In-situ synthesis of TiO2 rutile/anatase heterostructure by DC magnetron sputtering at room temperature and thickness effect of outermost rutile layer on photocatalysis

Non-Conventional Synthesis and Repetitive Application of Magnetic Visible Light Photocatalyst Powder Consisting of Bi-Layered C-Doped TiO2 and Ni Particles

In the current study, a non-conventional application of the magnetron sputtering technique was proposed. A four-step synthesis procedure allowed us to produce a magnetic photocatalyst powder consisting of bi-layered particles with carbon-doped TiO2 on one side, and metallic Ni on the other side. XRD, SEM and EDS methods were used for sample characterization. It was determined, that after the sputtering process optimization, the bandgap of carbon-doped TiO2 was reduced to approximately 3.1 eV and its light adsorption increased over the whole visible light spectrum. The repetitive Rhodamine B solution bleaching with magnetic photocatalyst powder and visible light showed interesting evolvement of photocatalyst efficiency. After the first cycle, Rhodamine B concentration was reduced by just 35%. However, after the second cycle, the reduction had already reached nearly 50%. Photocatalytic bleaching efficiency continued to improve rapidly until higher than 95% of Rhodamine B concentration reduction was achieved (at tenth cycle). For the next ten cycles, photocatalytic bleaching efficiency remained relatively stable. The initial gain in efficiency was attributed to the magnetic photocatalyst particle size reduction from an initial diameter of 100–150 µm to 5 µm. Naturally, the 20–30 times size reduction resulted in a remarkably increased active surface area, which was a key factor for the increased performance.

The Sensitization of TiO2 Thin Film by Ag Nanoparticles for the Improvement of Photocatalytic Efficiency

The formation of Ag nanoparticles on the surface of TiO2 (AgNP/TiO2) to enhance photocatalytic efficiency was studied. The Ag nanoparticles (AgNP) size, form, and distribution dependence on the initial thickness of Ag thin films, annealing temperature, and time were analyzed. The optimal annealing temperature of 400 °C and annealing time of 60 min were chosen to form AgNP from the initial Ag thin films with a thickness of 5, 7.5, and 10 nm. The formation of AgNP was done on amorphous TiO2 (a-TiO2), which crystallized into the anatase phase after the annealing. The photocatalytic efficiency (k–degradation rate constant, Defi–degradation efficiency) was evaluated by the photodegradation of Rhodamine B aqueous solution. The results suggested that the highest photocatalytic efficiency of Rhodamine B aqueous solution was reached where the average diameter (DA) of AgNP was ~38 nm (k38 = 0.017 min−1, Defi_38 = 63.5%), compared to 27 and 82 nm (k27 = 0.012 min−1, Defi_27 = 51.2% and k82 = 0.011 min−1, Defi_82 = 52.1%, respectively). The acquired results did not show clear correlation between the size and distribution of the AgNP on the TiO2 surface and photocatalytic efficiency. Nevertheless, the results suggest that AgNP can enhance the photocatalytic efficiency of TiO2 thin films (kTiO2 = 0.008 min−1, Defi_TiO2 = 36.3%).

Floating Carbon-Doped TiO2 Photocatalyst with Metallic Underlayers Investigation for Polluted Water Treatment under Visible-Light Irradiation

In the current study, we analysed the influence of metallic underlayers on carbon-doped TiO2 films for RhB decomposition and Salmonella typhimurium inactivation under visible-light irradiation. All the experiments were divided into two parts. First, layered M/C-doped-TiO2 film structures (M = Ni, Nb, Cu) were prepared by magnetron sputtering technique on borosilicate glass substrates in the two-step deposition process. The influence of metal underlayer on the formation of the carbon-doped TiO2 films was characterised by X-ray diffractometer, scanning electron microscope, and atomic force microscope. The comparison between the visible-light assisted photocatalytic activity of M/C-doped TiO2 structures was performed by the photocatalytic bleaching tests of Rhodamine B dye aqueous solution. The best photocatalytic performance was observed for Ni/C-doped-TiO2 film combination. During the second part of the study, the Ni/C-doped-TiO2 film combination was deposited on high-density polyethylene beads which were selected as a floating substrate. The morphology and surface chemical analyses of the floating photocatalyst were performed. The viability and membrane permeability of Salmonella typhimurium were tested in cycling experiments under UV-B and visible-light irradiation. Three consecutive photocatalytic treatments of fresh bacteria suspensions with the same set of floating photocatalyst showed promising results, as after the third 1 h-long treatment bacteria viability was still reduced by 90% and 50% for UV-B and visible-light irradiation, respectively. The membrane permeability and ethidium fluorescence results suggest that Ni underlayer might have direct and indirect effect on the bacteria inactivation process. Additionally, relatively low loss of the photocatalyst efficiency suggests that floating C-doped TiO2 photocatalyst with the Ni underlayer might be seen as the possible solution for the used photocatalyst recovery issue.

