Zeolites synthesis from phyllosilicates and their performance for CO2 adsorption.

Five phyllosilicates (kaolinite, montmorillonite, saponite, sepiolite and palygorskite) have been selected as starting materials for the synthesis of zeolites. Among them, kaolinite and montmorillonite display the lowest Si/Al molar ratio leading to aluminosilicates with high crystallinity. Thus, the hydrothermal treatment under basic conditions forms 4A zeolite when kaolinite is used as starting material while 13X zeolite is obtained when montmorillonite is used as starting material. The microporosity and CO2-adsorption capacity of the prepared zeolites are directly related to its crystallinity. Thus, in order to improve it, raw phyllosilicates were subjected to a microwave-assisted treatment to remove undesired Mg or Fe-species, which have a negative effect in the assembling of the zeolites by hydrothermal basic conditions in a second step. The highest adsorption value was 3.85 mmol/g at 25 °C and 760 mm of Hg for Mont-A-B sample after the consecutive treatments.

An advanced PdNPs@MoS2 nanocomposite for efficient oxygen evolution reaction in alkaline media.

In response to the increasing availability of hydrogen energy and renewable energy sources, molybdenum disulfide (MoS2)-based electrocatalysts are becoming increasingly important for efficient electrochemical water splitting. This study involves the incorporation of palladium nanoparticles (PdNPs) into hydrothermally grown MoS2via a UV light assisted process to afford PdNPs@MoS2 as an alternative electrocatalyst for efficient energy storage and conversion. Various analytical techniques, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and energy dispersive spectroscopy (EDS), were used to investigate the morphology, crystal quality, and chemical composition of the samples. Although PdNPs did not alter the MoS2 morphology, oxygen evolution reaction (OER) activity was driven at considerable overpotential. When electrochemical water splitting was performed in 1.0 M KOH aqueous solution with PdNPs@MoS2 (sample-2), an overpotential of 253 mV was observed. Furthermore, OER performance was highly favorable through rapid reaction kinetics and a low Tafel slope of 59 mV dec-1, as well as high durability and stability. In accordance with the electrochemical results, sample-2 showed also a lower charge transfer resistance, which again provided evidence of OER activity. The enhanced OER activity was attributed to a number of factors, including structural, surface chemical compositions, and synergistic effects between MoS2 and PdNPs.

Linear Polyethyleneimine-Based and Metal Organic Frameworks (DUT-67) Composite Hydrogels as Efficient Sorbents for the Removal of Methyl Orange, Copper Ions, and Penicillin V.

This research explores the integration of DUT-67 metal organic frameworks into polyethyleneimine-based hydrogels to assemble a composite system with enough mechanical strength, pore structure and chemical affinity to work as a sorbent for water remediation. By varying the solvent-to-modulator ratio in a water-based synthesis path, the particle size of DUT-67 was successfully modulated from 1 µm to 200 nm. Once DUT-67 particles were integrated into the polymeric hydrogel, the composite hydrogel exhibited enhanced mechanical properties after the incorporation of the MOF filler. XPS, NMR, TGA, FTIR, and FT Raman studies confirmed the presence and interaction of the DUT-67 particles with the polymeric chains within the hydrogel network. Adsorption studies of methyl orange, copper(II) ions, and penicillin V on the composite hydrogel revealed a rapid adsorption kinetics and monolayer adsorption according to the Langmuir's model. The composite hydrogel demonstrated higher adsorption capacities, as compared to the pristine hydrogel, showcasing a synergistic effect, with maximum adsorption capacities of 473 ± 21 mg L-1, 86 ± 6 mg L-1, and 127 ± 4 mg L-1, for methyl orange, copper(II) ions, and penicillin V, respectively. This study highlights the potential of MOF-based composite hydrogels as efficient adsorbents for environmental pollutants and pharmaceuticals.

Microwave-Assisted Synthesis of Zeolite A from Metakaolinite for CO2 Adsorption.

The global demand for energy and industrial growth has generated an exponential use of fossil fuels in recent years. It is well known that carbon dioxide (CO2) is mainly produced, but not only from fuels, which has a negative impact on the environment, such as the increasing emission of greenhouse gases. Thus, thinking about reducing this problem, this study analyzes microwave irradiation as an alternative to conventional heating to optimize zeolite A synthesis conditions for CO2 capture. Synthesis reaction parameters such as different temperatures (60-150 °C) and different time durations (1-6 h) were evaluated. The CO2 adsorption capacity was evaluated by CO2 adsorption-desorption isotherms at 25 °C and atmospheric pressure. The results showed that the synthesis of zeolite A by microwave irradiation was successfully obtained from natural kaolinite (via metakaolinization), reducing both temperature and time. Adsorption isotherms show that the most promising adsorbent for CO2 capture is a zeolite synthesized at 100 °C for 4 h, which reached an adsorption capacity of 2.2 mmol/g.

