Comparison between the effects of the addition of various cations via salt solution on the aggregation of silver nanoparticles synthesized via the reduction method

A general equation for determining average nanoparticle diameter is thus deduced.

λ_peak = 0.01D² + 0.0379D + 395.77 (1)

Where λ_peak is the peak absorbance wavelength and D is the diameter of the nanoparticles.

This equation appears to generate results that are in line with experiments described in the literature. Has a deduction for the uncertainty, which is 10 nm.

A selection of variables was controlled during this experiment to prevent aggregation.

To maintain stability with the nanoparticles, the ratio of AgN0₃ and NaBH₄ must be kept at 1:2; otherwise, aggregation may happen on its own. AgN0₃ and NaBH₄ solutions have and mM concentrations, respectively, for this experiment.

The aggregation will also occur if you keep stirring the NaBH₄ solution after you've added the last drop of AgN0₃. Therefore, stirring is stopped after adding the final depth of the AgN0₃ solution. Every freshly created batch of Ag-NP solution is left undisturbed for an hour while being watched to ensure that aggregation does not occur after stirring. Accumulation is observed in some collections, and those batches are rejected.

Ag-NP solutions can be created in 40 mL batches using the technique utilized in this experiment. The nanoparticle sizes within various collections may vary, possibly producing slightly different absorbance spectra due to the possibility of fluctuation in dripping AgN0₃ duration and random errors in measuring reactant volume. All successful batches are combined into one sizable beaker to achieve uniform average nanoparticle diameter throughout all experiments and constant absorbance spectra.

The scatter plot graph of the average peak SPR wavelength to particle size was used to depict this data. An equation was developed after a trend-line was placed against the graph.

As aggregation occurs as a result of the addition of salt solution, the colour of the nanoparticles changes from light yellow to dark yellow to light grey due to the localised surface plasm on resonance of silver nanoparticles.

The size of the nanoparticles can be determined by first determining the absorption spectrum of the nanoparticle solution using a UV spectrometer. According to Figure 4, the absorbance peak redshifts to higher wavelengths when aggregation and consequently particle size grow.

This experiment will consider two different independent variables.

 The first independent variable is ionic strength.Ionic strength is the first independent variable. Ionic strength is defined as \(\displaystyle\sum_{i=1}^{n}\) c_iz_i² where Ci is an ion's concentration, and Zi is the ion's ionic charge. The attention of the salt solution altered the additional salt solution's ionic strength will be changed from 0.2 M solutions to 1.0 M solutions in increments of 0.2 M.

The second independent variable will be ionic radii. Ionic radii will be changed by using different salts from period 1: LiCl, NaCl, KCl and NH₄Cl. In this way, due to the salts having the same ionic charge, ionic strength would be the same between all the salt solutions.

The preparation of the silver nanoparticle solution is as follows. 0.019 ± 0.002 g of NaBH₄ was added to 250 ± 0.8 mL distilled water to make a 2 mM NaBH₄ solution, while 0.017 ± 0.002 g of AgN0₃ was added to 100 ± 0.3 mL to make a 1 mM AgN0₃ solution.

With the heat turned off, 30 mL of NaBH₄ were placed into a 125 mL Erlenmeyer flask using a magnetic stir bar and stirrer at the highest speed. Then, using a dropper, 10 mL of AgN0₃ was added in drops at roughly one decline per second. After the AgN0₃ has been added and the magnetic stirrer has been turned off, the solution is seen to have a golden-yellow colour.

To ensure the silver nanoparticle solution does not further aggregate on its own, the now 40 mL batch is left sitting on the lab bench for one hour untouched. Collections in which aggregation continues will turn visibly black, while sets in which accumulation does not occur will experience no visible colour change. Figure 7 shows the comparison between a failed batch and a successful batch.

Due to their practical applications in a wide range of disciplines, nanoparticles are currently the focus of enormous scientific attention. Silver nanoparticles are widely used in medicine and have been shown to have antibacterial properties. Effective UV scatters been created using titanium oxide nanoparticles In sunblock. Even in clinical trials for cancer therapy, nanoparticles have been employed to colour-mark cancer cells.

It is evident that a lot of the characteristics that make nanoparticles so beneficial result from their small size. This has led me to choose aggregation as the subject of my extended essay. While adding salt solution would result in aggregation, little is known regarding the effects that altering the salt solution would have on aggregation. This experiment might lead to a better understanding of aggregation processes.

The reduction process, which grows nanoparticles from their smaller individual atoms, is a bottom-up strategy for producing nanoparticles. Due to its simplicity, low cost, controllability, and easy indication of synthesis success, this approach is constructive in synthesizing metallic nanoparticles.

The reduction process for the synthesis of silver nanoparticles begins with a solution of silver nitrate (AgN0₃), which is then mixed with a resolution of excess sodium borohydride (NaBH₄). The following redox reaction occurs in the answers.

AgNO₃ + NaBH₄ → Ag⁰ + ¹/₂ H₂ + ¹/₂ B₂H₆ + NaNO₃

In which the Ag⁺ ions in AgN0₃ are reduced into neutral Ag⁰ atoms.

The solution finally reaches the saturation limit due to the reaction, which causes an accumulation of Ago atoms. The Ag⁰ atoms then go through nucleation to form clusters, where up to twelve particles adhere to one another by Van Dal Waal's forces to prevent super-saturation. The groups then join forces with other groups and expand in size, a process known as aggregation.

