Fabrication Biowaste-Derived Carbon Quantum Dot/Calcium Oxide for Photodegradation of Methylene Blue under Visible Light

Abstract

In response to the significant environmental risks posed by the discharge of synthetic dyes into water bodies from the textile industry in Malaysia, this study presents a sustainable solution utilizing orange peel waste-derived carbon quantum dot (CQD) and calcium oxide (CaO) for the photodegradation of methylene blue (MB) under visible light. This approach not only addresses environmental contamination but also promotes the reuse of biowastes, aligning with circular economy principles and environmental sustainability. This research includes the CQD/CaO nanocomposites sourced from biomass wastes using a microwave-hydrothermal method, investigation on the dyes photodegradation efficiency under visible light, focusing on catalyst loadings and initial dye concentrations. Additionally, the kinetic studies and type of heterojunction were explored as well. Characterizations involve a range of techniques, including Fourier-transform infrared spectroscopy (FTIR), photoluminescence (PL) spectroscopy, and Diffuse reflectance ultraviolet-visible spectroscopy (DR UV-Vis). The CQD/CaO heterojunction significantly enhances photocatalytic efficiency by promoting charge separation and visible light absorption. PL analysis showed that the nanocomposite exhibits much lower PL intensity than pure CQD, indicating reduced electron-hole recombination. FTIR results confirm an increased surface hydrophilicity and the introduction of new hydroxyl groups, while UV-Vis analysis demonstrats a narrowed band gap and broader light absorption in the CQD/CaO nanocomposite. Together, these properties enable more efficient photodegradation of MB under visible-light illumination. Under optimized reaction conditions, specifically with a catalyst loading of 0.5 g/L, initial MB concentration of 15 ppm, at pH 7 and in the presence of 10 mL 5 mM H₂O₂, the CQD/CaO photocatalyst achieved a photodegradation efficiency of 72.61% within 3 hours of visible-light irradiation. The findings are expected to provide insights into the feasibility of deploying biowaste-derived materials for effective environmental remediation, offering a dual benefit of pollution reduction and waste management.