Temperature-Driven Phase Evolution and Physicochemical Property changes in TiO2 Nanoparticles

Abstract

TiO2 nanoparticles were synthesized by the sol–gel method and annealed at 450, 550, 650,
and 750 °C. This allowed examination of how temperature drives phase evolution and alters
structural, optical, vibrational, thermal, and electrochemical properties. X-ray diffraction (XRD)
analysis confirmed phase-pure anatase at 450 and 550 °C. At 650 °C a mixed anatase and rutile
structure appeared. At 750 °C there was complete conversion to the rutile phase is noted. Crystallite
size grew monotonically from 21.3 nm to 40.9 nm, while dislocation density and microstrain fell
sharply across the same range, indicating progressive defect annihilation. UV–Vis spectroscopy (UV-
Vis) revealed a systematic red-shift in the optical absorption edge from ~390 to ~416 nm. Fourier
Transform Infrared Spectroscopy (FTIR) showed progressive loss of surface hydroxyl groups and
organic residues, with the Ti–O lattice sharpening and intensifying at higher temperatures.
Photoluminescence (PL) measurements indicated a shift in emission followed by intensity quenching
at 750 °C due to reduced defect density. Raman spectra corroborated the XRD-determined phase
sequence and further confirmed the anatase to rutile phase transformation. Thermogravimetric
analysis (TGA) showed total weight loss falling from ~6% (450 °C) to ~0.5% (750 °C), confirming
the removal of adsorbed water and organic precursors with increasing crystallinity. Cyclic
voltammetry (CV) indicated that the 450 °C sample delivered the highest specific capacitance value
of 1.311 F g⁻¹ at 10 mV s⁻¹ due to its greater surface area and defect-rich anatase structure.
Electrochemical impedance spectroscopy confirmed the lowest charge-transfer resistance in the
450 °C sample. The 450 °C anatase sample additionally exhibited measurable antibacterial activity
against S. aureus, B. subtilis, and K. pneumoniae. Together, these results establish a consistent,
temperature-indexed property map that can guide the selection of TiO2 annealing conditions for
photocatalysis, energy storage, and optoelectronic applications.