Photocatalytic Activity For NO Removal Research Articles

TiO2 with exposed (001) facets/Bi4O5Br2 nanosheets heterojunction with enhanced photocatalytic for NO removal

A TiO2 with exposed (001) facets/Bi4O5Br2 nanosheets heterojunction (TNS/BOB) was fabricated via a hydrothermal and electrostatic self-assembly method. The photocatalytic activity for NO removal was evaluated under simulated solar light irradiation. Through optimizing the content of TNS nanosheets, the photo-oxidative NO removal rate of 15% TNS/BOB was increased by up to 54.3%. This value is much higher than that of the individual components TNS (31.1%) and BOB (37.7%). Through capturing experiments and electron spin resonance (ESR) measurements, the main active species in the photocatalytic process were identified as · and ·OH. Discrete Fourier transform computation results and ESR tests revealed that the photo-induced electrons in TNS should recombine with the holes in BOB, leading to effectively promoted charge separation at the TNS/BOB interface through the Z-type charge transfer. This work showed that with appropriate facet control and heterojunction design TiO2 can be used as an effective visible-light photocatalyst material.

Facile synthesis of novel Mn-doped Bi4O5Br2 for enhanced photocatalytic NO removal activity

This study investigates the photocatalytic activity of a novel Mn-doped Bi4O5Br2 material prepared via a facile synthesis process. The experimental and theoretical results confirm that Mn doping enhances the efficiency of NO removal over a Bi4O5Br2 catalyst under visible light irradiation. The SEM (scanning electron microscopy), BET (Brunauer-Emmet-Teller), XRD (X-ray diffraction) analyses show that neither the surface morphology nor the phase of the photocatalytic material changes after the incorporation of Mn. The ESR (electron spin resonance) and UPS (Ultraviolet photoelectron spectroscopy) results show that the electrons in the CBM (conduction band minimum) can be directly captured by O2 to produce large amounts of •O2 radicals, and •OH radicals are formed via the route of •O2−→H2O2→•OH. The higher efficiency of Mn-doped Bi4O5Br2 is driven by the reduced band gap, widened visible light absorption range, higher intensity of visible light absorption, and enhanced separation efficiency of electrons and holes in this material compared with those of pristine Bi4O5Br2.

Enhancement of photocatalytic NO removal activity of g-C3N4 by modification with illite particles

The modification of illite particles could enhance the photocatalytic NO removal activity of g-C3N4.

La-Doped ZnWO4 nanorods with enhanced photocatalytic activity for NO removal: effects of La doping and oxygen vacancies

La3+-Doped ZnWO4 nanorods were prepared via a hydrothermal method for the photocatalytic NO removal under simulated solar light irradiation.

Enhancing Photocatalytic Activity of NO Removal through an In Situ Control of Oxygen Vacancies in Growth of TiO2

AbstractAlthough defects play an important role in the photocatalytic activity of TiO2, the mechanism of the photocatalytic activity related to different defects remains disputable. Moreover, the reported methods to introduce defects raise the preparation cost. In this work, different types of defects including O‐vacancy cluster, surface O‐vacancy, and bulk O‐vacancy defects are in situ introduced in TiO2 by controlling the crystallization temperature. The medium‐degree crystallinity TiO2 sample mainly containing surface O‐vacancies exhibits the best NO removal activity. The systematic study of photocatalytic mechanism demonstrates that the surface O‐vacancies significantly promote the adsorption of H2O molecules and improve charge transfer to the adsorbed H2O forming ·OH, thus dramatically enhancing the photocatalytic NO removal activity. On the contrary, bulk O‐vacancies neither help the adsorption of H2O molecules, nor improve the charge transfer to H2O.

Facile Synthesis of Ternary g-C3N4@BiOCl/Bi12O17Cl2 Composites With Excellent Visible Light Photocatalytic Activity for NO Removal.

