二氧化锰作为重要过渡金属氧化物具有储备丰富、环境友好、工作电压窗较宽等优点, 在电极材料、电致变色、催化、生物传感器等领域都有广泛的应用前景[1,2,3]。二氧化锰经常含有少量的其它锰氧化物和化合水[4], 分子式表示为MnOx (x<2)[5,6]。将二氧化锰纳米化后, 其颗粒尺寸变小、比表面积增大[7], 从而使离子的传输速率、催化效率等都有了进一步的提升。除上述原因外, 纳米二氧化锰多变的晶型也是它受到研究人员重视的主要原因之一。二氧化锰有α、β、δ等晶型, 按[MnO6]的连接方式不同, 又可分为链状或隧道状结构[5,6]。这些原因促使纳米二氧化锰在能源、光电、环境、生物医学等领域有着广泛的应用。
1 纳米二氧化锰的制备方法
1.1 水热法
水热法是指在一定温度的密闭条件下, 以水为溶剂的溶液产生压力, 使得反应物之间发生反应从而生成特定产物的制备方法[11]。水热法有诸多优点, 例如不受模板的约束、初始反应物不必具有可溶性; 通过选择适合的温度、时间等, 可以较为方便地合成纳米材料; 在密闭空间进行合成, 最大限度地减少了外界的干扰, 极大地提高了生成产物的纯度, 是一种在实际操作中较为常用的合成方法。水热合成法制备的纳米二氧化锰材料具有纯度高、分散性好、晶型完整、晶粒大小可控等优点。但由于要保持高温高压的合成环境, 较其它合成方法更繁琐。Zhao等[12]将制备好的中空碳纳米纤维加入到KMnO4溶液中, 经120 ℃水热反应2 h合成了表面有δ-MnO2纳米片的中空碳纳米纤维, 得到了可用于高性能非对称超级电容器的超薄MnO2纳米薄片/中空碳纳米纤维的纳米复合材料。Wu等[13]利用沸石咪唑酯框架材料作为自模板, 在碳布上水热制备了MnO2空心纳米片结构, 纳米片厚度为10 nm左右, 制备过程如图1所示。MnO2空心多面体具有较大的比表面积, 易于实现电解质的渗透、抑制体积膨胀, 而碳布基板促进电子传输, 进一步提高了锌离子的存储性能。Lu等[14]以KMnO4和乙醇混合溶液为反应溶液, 经120 ℃水热反应2 h后得到了直径为12 nm的α-MnO2纳米线, 并将其应用在Li-O2电池的电催化中。利用水热合成方法可以制备形貌各异的二氧化锰纳米结构, 除上述所提到的结构外, 还有纳米颗粒、纳米棒、纳米晶须、纳米管、纳米花束以及球壳结构等[15,16,17,18,19,20]。
图1
1.2 溶胶-凝胶法
作为一种常见的材料合成工艺, 溶胶-凝胶法主要是通过水解缩聚金属醇盐或无机盐并使其逐渐变成凝胶, 经过相应处理后得到粉体材料的合成方法[21]。溶胶-凝胶法制备的产物具有化学尺度的均匀分散性以及高纯度。但由于反应周期长, 煅烧过程会产生团聚, 因此通常与其它合成方法例如模板法等相结合使用[22], 以改善溶胶-凝胶法自身的不足, 制备出较为完善、规整的纳米材料。Wang等[23]将溶胶-凝胶法与模板法相结合, 首先配制Mn(CH3COO)2、柠檬酸和正丙醇的混合溶液, Mn2+与柠檬酸的摩尔比为1 : 2, 通过添加NH3·H2O调节pH至8.5。将该混合溶液在80 ℃下加热醚化, 提取过量的正丙醇。当溶液变成透明的粘性溶胶时, 将溶胶倒入制备好的多孔氧化铝(AAO)中, 80 ℃常压干燥2 h, 400 ℃加热12 h, 得到MnO2纳米线。图2(a, b)分别是利用磷酸将AAO扩孔20 min获得的模板A和扩孔40 min获得的模板B生成的MnO2纳米线的扫描电镜照片。赵娜英等[24]配制Mn(CH3COO)2、柠檬酸和La(NO3)3·6H2O混合溶液, 并用NH3·H2O调节溶液pH至6, 在80 ℃加热、110 ℃脱水, 煅烧10 h, 90 ℃酸化, 洗涤至中性后, 干燥, 获得镧掺杂MnO2复合材料。李哲等[25]以Mn(CH3COO)2、柠檬酸和硅藻土作为原料, 用溶胶-凝胶法制备出纳米MnO2和纳米MnO2负载硅藻土的复合材料并将其用于吸附苯酚。
图2
1.3 化学沉淀法
