Progetti di ricerca

Carbon-based amendments are increasingly explored as sustainable technologies for restoring degraded or metal-contaminated soils. Among these, microalgal-based carbon–encapsulated iron nanoparticles (ME-nFe) and biochar (BC 600 °C), represent conceptually different but complementary approaches. Both materials are produced from biomass residues, offer… Leggi tutto sorptive and stabilizing capacities, and hold promise for mitigating the mobility and ecological risk of heavy metals in soils. ME-nFe are produced through Hydrothermal Carbonization of microalgal biomass pre-impregnated with Fe(NO3)3 9H2O. HTC is conducted in water at relatively mild temperatures (225 °C) and autogenous pressure, making it a low-energy thermochemical process. From a circular-bioeconomy perspective, HTC allows the valorisation of microalgal biomass from wastewater treatment or commercial production. Algae offer inherent advantages: high protein and polysaccharide content, abundant oxygenated functional groups, and the ability to incorporate nutrients from waste streams. During HTC, the organic matrix undergoes dehydration and polymerization, forming a hydrochar where iron species nucleate as finely dispersed Fe⁰, Fe₂O₃ and Fe₃O₄ nanodomains. The coexistence of zero-valent iron and iron oxides provides both reductive and sorptive mechanisms, relevant for transforming and immobilizing metals as Cr(VI), Pb²⁺, Zn²⁺ and Cu²⁺. The microalgalderived carbon matrix introduces mesopores and macropores, as well as carboxyl, hydroxyl and phenolic groups contributing to cation exchange and surface complexation. Biochar from second generation feedstocks is produced at 400-600 °C in nitrogen atmosphere. The material generated by pyrolysis at such temperatures is highly aromatized, thermally stable and chemically inert. It exhibits a well-developed microstructure, a conductive carbon matrix capable of mediating electron-transfer reactions, the ability to stimulate electroactive microorganisms and influence soil redox dynamics. Unlike HTC, pyrolysis is more energy-intensive and requires pre-drying of biomass. However, it produces a more porous, more stable and often more adsorptive carbon material. Its microporosity is especially relevant for trapping small metal ions or facilitating complexation with functional groups on internal surfaces. Both ME-nFe and biochar can contribute to metal immobilization and overall soil-quality improvement, but they do so through mechanisms shaped by their distinct structural and chemical features. The two materials differ in both specific surface areas and porosity. The ME-nFe are dominated by mesopores, whereas micropores prevail in the biochars. The ME-nFe are expected to immobilize metals primarily through surface complexation on oxygenated functional groups, redox reactions driven by Fe⁰ and mixed-valence iron oxides, and co-precipitation onto iron hydroxides formed in situ. Their mesoporous structure provides larger pore channels that facilitate diffusion and contact between metals and reactive iron phases, while the magnetic microdomains can promote localized redox cycling. The carbon matrix contributes additional binding sites and can moderately enhance the soil’s cation exchange capacity (CEC). ME-nFe should be most effective where reactivity, reduction of oxidized metal species, and rapid surface interactions are required. In contrast, biochar possesses a network of micropores creating extensive internal surface area at the nanoscale and promote adsorption of dissolved metal ions. The biochar’s alkaline and aromatic carbon matrix can contribute to surface precipitation, cation exchange, and moderate pH buffering, decreasing metal mobility. Its carbon matrix improves soil aggregation, structure, and water retention, and provides microhabitats stimulating beneficial microbial populations. Biochar should contribute more strongly to long-term soil stabilization rather than rapid redox-driven transformations.