Abstract

Interfacial reactions at solid-water interfaces control mineral formation, solid structure transformation, and surface reactivity in aqueous environments. These reactions are often governed by local water chemistry near the material surface, which can differ from the bulk solution chemistry. Therefore, understanding and controlling interfacial properties can direct solid formation toward either scale inhibition or resource recovery. This advanced knowledge provides a basis for designing materials that remove contaminants, recover resources, and mediate environmentally relevant reactions. The objectives of this dissertation address interfacial reactions in forming and transforming solids for three environmental systems. (1) Nitrogen (N) and phosphorus (P) recovery system: Human activities have increased the levels of N and P in sewage and agricultural runoff, creating environmental problems such as harmful algal blooms, while also depleting natural nutrient deposits. (2) Carbon dioxide storage and utilization system: Effectively reducing carbon dioxide release to the atmosphere requires new materials that can capture and store carbon in reusable or stable forms. (3) Redox transformation of engineered nanomaterial systems: Reactive solid-water interfaces can transform aqueous species and alter the fate of contaminants and metals in natural and engineered water systems. Across these different problems, controlled solid formation and interfacial transformation provide a promising approach because they remove dissolved species from water while producing solid products or reactive surfaces with environmental value. This dissertation consists of four parts. First, we examined the molecular-scale interfacial reactions in struvite nucleation on biopolymer surfaces. While struvite (NH4MgPO4·6H2O) precipitation enables simultaneous N and P removal with potential fertilizer reuse, conventional bulk precipitation often requires harsh chemical input, leading to uncontrolled scale formation. To improve control over mineral formation, diverse biopolymer surfaces were evaluated as hydrated interfaces for directing heterogeneous struvite nucleation. To examine struvite nucleation and growth behavior on different biopolymer surfaces, time-resolved grazing-incidence small-angle X-ray scattering (GISAXS) was used. Especially on the alginate surface, we quantified local chemistry near the alginate-water interface using surface-enhanced Raman spectroscopy (SERS). Combined with simulations, these measurements revealed local supersaturation regimes that were not predicted from bulk solution chemistry. Incorporating this quantified local chemistry into classical nucleation theory proved that local ion distribution strongly controlled the apparent interfacial energy and heterogeneous struvite nucleation on alginate surfaces. The second part of this dissertation developed mineral–hydrogel composites for simultaneous ammonium and phosphate recovery. Building on the interfacial understanding of struvite nucleation, alginate hydrogel matrices containing calcium phosphate and struvite mineral seeds were designed to localize favorable mineral formation within recoverable composite materials. These pre-existing mineral seeds can reduce the energy barrier for nucleation and drive heterogeneous nucleation inside the hydrogel. Furthermore, the relatively large size of composites facilitates easy harvesting of the final solid nutrient products and potential reuse of the composites. The nutrient removal and recovery performance of these composites was evaluated under different water chemistries, and the environmental implications of using recovered nutrient products were assessed. The third part of this dissertation expanded the mineral–hydrogel composite platform to carbon dioxide storage and utilization. Amine-functionalized alginate hydrogel composites were developed by integrating calcium carbonate seeds with polyethyleneimine co-crosslinking. Calcium carbonate (CaCO3) provided a solid inorganic phase for carbon storage, while amine functional groups enhanced CO2 hydrolysis to bicarbonate. The synergetic effects of amine functionality and CaCO3 mineral seeds were systematically evaluated to determine their impact on capture efficiency, mineral stability, and reusability. These results demonstrate that soft polymer matrices with mineral seeds can be integrated to design solid-forming composite materials for carbon-related environmental applications. The final part of this dissertation extended solid–water interfacial chemistry to defect-mediated reactivity in functional inorganic oxides using barium titanate (BaTiO3, BTO) as an emerging reactive dielectric oxide interface in aqueous environments. BTO has gained attention in water treatment because its ferroelectric properties can influence interfacial reactions. Under saline and sulfate-rich conditions, BTO underwent ion-specific surface transformation that enhanced reactive oxygen species generation and altered manganese (Mn) redox cycling. These changes were linked to sulfate-induced surface reconstruction, defect formation, and changes in dielectric response. Nanoscale BTO thin films were further used to examine how aqueous electrolytes affect the interfacial stability and structural evolution of freestanding oxide materials. Overall, this dissertation holistically explored solid formation and transformation at environmental interfaces using thermodynamics and kinetics, local chemistry analyses, and structural characterization. These studies advance interfacial design strategies for clean water, resource recovery, and environmentally relevant solid–water reactions.

Committee Chair

Young-Shin Jun

Committee Members

Alexandra Rutz; Srikanth Singamaneni; Yinjie Tang; Zhen (Jason) He

Degree

Doctor of Philosophy (PhD)

Author's Department

Energy, Environmental & Chemical Engineering

Author's School

McKelvey School of Engineering

Document Type

Dissertation

Date of Award

8-17-2026

Language

English (en)

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Available for download on Monday, August 14, 2028

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