One-dimensional titanium dioxide (TiO2) based mostly nanomaterials akin to nanorods, nanotubes and nanowires, occupy an necessary place within the business as a consequence of their wonderful physicochemical properties, excessive side ratio, massive particular floor space, and wonderful stability [1], [2], [3], [4]. The polymorphism function of TiO2 contributes to the various purposes of one-dimensional TiO2 nanomaterials in several areas[5], [6]. As an illustration, TiO2(B) (TB) is extensively used as adverse electrode materials in lithium-ion batteries due to its open construction, good lithium-ion embedding and desorption efficiency [7], [8], [9]. The nanostructures of anatase TiO2 (TA), rutile TiO2 (TR), and their heterojunctions are often utilized in photocatalysis as a consequence of their distinctive digital constructions in addition to structural stability [10], [11], [12], [13], [14]. Subsequently, in sensible purposes, it’s desired to exactly fabricate TiO2-based nanomaterials with managed crystal part, morphology, and even atomic construction. Heating-induced part transition of H2Ti3O7 (HT) precursors is a prevalent technique for making ready one-dimensional TiO2-based nanomaterials. Nevertheless, this seemingly easy technique is, the truth is, extremely intricate on the microscopic stage, because it entails a posh course of together with not solely compositional change as a consequence of dehydration but in addition atomic construction variation amongst totally different TiO2 phases. Subsequently, to comprehensively perceive the atomic mechanism of the part transformation technique of TiO2-based nanomaterials is sort of difficult, which is the premise for acquiring TiO2 nanomaterials with desired constructions.
To disclose the structural transition mechanism, great developments have been made within the structural transition research of titanate nanomaterials via a wide range of spectroscopy strategies (X-ray diffraction [15], Raman spectroscopy [16], [17], synchronous thermal evaluation [18], and so forth.). As evidenced by a earlier research via X-ray diffraction technique [19], each the TA and TB phases had been detected after annealing HT at elevated temperatures, coexisting inside a broad experimental situation vary [20]; and a basic statistical regularity was efficiently obtained that the transformation of HT to TA part could occur immediately, or entails TB because the intermediate part [21]. However the detailed atomic construction evolution stays obscure, and lots of essential points stay to be clarified, as a consequence of lack of in situ structural evolution info on the atomic scale.
Prior to now a long time, the development of the in situ transmission electron microscopy (TEM) technique has made it attainable for direct visualization of atomic structural and composition evolution of nanostructured supplies with a excessive spatial and temporal decision underneath totally different exterior environments [22], [23], [24], [25], [26], [27], [28], [29], [30], [31], akin to crystal nucleation [32], crystal progress [33], [34], [35], part transition [36], and floor reconstruction [37], [38], [39], [40], [41], and so forth [42]. Fei et al. have efficiently utilized the in situ TEM in finding out structural evolution of Na0.8Ti4O8 nanorods at elevated temperatures [43]. Lei et al. studied the part transformation of one-dimensional H2Ti3O7 nanofibers to TiO2(B) with in-situ SAED mixed theoretical calculation [44]. They’ve additionally analyzed the crystallographic orientation relationship of the coherent and incoherent interfaces between TA and TB part fabricated by annealing H2Ti3O7 nanofibers [45]. Nevertheless, many essential points stay to be solved. The nucleation and progress pathways throughout the part transformation are nonetheless unclear, and the detailed structural transition course of and the essential elements stays to be clarified. As well as, the direct TEM statement of the structural evolution of HT nanotubes are thought-about very difficult, as a result of the ultra-thin HT nanotube wall (often 2–3 atomic layers) is extraordinarily sensitivity to e-beam irradiation [19].
Herein, utilizing environmental transmission electron microscopy (ETEM), we in situ studied the dynamic part transition of titanate nanotubes at elevated temperatures. By utilizing a quick CMOS digital camera and a low electron dose to attenuate the electron beam irradiation harm, the structural evolution of hydrogenated titanate to TiO2 was noticed at atomic stage, which underwent a two-step part transition course of, consisting of an oblique HT-to-TB nucleation course of through nonuniform dehydration and atomic rearrangement, and a direct TB-to-TA nucleation and interface migration course of. With additional evaluation by HRTEM, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and thermogravimetry-differential scanning calorimetry (TG-DSC), an entire part transition mechanism from HT nanotubes to TB and TA nanocrystals was proposed.
