Abstract

Introduction

Wastewater in area of focus

Nanotechnology in water purifcation

Nano‑adsorption

Microbial agent

Nanocomposites

Types of nanocomposites

Synthesis modes for nanocomposites

Graphene oxide‑based composites as a disinfectant

Zinc oxide nanocomposites as disinfectant

Copper oxide nanocomposites

Silver/silver oxide nanocomposites

Titanium oxide nanocomposites

Discussion

Conclusion

References

Abstract

     Water is crucial for the existence of life. The world, however, is facing a global water crisis. There are variety of microorganisms, gases and other toxins responsible for water contamination. Various types of nanomaterials exist that have enormous potential to treat contaminated water (water containing metal toxins or specific organic or inorganic impurities) due to their unique properties such as a high surface area and their ability to work effectively even at low concentrations. In recent years, scientists have been giving considerable attention to the application of nanocomposites for water purification, wastewater treatment, microorganism elimination, chemical contaminants, heavy metals removal and so forth. The incorporation of different nanofillers such as carbon nanotubes, graphene oxide, 2D materials, zinc oxide, titanium dioxide, copper and silver nanoparticles into polymeric materials has facilitated important advances, such as suppressing the accumulation of pollutants and foulants, improving the hydrophilicity, increasing the efficiency and improving the mechanical properties. This review discusses leading advances in the development of nanocomposites for antimicrobial and wastewater treatment with the aim of providing an improved understanding of nanocomposites and their applications in antimicrobial and wastewater treatment.

Introduction

     Water is a basic requirement for human life. However, we are far from meeting global requirements for clean water, and this issue will continue to grow over the time (Hillie and Hlophe 2007; Elwakeel et al. 2020b). The demand of clean drinking water is rising as a result of the deterioration of water quality, global climate change and population growth (Tchobanoglous et al. 1991; Elwakeel et al. 2020d). Emissions of organic dyes and heavy metal ions from the paper, leather and textile industries are a serious problem, as they are potentially mutagenic and carcinogenic. To meet environmental requirements, wastewater contaminated with these organic and inorganic species need to be treated before being discharged (Santhosh et al. 2016; Elwakeel et al. 2021). Heavy metals are widely used in various industries for many purposes, including mining and pigment production. Synthetic dyes are also an important type of pollutant, and their sources for water contamination include the textile, pulp and paper, tinting, printing, painting and tanning industries. The removal of dye from such wastewater is a challenging task, as pigments and synthetic dyes are biodegradation-resistant and remain in the environment for a long time. The destruction and handling of organic dyes is therefore an important issue, and a cost-efective method for removing dye substances from wastewater has been developed (Santhosh et al. 2016; Elwakeel et al. 2018).

Conclusion

     This paper explores the existing nanocomposites used to extract heavy metal ions and dyes from wastewater as efective adsorbents. This article addressed recent developments in nanomaterials as economical and environmentally sustainable water purifcation adsorbents. This review highlights fve commonly used nanomaterials/nanoparticles that are used in most existing nanocomposites. In this review, we concluded that TiO2-based nanocomposites have been used for photodegradation activity by most of the researchers in the literature. Silver-based nanocomposites are mostly used for antimicrobial activity. Silver and GO-based nanocomposites were used for the removal of green dye, anionic dye and Cu(II). Copper-based nanocomposites are mostly used for adsorption and photodegradation activity. Zinc oxide nanocomposites are used for adsorption, antimicrobial and photodegradation activity. Finally, we concluded that GO also greatly contributes to the improvement of other materials’ efciency. Further, much needs to be done to control the two-dimensional GO sheets for advanced technologies in the future. There are many challenges and obstacles associated with handling wastewater, and many precautions are required to prevent environmental and health problems. Therefore, new modern wastewater treatment equipment should be versatile, low-cost and commercially efective.

