Free-standing single-walled carbon nanotube-CdSe quantum dots hybrid ultrathin films for flexible optoelectronic conversion devices

In this work, we described a facile route for the fabrication of free-standing single-walled carbon nanotubes (SWCNT)-CdSe quantum dots (QDs) hybrid ultrathin films and investigated their optoelectronic conversion properties. A free-standing SWCNT film with thickness of ～36 nm was firstly prepared via vacuum filtration. The film was then immersed into the pre-synthesized oleic acid-capped CdSe QDs (average diameter of 3.5 nm) solution, where CdSe QDs anchored spontaneously onto the surface of SWCNT film to produce SWCNT-CdSe QDs hybrid film. By using pure SWCNT films in different thicknesses as bottom and top electrodes, a flexible all-carbon electrode optoelectronic conversion device with sandwich structure of SWCNT film (thickness of ～200 nm)/SWCNT-CdSe QDs hybrid film (thickness of ～36 nm)/SWCNT film (thickness of ～36 nm) was constructed to generate optoelectronic conversion under illumination of solar-simulated light. Our results demonstrated that the all-carbon electrode structure was effective for charge separation and a sensitive and stable photocurrent signal could be produced in such a device. In addition, our SWCNT-CdSe QDs hybrid film exhibited high flexibility and durability. No clear change in the resistance of the film was detected under bending in various bending angles.     

Synthesis and characterization of water soluble choline labeled cadmium selenide/zinc selenide/zinc sulfide luminescent quantum dots

Water soluble choline-labeled CdSe/ZnSe/ZnS quantum dot (QD) bioconjugates were synthesized by attaching a thiolated choline analogue to the core-shell QD surface. Characterization was conducted by absorption and luminescence spectroscopy and scanning electron microscopy. QDs with diameters of 5–6 nm resulted and exhibited a luminescence maximum at 663 nm in aqueous solution.     

One-Pot Synthesis of Biocompatible CdSe/CdS Quantum Dots and Their Applications as Fluorescent Biological Labels

We developed a novel one-pot polyol approach for the synthesis of biocompatible CdSe quantum dots (QDs) using poly(acrylic acid) (PAA) as a capping ligand at 240°C. The morphological and structural characterization confirmed the formation of biocompatible and monodisperse CdSe QDs with several nanometers in size. The encapsulation of CdS thin layers on the surface of CdSe QDs (CdSe/CdS core–shell QDs) was used for passivating the defect emission (650 nm) and enhancing the fluorescent quantum yields up to 30% of band-to-band emission (530–600 nm). Moreover, the PL emission peak of CdSe/CdS core–shell QDs could be tuned from 530 to 600 nm by the size of CdSe core. The as-prepared CdSe/CdS core–shell QDs with small size, well water solubility, good monodispersity, and bright PL emission showed high performance as fluorescent cell labels in vitro. The viability of QDs-labeled 293T cells was evaluated using a 3-(4,5-dimethylthiazol)-2-diphenyltertrazolium bromide (MTT) assay. The results showed the satisfactory (>80%) biocompatibility of as-synthesized PAA-capped QDs at the Cd concentration of 15 μg/ml.     

Temperature dependent synthesis and optical properties of CdSe quantum dots

The CdSe quantum dots (QDs) were synthesized at various temperatures in aqueous solution. The as-synthesized QDs were characterized by X-ray diffraction (XRD) method and transmission electron microscopy (TEM), and their optical properties were assessed via ultraviolet–visible (UV–vis) absorption spectrum and fluorescence spectrum. The results showed that the reaction temperature could significantly influence the band gap, particle size, and spectral behaviors of the QDs. With the increase of the temperature from room temperature to 90 °C, the band gap of the QDs linearly decreased, corresponding to an essential increase of particle size as well as variable spectral behaviors. In particular, the starting temperature had an important effect on the QDs synthesis and their optical properties. From a viewpoint of wide controls of fluorescence color and intensity, a reaction temperature range of 17–90 °C was appropriate for the synthesis of the CdSe QDs.     

Improving the synthesis of single-walled carbon nanotubes by pulsed arc discharge in air by preheating the catalysts

Single-walled carbon nanotubes (SWCNTs) were synthesized in reduced pressure air using pulsed arc discharge after preheating the catalyst. Our experimental results revealed that preheating the catalysts can assist the synthesis of SWCNTs in air under a pressure of 5-10 kPa. The SWCNTs have a diameter of 1.5-2 nm and length can reach several micrometers. The consumption rate of the anode and the production rate of CNTs and SWCNTs in air are lower than in helium atmosphere at the same pressure, respectively. Further experiment demonstrates that 600 °C is optimum temperature for preheating the catalysts to synthesize SWCNTs in air.     

