In this work, the novel macro-mesoporous TiO2 microspheres (MMTMs) have been synthesized via a spray drying route with fumed silica (FS) as template, followed by calcination and etching. The as-synthesized MMTMs have unique bimodal porous structures of macropores origin from FS template and mesopores accumulated by TiO2 nanoparticles. The macro-mesoporous structure endows the TiO2 microspheres with better surface area and wonderful light scattering property. When MMTMs are employed as the photoelectrodes of dye-sensitized solar cells, short-circuit current and open-circuit voltage are both improved and the high power conversion efficiency of 8.68% is obtained eventually, which is much higher than P25 photoelectrode. The excellent performance can be attributed to the excellent light-scattering property, better diffusion of electrolyte as well as superior electron transport owing to the unique bimodal pore structure and the dense packed of the internal nanoparticles of MMTMs.

SnOx nanocrystalline aggregates (NAs) encapsulated by an amorphous TiO2 layer have been successfully designed by a one-step flame spray pyrolysis (FSP). The synthesized SnOx NAs@TiO2 with different degrees of aggregations were composed of SnOx nanocrystallites ranging from 5 nm to 10 nm and a TiO2 layer with a thickness of 1–5 nm. The encapsulated TiO2 layer was introduced in situ by incorporating TiCl4 into the downstream of an FSP reactor, where TiO2 nucleated and grew in the surface of the SnOx NAs. The hydrolysis temperature of TiCl4 in a flame was controlled to synthesize amorphous TiO2 with intrinsic electrochemical features. As an anode in LIBs (Li-ion batteries), the SnOx NAs@TiO2 electrode showed superior cycle life and rate performance (capacity of 350 mA h g−1 after 300 cycles and 332 mA h g−1 at 1 A g−1) compared to pure SnOx or TiO2 electrodes. The remarkably enhanced Li+ storage performance is mainly attributed to the nanoscale of nanocrystalline aggregates, the core–shell structure of SnOx@TiO2 and the amorphous state of TiO2.

The rational design of nanoheterostructured materials has attracted much attention because of its importance for developing highly efficient LIBs. Herein, we have demonstrated that internal Mo6+ doped TiO2 nanocrystals in situ decorated with highly dispersed MoO3 clusters have been realized by a facile and rapid flame spray pyrolysis route for electrochemical energy storage. In such intriguing nanostructures, internal Mo6+ doping can improve the conductivity of electrode materials and facilitate rapid Li+ intercalation and ion transport and the heteroassembly of highly dispersed ultrafine MoO3 clusters with excellent electrochemical activity endows the TiO2 with extra Li+ ion storage ability as well as incorporates Mo6+. Thus, the as-prepared nanohybrid electrodes exhibit a high specific capacity and superior rate capability due to the maximum synergetic effect of TiO2, Mo6+ and ultrafine MoO3 clusters. Moreover, the aerosol flame process with a unique temperature gradient opens a new strategy to design novel hybrid materials by the simultaneous doping and heteroassembly engineering for next-generation LIBs.

The design and engineering of multifunctional nanostructures with multiple components and synergistic properties are in urgent demand for variety of acceptable biosensing platforms, enabling users to fulfill multiple tasks in a single nanosystem. Herein, we report using an asymmetric hematite–silica hybrid of Janus γ-Fe2O3/SiO2 nanoparticles (JFSNs) as a multifunctional biosensing platform for sensitive colorimetric detection of H2O2 and glucose. It was demonstrated that JFSNs exhibit an intrinsic peroxidase-like catalytic activity. Compared with natural enzyme, JFSNs nanoenzymes could be used over a wider range of pH and temperatures and were more stable over time. Importantly, besides its excellent catalytic activity, the asymmetric properties of the Janus nanoparticle enable it to form the multiple functional utilities for various biosensing applications, including the ease of surface modification without deactivation of catalytic activity and recoverable use by magnetic separation. Thus, we utilized JFSNs with glucose oxidase (GOx) immobilization for glucose-sensitive colorimetric detection, which exhibited both catalytic activity of glucose oxidase and peroxidase with high selectivity and acceptable reproducibility. By combining these two analysis systems into Janus particles, an all-in-one and reusable sensor for blood glucose was formed and has the capability for determination of glucose in complex samples such as serum. These results suggest that such Janus nanosystems have the potential to construct robust nanoarchitecture with multiple functionalities for various biosensing applications.Keywords: colorimetric biosensor; glucose; hematite−silica; hydrogen peroxide; Janus nanoparticle;

Sn@Ni3Sn4 embedded nanocable-like carbon hybrids have been successfully prepared through a novel gas-phase route. The introduced Ni3Sn4 layer not only suppresses the tin-induced volume expansion, but also provides more voids and vacancies in the interior of the nanocables. When used as the anode in LIBs, the Sn@Ni3Sn4/C hybrids exhibit a long cycle life (360 mA h g−1 at 1 A g−1 after 1500 cycles).

