Abstract

1. Introduction

2. Experimental

3. Results and discussion

4. Conclusion

Conflict of Interest

Supplementary Information

References

Abstract

     This study investigates the effect of graphene oxide (GO) on the mechanical and corrosion behavior, antibacterial performance, and cell response of Mg—Zn—Mn (MZM) nanocomposite. MZM/GO nanocomposites with different amounts of GO (i.e., 0.5wt%, 1.0wt%, and 1.5wt%) were fabricated by the semi-powder metallurgy method. The influence of GO on the MZM nanocomposite was analyzed through the hardness, compressive, corrosion, antibacterial, and cytotoxicity tests. The experimental results showed that, with the increase in the amount of GO (0.5wt% and 1.5wt%), the hardness value, compressive strength, and antibacterial performance of the MZM nanocomposite increased, whereas the cell viability and osteogenesis level decreased after the addition of 1.5wt% GO. Moreover, the electrochemical examination results showed that the corrosion behavior of the MZM alloy was significantly enhanced after encapsulation in 0.5wt% GO. In summary, MZM nanocomposites reinforced with GO can be used for implant applications because of their antibacterial performance and mechanical property.

Introduction

     Currently, because magnesium (Mg) alloys have more benefits than common metallic materials, ceramics, and biodegradable polymers, their biomedical applications have been increasing. In terms of mechanical features, metals have higher mechanical strength and fracture toughness than ceramics or polymers; thus, metals are more appropriate for load-bearing usages than ceramics or polymers [1–2]. The density of human cortical bone (1.75 g/cm3 ) is similar to the density of Mg (1.738 g/cm3 ) and Mg alloys (1.75–1.85 g/cm3 ) but lower than the density of biomedical titanium alloy Ti6Al4V (4.47 g/cm3 ) [3–4]. In terms of biocompatibility, certain amounts of Mg ions in the human body are connected with many metabolic reactions and biological mechanisms [5–6]. Mg alloys are suitable orthopedic and cardiovascular implants because further surgery to remove them is not needed [7–8]. However, an important drawback of Mgbased implants is that they do not have good resistance against corrosion in physiological environments [9]. Mechanical strength could be significantly reduced by rapid and uncontrollable corrosion processes, which leads to premature failure [10]. Moreover, the health of patients who have such implants could be at risk because of the evolution of hydrogen gas and alkalinization of the environments close to the interface between implant and tissue [11]. Therefore, to achieve the secure deployment of biomedical devices, the degradation/corrosion rate of Mg alloys needs to be controlled [12]. In this context, several methods, such as alloying, powder metallurgy (PM), and surface modification strategies, have been used in an extensive number of studies that aimed to solve the problem of corrosion in Mg alloys [13–14]. Among the best methods to enhance the corrosion resistance of porous Mg are PM processes, such as mechanical alloying [15–17].

Conclusion

     In this study, using the semi-powder metallurgy method, different contents of GO were embedded in the Mg–Zn–Mn (MZM) matrix to prepare MZM/xGO nanocomposites for orthopedic applications. The corrosion performance and the 24 20 16 12 8 4 0 0 −0.5 −1.0 −1.5 −2.0 Extension / mm MZM/GO Graphene oxide Graphene oxide Graphene oxide Graphene oxide Crack Crack (a) (c) 1.5GO 0.5GO 1GO MZM (b) MZM composite MZM/0.5GO MZM/1GO MZM/1.5GO 49 59 63 64 Compression strength / N 4820 17810 19960 9620 1.12 1.31 1.44 0.72 Force / (10 3 N) Micro hardness, HV Extension / mm Material nanocomposite Fig. 10.    (a) Typical compressive curves and (b) hardness and compressive strength values of the MZM/xGO nanocomposites; (c) schematic diagram of the crack deflection toughening mechanisms of GO in the MZM/xGO nanocomposites. S. Jabbarzare et al., Effect of graphene oxide on the corrosion, mechanical and biological properties of Mg-based … 317 mechanical and biological characteristics of the MZM/xGO nanocomposites were analyzed. The microstructural assessment showed that a uniform distribution was achieved in the MZM/0.5GO and MZM/1GO nanocomposite specimens. However, agglomeration was observed in the MZM/1.5GO nanocomposite specimen. The results showed that the GO content, hardness value, and compressive strength are positively associated. In this context, the MZM/1GO nanocomposite has higher hardness value and compressive strength than the Mg-based nanocomposite without GO. The MZM/ 0.5GO nanocomposite exhibited a nearly comparable corrosion resistance to the MZM/1GO nanocomposite, even though the incorporation of more GO has an unfavorable effect on the Rct value of the MZM matrix. The MTT assay results showed that the MZM/1GO nanocomposite increased the MG63 cell viability and ALP activity, indicating the increasing level of osteogenesis. The results of the analysis of antibacterial activity showed that the MZM/1.5GO nanocomposite had a noticeable effect on antibacterial effectiveness toward bacteria, including Salmonella–Shigella and Klebsiella pneumoniae. In summary, the results indicate the possibility of utilizing the MZM/1GO nanocomposite for implant applications with effective anti-infection characteristics.

