Abstract

1. Introduction

2. Experimental

3. Results and discussion

4. Conclusion

Conflict of Interest

Supplementary Information

References

Abstract

     This study investigates the effect of graphene oxide (GO) on the mechanical and corrosion behavior, antibacterial performance, and cell response of Mg—Zn—Mn (MZM) nanocomposite. MZM/GO nanocomposites with different amounts of GO (i.e., 0.5wt%, 1.0wt%, and 1.5wt%) were fabricated by the semi-powder metallurgy method. The influence of GO on the MZM nanocomposite was analyzed through the hardness, compressive, corrosion, antibacterial, and cytotoxicity tests. The experimental results showed that, with the increase in the amount of GO (0.5wt% and 1.5wt%), the hardness value, compressive strength, and antibacterial performance of the MZM nanocomposite increased, whereas the cell viability and osteogenesis level decreased after the addition of 1.5wt% GO. Moreover, the electrochemical examination results showed that the corrosion behavior of the MZM alloy was significantly enhanced after encapsulation in 0.5wt% GO. In summary, MZM nanocomposites reinforced with GO can be used for implant applications because of their antibacterial performance and mechanical property.

Introduction

     Currently, because magnesium (Mg) alloys have more benefits than common metallic materials, ceramics, and biodegradable polymers, their biomedical applications have been increasing. In terms of mechanical features, metals have higher mechanical strength and fracture toughness than ceramics or polymers; thus, metals are more appropriate for load-bearing usages than ceramics or polymers [1–2]. The density of human cortical bone (1.75 g/cm3 ) is similar to the density of Mg (1.738 g/cm3 ) and Mg alloys (1.75–1.85 g/cm3 ) but lower than the density of biomedical titanium alloy Ti6Al4V (4.47 g/cm3 ) [3–4]. In terms of biocompatibility, certain amounts of Mg ions in the human body are connected with many metabolic reactions and biological mechanisms [5–6]. Mg alloys are suitable orthopedic and cardiovascular implants because further surgery to remove them is not needed [7–8]. However, an important drawback of Mgbased implants is that they do not have good resistance against corrosion in physiological environments [9]. Mechanical strength could be significantly reduced by rapid and uncontrollable corrosion processes, which leads to premature failure [10]. Moreover, the health of patients who have such implants could be at risk because of the evolution of hydrogen gas and alkalinization of the environments close to the interface between implant and tissue [11]. Therefore, to achieve the secure deployment of biomedical devices, the degradation/corrosion rate of Mg alloys needs to be controlled [12]. In this context, several methods, such as alloying, powder metallurgy (PM), and surface modification strategies, have been used in an extensive number of studies that aimed to solve the problem of corrosion in Mg alloys [13–14]. Among the best methods to enhance the corrosion resistance of porous Mg are PM processes, such as mechanical alloying [15–17].

Conclusion

     In this study, using the semi-powder metallurgy method, different contents of GO were embedded in the Mg–Zn–Mn (MZM) matrix to prepare MZM/xGO nanocomposites for orthopedic applications. The corrosion performance and the 24 20 16 12 8 4 0 0 −0.5 −1.0 −1.5 −2.0 Extension / mm MZM/GO Graphene oxide Graphene oxide Graphene oxide Graphene oxide Crack Crack (a) (c) 1.5GO 0.5GO 1GO MZM (b) MZM composite MZM/0.5GO MZM/1GO MZM/1.5GO 49 59 63 64 Compression strength / N 4820 17810 19960 9620 1.12 1.31 1.44 0.72 Force / (10 3 N) Micro hardness, HV Extension / mm Material nanocomposite Fig. 10.    (a) Typical compressive curves and (b) hardness and compressive strength values of the MZM/xGO nanocomposites; (c) schematic diagram of the crack deflection toughening mechanisms of GO in the MZM/xGO nanocomposites. S. Jabbarzare et al., Effect of graphene oxide on the corrosion, mechanical and biological properties of Mg-based … 317 mechanical and biological characteristics of the MZM/xGO nanocomposites were analyzed. The microstructural assessment showed that a uniform distribution was achieved in the MZM/0.5GO and MZM/1GO nanocomposite specimens. However, agglomeration was observed in the MZM/1.5GO nanocomposite specimen. The results showed that the GO content, hardness value, and compressive strength are positively associated. In this context, the MZM/1GO nanocomposite has higher hardness value and compressive strength than the Mg-based nanocomposite without GO. The MZM/ 0.5GO nanocomposite exhibited a nearly comparable corrosion resistance to the MZM/1GO nanocomposite, even though the incorporation of more GO has an unfavorable effect on the Rct value of the MZM matrix. The MTT assay results showed that the MZM/1GO nanocomposite increased the MG63 cell viability and ALP activity, indicating the increasing level of osteogenesis. The results of the analysis of antibacterial activity showed that the MZM/1.5GO nanocomposite had a noticeable effect on antibacterial effectiveness toward bacteria, including Salmonella–Shigella and Klebsiella pneumoniae. In summary, the results indicate the possibility of utilizing the MZM/1GO nanocomposite for implant applications with effective anti-infection characteristics.

