[0001] The present invention relates to a method for the preparation of a boron-carbon doped nanomaterial and to a method for the preparation of an electrode comprising nanostructures of said boron-carbon doped material. The invention also relates to the material and electrodes resulting from said methods and to the use of said electrode as electrocatalyst, capacitator or in an electrochemiluminescent sensor.
1. Method for the preparation of a boron-doped carbon nanodot material comprising the steps of: (i) providing an aqueous solution comprising an alpha amino acid, boric acid and a polyamine compound for forming carbon nanodots having amino end groups, wherein the molar ratio of alpha amino acid to boric acid is 2:1, the molar ratio of alpha amino acid to primary amine groups in the polyamine compound is essentially 1:2 and the concentration of alpha amino acid is comprised between 2 mM and 6 mM; (ii) heating the solution provided in step (i) in a closed vessel at a temperature of between 180 °C and 250 °C so as to avoid the evaporation of water as the solvent. 2. Method according to claim 1 wherein the heating step (ii) satisfies one or more of the following conditions (a) to (d): (a) the heating step is carried out at a temperature of 235 °C; (b) the heating step is carried out at a pressure of between 1 bar and 20 bars; (c) the reaction time is between 150 and 200 seconds; (d) the heating step (ii) is carried out under microwave irradiation; (e) the alpha amino acid is arginine; (f) the polyamine compound is 3,3' diamino-N-methyldipropylamine; (g) the concentration of alpha amino acid is about 4 mM. 3. Method according to any one of claims 1 to 2 further comprising the steps of: (iii) diluting the product resulting from step (ii) in water; (iv) removing solid particles having an average size higher than 100 nm from the product resulting from step (iii); so as to produce a solid fraction consisting of said solid particles and a liquid fraction comprising the boron-doped carbon nanodot material; and (v) removing the suspended colloidal particles from the liquid fraction resulting from step (iv). 4. Product obtainable by the method as defined in any one claims 1 to 3. 5. Boron-doped carbon nanodot material having free amine end groups for forming diazonium end groups characterized in that: (i) said material exhibits a fluorescence emission peak at about 360 nm when irradiated with light of a wavelength of about 310 nm; and/or (ii) 100 moles of said material substantially consist of from 40 to 50 moles of carbon atoms, from 5 to 15 moles of hydrogen atoms, from 15 to 25 moles of nitrogen atoms and from 10 to 40 moles of oxygen and/or boron atoms; and/or (iii) said material exhibits infrared absorption peaks at one or more wavelengths selected from the group consisting of 3480 cm<-1>, 2950 cm<-1>, 1715 cm<-1>, 1450 cm<-1>, 1377 cm<-1>, 1383 cm<-1> and 801 cm<-1>; and/or (iv) said material has an average particle size of between 10 and 50 nm as measured by dynamic light scattering; and/or (v) said material exhibits a zeta potential lower than -5 mV at pH values higher than 6 at a concentration of boron-doped carbon nanodot material in water of 1.30 mg per mL. 6. Aqueous composition comprising the material of claim 5. 7. Method for the preparation of an electrode comprising the steps of: (i) submitting a product as defined in claim 4 or an aqueous composition as defined in claim 6 to reaction conditions suitable for converting at least one amine group of the boron-doped carbon nanodot material in a diazonium group; (ii) providing an electrode support consisting essentially of a carbon material; (iii) contacting the electrode support provided in step (ii) with the product or composition provided in step (i) while applying a potential being equal to or inferior to -0.7 V, so as to promote the grafting of the boron-doped carbon nanodot material comprised in the mixture resulting from step (i) on the surface of the electrode support such that the grafted boron-doped carbon nanodot material has a height inferior to 2 nm as measured by atomic force microscopy. 8. Method according to claim 7 wherein step (i) comprises contacting the product as defined in claim 4 or the aqueous composition as defined in claim 6 with sodium nitrite in the presence of an acid. 9. Method according to any one of claims 7 to 8 wherein the electrode support of step (ii) consists essentially of graphite. 10. Method according to any one of claims 7 to 9 wherein step (iii) comprises applying at least 40 cycles of potential cycling between 0 and -0.8 V at 100 mV/s scan rate; or, alternatively, applying a potential equal to -0.7 V for a period of time of at least 800 seconds. 11. Electrode obtainable according to the method of any of claims 7 to 10. 12. Electrode comprising a boron-doped carbon nanodot material grafted on a carbon material characterized in that: (i) said electrode exhibits Raman absorption peaks at one or more wavelengths selected from the group consisting of 500 cm<-1>, 1230 cm<-1>, 2911 cm<-1> and 2965 cm<-1>; and/or (ii) said electrode exhibits a charge resistance for electron transfer of about 240 Ω as measured by electrochemical impedance spectroscopy; and/or (iii) said electrode exhibits a reduction potential of about 0.1 V and an oxidation potential of about 0.4 V as measured by cyclic voltammetry using a Ag/AgCI reference electrode and a platinum wire counter electrode at 10 mV/s scan rate in 0.1 M phosphate buffer of pH 7.4 containing 0.1 M KCI; and/or (iv) said material exhibits a capacitance higher than 1000 µF per cm<2> at a scan rate of 0.005 V/s as measured by cyclic voltammetry. 13. Use of an electrode as defined in claim 11 or in claim 12 as capacitator, or as electrocatalyst, or as electrochemiluminescent electrode.