This study presents a novel method for the development of TiO₂/reduced graphene oxide (rGO) nanocomposites for photocatalytic degradation of dyes in an aqueous solution. The synergistic integration of rGO and TiO₂, through the formation of Ti–O–C bonds, offers an interesting opportunity to design photocatalyst nanocomposite materials with the maximum absorption shift to the visible region of the spectra, where photodegradation can be activated not only with UV but also with the visible part of natural solar irradiation. TiO₂@rGO nanocomposites with different content of rGO have been self-assembled by the hydrothermal method followed by calcination treatment. The morphological and structural analysis of the synthesized photocatalysts was performed by FTIR, XRD, XPS, UV-Vis DRS, SEM/EDX, and Raman spectroscopy. The effectiveness of the synthesized nanocomposites as photocatalysts was examined through the photodegradation of methylene blue (MB) and rhodamine B (RhB) dye under artificial solar-like radiation. The influence of rGO concentration (5 and 15 wt.%) on TiO₂ performance for photodegradation of the different dyes was monitored by UV-Vis spectroscopy. The obtained results showed that the synthesized TiO₂@rGO nanocomposites significantly increased the decomposition of RhB and MB compared to the synthesized TiO₂ photocatalyst. Furthermore, TiO₂@rGO nanocomposite with high contents of rGO (15 wt.%) presented an improved performance in photodegradation of MB (98.1%) and RhB (99.8%) after 120 min of exposition to solar-like radiation. These results could be mainly attributed to the decrease of the bandgap of synthesized TiO₂@rGO nanocomposites with the increased contents of rGO. Energy gap (E_g) values of nanocomposites are 2.71 eV and 3.03 eV, when pure TiO₂ particles have 3.15 eV. These results show the potential of graphene-based TiO₂ nanocomposite to be explored as a highly efficient solar light-driven photocatalyst for water purification.

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. Among them organic micropollutants (OMPs) are considered a significant threat to aquatic ecosystems. The efficient removal of this persistent pollutants from wastewater is nowadays commonly considered in water treatment technologies. Utilizing photocatalysis by harvesting solar energy as an inexhaustible source, represents a facile and easy to upscale solution, for removing persistent pollutants and other emerging contaminants. In the recent decade, graphene-based titanium dioxide catalyst (rGO@TiO₂) has received a lot of attention as an effective material for the degradation in the enviroment. This review summarizes the recent progress in preparing rGO@TiO₂ nanocomposites and their utilization for purification purposes. Its main advantage over many other photocatalysts is its easy preparation, low toxicity, and reasonable photo-activity in a specific solar light spectrum.

In this work, nanocomposites based on titanium dioxide and reduced graphene oxide (TiO₂@rGO) with different weight percentages of rGO (4, 8, and 16 wt%) were prepared by the hydrothermal/solvothermal synthesis method and thermally treated at 300 °C. The prepared nanocomposites were explored for the removal of methylene blue dye (MB) in the presence of simulated solar illumination as well as natural sunlight. The structural, morphological, chemical, and optical properties of the as-synthesized TiO₂@rGO nanocomposites were characterized. The obtained results of the graphene-based nanocomposite materials indicated the existence of interactions between TiO₂ and rGO, i.e., the Ti–O–C bond, which confirmed the successful integration of both components to form the TiO₂@rGO nanocomposites. The addition of rGO increased the specific surface area, decreased the band gap energy, and increased the photocatalytic degradation efficiency of MB from water compared to TiO₂ nanoparticles. The results of photocatalytic activity indicated that the amount of rGO in the prepared TiO₂@rGO nanocomposites played a significant role in the application of different photocatalytic parameters, including the initial dye concentration, catalyst concentration, water environment, and illumination source. Our studies show that the reinforcement of the nanocomposite with 8 wt% of rGO allowed us to obtain the maximum photocatalytic decomposition performance of MB (10 mg·L⁻¹) with a removal percentage of 99.20 after 2 h. Additionally, the obtained results show that the prepared TiO₂@rGO_8 wt% nanocomposite can be used in three consecutive cycles while maintaining photocatalytic activity over 90%.

