Photocatalytic NO Removal Research Articles

Fabrication of 1D/2D BiPO4/g-C3N4 heterostructured photocatalyst with enhanced photocatalytic efficiency for NO removal

The visible light photocatalytic removal of NO in air is a promising way. BiPO4 is restricted by its wide band gap and can only be responded to ultraviolet light. Herein, 1D BiPO4 nanorod/2D g-C3N4 heterostructured photocatalyst was successfully synthesized via a facile one-step hydrothermal process for efficient visible light photocatalytic removal of NO. With simulated sunlight irradiation, the photocatalytic NO removal activity of the BiPO4/g-C3N4 (64%) is much higher than that of the pure BiPO4 (7.2%) and g-C3N4 (50%). Its excellent photocatalytic performance was ascribed to broadening the light response range to visible light and boosting the separation and transfer of photogenerated electrons and holes. The NO photocatalytic removal mechanism was proposed by the free radical trapping experiment and in situ DRIFTS research. The present study might induce a new means to design BiPO4-based heterostructured photocatalysts for the removal of NO from air pollution under simulated solar light irradiation.

Rational design of n-Bi12TiO20@p-BiOI core–shell heterojunction for boosting photocatalytic NO removal

Bismuth titanate (Bi12TiO20) with unique sillenite structure has been shown to be an excellent photocatalyst for environmental remediation. However, the narrow light-responsive range and rapid recombination of photoinduced electrons-holes limit the photocatalytic performance of Bi12TiO20. To overcome the limitations, a practical and feasibleway is to fabricate heterojunctions by combining Bi12TiO20 with suitable photocatalysts. Here, using a facile chemical precipitation method, a novel and hierarchical core–shell structure of n-Bi12TiO20@p-BiOI (BTO@BiOI) heterojunction was rationally designed and synthesized by loading BiOI nanosheets on BTO nanofibers. The constructed BTO@BiOI composites exhibited significant charge transfer ability due to the synergistic effects of the built-in electric field between BTO and BiOI as well as close interfacial contacts. In addition, the narrow bandgapcharacteristics of the BiOI led to wide light absorption ranges. Therefore, the BTO@BiOI heterojunction exhibited an improved photocatalytic performance under visible light irradiation. The NO removal efficiency of optimal BTO@BiOI was 45.7%, which was significantly higher compared tothat of pure BTO (3.6%) or BiOI (23.1%). Moreover, the cycling experiment revealed that BTO@BiOI composite has a good stability and reusability. The possible mechanism of photocatalytic NO oxidation over BTO@BiOI was investigated in detail.

Porphyrin-based Ti-MOFs conferred with single-atom Pt for enhanced photocatalytic hydrogen evolution and NO removal

A robust and efficient titanium metal–organic framework (TMF-Pt) with a single-atom Pt embedded PtII tetrakis(4-carboxyphenyl)porphyrins (PtTCPP) as linking groups and Ti-oxo molecular clusters as metal nodes was successfully fabricated for the first time, which have been confirmed by aberration-correction scanning transmission electron microscopy (HAADF-STEM) and synchrotron-radiation-based X-ray absorption fine-structure spectroscopy (XAFS), and was applied to photocatalytic hydrogen production and NO removal. It was worth noting that the TMF-Pt exhibited an extremely high hydrogen evolution activity (15456 µmol·g−1·h−1) and NO removal rate (70.3%) in comparison with most of the reported MOFs-based photocatalysts, which could be ascribed to the very high atom-utilization efficiency of single-atom Pt along with a high charge carriers separation efficiency and the Ti-oxo clusters as an alternative to the very famous TiO2 photocatalyst. The results provided us with a novel strategy that introducing single-atom Pt into the center of the porphyrin skeleton could integrate the broad light-harvesting porphyrin unite with the very high atom-utilization efficiency single-atom Pt to further improve the photocatalytic performance ultimately.

