Alexandre V. Vorontsov

Gas-phase photocatalytic oxidation of diethyl sulfide over TiO2: kinetic investigations and catalyst deactivation

Abstract The gas-phase heterogeneous photocatalytic oxidation of diethyl sulfide (DES), a simulant for chemical agent mustard gas, was investigated in a batch reactor using detection of gaseous products and FT-IR identification of surface species. Acetaldehyde and ethylene were detected as gaseous intermediates and diethylsulfone and carboxylates were detected as surface intermediate products. It was found that DES is oxidized completely and the final products of its oxidation are carbon dioxide, water and surface sulfate species. Deactivation of the TiO 2 photocatalyst was evidenced by increased time of DES complete mineralization in consecutive treatment of fixed amount of DES in the batch reactor. Carbonate and sulfate species were detected on the TiO 2 surface after complete DES oxidation by means of FT-IR diffuse reflectance spectroscopy. These structures turned out to be responsible for TiO 2 deactivation.

Pathways of photocatalytic gas phase destruction of HD simulant 2-chloroethyl ethyl sulfide

Abstract Photocatalytic oxidation of HD simulant, 2-chloroethyl ethyl sulfide (CEES), was studied in a specially designed coil and flow photocatalytic reactor by means of GC-MS and FTIR techniques. TiO 2 Hombikat UV 100 photocatalyst was deactivated after a few hours of operation, which was signaled by the appearance of incomplete oxidation products in the reactor effluent and accumulation of incomplete oxidation products on the TiO 2 surface. Complete reactivation of the photocatalyst was achieved by washing the photocatalyst with water. Compared to diethyl sulfide, CEES showed lower reactivity in photocatalytic oxidation and was accumulated on the TiO 2 surface after catalyst deactivation. Without UV irradiation, hydrolysis of CEES proceeded on the TiO 2 surface. Major gaseous products of CEES incomplete photocatalytic oxidation are acetaldehyde, chloroacetaldehyde, SO 2 , diethyl disulfide, and chloroethylene. Surface products extracted from the TiO 2 surface with acetonitrile and water include mainly 2-chloroethyl ethyl sulfoxide and ethanesulfinic and ethanesulfonic acids, as well as diethyl di-, tri-, and tetrasulfides mono and disubstituted in the β position with a chlorine or hydroxyl group. While surface monodentate sulfates can be removed upon washing, surface bidentate species stayed on the surface and possibly contribute to the permanent catalyst deactivation.

COMPARATIVE STUDY ON PHOTOCATALYTIC OXIDATION OF FOUR ORGANOPHOSPHORUS SIMULANTS OF CHEMICAL WARFARE AGENTS IN AQUEOUS SUSPENSION OF TITANIUM DIOXIDE

Abstract Photocatalytic oxidation by oxygen of air was carried out for dimethyl methyl phosphonate (DMMP), trimethyl phosphate (TMP), triethyl phosphate (TEP), and diethyl phosphoramidate (DEPA) in different concentration. The initial rate of organophosphorus compounds consumption increases with the initial concentration at relatively low concentrations but decreases at higher initial concentrations. If the concentration is higher than the concentration in maximum, the rate decreases because of the lack of adsorbed oxygen. These summit-like dependences are well approximated by one site Langmuir–Hinshelwood equation with competitive adsorption of oxygen and organophosphorus compound. Parameters of the Langmuir–Hinshelwood equation are reported. Complete mineralization of the organophosphorus compounds at the end of reaction was evidenced by the total organic carbon concentration profiles. These profiles have sigmoidal shape. GC–MS technique was used to identify intermediates of TEP and TMP oxidation. The main intermediates are dimethyl phosphate and methyl phosphate in the case of TMP and diethyl phosphate and ethyl phosphate in the case of TEP. The set of intermediates shows that photocatalytic oxidation proceeds primarily at α carbon atoms of TEP. The distribution of intermediates corroborates that photocatalytic oxidation is initiated by reaction with hydroxyl radicals.

Correlation of TiO2 photocatalytic activity and diffuse reflectance spectra

Abstract Photocatalytic activity of TiO 2 samples prepared by aqueous hydrolysis of TiCl 4 and deposition with NH 3 in gaseous acetone photocatalytic oxidation has been found dependent on calcination temperature. The activity reaches its maximum at calcination temperature 450°C and then decreases, all the samples being anatase. The photocatalytic activity of the samples in a series of different calcination temperatures correlates well with reflectance of the samples in the visible light region. The increase in calcination temperature from 320 to 500°C results in the growth of TiO 2 crystallites, decrease in BET surface area, slight changes in lattice parameters, and removal of weak surface Bronsted acid centers that are speculated to be OH groups. TiO 2 prepared by deposition with NaOH exhibits much higher photocatalytic activity. The only paramagnetic species detected in the TiO 2 samples was NO that resulted from oxidation of lattice-captured NH 3 . No NO was detected in TiO 2 prepared by deposition with NaOH. The concentration of NO increases steadily with calcination temperature as indicated by ESR spectra. The observed correlation of diffuse reflectance and photocatalytic activity was attributed to opposite effects of the increase of crystallinity and removal of surface water and hydroxyl groups.

