rGO Nanosheets Research Articles

Rough edges of reduced graphene oxide (rGO) sheets elicit anticancerous activities: An in vitro study

In this study, reduced graphene oxide nanosheets (rGO) were synthesized using a chemical bottom-up technique of modified Hummer’s method. The as-synthesized graphene sheets were characterized optically by Fourier Transform Infra Red spectroscopy (FTIR) and Raman spectroscopy. The morphological characterizations were performed using Field-Emission Scanning Electron Microscopy (FE-SEM), High-Resolution Transmission Electron Microscopy (HR-TEM), Atomic Force Microscopy (AFM) and Confocal Microscopy, respectively. It could be evident from the images that wrinkles and surface corrugation are clearly visible from the morphological analysis. The biomedical applications of rGO nanosheets have been studied in the cancer cell lines of A375 and A549 cells at the in-vitro conditions. MTT assay and live dead assay results clearly indicated that rGO exhibited robust anticancerous activities against the chosen cell lines. Although, it could not elicit any antimicrobial activity at the selected doses. Understanding the primary mechanism and the underlying phenomenon involving the interaction of the rGO nanosheets with the cell systems reveals the potentialities of the nanosheet in designing future-based anticancerous therapeutics at the nanoscale level.

Controlling the Formation of Electroactive Graphene-Based Cementitious Composites: Towards Structural Health Monitoring of Civil Structures.

The development of composites combining multiple components each one imparting a specific function to the ensemble is highly sought after for disruptive applications in chemistry and materials science, with a particular importance for the realization of smart structures. Here, we report on the development of an unprecedented multifunctional cementitious composite incorporating reduced graphene oxide (rGO). By design, this material features significantly enhanced electrical properties while retaining the excellent cement's hydration and microstructure. The multiscale investigation on the chemical and physical properties of the dispersion made it possible to establish an efficient preparation protocol for rGO aqueous dispersion as well as rGO-based cementitious composites using a commercial poly(carboxylate ether)-based superplasticizer. The conduction mechanisms within the matrix of rGO containing mortars were unraveled by electrochemical impedance spectroscopy revealing conductive paths originating from bulk cement matrix and rGO nanosheets in composites with rGO loadings as low as 0.075 wt. %. For this rGO loading, we observed the reduction of the resistivity of bulk cement mortar layers from 18.3 MΩ cm to 2.8 MΩ cm. Moreover, the addition of 0.2 wt. % of rGO resulted in the formation of rGO conductive paths with the resistivity of 51.1 kΩ cm. These findings represent a major step forward towards the practical application of graphene-based materials in structural health monitoring of concrete structures.

Zn/Ni composite coating modified by reduced graphene oxide and layered double hydroxide with synergistic effect for superior corrosion protection of Mg alloys

In this work, layered double hydroxide (LDH) and reduced graphene oxide (rGO) were incorporated into Zn/Ni matrix coating by cold-spraying on the surface of Mg alloys. Inside the resulting GLG@Zn/Ni coating, LDH/rGO are homogeneously dispersed and inner-connected to a protective network. Compared with other coatings without LDH or rGO nanosheets, the GLG@Zn/Ni coating shows the best corrosion resistance, with a high self-corrosion potential at − 1.174 V (vs. − 1.471 V for Mg), a decent self-corrosion current density of 344.7 μA·cm−2 (vs. 878.3 μA·cm−2 for Mg), and the longest available protection (>720 h) against corrosion. Electrochemical and morphological characterizations reveal a synergistic effect of the coating compositions in enhancing corrosion resistance. In detail, the LDH/rGO network inside the coating restricts the penetration of the corrosive medium, particularly for LDH, which has the capacity to capture corrosive Cl− ions. Meanwhile, Ni promotes the conversion of Zn into passivation layers, which then spread to fill the corrosion pores and interphase cracks. This transformation ultimately leads the GLG@Zn/Ni coating to become a unified whole, providing excellent corrosion resistance.

