Photocatalytic Reduction Of Nitrate Research Articles

Nanoarchitectonics of S-Scheme Heterojunction Photocatalysts: A Nanohouse Design Improves Photocatalytic Nitrate Reduction to Ammonia Performance.

Photocatalytic nitrate reduction reaction (NitRR) is a promising route for environment remediation and sustainable ammonia synthesis. To design efficient photocatalysts, the recently emerged nanoarchitectonics approach holds great promise. Here, we report a nanohouse-like S-scheme heterjunction photocatalyst with high photocatalytic NitRR performance. The nano-house has a floor of plate-like metal organic framework-based photocatalyst (NH2-MIL-125), on which another photocatalyst Co(OH)2 nanosheet is grown while ZIF-8 hollow cages are also constructed as the surrounding wall/roof. Experimental and simulation results indicate that the positively charged, highly porous and hydrophobic ZIF-8 wall can modulate the environment in the nanohouse by (i) NO3 - enrichment/NH4 + discharge and (ii) suppression of the competitive hydrogen evolution reaction. In combination with the enhanced electron-hole separation and strong redox capability in the NH2-MIL-125@Co(OH)2 S-scheme heterjunction confined in the nano-house, the designed photocatalyst delivers an ammonia yield of 2454.9 μmol g-1 h-1 and an apparent quantum yield of 8.02 % at 400 nm in pure water. Our work provides new insights into the design principles of advanced photocatalytic NitRR photocatalyst.

Nanoarchitectonics of S‐Scheme Heterojunction Photocatalysts: A Nanohouse Design Improves Photocatalytic Nitrate Reduction to Ammonia Performance

AbstractPhotocatalytic nitrate reduction reaction (NitRR) is a promising route for environment remediation and sustainable ammonia synthesis. To design efficient photocatalysts, the recently emerged nanoarchitectonics approach holds great promise. Here, we report a nanohouse‐like S‐scheme heterjunction photocatalyst with high photocatalytic NitRR performance. The nano‐house has a floor of plate‐like metal organic framework‐based photocatalyst (NH2‐MIL‐125), on which another photocatalyst Co(OH)2 nanosheet is grown while ZIF‐8 hollow cages are also constructed as the surrounding wall/roof. Experimental and simulation results indicate that the positively charged, highly porous and hydrophobic ZIF‐8 wall can modulate the environment in the nanohouse by (i) NO3− enrichment/NH4+ discharge and (ii) suppression of the competitive hydrogen evolution reaction. In combination with the enhanced electron‐hole separation and strong redox capability in the NH2‐MIL‐125@Co(OH)2 S‐scheme heterjunction confined in the nano‐house, the designed photocatalyst delivers an ammonia yield of 2454.9 μmol g−1 h−1 and an apparent quantum yield of 8.02 % at 400 nm in pure water. Our work provides new insights into the design principles of advanced photocatalytic NitRR photocatalyst.

Advancing the Understanding of Photocatalytic Nitrate Reduction for Ammonia Synthesis: Copper Catalysts and Formic Acid Synergy

Advancing the Understanding of Photocatalytic Nitrate Reduction for Ammonia Synthesis: Copper Catalysts and Formic Acid Synergy

How Plasmon Ag Nanoparticles can Enhance the Power Performance of a Thermoelectric Generator.

The development of wearable thermoelectric generators (wTEG) represents a promising strategy to replace batteries and supercapacitors required to supply electrical energy for portable electronic devices. However, the main drawback of wTEGs is that the thermal gradient between the skin and the ambient is minimal, reducing the power output produced by the generator. Therefore, it is necessary to improve the thermal management of wTEG in order to increase its efficiency. This work deals with the preparation of a thermoelectric generator that harnesses the plasmonic heating effect to enhance the thermal gradient of the final device. The thermoelectric layer is created through the in situ polymerization of terthiophene (3T) within a polyurethane matrix, utilizing silver (Ag) (I) and copper (II) perchlorate as oxidants. The plasmonic film, composed of Ag-NP (nanoparticles), is formed via photocatalytic reduction of silver nitrate in the presence of titanium oxide. These layers are then meticulously assembled to yield the hybrid plasmonic/thermoelectric generator.