Abstract

     Circular economy approaches are commonly depicted by two cycles, where the biological cycle is associated with regeneration in the biosphere and the technical cycle with reuse, refurbishment, and recycling to maintain value and maximize material recovery. This work, instead, presents an alternative vision to the management of carbon-based materials that integrates the two cycles and enables the phasing-out of fossil carbon from the material system. The aim is to investigate the benefits and global potential of a co-recycling system, as an alternative to conventional recycling systems that separate biomass-based materials (e.g., wood, paper) from fossil-based materials (e.g., plastics). Thermochemical recycling technologies enable the conversion of carbon-based waste materials into high-quality synthetic products, promoting circularity and avoiding carbon losses such as carbon emissions and waste accumulation in landfills and nature. Here, the construction and analysis of co-recycling scenarios show how the deployment of thermochemical recycling technologies can decouple the material system from fossil resource extraction. Furthermore, energy use is reduced if pyrolysis and/or gasification are included in the portfolio of recycling technologies. In a decarbonized energy system, deployment of co-recycling can lead to near-zero carbon emissions, while in more carbon-intensive energy systems the choice of thermochemical recycling route is key to limiting carbon emissions.

Introduction

     Carbon-based fuels (mainly fossil fuels but also biomass) account for about 90% of the current global primary energy supply. Carbon is also a building block in a wide range of materials (carbon-based materials; C-materials) used in society. While fossil fuel use is the main cause of anthropogenic greenhouse gas (GHG) emissions, and a transition away from the use of such fuels is essential to limit the global temperature increase to 1.5 °C (IPCC et al., 2018), the production and use of materials such as plastics, cement and steel entail significant GHG emissions (IEA, 2018; Jambeck et al., 2015). The use of biomass-based products can effectively reduce the use of fossil fuels and GHG-intensive materials. There is also scope for substituting existing biobased products with more benign products. For example, cellulose-based textiles can replace cotton which is associated with soil and water depletion, as well as harmful impacts on human health and biodiversity due to excessive use of pesticides and fertilizers (IPCC et al., 2019c; Niinimäki et al., 2020). However, the biomass supply potential is limited by resource constraints (Gerten, 2018) and implications of expanded biomass use for mitigation and other objectives depend on many factors, including soil and climate conditions, biomass type, land management system, scale and pace of deployment, and influence on land use (Calvin et al., 2021). For instance, cropland expansion for energy crop production may cause deforestation, with consequent GHG emissions and negative impacts on biodiversity (IPCC et al., 2019b).

Conclusion

     A co-recycling scenario utilizing advanced thermochemical recycling is proposed and analyzed. The results show that such a scenario can combine natural and synthetic C-materials in the same recycling scheme and that enables to decoupling of the Carbon Material System from the extraction of fossil resources, as well as minimizing waste generation. Advanced thermochemical recycling enables the recovery of any carbon flow (CO2, natural or synthetic, losses, etc.) and the production of high-quality products. A focus on carbon recycling, instead of material recycling, can improve C-materials (wood, paper, plastics, and textiles) resource management, by increasing the resource utilization from 0.7 to 1.1 tC-material/tCRtM, i.e., producing more C-materials than resources used, as well as reducing the CMS losses by half.

Abstract

I. INTRODUCTION

II. EXPERIMENTAL DETAILS

III. RESULTS

IV. DISCUSSION

V. CONCLUSION

REFERENCES

Abstract

     Nanocomposites have been developed as the third-generation insulating materials. This article introduces the crosslinked polyethylene (XLPE) nanocomposite dielectric doped with a small amount of nano-hexagonal boron nitride ( h -BN), which exhibits excellent insulation properties under high dc voltage. The test results show that XLPE/ h -BN nanocomposites possess significant improvements in dc breakdown strength and 0.1 wt% nano h -BN doping can actually increase the dc breakdown strength by 39%. The space charge properties of the XLPE/ h -BN obtained by the pulsed electro-acoustic (PEA) measurements and the direct current integrated charge [DCIC- Q(t) ] measurements show that the positive homocharge injection under dc voltage is obviously suppressed, and the electrical conductivity under relatively high electric field decreases. The thermally stimulated current results show that the nano h -BN doping introduces only deep charge traps (above 1 eV) to the XLPE matrix. The trap energy is deeper than that of the original traps, and this is the main factor leading to the improvement of the dc insulation properties. Besides, the doping of h -BN does not introduce impurities or change the crystallinity of XLPE. This article presents the novel XLPE/ h -BN nanocomposites with excellent dc insulation properties and indicates the large potential of the nano h -BN-doped insulation materials.

