Post-grafting Method Research Articles

Fabrication of isocyanate‐based polyimide foam by a postgrafting method

ABSTRACTDensity and flame retardancy controlled isocyanate‐based polyimide foam was prepared by a postgrafting method. The first solution containing prepolymer that was synthesized by dianhydride and overdose isocyanates was added into the second solution containing dianhydride derivatives, water, catalysts, and surfactants. The possible reactions during preparation are discussed. The obtained Fourier transform infrared spectra indicate that an increased amount of imide rings was generated with increasing molar ratio of the anhydride/isocyanate groups. The size and walls of the cells became smaller and thinner with less carbon dioxide (CO2) escaping into the air during the first solution preparation process, as shown in scanning electron microscopy images. The thermogravimetric analysis curves demonstrated that the 5% weight loss temperature (T5%) was greater than 289 °C, and the residual weight retention at 800 °C was more than 45%. In addition, differential thermogravimetry curves demonstrated that the thermal stability decreased with more byproducts in polyimide foams. The limiting oxygen index increased gradually from 30.63% ± 0.56 to 48% ± 0.50 with increasing molar ratio of the anhydride/isocyanate groups. Meanwhile, the density of obtained polyimide foams ranged from 38.31 kg/m3 ± 0.90 to 99.53 kg/m3 ± 10.85. When the molar ratio of anhydride/isocyanate groups ranged from 0.4 to 0.8, the prepared isocyanate‐based polyimide foams all exhibit both great flame retardancy and lower density. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44240.

Preparation of amidoxime functionalized SBA-15 with platelet shape and adsorption property of U(VI)

Abstract A novel amidoxime (AO) functionalized SBA-15 (AO@SBA-15) with platelet shape and short channels, was prepared by the amidoximation reaction of hydroxylamine with cyanoethyl (CN) functionalized SBA-15 (CN@SBA-15) under N 2 atmosphere. The precursor CN@SBA-15 was initially synthesized by co-condensation of tetraethoxysilane with 2-cyanoethyltriethoxysilane (CTES) using a triblock copolymer (P123) as a structural directing agent in acid medium or via the post-grafting of CTES onto SBA-15 with short channels. The AO@SBA-15 with platelet shape and short channels was employed as an adsorbent to remove U(VI) from an aqueous solution. The g-AO@SBA-15 (precursor prepared by post-grafting method) has higher adsorption capacity (625 mg g −1 ) than that of c-AO@SBA-15 (precursor prepared by co-condensation method) (516 mg g −1 ) at an optimum pH of 6, but with one more preparation step. Results indicated that both the adsorbents showed fast adsorption rate, high selectivity to Na + , K + , Mg 2+ , and Ca 2+ , and reusability for uranium extraction. Therefore, AO-functionalized SBA-15 with short channels is a promising adsorbent to remove uranium ion from an aqueous solution.

Fluorescence emission properties of rhodamine B encapsulated organic-inorganic hybrid mesoporous silica host

Mesoporous silica material can be viewed as an ideal solid host for constructing desirable dye laser with tunable wavelength range. In this investigation, Rhodamine B molecules were successfully encapsulated into the pore of highly ordered MCM-41 and Phenyl-functionalized MCM-41 mesoporous silica by using a simple and facile postgrafting method. The as-gained Rhodamine B encapsulated mesoporous silica materials were successfully characterized by Fourier transform infrared spectroscopy, nitrogen adsorption-desorption and small angle X-ray diffraction. Particularly, the optical absorption and electrochemical behaviors investigated by UV-vis absorption spectra and electrochemical cyclic voltammogram indicate that the difference on the hydrophillic nature of different mesoporous silica hosts has great influence on the existence state of Rh B molecules, resulting lead to strong fluorescence and obvious blue-shift of the encapsulated Rhodamine B molecules in the proposed organic-inorganic hybrid mesoporous. Furthermore, it was pointed out that the significant host-guest interactions of mesoporous silica and Rhodamine B are related not only to the structure, but also to the environmental and surrounding polarity of the materials.

