【作者】 马薇；

【导师】 姚秉华；

【作者基本信息】 西安理工大学 ， 环境科学与工程， 2022， 博士

【摘要】 化石能源危机和环境污染成为制约人类社会可持续发展的两大难题,尤其是水环境污染问题,水环境中有机污染物的存在和消除已成为环境催化领域的研究热点。压电催化是一种新兴的高级氧化技术,该技术利用压电材料将机械能转化为化学能,在有机污染物降解方面显示出巨大的应用潜力。近年来,二维过渡金属二硫族化合物(TMDs)具有大的比表面积,良好的柔韧性,优异的机械、电子和压电性能,是一类非常有前景的能量收集与转换材料。其中,半导体特性的钼基TMDs(MoX2(X=S,Se))表现出与传统压电材料相当的高压电性能,并且具有较高的载流子浓度和迁移率,是催化应用的理想候选材料。但钼基压电催化剂仍然面临着仅奇数层有压电催化活性、层数难以精确控制、活性边缘位点有限、电导率低、结构稳定性差、难回收利用等问题。如何通过结构和性能调控优化压电催化剂的活性和稳定性,提高能量转换效率,一直是该领域的研究热点和难点。本论文主要围绕高效钼基压电催化剂的设计与微观结构构筑,分别通过缺陷工程、构筑层级中空结构、化学剥离及设计压电催化活性膜等方法成功制备了四种高效、稳定的钼基压电催化剂,深入分析了压电催化活性增强的机理,提出了高效压电催化剂设计与构筑的新策略,以期推进压电催化技术在有机污染物去除领域的实际应用。主要研究内容如下:1.通过水热法制备了富缺陷和无缺陷MoS2纳米片(NSs)(MoS2 NSs)压电催化剂,探究了缺陷对压电催化性能的影响。SEM和TEM表征结果表明富缺陷MoS2 NSs含有大量的奇数层结构和孔缺陷,这不但增加了片层结构的不对称性提升了压电性能,而且提供了更多的催化活性边缘位点。富缺陷MoS2 NSs更大的比表面积也促进了反应物分子的吸附。压电催化降解实验表明,与无缺陷MoS2 NSs相比,富缺陷MoS2 NSs对环丙沙星(CIP)表现出最优异的降解性能,30 s内可降解99.1%的CIP。同时,富缺陷MoS2 NSs对磺胺二甲基嘧啶(SMZ)、四环素(TC)和土霉素(OTC)也表现出较好的降解性能,降解率分别为40.0%、87.9%和91.5%。自由基捕获实验证明,·OH是富缺陷MoS2 NSs反应体系的主要活性物种。通过HPLC-MS鉴定了 CIP降解的中间产物,提出了三种可能的降解途径,主要以羟基化作用导致哌嗪环的去除和喹诺酮基团的氧化裂解为主。2.采用溶剂热法制备了具有不同长径比的层级MoS2纳米管(NTs)(MoS2 NTs)压电催化剂。表征结果证实纳米管是由单层/少层MoS2纳米片自组装而成的层级多孔结构,在有效抑制纳米片堆积团聚的同时,又可以充分发挥压电性能。具有大长径比的MoS2 NTs-13直径在200～250 nm之间,长度大于2 μm,壁厚在38 nm左右,并且具有更大的比表面积(85.83 m2g-1),可以暴露更多的催化活性边缘位点。由于富缺陷MoS2 NSs对SMZ的降解性能较差,因此对比研究了富缺陷MoS2 NSs、MoS2 NTs-10和MoS2 NTs-13对SMZ的降解性能。实验结果表明MoS2 NTs-13表现出最优的SMZ降解性能,在10 min内可降解93.3%的SMZ,该反应体系的主要活性物种是·OH和·O2-。通过HPLC-MS检测到SMZ降解的6种中间产物,主要的分解机制包括SO2去除、嘧啶环和苯胺环裂解以及甲基和氨基的氧化。3.通过HNO3辅助剥离的策略制备了 AB-堆叠超薄MoSe2纳米片(MoSe2 NSs)压电催化剂。SEM、TEM、N2吸附-解吸实验、接触角测试和交流阻抗测试结果表明MoSe2 NSs-10具有超薄的层状结构,大的比表面积,良好的亲水性和导电性。SEM-EDS、XPS和EPR表征结果均证实MoSe2 NSs-10中含有大量的Se空位。PFM测试发现MoSe2 NSs-10呈现出典型的蝴蝶形振幅曲线和150°电畴翻转,证实了层间滑移引起的面外铁电性。降解实验表明,MoSe2 NSs-10对TC的降解效率最高,TC、OTC、SMZ和CIP的降解率分别为93.9%、89.9%、19.8%和88.9%,·OH和·O2-是该催化体系的主要活性自由基。基于HPLC-MS鉴定了中间产物,提出了 TC在MoSe2 NSs-10压电催化体系中的降解途径。4.采用静电纺丝技术制备了一系列柔性E-MoS2/PVDF静电纺纤维膜(EFMs)(E-MoS2/PVDF EFMs),以进一步推进压电催化剂的实际应用。SEM、TEM表征和导电性测试结果表明,与纯PVDF EFMs相比,10.0 wt%E-MoS2/PVDF EFMs具有不均匀的纤维直径,大量超薄的E-MoS2纳米片暴露于纤维表面,为催化反应提供了丰富的活性边缘位点,也使纤维膜的导电性明显增强。此外,E-MoS2纳米片的成核作用使PVDF中压电性β相的含量增大至94.1%。无机和有机压电材料呈现出优异的协同催化效果,10.0 wt%E-MoS2/PVDF EFMs表现出最优的OTC降解性能,24 min内OTC的降解率达到93.1%,TOC矿化率达到68.5%,·OH和·O2-是该反应体系的主要活性物种。对TC、SMZ和CIP的降解率分别为91.6%、19.9%和84.4%。采用HPLC-MS检测到OTC降解的9种中间产物,主要的分解机制包括逐步羟基化、去甲基化、脱羰和开环反应。更多还原

【Abstract】 Fossil energy crisis and environmental pollution have become two major problems restricting the sustainable development of human society,especially for water environment pollution.The existence and elimination of organic pollutants in the water environment have become a research hotspot in the field of environmental catalysis.Piezocatalysis is an emerging advanced oxidation technology,which uses piezoelectric materials to convert mechanical energy into chemical energy,showing great application potential in degradation of organic pollutants.In recent years,two-dimensional transition metal dichalcogenides(TMDs)have become a kind of promising energy harvesting and conversion materials due to their large specific surface area,good flexibility,and excellent mechanical,electronic and piezoelectric properties.Among them,semiconducting molybdenum-based TMDs(MoX2(X=S,Se))exhibit high