Facile fabrication of AgI/Sb2O3 heterojunction photocatalyst with enhanced visible-light driven photocatalytic performance for efficient degradation of organic pollutants in water

The construction of heterojunction is considered as a promising approach to designing highly effective visible-light driven photocatalysts. In this research, the AgI/Sb₂O₃ heterojunction photocatalyst was synthesized by a simple in situ deposition-precipitation procedure, which was supported by XPS results. Among the prepared samples, the 60% AgI/Sb₂O₃ samples exhibited the best ARG degradation ratio (98.3%) in 1 h under visible light irradiation, while the pure Sb₂O₃ and AgI exhibited almost none photocatalytic performance. The trapping experiments and EPR proved that the photo-generated ·O₂^- and ·OH made major contributions to the photocatalytic degradation of ARG by the 60% AgI/Sb₂O₃ samples. The enhanced photocatalytic performance of AgI/Sb₂O₃ heterojunction photocatalysts was ascribed to that the e^- produced in the CB of AgI would be transferred to the empty CB of Sb₂O₃, which could effectively promote separation of photo-induced carries. More importantly, the transfer of electrons from AgI to Sb₂O₃ would be in favor of restraining the reduction of Ag⁺ to Ag⁰ resulting in the good stability of heterojunction photocatalysts. The heterojunction photocatalyst provided in this work might be a prospective candidate for decontamination of water.

A roadmap of strain in doped anatase TiO2

Anatase titanium oxide is important for its high chemical stability and photocatalytic properties, however, the latter are plagued by its large band gap that limits its activity to only a small percentage of the solar spectrum. In that respect, straining the material can reduce its band gap increasing the photocatalytic activity of titanium oxide. We apply density functional theory with the introduction of the Hubbard + U model, to investigate the impact of stress on the electronic structure of anatase in conjunction with defect engineering by intrinsic defects (oxygen/titanium vacancies and interstitials), metallic dopants (iron, chromium) and non-metallic dopants (carbon, nitrogen). Here we show that both biaxial and uniaxial strain can reduce the band gap of undoped anatase with the use of biaxial strain being marginally more beneficial reducing the band gap up to 2.96 eV at a tensile stress of 8 GPa. Biaxial tensile stress in parallel with doping results in reduction of the band gap but also in the introduction of states deep inside the band gap mainly for interstitially doped anatase. Dopants in substitutional positions show reduced deep level traps. Chromium-doped anatase at a tensile stress of 8 GPa shows the most significant reduction of the band gap as the band gap reaches 2.4 eV.

Hydrothermal in situ synthesis of Rb and S co-doped Ti-based TiO2 sheet with a thin film showing high photocatalytic activities

TiO2 is considered as one of the most promising semiconductor photocatalysts used to degrade organic pollutants. Element doping has a good effect on improving the properties of TiO2. Herein, by using Rb2SO4, we explored the in situ synthesis of Ti-based TiO2 sheets with a thin film through a hydrothermal reaction. Then, the photocatalyst was successfully fabricated by calcination. All samples were characterized by FT-IR, XRD, SEM, XPS, PL and UV-vis DRS measurements. The results indicate that the S doping together with surface hydroxyl groups lead to the band gap narrowing. S and a trace amount of Rb element can enable the formation of uniform microspheres on the surface of the Ti plate and the major phase transformed from titanium to anatase. The band gap absorption extended from 400 nm to 600 nm. The photocatalytic properties were investigated by performing the degradation of methyl orange (MO) and 4-chlorophenol (4-CP) in the aqueous solutions under UV and simulated sunlight. In the series of TiO2 photocatalysts, Rb/S/TiO2-48 shows the best photocatalytic efficiency and good photocatalytic performance on recycling. Interestingly, when H2O2 was added to the MO aqueous solution, a synergistic effect of the TiO2 thin film and H2O2 on degrading the pollutant was observed.