Invited review and perspectiveHollow spherical titanium dioxide nanoparticles for energy and environmental applications
Graphical abstract
Introduction
Titanium dioxide (TiO2) is a multifunctional material used in pigments, cosmetics, and food additives since the early twentieth century (Chen & Mao, 2007). TiO2 has recently shown promise in energy and environmental applications, such as solar cells (Bai, Mora-Seró, De Angelis, Bisquert, & Wang, 2014), photocatalysts (Ma et al., 2014), and batteries (Su et al., 2012, Yang et al., 2009). TiO2 exhibits unique optical, electrical, and chemical properties, and is non-toxic and widely abundant (Su, Lu, Tian, Ma, & Gong, 2013). Many strategies have been proposed for improving the performance of TiO2 in energy and environmental applications, with fine control of its morphology being one of the most effective (Osterloh, 2013). TiO2 nanospheres (Kim et al., 2009), nanorods/nanowires/nanobelts (Hoang et al., 2012, Liu and Aydil, 2009, Tian et al., 2014, Zhou et al., 2013), and nanotubes (El Ruby Mohamed and Rohani, 2011, Lee et al., 2014, Paramasivam et al., 2012) have all been synthesized, and have exhibited favorable properties in various applications. Hollow spherical TiO2 structures possess large specific surface areas, enhanced light scattering properties, and their inner and outer surfaces can be controlled and selectively functionalized. Hollow spherical TiO2 has shown good performance in energy and environmental applications.
In this review we discuss approaches for synthesizing hollow spherical TiO2 materials, including templating and solvothermal methods. The application of hollow spherical TiO2 in dye-sensitized solar cells (DSSCs), photocatalysts, and batteries is then reviewed. Directions for future research on TiO2 hollow spheres are finally discussed.
Section snippets
Templating method
This method for synthesizing hollow spherical TiO2 nanoparticles involves coating TiO2 precursors onto polymer beads or inorganic nanoparticles, which act as sacrificial templates. The template is subsequently removed by annealing or chemical etching. The particle size and dispersibility and surface properties of the template greatly affect the properties of the resulting hollow spherical TiO2 nanoparticles. Tuning the geometries or functionalizing the surfaces of carefully selected templates
DSSCs
Solar cells convert solar energy into electricity, and are a promising alternative to fossil fuel reserves for meeting increasing energy demands. DSSCs have attracted tremendous attention and development since their first report, which utilized mesoporous TiO2 of large surface area (O’Regan & Grätzel, 1991).
A typical DSSC (Fig. 6) contains a mesoporous metal oxide (usually TiO2) deposited on a transparent conducting substrate (Hagfeldt, Boschloo, Sun, Kloo, & Pettersson, 2010). The mesoporous
Conclusions and perspectives
This review covers synthetic approaches for hollow spherical TiO2 nanoparticles, and their performance in DSSCs, photocatalysts, and batteries. However, the application of TiO2 hollow spheres is not limited to these. They have also been investigated as sensors (Yang, Hu, Cao, Yuan, & Xu, 2010), heterogeneous water treatment catalysts (Linley, Leshuk, & Gu, 2013), and membrane components (Liu, Jiang, Wang, & Yang, 2013). The high activity of TiO2 hollow spheres in these applications results from
Acknowledgements
We acknowledge the National Natural Science Foundation of China (Nos. U1463205, 21222604, 51302185), Program for New Century Excellent Talents in University (No. NCET-10-0611), Scientific Research Foundation for the Returned Overseas Chinese Scholars (MoE), and Program of Introducing Talents of Discipline to Universities (No. B06006) for financial support.
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Crystallization of hollow TiO<inf>2</inf> into anatase at mild conditions, for improved surface recognition in selective photocatalysis
2022, Applied Catalysis A: GeneralCitation Excerpt :Hollow spheres based on TiO2, of nanometric or micrometric size, have been widely described in the literature as photocatalysts of high photonic efficiency [1–4]. This is due to the several advantages that characterize these structures, namely, high capacity for multiple diffraction and reflection light processes, chemical stability, low cost, large surface area, low density and high shell permeability [2,5–7]. Crystallinity is one of the most important factors for obtaining a TiO2 photocatalyst with high photonic efficiency.
Hollow structures of Ti<inf>n</inf>O<inf>m</inf> systems with m ≈ 2n: A density functional theoretical study
2022, Journal of Physics and Chemistry of SolidsCitation Excerpt :Although these methods have proven to be robust for the synthesis of THS, they also present some difficulties, such as the high cost of the materials used as templates and the need for numerous steps in the synthesis process, which has led some scientists to explore template-free methods [7,17]. Whatever the method used, these THS are revolutionizing several applications [18], where their use in electrochemiluminescence to detect cholesterol [8], chloramphenicol [15], prostate protein antigen in serum [19] or diclofenac [20] stands out. Besides, these THS are also being considered for applications in energy systems such as dye-sensitized solar cells (DSSCs) [4,7], a class of photovoltaic devices based on nanocrystalline porous films with dye molecules absorbed on the surface; lithium-ion batteries [21–23], the most promising energy storage technologies for electric and hybrid vehicles as well as renewable energy systems such as wind and solar energy generators; and lithium-sulfur (Li–S) batteries [24], the most promising alternatives for lithium-ion batteries.
Latest progress on the key operating parameters affecting the photocatalytic activity of TiO<inf>2</inf>-based photocatalysts for hydrogen fuel production: A comprehensive review
2021, FuelCitation Excerpt :A noticeable enhancement of around 3303.85 μmol/g h of H2 was mainly ascribed to the role of 2D Ni2P and Ti3+ in facilitating the electron diffusion, Z-scheme mechanisms in enhancing the charge separation efficiency, and improving light absorption and utilization through the formation of nanotubes structure and oxygen vacancy. Furthermore, the fabrication of TiO2 hollow-sphere has been extensively reported as an effective way to enhance its photocatalytic activity because it can offer large specific surface areas and improve the light scattering properties of TiO2 [320]. For instance, Jiang et al. [321] boosted the photocatalytic activity of TiO2 hollow sphere for hydrogen production under solar light irradiation by dual cocatalysts (Ag and RuO2).
Highly photoactive TiO<inf>2</inf> microspheres for photocatalytic production of hydrogen
2019, International Journal of Hydrogen EnergyCitation Excerpt :These hierarchical structures have high surface-volume ratios, retain a significant surface area with good crystallinity, reduce recombination possibilities as they promote electron-hole separation by increasing electron delocalisation, and in addition normally have micrometric dimensions which facilitate their separation by simple filtration [14–20]. Numerous studies have been published on the synthesis of hierarchical TiO2, generally of hollow microspheres by templating or solvothermal methods [21]. In this respect, K. Yan and G. Wu published a recent review in which they compiled the different methods to obtain TiO2-hollow microsphere based materials and the application of these materials in photocatalytic hydrogen production [22].
Synthesis of 3D CQDs/urchin-like and yolk-shell TiO<inf>2</inf> hierarchical structure with enhanced photocatalytic properties
2019, Ceramics InternationalCitation Excerpt :However, the small particles still have some problems, such as serious aggregation, bad dispersion stability and difficulty to be separated and recycled. In comparison, the synthesis of hierarchical TiO2 structures assembled by small nanosheets and nanowires is a more promising way to solve these problem, since they have good dispersion and stability during the cyclic reaction, and also show higher photocatalytic activity owing to their increased specific surface area [26,27]. In particularly, according to our previous study [28], the three-dimensional urchin-like and yolk-shell TiO2 microspheres with internal cavity and large surface area can significantly facilitate the light absorption and enlarge the contact area with contaminants.