Huang Kun, Qi Jian, Liu Xue-xin, Liu Yu-feng, Li Wei-hong, Yang Zhan-lan, Weng Shi-fu, Xu Yi-zhuang, Wu Jin-guang
College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China.
Guang Pu Xue Yu Guang Pu Fen Xi. 2008 Sep;28(9):2038-43.
The formation of W/O microemulsions in the extraction system TBP-Pd(II)-HCl was investigated. The solution structural evolution of the palladium loaded organic phases, with the variation in the content of acid into the organic phases, was characterized by various spectroscopic techniques such as DLS, FTIR and 31P-/1H NMR. The results indicated that (1) the extraction behaviors of palladium was related to the formation of W/O microemulsion structure in the loaded organic solutions. Because of the co-extraction of hydrochloric acid, there formed the microscopic aggregates in the loaded organic phases. (2) The variation in the HCl content in organic phase resulted in corresponding changes in solution structure. With the increase in the HCl content, the average radii of nanoscopic aggregates in the organic phases increased and then decreased. The extraction of HCl into the organic phase exhibited a distinct impact on the O-H stretching vibration and O-H-O bending vibration of water molecules in the microscopic W/O micelles. FTIR spectra of the organic phase saturated with acids show that the broad band of O-H stretching vibration of water extended to a very wide range and overlaped with the C-H stretching vibration bands. The higher the acid concentration in the organic phase was, the greater the overlapping. On the other hand, it was also observed that a remarkable change appeared in the O-H-O bending vibration of water and the stretching vibration of P=O in TBP molecules shifted to lower frequency. With the increase in acid content in the TBP organic phases, the observed 31P NMR chemical shifts decreased and varied to up-field; whereas the 1H NMR chemical shift of H+ increased and even became larger than that of deuterium chloride-d at a lower frequency field. The changes in delta 31P to opposite direction of delta H+ means that TBP molecules were associated with acid protons and water molecules in microemulsion pools to form RP=O x H+ or RP=O x H3O+, and then interacted with PdCl4(2-) complex ions, which finally led to the extraction of palladium into the organic phase. (3) When forming the W/O reversed micelles/microemulsions, the concentration of acid within the microscopic micelles was even higher than that of saturated concentrated hydrochloric acid. It was the microscopic structural changes in organic phase microemulsion "water pool" that resulted in the corresponding variations in the palladium extraction behaviors.
研究了萃取体系TBP-Pd(II)-HCl中W/O微乳液的形成。通过动态光散射（DLS）、傅里叶变换红外光谱（FTIR）和31P-/1H核磁共振等多种光谱技术，表征了负载钯有机相的溶液结构随有机相中酸含量变化的演变。结果表明：（1）钯的萃取行为与负载有机溶液中W/O微乳液结构的形成有关。由于盐酸的共萃取，负载有机相中形成了微观聚集体。（2）有机相中HCl含量的变化导致溶液结构相应改变。随着HCl含量的增加，有机相中纳米聚集体的平均半径先增大后减小。HCl萃取到有机相对微观W/O胶束中水分子的O-H伸缩振动和O-H-O弯曲振动有显著影响。饱和酸的有机相的FTIR光谱表明，水的O-H伸缩振动宽带扩展到很宽的范围，并与C-H伸缩振动带重叠。有机相中酸浓度越高，重叠越大。另一方面，还观察到水的O-H-O弯曲振动出现显著变化，TBP分子中P=O的伸缩振动向低频移动。随着TBP有机相中酸含量的增加，观察到的31P NMR化学位移减小并向上场变化；而H+的1H NMR化学位移增加，甚至在较低频率场变得比氯化氘-d的化学位移更大。31P的δ值与H+的δ值变化方向相反，这意味着TBP分子与微乳液水池中的酸质子和水分子缔合形成RP=O x H+或RP=O x H3O+，然后与PdCl4(2-)络合离子相互作用，最终导致钯萃取到有机相中。（3）形成W/O反胶束/微乳液时，微观胶束内的酸浓度甚至高于饱和浓盐酸的浓度。正是有机相微乳液“水池”的微观结构变化导致了钯萃取行为的相应变化。
