title: Removal of sulfamethoxazole from solution by raw and chemically treated walnut shells.
abstract: OBJECTIVE
  The sorption of sulfamethoxazole, a frequently detected pharmaceutical compound in the environment, onto walnut shells was evaluated.
  
  
  METHODS
  The sorption proprieties of the raw sorbent were chemically modified and two additional samples were obtained, respectively HCl and NaOH treated. Scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and thermogravimetric (TG/DTG) techniques were applied to investigate the effect of the chemical treatments on the shell surface morphology and chemistry. Sorption experiments to investigate the pH effect on the process were carried out between pH 2 and 8.
  
  
  RESULTS
  The chemical treatment did not substantially alter the structure of the sorbent (physical and textural characteristics) but modified the surface chemistry of the sorbent (acid-base properties, point of zero charge-pH(pzc)). The solution pH influences both the sorbent's surface charge and sulfamethoxazole speciation. The best removal efficiencies were obtained for lower pH values where the neutral and cationic sulfamethoxazole forms are present in the solution. Langmuir and Freundlich isotherms were applied to the experimental adsorption data for sulfamethoxazole sorption at pH 2, 4, and 7 onto raw walnut shell. No statistical difference was found between the two models except for the pH 2 experimental data to which the Freundlich model fitted better.
  
  
  CONCLUSIONS
  Sorption of sulfamethoxazole was found to be highly pH dependent in the entire pH range studied and for both raw and treated sorbent.
authors: REQUIMTE/Departamento de Engenharia Química, Instituto Superior de Engenharia do Porto, Rua Dr. António Bernardino de Almeida 431, 4200-072 Porto, Portugal. slt@isep.ipp.pt
authors: Salomé
authors: S
authors: Teixeira
authors: Cristina
authors: C
authors: Delerue-Matos
authors: Lúcia
authors: L
authors: Santos
mesh_terms: D000327:Adsorption; D000890:Anti-Infective Agents / Q000032:analysis / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D031324:Juglans / Q000737:chemistry*; D008956:Models, Chemical; D013420:Sulfamethoxazole / Q000032:analysis / Q000737:chemistry*; D018508:Water Purification / Q000379:methods*
chemical_list: D000890:Anti-Infective Agents; D013420:Sulfamethoxazole