Reduced graphene oxide and ZnO decorated graphene for biomedical applications

The ability of graphene-based materials to enhance the conventional antibiotic resistance is well known and researchers have been interested in improving their antibacterial activity. The reduction of graphene oxide by eco-friendly reducing agents is of great interest on the basis of environmental and human health aspects. Herein we report the synthesis of two forms of graphene derivatives namely, reduced graphene oxide (RGO) through reduction using potato starch and zinc oxide decorated RGO (ZnO-RGO). In the case of ZnO-RGO, the reduction of graphene oxide and the conversion of ZnO to nano ZnO occur simultaneously. The characterization of all the graphene based materials and nanocomposites developed were carried out using FT-IR, XRD, Raman spectra and TEM techniques. The antibacterial activity of these modified materials against E. coli was also studied by well diffusion method. Our results show that ZnO-RGO is more efficient than RGO in their antibacterial properties which we attribute to the synergistic effect of ZnO and RGO towards the bacteria in the nanocomposite. Further we find that the antibacterial effect of ZnO-RGO towards E. coli is due to the disruption of the bacterial cell which could be confirmed by AFM images. Considering the fact that graphene-based materials are less toxic towards mammalian cells, both RGO and ZnO-RGO we have developed can find applications in the field of medicine and life sciences.     

Nanocrystalline transition metal oxides and their composites with reduced graphene oxide and carbon nanotubes for photocatalytic applications

Transition metal oxide nanoparticles (CuO, ZnO & Fe₂O₃) and mixed metal oxides CuO. ZnO.Fe₂O₃ were fabricated by facile co-precipitation approach for photocatalytic treatment of organic dyes. The structural features, phase purity, crystallite size and morphology of individual and mixed metal oxides were analysed by X-rays diffraction patterns (XRD) and scanning electron microscopic (SEM) analysis. Electrical behaviour of CuO, ZnO, Fe₂O₃ and mixed metal oxides CuO. ZnO.Fe₂O₃ was explored by current-voltage (I-V) measurements. Functional groups present in the synthesized metal oxides were investigated by Fourier transform infrared spectroscopy (FTIR) which ensures the existence of M-O functional groups in the samples. The optical bandgap analysis was carried out by UV–visible spectroscopic technique which revealed that the blend of three different transition metal oxides reduced the bandgap energy of mixed metal oxides. The reason behind this reduced bandgap energy is formation of new electronic state which arises due to the metal-oxygen interactions. Moreover, the nanocomposites of CuO.ZnO.Fe₂O₃ with reduced graphene oxide (rGO) and carbon nanotubes (CNTs) were prepared to study the effect of the carbonaceous materials on the rate of photodegradation. These carbonaceous nanomaterials have plethora properties which can bring advancement in sector of photocatalytic treatment of wastewater. The photocatalytic experiments were performed using methylene blue (MB) as standard dye for comparative study of metal oxides and their composites with rGO and CNTs. The percentage degradation of methylene blue (MB) by nanocomposite CuO.ZnO.Fe₂O₃/rGO is 87% which is prominent among all samples. This result ascribed the photocatalytic aspects of reduced graphene oxide along with mixed metal oxides.     

CuxNi1-xO nanostructures and their nanocomposites with reduced graphene oxide: Synthesis,characterization, and photocatalytic applications

NiO nanostructure was synthesized using a simple co-precipitation method and was embedded on reduced graphene oxide surface via ultrasonication. Structural investigations were made through X-ray diffraction (XRD) and functional groups were confirmed by Fourier transform infrared spectroscopy (FTIR). XRD analysis revealed the grain size reduction with doping. Fourier transform infrared spectroscopy confirmed the presence of metal-oxygen bond in pristine and doped NiO nanostructure as well as the presence of carbon containing groups. Scanning electron microscopy (SEM) indicated that the particle size decreased when NiO nanostructure was doped with copper. BET surface area was found to increase almost up to 43 m²/g for Cu doped NiO nanostructure/rGO composite. Current-voltage measurements were performed using two probe method. UV–Visible spectroscopic profiles showed the blue and red shift for Cu doped NiO nanostructure and Cu doped NiO Nanostructure/rGO composite respectively. Rate constant for Cu doped NiO nanostructure/rGO composite found to increase 4.4 times than pristine NiO nanostructure.     