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

     Two dimensional nanomaterials, such as graphene and MXene, have been widely used to fabricate high performance nanocomposite films owing to their unique structure and excellent physiochemical properties, showing enormous potential applications in many areas. However, the existing voids and wrinkling in the nanocomposite films inevitably impedes realizing the high performance of the nanocomposite films during the assembly process of graphene and MXene nanosheets. Nacre provides an inspiration for fabricating high performance graphene and MXene nanocomposite films through constructing a high alignment structure and strong interface interactions. In this review, we summarize the preparation approaches of graphene and MXene nanocomposite films and discuss the mechanical properties. Then, several effective strategies for assembling graphene and MXene nanosheets have been concluded and discussed. Meanwhile, we also summarize and discuss the applications of graphene and MXene nanocomposite films including electromagnetic interference (EMI) shielding and thermal management. Finally, outlooks and challenges are proposed to promote their progress and applications in the future.

Introduction

     Since the first discovery of graphene in 2004, graphene has gradually aroused widespread attention [1]. Due to the outstanding mechanical, electrical and thermal properties, graphene has been applied in flexible electronic devices, aerospace and thermal management fields in the past decade [2], [3], [4], [5], [6]. For instance, the single-layer graphene has a Young’s modulus of 1.0 TPa [7] and a superhigh thermal conductivity of about 5300 W/mK [8] at room temperature, demonstrating enormous practical potentiality in the above mentioned fields. Before realizing these applications, it is crucial to assemble graphene nanosheets into high performance graphene nanocomposites including one dimensional (1D) fiber, two dimensional (2D) film and three dimensional (3D) bulk. Especially, high performance graphene nanocomposite films have gained enormous attention. However, it is difficult to achieve high performance nanocomposite films due to weak interaction between adjacent graphene nanosheets. Graphene oxide (GO) is a usual precursor for obtaining graphene with plentiful surface terminating groups, which can easily interact with various materials for preparing nanocomposite films [9,10]. Meanwhile, in recent years, MXene, a novel two dimensional (2D) materials, shows promising electrical and thermal properties, which shows promising application in aerospace field [11], [12], [13], [14], [15], [16]. Indeed, compared with graphene, the intrinsic mechanical and thermal conductivity properties and stabilities of MXene is relatively poor. Furthermore, the easily oxidizable characteristics and thermal vulnerability of MXene may restrict its practical applications. However, compared with graphene, MXene has plentiful surface functional groups, which is an ideal building block for fabricating nanocomposite films without chemical modification any more.

Summary and outlook

     In the past several years, two dimensional materials such as graphene and MXene have been widely studied owing to the excellent physiochemical properties. In this review, we have focused on the preparation methods, assembling strategies and mechanical properties of graphene and MXene nanocomposite films. Moreover, we have also discussed the applications of obtained graphene and MXene nanocomposite films such as EMI shielding and thermal conductivity. Various methods such as VAF, blade coating, drop casting and LbL have been used to prepare high performance graphene and MXene nanocomposite films. However, as aforementioned, the existing voids and wrinkling are harmful for the mechanical properties of graphene and MXene nanocomposite films. Hence, several strategies for fabricating high performance graphene and MXene nanocomposite films are proposed.

This article reports the effects of different dosages of silane coupling agent (KH-550) on the properties of geopolymer that have been cured for 360 days. The mineral phase formation and microstructure changes of geopolymer were analyzed combined with mechanical properties, XRD, FT-IR, SEM and 29Si NMR. The results show that adding an appropriate amount of silane coupling agent can improve the toughness of geopolymer, and the best performance is obtained when the silane coupling agent content is 0.1 wt%. The highest compressive strength and flexural strength of geopolymer samples containing 0.1 wt% silane coupling agent cured for 90 days reached 51.4 MPa and 12.93 MPa, respectively. The gel phase in the geopolymer is significantly enriched after adding silane coupling agent. Combined with 29Si NMR analysis, it can be seen that the doping of silane coupling agent promotes the polymerization reaction, and gradually develops towards low-aluminum bonded silica and Q4(0Al) structure. The decrease in Q4(0Al) structure of the geopolymer samples cured for 360 days indicates the weakening of the geopolymerization reaction and also explains the decrease in strength after long-term curing.

