Showing papers by "Hua Zhang published in 2020"

Phase engineering of nanomaterials

Abstract: Phase has emerged as an important structural parameter — in addition to composition, morphology, architecture, facet, size and dimensionality — that determines the properties and functionalities of nanomaterials. In particular, unconventional phases in nanomaterials that are unattainable in the bulk state can potentially endow nanomaterials with intriguing properties and innovative applications. Great progress has been made in the phase engineering of nanomaterials (PEN), including synthesis of nanomaterials with unconventional phases and phase transformation of nanomaterials. This Review provides an overview on the recent progress in PEN. We discuss various strategies used to synthesize nanomaterials with unconventional phases and induce phase transformation of nanomaterials, by taking noble metals and layered transition metal dichalcogenides as typical examples. Moreover, we also highlight recent advances in the preparation of amorphous nanomaterials, amorphous–crystalline and crystal phase-based hetero-nanostructures. We also provide personal perspectives on challenges and opportunities in this emerging field, including exploration of phase-dependent properties and applications, rational design of phase-based heterostructures and extension of the concept of phase engineering to a wider range of materials. Properties of nanomaterials respond to changes in the material’s phase, as well as changes in size, composition and morphology. This Review discusses the most recent developments in phase engineering of nanomaterials to afford conventional and unconventional crystal phases, amorphous phases and amorphous–crystalline heterophases.

Layered Transition Metal Dichalcogenide-Based Nanomaterials for Electrochemical Energy Storage.

Abstract: The rapid development of electrochemical energy storage (EES) systems requires novel electrode materials with high performance. A typical 2D nanomaterial, layered transition metal dichalcogenides (TMDs) are regarded as promising materials used for EES systems due to their large specific surface areas and layer structures benefiting fast ion transport. The typical methods for the preparation of TMDs and TMD-based nanohybrids are first summarized. Then, in order to improve the electrochemical performance of various kinds of rechargeable batteries, such as lithium-ion batteries, lithium-sulfur batteries, sodium-ion batteries, and other types of emerging batteries, the strategies for the design and fabrication of layered TMD-based electrode materials are discussed. Furthermore, the applications of layered TMD-based nanomaterials in supercapacitors, especially in untraditional supercapacitors, are presented. Finally, the existing challenges and promising future research directions in this field are proposed.

Stretchable, self-healing and tissue-adhesive zwitterionic hydrogels as strain sensors for wireless monitoring of organ motions

Abstract: Skin-inspired sensors have great potential applications in wearable and implantable devices to monitor human motions. Robust tissue adhesion, fatigue resistance, and biocompatibility are desired for in situ signal capture and wireless transmission. Inspired by the mussel and zwitterionic adhesion mechanisms, we prepared novel stretchable, self-healing and polydopamine zwitterionic nanocomposite hydrogels that provide reversible and robust adhesion to tissues with a strength up to 19.4 kPa and a strain sensitivity of 4.3. The hydrogel sensors robustly adhere to organs like the heart, liver, and lungs to capture signals for remote monitoring and diagnostics through wireless transmission.

Ultrathin Ni(0)‐Embedded Ni(OH)2 Heterostructured Nanosheets with Enhanced Electrochemical Overall Water Splitting

Abstract: The efficiency of splitting water into hydrogen and oxygen is highly dependent on the catalyst used. Herein, ultrathin Ni(0)-embedded Ni(OH)2 heterostructured nanosheets, referred to as Ni/Ni(OH)2 nanosheets, with superior water splitting activity are synthesized by a partial reduction strategy. This synthetic strategy confers the heterostructured Ni/Ni(OH)2 nanosheets with abundant Ni(0)-Ni(II) active interfaces for hydrogen evolution reaction (HER) and Ni(II) defects as transitional active sites for oxygen evolution reaction (OER). The obtained Ni/Ni(OH)2 nanosheets exhibit noble metal-like electrocatalytic activities toward overall water splitting in alkaline condition, to offer 10 mA cm-2 in HER and OER, the required overpotentials are only 77 and 270 mV, respectively. Based on such an outstanding activity, a water splitting electrolysis cell using the Ni/Ni(OH)2 nanosheets as the cathode and anode electrocatalysts has been successfully built. When the output voltage of the electrolytic cell is 1.59 V, a current density of 10 mA cm-2 can be obtained. Moreover, the durability of Ni/Ni(OH)2 nanosheets in the alkaline electrolyte is much better than that of noble metals. No obvious performance decay is observed after 20 h of catalysis. This facile strategy paves the way for designing highly active non-precious-metal catalyst to generate both hydrogen and oxygen by electrolyzing water at room temperature.

