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Abstract It is known that the world scenario is one of constant search for sustainable technologies that can reduce the emission of carbon dioxide (CO2) in the atmosphere. This is because CO2 is seen as the main responsible for the increase in the generation of greenhouse gases, which leads to global warming and climate change. The development of efficient adsorbents for CO2 capture is a current challenge. MCM-41 and SBA-15 were synthesized in a microwave reactor and used as adsorbents in this work. Microwave irradiation presents itself as an easy synthesis strategy with less preparation time and energy requirement. The silica synthesis period was extremely reduced (1 h) at a temperature of 60 and 80 °C in the microwave reactor, obtaining silica with good textural and chemical properties. The CO2 adsorption isotherms were performed at 0, 25, and 40 °C at 1 bar. The MCM-41 and SBA-15 present favorable results for CO2 capture processes, showing that pure silica synthesized by microwave already obtains promising results, reaching a maximum adsorption capacity of 2.16 mmol g−1 (1 bar—0 °C) and a good fit for the Langmuir, DsL and Toth models. Furthermore, to increase CO2 adsorption, the mesoporous silica was also modified via impregnation with branched polyethylene diamine (PEI) or tetraethylenepentamine (TEPA). It is worth mentioning that microwave irradiation reduced the synthesis steps and improved the properties and adsorption capacity of the silica. This work opens new opportunities in the efficient preparation of materials that require optimizing the adsorbent synthesis process. Graphical Abstract

The synthesis of PCH from natural bentonite produces a porous heterostructure material effective for the adsorption of glyphosate from water. The adsorption process takes place through an interaction between the silanol group of montmorillonite and/or the PCH adsorbent with the functional groups of glyphosate. The glyphosate adsorption isotherms, recorded for all the studied samples, have been established to be of Langmuir type. The kinetic of the herbicide adsorption on the PCH was best described by the pseudo-second-order model. With the increase in temperature from 25 to 50 °C, the sorption capacities of the materials studied towards glyphosate increased. The process of glyphosate adsorption was found to be endothermic and spontaneous in nature, as indicated by positive values of ΔH and negative values of ΔG. According to the results obtained, the herbicide sorption was more effective in a basic environment. The maximum amount of adsorbed glyphosate is almost doubled with PCH from 13.5 mg/g of natural clay to 27.5 mg/g of PCH. This study was partially funded by project RTI2018-099668-BC22 of Ministerio de Ciencia, Innovación y Universidades, and project UMA18-FEDERJA-126 of Junta de Andalucía and FEDER funds. Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature and Funding for open access charge: Universidad de Málaga / CBUA.

A series of tetrametallic hydrotalcite with different Ni loading, were synthesized by coprecipitation method. Then, these hydrotalcites were calcined in their respective metal oxides and were used as catalysts in the etherification reaction for the synthesis of polyglycerols. The effect of Ni loading on the structural and textural features was investigated by various techniques such as X-ray diffraction (XRD), thermogravimetric analysis TG–DSC–MS, temperature-programmed reduction (H2-TPR), temperature-programmed desorption (NH3-TPD) and 1-butene isomerization as a model reaction to probe acid–base character of catalysts. Mixed oxides derived from hydrotalcites are found to be active and suitable, via solvent free, in the glycerol etherification reaction. A gradual enhance of glycerol conversion is revealed when increasing the Ni/Mg molar ratio and the most active catalyst found is HTc-Ni75% with full selectivity to diglycerol.

Geopolymers are a class of inorganic polymers that have attracted attention in recent years, especially in the construction sector, due to their promising mechanical properties, as well as simple and low-cost fabrication. These materials also stand out for being more environmentally friendly, not only because of their lower CO2 emissions during production, but also because industrial by-products can be incorporated in their synthesis. Recent studies have investigated porous geopolymers, allowing expansion of their potential use to several other applications. Meanwhile, application of GPs to efficient water and wastewater treatments, such as nanofiltration and advanced oxidation processes, remains a challenge, especially due to high operational costs. Thus, this paper provides a comprehensive review of the current state of knowledge of geopolymers produced from aluminosilicate wastes, showing the main promising advances in their applications in three technological fields: (1) adsorption, (2) membrane filtration and (3) catalysis (as both catalyst or catalyst support).

