Synthesis of single-crystalline hollow β-FeOOH nanorods via a controlled imcomplete-reaction coure

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Synthesis of single- crystalline hollow β- FeOOH nanorods via a controlled imcomplete- reaction coure 溶溶溶溶溶溶溶溶

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溶液合成方法举例. Synthesis of single-crystalline hollow β-FeOOH nanorods via a controlled imcomplete-reaction coure. Abstract. Single-crystalline β -FeOOH hollow nanorods have been synthesized though a two-step route. The formation process of hollow space is from inside to outside. - PowerPoint PPT Presentation

Transcript of Synthesis of single-crystalline hollow β-FeOOH nanorods via a controlled imcomplete-reaction coure

Page 1: Synthesis of single-crystalline hollow β-FeOOH nanorods via a controlled imcomplete-reaction coure

Synthesis of single-crystalline hollow β-FeOOH nanorods via a controlled imcomplete-reaction coure

溶液合成方法举例

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Abstract

•Single-crystalline β-FeOOH hollow nanorods have been synthesized though a two-step route. The formation process of hollow space is from inside to outside.

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• Recently, much effort has been devoted to synthesis of hollow inorganic materials because of their low density and high surface area compared with bulk materials. These materials may be find a wide range of potential applications in many areas, such as catalysts, potential drug carriers, coatings, low-density materials and nano-reactor.Many hollow inorganic materials including metals, non-oxides and metal oxides have been synthesized.

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• The general approach for synthesizing such materials is based on the use of hard-template or soft-template such as polystyrene beads, colloid particles, emulsions, vesicles and droplets. Moreover, most of products are polycrystalline submicrometer spheres aggregated of nanoparticles. To my best knowledge,only several non-sphere and single-crystalline hollow structures have been prepared.

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• In this paper, we present a novel selftemplate route for fabricating single-crystalline β-FeOOH hollow nanorods with length in the range of 70-110 nm and width in the range of 20-30 nm. Hollow cavitys will be gained by controlling the degree of the phase transition from Fe(OH)3 to β-FeOOH and the Ostwald ripening process happening at the interior of nanorods.

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Ostwald ripening process • Many small crystals form in a system initially

but slowly disappear except for a few that grow larger, at the expense of the small crystals. The smaller crystals act as "nutrients" for the bigger crystals. As the larger crystals grow, the area around them is depleted of smaller crystals

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Explanation for the occurrence of Ostwald ripening

• Larger crystals are more energetically favored than smaller crystals. While the formation of many small crystals is kinetically favored, (i.e. they nucleate more easily) large crystals are thermodynamically favored. Small crystals have a larger surface area to volume ratio than large crystals. Molecules on the surface are energetically less stable than the ones already well ordered and packed in the interior. Large crystals, with their greater volume to surface area ratio, represent a lower energy state. Thus, many small crystals will attain a lower energy state if transformed into large crystals and this is what we see in Ostwald ripening.

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Pictorial example of crystal ripening from a precipitate

 Day 6.

A single crystal has appeared in the precipitate. The precipitate feeds the growth of the crystal and a zone of depletion appears around the crystal as it grows. This depletion zone looks like a halo around the crystal.

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Day 10

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Day 13

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Day 16

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配置 CS 溶液(壳聚糖的醋酸溶液)

2mLCS 溶液15mL0.3mol/L FeCl3 溶液15mL 正丙醇 0.408g 尿素82 2℃ h

黄色沉淀

乙醇洗涤、干燥

高压釜内乙醇热

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产物的表征采用以下仪器和条件• ( 1 ) XRD:Rigaku D/max-γA200,CuKα, • ( 2 ) TEM: JEM-100CXII, 加速电压 80kV• ( 3 ) HRTEM: Technai F30, 加速电压 300kV• ( 4 ) FT-IR: Bio-Rad model FTS-165 IR 红外

