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Graphene photocatalysts 5

,†
,†
Luisa M. Pastrana-Martínez* , Sergio Morales-Torres* ,
†
†
José L. Figueiredo , Joaquim L. Faria , Adrián M.T. Silva †
†
*University of Granada, Granada, Spain, Universidade do Porto, Porto, Portugal
5.1 Introduction

Significant attention is being paid to the development of renewable and green technol-
ogies because of the increased energy demand and persistent environmental pollution.
From this perspective, the sun, a free, clean, and inexhaustible resource, is regarded
as a promising option [1–3]. New photocatalytic technologies are being developed to
transform renewable energy (i.e., solar light) into chemical fuels and products, such
as photocatalytic water splitting and carbon dioxide (CO 2 ) reduction, among others
[4–6]. Photocatalytic water splitting is aimed at the production of hydrogen (H 2 ) using
natural renewable resources like water and the sun. Moreover, by using solar energy,
the photocatalytic reduction of CO 2 can transform a harmful greenhouse gas (i.e., CO 2 )
into valuable solar fuels such as methane (CH 4 ) and methanol (CH 3 OH) [2,4,5,7].
Various developments over the past four decades, particularly in regard to energy
and environmental applications, have shown great potential for semiconductor pho-
tocatalysis to be a low-cost, environmentally friendly treatment technology [8,9].
However, some limitations are still associated with photocatalysts, such as their in-
ability to use visible light efficiently and their poor stability. Recent efforts have been
devoted to the development of novel composite photocatalysts with the notion of in-
creasing the efficiency of solar energy conversion.
2
Graphene, a 2D monolayer of sp carbon atoms with a hexagonal packed lattice
structure, was a breakthrough discovery in 2004, and it is now set to exceed all other
carbon allotropes in material science and technology [10]. This material exhibits many
interesting properties, such as high mechanical strength, superior thermal conduc-
tivity, outstanding transparency, a huge specific surface area, and excellent charge
transport [11,12]. Graphene and its derivatives (e.g., graphene oxide, GO; and re-
duced graphene oxide, rGO) have stimulated interest in the design of sophisticated
high-performance graphene-based composite materials for different applications, such
as sensors [13], energy storage devices [14], bio-applications [15], and particularly
graphene-based photocatalysts with improved solar-to-fuel conversion efficiency [16].
Graphene derivatives have been shown to induce some beneficial effects on the pho-
tocatalytic performance of semiconductor catalysts by creating synergies between the
semiconductor and the carbon phases. This effect is attributed mainly to a decrease
in the band gap energy of the composite catalyst, an enhancement of the adsorptive
properties, and the charge separation and transportation properties.
This chapter focuses on the current status of graphene-based composites applied
in photocatalysis for energy applications, including photocatalytic water splitting and

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