Photocatalytic Ammonia Synthesis Research Articles

Boosting photocatalytic reduction of nitrate to ammonia enabled by perovskite/biochar nanocomposites with oxygen defects and O-containing functional groups

Photocatalytic ammonia synthesis from waste nitrate has emerged as a promising strategy in water treatment; however, the conversion and selectivity still remain a great challenge. Herein, recyclable magnetic perovskite (LaFeO3)/biochar nanocomposites were successfully synthesized by the co-pyrolysis of the lotus biomass and Fe/La salts without extra organic complexants. Results showed that the lotus interacted with the iron ions (Fe3+) and the lanthanum ions (La3+) changing the surface and structural characteristics of catalysts. Oxygen defects of LaFeO3 were enhanced due to biomass introduction, which accelerated the separation of electron-hole pairs. On the other hand, Fe/La salts participated in the modification process of the biochar surface during the carbonization, which promoted the exposure of oxygen-containing functional groups and aromatic structures facilitating the nitrate adsorption. Notably, the redox-active quinone/phenol groups on the biochar surface contributed to the photogenerated electrons exchange favoring the ammonium ion (NH4+) selectivity as direct electron donor. Nitrate conversion reached 98% and ammonia selectivity reached 97% over the LaFeO3/biochar photocatalyst under visible light irradiation, when the mass ratio of lotus and Fe/La salts was optimized. Our findings may potentially provide a green and cost-effective way for ammonia recovery from nitrate contaminants.

Enhanced photocatalytic ammonia synthesis over a Bi/carbon cloth float: triphase reaction system-assisted N2supply and photothermal co-activation

A novel Bi/CC float is designed to construct a gas–solid–liquid triphase reaction system for improved photocatalytic ammonia synthesis.

Active Site Engineering in Heterovalent Metal Organic Frameworks for Photocatalytic Ammonia Synthesis

Active Site Engineering in Heterovalent Metal Organic Frameworks for Photocatalytic Ammonia Synthesis

Modular assembly of electron transfer pathways in bimetallic MOFs for photocatalytic ammonia synthesis

Our work proposed the EPE strategy for the sustainable development of MOF-based photocatalysts with concerted electron transfer and utilization.

Multi-stepwise electron transfer via MOF-based nanocomposites for photocatalytic ammonia synthesis

Our study proposed a multi-stepwise electron transfer strategy to offer a method for designing MOF-based nanocomposite photocatalysts with the intensified electron transfer process.

Efficient full-spectrum driven ammonia synthesis over heterostructured TiO2 nanosheet arrays.

Here, we report that efficient photocatalytic ammonia synthesis was realized across the entire solar spectrum by using Ru modified anatase/TiO2(B) heterostructured nanosheet arrays. The superior NH3 production rates of 2004 μg h-1 g-1 and 521 μg h-1 g-1 were achieved under visible light (400 nm) and near-infrared-light (1550 nm) irradiation, respectively.

Photocatalytic Ammonia Synthesis: Mechanistic Insights into N2 Activation at Oxygen Vacancies under Visible Light Excitation

Photocatalytic Ammonia Synthesis: Mechanistic Insights into N₂ Activation at Oxygen Vacancies under Visible Light Excitation

Carbon defective carbon nitride with large specific surface area by hot oxygen etching for promoting photocatalytic performance

Defect engineering is an extremely powerful strategy for carbon nitride materials. In our paper, carbon defective-carbon nitride (V-g-C3N4) with a large specific surface area (555.3 m2 g−1) was prepared by multiple thermal and oxygen etching using urea as a precursor. The photocatalytic performance of the materials was evaluated by synthetic ammonia under visible light and full spectrum. Under visible light, V-g-C3N4 can produce 3.60 mmol/h/g of NH3, which is approximately ~ 3.24 times higher than that of g-C3N4. Under the sunlight, V-g-C3N4 can produce 21.35 mmol/h/g of NH3. Particularly, positron annihilation lifetime spectroscopy (PALS) was used to confirm the type of vacancies. The experimental results show that the method of multiple calcinations not only can successfully introduce the carbon vacancy into the polymerization network structure of carbon nitride, resulting in a large number of active sites are added for the reaction of ammonia synthesis, but also can expand the bandgap from 2.82 eV to 3.03 eV. In addition, After g-C3N4 was exposed to high temperature and weak oxygen three times, its structure became loose and porous, which also provides more active sites for the reaction. Herein, these findings provide a novel concept of introducing carbon vacancies to promote the efficiency of photocatalytic ammonia synthesis.

