Rapid synthesis of MXenes at room temperature

Ti₃C₂, one of the most studied MXenes (M is an early transition metal, and X is either C or N), has attracted considerable attention due to their excellent electrical conductivity, hydrophilicity, and catalytic activity. To date, most MXenes are prepared from powders and chemical etching under conditions of either long duration (generally ≥8?h) or high temperature (generally ≥35°C). In this study, Ti₃C₂ with –F and –O/–OH terminal groups was successfully obtained by electrochemically etching porous Ti₃AlC₂ sheet electrodes in NH₄HF₂ solution at room temperature. The reaction mechanism and the effect of voltage were demonstrated. Electrochemical etching could induce subsequent over-etching to generate carbide-derived carbons.     

Synthesis of monodispersed CdSe nanocrystals in poly(styrene-alt-maleic anhydride) at room temperature

Nanocomposite of CdSe/poly(styrene-alt-maleic anhydride) (PSM) was successfully prepared via an in situ reaction process at room temperature and ambient pressure. Transmission electron microscopy (TEM) analysis revealed that CdSe nanoparticles with a small size and narrow size distribution were obtained. The obtained nanocomposite was also characterized by FT-IR, XRD, ultraviolet-visible, and fluorescence spectroscopy.     

Environmentally friendly aqueous solution synthesis of hierarchical CaWO4 microspheres at room temperature

An environmentally friendly route for the synthesis of hierarchical CaWO4 microspheres with novel morphology at room temperature has been successfully developed. CaCl2 and Na2WO4 were used as reaction regents, and distilled water was used as an environmentally friendly solvent. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and photoluminescence spectroscopy. This green wet-chemical route provides a simple, one-step, low-cost approach for the large-scale synthesis of hierarchical CaWO4 microspheres with relatively uniform diameters of 3-6 microm. The hierarchical microspheres are built up with numerous nanorods with an average diameter of 50 nm, which are radially oriented to the microsphere center. SEM observations of different intermediates indicate the possible growth process, in which the hierarchical structure growth is from nuclei through kayak-like, rod-like, peanut-like, dumbbell-like, and peach-like structures to final microspheres, via "self-assembled preferential end growth" of kayak-like particles in aqueous solution. The hierarchical CaWO4 microspheres exhibit a strong, broad blue emission peak of 412 nm.     

Deposition of copper sulfide hollow nanospheres in aqueous solution at room temperature

Uniform copper sulfide hollow nanospheres were obtained in high yield by reacting copper nitrate with thioacetamide in water at room temperature under the assistance of sodium dodecyl sulfate (SDS). The spheres (average diameter of ca. 200 nm) displayed big cavity while their surface were constructed by randomly stacked nanoflakes. The products were characterized by X-ray diffraction (XRD), energy-dispersive X-ray spectrometry (EDX), field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). SDS was found to play a key role in the synthesis process while a four-step mechanism was proposed to explain the formation of hollow nanospheres. The influence of SDS concentration on the size and shape of the product has also been investigated in detail.     

Effect of different aqueous synthesis parameters on the size of CdSe nanocrystals

The variation of CdSe nanoparticle size as a function of synthesis conditions is presented. Cadmium sulphate (CdSO₄), cadmium chloride (CdCl₂) and sodium selenosulphate (Na₂SeSO₃) solutions were used as precursors. Nanoparticles were synthesized by aqueous chemical methods. The synthesis parameters studied were pH, Cd:Se ratio and the type of stabilizing agent. Three different stabilizing agents were used, thioglycolic acid, mercaptoethanol and poly(vinyl pyrrolidone). Fourier transform infrared spectroscopy results confirmed the presence of the stabilizing agent on the surface of the nanoparticles. Ultraviolet visible and X-ray powder diffraction measurements were used to estimate the trend of size variations of the particles with different synthesis parameters, which agreed fairly by both techniques and the crystal structure. Additionally, the size of the nanoparticles was obtained by transmission electron microscopy measurements. Whilst the effect of pH was different for each of the different stabilizing agents due to the different chemical groups in the thiol compounds and the size of the nanoparticles varied with the used stabilizing agents, the effect of Cd:Se ratio in the size of nanoparticles showed the same tendency for the several stabilizing agents.     

