Jiugang Hu

Microscopic Insights into Extraction Mechanism of Copper(II) in Ammoniacal Solutions Studied by X-ray Absorption Spectroscopy and Density Functional Theory Calculation

A microscopic investigation on the extraction process of copper(II) in ammoniacal solutions has been performed by X-ray absorption spectroscopy (XAS) and density functional theory (DFT) calculation. The structural change of copper(II) species in ammoniacal solution has been derived from X-ray absorption near-edge spectroscopy (XANES) by principal component analysis and linear combination fitting. It was found that the coordination structure of the extracted copper complex in the organic phases is planar square and independent of the aqueous pH, whereas the geometries of copper(II) species in ammoniacal solutions changed from axially elongated octahedron to distorted planar square with increase of pH. The coordination geometry and structural parameters of copper(II) species were further obtained by extended X-ray absorption fine structure (EXAFS) fitting and DFT calculation with the B3LYP functional. These results reveal that the formation of tetracoordinated copper(II) ammine species can evidently inhibit the copper extraction reaction. Thus, the extraction mechanism of copper(II) in ammoniacal solutions has been elucidated in view of the microscopic structural aspects of copper species in both organic phase and ammoniacal solutions.

Hydrophobic ligand-mediated hierarchical Cu nanoparticles on reduced graphene oxides for SERS platform

Hierarchical Cu nanoparticles/rGO (CuNPs/rGO) composites were synthesized through the kinetic reaction mediated by hydrophobic methyl trioctyl ammonium chloride (A336) and 2-hydroxy-5-nonyl-acetophenone oxime (LIX84I). The CuNPs/rGO composites were characterized by scanning electron microscopy (SEM), transmission electron microscope (TEM), and X-ray diffraction (XRD), and used as substrates for surface-enhanced Raman scattering (SERS) measurements. The hierarchical CuNPs/rGO composites formed with A336 were assemblies of Cu nanosubunits with a crystal size of 5–10 nm and some observable pinholes, whereas compact Cu nanospheres and nanorods on rGO sheets were formed with LIX84I. Therefore, a hydrophobic ligand-mediated kinetic mechanism was proposed. A synergetic effect on SERS performance was observed for CuNPs/rGO composites and the ratio between CuNPs and rGO was optimized. Moreover, the SERS activity of CuNPs/rGO-A336 was much stronger than CuNPs/rGO-LIX84I owing to the hierarchical structure of CuNPs/rGO-A336. For the CuNPs/rGO-A336 substrate, the detection limit reached 10−8 mol L−1 for R6G molecules, and quantitative SERS analysis was achieved. The CuNPs/rGO-A336 substrate showed good reproducibility and a high enhancement factor of 2.75 × 106, which is superior to other Cu-based substrates in the literature.

Investigation of intermolecular interactions of mixed extractants of quaternary phosphonium or ammonium chlorides and bis(2,4,4-ethylhexyl)phosphoric acid for metal separation

Mixed extractants composed of di(2-ethylhexyl)phosphoric acid (P204) and ionic liquids (trihexyl(tetradecyl)phosphonium chloride (IL101) or methyltrioctylammonium chloride (A336)) for Zn(II)/Cu(II) separation were investigated. An antagonistic effect can be found for the extraction of both zinc and copper when mixing ionic liquids with P204, especially for Cu(II), thus the Zn(II)/Cu(II) separation can be greatly improved by adjusting the kinds and mole fractions of ionic liquids in the mixed extractants. Attenuated total reflection infrared (ATR-IR) and nuclear magnetic resonance (NMR) spectroscopies elucidate that the diverse intermolecular interactions between P204 and ionic liquids can be tailored by changing their compositions. Two-dimensional correlation analysis on IR spectra further extracts the overlapped structural information of the mixed extractants. And the dependence of metal extraction on intermolecular interactions has been elucidated.

