Feed Ratio Of Precursors Research Articles

Facile microwave synthesis of carbon dots powder with enhanced solid-state fluorescence and its applications in rapid fingerprints detection and white-light-emitting diodes

In this report, we successfully developed a simple and fast MW-assisted method for preparing CDs with strong solid-state fluorescence (SSF) by using phthalic acid and piperazine as precursors. The prepared p-CDs can be obtained in high yield (48.7%) and emit bright yellow-green SSF under 365 nm UV light. The absolute PL quantum yield (PLQY) of p-CDs in solid state was measured to be 20.5%, which is much higher than that in aqueous solution. This interesting phenomenon shows that p-CDs not only successfully conquer the aggregation-caused fluorescence quenching (ACQ) effect, but also achieve enhanced fluorescence emission, which was rarely reported in previous literatures as CDs in solid state always reduce their fluorescence emission due to the excessive resonance energy transfer (RET) or direct π-π interactions. In addition, the relationship between the feed ratio of precursors and optical properties of the CDs were also investigated detailedly. Based on their strong SSF, the p-CDs were successfully used in rapid latent fingerprints detection and white light-emitting diodes (WLEDs) preparation with high quality. In summary, this research not only developed a new type of CDs with strong enhanced SSF, but also offered a valuable reference for design SSF-emitting CDs with high yield.

Facile Synthesis of Composition‐Controlled Graphene‐Supported PtPd Alloy Nanocatalysts and Their Applications in Methanol Electro‐Oxidation and Lithium‐Oxygen Batteries

A new and simple approach is reported for the synthesis of uniformly dispersed PtPd alloy nanocatalysts supported on graphene nanoplatelets (GNPs) (PtPd-GNPs) through the introduction of bifunctional materials, which can modify the GNP surface and simultaneously reduce metal ions. With the use of poly(4-styrenesulfonic acid), poly(vinyl pyrrolidone), poly(diallyldimethylammonium chloride), and poly(vinyl alcohol) as bifunctional materials, PtPd-GNPs can be produced through a procedure that is far simpler than previously reported methods. The as-prepared nanocrystals on GNPs clearly exhibit uniform PtPd alloy structures of around 2 nm in size, which are strongly anchored and well distributed on the GNP sheets. The Pt/Pd atomic ratio and loading density of the nanocrystals on the GNPs are controlled easily by changing the metal precursor feed ratio and the mass ratio of GNP to the metal precursor, respectively. As a result of the synergism between Pt and Pd, the as-prepared PtPd-GNPs exhibit markedly enhanced electrocatalytic performance during methanol electro-oxidation compared with monometallic Pt-GNP or commercially available Pt/C. Furthermore, the PtPd-GNP nanocatalysts also show greatly enhanced catalytic activity toward the oxygen reduction/evolution reaction in a lithium-oxygen (Li-O2 ) process, resulting in greatly improved cycling stability of a Li-O2 battery.

Synthesis, characterization of dextran hydrogels and their in vitro release of gentamycin sulphate.

This study reports on the synthesis and characterization of biodegradable dextran-allyl isocyanate-ethylamine (Dex-AE)/polyethylene glycol-diacrylate (PEGDA) hydrogels for the controlled release of gentamycin sulphate (GS) and in vitro inhibition of organisms. The Dex-AE precursor was prepared through a 2-step chemical modification and characterized by Fourier transform infrared spectroscopy (FTIR). Scanning electron microscopy (SEM) results revealed that an increase in Dex-AE content led to an initial decrease in pore size of the Dex-AE/PEGDA hydrogels, but a further increase in Dex-AE content resulted in a slightly increase of pore size. The swelling data indicated that the swelling ratio depended on the precursor feed ratio. GS was incorporated into the hydrogels through 2 different methods, i.e., immersed and crosslinked. The crosslinked GS-Dex-AE/PEGDA hydorgels exhibited stronger antimicrobial activities against Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa. Finally, the viscoelastic properties of crosslinked GS-Dex-AE/PEGDA hydorgels were investigated.

Microwave-Controlled Facile Synthesis of Well-Defined PbS Hexapods

Controlled synthesis of well-defined PbS nanostructures in terms of size and shape has been strongly motivated by their potential applications ranging from solar photovoltaics to near-infrared optics. Hereby, we report a facile microwave-assistant method for ultrafast fabrication of PbS nanostructures, by which uniform PbS hexapods with six arms stretching along six (100) directions of the crystal seeds have been easily synthesized within minutes. Various morphologies including rectangle plates, uniform cubes as well as nanoparticles were obtained by tuning the parameters for the formation of PbS nanocrystals. The results reveal that both concentration and feed ratio of precursors determine the growth of PbS nanocrystals significantly. And higher initial precursor concentration favors the formation of the hexapod structures. The process of crystal growth is monitored through scanning electron microscopy of PbS from different durations of the reaction. This controlled ultrafast synthesis of PbS structures at nanometer and micrometer scale with various morphologies may be promising in large scale fabrication of nanostructures. Based on the systematically study of the growth process, a possible mechanism for the formation of the hexapod-like structure is discussed.

