Latest ArticlesPhotocatalytic water splitting utilizing solar energy is considered as one of the most ideal strategies for solving the energy and environmental issues. Recently, two-dimensional (2D) materials with an intrinsic dipole show great chance to achieve excellent photocatalytic performance. In this work, blue-phase monolayer carbon monochalcogenides (CX, X = S, Se) are constructed and systematically studied as photocatalysts for water splitting by performing first-principles calculations based on density functional theory. After confirming the great dynamical, thermal, and mechanical stability of CX monolayers, we observe that they possess moderate band gaps (2.41 eV for CS and 2.46 eV for CSe) and high carrier mobility (3.23 × 104 cm2 V-1 s-1 for CS and 4.27 × 103 cm2 V-1 s-1 for CSe), comparable to those of many recently reported 2D photocatalysts. Moreover, these two monolayer materials are found to have large intrinsic dipole (0.43 D for CS and 0.51 D for CSe), thus the build-in internal electric field can be selfintroduced, which can effectively drive the separation of photongenerated carriers. More importantly, the well-aligned band edge as well as rather pronounced optical absorption in the visible-light and ultraviolet regions further ensure that our proposed CX monolayers can be used as high efficient photocatalysts for water splitting. Additionally, the effects of external strain on the electronic, optical and photocatalytic properties of CX monolayers are also evaluated. These theoretical predictions will stimulate further work to open up the energy-related applications of CX monolayers.
Transition-metal oxides are considered to be a promising anode material for lithium-ion batteries (LIBs) due to their high capacities, low cost, and ease of synthesis. Herein, a hybrid nanosheet composed of uniform MoO2 nanoparticles (NPs) homogeneously immobilized on the reduced graphene oxide nanosheets (MoO2 NP@rGO) is first synthesized by a self-templating and subsequent calcination treatment. The unique two-dimensional hybridnanosheets provides several merits. rGO can be used as a favorable support for the loading of electrochemically active MoO2 NPs. Meanwhile, MoO2 NPs can effectively prevent the stacking of the rGO. The effective combination of MoO2 NPs and rGO nanosheets furnish additional electrochemically interfacial active sites for extra lithium ion storage. Noticeably, the as-fabricated hybrid nanosheets deliver a reversible capacity of 641 mAh/g after 350 cycles at a current density of 1000 mA/g with a good rate capability. The greatly enhanced lithium storage properties of MoO2 NP@rGO indicate the importance of elaborate construction of novel hybrid hierarchical structures.
Encapsulation and controlled release of volatile molecules such as fragrances in a designed manner is important but challenging for the flavor and fragrance industry. Here, we report the tuning release of volatile molecules by postsynthetic modification of an amine-terminated metal-organic framework (MOF) MIL-101-NH2. By amidation, we obtained three MIL-101 MOFs, the trimethylacetamide-terminated TC-MIL-101, the benzamide-terminated BC-MIL-101, and the oxalic acid monoamide-terminated OC-MIL-101. All the MOFs can efficiently encapsulate volatile molecules. Moreover, we demonstrate that the release profile of volatiles can be widely tuned to sustain the release in several days to months and even over a year using different modified MIL-101 MOFs. We show that the release profiles are correlated with the binding energies between the guest volatiles and pores in MOFs. The pore diffusion and the synergistic transport are the rate-limiting step of the guest molecules from the modified MOFs.
Photoelectrochemical (PEC) water splitting is a promising technology to use solar energy. However, current metal oxides photoanode face the problem of sluggish water oxidation kinetic. In this study, we propose that the sluggish water oxidation process will cause slow mass transfer efficiency, which are rarely considered previously, especially at large bias and strong illumination. Mass transfer refers to the migration of reactants (like H2O and OH-) to the photoanode surface, reaction with holes and diffusion of products (like radical and O2) to the bulk of the electrode. If the migration and diffusion are not fast enough, the mass transfer will inhibit the increase of PEC activity. This problem will be more apparent for nanorod arrays (NRAs), where the space among the NRAs is related narrow. Herein, we solve this problem by decorating the surface of the photoanode by NiO clusters with Ni3+ state as water oxidation cocatalysts. This work studies the PEC process from the viewpoint of mass transfer and firstly demonstrates that mass transfer in NRAs structure can be promoted by using Ni-based water oxidation cocatalyst.
