Size- and shape-controlled synthesis of ZnSe nanocrystals using SeO2 as selenium precursor

Here we report a low-cost and "green" phosphine-free route for the size- and shape-controlled synthesis of high-quality zinc blende (cubic) ZnSe nanocrystals. To avoid the use of expensive and toxic solvents such as trioctylphosphine (TOP) or tributylphosphine (TBP), SeO(2) was dispersed in 1-octadecene (ODE) as a chalcogen precursor. It has been found that the temperature and the surface ligand influenced the nucleation, the reaction speed and the formation of different shapes. Absorption spectroscopy, fluorescence spectroscopy, powder X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used for the characterization of the as-synthesized ZnSe nanocrystals. The size-dependent photoluminescence (PL) range of the as-prepared ZnSe nanocrystals was between 390 and 450 nm, with the PL full width at half-maximum (FWHM) well controlled between 14 and 18 nm and PL quantum yields reached up to 40% at room temperature. Moreover, this new selenium precursor can be used to form tetrapod-shaped ZnSe nanocrystals when zinc acetylacetonate was introduced as the zinc precursor with a one-pot method.     

Synthesis of oleylamine capped copper nanocrystals via thermal reduction of a new precursor

The present investigation reports the novel synthesis of copper nanocrystals using thermal reduction, and their physicochemical characterization. The copper nanocrystal powder has been prepared using [bis(2-hydroxyacetophenato)copper(II)] as a precursor. The effect of oleylamine and triphenylphosphine on the particle morphology has been investigated. Transmission electron microscopy (TEM) analysis has demonstrated that the copper nanocrystals have an average diameter of about 3 nm. The as-prepared copper nanocrystals were characterized by XRD, SEM, TEM, EDX, UV–Vis and FTIR.     

An anhydrous precursor approach to BaYF5-based upconverting nanocrystals

With an objective to have easy access to high quality BaYF₅ matrix, we report here new anhydrous precursors of barium and yttrium which show a good compatibility in terms of co-thermal decomposition. These complexes not only fill the void of precursors for Ba-based upconverting (UC) nanomaterials but also provide a way to minimize the –OH concentration around these nanocrystals (NCs) to enhance their UC efficiency without requiring the usual core-shell structure. The precursors and the BaYF₅ NCs co-doped with Yb³⁺/Tm³⁺ ions were thoroughly characterized. The NCs were studied for upconversion properties and preliminary results are presented here. On the basis of these results, a mechanism for the energy transfer in Yb–Tm system is proposed.     

The synthesis of a [2.2]paracyclophane-derived secondary phosphine oxide and a study of its reactivity

A planar chiral secondary phosphine oxide based on [2.2]paracyclophane was synthesized and its chemistry investigated; it was shown to be a competent pre-ligand in palladium(0)-mediated reactions, and displayed promising activity in gold(I)-catalysed cyclisations. The secondary phosphine oxide could be transformed into a collection of P-stereogenic tertiary phosphine oxides. These are rare examples of the planar chirality of [2.2]paracyclophane being combined with a P-stereogenic centre. Unfortunately, epimerisation of the phosphorus stereocentre during reduction limits the use of this chemistry.     

Synthesis and size control of luminescent ZnSe nanocrystals by a microemulsion-gas contacting technique

A scalable method for controlled synthesis of luminescent compound semiconductor nanocrystals (quantum dots) using microemulsion-gas contacting at room temperature is reported. The technique exploits the dispersed phase of a microemulsion to form numerous identical nanoreactors. ZnSe quantum dots were synthesized by reacting hydrogen selenide gas with diethylzinc dissolved in the heptane nanodroplets of a microemulsion formed by self-assembly of a poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) amphiphilic block copolymer in formamide. A single nanocrystal is grown in each nanodroplet, thus allowing good control of particle size by manipulation of the initial diethylzinc concentration in the heptane. The ZnSe nanocrystals exhibit size-dependent luminescence and excellent photostability.     

Size-controlled synthesis of orderly organized cube-shaped lead sulfide nanocrystals via a solvothermal single-source precursor method

Monodisperse cube-shaped lead sulfide (PbS) nanocrystals were successfully synthesized by virtue of a solvothermal single-source precursor method at mild reaction conditions. These resulted PbS nanocrystals have the average size in a range of 10 nm and a uniform cubic shape, shown by TEM and HRTEM, respectively. Due to their narrow size distribution, orderly self-organized arrays on a large scale can be easily obtained. Experimental results indicate that several factors, such as coordinating ability of the solvent, carbon number of the substitute alkyls (n), reaction temperature, and concentration of the precursor, play key roles in the final size and size distribution of PbS nanocrystals. This finding will enhance our understanding for the formation mechanism of nanostructured materials with special shapes.     

