In recent years, metal organic frameworks (MOFs) have become emerging materials. Their applications in various fields are increasingly reported due to their special structure and excellent physical and chemical properties. Zeolitic imidazolate framework (ZIF) is a sub-system of MOF with good stability and similar structure to conventional type of zeolites. A variety of ZIF crystals have been obtained by adjusting metal ions as well as organic ligands. Through investigation, we found that the literature on gas sensing mainly focuses on the complexes of ZIF-8 and derivatives of ZIF-67, and there were also some reports on the application of other ZIF materials in gas response. In this paper, the reports of ZIF materials in the direction of gas sensing in recent years are summarized. By summarizing and considering the existing studies, it can help us better understand the current progress and limitations of ZIF materials in the development of gas sensing, and provide some possible development directions or ideas for the future development of ZIF materials.

The development of efficient photodetectors for color recognition is of great importance for many applications. In this paper, we report a novel bipolar dual-broadband photodetector equipped with a perovskite heterojunction, with bidirectional broadband responses in the short-wavelength and long-wavelength regions at zero bias voltage, enabled by a charge separation reversion mechanism. The unique aerosol–liquid–solid technique allowed the perovskite heterojunction to be fabricated by successively depositing wide-bandgap perovskite (WBP) and narrow-bandgap perovskite (NBP) layers directly on the transparent substrate. For photodetectors based on the perovskite heterojunctions, the short-wavelength photons were depleted by the bottom WBP layer and generated negative responses, while the long-wavelength photons were absorbed by the top NBP layer and generated positive responses. Moreover, the demarcation wavelength between the bipolar responses and the cut-off wavelength can be easily tuned by adjusting the bandgaps (or compositions) of the bottom and top perovskite layers.

Scintillators are widely used for x-ray detection in various fields, such as medical diagnostics, industrial inspection and homeland security. Nanocrystals (NCs) of metal halide perovskites (MHPs) and their analogues showed great advantages as x-ray scintillators due to their cheap manufacturing, fast decay time, and room temperature scintillation from quantum confinement effect. However, there are still many challenges unsolved for further industrialization. Herein, it is necessary to summarize the progress of scintillators based on NCs of MHPs and their analogues. In the first section, the scintillation mechanism and key parameters are outlined. Then, various NCs of MHPs and their analogues used as scintillators are reviewed. Finally, the challenges and outlook are discussed. It is believed that NCs of MHPs and their analogues are favorable for large-area and flexible x-ray detectors.

Graphene-based thermal rectification was investigated by measuring the thermal transport properties of asymmetric suspended graphene nanomesh devices. A sub-10 nm periodic nanopore phononic crystal structure was successfully patterned on the half area of the suspended graphene ribbon by helium ion beam milling technology. The ‘differential thermal leakage’ method was developed for thermal transport measurement without disturbance from the leakage of electron current through the suspended graphene bridge. A thermal rectification ratio of up to 60% was observed in a typical device with a nanopore pitch of 20 nm. By increasing the nanopore pitch in a particular range, the thermal rectification ratio showed an increment. However, this ratio was degraded by increasing the environmental temperature. This experiment suggests a promising way to develop a high-performance thermal rectifier by using a phononic crystal to introduce asymmetry on homogeneous material.

This work reports a key factor, the H2SO4 concentration, in controlling the physicochemical properties of titanium dioxide (TiO2) photocatalysts during the sol–gel synthesis. The photocatalysts synthesized using different concentrations of H2SO4 possess specific anatase/rutile ratios and crystallite sizes as well as surface areas, resulting in different photocatalytic performance in the degradation of formic acid in solution. The best photocatalytic performance is observed for the TiO2 photocatalyst containing a relatively high percentage of the rutile phase (∼84%), which is obtained from the sol–gel synthesis without H2SO4.

Natural fibers and materials are well known for adsorption studies, whereas synthetic fibers have not received enough attention in this field. Therefore, an attempt is made here to study the adsorption properties of synthetic poly(methyl methacrylate) (PMMA) nanofibers and methods for improving or modifying their adsorption properties. PMMA nanofibers are prepared by the most recent electrospinning technique and the structural, and hence, the adsorption properties of the PMMA nanofibers are modified by preparing them in surface-roughened and coaxial hollow forms through electrospinning. Studies of the adsorption of methylene blue (MB) and brilliant green (BG) dyes by the three types of PMMA nanofiber demonstrate that all the PMMA nanofibers show a certain amount of adsorption. Fiber samples that had adsorbed MB and BG were subjected to various adsorption isotherms which confirmed the multilayer adsorption properties of the fiber samples by satisfying various isotherms, mainly the Freundlich and Elovich adsorption isotherms. Kinetic studies of pure and structurally modified PMMA nanofibers that had adsorbed MB and BG dyes proved that the intraparticle diffusion model applied to these fiber samples. Here, it is also shown that the adsorption properties of electrospun synthetic fibers can be further improved by structural modification using the possibilities of electrospinning.