Reduced graphene oxide-ZnO hybrid composites as photocatalysts: The role of nature of the molecular target in catalytic performance

Spurred by controversial literature findings, we enwrapped reduced graphene oxide (rGO) in ZnO hierarchical microstructures (rGO loadings spanning from 0.01 to 2 wt%) using an in situ synthetic procedure. The obtained hybrid composites were carefully characterized, aiming at shining light on the possible role of rGO on the claimed increased performance as photocatalysts. Several characterization tools were exploited to unveil the effect exerted by rGO, including steady state and time resolved photoluminescence, electron microscopies and electrochemical techniques, in order to evaluate the physical, optical and electrical features involved in determining the catalytic degradation of rhodamine B and phenol in water.Several properties of native ZnO structures were found changed upon the rGO enwrapping (including optical absorbance, concentration of native defects in the ZnO matrix and double-layer capacitance), which are all involved in determining the photocatalytic performance of the hybrid composites. The findings discussed in the present work highlight the high complexity of the field of application of graphene-derivatives as supporters of semiconducting metal oxides functionality, which has to be analyzed through a multi-parametric approach.     

A novel photocatalyst AgBr/ZnO/RGO with high visible light photocatalytic activity

A novel ternary photocatalyst AgBr/ZnO/RGO, where AgBr/ZnO is supported on reduced graphene oxide, is synthesized via a facile hydrothermal–impregnation method. The resultant composite presents a lamellar structure with AgBr nanoparticles homogeneously dispersing on the surface. The photocatalytic experiment for methyl orange dye degradation under visible light irradiation shows that ternary composite AgBr/ZnO/RGO has an activity 12.8 times and 2.3 times higher than binary photocatalysts ZnO/RGO and AgBr/ZnO respectively. More importantly, the ternary composite also demonstrates a good photostability. Metallic Ag is produced during the photocatalytic process, which may serve as the electron transfer mediator in the vectorial Z-scheme transfer of photogenerated charge carriers at the interface of AgBr/ZnO/RGO. The effective separation of photogenerated electrons and holes was proposed to be responsible for the enhancement of visible light photoactivity.     

Reduced graphene oxide coated Fe-soc as a cathode material for high-performance lithium-sulfur batteries

To solve the problem of the rapid decrease in capacity caused by poor conductivity, polysulfide shuttling, and the volume expansion associated with the reaction process, we attempt to use metal-organic framework (MOF) Fe-soc coated with reduced graphene oxide through electrostatic adsorption as a sulfur carrier material for lithium sulfur batteries. The research results show that S/Fe-soc@rGO has a high initial discharge specific capacity of 1634.3 mA h g⁻¹ with a stable specific capacity retention rate of 865.3 mA h g⁻¹ after 80 cycles and displays enhanced rate performance with high discharge specific capacities of 638.8 and 334.3 mA h g⁻¹ after 200 cycles at 0.5 and 1 C, respectively. Fe-soc has unsaturated metal sites can adsorb sulfur and polysulfide, effectively bind polysulfide, symmetrical stable structure is conducive to speed up the electron and ion transmission efficiency while buffering the volume expansion during charge and discharge. In addition, reduced graphene oxide as a coating layer can better assist Fe-soc to increase the utilization rate of sulfur, and improve the conductivity of the cathode material, thereby improving the cycle performance and rate performance of lithium-sulfur batteries. This article is also expected to stimulate the application of MOF derivatives in energy storage materials.     

