ZnO thin films manifest interesting electrical and optical features upon incorporation of metal atoms. To widen its absorption window from ultra violet (UV) to visible region, among various strategies, the incorporation of other metal into plain ZnO thin films to modulate band gap is an effected strategy. But, wide optical band gap of plain ZnO limits its large scale practical utility as it is only active in ultraviolet (UV) region of light. Since, Fujishima and Honda has demonstrated the use of TiO 2 for PEC water splitting 6, a variety of transition metals based semiconductors, such as metal oxides 7, 8, 9, 10, 11, 12, 13, metal nitrides, and sulfides/selenides 14, 15, 16, have been extensively investigated as photoanodes for PEC cells.Īmong various semiconductors, ZnO has been widely explored as photoanodes due to its non-toxic, abundant, thermal and chemical stability and suitable optical band edges 17, 18, 19, 20, 21, 22, 23. Hydrogen generation as a clean fuel from solar energy through photoelectrochemical (PEC) water splitting is regarded as one of the most efficient strategy 3, 4, 5. The US Environmental Protection Agency (EPA) applies an emissions limit on chrome 6 from hard chrome plating facilities.Solar energy utilization has become the topic of research interest worldwide in order to cope with environmental issues and energy crisis 1, 2.
Cr 6 to cr 3 skin#
Other adverse health effects associated with chromium-6 exposure, according to the US National Institute for Occupational Safety and Health (NIOSH), include skin irritation or ulceration, allergic contact dermatitis, occupational asthma, nasal irritation and ulceration, perforated nasal septa, rhinitis, nosebleed, respiratory irritation, nasal cancer, sinus cancer, eye irritation and damage, perforated eardrums, kidney damage, liver damage, pulmonary congestion and edema, epigastric pain, and erosion and discoloration of one's teeth. Hexavalent chromium is classified as a human carcinogen based on excess lung cancer found in heavily exposed workers through inhalation in chrome plating and chromate pigment production. Levels of chromium in these conditions are usually well-below those that would be considered dangerous. In drinking water the level of chromium is usually low as well. The level of chromium in air and water is generally low. People who smoke tobacco also have a higher chance of exposure to chromium. Hexavalent chromium is a danger to human health, mainly for people who work in the steel and textile industry. Only a small part of the chromium that ends up in water will eventually dissolve. In water chromium will absorb on sediment and become immobile. Chromium in soils strongly attaches to soil particles and as a result it will not move towards groundwater. Most of the chromium in air will eventually settle and end up in waters or soils. Most industrial output is to water but coal burning also increases air concentration. Hexavalent chromium finds its way into the environment naturally or through manufacturing activities. The use of chromium in welding produces hexavalent chromium as a by-product. Hexavalent chromium is used to produce CCA (chromated copper arsenate) that is applied as a preservative in the treatment of structural timber. It is used in chrome plating and as an alloy in the production of stainless steel, as well as in anti-corrosion and conversion coatings. Its properties include corrosion-resistance, durability and hardness. However, its ease of reaction with other elements is the main reason why hexavalent chromium is considered a major health hazard. This ability to react can produce hard coatings. It can easily gain electrons from other elements, meaning that it can easily react with them. Hexavalent chromium occurs naturally but it is usually produced by industrial process. The most common forms of chromium in the environment are trivalent chromium (chromium-3), hexavalent chromium (chromium-6) and the metal form of chromium (chromium-0). Chromium is unstable in oxygen, it immediately produces a thin oxide layer that is impermeable to oxygen and protects the metal below. It does not tarnish in air, when heated it burns and forms the green chromic oxide. Its colour is silver-grey and it can be highly polished. Chromium is a lustrous, brittle, hard metal.
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