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Tenebrio molitor feces derived biochar for CO2 capture and stability

https://doi.org/10.1039/D2RA03575H

Tenebrio molitor feces derived biochar samples were prepared by KOH activation at different temperatures (600, 700 and 800  °C)

“CO2 capture capacity tests of TMFB and activated TMFB were performed and the experimental data were fitted by both Freundlich (Fig. 3a) and Langmuir (Fig. 3b) models.50 The adsorption equation parameters were reported in Table S3. Apparently, the CO2 capture capacities of TMFB and activated TMFB were positively correlated with the PCO2, which was consistent with the PCO2 being the thermodynamic driving force of the adsorption process. The fitted curves of both Freundlich and Langmuir models showed good agreement with the experimental adsorption isotherms of TMFB and activated TMFB, with fitted correlation coefficients (R2) larger than 0.98. For activated TMFB, Freundlich equation seemed to be more appropriate for the entire partial pressure range, implying that heterogeneous adsorption was distributed on the biochar surface.51 Since the n parameter was always larger than 1, the CO2 adsorption on activated TMFB was mainly physical.”

“The CO2 capture capacities of TMF, TMFB-600A, TMFB-700A, and TMFB-800A at 0.1 MPa were 1.64, 2.09, 3.05, and 2.59 mol kg−1, respectively. Among activated TMFB, TMFB-700A exhibited the best capture capacity. It can be seen from Fig. 3c that all biochars exceed 90% of their maximum capture capacities after 20 min, showing a rapid adsorption speed. TMFB-700A also exhibited the largest capture capacity in gravimetric CO2 adsorption test. Its saturation value of 2.9 mol kg−1 at 30 min was consistent with the capture isotherm. In addition, TMFB-700A was selected for further evaluation of its CO2 adsorption and desorption cycling stability (Fig. 3d). TMFB-700A maintained more than 99% of its initial capture capacity for 10 consecutive cycles, indicating that it can be regenerated easily and had excellent adsorption–desorption kinetics. Compared with the CO2 capture performance of other biochar materials currently reported in Table S4, TMFB-700A showed superior performance. The excellent CO2 capture performance of TMFB-700A should be attributed to the high specific surface area and well-developed pore structure. Besides, it could also be due to the following factors: (1) O-containing (i.e., carbonyl, ether, carbonyl, and hydroxyl) or N-containing (amino) functional groups on the surface of biochar produced strong electrostatic interactions with CO2 molecules and provide additional adsorption sites.52 (2) The N-containing sites (pyridine N, oxidized N, and graphitic N) not only enhanced the surface affinity between basic sites and CO2 but also generated π interactions with CO2.53,54 (3) Alkali metals on the biochar surface decorated as electron donors enhanced the adsorption of CO2 as electron acceptors.55

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