A novel one-step, vapor-fed aerosol flame synthetic process (VAFS) has been developed to prepare Ti3+ self-doped titanium dioxide (TiO2). The freshly formed TiO2 was in situ surface hydrogenated during the condensation stage by introducing H2 above the flame, and Ti3+ ions were created near the surface of TiO2. The relative content of Ti3+ ions near the surface of TiO2 is estimated to be 8%. Because of the high absorption of visible light and suppression of charge recombination, the photocurrent density and decomposition of MB under visible light irradiation were remarkably enhanced. This study demonstrates a simple, potential method to produce Ti3+ self-doped TiO2 with effective photoactivity in visible light.

Novel SnO2 nanorod@TiO2 hybrid materials have been designed and synthesized by in situ coating a layer of TiO2 on the surface of the SnO2 nanorods using a modified flame spray pyrolysis (FSP) approach. The as-prepared SnO2 nanorod@TiO2 hybrid materials have a length of up to about 150 nm and a diameter of about 40 nm. TiO2 is uniformly coated on well-crystallized SnO2 nanorods with a thickness of about 10 nm. The dye-sensitized solar cell (DSC) properties of the SnO2 nanorod@TiO2 hybrid materials were investigated. Owing to the superior light scattering effect, advantages of suppression charge recombination, and increased dye loading, the power conversion efficiency (η) of the SnO2 nanorod@TiO2 hybrid material electrode is 6.98%, much higher than that of the SnO2 nanorods electrode (3.95%) and P25 electrode (5.27%).

Enhanced electron concentration derived from Ta5+ doping is responsible for the open-circuit voltage improvement due to the upward shift of the Fermi level, but the oxygen defects generated retard the negative shift of the Fermi level. By mediating the trap states, highly efficient DSSC devices could be achieved.

Branch-type SnO2 nanowires with high crystallinity have been successfully prepared by a rapid and continuous flame spray pyrolysis (FSP) route. The SnO2 branch has an average diameter of 15–20 nm and a length of 200–700 nm. As is known, this is the first time one dimensional SnO2 nanowires with branch-type nanostructures have been synthesized using flame synthesis. The average growth rate of nanowires could reach 1 μm s−1, which is thousand times faster than other methods. Interestingly, it is found that Au nanoclusters appear at the tip of SnO2 nanowires. An in situ Au-catalyzed vapour–liquid–solid (VLS) model is proposed to explain the growth mechanism of branch-type SnO2 nanowires in flame. As photoanodes, the DSSCs based on branch-type SnO2 nanowires (with TiCl4 post-treatment) show a higher short-circuit current (JSC = 10.60 mA cm−2) and a superior power conversion efficiency of 4.23%, improved by 99.5% compared to pure SnO2 nanoparticles (2.12%). The efficiency improvement could be attributed to the unique branch-type nanowire architecture, which provides a highly efficient electron channel and excellent ability of light scattering.

Double-faced γ-Fe2O3||SiO2 nanohybrids (NHs) and their in situ selective modification on silica faces with the 3-methacryloxypropyltrimethoxysilane molecules have been successfully prepared by a simple, rapid and scalable flame aerosol route. The double-faced NHs perfectly integrate magnetic hematite hemispheres and non-magnetic silica parts into an almost intact nanoparticle as a result of phase segregation during the preparation process. The unique feature allows us to easily manipulate these particles into one-dimensional chain-like nanostructures. On the other hand, in situ selectively modified double-faced γ-Fe2O3||SiO2 NHs possess excellent interfacial activities, which can assemble into many interesting architectures, such as interfacial film, magnetic responsive capsules, novel magnetic liquid marbles and so forth. The modified NHs prefer to assemble at the interface of water–oil or oil–water systems. It is believed that the highly interfacial active NHs are not only beneficial for the development of interface reaction in a miniature reactor, but also very promising functional materials for other smart applications.

