Reduced graphene oxide loaded sulfated titania mediated photocatalytic degradation of Reactive Red 120 dye under UV-A and solar light

Abstract

Industries such as textiles, leather, and plastics contribute significantly to water pollution through the discharge of toxic dyes and chemicals, posing environmental and health risks. Traditional wastewater treatment methods often fall short of removing complex pollutants efficiently. Photocatalysis, particularly using TiO₂-based catalysts, has emerged as a sustainable solution for water purification. This work focuses on the synthesis of rGO/TiO₂-SO₄²⁻ photocatalysts and their evaluation for degrading Reactive Red 120 (RR 120) dye under UV-A and solar light. Structural and optical characterizations were conducted, and enhanced degradation performance was observed compared to TiO₂-SO₄²⁻. The crystal phase and degree of crystallinity of both TiO₂-SO₄²⁻ and rGO/TiO₂-SO₄²⁻ photocatalysts were confirmed via XRD analysis. Raman analysis identified peaks at 143, 393, 514, and 632 cm⁻¹ for TiO₂-SO₄²⁻, corresponding to the anatase phase. For rGO/TiO₂-SO₄²⁻, the D-band (1342 cm⁻¹) and G-band (1582 cm⁻¹) of rGO were additionally observed, while the TiO₂ modes were suppressed. SEM images showed spherical particle aggregation for TiO₂-SO₄²⁻ and clusters of these particles on rGO sheets for rGO/TiO₂-SO₄²⁻, suggesting enhanced dye molecule absorption. TEM and HR-TEM analysis confirmed the presence of spherical TiO₂-SO₄²⁻ particles on rGO sheets, with lattice fringes corresponding to TiO₂-SO₄²⁻, indicating successful composite formation. EDS and elemental mapping confirmed the presence of carbon (C), oxygen (O), sulfur (S), and titanium (Ti) in the rGO/TiO₂-SO₄²⁻ photocatalyst, further verifying its composition. The XPS spectra provided additional confirmation of the elemental composition and interactions between the rGO and TiO₂-SO₄²⁻ components. The photocatalytic activity of TiO₂-SO₄²⁻ and rGO/TiO₂-SO₄²⁻ photocatalysts was studied using Reactive Red 120 (RR 120) dye under UV-A light and sunlight. The rGO/TiO₂-SO₄²⁻ catalyst exhibited superior performance, achieving nearly 100 % degradation under UV-A light in 50 min and 99.3 % under sunlight in 180 min. Reusability tests showed stable performance over multiple cycles, with minimal degradation loss. The degradation pathway is also proposed using GC–MS analysis. Scavenger experiments revealed that superoxide radicals (O₂^•−) were the primary active species in the photodegradation process. These findings highlight the potential of rGO/TiO₂-SO₄²⁻ photocatalysts for efficient wastewater treatment applications.