纳米MnO_2粉体的固相合成及其电化学性能 (Ⅲ)固相氧化还原反应合成纳米α-MnO_2的性能

纳米材料在光、电、磁方面的特性使其在催化,磁性材料,传感器,医学,生物学等方面有特殊应用．纳米材料比常规电极在电化学性能方面有一定的优越性［１～５］．已成功地合成出多种纳米材料［６,７］．本文采用固相氧化还原反应体系直接合成出纳米αＭｎＯ２,并用Ｘ...     

聚多巴胺还原高锰酸钾制备二氧化锰阵列纳米管

以通过水热法在石英玻璃片表面合成的ZnO纳米棒为模板,在其表面生成聚多巴胺薄膜,然后与KMnO4反应,制备了MnO_2阵列纳米管。经表征发现,制备的MnO_2纳米管形态良好,在基底表面的附着力强;所制备的MnO_2为非晶型。由于ZnO模板易合成、易去除、形态好,且聚多巴胺薄膜的生成方法也很简便易行,使得该制备MnO_2纳米管阵列的方法具有简便、快捷、适用性广等的特性,对MnO_2新形态纳米结构的构建具有一定的启示作用。     

Generating MnO2 nanoparticles using simulated amorphization and recrystallization

Models of MnO2 nanoparticles, with full atomistic detail, have been generated using a simulated amorphization and recrystallization strategy. In particular, a 25,000-atom "cube" of MnO2 was amorphized (tension-induced) under molecular dynamics (MD). Long-duration MD, applied to this system, results in the sudden evolution of a small crystalline region of pyrolusite-structured MnO2, which acts as a nucleating "seed" and facilitates the recrystallization of all the surrounding (amorphous) MnO2. The resulting MnO2 nanoparticle is about 8 nm in diameter, conforms to the pyrolusite structure (isostructural with rutile TiO2, comprising 1 x 1 octahedra) is heavily twinned and comprises a wealth of isolated and clustered point defects such as cation vacancies. In addition, we suggest the presence of ramsdellite (2 x 1 octahedra) intergrowths. Molecular graphical snapshots of the crystallization process are presented.     

Enhancement of the electrocapacitive performance of manganese dioxide by introducing a microporous carbon spheres network

An amorphous MnO(2)·nH(2)O/microporous carbon spheres (α-MnO(2)·nH(2)O/MCS) composite electrode material is prepared by a chemical co-precipitation method. It is observed that the amorphous MnO(2) particles are deposited on the surface of the MCS, which form a network with a uniquely developed three-dimensional open porous system containing macropores, mesopores and micropores. The electrochemical measurements reveal that the composite electrode material presents a much more stable and reversible capacitance behavior compared to the pure α-MnO(2)·nH(2)O in 1 M of Na(2)SO(4) electrolyte. The composite containing 25 wt% MCS exhibits optimal specific capacitance of 218.2 F g(-1) at 2 mV s(-1), and is still as high as 112.4 F g(-1) at 100 mV s(-1), while a drastic reduction from 197.0 F g(-1) at 2 mV s(-1) to only 40.7 F g(-1) at 100 mV s(-1) occurs for the pure α-MnO(2)·nH(2)O. The composite also shows a rather high electrode-specific capacitance of 3.13 F cm(-2) and a long cycle life. The remarkable enhancement in the electrochemical performance is mainly attributed to the microporous structure of the MCS contributing to the deposition of MnO(2) particles on the surface of the MCS, and the uniquely developed porous network of the composite facilitating the rapid transport of the electrolyte. These factors result in the high electrochemical utilization of MnO(2), a great reduction of the equivalent series resistance, and hence the relatively high and stable electrochemical behavior.     

聚乙撑二氧噻吩/二氧化锰纳米复合物的界面聚合制备及其电化学性能

采用界面聚合法制备聚3,4-乙撑二氧噻吩/二氧化锰(PEDOT/MnO2)纳米复合物. 通过红外(IR)光谱、X射线衍射(XRD)、BET比表面积、扫描电子显微镜(SEM)和透射电子显微镜(TEM)对样品进行表征. 结果表明, 产物是具有丰富的多孔孔道结构的无定型纳米材料, 孔径主要分布在5-25 nm范围内, 比表面积可达98 m2·g-1. 同时用循环伏安(CV)、恒流充放电和交流阻抗(EIS)等电化学测试表明, 在0.5 mol·L-1 Na2SO4溶液中, -0.2 - 0.8 V(vs SCE)的电化学窗口下, PEDOT/MnO2纳米复合物显示出良好的电化学性能, 当电流密度为0.5 A·g-1时, 所制备的PEDOT/MnO2单电极比容量达196.3 F·g-1, 500次循环后样品放电比容量保持90%左右.     