化学沉淀法在高纯度纳米粒子液相合成中应用较为广泛, 是指在水溶液中通过调节反应条件将溶解于其中的金属盐转变为难溶化合物或水合氧化物而析出, 经过进一步处理得到纳米材料的方法[26]。化学沉淀法包括共沉淀法、均匀沉淀法、氧化水解法、还原法等。化学沉淀法有反应温度较低、操作简单、成本低等优点, 但也存在诸如生成物均匀性较差、易发生硬团聚等缺点。通过改变反应物浓度、调节溶液pH可以有效改善这一情况, 化学沉淀法为批量生产纳米材料提供了很好的选择。Li等[27]利用化学氧化聚合法获得Ti3C2Tx@PDA(聚多巴胺)粉末, 将其溶于超纯水中, 加入KMnO4溶液, 以十六烷基三甲基溴化铵(CTAB)和聚乙二醇(PEG)作为表面活性剂, 利用液相共沉淀法制备不同形貌的Ti3C2Tx@MnO2复合材料。其中MnO2的形貌包括纳米片状、米粒状、纳米花状、纳米线状。米粒状MnO2长度约为100 nm, 纳米片状则可以在表面活性剂的作用下团聚成纳米花状, 其直径为100 nm。Mahamallik等[28]利用KMnO4和MnCl2·4H2O (摩尔比2 : 3)通过氧化还原共沉淀法合成了MnO2纳米片。在磁力搅拌下, 将KMnO4溶液(2 mmol/L, 100 mL)以5 mL/min的速率滴加入MnCl2溶液(3 mmol/L, 100 mL)中, 分离出棕色沉淀, 在90 ℃温度下干燥4 h, 再一次将干燥的固体通过搅拌重新分散在水中, 经适当清洗得到上清液, 用离心法将物料从液体中分离出来, 在90 ℃下干燥12 h, 即得到具有微孔结构的MnO2纳米片, 其比表面积为301 m2/g, 孔径为0.364 nm (图3)。
图3
1.4 固相合成法
固相合成法是采用较低温度通过固化反应生成纳米二氧化锰的合成方法, 反应过程主要是通过固体反应物高速球磨等。因实验方法简单、环境污染较小、生成物产量高、反应选择性较好, 固相合成法为纳米材料的合成提供了一种简单、高效、低价的方法。但由于二氧化锰本身的固有特性, 采用此方法不宜合成单晶型的纳米级产物。吴昊天等[29]按照一定比例混合KMnO4和MnCl2·4H2O, 在研钵中研细, 80 ℃水浴3 h, 离心洗涤后, 80 ℃烘干获得纳米棒状MnO2。随着反应物MnCl2·4H2O比例的不断增大, 获得纳米棒状MnO2的直径与长度都不断增大, KMnO4和MnCl2·4H2O的摩尔比为2:2、2:3、2:4时产物的长径比分别为7、9、12。龚良玉[30]利用表面活性剂辅助固相合成法制备了直径为10~ 15 nm、长度为100~150 nm的α-MnO2纳米棒。李娟等[31]将摩尔比相同的Mn(CH3COO)2与柠檬酸混合均匀, 于玛瑙研钵中研磨30 min以上。待体系颜色不再变化时, 在50~60 ℃反应10 h, 在马弗炉中300 ℃煅烧10 h。之后在2 mol/L H2SO4中于80~90 ℃酸化处理1~2 h, 冷却后用蒸馏水洗涤至中性, 105 ℃烘干10 h, 取出研细, 所得产物是粒径为20~30 nm的球形纳米γ-MnO2颗粒。
2 纳米二氧化锰的应用
2.1 储能电极
二氧化锰可作为电池的正极材料[32], 较广泛地应用于锌/二氧化锰电池、镁/二氧化锰电池和碱性锌/二氧化锰电池等。因二氧化锰的电容性较好, 在超级电容器中可替代高价的氧化钌作为电极材料。Wang等[16]利用微波辅助水热法制备直径为200 nm的纳米花状δ-MnO2, 并将其作为超级电容器的电极材料。在1 mol/L Na2SO4电解质溶液中, 2.1 A/g的电流密度下测得其电容与循环性能如图4所示。δ-MnO2在初始400次循环中比电容快速降低, 可能是由于材料的循环收缩和膨胀以及材料在集流器上的弱结合造成电极中松散材料出现损失。经过400次循环后, 材料的比电容保持相对稳定。经过5000次循环后, 比电容为初始值的89%, 表明该材料具有良好的充放电循环稳定性。Shafi等[33]用化学沉淀法合成了α-MnO2纳米晶, 对制备的样品进行不同温度的退火处理, 并进行电化学性能测试。结果显示, MnC4.5即纯相α-MnO2纳米晶是超级电容器较佳的电极材料。在MnO2的不同晶型中, α-MnO2在超级电容器中应用较为广泛。近年来随着技术的不断进步, 纳米MnO2在电极材料方面的应用更加多样, 涵盖面也更加广泛[34,35,36]。由于二氧化锰的晶型复杂, 随着反应条件的改变极易发生变化, 且随着对储能材料性能要求的不断提高, 单一材料已不能满足当前对能量密度等的需求, 调控二氧化锰的晶型和制备复合材料成为当前的研究重点。含锰复合氧化物作为电池正极材料的应用较广泛, 其中LiMn2O4正极材料为尖晶石结构, 理论容量为148 mAh/g; 以高纯度的Mn3O4作为原料, 可进一步提高其容量并改善循环稳定性, 主要是因为Mn3O4与LiMn2O4有类似的结构, 制备过程中结构不会发生剧烈变化[37]。LiMnPO4正极材料为橄榄石结构, 结构较稳定, 能量密度与放电平台均比相同结构的LiFePO4高, 但其导电性能与倍率性能较差, 循环稳定性不高[38]。针对上述问题, 科研工作者发现通过纳米化以及对晶面进行筛选可以改善这一情况, 从而提高其电化学性能[39]。上述材料作为锂离子动力电池的正极材料已有产业化应用, 在新能源汽车领域具有良好的应用前景。
