Two-Dimensional Amorphous Titanium Dioxide/Silver (TiO2/Ag) Nanosheets as a Surface-Enhanced Raman Spectroscopy Substrate for Highly Sensitive Detection.

For the purpose of investigating the chemical enhancement of amorphous semiconductors as well as increasing the sensitivity of the surface-enhanced Raman spectroscopy (SERS) substrate, titanium dioxide (TiO2) precursors were calcined at different temperatures to generate crystallized TiO2 (c-TiO2) and amorphous TiO2 (a-TiO2) nanosheets, respectively. Afterward, a two-dimensional (2D) a-TiO2/Ag nanosheet SERS substrate was successfully fabricated using electrostatic interaction between a-TiO2 and Ag nanoparticles. In order to demonstrate a greater SERS sensitivity on a-TiO2/Ag compared to either c-TiO2 or Ag nanoparticles alone, the SERS probe molecules rhodamine 6G (R6G) and malachite green (MG) were utilized. Based on the results of SERS detections for probe molecules and contaminants, it demonstrates that a-TiO2/Ag nanosheets produce highly sensitive and repeatable Raman signals. The detectable concentration limits for R6G and MG were found to be 10-11 M and 10-10 M, respectively. And it has been determined that the system exhibits an enhancement factor (EF) of up to 1 × 108. The limit of detection for 4-mercaptobenzoic acid and alizarin red can both reach 1 × 10-8. Furthermore, a finite-difference time-domain simulation is performed in order to evaluate the magnetic field strength generated by Ag nanoparticles. As a result of the simulation, it is evident that the actual EF is smaller than the calculated one, leading support to the view that a-TiO2 nanosheets have a beneficial effect on the chemical enhancement of SERS.

Self-Assembled Three-Dimensional Polyamide/Silver Nanoparticle Pore Array as a Highly Sensitive and Reproducible SERS Substrate for Pesticide Detection in Water.

In this study, silver nanoparticles (AgNPs) are self-assembled onto the polyamide (PA) pore array through hydrogen bonding, resulting in and optimizing the PA/Ag 3D pore array substrates. The best surface-enhanced Raman scattering (SERS) substrate is obtained with a pore depth of 500 nm in the PA array, 30 nm AgNPs, at a pH of 5.0, and a 24 h assembly time. The SERS performance of the substrates is assessed using rhodamine 6G (R6G) as a probe molecule. The detection limit of the R6G molecule reaches 10-13 M, and the relative standard deviation is under 20%, indicating good enhancement ability and reproducibility. Furthermore, label-free detection of pesticide contaminant diquat with a detection limit of 2.69 × 10-9 M is achieved using the optimized 3D substrate, which meets environmental monitoring requirements for drinking water. The findings demonstrate that this 3D SERS substrate has promising potential for use and development in the fields of contaminant detection and chemical sensing.

Glucose sandwich assay based on surface-enhanced Raman spectroscopy.

A facile and sensitive glucose sandwich assay using surface-enhanced Raman scattering (SERS) has been developed. Glucose was captured by 3-aminopheyonyl boronic acid (APBA) modified Ag nanoparticles decorated onto a polyamide surface. Then, Ag nanoparticles modified with 3-amino-6-ethynylpicolinonitrile (AEPO) and APBA were used as SERS tags. APBA forms specific cis-diol compounds with glucose molecules avoiding interference by other saccharides and biomolecules in urine enabling its selective detection. As the actual Raman reporter, AEPO exhibited a distinctive SERS peak in the Raman silent region, thus increasing the sensitivity of the glucose detection to 10-11 M. Additionally, the developed SERS assay was reusable, and its applicability in artificial urine samples demonstrated future clinical utility confirming the potential of this innovative technology as a diagnostic tool for glucose sensing.

The antibacterial activity and mechanism of imidazole chloride ionic liquids on Staphylococcus aureus.

Ionic liquids (ILs) have garnered increasing attention in the biomedical field due to their unique properties. Although significant research has been conducted in recent years, there is still a lack of understanding of the potential applications of ILs in the biomedical field and the underlying principles. To identify the antibacterial activity and mechanism of ILs on bacteria, we evaluated the antimicrobial potency of imidazole chloride ILs (CnMIMCl) on Staphylococcus aureus (S. aureus). The toxicity of ILs was positively correlated to the length of the imidazolidinyl side chain. We selected C12MIMCl to study the mechanism of S. aureus. Through the simultaneous change in the internal and external parts of S. aureus, C12MIMCl caused the death of the bacteria. The production of large amounts of reactive oxygen species (ROS) within the internal parts stimulated oxidative stress, inhibited bacterial metabolism, and led to bacterial death. The external cell membrane could be destroyed, causing the cytoplasm to flow out and the whole cell to be fragmented. The antibacterial effect of C12MIMCl on skin abscesses was further verified in vivo in mice.