Structural insights into the extraction mechanism of cobalt(II) with dinonylnaphthalene sulfonic acid and 2-ethylhexyl 4-pyridinecarboxylate ester

Abstract In this work, to elucidate the synergistic extraction mechanism of cobalt(II) with dinonylnaphthalene sulfonic acid (HDNNS) and 2-ethylhexyl 4-pyridinecarboxylate ester (L), hexaaquacobalt(II) naphthalene-2-sulfonate (compound 1) was prepared using naphthalene-2-sulfonic acid (HNS, the short chain analog of HDNNS) and di-methyl isonicotinate tetraaquacobalt(II) naphthalene-2-sulfonate (compound 2) was prepared using methyl isonicotinate (LI, a short chain analog of 2-ethylhexyl 4-pyridinecarboxylate ester) and HNS; the compounds were studied by single crystal X-ray diffraction. Moreover, 2 and the actual extracted cobalt(II) complex were further investigated by Fourier transform infrared spectroscopy (FT-IR) and electrospray ionization mass spectrometry (ESI-MS). The results indicated that the actual extracted cobalt(II) complex possesses a similar coordination structure as 2. Combined with the results obtained by single crystal X-ray diffraction of 1 and 2, FT-IR and ESI-MS of 2 and the actual extracted cobalt(II) complex, it is reasonable to conclude that the extracted cobalt(II) complex with the actual synergistic mixture is much more stable than the cobalt(II) complex with HDNNS alone. Therefore, the extraction selectivity cobalt(II) is effectively enhanced with the addition of 2-ethylhexyl 4-pyridinecarboxylate ester to HDNNS.

Twinned copper nanoparticles modulated with electrochemical deposition for in situ SERS monitoring

The earth-abundant copper nanoparticles were synthesized on glass carbon electrode as SERS substrate by electrochemical deposition method. Both deposition potential and time were used to modulate the microstructure and SERS activity of copper electrodeposits. The aggregation and evolution behaviors of the deposited copper nanoparticles were elucidated. An interesting dependence of SERS activity on the obtained copper deposits was observed. When deposition potential becomes more negative, the SERS activity of the copper deposits obtained at 150 s diminishes gradually until it reaches to a minimum value at −0.8 V, and then dramatically strengthens again. However, the SERS activity of copper deposits obtained at −0.9 V rapidly is enhanced as deposition time increases and reaches to a maximum value at about 150 s, then gradually weakens and even vanishes at 900 s. The SERS performance of Cu nanoparticles depends on their grain size and the intergranular gaps, which are able to offer “hot spots” for Raman enhancement. Especially, the formed peanut-like Cu nanoparticles are advantageous for the reliable and reproducible SERS detection. Owing to their good SERS activity and potential catalytic property, the copper deposits are successfully employed to in situ monitoring of the electrocatalytic reduction process of nitrate.

Insights into the extraction mechanism from the coordination chemistry of copper(II) with a synergistic mixture which mimics Versatic10 and 2-ethylhexyl 4-pyridinecarboxylate ester

Abstract In the present work, a copper(II) synergist complex with methyl isonicotinate (LI, a short chain analog of 2-ethylhexyl 4-pyridinecarboxylate ester) and isobutyric acid (HBI, a short chain analog of Versatic10) was synthesized and studied by X-ray single-crystal diffraction. The results indicated that the copper(II) synergist complex obtained with isobutyric acid and methyl isonicotinate crystallizes in the monoclinic C2/c space group and confirmed the composition [Cu(BI)2(LI)]2. The crystal structure consisted of centrosymmetric dimeric units, in which the two Cu ions are bridged in pairs by four carboxylate groups of the deprotonated isobutyric acid. In order to bridge the gap between the solid-state structure of the copper(II) synergist complex obtained with isobutyric acid and methyl isonicotinate and the solution structure of the extracted copper(II) complex in the non-polar organic phase, the two copper(II) complexes were further investigated by Fourier transform infrared spectroscopy (FT-IR) and electrospray ionization mass spectrometry (ESI-MS). The results indicated that the extracted copper(II) complex in the non-polar organic phase has a similar coordination structure as the copper(II) synergist complex obtained with isobutyric acid and methyl isonicotinate.