Functional Groups Of Graphene Oxide Research Articles

Theoretical and experimental study on efficient thorium removal from aquatic environment using phosphate-modified graphene oxide polymeric beads

AbstractThorium is an element of immense importance in nuclear industry due to lower environmental impact compared to fossil fuels and conventional nuclear power. In the present study, highly selective adsorption of Th4+ on phosphate modified graphene oxide polymeric beads was investigated. The interaction of –PO4, –OH and –O– functional groups of graphene oxide with thorium ion was thoroughly investigated using Density Functional Theory. The adsorption induced density difference was utilized to investigate the bonding characteristics. The affinity of the Th4+ ions was obtained as –PO4 > –OH > –O– group of the phosphate modified graphene oxide. Phosphate modified Graphene oxide embedded in Calcium alginate matrix was characterized using ATR-FTIR, XRD, SEM and Raman spectroscopy. Highly efficient (> 93%) uptake of thorium at pH 5 with fast rate of sorption (< 5 min) was observed in the batch sorption studies.

Graphene Oxide/Black Phosphorus Functionalized Collagen Scaffolds with Enhanced Near-Infrared Controlled In Situ Biomineralization for Promoting Infectious Bone Defect Repair through PI3K/Akt Pathway.

Infectious bone defects resulting from surgery, infection, or trauma are a prevalent clinical issue. Current treatments commonly used include systemic antibiotics and autografts or allografts. Nevertheless, therapies come with various disadvantages, including multidrug-resistant bacteria, complications arising from the donor site, and immune rejection, which makes artificial implants desirable. However, artificial implants can fail due to bacterial infections and inadequate bone fusion after implantation. Thus, the development of multifunctional bone substitutes that are biocompatible, antibacterial, osteoconductive, and osteoinductive would be of great clinical importance. This study designs and prepares 2D graphene oxide (GO) and black phosphorus (BP) reinforced porous collagen (Col) scaffolds as a viable strategy for treating infectious bone defects. The fabricated Col-GO@BP scaffold exhibited an efficient photothermal antibacterial effect under near-infrared (NIR) irradiation. A further benefit of the NIR-controlled degradation of BP was to promote biomineralization by phosphorus-driven and calcium-extracted phosphorus in situ. The abundant functional groups in GO could synergistically capture the ions and enhance the in situ biomineralization. The Col-GO@BP scaffold facilitated osteogenic differentiation of bone marrow-derived mesenchymal stem cells (BMSC) by leveraging its mild photothermal effect and biomineralization process, which upregulated heat shock proteins (HSPs) and activated PI3K/Akt pathways. Additionally, systematic in vivo experiments demonstrated that the Col-GO@BP scaffold obviously promotes infectious bone repair through admirable photothermal antibacterial performance and enhanced vascularization. As a result of this study, we provide new insights into the photothermal activity of GO@BP nanosheets, their degradation, and a new biological application for them.

Evolution of Oxygen Content of Graphene Oxide for Humidity Sensing.

Graphene oxide (GO) has shown significant potential in humidity sensing. It is well accepted that the oxygen-containing functional groups in GO significantly influence its humidity sensing performance. However, the relationship between the content of these groups and the humidity sensing capability of GO-based sensors remains unclear. In the present work, we investigate the role of oxygen-containing functional groups in the humidity sensing performance by oxidizing graphite with mesh numbers 80-120, 325, and 8000 using the Hummers method, resulting in GO-80, GO-325, and GO-8000. Infrared spectroscopy (IR) and X-ray photoelectron spectroscopy (XPS) were used to identify the types and quantification of oxygen-containing functional groups. Molecular dynamics simulation is used to simulate the adsorption energy, intercalation dynamics, and hydrogen bonding of water molecules. Electrochemical tests were used to compare the adsorption/desorption time and response sensitivity of graphene oxide to humidity. It is proposed that hydroxyl and carboxyl groups are the main contributing groups to humidity sensing. GO-8000 shows a relatively fast response time, but the large number of carboxyl groups will hinder intercalation of water molecules, thus exhibiting lower sensitivity. This research provides a reference for the future development of graphene-based sensors, catalysts, and environmental materials.