Facile synthesis of efficient Co3O4 nanostructures using the milky sap of Calotropis procera for oxygen evolution reactions and supercapacitor applications.

The preparation of Co3O4 nanostructures by a green method has been rapidly increasing owing to its promising aspects, such as facileness, atom economy, low cost, scale-up synthesis, environmental friendliness, and minimal use of hazardous chemicals. In this study, we report on the synthesis of Co3O4 nanostructures using the milky sap of Calotropis procera (CP) by a low-temperature aqueous chemical growth method. The milky sap of CP-mediated Co3O4 nanostructures were investigated for oxygen evolution reactions (OERs) and supercapacitor applications. The structure and shape characterizations were done by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS) techniques. The prepared Co3O4 nanostructures showed a heterogeneous morphology consisting of nanoparticles and large micro clusters. A typical cubic phase and a spinel structure of Co3O4 nanostructures were also observed. The OER result was obtained at a low overpotential of 250 mV at 10 mA cm-2 and a low Tafel slope of 53 mV dec-1. In addition, the durability of 45 hours was also found at 20 mA cm-2. The newly prepared Co3O4 nanostructures using the milky sap of CP were also used to demonstrate a high specific capacitance of 700 F g-1 at a current density of 0.8 A g-1 and a power density of 30 W h kg-1. The enhanced electrochemical performance of Co3O4 nanostructures prepared using the milky sap of CP could be attributed to the surface oxygen vacancies, a relatively high amount of Co2+, the reduction in the optical band gap and the fast charge transfer rate. These surface, structural, and optical properties were induced by reducing, capping, and stabilizing agents from the milky sap of CP. The obtained results of OERs and supercapacitor applications strongly recommend the use of the milky sap of CP for the synthesis of diverse efficient nanostructured materials in a specific application, particularly in energy conversion and storage devices.

Transforming NiCo2O4 nanorods into nanoparticles using citrus lemon juice enhancing electrochemical properties for asymmetric supercapacitor and water oxidation.

Recently, the nanostructured nickel-cobalt bimetallic oxide (NiCo2O4) material with high electrochemical activity has received intensive attention. Beside this, the biomass assisted synthesis of NiCo2O4 is gaining popularity due to its advantageous features such as being low cost, simplicity, minimal use of toxic chemicals, and environment-friendly and ecofriendly nature. The electrochemical activity of spinel NiCo2O4 is associated with its mixed metal oxidation states. Therefore, much attention has been paid to the crystal quality, morphology and tunable surface chemistry of NiCo2O4 nanostructures. In this study, we have used citrus lemon juice consisting of a variety of chemical compounds having the properties of a stabilizing agent, capping agent and chelating agent. Moreover, the presence of several acidic chemical compounds in citrus lemon juice changed the pH of the growth solution and consequently we observed surface modified and structural changes that were found to be very effective for the development of energy conversion and energy storage systems. These naturally occurring compounds in citrus lemon juice played a dynamic role in transforming the nanorod morphology of NiCo2O4 into small and well-packed nanoparticles. Hence, the prepared NiCo2O4 nanostructures exhibited a new surface-oriented nanoparticle morphology, high concentration of defects on the surface (especially oxygen vacancies), sufficient ionic diffusion and reaction of electrolytic ions, enhanced electrical conductivity, and favorable reaction kinetics at the interface. The electrocatalytic properties of the NiCo2O4 nanostructures were studied in oxygen evolution reaction (OER) at a low overpotential of 250 mV for 10 mA cm-2, Tafel slope of 98 mV dec-1, and durability of 40 h. Moreover, an asymmetric supercapacitor was produced and the obtained results indicated a high specific capacitance of (Cs) of 1519.19 F g-1, and energy density of 33.08 W h kg-1 at 0.8 A g-1. The enhanced electrochemical performance could be attributed to the favorable structural changes, surface modification, and surface crystal facet exposure due to the use of citrus lemon juice. The proposed method of transformation of nanorod to nanoparticles could be used for the design of a new generation of efficient electrocatalyst materials for energy storage and conversion uses.

Modification of the Textural Properties of Chitosan to Obtain Biochars for CO2-Capture Processes.