Advancement of Bismuth‐Based Materials for Electrocatalytic and Photo(electro)catalytic Ammonia Synthesis

AbstractAmmonia (NH3) plays a vital role in the fertilizer industry, nitrogen‐containing chemical production, and hydrogen storage. The development of electrocatalytic and photo(electro)catalytic nitrogen reduction reaction (NRR) to synthesize NH3 are desirable, which are more environmentally friendly than the conventional Haber–Bosch process. Due to the strong nonpolar bonding of the NN bond, the discovery of efficient catalysts is essential to overcome the high kinetic barrier. Here, bismuth‐based materials that show proven activities for NRR are highlighted. The fundamental knowledge, including thermodynamics, mechanisms, reaction systems, evaluation aspects of NRR, and product quantification, is introduced. Together with scientific reasoning and exhibited activities, the strategies for improving the performance are discussed in detail. Perspective and outlook, as well as the opportunities to further develop bismuth‐based materials for NH3 synthesis, are provided. This review aims to provide a comprehensive understanding of the advancement in this field and serves as a guide for the future design of highly efficient NRR catalysts.

Electronic and Interface Regulation of Wurtzite Surfaces Promotes Photocatalytic Ammonia Synthesis under Visible Light Irradiation

Electronic and Interface Regulation of Wurtzite Surfaces Promotes Photocatalytic Ammonia Synthesis under Visible Light Irradiation

Boosting Nitrogen Activation via Bimetallic Organic Frameworks for Photocatalytic Ammonia Synthesis

Photocatalytic ammonia synthesis from N2 is a carbon-neutral strategy, although its efficiency is impeded by the activation of inert N≡N triple bonds. In N2 activation, the electron acceptance process is often strongly coupled with the electron donation process, leading to a high potential activation energy barrier and low photocatalytic activity. Herein, we proposed a strategy to decouple these two processes by bimetallic organic frameworks (BMOFs) for boosting N2 activation. The rationally designed BMOFs are composed of two functional metal nodes, in which the hard acid metal node with a high ionization potential (In) accepts the electron from N2 and the soft acid metal node with a low In donates the electron to N2. Owing to the bimetal synergistic effect, the potential activation energy barrier of N2 is reduced, as confirmed by the in situ Fourier transform infrared (FTIR) spectra and density functional theory (DFT) calculations. Via testing six kinds of bimetal combinations, it is found that, as the ionization potential difference (ΔIn) between the two metals is ≥6 eV and the proportion of high In metal reaches ∼20%, the bimetal synergistic effect becomes dominant. In all the as-prepared BMOFs, the optimal BMOF(Sr)–0.2Fe photocatalyst exhibits an NH3 evolution rate up to 780 μmol g–1 h–1. This work may unveil a corner of the hidden mechanism for the chemical bond activation in a broad range of catalytic processes.

3D hollow Bi2O3@CoAl-LDHs direct Z-scheme heterostructure for visible-light-driven photocatalytic ammonia synthesis

In this paper, the novel 3D hollow Z-scheme heterojunction photocatalysts based on Bi2O3 and CoAl layered double hydroxides (Bi2O3@CoAl-LDHs) were prepared for efficient visible-light-driven photocatalytic ammonia synthesis. The synthesized nanohybrid exhibits excellent photocatalytic ammonia synthesis performance (48.7 μmol·L−1·h−1) and structural stability, which is primarily attributed to the fact that Z-scheme heterojunction significantly enhanced lifetime of photogenerated carriers (6.22 ns) and transfer efficiency of surface photogenerated electrons (72.5%). Strict control experiments and nitrogen isotope labeling results show that nitrogen and hydrogen in the produced ammonia come from nitrogen and water in the reactant respectively. Electron paramagnetic resonance (EPR) experiments and density functional theory (DFT) calculations further reveal that the built-in electric field due to the difference between Bi2O3 and CoAl-LDHs is the key to constructing the Z-scheme heterojunction. In addition, results of partial density of states (PDOS) show that Co in Bi2O3@CoAl-LDHs composite is the active site for photocatalytic N2 fixation.