Magnetically recyclable Ni1-xCdxCeyFe2-yO4-rGO nanocomposite photocatalyst for visible light driven photocatalysis

In this study, a magnetically recyclable Ni_1-xCd_xCe_yFe_2-yO₄-rGO (x, y = 0.05) (NCCF-rGO) nanocomposite photocatalyst has been prepared by following a facile in-situ co-precipitation method combined with ultra-sonication means. The as-synthesized magnetically separable NCCF-rGO nanocomposite photocatalyst efficiently degrades methylene blue (MB) dye in comparison to bare Ni_1-xCd_xCe_yFe_2-yO₄ (x, y = 0.05) (NCCF) nanoparticles (NPs) under visible light irradiation. The photo-degradation rate of MB with NCCF-rGO was ~9 times higher than NCCF nanoparticles (NPs). This enhanced photocatalytic performance of NCCF-rGO photocatalyst was due to the presence of reduced graphene oxide, which greatly help in production of photoactive species by reducing the rate of electro-hole pair recombination. The role of photoactive species that were responsible for the photocatalytic degradation of methylene blue has also been investigated. The as-synthesized NCCF-rGO photocatalyst expressed superb chemical stability and photocatalytic activity even after seven cycle runs. Moreover, the NCCF-rGO nanocomposite worked at all pH values and showed good acid resistance. In particular, the as-synthesized NCCF-rGO photocatalyst could be collected for the next cycle run by simply applying an external magnetic field. Hence, the NCCF-rGO nanocomposite could have potential use in organic dyes contained wastewater treatment.     

Reduced graphene oxide/carbon nanotubes reinforced calcium phosphate cement

Improving the mechanical properties of calcium phosphate cement (CPC) will be helpful for expanding its application range in the treatment of bone defect. In this work, reduced graphene oxide (RGO), which has two-dimensional structure and excellent mechanical properties, and carbon nanotubes (CNTs) were used as toughening materials collectively, to enhance the mechanical properties of CPC. Setting time, morphology and mechanical properties of CPC were analyzed. The two dimensional structure of RGO could increase the interface area between RGO and substrate, which achieved an effective transfer of load between substrate and RGO. Moreover, by reasons of bridging cracks, preventing crack extension, pulling out from substrate and interface debonding, the flexural strength and compressive strength of CPC were increased by 67.1% ± 4.8% and 76.4% ± 10.6% respectively. Therefore, the CPC composite we studied has potential to be used as load-bearing substitution in bone defects.     

Developing titania-hydroxyapatite-reduced graphene oxide nanocomposite coatings by liquid flame spray deposition for photocatalytic applications

Nanostructured titania has been extensively investigated for photocatalytic applications. Persistent challenge yet is how to effectively promote adhesion of microorganisms on the material surface for consequent enhanced photocatalytic disinfection. Here we report fabrication and characterization of titania-based nanocomposite coatings with addition of hydroxyapatite-reduced graphene oxide (HA-rGO). The nano features of TiO₂, HA, and rGO were well retained during liquid flame spray deposition. Photocatalytic activities of the coatings were examined by degradation of methylene blue and sterilization testing of Escherichia coli bacteria. Addition of HA-rGO effectively increased the specific surface area of the coatings and markedly enhanced adherence of the bacteria for subsequent extinguishment. The TiO₂–10 wt.% (HA-rGO) coating showed the best photocatalytic performances and further overloading of HA-rGO resulted in enwrapping of TiO₂ particles, resulting in deteriorated degradation activity. The results give clear insight into fabrication of novel photocatalytic nanocomposites by suspension thermal spray route for enhanced performances.     

