(4nq) Exploring Interfacial Chemistry of Natural and Engineered Materials to Address Grand Challenges Related to Carbon Dioxide Removal and Water Remediation

Since the Industrial Revolution, human society has rapidly developed and flourished. However, this progress has led to interconnected challenges, particularly in the areas of water, energy, and the environment, which pose significant threats to sustainability. These grand challenges are intricately linked, highlighting the importance of addressing them through the water-energy-environment (WEE) nexus. This approach emphasizes the interconnections between these sectors.

For instance, the unprecedented accumulation of CO₂ in the atmosphere has accelerated global warming and triggered environmental issues such as droughts and floods. This water resource insecurity has driven the need for water recycling. Concurrently, a new class of anthropogenic contaminants, including pharmaceuticals, personal care products (PPCPs), heavy metals, herbicides, pesticides, and per- and polyfluoroalkyl substances (PFAS), has accumulated in natural water bodies. Known as emerging contaminants, these substances can pose severe ecological and human health risks.

To mitigate climate change, we must not only reduce CO₂ emissions but also remove previously emitted CO₂ from the atmosphere. In-situ carbon mineralization is a critical technology for carbon dioxide removal (CDR), offering a thermodynamically favorable reaction to store CO₂ permanently in solid form. Water plays a pivotal role in the interactions at rock-H₂O-CO₂ interfaces during this process. However, the kinetics and mechanisms of interfacial reactions in the mineral-aqueous phases with various compositions need further understanding. Additionally, in-situ carbon mineralization requires substantial water usage, making water security imperative. The process of water usage and recycling can lead to the accumulation of ions, including heavy metals, and the spread of organic pollutants, intensifying concerns about water security. Furthermore, injecting fluid consisting of CO₂ and H₂O for in-situ carbon mineralization can also introduce these contaminants into clean groundwater reservoirs, potentially causing ecological and human health problems.

My research aims to tackle these multifaceted issues by investigating the interfacial reactions and transport behaviors of CO₂ and emerging contaminants at natural or engineered solids and aqueous phases within the WEE nexus, especially in the context of geological CO₂ storage involving water usage. The specific objectives are:

Objective 1: To estimate the reservoir’s reactivity and potential for CO₂ storage, I study the interfacial reactions and transport behavior at CO₂-rich fluid and ultramafic/mafic rock interfaces, particularly under far-from-equilibrium conditions. Using spectroscopic analyses such as ICP-OES, XRD, and XPS, I aim to understand reaction parameters, primary mineral phases involved, and phase evolution during the reaction. This research provides insights into geological CO₂ storage regarding storage potential, reaction kinetics, water chemistry evolution, and related economic and safety considerations.

Objective 2: Investigating different reaction pathways of CO₂ mineralization at CO₂-rich fluid and ultramafic rock interfaces, I focus on direct carbonation under various pH conditions. pH is a critical parameter controlling the carbon mineralization process. Groundwater at ultramafic/mafic reservoirs naturally has high pH due to dissolved alkaline cations from the rock matrix, creating a pH gradient from the injection site. This study aims to understand the implications of alkaline pH during geological CO₂ storage and the mechanisms driving reactions at the interface.

Objective 3: At the interface of mineral matrices and aqueous phases, dissolved divalent cations like Mg and Ca can react with dissolved CO₂ to form solid carbonate phases. Interfacial energy plays a role in the nucleation and growth of these solid products. Subsurface conditions feature various mineral phases with different interfacial energies, affecting the mineral trapping step and pore network. This research aims to understand the fundamental interaction behaviors during the heterogeneous nucleation and growth of hydrated MgCO₃ (nesquehonite). The study explores the effects of different mineral surfaces and background ions, providing insights into pore network evolution and mineral surface changes.

Objective 4: Within the WEE nexus, using water sources free from emerging contaminants during in-situ carbon mineralization is crucial to prevent ecological and human health problems. This objective involves preparing engineered materials to adsorb various emerging contaminants and understanding their mechanisms and transport behaviors. The study explores the relationship between surface functionality and emerging contaminants, as well as the effects of different background ions. Additionally, it examines the efficiency and process design of different porous materials, and strategical directions for material development based on insights from this research.

Future research should focus on expanding studies of interfacial reactions and transport behaviors under diverse conditions related to real-world scenarios, while utilizing the obtained insights to develop integrated approaches for addressing the interconnected grand challenges with enhanced performance.