Hang-Beom Bu

Hydrothermal synthesis of thiol-capped CdTe nanoparticles and their optical properties

Water soluble nanoparticles (NPs) with a high emission property were synthesized via hydrothermal routes. In this report, we chose thiol ligand N-acetyl-L-cysteine as the ideal stabilizer and have successfully employed it to synthesize readily size-controllable CdTe NPs in a reaction of only one step. Hydrothermal synthesis of CdTe NPs has been carried out in neutral or basic conditions so far. We found out that the pH value of precursor solutions plays an important role in the uniformity of the particle size. Actually, high quality CdTe NPs were synthesized under mild acidic conditions of pH 5. The resultant NPs indicated good visible light-emitting properties and stability. Further, the experimental results showed that the reaction temperature influenced significantly the growth rate and the maximum size of the NPs. The CdTe NPs with a high photoluminescence quantum yield (the highest value: 57%) and narrower half width at half maximum (the narrowest value: 33 nm) were attained in very short time, within 40 minutes, reaching diameters of 2.3 to 4.3 nm. The PL intensity was increased with an increase in the reaction time, reflecting the suppression of nonradiative recombination processes. Furthermore, the formation of CdTe/CdS core-shell structures was discussed from the viewpoint of PL dynamics and X-ray diffraction studies.

Preparation of highly luminescent hybrid gel incorporating NAC-capped CdTe quantum dots through sol–gel processing

Highly photoluminescent gel was prepared by embedding water soluble quantum dots (QDs) in an inorganic–organic hybrid gel matrix using a conventional sol–gel process. Aminopropyltrimethoxysilane and citric acid (CA) were found to be the best combination for the gel preparation. 13C-NMR and FT-IR studies indicated hydrogen bond formation between the amine group of APS and the carboxyl group of CA. IR-light radiation curing was comparable to thermal curing and reduced the gelation time to a considerable extent (71 %). The resulting composite formed a hybrid gel phosphor with excellent transparency by embedding CdTe QDs into the matrix and emitted light of various colors with high photoluminescence efficiency (40 %). The gel phosphor retained the PL properties after storage in air for one year. In addition, the strength of the hybrid phosphor was demonstrated by a coin-flipping test.

Microwave-assisted hydrothermal synthesis of highly luminescent ZnSe-based quantum dots with a quantum yield higher than 90%

Highly luminescent ZnSe-based quantum dots (QDs) were synthesized by a microwave-assisted hydrothermal method. The characteristics of the ZnSe precursor solution strongly influenced the photoluminescence (PL) quantum yields (QYs) of the QDs. The PL QY of ZnSe-core QDs synthesized under the optimum conditions reached 60%. Furthermore, the PL QY further increased to higher than 90% when a ZnS shell was applied to prepare ZnSe/ZnS-core/shell QDs.

Electrochemical Polymerization of 1,10‐Decanedithiol in CH3CN at Constant Current

Full Paper: The addition polymerization of N,N-diglycidyl aniline (DGA) and disecondary diamines leads to linear addition polymers with molecular weights ranging from 2 500 to 9 100 Da respectively. Their relatively broadmolecular weight distribution (M w /M n = 5.5 to 17) is caused by the formation of small amounts of cyclic oligomers. Surprisingly, the addition polymerization of primary monoamines and DGA results in the formation of oligomers only. These oligomers have molecular weights between 684 and 1 165 g.mol - 1 . 1 3 C NMR spectra proof that during addition reaction no side-reaction took place and that the epoxide end groups were completely consumed. Obviously, the addition products mainly consist of cyclic oligomers. In the MALDI-TOF mass spectra cyclic oligomers of repeat units between n = 1 and n = 7 were observed. The kinetics of the addition polymerization can be described by both a formal model and the smallest necessary set of elementary reactions. In order to find the optimum parameters, the set of differential equations was solved numerically by multivariate non-linear regression. The perfect agreement between model calculations and experimental curves allows reliable predictions of the reaction behavior for arbitrary temperature-time profiles.

Electrochemical polymerization of 1,10-decanedithiol in CH2Cl2 and additive effect of benzylmercaptan

Abstract Synthesis of polymers containing disulfide bonds in the main chain by electrochemical polymerization of 1,10-decanedithiol (DEDT) in dichloromethane (CH 2 Cl 2 ) was investigated. The resulting poly(DEDT) was also investigated under constant current electrolysis. It is observed that the number-average molar mass ( M n ) of the polymer increases as a function of time (i.e. as a function of the Faradaic charge passing through the circuit), as opposed to what was observed in acetonitorile (CH 3 CN). These results are attributed to the solubility of the product, poly(DEDT) of the reaction in CH 2 Cl 2 , while it is insoluble in CH 3 CN. In the polymerization of DEDT in CH 2 Cl 2, the relation between the M n of the polymer and Faradaic charge showed the features of a stepwise polymerization process (which proceeds by the stepwise reaction between the functional groups of the reactants). The cleavage of the disulfide bond in the polymer was found to take place mainly at the anode via an oxidation process. By the addition of benzylmercaptan (BzSH), the molar mass of the polymer could be regulated. The benzylthiyl group derived from BzSH could be introduced at the polymer chain end.