Covalency competition dominates the water oxidation structure–activity relationship on spinel oxides

Abstract: Spinel oxides have attracted growing interest over the years for catalysing the oxygen evolution reaction (OER) due to their efficiency and cost-effectiveness, but fundamental understanding of their structure–property relationships remains elusive. Here we demonstrate that the OER activity on spinel oxides is intrinsically dominated by the covalency competition between tetrahedral and octahedral sites. The competition fabricates an asymmetric MT−O−MO backbone where the bond with weaker metal–oxygen covalency determines the exposure of cation sites and therefore the activity. Driven by this finding, a dataset with more than 300 spinel oxides is computed and used to train a machine-learning model for screening the covalency competition in spinel oxides, with a mean absolute error of 0.05 eV. [Mn]T[Al0.5Mn1.5]OO4 is predicted to be a highly active OER catalyst and subsequent experimental results confirm its superior activity. This work sets mechanistic principles of spinel oxides for water oxidation, which may be extendable to other applications. Spinel oxides have attracted interest as water oxidation catalysts due to their efficiency and cost-effectiveness. Now, the covalency competition between tetrahedral and octahedral sites is shown to dominate the OER activity on spinel oxides, and the design principle is used to predict and confirm the superior activity of [Mn]T[Al0.5Mn1.5]OO4.

Ethylene Selectivity in Electrocatalytic CO2 Reduction on Cu Nanomaterials: A Crystal Phase-Dependent Study.

Abstract: The crystal phase of metal nanocatalysts significantly affects their catalytic performance Cu-based nanomaterials are unique electrocatalysts for CO2 reduction reaction (CO2RR) to produce high-value hydrocarbons However, studies to date are limited to the conventional face-centered cubic (fcc) Cu Here, we report a crystal phase-dependent catalytic behavior of Cu, after the successful synthesis of high-purity 4H Cu and heterophase 4H/fcc Cu using the 4H and 4H/fcc Au as templates, respectively Remarkably, the obtained unconventional crystal structures of Cu exhibit enhanced overall activity and higher ethylene (C2H4) selectivity in CO2RR compared to the fcc Cu Density functional theory calculations suggest that the 4H phase and 4H/fcc interface of Cu favor the C2H4 formation pathway compared to the fcc Cu, leading to the crystal phase-dependent C2H4 selectivity This study demonstrates the importance of crystal phase engineering of metal nanocatalysts for electrocatalytic reactions, offering a new strategy to prepare novel catalysts with unconventional phases for various applications

Ag@MoS2 Core-Shell Heterostructure as SERS Platform to Reveal the Hydrogen Evolution Active Sites of Single-Layer MoS2.

Abstract: Understanding the reaction mechanism for the catalytic process is essential to the rational design and synthesis of highly efficient catalysts. MoS2 has been reported to be an efficient catalyst toward the electrochemical hydrogen evolution reaction (HER), but it still lacks direct experimental evidence to reveal the mechanism for MoS2-catalyzed electrochemical HER process at the atomic level. In this work, we develop a wet-chemical synthetic method to prepare the single-layer MoS2-coated polyhedral Ag core-shell heterostructure (Ag@MoS2) with tunable sizes as efficient catalysts for the electrochemical HER. The Ag@MoS2 core-shell heterostructures are used as ideal platforms for the real-time surface-enhanced Raman spectroscopy (SERS) study owing to the strong electromagnetic field generated in the plasmonic Ag core. The in situ SERS results provide solid Raman spectroscopic evidence proving the S-H bonding formation on the MoS2 surface during the HER process, suggesting that the S atom of MoS2 is the catalytic active site for the electrochemical HER. It paves the way on the design and synthesis of heterostructures for exploring their catalytic mechanism at atomic level based on the in situ SERS measurement.

