Mesoporous Silica HMS Research Articles

Removing Pb2+ by Adsorption over Thiol-Functionalized Mesoporous Silica

A thiol-functionalized HMS mesoporous silica was synthesized with thiolsilane. FTIR characterization suggests that thiol group has been anchored on the surface of HMS. SH-HMS performs better than HMS in adsorption of lead ion from water. The adsorption ratio on SH-HMS monotonously increases with adsorption time, which is beyond 95.5% after 5 min of adsorption time and be close to the equilibrium state. It decreases with pH value while increases with adsorbent dosage. Furthermore, the increment of lead initial concentration leads to decrease the adsorption ratio while increase the adsorption quantity. Adsorption ratioof 100 % can be obtained under following conditions: pH 6, 30 min of adsorption time, 8 g L–1 of adsorbent dosage, and 40 mg L–1 of initial lead concentration. The relationship between the adsorptive quantity and equilibrium adsorption concentration is in good accordance with both of the Langmuir isotherm model and the Freundlich model.

Improvement of dissolution of poorly soluble glimepiride by loading on two types of mesoporous silica carriers

The aim of the present study was to evaluate the potential of MCM-41 and HMS mesoporous silica particles as efficient carriers for poorly soluble drug, such as glimepiride (BCS, class II). In vitro release tests performed at pH 7.4 showed practically complete release of the drug in two hours from both carriers, whereas the dissolution of pure glimepiride reached only 30% for the same time. The results from our study suggested that the improved solubility was probably due to a significant decrease in drug crystallinity degree. The beneficial safety profile of the glimepiride-loaded MCM-41 and HMS particles was proved on human endothelial EA.hy926 and hepatotoma HepG2 cells. Our findings suggest that the newly developed formulations might be considered as promising and safe delivery systems for poorly soluble drug like glimepiride.

Ti-Doped Pd-Au Catalysts for One-Pot Hydrogenation and Ring Opening of Furfural

Pd-Au bimetallic catalysts with different Pd/Au atomic ratios, supported on ordered structured silica (Hexagonal mesoporous silica—HMS, or Santa Barbara Amorphous-15—SBA-15) were evaluated for one-pot hydrogenation of furfural to 1,2-pentanediol. The surface and structural properties of the catalysts were deeply investigated by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), N2 adsorption isotherms (BET), Infrared spectroscopy (IR), and acid capacity measurements. XPS studies revealed that Ti doped supports had higher dispersion of the active phase, particularly in the case of Pd-Au materials in which Ti played an important role in stabilizing the metallic species. Among the various process conditions studied, such as temperature (160 °C), catalyst amount (10% w/w), and reaction time (5 h), H2 pressure (500 psi) was found to improve the 1,2-pentanediol selectivity. The SBA silica bimetallic Ti-doped system showed the best performance in terms of stability and reusability, after multiple cycles. Under specific reaction conditions, the synergism between Pd-Au alloy and Ti doping of the support allowed the ring opening pathway towards the formation of 1,2-pentanediol in furfural hydrogenation.

Removal of Cationic Dyes, Heavy Metal Ions, and CO2 Capture by Adsorption on Mesoporous Silica HMS

Mesoporous silica with wormhole framework structure (HMS-OH) and its amine-functionalized material (HMS-NH2) were prepared through an electrically neutral assembly pathways, post-grafting process of 3-aminopropyltriethoxysilane (APTES), respectively. Their adsorption behaviors toward cationic dyes as well as heavy metal ions in aqueous system and the capture capacities for CO2 molecules all have been investigated. As-synthesized HMS-OH showed a high removal efficiency and rapid sorption rate to cationic dyes because of large surface area and versatile pore structure. HMS-NH2 exhibited better heavy metal ions and more CO2 gas sorption capacities due to the intrinsic property of amine groups grafted on the surface. The adsorption isotherms of methylene blue (MB) onto HMS-OH, Cu(II) onto HMS-NH2 were fitted with Langmuir model and kinetic processes followed well the pseudo-second order pattern. There results revealed that both HMS-OH and HMS-NH2 had a potential application in the treatment of cationic dyes, heavy metal ions, and greenhouse gas CO2.

