Preparation Of Nanosized Ecomaterials And Removal Of Typical Heavy Metals And Organic Dyes From Aqueous Solution

Water pollution,one of the main environmental problems currently faced by humanity,not only exacerbates the shortage of water resources,but also poses a serious threat to the ecological environment and human health.The types and properties of pollutants in different polluted water bodies vary greatly.Therefore,it is imperative to develop new materials and methods for the treatment and remediation.Heavy metals and organic dyes are the most common and typical types of pollutants,and are characterized by strong toxicity,high stability and difficulty in removal.Nanosized ecomaterials are promising candidates for the treatment of heavy metals and organic dyes,due to their large specific surface area,strong reactivity,tunable morphology,and unique performance and mechanisms in water treatments such as adsorption and advanced oxidation.This dissertation focuses on the water pollution of heavy metals and organic dyes,as well as the shortcomings of some ecomaterials in treatment of heavy metals and organic dyes.A series of nanosized ecomaterials are designed and prepared,and their removal performance and mechanisms to typical heavy metals and organic dyes are also systematically investigated.The main results are summarized as follows:1.Heavy metals and different types of organic dyes often coexist in the effluents with a central discharge of industry wastewaters.The physicochemical properties of heavy metals and organic dyes are quite distinct,such as molecular size,chemical composition and structure,and charge state.Threrefore,their simultaneous removal is a grand challenge.Due to the non-degradability of heavy metals,adsorptive treatment could be an effective way for simultaneous removal of coexisting heavy metals and organic dyes.In this regard,in Chapter 2 of this dissertation,a hydrochar and MgAl layered double hydroxide（HC-MgAlLDH）nanocomposite was successfully fabricated by a facile one-step hydrothermal route,and used for adsorptive removal of the anionic dye Congo red（CR）,cationic dye Methylene blue（MB）,and heavy metal Pb（II）.The removal performances of the nanocomposite for the three targets were systematically investigated by batch adsorption experiments,and their removal mechanisms were also explored by a variety of characterization techniques.The results reveal that the maximum Langmuir removal capacity to single CR,MB or Pb（II）is 348.78,256.54,or 33.55 mg/g,respectively.In the multi-pollutant systems,the nanocomposite not only shows the high-level removals for CR and MB,but also an enhanced removal for Pb（II）,showing great potential for simultaneous treatment of the coexisting heavy metals and different types of organic dyes.The positively charged MgAlLDH and negatively charged HC,combined with abundant aromatics ring structures on HC,make the nanocomposite become an efficient and multifunctional adsorbent for coexisting anionic CR,cationic MB,and heavy metal Pb（Ⅱ）.The removal of CR,MB,and Pb（Ⅱ）involves a series of interactions,such as electrostatic attraction,π-π interaction,and coordinative adsorption.In addition,Pb（Ⅱ）can interact with the dyes and form Pb complexes and PbSO4 precipitates on the nanocomposite surfaces,thereby enhancing Pb（Ⅱ）removal in the multi-pollutant systems.Therefore,the HC-MgAlLDH nanocomposite can be potentially applied for adsorptive treatment of the wastewaters containing heavy metals and different types of organic dyes.2.Organic dyes in industry wastewaters usually have complex composition and low biodegradability,and thus degradation of the organic dyes into harmless products through advanced oxidation processes is a feasible solution.Heterogeneous Fenton oxidation is one of the processes for efficient degradation of organic dye pollutants,using the strong oxidizing species generated from the catalysis of H₂O₂ by solid phase catalyst The key of heterogeneous Fenton process is to synthesize high-performance catalysts.Delafossite（CuFeO₂）is a typical binary metal oxide and theoretically should be an excellent heterogeneous Fenton catalyst.However,CuFeO₂ nanocrystals usually possess high surface energy and tend to agglomerate,thereby dramatically blocking the active sites.To this end,in Chapter 3,a novel CuFe02 nanosheet with good dispersity was successfully prepared by a simple hydrothermal method with montmorillonite as an assistant reagent,and