The Effect of Cube Shape and Size on Optical Properties The optical properties of silver nanocubes depend on their size, with the surface plasmon resonance peak of the cubes shifting to longer wavelengths as the nanocube diameter increases.
Due to the cubic shape, however, silver nanocubes have optical properties that are different than similarly-sized nanospheres. For example, the silver nanocubes have sharp corners and edges that give rise to additional plasmonic modes that occur at different resonance wavelengths in the spectrum.
For nanocubes with small dimensions, such as the 40 nm-diameter nanocubes shown below, these plasmon modes are bunched together and the extinction peak of the first highest resonance wavelength dipole mode dominates. As the size of the nanocubes increases, the resonance wavelengths of the higher order plasmonic modes become more separated and distinct, and increase in intensity in spectrum. As shown below, the extinction peaks of these higher plasmonic modes appear in the visible and near infrared regions of the spectrum.
This absorption peak becomes broad and relatively less intense as the cube size increases. As a result of these multiple plasmonic modes, nanocubes between nm size are bichromic, exhibiting different colors depending on whether the sample is transmitting or scattering incident light. Qiang Zhang, Christine H. Langmuir , 28 24 , Chemistry of Materials , 22 24 , The Journal of Physical Chemistry C , 50 , Sheng Peng and Yugang Sun.
Chemistry of Materials , 22 23 , Journal of the American Chemical Society , 32 , The Journal of Physical Chemistry C , 14 , The Journal of Physical Chemistry C , 10 , The Journal of Physical Chemistry C , 0. The chemical reduction is one of the most commonly used methods for the synthesis of silver nanoparticles by inorganic and organic reducing agents.
Different shapes of silver nanoparticles synthesized with various chemical reductants 3. Synthesis of spherical silver nanoparticles The spherical silver nanoparticles were synthesized using the reducing agents such as ascorbic acid, sodium citrate, NaBH4, thiosulfate, and polyethylene glycol.
In addition to that, the use of the surfactants such as citrate, polyvinylpyrolidone PVP , cetyltrimethylammonium bromide CTAB , and polyvinyl alcohol PVA for interactions with particle surfaces can stabilize particle growth and protect particles from sedimentation and agglomeration [ 13 , 14 , 15 , 16 , 17 ].
Then, Silver nanorods were grown in the solution with the injection of silver seeds at the growth medium containing silver nitrate and sodium citrate and then irradiated for 24 h using a halogen lamp and a bandpass filter to selectively tune. This photomediated method provided an elegant method for controlling the architectural parameters of the resulting silver nanostructures [ 18 ].
Then solution of ice cold of NaBH4 was added while stirring. To synthesize Ag nanorods of at three different aspect ratios, three stock solutions of AgNO3, ascorbic acid, and the surfactant cetyltrimethylammonium bromide CTAB were prepared separately. These stock solutions were mixed at certain quantities properly.
Thereafter, 1. The color of each nanorod solutions depends on the seed concentrations added in the final solution [ 19 ]. Then, sodium borohydride reducing agent solution was injected to the above solution all at once while stirring vigorously.
The solution color was changed to light yellow. The entire solution was heated under continuous stirring on magnetic stirrer. Then, AgNO3 and ascorbic acid solution were added. And then, the seed solution was added and at last, few drops of NaOH were added to maintain constant pH and stirred well. Figure 1. A TEM image of the silver seed nanoparticles. D Selective-area electron diffraction SAED pattern of a single silver nanorod, showing the interpenetration.
Synthesis of silver nanowires Sun et al. The silver nanowires with diameters of 20 nm and aspect ratios up to have obtained by adding 2. They used polyvinylpyrrolidone as stabilizing and capping agent combined with sodium chloride and potassium bromide salts, ethylene glycol was used as both solvent and a reducing agent, and silver nitrate was used as a silver precursor. They determined that the diameter and uniformity of silver nanowires can be controlled by adjusting the concentration of AgNO3 and [PVP] to [AgNO3] molar ratio keeping the other parameters constant.
Figure 2. Synthesis of cubic silver nanoparticles The synthesis of cubic silver nanoparticles was achieved by the reduction of silver nitrate using ethylene glycol in the presence of polyvinylpyrrolidone PVP. In polyol process, ethylene glycol containing hydroxyl groups have functional structure as both solvent and reducing agent.
Polyvinylpyrrolidone as capping agent was used to constitute the cubic shape. Molar ratio of the PVP and silver ions determines the shape of the product [ 24 , 25 , 26 ]. The inset shows the electron diffraction pattern obtained by aligning the electron beam perpendicular to one of the square faces of a Ag nanocube.
The XRD pattern recorded from the same batch of sample is displayed in Fig. Two peaks can be assigned to the , planes of pure fcc Ag respectively. Figure 1d shows the optical extinction spectrum of Ag nanocubes. The peaks located at nm and nm may be induced by the dipole resonance and quadrupole resonance of Ag nanocubes respectively, which are consistent with previous report Figure 1 a SEM images of a typical sample of Ag nanocubes taken at 90 min, and the inset shows the high-magnification SEM image of a single Ag nanocube.
