Functionalized Graphene Derivatives and TiO2 for High Visible Light Photodegradation of Azo Dyes

Abstract

Functionalized graphene derivatives including graphene oxide (GO), reduced graphene oxide (rGO), and heteroatom (nitrogen/sulphur (N/S) or boron (B))-doped graphene were used to synthesize composites with TiO2 (T). The photocatalytic performance of composites was assessed for the degradation of Orange G dye (OG) under simulated solar light. All the prepared graphene derivatives—TiO2 composites showed better photocatalytic performance than bare TiO2. A higher photocatalytic activity was found for the composites containing GO and N/S co-doped rGO (kapp = 109.2 × 10−3 and 48.4 × 10−3 min−1, for GO-T and rGONS-T, respectively). The influence of both initial solution pH and the reactive species involved in the OG degradation pathway were studied. The photocatalytic activity of the samples decreased with the increase of the initial pH (from 3.0 to 10.0) due to the occurrence of electrostatic repulsive forces between the photocatalysts surface and the molecules of OG, both negatively charged. The use of selective scavengers showed that although the photogenerated holes dominate the degradation mechanism, radicals and singlet oxygen also participate in the OG degradation pathway. In addition, reutilization experiments indicated that the samples were stable under the reaction conditions used.

Photocatalytic Perfomance of ZnO-Graphene Oxide Composites towards the Degradation of Vanillic Acid under Solar Radiation and Visible-LED

“…Normally, metal oxides such as titanium dioxide (TiO 2 ), zinc oxide (ZnO), zirconia (ZrO 2 ), tungsten trioxide (WO 3 ), and vanadium oxide (V 2 O 5 ), have been used as semiconductor photocatalysts for water and air decontamination, as well as for energy applications [9][10][11][12]. ZnO is an n-type semiconductor with a band gap ca.…”

One-Pot Thermal Synthesis of g-C3N4/ZnO Composites for the Degradation of 5-Fluoruracil Cytostatic Drug under UV-LED Irradiation

“…The photodegradation of 5-FU was assessed at different pH values, i.e., 3.0, 6.3 (natural), and 9.0, by adding HCl 0.1 M or NaOH 0.1 M, respectively. The photocatalytic degradation pathway of 5-FU was evaluated using methanol (MeOH, 1.0 mM), furfuryl alcohol (FFA, 1.0 mM), and ethylenediaminetetraacetic acid (EDTA, 1.0 mM), as radical, singlet oxygen ( 1 O 2 ), and hole scavengers, respectively [ 40 , 41 ].…”

Recent progress in semiconductor/graphene photocatalysts: synthesis, photocatalytic applications, and challenges

“…For instance, the photodegradation efficiency of Orange G dye over GO–TiO 2 and its heteroatom doped variant rGO(NS)–TiO 2 photocatalysts was greatly affected by the medium pH. 83 At low pH values, the surface of the catalyst becomes positively charged that facilitates its attraction with the negatively charged dye molecules; however, at higher pH values the photocatalytic activity was reduced. In another study, MB dye photo degradation improved with raising the pH value due to the increased attraction between the cationic dye and ZnO/graphene/TiO 2 photocatalyst (pH pzc = 6.4); however, at pH > 11.0, OH − competes with the photocatalyst in attracting the cationic MB molecules resulting in lower decomposition efficiency, Fig.…”