Functionalized hectorite clay mineral for Ag(I) ions extraction from wastewater and preparation of silver nanoparticles supported clay

A novel clay mineral-based adsorbent for Ag(I) ions extraction was obtained by modifying hectorite with 2-(3-(2-aminoethylthio)propylthio)ethanamine (AEPE-hectorite). The modified hectorite was used to recover Ag(I) ions from wastewater for further preparation of silver nanoparticles supported hectorite. The parameters affecting silver ions extraction by AEPE-hectorite were investigated. The adsorbent could extract Ag(I) ions from solution in a wide pH range (1–8) and high extraction efficiencies were achieved in the solution pH ranged from 4 to 9. AEPE-hectorite showed a good selectivity toward Ag(I) ions over Co(II), Ni(II) and Cd(II) ions and the solution ionic strength had no significant effect on extraction efficiency. The adsorption of Ag(I) ions onto AEPE-hectorite followed the Freundlich isotherm model with maximum adsorption capacity observed in the experiment of 49.5 mg g^− 1. The adsorbent was successfully used to recover silver ions from a wastewater containing high concentration of silver and silver nanoparticles supported hectorite was obtained after reducing with NaBH₄. These results show an alternative in the preparation of silver nanoparticles supported clay.     

Graphene supported Ru@Co core–shell nanoparticles as efficient catalysts for hydrogen generation from hydrolysis of ammonia borane and methylamine borane

Well-dispersed graphene supported Ru@Co core–shell nanoparticles were synthesized by one-step in situ co-reduction of aqueous solution of ruthenium(III) chloride hydrate, cobalt(II) chloride hexahydrate and graphite oxide (GO) with ammonia borane under ambient condition. The as-synthesized nanoparticles exert excellent catalytic activities, with the turnover frequency (TOF) value of 344 mol H₂ min^− 1 (mol Ru)^− 1 for catalytic hydrolysis of ammonia borane, which is the second highest value ever reported. The as-synthesized catalysts exert superior catalytic activities than the monometallic (Ru/graphene), alloy (RuCo/graphene), and graphene-free Ru@Co counterparts towards the hydrolytic dehydrogenation of AB. Moreover, the catalytic hydrolysis of MeAB at room temperature was also studied. These Ru@Co NPs are a promising catalyst for amine-borane hydrolysis and for developing a highly efficient hydrogen storage system for fuel cell applications.     

Highly efficient oxidation of diphenylmethane to benzophenone employing a novel ruthenium catalyst with tert-butylhydroperoxide under mild conditions

The ruthenium complex Ru(bpbp)(pydic) (bpbp = 2,6-bis(1-phenylbenzimidazol-2-yl), pydic = pyridine-2,6-dicarboxy acid) has been synthesized and tested in the selective oxidation of diphenylmethane to benzophenone utilizing tert-butylhydroperoxide as the terminal oxidant. The influence of various reaction parameters such as temperature, catalyst amount and nature of solvent on the activity and selectivity was evaluated. Diphenylmethane was converted with 94% conversion and 100% selectivity to benzophenone under the optimized reaction conditions, in which the turnover number (TON) of catalyst reached 94,000. Moreover, a plausible reaction mechanism through redox ruthenium species was proposed.     

Synthesis,characterization and alcohol sensing property of Zn-doped SnO2 nanoparticles

The Zn-doped SnO₂ nanoparticles synthesized by the chemical co-precipitation route and having dopant concentration varying from 0 to 4 at%, were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM) for structural and morphological studies. XRD analyses reveal that all the samples are polycrystalline SnO₂ having tetragonal rutile structure with nanocrystallites in the range 10–25 nm. The TEM images show agglomeration of grains (cluster of primary crystallites). A corresponding selected area electron diffraction pattern reveals the different Debye rings of SnO₂, as analyzed in XRD. Alcohol sensing properties of all the Zn-doped samples were investigated for various concentrations of methanol, ethanol and propan-2-ol in air at different operating temperatures. Among all the samples examined, the 4 at% Zn-doped sample exhibits the best response to different alcohol vapors at the operating temperature of 250 °C. For a concentration of 50 ppm, the 4 at% Zn-doped sample shows the maximum response 85.6% to methanol, 87.5% to ethanol and 94.5% to propan-2-ol respectively at the operating temperature of 250 °C. A possible reaction mechanism of alcohol sensing has been proposed.     

