High Degree Of Exfoliation Research Articles

A novel water‐based mechanochemical approach for surface modification of graphene platelets and their epoxy nanocomposites

AbstractGraphene (nano) platelets (GPs) are cost‐effective and possess high structural integrity, but their limited surface functional groups hinder their compatibility with polymers. In this study, an eco‐friendly, water‐based mechanochemical approach was developed to modify GPs with polyacrylamide (PAM), creating PAM graphene platelets (PAM‐GPs) with a grafting ratio of approximately 15%. The platelet was measured to be a few nanometers in thickness, and the grafted PAM provides abundant functional groups, including amide groups, which enhance compatibility with polymers. A typical polymer, bisphenol‐A epoxy, was compounded with PAM‐GPs, resulting in a high degree of exfoliation and dispersion of PAM‐GPs within the matrix. The resulting epoxy/PAM‐GP composites exhibited significantly improved mechanical properties, including an 18% increase in Young's modulus and a substantial enhancement in fracture toughness, with a 71% increase at a low filler fraction of 0.5 wt%. These improvements are attributed to the effective interfacial interaction between the PAM‐GPs and the epoxy matrix, facilitated by the grafted functional groups. This study highlights the potential of PAM‐GPs as toughening fillers for epoxy composites, emphasizing their applicability in enhancing the durability and performance of structural components in industrial applications.Highlights Polyacrylamide (PAM)‐modified graphene platelets by a water‐based approach. A strong interface promoted exfoliation and dispersion of platelets. PAM‐modified platelets improved epoxy modulus and toughness. Fractographic analysis unveils toughening mechanisms.

Fabrication of co-continuous morphology of polysulfone/nylon 6, 6 nanocomposites by varying the concentration of organically modified clay content

A unique morphology was fabricated using melt mixing of polysulfone (PSU) and nylon 6, 6, as well as organically modified clay to produce two blended nanocomposite compositions (80/20 and 60/40 w/w) of polysulfone and nylon 6, 6. The morphology of PSU/Nylon 6, 6 blend nanocomposites with various amounts of clay has been examined using scanning electron microscope (SEM), transmission electron microscope (TEM), and wide-angle X-ray diffraction (WAXD). In the case of 80/20 (w/w) PSU/Nylon 6, 6 without clay, the Nylon 6, 6 is dispersed in the PSU matrix with an average particle size of about 6.81 micrometers (μm). After adding clay (2%, 4%, and 8%), the domain size of nylon 6, 6 decreases, although the decrease rate is much slower than initially observed. However, we discovered that when the organoclay level exceeds 2%, the matrix-domain structure transforms into a co-continuous morphology for the 60/40 (w/w) blends. The TEM studies clearly demonstrate that the organoclay preferentially positions itself in the nylon 6, 6 phase, exhibiting a high degree of exfoliation, while the PSU phase of the nanocomposites remains devoid of clay, irrespective of the amount present. This study indicates that the size of clay platelets dispersed in the PSU/Nylon 6, 6 blend plays an important role in determining the morphology and stability of these blends. Moreover, the co-continuous structures were stable against further annealing at high temperatures, thus inhibiting the coalescence of the dispersed phase in addition to reducing interfacial tension.

Reaction mechanism of exfoliation degree and high temperature surface oxidation metamorphism of 2D Ti3C2Tx on thermal decomposition of various energetic materials

