The dual-functionality sensor derived from semiconductor metal
oxides operating at low temperature for low power consumption and
robust stability toward humidity is a striking platform for economic
and indoor air-quality monitoring. Therefore, in this work, temperature-dependent
selectivity and robust stability toward carbon monoxide (CO), toluene
(C7H8), and p-xylene (C8H10) are displayed by various TiO2 nanostructures
synthesized following a facile hydrothermal method. The X-ray diffraction
patterns confirmed the tetragonal structure of anatase TiO2. Surface studies confirmed the different morphologies, such as nanoparticles
(TiO2 nanoparticles (TNPs)), nanowires (TiO2 nanowires (TNWs)), and sea-urchin-like hierarchically (HHC) arranged
TiO2 nanostructures. Relatively high surface area and interconnected
pore distribution were witnessed for TNWs and HHC nanostructures as
compared to TNPs. In situ photoluminescence and X-ray photoelectron
spectroscopy analyses confirmed the defect states of the nanostructures,
and the TNWs possessed the highest concentration of oxygen vacancies
and Ti3+, which influenced the dual-selectivity functionality
of TNW toward C7H8 and C8H10 at 25 and 125 °C, respectively. Additionally, at an optimum
working temperature of 25 °C, a response of 2.46 toward 20 ppm
CO was witnessed for the HHC-based sensor and was attributed to the
available surface area and active sites presented by the hierarchically
arranged nanostructures. Cross-sensitivity measurements were conducted
in the presence of interfering gases, which showed negligible cross-responses.
The long-term stability in the presence of relative humidity and the
sensing mechanism underlying the fascinating dual functionality for
C7H8 and C8H10 vapor detection
were discussed in detail. These findings showed that the current sensors
can be employed for detection of C7H8 and C8H10 in a vastly robust and selective way with insignificant
interference from ambient humidity.
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