PhD Thesis Defense | Francesco Coin

Development and Characterization of Novel Eco-Friendly Adsorbents Based on Pectin Composites and PVA Mats to Remediate Water from Emerging Pollutants SUMMARY

This PhD thesis, “Development and Characterization of Novel Eco-Friendly Adsorbents Based on Pectin Composites and PVA Mats to Remediate Water from Emerging Pollutants”, addresses water contamination by emerging pollutants such as heavy metals, pharmaceuticals/antibiotics, and pesticides. These species can be persistent and toxic even at trace concentrations and are not efficiently eliminated by conventional wastewater treatment plants. The thesis therefore pursues adsorption as a sustainable remediation strategy, aiming to create materials that are effective, reusable, and environmentally responsible while also clarifying how molecular interactions control macroscopic removal performance.

Three complementary material platforms are developed and assessed: low-methoxyl pectin (a plant-derived polysaccharide rich in carboxyl groups), the metal–organic framework Basolite F300® (Fe–BTC), and electrospun poly(vinyl alcohol) (PVA) nanofiber mats. Materials are fabricated in practical, recoverable forms (films, foams, and mats) and characterized with a broad toolbox spanning structure, chemistry, and dynamics, including techniques such as X-ray diffraction, FT-IR spectroscopy, microscopy, thermal analysis (DSC), and broadband dielectric spectroscopy, together with contaminant quantification methods for adsorption testing. A major part of the thesis clarifies how pectin chemistry and hydration govern adsorption. Because pectin is water-soluble, it is insolubilized mainly by Ca2+ ionic crosslinking, producing networks whose structure depends on crosslinking conditions and water content. Calcium-crosslinked pectin matrices remove Zn2+ via a combination of ion exchange and coordination to pectin carboxylates. By varying the crosslinking level and hydration state, the work shows that water is not merely a transport medium: it actively reorganizes pectin structure and thereby modulates the accessibility and effectiveness of binding sites. To exploit MOF porosity in a usable format, Fe–BTC is immobilized within calcium-crosslinked pectin, overcoming practical limitations of MOF powders such as aggregation, difficult recovery, and the risk of secondary contamination by fine particles. Composite films (solvent casting) and highly porous foams (freeze-drying) show stable structural integration and improved porosity. These hybrids combine the sustainability and metal-binding functionality of pectin with the high internal surface area and open metal sites of Fe–BTC, leading to improved adsorption performance for multiple contaminant classes, including zinc, paraquat, and tetracycline. In parallel, the thesis develops high-surface-area PVA adsorbents fabricated by electrospinning. Because PVA dissolves in water, the mats are stabilized using a green citric-acid esterification crosslinking strategy that also introduces additional carboxylate groups. Europium is incorporated either by post-doping or by in situ incorporation during electrospinning, creating extra complexation sites and strengthening interactions with antibiotics (notably tetracycline and ciprofloxacin). The mats are reusable over several cycles and maintain performance even in the presence of co-contaminants (e.g., dyes and pesticides), with in situ europium incorporation providing superior distribution and adsorption efficiency. Finally, the thesis connects adsorption outcomes to fundamental water dynamics: DSC and broadband dielectric spectroscopy demonstrate that water confined in pectin nanochannels and Fe–BTC pores undergoes glass transitions in the 170–200 K range, offering mechanistic insight into hydration-controlled structure and performance and contributing to the broader debate on water’s glass transition.