Kaiqiang Liu

Porous Nickel–Iron Oxide as a Highly Efficient Electrocatalyst for Oxygen Evolution Reaction

A porous Ni–Fe oxide with improved crystallinity has been prepared as a highly efficient electrocatalytic water oxidation catalyst. It has a small overpotential, a low Tafel slope, and an outstanding stability. The remarkably improved electrocatalytic performance is due to the porous structure, high extent homogeneous iron incorporation, ameliorative crystallinity, and the low mass transfer resistance.

New Dicholesteryl-Based Gelators: Chirality and Spacer Length Effect

Eight new diacid amides of dicholesteryl L(D)-alaninates were designed and prepared. The compounds with spacers containing three, four, five, or six carbon atoms and L-alanine residues are denoted as 1a, 2a, 3a, and 4a, respectively, and those containing D-alanine residues are denoted as 1b, 2b, 3b, and 4b, respectively. A gelation test revealed that a subtle change in the length of the spacer and an inverse in the chirality of the amino acid residue can produce a dramatic change in the gelation behavior of the compounds and the microstructures of the gels, as revealed by SEM, XRD, and CD measurements. Importantly, for the compounds 1 and 2, those containing d-alanine residues (1b, 2b) are more efficient gelators than their analogues with opposite chirality (1a, 2a). For the compounds of longer spacers (3, 4), however, those containing l-alanine residues (3a, 4a) are superior to the corresponding ones with d-alanine residues (3b, 4b). Very interestingly, of the 139 gel systems studied, at least 11 of them gel spontaneously at room temperature. Studies of the rheological properties of the example systems of these gels demonstrated that change in the spacer lengths of the gelators has a great effect upon the mechanical properties of the corresponding gels, and the studies also revealed the thixotropic properties of the gels. Furthermore, it was observed that 4a forms water-in-oil gel emulsions with some organic solvents by simple agitating the systems at room temperature.

Simple design but marvelous performances: molecular gels of superior strength and self-healing properties

Four nitrobenzoxadiazole (NBD)-containing cholesteryl (Chol) derivatives were prepared, and their gelation behaviors were tested. It was demonstrated that the compounds show a remarkable gelling ability. In particular, a subtle change in the length of the spacers connecting the two structural units of the compounds, which are NBD and Chol, respectively, produced a dramatic change in the gelation ability and the gel properties of the compounds. As for gelation, compound 1 is much more powerful than others, especially in the gelation of methanol-containing organic mixtures. It is to be noted that the gel of 1/pyridine–methanol exhibits superior mechanical strength with a yield stress higher than 6300 Pa at a gelator concentration of 2.5% (w/v), and the value exceeds 23 000 Pa when the gelator concentration reaches 5.0% (w/v), a result never reported before in the field of molecular gels based on low-molecular mass gelators (LMMGs). More importantly, the gel shows a rapid self-healing property as evidenced by the fact that the gel heals up immediately upon cutting, provided the segments from the cutting are squeezed together. No doubt, our findings establish a benchmark for LMMG-based molecular gels in their rheological performances. FTIR, 1H NMR and XRD studies revealed that intermolecular hydrogen bonding and π–π stacking are two of the main driving forces to promote the gelation of the system and the self-assembling of the molecules of the gelator.

Hierarchical Co(OH)F Superstructure Built by Low-Dimensional Substructures for Electrocatalytic Water Oxidation

The development of new materials/structures for efficient electrocatalytic water oxidation, which is a key reaction in realizing artificial photosynthesis, is an ongoing challenge. Herein, a Co(OH)F material as a new electrocatalyst for the oxygen evolution reaction (OER) is reported. The as-prepared 3D Co(OH)F microspheres are built by 2D nanoflake building blocks, which are further woven by 1D nanorod foundations. Weaving and building the substructures (1D nanorods and 2D nanoflakes) provides high structural void porosity with sufficient interior space in the resulting 3D material. The hierarchical structure of this Co(OH)F material combines the merits of all material dimensions in heterogeneous catalysis. The anisotropic low-dimensional (1D and 2D) substructures possess the advantages of a high surface-to-volume ratio and fast charge transport. The interconnectivity of the nanorods is also beneficial for charge transport. The high-dimensional (3D) architecture results in sufficient active sites per the projected electrode surface area and is favorable for efficient mass diffusion during catalysis. A low overpotential of 313 mV is required to drive an OER current density of 10 mA cm-2 on a simple glassy carbon (GC) working electrode in a 1.0 m KOH aqueous solution.

Novel Dimeric Cholesteryl Derivatives and Their Smart Thixotropic Gels

Three novel LS(2)-type dimeric-cholesteryl derivatives (1-3), where S is a steroidal residue and L stands for a linker connecting the two S residues and contains three benzene rings and two amide and two carbamate groups, were designed and prepared. The compounds can gel a wide variety of organic solvents via three different ways, including mixing at room temperature, a heating-cooling cycle, and ultrasound treatment. SEM measurements revealed that the structures and the concentrations of the gelators, the nature of the solvent, and the preparation method employed have a great effect on the morphologies of the gel networks. It was revealed that 1 is a supergelator for DMSO (cgc = 0.04% w/v) and that the 1/DMSO gel can be prepared via any of the three methods mentioned above. Furthermore, the gel possesses excellent mechanical strength and a very smart thixotropic property. FT-IR and temperature- and concentration-dependent (1)H NMR spectroscopy studies revealed that hydrogen bonding and π-π stacking among the molecules of 1 are two important driving forces for the physical gelation of DMSO. In addition, XRD analysis confirmed the layered packing structure of 1 in its DMSO gel.

