Abundant Surface Active Sites Research Articles

2D Polymers as Emerging Materials for Photocatalytic Overall Water Splitting.

Converting solar energy into storable and transportable chemical fuels using artificial photosynthetic systems can provide an alternative route to the current unsustainable use of fossil fuels, addressing the worldwide energy crisis and environmental issues. Recently, semiconducting polymers have emerged as a very promising class of photocatalysts for water splitting as their electronic and structural properties can be conveniently controlled and systematically designed at a molecular level. Among the various polymer photocatalysts that are reported so far, 2D polymer nanosheets are particularly interesting and gaining more attention. The 2D planar structure offers unique features such as high surface area, abundant surface active sites, efficient charge separation, and facile formation of heterostructures. The design and synthesis of 2D polymer nanosheets have greatly advanced the research in photocatalytic overall water splitting. Here, recent advances in developing photocatalysts based on 2D polymer nanosheets for photocatalytic overall water splitting are highlighted. Specifically, the existing approaches to tune their electronic structures and surface active sites for photocatalysis are discussed. Future opportunities and challenges for developing 2D polymers for photocatalytic overall water splitting are also included.

Shape-Controlled Synthesis of Platinum-Copper Nanocrystals for Efficient Liquid Fuel Electrocatalysis.

Well-defined noble metal nanomaterials are attractive as catalysts for various applications because of abundant surface-active sites. However, the shape-controlled synthesis of high-performance Pt-based nanocatalysts remains a forbidden challenge. We herein demonstrate a versatile approach for realizing the systemically controlled syntheses of bimetallic Pt-Cu nanocrystals (NCs) from concave nanocubes (CNCs), to excavated nanocubes, to tripods via simply switching the amount of glycine (reducing agent). These Pt-Cu nanostructures supply a desirable platform for carrying out the structure-dependent electrocatalytic studies in the liquid fuel electro-oxidation. Impressively, all of the Pt-Cu NCs show high activity and outstanding durability for alcohol oxidation. In particular, the Pt-Cu CNCs display unprecedent high activity toward MOR and EOR, which are found to be 2041.1 and 5760.9 mA mg-1 in mass activity, 7.9- and 11.5-folds greater than the commercial Pt/C catalysts, respectively, showing a promising class of electrocatalysts for fuel cells. This work sheds great promise for optimizing the electrochemical catalysis by precisely modulating the structure of catalysts.

High-performance supercapacitor based on three-dimensional flower-shaped Li4Ti5O12-graphene hybrid and pine needles derived honeycomb carbon

A three-dimensional (3D) flower-shaped Li4Ti5O12-graphene (Gr) hybrid micro/nanostructures and pine needles derived carbon nanopores (PNDCN) has been prepared by using the effective hydrothermal process. Due to the unique micro/nanostructures which can provide abundant surface active sites, the obtained 3D Li4Ti5O12-Gr displays a high specific capacitance of 706.52 F g−1 at 1 A g−1. The prepared PNDCN also exhibits high specific capacitance of 314.50 F g−1 at 1 A g−1 benefiting from its interconnected honeycomb-like hierarchical and open structure, which facilitates the diffusion and reaction of electrolyte ions and enables an isotropic charging/discharging process. An asymmetric supercapacitor utilizing Li4Ti5O12-Gr as positive electrode and PNDCN as negative electrode has been fabricated, it delivers a high energy density of 35.06 Wh kg−1 at power density of 800.08 W kg−1 and outstanding cycling stability with 90.18% capacitance retention after 2000 cycles. The fabrication process presented in this work is facile, cost-effective, and environmentally benign, offering a feasible solution for manufacturing next-generation high-performance energy storage devices.

Facile construction of pompon-like PtAg alloy catalysts for enhanced ethylene glycol electrooxidation

In the drive toward energy crisis, direct ethylene glycol cells have received a great deal of attention, but its commercial development has been greatly restricted due to the lack of cost-effective anodic catalysts. Therefore, it is essential to design a suitable catalyst with excellent performance. To this end, we herein report a facile one-pot tactic for successfully synthesizing the pompon-like PtAg nanocrystals (NCs) with marvelous electrocatalytic activity and amazing long-term stability. More specifically, the results have proved that the pompon-like PtAg possessed the superior mass activity of 5042.9 mA mg−1 towards ethylene glycol oxidation reaction (EGOR) under the alkaline condition, 5.4-fold enhancements than that of commercial Pt/C. Upon the basis of our investigation, we attributed the better catalytic activity to abundant available surface active sites and synergistic effect, as well as the brushy hairs on the surface of PtAg NCs. There is no doubt that the as-obtained nanocatalysts show a great prospect for serving as excellent anode catalyst in fuel cells and beyond.

