KOH/NaOH mixture as new chemical activation approach

What is it about?

To produce activated carbon, the raw material (e.g. biomass) is thermally decomposed through carbonisation – a charring process to convert biomass into char by pyrolysis. Then, the char is ‘activated’ via physical or chemical activation to increase the char porosity. Physical activation uses carbon dioxide or steam as activating agents while chemical activation is performed using chemicals (e.g. alkali metal hydroxides and carbonates) to produce activated carbon. Chemical activation shows advantages over physical activation in requiring lower activation temperature (450–700 °C) and producing higher yield of activated carbon. Our previous study showed that the use of chemical mixture seemed to have a beneficial effect in increasing the surface area and porosity of the resulting activated carbon. The above findings provide the motivation for this study, which was performed to convert banana peel into activated carbon using microwave pyrolysis with emphasis on the utilisation of hydroxides mixture as an activating agent. The effects of various process parameters (i.e. microwave power, microwave irradiation time, chemical impregnation ratios and types of chemical used for activation) on the yield and characteristic of activated carbon obtained were investigated with the intention to explore the potential of using this pyrolysis approach to produce activated carbon of improved quality.

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Why is it important?

Activated carbon with high BET surface area, total pore volume, carbon and fixed carbon contents was produced using hydroxide mixture as a chemical activating agent over a chemical impregnation ratio of 1.0, 700 W of microwave power, and 10 mins of microwave irradiation time. It showed a micro-mesoporous surface (i.e. small pores presence on large pores) with a high removal percentage (up to 90%) on malachite green dye. Our results demonstrated that the use of microwave pyrolysis combining with chemical activation using KOH/NaOH mixtures as chemical activating agent shows exceptional promise to produce AC as dye adsorbent.