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Preparation of silver colloids with improved uniformity and stable surface-enhanced Raman scattering.

Meng W, Hu F, Jiang X, Lu L - Nanoscale Res Lett (2015)

Bottom Line: Silver colloids of uniform shape and size are prepared by a two-step reduction.Small silver particles form initially by the rapid reduction of silver nitrate with sodium citrate at 100°C and then grow at 92°C.The reaction processes and resulting silver colloids are characterized by transmission electron microscopy, ultraviolet-visible absorption spectrophotometry, zeta-potential measurements, and Ag(+) concentration analysis.

View Article: PubMed Central - PubMed

Affiliation: School of Sciences, China Pharmaceutical University, Nanjing, 211198 China ; Key Laboratory for Soft Chemistry and Functional Materials of Ministry Education, Nanjing University of Science and Technology, Nanjing, 210094 China.

ABSTRACT
Silver colloids of uniform shape and size are prepared by a two-step reduction. Small silver particles form initially by the rapid reduction of silver nitrate with sodium citrate at 100°C and then grow at 92°C. The reaction processes and resulting silver colloids are characterized by transmission electron microscopy, ultraviolet-visible absorption spectrophotometry, zeta-potential measurements, and Ag(+) concentration analysis. The surface-enhanced Raman scattering (SERS) activity of the silver colloids is then investigated, using crystal violet (CV) as a SERS probe. The silver colloids exhibit uniform shape and size and stable SERS activity. The average size of the silver particles is 47 nm (14% relative standard deviation), while the average sizes of the silver colloids prepared at 100°C and 92°C are 41 (30%) and 71 nm (33%), respectively.

No MeSH data available.


TEM images of reaction aliquots: (a) sample A at stage 1; (b) sample A at stage 2; (c) sample A at stage 3; (d) sample B at stage 1; (e) sample B at stage 2; (f) sample B at stage 3; (g) sample C at stage 2; (h) sample C at stage 3; (i) sample D at stage 3.
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Fig2: TEM images of reaction aliquots: (a) sample A at stage 1; (b) sample A at stage 2; (c) sample A at stage 3; (d) sample B at stage 1; (e) sample B at stage 2; (f) sample B at stage 3; (g) sample C at stage 2; (h) sample C at stage 3; (i) sample D at stage 3.

Mentions: The time evolution of λmax, absorption at λmax, and Ag+ concentration for sample A are shown in Figure 1a. The reaction can be divided into three stages: nucleation of silver and formation of silver seeds (1), growth of silver seeds (2), and dispersion of silver particles (3). During stage 1 (0 to 4 min), the solution is initially colorless with little absorption and then becomes faintly yellow and weakly absorbs at 398.5 nm. About 5% of Ag+ is reduced in the first 4 min. TEM images show that the size of the silver seeds is approximately 10 nm at the end of stage 1 (Figure 2a). During stage 2 (4 to 11 min), the reduction of Ag+ accelerates because of catalysis by the silver particles [20]. The rapid increase in λmax and absorbance at λmax indicates the growth of silver seeds, which makes the solution turn gray yellow. It is difficult to exclusively restrict growth to molecular addition during stage 2, as evidenced by the particles (approximately 10 nm, see Figure 2c) existing in the final silver colloids. During stage 2, silver nuclei continue to form, creating more silver seeds, which grow by molecular addition, as shown by TEM (Figure 2b). Large and small silver particles form simultaneously, so stage 2 does not solely involve the growth of silver seeds. It should instead be seen as a continuous formation-and-growth stage for silver seeds. At 11 min, the λmax blue shifts, and the reaction begins stage 3. About 20% Ag+ remains at this point. Ag+ continues to reduce as stage 3 progresses: λmax shifts from 426 to 413 nm, and the absorbance intensity increases. This indicates that some silver particles aggregate into larger particles during stage 2, and that dispersion dominates stage 3. Figure 2c shows that the product is a mixture of quasi-spherical and rod-like particles [21] with an average size and relative standard deviation of 41 nm and 30%, respectively. These sizes are calculated from average values of the long and short axes of >100 particles. The continuous formation of silver seeds during stage 2 yields the wide distribution of shapes and sizes observed in the final product.Figure 1


Preparation of silver colloids with improved uniformity and stable surface-enhanced Raman scattering.

