Profitable Fischer Tropsch realization via CO2–CH4 reforming; an overview of nickel–promoter–support interactions

Environmental pollution, climate change, and fossil fuel extinction have aroused serious global interest in the search for alternative energy sources. The dry reforming of methane (DRM) could be a good technique to harness syngas, a starting material for the FT energy process from greenhouse gases. Noble metal DRM catalysts are effective for the syngas generation but costly. Therefore, they inevitably, must be replaced by their Ni-based contemporaries for economic reasons. However, coking remains a strong challenge that impedes the industrialization of the FT process. This article explains the secondary reactions that lead to the production of detrimental graphitic coke deposition on the surface of active nickel catalyst. The influence of nickel particle size, impact of extra surface oxygen species, interaction of Ni catalysts with metal oxide supports/promoters, and larger fraction of exposed nickel active sites were addressed in this review. Size of active metal determines the conversion, surface area, metal dispersion, surface reactions, interior diffusion effects, activity, and yield. The influence of oxygen vacancy and coke deposition on highly reported metal oxide supports/promoters (Al₂O₃, MgO and La₂O₃) was postulated after studying CIFs (crystallographic information files) obtained from the Crystallography open database (COD) on VESTA software. Thus, overcoming excessive coking by La₂O₃ promotion is strongly advised in light of the orientation of the crystal lattice characteristics and the metal–support interaction can be used to enhance activity and stability in hydrogen reforming systems.

Particle size increases during agglomeration, which causes catalyst deactivation. Reducible metal oxide restricts metal growth, hence reducing the sintering.     

Li-based layered nickel–tin oxide obtained through electrochemically-driven cation exchange

The Li-based layered nickel-tin oxide Li_0.35Na_0.07Ni_0.5Sn_0.5O₂ has been synthesized via electrochemically-driven Li⁺ for Na⁺ exchange in O3-NaNi_0.5Sn_0.5O₂. The crystal structure of Li_0.35Na_0.07Ni_0.5Sn_0.5O₂ was Rietveld-refined from powder X-ray diffraction data (a = 3.03431(7) Å, c = 14.7491(8) Å, S. G. R$\bar{3}$m). It preserves the O3 stacking sequence of the parent compound, but with ∼13% lower unit cell volume. Electron diffraction and atomic-resolution scanning transmission electron microscopy imaging revealed short-range Ni/Sn ordering in both the pristine and Li-exchanged materials that is similar to the “honeycomb” Li/M ordering in Li₂MO₃ oxides. As supported by bond-valence sum and density functional theory calculations, this ordering is driven by charge difference between Ni²⁺ and Sn⁴⁺ and the necessity to maintain balanced bonding for the oxygen anions. Li_0.35Na_0.07Ni_0.5Sn_0.5O₂ demonstrates reversible electrochemical (de)intercalation of ∼0.21 Li⁺ in the 2.8–4.3 V vs. Li/Li⁺ potential range. Limited electrochemical activity is attributed to a formation of the surface Li/Ni disordered rock-salt barrier layer as the Li⁺ for Na⁺ exchange drastically reduces the energy barrier for the Li/Ni antisite disorder.

Layered O3-Li_0.35Na_0.07Ni_0.5Sn_0.5O₂ cathode material was obtained by electrochemically-driven Li for Na exchange. The exchange process was comprehensively studied via a combination of transmission electron microscopy techniques.     

Formation of nickel–cobalt sulphide@graphene composites with enhanced electrochemical capacitive properties

Here, nickel–cobalt sulphide particles embedded in graphene layers (porous Ni–Co–S@G), were successfully prepared by one-step annealing of metallocene/metal–organic framework (MOF) hybrids involving simultaneous carbonization and sulfidation. Benefiting from the porous structure, highly conductive graphene layers and large loading of super-capacitive Ni–Co–S, the obtained Ni–Co–S@G composites exhibited excellent electrochemical performance with a specific capacitance of 1463 F g⁻¹ at a current density of 1 A g⁻¹. A flexible solid-state asymmetric supercapacitor (ASC), assembled with Ni–Co–S@G and active carbon, demonstrated a high energy density of 51.0 W h kg⁻¹ at a power density of 650.3 W kg⁻¹. It is noteworthy that the ASC offered robust flexibility and excellent performance that was maintained when the devices were bent at various angles. The results indicate that the as-prepared materials could potentially be applied in high-performance electrochemical capacitors.

