Charging characteristics of long distance accumulator for underwater electro-hydraulic control system.

Long distance accumulators are widely used in underwater electro-hydraulic control systems. However, as the working depth increases, the underwater umbilical cable becomes longer. The actual physical properties of the gas in the accumulator change. These factors affect the charging characteristics of the accumulator. To address the above issues, a simulation model of the charging of the long distance accumulator under real operating conditions is developed. Among them, the real properties of the gas inside the accumulator were calculated using the Redlich-Kwong-Soave method. The coefficient of friction within the umbilical cable is based on the Reynolds number and relative roughness. The simulation data were compared with the experimental results in the South China Sea to verify the accuracy of the simulation model. The effects of key factors on the charging characteristics of the long distance accumulators were also analyzed. The results show that the simulation results are in good agreement with the experimental results. The law of accumulator charging was analyzed: the greater the pressure of the gas source, the smaller the accumulator charging time; the greater the working water depth, the shorter the accumulator charging time. The research provides guidance for the design of long distance accumulators.

Preparation of Carbon Dots from PET Waste by One-step Hydrothermal Method and its Application in Light Blocking Films and LEDs.

An environmentally friendly PET-based Carbon Dots (PET-CDs) with excellent fluorescence properties were prepared with waste PET bottle, pyromellitic acid and ammonia water as raw materials by one-step hydrothermal method. The preparation mechanism of PET-CDs was as follows: PET first underwent ammonolysis reaction to produce terephthalic acid diamide and ethylene glycol, and then dehydrated and carbonized with pyromellitic acid to form PET-CDs. The as-prepared PET-CDs exhibit excitation-independent emission properties in the range from 340 to 440 nm, and the fluorescence quantum yield is as high as 87.36%. In terms of structure, PET-CDs is a spherical structure with an average particle size of 2.0 nm, and its surface contains carboxyl and amino groups. The PET-CDs were dispersed in a PVA matrix to obtain an light blocking films(LBFs) for 250-450 nm light with excellent properties, and its transparency for 450-700 nm light is good. In addition, PET-CDs was used in the fields of LED, and it was found that the color coordinate for the LED assembled with PET-CDs and 395 nm LED chips is (0.55, 0.44) and the correlated color temperature is 2018 K.

Solvothermal preparation of nitrogen-doped carbon dots with PET waste as precursor and their application in LEDs and water detection.

Developing novel, alternative ways to recycle PET waste, which has an important influence on reduction of landfilling and CO2 emissions, has always been a research hot spot for industry and academy. In this work, PET waste was adopted as precursor for the preparation of nitrogen-doped Carbon Dots (NCDs). Firstly, PET oligomers were obtained by alcoholysis of PET waste with ethylene glycol. Then, the mixture without isolation and purification as well as pyromellitic acid dianhydride and urea were adopted as precursors for the preparation of NCDs by solvothermal method with tetrahydrofuran (THF) as solvent. The as-prepared NCDs has a spherical structure with an average particle size of 2.3 nm. What is more, NCDs exhibit excitation-independent emission properties, the largest excitation peak and emission peak of NCDs located in 360 nm and 470 nm, and the fluorescence quantum yield is 48.16 %. In term of application, NCDs are dispersed in PMMA and loaded on 365 nm and 430 nm LED chips to obtain LED devices emitting yellow light ((0.55, 0.44), 2018 K) and warm white light ((0.37, 0.31), 3783 K), respectively. In addition, NCDs could be adopted as fluorescent probe for the construction of sensor for water in organic solvents based on dynamic quenching of NCDs, and the limit of detection (LOD) is 0.00001 %.

Mechanical, Thermal Stability, and Flame Retarding Properties of Phosphorus-Modified PET Blended with DOPO-POSS.

