Catalysis Today
2020
Controlling the surface chemistry of graphene oxide: Key towards efficient ZnO-GO photocatalysts
SANDRA VÍCTOR-ROMÁN; ENRIQUE GARCÍA-BORDEJÉ; JAVIER HERNÁNDEZ-FERRER; JOSÉ M. GONZÁLEZ-DOMÍNGUEZ; ALEJANDRO ANSÓN-CASAOS; ADRIÁN M.T. SILVA; WOLFGANG K. MASER; ANA M. BENITO

Highlights

• Development of ZnO-GO hybrids for enhanced photocatalysis.

• ZnO-GO catalysts show high efficiency at low concentration.

• Surface chemistry of GO key for establishing photoinduced charge-transfer interface interactions with ZnO.

• Interface interactions between ZnO and GO responsible for photocatalysis enhancement.

Abstract

Graphene oxide (GO) and related materials are widely reported to enhance the photocatalytic activity of zinc oxide. However, the origin of the observed performance improvements remains elusive and studies contributing to a deeper understanding of this critical issue are largely missing. In this work, we have prepared a set of benchmark ZnO-GO hybrid materials in order to systematically put under closer scrutiny the influence of the surface chemistry of GO on the photocatalytic degradation of methylene blue. The set of ZnO-GO hybrids has been synthesized in an ultrasonication process involving ZnO nanoparticles obtained in a microwave synthesis process and GO with three distinct oxidation degrees, employed in three different loading fractions. Structural and physical-chemical characterization by XRD, FTIR, Raman, UV–vis, photoluminescence and spectroscopy and XPS, consistently demonstrate the importance of the surface chemistry of GO for establishing photo-induced charge-transfer interface interactions with ZnO, facilitating the enhancement of the catalytic activity of the ZnO-GO catalyst. Optimized interface interactions thus enabled the design of a ZnO-GO catalyst exhibiting a conversion rate of 80% obtained in a time of 70 min and at a catalyst concentration of only 0.045 mg/mL.

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Photoelectrochemical measurements

Fluorinated tin oxide (FTO) substrates of 2.5 x 1 cm (Solems SA, France) were sonicated in isopropanol for 5 min before spraying. ZnO films were prepared by spraying a ZnO (or ZnO-GO) suspension in ethanol (0.5 mg/ml) onto the FTO substrates using an automatized spray coater (Nadetech ND-SP, Spain), covering an area of 0.7 cm2.

Keywords: Graphene oxide; Zinc oxide; ZnO-GO hybrid; Photocatalysis; Surface chemistry