【作者】 刘海；

【导师】 张建； 梁爽； 谢慧君；

【作者基本信息】 山东大学 ， 环境工程， 2017， 博士

【摘要】 人工湿地作为一种投资低、运行稳定、管理方便的生态污水处理技术,已广泛应用于发展中地区流域水污染治理、再生水回用及生态修复等领域。湿地植物作为人工湿地的核心组成部分之一,可直接吸收污染物、根系泌氧、提供微生物附着位点等积极作用。随着湿地工程的不断推广应用,每年大量废弃的季节性湿地植物导致巨大的资源浪费和二次污染问题,威胁着人工湿地大型工程的可持续稳定运行。探索湿地植物的资源化利用,使其"变废为宝、化害为利"具有重大的现实和战略意义。重金属污染具有高毒性、持久性、生物蓄积性、致癌性和基因诱变性等特性,己经成为全球水污染主要问题之一。活性炭吸附是处理重金属污水的有效技术,但活性炭较高的制备成本和较低的吸附容量限制了它的广泛应用。因此,本研究拟利用湿地植物为活性炭原料,采用新型活化法和简易改性方法提高活性炭对重金属的吸附性能,实现湿地植物秸秆高价值回收利用。本研究基于维管束植物茎叶多孔的特征,研发了高价值湿地植物基活性炭制备技术;评估了磷酸高温聚合反应对活性炭理化性能的影响,解析了磷酸活化过程官能团生成的控制因素,剖析了磷酸活化法制备秸秆基活性炭的机理;通过磷酸活化法糖基和多元醇基活性炭的制备,证实了磷酸酯的形成能促进活性炭表面官能的生成;通过评估有机磷酸酯新型活化法的可行性,研发了多种高Pb(Ⅱ)吸附性能的湿地植物基活性炭吸附剂,通过原位季戊四醇改性法强化了有机磷酸酯生成技术,研发了提升活性炭Ni(Ⅱ)吸附容量的简易改性方法;通过原位酒石酸改性法改善了有机磷酸的生成和造孔作用,研发了保持活性炭孔隙率和提升活性炭Cr(VⅥ)去除率的改性方法。取得的主要研究结论如下:(1)磷酸不同维度的高温聚合方式和秸秆浸渍效果决定了活性炭的孔隙结构和表面官能团含量。制备的磷酸活性炭(SBET,1114 m2/g)和焦磷酸活性炭(940 m2/g)比聚偏磷酸活性炭(279 m2/g)和亚磷酸活性炭(125 m2/g)具有更发达的孔隙结构;焦磷酸对莲秆的木质纤维素结构具有最强的解聚和水解作用,制备的焦磷酸活性炭(4.156 mmol/g)比磷酸活性炭(2.486 mmol/g)具有更高的表面官能团含量;偏磷酸活性炭保持了炭先驱体的初始形貌;亚磷酸活性炭具有最规整的芳香性结构。磷酸高温聚合作用促进了木质纤维素的解聚和水解作用,浸渍过程形成的低聚磷酸酯化合物促进了活性炭表面官能团的生成。(2)磷酸活化法过程中低聚磷酸酯的生成能促进活性炭表面官能团化。制备的芦苇基活性炭(1057 m2/g)孔隙率比糖基活性炭(12-698 m2/g)更为发达,但糖基活性炭表面官能团含量和Ni(Ⅱ)吸附容量比芦苇基活性炭分别多55-75%和45-70%。低聚糖制备的活性炭含有更高的表面官能团含量,进而采用了具有更低稳定度的多元醇作为活性炭先驱体。以木糖醇为炭先驱体优化磷酸活化法制备参数,通过分析炭材料的收率和官能团含量,发现了活化温度350℃和浸渍比1.5时可制备最佳的木糖醇基活性炭。在此优化条件下批次制备了 3C至6C的多元醇基活性炭,它们比芦苇基活性炭表面官能团含量多50-90%,验证了低聚磷酸酯的生成能促进磷酸活化法活性炭官能团的生成。(3)磷酸酯新型活化法可制备出价廉和高Pb(Ⅱ)吸附性能的莲秆基活性炭。七种不同的正磷酸酯和亚磷酸酯活化法都显著提升了活性炭的比表面积、收率和表面官能团含量。正磷酸酯活化法制备的活性炭具有更多的官能团,磷酸三甲酯活化法制得的活性炭官能团含量最高(6.01 mmol/g)。依据活活性炭的收率和官能团含量,磷酸三甲酯和三丁酯活化法制备的活性炭性能最为优异。磷酸三甲酯活性炭(345 m2/g)和磷酸三丁酯活性炭(541 m2/g)的孔隙率远低于磷酸活性炭(1418 m2/g),但它们表面官能团含量比磷酸活性炭高70-80%。磷酸三甲酯活性炭和磷酸三丁酯活性炭的Pb(Ⅱ)吸附容量比常规磷酸活性炭高65-75%,证实了Pb(Ⅱ)吸附主要由活性炭化学性能控制,吸附机理主要包括静电引力、离子交换和表面络合作用。(4)季戊四醇原位改性法简化了常规活性炭改性工艺,提升了莲秆基活性炭的Ni(Ⅱ)吸附性能。季戊四醇原位改性法促进了磷酸活化过程中磷酸酯的产生,进而强化了活性炭表面官能团的生成。这一系列的反应促使了交联结构的生成,极大的降低了活性炭的孔隙率,但改性后的活性炭表面氧含量和总官能团量都提升了 80%。在三个不同背景离子强度下(0、100和1000 mMNaCl),改性活性炭的最大Ni(Ⅱ)吸附量比原炭高30-60%,证实了化学吸附是Ni(Ⅱ)吸附的主要机理,主要包括阳离子交换、静电吸引和表面络合。该方法比常规"先制备,后改性"方法更为简易和高效,是一种有前景的重金属吸附剂制备/改性方法。(5)酒石酸原位改性法和官能团掩蔽法提升了茭白基活性炭的Gr(Ⅵ)吸附性能。酒石酸掺杂量梯度对比实验显示,30mmol/10g茭白为最优的酒石酸掺杂量。原炭和改性炭具有相似的孔隙结构(～1200 m2/g),但改性炭官能团含量提高了 60%,进而对Cr(Ⅵ)的吸附量提升了 20-30%。通过掩蔽活性炭的羧基和羟基,降低了活性炭和Cr(Ⅵ)间的静电斥力,进一步将Cr(VⅥ)和总Cr的去除效率提升了 10-15%。活性炭表面80%的Cr以Cr(Ⅲ)形式存在,说明了"Cr(Ⅵ)吸附、Cr(Ⅵ)还原和Cr(Ⅲ)再吸附"是活性炭对Cr(Ⅵ)去除机理。更多还原

【Abstract】 As a kind of ecological wastewater treatment technology,constructed wetland has advantages of low capital cost,stable operation and easy management,which has been successfully applied for wastewater reuse,ecological restoration and wastewater treatment in developing regions.As one of the most important components of constructed wetland,plants can assimilate directly pollutants,provide oxygen through radial oxygen loss,and facilitate microbial activities by providing habitats.Along with the application of constructed wetland,large abundant of biomass is producing annually from the withered plants,which results in the problems of resources waste and second pollution in constructed wetland without reasonable disposal and treatment.Thus,it is necessary to explore efficient recovery and utilization technologies of the biomass.Heavy metal pollution in water environment has been regarded as a universal problem due to