Unsupported CuFe bimetallic nanoparticles for higher alcohol synthesis via syngas

CuFe bimetallic nanoparticles were synthesized by co-reduction method as model catalysts for HAS. Cu contacted with Fe component in the form of Cu–Fe alloy, CuFe₂O₄ and Cu(Fe)–CuFe₂O₄ interface in the fresh CuFe sample. However, Cu/Fe₃O₄ and Cu/FeC_x composites formed after activation. Cu–FeC_x center benefited alcohol formation which led to higher selectivity to total alcohol for CuFe than that for Fe and physical mixture of Fe and Cu nanoparticles. In addition, CuFe showed very high C_6 +OH selectivity in alcohol distribution and 33 wt.%–74 wt.% was achieved, demonstrating the potential for direct synthesis of C_6 +OH from syngas.     

New trinuclear dendritic complexes with [Ru(tpy)(bpy)X]n + (X = Cl,H2O; n = 1, 2) for enhanced water oxidation and light-driven alcohol oxidation

A symmetric trinuclear ruthenium complex with [Ru(tpy)(bpy)(Cl)]⁺ (tpy = 2,2′:6′,2″-terpyridine; bpy = 2,2′-bipyridine) connected by 2,4,5-trimethylbenzene was easily prepared. The complex showed effective chemical water oxidation and light-driven oxidation activity of alcohols to corresponding aldehydes in water. When Cl⁻ is replaced by H₂O, the resulting complex exhibited over a twofold increase in O₂ evolution activity compared with its parent complex. Moreover, compared with equimolar ruthenium amounts of the mononuclear complex with the H₂O ligand, the trinuclear ruthenium complex with the conjugated ligand motif also displayed a two time increase in water oxidation activity.     

Poly (styrene-co-divinylbenzene) amine functionalized polymer supported ruthenium nanoparticles catalyst active in hydrogenation of xylose

Poly (styrene-co-divinylbenzene) amine functionalized polymer supported ruthenium nanoparticles catalyst is evaluated first time in selective hydrogenation of xylose to xylitol. The catalyst Ru/PSN is characterized by different techniques such as X-ray powder diffraction, transmission electron microscopy and CO chemisorption. To develop our understanding for the activity of catalyst Ru/PSN, xylose hydrogenation experiments were carried out using catalyst of Ru/PSN with different ruthenium loading (from 1.0% to 3.0%), at different temperatures (from 100 to 140 °C) and hydrogen pressures (from 30 to 55 bar). For deactivation test, the catalyst of Ru/PSN recovered from the product solution was reused up to the four times.     

Formation of RuO2 nanoparticles by thermal decomposition of Ru(NO)(NO3)3

A simple one-pot synthesis of RuO₂ nanoparticles by the thermal decomposition of ruthenium nitrosyl nitrate [Ru(NO)(NO₃)₃] up to 800 °C was investigated. The RuO₂ phase was characterized by XRD, SAXS, FE SEM/EDS, Raman, DTA/TGA and FT-IR techniques. Broadening of prominent diffraction lines (110), (101) and (211) was used to estimate nanocrystallite sizes in RuO₂ particles. FE SEM showed the formation of RuO₂ plates at 400 °C which consisted of RuO₂ nanoparticles of about 15–25 nm in size. At 800 °C RuO₂ nanoparticles showed the sintering effect and some of them increased in size to about 200 nm. Raman and FT-IR spectra consolidated the findings. Moreover, DTA curves showed the decomposition and release of NO and NO₃⁻ groups to be a stepwise process.     

Synthesis,structures and catalytic activities of half-sandwich ruthenium complexes based on Schiff Base ligands

A series of half-sandwich ruthenium(II) complexes containing Schiff-base ligands [Ru(p-cymene)LCl] [HL = (E)-4-X-2-((phenylimino)methyl)phenol, X = H (2a); X = CH₃ (2b); X = Cl (2c) and X = Br (2d)] have been synthesized and fully characterized by ¹H and ¹³C NMR spectra, elemental analyses and infrared spectrometry. Moreover, the molecular structures of ruthenium complexes 2b and 2c were confirmed by single-crystal X-ray diffraction methods. These half-sandwich ruthenium complexes are highly catalyzed hydrogenation of nitroarenes to aromatic anilines to proceed in the presence of sodium borohydride reducing agent in ethanol solvent. Notably, complex 2c was found to be a very efficient catalyst toward reduction of nitroarene compounds with wide functional group compatibility and substrate scope.     

