# Recent Strategies for Environmental Remediation of Organochlorine Pesticides
## 5 Photocatalysts for Pesticides Degradation
### Graphene Oxide-Based Photocatalyst for Pesticide Degradation  
The use of graphene oxide in heterogeneous photocatalysis for degrading organochlorine pesticide was favored due to its large surface area. It is metal free, since it contains only carbon, hydrogen and oxygen and can disperse easily in water [125]. Delocalization of conjugated \(\pi\) (pie) electrons throughout its layers have positive impact on charge transport. In addition, the presence of functional group such as OH and COOH, hydrophilicity, low conductivity and chemical stability are desirable properties of graphene oxide. In actual fact, graphene oxide is mostly used as co-catalyst because limited information is available about its ability to be activated by light [126]. However, it has been reported that their presence significantly improved the photocatalytic removal efficiency. This can be attributed to the role played in adsorbing the pollutant, acting as an electron acceptor, surfactant and support for the semiconductor [127; 128; 129]. Graphene oxide can be reduced to form reduced graphene oxide [130; 131]. Both graphene oxide and reduced graphene oxide have similar properties; however, reduced graphene oxide have high defects and low oxygen-to-carbon ratio unlike graphene oxide that has high oxygen-to-carbon ratio. Apart from this, graphene oxide has the appearance of brown powder, whereas reduced graphene oxide is a black powder. Either of the two could be combined with other semiconductors to degrade organochlorine pesticides with improved degradation efficiency [130; 132]. The improved efficiency could be attributed to better light absorption, narrowed band gap, limited recombination of charge carrier and improved separation of charge carrier [133]. Graphitic oxide and graphene oxide have been used to degrade 4-chlorophenol in water. About 92 and 97% were successfully degraded at optimum conditions, respectively [125]. [PERSON] et al. [134], prepared nanocomposite from both titanium oxide and graphene oxide which was used to degrade two poisonous insecticides (imidazoldoprid and carbaryl).The prepared nanocomposites possessed smaller band gap and superior photodegradation of the insecticides than ordinary graphene oxide or pure titanium oxide. In a similar study, [PERSON] et al. [107] prepared nanocomposite of Ni, Co and La supported on graphene oxide through microwave method. This catalyst was utilized to degrade 2-chlorophenol under sunlight irradiation. Within 300 min, 71% of the organochlorine was destroyed. However, when the experiment was carried out without graphene oxide, about 57% degradation was obtained within the same time. The presence of graphene oxide in the nanocomposite resulted in the lowering of the ability of holes and electrons to recombine and charge transfer efficiency was tremendously enhanced. [PERSON] et al. [79] also degraded four different pesticides (atrazine, isoproturon, alachlor and diuron) from water, by using a nanocatalyst made from the combination of titanium oxide and graphene oxide. It was observed from their investigations that the photocatalytic efficiency of this nanocomposite was not affected by water matrix variation. There was an enhanced degradation when ultra-pure water and natural water were separately used. Conversely, the photocatalytic efficiency of pure titanium oxide catalyst was altered with change in water matrix. Visible light irradiation was used throughout the experiment. Similarly, [PERSON] et al. [88] destroyed fenitrothion, which is an organochlorine pesticide, by using mesoporous GO-Fe3O4/TiO2 as a visible light active photocatalyst.