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Performance of various commercial TiO <sub/>2</sub> in photocatalytic degradation of a mixture of indoor air pollutants: Effect of photocatalyst and operating parameters
摘要： Photocatalytic oxidation (PCO) air cleaners can be installed in air handling units to reduce occupants’ exposure to hazardous gases, boost indoor air quality, and concomitantly lower HVAC energy consumption by lowering the required ventilation rate. In this work, photocatalytic activity of four commercialized titanium dioxide photocatalysts (P25, PC500, UV100, and S5-300A) for treating a mixture of seven prevalent volatile organic compounds (VOCs) were assessed in a continuous flow reactor. The impacts of major experimental factors namely concentration (15-100 ppb), relative humidity level (0-60% at 23?C), and residence time (0.012-0.05 s) on the removal efficiency and by-products generation were examined. Photocatalysts were characterized by X-ray diffraction (XRD), nitrogen adsorption-desorption, Fourier transform infrared (FTIR), and scanning electron microscopy (SEM). UV100 possessed the highest values for total VOC removal efficiency, which could be attributed to its large surface area, high porosity, good crystallinity, and large population of surface hydroxyls. Regarding relative humidity, two dominant trends were found: i) increasing the humidity resulted in lower removal efficiencies, or ii) existence of an optimum humidity level in some cases. The treatment efficiency followed the order: alcohols > ketones > aromatics > alkanes. The main by-products in the gas phase were formaldehyde, acetaldehyde, acetone, and propionaldehyde.
关键词： titanium dioxide,volatile organic compounds,indoor air quality,photocatalytic oxidation,relative humidity,residence time,by-products
更新于2025-09-23 15:22:29
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[IEEE 2018 International Conference on Numerical Simulation of Optoelectronic Devices (NUSOD) - Hong Kong, China (2018.11.5-2018.11.9)] 2018 International Conference on Numerical Simulation of Optoelectronic Devices (NUSOD) - Modeling Modal Properties of Antiresonant VCSEL with Bessel Expansion Transfer Method
摘要： We study optical properties of an ARROW-VCSEL, in which the anti-resonant effect is provided by an oxide island manufactured with planar oxidation inside the optical cavity. We implement a novel Bessel Expansion Transfer Method to show how this effect alters the nature of the laser modes by forcing qualitative change in the optical field profiles.
关键词： single-mode,resonance,ARROW-VCSEL,Bessel expansion,modal transfer method,orthogonality,oxidation
更新于2025-09-23 15:22:29
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Monolayer Epitaxial Heterostructures for Selective Visible-Light-Driven Photocatalytic NO Oxidation
摘要： Construction of vertical heterostructures by stacking two-dimensional (2D) layered materials via chemical bonds can be an effective strategy to explore advanced solar-energy-conversion systems. However, it remains a great challenge to fabricate such heterostructures based on conversional oxide-based compounds, as they either do not possess a 2D layered structure or are not suitable for epitaxial growth due to large lattice mismatch. Here, a vertical heterostructure of bismuth oxyhalide semiconductors fabricated through a heteroepitaxial anion exchange method is reported. Monolayer Bi2WO6 is epitaxially grown on the exposed surface of BiOI to inhibit photocorrosion and introduce active sites. Theoretical and experimental results reveal that electrons generated under visible-light irradiation can directly transfer to surface coordinatively unsaturated (CUS) Bi atoms, which contribute to the adsorption and activation of reactant molecules. As a result, the Bi2WO6/BiOI vertical heterostructures exhibit significantly enhanced visible-light-driven NO oxidation activity compared with BiOI and Bi2WO6.