Introduction

Concrete is one of the most widely used building materials, traditionally produced by using ordinary portland cement (OPC) as major binder. However, the environmental problems caused by the emission of large amounts of carbon dioxide (CO2) during the production of cement have attracted more and more attention [[1], [2], [3], [4], [5]]. The production of 1 ton of cement is accompanied by the production of 0.6–1 ton of CO2, and it is accompanied by the production of other harmful gases [6,7]. This promotes the use of geopolymer, a new type of green cementitious material, and readily available raw materials such as metakaolin (MK), fly ash (FA) and ground blast furnace slag powder (GGBS) can be used for preparation. In addition, geopolymer can also reduce CO2 emissions by 26–45% without losing economic benefits [8,9]. The excellent properties of geopolymer gradually make it an alternative to OPC [10]. Recently, more researches have shown that the use of alkaline activators can activate cementitious materials, and can directly prepare geopolymer concrete without using OPC [[11], [12], [13]]. The zeolite-like gel (N-A-S-H) with a high degree of polymerization can be produced through the polymerization reaction of the silico-alumina material under alkaline conditions. The basic structure of geopolymer is a three-dimensional network structure with random distribution of [SiO4]4- and [AlO4]5- tetrahedron, and alkali metals distribute between network pores to balance the electric charge [14].

1- Introduction

2- Modeling of FG-CNTRC laminated cylindrical shells with NPR

3- Solution procedure

4- Numerical results and discussion

5- Concluding remarks

References

Abstract

This paper presents an investigation on the nonlinear flexural vibrations of carbon nanotube-reinforced composite (CNTRC) laminated cylindrical shells with negative Poisson’s ratios in thermal environments. The material properties of the CNTRCs are temperature-dependent and the functionally graded (FG) in a piece-wise pattern in the thickness direction of the shell. An extended Voigt (rule of mixture) model is employed to estimate the CNTRC material properties. The motion equations for the nonlinear flexural vibration of FG-CNTRC laminated cylindrical shells are based on the Reddy’s third order shear deformation theory and the von Kármán-type kinematic nonlinearity, and the effects of thermal environmental conditions are included. The nonlinear vibration solutions for the FG-CNTRC laminated cylindrical shells can be obtained by applying a singular perturbation technique along with a two-step perturbation approach. The effects of material property gradient, the temperature variation, shell geometric parameter, stacking sequence as well as the end conditions on the vibration characteristics of CNTRC laminated cylindrical shells are discussed in detail through a parametric study. The results show that negative Poisson’s ratio has a significant effect on the linear and nonlinear vibration characteristics of CNTRC laminated cylindrical shells.

Introduction

Composite laminated shell structures are widely used in structural applications owing to their specific higher strength-to-weight and stiffness-to-weight ratios, improved chemical and environmental resistance and the ability to tailor properties. These shell structures may be exposed to combined action of loading and various environmental conditions during their service life. This may lead to large amplitude vibration of the shells where the shell deflection may be in the order of the shell thickness. In this regard, the nonlinear vibration of composite laminated shells in thermal environments is an important consideration in engineering analysis and design. Many studies have been carried out on the nonlinear vibration behavior of composite laminated shells [1–6]. As pointed out by Shen [6], unlike in the cases of composite laminated plates, there are unresolved discrepancies between the vibration results obtained by different authors for composite laminated cylindrical shells, in particular for the cases of angle-ply laminated cylindrical shells. With growing interest in the development and manufacturing of high-performance and lightweight composite shells, auxetic composite materials and structures appear to be potential candidates. A consequence of material possessing a negative Poisson’s ratio (NPR) is that many of its mechanical properties are predicted to be enhanced by classical elasticity theory. The auxetic materials have a wide variety of multifunctional applications, for example, in energy storage, biomedical, acoustics, photonics, and thermal management [7]. There are two ways to construct auxetic structures. One way is to use auxetic metamaterial as sandwich core [8]. Another way is to change the stacking sequence and orientation of the laminates to obtain auxetic laminated shells. The production of larger values of negative Poisson’s ratio requires both a particular stacking sequence and the individual ply material being highly anisotropic [9].

