Photocatalysts For NO Removal Research Articles

S-scheme Bi12TiO20/Bi4Ti3O12 heterojunction immobilized on 3D-printed support as a monolithic photocatalyst for NO removal

Photocatalysis is recognized as one of the most promising techniques for environment purification. However, the inconvenient recovery of powder photocatalysts significantly impeded their practical applications. Immobilization of the photocatalysts on supports to form monolithic photocatalysts is an effective method to solve this problem. Herein, a monolithic photocatalyst Bi12TiO20/Bi4Ti3O12/SiOC is fabricated by growing optimal Bi12TiO20/Bi4Ti3O12 S-scheme heterojunction onto 3D-printed porous SiOC support. On one side, S-scheme heterojunction facilitates the separation of photoinduced electrons and holes while retaining their strong redox ability. On the other side, the porous structure favors mass transport and improves light harvesting by reflecting the light several times. Under simulated solar light irradiation, the NO removal efficiency of the monolithic photocatalyst Bi12TiO20/Bi4Ti3O12/SiOC is 16.4 %. Furthermore, the composite has good stability and reusability, suggesting its great potential in practical application. The possible photocatalytic mechanism is proposed according to systematic experiments and density functional theory (DFT). This work provides a rational reference for constructing efficient photocatalysts for environmental purification.

Metal Bi Loaded Bi2Ti2O7/CaTiO3 for Enhanced Photocatalytic Efficiency for NO Removal under Visible Light

NO has caused many serious environmental problems and even seriously threatened human health. The development of a cheap and efficient method to remove NO from the air has become an urgent need. In this paper, a novel nanocomposite metal-semiconductor photocatalyst Bi-Bi2Ti2O7/CaTiO3 was prepared. Compared to the original Bi2Ti2O7/CaTiO3, the modification by the metal Bi increased its photocatalytic activity from 25% to 64% under visible light irradiation. The improved photoactivity owns to the SPR effect and the electron capture effect of Bi metals in metal-semiconductor loaded systems improving the separation efficiency of electron-hole pairs and significantly improving the light absorption capacity of the composite photocatalyst. The capture experiment of active species showed that •OH, •O2−, h+ and e− are the main active species in the photocatalytic conversion of NO. This work provides new insights into the conformational relationships of Ti-based photocatalysts for NO removal.

Infrared light utilization based on pyroelectric effect to improve the efficiency and stability of BaTiO3 for photocatalytic NO removal

Photocatalysis is a promising method for removing nitrogen oxides outdoor, However, the wide band gap of most photocatalysts usually causes the limited solar spectral response, which hinders the practical application of photocatalysts. In this paper, Sm0.5Sr0.5CoO3(SSC5) with good photothermal conversion performance is combined with BaTiO3 for the effective utilization of sunlight as well as the prohibition of photogenerated carrier recombination. The introduce of SSC5 can rapidly improve the surface temperature of BaTiO3 photocatalyst, which results in the increase of NO activation molecules and the generation of pyroelectric built-in electric field in BaTiO3. Therefore, the photogenerated carrier can be fast migrated and separated. The performance of 3 wt% SSC5/BaTiO3 is improved by 15% compared with the original sample. More interestingly, SSC5/BaTiO3 exhibits good stability compared with pristine BaTiO3. To analyse the reason for the improved stability, the energy of the reaction process on the catalyst surface was also simulate by DFT calculations. The results imply that the increased stability of SSC5/BaTiO3 may rely on the transfer of holes on the BaTiO3 to the SSC5. This study provides some new insights to the design of efficient and stable photocatalysts for NO removal in the environment.

Bi12TiO20-TiO2 S-scheme heterojunction for improved photocatalytic NO removal: Experimental and DFT insights

The fabrication of step-scheme (S-scheme) photocatalysts with superior redox ability for air purification is very important but remains a challenge. In this study, an S-scheme Bi12TiO20-TiO2 heterojunction is prepared for photocatalytic NO removal. The optimized Bi12TiO20-TiO2 heterojunction shows higher NO removal efficiency (42.6 %) than that of pristine Bi12TiO20 (8.7 %) and TiO2 (21.4 %) under simulated solar light irradiation. The enhanced photocatalytic activity can be attributed to the efficient separation and transfer efficiency of photoinduced electrons-hole pairs, enhanced redox ability, and increased NO adsorption capacity induced by S-scheme heterojunction between Bi12TiO20 and TiO2. The S-scheme charge transfer mechanism on Bi12TiO20-TiO2 heterojunction is proposed based on characterizations and theoretical calculations. The NO conversion process is investigated using in-situ Fourier transform infrared spectroscopy (in-situ FTIR). This study provides new insights for exploring highly efficient photocatalysts for NO removal.