Ni–Co–S@graphene composites, derived from a metallocene/MOF precursor, presents high energy density and excellent cycling stability.     

Preparation of terpyridine-functionalized paramagnetic nickel–zinc ferrite microspheres for adsorbing Pb(ii), Hg(ii), and Cd(ii) from water

A paramagnetic microsphere combining special functional groups may be one kind of the most promising methods for heavy metal adsorption, due to their specific separation capacity, selectivity and reusability. In this study, a novel terpyridine-based magnetic solid-phase adsorbent (TPY-M) is successfully constructed. The paramagnetic Ni_0.25Zn_0.75Fe₂O₄ microsphere (M) is synthesized and applied as a magnetic core, and is functionalized by terpyridine (TPY) groups. The naked magnetic core and TPY-M are characterized by vibration sample magnetism (VSM), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), and Fourier-transform infrared spectroscopy (FT-IR) techniques. Some parameters of the TPY-M samples are evaluated as potential adsorbents for heavy metal ions in various aqueous solutions. The adsorption capacities of TPY-M for Pb(ii), Hg(ii) and Cd(ii) were 64.75 mg g⁻¹, 33.94 mg g⁻¹ and 24.64 mg g⁻¹ under given conditions, respectively. In the case of Pb(ii), some influencing factors on the TPY-M adsorbent are investigated, including the pH, adsorption time, and ion concentrations. The adsorbent can be easily regenerated by HCl solution after use. The adsorbent revealed good adsorption performance in some real water samples.

A paramagnetic microsphere combining special functional groups may be one kind of the most promising methods for heavy metal adsorption, due to their specific separation capacity, selectivity and reusability.     

Theoretical analysis of sulfuric acid–dimethylamine–oxalic acid–water clusters and implications for atmospheric cluster formation

In recent years, organic compounds potentially involved in atmospheric particle formation have received increased attention. However, the contributions of organic acids as precursors in nucleation remain ambiguous. In this study, the low-lying structures and thermodynamics of the sulfuric acid–dimethylamine–oxalic acid–water system are obtained at the M06-2X/6-311+G(2d,p) level, and the single point energy of the clusters has been calculated at the DF-LMP2-F12/VDZ-F12 level. The formations of the multicomponent clusters are predicted based on thermodynamics, involving proton transfer and hydrogen bonding interactions. Oxalic acid can synergistically promote the formation of the sulfuric acid–dimethylamine–oxalic acid–water system while inhibiting this with the addition of more sulfuric acid molecules. The results of hydrate distribution show that un-hydrate clusters play a dominant role during formation. Moreover, dimethylamine and oxalic acid have similar effects on Rayleigh scattering properties, and the clusters involving complex mixtures of compounds can have high optical activities.

The structure of SA₂.DMA.OA.W₄ cluster.     

Flowery nickel–cobalt hydroxide via a solid–liquid sulphur ion grafting route and its application in hybrid supercapacitive storage

In our research, a two-step solid–liquid route was employed to fabricate flowery nickel–cobalt hydroxide with sulphur ion grafting (Ni1Co2–S). The utilization of NaOH/agar and Na₂S/agar could efficiently retard the release rates of OH⁻ or S²⁻ ions at the solid–liquid interface due to strong bonding between agar hydrogel and these anions. Ni1Co2–S generally displays ultrathin flowery micro-frame, ultrathin internal nanosheets and expanded pore size. Besides, the introduction of suitable sulphide species into nickel–cobalt hydroxide could improve its conductivity due to the lower band gap of Ni–Co sulphide. The supercapacitive electrode Ni1Co2–S presented capacitance of 1317.8 F g⁻¹ (at 1 A g⁻¹) and suitable rate performance (77.9% at 10 A g⁻¹ and 59.3% at 20 A g⁻¹). Furthermore, a hybrid supercapacitor (HSC) was developed utilizing positive Ni1Co2–S and negative activated carbon electrodes. As expected, the HSC device exhibited excellent specific capacitance (117.1 F g⁻¹ at 1 A g⁻¹), considerable energy densities (46.7 W h kg⁻¹ at 0.845 kW kg⁻¹ and 27.5 W h kg⁻¹ even at 9 kW kg⁻¹) and suitable cycling performance, which further illuminated the high energy storage capacity of Ni1Co2–S.

