Photocatalytic oxidation of cationic dyes in single and binary solutions in presence of Zn-Cd oxides obtained from calcined LDH.

Abstract

In the present paper, zinc and cadmium layered double hydroxides (ZnCd-LDH) have been prepared through co-precipitation route then calcined at different temperatures. Their photocatalytic activity was determined by photodegradation of industriel toxic dyes (rhodamine B (RB) and crystal violet (CV)) in single and binary solutions illuminated with UVA or sunlight irradiation. It was found that the highest photodiscoloration efficiency was obtained for the nanomaterial heated at 700 °C (ZnCd-700). The physicochemical properties of ZnCd-LDH and ZnCd-700 were determined by PXRD, FTIR, DSC, TG/DTG, and DRS-UV-Vis. By heating the ZnCd-LDH material, some demixtion to ZnO and CdO phases occurred, corresponding to a band gap energy value of 2.93 eV for the formed zinc oxide nanoparticles. The results revealed that with 1 g·L-1 of ZnCd-700 dose, the photodiscoloration of dyes was enhanced significantly where in single solution, it was > 83.9% and ≥ 98.0% in 90 min of UVA ilumination and sunlight, respectively. Whereas, the removal of CV and RB was > 89.7% and ≥ 98.7% in binary solution under UVA and solar irradiations, respectively. The superoxide anion radical (O2•-) was identified as the most influential reactive species for dyes degradation. In binary solution, the CV dye was photodiscolored faster than RB while in single solution, the result was the opposite. The re-use study of ZnCd-700 as photocatalyst showed a slight decrease of dyes discoloration varying between 1.4 and 7.1% from the second to the fourth use.