The history of photocatalytic oxidation technology, the introduction of photocatalytic oxidation tec

In 1972, Fujishima and Honda discovered the photocatalytic cracking of water reaction on the N-type semiconductor TiO2 electrode, and published "Electrochemical Photolysis of Water at a Semiconductor Electrode" in Nature, which ushered in a new era of multiphase photocatalysis.

1976 John h .Carey et al. studied the photocatalytic oxidation of polychlorinated biphenyls, which is considered to be the first research work of photocatalytic technology in the elimination of environmental pollutants.

In 1977, Yokotat et al. found that TiO2 has photocatalytic activity for propylene epoxidation under light conditions, which broadened the application range of photocatalysis and provided a new idea for the oxidation of organic matter. Since 1983, Pruden and Alkanes.

Olefins and aromatic hydrocarbons.

The photocatalytic oxidation of a series of pollutants such as chloride has been continuously studied, and it has been found that the reactants can be rapidly degraded. In 1989, et al. found that the semiconductor photocatalytic process of organic matter consists of hydroxyl radicals.

OH), the addition of H2O2 to the system can increase the concentration of ·OH. Entered the 90s, with the development of nanotechnology.

The rise of photocatalytic technology in environmental protection, health care, organic synthesis and other aspects of the application of research has developed rapidly, nanoscale photocatalysts.

has become one of the most active research areas in the world.

Photochemical and photocatalytic oxidation is an advanced oxidation technology that has been studied a lot. The so-called photocatalytic reaction is a chemical reaction carried out under the action of light. Photochemical reactions require molecules to absorb electromagnetic radiation of a specific wavelength, which is stimulated to produce an excited state of the molecule, and then a chemical reaction occurs to form a new substance, or to become an intermediate chemical product that initiates a thermal reaction.

The activation energy of photochemical reactions is the same as the energy of photons, and photoelectric conversion and photochemical conversion have always been very active research fields in the utilization of solar energy. Photocatalytic oxidation technology uses photo-excited oxidation to combine oxidants such as O2 and H2O2 with light radiation. The light used is mainly ultraviolet light, including UV-H2O2, UV-O2 and other processes, which can be used to treat refractory substances such as CHCL3, CCL4 and PCBs in sewage.

In addition, in the Fenton system with ultraviolet light, there is a synergistic effect between ultraviolet light and iron ions, which greatly accelerates the rate of hydroxyl radical formation by the decomposition of H2O2 and promotes the oxidative removal of organic matter.

Photodegradation usually refers to the gradual oxidation of organic matter into low-molecular intermediate products under the action of light, and finally produces CO2, H2O and other ions such as NO3-, PO43-, Cl-, etc. The photodegradation of organic matter can be divided into direct photodegradation and indirect photodegradation. The former refers to the chemical reaction that occurs in the first step after the organic molecules absorb light energy.

The latter is the absorption of light energy by certain substances in the surrounding environment into an excited state, and then induces a series of organic pollution reactions. Indirect photodegradation is more important for organic pollutants that are difficult to biodegrade in the environment.

Pathways for the degradation of pollutants by photochemical reactions, including photochemical oxidation processes without catalysts and with catalyst participation. The former mostly uses oxygen and hydrogen peroxide as oxidizing agents to oxidize and decompose pollutants under ultraviolet light; The latter, also known as photocatalytic oxidation, can generally be divided into two types: homogeneous and heterogeneous catalysis. In heterogeneous photocatalytic degradation, Fe2+ or Fe3+ and H2O2 are used as the medium to produce ·ho through the photo-fenton reaction to degrade the pollutants, and the more common in heterogeneous photocatalytic degradation is to add a certain amount of photosensitive semiconductor materials to the polluting system, and at the same time combine a certain amount of light radiation to excite the photosensitive semiconductor under the irradiation of light to produce electron-null bright hole pairs, and the dissolved oxygen and water molecules adsorbed on the semiconductor interact with electron-hole to produce · Ho and other highly oxidizing free spike jujube broad group, and then through the addition of hydroxyl groups between the pollutant and the contaminant, substitution, electron transfer equation contaminant all or nearly all mineralization.

