Spontaneous Cross-linking for Fabrication of Nanohybrids Embedded with Size-Controllable Particles

This paper reports a versatile method to fabricate robust carbon/metal hybrids with ultrasmall particle and highly developed porous structure through a scalable and facile way. Alginate is used as the precursor for it could perform cross-linking reaction with different polyvalent metal ions to form gels. After simple freeze-drying and carbonization of the alginate-derived gels, we obtained the carbon/metal hybrids with fine nanostructure. Eleven kinds of metal ions were introduced to form gels and five kinds of the gels were carbonized to produce the carbon/metal hybrids. By adjusting the reaction condition, we could tune the size of the nanoparticles in the obtained hybrids. The obtained SnO₂/C hybrid shows outstanding specific capacity, rate performance, and long cycle life when it is used as the anode materials of lithium ion batteries. The ultrasmall active nanoparticles were uniformly dispersed within an interconnected pore framework. It ensured a short diffusion and transportation distance of electrolyte ions to the surfaces of active nanoparticles. In addition, the robust carbon framework comprises of quasigraphitic carbon layers. It contributed to the high rate performance by providing excellent conductive pathways for electrons within the electrodes. This work provides a general method for fabrication of carbon/metal (oxide) hybrids with fine nanostructure for application in energy storage

“Egg-Box”-Assisted Fabrication of Porous Carbon with Small Mesopores for High-Rate Electric Double Layer Capacitors

Here we report a method to fabricate porous carbon with small mesopores around 2–4 nm by simple activation of charcoals derived from carbonization of seaweed consisting of microcrystalline domains formed by the “egg-box” model. The existence of mesopores in charcoals leads to a high specific surface area up to 3270 m² g^–1, with 95% surface area provided by small mesopores. This special pore structure shows high adaptability when used as electrode materials for an electric double layer capacitor, especially at high charge–discharge rate. The gravimetric capacitance values of the porous carbon are 425 and 210 F g^–1 and volumetric capacitance values are 242 and 120 F cm^–3 in 1 M H₂SO₄ and 1 M TEA BF₄/AN, respectively. The capacitances even remain at 280 F g^–1 (160 F cm^–3) at 100 A g^–1 and 156 F g^–1 (90 F cm^–3) at 50 A g^–1 in the aqueous and organic electrolytes, demonstrating excellent high-rate capacitive performance

Facile Self-Cross-Linking Synthesis of 3D Nanoporous Co₃O₄/Carbon Hybrid Electrode Materials for Supercapacitors

A hybrid electrode material with ultrafine Co₃O₄ nanoparticles embedded throughout a hierarchically nanoporous graphitic carbon matrix has been obtained via a facile self-cross-linking route. Sodium alginate, a biopolymer with an ability of cross-linking with multivalent cobalt cations to form ordered microcrystalline zones, is used as a carbon source to produce nanoporous carbon frameworks of the hybrids. Ultrafine Co₃O₄ nanoparticles with tunable particle size (3–30 nm) are in situ grown within the nanoporous graphitic carbon frameworks by a simple carbonization of Co-cross-linked alginate. The obtained hybrid electrodes exhibit high specific capacitance of 645, 548, 486, and 347 F/g at scan rates of 5, 10, 20, and 50 mV/s, respectively, and excellent cycle performance with only 1% fading in capacitance after 10 000 cycles at a high current density of 20 A/g. Such excellent capacitive performance is ascribed to the collaborative contributions of well-dispersed ultrafine Co₃O₄ nanoparticles and conductive nanoporous carbon frameworks

Three-Dimensional CdS/Au Butterfly Wing Scales with Hierarchical Rib Structures for Plasmon-Enhanced Photocatalytic Hydrogen Production

Localized surface plasmon resonance (LSPR) of plasmonic metals (e.g., Au) can help semiconductors improve their photocatalytic hydrogen (H₂) production performance. However, an artificial synthesis of hierarchical plasmonic structures down to nanoscales is usually difficult. Here, we adopt the butterfly wing scales from Morpho didius to fabricate three-dimensional (3D) CdS/Au butterfly wing scales for plasmonic photocatalysis. The as-prepared materials well-inherit the pristine hierarchical biostructures. The 3D CdS/Au butterfly wing scales exhibit a high H₂ production rate (221.8 μmol·h^–1 within 420–780 nm), showing a 241-fold increase over the CdS butterfly wing scales. This is attributed to the effective potentiation effect of LSPR introduced by multilayer metallic rib structures and a good interface bonding state between Au and CdS nanoparticles. Thus, our study provides a relatively simple method to learn from nature and inspiration for preparing highly efficient plasmonic photocatalysts