WS2 incorporated PANI-rGO nanocomposites tailored for inflated thermal, optical and electrical properties used as ETL for OLEDs

This work reports on the synthesis of polymeric PANI-rGO-WS2 (PGW) nanocomposites were synthesized with varying concentrations of WS2 via chemical oxidative polymerization. FESEM images elucidated that the surface morphology of PGW3 carried a structure comprising of PANI nanofibers embedded on the top of the overlapped rGO and WS2 nanosheets. XRD and FTIR spectroscopy showed the molecular interaction among the constituents and affirmed the formation of PGW nanocomposite. UV–Vis. spectroscopy revealed the absorption of light in visible region with the for PGW3 nanocomposite. Photoluminescence spectroscopy showed light absorption in blue color region with excellent color purity. TGA showed the optimized PGW3 nanocomposite has inflated thermal stability. Current density for PGW3 nanocomposite was examined using J-V characteristic curve and found 96% higher than polyaniline. The increased conductivity and high electron-hole recombination rate attributed to the formation of enhanced charge transport network in PGW3 nanocomposite. These results evinced the optimized PGW3 nanocomposite as an ETL for OLED applications.

Non-covalent functionalization of surfactant-assisted graphene oxide with silver nanocomposites for highly efficient photocatalysis and anti-biofilm applications

This study presents a comprehensive investigation on the synthesis and characterization of surfactant-assisted graphene oxide non-covalent functionalized silver nanocomposites (rGS-AgNPs) for achieving remarkable photocatalytic and anti-biofilm properties. The approach involves using an anionic surfactant (sodium lauryl sulfate (SLS)), silver nitrate (AgNO3), and reduced graphene oxide (rGO) as stabilizing/reducing agents, metal precursors, and supporting materials, respectively. Different composites were prepared by varying the concentration of AgNO3, resulting in rGS-AgNPs composites with concentrations of 0.9 × 10−3 mM, 1.8 × 10−3 mM, and 2.7 × 10−3 mM. Characterization techniques including XRD, FTIR, SEM, and TEM/EDS analysis confirmed the formation of face-centered cubic AgNPs and amorphous rGO structures. The composites exhibited a firm binding of the surfactant and AgNPs on the surface of rGO nanosheets, resulting in efficient anti-biofilm and photocatalytic activity. The size of the supported AgNPs on rGO/SL was found to be 8–10 nm. The rGS-AgNPs composites displayed significantly improved anti-biofilm and photocatalytic performance, attributed to the increased surface area of AgNPs. Moreover, the photocatalytic efficiency of the rGS-AgNPs composites reached 96.48 % within 60 min, outperforming pure AgNPs. The synthetic producre and practical applications will be utilized for biosensors, food packing technology, biomedical and pharmaceutically valuable reactions.

Facile ultrasound assisted in-situ synthesis of novel redox-active ferrocenyl-based nanocomposite: Applicable to energy storage

Organometallic compounds, especially ferrocene (Fc) due to their outstanding properties and excellent stable redox features, are appearing as ideal electrode materials for supercapacitors. In this research work, an ultrasonic solvent-substitution route was applied for the in situ synthesis of Fc nanophere on reduced graphene oxide (rGO) nanosheets. Then, the Fc-containing porous organic polymer (POP) was prepared by using a Schiff base reaction. Finally, we prepared a novel redox-active battery-type ternary rGO-Fc/POP nanocomposite via the self-assembly route to obtain a highly efficient Fc host for energy storage devices. Owing to the porous structure and the fast faradaic redox reactions of Fc units, the final nanocomposite shows a high specific capacity of 655.5 mAh g−1 at 2.5 A g−1 and 5 % capacity loss after 5000 cycles. A symmetric supercapacitor (SSC) based on rGO-Fc/POP as both anode and cathode can be acted on in a wide electrochemical window up to 1.8 V and attains excellent cycling performance (93 % remained after 3000 cycles). Also, our SSC cell exhibits high energy and power densities of 101.7 Wh kg−1 and 25.92 kW kg−1, respectively. This research provides a route to increase the electrochemical properties of redox-active battery-type electrode materials for high-performance SCs.