In this study, novel two-dimensional (2D) g-C3N4@BiOCl/Bi12O17Cl2 composites have been fabricated through a facile deposition-precipitation process. The as-prepared photocatalysts were characterized by XRD, SEM, TEM, XPS, UV-vis DRS, PL, Photocurrent, EIS, ESR, and N2 adsorption-desorption. The photocatalytic activities were investigated through NO removal test in gas under visible light irradiation (λ > 420 nm). The g-C3N4@BiOCl/Bi12O17Cl2 composites exhibit enhanced visible light absorption and photo-induced electron-hole separation efficiency, compared with pristine g-C3N4 and BiOCl/Bi12O17Cl2. The intimated contact interfaces between g-C3N4 and BiOCl/Bi12O17Cl2 nanosheets are responsible for the more efficient photochemical interactions. The present work provides a new direction to develop a class of ternary g-C3N4-based visible-light-driven photocatalysts for environmental purification.

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.

Improved photocatalytic NO removal activity of SrTiO3 by using SrCO3 as a new co-catalyst

In this study, SrTiO3 catalyst decorated with SrCO3 was prepared by one step in-situ pyrolysis and was used for the photocatalytic removal of NO. The presence of SrCO3 not only improved the photocatalytic activity of SrTiO3 but also inhibited the deactivation of SrTiO3 during NO removal. In photocatalytic process, the photogenerated electrons in CB of SrTiO3 could migrate to the CB of SrCO3. Meanwhile, strong O2 adsorption on the SrCO3 surface would increase the production of O2−. Moreover, SrCO3 could increase the surface acidity of SrTiO3, which would increase the NO adsorption and facilitate the oxidation of NO. The experimental data suggested that SrCO3 functions as surface deposited noble metals without the shortcomings caused by noble metals. Overall, the prepared SrCO3 looks promising as environmentally friendly and economic substitute to noble metals.

Oxygen vacancy engineering of Bi2O3/Bi2O2CO3 heterojunctions: Implications of the interfacial charge transfer, NO adsorption and removal

Efficient enrichment of targeted gaseous pollutants and fast diffusion rates of charge carriers are essential for the photocatalytic removal of nitric oxides at ambient concentration levels. Here we demonstrate that the construction of nano-structured Bi2O3/Bi2O2CO3 heterojunctions with oxygen vacancies, increasing the photocatalytic NO removal activity, durability and selectivity for final products nitrate formation. Combining the experimental and density-functional theory calculations, it was elucidated that the presence of surface oxygen vacancies not only work as adsorption sites of low concentration NO, but also offer an intimate and integrated structure between surface defects and the light-harvesting heterojunctions, which can facilitate solar energy conversion and charge carrier transfer (more than 2 times). Control experiments with pristine Bi2O3/Bi2O2CO3 also confirmed the crucial role of surface oxygen vacancies on the improvement of NO adsorption and removal ability during the photocatalytic degradation process. We explain the enhanced removal of NO through the synergistic effect of oxygen vacancy and heterojunction, which not only guaranteed the generation of more OH radicals, but also provided another route to produce hydrogen peroxide. Our findings may provide an opportunity to develop a promising catalyst for air pollution control.

Controllable Synthesis of Core–Shell Bi@Amorphous Bi2O3 Nanospheres with Tunable Optical and Photocatalytic Activity for NO Removal

The size, morphology, and structure of a Bi nanoparticle can significantly affect its photocatalytic performance. In this study, core–shell structured Bi@amorphous Bi2O3 nanospheres were synthesized through a one-step solvothermal method, and the reaction mechanisms on NO removal were proposed. It was found that Bi nanoparticles can generate charge carriers by surface plasma resonance (SPR) under visible light irradiation, while the surface amorphous Bi2O3 layer can facilitate the charge carriers’ separation. The Bi@Bi2O3 sample with the synthesis time of 18 h exhibited superior visible light photocatalytic activity for NO degradation, attributed to the suited size and suitable amorphous Bi2O3 layer. •O2–, 1O2, and •OH radicals were identified as the main reactive species involved in the photocatalysis processes. Moreover, the enhancement mechanisms of photocatalytic NO removal over Bi@Bi2O3 samples were discussed. This study demonstrated that the fabrication of core–shell structured Bi@Bi2O3 is a good st...

