Alkyl substituents of P,S,N-containing organic ligands influencing the uptake of Au3+ and Pt2+ ions over a hydrophobic hypercrosslinked polymeric sorbent

Abstract

To increase the uptake efficiency towards Au3+ and Pt2+ ions, a hydrophobic hypercrosslinked polymeric sorbent (Purosorb™ PAD600, Purolite®) was impregnated with P,S,N-containing organic ligands: diethyldithiophosphoric acid (DEDTP), diisopropyldithiophosphoric acid (DIPDTP), diisobutyldithiophosphoric acid (DIBDTP), and 2-amine-1-methylbenzimidazole (MAB). Two stable polymorphs of 2-amino-1-methylbenzoazolium chloride monohydrate were formed and structurally analyzed by X-ray diffraction. The successful impregnation of organic ligands on the polymeric sorbent was confirmed by SEM, EDS and FTIR spectroscopy. The impregnation of the selected organic ligands significantly increased the uptake efficiency for Au3+ and Pt2+ ions of the polymeric sorbent. The uptake of Au3+ and Pt2+ ions is spontaneous, exothermic and obeys a pseudo-second-order kinetics, suggesting a complex uptake mechanism that includes a precipitation process dominating over both physical adsorption and strong chemical interaction. The highest uptake rates for Au3+ and Pt2+ ions were observed with PAD600-DIPDTP (3.71 mmol g−1) and PAD600-MAB (1.57 mmol g−1), respectively. The uptake ability of the selected organic ligands is discussed based on their electronic structure and type of alkyl groups, number and nature of donor atoms, hydrophobic and stereochemical parameters, chelate formation, possibility of the formation of poorly soluble compounds, dissociation constant, acid-base properties and synthesis conditions (pH, temperature, concentration, etc.). A complete desorption (>99%) of Au3+ and Pt2+ ions was achieved by introducing 60 mg L−1 of SC(NH2)2 solution (0.3 M H2SO4). The uptake efficiency of the Au3+ and Pt2+ ion was decreased by 10% in six successive adsorption–desorption cyclic runs due to the release of the impregnated organic ligands into the aqueous solution. The inexpensive, efficient and recyclable sorbents could be used for the uptake of various noble metals.