the catalytic performance and mechanism of the CuFeO₂ nanosheet for degradation of dye pollutant methyl orange catalyzed by H₂O₂ were systemically investigated.Results show that the montmorillonite plays key roles in isolation and dispersion of the forming CuFeO₂ nanosheet,effectively avoiding the CuFeO₂ aggregation.The montmorillonite is gradually dissolved and releases silicates to regulate the morphogenesis of the nanosheet-like CuFeO₂.For catalytic degradation of methyl orange,the CuFeO₂ nanosheet not only shows a much better catalytic performance than the CuFeO₂ nanopolyhedra synthesized via a conventional hydrothermal method,but also maintains high catalytic activity in a wide pH range of 3-9.In addition,the degradation efficiency of methyl orange is up to 86%after five cycles.Moreover,inorganic anions such as NO3-,HCO3-,and SO42that may inhibit the activities of the free radicals during the catalytic reaction exert a minor influence on the catalytic degradation.The free radical quenching experiments confirm that ·OH is the major radical in the heterogeneous Fenton system.X-ray photoelectron spectroscopy analyses show that the high catalytic activity of CuFeO₂ nanosheet mainly originates from the synergistic effects of Fe³⁺/Fe²⁺ and Cu⁺/Cu²⁺redox cycles on the CuFeO₂ nanosheet surfaces.Due to the facile synthesis and good catalytic performance,the CuFeO₂ nanosheet could be further employed in practical wastewaters as a high-performance heterogeneous Fenton catalyst.3.In addition to the heterogeneous Fenton process,persulfate-based advanced oxidation is also an important method for efficient treatment of organic dyes.Binary transition metal sulfides such as chalcopyrite（CuFeS2）are ideal catalysts for persulfate-based advanced oxidation due to the synergistic catalytic effect between different metal ions and the electron-donating effect of reduced sulfur on the redox cycle.In this context,in Chapter 4,a chalcopyrite hierarchical microsphere was prepared by solvothermal method,and its catalytic performance and mechanism in activating peroxymonosulfate for degradation of organic dye Rhodamine B were systematically investigated.The results show that the chalcopyrite microsphere exhibits high catalytic activity in a wide pH range and in the presence of coexisting anions,and the degradation efficiency of Rhodamine B reaches 57.5%after 5 catalytic cycles.Moreover,the catalytic degradation of Rhodamine B can be enhanced by elevating the reaction temperature,ultrasonic treatment,or sunlight irradiation.The main active free radical in this system is confirmed as SO4·-.The high catalytic activity of the chalcopyrite microspheres is ascribed to the synergistic effects of Fe³⁺/Fe²⁺and Cu⁺/Cu²⁺redox cycles.In addition,the S^2-,S₂^2-,S_n^2-and S0 in the structure of chalcopyrite act as electron donors and play a key role in accelerating the redox cycles of Fe³⁺/Fe²⁺and Cu⁺/Cu²⁺.This study provides an efficient catalyst for degradation of organic dyes by activation of potassium peroxymonosulfate.4.In addition to the pollution of organic dyes and heavy metal Pb in industrial wastewater,antimony（Sb）pollution in groundwater is also a great environmental concern.Permeable reactive barriers（PRB）are one of the common methods for treatment of groundwater pollution,and the active medium materials in PRB are the key to adsorptive immobilization of pollutants.Bone char,with hydroxyapatite as its main component,is a calcined product of broken animal bones at 500-700℃ and possesses rich sources,good renewability,and excellent permeability.Therefore,it is a promising reactive material for PRB systems.However,due to its limited specific surface areas and surface active sites,bare bone char shows low removal performance for antimony.To this problem,in Chapter 5,an FeS@bone char composite was prepared by loading FeS nanoparticles onto bone char,and used as an adsorbent for antimony（Sb（V））based on the strong chemical affinity of nanosized FeS for chalcophile elements such as Sb.The results show that the Sb（V）removal capacity increases by 2.4 times and reaches 1601.67 μg/g after the FeS modification.In addition,the FeS@bone char composite exhibits high removal performance for Sb（V）at pH 5-11 and in the presence of anions.Considering the simple modification and good removal performance,the FeS@bone char composite could be potentially used as an active material in PRB for remediation of groundwater Sb（V）pollution.