RESUMEN
A comparative study of the synthesis of TiO2 nanorods on fluorine-doped tin oxide (FTO) glass, Si, SiO2, Si/Ta, Si/TiN, Si/TiN/Ti and Si/HFO2 substrates by hydrothermal reaction is presented. Detailed analysis on the growth of TiO2 on pre-annealed Si/TiN/Ti and HfO2 (HFO) surfaces is also given. For Si/TiN/Ti, a pre-annealing procedure led to the transformation of Ti to a TiO2 layer which acts as a seed for aligned growth of TiO2 nanorods. In contrast, Si/HFO does not provide a nucleation site for the formation of aligned nanorods. Various samples were prepared by varying the synthesis conditions, i.e. pre- and post-annealing temperatures and hydrothermal reaction time to figure out the optimum conditions which lead to unidirectional and highly aligned nanorods. X-ray diffraction, scanning electron microscopy, ultraviolet-visible spectroscopy and Raman spectroscopy were used to study structural, morphological and optical properties of synthesized samples. It is found that TiO2 nanorods exhibit a rutile phase on the Si/Ti/TiN and Si/HFO substrates, but highly oriented vertical growth of nanorods has been observed only on pre-annealed Si/TiN/Ti substrates. On the other hand, TiO2 nanorods form dandelion-like structures on Si/HFO substrates. Growth of vertically oriented TiO2 nanorods on Si/TiN/Ti is attributed to the TiO2 seed layer which forms after the process of pre-annealing of substrates at a suitable temperature. Variation in hydrothermal reaction time and post-annealing temperature brings further improvement in crystallinity and morphology of nanorods. This work shows that the pre-annealed Si/TiN/Ti substrate is the optimal choice to achieve vertically oriented, highly aligned TiO2 nanorods.
RESUMEN
The photoinduced synthesis of zinc oxide nanoparticles (ZnO NPs) was carried out to unveil the effects of change in wavelength of photons. ZnO NPs were synthesized by the coprecipitation technique exposed to different light regimes [dark environment, daylight, and blue-, green-, yellow-, and red-colored light-emitting diodes (LEDs)] at room temperature. X-ray diffractogram (XRD) revealed the wurtzite structure of ZnO NPs. A small change in the size of ZnO NPs (17.11-22.56 nm) was observed with the variation in wavelength of lights from 350 to 700 nm. Spherical to hexagonal disks and rodlike surface morphologies were observed by scanning electron microscopy (SEM). The elemental composition and surface chemistry of NPs were studied by energy-dispersive X-ray diffractive (EDX) and Fourier transform infrared (FTIR) spectra. Maximum free radical quenching activity, cation radical scavenging, and total antioxidant capacity were found in ZnO NPs synthesized under green light (28.78 ± 0.18, 30.05 ± 0.21%, and 36.55 ± 2.63 µg AAE/mg, respectively). Daylight-synthesized NPs (DL-ZNPs) showed the greatest total reducing potential (15.81 ± 0.33 µg AAE/mg) and metal-chelating activity (37.77 ± 0.31%). Photoinduced ZnO NPs showed significant enzyme inhibitory effects on amylase, lipase, and urease by red-light NPs (87.49 ± 0.19%), green-light NPs (91.44 ± 0.29%), and blue-light NPs (92.17 ± 0.34%), respectively. Photoinduced ZnO NPs have been employed as nanozymes and found to exhibit intrinsic peroxidase-like activity as well. Blue-light-synthesized ZnO NPs displayed the strongest antibacterial activity (23 mm) against methicillin-resistant Staphylococcus aureus (MRSA). This study can be considered as a novel step toward the synthetic approach using LEDs to synthesize ZnO NPs with specific physicochemical properties and extends a great prospect in the environmental chemistry, food safety, and biomedical fields as nanozyme, antioxidant, antibacterial, anti-α-amylase, antiurease, and antilipase agents.
RESUMEN
We present the frequency- and temperature-dependent dielectric response of Eu1-x Ba x TiO3 (0 ⩽ x ⩽ 0.5) in detail. Excluding grain boundary effects, four relaxation mechanisms were observed. Relaxation dynamics were observed to arise due to hopping conduction associated with defects, namely oxygen vacancies as well as Eu3+ and Ti3+ ions. Dielectric relaxation analysis led to the identification of Ti ions in two different environments with different relaxation rates in the overall EuTiO3 perovskite structure. The emergence of another relaxation mechanism associated with ferroelectric order as a consequence of the formation of polar regions was also observed for higher Ba concentrations. The addition of Ba led to the identification of relaxation dynamics associated with hopping conduction between Eu ions, Ti ions (in the regions with and without oxygen vacancies) and with the formation of ferroelectric polar regions. Furthermore, the polydispersivity and relaxation times were extracted within the framework of the modified Debye model. Relaxation times have been observed to increase with a decrease in temperature while larger values of polydispersivity reveal a wide distribution of relaxation times due to the presence of lattice parameter and energy barrier distributions.