Photodegradation of Congo Red by Modified P25-Titanium Dioxide with Cobalt-Carbon Supported on SiO2 Matrix, DFT Studies of Chemical Reactivity

Congo red is a hazardous material in the environment. The present work describes the synthesis of TiO2/CoC@SiO2-bipy (1) and TiO2/CoC@SiO2-phen (2) nanocomposites for the photodegradation of azo-dye Congo red (CR) dye in aqueous solution, by combining pure TiO2 with CoC@SiO2-bipy (s1) and CoC@SiO2-phen (s2) nanoparticles. The prepared nanocomposites were evaluated in term of photocatalytic activity rates in aqueous solution using CR. The nanocomposites TiO2/CoC@SiO2-bipy (1) and TiO2/CoC@SiO2-phen (2) were prepared from TiO2 (75%) and CoC@SiO2-bipy (s1) or CoC@SiO2-phen (s2) (25%) (weight ratio). Ultra-sonication and milling were used to prepare the heterogeneous nano catalysts. The pH, initial dye concentration, and catalyst dosage appeared to have a significant impact on the photocatalytic degradation performance. Molecular oxygen and other active species played a significant role in the photocatalyst degradation of CR with sunlight energy (UV-index 5.0). The chemical reactions were accelerated depending upon electrophilicity (omega) and energy gap (E-g) of azo dye species CR-N=N, CR-N=NH and CR=N-NH species which were calculated by density function theory (DFT). It can be concluded that the rate of electron-hole recombination of the TiO2 catalyst, when adding CoC@SiO2-bipy (s1) or CoC@SiO2-phen (s2), not only enhances the degradation but also effectively removes toxic dye molecules and their by-products. The newly prepared TiO2/CoC@SiO2-bipy (1) nanocomposites showed increased photocatalytic efficiency at low catalyst dose and faster rate of degradation of Congo red compared to TiO2/CoC@SiO2-phen (2) and TiO2 catalysts. The novel catalysts (1) and (2) can be easily separated by centrifugation and filtration, from the reaction mixture compared to TiO2.