Degradation Of Organic Dyes By Ultrasonic-Fe-TiO₂

With the rapid development of modern society and economy,industrial demand is increasing,and the problem of water pollution is aggravated,which has seriously affected our daily life and even survival.However,traditional crafts have many difficult problems,such as huge energy consumption and repeated pollution,etc.,so we must develop an energy-saving,environmentally-friendly and effective treatment method.As an emerging oxidation process with great potential,AOPs（Advanced oxidation processes）can use the strong oxidizing hydroxyl radicals（·OH）produced by cavitation to oxidize and decompose macromolecular organic compounds in the water to obtain environmentally friendly degradation products,such as water,carbon dioxide and so on.In this paper,the Fe3+ doped modified TiO2 crystal was used as the ultrasonic catalyst in this experiment,and the organic dye was degraded under the combined force of ultrasonic radiation and mechanical stirring.（1）In this study,rhodamine B（RB）,methyl orange（MO）and methylene blue（MB）were used as single-component organic dyes.250 mL of each of their aqueous solutions were added to Fe-TiO2 nanoparticles,and the reaction was carried out in a three-necked glass container were placed in an ultrasonic cleaning machine filled with water,and the six probes at the bottom were ultrasonic radiation source.Samples were taken every 30min during 2h of the reaction,and the detections were carried out after centrifugation by UV-visible spectrophotometer（UV-Vis）.Then corresponding curves were made for analysis according to the calculated degradation rate values.First of all,through the three modes of dyes at different initial concentrations（5,10,15,20 mg/L）,the addition amount of Fe-TiO2 nanoparticles（0.25,0.50,0.75,1.00 g/L）,ultrasonic frequency（25,40,59,80 kHz）and stirring speed（100,300,500,700 r/min）,the correspondingly obtained degradation of the optimal conditions for single-component organic dyes were 10 mg/L,0.5 g/L,40 kHz and 500 r/min,respectively.It was also found that the final degradation rate of RB among the three was the highest,which may be due to the fact that RB is not an azo dye,and its structure is not as stable as MO and MB and easy to react.As a cationic dye,it is easier to adsorb and react with negatively charged catalyst particles.Finally,by adding isopropanol（IPA）,the degradation rates of RB,MO and MB were significantly reduced,which confirmed the free radical attack theory in the degradation process.（2）Based on the degradation of single-component organic dyes,mixed-mode dyes were used to explore the catalytic reaction of binary components.Firstly,the RB with the highest degradation rate was mixed with the MO of the heteroelectricity and the MB of the same electricity.The ultraviolet spectrum proved that no chemical reaction occurred,in other words,no new substances were generated to interfere with the experiment.Secondly,there was no obvious difference between RB and MB in a separate system and the binary system,which was an invalid mixture.Finally,RB and MO were mixed in a ratio of 1:1 and the degradation rates both changed,which indicated that in a mixed system with opposite electronegativity,the two interacted and had a certain impact on each other’s degradation.（3）Taking the mixed system of RB and MO as the research object of binary component organic dyes,the effects of nanoparticles concentration,radiation frequency and solution concentration on the degradation of the binary system were investigated respectively,and obtained the degradation binary component,and best conditions correspond to:0.5 g/L,40 kHz and 10 mg/L.Under these conditions,by comparing the degradation of RB and MO in the single component,it was found that the degradation efficiency of MO in the binary component was increased by 12.8%,while the degradation rate of RB was slightly reduced from 99.5%to 93.3%.It was speculated that MO used part of the ·OH produced by RB to promote its catalytic process in the mixed system,and this part of ·OH will have a certain inhibitory effect on the degradation of RB.Through a series of studies in this article,it is proved that Fe-TiO2 assisted ultrasonic combined stirring is an efficient method for the degradation of organic dyes,which provides a new idea for wastewater treatment and lays a foundation for the degradation and mechanism research of mixed dyes.