Piezoelectric Activation Of Persulfate By Supported MoS₂ Composites For Degradation Of Aqueous Dye Pollutants

In recent years,the advanced oxidation technology based on persulfate（PS）has received widespread attention in the field of sewage treatment.By activating persulfate to produce highly reactive free radicals,it can efficiently degrade aqueous pollutants.However,traditional activation methods such as heat,alkali,and radiation generally have the disadvantages of high energy consumption or low activation efficiency.Currently,most reports on the degradation of aqueous pollutants through PS activated by piezocatalyst are conducted under ultrasonic-wave or vigorous stirring,where piezocatalyst are suspended and dispersed in the water.This not only makes it difficult to recover the materials,but also causes secondary pollution.In this thesis,three different methods were used to synthesize and screen the most piezoelectrically active layered MoS₂.Its activity in activating peroxymonosulfate（PMS）for the degradation of dye pollutants was systematically studied.Furthermore,it was loaded onto a porous ceramic support and combined with a filter tube to achieve modularization.The performance of piezocatalyst and PMS activation was studied under simulated scaleup conditions.The main work and results of this thesis are as follows:（1）Three different methods were used to synthesize MoS₂with a layered structure,including calcination,precipitation,and hydrothermal methods.It was found that pure 2H-phase MoS₂with less obvious layered structures could be obtained through calcination at 650℃for 10 hours.The MoS₂synthesized by the precipitation method had a mixed phase of 1T/2H,with a phase composition of 37%1T-phase and 63%2H-phase,and a more obvious layered structure.The content of 2H-phase in MoS₂synthesized by the hydrothermal method increased with the increase of temperature,and pure 2H-phase MoS₂could be obtained at 220℃.The addition of 1-butyl-3-methylimidazolium chloride（Bmim Cl）as a template agent resulted in MoS₂nanoflower with more abundant layered structures and active sites than other samples.（2）The piezocatalytic activities of different layered MoS₂in the degradation of Rhodamine B（Rh B）were compared.The study found that H-MoS₂NFs-220 synthesized with the addition of a template agent under hydrothermal conditions at 220℃exhibited the best piezocatalytic activity.Based on desorption experiments,H-MoS₂NFs-220 exhibited a dual-coupling effect of strong adsorption and piezocatalytic degradation performance,which could degrade 100%of 20 ppm Rh B during 10 minutes under ultrasonic action.The optimal PMS dosage was found to be 150 mg,and UW/H-MoS₂NFs-220/PMS could degrade 100%of Rh B during only 5 minutes.Free radical capture experiments and electron paramagnetic resonance（EPR）demonstrated that the main active species of H-MoS₂NFs-220 were·OH,while UW/H-MoS₂NFs-220/PMS mainly generated·OH and·SO₄^-as active species.The degradation activity significantly decreased after suppressing the electron production,indicating that e^-produced by piezoelectric effect was a key factor in the generation of·OH and·SO₄^-.After 5 cycles of testing,UW/H-MoS₂NFs-220/PMS could maintain over 87%of its degradation activity,showing good stability.（3）H-MoS₂NFs-220 was successfully loaded onto a porous ceramic via a hydrothermal route.It was found that cordierite honeycomb ceramic caused the formation of Fe_0.96S in MoS₂,which was unfavorable for its growth,while pure aluminum oxide foam ceramic was more stable.By adjusting the precursor concentration,different loading amounts could be obtained,among which MA-5 had the highest loading amount（0.87 wt%）.（4）The degradation performance of alumina ceramic-supported MoS₂under ultrasonic-wave was improved while increasing loading amount,and MA-5 achieved the highest loading（0.87 wt%）.Under ultrasonic action,MA-5 was able to degrade 69%of Rh B（100 ml,20 ppm）within 60 minutes.When used as a catalytic reaction unit for degradation studies under flowing water,it was found that excessive flow rate caused local turbulence and reduced reaction activity.The optimal flow rate was 580 L·h^-1.Addition of PMS improved degradation performance,which increased with increasing temperature and number of units used,but excessive PMS（>1.25 m M）reduced removal efficiency.The utilization efficiency of PMS in this system was 41.2%,higher than in other systems.The piezoelectric effect of MA-5under vortex increased the utilization efficiency of PMS.In cycling experiments,it was found that after calcination to remove organic residues on the surface of the unit,MA-5 exhibited good cyclic stability.