Microalgal Biodiesel Fuels: Spectroscopic and Physicochemical Characterization and Life-Cycle Assessment toward CO ₂ Mitigation

Marine microalgae provide a reliable, carbon-neutral pathway for renewable fuel production and serve as promising feedstocks for sustainable energy. This study examines Nannochloropsis oculata (N. oculata) as a marine feedstock by integrating physicochemical characterization, multispectral scrutiny, and a cradle-to-grave life cycle assessment to establish its suitability as a sustainable fuel source. The FTIR analyzer confirmed ester functional group formation through a strong carbonyl peak at 1741 cm–1. The GC–MS spectrometer demonstrated that the biodiesel exhibited a FAME content of 94.47 wt %, predominantly composed of C12–C23 methyl esters. UV–vis spectroscopy indicated low aromatic content, and the photoluminescence spectra yielded a 3.24 eV band gap and a 52% quantum yield, illustrating a rapid, noninvasive approach for investigating fuel purity via photoluminescence emission and band gap analysis. The biodiesel met ASTM criteria with a viscosity of 4.59 mm2/s, a density of 0.886 g/cm3, and a calorific value of 40.5 MJ/kg. The Life-Cycle assessment demonstrated 50–70% lower GHG emissions relative to fossil diesel fuel and a net CO2 sequestration of 1.4–1.7 kg per kilogram of biodiesel. Correlating spectral fingerprints with environmental metrics enables an integrated assessment of the quality and sustainability. The findings demonstrate that marine microalga biodiesel derived from N. oculata exhibits high molecular integrity, regulatory compliance, and significant carbon reduction, supporting its potential role in renewable fuel development.