Nitrogen Adsorption-desorption Measurements Research Articles

Dissolution kinetics studies of kaolin ore as raw material for mesoporous silica by acid leaching

ABSTRACT The high demand for nanoporous silica materials makes it worthwhile to further explore new, cheap and environmentally friendly resources. In this study, the selective acid dissolution of an indigenous kaolin ore after thermal activation for the preparation of mesoporous silica nanoparticles was reported. Experimental parameters (acid concentration, liquid/solid ratio and temperature) were optimised and resultant solid was characterised by X-ray diffraction; scanning and transmission electron microscopy and nitrogen adsorption–desorption measurements. The products were found to be nanoporous with pore sizes of 0.402 and 0.129 cm3 g–1, with specific surface areas of 45.23 and 16.89 m2 g–1, respectively. The pore development follows the Avrami model with parameter model n values of 0.80 and 0.63, and calculated apparent activation energies of 7.22 and 22.81 kJ mol–1 for hydrochloric and sulphuric acid respectively, suggesting that the leaching activity is controlled by diffusion processes. The products as characterised demonstrated the vast potential of kaolinite in the development of mesopore materials for diverse industrial applications.

Development of Bi2O3/MoSe2 mixed nanostructures for photocatalytic degradation of methylene blue dye

Herein, we demonstrate the sample and low coast hydrothermal synthesis of a nanocomposite of Bi2O3/MoSe2 for hybrid photocatalyst. The structure of as-synthesized samples was characterized by using several techniques, including XRD spectroscopy, Raman spectroscopy, XPS, SEM, BET, and UV-visible absorption spectroscopy. The nitrogen adsorption–desorption measurements show that the samples have a mesoporous texture with slits like pores. The Bi2O3/MoSe2 nanocomposite had BET surface areas of 36.439 m2/g, which were more than those of Bi2O3 (18.342 m2/g) and MoSe2 (12.923 m2/g). Under visible illumination, the photocatalytic activities of pure samples ( Bi2O3 and MoSe2) and the hybrid Bi2O3/MoSe2 sample for the disintegration of methylene blue were assessed. The results show that the Bi2O3/MoSe2 sample showed the highest photocatalytic degradation efficiency (i.e. 96.5% after an exposure time of 80 min). The increased photocatalytic activity is due to the mixed sample's high crystallinity and surface area, as well as the small particle size.

Study of the catalytic properties of MgNi(Cu)Al LDH in the one-pot cascade oxidation-Knoevenagel condensation reaction

In this work, the structural and bifunctional catalytic properties of MgNi(Cu)Al layered double hydroxides (LDH) with different molar ratios between the cations were studied. The LDH materials were prepared by co-precipitation and were characterized using X-ray fluorescence (XRF), X-Ray diffraction (XRD), diffuse reflectance infrared Fourier-transform spectroscopy (DRIFT), diffuse reflectance ultraviolet-visible spectroscopy (DR-UV-VIS), scanning electron microscopy (SEM), nitrogen adsorption-desorption and acidity-basicity measurements. They were tested in a one-pot cascade oxidation-Knoevenagel condensation reaction used to synthesize 2-Benzoyl-3-phenylprop-2-enenitrile also known as 2-Benzoyl-3-phenylacrylonitrile (BPA). This involved the benzyl alcohol (BnOH) oxidation under an oxygen atmosphere followed by the Knoevenagel condensation of benzaldehyde with 3-oxo-3-phenylpropanenitrile also known as benzoyl acetonitrile (BzACN). Three different non-polar solvents, i.e., toluene, benzene and 1,3,5-trimethylbenzene (mesitylene), were used as reaction media. For the LDH catalysts containing both nickel and copper, the alcohol conversion and BPA yield increased with Ni/Cu molar ratio. The acid-base properties of the solids and the nature of the solvent strongly influence the reaction performance.

