Project description:The agglomeration of reduced graphene oxide (rGO) in water makes the development of rGO inks for supercapacitor printing challenging. Cellulose nanofiber (CNF), a biodegradable and renewable nanomaterial, can act as a nanospacer, preventing the agglomeration and restacking of rGO flakes. In this work, rGO/CNF films were fabricated using an environmentally friendly water-based rGO/CNF ink. In the absence of an additional binder/surfactant, the rGO/CNF films demonstrated remarkably enhanced hydrophilicity while retaining good electrical conductivity. The concentration of CNF was varied to observe the variation in the electrochemical performance. At a current density of 1 mA/cm2, the rGO/CNF-15 film exhibited a maximum areal capacitance of 98.61 mF/cm2, closely matching that of pure rGO films. Because of its excellent electrical performance, ease of manufacturing, and environmental friendliness, this water-based rGO/CNF ink may have promising applications in the printing of supercapacitor electrodes.
Project description:Alternative green binders processable in water are being investigated for the development of more efficient and sustainable supercapacitors. However, their electrochemical performances have fallen within or below the average of commercially available devices. Herein, an optimised gelled mixture of graphene oxide (GO) and starch, a biopolymer belonging to the family of polysaccharides, is proposed. The molecular interactions between the two components enhance electrodes structure and morphology, as well as their thermal stability. GO, thanks to its reduction that is initially triggered by reactions with starch and further progressed by thermal treatment, actively contributes to the charge storage process of the supercapacitors. The optimised electrodes can deliver a specific capacitance up to 173.8 F g−1 while providing good rate capabilities and long-term stability over 17,000 cycles. These are among the best electrochemical performances achieved by environmentally friendly supercapacitors using a biomaterial as a binder. Environmentally friendly binders for energy materials may improve sustainability, but can suffer from poor performance. Here a gel derived from graphene oxide and starch is used as a hybrid binder for supercapacitors, providing good rate performance and stability over 17,000 cycles.
Project description:Poly(lactic acid) (PLA) electrospun membranes immobilized with Zeolitic imidazole framework/graphene oxide hybrid (ZIF-8@GO) are fabricated via electrospinning. At first, ZIF-8@GO is synthesized by the in situ growth method. The UV-visible light (UV-vis) result demonstrates that ZIF-8@GO has a narrower band gap than ZIF-8. The performance of the obtained composite membrane is investigated by scanning electron microscope, Fourier transform IR spectroscopy, tensile test, water contact angle, and methylene blue (MB) removal test. The results demonstrate that the degradable PLA/ZIF-8@GO electrospun membrane shows enhanced tensile strength than neat PLA. The composite membrane also shows great MB removal ability by adsorption and photocatalytic degradation. The MB removal efficiency could reach over 90% at very low ZIF-8@GO concentration (0.06 mg/mL).
Project description:Janus membranes with asymmetric surface wettability have been extensively utilized in various fields, including fog harvesting, because of their novel liquid transport properties. However, Janus membranes have an inherent disadvantage in terms of aerodynamic efficiency in harvesting fog because of the clogged water bridges caused by the small pore size. In the present work, we applied Janus wettability to mesh geometry with systematically varying hole sizes. For a clogged mesh with a small hole size, capillary water transport to the mesh back via the wettability gradient in the direction of fog flow helps harvest more fog by enhancing water drainage, similarly to the Janus membrane. The advantage of the capillary water transport extends to a clog-free mesh with larger hole sizes but more preferably to a Janus mesh with a superhydrophilic back, which presents the highest level of fog-harvesting yield because of the fast shedding frequency and short onset time. In contrast, a Janus mesh with a superhydrophobic front, which also has a wettability gradient along the fog flow, produces a lower fog-harvesting performance, particularly at slow fog speeds, because of the dropwise deposition of large water drops that locally disturb fog flow around a protruding water surface. On the other hand, the other type of Janus mesh with a superhydrophilic front is observed to minimize this disadvantage in the local fog flow by virtue of the filmwise deposition. It is also found that some Janus treatments can help protect mesh holes from clogging up by either forming a thin water meniscus or resisting water transport through the mesh holes.
Project description:Access to clean water is a global challenge, and fog collectors are a promising solution. Polycarbonate (PC) fibers have been used in fog collectors but with limited efficiency. In this study, we show that controlling voltage polarity and humidity during the electrospinning of PC fibers improves their surface properties for water collection capability. We experimentally measured the effect of both the surface morphology and the chemistry of PC fiber on their surface potential and mechanical properties in relation to the water collection efficiency from fog. PC fibers produced at high humidity and with negative voltage polarity show a superior water collection rate combined with the highest tensile strength. We proved that electric potential on surface and morphology are crucial, as often designed by nature, for enhancing the water collection capabilities via the single-step production of fibers without any postprocessing needs.
