Abstract

     Two dimensional nanomaterials, such as graphene and MXene, have been widely used to fabricate high performance nanocomposite films owing to their unique structure and excellent physiochemical properties, showing enormous potential applications in many areas. However, the existing voids and wrinkling in the nanocomposite films inevitably impedes realizing the high performance of the nanocomposite films during the assembly process of graphene and MXene nanosheets. Nacre provides an inspiration for fabricating high performance graphene and MXene nanocomposite films through constructing a high alignment structure and strong interface interactions. In this review, we summarize the preparation approaches of graphene and MXene nanocomposite films and discuss the mechanical properties. Then, several effective strategies for assembling graphene and MXene nanosheets have been concluded and discussed. Meanwhile, we also summarize and discuss the applications of graphene and MXene nanocomposite films including electromagnetic interference (EMI) shielding and thermal management. Finally, outlooks and challenges are proposed to promote their progress and applications in the future.

Introduction

     Since the first discovery of graphene in 2004, graphene has gradually aroused widespread attention [1]. Due to the outstanding mechanical, electrical and thermal properties, graphene has been applied in flexible electronic devices, aerospace and thermal management fields in the past decade [2], [3], [4], [5], [6]. For instance, the single-layer graphene has a Young’s modulus of 1.0 TPa [7] and a superhigh thermal conductivity of about 5300 W/mK [8] at room temperature, demonstrating enormous practical potentiality in the above mentioned fields. Before realizing these applications, it is crucial to assemble graphene nanosheets into high performance graphene nanocomposites including one dimensional (1D) fiber, two dimensional (2D) film and three dimensional (3D) bulk. Especially, high performance graphene nanocomposite films have gained enormous attention. However, it is difficult to achieve high performance nanocomposite films due to weak interaction between adjacent graphene nanosheets. Graphene oxide (GO) is a usual precursor for obtaining graphene with plentiful surface terminating groups, which can easily interact with various materials for preparing nanocomposite films [9,10]. Meanwhile, in recent years, MXene, a novel two dimensional (2D) materials, shows promising electrical and thermal properties, which shows promising application in aerospace field [11], [12], [13], [14], [15], [16]. Indeed, compared with graphene, the intrinsic mechanical and thermal conductivity properties and stabilities of MXene is relatively poor. Furthermore, the easily oxidizable characteristics and thermal vulnerability of MXene may restrict its practical applications. However, compared with graphene, MXene has plentiful surface functional groups, which is an ideal building block for fabricating nanocomposite films without chemical modification any more.

Summary and outlook

     In the past several years, two dimensional materials such as graphene and MXene have been widely studied owing to the excellent physiochemical properties. In this review, we have focused on the preparation methods, assembling strategies and mechanical properties of graphene and MXene nanocomposite films. Moreover, we have also discussed the applications of obtained graphene and MXene nanocomposite films such as EMI shielding and thermal conductivity. Various methods such as VAF, blade coating, drop casting and LbL have been used to prepare high performance graphene and MXene nanocomposite films. However, as aforementioned, the existing voids and wrinkling are harmful for the mechanical properties of graphene and MXene nanocomposite films. Hence, several strategies for fabricating high performance graphene and MXene nanocomposite films are proposed.

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.

1- Introduction

2- Experimental investigation

3- Procedure and Calculations

4- Results and discussion

5- Conclusion

References

Abstract

Nanofluids have attracted huge attention because of their effective physical and thermal properties. One of many applications of nanofluids is the enhancement of the thermal performance of heat exchangers. In the current study, an experimental investigation has been conducted for studying the effects of graphene nanofluids on the convective heat transfer in a vertical shell and tube heat exchanger. Graphene flakes were prepared using graphite foam that is derived from sugar as a raw material. The prepared Graphene flakes have been characterized using scanning electron microscopy, X-ray diffraction, atomic force microscopy, and Raman spectroscopy. The graphene nanofluid has been used in the tube side of the heat exchanger to enhance its heat transfer performance. Different parameters such as nanofluids’ concentration, flow rate and inlet temperature were studied and their effects on heat transfer coefficient and thermal efficiencies are discussed. The results show that using of graphene/water nanofluids enhances the thermal performance of the vertical shell and tube heat exchanger. A maximum increase in the heat transfer coefficient of 29% was achieved using 0.2% graphene/water nanofluids. Furthermore, the mean thermal efficiency of the heat exchanger was enhanced by 13.7% by using graphene/ water nanofluid.

