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The goal of this paper is to fabricate innovative diaphragm headphones using graphene oxide paper (GOP) and GOP/epoxy nanocomposites (GOPC). Initially, graphene oxide suspension is fabricated, and the vacuum filtration method is adopted to make GOP. Then, vacuum bag molding is used to fabricate GOPC from GOP. Hot pressing and associated molds are adopted to fabricate line-indented (GOPC-L) or curve-indented patterns (GOPC-C) on the GOPC. The performances of one kind of GOP and three kinds of GOPC diaphragm headphones are analyzed based on their sound pressure level (SPL) curves achieved by the Soundcheck measurement system. There are four important processing parameters that will influence the performance of the diaphragm, including material type GOP versus GOPC, indented pattern type, sonication time on suspension, and graphene weight fraction in suspension. Compliances of various diaphragms are measured by the Klippel LPM laser measurement system. The results indicate that effects of sonication time and graphene weight fraction on SPL of GOP and GOPC headphones are in reverse, and this is associated with their difference on compliance (modulus), mass, damping ratio, and microstructure uniformity. Either GOPC-L or GOPC-C seems to improve the microstructure of the GOPC, and leads to better SPL performance. The correlation between the previous four factors and SPLs of four kinds of diaphragm headphones is proposed by using scanning electron microscope (SEM) to examine the microstructure of these diaphragms. [ABSTRACT FROM AUTHOR]

This paper discusses the results of the micro-Raman analysis performed on paper-like graphene oxide (GO) samples consisting of many functionalised graphene layers and annealed at moderate temperatures (≤500 °C) under vacuum conditions (p ≃ 10−4 mbar). The analysis of the standalone samples revealed that the obtained material is characterised by a noticeable disorder level but still stays below the commonly accepted threshold of high or total disorder. GO formed in a simple way showed two spectral bands above 1650 cm−1 recorded very rarely or not at all and their origin has been discussed in detail. The results also confirmed the metastable character of multilayer GO after the annealing process at moderate temperatures as the C/O ratio was kept between 2 and 3 and the spectral features were stable within the annealing temperature range. [ABSTRACT FROM AUTHOR]

Thermal annealing is a convenient, low-cost, and versatile route to fine-tune the physicochemical properties of graphene oxide paper (GOP) toward various applications. Therefore, a thorough monitoring of the thermal decomposition of GOP is generally required for a precise and safe adjustment of its properties. From this perspective, thermogravimetry analysis (TG-A) is employed to scrutinize the multi-step thermal decomposition process of GOP under a nitrogen atmosphere. GOP is elaborated from modified hummers graphene oxide (GO). Nonisothermal TG-A is carried out for the as-prepared GOP at different heating rates. Activation energy is assessed for the overall decomposition process by several isoconversional models. Derivative thermogravimetry (D-TG) curves are derived numerically from TG-A data. To find the number of reactions involved, D-TG curves are deconvoluted into individual peaks by the well-known Fraser–Suzuki function. The obtained results show that the thermal decomposition of GOP consists mainly of six reactions: physisorbed water dehydration, rearrangement and elimination of oxygen functional groups, disproportionation reaction, chemisorbed water dehydration, desulfonation, and degradation of the carbon framework. Furthermore, kinetic triplets for each of the individual reactions are figured out by coupling the Vyazovkin nonlinear method with the compensation effect. [ABSTRACT FROM AUTHOR]

This article discusses the morphology and thermomechanical properties of graphene oxide (GO) paper sheets and GO paper composites reinforced with carbon fibers. GO paper was fabricated using GO paste obtained by the condensation of GO aqueous solution synthesized using the Hummers' method. Carbon fibers were implemented to improve the mechanical properties of the pristine GO paper. All the investigated papers were subjected to thermal treatment to check thermo-related morphological and mechanical properties. The results presented in this study allowed for the deeper insight into morphological, structural, and mechanical volume and surface-related properties of pristine GO and GO-based composite materials reinforced with carbon fibers. We showed that there are two important factors that should be taken into consideration for the design and fabrication of GO-based papers. These factors were the concentration of the reinforcing agent and the thermal reduction of the papers. Both factors have influenced the final properties of the resulting GO-based papers. For the first time, it was revealed how the addition of the reinforcing material affects the GO paper thermal expansion coefficient. [Display omitted] [ABSTRACT FROM AUTHOR]

