Studies of amine functionalized biochar based desiccated coconut waste for carbon dioxide adsorption

Environmental problems such as climate and global warning caused by greenhouse gases, mainly CO₂, have become a worldwide topic of concern. Adsorption is a promising method for CO₂ capture. In this research, a series of amine functionalized on biochar based desiccated coconut waste (amine-biochar @ DCW) namely ethylenediamine functionalized biochar@DCW (eda-BIOCHAR@DCW), diethylenetriamine functionalized biochar@DCW (DETA-biochar@DWC). triethylenetetramine functionalized biochar@DCW (TETA-biochar@DCW), tetraethylenepentamine functionalized biochar@DCW (TEPA-biochar@DCW), and pentaethylenehexamine functionalized biochar@DCW (PEHA-biochar@DCW) adsorbents were synthesized and characterized. From the Scanning Electron Microscopy (SEM) dan Braeuer-Emmett-Teller (BET) analysis, series of amine-biochar@DCW adsorbents had better developed pore structure and larger specific surface area than that of pristine desiccated coconut waste (DCW). Besides, Energy Dispersive X-ray (EDX) dan Fourier Transform Infrared Spectroscopy (FTIR), confirmed the successful functionalization of series of amine towards biochar based desiccated coconut waste (biochar@DCW). From the CO₂ adsorption experiment, TETA-biochar@DCW had higher CO₂ adsorption capacity (61.78 mg/g) as it has the largest specific surface area and highest total pore volume with 31.7 m2/g dan 0.0029 cm2/g, respectively. The best ratio of biochar@DCW: anime for the CO₂ adsorption is 1:2. The absorption kinetics on the TETA-biochar@DCW was best fitted by the pseudo-second model, suggesting the adsorption process occurs through chemisorption. Furhermore, TETA-biochar@DCW depicts high selectivity towards CO₂ gas and good reusability after five CO₂ adsorption-desorption cycles. From theoretical study using Density Functional Theory (DFT) approach reveals that TETA-biochar@DCW as the reactive and stable adsorbent for CO₂ adsorption. Analysis from the geometry optimization and frontier molecular orbital (FMO) proved that TETA-biochar@DCW as stable adsorbent because it has the lowest total energy and dipole moment and has large energy gap after the CO₂ adsorption occurs. While, the study of molecular electrostatic potential (MEP) shows that TETA-biochar@DCW is a reactive CO₂ adsorbent with the highest electrostatic potential value (7.146 e -2 eV) compared with other amine-biochar@DCW adsorbents, suggesting the strong adsorption of TETA-biochar@DCW towards CO₂ gases. Outcomest from theoretical study well support the findings from experimental which showed TETA-biochar@DCW as optimum adsorbent for CO₂ due to its great physicochemical properties and its reactive molecular characteristics. As conclusion, TETA-biochar@DCW can be used as an alternative adsorbent for CO₂ adsorption.