Phase Engineering of Titanium Oxynitride System and Its Solar Light-Driven Photocatalytic Dye Degradation, H₂ Generation, and N₂ Fixation Properties

Abstract

In the present work, a phase engineering strategy is explored toward forming a titanium oxynitride (TiO x N y ) phase by nitriding a sol–gel-derived TiO2-based precursor at different nitridation temperatures ranging from 450 °C to 950 °C in an ammonia gas environment. The evolved Ti-oxynitride phase is confirmed using XRD, Rietveld refinement, micro-Raman, and HRTEM lattice fringes analysis. Various physicochemical properties of the Ti-oxynitride phase are investigated in comparison with the Ti-oxide and nitride phases obtained in this study. The XPS analysis of oxynitride phase shows dual +3/+4 oxidation states of Ti, which can be attributed to Ti–N and Ti–O network in the oxynitride system. The optical absorption and band gap energy of Ti-oxynitride are found to be favorably altered, compared to the typical Ti-oxides, which are attributed to the plasmonic material-like feature of Ti-nitride phase in the system. From the time-resolved photoluminescence spectra, lifetime of the excited carriers in oxide, nitride, and oxynitride systems is estimated to be ∼3.89, 3.83, and 4.59 ns, respectively, which ascribed to the Ohmic-interface-driven improved electron delocalization in oxynitride phase and corroborated with various photoelectrochemical analysis using voltammetry (cyclic and linear sweep), impedance, and photocurrent measurements. The photocatalytic dye degradation (expressed as a percentage), H2 evolution (in units of μmol g–1 h–1) and NH3 formation (in units of μmol g–1 h–1) over the developed Ti-oxynitride system (∼91–96/1278.2/215) is found to be improved compared to the sole oxide (∼85–88/458.6/102) and nitride (∼79–77/619.32/174) systems. The UV–visible light to H2 conversion efficiency of the developed oxynitride system is estimated to be ∼2.55%. The manifested improved photocatalytic efficiency of oxynitride could be attributed to the synergy of oxide-nitride phases facilitating the effective light harvesting properties via plasmonic features and inter/intratransfer of charge carriers in the system via Ohmic contacts, which eventually promote the multifacet redox reactions toward various photocatalytic applications, as demonstrated in this study.

Mechanistic Insights into the Phase Formation of an Atypical Iron Oxynitride (FexOyNz) System and Its Multifunctional Photocatalytic Applications

“…However, the major peaks corresponding to A 1g and E g bands of Fe x O y N z largely match with iron nitride because the vibration of both Fe–O and Fe–N bonding is in close proximity. These similar observations have also been reported in the titanium oxynitride systems as well. , …”

Oxynitride from Oxide versus Nitride: Manifesting Competitive and Synergistic Properties in Titanium Oxynitride for Solar‐Driven Water Splitting and Nitrogen Fixation

“…[21] Accordingly, titanium oxynitride forms with the lattices of Ti-N and Ti-O matching the crystal structure of the respective stable nitride (TiN) and oxide phases (TiO 2 ), rather than having its own distinct crystal structure. [22] Therefore, confirming the formation of unary-metal oxynitride often relies on observing XRD peaks corresponding to the nitride and oxide phases referring to the formation metal oxynitride structure. Both survey spectra (Figure 2a) confirm the presence of all respective elements in the TiO x N y systems obtained.…”