Palladium Nanoparticles Embedded Nutshell-like Bi2WO6 as an Efficient and Stable Visible-Light-Responsive Photocatalysts for NO Removal

Palladium Nanoparticles Embedded Nutshell-like Bi₂WO₆ as an Efficient and Stable Visible-Light-Responsive Photocatalysts for NO Removal

The electronic and optical properties of Au decorated(1 0 [formula omitted] 4) dolomite surface: A first principles calculations

The electronic and optical properties before and after Au decoration on (101¯4) surface of dolomite were investigated based on first principles calculations. The electronic structure analysis indicates that the band gap decreases from 4.25 eV (pristine) to 0.81 eV (1 Au decorated case), and the work functions increase from 2.41 eV to 3.53 eV. The density of states analysis revealed that the band gap decrease is mainly attributed to the Au 5d doping states in the forbidden band gap. Moreover, an additional peak located at 310 nm of polarization direction on E//c appears after Au decoration, resulting in the increased absorption intensity in the ultraviolet and visible range. By comparing the redox potential with that of different kinds of pollution gas, it can be found that the Au decorated dolomite might be a good photocatalyst for NO removal. The above results indicate that the Au decorated dolomite could be used in visible light photocatalysis or photovoltaic applications due to its semiconductor characteristics and suitable redox potentials.

Oxygen defect-induced NO− intermediates promoting NO deep oxidation over Ce doped SnO2 under visible light

A Ce doped SnO2 (Ce-SnO2) photocatalyst was constructed under the argon atmosphere with abundant oxygen vacancies (OVs) for adsorption and activation of NO and O2, aiming to promote NO deep oxidation removal efficiency under different relative humidity. It was found that the incorporation of cerium ions into SnO2 could results in the generation of OVs under argon atmospheres, which further promoted NO deep oxidation under visible light irradiation. The theoretical calculations results and in-situ DRIFTS demonstrated that NO was actively adsorbed at OVs sites to form the NO− intermediate and finally transformed to the harmless nitrate and nitrite products by the activated reactive oxygen species (ROS) at OVs sites. This process could occur continuously since more OVs were formed under visible light irradiation. This study maybe provides a new approach to design and synthesize high-efficient photocatalysts for NO removal.

Layered double hydroxide nanosheets as efficient photocatalysts for NO removal: Band structure engineering and surface hydroxyl ions activation

We demonstrated the partial Ni2+ substitution for Mg2+ in Mg2Al-layered double hydroxide nanosheet (Ni/LDH) significantly improved its photocatalytic performance in removing the ppb-level NO pollutant from air. With 25 % of Mg2+ substituted, the Ni/LDH delivered the highest NO removal efficiency of 42.10 % (87.2 % of them were mineralized to nitrate) under UV-light irradiation. Such a robust performance with the low energy input (8 W) made Ni/LDH among the top photocatalysts for NO removal. We evidenced the OH− carried by Ni/LDH transformed to ·OH radicals by trapping the photoexcited holes. This unique feature was intriguing as the OH− at layer surfaces of LDH were abundant, fully exposed and dynamically supplemented by atmospheric water, which endowed Ni/LDH with superior ·OH production capability even under low atmospheric moistures. The positive contribution of Ni2+ arose from its function in optimizing band structure and activating the OH− of LDH, leading to enhanced reactive oxidative species production.

Sb2WO6/BiOBr 2D nanocomposite S-scheme photocatalyst for NO removal

Photocatalysis technology is an efficient method for removing nitrogen oxides at low concentrations. Herein, dimension-matched Sb2WO6/BiOBr photocatalysts were synthesized at room temperature via precipitation-deposition way. Under visible light irradiation, the as-obtained Sb2WO6/BiOBr photocatalysts showed enhanced photocatalytic performance compare with the pure Sb2WO6 and BiOBr for removal of NO. The optimal ratio for photocatalytic performance of Sb2WO6/BiOBr composite was found to be 30 wt.% of Sb2WO6, which showed excellent recycling property even after 5 runs. Moreover, in situ DRIFT was carried out to reveal the time-dependent evolution of reaction intermediates during photocatalytic NO oxidation. The probable photocatalytic mechanism was considered based on the active species capture experiments. The enhanced photocatalytic performance for the Sb2WO6/BiOBr composite photocatalyst perhaps is attributed to the interaction between BiOBr and Sb2WO6 and S-scheme charge transfer path.