Lewis acid-rich SrFexTi1−xO3/TiO2 to enhance the photocatalytic reduction of nitrate to N2

The photocatalytic reduction of nitrate has received considerable attention due to its high efficiency and environmentally friendly nature. The excessive addition of hole scavengers is the most commonly used method to increase the nitrate reduction efficiency. However, achieving high selectivity in the photocatalytic reduction of nitrate to N2 with low concentration of hole scavengers remains challenging. In this study, the SrFexTi1−xO3/TiO2 S-scheme heterojunction photocatalysts with many Lewis acidic adsorption sites have been developed. The experimental results demonstrated that the incorporation of 6% Fe into SrFe0.06Ti0.94O3/TiO2 (SFTO6) resulted in the nitrate conversion rate of 97.68% and the N2 selectivity reached 96.35% with 25 mmol/L formic acid. Moreover, it also exhibited excellent stability and recycle ability. After 5 cycles, SFTO6 still exhibited a stable photocatalytic denitration efficiency of 92.94%, highlighting its potential for practical application. Through comprehensive mechanistic investigations, enhancing direct reduction process is considered the key to its high reduction efficiency with low formic acid. And the Lewis acidic adsorption sites enhance N2 selectivity by enriching NOx− on the surface of the material. Overall, this study provides a novel approach for achieving efficient photocatalytic reduction of nitrate to N2 under conditions with low concentration of hole scavengers.

Photocatalytic Nitrate Reduction over TiO2 Layers on Glass Rings Generated by Dip‐Coating

AbstractThe support of powdered catalysts on mold bodies facilitates their handling and reusability. In case of photocatalytic applications, such as enhanced water purification processes, transparent supports with thin layers of the active material are desirable to obtain an optimal light efficiency. For the generation of such layers a precise control of layer thickness is crucial. Here, a multi‐step dip‐coating approach for the generation of TiO2 layers with varying thickness on glass rings is reported. Additionally, the coated glass rings were tested in the photocatalytic reduction of nitrate in aqueous solution under simulated sunlight.

Charge Photoaccumulation in Covalent Polymer Networks for Boosting Photocatalytic Nitrate Reduction to Ammonia.

In the design of photoelectrocatalytic cells, a key element is effective photogeneration of electron-hole pairs to drive redox activation of catalysts. Despite recent progress in photoelectrocatalysis, experimental realization of a high-performance photocathode for multi-electron reduction of chemicals, such as nitrate reduction to ammonia, has remained a challenge due to difficulty in obtaining efficient electrode configurations for extraction of high-throughput electrons from absorbed photons. This work describes a new design for catalytic photoelectrodes using chromophore assembly-functionalized covalent networks for boosting eight-electron reduction of nitrate to ammonia. Upon sunlight irradiation, the photoelectrode stores a mass of reducing equivalents at the photoexcited chromophore assembly for multielectron reduction of a copper catalyst, enabling efficient nitrate reduction to ammonia. By introducing the new photoelectrode structure, it is demonstrated that the electronic interplay between charge photo-accumulating assembly and multi-electron redox catalysts can be optimized to achieve proper balance between electron transfer dynamics and thermodynamic output of photoelectrocatalytic systems.

Unraveling Rigidified Superexchange Couplings in Organic Donor–Acceptor Polymers for Boosting the Photocatalytic Reduction of Nitrate

Unraveling Rigidified Superexchange Couplings in Organic Donor–Acceptor Polymers for Boosting the Photocatalytic Reduction of Nitrate

Efficient photocatalytic reduction of nitrate byproducts during anammox process by novel extracellular polymeric substances-embedded NH2-MIL-101(Fe) photocatalysts