Effects of different amounts of APTES on physicochemical and structural properties of amino-functionalized MCM-41-MSNs

Mesoporous silica nanoparticles (MSNs) are frequently functionalized to be used for specific applications, including catalysis and biomedical engineering. In this research, MCM-41-MSNs were synthesized by the sol–gel method and were functionalized with different quantities of (3-aminopropyl) triethoxysilane (APTES) using a post-grafting method to determine the physicochemical and structural changes in the MSNs. The functionalized materials were assessed by different characterization techniques, namely, TGA, FTIR, BET, SEM, TEM, DLS, zeta potential, SAXS, XRD and XPS. The FTIR data confirmed the presence of amino groups on the MSN surfaces, and the results from the XPS, TGA and zeta potential demonstrated that the APTES concentration during post-grafting directly affects the quantity of amino groups bound to the MSNs. The SAXS, TEM and nitrogen adsorption–desorption analyses showed that as the amount of APTES in the MSNs increases, the mesoporous structure become more disordered.

Amplified spontaneous emission from DCJTB encapsulated in mesostructured composite silica SBA-15.

Amplified spontaneous emission (ASE) characteristics of a red dye 4-(Dicyanomethylene)-2-t-butyl-6-(1,1,7,7- etramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) encapsulated in a highly ordered mesoporous SBA-15 were studied. The mesoporous composite silica film loaded with organic dye has been successfully synthesized by a solgel reaction process and a simple postgrafting method at room temperature. The spectrum narrowing phenomena has been observed when the composite film is pumped at λp=532 nm by a Nd:YAG ed laser. There is a substantial reduction in the full width at half-maximum of the emitting light, which is one of the signatures of the presence of ASE. The ASE threshold and net gain, respectively, reached 0.03 mJ pulse^-1 and 34.7 cm^-1 for the DCJTB encapsulated in mesoporous SBA-15 film. The optimized ASE properties owe much to the effects of the better spatial confinement of the molecules in the ordered mesoporous structure of the host SBA-15.

Dihydroxy bezladely derivatives functionalized mesoporous silica SBA-15 for the sorption of U(VI)

Three different modified SBA-15 have been synthesized by a post-grafting method using 3,4-dihydroxy benzaldehyde (OHBA), 2,4-dihydroxy benzaldehyde (MHBA), 2,4-dihydroxy acetophenone (RATP). These materials were characterized by NMR, TEM, FT-IR and elemental analysis. Batch experiments have been conducted to study the effects of pH, temperature, adsorbent dosage, ionic strength, shaking time, initial concentration of metal ion, and coexisting ions on uranium(VI) sorption behaviors of pure and functional SBA-15. In addition, the adsorption of U(VI) could be well-described by the Langmuir, Freundlich isotherms and pseudo-second kinetic models. The results suggest the sorption capacity and selectivity of SBA-15 were improved after functionalization.

Release of flurbiprofen using of SBA-15 mesoporous silica: Influence of silica sources and functionalization

In the present study, SBA-15 silica materials synthesized from different silica sources (S15T and S15S) and functionalized by post-grafting method with trimethylmethoxysilane (F-S15T and F-S15S) were compared as drug carriers for flurbiprofen (FBP). The physical state of the drug in the samples was characterized by differential scanning calorimetry (DSC) and X-ray diffractometry (XRD). The results showed that the FBP molecules were not arranged in a crystalline form after incorporation of FBP into the pores of the SBA-15 samples. Surface functionalization resulted in decreased surface area, pore size, and pore volume of S15T and S15S, which decreased the drug-loading capacity from 27.09% to 13.59% and from 16.96% to 9.19%, respectively. The in vitro drug release testing demonstrated that functionalized SBA-15 samples showed slower release rates compared to the non-functionalized samples. The results indicate that F-S15T (which had the smallest pore size) showed controlled drug release profiles without burst-release while the other silica samples showed faster release profiles than F-S15T, indicating that pore size and hydrophobicity influenced the rate of the drug release process. The drug release mechanism of all the samples was found to be Fickian diffusion.