Highly efficient photocatalytic NO removal and in situ DRIFTS investigation on SrSn(OH)6

A novel SrSn(OH)6 photocatalyst with large plate and particle size were synthesized via a facile chemical precipitation method. The photocatalytic activity of the SrSn(OH)6 was evaluated by the removal of NO at ppb level under UV light irradiation. Based on the ESR measurements, SrSn(OH)6 photocatalyst was found to have the ability to generate the main active species of O2•−, •OH and 1O2 during the photocatalytic process. Moreover, SrSn(OH)6 photocatalyst not only exhibits high photocatalytic activity for NO removal (79.6%), but also has good stability after five cycles. The in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was used to investigate the NOx transfer pathway and the intermediate products distribution during the adsorption and photocatalytic NO oxidation process. The present work not only provides an efficient material for air pollutants purification at room temperature but also in-depth understanding of the mechanism involved in the photocatalytic NO removal process.

Ti3C2@TiO2/g-C3N4 heterojunction photocatalyst with improved charge transfer for enhancing visible-light NO selective removal

Control of Nitrogen dioxide (NO2) byproducts is of great importance for the photocatalytic NO removal and environmental remedy. However, individual semiconductor photocatalysts generally show limited capabilities for selective NO removal due to severe charge recombination and inadequate redox potentials. Herein, the cotton-like g-C3N4 was modified with Ti3C2@TiO2 to construct a heterojunction photocatalyst Ti3C2@TiO2/g-C3N4, which showed outperformed photocatalytic NO removal and MB degradation abilities compared to the individual photocatalysts under visible light irradiation. The UV–vis absorption spectra and photoluminescence (PL) spectra confirmed that Ti3C2@TiO2/g-C3N4 photocatalyst was endowed with superior light utilization and separation/transfer ability of charge carriers due to the presence of n-n heterojunction and Schottky barrier. Furthermore, the g-C3N4, Ti3C2, and TiO2 were closely contacted showing a high specific surface area, which promoted the charge transfer and the exposure of more active sites, further inducing the formation of more active species. Therefore, the designed photocatalyst delivered a high removal rate of NO and a suppressed discharge of NO2. Notably, the photocatalyst Ti3C2@TiO2/g-C3N4 also presented superior NO removal ability during the cycling experiment, indicating their outstanding stability and recyclability. Besides, the effects of active species were monitored using a trapping experiment to propose probable photocatalytic mechanism. This study could shed a new light to the design of photocatalyst for air purification in the future.

Effect of synergy between oxygen vacancies and graphene oxide on performance of TiO2 for photocatalytic NO removal under visible light

It is important to find an effective way to enhance the photocatalytic NO removal efficiency of black-TiO2. In this work, we used a simple hydrothermal method to synthesize the black TiO2-GO composite. One of the black TiO2-GO composites, B-TiO2-3GO (black TiO2-GO composites with graphene content of 3 wt%), exhibits remarkably high activity toward the photocatalytic removal of NO, with a NO conversion rate of 50.4% which is greater than that of pure black TiO2 (33.9%). The experimental results revealed that the TiO2-GO nanocomposite photocatalyst has the high absorption ability from large surface area and well mobility of charge carriers, which can enhance its photocatalytic activity. What’s more, the UV–vis (DRS)spectra, XPS and NO-TPD-MS indicated that the synergy between H2O2, oxygen vacancies and GO. Finally, a possible photocatalytic NO removal mechanism over the B-TiO2-GO composite is also presented based on the results of the band structures, the free radical capture experiments and electron spin resonance (ESR) tests. This work would provide a strategy to design HNO3/H2O2-resistant deNOx photocatalyst in the pollutant purification field.

The photocatalytic efficiency enhancement of Bi4O5Br2 by Li-intercalation for NO removal

In this study, authors report a facile method to improve the photocatalytic NO removal efficiency by simple Li-intercalation after the growth process of Bi4O5Br2. By combining experimental and theoretical analyses, the synergistic effects of more defects on the surface, adjustable photon absorption edge and intensity, prolonged lifetime of the photo-induced charge carriers and suitable redox potential lines are responsible for the photocatalytic efficiency improvement. This work proposes a new and promising method to modulate the efficiency of the Bi4O5Br2 photocatalyst by post-synthetic Li-intercalation and illustrates a deeper understanding of the improved photocatalytic efficiency.

