One-pot biosynthesis of Bio-PdZnO bimetallic nanoparticles for efficient p-nitrophenol remediation in water

The degradation of toxic organic pollutants such as p-nitrophenol (PNP) remains a persistent challenge in wastewater and industrial effluent treatment due to their toxicity and resistance to conventional treatment processes. Eco-friendly treatment strategies that integrate biological and nanotechnological approaches are required. This study investigates biosynthesis of a bimetallic bio-nanocomposite, Bio-PdZnO, synthesized in one-pot biogenic route, for effective PNP remediation under visible light irradiation. Aerobic microbial granules were cultivated in a laboratory-scale sequencing batch reactor (SBR) for 30 days, operated at four cycles per day. Bioreduction of PdZnO was facilitated by biogenic hydrogen generated during microbial fermentation, resulting in the formation of Bio-PdZnO granules. The removal performance of PNP was evaluated using adsorption isotherm and kinetic models by varying key parameters, including nanocomposite ratio, PNP concentration, nanocomposite dosage, temperature, and contact time. Comprehensive characterization using FESEM-EDAX, XRD and XPS confirmed the structural stability, elemental composition and effective formation of metal-granule complexes, A maximum p-Nitrophenol removal efficiency of 85% was achieved under optimized conditions (PNP concentration: 20 mg L⁻¹; contact time: 6 h, extended to 24 h to confirm complete degradation; nanocomposite dosage: 0.8 g; Bio-PdZnO granule ratio: 1:4). HRMS analysis indicated the formation of less toxic intermediates after degradation of PNP, spectrum peaks were found at m/z 110, 115,126, 128, 133.05, 135.03 and 141.94 suggesting the presence of degradative by-products, such as Benzoquinone, hydroquinol, hydroquinone, catechol, or simple organic acids confirming effective transformation of PNP. Phytotoxicity assessment using Solanum lycopersicum (tomato) seeds showed enhanced root and shoot growth upon treatment with Bio-PdZnO-treated filtrate and disposed Bio-PdZnO granules. Bio-PdZnO bio-nanocomposite demonstrated effective and sustainable removal of PNP from water. Treated filtrate and diposed Bio-PdZnO granules promoting plant growth, suggesting potential use as a Bio-fertilizer. The integration of biological granules with bimetallic Pd and Zn nanostructures offers most promising, scalable approach for wastewater treatment, highlighting the potential of Bio-PdZnO for broader environmental remediation applications.