Influence of Rapid Heat Treatment on the Photocatalytic Activity and Stability of Strontium Titanates against a Broad Range of Pollutants

Strontium titanate (STO) photocatalysts were prepared via a slightly modified Pechini sol–gel method. A unique rapid calcination technique with a short exposure time was used to obtain crystalline products. The samples were characterized by X-ray diffractometry, scanning electron microscopy, diffuse reflectance spectroscopy, infrared spectroscopy, nitrogen adsorption–desorption measurements, and X-ray photoelectron spectroscopy. Their photocatalytic activity was evaluated by the photocatalytic oxidation of phenol, oxalic acid, and chlorophenol under UV light irradiation using commercial STO as a reference. These pollutants, together with glucose and propanol, were used to investigate the stability of the samples against various functional groups. All our samples exhibited higher photocatalytic activity than the commercial STO reference. With increasing calcination temperature, the crystallinity and primary crystallite sizes increased while the band gaps and specific surface areas decreased. The photocatalytic activity of the most efficient sample was explained by the presence of SrCO3 on its surface. The STO catalysts were highly stable as they largely retained their crystalline composition after exposure to chemicals with different functional groups. Finally, we compared the costs associated with the unique calcination technique with a more conventional one and found that our method is ~35% more cost-effective.

Efficacy of Olive Stones and Corncobs Crystalline Silica Nanoparticles (SiO2, NPs) Treatments on Potato Tuber Moths (Phthorimaea Operculella)

Morphological and microstructural properties of silica (SiO2) are essential factors that need to be considered during the experimental applications. In this report, SiO2 nanoparticles (NPs) have been prepared at different concentrations from SiO2 powder derived from olive stones and corncobs by an alkali leaching extraction method. Thermal treatment has been used to modify the morphological and microstructural properties of the extracted SiO2. X-ray diffraction (XRD) shows that the extracted amorphous SiO2 has been transformed into a crystalline phase after the thermal treatment. Nitrogen adsorption–desorption measurements revealed significant reduction in both the specific surface area (SABET) and the total pores volume (Vtotal) of the derived SiO2 samples after the thermal treatment. The acquired thermal treatment properties of SiO2 found to have high impacts on the influence of the SiO2 NPs on the survival and development of larvae and pupae of P. opercullela. SiO2 NPs prepared from the crystalline silica samples exhibited less efficiency on suppressing potato tuber moth comparing to SiO2 NPs of the amorphous silica powders. Varied effects on biological parameters including larvae mortality, pupae weight, larval and pupal development time, fecundity and fertility are also linked to the SiO2 NPs source type and showed concentration depending manner effects. SiO2 NPs are conditionally effective as an alternative pesticide against P. opercullela, based on their sources, mesoporous structures and concentrations.

Structure of Y0.75La0.25PO4·0.67H2O rhabdophane nanoparticles synthesized by the hydrothermal microwave method

Nanopowders with a rhabdophane structure of nominal composition Y0.75La0.25PO4·0.67H2O were obtained by hydrothermal-microwave synthesis. The monoclinic structure of rhabdophane was refined by the Rietveld method within the C2 (5) space group. The nanopowders were studied by X-ray diffraction (XRD), transmission electron microscopy (TEM) and electron microdiffraction (selected area electron diffraction, SAED), small angle X-ray scattering (SAXS), thermal analysis, low-temperature nitrogen adsorption-desorption measurements for analysis of surface area and porosity (ASAP) and pycnometric density measurements. These methods showed the formation of rod-like single-crystal rhabdophane nanoparticles with isolated pores inside the nanoparticles. To describe the formation of such nanoparticles, a mechanism of coherent-accommodative intergrowth of nanoscale clusters with rhabdophane structure is proposed.

Preparation and Characterization of CuO/Clay Composite for Methyl Orange Photodegradation

This study reports on the preparation and characterizations of CuO/clay composite and its application for methyl orange (MO) photodegradation. The raw material of natural clay was obtained from Takalar District, South Sulawesi Province of Indonesia. CuO were incorporated in clay by impregnation method, with natural clay was intercalated using CMC before. The new composite was characterized by SEM, nitrogen adsorption-desorption measurements, and XRD. The results from SEM analysis revealed that there is a change in the surface morphology of the sample before and after impregnation, the clay becomes more porous and expands. XRD results show the CuO/clay composite has a monoclinic crystal structure. As for the sample surface area based on BET analysis using t-plot method, the surface area decreased after the CuO impregnated and the pore distribution using BJH analysis decrease, it indicates that CuO was successfully impregnated into the clay. The amount of CuO that was successfully impregnated into clay based on EDX analysis was 26.72%. The composite was successfully used as a photocatalyst in the MO degradation, showing a degradation ability of 85.84% with a composite mass of 500 mg with a contact time of 180 minutes.

