Search

Abstract: TiO x , VO x and TiO x –VO x oxides were highly dispersed at different metal loadings on the mesoporous silica SBA-15 by the molecular designed dispersion (MDD) method. A combination of different techniques (N2-sorption, FT-Raman, TPR, UV–vis-DR) was used to verify the nature of the vanadia and/or titania species on the surface of the mesoporous support. Temperature-programmed desorption (NH3-TPD) was applied to characterise the surface acidity of these catalysts. Vanadia and titania were found to be present as isolated species, even at high metal oxide concentrations. The supported catalysts were tested in the selective catalytic reduction (SCR) of NO with ammonia. Among the studied samples, the highest activity was found for TiO x –VO x mixed oxides on SBA-15. The catalytic activity results were discussed in terms of loading and metal dispersion on the support material. [Copyright &y& Elsevier]

Abstract: The thermal stability of Na2Ti3O7 and Na2Ti6O13, together with that of their protonated forms was investigated. The influence of temperature on the structural behaviour of tri- and hexa-titanates was studied using DTG, XRD, FTIR and FT-Raman. These results were correlated with the nature of the exchangeable cations using elemental analysis and N2-sorption. The tunnel structure of Na2Ti6O13 revealed a higher thermal stability compared to the layered structure of Na2Ti3O7 that shows traces of dimerisation above 800°C. The sodium forms were observed to be more thermally stable compared to their protonated forms. However, analysis show that ‘H2Ti6O13’ is much more thermally stable than the layered H2Ti3O7 which go through structural changes above 250°C and suffer a complete structural collapse into anatase/rutile above 800°C. It was obvious that thermal stability was significantly influenced by the nature of the exchangeable cations and the degree of ion-exchange. [Copyright &y& Elsevier]

Iron species were loaded into the mesopores of MCM-41 spheres by incipient wetness impregnation procedure with Fe(ACAC)3 as the precursor. The magnetism of the samples was studied by vibrating sample magnetometer (VSM), diffuse reflectance ultraviolet–visible (DRUV-vis) spectra and Mossbauer spectra. The results show that the magnetic behavior of the iron-loaded MCM-41 spheres depends on the content of iron loading, valence, and coordination state of iron ions, testing temperature and the atmosphere for the pyrolysis of the iron precursor. [Copyright &y& Elsevier]

Carbonation-cementation and bulk reaction mechanisms are studied in systems containing closely packed mixes of particulate Fe (0) (~10 μm) and Ca(OH) 2 (0%, 5%, 10% and 15% w/w of Ca(OH) 2) subjected to elevated CO 2 -pressure (1, 5, 10, and 20 barg) and temperature (30 °C and 60 °C). Solid solutions of (Ca x Fe 1-x)CO 3 series minerals are observed through shifting and broadening of XRD-reflections with variations in Ca(OH) 2 content, CO 2 -pressure and temperature. The product morphologies varied from rhombohedral in non-Ca(OH) 2 systems, to distorted rhombohedral (at 60 °C) and scalenohedral (at 30 °C) in the systems containing Ca(OH) 2. An X-ray diffraction-based interpolation method is developed to discern mixed and end-member carbonates for more accurate bulk phase quantification. Based on these observations, variations in cementation performances are explained. Exceptional formation of an Fe-LDH and a (Ca,Fe)-LDH has also been observed in some systems. Interestingly, these LDH phases were stable even after being exposed to ambient conditions for more than 75 days. [Display omitted] • Ca x Fe 1-x CO 3 (0 ≤ x ≤ 1) series cement formed by accelerated carbonation. • Fe substitution increases with carbonation temperature and CO 2 pressure. • More carbonate ≠ more strength. Microstructure/morphology are important. • XRD Rietveld interpolation method to quantify proportion and bulk compositions. • Formation of Ca,Fe-carbonate-hydroxide hydrate (LDH) stable for at least 75 days. [ABSTRACT FROM AUTHOR]