Water pollution has become a serious environmental issue. The textile industries using textile dyes are considered to be one of the most polluting of all industrial sectors. The application of solar-light semiconductor catalysts in wastewater treatment, among which TiO₂ can be considered a prospective candidate, is limited by rapid recombination of photogenerated charge carriers. To address these limitations, TiO₂ was tailored with graphitic carbon nitride (g-C₃N₄) to develop a heterostructure of g-C₃N₄@TiO₂. Herein, a simple hydrothermal synthesis of TiO₂@g-C₃N₄ is presented, using titanium isopropoxide (TTIP) and urea as precursors. The morphological and optical properties and the structure of g-C₃N₄, TiO₂, and the prepared heterostructure TiO₂@g-C₃N₄ (with different wt.% up to 32%), were analyzed by various laboratory methods. The photocatalytic activity was studied through the degradation of methylene blue (MB) aqueous solution under UV-A and simulated solar irradiation. The results showed that the amount of g-C₃N₄ and the irradiation source are the most important influences on the efficiency of MB removal by g-C₃N₄@TiO₂. Photocatalytic degradation of MB was also examined in realistic conditions, such as natural sunlight and different aqueous environments. The synthesized g-C₃N₄@TiO₂ nanocomposite showed superior photocatalytic properties in comparison with pure TiO₂ and g-C₃N₄, and is thus a promising new photocatalyst for real-life implementation. The degradation mechanism was investigated using scavengers for electrons, photogenerated holes, and hydroxyl radicals to find the responsible species for MB degradation.

The three-component hybrid (rGO/TiO₂/CN) nanocomposite was prepared in order to enhance the photocatalytic properties of anatase TiO₂ nanoparticles (NPs) under solar-like irradiation. The rGO/TiO₂/CN was prepared in a mixture of the reduced graphene oxide (rGO, 8 wt%), anatase TiO₂ nanoparticles (NPs), and graphitic carbon nitride (g-C₃N₄, 16 wt%). It was self-assembled through the one-step hydrothermal method, followed by an annealing process. The photocatalyst was thoroughly characterized by means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), the Brunauer-Emmett-Teller (BET) nitrogen adsorption/desorption technique and UV-Vis diffuse reflectance spectroscopy (DRS). The photocatalytic activity of the TiO₂, TiO₂/rGO, TiO₂/CN and hybrid rGO/TiO₂/CN nanocomposite was studied through the degradation of a rhodamine B (RhB) aqueous solution under solar-like irradiation. The results showed that the highest photocatalytic activity was achieved by the rGO/TiO₂/CN mixture, which can be attributed to the synergistic effect of the incorporation of both rGO and g-C₃N₄ with TiO₂. Further, the influence of the pH value of the RhB dye aqueous solution and different water matrix (Milli-Q, tap, and alkaline water) on the photocatalytic efficiency of the rGO/TiO₂/CN nanocomposite was examined. In addition, a recycle test was performed for hybrid rGO@TiO₂/CN to investigate the effectiveness of the photodegradation of RhB dye in three successive cycles. The conducted results indicate that the pH value of RhB dye aqueous solution and water matrices play an important role in the photocatalytic degradation rate.

This work presents the immobilisation of titanium dioxide (TiO₂) nanoparticles (NPs) and reduced graphene oxide (rGO)-TiO₂ nanocomposite on glass sheets for photocatalytic degradation of methylene blue (MB) under different radiation sources such as ultraviolet and simulated solar radiation. The TiO₂ NPs and rGO-TiO₂ nanocomposite were synthesised through a simple hydrothermal method of titanium isopropoxide precursor followed by calcination treatment. Deposition of prepared photocatalysts was performed by spin-coating method. Additionally, ethylene glycol was mixed with the prepared TiO₂ NPs and rGO-TiO₂ nanocomposite to enhance film adhesion on the glass surface. The photocatalytic activity under ultraviolet and simulated solar irradiation was examined. Further, the influence of different water matrices (milli-Q, river, lake, and seawater) and reactive species (h⁺, ^•OH, and e⁻) on the photocatalytic efficiency of the immobilised rGO/TiO₂ nanocomposite was careful assessed. MB dye photocatalytic degradation was found to increase with increasing irradiation time for both irradiation sources. The immobilisation of prepared photocatalysts is very convenient for environment applications, due to easy separation and reusability, and the investigated rGO/TiO₂-coated glass sheets demonstrated high efficiency in removing MB dye from an aqueous medium during five consecutive cycles.