Calix[4]arene-based supramolecular gels with unprecedented rheological properties

A novel calix[4]arene-based dimeric-cholesteryl derivative was synthesized, and its gelation behaviour in thirty organic solvents was investigated. It has been shown that the compound cannot gel any of the pure solvents tested. However, it gels a mixture of solvents n-decane and acetonitrile efficiently, provided the volume ratio of the two solvents in a mixture is within 9 : 1 and 3 : 2. AFM and SEM measurements revealed that the molecules of the compound aggregate into micro-/nano-rods first, then fine fibers, and then thick fibers, and finally networked structures in the mixture solvents. Interestingly, the gel with a composition of 1 to 1 (Vn-Decane:VAcetonitrile) and 2.5% (w/v) of the compound exhibits super-smart and fully reversible thixotropic properties, a phenomenon never reported before. Furthermore, the mechanical strength of the gel could be easily adjusted by altering the concentration of the gelator and the composition of the mixture solvents. Further interrogation of the gel revealed that structurally the gel is a gel-emulsion with acetonitrile dispersed in n-decane, a rarely found O/O (oil in oil) gel-emulsion which may find uses in the templated preparation of low-density materials with complicated internal structures.

Tellurium-Assisted Epitaxial Growth of Large-Area, Highly Crystalline ReS2 Atomic Layers on Mica Substrate.

Anisotropic 2D layered material rhenium disulfide (ReS2 ) with high crystal quality and uniform monolayer thickness is synthesized by using tellurium-assisted epitaxial growth on mica substrate. Benefit from the lower eutectic temperature of rhenium-tellurium binary eutectic, ReS2 can grow from rhenium (melting point at 3180 °C) and sulfur precursors in the temperature range of 460-900 °C with high efficiency.

New dicholesteryl-based gelators: gelling ability and selective gelation of organic solvents from their mixtures with water at room temperature

Four new diacid amides of dicholesteryl L-phenylalaninate were designed and prepared. The compounds with spacers containing three, four, five, or six carbon atoms are denoted as 1–4, respectively. Gelation tests showed that the four compounds are versatile organogelators, and a subtle change in the length of the spacer can produce a dramatic change in the gelation behaviors of the compounds, as well as the micro-structures of the gel networks as revealed by SEM and XRD measurements. Within the 77 gel systems studied, at least seven of them, including 2/kerosene, 2/toluene, 2/xylene, 3/kerosene, 3/1-pentanol, 3/1-hexanol and 3/1-heptanol, gel spontaneously at room temperature. Furthermore, 2 and 3 can be used for the selective gelation of xylene or kerosene from their mixtures with water. Importantly, heating and cooling cycle or addition of a co-solvent is not necessary for the selective gelation. Furthermore, the gels of 2/xylene are mechanically strong enough for separation, and thereby it is believed that 2 is a strong candidate for the practical separation of xylene from its mixture with water. FT-IR and temperature-dependent 1H NMR measurements demonstrated that inter-molecular hydrogen bonding plays an important role for the formation and maintenance of the gel networks.

Novel dimeric cholesteryl-based A(LS)2 low-molecular-mass gelators with a benzene ring in the linker.

Three novel dimeric cholesteryl-based A(LS)(2) low-molecular-mass organic gelators (LMOGs) with phthaloyl, isophthaloyl, or terephthaloyl moieties in the linkers were designed and prepared. According to the linker structures, the compounds are denoted as 1 (o-), 2 (m-), and 3 (p-), respectively. Gelation tests revealed that the difference of relative positions of two cholesterol moieties in the benzene ring can produce a dramatic change in the gelation behaviors of the compounds. Importantly, 2 and 3 are more efficient gelators than 1, and their self-assembly behaviors are also very different from each other as revealed by scanning electron microscopy (SEM) measurements. Very interestingly, 2 gels xylene spontaneously at room temperature, and the sol-gel phase transition of the system is mechanically controllable. FTIR and (1)H NMR spectroscopy studies revealed that hydrogen bonding and pi-pi interactions between the molecules of the gelators play an important role in the formation and maintenance of the gels. The X-ray diffraction (XRD) analysis revealed that in the gel of 2/benzene, 2 aggregated into a layered structure with an interlayer distance of 3.54 nm, which is just the length of 2.

New dimeric cholesteryl-based A(LS)2 gelators with remarkable gelling abilities: organogel formation at room temperature.

Three new dimeric cholesterol-based compounds of A(LS)(2) type, where A stands for aromatic component, S steroid moiety, and L a linker connecting the two units, have been designed and prepared. Gelation test in 30 solvents demonstrated that the compounds can gel some of the solvents and form 37 gels, of which 16 form spontaneously at room temperature (~25 °C). These gels possess smart thixotropic properties as revealed by rheological studies. FTIR and (1)H NMR measurements revealed that hydrogen bonding is an important driving force for the formation of the gel networks. XRD analysis demonstrated that unlike commonly found layered structures adopted by dimeric cholesterol-based low-molecular mass gelators (LMMGs), one of the gelators created in this study adopts a hexagonal packing structure in its benzene gel.