**1. Introduction**

The world is facing serious water scarcity problem and thus protection of fresh water resources is critical in sustainable development of the society. Water pollution causing severe health issues because of waterborne diseases such as cholera, diarrhea, typhoid, and hepatitis leading to human sickness and deaths of (> 14,000)

people/day globally [1]. Major water contaminants stemmed from pesticides, textile dyes and a bunch of different chemicals often end up in water bodies or rivers [2, 3]. Textile industries generally uses many colored dye effluents, 65–75% of them belong to azo dyes and annually ~12% of these dyes were lost during manufacturing and the processing operations [4]. The direct discharge of pollutant dyes or pharmaceuticals release toxic or carcinogenic substances into the aqueous environment leading to severe dangers and environmental disasters. To overcome these issues, globally various physical, chemical and biological processes have been used such as precipitation, adsorption (activated carbon), air stripping, coagulation, reverse osmosis, and membrane ultrafiltration, however, these conventional techniques are non-destructive, or often transfer the organic compounds from one phase to another phase triggering secondary pollution [5–7].

Ever since the discovery of water splitting via semiconductor photocatalysis by Fujishima and Honda [8], this technology has gained intense research interests due to potential applications in various fields including sustainable energy conversion, degradation of organic pollutants, bacterial elimination, CO2 reduction, air purification, antibacterial, organic reactions and self-cleaning etc. (**Figure 1**) [9–11]. Visible light driven (VLD) photocatalyst which can directly harvest solar energy to remove various toxic organic pollutants from water through the advanced oxidation processes is a relatively new and active research area in this field. Till date, titanium dioxide (TiO2) is the mostly used photocatalysts because of low cost, superior physicochemical properties and environmental sustainability. However, TiO2 has one major drawback of wide band gap (only absorb ultraviolet light <4% of solar spectrum) and limited its use under direct sunlight. In this regard, various other semiconductor nanomaterials have been exemplified as photocatalyst systems such as SnO2, ZnO, WO3, Fe2O3, BiVO4, Ag3PO4, BiOCl and BiOBr, etc. for photocatalytic water

**Figure 1.** *The diverse applications of photocatalysis.*

*Graphene Related Materials and Composites: Strategies and Their Photocatalytic Applications… DOI: http://dx.doi.org/10.5772/intechopen.102404*

**Figure 2.**

*Development of graphene based composites with different materials.*

decontamination [11–13]. The practical utility of these semiconductors catalysts is restricted by low its absorption coefficient, high rate of recombination of electron– hole pairs and variance with the solar spectrum [14, 15]. In order to overcome these issues, a different strategy including Z-Scheme semiconductor photocatalyst [16], metal doping in semiconductor [15], semiconductor-heterostructures or nanocomposites [16–18] have been proposed. In the past decade, metal-doped-graphene or related materials have fascinated intense interests because of its potential for environmental purification and converting photon energy into chemical energy. This process obeys one of the 'Green Chemistry Principle', and widely applied for the degradation of hazardous pollutants. However, in the practical applications was restricted due to the failure to absorb visible light. Therefore, development of novel catalysts that can meet these technical needs is still a daunting challenge. It is in no doubt that the innovations of graphene-based material (GRM) will brings about massive opportunities in nurturing science and technology (**Figure 2**). Due to its exceptional atom-thick 2D structure containing sp2 bonded arrangement of carbon atoms in a hexagonal lattice, the high specific surface area, conjugated aromatic system, admirable mechanical properties, and robust physicochemical stability and greater electron mobility, graphene is regarded as an ideal high-performance candidate for many photocatalyst systems [19, 20]. A series of different carbon materials, such as activated carbon, porous carbon, carbon nanotubes, graphene and graphitic-carbon nitride can be used as catalyst supports.

In this book chapter we focus on graphene and related materials (graphene oxide and reduced graphene oxide and derivatives) which has emerged to be excellent promoters in photocatalytic reactions because of their low cost, unique physicochemical properties, surface area, electronic conductivity, mechanical flexibility and ionic

mobility. These significant features together with high stability enabling them to produce hybrids or nanocomposites photocatalysts with enhanced performances for degradation of organic pollutants (dyes, pharmaceutical wastes, pesticides etc.) in water. Advanced oxidation processes (AOP) for waste water treatment mainly relies on generation of photo-induced-charge carriers (electron and holes), and utilizing them to produce highly active reactive oxygen species (ROS). The as produced ROS radicals generally function as ultimate oxidants in photochemical reactions and subsequently degrade the organic pollutants in water. This book chapter highlights historical background, synthesis strategies and overview of graphene-related materials to produce composite photocatalysts, enabling application in environmental remediation. Finally, the remarks pertaining to state-of-art advancements, challenges and future perspectives have been discussed.
