应用纳米零价铁富集银的研究

大量研究表明,纳米零价铁（nanoscale Zero-Valent Iron,nZVI）对水中重金属,尤其是金、银等稀贵金属,有良好的分离富集作用.利用纳米零价铁反应器证明了nZVI可从废水中分离低浓度的银离子（Ag⁺）,并生成高含量的“银矿石”.此外,也证明了反应区氧化还原电位能够反映nZVI与Ag⁺的反应速率和分离效率.利用X射线衍射仪、X射线光电子能谱和高分辨透射电子显微镜等手段对反应产物进行表征,证实了Ag⁺可被nZVI还原为单质银,并以纳米颗粒的形式（<10 nm）沉积在nZVI表面.与其他材料（常见吸附/还原材料）相比,nZVI具有效率高,受pH影响小的优点.研究结果表明,nZVI是一种能够高效富集痕量银资源并产生高价值纳米银的材料.     

硫化零价铁去除水中污染物的效能及交互机制

如何同步提升零价铁去除水中污染物的反应速率和电子选择性已成为近年研究热点。基于无氧体系下硫化能通过抑制零价铁与水之间的副反应而改善体系还原除污染物效能,系统概括了不同硫化方式、硫化药剂和硫化程度合成的硫化零价铁理化特征,并揭示了其与硫化零价铁在不同水氧环境下去除不同污染物反应活性和电子选择性的交互机制。硫化能够主要通过调控界面亲疏水和导电性能而实现改善零价铁除污染的效能,其提升表现主要依赖于硫化程度,而与硫化方式、硫化药剂相关性较低。最后,展望了基于硫化零价铁的水污染控制技术在地下水修复和工业废水处理的应用前景。     

纳米零价铁去除水体中砷的效能与机理

全球超过一亿人受到高毒性、难处理的砷污染引发的饮用水安全的威胁,解决砷污染问题迫在眉睫而又任重道远。纳米零价铁(nZVI)能高效去除重(类)金属、硝酸盐、磷酸盐、高氯酸盐、卤代物、多环芳烃、偶氮染料和苯酚等污染物,成为广泛应用的工程纳米材料之一,在全球已有近60例的环境原位修复和废水处理工程案例。其独特的纳米级核壳结构和表面性质使其能够通过吸附、还原和沉淀等多种作用高效去砷。本文综述了近年来nZVI及其改性材料去除水中砷的研究进展,探讨了nZVI去除水中As(Ⅲ)和As(Ⅴ)的反应机理,归纳了不同反应条件(初始pH值、反应时间、nZVI投加量、砷初始浓度、共存离子和有机质)对去除效果的影响,总结了nZVI改性材料(多孔材料负载改性nZVI、金属掺杂改性nZVI、表面稳定剂改性nZVI和绿色合成nZVI)对砷的去除效率,展望了纳米零价铁去除砷的发展方向和所面临的挑战。     

功能性纳米零价铁的构筑及其对环境放射性核素铀的富集应用研究进展

随着核能的广泛应用和核技术的快速发展,环境中放射性核素铀的污染日益严峻.纳米零价铁（Nanoscale Zero Valent Iron：nZVI）因其具有廉价、制备简便、高表面活性及对铀高效的吸附性能等特性而逐渐成为环境中铀污染处理的良好材料.采用可行的方法制备纳米零价铁复合材料,借助单体材料之间的协同效应可进一步提高材料对铀酰的吸附性能.因此,纳米零价铁复合材料的制备以及应用成为近期环境科学领域的研究热点之一.针对纳米零价铁及其复合材料对环境中铀酰的去除研究进行了概述和展望,包括纳米零价铁及其复合材料的制备方法、去除效果及去除机理,并且简要探讨了纳米零价铁及其复合材料在环境放射性污染治理的应用前景,以期为今后的深入研究和实际应用提供参考依据.     

