层板剥离水滑石的制备及影响因素

采用阴离子表面活性剂N-月桂酰基谷氨酸(LG)为插层分子，研究了烷烃-LG-水(O/W)微乳液中烷烃量的变化对插层水滑石层间距的影响，同时研究了烷烃分子大小和水滑石层板阳离子不同对水滑石剥离难易程度的影响。实验表明，随着微乳液中烷烃含量的增加，制备得到了由插层到层板剥离的水滑石，并且烷烃的链长越长，水滑石的剥离越容易实现。层板化学组成对剥离难易程度也有影响，难易程度依次是Mg/Al-LDH，Zn/Al-LDH和Ni/Al-LDH。     

超分子结构水杨酸根插层水滑石的组装及结构与性能研究

以锌铝水滑石ZnAl-CO3 LDHs为前体（主体），以乙二醇为分散介质，用离子 交换法组装了水杨酸根（客体）插层水滑石ZnAl-[o-HO(C6H4)COO]LDHs，并用XRD ，FT-IR，TG-DTA等手段对样品进行了表征。结果表明，能过控制离子交换条件， 水杨酸根阴离子可取代锌铝水滑石前体层间的CO3^2-离子，组装得到晶体结构良好 的水杨酸根插层水滑石。通过研究发现，主体水滑石层板与客体以静电力和氢键相 互作用，得到的超分子结构材料紫外阻隔作用增强并具有较好的稳定性，从而成为 一种集屏蔽和吸收双重功能的新型无机-有机得合紫外阻隔材料。     

表面预处理对镁铝水滑石结构性质和缓释性能影响

以Mg-Al-NO3水滑石(LDHs)为载体,将5-氟尿嘧啶(5-FU)通过离子交换法插入其层间,得5-FU/LDHs缓释材料。并对水滑石表面进行弱酸预处理改性,利用XRD、FTIR、TG-DSC、SEM和零电荷点(pHPZC)等表征手段,考察酸预处理对水滑石表面化学性质及微观结构的影响。结果表明,5-FU/LDHs的层间距从0.858 nm扩大到1.064 nm,层间5-FU2阴离子与主体层板通过氢键与静电作用,以呈一定角度单层交替排列于层间。酸预处理的水滑石粒径变小,层板正电荷密度增大。5-FU的释放机理是物理扩散、离子交换和药物溶解等协同作用,酸预处理可提高水滑石的缓释性能和稳定性。     

金属氢氧化物直接制备对苯二甲酸插层水滑石及其应用

以新制备的Mg(OH)_2和Al(OH)_3滤饼与对苯二甲酸通过水热反应制备了对苯二甲酸插层水滑石(TALDHs).使用X射线衍射(XRD)、热重-差热分析、扫描电镜(SEM)等技术对TA-LDHs与碳酸根型水滑石(CO3-LDHs)进行对比研究,结果显示,对苯二甲酸离子成功插入到LDHs层间,产物结构完整、晶相单一,所制得的TA-LDHs为片状.CO3-LDHs和TA-LDHs分别作为纳米填料,以两种不同的添加方式制备聚对苯二甲酸乙二醇酯(PET)/LDHs纳米复合材料.对复合材料进行XRD和SEM研究,结果表明在酯交换反应前添加2%TA-LDHs所制备的PET/LDHs纳米复合材料的层板被部分剥离,分散性最好.     