Abstract

I. INTRODUCTION

II. EXPERIMENTAL DETAILS

III. RESULTS

IV. DISCUSSION

V. CONCLUSION

REFERENCES

Abstract

     Nanocomposites have been developed as the third-generation insulating materials. This article introduces the crosslinked polyethylene (XLPE) nanocomposite dielectric doped with a small amount of nano-hexagonal boron nitride ( h -BN), which exhibits excellent insulation properties under high dc voltage. The test results show that XLPE/ h -BN nanocomposites possess significant improvements in dc breakdown strength and 0.1 wt% nano h -BN doping can actually increase the dc breakdown strength by 39%. The space charge properties of the XLPE/ h -BN obtained by the pulsed electro-acoustic (PEA) measurements and the direct current integrated charge [DCIC- Q(t) ] measurements show that the positive homocharge injection under dc voltage is obviously suppressed, and the electrical conductivity under relatively high electric field decreases. The thermally stimulated current results show that the nano h -BN doping introduces only deep charge traps (above 1 eV) to the XLPE matrix. The trap energy is deeper than that of the original traps, and this is the main factor leading to the improvement of the dc insulation properties. Besides, the doping of h -BN does not introduce impurities or change the crystallinity of XLPE. This article presents the novel XLPE/ h -BN nanocomposites with excellent dc insulation properties and indicates the large potential of the nano h -BN-doped insulation materials.

Introduction

     NANOCOMPOSITES have excellent dielectric properties and have become the third-generation insulating materials [1]. Nano-doping can improve corona resistance and electrical tree characteristics as well as regulate dielectric properties of the polymer matrix. More importantly, the dc insulation properties can be enhanced to various degrees by inorganic nanoparticle doping, such as the suppression of the charge injection and transportation, as well as the increase of the breakdown strength. With the construction of high-voltage direct current (HVDC) transmission line in a large scale, the power industries have proposed stricter requirements on the dc insulation performance of insulating materials. Therefore,nanocomposite dielectrics may be more suitable for dc insulation systems in the future, and nanocomposite materials with higher insulation performance need to be continuously developed. For example, crosslinked polyethylene (XLPE)- based nanocomposites are expected to be used in the new generation of HVDC cable.

Conclusion

     The XLPE/h-BN nanocomposite with high dc breakdown strength and suppressed charge injection features were introduced in this study. It is useful to reach the conclusions as follows.

     1) XLPE/h-BN nanocomposite samples with loading content ranging from 0.1 to 3 wt% were prepared successfully. The dc Eb of the nanocomposite sample shows at most a 39% increase under 0.1 wt% loading.

     2) The effect of h-BN doping on the charge trap characteristics of XLPE is a significant increase in the density of deep traps, and this is the main cause for the improvement of dc insulation properties.

Abstract

     Synthesis and characterization of new polybutadiene-based polyurethane, graphene quantum dot-MnO2 nanoparticles, and relative nanocomposites were set as the aim of current artwork. For this purpose, a one-pot polymerization approach was employed in preparation of polyurethane through the reaction of amine polyol and toluene diisocyanate (TDI) in presence of DBTDL catalyst. Nanocomposites were synthesized using 1 to 3 incorporation percent of graphene quantum dot-MnO2 nanoparticles in polymer matrix. 1H-NMR and FT-IR spectroscopies confirmed successful synthesis of reaction products including graphene quantum dot-MnO2, polyurethane, and nanocomposites. UV-vis and PL spectrophotometry techniques were applied for achieving optical information of samples. Optical properties of nanocomposites were reserved properly with no great quenching. Thermal stabilities, degradation rates, and thermal characteristics of polyurethane and nanocomposites were investigated using TGA/DTG and DSC analysis. Thermal stability showed direct relationship to nanoparticle content, and 3%wt nanocomposite showed improved thermal behaviour in comparison with pure PU. SEM, XRD, and AFM techniques proved successful nanocomposite synthesis with detecting nanoparticle species and fine nanoparticle dispersion with improved topographic and morphologic characteristics making GQD-MnO2 polyurethane nanocomposites a good candidate for using in optical active and thermal stable coatings.

Introduction

     At a time when socioenvironmental problems of polluting industries are the focus of legislators, the general trend is toward the production of new products from recycled materials, especially waste materials. In the case of polybutadiene, because of most usage in tire production in crosslinked form with sulfur or carbon dioxide, it does not seem so reasonable to pay attention on polybutadiene recycling, at least until recognition of successful separation approaches. However, crude polybutadiene itself faced some issues of processability like high molecular weight, high viscosity, low solubility, and high molding that can be solved for usage in wide speared areas with chain modification [1–4].

      Based on a common belief in green chemistry, it is much more beneficial to produce high-performance polymers form existing low-use ones than new starting monomers. With this respect, chemical modification of polybutadiene chain could make possible goals like raising polymer applications, introducing high-performance polymers, and preventing overproduction of new polymers with optimistic perspective to polybutadiene recycling [5, 6].