Theoretical design and experimental investigation on highly selective Pd particles decorated C3N4 for safe photocatalytic NO purification

Rational design of highly active and selective photocatalyst for NO removal is significant for the commercial application of photocatalytic technology because the secondary byproduct caused by insufficient and non-selective pollutant oxidation process is a major challenge. In this work, Pd nanoparticles decorated C3N4 (PdCN) is designed by density functional theory (DFT) at first. The PdCN exhibits superiority to CN in terms of both kinetics and thermodynamics performances, as reflected in the lower activation barrier of rate-determining step and higher selectivity for the final product (nitrate) instead of toxic intermediate (NO2). The as-designed highly selective and efficient photocatalyst is then fabricated by a facile method with an extremely low content of Pd particles supported on C3N4. Compared to bare CN, the synthesized PdCN exhibits highly enhanced purification of NO in air and strong inhibition of toxic NO2 by-product as supported by in-situ DRIFTS investigation, which is consistent with the theoretical prediction. This work is a typical demonstration of setting up a bridge between theory and experiment to give a promising way to the rational design of advanced photocatalysts and atomic understanding of the reaction mechanism.

A direct Z-scheme Bi2WO6/NH2-UiO-66 nanocomposite as an efficient visible-light-driven photocatalyst for NO removal.

To explore an efficient photocatalyst for NO pollution, a direct Z-scheme photocatalytic system is successfully fabricated by coupling Bi2WO6 with NH2-UiO-66 via a simple hydrothermal synthesis technique. The Z-scheme system promotes the NO photocatalytic oxidation activity with an optimum NO removal rate of 79%, which is 2.7 and 1.2 times that obtained by using only pristine Bi2WO6 and NH2-UiO-66, respectively. Simultaneously, superior selectivity for converting NO to NO3−/NO2− is observed. The enhanced photocatalytic performance of the Bi2WO6/NH2-UiO-66 hybrids is attributed to the following two aspects: (i) large specific area of NH2-UiO-66, which exposes more active sites and is beneficial to the adsorption and activation of NO; (ii) outstanding Z-scheme structure constructed between BiWO6 and NH2-UiO-66, which can improve the efficiency of the separation of electron–hole pairs and preserves the strong oxidation ability of hybrids. ESR analysis shows that ·O2− and ·OH contribute to NO removal. A possible photocatalytic mechanism of NO oxidation on the direct Z-scheme photocatalyst (BWO/2NU) under visible light irradiation is proposed. This work displays the BWO/2NU hybrid's potential for treating low-concentration air pollutants, and the proposed Z-scheme photocatalyst design and promotion mechanism may inspire more rational synthesis of highly efficient photocatalysts for NO removal.

Ultrathin bismuth oxyhalides solid solution nanosheets with oxygen vacancies for enhanced selective photocatalytic NO removal process

Photocatalytic NO removal is an oxidation reaction where the NO2 or NO3− can be generated during the selective or non-selective NO removal process. For enhanced photocatalytic NO removal ability, photocatalysts were required stronger molecular oxygen activation activity for stronger oxidizability. Solid solution structure is confirmed as an efficient strategy to achieve induced molecular oxygen activation capacity. In this work, ultrathin structural BiOBr0.5I0.5 with oxygen vacancies (BiOBr0.5I0.5-U) was prepared and it showed obvious enhanced photocatalytic efficiency for NO removal than unmodified BiOBr0.5I0.5. The photocatalytic NO removal mechanism was confirmed through efficient methods. The enhanced generation ability for superoxide and singlet oxygen due to the ultrathin structure of BiOBr0.5I0.5-U was confirmed evidentially. The improved molecular oxygen activation activity supported the improved selective NO removal efficiency. This study could provide a new thought for the design of efficient bismuth oxyhalide photocatalysts for NO removal.

Photocatalytic Nitrogen Oxide Removal Activity Improved Step-by-Step through Serial Multistep Cu Modifications.

Previous research has evidenced the insufficient efficiency in a one-step modified photocatalyst for NO removal. In this article, a serial multistep modification was explored to improve the NO removal activity of g-C3N4. In the experiment, a g-C3N4 photocatalyst has been successfully modified by Cu elements three times on one continuous process. Meanwhile, results showed that the serial multistep modifications could improve NO removal activity by g-C3N4 step by step. The main active species in the g-C3N4 system were h+ and •O2- but they were h+ and •OH in the three-modified g-C3N4 systems. Moreover, different mechanisms of activity improvement caused by the modified Cu in the serial-modified samples were identified. In the first modified sample, Cu2+ can decompose H2O2 molecules into •OH via a Fenton-like reaction. In the second modified sample, the H2O2 molecule is activated by Cu0 and decomposed into •OH by the generated photoelectrons. After the third modification, the synergistic effects of the N vacancy and Cu0 were identified, which significantly enhanced the photocatalytic NO removal activity of g-C3N4. This study proposed that the serial multistep modification can be a promising method to improve the NO removal activity of g-C3N4 stage-by-stage.