Anaerobic ammonium oxidation (anammox) is an efficient nitrogen removal process; however, nitrate byproducts hampered its development. In this study, extracellular polymeric substances (EPS) were embedded into NH2-MIL-101(Fe), creating NH2-MIL-101(Fe)@EPS to reduce nitrate. Results revealed that chemical nitrate reduction efficiency of NH2-MIL-101(Fe)@EPS surpassed that of NH2-MIL-101(Fe) by 17.3 %. After adding 0.5 g/L NH2-MIL-101(Fe)@EPS within the anammox process, nitrate removal efficiency reached63.9 %, consequently elevating the total nitrogen removal efficiency to 92.4 %. 16S rRNA sequencing results elucidated the predominant role of Candidatus Brocadia within NH2-MIL-101(Fe)@EPS-anammox system. Concurrently, sufficient photogenerated electrons were transferred to microorganisms, promoting the growth of Desnitratisoma and OLB17. Additionally, photogenerated electrons activated flavin and Complex III, thereby up-regulating crucial genes involved in intra/extracellular electron transfer. Subsequently, denitrification and dissimilatory nitrate reduction to ammonium were activated to reduce nitrate. In summary, this study achieved a notable rate of photocatalytic nitrate reduction within anammox process through the NH2-MIL-101(Fe)@EPS photocatalysts.

Wide pH photocatalytic nitrate reduction at adaptive microenvironment-dominated liquid–liquid-solid trilayer reaction interfaces

Developing highly efficient photocatalysts with a wide pH application range is the key to achieving widespread practical application of photocatalytic denitrification. However, the current study neglects the limitations of diffusion and mass transfer efficiency in the reaction interfacial microenvironment on high activity and selectivity, resulting in the inability to achieve the ideal results. Herein, the photocatalytic NO3– reduction system with a microenvironment-dominated trilayer reaction interface of liquid (external liquid)-liquid (adaptive interfacial microenvironment)-solid (Br-Bi2WO6-x photocatalysts with different charge transfer mechanisms under acid/base conditions and hydrophilic surfaces) (LEL-LIM-S) was successfully constructed. The interfacial microenvironment in the system can self-adapt and adjust its ion composition according to the changes in the pH environment, which facilitates timely supplementation of NO3–/HCOO– required for the reaction from external liquid, thus maintaining the relative stability of the microenvironment and achieving an excellent NO3– removal rate of over 90 % in a wide pH range from 3 to 9. Meanwhile, the trilayer reaction interface of LEL-LIM-S collectively constitutes a unique carrier shuttle and molecular reaction channel from the catalyst interior to the surface contaminants. Highly selective NO3– to NH3 conversion (NH3 selectivity of 91.7 %, NH3 yield of 750 μmol g-1h−1) could be accomplished utilizing this channel.

Present State and Future Outlook of Ammonia Production through Photocatalytic Nitrate Reduction

Ammonia (NH3) production has gained increasing attention owing to its versatility in both industrial and agricultural applications, as well as its potential as a next‐generation energy carrier with a high hydrogen density. Given the energy‐intensive and environmentally impactful nature of the Haber–Bosch process, there is a pressing need for a sustainable NH3 synthesis method under ambient conditions. Nitrate (NO3−) emerges as a compelling nitrogen source due to its numerous advantages over inert nitrogen (N2) gas, such as its relatively low dissociation energy and high aqueous solubility. Moreover, NO3− is a common contaminant found in wastewater, posing a threat to aquatic ecosystems. The photocatalytic NO3− reduction to NH3, which utilizes sunlight to convert contaminants into value‐added chemicals, aligns perfectly with the need for sustainable solutions. This perspective reviews the latest advancements in the field of photocatalytic NO3− to NH3 conversion. The mechanism behind the conversion of NO3− to NH3 is briefly explained, and photocatalysts exhibiting high selectivity and activity in NH3 production, along with other influential factors, are summarized. Additionally, current challenges and future prospects within this field are discussed.This perspective will provide a valuable guidance for future research in the realm of photocatalytic NH3 production via NO3− reduction.

