Gang Ou

Graphene-based Recyclable Photo-Absorbers for High-Efficiency Seawater Desalination

Todays scientific advances in water desalination dramatically increase our ability to transform seawater into fresh water. As an important source of renewable energy, solar power holds great potential to drive the desalination of seawater. Previously, solar assisted evaporation systems usually relied on highly concentrated sunlight or were not suitable to treat seawater or wastewater, severely limiting the large scale application of solar evaporation technology. Thus, a new strategy is urgently required in order to overcome these problems. In this study, we developed a solar thermal evaporation system based on reduced graphene oxide (rGO) decorated with magnetic nanoparticles (MNPs). Because this material can absorb over 95% of sunlight, we achieved high evaporation efficiency up to 70% under only 1 kW m(-2) irradiation. Moreover, it could be separated from seawater under the action of magnetic force by decorated with MNPs. Thus, this system provides an advantage of recyclability, which can significantly reduce the material consumptions. Additionally, by using photoabsorbing bulk or layer materials, the deposition of solutes offen occurs in pores of materials during seawater desalination, leading to the decrease of efficiency. However, this problem can be easily solved by using MNPs, which suggests this system can be used in not only pure water system but also high-salinity wastewater system. This study shows good prospects of graphene-based materials for seawater desalination and high-salinity wastewater treatment.

Arc-Melting to Narrow the Bandgap of Oxide Semiconductors

The bandgap of a series of oxide semiconductors is narrowed by a quick and facile arc-melting method. A defective structure is formed in the fast melting and cooling process without changing its phase structure. Enhanced optical and electrical properties are found in the arc-melted oxide, such as enhanced photocatalytic properties of the arc-melted ZnO under visible light.

High conductivity of La2Zr2O7 nanofibers by phase control

We report an oxygen ionic conductivity of 0.016 S cm−1 in La2Zr2O7 nanofibers at 500 °C, which is ∼400 times higher than traditional La2Zr2O7 bulk materials. The highly enhanced conductivity of our La2Zr2O7 nanofibers can mainly be attributed to a novel mixed phase structure. We found that a defect fluorite to pyrochlore phase transition occurred at 875 °C. By precise control of calcination conditions, we successfully tuned the ratio of defect fluorite and pyrochlore phases, and further demonstrated that nanofibers with a mixed phase structure have higher conductivity due to an interface lattice mismatch between the two phases. The remarkably high conductivity and facile manufacturing of the La2Zr2O7 nanofibers make them a promising material for high performance SOFCs and oxygen sensors. Moreover, our study provides a new strategy to design solid electrolytes with high conductivity by phase control.

Photothermal therapy by using titanium oxide nanoparticles

The photothermal therapy (PTT) technique is regarded as a promising method for cancer treatment. However, one of the obstacles preventing its clinical application is the non-degradability and biotoxicity of the existing heavy-metal and carbon-based therapeutic agents. Therefore, a PTT material with a high photothermal efficiency, low toxicity, and good biocompatibility is urgently wanted. Herein, we report a titanium oxide-based therapeutic agent with a high efficacy and low toxicity for the PTT process. We demonstrated that Magnéli-phase Ti8O15 nanoparticles fabricated by the arc-melting method exhibit >98% absorption of near infrared light and a superior photothermal therapy effect in the in vivo mouse model. The Ti8O15 nanoparticle PTT material also shows a good biocompatibility and biosafety. Our study reveals Magnéli-phase titanium oxide as a new family of PTT agents and introduces new applications of titanium oxides for photothermal conversion.

Ultralight, scalable, and high-temperature–resilient ceramic nanofiber sponges

Scalable synthesis of ultralight, multifunctional, and high-temperature resilient ceramic nanofiber sponges by blow-spinning. Ultralight and resilient porous nanostructures have been fabricated in various material forms, including carbon, polymers, and metals. However, the development of ultralight and high-temperature resilient structures still remains extremely challenging. Ceramics exhibit good mechanical and chemical stability at high temperatures, but their brittleness and sensitivity to flaws significantly complicate the fabrication of resilient porous ceramic nanostructures. We report the manufacturing of large-scale, lightweight, high-temperature resilient, three-dimensional sponges based on a variety of oxide ceramic (for example, TiO2, ZrO2, yttria-stabilized ZrO2, and BaTiO3) nanofibers through an efficient solution blow-spinning process. The ceramic sponges consist of numerous tangled ceramic nanofibers, with densities varying from 8 to 40 mg/cm3. In situ uniaxial compression in a scanning electron microscope showed that the TiO2 nanofiber sponge exhibits high energy absorption (for example, dissipation of up to 29.6 mJ/cm3 in energy density at 50% strain) and recovers rapidly after compression in excess of 20% strain at both room temperature and 400°C. The sponge exhibits excellent resilience with residual strains of only ~1% at 800°C after 10 cycles of 10% compression strain and maintains good recoverability after compression at ~1300°C. We show that ceramic nanofiber sponges can serve multiple functions, such as elasticity-dependent electrical resistance, photocatalytic activity, and thermal insulation.

