Boric acid templating synthesis of highly-dense yet ultramicroporous carbons for compact capacitive energy storage.

Carbon-based supercapacitors have shown great promise for miniaturized electronics and electric vehicles, but are usually limited by their low volumetric performance, which is largely due to the inefficient utilization of carbon pores in charge storage. Herein, we develop a reliable and scalable boric acid templating technique to prepare boron and oxygen co-modified highly-dense yet ultramicroporous carbons (BUMCs). The carbons are featured with high density (up to 1.62 g cm-3), large specific surface area (up to 1050 m2 g-1), narrow pore distribution (0.4-0.6 nm) and exquisite pore surface functionalities (mainly -BC2O, -BCO2, and -COH groups). Consequently, the carbons show exceptionally compact capacitive energy storage. The optimal BUMC-0.5 delivers an outstanding volumetric capacitance of 431 F cm-3 and a high-rate capability in 1 M H2SO4. In particular, an ever-reported high volumetric energy density of 32.6 Wh L-1 can be harvested in an aqueous symmetric supercapacitor. Our results demonstrate that the -BC2O and -BCO2 groups on the ultramicropore walls can facilitate the internal SO42- ion transport, thus leading to an unprecedented high utilization efficiency of ultramicropores for charge storage. This work provides a new paradigm for construction and utilization of dense and ultramicroporous carbons for compact energy storage.

Substituting inert phosphate with redox-active silicate towards advanced polyanion-type cathode materials for sodium-ion batteries.

Polyanion-type phosphate materials with Na-super-ionic conductor structures are promising for next-generation sodium-ion battery cathodes, although the intrinsically low electroconductivity and limited energy density have restricted their practical applications. In this study, we put forward substituting an inert phosphate with a redox-active silicate to improve the energy density and intrinsic electroconductivity of polyanion-type phosphate materials, thus enabling an advance in sodium-ion battery cathodes. As a proof of concept, some of the phosphate of Na3V2(PO4)3 was replaced by silicate to fabricate Na3V2(PO4)2.9(SiO4)0.1, which exhibited a higher average discharge voltage of 3.36 V and a higher capacity of 115.8 mA h g-1 than pristine Na3V2(PO4)3 (3.31 V, 109.6 mA h g-1) at 0.5 C, therefore improving the energy density. Moreover, the introduced silicate enhanced the intrinsic electroconductivity of Na3V2(PO4)3 materials, as confirmed by both theoretical simulation and electrochemical measurements. After pairing with a commercial hard carbon anode, the optimized Na3V2(PO4)2.9(SiO4)0.1 cathode enabled a stable-cycling full cell with 90.1% capacity retention after 300 cycles at 5 C and a remarkable average coulombic efficiency of 99.88%.

Direct epitaxial growth of nickel phosphide nanosheets on nickel foam as self-support electrode for efficient non-enzymatic glucose sensing.

Design and develop of cost-effective non-enzymatic electrode materials is of great importance for next generation of glucose sensors. In this work, we report a high-performance self-supporting electrode fabricated via direct epitaxial growth of nickel phosphide on Ni foam (Ni2P/NF) for nonenzymatic glucose sensors in alkaline solution. Under the optimal conditions, the uniform Ni2P nanosheets could be obtained with an average thickness of 80 nm, which provides sufficient active sites for glucose molecules. As a consequence, the Ni2P/NF electrode displays superior electrochemistry performances with a high sensitivity of 6375.1µA mM-1cm-2, a quick response about 1 s, a low detection limit of 0.14µM (S/N = 3), and good selectivity and specificity. Benefit from the strong interaction between Ni2P and NF, the Ni2P/NF electrode is also highly stable for long-term applications. Furthermore, the Ni2P/NF electrode is capable of analyzing glucose in human blood serum with satisfactory results, indicating that the Ni2P/NF is a potential candidate for glucose sensing in real life.

A single molecular sensor for selective and differential colorimetric/ratiometric detection of Cu2+ and Pd2+ in 100% aqueous solution.