关键词： epitaxial heterostructures,NO oxidation,photocatalysis,Bi2WO6,BiOI
更新于2025-09-23 15:22:29
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Mechanisim investigation on the enhanced and selective photoelectrochemical oxidation of atrazine on molecular imprinted mesoporous TiO2
摘要： In this work, enhanced and selective photoelectrochemical (PEC) oxidation of atrazine was realized on molecular imprinted mesoporous TiO2 (MI-meso-TiO2). The investigation revealed that, for one hand, the surface MI sites could function as surface defects for accelerating the separation of photogenerated holes and electrons, leading to enhanced generation of hydroxyl radicals. For the other hand, the MI sites showed enhanced binding affinity toward atrazine, resulted from the formation of multiple hydrogen bonds and halogen bonds etc., which was testified by in situ ATR-FTIR spectra. It led to the enhanced adsorption and improved local concentration of atrazine on the electrode surface. Both the two factors contributed to the improved PEC oxidation activity for atrazine on MI-meso-TiO2 compared with that on meso-TiO2. Moreover, the high binding affinity between MI sites and atrazine resulted in the selective recognition ability toward atrazine in the presence of the coexisting pollutants, so that selective PEC oxidation of atrazine in complex polluted water samples was successfully achieved on MI-meso-TiO2 with the apparent rate constant of 0.25 h-1, whereas that on meso-TiO2 was only 0.08 h-1. This work provided something new for explaining the selective and enhanced PEC performance on molecular imprinting catalyst.
关键词： mesoporous TiO2,molecular imprint,selective photoelectrochemical oxidation,atrazine
更新于2025-09-23 15:22:29
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Charge-state analysis of small barium-oxide clusters by X-ray absorption spectroscopy
摘要： Small barium-oxide clusters BamOn+ are studied by mass spectrometry and X-ray absorption spectroscopy to discuss stability of the clusters and oxidation state of constituent atoms. It is found that clusters with bulk composition, n = m, are stable, which can accommodate one or two excess oxygen atoms additionally as manifested by n = m + 1 and m + 2 species in the mass spectrum. XAS spectra of Ba2O2+ and Ba2O3+ reveal that the oxidation state of barium atoms stays at +2 (the bulk BaO value) even after binding excess oxygen, whereas spectral features originating from oxygen exhibit composition dependence. The present finding suggests that stoichiometric small barium-oxide clusters bind less-negatively-charged oxygen atoms without change in the charge state of barium.
关键词： X-ray absorption spectroscopy,charge state,barium-oxide clusters,oxidation number
更新于2025-09-23 15:22:29
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Thermal and Photocatalytic Reactions of Methanol and Acetaldehyde on Pt-Modified Brookite TiO <sub/>2</sub> Nanorods
摘要： The influence of adding Pt on the catalytic and photocatalytic activity of monodispersed brookite phase TiO2 (B-TiO2) nanorods (NRs) was investigated. Pt was deposited on the NRs by photo-deposition in solution and the Pt-modified NRs were characterized using XPS, STEM, and LEIS. The thermal and photocatalytic activity of the Pt-modified NRs were then evaluated using temperature-programmed desorption (TPD) in ultra-high vacuum (UHV). It was found that while Pt primarily acted as a site blocker for thermal reactions, Pt also acted as a recombination center for photogenerated electrons and holes, resulting in suppressed photocatalytic activity. Upon pretreatment with O2, however, the Pt-modified NRs exhibited enhanced photoactivity, indicating that adsorbed oxygen prevents electron-hole recombination by reacting with photogenerated conduction band electrons from the B-TiO2 to produce stable superoxide species on the Pt surface deposits. These results clearly demonstrate how the dynamics of charge carriers at the oxide surface may be altered by metal deposits such as Pt, as well as by the presence of adsorbed species on the metal surface.
关键词： brookite,acetaldehyde,photo-oxidation,TiO2,TPD,UHV,methanol,Pt
更新于2025-09-23 15:21:21
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CoGe surface oxidation studied using X-ray photoelectron spectroscopy
摘要： Cobalt germanides have been widely studied as semiconductor contact materials, but recent theoretical studies suggest that they may also be excellent catalysts for methane steam reforming with stabilities and activities comparable to more expensive noble metal catalysts. We have sputter deposited CoGe alloy films and characterized their structure and morphology after post-deposition annealing in high vacuum up to 1000 °C. We used X-ray photoelectron spectroscopy to study the initial oxidation of amorphous and crystalline CoGe alloy surfaces under low pressures of O2 and H2O. The oxidation rate in O2 was found to be faster for an amorphous CoGe surface compared to a crystalline surface. We also found that there was little difference in the oxidation rate in H2O for either amorphous or crystalline surfaces. During O2 oxidation, the crystalline surface preferentially forms GeO and the amorphous surface preferentially forms GeO2. We have also observed preferential oxidation of Ge in the CoGe thin films. During temperature programmed desorption studies, we found that GeO desorption begins near 350 °C and that GeO2 decomposes to GeO and desorbs near 700 °C. More studies of CoGe catalysts are warranted, however GeO desorption may be a concern under reaction conditions when the film is subjected to an oxidizing environment.
