[Show abstract][Hide abstract] ABSTRACT: Hydrogenated black titania, with a crystalline core/amorphous shell structure, has attracted global interests due to its excellent photocatalytic properties. However, the understanding on its structure-property relationships remains a great challenge and more effective method to produce hydrogenated titania is desirable. Herein, we report a TiH2 assisted reduction method to synthesize a bluish hydrogenated titania (TiO2-x:H) that is highly crystallized. The characteristic amorphous shells, which are essential for the enhancement of solar absorption and photocatalysis in many reported hydrogenated titania, are completely removed by hydrogen peroxide. The blue TiO2-x:H sample without amorphous shells delivers not only significantly improved visible- and infrared-light absorption but also greatly enhanced photocatalytic activity compared to the pristine TiO2. Its water decontamination is 2.5 times faster and the hydrogen production was 1.9-fold higher over the pristine TiO2. Photoelectrochemical measurement reveals that the reduced samples exhibit greatly improved carrier density and photocurrent (a 4.3-fold increase) compared with the original TiO2. This work develops a facile and versatile method to prepare hydrogenated titania and proposes a new understanding on the hydrogenated titania that doped hydrogen atoms, instead of the amorphous shells, are essential to its high photocatalytic performance.
[Show abstract][Hide abstract] ABSTRACT: Black titania with increased solar light absorption and enhanced photocatalytic and photoelectrochemical (PEC) performance has attracted enormous attention, stimulating us to explore the blackening of other wide band-gap oxide semiconductors for enhanced properties. Herein, we report the synthesis of black reduced Nb2O5 nanorods (r-Nb2O5) with an active exposed (001) surface and its enhanced PEC property for the first time. Black r-Nb2O5 nanorods were obtained by molten aluminum reduction of pristine Nb2O5 in a two-zone furnace. Different from the black titania, r-Nb2O5 nanorods are well-crystallized without a core-shell structure, which makes them be outstanding in photocatalytic stability. Substantial Nb4+ cations and oxygen vacancies are introduced into r-Nb2O5, resulting in the enhanced absorption in both visible and near-infrared regions and the improved charge separation and transport capability. The advantage of the r-Nb2O5 was also proved by performing efficient photoelectrochemical performance (138 times at 1.23 VRHE) and higher photocatalytic hydrogen-generation activity (13 times) than pristine Nb2O5. These results indicate that black r-Nb2O5 is a promising material for PEC application and photocatalysis.
No preview · Article · Jan 2016 · Dalton Transactions
[Show abstract][Hide abstract] ABSTRACT: Increasing the electrical conductivity of pseudocapacitive materials without changing their morphology is an ideal structural solution to realize both high electrochemical performance and superior flexibility for all solid state supercapacitor (ASSSC). Here, we fabricate a flexible ASSSC device employing black titania (TiO2-x:N) decorated two dimensional (2D) NiO nanosheets as positive electrode and mesoporous graphene as negative electrode. In this unique design, NiO nanosheets are pseudocapacitive materials and TiO2-x:N nanoparticles serve as conductive agent. Owing to the excellent electrical conductivity of TiO2-x:N and well defined “particle on sheet” planar structure of NiO/TiO2-x:N composites, 2D morphology of decorated NiO nansheets is completely retained, which efficiently reinforces the pseudocapacitive activity and flexibility of the whole all solid state device. The maximum specific capacitance of fabricated NiO/TiO2-x:N//mesoporous graphene supercapacitor can reach up to 133 Fg-1, which is 2 and 4 times larger than the values of NiO based ASSSC employing graphene and carbon black as conductive agent, respectively. In addition, the optimized ASSSC displays intriguing performances with an energy density of 47 Wh kg-1 in a voltage region of 0-1.6 V, which is, to the best our knowledge, a highest value for the flexible ASSSC devices. The impressive results presented here may pave the way for promising applications of black titania in high energy density flexible storage systems.
[Show abstract][Hide abstract] ABSTRACT: Substantially different from traditional combinatorial-treatment of photothermal therapy (PTT) and photodynamic therapy (PDT) by using multi-component nanocomposite under excitation of separate wavelength, a novel single near infrared (NIR) laser-induced multifunctional theranostic nanoplatform has been rationally and successfully constructed by a single component black titania (B-TiO2-x) for effective imaging-guided cancer therapy for the first time. This multifunctional PEGylated B-TiO2-x shows high dispersity/stability in aqueous solution, excellent hemo/histocompatibility and broad absorption ranging from NIR to ultraviolet (UV). Both in vitro and in vivo results well demonstrated that such a novel multifunctional theranostic nanoplaform could achieve high therapeutic efficacy of simultaneous and synergistic PTT/PDT under the guidance of infrared thermal/photoacoustic (PA) dual-modal imaging, which was triggered by a single NIR laser. This research circumvents the conventional obstacles of using multi-component nanocomposites, UV light and high laser power density. Furthermore, negligible side effects to blood and main tissues could be found in 3 months’ investigation, facilitating its potential biomedical application.
