Photocatalysis
Photocatalysis is a rapidly developing field of research with a high potential for a wide range of industrial applications, which include mineralization of organic pollutants, disinfection of water and air, production of renewable fuels and organic syntheses.
The word “photocatalysis” is of Greek origin and composes of two parts : the prefix “photo” (phos : light) and the word “catalysis” (katalyo : break apart,decompose). The main difference between a conventional thermal catalyst and a photocatalyst is that the former is activated by heat whereas the latter is activated by photons of appropriate energy.
Photocatalysis refers to the oxidation and reduction reactions on semiconductor surfaces, mediated by the valence band holes and conduction band electrons, which are generated by the absorption of ultraviolet or visible light radiation. Pairs of photo-generated hole (h+) and electron (e-) induce the formation of aggressive species such as hydroxyl or superoxide radicals from the moisture and atmospheric oxygen. These species are strong enough to oxidize and decompose organic materials or smelling gas and kill bacteria (see Fig 1). Several metal
The hydroxyl radical is the most important reactive species responsible for the destruction of the organic pollutant.
1.2.1.2. Sonolytic
That familiar fizzing you hear when you drop an Alka Seltzer tablet into a glass of water is the result of a chemical reaction, and chemical reactions are extremely prevalent when it comes to what living things do to carry out life processes. In addition, environmental conditions can alter the results of chemical reactions, and in this lab, we will be answering the
The purpose of the experiment is to study the rate of reaction through varying of concentrations of a catalyst or temperatures with a constant pH, and through the data obtained the rate law, constants, and activation energies can be experimentally determined. The rate law determines how the speed of a reaction occurs thus allowing the study of the overall mechanism formation in reactions. In the general form of the rate law it is A + B C or r=k[A]x[B]y. The rate of reaction can be affected by the concentration such as A and B in the previous equation, order of reactions, and the rate constant with each species in an overall chemical reaction. As a result, the rate law must be determined experimentally. In general, in a multi-step reac...
Chemiluminescence is the production of light from a chemical reaction. This phenomenon is caused by the fall of an electron from a higher energy shell back to its ground state, its normal, lower energy shell. An electron is promoted to a higher energy level when it absorbs energy, causing the electron to be in an excited state. When the electron falls back down, the absorbed energy is released as a photon, a packet of energy in the form of electromagnetic energy. If the wavelength of this energy is within the visible spectrum, it is seen as light.
In order to gain strong insight into the surface chemistry of silica we have perform a thorough literature search. Our goal is to identify the pioneer research performed on silica and silica supported catalyst. Particular interest lies in silica-water-cobalt and silica-alcohol-cobalt systems. This study is both on macro and micro level so that a complete theoretical base can be established. From this theoretical knowledge, key areas to look upon will be identified and a design of experiments will be established. The goal is to develop a both efficient and effective product (catalyst) using a novel methodology developed from past research.
Oxidation-reduction reactions can be used to stereochemically control and produce many different organic molecules. The oxidation step in this process increases the number of carbon oxygen bonds by losing a hydrogen and breaking that bond. Through the reduction step, carbon-oxygen bond is broken and the hydrogen is returned.
One type of reaction that produces chloromethane is a photochemical reaction. Photochemical reactions occur because light shines down upon the reaction and provides the heat and energy required to start the reaction. When the light comes into contact with diatomic chlorine, the reactions begins; Cl2 → 2Cl●. A free radical reaction follows. Free radical reactions are reactions that involve free radicals. Free radicals are singular atoms or molecules that have one unbonded electron, which is denoted with a ●, or dot, next to the element or molecule. The second step commences when one of the original radical chlorine atoms combines with methane to create a radical methyl group and hydrochloric acid; CH4 + Cl● → CH3● + H Cl. The radical methyl group then becomes an intermediate when it becomes a product along with diatomic chlorine to finally produce chloromethane and a radical chlorine;CH3● + Cl2 → CH3Cl + Cl●. Methylation takes place during this third step in the photochemical process also. Methylation is the addition or subtraction, in this case addition, of a methyl group into a re...
Predictions may be made about the suitability of possible catalysts by assuming that the mechanism of catalysis consists of two stages, either of which can be first:
In this experiment, the calcium carbonate was in the form of marble chips. The calcium carbonate reacted with hydrochloric acid when the acid was poured into marble chips. Due to calcium carbonate’s higher reactivity, it displaced hydrogen in the hydrochloric acid. As a result, products of calcium chloride, carbon dioxide and water were formed. As the chemical reaction occurred, the water in the measuring cylinder was displaced and gas bubbles that were blowing out represented carbon dioxide.
Photosynthetic pigments are essential for life because they allow photosynthesis to occur by capturing sunlight which is then used alongside carbon dioxide and water to form organic compounds such as glucose and oxygen. The pigments allow the conversion of light energy to chemical energy which other organisms can benefit from. Oxygen is utilised by other organisms in aerobic respiration. The different pigments present in the chloroplasts allow a wide variety of wavelengths of light to be absorbed for efficient photosynthesis and provide colours to the plant to attract pollinators.
1999, 71, 181-215. Minear, R., Amy, G.. Water Disinfection and Natural Organic Matter: History and Overview. ACS Symposium Series -. 1996, 649, 1-9. Richardson, S. Water Analysis: Emerging Containments and Current Issues. Journal of Analytical Chemistry. 2003, 75, 2831-2857.
The output phosphor, made of zinc cadmium sulfide, is where the electrons produced through photoemission will interact and produce light. It is extremely important that the path of the electrons from the photocathode to the output phosphor be precise.
Plontke, R. (2003, March 13). Chemnitz UT. TU Chemnitz: - Technische Universität Chemnitz. Retrieved April 1, 2014, from http://www.tu-chemnitz.de/en/
The photovoltaic effect, electricity can be created directly from sunlight. Some semi-conductor materials that are exposed to sunlight can create electron-hole pairs, which can be collected to produce electricity. This occurs when photons have energy above a certain threshold. These photons have shorter wavelengths. In silicon, the threshold for electron-hole production is in the infrared region of the electromagnetic spectrum.
Today, the phenomenon has many practical applications such as alarm systems that activate when the flow of light is interrupted. Photoelectricity also helps explain the physics of photosynthesis, by which plants make their own food. It's truly evident that the photoelectric effect and its explanation played an important historical role in science.
There are many different ways that we as the earths population are destroying the environment. For example, the tall cooling towers used by industries. They do not remove pollutants but simply push them higher into the atmosphere, in this way they reduce their concentration at that particular area. The pollutants may then travel over large distances and produce negative effects in areas far away from the original site.