Ajumobi Oluwole, Wang Borui, Farinmade Azeem, He Jibao, Valla Julia A, John Vijay T
Department of Chemical & Biomolecular Engineering, Tulane University, 6823 St. Charles Avenue, New Orleans, Louisiana 70118, United States.
Coordinated Instrumentation Facility, Tulane University, 6823 St. Charles Avenue, New Orleans, Louisiana 70118, United States.
Energy Fuels. 2023 Jul 26;37(16):12079-12088. doi: 10.1021/acs.energyfuels.3c01318. eCollection 2023 Aug 17.
Polymeric amine encapsulation in high surface area MCM-41 particles for CO capture is well established but has the drawback of leaching out the water-soluble polymer upon exposure to aqueous environments. Alternatively, chemical (covalent) grafting amine functional groups from an alkoxysilane such as 3-aminopropyltriethoxysilane (APTES) on MCM-41 offer better stability against this drawback. However, the diffusional restriction exhibited by the narrow uniform MCM-41 pores (2-4 nm) may impede amine functionalization of the available silanol groups within the inner mesoporous core. This leads to incomplete amine functionalization and could reduce the CO adsorption capacity in such materials. Our concept to improve access to the MCM-41 interior is based on the incorporation of nanostraws with larger inner diameter (15-30 nm) to create a hierarchical porosity and enhance the molecular transport of APTES. Halloysite nanotubes (HNT) are used as tubular straws that are integrated into the MCM-41 matrix using an aerosol-assisted synthesis method. Characterization results show that the intrinsic structure of MCM-41 remains unaltered after the incorporation of the nanostraws and amine functionalization. At an optimal APTES loading of 0.5 g ( = 2.0), the amine-functionalized composite of MCM-41 with straws (APTES/M40H) has a 20% higher adsorption capacity than the amine-modified MCM-41 (APTES/MCM-41) adsorbent. Furthermore, the CO adsorption capacity APTES/M40H doubles that of APTES/MCM-41 when normalized based on the composition of MCM-41 in the composite particle with straws. The facile integration of nanostraws in MCM-41 leading to hierarchical porosities could be effective toward the mitigation of diffusional restriction in porous materials with potential for other catalytic and adsorption technologies.
将聚合胺封装在高比表面积的MCM - 41颗粒中用于捕获CO已经得到了广泛认可，但存在一个缺点，即暴露于水环境时水溶性聚合物会浸出。另外，通过化学（共价）接枝法将胺官能团从诸如3 - 氨丙基三乙氧基硅烷（APTES）的烷氧基硅烷接枝到MCM - 41上，能更好地克服这一缺点。然而，狭窄均匀的MCM - 41孔（2 - 4纳米）所表现出的扩散限制可能会阻碍内介孔核内可用硅醇基团的胺官能化。这会导致胺官能化不完全，并可能降低此类材料的CO吸附容量。我们改善进入MCM - 41内部的方法是基于引入内径更大（15 - 30纳米）的纳米管，以形成分级孔隙率并增强APTES的分子传输。埃洛石纳米管（HNT）用作管状纳米管，通过气溶胶辅助合成方法将其整合到MCM - 41基质中。表征结果表明，引入纳米管和胺官能化后，MCM - 41的固有结构保持不变。在最佳APTES负载量为0.5克（= 2.0）时，带有纳米管的MCM - 41胺官能化复合材料（APTES/M40H）的吸附容量比胺改性的MCM - 41（APTES/MCM - 41）吸附剂高20%。此外，当基于含纳米管的复合颗粒中MCM - 41的组成进行归一化时，APTES/M40H的CO吸附容量是APTES/MCM - 41的两倍。纳米管在MCM - 41中的简便整合导致分级孔隙率，对于减轻多孔材料中的扩散限制可能是有效的，这在其他催化和吸附技术中具有潜力。
