Search

Background Nanotechnology has been in the limelight since its emergence and its products affect everyday lives. Nanomaterials are characterized by features such as size and shape, thus rendering their possible number essentially unlimited, which in turn makes them difficult to study and categorize regarding possible dangers. This work suggests that grouping could allow studying them with limited testing efforts without endangering safety. Methods Initially, the materials are identified and grouped according to their applications in health/medicine, as well as on their environmentally-friendly potential. The materials are then categorized using various toxicity classification methods to identify those with highest risks and group them with others that demonstrate similar behavior. Results The materials studied show promising uses in diagnostics, drug delivery, biosensors, water purification, oil spill cleaning, emission control and other fields. The toxicity risk assessment shows that the majority pose little to moderate risk, however there are certain materials that can be extremely hazardous or even cause death under specific circumstances. A risk mitigation plan was also developed. Conclusions Nanomaterials applications, including drug delivery, cancer treatment, waste treatment, solar energy generation etc. can be very beneficiary, but at the same time, these materials can be extremely harmful or even cause death, thus making the need to prioritize research on high risk materials crucial. A clear regulatory framework that addresses both benefits and risks and communicates that information effectively should play an important part in European and worldwide efforts. General significance The risk analysis validated the impression that there is limited research on nanomaterial toxicity risks, which calls for a more organized approach. The framework outlined in this work can be utilized by researchers as well as government bodies, in order to form regulatory policies and adopt a universally accepted labeling system. This article is part of a Special Issue entitled "Recent Advances in Bionanomaterials" Guest Editor: Dr. Marie-Louise Saboungi and Dr. Samuel D. Bader.

A simple solvothermal impregnation method was used to prepare ZnO nanoparticles supported on MCM-41 and SBA-15. X-ray powder diffraction, N2 adsorptiondesorption, Electron Probe Micro Analysis (EPMA), and UVvis spectroscopy were used to characterize the prepared materials. The influence of the ZnO loading of different supports on the structural characteristics and the photocatalytic activity toward degradation of methylene blue in water under ultraviolet irradiation were investigated. Wide angle X-ray diffraction and UVvis Diffuse Reflectance confirmed the existence of ZnO phase. A much smaller influence of impregnation with ethanolic zinc salt solution on the porosity was observed for SBA-15 compared with MCM-41. Finally, the adsorption and photocatalytic activity of the ZnO/mesoporous materials depend on porous characteristics of the support materials.

Sn4+-containing LDH was prepared using the co-precipitation method at constant pH, and characterized using X-ray diffraction, UV–vis diffuse reflectance spectroscopy and TG/DTG methods. The obtained product was further exposed to different thermal treatments in order to obtain nano-sized coupled ZnO/SnO2 systems with enhanced photocatalytic performances than the ones obtained by mixing the two semiconductor oxides. The formation of a well-defined ZnO/SnO2 system and the crystallite size, fully investigated using XRD, micro-Raman scattering and UV–vis DR techniques, were found to be influenced by the nature of the precursors and the calcination temperature. The photocatalytic activity of the ZnO/SnO2 systems, evaluated for the photodegradation of methyl orange (MO) dye, was studied as a function of the initial pH, catalyst loading and the calcination temperature. The metal dispersion supplied by layered structures proved to be an advantage when preparing coupled ZnO/SnO2 systems, the photocatalytic activity being ∼2.3 times higher comparing with the physical mixtures performances. The maximum photocatalytic activity of the coupled ZnO/SnO2 system having a layered precursor was observed when using neutral pH, at a catalyst loading of 1 g/L calcined at 600 °C for 4 h.

Porous clay heterostructures (PCH), obtained on the basis of synthetic saponite, were modified with copper and iron ions by an ion-exchange method and tested as catalysts for the selective reduction of NO with ammonia (NH 3 -SCR). Transition metal ions were introduced into H + and NH 4 + forms of PCH. The catalysts were characterized with respect to their texture (BET), composition (EPMA), coordination of transition metals (UV–vis-DRS) and surface acidity (FT-IR, NH 3 -TPD). The PCH-based catalysts have been found to be active, selective and stable in the NH 3 -SCR process. The Cu-containing catalysts effectively operated at temperatures significantly lower than the Fe-modified samples. The catalyst obtained by exchanging copper ions in the ammonium form of PCH was considerably more active compared to the sample obtained from H + -PCH.