Synthesis of MnOx/reduced graphene oxide nanocomposite as an anode electrode for lithium-ion batteries

We report the high performance of the manganese oxide/reduced graphene oxide (MnOx/rGO) nanocomposite as an anode electrode of a lithium-ion battery. The composite is synthesized by a low temperature (83 °C) chemical solution reaction, and shows relatively high specific capacities (660 mAh g⁻¹) after 50 cycles. For MnOx/rGO composites, the cycling stability is increased remarkably as compared to that seen with individual MnOx, and this is due to the synergistic effects of both the components in the composite. The rGO acts as a conductive buffer layer that suppresses the volume change of MnOx, and simultaneously promotes the conductivity of MnOx. The functional groups of graphene oxide facilitate MnOx formation at low temperature, and this retains the MnOx-graphene oxide connection, thus improving the capacity and cycling stability.     

Reduced graphene oxide/hierarchal spinel nickel cobaltite nanoflowers composites for supercapacitor electrodes with ultrahigh capacitive and excellent rate performance

Researchers are extensively investigating transition metal oxides due to their unique porous architectural structure and remarkable electrochemical properties, which are suitable to boost the energy storage capabilities. In present work, facile chemical route was used to synthesize hierarchal spinel nickel cobaltite nanoflowers anchored reduced graphene oxide (NiCo₂O₄-rGO) as high performance electrode material. NiCo₂O₄ anchored rGO demonstrated specific capacitance of 2695 Fg^-1 at 1 Ag^-1, which is greater than pristine NiCo₂O₄ nanoflowers specific capacitance. NiCo₂O₄-rGO showed excellent stability and retention capability of 96% after 2500 cycles at 5 Ag^-1. Furthermore, NiCo₂O₄–rGO exhibited maximum energy density of 93.57 WhKg^?1 at power density of 250 WKg^-1. We have achieved specific capacitance and retention capability which is higher than previously reported results. This enhancement is mainly attributed to the spinel structure of NiCo₂O₄ and its robust structural affinity with rGO. Moreover, rGO possesses extended surface area provided ample of active sites and exceptional synergetic effect which helped to enhance the induction and consequently transportation of e^?/h⁺. More importantly due to its special morphological effects, in future NiCo₂O₄ anchored rGO nanoflowers may open new avenue in research but also used as an efficient electrode material for the construction of high performance supercapacitors.     

Mesoporous yolk-shell structure Bi2MoO6 microspheres with enhanced visible light photocatalytic activity

Mesoporous yolk-shell structure Bi₂MoO₆ (BMO-YS) microspheres were successfully synthesized via a facile solvothermal route in Bi₂MoO₆ precursor solution. The morphology, structure and photocatalytic performance of the BMO-YS in the degradation of Rhodamine B (RhB) were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, nitrogen adsorption–desorption, UV–vis absorption spectroscopy and electrochemical impedance spectra, respectively. The as-prepared BMO-YS mainly consists of microspheres with diameters of about 1.5 μm. The photocatalytic studies reveal that the BMO-YS not only exhibits optimum photocatalytic performance, which may be attributed to the excellent charge separation characteristics and the enhanced light absorption offered by its unique yolk-shell structure, but also possesses excellent recyclability for photocatalysis.     

Bifunctional ternary manganese oxide/vanadium oxide/reduced graphene oxide as electrochromic asymmetric supercapacitor