不同工作介质下二氧化锰/膨胀石墨复合材料的电化学电容器行为

研究了氧化还原法制备二氧化锰/膨胀石墨复合材料用作电化学电容器, 利用热重分析、比表面及X射线衍射方法对材料的组成及结构进行了表征, 利用三电极循环伏安及充放电循环法研究了材料在硫酸钠、氯化钠、氯化钾及硝酸钾不同电解质中的电化学行为. 研究结果表明, 二氧化锰以非晶态的形式在复合材料中存在, 膨胀石墨起良好电导作用, 随其用量的增加, 复合材料的比表面下降, 但二氧化锰的比电容增加. 不同工作介质中电化学行为显示, 复合材料电化学行为的不同主要跟阳离子的种类有关. 在钠离子电解质中, 复合材料电极体现较高的表观电容和真实电容, 在钾盐电解质体系中, 复合材料电极的电流响应速度比较快, 这是由于钠盐和钾盐溶液具有不同的水合数、水合半径和电导率. 当复合材料中膨胀石墨的用量为24%左右时, 复合材料在2 mV/s扫描速度下, 在1 mol/L Na₂SO₄溶液中体现的比电容为220 F/g, 复合材料显示优良的循环性能.     

Interface synthesis of mesoporous MnO2 and its electrochemical capacitive behaviors

Mesoporous MnO(2) has been synthesized by means of a novel, facile, and template-free method by virtue of a soft interface between CCl(4) and H(2)O without any surfactants or organometallic precursors or ligands. X-ray diffraction spectroscopy, Fourier transform infrared spectroscopy analysis, scanning electron microscopy, and an ASAP2010 autoadsorption analyzer were applied to investigate the composition and microstructure of the as-synthesized MnO(2). The structure characterizations indicated a good mesoporous structure for as-prepared MnO(2) with an adsorption average pore diameter of 9.7 nm, mesoporous volume of 0.58 cm(3) g(-1), and Brunauer-Emmett-Teller specific surface area of 239 m(2) g(-1). Electrochemical properties of the mesoporous MnO(2) were elucidated by cyclic voltammograms, galvanostatic charge-discharge, and electrochemical impedance spectroscopy in 1 M Na(2)SO(4) electrolyte. Electrochemical data analysis demonstrated that as-synthesized MnO(2) had good capacitive behavior due to its unique mesoporous structure. A specific capacitance of ca. 220 F g(-1) could still be delivered for the mesoporous MnO(2) even at a scan rate of 100 mV s(-1).     

热处理对线团状二氧化锰结构及其电化学性质的影响

以氯化锰与高锰酸钾为原料, 在低浓度下大数量合成由无数片状纳米层组成的线团状二氧化锰粒子. 采用X衍射, 扫描电镜, 液氮等温吸附脱附、循环伏安、交流阻抗及恒流充放电等方法研究了温度对产物结构及电化学性质的影响. 结果表明处理温度升高, 微孔减少, 比表面积减小, 孔径变大, 在300 ℃以下二氧化锰粒子的结构保持无定型结构. 交流阻抗测试显示随着处理温度的升高, 样品的法拉第电荷传递能力和离子在电解液与活性材料界面的扩散能力均得到提高. 比电容测试显示在200 ℃处理的二氧化锰具有最高的比电容, 以1 mol·L^-1 Na₂SO₄为工作介质, 扫速为2 mV·s^-1时, 其比电容是210.6 F·g^-1. 该研究表明: 材料的电化学性质可以通过热处理进行调整, 适当的热处理能提高该材料作为超级电容器活性材料的性质.     