Achieving higher and faster energy release processes is a major research goal for energetic materials (EMs). Typically, EMs enhance their overall performance by incorporating catalysts. The novel two-dimensional layered MXenes, such as Ti3C2Tx, have shown significant potential as additives for ammonium perchlorate (AP). However, there is limited research on the impact of the exfoliation degree and high temperature oxidation of Ti3C2Tx MXene catalyst on the pyrolysis and combustion of different types of EMs. In this study, ultrathin Ti3C2Tx (U–Ti3C2Tx) MXene with a high exfoliation degree of approximately 20–80 nm was obtained through hydrofluoric acid (HF) etching, dimethyl sulfoxide (DMSO)-assisted layer expansion and ultrasonic peeling. The catalytic performance of MXenes on the thermal decomposition of three types of EMs (dihydroxylammonium 5, 5′-bistetrazole-1, 1′-diolate (TKX-50), cyclotetramethylene tetranitroamine (HMX), and AP) was evaluated. Results showed that 4 wt% U–Ti3C2Tx can reduce the decomposition peak of TKX-50 by 33.6 °C and decreases the high temperature decomposition (HTD) peak of AP by 45.5 °C, indicating superior catalytic performance compared to non-exfoliated Ti3C2Tx MXene. However, it had insignificant effect on HMX. Surface chemical analysis, electrochemical characterization, thermal decomposition of gaseous products analysis and material studio simulation all confirmed that high exfoliation U–Ti3C2Tx MXene exhibited better stability and electrical conductivity, facilitating the acceleration of the H+ transfer process and rapid gas release from EMs. Additionally, ignition tests demonstrated that high exfoliation U–Ti3C2Tx could effectively participate in the ignition process of EMs. The characterization and thermal analysis of Ti3C2Tx products after high temperature and oxidation treatment indicated that the catalytic activity is weakened due to high temperature crystal collapse and surface oxidation to TiOx metamorphism. This study provides new insights for the application of MXene catalysts in EMs.

The effect of controlled intercalation on the mechanical performances and dimensional accuracy of material extrusion additive manufactured poly(lactic acid)/organo-montmorillonite nanocomposites

Although the material extrusion-based 3D printing (MEX-3DP) has the ability to construct functional complex nanocomposites based on two-dimensional (2D) nanomaterials, however, the interplay of exfoliation degree of 2D materials and MEX-3DP parameters has not been elucidated, which seriously limits the further design and application of MEX-3DP 2D materials towards low-cost device fabrication. In this report, we use the well-studied organo-montmorillonite (MMT) as model materials and systematically studied the effect of various intercalation degrees on the mechanical and geometrical performance of MEX-3DP organo-MMT reinforced poly (lactic acid) nanocomposites. It was elucidated that, different from traditional injection moulding process, the best performance of MEX-3DP samples is obtained from completely exfoliated organo-MMT. The effect of the intercalation degrees is correlated with the melt flowability, thermal expansion and the resulting voids size that essential for MEX-3DP processes. The structure and rheology analysis demonstrate that the high exfoliation degree of 2D materials is essential to compensate the weak interfacial bonding or shrinkage-induced poor mechanical properties. The findings provide a detailed insight into the 2D materials exfoliation on the MEX-3DP quality, which is meaningful for engineers willing to design MEX-3DP functional 2D materials, for next generation disruptive technologies and applications.

Optimized time dependent exfoliation of graphite for fabrication of Graphene/GO/GrO nanocomposite based pseudo-supercapacitor

High capacitance devices (Supercapacitors) fabricated using two-dimensional materials such as Graphene and its composites are attracting great attention of the research community, recently. Synthesis of 2D materials and their composites with high quality is desirable for the fabrication of 2D materials-based supercapacitors. Ultrasonic Assisted Liquid Phase Exfoliation (UALPE) is one of the widely used techniques for the synthesis of graphene. In this article, we report the effect of variation in sonication time on the exfoliation of graphite powder to extract a sample with optimal properties well suited for supercapacitors applications. Three different graphite powders (hereafter termed as sample A, sample B, and sample C) were sonicated for duration of 24 h, 48 h and 72 h at 60 °C. The exfoliation of graphite powder into graphene, GO and GrO was studied using XRD and RAMAN. AFM and SEM were further used to examine the layered structure of the synthesized nanocomposite. UV–visible spectroscopy and cyclic voltammetery were used to measure the band gaps, and capacitive behavior of the samples. Sample B exhibited a remarkable specific capacitance of 534.53 F/g with charge specific capacity of 530.1 C/g at 1 A/g and energy density of 66 kW/kg. Power density varied 0.75 kWh/kg to 7.5 kWh/kg for a variation in current density from 1 to 10 A/g. Sample B showed capacitive retention of 94%, the lowest impedance and highest degree of exfoliation and conductivity as compared to the other two samples.