Three chitosans with different morphologies have been used (commercial chitosan powder, chitosan in film form and chitosan in globular form synthesized by the freeze-dried method) for the synthesis of biochars. The pyrolytic treatment has revealed that the biochar synthesized from the chitosan formed by the freeze-dried method reaches the highest CO2-adsorption capacity (4.11 mmol/g at 0 °C and a pressure of 1 bar) due to this adsorbent is highly microporous. Moreover, this biochar is more resistant to the pyrolytic treatment in comparison to the biochars obtained from the commercial chitosan and chitosan in the form of film. CO2-adsorption studies at different temperatures have also shown that the adsorption capacity diminishes as the adsorption temperature increases, thus suggesting that the adsorption takes place by a physical process.

Facile deposition of palladium oxide (PdO) nanoparticles on CoNi2S4microstructures towards enhanced oxygen evolution reaction.

Strong demand for renewable energy resources and clean environments have inspired scientists and researchers across the globe to carry out research activities on energy provision, conversion, and storage devices. In this context, development of outperform, stable, and durable electrocatalysts has been identified as one of the major objectives for oxygen evolution reaction (OER). Herein, we offer facile approach for the deposition of few palladium oxide (PdO) nanoparticles on the cobalt-nickel bi-metallic sulphide (CoNi2S4) microstructures represented as PdO@ CoNi2S4using ultraviolet light (UV) reduction method. The morphology, crystalline structure, and chemical composition of the as-prepared PdO@ CoNi2S4composite were probed through scanning electron microscopy, powder x-ray diffraction, high resolution transmission electron microscopy, energy dispersive spectroscopy and x-ray photoelectron spectroscopy techniques. The combined physical characterization results revealed that ultraviolet light (UV) light promoted the facile deposition of PdO nanoparticles of 10 nm size onto the CoNi2S4and the fabricated PdO@ CoNi2S4composite has a remarkable activity towards OER in alkaline media. Significantly, it exhibited a low onset potential of 1.41 V versus reversible hydrogen electrode (RHE) and a low overpotential of 230 mV at 10 mA cm-2. Additionally, the fabricated PdO@ CoNi2S4composite has a marked stability of 45 h. Electrochemical impedance spectroscopy has shown that the PdO@CoNi2S4composite has a low charge transfer resistance of 86.3 Ohms, which favours the OER kinetics. The PdO@ CoNi2S4composite provided the multiple number of active sites, which favoured the enhanced OER activity. Taken together, this new class of material could be utilized in energy conversion and storage as well as sensing applications.

Bimetallic Niobium-Based Catalysts Supported on SBA-15 for Hydrodeoxygenation of Anisole.

The effect of adding iron, cobalt or nickel to a prepared niobium-supported catalyst using mesoporous silica SBA-15 as a support was evaluated in the hydrodeoxygenation (HDO) reaction of anisole, chosen as a model compound in lignocellulosic biomass derived bio-oil. HDO activity as well as selectivity toward O-free products were highly dependent on the catalyst formulation: Ni incorporation showed the highest anisole conversion and selectivity to deoxygenated products, followed by Co and Fe counterparts. The activity was explained in terms of acidity, metal surface exposure and reducibility as a function of the interaction between the phases present. Regarding the characterization results, the better performance of NiNb/SBA-15 was associated with its lower acidity, higher Nb/Si surface exposure, NbO2/Nb2O5 ratio and better interaction between Ni and Nb species.

Au-Decorated Ce-Ti Mixed Oxides for Efficient CO Preferential Photooxidation.

We investigated the photocatalytic behavior of gold nanoparticles supported on CeO2-TiO2 nanostructured matrixes in the CO preferential oxidation in H2-rich stream (photo-CO-PROX), by modifying the electronic band structure of ceria through addition of titania and making it more suitable for interacting with free electrons excited in gold nanoparticles through surface plasmon resonance. CeO2 samples with different TiO2 concentrations (0-20 wt %) were prepared through a slow coprecipitation method in alkaline conditions. The synthetic route is surfactant-free and environmentally friendly. Au nanoparticles (<1.0 wt % loading) were deposited on the surface of the CeO2-TiO2 oxides by deposition-precipitation. A benchmarking sample was also considered, prepared by standard fast coprecipitation, to assess how a peculiar morphology can affect the photocatalytic behavior. The samples appeared organized in a hierarchical needle-like structure, with different morphologies depending on the Ti content and preparation method, with homogeneously distributed Au nanoparticles decorating the Ce-Ti mixed oxides. The morphology influences the preferential photooxidation of CO to CO2 in excess of H2 under simulated solar light irradiation at room temperature and atmospheric pressure. The Au/CeO2-TiO2 systems exhibit much higher activity compared to a benchmark sample with a non-organized structure. The most efficient sample exhibited CO conversions of 52.9 and 80.2%, and CO2 selectivities equal to 95.3 and 59.4%, in the dark and under simulated sunlight, respectively. A clear morphology-functionality correlation was found in our systematic analysis, with CO conversion maximized for a TiO2 content equal to 15 wt %. The outcomes of this study are significant advancements toward the development of an effective strategy for exploitation of hydrogen as a viable clean fuel in stationary, automotive, and portable power generators.

