Since the past few decades, textile wet processing and finishing industries are strongly dependent on synthetic dyes that severely contaminating water along with other very harmful organic pollutants. Cleansing of industrial wastewater is attracting more importance in present days due to toxic, low biodegradable, high persistence and carcinogenic nature of dye pollutants. Removal of these complex dye molecules is compulsory before their emergence into the environmental streams [1, 2]. These are degraded naturally under alkaline conditions, ultraviolet (UV) light illumination, high temperature, and other radical initiators. Unfortunately, by-products from these processes are more hazards than original dyes to the environment . Thus, for removing dyes from textile wastewater, an effective and economical treatment technique is needed. In view of this, various conventional methods have been developed to remove these most harmful and complex structured dye molecules from waste water such as adsorption on carbon materials, coagulation, flocculation, reverse osmosis (RO), biodegradation, membrane filtration, ozonation, advanced oxidation process (AOP) etc [4, 5]. Among these, AOP is largely adopted method for remediation of dye contaminated effluents because of their flexibility, efficacy and relatively low expensive . AOP covers wide variety of treatment techniques; among those approaches, semiconductor-mediated photocatalytic oxidation has been used extensively to abolish the recalcitrant organic pollutants from its contaminated wastewater. With this process degradation of a broad array of organic pollutants is possible which finally turns into H2O, CO2, etc through oxidation-reduction interactions between organic pollutants with photogenerated reactive oxygen species .
In particular, Titania (TiO2) has been generally admitted as a promising photocatalyst for the decomposition of hazardous environmental impurities owing to its unique physical and chemical properties . However, due to large band gap energy 3.2 eV (anatase TiO2) and poor electron mobility, it shows very limited photosensitization in the visible range of Earth’s solar spectrum. To overcome the grand challenges, several efforts have been made by researchers such as transition and noble metals doping [9, 10], semiconductors coupling , surface polymer sensitization [12, 13] and combination with carbonaceous materials . In particular, metal ion doping of TiO2 along with carbonaceous material combination is the emerging area at present in the photocatalysis. Doping can narrow the band gap and carbonaceous material can limit the charge carriers (e− - h+ pair) recombination . There are several investigators reported doping of TiO2 lattice with numerous transition metal ions i.e., Cr, Cu, Zr, Ce, Sn, Fe, Ni etc . Presently, as compare with many dopants, Nb doped TiO2 has attracted greater attention because of its utilization in various applications like photocatalysis, dye sensitized solar cells, sensors, fuel cell catalysis, and transparent conductive films . It is mainly due to the ionic radius of Nb5+ (0.064 nm) is significantly larger than Ti4+ (0.0605 nm) which effectively constricts the band gap of TiO2 to enlarge its adsorption in visible region and on the other side metals are thermally unstable as well as effortless to cause the charge carriers recombination .
Given on this obstacle, several researchers investigated and achieved efficient photocatalyst by providing 2-Dimensional support to TiO2 nanoparticles such as multiwall carbon nanotubes because of its multiple grapheme layers contacts with TiO2 allows electrons can flow through, which accelerate the photogenerated charge separation more favorably . Significant results have been obtained using graphene as 2-dimensional supporting material to catalyst due to that this material has a single atomic thick two-dimensional hexagonal lattice sheet structure aligned by a sp2-hybridized carbon network and its wide variety of features such as electrical, thermal, mechanical, etc . Additionally, the surface of graphene can be easily fabricated with different functional groups in contrast to carbon nanotubes. It is a 0 eV bandgap semiconductor  with high charge carrying property , high specific area (2600 m2g− 1) , high adsorption capacity and can be produced efficiently through “graphite oxide” intermediate from inexpensive natural graphite . Because of the hydrophobic nature of graphene, strong intercalation of metal oxide on graphene surface is difficult. In spite of this, chemically modified graphene-based materials like Graphene Oxide (GO) and reduced Graphene Oxide (rGO) drawing more attention in semiconductor photocatalysis as supporting material. The existing oxygen functionalities in GO and rGO, like carbonyl (C = O), hydroxyl (O-H), epoxide (C-O-C) groups making graphene to display wonderful hydrophilic character and good intercalation chemistry . It appears reasonable to conceive that much greater advancement in photocatalytic performance of Nb doped TiO2 (NT) can be achieved by the novel Nb doped TiO2/rGO composite materials with high interfacial contact and potential.
Herein, this paper demonstrated that synthesis of Nb-doped TiO2/rGO (NTG) nanocomposite by altering the GO loads using a modified sol-gel method via in situ process at low temperature, which is industrially scalable. Improvement in the photocatalytic efficiency of NTG catalysts caused by GO insertion was orderly investigated depending upon the electronic structure, optical absorption, microstructure, and electrochemical behaviours. The photocatalytic activity of the NTG nanocomposites was assayed by degrading the Rhodamine B (RhB) under visible light exposure.
RhB is a Xanthene group dye that is broadly using as a colouring compound in the manufacturing industries such as textiles, food products, paper, pharmaceutical, and dye laser production. Besides, also used for visual identification to illustrate the rate, flow path, and movement within water. As a consequence, it has been confirmed that polluted water with Rhodamine dyes could cause subcutaneous tissue borne sarcoma which is extremely fatal. Furthermore, other types of toxicities like reproductive and neurotoxicity have been thoroughly and intensively inspected as well as verified by the exposure of these dyes .