Facile Fabrication of a Photocatalyst of Ta₄N₅Nanocolumn Arrays by Using Reactive Sputtering

Abstract

This paper reports a facile fabrication method for robust and separated polycrystalline Ta 4 N 5 nanocolumn arrays on a FTO/glass substrate that involves using reactive sputtering, which provides an alternative approach to fabricating nitrides without using caustic NH 3 gases. The bandgap of Ta 4 N 5 nanocolumns made at 600 • C was observed to be approximately 2.5 eV. The excellent photodegradation performance was demonstrated in an environment with a pH of 10, in which approximately 80% of methylene blue (5 ppm) was photodegraded in 90 min. The incident photon-to-current efficiency of the 600 • C sample showed equivalent or superior characteristics compared with the Ta 3 N 5 and IrO 2 /Ta 3 N 5 thin films reported in the literature. The photoelectrochemical current measurement also demonstrated the stability of the sample. These features suggest that Ta Photodecomposition of organic pollutants that entails using longlasting solar power is one of the most sustainable applications of photocatalysis, 1 in addition to photocatalytic water splitting for hydrogen (H 2 ) production.2,3 Although various semiconductors have been proposed for such applications, most of these semiconductors exhibited various problems and limitations; for example, PbS and CdS 4,5 are toxic and easily photocorroded in a solution; ZnO is photocorrosive 6 and difficult to synthesize using solution-based processes because of its low solubility in water;7 Fe 2 O 3 , SnO 2 , and WO 3 require additional power to trigger harvesting of H 2 because of the unsuitable conduction band edges. 8 TiO 2 has been the most studied photocatalyst, 9,10 but exhibits excellent photocatalytic activity only under ultraviolet (UV) irradiation because of its wide bandgap (approximately 3.2 eV for anatase and 3.0 eV for rutile 9 ). A desirable photocatalytic process should occur in the visible light range, which comprises the prevailing portion (approximately 43%) of the solar spectrum. 3,11Tantalum nitride, existing in various stable and metastable phases, 12,13 represents another promising material system because it exhibits various favorable properties. The microstructure, as well as the mechanical and electrical properties, can be modulated within a wide range, depending on the deposition techniques 14 and the stoichiometry of nitrogen. 19,[24][25][26] and photodecomposition of organic pollutants. In particular, Ta 3 N 5 has received considerable attention because of its advantageous band structure (E g ∼ = 1.5 eV-2.1 eV).19,27-30 Studies have typically synthesized Ta 3 N 5 by using a two-step approach; Ta 2 O 5 was first grown, and subsequent nitridation was employed to obtain Ta 3 N 5 in a moisturized NH 3 atmosphere. 25,[30][31][32][33] This method typically exhibited the poor control of film thickness and structural discontinuities during oxidation and nitridation. 31 Consequently, high defect densities of Ta 3 N 5 were attained, thus compensating the photoelectrochemical (PEC) performance. 34 In addition, the chemical and functional instability of Ta 3 N 5...

Photocatalytic and photoelectrochemical performance of Ta3N5 microcolumn films fabricated using facile reactive sputtering

“…Furthermore, a previous study demonstrated that the chemical environment (i.e., pH level) of photocatalysis is crucial for efficiency. 56 Our earlier study 24 showed that a pH value of approximately 10 was optimal for FIG. 4. AES spectra of the Ta 3 N 5 microcolumns.…”

A Selective Synthesis of TaON Nanoparticles and Their Comparative Study of Photoelectrochemical Properties

“…Although it has been reported that tantalum based photocatalysts (Ta 2 O 5 , [52,53] and its nitrogen substituted compounds [54,55]) can degrade MB, the mechanism of the photocatalytic activity on Ta 3 N 5 or comparing it with Ta 2 O 5 is not yet reported. A preliminary analysis of the possible mechanism of photodegradation based on reports using these and other photocatalysts used in MB photodegradation is therefore presented here first.…”