Ultrathin Bi2WO6 nanosheet decorated with Pt nanoparticles for efficient formaldehyde removal at room temperature

Two-dimensional (2D) ultrathin bismuth tungstate (Bi2WO6) nanosheets (BWO-NS) with a thickness of approximately 4.0 nm were synthesized by a one-step hydrothermal method, and decorated with platinum (Pt) nanoparticles (NPs) via an impregnation/borohydride-reduction approach. The as-prepared ultrathin Pt-BWO-NS exhibited superior catalytic activity for removing gaseous formaldehyde (HCHO) at ambient temperature, in comparison with bulk counterpart with Bi2WO6 sheet thickness of tens of nanometers. The ultrathin structure endowed the Pt-BWO-NS sample with larger specific surface area, which can provide abundant surface active sites for HCHO adsorption and facilitate the homogeneous dispersion of Pt NPs. X-ray photoelectron spectroscopy and hydrogen temperature-programmed reduction analyses revealed the interaction between the Bi2WO6 support and Pt species, which is crucial for activating surface oxygen atoms to participate in the catalytic HCHO oxidation process. By conducting in situ diffuse reflectance infrared Fourier transform spectroscopy under different atmospheres, i.e., gaseous HCHO in nitrogen or oxygen (O2), the reaction mechanism and the role of O2 were elucidated, with dioxymethylene, formate and linearly adsorbed carbon monoxide identified as the main reaction intermediates. This study may provide new enlightenment on fabricating novel 2D nanomaterials for efficient indoor air purification and potentially other environmental applications.

Ag@AgCl decorated graphene-like TiO2 nanosheets with nearly 100% exposed (0 0 1) facets for efficient solar light photocatalysis

The large scale, ultrathin and (0 0 1) facet exposed anatase two-dimensional (2D) graphene-like TiO2 nanosheets were synthesized by hydrogen-bonding-mediated. The products were employed as scaffolding and deposited Ag@AgCl nanoparticles. The crystalline phase, morphologies and optical properties of as-prepared sample were surveyed. The results indicated that the as-prepared TiO2 nanosheets only have few nanometers thick. The Ag@AgCl nanoparticles were also successfully introduced into the surface of TiO2 nanosheets. By the modified of Ag@AgCl and significant enhanced the absorption spectrum in the visible light region. To assess the photocatalytic activities of as-prepared samples, the methylene blue (MB), methyl orange (MO) and rhodamine B (RhB) were employed to simulate the pollutants. The Ag@AgCl/TiO2 exhibited excellent photocatalysis under solar irradiation. There results suggested that, Ag@AgCl/TiO2-0.6 photocatalyst has suitable size of Ag@AgCl particles, large surface areas, abundant surface active sites and effective photogenerated electron-hole pair's separation, which significant improve the photocatalytic activities.

Evaluation of Mechanism on Selective, Rapid, and Superior Adsorption of Congo Red by Reusable Mesoporous α-Fe2O3 Nanorods

A large scale synthesis of mesoporous hematite (α-Fe2O3) nanorods with a high surface area of 98 m2/g and an average pore size of ∼26 nm was used for adsorption studies for pollutant dye removal. The nanorods exhibited rapid, superior, and selective adsorption efficiency toward Congo red, an organic dye present in wastewater. Highly selective adsorption capability of the mesoporous α-Fe2O3 nanorods has been attributed to the presence of abundant surface active sites with porous networks which make it highly water dispersible facilitating the formation of H-bonding and coordination effect between the -NH2 group of Congo red with its surface -OH groups and Fe3+, respectively. Adsorption studies concerning the effect of contact time, initial dye concentration, dosage of adsorbent, and effect of pH on adsorption kinetics were explored in addition to the desorption process investigation regarding the effect of solution pH from acidic to alkaline. To unravel the unresolved phenomenon toward selective adsorption...