In this paper, we have demonstrated a hierarchical architecture assembly from Sn-filled CNTs, which was in situ deposited on Cu foils to form binder-free electrode by incorporating flame aerosol deposition (FAD) with chemical vapor deposition (CVD) processes. The reversible capacity of Sn-filled CNTs hierarchical architecture anode exhibited above 1000 mA h g–1 before 30th cycle and stabilized at 437 mA h g–1 after 100 cycles at a current density of 100 mA g–1. Even at as high as 2 A g–1, the capacity still maintained 429 mA h g–1. The desirable cycling life and rate capacities performance were attributed to great confinement of tin in the interior of CNTs and the superior conducting network constructed by the 3D hierarchical architecture. The novel, rapid and scalable synthetic route was designed to prepare binder-free electrode with high electrochemical performance and avoid long-time mixing of active materials, binder, and carbon black, which is expected to be one of promising preparation of Sn/C anodes in lithium-ion batteries.Keywords: binder-free electrode; deposition; flame synthesis; hierarchical architecture; lithium-ion batteries; Sn-filled CNTs;

In this paper, novel core–shell α-Fe2O3/SnO2 heterostructures (HSs) are successfully prepared by a one-step flame-assisted spray copyrolysis of iron and tin precursor. The effect of SnO2 component is investigated for the evolution of phase composition and morphology in detail. For the first time, it is noted that SnO2 as a dopant can effectively promote the phase transition of γ-Fe2O3 to α-Fe2O3 during flame synthesis. A phase-segregation induced growth mechanism is proposed to explain the formation of a unique core–shell structure. Such core–shell HSs as LIB anode materials exhibit an enhanced lithium storage capacity in comparison to pure Fe2O3 and SnO2. This enhancement could be ascribed to the synergetic effect of both single components as well as the unique core–shell HSs.

A novel one-step and template-free preparation process had been developed to synthesize TiO2 hierarchically porous hollow spheres (HPHSs) by mixed solvents assisted flame spray pyrolysis (FSP). The as-obtained TiO2 HPHSs had hierarchically porous hollow structure such as central cavities, macropores on shells, and mesopores accumulated by TiO2 nanocrystallites. The unique hierarchically porous structure endowed the TiO2 spheres with high specific surface area and excellent light scattering property. A mechanism of the formation of TiO2 HPHSs depending on the competition between chemical reaction rate and diffusion rate of the components of the precursor was proposed, in which mixed solvents and short flame residence time were of importance. Furthermore, the dye-sensitized solar cells (DSSCs) performance of TiO2 HPHSs as light scattering layer was investigated. The photoelectric conversion efficiency (η) was improved by 38.2% (from 5.00% to 6.91%), comparing to that of single layer P25 films.

Air stable Co3Fe7–CoFe2O4 nanoparticles have been synthesized via one-step flame spray pyrolysis of a mixture of Fe/Co precursor solution under stronger reducing atmosphere. The as-synthesized nanoparticles with diameters of 20–80 nm showed a typical core shell structure and high stability for being one month in air, whose metallic Co3Fe7 cores were protected against oxidation by a surface shell of about 2–4 nm cobalt iron oxide (CoFe2O4). The ratio of metallic Fe/Co alloy nanoparticles was 7:3. The alloy nanoparticles exhibited enhanced saturation magnetization (126.1 emu/g), compared with flame sprayed iron nanoparticles with the same conditions. The formation process of metallic alloy nanoparticles with core–shell structure was investigated, which included three stages: flame combustion, reducing, and surface oxidation during the flame process. It is reckoned that such a continuous production approach is an effective way to produce the stable Co3Fe7 alloy nanoparticles with high saturation magnetization.

A one-step method for continuous large-scale synthesis of well-defined hollow titania spheres was established by feeding titanium tetrachloride mixed with ethanol vapor to a facile diffusion flame. A mixture of TiCl4 and C2H5OH vapor was transported at 100 m/s into a flame reactor and condensed into mesoscale droplets due to Joule–Thomson cooling and the entrainment of cool gases into the expanding high-speed jet. Hollow crystalline TiO2 spheres with good thermal stability were formed after the hydrolysis of TiCl4 in the H2/air flame at about 1500 °C. Structural characterization indicates that the hollow spheres, with uniform diameter of 300 nm and shell thickness of 35 nm, consist of 20–30 nm TiO2 nanocrystallites. A formation mechanism of the hollow spheres was proposed, involving the competition between chemical reaction and diffusion during the flame process. The present study provides a new pathway for continuous and large-scale engineering of hollow nanomaterials.Hollow crystalline TiO2 spheres with good thermal stability were prepared by the hydrolysis of TiCl4 in the H2/air flame at about 1500 °C. The hollow spheres, with uniform diameter of 300 nm and shell thickness of 35 nm, consist of 20–30 nm TiO2 nanocrystallites. The present study provides a new pathway for continuous and large-scale engineering of hollow nanomaterials.