• Strategies to improve efficiency and selectivity of photocatalytic CO 2 reduction. • Pt nanoparticles to tune selectivity toward CO, Pd nanoparticles toward methane. • Surface plasmon resonance effect and charge separation of metal nanoparticles. • High turnover frequencies for both CO and methane. • Extensive Finite Element Method (FEM) modeling to study plasmonic mechanisms. A Ti-Beta zeolite was used in gas phase photocatalytic CO 2 reduction to reduce the charge recombination rate and increase the surface area compared to P25 as commercial benchmark, reaching 607 m2 g−1. By adding Pt nanoparticles, the selectivity can be tuned toward CO, reaching a value of 92% and a turnover frequency (TOF) of 96 µmol·g cat −1·h−1, nearly an order of magnitude higher in comparison with P25. By adding Pd nanoparticles the selectivity can be shifted from CO (70% for a bare Ti-Beta zeolite), toward CH 4 as the prevalent species (60%). In this way, the selectivity toward CO or CH 4 can be tuned by either using Pt or Pd. The TOF values obtained in this work outperform reported state-of-the-art values in similar research. The improved activity by adding the nanoparticles was attributed to an improved charge separation efficiency, together with a plasmonic contribution of the metal nanoparticles under the applied experimental conditions. [ABSTRACT FROM AUTHOR]

A series of ZnTi layered double hydroxides (LDH) with different Zn/Ti ratios are prepared and used as catalysts for photodegradation of salicylic acid (SA) under visible light. The catalysts are characterized by X-Ray diffraction, diffuse reflectance infrared Fourier transform spectroscopy, UV–vis diffuse reflectance spectroscopy, thermogravimetry, electron paramagnetic resonance and N 2 adsorption-desorption. The results show that SA anions bind to the LDH surface and that an electron can be excited from the HOMO in the adsorbed molecules to the conduction band of the LDH under visible light illumination. This charge transfer further leads to an effective photodegradation and mineralization of SA with better conversion results than on P25 titania. Key factors influencing the charge-transfer process in LDH are the high surface area and the Ti/Zn ratio of the LDH materials. The combination of highly dispersed Zn2+ and Ti4+ cations in the brucite-like sheets of the LDH allows for a better charge separation, which also accounts for the high photocatalytic activity. The present results show that superoxide radicals play a role in the visible-light induced degradation of SA on LDH, while no •OH radicals are formed. In contrast to LDH, the light-induced degradation pathway of SA over P25 titania leads to the formation of CO 2 −, a relatively stable anion that may hamper further conversion to CO 2 and hence limit the photocatalytic performance. The introduction of an electron acceptor, such as peroxydisulfate, further improves the degradation and mineralization of SA over LDH, but care should be taken not to use an electron acceptor that can easily adsorb to the LDH surface, such as H 2 O 2. ZnTi LDH are thus very promising alternatives to TiO 2 for the photodegradation of colorless organic pollutants, such as SA, under visible light irradiation. Unlabelled Image • ZnTi layered double hydroxides (LDHs) allow mineralization of salicylic acid under visible light. • Visible light induces charge transfer from the adsorbed molecule to the semiconductor. • The Ti/Zn ratio and specific surface area of ZnTi LDH influence the photoactivity. • Photodegradation of SA involves different radical intermediates in LDH than in titania. [ABSTRACT FROM AUTHOR]

Schematic diagram of the proposed reaction processes and the reaction products. • FeCO 3 scale common to multiple Fe-particles (10 μm) cements them together. • Cement properties vary with scale microstructure based on CO 2 -pressure/temperature. • Up to 28 % FeCO 3 in bulk product within 4 h of carbonation (Rietveld analyses). • Needle shaped FeCO 3 crystals observed at 30 °C, rhombohedral crystals at 60 °C/90 °C. • FeCO 3 content always increases with CO 2 -pressure, temperature needs optimization. FeCO 3 scaling is utilised in a system of closely packed wet Fe-particles (10 μm) to prepare blocks composed of unreacted Fe-cores connected by a 'cementing matrix of FeCO 3 scales'. Within four hours of carbonation at different temperatures (30 °C – 90 °C) and CO 2 -pressures (1 barg–20 barg), a compressive strength of up to 160 MPa, and a siderite (FeCO 3) content of up to 28 % is observed. Typical rhombohedral and atypical needle-shaped FeCO 3 crystal morphologies are observed. The dependence of phase composition/morphologies on reaction conditions/processes is discussed. This study is proposed as a prelude towards utilisation of Fe-rich industrial wastes for cementation. [ABSTRACT FROM AUTHOR]

