Functionalized Graphene Oxide Nanostructures Enhance Targeted Drug and Gene Delivery, Immunomodulation, Photothermal/Photodynamic Therapy, and Cancer Theranostics.

Synthesis and characterization of graphene oxide, tin oxide, and reduced graphene oxide-tin oxide nanocomposites

Event Abstract Back to Event Gene therapy nanovehicle prospect based on graphene oxide (GO), citric acid (CA) and polyethylene glycol diamine (PEGDA) Bexi Bustillo1, Leticia Arregui1 and Ferdinando Tristán1 1 UAM Cuajimalpa, Natural sciences and engineering, Mexico Introduction: Gene therapy is defined by the intentional modulation of gene expression in cells to treat specific diseases and it has had problems during application in patients, particularly in gene delivery[1]. Due to its physicochemical, and mechanical properties, graphene oxide (GO) has been extensively explored in many fields and it has emerged as a prospect in biomedicine for drug and gene delivery[2],[3]. In this work, we obtained a conjugate based on GO, citric acid and polyethyleneglycol diamine (PEGDA) as a prospect for biocompatible gene delivery vector. Materials and Methods: GO was obtained from expanded graphite by using a modified version of Hummer's method. CA was covalently attached to carboxilated GO; next, PEGDA was added in order to obtain free amine groups. Every step of the synthesis was characterized using several techniques (FTIR, AFM, Zeta potential). The cytotoxicity of synthesized materials was evaluated by Alamar blue assay. Agarose gel electrophoresis analysis at different (w/w) ratios was used to explore the plasmid-nanovehicle complex formation. Results: GO showed typical IR bands at 3320 cm-1 for O-H bond; 1720-1740 cm-1 for C=O; 1250 cm-1 for C-O corresponding to O-H and -COOH functional groups. After PEGD functionalization, 1630-1695 cm-1 bands for the amide bond in the GO-CA-PEGDA conjugate was identified. GO thickness by AFM micrographs was ~ 1.1 nm. No significant difference in viability was found amongst control, GO and GO derivatives treated cultures by Alamar blue assay. Zeta potential measurements showed that all the modifications decreased negative charge of GO, which is helpful for the interactions with DNA. Discussion: CA covalent attachment to GO as well as attachment of PEGDA amine groups was confirmed by FTIR where typical adsorption bands were observed. The ratio C/O and C/N was evaluated by elemental analysis indicating the positive functionalization with PEGDA. AFM results indicated that synthesized GO can be found as monolayers and functionalization with PEGDA modifies the texture of the surface of GO derivatives. The surface charge of GO and GO derivatives was modified due to the functionalization. GO, GO-CA and GO-CA-PEGDA conjugates do not induce cytotoxicity. Conclusion: Amine terminated nanovehicles are very useful to design gene and drug delivery systems[4]. Regardless of the extensive interest in biomedical applications of nanovehicles there is concern regarding toxicity. That is why the main purpose was to prepare a novel prospect of biocompatible gene delivery system based on GO, CA and PEGDA. CA was expected to generate branches onto GO surface and enhance amide bonding with PEGDA. All these materials were chosen due to their good water solubility, low toxicity and biocompatibility, making this system a good candidate for gene delivery.

The synthesis of graphene oxide (GO)–polystyrene (PS) Pickering emulsions, as environment‐friendly nanostructures suitable for novel applications, has received significant attention in recent years. In this work, the synthesis and characterization of GO–PS nanocomposites through seeded emulsion polymerization and the selective light reflection properties of dry films have been reported. Amphiphilic molecule sulfonated 3‐pentadecyl phenol was used as a co‐surfactant to stabilize GO dispersions during the emulsion polymerization process. The particle size of the dispersions as measured by dynamic light scattering decreases from 540 nm, for PS without any GO, to 88 nm with 1 wt% GO content. Scanning electron microscopy studies show a uniform size distribution of the composite particles prepared with GO. The dried films show a structural color that varies with the GO content. The self‐assembly behavior of the dried film was further studied using reflectance spectroscopy, which shows a red shift of the reflectance maximum from 440 to 538 nm as the GO loading was increased from 0.2 to 0.5 wt%, respectively, indicating a different microstructure. X‐ray diffraction, transmission electron microscopy (TEM) and atomic force microscopy (AFM) were used to study the morphology and structure of the composite particles on drying. The AFM study confirms the non‐spherical shape of the particles. Thermogravimetric analysis shows improved thermal decomposition characteristics of the nanocomposite films. Copyright © 2015 John Wiley & Sons, Ltd.