Reaction of secondary phosphine oxides with acylacetylenes

Secondary phosphine oxides reacted with 1-alkanoyl-2-phenylacetylenes in chemoselective fashion under mild conditions (20°C, THF) in the absence of a catalyst (diphenylphosphine oxide) or in the presence of potassium hydroxide [bis(2-phenylethyl)phosphine oxide] to give 1-alkyl-1-diphenyl(or 2-phenylethyl)-phosphoryl-3-phenylprop-2-yn-1-ols in up to 96% yield. The reaction of diphenylphosphine oxide with 1-alkanoyl-2-phenylacetylenes in the system KOH-THF (20°C) afforded not only adducts at the carbonyl group but also products of double α,β-addition at the triple bond, 2,3-bis(diphenylphosphoryl)-3-phenylpropan-1-ones.     

Effective photocatalytic degradation of organic pollutant by ZnS nanocrystals synthesized via thermal decomposition of single-source precursor

2-Aminocyclopentene-1-dithiocarboxylate complex of zinc(II) has been synthesized and found to be an effective single-source precursor for the preparation of ZnS NCs (rod and sphere) by the use of ethylenediamine and hexadecylamine as structure directing solvents. Structural characterizations were carried out using XRD, TEM and BET measurements and the optical properties by UV-Vis and PL spectroscopic techniques. The prepared ZnS NCs show effective photocatalytic activity towards the degradation of Rose Bengal dye (RB) under light irradiation for their probable application in waste water treatment. The degradation mechanism of RB dye under light irradiation is established by terephthalic acid photoluminescence probing technique.     

Reaction of secondary phosphine chalcogenides with diallylamine

Diphenyl- or bis(2-phenylethyl)phosphine sulfides and -phosphine selenides react with diallylamine under radical initiation (UV or AIBN) to afford the corresponding diadducts and tetrahydropyrrolylmethyl phosphine chalcogenides. The yield and the ratio of the products depend on the structure of the starting secondary phosphine chalcogenides.     

Control of reactivity of phosphine imides by intramolecular coordination with an organoboryl group

Phosphine imides with a boryl substituent 3–5 were synthesized. Their structures were revealed to have a tetracoordinated boron and a phosphorus atom, featuring the N–B coordination by X‐ray crystallographic analysis and NMR spectroscopy. The phosphine imide moiety was persistent to hydrolysis, methylation, and the aza‐Wittig reaction. The N–B coordination remained intact upon treating with pyridine or fluoride ion. © 2012 Wiley Periodicals, Inc. Heteroatom Chem 23:429–434, 2012; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.21033     

Optical and photocatalytic properties of heavily F(-)-doped SnO2 nanocrystals by a novel single-source precursor approach

Heavily F-doped SnO(2) nanocrystals were successfully prepared by a novel synthetic approach involving low-temperature oxidation of a Sn(2+)-containing fluoride complex KSnF(3) as the single-source precursor with H(2)O(2). The F-doped SnO(2) powder was characterized by powder X-ray diffraction, TG-MS, BET surface area, diffuse reflectance spectroscopy, XPS, PL, FTIR spectroscopy, Raman spectroscopy, EPR spectroscopy, SEM, and TEM. Broadening of the diffracted peaks, signifying the low crystallite size of the products, was quite evident in the powder X-ray diffraction pattern of SnO(2) obtained from KSnF(3). It was indexed in a tetragonal unit cell with lattice constants a = 4.7106 (1) ? and c = 3.1970 (1) ?. Agglomeration of particles, with an average diameter of 5-7 nm, was observed in the TEM images whose spotwise EDX analysis indicated the presence of fluoride ions. In the core level high-resolution F 1s spectrum, the peak observed at 685.08 eV was fitted by the Gaussian profile yielding the fluoride ion concentration to be 21.23% in the SnO(2) lattice. Such a high fluoride ion concentration is reported for the first time in powders. SnO(2):F nanocrystals showed greater thermal stability up to 300 °C when heated in a thermobalance under flowing helium, after which generation of small quantities of HF was observed in the TG coupled mass spectrometry analysis. The band gap value, estimated from the Kubelka-Munk function, showed a large shift from 3.52 to 3.87 eV on fluoride ion doping, as observed in the diffuse reflectance spectrum. Such a large shift was corroborated to the overdoped situation due to the Moss-Burstein effect with an increase in the carrier concentration. In the photoluminescence (PL) spectrum, SnO(2):F nanocrystals exhibited a broad green emission arising from the singly ionized oxygen vacancies created due to higher dopant concentration. The evidence for singly ionized vacancies was arrived from the presence of a signal with a g value of 1.98 in the ESR spectrum of SnO(2):F at room temperature. The disordered nature of the rutile lattice and the enormous oxygen vacancies created due to fluoride ion doping were evident from the broad bands observed at 455, 588, and 874 cm(-1) in the room-temperature Raman spectrum of SnO(2):F. As the consequence of the oxygen vacancies, F-doped SnO(2) was examined for the function as a photocatalyst in the degradation of aqueous RhB dye solution under UV irradiation. A very high photocatalytic efficiency was observed for the F-doped SnO(2) nanocrystals as compared to pure SnO(2). The BET surface area of pure SnO(2) was quite high (207.81 m(2)/g) as compared to the F-doped SnO(2) nanocrystals (45.16 m(2)/g). Pore size analysis showed a mean pore diameter of 1.97 and 13.97 nm for the pure and doped samples. The increased photocatalytic efficiency was related to the very high concentration of oxygen vacancies in SnO(2) induced by F doping.     