piezoelectric properties comparable to those of traditional piezoelectric materials,and have high carrier concentration and mobility,which make them ideal candidates for catalytic applications.However,molybdenum-based piezocatalysts still face the problems of only odd number of layers exhibiting piezocatalytic activity,difficulty of precisely control the number of layer,limited active edge sites,low electrical conductivity,poor structural stability,and difficulty in recycling.How to optimize the activity and stability of piezocatalysts and improve energy conversion efficiency through structure and property modulation has always been a research hotspot and difficulty in this field.This dissertation mainly focuses on the design and microstructures construction of high-performance molybdenum-based piezocatalysts.Four efficient and stable molybdenum-based piezocatalysts have been successfully prepared through defect engineering,construction of hierarchical hollow structures,chemical exfoliation and design of piezocatalytic active menbranes.Moreover,the underlying mechanisms of piezocatalytic activity enhancement have been deeply analyzed to provide novel strategies for high-performance piezocatalysts design and construction,which will promote the practical application of piezocatalytic technology in the field of organic pollutant removal.The main research contents are as follows:1.Multi-flaw and flaw-free MoS2 nanosheets(NSs)(MoS2 NSs)piezocatalysts were prepared by hydrothermal method,and the effect of flaws on piezocatalytic performance was investigated.SEM and TEM characterization results demonstrated that multi-flaw MoS2 NSs had abundant odd numbers of atomic layers and pore flaws,which not only increased the asymmetry of layered structure to improve piezoelectric properties,but also provided more catalytic active edge sites.The larger specific surface area of multi-flaw MoS2 NSs also facilitated the adsorption of reactant molecules.The piezocatalytic degradation experiments showed that compared with flaw-free MoS2 NSs,multi-flaw MoS2 NSs exhibited the best degradation performance for ciprofloxacin(CIP),decomposing 99.1%of CIP in 30 s.Meanwhile,multi-flaw MoS2 NSs also showed good degradation performance for sulfamethazine(SMZ),tetracycline(TC)and oxytetracycline(OTC),and the degradation rates were 40.0%,87.9%and 91.5%,respectively.Radical trapping experiments demonstrated that ·OH was the main active species in multi-flaw MoS2 NSs reaction system.The intermediates of CIP degradation were identified by HPLC-MS,and three possible degradation pathways were proposed,which were mainly based on hydroxylation leading to removal of the piperazinyl ring and oxidative cleavage of quinolone moiety.2.Hierarchical MoS2 nanotubes(NTs)(MoS2 NTs)piezocatalysts with different aspect ratios were prepared by solvothermal method.The characterization results confirmed that the nanotubes possessed hierarchical porous structures self-assembled from single/few-layer MoS2 nanosheets,which could effectively suppress the stacking and agglomeration of nanosheets while fully demonstrate their piezoelectric properties.MoS2 NTS-13 with large aspect ratio had a