Unraveling the infrared spectrum of graphene oxide

The applicability of infrared spectroscopy toward graphene oxide (GO) and its derivatives is currently very limited, because the exact location of absorbance bands, originated by the main functional groups of GO, in the spectrum is still under debate. This obstacle leads to widespread misinterpretation of FTIR spectra in literature, and to invalid conclusions on attaining target functionalization reactions. In this work, by involving GO in four types of reactions, for the first time, we identify absorbance bands, originated by the main functional groups of GO: epoxides and tertiary alcohols. Also, we identify the bands, associated with carboxyl and carboxylate groups. In addition, we reconfirm the band assignment for absorbed water molecules (1619 cm−1) and covalent sulfates (1221 cm−1 and 1410 cm−1). Finally, we show conditions for appearance, and the exact position of the band of the C=C bond stretch. All together we accurately assign eight previously unidentified or incorrectly assigned absorbance bands in the fingerprint region of the spectrum, plus three bands which appear in the spectra of specific forms of GO. The assignment of the bands is independently confirmed by the 13C SSNMR spectroscopy. Summing up the newly assigned and the re-confirmed bands, for the first time, we report a complete library of the main absorbance bands in the FTIR spectrum of GO and GO derivatives.

Electrocatalytic tungsten boride quantum dots anchored reduced graphene oxide as the desolvation promotor for efficient sulfur redox kinetics

Lithium-sulfur (Li-S) batteries boast a multitude of compelling attributes, chief among them being their exceptional energy density and relatively low raw material costs. However, the sluggish redox kinetics of sulfur stemming from the considerable desolvation energy barrier and the notorious shuttle effect of lithium polysulfides, pose significant challenges in the commercialization of Li-S batteries. In this work, ultra-fine WB quantum dots were in-situ and uniformly dispersed on reduced graphene oxide nanosheets (WB-rGO) by mild melting-salt method, in which the abundant oxygen-containing functional groups in graphene oxide effectively prevent the agglomeration of WB. Such ultra-fine WB quantum dot as well as dual-active sites stemming from W and electronics-deficient B, confer the WB-rGO composite with improved electrochemical active surface area for dissociating Li+-solvents molecules and catalyzing polysulfides transformations, thus improving cycling and rate performance of Li-S battery. Hence, the cells with WB-rGO@PP maintained a stable long-term cycling (650 mAh g−1 after 900 cycles at 1 C with an average decay rate of 0.038 % per cycle) and an impressive rate capability (740 mAh g−1 at 4 C). Even at a sulfur loading of 4.7 mg cm−2, the cell performed a high areal capacity of 3.6 mAh cm−2 after 200 cycles.

Chemical stitching of a reduced and fluorine decorated graphene oxide quilt

This work demonstrated the possibility of obtaining continuous thin transparent films of reduced graphene oxide of large size. The process of chemical interaction of individual graphene oxide microsheets is implemented in a planar version on a silicon substrate with an oxide layer during preheating and subsequent reduction under hydrothermal conditions. Based on the results of thermal analysis, in situ X-ray diffraction, and results of XPS, a model of the chemical interaction of functional groups of graphene oxide during its primary thermal and subsequent hydrothermal treatment is proposed. The thin films obtained in this work were transferred to a measuring structure and their conductive properties were measured in planar and vertical geometries.

