Surface Modification of Porous Carbon Nanomaterials for Water Vapor Adsorption

In order to make porous carbon nanomaterial more suitable for the adsorption thermal energy storage field, it is necessary to modify the carbon nanomaterial to enhance water vapor adsorption capacity. This work investigated the influence of anionic surfactant sodium dodecylbenzenesulfonate (SDBS) modification on the physicochemical properties of coffee-shell carbon nanomaterials (CCNMs). The physicochemical properties of carbon nanomaterials were characterized. Water vapor adsorption isotherm, thermodynamics, and kinetics were analyzed to investigate further adsorption behavior over the CCNMs. The results suggest that the highest adsorption capacity of water vapor for modified CCNM (SDBS-CCNM) is up to 833.2 mg/g, with 2% SDBS mass fraction, 500 degrees C calcination temperature, and 30 min calcination time. However, its BET specific surface area and average pore size are only 2018 m2/g and 1.915 nm, respectively. On the other hand, the modification improved the amount of total surface oxygen-containing functional groups (SOFGs), mainly phenolic hydroxyl of SDBS-CCNM, compared with unmodified CCNM, which is conducive to water vapor adsorption on SDBS-CCNM under lower relative pressure. And water contact angles are less than 34 degrees. Furthermore, the dynamic adsorption process of water vapor on CCNMs was described by the Bangham model, which suggests that surface adsorption center sites of SDBS-CCNMs play a significant role in the water vapor adsorption process under lower relative pressure. As relative pressure increases, water molecules form clusters around the water molecules previously adsorbed at the active site through hydrogen-bonding interaction. When the clusters are large enough, water molecules begin to fill the pores of the CCNMs until the adsorption process becomes saturated. All the above results indicate that carbon nanomaterials are hydrophilic. Thus, the modified CCNM obtained in the present work can be a potential carbon nanomaterial with an excellent adsorption capacity for adsorption thermal energy storage.