Introduction

     NANOCOMPOSITES have excellent dielectric properties and have become the third-generation insulating materials [1]. Nano-doping can improve corona resistance and electrical tree characteristics as well as regulate dielectric properties of the polymer matrix. More importantly, the dc insulation properties can be enhanced to various degrees by inorganic nanoparticle doping, such as the suppression of the charge injection and transportation, as well as the increase of the breakdown strength. With the construction of high-voltage direct current (HVDC) transmission line in a large scale, the power industries have proposed stricter requirements on the dc insulation performance of insulating materials. Therefore,nanocomposite dielectrics may be more suitable for dc insulation systems in the future, and nanocomposite materials with higher insulation performance need to be continuously developed. For example, crosslinked polyethylene (XLPE)- based nanocomposites are expected to be used in the new generation of HVDC cable.

Conclusion

     The XLPE/h-BN nanocomposite with high dc breakdown strength and suppressed charge injection features were introduced in this study. It is useful to reach the conclusions as follows.

     1) XLPE/h-BN nanocomposite samples with loading content ranging from 0.1 to 3 wt% were prepared successfully. The dc Eb of the nanocomposite sample shows at most a 39% increase under 0.1 wt% loading.

     2) The effect of h-BN doping on the charge trap characteristics of XLPE is a significant increase in the density of deep traps, and this is the main cause for the improvement of dc insulation properties.

Abstract

1. Introduction

2. Experimental section

3. Results and discussion

4. Conclusions

Acknowledgment

References

Abstract

     The addition of graphene as an efficient nano-filler to different polymer matrices lead to a substantial improvement in different physical properties which, as a result, pave the way towards promising applications. In this work, Polystyrene (PS) was reinforced with different low loadings of graphene oxide (GO). The latter was prepared according to the Hummers method. The incorporated weight fractions were (0.01, 0.05, 0.1, 0.25, 1.0) wt. %. Solution blending was the adopted approach to prepare the nanocomposites. The resulted nanocomposites were characterised compared to the neat polymer. Many tools were employed to investigate the structure, morphology, thermal, and thermo-mechanical behaviour of GO, neat polymer, and the nanocomposites. The structural and morphological outcome for GO and PS was confirmed compared to the literature. The outcome confirmed as well the good dispersion of GO nano-sheets in the PS. The thermal and thermo-mechanical properties were enhanced for the nanocomposites compared to the neat polymer. The results emphasised the improvement of nanocomposites’ performance as the inclusion of GO went higher.

Introduction

     Carbon based nano-fillers for a range of applications have recently attracted a considerable attention due to their exceptional mechanical and physical properties such as high strength, high stiffness and high thermal and electrical conductivities. Many of research groups have prepared and study the features of these materials according to their low cost, low weight and ease of processing.[1] Graphite, fullerene, carbon nano-tubes and the recently discovered material, graphene, are derived from this fascinating material, carbon, and they are the most widely studied allotropes of interest to technologists and researchers due to their unique applications in various fields.

     Graphene is a planar honeycomb lattice that is a two dimensional, one atom thick carbon sheet. Its properties include high thermal conductivity, high intrinsic electron mobility, optical transmittance of 98%, large specific surface area and high Young’s modulus.[3] These properties offer graphene the potential for numerous different applications in many disciplines such as sensors, energy conversion, storage devices, solar cells and reinforced composites.[4] To enable the exploitation of these unique properties in applications, graphene and its derivatives have been successfully prepared using different routes such as bottom-up chemical vapour deposition and top down exfoliation of graphite by means of oxidation, intercalation and/or sonication.[5] As a consequence of their high G-G interactions (kind of non-covalent interaction between electron rich G system and another molecule), graphene sheets are not directly mixed with the polymer matrices to produce polymer nanocomposites as the graphene sheets tend to stack into large aggregates. For this reason, graphene oxide is usually incorporated into polymer matrices for making high quality polymer nanocomposites, as it has better compatibility with polymers, forms a uniform dispersion and offers a possibility of mass production.

