Sustainable Gel-Less Synthesis of Sub-1-μm-Thick All-Silica CHA Zeolite Membranes for Efficient CO₂ Capture

Carbon capture and storage are extensively recognized as promising technologies for relieving climate change. All-silica CHA (Si-CHA) zeolite membranes have an extremely attractive CO₂ separation performance and high resistance to humidity and CO₂ partial pressures. However, it remains an environmental issue for synthesizing Si-CHA zeolite and zeolite membranes by the conventional route because a large amount of gel containing toxic fluorite is used. Herein, we have reported a sustainable gel-less synthesis approach to fabricate uniform and sub-1-micron Si-CHA zeolite membranes. The sustainability and economy of membrane synthesis by the current approach can be improved since the amount of gel is saved by up to 95% and no fluoride is used compared with the conventional approach. Moreover, a formation mechanism of Si-CHA zeolite membranes is proposed. The effects of synthesis temperature, time, seeding layer, and gel composition on membrane formation are investigated. Thin Si-CHA membrane prepared under optimized conditions shows a notable CO₂ permeance of 1.3 × 10^-6 mol/(m² s Pa) and a CO₂/N₂ selectivity of 31 in an equimolar CO₂/N₂ mixture. Such a separation performance of the current membrane surpasses that of the reported membranes. The membrane also displays excellent separation performance in CO₂/CH₄ mixtures. The environmentally friendly gel-less synthesis approach is promising to produce Si-CHA zeolite membranes on a large scale for practical applications of the CO₂ capture from flue gas, natural gas, and biogas.