     Double-bond scission of polybutadiene chain usually occurs through chain oxidation using hydrogen peroxide, metachloroperbenzoic acid, and dimethyl dioxirane. The molecular weight could be engineered by peracid/double-bond unit ratio [7, 8]. Carbonyl functionalized polybutadiene derived from chain cutting down process is an attractive procedure for polyurea and polyurethane synthesis [9, 10].

Conclusion

     At the beginning of this research, graphene quantum dot was successfully prepared by hydrothermal method and coprecipitation approach in order to have GQD-MnO2 nanoparticle synthesis. GQD and GQD-MnO2 nanoparticle accurate synthesis approved by FT-IR spectroscopy, and optical properties of nanoparticles were investigated with UV-vis and PL techniques. In the following, PU-GQD-MnO2 nanocomposite was prepared through an in situ polymerization reaction of synthesized polyol and TDI diisocyanate in presence of different GQD-MnO2 nanoparticle percent. PU-GQD-MnO2 nanocomposite synthesis was confirmed using FT-IR technique. Also, it was resulted from UV-vis and PL analysis that nanocomposites excellently reserved their optical characteristics. Thermal property improvement of nanocomposites was observed using TGA/DTG and DSC methods. Finally, SEM, XRD, and AFM investigations resulted satisfying nanocomposite synthesis, fine nanoparticle distribution, and morphologic and topographic property improvement in nanocomposites in comparison with pure PU.

Highlights

Abstract

Graphical abstract

Keywords

1. Introduction

2. Experimental

3. Results and discussion

4. Conclusions

Declaration of Competing Interest

Acknowledgement

Declaration of Competing Interest

Data Availability

Appendix A. Supplementary material

References

Abstract

Ring-opening polymerization of benzoxazine monomers is a complex process and various chemical structures including N,O-acetal structures, phenolic Mannich structures and arylamine Mannich structures are formed in polybenzoxazines. To understand the polymerization mechanism, the effects of temperature, time and solvent polarity on the polymerization routes, chemical structures and thermal properties were studied. It was discovered that the N,O-acetal structures and the phenoxy structures can be obtained in a low-polarity solvent like dichloromethane at low temperature (−20 °C) with the aid of PCl5, while the arylamine Mannich structures can be readily generated in polar solvent like N,N-Dimethylformamide at high temperature (>80 °C) in the presence of PCl5. However, the phenolic Mannich structures can be directly formed at high temperature (>180 °C) without any catalysts. Upon prolonging the reaction time or elevating the temperature, the phenoxy structures easily rearranged into the N,O-acetal structures or the arylamine Mannich structures. Further increasing the temperature will cause the arylamine Mannich structures to rearrange into the phenolic Mannich structures and even the phenolic methylene structures. Therefore, both phenoxy structures and N,O-acetal structures showed poor thermal stability; while the arylamine Mannich structures possessed lower initial decomposition temperature but higher char yield compared with the phenolic Mannich structures because of the formation of thermally unstable iminium ions and the anchoring of dangling aniline moieties.

1. Introduction

Polybenzoxazines (PBzs) are formed by the ring-opening polymerization (ROP) of nitrogen and oxygen containing six-membered heterocyclic compounds, 3,4-dihydro-2H-1,3-benzoxazines. They are labeled as a kind of new high-performance thermosetting resins that possess good properties similar to or even higher than phenolic resins and satisfactory processability resembling epoxy resins [1–6]. Polybenzoxazines have aroused high research enthusiasm in academic communities and drawn much attention from industries because of their well-known merits: high strength, high modulus, good thermal stability, flame retardance, good dielectric properties, good dimensional stability, low water uptake, outstanding processability and tremendous design flexibility [7–12]. More recently, polybenzoxaiznes have found many functional applications such as shape memory, self-healing, catalyst support, pollution treatment, super capacitor, CO2 absorption and corrosion prevention [13–19]. Additionally, polybenzoxazines are of great potential in the future application as the fossil resources are decreasing rapidly but the amines and phenols that can be used to synthesize benzoxazine monomers are abundant and reproducible in nature [20–24].

1- Introduction

2- Experimental section

3- Results and discussion

4- Conclusion

References

Abstract

A series of hemiphasmidic luminescent liquid crystalline polymers, in which the hemiphasmidic mesogen containing cyanostilbene were linked to the polymethacrylate main-chains via flexible spacers with different lengths, named poly {(Z)-m-(4-(1-cyano-2-(3,4,5-tris(octyloxy)phenyl)vinyl)phenoxy)alkyl methacrylate} (donated as Pr-m, m = 2, 4, 6, 8, 10) were synthesized via free radical polymerization. The phase structures and photophysical properties of Pr-m were investigated in detail by a combination of techniques including differential scanning calorimetry (DSC), polarizing optical microscopy (POM), small-angle X-ray scattering (SAXS), UV–Vis absorption spectra (UV–Vis spectra), photoluminescence spectra (PL spectra) and particle size analyzer. The results revealed that the phase structures of Pr-m transformed from hexagonal columnar phase (m = 2, 4) to smectic A phase (m = 6, 8, 10) with the increasing of flexible spacer length. All of the polymers featured similar AIEE properties, however, the solid state quantum yields of Pr-m decreased with the increasing flexible spacer length, and the solid quantum yields of Pr-m decreased from 8.55 (Pr-2) to 3.71 (Pr-10) with the increasing flexible spacer length.

