Towards cost-effective CO₂ adsorption materials: Case of CuBTC - Hydrochar composite

This study focuses on synthesizing composite materials of biochar/hydrochar derived from rice straw and Copper benzene-1,3,5-tricarboxylate (CuBTC), a commercialized metal-organic framework, to enhance CO2 adsorption. The composite was synthesized using an electrochemical method based on CuBTC, biochar and hydrochar. The composite materials exhibited a significant increase in adsorption efficiency, with the combination of hydrochar and CuBTC showing the highest efficiency at 26%, compared to 3-4% and 15% for biochar/hydrochar and CuBTC alone, respectively. These composite materials have good promise for highly selective CO2/N-2 separation at room temperature. The SEM results showed that the hydrothermal method produced hydrochar that was small, uniform, and spherical in shape, which facilitated its combination with CuBTC. EDS chemical composition analysis indicated that the C:Cu ratio in biochar was 5:1, while in hydrochar, it was approximately 1.5:1. Moreover, the combination of hydrochar and CuBTC significantly increased the surface area of the material. Specifically, the surface area increased from 187 to 635 m(2)g(-1) and 164-795 m(2)g(-1) for biochar and hydrochar, respectively. Moreover, the microcapillary structure of the composite was also improved compared to the parent materials, which enhanced the CO2 adsorption capacity. Both chemical adsorption from surface functional groups and physical adsorption through the proliferation of micro capillaries and the Van der Walls effect can collectively explain the CO2 adsorption using the CuBTC-Hydrochar composite. Additionally, the composite of biochar/hydrochar with CuBTC reduced the sensitivity of CuBTC to moisture exposure, offering high practical applicability of the composite. The use of rice straw, an abundant by-product in Vietnam, along with the application of an electrochemical method, constitutes the novel and valuable contribution of this study.