Translation of a solution-based biomineralization concept into a carrier-based delivery system via the use of expanded-pore mesoporous silica

Mineralization of collagen fibrils using solution-based systems containing biomimetic analogs of matrix proteins to stabilize supersaturated calcium phosphate solutions have been predictably achieved in vitro. Solution-based systems have limitations when used for in-situ remineralization of human hypomineralized tissues because periodic replenishment of the mineralizing solution is infeasible. A carrier-based platform designed for delivering mineral precursors would be highly desirable. In the present work, mesoporous silica nanoparticles with expanded pores (eMSN; 14.8nm) were synthesized. Polyacrylic acid–stabilized amorphous calcium phosphate (PA–ACP) was generated from a supersaturated calcium and phosphate ion-containing solution, and chosen as the model mineralizing phase. After amine functionalization (AF) of the eMSN through a post-grafting method, the positively-charged AF-eMSN enabled loading of PA–ACP by electrostatic interaction. In-vitro cytotoxicity testing indicated that PA–ACP@AF-eMSN was highly biocompatible. The release kinetics of mineralization precursors from PA–ACP@AF-eMSN was characterized by an initial period of rapid calcium and phosphate release that reached a plateau after 120h. Intrafibrillar mineralization was examined using a 2-D fibrillar collagen model; successful mineralization was confirmed using transmission electron microscopy. To date, this is the first endeavor that employs expanded-pore mesoporous silica to deliver polymer-stabilized intermediate precursors of calcium phosphate for intrafibrillar mineralization of collagen. The carrier-based delivery system bridges the gap between contemporary solution-based biomineralization concepts and clinical practice, and is useful for in-situ remineralization of bone and teeth. Statement of significanceConcepts of collagen biomineralization have been reasonably well established in the past few years and intrafibrillar mineralization of collagen fibrils can be predictably achieved with analogs of matrix proteins using solution-based systems. However, solution-based systems have their limitations in clinical applications that require direct application of mineralization precursors in-situ because periodic replenishment of the mineralizing solution is impossible. The present work presents for the first time, the use of amine-functionalized mesoporous silica with expanded pores for loading and release of polyacid-stabilized amorphous calcium phosphate mineralization precursors, and for intrafibrillar mineralization of type I collagen fibrils. This strategy represents an important step in the translational application of contemporary biomineralization concepts for in-situ remineralization of bone and teeth.

AMINE MODIFIED MESOSTRUCTURED SILICA NANO PARTICLES ENHANCED ADSORPTION OF PHENOL

Mesoporous silica nanoparticles (MSN) were synthesized and modified with (3-aminopropyl) triethoxysilane (APTES) using co-condensation (co-MSN) and post-grafting (post-MSN) methods. Both modification methods seem to alter the crystallinity, surface area, and pore volume as compared to the unmodified MSN. The activity of all MSNs was tested for the adsorptive removal of phenol. Co-MSN showed significantly good adsorptivity towards 10 mg L-1 of phenols, followed by post-MSN and MSN. It was found that the highest activity of co-MSN was resulted from the additional higher adsorption energy from the quaternary alkylammonium groups (Si–C–C–C–[N+–(CH3)3]) of cationic template and also from the amine group of the APTES functionalization, which showed more advantages as compared to post-MSN and MSN.

Synthesis and characterization of Ni and Zn Schiff base complexes supported on modified MCM-41 as reusable catalysts for various oxidation reactions

Using post grafting method, two hybrids composite materials were prepared by anchoring Nickel and Zinc Schiff base complexes onto amino-modified MCM-41(Ni-MCM-41 and Zn-MCM-41). The prepared catalysts have been characterized by FT-IR spectroscopy, thermogravimetric analysis, and transmission electron microscopy, powder X-ray diffraction and N2 adsorption–desorption isotherms. The catalysts showed excellent catalytic efficiency in oxidation reaction of sulfides to sulfoxides and oxidative coupling of thiols to their corresponding disulfides using urea hydrogen peroxide as oxidant under mild reaction conditions. The supported Schiff base complexes can be recovered easily and reused many times without significant loss in catalytic activity and selectivity.