Introduction

Over the past few decades, liquid crystals (LCs) have been widely studied as a type of functional material [1-9]. A substantial number of LCs have been synthesized, and their physical and chemistry properties have been investigated because the LCs show excellent anisotropic physical properties that can be used in many classical fields, such as stimuli-responsive [10-12], information storage [3, 4], and photomechanical materials [13, 14] etc. Among various applications of LCs, display materials is always the most important application direction of LCs. However, the conventional liquid crystal materials are non-self-luminescent, so that a backlight needs to be added in the liquid crystal display device, which violates the development trend of energy saving and thinning of liquid crystal display device [15]. Therefore, new strategy toward more efficient liquid crystal display device is highly desirable. Luminescent liquid crystals (LLCs), which combines optoelectronic characteristics of luminescent materials with the unique properties of anisotropic fluids, is expected to be an effective way to solve those problems mentioned above. LLCs can overcome the shortcomings of traditional liquid crystals as display materials and enjoy tremendous advantages for the construction of linear or circular polarized light emitting materials [16, 17]. In view of the traditional luminogens, researchers have tried to construct fluorescent liquid crystal materials [18-20]. However, due to the aggregation caused quenching (ACQ) effect, these fluorescent liquid crystal materials usually emit strong fluorescence only in dilute solution while hardly emit light in aggregate state, which makes the preparation of LLCs with excellent performance intractable [21-24].

1- Introduction

2- Materials and methods

3- Results and discussion

4- Conclusions

References

Abstract

Traditional wastewater treatment plants cannot completely remove trace pharmaceutical and personal care products. In particular, quinolone antibiotics are mainly adsorbed on microbial cell surfaces in excess sludge and are released into the water environment during agricultural supplementation, mainly due to the exfoliation of extracellular polymeric substances (EPS) caused by changes in environmental conditions. Here, the occurrence of seven typical quinolone antibiotics from three generations in excess sludge was investigated at trace concentrations using ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). EPS facilitated adsorption independent of pH and quinolone antibiotic type, and the solid-liquid distribution coefficient decreased markedly as pH increased (pH 5–9, range of municipal wastewater). Metal ions bound in EPS were predominantly responsible for the adsorption of antibiotics in sludge, rather than the macroscopic size of the sludge floc. pH affected patterns of quinolone antibiotics, the zeta potential of sludge floc, and the contents of metal ions contained in sludge. The adsorption capacity of antibiotics first increased and then decreased with increasing pH in the range of pH 3–11, reaching a maximum (20,506, 14,458, 10,689, 22,854, 20,302, 8494, and 29,547 L/kg for CIP, ENR, LOM, MOX, NOR, OFL, and SAR, respectively) near pH 5, at which the cationic bridging of Ca2+ and Mg2+ bound in EPS played a major role owing to their larger ion radius and higher contents in excess sludge. Due to high surface heterogeneity of sludge, the Freundlich model was more suitable than the Langmuir model for describing the adsorption behavior of quinolone antibiotics. These results provide further insight into the release of quinolone antibiotics adsorbed in excess sludge, with potential implications for the agricultural use of sludge.

Introduction

Trace pharmaceutical and personal care products (PPCPs) have been detected in environmental media such as surface water, groundwater, and soil. Although the concentration of PPCPs related to human activities is usually on the order of nanograms to micrograms per liter in the water environment [1–5], many PPCPs are discharged continuously into the environment, causing potential risks for human health and the environment due to their ongoing utilization [6–9]. Wastewater treatment plants (WWTPs) are one of the main point sources of PPCP discharge into the environment [10], as it is difficult to biochemically degrade these substances during the conventional wastewater treatment process [11]. As a result, except for a small amount of PPCPs that are released into the atmosphere by escape, some portion of PPCPs remains in the effluent of the wastewater treatment plant, with the remainder present in excess sludge due to adsorption or dissolution [12]. The Water Pollution Prevention Action Plan promulgated in April 2015 in China stipulates that treated sludge cannot contain potential environmental pollutants [13]. When excess sludge containing PPCPs is used for land use and agricultural production activities such as fertilization, PPCPs in the sludge may be released into the environment as the external environment changes [10,14–19], thereby contaminating surface water and groundwater [4,12,18–20]. In recent years, quinolone antibiotics have been one of the most widely used antibiotics in veterinary and medical applications [21]. In China, they are widely used in human clinical settings and livestock breeding for disease prevention, with livestock and poultry farming accounting for about 50% of their use [22]. Moreover, the consumption of quinolone antibiotics has increased significantly; for example, the annual consumption of quinolone antibiotics in humans and animals in 1998 was 1,350 and 470 tons respectively [23], while the annual consumption of ciprofloxacin, norfloxacin, ofloxacin, lomefloxacin, and enrofloxacin in China in 2013 for both humans and animals reached 5340, 5440, 5110, 1250, and 5180 tons, respectively [22].