Tuning the textural properties of HMS mesoporous silica. Functionalization towards CO2 adsorption

HMS mesoporous silica materials were prepared using different amines as structure directing agents. Textural properties showed a clear dependence on the molecule used, with too long and too short amines yielding significantly distorted structures.CO2 adsorbents were obtained by loading additional amino groups on supports before (as made) or after removing the structure directing agent (extracted and calcined). Organic loading was performed by grafting with diethylenetriamine-trimethoxysilane (DT) and by impregnation with polyethyleneimine (PEI). CO2 adsorption analyses showed a higher CO2 uptake and amine efficiency (defined as the molar ratio CO2/N) for uniformly-structured adsorbents. Besides, as-made materials showed the best CO2 adsorption properties due to a synergistic effect between loaded amines and those already present in the support.The influence of adsorption temperature, operation cycles and CO2 concentration was also studied. A maximum CO2 uptake of 4.19 mmol CO2/g (184 mg CO2/g) was registered in pure CO2 (90 °C, 1 bar), while a value of 1.80 mmol CO2/g was found in direct air capture conditions (400 ppm CO2, 45 °C, 1 bar).

Facile fabrication of NaCl-added mesoporous silica HMS composite and its humidity responsing performance

A humidity-responsive material of NaCl-added mesoporous silica HMS composite was obtained successfully by a facile grind method where mesoporous silica HMS had been synthesized via a sol–gel route. Under room temperature, the sample of NaCl-added HMS with NaCl content of 0.2 g/g showed excellent humidity sensitivity. The impedance decreased linearly by more than four orders of magnitude from 11 to 95% relative humidity and the response time was about 18 s. In addition, the effect of pore order in mesoporous silica on its humidity-sensitive properties was discussed and complex impedance spectra were investigated to validate the humidity-sensing mechanism of Na-HMS(0.2).

Facile one-pot synthesis of highly dispersed Ni nanoparticles embedded in HMS for dry reforming of methane

Mesoporous silica-supported Ni can serve as alternative effective catalysts for dry reforming of methane. However, conventional synthesis method requires long synthetic time and high cost, and the resulting catalysts show unsatisfactory catalytic stability due to coking and sintering. In this paper, we reported a facile, low-cost and environmental benign method to introduce Ni species into HMS mesoporous silica (Ni-HMS) in a self-assembled way. FT-IR, H2-TPR, and TEM manifested that the obtained Ni-HMS established uniform distributed Ni particles (3.9±0.5nm) and strong metal-support interaction derives from Si-O-Ni bonding. The dry reforming of methane results demonstrated that the Ni-HMS showed more active and stable catalytic performance than that of Ni impregnated HMS catalyst (Ni/HMS). Notably, the catalytic activity was well maintained even after reacting at 700°C for 100h. HAADF-STEM and TG-DSC revealed that coking and sintering were unnoticeable over the endurance-tested Ni-HMS catalysts. The strong anchor effect of pore wall to Ni nanoparticles inherent to the one-pot synthesis was suggested to be the original reason for enhanced resistance toward coking and sintering.

Conditions of deposition of TiCl4 used in preparing the silylated Ti-HMS and their effect on catalytic epoxidation of propylene

Silylated Ti catalysts based on hexagonal mesoporous silica (Ti-HMS) were prepared by chemical vapor deposition of TiCl4 on HMS silica modified by vapor silylation. The influence of TiCl4 deposition conditions on surface properties and catalytic performance of the catalysts were investigated. Among the methods used to characterize the catalysts were N2-adsorption, Inductively coupled plasma-atomic emission spectrometry (ICP-AES), Ultraviolet-visible spectroscopy (UV-Vis), Raman spectroscopy. Catalytic activity was evaluated in the epoxidation of propylene using cumene hydroperoxide (CHP) as oxidant. Most of Ti ions in HMS mesoporous silica occupy tetrahedral sites and these sites are responsible for the efficient epoxidation activity. The Ti content incorporated in silica decreases with increasing calcination temperature. The experiments indicated 400°C as an appropriate deposition temperature since higher deposition temperatures favor the formation of low active Ti species. A deposition time of 2 h is a sufficient time interval for incorporating Ti into HMS mesoporous silica. A suitable calcination temperature can be estimated as 700°C while higher calcination temperatures promote the formation of low active Ti species. Propylene oxide in high yields (> 95%) can be obtained in the epoxidation of propylene over the catalysts described in the work. The mechanism proposed for the deposition reaction suggests that the incorporation of Ti into HMS is due to silica interaction of Si-OH with TiCl4, chlorination removes Cl-containing Ti species and in this way decreases the Ti content of catalysts at high deposition temperatures.