In this study, an antidroplet flame retardant system based on FRPET (phosphorus-containing copolyester) is constructed with DOPO-POSS (polyhedral oligomeric silsesquioxane containing DOPO) as an additive flame retardant. It is demonstrated that DOPO-POSS has good dispersibility at a lower amount. When the amount of DOPO-POSS is 9 wt %, the residual char of DOPO-POSS/FRPET at 700 °C increases to 23.56 from 18.16% of FRPET, and the maximum thermal weight loss rate also reduces. What is more is that the limiting oxygen index increases to 33 from 26% of FRPET. The flame burning time is shortened to 4.95 from 20.8 s, the phenomenon of self-extinguishing of the fire occurs, and the vertical combustion level is increased from V-2 to V-0. Compared with FRPET, the peak of the heat release rate decreases by 66.0%, the total heat release decreases by 32.4%, the flame retardancy index (FRI) reaches an excellent value, and the condensed-phase products significantly improve. The Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy-energy dispersive X-ray spectrometry (SEM-EDX), thermogravimetric-FTIR (TG-FTIR), and pyrolysis-gas chromatograph/mass spectrometry (Py-GC/MS) results indicate that DOPO-POSS contributes to the formation of char layers and decomposes to generate free radicals with a quenching effect. In a word, DOPO-POSS is an effective radical trapper and charring agent for PET and exerts a flame retardancy effect in gaseous and condensed phases simultaneously.

Preparation of Carbon Dots with Ultrahigh Fluorescence Quantum Yield Based on PET Waste.

Environmentally friendly polyethylene terephthalate-based carbon dots (PET-CDs) with ultrahigh fluorescence quantum yield were prepared with waste PET textiles as raw materials. First, oligomers were prepared from the reaction of waste PET textile and ethylene glycol by the microwave method. Then, the mixture without isolation and purification as well as pyromellitic acid and urea were adopted as precursors for the preparation of PET-CDs by the hydrothermal method. It was found that the as-prepared PET-CDs had a spherical structure with an average particle size of 2.8 nm. The carbon core of PET-CDs was a graphene-like structure doped with nitrogen atoms in the form of pyrrole nitrogen and the surface contained -NH2, which is convenient for modification and functionalization with various materials in the form of chemical bonds. The as-prepared PET-CDs exhibit excitation-independent emission properties in the range from 340 to 440 nm, and the best excitation and emission wavelengths of PET-CDs are 406 and 485 nm, respectively, while the fluorescence quantum yield is 97.3%. In terms of the application, the as-prepared PET-CDs could be adopted as a fluorescence probe for the detection of Fe3+, and the limit of detection is as low as 0.2 µmol/L. The mechanism of PET-CDs by Fe3+ was found to be the static quenching mechanism. In addition, PET-CDs can be used in LEDs and fluorescent anticounterfeiting.

High-Temperature-Resistant, Clean, and Environmental-Friendly Fracturing Fluid System and Performance Evaluation of Tight Sandstone.

Hydraulic fracturing, as an oil-water well stimulation and injection technology, is particularly important in the production and stimulation of low-permeability oil and gas fields, and the performance of the fracturing fluid directly affects the success of the fracturing operation. Compared with traditional water-based fracturing fluids, clean fracturing fluids have the advantages of strong sand-carrying ability and easy gel breaking with no residue. Aiming at the problem of poor temperature resistance and shear resistance of the clean fracturing fluid, based on previous research, this paper selects a high-temperature-resistant clean fracturing fluid system and evaluates the performance of the system. The research results show that the system has better rheological properties, better sand-carrying performance, shorter gel-breaking time, and less damage to the reservoir.

Simultaneously Enhancing the Fire Retardancy and Heat Resistance of Stereo-Complex-Type Polylactic Acid.

Polylactic acid (PLA) is considered to be the material with great application potential in the 21st century which has aroused wide research interest. However, PLA is a highly flammable material and exhibits low heat distortion temperature, which greatly limits its application in many fields. In this work, aluminum diethyl phosphinate (ADP) and poly (d-lactic acid) (PDLA) are used to improve fire retardancy and heat resistance of poly (l-lactic acid) (PLLA). PLLA/PDLA with the presence of 15 wt % ADP exhibited the limiting oxygen index (LOI) value at 26%, and the peak heat release rate (pHRR) and total heat release decreased, respectively, by 14.03 and 24.42% from 500 to 429 kW/m2 and 86 to 65 MJ/m2. The melt dripping phenomenon was suppressed obviously. The addition of ADP realized the flame-retardant effect from both the condensed phase and gas phase. Moreover, the results showed that the addition of ADP promoted the formation of stereo crystals and increased the crystallization temperature to 175 °C. The heat distortion temperature (HDT) of the PLLA/PDLA sample with 15 wt % ADP can be as high as 170.4 °C, which marks significant improvement in the heat resistance of PLA. The mechanical property test results showed that ADP has little effect on the mechanical properties of the composites. This work opens a window to realize the heat-resistant and anti-dripping fire-retardant PLA.