A Novel Naphthalene-Immobilized Nanoporous SBA-15 as a Highly Selective Optical Sensor for Detection of Fe(3+) in Water.

A novel organic-inorganic hybrid optical sensor (SBA-NCO) was designed and synthesized through immobilization of isocyanatopropyl-triethoxysilane and 1-amino-naphthalene onto the surface of SBA-15 by post-grafting method. The characterization of materials using XRD, TEM, N2 adsorption-desorption, and FT-IR techniques confirmed the successful attachment of organic moieties and preserving original structure of SBA-15 after modification step. Fluorescence experiments demonstrated that SBA-NCO was a highly selective optical sensor for the detection of Fe(3+) directly in water over a wide range of metal cations including Na(+), Mg(2+), Al(3+), K(+), Ca(2+), Cr(3+), Mn(2+), Fe(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+), Hg(2+),and Pb(2+) in a wide pH values.

ChemInform Abstract: A Highly Efficient, Enantioselective and Recyclable Mesoporous Silica‐Based Mn(II) Catalyst for Asymmetric Oxidation of Thioanisole.

The development of environmentally benign reactions is an important goal in synthetic organic chemistry and chemical engineering. However, catalytic enantioselective oxidations using transition-metal complexes are limited when the oxidant is hydrogen peroxide. A hydrazone based asymmetric ligand (H2L) was used to prepare a heterogeneous catalyst by the immobilization of its manganese complex, [{Mn(H2O)2Cl2}2(H2Btar)] (1), on mesoporous support SBA-15 via the post grafting method (H2L = 2,3-O-4-hydroxybenzhydrazidebenzylidene-D-tartrate). The heterogeneous asymmetric catalyst 1-SBA15 was characterized by elemental analysis; small angle X-ray diffraction (SAX), scanning electron microscopy (SEM), nitrogen sorption measurement, Fourier transform infrared spectroscopy and EPR spectroscopy. The asymmetric oxidation of thioanisole (PhSMe) was achieved with hydrogen peroxide in the presence of 1-SBA15 in excellent conversion and enantioselectivity (>99% ee). Compared to a homogeneous catalyst, the heterogenized catalyst is more stable and can be recycled four times without any significant loss of activity. Immobilization of complex 1 onto SBA-15 increased the selectivity toward sulfone in the oxidation.

Complexes of N,N-bis (salicylidene)4,5-dimethyl-1,2-phenylenediamine immobilized on porous nanomaterials: Synthesis, characterization and study of their antimicrobial activity

A new hybrid antibacterial material was developed by post synthesis grafting method. 3-aminopropyl triethoxysilane (3-APTES) was first anchored over MCM-41 and NaY Zeolite upon reaction with transition metal (M = Mn(II), Co(II) and Cu(II)) complexes of tetradentate Schiff base ligand L: (C22H20N2O2). The prepared materials were characterized by several techniques: chemical analysis, diffuse reflectance spectroscopy (DRS), Fourier transfer infrared (FT-IR), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and Burner–Emmet–Taller(BET). The in vitro antibacterial activity of these compounds was evaluated against Staphylococcus aureus (S. aureus) and Bacillus subtilis (B. subtilis), as Gram-positive bacteria, and further against Escherichia coli (E. coli) and Pseudomonas aeruginosa (P. aeruginosa), as Gram-negative bacteria. Then, the results were compared with standard drugs. The analysis revealed that hybrid materials that prepared by immobilization Schiff base in porous materials show fine inhibition on bacterial growth till 24 h.

