Kateřina Macounová

Kinetics of photocatalytic degradation of diuron in aqueous colloidal solutions of Q-TiO2 particles

Abstract Kinetics of the photocatalytic degradation of a phenylurea herbicide diuron in aqueous colloidal solutions of Q-TiO 2 nanoparticles was analyzed in detail applying a model of parallel consecutive reactions of the first-order. The found mechanism was compared with the reaction pathways of electrochemically assisted photoprocesses on illuminated TiO 2 layers, polarized by external voltage, in various solvents. While a reductive dechlorination on benzene ring of diuron represented the major pathway in acetonitrile, a consecutive oxidative demethylation on the aliphatic side chain was mainly observed in water.

Dramatically enhanced cleavage of the C-C bond using an electrocatalytically coupled reaction.

This paper describes a generalized approach for the selective electrocatalytic C-C bond splitting in aliphatic alcohols at low temperature in aqueous state, with ethanol as an example. We show that selective C-C bond cleavage, leading to carbon dioxide, is possible in high pH aqueous media at low overpotentials. This improved selectivity and activity is achieved using a solution-born co-catalyst based on Pb(IV) acetate, which controls the mode of the ethanol adsorption so as to facilitate direct activation of the C-C bond. The simultaneously formed under-potentially deposited (UPD) Pb and surface lead hydroxide change the functionality of the catalyst surface for efficient promotion of CO oxidation. The resulting catalyst retains an unprecedented ability to sustain the full oxidation reaction pathway on an extended time scale of hours as opposed to minutes without addition of Pb(IV) acetate.

Photodegradation of metamitron (4-amino-6-phenyl-3-methyl-1,2,4-triazin-5(4H)-one) on TiO2

Abstract Photodegradation of metamitron in aqueous solution (i) on a plate photoreactor with immobilized TiO2 layer and (ii) in a tube photoreactor in the presence of quantum sized Q-TiO2 particles was investigated and compared. Both processes, heterogeneous photocatalysis and homogeneous direct photolysis, took part on the overall photodegradation of metamitron. Deaminometamitron (6-phenyl-3-methyl-1,2,4-triazin-5(4H)-one), hydroxymetamitron (4-amino-6-(2′-hydroxyphenyl)-3-methyl-1,2,4-triazin-5(4H)-one) and deaminohydroxymetamitron (6-(2′-hydroxyphenyl)-3-methyl-1,2,4-triazin-5(4H)-one) were identified as main products. A reaction scheme of these phototransformations was proposed.

Photocatalytic degradation of diuron [3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea] on the layer of TiO2 particles in the batch mode plate film reactor

The photocatalytic degradation of diuron in aqueous solution on TiO 2 layer of a batch mode plate reactor irradiated with ultraviolet sun-bed tubes was investigated. Dependence of the reaction rate on the diuron concentration (in the range of 0.8-8.0x10 -5 mol/dm 3 ) and on the light intensity (0.8-2.7x10 -9 einstein/cm 2 .s) but independence on the flow rate (2.5-3.6 dm 3 /min) were found. A reaction scheme was proposed following the main identified primary (3-(3,4-dichlorophenyl)-1-methyl-1-formylurea and 3-(3,4-dichlorophenyl)-1-methyl-urea) and secondary (3-(3,4-dichlorophenyl)-1-formylurea and 3,4-dichloro-phenylurea) products.

Electrochemical Water-Splitting Based on Hypochlorite Oxidation

Effective catalytic water-splitting can be electrochemically triggered in an alkaline solution of sodium hypochlorite. Hypochlorite oxidation on polycrystalline platinum yields ClO· radicals, which initiate a radical-assisted water-splitting, yielding oxygen, hydrogen peroxide, and protons. The efficiency of the O2 production corresponds to about two electrons per molecule of the produced O2 and is controlled primarily by the hypochlorite concentration and pH.

Electrochemical Behavior of Nanocrystalline Ru0.8Me0.2O2 − x ( Me = Fe , Co , Ni ) Oxide Electrodes in Double-Layer Region

Nanocrystalline oxides with average chemical composition corresponding to Ru 0.8 Me o.2 O 2-x (Me = Fe, Co, Ni) were prepared by the sol-gel approach. All prepared materials were of single-phase character with rutile-type structure. The effect of nanocrystal size and nature of doping cation on electrochemical supercapacitor behavior was studied by means of cyclic voltammetry and electrochemical impedance. The specific capacitance of the Ru-based oxides increases by doping with lower-valence cation from ca. 22 μF cm -2 of actual electrode surface area observed for pure RUO 2 to 230 μF cm -2 in the case of Ni doped material. The improved capacitance behavior of the doped materials is ascribed to improvement of transport properties of the oxide structure enabling easier diffusion of compensating protons.