Stability studies of CdSe nanocrystals in an aqueous environment

In this paper, CdSe nanocrystal dissolution in an aqueous solution was studied. It was found that light is a key factor affecting the dissolution of nanocrystals. In the presence of light, the electrons generated from CdSe nanocrystals reduce water to hydrogen and hydroxide ions (OH-) while photo-generated holes oxidize CdSe to Cd2+ and elemental Se. The dissolution was accelerated in an acidic medium while moderate alkalinity (pH=10.3) can slow down the dissolution possibly due to precipitation of nanocrystals. This study has strong implications for the use of these crystals in aqueous environments (bioimaging and dye-sensitized solar cells).     

A nonaqueous solution route to synthesis of polyacrylamide-silver nanocomposites at room temperature

Polyacrylamide-silver nanocomposites with silver nanoparticles well dispersed in polyacrylamide matrix were synthesized for the first time by γ-irradiation at ambient conditions in alcohol solvent. X-ray powder diffraction (XRD) showed that the samples consisted of two phases, metallic silver and polyacrylamide. The amount of silver present as metallic species in polyacrylamide matrix was measured by precipitation titration. Transmission electron microscopy (TEM) was used to study the morphology and size distribution of silver nanoparticles. Infrared (IR) spectrum confirmed the polymerization of acrylamide monomer and the formation of polyacrylamide in ethanol upon γ-irradiation.     

Thin and superthin photoconductive CdSe films deposited at room substrate temperature

Low conductive and photosensitive CdSe films were deposited on substrates at room temperature. X-ray diffraction spectra showed a microcrystalline cubic structure for film thicknesses greater than 20 nm and an amorphous structure for film thicknesses below 10 nm. An optical band gap, E _g ⁰ , of 1.6 eV was determined using the Tauc-dependence usually employed for amorphous semiconductors. The dark conductivity, , of 10^{–9 –1} cm^–1 was measured in the as-deposited state, but an increase of five orders of magnitude was observed after heating the layer above 450 K. High photosensitivity was observed under illumination with white light as well as with monochromatic light over a wide spectral region (400–750 nm). A conclusion is reached concerning the existence of compensated donor and acceptor defects in the as-deposited state.     

A mild phosphine-free synthesis of alkylamine-capped CdSe nanocrystals

A new phosphine-free approach has been developed to synthesize high-quality cadmium selenide (CdSe) nanocrystals with cubic zinc-blende structure, by using the highly reactive selenium (Se) precursor at milder temperature than that used in the traditional phosphine route. This Se precursor was obtained from the reduction of Se powder by sodium borohydride in N,N-dimetbylformamide, in the absence of phosphine. Without the addition of other long-chain coordinating substances in this approach, the alkylamines such as dodecylamine (DDA) and octylamine (OA) were used as reaction solvents, and they also acted as surface capping reagents to produce DDA-capped and OA-capped CdSe NCs, respectively. The rapid nucleation and slow growth were observed by ultraviolet-visible absorption spectrum. The resulting OA-capped CdSe NCs grew faster compared with DDA-capped CdSe NCs under the same other conditions. These as-synthesized CdSe nanocrystals showed relatively narrow size distribution and high photoluminescence quantum efficiency (up to 9.4% for OA-capped CdSe NCs). This mild approach is low cost, relatively low danger and high production yield (approximately 80%), indicating that it is very effective for the phosphine-free synthesis of alkylamine-capped CdSe nanocrystals.     

Precursor compound enabled formation of aqueous-phase CdSe magic-size clusters at room temperature

The formation pathway of aqueous-phase colloidal semiconductor magic-size clusters(MSCs)remains unrevealed.In the present work,we demonstrate,for the first time...     

