Theoretically predicted effect of odd-even pattern of electron pairing on behavior of gold clusters in polyaniline/Au N (N = 0 to 8) has been confirmed experimentally. In these composites the atomic Au clusters with even number of atoms exhibit higher catalytic activity for electrochemical oxidation of n-propanol in 1 M NaOH than the odd-number atoms clusters. Also, infrared spectroscopy shows that even numbered PANI/Au N composites affect the N-H stretching vibration more strongly than the corresponding odd numbered ones. This behavior matches the theoretically predicted variations of HOMO-LUMO gap energy and the stability of the atomic Au clusters. It also agrees with the earlier experimental work in which the UPS spectra of isolated, mass-selected Au clusters have been reported.

Atom-by-atom deposition of gold into polyaniline (PANI) through a repeated cyclic pathway has been reported previously by us. It was noticed that the efficiency of the preparation was complicated by concurrent oxidative degradation of PANI in the course of the gold deposition process, resulting in the loss of the deposited matrix. The primary objective of this research was to minimize the loss of the matrix by separating the PANI degradation and the atomic gold deposition parts of the cycle. The overoxidation of PANI was performed as a preconditioning step, prior to the gold deposition cycles. The FTIR spectra obtained after preconditioning on the stabilized PANI film show that the imine attachment sites for the chloroaurate anion are still available.. The presence of the deposited gold on the cyclic voltammograms of the PANI film could be easily observed. The work function of the prepared composite films increased linearly with the logarithm of number of gold deposition cycles.Recently, we reported on a deposition of one atom of gold per imine site on PANI that followed a cyclic pathway in which the electrochemical control of the redox state of the PANI film was maintained throughout the deposition cycle. 1 Previously, for each cycle, the potential of the PANI film was held at +0.8 V for 300 s in a specially designed flow through cell, in order to keep it in a fully oxidized state while exposing it to solution of AuCl 4 − to form a stoichiometric PANI*AuCl 4 − complex. After all the excess AuCl 4 − was thoroughly rinsed away, the AuCl 4 − retained by the PANI was reduced to atomic gold by sweeping the potential to −0.2 V. It is assumed that the atom(s) of metallic gold remain at or close to the imine sites of PANI, which are then again available for AuCl 4 − complexation in the next gold deposition cycle. The localization of the metallic gold is assumed to be aided by formation of the local contact potential between Au and the imine site. Maintaining the high oxidation state of PANI was essential in order to avoid the spontaneous reduction of chloroaurate. 2,3 In the original process, 1 the atomic gold deposition and the oxidative degradation of PANI at +0.8 V were occurring simultaneously making it difficult to gain clear information on the impact of the deposited gold on the electrochemical behavior of PANI. The degradation process is caused by breaking of the polymer chains due to formation of quinones or quinone imines resulting in the loss of the material. 4 The rate of the degradation depends on several factors including the type of the anion in the acidic media, 5-7 the length of time the film is held at the overoxidation potential, 8 the magnitude of the applied potential, 9 and the thickness of the film. 10 The degradation of PANI follows a first order kinetics, 11 so most of the damage will occur early, reaching a stable material. It has been shown that HCl promotes degradation faster than any other acids. 6 Therefore the preconditioning degradation in HCl has been incorporated into the preparative pro...

Polyaniline (PANI) has been an effective matrix for hosting and preserving metal nanoclusters. In the case of gold, the tetrachloroaurate anion (AuCl4−) has a high affinity for the imine sites of PANI. Upon contact with PANI, AuCl4− is spontaneously reduced to metallic gold, but the size of the formed Au clusters cannot be precisely controlled. Herein, we report on the electrochemical method of controlled deposition of one atom by one atom of gold per imine site of PANI. By controlling the potential, we keep PANI in an oxidized state while exposing it to a solution of AuCl4− to form a PANI∗AuCl4− complex, which is reduced to atomic gold by sweeping the potential negative. This frees up the imine sites of PANI again and makes them accessible for the next Au deposition cycle. The repeated deposition of Au atoms follows a cyclic pathway. The amount of gold deposited using this method is consistent for each repeated cycle.

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