With the rapid development of graphene industry, low-cost sustainable synthesis of monolayer graphene oxide (GO) has become more and more important for many applications such as water desalination, thermal management, energy storage and functional composites. Compared to the conventional chemical oxidation methods, water electrolytic oxidation of graphite-intercalation-compound (GIC) shows significant advantages in environmental-friendliness, safety and efficiency, but suffers from non-uniform oxidation, typically ~50 wt.% yield with ~50% monolayers. Here, we show that water-induced deintercalation of GIC is responsible for the non-uniform oxidation of the water electrolytic oxidation method. Using in-situ experiments, the control principles of water diffusion governing electrochemical oxidation and deintercalation of GIC are revealed. Based on these principles, a liquid membrane electrolysis method was developed to precisely control the water diffusion to achieve a dynamic equilibrium between oxidation and deintercalation, enabling industrial sustainable synthesis of uniform monolayer GO with a high yield (~180 wt.%) and a very low cost (~1/7 of Hummers’ methods). Moreover, this method allows precise control on the structure of GO and the synthesis of GO by using pure water. This work provides new insights into the role of water in electrochemical reaction of graphite and paves the way for the industrial applications of GO.

Graphene oxide (GO) has become one of the emerging and important sole photocatalyst nanomaterials in recent years due to its exceptional/tunable optoelectronic properties, multifunctionality, and eco‐friendly nature. However, challenges remain in tuning surface chemistry, tailoring the band gap, developing doping strategies, and understanding the sole photocatalytic mechanism. This contribution investigated the synthesis of GO via the improved Hummers method by varying the ratio of the oxidizing agents (K2Cr2O7:KMnO4), as well as modifications by nitrogen (N) and boron (B) doping in view of its applications in photocatalytic degradation of organic dye pollutants. Furthermore, changes in surface chemistry, optical, compositional, morphological, and structural properties are investigated to understand the photocatalytic mechanism. The synthesized GO showed a broad spectrum of light absorption with a tunable band gap of 2.4–4.3 eV and exhibited more than 91% degradation of methylene blue dye under direct sunlight. However, the photocatalytic activity decreased after N and B doping attributed to reduced oxygen‐containing functional groups, low surface area, and dopants‐induced bonding configurations within the GO structure. This study provides a new insight into replacing metallic semiconductor photocatalysts with highly affordable, environmentally friendly, and potent metal‐free GO photocatalysts.

In today's technology, carbon-based materials (such as graphene, graphene oxide, carbon nanotubes, etc.) have become one of the most important research areas due to a large number of applications. Graphene oxide (GO) is being investigated in many applications, especially in the energy field. In this study, GO was synthesized by a modified Hummer’s method. After the synthesis of GO, nickel addition to the struc-ture was made by the hydrothermal method. The morphological and structural prop-erties of the synthesized GO were characterized by scanning electron microscope (SEM), X-ray powder diffraction (XRD) and Brunauer–Emmett–Teller (BET). Ac-cording to the BET results, the surface areas of untreated GO and Ni-doped graphene oxide after heat treatment at 360°C (Ni-doped GO 360) were calculated as 3.22 m2 g-1 and 228 m2 g-1, respectively. Electrochemical properties of GO and Ni-doped GO 360 were analyzed using cyclic voltammetry (CV), long term charge/discharge analysis and impedance spectroscopy. At the end of 1000 cycles, it was determined that the Ni-doped GO 360 electrode retained 76% of its initial capacitance.