合成路径对超级电容器用二氧化锰性质的影响

研究了不同合成路径对二氧化锰结构及电化学性能的影响. 路径1为将0.15 mol/L醋酸锰溶液加入到0.1 mol/L高锰酸钾溶液中; 路径2中, 物料的加料方式与路径1相反. X射线衍射和扫描电镜测试表明合成的产物均为无定型α-MnO2, 晶粒尺寸为200～300 nm. 氮吸附曲线测试结果表明: 路径1所得的二氧化锰具有较大的比表面积(329 m2/g), 其孔径分布比较均一, 孔径6～12 nm, 孔体积较小(0.45 cm3/g); 路径2所得的二氧化锰比表面积较小(298 m2/g), 具有从微孔到大孔的连续分布孔, 平均孔径11.4 nm, 孔体积较大(0.66 cm3/g). 交流阻抗和循环伏安电化学测试结果显示: 路径2所得样品具有较大的法拉第阻抗, 在较低扫描速度下(2 mV•s－1), 其比电容(203 F•g－1)比路径1所得MnO2高(189 F•g－1), 路径1所得二氧化锰的比电容随扫描速度变化的趋势较小. 恒流充放电测试显示路径1合成的二氧化锰具有较好的功率特性. 在2 A•g－1的电流密度下, 其比容量为0.1 A•g－1电流密度下的96.3%, 而路径1的样品的容量保持率为92.5%. 造成上述结果差异的原因是由于不同合成路径导致二氧化锰存在不同的孔结构特征所致.     

MnO2-embedded-in-mesoporous-carbon-wall structure for use as electrochemical capacitors

We present an in situ reduction method to synthesize a novel structured MnO(2)/mesoporous carbon (MnC) composite. MnO(2) nanoparticles have been synthesized and embedded into the mesoporous carbon wall of CMK-3 materials by the redox reaction between permanganate ions and carbons. Thermogravimetric analysis (TG), X-ray photoelectron spectrum (XPS), X-ray diffraction (XRD), nitrogen sorption, transmission electron microscopy (TEM), and cyclic voltammetry were employed to characterize these composite materials. The results show that different MnO(2) contents could be introduced into the pores of CMK-3 treated with different concentrations of potassium permanganate aqueous solution, while retaining the ordered mesostructure and larger surface area. Increasing the MnO(2) content did not result in a decrease in pore size from the data of nitrogen sorption isotherms, indicating that MnO(2) nanoparticles are embedded in the pore wall, as evidenced by TEM observation. We obtained a large specific capacitance over 200 F/g for the MnC composite and 600 F/g for the MnO(2), and these materials have high electrochemical stability and high reversibility.     

石英晶体微天平分析不同介孔二氧化锰材料的电化学性能

以碳酸锰(MnCO3)为前体,空气氛围下采用不同温度(300℃、350℃、400℃)煅烧, 制备了3种介孔二氧化锰(MnO2)材料,分别与粘结剂混合喷涂至石英晶片作为电极,利用石英晶体微天平(QCM)监测了3种材料在0.1 mol/L Na2SO4溶液中随循环伏安过程的电化学性能变化.分析结果表明,3种材料在首圈循环中都呈现出显著的质量增加,发生了不可逆反应过程; 300℃煅烧制备的MnO2材料具备更好的电化学稳定性和容量保持能力.将300℃, 350℃和400℃煅烧的MnO2各自作为正极与活性炭负极组成超级电容器, 进行充放电测试,首圈均有35％～40％的容量损失; 三者稳定循环时放电容量分别为15.9, 12.9和11.7 mA h/g.QCM的分析与充放电测试结果相一致,表明QCM可用于比较不同介孔二氧化锰材料的电化学性能.     

空心ZnMn2O4纳米球和纳米立方体的室温合成及氧还原催化性能

室温条件下,在含有Zn2+的溶液中,以空心结构的MnO2作为前驱体,使用NaBH4作为还原剂,合成了尖晶石型的ZnMn2O4纳米空心球和纳米空心立方体. 通过XRD,SEM,TEM,BET等测试手段对合成产物的结构、形貌、组成、表面性质进行了表征. 实验结果表明,所制备的空心结构ZnMn2O4纳米球和纳米立方体的尺寸在400?600 nm, 空心结构的壳层是由5?6 nm颗粒紧密堆积而形成,厚度约为40 nm. 将所制备的纳米ZnMn2O4空心结构应用于氧还原（ORR）反应中,研究了其在碱性溶液中的氧还原电催化性能,结果显示,相对于ZnMn2O4纳米空心立方体,ZnMn2O4纳米空心球在氧还原反应中表现出较大的电流密度和高的电子转移数 (n=3.5), 具有较好的氧还原电催化性能,有望成为一种新型的氧还原电极电催化剂.     