its high toxicity,persistence,bioaccumulation,carcinogenicity,and teratogenicity.Adsorption onto activated carbon(AC)is an effective way for treatment of heavy metal-polluted wastewater,but its wide application is limited by the relatively high preparation cost and low adsorption ability.Therefore,this study aims to explore new activation or facile modification methods to enhance the adsorption abilities of wetland plants-based ACs towards heavy metal ions.Based on the well-developed aeration tissues of wetland plants,they were utilized as carbon precursors to fabricate ACs.The effect of polymerization of phosphorus oxyacids at high temperatures on the textural property and surface chemistry of AC was investigated to further study the mechanisms of phosphoric acid activation and to find primary factors for controlling the formation of surface functionality of AC.Carbohydrates and polyhydric alcohols were employed as precursors to prepare ACs via phosphoric acid activation to verify that carbohydrates and alcohols hydrolyzed from lignocellulosic materials duing phosphoric acid impregnation promoted the creation of functional groups.Organic phosphates activations were explored to develop ACs from lotus stalk,and they were promising adsorbents for Pb(II)removal with excellent adsorption abilities.Pentaerythritol was employed to modify AC during phosphoric acid activation to promote the formation of organic phosphates,and this method simplified the conventional modification method and significantly improved the Ni(Ⅱ)adsorption ability of AC.In situ modification with tartaric acid of AC during phosphoric acid activation improved the formation of organic phosphates and pore-forming effect,and this method maintained the porosity of AC and enhanced Cr(VI)removal performance of AC.(1)The porosity and functionality of ACs were determined by the polymerization degree of phosphoric acid at different latitudes and impregnation effect of lignocellulosic materials.AC-H3PO4(SBET,1114 m2/g)and AC-H4P2O7(940 m2/g)exhibited better developed porosities than AC-(HPO3)n(279 m2/g)and AC-H3PO4(125 m2/g).H4P2O7 yielded the strongest corrosion and hydrolysis for lotus stalk,resulting in the higher content of functional groups of AC-H4P2O7(4.156 mmol/g)than AC-H3PO4(2.486 mmol/g).(HPO3)n maintained the structure of AC as its starting material after activation.AC-H3PO3 had the most dimensions of crystallites perpendicular to aromatic layers.It suggested that polymerization of phosphoric acid promoted the depolymerization and hydrolysis of lignocellulosic materials,and the formation of low-polymerized organic phosphates enhanced the creation of functional groups for ACs.(2)The creation of functional groups for ACs was induced by low-polymerized organic phosphates during phosphoric acid activation.Carbohydrates-based ACs had much lower surface area(12-698 m2/g)than Phragmites australis-based AC(1057 mg),but they exhibited 60-75%higher contents of functional groups.The monosaccharide yielded AC with higher functional groups content than disaccharide and polysaccharide,hence some chain-like polyhydric alcohols with lower stability were utilized as carbon precursors.Xylitol was used as precursor to optimize the preparation