Engineering grain boundaries at the 2D limit for the hydrogen evolution reaction.

Abstract: Atom-thin transition metal dichalcogenides (TMDs) have emerged as fascinating materials and key structures for electrocatalysis. So far, their edges, dopant heteroatoms and defects have been intensively explored as active sites for the hydrogen evolution reaction (HER) to split water. However, grain boundaries (GBs), a key type of defects in TMDs, have been overlooked due to their low density and large structural variations. Here, we demonstrate the synthesis of wafer-size atom-thin TMD films with an ultra-high-density of GBs, up to ~1012 cm−2. We propose a climb and drive 0D/2D interaction to explain the underlying growth mechanism. The electrocatalytic activity of the nanograin film is comprehensively examined by micro-electrochemical measurements, showing an excellent hydrogen-evolution performance (onset potential: −25 mV and Tafel slope: 54 mV dec−1), thus indicating an intrinsically high activation of the TMD GBs. Transition metal dichalcogenides demonstrate fascinating capabilities for electrocatalytic H2 evolution, although the activities vary widely depending on nanomaterial sites available. Here, authors show the grain boundaries of atomically thin MoS2 to be especially active sites for H2 evolution.

Ligand-Exchange-Induced Amorphization of Pd Nanomaterials for Highly Efficient Electrocatalytic Hydrogen Evolution Reaction.

Abstract: Various kinds of amorphous materials, such as transition metal dichalcogenides, metal oxides, and metal phosphates, have demonstrated superior electrocatalytic performance compared with their crystalline counterparts. Compared to other materials for electrocatalysis, noble metals exhibit intrinsically high activity and excellent durability. However, it is still very challenging to prepare amorphous noble-metal nanomaterials due to the strong interatomic metallic bonding. Herein, the discovery of a unique thiol molecule is reported, namely bismuthiol I, which can induce the transformation of Pd nanomaterials from face-centered-cubic (fcc) phase into amorphous phase without destroying their integrity. This ligand-induced amorphization is realized by post-synthetic ligand exchange under ambient conditions, and is applicable to fcc Pd nanomaterials with different capping ligands. Importantly, the obtained amorphous Pd nanoparticles exhibit remarkably enhanced activity and excellent stability toward electrocatalytic hydrogen evolution in acidic solution. This work provides a facile and effective method for preparing amorphous Pd nanomaterials, and demonstrates their promising electrocatalytic application.

Ionic liquid induced highly dense assembly of porphyrin in MOF nanosheets for photodynamic therapy

Abstract: Two-dimensional (2D) metal-organic framework (MOF) nanosheets have emerged as a new member of 2D nanomaterials for molecular sieving, energy conversion and storage, catalysis and biomedicine. In this paper, a highly dense assembly of porphyrin achievable in porphyrin-integrated MOF nanosheets induced by an ionic liquid is obtained by sonication exfoliation of its bulk crystals. The 2D layered structure MOF, [BMI]2[Ca3(H2TCPP)2(μ2-OH2)2(H2O)2] (1), was firstly prepared by using the ionic liquid assisted synthetic method (H6TCPP = meso-tetra(carboxyphenyl) porphyrin, BMI = 1-butyl-3-methylimidazolium). The laminated layers in 1 clearly indicate a weak interlayer non-covalent interaction but a strong metal-carboxylate bonding within the layers, which facilitates the exfoliation of 1 to form 2D MOF nanosheets (1 NSs). Powder X-ray diffraction (PXRD), high-resolution transmission electron microscopy (HR-TEM) and fast Fourier transform (FFT) patterns revealed that 1 NSs could maintain their crystalline structure after exfoliation. These MOF nanosheets exhibited excellent aqueous dispersibility, biodegradability and high cytotoxicity under light irradiation against MCF-7 cells.

Rational Design of MOF-Based Hybrid Nanomaterials for Directly Harvesting Electric Energy from Water Evaporation.

