Utilization of acai stone biomass for the sustainable production of nanoporous carbon for CO2 capture

Abstract Porous carbon materials with a tunable porosity and degree of graphitization were successfully synthesized using acai stone as a precursor. The acai stone was chosen due to the large volume of waste generated during the processing of acai fruit (>85% of the fruit), which has become a great concern to the population of the Amazon region in Brazil. To that end, the biomass waste was carbonized at 600 °C, and its porosity was further developed by either KOH or CO2 activation. Additionally, catalytic-induced graphitization was performed to increase the amount of graphitic domains. The increase in the porosity observed with KOH activation was larger compared with that achieved with CO2; however, CO2 activation allowed better control of the formation of small micropores. The best CO2 sorption performance was observed for the materials activated by KOH, and this performance was strongly correlated with the amount of ultramicropores. The CO2 adsorption capacity reached up to 6.1 mmol·g−1, while surface areas between 760 and 3250 m2·g−1 were obtained among the activated carbon materials. The degree of graphitization reached up to 64% of graphite, and the mesopore volume of all of the materials was significantly improved when compared to that of the carbons activated by either KOH or CO2. It is important to emphasize that both the activated and graphitized carbon presented herein can be applied to other strategic areas, such as in the energy sector and for water treatment and catalysis, and these areas potentially represent sustainable destinations for this abundant biomass waste.