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Study On Photocatalytic Degradation Of Dyes By Al2o3

2011/4/7 13:20:00 65

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In recent years, some semiconductor materials have been used as photocatalyst to treat pollutants. energy More and more attention has been paid to development, organic synthesis and other fields. The method has the advantages of simple process and low cost. It can completely decompose most of the toxic organic compounds which can not be degraded or biodegraded at room temperature. At present, TiO2 is used more frequently because of its high catalytic activity and good stability. However, because of its wide bandgap (3.2eV), it can only absorb ultraviolet light with wavelengths of less than 387nm, and has low utilization rate of sunlight and natural light. Therefore, it is still an important research topic to develop new photocatalyst or improve catalytic efficiency. In this paper, Al203 prepared by liquid heating method is used as light. Catalyzer It has good photocatalytic activity for malachite green, phenolpride red and methyl violet, and its performance is stable and can be reused. The preparation method is simple, the reaction time is short, and the cost is low. It has certain application value to dye industry wastewater treatment.

1 experimental part

One point one instrument And reagent

TU-1901 dual beam ultraviolet visible spectrophotometer (Beijing Puhua General Instrument Co., Ltd.); pHS-3 precision acidity meter (Shanghai magnetic instrument factory); XMT-9000 muffle furnace (Beijing Tai Guang Energy Saving Technology Co., Ltd.). Malachite green, phenolic flower red, methyl violet, amino black, indigo two sulfonic acid, bright green, Luo Danming B aqueous solution, the concentration is 30mg / L. The chemical reagents used are all analytical pure, and the experimental water is distilled water.

1.2 preparation of three oxidized two aluminum

Method 1: weigh a certain amount of AlCl3. Dissolve in distilled water to prepare solution. The AI (OH) 3 colloid was produced by slowly dropping dilute ammonia water under the condition of rapid stirring, and then filtered and washed with absolute alcohol and water to cl- without any cl-. The product was calcined at 450 degrees Celsius in muffle furnace and finely studied with agate mortar, marked as Al2O3 (1).

Method two: a certain amount of sodium hydroxide is dissolved in water, the concentration is about 30mol / L, heated to boiling, then the aluminum hydroxide is called 1.3:1, dissolved in sodium hydroxide solution, diluted to a certain concentration, filtered back. The sodium aluminate with a concentration of about 2 mol / L was added to four flasks. The temperature was kept at about 15~20 degrees Celsius. When the mixture was vigorously stirred, the CO2 of 0.3 ~ 0.5m3 / h was flown to the vicinity of 10.5 ~ 1L. The gel was calcined at 4H at 450 degrees centigrade, and the product was fully refined with agate mortar. The product was labeled Al203.

Method three: use Al2O3 in laboratory chromatography and label it as A1203 (3); and then Al2O3. 4h was fired at 450 degrees Celsius in a man muffle furnace and labeled as Al2O3 (4).

1.3 experimental method

The amount of 50mL organic dye was measured in the 100 mL beaker. 0.030g Al2O3 samples were added to the beaker and irradiated with different light sources for a certain time. The upper layer was collected for the night. The absorbance A was measured at the maximum absorption wavelength of the dye, the decolorization rate of the dye was D=[(A0-A)]/A0X100%, A0 was the absorbance of the dye solution before illumination, and the photocatalytic activity of the Al203 was characterized by the decolorization rate of the dye. The dye solution and the original solution after photocatalytic reaction were analyzed by UV Vis spectroscopy to determine whether the dye in the solution was degraded.

2 results and discussion

2.1 photocatalytic activity of A1203 prepared by different methods
The photocatalytic activity of Al2O3 prepared by the 3 methods is shown in Table L according to the experimental method. The 3H is irradiated with the same light source. It can be seen from Table L that Al2O3 (1) decolorization of amino black and indigo two sodium sulfonate is more obvious under the sunlight. Al203 (2) has a good decolorization effect on Malachite Green, phenolsulfonated red and methyl violet, while the decolorization of dyes is not obvious either directly using laboratory Al2O3 or activated laboratory Al203. The reason may be that the Al2 03 has different photocatalytic activity for different dyes because of its particle size or structure. In this paper, Al203 (2) is used as catalyst.

