Mesoporous waffle-like N-doped carbon with embedded Co nanoparticles for efficiently electrocatalytic oxygen reduction and evolution.

Rational design and facile preparation of high-performance carbon-based eletrocatalysts for both oxygen reduction and evolution reactions (ORR and OER) is crucial for practical applications of rechargeable zinc-air batteries. Inspired by the fact that the metallic Co catalysis on the formation of carbon nanotubes (CNTs), this work develops a facial compression-pyrolysis route to synthesize a mesoporous waffle-like N-doped carbon framework with embedded Co nanoparticles (Co@pNC) using a Co metal-organic framework and melamine as precursors. The unique porous waffle-like carbon framework is built up of interwoven N-doped CNTs and graphene nanosheets, which offers abundant catalytic-active sites and rapid diffusion channels for intermediates and electrolyte. The optimized Co@pNC shows excellent bifunctional ORR/OER electrocatalytic activity in alkaline media with a half-wave potential (E1/2) of 0.85 V for ORR and a small potential gap of 0.70 V between ORR E1/2 and OER potential at 10 mA cm-2. Its assembled battery exhibits a peak power density up to 150.3 mW cm-2, an energy density of 928 Wh kgZn-1 and superb rate capability. It highlights a facile component and architecture strategy to design high-performance carbon-based eletrocatalysts.

Activation of Carbonyl Oxygen Sites in ß-Ketoenamine-Linked Covalent Organic Frameworks via Cyano Conjugation for Efficient Photocatalytic Hydrogen Evolution.

2D covalent organic frameworks (COFs) are drawing intense attention in heterogenous photocatalysis due to their porous, crystalline, and tailor-made structures. For highly efficient solar-to-chemical energy conversion, revealing and modulating active centers in the skeletons of COFs are of great importance but encounter severe challenges. Herein, it is demonstrated that cyano conjugation on a typical ß-ketoenamine-linked COF via aldehyde-imine Schiff-base condensation contributes to an enhanced stable photocatalytic H2 -evolution rate of 1.8 mmol h-1 g-1 (λ > 420 nm) with a superior apparent quantum yield of 2.12% at 420 nm, compared to pristine COFs. Both experimental results and density functional theory calculations disclose that the cyano conjugation can efficiently improve photoinduced charge separation and effectively decrease the energy barrier for H-intermediate generation on the carbonyl oxygen sites of the functionalized COFs. These findings present a precise organic functionalization strategy to optimize active centers on COF-based photocatalysts for the practical applications.

Integrating CuInSe2 nanocrystals with polymeric carbon nitride nanorods for photocatalytic water splitting.

Developing photocatalysts with improved photoactivity and efficiency has remained an enduring theme both fundamentally and technologically in the field of photocatalysis. Polymeric carbon nitride (CN) has been widely exploited as an earth-abundant photocatalyst for water redox reactions. Nevertheless, the limited visible-light utilization rate and the high recombination rate of photoinduced charge carriers give rise to the moderate photocatalytic reactivity of CN in water splitting. Herein, p-type CuInSe2 nanocrystals are prepared by a solvothermal approach and then immobilized with n-type CN nanorods through self-assembly and thermal treatment process, forming a CuInSe2/CN hybrid photocatalyst. Benefiting from the p-n heterojunction, a 3% CuInSe2/CN nanocomposite photocatalyst exhibits a three-fold increase in the hydrogen evolution rate (HER) compared to that of bare CN nanorods owing to the strengthened visible-light capturing capability and improved separation rate of photoexcited charge carriers. This work paves new avenues for the construction of p-n heterojunction photocatalysts for solar fuel production.

Silica-coated bismuth sulfide nanorods as multimodal contrast agents for a non-invasive visualization of the gastrointestinal tract.

