Organic waste gas VOC treatment - photocatalytic oxidation equipment

1Photocatalytic oxidation equipmentIntroduction

The photocatalytic purification technology mainly utilizes the photocatalyst titanium dioxide (TiO2) to absorb external radiation light energy and directly convert it into chemical energy. When light with energy greater than the bandgap width irradiates a semiconductor, the light excites electrons to transition to the conduction band, forming conduction band electrons (e -), while leaving hole orders (h+) in the valence band. Due to the discontinuity of semiconductor energy bands, electrons and holes have longer lifetimes. They can move under the action of an electric field or through diffusion, undergo redox reactions with substances adsorbed on the surface of semiconductor catalyst particles, or be captured by surface lattice defects. Holes and electrons can also directly recombine inside or on the surface of catalyst particles. Holes can react with HO - or H2O adsorbed on the surface of catalyst particles to generate free radicals HO ·. HO · is a highly active particle that can selectively oxidize various organic compounds and mineralize them.

2、 Purification principle of photocatalytic oxidation equipment

The essence of photocatalytic reaction is the oxidation-reduction reaction carried out in photoelectric conversion. according tosemiconductorWhen a semiconductor (photocatalyst) absorbs a photon with an energy greater than its bandgap energy (Eg), the electron (e -) will transition from the valence band to the conduction band, leaving a positively charged hole (e -) on the valence band. Valence band holes have strong oxidizing properties, while conduction band electrons have strong reducing properties. They can directly react with reactants and also react with other electron donors and acceptors adsorbed on photocatalysts. For example, holes can cause oxidation, and electrons can reduce O2 in the air, generating H2O2, · OH groups, and · H2O. These groups have strong oxidation ability and can effectively oxidize organic pollutants, ultimately decomposing them into CO2 and H2O, achieving the goal of eliminating VOCs.

Generally, nano semiconductor particles are used as photocatalysts because: ① blue shift of the absorption edge is caused by quantum size confinement; ② Compared with bulk materials, the cooling rate of hot charge carriers in quantum wells decreases, resulting in improved quantum efficiency; ③ The quantum size effect of nano TiO2 causes its conductivity and valence energy levels to become separate, the energy gap to widen, the conductivity potential to become more negative, and the valence potential to become corrected, which gives it stronger redox ability and greatly improves its catalytic activity; ④ Nanoparticles have a larger specific surface area, which gives them a stronger ability to adsorb organic compounds, which is very beneficial for catalytic reactions. The smaller the particle size, the lower the probability of electron hole recombination, and the better the charge separation effect, thereby improving catalytic activity.

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