Silver embedded in defective twin brush-like ZnO for efficient and stable photocatalytic NO removal

Solar photocatalysis is a clean and sustainable approach for removing atmospheric NO, but suffers from unsatisfactory removal efficiency. Efficient charge separation and surface reaction are critical factors ensuring the efficiency of solar energy conversion by photocatalysts. To achieve efficient charge steering and an enhanced surface reaction, we synthesized a bicomponent photocatalyst consisting of multivalent Ag species embedded in defect-rich twin-brush ZnO (Ag/TB-ZnO) with strong metal-support interaction (SMSI). The optimum Ag/TB-ZnO with silver loading of 2.0 wt.% achieved NO oxidation efficiency of 71.0% under a GHSV of 1,200,000 mL h−1 g−1, and NO3− selectivity of 94.8%. Outstanding stability of up to 4 h was demonstrated. This superior performance was attributed to the enhanced efficacy of charge separation and surface reaction by the SMSI effect, surface plasmon resonance effect of metallic Ag and the efficient activation of oxygen species through vacancy-rich TB-ZnO.

The effect of excitation light source and humidity to photocatalytic activity of g-C3N4 nanosheets for NO removal

Introduction: Photocatalysis using nanostructured semiconductors is the potential strategy to solve the problem of environmental pollution. Besides traditional semiconductor materials, the novel polymeric metal-free semiconductor g-C3N4 has emerged as a potential substitute material because of its many outstanding features.
 Methods: This study successfully synthesized two dimensions (2D)-structured g-C3N4 nanosheets by a simple thermal-exfoliation method with annealing route at 2 oC/min. Firstly, melamine was placed in a ceramic crucible with cover and then undergone the annealing route at 550 oC for 2 h to develop into the g-C3N4 bulk. Then the assynthesized g-C3N4 bulk was further annealed without the cover at 550 oC for 2 h to form the final product, g-C3N4 nanosheets.
 Results: The results of XRD patterns and FTIR spectra show two typical diffractions peaks and chemical bonds that characterize the g-C3N4 matrix. The TEM images demonstrated that the as-prepared g-C3N4 possesses 2D-structured material, including several singly exfoliated sheets with a width of around several hundred nanometers. The photocatalytic NO removal efficiency of g-C3N4 nanosheets is highest at 48.27% under 30 min solar irradiation at 70% humidity. Meanwhile, the NO2 conversion yield is very low, only 9.44%, much smaller than the NO decomposition efficiency to form NO3 􀀀 ion products. The results of trapping tests indicated that the hole plays the most critical role in the photocatalytic process of g-C3N4 nanosheets. Especially, the photocatalytic NO removal efficiency still achieves 45.03% after the recycling test. Moreover, all characteristic peaks and chemical bonds in material remain even undergoing fifth times reuse as the results of XRD and FTIR.
 Conclusion: From various modern analytic characterization methods and photocatalytic investigation, we can concluse that g-C3N4 nanosheets are very stable and possible to apply in practical applications to decompose NO gas at atmospheric conditions.

Optimizing the Electronic Structure of BiOBr Nanosheets via Combined Ba Doping and Oxygen Vacancies for Promoted Photocatalysis

The promotion of BiOBr via simultaneous alkaline earth metal (Ba) doping and massive oxygen vacancies (OVs) was for the first time investigated toward the photocatalytic removal of NO in air. The a...

