Aqueous secondary organic aerosol formation from the direct photosensitized oxidation of vanillin in the absence and presence of ammonium nitrate

Vanillin (VL), a phenolic aromatic carbonyl abundant in biomass burning emissions, forms triplet excited states (3VL∗) under simulated sunlight leading to aqueous secondary organic aerosol (aqSOA) formation. Nitrate and ammonium are among the main components of biomass burning aerosols and cloud or fog water. Under atmospherically relevant cloud and fog conditions, solutions composed of either VL only or VL with ammonium nitrate were subjected to simulated sunlight irradiation to compare aqSOA formation via the direct photosensitized oxidation of VL in the absence and presence of ammonium nitrate. The reactions were characterized by examining the VL decay kinetics, product compositions, and light absorbance changes. Both conditions generated oligomers, functionalized monomers, and oxygenated ring-opening products, and ammonium nitrate promoted functionalization and nitration, likely due to its photolysis products (⚫OH, ⚫NO2, and NO2- or HONO). Moreover, a potential imidazole derivative observed in the presence of ammonium nitrate suggested that ammonium participated in the reactions. The majority of the most abundant products from both conditions were potential brown carbon (BrC) chromophores. The effects of oxygen (O2), pH, and reactants concentration and molar ratios on the reactions were also explored. Our findings show that O2 plays an essential role in the reactions, and oligomer formation was enhanced at pH <4. Also, functionalization was dominant at low VL concentrations, whereas oligomerization was favored at high VL concentrations. Furthermore, oligomers and hydroxylated products were detected from the oxidation of guaiacol (a non-carbonyl phenol) via VL photosensitized reactions. Last, potential aqSOA formation pathways via the direct photosensitized oxidation of VL in the absence and presence of ammonium nitrate were proposed. This study indicates that the direct photosensitized oxidation of VL may be an important aqSOA source in areas influenced by biomass burning and underscores the importance of nitrate in the aqueous-phase processing of aromatic carbonyls.

Photolysis of the Insensitive Explosive 1,3,5-Triamino-2,4,6-trinitrobenzene (TATB)

The explosive 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) is of particular interest due to its extreme insensitivity to impact, shock and heat, while providing a good detonation velocity. To determine its fate under environmental conditions, TATB powder was irradiated with simulated sunlight and, in water, under UV light at 254 nm. The hydrolysis of particles submerged in neutral and alkaline solutions was also examined. We found that, by changing experimental conditions (e.g., light source, and mass and physical state of TATB), the intermediates and final products were slightly different. Mono-benzofurazan was the major transformation product in both irradiation systems. Two minor transformation products, the aci-nitro form of TATB and 3,5-diamino-2,4,6-trinitrophenol, were detected under solar light, while 1,3,5-triamino-2-nitroso-4,6-dinitrobenzene, 1,3,5-triamino-2,4-dinitrobenzene and mono-benzofuroxan were produced under UV light. The product identified as 3,5-diamino-2,4,6-trinitrophenol was identical to the one formed in the dark under alkaline conditions (pH 13) and in water incubated at either 50 °C or aged at ambient conditions. Interestingly, when only a few milligrams of TATB were irradiated with simulated sunlight, the aci-isomer and mono-benzofurazan derivative were detected; however, the hydrolysis product 3,5-diamino-2,4,6-trinitrophenol formed only much later in the absence of light. This suggests that the water released from TATB to form mono-benzofurazan was trapped in the interstitial space between the TATB layers and slowly hydrolyzed the relatively stable aci-nitro intermediate to 3,5-diamino-2,4,6-trinitrophenol. This environmentally relevant discovery provides data on the fate of TATB in surface environments exposed to sunlight, which can transform the insoluble substrate into more soluble and corrosive derivatives, such as 3,5-diamino-2,4,6-trinitrophenol, and that some hydrolytic transformation can continue even without light.

Two-dimensional ultrathin MoS2 modified hydrogenated TiO2 nanoparticles for superior photocatalytic degradation under simulated sunlight

In this study, we firstly synthesized hydrogenated TiO2 nanoparticles (HT) by calcining P25, and on the basis of HT, MoS2/hydrogenated TiO2 binary composites with different component ratios (MHT-20%, MHT-30% and MHT-35%) were controlled prepared. Uv-vis DRS showed that the HT nanoparticles exhibited stronger absorption towards visible light compared to P25, and the introduction of two-dimensional ultrathin MoS2 nanosheets further enhanced the visible light absorption ability of MHT composites. Under simulated sunlight irradiation, the removal test of methylene blue (MB) in the present of various photocatalysts indicated that the catalytic performance of HT sample was better than that of P25, and MHT binary composites displayed more excellent photocatalytic performance. A maximum removal efficiency of MB reached 95% within 4 h over MHT-30% photocatalyst. In addition, repeated photodegradation studies and composition analysis of MHT-30% before and after photocatalytic reaction showed that MHT-30% photocatalyst exhibited good stability, and the removal rate of MB still reached 88% in four cycles. The improved and stable photocatalytic performance of MHT-30% can be attributed to band matching and tight interface bonding between MoS2 and HT, which accelerated the electron transfer and broaden the visible-light response range.

Photoelectrochemical and Photo-Fenton Mechanism of Enhanced Visible Light-Driven Nanocatalyst Synthesis of ZnFe2O4/BiOI

Based on the fact that the photo-Fenton process can directly use solar energy to degrade various pollutants, it has received widespread attention. However, it has attracted widespread attention due to the rapid recombination of photo-generated carriers and the low light response range. Therefore, the construction of a Z-scheme heterojunction in this paper can effectively enhance the electron-hole separation, increase the reduction and oxidation potential, and enhance the redox capability of the photocatalyst. This paper reports the successful preparation of visible-light-induced ZnFe2O4/BiOI composite photocatalyst. There is a Z-scheme heterojunction structure of ZnFe2O4 and BiOI. At the same time, the PL and UV absorption spectra showed that the light absorption performance of the composite nanomaterials was enhanced, the photo-generated carriers recombination rate was reduced, and the photo-Fenton performance was also significantly improved. And the photocurrent of ZnFe2O4/BiOI is more than 29 times that of pure ZnFe2O4. In addition, ZnFe2O4/BiOI can degrade the simulated pollutant RhB 100% within 20 min under simulated sunlight. It shows that ZnFe2O4/BiOI binary composite has excellent photo-Fenton properties. In addition, ZnFe2O4/BiOI still maintains a high photo-Fenton ability after three cycles. Therefore, it has potential application prospects of the industrial photodegradation of organic pollutants.

Carbon nanotubes as electronic mediators combined with Bi2MoO6 and g-C3N4 to form Z-scheme heterojunctions to enhance visible light photocatalysis

In this paper, Z-scheme Bi2MoO6/CNTs/g-C3N4 composite-photocatalysts were prepared through a simple hydrothermal method. The analysis was performed by XRD, FT-IR, SEM, EDS, TEM, HRTEM, XPS, BET, UV-Vis diffuse reflectance and PL spectrums. Various analyses show that CNTs not only act as excellent charge transfer bridges, but also enable the formation of a Z-scheme of charge transfer mechanism between Bi2MoO6 and g-C3N4. This process not only effectively isolates electrons and holes, but also prolongs electron-hole pair lifetimes, resulting in a substantial improvement in the photocatalytic performance of the composite photocatalyst. Best photocatalytic degradation performance was shown by Bi2MoO6/CNTs/g-C3N4 composite photocatalyst under simulated sunlight, while the composite photocatalyst still maintained extremely high degradation performance in cycling tests.