Fabrication of an Ag-based SERS nanotag for histamine quantitative detection.

A crucial issue in analytical science and physiology is the detection of histamine with high sensitivity, specificity and credibility, which served as an important neurotransmitter in biofluids. Despite the high sensitivity of surface-enhanced Raman spectroscopy (SERS) at the level of single molecule, there are still challenges in providing high sensitivity for histamine with a small cross section. For the selective detection of histamine using SERS, a highly sensitive sandwich structure substrate combining Fe3O4 and an Ag-based SERS nanotag was developed. The Fe3O4@SiO2-COOH served as a capture component for enriching histamine. Upon functionalized Ag nanoparticles with glycine (Gly) and (3-Aminopheyonyl) boronic acid (APBA), they were then used to connect with histamine and serve as a SERS nanotag, respectively. A linear relationship between the Raman intensity and the histamine concentration was observed over the range 10-4-10-8 M with a limit of detection of 7.24 × 10-9 M. This methodology also exhibited good selectivity in the presence of other neurotransmitters. With our new approach, histamine can be detected sensitively and reliably in fish samples, which indicates the potential prospect of an effective method for analyzing histamine in complex specimens.

Synthesis and properties of high performance thermoplastic polycarbonate polyurethane elastomers through a non-isocyanate route.

Thermoplastic polycarbonate polyurethane elastomers (TPCUEs) are synthesized through a solvent-free non-isocyanate melt polycondensation route. The route starts with the synthesis of 1,6-bis(hydroxyethyloxycarbonylamino)hexane (BHCH) from ethylene carbonate and 1,6-hexanediamine, and then the TPCUEs are prepared by the melt polycondensation of BHCH and polycarbonate diols (PCDLs). The TPCUEs are characterized by GPC, FT-IR, 1H NMR, XRD, AFM, DSC, TGA and tensile testing. The TPCUEs prepared have linear structures and high molecular weights, with Mn over 3.0 × 104 g mol-1. And these TPCUEs exhibit excellent thermal and mechanical properties, with T g ranging from -18 to -1 °C, T m ranging from 93 to 122 °C, T d,5% over 240 °C, tensile strength between 28.1-47.3 Mpa, elongation at break above 1000%, Young's modulus between 13.8-32.7 Mpa and resilience at 200% fixed-length between 70-90%, which makes them a promising alternative to products synthesized through the isocyanate route. In addition, the effects of the hard segment contents and the molecular weights of soft segment on the properties of TPCUEs are researched.

MIL-53(Al) catalytic synthesis of poly(ethylene terephthalate).

Poly(ethylene terephthalate) (PET) is one of the world's five major engineering plastics and is widely used in various fields. At present, the main catalysts used in the synthesis of PET are antimony, titanium, and aluminum metal compounds. Among them, antimony-based catalysts are poisonous and the titanium-based catalyst products are relatively yellow in hue. The aluminum-based catalyst has the advantages of low price and environmental friendliness, but current research shows that the organoaluminum catalyst has the problem of hydrolysis, and MIL-53 (Al) has good stability and will not affect the environment, so we add a catalyst before the esterification reaction, and uses thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscope (SEM), and N2 low-temperature physical adsorption characterizes the thermal stability and structure of MIL-53(Al). At the same time, the effects of different content, polycondensation time, before and after activation and polycondensation temperature on the properties of PET were investigated. The research results show that when the molar content of catalyst is 0.05% and the reaction temperature is 280 °C for 150 min, the product obtained is relatively excellent. The catalytic activity has almost no effect before and after activation, indicating that the polycondensation reaction is carried out on the surface of the catalyst. Therefore, MIL-53 (Al) has great potential in PET industrial catalysis.

Highly active Ce, Y, La-modified Cu/SiO2 catalysts for hydrogenation of methyl acetate to ethanol.

Rare earth element (Ce, Y, and La) modified Cu/SiO2 catalysts via hydrolysis precipitation and impregnation method were fabricated for the vapor-phase hydrogenation of methyl acetate to ethanol. LaO x showed the most pronounced promotion in the catalytic tests. After detailed characterizations, via N2 adsorption-desorption, XRD, N2O chemisorption, FTIR, H2-TPR, H2-TPD, TEM, XPS, and TG/DTA, we found that the addition of promoter LaO x can decrease the particle size while in turn, it can increase the dispersion of copper species. The strong interactions between copper and lanthanum atoms alter the surface chemical states of the copper species. This results in the generation of more Cu+ species and high S Cu + values, which are responsible for the excellent activity and stability during hydrogenation. In addition, the content of additive LaO x and reaction conditions (reaction temperature and LHSV) were optimized. Then, the long-term stability performance was evaluated over the selected catalyst in contrast with Cu/SiO2.