Recycling mine tailings present a good alternative to manage the waste generated from mining and mineral processing industries. The geopolymer technology provides a green solution to the utilization of mining tailings, avoiding its negative environmental impacts. In this study, we used phosphate mine tailings to produce a novel geopolymeric membrane useful for removing copper ions and humic acid from an aqueous solution. Hydrogen peroxide was used in different concentrations as a porogenic agent, and the membranes exhibited good compressive strength (11.15–43.67 MPa) and high BET surface area (321–384 m2 g−1), depending on the amount of hydrogen peroxide used in the synthesis. The hydraulic permeability of the membranes increased from 4.12 × 10−5 to 11.84 × 10−5 m s−1 bar−1 when H2O2 was added, but the rejection of copper and humic acid remained nearly the same. Copper ions are adsorbed on the membrane surface, while negligible adsorption was measured for humic acid. The geopolymeric membranes efficiently removed Cu2+ from water through the combined action of adsorption and rejection by the geopolymer inorganic membrane. The performance of the porous membrane in the removal of copper or humic acid from water increased by factors of 7–19 in comparison to the non-porous membrane.

Palygorskite (Pal) is a low-cost clay mineral material and was investigated in this study as a novel material for adsorptive desulfurization of petroleum refining fractions from the Clara Camarao Potiguar Refinery (RPCC) in Brazil. This clay mineral was characterized by X-ray fluorescence, X-ray photoelectron spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, thermogravimetry, zeta potential ($$\zeta$$) and N2 adsorption/desorption isotherm analyses. Palygorskite textural properties (specific surface area 156 m2 g−1, total pore volume 0.36 cm3 g−1) and specific surface chemistry activity with several metals were crucial to efficient adsorption, proposing that an interaction between adsorbate/adsorbent involves π-complexation mainly with Fe species. This material was used in raw and thermally activated forms to evaluate the adsorption capacity. Several kinetic and equilibrium models were used to assess the experimental data. The results showed high correlation to the pseudo-second order kinetic model for both adsorbents (R2 > 0.99), suggesting a chemisorption process as the determining step. Isotherm data were used to evaluate the equilibrium experimental data. Maximum adsorption capacity calculated from the Langmuir isotherm (R2 > 0.97) was 6.25 mg g−1 for raw-Pal at 318 K. The adsorption thermodynamic assessment of S-compounds indicated an endothermic process, and there was consequently an increase in spontaneity at higher temperatures. The adsorbent raw-Pal displayed good potential in the adsorption of sulfur compounds in real diesel fuel. Palygorskite stands out for being an abundant clay mineral in nature, environmentally safe, and with high possibility of its applications in adsorption and catalysis processes.

Mesoporous silica SBA-15 solids have been synthesized at different aging temperature with the goal of obtaining materials with different textural properties. The synthesized samples have been evaluated for their CO2 adsorption capacity. In order to increase the CO2 adsorption capacity and the CO2/N2 selectivity, the SBA-15 synthesized at different aging temperatures were functionalized via grafting with 3-aminopropyltriethoxysilane (APTES) and via impregnation with polyethyleniminethylenediamine branched (PEI) or tetraethylenepentamine (TEPA). In all cases, the adsorption isotherms of the amine functionalized silica are fitted to the Dualsite-Langmuir model, where physical and chemical adsorption sites are reported. The isotherms reveal that grafted-silicas with APTES displayed the coexistence of both adsorption sites, while the adsorption process of PEI or TEPA impregnated-silicas are mainly governed by chemical interactions. The adsorption isotherms show that the most promising adsorbent for CO2 capture in terms of CO2 adsorption capacity and CO2/N2 selectivity is the SBA synthesized at 393 K (aging temperature) and functionalized with TEPA (50 wt%) (SBA-393-50T). This sample reached a CO2 adsorption capacity of 2.83 mmol g−1 at 100 kPa and 338 K. The CO2 adsorption capacity of this material decreased around 5% after the first adsorption/desorption cycle, maintaining a constant value for successive cycles. SBA-393-50T also showed an outstanding CO2/N2 selectivity, increasing significantly as the CO2 concentration decreases.