Development of multifunctional graphene-based nanocomposites with synergistic effects of chemical and physical interactions

In this work, two types of graphene-based polyamide 66 (PA66) nanocomposites were prepared by in-situ polymerization. The effect of the surface functional groups of graphene oxide (GO) and the chemically modified GO (GO-DDA) on the structure and the properties of the nanocomposites were investigated. The nanocomposites achieved excellent enhancement in the properties. Compared to PA66/GO nanocomposites, PA66/GO-DDA nanocomposite showed higher Young’s modulus, tensile strength and thermal decomposition temperature at all the filler content. For example, at the filler content of 0.3 wt%, PA66/GO-DDA nanocomposite exhibited 92 % increase in the Young’s modulus, while PA66/GO nanocomposite exhibited 42 % increase. The thermal decomposition temperature was improved from 357 °C to 388 °C and to 383 °C by the incorporation of only 0.5 wt% of GO-DDA and GO, respectively. These results indicate the synergy reinforcement effect brought by the chemical interactions and the physical interactions between PA66 and GO-DDA.

Fabrication of highly flexible, wearable, free-standing symmetric supercapacitors with high voltage operation enabled by hierarchical graphene/cerium oxide/polypyrrole hybrid films

Flexible, free-standing supercapacitors play a significant role in the development of future wearable energy storage devices. Herein, we successfully fabricated the highly flexible and free-standing graphene/cerium oxide/polypyrrole hybrid films by thermal reduction of graphene oxide (GO) followed by the sol–gel synthesis of CeO2 and then the addition of PPy. By regulating oxygen functional groups in GO, the electronic conductivity and electroactive sites of the hybrid films are significantly controlled, leading to enhanced energy storage capability. Finally, a symmetric flexible supercapacitor (FSC) device was developed using the prepared films as electrodes. Resulting, the integrated symmetric GO-400/CeO2/PPy FSC manifests excellent areal capacitance of 49.0 mF cm−2 at 1 mA cm−2, with a durability of 83.1 % over 10,000 cycles. Specifically, the FSC exhibited capacitance retention of 77.2 % after 10,000 cycles under bending state with exceptional rate ability. Meanwhile, an impressive energy density of 19.69 µW h cm−2 was attained at a power density of 0.85 mW cm−2. Evidently, the synergistic interactions between GO and PPy nanosheets, along with CeO2 favour the rapid electron movement of electrode material for next-generation wearable, portable electronics.

Enhancing Efficiency and Stability in Carbon-Based Perovskite Solar Cells by Double Passivation with Ultralow-Cost Coal-Derived Graphene and Its Derivatives.

Coal-derived carbon nanomaterials possess numerous superior features compared to other classic carbon, such as readily accessible surfaces, tunable pore structure, and facile and precise surface functionalization. Therefore, the controllable preparation of coal-derived carbon nanomaterials is anticipated to be of great significance for the performance improvement and commercialization process of carbon-based perovskite solar cells (C-PSCs). In this study, we successfully synthesized highly stable and commercially valuable graphene oxide (GO) and reduced graphene oxide (rGO) utilizing coal. Compared to traditional methods and commercial graphene, the chemical oxidation and pyrolysis process used in this study is mild and simple, offering the advantages of controlled composition and the absence of other impurities. GO or rGO was incorporated into the top of the SnO2 electron transport layer (ETL) of C-PSCs. Under optimized conditions and ultraviolet-ozone (UVO) irradiation, the ultimate power conversion efficiency (PCE) increased from the unmodified 12.4 to 14.04% (based on rGO) and 15.18% (based on GO), representing improvements of 22 and 31%, respectively. The improved photovoltaic performance is mainly owing to enhanced charge transport capabilities, denser interfacial contacts, improved carrier separation properties, increased conductivity, and abundance of hydrophilic functional groups in GO, which can form more stable hydrogen bonds with SnO2. After being stored at room temperature and ambient humidity for 30 days, the modified, unpacked devices retained 87% of the highest power conversion efficiency (PCE). This study introduces a practical and manageable method to enhance the performance of C-PSCs by using functional carbon nanomaterials derived from coal.