Introduction

Heat exchangers are widely used by various types of industries to exchange heat between different fluids for waste heat recovery and utilities cost reduction. The thermal and physical properties of the heat transfer fluids are crucial factors that dedicate the efficiency of heat exchangers. During the last two decades, nanofluids have attracted a huge attention of researchers due to its enhanced thermal properties and flow characteristics [1]. These advantages make nanofluids promising heat transfer fluids to be used for heat transfer enhancement. Many experimental studies have been conducted for the evaluation of heat transfer characteristics of nanofluids in different types of heat exchangers [2–7]. These types of heat exchangers include plate heat exchangers [2], double pipe heat exchangers [3], and micro heat exchangers [6]. However, in open literature, similar studies on shell and tube heat exchangers are scarce. Thermal performance of a shell and tube heat exchanger was analytically investigated by Shahrul et al. using nanofluids of four different types of nanoparticles, Fe3O4, ZnO, TiO2, CuO, and Al2O3 [8].

1. Introduction

2. Experimental

3. Results and discussion

4. Conclusions

Acknowldgement

Appendix A. Supplementary data

References

Abstract

Handling of petrochemical waste oil (PWO) is costly, tedious, and risky to human health and environment. Hence, upcycling of PWO for biomass conversion to platform chemicals would be very advantageous. Herein, a highly porous sheet-like structure of sulfonated graphene oxide (sGO) catalyst was synthesized from PWO. The synthesized sGO possessed high surface area (246.2 m2 g1) due to its mesoporosity and high content of sulfonic groups (2.4 mmol g−1) grafted onto its surface. As its application, the synthesized sGO was employed to convert fructose to levulinic acid (LA) within deionized water. The high yield (61.2 mol %) of LA was obtained under a condition of 160 °C, 1 h, and 6 g g−1 fructose to sGO weight ratio. It can be reused several times (5 runs) with no severe degradation of catalytic activity. Therefore, the sGO derived from petrochemical waste oil would be considered as an environmentally benign catalyst for producing platform chemicals, i.e. LA from fructose and other biomass derivatives.

Introduction

Heavy reliance on depleting fossil resources to produce platform chemicals and fuels contributes to the economic dilemma and rising emission of greenhouse gases [1-3]. Hence, alternative ways including utilization of biomass in integrated biorefineries have been explored to compete with fossil-based refineries [4]. Biomass is a renewable resource that can be exploited to produce many high value-added products, i.e. alcohol, 5- hydroxymethylfurfural (5-HMF), furfural, formic acid (FA) and levulinic acid (LA) [5, 6]. LA is considered as top ten platform chemicals, which could be further utilized to produce succinic acid, resins, polymers, herbicides, pharmaceuticals, flavoring agents, solvents, plasticizers, anti-freeze agents and biofuels/oxygenated fuel additives [3, 7]. Generally, conversion of biomass into LA involves multiple steps, which are (1) hydrolysis of cellulose to glucose, (2) isomerization of glucose to fructose, (3) dehydration of fructose to HMF, and (4) further hydrolysis to form equimolar LA and FA [2, 8]. These processes are often realized through chemical or enzymatic routes. Nevertheless, the chemical route has been recognized as high potential for commercially viable LA production [9, 10].

In the past, homogeneous acid catalysts (e.g. H2SO4, HCl, H3PO4) were used to ensure a high conversion of reactants because of lower mass transfer resistance [11]. However, those acidic catalysts are corrosive, detrimental to the environment, and non-recyclable [8, 10, 12]. Hence, heterogeneous solid acid catalysts, such as ion-exchange resins, sulfated metal oxides, modified mesoporous silica, zeolites, and natural clays have been developed to overcome the disadvantages of those homogeneous acid catalysts [13, 14]. Recently, several of these types of catalysts have been used for conversion of fructose to LA from actual biomass [15-17].