1- Introduction

2- Modelling and deformation mechanism

3- Characterization of mechanical properties

4- Conclusions

References

Abstract

Artificial auxetic materials with negative Poisson’s ratio enable distinctive elastic response in the direction orthogonal to the loaded direction, i.e. shrinking when compressed and expanding when stretched, compared to conventional materials. Such distinctive mechanical characteristic makes auxetic materials unique in practice. Current studies in this aspect focus mainly on the realization of beam-dominated microstructures such as re-entrant and chiral lattices and of cellular microstructures with orthogonal elliptical hole pattern. In this study, a novel two-dimensional auxetic microstructure is designed by introducing peanut-shaped holes in solid bulk matrix. Compared to the microstructure with elliptical hole pattern, the present design can produce slightly larger negative Poisson’s ratio and achieve significantly lower stress level. The samples consisting of a number of centimeter-scale unit cells with the peanut-shaped holes are fabricated efficiently via additive manufacturing technique. Experiment and finite element simulation of tensile test are carried out on the specific sample to demonstrate the auxetic effect of the present design and simultaneously verify the computational model. Finally, effects of some parameters on Poisson’s ratio, which may control the auxetic behavior of the present microstructure, are discussed for better understanding deformation mechanism of the proposed auxetic material.

Introduction

The concept of metamaterials with specially designed artificial microstructure made by additive manufacturing technology has recently received more and more attention because of its unconventional physical properties that are previously inaccessible in conventional materials [1–4]. With these man-made metamaterials, engineering materials with various properties have been developed including negative Poisson’s ratio (auxetic properties) [5–11], zero/negative thermal expansion materials [12,13], cloaking materials [14,15], phononic materials [16–19], twistable materials [20,21], and materials with vibration absorption [22,23]. Among these examples, mechanical consistence between longitudinal and orthogonal transverse elastic deformations has been achieved in two-dimensional (2D) and three-dimensional (3D) cellular metamaterials with well-designed cellular topologies [24], i.e. re-entrant shape (Fig. 1a), chiral shape (Fig. 1b) and elliptical hole shape (Fig. 1c) [5–11]. In the static case, such mechanical consistence is conflicted to the fact that a conventional elastic solid cannot expand or shrink laterally when stretched or compressed longitudinally (Fig. 1d) [6,25,26]. It has been revealed that the auxetic behavior of a material can be regarded as a consequence of rotation of elastic cell when it is subjected to a compressive or tensile load [5]. Therefore, auxetic structures with negative Poisson’s ratio are beneficial to enhancing shear rigidity, indentation resistance, toughness, energy dissipation ability and acoustic absorption ability in various applications [27–31]. However, the current re-entrant and chiral metamaterials [9,10] with negative Poisson’s ratio are generally designed to have beamdominated microstructures with bending dominated topologies. As a result, they are known to have low macroscopic stiffness, high flexibility, and high porosity. More seriously, joints with sharp corners in the re-entrant and chiral auxetic structures could lead to high stress concentration [32]. As an alternative to the beam-dominated auxetic microstructures, the orthogonal elliptical hole pattern in solid material was revealed to be beneficial in achieving controllable auxetic response. However, the elliptical hole usually leads to high stress level too. In order to achieve the balance of stiffness and flexibility, and meanwhile possess smoothed boundary and controllable porosity, in this study, a new two-dimensional elastic cellular metamaterial with a negative Poisson’s ratio is designed, fabricated, and characterized.