Conclusions

     In this study, different low loadings of GO were incorporated homogenously into a PS matrix and different structural, thermal properties were studied as well as the nanomechanical behaviour for the polymer, and the nanosheets imaged in the cryogenically fractured surface. The incorporation of low loadings of the GO led to improvement in thermal and thermomechanical performance as the results of TGA, DSC and DMA indicated. As the homogenous dispersion for the nanosheets in the polymer matrix is a prerequisite for a good performance, this kind of dispersion was verified via different microscopic techniques carried out in this study. These techniques included OM, SEM and TEM. According to the very low weight fractions used in this study, no sharp peaks of GO appeared in Raman spectroscopy for the nanocomposites. Weak shoulders appeared in FTIR diagram and tiny humps can be seen in the curves of XRD. These can be attributed to the low loadings of GO in the PS that led to dilution of GO in the polymer matrix. In general, the incorporation of GO in PS using low loadings led to improve thermal and thermomechanical performance for the nanocomposites compared to the neat polymer. Td, Tg, and storage modulus were increased as the weight fraction of GO went higher.

Highlights

Abstract

Graphical abstract

Keywords

1. Introduction

2. Green synthesis of fluoroquinolone derivatives

3. Recent advances in green synthesis of fluoroquinolone derivatives and their role in anti-infective field

4. Applications of fluoroquinolones

5. Conclusion

6. Future aspects

CRediT authorship contribution statement

Declaration of competing interest

Acknowledgements

Abbreviations

References

Abstract

Fluoroquinolones are of pivotal interest for scientists because of their excellent pharmacological and pharmacokinetic profiles. They have a broad spectrum of antimicrobial activity and show several promising features such as, greater bioavailability, admirable tissue penetration and comparatively lower incidence of antagonistic and lethal effects. These have made the compounds highly desirable to combat several infectious diseases. Various synthetic conventions have been established to hasten the fluoroquinolone’s amination rate and to improve yield. Such methods have significant disadvantages including, costly reagents, usage of vast quantities of harmful solvents, excessive heat and sideways reactions. These drawbacks aren’t appropriate in current pharmaceutical market. Hence, it is highly desirable to develop a newer green and more efficient process for fluoroquinolones synthesis. Green chemistry methodology endeavours to achieve sustainability at the molecular level. The field of green chemistry has shown how chemists can design next-generation products and processes to make them more cost-effective while being virtuous for human health and the environment. This graphical review demonstrates the current developments in the synthesis of fluoroquinolones employing the principles of green chemistry by using the novel, recyclable and environmental-friendly catalysts and solvents.

1. Introduction

The growing prevalence of bacterial and fungal resistance to a wide number of anti-microbial mediators in both community and hospital-acquired infections has become a significant and global well-being issue with approximately 15 million deaths per annum, as currently, accessible medicines may no longer be successful for resistant infections as a consequence of pathogenic microbes implementing a range of strategies to solve these problems [1]. This unwanted occurrence encouraged the researchers to focused on the advancement of newer materials from bio renewable and sustainable sources because of great concerns about the environment, waste accumulation and destruction and the inevitable depletion of fossil resources [2]. Green chemistry is a modern area of chemistry that is rapidly emerging. Its growing significance is in making the use of maximum available resources in such a way that the production of chemical waste is negligible or minimal. This is one of the superlative possible replacements for conventional methods of chemical synthesis. Through using the green methodology, we can’t only evade the usage of harmful and noxious chemicals, but also prevent the development of by-products. Therefore, they are flawlessly responsive to combinatorial synthesis automation. Gedye and Giguere, in 1986, first announced that the organic synthesis under microwave irradiation could be performed very quickly [3]. Microwave irradiation technique is another form of heating, based upon the capability of analogues to convert electromagnetic energy into heat. This approach will help to increase the rates of chemical reactions, yields and safer materials [4].

Highlights

Abstract

Keywords

1. Introduction

2. Methodology

3. Results and discussion

CRediT authorship contribution statement

Declaration of competing interest

Acknowledgement

Appendix A. Supplementary data

Disclaimer

Research Data

References

ABSTRACT

We implement oceanic dimethylsulfide (DMS) emissions and its atmospheric chemical reactions into the Community Multiscale Air Quality (CMAQv53) model and perform annual simulations without and with DMS chemistry to quantify its impact on tropospheric composition and air quality over the Northern Hemisphere. DMS chemistry enhances both sulfur dioxide (SO2) and sulfate (SO2− 4 ) over seawater and coastal areas. It enhances annual mean surface SO2 concentration by +46 pptv and SO2− 4 by +0.33 μg/m3 and decreases aerosol nitrate concentration by − 0.07 μg/m3 over seawater compared to the simulation without DMS chemistry. The changes decrease with altitude and are limited to the lower atmosphere. Impacts of DMS chemistry on SO2− 4 are largest in the summer and lowest in the fall due to the seasonality of DMS emissions, atmospheric photochemistry and resultant oxidant levels. Hydroxyl and nitrate radical-initiated pathways oxidize 75% of the DMS while halogeninitiated pathways oxidize 25%. DMS chemistry leads to more acidic particles over seawater by decreasing aerosol pH. Increased SO2− 4 from DMS enhances atmospheric extinction while lower aerosol nitrate reduces the extinction so that the net effect of DMS chemistry on visibility tends to remain unchanged over most of the seawater.