Highly sensitive and selective gas sensor based on SnO2/Fe2O3@rGO nanocomposite for detection of formaldehyde

A highly sensitive and selective HCHO gas sensor based on SnO2/Fe2O3 nanocomposites decorated with reduced graphene oxide (rGO) nanosheets was prepared through the microwave-assisted hydrothermal method. The obtained products were characterized by X-ray diffraction and scanning electron microscopy. The gas sensing results show that the SnO2/Fe2O3@rGO sensor, with high response of 11.21 to HCHO gas, short response time of 32 s, short recovery time of 33 s, and good repeatability, is superior to single-component sensor SnO2@rGO. It can be inferred that the heterojunction effect among SnO2, Fe2O3 and rGO could facilitate the electron transfer, thus enhance the gas response to HCHO. The results may open an avenue for SnO2/Fe2O3@rGO as a promising sensor to detect toxic gas.

Rapid ultrasound driven self-assembled nanoarchitectonics iron oxide-reduced graphene oxide as an anode for Li-ion battery and its electrochemical performance studies

With the scope of identifying an effective nanomaterial as an anode for Li-ion battery under economic synthesis factors, here, high crystalline mesoporous magnetite nanoparticles (m-Fe3O4 NPs) with an average diameter of 45 ± 10 nm were successfully synthesized through facile, one-pot sonoelectrochemical method in 15 min, and it was structurally anchored into sonochemically exfoliated reduced graphene oxide nanosheets (m-Fe3O4@rGO). The morphological studies through FESEM and HRTEM analysis confirm that the m-Fe3O4 were well anchored into rGO nanosheets, and it has maximum magnetic saturation value of 39 emu g−1 and high surface area of 254 m2 g−1. The performance analysis results of m-Fe3O4@rGO nanocomposite as an anode material in half-cell configuration with Li-metal had demonstrated that around 11 % enhancement in first discharge capacity (1440.79 mAh g−1 at 0.2 A g−1 current density), ~50 % increased rate capability (356 mAh g−1 at 5.0 A g−1 current density) than bare m-Fe3O4 electrode and had maintained nearly 441 mAh g−1 after 500 cycles at 2.0 A g−1 current density. These results suggest that the sonochemical method could be a better alternate method when compared to other time-consuming processes like solvothermal method where high temperature is required to fabricate effective nanocomposite for high-rate performance in real time applications of Li-ion battery.

Two-dimensional layered rGO-MoS2 heterostructures decorated with Fe3O4 nanoparticles as an electrochemical sensor for detection of para-nitrophenol

In this study, reduced graphene oxide–molybdenum disulfide/iron oxide (rGO-MoS2/Fe3O4) nanocomposite, in which rGO nanosheets act as a substrate for Fe3O4 nanoparticles and the MoS2 nanostructure, was synthesized. The rGO-MoS2/Fe3O4 nanocomposite was synthesized with use of molybdenum disulfide, iron(III) chloride hexahydrate, and graphite oxide powder by application of the microwave method. The hexagonal structure of rGO-MoS2 along with the cubic geometry of Fe3O4 was confirmed by X-ray diffraction, while the decoration of the layered structure of rGO-MoS2 with Fe3O4 nanoparticles was visualized in scanning electron microscopy images of the nanocomposite. Increase in the intensity of the D band of the nanocomposite, when compared with rGO, in Raman spectra further indicated that the presence of Fe3O4 and MoS2 induced non-graphitic defects in the nanocomposite. The as-prepared sensor was applied for the electrochemical sensing of p-nitrophenol. Cyclic voltammetry was used to study the behavior of p-nitrophenol, while differential pulse voltammetry was used for a concentration study. Real samples of water, viz., distilled water, tap water, and river water, were used for this study. The detection limit obtained was 0.8 μM, and good sensitivity of 0.71 μA μM−1 cm−2 was achieved. This study provides motivation for the use of nanocomposites of carbon and transition metal dichalcogenides over use of metal-based nanoparticles.