Molecular dynamics simulation performed by the DFT/ONIOM method and X-ray photoemission spectroscopy (XPS) data were employed for studying the adsorbate-adsorbent interaction system in diesel desulfurization over Ag/MCM-41 produced from beach sand silica (MPI). The morphology and structure of the materials were characterized via powder X-ray diffraction (XRD), scanning transmission electron microscopy (STEM) and field emission scanning electron microscopy (FESEM) together with energy dispersive spectrometry (EDS) analysis. The results proved a high dispersion of different Ag nanodomains onto MCM-41 and their chemical interaction with support and sulfur compounds by π-complexation. The best fit of kinetic and equilibrium data to pseudo-second order (R2 > 0.99) and Langmuir models (R2 > 0.98), respectively, demonstrate the occurrence of chemisorptive/catalytic interactions with organosulfur compounds, as seen in the XPS results. Its adsorption capacity (qm = 31.25 mgS/g) was 10 times higher than that obtained for pure MCM-41 and double the qm for Ag/MCM-41(C) adsorbent from commercial silica. The computational modeling approach provided valuable insight towards molecular level understanding of the mechanism in aromatic S-compounds adsorption over functionalized MCM-41 and the role of Ag species in this process.

In this work, amine-grafted mesoporous silica were investigated using a adsorption microcalorimetry and supplementary techniques in order to study the influence of increasing the density of grafted amine on the CO2 binding mechanisms. A Tian–Calvet microcalorimeter coupled to a manometric setup was used to evaluate the energetic heterogeneity of adsorption sites and to calculate the thermokinetic parameter from the differential enthalpy curves. With such device, equilibrium adsorption isotherms of CO2 were simultaneously measured at 25 °C for all samples up to 1 bar. The adsorption microcalorimetric study suggests a change in active sites distribution as the density of grafted amines increases. The maximum thermokinetic parameter of 471 s for the pure silica support at 30.7 kJ mol−1 suggests that physisorption is the dominant binding mechanism. A different behavior occurs with the grafted samples: they have considerably higher enthalpy values corresponding to the formation of reacted species on the surface (chemisorbed CO2), which depend on grafted amine density and available free surface silanols. Kinetics of formation of chemisorption products, together with hindered CO2 diffusion, seriously impair the approach to equilibrium, which leads to a decrease in uptake upon isothermal pressure-swing cycles at low temperatures (25 °C). CO2 could be successfully desorbed at 120 °C from the sample with highest uptake (MSG60), which showed a constant uptake for three adsorption–desorption cycles using only vacuum at 50 °C.

Production of glycerol oligomers by heterogeneous catalysis is being studied as an option for valorization of this biodiesel by-product. In this study, the catalytic activity of dolomite and the effects of parameters such as catalyst loading, reaction temperature, and reaction time were evaluated. Reusability and stability test were also performed. The material was tested as-received and after a thermal treatment, being characterized by XRD, FTIR, N2 adsorption–desorption, SEM, CO2-TPD and TG/DTG. Reaction products were analyzed by GC-FID for oligomers composition and ICP to verify metallic species leaching. The thermal treatment led to a decrease of the particle size, increase of the specific surface area and improved basicity. Calcined dolomite showed better catalytic performance than natural dolomite, leading to almost 80% glycerol conversion and selectivities for diglycerol and triglycerol of 51% and 3%, respectively. Kinetic test revealed that the reaction is slow along the first hours and later the reaction rate increases. Ca and Mg are leached to the reaction medium but the catalyst could be reused up to 2 cycles, with similar diglycerol yield. The reaction conditions for this material are less severe than those reported previously, which added to the low cost and reusability capacity turns suitable for glycerol oligomerization process.

