A novel solid-state approach for enhancing the antimicrobial and colorimetric properties of pine sawdust using selenium nanoparticles

A novel and sustainable approach was developed to fabricate multifunctional pine sawdust (PS) with enhanced antimicrobial and coloration properties through the in-situ synthesis and deposition of selenium nanoparticles (SeNPs) on the sawdust surface for the first time. Sodium hydrogen selenite and ascorbic acid were employed as precursor and reductant, respectively, using a solid-state reduction technique at room temperature. The solid-state reduction method enables a one-step, solvent-free synthesis of SeNPs directly on sawdust, in line with green chemistry principles. Unlike liquid-phase methods, the solid matrix limits nucleation and growth, minimizing NPs mobility and therefore aggregation and agglomeration without the need for stabilizers. Transmission electron microscopy (TEM) revealed that the SeNPs were uniformly distributed on PS surfaces in spherical form, with sizes ranging from 3 to 68 nm depending on precursor concentration. X-ray diffraction (XRD) confirmed the presence of crystalline SeNPs and successful deposition on the PS. Colorimetric analysis demonstrated that SeNPs imparted vivid orange shades to PS, with color strength (K/S) increasing proportionally with SeNP concentration up to an optimal level, beyond which aggregation decreased color intensity. The PS deposited with SeNPs (SeNPs-PS) exhibited remarkable antimicrobial activity against both Gram-positive (Bacillus cereus, Micrococcus albus) and Gram-negative (Escherichia coli, Pseudomonas aeruginosa) bacteria, as well as potent antifungal effects against Aspergillus niger, Aspergillus flavus, and Aspergillus ochraceus. The strongest inhibition zones (up to 38 mm) were observed for A. niger. Overall, this eco-friendly fabrication route transforms waste sawdust into a multifunctional bio-composite with promising antimicrobial and aesthetic applications in sustainable materials and wood-based industries.