Influence of ZnO doping on structural, optical and pH-stimulus characteristics of silica-titania nanocomposite matrix

In-situ sol-gel procedure is used to synthesize the silica-titania nanocomposite (SiO2-TiO2) as host matrix which is doped with ZnO and heated at 300 °C for 1 h for homogeneous and stable matrix surface. The mixture of organic dyes i.e. cresol red, bromophenol blue, phenol red and phenolphthalein is encapsulated within ZnO:SiO2-TiO2 nanocomposite for the evaluation of sensing activity at dynamic pH range 1–12. Microscopic findings showed that the synthesized nanocomposites have homogeneous crack-free porous coating with low roughness value of 9.7–7.6 nm. XRD analysis shows the formation of new phase ZnSiO3 after ZnO doping and heat treatment along with anatase phase of titania and silica. TEM analysis confirmed the spherical nanoparticles. The heterogeneous bonding of synthesized Zn:SiO2-TiO2 composites is investigated by FTIR. Surface analysis confirmed that prepared nanocomposites have high surface area, large pore diameters and mesoporous nature, which is desirable for good sensing behavior. Optical studies show that low refractive index (1.33–1.39) transparent nanocomposites (92–62% transparency in the visible range) are promising for sensing applications. TGA analysis shows that SiO2-TiO2 nanocomposites after ZnO doping and heat treatment are thermally stable. The fast response 0.15 s of the ZnO:SiO2-TiO2 nanocomposite coated fiber optic sensor is optimized at pH 12. The observed sensitivity is of 15 counts/pH with repeatability of 93% at 440 nm. Keywords: Silica-titania nanocomposite, ZnO doping, Structural and optical properties, Fiber optic sensin