The information provided is given as reference. The gas molecules of Nitrogen dioxide (NO2) are not benefit to the human, plant, and animals. The gas can cause various problems, such as negative effect to lungs, smog rain, and is mainly fashioned from the burning of fossil fuels inside the combustion engines, alongside the other forms of NOx, such as NO and N2O.

Photocatalysis is a great technology to treat wastewater with environmental protection, more straightforward operation, high mineralization rate, and strong oxidation ability to efficiently remove the low concentration of organic pollutants in water.Tungsten trioxide (WO3) is a promising candidate for photocatalyst owing to its narrow energy gap (2.4–2.8 eV), high oxidation potential (+3.1–3.2 VNHE) of the valence band (VB), which is further meritorious for inducing the performance under visible light. WO3 is a widely studied metal oxide semiconductor for many cutting-edge applications such as photo/electrocatalysis, energy storage, smart window, antibacterial, anticancer agents, and pathogens control. Zinc tungstate (ZnWO4) has a wide band gap (about 3.8–5.7 eV) and possesses matched band structures with WO3. The introduction of ZnWO4 not only significantly promotes electron-hole separation but also broadens the absorption edge of WO3 and increases light absorption. Moreover, the addition of noble metal silver (Ag) can improve visible-light photocatalytic efficiency due to the increase of electron-transfer between semiconductor and noble metal.

Electrochromic (EC) materials have received distinguished attention because of their potential applications in smart windows, displays, and antiglare rearview mirrors. More interestingly, the electrochromic smart windows are considered being able to provide indoor comfort and reduce energy consumption in buildings because it could exhibit an ability to regulate the amount of sunlight entering the buildings. To achieve the excellent energy-saving effect, electrochromic smart windows should be able to adjust to near-infrared light along with visible light due to its broad range in sunlight.

Global energy demand, mainly based on unsustainable fossil fuels, has grown considerably during the last decades. Moreover, the emission of green house gases had caused environmental pollution and global warming.