Showing papers in "Journal of Materials Science in 2018"

Zinc oxide nanoparticles: a review of their biological synthesis, antimicrobial activity, uptake, translocation and biotransformation in plants

Abstract: Over the past decade, incorporation of nanomaterials into agricultural practices like nanofertilizers and nanopesticides has gained a lot of attention. Progress and application of fertilizers in nanoforms are one of the effective options for considerable improvement of the agricultural yield worldwide. Zinc oxide nanoparticles (ZnO NPs) are considered as a biosafe material for biological species. Earlier studies have shown the potential of ZnO NPs in stimulation of seed germination and plant growth as well as disease suppression and plant protection by its antimicrobial activity. However, both positive and negative effects of ZnO NPs on plant growth and metabolism at various developmental periods have been documented. Uptake, translocation and accumulation of ZnO NPs by plants depend upon the features of NPs as well as the anatomy of the host plant. This review summarizes the applications of ZnO NPs as nanofertilizer in crop production and also attempts to examine and record the possible mechanism of antimicrobial activity of ZnO NPs. Biological synthesis of ZnO NPs and their uptake, translocation and biotransformation in plants via various routes have also been examined.

Understanding and mitigating hydrogen embrittlement of steels: a review of experimental, modelling and design progress from atomistic to continuum.

Abstract: Hydrogen embrittlement is a complex phenomenon, involving several length- and timescales, that affects a large class of metals. It can significantly reduce the ductility and load-bearing capacity and cause cracking and catastrophic brittle failures at stresses below the yield stress of susceptible materials. Despite a large research effort in attempting to understand the mechanisms of failure and in developing potential mitigating solutions, hydrogen embrittlement mechanisms are still not completely understood. There are controversial opinions in the literature regarding the underlying mechanisms and related experimental evidence supporting each of these theories. The aim of this paper is to provide a detailed review up to the current state of the art on the effect of hydrogen on the degradation of metals, with a particular focus on steels. Here, we describe the effect of hydrogen in steels from the atomistic to the continuum scale by reporting theoretical evidence supported by quantum calculation and modern experimental characterisation methods, macroscopic effects that influence the mechanical properties of steels and established damaging mechanisms for the embrittlement of steels. Furthermore, we give an insight into current approaches and new mitigation strategies used to design new steels resistant to hydrogen embrittlement.

A review of the synthesis and characterization of anion exchange membranes

Abstract: This review highlights advancements made in anion exchange membrane (AEM) head groups, polymer structures and membrane synthesis methods. Limitations of current analytical techniques for characterizing AEMs are also discussed. AEM research is primarily driven by the need to develop suitable AEMs for the high-pH and high-temperature environments in anion exchange membrane fuel cells and anion exchange membrane water electrolysis applications. AEM head groups can be broadly classified as nitrogen based (e.g. quaternary ammonium), nitrogen free (e.g. phosphonium) and metal cations (e.g. ruthenium). Metal cation head groups show great promise for AEM due to their high stability and high valency. Through “rational polymer architecture”, it is possible to synthesize AEMs with ion channels and improved chemical stability. Heterogeneous membranes using porous supports or inorganic nanoparticles show great promise due to the ability to tune membrane characteristics based on the ratio of polymer to porous support or nanoparticles. Future research should investigate consolidating advancements in AEM head groups with an optimized polymer structure in heterogeneous membranes to bring together the valuable characteristics gained from using head groups with improved chemical stability, with the benefits of a polymer structure with ion channels and improved membrane properties from using a porous support or nanoparticles.

Surface modification of hexagonal boron nitride nanomaterials: a review

Abstract: Hexagonal boron nitride (h-BN) nanomaterials, such as boron nitride nanotubes, boron nitride nanofibers, and boron nitride nanosheets, are among the most promising inorganic nanomaterials in recent years. Their unique properties, including high mechanical stiffness, wide band gap, excellent thermal conductivity, and thermal stability, suggest many potential applications in various engineering fields. In particular, h-BN nanomaterials have been widely used as functional fillers to fabricate high-performance polymer nanocomposites. Like other nanomaterials, prior to their utilization in nanocomposites, surface modification of h-BNs is often necessary in order to prevent their strong tendency to aggregate, and to improve their dispersion and interfacial properties in polymer nanocomposites. However, the high chemical inertness and resistance to oxidation of h-BNs make it rather difficult to functionalize h-BNs. The methods frequently used to oxidize graphitic carbon nanomaterials are not quite successful on h-BNs. Therefore, many novel approaches have been studied to modify h-BN nanostructures. In this review, different surface modification strategies were discussed including various covalent and non-covalent surface modification strategies through wet or dry chemical routes. Meanwhile, the effects of these surface modification methods on the resulting material structures and properties were also reviewed. At last, a number of theoretical studies on the reactivity of h-BNs with different chemical agents have been conducted to explore new surface modification routes, which were also addressed in this review.

