First example of ZnO-TiO2 nanocomposites by Chemical Vapor Deposition: structure, morphology, composition and gas sensing performances

ZnO-TiO2 nanocomposites were synthesized by an innovative chemical vapor deposition (CVD) strategy, based on the initial growth of ZnO nanoplatelets (host) and the subsequent dispersion of TiO2 nanoparticles (guest). Ti(OiPr)2(dpm)2 and Zn(hfa)2âTMEDA (OiPr: iso-propoxy; dpm: 2,2,6,6-tetramethyl- 3,5-heptanedionate; hfa: 1,1,1,5,5,5-hexafluoro-2,4-pentanedionate; and TMEDA: N,N,N',N'-tetramethylethylenediamine) were adopted as Ti and Zn molecular sources, respectively. The syntheses were performed in nitrogen plus wet oxygen atmospheres at relatively low temperatures (350-400 °C) on Si(100) and Al2O3 substrates, avoiding ex-situ thermal treatment to preserve the chemical identity of the host and guest phases. The process resulted in the formation of ZnO-TiO2 nanocomposite deposits with an average thickness of 140 nm, whose characteristics were directly affected by the host matrix porosity and the guest amount and dispersion, tailored by varying the TiO2 deposition time. In this framework, particular attention was devoted to the investigation of the composite chemico-physical properties as a function of the adopted processing parameters. Furthermore, the gas sensing performances of the nanocomposites in the detection of volatile organic compounds (CH3COCH3, CH3CH2OH, and CO) resulted in being directly dependent on their composition and morphology, revealing better performances than the pristine ZnO systems. These results disclose intriguing perspectives for the development of sensing devices for environmental purposes and food control monitoring.