1- Introduction

2- Chemistry of geopolymers

3- Method and analysis section

4- Synthesis of geopolymers and mechanisms involved

5- Use of industrial waste as filler for the fabrication of crystalline metakaolin-based geopolymer

6- Result and discussion on applications driven by the surface chemistry of geopolymers in water

7- Barriers to utilization

8- Future research and prospects

9- Conclusion

References

Abstract

Geopolymer is a ceramic material, most often amorphous; finds applications in fire- and heat-resistant coatings and adhesives, medicines, refractory ceramics and binders, and manufacturing of radioactive waste container. Over the last decade, new cement based on geopolymers has been developed. Most relevant to this review is the fact that its porous nature and chemical similarity to zeolites is being employed for applications pertaining to wastewater treatment. Most of the work has been on the adsorptive treatment of water. However, using chemical reasoning and literature available we show that geopolymers have relevance for further activity on additional areas of relevance to waste water treatment such as photocatalysis, disinfection, and H2-energy production from waste water etc. These applications would depend strongly on the properties of geopolymers, which in turn would rely on the precursors employed and the synthetic methods used. The relevance of geopolymers for cleaner production is also highlighted. The use of fly ashes and metakaolin composites for the fabrication and surface tailoring of geopolymers (perhaps using relevant surfactants) is suggested as a plausible step in the right direction. Given the critical analysis of the state of the art, and the plausible directions identified, this article will benefit environmental scientists, engineers and chemists interested in deploying geopolymers for environmental remediation purposes. However moving forward, barriers are to be anticipated for the large scale implementation of geopolymers. Several barriers (e.g. legal, economical, technocrats and synthetic challenges) that are likely to hinder future research and translation are highlighted.

Introduction

Heavy metal removal and organic molecule degradation from wastewater have become a major topic of the public interest, due to their relevance to health and environment. Heavy metal and hazardous organic molecules are known to be toxic and a precursor to ill-health of the populace (Jaishankar et al., 2014). They are primarily released into the environment through human/industrial activities (Azimi et al., 2017). Hence research on multifunctional materials which relates to simultaneous environmental remediation and energy production are relevant to contemporary technologies connected with cleaner production. Geopolymers are a promising category of materials, for the removal of toxic substances from industrial and household effluents. It is usually prepared from a rather simple and eco-friendly reaction between an alkali such as NaOH/Na2SiO3 or KOH; and Al and Si source (s), making it a material amenable to clean production. Geopolymers obtained thus are often applied for the removal of metal ions such as Cs+ , Pb2+, Cd2+ etc. from wastewater. Geopolymers have come a long way, since their first discovery four decades ago (Davidovits, 1976). It has gained attention primarily because of the ease with which it can be synthesized with little or zero emission of green house gases (CO2. SO2, NOx etc.) (Noor ul et al., 2016). This coupled with its properties which include toughness, fire and heat resistance (i.e. its refractory nature), radiation hardness (making it relevant for radioactive waste containment) and pozzolanic action (Carsten, 2013), make geopolymers truly multifunctional.

We report a facile route for the synthesis of hyperbranched polyamido-graphenes (HBP(A-G)) as non-metallic high capacity electrodes for charge storage in supercapacitors. HBP(A-G) were synthesized by Michael addition of polyamines, ethylene diamine (EDA), diethylene triamine (DETA), triethylene tetraamine (TETA), to acrylamide grafted graphene oxide, followed by reduction in situ. A 3D network of stiff graphene sheets connected by flexible polyamine chain was formed. Hyperbranching increased d-spacing and BET surface area of graphene stacks, which enhanced accessibility of sites for ion storage, and prevented restacking. HBP(A-G) electrodes displayed electric double layer capacitance behaviour with excellent specific capacitance. The charge storage capacity of the electrodes increased with an increase in the amine chain length. Specific capacitance of electrodes containing HBP(TETA-G) was found to be 269 F g-1 in a symmetric two electrode electrochemical cell, using 1 M H2SO4 electrolyte at a current density of 1 A g-1 for voltage range of 0- 1 V. An increase in the length of amine chains improved ion mobility, lowered equivalent distributed resistance and time constant of the electrodes. The time constant of HBP(TETA-G) capacitor was only 538 ms. Hydrophilic amine linkages on graphene backbone provided stability against electrode volume changes during charging and discharging and gave 89 % capacity retention over 10,000 cycles at 10 A g-1 current density for HBP(TETA-G) electrodes. HBP(A-G) electrodes demonstrated superior performance as electrodes for supercapacitors and has shown potential for use in other electrochemical applications. Graphical abstract Symmetric supercapacitor fabricated using hyperbranched poly(amidographene)s, synthesized via novel route by Michael addition of polyamines to acrylamide-grafted-graphene oxide followed by in situ reduction to graphene, gave high specific capacitance with good energy density.