Reduction of CuO Butterfly Wing Scales Generates Cu SERS Substrates for DNA Base Detection

We prepare three-dimensional Cu plasmonic structures via a reduction of CuO photonic crystals replicated from butterfly wing scales. These Cu superstructures with high purity provide surface-enhanced Raman scattering (SERS) substrates for the label-free detection of DNA bases down to a micromolar level, which is achieved for the first time on Cu and even comparable to the detection-sensitivity for DNA bases on some Ag substrates. The generation of such superstructures has provided a substantial step for the biotemplated SERS substrates with high sensitivity, high reproducibility, and ultra-low cost to detect biomolecules, and presented affordable high-quality routine SERS consumables for corresponding biolaboratories

Bioinspired Fabrication of Hierarchically Structured, pH-Tunable Photonic Crystals with Unique Transition

We herein report a new class of photonic crystals with hierarchical structures, which are of color tunability over pH. The materials were fabricated through the deposition of polymethylacrylic acid (PMAA) onto a Morpho butterfly wing template by using a surface bonding and polymerization route. The amine groups of chitosan in Morpho butterfly wings provide reaction sites for the MAA monomer, resulting in hydrogen bonding between the template and MAA. Subsequent polymerization results in PMAA layers coating homogenously on the hierarchical photonic structures of the biotemplate. The pH-induced color change was detected by reflectance spectra as well as optical observation. A distinct U transition with pH was observed, demonstrating PMAA content-dependent properties. The appearance of the unique U transition results from electrostatic interaction between the −NH₃⁺ of chitosan and the −COO^– groups of PMAA formed, leading to a special blue-shifted point at the pH value of the U transition, and the ionization of the two functional groups in the alkali and acid environment separately, resulting in a red shift. This work sets up a strategy for the design and fabrication of tunable photonic crystals with hierarchical structures, which provides a route for combining functional polymers with biotemplates for wide potential use in many fields

Light-Driven Overall Water Splitting Enabled by a Photo-Dember Effect Realized on 3D Plasmonic Structures

Photoelectric conversion driven by sunlight has a broad range of energy/environmental applications (<i>e</i>.<i>g</i>., in solar cells and water splitting). However, difficulties are encountered in the separation of photoexcited charges. Here, we realize a long-range (∼1.5 μm period) electric polarization <i>via</i> asymmetric localization of surface plasmons on a three-dimensional silver structure (3D-Ag). This visible-light-responsive effectthe photo-Dember effect, can be analogous to the thermoelectric effect, in which hot carriers are thermally generated instead of being photogenerated. The induced electric field can efficiently separate photogenerated charges, enabling sunlight-driven overall water splitting on a series of <i>dopant-free commercial</i> semiconductor particles (<i>i</i>.<i>e</i>., ZnO, CeO₂, TiO₂, and WO₃) once they are combined with the 3D-Ag substrate. These photocatalytic processes can last over 30 h on 3D-Ag+ZnO, 3D-Ag+CeO₂, and 3D-Ag+TiO₂, thus demonstrating good catalytic stability for these systems. Using commercial WO₃ powder as a reference, the amount of O₂ generated with 3D-Ag+CeO₂ surpasses even its recently reported counterpart in which sacrificial reagents had to be involved to run half-reactions. This plasmon-mediated charge separation strategy provides an effective way to improve the efficiency of photoelectric energy conversion, which can be useful in photovoltaics and photocatalysis

Quantum Dots of 1T Phase Transitional Metal Dichalcogenides Generated <i>via</i> Electrochemical Li Intercalation

We prepare group VI transitional metal dichalcogenides (TMDs, or MX₂) from the 1T phase with quantum-sized and monolayer features <i>via</i> a quasi-full electrochemical process. The resulting two-dimensional (2D) MX₂ (M = W, Mo; X = S, Se) quantum dots (QDs) are <i>ca</i>. 3.0–5.4 nm in size with a high 1T phase fraction of <i>ca</i>. 92%–97%. We attribute this to the high Li content intercalated in the 1T-MX₂ lattice (mole ratio of Li:M is over 2:1), which is achieved by an increased lithiation driving force and a reduced electrochemical lithiation rate (0.001 A/g). The high Li content not only promotes the 2H → 1T phase transition but also generates significant inner stress that facilitates lattice breaking for MX₂ crystals. Because of their high proportion of metallic 1T phase and sufficient active sites induced by the small lateral size, the 2D 1T-MoS₂ QDs show excellent hydrogen evolution reactivity (with a typical η₁₀ of 92 mV, Tafel slope of 44 mV/dec, and <i>J</i>₀ of 4.16 × 10^–4 A/cm²). This electrochemical route toward 2D QDs might help boost the development of 2D materials in energy-related areas