Localization and Stabilization of Photogenerated Electrons at TiO2 Nanoparticle Surface by Oxygen at Ambient Temperature

Enhancement of light-driven adsorption efficacy through the integration of NiCo2O4 onto CeO2 for photo-ozone catalytic degradation of toluene

In this study, a co-catalytic route was explored to enhance the photo-ozone catalytic degradation of volatile organic compounds (VOCs). NiCo2O4 was loaded onto the surface of CeO2 nanoparticles to create a composite catalyst (10%NiCo2O4/CeO2). The integration of NiCo2O4 onto CeO2 enhanced the interaction between the catalyst and toluene, a representative VOC, resulting in significantly increased toluene adsorption without a corresponding increase in specific surface area. This integration also improved the utilization of charge carriers and conversion of ozone to O2-. Under visible light irradiation, H2O accumulated charge carriers at 10%NiCo2O4/CeO2's surface, facilitating both ozone utilization and toluene adsorption. Another benefit of NiCo2O4 loading was its ability to enhance the conversion efficiency of solar energy. Consequently, the toluene removal and mineralization efficiencies of 10%NiCo2O4/CeO2 were enhanced by 182% and 309% compared to CeO2, and by 201% and 357% compared to NiCo2O4, respectively. Overall, this study demonstrated a novel co-catalyst design strategy for enhancing the photo-ozone catalytic degradation of VOCs.

Optimization of Co3O4 surface sites for photo-ozone catalytic mineralization of dichloromethane

Obtaining high removal rate of chlorinated volatile organic compounds (CVOCs) and CO₂ selectivity with a low ratio of O₃/CVOC and energy consumption is challenging. Dodecylamine was used in this study to create active sites on Co₃O₄ for photo-ozone catalytic mineralization of dichloromethane (DCM). Amine-Co₃O₄-450 is a dodecylamine-modified sample with high density of Co³⁺, Co²⁺, and hydroxyl due to its nanosheet structure and exposed (112) facets. The optimized surface significantly enhanced the cleavage of the C-Cl bond at low temperatures. Photocatalysis primarily participated in the oxidation of intermediates following DCM dichlorination and significantly improved CO₂ selectivity. The respective DCM removal rate and mineralization efficiency of Amine-Co₃O₄-450 with an O₃/DCM molar ratio of 1.27 and one-sun irradiation were 14.9 and 15.0 times higher than the sum of those in the presence of light irradiation or O₃ alone. This finding indicated that a strong synergistic effect exists between O₃ and light.

Optimization of photothermal conversion and catalytic sites for photo-assisted-catalytic degradation of volatile organic compounds

Solar energy conversion is a promising strategy to enhance the elimination of volatile organic compounds (VOCs) and minimize power consumption. Herein, non-noble metal WC@WO₃ as cocatalyst was composited with CeO₂ to optimize photochemical and photothermal conversion for the catalytic ozonation of toluene and acetone. The photothermal conversion efficiencies of visible and infrared lights on 20%WC@WO₃-CeO₂ were 2.2 and 10.4 times higher than those on CeO₂, respectively, which indicates that the equilibrium temperature of the catalyst remarkably increased under full-spectrum light irradiation. Moreover, WC@WO₃ transferred electrons to CeO₂ in 20%WC@WO₃-CeO₂ and thus remarkably improved the activity of catalytic sites. The synergy factor of light and O₃ on 20%WC@WO₃-CeO₂ was 5.8, and the reaction rate of toluene and acetone reached 9274.5 and 35779.0 mg/(m³∙min), respectively. This work provides a low-cost and high-efficient catalyst for the utilization of solar energy for VOC control.

Conversion of methanol on rutile TiO2(110) and tungsten oxide clusters: 2. The role of defects and electron transfer in bifunctional oxidic photocatalysts

The photochemical conversion of organic compounds on tailored transition metal oxide surfaces by UV irradiation has found wide applications ranging from the production of chemicals to the degradation of organic pollutants e.g. in waste water treatment. Here, we present a systematic surface science-based study of the UV photoconversion of methanol on a rutile TiO2(110) surface. Under the used conditions, the dominant photoreaction is the photo-oxidation forming formaldehyde, that is drastically boosted by the presence of adsorbed oxygen as well as (sub-)surface defects such as oxygen vacancies and Ti3+ interstitials. Moreover, a photostimulated and Ti3+ mediated C-C coupling was observed leading to the production of ethene. We have further deposited tungsten oxide clusters on the rutile surface and examined the impact on the methanol photochemistry. In this case, the C-C coupling can be suppressed. Surprisingly, especially for high Ti3+ contents the population of the photochemical pathway is quenched in favor of the population of the thermal reaction yielding more methane from the deoxygenation reaction. So, the common concept that long time charge separation is efficient by combining two photocatalysts with similar band gaps, but different work functions in order to enhance photochemical yields is apparently too naive for certain systems. We attribute the loss of photoproducts with tungsten oxide coadsorption to the "pinning" of Ti3+ centers and a related enhancement of electron density near the oxide clusters which makes a concomitant recombination of the photochemical relevant holes with the excess surface electrons more likely.

Self-Doping Surface Oxygen Vacancy-Induced Lattice Strains for Enhancing Visible Light-Driven Photocatalytic H2 Evolution over Black TiO2

The synergistic effect of surface oxygen vacancy with induced lattice strains on visible light-driven photocatalytic H₂ evolution over black TiO₂ was investigated. Experimental measurements and theoretical calculations on the lattice parameters of black TiO₂ show that surface oxygen vacancies induce internal lattice strain during two-step aluminothermic reduction, which regulates the band structure and optimizes the photoinduced charge behavior of black TiO₂. The hydrogen evolution rate of black TiO₂ with strain modification shows a 12-fold increase to 1.882 mmol/g· h (equal to 4.705 μmol/cm²·h) under visible light illumination. The metastable state caused by the surface oxygen vacancies leads to the formation of a high-energy surface, which enhances visible light absorption and improves the photoinduced charge separation efficiency. Furthermore, the internal lattice strain provides the driving force and channel for the directional movement of photoinduced electrons from the bulk to the high-energy surface for photocatalytic H₂ evolution. This strategy provides a new method for designing a high-performance photocatalyst for H₂ production.

Platinum-enhanced amorphous TiO2-filled mesoporous TiO2 crystals for the photocatalytic mineralization of tetracycline hydrochloride

The adsorption ability and photoactivity of a photocatalyst largely determine the mineralization efficiency of antibiotics. Herein, aiming to enhance the adsorption and mineralization of antibiotics, we constructed a hierarchical porous core-shell structure by filling amorphous TiO₂ in the pores of Pt-doped mesoporous TiO₂ crystals (MCs). The physical-chemical properties of the prepared samples were investigated by surface photovoltage spectroscopy, X-ray photoelectron spectroscope, etc. Adsorption and photocatalysis experiments were conducted with tetracycline hydrochloride as the model antibiotic. Pt nanoparticles doped at the interface of the rutile-amorphous homojunction remarkably enhanced the built-in electric field. The enhanced electric field increased the hole transfer to the catalyst surface, and the Pt doping treatment promoted the growth of amorphous TiO₂ into the mesopores of the MCs. The optimization increased the surface area of the catalyst without increasing the thickness of the amorphous TiO₂ shell, thereby reducing the charge migration distance from the core-shell interface to the catalyst surface. The adsorption amount and mineralization efficiency of tetracycline hydrochloride for the porous core-shell composite were 6.7 and 3.8 times of those for MCs, respectively.