The rapid development of internet and internet of things brings new opportunities for the expansion of intelligent sensors, and acetone as a major disease detection indicator (i.e., diabetes) making it become extremely important clinical indicator. Herein, uniform mesoporous ZnO spheres were successfully synthesized via novel formaldehyde-assisted metal-ligand crosslinking strategy. In order to adjust the pore structure of mesoporous ZnO, various mesoporous ZnO spheres were synthesized by changing weight percentage of Zn(NO3)2·6H2O to tannic acid (TA). Moreover, highly active heterojunction mesoporous ZnO/Co3O4 has been fabricated based on as-prepared ultra-small Co3O4 nanocrystals (ca. 3 nm) and mesoporous ZnO spheres by flexible impregnation technique. Profit from nano-size effect and synergistic effect of p-n heterojunction, mesoporous ZnO/Co3O4 exhibited excellent acetone sensing performance with high selectivity, superior sensitivity and responsiveness. Typically, 5 wt% Co3O4 embedded mesoporous ZnO sphere showed prominent acetone response (ca. 46 for 50 ppm), which was about 11.5 times higher than that in pure ZnO sensing device, and it was also endowed high cyclic stability. The nanocrystals embedded hybrid material is expected to be used as promising efficient material in the field of catalysis and gas sensing.
A novel diselenide-containing crown ether (BC7Se2) was fabricated, which can polymerize to form cyclic oligomers through intermolecular dynamic covalent reaction by irradiation of visible light. The size and distribution of oligomers are related to the monomer concentration. The decomposition reaction of oligomers is controlled by topology and solvents. Furthermore, potassium cation can inhibit the polymerization of BC7Se2 and accelerate the decomposition of oligomers.
Aqueous electrolytes are safe, economic, and environmentally friendly. However, they have a narrow potential window. On the other hand, organic electrolytes exhibit good thermodynamic stability but are inflammable and moisture sensitive. In this study, we prepared water-PEG-lipid ternary electrolytes (TEs). To combine the advantages of water, polyethylene glycol (PEG) and propylene carbonate (PC). The nonflammable mixed electrolytes exhibited a wide potential window of about 2.8 V due to the beneficial effects of PEG and PC. Using these TEs, a lithium manganate–active carbon ion capacitor could be operated at 2.4 V with an energy density of 32 Wh/kg, based on the total active electrode material (current density of 3.3 mA/cm2). This value was significantly higher than that achieved using an aqueous electrolyte, thereby rationalizing the higher energy density.
The construction of nanostructured ion-transport channels is highly desirable in the design of advanced electrolyte materials, as it can enhance ion conductivity by offering short ion-transport pathways. In this work, we present a supramolecular strategy to fabricate a nanocomposite electrolyte containing highly ordered lamellar proton-conducting nanochannels, by the electrostatic self-assembly of a polyoxometalate H3PW12O40 (PW) and a comb copolymer poly(4-methlstyrene)-graft-poly(N-vinyl pyrrolidone). PW can effectively regulate the self-assembling order of polymer moieties to form a large-range lamellar structure, meanwhile, introducing protons into the nanoscale lamellar domains to build proton transport channels. Moreover, the rigid PW clusters contribute a remarkable mechanical reinforcement to the nanocomposites. The lamellar nanocomposite exhibits a conductivity of 4.3×10-4 S/cm and a storage modulus of 1.1×107 Pa at room temperature. This study provides a new strategy to construct nanostructured ion-conductive pathways in electrolyte materials.
The remarkable development of nanotechnology and nanoscience has greatly promoted the vigorous development of the field of nanomaterials. This study explores a porous cuboid Ni/NiO composite nanomaterial obtained by calcining NiC2O4·2H2O under a N2 environment. The composite affords direct electrochemical activity and good electrocatalytic properties. Compared to uncalcined precursor, the porous Ni/NiO obtained after calcination exhibited higher catalytic activity for glucose oxidation with higher sensitivity. Moreover, because of its regular cube structure the as-synthesized Ni/NiO exhibited improved electrochemical stability. Such porous Ni/NiO nanocubes represent promising glucose catalyst with high sensitivity and selectivity, improved stability and fast amperometric response.
The flourishing development in flexible electronics has provoked intensive research in flexible strain sensors to realize accurate perception acquisition under different external stimuli. However, building hydrogel-based strain sensors with high stretchability and sensitivity remains a great challenge. Herein, MXene nanosheets were composited into polyacrylamide-sodium alginate matrix to construct mechanical robust and sensitive double networked hydrogel strain sensor. The hydrophilic MXene nanosheets formed strong interactions with the polymer matrix and endowed the hydrogel with excellent tensile properties (3150%), compliant mechanical strength (2.03 kPa−1 in Young's Module) and long-lasting stability and fatigue resistance (1000 dynamic cycles under 1, 600% strain). Due to the highly oriented MXene-based three dimensional conductive networks, the hydrogel sensor achieved extremely high tensile sensitivity (18.15 in gauge factor) and compression sensitivity (0.38 kPa−1 below 3 kPa). MXene hydrogel-based strain sensors also displayed negligible hysteresis in electromechanical performance, typical frequent-independent feature and rapid response time to external stimuli. Moreover, the sensor exhibited accurate response to different scales of human movements, providing potential application in speech recognition, expression recognition and handwriting verification.
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