Effects of synthetic processes on the swelling capacity and modification mechanism of CMC-modified bentonite composites

Polymer-modified bentonite is widely utilized in wastewater treatments and barrier projects for contaminants due to its excellent performance. Despite numerous studies being conducted on the properties of different types of polymer-modified bentonite, the impact of synthetic processes has not been systematically explored. Hence, two common processes, the wet process and the semi-dry process, were investigated and compared. Sodium carboxymethyl cellulose (CMC)-modified bentonite was selected as an example here. Response surface methodology (RSM) was employed to develop relationship models of various factors versus the swell index. Specifically, the influence of modification temperature and stirring duration in the wet process, as well as pressure, moisture content, and ageing time in the semi-dry process were investigated. The feasibility and accuracy of the models were verified by the analysis of variance (ANOVA) and hypothesis testing. Results indicate that the semi-dry process leads to greater expansibility than the wet process. CMC dosage is a critical factor affecting performance. The following recommendations were made for the practical production: for the wet process, long-duration stirring at high temperature should be avoided at low CMC dosage, while the opposite is true at high CMC dosage (> 10%); for the semi-dry process, a longer ageing period should be selected at higher polymer contents, which can obviously improve the performance. Microscopic experiments were conducted to compare the differences in the modification mechanism of the two processes. Polymer/bentonite composites mainly form co-existing exfoliated and intercalated structures in wet and semi-dry processes, and the latter has a higher degree of exfoliation. The intensity of cationic bridging, hydrogen bonding, and group interaction between the polymer and bentonite is stronger when adopting the semi-dry process, resulting in better modification effects.

An efficient interface model to develop scalable methodology of melt processing of polypropylene with graphene oxide produced by an improved and eco‐friendly electrochemical exfoliation

AbstractThis study developed a scalable and straightforward adaptation methodology for melt processing of polypropylene (PP) to provide a high degree of exfoliation of multilayer graphene oxide (GO) by using a high‐shear mixer. GO was first produced by an improved and eco‐friendly electrochemical exfoliation by using an environmentally friendly aqueous methanesulfonic acid (MSA) and a sodium sulfate salt system to minimize the environmental impact. The produced GOs then were melt blended with PP and their mechanical, thermal, and morphological properties were investigated under different GO loadings to attain ideal configuration and increase interfacial interactions between polymer matrix and reinforcer. Comparisons were made by producing different PP composites using two different GO types produced in salt and acid environments. Additionally, by applying different voltages to salt system, the effect of applied voltage on the properties of both GO material and the composites were discussed. The characterization results indicated that GO obtained in MSA solution caused a 71% increase in flexural modulus and 46% in flexural strength with the addition of 1 wt% GO. The rheological characterization also showed that dispersion and viscosity improved with lower GO loadings compared to neat polymer by providing cost‐effective and scalable graphene manufacturing.

Effect of exfoliation degree on the performance of montmorillonite nanosheets

Montmorillonite (MMT) is easily exfoliated into two-dimensional(2D) nanosheets, which are widely used to prepare functional composites. However, there are few studies on the differences in the performance of MMT nanosheets (MMTNS) with different exfoliation degrees, which seriously limits the further breakthrough in the preparation of high-performance MMTNS based materials. In this work, some representative performance of MMTNS with different exfoliation degrees was investigated, and the performance was closely related with making functional composites. The exfoliation degrees of MMTNS were controlled by different ultrasonic exfoliation powers. The performance of MMTNS was studied by the measurements of atomic force microscopy (AFM), Zeta potential, turbidity, viscosity, scanning electron microscopy (SEM) and molecular dynamics simulation. The results show that MMTNS with high exfoliation degree had more negative electrical sites exposed and stronger repulsive potential energy between particles, which exhibited high surface negative electricity and excellent dispersion stability. Moreover, the MMTNS with high exfoliation degree had better gelling property. It can be seen that the “house-of-cards” structure in the structure after gelation of MMTNS with high exfoliation degree was more intensive. Also, with the increase of MMTNS exfoliation degree, its adsorption capacity for organic matter was better and its reaction with organic was more active. These findings might be helpful to select the suitable MMTNS for making functional composites by controlling its exfoliation degree.