掺杂MnO2土壤对多种雌激素化合物的吸附热力学特征及机理

通过析因实验设计优化了掺杂MnO2土壤对雌酮(E1)、雌二醇(E2)、17α-乙炔基雌二醇(EE2)、雌三醇(E3)和双酚A(BPA)等多种雌激素化合物的吸附条件,采用Langmuir吸附等温式和Gibbs方程考察了掺杂MnO2土壤吸附雌激素化合物的热力学规律和吸附过程的热力学性质,并利用傅里叶变换红外光谱对吸附机理进行了探讨,同时利用液相色谱-质谱联用技术对土壤中多种雌激素化合物的主要降解产物进行了定性分析.结果表明,雌激素化合物浓度和MnO2掺杂比例对雌激素化合物在掺杂MnO2土壤中的吸附量起显著的正效应,土壤质量对雌激素的吸附起负效应,土壤-水吸附体系的pH值对E2的吸附量起正效应而对E3起负效应.Langmuir吸附等温式能够描述雌激素在掺杂MnO2土壤中的热力学吸附行为(R2>0.99),吸附过程中雌激素化合物的ΔG均为负值,绝对值均小于40 kJ/mol,说明土壤吸附雌激素化合物为自发的物理吸附过程;掺杂MnO2土壤对雌激素的吸附既存在物理吸附作用,也存在化学降解作用.雌激素化合物的降解主要由于土壤中的有机碳增强了MnO2的导电性能,说明MnO2可以作为土壤固定化剂,能够有效地防止雌激素化合物因解吸作用而形成的"二次污染".     

镧掺杂的二氧化锰/碳纳米管电化学超级电容器复合电极

尽管在二氧化锰/多壁碳纳米管（MnO₂/MWCNTs）上获得了较高的比电容,低电导率仍是制约MnO₂担载量或膜厚度提高的主要障碍.另一个问题是MnO₂/MWCNTs的循环稳定性远低于活性炭.所以截止到目前这一新型材料的应用仍然受到很大的限制.本文采用原位还原的方法制备镧掺杂二氧化锰/多壁碳纳米管电化学超级电容器复合电极材料.分别通过透射电镜（TEM）、扫描电镜（SEM）、X射线衍射（XRD）和傅里叶变换红外（FTIR）光谱等技术对这些复合材料的形貌与结构进行了分析.采用循环伏安法、恒电流充放电法和交流阻抗法对其进行了电化学性能的研究.研究结果表明,通过还原MnO₄^-可以在MWCNTs上形成La掺杂MnO₂复合材料.La掺杂降低了复合电极的电阻,这是因为La的引入可以增大MnO₂的晶格缺陷,从而提高材料的电导率以及电极的电化学性能.因此La掺杂是克服MnO₂本征导电性差的有效途径之一.掺杂La可以在不增大电极电阻的情况下提高MnO₂的担载量或膜厚度.La掺杂的更重要的作用是使以MnO₂/MWCNTs作电极的对称电化学超级电容器的循环性能得到显著改善.此外,La掺杂也使复合电极的比电容得到一定程度的提高.     

Theoretical investigation of the reaction of Mn+ with ethylene oxide

The potential energy surfaces of Mn(+) reaction with ethylene oxide in both the septet and quintet states are investigated at the B3LYP/DZVP level of theory. The reaction paths leading to the products of MnO(+), MnO, MnCH(2)(+), MnCH(3), and MnH(+) are described in detail. Two types of encounter complexes of Mn(+) with ethylene oxide are formed because of attachments of the metal at different sites of ethylene oxide, i.e., the O atom and the CC bond. Mn(+) would insert into a C-O bond or the C-C bond of ethylene oxide to form two different intermediates prior to forming various products. MnO(+)/MnO and MnH(+) are formed in the C-O activation mechanism, while both C-O and C-C activations account for the MnCH(2)(+)/MnCH(3) formation. Products MnO(+), MnCH(2)(+), and MnH(+) could be formed adiabatically on the quintet surface, while formation of MnO and MnCH(3) is endothermic on the PESs with both spins. In agreement with the experimental observations, the excited state a(5)D is calculated to be more reactive than the ground state a(7)S. This theoretical work sheds new light on the experimental observations and provides fundamental understanding of the reaction mechanism of ethylene oxide with transition metal cations.     