图4
2.2 电致变色器件
电致变色是一种通过外加电压实现离子的注入与抽出, 从而达到颜色变化的现象[40,41]。由于电致变色材料具有在电场作用下改变颜色的特性, 在智能窗[42,43,44]、防眩后视镜[45]、显示器[46]以及防眩滑雪镜等方面均具有广泛的应用。纳米二氧化锰自身价态丰富, 颗粒尺寸较小, 比表面积较大, 离子、电子传输速率快, 因而适合应用于电致变色器件。但由于纯二氧化锰本身的颜色主要是在棕色和黄色之间变化, 光调制幅度较小, 需要将其与其它光调制幅度较大的材料进行复合。Zhou等[47]利用恒电位阳极电沉积法制备聚苯胺/二氧化锰(PANI/MnO2)杂化电致变色薄膜。PANI的电聚合和MnO2的电沉积同时发生, 合成的纳米MnO2可以作为氧化剂, 进一步改善PANI的化学聚合, 促进杂化膜的快速生长。这种独特的沉积机制产生的PANI/MnO2杂化电致变色薄膜较纯PANI膜在形貌、结构、电化学和电致变色性能上有巨大差异, 显示出更高的光学对比度、着色效率和循环稳定性(图5)。杂化膜的优异性能可以归功于其相互连接的纳米粒子的多孔形貌, 以及PANI与MnO2之间的施主—受体相互作用。Sakai等[48]通过将层状质子锰氧化物H0.13MnO2·0.7H2O降解为胶体单层, 合成了厚度为0.5 nm左右的MnO2纳米片。通过静电自组装的方法, 将MnO2纳米片沉积在氧化铟锡(ITO)透明导电玻璃上。相关电化学测试表明, 随着MnO2纳米片层数的增加, 氧化还原峰线性增强。尽管纳米片的规则堆积结构在最初的几个扫描周期中已经崩溃, 但是纳米片本身对CV循环保持稳定。MnO2纳米片电极表现出阳极电致变色, 着色效率高。吸光度的变化与MnO2纳米片的层数成正比, 通过控制MnO2纳米片的层数, 可以很容易地实现光密度的调控。Falahatgar等[49]采用浸涂溶胶-凝胶法在300 ℃的空气中, 于ITO玻璃上沉积了Zn和Mn摩尔比分别为8%、16%和25%的MnO2-ZnO纳米颗粒薄膜样品, 对薄膜的结构、表面、光学和电致变色性能进行了研究。测试结果表明, 制备的样品为无定形态, 在20和50 mV/s的扫描速率下, 薄膜的电致变色性能取决于Zn与Mn的组成比。
图5
图5
(a) PANI、(b) MnO2和(c) PANI/MnO2在不同电压下的紫外-可见光透过率光谱, (c)中的插图为PANI/MnO2杂化膜电沉积在ITO/玻璃上的褪色态(上, 浅绿黄色)和着色态(下, 深青绿色)的照片; (d) PANI、MnO2和PANI/MnO2杂化膜在λ680nm (-0.4 V/+0.4 V, 每周期60 s)的响应时间曲线[47]
Fig. 5
UV-Vis transmittance spectra of (a) PANI, (b) MnO2, and (c) PANI/MnO2 at different potentials with insets in (c) showing the photos of PANI/MnO2 hybrid film electrodeposited on ITO/glass at bleached (upper, light greenish yellow) and colored state (lower, dark bluish green), and (d) switching curves comparison between PANI, MnO2, and PANI/MnO2 hybrid films at λ680 nm (-0.4 V/+0.4 V, 60 s/cycle)[47]
2.3 催化剂
由于纳米二氧化锰具有良好的氧化还原特性以及特有的纳米尺寸效应, 因此在催化领域有较为广泛的应用。不同形貌的纳米二氧化锰的吸附效果有所差异并且对吸附物的影响较大, 目前主要是对反应条件进行精细化的控制, 生成特定的形貌从而满足相关催化需求。Lyu等[50]采用共沉淀法合成了MgAl层状双氢氧化物(LDHs)。LDHs在550 ℃的空气中煅烧10 h获得层状双氧化物(LDOs), 将制备的LDOs加入巯丙基三甲氧基硅烷(MPTS)甲苯溶液中, 在Ar气氛中回流, 过滤得到固体。用乙醇洗涤固体, 在80 ℃下干燥, 得到LDO-Si(SH)。将LDO-Si(SH)或LDO分散于0.1 mol/L KMnO4水溶液中, 然后在Ar气氛、80 ℃下剧烈搅拌。