Tin (Sn)-doped beta phase gallium oxide (β-Ga2O3) nanostructures at different Sn concentrations (0 to 7.3 at%) are synthesized using a facile hydrothermal method. The Sn-doped β-Ga2O3 nanostructures are characterized using scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy, and absorbance spectroscopy. In addition, their photocatalytic activity is evaluated by observing methylene blue degradation under ultraviolet light (254 nm) irradiation. The photocatalytic activity of the Sn-doped (0.7 at%) β-Ga2O3 nanostructures is significantly enhanced compared to that of intrinsic β-Ga2O3 nanostructures due to the elevated charge separation. Excessive Sn concentrations (exceeding 2.2 at%) above the solid solubility limit of the Sn in β-Ga2O3 nanostructures lead to SnO2 and SnO precipitation. The presence of SnO2 and SnO degrades the photocatalytic efficiency in the β-Ga2O3 nanostructures. The results suggest new opportunities for the synthesis of highly effective β-Ga2O3-based photocatalysts for applications in environmental remediation, disinfection, and selective organic transformations.
The photocatalytic activity is correlated with different parameters affecting the photocatalytic reactions; redox potential (RP), surface area (SA), crystal defect (CD), oxygen defect (OD), and grain-boundary induced defect (GD).
β-Ga 2 O 3 has attracted considerable attention as an alternative photocatalyst to replace conventional TiO 2 under ultraviolet-C irradiation due to its high reduction and oxidation potential. In this study, to enhance the photocatalytic activity of β-Ga 2 O 3 , nanofibers are formed via the electrospinning method, and Si atoms are subsequently doped. As the Si concentration in the β-Ga 2 O 3 nanofiber increases, the optical bandgap of the β-Ga 2 O 3 nanofibers continuously decreases from 4.5 eV (intrinsic) to 4.0 eV for the Si-doped (2.4 at. %) β-Ga 2 O 3 nanofibers, and accordingly, the photocatalytic activity of the β-Ga 2 O 3 nanofibers is enhanced. This higher photocatalytic performance with Si doping is attributed to the increased doping-induced carriers in the conduction band edges. This differs from the traditional mechanism in which the doping-induced defect sites in the bandgap enhance separation and inhibit the recombination of photon-generated carriers.
An ionic device using
a liquid Ga electrode in a 1 M NaOH solution
is proposed to generate artificial neural spike signals. The oxidation
and reduction at the liquid Ga surface were investigated for different
bias voltages at 50 °C. When the positive sweep voltage from
the starting voltage (
V
S
) of 1 V was applied
to the Ga electrode, the oxidation current flowed immediately and
decreased exponentially with time. The spike and decay current behavior
resembled the polarization and depolarization at the influx and extrusion
of Ca
2+
in biological synapses. Different average decay
times of ∼81 and ∼310 ms were implemented for
V
S
of −2 and −5 V, respectively,
to mimic the synaptic responses to short- and long-term plasticity;
these decay states can be exploited for application in binary electrochemical
memory devices. The oxidation mechanism of liquid Ga was studied.
The differences in Ga ion concentration due to
V
S
led to differences in oxidation behavior. Our device is beneficial
for the organ cell–machine interface system because liquid
Ga is biocompatible and flexible; thus, it can be applied in biocompatible
and flexible neuromorphic device development for neuroprosthetics,
human cell–machine interface formation, and personal health
care monitoring.
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