Hello,
Recently I have been attempting to synthesize graphitic carbon nitride for the purpose of photocatalytic conversion of carbon dioxide to methane under visible light.
The issue I am facing is that all my samples are greyish in color, rather than yellowish, and I believe the yellowish g-CN is needed for photocatalysis in the visible spectrum.
Has anybody faced a similar issue or could provide me with some insight as to why this is happening and how I could possibly improve my g-CN?
I have attached pictures of the samples I have obtained so far:
- Sample 1 - 50g of Urea at 600°C for 2.5H, heating rate of 10°C/min
- Sample 2 - 15g of Urea at 550°C for 3H, heating rate of 10°C/min
- Sample 3 - 15g of Urea at 600°C for 4H, heating rate of 10°C/min
From the literature I have read, I understood that the degree of polymerization (DP) determines the final band gap and color, and the DP could be varied by the temperature and time, and the precursor. This is why I performed the synthesis of sample 2 and 3 (one being 550 for 3H and the other 600 for 4H), but as you can see in the pictures, they appear to be more or less identical.
The FTIR graphs of these samples, all have the characteristic peaks for g-CN, but I have not been able to perform an XRD analysis yet.
Another related question I had is - Does the crucible material influence my product in any way? I am using a porcelain crucible.
Thank you,
Joshua Nigel
We also perform the synthesis with urea and it was yellowish. Two temperature ramps were used at constant speed of 60°C/min. The first ramp covered the
temperature range from room temperature (~18 °C) to 300 °C (this
temperature was kept for 3 min). The second ramp reached 600 °C and
that temperature was kept constant for 40 min. You can see more details in our article 10.1016/j.matchemphys.2019.121878.
I hope this answer helps
Best regard
Christian
Perform polymerization at temperature 520 to 530 oC for 4 hours. With increase of temperature and time its color with become greyish.
We also perform the synthesis with urea and it was yellowish. Two temperature ramps were used at constant speed of 60°C/min. The first ramp covered the
temperature range from room temperature (~18 °C) to 300 °C (this
temperature was kept for 3 min). The second ramp reached 600 °C and
that temperature was kept constant for 40 min. You can see more details in our article 10.1016/j.matchemphys.2019.121878.
I hope this answer helps
Best regard
Christian
All the 3 photographs showing the pyrolyzed urea or the obtained GCN looks fair and agreeable. If you want to rectify any errors then, check the grade of urea used, reduce the quantity of urea to 5-8g per batch, perform a simple post-pyrolysis step i.e washing the as-obtained material with 0.1M Nitric Acid and water to remove any alkaline species adsorbed.
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