Calcium-facilitated adsorption and precipitation of bacteria on the graphene oxide surface

Efficient removal of bacteria from aqueous environments is a hot research topic. Graphene oxide (GO) has been widely used due to its antimicrobial properties and high surface activity. However, GO alone could not remove bacteria from the aqueous environment through aggregation and precipitation. In this study, CaCl2 (Ca2+) was introduced into the process of bacterial removal by GO due to the negative charge on the surface of the removed bacteria (Sporosarcina pasteurii). The introduction of Ca2+ leads to the re-accumulation of GO layers, and the proportion of oxygen-containing functional groups in GO increases significantly. AFM and zeta potential results indicate a reduction in the negative charge on the GO surface in the presence of Ca2+, which reduces the electrostatic repulsion to bacteria. This leads to a gradual increase in the attractiveness of the GO surface and the adsorption of more bacteria. Ca2+ acts as a bridge, facilitating the sedimentation of GO and bacteria, resulting in the removal of bacteria from the water environment. The removal efficiency of GO against bacteria increased as the concentration of Ca2+ increased.

Triggering triboelectric nanogenerator antibacterial Activities: Effect of charge polarity and host material correlation

Triboelectric nanogenerators (TENGs) offer promising motion-driven energy harvesting for human–machine interactions, particularly in wearable healthcare and biomedical devices. However, direct skin contact demands addressing aggressive bacterial growth risks. The “triangle” interaction between bacteria, electrical stimulation, and host materials has been investigated comprehensively in the present study to facilitate appropriate self-antibacterial designs for TENGs. In so doing, it was revealed that the growth of negatively charged bacterial models (Escherichia coli and Staphylococcus aureus) was inhibited by induced positively charged substrates (Al or graphene oxide (GO)), regardless of the host material's composition due to the direct electrostatic interactions. Electron capture from the bacterial respiratory chain by the substrates leads to the interruption of the bacterial energy supply. In response to negative charges, however, an appreciable host-dependent antibacterial behaviour was observed, with Al showing a negligible bactericidal effect, while GO exhibited robust antibacterial properties. This effect was assigned to reactive oxygen species (ROS) generation, triggered by shuttling the negative charges to the oxygen functional groups in GO, suppressing bacterial growth efficaciously. The observed correlation between the electrostatic charge polarity and the material composition of the substrates (hosting the bacteria) highlights the superiority of ROS induction in the antibacterial properties of TENG. These findings pave the way for developing innovative approaches to control bacterial growth effectively and enhance the applicability of TENGs as advanced wearable devices with inherent antibacterial capabilities.

Fabrication optimization of polyethersulfone adsorptive mixed matrix membrane for enhanced dynamic methylene blue removal: Response surface methodology approach

AbstractIn the present study, the polyethersulfone (PES)/graphene oxide (GO)/polyethylene glycol 200 (PEG‐200) adsorptive mixed matrix membranes (AMMMs) were fabricated using a non‐solvent induced phase inversion method. According to the design of experiments using response surface methodology (RSM), PES concentration (15, 17.5, and 20%), PEG‐200 concentration as a pore former additive (0.5, 2.5, and 4.5%), and GO nanosheet loading percent (0, 0.5, and 1%) were varied during fabrication. A green solvent, dimethyl sulfoxide, was used as an alternative to conventional solvents, while it exhibited better membrane performance. Methylene blue (MB) removal was optimized in PES AMMM synthesis using RSM. Attenuated total reflectance Fourier transform infrared spectroscope confirmed the presence of GO functional groups in the optimum membrane. Scanning electron microscopy analysis revealed the optimum membrane was thicker than the neat membrane and atomic force microscopy analysis demonstrated higher surface roughness. The membranes hydrophilicity increased, with a decrease in water contact angle from 61.1 ± 0.2° (neat PES) to 54.4 ± 0.9° (optimal membrane). Pure water flux of 524.8 L m−2 h−1 and MB rejection of 97.46% were obtained for the optimum membrane. Furthermore, the optimum PES AMMM demonstrated a greater dynamic adsorption capacity in comparison to the unmodified PES membrane.Highlights The optimization of the polyethersulfone (PES) adsorptive mixed matrix membranes (AMMM) for methylene blue removal was performed utilizing the response surface methodology. The calculation of the dynamic adsorption capacity (DAC) was performed through the breakthrough curves. The integration of graphene oxide into the AMMM resulted in an enhanced DAC of the AMMM. The PES AMMM performance is based on Donnan electrostatic exclusion.

