Recently most of the chemical industries using several toxic substances such as chlorophenols, heavy metals, dioxins, polychlorinated biphenyls, asbestos, and dyes as in the form of solvents, and active ingredients for preparation of products [1]. After completion of chemical process, they are let out through our environment [2]. These toxic chemicals cause severe health issues in human beings such as skin infection, cancer, nervous problem, and waterborne disease [3].Even aquatic and terrestrial animals also affected and it reflects in ecological imbalance. Dyes are unavoidable necessary materials for our lifestyle. Nowadays, rhodamine B (RhB) is a widely used dye in medicine, biological staining, painting, printing, food, and leather industries [4]. It has highly colorant which leads to the carcinogenic/mutagenic to the living organisms [5]. RhB has a diminution of the light diffusion in water which reduces aquatic species photosynthesis and natural water purification [6]. Hence, RhB removal is very important from the environment water/industrial wastewater before deteriorating in the ecosystem.
Several methods such as adsorption, reverse osmosis, ion exchange, and biological methods were employed to the removal of RhB [7]. Photocatalytic degradation of dye molecules is one of the best methods compare to other techniques [8]. In photocatalysis,, many of the semiconductors like zinc oxide (ZnO), tungsten oxide (WO3), strontium titanate (SrTiO3), and titanium dioxide (TiO2) are acted as dynamic photocatalysts [9–12]. Among others, NiOis one of the semiconducting materials. It has a better chemical stability and adsorption property [13]. However, NiO has less absorption in the visible region and also limits the photocatalytic efficiency [14, 15].
On the other hand, g-C3N4 is a chemically stable and non-hazardous metal free semiconductor photocatalyst. Because, it has a band gap of 2.8 eV [16], which is responsible to absorb visible light region and it was suggested to be the best option to produce nano heterostructure. Moreover, g-C3N4 can be easily synthesized by using economically available precursors such as urea, melamine, cyanamide, and thiourea [17]. Though, NiO acts as a photocatalyst, the efficiency is low as compared with the g-C3N4 [18].Generally, bare metal oxides has some limitations regarding the charge separation and difficult to transfer and participate redox reaction [19]. To overcome this limitation, it is necessary to prepare new composites to further improve the photocatalytic efficiency of dye degradation [20–21]. Hence, combination of NiO and g-C3N4 could attain the efficient visible-light-driven photocatalytic activity without any additional oxidant [22].For example, recently, reported composite like MgO-g-C3N4, ZnO/g-C3N4, MnO2-g-C3N4 performed outstanding photocatalytic activity than their corresponding single entity [23–27]. In the present study NiO/g-C3N4, nanocomposite was synthesized by the simple mixing method and applied as photocatalyst to the RhBphoto degradation reaction assisted with visible light illumination.