Xiaoliang Fang

Single-crystal-like hematite colloidal nanocrystal clusters: synthesis and applications in gas sensors, photocatalysis and water treatment

A facile and efficient one-pot solvothermal synthetic route based on a simplified self-assembly is proposed to fabricate spherical hematite colloidal nanocrystal clusters (CNCs) of uniform shape and size. The as-prepared hematite CNCs are composed of numerous nanocrystals of approximately 20 nm in size, and present a single-crystal-like characteristic. A possible formation process based on the nucleation–oriented aggregation–recrystallization mechanism is proposed. Our experiments demonstrated that both the surfactant and the mixed solvent play very critical roles in controlling the size of primary nanocrystals and the final morphology of single-crystal-like spherical CNCs. Compared with other hematite nanostructures, the spherical hematite CNCs show outstanding performance in gas sensing, photocatalysis and water treatment due to their large surface area and porous structure. In addition, interesting tertiary CNCs formed by further assembly of secondary spherical CNCs were observed for the first time.

A multiple coating route to hollow carbon spheres with foam-like shells and their applications in supercapacitor and confined catalysis

Recent advances in the sol–gel process derived resorcinol-formaldehyde (RF) coating strategies offer new opportunities for the synthesis and applications of hollow carbon spheres (HCS). Due to the lack of an effective route for controlling the pore structures, the synthesis of RF resin derived HCS with a high specific surface area for promising applications is still a challenge. In this work, we present a facile and effective template-directed multiple coating route to synthesize RF resin derived HCS with foam-like shells (HCSF). The as-synthesized HCSF exhibit a significantly higher specific surface area (1286 m2 g−1) and larger pore volumes (2.25 cm3 g−1) than the RF resin derived HCS (639 m2 g−1 and 0.56 cm3 g−1). Our experiments demonstrated that the cationic surfactant CTAB plays a critical role in forming the foam-like pore structure. Compared with the RF resin derived HCS, the as-synthesized HCSF show advantageous performances in supercapacitor and confined catalysis due to their unique pore structures.

A Multi‐Yolk–Shell Structured Nanocatalyst Containing Sub‐10 nm Pd Nanoparticles in Porous CeO2

The fabrication of catalytically stable nanocatalysts containing fine noble metal nanoparticles is an important research theme. We report a method for the synthesis of a hierarchically structured Pd@hm‐CeO2 multi‐yolk–shell nanocatalyst (h=hollow; m=mesoporous) containing sub‐10 nm Pd nanoparticles from pre‐made hydrophobic Pd nanoparticles. In the developed method, monodisperse hydrophobic Pd nanoparticles are first reacted with an iron oxide precursor iron(III) acetylacetonate to allow the deposition of iron oxide on their surface. In a Brij 56–water–cyclohexane reverse micelle system, the surface growth of iron oxide is found to mediate and, thus, facilitate the encapsulation of hydrophobic Pd nanoparticles in SiO2 to yield Pd‐Fe2O3@SiO2 nanoparticles in a high concentration. After removal of Fe2O3 by acid, the obtained Pd@SiO2 core–shell particles are reacted solvothermally with Ce(NO3)3 in an ethylene glycol–water–acetic acid mixture to produce multi‐core–shell Pd@SiO2@m‐CeO2 nanospheres. In each multi‐core–shell Pd@SiO2@m‐CeO2 nanosphere, several Pd@SiO2 particles are separately embedded in mesoporous CeO2. After selective removal of silica by NaOH, Pd@SiO2@m‐CeO2 nanospheres are transformed into the multi‐yolk–shell Pd@hm‐CeO2 nanocatalyst. Even with a low Pd loading at 0.4 wt %, the as‐prepared multi‐yolk–shell Pd@hm‐CeO2 nanocatalyst displays high catalytic activity in CO oxidation with 100 % CO conversion at 110 °C. In comparison, under the same catalytic conditions, the same amount of the same‐sized Pd nanoparticles supported on SiO2 achieves 100 % CO conversion at 180 °C. More importantly, the multi‐yolk–shell structure of the Pd@hm‐CeO2 nanocatalyst significantly enhances the stability of the catalyst. No loss in catalytic activity was observed on the Pd@hm‐CeO2 nanocatalyst treated at 550 °C for six hours. The Pd@hm‐CeO2 nanocatalyst also exhibited excellent catalytic performance and stability in the aerobic selective oxidation of cinnamyl alcohol to cinnamaldehyde.

Hollow-in-hollow carbon spheres with hollow foam-like cores for lithium–sulfur batteries

Lithium-sulfur batteries have attracted increasing attention because of their high theoretical capacity. Using sulfur/carbon composites as the cathode materials has been demonstrated as an effective strategy to optimize sulfur utilization and enhance cycle stability as well. In this work, hollow-in-hollow carbon spheres with hollow foam-like cores (HCSF@C) are prepared to improve both capability and cycling stability of lithium–sulfur batteries. With high surface area and large pore volumes, the loading of sulfur in HCSF@C reaches up to 70 wt.%. In the resulting S/HCSF@C composites, the outer carbon shell serves as an effective protection layer to trap the soluble polysulfide intermediates derived from the inner component. Consequently, the S/HCSF@C cathode retains a high capacity of 780 mAh/g after 300 cycles at a high charge/discharge rate of 1 A/g.