Simple and Green Synthesis of Carbonized Polymer dots from Nylon 66 Waste Fibers and its Potential Application.

Carbonized polymer dots (CPDs) have attracted widespread attention owing to their unique properties and are usually prepared from monomers of polymers or polymers. To reduce the waste of high-value petropolymers and environmental pollution, a simple and green method for the preparation of CPDs using a hydrothermal technique based on the cross-linking enhanced emission effect was proposed, in which nylon 66 waste fibers were used as a precursor and glutaraldehyde as a cross-linking agent. The as-prepared CPDs possessed polymer/carbon hybrid structures with a 3.5 nm average diameter, and hydroxyl (-OH), carboxyl (-COOH), and amino (-NH2) groups were present on the surface of CPDs. It can be found that the as-prepared CPDs display excitation-dependent photoluminescence emission, which is mainly attributed to the molecular state luminescence center. Because the molecular state fluorescence of CPDs could be affected by the presence of Fe3+ and the change of pH values, the as-prepared CPDs can be used as a probe for the detection of the concentration of Fe3+ and the pH variations of solution. The fluorescence intensity of CPDs was selectively quenched by Fe3+ in the range from 1 to 145 µM. In virtue of the static quenching of CPDs by Fe3+, a sensing system was fabricated for the quantitative detection of Fe3+, and its limit of detection was 0.1 µM. Based on the electrostatic doping/charging of CPDs, a pH sensor was fabricated. It showed that the fluorescence intensity of CPDs decreased along with the increase of pH from 2.60 to 12.6. What is more, the CPDs were found to be an alternative to traditional fluorescent inks for encryption and information storage.

One-step preparation of red-emitting carbon dots for visual and quantitative detection of copper ions.

A one-step solvothermal method for the preparation of carbon dots with red fluorescence (R-CDs) was put forward, in which sodium citrate and formamide were chosen as precursors, while formamide was adopted as the solvent. The fluorescence emission peak of the as-prepared R-CDs remained the same (600 nm) when the excitation wavelength increased from 490 nm to 560 nm, and the fluorescence quantum yield is 35.3%. Furthermore, the fluorescence intensity of the as-prepared R-CDs could be selectively quenched by copper ions, and the mechanism of Cu2+ quenching R-CDs is the combination of static and dynamic quenching. As a result, the R-CDs were applied for the construction of a fluorescent sensor without any modification for the quantitative and visual detection of copper ions, which is a typical contaminant in water. The limit of detection for the fluorescent sensor was as low as 5 nmol/L, and it can be used to fast and directly confirm whether the content of copper ions in drinking water meets the criteria of the United States Environmental Protection Agency and the World Health Organization.

Author Correction: Creep in Primary Consolidation with Rate of Loading Approach.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Creep in Primary Consolidation with Rate of Loading Approach.

The debate on creep in primary consolidation is analysed with a power law model following an approach in which creep is considered as rate of loading. According to this approach, primary consolidation is one type of rate of loading. To verify this approach, two types of tests, standard oedometer test and oedometer test with drainage prevented, are conducted on three types of soils (two from NGES and the other from Port of Guangzhou). The result: creep exponents obtained from two kinds of tests agree well with each other. Moreover, the approach is further validated by tracking, for over 80 years, the data from settlement of the case history San Jacinto Monument, which is inconsistent with data calculated from the classical method. In the end, procedure of this approach, with which long term settlement is predicted, is illustrated, and this approach is compared with the classical method.

Enhanced Specific Capacitance of Few-Layer MoS2 Nanosheets via SDBS-Assisted Hydrothermal Method.