Introduction

The recovery and storage of electrical energy is one of the most important challenges facing our society that is progressing in the direction of harnessing renewable energy, use of hybrid vehicles, etc. Batteries and electrochemical capacitors are most common energy storage technologies [1]. The cutting-edge battery technology is not adequate for powering these applications, mainly due to slow charge/discharge time, short life and high cost. Electrochemical capacitors, also known as supercapacitors (SC) or ultracapacitors, combine the benefits of both, batteries and capacitors. Supercapacitors have much higher energy capacity than conventional capacitors, with similar rapid charge/discharge characteristics. Electric double layer capacitors (EDLC) are one type of SC containing high surface area material on which the charges accumulate. The other type of capacitor, known as pseudocapacitor, consists of conducting materials or those that undergo redox transformations [2]. Since pseudocapacitive materials have several times higher capacity, hybrid capacitators combing capacitive carbon based electrode with conductive or redox active materials have been in focus recently [3–7]. Graphene composed of sp2 hybridized (2D) carbon atoms has driven great interest in the field due to unique properties such as high surface area, excellent thermal and mechanical stability, high conductivity, etc., which makes it an ideal material for EDLC [8,9]. One of the disadvantages of graphene is, its tendency to stack thereby decreasing the accessible surface area and the performance [10]. Studies on derivatives of graphene with conducting polymers such as polyethylenedioxythiophene [11,12], polyaniline [13,14], polypyrrole [15–17] are reported with the aim of decreasing the stacking tendencies.

1- Introduction

2- Experimental

3- Results and discussion

4- Conclusion

References

Abstract

In this work, the bulk and surface composition of Fe3O4 supermagnetic nanoparticles were modified for efficient epoxy curing. The bare, ethylenediaminetetraacetic acid (EDTA) capped, and cobalt (Co)-doped EDTA capped Fe3O4 nanoparticles were synthesized electrochemically. The crystalline structure and phase information, surface capping, morphology and magnetization behavior of nanoparticles were studied by X-Ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), field-emission scanning electron microscopy (FE-SEM) and vibrating sample magnetometer (VSM), respectively. A low amount of the prepared nanoparticle (0.1 wt.%) was used in preparation of epoxy nanocomposites. Nonisothermal differential scanning calorimetry (DSC) under different heating rates was performed to study the potential of nanoparticles in curing epoxy resin with an aliphatic amine. The heat release data on nanocomposites suggest that EDTA capped Co-doped Fe3O4 considerably improved the curing reaction between epoxy resin and the curing agent. Calculations based on Cure Index approved qualitatively a shift from Poor to Good cure by concurrent lattice and surface modifications of magnetic nanoparticles. It is bielived that the approach used in this work can pave the way to enhance curability of epoxy nanocomposites by the combined modification of bulk and surface of nanoparticles.

Introduction

Addition of nanoparticles and their surface functionalization has been practised over the past three decades in order to enhance the ultimate properties and performance of organic coatings [1–5]. A Nevertheless, there is a need for looking at properties of coatings containing functionalized nanoparticles from a molecular perspective so as to be able to tune properties by controlling the curability of thermoset resins under the influence of surface-functionalized nanoparticles. The difficulty is that no molecular-level gauge is available for quantifying the status quo of cross-link density of thermoset nanocomposite to assess whether or not functionalized nanoparticles added to the system are reactive towards curing moieties [6–8]. The effect of surface modification of a wide variety of nanoparticles with low- and high-molecular weight molecules of amine, carboxylic and hydroxyl on the curability of epoxy resin was addressed in previous works of this group, which are including carbon nanotubes (CNTs) [9–11], graphene oxide (GO) nanoflakes [12–14], halloysite nanotubes (HNTs) [15–17], silica nanoparticles [18,19] and zinc oxide (ZnO) nanoparticles [20]. Reports suggest that surface functionalization of nanoparticles with high-molecular-weight ethylenediaminetetraacetic acid (EDTA) can affect ultimate properties of cross-linkable polymer nanocomposites. For instance, Syuhada et al. showed that EDTA surface-functionalized GO was dispersed well in chitosan matrix due to interaction of EDTA functional groups with chitosan [21]. Well-dispersed GO-EDTA in chitosan matrix led to facilitation of stress transfer resulting in 71% improvement in tensile strength compared to the neat chitosan film.

1. Overview

2. Properties of CFRP

3. Current Status of CFRP Application in Rail Transit Equipment

4. Principle of electromagnetic shielding

5. Simulation Research

6. Conclusion

7. References

The carbon fiber composite materials have been widely used in the field of rail transit.Carbon fiber body is more advantageous than traditional material especially in weight.This paper introduces main characteristics of carbon fiber composites and outlines the principles of electromagnetic shielding effectiveness.Electromagnetic shielding characteristics of carbon fiber reinforced polymer (CFRP) was studied through electromagnetic shielding simulation technology and test compared with aluminum, aluminum alloy and carbon steel. Some suggestions are provided in terms of the CFRP electromagnetic characteristics. This research sets a foundation for the EMC design for railway vehicles.

Overview

Modern railway vehicles have undertaken improvement and optimization in the aspects of rail transit, intelligence, safety and comfort, especially the high-speed EMU trains. However, speed increase will not only rely on the design of powerful traction system but also on the lightweight design which plays a vital role in this aspect.For the weight, stainless steel is better than weatherproof steel. Aluminum alloy is better than stainless steel. However, carbon fiber reinforced composite has better advantages over aluminum alloy. The application of composites in the high-speed railway vehicles has been gradually enlarged from carbody interior, components and materials of equipment inside vehicles to the carbody structure. Carbon fiber composite will bring rail transit industry into a new stage[1]-[2]. Although CFRP presents excellent properties in various aspects, there are still more aspects of carbody materials to be satisfied for high-speed trains, such as fire performance, thermal insulation properties, corrosion resistance characteristic and electromagnetic properties. Upon comparison with previous car bodies made from steel and aluminum alloy, however less attention is paid to electromagnetic shielding properties of CFRP vehicles.