Facile synthesis of CdSe nanocrystals for bulk-heterojunction solar cells

Oleic acid (OA)-capped cadmium selenide (CdSe) nanocrystals (NCs) have been synthesized via a new high-scale route. X-ray diffraction and transmission electron microscopy confirmed that rod-like hexagonal (wurtzite) CdSe NCs with an average size of 10 nm were obtained via this new route. The obtained CdSe NCs were treated individually with pyridine and tert-butylamine (t-BA) for ligand exchange. Fourier transform infrared spectra of the as-synthesized and treated CdSe NCs confirmed the removal of OA ligands from the surface of CdSe NCs after treatments with pyridine and t-BA. Bulk-heterojunction (BHJ) solar cell devices were prepared using untreated and surface treated CdSe NCs blended with poly (3-hexylthiophene-2,5-diyl) (P3HT) polymer. BHJ solar cell devices made from P3HT:(surface treated CdSe NCs) blends showed greater improvement in photovoltaic performances compared to P3HT:(untreated CdSe NCs) blend. The improvement in photovoltaic performances was due to the increase of electron mobility in P3HT:(CdSe NCs) blends after surface treatment of CdSe NCs.     

Large-area synthesis of carbon nanofibres at room temperature

Carbon nanotubes, first identified by Iijima, require for their production a source of elemental carbon and a transfer of energy that is specific to the type of source and the growth environment. Methods developed so far involve arc discharge, and vaporization using laser, pyrolysis and chemical vapour deposition of hydrocarbons. Here, we show growth of carbon nanofibres from radio-frequency plasma-enhanced chemical vapour deposition at room temperature, which was made possible by substituting the thermal energy requirements for the growth with plasma decomposition of methane on the Ni catalyst. Electron microscopy analysis provides evidence for a 'tip' growth model, with the Ni catalyst particle attached to the tip of the nanofibre. Energy-filtered imaging shows the Ni catalyst has a surface layer rich in carbon, consistent with the formation of a eutectic Ni-C droplet as a nucleation site for the carbon nanofibres, so that the carbon diffuses across the surface. The reduced distortion of the catalyst particles at low temperatures leads to a more uniform growth of the carbon nanofibres over large areas. The lower growth temperature allows for the removal of the silicon dioxide barrier layer associated with catalytic growth, and should allow in situ growth of nanofibres on relatively large areas of temperature-sensitive substrates, such as plastics, organics and even paper.     

Temperature-controlled synthesis of CdSe nanocrystals with narrow size distribution

CdSe quantum dots (QDs) with narrow size distribution and fine crystallinity were synthesized in paraffin liquid through temperature-control method. TEM, HRTEM, SEAD, XRD, PL and UV-VIS spectra were used to characterize the size, crystal structure and photoluminescence (PL) properties of CdSe nanocrystals. The PL spectra and TEM results revealed that the monodispersed and uniformed CdSe QDs with narrow size distribution were synthesized at a certain reaction temperature. HRTEM images combined with selected area electron diffraction (SAED) and XRD patterns illustrated that CdSe QDs showed near-perfect zinc-blende and wurtzite crystallinity at different temperatures. The Gibbs-Thomson calculation provided a thermodynamic explanation for obtaining the CdSe nanocrystals with narrow size distribution by temperature-control method.     

A surfactant-free recipe for shape-controlled synthesis of CdSe nanocrystals

We described surfactant-free recipes for the synthesis of CdSe nanocrystals (NCs) with well-controlled morphologies at a relatively low temperature. Dot-, rod-, tetrapod-and sphere-shaped CdSe NCs were prepared with trioctylphosphine oxide (TOPO) as a non-equilibrium solvent and trioctylphosphine selenide (TOPSe) and cadmium carboxylates as Se and Cd precursors, respectively. It was found that the morphology and stacking pattern of the CdSe NCs were related to the preparation conditions such as the concentration of the injected TOPSe(monomer concentration), reaction temperature and chain length of the cadmium carboxylate precursors. At a reaction temperature of 240?°C, CdSe NCs with a tetrapod selectivity of up to 85% were obtained in the presence of cadmium myristate under high concentrated TOPSe injection, and the in situ-formed myristic acid supplied the best acidic ligand with optimal amount to stabilize the anisotropic growth of the tetrapods. The intentional addition of more myristic acid in the reaction system would block the growth pathway of the tetrapods. Using cadmium laurate, cadmium palmitate and cadmium stearate as the cadmium precursors would reduce the formation of the tetrapods, showing the very low selectivity of the tetrapods.     