Single-step processing of copper-doped titania nanomaterials in a flame aerosol reactor

Synthesis and characterization of long wavelength visible-light absorption Cu-doped TiO2 nanomaterials with well-controlled properties such as size, composition, morphology, and crystal phase have been demonstrated in a single-step flame aerosol reactor. This has been feasible by a detailed understanding of the formation and growth of nanoparticles in the high-temperature flame region. The important process parameters controlled were: molar feed ratios of precursors, temperature, and residence time in the high-temperature flame region. The ability to vary the crystal phase of the doped nanomaterials while keeping the primary particle size constant has been demonstrated. Results indicate that increasing the copper dopant concentration promotes an anatase to rutile phase transformation, decreased crystalline nature and primary particle size, and better suspension stability. Annealing the Cu-doped TiO2 nanoparticles increased the crystalline nature and changed the morphology from spherical to hexagonal structure. Measurements indicate a band gap narrowing by 0.8 eV (2.51 eV) was achieved at 15-wt.% copper dopant concentration compared to pristine TiO2 (3.31 eV) synthesized under the same flame conditions. The change in the crystal phase, size, and band gap is attributed to replacement of titanium atoms by copper atoms in the TiO2 crystal.

Facile synthesis of red- to near-infrared-emitting CdTexSe1−x alloyed quantum dots via a noninjection one-pot route

Abstract High-quality CdTeSe colloidal nanocrystals with gradient distribution of components, consisting of Te-rich inner cores and Se-rich outer shells, were synthesized in a “green” solvent paraffin via a noninjection one-pot approach with the use of cadmium oxide (CdO), elemental tellurium, and elemental selenium as Cd, Te, and Se sources, respectively. All of these reactants were loaded at room temperature. This features synthetic reproducibility and large-scale capability. The bandgap engineering of the obtained CdTeSe QDs can be conveniently realized through the variation of growth temperature. Red- to near-infrared-emitting (620–780 nm) QDs with nearly identical particle sizes can be obtained when the reaction temperature was changed from 180 to 280 °C with the fixation of precursor feed ratio at 5Cd–0.5Te–0.5Se. The as-prepared CdTeSe QDs exhibit PL QY as high as 53%. The resulting CdTeSe QDs were characterized by UV–vis and photoluminescence spectroscopy, powder X-ray diffraction, transmission electron microscopy, and inductively coupled plasma atomic emission spectroscopy.

Synthesis, Characterization and Biocompatibility of Biodegradable Elastomeric Poly(ether-ester urethane)s Based on Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) and Poly(ethylene glycol) via Melting Polymerization

Poly(ether-ester urethane)s (PUs) multiblock co-polymers were synthesized from telechelic hydroxylated poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) and poly(ethylene glycol) (PEG) via a melting polymerization (MP) process using 1,6-hexamethylene diisocyanate (HDI) as a non-toxic coupling agent for the first time. The PHBHHx segments and PEG segments in the multiblock co-polymers behaved as a hard, hydrophobic and a soft, hydrophilic part, respectively. Their chemical structures and molecular characteristics were studied by gel-permeation chromatography (GPC), 1H-NMR and Fourier transform infrared spectroscopy (FT-IR). The PU produced via the MP method showed a higher molecular weight than those resulting from the solvent polymerization (SP) reported previously. Thermal properties showed enhanced thermal stability with semi-crystalline morphology via incorporation of PEG. The segments compositions evaluated from thermogravimetric analysis (TGA) two-step thermal decomposition profiles suggested that MP enhanced the reactivity of PEG compared with the SP process. It was in good agreement with those calculated from 1H-NMR, as well as the precursor feed ratio, respectively. Water contact angle measurements revealed that surface hydrophilicity of the PUs was enhanced by incorporating the PEG segment into PHBHHx polymer backbone. The mechanical properties assessment of the PUs recorded an improved and adjustable ductility and toughness than pure PHBHHx while preserving the tensile strength. Samples synthesized via MP were resistant to hydrolytic and lipase degradation, yet the multiblock co-polymers incorporating the highest amount of PEG degraded at the highest rate. SEM studies revealed that the surface of the PU films became increasingly porous as the degradation proceeded. Implantation of PU in mouse abdominal cavity indicated that tissue regeneration and tissue compatibility of PU film was better than that of PHBHHx-only film.

