Novel MgO–SnO<Subscript>2</Subscript> Solid Superbase as a High-Efficiency Catalyst for One-Pot Solvent-Free Synthesis of Polyfunctionalized 4<Emphasis Type="Italic">H</Emphasis>-pyran Derivatives

Abstract  

We report for the first time the hydrothermal synthesis of MgO–SnO₂ solid superbase using P123 as template. The basicity of the materials was determined by two approaches of Hammett indicators method and temperature-programmed desorption using CO₂ as adsorbate (CO₂-TPD). It was found that Mg/Sn molar ratio has an effect on MgO–SnO₂ basicity, and superbasicity was observed only at Mg/Sn molar ratio of 1. With variation of Mg/Sn molar ratio, superbase strength (H _-) was in the 26.5–33.0 range, showing superbasic value up to 0.939 mmol/g. The structure and texture of the as-prepared materials were studied by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and N₂ physio-adsorption methods. We detected particles of spherical morphology having diameter of ca. 150 nm. N₂ adsorption–desorption results suggested that the materials are of mesoporous structure, having specific surface area of 115.2 m²/g and average pore diameter of 6 nm. The superbase was found to exhibit excellent catalytic activity towards the one-pot synthesis of polyfunctionalized 4H-pyrans through the condensation of aldehydes, malononitrile, and an active methylene compound. Its excellent catalytic efficiency is related to its superbasicity of the MgO–SnO₂. The results provide a new route for the design and preparation of composite oxide superbases. Furthermore, the solid superbases will facilitate a strategy for high-efficiency synthesis of polyfunctionalized 4H-pyrans.     

Synthesis of SiO<Subscript>2</Subscript>–SnO<Subscript>2</Subscript> gels in water free conditions

A series of SiO₂–SnO₂ samples with various Sn/Si molar ratios (0.05–1.0) have been synthesized by the sol–gel technique from (Tetraethylorthosilicate) TEOS and Sn(CH₃COO)₄ precursors in water free conditions. The synthesis applied allowed obtaining the final product in monolithic (nonfractured upon drying) form with no use of drying control chemical additives. All samples are characterized by thermal analysis, XRD, and FTIR. The low temperature nitrogen adsorption measurements indicate the presence of both micro and mesopores. The samples containing less than 20 wt% of SnO₂ show much higher surface area than SiO₂ gel. The appearance of new bands at 1,048 and 882 cm⁻¹ in the FTIR spectra could be related to stretching vibrations of the three dimensional Si–O–Sn network, which suggests that tin component has replaced silicon atoms in Si–O–Si structure.     

Green synthesized Au–Ag bimetallic nanoparticles modified electrodes for the amperometric detection of hydrogen peroxide

Simple and eco-friendly electro deposition method was employed for the fabrication of Au–Ag bimetallic nanoparticles modified glassy carbon electrode. Nano Au–Ag film modified glassy carbon electrode surface morphology has been examined using atomic force microscopy. Electrodeposited Au–Ag bimetallic nanoparticles were found in the average size range of 15–50 nm. The electrochemical investigations of nano Au–Ag/1-butyl-3-methylimidazolium tetrafluoroborate-nafion film have been carried out using cyclic voltammetry and electrochemical impedance spectroscopy. The nano Au–Ag/1-butyl-3-methylimidazolium tetrafluoroborate-nafion film modified glassy carbon electrode holds the good electrochemical behavior and stability in pH 7.0 phosphate buffer solutions. The nano Au–Ag/1-butyl-3-methylimidazolium tetrafluoroborate-nafion modified glassy carbon electrode was successfully employed for the detection of H₂O₂ in the linear range of 1–250 μM in lab samples, and 1 × 10⁻³–2 × 10⁻² M in real samples, respectively.     

