Structural Properties of NdTiO2+xN1-x and Its Application as Photoanode

Mixed-anion inorganic compounds offer diverse functionalities as a function of the different physicochemical characteristics of the secondary anion. The quaternary metal oxynitrides, which originate from substituting oxygen anions (O^2–) in a parent oxide by nitrogen (N^3–), are encouraging candidates for photoelectrochemical (PEC) water splitting because of their suitable and adjustable narrow band gap and relative negative conduction band (CB) edge. Given the known photochemical activity of LaTiO₂N, we investigated the paramagnetic counterpart NdTiO_2+xN_1–x. The electronic structure was explored both experimentally and theoretically at the density functional theory (DFT) level. A band gap (E_g) of 2.17 eV was determined by means of ultraviolet–visible (UV–vis) spectroscopy, and a relative negative flat band potential of −0.33 V vs reversible hydrogen electrode (RHE) was proposed via Mott–Schottky measurements. ¹⁴N solid state nuclear magnetic resonance (NMR) signals from NdTiO_2+xN_1–x could not be detected, which indicates that NdTiO_2+xN_1–x is berthollide, in contrast to other structurally related metal oxynitrides. Although the bare particle-based photoanode did not exhibit a noticeable photocurrent, Nb₂O₅ and CoO_x overlayers were deposited to extract holes and activate NdTiO_2+xN_1–x. Multiple electrochemical methods were employed to understand the key features required for this metal oxynitride to fabricate photoanodes.

The structural properties of the prospective metal oxynitride NdTiO_2+xN_1−x were experimentally and theoretically investigated. The band edge positions make the compound theoretically suitable for overall photochemical water splitting.

TiNF and Related Analogues of TiO2 : A Combined Experimental and Theoretical Study

Aliovalent anion substitution in inorganic materials brings about marked changes in properties, as exemplified by N,F-codoped metal oxides. Recently, complete substitution of oxygen in ZnO by N and F was carried out to generate Zn₂ NF. In view of the important properties of TiO₂ , we have attempted to prepare TiNF by employing an entirely new procedure involving the reaction of TiN with TiF₄ . While the reaction at low temperature (450 °C) yields TiNF in the anatase phase, reaction at a higher temperature (600 °C) yields TiNF in the rutile phase. This is interesting since the anatase phase of TiO₂ also transforms to the rutile phase on heating. The lattice parameters of TiNF are close to those of the parent oxide. Partial substitution of oxygen in TiO₂ by N and F reduces the band gap, but complete substitution increases the value comparable to that of the oxide. We have examined properties of N,F-codoped TiO₂ , and more interestingly N,F-codoped Ti₃ O₅ , both with lower band gaps than the parent oxides. A detailed first-principles calculations has been carried out on structural and electronic properties of N,F-TiO₂ and the TiNF phases. This has enabled us to understand the effects of N,F substitution in TiO₂ in terms of the crystal structure, electronic structure and optical properties.

Nitrogen and Fluorine Codoped, Colloidal TiO2 Nanoparticle: Tunable Doping, Large Red-Shifted Band Edge, Visible Light Induced Photocatalysis, and Cell Death

Visible light photocatalysis by TiO₂ requires efficient doping of other elements with red-shifted band edge to the visible region. However, preparation of such TiO₂ with tunable doping is challenging. Here we report a method of making nitrogen (N) and fluorine (F) codoped TiO₂ nanoparticle with tunable doping between 1 and 7 at. %. The preparation of N, F codoped TiO₂ nanoparticle involves reaction of colloidal TiO₂ nanorods with an ammonium fluoride-urea mixture at 300 °C, and the extent of N/F doping is tuned by varying the amount of ammonium fluoride-urea and the reaction time. Resultant colloidal N, F codoped TiO₂ nanoparticles show doping dependent shifting of the band edge from the UV to near-IR region, visible light induced generation of reactive oxygen species (ROS), and visible light photodegradation of bisphenol A. A colloidal form of doped TiO₂ nanoparticle offers labeling of cells, visible light induced ROS generation inside a cell, and successive cell death. This work shows the potential advantage of anisotropic nanoparticle precursor for tunable doping and colloidal form of N, F codoped TiO₂ nanoparticle as a visible light photocatalyst.

The role of F-dopants in adsorption of gases on anatase TiO2 (001) surface: a first-principles study

Ti³⁺ induced by F-dopants plays an important role in enhancing interaction between gas molecules and TiO₂ surfaces.