1- Introduction

2- Deposition techniques for 3D printing of biomaterials

3- Materials for 3D printing of biomaterials

4- Applications of 3D printed biomaterials

5- 4D printing and its applications for biomaterials

6- Conclusions and future perspectives

References

Introduction

Three-dimensional printing (3D printing) or additive manufacturing (AM) promises to produce complex devices formulated from biomaterials and bioinspired materials from designs that are patient-specific. Since its advent as presurgical visualization technique and fabrication of tooling molds, 3D printing has evolved to yield bespoke devices, implants, scaffolds, diagnostic devices, and drug-delivery systems. As a result of recent public interest and affordable printing platforms, there is the desire to utilize this exciting technology for personalized health care. However, before AM can become a ubiquitous tool for the regeneration of complex tissues, such as bone, cartilage, muscles, vessels, nerves, and complex organs with multifaceted three-dimensional microarchitecture (e.g., kidneys, lymphoid organs), a number of technological limitations must be overcome. The development of advanced bioinks for 3D and 4D printing through the rational design of novel materials and their implementation as functional biomaterials through ever-expanding deposition techniques has improved the diversity and functionality of printed constructs outside of the traditional biofabrication window [1]. While there is the necessity for a compromise between suitability for purpose and biocompatibility, recent developments in materials science and bioink formulations have resulted in an improved range of solutions for biofabrication platforms. New biologically relevant printing formulations with highly consistent and accurate deposition parameters, attractive mechanical properties, high cytocompatibility, and the ability to modulate cellular functions are now being developed and offer prospects as biomaterials for use in a multitude of different applications; however, further work is needed before these novel materials become common place. In this chapter, we explore some of the approaches being pursued to achieve these targets in common 3D and 4D printing techniques, including an overview of the state-of-the-art technologies and formulations used in novel materials and bioinks, which are currently being developed, the techniques which are being utilized to produce 3D and 4D constructs, and the applications for which these new materials may be employed in. Key examples are highlighted to demonstrate the progress of this emerging technology and limitations to its development identified.

Keywords

1. Introduction

2. Graphene Oxide

3. Aerogels

4. Supercapacitor and Energy Storage

5. Supercapacitor applications of graphene and graphene oxide based aerogels

6. Conclusion

References

Abstract

Graphene and graphene-based materials have a high potential, especially in energy storage technology. Thanks to the three-dimensional (3D) structures developed with this material, their importance in the production and application of energy storage devices has increased. Studies on supercapacitor applications of graphene-based aerogels have begun to arouse interest in recent years. In this study, recent studies on aerogel supercapacitors, in which researchers have shown great interest, have been compiled and collected. In this study, production methods and properties of graphene oxide, properties and production of aerogels, production and applications of graphene/graphene oxide aerogels are discussed. In this way, the data is presented and discussed in an organized way for the researchers who study or who want to study in this field.

Introduction

Today’s rapidly depleted energy resources and the deteriorating ecological balance prioritized the need for energy storage systems. Moreover, the growing popularity of telecommunications equipment, backup storage devices, portable electronic devices, cardiac pacemakers and hybrid electric vehicles has aroused great interest towards energy storage devices. In this context, supercapacitors, which are mostly preferred among various energy storage devices, are electrochemical energy storage devices that cover the gap between batteries and dielectric capacitors with their high-power density, high specific energy and long life (>100,000 cycles) [1]. Furthermore, flexible solidstate supercapacitors are important for wearable electronic devices [[2], [3]].

Graphene, which come into prominence with wide specific surface area (SSA) (2630 m2 g−1 ), high electrical conductivity and chemical stability, as well as excellent mechanical, thermal and optical properties, has become popular especially for supercapacitors. However, a serious loss in surface area is observed due to the re-stacking of graphene layers during chemical reduction. The conversion of graphene nanotubes to graphene aerogel having a stable three-dimensional network solves this problem. The re-stacking problem resulting from π-π interactions between graphene layers and the Van der Waals forces are solved and the layers are chemically bonded together. Thus, the structure is intended to provide better performance in supercapacitors with much higher electronic conductivity, rapid charge transport between the layers and the resulting high surface area. The most interesting feature of GOs is that they are well protected by a hexagonal structure having functional groups such as hydroxyl, epoxide, carboxyl and some randomly distributed alkyl groups in the plane, together with a clear AB stacking order. Hydroxyl and epoxide functional groups are located close to each other in the basal planes, whereas carboxyl and alkyl groups are located at the edges of GO flakes. With longer oxidation times, hydroxyl groups are converted to more epoxide groups in the basal plane.