Ti3+ self-doped mesoporous black TiO2/SiO2 nanocomposite as remarkable visible light photocatalyst

Ti3+ self-doped mesoporous black TiO2/SiO2 composite is successfully synthesized by a solvothermal reaction, followed by calcination at 450°C and hydrogenation at 500°C. The structures and morphologies of the resultant samples are investigated. The consequences suggest that Ti3+ self-doped mesoporous black TiO2/SiO2 composites have a high surface area of ∼300m2g−1, a relative large pore size of ∼4nm and pore volume of ∼0.35cm3g−1. The introduction of SiO2 stabilizes the mesoporous networks and prevents the collapse of the channels during the calcination process, which not only improves the crystallinity of TiO2, but also maintains the mesoporous frameworks. The prepared composite with narrow bandgap of ∼2.79eV exhibits outstanding property for removal of dye and the production of H2 under AM 1.5 irradiation, which is higher compared with the pristine TiO2 composite. This is attributed to the Ti3+ self-doping reducing the bandgap and benefiting the absorption of visible light, the mesoporous frameworks favoring the diffusion of reactants and products, and providing abundant surface active sites.

Novel quantum dot and nano-sheet TiO2 (B) composite for enhanced photocatalytic H2 – Production without Co-Catalyst

Recently, the production of hydrogen through water splitting using titania (TiO2) as photocatalyst has received great attention in the new energy field. In this work, a single one-step hydrothermal method is used to synthesize ultra-thin TiO2 (B) nano-sheets, anatase TiO2, and their composite, using ethylene glycol (EG) and ethanol as the solvent. A new composite nanostructure with anatase TiO2 quantum dots grown on TiO2 (B) nano-sheets is obtained at certain ratios between EG and ethanol. Even without the help of co-catalyst, a high photocatalytic efficiency, about 45 times of that of rutile-anatase mixed Degussa P25, is observed in the TiO2 (B)-anatase composite nanostructure. The outstanding performance can be attributed to its large specific surface area, abundant surface active sites, mixed phase promoted efficient charge separation. Moreover, the properly aligned band structure, with the conduction band level of ultra-thin TiO2 (B) about 0.6 eV higher than that of the anatase, provides a large driving force for the reduction of water.

Core-shell iron oxide-layered double hydroxide: High electrochemical sensing performance of H2O2 biomarker in live cancer cells with plasma therapeutics

In this work, we develop a new type of multifunctional core-shell nanomaterial by controllable integration of CuAl layered double hydroxides (LDHs) over the surface of iron oxides (Fe3O4) nanospheres (NSs) to fabricate (Fe3O4@CuAl NSs) hybrid material with interior tunability of LDH phase and explore its practical application in ultrasensitive detection of emerging biomarker, i.e., H2O2 as cancer diagnostic probe. In addition, atmospheric pressure plasmas (APPs) have also been used as potential therapeutic approach for cancer treatment. Due to the synergistic combination of p-type semiconductive channels of LDHs with multi-functional properties, unique morphology and abundant surface active sites, the Fe3O4@CuAl NSs modified electrode exhibited attractive electrocatalytic activity towards H2O2 reduction. Under the optimized conditions, the proposed biosensor demonstrated striking electrochemical sensing performances to H2O2 including linear range as broad as 8 orders of magnitude, low real detection limit of 1nM (S/N = 3), high sensitivity, good reproducibility and long-term stability. Arising from the superb efficiency, the electrochemical biosensor has been used for in vitro determination of H2O2 concentrations in human urine and serum samples prior to and following the intake of coffee, and real-time monitoring of H2O2 efflux from different cancer cell lines in normal state and after plasma treatment. We believe that this novel nano-platform of structurally integrated core-shell nanohybrid materials combined with APPs will enhance diagnostic as well as therapeutic window for cancer diseases.