High visible-light photocatalytic performance of stable lead-free Cs2AgBiBr6 double perovskite nanocrystals

Lead halide perovskite nanocrystals (NCs) have been recognized as a rather competitive candidates for potential advanced optoelectronic applications. But the toxicity of lead and the intrinsic instability are the key concerns for their large-scale commercialization. For addressing these tricky issues, we synthesized lead-free all-inorganic Cs2AgBiBr6 double perovskite NCs adopting a facile hot injection approach. The as-prepared NCs could keep their structure stable either in air for more than two months or being heated at 300 °C in ambient atmosphere for 3 h. Moreover, Cs2AgBiBr6 NCs were investigated for photocatalytic NO removal under visible-light irradiation, achieving an exciting removal rate of 97%, which is much higher than the previous reports as we know. In addition, the Cs2AgBiBr6 NCs demonstrated outstanding recyclability for at least four cycles in NO removal. The photocatalytic mechanism of Cs2AgBiBr6 NCs was further proposed. This investigation offers a new environmental photocatalyst to purify the air.

Bi4O5Br2-based binary composites: Facile fabrication, characterization, and enhanced photocatalytic performance over NO removal

NOx at ppb level in atmospheric environment should be rationally treated through a suitable and efficient photocatalytic system. In the current study, oxygen-enriched oxybromide Bi4O5Br2 was modified with various amount of graphite graphene oxide via a facile in-situ precipitation route and resultant composites were systematically characterized by a series of analyses. The addition of graphite graphene oxide induced relatively small-sized Bi4O5Br2 nanosheets, thus causing expansion of band structures with stronger redox capabilities. In addition, the involvement of graphene oxide in composites also leaded to enlarged specific surfaces areas with abundant active sites, enhanced visible light harvesting, and strengthened charge carriers by heterojunction domains at interface, ensuring the improved photocatalytic NO removal efficiencies in comparison to bare Bi4O5Br2 under visible light. Moreover, the generation of toxic intermediate NO2 was obviously constrained. Eventually, these robust binary composites exhibited strong structural-stability and satisfactory reusability and a probable photocatalysis mechanism was speculated basing upon entrapping experiments and ESR results.

Insight into the role of copper in the promoted photocatalytic removal of NO using Zn2-xCuxCr-CO3 layered double hydroxide

In this work the ability of Zn2-xCuxCr-CO3 layered double hydroxides (LDHs) as highly efficient DeNOx photocatalysts was studied. LDHs with x = 0, 0.2 and 0.4 were prepared using a coprecipitation method. The samples were characterized by different techniques such as XRD, XPS, FT-IR, ICP-MS, TG, SBET, SEM and Diffuse reflectance (DR). The increased amount of copper ions in the LDH layers gave rise to slight changes in the structure and morphology and an important variation of the optical properties of the LDHs. The prepared ZnCuCr–CO3 photocatalysts exhibited favourable conversion efficiency (51%) and an extraordinary selectivity (97%) for the photochemical NO abatement. The photochemical mechanism was elucidated from DOS, EPR, Femtosecond transient absorption and in-situ DRIFTS studies. The results suggested that the presence of Cu2+ ions in the LDH framework introduced new states in the valence band states, thus favouring the production and mobility of e−/h+ charge carriers and a greater production of ⋅O2− and ⋅OH.

Light-storing assisted photocatalytic composite g-C3N4/Sr2MgSi2O7:(Eu,Dy) with sustained activity

The dependency of photocatalyst on light limits the large-scale application of photocatalysis technology. Thus, it was explored that the feasibility of the blue long afterglow phosphor and g-C3N4 for constructing a light-storing assisted photocatalytic composite with sustained activity in this study. The g-C3N4/Sr2MgSi2O7:(Eu,Dy) composite was prepared by a simple thermal polymerization method and the photocatalytic removal of NO under illumination and dark was studied. The experimental phenomena were explained from the aspects of optical properties, afterglow brightness and photoelectrochemical results. For the first time, the concept of cumulative pollutant degradation concentration(SC) was defined, which could be used as a quantitative index to evaluate the photocatalytic effect under illumination and dark. The results revealed that g-C3N4/Sr2MgSi2O7:(Eu,Dy) exhibited an enhanced photocatalytic activity under illumination due to the reduced recombination rate of carriers and the improved light absorption capacity. The existence of Sr2MgSi2O7:(Eu,Dy) as an internal light source endowed the composite with the ability to degrade pollutants continuously in the dark. The duration of photocatalysis in the dark was related to the brightness of afterglow and the photocatalytic activity. This study is helpful to promote the development of photocatalytic system with sustained activity.

