Direct sunlight photodegradation of congo red in aqueous solution by TiO2/rGO binary system: Experimental and DFT study

Abstract

Photolysis was employed to produce titanium dioxide (TiO2) with exposed (001) facets, which were then modified by incorporating reduce graphene oxide (rGO) sheets at (1, 3 and 5) wt.%.The chemical composition, optical properties, morphology, and electrochemical behavior of both the pure and composite nanomaterials were analyzed. The X-ray diffraction (XRD) and Raman spectroscopy techniques confirmed the formation of the anatase phase of TiO2 in the samples. The Debye Scherrer method was utilized to estimate the size of the particles. It was observed that the particle size decreased as the concentration of rGO increased; at 5 wt% rGO, the size was 11 nm. The morphology of the rGO/TiO2 nanocomposite was analyzed with transmission electron microscopy (TEM) which showed that TiO2 nanoparticles were dispersed on the surface of the rGO sheets. The analysis of the X-ray photoelectron spectrum (XPS) revealed that bonding of TiO2 with rGO occurred through the formation of Ti-C and Ti-O-C bonds. The results obtained from the diffuse reflectance spectroscopy (DRS) showed a decrease in band gap upon an increase in rGO concentration. Moreover, confirmation was obtained regarding the reduction of recombination carriers through the photoluminescence (PL) spectrum. The results indicated that the prepared nanocomposite had a high number of oxygen vacancies. The photodegradation mechanism of congo red dye under sunlight was studied by Liquid chromatography–mass spectrometry (LC-Mass) and scavenger effect. The photodegradation of congo red dye (CR) utilizing TiO2, both pure and incorporated with rGO, was observed under normal conditions in the presence of sunlight. The study revealed that the optimal condition for achieving maximum photodegradation of CR dye was pH = 7, 100 min, 50 ppm initial CR dye concentration and 10 mg of catalyst dosage. The photodegradation data illustrated that 5 wt% rGO doped TiO2 exhibits higher efficiency than other 3; 1 wt% rGO and pure TiO2. Finally, the improving breakdown of CR dye using direct sunlight showed high efficiency without leaving behind any secondary intermediates.