Few-layer MoS2 nanosheets have been successfully synthesized by a facile anionic surfactantassisted hydrothermal approach. The as-prepared samples are characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It is found that the anionic surfactant sodium dodecylbenzene sulfonate (SDBS) plays a crucial role in the formation of MoS2 nanosheets with few layers and rich exposed edges. The electrochemical performances of the as-prepared samples are evaluated by cyclic voltammogram, galvanostatic charge-discharge and electrochemical impedance spectroscopy. Compared with the pristine MoS2 without SDBS, the MoS2 nanosheets show a high specific capacitance of 223 F g-1 and its capacitance can still maintained a stable specific capacitance of 147 F g-1 after 500 cycles at 1 A g-1. The enhancement in supercapacitors is attributed to few-layer structure and exposed active edges, which enables fast electron transportation between the electrode and electrolytes. Therefore, the MoS2 nanosheets will be a suitable candidate for electrochemical supercapacitor applications.

A sensitive fluorescent sensor for the detection of trace water in organic solvents based on carbon quantum dots with yellow fluorescence.

The quantitative analysis of trace water in organic solvents has always been a research hotspot, and it is still in the development stage and needs to be continuously developed. In this study, a facile and rapid approach was developed for the preparation of carbon quantum dots (CQDs) with yellow fluorescence emission and ultrahigh absolute fluorescence quantum yields (92.6%). Compared to traditional organic fluorescent molecules, the preparation of CQDs is simpler, faster and more environmentally friendly. It is found that the fluorescent properties of CQDs are excellent in organic solvents and could be quenched by trace water, which makes them a promising material used without any modification for the detection of water in organic solvents. As a result, the as-prepared CQDs were adopted as fluorescent probes for the detection of water in organic solvents (ethanol, tetrahydrofuran, and 1,4-dioxane). The limit of detection was as low as 0.01%. To the best of our knowledge, this is the first time that CQDs have been used as water sensing fluorescent probes in organic solvents. The possible mechanism for trace water detection of the as-prepared CQDs in organic solvents is attributed to the specific water-fluorophore interaction and partially to the increase in polarity of the solvent caused by an increase in water concentration.

A sensitive biosensor for the fluorescence detection of the acetylcholinesterase reaction system based on carbon dots.

The carbon dots (C-dots) with high fluorescence quantum yield were prepared using hydrothermal method. C-dots have been adopted as probes for the fluorescence turn-off detection of H2O2 based on the special sensibility for the hydroxyl radical. And then the biosensors for the detection of substrate and enzymes activities were established in the acetylcholinesterase reaction system, which were related to the production of H2O2. Specifically, the proposed fluorescent biosensor was successfully applied to detect the concentration of choline (in the range from 0.025 to 50 µM) and acetylcholine (in the range from 0.050 to 50 µM), and the activity of choline oxidase (in the range from 1 to 75 U/L) and acetylcholinesterase (1 to 80 U/L). These results showed a sensitive, universal, nontoxic and eco-friendly detecting technique has been developed.

Preparation of electrophoretic nanoparticles for electronic paper.

As an electronic alternative for printed media, the E-paper has ultralow power consumption, reduced eyestrain, high contrast ratio. Electrophoretic displays are one of the most promising E-paper technologies, which are now widely used in consumer products. The properties of the electrophoretic display are mainly determined by the composition, size, light scattering properties, and density of the electrophoretic nanoparticles. First, we introduce the preparation of white and black electrophoretic nanoparticles, because the monochrome E-paper has achieved commercial success. Then the structure and properties of color electrophoretic nanoparticles for color E-paper products are discussed. In addition, the enhanced and novel electrophoretic nanoparticles are now propelling the development of next-generation E-paper with new applications. Finally, the active area of the preparation of electrophoretic nanoparticles is highlighted in terms of the development of future E-paper.

Synthesis of ultra-stable fluorescent carbon dots from polyvinylpyrrolidone and their application in the detection of hydroxyl radicals.