1- Introduction

2- Experimental

3- Results and discussion

4- Conclusions

References

ABSTRACT

Organic-based electrode materials for lithium-ion batteries (LIBs) are promising due to their high theoretical capacity, structure versatility and environmental benignity. However, the poor intrinsic electric conductivity of most polymers results in slow reaction kinetics and hinders their application as electrode materials for LIBs. A binder-free self-supporting organic electrode with excellent redox kinetics is herein demonstrated via in situ polymerization of a uniform thin polyimide (PI) layer on a porous and highly conductive carbonized nanofiber (CNF) framework. The PI active material in the porous PI@CNF film has large physical contact area with both the CNF and the electrolyte thus obtains superior electronic and ionic conduction. As a result, the PI@CNF cathode exhibits a discharge capacity of 170 mAh·g−1 at 1 C (175 mA·g−1 ), remarkable rate-performance (70.5% of 0.5 C capacity can be obtained at a 100 C discharge rate), and superior cycling stability with 81.3% capacity retention after 1,000 cycles at 1 C. Last but not least, a four-electron transfer redox process of the PI polymer was realized for the first time thanks to the excellent redox kinetics of the PI@CNF electrode, showing a discharge capacity exceeding 300 mAh·g−1 at a current of 175 mA·g−1 .

Introduction

Lithium-ion batteries (LIBs) have played an essential role on energy storage for portable electronic devices in recent decades. However, the ever-growing energy storage demands, especially those driven by electrical vehicles and grid-scale storage of renewable electricity, have generated a great concern not only over the energy density and power density, but also the safety, cost, and sustainability of LIBs [1, 2]. Considering the elaborate preparation process, limited resource and environmental and safety issues of the conventional inorganic battery electrode materials, organic materials are intriguing alternatives for sustainable batteries [3, 4] because of the potentially low-cost, high safety, recyclablility, design diversity of molecular structures, and high theoretical capacities due to low formula weight and capability of multiple electron transfer [5–8]. The development of organic compounds as electrode material actually started as early as that of the inorganic materials [9], but the progress is lagging behind due to the tremendous success of inorganic intercalation compounds in the late 1980’s [10]. The main problem of most organic materials is their electronic insulating nature. This means that a large amount of conductive carbon (usually more than 30 wt.%) is normally required for the preparation of an organic electrode using the typical slurry coating method [11]. When the mass of the conductive carbon, the polymer binder and the Al current collector is considered, the practical energy density of organic electrodes is quite low [7]. Besides, uniform distribution and good physical contact of organic active materials and the conductive additive in the electrode is often difficult to achieve with the slurry coating method, resulting in low utilization of the active material and poor rate performance [12]. Polyimide (PI), an important engineering plastic with excellent mechanical strength and outstanding thermal stability, belongs to the category of organic carbonyl compounds, which bear high theoretical capacity for storage of lithium ion [13, 14]. Li ions reversibly that absorb or desorb on oxygen atoms as the carbonyl groups are reduced or oxidized [15]. This process is also known as enolation [15, 16]. Theoretically, PI polymers with 1 mole of repeating units can react to 4 moles of Li ions, resulting in a theoretical capacity of ~ 400 mAh·g−1. However, redox processes beyond two-electron transfer reaction have not been reported for PI electrodes in LIBs. It was predicated that four-electron redox process is nearly impossible to be realized reversibly because deep enolation would damage the molecular structure of PI materials [12, 15]. Furthermore, reaction kinetics of PI electrodes needs to be improved for practical considerations [17].

Introduction

Experimental

Results

Discussion

Conclusions

References

Abstract

A solid-state photoelectrochemical (SSPEC) cell is an attractive approach for solar water splitting, especially when it comes to monolithic device design. In a SSPEC cell the electrodes distance is minimized, while the use of polymer-based membranes alleviates the need for liquid electrolytes, and at the same time they can separate the anode from the cathode. In this work, we have made and tested, firstly, a SSPEC cell with a Pt/C electrocatalyst as the cathode electrode, under purely gaseous conditions. The anode was supplied with air of 80% relative humidity (RH) and the cathode with argon. Secondly, we replaced the Pt/C cathode with a photocathode consisting of 2D photocatalytic g-C3N4, which was placed in tandem with the photoanode (tandem-SSPEC). The tandem configuration showed a three-fold enhancement in the obtained photovoltage and a steady-state photocurrent density. The mechanism of operation is discussed in view of recent advances in surface proton conduction in absorbed water layers. The presented SSPEC cell is based on earth-abundant materials and provides a way towards systems of artificial photosynthesis, especially for areas where water sources are scarce and electrical grid infrastructure is limited or nonexistent. The only requirements to make hydrogen are humidity and sunlight.

