Full Length ArticleHierarchical Fe2O3 nanorods/TiO2 nanosheets heterostructure: Growth mechanism, enhanced visible-light photocatalytic and photoelectrochemical performances
Graphical abstract
Introduction
In recent decades, titanium dioxide (TiO2) as a typical semiconductor material exhibits the wide potential applications in water splitting [1], [2], gas sensors [3], [4], photocatalysis [5], [6], photovoltaic and PEC cells fields [7], [8], due to its super properties such as proper electronic band structure, non-toxicity, low-cost, excellent catalytic activity and good chemical stability. However, TiO2 possesses a large band gap (Eg = 3.2 eV for anatase TiO2 and Eg = 3.0 eV for rutile TiO2), which restricts its light absorption only in the ultraviolet region (about 3–5% of the solar spectrum), resulting in a low effective utilization of solar light. Moreover, TiO2 has a relatively high recombination rate of photogenerated electrons and holes, which will reduce its photocatalytic and PEC performances owing to the poor quantum efficiency. Therefore, numerous research efforts have been focused on modifying TiO2 to extend its optical response towards visible light region and to enhance the efficient electron-hole separation.
Up to now, many narrow-band gap semiconductors have been developed to resolve the above drawbacks of TiO2, such as CdS [9], CdSe [10], PbS [11], In2S3 [12], Fe2O3 [13], and so on. Among these semiconductors, Fe2O3 as an environmental friendly material has recently been widely used to improve the photocatalytic and PEC performances of TiO2, because of its high visible-light absorption capacity, excellent chemical stability and low-cost [13], [14], [15], [16], [17], [18], [19], [20], [21], [22]. By the fabrication of Fe2O3/TiO2 heterostructure, the optical response of composites can extend towards visible light region, and the electron-hole separation can be effectively facilitated owing to the establishment of internal electric field. Sun et al. synthesized zero-dimensional Fe2O3/TiO2 nanopaticles via a calcining method, which exhibited enhanced photocatalytic and PEC performances [13]. Song et al. prepared one-dimensional Fe2O3/TiO2 photoeletrode via a hydrothermal method, which exhibited excellent photoelectric and water-splitting properties [14]. Chen et al. prepared one-dimensional core-shell Fe2O3/TiO2 photocatalyst via a hydrothermal method, which exhibited good visible-light response and excellent photocatalytic activity for Rhodamine B [15]. However, previous studies mainly focused on fabricating Fe2O3/TiO2 heterostructure on the basis of zero- and one-dimensional TiO2 nanomaterials, but there are few reports on fabricating Fe2O3/TiO2 heterostructure on the basis of two-dimensional (2D) TiO2 nanomaterials.
Recently, 2D TiO2 nanomaterials have been considered as the promising photocatalyst and photoanode candidates due to the proper electronic band structure and unique surface structure characteristics, especially for the 2D TiO2 NSs with dominant high-energy {0 0 1} facets [23], [24], [25], [26], [27], [28]. Firstly, the high-energy {0 0 1} facets have higher surface energy to be suit for adsorbing the pollutants, simultaneously which can provide more active sites for PEC reaction [23], [24], [25], [26]. In addition, the different conduction band (CB) and valence band (VB) of {0 0 1} facets and {1 0 1} facets that can effectively promote the internal carriers transport and photogenerated electron-hole separation, which is more favorable for improving the photocatalytic and PEC properties of TiO2 based materials [27], [28]. On the basis of above advantages, a 3D Fe2O3/TiO2 heterostructure by modifying Fe2O3 nanomaterials on the high-energy {0 0 1} facets exposed TiO2 NSs should have a more excellent photocatalytic and PEC performances. Unfortunately, it is still lack of the relevant investigation on 3D Fe2O3/TiO2 (NSs) heterostructure, so far the growth evolution of Fe2O3 nanomaterials onto TiO2 NSs and the optical, photocatalytic and PEC properties of 3D Fe2O3/TiO2 (NSs) composites have not yet been well known.
Herein, in present paper we employ the uniform and large high-energy {0 0 1} facets exposed TiO2 NSs as synthetic template to fabricate a novel 3D Fe2O3 NRs/TiO2 NSs heterostructure by the simple hydrothermal and chemical bath deposition (CBD) methods. The growth evolution of Fe2O3 nanomaterials onto TiO2 NSs are regulated by controlling the CBD time. The as-prepared 3D Fe2O3/TiO2 composites display pure phase, high crystallinity and good visible-light response. What is more, all Fe2O3/TiO2 composites exhibit significantly enhanced photocatalytic and PEC performances than pure TiO2 NSs. The present research can offer a simple route for designing a 3D Fe2O3/TiO2 heterostructure to effectively enhance the photoelectric properties of TiO2 based semiconductor materials.
Section snippets
Fabrication of 3D Fe2O3 NRs/TiO2 NSs heterostructure
In this experiment, all reagents used were of the purest grade available. Firstly, the pure TiO2 NSs were prepared on FTO substrate by the hydrothermal method using a solution of 0.25 g ammonium fluorotitanate (H8F6N2Ti) and 0.5 ml tetrabutyl titanate (C16H36O4Ti) in the mixed solution of 15 ml deionized water and 15 ml hydrochloric acid (HCl) at 170 °C for 12 h. Then, the Fe2O3 NRs were assembled onto TiO2 NSs by the CBD method without any template and precipitating agent. Typically, TiO2 NSs
Results and discussion
Fig. 1 shows the XRD patterns of FTO (curve A), TiO2 NSs (curve B) and 3D TiO2/Fe2O3 composites (curve C). For TiO2 NSs, besides the identified peaks of FTO, all of the diffraction peaks can well correlate to anatase TiO2 (JCPDS card no. 21-1272) and no impurity phase is found, which indicates the as-prepared TiO2 NSs have a pure anatase phase. Furthermore, the (1 0 1) diffraction peak has the highest intensity, which indicates the TiO2 NSs are highly oriented in the (1 0 1) direction. For 3D Fe
Conclusions
In summary, a novel 3D Fe2O3/TiO2 heterostructure is fabricated by the facile hydrothermal and CBD methods. During the growth process, Fe2O3 nanomaterials preferentially grow on the low-energy {1 0 1} facets of TiO2 NSs, and the growth evolution of that can be regulated by controlling the CBD time. Compared with pure TiO2 NSs, Fe2O3/TiO2 composites exhibited the significantly enhanced photocatalytic and PEC performances, owing to the larger BET surface area, better optical absorption and
Acknowledgments
Ruina Zhang and Meiling Sun contributed equally to this work. This work was supported financially by Natural Science Foundation of Shandong Province, China (Nos. ZR2016FB16), Higher Education Research and Development Program of Shandong Province (Nos. J18KA242).
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