Reaction of divinyl selenide with secondary phosphine chalcogenides

Under the conditions of free-radical initiation (AIBN, UV irradiation), divinyl selenide regioselectively reacts with secondary phosphine sulfides and phosphine selenides to afford, depending on the ratio of the reagents, mono- or diadducts mainly of the anti-Markownikoff structure. The conditions which allow obtaining the diadducts in up to 97% yield are found. By the example of 2-{[2-(diphenethylphosphoroselenoyl) ethyl]selanyl}ethyl(diphenethyl)phosphine selenide the diadducts were shown to react with aqueous hydrogen peroxide at 53–56°C to give vinyl(diphenethyl)phosphine oxide in 76% yield.     

Reaction of divinyl telluride with secondary phosphine chalcogenides

Divinyl telluride reacted with 2 equiv of diphenylphosphine sulfide in the presence of AIBN as radical initiator (63–68°C) to give the corresponding anti-Markovnikov adduct in 68% yield with high regioselectivity. Treatment of the addition product with aqueous hydrogen peroxide at room temperature afforded 71% of vinyldiphenylphosphine oxide. Radical addition of diphenylphosphine selenide to divinyl telluride (AIBN, 63–68°C) led to the formation of 1,1,3,3-tetraphenyldiphosphoxane 1,3-diselenide in 82% yield.     

Controllable synthesis of MnS nanocrystals from a single-source precursor

A facile single-source precursor method has been applied for the selective synthesis of MnS nanocrystals (NCs) with well-defined shapes and crystal structures such as hexapod, octahedral, hexagonal shaped α-MnS NCs, and pencil-shaped γ-MnS NCs. The effects of the composition of precursor, reaction temperature, and the heating rate on the morphologies, and crystal structures of MnS NCs were systematically studied for the first time.     

Improved synthetic routes to methylene-bridged P-chiral diphosphine ligands via secondary phosphine–boranes

Improved methods for the preparation of methylene-bridged diphosphine ligands are described. Both enantiomers of the key intermediate tert-butylmethylphosphine–borane were prepared via resolution or by the conversion of one enantiomer into the opposite enantiomer. The precursor borane complexes of bis(tert-butylmethylphosphino)methane (t-Bu-MiniPHOS), bis((1,1,3,3-tetramethylbutyl)methylphosphino)methane (t-Oct-MiniPHOS), and (tert-butylmethylphosphino)(di-tert-butylphosphino)methane (trichickenfootphos) were prepared in good yields and enantiopure form.     

Synthesis of branched gold nanocrystals by a seeding growth approach

Synthesis of branched gold nanocrystals by a seeding growth approach is described. In this process, HAuCl4 aqueous solution was supplied stepwise to grow the gold seeds (approximately 2.5 nm) into larger nanoparticles with a highly faceted particle structure (approximately 15-20 nm in diameter). Sodium dodecyl sulfate (SDS) served as a capping agent to facilitate the formation of highly faceted nanoparticles, and ascorbic acid was used as a weak reducing agent. The highly faceted nanoparticles then transformed into branched nanocrystals (approximately 40 nm in length) by further addition of the SDS-HAuCl4 solution and ascorbic acid for particle growth. The branched nanocrystals show bipod, tripod, tetrapod, and pentapod structures and are composed of mainly (111) lattice planes. These multipods appear to grow along the twin boundaries of the initially formed highly faceted gold nanoparticles, as the twin boundaries on the pods originate from the centers of the branched nanocrystals. The concentration of ascorbate ions in the solution was found to have a profound influence on branch formation. These branched nanocrystals are stable to storage at low temperature (that is, 4 degrees C), but they may slowly evolve into a multitwinned faceted crystal structure (that is, pentagonal-shaped decahedral structure) when stored at 30 degrees C.     