关键词： Oxidation,Cobalt germanium,Temperature programmed desorption,Atomic force microscopy,X-ray photoelectron spectroscopy,X-ray diffraction
更新于2025-09-23 15:21:21
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Electrode-free anodic oxidation nanolithography of low-dimensional materials
摘要： Scanning probe lithography based on local anodic oxidation (LAO) provides a robust and general nanolithography tool for a wide range of applications. Its practical use, however, has been strongly hampered due to the requirement of a pre-fabricated micro-electrode to conduct the driving electrical current. Here we report a novel electrode-free LAO technique, which enables in-situ patterning of as-prepared low-dimensional materials and heterostructures with great flexibility and high precision. Unlike conventional LAO driven by a DC current, the electrode-free LAO is driven by a high-frequency (>10 kHz) AC current applied through capacitive coupling, which eliminates the need of a contacting electrode and can be used even for tailoring insulating materials. Using this technique, we demonstrated flexible nanolithography of graphene, hexagonal boron nitride (hBN), and carbon nanotubes (CNTs) on insulating substrates with ~10-nanometer precision. In addition, the electrode-free LAO exhibits high etching quality without oxide residues left. Such an in-situ and electrode-free nanolithography with high etching quality opens up new opportunities for fabricating ultraclean nanoscale devices and heterostructures with great flexibility.
关键词： electrode-free local anodic oxidation,graphene,high-frequency AC voltage,low-dimensional materials,Scanning probe lithography
更新于2025-09-23 15:21:21
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Oxidation of P700 Ensures Robust Photosynthesis
摘要： In the light, photosynthetic cells can potentially suffer from oxidative damage derived from reactive oxygen species. Nevertheless, a variety of oxygenic photoautotrophs, including cyanobacteria, algae, and plants, manage their photosynthetic systems successfully. In the present article, we review previous research on how these photoautotrophs safely utilize light energy for photosynthesis without photo-oxidative damage to photosystem I (PSI). The reaction center chlorophyll of PSI, P700, is kept in an oxidized state in response to excess light, under high light and low CO2 conditions, to tune the light utilization and dissipate the excess photo-excitation energy in PSI. Oxidation of P700 is co-operatively regulated by a number of molecular mechanisms on both the electron donor and acceptor sides of PSI. The strategies to keep P700 oxidized are diverse among a variety of photoautotrophs, which are evolutionarily optimized for their ecological niche.
关键词： photosynthesis,reactive oxygen species,photoinhibition,P700 oxidation,photosystem I
更新于2025-09-23 15:21:21
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Effect of thermal oxidation temperatures on the phase evolution and photocatalytic property of tungsten-doped TiO <sub/>2</sub> thin film
摘要： Tungsten-doped titanium dioxide (W-TiO2) thin films were successfully prepared on glass substrates by sputtering thermally oxidized W-doped titanium films in air. Tungsten-doped titanium films were deposited using a DC and RF magnetron cosputtering system. The effects of annealing treatment and W content on the W-TiO2 film microstructure were investigated. The crystalline structures, morphological features, and photocatalytic activity of the annealed W-TiO2 films were systematically studied by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and ultraviolet spectrophotometry. The results indicated that annealing at 550 °C clearly induced the formation of an anatase and rutile phase mixture in the 5.5 at. % W-TiO2 films, which directly affected photocatalytic activity. The W-TiO2 films showed good photocatalytic activity under UV-light irradiation, with a higher rate of methylene blue dye degradation than in the case of undoped TiO2.
关键词： photocatalytic activity,tungsten-doped titanium dioxide,thermal oxidation,methylene blue degradation,thin films
更新于2025-09-23 15:21:21