Electrochemical Study Of Silica Film With Ordered Nanochannles

The diameter of nanochannel is in the range of 1-100 nm and its depth is much larger than diameter. Due to its controlled size, large surface area and ease of surface modification, it has been the important research object in areas including chemistry, materials and life science. Nanochannel has potential applications in analysis, separation, single-molecule detection, drug delivery, modeling of natural ion channels and synthesis of other materials.Inspired by natural bio-nanochannels, various solid state nanochannels have been fabricated with the advanced physical and chemical technologies. Ordered and vertical silica nanochannel has several advantages, such as physical and chemical stability, easy preparation and reproducibility. This thesis studiedmolecule transport and electroactive materials loading within the ordered silica nanochannel.The permselectivity of silica film with ordered nanochannels was studied and the transport of probes with different charge can be modulated by its surface charge and the ion strength of electrolyte. The surface of silica is covered with silanols and its isoelectric point is in the range of 2-3, hence the surface of silica was negatively charged in solution at pH larger than 3. The surface of silica became positively charged after modification with (3-aminopropyl)triethoxysilane (APTS), in which the transport of charged molecules was reversed. In addition, the electric double layer (EDL) in silica nanochannels with diameter of 2-3 nmtend to overlap when the concentration of electrolyte is less than 0.1 M. Hence, the transport of co-ionsin silicananochannles was disfavoredunderthe low ion strength.An AND molecule logic gate was designed based on the electrochemical current rectification (ECR) of 11-ferrocenyl-l-undecanethiolate (C11FcSH) self-assembled monolayer on gold electrode covered with ordered and vertical silica nanochannelsfilm. Because the redox potential of C11FcSH is positive than that of potassium ferrocyanide (Fe(CN)64-) probe, only the anodic current of redox probe can pass through the underlying electrode.The degree of ECR can be evaluated by ratio of cathodic and anodic peak current (Ipc / Ipa). The value of Ipc / Ipabecame smallar with the increase of Fe(CN)64- concentration, and the cathodic peak current disappeared when the concentration ofFe(CN)64-was larger than 90 (μM.Under low ion strength, the amount of Fe(CN)64-which could cross into silica nanochannels reacting with C11FcSH decreased due to the overlap of EDL.Hence, the value of Ipc I ipaalso decreased with increasingthe electrolyte concentration. And the cathodic peak current disappeared with the concentration of NaClO4 larger than 0.1 M. Thus, an AND logic gate was obtained with the two inputs including concentration of Fe(CN)64" probe and NaC104.Polyaniline-mesoprous silica film (PANI-MSF) hybrid material was fabricated, in which MSF with channels perpendicular to the substrate electrode serves as the hard template. The growth of PANI can be completely controlled within the channels of MSF by simply adjusting the concentration of aniline monomer and electrochemical polymerization time. The as-prepared PANI-MSF hybrid materials exhibited a good electrocatalytic activity toward oxidation of ascorbic acid (AA) and can be used to detect AA in the range of 0.1-1.0 mM.PANI-MSF can also be employed as a pH potentiometric sensor and displayed a near Nernstian response to the solution pH in the range of 3-9.The loading of metal nanoparticles in channels of silicaand their electrocatalytic, electrochemical sensing performance were studied. Firstly, silica nanochannels were modified with some other groups which can react with metal precursor. Subsequently, metal nanoparticles wereformed in silica channels after chemical reduction. Experimentally, the nanochannel surface was functioned with a layer of APTS which displayed a strong electrostatic interaction with AuCl4-, eventually resulting in the confinement of Au nanoparticles with a narrow size distribution inside the channels after chemical reduction.Furthermore, based on the previous work, we demonstrated a facile method for loading polyaniline and platinum nanoparticles in silica channels. The secondary amines and tertiary imines on PANI backbone can readily complex with PtCl62-ions, which can be further reduced to generate Pt nanoparticles. The obtained Pt nanoparticles@PANI/MSF (PtNPs@PANI/MSF) hybrid material displayed a good electrocatalytic activity toward oxidation of H2O2 and can be used to detect H2O2 in a wide concentration range (1.0μM-2.0 mM) with a high sensitivity (50 μA mM-1) and a low detection limit (0.24 μM, S/N = 3).