Microporous hydrophilic super-oxidized carbons with high surface area for removal of copper ions

Super-oxidized porous carbons produced from reduced graphene oxide have been demonstrated recently to show unique sorption properties. Here we report experiments with identical oxidative treatment applied to four very different types of porous carbon materials with extremely broad range of specific surface area (SSA) ∼350–3400 m2 g−1. It is demonstrated that KOH-activated carbons can be oxidized to the same degree as graphene oxide (GO) while preserving a larger part of SSA. Prolonged oxidation with ammonium persulfate resulted in extraordinary high degree of oxidation with C/O ratio reaching 2.1. Precursor carbons with largest share of micropores are found to be more stable against oxidative treatment, while single-walled carbon nanotubes (SWCNT's) are oxidized to much less extent. While mesopores collapse, micropores survive strong oxidation treatment providing materials with rather narrow pore size distribution and high (for given oxidation degree) BET SSA up to ∼1150 m2 g−1. Super-oxidized porous carbons (SOPC's) show a high abundance of hydroxyl, epoxide, carbonyl, and carboxyl functional groups (similar to GO). As a result of oxidation, the hydrophobic carbons are converted into hydrophilic materials. Characterization shows that many properties of SOPC (e.g. degree of oxidation, type of functional groups, thermal stability etc.) are rather similar to GO, except for three-dimensional porous structure which can be considered an advantage for sorbent applications. SOPC's demonstrate superior sorption capacity for Cu(II) (up to ∼105 mg g−1), which is 8-fold higher than the value for non-oxidized precursor.