parameters,and the optimized conditions were activation temperature of 350℃ and phosphoric acid to xylitol impregnation ratio of 1.5 considering their yields and functional groups contents.Different polyhydric alcohols were used to prepare ACs at the optimized conditions,and the produced ACs exhibited 50-90%more surface functional groups than Phragmites australis-based AC.These results demonstrated that the formation of organic phosphates improved the creation of functional groups of AC during phosphoric acid activation.(3)Organic phosphates activations was used to fabricate ACs from lotus stalk with low cost and high Pb(Ⅱ)adsorption abilities.Seven phosphate and phosphite esters activations dramatically enhanced the porosity,yield and surface functionality of ACs.The ACs with phosphate esters activations showed higher surface functional groups contents,and AC with trimethyl phosphate activation had the highest value(6.00 mmol/g).It was suggested that trimethyl phosphate and tributyl phosphate activations produced ACs with the better properties considering their yields and functional groups contents.ACs with trimethyl phosphate(345 m2/g)and tributyl phosphate(541 m2/g)activations exhibited much lower surface area than AC with phosphoric acid activation(1418 m2/g),but they contained 70-80%higher functional groups,and had 65-75%higher Pb(Ⅱ)adsorption capacities.These results indicated that Pb(Ⅱ)adsorption was controlled by the surface chemistry of ACs,and the main adsorption mechanisms were electrostatic attraction,cation exchange and surface ccomplexation.(4)The Ni(Ⅱ)adsorption ability was improved by a simplified modification of lotus stalk-based AC with pentaerythritol during phosphoric acid activation.Pentaerythritol promoted the formation of organic phosphates,and hence enhanced the creation of functional groups for AC.These reactions resulted in the formation of highly cross-linked structure,and then dramatically decreased the porosity of the resulting AC.Nevertheless,the surface oxygen atomic content and functional groups content of AC after modification were improved 80%.Under three ionic strengths(0,100,and 1000 mM NaCl),the Ni(Ⅱ)adsorption capacities of the modified AC were improved 30-60%.It was also indicated that Ni(Ⅱ)adsorption onto ACs was controlled by chemical adsorption,and the major mechanisms were cation exchange,electrostatic attraction and surface complexation.(5)The Cr(Ⅵ)removal performance was enhanced by in situ modification of Zizania caduciflora based-AC with tartaric acid during phosphoric acid activation and functional groups blocking.The optimized additive amount of tartaric acid was 30 mmol/10 g precursor.ACs with and without modification had slightly differences in porosities,but the modified AC contained 60%more surface functional groups,and had 20-30%higher Cr(Ⅵ)removal efficiency than original AC.After reducing the electrostatic attraction between the Cr(Ⅵ)and ACs’ surfaces by blocking their carboxyl and hydroxyl groups,the Cr(Ⅵ)removal was further enhanced 10-15%.About 80%Cr adsorbed on the carbon’s surface was present as Cr(Ⅲ),which indicated that the mechanisms for Cr(Ⅵ)removal by ACs were "Cr(Ⅵ)adsorption,Cr(Ⅵ)reduction and Cr(Ⅲ)adsorption".更多还原