纳米零价铁复合材料制备、稳定方法及其水处理应用

纳米零价铁(nZVI/Fe⁰)因极高的催化活性和经济适用性备受关注,但实际推广中受团聚性和空气不稳定性等限制。为解决这些问题,近年来国内外学者研究开发了系列纳米零价铁的复合材料和稳定方法,在制备方法、基体材料和环境修复方面均有了较大进展。本文对近五年的研究成果进行汇总,从复合载体研究、稳定方法和水环境应用三个方面对纳米零价铁复合材料研究进行较全面的综述和展望。在纳米零价铁负载方面,本文对聚合物载体、黏土矿物、碳材料和金属氧化物载体的相关研究进行了总结;在颗粒稳定性方面着重讨论了复合金属、表面涂层、硫化方面的新成果;在水环境应用方面,本文指出纳米零价铁主要通过吸附、还原、络合、共沉淀、电化学反应、(类)芬顿氧化等过程实现水中的重金属以及有机物的去除,光、热、电、超声、微波的引入可显著增强水体中污染物的处理效果。     

还原氧化石墨烯负载零价铁的合成及对TNT废水处理

选取比表面积大且导电性能优良的还原氧化石墨烯（rGO）作为支撑材料,负载还原性强但极易团聚的纳米零价铁（nZVI）,制得还原氧化石墨烯负载零价铁（nZVI/rGO）复合材料.通过X射线衍射（XRD）、傅里叶变换红外光谱（FTIR）、扫描电子显微镜（SEM）与X射线光电子能谱（XPS）等测试手段对零价铁的负载情况、材料表面微观形貌与反应前后nZVI/rGO材料表面铁元素的含量与组成进行表征.考察了溶液初始pH值、材料投加量和理论零价铁负载量等因素对nZVI/rGO去除2,4,6-三硝基甲苯（TNT）的影响,研究了nZVI/rGO材料去除TNT的反应机理.通过正交实验可知,nZVI/rGO对含TNT废水的处理在较宽的反应条件范围内都可达到处理要求,在理论零价铁的负载量为3.0 g/g rGO,溶液初始pH为6,材料投加量为40 g/L时效果最佳,可将废水中TNT处理到检出限0.1 mg/L以下.     

纳米零价铁活化分子氧原理及降解有机污染物性能增强策略

纳米零价铁直接还原降解有机污染物运行长效性差,且不能矿化有机污染物.利用纳米零价铁还原活化分子氧生成活性氧物种可以氧化甚至矿化有机污染物.在最近的研究中,作者提出了纳米零价铁活化分子氧的双途径机理,即铁核电子转移到氧化铁壳表面的双电子还原活化分子氧途径和氧化铁表面结合态亚铁离子的单电子还原活化分子氧途径,阐释了纳米零价铁核壳结构依赖的分子氧活化降解有机污染物性能机制及性能增强策略.证实在纳米零价铁活化分子氧体系添加少量亚铁离子能在零价铁表面形成更多的结合态亚铁,显著增强纳米铁表界面活性氧物种生成量;同时,在纳米零价铁活化分子氧体系中引入少量有机或无机配体亦可提高活性氧物种产生效率,从而增强有机污染物降解性能.最后讨论了典型环境因素如pH值、共存离子、天然有机物等影响纳米零价铁活化分子氧降解有机污染物性能的规律.     

纳米零价铁与重金属的反应:“核-壳”结构在重金属去除中的作用

重金属是一类毒性较高、处理难度较大的环境污染物.纳米零价铁因为具有高效分离、固定重金属的潜能而受到广泛关注.其独特的纳米级核壳结构和表面性质使纳米零价铁能够通过吸附、还原和沉淀等多种作用高效去除重金属.现代仪器分析手段的进步,特别是高分辨电子显微成像技术的发展,为深入研究纳米零价铁的微观结构以及纳米零价铁与重金属的作用机理开辟了新的视角.本文重点讨论了纳米零价铁的结构、性质及其在重金属去除中的作用.研究借助高分辨率的球差校正扫描透射电镜(Cs-STEM)成像,配合高灵敏度的X射线能谱仪(XEDS)进行化学分析,旨在更好地了解纳米零价铁的精细结构及其与重金属的界面反应过程和机理.在深入理论研究的同时,通过"小试—中试—工程"逐级放大的方法,系统论证了纳米零价铁处理重金属废水的可行性.结果表明,纳米零价铁可有效、同步去除实际废水中铜、砷、铅、锌等多种重金属,并具有较高的去除负荷.     