The scale bar is nm and 50 nm respectively. The inset shows the electron diffraction pattern obtained by directing the electron beam perpendicular to one of the square faces of a Ag nanocube.
The scale bar is nm. Full size image In order to know the detail of growth process, Ag nanocubes taken at different stages of a synthesis are obtained and investigated by TEM, as illustrated in Fig.
It can be observed that there are irregular nanoparticles in Fig. The light yellow color of the solution see supplementary information Fig. Although twinned and single-crystal Ag seeds coexist in the solution in the early stage, twinned nanoparticles are the most abundant nanostructure due to the fact that their surface energies are relatively lower than that of single-crystal As a result, single-crystal seeds are the primary seeds.
The reduced Ag atoms continuously deposit on these crystal seeds. As shown in Fig. The edge size is about 60 nm, with a standard deviation of 10 nm. With the reaction proceeding, the size of these nanocubes will be increased by absorbing the reduced Ag atoms while the shape is kept the same.
It can be seen from Fig.The unconventional methods contain laser ablation, radiocatalysis, vacuum evaporation of metal, irradiation, photolithography, electrodeposition and the electrocondensation. Langmuir , 28 24 , Journal of the American Chemical Society , 32 ,
Rycenga, M. Chemistry of Materials , 30 14 , The Effect of Cube Shape and Size on Optical Properties The optical properties of silver nanocubes depend on their size, with the surface plasmon resonance peak of the cubes shifting to longer wavelengths as the nanocube diameter increases. Green synthesis of different shape Ag-NPs and their antibacterial activity .
The edge size of nanocubes is 85 nm in Fig. Among the variety of shaped silver nanoparticles, silver nanocubes have received particular interest due to their distinctive morphology. Thus, to obtain Ag nanocubes, both single twinned and multiple twinned seeds should be effectively eliminated. In addition, the obtained nanostructures are almost always polycrystalline. Several hypotheses have been proposed regarding the role of Cl—; however, there is still no consensus regarding the exact influence of Cl— in the shape-controlled synthesis of Ag nanocubes.
The entire solution was heated under continuous stirring on magnetic stirrer. Ex situ experiments probed the evolution of Cl— during the growth of Ag nanocubes, which involves the initial formation of AgCl nanocubes, and their subsequent dissolution to release Cl—, which adsorbs onto the surfaces of single crystal seeds to impact shape evolution through apparent thermodynamic control. Meanwhile, enhanced local electromagnetic fields at the 8 vertices of cube can enhance optical nonlinear process Chemistry of Materials , 22 23 ,
Green synthesis of different shape Ag-NPs and their antibacterial activity . Although the lithographic fabrication can control the shape of metal nanostructure, the lithographic techniques such as electron beam lithography, or focused ion beam lithography are complex, expensive, and require highly specialized facilities. As multiple twinned and single twinned seeds have more defects and lower surface energy compared with single-crystal seeds, the twinned seeds are more favorable for the deposit of reduced Ag atoms. As shown below, the extinction peaks of these higher plasmonic modes appear in the visible and near infrared regions of the spectrum. Due to the cubic shape, however, silver nanocubes have optical properties that are different than similarly-sized nanospheres.
From electrical switches, solar panels to chemical-producing catalysts and antimicrobial activity, the silver nanoparticle is an essential component in many industries. Molar ratio of the PVP and silver ions determines the shape of the product [ 24 , 25 , 26 ]. The change of reaction temperature can also affect the shape of final products, which can be clearly observed in Fig.
Figure 1d shows the optical extinction spectrum of Ag nanocubes. Among the four different shaped AgNPs, the flower shape AgNPs exhibited the best results and led to the fastest bactericidal activity against all the tested strains at similar bacterial concentrations Figure 6 [ 84 ].
Nanoparticle research is currently an area of intense scientific research, due to a wide variety of potential applications in fields such as healthcare, cosmetics, food and feed, environmental health, mechanics, optics, biomedical sciences, chemical industries, electronics, space industries, drug-gene delivery, energy science, optoelectronics, catalysis, single electron transistors, light emitters, nonlinear optical devices, and photo-electrochemical area. The laser ablation method, which has several types of different applications, is another method to study the synthesis of silver nanoparticles Ag-NPs. The formation of cubes is independent of the source of AgCl, indicating temporal control of the Cl— chemical potential in solution leads to high-yield synthesis of Ag nanocubes. We ascribe this phenomenon to the increased growth rate of nanocubes. Thus, to obtain Ag nanocubes, both single twinned and multiple twinned seeds should be effectively eliminated.
As shown in Fig. Chemistry of Materials , 30 14 , TEM and SEM studies have shown that the presence of reducing agent in a plant-mediated synthesis of Ag-NPs, where the plant extract acts as reducing agents, shapes the nanoparticle during its growth.
Therefore, reaction conditions such as temperature and ratio of PVP to AgNO3 in the system should be kept at suitable values to maintain the uniformity of Ag nanocubes.