【作者】 金华；

【导师】 董军；

【作者基本信息】 吉林大学 ， 环境工程， 2020， 博士

【摘要】 随着医药、化工、印染等行业的蓬勃发展,水体中难降解有机污染物种类和浓度与日俱增,利用单一水处理技术治理出现很多局限性和缺陷,有的已经无法达到国家规定的排放标准。而应用现有的、相对成熟的单元水处理技术优化组合成为耦合水处理技术便成为解决单一技术缺陷的有效途径。其中,以光催化氧化为主体的组合工艺逐渐成为极具应用前景的耦合水处理技术的发展方向。在这类组合工艺中,光催化/Fenton耦合技术因能耗低、能在常温常压下进行,更适合实际工程应用。但该技术在使用过程中仍然存在可见光利用率低、催化剂难回收、反应依赖酸性环境、影响因素及微观作用机制理论依据少等不足。针对上述问题,有必要对现有光催化/Fenton耦合技术进行相应改进,满足当前日益严格的水质排放标准和人们对安全水质环境的迫切需求。本论文从复合催化材料的设计制备及组合工艺的构建两方面着手,对上述耦合技术进行改进,具体实施方式如下:采用可见光响应型光催化剂Ag₃PO₄替换紫外光响应型光催化剂TiO₂,并将Ag₃PO₄与Fe₃O₄/GO复合来提高催化剂的稳定性及循环利用性。采用能够产生SO₄^-·的过硫酸盐（PDS）替换传统Fenton体系中产生·OH的H₂O₂,来延长活性物种的寿命、拓宽体系pH适用范围、提高氧化降解能力。所制备的Ag₃PO₄/Fe₃O₄/GO兼具可见光与PDS双重催化活性,即:在可见光照射下,可作为光催化剂降解污染物;在PDS存在条件下,可作为PDS催化剂降解污染物;在可见光与PDS共存条件下,可作为双效催化剂协同降解污染物。通过该双效催化剂将Ag₃PO₄光催化和PDS催化以非均相催化形式结合构成一个以光催化氧化为主导并有过硫酸盐催化氧化的可见光-过硫酸盐耦合（Vis-PDS）体系。该耦合技术能够有效利用可见光,催化剂易于分离、回收,pH适用范围广,在不同条件下可以通过不同的作用机制发挥高效降解污染物的作用。研究过程中获得以下主要成果:1.以Ag₃PO₄为主体材料,充分利用Fe₃O₄/GO的PDS催化活性、磁回收性、导电性及大比表面积等特性,将二者有机结合成为Ag₃PO₄/Fe₃O₄/GO复合材料。通过多种表征手段对材料的结构信息及组成、形貌、纳米结构、元素及分布、表面元素的氧化态及磁性等理化性质进行鉴定分析;以罗丹明B（RhB）及对氯苯酚（p-CP）为目标污染物,考察了Ag₃PO₄/Fe₃O₄/GO的光催化性能、PDS催化性能及在耦合体系中的增效性。明确了双效催化剂的微观结构与催化性能之间的构-效关系,并以光催化及PDS催化机理为基础,提出了Vis-PDS耦合体系协同降解污染物的微观作用机制。2.探明了Fe₃O₄/GO的引入能够有效增强Ag₃PO₄在可见光区的吸光能力及光催化反应性,且Ag₃PO₄/Fe₃O₄/GO的光催化性能与Fe₃O₄/GO的质量分数有关。Ag₃PO₄/Fe₃O₄/GO的耐热性好、光催化活性及结构稳定性相对较好,光催化反应过程中存在一定程度的光腐蚀现象。基于Ag₃PO₄/Fe₃O₄/GO的光催化体系以h⁺和O₂^-·起主要作用,·OH起次要作用。3.揭示了Ag₃PO₄/Fe₃O₄/GO光催化降解RhB的机理。GO保留了Ag₃PO₄纳米粒子的活性中心,促进了催化剂对有机污染物的高效分解;GO与Ag₃PO₄构建成p/n异质结结构,促进了电荷分离,并延长光生载流子的寿命;Fe₃O₄/GO表面的光生e^-将催化剂表面吸附的O₂还原为O₂^-·,O₂^-·作为氧化剂降解污染物;Ag₃PO₄价带上的h⁺则直接氧化分解污染物,同时还可以将催化剂表面的OH^-和H₂O氧化生成·OH,来降解污染物。4.探明了Ag₃PO₄/Fe₃O₄/GO具有优于Fe₃O₄/GO的PDS催化活性,且催化性能、催化剂的特征基团及分子结构具有较好的稳定性。催化剂材料中的Ag⁺与Fe²⁺共同发挥PDS催化剂的作用,且Ag⁺对PDS的催化作用更显著。Ag₃PO₄/Fe₃O₄/GO催化PDS体系的主要活性基团为SO₄^-·和·OH。5.阐明了基于Ag₃PO₄/Fe₃O₄/GO的Vis-PDS耦合体系通过协同作用有效增强了体系的反应活性,协同系数η_Syn最高达59.8%。Fe₃O₄/GO与Ag₃PO₄的质量比对耦合体系的催化性能有影响,Ag₃PO₄/Fe₃O₄/GO-0.05的协同催化性能最佳。Ag₃PO₄/Fe₃O₄/GO在耦合体系中的活性、表面元素组成及各元素的氧化态在反应前后均比较稳定,催化剂中Ag、Fe元素在整个反应过程中仅有少量流失。6.确定了催化剂用量、初始pH、污染物浓度及PDS浓度等动力学反应参数对三种催化体系的影响,耦合体系的pH范围更加宽泛,PDS用量更少。另外,Vis-PDS耦合体系的运行模式为同时运行时,降解效率最高。常见无机离子对耦合体系的催化性能有不同程度的抑制作用,阴离子抑制作用显著,顺序为:CO₃^2->HCO₃^->NO₃^->SO₄^2-;阳离子Mn²⁺和Mg²⁺抑制作用不明显。7.阐释了h⁺、SO₄^-·、·OH、¹O₂以及O₂^-·五种活性基团在耦合体系降解p-CP过程中起作用,贡献率按照h⁺>SO₄^-·>·OH>¹O₂>O₂^-·排序。在此基础上结合半导体类型、光生e^--h⁺对的分离程度等方面详细阐明耦合体系的增效作用机理;并从化学动力学角度,利用电极电势作为判据,明确耦合体系中Ag²⁺+Fe²⁺→Ag⁺+Fe³⁺反应的正向进行,解释了Ag⁺与Ag²⁺、Fe²⁺与Fe³⁺的循环反应的存在可以有效促进Ag⁺与Fe²⁺的再生,保持催化剂的催化活性及稳定性。探讨了p-CP在耦合体系中的反应限度及矿化率,解析了耦合体系降解p-CP的主要中间产物为2-丁烯酸、对苯醌及癸酸,并对降解途径进行了理论推测。更多还原

【Abstract】 With the rapid development of medicine,chemical industry,printing and dyeing and other industries,the types and concentrations of refractory organic pollutants in water are increasing day by day.Some single water treatment technologies which have many limitations and defects,have been unable to meet the national emission standards.It has become an effective way to solve the defects of single technology by using the existing and relatively mature single water treatment technology as the coupling water treatment technology.Among them,the combination process with photocatalytic water treatment technology as the main body has gradually become the development direction of coupling water treatment technology with great application prospect.In such combination process,photocatalytic/Fenton coupling technology is suitable for practical engineering applications because of low energy consumption and normal temperature and