The Ni1Co2–S material fabricated via a solid–liquid route achieves high-performance supercapacitive storage.     

Bifunctional nickel–iminodiacetic acid-core–shell silica nanoparticles for the exclusion of high molecular weight proteins and purification of His-tagged recombinant proteins

Herein, silica nanoparticles were synthesized and chemically modified with iminodiacetic acid (IDA) and Ni²⁺ ions surrounded by a bis-acrylamide polymeric shell to obtain a new core–shell immobilized metal affinity chromatography (IMAC) based material. These Ni²⁺–IDA-core–shell silica nanoparticles (Ni²⁺–IDA-CSS-NP) represent a new alternative for purification of His-tagged proteins and exclusion of high molecular weight (HMW) proteins at the same time. Nanoparticles presented a final size of 479.6 ± 6.9 nm determined by dynamic light scattering (DLS) and a surface charge of −37.2 ± 0.5 mV. Successful incorporation of the different compounds at every phase of synthesis was evidenced by ATR-FTIR analysis. Ni²⁺–IDA-CSS-NP were used for isolation of His-tagged spo0F (6His-spo0F) from E. coli lysate. Ni²⁺–IDA-CSS-NP presented a capacity of 4.16 ± 0.45 μg mg⁻¹. Purification of 6His-spo0F with high selectivity and the effective exclusion of HMW proteins were evidenced by SDS-PAGE and validated through mass spectrometry analysis.

Silica nanoparticles were synthesized and chemically modified with iminodiacetic acid (IDA) and Ni²⁺ ions surrounded by a bis-acrylamide polymeric shell to obtain a new core–shell immobilized metal affinity chromatography (IMAC) based material.     

Spontaneous alloying of ultrasmall non-stoichiometric Ag–In–S and Cu–In–S quantum dots in aqueous colloidal solutions

The effect of spontaneous alloying of non-stoichiometric aqueous Ag–In–S (AIS) and Cu–In–S (CIS) quantum dots (QDs) stabilized by surface glutathione (GSH) complexes was observed spectroscopically due to the phenomenon of band bowing typical for the solid–solution Cu(Ag)–In–S (CAIS) QDs. The alloying was found to occur even at room temperature and can be accelerated by a thermal treatment of colloidal mixtures at around 90 °C with no appreciable differences in the average size observed between alloyed and original individual QDs. An equilibrium between QDs and molecular and clustered metal–GSH complexes, which can serve as “building material” for the new mixed CAIS QDs, during the spontaneous alloying is assumed to be responsible for this behavior of GSH-capped ternary QDs. The alloying effect is expected to be of a general character for different In-based ternary chalcogenides.

The effect of spontaneous alloying of aqueous glutathione-capped Ag–In–S and Cu–In–S quantum dots (QDs) into quaternary Cu(Ag)–In–S QDs is reported.     

Comparative advantages of Zn–Cu–In–S alloy QDs in the construction of quantum dot-sensitized solar cells

Alloyed structures of quantum dot light-harvesting materials favor the suppression of unwanted charge recombination as well as acceleration of the charge extraction and therefore the improvement of photovoltaic performance of the resulting solar cell devices. Herein, the advantages of Zn–Cu–In–S (ZCIS) alloy QD serving as light-harvesting sensitizer materials in the construction of quantum dot-sensitized solar cells (QDSCs) were compared with core/shell structured CIS/ZnS, as well as pristine CIS QDs. The built QDSCs with alloyed Zn–Cu–In–S QDs as photosensitizer achieved an average power conversion efficiency (PCE) of 8.47% (V_oc = 0.613 V, J_sc = 22.62 mA cm⁻², FF = 0.610) under AM 1.5G one sun irradiation, which was enhanced by 21%, and 82% in comparison to those of CIS/ZnS, and CIS based solar cells, respectively. In comparison to cell device assembled by the plain CIS and core/shell structured CIS/ZnS, the enhanced photovoltaic performance in ZCIS QDSCs is mainly ascribed to the faster photon generated electron injection rate from QD into TiO₂ substrate, and the effective restraint of charge recombination, as confirmed by incident photon-to-current conversion efficiency (IPCE), open-circuit voltage decay (OCVD), as well as electrochemical impedance spectroscopy (EIS) measurements.