Combined Anti-Angiogenic and Anti-Inflammatory Nanoformulation for Effective Treatment of Ocular Vascular Diseases.

Ocular vascular diseases are the major causes of visual impairment, which are characterized by retinal vascular dysfunction and robust inflammatory responses. Traditional anti-angiogenic or anti-inflammatory drugs still have limitations due to the short-acting effects. To improve the anti-angiogenic or anti-inflammatory efficiency, a dual-drug nanocomposite formulation was proposed for combined anti-angiogenic and anti-inflammatory treatment of ocular vascular diseases. CBC-MCC@hMSN(SM) complex nanoformulation was prepared by integrating conbercept (CBC, an anti-angiogenic drug) and MCC950 (MCC, an inhibitor of inflammation) into the surface-modified hollow mesoporous silica nanoparticles (hMSN(SM)). CBC-MCC@hMSN(SM) complex nanoformulation was then characterized by Fourier transform infrared spectroscopy, transmission electron microscopy, zeta potentials, and nitrogen adsorption-desorption measurement. CBC and MCC release profile, cytotoxicity, tissue toxicity, anti-angiogenic effects, and anti-inflammatory effects of CBC-MCC@hMSN(SM) were estimated using the in vitro and in vivo experiments. CBC-MCC@hMSN(SM) complex had no obvious cytotoxicity and tissue toxicity and did not cause a detectable ocular inflammatory responses. CBC-MCC@hMSN(SM) complex was more effective than free CBC or MCC in suppressing endothelial angiogenic effects and inflammatory responses in vitro. A single intraocular injection of CBC-MCC@hMSN(SM) complex potently suppressed diabetes-induced retinal vascular dysfunction, choroidal neovascularization, and inflammatory responses for up to 6 months. Combined CBC and MCC nanoformulation provides a promising strategy for sustained suppression of pathological angiogenesis and inflammatory responses to improve the treatment outcomes of ocular vascular diseases.

Separation of Panax notoginseng saponins on modified rosin ester-bonded silica stationary phase and its mechanism

A column prepared using a unique three-membered phenanthrene skeleton of rosin has complementary selectivity to a C18 column for some separation tasks. In this study, propylene pimaric acid (16-hydroxyethyl acrylate-34-n-butyl) ester (BRB) and propylene pimaric acid (16-hydroxyethyl acrylate-34-dodecyl) ester (BRLA) were used as functional ligands to prepare two novel stationary phases, namely BRB@SiO2 and BRLA@SiO2, through a “thiol-ene” click chemistry reaction. The characterization results of Fourier transform infrared spectroscopy, thermogravimetric analysis, nitrogen adsorption-desorption measurements, and contact angle tests showed that the BRB@SiO2 and BRLA@SiO2 stationary phases were successfully prepared. In addition, the performance of the columns was evaluated using the Tanaka test and hydrophobic subtraction model, which showed that the stationary phases exhibited typical reversed-phase chromatography performance and good hydrophobicity, hydrophobic selectivity, and steric selectivity. The changes in the retention of Panax notoginseng saponins on a column under different chromatographic conditions (acetonitrile content, flow rate, and column temperature) were investigated. The separation effect of BRB@SiO2 and BRLA@SiO2 columns on P. notoginseng saponins was better than that of the C18 column and the BRLA@SiO2 column could replace the C18 column for the detection of P. notoginseng saponins.

