In situ construction of biocompatible Z-scheme alpha-Bi2O3/CuBi2O4 heterojunction for NO removal under visible light

The design of efficient, stable and biocompatible photocatalysts for air purification is still a challenge. In this work, we report a Z-scheme alpha-Bi2O3/CuBi2O4 composite with high-quality interfaces using an in situ synthesis method. The alpha-Bi2O3/CuBi2O4 displays significantly enhanced photocatalytic activity for NO removal (30 %) in comparison with alpha-Bi2O3 (17 %) under visible light irradiation. Based on characterizations, theoretical calculations and ESR tests, the Z-scheme migration mechanism of photoinduced electrons and holes on alpha-Bi2O3/CuBi2O4 heterojunction was proposed. The formation of intermediates and products was monitored by in situ DRIFTS. The NO adsorption and activation on alpha-Bi2O3/CuBi2O4 surface are more favorable than that on alpha-Bi2O3 surface. The alpha-Bi2O3/CuBi2O4 also shows high selectivity for the conversion of NO to NO- 3. Moreover, the cytotoxicity of alpha-Bi2O3/CuBi2O4 exposed to human alveolar epithelial cell has been evaluated for its potential application in air purification. This work provides a new perspective regarding the design of Z-scheme heterojunctions by an in situ method and a promising photocatalyst suitable for air pollution control

Chemical etching fabrication of uniform mesoporous Bi@Bi2O3 nanospheres with enhanced visible light-induced photocatalytic oxidation performance for NOx

Bulk materials with a microporous structure are adverse to light adsorption, photoelectron and reactant transport in a photocatalytic reaction. Mesoporous photocatalysts have shown many marked advantages in photo catalytic fields. Herein, uniform mesoporous Bi@Bi2O3 nanospheres were fabricated by HCl-ethanol chemical etching at low temperature (60 degrees C). The obtained mesoporous photocatalysis increased the NO removal efficiency (16%) and inhibited toxic NO2 generation (3%) under visible light irradiation. Further oxidation of Bi and calcination at high temperatures were avoided during template removal. Moreover, the as-prepared sample possessed a remarkably narrower pore size distribution (3.2-3.9 nm) and stronger light and NO adsorption ability than the bulk microporous Bi@Bi2O3. Work function and the electron spin resonance test results also indicated that the position of the entire energy bands on Bi2O3 was lowered. The amount of reactive oxygen species generated over the uniform mesoporous structure was higher than that over bulk Bi@Bi2O3. However, photoelectrochemical measurements indicated that the separation efficiencies of the photo-generated carriers were not improved over the uniform mesoporous Bi@Bi2O3. Comprehensive studies have shown that the oxi-dation ability rather than the enhanced separation efficiency of charge carriers accounted for the enhanced photocatalytic activity. This work elucidates the roles of a uniform mesoporous structure in NOx photocatalytic oxidation and provides an efficient strategy for structural engineering in preparing highly reactive and practical photocatalysts

Heterogeneous activation of peroxymonosulfate by LaFeO3 for diclofenac degradation: DFT-assisted mechanistic study and degradation pathways

A perovskite oxide, LaFeO3 (LFO), was synthesized and evaluated as a heterogeneous catalyst to activate peroxymonosulfate (PMS) for the oxidative degradation of diclofenac (DCF), a non-steroidal anti-inflammatory drug. It was observed that the catalytic activity of LFO was much higher than that of Fe2O3. LFO catalyzed PMS to degrade DCF with a turnover frequency (2.02 x 10(-3) min(-1))which is 17-fold higher than that of Fe2O3. Both sulfate and hydroxyl radicals were identified during LFO-activated PMS process by electron spin resonance (ESR). Radical competitive reactions indicate sulfate radicals played a major role in DCF degradation by LFO/PMS process. The PMS decomposition can be attributed to the formation of an inner-sphere complexation between the Fe (III) sites on LFO surface and PMS. Theoretical calculations illustrated the strong interaction between PMS and Fe (III) and electron transfer from PMS to Fe (III). Hydrogen temperature-programmed reduction (H-2-TPR) indicates that the LFO perovskite oxide is capable of facilitating an easier reduction of Fe (III) to mediate a redox process. Oxygen temperature-programmed desorption (O-2-TPD) suggests much more oxygen vacancies exist in LFO than in Fe2O3. Oxygen vacancies are favorable for the formation of chemical bond between Fe (III) and PMS and the activation of PMS. In situ ATR-FTIR analysis of LFO surface during PMS decomposition implies Fe (III)-Fe(II)-Fe (III) redox cycle was believed to account for the generation of sulfate radical. The intermediates generated during DCF degradation were identified and the possible degradation pathways were advanced in LFO/PMS system

Enhanced peroxymonosulfate activation by Cu-doped LaFeO3 with rich oxygen vacancies: Compound-specific mechanisms