Pd and PdAu catalysts supported over 3-MPTES grafted HMS used in the HDS of thiophene

Palladium and bimetallic palladium-gold catalysts were supported over mesoporous silica HMS grafted with variable amount of mercaptopropyl groups corresponding to different molar ratio of the SH group over the metal, molesSH/molesmetal=2, 4, 7, 9. The obtained catalysts, characterized by XRD and XPS techniques were tested in the hydrodesulphurization (HDS) reaction of thiophene. Generally speaking, all the bimetallic catalysts were more active as compared to the monometallic ones. The support modification affected the structure of the fresh (calcined) and reduced catalysts. Supporting the metals over the bare HMS, through deposition–precipitation with urea, produced a drastic decrease of the surface area at variance with the catalysts supported over the functionalized HMS which maintained fairly high surface areas. According to the XRD, the introduction of the SH groups contributed to the better dispersion of the PdO and metallic gold in the calcined samples. Upon hydrogen treatment the supported metals transformed into small particles of gold enriched alloy leading to high activity and lower catalyst deactivation. The promotion of the catalytic behaviour increased with the increase of the SH loading up to a molar ratio, molesSH/molesmetal=7. Above this value, the beneficial effect started diminishing. Based on the XPS and the XRD results, the catalytic behaviour was correlated with the structure and surface composition of the supported species, governed by the interaction between the metals and the mercaptogroups.

Tuning the hydrophobicity of mesoporous silica materials for the adsorption of organic pollutant in aqueous solution

The ability of various as-prepared and organically modified MCM-41 and HMS mesoporous silica materials to behave as efficient adsorbents for organic pollutants in aqueous solution was investigated by using different surface functionalization procedures, so as to adjust their hydrophilic/hydrophobic balance. The hydrophilic and organophilic properties of the parent silica materials and their corresponding surface functionalized counterparts were studied by using water and toluene adsorption isotherms. Their quantification was determined by the hydrophobic static index value (HI static), as well as by the silanol and organic group densities after the functionalization step. A clear correlation could be found between the HI static values and either the superficial silanol density, or the amount of organic moieties grafted or incorporated to the silica materials. For the highly organically functionalized samples, the residual superficial silanol groups (<50%) are sufficiently isolated from each other so as to prevent the water capillary condensation within the pores, thereby leading to an increased hydrophobic character of the resulting mesoporous silica. Those hydrophobic samples, for which the water liquid meniscus formation within the mesopores was minimized or avoided, exhibited a storage capacity for an organic pollutant (N,N-diethyl-m-toluamide, DEET) in aqueous solution more than 20 times higher than that of the corresponding unmodified sample, independently of the silica nature (MCM-41 or HMS). For all calcined and silylated samples, the DEET maximum adsorption capacities determined by the Langmuir model could be correlated with the silica surface coverage by trimethylsilyl groups and thus with the remaining silanol amount.

Sulfated ZrO&lt;sub&gt;2&lt;/sub&gt; Supported on HMS Mesoporous Silica for Catalytic Epoxidation of Soybean Oil

Sulfated zirconia supported on HMS mesoporous silica (SZ-HMS) was prepared and evaluated by catalytic epoxidation of soybean oil. The preparation procedure of SZ-HMS included soaking of HMS with ZrOCl2, and then sulfating with H2SO4. The samples were characterized by IR, XRD, and N2-adsorption. SZ-HMS kept the typical mesoporous crystalline as well as pore structure and exhibited an excellent catalytic performance for the epoxidation of soybean oil. The best catalytic activity, 4.4 of epoxy value, is acquired over the SZ-HMS sample prepared by 0.2 mol/L of ZrOCl2 concentration, 0.75 mol/L of H2SO4 concentration, and 823 K of calcination temperature.

Preparation of a kind of mesoporous carbon and its performance in adsorptive desulfurization

Carbon materials were prepared using mesoporous silica HMS with different pore sizes as the hard templates and water-soluble phenolic resin as the carbon source. The obtained materials were characterized by powder X-ray diffraction, transmission electron microscopy and N 2 physical adsorption, and were used in adsorptive desulfurization. It has been shown that the carbon material prepared using HMS with larger pore size (>3 nm) presented uniform wormlike mesopore of 2.3 nm and large BET surface area (1903 m 2/g). The mesoporous carbon was an excellent adsorbent to remove the refractory sulfur compound in diesel, especially dibenzothiophene and 4, 6-dimethyldibenzothiophene.