Qualitative and Quantitative Analysis of the Product and By-Products from Transesterification between Phenol and Dimethyl Carbonate.

By-products (phenyl salicylate, phenyl 4-hydroxybenzoate, and xanthone) from transesterification between phenol and dimethyl carbonate (DMC) were qualitatively analyzed by gas chromatography-mass spectrometry, and a gas chromatographic method with directed injection for simultaneous quantitative analysis of the product (DPC) and by-products of the transesterification has been established. Based on the results of qualitative and quantitative analyses, the mechanism of the by-products generation was preliminarily deduced. The sample for quantitative analysis was directly diluted in acetone, and related compounds were separated on an HP-5 capillary column and detected by a hydrogen flame ionization detector (FID). The product and by-products were well separated, the correlation coefficients (r) within the concentration range of 1.0 µg/mL-100 µg/mL were ≥0.9997, the relative standard deviations were between 0.5% and 4.4%, spiked recoveries were between 91.5% and 105.6%, and detection limits were between 0.11 and 0.18 µg/mL. The established method is simple, rapid, accurate, sensitive, and highly specific. It is suitable for simultaneous qualitative and quantitative analyses of the product and by-products of transesterification between phenol and DMC.

Highly effective transformation of methyl phenyl carbonate to diphenyl carbonate with recyclable Pb nanocatalyst.

Diphenyl carbonate (DPC) is a type of versatile industrial chemical, and the disproportionation of methyl phenyl carbonate (MPC) is a key step to produce DPC. However, the design and formulation of a catalyst for the efficient synthesis of DPC is a major challenge due to its small equilibrium constant. The support material is a critical factor influencing the performance of Pb nanocatalysts. Thus, a series of Pb-based catalysts over MgO, ZrO2, SiO2, TiO2 and Al2O3 were prepared to investigate the effect of the support materials on the physicochemical properties and catalytic performances for the conversion of MPC to effectively synthesize DPC. The catalysts were well characterized by XRD, BET, TEM, XPS, ICP-OES, H2-TPR, Py-IR and NH3-TPD. The results showed that the nature of the support obviously affected the structural properties and catalytic performances, and Pb was dispersed better on SiO2, TiO2, ZrO2 and MgO than on Al2O3, and showed stronger metal-support interaction over MgO and ZrO2. The activity results revealed that PbO/MgO and PbO/ZrO2 exhibited higher catalytic activities because they contained higher Pb dispersion and more Lewis acid sites, and the catalytic activities followed the order PbO/MgO > PbO/ZrO2 > PbO/SiO2 > PbO/Al2O3 > PbO/TiO2. On the contrary, PbO/MgO and PbO/ZrO2 exhibited better reusability due to strong interaction between the highly dispersed Pb and the supports, and the activity decrease in the case of PbO/SiO2, PbO/Al2O3 and PbO/TiO2 mainly resulted from the Pb leaching loss. This work would contribute to exploiting novel catalytic materials in a wide range of applications for the efficient synthesis of organic carbonates.

Influence of coordinating groups of organotin compounds on the Fries rearrangement of diphenyl carbonate.

In this paper, the Fries rearrangement of diphenyl carbonate (DPC) catalyzed by organotin compounds with different coordination groups was studied for the first time. The electronic effect and steric hindrance of the coordinating groups were discussed with respect to the reactivity of DPC rearrangement. The results showed that both the electronic effect and steric hindrance of the coordinating groups influenced the acidity of the active tin centers and then affected the catalytic performance of organotin as a Lewis acid for the rearrangement of DPC, and the influence of the electronic effect is greater than that of steric hindrance. The catalytic activity is in the order of BuSnO(OH) > Bu2SnO > Bu2Sn(OCOC11H23)2 > BuSnCl3 > Bu3SnOSnBu3 > Bu3SnCl, and Bu2SnO showed the best catalytic activity due to its strong electron absorption effect, small steric hindrance, and good stability. Under the optimum reaction conditions, the conversion of DPC was up to 93%, and the yields of phenyl salicylate (PS) and xanthone (XA) were 62% and 28%, respectively. In addition, a reaction mechanism of DPC rearrangement catalyzed by the organotin compounds was speculated. This research can provide vigorous theoretical data support to control the byproducts produced by DPC rearrangement in the process of DPC synthesis. It also provides a new route for the preparation of PS and XA.