Enhanced photocarrier separation in Br substitution-induced [W(VI)O6−x] units for highly efficient photocatalytic nitrate reduction under alkaline conditions

Photocatalytic nitrate (NO3-) reduction is considered a promising green and non-polluting technology to solve the nitrate pollution of groundwater and surface water. Herein, a novel Br-substituted Bi2WO6−x ultrathin nanosheets were prepared by a simple hydrothermal method in a strong acid environment containing sixteen alkyl three methyl bromide (CTAB). The catalytic system solves the problems of low carrier separation efficiency, poor performance under alkaline conditions, and a hard-to-activate N = O bond, achieving efficient NO3- removal under alkaline conditions along with high N2 selectivity. It was confirmed that Br-substituted Bi2WO6−x produced the [W(VI)O6−x] units with a strong electron-withdrawing property by changing the polarity of the O-W-O bond. As a result, the effective space charge separation caused by the change of the W valence state and the spontaneous fracture behavior of the N = O bond improved the carriers utilization efficiency and distinctly reduced the reaction energy consumption, synergistically achieving excellent performance.

Photocatalytic ammonia synthesis from nitrate reduction on nickel single-atom decorated on defective tungsten oxide

Photocatalytic reduction of waste nitrate (NO3-) into value-added ammonia (NH3) under ambient conditions has enormous advantages over the Haber-Bosch process. However, weak adsorption capacity and low efficiency of photocatalysts limit its large-scale application. Here, Ni single-atom (SA) on defective WO3 (Ni/HxWO3−y) hybrids with abundant oxygen vacancies (OVs) are synthesized by a facile H-spillover process, which exhibits a high NH3 rate of 10.5 mmol gcat-1 h-1 and 98.26 % NH3 selectivity. In situ characterizations and theoretical calculations demonstrate the activity mainly derives from the synergetic effect of OVs and Ni SAs. That is, (1) photogenerated electrons and adsorbed NO3- transfer from OVs to Ni SAs; (2) the strong hybridizations of Ni 3d - O 2p orbitals of NO3- accelerate electron transfer from Ni SAs to NO3-; (3) Ni SAs effectively reduce the free energy of the rate-limiting step (NO2* → NO*) of HxWO3−y. In simulated wastewater, the durable performance of Ni/HxWO3−y hybrids proves great potential in industrial applications.

Atomically isolated copper on titanium dioxide for ammonia photosynthesis via nitrate reduction with unprecedently high apparent quantum yield

Photocatalytic nitrate (NO3) reduction to NH3 (PcNRA) is a sustainable alternative that is considered advantageous over N2 fixation, which suffers from the high dissociation energy and sluggish activation of inactive N2. Although PcNRA has recently been shown to achieve excellent selectivity, its sluggish kinetics restrict the NH3 production efficiency. Herein, we present a single-atom Cu-incorporated TiO2 nanosheet (Cu-TNS) photocatalyst for efficient and selective PcNRA. Single Cu atoms displacing Ti sites accumulate photogenerated electrons, ensuring efficient charge separation and surface NO3 reduction. Moreover, introducing Cu atoms into the TiO2 matrix induces spontaneous defect formation, resulting in oxygen vacancies and lattice strain that promote NO3 adsorption and activation. The simultaneous presence of single Cu atoms and structural defects in Cu-TNS synergistically stimulates PcNRA, leading to a 62-fold enhancement over pristine TiO2 in NH3 production with 97.6% selectivity and an unprecedently high apparent quantum yield of 11.7% at 330 nm under optimized conditions.