A bifunctional ternary manganese oxide/vanadium oxide/reduced graphene oxide (MnO₂/V₂O₅/rGO) was developed for asymmetric electrochromic supercapacitor (EC-SC) application. The elemental mapping revealed uniformly distributed MnO₂, V₂O₅ and rGO, depicting homogenous synthesis of the hybrid composite. The phase composition, vibration modes and valance state of the ternary composite were analyzed via X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) analysis, respectively. Interestingly, the as-prepared MnO₂/V₂O₅/rGO composite disclosed tremendous C_sp of 1403.5 F/g, which was higher compared to MnO₂/V₂O₅ (801.1 F/g), V₂O₅ (613.1 F/g), MnO₂ (126.7 F/g) and rGO (60.7 F/g). MnO₂/V₂O₅/rGO that appeared in dark green switched its visual color to orange at the charged state, confirming the electrochromic property. The bifunctional manganese oxide/vanadium oxide/reduced graphene oxide//copper-based metal-organic framework/reduced graphene oxide (MnO₂/V₂O₅/rGO//MrGO) asymmetrical EC-SC device revealed outstanding cycling stability (90.3% charge retention over 5000 cycles), tremendous specific capacitance (652.7 F/g) and maximum specific energy (60.4 Wh/kg). MnO₂/V₂O₅/rGO//MrGO asymmetrical EC-SC device demonstrated reversible color changes from dark green to orange at the discharged and charged states, respectively. The significantly great electrochromic and supercapacitive performance revealed that MnO₂/V₂O₅/rGO//MrGO is an outstanding electroactive candidate for the next generation of electrochromic supercapacitors.     

Enhanced visible light photocatalytic performance of Sr0.3(Ba,Mn)0.7ZrO3 perovskites anchored on graphene oxide

In search of better materials for visible light photocatalytic performance, perovskite Sr_0.3(Ba/Mn)_0.7ZrO₃ nanopowders anchored on graphene oxide were synthesized for the evaluation of their photocatalytic activity against methylene blue (MB). The chemical coprecipitation method was used to synthesize SrZrO₃ (SZO) and a series of doped derivatives having a nominal composition of Sr_1-x(Ba,Mn)_xZrO₃ (x = 0.1–0.9) at an annealing temperature of 700 °C for 12 h. However, Sr_0.3(Ba,Mn)_0.7ZrO₃ with a bandgap value of 3.50 eV was further processed for the formation of composite with graphene oxide (GO) owing to its lowest bandgap value in the synthesized series. The inclusion of larger Ba²⁺ cations in the lattice resulted in the redistribution of cations creating antisite defects which were evident from the shrinkage of the lattice. The incorporation of Mn²⁺ resulted in the hybridization of Mn²⁺ (3d) orbitals with the split Zr⁴⁺ (4d) orbitals. This reduced the bandgap and composite formation with GO further enhancing the delocalization of excited electrons to GO hence, reducing electron-hole recombination. Adsorption assisted photocatalysis under a 100 W tungsten lamp was performed using the designed catalysts for the removal/degradation of MB. The π-π conjugation and the ionic interactions were found responsible for the adsorption of MB at the GO surface. High surface coverage, initial dye concentrations, heterogeneous catalyst surface, weak van der Waals interactions, pH and availability of ?OH radicals were found to be the decisive factors for the removal/degradation process. Improved charge separation enhances the generation of ?OH and better performance of the GO composites as opposed to the pristine strontium zirconate perovskites.     

Surfactant-free synthesis of homogeneous nano-grade cadmium sulfide grafted reduced graphene oxide composite as a high-activity photocatalyst in visible light

Zero-dimensional cadmium sulfide (CdS) nanoparticles with small size (∼50 nm) were grafted on the two-dimensional reduced graphene oxide (RGO) nanosheet via a facile hydrothermal method without any surfactant to synthesize CdS@RGO nanocomposites in this paper. The structural analysis confirms the strong attachment and interaction between CdS and RGO in CdS@RGO photocatalyst, which leads to a higher photocatalytic efficiency (95.3%) with superior anti-corrosion stability (almost no change of efficiency over three repeated experiments) to that of pure CdS in visible light. The unique hybrid nanostructure of CdS@RGO can effectively prevent the self-corrosion of CdS and facilitate the separation of electron-hole pairs. Consequently, these outstanding photocatalytic performances of CdS@RGO endow it with a promising prospect for the degradation of organic pollutants and this work can be extended to other graphene-based inorganic semiconductor composites.     

