Valorization of African walnut (Tetracarpidium Conophorum) husks for green synthesis of silver nanoparticles and sustainable control of indoor mycotoxigenic fungi

Abstract

Indoor mycotoxigenic fungi constitute serious health and building damage risks for occupants and this calls for the implementation of environmentally friendly methods to solve this problem. This research focused on developing silver nanoparticles through green methods which used African walnut Tetracarpidium conophorum husk extract as a source material for testing their ability to kill indoor toxic molds. The process of synthesizing AgNPs involved using walnut husk extract to create silver nanoparticles through photo-activation which researchers then studied using various techniques including UV–Vis spectroscopy and Fourier Transform Infrared FTIR spectroscopy and Energy Dispersive X-ray EDX analysis and Transmission Electron Microscopy TEM analysis. UV–Vis spectroscopy confirmed nanoparticle formation via surface plasmon resonance (SPR) at 430 nm. FTIR analysis identified key functional groups (N–H amines/amides: 3778.31 and 3376.0 cm −1 ; C–H alkyl stretches: 2918.0 and 2853.01 cm −1 ; C=O carbonyl groups: 1595.0 and 1032.0 cm −1 ) responsible for bio-reduction and stabilization. EDX confirmed silver as the predominant element (75.20% by mass). TEM revealed predominantly spheroidal nanoparticles with well-defined edges at 20–50 nm scale, and SAED confirmed fcc crystallinity through four distinct diffraction rings indexed to the (200), (220), (311), and (400) planes of silver. The AgNPs demonstrated exceptional antifungal activity with mycelial inhibition rates of 97.94, 95.05, and 98.01% at 50 µg/mL and 98.38, 98.19, and 98.25% at 100 µg/mL against Aspergillus flavus, Aspergillus fumigatus , and Aspergillus salisburgensis , respectively. In contrast, the silver nitrate precursor showed only 14.20–48.30% inhibition, and the plant extract alone exhibited only 7.30–9.50% inhibition, confirming the nanoparticulate form as essential for high antifungal efficacy. This study demonstrates for the first time that T. conophorum husk waste can be valorized for eco-friendly AgNP synthesis, yielding highly potent antifungal agents against indoor mycotoxigenic Aspergillus species. These results support the application of T. conophorum husk-derived AgNPs in the development of sustainable antimicrobial building materials, coatings, and surface treatments for indoor mold control.