In vitro degradability and bioactivity of oxidized bacterial cellulose-hydroxyapatite composites.

Hydroxyapatite-associated bacterial cellulose (BC/HA) is a promising composite for biomedical applications. However, this hybrid composite has some limitations due to its low in vivo degradability. The objective of this work was to oxidize BC and BC/HA composites for different time periods to produce 2,3 dialdehyde cellulose (DAC). The BC and oxidized BC (OxBC) membranes were mineralized to obtain the hybrid materials (BC/HA and OxBC/HA) and their physico-chemical, degradability, and bioactivity properties were studied. The results showed that OxBC/HA was more bioactive and degradable than BC/HA, which isa function of the degree of BC oxidation. High glucose levels in the BC degradation were observed as a function of oxidation degree, and other products, such as butyric acid and acetic acid resulted from DAC degradation. Therefore, this chemical modification reaction favors BC degradation, making it a good biodegradable and bioactive material with a potential for bone regeneration applications.

Photocatalyzed preferential oxidation of CO under simulated sunlight using Au-transition metal oxide-sepiolite catalysts.

In the present study a series of Au-transition metal oxides supported on a clay mineral such as sepiolite were tested in the preferential oxidation of CO in an excess of H2 under simulated solar light irradiation and in the absence of light, at 30 °C and atmospheric pressure. Transition metal oxides (ZnO, Fe2O3, NiO, MnO2, and Co3O4) were dispersed over the sepiolite surface where, subsequently, Au nanoparticles with an average particle size between 2 and 3 nm were successfully deposited-precipitated. The obtained photocatalysts were characterized by XRD, XRF, DRUV-Vis, N2 adsorption-desorption and HRTEM in order to evaluate the optical, structural and chemical properties of the prepared samples. Despite the low amount of gold (nominal 1.0 wt%), the catalysts exhibited an outstanding behavior under light irradiation, with reaction rates between 4.5 and 5.2 mmol COox gcat-1 h-1 for the Au-NiSep, Au-CoSep and Au-ZnSep samples. These photocatalysts exhibited a high dispersion of the respective transition metal oxides over the sepiolite support and the presence of low-coordinated hemispherical gold nanoparticles. The superior photocatalytic efficiency of these samples was ascribed to the reduction of the electron-hole pair recombination of photogenerated charge carriers by the excitation of the localized surface plasmon resonance of the Au nanoparticles. The BET surface area and the gold particle size seemed to be relevant factors affecting the catalytic performance.

CO Preferential Photo-Oxidation in Excess of Hydrogen in Dark and Simulated Solar Light Irradiation over AuCu-Based Catalysts on SBA-15 Mesoporous Silica-Titania.

In this work, SBA-15 silica and silica-titania have been used as supports for photocatalysts based on AuCu alloy (Au:Cu = 1) to be used in the preferential oxidation of CO (CO-PROX) in excess of hydrogen at room temperature and atmospheric pressure both in the dark and under simulated solar light irradiation. To study their textural, structural, chemical and optical properties, the samples were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), adsorption-desorption of N2 at -196 °C, 13C and 29Si solid state nuclear magnetic resonance (NMR), X-ray photoelectron spectroscopy (XPS) and diffuse reflectance ultraviolet-visible (DRUV-vis) spectroscopy. Titanium was present mainly in the form of titania aggregates, but also as small particles interacting with the SBA support. In both catalysts, the metal alloy nanoparticles displayed an average size of 4 nm as demonstrated by TEM measurements. AuCu/Ti-SBA turned out to be photoactive and selective in the photo-CO-PROX reaction showing the highest activity, with conversion and selectivity towards CO2 of 80%, due both to the presence of titania incorporated in SBA-15 and to the synergistic effect of Cu when alloyed with Au.

Au and AuCu Nanoparticles Supported on SBA-15 Ordered Mesoporous Titania-Silica as Catalysts for Methylene Blue Photodegradation.

