Bimetallic Ni–Co‐based metal–organic framework: An open metal site adsorbent for enhancing CO 2 capture

An open metal site framework named UTSA‐16 was synthesized and modified as a high‐capacity adsorbent for reversible CO 2 capture. Partial substitution of intrinsic Co 2+ sites of UTSA‐16 with Ni 2+ centres was realized in the molar composition range 0–75% Ni with the aim of increasing CO 2 uptake. Synthesized bimetallic Ni x ‐UTSA‐16 ( x  = 0, 20, 50, 75) materials were characterized using various techniques to assess the influence of chemical composition on CO 2 binding affinity and any subsequent physical change in morphology, crystal size and porosity on the total uptake. Experimental isotherm adsorption studies showed the following trend for CO 2 adsorption capacity employing the Ni x ‐UTSA‐16 series: Ni20‐UTSA‐16 > UTSA‐16 > Ni50‐UTSA‐16 > Ni75‐UTSA‐16. According to the dynamic breakthrough CO 2 profiles measured for a mixture of CO 2 and CH 4 (15/85 molar ratio), Ni20‐UTSA‐16 exhibited 2 times the breakthrough time with 1.5 times the loading capacity at 75 Nml min −1 feed flow rate, compared to the parent UTSA‐16. In addition, the Ni20‐UTSA‐16 bimetallic metal–organic framework exhibited lower isosteric heat of adsorption compared to UTSA‐16 (Δ H ave  = 28.54 versus 46.85 kJ mol −1 ). As a result, more than 95% of its capacity was restored by applying a partial vacuum for only 1 h at room temperature without involving any other time‐ and energy‐consuming regenerative step.