Thickness regulation of graphitic carbon nitride and its influence on the photocatalytic performance towards CO2 reduction

Graphitic carbon nitride (g-C3N4) has been widely investigated in photocatalysis due to its excellent semiconductor properties. Though various strategies have been used to optimize the catalytic activity of g-C3N4, the influence of thickness itself on the photoelectric properties and CO2 reduction activity of g-C3N4 is still unclear. In this work, g-C3N4 with various thickness were successfully prepared by high-temperature exfoliation, and applied for the photoreduction of CO2. It was found that the conduction band (CB) of g-C3N4 samples shifted to negative position with decreasing thickness due to quantum confinement effect. Meanwhile, the more negative CB position endowed g-C3N4 with higher reduction potential that favors the reduction of CO2. Moreover, the specific surface area remarkably increased with higher exfoliation degree accompanied by more exposed active sites. The thinner g-C3N4 thickness also led to the exposure of ample edge amino groups that are beneficial for CO2 adsorption. Furthermore, the high-temperature exfoliation were also benefit for optimizing the crystal structure of g-C3N4 and reducing defect structures, which significantly inhibits the recombination of electron-hole pairs and facilitates the migration of charge carriers. These merits of g-C3N4 with high exfoliation degree synergistically catalyze the photoreduction of CO2 with high efficiency.

A prospect of cost-effective handling and transportation of graphene oxides: folding and redispersion of graphene oxide microsheets

Controlling the assembly of 2D materials such as graphene oxides (GO) has a significant impact on their properties and performance. One of the critical issues on the processing and handling of GO is that they need to be in dilution solution (0.5 to 2.5 wt%) to maintain their high degree of exfoliation and dispersion. As a result, the shipment of GO in large quantity involves a huge volume of solvent (water) and thus the transportation costs for large sales volume would become extremely high. Through cross-sectional scanning electron microscopy and polarized optical microscopy together with x-ray diffraction and small-angle x-ray scattering studies, we demonstrated that the assembly and structure of GO microsheets can be preserved without restacking, when assembled GO via water-based wet spinning are re-dispersed into solution. A couple of alkyl ammonium bromides, CTAB and TBAB, as well as NaOH, were examined as coagulants and the resulting fibers were redispersed in an aqueous solution. The redispersed solution of fibers that were wet-spun into the commonly used CTAB and TBAB coagulation baths, maintained their physico-chemical properties (similar to the original GO dispersion) however, did not reveal preservation of liquid crystallinity. Meanwhile, the redispersed fibers that were initially spun into NaOH coagulation bath were able to maintain their liquid crystallinity if the lateral size of the GO sheets was large. Based on these findings, a cost-effective solid handling approach is devised which involves (i) processing GO microsheets in solution into folded layers in solid-state, (ii) transporting assembled GO to the customers, and (iii) redispersion of folded GO into a solution for their use. The proposed solid handling of GO followed by redispersion into solution can greatly reduce the transportation costs of graphene oxide materials by reducing the transportation volume by more than 90%.

