E. Pulido Melián

Comparative study of nanocrystalline titanium dioxide obtained through sol-gel and sol-gel-hydrothermal synthesis.

TiO2 particles were prepared by sol-gel method alone and by sol-gel method combined with hydrothermal treatment. The structural and photocatalytic properties of the two series of photocatalysts were compared. XRD studies revealed that rutilization was faster in the series of photocatalysts, which had been additionally subjected to a hydrothermal process (SG-HT). The hydrothermally treated photocatalysts also displayed a higher specific surface area than those which had only been synthesized using the sol-gel process (SG) and subjected to low calcination temperatures of up to 873 K, while this tendency was inverted at higher temperatures. In accordance with the above observation, the hydrothermally treated series of photocatalysts had a lower particle size than the SG series calcined immediately after the sol-gel process up to 873 K, with this relation being inverted for the highest two temperatures which were studied (973 K and 1023 K) and which saw the commencement of rutilization. Increases in average particle size were observed for both series, with a polyhedral morphology seen as calcination temperature rose. FTIR studies highlighted the presence of the band at 2351 cm(-1) in the SG-HT photocatalysts, characteristic of surface-adsorbed CO2. This was not seen in the SG or P25 photocatalysts. In terms of photoreactivity, the best photocatalyst in the SG-HT series was that calcined at 923 K and in the SG series at 1023 K (SG-1023). Comparing these two photocatalysts and the commercial P25 photocatalyst, SG-1023 was found to be the most photoactive in both the photodegradation and the mineralization of phenol.

Adsorption and Photocatalytic Degradation of Phthalic Acid on TiO2 and ZnO

Abstract The photocatalytic degradation of phthalic acid (H2Ph) with TiO2 (Degussa P-25) and ZnO (Aldrich) at different pHs and substrate concentrations (10-150 ppm) has been studied. The concentration and mineralization of H2Ph has been monitored. Results in optimal conditions are: ko = 6.63 · 10-4 s-1, %TOC = 86.02 for TiO2 and ko = 12.7 · 10-4 s-1, %TOC = 81.90 for ZnO. Dissolved zinc was monitored during reaction. Zinc concentration in solution showed a maximum when that of the organic compound was at its minimum. At this step zinc in solution decreases. Catalyst solubility, catalyst photocorrosion and extraction by the substrate, could be main processes explaining dissolved zinc concentration along the reaction. Adsorption and rate constants have been obtained by using the Langmuir-Hinselwood model. Adsorption constants in the dark and adsorption constants obtained from Langmuir-Hinselwood kinetic model have been compared. The adsorption constant values in TiO2 studies are greater than in ZnO ones. Considering the relationship between degradation rate and surface bonding FTIR studies have been performed. FTIR results show that H2Ph molecule interacts with ZnO and TiO2 surfaces. In both cases, H2Ph interaction occurred by means of the formation of a phthalate.

Valorisation of a by-product from the TiO2 pigment industry for its application in advanced oxidation processes

AbstractThe aim of this study was to find a recycling use for waste material (WTiO2) that results from the extraction process of TiO2 from ilmenite in the pigment industry. In view of its high TiO2 content, the photocatalytic activity of this material was tested in the degradation of humic and fulvic acid substances (HFAs) and showed low levels of photoactivity, as was the case for the commercial photocatalyst Aeroxide TiO2 P25 (P25). However, due to its high Fe3+ content, an important application was observed for WTiO2 as an HFA coagulant and catalyst in Fenton and photo-Fenton processes. A two-stage process of coagulation and photo-Fenton treatment was subsequently designed and conducted at laboratory and small pilot scale. High percentages (above 95%) were obtained in total organic carbon (TOC) removal.