Synthesis, Characterization, and Microwave Absorption Property of the SnO2 Nanowire/Paraffin Composites

In this article, SnO₂ nanowires (NWs) have been prepared and their microwave absorption properties have been investigated in detail. Complex permittivity and permeability of the SnO₂ NWs/paraffin composites have been measured in a frequency range of 0.1–18 GHz, and the measured results are compared with that calculated from effective medium theory. The value of maximum reflection loss for the composites with 20 vol.% SnO₂ NWs is approximately −32.5 dB at 14 GHz with a thickness of 5.0 mm.     

Interconnected SnO2/graphene+CNT network as high performance anode materials for lithium-ion batteries

As a metal oxide with a high theoretical capacity, SnO₂ is considered to be one of the promising alternative anode materials in lithium-ion batteries. However, the pulverization of electrodes caused by the large volume expansion of SnO₂ during repeated charge/discharge hinders its practical application. Here, SnO₂ nanoparticles decorated on a 3D carbon network structure formed by the interconnection of graphene and CNT (SnO₂/G + CNT), which is designed and successfully synthesized via in situ chemical synthesis and thermal treatment. In this structure, the SnO₂ with nanosized can increase energy storage points and decrease the ions transport length, the carbon network can build a high conductive network that facilitates electron transport and alleviate the volume expansion to prevent electrode pulverization. In addition, graphene has a high specific surface area effect that facilitates lithium-ion storage, and the CNT also supports the graphene frame to make the carbon skeleton structure more stable, and provides a large number of ion transport channels, increasing the active sites of the reaction. Due to this excellent structure with synergistic effects, the SnO₂/G + CNT electrode exhibits superior reversible capacity (1227.2 mAh g^-1 at 0.1 A g^-1 after 200 cycles), superior rate capacity (549.3 mAh g^-1 at 3.0 A g^-1) and long cycle stability (1630.1 mAh g^-1 at 0.5 A g^-1 after 1000 cycles).     

Preparation and electrochemical performance of SnO2@carbon nanotube core–shell structure composites as anode material for lithium-ion batteries

Carbon nanotube-encapsulated SnO₂ (SnO₂@CNT) core–shell composite anode materials are prepared by chemical activation of carbon nanotubes (CNTs) and wet chemical filling. The results of X-ray diffraction and transmission electron microscopy measurements indicate that SnO₂ is filled into the interior hollow core of CNTs and exists as small nanoparticles with diameter of about 6 nm. The SnO₂@CNT composites exhibit enhanced electrochemical performance at various current densities when used as the anode material for lithium-ion batteries. At 0.2 mA cm^?2 (0.1C), the sample containing wt. 65% of SnO₂ displays a reversible specific capacity of 829.5 mAh g^?1 and maintains 627.8 mAh g^?1 after 50 cycles. When the current density is 1.0, 2.0, and 4.0 mA cm^?2 (about 0.5, 1.0, and 2.0C), the composite electrode still exhibits capacity retention of 563, 507 and 380 mAh g^?1, respectively. The capacity retention of our SnO₂@CNT composites is much higher than previously reported values for a SnO₂/CNT composite with the same filling yield. The excellent lithium storage and rate capacity performance of SnO₂@CNT core–shell composites make it a promising anode material for lithium-ion batteries.     

Synthesis and characterization of Sb–SnO2/kaolinites nanoparticles

In this paper, we reported the synthesis of composite conductive powders of antimony-doped tin oxide (Sb–SnO₂) coated onto kaolinite. Structure and morphology of the samples were systematically characterized by X-ray diffraction (XRD), scanning electronic microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), Fourier transform infrared (FTIR) and X-ray photoelectron spectrum (XPS). The results showed that Sb–SnO₂ nanoparticles (< 10 nm) were successfully coated as thin layers on the surface of kaolinite. The antimony-doped tin oxide/kaolinite (ATK) composites retained the flake morphology like the original kaolinite and had a resistivity of 273.2 Ω·cm. Sb–SnO₂ layers were proved to attach to the kaolinite surface via the Sn–O–Si or Sn–O–Al bonds. The growth mode of Sb–SnO₂ layers onto the kaolinite was investigated.     

