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Cigarette filters were utilized as carbon source for the production of solid carbon acid catalysts. In this study, the process of carbonization and simultaneous sulfonation via hydrothermal treatment was employed. The catalysts were prepared by mixing cigarette filters and sulfuric acid at temperatures of 100, 150, and 190 °C for durations ranging from 2 to 8 h. It was observed that the highest conversion of oleic acid occurred when the catalyst was synthesized at 190 °C for 4 h. The optimized conditions for the esterification reaction using this catalyst included an oleic acid to methanol molar ratio of 1:12, a catalyst loading of 5 wt%, and a temperature of 100 °C for 1 h. Additionally, the catalyst was successfully reused four times without significantly impacting the reaction yield. These findings highlight a promising approach for the utilization of waste materials, with immediate implications for waste management practices and positive environmental impacts., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

The increase in burning, deforestation, and the exorbitant use of fossil fuels have contributed to the increase in carbon dioxide emissions; this gas is responsible for the intensification of the greenhouse effect and radical climate changes. In this way, it becomes necessary to find alternatives to reduce its emission. Porous carbon materials synthesized from lignocellulosic waste can be employed in technologies for capture and utilization of CO 2 due to the advantages such as selectivity, low-cost synthesis, high surface area and pore volume, and thermal and chemical stability. Considering the availability of Brazil nut biomass residues in the Amazon region, this article proposes to synthesize activated carbon from the lignocellulosic residue using physical and chemical activation methods for CO 2 capture. The analysis of N 2 adsorption-desorption isotherms proves the predominance of a microporous structure when using the two synthesis methods described here. In physical activation, the surface area was 912 m 2 /g, while, in chemical activation, it was 1421 to 2730 m 2 /g. The sample treated via the chemical method (BS6-K1) showed better performance in CO 2 adsorption, with adsorption results of 3.8 and 6 mmol/g of CO 2 at 25 ℃ and 0 °C, respectively, at 101 kPa. CO 2 adsorption capacity is due to the high volume of ultramicropores. It is believed that the microporous carbon material synthesized from Brazil nut residues is an alternative precursor for carbon materials used as CO 2 capture., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Acai seed was used herein as an Amazon biomass waste for the synthesis of activated and modified carbon in order to find a possible use for the large volume of residues generated during the processing of this fruit and to add value to this residue. Activated carbon materials were used to remove Pb 2+ , Fe 2+ , and Mg 2+ metal ions from water. The efficiency of removal of these ions by the acai seed activated carbon was compared with that by commercial activated carbon. Activated carbon materials were prepared by carbonization and chemical activation using two KOH impregnation ratios, namely 1:1 (ACK1) and 5:1 (ACK5), by mass. These samples were modified by treatment with nitric acid under microwave heating (ACK1-M) and (ACK5-M), respectively. The result of the elemental analysis indicated that this biomass has carbon and sulfur contents of 43.29% and 0.10% wt, respectively. The textural parameters showed that the obtained activated carbon samples presented high surface areas between 1462 and 2774 m 2  g -1 . Raman analysis revealed the different degrees of graphitization of the activated carbon materials. Boehm titration identified the presence of phenolic, carboxylic, and lactonic groups in samples that were confirmed by Fourier transform infrared spectroscopy. In the metal adsorption tests, ACK5-M showed better removal efficiency, reaching 86% removal for Pb 2+ , 69% for Fe 2+ , and 8% for Mg 2+ in 1 h of contact time; these results were superior to those obtained for commercial carbon. The results indicated that acai seed can be used for the production of activated carbon and can also be used for metal removal., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020. Published by Elsevier Ltd.)