Optimizing the micro/mesoporous structure of hierarchical graphene aerogel for CO2 capture by controlling the oxygen functional groups of graphene oxide

BackgroundGraphene aerogels as solid porous adsorbents are great candidates for CO2 adsorption based on their tunable hierarchical pore structure and oxygenated groups on graphene oxide can control the self-assembly and pore structure of graphene aerogels. MethodsModified Hummer's method was used to synthesize graphene oxides by using various levels of H2SO4, KMnO4, and H2O2 and 3D graphene aerogels were synthesized via the hydrothermal and freeze-drying method. FTIR, RAMAN, XRD, FE-SEM, and BET analysis were used for characterizations. Significance findingsThe effect of graphite oxidation conditions on the hierarchical porous structure of graphene aerogel for CO2 adsorption was investigated. The graphene aerogel with the high meso and micro surface areas and the highest Sm/ST value (micro surface area/total micro and meso surface area) of 33% and also, the adequate macropores was achieved using high dosage of H2SO4 in the graphene oxidation process led to the highest CO2 adsorption capacity of 1.72 mmol/g. increasing the H2O2 dosages increased the macropores in the aerogel structure and improved the value of Sm/ST leading to an increase in the CO2 adsorption capacity. The high content of KMnO4 led to low Sm/ST value and fewer macropores and decreased the CO2 adsorption capacity (1.04 mmol/g).

REDUCED GRAPHENE OXIDE NANOSHEETS DERIVED FROM IRAQI RHUS CORIARIA (L.) FRUITS WERE EVALUATED FOR THEIR ANTICANCER AND ANTIBACTERIAL PROPERTIES

In this study, reduced graphene oxide nanosheets (rGO) were biosynthesized using the methanolic extract of Iraqi Rhus coriaria (L.) fruits with substantial bioreduction capabilities. The GC-MS analysis of the methanolic extract of Iraqi Rhus coriaria (L.) fruits was used to determine the synthesis mechanism of rGO nanosheets. The synthesized graphene oxide (GO) and the biosynthesized methanolic extract of Iraqi Rhus coriaria (L.) fruits-rGO nanosheets (MERCF-rGO) were characterized using UV-Vis at 226 nm, and 238 nm, respectively. FTIR explained the functional groups of GO and MERCF-rGO nanosheets, XRD spectra of the GO and MERCF-rGO show the sizes at 10.42 nm, and 4.07 nm, TEM observed the size of GO and MERCF-rGO at 15.54 nm and 9.6 nm. As well as FESEM of GO and MERCF-rGO was carried out to explain sheet shape about them. Raman spectroscopy of GO and MERCF-rGO displayed the two peaks D at (1353 cm-1, 1336 cm-1) and G at (1597 cm-1, 1594 cm-1) respectively. MERCF-rGO nanosheets showed activity against antibacterial gram-positive (Staphylococcus aureus) and gram-negative (Escherichia coli), cytotoxicity by MTT assay against breast cancer MCF-7 cell line IC50 at 251.99 μg/mL, genotoxicity fragmented DNA of MCF-7 by comet assay. Comprehensively, the green synthesis of rGO is safe, the lowest cost and developable biogenic nano-formulation of Iraqi Rhus coriaria (L.)–rGO owns antibacterial and anticancer therapeutic applications.

Role of oxygen functional groups and attachment of Au nanoparticles on graphene oxide sheets for improved photodetection performance.

