Highly-Controlled Soft-Templating Synthesis of Hollow ZIF-8 Nanospheres for Selective CO₂ Separation and Storage

Global warming is an ever-rising environmental concern,and carbondioxide (CO2) is among its major causes. Different technologies,including adsorption, cryogenic separation, and sequestration, havebeen developed for CO2 separation and storage/utilization.Among these, carbon capture using nano-adsorbents has the advantagesof excellent CO2 separation and storage performance aswell as superior heat- and mass-transfer characteristics due to theirlarge surface area and pore volume. In this work, an environmentallyfriendly, facile, bottom-up synthesis of ZIF-8 hollow nanospheres(with reduced chemical consumption) was developed for selective CO2 separation and storage. During this soft-templating synthesis,a combined effect of ultra-sonication and low-temperature hydrothermalsynthesis showed better control over an oil-in-water microemulsionformation and the subsequent growth of large-surface-area hollow ZIF-8nanospheres having excellent particle size distribution. Systematicstudies on the synthesis parameters were also performed to achievefine-tuning of the ZIF-8 crystallinity, hollow structures, and spheresize. The optimized hollow ZIF-8 nanosphere sample having uniformsize distribution exhibited remarkable CO2 adsorption capability(& SIM;2.24 mmol g(-1) at 0 & DEG;C and 1.75 bar),a CO2/N-2 separation selectivity of 12.15, agood CO2 storage capacity (1.5-1.75 wt %), and anexcellent cyclic adsorption/desorption performance (up to four CO2 adsorption/desorption cycles) at 25 & DEG;C. In addition,the samples showed exceptional structural stability with only & SIM;15%of overall weight loss up to 600 & DEG;C under a nitrogen environment.Therefore, the hollow ZIF-8 nanospheres as well as their highly controlledsoft-templating synthesis method reported in this work are usefulin the course of the development of nanomaterials with optimized propertiesfor future CO2 capture technologies.