Non-invasive and real-time imaging of the gastrointestinal (GI) tract is particularly desirable for research and clinical studies of patients with symptoms arising from gastrointestinal diseases. Here, we designed and fabricated silica-coated bismuth sulfide nanorods (Bi2S3@SiO2 NRs) for a non-invasive spatial-temporally imaging of the GI tract. The Bi2S3 NRs were synthesized by a facile solvothermal method and then coated with a SiO2 layer to improve their biocompatibility and stability in the harsh environments of the GI tract, such as the stomach and the small intestine. Due to their strong X-ray- and near infrared-absorption abilities, we demonstrate that, following oral administration in mice, the Bi2S3@SiO2 NRs can be used as a dual-modal contrast agent for the real-time and non-invasive visualization of NRs distribution and the GI tract via both X-ray computed tomography (CT) and photoacoustic tomography (PAT) techniques. Importantly, integration of PAT with CT provides complementary information on anatomical details with high spatial resolution. In addition, we use Caenorhabditis Elegans (C. Elegans) as a simple model organism to investigate the biological response of Bi2S3@SiO2 NRs by oral administration. The results indicate that these NRs can pass through the GI tract of C. Elegans without inducing notable toxicological effects. The above results suggest that Bi2S3@SiO2 NRs pave an alternative way for the fabrication of multi-modal contrast agents which integrate CT and PAT modalities for a direct and non-invasive visualization of the GI tract with low toxicity.

Interstratified nanohybrid assembled by alternating cationic layered double hydroxide nanosheets and anionic layered titanate nanosheets with superior photocatalytic activity.

Oppositely charged 2D inorganic nanosheets of ZnAl-layered double hydroxide and layered titanate were successfully assembled into an interstratified nanohybrid through simply mixing the corresponding nanosheet suspensions. Powder X-ray diffraction and high-resolution transmission electron microscope clearly revealed that the component nanosheets in the as-obtained nanohybrid ZnAl-Ti3O7 retain the 2D sheet skeletons of the pristine materials and that the two kinds of nanosheets are well arranged in a layer-by-layer alternating fashion with a basal spacing of about 1.3 nm, coincident with the thickness summation of the two component nanosheets. The effective interfacial heterojunction between them and the high specific surface area resulted in that the nanohybrid exhibits a superior photocatalytic activity in the degradation of methylene blue with a reaction constant k of 2.81 × 10(-2)min(-1), which is about 9 and 4 times higher than its precursors H2Ti3O7 and ZnAl-LDH, respectively. Based on UV-vis, XPS and photoelectrochemical measurements, a proposed photoexcitation model was provided to understand its photocatalytic behavior.

Facile synthesis of TiO2 microspheres with reactive (001) facets for improved photocatalytic performance.

Anatase TiO2 microspheres with a high percentage of exposed (001) facets were synthesized by a template-free hydrothermal method without using concentrated hydrofluoric acid. The influence of various experiment conditions, such as hydrothermal temperature, acid condition, reaction time, etc., on the morphology of the final products was investigated in detail. The formation mechanism of the microspheres was deduced according to the XRD, SEM, TEM, and HRTEM characterizations. The as-obtained microspheres exhibited superior photocatalytic activity in the degradation of Acid Red 88 compared to TiO2 without exposed (001) facet.

Origin of the enhanced visible-light photocatalytic activity of CNT modified g-C3N4 for H2 production.

Graphitic carbon nitride (g-C3N4) hybridized with a small number of multi-walled carbon nanotubes (CNT) was synthesized using cyanamide as precursor. The optimal CNT content is found to be ∼0.2 wt% in the composite, which displays a 2.4-fold enhancement in photocatalytic water splitting over pure g-C3N4. Characterizations by a series of joint techniques including Raman spectra, UV/vis diffuse reflectance spectra, steady and time-resolved fluorescence emission spectra, and photocurrent responses were carried out, aiming to reveal the determinative factor for the improved visible-light response. Our results indicate that the increased photoactivity originates from the enhanced charge-transfer effect due to the intimate interactions between g-C3N4 and conjugated CNT. The presence of CNT in the hybrids is beneficial for improving electron-hole separation on the excited g-C3N4 by prolonging the lifetimes of charge carriers and improving the population distribution of short-lived and long-lived charge carriers.

A facile approach to synthesize novel oxygen-doped g-C3N4 with superior visible-light photoreactivity.

O-doped g-C(3)N(4) was synthesized for the first time by a facile H(2)O(2) hydrothermal approach. The O-doping in the g-C(3)N(4) lattice could induce intrinsic electronic and band structure modulation, resulting in its absorbance edge up to 498 nm and enhanced visible-light photoactivity, consequently.

Heterostructured Tin oxide-pillared tetratitanate with enhanced photocatalytic activity.