Fabrication of MWCNTs/rGO/PPy ternary composites for excellent electromagnetic absorption

With the development of radar stealth technology and electronic communication technology, electromagnetic (EM) wave absorbing materials with lightweight and broad absorbing bandwidth are widely expected. In this study, the multi-walled carbon nanotubes (MWCNTs)/reduced graphene oxide (rGO)/polypyrrole (PPy) ternary composites were prepared by in-situ polymerization under hydrothermal conditions. The effects of carbon substrate of MWCNTs/rGO and the content of PPy on the microwave absorption (MWA) properties of the ternary composites and the corresponding attenuation mechanism were investigated. The results showed that MWCNTs and rGO nanosheets interweave together to form a relatively uniform micro-network structure with even wrapping of PPy on the surface of MWCNTs/rGO substrate. The adjustable amount of PPy optimizes the impedance matching and EM wave attenuation capacity. The composites achieve effective absorption bandwidth (EAB) of 4.6 GHz at 2.1 mm, and the minimum reflection loss (RLmin) value of −57 dB at 15.8 GHz. The multi-void network structures formed by MWCNTs and lamellar rGO and the interfacial polarization between MWCNTs/rGO composite carbon substrate and PPy can effectively decay EM wave absorption, thus improving the MWA performance of the composites. This work provides an effective reference for the application of multi-component carbon composites in the field of microwave absorption.

Harvesting visible light for enhanced catalytic degradation of wastewater using TiO2@Fe3O4 embedded on two dimensional reduced graphene oxide nanosheets

Carbon-integrated binary metal oxide semiconductors have gained prominence in the last decade as a better material for photocatalytic wastewater treatment technology. In this regard, this research describes the investigation of the binary metal oxide TiO2@Fe3O4 embedded on reduced graphene oxide (rGO) nanosheets synthesized through a combination of sol-gel, chemical precipitation, and Hummer's processes. Besides, the catalyst is applied for the photocatalytic degradation of organic chlorophenol pollutants. The characterized diffraction results showed the peak broadening of the rGO-TiO2@Fe3O4 composite formed with tetragonal and cubic structures having small crystallite sizes. The TEM observation shows an enormous miniature of TiO2@Fe3O4 nanospheres spread on the folded 2D-rGO nanosheets with a large BET surface area. The XPS result holds the mixed phases of Fe3O4 and Fe2O3. Finally, the catalyst demonstrated a low band gap with extended light absorption towards visible light irradiation. The synergistic interactions between Fe3+ and Fe2+ improved the visible light activity due to the incorporation of rGO, and also possessed good recycling capacity. The increased mobility of electrons at the interfaces of TiO2 and Fe3O4 due to the mixing of rGO results in the separation of charge carriers by elevating the photocatalytic degradation efficiency of chlorophenol.

Interface-induced efficient adsorption and photocatalytic degradation of organic pollutants using rGO/SnO2 nanocomposites: exploring the role of rGO concentration at the interface

This study presents the synthesis and characterization of rGO/SnO2 nanocomposites and investigates their efficacy in the adsorption and photocatalytic degradation of organic contaminants. The nanocomposites were synthesized via a one-step hydrothermal route, which is an environmentally friendly method without the use of hazardous reducing agents. The incorporation of rGO onto SnO2 nanostructures led to bandgap modification and increased specific surface area, synergistically enhancing the adsorption and photocatalytic properties of the nanocomposites. The influence of varying rGO concentrations on the performance of the nanocomposite was systematically examined. An optimal weight ratio of 15% of rGO was identified, providing the most effective adsorption-photodegradation synergy, resulting in the rapid degradation of organic contaminants under simulated sunlight irradiation. The nanocomposites demonstrated high degradation rates for a mixture of rhodamine B (RhB) and methylene blue (MB) dyes within 50 min. Scavenger experiments identified superoxide anion radicals (O 2 •−) and hydroxyl free radicals (OH•) as the primary active species involved in the photocatalytic degradation process. Furthermore, the study explored the influence of initial dye concentration and photocatalyst mass under optimized conditions. The interfacial contact between rGO nanosheets and SnO2 nanostructures played a crucial role in enhancing the photocatalytic performance by facilitating efficient charge carrier separation. The results indicated the efficient degradation of high concentrations of dyes and demonstrated the potential of rGO/SnO2 nanocomposites for real-world wastewater treatment applications. Overall, this study highlights the remarkable adsorption-photocatalytic synergy of rGO/SnO2 nanocomposites, offering a promising solution for the simultaneous degradation of mixed organic contaminants.