锌铝水滑石层板与层间离子调变及其光催化性能研究

采用双滴共沉淀法,结合水滑石层板阳离子和层间阴离子调变,制备十种锌铝水滑石,运用X射线衍射(XRD)、红外光谱(FT-IR)和差热分析(DTA)技术对合成样品的结构进行表征,考察了催化剂种类和用量、光照时间等变量对水滑石光催化降解罗丹明B的影响。研究结果表明,合成产物均具有典型水滑石特征衍射峰,调变阳离子种类合成的六种水滑石中,Zn-Al-Ni-CO₃-LDHs的催化效果最好;不同阴离子插层水滑石中,以ZnAl-CO₃-LDHs的光催化效果最佳;最佳反应条件为:催化剂用量0.1 g,光照时间65 min,两种水滑石材料光催化降解率可达82%以上。     

表面活性剂和硅烷偶联剂复合改性水滑石的表面性质

采用十二烷基硫酸钠(SDS)和3-氨丙基三乙氧基硅烷(KH550)、乙烯基三乙氧基硅烷(KH151)对锌铝水滑石进行有机改性,得到插层改性与表面改性结合的聚合物/锌铝水滑石复合材料。XRD、FTIR及计算机模拟的分析结果表明,SDS已垂直插入水滑石层间,层间距达到2.70 nm,KH550及KH151只是覆盖在水滑石表面,与层板表面羟基进行偶联。反相气相色谱的结果表明,复合材料的表面能(γsd)均比水滑石小,其中KH151-SDS-LDHs及KH550-SDS-LDHs的表面能较接近,由材料表面的酸碱常数,判断出SDS-LDHs表面趋于两性,KH151-SDS-LDHs及KH550-SDS-LDHs表面偏碱性,适于做碱性聚合物的填料。     

表面预处理对镁铝水滑石结构性质和缓释性能影响

以Mg-Al-NO₃水滑石（LDHs）为载体,将5-氟尿嘧啶（5-FU）通过离子交换法插入其层间,得5-FU/LDHs缓释材料。并对水滑石表面进行弱酸预处理改性,利用XRD、FTIR、TG-DSC、SEM和零电荷点（pHPZC）等表征手段,考察酸预处理对水滑石表面化学性质及微观结构的影响。结果表明,5-FU/LDHs的层间距从0.858nm扩大到1.064nm,层间5-FU₂阴离子与主体层板通过氢键与静电作用,以呈一定角度单层交替排列于层间。酸预处理的水滑石粒径变小,层板正电荷密度增大。5-FU的释放机理是物理扩散、离子交换和药物溶解等协同作用,酸预处理可提高水滑石的缓释性能和稳定性。     

二元类水滑石层板组成、结构与性能的理论研究

采用晶体学理论建立二元类水滑石(LDHs)微观结构模型与静电势能模型，将层板金属离子间距、层板电荷密度、层间阴离子间距等微观结构参数定量化，并将层间阴离子的静电势能表示成层板金属离子半径和物质的量之比、插层阴离子尺寸和电荷的函数。研究结果表明：LDHs层板金属离子间距应用离子紧密堆积来估算和孔径按阴离子平面六方点阵分布来计算是可行的；调变层板金属离子种类与物质的量之比影响层间阴离子的稳定性，势能计算值与文献报道的LDHs热稳定性次序一致。所以该模型可用于预测LDHs的微观结构参数以及热稳定性，为新型层状双羟基材料的定向合成提供思路。     

PVC/插层稀土类水滑石的热稳定性能研究

以山梨酸、La(NO_3)_3,Al(NO_3)_3,Mg(NO_3)_2和Na OH为主要原料合成了山梨酸插层镁铝镧类水滑石(Mg Al La-SA LDHs),通过X射线衍射(XRD)、红外光谱(FT-IR)进行结构表征。采用刚果红法、热老化烘箱法、转矩流变法、电导率法等研究了山梨酸插层类水滑石及与季戊四醇、硬脂酸锌复合后添加到聚氯乙烯(PVC)的热稳定性能。结果表明:山梨酸插层类水滑石可有效地延长PVC热稳定时间,抑制初期着色,降低加工能耗,热降解活化能较纯PVC提高了6.59 k J·mol~(-1)。按质量份数1/4/1与季戊四醇、硬脂酸锌复合后,热降解活化能较复合前提高了13.96 k J·mol~(-1),热稳定效果更优。     

