Chemistry, Physics and Technology of Surface

ISSN 2518-1238 (Online), ISSN 2079-1704 (Print)

Recently, specific carbon-based nanomaterials (quantum dots, CDs) became highly attractive due to their low toxicity, good biocompatibility, chemical inertness, high photostability and fluorescence. Doping with some heteroatoms was found to be an effective approach to improve their luminescence. Besides, using the surface of silica as a support might facilitate the nanodots formation and expand the application area of carbon-silica composites. Recent advancements in synthesis of luminescent silica/CDs composites revealed great potential of such systems in bioimaging, sensor, as well as in solid-state lightning applications. Most of the synthetic methods are still relatively complex and costly. Here, the simple and inexpensive route to produce luminescent silica-based nanomaterials was used. The aim of this work was to study the luminescent properties of the materials obtained by pyrolysis of citric acid ureates at the nanosilica surface.

Fumed silica was used as a support material. The salts with various ratios of citric acid and urea were obtained either in aqueous or alcohol solution, and they were further deposited on silica surface. The resulting material was then heat treated at the temperature of up to 270 °C, and the absorption and photoluminescence spectra for the samples obtained were collected and analyzed.

The results have shown that irrespective of the solvent used, both dried and pyrolyzed samples possess the luminescent properties, with quantum yield of photoluminescence being within 7–11 %. The change of the citric acid-to-urea ratio in aqueous solution within 1:(1÷3) doesn’t affect the luminescent properties of dried samples, but further pyrolysis at 270 °C reduces the photoluminescence intensity. The solvent change to ethanol has an ambiguous influence on the luminescent properties of dried silica samples with different citric acid-to-urea ratio applied, however, further thermal treatment at 270 °C results in the formation of the materials with almost the same luminescence properties. Within the citric acid-to-urea ratios and the solvents used, as well as the heat treatment regimes applied, the variant with the 1:1 salt in the alcohol solution applied to the silica surface with further drying and heat treatment at 270 °C was found to be the most suitable.

1. Yang Z., Li Z., Xu M., Ma Y., Zhang J., Su Y., Gao F., Wei H., Zhang L. Controllable synthesis of fluorescent carbon dots and their detection application as nanoprobes. Nano-Micro Lett. 2013. 5(4): 247. https://doi.org/10.1007/BF03353756

2. Zheng X.T., Ananthanarayanan A., Luo K.Q., Chen P. Glowing graphene quantum dots and carbon dots: properties, syntheses, and biological applications. Small. 2015. 11(14): 1620. https://doi.org/10.1002/smll.201402648

3. Du W., Xu X., Hao H., Liu R., Zhang D., Gao F., Lu Q. Green synthesis of fluorescent carbon quantum dots and carbon spheres from pericarp. Sci. China Chem. 2015. 58(5): 863. https://doi.org/10.1007/s11426-014-5256-y

4. Qian Z., Shan X., Chai L., Ma J., Chen J., Feng H. Si-doped carbon quantum dots: a facile and general preparation strategy, bioimaging application, and multifunctional sensor. ACS Appl. Mater. Interfaces. 2014. 6(9): 6797. https://doi.org/10.1021/am500403n

5. Anilkumar P., Wang X., Cao L., Sahu S., Liu J.-H., Wang P., Korch K., Tackett K.N., Parenzan A., Sun Y.-P. Toward quantitatively fluorescent carbon-based «quantum» dots. Nanoscale. 2011. 3(5): 2023. https://doi.org/10.1039/c0nr00962h

6. Yang C., Thomsen R.P., Ogaki R., Kjems J., Teo B.M. Ultrastable green fluorescence carbon dots with high quantum yield for bioimaging and use as theranostic carriers. J. Mater. Chem. B. 2015. 3: 4577. https://doi.org/10.1039/C5TB00467E

7. Cao L., Yang S-T., Wang X., Luo P.G., Liu, J.-H. Sahu S., Liu Y., Sun Y.-P. Competitive performance of carbon "quantum" dots in optical bioimaging. Theranostics. 2012. 2(3): 295. https://doi.org/10.7150/thno.3912