In this instance, sodium borohydride serves as a surfactant as well. Excess NaBH₄ acts as a surfactant once the silver nanoparticles have amassed to a particular size, adsorbing each nanoparticle with several BH_4^- anions and preventing further aggregation because the BH₄^- anions would otherwise reject each other by repulsive electrostatic forces.

Nanoparticles are described as particles with one or more dimensions that range in size from one to one hundred nanometers (nm). By sharing some features of both bulk materials and molecule structures because to their particular size, they serve as a bridge between the two. For instance, unlike bulk materials, nanoparticles frequently depend on size and shape to exhibit specific features, such as their optical qualities. Even though gold is golden in colour in bulk, gold nanoparticles dispersed in a solution, for example, show colour variations based on their diameter, starting with a bright red colour and changing into dark purple as the particle size grows, as shown in figure 1.

Monodispersed silver nanoparticles have the unique optical feature of darkening the colour of the solution from a bright yellow to a dark grey as they accumulate. Because of confined surface plasmon resonance, this optical characteristic exists.

The collective oscillation of electrons on a metallic nanoparticle brought on by light is known as localized surface plasmon resonance. The electrons on a metallic nanoparticle delocalize and oscillate when exposed to light at a specific frequency, creating an electric field that is the opposite of the light waves and absorbing electromagnetic waves of the same frequency. These oscillations are sensitive to the surrounding conditions, particularly the particle size and the medium in which the nanoparticles are disseminated. Because of their small size, nanoparticles frequently have localized surface plasmon resonances that oscillate at visible light wavelengths, absorbing that wavelength of light. The distributed nanoparticle solutions experience a colour shift as a result.

This experiment will consider two different dependent variables.

The first dependent variable is the rate at which the silver nanoparticles aggregate after being added to the salt solutions. The relative absorbance at A = 407.0 nm is measured once every five seconds over one minute to detect variations in pace. Finding the rate of dropping relative absorbance acts as an equivalent indicator of the aggregation rate since A = 407.0 nm is close to the peak of the absorbance spectra, and the ridge flattens as the nanoparticle solution begins collection.

The total level of aggregation is the second dependent variable. The absorption spectra of the nanoparticle solution are captured using a spectrometer at t = 60 seconds. The equation would then be applied to this final spectrum to get the average nanoparticle diameter, allowing comparisons between various salt solutions and concentrations.

The following research question was sparked by this experiment: "How does the addition of various cations via salt solution impact the rate and overall degree of aggregation of silver nanoparticle solution generated by the reduction method?

Silver nanoparticles are created when a silver precursor solution, such as AgN0₃, is combined with a potent reducing agent, such as Na₈H₄. In a procedure known as aggregation, the agent breaks down silver ions into neutral atoms. The extra BH^4- anions surround the freshly formed silver nanoparticles and establish an electrostatic-repellent barrier to stop further aggregation. These charges are suppressed, and collection is permitted by the presence of hydrated cations in the addition of salt solution. While comparisons between various salt solutions are not well-documented in the literature, adding salt solution would result in aggregation. I decided to look into this study subject because there isn't much information available in this field and because scientists are becoming increasingly interested in nanoparticles and nanotechnology.

In this experiment, salt solutions of LiCl, KCl, NH₄Cl, and NaCl in volumes of 0.2 mL, 0.4 mL, 0.6 mL, 0.8 mL, and 1.0 mL were introduced to samples of silver nanoparticle solutions. The size of the aggregated nanoparticles was determined by the measurement of an absorbance spectrum obtained by a spectrometer and recorded a minute after the addition of salt solution. Comparing relative absorbance at different wavelengths also allows one to compare aggregation rates. ii. = 407.0 nm. It has been discovered that an increase in ionic strength causes an increase in the rates and total amounts of accumulation. The highest degree and expansion rate are caused by KCl, followed by NH₄Cl, NaCl, and inlining. It is discovered that ionic strength is not the critical element in determining aggregation.

It is evident that the size of the nano particle can be determined by analysing the absorption spectra of a solution because size is the primary determinant of the wavelength induced by LSPR. This is crucial because it provides a way to use a visible-light spectrometer, which is frequently found in high school laboratories, to measure the size of my produced nanoparticles.

How does the rate and overall level of aggregation of the silver nanoparticle solution produced using the reduction process change when different cations are added via salt solution?

According to published research, using Mie's Scattering Theory, one may quantitatively determine the nanoparticle size given the absorption spectrum.

\(w = {(\varepsilon _0\ +\ 2n^2)cmu{_F} \over 2N_ce^2 D}\)

Where w is the spectrum's full width at half maxima peak, D is the diameter of a nanoparticle, and ε₀, n, c, m, U_f, Nc, and e stand for the frequency-independent parts of complex forms of the dielectric constant, water's refractive index, the mass of an electron's speed of light, the electron's velocity at the Fermi energy, the number of electrons per unit volume, and the electron charge, respectively.

However, this experiment cannot use that equation due to technical restrictions. Data collection on wavelengths outside the visible spectrum, most notably below A = 400 nm, is not possible because all that is accessible is a visible light spectrometer. As can be observed from Figure 1, the minimum point of the peak is in the 300–400 nm region, making it impossible to determine the specific absorbance at that location.

As a workaround, I gathered information from Cytodiagnostics, a biotechnology business that creates its silver nanoparticle solutions using a similar technique. Figure 5, in particular, released by Cytodiagnostics, shows the link between average nanoparticle diameter and peak absorption wavelength: