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![(a) 1D in-plane GISAXS patterns of EASA films with C 22 TAB and C 24 TAB deposited at a potential of −1.25 V (vs Ag/Ag + ) for 20 s on ITO electrodes [inset: 2D GISAXS patterns for (i) C 22 TAB-and (ii) C 24 TAB-templated EASA films] and a (b) plot of pore spacing (nm) of the 10 reflection and pore diameter (nm) determined using EP as a function of surfactant chain lengths of EASA films grown with C 14 TAB, 32 C 16 TAB, C 18 TAB, C 20 TAB, C 22 TAB, and C 24 TAB. Furthermore, the GISAXS data are given in the Supporting Information (Figures S10−S13).](publication/358455017/figure/fig1/AS:1156035591061505@1652631771472/a-1D-in-plane-GISAXS-patterns-of-EASA-films-with-C-22-TAB-and-C-24-TAB-deposited-at-a.png)
(a) 1D in-plane GISAXS patterns of EASA films with C 22 TAB and C 24 TAB deposited at a potential of −1.25 V (vs Ag/Ag + ) for 20 s on ITO electrodes [inset: 2D GISAXS patterns for (i) C 22 TAB-and (ii) C 24 TAB-templated EASA films] and a (b) plot of pore spacing (nm) of the 10 reflection and pore diameter (nm) determined using EP as a function of surfactant chain lengths of EASA films grown with C 14 TAB, 32 C 16 TAB, C 18 TAB, C 20 TAB, C 22 TAB, and C 24 TAB. Furthermore, the GISAXS data are given in the Supporting Information (Figures S10−S13).
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Context 1
... pore ordering and alignment in mesoporous silica were determined by GISAXS measurements. The 1D in-plane scattering pattern for the EASA film grown with C 22 TAB is shown in Figure 1, and contains the typical peaks for mesoporous materials with a hexagonal arrangement of cylindrical pores in P6mm symmetry, namely the SBA-15 34,35 and MCM 36,37 families of materials. The incident beam angle found to provide the most intense diffraction features was 0.25°, and the 10, 11, 20, and 21 peaks were observed at 2.00, 3.43, 3.96, and 5.22°, respectively. ...
Context 2
... set of peaks was observed for films produced with the surfactants from C 14 −C 22 . In contrast, the addition of C 24 TAB to the sol electrolyte resulted in a disordered sol−gel film, as indicated by the 1D inplane GISAXS data shown in Figure 1. A clear reduction in the intensity of the broad 10 diffraction peak and a total loss of the 11 and 20 diffraction peaks were observed, indicating a significant loss of the hexagonal order. ...
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... 2D GISAXS image of the EASA film templated with C 22 TAB is presented in the insets to Figure 1i. The four inplane spots in the horizontal plane relate to the 10, 11, 20, and 21 reflections discussed in the previous paragraph. ...
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... et al. 31 reported similar GISAXS features for C 16 TABgenerated EASA films due to the growth of silica spheres at the surface with random alignment of the hexagonal pores. The second inset to Figure 1ii illustrates the 2D GISAXS data obtained for the EASA film templated with C 24 TAB after surfactant removal. The position of the 10 diffraction spots in the horizontal plane shows this film also has vertically aligned pores, but the hexagonal domains have very little longer-range order, which also accounts for the low intensity of the 1D GISAXS pattern. ...
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... pore spacings as a function of the surfactant chain length (C 14, C 16 , C 18 , C 20 , C 22 , and C 24 ) for a range of EASA films are also shown in Figure 1. An increase in the pore spacing values upon increasing the surfactant size is observed. ...
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... be removed using a sticky tape (Supporting Information, Figure S14), or reduced by either optimizing the sol composition, or adjusting the deposition potential and time. ...
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... further investigate the porous silica structure, TEM samples were prepared using EASA films prepared from C 22 TAB and C 24 TAB. The GISAXS data (Figure 1) suggested that the strong hexagonal order found with C 16 TAB could be maintained to C 22 TAB, but that with C 24 TAB experienced loss of order. The images in Figure 3 support this finding because the mesopores in the C 22 TAB-derived silica film have vertical orientation with large hexagonal domains across the film. ...
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... it is also noticed that the pore diameter increases steadily upon increasing the carbon units in the surfactant chain. This compared well with the GISAXS-derived pore spacing in Figure 1, and shows a fairly consistent trend. In brief, the asprepared silica films containing surfactants have a strong suppression of the electrochemical current with the charged probes, showing the films to have a good coverage. ...
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... Tetraethoxysilane (TEOS, 98%, Alfa Aesar, Leicestershire, UK), ethanol (99.8%, Fisher, Leicestershire, UK), NaNO3 (98%, Timstar, Shrewsbury, UK), eicosyltrimethylammonium bromide (C20TAB, synthesised in-house [31]), HCl (37%, Fisher, Leicestershire, UK), hexaamine ruthenium (Aldrich, St. Louis, MO, USA) and deionised water (18 MΩ cm, Select Fusion purifier, Willoughby, OH, USA) were used as reagents. Indium tin oxide (ITO) coated on glass (surface resistivity 20 Ω sq −1 , Ossila Technologies, Sheffield, UK) was used for the working electrodes. ...