1- Introduction

2- Experimental

3- Results and discussion

4- Conclusions

References

Abstract

To develop effective strategies for removing phenolic compounds, in-situ graphene oxide/manganese oxide (GO/MnOX, X = 2, 3/4) composites were fabricated via a sustainable method by synchronously utilizing manganese ions and acidic liquid waste during synthesis of GO. Comparatively, traditionally ex-situ GO/MnO2 composites were synthesized to verify the difference between in-situ and ex-situ synthesis. Based on the schematic and mass flow analysis, in-situ synthesis exhibited better atom economy and less waste emission than ex-situ synthesis. Then, the results of batch experiments exhibited that GO/MnOX composites possessed higher removal efficiency and wider pH range for p-cresol (p-CR) and p-tert-butylphenol (p-TBP) than GO/MnO2 composites. The maximum removal capacities of GO/MnOX composites were 107.68 mg/g for p-CR and 135.41 mg/g for p-TBP. And GO/MnOX composites could retain high removal efficiency for p-TBP (>90%) after five recycles. For in-situ GO/MnOX composites, GO sheets not only promoted the adsorption of phenolic compounds and by-products, but also enhanced the oxidation capacity of MnOX via an electron transfer interaction. Especially, the detection of ring cleavage products indicated further oxidation for p-TBP. Possessing an eco-friendly fabrication strategy and augmented adsorption-oxidation capability, in-situ GO/MnOX composites are expected to be applied in the removal of phenolic compounds.

Introduction

Phenolic compounds have given rise to emerging concerns regarding human health and ecosystems due to their widespread use in the pharmaceutical, petroleum and petrochemical, pesticide, plastic, and paper industries (Danquah et al., 2018). Consisting of a hydroxyl group bonded directly to a benzene ring, phenolic compounds possess a stable conjugated system, leading to biological accumulation and poor biodegradability (Ou et al., 2018). Thus, an urgent need exists to develop an efficient method for removing phenolic compounds (Villar da Gama et al., 2018; Zhong et al., 2018). Various methods, including chemical oxidation (Jiang et al., 2015), adsorption (Villar da Gama et al., 2018), and membrane separation (Zagklis and Paraskeva, 2015), have been reported to remove phenolic compounds. Among them, oxidation constitutes an effective and attractive method due to the potential to disrupt the structural stability of pollutants (Wang et al., 2015). Manganese oxides, ubiquitous in natural soil and synthetic materials, are traditional and cost-effective adsorbents and oxidants in wastewater treatment. Especially, manganese oxides are able to oxidize various aromatic Lewis bases, such as phenolic and aniline compounds (Grebel et al., 2016; Wang et al., 2018b). Previous studies demonstrated that phenolic compounds are susceptible to oxidation by manganese dioxide (MnO2) through sequential one electrontransfer reactions, forming a series of intermediate products (Abdullah et al., 2017; Remucal and Ginder-Vogel, 2014). However, the intermediate products, such as phenolic multimer and benzoquinones, would be released back into the aqueous solution.

1- Introduction

2- Materials and methods

3- Results and discussion

4- Discussion

5- Conclusions

References

Abstract

In this study, the influences of ultrasonic and surfactants on the dispersion of graphene sheets in water were evaluated using UV–vis spectroscopy, and homogenous dispersions of graphene sheets in water were obtained by using sodium dodecyl benzene sulfonate (SDBS). Then, the highly dispersed graphene sheets were introduced to cement paste through high-speed mixing, and the mechanical and microstructural properties of graphene-modified cement material was evaluated. Experiment results indicated that the addition of 0.025 wt% graphene sheets increased the 7-day composite compressive strength by 14.9%, the flexural strength by 23.6% and direct tensile strength by 15.2%. X-ray diffraction (XRD) analysis showed that the addition of graphene sheets lowered the orientation index of calcium hydroxide (CH) crystals significantly. Moreover, mercury intrusion porosimetry (MIP) and microscope imaging (SEM) indicated that a high degree of dispersion of graphene sheets was achieved, and the two-dimensional graphene sheets promote hydration and suppress the extension process of cracks.

Introduction

As a main component of concrete, cement is the most widely used binder material in the world. However, one of cementitious materials’ biggest drawbacks is their quasi-brittle nature and poor resistance to crack formation. Thus, many studies have been carried out to combine nano-fiber with cementitious composites to enhance their microstructure and mechanical properties, and results showed a small amount of carbon nanotubes (CNTs) can restrain the propagation of microcracks and improve the fracture toughness of the nanocomposites [1–3]. However, CNTs tend to agglomerate, hindering their dispersion in solvents because of their super high length-diameter ratio [4]. As a two-dimensional nanomaterial, graphene is the basic structural element of other allotropes, including graphite, CNTs and fullerenes [5,6]. The theoretical specific surface area (SSA) of graphene can reach 2630 m2 /g, which is much larger than that reported to date for CNTs [7]. In addition, it has an intrinsic tensile strength of 130 GPa and a Young’s modulus of 1 TPa [8]. Due to its remarkable mechanical performance, great attention is paid to the graphene as the nano reinforcing material in cement with greatest potential. Development of aqueous dispersions incorporating higher concentrations of graphene sheets would facilitate scalable production of graphene sheets modified concrete [9]. Thorough dispersion of graphene sheets in water is the key first step toward achieving uniform dispersions of graphene within cementitious composites [10]. Different surface treatments have been investigated for improving the hydrophilic property of graphene. Current processing methods involve acid treatment [2], oxidation via heating [11], ozone treatment [12] and silane treatment [13].