Transition metal loaded silicon carbide-derived carbons with enhanced catalytic properties

Carbide-derived carbons (CDC) with incorporated transition metal nanoparticles (～2.5 nm) were prepared using a microemulsion approach. Time-consuming post synthesis functionalization of the carbon support material can thus be avoided and nanoparticle sizes can be controlled by changing the microemulsion composition. This synthesis strategy is a technique for the preparation of highly porous carbon materials with a catalytically active component. In particular we investigated the integration of ruthenium, palladium, and platinum in a concentration ranging from 4.45 to 12 wt.%. It was found that the transition metal has a considerable influence on sorption properties of resulting nanoparticle-CDC composite materials. Depending on the used metal salt additive the surface area and the pore volume ranges from 1480 m²/g and 1.25 cm³/g for Pt to 2480 m²/g and 2.0 cm³/g for Ru doped carbons. Moreover, members of this material class show impressive properties as heterogeneous catalysts. The liquid phase oxidation of tetralin and the partial oxidation of methane were studied, and electrochemical applications were also investigated. Primarily Pt doped CDCs are highly active in the oxygen reduction reaction, which is of great importance in present day fuel cell research.     

Effect of concentration and degree of saturation on co-precipitation of catechin and poly(l-lactide) by the RESOLV process

Rapid expansion of subcritical solutions into liquid solvents (RESOLV) was able to consistently produce catechin (CTC)-loaded poly(l-lactide) (PLLA) nanoparticles. The effects of CTC concentration and processing conditions – pre-expansion temperature and pressure, and degree of saturation – on the size and morphology of CTC-loaded PLLA nanoparticles were investigated, as well as the loading capacity (LC), entrapment efficiency (EE), and release of CTC. RESOLV experiments were carried out with 0.1 wt% CTC + 0.2 wt% PLLA and 0.2 wt% CTC + 0.2 wt% PLLA solutions in mixtures of EtOH and CO₂ (3:2, wt/wt) with pre-expansion temperature and pressure of 60–100 °C and 265–325 bar, respectively. The obtained CTC-loaded PLLA nanoparticles were spherical, with average sizes, LC, and EE ranges of ∼30–40 nm, 2.4–7.3%, and 4.7–22.0%, respectively. CTC concentration, pre-expansion temperature, and degree of saturation had significant effects on LC and EE of CTC, without affecting the size of composite nanoparticles. The LC and EE of CTC increased with increasing pre-expansion temperature and degree of saturation, and with decreasing CTC concentration. The release profiles of CTC from the nanoparticles exhibited an initial stage of burst release (first 8 h) followed by a sustained release (∼1–9 days). Furthermore, the fraction of CTC being released from the nanoparticles decreased with increasing the degree of saturation of subcritical solutions prior to rapid expansion and with increasing the LC of CTC.     

The effect of the surface nanostructure and composition on the antiwear properties of zirconia–titania coatings

This study describes the preparation, surface imaging and tribological properties of titania coatings modified by zirconia nanoparticles agglomerated in the form of island-like structures on the titania surface. Titania coatings and titania coatings with embedded zirconia nanoparticles were prepared by the sol–gel spin coating process on silicon wafers. After deposition the coatings were heat-treated at 500 °C or 1000 °C. The natural tendency of nanoparticles to form agglomerates was used to build separated island-like structures unevenly distributed over the titania surface having the size of 1.0–1.2 μm. Surface characterization of coatings before and after frictional tests was performed by atomic force microscopy (AFM) and optical microscopy. Zirconia nanoparticles were imaged with the use of transmission electron microscopy (TEM). The tribological properties were evaluated with the use of microtribometer operating in ambient air at technical dry friction conditions under normal load of 80 mN. It was found that nanocomposite coatings exhibit lower coefficient of friction (CoF) and considerably lower wear compared to titania coating without nanoparticles. The lowering of CoF is about 40% for coatings heated at 500 °C and 33% for the coatings heated at 1000 °C. For nanocomposites the wear stability was enhanced by a factor of 100 as compared to pure titania coatings. We claim that enhanced tribological properties are closely related to the reduction of the real contact area, lowering of the adhesive forces in frictional contacts and increasing of the composite hardness. The changes in materials composition in frictional contact has secondary effect.     