Phase stability and high conductivity of ScSZ nanofibers: effect of the crystallite size

10 mol% Sc2O3-doped ZrO2 (10ScSZ) nanofibers were prepared through electrospinning followed by calcination. The phase structures and electrical conductivities of the nanofibers have been investigated as a function of the crystallite size. The cubic (c) phase can be stabilized in 10ScSZ nanofibers when the average crystallite size is smaller than 26 nm. The generated phase stability endows the nanofibers with an enhanced conductivity which increases with the decrease of crystallite size. As the average crystallite size decreased from 37 nm to 7 nm, the conductivity of the nanofibers increased by more than 20 times. An exceptionally high oxide ion conductivity of 0.023 S cm−1 for the nanofibers was observed at 500 °C, which is more than 900 times higher than that of bulk 10ScSZ.

Enhanced oxide-ion conductivity in highly c-axis textured La10Si6O27 ceramic

Here, we report a highly c-axis textured apatite-type La10Si6O27 ceramic with conductivity of 1.3 × 10−2 S cm−1 at 500 °C, which is an 11.2 times enhancement compared with isotropic La10Si6O27 ceramic. The highly c-axis textured La10Si6O27 was fabricated by a arc-melting process with a unilateral temperature gradient as the main driving force for the formation of the La10Si6O27 texture. The conductivity enhancement is mainly attributed to the enhanced mobility contribution along the c-axis with low activation energy and the relatively small grain boundary blocking effect along the c-axis.

Defective molybdenum sulfide quantum dots as highly active hydrogen evolution electrocatalysts

Molybdenum disulfide (MoS2), a promising non-precious electrocatalyst for the hydrogen evolution reaction with two-dimensional layered structure, has received increasing attention in recent years. Its electrocatalytic performance has been limited by the low active site content and poor conductivity. Herein, we report a facile and general ultrafast laser ablation method to synthesize MoS2 quantum dots (MS-QDs) for electrocatalytic HER with fully exposed active sites and highly enhanced conductivity. The MS-QDs were prepared by ultrafast laser ablation of the corresponding bulk material in aqueous solution, during which they were partially oxidized and formed defective structures. The as-prepared MS-QDs demonstrated high activity and stability in the electrocatalytic HER, owing to their very large surface area, defective structure, abundance of active sites, and high conductivity. The present MS-QDs can also find application in optics, sensing, energy storage, and conversion technologies.

Fabrication of high performance oxygen sensors using multilayer oxides with high interfacial conductivity

The effective enhancement of the ionic conductivity of solid oxide electrolytes by manipulating the multilayered hetero-nanostructures has been recognized for more than a decade; however, such fantastic nanostructures have not been applied for practical applications yet. Here we fabricated Ce0.8Sm0.1Nd0.1O2−δ/Al2O3 (SNDC/AO) multilayered electrolyte materials with high oxygen ionic conductivity and explored their applications in oxygen sensors with low operating temperature. The multilayer oxide electrolytes show a conductivity of 2 orders of magnitude higher than that of traditional yttria-stabilized zirconia (YSZ) ceramics at 400 °C, which endows the sensors with high performances including a rapid response (∼0.1 s), high sensibility (down to 1 vol%) and high cycling stability (no performance degradation after 1000 cycles), and most importantly, low operating temperature (200 °C lower relative to YSZ-based sensors). The excellent performances of our multilayered electrolytes can be attributed to their high interfacial conductivity and low activation energy which might be related to the highly disordered microstructures. This study shows good prospects for the efficient and practical use of multilayered oxide-based electrolytes for a range of applications including sensors, oxygen separation, solid oxide fuel cells (SOFCs) and solid oxide electrolysis cells (SOECs).

Residual stress-dependent electric conductivity of sputtered co-doped CeO2 thin-film electrolyte

Sm3+ and Nd3+ co-doped ceria thin-film electrolytes have been deposited on polycrystalline alumina substrates via RF magnetron sputtering. Electric conductivity is evaluated with respect to the residual stress in the film by sin2 ψ-methodology, indicating that an in-plane tensile stress is applied to the as-deposited film. The stress in the film increases as annealing temperature decreases, and there is an enlarged crystal lattice. The results also reveal that the annealed film with a greater stress shows a higher electric conductivity, which might be due to the lower activation energy. The conductivity of the film annealed at 600 °C is as high as 0.009 S cm−1 at 500 °C, and the residual stress is determined to be 542.70 MPa at room temperature.