Reoxidation of graphene oxide: Impact on the structure, chemical composition, morphology and dye adsorption properties

The chemical composition, oxidation degree, and sheet size strongly affect the properties of graphene oxide (GO). Therefore, much effort has been directed to improve the synthesis of GO and control its structure. Herein, we report the reoxidation of GO using milder conditions of a modified Hummers’ method, including shorter reaction times and a reduced proportion of chemicals to obtain the reoxidized GO (Ox-GO). The reoxidation impact was evaluated by studying the materials’ adsorption performance towards methylene blue (MB) and rhodamine B (RB). Compared to GO, Ox-GO presents a similar C/O ratio, increased interlayer spacing, smaller sheets with holes, a higher exfoliation degree, and slight differences in each oxygenated functional group. Our measurements evidence that Ox-GO has an MB adsorption capacity more than 30% higher than GO under different conditions of dye concentration and pH. Moreover, Ox-GO also shows a notable improvement in the RB removal for a high dye concentration, where the removal capacity is almost 40% higher than that of GO. The enhancements in the dyes’ removal are attributed to the increased accessible surface area of Ox-GO, which provides more sites for dyes’ adsorption.

Comparing the effect of nanoclays on the water-resistance of intumescent fire-retardant coatings

This paper reports a study into the effect of nanoclays on the water-resistance of the intumescent system ammonium polyphosphate/melamine/pentaerythritol/titanium dioxide/polymer (ethylene vinyl acetate (EVA) or styrene acrylate (SA). It has been established that adding nanoclay to a coating based on ethylene vinyl acetate increases the fire resistance limit of a metal plate by 30 %, and to a coating based on styrene acrylate – by 50 %. At the same time, coatings that include the EVA polymer are characterized by greater fire-retardant efficiency and less water resistance than coatings containing the SA polymer. It has been shown that intumescent coatings, regardless of the nature of the polymer, under the conditions of 80 % humidity over 800 days their reduce fire-protective properties by an average of 10 %. The loss of coating fire resistance occurs due to the leaching of pentaerythritol, ammonium polyphosphate, and polymer degradation by hydrolysis. The admixtures of nanoclays with a high degree of exfoliation to the studied system create a barrier effect and maximize the chemical formulation of the intumescent coating. The fireproof properties of coatings with organically-modified montmorillonite admixtures are maintained or reduced to 5 % under the conditions of 80 % humidity over 800 days. It has been determined that the direct effect of water on the coating over a period of more than 2 days leads to a significant decrease in the swelling coefficient of intumescent coatings, regardless of the content of a nanoclay admixture in their composition. At the same time, the half-decay period of coatings without nanoclay, calculated on the basis of solubility constant in water, is 0.5 days. For coatings, which include the admixtures of organically-modified nanoclays, the half-decay period increases to 2 days. The results reported in this paper could be recommended for designing water-proof fire-resistant reactive-type nano-coatings with prolonged service life.

Mechanism of strengthening and toughening of a nanostructured styrene-butadiene based block copolymer by oligostyrene-modified montmorillonites

The influence of oligostyrene-modified montmorillonite (OS-MMT) on the morphological, mechanical and fracture mechanical behaviour of a nanostructured styrene-butadiene based block copolymer were studied by using electron microscopy (TEM, SEM), small angle X-ray scattering (SAXS) and uni-axial tensile testing. The crack toughness behaviour of the block copolymer nanocomposites was evaluated with the essential work of fracture approach using a pseudo single specimen method. A high degree of exfoliation of MMT vis-a-vis well distributed tactoids with gallery spacings of ca. 10 nm could be observed. PS-phase specific nano-confinement of silicate tactoids could also be confirmed as indicated by the shift in the glass transition temperature (Tg-PS) of the PS-rich phase to higher temperatures. The Young's modulus and yield stress of the block copolymer nanocomposite (BCP-NC) increased with oligostyrene-MMT content without any compromise in the ductility/toughness. A maximum in the resistance to crack propagation (βwP) at 3 wt.-% of oligostyrene-MMT accompanied by a change in deformation mechanism from homogenous plastic flow (drawing and micro-necking of microdomains) in the BCP-NC with 0-1 wt.-% of OS-MMT to a craze-like deformation (microvoid formation and stretching of polymer fibrils) for the BCP-NC with 3–5 wt.-% of OS-MMT. Above 5 wt.-% OS-MMT content a tough-to-brittle type transition attributed to the μm-sized aggregates in combination with an increased content of rigid PS phase controlling the fracture process as in the BCP-NC with 10 wt.-% nanofillers could be ascertained.Thus, our study demonstrates the possibilities of simultaneous strengthening and toughening of block copolymers by incorporation of modified layered silicates via tuning the dynamics of “intercalation-exfoliation” and by phase-specific nano-confinement of silicates in the BCP-NC.