分析仪• ( 5 ) TGA: Mettler Toledo SDTA851e, N2, 升

温速率 20 /℃ min

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• 82℃ 保温 20min 后先得到无定型 Fe(OH)3

随着加热时间的延长,无 定 型 Fe(OH)3 纳 米 颗粒经过聚集 - 脱水过程形成多晶态 β-FeOOH 纳米棒

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• 醇热反应在 180℃ 进行 2h 后,由于纳米棒中Fe(OH)3 的分解,该纳米棒逐渐变成多孔棒。

Ostwald 熟化过程,结果多孔结构由内向外崩溃形成较大的中空结构。

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影响因素的研究• 壳聚糖和正丙醇在中空 β-FeOOH 纳米棒的形

成过程中起保护作用。研究还发现,如果将正丙醇换成乙醇,只能得到实心的颗粒。

• 影响材料形貌、粒度和结构的因素包括壳聚糖的用量、正丙醇与水的比例、反应温度和时间。如果实验中没有壳聚糖,反应的最终产物是 α-Fe2O3 ;

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Templates for Synthesizing Nanoparticles

溶液合成方法举例

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模板及其作用• 硬模板:阳极氧化铝( AAO ), 碳纳米管、线,其他。• 软模板:表面活性剂及其不同的聚集状态 高分子化合物 其他。

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硬模板 -纳米碳管

Carbon Nanotube

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硬模板 -氧化铝管的制备

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软模板 - 表面活性剂的特点• 阴离子表面活性剂:十二烷基硫酸钠 SDS ;

十二烷基苯磺酸钠 SDBS ; AOT

• 阳离子表面活性剂:三甲基十六烷基溴化铵CTAB

• 非离子表面活性剂: Triton-X :t-octyl-(OCH2CH2)xOH,

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表面活性剂的聚集状态• 胶束和反胶束:球形、棒状、片状胶束的形成

和表面活性剂浓度的关系。

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表面活性剂的聚集状态• 微乳液:表面活性剂 - 助表面活性剂 - 水

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Redox synthesis by NiSO4 and NaH2PO2 in cyclohexane-water-polyglycol emulsion

system

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将 Fe3+ 和 Fe2+ 混合溶液与阴离子表面活性剂 SDS 混合,通过烧结的陶瓷板向溶液中吹入高压空气,利用重力将多余的液体分离,得到稳定干燥的泡沫。将此干燥泡沫与氨溶液接触一定时间,发生水解。结果表 明 , 得 到 了FeOOH ,随后焙烧转化为 Fe2O3 。

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氧化氢氧化铁

FeOOH

Fe2O3

氧化铁

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溶液合成方法举例Shape control and associated magnetic properties of spinel cobalt ferrite nanocrystals

JACS 2004, 102, 126, 6164-6168

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合成基本思路

• 将非水解过程和晶种生长法结合,以铁、钴的乙酸乙酰盐为原料,利用非水解法先合成5nm 球状 CoFe2O4 ;再以它为晶种,生长得到较大的球状或立方状纳米晶。

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具体实验• 2mmol Co(acac)2 , 40mL 二 苯 醚 , 20mmol

1 , 2- 十六烷基二醇, 10mL 油酸, 18mL 十八 烯 胺 混 合 加 热 到 140℃ , 然 后 滴 加 由4mmol Fe(acac)3 和 30mL 二苯醚组成的混合溶 液 ; 迅 速 升 温 到 260℃ , 加 热 回 流30min 。最后,冷却到室温,加入乙醇,离心分离,得到 5nm 球状产物。

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具体实验• 取 100mg 上述产物作为晶种,在由 1mmol

Co(acac)2 、 2mmol Fe(acac)3 、 10mmol 1-十八醇、 5mL 油酸、 5mL 十八烯胺组成的混合溶液中,按照 10~15℃/min 速度升温到260℃ 并保温 30min 。冷却后,加入乙醇使之 沉 淀 。 如 此 , 就 可 以 得 到 8nm 球 状CoFe2O4 。

