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NOx emissions cause many negative impacts on the living environment. The photocatalysis of semiconductors is superior for nitric oxide (NO) degradation due to their low redox potential. In this report, we combine SnO2-x/g-C3N4 heterojunction photocatalyst toward the high selectivity into green products under visible light illumination. Results show that SnO2-x/g-C3N4 heterojunction degraded 40.8% of NO, which is 1.6 times higher than that of g-C3N4. In addition, the selectivity coefficient of SnO2-x/g-C3N4 is higher 3 times than both pure SnO2-x and g-C3N4. Furthermore, SnO2-x/g-C3N4 expresses a superior stability for NO photocatalytic-degradation after five cycles. The scavenger trapping test results, and electron spin resonance (ESR) analysis also provide more understanding of the charge transfer mechanism of materials. SnO2-x/g-C3N4 heterojunction shows a high removal efficiency of NO gas, making it an up-and-coming environmental treatment candidate.

Titania (TiO2) as a commercial photocatalyst has been continually struggling due to the limitation of ultraviolet light response and the high recombination rate of photoinduced carriers. The development of heterojunction nanostructures provides great promise to achieve the activation by visible light and suppress the photoinduced electron-hole pairs recombination. Herein, we synthesized a SnO2 and TiO2 nanotube heterojunction (SnO2/TNT) via a one-step hydrothermal strategy and systematically investigated NO photocatalytic degradation over the SnO2/TNTs heterojunction under visible light at the parts per billion level. Various physicochemical characterization techniques were conducted to verify the physical and chemical properties of the materials. For example, the morphology and lattice spacings of the materials were examined by high-resolution TEM (HR-TEM) images and selected area electron diffraction (SAED) pattern, X-ray photoelectron spectroscopy (XPS) was employed to study the oxidation states and propose the band alignment diagram of the SnO2/TNTs heterojunction, and photoluminescence spectroscopy was employed for understanding of carrier's trapping, migration and transfer. The photocatalytic results show that the SnO2/TNTs heterojunction exhibits the superior photocatalytic performance, and the photocatalytic degradation efficiency of NO can reach 60% under visible light with effective inhibition of NO2 production. The excellent photocatalytic ability is due to the low recombination rate of the photoinduced electron-hole pairs. Furthermore, a trapping experiment was combined with electron spin resonance (ESR) and utilized to identify the involvement of reactive radicals in the photocatalysis process suggesting that and OH mediated pathways play a predominant role in NO removal.

In this study, we classified the effect of the annealing temperature on silver-loaded TiO2 nanotubes (Ag/TNTs). X-ray diffraction results demonstrate that TNTs have a tendency of phase transformation owing to silver nanoparticles (Ag NPs). The Brunauer–Emmett–Teller method indicates that Ag/TNTs is a mesopore material and the surface area of Ag/TNTs decreases when the annealing temperature increases. This research concluded that the TNT structure begins to break at high annealing temperatures (>400 °C) and is completely broken at 500 °C. The average diameter of the Ag NPs in Ag/TNTs increases linearly with the annealing temperature. In addition, this study clearly explained the oxidation state transformation of Ag in Ag/TNTs under the impact of the annealing temperature, therein, the Ag0 state is transferred completely to Ag+ at 400 °C, and some Ag+ is oxidized to form Ag2+. The Ag/TNTs and Ag/TNTs annealed at 300 °C provided the good methylene blue photodegradation ability for 150 min under sunlight condition.

Enhancing and investigating the photocatalytic activity over composites for new models remains a challenge. Here, an emerging S-scheme photocatalyst composed of 2D/0D g-C3N4 nanosheets-assisted SnO2 nanoparticles (g-C3N4/SnO2) is successfully synthesized and used for degrading nitrogen oxide (NO), which causes negative impacts on the environment. A wide range of characterization techniques confirms the successful synthesis of SnO2 nanoparticles, g-C3N4 nanosheets, and 2D/0D g-C3N4/SnO2 S-scheme photocatalysts via hydrothermal and annealing processes. Besides, the visible-light response is confirmed by optical analysis. The S-scheme charge transfer was elucidated by Density-Functional Theory (DFT) calculation, trapping experiments, and electron spin resonance (ESR). We found that intrinsic oxygen vacancies of SnO2 nanoparticles and S-scheme charge transfer addressed the limitation of other heterojunction types. It is notable that compared pure SnO2 nanoparticles and g-C3N4, g-C3N4/SnO2 offered the best photocatalytic NO degradation and photostability under visible light with the removal of more than 40% NO at 500 ppb throughout the experiment. Benefiting from the unique structural features, the new generation architectural structure of S-scheme heterojunction exhibited potential photocatalytic activity and it would simultaneously act more promising for environmental treatment in the coming years.

