Methylene blue (MB, Figure 1) is a blue colored dye that can be used as a medication and as dye for dyeing leather and temporary hair. It is generally used in human and veterinary medicine for various therapeutic and diagnostic procedures such as a stain in bacteriology, as a redox coloring agent, as a targeting agent for melanoma, as an anti-methemoglobinemic, as an antiseptic and disinfectant, as a treatment for ifosfamide induced encephalopathy, as a treatment of vasoplegic associated with septic shock, and as a tracer in parathyroid surgery [1-3]. It has been also used for various other types of application inducing, redox indicator, peroxide generator, water testing, biological staining, and aquaculture. Moreover, the dose of MB (approximately 500 mg) in human bodies causes various types of side-effects such as headache, nausea, vomiting, chest pain, cyanosis, shortness of breath, and high blood pressure with some other side effects including hyperbilirubinemia, anemia, erythrocytic blister cells, skin discoloration, serotonin syndrome, red blood cell breakdown, and allergic reactions [4-6].

Hence, to lessen its drawbacks and for the protection of environment, the elimination of MB dye from aqueous solution is of the major concern for the scientist community. For this, a number of techniques, such as, membrane filtration [7], oxidation [8], reduction [9], flocculation [10], chemical precipitation [11], adsorption [12] and sonochemical [13] are available to tackle such type of pollutants. Among all these methods, photocatalysis is a significant method for the removal of organic pollutants and variety of semiconductor photocatalysts with different wavelengths are available in literature [14]. In solar energy, more than 43% of energy falls in the visible region and traditional photocatalysts, such as TiO₂ have a large band gap (3.2 eV) and they require Ultraviolet light for photocatalysis [15]. Thus, these semiconductor photocatalysts cannot utilize the solar energy (visible light) in the catalysis process and have motivated the scientist community to develop efficient photocatalysts which can utilize the visible light of solar energy.

In modern era, nanotechnology, an emerging science; has fascinated scientists due to its novel properties. Plasmonic based photo catalyst is a promising agent for the reduction of synthetic dyes [16]. Graphene consists of a single layer of sp² hybridized carbon atoms forming a two-dimensional (2D) hexagonal lattice and it possesses excellent properties such as high electron mobility, high young’s modulus, large specific surface area and excellent thermal conductivity [17,18]. Graphene oxide (GO) as shown in Figure 2, a monolayer sheet is in oxidized form and decorated by the oxygen-containing polar functionalities of graphite which can enhance its surface functionality and it can be widely used in a number of applications such as sensor, electronic, drug delivery, solar desalination, catalyst, biomedicine antibacterial coatings and water treatment [19-22].

In order to enhance the surface area of GO, reduction of oxygen containing groups is required. The reduction of these oxygen containing groups, i.e., GO into rGO can be carried out by using various chemicals such as hydrazine, hydroquinone, sodium borohydride etc. as a simple method [23,24]. But these chemicals are toxic and hazardous and also cause the secondary environment pollution [25]. Hence, the need of environmental protection has led to enhance the interest in eco-friendly method for the reduction of GO into rGO. Keeping this thing in mind, electroplating method has been used for the reduction of GO into rGO. Figure 3 describes the synthesis of rGO on stainless steel by using potentiostat techniques [26]. The GO possess negative charge so it is attracted towards anode and get reduced and finally becomes rGO. In this method no chemical is required, by using simple techniques rGO is deposited successfully on the stainless steel.

The required mass of rGO onto stainless steel can be altered by changing the synthesis procedure such as concentration of GO, electroplating time duration and applied voltage. Furthermore, the metal nanostructure has a suitable band position, Surface Plasmonic Resonance effect, photonic stability and its biocompatibility, which make them distinctive and acts as a substrate in the electron transfer reaction, which is necessary for the reduction of any reactant. The decoration of AgNWs onto the surface of rGO layer has been carried out in order to enhances its surface area. Also, the presence of AgNWs onto rGO is responsible for the tunning of band gap of material which has been confirmed from the Tauc plot. The optical band gap of rGO and rGO/AgNWs has been calculated from the UV-Vis absorption spectra by using the Tauc's equation [27]. Tauc plot of the bandgap of synthesized rGO and rGO/AgNWs nanocomposite is shown in Figure 4.

The bandgap of the rGO is found to be decreased from 2.69 eV to 1.74 eV in the presence of AgNWs. It is also confirmed that the bandgap decreases non-linearly by virtue of the presence of AgNWs. The results reveal that the presence of AgNWs onto rGO will be responsible for the decline in the wide-bandgap and enhancement in photocatalytic reduction activity. Hence, the synthesized GO/AgNWs nanocomposite has suitable band position, Surface Plasmonic Resonance effect, photonic stability and its biocompatibility.

The specific surface area is an important property of nanocomposite and play an important role in catalysis application.

In order to explore the Brunauer–Emmett–Teller (BET) surface area, N₂ adsorption and desorption has been performed and displayed in Figure 5. The isotherm curve of both rGO and rGO/AgNWs reveal that both the samples are porous in nature with a hysteresis loop at high partial pressures. The total active specific surface area of rGO is about 150.123 m²/g. However, the value of active specific surface area in case of rGO/AgNWs is increased as compared to rGO, which also confirms the porous nature of rGO/AgNWs nanocomposite as confirmed from FE-SEM micrographs.

It can be concluded that the problem related to deletion of methylene blue dye from aqueous solution has been resolved by using the photocatalyst based on reduced graphene oxide decorated with AgNWs. The modification of GO has been carried out by the reduction of GO into rGO through electroplating method without the usage of any toxic and hazardous chemicals. Moreover, the silver nanowires have been also decorated onto surface of rGO which increase its surface area, porosity and conductivity of the sample which is essential for photocatalyst in catalysis application. The rGO/AgNWs is efficient photocatalyst with tuneable band gap and higher surface area for the degradation of MB dye in aqueous solution. Furthermore, it is expected that this short note may provide the knowledge of promising photocatalyst based on rGO/AgNWs for effective photocatalytic degradation of methylene blue from the aqueous solution.

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this short communication.