Hybrid materials (HMs) based on a combination of bacterial cellulose (BC) and hydroxyapatite (HA) have demonstrated promising capabilities, especially for bone repair. The insertion of strontium into a BC/HA matrix has a role in the body related to bone remodeling. This study aimed to obtain HMs containing BC/HA doped with strontium ions (Sr2+) by two routes of synthesis, differing in the way strontium was inserted. The HMs produced were characterized to elucidate the morphology and metal/biopolymer interaction, and also strontium adsorption/desorption profiles were evaluated. The biomaterials produced were able to interact with Sr2+, showing a distinct adsorption/desorption profile for each material. BC/CaHA/Sr showed an ion exchange between Ca2+ present in hydroxyapatite by the Sr2+ in solution, characterized by mainly a physisorption mechanism. BC/SrAp demonstrated a chemical bond of Sr2+ on the BC surface by a chemisorption mechanism. The desorption study showed that the Sr release reached a plateau after 11 and 60 days and after 4 months, 91 and 6% of the adsorbed Sr2+ was released by BC/CaHA/Sr and BC/SrAp, respectively. These results suggest that the delivery of Sr2+ can be modulated during bone repair depending on the way Sr2+ is inserted into the hybrid matrix.

New ZrOxNy thin films were deposited via reactive RF magnetron sputtering on stainless steel substrate from a Y2O3-doped ZrO2 (3YSZ) target. In order to reduce their porosity and increase corrosion resistance, the films were annealed at 265 °C in an inert atmosphere at reduced pressure, increasing their density and corrosion resistance in saline solution. The crystal structure of the films was characterized by means of X-ray diffraction, the morphology via scanning electron microscopy and atomic force microscopy, and the chemical composition via X-ray photoelectron spectroscopy. The corrosion resistance was evaluated using electrochemical techniques based on linear polarization. The results show that the annealing treatment decreases the morphological imperfections of the coatings such as pores and cracks, which allows increasing the corrosion resistance of the substrate-coating system.

Cobalt phosphide catalysts supporting on SiO2 presenting different CoxPy stoichiometry were proved in hydrodeoxygenation (HDO) of two different model molecules present in biomass derived bio-oil such as phenol (Ph) and dibenzofuran (DBF). To investigate composition effects a series of cobalt phosphide catalysts presenting different initial P/Co atomic ratio were prepared. The catalysts were characterized by a range of techniques (N2 physisorption, XRD, TEM, NH3-TPD and XPS) and tested for DBF and Ph HDO activity and selectivity. Characterization results evidenced good textural properties, high dispersion of the active phase, as well as the presence of acid sites after P and Co incorporation. The highest activity was observed for catalysts containing an intermediate P/Co content were the CoP phase was the predominat one. Those catalyst containing Co2P or CoP2 phases were less active in these reactions.

In this work, solid wastes from the flocculation step of a drinking water treatment plant were used as starting material to obtain CO2 adsorbents upon thermal treatment and a pillaring strategy. Thermally treated solid waste and pillared materials were characterized by XRD, FTIR, TGA, N2 adsorption–desorption isotherms at 77 K, XPS and elemental analysis. From the characterization results, it was found that the introduction of silica pillars was successful, leading to heterostructured materials with higher specific surface area and pore volume. In order to improve the CO2 adsorption capacity, pillared materials were functionalized by grafting with (3-aminopropyl)triethoxysilane (APTES)and impregnation with polyethylenimine (PEI). Pillared materials could be loaded with up to 50 wt% PEI. PEI-impregnated pillared adsorbents were tested for CO2 adsorption at 298 and 348 K and CO2/N2 adsorption at 348 K using a Magnetic Suspension Balance equipped with a mixture gas dosing (Rubotherm, Germany). Langmuir and Sips models were used to fit monocomponent and mixture experimental data, considering two different sites for CO2 adsorption. At 1 bar, 50PEI-SiFe (loaded with 50 wt% PEI) adsorbed 2.5 and 3.6 mmol CO2 g−1 at 298 and 348 K, respectively and exhibited an extremely high CO2/N2 selectivity (above 150 mol CO2/mol N2 at 348 K). Nevertheless, PEI loaded adsorbents still exhibit a lower amine efficiency as compared to APTES-grafted counterparts, due to diffusion restrictions caused by the high viscosity of the impregnated polymer.

