The mechanical properties of carbon nanotube composites are mainly studied by experiment, theoretical analysis and numerical method. The common methods for the mechanical properties of carbon nanotubes include amplitude calculation, cantilever/simply supported beam model, and direct methods. The mechanical parameters of carbon nanotubes are derived by classical mechanics.Solid acid catalysts play a significant part in chemical and petroleum industries in hydrocarbon conversion reactions required in octane enhancement processes, such as cracking, isomerization and alkylation, which can form highly branched isoparaffins. Such reactions need strong or moderate acid catalysts.

WC-Co cemented carbide has widely used in machining, drilling, automotive, military, and aerospace owing to its excellent mechanical performances. Most research on cemented tungsten carbides with a cobalt binder (WC-Co cemented carbides) has focused on improving their strength, fracture toughness, and hardness.

As the demands for solar energy, pure air and water, and disposing of poisonous and hazardous pollutant are increasing, the use of semiconductor photocatalysts for environmental purification has attracted considerable attention due to their applicability for the removal of a wide variety of pollutants. Especially TiO2 has been studied widely in virtue of the high photocatalytic activity for organic pollutants such as RhB, tetracycline, phenol, and methylene blue under UV irradiation. Although TiO2 has various merits, the practical application of TiO2 is limited by its low photon utilization efficiency and the need for an ultraviolet excitation source which accounts for only a small fraction of solar light (approximately 5%).

Currently, due to the environmental situation worsening, in various countries and especially in the large cities, more and more funds have been allocated for the development of the green energy industry and environmentally friendly technologies. Hydrogen energy is an energy source that has increased its popularity in recent years. It is a clean energy source that can be used instead of fossil fuels. Hydrogen it can be used instead of fossil fuels due to its higher energy content and less environmental impact. The density of hydrogen is lower than the density of air. The gravimetric density of hydrogen energy is generally about seven times higher than the density of fossil fuels.

Cobalt tungstate (CoWO4) with monoclinic wolframite structure has been used in a wide range of potential applications including supercapacitors, photocatalysts, catalyst for oxygen evolution reaction (OER) and hydrogen production, microwave dielectric ceramics, photovoltaic electrochemical cells, among others. As electrochemical energy storage devices, batteries and supercapacitors have attracted significant attention due to their intrinsic characteristics of energy and power densities, cycling stabilities and charging-discharging rates.

A fabrication process of tungsten oxide (WO3) nanoplates with ammonium paratungstate has been performed, the product showed great photocatalytic activity due to the plate-like shape. Tungsten oxide (WO3) is a promising candidate for semiconductor gas sensors, electrochromic devices and photocatalysts. Structure and morphology of WO3 have obvious influences on its properties and applications. It has been reported that tungsten oxide with mixed structures exhibits poor optical properties, whereas the single-structure tungsten oxide, either hexagonal or cubic, exhibits noticeable absorption capacity.

As a hydrogen carrier for long-term sustainable energy supply, urea (CO(NH2)2) has been attracting increasing attention due to its stable, relatively non-toxic, non-flammable and renewable properties. Recently, the electrooxidation of urea has been used as an effective approach for hydrogen production as well as treatment of urea-rich wastewater.However, the current major challenge is to improve the catalytic activity and CO-tolerance of the catalyst.

Employing semiconductor powders as photocatalysis for the degradation of organic pollutants in water has received a lot attention in the last decade. Titanium dioxide (TiO2) inhibits amazing photocatalyst properties including high activity, chemical stability, and low cost. Nevertheless, the photocatalytic activity of TiO2 (with band gap of 3.2 eV and excited by photons with wavelengths under 387 nm) is still limited to irradiation by UV wavelengths, so that photocatalytic process does not occur effectively during the irradiation with solar light as only about 4% of the total radiation of the solar spectrum is in ultraviolet region. Thus, modification of TiO2 in the view to obtain a higher light absorption by shifting absorbance to the visible wavelengths has become the aim of many authors. One of the methods is the coupling of TiO2 with other semiconductors such as TiO2/CdS, TiO2/SnO2, TiO2/ZnO, and TiO2/WO3.

Photoelectrochemical (PEC) water-splitting technology is one of the most considerable technologies to synthesis H₂ gas as a clean energy. Titanium dioxide (TiO₂) has caught a lot attention as an effectual photoelectrode in PEC water-splitting for H₂ production owing to its unique and promising functional properties, such as high photocatalytic activity, long term photo-stability, superior oxidation ability, inertness to chemical environment, as well as low cost.

Tungsten oxide (WO3) is believed to be a remarkable and feasible photoactive material due to its stable physio-chemical characteristics under different reaction conditions. Furthermore, WO3 has a band gap energy around 2.6 eV. Nether less, bulk WO3 semiconductor, surface accumulation of photo generated charge carriers led to increase their recombination rate and eventually limiting the photocatalytic efficiency.