Mesoporous Silica Molecular Sieves Research Articles

Humidity-resistant hydrogen sensors based on rare-earth-doped tin dioxide nanofibers with hydrophobic mesoporous silica sieve encapsulation

Air humidity is a major factor that degrades the performance and long-term stability of metal-oxide-semiconductor (MOS) based gas sensors. In this work, we propose an encapsulation strategy by coating a mesoporous silica molecular sieve (SBA-15) on rare earth doped tin oxide (RE-SnO2) nanofibers for humidity-resistant hydrogen detection. In this design, the hydrophobic SBA-15 sieve layer effectively blocks the water molecules without affecting hydrogen diffusion, while the RE dopant greatly improves the responsivity and lowers down the operating temperature of the sensors, As a result, the Er-SnO2/SBA-15 and Tb-SnO2/SBA-15 sensors respectively show the maximum response values of 27.71 and 33.68 (to 10 ppm hydrogen at 280 °C, 4.67 and 5.67 times that of the bare SnO2 ones, respectively), short response/recovery time (< 1.0 s / < 1.0 s), as well as a low limit of detection for hydrogen (200 ppb) and a good gas selectivity. Under the protection of the SBA-15 sieve layer, the response retention of the sensors is significantly improved when the humidity increases from 25% to 85% RH (Er-doping, from 38.8% to 60.0%; Tb-doping, form 25.6–57.8%). Besides, further analysis on enhancement mechanism of response indicates that the SBA-15 coating contribute about 1/3 of the response enhancements via its own hydrogen physical adsorption capacity and the induced oxygen vacancies during the calcination processes.

Enhancements on volatile organic compounds (VOCs) adsorption and desorption performance of ZSM-5 by fabricating hierarchical MCM-41.

ZSM-5 zeolite has been considered a promising adsorbent for capturing VOCs. However, its hydrophilicity and narrow micropore structure limit their practical application especially under humid atmospheres. In this study, the pure silica mesoporous molecular sieve MCM-41 was assembled on ZSM-5 zeolite with different SiO2/Al2O3 ratios (SARs) via a surfactant-mediated recrystallization method. Then, its adsorption-desorption behaviors were investigated using n-hexane, toluene, and ethyl acetate as VOC model molecules. The results showed that the hydrophobicity of ZSM-5/MCM-41 composites and their VOC diffusion behaviors were significantly improved. Furthermore, the SARs of the ZSM-5 precursors had a remarkable influence on the adsorption performance of ZSM-5/MCM-41 composites. ZSM-5/MCM-41(130) was the optimum option, and its dynamic adsorption capacity for ethyl acetate (111.30 mg·g-1) was higher than that of the corresponding ZSM-5 zeolites even under statured humidity. Meanwhile, the ratios of dynamic adsorption capacities at humid and dry atmospheres (qs,wet/qs,dry) of ZSM-5/MCM-41(130) for n-hexane, toluene, and ethyl acetate were 84.89%, 61.46%, and 73.81% respectively. The results will provide guidelines for the preparation of hydrophobic adsorbents.

Synthesis of spherical amine-functionalized silica molecular sieve and application as selective adsorbents for aromatic hydrocarbons analysis

In this work, spherical amine-functionalized mesoporous silica (Sp-Amino-Si) molecular sieve was fabricated by an acid hydrothermal method using 3-aminopropyltriethoxysilane as a modifier and toluene as the solvent. The results of scanning electron microscopy, Barrett-Joyner-Halenda pore size distribution, Fourier transform-infrared spectroscopy, and low-angle X-ray diffraction patterns revealed that the Sp-Amino-Si was monodispersed microspheres with uniform and controllable pore sizes sharing two-dimensional hexagonal P6mm symmetry and a large number of amino groups. The Sp-Amino-Si molecular sieve was verified to be suitable for the selective separation of aromatic hydrocarbons (AMHs) containing two fused benzene rings among other compounds from environmental water matrix. Under the optimized conditions, the Sp-Amino-Si exhibited much higher adsorption efficiency for AMHs (above 88.19%), comparing to the original SBA-15 (below 44.52%). The maximum adsorption capacities for naphthalene, methyl naphthalene, 2-methyl naphthalene, and acenaphthene were 477.1, 1006.5, 893.3, and 1253.2 µg·g−1, respectively. The high selectivity of Sp-Amino-Si for the four AMHs attributed to the size sieving and p-π interactions between the lone pair electrons of amine groups and the π-electrons in AMHs molecules. The Sp-Amino-Si based solid-phase extraction coupled with high performance liquid chromatography detection method was constructed for the analysis of the four AMHs, and the recoveries of spiked AMHs ranged from 89.67% to 112.74% with a relative standard deviation lower than 5.75%. This study provides some inspiration and a reliable method for AMHs separation, removal, and analysis.