Precise location and regulation of active sites for highly efficient photocatalytic synthesis of ammonia by facet-dependent BiVO4 single crystals

Based on the characterizations of photo-deposition experiment, environmental transmission electron microscopy (ETEM) and scanning fluorescence X-ray microscopy (SFXM) for the in-situ photocatalytic nitrogen reduction reaction (pNRR) on different facets as well as theoretical calculation, we confirmed that the cycle of oxygen vacancy-V4+/V5+ (OV-V4+/V5+) on (040) facet is the exact active site for the photocatalytic NRR (pNRR) by bismuth vanadate (BiVO4) single crystal. V4+ plays the role of chemisorption of N2, V5+ is electron transfer bridge, and the photogenerated electrons trapped in OV provide the driving force for ammonia synthesis. (110) facet has only V5+, which can not produce the start-up step of chemisorption of N2, so it is the inert facet of pNRR. Thus, NRR activity increases linearly with the increase of (040)/(110) facet ratio by adjusting the active sites on (040) facet, and the highest activity can reach 103.4 μmol g−1 h−1 without sacrifice reagent. Based on the discussion of real active sites and their transformation in photocatalytic NRR by facet-dependent BiVO4, we not only analyze the essential reason why exposing specific facets can greatly improve the photocatalytic activity, but also put forward a new viewpoint on the activity control of photocatalytic ammonia synthesis.

Atomic-level insights into the activation of nitrogen via hydrogen-bond interaction toward nitrogen photofixation

Summary As the activation of N2 molecules is generally regarded as the bottleneck in N2 reduction, it is of significant importance to develop promising strategies to efficiently activate N2 molecules. Herein, we discovered an innovative approach to activate N2 molecules via hydrogen-bond interaction in N2 photofixation. Porous Cu with surface modification of S atoms (3%-S/Cu) exhibited remarkable catalytic activity and stability in N2 photofixation. Further mechanistic studies revealed that surface S atoms directly participated in the catalytic process by accepting and donating H atoms. In addition, the forming S–H bond significantly promoted the activation of N2 molecules via hydrogen-bond interaction, contributing to the enhanced catalytic activity.

Emerging Materials and Methods toward Ammonia-Based Energy Storage and Conversion.

Efficient storage and conversion of renewable energies is of critical importance to the sustainable growth of human society. With its distinguishing features of high hydrogen content, high energy density, facile storage/transportation, and zero-carbon emission, ammonia has been recently considered as a promising energy carrier for long-term and large-scale energy storage. Under this scenario, the synthesis, storage, and utilization of ammonia are key components for the implementation of ammonia-mediated energy system. Being different from fossil fuels, renewable energies normally have intermittent and variable nature, and thus pose demands on the improvement of existing technologies and simultaneously the development of alternative methods and materials for ammonia synthesis and storage. The energy release from ammonia in an efficient manner, on the other hand, is vital to achieve a sustainable energy supply and complete the nitrogen circle. Herein, recent advances in the thermal-, electro-, plasma-, and photocatalytic ammonia synthesis, ammonia storage or separation, ammonia thermal/electrochemical decomposition and conversion are summarized with the emphasis on the latest developments of new methods and materials (catalysts, electrodes, and sorbents) for these processes. The challenges and potential solutions are discussed.

TiO2 doped HKUST-1/CM film in the three-phase photocatalytic ammonia synthesis system

Photocatalytic synthesis of ammonia from N2 and H2O at room temperature and atmospheric pressure is considered to be a safe, clean and sustainable method. Due to the low solubility and diffusion coefficient of nitrogen in water, the rate of ammonia synthesis is significantly hindered. As a result, we develop a kind of thin film photocatalyst, which can be used in gas-liquid-solid three phase reaction system to solve this problem. The catalyst bases on HKUST-1 thin film with high nitrogen adsorption performance and supported with TiO2 nanoparticles with photocatalytic nitrogen fixation performance. The constructed binary composite photocatalyst has a stable structure under a 300 W xenon lamp, which exhibits good photoelectric conversion performance. While characterizing the structure and photoelectric performance of the material, the performance of photocatalytic ammonia synthesis was investigated. The highest ammonia synthesis efficiency was 0.048 μmol·h−1·cm−2, and its performance was 2.8 times that of TiO2/CM catalyst under the same conditions. The thin film catalyst does't contain any N substance and won't interfere with the ammonia synthesis reaction. The preparation process is simplified by directly using the copper source in the CM without additional metal reagent. Moreover, it provides a new idea for the design of photocatalytic catalysts for ammonia synthesis.

