Porous carbon nitride spheres from melamine-formaldehyde resin

Abstract

Recently, porous carbon nitrides attracted much more attention since they have high hardness and stability as well as high surface area. Spherical colloidal carbon nitride porous particles have, in particular, attracted the most attention because they represent a thermodynamically favorable state in terms of surface energy and are therefore relatively easy to synthesize. In this study, melamine-formaldehyde (MF) resins are used as precursors for synthesizing carbon nitride spheres. Carbon nitride microporous spheres (CNMSs) with very large surface area are synthesized by carbonizing melamine-formaldehyde spheres (MFSs). The CNMS synthetic process is facile and convenient to reproduce since it does not contain a hard template production step for generating micropores. The surface area of CNMSs is increased approximately 100 times after the carbonization process. Also, sub-nanometer sized pores in CNMSs offer potential use in gas separation and gas storage. It is found that CNMS has a hydrogen storage capacity of 1.9 wt\% at 77 K and 1 atm. The atomic structure of CNMSs is analyzed by $^{13}C$ MAS NMR and it is determined that the CNMSs consist of amorphous and graphite-like carbon atoms that have three distinct $sp^2$ carbon bonding configurations. Since melamine has nitrogen atoms and amine groups in its structure, MFSs are expected to be used in various fields including drug delivery. Amine groups on the surface of MFSs make the particles positively in water which is important in adsorbing small molecules such as DNA and protein. Size controlled MFSs were synthesized by varying the stirring RPM during the condensation step and the endocytosis of MFS in BV2 cell is observed by SEM. Rhodamine 6G adsorbed MFS was incubated with BV2 cell and transference of the small molecules from the particles to the cells is shown by confocal microscopy. Hollow and porous Ni-carbonitride spheres have been synthesized for the first time by nozzle spray pyrolysis (NSP) pr...