Organic dyes are used in many industries, e.g., textile, cosmetics and food. Hence, contamination of organic dyes to water sources is a critical issue. To reduce water pollution by organic dyes, we propose a paper-like adsorbent with a practical and economical production procedure. Subsequently, a flexible adsorbent was produced using a one-step approach by vacuum filtration of graphene oxide (GO) and iron oxide nanoparticles (Fe3O4-NPs) containing dispersion through a membrane and quoted as GO/Fe3O4 paper. For comparison, GO paper was also prepared using the same procedure. Both papers were characterized using UV–VIS absorption spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy, electron diffraction X-ray analysis, X-ray photoelectron spectroscopy, and powder X-ray diffraction techniques. At the steady-state conditions, GO/Fe3O4 and GO papers were performed as adsorbent for cationic dyes of methylene blue, neutral red, and anionic dyes of methyl orange and fluorescein. In general, the removal efficiency of GO/Fe3O4 paper was higher than that of GO paper for adsorption of all dyes and this adsorbent revealed satisfactory adsorption properties for cationic dyes when compared to anionic dyes. [ABSTRACT FROM AUTHOR]

A triboelectric nanogenerator (TENG) electrode sensitive to the adsorption of water molecules has been introduced to create a self-powered humidity sensor. Graphene oxide (GO) nanosheets and graphene oxide nanoribbon (GONR) possessing oxygenated functional groups, as well as high dielectric constants, have been proposed as appropriate candidates for this purpose. GO papers have been fabricated in three forms, i.e. pure GO paper, uniform composites of GONR and GO, and double-layer structures of GONR on top of GO. Results showed that all of the prepared paper-based TENGs revealed excellent performances by maximum output voltage above 300 V. As active humidity sensors, the maximum voltage response values of 57%, 124%, and 78% were obtained for GO, GONR+GO, and GONR/GO TENGs, respectively. Besides high sensitivity and precision of all variants, GO+GONR TENG demonstrated a rapid response/recovery behavior (0.3/0.5 s). This phenomenon can be attributed to the higher oxygenated groups and defects on the edges of GONR, which leads to facilitating the bulk diffusion of water molecules. Our results open new avenues of GONR application as an additive to enhance the performance of self-powered humidity sensors, as well as conventional hygrometers. [ABSTRACT FROM AUTHOR]

• Nacre-like GO-PTA paper is prepared by evaporation-induced self-assembly method. • Fire sensor-based GO-PTA exhibits ultrasensitive and durable warning response. • Enhancement in fire resistance of GO is attributed to in situ phosphorus doping. A novel nacre-like flame-retardant paper based on graphene oxide (GO), and phytic acid (PTA) is fabricated via evaporation-induced self-assembly. This facile method is time saving and low energy consuming. A facile approach is proposed to improve thermal oxidative stability of GO paper by in situ phosphorus doping during flame exposure. Then fire-alarm system is designed based on the high-temperature thermal reduction characteristic of GO. The GO paper functionalized with PTA (GO-PTA) can provide ultrasensitive, reliable and longtime fire early-warning signal. Fire alarm can be triggered at approximately 0.50 s when GO-PTA samples are attacked by fire. Phosphorus atoms are in situ doped into graphene layers during fire exposure, endowing GO-PTA paper with outstanding thermal oxidative stability, and thus alarm duration time of GO is greatly improved. The work develops advanced fire detection and early-warning sensors that provide reliable and continuous signals, which provide more available time for fire evacuation. [ABSTRACT FROM AUTHOR]