pressure.However,there are still some drawbacks in the application of the technology,such as the low utilization of visible-light,the difficulty of catalyst recovery,the dependence of acidic environment on the reaction,the lack of theoretical basis for influencing factors and micro mechanism.In view of the above disadvantages and deficiencies,it is necessary to improve the photocatalytic/Fenton coupling technology to meet the increasingly stringent water quality discharge standards and the urgent demand for safe water quality environment.In this work,the design and preparation of the composite catalytic materials and the construction of the combined process were carried out to improve the coupling technology.The specific implementation mode is as follows:The visible light responsive catalyst Ag₃PO₄ was used to replace the UV responsive catalyst TiO₂,and the combination of Ag₃PO₄/Fe₃O₄/GO was used to improve the stability and recycling of the catalyst.The persulfate which can produce SO₄^-·was used to replace H₂O₂ which can produce·OH in the traditional Fenton system,so as to prolong the life of the active species,widen the application range of pH and improve the oxidative degradation ability of the system.The prepared Ag₃PO₄/Fe₃O₄/GO has bifunctional catalytic activities of visible-light and persulfate,that is,under visible-light irradiation,it can be used as photocatalyst;in the presence of PDS,it can be used as PDS catalyst;under the coexistence of visible-light and PDS,it can be used as a bifunctional catalyst.Then,Ag₃PO₄ photocatalysis and PDS catalysis were combined in the form of heterogeneous catalysis through the bifunctional catalyst.The heterogeneous catalysis was dominated by photocatalysis and coexisted by persulfate catalytic oxidation（Vis-PDS）.The coupling technology can effectively utilize visible-light,the catalyst was easy to be separated and recovered,and the pH range was wide.Furthermore,it could play the role of efficient degradation of pollutants through different mechanisms under different conditions.The main innovative achievements of the research are as follows:1.The preparation of Ag₃PO₄/Fe₃O₄/GO composite took Ag₃PO₄ as the main material,making full use of the PDS catalytic activity,magnetic recovery,conductivity and large specific surface area of Fe₃O₄/GO.Moreover,the structure information,composition,morphology,nanostructure,element and distribution,oxidation state and magnetic properties of surface elements were identified and analyzed by various characterization methods.After that,taking rhodamine B（RhB）and p-chlorophenol（p-CP）as the target pollutants,the photocatalytic performance,PDS catalytic performance and synergistic effect of Ag₃PO₄/Fe₃O₄/GO were investigated.Based on the mechanism of photocatalysis and PDS catalysis,the mechanism of synergistic degradation of pollutants by Vis-PDS coupling system was proposed.2.The introduction of Fe₃O₄/GO can effectively enhance the absorbance of Ag₃PO₄ in visible-light region and the reaction activity.The photocatalytic property of Ag₃PO₄/Fe₃O₄/GO was related to the mass fraction of Fe₃O₄/GO.The heat resistance,photocatalytic activity and structural stability of Ag₃PO₄/Fe₃O₄/GO are relatively good.There was a certain degree of photo etching in the process of photocatalytic reaction.In the photocatalytic system,h⁺and O₂^-·played the major role,while·OH played