Controlled assembly of carbon nanotubes encapsulated with amphiphilic block copolymer

An amphiphilic diblock copolymer (PEtOz-PCL) based on hydrophilic poly(2-ethyl-2-oxazoline) (PEtOz) and hydrophobic poly(ε-caprolactone) (PCL) was adsorbed in aqueous phase on the surface of single-wall carbon nanotube to produce PEtOz-PCL-encapsulated SWCNTs (PEtOz-PCL/SWCNT) with the diameter about 30 nm. The Raman spectroscopy analysis indicated that the nanotubes were physically encapsulated by the block copolymer without chemical denaturation of the nanotube. PEtOz-PCL/SWCNTs exhibited pH-responsive reversible complexation with poly(acrylic acid) or poly(methacrylic acid) in aqueous phase due to the pH-dependent hydrogen bonding between the PEtOz outer shell of PEtOz-PCL/SWCNTs with carboxyl groups. In addition, by using PEtOz as a template for the formation of metal nanoparticles, Au and Pd nanoparticles were successfully hybridized with PEtOz-PCL/SWCNTs.     

Designed multifunctionalized magnetic mesoporous microsphere for sequential sorption of organic and inorganic pollutants

A novel magnetic microsphere with thiol-functionalized mesoporous shell was fabricated by using a colloidal chemical method and cationic surfactants (CTAB) as structure-directing agents. As a high performance adsorbent, these microspheres were examined for environmental protection applications to adsorb and remove toxic phenolic compounds and heavy metal ions, sequentially, in aqueous solution. The prepared nanocomposite microspheres were mesoporous and magnetizable, with a diameter of 350-400 nm, a high surface area of 913.14 m²/g, a pore size of 2.48 nm, and a saturation magnetization of 33.9 emu/g. These multifunctional microspheres showed excellent adsorptive capability towards toxic phenolic compounds and heavy metal ions (Hg²⁺, Pb²⁺). The cation micelle made of CTAB in the mesopores has great attractive power to phenolic compounds and the adsorption capacity was as high as 144.78 mg/g for 4-methyl-2,6-dinitrophenol. The thiol-functionalized magnetic mesoporous microsphere (TMMM) which had adsorbed phenolic compounds can further adsorb metal ions after removing CTAB. The adsorption capacity was 185.19 mg/g for Hg²⁺ and 114.7 mg/g for Pb²⁺. The TMMM can be easily removed from solution by an external magnetic field. These results suggest that this kind of nanocomposites is potentially useful materials for effectively adsorbing and removing different dangerous pollutants in aqueous solution.     

Impact of nanometal catalysts on the laser vaporization synthesis of single wall carbon nanotubes

The effects of catalyst particle size on the purity, yield, and purification efficiency of single wall carbon nanotubes (SWCNTs) synthesized via pulsed laser vaporization were investigated. The purity of as-produced SWCNT material synthesized using Ni and Co nanometal (∼13 nm diameter) catalyst particles was compared to material synthesized using conventional micronmetal (2-3 μm diameter) particles. The SWCNT material from nanometal catalysts demonstrated a 50% increase in SWCNT purity as assessed by optical absorption spectroscopy and thermogravimetric analysis (TGA). A change in the thermal oxidation properties was also observed with the nanometal-SWCNTs exhibiting a suppression of the exothermic oxidation of post-synthesis catalyst. Statistical analysis of the TGA residue yielded mean post-synthesis catalyst particle diameters of 18 ± 6 nm and 3 ± 1 nm for the micronmetal and nanometal produced material, respectively. When a thermal oxidation profile was performed, the micronmetal-produced material showed the typical decrease in SWCNT purity with increasing oxidation temperature while the nanometal-produced material showed increasing SWCNT purity with increasing temperature. Overall, the use of nanometal catalysts significantly increases synthesis yield and offers novel thermal oxidation procedures to thermally remove carbonaceous impurities without the aid of acid treatments for the development of potential large-scale purification processing.     

Surfactant-free assembling of functionalized single-walled carbon nanotube buckypapers

The electrical and textural properties of single-walled carbon nanotube buckypapers were tunned through chemical functionalization processes. Single-walled carbon nanotubes (SWCNTs) were covalently functionalized with three different chemical groups: Carboxylic acids (-COOH), benzylamine (-Ph-CH₂-NH₂), and perfluorooctylaniline (-Ph-(CF₂)₇-CF₃). Functionalized SWCNTs were dispersed in water or dimethylformamide (DMF) by sonication treatments without the addition of surfactants or polymers. Carbon nanotube sheets (buckypapers) were prepared by vacuum filtration of the functionalized SWCNT dispersions. The electrical conductivity, textural properties, and processability of the functionalized buckypapers were studied in terms of SWCNT purity, functionalization, and assembling conditions. Carboxylated buckypapers demonstrated very low specific surface areas (< 1 m²/g) and roughness factor (R_a = 14 nm), while aminated and fluorinated buckypapers exhibited roughness factors of around 70 nm and specific surface areas of 160-180 m²/g. Electrical conductivity for carboxylated buckypapers was higher than for as-grown SWCNTs, but for aminated and fluorinated SWCNTs it was lower than for as-grown SWCNTs. This could be interpreted as a chemical inhibition of metallic SWCNTs due to the specificity of the diazonium salts reaction used to prepare the aminated and fluorinated SWCNTs. The utilization of high purity as-grown SWCNTs positively influenced the mechanical characteristics and the electrical conductivity of functionalized buckypapers.     

