Ting-Ting Li

Facile synthesis of porous CuO polyhedron from Cu-based metal organic framework (MOF-199) for electrocatalytic water oxidation

Metal–organic frameworks (MOFs) have been demonstrated as suitable metal sources and sacrificial templates for the preparation of porous transition-metal oxide nanomaterials. Herein, porous CuO micro-polyhedra assembled from numerous nanoparticles are synthesized simply by employing a Cu-based MOF as a precursor via a one-step calcination process under an air atmosphere. Benefitting from their high porosity and large specific surface area, porous CuO materials exhibit excellent electrocatalytic performances toward water oxidation in pH 9.2 KBi solution. A low catalytic onset potential at 1.05 V vs. NHE (NHE = normal hydrogen electrode) is obtained based on electrochemical measurements. A faradaic efficiency of nearly 98% and a stable catalytic current density of 2.2 mA cm−2 are achieved under an applied potential of 1.30 V vs. NHE over an electrolysis period of 10 h. In addition, based on the Tafel plot, the required overpotentials are only ∼410 mV and ∼510 mV for achieving the catalytic current densities of 0.1 mA cm−2 and 1.0 mA cm−2, respectively. The excellent performances make it an appealing candidate as a potential catalyst for green energy applications.

A poly(2-(dimethylamino)ethyl methacrylate-co-methacrylic acid) complex induced route to fabricate a super-hydrophilic hydrogel and its controllable oil/water separation

Smart hydrogels, or stimulus–responsive (SR) hydrogels which are composed of three-dimensional networks with crosslinked hydrophilic polymer chains can display dramatic volume changes in response to external environments, such as temperature, pH and certain stimuli. Controllable and significant responses to environmental stimuli and super-hydrophilicity are crucial for versatility in terms of oil/water separation, especially. Thermo and pH dual-controllable oil/water separation materials are successfully fabricated by free radical polymerization of 2-(dimethylamino)ethyl methacrylate (DMAEMA) and methacrylic acid (MAA). The substrate of the stainless steel mesh was coated with the super-hydrophilic hydrogel film by simple immersion in an aqueous solution. The as-prepared mesh showed high hydrophobicity with an oil contact angle of about 151° underwater. More importantly, it can be used to separate oil/water mixtures like silicone oil. As shown, water can pass through the processed mesh in temperatures of less than 55 °C (pH 7) and pH values under pH 13 (T = 25 °C) when oil is intercepted on the mesh. Otherwise, the water retention capacity of the hydrogel is significantly reduced. The separation efficiency (98.35%) remains high after 15 uses and the mesh can be easily cleaned, stored, and reused. These properties render such thin films useful for applications to achieve various functional separation materials.

Self-healing supramolecular hydrogel of poly(vinyl alcohol)/chitosan carbon dots

Abstract Supramolecular hydrogels are non-covalent three-dimensional networked materials with many advantages compared to covalently cross-linked ones. In this present work, a supramolecular polymer hydrogel composed of poly(vinyl alcohol) (PVA) and chitosan carbon dots (CDs) was prepared by using the freezing/thawing method. To demonstrate the performance characteristics of such a polymer hydrogel, infrared spectrum, SEM, thermal analysis, swelling ratio, rheological study, self-healing test, etc., were adopted. The result showed that PVA/CDs supramolecular hydrogel not only has excellent self-healing property, but also has good thermal stability. This study work shows the great potential of the PVA/CDs hydrogel as an exciting polymer hydrogel material in the field of environmental management and biological medicine to design multifunctional materials. The simple nontoxic ingredients may also make the hydrogels suitable substitutes for biomedical applications pending further research.

Porous Co3O4 nanoparticles derived from a Co(II)-cyclohexanehexacarboxylate metal–organic framework and used in a supercapacitor with good cycling stability

Porous cobalt oxide materials have received great interest in recent years due to their potential application to supercapacitors. In this work, porous Co3O4 nanoparticles were prepared by the thermolysis of a Co(II)-based [Co3(cis-chhc)(H2O)6]n (cis-H6chhc = 1,2,3,4,5,6-cyclohexane-hexacarboxylic acid) metal–organic framework. Cyclic voltammetry and galvanostatic charge–discharge measurements were carried out to characterize the electrochemical performance of Co3O4 in a 2.0 M KOH electrolyte. The results demonstrate that the as-synthesized Co3O4 can be applied as a supercapacitor electrode. The porous Co3O4 electrode exhibits a specific capacitance of 148 F g−1 at a current density of 1 A g−1, and displays slightly enhanced capacitance after 2500 continuous charge–discharge cycles. This remarkable electrochemical performance suggests that the as-prepared porous Co3O4 material is potentially promising for applications in energy storage.

Self-supported hierarchical CuOx@Co3O4 heterostructures as efficient bifunctional electrocatalysts for water splitting

The preparation of low-cost and efficient bifunctional catalysts towards water splitting is essential for the production of clean H2 energy. Herein, a hierarchical Co3O4-decorated CuO–Cu2O nanorod core–shell structure was in situ grown on a Cu foam (denoted as CuOx@Co3O4 NRs/CF) and investigated as a bifunctional catalyst for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in alkaline solution. Benefiting from its large electrochemical surface area and the synergetic effects between the CuOx core and Co3O4 shell, CuOx@Co3O4 NRs/CF exhibited considerable catalytic activity, which resulted in a small overpotential of 240 mV for the OER and 242 mV for the HER at a current density of 50 mA cm−2, along with low Tafel slopes of 46 and 61 mV dec−1, respectively. Remarkably, CuOx@Co3O4 NRs/CF could continuously produce O2 or H2 for at least 24 h with negligible decline in catalytic activity, and it gave rise to high faradaic efficiencies of 99.7% and 96.4% for the OER and HER, respectively. The electrochemical performance of CuOx@Co3O4 NRs/CF was dramatically improved as compared to those of its CuOx NRs/CF counterpart and also most reported Cu-based water splitting electrocatalysts.

MOF-templated syntheses of porous Co3O4 hollow spheres and micro-flowers for enhanced performance in supercapacitors

Two kinds of MOF micro-precursors (Co-BTB-I, micro-spheres; Co-BTB-II, micro-flowers) are obtained with/without a surfactant by a simple and fast reaction. The hollow spherical morphology of Co-BTB-I-450 and the flower-like morphology of Co-BTB-II-450 are successfully preserved from the MOF-based template morphologies with highly crystalline Co3O4 nanoparticles. Compared to Co-BTB-II-450 materials and commercial Co3O4, the Co-BTB-I-450 electrode exhibits the best performance as an electrochemical supercapacitor with a specific capacitance of 342.1 F g−1 at 0.5 A g−1.