Abstract: The continuous exploration of clean-energy technology is critical for the sustainable development of society. The recent work on the electric energy harvesting from water evaporation has made a significant contribution to the utilization of clean energy for self-powering systems. Here, a novel metal-organic-framework-based hybrid nanomaterial is delicately designed and synthesized by the growth of UIO-66 nanoparticles on 2D AlOOH nanoflakes. Due to the combined merits from the 2D morphology, which is inherited from the AlOOH nanoflakes, and the high surface potential, which originates from the UIO-66 nanoparticles, the device made of the AlOOH/UIO-66 hybrid nanomaterials can harvest electric energy from natural water evaporation. An open-circuit voltage of 1.63 ± 0.10 V can be achieved on the prototype devices made of the hybrid nanomaterial. As a proof-of-concept application, a small electric appliance, e.g., a digital calculator, is powered up by a 3 × 3 device array connected in a combined series-parallel configuration.

A combined "eat me/don't eat me" strategy based on extracellular vesicles for anticancer nanomedicine.

Abstract: A long-term and huge challenge in nanomedicine is the substantial uptake and rapid clearance mediated by the mononuclear phagocyte system (MPS), which enormously hinders the development of nanodrugs. Inspired by the natural merits of extracellular vesicles, we therefore developed a combined "eat me/don't eat me" strategy in an effort to achieve MPS escape and efficient drug delivery. Methodologically, cationized mannan-modified extracellular vesicles derived from DC2.4 cells were administered to saturate the MPS (eat me strategy). Then, nanocarriers fused to CD47-enriched exosomes originated from human serum were administered to evade phagocytosis by MPS (don't eat me strategy). The nanocarriers were also loaded with antitumor drugs and functionalized with a novel homing peptide to promote the tumour tissue accumulation and cancer cell uptake (eat me strategy). The concept was proven in vitro as evidenced by the reduced endocytosis of macrophages and enhanced uptake by tumour cells, whereas prolonged circulation time and increased tumour accumulation were demonstrated in vivo. Specially, the strategy induced a 123.53% increase in tumour distribution compared to conventional nanocarrier. The study both shed light on the challenge overcoming of phagocytic evasion and provided a strategy for significantly improving therapeutic outcomes, potentially permitting active drug delivery via targeted nanomedicines.

Phase-Selective Epitaxial Growth of Heterophase Nanostructures on Unconventional 2H-Pd Nanoparticles

Abstract: Heterostructured, including heterophase, noble-metal nanomaterials have attracted much interest due to their promising applications in diverse fields. However, great challenges still remain in the rational synthesis of well-defined noble-metal heterophase nanostructures. Herein, we report the preparation of Pd nanoparticles with an unconventional hexagonal close-packed (2H type) phase, referred to as 2H-Pd nanoparticles, via a controlled phase transformation of amorphous Pd nanoparticles. Impressively, by using the 2H-Pd nanoparticles as seeds, Au nanomaterials with different crystal phases epitaxially grow on the specific exposed facets of the 2H-Pd, i.e., face-centered cubic (fcc) Au (fcc-Au) on the (002)h facets of 2H-Pd while 2H-Au on the other exposed facets, to achieve well-defined fcc-2H-fcc heterophase Pd@Au core-shell nanorods. Moreover, through such unique facet-directed crystal-phase-selective epitaxial growth, a series of unconventional fcc-2H-fcc heterophase core-shell nanostructures, including Pd@Ag, Pd@Pt, Pd@PtNi, and Pd@PtCo, have also been prepared. Impressively, the fcc-2H-fcc heterophase Pd@Au nanorods show excellent performance toward the electrochemical carbon dioxide reduction reaction (CO2RR) for production of carbon monoxide with Faradaic efficiencies of over 90% in an exceptionally wide applied potential window from -0.9 to -0.4 V (versus the reversible hydrogen electrode), which is among the best reported CO2RR catalysts in H-type electrochemical cells.

Selective Epitaxial Growth of Oriented Hierarchical Metal-Organic Framework Heterostructures

Abstract: Metal–organic framework (MOF) heterostructures have shown promising applications in gas adsorption, gas separation, catalysis, and energy, arising from the synergistic effect of each component. How...

Synthesis of Palladium-Based Crystalline@Amorphous Core-Shell Nanoplates for Highly Efficient Ethanol Oxidation.

