Photonic crystals have attracted extensive interest for the potential applications in manipulating light by nontraditional ways based on photonic band structure concepts. In this paper, 3D inverse-opal TiO 2 photonic crystals (TiO 2 -PCs) with designed photonic band gaps are prepared. It is worth noting that when the photonic band gaps of the TiO 2 -PCs are matched with the absorption peaks of the dyes (methyl orange, rhodamine B, and methylene blue), the photocatalytic activity of the corresponding sample is improved under simulated solar light (320 nm < λ < 800 nm) and visible light (420 nm < λ < 800 nm) irradiation. The enhancement could be attributed to the intensified dye sensitization as a result of slow photon effect on the edges of the photonic band gaps. Furthermore, the TiO 2 -PCs exhibit much higher photocatalytic activity and stability than TiO 2 nanoparticle film. It is believed that the presence of inverse opal structure plays an essential role in affecting the dye sensitization and photoreactivity, which could provide valuable information on the design of photocatalysts and set the foundation for the future environmental and energy technologies.
In order to exploit efficient photosensitizers with appropriate electronic states to enhance the transfer of electrons, ZnxCd1-xS/TiO2 nanocomposites were first synthesized by a simple hydrothermal method. The samples were characterized by X-ray diffraction, transmission electron microscopy, diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, electron spin resonance, and photoluminescence techniques. The results showed that the composite of the two inorganic semiconductors largely enhanced the photosensitized degradation of rhodamine B (RhB) under visible light irradiation (420 nm<λ<800 nm). These photocatalytic reactions were driven mainly by the light absorption of RhB molecules and to a lesser extent by the excitation of ZnxCd1-xS. They were supposed to arise mainly from the electron transferred from the adsorbed dye in its singlet excited state to the conduction band of ZnxCd1-xS and TiO2. Such a heterogeneous photocatalytic reaction has much significance in the degradation of organic pollutants in ordinary photocatalysis.
To fundamental understanding the effects of the deposited Pt and its deposition route on the photocatalytic reforming (PR) of glycerol for H 2 evolution over Pt/TiO 2 , several 1 wt% Pt/P25 (PT) samples were prepared by photo-deposition (PD, glycerol as hole scavenger) and impregnation-reduction deposition routes (IRD, NaBH 4 or H 2 /Ar as reductant) using H 2 PtCl 6 as the precursor. The samples were 10 characterized by XRD, UV-vis DRS, TEM and XPS, and the PR activities were examined and compared under ambient condition. The formation of photo-induced charge carriers (CCs) over PT was measured by photoluminescence technique using terephthalic acid as a probe molecule. The results indicated the reforming activity depends on both the nature of the light harvesting of P25 and the characteristics of cocatalyst Pt, including its chemical state, size, and the interaction with P25, which serves as the active sites 15 for H 2 evolution. Uniform Pt particles could be selectively and intimately deposited on P25 in Pt(0) state via in situ PD process (PT-S), while by IRD routes, Pt were randomly loaded with surface in Pt(0) and the bulk in Pt(II/IV) states. Unlike the Pt chemical state, the Pt sizes are less impacted by the deposition routes and are about 2 nm. Compared to P25, a low generation efficiency of CCs was observed on platinized samples due to the covering of the photo-active sites by Pt. Pt(0) exhibits higher light shielding 20 effect than Pt(II/IV). Meanwhile, the separation of CCs was promoted by Schottky barriers formed at PtTiO 2 interface. Photo-induced electrons can be trapped by the barriers and the process was favored by well-contacted Pt(0) and obstructed by the bulk Pt(II/IV) component. The promotion effect of Pt(0) prevails over its adverse effect. Thus, PT-S exhibited the highest PR activity as it only possesses Pt(0) demonstrating the advantage of PD process. Control test suggests Pt with this kind of feature can only be 25 achieved in a dilute suspension by PD route.
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