The characteristics of new types of coated wire potentiometric sensors based on composite coatings were compared with classical potentiometric sensors. The composite sensors contained respectively the clay montmorillonite (MM) and the zeolite NaY as the ionically conducting components, embedded in PVC based rubber phase membranes. The behavior of 20 basic medicinal drugs and 5 biogenic amines was studied on 9 potentiometric sensors of different composition. The behavior of 3 composite sensors, and 6 more classical PVC based sensors either of the "inner solution" or "coated wire" type were studied. The analytes were chosen to cover a wide log P range of, e.g. -1.54 (noradrenaline) up to +5.55 (promethazine). All sensors were tested using a high-throughput FIA-based method. The results were interpreted via statistical data analysis. The responses of all electrodes had a very high correlation to the log P of the analytes. This was also the case for the ion-pair based electrodes containing a specific cationic drug as the counterion. Classical ion-pair based sensors containing tetrakis (p-chlorophenyl) borate (TCPB) and a counterion with a high log P value (e.g. promazine) were the least sensitive. The composite-based sensors were the most sensitive. Coated wire electrodes were statistically shown to behave in the same way (selectivity and sensitivity) as inner solution electrodes. The results are discussed using a physico-chemical model. Practical applications of the most performant (composite) sensors are shown in HPLC detection of the pharmaceutical drugs and the biogenic amines. Detection limits in the 10-7 M regio (injected concentrations) are obtained for lipophilic drugs (log P > 2). © 2006 Elsevier Ltd. All rights reserved.

PHTS materials with combined micro- and mesoporosity and with different morphologies were synthesized. PHTS or Plugged Hexagonal Templated Silica is a plugged variant of SBA-15 containing extra silica nanoparticles (‘plugs’) inside the mesoporous channels. Utilising a low amount of TEOS and high stirring and aging temperatures, PHTS-particles with spherical morphology were synthesized for the first time. It was observed that the morphology changed gradually with increasing stirring temperature. It evolved from smooth rods (60∘C) to rough rods with a deposition of small particles on the surface (70∘C) and finally to spheres (80∘C). However, synthesis of materials at a stirring and aging temperature of 80∘C using larger amounts of silica source (TEOS) did not result in particles with spherical morphology. This demonstrates the profound impact of the amount of silica source, as well as the temperature. The results are explained by means of the cloud point of the surfactant and the balance between the rate of polymerization of the silica source and the rate of mesostructure formation. The prepared PHTS materials were characterized by XRD, N2 sorption and SEM.

Herein, we report the formation of a series of nanocomposites composed of LDH structures and TiO 2 with anatase crystal phase. The structure of the LDH clay was modulated by the insertion of different di-, tri- or tetravalent cations, such as Zn 2+ , Cu 2+ , Al 3+ , Fe 3+ or Ti 4+ , within the brucite-like sheets. Afterwards, the anatase seeds were deposited onto the LDH clays, obtaining new nanocomposite systems with tailored photocatalytic activity. In this way, the photoresponsive properties of the final nanocomposites were shifted from the UV to the visible range of the solar spectrum. The obtained nanocomposites were tested for the degradation of different organic pollutants, like phenol and methylene blue, under UV and visible light in aqueous media with different pH. The kinetic study showed that the TiO 2 @LDH nanocomposites are efficient for the phenol (and its intermediary species catechol and hydroquinone) and methylene blue photocatalytic degradation under both UV and Vis light illumination.

Thermally stable composite nanostructures of titanium dioxide (anatase) and silicate nanoparticles were prepared from Laponite clay and a sol of titanium hydrate in the presence of poly(ethylene oxide) (PEO) surfactants. Laponite is a synthetic clay that readily disperses in water and exists as exfoliated silicate layers of about 1-nm thick in transparent dispersions of high pH. The acidic sol solution reacts with the clay platelets and leaches out most of the magnesium in the clay, while the sol particles hydrolyze further due to the high pH of the clay dispersion. As a result, larger precursors of TiO2 nanoparticles form and condense on the fragmentized pieces of the leached silicate. Introducing PEO surfactants into the synthesis can significantly increase the porosity and surface area of the composite solids. The TiO2 exists as anatase nanoparticles that are separated by silicate fragments and voids such that they are accessible to organic molecules. The size of the anatase particle can be tailored by manipulating the experimental parameters at various synthesis stages. Therefore, we can design and engineer composite nanostructures to achieve better performance. The composite solids exhibit superior properties as photocatalysts for the degradation of Rhodamine 6G in aqueous solution.