Introduction

A fundamental societal concern is the impact of climate change on water quality and quantity [1]. It is also expected that the duration, magnitude and frequency of droughts on a worldwide basis will increase due to climate changes [2]. Water electrolysis is already an important and promising method for hydrogen generation and in the near future, clean water supplies will become a vital concern for this technology. Devices that can directly convert the solar energy to fuels, such as hydrogen, are highly desirable because the solar energy is absorbed and stored in the form of fuels in a single step [3e5]. Such “artificial photosynthesis” (AP) devices hold a great promise by mimicking nature in order to perform environmentally sustainable reactions, such as splitting water into O2 and H2, and CO2 fixation to sugars [6,7]. The device design is also very important and has an impact on the overall efficiency and cost [8]. Monolithic device designs, where the photoabsorbers are integrated together with the electrocatalysts, have certain advantages such as reduced area requirements, less frames and connections, as well as reduced footprint [9,10]. In our previous work [11], we demonstrated a monolithic solid-state photoelectrochemical (SSPEC) water electrolysis cell, in which the photoanode and cathode electrodes were attached to opposite sides of a Nafion-based polymer electrolyte membrane. The role of the membrane is to separate the evolved gaseous products, support and minimize the distance between the electrodes (down to a few mm) and provide protonic conductivity. The monolithic SSPEC cell was operated under asymmetric conditions i.e. 0.1 M Na2SO4 solution at the anode and gaseous Ar or air in the cathode compartment. There are a few more other works in the literature inspired by a polymer exchange membrane, PEM-like approach, where the photoanode is fed with a water stream [12,13]. Iwu et al. were the first to photoelectrolyze water vapor in an all-solid-state photoelectrochemical (PEC) cell [14], while Georgieva et al. have employed an all-solid-state PEC cell for the decomposition of organic vapors under UV and visible illumination [15]. Recently, the possibility of steam electrolysis in a high temperature PEC cell has been demonstrated by Brunauer and co-workers [16].

The concept of cosolvent exclusion was developed by a group of Timasheff’s laboratory in 1970-1990 and is currently used widely to explain the effects of a variety of cosolvents on the stability and solubility of macromolecules. Not surprisingly, these concepts have had substantial influence in the fields of formulation, protein folding and unfolding, but they have perhaps more surprisingly found their way into the field of chromatography. A variety of excluded cosolvents have been used to enhance binding and resolution of proteins and other macromolecules in ion exchange, hydroxyapatite, affinity, and hydrophobic interaction chromatography. These cosolvents include salting-out salts, amino acids and polymers, and frequently polyethylene glycol (PEG). A new mode of chromatography, termed “steric exclusion chromatography,” was recently introduced. It employs hydroxylated solid phase surfaces. Steric exclusion of the PEG stabilizes the association of macromolecules with the solid phase. Elution is achieved by reducing the PEG concentration. Magnetic particles are also used in this chromatography. This review summarizes the concepts of preferential cosolvent exclusion and its applications in column chromatography.

Introduction

The theoretical foundation and supporting data on protein solvent interactions were developed primarily by pioneering work conducted in Timasheff’s laboratory. Early studies focused on the mechanisms of protein denaturants, such as organic solvents and guanidine hydrochloride or urea, as they were found to play a critical role in understanding the unfolding and refolding pathways of proteins.1-6 These additives (cosolvents) exerted their effects at very high concentrations, where conventional stoichiometric binding measurements were neither practical nor meaningful. Timasheff’s group employed equilibrium experiments, for example, dialysis, which measured differences in cosolvent concentration between the vicinity (inside the dialysis bag) of protein molecule and the bulk phase (dialyzing solvent).7 At high cosolvent concentrations, many different interactions between the protein surface and cosolvent were found to occur.8-11 Water molecules, which were at high concentration in aqueous solution, were also bound to the protein or other macromolecules.12,13 All these interactions could cause difference in cosolvent concentration around the protein surface. These experiments provided a wealth of information about the effects of cosolvents on protein denaturation and stability in aqueous solution. Protein denaturants, for example, organic solvents and urea, were observed to bind to the proteins in the denatured, unfolded state at high cosolvent concentration, leading to stabilization of the denatured structure.1-6 Protein stabilizers, for example, sugars and polyols, were found to show lower cosolvent concentration inside the dialysis membrane than the dialyzing solvent.14-22 This showed that they were excluded from protein surfaces. Carpenter and Crowe and others23-27 demonstrated that these excluded cosolvents also stabilized proteins against freezethaw stresses, and they have since been shown to prevent proteolysis.28 Other important applications of preferentially excluded cosolvents are found in the field of chromatography. Chromatography plays an essential role in purification of biopharmaceuticals such as proteins, peptides, nucleic acids, and viruses. Affinity and hydrophobic interaction chromatography (HIC) permit the application of various excluded salts to modulate binding and elution. Anion and cation exchange chromatography are less tolerant of salts but invite application of nonionic and zwitterionic excluded cosolvents such as polyethylene glycol (PEG) and glycine. Many of these applications have been found particularly to enhance fractionation of native proteins from fragments and aggregates.