Hybrid materials of platinum nanoparticles and thiol-functionalized graphene derivatives

Hybrid materials of platinum nanoparticles (Pt-NP) and thiol-functionalized thermally reduced graphite oxide (TRGO-SH), were synthesized by thermal decomposition of the organometallic precursor methylcyclopentadienyl-trimethylplatinum(IV) in dispersions of TRGO-SH in the ionic liquid 1-n-butyl-3-methyl-imidazolium tetrafluoroborate under microwave-assisted heating conditions. For the kinetic stabilization of Pt-NPs on TRGO-SH no additional donor ligands were necessary. The ionic liquid acts as separator of the TRGO-SH graphene sheets and as kinetic stabilizing template in the Pt-nanoparticle formation process. Thiol-functionalization of thermally reduced graphite oxide was carried out using three different synthetic procedures: (1) ring opening of propylene sulfide; (2) xanthate grafting and reduction to thiol; (3) reduction, thioesterfication under Mitsunobu conditions and ester hydrolysis. These three different TRGO-SH materials (1), (2) and (3) had different sulfur contents (1.2, 2.5 and 14 wt.%, respectively) and were used as support materials for platinum nanoparticles. The loading of Pt-NPs on TRGO-SH (1), (2) and (3) was 3.2, 3.5 and 8.8 wt.% with particle diameters determined from transmission electron microscopy of (9 ± 4), (2.5 ± 0.9) and (5 ± 2) nm, respectively.     

A hybrid microreactor/microwave high-pressure flow system of a novel concept design and its application to the synthesis of silver nanoparticles

This article reports on a microreactor/microwave high-pressure flow hybrid apparatus of a novel concept design, which includes both the microreactor and a spiral reactor, and its efficient use in the synthesis of silver nanoparticles of relatively uniform sizes (4.3 ± 0.7 nm) under microwave irradiation. By contrast, under otherwise identical experimental conditions but with conventional heating, the nanoparticle size was non-uniform (8.3 ± 2.7 nm) and the spiral reactor walls were covered with a silver mirror deposit. Formation of the nanoparticles was monitored by UV–visible spectroscopy (plasmonic absorption band; LSPR), TEM and by small-angle X-ray scattering (SAXS). Both the spiral microreactor and the spiral quartz reactor of the hybrid system played an important role in the synthesis, with the microreactor providing the environment wherein mixing of the aqueous solution of [Ag(NH₃)₂]⁺ and the solution of glucose (the reducing agent) and poly(N-vinyl-2-pyrrolidone) (PVP; stabilizer/dispersing agent) occurred. The microwaves provided the thermal energy to effect a uniform growth of the silver nanoparticles at temperatures above 120 °C. Mixing the two solutions by conventional methods (no microreactor) failed to yield such nanoparticles even under microwave irradiation and no formation of a silver mirror occurred in the inner walls of the spiral reactor.     

High tensibility and pH-responsive swelling of nanocomposite hydrogels containing the positively chargeable 2-(dimethylamino)ethyl methacrylate monomer

Positively chargeable nanocomposite hydrogels (NC gels) were synthesized by in situ copolymerization of acrylamide (AM) and 2-(dimethylamino)ethyl methacrylate (DMAEMA) in an aqueous suspension of hectorite clay Laponite XLS. The stability of the Laponite suspension containing DMAEMA was monitored by its transmittance, viscosity and zeta potential. The polymerization was initiated either by redox or UV radiation to fabricate the NC gels. Elongation at break and tensile strength decreased with increasing DMAEMA content in monomers up to 17 mol%. As expected from the protonation of DMAEMA, the NC gels containing more than 5 mol% DMAEMA showed pH-responsive swelling; the gels were swollen at pH < 4 and shrunken at pH > 4. In comparison with the redox-initiated NC gels, the UV-initiated NC gels possessed a more homogeneous structure with higher transmittance, better mechanical properties, and a larger equilibrium swelling ratio at pH < 4.     

