Mesoporous silica: a suitable adsorbent for amines

Biogenic Amine Sensing Based on Rosamine a N-Methylpyridinium Derivative Supported on Silica Materials from Rice Husk

In this work new rosamine-silica composites were prepared and their sensing ability towards different amines was assessed. Rice husk wastes were used as a biogenic silica source. Silica was extracted by thermal treatment, before rice husk ash and after acid leaching with citric acid-treated rice husk ash. Mesoporous material (SBA-15) was also prepared using the extracted silica. The prepared materials were characterized by several techniques such as FTIR, XRD, SEM and N₂ adsorption. The materials were then used as adsorbents of the chromophore N-methylpyridinium rosamine (Ros4PyMe). The obtained loaded composites were tested in solution for amines sensing (n-butylamine, aniline, putrescine and cadaverine). The detection studies were analyzed by fluorescence and revealed 40% and 48% quenching in fluorescence intensity for the composite Ros4PyMe@SBA in the presence of the biogenic amines cadaverine and putrescine, respectively. The composite was also sensitive in the powder form, changing the color from violet to pale pink in the presence of putrescine vapors with a fast response (around 2 min), the process being reversible by exposure to air.

Quantitative Study of the Enhanced Content and Chemical Stability of Functional Groups in Mesoporous Silica by In-Situ Co-condensation Synthesis

The chemical stability and content of organic functional groups significantly affect the application of materials in the field of adsorption. In this study, we quantitatively studied the effect of in-situ co-condensation and post grafting on the physico-chemical properties and sorption properties of modified mesoporous silica. The results showed that the grafting method changed the morphology of mesoporous silica while the in-situ method kept the spherical morphology well, and the amino groups were both successfully introduced into the materials. Besides, the amino content of the material prepared by in-situ method (ami-MSN) was 2.71 mmol/g, which was significantly higher than the 0.98 mmol/g of the grafting method (ami-g-MS). Moreover, the chemical stability of functional groups in ami-MSN was much better than ami-g-MS. Furthermore, ami-MSN showed better capability in removing toxic metals of Pb, Cd, Ni, and Cu, and the removal efficiency of Pb reached 98.80%. Besides, ami-MSN exhibited higher dynamic CO2 adsorption of 0.78 mmol/g than ami-g-MS of 0.34 mmol/g. This study revealed the relationship between modification methods and the modification efficiency, functional groups stability, and sorption properties through quantitative comparative studies, which provided a reference for preparing modified mesoporous silica materials with high sorption properties.

Exceptional Packing Density of Ammonia in a Dual-Functionalized Metal-Organic Framework

We report the reversible adsorption of ammonia (NH₃) up to 9.9 mmol g^-1 in a robust Al-based metal-organic framework, MFM-303(Al), which is functionalized with free carboxylic acid and hydroxyl groups. The unique pore environment decorated with these acidic sites results in an exceptional packing density of NH₃ at 293 K (0.801 g cm^-3) comparable to that of solid NH₃ at 193 K (0.817 g cm^-3). In situ synchrotron X-ray diffraction and inelastic neutron scattering reveal the critical role of free -COOH and -OH groups in immobilizing NH₃ molecules. Breakthrough experiments confirm the excellent performance of MFM-303(Al) for the capture of NH₃ at low concentrations under both dry and wet conditions.

Application of surfactant-templated ordered mesoporous material as sorbent in micro-solid phase extraction followed by liquid chromatography-triple quadrupole mass spectrometry for determination of perfluorinated carboxylic acids in aqueous media

In the present study, micro-solid phase extraction (µ-SPE) followed by liquid chromatography-triple tandem mass spectrometery (LC-MS/MS) was developed for the determination of perfluorocarboxylic acids (PFCAs) at trace levels in water samples. The µ-SPE device comprised of a porous polypropylene membrane bag containing 5mg sorbent. The membrane bag acted as a clean-up filter and prevented matrix compounds from interfering with the extraction process. Analysis was carried out by LC-MS/MS in negative electrospray ionization mode. MS/MS parameters were optimized for multiple reaction monitoring. Calcined and non-calcined MCM-41, as silica-ordered mesoporous materials, were used as sorbents in µ-SPE for the extraction of five PFCAs-perfluoropentanoic acid (PFPA), perfluoroheptanoic acid (PFHpA), perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), and perfluorodecanoic acid (PFDA)-from aqueous media. The performances of these two sorbents were compared with other sorbents such as octadecylsilane (C18) modified silica, HayeSep-A, HayeSep-B, and Porapak-R. It was found that non-calcined MCM-41 showed better extraction performance for the analytes considered. Parameters influencing extraction efficiency, such as desorption time, extraction time, desorption solvent, and salt concentration, were investigated. The effect of the matrix on MS signals (suppression or enhancement) was also evaluated. Only minor effects on ionization efficiencies were observed. The developed method proved to be convenient and offered good sensitivity and reproducibility. The limits of detection ranged from 0.02 to 0.08ng L(-1), with a relative standard deviations between 1.9 and 10.5. It was successfully applied to the extraction of PFCAs in river and rain water samples. As expected from the ubiquitous nature of PFCAs, contamination at low levels was detected for some analytes in the samples (with the highest concentration recorded for PFOA). Satisfactory relative recoveries ranging between 64% and 127% at spiking levels of 10ng L(-1) of each analyte were obtained.

Nanocasting Synthesis of Ultrafine WO3 Nanoparticles for Gas Sensing Applications

Ultrafine WO3 nanoparticles were synthesized by nanocasting route, using mesoporous SiO2 as a template. BET measurements showed a specific surface area of 700 m 2/gr for synthesized SiO2, while after impregnation and template removal, this area was reduced to 43 m 2/gr for WO3 nanoparticles. HRTEM results showed single crystalline nanoparticles with average particle size of about 5 nm possessing a monoclinic structure, which is the favorite crystal structure for gas sensing applications. Gas sensor was fabricated by deposition of WO3 nanoparticles between electrodes via low frequency AC electrophoretic deposition. Gas sensing measurements showed that this material has a high sensitivity to very low concentrations of NO2 at 250°C and 300°C.