Nano

Graphene quantum dots (GQDs) have aroused widespread attention because of their remarkable properties and potential applications. Herein, we discuss both the top-down and bottom-up strategies for the synthesis of GQDs. Different processes are presented to study their characteristics and the influence on the final properties of GQDs. The respective advantages and disadvantages of these methods are summarized. With regard to some important or novel ones, mechanisms are proposed for reference. In addition, the application of GQDs in biosensors is highlighted in detail. At last, we put forward some problems to be solved and give a brief prospect in their future developments. This review is very useful for quickly gaining knowledge and experience for synthesizing GQDs and designing the related novel biosensors.

By adjusting the oxidation voltage, electrolyte, anodizing time and other parameters, TiO₂ nanotubes with high aspect ratio can be prepared by oxidation in organic system because anodic oxidation method has the advantage of simple preparation process, low material cost and controllable morphology. This review focusses on the influence of anodizing parameters on the morphology of TiO₂ nanotube arrays prepared by anodizing. In order to improve the photocatalytic activity of TiO₂ nanotubes under visible light and to prolong the life of photo-generated carriers, the research status of improving the photocatalytic activity of TiO₂ nanotubes in recent years is reviewed. This review focusses on the preparation and modification of TiO₂ nanotubes by anodic oxidation, which is helpful to understand the best structure of TiO₂ nanotubes and the appropriate modification methods, thus guiding the application of TiO₂ nanotubes in practical photocatalysis. Finally, the development of TiO₂ nanotubes is prospected.

The ability of neural networks to process information intelligently has allowed them to be successfully applied in the fields of information processing, controls, engineering, medicine, and economics. The brain-like working mode of a neural network gives it incomparable advantages in solving complex nonlinear problems compared with other methods. In this paper, we propose a feedforward DNA neural network framework based on an enzyme-free, entropy-driven DNA reaction network that uses a modular design. A multiplication gate, an addition gate, a subtraction gate, and a threshold gate module based on the DNA strand displacement principle are cascaded into a single DNA neuron, and the neuron cascade is used to form a feedforward transfer neural network. We use this feedforward neural network to realize XOR logic operation and full adder logic operation, which proves that the molecular neural network system based on DNA strand displacement can carry out complex nonlinear operation and reflects the powerful potential of building these molecular neural networks.

The novel Al-MOF@PPy@Au nanocomposites were synthesized by an in-situ growth method. The prepared Al-MOF@PPy@Au nanocomposites were characterized by Transmission Electron Microscope (TEM), Fourier Transform Infrared Spectrometer (FTIR), X-ray powder diffraction (XRD), Inductively Coupled Plasma (ICP) and X-ray photoelectron spectroscopy (XPS). The catalytic properties of the prepared Al-MOF@PPy@Au nanocomposites with different content of Au were investigated. The results illustrated that the Al-MOF@PPy@Au(G) with 27.80 wt.% (w/w) Au obtained good catalytic performance. P-nitrophenol (4-NP), methyl orange (MO), methylene blue (MB) and rhodamine B (RhB) were used to test the catalytic degradation of Al-MOF@PPy@Au(G) nanocomposites. The degradation efficiency of the Al-MOF@PPy@Au(G) nanocomposites for 4-NP, MO, MB and RhB reached 92.12%, 93.84%, 93.19% and 92.44% within 25 min, 7 min, 16 min and 2 min, respectively. The Al-MOF@PPy@Au(G) nanocomposites still have good degradation efficiency and good stability for 4-NP within one month being in water. The Al-MOF@PPy@Au(G) nanocomposites can be applied to the real water solution without causing the change of the degradation efficiency.