A series of mixed nanocomposite materials was synthetized, containing a Ferrite phase type Zn 1-x Ni x Fe 2 O 4 and a Freudenbergite phase type Na 2 Fe 2 Ti 6 O 16 , where x = 0; 0.2; 0.4; 0.6; 0.8; 1. The choice for this combination is based on the good adsorption properties of Freudenbergite for dye molecules, and the small bandgap energy of Ferrite spinel, allowing activation of the catalysts under visible light irradiation. A two steps synthesis protocol was used to obtain the smart-removal nanocomposites. Firstly, the spinel structure was obtained via the co-precipitation route followed by the addition of the Ti-source and formation of the Freudenbergite system. The role of cations on the formation mechanism and an interesting interchange of cations between spinel and Freudenbergite structures was clarified by a TEM-study. Part of the Ti4+ penetrated the spinel structure and, at the same time, part of the Fe3+ formed the Freudenbergite system. The photocatalytic activity was studied under visible light, reaching for the best catalysts a 67% and 40% mineralization degree for methylene blue and rhodamine 6G respectively, after 6 h of irradiation. In the same conditions, the well-known commercial P25 (Degussa) managed to mineralize only 12% and 3% of methylene blue and rhodamine 6G, respectively. Due to the remarkable magnetic properties of Ferrites, a convenient recovery and reuse of the catalysts is possible after the photocatalytic tests. Based on the excellent catalytic performance of the nanocomposites under visible light and their ease of separation out of the solution after the catalytic reaction, the newly developed composite catalysts are considered very effective for wastewater treatment. Image 1 • Novel smart-removal photocatalysts are developed for the use under visible light irradiation. • The formation mechanism of the nanocomposites are discussed and clarified. • The results show superior mineralization degree for the as-prepared nanocomposites compared to P25. • The magnetic separation allows recycling and the study of more cycles for a selected photocatalyst. [ABSTRACT FROM AUTHOR]

This paper investigates the structural and magnetic properties of a mixed series of ferrites having general formula Co 0.5 Zn 0.25 M 0.25 Fe 2 O 4 (M = Ni, Cu, Mn, Mg). Insights on surface chemistry, structural and morphological parameters are presented in order to achieve highly tuned ferrite systems with specific characteristics. The site occupancy of the cations in the spinel structure was determined using XAS, XRD and Raman spectroscopy. A 100% occupancy of the tetrahedral sites was observed for the Zn cations for all the samples. Co cations occupied the octahedral sites in proportion of 100% for Co–Zn–Cu, Co–Zn–Mg and around 80% for Co–Zn–Ni, Co–Zn–Mn. Ni cations were found only in the octahedral sites, while Cu 80% in the octahedral sites and Mn 60% in the octahedral sites. The cation distribution results were correlated with the magnetic properties data. At the same time, not only the cation distribution, but also the particles size distribution was observed to have a great influence on magnetic and optical properties of the ferrites. Given the importance of the surface chemistry of the nanoparticles, XPS and FT-IR analysis were used to prove the functionalization with groups belonging to the surfactant. Moreover, the peculiar behavior of manganese in spinel structures was clarified and the origin of the multiple states (Mn2+and Mn4+) was elucidated. Finally, parallels have been drawn between the use of different cations in mixed ferrites in order to gain specific properties. • Synthesis of novel mixed ferrites Co–Zn-M (M = Ni, Cu, Mn, Mg) is described. • Surface characterization techniques confirm the functionalization with organic groups. • X-ray absorption spectroscopy results revealed a peculiar behavior of Mn containing ferrite. • Magnetic properties as function of particles size and cation distribution are summarized. [ABSTRACT FROM AUTHOR]

