Bimetallic ZIFs based on Ce/Zn and Ce/Co combinations for stable and enhanced carbon capture

Abstract

Global warming leading to adverse climate changes has become a serious concern worldwide. Carbon capture through various technologies like adsorption has been found to be the most potential tool to address this phenomenon. In this work, novel, cost effective and green adsorbents like Zeolitic Imidazolate Frameworks (ZIFs) have been developed through simple protocols to give higher capture capacity and cyclic stability. Addressing global warming and mitigating climate change would provide the most conducive environment and ecosystem to promote efficiency, sustainability, and cleaner production in various processes. Also, carbon dioxide captured may be converted to clean fuels like Hydrogen through methanation. In this study, two bimetallic ZIFs, ((Ce,Zn)ZIF-8 and (Ce,Co)ZIF-67), were synthesized and chosen to compare with each other in terms of CC (Carbon Capture) performance. Response Surface Methodology (RSM), specifically Central Composite Design (CCD), was employed to aid in designing the carbon capture (CC) experiments. Four process parameters that influenced the CC performance were temperature, amount of adsorbent loaded, time of carbonation and effect of diethanolamine (DEA) loading. Both adsorbents showed good initial CC values with (Ce,Zn)ZIF-8 showing the better uptake value of 3.77 mmol/g than the uptake value of 3.55 mmol/g of (Ce,Co)ZIF-67. The highest absolute CC value of 4.55 mmol/g was given by 15% DEA loaded (Ce,Zn)ZIF-8 adsorbent. Temperature and DEA loading were the two most influential factors in CC uptake values, while the time of carbonation and amount of adsorbent had minimal effect individually. The pseudo-second-order and Avrami models best explained the CO2 uptake of (Ce,Zn)ZIF-8 and (Ce,Co)ZIF-67, respectively. Langmuir adsorption isotherm suited the experimental data well indicating a monolayer adsorption process. Both the adsorbents performed decently well when subjected to the cyclic adsorption process retaining up to 94% of their initial CO2 uptake over 15 cycles.