Hydrothermal Fabrication of High Specific Surface Area Mesoporous MgO with Excellent CO2 Adsorption Potential at Intermediate Temperatures

In this work, we report on a novel sodium dodecyl sulfate (SDS)-assisted magnesium oxide (MgO)-based porous adsorbent synthesized by hydrothermal method for intermediate CO2 capture. For industrial MgO, its CO2 adsorption capacity is normally less than 0.06 mmol g−1, with a specific surface area as low as 25.1 m2 g−1. Herein, leaf-like MgO nanosheets which exhibited a disordered layer structure were fabricated by the introduction of SDS surfactants and the control of other synthesis parameters. This leaf-like MgO adsorbent showed an excellent CO2 capacity of 0.96 mmol g−1 at moderate temperatures (~300 °C), which is more than ten times higher than that of the commercial light MgO. This novel mesoporous MgO adsorbent also exhibited high stability during multiple CO2 adsorption/desorption cycles. The excellent CO2 capturing performance was believed to be related to its high specific surface area of 321.3 m2 g−1 and abundant surface active adsorption sites. This work suggested a new synthesis scheme for MgO based CO2 adsorbents at intermediate temperatures, providing a competitive candidate for capturing CO2 from certain sorption enhanced hydrogen production processes.

Carrier Step-by-Step Transport Initiated by Precise Defect Distribution Engineering for Efficient Photocatalytic Hydrogen Generation.

Semiconductor photocatalysts have been widely used for solar-to-hydrogen conversion; however, efficient photocatalytic hydrogen generation still remains a challenge. To improve the photocatalytic activity, the critical step is the transport of photogenerated carriers from bulk to surface. Here, we report the carrier step-by-step transport (CST) for semiconductor photocatalysts through precise defect engineering. In CST, carriers can fast transport from bulk to shallow traps in the defective subsurface first, and then transfer to the surface active acceptors. The key challenge of initiating CST lies in fine controlling defect distribution in semiconductor photocatalysts to introduce the special band matching between the crystalline bulk and defect-controllable surface, moderate bridgelike shallow traps induced by subsurface defects, and abundant surface active sites induced by surface defects. In our proof-of-concept demonstration, the CST was introduced into typical semiconductor TiO2 assisted by the fluorine-assisted kinetic hydrolysis method, and the designed TiO2 can exhibit the state-of-the-art photocatalytic hydrogen generation rate among anatase TiO2 up to 13.21 mmol h-1 g-1, which is 120 times enhanced compared with crystalline anatase TiO2 under sunlight. The CST initiated by precise defect distribution engineering provides a new sight on greatly improving photocatalytic hydrogen generation performance of semiconductor catalysts.

Solvent-free catalytic synthesis and optical properties of super-hard phase ultrafine carbon nitride nanowires with abundant surface active sites

Hot-melt reduction solvent-free catalytic synthesis and optical property of ultrafine α/β-C3N4 nanowires with abundant surface active sites.

Water-soluble MoS3 nanoparticles for photocatalytic H2 evolution.

Polyvinylpyrrolidone (PVP)-modified MoS3 nanoparticles with unusual water solubility up to 1.0 mg mL(-1) were synthesized through a facile hydrothermal method in the presence of thioacetic acid. The amorphous nanoparticles wrapped by PVP have sizes of around 2.5 nm, which represent the smallest MoS3 clusters reported. The photocatalytic performance of the MoS3 nanoparticles was evaluated under visible light for H2 evolution using xanthene dyes as photosensitizers. The quantum efficiency of the optimized system for H2 evolution under green light irradiation (520 nm) is up to 36.2 %, which is comparable with those of other excellent photocatalytic systems involving earth-abundant catalysts. The excellent photocatalytic activity can be attributed to its good dispersion in water, amorphous nature and limited layers with abundant surface active sites, and possibly higher conduction band potential for proton reduction and larger indirect band gap for a longer lifetime of the excited electrons.

Pore-controlled synthesis of Mn2O3microspheres for ultralong-life lithium storage electrode

Mesoporous structures have attracted increasing interest in improving the cycling life and specific capacity of electrode materials. Mn2O3 microspheres with controlled pore size were successfully synthesized by morphology-conserved transformation at 500, 700 and 900 °C. Among them, mesoporous Mn2O3 microspheres annealed at 500 °C show the highest discharge capacity, the minor capacity fading per cycle and ultralong cycling life. It can realize 1000 stable charge/discharge processes with 125 mAh g−1 reversible capacity at current density of 1000 mA g−1. Meanwhile, at relatively low current density (200 mA g−1), it can deliver capacity of 524 mAh g−1 after 200 cycles. The remarkable electrochemical performance can result from the relatively high surface area and abundant surface active sites of mesoporous structure, which can enhance the continuous charge transfer kinetics, ion diffusion and capacity. The high cycling stability and long life span make mesoporous Mn2O3 microspheres promising electrode materials for electrochemical energy storage.