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%.

TiO2 reactivation in photocatalytic destruction of gaseous diethyl sulfide in a coil reactor

Abstract Diethyl sulfide (DES) photocatalytic oxidation was carried out in a flow research reactor with TiO2 Hombikat UV 100 deposited onto the internal surface of a Pyrex coil. The reactor allowed easy catalyst reactivation by washing with water. Mass transfer limitations were not detected in the reactor. Catalyst deactivated after several hours of complete DES mineralization, which was expressed by decrease of effluent CO2 concentration and appearance of gaseous intermediates. Catalyst reactivation was achieved by two procedures: (1) irradiating photocatalyst until complete mineralization of adsorbed organic products with subsequent water washing; and (2) immediate washing with water. The water used after the first procedure contained only H2SO4, while after the second procedure it contained organic intermediates. The second procedure was much faster. Lower water concentration and higher catalyst loading allowed longer catalyst stability in DES oxidation. Low feed DES concentration resulted in much longer deactivation. Twelve consecutive runs were done to test reactivation completeness. Some permanent catalyst deactivation was noted and explained by TiO2 etching with H2SO4. Gaseous and surface intermediate products were detected in the reactor effluent and catalyst wash water using solid phase microextraction (SPME) and trimethylsilyl derivatization. Main gaseous products were acetaldehyde, diethyl disulfide, ethylene, SO2, and main surface products were diethyl disulfide, diethyl trisulfide, 1,2-bis(ethylthio)ethane, ethanesulfinic, ethanesulfonic acids, diethyl sulfoxide, diethyl sulfone, and sulfuric acid.

Enhanced photocatalytic degradation of dimethyl methylphosphonate in the presence of low-frequency ultrasound

Mechanistic aspects of the role of 20 kHz ultrasonication in photocatalytic oxidation of dimethyl methylphosphonate (DMMP), a simulant for nerve chemical warfare agents, were studied in a batch reactor. We found that DMMP did not undergo mineralization under low frequency (20 kHz) ultrasonic irradiation. The increase of the rate of DMMP photocatalytic mineralization in the presence of ultrasound was not due to deagglomeration of TiO2, but was associated with enhanced mass transport of reagents. The same intermediate non-volatile products were detected in photocatalytic and sonophotocatalytic degradation. A kinetic model involving all stable intermediate species detected was introduced. Apparent rate constants of all stages of DMMP mineralization increase under sonication. A reaction route of DMMP mineralization without the formation of intermediate products appeared under ultrasonication. Such behaviour was attributed to enabling mass transport of DMMP into micropores and to the surface of TiO2.

Kinetic features of the steady state photocatalytic CO oxidation by air on TiO2

The paper reports quantum efficiency dependence of the steady state gas phase photocatalytic oxidation of CO over dispersed anatase on CO and CO2 concentrations, temperature and UV light intensity. A tentative mechanism of the process is proposed.

Air detoxification with nanosize TiO2 aerosol tested on mice

A method for fast air purification using high concentration aerosol of TiO(2) nanoparticles is evaluated in a model chemical catastrophe involving toxic vapors of diisopropyl fluorophosphate (DFP). Mice are used as human model in a closed 100 dm(3) chamber. Exposure of mice to 37 ppm of DFP vapor for 15 min resulted in acute poisoning. Spraying TiO(2) aerosol in 2 min after the start of exposure to DFP vapors resulted in quick removal of DFP vapors from the chambers air. Animals did not show signs of poisoning after the decontamination experiment and exposure to TiO(2) aerosol alone. Reactive oxygen species (ROS) and antioxidant activity (AOA) of mice blood plasma were measured for animals exposed to sound of aerosol generator, DFP vapors, TiO(2) aerosol and DFP vapors+TiO(2) aerosol. Reduced ROS and increased AOA were found for mice exposure to sound, DFP and TiO(2) aerosol. Exposure to DFP and decontamination with TiO(2) nanoparticles resulted in decreased AOA in 48 h following the exposure. The results suggest that application of TiO(2) aerosol is a powerful method of air purification from toxic hydrolysable compounds with moderate health aftermaths and requires further study and optimization.

Heterogeneous oxidation of ethanol over Cu(OH)2/α-Fe2O3 under visible light

A Cu(OH)2/α-Fe2O3 photocatalyst is shown to be active in the gas phase oxidation of ethanol under visible light. The calculated initial quantum efficiency of the ethanol photooxidation is 0.1-1%. However, ethanol is oxidized only into acetic acid, which deactivates the catalyst.