Graphene Oxide "Surfactant"-Directed Tunable Concentration of Graphene Dispersion

Graphene in 3D Bioprinting

Three-dimensional (3D) bioprinting is a fast prototyping fabrication approach that allows the development of new implants for tissue restoration. Although various materials have been utilized for this process, they lack mechanical, electrical, chemical, and biological properties. To overcome those limitations, graphene-based materials demonstrate unique mechanical and electrical properties, morphology, and impermeability, making them excellent candidates for 3D bioprinting. This review summarizes the latest developments in graphene-based materials in 3D printing and their application in tissue engineering and regenerative medicine. Over the years, different 3D printing approaches have utilized graphene-based materials, such as graphene, graphene oxide (GO), reduced GO (rGO), and functional GO (fGO). This process involves controlling multiple factors, such as graphene dispersion, viscosity, and post-curing, which impact the properties of the 3D-printed graphene-based constructs. To this end, those materials combined with 3D printing approaches have demonstrated prominent regeneration potential for bone, neural, cardiac, and skin tissues. Overall, graphene in 3D bioprinting may pave the way for new regenerative strategies with translational implications in orthopedics, neurology, and cardiovascular areas.

Unravelling the pseudocapacitive origin of graphene oxide-based aerogels by comparative insights

We reveal the intrinsic pseudocapacitive center of graphene-oxide-based aerogels by investigating different modified graphene skeletons from various approaches. A high proportion of carbonyl groups in carbon networks is shown to optimize the construction of rational pseudocapacitive sites by triggering reversible proton-induced surface reactions, leading to satisfactory electrochemical performance.

ZnO/Graphene Oxide on Halloysite Nanotubes as a Superabsorbent Nanocomposite Photocatalyst for the Degradation of Organic Dyes

Using renewable photocatalysts for pollutant degradation represents a promising approach to addressing environmental water challenges by harnessing solar energy without additional energy consumption. However, for the practical use of photocatalysts, it is necessary to improve catalyst efficiency, considering cost and biocompatibility. In this study, we developed a new superabsorbent photocatalyst for the degradation of organic dyes in water. Our photocatalyst comprises halloysite nanotubes (HNTs) with a large outer diameter and Si-O and Al-O groups on the outer and inner surfaces, respectively; graphene oxide (GO) possessing numerous sp2 bonds and light-conductive properties; and ZnO, which can degrade organic molecules via a photon source. By exploiting the superabsorbent properties of GOs for organic dyes and stabilizing ZnO nanoparticles on HNTs to inhibit aggregation, our photocatalysts demonstrated significantly improved degradability compared to ZnO nanoparticles alone and combinations of ZnO with HNTs or GO. The structural characteristics of the nanocomposites were characterized using SEM, EDX, Raman spectroscopy, and XRD. Their enhanced photocatalytic activity was demonstrated by the degradation of rhodamine b in water, showing 95% photodegradation under UV illumination for 60 min, while the ZnO nanoparticles showed only 56% dye degradation under the same condition. Additionally, the degradation rate was enhanced by four times. Furthermore, the catalysts maintained their initial activity with no significant loss after four uses, showing their potential for practical implementation in the mass purification of wastewater.

Humanoid shaped optical fiber plasmon biosensor functionalized with graphene oxide/multi-walled carbon nanotubes for histamine detection

Histamine is a biologically active molecule that serves as a reliable predictor of the quality of fish. In this work, authors have developed a novel humanoid-shaped tapered optical fiber (HTOF) biosensor based on the localized surface plasmon resonance (LSPR) phenomenon to detect varying histamine concentrations. In this experiment, a novel and distinctive tapering structure has been developed using a combiner manufacturing system and contemporary processing technologies. Graphene oxide (GO)/multi-walled carbon nanotubes (MWCNTs) are immobilized on the HTOF probe surface to increase the biocompatibility of biosensor. In this instance, GO/MWCNTs are deployed first, then gold nanoparticles (AuNPs). Consequently, the GO/MWCNTs help to give abundant space for the immobilization of nanoparticles (AuNPs in this case) as well as increase surface area for the attachment of biomolecules to the fiber surface. By immobilizing AuNPs on the surface of the probe, the evanescent field can stimulate the AuNPs and excite the LSPR phenomena for sensing the histamine. The surface of the sensing probe is functionalized with diamine oxidase enzyme in order to enhance the histamine sensor's particular selectivity. The proposed sensor is demonstrated experimentally to have a sensitivity of 5.5 nm/mM and a detection limit of 59.45 µM in the linear detection range of 0-1000 µM. In addition, the probe's reusability, reproducibility, stability, and selectivity are tested; the results of these indices show that the probe has a high application potential for detecting histamine levels in marine products.