过滤后的固体用热去离子水洗涤, 然后在90 ℃下真空干燥4 h, 得到LDH-Si(SH)-Mn或LDH-Mn。LDH-Mn和LDH-Si(SH)-Mn具有显著的乙苯转化率, 表明Mn物种主要负责氧化活性。在没有过氧化氢叔丁基(TBHP)作为引发剂的情况下, LDH-Si(SH)-Mn的乙苯转化率仅为0.7%, 而添加少量TBHP后转化率达到29.5%, 说明TBHP起到了启动催化剂的作用。Wang等[51]利用水热法和CCl4溶剂法分别制备了纳米棒状、类丝状、管状α-MnO2和花状球形Mn2O3, 如图6(a)所示。各个样品的催化性能为棒状α-MnO2>管状α-MnO2>花状Mn2O3>线状α-MnO2, 如图6(b)所示。α-MnO2纳米棒的优异的催化性能可能与高氧含量和良好的低温还原性有关, 这种一维锰氧化物材料在催化消除空气污染物中有较广阔的发展前景。
图6
图6
(a)纳米棒状、类丝状、管状α-MnO2和花状球形Mn2O3的SEM照片; (b)在甲苯浓度为10-3、甲苯/O2的摩尔比为1/400和空速为20000 mL/(g⋅h)的条件下甲苯的转化率随反应温度的变化曲线[51]
Fig. 6
(a) SEM images of rod-like α-MnO2, wire-like α-MnO2, tube-like α-MnO2, and flower-like Mn2O3; (b) Toluene conversion as a function of reaction temperature over the catalysts under the conditions of a toluene concentration of 10-3, toluene/ O2 = 1/400 (mol/mol), and a space velocity of 20000 mL/(g⋅h)[51]
2.4 生物传感器
生物传感器是一种结合对生物或生物衍生敏感元件的精密分析器件, 与理化换能器产生间断或连续的数字信号, 被分析物的含量由信号强度与被分析物成比例关系来确定。纳米二氧化锰由于具有宏观量子隧道效应、小尺寸效应等纳米效应, 能够增大电流响应, 降低检出限, 使检测的灵敏度大大提高, 近年来在生物传感器领域逐渐被大家重视并得到广泛应用。为了使生物传感器中的二氧化锰更好地与检测物接触, 可以将它与比表面积较大的其它材料进行复合或提高其自身的比表面积。Qi等[52]以MnO2纳米片作为辅助, 利用配体-DNA相互作用和基于荧光偏振的方法来检测Ag+。在预先形成的普罗黄素(配体)-DNA复合物中加入Ag+可诱导释放普罗黄素, 从而引起荧光极化的微弱变化, MnO2纳米片可以放大这种荧光变化。图7表明, 荧光偏振差值(ΔFP)与Ag+的浓度之间具有良好的线性关系。该方法进一步阐明存在MnO2纳米片时加入Ag+的过程中引起荧光偏振变化的机理。这些研究表明, 目前的MnO2纳米片辅助荧光偏振生物传感器是一种很有前途的检测环境水样中Ag+的工具。Xiao等[53]制备了一种基于PtAu合金和MnO2二元纳米复合材料修饰的石墨烯纸的新型柔性电化学传感器。通过一步无模板电沉积在衬底上生长珊瑚状PtAu-MnO2纳米复合材料, 使PtAu合金、MnO2与基体密切接触。柔性电极具有独特的结构和电化学性能, 如更好的均匀性、更大的活性比表面积和更快的电子转移。在非酶葡萄糖检测中, PtAu-MnO2二元纳米结构修饰的石墨烯纸表现出良好的传感性能。
图7
3 结语
虽然纳米二氧化锰的制备及应用取得了显著进展, 但仍需要研究纳米二氧化锰的可控制备方法及制备与性能之间的关系, 以期进一步提升性能, 满足更高的使用要求。当前含锰氧化物在电池正极材料的应用已经进入了产业化阶段。现有新能源汽车的发展大幅度提升了对电池正极材料的能量密度的要求, 而锂电池在向着高容量、低成本的发展过程中含锰复合材料起着重要推动作用。由于二氧化锰的晶型多变、反应过程中存在副反应, 使其发展存在诸多壁垒。为了改善二氧化锰材料的性能, 未来除了体相掺杂、表面包覆、使用梯度材料等方法, 还需要对材料的形貌与尺寸进行精细控制, 提高材料的循环性能。未来纳米二氧化锰的研究与高容量富锂正极/碳负极锂离子电池正极材料的发展密切相关, 将向着与其他材料复合的方向发展, 从而更好地满足正极材料对性能的需求。由于单一纳米二氧化锰作为电致变色材料的光调制幅度较小, 未来主要是与其它材料复合来增强材料的性能, 或者与光调制幅度较大的材料制备互补型电致变色器件来改善电致变色器件的性能。只有不断探索材料性能与材料自身的尺寸、晶型、形貌等之间的关系, 掌握其规律, 纳米二氧化锰才能被更好地开发与利用, 实现产业化应用。