Plastic concrete is used in the manufacture of cut off wall and its mechanical properties is important for performance of dam. In this paper, in order to investigate the durability and mechanical properties of plastic concrete, uniaxial and triaxial compressive strength tests were performed on plastic concrete specimens in different ages (7, 14, 28, 56 and 90 days) and different percentage of replacement cement by nano silica (0, 1.5, 3, 4.5 and 6%) and compressive strength, the stress–strain behavior, elastic modulus, shear strength parameters of plastic concrete have been evaluated. According to the result, as the age of the specimen increases, elastic modulus, compressive strength and triaxial strength of the plastic concrete enhances. Furthermore, although by increasing the amount of nano silica the strength parameters of plastic concrete are improved and workability of concrete is reduced and the amount of elastic modulus of the specimen is almost constant. The results of shear strength parameters also show that the addition of up to 3% of nano silica increases the cohesion and internal friction angle decreases and with over 3% nano silica this trend is reversed and cohesion decreases and friction angle increases.

Introduction

The rheology and permeability of various concrete and advantage of nano material as a partial replacement for cement is well established in previous papers [1–11]. Besides, plastic concrete of cut-off wall is buried inside the soil in geotechnical project [12–14]. Two main attributes are necessary. Firstly, they should have enough strength to bear the weight of the dam body and secondly, a low elastic modulus that works seamlessly integrated with the surrounding environment soil [15–19]. If the elastic modulus is much higher than the surrounding soil of cut-off wall, soil and wall do not have load bearing capacity for unified action and cut-off wall will be cracked and its performance will be lost. The high elastic modulus of normal concrete is the reason for not using normal concrete in making the cut-off wall. As a result, plastic concrete satisfies both of the above conditions, and so is used to construct a cut-off wall. The water to cement ratio of plastic concretes is usually considered in the range of 1.5–4 to achieve the low elastic modulus; however, in normal concretes, this range varies between 0.35 and 0.65 [16,20–24]. In the previous researches [25,26], the compressive strength parameters of plastic concrete are investigated by performing uniaxial compressive strength. They showed that the compressive strength of concrete specimens depends on various parameters such as cement and bentonite content, aggregate size and specimen age.

1- Introduction

2- Experimental

3- Results and discussion

4- Conclusions

References

Abstract

To develop effective strategies for removing phenolic compounds, in-situ graphene oxide/manganese oxide (GO/MnOX, X = 2, 3/4) composites were fabricated via a sustainable method by synchronously utilizing manganese ions and acidic liquid waste during synthesis of GO. Comparatively, traditionally ex-situ GO/MnO2 composites were synthesized to verify the difference between in-situ and ex-situ synthesis. Based on the schematic and mass flow analysis, in-situ synthesis exhibited better atom economy and less waste emission than ex-situ synthesis. Then, the results of batch experiments exhibited that GO/MnOX composites possessed higher removal efficiency and wider pH range for p-cresol (p-CR) and p-tert-butylphenol (p-TBP) than GO/MnO2 composites. The maximum removal capacities of GO/MnOX composites were 107.68 mg/g for p-CR and 135.41 mg/g for p-TBP. And GO/MnOX composites could retain high removal efficiency for p-TBP (>90%) after five recycles. For in-situ GO/MnOX composites, GO sheets not only promoted the adsorption of phenolic compounds and by-products, but also enhanced the oxidation capacity of MnOX via an electron transfer interaction. Especially, the detection of ring cleavage products indicated further oxidation for p-TBP. Possessing an eco-friendly fabrication strategy and augmented adsorption-oxidation capability, in-situ GO/MnOX composites are expected to be applied in the removal of phenolic compounds.