[Show abstract][Hide abstract] ABSTRACT: Black TiO2, with enhanced solar absorption and photocatalytic activity, has gained extensive attention, inspiring us to investigate the reduction of other wide-bandgap semiconductors for improved performance. Herein, we report the preparation of grey Ta2O5 nanowires with disordered shells and abundant defects via aluminum reduction. Its water decontamination is 2.5 times faster and hydrogen production was 2.3-fold higher over pristine Ta2O5. The reduced Ta2O5 also delivers significantly enhanced photoelectrochemical performance compared with the pristine Ta2O5 nanowires, including much higher carrier concentration, easier electron-hole separation and 11 times larger photocurrent. Our results demonstrate that Ta2O5 will have great potentials in photocatalysis and solar energy utilization after proper modification.
No preview · Article · Dec 2015 · ACS Applied Materials & Interfaces
[Show abstract][Hide abstract] ABSTRACT: Extraordinary tubular graphene cellular material of a tetrahedrally connected covalent structure was very recently discovered as a new supermaterial with ultralight, ultrastiff, superelastic and excellent conductive characteristics, but no high specific surface area will keep it from any next-generation energy storage applications. Herein, we prepare another new graphene monolith of mesoporous graphene-filled tubes instead of hollow tubes in the reported cellular structure. This graphene nanoporous monolith is also composed of covalently-bonded carbon network possessing high specific surface area of ~1,590 m(2) g(-1), and electrical conductivity of ~32 S cm(-1), superior to graphene aerogels and porous graphene forms self-assembled by graphene oxide. This 3D graphene monolith can support over 10,000 times its own weight, significantly superior to CNT and graphene cellular materials with a similar density. Furthermore, pseudocapacitance-active functional groups are introduced into the new nanoporous graphene monolith as an electrode material in electrochemical capacitors. Surprisingly, the electrode of 3D mesoporous graphene has a specific capacitance of 303 F g(-1) and maintains over 98% retention after 10,000 cycles, belonging to the list for the best carbon-based active materials. The macroscopic mesoporous graphene monolith suggests the great potential as an electrode for supercapacitors in energy storage areas.
[Show abstract][Hide abstract] ABSTRACT: Flexible/stretchable devices for energy storage are essential for future wearable and flexible electronics. Electrochemical capacitors (ECs) is an important technology for supplement batteries in energy storage and harvesting field, but are limited by relatively low energy density. Herein, we report a superelastic foam consisting of few-layer carbon nanowalls made from natural cotton as a good scaffold to growth conductive polymer polyaniline for stretchable, lightweight and flexible all-solid-state ECs. As-prepared superelastic bulk tubular carbon foam (surface area ~950 m2/g) can withstand >90% repeated compression cycling and support >45,000 times its own weight but no damage. The flexible device has a high specific capacitance of 540 F/g in weight of the total electrode materials, a specific energy of 25.5 Wh/kg and a power density of 28.5 kW/kg and withstands 5,000 charging/discharging cycles.
No preview · Article · Oct 2015 · ACS Applied Materials & Interfaces
[Show abstract][Hide abstract] ABSTRACT: Transition-metal perovskite oxides possess rich functionalities in the fields of ferroelectrics, piezoelectrics, superconductors, dielectrics, fuel cells and photocatalysis. Nano-facet control of the cubic ATiO3 (A: a divalent cation) phase, a typical perovskite oxide, may result in new properties or phenomena not observable in the bulk material. Herein, we first report a puzzle-like 3D hierarchical structure constructed with K0.5La0.5TiO3 nanosheets. Surprisingly, K0.5La0.5TiO3 has a cubic symmetry similar to a SrTiO3 perovskite. The unusual phase is synthesized by a simple one-pot hydrothermal strategy without using any structure-directing agent. After modest acidification, the assembled 3D hierarchical structure is etched into a core-shell nanostructure which consists of a crystalline K0.5La0.5TiO3 core and an amorphous TiO2 shell. The acid-treated sample exhibits remarkably enhanced photocatalytic H2 production, which is over 60 times higher than the pristine sample.