Nanostructures synthesised by hard-templating assisted methods are advantageous as they retain the size and morphology of the host templates which are vital characteristics for their intended applications. A number of techniques have been employed to deposit materials inside porous templates, such as electrodeposition, vapour deposition, lithography, melt and solution filling, but most of these efforts have been applied with pore sizes higher in the mesoporous regime or even larger. Here, we explore atomic layer deposition (ALD) as a method for nanostructure deposition into mesoporous hard templates consisting of mesoporous silica films with sub-5 nm pore diameters. The zinc oxide deposited into the films was characterised by small-angle X-ray scattering, X-ray diffraction and energy-dispersive X-ray analysis.
... 7 The lattice parameter of CTAB derived silica structures ranges from circa 3.8 nm for C 14 TAB to 5 nm for C 24 TAB, where the structure expands when made with a longer surfactant (until reaching a plateau). 13 One problem arising when using EASA is the formation of unwanted aggregates on the film. The electrochemically generated hydroxides not only drive polycondensation of silica at the electrode surface, but also in the bulk solution above. ...
... The transient has the same shape as the one obtained in the CTAB experiment. The elongation of the chain from 16 to 18 carbon atoms was expected to result in a slightly enlarged pore distance 13 . Once again, a contour plot of the horizontal scattering profiles was made, as shown in Figure S4. ...
The process of electrochemically assisted surfactant assembly was followed in real time by grazing incidence small angle X-ray scattering with the aim to deconvolute the formation of mesoporous silica film...
... The surfactant is removed from the mesopores by washing with an acidic alcoholic solution or calcination for 30 minutes to generate mesoporous silica films with vertical pore channels. We previously reported variations in those oriented mesoporous silica films that can be achieved with CnTAB surfactants from C14 to C24. 19 Faster ion diffusion rates were observed from a variety of redox probe molecules for films with increasing surfactant chain lengths, linked to increases in pore size. EASA most commonly uses C16TAB, resulting in small diameter pores of 2-3 nm diameter. ...
... Such rings from EASA films with C16TAB, C22TAB and C24TAB have previously been attributed to the presence of silica spheres on the surface of the film after formation in the bulk solution. 25,19 There are two ways to remove the surfactant template either by washing in an acidic alcoholic bath or calcination. The former method was applied and the resulting porous silica films were characterised by SEM (Fig. 2). ...
... Previous works have shown that mass transport of redox-active molecules through porous silica films is governed by diffusion processes. 19,12,25 Therefore, the charge transfer resistance 3-/4transporting through the silica films than that seen with the C18TAB and C18DMEAB ...
Production of mesoporous silica films with vertically oriented pores has been a challenge since interest in such systems developed in the 1990s. Vertical orientation can be achieved by the electrochemically assisted surfactant assembly (EASA) method using cationic surfactants such as cetyltrimethylammonium bromide (C16TAB). The synthesis of porous silicas using a series of surfactants with increasing head sizes is described, from octadecyltrimethylammonium bromide (C18TAB) to octadecyltriethylammonium bromide (C18TEAB). These increase pore size, but the degree of hexagonal order in the vertically aligned pores reduces as the number of ethyl groups increases. Pore accessibility is also reduced with the larger head groups.
... The pore dimension can be increased by swelling with mesitylene 47 or using surfactants with a longer alkyl chain. 48 The potentialities of oriented mesochannels in silica lms have been further exploited by covalent binding organofunctional species on the pore surface. One example of such applications is a surface modication with electroactive molecules, such as ferrocene. ...
... The arrows in the lower-right magnified panel represent the possible occurrence of interchannel microporosity originating from the overlapping of neighbouring pores during vertical contraction. Reproduced with permission from ref.48. ...
The synthesis of ordered mesoporous films via self-assembly represents one of the main accomplishments in nanoscience. In fact, controlling the complex chemical-physical phenomena that govern the process triggered by the solvent's fast evaporation during film deposition has represented a challenging task. Several years after the first articles on the subject, the research in the field entered a new stage. New advanced applications based on the peculiar properties of mesoporous films are envisaged while basic research is still going on, especially to clarify the mechanism behind self-organization in a spatially defined environment and the physics and chemistry in mesoscale porosity. This review has been dedicated to analysing the main trends in the fields and the perspective for future developments.
... Mesoporous silica lms synthesised with the surfactants C 18 TAB, C 20 TAB and C 22 TAB had larger pore diameters (2.8-4.4 nm) while retaining the ordered structure. 28 Herein, we report electrodeposition of AuNPs into mesoporous silica lm hard templates with pores below 10 nm. The templates have a 3-dimensional pore structure generated by evaporation induced self-assembly with commercial F127 as the surfactant and vertical pores generated by electrochemically assisted self-assembly with C 20 TAB as the surfactant. ...
... 33 Herein we used a longer alkyl chain C 20 TAB surfactant and silica lms were produced with vertical pore orientation and pore diameter $4 nm and lm thickness of 100-150 nm. 28 Nitrogen porosimetry experiments would require a large number of samples to be combined for sufficient material since the mesoporous silica lms in this work were approx. 1 Â 1.5 cm and 100-200 nm thick. Zhao et. ...
