Nitrogen configuration enriched N-doped activated carbon from spent tea leaves through an ammonia impregnation approach for CO2 adsorption

Abstract

An N configuration enriched N-doped activated carbon adsorbent was successfully synthesised using an ammonia-induced N impregnation step with spent tea leaves (STLs) as a carbon precursor. In this study, activated carbon (AC) has been synthesized using a two-step H₃PO₄ activation method. SEM, Raman spectroscopy, N₂ physisorption, ultimate elemental analysis, and XPS were employed to characterise the physicochemical features of the prepared adsorbent. According to the characterisation analysis, the characteristics of the prepared adsorbent solely (either high in the surface area or N-content) are not sufficient enough to achieve good uptake capacity, and this has been demonstrated using the un-doped AC (AC) and commercialised AC (CAC) with a high surface area and N-doped biochar (NC) with a high N content. Through a volumetric adsorption step, it was revealed that the N-doped AC (NA773C) exhibited an improved CO₂ adsorption uptake capacity of 2.66 mmol g⁻¹, which is about 78%, 400%, and 177% higher than those of NC, AC and CAC, respectively, at 298 K and under atmospheric pressure conditions. With the results obtained from the characterisation analysis, it was found that a high surface area, along with a high N–C composition possessed by NA773C compared to those of other adsorbents endowed it with a high CO₂ uptake capacity.