Formation and characterization of mononuclear and dinuclear manganese oxide-dioxygen complexes in solid argon

A manganese atom reacts with dioxygen to form the previously characterized MnO 2 molecule in solid argon under UV-visible light irradiation. Subsequent sample annealing allows the dioxygen molecules to diffuse and to react with MnO 2 to give the (eta (2)-O 2)MnO 2 complex, which is characterized to be a side-on bonded peroxo manganese dioxide complex. The manganese tetraoxide MnO 4, which was predicted to be less stable than the (eta (2)-O 2)MnO 2 isomer, was not observed. However, the (eta (2)-O 2)MnO 2 complex reacts with another weakly coordinated dioxygen to give the (eta (2)-O 2)MnO 4 complex via visible light irradiation, in which the manganese tetraoxide is coordinated and stabilized by a side-on bonded O 2 molecule. Manganese dimer reacts with dioxygen to form the cyclic Mn(mu-O) 2Mn cluster spontaneously upon annealing, which further reacts with dioxygen to give the (eta (2)-O 2) 2Mn(mu-O) 2Mn cluster, a side-on bonded disuperoxide complex with a planar D 2 h structure.     

MnO2/ZSM-5上臭氧协同催化去除甲醛的性能研究

采用浸渍法制备了不同MnO2负载量的催化剂,用BET分析、X射线衍射等手段对其进行了分析,并考察了在MnO2/ZSM-5催化剂上臭氧协同催化去除甲醛的性能.结果显示:相对于单一的MnO2和ZSM-5,MnO2/ZSM-5复合催化剂具有更高的催化活性,其中10%MnO2/ZSM-5性能最佳,一次性去除效率可达到47%左右,制备所得到的催化剂有较强的稳定性,连续工作120h去除效率基本不变.     

Mechanistic and kinetic studies of crystallization of birnessite

Kinetic and mechanistic features have been studied for the crystallization of birnessite in aqueous systems via different synthesis methods: the oxidation of Mn2+, reduction of MnO4-, and redox reaction between Mn2+ and MnO4-. For oxidation methods, a topotactical conversion from Mn(OH)2 to birnessite via feitknechtite (beta-MnOOH) is observed. In reduction methods, birnessite evolves from the initially produced amorphous manganese oxide (AMO gel). For redox methods, both mechanisms exist, with the latter prevailing. A liquid mechanism is proposed to describe the reduction and redox synthesis, which comprises three stages: an induction period, a fast crystallization period, and a steady-state period. The redox method is accompanied by the formation and phase transformation of feitknechtite to birnessite. A method combining IR and XRD quantitation is proposed to detect nuclei in the induction period. Crystallization rates and apparent energies of activation of crystallization for reduction and redox methods are determined.     

Cu掺杂对LaMnO3催化剂的结构和催化氧化性能的影响

采用非晶态多核配合的方法合成了La1-xCuxMnO3(x=0、0.05、0.1、0.2、0.3、0.4、0.5)系列催化剂, 并用X射线衍射(XRD)、透射电镜(TEM)、比表面测定仪(BET)等手段对催化剂的微观结构进行了表征. 研究了Cu掺杂对钙钛矿结构及其对CO催化氧化发光性能及催化氧化CO、CH4性能的影响规律. 结果表明, 当x≤0.1 时, Cu掺杂仍可形成单相的钙钛矿结构; 当x>0.1时, 过量掺杂的Cu以CuO杂相存在. Cu掺杂可改善La1-xCuxMnO3催化剂对CO和CH4的催化氧化活性. 经700 ℃焙烧3 h制备的La0.9Cu0.1MnO3催化剂具有最高CO催化氧化活性(T100%=170 ℃), 该结果与CO催化氧化发光结果一致.而La0.95Cu0.05MnO3催化剂对CH4的催化氧化活性最高(T95%=705 ℃).     

MnO2纳米粒子固载纤维素酶用于高效水解农业废弃物制备生物乙醇

纤维素酶是一种有效的纤维质类物质水解催化剂,工业应用时可通过固定化纤维素酶来降低其成本。本文将烟曲霉原变种JCF产生的纤维素酶固定在MnO2纳米颗粒上。 MnO2可提高纤维素酶的活性,并充当一个更好的载体。采用扫描电镜表征了所制MnO2纳米粒子及其负载纤维素酶的表面性质,以傅里叶变换红外光谱分析了固定在MnO2纳米粒子上纤维素酶的官能团性质。纤维素酶在MnO2纳米粒子上最大的固定化效率为75%。考察了固定化纤维素酶的活性、操作pH值、温度、热稳定性和重复使用性等性质。结果表明,所制固定化酶的稳定性比游离酶更高。固定于MnO2纳米粒子上的纤维素酶可用于纤维质类物质的水解反应,且能在较宽的温度和pH值范围内使用。表征结果证实了该催化剂具有非常高的催化纤维素类物质水解的活性。