参考文献
Nano-MnO2-mediated transformation of triclosan with humic molecules present: kinetics, products, and pathways
DOI:10.1007/s11356-018-1637-7
URL
PMID:29525863
[本文引用: 1]
It has been shown that manganese dioxide (MnO2) can mediate transformation of phenolic contaminants to form phenoxyl radical intermediates, and subsequently, these intermediates intercouple to form oligomers via covalent binding. However, the reaction kinetics and transformation mechanisms of phenolic contaminants with humic molecules present in nano-MnO2-mediated systems were still unclear. In this study, it was proven that nano-MnO2 were effective in transforming triclosan under acidic conditions (pH 3.5-5.0) during manganese reduction, and the apparent pseudo first-order kinetics rate constants (k = 0.0599-1.5314 h(-1)) increased as the pH decreased. In particular, the transformation of triclosan by nano-MnO2 was enhanced in the presence of low-concentration humic acid (1-10 mg L(-1)). The variation in the absorption of humic molecules at 275 nm supported possible covalent binding between humic molecules and triclosan in the nano-MnO2-mediated systems. A total of four main intermediate products were identified by high-resolution mass spectrometry (HRMS), regardless of humic molecules present in the systems or not. These products correspond to a suite of radical intercoupling reactions (dimers and trimers), ether cleavage (2,4-dichlorophenol), and oxidation to quinone-like products, triggered by electron transfer from triclosan molecules to nano-MnO2. A possible reaction pathway in humic acid solutions, including homo-coupling, decomposition, oxidation, and cross-coupling, was proposed. Our findings provide valuable information regarding the environmental fate and transformation mechanism of triclosan by nano-MnO2 in complex water matrices.
