Hong-Ping Lin

Tubules-Within-a-Tubule Hierarchical Order of Mesoporous Molecular Sieves in MCM-41

The recently discovered mesoporous aluminosilicate MCM-41 consists of hexagonal arrays of nanometer-sized cylindrical pores. It is shown that this material can be synthesized by cooperative condensation of silicate and cylindrical cationic micelles. Careful control of the surfactant-water content and the rate of condensation of silica at high alkalinity resulted in hollow tubules 0.3 to 3 micrometers in diameter. The wall of the tubules consisted of coaxial cylindrical pores, nanometers in size, that are characteristic of those of MCM-41. The formation of this higher order structure may take place through a liquid crystal phase transformation mechanism involving an anisotropic membrane-to-tubule phase change. The hierarchical organization of this “tubules-within-a-tubule” particle texture is similar to that of the frustules of marine diatoms.

Formation of Mesoporous Silica Nanotubes

[29] M. A. van Dijk, R. van den Berg, Macromolecules 1995, 28, 6773.[30] From the morphology of the polymer blend thin film, it was alreadypointed out that there is no clear affinity for one of the two hydropho-bic phases to preferentially wet the hydrophilic silicon substrate.[31] V. Z.-H.Chan,E. L. Thomas, R. G. H.Lammertink, M. A. Hempenius,G. J. Vancso, H. Wang,R. J. Composto, unpublished.[32] Auger electron spectroscopy (AES) data obtained for oxygen etchedPFS homopolymer are consistent with the XPS results. Depth profiling(argon ion sputtering) indicated an approximately 10 nm thin layerrich of iron, silicon, and oxide at the surface of the oxygen etchedpolymer film.[33] A. B. Fischer, J. B. Kinney, R. H. Staley, M. S. Wrighton, J. Am.Chem. Soc. 1979, 101, 6501.

Synthesis of CuO on mesoporous silica and its applications for coupling reactions of thiols with aryl iodides

Novel CuO on mesoporous silica is prepared under a convenient approach, and has been shown to be an efficient catalyst for cross-coupling reactions of thiols with aryl iodides with only 1.0-5.0 mol% catalyst loading.

Effect of delayed neutralization on the synthesis of mesoporous MCM-41 molecular sieves

Abstract We present a detailed study on the preparation of highly-ordered MCM-41 molecular sieves based on a new delayed neutralization process. Products synthesized from cationic surfactants with different carbon chain lengths (alkyltrimethylammonium salt), counterions and head groups gave almost constant wall thickness (about 1.7nm), small lattice contraction after calcination, and sharp pore size distribution. However, the structural order decreased with the decrease of the carbon chain length. Adding a proper amount of alcohols as cosurfactants would improve the XRD patterns of the surfactants with carbon chain lengths less than 14. A head group of larger size would shrink the pore size and damage somewhat the structural order of MCM-41 materials. The rate of acidification and the source of the acid did not have much effect on the XRD patterns of MCM-41, but would affect its morphology. The formation process and the nature of the MCM-41 product based on octadecyltrimethylammonium bromide (C18TMAB) are dependent on the synthetic temperature.

Control of morphology in synthesizing mesoporous silica

Mesoporous silica can be synthesized by either the alkaline route or the acidic route, both using surfactants as templates. Morphological transformations of mesoporous silica can produce various hierarchical orders. Different morphologies are produced under different synthetic conditions. In the alkaline route, the surfactant/silicate liquid crystal system undergoes phase transformation to form vesicles and further transforms to the hexagonal phase. The results are tubule-within-tubule and hollow pillar-within-sphere structures depending on cosurfactant/surfactant composition. Using nitric acid in the acidic route, one can obtain hierarchical ropes or gyroids depending on stirring conditions. Ammonia hydrothermal treatment can induce further morphological transformation to nanotubes of mesoporous silica.

