Carbothermally Derived Silicon Carbide Nanoparticles from Rice-Husk Silica: Structural, Optical and UV-LightDriven Photocatalytic Decolorization of Methylene Blue

Silicon carbide (SiC) nanoparticles were synthesized by carbothermal reduction of amorphous silica extracted from rice-husk ash with activated carbon at 1500°C for 5 h under flowing argon, using polyvinyl alcohol as a temporary binder. X-ray diffraction showed reflections consistent with cubic 3C-SiC, with a weak feature near 33.6° (2θ); the lattice parameter calculated from the indexed reflections is a = 4.3781(5) Å, and line-profile analysis gives a mean crystallite size of 19.5 ± 3.8 nm with a microstrain of 1.1 × 10 -3 . FTIR confirmed the Si–C stretching band at 872 cm -1 and also revealed a Si–O–Si band at 1092 cm -1 , indicating a residual silica/surface-oxide contribution; the product is therefore described as predominantly single-phase rather than phase-pure. Diffuse-reflectance data, converted using the Kubelka–Munk function and analysed using an indirect Tauc construction, gave an optical band gap of 2.17 eV, narrower than the reported bulk value for 3C-SiC and consistent with defect- and disorder-related tail states. SEM revealed irregular, densely agglomerated clusters of fine grains, with measured feature diameters of approximately 40, 210 and 398 nm in the representative micrographs. Under irradiation from a 300 W UV lamp, the SiC nanoparticles produced 52% methylene blue removal (10 mg L -1 , 30 mg catalyst per 50 mL) within 60 min, compared with 14% removal in the catalyst-free photolysis control, and the apparent pseudo-first-order rate constant was 0.0117 ± 0.0006 min -1 (R 2 = 0.987). The results demonstrate photocatalytic activity toward methylene blue under UV irradiation, while residual surface oxide, pronounced agglomeration, and possible charge-carrier recombination are identified as factors that may limit performance.