The template extraction of two porous clay heterostructures (PCHs), derived from natural montmorillonite (PMH) and synthetic saponite (PSH), has been studied. Extraction in methanol solvent in the presence of cations (H+) removes up to 90% of the templates in a reproducible way without a subsequent calcination step for both PMH and PSH. The extracted materials have a high surface area (896 m2 g−1 for PMH and 1122 m2 g−1 for PSH) and pore volume (0.84 cm3 g−1 for PMH and 1.13 cm3 g−1 for PSH) and are structurally very stable when exposed to hydrothermal conditions. The number of silanol groups on the surface of PCH materials have been titrated by a surface reaction with hexamethyldisilazane, followed by quantification of the liberated NH3. Based on this method both extracted PMH and PSH have slightly higher silanol numbers than their calcined forms, a very important feature with respect to the amount of catalytic sites that can eventually be grafted onto the surface. The hydrothermal stability under a N2 flow containing 25% steam for 5 days at different temperatures between 400 °C and 700 °C for both calcined and extracted PMH and PSH was investigated using X-ray diffraction and N2-adsorption data. A remarkable hydrothermal stability was observed for all samples until 600 °C, a promising characteristic for applications of porous clay heterostructures.

The thermal, hydrothermal, and mechanical stabilities of a wide range of ordered mesoporous materials, in particular, the molecular sieves MCM-41, MCM-48, HMS, FSM-16, KIT-1, PCH, and SBA-15, have been studied in detail using X-ray diffraction (XRD) and nitrogen sorption. The thermal stability was found to be strongly related to the wall thickness and the silica precursor used during synthesis, and the following stability trend was observed: MCM-41 (fumed silica), MCM-48 (fumed silica), KIT-1 (colloid silica) > SBA-15 (TEOS) > FSM-16 (layered silicate), PCH (layered silicate) > MCM-41 (TEOS), MCM-48 (TEOS), HMS (TEOS). The hydrothermal stability is influenced by the wall thickness and the polymerization degree and decreases according to the following trend: KIT-1 > SBA-15 > MCM-48 (fumed silica and TEOS), PCH > FSM-16, MCM-41 (fumed silica and TEOS), HMS. The mechanical stability is little influenced by the nature of the mesoporous molecular sieves. All materials collapsed at a maximum pelletizing press...

Titaniumoxide supported MCM-48 was prepared by a novel synthesis method, utilizing titanylacetyl-acetonate as the Ti source. The process consists of an adsorption and subsequent thermolysis of the Ti-complex. The interaction of the complex with the surface was studied by FTIR, TGA and chemical analysis. Further characterization was done by XRD, Raman, UV-DR and N2 adsorption measurements. The Ti-complex is irreversibly adsorbed on the MCM-48 surface by a hydrogen bonding mechanism independent of the Ti loading. During calcination, the supported TiO(acac)2 complex is converted towards supported titaniumoxide, whereby the Ti atoms are partly incorporated into the pore walls of MCM-48. The adsorption of TiO(acac)2 is an efficient way to create supported titaniumoxides with a high surface area.

High quality MCM-48 can be repeatedly and reproducibly prepared, as a novel method for the extraction, recuperation and re-use of the gemini surfactant has been optimized. Gemini surfactants have the general formula [CnH2n+1N+(CH3)2(CH2)sN+(CH3)2CmH2m+1]·2Br, and have been shown to produce MCM-48 in a very convenient way. In each cycle, more than 95 wt% of the surfactant is extracted under mild conditions. The extracted surfactant does not degenerate during this treatment and can be re-used many times. The MCM-48 produced by this soft extraction, has a narrower mesoporous pore size distribution and a larger pore radius than materials prepared by normal temperature-programmed calcination. The surface of the extracted MCM-48 still contains sufficient silanol groups, although some silanol groups have been replaced by methoxy groups. The number of silanols on the surface of the MCM-48 has been titrated by surface reaction with hexamethyldisilazane, followed by quantification of the liberated NH3.

AlOx coating is proposed as a possible method for vanadium passivation of the ultrastable zeolite Y (USY). Two coating methods are discussed: (i) the deposition of the [Al13O4(OH)(24)(H2O)(12)](7+) ([Al-13]) complex from aqueous solutions and (ii) the anchoring of alumoxane by in situ triisobutylaluminum hydrolysis followed by calcination. The properties and the efficiency in vanadium passivation of the coated materials have been investigated with DRS, ESR, XPS, FTIR, and sorption measurements. XPS revealed for all the coated samples an enrichment in the Al content in the near-surface region and differences in Al coordination geometry. Vanadyl(IV) etioporphyrin,the major contaminant in crude oil, was used to probe the trapping efficiency of the external AlOx layer. The [Al-13]-derived layer is homogeneously distributed and covers the external surface of the USY zeolite, following its topology, but without blocking its pores. About 80% of the offered vanadyl species have been preferentially trapped in this layer. The alumoxane-based method is less efficient in vanadium passivation, most probably because after calcination the aluminum species are heterogeneously distributed, both on the external surface and in the channels of USY zeolite.