Chiral bisphosphinite metalloligands derived from a P-chiral secondary phosphine oxide

Interaction of PdCl(2)(MeCN)(2) with 2 equiv of (S(P))-(t)BuPhP(O)H (1H) followed by treatment with Et(3)N gave [Pd((1)(2)H)](2)(micro-Cl)(2) (2). Reaction of 2 with Na[S(2)CNEt(2)] or K[N(PPh(2)S)(2)] afforded Pd[(1)(2)H](S(2)CNEt(2)) (3) or Pd[(1)(2)H)[N(PPh(2)S)(2)] (4), respectively. Treatment of 3 with V(O)(acac)(2) (acac = acetylacetonate) and CuSO(4) in the presence of Et(3)N afforded bimetallic complexes V(O)[Pd(1)(2)(S(2)CNEt(2))](2) (5) or Cu[Pd(1)(2)(S(2)CNEt(2))](2) (6), respectively. X-ray crystallography established the S(P) configuration for the phosphinous acid ligands in 3 and 6, indicating that 1H binds to Pd(II) with retention of configuration at phosphorus. The geometry around Cu in 6 is approximately square planar with the average Cu-O distance of 1.915(3) A. Treatment of 2 with HBF(4) gave the BF(2)-capped compound [Pd((1)(2)BF(2))](2)(micro-Cl)(2) (7). The solid-state structure of 7 containing a PdP(2)O(2)B metallacycle has been determined. Chloride abstraction of 7 with AgBF(4) in acetone/water afforded the aqua compound [Pd((1)(2)BF(2))(H(2)O)(2)][BF(4)] (8) that reacted with [NH(4)](2)[WS(4)] to give [Pd((1)(2)BF(2))(2)](2)[micro-WS(4)] (9). The average Pd-S and W-S distances in 9 are 2.385(3) and 2.189(3) A, respectively. Treatment of [(eta(6)-p-cymene)RuCl(2)](2) with 1H afforded the phosphinous acid adduct (eta(6)-p-cymene)RuCl(2)(1H) (10). Reduction of [CpRuCl(2)](x)() (Cp = eta(5)-C(5)Me(5)) with Zn followed by treatment with 1H resulted in the formation of the Zn(II) phosphinate complex [(CpRu(eta(6)-C(6)H(5)))(t)BuPO(2))](2)(ZnCl(2))(2) (11) that contains a Zn(2)O(4)P(2) eight-membered ring.     

Fluoride-assisted synthesis of anatase TiO2 nanocrystals with tunable shape and band gap via a solvothermal approach

A simple solvothermal approach employing oleic acid has been developed to prepare anatase TiO₂ nanocrystals with different shapes, which were tuned from nanorods to nano-ellipsoids by increasing the amount of NaF from 0 to 0.5 mmol, and the optical band gap decreased from 3.47 eV to 3.29 eV accordingly. However, when the fluoride was changed to NH₄F, the resultant TiO₂ nanocrystals possessed an anatase phase but weremade up of smaller-sized nanocrystals and nanorods, and the band gap was increased to 3.53 eV. The X-ray photoelectron spectroscopy (XPS) results illustrated an increase of fluorine content with an increasing amount of NaF could account for the variation of the shape and optical band gap of TiO₂ nanocrystals. Moreover, the absence of fluorine content brought about less change of shape and increase of optical band gap of the product synthesized in the presence of NH₄F. This result may offer another way to alter the shape and band gap of metal oxide nanocrystals with the assistance of fluoride.     

An approach to enhanced redispersibility of cellulose nanocrystals via freeze-drying their Pickering emulsions

To enhance the redispersibility of dried nanocellulose, cellulose nanocrystal (CNC) cryogels were produced by freeze-drying CNC-stabilized cyclohexane-in-water Pickering emulsions. The CNC cryogels were easily redispersed in water and organic solvents; thus, the approach proposed made it possible to significantly improve CNC redispersibility in aqueous and nonaqueous media.