Highly biocompatible and highly photostable fluorescent carbon dots (C dots) were obtained through a simple and nontoxic one-pot hydrothermal method. Polyvinylpyrrolidone, a common and low-cost biocompatibility reagent, was used as the only carbon source for the first time. The resulting water-soluble C dots showed a quantum yield of up to 23.58% with low cytotoxicity, favorable photoluminescent properties, and good photostability. Importantly, the fluorescence intensities of the C dots were quite stable in high-salt conditions and over a broad pH range (3.0-10.5). The as-prepared C dots have been demonstrated to be an excellent probe for hydroxyl radicals sensing based on the fluorescence quenching with great sensitivity and specificity. This opens up a new application field for C dots.

Fluorescent carbon dots for biolmaging and biosensing applications.

Due to the excellent biocompatibility, carbon dots (CDs), which are attracting considerable attention as new quantum-sized carbon-containing fluorescent nanoparticles, are becoming both an important class of imaging probes and a versatile platform for biosensors. In the process of transferring carbon dots from proof-of-concept studies to real bioimaging and biosensing applications, major advances have already been made in their synthesis, structure, properties, mechanism of fluorescence, and evaluation of biocompatibility and bio-applications. This review aims to summarize the recent developments and trends in carbon dots. Investigations of preparation methods, fluorescent properties and applications as biosensors and in bioimaging for carbon dots are described. In addition, this review highlights on the design and construct of a carbon dot fluorescent ratiometric biosensing platform for the detection of enzymatic activity, substrate and inhibitor concentrations related to the production or consumption of H2O2. This review provides perspectives on future opportunities and the remaining challenges confronting this research field.

An eco-friendly, simple, and sensitive fluorescence biosensor for the detection of choline and acetylcholine based on C-dots and the Fenton reaction.

A simple and novel method is proposed for the preparation of Carbon dots (C-dots) with excellent properties. We firstly demonstrated that the fluorescence of C-dots decreased apparently in the presence of H2O2 and Fe(2+). Based on the this finding, C-dots are successfully adopted as probes for the detection of H2O2. After the experimental conditions are optimized, the limit of detection (LOD) for H2O2 is found to be 0.1 µM. Furthermore, we established an eco-friendly, simple and sensitive biosensor for the detection of choline and acetylcholine (ACh) based on the detection of H2O2 using C-dots as probes. The detection limit for choline is 0.1 µM and the linear range is 0.1-40 µM. The detection limit for ACh is found to be 0.5 µM and the linear range is 0.5-60 µM. The excellent performance of the proposed biosensor shows that this method possesses the potential for practical application.

An overview on the pharmacokinetics of quantum dots.

Recent developments in nanotechnology have paved the way for using quantum dots (QDs) in nanodiagnostics and nanotherapeutics. Careful design and preparation of QDs are guided by these application-specific requirements. QDs will probably be one of the first nanomaterial to reach clinical applications, however many challenges in this field have yet to be overcome. In this article, we present an extensive review of the pharmacokinetic properties of QDs. The representative studies responsible for observing quantitative determination of QDs biodistribution in vivo are presented. The effects of size, surface chemistry, and target moiety on their pharmacokinetics are discussed. Finally, future directions for improving the pharmacokinetics of QDs and perspectives in the field are discussed. The understanding of its absorption, distribution, metabolism, and excretion from the body will provide important guidelines for the successful clinical use of QDs.

A new amperometric glucose biosensor based on one-step electrospun poly(vinyl alcohol)/chitosan nanofibers.

In this work, a new glucose amperometric biosensor was developed by directly electrospinning poly(vinyl alcohol)/chitostan nanofibers on the surface of the platinum electrode, in which glucose oxidase (GOD) was effectively immobilized in nanofibers by encapsulation. After been cross-linked in glutaraldehyde vapor and modified with a thin nafion film, the nanofibers (PVA/chitosan/GOD)/nafion electrode was used for glucose amperometric measurements. The electrospun nanofibrous enzyme membrane served as a better sensing element than the casing one due to the unique properties of nanofibers such as the special three-dimensional network structure, large pores, high porosity, and large surface to volume ratios. The as-prepared biosensor showed a wide linear calibration range, low detection limit, and low apparent Michaelis-Menten constant in the glucose determination. The stability, reproducibility and anti-interference capability of biosensor were also presented. Furthermore, the new biosensor was successfully applied to detect glucose in human serum samples.