Synthesis and Characterization of Silica Nanotube by Glycyldodecylamide as a Template

Abstract

Scheme 1. Schematic representation of tubular nanostructure by self assembled GDA amphiphilic templating process (left: SNT-1, right SNT-2) Many efforts have been devoted to synthesize various kind of inorganic nanotubes due to their numerous significant applications. Among them hollow silica nanotubes (SNTs) have drawn considerable interest because of their advantages such as biocompatiblity, controllable size, and accessible for the modification of surfaces increasing its utility in areas of nanofluidic, drug delivery, adsorption, catalysis, hydrogen storage, and bioseparation. Several methods have been developed for synthesizing hollow silica nanotube. However, normal synthetic methods of silica nanotube are mainly through the sol-gel transcription process using various kinds of templates. These methods relied on severe conditions such as extreme pH, difficult template preparation and high pressure. For synthesizing silica nanotube, an organic templates including biomolecules and lipids which leads to gelation through the self-assembly of amphiphiles is required. Nowadays, research has increasingly focused on finding new templates for producing well-defined structures in terms of pore diameters, wall thickness, and aspect ratios etc. But several difficulties lie on the high orderness and creation of well-defined morphology. One of attractive method for synthesizing silica nanotube is via neutral templating route due to formation of mesoporous structures with neutral amine and neutral silica precursors. Moreover this method is simple, based on ambient conditions facilitate easy recovery of the surfactant, yielding a thick silica wall and hydrothermally stable materials. This finding inspired us to develop a new glycyldodecylamide (GDA) surfactant as template for synthesis of silica nanotube. The aim of our study was to undertake bio-silication through assembly in an aqueous solution using glycyldodecylamide surfactant. Two types of silica nanostructure (SNT-1 and SNT-2) were synthesized with narrow (3 4 nm) and wide (45 nm) diameters, respectively by temperature dependent self assembly (Scheme 1). The silica nanotubes were synthesized by the hydrolysis of TEOS as a silica source after dissolving the surfactant in a water/ethanol (10: 1) solution. The XRD pattern of SNT-1 showed the broad band at the small-angle scattering regime (2θ < 2), which could indexed as a lattice constant, a = 4.1 nm (Figure S1 red line). The selfassembled GDA gel in a dry form also shows the periodical diffraction peaks, indicating its assembled structure as a lamellar organization (Figure S1 black line). The d-spacing of the aggregates were approximately 4.1, 2.06, 1.38, 1.05 nm and corresponded to the twice of the extended molecular length of GDA