Ultra-dispersive monolayer graphene oxide as water-based lubricant additive: Preparation, characterization and lubricating mechanisms

Although graphene oxide (GO) is deemed as an admirable lubricant additive to enhance the tribological properties of water, there remain great challenges in improving its dispersion stability and re-dispersity in water, and understanding the effects of dispersity and exfoliation degree on lubricity of GO. Herein, the functionalized GO (GO-EmimN(CN)2) with extraordinary dispersity, re-dispersity and high exfoliation degree is successfully prepared using 1-ethyl-3-methyl imidazolium dicyanamide as intercalator of multilayer graphene oxide (MGO). GO-EmimN(CN)2 as water-based lubricant additive dramatically decreases the wear rate and wear width of GCr15 steel by 74% and 40% compared to pure water, 53% and 45% to MGO respectively. Finally, lubricating mechanisms of GO-EmimN(CN)2 are determined and proposed via abundant surface analysis techniques.

In situ self-assembly of 3D hierarchical 2D/2D CdS/g-C3N4 hereojunction with excellent photocatalytic performance

A novel hierarchical 2D/2D CdS/g-C3N4 hybridarchitecture was synthesized via a hydrothermal method and then characterized by XRD, FTIR, SEM, EDS, UV–vis DRS, PL, BET, and EIS. The results showed the combination of CdS and g-C3N4 changed the growth orientation of dendritic CdS nanocrystallines and promoted the high degree of exfoliation of g-C3N4, which provided the close nanosheet/nanosheet 2D/2D contact interface and large specific surface area, resulting in the effective separation of the photo-generated carrier pairs. The photocatalytic activity of CdS/g-C3N4 was 6.93 and 3.64 times higher than that of the pure g-C3N4 and CdS samples, respectively, in the degradation of RhB under visible light irradiation. The CdS/g-C3N4 showed no obvious loss of the photocatalytic activity and little change of structure after three repeated runs, which is vital in the application of photocatalyst. This could be contributed to the reinforced hierarchical 3D architecture constructed through the dendritic CdS nanosheet penetrating into g-C3N4 interlayers. The possible mechanism for formation and photocatatlytic activity of the CdS/g-C3N4 architecture was proposed.

Cellulose acetate/layered double hydroxide adsorptive membranes for efficient removal of pharmaceutical environmental contaminants

The increasing amount of residual pharmaceutical contaminants in wastewater has a negative impact on both the environment and human health. In the present study, we developed new cellulose acetate/Mg-Al layered double hydroxide (Mg-Al LDH) nanocomposite membranes as an efficient method to remove pharmaceutical substances from wastewater. The morphology, porosity, surface properties and thermal stability of nanocomposite membranes containing various amounts of nanofiller were evaluated by scanning electron microscopy (SEM), X-ray microtomography (μCT), contact angle measurements and thermogravimetric analysis (TGA). The Mg-Al LDH nanofiller showed a high degree of exfoliation in the polymer matrix, evidenced by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The hydrodynamic properties and adsorption capacity were evaluated with pure water and aqueous solutions of two common drugs, diclofenac sodium (DS) and tetracycline (TC), and the nanocomposite membranes showed an improved permeability compared with neat cellulose acetate. The membrane prepared with 4 wt.% Mg-Al LDH loading exhibited the highest water flux compared with the pure polymer one (529 vs 36 L·m−2·h-1) and a tenfold increase in adsorption capacity for DS. This enhancement is attributed to electrostatic interactions between the negatively charged drug molecule and positively charged Mg-Al LDH layers. Conversely, in the case of TC, the increase in adsorption capacity was smaller and was assigned to hydrogen bonding interactions between the drug molecule and the nanofiller.