Abstract: Phase engineering of nanomaterials (PEN) offers a promising route to rationally tune the physicochemical properties of nanomaterials and further enhance their performance in various applications. However, it remains a great challenge to construct well-defined crystalline@amorphous core-shell heterostructured nanomaterials with the same chemical components. Herein, the synthesis of binary (Pd-P) crystalline@amorphous heterostructured nanoplates using Cu3- χ P nanoplates as templates, via cation exchange, is reported. The obtained nanoplate possesses a crystalline core and an amorphous shell with the same elemental components, referred to as c-Pd-P@a-Pd-P. Moreover, the obtained c-Pd-P@a-Pd-P nanoplates can serve as templates to be further alloyed with Ni, forming ternary (Pd-Ni-P) crystalline@amorphous heterostructured nanoplates, referred to as c-Pd-Ni-P@a-Pd-Ni-P. The atomic content of Ni in the c-Pd-Ni-P@a-Pd-Ni-P nanoplates can be tuned in the range from 9.47 to 38.61 at%. When used as a catalyst, the c-Pd-Ni-P@a-Pd-Ni-P nanoplates with 9.47 at% Ni exhibit excellent electrocatalytic activity toward ethanol oxidation, showing a high mass current density up to 3.05 A mgPd -1 , which is 4.5 times that of the commercial Pd/C catalyst (0.68 A mgPd -1 ).

Mechano-Responsive, Tough, and Antibacterial Zwitterionic Hydrogels with Controllable Drug Release for Wound Healing Applications.

Abstract: Acute wounds subject to frequent deformations are difficult to be treated because the healing process was easily interfered by external mechanical forces. Traditional wound dressings have limited efficacy because of their poor mechanical properties and skin adhesiveness and difficulty in the delivery of therapeutic drugs effectively. As such, tough and skin-adhesive wound dressings with sustainable and stimuli-responsive drug release properties for treatment of those wounds are highly desirable. For this purpose, we have developed a mechano-responsive poly(sulfobetaine methacrylate) hydrogel which aims to control the delivery of antibiotic drug upon application of mechanical forces. Diacrylated Pluronic F127 micelles were used as a macro-cross-linker of the hydrogel and loaded with hydrophobic antimicrobial drugs. The micelle-cross-linked hydrogel has excellent mechanical properties, with the ultimate tensile strength and tensile strain of up to 112 kPa and 1420%, respectively, and compressive stress of up to 1.41 MPa. Adhesiveness of the hydrogel to the skin tissue was ∼6 kPa, and it did not decrease significantly after repetitive adhesion cycles. Protein adsorption on the hydrogel was significantly inhibited compared to that on commercial wound dressings. Because of the mechano-responsive deformation of micelles, the release of drug from the hydrogel could be precisely controlled by the extent and cycles of mechanical loading and unloading, endowing the hydrogel with superior antibacterial property against both Gram-positive and Gram-negative bacteria. In addition, drug penetration into the skin tissue was enhanced by mechanical stress applied to the hydrogel. The micelle-cross-linked zwitterionic hydrogel also showed good cell biocompatibility, negligible skin irritation, and healing capacity to acute skin wounds in mice. Such a tough mechano-responsive hydrogel holds great promise as wound dressings for acute wounds subjected to frequent movements.

Heterophase fcc-2H-fcc gold nanorods.

Abstract: The crystal phase-based heterostructures of noble metal nanomaterials are of great research interest for various applications, such as plasmonics and catalysis. However, the synthesis of unusual crystal phases of noble metals still remains a great challenge, making the construction of heterophase noble metal nanostructures difficult. Here, we report a one-pot wet-chemical synthesis of well-defined heterophase fcc-2H-fcc gold nanorods (fcc: face-centred cubic; 2H: hexagonal close-packed with stacking sequence of "AB") at mild conditions. Single particle-level experiments and theoretical investigations reveal that the heterophase gold nanorods demonstrate a distinct optical property compared to that of the conventional fcc gold nanorods. Moreover, the heterophase gold nanorods possess superior electrocatalytic activity for the carbon dioxide reduction reaction over their fcc counterparts under ambient conditions. First-principles calculations suggest that the boosted catalytic performance stems from the energetically favourable adsorption of reaction intermediates, endowed by the unique heterophase characteristic of gold nanorods.