Efficient Visible Light Photocatalytic Oxidation of NO on Aerosol Flow-Synthesized Nanocrystalline InVO₄ Hollow Microspheres

In this study, aerosol flow-synthesized (AFS) nanocrystalline InVO4 hollow microspheres (AFS-InVO4) were used to oxidize gaseous NO at indoor air level under visible light and compared with hydrothermally synthesized InVO4 counterpart powder. Results revealed that the AFS-InVO4 hollow spheres exhibited higher photocatalytic activity than the hydrothermally synthesized counterpart. The photocatalytic activity enhancement could be attributed to the large surface area and special hollow structures, which were favorable for the diffusion of intermediates and the deactivation inhibition of photocatalyst during the photocatalytic reaction. Fourier transform infrared spectroscopy results confirmed the generation of nitric acid on the AFS-InVO4 surface during the photocatalysis of NO in the gas phase, suggesting that the oxidation of NO molecules was the major process in this photocatalytic reaction. Multiple runs of the photocatalytic NO removal revealed that the AFS-InVO4 hollow spheres were very stable during photocatalysis. This study presents a promising approach for scaling up industrial production of InVO4 hollow spheres with improved photocatalytic activity for indoor air purification

Efficient Visible Light Photocatalytic Removal of NO with BiOBr-Graphene Nanocomposites

In this study, we demonstrate that bismuth oxybromide and graphene nanocomposites (BGCs) exhibit superior performance on photocatalytic removal of gaseous nitrogen monoxide (NO) to pure BiOBr under visible light irradiation (λ > 420 nm). The photocatalytic NO removal rate constant of BGCs was 2 times that of pure BiOBr. The BGCs were prepared by a facile solvothermal route with using graphene oxide (GO), bismuth nitrite, and cetyltrimethyl ammonium bromide (CTAB) as the precursors. During the synthesis, both of the reduction of GO and the formation of BiOBr nanocrystals were achieved simultaneously. On the basis of the characterization results, we attributed the enhanced photocatalytic activity of the BGCs nanocomposites to more effective charge transportations and separations arisen from the strong chemical bonding between BiOBr and graphene, not to their light absorption extension in the visible region and higher surface area

Interfacial Hydrothermal Synthesis of Cu@Cu₂O Core−Shell Microspheres with Enhanced Visible-Light-Driven Photocatalytic Activity

In this study, core−shell Cu@Cu2O microspheres were synthesized with an interfacial hydrothermal method. The resulting products were systematically characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy. A core−shell Cu@Cu2O microsphere formation mechanism, which involved the in situ transformation of Cu to Cu2O, was proposed on the basis of the characterization results. That is, pure Cu microspheres were first formed through the reduction of copper(II) acetylacetonate. Then surface Cu was oxidatively transformed to a Cu2O shell, resulting in the Cu@Cu2O core−shell structure. The content of Cu2O shell in the composite microspheres increased with prolonged reaction time. The as-prepared Cu@Cu2O core−shell microspheres exhibited enhanced photocatalytic activity as compared to Cu2O on the degradation of gaseous nitrogen monoxide under visible light irradiation. The reasons for visible-light-driven photocatalytic activity enhancement on Cu@Cu2O core−shell microspheres were discussed. These Cu@Cu2O microspheres are ideal candidates for fundamental studies as well as catalytic, electronic, and magnetic applications

Efficient Photocatalytic Removal of NO in Indoor Air with Hierarchical Bismuth Oxybromide Nanoplate Microspheres under Visible Light

In this study, hierarchical bismuth oxybromide (BiOBr) nanoplate microspheres were used to remove NO in indoor air under visible light irradiation. The BiOBr microspheres were synthesized with a nonaqueous sol−gel method by using bismuth nitrate and cetyltrimethyl ammonium bromide as the precursors. On degradation of NO under visible light irradiation (λ > 420 nm) at 400 part-per-billion level, which is typical concentration for indoor air quality, these nonaqueous sol−gel synthesized hierarchical BiOBr microspheres exhibited superior photocatalytic activity to the chemical precipitation synthesized counterpart BiOBr bulk powder and Degussa TiO2 P25 as well as C doped TiO2. The excellent catalytic activity and the long-term activity of nonaqueous sol−gel synthesized BiOBr microspheres were attributed to their special hierarchical structure, which was favorable for the diffusion of intermediates and final products of NO oxidation. Ion chromatograph results confirmed that nitric acid was produced on the surface of BiOBr microspheres during the photooxidation of NO in gas phase. This work suggests that the nonaqueous sol−gel synthesized BiOBr nanoplate microspheres are promising photocatalytic materials for indoor air purification