Benefiting from the accelerative electron injection and retarded charge recombination, Zn–Cu–In–S alloy QD based QDSC achieved a PCE of 8.55%, which is 21%, and 82% higher than those of CIS/ZnS, and pristine CIS QDs based solar cells, respectively.     

Luminescence and photoelectrochemical properties of size-selected aqueous copper-doped Ag–In–S quantum dots

Ternary luminescent copper and silver indium sulfide quantum dots (QDs) can be an attractive alternative to cadmium and lead chalcogenide QDs. The optical properties of Cu–In–S and Ag–In–S (AIS) QDs vary over a broad range depending on the QD composition and size. The implementation of ternary QDs as emitters in bio-sensing applications can be boosted by the development of mild and reproducible syntheses directly in aqueous solutions as well as the methods of shifting the photoluminescence (PL) bands of such QDs as far as possible into the near IR spectral range. In the present work, the copper-doping of aqueous non-stoichiometric AIS QDs was found to result in a red shift of the PL band maximum from around 630 nm to ∼780 nm and PL quenching. The deposition of a ZnS shell results in PL intensity recovery with the highest quantum yield of 15%, with almost not change in the PL band position, opposite to the undoped AIS QDs. Size-selective precipitation using 2-propanol as a non-solvent allows discrimination of up to 9 fractions of Cu-doped AIS/ZnS QDs with the average sizes in the fractions varying from around 3 to 2 nm and smaller and with reasonably the same composition irrespective of the QD size. The decrease of the average QD size results in a blue PL shift yielding a series of bright luminophors with the emission color varies from deep-red to bluish-green and the PL efficiency increases from 11% for the first fraction to up to 58% for the smallest Cu-doped AIS/ZnS QDs. The rate constant of the radiative recombination of the size-selected Cu-doped AIS/ZnS QDs revealed a steady growth with the QD size decrease as a result of the size-dependent enhancement of the spatial exciton confinement. The copper doping was found to result in an enhancement of the photoelectrochemical activity of CAIS/ZnS QDs introduced as spectral sensitizers of mesoporous titania photoanodes of liquid-junction solar cells.

Colloidal size-selected copper-doped Ag–In–S quantum dots were produced directly in aqueous solutions by fractionation/redispersion with a plethora of emission colors and a top luminescence quantum yield of around 60%.     

Electrodeposited nickel–graphene nanocomposite coating: effect of graphene nanoplatelet size on its microstructure and hardness

In this study, the effect of graphene nanoplatelet (GNP) size on the microstructure and hardness of the electrodeposited nickel–graphene nanocomposite coatings were investigated. GNPs with different sizes were prepared by using a high energy ball milling technique. The experimental result revealed the high energy ball milling technique could reduce the size, increase the surface area, and improve the dispersion ability of GNPs. The microstructure, hardness, and components of the nanocomposite coatings were greatly affected by GNP sizes. The highest microhardness was measured to be 273 HV for the nanocomposite coatings containing 5 h-milled GNPs, which is increased up to ∼47% compared to pristine Ni coating. The enhancement in the hardness is attributed to the uniform dispersion of the small GNP sizes inside the Ni matrix and the Ni grain size reduction when using milled GNPs.

The effect of graphene nanoplatelet size on the microstructure and hardness of electrodeposited nickel–graphene nanocomposite coatings was investigated.     

Ultra-small aqueous glutathione-capped Ag–In–Se quantum dots: luminescence and vibrational properties

We introduce a direct aqueous synthesis of luminescent 2–3 nm Ag–In–Se (AISe) quantum dots (QDs) capped by glutathione (GSH) complexes, where sodium selenosulfate Na₂SeSO₃ is used as a stable Se²⁻ precursor. A series of size-selected AISe QDs with distinctly different positions of absorption and PL bands can be separated from the original QD ensembles by using anti-solvent-induced size-selective precipitation. The AISe–GSH QDs emit broadband PL with the band maximum varying from 1.65 eV (750 nm) to 1.90 eV (650 nm) depending on the average QD size and composition. The PL quantum yield varies strongly with basic synthesis parameters (ratios of constituents, Zn addition, duration of thermal treatment, etc.) reaching 4% for “core” AISe and 12% for “core/shell” AISe/ZnS QDs. The shape and position of PL bands is interpreted in terms of the model of radiative recombination of a self-trapped exciton. The AISe–GSH QDs reveal phonon Raman spectra characteristic for small and Ag-deficient tetragonal Ag–In–Se QDs. The ability of ultra-small AISe QDs to support such “bulk-like” vibrations can be used for future deeper insights into structural and optical properties of this relatively new sort of QDs.