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纳米晶体的生长速度决定了产品的形状。前驱体分解温度大约为 190℃ ;油酸是一种表面活性剂,起稳定纳米晶的作用;十八烯胺提供了形成尖晶石所必需的碱性环境;长链醇对于成核和生长也是必要的,它可以加速 CoFe2O4 纳米晶的形成;升温速度慢可以保证前驱体分解产生的金属离子浓度较低;而反应温度低可以降低晶体生长的速度。

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升温速度较快时,金属离子浓度相对增加,晶体生长速度增加,各个晶面的生长速度差异减小,导致晶体生长的方向性减小,得到球状产物。

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溶液合成方法举例Unidirectionally Aligned Copper

Hydroxide Crystalline Nanorods from

Two-Dimensional Copper Hydroxy Nitrate

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基本思路

• 以层状碱式硝酸铜为原料制备 1D Cu(OH)2 的研究。碱式硝酸铜具有与水镁石 Mg(OH)2 相似的层状结构,其中四分之一的 OH- 被 NO3-

代替。具有 2D 结构的 Cu2(OH)3NO3 与 NaOH

溶液发生阴离子交换,最终得到 1D 结构的Cu(OH)2 。

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层状结构示意图

R. Xu, H. C. Zeng, Chem. Mater., 2003, 15, 2040-2048

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管状结构

嵌入、柱撑、剥离

加热、卷曲

1342

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具体操作

• 将 2.5g 起始原料 Cu2(OH)3NO3 分散在蒸馏水中,然后加入 2mol/L 的 NaOH 溶液,隔绝空气,室温下,在圆底烧瓶中搅拌 48h ,得到蓝灰色沉淀,过滤、分别用蒸馏水、乙醇洗涤, 35℃真空干燥,得到产物。

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原料具有典型的层状结构。最终产物可以指标化为正交晶系Cu(OH)2 物相,与 JCPDS 卡片 13-420 一致。

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• FTIR 谱也证实了原 料 Cu2(OH)3NO3 直接转化 为Cu(OH)2 。图 b 中, 700cm-1 以下的吸收对应于 Cu-O振动,而 3303 和 3567cm-1处的吸收为 OH- 的振动。另外,图 a归于 NO3- 离子、处在 1340cm-1附近的吸收在图 b 中消失,表明 NO3-完全被 OH- 取代。

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溶液合成方法举例溶胶凝胶法 - 硬模板法合成 Eu2O3 纳米管

JACS 2004 , 126 , 5976-5977

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具体实验操作• 将硝酸铕溶解于蒸馏水中得到 0.01mol/L 溶液,

用氨水调节溶液酸碱性至近中性,按照 Eu/ 尿素 =1/20 的摩尔比加入尿素。然后,加入阳极氧化氧化铝模板。 80℃ 保温 72h 。取出模板,置于管式炉内,升温至 150℃ 保温 1小时,再升温至 700℃ 保温 10小时。

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产物的晶相分析在 Philips X’pert PRO 衍射仪上进行,产物为立方晶系 Eu2O3 ,晶胞参数 a=1.085nm ,与 JCPDS 标准卡 86-2476 一致。 为了进一步确定该纳米管的组成,进行了能谱分析, Eu 和 O 的原子个数比近似等于 2 : 3 。

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The function of the Al2O3 template

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模板中 Eu2O3 纳米管阵列的俯视图,纳米管竖直排列在模板上,几乎相互平行形成阵列,外径约 50~80nm ,与模板孔径尺寸相符。照片的放大相更清晰,几乎所有的孔中都填满了Eu2O3 纳米管。 TEM照片显示了孔的外径约 70nm ,壁厚约5nm 。

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TEM照片可以清晰地看到纳米管的开口,选区电子衍射中的衍射环表明形成了 Eu2O3 多晶,其中( 222 )晶面环特别亮,表示该晶体具有特定的生长方向。高分辨电子显微镜 HRTEM照片见图 b