1. Introduction

In the 30+ years since Charlson et al. (1987) hypothesized that biogenically-produced dimethyl sulfide (DMS) from marine phytoplankton participates in a negative climate feedback loop affecting cloud condensation nuclei and cloudiness, the study of DMS from the world’s oceans has been a vigorous area of research. Though the CLAW hypothesis (named after the authors of Charlson et al., 1987) has been criticized as too simplistic (Quinn and Bates, 2011), the resulting knowledge gained about the sources, oceanic concentrations, and emissions of oceanic DMS has enabled chemical transport and earth systems models to realistically simulate its impacts on air quality and climate. DMS in the ocean is produced from the breakdown of dimethylsulfoniopropionate (DMSP) generated from microalgal metabolic processes and exudation/mortality (Stefels et al., 2007). The concentration of DMS in seawater has been sampled extensively, leading to the construction of the Global Surface Seawater DMS Database (http://saga.pmel.noaa.gov/dms) and interpolated estimates of the global concentration distribution (Kettle et al., 1999; Kettle and Andreae, 2000). An updated climatology of oceanic DMS concentrations using over 47,000 measurements was reported by Lana et al. (2011).

Introduction

Materials and Methods

Results and Discussion

Conclusions

References

ABSTRACT

RNA molecules perform a variety of biological functions for which the correct three-dimensional structure is essential, including as ribozymes where they catalyze chemical reactions. Metal ions, especially Mg2þ, neutralize these negatively charged nucleic acids and specifically stabilize RNA tertiary structures as well as impact the folding landscape of RNAs as they assume their tertiary structures. Specific binding sites of Mg2þ in folded conformations of RNA have been studied extensively; however, the full range of interactions of the ion with compact intermediates and unfolded states of RNA is challenging to investigate, and the atomic details of the mechanism by which the ion facilitates tertiary structure formation is not fully known. Here, umbrella sampling combined with oscillating chemical potential Grand Canonical Monte Carlo/molecular dynamics simulations are used to capture the energetics and atomic-level details of Mg2þ-RNA interactions that occur along an unfolding pathway of the Twister ribozyme. The free energy profiles reveal stabilization of partially unfolded states by Mg2þ, as observed in unfolding experiments, with this stabilization being due to increased sampling of simultaneous interactions of Mg2þ with two or more nonsequential phosphate groups. Notably, these results indicate a push-pull mechanism in which the Mg2þ-RNA interactions actually lead to destabilization of specific nonsequential phosphate-phosphate interactions (i.e., pushed apart), whereas other interactions are stabilized (i.e., pulled together), a balance that stabilizes unfolded states and facilitates the folding of Twister, including the formation of hydrogen bonds associated with the tertiary structure. This study establishes a better understanding of how Mg2þ-ion interactions contribute to RNA structural properties and stability.

INTRODUCTION

RNA molecules have highly diverse structures ranging from simple helices to highly heterogeneous folded conformations that are essential for their wide range of cellular functions (1–3). Specifically, ribozymes, a distinct class of enzymes, exhibit complex tertiary structures and catalyze self-cleavage or the cleavage of phosphodiester bonds of substrate RNA, with metal ions typically playing a central role in the catalytic activity (4–6). To assume their tertiary structures, RNAs must overcome large unfavorable electrostatic interactions associated with their polyanionic phosphodiester backbone (7). To facilitate this, positively charged ions screen the highly negative potential, allowing the RNA secondary structures to collapse into compact tertiary conformations (8–11). Typically divalent ions, most often Mg2þ, facilitate the formation of tertiary interactions required for the full folding of RNA (12–14). However, the inability to visualize the ions during folding represents a key barrier to understanding the role of divalent ions in folding of RNA (15). Studies have used classical molecular dynamics (MD) or other theoretical approaches to investigate Mg2þ-RNA binding, but they were limited to native conformations because of their inability to overcome the issues associated with the Mg2þ exchange rates (16–22). The exchange rate of water complexed to Mg2þ is on the ms timescale (6.7 105 s 1 ), and the exchange rate of Mg2þ with phosphate is on the ms timescale (0.5–2.5 103 s 1 ) (23), which is beyond the timescale of typical atomistic MD simulations (20,24) such that only limited insights into Mg2þ-RNA interactions are accessible (25). Alternatively, simulations using coarse-grained models of nucleic acids provided insights into how Mg2þ can serve to nucleate the folding of key tertiary interactions with the Mg2þ-RNA interactions being dominated by specific interactions even in unfolded states (19,26).