Neodymium oxide (Nd2O3) coupled tubular g-C3N4, an efficient dual-function catalyst for photocatalytic hydrogen production and NO removal

Graphitic carbon nitride (g-C3N4) has emerged as a most promising photocatalyst, non-toxicity and low density, but it is plagued by low activity due to the small specific surface area and poor quantum efficiency. Morphological engineering and coupling with other materials to form hybrids have proven to be effective strategies for enabling high photocatalytic performances. Here, neodymium oxide (Nd2O3) coupled tubular g-C3N4 composites had been facilely synthesized by a solvent evaporation and high-temperature calcination method to realize efficient photocatalytic activity of hydrogen production and NO removal. A series of characterizations, such as XRD, ESR, in-situ DRIFTS, etc., were used to analyze the physical and chemical properties of the bifunctional photocatalyst, which demonstrated that the composite material had more active sites and a faster electron transfer rate. The optimal sample (1 wt% Nd2O3/CN-T) had a H2 generation rate of 4355.34 μmol·g−1·h−1, which was 9.46 times than that of original g-C3N4 obtained through heating melamine (CN-M). In addition, the NO removal rate was also 32.32% higher than that of original CN-M. On the basis of the above photocatalytic experimental results and characterizations, a possible mechanism or pathway was proposed and illustrated. This work could provide a feasible strategy to fabricate tubular g-C3N4-based composites with rare earth metal oxides (dual-factor regulation) to simultaneously enhance photocatalytic hydrogen production and NO removal efficiently (double application).

Synergistic photocatalytic NO removal of oxygen vacancies and metallic bismuth on Bi12TiO20 nanofibers under visible light irradiation

Tailoring the semiconductors with non-precious metals or defects have been demonstrated to be a fascinating and prospective approach for environmental remediation. In this work, Bi metal and oxygen vacancies (OVs) co-modified Bi12TiO20 nanofibers (Bi/BTO) photocatalysts were synthesized through electrospinning technique and subsequent chemical reduction method for the first time. The Bi/BTO composite photocatalysts exhibit significantly higher photocatalytic NO removal activity than that of pristine BTO under visible light irradiation. The improvement of photocatalytic performance is ascribed to the integrative effect of OVs and surface plasmon resonance (SPR) effect of Bi particles. The presence of OVs is confirmed by X-ray photoelectron spectroscopy and electron paramagnetic resonance spectroscopy. The density functional theory (DFT) calculations reveal that the OVs in BTO induce the formation of a defect level, which is beneficial to increase light absorption. In addition, Bi can act as an electron sink, boosting the separation of photoinduced electron-hole pairs. The trapping experiment and electron spin resonance spectra indicate that the main active species are ·O2− and h+. Moreover, the reaction process over 3% Bi/BTO is monitored by in situ infrared spectroscopy (in situ FTIR) and a reasonable photocatalytic mechanism of NO removal on Bi/BTO is proposed through a combination of experimental and theoretical results.

Synthesis of crystalline carbon nitride with enhanced photocatalytic NO removal performance: An experimental and DFT theoretical study

The pristine carbon nitride derived from the thermally-induced polymerization of nitrogen-containing precursors (e.g. cyanamide, dicyanamide, melamine and urea) displays low crystallinity because of the predominantly kinetic hindrance. Herein, we reported a modified molten-salts method to fabricate the crystalline carbon nitride under ambient pressure, which is expected to the large-scale production of crystalline carbon nitride. The obtained crystalline carbon nitride displayed about 3.0 times higher photocatalytic NO removal performance than that of pristine carbon nitride under visible light irradiation (λ < 400 nm). Detailed experimental characterization and theoretical calculation revealed the crucial roles of crystallinity in crystalline carbon nitride for the enhanced photocatalytic NO removal performance. This research provided deep insights into the crystallinity of carbon nitride for the enhanced photocatalytic performance.