Synthesis and Properties of Polyethylene Glycol Diacrylate /2-Hydroxyethyl Mathacrylate Hydrogels

The bioactive synthetic hydrogel materials were prepared with polyethylene glycol diacrylate (PEGDA) and 2-hydroxyethyl mathacrylate (HEMA) by UV photo-polymerization. The aim of this study was to prepare a scaffold material by combining HEMA into a composite polymeric PEGDA-based hydrogel, which were used as bioactive artificial cartilage. The structure and properties of the synthetic hydrogels were investigated in details using FTIR techniques. The swelling data indicated that the equilibrium water content depended on the precursor feed ratio. It was found that adding the HEMA into the PEGDA-based hydrogels was very helpful to improve the swelling properties.

Synthesis, characterization of biodegradable dextran–allyl isocyanate–ethylamine/polyethylene glycol–diacrylate hydrogels and their in vitro release of albumin

Based on dextran–allyl isocyanate–ethylamine (Dex-AE) and polyethylene glycol–diacrylate (PEGDA), a pH sensitive biodegradable hydrogel with improved protein release was prepared through UV photo-crosslinking. The Dex-AE precursor was prepared through a two-step chemical modification and characterized by FT-IR and 1H NMR. The effects of reaction conditions on the synthesis of Dex-AE were studied. The interior morphology data by scanning electron microscopy (SEM) revealed that an increase in Dex-AE content led to an initial decrease in pore size of the microstructure of the Dex-AE/PEGDA hydrogels, but a further increase in Dex-AE content resulted in a relatively looser network structure. The swelling data indicated that the swelling ratio depended on the precursor feed ratio and was correlated to the morphology of the microporous network structure. The pH sensitive property of the Dex-AE/PEGDA hydrogels was studied in different pH buffer solutions and was found that these hydrogels were pH sensitive due to the presence of ample pendant amino groups. The ionic strength data demonstrated that the Dex-AE/PEGDA hydrogels exhibit the highest swelling ratio in pure water, but the swelling ratio became lower as the ionic strength of the media increased. The in vitro albumin release from these hydrogels was examined in different pH (3.0, 7.4) buffer solutions. Both the protein loading and release data indicated that the Dex-AE/PEGDA hydrogels had more protein loading and sustained release capability than pure PEGDA hydrogel, and this ability increased as the Dex-AE composition increased; the Dex-AE/PEGDA hydrogel also showed a faster BSA release in a lower pH than a higher pH medium.

Synthesis and characterization of novel biodegradable unsaturated poly(ester amide)/poly(ethylene glycol) diacrylate hydrogels

AbstractA series of novel biodegradable hydrogels were designed and synthesized from four types of unsaturated poly(ester amide) (UPEA) and poly(ethylene glycol) diacrylate (PEG‐DA) precursors by UV photocrosslinking. These newly synthesized biodegradable UPEA/PEG‐DA hydrogels were characterized by their gel fraction (Gf), equilibrium swelling ratio (Qeq), compressive modulus, and interior morphology. The effect of the precursor feed ratio (UPEAs to PEG‐DA) on the properties of the hydrogels was also studied. The incorporation of UPEA polymers into the PEG‐DA hydrogels increased their hydrophobicity, crosslinking density (denser network), and mechanical strength (higher compressive modulus) but reduced Qeq. When different types of UPEA precursors were coupled with PEG‐DA at the same feed ratio (20 wt %), the resulting hydrogels had similar Qeq values and porous three‐dimensional interior morphologies but different Gf and compressive modulus values. These differences in the hydrogel properties were correlated to the chemical structures of the UPEA precursors; that is, the different locations of the >CC< double bonds in individual UPEA segments resulted in their different reactivities toward PEG‐DA to form hydrogels. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3932–3944, 2005

Enhancement of mechanical properties of organosilicon thin films deposited from diethylsilane

A strong demand exists for improved low-k intermetal dielectric materials, such as organosilicons, to enhance the performance of ultralarge scale integrated circuits. Pulsed-plasma enhanced chemical vapor deposition was used to deposit organosilicon thin films from diethylsilane and oxygen. Fourier-transform infrared (FTIR) analysis showed significant organic content as well as hydroxyl and silanol moieties in the as-deposited materials. FTIR showed a complete removal of hydroxyl groups after annealing at 400°C for 1h. This removal indicates a condensation reaction between proximal hydroxyl groups leading to the formation of additional Si–O–Si linkages, which would increase both the hardness and modulus of the film. Mechanical property measurements were in accordance with this hypothesis, as both the hardness and modulus increased by over 50% after annealing. Film structure and properties were strongly dependent on the precursor feed ratio.