Carbon dioxide mitigation

Due to technological advancement, energy consumption and demand have been increasing significantly, primarily satisfied by fossil fuel utilization. The dependence on fossil fuels results in substantial greenhouse gas emissions, with CO₂ being the principal factor in global warming. Carbon capture technologies are employed to mitigate the escalated CO₂ emissions into the atmosphere. Among various carbon capture methods, amine scrubbing is widely utilized because of its high CO2 capture efficiency and ease of adaptability to the existing power plants. This method, however, presents drawbacks, including increased toxicity, corrosiveness, and substantial freshwater use. To overcome these shortcomings and simultaneously develop an environmentally sustainable carbon capture solution, this study aims to evaluate the CO2 capture performance of seawater associated with polyvinylpyrrolidone (PVP) polymer-coated nickel nanoparticles (NiNPs) catalysts. Using high-speed bubble-based microfluidics, we investigated time-dependent size variations of CO2 bubbles in a flow-focusing microchannel, which is directly related to transient CO₂ dissolution into the surrounding solution. We hypothesize that the higher surface-to-volume ratio of polymer-coated NiNPs could provide a higher CO2 capture rate and solubility under the same environmental conditions. To test this hypothesis and to find the maximum performance of carbon capture, we synthesized polymer-coated NiNPs with different sizes of 5 nm, 10 nm, and 20 nm. The results showed that 5 nm polymer-coated NiNPs attained a CO₂ dissolution rate of 77% while it is 71% and 43% at 10 nm and 20 nm NPs, respectively. This indicates that our hypothesis is proven to be valid, suggesting that the smaller NPs catalyze CO2 capture effectively with using the same amount of material, which could be a game changer for future CO2 reduction technologies. This unique strategy promotes the future improvement of NiNPs as catalysts for CO2 capture from saltwater.

The atmospheric concentration of CO2 increased from 320 to 425 parts per million by volume (ppmv; 0.0425 vol.%) between 1960 and 2024. Sample CO2 reduction strategies include shifting to renewable energy sources and employing CO2 capture. CO2 capture from the air (also known as direct air capture; DAC) has recently received increased attention. CO2 has the potential to act as an asphyxiant at high concentrations, particularly in enclosed environments (e.g., spacecraft, submarines), requiring air revitalization to remove CO2. Hence, the U.S. Occupational Safety and Health Administration determined a permissible exposure limit of 5,000 ppmv CO2 (0.5 vol.%) throughout an 8-hour work shift. Considering the trace levels of CO2 and the presence of humidity in DAC and air revitalization applications, similar materials can be developed for implementation in both cases. CO2 capture involving amine-functionalized silica materials (“aminosilicas”) can achieve high CO2 uptakes at low concentrations due to high selectivity. Additionally, moisture in CO2-laden gases enhances the CO2 uptake and stability of aminosilicas. Therefore, this research investigated the potential of aminosilicas for removing CO2 from dilute streams, including DAC and air revitalization applications. Aminosilicas were produced using mesoporous silica supports with different particle sizes that were modified with tetraethylenepentamine (TEPA) or branched polyethylenimine (PEI) with different molecular weights (600, 1200, and 1800), or grafted with 3-aminopropyltrimethoxysilane (APTMS). The performance of aminosilicas was assessed to determine equilibrium CO2 adsorption capacity, adsorption kinetics, and cyclic stability.

Carbon capture and sequestration (CCS) has been considered a promising technology for mitigating heavy atmospheric carbon dioxide (CO2) concentration as an immediate response to global climate change and ocean acidification. Despite various previous studies on CCS, there has been a paucity of research to overcome many of the challenges. In geological carbon sequestration, there are two major issues in achieving a feasible means of storing CO2. The first is the slow reaction of carbonic acid (H2CO3) formation from the reaction between injected CO2 and brine. Another technical challenge to the realization of industrial-scale carbon sequestration is the drying-out of brine induced by CO2 advection. The resident brine near a wellbore area is rapidly evaporated while precipitating significant amounts of salt at pores when gaseous CO2 is continuously injected into these aquifers. On the other hand, in industrial post-carbon capture processes, monoethanolamine (MEA) has been dominantly used as an absorption solvent. However, it generates significant amounts of toxic wastewater containing chemicals difficult to treat. The objectives of this thesis are to address these challenges in CCS, making the CCS technology feasible and competitive. An innovative method for geologic carbon sequestration, namely nickel nanoparticles (Ni NPs) addition to the injection fluid was developed and evaluated, to address issues of the slow reaction in deep saline aquifers. The catalytic activity of Ni NPs was evaluated using the microfluidic technique to confirm their possibility of additive for enhancing CO2 hydration in deep saline aquifers. First of all, to achieve acceleration of CO2 dissolution under reservoir-specific conditions, the catalytic effect of Ni NPs was investigated by monitoring change in CO2 bubble size at various Ni NPs concentration, pH, and different levels of salinity. Then, steric stabilization of Ni NPs by adsorbing polymers has been studied to further enhance Ni NPs’ catalytic activity. Second, to overcome the brine drying-out challenge, a new strategy of sequential water injection with CO2 was proposed. This sequential injection strategy showed great potential for preventing aquifer formation damage by decreasing brine drying-out and enhancing CO2 dissolution significantly. Lastly, the CO2 capturing performance of Ni NPs as a possible additive in an MEA solvent was evaluated to meet CO2 reduction and environmental protection demands. The results were promising: the catalytic potential of Ni NPs accelerates the average CO2 absorption rate by 34% and 54% in the limited mixing and the high mixing conditions, respectively. The results presented in this dissertation could help alleviate global concerns raised by CCS technology and would offer strategies for stable CCS technology with improved efficiency.