Introduction

Result and discussion

Conclusion

Acknowledgment

Appendix A. Supplementary data

Research Data

References

Abstract

In this paper, the effect of Zr and Mn on the microstructure and first hydrogenation kinetic of TiFe alloy is reported. TiFe alloy to which Zr, Mn or a combination of both have been added were synthesized by induction melting. First hydrogenation of all alloys was performed at room temperature under 20 bar of hydrogen. We found that addition of manganese makes possible activation at room temperature, but kinetics was very sluggish. Alloy with 2 wt% Zr did not absorb hydrogen. However, with addition of 4 wt% Zr, the alloy absorbed 1.2 wt% of hydrogen. A synergetic effect was found when zirconium was added along with manganese. Alloy with 1 wt% Mn and 2 wt% Zr had better kinetics than the alloy having only Mn or only Zr. The maximum hydrogen capacity was also greater at ~1.8 wt% after 7 h. Combination of 4 wt% Zr and 2 wt% Mn absorbed 2 wt% of hydrogen in 5 h. The rate limiting step for each activated alloy was found to be diffusion controlled with decreasing interface velocity.

Introduction

Emission of greenhouse gases due to the intensive use of fossils fuel demands the development of alternative fuels [1,2]. Hydrogen fulfills the criteria as an alternative energy carrier due to its high energy density, availability and less impact on the environment when produced by renewable resources such as solar and wind energies [3,4]. One of the major challenges in the development of hydrogen economy is to store hydrogen safely and at low cost [5]. The solid-state hydrogen storage in metal hydrides presents some advantages over the conventional high-pressure cylinders and liquid hydrogen because of its high volumetric capacity, low pressure, and low temperature of operation [6e10]. Metal hydrides can also be used as a negative electrode in rechargeable batteries such as Ni-MH [11e13]. Two of the major characteristics of metal hydrides should have in order to fulfill the requirements for mobile and stationary applications are low cost and utilization in a practical range of temperature and pressure (0e100 C, 1e10 atm) [14e16].

1- Introduction

2- Materials and methods

3- Results

4- Discussion

References

Abstract

Objective. The aim of this study is to investigate bone healing ability of niobium-containing bioactive glasses in rat femur model with quantitative and qualitative measurements through x-ray computed microtomography.
Methods. Niobium-containing bioactive powders and scaffolds were produced by sol–gel route (BAGNb). Glasses without niobium addition were produced as well (BAG). Five groups were used: BAGNb powders, BAG powders, BAGNb scaffolds, BAG scaffolds and, as a control group, autogenous bone was used. Materials were implanted in the femur of male rats (Wistar Lineage n= 10) and the healing was observed after 15, 30 and 60 days. After the post-operative times, samples were scanned by X-ray microcomputed tomography where morphometric measurements and the mineral density were assessed in image software.
Results. No postoperative complications were observed after surgery. BAGNb glasses presented higher mineral deposition, which was observed in the relative volume of bone and the mineral density when compared BAG groups. In these parameters, no statistical difference was found between BAGNb and autogenous bone. The BAGNb powders presented a higher amount of mineralized tissue when compared to BAGNb scaffolds. The analysis oftrabecular structure showed lower trabecular formation in synthetic materials when compared to autogenous bone.
Significance. Niobium-containing bioactive glasses promoted bone formation comparable to that of the autogenous bone without compromising the quality of the formed bone.

Introduction

Bioactive glasses are a class of synthetic materials that may be used in bone regeneration applications in dentistry [1,2]. The osteoinductive and osteoconductive abilities [3] of these glasses are related to their ion release that promotes bone formation by way of two mechanisms, specifically 1) the formation of a carbonated hydroxyapatite layer in the surfaces of the particles [4] and 2) the upregulation of cell activity to stimulate the deposition of bone tissue [5]. Improvements in glass composition and structure may contribute to an improved release of bioactive ions and increased bone formation. The enhancement of bioactive glass composition and production may improve bone regeneration capacity. Niobium has been investigated as biomaterial to be used [6–9] due to its ability to promote mineral deposition [6,7,10,11]. The development of sol–gel-derived, niobium-containing bioactive glasses powders and scaffolds was previously shown [7] and increased mineralization ability was observed for niobium-containing grafts in vitro. Several approaches are used to promote the reestablishment of bone tissue for prosthetic rehabilitation, while autogenous bone remains the gold standard graft for maxillae and mandible reconstructions [12–15]. Synthetic bone substitutes have been used as alternatives that have ensured reduced patient morbidity [13] and comparable bone formation [14]. The placement of dental implants in edentulous patients is additionally related to improved health parameters and an increased quality of life, but may be limited in terms of efficacy by the absence of adequate quality and quantity of bone [15]. The aim of this study was to investigate the bone healing ability of niobium-containing bioactive glasses in a rat femur model according to quantitative and qualitative measurements obtained through X-ray computed microtomography. The working hypothesis is thatthe addition of niobium increased the bone regeneration ability promoted by sol-gel derived bioactive glasses.