Lanthanum-based metal organic framework (La-MOF) use of 3,4-dihydroxycinnamic acid as drug delivery system linkers in human breast cancer therapy

Metal organic frameworks (MOFs) have received a lot of attention in the research community due to their unique physical properties, which make them ideal materials for targeted drug delivery systems. In this paper, we describe the synthesis of a non-toxic La-based MOF with 3,4-dihydroxycinnamic acid (3,4-DHCA) as a linker. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), nitrogen adsorption–desorption measurements, and X-ray powder diffraction (XRD) have all been used to characterize it thoroughly. The La-based MOF showed good biocompatibility with the human breast cancer cell line MDA-MB-468. The ability of 3,4-DHCA to treat MDA-MB-468 cells was confirmed by 40.35% cell viability with La-based MOF. Based on the findings, La-based MOF can be recommended as a promising candidate for anticancer delivery.

Features of the surface layer structure of the magnetosensitive materials functionalized by silica with thiourea groups and their applying for selective Cu(II) and Au(III) ions removal

One-step sol–gel synthesis for covering magnetic particles with polysiloxane layers with ≡Si(CH2)3NHC(S)NHC2H5 groups has been proposed. Unique properties of this functional group, containing sulfur and nitrogen, and the developed approach open wide (and novel) opportunities for the controlled surface design. A number of factors affecting the characteristics of such materials and their sorption properties towards heavy metal ions were analyzed. Results of scanning and transmission electron microscopy studies, Fourier-transform infrared spectroscopy, nitrogen adsorption–desorption measurements, elemental analysis, thermogravimetric analysis, and X-ray powder diffraction analysis indicated that, depending on the ratio of core/shell components, the resulting spherical moieties with size of 35.1–43.1 nm, can form agglomerates of larger sizes. Packing of these aggregates offers porosity to such materials, having a dense or loose polysiloxane shell, with thiourea groups load of 0.67–1.05 mmol/g. The synthesized materials proved to be effective in extraction of Cu(II), Pb(II), Cd(II), Hg(II), Ag(I), Au(III), Zn(II) ions from aqueous solutions, as well as in selectively adsorption of Au(III) ions at pH = 3 and Cu(II) ions at pH = 5.5. X-ray photoelectron spectroscopy demonstrated different types of interactions between metal ions and the thiourea groups, depending on pH.

Optimization of Preparation Conditions of F-N-TiO2/AC Composite Photocatalyst for Degradation of Printing and Dyeing Wastewater

Abstract A novel composite photocatalyst loading titanium dioxide particles onto activated carbon and co-doping with fluorine and nitrogen (F-N-TiO2/AC) was synthesized using the impregnation-hydrothermal method for the degradation of printing and dyeing wastewater. The optimal preparation conditions of the composite photocatalyst were determined using orthogonal experiments. Through range analysis and variance analysis, the optimal preparation conditions were as follows: a molar ratio of anhydrous ethanol, glacial acetic acid, and tetrabutyl titanate of 3:175:100, and hydrothermal temperature of 150°C and hydrothermal time of 12 h. The catalyst prepared under these conditions showed high catalytic activity, with 100 % degradation of methyl orange when irradiated with a xenon lamp light source for 60 min, and the preparation conditions were feasible. The F-N-TiO2/AC composite photocatalysts were characterized using x-ray diffraction and nitrogen adsorption–desorption measurements. On the basis of this analysis, it was found that the doping of fluorine and nitrogen did not change the anatase structure of titanium dioxide but affected the grain growth and changed the structural properties of the F-N-TiO2/AC photocatalyst. Good reusability properties were also found.

Lotus-biowaste derived sulfur/nitrogen-codoped porous carbon as an eco-friendly electrocatalyst for clean energy harvesting

