Photocatalytic degradation of phenol using a new developed TiO2/graphene/heteropoly acid nanocomposite: synthesis, characterization and process optimization

A TiO2/graphene (TiO2/Gr) nanocomposite was synthesized using bottom-up assembly. The TiO2/Gr nanocomposite was modified with 12-tungstophosphoric acid (H3PW12O40, TiO2/Gr/xPW). The structural properties of the nanocomposite have been characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), zeta potential, Brunauer-Emmett-Teller (BET), Fourier transform infrared (FTIR), and diffuse reflectance spectra (DRS). Results of DRS showed a visible shift when the TiO2/Gr nanocomposite was modified with PW. The photocatalytic activity of the synthesized nanocomposite was measured by the degradation of phenol under visible and UV light irradiation. The effects of initial concentration of phenol, concentration of photocatalyst, reaction time, loading of PW and initial pH on phenol removal efficiency in batch experiments were investigated. The results showed that the degradation efficiency is decreased with an increase in initial concentration of phenol from 50 to 150 mg L-1 while pH did not show a significant impact. As a result, TiO2/Gr/xPW exhibited a higher visible-light photocatalytic activity in comparison with TiO2/Gr and pure TiO2 with the maximum degradation efficiency of 91, 68, and 15%, respectively. This clearly shows that among the modified composites, the catalyst with 20 wt% PW showed maximum visible shift. COD measurements under optimum conditions showed 78% phenol mineralization. And also, the reusability of the catalyst was proved when 80% degradation could be achieved after three consecutive batches.