Graphene oxide-P25 photocatalysts for degradation of diphenhydramine pharmaceutical and methyl orange dye

Abstract

Graphene oxide (GO) and the benchmark TiO2 photocatalyst (P25) were used to prepare different composites (GOP), by a simple method of mixing and sonication, varying the GO content and the heat-treatment temperature under nitrogen. The composites were characterized by thermogravimetric (TG) and differential thermogravimetric (DTG) analyses, scanning electron microscopy (SEM), physical adsorption of nitrogen, UV–Vis and IR diffuse reflectance spectroscopies (DRUV and DRIFT), and point of zero charge (pHPZC) measurements. The morphology, microporosity and SBET of the composites did not vary significantly in comparison to P25, while an increase of their mesoporosity and mesopore diameter were observed due to the formation of GO aggregates coated with P25 nanoparticles. The aggregates were stabilized by the formation of TiOC bonds, which in turn produced a narrowing of the band gap relative to P25. The surface chemistry of GOP composites varied with the GO content, being more acidic when higher GO content was used. The photocatalytic performance was evaluated for the degradation of diphenhydramine (DP) pharmaceutical and methyl orange (MO) dye under near-UV/Vis irradiation. The first order rate constant of MO photodegradation increased four times for some GOP composites with relation to P25 (i.e., from k=52×10−3 to 207×10−3min−1). Comparable efficiencies were observed when DP was used as model pollutant (i.e., around k=54×10−3min−1). The best performing photocatalyst was that containing 1.4wt.% GO and treated at 200–300°C. The improved performance was attributed to the reduction of GO during the thermal treatment and to the good contact between the TiO2 and the carbon phases.