Highly efficient (BiO)2CO3-BiO2-x-graphene photocatalysts: Z-Scheme photocatalytic mechanism for their enhanced photocatalytic removal of NO

NO removal is one of the most important issues in dealing with air pollution. In this report, Z-scheme (BiO)2CO3-BiO2-x-graphene (BOC-BiO2-x-GR) composite photocatalyst was designed for NO removal under simulated solar light irradiation. Characterizations of physical properties of the ternary composites revealed extended light absorption and high efficient electron-hole separation. Through the optimization of the BiO2-x content, we observed that the BOC-BiO2-x(35wt%)-GR composite exhibited superior photocatalytic activities in NO removal as compared to pure BOC, BiO2-x, and BOC-BiO2-x binary composites. Detailed microstructural observation showed that the BOC-BiO2-x heterojunction was formed between BOC (013) and BiO2-x (111) planes. The density of state (DOS) calculation revealed that due to the different hybridization conditions in the energy bands of BOC and BiO2-x, the Z-scheme charge transfer should be dominant at the heterojunction interface. The density functional theory (DFT) computation on the Fermi level results confirmed that energy band structure between BOC and BiO2-x is more in favor of the transfer of photo-generated electrons from CB of BOC to the VB of BiO2-x, which can be further enhanced by highly conductive GR sheets. The electron spin resonance (ESR) experiments results show that O2− and HO were produced during the photocatalytic process, which further provided evidences that the BOC-BiO2-x(35wt%)-GR composite works as a Z-scheme photocatalyst. This work indicates that Bi-based nanomaterials can be employed as a stable and high efficient solar light active photocatalyst for NO removal in air pollution control.

Synthesis of a Bi2O2CO3/ZnFe2O4 heterojunction with enhanced photocatalytic activity for visible light irradiation-induced NO removal

Although bismuth subcarbonate (Bi2O2CO3), a member of the Aurivillius-phase oxide family, is a promising photocatalyst for the removal of gaseous NO at parts-per-billion level, the large band gap of this material restricts its applications to the UV light region. The above problem can be mitigated by heterojunction fabrication, which not only broadens the light absorbance range, but also inhibits the recombination of photogenerated charge carriers. Herein, we implement this strategy to fabricate a novel Bi2O2CO3/ZnFe2O4 photocatalyst for NO removal under visible light irradiation and authenticate the formation of the above p-n heterojunction using an array of analytical techniques. Notably, the above composite showed activity superior to those of its individual constituents, and the underlying mechanisms of this activity enhancement were probed by density functional theory calculations and photocurrent measurements. Elevated electron/hole separation efficiency caused by the presence of an internal electric field at the Bi2O2CO3/ZnFe2O4 interface was identified as the main reason of the increased photocatalytic activity, with the main active species were determined as O2− and OH by electron spin resonance spectroscopy. Finally, cytotoxicity testing proved the good biocompatibility of Bi2O2CO3/ZnFe2O4. Thus, this work presents deep insights into the preparation and use of a green p-n heterojunction catalyst in various applications.

In situ fabrication of Bi2O2CO3/MoS2 on carbon nanofibers for efficient photocatalytic removal of NO under visible-light irradiation

A novel nanocomposite photocatalyst for NO removal, Bi2O2CO3-MoS2-CNFs, was fabricated by an efficient method. This new photocatalyst performed impressively in the removal of NO at low concentration (600ppb), with a maximum efficiency of 68% under visible-light irradiation, superior to most other visible-light photocatalysts. Its high performance was ascribed to the introduction of carbon nanofibers as carriers, and MoS2, which enhanced the absorption of visible light and accelerated the separation and transfer of electrons and holes. Photocurrent tests and electrochemical impedance spectroscopy also demonstrated that Bi2O2CO3-MoS2-CNFs had a high efficiency of interfacial charge separation, which is critical to improving the photocatalytic activity. Moreover, the membrane of the photocatalyst was stable and recyclable after multiple runs. All of these factors demonstrate its potential application in the removal of NO from air.