水环境中ZVI/氧化剂体系及其电子迁移作用机制

利用零价铁(Zero-Valent Iron,ZVI)去除水环境中的污染物成为近年来的研究热点。当O_2、H_2O_2等氧化剂存在时,ZVI、氧化剂与污染物之间的电子迁移机制非常复杂,ZVI和氧化剂之间的相互影响机制尚无定论。传统观点认为,O_2会促进ZVI钝化膜的形成并阻断电子传递从而降低ZVI的还原性能。然而O_2可在ZVI作用下通过双电子传输转化为H_2O_2,构成ZVI/O2类Fenton体系;在此基础上,利用额外加入H_2O_2、HSO_5~-、S_2O_8~(2-)等氧化剂,发展出了基于·OH或SO_4~(·-)的ZVI/氧化剂高级氧化体系(ZVI-AOPs),从而氧化降解有机污染物。有学者认为H_2O_2、KMnO_4、S_2O_8~(2-)等强氧化剂的加入反而可以加快ZVI腐蚀和失电子的速率,从而提高ZVI去除重金属等污染物的还原性能,该研究结论对钝化膜机制提出了挑战。ZVI与氧化剂的联合作用还可以实现同时还原去除重金属和氧化降解有机物,也可以对卤代有机物等抗氧化污染物实现先还原后氧化去除。本文综述了基于ZVI/氧化剂的高级氧化或还原体系及其电子迁移机制,同时对ZVI与氧化剂的联合作用体系作一总结,并就值得深入研究的问题进行了展望。     

纳米零价铁在水相反应中的表面化学和晶相转化

纳米零价铁在水相中的表面化学特性和晶相等性质变化,将影响其反应活性及环境归趋等.总结近期课题组关于纳米零价铁在水相中表面化学和晶相转化的研究进展,为纳米零价铁污染控制化学提供基础理论.重点探讨水中有无溶解氧、不同水力学条件复氧（静态和扰动）、重金属共存、无机阴离子共存对纳米零价铁颗粒表面化学特性和晶相转变的影响.同时也研究高分子电解质表面修饰后,颗粒在水相中表面及晶相的演变及对重金属去除性能的影响.研究表明,纳米零价铁与水相中的水分子、溶解氧、重金属离子及无机阴离子反应,零价铁失去电子演变为氧化铁、羟基氧化铁等;环境条件对颗粒结构性能产生影响,从而影响污染物去除效率及其在环境中的归趋.未来研究将重点探讨结构性能动态变化与不同污染物之间反应性能的影响,建立纳米颗粒的结构与性能之间关系模型,为纳米零价铁材料的环境应用提供理论依据.     

A carbanion induced synthesis of highly congested pyrazole and imidazole containing heterocycles

An efficient approach to the synthesis of highly congested di, penta and hexacyclic pyrazoles as well as imidazole fragment containing novel heterocyclic molecule has been developed through a carbanion induced transformation of suitably functionalized 2H-pyran-2-ones, benzo[h]chromene and thiochromeno[4,3-b]pyrans. Due to the presence of fluorescence, we report their prime application metal sensor as off/on switching in ferric ions.     

α-Amino acid derived enaminones and their application in the synthesis of N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates and other heterocycles

A new and simple synthesis of novel N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates, which exist in equilibrium with their 4-oxo tautomers, has been developed in two steps starting from N-protected α-amino acids. The key intermediates are enaminones, which can also be isolated, characterized, and used for the construction of other functionalized heterocycles, before they spontaneously decompose to pyrrole products. 4-Hydroxypyrroles are prone to partial aerial oxidation but can be efficiently alkylated or reduced to stable polysubstituted pyrrolidine derivatives.     

Specific intramolecular aromatic CH insertion of diazosulfonamides

The chemoselectivity in the intramolecular CH insertion of various diazosulfonamides has been experimentally studied. The results reveal that the aliphatic 1,4-, 1,5-, or 1,6-C(sp³)?H insertions of diazosulfonamides are not accessible, while the aromatic 1,5-C(sp²)?H insertion can be realized specifically by adjusting the diazo-adjacent group. In addition, the general chemoselectivities in the intramolecular CH insertions of diazosulfonyl compounds are summarized. Generally, diazosulfones undergo both aromatic 1,5-C(sp²)?H and aliphatic 1,5- and 1,6-C(sp³)?H insertions, while diazosulfonates undergo aliphatic 1,5- and 1,6-C(sp³)?H insertions. However, diazosulfonamides only undergo aromatic 1,5-C(sp²)?H insertion.     

