Multishell structured magnetic nanocomposites carrying a copolymer of pyrrole–thiophene for highly selective Au(iii) recovery

Abstract

Magnetic nanocomposites with surface containing multiform heteroatoms have great potential for metal-ion recovery with a high throughput. In this paper, a copolymer of pyrrole–thiophene (cPPyTh) is formed upon the Fe₃O₄/SiO₂ composite through chemical oxidation polymerization in aqueous medium, using a modified Fenton reagent (FeCl₃ plus H₂O₂) as the oxidant. The resulting Fe₃O₄/SiO₂/cPPyTh nanocomposites exhibit an enhanced acid resistance and an excellent adsorption performance for Au(III) recovery from multiionic aqueous solution. At room temperature, the adsorption capacity of Fe₃O₄/SiO₂/cPPyTh toward Au(III) can dramatically increase to 559.7 mg g⁻¹ within 5 min, and finally reach an equilibrium adsorption capacity of 845.9 mg g⁻¹. Also, Fe₃O₄/SiO₂/cPPyTh exhibits highly selective adsorption toward Au(III) versus interfering ions (Mg(II), Cu(II), Zn(II), As(V), Cd(II), and Pb(II)). After consecutive use for five times, the adsorption/recovery percentages of Au(III) from multiionic solution with Fe₃O₄/SiO₂/cPPyTh retain 93.3%/92.3%, showing a good reusability of the adsorbent. Compared with that of Fe₃O₄/SiO₂/polypyrrole, Fe₃O₄/SiO₂/polythiophene, and many other adsorbents in recent reports, the superior adsorption performance of Fe₃O₄/SiO₂/cPPyTh is attributed to the following facts: (i) the lowest unoccupied molecular orbital energy level with a relatively high upper band for cPPyTh is beneficial for Au(III) recovery upon Fe₃O₄/SiO₂/cPPyTh through an adsorption–reduction mechanism; (ii) the synergistic effect offered by the lower oxidation potential of pyrrole compared with thiophene but the higher affinity of S to gold ion species compared with N.