Due to fossil fuel consumption, the development of green and clean hydrogen energy sources is crucial. In this paper, a composite bifunctional catalyst comprised of Ni–Fe layered double hydroxide and multi-walled carbon nanotubes on nickel foam (LDHCN) were synthesized through a one-step hydrothermal method. The catalyst displayed excellent catalytic activity in both the hydrogen evolution reaction and oxygen evolution reaction. The composition and morphology of LDHCN were determined. Electrochemical testing was performed by building a parallel two-electrode electrolyzer (LDHCN‖LDHCN) that required a voltage of only 1.542V to drive 10 mA/cm². LDHCN‖LDHCN also maintained 100mA/cm² for at least 30 hours, indicating its excellent stability and activity. These results show that the material is viable for the highly efficient conversion and transport of hydrogen energy.

Surface and interface engineering have shown broad application prospect in energy conversion. Mo₂C-C/Sb₂S₃ composites have been synthesized by coupling Mo₂C-C composites and Sb₂S₃ nanowires with coupling agent. The performance of the devices has been investigated. Under irradiation by light source, the device showed better electrical contact, fast response speed (rise time 0.135s, decay time 0.132s) and larger on/off ratio ($1.5\times 10^2$) than the device which assembled by mechanical mixing ($1\times 10^2$) and pure Sb₂S₃ nanowires (47), respectively. The performance has been enhanced by modifying the surface and interface of materials. This approach provides a new idea to enhance the high-performance photodetectors and other inventive optoelectronic devices.

FeOOH nanorods (NRs) wrapped by reduced graphene oxide (rGO) were fabricated using a facile solvothermal method. When used as anode materials for lithium-ion batteries (LIBs), the FeOOH NRs/rGO composites show a higher capacity (490mAh g${}^{-1}$ after 100 cycles at a current density of 100mA g${}^{-1})$ and better rate capability than pure FeOOH NRs. The enhanced electrochemical performance can be ascribed to the hybrid structure of FeOOH and rGO. On one hand, the introduction of rGO can improve electronic conductivity and reduce charge-transfer resistance for electrode materials. On the other hand, the distinctive structure (FeOOH NRs surrounded by flexible rGO) can effectively buffer large volume change during the Li${}^{+}$ insertion/extraction process. Our work provides a feasible strategy to obtain high-performance LIBs.

The porous Pd-loaded In₂O₃ hollow spheres were successfully prepared by simple one-step method with the template of carbon spheres. The effect of calcination temperatures on morphology, composition and gas sensing performance of the as-obtained products was discussed by a series of test methods. The sample calcined at 550^∘C showed uniform porous hollow spheres with an average diameter of 100nm. Gas-sensing results exhibited that the Pd-In₂O₃ hollow spheres-based sensor possessed excellent sensing properties to formaldehyde, which include high response value (33), low working temperature (180^∘C) and fast response and recovery time (12s and 22s). The enhanced HCHO-sensing properties of Pd-In₂O₃ composites were attributed to the special porous and hollow structure, abundant oxygen vacancies and the catalysis of palladium. Pd-loaded In₂O₃ hollow spheres had been proved to be an ideal material for detecting HCHO at a low working temperature.

Rationally engineered anode materials with high specific capacities and rate capability are essential for lithium-ion batteries (LIBs). In this paper, a free-standing anode composed of Co₃S₄ nanosheets arrays and carbon cloth (abbreviated Co₃S₄@CC) was fabricated for high performance LIBs. The three-dimensional (3D) porous carbon cloth could not only improve the conductivity but also boost Li${}^{+}$ transfer and increase contact area for reactions. Besides, the porous thin Co₃S₄ nanosheets possessing strong interaction with carbon cloth by formation of C–S bond and high surface area could facilitate the mitigation of volume expansion and reduction of Li${}^{+}$ diffusion distance, coupling with efficient contact with electrolytes during cycling process. As expected, the freestanding Co₃S₄@CC anode presents pseudocapacitance-dominated storage behavior with a very high specific capacity of 847mAh g${}^{-1}$ at 250mA g${}^{-1}$ after 100 cycles and good rate capability for LIBs. This work provides an approach for designing metal sulfides with high capacities and rate capability for LIBs, especially flexible LIBs.