The quest to provide clean water has led to a tremendous boost in the synthesis of advanced photocatalysts that are able to decontaminate water by harvesting the solar energy. Herein, a tandem of Pt or both Pt-Ag nanoparticles on layered double hydroxides (LDH) photocatalysts were obtained via a green chemical procedure in which LDH serve a dual function of both facilitating the synthesis of nanoparticles of Pt and Ag and acting as a support. Detailed characterization showed that the LDH structure is well-retained, while small nanoparticles of Pt or Pt-Ag are formed and dispersed on the larger nanoparticles of the LDH. The effects of the heterometallic composition of the 2-D LDH layers (e.g. Zn2Al; Zn2FeAl) and the mono/bi-metal (Pt/Pt-Ag) identity on the solar-light-induced catalytic performances were investigated using p-nitrophenol (p-NPh) as a targeted pollutant. Pt-Ag synergistic activity was superior to Pt alone to promote p-NPh degradation and Pt-Ag/Zn2Al exhibited the best photocatalytic activity approaching 77% degradation and 71% mineralization of p-NPh, after 6 h under solar light, at room temperature. The introduction of Fe in the LDH layers caused a significant change in the degradation pathway of p-NPh and drastically decreased the catalytic response such that p-NPh mineralization was only 10% for Pt-Ag/Zn2FeAl. Even though UV–vis analysis showed that Pt-Ag/Zn2FeAl had a stronger absorption of the visible light than Pt-Ag/Zn2Al, the PL data indicated a significant increase in the photoluminescence signal for Pt-Ag/Zn2FeAl as compared to Pt-Ag/Zn2Al. This suggested a retard recombination of electrons-holes in Pt-Ag/Zn2Al and revealed the active role of the LDH multimetallic composition to establish an effective electronic coupling between the constituent nanounits. These findings may aid in the rational design of multimetallic heterostructures that can effectively harvest sunlight for environmental cleanup. Unlabelled Image • Pt or Pt-Ag nanoparticles on layered double hydroxides (LDH) by a facile synthesis. • Properties of Pt/LDH and Pt-Ag/LDH were confirmed by imperative measurements. • Pt-Ag synergistic activity is superior to Pt to promote p-nitrophenol degradation on a tandem photocatalysis. • LDH multimetallic compositions have an active role to establish the electronic coupling between the constituent nanounits. [ABSTRACT FROM AUTHOR]

Engineering bulk covalent organic frameworks (COFs) to access specific morphological structures holds paramount significance in boosting their functions in cancer treatment; nevertheless, scant effort has been dedicated to exploring this realm. Herein, silica core-shell templates and multifunctional COF-based reticulated hollow nanospheres (HCOFs) are novelly designed as a versatile nanoplatform to investigate the simultaneous effect of dual-drug chemotherapy and photothermal ablation. Taking advantage of the distinct structural properties of the template, the resulting two-dimensional (2D) HCOF, featuring large internal voids and a peripheral interconnected mesoporous shell, presents intriguing benefits over its bulk counterparts for cancer treatment, including a well-defined morphology, an outstanding drug loading capability (99.6%) attributed to its ultrahigh surface area (2087 m 2 /g), great crystallinity, improved tumor accumulation, and an adjustable drug release profile. After being loaded with hydrophilic doxorubicin with a remarkable loading capacity, the obtained drug-loaded HCOFs were coated with gold nanoparticles (Au NPs) to confer them with three properties, including pore entrance blockage, active-targeting capability, and improved biocompatibility via secondary modification, besides high near infrared (NIR) absorption for efficient photothermal hyperthermia cancer suppression. The resultant structure was functionalized with mono-6-thio-β-cyclodextrin (β-CD) as a second pocket to load docetaxel as the hydrophobic anticancer agent (combination index = 0.33). The dual-drug-loaded HCOF displayed both pH- and near-infrared-responsive on-demand drug release. In vitro and in vivo evaluations unveiled the prominent synergistic performance of coloaded HCOF in cancer elimination upon NIR light irradiation. This work opens up a new avenue for exciting applications of structurally engineered HCOFs as hydrophobic/hydrophilic drug carriers as well as multimodal treatment agents.

This study introduces solid-state tuning of a mesostructured cellular foam (MCF) to enhance hydrogen (H 2 ) storage in clathrate hydrates. Grafting of promoter-like molecules ( e.g. , tetrahydrofuran) at the internal surface of the MCF resulted in a substantial improvement in the kinetics of formation of binary H 2 -THF clathrate hydrate. Identification of the confined hydrate as sII clathrate hydrate and enclathration of H 2 in its small cages was performed using XRD and high-pressure 1 H NMR spectroscopy respectively. Experimental findings show that modified MCF materials exhibit a ∼1.3 times higher H 2 storage capacity as compared to non-modified MCF under the same conditions (7 MPa, 265 K, 100% pore volume saturation with a 5.56 mol% THF solution). The enhancement in H 2 storage is attributed to the hydrophobicity originating from grafting organic molecules onto pristine MCF, thereby influencing water interactions and fostering an environment conducive to H 2 enclathration. Gas uptake curves indicate an optimal tuning point for higher H 2 storage, favoring a lower density of carbon per nm 2 . Furthermore, a direct correlation emerges between higher driving forces and increased H 2 storage capacity, culminating at 0.52 wt% (46.77 mmoles of H 2 per mole of H 2 O and 39.78% water-to-hydrate conversions) at 262 K for the modified MCF material with fewer carbons per nm 2 . Notably, the substantial H 2 storage capacity achieved without energy-intensive processes underscores solid-state tuning's potential for H 2 storage in the synthesized hydrates. This study evaluated two distinct kinetic models to describe hydrate growth in MCF. The multistage kinetic model showed better predictive capabilities for experimental data and maintained a low average absolute deviation. This research provides valuable insights into augmenting H 2 storage capabilities and holds promising implications for future advancements., Competing Interests: The authors declare no competing financial interest., (This journal is © The Royal Society of Chemistry.)

