Manufacture and characterization of activated carbon from marigold straw (Tagetes erecta L) by H3PO4 chemical activation

• Marigold straw shows promise as an excellent raw material for producing porous activated carbon.
• The optimal conditions on preparation with phosphoric acid as activator have been found.
• The weight ratio of the activator to the raw material was the most influential factor for enhancing the properties of activated carbon.
• The marigold straw activated carbon has a great specific surface area with a majority of micropores.

Marigold straw shows promise as an alternative raw material for activated carbon production. This study investigated the adsorption performance of activated carbon prepared from marigold straw and evaluated the preferable conditions for preparation. Activated carbons were prepared from a new precursor marigold (Tagetes erecta L) straw with phosphoric acid activation, using H3PO4 as an activator in air to create an abundant pore structure. Results show a higher iodine adsorption value (1145.38 mg/g) for activated carbon with an activation time of 2 h at 400 °C with a 2:1 weight ratio of the activator to the raw material. This study also characterized preferable carbon through microstructure morphology, elemental analysis and physical adsorption of N2 at −196 °C. Findings reveal that part of the cellulose crystalline structure was destroyed, resulting in a significant increase in carbon content, from 46.73% to 74.55%. SEM photographs show that a porous structure formed during activation. The nitrogen adsorption–desorption isotherm illustrates a micropore structure and a Brunauer–Emmett–Teller (BET) surface area corresponding to 1344.23 m2/g, with a micropore surface area of up to1113.65 m2/g. This study also assessed the microporosity of activated carbon with a mean pore diameter of 0.59 nm using a micropore size distribution curve.

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