In this work, non-calcined Mg–Al and Zn–Al layered double hydroxides (LDHs) with molar ratio of 3:1 were investigated for the adsorption of bovine serum albumin (BSA). Both LDHs were synthesized using the co-precipitation method and were characterized by X-ray diffraction, N2 adsorption–desorption isotherm at −196 °C, elemental analysis and X-ray photoelectron spectroscopy. The adsorption of BSA was evaluated in a batch adsorption system to assess the influence of buffer solution and buffer pH, contact time and initial concentration. Fixed-bed adsorption experiments were also performed in order to evaluate the dynamic adsorption behavior of BSA on the LDH as well as the regenerability of this material. In the batch adsorption experiments, the maximum amount of BSA adsorbed was reached at its isoelectric point (pI = 4.8) with 50 mM acetate buffer for Mg–Al LDH and pH 6.7 with 50 mM 2-(N-morpholino)ethanesulfonic acid (MES) buffer for Zn–Al LDH. The Langmuir and Langmuir–Freundlich models provided maximum equilibrium adsorption capacity of 338.74 and 346.54 mg g−1for Zn-Al LDH, respectively, and 196.12 and 197.80, respectively, for Mg-Al LDH. Column experiments were carried out with a constant flow of 1 mL min−1, varying the feed concentration of BSA solutions from 1.0 to 2.0 mg mL−1. An average of 98 % of BSA injected into the column was retained, and a completely elution was reached using 50 mM sodium phosphate with pH 12.

In this work we have studied the CO2 adsorption capacity and CO2/CH4 separation on several APTES-grafted mesoporous silicas of SBA-15 type. The synthesis was modified in order to obtain pore expanded materials, and post synthesis functionalization was carried out by grafting with APTES (by immersion in 20 % v/v solution). The samples were characterized by elemental (CNH) analysis, X-ray diffraction, N2 adsorption–desorption isotherms at −196 °C, and TGA. To test the CO2 adsorption capacity and CO2/CH4 separation of all samples, a gravimetric method with a magnetic suspension balance (Rubotherm, Germany) was used. Monocomponent and mixture adsorption isotherms were measured at 25 °C. All isotherms were recorded to 10 bar. Monocomponent experimental data were fitted to Langmuir and Dual-site Langmuir models and the mixture experimental data were well fitted to Multiregion Extended Langmuir combined with Dualsite Langmuir model, achieving a good correlation between experimental and simulated data.

Ir and Pt have been tested as dopants for ruthenium sulfide supported on ordered SBA-15 mesoporous silica. The incorporation of Ir or Pt into RuS2/SBA-15 was found to enhance the activity in the gas-phase hydrodeoxygenation (HDO) of phenol carried out at 310 °C and 30 bar of total H2 pressure. X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy, temperature programmed desorption of NH3 and H2-temperature-programmed reduction of the sulfided catalysts were used to characterize the catalysts. XPS analysis of the spent catalysts confirmed the oxidation of ruthenium sulfide during HDO of phenol. The main factor that influences the catalyst activity was the surface exposure of the active phases, whereas the formation of oxysulfide species did not inhibit the HDO reaction., Thanks to MICINN for funding CTQ2012-37925-C03-03 and FEDER Projects, and Project of Excellence RNM 1565 of Junta de Andalucía for financial support. This study is also partially supported by the MICINN (ENE2007-67533-C02-01 Project) and CAM (S2009ENE-1743 Project).

Using a montmorillonite and the cationic surfactant hexadecyltrimethylammonium bromide (HDTMABr), a series of organoclays were synthesized with progressively increasing surfactant loads of between 0.2 and 4.0 times the cation exchange capacity of the starting clay. Different experimental techniques were used (thermal techniques, XPS, zeta potential) for characterizing the solids. The results obtained allowed to distinguish between the fraction of surfactant adsorbed by strong interactions and the fraction adsorbed by weak interactions. Adsorption isotherms of each of these processes were constructed, and were then adjusted using the Langmuir and Dubinin-Radusquevich adsorption models. Three types of interaction between the surfactant and the clay were identified and described, qualitatively and quantitatively. Two of these interactions, strong and weak, involve the hexadecyltrimethylammonium cation (HDTMA+). The third is a weak interaction involving the ion pair HDTMA+Br-. Fil: Naranjo, Pablo Matias. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Salta. Instituto de Investigación Para la Industria Química (i); Argentina Fil: Sham, Edgardo Ling. Universidad Nacional de Salta. Facultad de Ingenieria; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Salta. Instituto de Investigación para la Industria Química (i); Argentina Fil: Rodriguez Castellón, Enrique. Universidad de Malaga; España Fil: Torres Sanchez, Rosa Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico la Plata. Centro Tecnológico de Recursos Minerales y Cerámica (i); Argentina Fil: Farfan Torres, Elsa Monica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Salta. Instituto de Investigación Para la Industria Química (i); Argentina. Universidad Nacional de Salta. Facultad de Ciencias Exactas; Argentina