Brief History, Preparation Method, and Biological Application of Mesoporous Silica Molecular Sieves: A Narrative Review.

It has been more than 30 years since the first ordered mesoporous silica molecular sieve (MCM-41) was reported, but the enthusiasm for exploiting mesoporous silica is still growing due to its superior properties, such as its controllable morphology, excellent hosting capability, easy functionalization, and good biocompatibility. In this narrative review, the brief history of the discovery of mesoporous silica and several important mesoporous silica families are summarized. The development of mesoporous silica microspheres with nanoscale dimensions, hollow mesoporous silica microspheres, and dendritic mesoporous silica nanospheres is also described. Meanwhile, common synthesis methods for traditional mesoporous silica, mesoporous silica microspheres, and hollow mesoporous silica microspheres are discussed. Then, we introduce the biological applications of mesoporous silica in fields such as drug delivery, bioimaging, and biosensing. We hope this review will help people to understand the history of the development of mesoporous silica molecular sieves and become familiar with their synthesis methods and applications in biology.

Nanoengineered, magnetically guided drug delivery for tumors: A developmental study.

Fighting against tumors is an ongoing challenge in both medicinal and clinical applications. In recent years, chemotherapy, along with surgery, has significantly improved the situation to prolong life expectancy. Theoretically, and regardless of dosage, we now have drugs that are strong enough to eliminate most tumors. However, due to uncontrollable drug distribution in the body, it is difficult to increase treatment efficiency by simply increasing dosages. For this reason, the need for a drug delivery system that can release “bombs” at the target organ or tissue as precisely as possible has elicited the interest of researchers. In our work, we design and construct a silica-based nanocomposite to meet the above demand. The novel nanocomposite drug carrier can be guided to target tumors or tissue by a magnetic field, since it is constructed with superparamagnetic Fe3O4 as the core. The Fe3O4 core is clad in a mesoporous silica molecular sieve MCM-41 (represented as MS, in this article), since this MS has enormous ordered hexagonal caves providing sufficient space to hold the drug molecules. To modify the magnetically guided carriers so that they become both magnetically guided and light-responsive, benzophenone hydrazone is coupled into the molecular sieve tunnel. When a certain wavelength of light is imposed on the gating molecules, C=N double bonds vibrate and swing, causing the cavity that holds the drug molecules to change size and open the tunnels. Hence, the nanocomposite has the ability to release loaded drugs with light irradiation. The structure, loading abilities, and the size of the nanocomposite are inspected with a scanning electron microscope, a transmission electron microscope, thermogravimetry analysis, N2 adsorption/desorption, and dynamic light scattering The biocompatibility and in vitro drug molecule controlled release are tested with an SMMC-7721 cell line.

Phosphotungstic acid and propylsulfonic acid bifunctionalized ordered mesoporous silica: A highly efficient and reusable catalysts for esterification of oleic acid

In phosphotungstic acid aqueous solution, the ordered mesoporous silica molecular sieve (HPW/OMS-SO3H) simultaneously functionalized by phosphotungstic acid (HPW) and propyl sulfonic acid groups (-pr-SO3H) was successfully prepared via a one-pot co-condensation method. The skeleton of the materials was formed based on the simultaneous hydrolysis and co-condensation of 3-mercaptopropyltriethoxysilane (MPTES) and tetraethoxysilane (TEOS) using in situ oxidation of the thiol groups to sulfoacid groups with H2O2. The materials with an ordered 2D hexagonal mesoporous structure and a high specific surface area were confirmed by the results of small-angle XRD, N2 adsorption–desorption, and TEM. The spectroscopy of FT-IR, UV–Vis DRS, XPS, and Raman indicated that the active component of HPW and propylsulfonic acid groups successfully immobilized on the OMS support and a strong interaction existed among silicon hydroxyl and propylsulfonic acid groups with HPW. The esterification reaction of oleic acid with methanol to produce biodiesel over prepared catalyst showed excellent catalytic activity due to the synergistic effect between the HPW and propylsulfonic acid groups. The biodiesel yield of 95.3% was obtained by 0.3HPW/OMS-SO3H-5 catalyst under the optimum reaction conditions. The catalytic performance was not reduced significantly even after five cycles reused, because the strong interaction prevented acid-active component loss from the support. The activation energy of the reaction by the 0.3HPW/OMS-SO3H-5 materials was investigated, which obeyed the first-order kinetics.

