Effect of background electrolytes and pH on the adsorption of Cu(II)/EDTA onto TiO 2

Abstract

Cu(II)/EDTA adsorption onto TiO 2 has been studied with a variation of pH, ionic strength, and type of background electrolytes. Cu(II) adsorption onto TiO 2 increased as ionic strength increased when NaClO 4 was used as a background electrolyte. This can be explained by the increase of exp ( − F Ψ / R T ) as a part of the electrostatic correction within a surface complexation model. Model predictions described experimental adsorption trends. Types of background anions (ClO 4, Cl, NO 2, NO 3, SO 3, and PO 4) did not affect adsorption trends and adsorption amounts of Cu(II) onto TiO 2. However, different trends were observed with various types of background ions used as ionic strength in EDTA and Cu(II)–EDTA adsorption. EDTA adsorption was decreased by using Na 2SO 3 and Na 3PO 4 as background ions, while NaClO 4, NaCl, NaNO 2, and NaNO 3 showed negligible interference on the EDTA adsorption, which matched well with model predictions. The presence Na 2SO 3 and Na 3PO 4 also interfered with Cu(II)–EDTA adsorption, to a somewhat greater extent compared to EDTA adsorption, especially at lower pH. This interference was also noted in Cu(II)–EDTA adsorption with a variation of Cu(II)–EDTA concentration at constant ionic strength ( 3 × 10 −3 M ) by using Na 2SO 3 and Na 3PO 4, especially at lower ratios of Cu(II)–EDTA to Na 2SO 3 and Na 3PO 4. These results suggest that the ratio of Cu(II)–EDTA to Na 2SO 3 and Na 3PO 4 is an important factor for the controlling of competition between these background ions and Cu(II)–EDTA onto TiO 2. Model prediction generally matched well with experimental adsorption using NaClO 4, NaCl, NaNO 2, and NaNO 3 as backgrounds ions, while a severe deviation was observed in the presence of Na 2SO 3 and Na 3PO 4. These results suggest that the mobility of copper ions as Cu(II)–EDTA can be increased from polluted area in the presence of multivalent background ions, especially as the ratio of adsorbates/background ions decreased.