Introduction

Materials and method

Results and discussion

Conclusion

References

Abstract

Adsorption is one of the most commonly used methods for the wastewaters treatment. In this work, we studied the impact of experimental conditions on the adsorption of heavy metals M(II) (M=Cd, Ni, Cu, Pb and Zn) in batch system using chitin obtained from crab shells. This biomaterial is selected because of its low cost, availability and efciency. The M(II) adsorption was found to be dependent on the initial pH, contact time, initial concentration of M(II) and biomass dose. The kinetic models of Elovich, pseudo-frst-order and pseudo-second-order kinetic models were successfully applied, providing the best ftting of the experimental data. The Langmuir, Freundlich, Temkin and Dubinin–Radushkevich isotherms and the thermodynamic parameters were also discussed. The adsorption capacity peaks at: 50, 47.61, 43.4, 40 and 38.46 (mg L−1) for Pb(II), Cu(II),Ni(II), Cd(II) and Zn(II), respectively. The negative free energy (∆G°) and positive enthalpy (∆H°) indicated spontaneous and endothermic adsorption.

Introduction

The natural environment is constantly contaminated by various pollutants coming from industrial sectors, which in turn showed a considerable change. Toxic metals are widespread and hazardous and afect the environment with a negative impact on the ecosystem, causing dangerous diseases to both animals and humans. Among toxic metals, one can cite Cd, Hg, Pb, As, Cr and Cu (Salem et al. 2012) which must be removed before discharge to the aquatic environment. Unlike organic pollutants, heavy metals are refractory and cannot be degraded and accumulate in living organisms (Ali and Ateeg 2015). The elimination of metals has been the subject of several works using diferent techniques like ion electrodialysis (Esalah et al. 2000), sedimentation (Gupta et al. 2001), ion exchange (Da̧browski et al. 2004; Kang et al. 2008), biological operations (Rashid et al. 2014), coagulation/focculation (Yue et al. 2009), nanofltration (Hafane et al. 2000), solid-phase extraction (Khezami and Capart 2005), adsorption (Abolhasani and Behbahani 2015; Behbahani et al. 2014) and electrokinetic remediation (Sawada et al. 2004). However, all these techniques sufer from high costs of capital and operations as well as the elimination of metallic sludge (Malairajan 2011). On the other hand, the adsorption has become advantageous for removing toxic metals because of its environmentally friendly characteristic, efciency and low cost. In this regard, many marine wastes were used as adsorbents for both inorganic and organic pollutants (Copat et al. 2012; Izquierdo et al. 2014; Samiey and Ashoori 2012; Vilar et al. 2008).

Hydrate-based desalination (HBD) has been developed to obtain fresh water from seawater in an economic and environmental sustainable manner. As a low-pressure hydrate former for the HBD process, chlorodifluoromethane (R22) hydrates were formed in the pressure range of 1–6 bar under brine environments, aqueous NaCl and MgCl2 solutions. Synchrotron X-ray diffraction and Raman spectroscopy measurements revealed that the R22 hydrates formed with NaCl and MgCl2 show structure I and enclathration of R22 molecules into the large cages. These results also confirmed that the salt ions cannot be encaged in the gas hydrate framework, reflecting the ion exclusion behavior for HBD above the eutectic of water and hydrated salts. The formation kinetics of R22 clathrate hydrate in the presence of salts show that both the initial growth rate and pressure drop of the R22 hydrates heavily depend on the salinity of aqueous solutions. A new theoretical approach adopting the transient time-dependent apparent rate constant of hydrate formation with salts was proposed to predict the formation kinetics of R22 hydrates under brine environments, which was in good agreements with the experimental results. These results provide good information for separating ionic compounds from aqueous solutions by hydrate-based separation processes.