Selective Hydrogenation of the Carbonyls in Furfural and 5-Hydroxymethylfurfural Catalyzed by PtNi Alloy Supported on SBA-15 in Aqueous Solution Under Mild Conditions.

Valuable furfuryl alcohol (FFA) and 2,5-dihydroxymethylfuran (DHMF) could be produced by selective hydrogenation of biomass-derived furfural (FF) and 5-hydroxymethylfurfural (HMF) with high atom economy. In this study, SBA-15 (a kind of mesoporous silica molecular sieve)-supported low metal loading (3 wt% total metal content) PtNi alloy catalyst (PtNi/SBA-15) was synthesized via two steps, including the generation of PtNi alloy by hydrothermal method, and the immobilization of PtNi alloy on SBA-15. PtNi/SBA-15 has ordered mesoporous structure with high surface area, and high dispersion of the PtNi alloy with the formation of Ptδ−-Niδ+ surface pairs on SBA-15, which benefit hydrogen activation and selective carbonyl hydrogenation. The selective hydrogenation of FF and HMF over PtNi/SBA-15 in water solvent at 303 K with 1.5 MPa H2 within 2 h, could respectively yield 64.6% FFA with 77.0% selectivity, and 68.2% DHMF with 81.9% selectivity. Besides, PtNi/SBA-15 exhibited a satisfactory water resistance and stability after recycling at least five runs.

Polyol-pretreated SBA-16 supported Ni-Fe bimetallic catalyst applied in CO methanation at low temperature

• Polyols were used to pretreat the mesoporous silica molecular sieve SBA-16 to adjust the surface groups. • Bimetallic Ni-Fe catalysts with polyol-pretreated support were obtained. • The mechanism of how the polyols influence the surface SiOH groups and thus the metal particles distribution was figured out. • Catalysts with polyol-pretreated support lowered the minimum temperature for CO complete conversion to 230 °C from 290 °C. Polyols were used to pretreat the mesoporous silica molecular sieve SBA-16 and thus supported bimetallic Ni-Fe catalyst was prepared in order to address the low activity of CO methanation at lower temperature. The characterization of the pretreated support and catalysts indicated that the residual polyols release heat during combustion, which could provide energy for the decomposition of metal precursors, lowering the decomposition temperature and reducing the metal particle size. More importantly, the pretreatment of support with polyols could increase the isolated silicon hydroxyl, and strengthen the metal-support interaction, thus obtaining smaller metal particles. The smaller metal particles promoted the dissociation of reactant gas, as a result, Ni-Fe bimetallic catalyst with polyol-pretreated support could lower the minimum temperature for CO complete conversion from 290 °C to 230 °C while keeping CH 4 selectivity above 90%. Catalysts with polyol-pretreated support provide a new possibility for low-temperature CO methanation technology.

Polymer grafted mesoporous SBA-15 material synthesized via metal-free ATRP as pH-sensitive drug carrier for quercetin