Facile Microwave-Assisted Synthesis and Magnetic and Gas Sensing Properties of Fe₃O₄ Nanoroses

In this study, we developed a facile microwave-assisted ethylene glycol approach to synthesize Fe3O4 nanoroses in the presence of the PEO-PPO-PEO block copolymer (P123). The resulting products were systematically characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and Fourier transform infrared absorption spectroscopy (FT-IR). The characterization results revealed that the Fe3O4 nanoroses were formed by P123 directed assembly of nanoparticles under microwave irradiation. Besides size and morphology-dependent magnetic properties, the as-prepared nanocrystalline Fe3O4 nanoroses exhibited high sensitivity and good reversibility for gas-sensing of ethanol vapor at room temperature. Our results suggest these Fe3O4 nanoroses are promising materials for magnetic and sensing applications

Ultrasonic Spray Pyrolysis Synthesis of Porous Bi₂WO₆ Microspheres and Their Visible-Light-Induced Photocatalytic Removal of NO

In this study, porous Bi2WO6 microsphere photocatalysts were obtained via the ultrasonic spray pyrolysis method using bismuth citrate and tungstic acid as precursors in basic aqueous solution. The characteristics of the resulting samples were investigated in detail by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, N2 adsorption/desorption, X-ray photoelectron spectroscopy, and UV−vis diffuse reflectance spectroscopy. The resulting porous Bi2WO6 microsphere was of high crystallinity, which means fewer traps and stronger photocatalytic activity. The band-gap energy of Bi2WO6 microspheres estimated from the (αhν)2 versus photon energy (hν) plots was 2.92 eV. The formation of the porous structure in the as-prepared microspheres can be ascribed to the existence of citrate anions and in situ generated carbon residues that can serve as capping agents and templates, respectively, during the synthesis processes. It was found that the synthesis temperature was an important parameter controlling the morphology of the Bi2WO6 microspheres. As compared with the bulk Bi2WO6 sample, the resulting porous Bi2WO6 microspheres demonstrated superior photocatalytic activities on the removal of NO under either visible light or simulated solar light irradiation. The highest NO removal rates were 110 and 27 ppb/min for the porous Bi2WO6 sample under solar light and visible light (λ > 400 nm) irradiation, respectively. On the basis of the analysis of the characterization and experimental observations, a possible mechanism on the formation of porous Bi2WO6 microspheres was also proposed

Molecular, Seasonal, and Spatial Distributions of Organic Aerosols from Fourteen Chinese Cities

Organic aerosols were studied at the molecular level in 14 coastal and inland mega-cities in China during winter and summer 2003. They are characterized by the abundant presence of n-alkanes (annual average, 340 ng m-3), fatty acids (769 ng m-3), sugars (412 ng m-3), and phthalates (387 ng m-3). In contrast, fatty alcohols, polyols/polyacids, lignin and resin products, sterols, polycyclic aromatic hydrocarbons (PAHs), and hopanes were detected as relatively minor components. n-Alkanes show a weak odd/even carbon predominance (CPI = 1.1) and PAHs show a predominance of benzo(b)fluoranthene, suggesting a serious contribution from fossil fuel (mainly coal) combustion. Their concentrations (except for phthalates and polyols/polyacids) were 2−15 times higher in winter than summer due to a significant usage of coal burning and an enhancement of atmospheric inversion layers. Phthalates were found to be more abundant in summer than winter, probably due to enhanced vaporization from plastics followed by adsorptive deposition on the pre-existing particles. Concentrations of total quantified compounds are extremely high (∼10 μg m-3) in the midwest (Chongqing and Xi'an) where active industrialization/urbanization is going on. This study shows that concentrations of the compounds detected are 1−3 orders of magnitude higher than those reported from developed countries

