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.