Comparison of Amorphous and Crystalline Ni-MOFs for Environmental Applications

Amorphous and crystalline nickel-based metal-organic frameworks (Ni-MOFs) were prepared via a one-pot synthesis at room temperature in methanol using 2-methylimidazole as a ligand. The crystallinity was adjusted by varying the solvent volume, yielding an amorphous phase with higher surface area (≈242 m²g^-1) and a crystalline form with reduced porosity (≈22 m²g^-1). Comprehensive structural, morphological, and spectroscopic analyses confirmed distinct coordination environments, particle sizes and colloidal behaviors. Gas sorption measurements revealed enhanced CO₂ uptake in the amorphous Ni-MOF (≈9.5 cm³g^-1) compared to the crystalline sample (≈3.4 cm³g^-1), consistent with its greater pore volume and surface area. Photocatalytic degradation of methyl orange under 365 nm UV irradiation demonstrated faster activity for the amorphous material, with a pseudo-first-order rate constant of 0.0157 min^-1 versus 0.0035 min^-1 for the crystalline sample. These findings suggest that structural features such as higher surface area, pore volume, and possible disorder contribute to the improved gas sorption and photocatalytic response. The use of mild reaction conditions and a single solvent system offers a straightforward and energy-efficient approach for preparing functional MOFs with tunable crystallinity, applicable in environmental remediation contexts.