diameter of 200～250 nm,a length greater than 2 μm,a wall thickness of about 38 nm,and a larger specific surface area(85.83 m2g-1),which could expose more catalytic active edge sites.Due to the poor degradation performance of SMZ by multi-flaw MoS2 NSs,the degradation performance of multi-flaw MoS2 NSs,MoS2 NTs-10 and MoS2 NTs-13 towards SMZ was comparatively studied.The experimental results showed that MoS2 NTs-13 exhibited the best SMZ degradation performance,which could degrade 93.3%of SMZ within 10 min.The main active species in this reaction system were ·OH and ·O2-.Six intermediates of SMZ degradation were detected by HPLC-MS,and the main decomposition mechanisms included the removal of SO2,the cleavage of pyrimidine and aniline rings,and the oxidation of methyl and amino groups.3.AB-stacked ultrathin MoSe2 nanosheets(MoSe2 NSs)piezocatalysts were prepared via a HNO3-assisted exfoliation strategy.The results of SEM,TEM,N2 adsorption-desorption experiment,contact angle test and electrochemical impedance test showed that MoSe2 NSs-10 had an ultrathin layered structure,large specific surface area,good hydrophilicity and electrical conductivity.The results of SEM-EDS,XPS and EPR characterization confirmed that MoSe2 NSs-10 contained abundant Se vacancies.PFM measurements found that MoSe2 NSs-10 showed typical butterfly-shaped amplitude curves and 150° polar domain switching,which confirmed the out-of-plane ferroelectricity induced by interlayer sliding motion.Degradation experiments showed that MoSe2 NSs-10 exhibited the highest degradation efficiency for TC,the degradation efficiencies of TC,OTC,SMZ and CIP were 93.9%,89.9%,19.8%and 88.9%,respectively,·OH and ·O2-were the main active free radicals in this catalytic system.Based on the intermediates identified by HPLC-MS,the degradation pathway of TC in the MoSe2 NSs-10 piezocatalytic system was proposed.4.A series of flexible E-MoS2/PVDF electrospun nanofiber membranes(EFMs)(EMoS2/PVDF EFMs)were prepared by electrospinning technology to further promote the practical application of piezocatalysts.The results of SEM,TEM characterization and electrical conductivity test showed that,compared with pure PVDF EFMs,10.0 wt%E-MoS2/PVDF EFMs possessed non-uniform fiber diameters,many ultrathin E-MoS2 nanosheets were exposed on the surface of fiber,which provided abundant active edge sites for catalytic reactions and also significantly enhanced the electrical conductivity of the fiber membranes.In addition,the nucleation of E-MoS2 nanosheets increased the content of piezoelectric β phase in PVDF to 94.1%.Inorganic and organic piezoelectric materials showed excellent synergistic catalytic effect,10.0 wt%E-MoS2/PVDF EFMs showed the best OTC degradation performance,the degradation rate of OTC reached 93.1%within 24 min,and the TOC mineralization rate was 68.5%,·OH and ·O2-are the main active species in this reaction system.The degradation rates of TC,SMZ and CIP were 91.6%,19.9%and 84.4%,respectively.Nine intermediates of OTC degradation were detected by HPLC-MS,and the main decomposition mechanisms included stepwise hydroxylation,demethylation,decarbonylation and the ring-opening reactions.更多还原