General and Facile Syntheses of Metal Silicate Porous Hollow Nanostructures

Porous hollow nanostructures have attracted intensive interest owing to their unique structure and promising applications in various fields. A facile hydrothermal synthesis has been developed to prepare porous hollow nanostructures of silicate materials through a sacrificial-templating process. The key factors, such as the concentration of the free metal cation and the alkalinity of the solution, are discussed. Porous hollow nanostructures of magnesium silicate, nickel silicate, and iron silicate have been successfully prepared by using SiO(2) spheres as the template, as well as a silicon source. Several yolk-shell structures have also been fabricated by a similar process that uses silica-coated composite particles as a template. As-prepared mesoporous magnesium silicate hollow spheres showed an excellent ability to remove Pb(2+) ions in water treatment owing to their large specific surface and unique structures.

pH-induced simultaneous synthesis and self-assembly of 3D layered beta-FeOOH nanorods.

Higher-ordered architectures self-assembly of nanomaterials have recently attracted increasing attention. In this work, we report a spontaneous and efficient route to simultaneous synthesis and self-assembly of 3D layered beta-FeOOH nanorods depending on a pH-induced strategy, in which the continuous change of pH is achieved by hydrolysis of FeCl(3).6H(2)O in the presence of urea under hydrothermal conditions. The electron microscopy observations reveal that the square-prismic beta-FeOOH nanorods are self-assembled in a side-by-side fashion to form highly oriented 2D nanorod arrays, and the 2D nanorod arrays are further stacked in a face-to-face fashion to form the final 3D layered architectures. On the basis of time-dependent experiments, a multistage reaction mechanism for the formation of the 3D layered beta-FeOOH nanorods architecture is presented, involving the fast growth and synchronous self-assembly of the nanorods toward 1D, 2D, and 3D spontaneously. The experimental evidence further demonstrates that the urea-decomposition-dependent pH continuously changing in the solution, spontaneously altering the driving force competition between the electrostatic repulsive force and the attractive van der Waals force among the nanorods building blocks, is the essential factor to influence the self-assembly of the beta-FeOOH nanorods from 1D to 3D.

Self-supporting sulfur cathodes enabled by two-dimensional carbon yolk-shell nanosheets for high-energy-density lithium-sulfur batteries

How to exert the energy density advantage is a key link in the development of lithium–sulfur batteries. Therefore, the performance degradation of high-sulfur-loading cathodes becomes an urgent problem to be solved at present. In addition, the volumetric capacities of high-sulfur-loading cathodes are still at a low level compared with their areal capacities. Aiming at these issues, two-dimensional carbon yolk-shell nanosheet is developed herein to construct a novel self-supporting sulfur cathode. The cathode with high-sulfur loading of 5 mg cm−2 and sulfur content of 73 wt% not only delivers an excellent rate performance and cycling stability, but also provides a favorable balance between the areal (5.7 mAh cm–2) and volumetric (1330 mAh cm–3) capacities. Remarkably, an areal capacity of 11.4 mAh cm–2 can be further achieved by increasing the sulfur loading from 5 to 10 mg cm–2. This work provides a promising direction for high-energy-density lithium–sulfur batteries.One of the challenges facing lithium-sulfur batteries is to develop cathodes with high mass and high volume loading. Here the authors show that two-dimensional carbon yolk-shell nanosheets are promising sulfur host materials, enabling stable battery cells with high energy density.

Hierarchical porous carbon microrods composed of vertically aligned graphene-like nanosheets for Li-ion batteries

Preventing the stacking of ultrathin 2D carbon nanostructures is a very important research theme in the field of energy storage. In this work, hierarchical porous carbon microrods (HPCMs) composed of vertically aligned graphene-like nanosheets are successfully fabricated via a facile Mg(OH)2-templating method. The unique structure of the HPCMs is a desirable combination of 1D hierarchical structures, vertically aligned graphenes, and porous graphenes. With the hierarchical structure and pores, high specific surface area, large pore volume, and ideal charge transport and ion diffusion pathways, HPCMs are potential candidates for high-performance electrode materials. When used as an anode for Li-ion batteries, the HPCM electrode exhibits excellent capability (1150 mA h g−1 at 0.1 A g−1), rate performance (246 mA h g−1 at 10 A g−1), and cycling stability (833 mA h g−1 after 700 cycles at 1 A g−1), with measurements superior to those of natural graphite and many graphene-based anodes.

A facile one-pot synthesis of supercubes of Pt nanocubes

A facile one-pot synthetic strategy is developed to prepare high-quality Pt supercubes. The as-synthesized Pt supercubes are composed of the uniform Pt nanocubes arranged in a primitive cubic structure. The shape and size of the Pt superparticles are readily tuned by varying the structures of pyridyl-containing ligands used in the synthesis. The co-presence of CO and nitrogen-containing ligands is critical to the formation of Pt supercubes. While CO molecules play an important role in the synthesis of Pt nanocube, introducing nitrogen-containing ligands is essential to the successful assembly of those nanocubes into Pt supercubes. Our systematic studies reveal that the electrostatic attraction between positively charged ligands and negatively charged Pt nanocubes is the main driving force for the assembly of Pt nanocubes into supercubes. More importantly, the ligands within the Pt supercubes are readily removed at relatively low temperature to yield surface-clean supercubes which are expected to exhibit unique size-selective catalysis.

A cake making strategy to prepare reduced graphene oxide wrapped plant fiber sponges for high-efficiency solar steam generation

A facile method inspired by the cake making process is developed to fabricate reduced graphene oxide wrapped plant fiber sponges (PFS@rGO) through in situ coating and foaming. This method avoids the use of energy-intensive equipment for molding and drying, and hence has great potential in the production of large-sized rGO sponges. With a highly porous framework, good mechanical properties, efficient solar absorption, and low thermal conductivity, the as-fabricated hydrophilic and light-weight PFS@rGO readily floats on seawater and generates water vapor with a solar thermal conversion efficiency of 88.8% under 1 sun illumination.