PH-sensitive amphiphilic poly(2-(diethylamino)ethyl methacrylate) (PDEAEMA) were grafted from mesoporous silica molecular sieve SBA-15 surface via metal-free atom transfer radical polymerization (metal-free ATRP). The amino group was introduced onto SBA-15 surface by silane coupling agent KH-550, followed by the ATRP initiator SBA-15-Br was obtained after bromoisobutyryl bromide (BIBB) immobilized onto SBA-15 surface. The PDEAEMA grafted SBA-15 (SBA-15-g-PDEAEMA) inorganic–organic hybrid materials were prepared by surface initiated metal-free ATRP using SBA-15-Br as initiator, 10-phenylphenothiazine (PTH) as photocatalyst, 2-(diethylamino)ethyl methacrylate (DEAEMA) as the monomer. Then, the anticancer drug quercetin was loaded onto SBA-15-g-PDEAEMA hybrid material (SBA-15-g-PDEAEMA-Qu) and the controlled release of quercetin was investigated. The analytical results indicated that the ATRP initiator has been successfully anchored onto the SBA-15 surface and the ordered structure of the mesoporous material has been maintained. The kinetic plots and the curve of the relationship between Mn and monomer conversion illustrates that the polymerization process has the characteristics of “living”/controllable radical polymerization. The TGA results showed that the graft rate of organics in SBA-15 channel is 24.7%. In vitro cytotoxicity evaluation and cell uptake assay results indicated that the cytotoxicity of SBA-15-g-PDEAEMA to the L929 cells had completely disappeared on the 3rd day, SBA-15-g-PDEAEMA has good biocompatibility and can be endocytosed by L929 cells. The drug release rate of SBA-15-g-PDEAEMA hybrid material loaded with quercetin (SBA-15-g-PDEAEMA-Qu) at pH = 5.5 is significantly higher than that at pH = 7.4, the SBA-15-g-PDEAEMA hybrid material can be used as carrier for controlled drug release and has potential application prospects in clinical practice.

One‐Pot Synthesis of Propyl‐Sulfonic Phosphotungstic Dual‐Acid Functionalized Mesoporous Silica in Non‐Hydrochloric Acid Solution: Reusable Catalyst for Efficient Biodiesel Production

AbstractOrdered mesoporous silica molecular sieve (HPW/OMS‐SO3H), functionalized by phosphotungstic acid (HPW) and propyl sulfonic acid, was successfully synthesized using the green and efficient one‐pot co‐condensation method in a non‐hydrochloric acid solution. The materials, making HPW and propyl sulfonic acid successfully immobilized on the OMS supports, have ordered 2D hexagonal mesoporous structure. The catalyst showed excellent catalytic activity in the esterification of oleic acid with methanol due to the synergistic effect between the HPW and propyl sulfonic acid group. The catalytic performance not reduced significantly after five recycling reflected that the catalyst has excellent stability. The activation energy of esterification was calculated by detailed kinetic studies.

Study on SBA-15 as an effective sorbent for dye butyl rhodamine B

Nano mesoporous silica molecular sieve material SBA (Santa Barbara Amorphous)-15 was prepared by hydrothermal method and characterized by means of powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and nitrogen adsorption-desorption studies. Butyl rhodamine B (BRB) was adsorbed by the SBA-15. The impacts of solution acidity, adsorbent dosage, the initial concentration of butyl rhodamine B, contact time, and temperature on the effects of adsorption were studied and the optimum adsorptive conditions were obtained. The experimental results of adsorption showed that the optimal adsorptive conditions were: pH = 5.0, (SBA-15): BRB = 750: 1, room temperature 30 ± 1 °C and the contact time 20 min. At this time, the adsorption capacity is 1.30 mg/g and the adsorption ratio is 97.52%. Dynamic and thermodynamic properties of the adsorption for butyl rhodamine B by SBA-15 were studied, and the results showed that the adsorption of butyl rhodamine B by SBA-15 is a pseudo-second-order kinetic adsorption. The adsorption thermodynamic data showed that in the 4–30 °C interval ∆G0 0 showed that the adsorption of butyl rhodamine B by SBA-15 is an endothermic process. ΔS0 = 204.9 J / (mol · K) > 0 illustrated that the adsorption process is a reaction of entropy increase. In the 30–60 °C interval, ∆G0 < 0, the reaction can occur spontaneously. ΔH0 = −32.371 kJ/mol < 0 showed that the adsorption of butyl rhodamine B by SBA-15 is an exothermic process. ΔS0 = −30.2 J / (mol · K) < 0 illustrated that the adsorption process is a reaction of entropy decrease. ΔG0 is between −20 and −80 kJ/mol, showing that this adsorption is a coexisting of chemical and physical adsorption. The adsorption of butyl rhodamine B by SBA-15 satisfies the Freundlich adsorption isotherm and belongs to a heterogeneous adsorption.

