Photocatalytic degradation of naphthol blue from Batik wastewater using functionalized TiO2-based composites

This work provides a first-time comparative study examining the photocatalytic activity of functionalized TiO2-based composites to eliminate naphthol blue in Batik wastewater. Reduced graphene oxide (RGO) was synthesized by oxidizing solid graphite using the Hummers' method followed by sonication and reduction. N-doped TiO2 (N–TiO2) was synthesized from titanium tetrachloride (TiCl4) and urea (CH₄N₂O) precursors by the sol-gel method. N–TiO2 modified RGO (RGO/NT) was synthesized using a hydrothermal method from N–TiO2 and RGO. Prepared TiO2-based composites and commercial TiO2, for comparison were characterized using Fourier transform infrared spectrometer (FTIR), X-Ray diffractometer (XRD), scanning electron microscope-energy dispersive X-ray (SEM-EDX), and UV–Vis diffuse reflectance spectrometer (UV–Vis DRS). FTIR characterization indicated Ti–N bonding in N–TiO2 and RGO/NT. XRD patterns showed that commercial TiO2 had a rutile phase, while N–TiO2 and RGO/NT had an anatase phase with crystal sizes of 30.09, 16.28, and 12.02 nm, respectively. SEM results displayed the presence of small and glossy white N–TiO2 dispersed on the surface of RGO. Characterization using UV–Vis DRS showed that the band gap energy values for TiO2, N–TiO2, and RGO/NT were 3.25, 3.12, and 3.08 eV with absorption regions at the wavelengths of 382, 398, and 403 nm, respectively. The highest photocatalytic activity for RGO/NT for degrading naphthol blue was obtained at pH 5, with a photocatalyst mass of 60 mg, and an irradiation of 15 min. Photocatalytic degradation by RGO/NT on Batik wastewater under visible light showed higher effectivity than under UV light.