Layered Perovskite Pb2Bi4Ti5O18 for Excellent Visible Light-Driven Photocatalytic NO Removal

A grand challenge in photocatalysis is to seek chemically stable photcatalysts with minimized recombination of photoinduced charges in order to maximize the efficiency of the subsequent redox reactions. Because of the structural noncentrosymmetry, TiO2-based and lead-containing perovskite-type photocatalysts exhibit excellence in both stability and ferroelectricity to facilitate charge separation state. To extend their visible light activity, we use molten salts synthesis methodology to prepare Pb2Bi4Ti5O18 perovskites with various nanoscale morphologies and evaluated their visible light-driven photocatalytic activity for NO removal. The results show that perovskite Pb2Bi4Ti5O18 samples exhibit excellent stability as well as display over 50% NO removal efficiency under visible light in contrast to no more than 15% for commercial P25. A set of radical scavengers were used to probe the reaction mechanism. A bond-valence method was used to calculate the direction and magnitude of the dipole moments of the as...

Salt-assisted Synthesis of Hollow Bi2WO6 Microspheres with Superior Photocatalytic Activity for NO Removal

Hollow Bi2WO6 microspheres are successfully synthesized by a facile ultrasonic spray pyrolysis (USP) method using NaCl as a salt template. The as-prepared hollow microspheres assembled as nanoplates with dimensions of approximately 41–148 nm and are dispersed with non-uniform pores on the template surface. By swapping the salt template with KCl or Na2SO4, different morphologies of Bi2WO6 are obtained. The experimental results demonstrate that NaCl plays a key role on the formation of Bi2WO6 with hollow structures. The specific growth mechanism of hollow microspheres was studied in detail. The Bi2WO6 hollow microspheres exhibit an excellent photocatalytic efficiency for NO removal under solar light irradiation, which is 1.73 times higher than for the Bi2WO6 obtained in the absence of any salt template. This enhancement can be ascribed to the simultaneous improvement on the surface area and visible light-harvesting ability from the hollow structures. Electron spin resonance (ESR) results suggest that both radicals of •OH and •O2− are involved in the photocatalytic process over the BWO-NaCl sample. The production of •O2− radicals offers better durability for NO removal.

Modification of Bi2WO6 composites with rGO for enhanced visible light driven NO removal

AbstractBi2WO6‐rGO composites were synthesized through hydrothermal method. Its visible‐light‐driven photocatalytic properties were evaluated by the oxidation of nitrogen monoxide, which exhibited significantly enhancement on the photocatalytic performance comparing with Bi2WO6. Bi2WO6–2% rGO showed the highest photocatalytic activity for NO removal. The enhanced photocatalytic activity can be attributed to the increased light absorption and more effective charge transportation and separation arisen from the strong chemical bonding between Bi2WO6 and rGO. The results on the effects of H2O and SO2 concentration to NO removal efficiency indicate that the activity of Bi2WO6–2% rGO composite was suppressed by the coexisting of SO2 while promoted by H2O. In addition, the reaction mechanism of the photocatalytic oxidation of NO to NO2 was also discussed. © 2016 Curtin University of Technology and John Wiley & Sons, Ltd. © 2016 Curtin University of Technology and John Wiley & Sons, Ltd.

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...

In situ Fabrication of α-Bi2O3/(BiO)2CO3 Nanoplate Heterojunctions with Tunable Optical Property and Photocatalytic Activity.

Exploring the full potential use of heterojunction photocatalysts containing bismuth has attracted considerable interest in recent years. Fabrication of well-defined heterojunction photocatalysts with precise modulation of their chemical composition is crucial for tuning their optical properties and photocatalytic activity. In this study, we fabricated nanoplate α-Bi2O3/(BiO)2CO3 heterojunctions through in situ thermal treatment of (BiO)2CO3 nanoplates synthesized using a facile hydrothermal process. Characterization results showed that the as-prepared Bi2O3/(BiO)2CO3 heterojunctions possessed distinct crystal interface and exhibited pronounced structural and optical modulation, resulting in significant improvement of their photocatalytic activity for NO removal under simulated solar light irradiation compared with pristine (BiO)2CO3. Electron spin resonance spectroscopy showed that ⋅OH radicals were the major reactive species involved in NO degradation, which is consistent with the theoretical analysis. The heterojunction formation can not only broaden the light absorption range but also improve the charge separation of photo-induced electron–hole pairs. This study is an important advancement in the development of semiconductor heterojunctions towards achieving functional photocatalysts.

