Fossil fuels as the current major energy source has promoted many environmental issues due to the large-scale emission of CO2 and other pollutants. Issues brought by fossil fuels include global warming, climate change, and sea level rise. Solar energy as a clean energy source has caught great interest globally, and is belived to be a promising solution to climate change and fossil fuel depletion. Photoelectrochemical water splitting (PEC) is an effective solar conversion technology to store the energy in hydrogen gas (H2).

Nitrogen oxides (NOx) are produced from the emissions of stationary sources and automobiles. Direct emission of NOx into the atmosphere without purification will lead to photochemical smog, acid rain and even global warming. The selective catalytic reduction (SCR) of NO with NH3 is widely employed for reduction of NOx emissions from stationary sources like gas, oil and coal- fired power plants. The most common catalyst is vanadium well-dispersed on a titania support as V2O5-TiO2.

There are four main preparation methods of preparing tungsten copper: mixed-press sintering method, activation sintering method, infiltration method, and nano/ultrafine mixed powder sintering method.

Glycerol is a byproduct of overcapacity from biodiesel manufacture. Selective hydrogenolysis of glycerol to 1,3-propanediol (1,3-PDO) has seen an increasing industrial demand as the glycerol derived from biodiesel production. By the way, 1,3-PDO has been largely utilized in solvents, cosmetics, cleaning products, pharmaceutical industries, and organic synthesis intermediates.

Titanium dioxide (TiO2) heterogeneous photocatalysis is an advanced oxidation process that degrades a variety of organic compounds, such as synthetic dyes, phenols and chlorophenols, detergents, solvents. Sunlight as a possible source of irradiation makes TiO2 photocatalysis an attractive technology to degrade pollutants in air. However TiO2 only works in conjunction with irradiation of limited wavelength: TiO2 band gap (Eg ≈ 3.2 eV) requires λirr  < 385 nm, which rules out 95% of the solar spectrum.

Photoelectrochemical (PEC) water splitting is believed to be the cleanest, most efficient and sustainable routes to replace the current fossil fuel based energy. H2 produced via PEC water splitting efficiently converted into electricity using fuel cells. Metal oxide semiconductors are known to be suitable materials for PEC water splitting as they are inexpensive and very stable in aqueous solutions.

Hexagonal WO3 (h-WO3) has caught a great attention due to its unique tunnel structure. In h-WO3, six-membered rings composed of WO6 octahedra are arranged along the (001) plane by sharing corner oxygens, with formation of open tunnels that have a theoretical intracrystalline tunnel size of 0.39 nm, along the c-axis throughout the entire unit cell.

Milling processing is divided into down milling and up milling. Down milling is a milling method in which the rotation direction of the contact part of the milling cutter and the workpiece is the same as the cutting feed direction. Up milling is a milling method in which the rotating direction of the contact part of the milling cutter and the workpiece is opposite to the cutting feed direction.

Molybdenum disulfide(MoS2) is a kind of solid powder which is made from natural molybdenum concentrate powder by chemical purification and changing its molecular structure. It is black with slight silver gray, metallic luster, slippery to the touch, and insoluble in water.

Molybdenum disulfide (MoS2) is a type of transition metal sulfide with glossy lead gray solid powder. It is synthesized and appears black, which has stable chemical property.