Room temperature synthesis of 2D CuO nanoleaves in aqueous solution

A simple room temperature method was reported for the synthesis of CuO nanocrystals in aqueous solution through the sequence of Cu(2+) → Cu(OA)2 → Cu(OH)2 → Cu(OH)(2-)4 → CuO. Sodium oleate (SOA) was used as the surfactant and shape controller. The as-prepared samples were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), UV-visible absorption spectroscopy (UV-vis) and differential thermal analysis (DTA). It can be seen that 1D Cu(OH)(2) nanowires were first obtained from Cu(OA)(2) and, at room temperature, converted into 2D CuO nanoleaves (CuO NLs) in a short time under a weakly basic environment. On prolonging the reaction time, the top part of these 2D nanoleaves branched and separated along the long axis to form 1D rod-like nano-CuO because of the assistance of SOA. A possible transformation mechanism of Cu(OH)(2) to CuO nanostructures at room temperature in aqueous solution is discussed. The transformation velocity can be controlled by changing the pH value of the system. The prepared CuO NLs were used to construct an enzyme-free glucose sensor. The detecting results showed that the designed sensor exhibited good amperometric responses towards glucose with good anti-interferent ability.     

Highly luminescent monodisperse CdSe nanoparticles synthesized in aqueous solution

Simple routes to synthesize highly photoluminescent monodisperse thiol-capped CdSe nanoparticles are reported. The as-synthesized water-soluble CdSe nanoparticles possess higher photoluminescence quantum efficiency (up to 22%), smaller values of full width of half-maximum of photoluminescence spectra (down to 31 nm), higher photostability, and better monodispersity compared with the nanoparticles made from other aqueous routes. The quality of CdSe nanoparticles prepared by our route compares very favourably with those prepared in organic solution.     

A facile and green preparation of high-quality CdTe semiconductor nanocrystals at room temperature

One chemical reagent, hydrazine hydrate, was discovered to accelerate the growth of semiconductor nanocrystals (cadmium telluride) instead of additional energy, which was applied to the synthesis of high-quality CdTe nanocrystals at room temperature and ambient conditions within several hours. Under this mild condition the mercapto stabilizers were not destroyed, and they guaranteed CdTe nanocrystal particle sizes with narrow and uniform distribution over the largest possible range. The CdTe nanocrystals (photoluminescence emission range of 530-660?nm) synthesized in this way had very good spectral properties; for instance, they showed high photoluminescence quantum yield of up to 60%. Furthermore, we have succeeded in detecting the living Borrelia burgdorferi of Lyme disease by its photoluminescence image using CdTe nanocrystals.     

Controlled synthesis of pentagonal gold nanotubes at room temperature

Large quantities of pentagonal gold nanotubes have been synthesized by reducing chloroauric acid with silver nanowires in an aqueous solution of hexadecyltrimethylammonium bromide (CTAB) at room temperature. These gold nanotubes possess perfect structures, smooth surfaces, highly crystalline walls, and similar cross-sections to that of the silver template. In this process, the CTAB participation was found to be crucial for shape-controlled synthesis of pentagonal gold nanotubes. In the absence of CTAB, loose and hollow gold structures were routinely generated, while bundled gold nanotubes with rough surfaces were obtained by replacing the CTAB with poly(vinyl pyrrolidone) (PVP). The possible formation mechanism of pentagonal gold nanotubes has also been discussed on the basis of various growth stages studied by field-emission scanning electron microscopy (FE-SEM) images. In addition, the catalytic properties of these hollow nanostructures for hydrogen generation reaction from HCHO solution have also been investigated. They showed higher activity than that of spherical gold nanoparticles.