Meng W, Hu F, Jiang X, Lu L - Nanoscale Res Lett (2015)

TEM images of reaction aliquots: (a) sample A at stage 1; (b) sample A at stage 2; (c) sample A at stage 3; (d) sample B at stage 1; (e) sample B at stage 2; (f) sample B at stage 3; (g) sample C at stage 2; (h) sample C at stage 3; (i) sample D at stage 3.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4384897&req=5

Fig2: TEM images of reaction aliquots: (a) sample A at stage 1; (b) sample A at stage 2; (c) sample A at stage 3; (d) sample B at stage 1; (e) sample B at stage 2; (f) sample B at stage 3; (g) sample C at stage 2; (h) sample C at stage 3; (i) sample D at stage 3.
Mentions: The time evolution of λmax, absorption at λmax, and Ag+ concentration for sample A are shown in Figure 1a. The reaction can be divided into three stages: nucleation of silver and formation of silver seeds (1), growth of silver seeds (2), and dispersion of silver particles (3). During stage 1 (0 to 4 min), the solution is initially colorless with little absorption and then becomes faintly yellow and weakly absorbs at 398.5 nm. About 5% of Ag+ is reduced in the first 4 min. TEM images show that the size of the silver seeds is approximately 10 nm at the end of stage 1 (Figure 2a). During stage 2 (4 to 11 min), the reduction of Ag+ accelerates because of catalysis by the silver particles [20]. The rapid increase in λmax and absorbance at λmax indicates the growth of silver seeds, which makes the solution turn gray yellow. It is difficult to exclusively restrict growth to molecular addition during stage 2, as evidenced by the particles (approximately 10 nm, see Figure 2c) existing in the final silver colloids. During stage 2, silver nuclei continue to form, creating more silver seeds, which grow by molecular addition, as shown by TEM (Figure 2b). Large and small silver particles form simultaneously, so stage 2 does not solely involve the growth of silver seeds. It should instead be seen as a continuous formation-and-growth stage for silver seeds. At 11 min, the λmax blue shifts, and the reaction begins stage 3. About 20% Ag+ remains at this point. Ag+ continues to reduce as stage 3 progresses: λmax shifts from 426 to 413 nm, and the absorbance intensity increases. This indicates that some silver particles aggregate into larger particles during stage 2, and that dispersion dominates stage 3. Figure 2c shows that the product is a mixture of quasi-spherical and rod-like particles [21] with an average size and relative standard deviation of 41 nm and 30%, respectively. These sizes are calculated from average values of the long and short axes of >100 particles. The continuous formation of silver seeds during stage 2 yields the wide distribution of shapes and sizes observed in the final product.Figure 1

Bottom Line: Silver colloids of uniform shape and size are prepared by a two-step reduction.Small silver particles form initially by the rapid reduction of silver nitrate with sodium citrate at 100°C and then grow at 92°C.The reaction processes and resulting silver colloids are characterized by transmission electron microscopy, ultraviolet-visible absorption spectrophotometry, zeta-potential measurements, and Ag(+) concentration analysis.

View Article: PubMed Central - PubMed

Affiliation: School of Sciences, China Pharmaceutical University, Nanjing, 211198 China ; Key Laboratory for Soft Chemistry and Functional Materials of Ministry Education, Nanjing University of Science and Technology, Nanjing, 210094 China.

ABSTRACT
Silver colloids of uniform shape and size are prepared by a two-step reduction. Small silver particles form initially by the rapid reduction of silver nitrate with sodium citrate at 100°C and then grow at 92°C. The reaction processes and resulting silver colloids are characterized by transmission electron microscopy, ultraviolet-visible absorption spectrophotometry, zeta-potential measurements, and Ag(+) concentration analysis. The surface-enhanced Raman scattering (SERS) activity of the silver colloids is then investigated, using crystal violet (CV) as a SERS probe. The silver colloids exhibit uniform shape and size and stable SERS activity. The average size of the silver particles is 47 nm (14% relative standard deviation), while the average sizes of the silver colloids prepared at 100°C and 92°C are 41 (30%) and 71 nm (33%), respectively.

No MeSH data available.