Impregnation versus Bulk Synthesis: How the Synthetic Route Affects the Photocatalytic Efficiency of Nb/Ta:N Codoped TiO₂ Nanomaterials

Abstract

Selecting the proper doping strategy is essential to controlling the photocatalytic activity of TiO 2 -based nanomaterials. In this work, we compare impregnation and bulk synthesis methods for feeding titania nanocrystals with either Nb or Ta as transition metal dopant and N as nonmetal codopant.The resulting photocatalytic efficiency was tested toward ethanol degradation under either UV or simulated solar irradiation. Microstructure, morphology, and electronic properties at various length scales were deeply investigated and compared with DFT simulations. Instead, under UV irradiation, impregnated samples performed better than bulk synthesis ones, with Ta-doped powders being more efficient than Nb-doped and undoped TiO 2 . Under simulated solar irradiation, bulk synthesis Nbdoped materials were the most active ones, while all the impregnated samples were even less performing than the undoped TiO 2 reference. On the basis of XPS, EPR, DRS, and XRPD results, such differences were attributed to the bulk synthesis approach producing a more homogeneous distribution of guest dopants within the grains, in conjunction with a higher amount of intrinsic defects (such as O vacancies). Implications of these findings on the engineering of efficient titania photocatalysts are discussed.

Passivated co-doping approach to bandgap narrowing of titanium dioxide with enhanced photocatalytic activity

“…Experimental results on F-N codoped TiO2 showed strong visible-light absorption and high photocatalytic activity for p-chlorophenol [63], rhodamine B [63], acetaldehyde [64], trichloroethylene [64], and toluene [64] [67] were enhanced by the Nb-N co-doping under visible light. For Ta-N, the photocatalytic oxidation activity evaluated by the decompositions of oleic acid, SCN-, Br-, I- [68], ethanol [67] were enhanced by the Ta-N co-doping under visible light, when compared to N single doping.…”

On the Crystal Structural Control of Sputtered TiO2 Thin Films

“…Thus, the bombardment effect may not be a main factor for the formation of rutile phase during the sputtering process (we subsequently confirmed the weak influence of the bombardment effect by off-axis sputtering, as discussed in the following section). Such a growth behaviour can likely be attributed to the strong thermodynamic driving force towards the I4 1 /amd phase, which results in smaller critical radii of the crystal nuclei and accelerates nucleation over the growth process [12].…”

“…Currently, two approaches can be used to fabricate pure-phase sputtered TiO 2 films. One is to control the sputtering conditions such as the total gas pressure, substrate temperature and type of sputtering gas to selectively fabricate uniform coatings of rutile or anatase TiO 2 films [1]; the other is to use impurity doping to induce a phase transformation between the anatase and rutile phases [1,[7][8][9][10][11][12][13][14].…”

“…However, the bombardment effects have not been confirmed experimentally, and the mechanism by which the rutile or anatase TiO 2 phase grows during the sputtering process remains unknown. In the case of impurity doping, elements such as Mn [7], Fe [7], Cu [7], Ag [8], Ni [9] and Co [9] have been reported to enhance the phase transition from the anatase to the rutile phase, whereas other elements such as W [7], V [10], Si [11], Nb [12], Ta [12] and Cr [13] have been reported to suppress the anatase-to-rutile phase transition. On the basis of first-principles calculations, the room-temperature phase conversion of anatase to rutile TiO 2 using Co or Ni doping is attributed to the increased interaction between Co and Ni atoms, which results in the formation of a linear chain in the rutile phase [14].…”

Polymorphism and Structural Distortions of Mixed-Metal Oxide Photocatalysts Constructed with α-U3O8 Types of Layers

“…The carrier diffusion lengths, and charge carrier mobility are also critical to the material's photocatalytic performance [85,[92][93][94][95]. In addition, selecting a suitable doping strategy is essential to enhancing photocatalytic properties [96]. Common challenges for achieving water splitting with heterogeneous photocatalysts include rapid recombination of electrons/holes [97], hole/electron collection at particle surfaces [98], and improvement of the photocatalytic rates [99,100].…”