Adsorption behavior of one-dimensional coordination polymers [Cu(bipy)X]n (X = 2Cl− and SO42−) toward acid orange 7 and methyl orange

Abstract

A kind of one-dimensional coordination polymer, [Cu(bipy)X]_n (X = 2Cl⁻ or SO₄²⁻), was prepared by Cu²⁺ and 4,4′-bipyridine (bipy) through a facile method, and used as the adsorbent for removal of acid orange 7 (AO7) and methyl orange (MO) from water. Two kinds of anions, chloride ion and sulfate ion, were tested as the counter ion in preparing the [Cu(bipy)Cl₂]_n and [Cu(bipy)(SO₄)]_n to balance the positive charge of [Cu(bipy)]_n²⁺, to research the impact of anions on the adsorption performance of the [Cu(bipy)]_n²⁺. Compared to [Cu(bipy)Cl₂]_n, [Cu(bipy)(SO₄)]_n can remove the dyes better both from the view of the adsorption capacity and adsorption kinetic constant. The MO can be more easily adsorbed than AO7 by both adsorbents. The adsorption capacity of [Cu(bipy)Cl₂]_n for AO7 and MO reached 848 mg g⁻¹ and 1084 mg g⁻¹, respectively. However, the adsorption capacity of [Cu(bipy)(SO₄)]_n for AO7 and MO reached 3308 mg g⁻¹ and 1521 mg g⁻¹, respectively. The dominant adsorption mechanism of the two adsorbent in removing dyes was found to be ionic exchange and the ultra high adsorption capacity of [Cu(bipy)(SO₄)]_n for AO7 was attributed to the two-step adsorption process which can be observed from the adsorption isotherm. The mechanism of the second adsorption step was speculated to be hydrophobic adsorption and π–π interaction.