Recent research is focused on biomass-derived porous carbon materials for energy harvesting (hydrogen evolution reaction) because of their cost-effective synthesis, enriched with heteroatoms, lightweight, and stable properties. Here, the synthesis of porous carbon (PC) materials from lotus seedpod (LP) and lotus stem (LS) is reported by the pyrolysis method. The porous and graphitic structure of the prepared LP-PC and LS-PC materials were confirmed by field emission scanning electron microscopy, transmission electron microscopy with selected area electron diffraction, X-ray diffraction, and nitrogen adsorption-desorption measurements. Heteroatoms in LP-PC and LS-PC materials were investigated by attenuated total reflection-Fourier transform infrared and X-ray photoelectron spectroscopy. The specific surface area of LP-PC and LS-PC were calculated as 457 and 313 m2 g−1, respectively. Nitrogen and sulfur enriched LP-PC and LS-PC materials were found to be effective electrocatalysts for hydrogen evolution reactions. LP-PC catalyst showed a very low overpotential of 111 mV with the Tafel slope of 69 mV dec−1, and LS-PC catalyst achieved a Tafel slope of 85 mV dec−1 with a low overpotential of 135 mV. This work is expected to be extended for the development of biomass as a sustainable porous carbon electrocatalyst with a tunable structure, elements, and electronic properties. Furthermore, preparing carbon materials from the biowaste and applying clean energy harvesting might reduce environmental pollution.

Experimental and molecular modelling approach for rapid adsorption of Bisphenol A using Zr and Fe based metal–organic frameworks

The synthesized highly porous functionalized metal–organic frameworks (MOFs) are the solution for the rapid removal of toxic pollutants from wastewater. Bisphenol A (BPA) which consists of a derivative of phenol was identified as the primary pollutant in environmental waters and requires elimination for a sustainable and greener environment. In this work, we reported highly porous and stable Zr and Fe–based metal–organic frameworks as adsorbents for the removal of BPA in an aqueous solution. In this study, MIL–88(Fe) (MIL stands for Matériaux de l’Institut Lavoisier) and UiO–66(Zr) (UiO stands for University of Oslo) were synthesized by solvothermal techniques and characterized by fourier transformed infrared spectroscopy (FTIR), x–ray diffraction (XRD), energy–dispersive x–ray spectroscopy (EDX), field emission scanning electron microscopy (FESEM), scanning electron microscopy (SEM) and nitrogen adsorption–desorption measurements. MIL–88(Fe) and UiO–66(Zr)had 1242 and 1421 mg2/g surface area, respectively. In the experimental study, the UiO–66(Zr) and MIL–88(Fe)removed 99.25 and 98.36 % BPA, respectively. Compared to MIL–88(Fe), UiO–66(Zr) showed faster adsorption of BPA. The process was exothermic and spontaneous. The pseudo–second order model suited the kinetics studies well, while the Langmuir model fit the MIL–88(Fe) and UiO–66(Zr)isotherms. Molecular docking was used to study the surface interactions of MIL–88(Fe) and UiO–66(Zr) with BPA.The process involved van der Waals and hydrogen interactions between BPA with MIL–88(Fe) and UiO–66(Zr) surfaces. Both MOFs proved to have high efficacy and appropriateness for the practical application of BPA adsorption from an aqueous solution.

(3-Aminopropyl) triethoxysilane-functionalized silica nanocapsule adsorbent: Synthesis and analysis of physicochemical characteristics

3-aminopropyltriethoxysilane (APTES)-functionalized silica nanocapsule (A-SiNC) was prepared from a one-step synthesis process for the application of post-combustion carbon dioxide (CO2) capture. A-SiNC was synthesized from the microemulsion method by using cetyl trimethylammonium bromide (CTAB) as a cationic surfactant, toluene as co-solvent, APTES as an amine group, and tetraethyl orthosilicate (TEOS) as silica base. The synthesis and functionalization were carried out in a variation of APTES using Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), nitrogen adsorption-desorption measurements (BET), and transmission electron microscopy (TEM). The results showed that silica nanocapsules (SiNC) potential to react until a temperature of 166 ​°C, which indicates a stable thermal decomposition property. The surface area and surface morphology were influenced by the presence of an amino group as APTES loaded SiNC provides a different mechanism compared to blank SiNC. The close-packed structure was seen and proven in A-SiNC based on the observation from TEM.

