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

Abstract

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.

Visible-Light-Driven Photocatalytic Inactivation of Bacteria, Bacteriophages, and Their Mixtures Using ZnO-Coated HDPE Beads as Floating Photocatalyst

“…Prior to the ZnO deposition, the HDPE beads were precovered with a thin layer of Ni (thickness of about 100 nm) using magnetron with Ni target (purity 99.99%, Kurt J. Lesker Company, Clairton, PA, USA) powered by a direct current power source. Our previous study disclosed that metallic underlayers can have positive impacts on the bactericidal effect of the photocatalyst under visible-light irradiation [28]. During the process, HDPE beads were placed under the unbalanced magnetron with a circular Zn target (99.99% purity and 76 mm diameter, Kurt J. Lesker Company, Clairton, PA, USA) which was powered by an RF power source working at 150 W for 1 h. After that, the HDPE beads were flipped over, and ZnO film was deposited on the other side of the beads under the same conditions.…”

“…Meanwhile, some authors suggest that doping or other types of Ni and ZnO combination can be a suitable way to improve ZnO characteristics [24][25][26][27]. Moreover, our previous study revealed that Ni underlayer improves TiO 2 photocatalytic efficiency, which was applied as floating photocatalyst for Salmonella typhimurium inactivation under visible-light irradiation [28].…”

“…Part of HDPE beads was precovered by a thin nickel underlayer to test if it improves the photocatalytic activity in the case of ZnO. Our previous studies [28,44] showed that the metallic underlayer can positively affect photocatalytic performance under both UV-B and visible light irradiation. Additionally, some studies suggest that the recombination rate of electron-hole can be reduced and photocatalytic efficiency improved using metallic substrates and transition metals dopants [45][46][47].…”

Synthesis and Structure of Carbon‐doped TiO2 by Carbothermal Treatment

“…A sol-gel step is applied and the intermediate is calcined at comparably moderate temperatures between 400 • C and 500 • C. [21][22][23] Beside the well-established methods, alternatives are tested such as high-energy grinding of anatase in ethanol and subsequent calcination at 200 • C. [24] To address the problem of catalyst recovery new methods were applied recently aiming at the synthesis of TiO 2 combined with magnetic metals. Magnetron sputtering is applied to fabricate films of carbon-doped anatase with underlying nickel [25] or bi-layered particles. [26] Theoretical calculations regarding the influence of pblock elements on the optical absorption are thoroughly reviewed by Di Valentin et al [27,28] Several other sources as well as experimental results showing the influence of p-block elements are for instance reviewed in the publication of Dozzi et al [10] The influence of carbon on the band gap of TiO 2 is thoroughly discussed for both theoretical calculations and experimental work.…”

“…[ 24 ] To address the problem of catalyst recovery new methods were applied recently aiming at the synthesis of TiO 2 combined with magnetic metals. Magnetron sputtering is applied to fabricate films of carbon‐doped anatase with underlying nickel [ 25 ] or bi‐layered particles. [ 26 ]…”