Distinct adsorption enhancement of bi-component metals (cobalt and nickel) by Fireweed-derived carbon compared to activated carbon: Incorporation of surface group distributions for increased efficiency

The aim of this research is to report the superior capability of Fireweed (Chamerion angustifolium) carbons to adsorb metal ions, a distinct improvement compared to commercially available powdered activated carbon (PAC). The performance of three different carbons (PAC, AFWC and FWC, or amine-modified and unmodified Fireweed carbon) in the uptake of cobalt and nickel ions (Co(II) and Ni(II)) was studied and the efficacy of the carbons synthesized from Fireweed leaves was compared with that of PAC. The impact of the characteristics of the carbon on adsorption showed that surface group distributions were the prime factor in increased efficiency. AFWC demonstrated a distinct enhancement of adsorption and Langmuir capacity data showed a significant three- and fivefold increase in comparison to FWC and PAC, respectively. Pseudo second order kinetic curves indicated the rate limiting step could be chemisorption due to suspended amine-surface groups on AFWC. Interestingly, adsorption decreased with increasing ionic strength of the aqueous solution from 0.0095 to 0.95M (as NaCl) for AFWC, whereas adsorption increased with increasing ionic strength for FWC and PAC. An acidic eluent (1M HNO₃) desorbed ~97% of metal ions and phosphate oxyanion showed the least interference for AFWC samples. Evidence for an adsorption controlled mechanism was plausibly explained with analytical and spectroscopic techniques including X-ray photoelectron spectroscopy and thermal stability identified with differential scanning calorimetry thermogravimetric analysis. The results indicate the advantages of Fireweed carbons over PAC and open up the possibility of rapid and inexpensive materials processing to extract industrially important metals from water.