One-dimensional spindle-like BiVO4/TiO2 nanofibers heterojunction nanocomposites with enhanced visible light photocatalytic activity

One-dimensional spindle-like BiVO₄/TiO₂ nanofibers heterojunction nanocomposites with high visible light photocatalytic activity have been successfully obtained by combining the electrospinning technique and solvothermal method. The as-obtained products were characterized by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV–vis spectra and photoluminescence (PL) spectra. The results revealed that spindle-like BiVO₄ nanostructures were successfully grown on TiO₂ nanofibers. Photocatalytic tests showed that the BiVO₄/TiO₂ nanofibers heterojunction nanocomposites showed enhanced visible light photocatalytic activity than that of pure TiO₂ nanofibers, which might be attributed to the effective photogenerated electrons-holes separation based on the photosynergistic effect of the BiVO₄/TiO₂ heterojunction. Moreover, the BiVO₄/TiO₂ nanofibers heterojunction nanocomposites could be easily recycled without any decrease of the photocatalytic activity.     

Hollow ZnSnO3 cubes@carbon/reduced graphene oxide ternary composite as anode of lithium ion batteries with enhanced electrochemical performance

The ternary composite, carbon coated hollow ZnSnO₃ (ZS@C) cubes encapsulated in reduced graphene oxide sheets (ZS@C/rGO), was synthesized via low-temperature coprecipitation and colloid electrostatic self-assembly. The uniform carbon-coating layer not only plays a role in buffering the volume change of ZnSnO₃ cubes in the charging/discharging processes, but also forms three-dimensional network with the cooperation of graphene to maintain the structural integrity and improve the electrical conductivity. The results show that the reduced graphene oxide sheets encapsulated ZS@C microcubes with a typical core-shell structure of ~700 nm in size exhibit an improved electrochemical performance compared with bare ZS@C microcubes. The ZS@C/rGO electrode delivered an initial discharge capacity of 1984 mA h g⁻¹ at a current density of 0.1 A g⁻¹ and maintained a capacity of 1040 mA h g⁻¹ after 45 cycles. High specific capacity and superior cycle stability indicate that the ZS@C/rGO composite has a great potential for the application of lithium-ion anode material.     

Enhanced UV- and visible-light driven photocatalytic performances and recycling properties of graphene oxide/ZnO hybrid layers

Light induced catalytic processes have attracted significant attention during the last years for wastewater treatment due to their efficiency in decomposition of organic contaminants. In this study we report the synthesis of graphene oxide (GO)/ZnO hybrid layers with high photocatalytic efficiency using laser radiation. The results show that the hybrid layers exhibit much improved photodecomposition efficiency as compared to pure GO or ZnO both under UV and visible-light irradiation. The enhanced photocatalytic efficiency of the hybrid as compared to the reference pure ZnO and GO layers was attributed to the contribution of GO to the separation and transport of the photogenerated charge carriers. Additionally, under visible light irradiation the organic molecules can act as first sensitizers in the degradation process. The recyclability of the layers was also investigated through repetitive photodegradation cycles under UV- or visible-light irradiation. After consecutive degradation runs, the hybrid photocatalyst layers were still stable and retained high degradation efficiency, ensuring reusability. The photocatalytic activity of the layers was correlated with the gradual change of their chemical structure during consecutive degradation cycles. Owing to the high photodegradation efficiency, reusability, and ease of recovery the synthesised hybrid layers consisting of easily available materials are suitable for environmental purification applications.     

Reduced graphene oxide modified melamine sponges filling with paraffin for efficient solar-thermal conversion and heat management

A novel type of reduced graphene oxide(rGO) modified melamine sponges(rGS) filling with paraffin(rGS-pf) is developed for efficient solar-thermal conversion and heat management.The micro structures,filling and holding capacity of paraffin in porous rGS,solar-thermal energy conversion and energy harvesting efficiency of the prepared rGS-pf have been investigated systematically.The content of rGO nanosheets coated on the skeletons of rGS-pf is only 0.11%,while the loading content of paraffin in th...