Preparation of polycarbonate diols (PCDLs) from dimethyl carbonate (DMC) and diols catalyzed by KNO3/γ-Al2O3.

γ-Al2O3 loaded with potassium nitrate (KNO3/Al2O3) catalysts were prepared, characterized and employed as a type of heterogenous solid base catalyst in the synthesis of polycarbonate (1,4-butane carbonate)-diol (PBC-OH) via the transesterification of dimethyl carbonate (DMC) and 1,4-butanediol (BD). The relationship between physicochemical properties and catalytic performance for KNO3/Al2O3 in this transesterification reaction was investigated using various techniques. The results demonstrated that the performance of KNO3/Al2O3 catalysts was highly influenced by basic site amount and strength. The medium and strong basic sites were beneficial for this reaction. The catalyst with a KNO3 loading of 35% and a calcination temperature of 700 °C exhibited the best catalytic activity due to its highest basic site amount and appropriate base strength. The highest BD conversion and PBC-OH yield of 80.2% and 68.4% were obtained under optimal reaction conditions. Also, this solid base catalyst was successfully employed in the synthesis of copolycarbonate diols from DMC and two different diols. Different scanning calorimetry results indicated that the thermal properties of the copolycarbonate diols can be adjusted by regulating the average segment lengths, M n and copolymer composition structure.

Photolysis kinetics and influencing factors of bisphenol S in aqueous solutions.

The photodegradation of bisphenol S (BPS) in aqueous solutions was studied under different conditions. Photolysis and kinetics were investigated, as were the photolysis mechanism and the influences of initial pH value, light source, and environmental substances in water. The results showed that the photolysis of BPS occurred under UV light, and the rate increased with light source intensity. The photolysis of 5.0-50.0 mg/L BPS in water followed first-order kinetics: the rate was gamma = 0.0161C(BPS) under a 40-W UV-lamp, and the degradation half-life was 43.1 min. Due to its absorption of light, direct photolysis of BPS was a predominant pathway for BPS but was not obviously affected by reactive oxygen species. The results confirmed that the photolysis rates of BPS in alkaline water solution were faster than those in acidic and neutral water solution because of the ionization of BPS. The photodegradation rate of BPS increased in the presence of chloride and ferric ions, while the rate was inhibited by nitrate and phosphate in aqueous solution.

[Monitoring the synthesis of N,N-diphenyl urea by IR-online].

IR-online detector, React IRTM 4000, was used to monitor the synthesis of N,N-diphenyl urea from urea and aniline. The concentration changes of the reaction components were obtained according to the characteristic IR absorbance changes of the reactants (urea and aniline) at 1 420 and 1 270 cm(-1) respectively, the intermediate product (monophenylurea) at 1 339 cm(-1) as well as the product (N,N-diphenyl urea) at 1 312 cm(-1). In the present study, the result showed that the synthesis of N,N-Diphenyl urea was carried out by two steps. Firstly, the intermediate product monophenylurea was synthesized from urea and aniline, and then N, N-diphenyl urea was obtained by the reaction of monophenylurea with aniline. It was also shown that the IR-online detector was a fast, simple and exact technique to optimize the reaction time and so the reaction course could be easily controlled. The result of IR-online spectrometry was approved by offline reference high performance liquid chromatography (HPLC) method. As a result, the IR-online spectrometry was superior to HPLC method since it was a nondestructive method without the need to sample the reaction medium.

Kinetics and adsorption behavior of carboxymethyl starch on alpha-alumina in aqueous medium.

The adsorption of carboxymethyl starch (CMS) at the alpha-alumina/aqueous solution interface has been investigated through adsorption studies, electrokinetics mobility measurements, and FTIR spectroscopy. Zeta potential measurements show that the addition of CMS results in a more dramatic increase in the absolute zeta potential in the alkaline region, as well as a shift of the isoelectric point to lower values, indicating the adsorption of CMS from the aqueous solution onto the alumina surface. The positive hydrophilic surface sites of alumina are responsible for the adsorption of CMS molecules. The adsorption of CMS is possible after charge reversal by the addition of excess CMS. Nearly 30 min of contact time are found to be sufficient for the adsorption of CMS to reach equilibrium. CMS adsorption follows a Langmuir isotherm with adsorption capacities of 91.74 mg CMS per gram of alpha-alumina. For the adsorption of CMS, pseudo-second-order chemical reaction kinetics provides the best correlation with the experimental data. FTIR analysis indicated that CMS forms outer complexes with alumina surfaces depending on the shifting of the asymmetric and symmetric bands.