The availability of clean water is essential for humans wellbeing and the diverse biotic population in the environment. Menkind imposes a significant pressure on food supplies, natural resources, and other commodities. Large-scale anthropogenic activities, such as agriculture and industry, which are practiced to ensure population growth and survival, have caused several harmful environmental effects, including the discharge of pollutants into the aquatic environment. rGO-based TiO2 material is commonly used in light-driven photocatalysis of dyes in an aqueous medium. Because of exceptional properties, rGO-based oxide semiconductors promote electron separation, which results in boosting photo-driven reactions such as the degradation of carcinogenic dyes (e.g., methylene blue) and solar-fuel (hydrogen) production. Preparation of rGO-based TiO2 photocatalysts increases the specific surface area of the nanocomposite, consequently increasing the photocatalytic activity, which is why rGO-based semiconductor photocatalysts have been found to be promising in several applications.
Many studies using rGO@TiO2 nanocomposite were made to improve photocatalytic efficiency. Liu  treated Methylene Orange (MO) using rGO@TiO2 nanocomposite for 240 min exposing it to visible light (λ > 400 nm) irradiation and reported ~90% photodegradation of overall organic pollutant. Several authors report the photocatalytic degradation of methylene blue (MB) using rGO@TiO2 nanocomposites, among them Deshmukh et al.  who got maximum degradation of MB equal to 91.3% within 30 min of sunlight irradiation. In another study by Mohammadi et al. , photocatalytic degradation of MB using rGO@TiO2 composite was even better. 95% and 93% of the overall organic pollutant were removed within 30 min using irradiation from a 200 W Mercury short arc and Osram 500 W Xenon lamp with a cut-off UV filter at 400 nm, respectively.
The investigation of the long-term stability and reusability of prepared rGO@TiO2 photocatalyst is a crucial parameter for its practical application. The stability of prepared rGO@TiO2 photocatalyst is investigated between several consecutive cycles with the same photocatalytic tests. Wanag et al.  investigated the stability of prepared rGO@TiO2 photocatalyst under seven cycles. The obtained results show very high activity after five cycles. A substantial decrease in the photoactivity is noted after seventh cycles. Prepared rGO@TiO2 photocatalyst showed high stability during the photodegradation of MB dye.
TiO2 has a wide band gap energy (3.0–3.20 eV) which limits its absorption only in the UV region of the solar spectrum. The wavelengths and intensities of UV light irradiation significantly affect the photodegradation of pollutants in an aqueous medium. UV irradiation is thus more frequently practiced than sunlight as it has higher efficiency in the degradation of pollutants. Expanding the photocatalytic degradation of pollutants to visible irradiation is an important aspect to recon with if people want to commercialize the process. Such a system should be functional under natural sunlight as the irradiation source . The intensity of the light also affects the transition rate of electrons from the valence band (VB) to the conduction band (CB). Higher intensity usually leads to significantly higher degradation rates of the photocatalytic process. After saturation when the amount of photons is equal to TiO2 active sites, the rate of photogeneration becomes less dependent on the increase of the light intensity. Therefore, appropriate photon energy distribution contributes to the photodegradation rate . A surplus of photons of given energy cannot contribute to a higher photocatalytic degradation rate because of the limited amounts of active sites on the surface of the catalyst .