水滑石层间碘酸根离子的还原性机理研究

通过X射线衍射(XRD)和傅里叶变换红外(FTIR)光谱仪表征发现,经水合肼(N2H4·H2O)和亚硫酸钠(Na2SO3)两种还原剂处理碘酸根插层水滑石的产物分别为碘离子插层的水滑石(ZnAl-I LDHs)和硫酸根离子插层水滑石(ZnAl-SO4LDHs)。进一步研究表明,N2H4·H2O和水滑石的反应为D7模型的核外层扩散反应,N2H4·H2O在水滑石微球界面和IO3-发生反应。而Na2SO3则先进入了水滑石层间,然后与层间的IO3-反应,其模型符合D11动力学模型。     

Amine‐Assisted Syntheses of Carbonate‐Free and Highly Crystalline Nitrate‐Containing Zn‐Al Layered Double Hydroxides

Zn‐Al layered double hydroxides (LDHs), with nitrate as the charge balancing anion in the interlayer space, were synthesized by precipitation from homogeneous solution containing different amines [e.g., hexamethylenetetraamine (HMTA), diethylenediamine (DEDA), trimethylamine (TMA) and dimethylamine (DMA)]. The applied method does not require nitrogen atmosphere. The solution pH and concentration of different amines were varied in order to identify the controlling parameters and whether nitrate or carbonate are the interlayer anion. Particularly, the addition of amines turns out to be an effective tool for the synthesis of nitrate containing Zn‐Al LDHs independent from the nitrogen atmosphere. The structure, textural, composition, and morphological properties were investigated using the powder X‐ray diffraction (PXRD), thermogravimetric analysis (TGA), FT‐IR spectroscopy, and scanning electron microscopy (SEM). The analyses showed that the samples had high crystallinity and purity. The NO₃‐ZnAl LDHs samples show that LDH sheets are predominantly smooth textured and the thickness of LDH sheets are found to be around 23 nm. The results also indicate that this method successfully produces a NO₃^– form Zn‐Al LDH that is almost identical to the one synthesized by conventional methods.     

Synthesis and Characterization of [Zn‐Al] Layered Double Hydroxides: Effect of the Operating Parameters

In this study, [Zn‐Al] layered double hydroxides (LDHs ) were prepared using the coprecipitation method at constant pH . The synthesis parameters (including the aging time, synthesis pH , nature of the alkali, concentration of metallic salts, and the cationic molar ratio R = Zn/Al) were varied in order to elucidate their effect on the properties of the obtained materials. Different characterization techniques, namely X‐ray diffraction, Fourier transform infrared, thermogravimetric analysis‐differential thermogravimetry, transmission electron microscopy, energy‐dispersive X‐ray, inductively coupled plasma, and photoluminescence, were used in this study. It was found that obtaining well‐crystallized LDHs requires (i) an aging time of 24 h and (ii) a synthesis pH value in the range 8–12. Our results also show that the concentration of the cationic metallic salts has no influence on the structural properties of the LDHs . The use of NH₄OH as alkali for adjusting the pH value during the synthesis favors the formation of nitrated LDH phases while NaOH gives rise to carbonated ones. Moreover, it was found that irrespective of the molar cationic ratio used (between 1 and 5), [Zn‐Al] LDHs could be obtained. The sample synthesized at R = 2 exhibited the best crystallinity.     

Adsorption of Cr(VI) and Se(IV) from their aqueous solutions onto Zr4+-substituted ZnAl/MgAl-layered double hydroxides: effect of Zr4+ substitution in the layer

