Generally elevated (ranging from 50C to 90C) temperatures will offer the small and high density uniform particles. But not in much temperatures. In addition, the gold ions completely convert into gold nanoparticles. Also, the rate of the reaction will increased. The higher intensity may due to more absorption because of more surface area of nanoparticles. When the size of particles decreased the surface area increased.

The best temperature for synthesis of nanoparticles will differ for different concentration of precursor and reducing agent.

thank you Sir,I am qurious about an other point here ,at room temperature (T=30) there is more intensity of absorption and narrow peak width as compared to (T=40),however,there is increase in intensity at 60C,and further increase at 80C...so what could be the reason that absorption decrease first with increase in temperature ,than increase in a predictable direct relation with temperature...it is also requested to send me some papers related to temperature effect

increase in intensity shows increase in the formation of gold nanoparticles with increase of temperature upto 100C (when no of particles increases the absorbency get increased hence u get higher intensity).

check the stability of the solution after 100C because at temperature >100C u may get smaller particles, it tends to get agglomerate has it as higher surface area hence it gets settled down at the bottom so you may get decrease in intensity. if that is the case try with capping agents with different percentage to overcome it to get the right answer.

all the best.

Hello Aiman

Your question does not show details and sources of deposition. Assuming you want deposit gold from gold compound in solution or from gaseous compounds, the following should be considered:

- With higher temperature we expect higher reaction rate. With higher reaction rate we normally get smaller particles (assuming no sintering between particles occurs at higher temperature).

Increasing temperature gives smaller particles, but may again sinter them (after formation) into larger ones. Care should be taken

Is this relevant to your question?

I think the difference in absorption is due to the nanoparticles forming different shapes at different temperatures. I learned about this in a physics of materials class, but I forget the conditions for forming the different shapes. Some of the shapes are rods, cubes, cages, triangles, and spheres.

Also something to note is that the particles are not actually "absorbing" the light in the same sense as other molecules. The peak that you see is called the "plasmon resonance band." These are the wavelengths of light that resonate with the "electron sea" of the metal nanoparticle.

Reported temperature in most of publication is 40 to 60 degree Celsius.use low concentration solution of Ag salt,as more ions leads bigger particles and made complications in observations.

The one-pot synthesis of gold nanoparticles (AuNPs) mediated by poly(dimethylaminoethyl methacrylate) homopolymer, without the use of a reducing agent, has been studied under different temperatures. The obtained results show that the higher is the temperature, during nanoparticle synthesis, the faster is nanoparticle creation and the more uniform are the produced nanoparticles. The kinetic studies on the nanoparticles synthesis were performed mainly by light scattering techniques. The obtained results indicate that at elevated temperatures the synthesis takes place in three steps, while at lower temperatures the followed synthetic pathways are more complex. Finally, the development of gold nanoparticles was also followed by UV–vis absorption measurements, indicating a good agreement between the two techniques.