Highly active and selective copper-containing HMS catalyst in the hydrogenation of dimethyl oxalate to ethylene glycol

Abstract Copper-containing mesoporous silica HMS catalysts were prepared by an impregnation method. The surface structures of these catalysts were characterized by N 2 -physisorption, X-ray diffraction, transmission electron microscopy, H 2 temperature-programmed reduction, Fourier transform infrared spectroscopy, N 2 O titration and X-ray photoelectron spectroscopy. The results show that the copper-containing HMS catalysts exhibit superior catalytic performance in the selective hydrogenation of dimethyl oxalate to ethylene glycol compared to the commercial silica-supported ones obtained by the same method. The dimethyl oxalate conversion can reach 100% and the ethylene glycol selectivity can reach 92% at 473 K with 2.5 MPa H 2 pressure and 0.2 h −1 liquid hour space velocity of dimethyl oxalate over the 5 wt.% Cu-HMS catalyst. The enhanced catalytic performance of copper-HMS catalysts may be attributed to the homogeneous dispersion and uniformity of the active copper species and to the larger copper surface areas attained on the HMS supports with large pore diameters and surface areas.

Propane oxidative dehydrogenation over vanadia catalysts supported on mesoporous silicas with varying pore structure and size

The structural characteristics and the performance of vanadia catalysts (0.7–8 wt.% V) supported on mesoporous (MCM-41, HMS, MCF, SBA-15), microporous (silicalite) and non-porous (SiO 2) silicas in oxidative dehydrogenation of propane were investigated. The structure of vanadia species, the redox and the acidic properties of the catalysts were studied using in situ Raman spectroscopy, TPD- NH 3 and H 2-TPR. The only vanadia species detected on the surface of HMS and MCM-41 for V loadings up to 8 wt.% were isolated monovanadates indicating high vanadia dispersion. Additional bands ascribed to V 2O 5 nanoparticles were evidenced in the case of SBA-15 and MCF supported catalysts while these bands were the only ones identified on the surface of the catalysts supported on silicalite and non-porous silica. The catalysts supported on mesoporous HMS and MCM-41 materials showed the best performance achieving high propane conversions (35–40%) with relatively high propene selectivities (35–47%). Lower activity due to the lower degree of vanadia dispersion, caused by the partial destruction of the pore structure was observed for the SBA-15 and MCF supported catalysts. The degree of dispersion of the V species on the catalyst surface and not the pore size and structure of the mesoporous support or the acidity/reducibility characteristics mainly determine the catalytic activity towards propene production. In addition, it was shown that the pore structure and size of the mesoporous supports did not have any significant effect in the turnover rates (TOF values) of propane conversion (and propene formation at low propane conversion, below ca. 10%). However, the highest propene yield (up to 19%) and stable catalytic behavior was attained for catalysts supported on HMS mesoporous silica, and especially for those combining framework mesoporosity and textural porosity (voids between primary nanoparticles).

Sorption of reactive dyes from aqueous solutions by ordered hexagonal and disordered mesoporous carbons

In the present study two synthetic mesoporous carbons, a highly ordered CMK-3 sample with hexagonal structure and a disordered mesoporous carbon (denoted DMC) were investigated for the sorption of Remazol Red 3BS (C.I. 239) dye in comparison to three commercial activated carbons and a HMS mesoporous silica with a wormhole pore structure. The structural, porosity and surface characteristics of the materials were evaluated using XRD, TEM, N 2 porosimetry, FT-IR spectroscopy and zeta-potential measurements. Optimal dye sorption occurred at pH ∼2. Equilibrium sorption data followed the Langmuir model and showed that the two synthetic mesoporous carbons exhibit higher sorption capacities ( q max ∼ 500–580 mg/g at 25 °C) in comparison to the commercial activated carbons which possessed either microporous (Takeda 5A and Calgon carbon) or combined micro-/mesoporous (Norit SAE-2) structures and to the HMS mesoporous silica. Thermodynamic parameters as the change in free energy, enthalpy, and entropy of sorption were also estimated. Kinetic studies were carried out and showed a rapid sorption of dye in the first ca. 30 min while equilibrium was reached after ca. 3 h. The sorption kinetics of dye was best described by a second-order kinetic model. A surfactant enhanced carbon regeneration (SECR) technique was used to regenerate the dye-loaded carbon sorbents.