Carbon coated porous tin peroxide/carbon composite electrode for lithium-ion batteries with excellent electrochemical properties

A porous tin peroxide/carbon (SnO₂/C) composite electrode coated with an amorphous carbon layer is prepared using a facile method. In this electrode, spherical graphite particles act as supporter of electrode framework, and the interspace among particles is filled with porous amorphous carbon derived from decomposition of polyvinylidene fluoride and polyacrylonitrile. SnO₂ nanoparticles are uniformly embedded in the porous amorphous carbon matrix. The pores in amorphous carbon matrix are able to buffer the huge volume expansion of SnO₂ during charge/discharge cycling, and the carbon framework can prevent the SnO₂ particles from pulverization and re-aggregation. The carbon coating layer on the outermost surface of electrode can further prevent porous SnO₂/C electrode from contacting with electrolyte directly. As a result, the repeated formation of solid electrolyte interface is avoided and the cycling stability of electrode is improved. The obtained SnO₂/C electrode presents an initial coulombic efficiency of 77.3% and a reversible capacity of 742 mA h g⁻¹ after 130 cycles at a current density of 100 mA g⁻¹. Furthermore, a reversible capacity of 679 mA h g⁻¹ is obtained at 1 A g⁻¹.     

Synthesis of TiO2(B)/SnO2 composite materials as an anode for lithium-ion batteries

A TiO₂(B) nanosheets/SnO₂ nanoparticles composite was prepared by the hydrothermal and chemical bath deposition (CBD) methods, and its electrochemical properties were investigated for use as the anode material of a lithium-ion battery. The as-prepared composites consisted of monoclinic-phase TiO₂(B) nanosheets and cassiterite structure SnO₂ nanoparticles, in which SnO₂ nanoparticles were uniformly decorated on the TiO₂(B) nanosheets. The TiO₂(B)/SnO₂ composites showed a higher reversible capacity and better durability than that of the pure TiO₂(B) for use as a battery anode. The composite electrodes exhibiting a high initial discharge capacity of 2239.1 mAh g⁻¹ and a discharge capacity of more than 868.7 mAh g⁻¹ could be maintained after 50 cycles at 0.1 C in a voltage range of 1.0–3.0 V at room temperature. The results suggest that TiO₂(B) nanosheets coated with SnO₂ could be suitable for use as a stable anode material for lithium-ion batteries. In addition, the coulombic efficiency of the nanosheets remains at an average of 93.1% for the 3rd–50th cycles.     

Fabrication of porous carbon monoliths with a graphitic framework

Macro/mesoporous carbon monoliths with a graphitic framework were synthesized by carbonizing polymeric monoliths of poly(benzoxazine-co-resol). The overall synthesis process consists of the following steps: (a) the preparation of polymeric monoliths by co-polymerization of resorcinol and formaldehyde with a polyamine (tetraethylenepentamine), (b) doping the polymer with a metallic salt of Fe, Ni or Co, (c) carbonization and (d) the removal of inorganic nanoparticles. The metal nanoparticles (Fe, Ni or Co) formed during the carbonization step catalyse the conversion of a fraction of amorphous carbon into graphitic domains. The resulting carbon monoliths contain >50 wt.% of graphitic carbon, which considerably improves their electrical conductivity. The use of tetraethylenepentamine in the synthesis results in a nitrogen-containing framework. Textural characterization of these materials shows that they have a dual porosity made up of macropores and mesopores (∼2–10 nm), with a BET surface area in the 280–400 m² g⁻¹ range. We tested these materials as electrodes in organic electrolyte supercapacitors and found that no conductive additive is needed due to their high electrical conductivity. In addition, they show a specific capacitance of up to 35 F g⁻¹, excellent rate and cycling performance, delivering up to 10 kW kg⁻¹ at high current densities.     

