Heterogeneous photocatalytic degradation over titanium dioxide of touene in gas phase and diphenhydramine in liquid phase

Abstract

Scientific studies on photocatalysis started about two and a half decades ago. Titanium dioxide (TiO2), which is one of the most basic materials in our daily life, has emerged as an excellent photocatalyst material for environmental purification. In this study, current progress in the area of TiO2 photocatalysis, mainly photocatalytic air and water purification are discussed together with some fundamental aspects. In the air purification line it was set-up an installation for descontamination of toluene in gas phase. It was explained the experimental method to carry out different experiments and the experiments performed. Moreover, it was created a new chromatographic method to analyze toluene in GC-2010. Best results showed 97% of recovery with 0.5 L/min of toluene during 10 minutes and it desorbed with Vortex during 10 minutes without photocatalytic reaction. But after some deficiencies were found in the installation and in this work it were proposed some enhancement options to study different variables involved in photocatalytic process in gas phase (photolysis, adsorption, total flow rate, radiation and concentration of pollutant). In the water purification line the degradation of diphenhydramine hydrochloride (DPH) by TiO2 photocatalysis was studied under different radiation sources: UVC (λ=254 nm), black blue lamps (BLB, λ=365 nm), simulated solar radiation (SB, Solarbox) and CPCs, at pilot plant scale with sunlight. Photolysis shows an important role in the DPH abatement under UVC radiation (31.5% of DPH conversion) but mineralization was not observed. Different TiO2 concentrations (0.05, 0.1 and 0.4 g/L) were used in SB device and the best results were obtained for 0.4 g/L: 35.7% of DPH conversion and 9.8% of TOC removal, after 60 min of irradiation. The UV-Vis/H2O2/TiO2 process represents an improvement with respect to the photocatalytic process (without H2O2). Thus, at 60 min with 150 mg/L of H2O2, 62.6% of DPH conversion (kinetic constant 15.05 ·10-3 h-1) in SB was achieved instead of 35.7% obtained without H2O2. Concerning the energy consumption in the useful wavelength range, SB and BLB reactors displayed the best ratios (mg DPH removed/kJ): 0.10 and 0.12, respectively, with 0.4 g/L of TiO2. Finally, reaction intermediates were identified and DPH photo-degradation pathway was proposed. Keywords: air purification, water purification, toluene, diphenhydramine hydrochloride, titanium dioxide, UVC, BLB, SB, CPC.