Functional Starch and Applications in Food by Unknown

Author:Unknown
Language: eng
Format: epub
ISBN: 9789811310775
Publisher: Springer Singapore

4.4.2.2 Chemical Activation

Compared with physical activation, chemical activation is the preferred method to obtain high-performance porous carbon from different materials. The most commonly used chemical activation agents are KOH, NaOH, H3PO4, ZnCl2, K2CO3, and Na2CO3 [44, 61–64]. During the preparation of supercapacitors from cationic starch using KOH, ZnCl2, and ZnCl2/CO2 activation, hysteresis is mainly due to factors such as the asymmetric slit-shape pores and the presence of ink bottle-type pores [65]. In addition, KOH-activated starch is quite different to the others in terms of its surface morphology characteristics, as it has a number of shallow concave round pores on the surface, which may be suitable for ion mobility and storage. H3PO4 is the preferred chemical activator as the activation conditions are milder. H3PO4 can be recovered, and the corresponding porous carbon has a high yield and well-developed pore structure. When starch was directly impregnated with H3PO4, starch particles assembled together, and H3PO4 interacted with them to form phosphate and polyphosphate bridges. The pores were generated through dehydration reactions between acid molecules upon heating. The pore structures were created by the insertion of phosphate groups during the dilation processes [66].

High concentrations of acid and base are usually used to destroy the intermolecular hydrogen bond interactions and crystallization regions, which then facilitates the chemical reaction between the starch and modifiers [67]. A base can weaken the intermolecular interactions of the starch molecules and facilitate the reaction between starch and modifiers. When the modifier/starch mole ratio was increased, the porous structure was maintained, and when the NaOH concentration was increased to a high level, the porous structure was destroyed and disappeared [68].

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