Preparation of triangular silver nanoplates by silver seeds capped with citrate-CTA

Abstract

Due to the competitive growth on the crystal face of seed, it is always difficult to control the morphology of the formation of nanoparticles precisely by a seed-mediated growth method. Herein, we provided a simple but effective technique to synthesize silver nanotriangles using a new silver seed that is capped with citrate-CTA⁺ (CTA⁺ is cetyltrimethyl ammonium cation). Compared to the preparation of silver nanoparticles (AgNPs) by a conventional seed-mediated method, in this paper, we presented a growth technique with two distinct innovative changes. First, the concentrations of CTAB that we added in silver seed collosol have a significant impact on the size distribution, and silver nanotriangles, nanorods, and nanospheres could be obtained by adjusting the CTAB concentration. Second, the seed prepared by our method has a longer use time, and silver nanotriangles, nanospheres, and nanorods could be prepared by adjusting the aged time of the seed colloid. We have also shown a simple way to control the morphology of silver nanoparticles in almost the same reactive medium by varying the NaOH concentration. Using the new silver seed capped with citrate-CTA⁺, we obtained triangular silver nanoparticles with relatively high regularity. Based on the limited experimental results and IR analysis, a possible mechanism was preliminarily proposed to explain the formation of the seed and the truncated triangular AgNPs.

Fig. 1. The influence of different concentrations of CTAB on the formation of the seed and AgNPs. (a) UV-vis spectra of the seed added different concentrations of CTAB. (b) UV-vis spectra of growth solution prepared by the seed that was added different concentrations of CTAB and aged for 20 min. (c) TEM image of silver seeds prepared by adding 0.96 mM CTAB. (d) TEM image of silver seeds prepared by adding 1.90 mM CTAB.

Fig. 2. The influence of the aging time of silver seed on the morphology and size of AgNPs: (a) UV-vis spectra of the seed colloidal solution at different aging times; (b) and (c) UV-vis spectra of growth solution prepared by the seed with the aging times from 0 to 60 min and 2 to 24 h; (d) the hydrodynamic size distribution (by DLS) of silver nanoplates prepared by the seed with different aging times; (e) and (f) TEM image and size distribution of triangular silver nanoplates prepared by the seed aged for 3 h.

Fig. 3. The influence of the concentrations of NaOH on the morphology of AgNPs: UV spectra of growth solution with different concentrations of NaOH, (a) 5.1 mM to 15 mM, (b) 20 mM to 51 mM; (c) the pH of the growth solution with different concentrations of NaOH. (d) TEM image of nanorods prepared by the growth solution of 30 mM NaOH.

Fig. 4. The influence of aging time of growth solution on the morphology of silver nanoplates: (a) UV-vis spectra of growth solution aged for different times; (b) photos of growth solution at different aging times (see the vertical axis) and photos of growth solution prepared respectively by the seed at different aging times (see the horizontal axis); TEM image of silver nanoplates prepared by the seed aged for 3 h: (c) the growth solution aging time was 24 h and (d) the growth solution aging time was 3 d.

Fig. 5. A schematic illustrating the formation of silver seed in the solution containing CTAB.

Fig. 6. FTIR spectra of triangular silver nanoplates by the silver seed capped with citrate-CTA⁺: (1) CTAB, (2) sample of silver nanoplates, (3) mixture of CTAB and citrate, and (4) citrate.

Fig. 7. A schematic illustrating the formation of triangular silver nanoplates by the orientated stacking and growth of the seed.