Performance And Mechanism Of Ultrasonically Driven Multi-phase MoS₂/Fe₃O₄ Piezoelectric Fenton Material For The Degradation Of Sildenafil

Sildenafil is a phosphodiesterase-5 selective inhibitor（PDE-5i）that enters the environment with human metabolism and seriously harms aquatic ecosystems during the New coronavirus pandemic due to its massive abuse and endocrine-disrupting effects.For the purification of such organic pollutants in the aqueous environment,ultrasound US（Ultrasound）-assisted Fenton technology based on conventional Fenton catalytic materials can effectively degrade such organic contaminants,but the traditional Fenton catalytic materials still suffer from low utilization of ultrasonic cavitation,low exposure of catalyst active sites,difficult neutral initiation and weak catalyst piezoelectric effect.To address these defects,surface mesoporous Fe₃O₄spherical piezoelectric Fenton materials were first constructed by the solvothermal method to enhance ultrasonic cavitation utilization.Then,the MoS₂/Fe₃O₄piezoelectric Fenton composites were constructed by chemical self-assembly route to enhance the catalyst active sites and solve the neutral initiation proble.Finally,different phase MoS₂/Fe₃O₄heterojunction piezoelectric Fenton catalysts were constructed by interfacial polarization engineering to enhance the piezoelectric polarization effect of the material system and strengthen its piezoelectric Fenton degradation efficacy of sildenafil.And the modulating effects of different phase MoS₂complexes on the conversion rate of Fe³⁺to Fe²⁺,interfacial charge transfer efficiency,ultrasonic cavitation utilization,free radical intensity,and the sildenafil degradation efficiency were investigated in depth.The results of this thesis provide a theoretical basis and technical support for the sildenafil-like refractory organic compounds based on ultrasound-driven piezoelectric Fenton material catalysis.Firstly,a surface mesoporous Fe₃O₄spherical material was constructed to investigate the effect of surface structure on the ultrasonic cavitation utilization and sildenafil degradation efficiency of single-component piezoelectric Fenton catalysts.The material characterization results show that the material has an abundant surface mesoporous structure and a large amount of defective oxygen,which contributes to the improvement of interfacial charge transfer efficiency,ultrasonic cavitation utilization and piezoelectric Fenton catalysis efficiency.The results of ultrasound-driven piezoelectric Fenton catalytic degradation of sildenafil showed that under the experimental conditions of initial H₂O₂concentration of 20 m M/L,initial p H=3,ultrasound intensity of 300 W,sildenafil concentration of 50 g/L and catalyst dosing of 0.2 g.The degradation of sildenafil by spherical mesoporous Fe₃O₄was 90%after 120 min of ultrasound-driven piezoelectric Fenton action（only 75%for commercially available Fe₃O₄under the same conditions）with a maximum kinetic constant(k=0.02294 min^-1).The PFM results showed that the piezoelectric response value of spherical mesoporous Fe₃O₄was about 30 pm/V,and the piezoelectric effect was relatively obvious.The construction of the surface structure could effectively enhance the degradation efficiency of the catalyst for sildenafil.To further improve the degradation efficiency of spherical mesoporous Fe₃O₄piezoelectric Fenton catalysts for sildenafil and to solve the neutral initiation problem of the catalytic system,MoS₂/Fe₃O₄composite piezoelectric Fenton catalytic materials were prepared by chemically self-assembling MoS₂with the prepared spherical mesoporous Fe₃O₄materials.The material characterization results showed that it possesses a more abundant surface structure and active sites.The XPS results showed that charge transfer channels dominated by Fe-S-Mo bonds are formed at the two-phase interface of the composite.The results of sildenafil degradation experiments showed that the MoS₂/Fe₃O₄piezoelectric Fenton catalytic material achieved 93%degradation of sildenafil in 60 min at dosing amount of 0.4 g,an initial H₂O₂concentration of 40 m M/L,a sildenafil concentration of 50 g/L,a p H of 7,and an ultrasonic intensity of 300 W.Compared with the spherical mesoporous Fe₃O₄piezoelectric Fenton catalytic material,the degradation effect was significantly enhanced.Zeta potential characterization