Study of surface heterogeneity and nitrogen functionalizing of biochars: Molecular modeling approach

The functionality of biochar surfaces depends on the nature of the feedstock, pyrolysis temperature, and residence time. In this study, molecular modeling was used to determine the types of functionalization that could enhance adsorption and to pre-screen the target adsorbate for the sake of minimizing experimental time. The impact of a single functional group and interaction between them (including nitrile, methyl, ether, furan, carboxyl, hydroxyl, amine, and amide) on the adsorption of target adsorbate onto biochar was investigated. Among biochars inherent functional groups simulated, the lowest energy of adsorption (highest adsorption) occurred with carboxyl and hydroxyl for CO2 adsorption due to hydrogen bonding. The simulations showed adding amine/amide functional groups to the biochar surface enhanced CO2 adsorption, because of stronger bonding. The simulation results were compared against experimental results and the thermodynamic properties were satisfactorily matched. The overall heat of adsorption of H2S was lower than CO2, but the average Gibbs free energy was approximately the same, indicating CO2 could replace H2S in initial screening adsorption experiments for this type of biochar, reducing costs, risk and toxicity concerns of using H2S. This is an example of potentially how the models can be used to better design experiments. (C) 2020 Elsevier Ltd. All rights reserved.