The direct reduction of graphene oxide (GO) by hydroiodic acid is an established method to produce iodine functionalized reduced GO (I-rGO). However, the stability of the iodine species within I-rGO upon heating and dispersing into different solvents, as required for many applications, has not been examined. Herein we examined the stability of I-rGO and utilized it to promote self-assembled nanoenergetic composites. I-rGO intercalated with polyiodide was found to be unstable at elevated temperature and when dispersed in organic solvents. The I-rGO exhibited excellent dispersion in dimethylformamide but resulted in a loss of iodine content as exfoliation released weakly-bound intercalated iodine species. The dispersed I-rGO was utilized as a scaffold to self-assemble I-rGO/Al and I-rGO/Al/Bi2O3 nanoenergetic composites. The I-rGO both prevented the phase separation of Al and Bi2O3 particles and provided a source for reactive iodine to etch the alumina shell surrounding Al fuel nanoparticles. Differential scanning calorimetry showed that the use of the I-rGO assembly template reduced the temperature of initiation and peak reaction and produced 70% greater energy release than randomly mixed Al/Bi2O3 nanoenergetic powder. In fact, 95% of the exothermal energy released by the reaction occurred while Al was in the solid state, suggesting that the reaction between free iodine and alumina was significant enough to greatly reduce the diffusion barrier between solid Al fuel and surrounding oxidizer. Further, the underlying conductive I-rGO scaffold reduces electrostatic discharge sensitivity of the nanoenergetic composite by almost four orders of magnitude.

Experimental data and a supporting model are presented for the formation of voids in InN nanorods grown by selective area hydride vapor phase epitaxy on patterned GaN/c-Al2O3 templates. It is shown that these voids shape, due to a high lattice mismatch between InN and GaN materials, starts from the base and extends up to a half of the total length of the nanorods. When the effect of the mismatch between substrate and nanorods becomes weaker, the hollow nanotubes close up at the top and further growth proceeds in the standard nanowire geometry without voids. This effect is observed within a wide range of growth conditions during the InN synthesis and must be taken into account for controlling the final structure of InN nanorods for different device applications.

Nano-sized extracellular vesicles have become an interesting target for fluorescent labelling due to their complex roles within cellular processes. Extracellular vesicles are released by most cells, including bacteria and mammalian and have demonstrated clear involvement within cellular, as well as patho-physiological processes. They contain information about the cell they originate from and communicate between cells making them promising disease biomarkers and vehicles for drug delivery. Many strategies have been used to fluorescently label extracellular vesicles to track or identify unknown cellular processes. Various targetable proteins are embedded in their membrane enabling them to be fluorescently labelled for detection and identification purposes. The fluorescent probes used for biosensing and bioimaging include organic dyes, fluorescent proteins, metal nanoparticles and quantum dots. Commonly used organic dyes and fluorescent proteins have inherent issues with stability and photobleaching. Quantum dots, however, exhibit high quantum yields, have broad excitation wavelengths and do not photobleach. The tuneable size of the quantum dots corresponds to emission wavelengths and can therefore be used in multiplexing or parallel detection of different targets. Semiconducting quantum dots can be modified with targetable proteins that make them ideal labelling agents. This review introduces extracellular vesicles and state-of-the-art use of quantum dots for bioimaging and biosensing.

In this paper we revisit the structure of graphene oxide, and determine the pure and truly representative structures for graphene nanoflakes using machine learning. Using 20 396 random configurations relaxed at the electronic structure level, we observe the presence of hydroxyl, ether, double bonds, aliphatic (cyclohexane) disruption, defects and significant out-of-plane distortions that go beyond the Lerf–Klinowski model. Based on an diverse list of 224 chemical, structural and topological features we identify 25 archetypal ‘pure’ graphene oxide structures which capture all of the complexity and diversity of the entire data set; and three prototypes that are the truly representative averages in 224-dimensional space. Together these 28 structures, which are shown to be largely robust against changes in thermochemical conditions modeled using ab initio thermodynamics, can be downloaded and used collectively as a small data set for with a fraction of the computational cost in future work, or independently as an exemplar of graphene oxide with the required oxidation.