The effects of processing parameters on fatigue lives of graphene oxide papers (GOP) and reduced GOP (RGOP) are investigated. The fabrication method could be either vacuum filtration or pressure filtration, and the important processing parameters include graphene weight fraction in suspension, sonication time for suspension and pressure value for pressure filtration. Fatigue performance of the papers are studied by strain‐controlled fatigue test. Under vacuum filtration method, fatigue lives of both GOP and RGOP decrease with increasing graphene weight fraction. The longest fatigue life is 403 284 cycles for the GOP under highest power sonication time and lowest graphene weight fraction. Fatigue lives of most GOP increase with increasing sonication time up to medium level. Under pressure filtration method, all GOP have shorter fatigue lives than those by vacuum filtration. Scanning electron microscopy is employed to carefully analyse the failed papers in order to clarify the fatigue failure mechanism. [ABSTRACT FROM AUTHOR]

Flame-retardant silane-grafted-graphene oxide (silane-GO) papers are fabricated via a green and versatile silane-assisted assembling strategy, and their use as early fire alarm sensors are investigated. Different silane molecules with alkoxy groups can react with GO in aqueous solution via hydrolysis and condensation reactions and thus assemble into the aligned silane-GO papers. The silane-GO papers exhibit good mechanical flexibility, strong acidic/alkaline tolerance, excellent flame resistance and improved thermal stability at low silane content in comparison with pure GO paper. Structure observation and analysis disclose that a compact nano-silica protective layer transformed from the grafted silane molecules during combustion is formed to inhibit the thermal degradation of GO sheet effectively. Furthermore, the insulating silane-GO paper can be thermally reduced into the conductive reduced GO network after encountering high-temperature or flame situation, thus providing ideal early fire alarm response, i.e. rapid flame detecting response time of ∼1.6 s and fire early warning response of ∼5 s when attach on the heat resistor. These results suggest that the silane-GO papers are promising for development of advanced materials as smart sensors in early fire alarm applications. A facile and green silane-assisted assembling technique was developed to fabricate flame-retardant graphene oxide papers, showing fast flame detection and ideal early warning response. Image 1 • A facile silane-assisted assembling strategy was developed to fabricate flame-retardant graphene oxide (silane-GO) papers. • Different silane molecules with alkoxy groups were assembled well onto the aligned silane-GO papers. • The silane-GO papers exhibited good mechanical flexibility, strong acidic/alkaline tolerance, and excellent thermal stability and flame resistance. • The related flame-retardant mechanisms were analyzed and discussed. • The silane-GO papers showed fast fire alarm response due to temperature-triggered sensitive resistance transition, showing promising for fire safety and prevention. [ABSTRACT FROM AUTHOR]

Abstract In this study, cathodic electrodeposition of manganese oxide onto reduced graphene oxide paper is carried out to prepare flexible and binder-free electrodes for electrochemical capacitors. Effects of electrodeposition potential and the amount of deposited mass on the electrochemical performance are examined. Hausmannite phase manganese oxide coated electrodes exhibit promising performance in charge-discharge and cyclic voltammetry measurements with specific capacitance of 546 F g−1 at current density of 0.5 A g−1 and 308 F g−1 at scan rate of 1 mV s−1, respectively. During potential cycling, phase transformation of Mn 3 O 4 to mixed-valent MnO x is observed. Consequently, MnO x nanostructures on self-standing reduced graphene oxide electrodes have 154% capacitance retention at 10000 cycles of cyclic voltammetry. Graphical abstract Image [ABSTRACT FROM AUTHOR]

