RESUMO
To explore green gold leaching reagents, a series of imidazolium cyanate ionic liquids (ILs), 1-ethyl-3-methyl-imidazolium cyanate ([C2MIM][OCN]), 1-propyl-3-methyl-imidazolium cyanate ([C3MIM][OCN]) and 1-butyl-3-methyl-imidazolcyanate ([C4MIM][OCN]) were synthesized and characterized by Nuclear Magnetic Resonance (NMR), Fourier Transform Infrared Spectroscopy (FTIR) and thermogravimetric (TG) analysis. In this research, the imidazolium cyanates were utilized as a solute, which not only decreased the usage of ILs but also increased their gold dissolution capability. The gold dissolution performances of three imidazolium cyanates were characterized by dynamic leaching test and Scanning Electron Microscopy (SEM). The results show that the all three imidazolium cyanates had a gold dissolution ability, and the shorter the carbon chain on the imidazole ring in imidazolium cyanate, the faster the gold dissolution rate. The gold dissolution performance of [C2MIM][OCN] was the best, and the weight loss of gold leaf was 2.9 mg/cm2 at 40 °C after 120 h dissolution in [C2MIM][OCN] mixed with 10 wt. % water. Besides this, the gold dissolution rate increased with the increase in the concentration of imidazolium cyanates as well as the reaction temperature. The gold dissolution performances of imidazolium cyanates in different solvents including water, acetonitrile, dimethyl sulfoxide (DMSO) and dimethylformamide (DMF) were also investigated, and the weaker the polarity of the solvent, the more conducive it was to the gold dissolution reaction. The mechanism of gold dissolution by imidazolium cyanates was investigated through NMR spectroscopy and Electrospray Ionization Mass Spectrometry (ESI-MS). It was inferred that during the process of gold dissolution, Au was oxidized to Au+ and the imidazolium cations were deprotonated to form N-heterocyclic carbenes, which coordinated with gold to form gold complexes and achieve gold dissolution.
RESUMO
Graft modification is an effective approach to improve the water solubility and molecular weight of chitosan. This work investigated the effect of grafting rate on water solubility of chitosan-grafted polyacrylamide (Chi-g-PAM) using molecular dynamics simulations. The intramolecular and intermolecular interaction between Chi-g-PAM with the grafting rate of 100%-250% and water together with the conformation change were analyzed by radial distribution function (RDF), radius of gyration, solvation free energy (ΔGSFE), mean square displacement, diffusion coefficient and shear viscosity. The results showed that the intramolecular hydrogen bonding of Chi-g-PAM was the dominant factor affecting its water solubility. While the grafting rate of Chi-g-PAM increased from 100% to 250%, the RDF of Chi-g-PAM decreased from 5.39 to 3.57 between O-H at 2.0 Å and 2.60 to 1.30 between N-H at 2.1 Å. The interaction between Chi-g-PAM and water increased with grafting rate as the absolute value of ΔGSFE for Chi-g-PAM increased from 432.917 kcal/mol to 858.749 kcal/mol. The solubility of Chi-g-PAM in acidic solution was much better than that of Chi-g-PAM in aqueous solution. Our work on the fundamental insights into the effect of grafted molecular structure of chitosan-based copolymer on its solubility will benefit the development of environmentally friendly chitosan-based flocculants.
