Structural evolution and optical properties of C-coated TiO2 nanoparticles prepared by laser pyrolysis

Laser oxidative pyrolysis synthesis and annealing of TiO2 nanoparticles embedded in carbon–silica shells/matrix

“…Generally, the mean crystallite size values of each phase extracted with the aid of Scherrer equation from the anatase (1 0 1) and rutile (1 1 0) XRD peaks (Table 2) can be correlated with those from the presented TEM images, where much smaller nanoparticle populations were considered. A clear tendency of the rutile to anatase ratio (as well as the carbon content) to decrease with the increasing amount of injected air through the second annular nozzle can be observed and was also reported by us in [24]. This effect can be related to the role of carbon in the enhancing the transformation of anatase to rutile through the formation of oxygen vacancies [36], correlated with the high temperatures in the flame environment.…”

“…A more detailed structure can be visualized in the right down corner HR-TEM inset from the same image, where the (1 0 1) anatase planes can be identified, delimited by turbostratic graphite units composed from short packed graphenes (spaced at ∼3.6-4Å) mixed with more disordered zones (possibly containing amorphous silica). The presence of turbostratic carbon on the surface of laser-assisted synthesis of titania nanocrystals was also reported by us in [24,32]. In the same Fig.…”

“…8a. Their ultraviolet absorption peaks are positioned around 330 nm, a value close to those measured for TiO 2 @C laser-synthesized nanocomposites [24]. A clear enhanced visible light absorption can be observed for the annealed silica-containing nanopowders (especially for TLOP 6(H) and TLOP 7(H) particles), when compared with the calcined reference sample TLOP 01(H), even if their atomic carbon concentration are quite similar (between 10.2% and 12.3% as can be seen in Table 2).…”

“…The elemental composition (extracted for the mediated EDX analyses) presented in Table 2 proves the presence of carbon in all samples and points out the ethylene as their main source. The formation of carbonaceous material as a result of a partial ethylene decomposition is an indicator for the oxygen deficiency in the reactive mixtures used in our laser pyrolysis experiments and was reported by us in [24,34] for nanotitania-based particle synthesis using the same method, Ti precursor and sensitizer. Following all these considerations, the titania-based core-shell nanostuctures genesis can be explained starting from the hot freshly formed titania nanoparticles in the flame central zone which act as catalytic surfaces for the deposition of carbonaceous layer provided by ethylene decomposition, combined (for the TLOP 6,7 and 8 experiments) with the amorphous silica from HMDSO (introduced through the annular nozzle) oxidation.…”

“…The coating of pre-formed TiO 2 nanoparticles with disordered carbon was also successfully achieved using C 2 H 2 in a CVD process, resulting again an increasing visible-light photocatalytic activity against phenol [22]. One-step gas-phase synthesis of TiO 2 @C nanostructured particles was reported using low oxidant concentration from TTIP and C 2 H 2 in flame aerosol reactor [23] or from TiCl 4 and C 2 H 4 with/without C 2 H 2 by laser pyrolysis [24]. Recently, carbon-incorporated TiO 2 microspheres prepared by flame-assisted hydrolysis of TBOT proved enhanced H 2 production from water (when compared with TiO 2 P25) during simulated solar light irradiation [25].…”