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4.
2.
4.
1 Catalyst
The influence of the nature of the photocatalyst on the catalytic performance is an indicator that cannot be ignored.
The particle size and specific surface, surface hydroxyl and mixed crystal effects are the factors that affect the activity of the catalyst
.
The smaller the catalyst particle and the larger the specific surface area, it will help the adsorption of the reactants, and the greater the reaction rate and efficiency.
4.
2.
4.
2 Light source and intensity
The light source selection is based on: one is to choose the most suitable light source according to the absorption spectrum, state and concentration of the reactants and products over time; the other is to choose the light source according to the light intensity, because the light intensity determines the emission of photons It also determines the chemical transformation rate of the reaction; the geometry is the third important factor in the selection of the light source.
The geometry of the lamp has a great relationship with the shape of the reactor.
The light source can be a point light source or a long shape.
Light source
.
Photovoltage spectroscopy analysis shows that due to the influence of impurities on the surface of titanium dioxide and lattice defects, it has photocatalytic activity in a larger wavelength range.
Light intensity is an important parameter of the photocatalytic degradation reaction.
As the light intensity increases, the number of photons irradiated on the surface of the catalyst also increases, resulting in more electron-hole pairs
.
In fact, when other conditions are fixed, the intensity of light determines the number of photo-generated holes and thus the number of photoactive species
① At low light intensity, V changes with I and is a constant;
② When the light intensity is medium, both V and Φ change with I;
③When the light intensity is high, V is a constant, and Φ changes with 1/I
.
4.
2.
4.
3 Additional oxidant
In order to ensure the effective progress of the photocatalytic reaction, it is necessary to reduce the simple recombination of photogenerated electrons and holes.
Since the oxidant is an effective capture agent for photogenerated electrons, the addition of an oxidant can increase the rate and efficiency of photocatalytic oxidation.
It has been found to promote light Oxidants for catalytic oxidation include O 2 , H 2 O 2 , S 2 O, IO, Fe 2 O 3 and the like
.
Many studies have shown that the rate of photooxidation of organics on the catalyst surface is limited by the rate of electron transfer to O 2.
4.
2.
4.
4 pH
The surface charge of TiO 2 is greatly affected by the pH value.
The zero point of TiO 2 in the aqueous solution is about pH=6.
25.
When the solution pH is less than 6.
25, the TiO 2 surface is positively charged.
When the solution pH> 6.
25, the TiO 2 surface Negatively charged, surface charge affects the adsorption of organic matter, so the pH value has a greater impact on photocatalytic degradation
.
The higher rate of photocatalytic oxidation may occur at both low pH and high pH, and changes in pH have different effects on the degradation of different reactants
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2.
4.
5 Temperature
It is generally believed that the liquid phase photocatalytic reaction is not sensitive to temperature changes, because the apparent activation energy of the photocatalytic reaction is low
.
From a macro point of view, on the one hand, increasing the temperature may accelerate the oxidation rate of surface organic substances, on the other hand, it will also reduce the adsorption related to organic substances and O 2.
4.
2.
4.
6 Salt
The influence of soluble salts in water on the photocatalytic degradation of organic matter is complicated.
It is related to the type of salt.
There may be both competitive adsorption and competitive reaction, and it is related to the specific conditions of the reaction
.
The research showed Tongji University, of Na + , of Mg 2+ , CI - , SO .
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2.
4.
7 The influence of the concentration of organic matter
The effect of reactant concentration on degradation rate is similar to that of light intensity
.
It is generally believed that when the concentration of the reactant is low, the degradation rate is proportional to the concentration, that is, V=KC