One of the materials that has attracted the attention of nanotechnology researchers today is graphene oxide (GO). GO was first developed by Oxford chemist Benjamin C. Brody in 1859 by processing graphite with a mixture of potassium chlorate and smoky nitric acid. GO, formerly known as graphite acid, is a combination of carbon, oxygen, and hydrogen in variable ratios obtained by refining graphite with strong oxidants and acids to decompose excess metals. The oxidized product is a yellow solid with a C: O ratio between 2.1 and 2.9 that maintains the structure of the graphite layer but at a much larger and irregular distance (Januário et al., 2021). GO is a two-dimensional, monolayer material with a hexagonal and crystalline structure that has oxygen groups on its plates and its high biocompatibility and biodegradability has made it one of the nanomaterial substrates for stabilizing and transporting enzymes. In recent years, researchers have used the substance in both medical and pharmaceutical technologies and industrial applications (Abdelhamid & Hussein, 2021). The use of GO for a glucose sensor was first reported in 2009 (Karki et al., 2020). GO has been used in various fields, including in the manufacture of sensors, due to its outstanding chemical, electrical and optical properties, as well as its high oxygen content. Also as an antimicrobial agent for biomedical applications, as well as nanofillers for membranes was used in wastewater treatment. The future of GO-based membranes for the treatment of water-contaminated water is also presented. GO sheets are used to make materials such as paper, membranes, thin films, and composites. Initially, graphene oxide was considered as a possible intermediate for the production of graphene (Januário et al., 2021). Biochemical and biomedical applications of GO rely heavily on the interactions of biomolecules with it (Zhang et al., 2012). This carbon-based nanoparticle is also used as a drug carrier (Abdelhamid & Hussein, 2021). Chemical vapor deposition and thermal peeling, microchannel peeling of graphite, and direct synthesis and chemical peeling of graphite, are common methods for GO synthesis developed by Brody Stedemiz and Hummer (Ciszewski & Mianowski, 2013). The method chosen in present study for GO synthesis is the modified Hammers method, in which the synthesis duration was shorter and the process was easier. And 0.5 g sodium nitrate were mixed with 23 mL sulfuric acid in a 500 mL flask place in. To synthesize GO, 0.5 g of natural graphite powder and 0.5 g of NaNo3 mixed with 23 ml of sulfuric acid in a 500 mL flask placed in an ice bath (below 20 °C) for 4 hours with stirring. 3 grams of potassium permanganate was added to the flask and the solution was stirred for one hour. The temperature was increased to 35 °C and the solution was stirred for another one hour. 46 mL of distilled water was added slowly and the temperature was increased to 95 °C without boiling for 2 hours. The solution was left to reach the same room temperature. 100 mL distilled water was added and stirred for an hour. 10 mL hydrogen peroxide (0.30%) was added to the solution and stirred for an hour. The solution was centrifuged at 5000 rpm for 7 minutes and the supernatant was removed. 30 mL distilled water and 10 mL HCl (0.37%) was added to the precipitate and the solution was centrifuged. This procedure was carried out for 3 times. The obtained precipitate was evaluated using x-ray diffraction pattern (XRD), scanning electron microscope (SEM) and fourier transform infrared spectroscopy (FTIR) to demonstrate whether the precipitated material was GO nanoparticles. The XRD pattern for GO (Figure 1), SEM image (Figure 2) and The FTIR spectra confirmed the fabrication of GO (Figure 3). We have shown that our modified Hummer method for GO synthesis, is a convenient and cost-effective synthesis of GO nanoparticle.

The modified Graphene Oxide (GO) synthesis methods used over the past sixty years is contributed mainly to improving its characteristics and increasing its advanced applications. Therefore, in this work, modifying Hummer’s Method via oxidizing graphite flakes using one type of acid (H₂SO₄) was performed without any chemical agents. Also, ultra-sonication and filtration were implemented with optimal parameters (50 kHz frequency during 120 minutes at room temperature 30 ^oC) to prepare GO nanosheets. These procedures improved GO characteristics via analyzing; Particle size, X-ray diffraction pattern (XRD), Ultra-violet visible (UV-vis) absorption, and Scanning Electron Microscopy (SEM). The obtained results showed that the characteristics of GO nano-sheets had met the preparation requirements, such as reducing the average diameter of GO nano‑sheets from 313 nm to 94 nm. Moreover, characterizing the diffraction angle of GO at 9.86^o and the optimal absorption by UV-vis achieved at 230 nm. The synthesis and exfoliation of GO nano-sheets were carried out with fewer impacts of toxicity using distilled water. Finally, this GO synthesis in the lab might be used to make a variety of nanocomposites.

Kinetic study of graphene oxide synthesis by electrochemical exfoliation of graphite

The improved Hummers’ synthesis of graphene oxide (GO) from graphite is investigated to monitor how the functional groups form during the synthesis steps. To achieve these, samples are taken after every preparation step and analyzed with TG–DTA/MS, FTIR, XRD and SEM–EDX techniques. It was found that the main characteristic mass loss step of GO was around 200 °C, where at first the carboxyl and lactone groups were released, and the evolution of sulfonyl groups followed them right away in a partially overlapping step. It became clear that in the as-prepared acidic GO sample the presence of H2SO4 originating from the reaction solution was still dominant. The functional groups were formed only after washing the as-prepared GO with HCl. The consecutive washing step with distilled water did not alter the functional groups or the thermal properties significantly; however, it made the GO structure more ordered. The reduction of the GO structure back to reduced GO resulted in the loss of the functional groups, and a graphitic material was obtained back.

