(494c) Transition Metal Doping for Enhancing CO2 capture Capacities in MOFs

In the face of escalating concerns over anthropogenic carbon dioxide (CO₂) emissions and their profound impact on global climate change, urgent attention is needed towards the development of effective CO₂ capture strategies. While transitioning from carbon-based energy sources to carbon-neutral or negative-emission alternatives is ideal, it presents significant challenges requiring substantial modifications to existing energy infrastructures. Moreover, many cleaner alternative technologies are still in the early developmental stages, limiting their immediate industrial adabtability. Consequently, the importance of carbon capture technologies capable of capturing CO₂ from current emission sources remains paramount. Among the extensively researched carbon capture approaches post-combustion CO₂ capture using porous adsorbents is one of the maor potential techniques, focusing on capturing CO₂ from flue gas at pressures around 100 kPa and partial pressures of CO₂ around 15 kPa. Here, the adsorptive qualities are heavily influenced by the chemical composition of the adsorbent's pore surface, with materials featuring highly functionalized surfaces exhibiting enhanced adsorption capabilities. This study explores Metal-Organic Frameworks (MOFs), a class of porous materials renowned for their tunable properties, high surface areas, and versatile functionalities, making them promising candidates for CO₂ capture and storage.

Specifically, the research entails synthesizing and characterizing three MOFs—aluminum fumarate, MIL–100(Fe), MOF–801, assessing their CO₂ capture capacities across a pressure range (0 to 110 kPa) at temperatures of 5, 15, and 25 °C. Structural and morphological features of the synthesized materials were investigated using scanning electron microscopy and X-ray diffraction techniques, while nitrogen adsorption/desorption experiments probed their porous properties. Subsequently, various variants of the selected MOFs were synthesized through in-situ transition metal doping. Nickel and cobalt were chosen as the transition metals for this process. The Ni²⁺ and Co²⁺ doped variants were synthesized using the same procedure as the parent MOFs, with the addition of 10% Ni2+ and Co2+ salts to the precursor solutions. Subsequently, the modified samples underwent material characterizations to ensure their structural stability and porosities, followed by testing for their CO₂ capture capabilities.

Results indicated that both Ni²⁺ and Co²⁺ enhancements improved the CO₂ capture capacities of the parent MOFs. Notably, the Ni²⁺ doped samples exhibited superior CO₂ capture capacities compared to the Co²⁺ doped ones. Specifically, Ni²⁺ doped aluminum fumarate demonstrated approximately 32% (2.5 mmol/g) more CO₂ capture capacity than the parent counterpart (1.9 mmol/g) at 25°C and 110 kPa. Similarly, under same operating condition, for MOF-801 (CO₂ capture capacity: 1.24 mmol/g) and MIL-100(Fe) (CO₂ capture capacity: 1.44 mmol/g), the Ni²⁺ doped samples showed 26% and 31% higher CO2 capture capacities, respectively. In contrast, the Co²⁺ doped samples exhibited CO₂ capture capacities of 2.35 mmol/g, 1.42 mmol/g, and 1.78 mmol/g for aluminum fumarate, MOF-801, and MIL-100(Fe), respectively, at 25°C and 110 kPa.These findings hold significant implications for advancing sustainable carbon capture technologies across diverse industrial applications.