Smart adsorbents for CO 2 capture: Making strong adsorption sites respond to visible light
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Published online 21 August 2020 | https://doi.org/10.1007/s40843-020-1423-8
Smart adsorbents for CO2 capture: Making strong adsorption sites respond to visible light †
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Qiu-Rong Wu , Peng Tan , Chen Gu, Rui Zhou, Shi-Chao Qi, Xiao-Qin Liu, Yao Jiang and * Lin-Bing Sun ABSTRACT Due to the good controllability and high energy efficiency in adsorption processes, photoresponsive adsorbents are intriguing for CO2 capture. Nevertheless, most reported photoresponsive adsorbents are designed based on weak adsorption sites, regulating CO2 adsorption through structural change or steric hindrance. In addition, ultraviolet (UV) light is commonly involved in the regulation of adsorption capacity. Here we report for the first time the smart adsorbents for CO2 capture, which makes strong adsorption sites respond to visible (Vis) light. The adsorbents were fabricated by introducing primary amine and Dispersed Red 1 (DR1, a kind of push-pull azobenzene that responds to Vis light rapidly) units to mesoporous silica, which act as strong adsorption sites and triggers, respectively. The primary amine sites make the adsorbents highly selective in the adsorption of CO2 over CH4. Without light irradiation, azobenzene is in the form of trans configuration, which leads to decreased electrostatic potential of primary amines and subsequently, exposure of active sites and liberal adsorption of CO2. Upon Vislight irradiation, cis isomers are formed, which results in increased electrostatic potential of primary amines and subsequently shelter of active sites. Even on such strong adsorption sites, the alteration of CO2 adsorption capacity can reach 40% for the adsorbent with and without Vis-light irradiation. Moreover, the trans/cis isomerization of DR1 units can be triggered reversibly by Vis light. The present smart system endows adsorbents with selective adsorption capacity and avoids the employment of UV light, which is unlikely to be achieved by conventional photoresponsive adsorbents. Keywords: CO2 adsorption, strong adsorption sites, selective adsorption, push-pull azobenzene, visible light response
INTRODUCTION Natural gas has attracted increasing attention as a cleaner energy source compared with other fossil fuels [1–5]. Methane (CH4) is the active component of natural gas and carbon dioxide (CO2) is a predominant impurity. The coexistence of CO2 is almost unavoidable regardless of the geographical origin, which not only reduces the calorific value of natural gas but also leads to the corrosion of equipment [6–8]. To remove CO2, amine scrubbing is currently employed in industry [9–11]. Albeit effective, this technique has some shortcomings like high energy consumption for regeneration and corrosiveness of aqueous amine solutions [12]. In recent years, adsorption using porous solid adsorbents such as zeolites [13], activated carbons [14], and metal-organic frameworks (MOFs) [15–18] is of great interest as an alternative for CO2 capture. Currently, pressure and temperature swings are the two typical approaches used to vary the adsorp
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