The Wheeler-Jonas model is well known for its good prediction of breakthrough times for organic vapors on activated carbon beds. However, it is valid only in dry conditions: no prewetting of the filter and no humidity in the ambient air during use. One of the parameters that is likely to be influenced is the overall mass transfer coefficient kv. By measuring over 200 breakthrough times, with 7 different vapors on 4 different types of activated carbon, a simple but satisfactory model for the influence of moisture on kv was established. The only items of information needed, compared with the application of the Wheeler-Jonas equation under dry circumstances, are the water isotherm and the total pore volume of the activated carbon.

Silica pillared montmorillonite has been synthesized using aminopropyltriethoxysilane (APTS), the organic part of which is removed upon calcination. A good intercalation has been established as determined by X-ray diffraction, thermogravimetric analysis and fourier-transform infrared measurements. The concentration of the APTS solution has an influence on the density of the pillars in the interlayer space. In case of enhanced APTS concentration, a material with lower surface area and pore volume is obtained, due to the clay interlayer space being completely occupied by silica pillars. Therefore a templated synthesis method is applied in order to reduce the density of the pillars between the clay sheets. By a pre-intercalation of the clay with cetyltrimethylammonium ions prior to the modification with APTS, the clay sheets are driven apart allowing a more easy intercalation of the APTS molecules. Analysis results show an increase in interlayer free spacing (IFS) to a value of 7.4 A probably due to the insertion of two layers of silica (—Si—O—Si—) between the clay sheets. A maximal surface area of 252 m2/g and a micropore volume of 0.072 cc/g can be obtained in case of the templated synthesis method.

Changing the surface characteristics of silicon or mixed Si-Al oxides has created new prospects in both catalysis and separation technology. This review presents the surface modification of these materials by silylation over a wide range of pore sizes. The influence on the porosity, the adsorption characteristics and thermodynamic background of these modifications are summarised. The reaction mechanisms are reviewed for a wide range of silylation reagents.

The pillaring of (NO3)-ZnAl-LDHs with the polyoxometalates (POMs) [PV2W10O40]5−, [Mo7O24]6−, [V10O28]6− and [H2W12O40]6−, using large organic anions like terephthalate for pre-swelling the LDH structure forms a promising method for the controlled creation of small micropores. The use of the terephthalate precursor ((T)-ZnAl-LDH) avoided almost completely the formation of undesired side phases during pillaring, although anion exchange with the large POM complexes proceeded with more difficulty than in the case where (NO3)-LDHs were used as a starting material. Direct pillaring via the (NO3)-LDHs resulted in multiphased materials, and no correlation was found between the M(II)/M(III) ratios in the starting LDHs and the created porosity. For the [POM]-ZnAl-LDHs pillared via the terephthalate precursor, the layer charge density arising from the amount of isomorphically substituted Al3+ in the LDH layers forms the crucial parameter with regard to the created microporosity. Improving the surface area (SA) and micropore volume (μPV) values was accomplished by lowering the charge density on the LDH layers (increasing the Zn2+/Al3+ ratio). In this way, a [PV2W10O40]-ZnAl-LDH (Zn2+/Al3+ = 4.26) with a SA (BET) of 166 m2/g and a μPV of 0.047 cm3/g was formed. For the different types of pillars, small micropores were formed due to the pillaring process. In the case of the smaller POM complexes [Mo7O24]6+ and [V10O28]6+, an increase in μPV and SA was not accompanied by a detectable shift in average pore size, which was the case for the second group of complexes, [PV2W10O40]5− and [H2W12O40]6−. Due to their larger dimensions, mainly micropores between 0.71 and 1.06 nm were created at high Zn2+/Al3+ ratios, together with a substantial amount of pores smaller than 0.71 nm.

Over the last ten years, the concept of pillaring has frequently been applied on layered double hydroxides (LDHs). Due to the variety of possible anionic pillaring species and the adjustable layer charge density, LDHs offer good perspectives with regard to the creation of porous adsorbents and catalysts. But despite these possibilities, their porosity properties can still not compete with those of industrially applicable materials like zeolites. In this study, theoretical calculations based on geometrical models and performed on both Fe(CN)6-MgAl-LDHs (A) and [PV2W10 O40]-ZnAl-LDHs (B) were reported. Properties such as the micropore volume and the interpillar distance were calculated, and compared to experimental data. For a M(II)/M(III) ratio in the layers of 3, the theoretical maximum micropore volumes were 0.3843 cm3/g (A) and 0.1497 cm3/g (B), respectively. By implementing parameters like the stack size, pillars on the outside of the stacks and the possibility of collapse, the model was adjusted in order to create a realistic picture of the microstructure of pillared LDHs. This led to a better understanding of the limiting factors, and gave an explanation for the relatively low micropore volumes of pillared LDHs. For the Fe(CN)6-MgAl-LDHs, small interpillar distances were responsible for the partial inaccessibility of the interlayer regions by N2. This effect was the most pronounced for high charge density LDHs. The situation for the [PV2W10O40]-ZnAl-LDHs is more complex. Probably due to an incomplete pillaring process, the theoretical maximum values are not reached.

