Ag 2 O does not create an effective p–n junction with TiO 2 but is phototransformed into silver nanoparticles during the photocatalytic process. The resulting nanoparticles increase the photoactivity of the system in hydrogen evolution.
Understanding of the TiO 2 -assisted phototransformations observed for fundamentally important derivatives of Rhodamine B is expected to bring consistent and eventually comprehensive knowledge on behavior of this dye. The photocatalytic transformations of Rhodamine B in solution irradiated with visible light embrace an N-deethylation process eventually forming Rhodamine-110 rather than degradation of the chromophore. The N-deethylation of Rhodamine B was studied in solution and for the first time in the solid state. In this work, the influence of the wavelength of incident light on the photocatalytic processes involving Rhodamine dyes, is presented. The results indicate that the selection of wavelength is crucial to govern the pathway of RhB degradation. The N-deethylation process does not involve reactive oxygen species, as assumed in literature, but the photoinduced electron transfer between the adsorbed RhB molecule and the TiO 2 support, followed by radical transformations of the dye, plays a key role.
This work is focused on photocatalytic properties of titanium dioxide thin coatings modified with silver nanostructures (AgNSs) and graphene oxide (GO) sheets which were analyzed in processes of chemical transformations of rhodamine B (RhB) under ultraviolet (UV) or visible light (Vis) irradiation, respectively. UV-Vis spectroscopy was applied to analyze the changes in the RhB spectrum during photocatalytic processes, revealing decolorization of RhB solution under UV irradiation while the same process coexisting with the transformation of RhB to rhodamine 110 was observed under Vis irradiation. The novelty of this study is the elaboration of a methodology for determining the parameters characterizing the processes occurring under the Vis irradiation, which enables the comparison of photocatalysts’ activity. For the first time, the method for quantification of rhodamine B transformation into rhodamine 110 in the presence of a semiconductor under visible light irradiation was proposed. Photocatalysts with various surface architectures were designed. TiO2 thin coatings were obtained by the sol-gel method. GO sheets were deposited on their surface using the dip-coating method. AgNSs were photogenerated on TiO2 or grown spontaneously on GO flakes. For characterization of obtained photocatalysts, scanning electron microscopy (SEM), X-ray diffraction (XRD) and diffuse-reflectance spectroscopy (DRS) techniques were applied. The results indicate that the surface architecture of prepared coatings does not affect the main reaction path but have an influence on the reaction rates and yields of observed processes.
In this work, the application of highly defective cobalt and copper tungstates was proposed for photocatalytic CO2 reduction. The materials were synthesized by hydrothermal method and characterized with SEM, EDS, XRD, XPS and DRS techniques. Studied materials were examined in photocatalytic CO2 reduction to CO in the gas phase, as bare photocatalysts and in mixtures with TiO2. The behavior of the junctions between the mixture components was determined using photoelectrochemical, spectroelectrochemical and surface photovoltage measurements. These studies reveal different types of junctions for the synthesized materials (disturbed S-scheme for CoT/TiO2 and type-I for CuT/TiO2). It was found the CuT/TiO2 mixture is more effective than CoT/TiO2 due to lower recombination rates of photogenerated charge carriers and the presence of a larger number of W5+ and Cu2+ active centers.
The composites of ZnFe2O4 (ZFO) with TiO2 (anatase, rutile) were synthesized and tested towards the photocatalytic reduction of CO2 to CO in the gas phase. ZFO was obtained through the precipitation from zinc and iron nitrates(V) precursors, followed by hydrothermal treatment, and its physicochemical properties were examined using XRD, FT-IR, XPS, SEM-EDS, and XRF techniques. ZFO was simply ground in the agate mortar with one of the TiO2 polymorphs, forming ZFO/anatase and ZFO/rutile. Spectroelectrochemical (SE-DRS), surface photovoltage (SPV), transient photocurrent and diffuse reflectance UV–vis spectroscopy (DRS) measurements were applied to understand the fate of photogenerated electrons and holes. The results point to the type-I heterojunction that is formed in the case of all ZFO/TiO2 systems. This type of band alignment is responsible for boosted photoactivity of the composites compared to the components used separately. The results confirm that the selection of anatase favours reaching higher yields of CO production, which is attributed rather to better electron mobility within anatase compared to rutile than to preferential, reducing properties of the rutile's conduction band.
The results of this work cover the influence of plasmonic (gold) and non-plasmonic (palladium) nanostructures on the photocatalytic activity and redox properties of titanium dioxide.
Understanding of the TiO2-assisted phototransformations observed for fundamentally important derivatives of Rhodamine B is expected to bring consistent and eventually comprehensive knowledge on behavior of this dye. The photocatalytic transformations of Rhodamine B in solution irradiated with visible light embrace an N-deethylation process eventually forming Rhodamine-110 rather than degradation of the chromophore. The N-deethylation of Rhodamine B was studied in solution and for the first time in the solid state. In this work, the influence of the wavelength of incident light on the photocatalytic processes involving Rhodamine dyes, is presented. The results indicate that the selection of wavelength is crucial to govern the pathway of RhB degradation. The N-deethylation process does not require reactive oxygen species, as assumed in literature, but the photoinduced electron transfer between the adsorbed RhB molecule and the TiO2 support, followed by radical transformations of the dye, plays a key role.
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