Chapter 1. Part I Hydrophobic Effects of o-Phenanthroline and 2, 2'-Bipyridine on Adsorption of Metal(II) Ions onto Silica Gel Surface
The effects of o-phenanthroline and 2,2'-bipyridine on the adsorption of metal(II) (Fe, Co, Ni and Cu) ions onto silica gel surface have been studied. The adsorption is expressed in terms of the measured concentrations of both metal and ligand at equilibrium. Each adsorption of the four metal ions is increased with the presence of the ligands. In addition, adsorption increases slowly with pH at low pH values and then increases rapidly up to near $pK_a$ value of silica gel (=6.5). The adsorption of each metal ion at low pH is increased with increased ligand concentration. However, at high pH the adsorptions of Fe(II) and Cu(II) are decreased with increased ligand concentration whereas the adsorptions of Co(II) and Ni(II) are always increased. At low pH values the ligand to metal ratio adsorbed on the silica gel surface is ca. 3:1 while at high pH values it is 1:1, 2:1, and 3:1, corresponding to the initial ligand to metal ion concentration ratio. The addition of ethanol to the phenanthroline-$SiO_2$ solution results in a decrease in the adsorption of phenanthroline. The effect of ethanol is also observed in the Fe(II)-phenanthroline-$SiO_2$ system. The behavior of the adsorption is interpreted qualitatively by hydrophobic expulsion, the formation of surface complexes, and electrostatic interaction. It is concluded that hydrophobic expulsion plays an important role in the adsorption of metal ions in the presence of hydrophobic ligands on silica gel surface.
Chapter 1. Part II Effects of complexing Ligands on Copper adsorption onto Silica Gel Surface
The effect of complexing ligands on the adsorption of Cu(II) was investigated from aqueous solution on silica gel. The ligands used were hydrophobic ionizable organic compounds such as terpyridine, pyridine, lutidine, aminomethyl pyridine, pyridine methanol, and picolinic acid, in addition to salicylic- and sulfosalicylic acid. In the absence of $Cu^{2+}$ ions, the adsorption of these hydrophobic ligands varied with pH. For terpyridine, pyridine and lutidine, adsorption maxima occurred near their respective $pK_a$ values and were mainly due to ion exchange reaction. In addition, the adsorption of these ligands at low pH was strongly attributed to hydrophobic interaction. The adsorption of aminomethyl pyridine increased with increasing pH over the entire pH ranges investigated. Picolinic acid was adsorbed mainly by hydrogen bonding either through N atom at low pH or through O atom at high pH. Pyridine methanol was adsorbed by hydrophobic interaction at low pH and by hydrogen bonding at high pH. For salicylic- and sulfosalicylic acid, the adsorption was very small over the entire pH ranges investigated.
The adsorption of Cu(II) was strongly affected by the presence of ligand. It was conspicuously enhanced for terpyridine, aminomethyl pyridine, and pyridine methanol, whereas it was attenuated for picolinic acid, salicylic acid, and sulfosalicylic acid. This effect of ligand was explained in terms of either the formation of ternary surface complex for the enhancement or the competition of dissolved ligands and silanol group toward $Cu^{2+}$ ions for the attenuation. For pyridine and lutidine, the adsorption of Cu(II) at low pH was explained by the formation of type B ternary surface complex. For pyridine methanol, the formation of cyclic ternary surface complex was proposed. The Stern model was used to model the adsorption data.
Chapter 2. Part I Europium(III) Luminescence Excitation Spectroscopy: Probe of Metal Ion Binding Sites of Macromolecules
The trivalent europium ($Eu^{3+}$) luminescence spectroscopy was applied to the investigation of metal binding sites in complex ligands. $Eu^{3+}$ is luminescent in aqueous solution and largely retains its luminescence even when it is bound by complex ligand system. Furthermore, it has strong affinity for water which is displaced only by negatively charged ligands such as deprotonated carboxylate moieties. Since $^7F_0$→$^5D_0$ $Eu^{3+}$ excitation spectra show one-to-one correspondence between the number of peaks in the spectra and the number of $Eu^{3+}$ species, these excitation spectra were used as luminescence probes of metal ion binding sites. The excitation spectra of Eu(III)-acetate complexes with the different L to M ratios were obtained and deconvoluted. It is found that three Eu(III)-acetate species can be present in equilibrium. The excitation spectra of several ligands and synthetic polymers having carboxylate groups were also obtained in a similar manner. It is interesting to note that the measurements of the luminescence lifetime for both poly acrylic acid and poly vinyl benzoic acid could give a good estimation of the primary water coordination number of $Eu^{3+}$. The $Eu^{3+}$ $^7F_0$→$^5D_0$ excitation spectra of Eu(III)-humate showed a somewhat broader single peak centered around 579.28 mm, suggesting that carboxylate groups are the major binding sites.
Chapter 2. Part II Development of Laser-induced Photoacoustic Spectroscopy (LPAS) for the speciation of Trace Elements in Aqueous Solutions
The performance of laser induced photoacoustic spectroscopy (LPAS) system constructed in our laboratory was tested. In this work, the experimental set-up was described. The linear correlation of PA signal to laser pulse energy was found to be in good agreement with theoretical considerations. The application of our LPAS system to aqueous $Pr^{3+}$ ion suggests that the minimal absorbance detectable for $Pr^{3+}$ ion is 4.3×$10^{-5}cm^{-1}$ at 588.8 nm, implying that the average accuracy obtained in the investigation for $Pr^{3+}$ ion corresponds to about 3% of water absorption at 588.8 nm. The average accuracy of 3% obtained with our LPAS system corresponds to able to detect an $Am^{3+}$ concentration of 2×$10^{-8}$ mol/L (ε=$400Lmol^{-1}cm^{-1}$t 503 nm) when the absorbance of water is about 2.6×$10^{-4}cm^{-1}$ at 503 nm. From this detectability, it is expected that the LPAS constructed in our laboratory can be applied to the speciation of transuranium elements in aqueous solutions.
본 연구에서는 레이저유도 광음향 분광기를 구성하고 이에 대한 성능시험을 수행하였다. 기기의 구성 및 단위 구성기기의 제작에 관한 상세한 내용이 기술되어 있으며, 구성된 기기의 측정감도가 기존의 일반적인 흡수분광기로 얻을 수 있는 것과 비교했을 때 100배 이상 높은 것으로 나타났다. 구성기기의 성능시험은 우선 오실로스코프를 사용하여 광음향신호가 측정되는지를 확인하였고, 레이저 펄스 에너지에 따른 광음향신호의 비례관계를 확인하였다. 측정감도에 대한 시험결과, $Pr^{3+}$ 이온용액을 사용하여 최저로 측정할 수 있는 흡수계수는 588.8nm에서 $4.3×10^{-5}cm^{-1}$였다. 이러한 측정감도는 물에 의한 광흡수로부터 발생되는 광음향신호의 약 3% 에 해당하는 시료의 광음향 신호까지를 측정할 수 있다는 의미로서, 이를 $Am^{3+}$ 이온 용액에 적용할 경우, 503nm 에서 몰흡광도가 $400 Lmol^{-1} cm^{-1}$ 이므로 측정가능한 $Am^{3+}$ 의 농도는 $2×10^{-8}$ mol/L 에 해당한다. 이는 국외에서 개발된 기기의 측정감도와 대등한 수준이었다.
본 연구 결과, 구성된 레이저유도광음향분광기기는 지하수중에 미량으로 존재하는 화학종의 화학적 상태 및 농도를 측정하는데 적용될 수 있음을 확인하였다.