Photocatalysis is an emerging tool used for the reduction of air pollutants. In the atmosphere, nitrogen oxide (NO) is one of the leading pollutants because of its detrimental effects on flora and fauna. This work introduces the photocatalytic NO degradation over Ag nanoparticles-decorated Bi2S3 nanorods. The XRD, FTIR, XPS, SEM, EDS, and TEM demonstrate the existence of the materials, with the morphology of Ag nanoparticles (NPs) loading on Bi2S3 nanorods. The increase in surface area and pore volume of Bi2S3 nanorods thanks to Ag is confirmed by nitrogen adsorption–desorption isotherm using BET. The NO removal efficiency over 3% Ag@Bi2S3 is 31.12%, while that of pure Bi2S3 is only 11.65%. The band bending and surface plasmon resonance (SPR) enhance the photocatalytic activity are confirmed by DRS and Mott–Schottky plot. The high stability of materials were surveyed by recycle test, XRD, and FTIR. The ESR and trapping experiments support to determine the unique photocatalytic mechanism of Ag@Bi2S3 via •HO2 radicals. This study provides an unique understanding about of Ag@Bi2S3 for nitrogen oxides (NO x ) degradation under solar light.

Photocatalytic materials present a robust approach in tackling pollutants in the air. However, the involving reactions and their associated toxicity, those are important for practical implications, have not been sufficiently reported. Here, we synthesize ZnSn(OH)6 and control its morphology by changing NaOH's dosage in a one-step hydrothermal growth. Combining results from density functional theory and experimentation, we initiatively show the roles of exposed facets, oxygen defects, metal terminated surface, and bandstructure of ZnSn(OH)6. By carefully characterizing reactions during DeNOx and DeVOC processes, this work enables a comprehensive understanding of photocatalytic activity against pollution of nitric oxide and VOCs. Also, a new systematic calculation of the apparent DeNOx index is introduced for evaluating the total toxicity. The trapping experiments reveal a balance in the involvement of e–, h+, •OH radicals in the photocatalytic DeNOx and DeVOC. Thus, our findings would enable an important understanding of addressing air pollution using high-performance photocatalysts and proper evaluation of total toxicity.

The increase of formaldehyde in the air causes many problems in the environment. The photocatalytic method is green, inexpensive, high sufficiency, but challenging to use because of photocatalysts’ wide bandgap working only under the UV light, which is accounted for less than 5% of the sunlight. Here, gold-assisted ZnSn(OH)6 microcubes (Au:cZHS) were produced by a hydrothermal process of cZHS, a well-known catalyst for NOx and VOCs removal. The existence and unique morphology of the Au:cZHS composites were confirmed by the characterizations of X-ray diffraction (XRD), Fourier transformation infrared spectroscopy (FTIR), Raman spectroscopy, field-emission scanning electron microscopy (FESEM), and high-resolution transmission electron microscopy (HRTEM). The band structure and charge-transfer processes of the materials were evaluated from the results of the UV–Vis diffuse reflectance spectroscopy (DRS), electrochemical impedance spectroscopy (EIS), and Mott–Schottky. These results indicated the Au:cZHS composites have a high sufficiency of charge transport and near-visible light absorption. The electron spin resonance (ESR) was also used to determine reactive oxygen species producing from photocatalytic reactions. In addition, the reaction rates and apparent quantum efficiency (AQE) were calculated for a better comparison with other studies. In addition, the 10% Au:cZHS removed more than 70% of 1 ppb formaldehyde (HCHO) under solar light. These results indicate that the Au:cZHS is a promising photocatalyst for air treatment.

Herein, Ag@SnO2 nanocomposite (NC) is prepared by UV-assisted depositing of Ag nanoparticles (NPs) onto hydrothermally synthesized SnO2 NPs surface without any additional assistance. To characterize the NC, transmission electron microscope (TEM) images, selected area electron diffraction (SAED), X-ray diffraction (XRD), and energy-dispersive X-ray (EDX) patterns are employed. The understanding of kinetics, photostability, and species lifespan in the NC are thoroughly studied with experiments and time-dependent electron spin resonance (ESR). The Ag@SnO2 exhibits an outstanding NO photocatalytic removal performance (70%) and low conversion of NO2 (4%) after 30 min under solar light. The Ag@SnO2 promises a potential application for air remediation.