Integrating low-dimensional graphene oxide (GO) with conventional Si technology offers innovative strategies for developing ultrafast wideband photodetectors. In this study, we synthesized GO and explored its potential application in broadband photodetection alongside silicon heterostructures. The as-synthesized GO contains various oxygen functional groups, as evidenced by X-ray photoelectron and Fourier transform infrared spectroscopy. These functional groups contribute to increased photo absorption, enhancing photodetection performance. The systematic reduction of these functional groups from the GO surface via thermal annealing decreases photo absorption and consequently lowers the photocurrent. This reduction diminishes photo absorption and amplifies the dark current by approximately 25 times, from 20 nA to 496 nA. This dark current increase is attributed to the electron mobility following the reduction of functional groups. However, attaching plasmonic gold nanoparticles (Au NPs) to the GO surface enhances UV-Vis absorption in the visible region, enabling broadband detection. The even distribution of attached Au NPs on the GO surface is confirmed through field emission transmission electron microscopy. While thermal annealing of GO diminishes the responsivity from 4.6 A W-1 to 3.0 A W-1, the attachment of Au NPs augments the responsivity by more than two-fold, reaching 10.0 A W-1. Thus, it highlights the importance of rich oxygen functional groups in GO and the attachment of Au NPs to achieve more efficient photo-sensing properties.

Investigating the Antibacterial Activities of Graphene Oxide Loaded Spiky Gold Nanocomposites via Chitosan linker

The graphene oxide (GO) loaded spiky gold (AuNS) nanocomposites were prepared by electrostatic interaction between negatively-charged GO nanosheets and positively-charged AuNS by the assistance of chitosan as linker molecules. The AuNS/GO nanocomposites exhibit a red-shift in the extinction spectra and a reduction in the zeta potential compared to those of the pristine AuNS due to the presence of oxygen-containing functional groups in GO. The bactericidal analysis demonstrates that the incorporation of GO greatly enhances the intrinsic antibacterial activities of AuNS. Besides, the AuNS with smaller size exhibit better bactericidal efficiency compared to that of AuNS with bigger size. Upon light irradiation, the AuNS/GO with the absorption peak close to the wavelength of excitation light (900 vs. 904 nm) demonstrates a noticeable improvement in the bactericidal efficiency which is attributed to the plasmon-induced photothermal effect. All these results suggest that the AuNS/GO nanocomposites can work as a promising functional material for both intrinsic and plasmon-induced antibacterial materials.

The Effect of Magnetic Stirring Duration and Ascorbic Acid Concentration on the Yield of Reduced Graphene Oxide Isolated from East Kalimantan Bituminous Coal

East Kalimantan bituminous coal has a carbon composition of 70.24%, indicating a crystal structure of graphite layers. This makes it a viable material for creating reduced graphene oxide (r-GO), which has multiple advantages in various properties and can be employed in numerous technological applications. RGO is obtained by nearly eliminating oxygen functional groups in graphene oxide (GO) through sonication for 3 hours at pH 4. The yield with the lowest value at a 30% concentration of ascorbic acid and 50 minutes of magnetic stirring was selected as optimal. To characterize the resulting product, FTIR was utilized and revealed that O-H (84.21%), C=C (63.04%), and C-O-C (61%) had the highest %T. Technical abbreviations were explained upon first use. Energy-dispersive X-ray (EDX) analysis demonstrated a 90.6% increase in carbon content from 40.159% in GO to 76.554% in r-GO. In parallel, oxygen content decreased from 40,973% in GO to 17.551% in rGO, marking a 57.16% decrease. The morphology of the resulting rGO closely resembled the reference. Additionally, rGO exhibited a C:O ratio of 4.378, surpassing the C:O ratio of GO, which was 1.02. RGO density and pH value were 1.45 g/cm3 and 2, respectively.