Electron beam lithography (EBL) was used for preparing nanostructured reduced patterns on the GO paper surface, while preserving its mechanical resistance and flexibility. Different EBL parameters, like dose and time of exposure for patterning were tested. SEM analysis showed the consequent increase of contrast of the reduced stripes on the patterned regions due to the increase of electron beam doses. Moreover, surface potential microscopy experiments also exhibited a clear contrast between the patterned and non-patterned regions. Structural analysis of the patterned paper through X-ray diffraction and nanoindentation showed that the interlayer distance between GO sheets decreases after reduction allowing the increase of the Hardness and Young modulus that makes this material able to be manipulated and integrated on different devices. Furthermore, we also observe that exposed areas to electron beam reduction process show an increase in the electrical conductivity up to 3 × 10 4 times. The developed flexible GO films can have interesting applications such as biosensors or templates for inducing tissue regeneration, by providing a surface with differently patterned cues with contrasting electron mobility. Preliminary in vitro studies with L929 fibroblasts support the cytocompatible nature of this patterned GO paper. [ABSTRACT FROM AUTHOR]

Through design hierarchical architectures and interlayer interaction, multifunctional macroscopic graphene oxide papers tend to attain outstanding mechanical properties. Three dimensional architectures functionalized graphene oxide papers are self-assembled with zirconium diboride particles and poly(vinyl alcohol, PVA) using vacuum assisted filtration method. Firstly, ternary graphene oxide micro-scale structures are achieved by the addition of zirconium diboride particles. Then, PVA is introduced to enhance the interface interaction between graphene oxide nanosheets and zirconium diboride particles. The results show significant enhancements in fracture strength (~ 200%) and tensile modulus (20–100%) are attained through synergistic effect of ternary graphene oxide structures and interlayer interaction between PVA, graphene oxide and zirconium diboride particles. [ABSTRACT FROM AUTHOR]

This work reports on deoxygenation thermokinetics involved in preparing freestanding deoxygenated graphene oxide paper (DGOP) and the degree of deoxygenation-electrical transport correlation. The differential scanning calorimetry (DSC) and thermomechanical analyzer (TMA) for dimensional change study revealed that the manifestation of graphene oxide paper (GOP) into DGOP is associated with the activation energy of 153.8 kJ/mol with releasing gaseous moieties in the range of 210–230 °C. With variation in deoxygenation temperature ranging from 50 to 250 °C, DGOP is altered from dark brown to black, indicating the thermal reduction of DGOP. Upon increasing the annealing temperature, the hydrophobicity and electrical conductivity of DGOP are significantly increased. DGOP-250 exhibited superhydrophobicity and electrical conductivity of 102.2° and 4.5 S/cm, respectively. Understanding the underlying controlled-thermokinetics in converting GOP into DGOP with DSC and TMA helps in fine-tuning the structural modification associated electrical transport and hydrophobicity, which is desirable for practical applications. [Display omitted] • Freestanding graphene oxide paper (GOP) preparation via vacuum-assisted filtration • GOP converts into DGOP with the activation energy of 153.8 kJ/mol • Deoxygenation is prominent in the range of 210-230 °C as per DSC and TMA study • Deoxygenation temperature (50 to 250 °C) altered DGOP from dark brown to black • DGOP-250 showed hydrophobicity and electrical conductivity of 102.2° and 4.5 S/cm [ABSTRACT FROM AUTHOR]

Graphene oxide (GO) papers are candidates for structural materials in modern technology due to their high specific strength and stiffness. The relationship between their mechanical properties and structure needs to be systematically investigated before they can be applied to the broad range fields where they have potential. Herein, the mechanical properties of GO papers with various thicknesses (0.5-100 μm) are investigated using bulge and tensile test methods; this includes the Young's modulus, fracture strength, fracture strain, and toughness. The Young's modulus, fracture strength, and toughness are found to decrease with increasing thickness, with the first two exhibiting differences by a factor of four. In contrast, the fracture strain slightly increases with thickness. Transmission electron, scanning electron, and atomic force microscopy indicate that the mechanical properties vary with thickness due to variations in the inner structure and surface morphology, such as crack formation and surface roughness. Thicker GO papers are weaker because they contain more voids that are produced during the fabrication process. Surface wrinkles and residual stress are found to result in increased fracture strain. Determination of this structure-property relationship provide improved guidelines for the use of GO-based thin-film materials in mechanical structures. [ABSTRACT FROM AUTHOR]