Aluminium pillared clays were synthesised under various experimental conditions starting from a sodium montmorillonite clay (Hithix). The influence of sonication, successive exchange and a constant pH during and after the intercalation process were investigated as important synthesis parameters in the optimisation of these materials. The concentration of aluminium in the pillaring solution, the ratio of Al/clay and the aging time and temperature were kept constant throughout this work. This optimisation is necessary in order to obtain high-quality Al-PILCs, as could be deduced from a theoretical study on the potential and limitations of pillared clay substrates. The ultrasonic treatment of the suspension during the synthesis is responsible for a significant increase in porosity. Despite the promising nature of the successive exchange technique, a reduction of the porosity is observed. Instead of a homogenisation process, an accumulation of aluminium in the interlayer space occurred. This expected homogenisation takes place when the synthesis of the pillared clay was carried out at constant pH. In this case, nitrogen BET surface areas of 458 m2/g and micropore volumes of 0.17 cm3/g were obtained after calcination of the intercalated clays at 400°C.

The preparation and characterization of porous ceramic membranes is presented. These membranes consist of a macroporous support system, with or without a mesoporous intermediate layer, and a microporous top layer. For the macroporous support membranes two manufacturing routes are described: a conventional and a RBAO (Reaction Bonded Aluminium Oxide) route. The mesoporous γ-Al2O3 layer is obtained by means of a sol-gel dipcoating technique. Three microporous top layers are considered: SiO2, Al2O3-pillared montmorillonite and Laponite. These top layers have different pore structures which results in different gas transport properties. A SiO2 membrane can be used for H2 removal from a gas mixture. Al2O3-pillared montmorillonite and Laponite membranes do not show specific gas separation properties. Dehydration of water/2-propanol mixtures by means of pervaporation also proved a different behavior for these microporous membranes.

Silylated silica surfaces have found many applications in the field of analytical chemistry (HPLC, Ion Exchange Chromatography, Size Exclusion Chromatography, GC), synthetic chemistry (heterogeneous catalysts, phase transfer catalysts), biochemistry (enzyme immobilization, affinity chromatography) and industries (composites, high-tech materials, semiconductor devices). In all cases, the knowledge of their chemical composition and surface characteristics is of great importance for the understanding and eventual improvement of their performance. This review presents a general description of the silica surface and a summary of the different modification techniques that have been developped to silylate oxide surfaces. The chlorosilylation of the silica surface (in liquid and gaseous phase) and the modification with aminosilanes are discussed in more detail, emphasizing the analysis techniques and skills that enable researchers to get a more profound insight into the reaction mechanisms and the nature...

The surface modification reaction of silica gel with aminoorganosilanes proceeds in two steps. For both the reaction step and the curing step, the chemical and physical interactions of the silane molecules with the silica surface have been modelled.From ethanol leaching tests, the reaction phase interaction, in dry conditions, may be characterized as 22% proton transfer, 10% hydrogen bonding and 68% siloxane bonding. The deposition of the aminosilane molecules is governed by the specific surface area and surface hydration. For the bifunctional N-beta-aminoethyl-gamma-aminopropyltrimethoxysilane, a two-step deposition is observed.The rate of siloxane bonding in the curing phase is limited by the number of alkoxy groups, and results in a turnover of the aminosilane molecules.A new application of aminosilane-modified silica gel is developed in converting the aminosilane layer to SiC. Thus, the liquid phase path of the chemical surface coating process, for the controlled synthesis of advanced ceramics, is set up.

