Introduction Of Organic Functional Groups Research Articles

Small angle X-ray scattering and positron annihilation spectroscopy of polyethyleneimine functionalized ordered mesoporous silica SBA-15 microstructure

Owing to its advantages of high specific surface area, large pore volume, adjustable pore size, good thermal stability and relatively low cost, SBA-15 has a wide range of application prospects in adsorption, separation, catalysis, nanomaterials and other fields. And the use of organic functional groups to modify SBA-15 has become one of the hot spots of research on materials, but the introduction of organic functional groups will inevitably affect the pore structure of material, affecting its performance. Therefore, how to more comprehensively characterize the pore structure of material has received much attention. In this work, small angle X-ray scattering (SAXS) technique is used to characterize the pore structure of PEI/SBA-15 mesoporous molecular sieve. The pore structure and periodicity information of PEI/SBA-15 are obtained by using correlation function and string length distribution theory, and compared with those obtained by positron annihilation lifetime spectroscopy (PALS) technique. The results show that the periodic structure of PEI/SBA-15 mesoporous molecular sieve does not change significantly with the increase of PEI mass percent, and the pore size of PEI/SBA-15 mesoporous molecular sieve only decreases from 8.3 nm to 7.6 nm by the chord length distribution function. Two long-life components<i>, τ</i><sub>3</sub> and <i>τ</i><sub>4</sub>, are obtained by PALS, and <i>τ</i><sub>3</sub> reflects the random pores structure in SBA-15 matrix, while <i>τ</i><sub>4</sub> denotes the size of SBA-15 hexagonal pores. Compared with the results of SAXS, the mesoporous pore size obtained by PALS technique shows the same trend. By combining SAXS technique and PALS technique, the evolution of material microstructure can be revealed in more depth, thus providing a unique method for studying the structural characterization of functional nanocomposites in the future.

Low-temperature hydrodeoxygenation of phenol using modified TiO2(B) nanosheets supported highly dispersed Pt catalyst

Catalytic hydrodeoxygenation (HDO) of oxygenated compounds is essential for chemical refining, which is always carried out under high temperature, hydrogen pressure or/and strong acids. Herein, we developed a novel Pt/TiO2(B) catalyst for the ambient HDO process. With the modified organic functional TiO2(B) nanosheets, the catalytic activity of Pt/TiO2(B) was significantly improved. Through the synergistic effect of highly dispersed Pt species and TiO2(B) supports, phenol was efficiently converted into cyclohexane and concomitant cyclohexanol under 50 °C and atmospheric hydrogen without extra acid. The characterizations of catalysts showed that the introduction of organic functional groups not only led to the formation of highly dispersed Pt species, but was also conducive to the yielding of key HDO intermediates. Due to the low CO bond energy of enol intermediates, the HDO of phenol could be carried out at mild conditions through the implementable CO bond cleavage of enol intermediates. This study provides a new understanding of the green HDO process and a novel approach for HDO catalyst development.

Improvement of Interaction in a Composite Structure by Using a Sol-Gel Functional Coating on Carbon Fibers.

The modification of carbon fibers for improving adhesion between fibers and an epoxy resin in composite materials has become the focus of attention. In this work the carbon fiber coating process has been devised in a way preventing the stiffening and clumping of fibers. To improve interactions between coated fibers and a resin in composites, four types of silica coatings with different organic functional groups (3-aminopropyl–coating 1, 3-mercaptopropyl–coating 2, 2-(3,4-epoxycyclohexyl) ethyl–coating 3, methyl–coating 4) were obtained. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to distinguish the changes of a carbon fibers surface after coating deposition. The thickness of the obtained coatings, including the diversity of thickness, was determined by transmission electron microscopy (TEM). The increase in surface free energy (SFE) of modified fibers, including the distinction between the polar and dispersive parts, was examined by wettability measurements using a tensometric test. The developed coating preparation process allowed to cover fibers separately with nanoscale silica layers, which changed their morphology. The introduction of organic functional groups resulted in surface free energy changes, especially an increase in specific polar surface energy components.

Donor–Acceptor‐Type Heptazine‐Based Polymer Networks for Photocatalytic Hydrogen Evolution

AbstractA heptazine‐based polymer network (HMP‐3) with a donor–acceptor (D–A) structure was prepared and tested as catalyst for photocatalytic hydrogen evolution from water. Compared to other heptazine‐based materials, which are typically prepared at high temperatures and have recently received much interest as metal‐free photocatalysts, the low‐temperature protocol applied here allows the defined introduction of organic functional groups within the polymer backbone. The structure of HMP‐3 contains alternating heptazine and benzothiadiazole moieties as electron acceptors connected by aminobenzene bridges as electron donors. The resulting material leads to enhanced hydrogen evolution compared to graphitic carbon nitride materials prepared at high temperatures (>500 °C) most probably because of the stabilization of photogenerated charge carriers in the D–A structure.

Thin film photochromic materials: Effect of the sol-gel ormosil matrix on the photochromic properties of naphthopyrans

Photochromic naphthopyran derivatives have been embedded in sol-gel prepared organically modified thin films. The introduction of organic functional groups into a silica matrix allows tailoring the surface of its pores and the polarity of the environment of the embedded host molecules. The photochromic properties of the naphthopyran molecules, such as the spectral properties of the coloured forms and the kinetics of the thermal bleaching, depend strongly on the polarity of the pores where the molecules are located and, hence, on the nature and loading of organic functional groups in the composition of the ormosil matrix. Important changes in the photochromic properties of the films have also been induced by modifications in the sol-gel preparation and processing parameters. The photostability of the photochromic molecules upon prolonged exposition to UV light is strongly related to the nature of the embedding ormosil matrix. The introduction of organic functional groups into the inner pore surface of the matrix, where the dye molecules will be located, affects the stability of the molecules, in terms of the effectiveness of the interaction between the photochromic molecules and the pore surface.

Photostability of a photochromic naphthopyran dye in different sol-gel prepared ormosil coatings

A photochromic naphthopyran derivative was embedded in sol-gel prepared thin ormosil films. The resulting samples show high transparency and exhibit a strong red colouration upon irradiation with UV light. The photostability of the photochromic molecules is strongly related to the nature of the embedding ormosil matrix. The introduction of organic functional groups into the inner pore surface of the matrix allows tailoring the chemical environment where the dye molecules will be allocated, in terms of the effectiveness of the interaction between the photochromic molecules and the Si-OH groups on the surface of the pores, affecting the stability of the molecules upon prolonged exposition to UV light.

The role of organic groups in ormosil matrices in the photochromism of naphthopyrans in sol–gel thin films

Photochromic 3,3-diphenyl-3H-naphtho[2,1-b]pyran molecules were embedded in sol–gel prepared thin organically modified silica films. The introduction of organic functional groups into a silica matrix allows the surfaces of its pores to be tailored and thus the polarity of the pores to be modified. The photochromic properties of the naphthopyran molecules, such as the spectral properties of the colored forms and the kinetics of thermal bleaching, were found to depend strongly on the polarity of the pores in which the molecules are located and hence, on the nature and loading of the organic groups (Me, Ph or iBu) in the ormosil matrix. The large isobutyl substituents showed the largest reduction in the polarity of the pore, due to the effective screening of the polar OH groups at the surfaces of the pores. Hence, the absorption band of the open colored form of the photochromic dye could be adjusted by as much as 35 nm in the yellow-to-orange range by changing the composition of the embedding matrix. Reducing the polarity of the pore walls in the ormosil matrix resulted in a substantial acceleration of the bleaching kinetics of the photochromic effect.