2.2 effect of different light sources on dye decolorization rate
Sunlight, infrared and ultraviolet light are used as the light source respectively. The results are shown in Table 2. It can be seen from table 2 that the 3 kinds of light sources have the best decolorization effect with sunlight. This may be related to the characteristics of the light source and the band gap Eg of Al203. Because the wavelength of the solar radiation is the widest range, besides visible light, infrared light and high energy ultraviolet and near ultraviolet light, it can be absorbed more by Al2O3 than pure ultraviolet and infrared lamps. {page_break}

2.3 effect of catalyst and light conditions on dye decolorization rate
Taking sunlight as the light source, the experimental results are shown in Table 3. (1) when no catalyst was irradiated with sunlight, several dyes were not decolorization, indicating that all kinds of dyes were relatively stable under normal conditions. (2) catalysts had a certain decolorization of various dyes, which was due to the adsorption of dyes on the catalyst surface. In photocatalytic reaction, the first adsorption of reactants on the surface of catalyst is often a necessary step forward, and then the photocatalytic degradation reaction occurs on the surface of photocatalyst or from several atoms on the surface. (3) with the addition of catalyst and light, the dye decolorization is obvious, indicating that Al2O3 does play a role as a photocatalyst.

2.4 effect of illumination time on dye decolorization rate
According to the experimental method, the decolorization rate of malachite green varies with time under the sunlight, as shown in Fig. L. The results showed that under the experimental conditions, the decolorization rate of 3H dye was more than 90% and basically decolorization.

The formation of Al2O3 thin layer is relatively dense, which can absorb all the photons arriving on the surface. The OH produced on the thin surface remains basically constant, and the rate of photoff reduction varies little, almost completely, and tends to a certain value.

Effect of 2.6 pH on dye decolorization rate
HC1 and NaOH were used to regulate the pH value of malachite green dye solution and sunlight as the light source. The results showed that in the range of pH8 to 10, the dye decolorization rate was the highest, reaching 93% ~ 96%. The reason is that the electron hole pair produced by Al203 powder under the light condition acts on the interaction of dissolved oxygen and water to produce highly reactive chemical OH radicals, while H+ and OH are also produced. The pH value in the solution will affect the generation of H+ and OH-, thereby affecting the number of OH and the efficiency of photocatalytic reaction.
2.7 effect of added substances on dye decolorization rate
In malachite green dye solution, Al203 catalyst was added, then lmL8mg / L Fe 3+, lmL 3%H202, lmL 0.2mg / mLA g+ were added, and 0.2mg / mLA was added. At the same time, no addition of the catalyst was compared. After sunlight irradiation, the samples were analyzed. The results showed that the decolorization rate of malachite green was 16.56% and 19.27% when no accelerator was added, and the decolorization rate of the dye was 5.31%. When the catalyst is present, the decolorization rate of H20 2 is not very great. It may be that the decolorization rate is almost complete. However, adding Ag+, Mg2+ has a slight decrease in the dye decolorization rate, which indicates that it has no photocatalytic effect and Fe3+ catalysis.
2.8 UV visible spectrum analysis of dye solution
UV Vis absorption spectra of malachite green solution and photocatalytic decolorizing solution were determined as shown in Fig. 3. It is obvious that the curve 3 not only absorbs light to zero, but also has a large change in the absorption peak of the UV and visible region compared with the original solution, which indicates that the A1203 (2) prepared by the experiment actually degrades the dye in the sunlight.

2.9 stability of catalyst
The used Al2O3 was washed 3 times with distilled water, washed two times with anhydrous alcohol, and dried naturally. According to the experiment 1.3, the malachite green solution was tested (sunlight 3h, solution pH9), the decolorization rate was 94.1%, and its catalytic activity was basically unchanged compared with that before. Therefore, the Al2O3 photocatalyst prepared by liquid heating method has stable performance and can be reused.