Nanocomposites and nanomaterials
Ex-situ vs. in-situ fabrication routes for luminescent nanocomposites C-dots/porous silica
G.Yu. Rudko1,2, O.F. Isaieva1,2, A.V. Vasin1,3, D.V. Kysil1, E.G. Gule1, A.N. Nazarov1,3, B. Capoen4, M. Bouazaoui4, H. El Hamzaoui4, S.V. Sevostianov5
1 V. Lashkaryov Institute of Semiconductor Physics of National Academy of Sciences of Ukraine, 45, Pr. Nauky, Kiev, 03028, Ukraine.
E-mail: oksana.isaieva@isp.kiev.ua 
2 National University “Kyiv-Mohyla Academy”, Skovorody, 2, Kiev, 04070, Ukraine.
3 National Technical University Igor Sikorsky Kyiv Polytechnic Institute”, Kyiv 03056, Ukraine
4 Univ-Lille, CNRS, UMR8523 – Physique des Lasers AtomesetMolequles, CERLA/IRCICA, F-59000, Lille, France.
5 Chuiko Institute of Surface Chemistry of NASU, Kyiv, Ukraine.

It is known that carbon nanodots are effective light emitters. Colloidal solutions of carbon nanodots demonstrate quantum yield 90 % and above. Thus, they are promising candidates for the fabrication of light-emitting devices as well as for bio-medical applications, such as disease diagnostics. Among the advantages of these nano-objects one must mention their comparative cheapness, environmentally friendly fabrication routes, ability to control their color properties of emission. Therefore, carbon nanoobjects attract a lot of research attention nowadays.
Recently a new method of carbon nanostructures synthesis using a porous SiO2 matrix has been advanced [1]. Carbon nanoparticles were synthesized within the pores of SiO2 matrix.  The silica sample was soaked in the solution of sucrose (С₁₂Н₂₂О₁₁) that served as a carbon source, diluted in dimethyl sulfoxide (DMSO, (CH₃)₂SO). Synthesis of carbon nanoparticles was performed by thermolysis of the solution at temperature 170-180 0C. Thus, the pores restricted the size of the synthesized nanoparticles and the nanodots. This method is the in-situ growth.
In the present study we used both the above in-situ method and the alternative ex-situ method of carbon nano-objects fabrication. The latter method implies the growth of carbon nanoobjects by more standard colloidal route (using the same organic source of carbon and solvent). The first step was the thermolysis of sucrose/DMSO solution that resulted in the formation of concentrated colloid of luminescent carbon nanoparticles. Then the porous silica matrix has been infiltrated by this colloidal solution. Obviously, the sizes of the ready nanoparticles, that were incorporated into the porous silica were limited by the sizes of the pores. To compare the properties of nanoparticles grown by these two routes we washed out the nanoparticles from the porous silica/nanoparticles solid composites obtained either by in-situ or ex-situ methods, and studied the optical properties of the solutions obtained. The photoluminescence excitation and emission spectra of these colloidal solutions of carbon nanoparticles synthesized by two methods were studied. It is shown that the synthesis method does not significantly affect the spectral characteristics of the obtained nanoparticle solutions. In particular, when the porous SiO2 matrix with a pore size of 7 nm was used, the spectral characteristics of nanoparticles synthesized by both methods completely coincide. When the porous SiO2 matrix with a pore size of 40 nm was used, the position of the PL spectrum maximum for nanoparticles synthesized by the in situ method is slightly shifted to the long-wavelength region. Thus, both methods provide nanoparticles with almost the same properties.
When porous SiO2 with a larger pore size is used, emission spectrum of carbon nanoparticles is characterized by larger half-bandwidth and the position of the maximum is red-shifted as compared with the spectrum of nanoparticles obtained using a matrix with the smaller pore size. Both features point to the formation of nanoparticles of larger sizes and larger dispersion of nanoparticles sizes. 
In summary, the luminescent properties of the nanoparticles obtained depend rather on the size of pores in SiO2 than on synthesis route. Both methods demonstrated the effect of the size of carbon nanoparticles on emission spectra, i.e. broadening and noticeable blue shift of emission band in larger nanoparticles.

1.	Vasin A., Kysil D., Sevostianov S., Isaieva O., Rudko G., Capoen B., Bouazaoui M., Hamzaoui H., Tertykh V., Starik S., Nazarov A. Liquid-Phase Synthesis of Hydrophilic Luminescent Carbon Dots Using Porous Silica as a Nanotemplate // Phys. Status Solidi A-2021.-218, № 15. Р. 2000817.