The Nanocrystalline SnO2–TiO2 System—Part I: Structural Features

The phases present and their crystal structure and microstructure in the nanocrystalline SnO₂–TiO₂ system were studied in the compositional range Sn_1?xTi_xO₂ (0.0 ≤ x ≤ 0.9). There is an apparent increase in the solubility limits in the solid solution compared to bulk crystalline SnO₂–TiO₂. No two phase region was observed with increasing TiO₂ content. Electron energy loss spectroscopy, infrared spectroscopy (FTIR), and X‐ray diffraction (XRD) of the nanopowders showed that the apparent increase in solubility is related to the systematic Ti⁴⁺ segregation on the particle surface (surface excess) at the SnO₂‐rich side, avoiding the nucleation of a second phase even at high Ti⁴⁺ contents. Is this finding in accord with Raman spectra, which suggest localized Ti‐rich sites in the absence of a second crystalline phase. Ti⁴⁺ surface excess is also lead to a modification of the surface hydroxyls and a decrease in the crystallite size of the nanoparticles (with a concomitant increase in surface area), with expected implications to catalytic and sensorial properties of these nanoparticles.     

Enhancement of Sm3+ emission by SnO2 nanocrystals in the silica matrix

Silica xerogels containing Sm³⁺ ions and SnO₂ nanocrystals were prepared in a sol–gel process. The image of transmission electron microscopy (TEM) shows that the SnO₂ nanocrystals are dispersed in the silica matrix. The X-ray diffraction (XRD) of the sample confirms the tetragonal phase of SnO₂. The xerogels containing SnO₂ nanocrystals and Sm³⁺ ions display the characteristic emission of Sm³⁺ ions (⁴G_5/2 → ⁶H _J (J = 5/2, 7/2, 9/2)) at the excitation of 335 nm which energy corresponds to the energy gap of the SnO₂ nanocrystals, while no emission of Sm³⁺ ions can be observed for the samples containing Sm³⁺ ions. The enhancement of the Sm³⁺ emission is probably due to the energy transfer from SnO₂ nanocrystals to Sm³⁺ ions.     

Novel bismuth/multi-walled carbon nanotubes-based electrochemical sensor for the determination of neuroprotective drug cilostazol

A very sensitive electrochemical sensor has been developed by modification of glassy carbon electrode (GCE) with nanoparticles of bismuth (III) oxide (Bi₂O₃) and multi-walled carbon nanotubes (MWCNTs). The sensor was applied for the determination of cilostazol, cyclic nucleotide phosphodiesterase inhibitors in pharmaceutical formulation and human plasma. The voltammetric responses were compared with those obtained at bare GCE under optimum conditions. The cyclic and square-wave voltammograms of cilostazol showed 3.3 and 4.9 times enhancement in the oxidation peak current at MWCNTs–Bi₂O₃/GCE as compared to a bare GCE. Bi₂O₃–MWCNTs/GCE showed a linear response for cilostazol in standard solution over the concentration range of 0.8–13 μg mL⁻¹ with the detection limit 0.76 μg mL⁻¹, whereas human plasma over the concentration range 0.8–12.5 μg mL⁻¹ with the detection limit 0.66 μg mL⁻¹.     

Evaluation of physicochemical and biological properties of SnO2 and Fe doped SnO2 nanoparticles

