Comprehensive understanding of the formation process on monodisperse resorcinol-formaldehyde polymer and carbon spheres and their use as substrates for surface-enhanced Raman spectroscopy

The synthesis of nitrogen-doped polymer (resorcinol-formaldehyde) and carbon spheres (denoted as N-RFS and N-CS, respectively) was carried out via an alkaline-based condensation reaction, with emphasis on high monodispersibility and precise size control. The particle size can be controlled in the range of 0.16-1.8 mu m by simply adjusting the experimental conditions, i.e., the concentrations of the monomers including resorcinol and formaldehyde, the reaction temperature, the methanol volume fraction and the concentration of a catalyst/nitrogen source (ammonia hydroxide). The correlations between the synthetic conditions and the particle size are established and elucidate the mechanism of the particle size control, in turn enabling prediction of the particle size at a set experimental parameter. Due to the outstanding thermal stability of N-RFS, the converted N-CS can be generated uniformly with high yield. With their high monodispersity, versatile synthesis procedure and close-packing ability, both the N-RFS and their corresponding N-CS in this work may offer remarkable flexibility in the design of periodic arrayed substrates for surface-enhanced Raman spectroscopy (SERS).