Ternary Nanocomposite of Activated Charcoal/Reduced Graphene Oxide-Silver Nanoparticles [ACH/Ag@rGO] as a Novel Platform for the First Sensitive Prucalopride Drug Detection in Generic and Innovator Tablets and Human Plasma

Ag@rGO nanocomposite was prepared using an in situ reduction approach of silver ions and the as-synthesized graphite oxide (GO). TEM analysis reveals the crumpled and folded layered structure of rGO with homogeneous dispersed spherical Ag NPs on these rGO nanosheets. The intensity ratio of the D to G bands (ID/IG) in Raman spectra for Ag@rGO indicates a large defect due to Ag NPs intercalation and deposition on rGO surface. XRD pattern indicates the face centered cubic crystal structure of Ag with average crystalline size of 19.63 nm. An electrochemical sensor based on Ag@rGO is first designed for Prucalopride drug oxidation and characterized applying EIS and cyclic voltammetry. Its electrocatalytic effect was enhanced upon utilizing a characterized activated charcoal (ACH) as an electro-modified carbon nanomaterial for CPE. The ternary nanocomposite [ACH/Ag@rGO] as a platform of CPE supposed three times higher response to Prucalopride compared to CPE. Prucalopride was quantified over wide linear ranges of (5.0 × 10−9– 1 × 10−6 M) and (2.0 × 10−8– 1.4 × 10−6 M), with LOD values of 7.95 × 10−10 M and 8.51 × 10−9 M in bulk form and spiked human plasma, respectively. This sensor can thus be adopted easily for the quality control analysis of Prucalopride in formulation and human plasma and for pharmacokinetic study.

Dual‐laser pulse‐patterned α‐Co(OH)2/rGO heterointerface for accelerated water oxidation and surface phase‐transition via in‐situ Raman spectroscopy

AbstractThe dynamic surface reconstruction of electrodes is a legible sign to understand the deep phase‐transition mechanistic and electrocatalytic origin during the oxygen evolution reaction (OER). Herein, we report a dual‐laser pulse‐patterned heterointerface of α‐Co(OH)2 and reduced graphene oxide (rGO) nanosheets via pulsed laser irradiation in liquid (PLIL) to accelerate OER kinetics. α‐Co(OH)2 was formed from the OH− ions generated during the PLIL of GO at neutral pH. Co2+ modulation in tetrahedral coordination sites benefits as an electrophilic surface for water oxidation. Few d‐vacancies in Co2+ increase its affinity toward oxygen, lowering the energy barrier and generating many CoOOH and CoO2 active sites. rGO with an ordered π‐conjugated system aids the surface adsorption of OOH*, O*, and OH* during OER. α‐Co(OH)2 surface phase‐transition and OER mechanistic steps occurred via phase‐reconstruction to CoOOH and CoO2 reactive intermediates, uncovered using in situ electrochemical–Raman spectroscopy. Our findings in the dual‐laser pulse strategy and the surface reconstruction correlation in active OER catalysts pave the path for paramount in multiple energy technologies.image

Hydrothermal integration of MoO2–MoS2@rGO nanoframe networks: A promising approach for efficient bacterial disinfection in wastewater

The efficient disinfection of bacterial contaminants in wastewater is a critical challenge in the field of environmental remediation. Herein, we present a novel approach for efficient bacterial disinfection using hydrothermally integrated MoO2–MoS2@rGO nanoframe networks. The developed nanoframe networks exhibit a unique architecture comprising of molybdenum dioxide (MoO2) and molybdenum disulfide (MoS2) impregnated on algae biomass reduced graphene oxide (rGO). The as-synthesized nanoframe networks demonstrate exceptional antibacterial activity against Escherichia coli bacteria. The disinfection efficiency was evaluated by measuring the bacterial viability and observing the morphological changes using scanning electron microscopy. The MoO2–MoS2@rGO nanoframe networks exhibited a remarkable antibacterial effect, achieving a high disinfection rate of 95.8% within a short contact time of 10 min. The efficient bacterial disinfection capability of the nanoframe networks can be attributed to the synergistic effects of MoO2, MoS2, and rGO components. The MoO2 nanoparticles generate reactive oxygen species (ROS), persuading oxidative stress and leading to bacterial inactivation. The MoS2 nanoparticles possess inherent antibacterial properties through the release of Mo and S ions. The rGO nanosheets provide a conductive and stable platform, facilitating the charge transfer during the antibacterial process. Furthermore, the hydrothermal integration method enables easy scalability and cost-effectiveness of the MoO2–MoS2@rGO nanoframe networks. The nanoframe networks can be easily recovered and reused, reducing waste generation and promoting sustainability. Overall, this study presents a promising approach for efficient bacterial disinfection in wastewater using hydrothermally integrated MoO2–MoS2@rGO nanoframe networks. The remarkable antibacterial performance, along with the advantages of scalability and reusability, makes these nanoframe networks a potential candidate for practical applications in environmental remediation and water treatment processes.

