Effects of catalyst thickness on the fabrication and performance of carbon nanotube-templated thin layer chromatography plates

Abstract

The effects of iron catalyst thickness on the fabrication and performance of microfabricated, binder-free, carbon nanotube (CNT)-templated, thin layer chromatography (TLC) plates are demonstrated. The iron catalyst was deposited at thicknesses ranging from 4 to 18 nm in increments of 2 nm. Its thickness plays a key role in governing the integrity and separation capabilities of microfabricated TLC plates, as determined using a test dye mixture. Atomic force microscopy and scanning electron microscopy show that smaller and more numerous catalyst nanoparticles are formed from thinner Fe layers, which in turn govern the diameters and densities of the CNTs. The average diameter of the Fe nanoparticles, Dp, is approximately six times the initial Fe film thickness, tFe: Dp ≈ 6tFe. After deposition of relatively thick silicon layers on CNTs made with different Fe thicknesses, followed by oxidation, all of the resulting CNT-templated SiO2 wires had nearly the same diameter. Consequently, their surface areas were very similar, although their areal densities on the TLC plates were not because thinner catalyst layers produce denser CNT forests. For tFe = 6 nm, nanotube growth appears to be base growth, not tip growth. Best TLC separations of a test dye mixture were obtained with plates prepared with 6 or 4 nm of catalyst. Calculations suggest a loss of surface area for TLC plates made with thicker Fe layers as a result of fewer, thicker CNTs, where the density of silica nanotubes (device surface area) goes approximately as 1/tFe2. While the focus of this paper is toward a greater understanding of the processing conditions that lead to the best TLC plates, a baseline separation of three analgesics (caffeine, phenacetine, and propyphenazone) is shown on a normal phase TLC plate grown with 6 nm of iron.

Atomic layer deposition of aluminum-free silica onto patterned carbon nanotube forests in the preparation of microfabricated thin-layer chromatography plates

“…TLC plates were microfabricated using the methods described previously up through the growth of patterned CNT forests [11][12][13]30]. The mask used to make the plates in this study had zig-zag features that produced 3-µm wide hedges, 4.24-µm channel widths, and 50 µm channels as shown in Figure 1.…”

“…It complicates the synthesis of the plates and limits their potential acceptance -normal phase (pure) silica is by far the most common TLC stationary phase. In addition to an exploration of different microfabrication schemes, we have reported the detailed characterization of the materials in our TLC plates [13,[25][26][27][28][29] and the effects of Fe layer thickness on nanoparticle size and CNT forest growth [30].…”

Chemical Separation on Silver Nanorods Surface Monitored by TOF-SIMS

“…This causes some inhomogeneity in separation zone leading to zone spreading. Some separation specific, nanotextured films, preparation methods have already been documented in the articles published by Linford research group [24][25][26][27]. In the next step various PDMS microfluidic channel designs based on hydrogel procedure preparation will be examined [28] followed by an integration of nanostructured functional films into miniaturized systems.…”

Microfabrication, separations, and detection by mass spectrometry on ultrathin-layer chromatography plates prepared via the low-pressure chemical vapor deposition of silicon nitride onto carbon nanotube templates

“…These include glancing angle deposition (GLAD) [1][2][3], monoliths [4][5][6][7][8][9][10], and electrospun polymers [11][12][13][14]. To this end, patterned, infiltrated, microfabricated carbon nanotube (CNT)-templated UTLC plates based on a zigzag geometry have also been introduced [15][16][17][18][19].…”

“…Various inorganic materials have been investigated for the conformal coating of CNTs in UTLC plate microfabrication, starting with the low-pressure chemical vapor deposition (LPCVD) of silicon [15,16]. In this rapid deposition process, the silicon adhered conformally and directly to the CNTs.…”