hello
i have synthesized titanium dioxide by sol gel route and i try to test it for photocatalyitc reaction with Rhodamine6G.
i take 0.05g of catalyst in 50mL of R6G with concentration of 20ppm.
during photocatalytic test i take samples every 5 minutes until 35 minutes then all the simples are centrifuged to pass them in UV-VIS aparatus.
the results show for the first two simples (5min and 10min) 2ppm of concentration of R6G and then this concentration increase with time untill 14ppm for the last mesure corresponds to 30 minute????
why we an increase of concentration of R6G with time ??? this result is unlogical???
This image show absorbance and concentration in function of time.
The four last simples are centrifuged second time and then measure absorbance to confirm the measure.
At what wavelength is the absorbance of the solution being monitored?
Is there scattering contribution to the measured absorbance?
I am hoping that there is no scattering in your sample.
You may be measuring absorbance in the wavelength region where both R6G and degraded product absorb. At that wavelength if the extinction coefficient of degraded R6G is greater than R6G then it will give you enhanced absorbance.
At isosbestic point, the absorbance of the solution will not change with time as the reaction proceeds. It will remain same throughout. The decrease in absorbance due to decreasing reactant concentration is compensated by the increase in product absorbance due to increased product concentration.
A(lambda) = (e1c1 + e2c2) l
At isosbestic point, c1 decrease is compensated by c2 increase.
The previous suggestions could be assessed if you could upload a spectrum.
And how we can avoid this isosbestic point during photo catalytic test??
Isosbestic point exists at a particular wavelength for a given sample under given set of conditions. It can be avoided by changing the wavelength.
How I now if I have scatter in my simple??
I think in the first 10 minutes when I take a simple I take with it an amount of catalyst and then the reaction is not achieved??
Is that possible???
Scatter is manifest as a background...... if you post a spectrum, I can immediately tell you if you have scatter, and isosbestic point.... etc. etc.
Scattering shows 1/(lambda)^4 dependence I.e., as the wavelength decreases scattering increases. One sees less scattering at longer wavelength and greater scattering at shorter wavelength.
Scattering depends on the size of the particles and the wavelength of light.
Rayleigh Scattering shows a 1/(lambda)^4 dependence. This is dominant when the scatterers are smaller than the wavelength of light. (e.g. why the sky is blue). When the particles are closer to the wavelength of light, Mie scattering is dominant, and when there is a range of sizes, a largely wavelength independent response is seen (e.g why clouds are white or why microparticle or aggregated nanoparticle suspensions appear milky).
Yes Hugh J Byrne is correct. It is Rayleigh Scattering that shows 1/(Lambda)^4 dependence and it happens when the particle size
Thank you
I have data of absorbance in function of time. That correspond to concentration of solution with time. Can I show you this figures I we need it ??
The absorbance is monitored in 527.0 nm which corresponds to R6G.
It would be helpful if you can show the absorption spectra as a function of time.
so i need to show spectra in nanometer as fuction of time ???
thank you
Ok tomorrow i will postulate this type of graph
But I have another problem in the R6G when the sample is taken and then a UV-VIS gives a value firstly and then the analyzed sample is taken and stirred with hand and then passed for a second time the value of l The absorbance obtained is lower
can you explain me this results please??
thank you very much
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