Graphene Oxide (GO) is one of the common members of the graphene family owing to its unprecedented and unique properties. These properties attract researchers to use GO in several potential applications such as a transparent electrode in light-emitting diodes (LED), biosensors and solar cells, etc. In this work, GO was produced through the oxidation of graphite by potassium permanganate using modified Hummer’s method and this was followed by ozone treatment. The crystallographic structure, chemical properties, surface morphologies, and optical properties of before and after treatment of GO were determined by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and UV- visible spectroscopy. The FTIR observation confirmed the formation of GO from graphite flakes. XRD results showed peak at11.6˚ with a different interlayer spacing of 0.7nm and 0.8nm for GO and ozone-treated graphene oxide (O- GO) respectively. While for both GO and O- GO all the peaks were at the same position. Further, SEM micrographs of GO exhibited the multilayered graphene oxide with variable thickness. While the rough surface of O- GO suggests the reduction of GO particle size due to ozonation. Ultraviolet-visible spectra of GO at 223.2 nm was noted which is attributed to atomic C- C bonds but O- GO exhibited the peak shift at 232.7 nm thereby suggesting a higher surface area.

Graphene is a promising candidate for making next-generation nanotechnology devices due to its outstanding properties in terms of physical, chemical, mechanical aspects. Based on the theoretical point of view, graphene is a two-dimensional (2D) crystal structure with sp2 hybridized carbon atoms arrangement and has attracted extensive attention in a considerable number of applications such as solar energy, sensor and energy storage, naming a few. Herein, graphene oxide (GO) is synthesized from graphite flakes using the Improved Hummer's method. The results demonstrated the comparison of synthesized GO samples based on stirred duration of 6 h and 72 h. The FTIR results proved that the 72 h GO sample was well-bonded with the C-O functional group, signifying the successful synthesis of GO under an extended stirred duration. The FESEM images showed that the synthesized GO was well-arranged in crystal lattice of graphene sheets whereas the EDX result showed that higher atomic % of Oxygen, O2 was obtained with a longer stirred duration due to the high opportunity for oxygenated bonded to occur on the C-C functional group.

Graphene oxide (GO) and reduced graphene oxide (rGO) synthesised from GO, has a promising future in fields ranging from electronics to energy technologies[1]. GO may be synthesized by the modified Hummer’s method[2], where a mixture of potassium permanganate and concentrated sulfuric acid forms the ground pillar for the oxidation of graphite to GO. rGO can be synthesized by a broad range of methods, with the chemical and the thermal reduction routes being very common[3]. The synthesis mechanism of GO by the modified Hummer’s method is still unknown, even though the active oxidizing species dimanganese heptoxide has been suggested as the main redox active specie[4]. The mechanism of the thermal reduction of GO to rGO is also unknown. We present results from i n situ synchrotron X-ray diffraction (XRD) experiments of syntheses and thermal reduction of GO. The in situ synthesis of GO was performed by placing a mixture of permanganate and sulphuric acid in a capillary next to graphite. The synthesis was then initiated by gently pushing the fluid mixture into the powder with N2 gas. The in situ XRD of the GO synthesis showed how the oxidation reaction proceeds in three separate stages, as seen in Figure 1. The first stage was the dissolution of potassium permanganate, followed by an intercalation stage and subsequent formation of crystalline material. The GO 001 diffraction peak was observed early during the synthesis, in the second stage, and the intensity of the 001 diffraction increased during the third stage. The in situ XRD results of the thermal reduction of GO to rGO showed a dependence on the temperature ramping and addition of diamond powder. Syntheses were measured at 1, 5, 10, 20 and 50 °/min temperature ramps. The syntheses were performed in a capillary with GO being heated by a hot air blower under constant N2 flow. Three stages were observed for the reduction process; a GO stage, an amorphous stage and a rGO stage. The change in stage was defined from the changing of the d-value of the initial 001 GO peak, see Figure 2. The initial GO diffraction pattern changed during the heating and more diffraction peaks were observed. The results showed that the nature of the rGO material depends heavily on both temperature and additives. These in situ XRD studies revealed the crystalline intermediates and final product of synthesis by a modified Hummer’s method and the diffractional change during the thermal reduction of GO. The stages observed for both syntheses illuminate how important it is to consider the experimental parameters dependent on the application; they might even have to be optimized separately. As the future use of GO and rGO is expanding and the commercialization of these products are enhanced, the syntheses mechanisms may be of increasing interest. [1] M. Segal, Nat Nano, 4 (2009) 612-614. [2] Hummer and Offeman, J. Am. Chem. Soc. (1958) 1339-1339 [3] Pei and Cheng, Carbon (2012) 3210-3228 [4] Dreyer, Park, Bielawski and Ruoff, Chem. Soc. Rev. (2010) 228-240 Figure 1

