Chemical activation of cotton fibers with varied regents induces distinct morphology of activated carbon and adsorption capacity of methylene blue.

Some biomasses like cotton contain natural fibrous structures. This is a desirable structural feature for exposure of adsorption sites on cotton-derived activated carbon (AC). This was verified herein by conducting activation of cotton with ZnCl2, H3PO4, K2C2O4, or KOH, probing whether structural transformation during activation could be confined inside a cotton fiber. The results indicated that ZnCl2 showed the highest capability for generating pores (1432.8 m2·g-1), especially mesopores (> 50 %). This resulted from its highest activity for catalyzing the aromatization reactions associated with deoxygenation during the activation (C/O of 13.1 versus C/O of ca. 3.6 for counterparts). The intensive cracking from the potassium activators interfered with aromatization, retaining more oxygen but diminished pore development (ca. 1000 m2·g-1), especially mesopores (< 7 %). Furthermore, ZnCl2 catalyzed condensation of intermediates bearing CO and C-O-C, but KOH or K2C2O4 could not. ZnCl2 activation retained the fibrous structure of resulting activated carbon but induced the merge of fiber with the help of the formed reactive carbon cation, while H3PO4 led to the full deformation of fibers. Reactive "fiber intermediates" could also form in activation with KOH but not with K2C2O4, as K2C2O4 only catalyzed the transformation of inner structures. This work supports cotton pretreatment and chemical activation as a promising technique for creating porous AC with high adsorption capacity.