Adsorption of pyridine on copper-silica catalysts is studied by differential scanning calorimetry (DSC) and Fourier transform-infrared/photoacoustic spectroscopy (FT-IR/PA), in the region of mid-frequency vibrations as well as in the region of hydroxyl groups. The adsorption of pyridine on copper-silica catalysts shows three modes of sorption in the 1650-1400 cm −1 region: physisorption or hydrogen-bonded (HPY), and two sites of Lewis acid sorption (LPY(I) and LPY(II)). The Lewis band at 1609 cm −1 was very strong compared with the 1450 cm −1 band since the former band showed a shift to higher wavenumbers whereas the latter showed a shift to lower wavenumbers. A relationship was found between the DSC scans, in the low temperature range (240-140°C), and the 1450-1443 cm −1 band. On the other hand, the high temperature DSC scans (400-360°C) were correlated with the behaviour of the 1609–1612 cm −1 band. The volumetric results of pyridine adsorption on 9 and 15 wt.% Cu catalysts show a constant behaviour; however, this constancy was also reflected by carbon monoxide adsorption, demonstrated by a similar behaviour of both 2128 and 2259 cm −1 bands. This was attributed to the blocking of the small pores of silica earlier at the 9 wt.% Cu loading. A new broad band at 2248–2259 cm −1 , not identified in the ion-exchange catalysts, was obtained and attributed to CO adsorbed on agglomerated copper clusters.

Recently, the development of carbon molecular sieves (CMS) for the separation of various gases, particularly air into oxygen and nitrogen, has gained widespread attention. In this paper, a simple method was presented for preparing carbon molecular sieves. Carbonized walnut shells were impregnated with a small amount of potassium hydroxide (KOH) and pyrolysed. In this way, the pore size can be easily controlled in the range around 0.5 nm. The produced samples were further modified by a carbon deposition to form the final CMS. 3-methylpentane (3-MP) was used as a carbon source for the deposition. The CMS samples were characterized by the adsorption of nitrogen, oxygen, and a series of molecular probes to estimate the surface area, pore volume, and the pore size distributions. Due to the small pore entrances, only a very small nitrogen adsorption was found on the CMS at 77 K. Therefore, the oxygen adsorption isotherms at 77 K were used to calculate the surface area and pore volume. We are able to prepare CMS with a narrow pore size distribution in the range 0.33–0.43 nm and with an oxygen-to-nitrogen separation selectivity, D O 2 D N 2 , as high as 9.2.

The adsorption of the cationic surfactant cetyltrimethylammonium bromide (CTAB) on silica gel and on molybdenum-modified silica gel substrate, in the solid state, was studied by differential scanning calorimetry and Fourier transform IR photoacoustic spectroscopy (FTIR-PA) techniques. Examination of the solid state IR spectra of CTAB absorbed onto molybdenum—silica substrate, as a function of temperature, shows a new band at 938 cm −1 shifted to 961 cm −1 (during the temperature flow), representing a chemisorption via the interaction of the head group of the surfactant (CH 3 ) 3 N + and MoO stretching vibration species. In the presence of NaCl, shifting of the high temperature exothermic peak at 411°C to 451°C was obtained, providing an enhancement of cetyltrimethylammonium chloride adsorption onto molybdenum—silica substrate and a considerable reduction in the Δ H value is observed. This decrease in the Δ H value was obtained as a result of the interference of the less reactive site Na + ions in the adsorption, because of substitution of Na + for Mo 6+ ions.

Zn/Al-LDHs with cationic ratio of 1–4 were prepared by the co-precipitation method at constant pH. The XRD patterns showed that additional phase is present in all samples due to the lattice strains created when more Zn2+ is added and the longer periods of hydrothermal treatment. The as-synthesized samples were calcined at different temperatures and the phase transformations were fully investigated by XRD, IR, TG/DTG, UV–vis-DR, N2 adsorption/desorption, SEM and EDX methods. Infrared spectroscopy revealed that the characteristic layered double hydroxide structure is not fully destroyed. The EDX analysis showed that the increase of the calcination temperature leads to a diffusion of the Zn2+ cations to the surface of the particles. The photocatalytic activity was evaluated for the degradation of the methyl-orange dye. The band gap energy decreases as the calcination temperature increases indicating that less energy is needed for the photocatalytic process. The photocatalytic activity increases with the increase of the cationic ratio and the calcination temperature. 93% of the dye could be removed by the Zn/Al-LDH with the cationic ratio of 4 and calcined at 500 °C.

This report describes the synthesis and photocatalytic behavior of TiO 2 /SiO 2 mesoporous materials prepared by acid catalyzed sol-gel method. The properties of ordered TiO 2 /Si-MCM-41 and TiO 2 /Si-SBA-15 materials were identified by XRD, N 2 sorption measurements and chemical analysis. It has been shown that the photocatalytic degradation of rhodamine 6G in aqueous solution is depending on the titania loading, titania nanoparticles size and the location of the titania clusters on the external surface or in the inner pore walls.