In Situ Growth of Perovskite on 2D Hydrothermal Carbonation Carbon for Photocatalytic Reduction of Nitrate to Ammonia

In Situ Growth of Perovskite on 2D Hydrothermal Carbonation Carbon for Photocatalytic Reduction of Nitrate to Ammonia

Synergistic effect of oxygen vacancies and built-in electric field in GdCrO3/BiVO4 composites for boosted photocatalytic reduction of nitrate in water

As a promising approach for nitrate nitrogen removal in water, photocatalysis required sufficient photogenerated charges to achieve a high photocatalytic efficiency. Herein, a novel GdCrO3/BiVO4 composite was prepared by the solid-state combustion method combined with hydrothermal treatment. The synergistic effect of oxygen vacancies introduced by chemical reduction method and built-in electric field formed in GdCrO3/BiVO4 heterostructures suppressed the charge recombination, which eventually improved the photocatalytic activity. Effects of photocatalyst composition, HCOOH dosage and oxygen vacancy concentration on photocatalytic activity were investigated. It was found that 0.30-GdBiOVs composites exhibited highest photocatalytic activity with nitrate removal ratio of 97.05% and N2 selectivity of 92.76% in 40 min. Moreover, end-products of nitrate nitrogen elimination and stability of photocatalysts were revealed. The existences of oxygen vacancies and built-in electric field were confirmed by EPR and HRTEM analyses. Ultimately, the possible mechanisms of nitrate nitrogen elimination were clarified.

Synergistic effect of single-atom Cu and hierarchical polyhedron-like Ta3N5/CdIn2S4 S-scheme heterojunction for boosting photocatalytic NH3 synthesis

Achieving synergy between single atomic site and charge transfer in heterojunction is significant for synthesising photocatalysts with excellent properties. In this paper, single atom Cu/Ta3N5/CdIn2S4 S-scheme hierarchical polyhedrons (SACu/TN/CIS SHPs) have been successfully synthesized by a three-step simple chemistry process. We dive into the improvement of photocatalytic activity in the synergistic effect of SACu and S-scheme. The excellent charge separation and reducing the energy barrier during the ammonium production reaction in the synergistic effect were confirmed by density functional theory (DFT) calculations and physicochemical mechanistic investigations. Electron spin resonance (ESR) corroborated production of reducing agent to accelerate the progress of NO3− to NH3. Under light conditions, the NH3 production rate for SACu/TN/CIS SHPs is an astonishing ∼43.6 times higher than that of original Ta3N5. This report not only recommends an efficient catalyst under visible light, but also proposes an advantageous solution for photocatalytic nitrate reduction in natural conditions.

Efficient nitrate reduction in water using an integrated photocatalyst adsorbent based on chitosan-titanium dioxide nanocomposite.

Globally, there exists a huge concern on the increased discharge of nitrates to the natural water resources out of various anthropogenic activities as it causes serious environmental pollution and associated harmful effects. In the present work, sol-gel-derived functional nanocomposites based on silver (Ag) and nitrogen (N)-doped titanium dioxide (TiO2)-coated chitosan nanocomposites were successfully synthesized in the form of beads, and their application for the reduction of nitrates in water was studied. The synthesized nanocomposite beads were characterized for their structural, textural, and morphological features using X-ray diffraction analysis, Fourier transform infrared spectroscopy, UV-visible spectroscopy, BET surface area analysis, Scanning electron microscopy, Transmission electron microscopy, and X-ray photoelectron spectroscopy. A uniform coating of doped titania species on the chitosan porous structure was achieved through electrostatic interaction. Adsorption/photocatalytic reduction of nitrates was further carried out using functional nanocomposite beads by monitoring the nitrate concentration of the model contaminated water, in an adsorption study under dark condition and photocatalytic study under UV/sunlight for a definite time period. Drying conditions of the nanocomposite beads were found to have a significant effect on the adsorption cum photocatalytic efficiencies of the nanocomposite. The freeze-dried chitosan-titania nanocomposite beads containing 0.5mol% Ag exhibited an adsorption efficiency of ~ 43.5% (under dark for 30min) and photocatalytic reduction capability of ~ 95% (under sunlight for 2h), whereas the oven dried beads of the same composition exhibits adsorption and photocatalytic efficiencies of 40% (under dark for 30min) and 70% (under UV light for 2h) respectively, towards the reduction of nitrate ions in an aqueous solution. Continuous flow adsorption cum photocatalytic study using the oven-dried nanocomposite beads was also carried out with the help of an experimental setup fabricated in-house and under varying experimental conditions such as flow rate, bed height, and concentration of feed solution. Nitrate reduction efficiency of 87.6% and an adsorption capacity of 7.9mgg-1 were obtained for the nanocomposite beads in the continuous flow adsorption cum photocatalysis experiment for up to 8h when using an inlet concentration of 100ppm, bed height 12cm, and flow rate 5.0mLmin-1. A representative fixed-bed column adsorption experiment performed with oven dried nanocomposite beads in a real groundwater sample collected from the Palakkad District of Kerala shows promising results for nitrate reduction (85.9% efficiency) along with a significant removal rate for the other anions as well. Thus, the adsorption cum photocatalytic nitrate reduction efficiency of the functional nanocomposite material makes them suitable for the reduction of nitrates from water/wastewater through an integrated nanocomposite approach.