Enhanced photocatalytic performance and stability of multi-layer core-shell nanocomposite C@Pt/MoS2@CdS with full-spectrum response

The nanocomposite material C@Pt/MoS 2 @CdS was prepared by a simple microwave-assisted hydrothermal method combined with photoreduction method. The crystal structure, microstructure, and surface physical chemistry properties of the material were analyzed by X-ray diffraction (XRD), ultraviolet–visible diffuse reflectance absorption spectroscopy (UV–vis/DRS), X-ray photoelectron energy spectroscopy (XPS), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HR-TEM), nitrogen adsorption–desorption measurement, photoluminescence spectroscopy (PL), and electrochemical tests. As a result, this material has full-spectrum light absorption property and the composited CdS presents a good hexagonal phase. Moreover, the composite material presents a nanorod-like multi-layer core-shell structure, wherein the rod-like MoS 2 @CdS surface is covered with Pt and C. The formation of the multi-layer core-shell structure increases the specific surface area of as-composite material and strengthens its light absorption performance. The electrochemical impedance and transient photocurrent test results show that C@Pt/MoS 2 @CdS has the highest charge separation efficiency and enhanced photocurrent density compared with other systems. Photogenerated charge carriers have higher separation efficiency, and photogenerated electrons and holes exhibit longer life. During the photocatalysis experiments, the nanocomposite C@Pt/MoS 2 @CdS shows enhanced photodegradation activity under multi-modal photocatalytic experiments and excellent stability under visible light irradiation. In addition, C@Pt/MoS 2 @CdS has a strong photocatalytic water splitting ability. Under the same experimental conditions, its hydrogen production is 60 times that of commercially available P25. Through capture experiments, the reactive species in the photocatalytic reaction process were determined, and the possible photocatalytic reaction mechanism of this multi-layer core-shell C@Pt/MoS 2 @CdS nanocomposite was inferred. • Constructed a multi-layer core-shell structure photocatalytic composite material. • Improved the photocatalytic activity and stability of CdS-based photocatalyst. • The hydrogen production of C@Pt/MoS 2 @CdS was approximately 60 times that of commercially available P25. • Recombination rate of photogenerated charge carriers was effectively restrained.

Phosphate Adsorption onto an Al-Ti Bimetal Oxide Composite in Neutral Aqueous Solution: Performance and Thermodynamics

Phosphorus (P) pollution and phosphorus recovery are important issues in the field of environmental science. In this work, a novel Al-Ti bimetal composite sorbent was developed via a cost-effective co-precipitation approach for P removal from water. The adsorptive performance and characteristics of P onto Al-Ti sorbent were evaluated by batch adsorption experiments. The effects of Al:Ti molar ratio, initial P concentration and reaction temperature were investigated. The microstructural characteristics of the Al-Ti sorbent were confirmed by scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis, Fourier transform infrared (FTIR) spectroscopy, and nitrogen adsorption-desorption measurements. Kinetic studies showed that the adsorption of P on Al-Ti oxide proceeds according to pseudo-second-order kinetics. The maximum adsorption capacity of phosphate on the Al-Ti oxide calculated from linear Langmuir models was 68.2 mg-P/g at pH 6.8. The Al-Ti oxide composite sorbent showed good potential for P recovery, owing to its large adsorption capacity and ease of regeneration.

Tunable synthesis, characterization, and CMP performance of dendritic mesoporous silica nanospheres as functionalized abrasives