Efficient adsorption and photocatalytic degradation of organic pollutants diluted in water using the fluoride-modified hydrophobic titanium oxide photocatalysts: Ti-containing Beta zeolite and TiO 2 loaded on HMS mesoporous silica

Using the F − media, the hydrophobic zeolite and mesoporous silica can be synthesized. These hydrophobic porous materials exhibit the high ability for the adsorption of organic compounds diluted in water and become the useful supports of photocatalyst. The hydrophobic Ti-Beta(F) zeolite prepared in the F − media exhibited high efficiency than the hydrophilic Ti-Beta(OH) zeolite prepared in OH − media for the liquid-phase photocatalytic degradation of 2-propanol diluted in water to produce CO 2 and H 2O. The TiO 2 loaded on the hydrophobic mesoporous silica HMS(F) (TiO 2/HMS(F)), which was synthesized using tetraethyl orthosilicate, tetraethylammonium fluoride as the source of the fluoride and dodecylamine as templates, also exhibited the efficient photocatalytic performance for the degradation. The amount of adsorption of 2-propanol and the photocatalytic reactivity for the degradation increased with increasing the content of fluoride ions on these photocatalysts. The efficient photocatalytic degradation of 2-propanol diluted in water on Ti-Beta(F) zeolite and TiO 2/HMS(F) mesoporous silica can be attributed to the larger affinity for the adsorption of propanol molecules on the titanium oxide species depending on the hydrophobic surface properties of these photocatalysts.

Functionalized HMS mesoporous silica as solid phase extractant for Pb(II) prior to its determination by flame atomic absorption spectrometry

In this work, a mesoporous silica has been chemically modified with 5-mercapto-1-methyl-1-H-tetrazol using the homogeneous route (MTTZ-HMS). This synthetic route involved the reaction of 5-mercapto-1-methyl-1-H-tetrazol with 3-chloropropyltriethoxysilane, prior to immobilization on the support. The resulting material has been characterized and employed as solid phase extractant for Pb(II). The effect of several variables (stirring time, pH, temperature, metal concentration, presence of other metals) has been studied using batch and column techniques. In batch experiments, 15 min stirring time, 55 degrees C and pH 8 were the optimal conditions for Pb(II) adsorption. In column experiments, sorption was quantitative for 1000 mL of 2.41 x 10(-4 )mM of Pb(II) solution and adsorbed ions were eluted out by 5 mL of 1 M HCl (preconcentration factor of 200). Spiked tap water was used for the preconcentration and determination of Pb(II) by flame atomic absorption spectrometry, and a 100% recovery was obtained. The LOD and LOQ values of the proposed method were found to be 3.52 x 10(-3) and 4.20 x 10(-3 )mM, respectively. The RSD for three preconcentration experiments was found to be <or= 2%. The linear working range for measurements was between 2 x 10(-3 )and 0.14 mM (y = 0.0136x + 0.0007, R(2 )= 0.9999).

Synthesis and Photocatalytic Activity of TiO&lt;sub&gt;2&lt;/sub&gt; Nanoparticles Loaded on the Fluorine-Modified Hydrophobic Mesoporous Silica

The fluorine-modified mesoporous silica HMS(F20) was synthesized by using the mixture of TEFS(SiF(OC2H5)3) and TEOS(Si(OC2H5)4) as the silica source. The specific surface and pore size distribution were characterized by N2 adsorption and the hydrophilic-hydrophobic property was measured by water adsorption. The photocatalytic activities of TiO2 nanoparticles loaded on HMF(F20) and HMS were investigated for the degradation of iso-butanol diluted in water. The results show that the fluorine-modified mesoporous silica HMS(F20) has higher hydrophobic property than HMS and the TiO2/HMS(F20) exhibits the higher photocatalytic activity than TiO2/HMS. The hydrophobic mesopores benefit the condensation of hydrophobic organic compounds diluted in water, which results in higher photocatalytic degradation efficiency.

Visible-light-responsive photocatalytic reaction on tetrahedrally-coordinated chromium oxide moieties loaded on ZSM-5 zeolites and HMS mesoporous silica: partial oxidation of propane

Chromium oxide (Cr-oxide) moieties loaded on ZSM-5 zeolites and HMS mesoporous silica molecular sieves were prepared by an impregnation method and characterized by various spectroscopic methods (XRD, XAFS, UV-Vis, photoluminescence) and their photocatalytic reactivities for partial oxidation of propane under visible light irradiation were investigated. The local structure of Cr-oxide species depended to a large extent on the zeolite types and Si/A1 ratios of zeolites. Tetrahedrally-coordinated isolated Cr-oxide moieties can be loaded on HMS and ZSM-5 having the higher Si/A1 ratios. On these catalysts, in the presence of propane and O2, a partial oxidation proceeded under visible light irradiation to produce acetone with high selectivity. The charge-transfer excited state of the tetrahedral Cr-oxide moieties plays a significant role in the selective photocatalytic reactions under visible light irradiation.