Mesoporous titania was synthesised following the Evaporation-Induced Self-Assembly method. The structures had to be thermally stabilised in order to possess photocatalytic activity, since the photocatalytic active anatase phase needs to be accessible. The photocatalytic activity of the materials was tested by the photodegradation of rhodamine 6G. The stabilisation of the mesoporous structure is done by a post-modification in basic medium. A comparison was made between NH 4 OH and NaOH as post-modification base. The results show that post-modification with NaOH is better than NH 4 OH and leads also to a better photocatalyst.

A multistep deposition of anatase nanoparticles was employed to incorporate high amounts of titania into the mesopores of SBA-15. Anatase nanoparticles were synthesized and deposited following the Acid Catalyzed Sol Gel method. With this method, the size of the anatase nanoparticles can be controlled and therefore, the titania loading into the mesopores of SBA-15 can be controlled. Through multistep deposition of anatase nanoparticles, a further increase of titania loading into the mesoporous channels can be obtained. For the degradation of Rhodamine-6G, the samples synthesized by multistep deposition showed an enhanced photocatalytic activity.

Properties of SBA-15 materials modified by the impregnation of vanadium silicalite-1 zeolite-like nanoparticles (SBA-VS) have been studied. The influence of the amount and concentration of impregnated nanoparticles on the structural characteristics were studied by N2-sorption measurements, TEM and HRSTEM. Increasing the amount of nanoparticles on the SBA-15 material has large consequences on the ratio of open to narrowed mesopores, the micro- and mesopore volume and the vanadium content. The influence of the impregnated nanoparticles on mobility of guest molecules in the different SBA and SBA-VS materials was studied with help of pulsed field gradient nuclear magnetic resonance. Strong effects on molecular translational diffusion produced by loading were observed. Interpretation is given in terms of structure changes and molecular exchange between the meso- and macropores.

Transition metal oxides (Cu, Cr and Fe) were deposited on various mesoporous silicas (MCM-48, SBA-15, MCF and x-MSU) by an impregnation method. Electron microprobe analysis, BET, UV-VIS-DRS and temperature programmed desorption of NH3 were used for the characterization of the samples. The modified mesoporous silicas were tested as catalysts of the N2O decomposition and the N2O reduction using ammonia and methane. The Cu-containing samples presented the highest catalytic activity in the N2O decomposition, while the Cr- and Fe-modified materials were more active in the reduction of nitrous oxide with NH3 and CH4. The type of the silica support strongly influenced the catalytic performance of the studied materials.

The most recent developments in the formation of new mesoporous templated zeolitic materials, characterized by surfaces of more than 1000 m(2)/g, are discussed in this paper. By adapting the synthesis parameters, such as type of silicium source, type of template, pH, temperature, em leader different materials can be synthesized with varying porosity and crystallinity. Besides the synthesis, much attention is focused on the activation of their surfaces by incorporation methods or deposition processes towards catalytic applications. Finally, the stability of the different materials, one of the critical parameters to potential industrial applications, is compared and evaluated.

Hexagonal MCM-41 can be transformed into cubic MCM-48 and finally into spherical particles by the addition of alcohol during the synthesis of a mesoporous silica material. X-ray diffraction suggests that the structure of these spherical particles is of the MCM-41 type. Transmission electron microscopy however reveals that the structure of the mesoporous silica spherical particles consists of a core in the form of a truncated octahedron with an MCM-48 cubic structure and radial pores grown on the surfaces of the truncated octahedron. Spherical MCM particles therefore consist of a mixture of cubic and hexagonally arranged pores.

The increasing awareness of the need to create green and sustainable production processes in all fields of chemistry has stimulated materials scientists to search for innovative catalysts supports. These new catalytic supports should allow the heterogenization of most catalytic processes, increasing the efficiency and selectivity of the synthesis and reducing waste and byproducts. Following the development of several micellar templated structures, such as M41S, FSM-16, HMS, MSU-x, and SBA-x, it is a crucial next step to create support materials, consisting of a composite matrix with combined micro- and mesoporosities and a sufficient stability to withstand most industrial treatments. We describe in this paper the very first development of a hexagonal material with large pore diameters and thick walls (4 nm), containing internal microporous silica nanocapsules. These plugged hexagonal templated silicas (PHTS) have two types of micropores (originating from the walls and the nanocapsules respectively) and a tunable amount of both open and encapsulated mesopores. The micropore volumes have a high value (up to 0.3 cm3/g) and the total pore volume exceeds 1 cm3/g. The obtained materials are much more stable than the conventional micellar templated structures known so far, and can easily withstand severe hydrothermal treatments and mechanical pressures.

