DOI: https://doi.org/10.55373/mjchem.v28i3.250

Keywords: Green synthesis, Carrageenan, photodegredation, anti-oxidant, methylene blue

Abstract

In present study, the green synthesized maghemite (γ-Fe₂O₃) nanoparticles from brown (FB) and green (FG) variants of Kappaphycus alvarezii possess enhanced photocatalytic degradation of methylene blue with anti-oxidant potential. The nanocomposites were synthesized through chemical co-precipitation method using crude carrageen extract derived from both the variety form of macroalgal biomass. The synthesized nanoparticles FG and FB has been characterized with major analytical analysis. UV-Vis spectroscopy showed a characteristic absorption peak at 344 nm highlights the ligand transition change from O²⁻ to Fe³⁺ through the ligand-to-metal charge transfer with a direct band gap of 3.12 eV. XRD analysis of the nanocomposites observed with a cubic spinel structure with a lattice parameter of approximately 8.35 Å and crystallite sizes of 4.82 nm (FB) and 5.07 nm (FG). The frequency size distribution of the nanocomposites through SEM imaging revealed a narrow, unimodal particle size distribution in the 2–11 nm range. Antioxidant assays demonstrated dose-dependent DPPH radical scavenging of FG nanocomposite possess a lower IC₅₀ of 8.5 ppm with 82.4 ± 1.5% scavenging at 50 ppm. Photocatalytic evaluation under visible light selected the FG nanocomposite for superior stability of 90.132% methylene blue degradation in 90 minutes at optimal 10 ppm nanoparticle with a pseudo-first-order rate constant of 0.0285 min⁻¹ and a 1.18-fold enhancement over the carrageenan-only control. Moderate loading maximized efficiency through enhanced reactive oxygen species generation and interfacial charge separation greater loading (50 ppm) reduced performance (k = 0.0218 min⁻¹) due to aggregation and light scattering.