Continuous advances on Pseudo-anti-galvanic reaction research have been achieved by a joint team which is mainly composed of Prof. WU Zhikun group at Institute of Solid State Physics, Hefei Institutes of Physical Science and CAS's member YANG Jinlong group from University of Science and Technology of China.
Relevant works have been published in Acta Chimica Sinica and Journal of the American Chemical Society, respectively.
The galvanic reaction (GR), named after Italian scientist Luigi Galvani (1737-1798), is referred to the spontaneous reduction of a noble-metal cation by a less noble metal in solution. In 2012, the reaction opposite GR was proposed and confirmed by WU¡¯s group. They found the reduction of metal ions by more noble metals as the size of metal decreasing, and defined it as anti-galvanic reaction (AGR). Subsequently, they conducted a series of research on the mechanisms and applications of AGR.
Recently, they found that metal nanoclusters could react with the same metal complexes (ions), which was different from either GR or AGR. This new reaction was dubbed Pseudo-anti-galvanic reaction (Pseudo-AGR). Upon its report, AGR was recognized as a unique way to tune the metal structure at nanoscale by the experts and colleagues in the field. However, the potential of Pseudo-AGR is yet to be explored.
On one hand, the above findings on Pseudo-AGR paved the way for further research on precisely modulating of the nanoparticles structure in a controlled manner, which is a challenging and inspiring topic.
Although the single or few metal-atom tailoring of metal nanoparticles with the remnant structure untouched has recently been accomplished, module replacement (MR), which is the local structural replacement involving over three net metal atoms, has not been hitherto achieved yet.
Recently, for the first time, the joint team fulfilled the MR of the Au48(CHT)26 (CHT: cyclohexanethiolate) nanoclusters by a Pseudo-AGR process and obtained another novel Au37(CHT)23 nanoclusters. The MR product Au37(CHT)23 shared a similar Au31(CHT)12 unit with its predecessor Au48(CHT)26, however the former differed from the latter in the remnant section (Au6(CHT)11 vs Au17(CHT)14).
Interestingly, the MR weakened the photoluminescence but strengthened the photothermy in this work, indicating that the two effects were in a balance and could be at least partly converted to each other for nanoclusters.
This work has important implications for future tuning of the structures and in-depth understanding of the interactions between various properties as well.
On the other hand, Pseudo-AGR process had also played a significant role in WU group¡¯s observation on structural oscillation in nanoparticles. Oscillation is a common phenomenon in nature, found in a large range of systems from large celestial bodies to small atoms. However, the atomically precise observation of structural oscillation in nanoparticles has not been reported so far.
WU¡¯s group simultaneously synthesized a pair of nanocluster isomers Au28i and Au28ii via a Pseudo-AGR process.
Note that, they are the fourth pair of structural isomers reported so far, and the first and the second pair of structural isomers were also reported by WU group.
Very interestingly, the structures of the two isomers could oscillate for at least 10 cycles, driven by dissolution and crystallization processes.
Moreover, the transformation from Au28ii to Au28i was solvent dielectric constant-dependent and exhibited deuteration effect: the larger the dielectric constant, the faster the structure transformation. Au28ii showed enhanced photoluminescence compared with Au28i although they have identical metal kernel but different outer staples. The rigid structure on the shell explained the extensive emission on the basis of a previous work from WU's group. The oscillation between two isomers with a dramatic fluorescence difference might have potential applications in converting, sensing, etc.
These works were supported by the National Natural Science Foundation of China, Natural Science Foundation of Anhui Province, the CAS/SAFEA International Partnership Program for Creative Research Teams and the CASHIPS Director¡¯s Fund.
Link to the papers:
Module Replacement of Gold Nanoparticles by a Pseudo-AGR
Structural Oscillation Revealed in Gold Nanoparticles
Figure 1. The illustration of galvanic reaction, anti-galvanic reaction, and Pseudo-AGR of certain metal Mi in the metal activity sequence (only six metals were shown) (the last two reactions were named by WU¡¯s group; x represents a positive integer, and y represents a positive integer or decimal).
Figure 2. Module replacement process and its influences on photothermy and photoluminescence (left), cover image (right). (Image by XIA Nan)
Figure 3. (A) The comparison of the structures of Au28 isomers, (B) the UV-vis-NIR monitoring of the reversible transformation between Au28 isomers, (C) solvent and deuteration dependent transformation rates from Au28ii to Au28i, (D) Photoluminescence spectra of Au28isomers. (Image by XIA Nan)