The photocatalyst was discovered in 1967 by Professor Akira Fujishima, who was a graduate student at the University of Tokyo at the time. In one experiment, titanium oxide single crystals placed in water were irradiated with light, and it was found that the water was broken down into oxygen and hydrogen. This effect is used as " Hondo · The Fujishima Effect is known as the "honda-fujishima effect", a name that combines the names of Professor Fujishima and his instructor at the time--- Kenichi Honda, president of Tokyo Polytechnic University.

Because the oxidative decomposition reaction is promoted by the power of light, the titanium oxide in this phenomenon was later called a photocatalyst. This phenomenon is equivalent to the conversion of light energy into chemical energy, and in the context of the oil crisis at the time, the world was looking forward to finding new energy, so this technology attracted attention as an epoch-making method for extracting hydrogen from water, but because it was difficult to extract large amounts of hydrogen in a short period of time, it was not possible to use it in the development of new energy sources, so it quickly cooled down after a sensation.

In 1992, the first international symposium on titanium dioxide photocatalyst was held in Canada, and Japanese research institutions published many new ideas about photocatalysts and put forward research results applied to nitrogen oxide purification. Therefore, the number of titanium dioxide-related patents is also the largest, and other catalyst-related technologies cover the process of catalyst blending, catalyst structure, catalyst support, catalyst fixation method, catalyst performance test, etc. As a result, research on the use of photocatalysts in the fields of antibacterial, antifouling, and air purification has increased dramatically, with a total of 10,717 patents filed for photocatalysts from 1971 to June 2000.

The wide application of titanium dioxide tio 2 photocatalyst will bring people a clean environment and a healthy body.

The length of an object is 10 -6 meters, which is called a micrometer. mm), 10 -9 meters is called nanometer (nanometer; nm)。Various application materials will also gradually enter the nano era from micrometers. Nanomaterials are composed of a grain size of 1 100 nm in height of the particle state.

The particle size is extremely fine, with a large specific surface area, and as the particle size decreases, the percentage of surface atoms increases. The phenomenon of high surface energy is caused on the surface due to the incomplete coordination of a large number of atoms. The proportion of surface energy to total energy is greatly increased, so that nanomaterials have the characteristics of adsorption, light absorption, and melting point change.

Using the technology and characteristics of nano-ultrafine particles, the catalyst technology that the material itself does not participate in the reaction at all, but can promote and increase the reaction energy to catalyze the target reaction has been applied to the environmental cleaning effect, so as to accelerate the reaction of harmful or toxic substances into stable and harmless substances and achieve environmental protection effects.

Nano titanium dioxide photocatalyst is a substance that does not change itself under the irradiation of light, but can promote chemical reactions, just like chlorophyll in plant photosynthesis. TIO2 photocatalyst can produce antibacterial, deodorant sail staring, oil decomposition, mildew and algae, and air purification under the irradiation of sunlight or indoor fluorescent lamps.

Photocatalytic technology is a green technology with important application prospects in the field of energy and environment. Photocatalytic Technology (Introductory Edition) systematically expounds the working principle, application objects and research progress of photocatalytic technology in the field of environment and energy. In particular, the research progress of photocatalytic reactors for different applications is summarized and discussed.

It reflects the latest research results and future development directions in the field of photocatalytic reaction engineering.

Photocatalyst is a portmanteau of photo=light + catalyst. Photocatalyst is a kind of substance that does not change under the irradiation of light, but can promote chemical reactions, photocatalyst is the use of light energy existing in nature to convert the energy required for chemical reactions, to produce a catalytic effect, so that the surrounding oxygen and water molecules are excited into free negative ions with great oxidizing force. It can decompose almost all organic substances and some inorganic substances that are harmful to the human body and the environment, which can not only accelerate the reaction, but also use the fixed substances of nature without causing waste of resources and additional pollution.

The most representative example is photosynthesis in plants, which absorbs carbon dioxide and converts light energy into oxygen and organic matter.