In the past decade, MXenes, a new class of advanced functional 2D nanomaterials, have emerged among numerous types of electrode materials for electrochemical energy storage devices. MXene and their composites have opened up an interesting new opportunity in the field of functional materials, owing to their transition metal nitrides/carbides/carbonitride-based unique layered structures, higher electrical and thermal conductivity, higher charge carrier mobility, high negative zeta-potential, high mechanical properties, tunable bandgap, superior hydrophilicity, metallic nature and rich surface chemistry, which enhance the number of metal active redox sites on the surface and short ion diffusion path. However, in the case of electrochemical energy storage applications, the unavoidable problem of aggregation and nanosheet restacking significantly reduces the accessibility of the active surface sites of MXene materials for electrolyte ions. Currently, there is a number of research efforts devoted to solutions in order to avoid these deficits. This Review complies extensively with the recent advances in the application of MXene-based materials in the energy storage devices such as batteries and supercapacitors. Particular attention is paid to the understanding of the relation of MXenes chemical composition, and morphology with their electrochemical performances. Moreover, the challenges of MXenes and MXene-based composited for the commercial application are considered and the ways to overcome their drawbacks are provided. Finally, opportunities given with MXenes for future research on novel energy storage materials are highlighted.

The features of the properties and creation of nanocomposite metal oxide materials, especially TiO₂, ZnO, SnO₂, ZrO₂, and Fe₃O₄, and their applications for ecology are considered in the article. It is shown that nanomaterials based on them are very promising for use in the ecological direction, especially as sorbents, photocatalysts, and sensitive layers of gas sensors. The crystallochemical characteristics, surface structure, and surface phenomena that occur when they enter the water and air environment are given for these metal oxides, and it is shown that they play a significant role in obtaining the sorption and catalytic characteristics of these nanomaterials. Particular attention is paid to the dispersion and morphology of metal oxide particles by which their physical and chemical properties can be controlled. Synthesis methods of metal oxide nanomaterials and ways for creating of nanocomposites based on them are characterized, and it is noted that there are many methods for obtaining individual nanoparticles of metal oxides with certain properties. The main task is the correct selection and testing of parameters. The prospects for the production of metal oxide nanocomposites and their application for environmental applications are noted, which will lead to a fundamentally new class of materials and new environmental technologies with their participation.

This paper provides a summary of the recent developments with promising 2D MXene-related materials and gives an outlook for further research on gas sensor applications. The current synthesis routes that are provided in the literature are summarized, and the main properties of MXene compounds have been highlighted. Particular attention has been paid to safe and non-hazardous synthesis approaches for MXene production as 2D materials. The work so far on sensing properties of pure MXenes and MXene-based heterostructures has been considered. Significant improvement of the MXenes sensing performances not only relies on 2D production but also on the formation of MXene heterostructures with other 2D materials, such as graphene, and with metal oxides layers. Despite the limited number of research papers published in this area, recommendations on new strategies to advance MXene heterostructures and composites for gas sensing applications can be driven.

This paper aims to provide a large coverage of recent developments regarding environmental monitoring using metal oxide-based sensors. Particular attention is given to the detection of gases such as H₂, CO_x, SO_x, NO_x, and CH₄. The developments and analyses of the design of sensors and types of metal oxide sensing materials are emphasized. The sensing mechanisms and peculiarities of metal oxides used in chemoresistive sensors are provided. The main parameters that affect the sensitivity and selectivity of metal oxide sensors are indicated and their significance to the sensor signal is analyzed. Modern data processing algorithms, employed to optimize the measurement process and processing of the sensor signal, are considered. The existing sensor arrays/e-nose systems for environmental monitoring are summarized, and future prospects and challenges encountered with metal oxide-based sensor arrays are highlighted.

The effect of precursors on the characteristics of tin oxide obtained by chemical vapor deposition (CVD) method was investigated. The synthesis of nanosized tin(IV) oxide was carried out with the use of two different precursors: tin(II) oxalate obtained using tin chloride(II) and oxalic acid; tin(II) oxalate obtained using tin chloride(II); and ammonium oxalate. The synthesized tin(IV) oxide samples were studied by electron microscopy, X-ray diffraction and optical spectra. The lattice parameters of tin(IV) oxide samples were defined, the bandgap of samples were calculated.