No preview · Article · Oct 2015 · Dalton Transactions
[Show abstract][Hide abstract] ABSTRACT: A facile, high yield ZnCl2/KCl molten-salt route is developed to fabricate black titania hexagonal nanosheets under atmospheric pressure and low temperature (400 °C). After post-annealing, the black titania possesses a tunable phase composition and enhanced visible light photocatalytic activity, accompanied with a controllable morphology transformation from hexagonal nanosheets to nanorods.
[Show abstract][Hide abstract] ABSTRACT: Black titania has attracted enormous attention due to its enhanced photocatalytic activity via increased solar absorption, but few studies extended the investigations to other wide band-gap titanates. Herein, strontium titanate (SrTiO3), a typical ternary titanate with more potential in photocatalysis, is selected as the target material. Black SrTiO3 nanocrystals were obtained by molten aluminum reduction of solution-processed pristine SrTiO3 in a two-zone furnace. Different from the black titania, black SrTiO3 nanocrystals are well-crystallized and have no core-shell structure. Substantial Ti3+ cations and oxygen vacancies are introduced into SrTiO3 after aluminum reduction, which results in enhanced absorption in both visible and near-infrared regions, and improved charge separation and transport. The photocatalytic hydrogen-generation and photoelectrochemical investigations demonstrate that black SrTiO3 exhibits an impressive improvement (2.5 times and 2.4 times at 1.23 VRHE, respectively) compared with white SrTiO3.
[Show abstract][Hide abstract] ABSTRACT: Carbon microtube/graphene (CMT/GR) hybrid structures were prepared from a natural biomass material (absorbent cotton) by the carbonization and continuous chemical vapour deposition (CVD) of graphene at 1200 °C. The graphene nanosheets deposited by CVD had a few-layer structure and were uniformly coated on the surface of the CMTs. The CMT/GR composite had a hollow tubular structure, a specific surface area of about 312 m2 g-1 and was highly hydrophobic (contact angle about 128°). The CMT/GR hybrid acted as a thermally conductive supporting framework and organic octadecanoic acid (OA) was easily impregnated into the CMT/GR structure by capillary forces. The CMT/GR/OA composite had a thermal conductivity of about 0.69 W m-1 K-1 at a CMT/GR loading fraction of about 10 wt%, which is about 4.3 times larger than that of OA (about 0.16 W m-1 K-1). The CMT/GR/OA composite had a high heat storage capacity of about 174 J g-1, very close to the value of OA (about 186 J g-1) and showed good thermal reliability even after 500 melting/freezing cycles. This method produces novel shape-stabilized phase change materials for use in thermal energy storage applications and has given new insights into the design and preparation of CMT/GR hybrid structures from natural resources. This journal is
No preview · Article · Aug 2015 · Journal of Materials Chemistry A
[Show abstract][Hide abstract] ABSTRACT: To utilize visible-light solar energy to meet environmental and energy crises, black TiO2 as a photocatalyst is an excellent solution to clean polluted air and water and to produce H2. Herein, black TiO2 with a crystalline core–amorphous shell structure reduced easily by CaH2 at 400 °C is demonstrated to harvest over 80 % solar absorption, whereas white TiO2 harvests only 7 %, and possesses superior photocatalytic performances in the degradation of organics and H2 production. Its water decontamination is 2.4 times faster and its H2 production was 1.7 times higher than that of pristine TiO2. Photoelectrochemical measurements reveal that the reduced samples exhibit greatly improved carrier densities, charge separation, and photocurrent (a 4.5-fold increase) compared with the original TiO2. Consequently, this facile and versatile method could provide a promising and cost-effective approach to improve the visible-light absorption and performance of TiO2 in photocatalysis.
[Show abstract][Hide abstract] ABSTRACT: Supercapacitors suffer either from low capacitance for carbon or derivate electrodes or from poor electrical conductivity and electrochemical stability for metal oxide or conducting polymer electrodes. Transition metal nitrides possess fair electrical conductivity but superior chemical stability, which may be desirable candidates for supercapacitors. Herein, niobium nitride, Nb4N5, is explored to be an excellent capacitive material for the first time. An areal capacitance of 225.8 mF cm−2, with a reasonable rate capability (60.8% retention from 0.5 to 10 mA cm−2) and cycling stability (70.9% retention after 2000 cycles), is achieved in Nb4N5 nanochannels electrode with prominent electrical conductivity and electrochemical activity. Faradaic pseudocapacitance is confirmed by the mechanistic studies, deriving from the proton incorporation/chemisorption reaction owing to the copious +5 valence Nb ions in Nb4N5. Moreover, this Nb4N5 nanochannels electrode with an ultrathin carbon coating exhibits nearly 100% capacitance retention after 2000 CV cycles, which is an excellent cycling stability for metal nitride materials. Thus, the Nb4N5 nanochannels are qualified for a candidate for supercapacitors and other energy storage applications.