A direct aqueous synthesis, composition- and size-dependent absorption, photoluminescence, and vibrational properties of ultra-small glutathione-capped Ag-deficient Ag–In–Se quantum dots are reported.     

Ammonia borane dehydrogenation and selective hydrogenation of functionalized nitroarene over a porous nickel–cobalt bimetallic catalyst

The hydrolysis of ammonia borane is a promising strategy for hydrogen energy exploration and exploitation. The in situ produced hydrogen could be directly utilized in hydrogenation reactions. In this work, a bimetallic nickel–cobalt material with porous structure was developed through the pyrolysis of ZIF-67 incorporated with Ni ions. Through the introduction of Ni(NO₃)₂ as an etching agent, the ZIF-67 polyhedrons were transformed into hollow nanospheres, and further evolved into irregular nanosheets. The bimetallic NiCo phase was formed after pyrolysis in a nitrogen atmosphere at high temperature, with the decomposition and release of organic ligands as gaseous molecules under flowing nitrogen. The obtained bimetallic NiCo porous materials show superior catalytic performance towards hydrolytic dehydrogenation of ammonia borane, thereby nitrobenzene with reducible functional groups can be reduced with high selectivity to the corresponding aniline.

Porous nickel–cobalt bimetallic catalyst realizes selective hydrogenation of nitrobenzene with in situ produced hydrogen through hydrolysis of ammonia borane.     

Copper–ligand clusters dictate size of cyclized peptide formed during alkyne–azide cycloaddition on solid support

Peptide and peptidomimetic cyclization by copper-catalyzed alkyne–azide cycloaddition (CuAAC) reaction have been used to mimic disulfide bonds, alpha helices, amide bonds, and for one-bead-one-compound (OBOC) library development. A limited number of solid-supported CuAAC cyclization methods resulting in monomeric cyclic peptide formation have been reported for specific peptide sequences, but there exists no general study on monocyclic peptide formation using CuAAC cyclization. Since several cyclic peptides identified from an OBOC CuAAC cyclized library has been shown to have important biological applications, we discuss here an efficient method of alkyne–azide ‘click’ catalyzed monomeric cyclic peptide formation on a solid support. The reason behind the efficiency of the method is explored. CuAAC cyclization of a peptide sequence with azidolysine and propargylglycine is performed under various reaction conditions, with different catalysts, in the presence or absence of an organic base. The results indicate that piperidine plays a critical role in the reaction yield and monomeric cycle formation by coordinating to Cu and forming Cu–ligand clusters. A previously synthesized copper compound containing piperidine, [Cu₄I₄(pip)₄], is found to catalyze the CuAAC cyclization of monomeric peptide effectively. The use of 1.5 equivalents of CuI and the use of DMF as solvent is found to give optimal CuAAC cyclized monomer yields. The effect of the peptide sequence and peptide length on monomer formation are also investigated by varying either parameter systemically. Peptide length is identified as the determining factor for whether the monomeric or dimeric cyclic peptide is the major product. For peptides with six, seven, or eight amino acids, the monomer is the major product from CuAAC cyclization. Longer and shorter peptides on cyclization show less monomer formation. CuAAC peptide cyclization of non-optimal peptide lengths such as pentamers is affected significantly by the amino acid sequence and give lower yields.

We report the heterogeneous controlled formation of monomeric cyclic peptides by CuAAC reaction using cooper–piperidine complexes.     