The type, morphology, structure, size and distribution, surface chemistry, and mechanical behavior of particle abrasives play a key role in advanced chemical mechanical polishing (CMP) applications. In this work, dendritic mesoporous silica (D-mSiO2) nanospheres with tunable structures were synthesized via a modified n-hexane/water biliquid system coupled with a shearing assisted interfacial coassembly method. The resulting samples were characterized in terms of transmission electron microscopy, scanning electron microscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy, powder X-ray diffraction, and nitrogen adsorption-desorption measurements. The spherical D-mSiO2 products presented three-dimensional and center-radial structures with particle size of 30–140 nm, pore diameter of 3–9 nm, surface area of ~780 m2/g, and pore volume of ~1.5 cm3/g. The elastic property and compressive elastic modulus of D-mSiO2 nanospheres were investigated by atomic force microscopy (AFM) nanoindentation. Oxide-CMP performances of the series of D-mSiO2 nanospheres as functionalized abrasives were tracked via high-resolution AFM and interferometric microscopy. The subtle differences of surface characteristics were systematically compared in terms of roughness, topographical variation, and image surface area difference (SAD). Sub-100 nm D-mSiO2 nanospheres achieved superior CMP qualities with the decreased surface roughness (less than 0.2 nm Rq and 0.3 nm Rz, within 5.0 × 5.0 µm2), the reduced maximum peak height/minimum valley depth (less than 0.5 nm), as well as the low image SAD (less than 0.009%). Furthermore, the interfacial contact behavior, water-involved tribochemical wear, and material removal mechanism of D-mSiO2 nanoabrasives were also discussed. The investigations are expected to open up the possibility of utilizing D-mSiO2 nanospheres as novel abrasives for advanced CMP applications.

Effect of (3-aminopropyl)triethoxysilane on dissolution of silica nanoparticles synthesized via reverse micro emulsion.

Silica nanomaterials have been studied based on their potential applications in a variety of fields, including biomedicine and agriculture. A number of different molecules have been condensed onto silica nanoparticles' surfaces to present the surface chemistry needed for a given application. Among those molecules, (3-aminopropyl)triethoxysilane (APS) is one of the most commonly applied silanes used for nanoparticle surface functionalization to achieve charge reversal as well as to enable cargo loading. However, the colloidal stability of APS-functionalized silica nanoparticles has not been thoroughly studied, which can be problematic when the high reactivity of amine groups is considered. In this study, four different types of silica nanoparticles with varied location of added APS have been prepared via a reverse micro emulsion process, and their colloidal stability and dissolution behavior have been investigated. Systematic characterization has been accomplished using transmission electron microscopy (TEM), silicomolybdic acid (SMA) spectrophotometric assay, nitrogen adsorption-desorption surface area measurement, and aerosol ion mobility-mass spectrometry to track the nanoparticles' physical and chemical changes during dissolution. We find that when APS is on the interior of the silica nanoparticle, it facilitates dissolution, but when APS is condensed both on the interior and exterior, only the exterior siloxane bonds experience catalytic hydrolysis, and the interior dissolution is dramatically suppressed. The observation and analyses that silica nanoparticles show different hydrolysis behaviors dependent on the location of the functional group will be important in future design of silica nanoparticles for specific biomedical and agricultural applications.

Ce-Containing MgAl-Layered Double Hydroxide-Graphene Oxide Hybrid Materials as Multifunctional Catalysts for Organic Transformations.

The combination of layered double hydroxides (LDH) with graphene oxide (GO) enables the formation of nanohybrids with improved properties. This work focuses on the structural and catalytic properties of Ce-containing MgAl LDH-GO composites bearing different concentrations of GO in the range of 5–25 wt.%. The synthesis of the composites was performed by co-precipitating the LDH phase in the presence of GO, while their characterization was performed using XRF, XRD, DRIFT, Raman, SEM, nitrogen adsorption-desorption, and acidity-basicity measurements. The LDH-GO composites, showing redox, basic, and acid catalytic functions, were tested in two different types of organic transformations: (i) Knoevenagel condensation and (ii) one-pot cascade oxidation-Knoevenagel condensation. (i) The cinnamic acid was synthesized by the Knoevenagel condensation of benzaldehyde with diethylmalonate. The composites showed catalytic performances in strong contrast to neat LDH or GO, suggesting a synergistic interaction between the two components. During Knoevenagel condensation, the catalytic activity increased with the GO content in the hybrids up to 15 wt.% and decreased afterwards. (ii) 2-Benzoyl-3-phenylacrylonitrile was synthesized by the aerobic oxidation of benzyl alcohol followed by the Knoevenagel condensation with benzoyl acetonitrile using three different non-polar solvents, i.e., toluene, benzene, and mesitylene. The conversion of benzyl alcohol was higher for the hybrid materials compared to the individual components but decreased with the increase of the graphene oxide concentration.