Branch-type SnO2 nanowires with high crystallinity have been successfully prepared by a rapid and continuous flame spray pyrolysis (FSP) route. The SnO2 branch has an average diameter of 15–20 nm and a length of 200–700 nm. As is known, this is the first time one dimensional SnO2 nanowires with branch-type nanostructures have been synthesized using flame synthesis. The average growth rate of nanowires could reach 1 μm s−1, which is thousand times faster than other methods. Interestingly, it is found that Au nanoclusters appear at the tip of SnO2 nanowires. An in situ Au-catalyzed vapour–liquid–solid (VLS) model is proposed to explain the growth mechanism of branch-type SnO2 nanowires in flame. As photoanodes, the DSSCs based on branch-type SnO2 nanowires (with TiCl4 post-treatment) show a higher short-circuit current (JSC = 10.60 mA cm−2) and a superior power conversion efficiency of 4.23%, improved by 99.5% compared to pure SnO2 nanoparticles (2.12%). The efficiency improvement could be attributed to the unique branch-type nanowire architecture, which provides a highly efficient electron channel and excellent ability of light scattering.

Novel SnO2 nanorod@TiO2 hybrid materials have been designed and synthesized by in situ coating a layer of TiO2 on the surface of the SnO2 nanorods using a modified flame spray pyrolysis (FSP) approach. The as-prepared SnO2 nanorod@TiO2 hybrid materials have a length of up to about 150 nm and a diameter of about 40 nm. TiO2 is uniformly coated on well-crystallized SnO2 nanorods with a thickness of about 10 nm. The dye-sensitized solar cell (DSC) properties of the SnO2 nanorod@TiO2 hybrid materials were investigated. Owing to the superior light scattering effect, advantages of suppression charge recombination, and increased dye loading, the power conversion efficiency (η) of the SnO2 nanorod@TiO2 hybrid material electrode is 6.98%, much higher than that of the SnO2 nanorods electrode (3.95%) and P25 electrode (5.27%).

Enhanced electron concentration derived from Ta5+ doping is responsible for the open-circuit voltage improvement due to the upward shift of the Fermi level, but the oxygen defects generated retard the negative shift of the Fermi level. By mediating the trap states, highly efficient DSSC devices could be achieved.

SnOx nanocrystalline aggregates (NAs) encapsulated by an amorphous TiO2 layer have been successfully designed by a one-step flame spray pyrolysis (FSP). The synthesized SnOx NAs@TiO2 with different degrees of aggregations were composed of SnOx nanocrystallites ranging from 5 nm to 10 nm and a TiO2 layer with a thickness of 1–5 nm. The encapsulated TiO2 layer was introduced in situ by incorporating TiCl4 into the downstream of an FSP reactor, where TiO2 nucleated and grew in the surface of the SnOx NAs. The hydrolysis temperature of TiCl4 in a flame was controlled to synthesize amorphous TiO2 with intrinsic electrochemical features. As an anode in LIBs (Li-ion batteries), the SnOx NAs@TiO2 electrode showed superior cycle life and rate performance (capacity of 350 mA h g−1 after 300 cycles and 332 mA h g−1 at 1 A g−1) compared to pure SnOx or TiO2 electrodes. The remarkably enhanced Li+ storage performance is mainly attributed to the nanoscale of nanocrystalline aggregates, the core–shell structure of SnOx@TiO2 and the amorphous state of TiO2.

Sn@Ni3Sn4 embedded nanocable-like carbon hybrids have been successfully prepared through a novel gas-phase route. The introduced Ni3Sn4 layer not only suppresses the tin-induced volume expansion, but also provides more voids and vacancies in the interior of the nanocables. When used as the anode in LIBs, the Sn@Ni3Sn4/C hybrids exhibit a long cycle life (360 mA h g−1 at 1 A g−1 after 1500 cycles).