Self-assembly of guanosine into carbon-based multilayer materials

We report the utilization of guanosine as a supramolecular precursor that unprecedentedly renders the formation of carbon-based multilayer materials with naturally high-level nitrogen doping. As a proof-of-concept, the porous carbon multilayers after anchoring 0.5 wt% Rh electrocatalysts displayed an excellent hydrogen evolution reaction activity.

Improved Dispersibility of Graphene in an Aqueous Solution by Reduced Graphene Oxide Surfactant: Experimental Verification and Density Functional Theory Calculation

It is difficult to disperse graphene flakes well in an aqueous solution while maintaining conductivity due to its high hydrophobicity. Herein, we demonstrated that a well-dispersed state of graphene in an aqueous solution was realized by using reduced graphene oxide (rGO) with a suitable content of oxygen-functional groups. A rGO-dispersed graphene (rGO/G) film was fabricated from the graphene dispersion with good conductivity by using rGO with a C/O ratio of 2.48 as the surfactant. Also, the prepared rGO/G aerogel has a broad prospect. Density functional theory calculation revealed that the strong electrostatic repulsion, which was more potent than the van der Waals force and the π-π interaction, was the primary driving force promoting the dispersibility of graphene in an aqueous solution. Furthermore, the repulsion of the rGO/G dispersion decreased with the reduction of the oxygen-functional groups of rGO. Therefore, applying rGO with an appropriate content of oxygen-functional groups is an alternative option to improve the dispersibility of graphene in an aqueous medium while maintaining its original properties, from which many potential applications could be expected.

Redispersible Reduced Graphene Oxide Prepared in a Gradient Solvent System

We designed a gradient solvent strategy for the reduction of graphene oxide, matching the hydrophilic properties of graphene oxide (GO) and reduced graphene oxide (RGO), respectively. A third solvent was added dropwise to regulate the hydrophilic variation of the continuous gradient system which maintained the whole reduction process without aggregation, and the obtained RGO dispersions could maintain stability for a long time. The separated RGO solid powder can be directly ultrasonically redispersed in N-methyl-pyrrolidone (NMP) with an average particle size as low as 200 nm. Furthermore, RGO with a high C/O ratio of 13.75 was prepared on the basis of the gradient solvent system. Using different structures of dispersants and polymers as representatives, we employed successive solvent rinsing, thermal solvent extraction, and thermal treatment to study adsorption and desorption. It was found that the above measures differed significantly in the removal of surface sorbates. The selected fatty alcohol polyoxyethylene ether (AEO) series achieved a good balance between the system dispersion and surface adsorbate removal. The conductivity was originally 5236 S m^-1, and it increased from 9024 to 18,000 S m^-1 after thermal treatment at 300 and 500 °C, respectively.

Roles of Graphene Oxide in Heterogeneous Photocatalysis

Graphene oxide (GO) has been widely utilized as the precursor of graphene (GR) to fabricate GR-based hybrid photocatalysts for solar-to-chemical energy conversion. However, until now, the properties and roles that GO played in heterogeneous photocatalysis have remained relatively elusive. In this Review, we start with a brief discussion of synthesis and structure of GO. Then, the photocatalysis-related properties of GO, including electrical conductivity, surface chemistry, dispersibility, and semiconductor properties, are concisely summarized. In particular, we have highlighted the fundamental multifaceted roles of GO in heterogeneous photocatalysis, which contain the precursor of GR, cross-linked framework for constructing aerogel photocatalyst, macromolecular surfactant, two-dimensional growth template, and photocatalyst by itself. Furthermore, the future prospects and remaining challenges on developing effective GO-derived hybrid photocatalysts are presented, which is expected to inspire further research into this promising research domain.

Recent Studies on Dispersion of Graphene-Polymer Composites

Graphene is an excellent 2D material that has extraordinary properties such as high surface area, electron mobility, conductivity, and high light transmission. Polymer composites are used in many applications in place of polymers. In recent years, the development of stable graphene dispersions with high graphene concentrations has attracted great attention due to their applications in energy, bio-fields, and so forth. Thus, this review essentially discusses the preparation of stable graphene-polymer composites/dispersions. Discussion on existing methods of preparing graphene is included with their merits and demerits. Among existing methods, mechanical exfoliation is widely used for the preparation of stable graphene dispersion, the theoretical background of this method is discussed briefly. Solvents, surfactants, and polymers that are used for dispersing graphene and the factors to be considered while preparing stable graphene dispersions are discussed in detail. Further, the direct applications of stable graphene dispersions are discussed briefly. Finally, a summary and prospects for the development of stable graphene dispersions are proposed.