Graphene oxide paper (GOP) is a composite material fabricated from graphene oxide (GO) solution. In addition, it can be a novel and potential material for application on the separation of water vapor from gaseous steam or larger alkali ions from aqueous solution. GOP could be used as electricity and thermal storage materials. The preparation of GO commonly uses high purity natural or artificial graphite. It is difficult to prepare GOP from artificial graphite powder due to the cost of $1,450 US/ton. In this study, we tried to prepare GOPs from homemade graphene sheets containing carbon materials (GSCCMs) and evaluate the thermal properties of GSCCM derived GOPs. Results show that GSCCM derived GOPs have a higher phase transition temperature, and the average mesophase phase change enthalpy is 9.41 J/g, which is 2.87 times higher than graphite derived GOP. Therefore, to prepare GOP from GSCCMs could highly reduce the cost. [ABSTRACT FROM AUTHOR]

Graphene oxide (GO) is an insulator and should be converted to reduced graphene oxide (rGO) paper structure by reduction to provide electrochemical activity. This work maintains an essential route to fabricate rGO paper. Hence, the first aim of this study is to produce rGO paper by one-step electrochemical reduction of GO paper by the optimization of quality parameters. Humidity actuators produce mechanical feedback if the moisture is exposed to their surface. To provide this kind of response, Janus materials are good nominated due to their asymmetric surface character in terms of hydrophilicity. GO paper can be performed for this application by converting one side to rGO layers. By this approach, hydrophobic rGO and hydrophilic GO sheets of the Janus system are generated, in which moisture flow swells the GO side and causes bending motion of the material through the rGO layer. In this work, Janus GO/rGO paper has been prepared by one-step electrochemical reduction of one side of the GO paper. Characterization of the samples has been carried out using numerous techniques. Humidity actuator experiments have indicated that Janus GO/rGO paper is acting circularly and there is an exponential relationship between relative humidity and circularly-oriented bending angle of the actuator. [Display omitted] • Preparation of rGO paper by one-step electrochemical reduction route. • Fabrication of Janus GO/rGO paper by electrochemical reduction of one side of GO paper. • Circular actuation of GO/rGO paper proportional to moisture content. • High stability and reproducibility of Janus GO/rGO paper as a humidity actuator. [ABSTRACT FROM AUTHOR]

Colloidal suspensions of glutaraldehyde (GA) crosslinked or grafted graphene oxide (GO) sheets were fabricated by simply tailoring the feed sequence. The different structures were confirmed by Fourier transform infrared spectra and X-ray diffraction. As demonstration of the utilities, the different colloidal suspensions were used to prepare free-standing papers by flow-directed filtration and poly(vinyl alcohol) (PVA)-based nanocomposite films by casting. Free-standing papers from GA crosslinked GO sheets exhibited better mechanical properties than unmodified GO paper, while nanocomposite films from GA grafted GO exhibit higher tensile strength and Young's modulus. [ABSTRACT FROM AUTHOR]

A facile route for the large scale production of graphene oxide (GO) papers and their mechanical enhancement has been presented in this work. The novel paper-like GO made from individual GO sheets in aqueous suspension can be achieved in large scale by a simple drop casting method on hydrophobic substrates. Significant enhancement in mechanical stiffness (341%) and fracture strength (234%) of GO paper have been achieved upon modification with a small amount (less than 10 wt%) of glutaraldehyde (GA). The cross-linking reaction takes place between hydroxyl groups on the surface of GO and aldehyde groups of GA, through forming hemiacetal structure, which can result in distinct mechanical enhancement of the GO papers. [ABSTRACT FROM AUTHOR]