Hydrotalcite-like compounds (layered double hydroxides, LDHs) containing varying amounts of Al(3+), Zr(4+), and Zn(2+) or Mg(2+) in the metal hydroxide layer have been synthesized and characterized by various physicochemical methods. The adsorption behavior of uncalcined (as-synthesized) and calcined LDHs have been investigated for Cr(2)O(7)(2-) and SeO(3)(2-). The mixed oxides, obtained on calcination at 450 degrees C, exhibit high adsorption capacities for Cr(2)O(7)(2-) (1.6-2.7 meq/g) and SeO(3)(2-) (1.1-1.5 meq/g), where adsorption occurs through rehydration. Substitution of Zr(4+) in the LDHs, for either M(2+) or Al(3+) ions, increases the adsorption capacity up to 20%, thus providing an alternative way to enhance the adsorption capacity of this type of material. The high adsorption capacity of these materials could be successfully used for removal of undesirable anions from water and also for synthesis of intercalated materials with tailored acidobasicity.     

Thermally Induced Growth of ZnO Nanocrystals on Mixed Metal Oxide Surfaces

An in situ method for the growth of ZnO nanocrystals on Zn/Al mixed metal oxide (MMO) surfaces is presented. The key to this method is the thermal treatment of Zn/Al layered double hydroxides (Zn/Al LDHs) in the presence of nitrate anions, which results in partial demixing of the LDH/MMO structure and the subsequent crystallization of ZnO crystals on the surface of the forming MMO layers. In a first experimental series, thermal treatment of Zn/Al LDHs with different fractions of nitrate and carbonate in the interlayer space was examined by thermogravimetry coupled with mass spectrometry (TG‐MS) and in situ XRD. In a second experimental series, Zn/Al LDHs with only carbonate in the interlayer space were thermally treated in the presence of different amounts of an external nitrate source (NH₄NO₃). All obtained Zn/Al MMO samples were analysed by electron microscopy, nitrogen physisorption and powder X‐ray diffraction. The gas phase formed during nitrate decomposition turned out to be responsible for the formation of crystalline ZnO nanoparticles. Accordingly, both interlayer nitrate and the presence of ammonium nitrate led to the formation of supported ZnO nanocrystals with mean diameters between 100 and 400 nm, and both methods offer the possibility to tailor the amount and size of the ZnO crystals by means of the amount of nitrate.     

Thermal and photocatalytic behavior of Ti/LDH nanocomposites

The development of nanocomposite photocatalyst based on layered double hydroxides (LDHs) associated with TiO₂ was the subject of this research. The thermally activated Zn–Al LDHs were selected as catalyst support precursor because of their proven photocatalytic activity and therefore their possible contribution to overall activity of novel Ti–Zn–Al nanocomposite. The catalyst precursor (Zn–Al LDH) was synthesized by low supersaturation coprecipitation method, and its association with active TiO₂ component targeting the formation of novel Ti–Zn–Al nanocomposite was achieved by wet impregnation. Simultaneous thermal analysis (TG–DTA) was used to investigate the thermal behavior of Zn–Al LDH and Ti–Zn–Al LDHs. Complementary, morphology, texture, and structure characterization was carried out. The photocatalytic test reaction was performed under UV light using the methylene blue degradation. The results confirmed a successful impregnation of TiO₂ on catalyst support precursor Zn–Al–LDH followed by considerable change in morphology and structure of Zn–Al LDH precursor. It was concluded that the synergic effect between TiO₂ and Zn–Al LDH precursor contributes to the overall photocatalytic activity.     

Synthesis of heptamolybdate‐intercalated MgAl LDHs and its application in polyurethane elastomer

