SYNTHESIS AND CHARACTERIZATION OF ZNO/TIO₂ NANOPARTICLES: STRUCTURAL, OPTICAL, AND PHOTOCATALYTIC PROPERTIES
Keywords:
ZnO nanoparticles; TiO₂ nanoparticles; ZnO/TiO₂ nanocomposite; heterojunction photocatalysis; charge separation; X-ray diffraction; optical band gap; photocatalytic dye degradation; wastewater treatmentAbstract
Zinc oxide, titanium dioxide (TiO₂), and ZnO/TiO₂ nanocomposites were synthesised by a controlled chemical route, and their structural, optical, and photocatalytic properties were systematically characterised in order to establish a coherent structure–property–performance relationship. ZnO nanoparticles were prepared by a pH-controlled hydrothermal route, TiO₂ was obtained from a titanium alkoxide precursor and crystallised by calcination, and the composite was formed in situ by dispersing pre-formed ZnO in ethanol, adjusting the pH, and adding a titanium precursor before calcination at 500 °C for 2 h.
X-ray diffraction confirmed that the composite consisted of hexagonal wurtzite ZnO (JCPDS 36-1451) and anatase TiO₂ (JCPDS 21-1272) as separate phases, with no detectable impurity or zinc titanate phase; the crystallite size of the composite was smaller than that of pristine ZnO, consistent with the incorporation of TiO₂ within the ZnO matrix. Scanning electron microscopy and energy-dispersive X-ray spectroscopy provided the particle morphology, agglomeration behaviour, and elemental composition, while Fourier transform infrared spectroscopy confirmed the metal–oxygen bonding and Ti–O–Zn linkages of the composite.
Optical characterisation showed strong ultraviolet absorption, with the absorption edge of the composite displaced relative to the pristine oxides and the band gap decreasing from 3.48 eV for pure ZnO to 3.05 eV as the TiO₂ volume ratio increased; photoluminescence measurements indicated a change in emission intensity, interpreted in terms of charge-carrier recombination. The composite degraded the model organic dye more efficiently than either pristine oxide under identical conditions, and the kinetics followed a pseudo-first-order model. The enhancement is attributed to the staggered (type-II) band alignment at the ZnO/TiO₂ heterojunction, which spatially separates photogenerated electrons and holes, prolongs carrier lifetime, and improves interfacial charge transfer to adsorbed species.
The results establish a coherent structure property performance relationship and support the use of low-cost, chemically and thermally stable ZnO/TiO₂ nanocomposites for the removal of organic pollutants from contaminated water.
