TiO2/Au/TiO2 multilayer thin-film photoanodes synthesized by pulsed laser deposition for photoelectrochemical degradation of organic pollutants

Abstract

Most commonly employed anodes for photoelectrochemical degradation of organic contaminants in water are too thick, resulting in a lower degradation efficiency due to an excessive electron-hole recombination. Multilayer-type TiO2/Au/TiO2 nanocomposites have been prepared as photoanode thin films by pulsed laser deposition (PLD). The films were composed of six TiO2 and five Au alternate layers, with total thickness of about 212 nm, aimed to optimize the absorption of photons and minimize the recombination. The influence of gold on the optical, structural, and chemical properties of the semiconductor nanocomposites was investigated. The band gap determined from Tauc model was 3.22 eV, close to that obtained by spectroscopic ellipsometry and lower than that of the TiO2 film, revealing an enhancement of visible light absorption. The catalytic performance of PLD films was evaluated by using them as anodes in electro-oxidation (EO) and photoanodes in photoelectrocatalysis (PEC) to degrade 39-157 mg L -1 paracetamol in sulfate medium. The drug removal was very slow in EO, due to the low ability to form • OH on the anode surface, which was significantly enhanced upon UVA irradiation in PEC. The presence of Cl − allowed a faster degradation by produced active chlorine. Finally, a hybrid process involving PEC + photoelectro-Fenton (PEF) with an air-diffusion cathode yielded total paracetamol decay in 4-5 min at an anodic potential of +4.0 V because of the efficient • OH generation from Fenton's and photo-Fenton reactions. Hydroquinone, p-benzoquinone and hydroxylated products were detected during EO and PEC. The generation of active chlorine was confirmed by identifying a chlorinated derivative, N-(4-chloro-2-hydroxyphenyl)acetamide, in PEC + PEF treatment.

Nanoparticles in Agroindustry: Applications, Toxicity, Challenges, and Trends

“…The degradation processes of the catalysts mentioned above are mainly carried out in wastewater treatments to remove recalcitrant and persistent pollutants such as dyes and pharmaceutical compounds, and the catalysts even work as disinfection agents [ 23 , 24 , 25 , 26 ]. The remaining effluents are used for watering some crop fields without any proper legislation [ 27 , 28 ], and no toxicology studies are well substantiated yet, because the remained NPs in the effluents are considered not dangerous in low concentrations.…”

Photo-Chlorine Production with Hydrothermally Grown and Vacuum-Annealed Nanocrystalline Rutile

“…The production of chlorine from the ubiquitous sources of seawater and solar (or synthetic LED) radiation via photoelectrocatalysis could be beneficial in specific applications. There is also evidence in the literature on the applications of chlorine intermediates in the related photoelectrochemical pollutant degradation in chloride containing media [26][27][28]. The two biggest limitations preventing photoelectrocatalysis becoming a common industrial technique (e.g.…”

Hazardous wastes treatment technologies

“…The result showed 88% removal of antibiotics at optimum current density of 5 mA/cm 2 and pH 6.23. Olvera‐Rodriguez et al (2019) studied the effect of Au on the optical property of multilayered TiO 2 /Au/TiO 2 nanocomposite and subsequent electro‐oxidation of p‐acetamol. Results showed enhanced oxidation of p‐acetamol with the production of intermediates including hydroquinone, p‐benzoquinone, and hydroxylated.…”