Sulfonic acid (-HSO3) functionalization effect on graphene oxide membrane by (3 mercaptopropyl) trimethoxysilane and their applications in hydrogen membrane fuel cells

Conventional proton exchange membrane fuel cells (PEMFCs) use a perfluorinated ionomer membrane, e.g., Nafion®, which is expensive and subject to a rigorous synthesis process. Graphene oxide membrane (GOM) is acknowledged as a promising alternative electrolyte due to its hydrophilic nature and attractive proton conductivity in wet conditions. However, GOM loses its negative surface functional groups by hydrogen gas at the anode during operation in PEMFCs, resulting in increased electronic conductivity. In addition, two-dimensional graphene oxide (GO) nanosheets exhibited a larger anisotropy difference in proton conductivity compared to Nafion®. In this study, (3-mercaptopropyl)trimethoxysilane (MPTS, HS(CH2)3Si(OCH3)3) was reacted with the surface of GO nanosheet (M-GOM) by vigorous stirring, where unreacted MPTS was partially removed by a rinsing cycle except the M-GOM powder. Reactive MPTS has two essential reactions which were carried out by forming a hydrolysis reaction (Si-OCH3 to Si-OH) and a condensation reaction (Si-OH to Si-O-Si). The thiol groups of MPTS were oxidized to sulfonic acid groups (-HSO3) to provide high proton conducting stations with GO functional groups (M-GOM/oxid) and compared with non-oxidized thiol groups in a GO matrix (M-GOM/unoxid). The superior –HSO3 effect on M-GOM have reported for proton conductivity, physicochemical properties, ion exchange capacity, thermal stability, gas permeability and fuel cell performance. Furthermore, a hydrogen-permeable metal layer was deposited by a DC magnetron sputter to increase mechanical strength and reduce fuel crossover. A dual-layer membrane composed of M-GOM/unoxid or M-GOM/oxid and Pd thin film was analyzed as an electrolyte for a hydrogen membrane fuel cell (HMFC), which simultaneously performs two roles, an anode catalyst and an electrolyte.

Improving the interfacial properties of PVA fiber and cementitious composite: Design and characterization

Poly vinyl alcohol (PVA) fiber has been widely applied to improve the ductility of cementitious materials, and the overall performance of fiber reinforced cementitious materials largely depends on the interfacial properties of the fiber and cementitious matrix. In this work, a novel design of graphene oxide (GO) modified PVA fiber is proposed to improve the interfacial properties of PVA fiber and cementitious matrix. It is found that the interaction between GO and PVA fiber forms the hydrogen bond and enables the GO to form a tight three-dimensional bonding on the surface of the PVA fiber. Meanwhile, the oxygen-containing functional groups of GO could form chemical bond with the hydration products and promote the formation of denser microstructure at the interface. Therefore, the introduction of GO prominently improves the interfacial properties of PVA fiber and cementitious matrix, which is verified by the characterizations on the microstructures and morphologies. Furthermore, it is found that GO remarkedly improves the interfacial mechanical properties and results that a zone with the enhanced mechanical properties appears near the interface, verified by the characterizations on the micro-mechanical properties including fracture toughness near the interface.

High-efficiency recyclable reduced graphene oxide-tin oxide nanocomposite catalyst for esterification

Graphene oxide (GO) possesses 2D nanostructures and was synthesized indigenously via the enhanced Hummer method. It is well-accepted that the redox approach is a distinctive technique to fabricate GO on an expanded scale. Here, reduced graphene oxide-tin oxide (SnO2-rGO) nanocomposite material was produced for application as an efficient heterogeneous solid acid catalyst esterification reaction. Fourier transform infrared analysis was carried out to validate the incidence of oxygen functional groups in GO and SnO2-rGO nanocomposite. The Raman spectra of GO and SnO2-rGO nanocomposite have been simulated to get stable structure and functional groups. To get surface morphological and structural features, powder X-ray diffraction, scanning electron microscope-energy dispersive X-ray spectra, transmission electron microscope and high resolution-TEM analysis, and thermogravimetric analysis were delineated during this experimental study. It is seen that the catalyst has high efficiency for esterification reaction. The maximum efficiency (96% yield) was obtained when a 1:3 (acetic acid to benzyl alcohol) molar ratio, catalyst (25 mg), temperature (60 0C), and time (4 h) were maintained. The SnO2-rGO nanocomposite was recycled several times with a minimal loss of its efficiency.