Intercalation and conversion reactions of nanosized β-MnO2 cathode in the secondary Zn/MnO2 alkaline battery
A three-dimensional graphene/ CNT/MnO2 hybrid as supercapacitor electrode
General synthesis of MnOx (MnO2, Mn2O3, Mn3O4, MnO) hierarchical microspheres as lithium-ion battery anodes
Manganese oxide porous crystals
Manganese oxide minerals: crystal structures and economic and environmental significance
Interfacial synthesis of δ-MnO2 nano-sheets with a large surface area and their application in electrochemical capacitors
Preparation of manganese dioxide for oxygen reduction in zinc air battery by hydro thermal method
Characterization of MnO2 aerogels prepared via supercritical drying technique
Synthesis and electochemical capacity of MnO2/SMWCNT/PANI ternarycomposites
Continuous hydrothermal synthesis of inorganic nanoparticles: applications and future directions
DOI:10.1021/acs.chemrev.6b00417
URL
PMID:28771006
[本文引用: 1]
Nanomaterials are at the leading edge of the emerging field of nanotechnology. Their unique and tunable size-dependent properties (in the range 1-100 nm) make these materials indispensable in many modern technological applications. In this Review, we summarize the state-of-art in the manufacture and applications of inorganic nanoparticles made using continuous hydrothermal flow synthesis (CHFS) processes. First, we introduce ideal requirements of any flow process for nanoceramics production, outline different approaches to CHFS, and introduce the pertinent properties of supercritical water and issues around mixing in flow, to generate nanoparticles. This Review then gives comprehensive coverage of the current application space for CHFS-made nanomaterials including optical, healthcare, electronics (including sensors, information, and communication technologies), catalysis, devices (including energy harvesting/conversion/fuels), and energy storage applications. Thereafter, topics of precursor chemistry and products, as well as materials or structures, are discussed (surface-functionalized hybrids, nanocomposites, nanograined coatings and monoliths, and metal-organic frameworks). Later, this Review focuses on some of the key apparatus innovations in the field, such as in situ flow/rapid heating systems (to investigate kinetics and mechanisms), approaches to high throughput flow syntheses (for nanomaterials discovery), as well as recent developments in scale-up of hydrothermal flow processes. Finally, this Review covers environmental considerations, future directions and capabilities, along with the conclusions and outlook.
Nanocomposites of hierarchical ultrathin MnO2 nanosheets/hollow carbon nanofibers for high-performance asymmetric supercapacitors
Boosted Zn storage performance of MnO2 nanosheet-assembled hollow polyhedron grown on carbon cloth via a facile wet-chemical synthesis
DOI:10.1002/cssc.201903006
URL
PMID:31797574
[本文引用: 3]
Aqueous zinc-ion batteries (ZIBs) have been considered as prospective alternatives for lithium-ion batteries, which are able to serve as power sources for next-generation wearable and flexible devices, owing to the merits of abundant zinc resources and high safety of aqueous electrolyte. However, the lack of suitable cathode materials with flexibility for ZIBs hinders their further application. Herein, a novel cathode material [i.e., MnO2 nanosheet-assembled hollow polyhedron anchored on carbon cloth (MnO2 /CC)] was prepared through a rapid hydrothermal method by using ZIF-67 as self-sacrificing template. When tested in an aqueous ZIB, the MnO2 /CC delivered a high reversible capacity of 263.9 mAh g(-1) at 1.0 A g(-1) after 300 cycles, far exceeding those of the commercial MnO2 electrode. More importantly, benefiting from the unique structural advantages, a flexible ZIB assembled based on the MnO2 /CC displayed a stable output voltage of 1.53 V and a specific capacity of 91.7 mAh g(-1) at 0.1 A g(-1) after 30 cycles. It also successfully lit LED bulbs even under different bending angles, showing good flexibility. This research contributes to the development of MnO2 -based cathode materials for high-performance flexible ZIBs.
Synthesis of α-MnO2 nanowires via facile hydrothermal method and their application in Li-O2 battery
Investigating the effect of MnO2 band gap in hybrid MnO2-Au materials over the SPR-mediated activities under visible light
Synthesis of δ-MnO2 with nanoflower-like architecture by a microwave-assisted hydrothermal method. Journal of Sol-Gel Science and
Hydrothermal synthesis and characterization of surface-modified δ-MnO2 with high Fenton-like catalytic activity
Preparation of Fe-MnO2/RGO electrode and electrochemical properties
Preparation of MnO2/porous carbon material with core-shell structure and its application in supercapacitor