High Selectivity of Visible-Light-Driven La-doped TiO2 Photocatalysts for NO Removal

Semiconductors mediated by rare earth metals (REMs) have attracted attention with regard to the degradation of pollutants. In order to enhance the visible response of TiO2, La-doped TiO2 (La-TO) photocatalysts with visible-light-driven capacity for NO removal were successfully synthesized in this study via a facile sol-gel method followed by calcination. A series of La-TiO2 samples with differing weight ratios were evaluated for their photocatalytic performances. It was found that 3% La integrated with TiO2 (in mass ratio) could enhance the removal efficiency of NO (up to 32%) under solar light, which is more than twice that seen with pure TiO2. The resulting products were characterized by a series of techniques, such as XRD, FTIR, UV-vis DRS, BET and (photo)electrochemical analysis. The results indicated that La-doped TiO2 can harvest visible light due to the relatively narrow band gap (from 2.98 to 2.75 eV). More importantly, La dopant improved electron-hole separation and suppressed charge carrier recombination, due to the synergistic effect. Furthermore, La-doped TiO2 increased the photo-oxidation efficiency of the transformation from NO to NO3–, owing to inhibition of the production of intermediate NO2 (0.02%). To the best of our knowledge, this study is the first time that La-doped TiO2 has been used to eliminate NO (at the ppb level) in the atmosphere. This study provides a facile and controllable route to fabricate La-TO photocatalyst for NO abatement with high selectivity of NO2 under visible light.

Lower treating temperature leading to higher air purification activity

Polymeric graphitic carbon nitride is an efficient visible-light photocatalyst for NO removal which can be prepared by precursors rich in C and N elements, such as melamine, dicyandiamide, urea, and thiourea et al. The method of synthesizing carbon nitride from melamine and dicyandiamide has much higher yield and, whereas the photocatalytic efficiency of the product was lower than that of synthesizing from urea and thiourea. In present work, the photocatalytic performance of carbon nitride prepared from dicyandiamide was significantly improved; melem/g-C3N4 was prepared from dicyandiamide under lower temperature with superior performance on NO purification than pure carbon nitride (g-C3N4). Suitable depolymerization ratio and surface protonation status could bring about higher photocatalytic activity through XPS characterizations. Through the SEM images, two kinds of morphology nanorod carbon nitride and bulk carbon nitride cross each other together and the ratio variation are consistent with reaction temperature and time. The different band gap structure between g-C3N4 and melem could drive the photogenerated electron-hole separation due to the offsets and lead to higher NO removal efficiency. This heterojunction consisted of melem and g-C3N4 was developed here just by adjusting reaction temperature and time, which could open up a new possibility for air purification in a low cost way.

Plasmonic Ag-TiO2 − x nanocomposites for the photocatalytic removal of NO under visible light with high selectivity: The role of oxygen vacancies

Integration of semiconductors with plasmonic noble metal nanoparticles for visible- light driven photocatalysis has become an interesting research field recently. In this work, Ag-TiO2−x nanocomposites were successfully synthesized via a facile photochemical reduction process followed by post-annealing. The deposition of Ag nanoparticles greatly increases the light absorption and charge separation. Compared with commercial P25, the Ag-TiO2−x nanocomposites are not only superior in visible-light photocatalytic NO removal, but also in inhibiting the production of NO2, whose toxicity is 4–5 times higher than NO. As confirmed by gas chromatography, the photo-oxidation of NO and selective photo-reduction of NO to N2 occur simultaneously during the process of NO removal by Ag-TiO2−x. The oxidation of NO was due to the synergic effect between h+ and O2−; while the selective photo-reduction was resulted from introduced oxygen vacancies in TiO2. In addition, the light wavelength dependence measurement reveals that the surface plasmon resonance effect of Ag is responsible for the improvement of the visible-light photoactivity. The present study will provide an alternative approach to design highly selective photocatalysts for NO removal under visible-light.

Plasmonic Bi/ZnWO4 Microspheres with Improved Photocatalytic Activity on NO Removal under Visible Light

In this work, bismuth (Bi) nanoparticle anchored ZnWO4 microspheres (Bi/ZnWO4) were prepared and used as robust and efficient photocatalysts for NO removal at parts-per-billion level under visible light irradiation. The as-synthesized composite with a proper mass ratio of Bi (50%) displayed a higher reaction rate (0.067 min–1) than its single counterparts ZnWO4 (0.004 min–1) and Bi (0.027 min–1), respectively. Due to the surface plasmon resonance (SPR) effect of Bi nanoparticles, the Bi/ZnWO4 composites showed broad light absorption in the visible spectrum. Moreover, the formation of the Bi/ZnWO4 heterointerface promoted the separation of photoexcited electron–hole pairs, which is demonstrated by the increased photocurrent density in comparison to the pristine materials. The above characteristics endowed the Bi/ZnWO4 composites with superior photocatalytic activity for NO removal. The radical scavanger tests revealed that the superoxide radical was the main active species to initiate NO oxidation, while t...