In recent decades, nanoparticle synthesis has been used for various physical and chemical methods. However, different toxic chemicals are used during this synthesis process to address these concerns, which has multiple effects on environmental toxicity and high cost. To avoid these problems, we need a cost-effective and environmentally friendly approach. In this study, green synthesis was used to make tin oxide (SnO₂) and ferrous doped tin oxide (SFO) nanoparticles (NPs) from Morinda citrifolia leaf extracts. The X-ray diffraction patterns of SnO₂ and SFO NPs reveal a tetragonal crystalline structure. From the FESEM image of synthesized SnO₂ and SFO NPs, their spherical structure and chemical composition were identified by EDX spectrum. Through the DLS spectrum, the hydrodynamic size was observed at 66 and 61 nm for SnO₂ and SFO NPs, respectively. In the FTIR spectrum, the O–Sn–O stretching vibration peak arises at (606 & 509 cm^?1 for SnO₂ NPs) and (613 & 538 cm^?1 for SFO NPs). Photoluminescence is used in materials to detect surface defects and impurity levels. The antibacterial activity of the SnO₂, SFO NPs, and conventional antibiotics like amoxicillin NPs is effectively inhibited against S. aureus and E. coli bacterial strains. SFO NPs exhibit a higher antibacterial activity as compared to SnO₂ and amoxicillin. The anticancer efficacy of increased SFO NPs compared to SnO₂ NPs was tested against (MDA-MB-237) human breast cancer cells. These results suggest that Fe ions modified SnO2 NPs could be used in healthcare industrial applications to improve human health.     

Optimization of Opto-Electrical and Photocatalytic Properties of SnO<Subscript>2</Subscript> Thin Films Using Zn<Superscript>2+</Superscript> and W<Superscript>6+</Superscript> Dopant Ions

Abstract  

A series of Zn²⁺ and W⁶⁺ doped tin oxide (SnO₂) thin films with various dopant concentrations were prepared by spray pyrolysis deposition, and were characterized by X-ray diffraction, atomic force microscopy, contact angle, absorbance, current density–voltage (J–V) and photocurrent measurements. The results showed that W⁶⁺ doping can prevent the growth of nanosized SnO₂ crystallites. When Zn²⁺ ions were used, the crystallite sizes were proved to be similar with the undoped sample due to the similar ionic radius between Zn²⁺ and Sn⁴⁺. Regardless of the dopant ions’ type or concentration, the surface energy has a predominant dispersive component. By using Zn²⁺ dopant ions it is possible to decrease the band gap value (3.35 eV) and to increase the electrical conductivity. Photocatalytic experiments with methylene blue demonstrated that with zinc doped SnO₂ films photodegradation efficiencies close to 30% can be reached.     

Effects of the geometry and operating temperature on the stability of Ti/IrO<Subscript>2</Subscript>–SnO<Subscript>2</Subscript>–Sb<Subscript>2</Subscript>O<Subscript>5</Subscript> electrodes for O<Subscript>2</Subscript> evolution

Ternary IrO₂–Sb₂O₅–SnO₂ anode has shown its superiorities over IrO₂ and many other electrocatalysts for O₂ evolution, in terms of electrochemical stability, activity and cost. The performance of IrO₂–Sb₂O₅–SnO₂ anodes is affected by its electrochemical properties and operating conditions. In this paper, the electrochemical stability and activity of the Ti/IrO₂–Sb₂O₅–SnO₂ anodes prepared with three different geometries were investigated under different operating conditions. It was found that anodes with large mean curvature have high electrochemical stability. Although increasing temperature results in a decrease in the stability of Ti/IrO₂–Sb₂O₅–SnO₂, the anode with a mean curvature of 200 m⁻¹ still shows acceptable service life even at 70 °C. This tolerance of high temperature was attributed to the thermal expansion difference between the substrate and the coating layer, the redox window for Ir(V)/Ir(IV) conversion, and the redox reversibility of Sb and Sn species in the coating layer.     