One step synthesis of bifunctional iron-doped manganese oxide nanorods for rechargeable zinc-air batteries
Electrochromic properties of Sol-Gel prepared hybrid transition metal oxides - a short review
DOI:10.1016/j.jsamd.2017.08.005 URL [本文引用: 1]
Carbon as amorphous shell and interstitial dopant in mesoporous rutile TiO2: bio-template assisted Sol-Gel synthesis and photocatalytic activity
DOI:10.1016/j.apsusc.2016.09.145 URL [本文引用: 1]
Sol-Gel template synthesis of highly ordered MnO2 nanowire arrays
Synthesis of layered double hydroxides containing Mg2+, Zn2+, Ca2+ and Al3+ layer cations by co-precipitation methods-a review
Manganese dioxide morphology on electrochemical performance of Ti3C2Tx@MnO2 composites
Tetracycline degradation in aquatic environment by highly porous MnO2 nanosheet assembly
A review on mechanistic understanding of MnO2 in aqueous electrolyte for electrical energy storage systems
Structural evolution of tetragonal MnO2 and its electrochemical behavior
Mechanism of Zn insertion into nanostructured δ-MnO2: a nonaqueous rechargeable Zn metal battery
Silver nanowire/MnO2 nanowire hybrid polymer nanocomposites: materials with high dielectric permittivity and low dielectric loss
DOI:10.1021/acsami.6b14948
URL
PMID:28378996
[本文引用: 1]
This study reports the fabrication of hybrid nanocomposites based on silver nanowire/manganese dioxide nanowire/poly(methyl methacrylate) (AgNW/MnO2NW/PMMA), using a solution casting technique, with outstanding dielectric permittivity and low dielectric loss. AgNW was synthesized using the hard-template technique, and MnO2NW was synthesized employing a hydrothermal method. The prepared AgNW:MnO2NW (2.0:1.0 vol %) hybrid nanocomposite showed a high dielectric permittivity (64 at 8.2 GHz) and low dielectric loss (0.31 at 8.2 GHz), which are among the best reported values in the literature in the X-band frequency range (8.2-12.4 GHz). The superior dielectric properties of the hybrid nanocomposites were attributed to (i) dimensionality match between the nanofillers, which increased their synergy, (ii) better dispersion state of AgNW in the presence of MnO2NW, (iii) positioning of ferroelectric MnO2NW in between AgNWs, which increased the dielectric permittivity of nanodielectrics, thereby increasing dielectric permittivity of the hybrid nanocomposites, (iv) barrier role of MnO2NW, i.e., cutting off the contact spots of AgNWs and leading to lower dielectric loss, and (v) AgNW aligned structure, which increased the effective surface area of AgNWs, as nanoelectrodes. Comparison of the dielectric properties of the developed hybrid nanocomposites with the literature highlights their great potential for flexible capacitors.
Integrated design of MnO2@carbon hollow nanoboxes to synergistically encapsulate polysulfides for empowering lithium sulfur batteries
Fabrication of scandium-doped lithium manganese oxide as a high-rate capability cathode material for lithium energy storage
Porous nest-like LiMnPO4 microstructures assembled by nanosheets for lithium ion battery cathodes
An underlying intercalation ion for fast-switching and stable electrochromism
Electrochromic triphenylamine-based cobalt (II) complex nanosheets
Normally transparent smart window based on electrically induced instability in dielectrically negative cholesteric liquid crystal
Achieving rapid Li-ion insertion kinetics in TiO2 mesoporous nanotube arrays for bifunctional high-rate energy storage smart windows
DOI:10.1039/c7nr07703c
URL
PMID:29384164
[本文引用: 1]
Smart electrochromic windows integrated with electrochemical energy storage capacity are receiving increasing interest for green buildings. However, the fabrication of bifunctional devices that demonstrate high-rate capability with stable and desirable optical modulation still remains a great challenge. Herein, a facile sacrificial template-accelerated hydrolysis approach is presented to prepare a designed lithium-ion insertion-type material layer on a fluorine-doped tin oxide substrate, with TiO2 mesoporous nanotube array (MNTA) film as an example, with rapid Li-ion insertion kinetics and without sacrificing window transparency, to meet requirements. A bifunctional device is assembled to exhibit the optical-electrochemical superiority of MNTA nanostructures. The as-assembled bifunctional smart window exhibits strong electrochromic contrast and high-rate capability in the fast galvanostatic charge/discharge process. For instance, at 1 A g(-1), it completes the charge or discharge process within only 232 s and delivers a high, reversible and stable specific capacity of 60 mA h g(-1), accompanying obvious transmittance modulation in the visible spectrum, with a typical value of ca. 30.4% at 700 nm, and strong color changes between deep blue and transparency.