Applications of ferroelectric materials in modern microelectronics will be greatly encouraged if the thermal incompatibility between inorganic ferroelectrics and semiconductor devices is overcome. Here, solution-processable layers of the most commercial ferroelectric compound ─ morphotrophic phase boundary lead zirconate titanate, namely Pb(Zr0.52Ti0.48)O3 (PZT) ─ are grown on silicon substrates at temperatures well below the standard CMOS process of semiconductor technology. The method, potentially transferable to a broader range of Zr:Ti ratios, is based on the addition of crystalline nanoseeds to photosensitive solutions of PZT resulting in perovskite crystallization from only 350 °C after the enhanced decomposition of metal precursors in the films by UV irradiation. A remanent polarization of 10.0 μC cm−2 is obtained for these films that is in the order of the switching charge densities demanded for FeRAM devices. Also, a dielectric constant of ~90 is measured at zero voltage which exceeds that of current single-oxide candidates for capacitance applications. The multifunctionality of the films is additionally demonstrated by their pyroelectric and piezoelectric performance. The potential integration of PZT layers at such low fabrication temperatures may redefine the concept design of classical microelectronic devices, besides allowing inorganic ferroelectrics to enter the scene of the emerging large-area, flexible electronics.

This work presents some applications of ZrO2 supported over SBA-15 silica as promoter of sulfated zirconia and as support from CuO/CeO2 catalytic system for preferential oxidation of CO to CO2 in hydrogen rich streams, used as feed for proton exchange membrane fuel cells (PEMFC). Different amounts of ZrO2, from 10 to 30 wt.% were incorporated. These prepared materials were characterized by powder XRD, adsorption-desorption of N2 at 77 K, transmission and scanning electron microscopy (TEM and SEM) and X-rays photoelectron spectroscopy (XPS). The acidity was studied by thermo-programmed desorption of ammonia (NH3-TPD). These materials were tested, after treatment with H2SO4, by 2-propanol dehydration and 1-butene isomerization catalytic tests. The samples were found quite good catalyst with strong acid sites, the sample with 20 wt.% of ZrO2 being the better performing sample. Finally this material was successfully used as support for a CuO/CeO2 system, with 6 wt.% of Cu and 20 wt.% of Ce. The resulting catalyst was tested in the preferential oxidation of CO (CO-PROX) attaining conversions close to 100% and high selectivity to CO2.

The synthesis and characterization of cadmium sulphide (CdS) quantum dots, conjugated in a porous phosphate heterostructure functionalized with aminopropyl groups is described. The resulting material has fluorescence properties with maximum emission intensity at 575 nm. The fluorescent materials are not soluble in water and exhibit high stability in aqueous solution in the pH ranges from 2 to 9. Energy dispersive X-ray spectroscopy confirmed the qualitative elemental composition of the synthesized materials and X-ray photoelectron spectra showed a surface S/Cd atomic ratio of 1.09. SEM images show that the materials are amorphous, possessing porous with sizes of several tens nanometres, homogeneous and exhibit a layered morphology. The adsorption-desorption analysis by N(2) at 77 K showed the accessibility of the CdS quantum dots onto the pores of the structure. The CdS quantum dots were stabilized by mercaptopropionic acid and bounded to the host materials by amine groups.

Three series of vanadium-containing silica catalysts (2–7.6 wt% V) have been prepared by varying the synthesis method. In all cases, conversion values in the oxidative dehydrogenation of propane increase with the temperature, vanadium loading and reducibility. For impregnated and anchored catalysts, a relationship between the selectivity towards propene and the effective acidity, as determined in the dehydration of 2-propanol, can be established.