Effect of oxygen vacancies and its quantity on photocatalytic oxidation performance of titanium dioxide for NO removal

In this work, black TiO2 catalysts containing a large number of oxygen vacancies were prepared by sol-gel and calcination methods. The catalytic activity of the photocatalysts was evaluated by photocatalytic oxidation removal of NO. We found that black TiO2 calcined at 400 °C in an N2 atmosphere with appropriate oxygen vacancy removes up to 71.3 % of NO in 90 min under the illumination of UV light, which was significantly better than other samples. The prepared catalyst was characterized by X-ray diffraction, Raman spectroscopy, UV–vis, XPS, EPR, BET surface area analysis and Photo-electrochemical test. These results showed that oxygen vacancies played an important role in the photocatalytic NO removal process. An appropriate amount of oxygen vacancies in catalyst benefits the aggregation of electrons in oxygen vacancies and a large number of electrons reacted with H2O2 and NO under UV light, thereby the activity enhanced. It was also found through EPR that the number of oxygen vacancies increased with the rise of temperature, which means that the number of oxygen vacancies would affect the catalyst performance.

Selective Bonding Effect of Heterologous Oxygen Vacancies in Z-Scheme Cu2O/SrFe0.5Ta0.5O3 Heterojunctions for Constructing Efficient Interfacial Charge-Transfer Channels and Enhancing Photocatalytic NO Removal Performances.

An interfacial structure is crucial to the photoinduced electron transport for a heterostructure photocatalyst. Constructing an interfacial electron channel with an optimized interfacial structure can efficiently improve the electron-transfer efficiency. Herein, the rapid electron-transfer channels were built up in a Cu2O/SrFe0.5Ta0.5O3 heterojunction (Cu2O/SFTO) based on the selective bonding effect of heterologous surface oxygen vacancies in the SFTO component. The heterologous surface oxygen vacancies, namely, VO-Fe and VO-Ta, respectively, adjacent to Fe and Ta atoms, were introduced into fabricating the Z-scheme Cu2O/SFTO heterojunction. Compared with sample Cu2O/SFTO with VO-Fe, the photocatalytic NO removal efficiency of sample Cu2O/SFTO with VO-Fe and VO-Ta was increased by 22.5%. The enhanced photocatalytic performance originated from the selective bonding effect of heterologous VO-Fe and VO-Ta on the interfacial electron-separating and -transfer efficiency. VO-Fe is the main body to construct the interfacial electron-transfer channels by forming interfacial Fe-O-Cu(I) bonds, which causes lattice distortion at the interface, and VO-Ta can optimize the structure of interfacial channels by balancing the electron density of SFTO to control the average space of the interface transition zone. This research provides a new cognitive perspective for constructing double perovskite oxide-based heterostructure photocatalysts.

Reductant-free synthesis of oxygen vacancies-mediated TiO2 nanocrystals with enhanced photocatalytic NO removal performance: An experimental and DFT study

Herein, we developed a reductant-free strategy to fabricate oxygen vacancies-mediated (OVs-mediated) TiO2 nanocrystals. Different from the conventional reduction process, OVs-mediated TiO2 were synthesized via a low-temperature calcination in nitrogen atmosphere assisted solvothermal process. Firstly, the pristine TiO2 was synthesized by solvothermal process using the tetra-n-butyl titanate as precursor and ethanol as solvent. Because of the organic precursor and solvent, the obtained pristine TiO2 was inevitably carbon-doped. Then, low-temperature calcination in nitrogen atmosphere instead of reducing gas atmosphere was carried out to introduce the OVs into the pristine TiO2. Experimental and theoretical results revealed that the intrinsic carbon-doping was conducive to the formation of OVs. Moreover, the obtained OVs-mediated TiO2 exhibited outstanding photocatalytic performance in comparison with the commercial P25, which was attributed to the crucial roles of OVs. This work not only provided a novel synthesis of OVs-mediated TiO2, but also contributed to understanding the crucial roles of OVs.