Secondary Formation and Impacts of Gaseous Nitro-Phenolic Compounds in the Continental Outflow Observed at a Background Site in South China

Nitro-phenolic compounds (NPs) have attracted increasing attention because of their health risks and impacts on visibility, climate, and atmospheric chemistry. Despite many measurements of particulate NPs, the knowledge of their gaseous abundances, sources, atmospheric fates, and impacts remains incomplete. Here, 18 gaseous NPs were continuously measured with a time-of-flight chemical ionization mass spectrometer at a background site in South China in autumn and winter. Abundant NPs were observed in the continental outflows from East Asia, with a total concentration up to 122.1 pptv. Secondary formation from the transported aromatics dominated the observed NPs, with mono-NPs exhibiting photochemical daytime peaks and nighttime enrichments of di-NPs and Cl-substituted NPs. The budget analysis indicates that besides the •OH oxidation of aromatics, the NO3• oxidation also contributed significantly to the daytime mono-NPs, while the further oxidation of mono-NPs by NO3• dominated the nocturnal formation of di-NPs. Photolysis was the main daytime sink of NPs and produced substantial HONO, which would influence atmospheric oxidation capacity in downwind and background regions. This study provides quantitative insights on the formation and impacts of gaseous NPs in the continental outflow and highlights the role of NO3• chemistry in the secondary nitro-aromatics production that may facilitate regional pollution

Atmospheric Peroxides in a Polluted Subtropical Environment: Seasonal Variation, Sources and Sinks, and Importance of Heterogeneous Processes

Hydrogen peroxide (H₂O₂) and organic peroxides play an important role in atmospheric chemistry, but knowledge of their abundances, sources, and sinks from heterogeneous processes remains incomplete. Here we report the measurement results obtained in four seasons during 2011–2012 at a suburban site and a background site in Hong Kong. Organic peroxides were found to be more abundant than H₂O₂, which is in contrast to most previous observations. Model calculations with a multiphase chemical mechanism suggest important contributions from heterogeneous processes (primarily transition metal ion [TMI]-HOx reactions) to the H₂O₂ budget, accounting for about one-third and more than half of total production rate and loss rate, respectively. In comparison, they contribute much less to organic peroxides. The fast removal of H₂O₂ by these heterogeneous reactions explains the observed high organic peroxide fractions. Sensitivity analysis reveals that the role of heterogeneous processes depends on the abundance of soluble metals in aerosol, serving as a net H₂O₂ source at low metal concentrations, but as a net sink with high metal loading. The findings of this study suggest the need to consider the chemical processes in the aerosol aqueous phase when examining the chemical budget of gas-phase H₂O₂

Molecular Characterization of Oxygenated Organic Molecules and Their Dominating Roles in Particle Growth in Hong Kong

Oxygenated organic molecules (OOMs) are critical intermediates linking volatile organic compound oxidation and secondary organic aerosol (SOA) formation. Yet, the understanding of OOM components, formation mechanism, and impacts are still limited, especially for urbanized regions with a cocktail of anthropogenic emissions. Herein, ambient measurements of OOMs were conducted at a regional background site in South China in 2018. The molecular characteristics of OOMs revealed dominant nitrogen-containing products, and the influences of different factors on OOM composition and oxidation state were elucidated. Positive matrix factorization analysis resolved the complex OOM species to factors featured with fingerprint species from different oxidation pathways. A new method was developed to identify the key functional groups of OOMs, which successfully classified the majority species into carbonyls (8%), hydroperoxides (7%), nitrates (17%), peroxyl nitrates (10%), dinitrates (13%), aromatic ring-retaining species (6%), and terpenes (7%). The volatility estimation of OOMs was improved based on their identified functional groups and was used to simulate the aerosol growth process contributed by the condensation of those low-volatile OOMs. The results demonstrate the predominant role of OOMs in contributing sub-100 nm particle growth and SOA formation and highlight the importance of dinitrates and anthropogenic products from multistep oxidation