A series of chromium supported mesoporous MCM‐41 silica catalysts (0.5–6 wt% Cr) were prepared and tested in the oxidative dehydrogenation of propane between 350 and 550°C. The catalytic activity, observed at temperatures as low as 350 °C, can be well explained on the basis of the existence of highly dispersed and reducible chromium species.

Four molybdotellurates containing the 1-methylimidazolium, 2-methylimidazolium and 4-methylimidazolium cations have been synthesized and their structures: [2-H2-methyl-imz]6[TeMo6O24 ]·2H2O (2), [2-H2-methyl-imz]6[TeMo6O24 ]·2(2-H-methyl-imz)·2H2O (3) and [4-H2-methyl-imz]6[TeMo6O24 ]·Te(OH)6 (4) determined by X-ray diffraction methods. The protonated organic bases are bonded to the anion in the crystal by hydrogen bonds, except for (4) where the crystal structure consists of discrete [TeMo6O24]6− anions and Te(OH)6 units, both bonded to 4-methylimidazolium cations by hydrogen bonds. The hydrogen bonds were studied as a function of the unit charge of the oxygen atoms of the [TeMo6O24]6− anion. Distortions of the central octahedron of polyanions of formula [XMo6O24]n− (X=AlIII, MoVI, TeVI and IVII), and polyanions of formula [H6YMo6O24]n−, (Y=CoII, CuII, ZnII, CrIII, RhIII and PtIV) are discussed. 95Mo n.m.r spectroscopy of compounds [1-H2-methyl-imz]6[Te-Mo6O24]·Te(OH)6 (1), (2) and (4) indicates the existence of an octahedral oxygen atom arrangement around the molybdenum and a pH variation experiment, carried out with compound (1), confirmed the existence of hydrolytic processes of the compounds in aqueous solution. 125Te n.m.r. studies permitted identification of the Te atom in the [TeMo6O24]6− kernel in all compounds; the presence of two different Te(OH)6 moieties in compounds (1) and (4) was also detected. The similarity between the spectra of both compounds could indicate that (1) has the same structural arrangement as (4). Finally, the thermal behaviour and the thermal stabilities of the complexes as a function of the organic cation were studied.

Tungstotellurates of the organic imidazolium and 4-methyl-imidazolium cations have been prepared and characterized by X-ray diffraction and i.r. spectroscopy. The [TeW6O24]6− anion is formed by close packing of oxygen atoms with Te and W atoms in distorted octahedral voids. In both compounds the organic cations are involved in hydrogen bonds, to the [TeW6O24]6− anion in [H2imz]6[TeW6O24] · 2(Himz) (1) and to Te(OH)6 units in [4-H2-methyl-imz]6[TeW6O24] · Te(OH)6 (2). Solution studies of (1) and (2) by 1H-, 183W- and 125Te-n.m.r. have been carried out. Thermogravimetric (t.g.) and calorimetric (d.s.c.) analyses were performed for both compounds.

The present study investigates systematically, how the electrical properties of thin films consisting of silicon nanoparticles are affected by an organic monolayer coating the particles. Therefore, films of as-prepared silicon nanoparticles with a size of about 23 nm as well as freshly etched ones, both terminated with hydrogen, are compared with films of silicon nanoparticles functionalized with different 1-alkenes. It is found that the activation energy of the electron transport through the nanoparticle films scales with the thickness and permittivity of the respective organic monolayer.

Refluxing chromium (III) acetate with a Na+-montmorillonite suspension gives rise to the intercalation of linear Cr(III) polyhydroxo-acetate oligomers. Thermally stable chromia pillared mont-morillonite materials are obtained upon calcination under ammonia up to 625°C, and basal expansions up to 6 A are maintained. The porous materials retain high surface areas (366–464 m2 g−1), a micropore volume of 0.1 cm3 g−1 and narrow pore size distributions centered between 7.5 and 12 A. The most thermally stable materials in air were those prepared under ammonia at 625°C, containing NH4+ as the exchangeable ion.