Direct photocatalytic reduction of CO 2 has become an highly active field of research. It is thus of utmost importance to maintain an overview of the various materials used to sustain this process, find common trends, and, in this way, eventually improve the current conversions and selectivities. In particular, CO 2 photoreduction using plasmonic photocatalysts under solar light has gained tremendous attention, and a wide variety of materials has been developed to reduce CO 2 towards more practical gases or liquid fuels (CH 4 , CO, CH 3 OH/CH 3 CH 2 OH) in this manner. This Review therefore aims at providing insights in current developments of photocatalysts consisting of only plasmonic nanoparticles and semiconductor materials. By classifying recent studies based on product selectivity, this Review aims to unravel common trends that can provide effective information on ways to improve the photoreduction yield or possible means to shift the selectivity towards desired products, thus generating new ideas for the way forward., (© 2023 Wiley-VCH GmbH.)

Silver nanoparticles are widely used in the field of plasmonics because of their unique optical properties. The wavelength-dependent surface plasmon resonance gives rise to a strongly enhanced electromagnetic field, especially at so-called hot spots located in the nanogap in-between metal nanoparticle assemblies. Therefore, the interparticle distance is a decisive factor in plasmonic applications, such as surface-enhanced Raman spectroscopy (SERS). In this study, the aim is to engineer this interparticle distance for silver nanospheres using a convenient wet-chemical approach and to predict and quantify the corresponding enhancement factor using both theoretical and experimental tools. This was done by building a tunable ultrathin polymer shell around the nanoparticles using the layer-by-layer method, in which the polymer shell acts as the separating interparticle spacer layer. Comparison of different theoretical approaches and corroborating the results with SERS analytical experiments using silver and silver-polymer core-shell nanoparticle clusters as SERS substrates was also done. Herewith, an approach is provided to estimate the extent of plasmonic near-field enhancement both theoretically as well as experimentally.

Mesoporous SBA-16 and SBA-15 were studied in order to control their possible morphologies. SBA-16 is synthesized using a silicon source (tetraethoxysilane, TEOS) and a ternary system consisting of surfactant F127 (EO106PO70EO106), water, and butanol. The same ternary system, with higher butanol concentration, is used to form SBA-15 material as well. An increase of the TEOS concentration results in a morphology shift of SBA-16 from micron-sized spheres, over randomly shaped aggregated particles, to macrospheres with a size of 15 mm. An identical increase in TEOS concentration also results in the formation of SBA-15 macrospheres, which can be controlled in size. Micron-sized spheres of SBA-15 were formed using a quaternary system of surfactant P123 (EO20PO70EO20), cetyltrimethylammonium bromide (CTAB), ethanol, and water. All mesoporous silica materials were characterized using SEM, XRD, and N2 sorption techniques.

Four various mesoporous silicas (MCM-48, SBA-15, MCF, and MSU) were modified by the molecular designed dispersion method using Fe(acac)3, Cr(acac)3, and Cu(acac)2 complexes. The deposition was performed at the same concentration of the metal acetylacetonate (acac) complex in a toluene solution. All as-synthesized samples were investigated by diffuse reflectance infrared Fourier transform spectroscopy, Fourier transform infrared photoacoustic spectroscopy, and thermogravimetric analysis. The calcined materials were studied with respect to their textural properties (Brunauer-Emmett-Teller adsorption isotherm) and chemical composition (electron microprobe analysis). It allowed elucidation of the mechanism of interaction between the acac complex and the silanol groups. For the MCM-48, SBA-15, and MCF materials, the formation of hydrogen bonding was found for the chromium- and copper-modified samples, whereas the Fe-containing materials showed the ligand exchange mechanism. The strong interaction of the MSU support and the different acetylacetonate complexes, resulting in a loss of at least one acac ligand, was observed. The mesoporous silicas modified with transition metal oxides were studied by UV-vis-DR spectroscopy. The different metal dispersions were found for the samples containing various transition metal oxides.