Green Synthesis of Biopolymer-Encapsulated Metal Nanoparticles in Soil Remediation Systems

Thesis Abstract

Soil contamination by organic and inorganic pollutants poses significant risks to ecosystem health and human well-being, necessitating remediation strategies that are effective, sustainable, and scalable. This study addresses the environmental and economic limitations of conventional remediation approaches by exploring the green synthesis of biopolymer-encapsulated metal nanoparticles (Biopol-Ag/Fe, for example) and their application in soil remediation systems. The aim is to evaluate whether biopolymer encapsulation enhances the stability, transport, and remediation efficiency of metal nanoparticles while reducing ecotoxicity and synthesis costs. Specific objectives include (i) to optimize a green synthesis protocol for metal nanoparticles using agro-waste-derived biopolymers (chitosan, alginate, and cellulose derivatives) as encapsulants; (ii) to characterize nanoparticle size, morphology, and surface chemistry using TEM, SEM-EDS, XRD, FTIR, and Zeta potential measurements; (iii) to assess the remediation performance against representative contaminants (polycyclic aromatic hydrocarbons, polychlorinated biphenyls, and heavy metals such as lead and arsenic) in controlled soil microcosms; (iv) to evaluate transport, retention, and aggregation behavior in heterogeneous soil matrices through column studies and breakthrough curve analysis; (v) to model degradation kinetics and contaminant desorption using a dual-transport reactive-adsorption framework; and (vi) to conduct a preliminary ecotoxicological assessment on soil microbial communities and Collembola to gauge environmental safety. Methodologically, the study employs a mixed-methods design anchored in systems thinking and the Theory of Planned Behavior to interpret remediation adoption potential. An initial laboratory synthesis phase will produce Biopol-encapsulated nanoparticles via green reducing agents (plant extracts) and biopolymer matrices, with particle concentrations ranging from 0.5 to 5.0 g/L. Characterization will involve Transmission Electron Microscopy (TEM), Scanning Electron Microscopy with Energy-Dispersive X-ray Spectroscopy (SEM-EDS), X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), and dynamic light scattering for hydrodynamic diameter and zeta potential. Soil microcosm experiments will utilize standardized agricultural soil collected from three distinct sites (sandy, clay, and loam) with contaminant loadings adjusted to realistic field concentrations PAHs at 50 mg/kg, PCBs at 20 mg/kg, lead at 400 mg/kg, and arsenic at 100 mg/kg. Each treatment will include controls (no treatment, bare nanoparticles) and triplicate replicates, totaling 42 microcosms. Column studies will simulate leaching under unsaturated flow to obtain breakthrough curves over a 60-day period. Analytical quantification of contaminants will be performed by GC-MS for organics and ICP-MS for metals, with confirmatory LC-MS for selected PCBs. Reactive transport modeling will implement a dual-porosity Advection-Dispersion-Reaction (ADR) framework integrated with a Langmuir–Freundlich isotherm to describe adsorption and desorption dynamics. Statistical analyses will include one-way and two-way ANOVA to compare remediation efficiency across soil types and treatments, followed by post hoc Tukey tests. Multivariate redundancy analyses will relate nanoparticle characteristics to remediation outcomes and microbial community shifts, informed by 16S rRNA gene sequencing and qPCR quantification of key functional genes. The theoretical framework combines Green Chemistry principles with heterogeneous catalysis theory and reactive transport concepts, supplemented by the Ecotoxicology Bio-Risk Model to interpret ecological safety data. Expected findings include (i) a reproducible, cost-effective green synthesis route yielding Biopol-encapsulated nanoparticles with uniform size distributions (50–120 nm) and favorable zeta potentials (+20 to +40 mV) that enhance stability in soil pore waters; (ii) superior sorption and accelerated degradation rates for PAHs and PCBs in encapsulated systems relative to bare nanoparticles, with reduced metal leaching under hydraulic forcing; (iii) distinct transport behavior across soil textures, with clay-rich matrices showing pronounced retardation and lower desorption volatility; (iv) kinetic parameters indicating pseudo-first-order sorption and pseudo-second-order degradation with half-lives shortened by 30–60% compared with controls; and (v) minimal adverse effects on non-target soil microbiota at effective remediation concentrations, suggesting acceptable environmental risk. The study contributes to knowledge by integrating green synthesis, biopolymer encapsulation, and environmentally conscious remediation modeling to produce a practical, scalable approach for in situ soil remediation. It provides a robust experimental framework linking nanoparticle physicochemical properties to remediation performance and ecological safety, advancing understanding of sustainable nanoremediation. Conclusions are expected to recommend optimized, site-specific formulations of biopolymer-encapsulated nanoparticles for field-scale soil remediation, with guidance on regulatory and risk assessment considerations, and directions for future research into long-term ecological outcomes and lifecycle assessment.