Abstract The Zn0.5Cd0.5S/ZnO/carbon xerogel photocatalyst was synthesized through the thermal treatment of ZnO, CdS, and a low-cost carbon xerogel matrix at high temperature (600 ºC). ZnO is one of the most widely used photocatalysts, but it has low visible-light absorption, while Zn0.5Cd0.5S is a visible-light active photocatalyst, which can be used as a co-catalyst to enhance photoactivity under natural radiation and promote charge separation through the creation of Z-scheme heterojunctions. The further addition of the carbon xerogel can be justified by its highly developed porous structure and ability to capture photogenerated electrons, which will also promote charge separation. The creation of the hexagonal Zn0.5Cd0.5S and ZnO phases was confirmed through the X-ray diffractometry technique. The addition of the carbon xerogel led to an increase in the specific surface area of the XC/ZnO (630%) and XC/ZnO-Zn0.5Cd0.5S (320%) and a decrease in particle size when compared to the pure ZnO. Regarding the photocatalytic performance of the materials, the Zn0.5Cd0.5S/ZnO/carbon xerogel displayed an enhanced photocatalytic activity for 4-chlorophenol degradation, with 84% degradation after 300 minutes of artificial solar irradiation. The enhanced photoactivity of the Zn0.5Cd0.5S/ZnO/carbon xerogel composite was further confirmed by chronoamperometry, as the composite presented higher photocurrent generation under light irradiation.

The influence of different supporting electrolytes as well as of different current densities on RO16 dye electrochemical oxidation using BDD electrodes has been systematically studied. The RO16 azo-dye electrooxidation experiments were performed at different current densities and three different supporting electrolytes: H2SO4 0.1 mol L-1, HClO4 0.1 mol L-1 and K2SO4 0.1 mol L-1. The results showed that a higher degradation for reactive azo dye RO16 was observed for the K2SO4 (pH=10) supporting electrolyte for a current density of 100 mA cm-2. This behavior can be associated with the deprotonation effect of the dye molecule, which can facilitate breakdown of the molecule, specifically the azo bond making color removal more efficient. In addition, in this pH there is a greater amount of hydroxyl ion (OH-) available increasing the hydroxyl radical formation.

This paper reports the electrochemical degradation of the azo dye Ponceau 2R under galvanostatic electrolysis in the 1 to 200 mA cm-2 range at room temperature using dimensionally-stable anodes of oxygen (DSA-O2), chlorine (DSA-Cl2) and a titanium electrode of platinum coated with platinum oxide (Ti/Pt). The methodology applied was efficient for removing the color of the Ponceau 2R and the highest percentage removal of total organic carbon was obtained at 200 mA cm-2. Despite not having been observed complete mineralization, approximately80% removal of aromatic rings was estimated, resulting in drastic reduction of toxicity of the sample.