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Some core±shell semiconductor nanocrystals, such as CdSe/ CdS and CdS/ZnS, show high luminescence properties and stability against photo-oxidation due to passivation of the nanocrystal surface. The surfaces of these nanocrystals are capped with an inorganic shell with wider bandgaps, e.g., CdS or ZnS, which have been widely used in light-emitting diodes (LEDs) [1] and biological labeling. [2] Because the inorganic shell provides a passivation of the nanocrystal surface, which effectively eliminates, to a great extent, the dangling bonds or coordination sites that form traps for photogenerated carriers, photogenerated carriers inside the nanocrystals will be mostly confined in the core, resulting in a higher quantum yield (QY). Among such core±shell systems, CdSe/CdS and CdSe/ZnS have been intensively studied over the past decade. As reported in the literature, the photoluminescence (PL) quantum yields for as-prepared core±shell nanocrystals at room temperature are 10±80 % in the spectral range of 470 to 630 nm; the nanocrystals were synthesized via an organometallic approach [3] and its alternative routes.[4] Until now, emission of pure blue color (PL peak~455 nm) has not been reported for CdSe/CdS or CdSe/ZnS core±shell nanocrystals because it is difficult to synthesize extremely small (< 1.6 nm diameter) nanocrystals of CdSe with narrow size distributions by the above-mentioned organometallic approaches and their alternative routes.[5] Generally, they are produced at relatively low temperatures (90±140 C) and a long reaction time.[6] However, lower temperatures will lead to a longer nucleation time, which results in polydisperse nanocrystals. Hence, it is a challenge to prepare extremely small nanocrystals of CdSe with narrow size distributions and CdSe/CdS core±shell nanocrystals whose emission is pure blue, through organometallic approaches and their alternative routes. Previously, we have prepared highly luminescent and nearly monodisperse CdS nanocrystals by a two-phase approach under mild conditions (< 100 C) [7] and found that a slow nucleation does not always lead to polydisperse colloids if the growth time of the nanocrystals is very long. Since decomposition rates of selenourea and thiourea are controllable by changing the reaction temperature, the size of the nanocrystals and their distribution can be controlled through tuning a balance between nucleation and growth. Herein, we took advantage of an autoclave to obtain a high temperature and pressure for the nucleation and growth of CdSe and CdSe/ CdS core±shell nanocrystals. The extremely small CdSe and highly luminescent CdSe/CdS core±shell quantum dots with CdSe cores ranging in diameter from 1.2 to 1.5 nm were synthesized in a two-phase system in the autoclave. Cadmium myristate (Cd-MA) and selenourea (thiourea) were used as a source of cadmium and selenium (sulfur), respectively. Oleic acid (OA) was used as the only capping agent. A solution of Cd-MA and OA in toluene and a solution of selenourea (or thiourea) in water were mixed and heated in ...

Macroporous materials are a class of absorbents used for oil spill cleanup. In this article, novel macroporous and hydrophobic polyvinyl formaldehyde (PVF-H) sponges were prepared by the reaction of stearoyl chloride with hydroxyl groups of hydrophilic PVF sponge at different temperatures. Attenuated total reflectance-infrared (ATR-IR) spectroscopy confirmed the successfully anchoring of hydrophobic stearoyl groups on the PVF networks. Scanning electron microscopy (SEM) images demonstrated that the as-prepared PVF-H had interconnected open-cell structures, and mercury intrusion porosimetry indicated that the average pore size ranged from 60 to 90 μm and porosity was greater than 94.8%. Such PVF-H sponges can absorb oil products effectively, such as toluene, n-hexane, kerosene, soybean oil, hydraulic oil, and crude oil up to 13.7 g·g(-1) to 56.6 g·g(-1), and this level of absorption was approximately 2-4 times higher than that absorbed by commercial polypropylene nonwoven mat. In low-viscosity oils, the samples can reach the saturated absorption amount only in 1 min, but in higher-viscosity oils, absorption equilibrium can be reached in 10 min. In a simulated oil slick system, these macroporous and hydrophobic sponges can still maintain high oil absorption capacities within the range of 14.4 g·g(-1) to 57.6 g·g(-1), whereas a relatively low absorption rate (approximately 20 min) indicated high absorption performance and excellent selectivity in the oil-water mixture. In addition, the absorbed oils were collected effectively only through a simple squeeze. The PVF-H sponges were subjected to 35 absorption-squeeze cycles and exhibited good reusability and 90% recovery for oils. The samples prepared at different temperatures differed in their absorption capacities to some extent. However, this new kind of macroporous and PVF-H sponges had excellent absorption performance on oil products.

