Investigation of Calcination and O2 Plasma Treatment Effects on TiO2-Supported Palladium Catalysts

Dye wastewater degradation by the synergetic effect of an atmospheric pressure plasma treatment and the photocatalytic activity of plasma-functionalized Cu‒TiO2 nanoparticles

In this paper, the photocatalytic activity of plasma-functionalized Cu-doped TiO₂ nanoparticles (NPs) and the oxidization process of atmospheric pressure plasma jet were combined for the degradation of reactive red-198 (RR-198) in aqueous solution. The first part of the study was thus devoted to subject Cu-‒TiO₂ NPs synthetized by the sol-gel method to various plasma treatments operating in air, argon, oxygen and nitrogen to improve their degradation efficiency. The physicochemical properties of the NPs were then assessed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) measurements. XRD results indicated the predominant presence of the anatase phase which is the most photoactive form of TiO₂. The XPS analysis revealed that the different plasma treatments triggered the formation of oxygen vacancies, Ti³⁺ oxidation state and Cu²⁺ oxidation state on the surface of Cu-‒TiO₂ NPs. These changes, known to prevent the recombination of electron-hole pair, have led to a reduction in the bandgap that was more pronounced for the N₂ plasma-treated NPs. The second part of the paper explored the actual degradation of RR-198 in aqueous solution by an Ar plasma treatment alone or combined with the plasma pre-treated Cu-‒TiO₂ NPs. Optical emission spectroscopy (OES) and spectrophotometric analyses showed that the synergetic effect of Ar plasma and N₂ plasma-treated NPs produced the highest concentration of OH^• radicals and H₂O₂ species which led to the highest RR-198 degradation efficiency. This was further confirmed by pH, electrical conductivity and total organic carbon (TOC) removal measurements. The degradation of RR-198 was determined using UV-Vis spectroscopy and high-performance liquid chromatography (HPLC). Overall, it can be concluded that plasma-assisted processes illustrated by a combination of a direct plasma treatment with plasma-functionalized Cu-‒TiO₂ NPs can be used in various textile and pharmaceutical industries as a highly effective treatment of their effluents before discharging.

Formation of oxygen vacancies and Ti(3+) state in TiO2 thin film and enhanced optical properties by air plasma treatment

This is the first time we report that simply air plasma treatment can also enhances the optical absorbance and absorption region of titanium oxide (TiO₂) films, while keeping them transparent. TiO₂ thin films having moderate doping of Fe and Co exhibit significant enhancement in the aforementioned optical properties upon air plasma treatment. The moderate doping could facilitate the formation of charge trap centers or avoid the formation of charge recombination centers. Variation in surface species viz. Ti³⁺, Ti⁴⁺, O²⁻, oxygen vacancies, OH group and optical properties was studied using X-ray photon spectroscopy (XPS) and UV-Vis spectroscopy. The air plasma treatment caused enhanced optical absorbance and optical absorption region as revealed by the formation of Ti³⁺ and oxygen vacancies in the band gap of TiO₂ films. The samples were treated in plasma with varying treatment time from 0 to 60 seconds. With the increasing treatment time, Ti³⁺ and oxygen vacancies increased in the Fe and Co doped TiO₂ films leading to increased absorbance; however, the increase in optical absorption region/red shift (from 3.22 to 3.00 eV) was observed in Fe doped TiO₂ films, on the contrary Co doped TiO₂ films exhibited blue shift (from 3.36 to 3.62 eV) due to Burstein Moss shift.

Promotion effects of plasma treatment on silica supports and catalyst precursors for cobalt Fischer–Tropsch catalysts

Glow discharge plasma would modify the surface hydrophilicity of support; the plasma treated catalysts showed much higher FTS activity.