the secondary role.3.The mechanism of photocatalytic degradation of RhB by Ag₃PO₄/Fe₃O₄/GO was revealed.That was,GO retained the active center of Ag₃PO₄ nanoparticles and promoted the efficient decomposition of organic pollutants.The p/n heterojunction constructed by GO and Ag₃PO₄ promoted charge separation and prolongs the lifetime of photocarriers.Meanwhile,the photogenerated e^-on Fe₃O₄/GO reduced the O₂adsorbed on the catalyst surface to O₂^-·,which is an oxidant and can degrade pollutants.The h⁺on the valence band of Ag₃PO₄ oxidized and decomposed the pollutants directly.Meanwhile,it can oxidize the OH^-and H₂O on the catalyst surface to generate·OH to degrade the pollutants.4.It had been proved that Ag₃PO₄/Fe₃O₄/GO possessed better PDS catalytic activity than Fe₃O₄/GO,and the catalytic performance,characteristic groups and molecular structure of the catalyst were stable.Ag⁺and Fe²⁺in the catalyst material played the role of PDS catalyst together,and the catalytic capacity of the former on PDS was more significant.In addition,SO₄^-·and·OH were the main active groups of PDS catalytic system.5.It was clarified that the coupling system can effectively enhance the reactivity through synergism,and the synergy coefficient Syn was 59.8%.The mass ratio of Fe₃O₄/GO to Ag₃PO₄ had an effect on the catalytic performance of the coupling system,and the synergistic catalytic performance of Ag₃PO₄/Fe₃O₄/GO-0.05 was the best.Moreover,the activity,surface element composition and oxidation state of the catalyst in the coupling system were stable before and after reaction.Only a small amount of Ag and Fe elements in the catalyst were lost during the whole reaction process.6.The effects of kinetic parameters such as catalyst dosage,initial pH,concentration of pollutant and PDS on the three catalytic systems were determined.Compared with the single system,the pH range of the coupling system is wider,PDS consumption is less,and oxidation degradation capacity is stronger.The operation mode of the coupling system was the highest when it operated simultaneously.In addition,the common inorganic ions had different degrees of inhibition on the catalytic performance of the coupling system,the anion inhibition was significant which was in the following order:CO₃^2->HCO₃^->NO₃^->SO₄^2-.However,the inhibition of Mn²⁺and Mg²⁺was not obvious.7.It was explained that h⁺、SO₄^-·、·OH、¹O₂ and O₂^-·played a role in the degradation of p-CP by coupling system and the contribution rates are ranked according to h⁺>SO₄^-·>·OH>¹O₂>O₂^-·order.On this basis,the synergistic mechanism of the coupling system was expounded in detail according to the semiconductor type and the degree of separation of photo generated e^--h⁺pairs.From the perspective of chemical kinetics,electrode potential was used as criterion the to determine the forward reaction of Ag²⁺+Fe²⁺→Ag⁺+Fe³⁺in the coupling system.It was explained that the circulation reaction of Ag⁺and Ag²⁺,Fe²⁺and Fe³⁺could promote the regeneration of Ag⁺and Fe²⁺effectively and maintain the catalytic activity and stability of the catalyst.Finally,the reaction limits and mineralization rates of p-CP in coupling system were discussed.The main degradation intermediates of p-CP in the coupling system were analyzed as 2-butenoic acid,p-Benzoquinone and decanoic acid,and the degradation pathways were theoretically speculated.更多还原