Consequences of Nitrogen Doping and Oxygen Enrichment on Titanium Local Order and Photocatalytic Performance of TiO₂ Anatase

Abstract

Extended X-ray Absorption Fine Structure (EXAFS) investigation of the oxygen-rich titania formed via the thermal treatment of N-doped TiO 2 has revealed that the removal of N-dopants is responsible for the creation of defect sites in the titanium environment, thus triggering at high temperatures (500-800 o C) the capture of atmospheric oxygen followed by its diffusion towards the vacant sites and formation of interstitial oxygen species. The effect of the dopants on Ti coordination number and Ti-O int and TiN int bond distances has been estimated. The photocatalytic p-cresol degradation tests have demonstrated that the interband states formed by the N-dopants contribute to a greater extent to the visible-light activity than the oxygen interstitials do. However, under the UV irradiation the oxygen-rich titania shows higher efficiency in the pollutant degradation, while the N-dopants in N-TiO 2 play the role of recombination sites. On the other hand, the presence of the surface nitrogen species in TiO 2 is highly beneficial for the application in partial photooxidation reactions, where N-TiO 2 demonstrates a superior selectivity of 5-hydroxymethyl furfural (HMF) oxidation to 2,5furandicarboxaldehyde (FDC). Thus, this work underlines the importance of a rational design of non-metal doped titania for photocatalytic degradation and partial oxidation applications, and it establishes the role of bulk defects and surface dopants on the TiO 2 photooxidation performance.

Photocatalytic Oxidation of HMF under Solar Irradiation: Coupling of Microemulsion and Lyophilization to Obtain Innovative TiO2-Based Materials

“…The results showed that high specific surface area, low crystallinity, and reduced hydroxylation degree of synthesized TiO 2 are among the influencing parameters, showing a less significant effect on the over-oxidation of HMF to CO 2 and H 2 O through the formation of DFF and some aliphatic intermediates. This has also been confirmed in other studies using differently synthesized titania [ 20 , 36 , 37 ]. A tendency to mineralization is an expected feature since, under UV light, TiO 2 in water media is known to generate • OH, • O 2 − , and HO • 2 radicals, leading to a complete oxidation of aliphatic and aromatic compounds [ 38 , 39 ].…”

Selective photocatalytic oxidation of 5-hydroxymethyl-2-furfural in aqueous suspension of polymeric carbon nitride and its adduct with H2O2 in a solar pilot plant

“…If the control over the HMF to FDC oxidation selectivity is relatively easily achieved in organic solvents, where hydroxyl radicals are not produced [23], carrying out the same reaction in water is a more complicated task. Low-crystalline and N-doped TiO2 were found to be suitable photocatalysts for this oxidation reaction under UV-light in aqueous medium, however they provided selectivity of only 30-40 % [19,24]. The application of polymeric carbon nitride (PCN) not only allowed to increase this value up to 50 %, but also to use efficiently natural sunlight [21].…”

Effect of Substituents on Partial Photocatalytic Oxidation of Aromatic Alcohols Assisted by Polymeric C3N4

“…In fact, the formation of highly oxidative hydroxyl radicals readily occurs on the surface of inorganic semiconductor photocatalysts having high VB potential. [17] Numerous approaches including non-metal doping [18] and using low-crystalline TiO2 [19] were intended to enhance the selectivity of alcohols partial oxidation. However, it was not possible to completely avoid the formation of by-products and substrate mineralisation, hence a selectivity far below 100 % was usually obtained.…”