Photocatalytic activity of graphene oxide-TiO2 thin films sensitized by natural dyes extracted from Bactris guineensis.

William Vallejo,Patricia Quintana,Carlos Díaz-Uribe,Carlos Grande,Angie Rueda

doi:10.1098/rsos.181824

Abstract

This study synthesized and characterized composites of graphene oxide and TiO2 (GO–TiO2). GO–TiO2 thin films were deposited using the doctor blade technique. Subsequently, the thin films were sensitized with a natural dye extracted from a Colombian source (Bactris guineensis). Thermogravimetric analysis, X-ray diffraction, Raman spectroscopy, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and diffuse reflectance measurements were used for physico-chemical characterization. All the samples were polycrystalline in nature, and the diffraction signals corresponded to the TiO2 anatase crystalline phase. Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR) verified the synthesis of composite thin films, and the SEM analysis confirmed the TiO2 films morphological modification after the process of GO incorporation and sensitization. XPS results suggested a possibility of appearance of titanium (III) through the formation of oxygen vacancies (Ov). Furthermore, the optical results indicated that the presence of the natural sensitizer and GO improved the optical properties of TiO2 in the visible range. Finally, the photocatalytic degradation of methylene blue was studied under visible irradiation in aqueous solution, and pseudo-first-order model was used to obtain kinetic information about photocatalytic degradation. These results indicated that the presence of GO has an important synergistic effect in conjunction with the natural sensitizer, reaching a photocatalytic yield of 33%.

Highlights

In recent decades, the increased concentration of organic dyes in water has been a problem of growing concern; the textiles, paper and plastics industries use dyes in the manufacture of their products and consume a large quantity of water, increasing quantities of these pollutants in the final effluent [1,2]
According to data reported by Stengl et al about the influence of the GO in the photocatalytic activity of TiO2, the reduction in the surface area could be due to an agglomeration given by the carbonaceous material, in which the GO is completely covered by semiconductor particles
The present study synthesized TiO2 –GO composites and studied the natural dye sensitization of TiO2 – GO thin films with natural dyes extracted from B. guineensis

Summary

Introduction

The increased concentration of organic dyes in water has been a problem of growing concern; the textiles, paper and plastics industries use dyes in the manufacture of their products and consume a large quantity of water, increasing quantities of these pollutants in the final effluent [1,2]. Recent studies have demonstrated that heterogeneous photocatalysis is a promising technology as an alternative for water purification, especially in reducing the concentration of dyes in wastewater by the use of different kinds of semiconductors under a specific radiation source [3,4,5]. Recent study has reported the improvement of the photocatalytic activity of TiO2 using Syzygium cumini as a natural sensitizer [26]. The modification of semiconductors with electron-donating materials (e.g. graphene, graphene oxide (GO) and other carbon materials) is another approach to improving the catalyst efficiency This kind of donating materials reduces the recombination rate of electron–hole pairs by increasing the charge-carrier mobility [28]. Stengl et al [32] obtained TiO2/graphene nanocomposites by thermal hydrolysis of suspension with graphene nano-sheets, and titania-peroxo complex provided a good photocatalytic activity in the decomposition of butane under UV and visible light

Methods

Results

Conclusion