Ettireddy P. Reddy

Sonophotocatalytic destruction of organic contaminants in aqueous systems on TiO2 powders

Abstract The effect of ultrasound on the photodegradation of salicylic acid on four commercial titania powders was studied. The system exhibiting the highest enhancement was isolated. The use of ultrasound during photocatalysis had a pronounced effect on the rate and efficiency of salicylic acid destruction as compared with UV-light photocatalysis alone. The possible reasons of the increased activity under ultrasonication were proposed: aggregate breakage and photocatalytic utilization of species produced by the ultrasound. The combination of the action of ultrasonic waves and UV-assisted photocatalysis yielded synergistic effects for the catalysts with smaller particle size (such as Hombikat), while no enhancement was observed for the largest particle size photocatalyst (Aldrich anatase). Degussa P25 exhibited the highest overall activity for the degradation of salicylic acid and moderate enhancement of activity by ultrasound. The presence of intermediates in the bulk solution was observed during the purely photocatalytic degradation of phenol. The presence of ultrasound, however, allows to eliminate the toxic intermediates by the sonolysis in the bulk solution.

Routes of photocatalytic destruction of chemical warfare agent simulants

Selected imitants of chemical warfare agents such as dimethyl methylphosphonate (DMMP), diethyl phosphoramidate (DEPA), pinacolyl methylphosphonate (PMP), butylaminoethanethiol (BAET) were subjected to photocatalytic and sonophotocatalytic treatment in aqueous suspensions of TiO2. Complete conversion of the same mass of imitants to inorganic products was obtained within 600 min for DMMP, DEPA, PMP, but required a longer time for BAET. Sonolysis accelerated photodegradation of DMMP. No degradation was observed without ultraviolet illumination. Final products of degradation were PO43−, CO2 for DMMP and PMP, PO43−, NO3− (25%), NH4+ (75%), CO2 for DEPA, and SO42−, NH4+, CO2 for BAET. The number of main detected intermediate products increases in the order DMMP (7), DEPA (9), PMP (21), and exceeds 34 for BAET. Degradation of DMMP mainly proceeds through consecutive oxidation of methoxy groups and then the methyl group. Dimethyl hydroxymethylphosphonate and dimethylphosphate testify to the parallel oxidation of the methyl group. Destruction of DEPA mainly starts with cleavage of the P–NH2 bond to form diethyl phosphate, which transforms further into ethyl phosphate. Oxidation of α and β carbons of ethoxy groups to form ethylphosphonoamidate, hydroxyethyl ethylphosphonoamidate and other products also contributes to the destruction. Photocatalytic degradation of PMP mainly starts with oxidation of the pinacolyl fragment, methylphosphonic acid and acetone being the major products. Oxidation of BAET begins with dark dimerization to disulfide, which undergoes oxidation of sulfur forming sulfinic and sulfonic acids as well as oxidation of carbons to form butanal, aminobutane, etc., and cyclic products such as 2-propylthiazole. A scheme of degradation was proposed for DMMP and DEPA, and starting routes for PMP and BAET. Quantum efficiencies of complete mineralization calculated as reaction rate to photon flux ratio approximate 10−3%.

Synthesis, Characterization and Photocatalytic Activity of Titania Loaded Cd-MCM-41

Catalysts consisting of cadmium incorporated into MCM-41 mesoporous molecular sieves (Cd-MCM-41) with Si/Cd = 80 have been synthesized by the hydrothermal method using cadmium acetate as the source of cadmium. This was then loaded with titania via the sol-gel method to explore the photoactivity in UV light. These two materials were characterized by various physicochemical techniques such as N2 physisorption, O2 chemisorption, diffuse reflectance UV-vis, X-ray diffraction (XRD), Raman and X-ray photoelectron spectroscopy (XPS). The pore size of the Cd-MCM-41 was higher and the BET surface area was lower than those commonly found in our siliceous MCM-41. This is due to the partial pore breakage, as recorded by pore size distribution analysis. The oxygen chemisorption results shows that the dispersion of cadmium is quite high, and decreased after loading of titania. The XRD patterns of Cd-MCM-41 and 25%TiO2/Cd-MCM-41 are similar to those of siliceous MCM-41; however, the intensity of the d100 peak is decreased and the unit-cell parameter increased with titania loading. Raman spectra could not detect any peaks, whereas peaks were detected at 144, 397, 518 and 641 cm-1 with loading of titania, these peaks being associated with the anatase phase of titania. The surface composition and binding energy of the Cd 3d5/2 peak for Cd-MCM-41 and 25%TiO2/Cd-MCM-41 was analyzed by XPS and showed considerable infusion of cadmium ions on to the surface upon loading of titania. The Cd/Si surface atomic ratio measured by XPS increases 10 times with loading of titania on Cd-MCM-41, indicating that the two separate surface electronic levels such as Cd-O-Si and Cd-O-Ti were found for 25%TiO2/Cd-MCM-41. The 25%TiO2/Cd-MCM-41 showed higher activity than 25%TiO2/MCM-41 for photocatalytic degradation of formic acid. The activity results are compared with the pure titania based on the transformation per site of Ti.