In this work, the application of high-power LED_365nm and commercial, low-price LED_398nm for heterogeneous photocatalysis with TiO₂ and ZnO photocatalysts are studied and compared, focusing on the effect of light intensity, photon energy, quantum yield, electrical energy consumption, and effect of matrices and inorganic components on radical formation. Coumarin (COU) and its hydroxylated product (7-HC) were used to investigate operating parameters on the ^•OH formation rate. In addition to COU, two neonicotinoids, imidacloprid and thiacloprid, were also used to study the effect of various LEDs, matrices, and inorganic ions. The transformation of COU was slower for LED_398nm than for LED_365nm, but r₀^7-HC/r₀^COU ratio was significantly higher for LED_398nm. The COU mineralization rate was the same for both photocatalysts using LED_365nm, but a significant difference was observed using LED_398nm. The impact of matrices and their main inorganic components Cl⁻ and HCO₃⁻ were significantly different for ZnO and TiO₂. The negative effect of HCO₃⁻ was evident, however, in the case of high-power LED_365nm and TiO₂, and the formation of CO₃^•− almost doubled the r₀^7-HC and contributes to the conversion of neonicotinoids by altering the product distribution and mineralization rate.

In this work a poly(3,4-ethylenedioxythiophene) (PEDOT)/iron oxalate composite was synthesized by electrochemical polymerization. The layer was deposited potentiostatically from the monomer-containing solution in the presence of iron(II) oxalate. Similarly to the polypyrrole/iron oxalate electrode – presented in a recent paper – the layer gave a negative photocurrent, which depended on the oxygen concentration of the electrolyte. This cathodic photocurrent – taken as the differences between the values registered under illumination and in the dark at −750 mV potential on the cathodic part of the voltammetric cycles – confirmed the sensitivity of the PEDOT/iron oxalate electrode for dissolved oxygen. Stationary photocurrents were determined also from chronoamperometric measurements, and they exhibited a linear behaviour with the dissolved oxygen concentration to below 1 ppm. The photo-effect of the PEDOT/iron oxalate layer can be attributed to the excitation of the neutral form of the film.