Synergistic effect of oxygen-containing functional groups and MnₓOᵧ for efficient CH 4 /N 2 separation on coconut-shell activated carbon

Abstract

A hydrothermal-modification strategy was adopted to anchor manganese oxide (Mn x O y ) nanoparticles over the coconut shell activated carbon (CSAC) for CH 4 /N 2 separation. Systematic investigations were carried out on the effects of type and amount of manganese salts on the adsorption performance. Dynamic breakthrough experiments showed that CSAC-KMnO 4 prepared by modification with KMnO 4 exhibited the optimal CH 4 adsorption performance with a breakthrough time of 131 s, which was approximately 40% longer than that of pristine CSAC. At 273 K and 100 kPa, its saturated CH 4 uptake was as high as 110.7 cm 3 g -1 , 2.92 times that of pristine CSAC.Comprehensive characterization techniques revealed that highly dispersed Mn x O y nanoparticles exhibited the mixed valence states of Mn 2+ /Mn 3+ , and their abundant unsaturated coordination adsorption sites induced polarization of CH 4 molecules, leading to enhanced van der Waals interaction and high adsorption capacity. Moreover, the strong oxidizing property of Mn 7+ could etch pores of the activated carbon skeleton, introducing more COOH, C=O and C-O-C groups, thereby further enhancing the polarity with increased CH 4 uptake. This work provided a new design pathway for high-efficient separation of CH 4 /N 2 .