Introduction

Over the past several decades, demand for fresh water has continuously increased throughout the world as a result of sustained population growth and improved living standards [1–4]. At the same time, the availability of good quality water is central to sustainable development and further improvements in quality of life. Given the limited availability of fresh water resources, and unreliable water quality for industrial and human needs, desalination technologies involving processes to recover pure water from sea water, have attracted considerable attention [5–10]. Fundamentally, desalination technology removes salts from sea water to provide fresh water, and various approaches have been proposed over the last several decades to accomplish this, with a range of efficiencies, performance and cost. Gas hydrates are ice-like inclusion compounds comprised of a ‘host’ water-framework and small ‘guest’ molecules such as methane, ethane, carbon dioxide, etc. Hydrate structures are typically categorized based on differences in the size and shape of the hydrate cages. Huge amounts of gaseous molecules can be selectively stored in the hydrate cages [11–23]. For this reason, gas hydrates are currently considered one of the promising functional materials in the energy and environmental fields because of their possible applications for gas storage and transportation [24–27], carbon capture and sequestration [28–32], the selective separation of gas species [33–38], and desalination [39–41]. Among the various desalination approaches, hydrate-based desalination (HBD) technology is a promising method for recovering fresh water from sea water. The key mechanism of the HBD technology is a simple temperature- and pressure-dependent phase transition from liquid to solid. HBD technology is considered a novel method for reducing the energy costs of desalination, and increasing the level of freshwater recovery. In addition, HBD technology is also regarded as an environmental-friendly method because hydrates can be directly formed from seawater under low-temperature and high-pressure conditions [39–41]. However, achieving the appropriate high-pressure condition for gas hydrate formation is a major obstacle to improving hydrate formation efficiency, and accordingly, the development of an efficient way to form gas hydrates under more moderate conditions is one of the key objectives of current research

We report a facile route for the synthesis of hyperbranched polyamido-graphenes (HBP(A-G)) as non-metallic high capacity electrodes for charge storage in supercapacitors. HBP(A-G) were synthesized by Michael addition of polyamines, ethylene diamine (EDA), diethylene triamine (DETA), triethylene tetraamine (TETA), to acrylamide grafted graphene oxide, followed by reduction in situ. A 3D network of stiff graphene sheets connected by flexible polyamine chain was formed. Hyperbranching increased d-spacing and BET surface area of graphene stacks, which enhanced accessibility of sites for ion storage, and prevented restacking. HBP(A-G) electrodes displayed electric double layer capacitance behaviour with excellent specific capacitance. The charge storage capacity of the electrodes increased with an increase in the amine chain length. Specific capacitance of electrodes containing HBP(TETA-G) was found to be 269 F g-1 in a symmetric two electrode electrochemical cell, using 1 M H2SO4 electrolyte at a current density of 1 A g-1 for voltage range of 0- 1 V. An increase in the length of amine chains improved ion mobility, lowered equivalent distributed resistance and time constant of the electrodes. The time constant of HBP(TETA-G) capacitor was only 538 ms. Hydrophilic amine linkages on graphene backbone provided stability against electrode volume changes during charging and discharging and gave 89 % capacity retention over 10,000 cycles at 10 A g-1 current density for HBP(TETA-G) electrodes. HBP(A-G) electrodes demonstrated superior performance as electrodes for supercapacitors and has shown potential for use in other electrochemical applications. Graphical abstract Symmetric supercapacitor fabricated using hyperbranched poly(amidographene)s, synthesized via novel route by Michael addition of polyamines to acrylamide-grafted-graphene oxide followed by in situ reduction to graphene, gave high specific capacitance with good energy density.

Introduction

The recovery and storage of electrical energy is one of the most important challenges facing our society that is progressing in the direction of harnessing renewable energy, use of hybrid vehicles, etc. Batteries and electrochemical capacitors are most common energy storage technologies [1]. The cutting-edge battery technology is not adequate for powering these applications, mainly due to slow charge/discharge time, short life and high cost. Electrochemical capacitors, also known as supercapacitors (SC) or ultracapacitors, combine the benefits of both, batteries and capacitors. Supercapacitors have much higher energy capacity than conventional capacitors, with similar rapid charge/discharge characteristics. Electric double layer capacitors (EDLC) are one type of SC containing high surface area material on which the charges accumulate. The other type of capacitor, known as pseudocapacitor, consists of conducting materials or those that undergo redox transformations [2]. Since pseudocapacitive materials have several times higher capacity, hybrid capacitators combing capacitive carbon based electrode with conductive or redox active materials have been in focus recently [3–7]. Graphene composed of sp2 hybridized (2D) carbon atoms has driven great interest in the field due to unique properties such as high surface area, excellent thermal and mechanical stability, high conductivity, etc., which makes it an ideal material for EDLC [8,9]. One of the disadvantages of graphene is, its tendency to stack thereby decreasing the accessible surface area and the performance [10]. Studies on derivatives of graphene with conducting polymers such as polyethylenedioxythiophene [11,12], polyaniline [13,14], polypyrrole [15–17] are reported with the aim of decreasing the stacking tendencies.