Yongbing Lou

Plasmonic Cu2−xS Nanocrystals: Optical and Structural Properties of Copper-Deficient Copper(I) Sulfides

Cu(2-x)S (x = 1, 0.2, 0.03) nanocrystals were synthesized with three different chemical methods: sonoelectrochemical, hydrothermal, and solventless thermolysis methods in order to compare their common optical and structural properties. The compositions of the Cu(2-x)S nanocrystals were varied from CuS (covellite) to Cu(1.97)S (djurleite) through adjusting the reduction potential in the sonoelectrochemical method, adjusting the pH value in the hydrothermal method and by choosing different precursor pretreatments in the solventless thermolysis approach, respectively. The crystallinity and morphology of the products were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM), which shows that most of them might be of pure stoichiometries but some of them are mixtures. The obtained XRDs were studied in comparison to the XRD patterns of previously reported Cu(2-x)S. We found consistently that under ambient conditions the copper deficient Cu(1.97)S (djurleite) is more stable than Cu(2)S (chalcocite). Corroborated by recent computational studies by Lambrecht et al. and experimental work by Alivisatos et al. This may be the reason behind the traditionally known instability of the bulk Cu(2)S/CdS interface. Both Cu(2)S and the copper-deficient Cu(1.97)S have very similar but distinguishable electronic and crystal structure. The optical properties of these Cu(2-x)S NCs were characterized by UV-vis spectroscopy and NIR. All presented Cu(2-x)S NCs show a blue shift in the band gap absorption compared to bulk Cu(2-x)S. Moreover the spectra of these Cu(2-x)S NCs indicate direct band gap character based on their oscillator strengths, different from previously reported experimental results. The NIR spectra of these Cu(2-x)S NCs show a carrier concentration dependent plasmonic absorption.

Meta and para effects in the ultrafast excited-state dynamics of the green fluorescent protein chromophores

Femtosecond transient absorption and fluorescence upconversion experiments have been performed to investigate the photoinduced dynamics of the meta isomer of the green fluorescent protein chromophore, m-HBDI, and its O-methylated derivative, m-MeOBDI, in various solvent mixtures at neutral, acidic, and basic pH. The para isomer, p-HBDI, and its O- and N-methylated derivatives, p-MeOBDI and p-HBDIMe(+), were also studied for comparison. In all cases, fast quenching of the excited S1 state by internal conversion (IC) to the ground state was observed. In the para compounds, IC, presumably promoted by the internal twisting, arises in <1 ps. A similar process takes place in the meta compounds in nonaqueous solvents but with notably slower kinetics. In aqueous solutions, the meta compounds undergo ultrafast intermolecular excited-state proton transfer that competes with isomerization.

Catalytic activation of core-shell assembled gold nanoparticles as catalyst for methanol electrooxidation

This paper describes the results of an investigation of the evolution and the reconstitution of core-shell assembled gold nanoparticles in electrocatalytic activation for methanol electrooxidation. The aim is to probe the structural and morphological reconstitution upon the catalytic activation. Gold nanoparticles of 2-nm core size are linked by 1,9-nonanedithiolates into a network thin film on planar substrate, and are explored as a model system of core-shell nanostructured catalysts. This system is probed using three characterization techniques: electrochemical quartz-crystal nanobalance (EQCN), infrared reflection spectroscopy (IRS), and atomic force microscopy (AFM). The EQCN detected two types of mass changes across the nanostructured catalysts. One corresponds to shell desorption upon the oxidative potential-driven activation, and the other relates to the formation of surface oxygenated species during the catalytic oxidation of methanol. IRS provided two pieces of evidence for the shell reconstruction upon the activation. One is indicative of the desorption of the shell thiolates, and the other relates to the interparticle electronic effect. AFM revealed morphological changes of the nanoparticle assemblies in terms of the film smoothness and the particle size that are dependent on the thickness of the nanoparticle assembly. While thick films displayed enlarged nanoparticle features, thinner films exhibited a relatively smaller evolution. The catalytic activity is associated with the partial or even complete desorption of network shell components accompanied by the formation of surface oxygenated species, a reconstitution process that may have important implications to the delineation of design and preparation parameters of nanoporous and highly active nanoscale catalysts.

Gold–platinum alloy nanoparticle assembly as catalyst for methanol electrooxidation

This paper describes preliminary findings of a thiolate-capped gold–platinum alloy nanoparticle assembly (metallic core and organic shell) as a novel catalyst for electrooxidation of methanol.

Evaluation of the photoinduced electron relaxation dynamics of Cu1.8S quantum dots

Cu1.8S quantum dots were prepared by using a single-source-precursor type method and investigated in the light of opto-electronic applications. With femtosecond time-resolved transient absorption measurements, the electron relaxation as well as their trapping dynamics could be evaluated. The measurements reveal that the largest and the smallest QD samples prepared exhibit the longest mobility lifetimes, and that the electron-hole relaxation dynamics is strongly dependent on the occurrence of trapping sites. Based on the argument of optical response, it appears that the largest prepared Cu1.8S QDs with band gap energy of 2.35 eV are preferred candidates for opto-electronic device fabrication.

