Hello

I am wondering if you are using a closed crucible with a lid to prepare g-C3N4. Try using a closed lid crucible and and perform pyrolysis.

Hope it should work.

Regards.

Best way of preparing such nitrides is by heating the precursor in vacuum atmosphere. Usual problem associated with the preperation of carbon nitride material is decomposition of carbon and associated nitrogen chains during calcination in air atmosphere. Hence, vacuum system can circumvent such situation.

another system u can try is closed system where, the accessibility of air/O2 is less. In such a system dont forget to use higher amount of precursor.

Hi dear Athanasia Petala

I can not say for sure but this is most likely due to a laboratory error. please read the following article. It may be useful.

10.1039/C1JM12620B

I would like to suggest you that try in inert atmospheres (Ar/N2 gas). It will also reduce the carbon oxidation during pyrolysis.

Use slow heating rate (2.5 C/min)

Dear Athanasia Petala

The efficiency of urea conversion to g-C3N4 is generally very low. You can use melamine for preparation of this semiconductor with efficiency of about 40%. For more information, please read the enclosed review paper about g-C3N4.

You need to use atleast 10g Urea. Or can use Melamine.

I am agree with Dr. Muhammad Tahir.

What is the duration? and heat rate?

Heat under under inert atm (N2) for not more than 2 h with heat rate of 2.5 to 5 oC/ min. Remember yield will be very low using Urea. Melamine relatively better.

Try changing your precursor from urea to melamine (better yields than urea) , avoid smaller amounts of precursor (~10g should be fine), perform the pyrolysis using crucibles with lids and a slow ramping rate is also recommended. You can also do your reaction under inert conditions as previously suggested.

Good luck

Cover it with a quartz or ceramic material. 3C per min. For 10 g, 2 hours will do the trick.

Athanasia Petala

1. Use 50 ml crucible with lid

2. Take 10 g of Urea (Do not completely fill the crucible, leave more then quarter volume for condensation reaction)

3. Cover with lid

4. Then wrap with aluminium paper (It will further enhance the yield)

For reference, have a look at the attached photographs

Hi dear friends.

I am preparing g-C3N4 by heating Urea getting white, while heating thiourea and melamine i am getting yellow g-c3N4, which one will be good.?

Plz let me know that i proceed any one?

abdul Khaliq Jan

Hi!

quality g-C3N4 is yellow, if it is white then it means that the condensation reaction wasn't completed at all and you can't use it as visible-light semiconductor. Visible-light semiconductor can absorb at least wavelength above 400 nm, mostly 420+ nm, it means that they have yellow color. TiO2 is white because its absorption starts from UV. By increasing temperature up to 600-700 °C you can shift the band gap to even higher wavelengths than 450 nm (2.75 eV), g-C3N4 prepared at 550 °C see in text below.

In your case you need to increase the time or increase the temperature. The common preparation procedure is: 550 °C for 2-3 hours with heating rate like 3 °C/min, don't forget to use crucible with a cover. The problem with urea is its very low yield compared with e.g. melamine. The yield by using melamine is mostly even around 50 %. In the case of urea the yield was about 5 % and less. One of many intermediates between urea and the final g-C3N4 is melamine. By using melamine you won't lose as much of precursor as when you start from urea.

More about shifting band gap by increasing temperature and other properties such as surface area, ration C/N, etc.: 10.1016/j.matchemphys.2017.03.008

Dear friend

Thank you for valuable information,

actually one of my labfellow told me that urea produce white color g-C3N4 and that is better one. But i am agree with your statement that yellow color is good.

Recently i am facing another isse,

that the g-C3N4 doesnt stuck tight and are washed away during electocurrent determination process (PEC), although i am using nafio or PVP binders.

also the photo-electrode show small photo-current.

please send me your email that i communicate you some points.

Regards

thanks for your response.

[email protected]

Hello,

The color of g-C3N4 depends on the temperature and the time. Many people produce also so called exfoliated g-C3N4 (white, light yellow), which means that by thermal, chemical or another exfoliation method, the bulk lamelar (yellow) g-C3N4 is broken to smaller pieces. If this happen the electron delocalization is limited and thus exfoliated g-C3N4 can't absorb wavelength with lower energy (i.e. higher wavelength). By synthesizing g-C3N4 you are going to do exactly the opposite, you are enlarging layers by connecting of more tri-s-triazine units together and the extended layers increase also the electron delocalization, which can be observed by red shift in UV-Vis spectrum and in decrease of photoluminiscence emission, i.e. lower probability of electron-hole recombination. Slow heating rate also means less defects in strucutre.