• GO-PA paper is prepared by an evaporation-induced self-assembly method. • Fire sensor based GO-PA exhibits ultrasensitive and durable warning response. • Enhancement in fire resistance of GO is attributed to in situ phosphorus doping. Although traditional fire detectors are widely used in many occasions, they still show some limitations, such as slow fire response and poor resistance to severe conditions. Thus, it is urgent to design and exploit early fire-warning device with ultrafast response and flame-retardant ability to provide timely and fast alarm. Herein, graphene oxide paper functionalized with phosphoric acid (GO-PA) is fabricated by a facile and environmentally friendly water evaporation-induced self-assembly approach. Based on the flame-induced electrical resistance transformation characteristic of GO-PA, a fire-warning detector is designed to reliably monitor early fire. Fire alarm can be triggered within 0.5 s when GO-PA samples are attacked by fire. The GO-PA composite paper is more sensitive than GO-based fire sensors reported in the literature. Phosphorus atoms are in situ doped into graphene structure during flame exposure. Combustion reaction of GO is significantly retarded by the incorporated PA, thus fire duration time of GO is greatly improved. This work paves a new way to improve fire detection performance of GO-based sensors. This work provides a guide for the development of advanced fire detection and early-warning sensors to provide reliable and continuous alarm signals. [ABSTRACT FROM AUTHOR]

• A biphasic Graphene oxide/chitosan paper was developed for water treatment. • The presence of chitosan renders high water stability to the hybrid structure. • The biphasic paper can absorb both anionic and cationic dyes and kill bacteria. A bi-phasic and water-stable GO paper was developed based on a simple casting method and the addition of a chitosan (CH) coating layer. While pure GO paper re-dispersed after water immersion water becoming a powder, the bi-phasic GO/CH paper presented water stability. The stable GO/CH paper was able to adsorb both anionic and cationic dyes showing a maximum monolayer adsorption capacity (q m) of 103 mg/g and 232 mg/g for Methylene Blue and Methyl Orange, respectively. The biocidal behavior of GO and CH was rendered to the paper presenting antibacterial capacity against Staphylococcus Aureus and Escherichia coli under continuous agitation. These results show that our GO/CH paper can be a viable material for water treatment. [ABSTRACT FROM AUTHOR]

Graphene oxide (GO) paper with outstanding integrated multiple functionalities (good mechanical performance, thermal stability and flame resistance, etc.) is strongly needed for numerous potential applications in cutting-edge fields. In this work, we report a facile and green process to fabricate GO-based nanocomposite papers via introducing functionalized silica (f-SiO 2) nanoparticles. The results reveal that addition of f-SiO 2 produces simultaneous improvements in mechanical strength, stiffness and flame resistance for GO paper. With incorporation of 10 wt% f-SiO 2 , the tensile strength, elastic modulus and toughness of the GO/f-SiO 2 nanocomposite papers can be increased by about 51%, 317%, and 69%, respectively. Various characterizations disclose that hydrogen bonds and covalent interactions between GO sheets and f-SiO 2 mainly contribute to the effective load transfer and energy dissipation between them, and thus leading to the improvements of mechanical properties. Based on the structural observation and analysis, the improved flame resistance of the GO/f-SiO 2 papers should be attributed to the formation of rGO/SiO 2 protective char, which are derived from the decomposition and redeposition of the grafted silane molecules and inorganic SiO 2 and thermal reduction of GO into rGO. Our results suggest that the mechanical and thermal properties of GO papers can be tuned by introducing inorganic/organic f-SiO 2 , providing a new route for the rational designing and development of mechanically flexible and flame-retardant GO-based nanocomposite paper materials. • Graphene oxide/APTS modified silica nanocomposite papers were designed and synthesized. • The obtained nanocomposite papers show simultaneous improved mechanical properties and flame resistance. • The enhanced hydrogen bonds and covalent interactions between graphene oxide sheets and nanoparticles contribute to the improved mechanical properties. • The formation of SiO 2 protective layer derived from the decomposition of grafted silane molecules endows GO/f-SiO 2 papers an attractive flame retardant property. [ABSTRACT FROM AUTHOR]