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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.

The facile fabrication of g-C3N4/SnO2 S-scheme heterojunctions for photocatalytic removal of NO under visible light is reported. Optical and electrochemical investigations indicate the formation of these heterojunctions that enable bending at the interface of g-C3N4 and SnO2 and give rise to an efficient separation. A high photocatalytic 500-ppb NO removal performance of 35% and low NO2 generation of 2% are realized after 30 min of visible light irradiation upon the g-C3N4/SnO2 heterojunction with 30% of g-C3N4 addition. In contrast, the bare g-C3N4 extensively produces NO2 greater than 12% compared to 30% from the g-C3N4 sample. This study also shows that the g-C3N4/SnO2 heterojunction is a stable catalyst system and superoxide radicals play a crucial role in the photocatalytic NO removal. Since the preparation of the g-C3N4/SnO2 heterojunction reported in this work is straightforward, it can potentially enable the preparation of highly robust visible-light-driven photocatalysts to remove NO pollution.

Photocatalysis has been studied and considered as a green and practical approach in addressing environmental pollution. However, factors that affect photocatalytic performance have not been systematically studied. In this work, we have presented a comprehensive roadmap for characterizing, interpreting, and reporting semiconductors' electrical and optical properties through routinely used techniques such as diffuse reflectance spectroscopy, electrochemical techniques (Mott-Schottky plots), photoluminescence, X-ray photoelectron spectroscopy, and ultraviolet photoelectron spectroscopy in the context of photocatalysis. Having precisely studied the band structure of three representative photocatalysts, we have presented and highlighted the essential information and details, which are critical and beneficial for studies of (1) band alignments, (2) redox potentials, and (3) defects. Further works with a comprehensive understanding of the band structure are desirable and hold great promise.

The pursuit of robust photocatalysts that can completely degrade organic contaminants with high performance as well as high energy efficiency, simplicity in preparation, and low cost is an appealing topic that potentially promotes photocatalysts for being used widely. Herein, we introduce a new and efficient SnO2/Bi2S3/BiOCl–Bi24O31Cl10 (SnO2/Bi2S3-Bi25) composite photocatalyst by taking advantage of the robust, simple, and potentially scalable one-pot synthesis, including the hydrothermal process followed by thermal decomposition. Interestingly, we observed the formation of BiOCl–Bi24O31Cl10 (abbreviated as Bi25) heterojunctions derived from reactions between Bi2S3 and SnCl4·5H2O precursor solutions under the hydrothermal condition and thermal decomposition of BiOCl. This Bi25 heterojunction acts as an interface to reduce the recombination of photogenerated electron–hole (e––h+) pairs as well as to massively enhance the visible light harvesting, thereby significantly enhancing the photocatalytic degradation performance of the as-prepared composite photocatalyst. In detail, the photocatalytic degradation of Rhodamine B (RhB) activated by visible light using 15% SnO2/Bi2S3-Bi25 shows the efficiency of 80.8%, which is superior compared to that of pure Bi2S3 (29.4%) and SnO2 (0.1%). The SnO2/Bi2S3-Bi25 composite photocatalyst also presents an excellent photostability and easy recovery from dye for recycling. The trapping test revealed that the photogenerated holes play a crucial factor during the photocatalytic process, whereas superoxide radicals are also formed but not involved in the photocatalytic process. Successful fabrication of SnO2/Bi2S3-Bi25 composite photocatalysts via a straightforward method with drastically enhanced photocatalytic performance under visible light activation would be useful for practical applications.

Photocatalysis has been studied and considered as a green and effective approach in addressing environmental pollution. However, factors that affect photocatalytic performance have not been systematically studied. In this work, we have presented a comprehensive roadmap for characterizing, interpreting, and reporting semiconductors' electrical and optical properties through routinely used techniques such as diffuse reflectance spectroscopy (DRS), electrochemical techniques (Mott-Schottky plots), photoluminescence (PL), X-ray photoelectron spectroscopy (XPS ), and ultraviolet photoelectron spectroscopy (UPS) in the context of photocatalysis. Having deeply and precisely studied the band structure of three representative photocatalysts, we have presented and highlighted essential information and details, which are critical and beneficial for studies of (1) band alignments, (2) redox potentials, and (3) defects. Further works with a comprehensive understanding of band structure are desirable and hold great promise.