FeN4 active sites generated on dipyridylpyridazine functionalized reduced graphene oxide for high-performance air electrode in a Zn-air battery

The growing global electricity demand requires the development of cost-effective energy conversion and storage systems, integrating inexpensive, eco-friendly, and high-efficiency catalysts. Oxygen reduction reaction (ORR) is considered crucial process to achieve high-power-density fuel cells and Zn-air batteries (ZABs). The latter have attracted the attention of scientific community due to its high theoretical energy density, reliable safety and low-cost. However, several limitations must be overcome, designing ORR catalysts thought versatile and economical synthetic routes. In this sense, the non-noble iron–nitrogen-carbon materials (FeNC) have been reported as the most potential candidates for attaining superior activity toward ORR in substitution of the high-priced commercial Pt-C catalysts. Herein, Diels-Alder surface adducts based on dipyridylpyridazine units have been created along 2D surface of reduced graphene oxide (rGO) nanosheets for the controlled generation of FeN4 active sites at the edges through successive solvent-free mechanochemical reactions and an additional thermal treatment. The optimized catalyst provided high content of pyridinic-N, graphitic-N and Fe2+ species, contributing to the excellent activity delivered as electrocatalyst for ORR processes. In addition, a flooded ZAB assembled with this material as cathodic/air electrode exhibited excellent specific capacities of 4.94 and 2.77 A·h·g−1 at -1 and -5 mA, respectively, improving the catalytic performance obtained for the 10 wt% Pt-C benchmark electrocatalyst.

Gelatin-assisted fabrication of reduced nanographene oxide for dual-modal imaging of melanoma cells

In this work we report a gelatin-based, simple two-steps approach for fabrication of reduced graphene oxide (rGO-GEL) possessing high stability and biocompatibility, as novel label-free intracellular contrast agents. Gelatin, a biopolymer that is known for its versatility, was employed not only to biocompatibilize the rGO, but also to prevent the aggregation of the GO nanosheets during the reduction process. To confirm the successful reduction process and the attachment of the gelatin to the rGO nanosheets, we employed multiple spectroscopic analyses such as FT-IR, Raman, UV–VIS and photoluminescence, while the morphology and the lateral dimensions of the resulting hybrid rGO-GEL were investigated by Scanning-Transmission Electron Microscopy (STEM). Cellular toxicity test proved that the rGO-GEL nanoflakes are nontoxic for melanoma B16-F10 cells, even at high concentrations. Finally, the intracellular tracking after 24 h of treatment was performed by non-invasive Super-resolution re-scan confocal microscopy as well as Confocal Raman imaging, thus implementing our nanoflakes as a suitable contrast agent candidate for cellular imaging of interest.

The degradation of bisphenol-A organic pollutant using the dispersal of TiO2 nanorods onto the partial reduction of graphene oxide nanosheets

The notion of innovative combinations of semiconducting metal oxides for photocatalytic destruction is a key factor in the removal of environmental contaminants. However, for the first time, the combination was made possible for the aforementioned reason by embedding one-dimensional titanium dioxide (TiO2) semiconductor nanorods on two-dimensional rGO (reduced graphene oxide) nanosheets utilizing hydrothermal and a modified Hummers' method. By applying several sophisticated procedures, the properties of these catalysts were found, and then the degradation of BPA (bisphenol-A) was examined with UV and visible light sources. Further, all the analyses were performed on pure TiO2 material. As a result of the synergistic interaction between TiO2 and rGO, the rGO-TiO2 catalyst produced a favorable photocatalytic outcome. The structural investigation of rGO-TiO2 has confirmed that the TiO2 was in anatase phase along with GO and rGO peaks, and the morphological characterization showed that the TiO2 nanorods were integrated randomly into the rGO nanosheets along with defective sites. Also, adding rGO to TiO2 causes charge separation, and π–π interactions to improve the visible light absorption range. In this study, the main model organic component in the photocatalytic degradation is bisphenol-A (BPA). During visible light irradiation, the OH radicals were finally produced by the redox reactions. Furthermore, the rGO surface adsorbs the phenol molecules due to graphene π–π interactions, thus narrowing the band gap and increasing the efficiency of BPA degradation.