Protein adsorption has a vital role in biomaterial surface science because it is directly related to the hemocompatibility of blood-contacting materials. In this study, monomethoxy poly(ethylene glycol) (mPEG) with two different molecular weights was grafted on polyethylene as a model to elucidate the adsorption mechanisms of plasma protein through quartz crystal microbalance with dissipation (QCM-D). Combined with data from platelet adhesion, whole blood clotting time, and hemolysis rate, the blood compatibility of PE-g-mPEG film was found to have significantly improved. Two adsorption schemes were developed for real-time monitoring of protein adsorption. Results showed that the preadsorbed bovine serum albumin (BSA) on the surfaces of PE-g-mPEG films could effectively inhibit subsequent adsorption of fibrinogen (Fib). Nonspecific protein adsorption of BSA was determined by surface coverage, not by the chain length of PEG. Dense PEG brush could release more trapped water molecules to resist BSA adsorption. Moreover, the preadsorbed Fib could be gradually displaced by high-concentration BSA. However, the adsorption and displacement of Fib was determined by surface hydrophilicity.

Well‐defined diblock poly(L‐lactide)‐block‐poly(dimethylamino‐2‐ethyl methacrylate) (PLLA‐b‐PDMAEMA) copolymers were synthesized by combining ROP of LLA and ATRP of DMAEMA, from a dual‐initiator 2‐hydroxylethyl 2‐bromoisobutyrate. The molecular characterization of these diblock copolymers was performed using 1H NMR, FT‐IR, and GPC‐MALLS analysis. The responsive behavior of these diblock copolymers in aqueous solutions at different pH and temperatures were investigated using DLS. Results show that both higher pH and temperature result in a higher degree of neutralization, weaker hydrogen bonding, and micellar aggregation. As observed by TEM, changes in micellar morphology are in accordance with DLS results. magnified image

“Nano-onions” with multifold alternating CdS/CdSe or CdSe/CdS structure have been synthesized via a two-phase approach. The influences of shell on photoluminescence (PL) quantum yields (QYs) and PL lifetimes are investigated and discussed. It is found that the outmost shell plays an important role in the PL QYs and PL lifetimes of the multishells “onion-like” nanocrystals. The PL QYs and PL lifetimes fluctuate regularly with CdSe and CdS shells. The PL QY increases when the nanocrystals have an outmost CdS shell; however, it decreases dramatically with the outmost CdSe shell. The trend of the change of PL lifetimes is consistent with that of the QYs. The crystal structure and composition of the novel nano-onions are characterized by transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectra techniques.

Biocompatible and zwitterionic poly(sulfobetaine methacrylate) (PSBMA) was grafted onto the surface of initiator-modified silica nanoparticles via surface-initiated atom transfer radical polymerization. The resultant samples were characterized via nuclear magnetic resonance, Fourier transform infrared spectroscopy, transmission electron microscopy, and thermogravimetric analysis. Their molecular weights and molecular weight distributions were determined via gel permeation chromatography after the removal of silica by etching. Moreover, the phase behavior of these polyzwitterionic-grafted silica nanoparticles in aqueous solutions and stability in protein/PBS solutions were systematically investigated. Dynamic light scattering and UV-visible spectroscopy results indicate that the silica-g-PSBMA nanoparticles exhibit an upper critical solution temperature (UCST) in aqueous solutions, which can be controlled by varying the PSBMA molecular weight, ionic strength, silica-g-PSBMA nanoparticle concentration, and solvent polarity. The UCSTs shift toward high temperatures with increasing PSBMA molecular weight and silica-g-PSBMA nanoparticle concentration. However, increasing the ionic strength and solvent polarity leads to a lowering of the UCSTs. The silica-g-PSBMA nanoparticles are stable for at least 72 h in both negative and positive protein/PBS solutions at 37 °C. The current study is crucial for the translation of polyzwitterionic solution behavior to surfaces to exploit their diverse properties in the development of new, smart, and responsive coatings.

Hybrid organic/inorganic white light-emitting diodes (LEDs) were fabricated of semiconductor polymer poly(N-vinylcarbazole) (PVK) doped with CdSe/CdS core–shell semiconductor quantum dots (QDs). The device, with a structure of indium–tin-oxide (ITO)|3,4-polyethylene–dioxythiophene–polystyrene sulfonate (PEDOT:PSS)|PVK:CdSe/CdS|Al, emitted a pure white light spanning the whole visible region from 400 to 800 nm. The Commission Internationale del’Eclairage coordinates (CIE) remained at x = 0.33,y = 0.34 at wide applied voltages. The maximum brightness and electroluminescence (EL) efficiency reached 180 cd m−2 at 19 V and 0.21 cd A−1 at current density of 2 mA cm−2, respectively. The realization of the pure white light emission is attributed to the incomplete energy and charge transfer from PVK to CdSe/CdS core–shell QDs.