Novel activated carbon route to low-cost geopolymer based porous composite with high mechanical resistance and enhanced CO2 capacity

Abstract Geopolymers are regarded as zeolite-like structure materials but do not exhibit satisfactory zeolite-like capabilities because of their limited porosity and surface area. Geopolymer-zeolite composites have been prepared by embedding zeolite powders into the geopolymer matrix or through the in-situ hydrothermal route, however, it is challenging to obtain both the sufficient mechanical resistance as well as porosity. In this study, a novel activated carbon route was proposed for the first time to overcome the above drawbacks via a facile two-step reaction of activated carbon embedded polycondensation and hydrothermal crystallization. The initiative incorporation of activated carbon into the geopolymer generated an interface in the matrix and improved the porosity of the composite simultaneously, the mechanical resistance loss caused by the interface was effectively mitigated by increasing the alkalinity of the activator. The hydrothermal product exhibited an enhanced specific surface area of 256.24 m2/g due to the improvement of zeolite yields with the aid of the deliberate interface. The hydrothermal zeolite formation process didn't affect the mechanical resistance because the zeolite in the matrix was combined with the geopolymer through [SiO4]4- and [AlO4]5- tetrahedral by sharing the bridging oxygens. This finally resulted in an excellent compressive strength of 23.1 MPa and enhanced CO2 capacity of 60.14 cc/g at 1 atm and 35 °C, both of which are higher than those of geopolymer-based adsorbents reported for CO2 capture to date.