and experimental results demonstrate that MoS₂/Fe₃O₄can maintain its surface stable Fe cycle by maintaining an acidic microenvironment even in neutral solutions.The PFM results yielded a piezoelectric response value of about 56 pm/V for the MoS₂/Fe₃O₄composites,significantly improving the piezoelectric performance compared with the spherical mesoporous Fe₃O₄material.Similarly,they demonstrated that the enhanced piezoelectric polarization effect could effectively enhance the catalyst degradation efficiency for sildenafil.To further improve the degradation efficiency of MoS₂/Fe₃O₄composite piezoelectric Fenton catalytic materials for sildenafil,and to investigate the effects of different phase MoS₂on the surface polarization and piezoelectric effects of the composites,three distinct phases of MoS₂composite piezoelectric Fenton catalytic materials with 1T MoS₂/Fe₃O₄,1T-2H MoS₂/Fe₃O₄and 2H MoS₂/Fe₃O₄were constructed using interfacial polarization engineering.The results of sildenafil degradation experiments showed that the degradation efficiency of sildenafil was1T MoS₂/Fe₃O₄>1T-2H MoS₂/Fe₃O₄>2H MoS₂/Fe₃O₄in descending order for the three.The degradation efficiency of 1T MoS₂/Fe₃O₄piezoelectric Fenton material for sildenafil was close to 100%after 30 min of degradation at a catalytic material dosage of 0.4 g,an initial H₂O₂concentration of 40 m M/L,a sildenafil concentration of 50 g/L,a p H of 7,and an ultrasonic intensity of 300 W.The results of radical masking experiments showed that·OH was the dominant radical in the 1T MoS₂/Fe₃O₄piezoelectric Fenton catalytic system,and the order of radical activity was·OH>·O₂^->h⁺>¹O₂.The 1T MoS₂/Fe₃O₄has the best piezoelectric response strength,with a piezoelectric response value of about 133pm/V.The piezoelectric performance is significantly improved again.The material characterization results show that the presence of the metallic phase nature of 1T MoS₂in 1T MoS₂/Fe₃O₄can effectively enhance the charge transfer and transport efficiency,leading to an enhanced piezoelectric polarization effect of the composite while accelerating the conversion efficiency of Fe³⁺to Fe²⁺,thus further enhancing its sildenafil degradation efficiency.Finally,in order to reveal the catalytic mechanism of the composite piezoelectric Fenton catalytic materials,theoretical calculations of three different phases MoS₂/Fe₃O₄heterojunction piezoelectric Fenton catalytic materials were carried out using the first-nature principle DFT.Firstly,the results of the work function calculations show that the 1T MoS₂/Fe₃O₄piezoelectric Fenton catalytic material differs from the other two materials in that the trend of piezoelectric polarization charge transfer direction is different.The electron transfer of 1T MoS₂/Fe₃O₄tends to Fe₃O₄,leading to an increase in the conversion efficiency between Fe³⁺and Fe²⁺,which directly leads to the enhancement of the Fenton interaction.Due to the accelerated electron transfer,its hole accumulation is accelerated simultaneously,further promoting the piezoelectric polarization effect while improving the ultrasonic utilization efficiency.The bonding and anti-bonding of each elemental electron orbital is calculated by density of states analysis,and the results show that it effectively forms a heterogeneous structure,and it is inferred that there is a strong covalent hybridization between Fed electron orbital as well as Sp electron orbital,i.e.,a covalent hybridization orbital is formed between F_ed-S_p-Mo_dor O_2p-F_ed-S_p,which is the primary source of electrons in the polarized carriers under the effect of piezoelectric polarization.The polarized electrons further enhance the cyclic reaction between Fe³⁺and Fe²⁺.By quantum chemical calculations of the contaminant sildenafil molecule,C18（0.0552）,C15（0.0319）,C10（0.0372）,N30（0.0559）and N9（0.0405）were considered as the preferred radical reaction in the condensed Fukui index value（CFF）of f₀sites,indicating that these sites are most vulnerable to attack by various reactive radicals in the early stage of the reaction.The specific ring-opening break location of the sildenafil molecule could be determined by calculating the CFF of different reaction types,and the degradation pathway of the sildenafil molecule consistent with the quantitative calculation was further verified by high-performance liquid-liquid mass spectrometry.