A novel salicylaldehyde bis-Schiff-base probe decorated with imidazolium ionic liquid moieties at both ends (SAS-IMIs) was designed and facilely synthesized as a colorimetric/ratiometric sensor to visually detect Cu2+ and Pd2+ in pure aqueous media. Due to the positively charged characters of its head and tail, the SAS-IMIs exhibited high water solubility with a potential advantage in minimizing the self-aggregation. More importantly, simply by varying the solution pH, colorimetric/ratiometric sensing detection of individual metal ion (Cu2+ or Pd2+) was realized without any mutual interference. Subsequently, sensitive, selective, and differential detections for Cu2+ (LOD: 0.080 µM) and Pd2+ (LOD: 0.076 µM) in 100% aqueous solutions were achieved, which proved to be applicable for real water samples. Results from density functional theory (DFT) calculations unveiled the Cu2+/Pd2+-binding properties of SAS-IMIs, which were in accordance with the experimental observations. Furthermore, a SAS-IMIs-based solid phase sensor was fabricated, which manifested satisfactory detection abilities for Cu2+ and Pd2+.

Transition-Metal Ion-Doped Flower-Like Titania Nanospheres as Nonlight-Driven Catalysts for Organic Dye Degradation with Enhanced Performances.

Titania has recently been identified as a new and effective nonlight-driven catalyst for degradation of organic pollutant with the use of H2O2 as an oxidant; however, either relatively low surface area or lack of diversity in chemical composition largely limits its catalytic performance. In this work, a series of transition-metal ion (Mn2+, Co2+, Ni2+, and Cu2+)-doped titania nanomaterials with regular flower-like morphology, good crystallinity (anatase), and large specific surface areas (71.4-124.4 m2 g-1) were facilely synthesized and utilized as catalysts for methylene blue (MB) degradation in the presence of H2O2 without light irradiation. It was revealed that the doping of transition-metal ions (especially Mn2+) into titania could significantly improve the catalytic efficiency. At 30 °C, 10 mL of MB with a concentration of 50 mg L-1 could be completely degraded within 60-100 min for these doped samples, whereas the removal rate was only 35.1% within 100 min with the use of pure flower-like titania. Temperature-dependent kinetic studies indicated that the presence of transition-metal ion dopants could markedly lower the activation energy and thus resulted in enhanced catalytic performances. Test of reusability exhibited that these doped catalysts could well keep their original catalytic activities after reuse for several cycles, indicating their excellent catalytic durability.

Partial-Redox-Promoted Mn Cycling of Mn(II)-Doped Heterogeneous Catalyst for Efficient H2O2-Mediated Oxidation.

The development of a heterogeneous catalyst with high catalytic activity and durability for H2O2-mediated oxidation is one of the most important industrial and environmental issues. In this study, a Mn(II)-doped TiO2 heterogeneous catalyst was developed for H2O2-mediated oxidation. The TiO2 substrate-dependent partial-redox behavior of Mn was identified on the basis of our density functional theory simulations. This unique redox cycle was induced by a moderate electron transfer from Ti to Mn, which compensated for the electron loss of Mn and finally resulted in a high-efficiency cycling of Mn between its oxidized and reduced forms. In light of the theoretical results, a Mn(II)-doped TiO2 composite with well-defined morphology and large surface area (153.3 m2 g-1) was elaborately fabricated through incorporating Mn(II) ions into a TiO2 nanoflower, and further tested as the catalyst for oxidative degradation of organic pollutants in the presence of H2O2. Benefiting from the remarkable textural features and excellent Mn cycling property, this composite exhibited superior catalytic performance for organic pollutant degradation. Moreover, it could retain 98.40% of its initial activity even in the fifth cycle. Our study provides an effective strategy for designing heterogeneous catalytic systems for H2O2-mediated oxidations.

On the Mechanism of the Improved Operation Voltage of Rhombohedral Nickel Hexacyanoferrate as Cathodes for Sodium-Ion Batteries.

