Amine-functionalisation of Ni-DOBDC MOF for CO₂ adsorption

Biogas is a sustainable energy source substitute for fossil fuels. However, biogas possesses a relatively high carbon dioxide content (CO₂) to methane (CH₄), which is undesirable as it can damage the engine through corrosion and deposition. Adsorption techniques have been widely employed to extract CO₂ from biogas using Metal-Organic Frameworks (MOFs) modified with polar groups such as amines to increase their capacity for CO₂ adsorption. Hence, the aim of this study is to investigate how ethylenediamine (EDA) modification affects the CO₂ adsorption performance of Ni-based MOF. Ni-DOBDC was synthesised using hydroxylated terephthalic acid (2,5-dihydroterephthalic acid, DOBDC) as ligand and post-synthetically modified with 15 % w/w EDA. Ni-DOBDC and its EDA-modified form were characterised using XRD, FTIR, N₂-physisorption, SEM-EDX, and CO₂-TPD to investigate the physicochemical properties, which were then employed as CO₂ adsorbent in CO₂/CH₄/N₂ (30:60:10) biogas model. The CO₂ adsorption test results showed that EDA-modified Ni-DOBDC exhibits an improved adsorption capacity (11.80 mmol/g) compared to pristine Ni-DOBDC (8.71 mmol/g), with highest selectivity towards CO₂ when imposed to biogas model at 70 °C. Analysis on the adsorption isotherm, kinetics, and reusability test were also conducted to understand the stability and adsorption mechanism of CO₂ within MOF.