The photocatalytic degradation of methylene blue (MB) dye has been performed under UV irradiation in aqueous suspension, employing photocatalysts based on Au (1.5 wt %) and AuCu (Au/Cu = 1, 2.0 wt %), and supported on SBA-15-ordered mesoporous silica, with and without titania (Si/Ti = 3), in order to evaluate the versatility of this mesoporous support in this type of reaction of great impact from the environmental point of view. Samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), N2 adsorption-desorption at -196 °C, and X-ray photoelectron spectroscopy (XPS), so as to study their structural, optical, and chemical properties. All the prepared catalysts were found to be active in the test reaction. The bimetallic AuCu-based catalysts attained very high MB degradation values, in particular AuCu/SBA-15 titania-silica sample reached 100% of dye oxidation after the monitored reaction period (120 min).

Lamellar zirconium phosphates to host metals for catalytic purposes.

In the present study a porous lamellar zirconium phosphate heterostructure (PPH) formed from zirconium(iv) phosphate expanded with silica galleries (P/Zr molar ratio equal to 2 and (Si + Zr)/P equal to 3) was prepared to host noble metals. Textural and structural characterization of PPH-noble metal materials was carried out in order to elucidate the location and dispersion of the metallic particles and the properties of the resulting material to be used in catalytic processes. In the present paper, their activity in the catalytic hydrodeoxygenation (HDO) reaction of dibenzofuran (DBF) was evaluated. X-ray diffraction (XRD), solid state nuclear magnetic resonance (NMR) and X-ray photoelectron spectroscopy (XPS) evidenced that the structure of the pillared zirconium phosphate material was not modified by the incorporation of Pt and Pd. Moreover, transmission electron microscopy (TEM) showed a different dispersion of the noble metal. The acidity of the resulting PPH-noble metal materials also changed, although in all cases the acidity was of weak nature, and the incorporation of noble metals affected Brønsted acid sites as observed from 31P NMR spectra. In general, the textural, structural and acidic properties of the resulting materials suggest that PPH can be considered a good candidate to be used as a catalytic support. Thus, the catalytic results of the PPH-noble metal samples indicated that the Pd sample showed a stable behavior probably ascribed to a high dispersion of the active phase. However, the Pt sample suffered from fast deactivation. The selectivity to the reaction products was strongly dependent on the noble metal employed.

2D corrugated magnesium carboxyphosphonate materials: topotactic transformations and interlayer "decoration" with ammonia.

In this paper we report the synthesis and structural characterization of the 2D layered coordination polymer Mg(BPMGLY)(H(2)O)(2) (BPMGLY = bis-phosphonomethylglycine, (HO(3)PCH(2))(2)N(H)COO(2-)). The Mg ion is found in a slightly distorted octahedral environment formed by four phosphonate oxygens and two water molecules. The carboxylate group is deprotonated but noncoordinated. This compound is a useful starting material for a number of topotactic transformations. Upon heating at 140 °C one (of the two) Mg-coordinated water molecule is lost, with the archetype 2D structure maintaining itself. However, the octahedral Mg in Mg(BPMGLY)(H(2)O)(2) is now converted to trigonal bipyramidal in Mg(BPMGLY)(H(2)O). Upon exposure of the monohydrate Mg(BPMGLY)(H(2)O) compound to ammonia, one molecule of ammonia is inserted into the interlayer space and stabilized by hydrogen bonding. The 2D layered structure of the product Mg(BPMGLY)(H(2)O)(NH(3)) is still maintained, with Mg now acquiring a pseudo-octahedral environment. All of these topotactic transformations are also accompanied by changes in hydrogen bonding between the layers.

"Breathing" in adsorbate-responsive metal tetraphosphonate hybrid materials.

The structures of various layered calcium tetraphosphonates (CaH6DTMP; H8DTMP=hexamethylenediamine tetrakis(methylenephosphonic acid)), have been determined. Starting from CaH6DTMP.2H2O, thermal treatment and subsequent exposure to NH3 and/or H2O vapors led to four new compounds that showed high storage capacity of guest species between the layers (up to ten H2O/NH3 molecules) and a maximum volume increase of 55 %. The basic building block for these phosphonates consists of an eight-membered ring chelating Ca2+ through two phoshonate groups, and the organic ligand is located within the layers, which are held together by hydrogen bonds. The structural analysis revealed that the uptake/removal of guest species (H2O and NH3) induces significant changes in the framework not only by changing the interlayer distances but also through important conformational changes of the organic ligand. An anisotropic breathing motion could be quantified by the changes of the unit-cell dimensions and ligand arrangements in four crystalline derivatives. Complete characterization revealed the existence of interconversion reactions between the different phases upon gas uptake and release. The observed behavior represents, to the best of our knowledge, the first example of a breathing-like mechanism in metal phosphonates that possess a 2D topology.