Boosting light harvesting and charge separation over hollow double-shelled Ag@SrTiO3-TiO2 with Z-scheme heterostructure for highly efficient photocatalytic reduction of nitrate to N2

Hollow double-shelled Ag@SrTiO3-TiO2 with Z-scheme heterostructure was constructed for highly efficient photocatalytic reduction of nitrate to N2. The 3D finite-difference-time-domain analysis indicated that hollow double-shelled structure improved light harvesting due to multiple reflections. Photo-generated electrons transfer from SrTiO3 to Ag0 caused by electron sink effect were utilized to reduce nitrate, while photo-generated electrons of TiO2 migrated to SrTiO3 via transport bridge of Ti3+ defects for electron–hole recombination. Such charge carriers migration pathway facilitated the construction of Z-scheme heterostructure, which enhanced charge separation yet still retained high redox powers. Both photogenerated electrons and CO2− played important role in photocatalytic denitrification. Furthermore, Ag0 acted as co-catalyst which not only promoted photogenerated electrons transfer to nitrate but also enhanced nitrate conversion selectivity to N2. Combining the above advantages, nitrate removal rate and the nitrogen selectivity reached 97.2 % and 98.8 % within 60 min, respectively. Even after five cycles, it still remained satisfied photocatalytic activity and stability. In summary, this work proposed a feasible strategy to construct Z-scheme hollow double-shelled photocatalyst for efficient photocatalytic denitrification.

ZnS quantum dots implanted polyaniline-wrapped corn straw catalysts for efficient photocatalytic nitrate reduction without external addition of hole scavengers

Photocatalytic reduction to harmless nitrogen gas is considered a promising method for the removal of nitrate from water. However, achieving high efficiency of photocatalytic nitrate reduction, especially without the assistance of a hole scavenger, remains a critical issue. Herein, PANI-CS (PC) is prepared by in-situ polymerization of aniline on the surface of biomass corn straw, and then ZnS QDS is loaded to synthesize ZnS QDs-PANI-CS (ZPC) catalysts for photocatalytic reduction of nitrate. The optimized ZPC shows highly selective and efficient photocatalytic reduction of NO3– without extra sacrificial agents, with the 0.8% ZPC delivering an excellent nitrate removal rate of 98.4% and N2 selectivity of 96.8%. Outstanding catalytic performance is attributed to the ZPC having higher electron mobility and longer electron lifetime. Additionally, ZnS QDs induce the conversion of the quinone ring of PANI to the benzene ring, thereby improving the reducibility of the catalyst. Most importantly, The carbon–sulfur double bond on the ZnS quantum dots and the bicarbonate on the surface of the straw are the sources of formic acid, which provides great help for the production of CO2•- with reduction activity. The introduction of ZnS QDs also enriches the Lewis acid sites on the ZPC surface, thereby enhancing the N2 selectivity, and simultaneity, the stability of the composite is consolidated due to the formation of N-Zn covalent bonds, laying the foundation for the commercialization of the catalyst. This work introduces the characteristics of self-produced formic acid into photocatalysts through ingenious design, which provides a new idea for the photocatalytic treatment of nitrate wastewater.