Publisher Summary This chapter discusses different strategies for increasing the structural and chemical stability of pure silica MCM-48. Thickening of the walls, using tetrachlorosilane (SiCl 4 ) and water, results in a wall thickening of 50%. It also strongly improves the mechanical stability of the samples. A partial hydrophobization with an amphiphilic silane, such as dimethyldichlorosilane, has extremely beneficial effects on the thermal, mechanical, and hydrothermal stability of the samples and strongly reduces the leaching of the active centers. Both wall thickening and hydrophobization can be combined into one simple postsynthesis treatment. Such treatments will be necessary for allowing a practical (industrial) use of the MCM-48 support as catalysts support or adsorbent.

Publisher Summary This chapter discusses the hydrothermal synthesis of vanadium-containing microporous aluminophosphates through the design of experiments approach. An experimental design has been applied to the hydrothermal synthesis of VAPO-11 molecular sieve (AEL structure) from a VOSO 4. 5H 2 O·Al(iPrO) 3 ·Pr 2 NH·H 2 O gel. Statistical models that relate the selected synthesis variables with the crystallinity are proposed. The optimal synthesis conditions for the two structures (single phase or physical mixture with the AFO (VAPO-41) structure) are inferred from the models and compared with the data on single-phase synthesis. Highly crystalline single-phase VAPO-11 can be best prepared at 170°C from a synthesis gel with low vanadium content and high water content.

Publisher Summary This chapter describes the synthesis of mesoporous aluminosilicate FSM-materials derived from synthetic and natural Saponite. A new successful synthesis route for the preparation of FSM-16 is developed using leached Saponite, in combination with cetyltrimethyl ammoniumbromide as structure-directing agent. Acid treatment of the clays allows the formation of mesoporous aluminosilicate hexagonal structures (M41S family) with high porosity, high specific surface area, high pore-wall thickness, a narrow pore-size distribution, and uniform pore-size distributions. Using natural clays as silica source is of great interest in an economical and ecological way while the aluminium present in the clay and finally in the mesoporous structure is an additional advantage looking to acid catalysis.

Silica-, alumina-, and zirconia-supported tantalum oxide and supported vanadia-tantala mixed oxide catalysts were investigated by XRD, UV−vis-DR, FTIR, and FT-Raman spectroscopy to determine the nature of the surface tantala species. Two types of surface TaOx species were identified. On the SiO2 support, at low coverages tetrahedral TaO4 species exist, with a TaO bond and three bridging Ta−O-support bonds. At higher coverages, octahedral TaO6 species occur. On Al2O3 and ZrO2 both surface species exist already at considerably low Ta loading. The acidic properties of the catalysts were investigated by an FTIR study of adsorbed pyridine. Supported tantala is clearly more Lewis acidic in comparison to vanadia. The oxidation of methanol was used to probe the catalytic performance of the supported oxide species and from the activity and product distribution it is concluded that supported tantala predominantly shows acidic over redox behavior.

Publisher Summary This chapter discusses the pore size engineering of mesoporous MCM-48 materials using several additives during the synthesis. Dimethyltetradecyl amine (DMTDA) is a convenient expander, resulting in a MCM-48 structure with a pore size enlargement from 1.7 nm to 2.4 nm pore radius. A wide range of dimethylalkyl amines, with varying chain length is applied as swelling agents. Other additives, such as ethanol and decane, are also found to be suitable for the synthesis of large pore MCM-48. The influence of the chain length and the effect of the molar ratio of amine or surfactant on the crystallinity and pore size of the MCM-48 are also studied.

Publisher Summary This chapter discusses the synthesis and hydrothermal stability of directly usable hexagonal mesoporous silica (HMS) by efficient primary amine template extraction in acidified water. This very efficient extraction (100%) does not affect the physical properties of the resulting mesostructure. Compared to the ethanol-extracted HMS, no subsequent calcination step is required to remove the surface ethoxy groups produced during the ethanol extraction. The recovered surfactant can be easily re-used in a fresh synthesis. An improved hydrothermal stability is also observed after using the acidified water-extraction procedure.

Publisher Summary This chapter describes a controlled dispersion of Al 3+ onto a silica mesoporous material. A pure silica MCM-48 is activated by a controlled dispersion of Al onto the substrate surface performed by the anchoring of the Al(acac) 3 complex onto the surface silanols. A calcinations step removes the organic ligands. The characteristics of the final structure are evaluated by comparison with Al incorporated MCM-48. The type and concentration of Lewis/BrOnsted acid sites are also investigated by the adsorption of ammonia (NH 3 ) and acetonitrile-d3 (CD 3 CN).