Sulfur and phosphorus co-doped nickel–cobalt layered double hydroxides for enhancing electrochemical reactivity and supercapacitor performance

Layered double hydroxides (LDHs) have drawn significant interest as emerging active materials for advanced energy storage devices; however, their low electric and ionic conductivity limit their applications. In this study, we report sulfur (S) and phosphorus (P) co-doped NiCo LDH nanoarrays prepared via a facile phosphor–sulfurization process to impart diverse co-doping effects. Combining the benefits of their unique hierarchical structure and reduced charge transfer resistance, the S and P co-doped NiCo LDH (NiCo LDH-SP) nanoarrays realize faster and more efficient redox reactions and achieve enhanced surface reactivity, thereby resulting in a performance superior to that of pristine NiCo LDH. Therefore, a NiCo LDH-SP shows an ultra-high specific capacitance of 3844.8 F g⁻¹ at a current density of 3 A g⁻¹ and maintains a specific capacitance of 2538.8 F g⁻¹ at a high current density of 20 A g⁻¹. Additionally, an asymmetric supercapacitor, assembled with the NiCo LDH-SP as the cathode and activated carbon (AC) as the anode (NiCo LDH-SP//AC), shows a high energy density of 74.5 W h kg⁻¹ at a power density of 0.8 kW kg⁻¹ and outstanding cycling stability, thereby retaining ∼81.3% of its initial specific capacitance after 5000 cycles. This study presents a facile and promising strategy for developing LDH-based electrode materials with excellent electrochemical performance for advanced energy storage applications.

The optimized sulfur and phosphorus co-doped NiCo LDH reduces charge transfer resistance and realizes efficient redox reaction, achieving an outstanding specific capacitance of 3844.8 F g⁻¹ at 3 A g⁻¹.     

Electrochemical oxidation of boron-doped nickel–iron layered double hydroxide for facile charge transfer in oxygen evolution electrocatalysts

The oxygen evolution reaction (OER) is the key reaction in water splitting systems, but compared with the hydrogen evolution reaction (HER), the OER exhibits slow reaction kinetics. In this work, boron doping into nickel–iron layered double hydroxide (NiFe LDH) was evaluated for the enhancement of OER electrocatalytic activity. To fabricate boron-doped NiFe LDH (B:NiFe LDH), gaseous boronization, a gas–solid reaction between boron gas and NiFe LDH, was conducted at a relatively low temperature. Subsequently, catalyst activation was performed through electrochemical oxidation for maximization of boron doping and improved OER performance. As a result, it was possible to obtain a remarkably reduced overpotential of 229 mV at 10 mA cm⁻² compared to that of pristine NiFe LDH (315 mV) due to the effect of facile charge-transfer resistance by boron doping and improved active sites by electrochemical oxidation.

An electrochemically oxidized boron-doped NiFe LDH electrocatalyst was prepared and the electrocatalyst showed improved water oxidation performance.     

Magnetic graphene oxide-ultrathin nickel–organic framework composite for the extraction and determination of epoxiconazole in food samples

In this work, a magnetic graphene oxide-ultrathin metal–organic framework composite (Fe₃O₄@SiO₂-GO-Ni-MOF) was synthesized for the first time. Employing Fe₃O₄@SiO₂-GO-Ni-MOF composite as extractant, a novel method for the separation and analysis of the pesticide epoxiconazole was established with the assistance of high performance liquid chromatography (HPLC). The adsorption mechanisms were studied including by adsorption kinetics, thermodynamic parameters and adsorption isotherms. The experimental results showed that this method was convenient, operable, effective and practical for the extraction and determination of epoxiconazole in real samples.

Schematic illustration for the MSPE procedures.     

Evaluating the cytotoxicity of Ge–Sb–Se chalcogenide glass optical fibres on 3T3 mouse fibroblasts

