Effect of oxidation of activated carbon on its enrichment efficiency of metal ions: comparison with oxidized and non-oxidized multi-walled carbon nanotubes

The effect of oxidation of activated carbon (AC) with various oxidizing agents (nitric acid, hydrogen peroxide, ammonium persulfate) on preconcentration of metal ions (Cr3+, Mn2+, Pb2+, Cu2+, Cd2+ and Zn2+) from environmental waters prior to their flame atomic absorption spectroscopic analysis was investigated. The highest recoveries and adsorption capacities towards metal ions were achieved when using nitric acid-oxidized AC (sorbent AC-NA) as preconcentrating sorbent at pH 9. A preconcentration procedure was optimized using AC-NA as sorbent, which was then compared with non-oxidized AC in terms of analytical performance of the preconcentration method. Higher sensitivity, lower detection limits and wider linear ranges were achieved when AC-NA was used. The analytical performance of the method using AC-NA as preconcentrating sorbent was also compared with nitric acid-oxidized multi-walled carbon nanotubes (sorbent MWCNT-NA) and non-oxidized multi-walled carbon nanotubes (sorbent MWCNT). The analytical performance of the preconcentration method using AC-NA was close to MWCNT-NA, but AC-NA was better than non-oxidized MWCNT. Application of the optimized preconcentration method (using AC-NA sorbent) to environmental waters (tap water, reservoir water, stream water) gave spike recoveries of the metals in the range 63-104%.