An excellent novel laminar and hierarchical polyethyleneimine cross-linked graphene oxide/titanium dioxide (GO–TiO₂–PEI) membrane was successfully prepared by vacuum filtration technology using polyethyleneimine (PEI) as the cross-linking agent and a GO–TiO₂ nanocomposite as the substrate. The resultant membrane (GO–TiO₂–PEI) displayed a favorable antifouling performance with bovine serum albumin (BSA) and showed good hydrophilicity and wettability, with a static water contact angle of 13.2^∘. The stability of the GO–TiO₂–PEI membrane in aqueous solution obviously improved with the cross-linking of PEI compared with that of the GO and GO–TiO₂ membranes. The GO–TiO₂–PEI membrane also exhibited a satisfactory water flux of 48.6L m${}^{-2}$ h${}^{-1}$ bar${}^{-1}$. The GO–TiO₂–PEI membrane exhibited a good performance for effectively separating different dyes including methylene blue (MB), rhodamine B (RB), methyl orange (MO), sunset yellow (SY), new coccine (NC) and amaranth. All the above results suggested that the GO–TiO₂–PEI membrane could be used as an excellent stable hydrophilic membrane for efficiently separating dyes from aqueous solution.

A new noninvasive glucose sensor is developed based on Co₃O₄ particles (Co₃O₄ NPs), which are synthesized by a single-step hydrothermal method with uniform structure and size. The electrochemical measurements reveal that the device exhibits outstanding performance for glucose detection, achieving a maximal sensitivity of 2495.79$\mu$A mM${}^{-1}$ cm${}^{-2}$ with a high $R^2$ of 0.99575, a ultra-low detection limit of 9.3nM with a signal-to-noise of 3 and linear range up to 3mM. The noninvasive glucose sensor can respond swiftly and selectively due to the high electrocatalytic activity of Co₃O₄ NPs. The sensor also shows its high sensitivity and selectivity in detecting glucose levels in human blood serum and saliva sample, confirming the application potential of Co₃O₄ NPs in noninvasive detection of glucose.

In order to realize the rational utilization of wastewater treatment, an efficient and conductive 3D hierarchical flowers globose nanostructure of Bi₂WO₆/C is explored from the withered peach blossom for removing the contaminants. As a consequence, Bi₂WO₆/C shows a better degradation efficiency for tetracycline (TC) than Bi₂WO₆ (49%) under visible light, when the mass ratio of Bi₂WO₆ to C is 6:1. Additionally, photoelectrochemical measurements proved that the separation efficiency of electron–hole pairs of Bi₂WO₆ is enhanced by the introduction of biomass carbon, due to its good electron transmission ability. Moreover, the mechanism exploration experiment showed that $\cdot {\mathrm{\text{O}}}_2^{-}$ was the main activity species. Meanwhile, the photocatalytic electron transfer mechanism was also investigated. The favorable photocatalytic performances make the waste biomass carbon act as a new resource for being applied to antibiotic wastewater treatment.

In this work, innate free-standing and flexible anode composed of entangled N-doped carbon nanotubes (CNTs) is fabricated by a facile annealing method following a simple compression without needing any tedious processing operations. The well cross-linked CNTs of the resultant free-standing anode enable robust diffusion channels for lithium ions and high flexibility. Served as the anode in lithium-ion batteries (LIBs) without the utilization of binder and current collector, the fabricated free-standing electrode can deliver a reversible area capacity of 2.14mAhcm${}^{-2}$ at 1mAcm${}^{-2}$ with superior cycling stability and excellent rate capability. The obtained reversible area capacity for the fabricated free-standing electrode material is much higher than that of the commercial graphite anode ($\sim 0.6$mAhcm${}^{-2}$ at 1mAcm${}^{-2}$). Furthermore, the assembled full flexible battery utilizing the fabricated free-standing electrode also exhibits attractive performance and can substantially supply power for an electronic watch at flat and 180^∘ bending positions, indicating the promising application in flexible electronic devices.