Activated carbon produced from paulownia sawdust for high-performance CO2 sorbents

Carbon dioxide is a major green house gas emitted by the combustion of fossil fuels (coal, oil and natural gas) in industrial plants [1], [2]. Therefore the control of anthropogenic CO₂ emissions is a crucial matter for its significant role in global climate change. In recent years, much research has been directed toward the development of new technologies for CO₂ capture and its storage [3]. For the capture of CO₂, traditional technologies mainly include absorption and adsorption-coupled membrane separation. Adsorption processes using novel solid sorbents capable of reversibly capturing CO₂ have many potential advantages, such as reduced energy for regeneration, great capacity, excellent selectivity, ease operability, etc. [4]. Up to now, several kinds of solid adsorbents have been investigated, which include carbonaceous adsorbents [5], [6], zeolites and mesoporous silicates [7], [8], organic solids [9], and metal-organic frameworks [10], [11]. Among them, carbonaceous adsorbents, especially porous activated carbons (ACs), have already been highlighted owing to their high specific surface area, excellent thermal and chemical stability, easy-to-design pore structure, and low energy requirements for regeneration [12], [13], [14]. It is well known that ACs can be prepared by pyrolysis from a wide range of different carbon-containing source materials [15]. So far, many biomass-derived ACs, such as from bamboo [14], sawdust [16], algae [17], wood [18], celtuce leaves [19], carpet [20], anthracites [21], etc., have been prepared by carbonization and activation for CO₂ adsorption. However, it should be noted that the preparation of many of the biomass-derived ACs involves two-step processes consisting of carbonization and subsequent activation, and they still display the unsatisfied CO₂ absorption capacity (normally lower than 6.0 mmol/g) at 0 °C [16].

In this work, porous ACs with high specific surface areas and abundant micropores were prepared using porous paulownia sawdust as the carbon precursor via a simple one-step carbonization-activation. Also, the effects of the preparation parameters (the mass ratio between KOH activator and paulownia sawdust, the activation temperature and the activation time) on the porous structures of as-made ACs and the corresponding CO₂ absorption capacity were investigated. The results show that the AC prepared at the optimized conditions (the mass ratio is 4, the activation temperature is 700 °C at the activation time is 1 h) has the most micropores, enabling the maximum CO₂ uptake of 8.0 mmol/g at 0 °C and 1 bar. However, the highest CO₂ adsorption capacities reported for activated carbon under ambient conditions is 8.9 mmol g at 0 °C [22].