Synthesis and characterization of black TiO2 nanoparticles by pulsed laser irradiation in liquid

Modified TiO₂ (black TiO₂) nanoparticles (NPs) produced by different methods showed enhanced visible light absorption than ordinary white TiO₂ NPs. Pulsed laser ablation in liquid (PLAL) is a promising technique for synthesizing nanostructures due to its simplicity, less usage of toxic reagents and absence of costly vacuum systems. In the present study, black TiO₂ NPs synthesized by pulsed laser irradiation is examined for their structure, morphology and optical properties. Nanoparticles of modified TiO₂ were prepared by pulsed laser ablation in liquid technique by irradiating white TiO₂ powder in water using an Nd:YAG laser (532 nm, 10 ns, 10 Hz). Characterization of morphology of the nanoparticles by scanning electron microscopy (SEM) showed a change in morphology by laser irradiation for TiO₂ nanoparticles. Crystalline structure was determined by X-ray diffraction (XRD) in which the major anatase phase in white TiO₂ was changed to rutile during irradiation and for longer irradiation, rutile became the major phase. Most of the vibrational peaks for TiO₂ were identified in Raman spectra. Ti 2p and O 1s binding energy analysis by X-ray photoelectron spectroscopy (XPS) for black TiO₂ (90 min) showed changes of 0.5 eV and 0.7 eV respectively compared to the white TiO₂ due to their change in chemical states. Optical absorption and band gap evaluation were done using the diffuse reflectance spectra measurements that showed enhanced absorption in the visible range for all the laser irradiated nanoparticles and a decrease in the bandgap from 2.98 eV of white TiO₂ to 1.84 eV for black TiO₂. Synthesis of black TiO₂ at normal atmospheric conditions by irradiation of TiO₂ in liquid using 532 nm laser output which is a very common Nd:YAG wavelength is reported for the first time.