We reported a rhombohedral Na-rich nickel hexacyanoferrate (r-NiHCF) with high discharge voltage, which also possesses long cycle stability and excellent rate capability when serving as the cathode material of Na-ion batteries. First-principles calculations suggest that the high working voltage of r-NiHCF is correlated to the asymmetric residence of Na+ ions in the rhombohedral framework in parallel with the low charge density at the Fe2+ ions. In both aqueous and ether-based electrolytes, r-NiHCF exhibits higher voltage than that of cubic NiHCF. Rate and cycle experiments indicate that r-NiHCF delivers a specific capacity of 66.8 mAh g-1 at the current density of 80 mA g-1, which is approximate to the theoretical capacity of r-NiHCF. A capacity retention of 96% can be achieved after 200 cycles. The excellent stability of r-NiHCF can be assigned to the absence of rhombohedral-cubic phase transition and negligible volume variation during electrochemical redox, as proven by the ex situ XRD patterns at different depths of charge/discharge and the DFT calculations, respectively.

Selective Adsorption of Gd(3+) on a Magnetically Retrievable Imprinted Chitosan/Carbon Nanotube Composite with High Capacity.

A novel magnetic imprinting nanotechnology for selective capture of Gd(3+) from a mixed solution of rare earth ions was developed by simply adding Gd(3+)-imprinted chitosan/carbon nanotube nanocomposite (IIP-CS/CNT) and silica-coated magnetite nanoparticle (SiO2@Fe3O4). The IIP-CS/CNT was prepared for the first time via a facile "surface deposition-crosslinking" method, exhibiting a well-defined coating structure. Interestingly, the neighboring IIP-CS/CNT monomers were held together as bundles, like a network, containing abundant interstitial spaces. When IIP-CS/CNT and SiO2@Fe3O4 were dispersed in a mixed solution of rare earth ions, the magnetic SiO2@Fe3O4 submicrospheres would be trapped in or adhere to the IIP-CS/CNT network, leading to the magnetization of IIP-CS/CNT; meanwhile, Gd(3+) ions could be selectively captured by the magnetized IIP-CS/CNT. Saturation adsorption capacity for Gd(3+) was up to 88 mg g(-1) at 303.15 K, which is significantly higher than the Gd(3+) adsorption capacities for the reported rare earth ion-imprinted adsorbents over recent years. The selectivity coefficients relative to La(3+) and Ce(3+) were 3.50 and 2.23, respectively, which are very similar to those found for other reported CS-based imprinted materials. Moreover, the imprinted adsorbents could be easily and rapidly retrieved by an external magnetic field without the need of additional centrifugation or filtration, greatly facilitating the separation process. Test of reusability demonstrated that the magnetized IIP-CS/CNT could be repeatedly used without any significant loss in binding capacity. Overall, this work not only provides new insights into the fabrication of magnetic imprinted CS-based composite, but also highlights its application for selective adsorption toward rare earth ions.

Enabling prominent high-rate and cycle performances in one lithium-sulfur battery: designing permselective gateways for Li(+) transportation in Holey-CNT/S cathodes.

A cathode material composed of h-CNT/S/ZrO2 is developed for lithium-sulfur batteries. By incorporating ZrO2 into the S-incorporated h-CNT, permselective gateways for free Li(+) transportation can be assembled at the mesopore openings, which deny the penetration of lithium polysulfides. At the ultrahigh rate of 10 C, the discharge capacity averages to be 870 mA h g(-1) within 200 cycles.

Synthesis of hybrid silica materials with tunable pore structures and morphology and their application for heavy metal removal from drinking water.

Porous silica materials S8, S12, S16, and SBA with controllable pore structures and morphology were synthesized by varying the type or alkyl chain length of the surfactant. Diverse amino-functionalized organic-inorganic hybrid porous materials were then prepared by post-grafting. Depending on the relation between the pore diameter of the porous silica materials and the size and content of the moiety to be grafted, the functionalized materials exhibited varying degrees of decline of structure properties, i.e. regular arrangement of pores, specific surface area, pore size, and pore volume. The hybrid silica materials have been employed as heavy metal ions adsorbents from simulated drinking water at room temperature. The results indicated that the diverse pore structures and different amino group densities influence the heavy metal ions adsorption of functionalized silicas significantly. The best adsorbent was found to be monoamino-functionalized silica S16-1N, which could effectively remove heavy metal Cd(II), Pb(II), Fe(III), as well as Mn(II). The good performance can be attributed to the accessibility of effective amino groups in the pores, as well as the suitable pore structure with high specific surface area of 728 m(2)/g and total pore volume of 0.34 cm(3)/g.