Enhanced visible-light-driven photocatalytic removal of NO: Effect on layer distortion on g-C3N4 by H2 heating

We report a simple strategy for realizing the tunable structure distortion of graphitic carbon nitride (g-C3N4) layers by H2 post calcination to improve the intrinsic electronic structure and the photocatalytic performances of g-C3N4 samples. In comparison with the O2 or N2 post treatment, the H2-modified g-C3N4 develops new optical absorption above 460nm and enhances photocatalytic activity for NO removal. The combined characterization results reveal that H2 heating induced the structure distortion of g-C3N4 layers is originated from the creation of amino groups within the structure and generation of the strong hydrogen bonding interactions between layers. The distorted structure allows n–π* electron transitions in g-C3N4 to increase visible-light absorption. The structure distortion also enables more electrons to be available for initiating the photocatalytic reaction and the separation of photogenerated charge carriers in g-C3N4. This work provides a simple strategy for realizing the tunable structure distortion of g-C3N4 layers to adjust its electronic structure and photocatalysis.

Facile synthesis of porous graphene-like carbon nitride (C6N9H3) with excellent photocatalytic activity for NO removal

We reported the possible synthesis of a new porous graphene-like carbon nitride (C6N9H3) by simply adding hydrochloric acid in the precursor of block g-C3N4. The formation of the porous graphene-like C6N9H3 can be attributed to the change in the thermal condensation modal of the precursor and the acidic condition induced by Cl− and H+. The photocatalytic activity of the samples was evaluated by the removal of NO under visible light illumination. We found that the porous graphene-like C6N9H3 exhibited enhanced photocatalytic activity compared to the block g-C3N4. We also researched the removal mechanism and found that the removal of NO in our systems was due to the synergic effect of h+ and O2−. This study could shed light on the design of efficient photocatalysts and facilitate a deep understanding of the NO removal mechanism through photocatalytic technology.

Green synthesis of a self-assembled rutile mesocrystalline photocatalyst

This paper reports a simple and environmentally benign approach for the synthesis of photocatalytically active rutile TiO2 mesocrystals. It is a microwave-assisted hydrothermal method involving titanium(III) chloride as the only reactant. The resulting 1D rutile nanowires can easily assemble into 3D hierarchical architectures without the help of surfactants or additives. The average aspect ratio for the nanowires is 267. The BET specific surface area of the mesocrystals is 16 m2 g−1. The optical band energy of the product exhibits an obvious red-shift of 0.2 eV with aspect to that of pure rutile TiO2. This red-shift effect may be ascribed to the high aspect ratio of rutile nanowires. The products show excellent photocatalytic activity for NO removal in air and the activity is well maintained after three cycles. Gold modification on the rutile TiO2 results in a 50% improvement in the photocatalytic performance.

Role of oxygen vacancy in the plasma-treated TiO 2 photocatalyst with visible light activity for NO removal

The photocatalytic activity for NO removal under an oxidative atmosphere has been studied over commercial TiO 2 and plasma-treated TiO 2 powders. By the plasma treatment, the photocatalytic activity for NO removal appeared in the visible light region up to 600 nm without a decrease in the ultraviolet light activity. It was found that the NO was removed as nitrate (NO 3 −) by photocatalytic oxidation over the TiO 2 powders, where NO 3 − was accumulated. No difference in the crystal structure, the crystallinity, and the specific surface area was observed between the raw TiO 2 and the plasma-treated TiO 2 photocatalysts. In electron spin resonance (ESR) measurements, a sharp signal at g=2.004, which was identified as the electrons trapped on oxygen vacancies, was detected only for plasma-treated TiO 2 under visible light irradiation. The saturated intensity of the ESR signal at g=2.004 was proportional to the removal percentage of nitrogen oxides, suggesting that the number of trapped electrons determined the activity for the photocatalytic oxidation of NO to NO 3 −. The appearance of the visible light activity in the plasma-treated TiO 2 photocatalyst was ascribed to the newly formed oxygen vacancy state between the valence and the conduction bands in the TiO 2 band structure.