Fabrication and optical characterizations of Yb,Er codoped CaF2 transparent ceramic

Nanoparticles of Yb, Er codoped calcium fluoride were obtained by a co-precipitation method. Scanning electron microscope (SEM) and X-ray powder diffraction (XRD) analysis showed that the obtained nanoparticles were single fluorite phase with grains size around 30–50 nm. Yb, Er:CaF₂ transparent ceramics were fabricated by hot pressing (HP) the nanoparticles at a temperature of 800 °C in a vacuum environment. For a 2 mm thickness ceramic sample, the transmittance at 1200 nm reached about 83%. Microstructures were characterized using SEM analysis, and the average grain size was about 700 nm. Grain boundaries of the ceramic sample were clean and no impurities were detected. The absorption, upconversion and infrared emission spectra of transparent ceramic sample under 978 nm excitation were measured and discussed.     

New approach for highly selective hydrogenation of phenol to cyclohexanone: Combination of rhodium nanoparticles and cyclodextrins

The effect of cyclodextrins on the activity and selectivity of a catalytic system based on rhodium nanoparticles stabilized by polyacrylic acid (PAA) in the hydrogenation of phenol in aqueous solution and ionic liquid was reported. It was found that the reaction medium and the nature of the cyclodextrin (CD) essentially affect the rate of reaction and the distribution of reaction products. The use of the system based on rhodium nanoparticles stabilized by cyclodextrins makes it possible to rapidly and efficiently prepare cyclohexanone from phenol with yields up to 100% under relatively mild conditions (1 h; T = 80°°C, p(H₂) = 10–40 bars).     

Synthesis and catalytic properties of novel POM@TiO2 composite materials

Donor–π-bridge–acceptor (D–π–A) type polyoxometalates (POMs) were self-assembled for the first time on the surface of titanium dioxide (TiO₂) nanoparticles through the layer-by-layer (LBL) method. The obtained composite materials POM@TiO₂ were characterized by Transmission electron microscopy (TEM), Fourier transform IR spectroscopy (FTIR), Raman spectrum and energy dispersive X-ray (EDX) spectroscopy. Catalytic properties of POM@TiO₂ were also investigated by treating organic pollutants (typically, removal of 40 mL 20 mg L^− 1 methylene blue (MB) by 10 mg POM@TiO₂ was up to 99.5% within 3 min under ambient conditions and the photodegradation efficiency was obviously higher than bare TiO₂ nanoparticles under irradiation).     

In vivo evaluation of hydrogels of polyvinyl alcohol with and without carbon nanoparticles for osteochondral repair

Polyvinyl alcohol (PVA) hydrogels both pure and reinforced with two types of carbon nanoparticles (nanotubes and nanofibres) were studied as a candidate material for osteochondral defect repair. The carbon nanoparticles produced by chemical vapour deposition were characterised by Raman spectroscopy, field emission scanning electron microscopy and high-resolution transmission electron microscopy. The hydrogels were surgically implanted in osteochondral defects in the articular cartilage of rats and, after 3 and 12 weeks of follow-up, examined by scanning electron microscopy (SEM), optical microscopy (OM), creep indentation test (CIT) and X-ray fluorescence (XRF). No sign of tissue adhesion or abrasive wear could be seen by SEM. OM revealed dense connective tissue at the interface after 3 weeks and neoformed bone tissue without significant inflammatory process after 12 weeks. Dense connective tissue could be seen at the pure-PVA/tissue interface after 12 weeks, but not at the carbon reinforced-PVA/tissue interface after the same follow-up time. The hydrogel creep modulus increased with follow-up time. XRF revealed an increasing concentration of calcium and phosphorus in the implants over time, a phenomenon more pronounced for the hydrogels with carbon nanofibres. The results suggest that PVA hydrogel with carbon nanoparticles elicits a stronger biological response than pure hydrogel.     

Synthesis and optical characterization of Er-doped bismuth titanate nanoparticles grown by sol–gel hydrothermal method

The Er³⁺-doped bismuth titanate (Bi₄Ti₃O₁₂, BIT) nanoparticles were synthesized by a combined sol–gel and hydrothermal method under a partial oxygen pressure of 30 bar. The composition and morphology were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Raman scattering. They showed pure and homogeneous spherical BIT nanoparticles with a size below the 30 nm. The incorporation of Er ions showed a strong decrease in the lattice parameters, as well as averaged particle size. The photoluminescence up-conversion (excitation wavelength =1480 nm) showed an enhancement of the infrared emission (980 nm) as Er concentration increased, achieving a maximum for 6% mol, while photoluminescence spectra (excitation wavelength =473 nm) showed a strong green emission (529 and 553 nm) with a maximum at 4% mol.