Introduction

Phenolic compounds have given rise to emerging concerns regarding human health and ecosystems due to their widespread use in the pharmaceutical, petroleum and petrochemical, pesticide, plastic, and paper industries (Danquah et al., 2018). Consisting of a hydroxyl group bonded directly to a benzene ring, phenolic compounds possess a stable conjugated system, leading to biological accumulation and poor biodegradability (Ou et al., 2018). Thus, an urgent need exists to develop an efficient method for removing phenolic compounds (Villar da Gama et al., 2018; Zhong et al., 2018). Various methods, including chemical oxidation (Jiang et al., 2015), adsorption (Villar da Gama et al., 2018), and membrane separation (Zagklis and Paraskeva, 2015), have been reported to remove phenolic compounds. Among them, oxidation constitutes an effective and attractive method due to the potential to disrupt the structural stability of pollutants (Wang et al., 2015). Manganese oxides, ubiquitous in natural soil and synthetic materials, are traditional and cost-effective adsorbents and oxidants in wastewater treatment. Especially, manganese oxides are able to oxidize various aromatic Lewis bases, such as phenolic and aniline compounds (Grebel et al., 2016; Wang et al., 2018b). Previous studies demonstrated that phenolic compounds are susceptible to oxidation by manganese dioxide (MnO2) through sequential one electrontransfer reactions, forming a series of intermediate products (Abdullah et al., 2017; Remucal and Ginder-Vogel, 2014). However, the intermediate products, such as phenolic multimer and benzoquinones, would be released back into the aqueous solution.

1- Introduction

2- Experimental section

3- Results and discussion

4- Conclusions

References

Abstract

At present, infrared stealth materials for advanced detection and stealth technology is usually prepared with low emissivity coating on the surface, but there are very few efficient infrared stealth materials based on textiles with lightweight and flexible features. In this paper, we designed a carbon nanotube-doped aerogel (CNTAs) sandwich structure on polyimide (PI) fabric by hot pressing and then coated with a low emissivity Al-doped ZnO (ZAO) on the outer surface. The surface emissivity lower than 0.5 due to the existence of ZAO and the thermal conductivity of the intermediate interlayer aerogels as low as 0.013 W/(m·K). Additionally, through experiments, theoretical derivation and simulation analysis, we found the resultant composite demonstrated a high infrared stealth performance with super insulation effect, implying it will have a fine prospect in infrared stealth and thermal insulation protection fields with its unique structure and excellent properties.

Introduction

With the rapid development of infrared (IR) detection systems and the improvement of detection accuracy, the security and survival of military equipment and facilities have been seriously threatened [1-3]. Therefore, IR stealth provides a guarantee for the survival of soldiers and weapons, and plays an extremely important role in the battlefield [4, 5]. However, all objects above absolute zero will emit IR radiation [6], and IR detection just relies on the difference in IR radiation between the target and the background to detect the target [1]. Needless to say, soldiers and weapons often have higher temperatures than their environment, especially at night, as they will exhibit high brightness on an infrared thermal imaging in contrast with the background[6]. According to Stefan-Boltzmann’s law[7], there are two main methods to reduce the infrared radiation of the target: one is to reduce the emissivity of the target surface; the other is to control the temperature of the target surface. Therefore, take these two factors into account; the key to stealth technique is to prepare a functional composite with isolate heat structure inside combining with low surface emissivity outside. This functional composite can not only used in infrared stealth fields, but also in high-temperature environments such as steelmaking, ironmaking, and firefighting when based on textiles as it has a good heat isolation function with flexible and lightweight features[8]. This composite can also be used in the energy-saving fields like building upholstery [8, 9]. Therefore, the development of infrared stealth material based on textiles with excellent thermal insulation properties is great significance, while fire retardancy, resilience and flexibility are also demanded in practical use [8, 10].