Effect of CdSe quantum dots on the performance of hybrid solar cells based on ZnO nanorod arrays

This paper reports the fabrication and interface modification of hybrid inverted solar cells based on ZnO nanorod arrays and poly (3-hexylthiophene). CdSe quantum dots (QDs) are grafted to the ZnO nanorod array successfully by bifunctional molecule mercaptopropionic acid to enhance the device performance. The power conversion efficiency of the device is increased by 109% from 0.11% to 0.23% under simulated 1 sun AM 1.5 solar illumination at 100 mW/cm² after the modification. The grafting of CdSe QDs effectively enhanced the excition generation and dissociation on the organic/inorganic interface. This work may provide a general method for increasing the efficiency of organic–inorganic hybrid solar cells by interface modification.     

Metal catalyst-free mist flow chemical vapor deposition growth of single-wall carbon nanotubes using C60 colloidal solutions

Metal catalyst-free mist flow chemical vapor deposition (CVD) growth of single-walled carbon nanotubes (SWCNTs) with C₆₀ fullerenes has been investigated by using an aqueous colloidal C₆₀ solution. Under the optimum reaction condition, relatively uniform SWCNTs with a mean diameter of 1.28 nm can be synthesized without any treatments of C₆₀ prior to CVD. Cap opening, nucleation and the growth of SWCNTs have been occurring almost simultaneously during the present CVD. C₆₀ can be used as the seeds (i.e., end-caps) of SWCNTs, in which oxygen atoms from water molecules provide etching of C₆₀ into caps. Furthermore, the coalescence of C₆₀ caps into a larger one leads to the growth of SWCNTs with larger diameters.     

谷氨酰胺为稳定剂制备硒化镉纳米晶及光谱性质研究

以谷氨酰胺(Gln)为稳定剂合成了硒化镉纳米晶,利用X-射线粉末衍射(XRD)和透射电镜(TEM)对纳米晶结构进行了表征,粒径约为20 nm。通过紫外-可见吸收光谱、激发光谱与发射光谱研究了纳米晶光谱特性。实验结果表明,反应温度过高、反应时间过长都会破坏谷氨酰胺(Gln)的稳定作用,使CdSe聚集,影响其荧光性质。而聚乙二醇(PEG)的加入会使纳米晶的荧光发射明显加强,而且发射峰峰形尖锐。     

CdSe量子点标记免疫球蛋白及光谱性质研究

以巯基乙酸为稳定剂合成了CdSe量子点,利用X-射线粉末衍射(XRD)和透射电镜(TEM)对量子点结构进行了表征,粒径约为5 nm。以碳二亚胺为缩合剂将量子点与免疫球蛋白共价连接,光谱实验结果表明CdSe量子点与免疫球蛋白有效结合,其荧光发射峰发生了红移,而半峰宽和发射强度没有明显变化。     

Production of single-walled carbon nanotubes with narrow diameter distribution using iron nanoparticles derived from DNA-binding proteins from starved cells

Iron nanoparticles derived from DNA-binding proteins from starved cells (Dps) were used to grow single-walled carbon nanotubes (SWCNTs) with narrow diameter distribution. An atomic force microscopy, Raman spectroscopy, and photoluminescence were used for evaluation of diameter or chirality distribution of the SWCNTs. We found that thin SWCNTs (1.1 nm diameter) were grown from the large Dps-derived nanoparticles (2.4 nm diameter) on and above the substrates. From the size comparison with ferritins and Co-filled apoferritins, we also found that SWCNTs become thinner as the catalyst becomes smaller. The synthesis of smaller catalysts (ca. 1 nm diameter) and their use for growth becomes crucial for the control of SWCNT diameter.     

Improved performance of dense TiO2/CdSe coupled thin films by low temperature process

Dense TiO₂ and TiO₂/CdSe coupled nanocrystalline thin films were synthesized onto ITO coated glass substrate by chemical route at relatively low temperature (≤100 °C). TiO₂ films were nanocrystalline and crystallinity disappears after CdSe deposition as evidenced by X-ray powder diffraction. Surface morphology and physical appearance of films were studied from SEM and actual photo-images, reveals dense nature of TiO₂ (10-12 nm spherical grains, faint violet) and CdSe (80-90 nm spherical grains, deep brown), respectively. Presence of two absorption edges in UV spectra implies existence of separate phases rather than composite formation. TiO₂ film was found to have higher water contact angle (71°) than TiO₂/CdSe (61°) and CdSe (56°). I-V and stability tests of photo-electrochemical cells were performed with TiO₂ and TiO₂/CdSe film electrodes (under light of illumination intensity 80 mW/cm²) in lithium iodide as an electrolyte using two-electrode system.     