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.

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-C

This chapter compares the properties of different light sources. A comprehensive comparison reports the advantages and disadvantages of chemical reduction and photoreduction methods. The role of light in the nanoparticle formation mechanism is proposed with the evidence from previous studies. Interestingly, the factors affecting the properties of nanoparticles, such as light sources, photoreduction time, and chemical concentration, are reviewed and evaluated. This chapter also provides examples of the synthesis of nanoparticles via the photoreduction method. In addition, a comprehensive comparison discriminates the chemical reduction and photoreduction methods with clear examples of their advantages and disadvantages. Finally, the potential of the photoreduction method is described to support the readers’ perspective in the green synthesis of nanomaterials.

This is the first time the SnO2/PANI nanocomposite was utilized for the nitrogen oxide (NO) photocatalytic degradation. In addition, the properties of the SnO2/PANI nanocomposite were deeply studied by various characterizations. The results showed that the photostability of PANI has been improved and the SnO2/PANI nanocomposite demonstrated the efficient NO photocatalytic degradation. Notably, in this work, the adsorption and photocatalytic mechanisms, polymer photodegradation, and the band structure of the SnO2/PANI nanocomposite were fully and systematically investigated via experimental measurements and density functional theory (DFT).

Tin oxide nanoparticles (SnO2 NPs) with a diameter less than 10 nm are usually used in waste water treatment via the photocatalytic reaction. However, SnO2 nanoparticles were not clearly studied for this NO photodegradation. In this study, SnO2 NPs were hydrothermally prepared and measured via characterization techniques such as high-resolution transmission electron microscope (HR-TEM) and high-resolution X-ray photoelectron spectroscopy (HR-XPS). This is the first report of using SnO2 NPs for NO photodegradation. The results show that the NO photodegradation result showed that SnO2 NPs degraded 63.37% NO (higher than approximately 2 times compared with P25 catalyst) after 30 min under solar light and the NO2 yield is only 1.66%. Moreover, SnO2 nanoparticles are very stable indicating NO gas photodegradation efficiency about 58.96% after five photocatalytic cycles. In addition, reactive radicals in the photocatalysis processes were identified via the trapping experiment and electron spin resonance (ESR) study. Based on the aforementioned experimental results, a detailed photocatalytic mechanism was systematically investigated. The high photocatalytic performance and the stability of SnO2 NPs under solar light will open to a promising application.

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.

Here, we synthesized copper(I) oxide and titanium dioxide nanotubes (TNTs) heterojunctions (HJs) by a photoreduction method using a low-power UV lamp without involving any additional steps, such as chemical reduction, surfactant, or protection agents. Transmission electron microscopy, X-ray diffraction, Raman scattering, X-ray photoelectron spectroscopy, diffuse reflectance spectra, and photoluminescence spectroscopy were carried out to verify the formation of a HJ between the Cu2O nanoparticles (Cu2O NPs) and TNTs. The efficiency and the rate of methylene blue photo-degradation over the Cu2O/TNTs HJ were found to be nearly double and triple compared to the isolated TNTs. The enhanced efficiency is attributed to the narrow band gap and defect states caused by the oxygen vacancies in the vicinity of HJs. Moreover, the type II band alignment of Cu2O NPs and TNTs naturally separates the photo-generated carriers and constrains the recombination process owing to the internal electric field across the Cu2O/TNTs interface.

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.

Titania (TiO

Here, we synthesized copper(i) oxide and titanium dioxide nanotubes (TNTs) heterojunctions (HJs) by a photoreduction method using a low-power UV lamp without involving any additional steps, such as chemical reduction, surfactant, or protection agents. Transmission electron microscopy, X-ray diffraction, Raman scattering, X-ray photoelectron spectroscopy, diffuse reflectance spectra, and photoluminescence spectroscopy were carried out to verify the formation of a HJ between the Cu