Heptamolybdate (Mo₇O₂₄^6?) was intercalated in the interlayer space between MgAl‐layered double hydroxides (Mo‐MgAl LDHs) by the hydrothermal and ion exchange method, and then polyurethane elastomer (PUE) based composites were prepared by the prepolymerization method with different amounts of Mo‐MgAl LDHs. X‐ray diffraction (XRD), Fourier transform infrared (FTIR) spectra, laser Raman spectroscopy (LRS), and scanning electron microscopy (SEM) were employed to characterize the obtained LDHs. The performance of the PUE/LDHs were evaluated by measuring their thermal gravimetric, heat release rate (HRR), and smoke density (Ds). The results show that PUE/LDH composites exhibit a lower peak heat release rate (pk‐HRR), Ds, and a prolonged combustion time, in comparison with neat PUE. Comparison between NO₃‐MgAl LDHs and Mo‐MgAl LDHs containing composites show that the introduction of Mo⁶⁺ is able to facilitate flame retardance and smoke suppression efficiency, which results mainly from the presence of MoO₃ derived from the decomposition of Mo₇O₂₄^6? intercalated LDHs. Mo‐MgAl LDHs reduce the pk‐HRR of composites by 39% with only 1 wt.% content, and the maximum Ds of composites is reduced to a minimal value of 274 with 10 wt.% Mo‐MgAl LDHs. More importantly, LDHs would improve the mechanical properties at a low content. The experimental results reveal the potential of Mo₇O₂₄^6? intercalated LDHs to improve both the flame retardancy and smoke suppression of PUE. Copyright © 2015 John Wiley & Sons, Ltd.     

Photooxidation of polypropylene/layered double hydroxide nanocomposites: Influence of intralamellar cations

The influence of layered double hydroxides (LDHs) on the photooxidation of polypropylene (PP)/LDH nanocomposites was studied under irradiation at long wavelengths (λ > 300 nm, 60 °C and in the presence of oxygen). The influence of hybrid LDHs containing different divalent cations (Mg, Zn or both Mg and Zn) on the photooxidation mechanism of PP and on the rates of oxidation of the matrix was characterised based on infrared analysis. The presence of LDHs modifies the photoproducts accumulating in the PP and the rates of oxidation of PP were changed depending on the divalent cations in the LDH layers. Whereas natural clays, such as montmorillonite (MMt), can lead to a faster degradation of the materials, LDHs (Zn₂-Al-DS, for example) appear to have no inductive effect on polymer oxidation.     

不同锌铝比水滑石的合成及其吸附脱除水中邻苯二甲酸性能

采用共沉淀法合成一系列具有不同锌铝比的水滑石,并利用X射线衍射(XRD)、扫描电镜(SEM)、热重(TG)、氮气吸脱附及电感耦合等离子体质谱(ICP-MS)等表征手段对其结构与组成进行了测试。将上述水滑石材料用于吸附脱除水中邻苯二甲酸污染物,考察了不同锌铝比水滑石吸附邻苯二甲酸性能的差异。结果表明,在较低锌铝比时,随着水滑石锌铝比的增加,其对邻苯二甲酸的吸附量逐渐增大;当锌铝比较大时(6),随着锌铝比的增加,水滑石的吸附量基本保持不变。进一步选取锌铝比为6的水滑石,分别对其吸附邻苯二甲酸的动力学和热力学进行了研究,发现其吸附等温线和吸附动力学数据分别符合Freundlich等温吸附模型和准二级动力学模型,且循环吸附性能较好。     

不同锌铝比水滑石的合成及吸附脱除水中邻苯二甲酸性能的研究

采用共沉淀法合成一系列具有不同锌铝比的水滑石,并利用X射线衍射（XRD）、扫描电镜（SEM）、热重（TG）、氮气吸脱附及电感耦合等离子体质谱（ICP-MS）等表征手段对其结构与组成进行了测试。将上述水滑石材料用于吸附脱除水中邻苯二甲酸污染物,考察了不同锌铝比水滑石吸附邻苯二甲酸性能的差异。结果表明,在较低锌铝比时,随着水滑石锌铝比的增加,其对邻苯二甲酸的吸附量逐渐增大;当锌铝比较大时（>6）,随着锌铝比的增加,水滑石的吸附量基本保持不变。进一步选取锌铝比为6的水滑石,分别对其吸附邻苯二甲酸的动力学和热力学进行了研究,发现其吸附等温线和吸附动力学数据分别符合Freundlich等温吸附模型和准二级动力学模型,且循环吸附性能较好。