A novel carbon microspheres@SnO2/reduced graphene composite as anode for lithium-ion batteries with superior cycle stability

Many advantages made SnO₂ a potential anode for lithium-ion batteries, but huge volume expansion during cycling seriously impeded its practical application. Here, a novel double-carbon structure with low graphene weight proportion was successfully prepared using a facile hydrothermal method to enhance the long-cycle stability of SnO₂ as anodes for lithium-ion batteries. In this structure, SnO₂ nanoparticles were formed around the surface of the carbon microspheres (CMS), and the reduced graphene (GR) shuttled through the outer layer. As anodes for lithium-ion batteries, the SnO₂ protected by dual carbon (CMS@SnO₂/GR) exhibited outstanding cycle performance with an initial reversible capacity of 789.5 mAh g^-1 and the reversible capacity retention rate of 68.6% after 350 cycles at 200 mA g^-1. The abundance free space among CMS, nano-scale, and the excellent flexibility of graphene were all contributed to alleviating the volume variation of CMS@SnO₂/GR during the lithiation and delithiation.     

SnO2–graphene–carbon nanotube mixture for anode material with improved rate capacities

SnO₂–graphene–carbon nanotube (SnO₂–G–CNT) mixture is synthesized using graphene oxide as precursor for application as anode material in rechargeable Li ion batteries. It is shown that the SnO₂ nanoparticles of 3–6 nm in diameter are not only attached onto the surface of graphene sheets by anchoring with surface functional groups, but they also are encapsulated in pore channels formed by entangled graphene sheets. The incorporation of carbon nanotubes reduces the charge transfer resistance of the anode made from the mixture through the formation of 3D electronic conductive networks. The SnO₂–G–CNT anodes deliver remarkable capacities of 345 and 635 mAh g⁻¹ at 1.5 and 0.25 A g⁻¹, respectively. Flexible electrodes consisting of highly-aligned SnO₂–G–CNT papers are also prepared using a simple vacuum filtration technique. They present a stable capacity of 387 mAh g⁻¹ at 0.1 A g⁻¹ after 50 cycles through the synergy of the high specific capacity of SnO₂ nanoparticles and the excellent cycleability of G–CNT paper.     

Carbon nanotube capsules encapsulating SnO2 nanoparticles as an anode material for lithium ion batteries

Carbon nanotubes capsules (CNCs) with compact, stout walls and tunable sizes were fabricated by using self-assembly of acid modified carbon nanotubes in a water-in-oil emulsion system. The effect of ultrasonic power on the formation and size of CNCs were investigated. On the basis of fabrication of CNCs, CNCs encapsulating SnO₂ nanoparticles were prepared as anode material for lithium ion batteries. The morphologies, structural characteristics and electrochemical performances of CNCs and CNCs encapsulating SnO₂ nanoparticles were systemically investigated by FE-SEM, TEM, XRD and a series of electrochemical testing techniques. The results showed that the encapsulation amount of SnO₂ in CNCs had a great influence on the reversible capacity and cycle performance of the composites. The composite with appropriate amount of SnO₂ exhibited a high reversible capacity of 383 mAh g⁻¹ and an excellent cyclability with only 0.4% capacity loss/cycle in that CNCs not only could provide high electric conductivity for composites but also effectively accommodate the volume change of SnO₂ during the cycling processes.     

Direct synthesis of graphitic carbon nanostructures from saccharides and their use as electrocatalytic supports

An easy method is described for fabricating graphitic carbon nanostructures (GCNs) from a variety of saccharides; i.e., a monosaccharide (glucose), a disaccharide (sucrose) and a polysaccharide (starch). The synthesis scheme consists of: (a) impregnation of saccharide with Ni or Fe nitrates, (b) heat treatment under inert atmosphere (N₂) up to 900 °C or 1000 °C and (c) oxidation in liquid phase to selectively recover the graphitic carbon. This procedure leads to GCNs with a variety of morphologies: nanopipes nanocoils and nanocapsules. Such GCNs have a high crystallinity, as shown by TEM/SAED, XRD and Raman analysis. The GCNs were used as supports for platinum nanoparticles, which were well dispersed (Mean Pt size  2–3 nm). Electrocatalysts thus prepared have electrocatalytic surface areas in the 70–95 m² g⁻¹ Pt range and exhibit high catalytic activities towards methanol electrooxidation.