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.

The advanced synthesis and development of raw graphene based on various significant functionalization has been outstanding in the wastewater treatment compared to the other alternatives such as carbon nanotubes and other carbon nanomaterials. Nano size graphene is known to possess large surface area and some promising properties in terms of mechanical, electrical, chemical and magnetism. Besides, the graphene can be generated via both Top-down and Bottom-up methods such as chemical exfoliation, chemical vapor deposition and other techniques so that it can be further functionalized to form graphene oxide-based nanomaterials. Hence, graphene oxide-based nanomaterials are discovered to be useful in the application of heavy metal removal from wastewater. In short, this paper critically reviewed on the synthesis method of graphene and application of graphene oxidebased nanomaterials in the term of heavy metal removal. The advantages, drawbacks, comparison of the data efficiencies, and research requirements are further highlighted, elaborated and discussed detailly. Lastly, the future challenges of graphene are elaborated. Therefore, it can be guaranteed that the wastewater discharged should be detected with the minimum or none of the heavy metals so that minimum effects on the ecosystem is discovered.

Introduction

Graphene can be extracted from graphite and it is merely a sheet of graphite. It is defined as a single layer of sp2 bonded carbon atoms in hexagonal lattice arrangement. At the same time, graphene possesses few promising properties such as good electronic properties caused by the bonding and anti-bonding of the pi orbitals. Furthermore, graphene is clarified to be the strongest substance in terms of mechanical strength since it possesses high tensile strength and it is light in weight. For instance, it is more than 40 times stronger than diamond and more than 300 times stronger than A36 structural steel, at 130 GPa[1]. Meanwhile, for the optical properties, high absorption of white light up to 2.3% is capable to be observed from graphene. Besides of the impressive properties, appropriate method to produce graphene must be taken into consideration. There are two different type of methods to produce graphene which are exfoliation methods and direct growth of graphene layer which can be known as Top-down and Bottom-up methods respectively[2]. Methods to generate graphene include “Scotch Tape Method”, dispersion of graphite, exfoliation of graphite oxide, epitaxial growth and lastly chemical vapor deposition (CVD)[3]. However, improved Hummers method which falls under method of dispersion of graphite is widely used since it is an improved method which excludes the usage of toxic chemical and at the same time enhances the reaction performance[4].

چکیده

توسعه و سنتز پیشرفته ی گرافن خام بر اساس عملکردهای مختلف و قابل توجه در زمینه ی تصفيه فاضلاب، در مقایسه با سایر راهکارهاي جايگزين (مانند نانولوله هاي كربني و ساير نانو مواد كربني)،بسيار چشمگير بوده است. گرافن در ابعاد نانو داراي مساحت سطح بزرگ و برخي ويژگي هاي نويد بخش از نظر مكانيكي، شيميايي،الكتريكي و مغناطيسي است.علاوه بر اين گرافن مي تواند از هر دو روش پايين به بالا و بالا به پايين ،مانند لايه برداري شيميايي،رسوب دهی شیمیایی بخار و روش های دیگر تولید شود بنابراین ، بنابراین نانو‌مواد بر پایه ی اکسید گرافن برای حذف فلزات سنگین از فاضلاب مفید در نظر گرفته شده اند . به طور خلاصه این مقاله مروری است بر روی روش های سنتز گرافن وکاربرد نانو مواد برپایه ی اکسید گرافن د رحذف فلزات سنگین. در این مقاله فواید،نقص ها و مقایسه ی بازده ی داده ها و تحقیقات مورد نیاز، بیشتر برجسته شده و با جزییات توضیح داده شده و مورد بحث قرارگرفته است. در آخر چالش های آینده ی گرافن مورد بررسی قرار گرفته است. بنابراین می توان تضمین کرد که تخلیه ی فاضلاب باید با حداقل مقدار فلز سنگین یا بدون آن در نظر گرفته شود تا کمترین اثر را روی اکو سیستم بگذارد.

