Synthesis and photocatalytic activity of sulfate modified Nd-doped TiO2 under visible light irradiation

The Influence of Nd and Sm on the Structure and Properties of Sol-Gel-Derived TiO2 Powders

TiO₂ nanopowders modified by Nd and Sm were prepared using the sol-gel technique. It was found by XRD analysis that the samples containing Sm are amorphous up to 300 °C, while those with Nd preserve a mixed organic-inorganic amorphous structure at higher temperatures (400 °C). The TiO₂ (rutile) was not detected up to 700 °C in the presence of both modified oxides. TiO₂ (anatase) crystals found at about 400 °C in the Sm-modified sample exhibited an average crystallite size of about 25-30 nm, while doping with Nd resulted in particles of a lower size-5-10 nm. It was established by DTA that organic decomposition is accompanied by significant weight loss occurring in the temperature range 240-350 °C. Photocatalytic tests showed that the samples heated at 500 °C possess photocatalytic activity under UV irradiation toward Malachite green organic dye. Selected compositions exhibited good antimicrobial activity against E. coli K12 and B. subtilis.

Tuning the photoactivity of TiO2 nanoarchitectures doped with cerium or neodymium and application to colour removal from wastewaters

The impact of cerium (Ce) and neodymium (Nd) rare-earth metal doping of TiO₂ prepared by the hydrothermal method was investigated to tailor effective photocatalytic degradation of coloured wastewater under UV or visible illumination. The hydrothermal treatment of TiO₂ decreased the pH_pzc from 6.3 to 3.1-3.8 favouring the affinity for cationic water contaminants. Doping with Ce and Nd modified the crystallinity and the morphology of the photocatalysts and significantly increased the BET surface area and the adsorption capacity of cationic dyes. The photocatalytic activity under UV light irradiation decreased due to shielding of the catalyst active area by excessive amount of dye adsorbed. Conversely, the photocatalytic activity of the Ce and Nd doped TiO₂ increased under visible light irradiation by 1.2 times as a result of the dye photosensitization effect. It was demonstrated that two-steps dark adsorption and photocatalytic reaction or one-step simultaneous adsorption and reaction can produce significantly different results for the photocatalytic degradation of dyes in coloured waters, the rate being controlled by the competitive adsorption of the reacting organics and the H₂O/OH^- species. The reaction is driven by the radical oxygen species (ROS) formed on the catalyst surface the nature of which, differs under UV or visible light irradiation. The Ce-doped TiO₂ and Nd-doped TiO₂ photocatalysts with 0.5% rare-earth content were found to be efficient in the degradation of MB in aqueous solution, removing the colour and reducing the toxicity of wastewaters.

Synergistic Mechanism of Rare-Earth Modification TiO2 and Photodegradation on Benzohydroxamic Acid

Rare earth elements are plentiful in Gannan area, China, and there is a large amount of wastewater from all kinds of mines. In this paper, rare-earth modification TiO2 composites (RE/TiO2, RE = La, Ce, Gd, Yb) was studied by theory computation and experimental performance. The prepared RE/TiO2 was investigated for the degradation of benzohydroxamic acid (BHA) as a typical residual reagent in wastewater from beneficiation. The crystallinity, morphology, specific surface area, light absorption, and composition of compound were investigated by various techniques. As a result of computation and experimentation, four different electron configurations of rare earth all retained the anatase phase of TiO2 and reduced the band gap of TiO2 to some degree compared with pure TiO2. Different rare-earth elements and calcination temperatures resulted in different removal effects on BHA. The optimum doping contents were 0.75% (500 °C), 0.20% (500 °C), 0.70% (500 °C) and 0.50% (450 °C) for La, Ce, Gd, Yb respectively. All the RE/TiO2 composites studied in this research still possessed good photoactivity after four runs, which supports the theoretical and practical basement for the photocatalytic treatment of mining and metallurgy wastewater.

Influence of the preparation method on the photocatalytic activity of Nd-modified TiO2

Nd-modified TiO2 photocatalysts have been obtained via hydrothermal (HT) and sol-hydrothermal (SHT) methods. The as-prepared samples were characterized by X-ray diffraction (XRD), BET surface area measurements, scanning electron microscopy (SEM), diffuse reflectance spectroscopy (DRS), luminescence spectroscopy and X-ray photoelectron spectroscopy (XPS). The photocatalytic activity of the synthesized samples was evaluated by the degradation of phenol in aqueous solution under irradiation with UV-vis (λ > 350 nm) and vis (λ > 420 nm) light, as well as by the degradation of gaseous toluene under irradiation with vis (λmax = 415 nm) light. It was found that Nd-modified TiO2 is an efficient photocatalyst for the degradation of phenol and toluene under visible light. XPS analysis revealed that the photocatalyst prepared via HT method contains a three-times higher amount of hydroxy groups at the surface layer and a two-times higher amount of surface defects than that obtained by the SHT method. The photocatalytic efficiency of phenol and toluene degradation under vis irradiation in the presence of 0.25% Nd-TiO2(HT) reached 0.62 and 3.36 μmol·dm-1·min-1, respectively. Photocatalytic activity tests in the presence of Nd-TiO2 and scavenger confirm that superoxide radicals were responsible for the visible light-induced degradation of the model pollutant in aqueous solution.