Highly effective esterification of lignin to produce a pharmaceutical intermediate using novel silica mesoporous molecular sieves as catalysts

The use of lignin to prepare fine chemicals is a hot research topic. Here, we propose a strategy for esterification of the syringyl group, which is abundant in lignin, to produce 3,4-dimethoxyphenyl acetic acid ester. Lignin reacts with alcohols over acidic pure silica catalyst, L-MCM-41, to generate 3,4-dimethoxyphenyl acetic acid esters. The esterification yield from alkali lignin (Indulin AT) reached more than 60%. Furthermore, L-MCM-41 was easily and quickly prepared using hydroxyl free radicals. The obtained L-MCM-41 exhibited enhanced Lewis acidity and stability compared to silica MCM-41 derived from a traditional hydrothermal system. The enhanced Lewis acidity of the surface silicon atoms of L-MCM-41 can be attributed to the electron-withdrawing effect of abundant geminal hydroxyl groups that they bear. Based on spectroscopic data and the concentration of hydroxyl free radicals, the mechanism underpinning the enhanced acidity and stability of the mesoporous silica molecular sieves is proposed. This work enables production of fine chemicals using lignin as feedstock and provides a reliable and simple method for the synthesis of strongly acidic mesoporous silica molecular sieves.

Improved structural stability and catalytic performance for CH4 reforming reaction of mesoporous MCM-41 analogs prepared by zeolitic subunits of MOR desilication

We demonstrated a new strategy for the preparation of highly stable mesoporous molecular sieves (TMM) by the desilication of MOR zeolite and self-assembling of the zeolite subunits in Na2O•(3.3–3.4) SiO2 aqueous solution. Na2O•(3.3–3.4) SiO2 in the aqueous solution plays two roles in the synthesis, one was providing a moderate alkaline medium with buffering effect for the desilication of MOR zeolite, other one was supplementing silica source. The desilication conduction of MOR zeolite was optimized by the adjustment of reaction temperature and time, pH in the solution. TMM were characterized by X-ray diffraction (XRD), N2 adsorption/desorption (BET), Fourier transformed infrared (FT-IR) and transmission electron microscopy (TEM). The characterization results showed that the characteristics of MOR zeolite, such as double six-membered or five-membered ring subunits, were still preserved in TMM, and TMM possessed well-ordered mesostructure of MOR zeolite crystals. Compared with the pure silica mesoporous molecular sieve (MCM-41, 4-day), the hydrothermal stability of TMM (17-day) was increased by 100% with refluxed water. The significantly improving of TMM hydrothermal stability was due to increase the surface hydrophobicity and the ratio of T12-ring, and decreased remarkably number of hydrophilic silanol groups. After hydrothermal treatment for 17-day, TMM also exhibited more efficient catalytic activation than MCM-41 treated for 4-day in CO2 reforming of methane reaction (700 °C). The 5 wt% Ni/TMM-17d-Glu (5 wt% Ni, loading) catalysts prepared by Glucose modified impregnation method exhibited excellent catalytic activity, which were providing 58% CO2 and 47% CH4 conversions at 700 °C.

Electrochemical Detection of Dopamine at a Gold Electrode Modified with a Polypyrrole⁻Mesoporous Silica Molecular Sieves (MCM-48) Film.

A gold electrode modified with a polypyrrole–mesoporous silica molecular sieves (polypyrrole—MCM-48) nanostructure film was used for the electrochemical determination of small concentrations of dopamine (DA) by cyclic voltammetry and square-wave voltammetry techniques. This electrode showed good electrocatalytic activity for the oxidation of dopamine. The oxidation potential of dopamine was decreased significantly compared with that obtained at the bare gold electrode. The observed linear range for the determination of the dopamine concentration, without interferents through cyclic voltammetry measurements, was from 10 μM to 1.2 mM (R2 = 0.9989) for the gold electrode modified with the polypyrrole—MCM-48 nanostructure, with a detection limit of 2.5 μM. In the case of square-wave voltammetry, the linear range was 2–250 μM, with a correlation coefficient of 0.9996, and the detection limit was estimated to be 0.7 μM. The effects of interferents, such as ascorbic acid (AA) and uric acid (UA), on the electrochemical detection of dopamine were also examined. The modified electrode can successfully separate the oxidation potentials for ascorbic acid and dopamine, shifting the oxidation peak potential of ascorbic acid to a more positive potential, and significantly decreasing the peak current. The presence of ascorbic acid increased the sensitivity of dopamine determination at the modified electrode, and the detection limit was estimated to be 0.5 μM with 0.1 mM ascorbic acid to imitate physiological solutions. Additionally, studies showed that the presence of uric acid does not affect the electrochemical detection of dopamine. The modified electrode can be successfully applied for the quantitative analysis of dopamine both with and without interferents.