Progress and challenges in photocatalytic ammonia synthesis

This review puts forward a few critical issues existing in nitrogen photoreduction apart from discussion of the efficient strategies for improvement of NH3 synthesis.

Phase-selective active sites on ordered/disordered titanium dioxide enable exceptional photocatalytic ammonia synthesis.

Photocatalytic N2 fixation to NH3via defect creation on TiO2 to activate ultra-stable N Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> N has drawn enormous scientific attention, but poor selectivity and low yield rate are the major bottlenecks. Additionally, whether N2 preferentially adsorbs on phase-selective defect sites on TiO2 in correlation with appropriate band alignment has yet to be explored. Herein, theoretical predictions reveal that the defect sites on disordered anatase (Ad) preferentially exhibit higher N2 adsorption ability with a reduced energy barrier for a potential-determining-step (*N2 to NNH*) than the disordered rutile (Rd) phase of TiO2. Motivated by theoretical simulations, we synthesize a phase-selective disordered-anatase/ordered-rutile TiO2 photocatalyst (Na-Ad/Ro) by sodium-amine treatment of P25-TiO2 under ambient conditions, which exhibits an efficient NH3 formation rate of 432 μmol g−1 h−1, which is superior to that of any other defect-rich disordered TiO2 under solar illumination with a high apparent quantum efficiency of 13.6% at 340 nm. The multi-synergistic effects including selective N2 chemisorption on the defect sites of Na-Ad with enhanced visible-light absorption, suitable band alignment, and rapid interfacial charge separation with Ro enable substantially enhanced N2 fixation.

Functional group defect design in polymeric carbon nitride for photocatalytic application

Defects are conventionally considered as the active sites in heptazine-based polymer melon (also known as graphitic carbon nitride, g-C3N4) for photocatalysis and are rationally incorporated for improving the intrinsic photocatalytic ability. The rise of group functionalized g-C3N4 based on defect engineering has set off a new wave of research in recent years, especially in photocatalysis. In this review, the recent process in functional group defect strategies to design high-efficiency g-C3N4-based photocatalysts, including cyanamide/cyano moiety, urea group, oxygen-containing groups (—OH, —COOH), and aromatic motifs, has been strictly analyzed so as to inspire critical thinking about the efficient methodology for the rational design of polymeric photocatalysts. The applications of the group functionalized g-C3N4 in photocatalytic water splitting, CO2 reduction, H2 evolution, ammonia synthesis, H2O2 production, and disinfection are summarized. The current challenges and future promising applications of the group functionalized g-C3N4 materials for advanced catalysts are also discussed.

Computational Study of Transition-Metal Substitutions in Rutile TiO2 (110) for Photoelectrocatalytic Ammonia Synthesis

Synthesis of ammonia through photo- and electrocatalysis is a rapidly growing field. Titania-based catalysts are widely reported for photocatalytic ammonia synthesis and have also been suggested as electrocatalysts. The addition of transition-metal dopants is one strategy for improving the performance of titania- based catalysts. In this work, we screen d-block transition- metal dopants for surface site stability and evaluate trends in their performance as the active site for the reduction of nitrogen to ammonia on TiO2. We find a linear relationship between the d-band center and metal substitution energy of the dopant site, while the binding energies of N2, N2H, and NH2 all are strongly correlated with the cohesive energies of the dopant metals. The activity of the metal-doped systems shows a volcano type relationship with the NH2 and N2H energies as descriptors. Some metals such as Co, Mo, and V are predicted to slightly improve photo- and electrocatalytic performance, but most metals inhibit the ammonia synthesis reaction. The results provide insight into the role of transition-metal dopants for promoting ammonia synthesis, and the trends are based on unexpected electronic structure factors that may have broader implications for single-atom catalysis and doped oxides.