[Show abstract][Hide abstract] ABSTRACT: Black TiO2, with increased solar light absorption and enhanced photocatalytic and photoelectrochemical (PEC) performance, has attracted enormous attention, stimulating us to explore the blackening of other oxide semiconductors for enhanced properties. Here, we report the fabrication of black nanostructured Nb2O5 and its enhanced PEC property for the first time. We successfully prepare oxygen-deficient black Nb2O5 nanochannels, which contain considerable amount of oxygen vacancies (Nb4+ sites) serving as shallow donors. The black Nb2O5 exhibits strong visible and infrared light absorption, which can absorb 75.5% solar energy superior to 5.7% for pristine Nb2O5. The PEC performance of black Nb2O5 photoanode is significantly enhanced with a relatively large photocurrent of 1.02 mA cm-2 and high applied bias photon-to-current efficiency (ABPE) of 0.345%, in comparison with the poor performance of pristine Nb2O5 (0.084 mA cm-2 photocurrent and 0.056% ABPE). These results indicate that black Nb2O5 is a promising material for PEC application and solar energy utilization.
[Show abstract][Hide abstract] ABSTRACT: A novel architecture of graphene wrapped copper-nickel (Cu-Ni) nanospheres (NSs)/graphene film was proposed to be TCO- and Pt-free counter electrode (CE) with high electrocatalytic activity for dye-sensitized solar cells (DSSCs). The novel architecture CE is composed of highly conductive graphene film, Cu-Ni alloy NSs and the wrapping graphene on the surface of alloy NSs. The graphene film as an electrically conductive layer was synthesized by chemical vapor deposition (CVD) on the insulating SiO2 substrate, and graphene wrapped Cu-Ni alloy catalyst NSs on the graphene film were in-situ formed by the reduction of Cu-Ni acetate and graphene growth using CVD. The graphene wrapped Cu-Ni NSs/graphene film CE shows much superior electrocatalytic activity, compared with graphene film, and the power conversion efficiency of 5.46% was achieved in DSSC devices, which is close to that of Pt/FTO electrode (6.19%). Therefore, the novel architecture of graphene wrapped Cu-Ni NSs/graphene film CE may be used as Pt- and TCO-free CEs for low-cost, high performance DSSCs.
[Show abstract][Hide abstract] ABSTRACT: Colored titania has attracted enormous attentions due to its visible light absorption and wide range of applications. Here, we demonstrate an effective approach to obtain colored titania with enhancing solar absorption by introducing disorder in the surface of titania through Al reduction. As prepared black TiO2−x possesses solar energy absorption up to 88%. The recombination centers of light-induced electrons and holes are reduced in acid solution, which ensures the excellent photocatalytic activity of the black TiO2 −x in the photo-oxidation of organic molecules in water.
Full-text · Article · Nov 2014 · Catalysis Communications
[Show abstract][Hide abstract] ABSTRACT: Three-dimensional elastic macroscopic graphene network (3D-GN) is prepared with the assistance of porous SiO2 ceramic substrates by using ambient pressure chemical vapor deposition, which is suitable for thermal management application. The free standing elastic macroscopic 3D-GN possesses excellent electrical, mechanical and thermal transfer properties.
[Show abstract][Hide abstract] ABSTRACT: Graphene/ceramic composites are proposed by directly depositing graphene on the insulating Al2O3 particles by chemical vapor deposition without any metal catalysts. Carbothermic reduction occurring at the Al2O3 surface is vital during the initial stage of graphene nucleation and the graphene sheet can connect with neighboring sheets to completely cover Al2O3 particles. The quality and layer number of graphene on Al2O3 can be finely tailored by changing the growth temperature and gas ratio. Graphene coated Al2O3 (G-Al2O3) composites are used as effective fillers of stearic acid (SA) to increase the thermal transport property. By the optimization of the layer number of graphene, size of Al2O3 particles and ratio of G-Al2O3/SA in a quantitative, their thermal conductivities significantly increase up to 11 folds from 0.15 to 1.65 W m−1 K−1. The great improvement is attributed to the high thermal transfer performance of graphene and excellent wettability between graphene and SA. When the G-Al2O3/SA composites with the graphene coated porous Al2O3 foam, the thermal conductivity further reaches to 2.39 W m−1 K−1, and the corresponding latent heat is 38 J g−1. It demonstrates the potential applications of graphene in thermal transport and thermal energy storage devices.