1- Introduction

2- Experimental

3- Results and discussion

4- Conclusions

References

Abstract

Memories based on graphene that could be mass produced using low-cost methods have not yet received much attention. Here we demonstrate graphene ferroelectric (dual-gate) field effect transistors. The graphene has been obtained using electrochemical exfoliation of graphite. Field-effect transistors are realized using a monolayer of graphene flakes deposited by the Langmuir-Blodgett protocol. Ferroelectric field effect transistor memories are realized using a random ferroelectric copolymer poly(vinylidenefluoride-co-trifluoroethylene) in a top gated geometry. The memory transistors reveal ambipolar behaviour with both electron and hole accumulation channels. We show that the non-ferroelectric bottom gate can be advantageously used to tune the on/off ratio.

Introduction

Graphene holds great promise for microelectronic applications.1–5 Digital memories based on graphene have been proposed and different graphene memory concepts based on charge trapping6–9 and ferroelectric gating10–16 have been demonstrated. There have been many efforts to integrate ferroelectrics (both organic and inorganic) with graphene for non-volatile memory applications.17 In all cases a transistor is used with a planar structure. The ferroelectric memories have been realized using graphene obtained from either mechanical exfoliation or chemical vapour deposition (CVD). Due to good mechanical properties and flexibility, graphene has been suggested for low-cost, flexible electronics. Mechanically exfoliated graphene, however, does not meet the up-scaling and industrial production demand. CVD growth wherein an organic precursor is decomposed at elevated temperatures on a Cu or Ni foil,18 requires post-growth transfer of graphene to a target substrate using a sacrificial transfer layer and wet etching of the metal foil. 19–21 The etching process is typically done in an aqueous acidic environment. As a result, transferred CVD graphene is usually highly doped and exhibit a large uncontrolled shift in the Dirac voltage. The lack of control over the Dirac voltage results in typically absence of electron channel in the transistor, as well as the reliability and irreproducibility issues in the performance of discrete graphene memories. Moreover, the thermal budget (process temperature and time) for CVD-grown graphene is incompatible with low-cost and low-temperature technologies.22–25 For lowcost, flexible electronic applications, a low-temperature solution-based graphene production technology is still needed, which eventually enables solution-processed graphene ferroelectric transistors. Viable solution processed memories based on low-cost graphene have not been demonstrated yet. Recently, low-cost graphene mass production methods have been proposed that yield high-quality graphene sheets at low temperatures particularly suitable for applications in disposable and printed electronics. Electrochemical (EC) exfoliation of graphite sheets in aqueous solutions has been demonstrated as an effective and high yielding route toward up-scaled graphene fabrication.26–29 It has been shown that EC-exfoliation in electrolytes leads to flakes with large lateral size of up to 44 μm and typically less than 3 layers. EC-exfoliated graphene flakes have a low oxidation degree (a carbon/oxygen ratio of 17.2). The reported hole mobility in EC-exfoliated graphene is about 300 cm2 /Vs, much lower than that of CVD graphene however suitable for low-cost printed electronic applications.30 Despite the potential of EC-exfoliated graphene for micro-electronic applications, functional devices such as memories have not been reported so far.

ABSTRACT:

We developed nanosized, reduced graphene oxide (nano-rGO) sheets with high near-infrared (NIR) light absorbance and biocompatibility for potential photothermal therapy. The single-layered nano-rGO sheets were ∼20 nm in average lateral dimension, functionalized noncovalently by amphiphilic PEGylated polymer chains to render stability in biological solutions and exhibited 6-fold higher NIR absorption than nonreduced, covalently PEGylated nano-GO. Attaching a targeting peptide bearing the Arg-Gly-Asp (RGD) motif to nano-rGO afforded selective cellular uptake in U87MG cancer cells and highly effective photoablation of cells in vitro. In the absence of any NIR irradiation, nano-rGO exhibited little toxicity in vitro at concentrations well above the doses needed for photothermal heating. This work established nano-rGO as a novel photothermal agent due to its small size, high photothermal efficiency, and low cost as compared to other NIR photothermal agents including gold nanomaterials and carbon nanotubes.

INTRODUCTION:

Photothermal therapy employs photosensitizing agents taken up by cells to generate heat from light absorption, leading to photoablation of the cancer cells and subsequent cell death. To avoid nonspecific heating of healthy cells, photosensitizers must show high absorption in the near-infrared (NIR) and selective uptake in cancerous cells in tumors over normal cells in healthy tissues. Deep penetration and little nonspecific photothermal heating in the NIR window are due to the transparency and low absorption of light by tissues in this optical window. Materials currently under investigation with high optical absorbance in the NIR region for photothermal therapy include gold nanoshells, gold nanorods, gold pyramids, single-walled carbon nanotubes (SWNTs), and multiwalled carbon nanotubes.

مقاله سال 2017

5th International Conference of Materials Processing and Characterization