Smart electrochromic windows to enhance building energy efficiency and visual comfort
Photoelectrochromic windows and displays
Nanotube-based ultrafast electrochromic display
Rapid one-pot electrodeposition of polyaniline/manganese dioxide hybrids: a facile approach to stable high-performance anodic electrochromic materials
Electrochromic films composed of MnO2 nanosheets with controlled optical density and high coloration efficiency
Electrochromic performance of Sol-Gel derived amorphous MnO2-ZnO nanogranular composite thin films
Silylated MgAl LDHs intercalated with MnO2 nanowires: highly efficient catalysts for the solvent-free aerobic oxidation of ethylbenzene
Manganese oxides with rod-, wire-, tube-, and flower-like morphologies: highly effective catalysts for the removal of toluene
DOI:10.1021/es204038j
URL
PMID:22413904
[本文引用: 3]
Nanosized rod-like, wire-like, and tubular alpha-MnO(2) and flower-like spherical Mn(2)O(3) have been prepared via the hydrothermal method and the CCl(4) solution method, respectively. The physicochemical properties of the materials were characterized using numerous analytical techniques. The catalytic activities of the catalysts were evaluated for toluene oxidation. It is shown that alpha-MnO(2) nanorods, nanowires, and nanotubes with a surface area of 45-83 m(2)/g were tetragonal in crystal structure, whereas flower-like spherical Mn(2)O(3) with a surface area of 162 m(2)/g was of cubic crystal structure. There were the presence of surface Mn ions in multiple oxidation states (e.g., Mn(3+), Mn(4+), or even Mn(2+)) and the formation of surface oxygen vacancies. The oxygen adspecies concentration and low-temperature reducibility decreased in the order of rod-like alpha-MnO(2) > tube-like alpha-MnO(2) > flower-like Mn(2)O(3) > wire-like alpha-MnO(2), in good agreement with the sequence of the catalytic performance of these samples. The best-performing rod-like alpha-MnO(2) catalyst could effectively catalyze the total oxidation of toluene at lower temperatures (T(50%) = 210 degrees C and T(90%) = 225 degrees C at space velocity = 20,000 mL/(g h)). It is concluded that the excellent catalytic performance of alpha-MnO(2) nanorods might be associated with the high oxygen adspecies concentration and good low-temperature reducibility. We are sure that such one-dimensional well-defined morphological manganese oxides are promising materials for the catalytic elimination of air pollutants.
MnO2 nanosheet-assisted ligand-DNA interaction-based fluorescence polarization biosensor for the detection of Ag+ ions
DOI:10.1016/j.bios.2016.08.093
URL
PMID:27614012
[本文引用: 3]
Silver (Ag(+)) ions are highly toxic to aquatic organisms and accumulate in the human body via the food chain. Therefore, the development of sensitive and selective quantitative analytical methods for detecting trace amounts of these ions is necessary. In the present study, a MnO2 nanosheet-assisted, ligand-DNA interaction and fluorescence polarization-based method was developed, for the first time, for sensitive detection of Ag(+). The addition of Ag(+) to the preformed proflavine-DNA complex induced the release of proflavine, which elicited weak changes in fluorescence polarization. The subsequent addition of MnO2 nanosheets magnified the observed changes, making this a feasible method for the detection of Ag(+). The calibration graphs indicated good linearity over the concentration ranges of 30-240nM for Ag(+), with a detection limit (S/N=3) of 9.1nM. This method additionally exhibits high selectivity. The mechanism underlying the changes in fluorescence polarization caused by the addition of Ag(+) in the presence of MnO2 nanosheets was further explored in this study. These findings demonstrate that the present MnO2 nanosheet-assisted fluorescence polarization biosensor may represent a promising tool for the detection of Ag(+) ions. The results for practical detecting Ag(+) proved that this biosensor can be applied to environmental water sample analysis.
Growth of coral-like PtAu-MnO2 binary nanocomposites on free-standing graphene paper for flexible nonenzymatic glucose sensors
DOI:10.1016/j.bios.2012.08.062
URL
PMID:23036772
[本文引用: 1]
The growing demand for compact point-of-care medical devices and portable instruments for on-site environmental sampling has stimulated intense research on flexible sensors that can be miniaturized and function under considerable physical deformation. We report a new type of flexible electrochemical biosensors based on free-standing graphene paper carrying binary nanocomposites of PtAu alloy and MnO(2). The coral-like PtAu-MnO(2) nanocomposites are grown on the substrate through one-step template-free electrodeposition, leading to an intimate contact between the PtAu alloy and MnO(2) matrix. The flexible electrode exhibits a unique set of structural and electrochemical properties such as better uniformity, larger active surface areas, and faster electron transfer in comparison with the control electrode prepared by tandem growth of MnO(2) network and PtAu alloy in two steps. In nonenzymatic amperometric glucose detection, the PtAu-MnO(2) binary nanostructure-decorated graphene paper has shown greatly enhanced sensing performance such as wide liner range (0.1 mM to 30.0 mM), high sensitivity (58.54 muA cm(-2) mM(-1)), low detection limit (0.02 mM, S/N=3), satisfactory selectivity, excellent reproducibility and stability, and tolerability to mechanical stress. The strategy of co-growth of metal and metal oxides on freestanding carbon substrates opens new possibility to develop high-performance flexible electrochemical sensors.