Graphene oxide (GO) sheets are emerging as a new class of carbocatalysts. Conventionally, researchers exfoliate graphite oxide into submicrometer-sized, water-dispersible flakes to produce these sheets. The presence of oxygen functional groups on the aromatic scaffold of GO allows these sheets to mediate ionic and nonionic interactions with a wide range of molecules. GO shows remarkable catalytic properties on its own and when hybridized with a second material. It is a perfect platform for molecular engineering. This Account examines the different classes of synthetic transformations catalyzed by GO and correlates its reactivity with chemical properties. First, we raise the question of whether GO behaves as a reactant or catalyst during oxidation. Due to its myriad oxygen atoms, GO can function as an oxidant during anaerobic oxidation and become reduced at the end of the first catalytic cycle. However, partially reduced GO can continue to activate molecular oxygen during aerobic oxidation. Most importantly, we can enhance the conversion and selectivity by engineering the morphology and functionalities on the G/GO scaffold. GO can also be hybridized with organic dyes or organocatalysts. The photosensitization by dyes and facile charge transfer across the graphene interface produce synergistic effects that enhance catalytic conversion. Using GO as a building block in supramolecular chemistry, we can extend the scope of functionalities in GO hybrids. The presence of epoxy and hydroxyl functional groups on either side of the GO sheet imparts bifunctional properties that allow it to act as a structural node within metal-organic frameworks (MOFs). For example, known homogeneous molecular catalysts can be anchored on the GO surface by employing them as scaffolds linking organometallic nodes. We have demonstrated that porphyrin building blocks with GO can lead to facile four-electron oxygen transfer reactions. We have also evaluated the advantages and disadvantages of GO as a catalytic material relative to other types of catalysts, both metallic and nonmetallic. Researchers would like to increase the potency of GO catalysts because many catalytic reactions currently require high loading of GO. Further research is also needed to identify a low-cost and environmentally friendly method for the synthesis of GO.

The synthesis of graphene oxide-coated mesoporous silica (MS_GO) with the template surfactant (Cetyltrimethylammonium Bromide) CTAB has been carried out. The effect of combining mesoporous silica and graphene oxide was studied by knowing the bonds, functional groups and crystalline structures. Functional groups C=O and C=C were formed at wave numbers 1,722, 1,617 and 1,647 cm−1, respectively, as a characteristic of GO compounds. XRD data showed that MS_GO has a more amorphous structure than graphite and GO due to the incorporation of silica onto the graphene oxide surface. The MS_GO synthesis was also applied as an adsorbent for methylene blue dye in water. The adsorption results showed that MS_GO was more effective than pure GO. The percent adorption efficiency (R %) of MS_GO against 10 ppm methylene blue was 93.1 % while that of pure GO was 91.5 %. The addition of mesoporous silica to graphene oxide makes MS_GO adsorbent more effective in adsorption dyes than pure GO, this is supported by the larger total surface area of BET MS_GO was 161.066 m2·g−1, while that of pure GO was 103.818 m2·g−1. HIGHLIGHTS Preparation of graphene oxide from graphite by the modified hummer method Mesoporous silica is synthesized with Graphene Oxide (GO) and occupies between GO layers in the GO interlayer space CTAB is used as a template and forms pores in the synthesis of layered Mesoporous Silica-Graphene Oxide (MS_GO) Graphene Oxide-Coated Mesoporous Silica will be applied for adsorption of methylene blue dye in water. The adsorption efficiency (% R) of GO against methylene blue is lower than % R of MS_GO against methylene blue GRAPHICAL ABSTRACT