8. Li X., Zhang S., Kulinich S.A., Liu Y., Zeng H. Engineering surface states of carbon dots to achieve controllable luminescence for solid-luminescent composites and sensitive Be²⁺ detection. Sci. Rep. 2014. 4: 4976. https://doi.org/10.1038/srep04976

9. Hu L., Sun Y., Li S., Wang X., Hu K., Wang L., Liang X., Wu Y. Multifunctional carbon dots with high quantum yield for imaging and gene delivery. Carbon. 2014. 67: 508. https://doi.org/10.1016/j.carbon.2013.10.023

10. Wei W., Xu C., Wu L., Wang J., Ren J., Qu X. Non-enzymatic-browning-reaction: a versatile route for production of nitrogen-doped carbon dots with tunable multicolor luminescent display. Sci. Rep. 2014. 4: 3564. https://doi.org/10.1038/srep03564

11. Dong Y., Pang H., Yang H.B., Guo C., Shao J., Chi Y., Li C.M., Yu T. Carbon-based dots co-doped with nitrogen and sulfur for high quantum yield and excitation-independent emission. Ang. Chem. Int. Ed. 2013. 52(30): 1.

12. Qu D., Zheng M., Du P., Zhou Y., Zhang L., Li D., Tan H., Zhao Z., Xied Z., Sun Z. Highly luminescent S, N co-doped graphene quantum dots with broad visible absorption bands for visible light photocatalysts. Nanoscale. 2013. 5: 12272. https://doi.org/10.1039/c3nr04402e

13. Kang M.S., Singh R.K., Kim T.H., Kim J.H., Patel K.D., Kim H.W. Optical imaging and anticancer chemotherapy through carbon dot created hollow mesoporous silica nanoparticles. Acta Biomater. 2017. 55: 466. https://doi.org/10.1016/j.actbio.2017.03.054

14. Wang Z., Xu C., Lu Y., Wu F., Ye G., Wei G., Sun T., Chen J. Visualization of adsorption: luminescent mesoporous silica-carbon dots composite for rapid and selective removal of U(VI) and in situ monitoring the adsorption behavior. ACS Appl. Mater. Interfaces. 2017. 9(8): 7392. https://doi.org/10.1021/acsami.6b13427

15. Xiang G., Ren Y., Zhang H., Fan H., Jiang X., He L., Zhao W. Carbon dots based dual-emission silica nanoparticles as ratiometric fluorescent probe for chromium speciation analysis in water samples. Can. J. Chem. 2018. 96(1): 72. https://doi.org/10.1139/cjc-2017-0472

16. Suzuki K., Malfatti L., Takahashi M., Carboni D., Messina F., Tokudome Y., Takemoto M., Innocenzi P. Design of carbon dots photoluminescence through organo-functional silane grafting for solid-state emitting devices. Sci. Rep. 2017. 7: 5469. https://doi.org/10.1038/s41598-017-05540-5

17. Nelson D.K., Razbirin B.S., Starukhi A.N., Eurov D.A., Kurdyukov D.A., Stovpiaga E.Yu., Golubev V.G. Photoluminescence of carbon dots from mesoporous silica. Opt. Mater. 2016. 59: 28. https://doi.org/10.1016/j.optmat.2016.03.051

18. Tian Y., Ran Z., Yang W. Carbon dot-silica composite nanoparticle: an excitation-independent fluorescence material with tunable fluorescence. RSC Adv. 2017. 7(69): 43839. https://doi.org/10.1039/C7RA07990G

19. Guo Z., Zhu Zh., Zhang X., Chen Y. Facile synthesis of blue-emitting carbon dots@mesoporous silica composite spheres. Solid State Sci. 2018. 76: 100. https://doi.org/10.1016/j.solidstatesciences.2017.12.011

20. Wang J., Zhang F., Wang Y., Yang Y., Liu X. Efficient resistance against solid-state quenching of carbon dots towards white light emitting diodes by physical embedding into silica. Carbon. 2018. 126: 426. https://doi.org/10.1016/j.carbon.2017.10.041