An effective active heterostructured photocatalyst of porous SnO(2)-pillared tetratitanate nanocomposite is synthesized by assembling tetratitanate nanosheets with SnO(2) nanoparticles via an exfoliation-restacking route. The nanocomposite was characterized by powder X-ray diffraction, high-resolution transmission electron microscope, thermogravimetric analysis, UV-vis DRS, X-ray photoelectron spectroscopy, and N(2) adsorption-desorption measurements. It was found that the pillared nanaocomposite is mesoporous with a gallery height of about 2 nm and a specific surface area of 154 m(2)/g. The pillared nanaocomposite exhibited enhanced photocatalytic activity in the photodegradation of Rhodamine B under UV light irradiation. The improved performance is attributed to the electronic coupling between the host and the guest components, as well as its high surface area and mesoporosity.

Controlled synthesis and electrochemical properties of Co3O4 hierarchical nanostructures from an urchinlike cobalt-hydroxide-carbonate precursor.

A large number of hierarchical Co3O4 nanostructures have been prepared via the thermal treatment of an urchinlike cobalt-hydroxide-carbonate precursor, which was obtained by simple hydrothermal treatment of CoCl2 solution in the presence of urea and K2SO4. The as-obtained cobalt-hydroxide-carbonate precursor has been characterized by XRD, SEM, TEM, XPS, IR and TGA. To study the formation process of this urchinlike precursor, the influences of experimental parameters, such as reaction time and inorganic salts, etc., on the morphology have been investigated during the synthesis. It was found that the morphology of cobalt-hydroxide-carbonate was strongly dependent on the sulfate. Calcination of the precursor at 350 degrees C led to the formation of well-defined hierarchical Co3O4 nanostructures with a surface area of 60 m2 g(-1). The electrochemical properties of Co3O4 nanostructures were also investigated.

Controllable assembly of WO3 nanorods/nanowires into hierarchical nanostructures.

The controlled synthesis of two novel h-WO3 hierarchical structures made of nanorods/nanowires has been successfully realized in a large scale via a simple hydrothermal method. It is demonstrated that the morphology of the final products is significantly influenced by adding different sulfates. The urchinlike and ribbonlike structures of WO3 can be selectively prepared by adding Rb2SO4 and K2SO4, respectively. The morphology evolvement and the growth mechanism were studied carefully. The sulfate-induced oriented attachment growth mechanism has been proposed for the possible formation mechanism of the ribbonlike sample. For urchinlike products, two growing stages are believed to be involved in the growth process. The current understanding of the growth mechanism of these nanostructures may be potentially applied for designing other oriented or hierarchical nanostructures based on 1D nanoscale building blocks through the direct solution-growth.

Great enhancement of photocatalytic activity of nitrogen-doped titania by coupling with tungsten oxide.

The TiO2-N-x%WO3 composite photocatalysts were prepared by introducing WO3 into nitrogen-doped TiO2. The composite catalysts present much higher photocatalytic activity than TiO2 and nitrogen-doped TiO2 under both ultraviolet and visible light irradiation. Diffuse reflectance UV-vis spectra, XPS analysis, and IR spectra show that the coordinated nitrogen species (or N-metal-O linkages) may contribute to the visible light photocatalytic activity. WO3 coupling increases the active nitrogen species and thus enhances the visible light activity of the composite photocatalysts. The superior activity of TiO2-N-x%WO3 composite photocatalysts upon UV light irradiation can be rationalized in terms of efficient charge separation and high adsorption affinity of WO3.

A simple hydrothermal method for the large-scale synthesis of single-crystal potassium tungsten bronze nanowires.

The large-scale synthesis of single-crystal K(x)WO(3) tungsten bronze nanowires has been successfully realized by a hydrothermal method under mild conditions. Uniform K(0.33)WO(3) nanowires with diameters of 5-25 nm and lengths of up to several micrometers are obtained. It is found that the morphology and crystallographic forms of the final products are strongly dependent on the sulfate and citric acid, which may act as structure-directing and soft-reducing agent, respectively. Some other influential factors on the growth of tungsten bronze nanowires, such as temperature and reaction time, are also discussed. It is worth noting that other alkali metal tungsten bronzes such as (NH(4))(x)WO(3), Rb(x)WO(3), and Cs(x)WO(3) could also be selectively synthesized by a similar route. Thus, this novel and efficient method could provide a potential mild route to selectively synthesize various tungsten bronze on-dimensional nanomaterials.