Synthesis and Characterization of TiO2@C Core−Shell Composite Nanoparticles and Evaluation of Their Photocatalytic Activities

TiO2@C core−shell composite nanoparticles were synthesized by a simple and efficient single-step method in a specially made Swagelok cell at different temperatures. The prepared samples were characterized by XRD, diffuse reflectance-UV−vis, Raman, TEM, HRTEM, and N2 adsorption−desorption methods. The carbon content in the samples can be varied with reaction time and temperature. It is evident from TEM analysis that the as-prepared samples are core−shell structures of TiO2, anatase phase, and C. The diameter of the TiO2@C nanoparticles is in the range of 15−35 nm. HRTEM results showed that a few graphitic layers were wrapped on the surface of TiO2, and these carbon layers are responsible for suppressing other phase formations of TiO2 even at high temperature. However, a few percentage points of the rutile phase are observed at high temperature (900 °C), evidenced from Raman analysis. The prepared samples were tested for their photochemical activities for 4-chlorophenol degradation. The sample prepared at 700 °C showed comparable activity for the degradation of 4-chlorophenol with that of Degussa P25. The photobleaching studies of methylene blue were also carried out under sunlight. It was found that the TiO2@C samples showed higher photocatalytic activity than Degussa P25.