Photoredox Reactions

AbstractThe development of metal‐free photocatalysts with high efficiency, stability, and broadband solar absorption is a major challenge to realize green and sustainable chemical development. Recently, metal‐free nanohybrids (BP/CN) composed of black phosphorus (BP) and polymeric carbon nitride (CN) are emerged as photocatalytic hybrids with broadband light‐harvesting capabilities and higher photocatalytic performance. Herein, the latest progress of BP/CN hybrids for multifarious photoredox reactions is summarized. The different heterojunction types of BP/CN hybrid photocatalysts, including type I, type II, and multicomponent heterojunctions, are illustrated. Furthermore, the relevant applications of BP/CN hybrid photocatalysts for photocatalytic water splitting, CO2 photoreduction, N2 fixation, H2O2 production, pollutant decomposition, and bacterial inactivation are discussed. An overview of the challenge in this area and the directions for the future is presented.

Monolayered g-C3N4 nanosheet as an emerging cationic building block for bifunctional 2D superlattice hybrid catalysts with controlled defect structures

New class of superlattice nanohybrids of interstratified graphitic-carbon nitride (g-C3N4)–transition metal dichalcogenide monolayers are synthesized by employing pH-controlled g-C3N4 nanosheet (NS) as an emerging cationic building block. The interstratification of g-C3N4 and MoS2 NSs leads to strong interfacial electronic coupling, creation of nitrogen vacancy, and stabilization of 1T′-MoS2 phase. The superlattice g-C3N4–MoS2 nanohybrids display remarkably enhanced bifunctionality as photocatalysts for visible light-induced N2 fixation and electrocatalysts for hydrogen evolution. Of prime importance is that the creation of nitrogen vacancy results in the significant improvement of selectivity for photocatalytic N2 fixation (582 μmolL−1h−1) over competitive photocatalytic H2 generation. This is attributable to promoted adsorption of nitrogen, provision of many active sites, and enhancement of charge transfer kinetics, charge separation, and visible light absorptivity. This study highlights that the application of g-C3N4 NS as a cationic building block provides valuable opportunity to widen the library of multifunctional NS-based superlattice nanohybrids.

Toward visible-light-assisted photocatalytic nitrogen fixation: A titanium metal organic framework with functionalized ligands

The fixation of atmospheric dinitrogen to ammonia is one of the most essential processes for sustaining life. Since the NN bond in dinitrogen is one of the strongest bonds in chemistry, it remains a grand challenge to develop efficient catalysts for fixation of N2 under ambient conditions. Herein we report for the first time on visible-light-assisted photocatalytic nitrogen fixation by metal organic framework material at room temperature and pressure. The Ti3+ species induced by electron transfer from ligand-to-metal charge transfer process provide active sites for N2 reduction. Furthermore, visible-light-assisted photocatalytic N2 fixation is achieved by ligands functionalization which extend the light harvesting of the MOF to visible region. The integration of Ti sites and amine-functionalized linkers in NH2-MIL-125 (Ti) shows the highest visible light photocatalysis efficiency at a rate of 12.3 μmol g−1 h−1. This Ti MOF system therefore shows a potential as a new design of combining light-harvesting and catalytic components in a single solid platform for green NH3 production.

Bandgap engineering via boron and sulphur doped carbon modified anatase TiO2: a visible light stimulated photocatalyst for photo-fixation of N2 and TCH degradation.

The present research reports the synthesis of two-dimensional (2D) sheet/flake-like nanostructures of crystalline carbon modified TiO2 (CT), B-TiO2 (B-CT), and S-TiO2 (S-CT) using a facile one-pot synthesis method. The crystallinity and phase purity (anatase) of the prepared nano-photocatalyst were characterised using X-ray diffraction, selected area electron diffraction (SAED) and high-resolution transmission electron microscopy (HRTEM) analysis. Furthermore, the morphological details and elemental content of the sample were studied via scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS), respectively. Additionally, the optoelectronic features of all of the prepared specimens were measured via UV-vis diffuse reflectance spectroscopy (DRS), photoluminescence (PL), impedance and Mott–Schottky studies. After successful characterisation, their photocatalytic performance was tested towards dinitrogen photo-fixation and tetracycline hydrochloride (TCH) degradation under visible light illumination. Moreover, the effective charge separation and greater availability of the active surface area led to the robust photocatalytic activity of the fabricated B-CT compared to the CT and S-CT samples, which correlates well with the PL, impedance and surface area analysis. B-CT displays the highest photocatalytic activity, i.e. 32.38 μmol L−1 (conversion efficiency = 0.076%) of ammonia production, and 95% tetracycline hydrochloride (10 ppm) degradation. Here, we have effectively designed a novel and productive pathway towards the enhancement of the photocatalytic performance of visible photon active TiO2-based materials for energy and environmental sustainability.

Preparation of a NiO/KNbO3 nanocomposite via a photodeposition method and its superior performance in photocatalytic N2 fixation

A p-NiO/n-KNbO3 heterojunction photocatalyst was synthesized via a photodeposition method and for the first time applied in photocatalytic N2 fixation under simulated sunlight.