Carboxylic acid-functionalized SBA-15 nanorods for gemcitabine delivery

The present study deals with the functionalization of mesoporous silica nanoparticles as drug delivery systems. Mono, di, and tri amino-functionalized SBA-15 nanorods were synthesized by post-grafting method using (3-aminopropyl) triethoxysilane, N-(2-aminoethyl-)3- aminopropyltrimethoxysilane, and 3-[2-(2-aminoethylamino) ethylamino] propyl trimethoxysilane, respectively. The carboxylic acid derivatives of the amino-functionalized samples were obtained using succinic anhydride. Tminopropyltrimethoxysilanehe obtained modified materials were investigated as matrixes for the anticancer drug (gemcitabine) delivery. The prepared samples were characterized by SAXS, N2 adsorption/desorption, SEM, transmission electron microscopy, thermogravimetric analysis, and FTIR and UV spectroscopies. The adsorption and release properties of all samples were studied. It was revealed that the adsorption capacity and release behavior of gemcitabine were highly dependent on the type of the introduced functional groups. The carboxylic acid-modified samples have higher loading content, due to the strong interaction with gemcitabine. The maximum content of deposited drug in the modified SBA-15 nanorods is close to 40 wt%. It was found that the surface functionalization leads toward significant decrease of the drug release rate. The carboxylic acid-functionalized samples have slower release rate in contrast with the amino-functionalized samples.

Titanium functionalized α-zirconium phosphate single layer nanosheets for photocatalyst applications

Titanium species were immobilized on α-ZrP nanosheets (ZrP–Ti) using a modified post-grafting method.

Piperazine and its carboxylic acid derivatives-functionalized mesoporous silica as nanocarriers for gemcitabine: adsorption and release study.

Piperazine-functionalized SBA-15 nanorods were synthesized by post grafting method with methyldimethoxysilylpropylpiperazine (MDSP). The carboxylic acid derivatives of piperazine-functionalized SBA-15 nanorods were obtained using two different kinds of precursors (bromoacetic acid and succinic anhydride). The prepared materials were used as nanocarriers for the anticancer drug (gemcitabine). The obtained samples were characterized by SAXS, N2 adsorption-desorption, SEM, TEM, DLS, thermogravimetric analysis, FTIR, Raman and UV spectroscopies. The adsorption and release properties of all samples were investigated. In vitro study included cell toxicity. It was found that the surface functionalization increases the interaction between the carrier and gemcitabine and results in the loading enhancement of the drug. In addition, the adsorption of gemcitabine on the modified mesoporous matrix depends on the type of the introduced functional groups. The carboxylic acid-modified samples have higher loading content, due to the strong interaction with gemcitabine. The maximum content of deposited drug in the modified SBA-15 nanorods is close to 36wt.% that it is related to PC2-SBA-15 sample which obtained using succinic anhydride. The obtained results reveal that the surface functionalization leads toward a significant decrease of the drug release rate without any appreciable cytotoxicity. No significant differences are observed among the drug release rate from the modified samples.

Bidentate salen Cu(II) complex functionalized on mesoporous MCM-41 as novel nano catalyst for the oxidative coupling of thiols into disulfides using urea hydrogen peroxide (UHP)

Functionalized Copper(II) complex into nano dimensional mesoreactor was successfully prepared. The Copper(II) complex with N–O donor Schiff base ligand was readily trapped into mesoporous silica MCM-41 through the post grafting method. N–O Chelating Schiff-base-MCM-41 has been derived from 5-bromo-salicylaldehyde and 3-aminopropyltriethoxysilane which was functionalized on MCM-41 via silicon alkoxide route. This compound was characterized by FT-IR, TGA, small angle X-ray diffraction patterns, ICP/MS analysis and N2 sorption–desorption analysis. The catalytic property of Cu–salen–MCM-41 was considered for the preparation of disulfides using urea hydrogen peroxide as oxidant. The reaction progress is simple and proceeds under mild and heterogeneous conditions in acetonitrile at the ambient of temperature. The corresponding disulfides have been achieved with high purity and good to excellent yields; also, no over oxidation to sulfoxide or sulfone was observed in all cases. The catalyst can be recovered and reused several times without significant loss of stability and activity.

