Valorization of African Walnut (Tetracarpidium Conophorum) Husks for Green Synthesis of Silver Nanoparticles and Sustainable Control of Indoor Mycotoxigenic Fungi

Indoor mycotoxigenic fungi pose significant health and structural risks to building occupants, necessitating sustainable remediation strategies. This study investigated the green synthesis of silver nanoparticles (AgNPs) using African walnut ( Tetracarpidium conophorum ) husk extract and evaluated their antifungal efficacy against indoor toxigenic molds. The AgNPs were synthesized through photo-activation of walnut husk extract with silver nitrate solution and characterized using UV-Vis spectroscopy, Fourier Transform Infrared (FTIR) spectroscopy, Energy Dispersive X-ray (EDX) analysis, and Transmission Electron Microscopy (TEM). UV-Vis spectroscopy confirmed nanoparticle formation with maximum absorbance at 430 nm, while FTIR analysis revealed the presence of functional groups including amines, amides, alkyl groups, and carbonyl compounds responsible for bio-reduction and stabilization. EDX analysis confirmed silver as the predominant element (75.20%), and TEM micrographs revealed predominantly spheroidal nanoparticles with well-defined edges. The biosynthesized AgNPs demonstrated exceptional antifungal activity against three mycotoxigenic Aspergillus species ( Aspergillus flavus -IDMM1 (PX430759), Aspergillus fumigatus- IDM2 (PX430757) and Aspergillus salisburgensis- IDM3 (PX430758) isolated from poorly ventilated indoor environments, achieving inhibition rates exceeding 95% at 50 µg/mL and 98% at 100 µg/mL. In contrast, the precursor silver nitrate and plant extract alone showed minimal antifungal activity (below 50%). These findings demonstrate that African walnut husk-derived silver nanoparticles represent a promising, eco-friendly alternative to conventional chemical biocides for controlling indoor mycotoxigenic fungi, with potential applications in the formulation of sustainable antimicrobial building materials.