Activation and adsorption performance of sewage sludge carbon for CO2: unusual enhancement effect of HF treatment?

Environmental Science: Nano Pub Date: 2021-05-07 DOI: 10.1039/D1EN00037C

Abstract

To understand the dependence of activation processes of sludge carbons on CO2 adsorption, five sludge carbons (SC1–SC5) were prepared by direct pyrolysis, pyrolysis–citric acid (CA) activation, pyrolysis–(CA + ZnCl2) activation, pyrolysis–(CA + ZnCl2 + KOH) activation and pyrolysis–(CA + ZnCl2 + KOH)–HF activation, respectively. It was unexpectedly found that the features of SC5 were very different from the others. Its specific surface area reached as high as 2654 mg g?1, being 4.2, 12.0, 71.5 and 88.4 fold that of SC4, SC3, SC2 and SC1, correspondingly. Moreover, many ultramicropores and C–F groups were formed, in addition to the intended desilication. These microstructural changes lead to a great adsorption capacity of 215.2 mg g?1 for CO2, which was 2.5, 8.9, 26.9 and 40.6 fold that of SC4, SC3, SC2 and SC1, respectively. The significant increase of the surface area was attributed to the combined activation effect of HF chemical etching on SC and the expansion of d002 interlayers of SC due to the physical action of SiF4 gas in HF activation. And, the enhancement of CO2 adsorption was demonstrated to be due to the formation of extensive CO2-philic expanded interlayer space-type micropores and C–F functional groups in SC5 activated by HF.

Graphical abstract: Activation and adsorption performance of sewage sludge carbon for CO2: unusual enhancement effect of HF treatment
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