... For template 2, in our recent published work, ellipsometric porosimetry with a toluene probe was used to investigate the pore structure of EASA lms grown with C 20 TAB. 28 Again the isotherm had Type IV characteristics and the $3.8 nm pore size is in accordance with the size from TEM image herein. The microscopic characterisation of hard templates conrmed the deposition of porous and homogenous silica lms. ...
Metallic nanostructures have widespread applications in fields including materials science, electronics and catalysis. Mesoporous silica films synthesised by evaporation induced self-assembly and electrochemically assisted self-assembly with pores below 10 nm were used as hard templates for the electrodeposition of Au nanostructures. Electrodeposition conditions were optimised based on pore orientation and size. The growth of nanostructures was initiated at the electrode surface as confirmed by microscopy. The hard templates and Au electrodeposits were characterised electrochemically as well as with X-ray diffraction, small angle scattering and transmission electron microscopy. Finally, mesoporous silica hard templates were removed by hydrofluoric acid etching and stable Au nanoparticles on different electrode surfaces were achieved.
Electrochemical sensors have become increasingly relevant in fields such as medicine, environmental monitoring, and industrial process control. Selectivity, specificity, sensitivity, signal reproducibility, and robustness are among the most important challenges for their development, especially when the target compound is present in low concentrations or in complex analytical matrices. In this context, electrode modification with Mesoporous Thin Films (MTFs) has aroused great interest in the past years. MTFs present high surface area, uniform pore distribution, and tunable pore size. Furthermore, they offer a wide variety of electrochemical signal modulation possibilities through molecular sieving, electrostatic or steric exclusion, and preconcentration effects which are due to mesopore confinement and surface functionalization. In order to fully exploit these advantages, it is central to develop reproducible routes for sensitive, selective, and robust MTF-modified electrodes. In addition, it is necessary to understand the complex mass and charge transport processes that take place through the film (particularly in the mesopores, pore surfaces, and interfaces) and on the electrode in order to design future intelligent and adaptive sensors. We present here an overview of MTFs applied to electrochemical sensing, in which we address their fabrication methods and the transport processes that are critical to the electrode response. We also summarize the current applications in biosensing and electroanalysis, as well as the challenges and opportunities brought by integrating MTF synthesis with electrode microfabrication, which is critical when moving from laboratory work to in situ sensing in the field of interest.
The removal of harmful organic dyes from aqueous solutions has drawn the attention of scientists because of the substantial threat they pose to society's worldwide health. Hence, it is crucial to design an adsorbent that is both very effective in removing dyes and has the benefit of being inexpensive. In the present work, Cs salts of tungstophosphoric acid (CPW) supported mesoporous Zr-mSiO2 (mZS) with varying extents of Cs ions have been prepared by a two-step impregnation technique. Accordingly, a lowering in the surface acidity modes was observed after Cs exchanged protons of H3W12O40 and formed salts immobilized on the mZS support. After exchanging the protons with Cs ions, the characterization results revealed that the primary Keggin structure was unaltered. Moreover, the Cs exchanged catalysts had higher surface area than the parent H3W12O40/mZS, suggesting that Cs reacts with H3W12O40 molecules to create new primary particles with smaller sizes possessing inter-crystallite centers with a higher dispersion degree. With an increase in Cs content and thus a decrease in the acid strength and surface acid density, the methylene blue (MB) monolayer adsorption capacities on CPW/mZS catalysts were increased and reached an uptake capacity of 359.9 mg g-1 for Cs3PW12O40/mZS (3.0CPW/mZS). The catalytic formation of 7-hydroxy-4-methyl coumarin was also studied at optimum conditions and it is found that the catalytic activity is influenced by the amount of exchangeable Cs with PW on the mZrS support, which is in turn influenced by the catalyst acidity. The catalyst kept approximately the initial catalytic activity even after the fifth cycle.
In the present work, we report a synthesis procedure for the preparation of vertically aligned mesoporous silica thin films containing long, nanometer-scale thin silver nanowires inside pores. The inter-channel nanowires had a fine crystalline structure and a diameter of no more than 2 nm. Despite the diameter being the edge of the theoretical possibility of synthesis, the nanowires were stable enough to be observed by transmission electron microscope and could be clearly observed. For the synthesis, we applied the idea of silica nanoreactors, and the procedure consists of two steps: fabrication of an initial organically-functionalized silica thin film containing silver ions distributed regularly inside vertically aligned pores and following thermal decomposition resulting in the decomposition of the organic anchoring groups and the formation of metallic crystalline nanowires from released silver atoms. Both the final nanocomposite and the initial material were studied by means of transition electron microscopy and electrochemical techniques: linear scan and differential pulse anodic stripping voltammetry. The crystallinity of silver nanowires inside silica mesopores was proved by electron diffraction. The spatial confinement realized by silica nanochannels facilitated the stabilization of relatively small and ultra-thin nanowires and the formation of a hexagonal P63/mmc silver crystalline structure instead of the more common Fm3m cubic.
