Enhanced Photocatalytic Activity of Electrospun β-Ga2O3 Nanofibers via In-Situ Si Doping Using Tetraethyl Orthosilicate

Abstract

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.

Impact of Al doping on a hydrothermally synthesized β-Ga2O3 nanostructure for photocatalysis applications

“…The pH value in the solution was adjusted to approximately 10 by adding an ammonium hydroxide solution (NH 4 (OH) 28 vol% in H 2 O) which was necessary to form b-Ga 2 O 3 nanostructures via a hydrothermal reaction. 26,27,31 To dope Al in the b-Ga 2 O 3 nanostructures with different concentrations, different amounts of aluminum nitrate nonahydrate (Al(NO 3 ) 3 $9H 2 O) (0.02, 0.064, 0.110, and 0.210 g for Al 0…”

“…The supersaturated mixed solution was transferred to a Teon-lined stainless-steel autoclave, thermally treated at 140 C for 10 h, and subsequently cooled down naturally to room temperature. 26,27,31 Aer the hydrothermal synthesis process, a-GaOOH nanostructures with different Al concentration were collected, washed three times with DI water, and then dried in an oven at 70 C for 6 h. It is noted that a-GaOOH nanostructures were precipitated in dissolved solutions (Ga(NO 3 ) 3 $xH 2 O) with an (NH 4 (OH)) alkali in this work, and it was reported that the a-GaOOH nanostructures were also precipitated in dissolved solutions (Ga(NO 3 ) 3 $xH 2 O) with other alkalis such as NaOH, KOH, NaHCO 3 , and Na 2 CO 3 . 32 In addition, the morphologies of the GaOOH were found to have signicantly different in terms of pH values.…”

“…24,25 Thus far, reports have indicated that dopants in Ga 2 O 3 have reduced the bandgap energy of Ga 2 O 3 , which reduce the benets of the high redox potential effects that Ga 2 O 3 posseses. [16][17][18][19][20][24][25][26][27] Therefore, it would be benecial to apply a dopant atom that could increase the Ga 2 O 3 bandgap with the dopant concentration. It has been reported that aluminum (Al) can increase the Ga 2 O 3 bandgap upon doping.…”

Crystallization, Phase Stability, Microstructure, and Chemical Bonding in Ga2O3 Nanofibers Made by Electrospinning

“…This is also seen in Raman spectroscopy data for the 800 °C samples as discussed in the section followed immediately after this. Overall, based on structural analysis, the as-deposited nanofibers are amorphous, which fully transform to crystalline β-phase Ga 2 O 3 nanofibers, which is in good agreement with the reports in the literature for Ga 2 O 3 nanofibers made by the electrospinning process. , Zhao also reported that, in order to obtain crystalline nanofibers, samples were annealed at 900 °C in air for 3 h . Similarly, Yoo et al obtained Si-doped β-Ga 2 O 3 nanofibers via the electrospinning method by thermal treatment 900 °C in air for 6 h. Thus, comparing our results with intrinsic Ga 2 O 3 nanofibers along with those reported on either intrinsic or doped Ga 2 O 3 nanofibers, we can conclusively indicate that a temperature on the order of 900-1000 °C for 2–3 h is optimum to realize crystalline β-phase Ga 2 O 3 nanofibers.…”

“…From group theory symmetry analysis, the number of expected optical vibrational modes of Ga 2 O 3 is 27, and among these vibrational modes, 15 are Raman active, while 12 are infrared active . Raman spectra of Ga 2 O 3 are classified into three regions: a high-frequency region (770–500 cm –1 ) which includes stretching and bending modes of GaO 4 tetrahedra, phonon modes in a middle frequency region (480–310 cm –1 ) due to deformation of GaO 6 octahedra, and phonon modes in a low-frequency region (below 200 cm –1 ) due to the oscillation and translation of Ga–O chains. , Figure shows the Raman spectra of as-prepared and thermally annealed samples. Corroborating with structural data, as-prepared samples (prior to heat treatment) exhibit broader peaks, indicating the amorphous nature of the nanofibers.…”