The reaction of gaseous pyrrole (pyr) with Cu2+ exchanged alumina- and chromia-pillared α-tin and α-zirconium phosphates has been investigated. Preliminary exchange with Cu2+ reveals differences in ordering in the two types of oxide-pillared materials, ascribed to differences in precursor insertion during their preparation. In both oxide-pillared types, the pyr rapidly polymerises in the pores (not on the surface). Optical spectra and XPS evidence point to the presence of more than one type of pyr polymer, and hence of a porous system. The optical properties are typical of mixed neutral and bipolaron states with the presence of low-oxidation level polypyrrole. Based on similarities in optical properties with zeolite analogues, it is suggested that the starting materials contain porous systems similar to both zeolite-Y and mordenite present together. As for zeolite-Y and mordenite analogues, the materials have negligible conductances ( < 10−9 Ω−1 cm−1), which is ascribed to the presence of only short polymeric pyr units.

The intercalation of amines into α-tin(IV) hydrogen phosphate, α-Sn(HP04)2·H20, (α-SnP) can occur to give mono- or bilayers of the guest molecule. The distribution and orientation of the amines is influenced by geometrical factors, acidity of the guest molecule and moreover, the degree of charge localisation of the guest organic cations. Regarding the monolayer formation, there are two possibilities. The first is that aromatic amines form monolayers with parallel orientation of the amine with respect to the phosphate layer, when the charge is delocalised over the aromatic ring. Monolayer formation with perpendicular orientation occurs when the positive charge is localised in opposite parts of the aromatic ring molecule. Bilayer formation occurs when the positive charge is localised in one part of the molecule and simultaneous interaction with two adjacent layers is not possible.

The intercalation of ferrocene and dimethylaminomethylferrocene into α-tin(IV) hydrogen phosphate (SnP) and α-vanadyl phosphate has been investigated. Successful intercalation of 0.81 mol of dimethylamino-methylferrocene into α-SnP by an acid-base reaction in aqueous medium to form a bilayer of protonated amines was achieved. However, ferrocene was not intercalated under the same conditions. Intercalation of α-vanadyl phosphate by 0.11 mol of ferrocene in acetonic medium at room temperature was effected by a redox topotactic reaction. The voluminous dimethylaminomethylferrocene was not intercalated into α-vanadyl phosphate.

The uptake of Ce3+, Nd3+, Gd3+, Er3+, and Lu3+ on vermiculite was studied using cation-exchange measurements, infrared spectroscopy (IR), and X-ray powder diffraction (XRD). The reaction was followed by measuring the amount of lanthanide ions (Ln3+) taken up by n-butylammonium-ex-changed vermiculite in relation to amount of Ln3+ salt added and the pH of the equilibrium solution. The amount of Ln3+ taken up in excess of the CEC value increased with the hydration energy of the lanthanide ion and with the pH of the n-butylammonium-exchanged vermiculite suspension. At equilibrium solution pHs of 3–4.5, the uptake of Ln3+ ions was only slightly greater than the CEC, whereas at pHs >4.5 the amount taken up by the vermiculite increased sharply. The uptake of Ln3+ ions beyond the CEC of the vermiculite is probably related to the hydrolysis of Ln3+ ions on the vermiculite interlayer surface. The appearance of a band at 1715–1720 cm−1 in the IR spectra of the Ln3+-exchanged vermiculite suggests a strongly acidic medium in the interlayer space. The Ln3+-exchanged vermiculites gave XRD patterns having 002/001 intensity ratios greater than that of Mg-exchanged vermiculite.

Monomers which contain unsaturated linkages and amine groups have been intercalated to form either mono- or bi-layers. The monomertrans-N,N′-diethyl-2-butene-1,4-diamine (NNBD) has been intercalated into α-tin(IV) hydrogen phosphate. The guest molecule, NNBD, forms a monolayer (d001 = 1.35 nm) in which the amine groups are paired to protons on opposite faces of the phosphate layers. The resultant compound has the formula Sn(C8H18N2)0.73(HPO4)2·H2O indicating that NNBD does not cover a large proportion of the available protons. 4-vinylpyridine slowly forms an intercalate in which the host molecule forms a bilayer (d001 = 1.56 nn). However, with 4-vinylpyridine there is surface modification in preference to intercalation.