Enhancing the TiO2-Ag Photocatalytic Efficiency by Acetone in the Dye Removal from Wastewater

Abstract

TiO2 nanoparticles synthesized by the sol-gel method and doped with Ag were characterized by SEM, EDAX, FTIR, BET, XRD and TEM, then tested in the photocatalytic degradation of methylene blue (MB) under UV irradiation. The experimental results indicate that the average size of the raw particles was 10 nm, and their size was increased by calcination. The photocatalytic degradation of MB on nanostructured TiO2-Ag shows a high degradation efficiency upon the addition of a photosensitizer. A parametric study of the process was performed and has revealed the optimal value of the photocatalyst dose (0.3 g L−1) at a MB concentration of 4 ppm. Afterwards, the effect of acetone as a photosensitizer was studied. A MB degradation mechanism was proposed to explain the synergy between the TiO2 and the silver nanoparticles in the degradation performance. Under the optimal experimental conditions, at photosensitizer doses of 0.1 and 0.2%, yields of 92.38% and 97.25% MB degradation were achieved, respectively. Kinetic models showed that, at 0.1% acetone concentration, the data fit the pseudo-first-order model, while at 0.2% acetone, the photodegradation mechanism fits a second-order model. The values of the apparent rate constants indicate that the reaction rate increased between 24 and 40 times in the presence of acetone on TiO2 and TiO2-Ag. The addition of acetone modified the photodegradation mechanism and the Ag-doped samples became more active. The results of recycling tests using calcined TiO2-Ag material clearly show that the material was highly photocatalytically stable for the MB degradation. According to experimental results, the dye degradation decreased from 97.25% to 92.39% after four consecutive cycles. This simple approach could be applied for the advanced cleaning of wastewater contaminated with dyes, in the perspective of its reuse.

Photocatalytic Oxygen Transfer as an Innovative Route for N2O Upgrading**

“…UV analyses performed on the catalyst showed that doping TiO 2 with silver allows to decrease the band gap energy of the semiconductor from 3.3 eV to 2.98 eV, thus increasing the photocatalytic activity of the material (Figures S2 and S3, Table S3). This phenomenon is also in accordance with the literature [28–32] . Indeed, Ag and TiO 2 form a Schottky barrier, that reduces the recombination rate of the e − /h + pairs, silver acting as an electron trap, [28,30,32] thanks to its lower Fermi level of 1.1 eV (Scheme 2).…”

“…After the reaction, the reactor was opened to air and the solution was filtered through a 0.20 μm syringe filter to remove the catalyst. The solution was then analysed by GC for quantification (details in the supporting information), and/or by 31 P NMR (spectra acquired on 400 MHz Bruker instruments at the Ecole Nationale Supérieure de Chimie de Rennes).…”

Room-Temperature Synthesis of Carbon Dot/TiO2 Composites with High Photocatalytic Activity

“…Qutub et al reported the use of CdS in improving the photocatalytic efficiency of TiO 2 in the visible region . Duduman et al used Ag-doped TiO 2 for dye degradation, and they found that the incorporation of Ag effectively improved the photocatalytic activity of TiO 2 by controlling the carrier charge recombination . Pandiyan et al reported the synthesis of the Ag–Sn bimetallic nanocomposite for the dye degradation in the visible region .…”

“…14 Duduman et al used Ag-doped TiO 2 for dye degradation, and they found that the incorporation of Ag effectively improved the photocatalytic activity of TiO 2 by controlling the carrier charge recombination. 15 Pandiyan et al reported the synthesis of the Ag−Sn bimetallic nanocomposite for the dye degradation in the visible region. 16 Hossein et al synthesized the graphene dot-grafted TiO 2 composite, which enhanced the photocatalytic efficiency by 85% under UV light illumination, because the graphene dot not only improved the charge transfer but also enhanced the absorption of the composite.…”

Photocatalytic oxygen transfer as an innovative route for N2O upgrading

“…This phenomenon is also in accordance with the literature. [28][29][30][31][32] Indeed, Ag and TiO 2 form a Schottky barrier, that reduces the recombination rate of the e -/h + pairs, silver acting as an electron trap. [28,30,32] According to several works, the silver species are composed of metal Ag 0 , which is known to stabilize the photocatalyst [33] and Ag + species, that come from partial oxidation of the photodeposited metal in air.…”