An EQCN assessment of electrocatalytic oxidation of methanol at nanostructured Au-Pt alloy nanoparticles

Abstract Alloy nanocrystals encapsulated with alkyl dithiolates (“core-shell” nanoparticles) serve as an intriguing class of nanostructured catalysts. This paper reports the preliminary results of an electrochemical quartz-crystal nanobalance (EQCN) investigation of mass transport associated with the catalytic activation and methanol oxidation at nanostructured Au–Pt nanocrystals. It is demonstrated that the catalytic activation and oxidation of methanol are accompanied by mass fluxes across the nanostructured film. The mass transport involves oxidation–reduction of surface oxygenated species, methanol adsorption and oxidation, solvent breath and product release. The implication of the EQCN results to the understanding of the core-shell nanostructured catalytic mechanism is discussed.

A competitive electrochemical immunosensor for the detection of human interleukin-6 based on the electrically heated carbon electrode and silver nanoparticles functionalized labels

A facile one-step electrochemical reduction method was developed to prepare electrochemically reduced graphene oxide (ERGO) and gold-palladium bimetallic nanoparticles (AuPdNPs) as the platform of immunosensor. A novel competitive electrochemical immunosensor was then proposed by combining the ERGO-AuPdNPs platform with silver nanoparticles (AgNPs) functionalized polystyrene bionanolabel for the sensitive detection of human interleukin-6 (IL-6). An electrically heated carbon electrode (HCPE) was introduced in the detection procedure of the immunosensor, and further improved the sensitivity. The immunosensor exhibited a wide linear response to IL-6 ranging from 0.1 to 100000 pg mL(-1) with a detection limit of 0.059 pg mL(-1). The proposed method showed good precision, broad linear range, acceptable stability and high reproducibility, and could be used for the detection of IL-6 in real samples, which possessed promising application in clinical research.

Structure modulation of manganese coordination polymers consisting of 1,4-naphthalene dicarboxylate and 1,10-phenanthroline.

Three new manganese coordination polymers, {[Mn2(1,4-NDC)2(phen)2](H2O)}n (1), [Mn2(1,4-NDC)2(phen)(H2O)]n (2) and {[Mn4(1,4-NDC)4(phen)4](DMF)2}n (3) (1,4-H2NDC = 1,4-naphthalene dicarboxylic acid; phen = 1,10-phenanthroline; DMF = N,N-dimethylformamide), have been synthesized solvo/hydrothermally. 1,4-NDC(2-) ligands adopt different coordination modes under different solvents and concentrations which promotes different crystal structure formation. X-ray crystal structural data reveal that compounds 1, 2 and 3 crystallize in monoclinic space groups C2/c, P21/c and C2/c, respectively. Compound 1 has Mn2 dimers connected by 1,4-NDC(2-) linkers, packing into a 2D structure in a grid pattern. Compound 2 has a three-dimensional (3D) structure which is constructed by Mn2 dimers and 1,4-NDC(2-) linkers. Each MnO4N2 node of compound 3 is linked to another by 1,4-NDC(2-) ligands to form a two-dimensional (2D) structure. Variable-temperature magnetic susceptibilities of compounds 1-3 exhibit overall weak antiferromagnetic coupling between the adjacent Mn(II) ions.

Spectroscopic investigation of II-VI core-shell nanoparticles: CdSe/CdS

CdSe and CdSe/CdS core/shell nanoparticles were prepared by a one-pot synthesis process. The CdSe/CdS core/shell nanoparticles showed red-shift absorption and emission spectra compared to the CdSe core. An optimal reaction time for CdS to form on the CdSe nanoparticles was evaluated and the highest photoluminescence yield of approximately equal to 20% was observed for the core/shell nanoparticles. Using nanosecond laser spectroscopy, the photoluminescence of CdSe nanoparticle was investigated and found to exhibit a monoexponential decay with a lifetime of 52.2 ns, while the photoluminescence of CdSe/CdS core/shell nanoparticles demonstrated biexponential decay characterised by a fast component around 25 ns and a slow component around 100 ns. The Stokes shift, photoluminescence yield, and lifetimes were correlated and attributed to the stress in the interface induced by the lattice mismatch of CdSe and CdS. The red-shift of the absorption and emission spectra of CdSe/CdS nanoparticles was discussed with the concepts of the quantum confinement and electronic confinement effects.

Near-infrared light-induced dissociation of zeolitic imidazole framework-8 (ZIF-8) with encapsulated CuS nanoparticles and their application as a therapeutic nanoplatform

Incorporation of CuS nanoparticles into the framework of ZIF-8 provides a chance to integrate near-infrared (NIR) light/low pH triggered release and chemo-photothermal therapy into one system. For the first time, we observed that the framework of ZIF-8 could be disintegrated at pH 7.4 under NIR laser irradiation.