Effect of graphene oxide with different exfoliation levels on the mechanical properties of epoxy nanocomposites

The surface of graphene oxide (GO) was covalently modified by two kinds of monofunctional poly(oxypropylene)amines with different molecular chain lengths. Thermogravimetric analysis and other relevant analysis confirmed that both monoamine molecules were successfully grafted onto GO nanosheets. The monoamine molecules with longer molecular chain functionalized GO showed better compatibility and higher degree of exfoliation in the epoxy matrix, achieving better enhancement of both strength and elongation at break. The tensile strength, elongation at break, flexural strength and dielectric constant of the epoxy nanocomposite exhibit 29, 77.9, 28.5 and 6000% (0.1 Hz) increase at 0.05 wt% loading fraction when compared with unmodified counterparts, respectively. Our results demonstrate a great potential for industrial applications.

Shape-Memory Epoxy Reinforced by Porous Graphite of Different Exfoliation Degrees

Epoxy-based shape memory polymer (ESMP) suffers from low mechanical strength, thermal stability and shape fixity ratio (Rf) which are restricting its practical applications. In order to reinforce the ESMP, in this research, porous graphite materials synthesized by low-temperature (250°C) reduction and exfoliation of graphite oxide (GO) were added into the polymer by a three-roll mill. The addition of porous graphite was proven to increase the thermal degradation temperature, storage modulus and Rf of ESMP. Different exfoliation degrees of the porous graphite resulted in different enhancement effects on the ESMP matrix. And the porous graphite with a higher exfoliation degree has a more efficient reinforcement on the polymer. Shape fixity tests indicated the porous graphite reinforced ESMP composites had higher Rf than pure ESMP. Shape memory tests showed the porous graphite with a lower exfoliation degree could delay the shape recovery of ESMP, while the porous graphite with a higher exfoliation degree resulted in a shorter shape recovery time than pure ESMP.

Structure and supercapacitor properties of few-layer low-fluorinated graphene materials

Graphene materials including porous few-layered graphenes are under focus of scientific community today. The great attention towards them is caused by their remarkable properties. Here, we use two different fluorinated graphite intercalation compounds with different fluorine content in their matrices to prepare thermally exfoliated fluorinated graphites and to investigate them in terms of their structural, spectroscopic and electrochemical properties as materials for use in supercapacitors. A higher temperature of low-fluorinated graphenes preparation resulted in higher exfoliation degree and higher gravimetric capacitance in supercapacitor appliances. More dramatic leap of gravimetric capacitance was observed after a treatment in a concentrated acid mixture of graphene material samples prepared at the highest temperature of thermolysis with highest exposition time.

Laponite crosslinked starch/polyvinyl alcohol hydrogels by freezing/thawing process and studying their cadmium ion absorption

In this study, Laponite RD (LRD) cross-linked hydrogels consisting of starch, polyvinyl alcohol (PVA) were prepared by freezing/thawing process and the influence of LRD content on structure and properties of hydrogels was investigated. FTIR showed a new structure of hydrogen bonding might result from cross-linking reactions between LRD and polymers. X-ray diffraction (XRD) analysis showed that high degree of exfoliation of LRD clay layers had occurred during the preparation of hydrogels. The synergistic effect of physical cross-linking by freeze/thaw cycles and by LRD led to more porous, uniform and stable network, which was shown in SEM images. The melting temperature decreased and thermal stability got improved with the increase of LRD content. Reswelling ratios of hydrogels had the highest value when LRD content was 10%. Additionally, cadmium ion absorption capacity of the hydrogel was studied and the results showed that increasing the concentration of LRD increased absorption ratio and amount of Cd2+ ion in the solution. In a word, LRD could be used as a physical crosslinker and reinforced agent for starch-PVA based hydrogels and the formed hydrogels could be used as novel type and high capacity absorbent materials in heavy metal removing processes.