In vivo cancer detection based on the mid-infrared molecular fingerprint of tissue is promising for the fast diagnosis and treatment of suspected cancer patients. Few materials are mid-infrared transmissive, even fewer, which can be converted into functional, low-loss optical fibres for in vivo non-invasive testing. Chalcogenide-based glass optical fibres are, however, one of the few. These glasses are transmissive in the mid-infrared and are currently under development for use in molecular sensing devices. The cytotoxicity of these materials is however unknown. The cytotoxicity of Ge–Sb–Se chalcogenide optical glass fibres on 3T3 mouse fibroblast cells is here investigated. Fibres exposed to four different pre-treatment conditions are used: as-drawn (AD), propylamine-etched (PE), oxidised-and-washed (OW) and oxidised (Ox). To achieve the latter two conditions, fibres are treated with H₂O₂(aqueous (aq.)) and dried to produce a surface oxide layer; this is either washed off (OW) or left on the glass surface (Ox). Cellular response is investigated via 3 day elution and 14 day direct contact trials. The concentration of the metalloids (Ge, Sb and Se) in each leachate was measured via inductively coupled plasma mass spectrometry. Cell viability is assessed using the neutral red assay and scanning electron microscopy. The concentration of Ge, Sb and Se ions after a 3 day dissolution was as follows. In AD leachates, Ge: 0.40 mg L⁻¹, Sb: 0.17 mg L⁻¹, and Se: 0.06 mg L⁻¹. In PE leachates, Ge: 0.22 mg L⁻¹, Sb: 0.15 mg L⁻¹, and Se: 0.02 mg L⁻¹. In Ox leachates, Ge: 823.8 mg L⁻¹, Sb: 2586.6 mg L⁻¹, and Se: 3750 mg L⁻¹. Direct contact trials show confluent cell layers on AD, PE and OW fibres after 14 days, while no cells are observed on the Ox surfaces. A >50% cell viability is observed in AD, PE and OW eluates after 3 days, when compared with Ox eluates (<10% cell viability). Toxicity in Ox is attributed to the notable pH change, from neutral pH 7.49 to acidic pH 2.44, that takes place on dissolution of the surface oxide layer in the growth media. We conclude, as-prepared Ge–Sb–Se glasses are cytocompatible and toxicity arises when an oxide layer is forced to develop on the glass surface.

We present a study that aims to evaluate the cytotoxicity of Ge₂₀Sb10Se₇₀ at% glass optical fibres on 3T3 mouse fibroblast cells. To observe the toxicity of these optical fibres, 3T3 fibroblast proliferation was investigated.     

Na–Ga–Si type-I clathrate single crystals grown via Na evaporation using Na–Ga and Na–Ga–Sn fluxes

Single crystals of a Na–Ga–Si clathrate, Na₈Ga_5.70Si_40.30, of size 2.9 mm were grown via the evaporation of Na from a Na–Ga–Si melt with the molar ratio of Na : Ga : Si = 4 : 1 : 2 at 773 K for 21 h under an Ar atmosphere. The crystal structure was analyzed using X-ray diffraction with the model of the type-I clathrate (cubic, a = 10.3266(2) Å, space group Pm$\bar{3}$n, no. 223). By adding Sn to a Na–Ga–Si melt (Na : Ga : Si : Sn = 6 : 1 : 2 : 1), single crystals of Na₈Ga_xSi_46−x (x = 4.94–5.52, a = 10.3020(2)–10.3210(3) Å), with the maximum size of 3.7 mm, were obtained via Na evaporation at 723–873 K. The electrical resistivities of Na₈Ga_5.70Si_40.30 and Na₈Ga_4.94Si_41.06 were 1.40 and 0.72 mΩ cm, respectively, at 300 K, and metallic temperature dependences of the resistivities were observed. In the Si L_2,3 soft X-ray emission spectrum of Na₈Ga_5.70Si_40.30, a weak peak originating from the lowest conduction band in the undoped Si₄₆ was observed at an emission energy of 98 eV.

Single crystals of a Na–Ga–Si clathrate, Na₈Ga_4.94Si_41.06, of size 3.7 mm were grown via the evaporation of Na from a Na–Ga–Si–Sn melt with the molar ratio of Na : Ga : Si : Sn = 6 : 1 : 2 : 1 at 873 K for 3 h under an Ar atmosphere.     

Photoinduced electron transfer in novel CdSe–Cu2Se type II core–shell quantum dots

Herein we report the synthesis, characterisation and electron transfer studies of CdSe–Cu₂Se QDs, a novel type II core–shell system. The synthesis was achieved by a high temperature organometallic method with oleylamine as ligand. Structural and optical properties of the nanostructures were investigated using X-ray diffraction, high resolution transmission electron microscopy, selected area electron diffraction, energy dispersive X-ray spectroscopy, inductive coupled plasma optical emission spectroscopy, cyclic voltammetry, X-ray photoelectron spectroscopy and absorption spectroscopy. The electron transfer dynamics were investigated by observing the variations in steady state and time resolved emission spectra in the presence of an electron acceptor-methyl viologen. Localization of electrons in the shells was evident from the studies performed indicating efficient charge separation.

Herein we report the synthesis, characterisation and electron transfer studies of CdSe–Cu₂Se QDs, a novel type II core–shell system.