Biosynthesis, characterization, optimization and toxicity studies: Simultaneously synthesized biogenic Pd/Fe bimetallic nanoparticle for the biodegradation of p-nitrophenol from aqueous solutions

In this study, simultaneous biogenic synthesis of Bio-S-PdFe bimetallic nanoparticles was achieved on the uppermost layer of aerobic microbial granules to aid biodegradation of p-nitrophenol (PNP) from aqueous solutions. Aerobic microbial granules were cultivated in SBR for 20 days, with 4-cycle lasting 6 h. The reduction of Bio-S-PdFe was mediated and accelerated by hydrogen gas (Bio-H₂) generated by the microbes during fermentation. Biogenic Bio-S-PdFe was used for PNP biodegradation, with the removal conditions optimized using RSM. Characterization techniques, including FESEM, EDAX, XRD, and XPS confirmed the formation of a metal granule complex. Bio-Pd achieved 80% PNP removal within 24 h. However, under optimized conditions, Bio-S-PdFe achieved complete PNP removal in 68 min. The degradation of PNP was analyzed using UV–Vis Spectroscopy and High-Resolution Mass Spectrometry of the degraded solution, as well as XRD and XPS analyses of the lyophilized granules. The degradation intermediates of p-nitrophenol were identified with mass values before degradation at 139.11 m/z and after degradation at 184, 155, 127, 113, and 110 m/z, respectively. Toxicity analysis after degradation was conducted using Chlorella sp., where the growth inhibition dropped significantly from 65 to 12%, indicating a substantial reduction in toxicity and ROS generation before degradation was found to be 3.26 and 1.44 after degradation showed reduction in cell death. Solanum lycopersicum (tomato) seeds also showed better root and shoot growth results in the Bio-S-PdFe-treated filtrate than pollutant PNP. Bio-S-PdFe effectively transformed PNP into much less harmful compounds in aqueous solutions, supporting its potential use in environmental remediation applications. This biomass along with palladium (Pd) and iron (Fe), convert and accelerate degradation through both biological and chemical mechanisms. This synergistic effect leads to faster and more complete pollutant breakdown, even in challenging environments.