Project description:A method was developed to pattern the surface of perfluorinated materials with graphene oxide thin film, and various biological applications of the patterned perfluorinated surface were illustrated. Perfluorinated surfaces such as Teflon, Cytop, and other perfluorinated materials are known to be both hydrophobic and oleophobic, with low adhesion for most materials. Modifying the perfluorinated surfaces has been difficult due to the extraordinary chemical inertness, which limits the applications of perfluorinated materials as anti-fouling substrates. Herein we successfully patterned Cytop surfaces with graphene oxide. Patterns of the graphene oxide thin film with feature dimension down to 40 microns were formed and remained stable on the Cytop surface against washing with water, ethanol and acetone. The graphene oxide thin film on the Cytop surface allowed non-specific protein adsorption. To illustrate the applications of the patterned Cytop surface, we used the patterned Cytop surface as the substrate to study the protein-protein interactions, stem cell culture, and stem cell proliferation.
Project description:A synchronous ion separation and electricity generation process has been developed using G-O membranes. In addition to the size effect proposed prevsiouly, the separation of ions can be attributed to the different interactions between ions and G-O membranes; the generation of electricity is due to the confinement of G-O membranes, and the mobility difference of ions. Efficient energy transduction has been achieved with G-O membranes, converting magnetic, thermal and osmotic energy to electricity, distinguishing this material from other commercial semi-permeable membranes. Our study indicated that G-O membranes could find potential applications in the purification of wastewater, while producing electricity simultaneously. With G-O membranes, industrial magnetic leakage and waste heat could also be used to produce electricity, affording a superior approach for energy recovery.
Project description:Recently, green-prepared oxidized graphenes have attracted huge interest in water purification and wastewater treatment. Herein, reduced graphene oxide (rGO) was prepared by a scalable and eco-friendly method, and its potential use for the removal of methylene blue (MB) from water systems, was explored. The present work includes the green protocol to produce rGO and respective spectroscopical and morphological characterizations, as well as several kinetics, isotherms, and thermodynamic analyses to successfully demonstrate the adsorption of MB. The pseudo-second-order model was appropriated to describe the adsorption kinetics of MB onto rGO, suggesting an equilibrium time of 30 min. Otherwise, the Langmuir model was more suitable to describe the adsorption isotherms, indicating a maximum adsorption capacity of 121.95 mg g-1 at 298 K. In addition, kinetics and thermodynamic analyses demonstrated that the adsorption of MB onto rGO can be treated as a mixed physisorption-chemisorption process described by H-bonding, electrostatic, and π - π interactions. These results show the potential of green-prepared rGO to remove cationic dyes from wastewater systems.
Project description:Wide bandgap oxidized graphenes have garnered particular interest among the materials explored for these applications because of their exceptional semiconducting and optical properties. This study aims to investigate the tunability of the related properties in reduced graphene oxide (rGO) for potential use in energy conversion, storage, and optoelectronic devices. To accomplish this, we scrutinized crucial parameters of the synthesis process such as reduction time and temperature. Our findings demonstrate that controlling these parameters makes it possible to customize the optical bandgap of reduced graphene oxide within a range of roughly 2.2 eV-1.6 eV. Additionally, we observed that reduced graphene oxide has strong and superior absorption in the visible region, which is attributable to the existence of OFGs and defects. Notably, our results indicate that the absorption coefficients of reduced graphene oxide are up to almost three times higher (7426 ml mg-1 m-1) than those observed in dispersions of exfoliated graphene and graphene oxide (GO). To complement our findings, we employed several spectroscopic and morphological characterizations, including scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and electrical measurements. The implications of our results are significant for the development and design of future semiconductors for energy conversion and optoelectronic applications.
Project description:Dry-spinning method is extensively employed in fiber industry, comparing to the counter-part of wet-spinning process, it has advantages of environmentally friendly, high yield rate and no need for purification. Here, we report the synthesis of graphene oxide (GO) fibers via dry spinning GO inks with extremely high concentrations. The proper rheology properties of such GO inks allow us to dry spin GO fiber directly. Various dry spinning conditions are investigated, and the relationship between mechanical performance and micro-structure of the obtained GO fiber are established. We found that the existence of larger GO liquid crystal domains does not necessarily result to higher mechanical properties, and it is because those large GO liquid crystal domains evolve into thick GO films during drying process and thus prevent the intimate compaction of the whole GOF and leave behind gaps. This is detrimental for the mechanical properties, and thus the dry spin GOF are much weaker than that of wet spin ones. Importantly, Barus effects, that generally arise during the melt spinning of polymers, were not observed, indicating that caution must be taken when classical polymer rheology theories are applied to investigate the dynamic behaviors of GO solution.