Effects of Alkali/Char Ratio and Activation Temperature on Ultramicropores of Rice Husk Active Carbon

doi:10.15541/jim20140251

Abstract

Abstract:

Porous carbons were prepared by KOH activation of rice husk char at alkali/char ratios of 0.6︰1 to 3︰1 and activation temperatures from 640℃ to 780 ℃. The obtained porous carbons were characterized using N₂ adsorption and desorption technique, CO₂ adsorption, TG-FTIR analyses. The results indicate that the ultramicropore size of the prepared porous carbons is mostly in the range of 0.42-0.70 nm. As the alkali/char ratio increases, the volume of ultramicropores first rises and then diminishes, whereas the volume of ultramicropores tends to decrease monotonously with the increase of activation temperature. A microporous carbon with ultramicropore volume of 0.149 mL/g, ultramicropore fraction of 36.3%, pore volume of 0.411 mL/g, and specific surface area of 774 m²/g, can be produced by activation at 640℃ at the alkali/char ratio of 1︰1. The ultramicropore volume of the porous carbons and their CO₂ uptake at 10⁴Pa display a strong linear relationship.

Key words: active carbon, ultramicropore, KOH, rice husk

CLC Number:

TQ424

LI Da-Wei, MA Teng-Fei, TIAN Yuan-Yu, ZHU Xi-Feng, QIAO Ying-Yun. Effects of Alkali/Char Ratio and Activation Temperature on Ultramicropores of Rice Husk Active Carbon[J]. Journal of Inorganic Materials, 2015, 30(1): 17-22.

Figures/Tables 6

Fig. 1 Characterizations for rice husk char and active carbons. (a) N2 adsorption/desorption isotherms; (b) Mesopore size distribution; (c) SEM image of rice husk char; (d) SEM image of K3-780

Table 1 Textural properties of rice husk char and active carbons

	Sample	S_BET / (m²·g^-1)	V_t / (cm³·g^-1)	V_micro / (cm³·g^-1)	V_meso / (cm³·g^-1)	V_{<0.7 nm} / (cm³·g^-1)	V_{<1 nm} / (cm³·g^-1)	(V_micro / V_t) /%	(V_{<0.7 nm} / V_t) /%
	RHC	114	0.069	0.051	0.018	—	—	—	—
Effects of KOH/char ratio	K0.6-780	678	0.359	0.262	0.097	0.120	0.156	73.0	33.4
	K1-780	1199	0.600	0.479	0.121	0.139	0.196	79.8	23.1
	K2-780	1842	0.828	0.802	0.026	0.088	0.126	96.9	10.6
	K3-780	2695	1.137	1.106	0.031	0.078	0.117	97.3	6.9
Effects of activation temperature	K1-640	774	0.411	0.302	0.109	0.149	0.190	73.5	36.3
	K1-710	1041	0.527	0.422	0.105	0.149	0.202	80.1	28.3
	K1-780	1199	0.600	0.479	0.121	0.139	0.196	79.8	23.1

Fig. 2 Effects of alkali/char ratio on pore size distributions of ultramicropores of active carbons

Fig. 3 Effects of activation temperature on pore size distributions of ultramicropores of active carbons

Fig. 4 Effects of heating temperature on mass and gaseous products of rice husk char (RHC) and KOH-containing char. (a) Thermogravimetric curves; FTIR spectra of gaseous products released at heating temperatures of 640℃(b), 710℃(c) and 780℃(d)

Fig. 5 Relation between ultramicropore volume and CO2 uptake at 104 Pa

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