Functionalized MCM-41 as a catalyst for the aldol condensation of 4-isopropylbenzaldehyde and propanal

Aldol condensation of 4-isopropylbenzaldehyde and propanal was carried out using functionalized MCM-41. The aldol condensations are usually performed using acidic or basic catalysts and due to this fact, the modification of MCM-41 was realized using post-grafting method by two acid groups (3-propylsulfoxy, 3-propylcarboxy) and one basic (the 3-(1,2-diethylamino)propyl) group. MCM-41 treated by sulfuric and nitric acid was also used. The prepared functionalized materials were characterized by BET, elemental analysis and UV–Vis spectroscopy. The optimal reaction conditions were found: the temperature of reaction mixture 100 °C, the molar ratio of reactants 4 isopropylbenzaldehyde:propanal = 1:2, the amount and the type of the catalyst: 50 wt% of MCM SO3H (compared to the amount of 4-isopropylbenzadehyde), the addition time of propanal 90 min and suitable solvent for the reaction was toluene. Using the optimal reaction conditions the yield of forcyclamenaldehyde was 45 %. The obtained results were compared to homogeneous catalysis with H2SO4 where the yield was 15 %.

A highly efficient, enantioselective and recyclable mesoporous silica-based Mn(ii) catalyst for asymmetric oxidation of thioanisole

The development of environmentally benign reactions is an important goal in synthetic organic chemistry and chemical engineering. However, catalytic enantioselective oxidations using transition-metal complexes are limited when the oxidant is hydrogen peroxide. A hydrazone based asymmetric ligand (H2L) was used to prepare a heterogeneous catalyst by the immobilization of its manganese complex, [{Mn(H2O)2Cl2}2(H2Btar)] (1), on mesoporous support SBA-15 via the post grafting method (H2L = 2,3-O-4-hydroxybenzhydrazidebenzylidene-D-tartrate). The heterogeneous asymmetric catalyst 1-SBA15 was characterized by elemental analysis; small angle X-ray diffraction (SAX), scanning electron microscopy (SEM), nitrogen sorption measurement, Fourier transform infrared spectroscopy and EPR spectroscopy. The asymmetric oxidation of thioanisole (PhSMe) was achieved with hydrogen peroxide in the presence of 1-SBA15 in excellent conversion and enantioselectivity (>99% ee). Compared to a homogeneous catalyst, the heterogenized catalyst is more stable and can be recycled four times without any significant loss of activity. Immobilization of complex 1 onto SBA-15 increased the selectivity toward sulfone in the oxidation.

Adsorption of tannic acid from aqueous solution by aminopropyl functionalized SBA-15

Tannic acid (TA) is generally considered as one of the refractory organic pollutants in water. In this study, aminopropyl functionalized SBA-15 (SBA-15-NH2) was prepared by post-grafting method and the adsorption behavior of TA on the synthetic adsorbent was investigated using batch experiments and adsorption kinetic tests. The adsorbent was characterized by a variety of experimental and spectroscopic techniques with respect to structural, porosity, and surface characteristics. Characterization results showed that SBA-15-NH2 has ordered mesoporous structure, BET surface area of 245.49 m2/g, and the pore volume of 0.43 cm3/g. Batch adsorption tests showed that SBA-15-NH2 adsorbent exhibited high adsorption affinity to TA with a maximum adsorption capacity of 272.4 mg/g. TA adsorption over the adsorbents could be well described by Freundlich adsorption model, suggesting that the adsorption process is heterogeneous. The hydrogen bonding ability and electrostatic interaction between the TA and aminopropyl groups further conformed by pH and ionic strength experiments. In addition, the adsorption process obeyed the pseudo-second-order kinetics and the rate constant decreased with initial TA concentration.