New pathway for the synthesis of gold and silver bimetallic nanocomplexes and their derivatives of polypyrrole nanorods (TM04096)

We report here the first electrochemical pathway to prepare Au- and Ag-containing bimetallic nanocomplexes with a mean diameter of 5 nm in 0.1 M HCl aqueous solutions without addition of any stabilizer. First, a silver substrate was roughened by a triangular-wave oxidation-reduction cycle (ORC) in an aqueous solution containing 0.1 M HCl. Silver-containing complexes were left in the solution after the ORC treatment. Then a gold substrate was subsequently roughened by the similar ORC treatment in this solution. Encouragingly, polypyrrole (PPy)-coated Au and Ag bimetallic nanocomposites with a nanorod structure and a diameter smaller than 15 nm can be prepared by the formation of self-assembled monolayers and orderly autopolymerization of pyrrole monomers on these bimetallic nanocomplexes, and further link them together.     

Cadmium selenide nanowires within core-shell cylindrical polymer brushes: Synthesis, characterization and the double-loading process

Cadmium selenide (CdSe) nanowires were successfully in situ fabricated, utilizing amphiphilic core-shell cylindrical polymer brushes (CPB) as well-defined single molecular templates. The hydrophilic polymer brush core acts as the nanoreactor for generating and shaping CdSe nanoparticles into nanowires via the absorption of cadmium ions by carboxylate groups in the core and subsequent introduction of H₂Se gas; the hydrophobic polymer brush shell protects the nanowires from agglomeration and renders the hybrid a soluble material. The formation of 170 nm-long CdSe nanowires proceeds simultaneously with the nucleation, growth and combination of CdSe nanoparticles. After the introduction of CdSe nanowires, the recuperated chemical structure of CPB facilitates a double-loading process, broadening the CdSe nanowire from 7.5 to 9.3 nm on an average. Both hybrids are soluble and stable in organic solvents for one year and a potential candidate of the nanoscale optic and electronic devices.     

Efficiency of C60 incorporation in and release from single-wall carbon nanotubes depending on their diameters

We show that the efficiency of incorporating C₆₀ in single-wall carbon nanotubes (SWCNTs) and that of the incorporated C₆₀’s release from the SWCNTs depend on the SWCNT diameter. Through transmission electron microscopy, we found that the C₆₀ incorporation efficiency reached its maximum at diameters of 1-2 nm, while the efficiency of C₆₀ release from SWCNTs in toluene was maximized at 3-5 nm. The difficulty of C₆₀ release from SWCNTs with diameters of 5-6 nm might reflect either the effective packing of C₆₀ inside SWCNTs or a flattened SWCNT structure. We occasionally observed C₆₀ molecules arranged in a line along the sidewall inside SWCNTs with large diameters/width (>7 nm), indicating that large diameter SWCNTs were sometimes flattened.     

Selective removal of metallic single-walled carbon nanotubes by combined in situ and post-synthesis oxidation

A combined in situ and post-synthesis gas phase oxidation approach for selective removal of metallic single-walled carbon nanotubes (m-SWCNTs) is reported. The in situ oxidation is performed by introducing a small amount of oxygen during the synthesis of SWCNTs by floating catalyst chemical vapor deposition, and the post-synthesis oxidation is conducted by heat-treating the synthesized SWCNTs in air at 400 °C. A combination of characterization techniques shows that m-SWCNTs were selectively removed as a result of their higher reactive activity to oxygen compared to semiconducting SWCNTs, and the diameter distribution of the SWCNTs is narrowed to a range of 1.5-2.0 nm. The mechanism of the combined in situ and post-synthesis oxidation approach is discussed.     

Compositional Dependence of CdSe Quantum Dot Formation on Silicate Host Glass Composition

Silicate glasses were synthesized with additional CdO and ZnSe of varying content. When CdO was added up to 3 mol% with the amount of ZnSe fixed at 1 mol%, absorption due to Se₂^? color centers significantly decreased and the color of glasses was bleached without any evidence of CdSe quantum dots (QDs). However, characteristic absorption due to CdSe QDs appeared without additional heat treatment when the ZnSe content exceeded 1.5 mol%, whereas the CdO content was fixed at 1 mol%. Raman spectra and transmission electron microscopy verified the formation of CdSe QDs. The role of CdO and ZnSe in CdSe QD formation has been discussed in relation to their structural contribution within silicate glasses.