Effect of mesoporous silica molecular sieve coating on nZVI for 2,4-DCP degradation: Morphology and mechanism during the reaction

Comparative analysis of reactivity for the removal of 2,4-DCP from water by degradation using mesoporous silica molecule sieve coating SiO2-coated nZVI were compared with those using uncoated nZVI. Reaction conditions of 2,4-DCP by nZVI and SiO2-coated nZVI and changes in solution with reaction progress were investigated. The effects of FeSO4·7H2O dosage, 2,4-DCP concentration, initial pH, and co-existing ions on the degradation activity in aqueous were investigated. Changes in pH, Fe2+ and Fe3+ concentration, and UV–vis spectra with reaction time during the whole reaction process were analyzed. Changes in the apparent properties of the uncoated and SiO2-coated nZVI during the entire reaction process were characterized. The experimental results showed that the removal rate distinguished exceeded about 45% when SiO2-coated nZVI was used in 2,4-DCP degradation research, and that high concentrations of Cl− could improve the 2,4-DCP removal rate obviously. The passivation due to the redox reaction of iron ion progressed on the nZVI surface for uncoated nZVI and on the outer layer of SiO2 amorphous coating for coated nZVI. The amorphous SiO2 coatings covered on the nZVI surface distinctly increased their oxidation resistance. It was confirmed that mesoporous silica molecule coating improved reducing capacity of nZVI.

Proton Activity in Nanochannels Revealed by Electron Paramagnetic Resonance of Ionizable Nitroxides: A Test of the Poisson–Boltzmann Double Layer Theory

Chemical and physical processes occurring within the nanochannels of mesoporous materials are known to be determined by both the chemical nature of the solution inside the pores/channels as well as the channel surface properties, including surface electrostatic potential. Such properties are important for numerous practical applications such as heterogeneous catalysis and chemical adsorption including chromatography. However, for solute molecules diffusing inside the pores, the surface potential is expected to be effectively screened by counter ions for the distances exceeding the Debye length. Here, we employed electron paramagnetic resonance spectroscopy of ionizable nitroxide spin probes to experimentally examine the conditions for the efficient electrostatic surface potential screening inside the nanochannels of chemically similar silica-based mesoporous molecular sieves (MMS) filled with water at ambient conditions and a moderate ionic strength of 0.1 M. Three silica MMS having average channel diamet...

A novel amine double functionalized adsorbent for carbon dioxide capture using original mesoporous silica molecular sieves as support

In order to relieve the amine agglomeration phenomenon in solid amine adsorbent and realize the efficient CO2 capture, a novel double-functionalized adsorbent was synthesized by grafting 3-aminopropyltriethoxysilane and impregnating tetraethylenepentamine, using original mesoporous silica molecular sieves as support. The effects of organic amine loading, gas flow rate and adsorption temperature on CO2 adsorption properties of adsorbent were studied. The results show that SBA-15(p)-AP-70T modified with 70% TEPA has the maximum N content (15.81 mmol/g) and the maximum saturated adsorption capacity (5.69 mmol/g) at 75 °C。Moreover, the CO2 adsorption capacity of this adsorbent can still remain about 5.2 mmol/g after 15 adsorption/desorption cycles. It is mainly because that the grafted APTES and residual P123 in the support pore provide space and hydrogen bonding functional groups for TEPA dispersion and fixation, while reduce the loss of TEPA during the cycle process. Therefore, compared with adsorbent modified by only TEPA, the adsorption capacity and stability of this adsorbent can be effectively improved. In addition, kinetic studies indicate that CO2 adsorption on SBA-15(p)-AP-70T is mainly chemisorption. According to the in situ DRIFTS results, CO2 adsorption mechanism on SBA-15(p)-AP-70T adsorbent is consistent with the zwitterion mechanism.