1- INTRODUCTION

2- EXPERIMENTATION

3- EXPERIMENTAL RESULTS

4- FUZZY LOGIC

5- DISCUSSION

6- CONCLUSIONS

REFERENCES

Abstract

The use of nanofluid in lubrication during machining of advanced engineering ceramics has been found to be highly efficient and eco‐friendly. This work involves experimental investigation of grinding Alumina (Al2O3) ceramic to determine the effect of the grinding variables. The grinding variables considered include depth of cut, feed rate, type of diamond wheel, and lubrication type. Moreover, the response parameters considered include grinding power, coefficient of friction, and surface quality. The responses obtained during the experiments were used to develop a fuzzy logic prediction model. The findings from this work can be concluded as follows: (a) The depth of cut and feed rate have direct proportional relationship with the grinding power and coefficient of friction. (b) The metallic bonded diamond wheel was found to have higher machining efficiency than the resinoid bonded one. (c) Higher number of diamond grits produces lower frictional coefficient. (d) The carbon nanotube based nanofluid when used in the minimum quantity lubrication (MQL) process proffers better lubrication capability than conventional flood cooling system. (e) The developed fuzzy logic models were found to have high prediction accuracies of 97.22%, 98.60%, and 96.8%, respectively, for grinding power, grinding force ratio, and surface roughness.

INTRODUCTION

Advanced engineering ceramics such as alumina, zirconia, silicon nitride etc have gained high popularity in biomedical and aerospace applications, due to their excellent hardness, high wear and thermal resistances, biocompatibility, and aesthetics. Among the conventional machining techniques used to machine advanced ceramics, surface grinding using diamond wheels is still the most efficient method utilized when processing the brittle materials. Studies have shown that machining takes up a bunch of the cost of producing advanced ceramic components. Due to their excessive hardness, there are many setbacks encountered during the machining of these kind of materials. Studies have shown that the difficulty encountered during the machining results about a great limitation to their extensive usage in various engineering fields. In addition, there is high rate formation of residual deformations such as macro and micro‐cracks, during machining of the brittle materials. These unwanted deformations have been found to deteriorate the quality of the manufactured components. As such, there is need to improve on the machining of these materials, especially improving the efficiency and achieving defect‐free components at lower costs.

INTRODUCTION

EXPERIMENTAL

RESULTS AND DISCUSSION

KINETIC STUDIES

CONCLUSIONS

REFERENCES

Abstract

The present paper aims to compare the corrosion protection performance of electrodeposited Ni‒P with Ni–P–C nanocomposite coatings in 3.5 wt % NaCl solution in order to assess the influence of carbon nanoparticles on corrosion behavior of these coatings, by the potentiodynamic polarisation Tafel curves and electrochemical impedance spectroscopic (EIS) techniques. The effect of heat treatment on the coatings performance was also studied. The results revealed that heat treated Ni–P–C nanocomposite coating in air at 673 K significantly improved resistance to corrosion compared with Ni–P coatings. This behavior was related to incorporation of carbon nanoparticles into Ni–P matrix using in-situ electrochemical reduction of L-lysine, which shift the corrosion potential (Ecorr) positively, also the corrosion current density (Icorr) and the double layer capacitance (Cdl) values decrease, the charge transfer resistance (Rct) and efficiencies of inhibition (IE, %) increase, indicating improvement in the corrosion resistance in seawater environment. Microstructure, phase change and chemical composition of the prepared coatings were studied using scanning electron microscopy (SEM), X-ray diffraction (XRD) and elemental microanalysis (EDX), respectively.

INTRODUCTION

Electrodeposited composite coatings based on a Ni–P alloy matrix containing different fine particles of nonmetallic, ceramic or polymer compounds [1‒10] have attracted attention in many industrial fields due to their good mechanical, chemical and electrocatalytic properties including enhanced wear resistance combined with a good corrosion resistance and especially high electrocatalytic activity for hydrogen evolution reaction (HER) in chlor-alkali industries and water electrolysis [11–17], when compared to pure nickel coatings. Ni–P coating with phosphorus content over 9 wt % are considered amorphous and possesses excellent mechanical properties such as corrosion resistance [18, 19]. This protective film can be deposited by electroplating and electroless plating onto a metallic or nonmetallic substrate to prevent attack by hostile environments [20].