The degradation reaction mechanisms of organic pollutants by peroxymonosulfate (PMS) activation processes remain controversial. In this study, Cu-doped LaFeO3 samples were prepared and used as heterogeneous catalysts of PMS for the degradation of pharmaceuticals. Compared to LaFeO3 (LFO), the increased catalytic activity of LaFe1-xCuxO3 (LFCO) samples was observed, among which LFCO-7.5 exhibited the best performance. The enhanced catalytic activity of LFCO-7.5 was attributable to the generation of abundant oxygen vacancies. Hydroxyl radicals, sulfate radicals, superoxide and singlet oxygen were detected in the LFCO-7.5/PMS system. However, selective effects of radical scavengers on the degradation of different pharmaceuticals and selective reactivity of singlet oxygen toward different pharmaceuticals indicate the existence of compound-specific degradation mechanisms in the LFCO-7.5/PMS system. Furthermore, possible degradation pathways of SDZ and the toxicity evolution were investigated during sulfadiazine (SDZ) degradation. This study further enhances our knowledge on the degradation reaction mechanisms of organic pollutants in PMS activation processes

Environment-Friendly Carbon Quantum Dots/ZnFe2O4 Photocatalysts: Characterization, Biocompatibility, and Mechanisms for NO Removal

A highly efficient and environmentally-friendly oxidation process is always desirable for air purification. This study reported a novel carbon quantum dots (CQDs)/ZnFe2O4 composite photocatalyst for the first time through a facile hydrothermal process. The CQDs/ZnFe2O4 (15 vol %) composite demonstrates stronger transient photocurrent response, approximately 8 times higher than that of ZnFe2O4, indicating superior transfer efficiency of photogenerated electrons and separation efficiency of photogenerated electron hole pairs. Compared with pristine ZnFe2O4 nano particles, CQDs/ZnFe2O4 displayed enhanced photocatalytic activities on gaseous NOx removal and high selectivity for nitrate formation under visible light (lambda > 420 nm) irradiation. Electron spin resonance analysis and a series of radical-trapping experiments showed that the reactive species contributing to NO elimination were center dot O-2(-) and center dot OH radicals. The possible mechanisms were proposed regarding how CQDs improve the photocatalytic performance of ZnFe2O4. The CQDs are believed to act as an electron reservoir and transporter as well as a powerful energy-transfer component during the photocatalysis processes over CQDs/ZnFe2O4. samples. Furthermore, the toxicity assessment authenticated good biocompatibility and low cytotoxity of CQDs/ZnFe2O4. The results of this study indicate that CQDs/ZnFe2O4 is a promising photocatalyst for air purification

Protonated g-C3N4/Ti( )(3+)self-doped TiO2 nanocomposite films: Room-temperature preparation, hydrophilicity, and application for photocatalytic NOx removal

Fabrication of photocatalysis films with good adhesion, hydrophilicity, and high activity on substrates at room temperature is essential for their application in air pollution control. Herein, functionalized transparent composite films containing ultrathin protonated g-C3N4 (pCN) nanosheets and Ti3+ self-doped TiO2 nanoparticles (pCN/TiO2) were fabricated on glass at room temperature. Thickness of the films measures 80 nm with surface roughness of 7.16 nm. The adhesion ability was attributed to the viscosity of TiO2 sol, which served as "chemical glue" in the films. The high photo-induced hydrophilicity demonstrated their self-cleaning potential. pCN/TiO2 films showed remarkably high visible-light-driven activity in terms of NO removal in a continuous-flow mode. Photoelectrochemical tests demonstrated the superior charge separation efficiency of pCN/TiO2 films compared with that of pristine TiO2. As identified by electron spin resonance spectra, center dot O-2(-) and center dot OH radicals were the key reactive species involved in NO removal. The possible mechanism for photocatalytic NO oxidation was proposed. Potential cytotoxicity of pCN/TiO2 films was evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay to ensure the biosecurity. This work provides a facile route to fabricate nanocomposite films under ambient temperature. The nanocomposite films were characterized by photo-induced hydrophilicity, high NO removal efficiency, and good biocompatibility, showing its potential in large-scale application

Visible-Light-Driven Nitrogen-Doped Carbon Quantum Dots/CaTiO₃ Composite Catalyst with Enhanced NO Adsorption for NO Removal

Nitrogen oxides (NO_<i>x</i>) have attracted extensive concerns as a secondary aerosol precursor in recent years. Solar-induced photocatalytic oxidation is a promising strategy for of NO_<i>x</i> removal nowadays. In this contribution, nitrogen-doped carbon quantum dots (N-CQDs)/CaTiO₃ composite was synthesized using a facile hydrothermal process. The incorporation of N-CQDs to CaTiO₃ facilitates the transfer of electrons and divorce of photogenerated carriers. NO temperature-programmed desorption (NO-TPD) demonstrated that the presence of N-CQDs was conducive to the NO adsorption in comparison with the pristine CaTiO₃. The composite catalyst demonstrated much better photocatalytic performance than CaTiO₃ and P25 did in regard to gaseous NO removal and NO₂ selectivity under visible light irradiation. Both •O₂^– and •OH are believed to make a major contribution to NO removal. The role of N-CQDs was unraveled in the photocatalytic reaction of NO elimination over N-CQDs/CaTiO₃ samples. This study provides insight into the composite catalyst N-CQDs/CaTiO₃ in photocatalytic reactions and applications