N-Heterocyclic carbene-palladacyclic complexes: synthesis,characterization and their applications in the C-N coupling and α-arylation of ketones using aryl chlorides

N-Heterocyclic carbene-palladacyclic complexes 3 were successfully achieved in a one-pot procedure under mild conditions. The structure of 3a was unambiguously confirmed by X-ray single crystal diffraction and it was an active catalyst in the Buchwald-Hartwig amination and α-arylation of ketones even at very low catalyst loadings (0.01?mol%).     

Selective synthesis of 4,5-dihydroimidazo- and imidazo[1,5-a]quinoxalines via modified Pictet–Spengler reaction

An efficient tandem approach for the selective synthesis of 4,5-dihydroimidazo[1,5-a]quinoxalines 6a–g and imidazo[1,5-a]quinoxalines 7a–h by the reaction of 2-imidazolyl anilines 4a–c with aryl aldehydes 5a–k under mild reaction conditions is described. Introduction of electron releasing alkyl groups in substrates 4a–b was found to be instrumental for the success of the reaction.     

Understanding the Diels-Alder reactivity of 1,2-azaborine analogues

The Diels-Alder reactivity of 1,2-heteroborines (H₄C₄B(H)X, X?=?NH, PH, AsH; O, S, Se) has been computationally explored by means of Density Functional Theory (DFT) calculations. The influence of the HB?=?X fragment on the reactivity of the system has been quantitatively analyzed in detail by means of the so-called Activation Strain Model (ASM) of reactivity. It is found that the interaction between these species and the dienophile is significantly stronger than that computed for their all-carbon isoelectronic counterpart, benzene. In addition, the strain energy plays a key role in the observed reactivity trends. The role of the aromaticity strength of these heteroarenes on the reactivity is also assessed.     

Synthesis of N-substituted carbazolones from α-iodo enaminones via Pd(0)-catalyzed intramolecular coupling under microwave irradiation

A variety of N-aryl and N-alkyl carbazolones were conveniently achieved in good to high yields via Pd₂(dba)₃-mediated intramolecular coupling of N-substituted α-iodo enaminones under microwave irradiation. The Pd(0)-catalyzed cyclization was found to proceed favorably with the more electron-deficient phenyl ring during the reactions involving unsymmetrical N,N-diaryl α-iodo enaminones. This unique property enables the construction of carbazolone skeleton containing nitro substituted benzenoid ring.     

Iodine-mediated oxidative Pictet-Spengler reaction using terminal alkyne as the 2-oxoaldehyde surrogate for the synthesis of 1-aroyl-β-carbolines and fused-nitrogen heterocycles

An efficient iodine-mediated oxidative Pictet-Spengler reaction in dimethyl sulphoxide (DMSO) using terminal alkynes as the 2-oxoaldehyde surrogate for the synthesis of aryl (9H-pyrido[3,4-b]indol-1-yl)methanones is described. The scope of the protocol includes the total synthesis of Fascaplysin, Eudistomins Y₁ and Y₂. The methodology is extended for preparing pyrrolo[1,2-a]-quinoxaline and indolo[1,5-a]quinoxaline derivatives. The utility of 1-aroyl-β-carbolines was demonstrated by performing palladium-catalyzed β-carboline directed ortho-C(sp2)-H functionalization of the phenyl ring with thiomethyl (SMe) group using DMSO as source and for accessing 4-aryl-canthin-6-ones.     

Facile synthesis of bicyclic 1-arylpyrazol-5-ones

In this Letter, we described a facile method for constructing fused bicyclic 1-arylpyrazol-5-one ring system. We employed various methylene-containing carboxylic acids as the substrates and proved that the pyrazolone ring closure requires activated methylene group in intermediate II. Accordingly, a series of structurally diversified, fused bicyclic 1-arylpyrazol-5-ones was prepared in moderate to high yields using the requisite substrates.     

Synthesis of substituted 2,4,5,6-tetrahydrocyclopenta[c]pyrazoles and 2,4,5,6-tetrahydropyrrolo[3,4-c]pyrazoles by intramolecular nitrilimine cycloaddition

Both substituted 2,4,5,6-tetrahydrocyclopenta[c]pyrazoles and 2,4,5,6-tetrahydropyrrolo[3,4-c]pyrazoles have been synthesized by the 3+2 intramolecular dipolar cycloaddition of nitrilimines to alkynes. This cyclization has been extended to more versatile 3-bromo derivatives by the use of alkynylbromides as dipolarophiles.