Cathodic electrophoretic deposited HA-rGO-ZnO ternary composite coatings on ZK60 magnesium alloy for enhanced corrosion stability

HA-rGO-ZnO ternary composite coatings were successfully prepared on ZK60 magnesium alloy using cathodic electrophoretic deposition method. XRD analysis proved the addition of ZnO nanoparticles induced a significantly reduced crystallinity in hydroxyapatite and the tensile strain values of HA-rGO-ZnO composite coatings gradually decreased as the content of ZnO increased. SEM analyses revealed that the HA and ZnO nanoparticles were anchored on rGO nanosheets and a closely-packed network of recrystallization needle-like ZnO and mineralization HA crystals was formed on the surface of HA-rGO-ZnO coated sample. The resulting composite coating exhibited a uniform and compact HA-rGO-16ZnO composite coating, with well adhered to the ZK60 magnesium alloy substrate. The HA-rGO-16ZnO coated sample exhibited the highest corrosion resistance with lowest icorr (1.12 × 10−6 A/cm2) and the highest Ecorr (−1.43 V/SCE) value when compared to HA-rGO-14ZnO and HA-rGO-18ZnO samples after immersion in a SBF for 10 min. Compared to HA-rGO-ZnO coated samples after 10 min of immersion in SBF, HA-rGO-ZnO coated samples after 3 days of immersion in SBF exhibited a remarkably improved corrosion resistance and rapid inducing of the apatite layer precipitated on the surface of the composite coatings. The microstructure and composition for the coated samples after 3 days of immersion in SBF also confirm that the presence of a apatite layer on the composite coatings. HA-rGO-18ZnO coated samples after 3 days of immersion in SBF showed the lowest icorr value, which indicating HA-rGO-18ZnO ternary composite coatings dramatically improved the formation ability of the apatite layer and led to an enhancement in the bioactivity. Accordingly, it is believed that the HA-rGO composite coating incorporated with ZnO will be a potential candidate for bone biomedical applications.

Engineering 2D/2D oxygen vacancy-rich CoAl LDH/rGO sheet-on-sheet heterostructures with improved charge storage for supercapacitors

Layered double hydroxides (LDHs) as electrode materials for supercapacitors still suffer from limited actual specific capacities and unsatisfactory cycling performance owing to their poor intrinsic electrical conductivity and insufficient electroactive sites. Herein, oxygen vacancy (Ov)-rich CoAl-LDH nanosheets are attached onto reduced graphene oxide (rGO) nanosheets to form 2D/2D Ov-CoAl-LDH/rGO sheet-on-sheet heterostructures via a facile precipitation-reduction reaction followed by hydrothermal treatment. The introduction of rich Ov defects in CoAl-LDHs enhances the electrical conductivity, while the attachment of Ov-CoAl-LDH nanosheets on the surface of rGO nanosheets not only reduces the aggregation of Ov-CoAl-LDH nanosheets and thus exposes abundant electroactive sites, but also maintains good structural stability. Theory calculations indicate that the Fermi-level difference of two components triggers interfacial charge separation while creating a built-in electric field at the Ov-CoAl-LDH/rGO interface, which favors rapid electron/ion migration and accelerates charge storage kinetics. The optimized Ov-CoAl-LDH/rGO nanocomposites deliver specific capacities of 984 C g−1 at 3 A g−1 and 708 C g−1 at 20 A g−1 and retain an initial capacity of 90 % after 10,000 cycles at 10 A g−1. These findings showcase a feasible strategy to endow 2D/2D LDHs/graphene heterostructures with enhanced charge storage performance.