A highly sensitive and moisture-resistant gas sensor for diabetes diagnosis with Pt@In2O3 nanowires and a molecular sieve for protection

Sensitive and selective detection of acetone in human exhaled breath plays an important role in the diagnosis of diabetes. However, obtaining a reliable response to ppb levels of acetone and avoiding cross-sensitivity due to the large amount of moisture in exhaled breath are still great challenges. In this work, a type of acetone sensor with ultrahigh sensitivity and moisture resistance is reported. Electrospun In2O3 nanowires with a controllable Pt core (Pt@In2O3 core-shell nanowires) are designed and prepared as sensitive layers. A mesoporous silica molecular sieve is further integrated as the moisture filter layer. The Pt@In2O3 core-shell nanowire-based sensor exhibits a highly improved response compared with a sensor based on pure In2O3 nanowires due to the probable increase in surface resistance and the introduction of p–n junctions after rational design of the structure. In addition, a good performance in terms of the fast dynamic process, selectivity and long-term stability is also achieved, and the detection limit can be as low as 10 ppb, which is much lower than the concentration level of 1.8 ppm in the exhaled breath of diabetic patients. The influence of the large amount of moisture is greatly weakened by using the molecular sieve as a moisture filter layer, leading to much improved sensitivity in clinical sample detection among healthy and diabetic patients. Based on the optimized composite structure of the Pt@In2O3 core-shell nanowire sensor and moisture filter layer, a simple portable sensing prototype is successfully fabricated. The reported Pt@In2O3 core-shell nanowires and the acetone sensing approach open up a new opportunity for a simple, inexpensive, and noninvasive diagnosis of diabetes.

Pd and Pt nanoparticles supported on the mesoporous silica molecular sieve SBA-15 with enhanced activity and stability in catalytic bromate reduction

Bromate is a highly carcinogenic disinfection by-product in drinking water. Catalytic reduction is an emerging technology that can effectively remove bromate from water without forming additional brines and sludges. In this study, Pd and Pt nanoparticles supported on SBA-15 were prepared for catalytic bromate reduction. The activity investigation results showed that the Pt/SBA-15 catalysts exhibited higher activities than the Pd/SBA-15 catalysts and the commercial 5% Pd/C catalyst, and the highest catalytic activity of 24.72 mg·min−1·gcat−1 was obtained using 4% Pt/SBA-15 as the catalyst. This activity is approximately 2.33- and 6.50-fold higher than the activities of the 4% Pd/SBA-15 and 5% Pd/C catalysts, respectively. Analysis of the intrinsic mechanism revealed that the activation energy of bromate reduction over the 4% Pt/SBA-15 catalyst was 47.31 kJ·mol−1, and the reaction followed the Langmuir-Hinshelwood mechanism, suggesting that the reduction of adsorbed bromate on the Pt surface rather than the diffusion process controlled the overall reaction rate. Catalytic bromate reduction was strongly dependent on the reaction pH, and the catalytic activity increased with decreasing pH. Bromate reduction was suppressed in the presence of coexisting anions, including PO43−, SO42−, and Cl−, and the inhibition effects followed the order of PO43− > SO42− > Cl−. Surprisingly, bromate removal was obviously enhanced when a low concentration (<1.5 mM) of nitrate coexisted in the reaction solution. In addition, the losses in catalytic activity and Pt after five repeated tests were only 7.8% and 2.6%, respectively, revealing the high stability of the 4% Pt/SBA-15 catalyst in the catalytic reduction of bromate.

Experimental research on purifying ultrafine nanoparticle by SBA-15 and its filtration mechanism

Airborne ultrafine nanoparticle (UFNP) is a key factor causing heavy haze pollution in Beijing-Tianjin-Hebei, which is very harmful to human health and the environment. Removal of environmental UFNPs by porous material is an important method of air purification treatment. However, the specific mechanism by which porous material filters UFNPs is not clear. In this study, UFNPs with 2–10 nm diameter were removed by SBA-15 mesoporous silica molecular sieves with different pore sizes, and the filtration mechanism was analyzed using transmission electron microscopy (TEM), specific surface area tests (BET), and X-ray photoelectron spectroscopy (XPS). The analyses showed a distinctive filtration of UFNPs over the interior mesopore channels. The removal efficiencies of SBA-15 with different pore sizes were also compared, demonstrating the influence of the pore size and structure on most penetrating particle size (MPPS). The UFNP filtration efficiency of SBA-15 increased with the increase of pore size. Moreover, SBA-15-14.6 could effectively purify UFNPs, and it had the highest fractional diffusive filtration efficiency of 98.79% and a total efficiency of 92.58% for UFNPs. This study provides a technical basis for the filtration of UFNPs using mesoporous materials.