Sulfated zirconia catalyst supported on MCM-41 mesoporous molecular sieve

Sulfated zirconia (SZ) was supported on siliceous hollow tubular MCM-41 mesoporous molecular sieve by using a one-step incipient wetness impregnation method with zirconium sulfate as the precursor. The SZ/MCM-41 catalyst was obtained by thermal decomposition of the precursor in air. The resultant catalyst was characterized with various techniques, such as nitrogen physisorption, X-ray diffraction, SEM, and TEM. It was shown that the well-ordered channels of MCM-41 support arranged in hexagonal arrays while the hollow tubular morphology was retained. Both tetragonal and monoclinic phases of zirconia were developed in the catalysts. With the addition of a proper amount of aluminum as a promoter, resulting in catalyst SZA/MCM-41, the transformation of zirconia from metastable tetragonal phase to monoclinic phase was retarded. The catalytic activity of SZA/MCM-41 catalyst in the isomerization of n-butane was dramatically improved in comparison to the activities of SZ/MCM-41 or SZA/silica.

Strong visible photoluminescence from SiO2 nanotubes at room temperature

The optical studies of SiO2 mesoporous materials with hierarchical tubules-within-tubule structure have been investigated by photoluminescence and Fourier-transform infrared transmittance (FTIR). Our results suggest that the radiative intensity can be strongly enhanced by annealing the samples in N2 environment. From the FTIR spectra, we have pointed out that the origin responsible for the strong emission is Si–OH complexes located on nanotube surface. It has been observed that after turning off the pumping laser, the photoluminescence signal of SiO2 nanotubes can persist for several seconds, which is much longer than that of most materials performed under similar conditions. We have found that the decay of the photoluminescence signal is due to the quantum tunneling process. These are triplet and singlet states of Si–OH complexes that are responsible for the observed persistent photoluminescence.

Innovative ligand-assisted synthesis of NIR-activated iron oxide for cancer theranostics

This work presents the development of a facile ligand-assisted hydrothermal reaction for the preparation of NIR-activated Fe(3)O(4) nanostructures that can directly upgrade the iron oxide with MR contrast ability to be a MRI/photothermal theranostic agent.

Counterion and alcohol effect in the formation of mesoporous silica

Abstract The adsorption of silicate anions onto the cationic micellar surface and the slow condensation of silicate species control the early phase of the alkaline synthesis of mesoporous materials. We found that there exists a well-defined induction time ( t p ) of the transition from clear solution to white precipitation gel. The induction time t p increases with the concentration of added salt NaX. At a fixed concentration of the salts, the t p decreases in the order: ClO 3 − >NO 3 − >Br − >SO 4 2− , SO 3 2− >Cl − >F − , with F − being the most effective ion in forming the hexagonal phase gel. The order in induction time reflects the strength in counter-ion binding of X − to micelles. The stronger adsorbing X − would block the adsorption of silicate ions on micelles and delay the formation of the silica–surfactant mesophases. The order of the ion series agrees with the Hofmeister series in many lyotropic systems such as in ion–protein and ion–surfactant interactions. Surfactant chain length and the addition of 1-alkanols affects the counterion adsorption behavior and they also have strong influences on the rate of formation of the silicate–surfactant mesophase.

Salt effect in post-synthesis hydrothermal treatment of MCM-41

Abstract Post-synthesis hydrothermal treatment of MCM-41 mesoporous silica provides a convenient method for pore expansion and silica wall thickening for improvement of its stability. The physical chemistry of the process is investigated by examining the effects of water content, salts and aluminum on pore expansion. A hydrothermal treatment at 150 °C in water or a salt solution leads to controlled pore expansion. The pore size and wall thickness vary with the kind of anion of the salt and their concentrations. The salt effect follows the well-known binding strength of the Hofmeister series of anion for the cationic surfactant, NO 3 − >Br − >Cl − >SO 4 2− ∼F − . It is proposed that an equilibrium of distributing surfactants inside the MCM-41 channels and in solution controls the pore size and wall thickness upon varying the salts. The anion (X − ) binds with cationic surfactant molecules (S + ) in solution to shift the equilibrium of surfactant/silicate binding leading to less surfactant and water in the pore, and hence less pore expansion. The effect of ammonia hydrothermal treatment is to shift the equilibrium to stronger surfactant/silicate binding and thus more pore expansion. At neutral condition, the wall thickness varies inversely with respect to the pore diameter. The wall thickness variation agrees with a model of elastic deformation of the wall silica materials at high temperature.