After exfoliation, you will obtain g-C3N4 "nanosheets", which can be observed by increased photoluminiscence because the probability of electron-hole recombination is increased and you will obtain surface area even up to 300 m2/g AND the color of g-C3N4 is changed from yellow to light yellow, because the orignal stucked layer structure is mostly removed. It is more likely that you obtained not g-C3N4, but mix of intermediates such as melam, dimelem, etc. with small portion of g-C3N4. It is hard to say without knowing the preparation procedure. But I guess that the specific surfacee area of such g-C3N4 won't be over 50 m2/g, which should suggest that the reaction wasn't completed. If you compare uncondensated g-C3N4 (white or yellow white) with exfoliated of fully condensated g-C3N4 (yellow) you will see a big difference thanks to also very high surface area, i.e. more active sites for reactions and less defects.

It is in our article where we compared bulk and exfoliated g-C3N4 at the range between 500-600 °C: 10.1016/j.materresbull.2017.12.049

Photocurrent is mostly always small for g-C3N4 because it has a lot of defects, it is not like graphene. To enhance photocurrent you can couple g-C3N4 with another semiconductor or do the exfoliation, which should decrease amount of defects as well. But if you start with urea to prepare g-C3N4 and then you are going to do also exfoliation, be prepared for really small yield of g-C3N4 nanosheets and many hours in lab.

I have never measured PEC, I am sorry I can't help you with this one.

If you have any questions, please feel free to contact me: [email protected]

Hi,

I try to synthesize g-C3N4 by using urea 550 oC for 2 hrs and i get black-grey color. I do not know why it become like that. Next, I calcined the urea at 550 oC for 2 hrs and it also turns out black-grey color. Is there any idea ?

If you're using Urea as the precursor in order to obtain graphitic carbon nitride (g-C3N4), you must make sure to use a crucible with lid. This is because, when the temperature approaches around 200+ degrees, nitrogen is formed and this atmosphere is necessary for the formation of the end product. Using a crucible without the lid will lead to the escape of the gases.

Dear friend, it is easy to prepare C3N4 the secret in behind is to cover the crucible during the heating process up to 550 oC for 2 h after reaching the 550 oC, you can use from 6-12 g from urea, thiourea, and melamine to reach the target

good luck

Ibrahim

You can use thiourea or melamine to synthesis g-C3N4. Besides, decreasing the temperature to 450 degree for 2 hours.

urea (CH4N2O) 50 g was taken from 250 ml alumina crucible. On the other hand, the alumina crucible was fully covered by the alumina foil. The covered crucible was inserted to furnace at 600 ◦C with the ramping rate 3 ◦C per minute. Besides, the reaction duration time was 2 hrs. Maintain temperature after decreasing 3 ◦C per minute.

Article Investigations on effect of graphitic carbon nitride loading...

Graphitic carbon nitride (g-C3N4) is a metal-free, intermediate band gap semiconductor that is readily produced via direct thermal polymerization of variety nitrogen-rich molecular precursors. This material is particularly attractive for environmental remediation and biocide applications due to its’ metal free composition, which could limit incidental toxicity, and the fact that it is photo responsive to visible wavelengths, allowing it to be easily employed in interior environments without the need for specialized light sources. Unfortunately, the potential utility of g-C3N4 is frequently compromised by relatively high recombination rates of photo generated charge carrier species and correspondingly low observed photo catalytic activities.

Briefly, a sample of 10 g of dried urea was placed in a covered 50 mL porcelain crucible and heated from 25°C to 575°C at a rate of 175°C/hour in a muffle furnace. The sample subsequently dwelled at 575°C for four hours and then was cooled to ambient temperature over 18 hours. The resulting pale yellow solid was collected and ground to produce approximately 0.5 grams of u-g-C3N4 as a free flowing powder.

For more relevant information please go throw this following link this research paper have very useful information: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5575986/

Hello

If the crucible is open; No product is obtained. Please put a cap on your crucible and try again.