Oxide-based RRAM materials for neuromorphic computing

Abstract: In this review, a comprehensive survey of different oxide-based resistive random-access memories (RRAMs) for neuromorphic computing is provided. We begin with the history of RRAM development, physical mechanism of conduction, fundamental of neuromorphic computing, followed by a review of a variety of RRAM oxide materials (PCMO, HfOx, TaOx, TiOx, NiOx, etc.) with a focus on their application for neuromorphic computing. Our goal is to give a broad review of oxide-based RRAM materials that can be adapted to neuromorphic computing and to help further ongoing research in the field.

Facile synthesis of cuboid Ni-MOF for high-performance supercapacitors

Abstract: Metal–organic frameworks (MOF) used directly in supercapacitors have attracted much attention for their special porous structure and potential high performance. Here, the Ni-MOF is fabricated by one-step facile hydrothermal method with a modification of mixed solution with DMF and water instead of pure DMF. After characterization, the Ni-MOF exhibits loosely stacked layer-cuboid structure with abundant mesoporous, which is beneficial for the charge transfer and ion transport for supercapacitors. In the three-electrode system, this Ni-MOF serving as working electrode shows remarkable specific capacitance of 804 Fg−1 at 1 Ag−1, excellent rate capacitance of 534 Fg−1 at 10 Ag−1, and with 302 Fg−1 retention after 5000 cycles, when measured in 2 M KOH electrolyte solution. To make a further research into the practical utility of the Ni-MOF, the Ni-MOF//AC asymmetrical supercapacitor device is assembled with the Ni-MOF and active carbon acted as positive and negative electrode materials, respectively. This device exhibits high specific energy of 31.5 Wh kg−1, at specific power of 800 W kg−1. All these results demonstrate that this Ni-MOF is a kind of promising electrode material for high-performance supercapacitors.

Superior strength and ductility of 316L stainless steel with heterogeneous lamella structure

Abstract: Strength and ductility are two of the most important mechanical properties for a metal, but often trade off with each other. Here, we report a 316L stainless steel with superior combinations of strength and ductility that can be controlled by fine-tuning its heterogeneous lamella structure (HLS). The HLS was produced by 85% cold rolling, which produced lamellar coarse grains sandwiched between mixtures of nano-grains and nano-twins. The HLS was fine-tuned by annealing at 750 °C for 5–25 min, which resulted in varying volume fractions of nano-grains, nano-twins, lamellar coarse grains, and recrystallized grains. During tensile testing, large amount of geometrically necessary dislocations were generated near the heterostructure interfaces to coordinate the deformation between soft domains and hard domains, which results in high back stress to achieve superior combination of strength and ductility. An optimal high yield strength of ~ 1 GPa with an elongation-to-failure of ~ 20% was obtained for an optimized HLS sample. Furthermore, the processing technique employed here is conducive to large-scale industrial production at low cost.

Review of recent achievements in self-healing conductive materials and their applications

Abstract: Self-healing materials have attracted increasing attention because of their wide range of applications. It can be expected to offer obvious advantages in conductive materials with self-healing properties, which are regarded as promising candidates for the fabrication of self-healing electronics, energy storage devices, sensors, anticorrosive coating and conductive adhesives. In this review, we focused on recent efforts to develop self-healing conductive composites including their preparation methods, properties and applications. The self-healing conductive materials were presented based on different conductive mediums, such as metal, carbon, conductive polymer, ionic liquids. In addition, their novel applications of the self-healing conductive materials in conductive coatings, energy storage devices and sensors are highlighted. Finally, the future challenges of conductive materials with self-healing properties are proposed.

Microstructures and mechanical properties of aligned electrospun carbon nanofibers from binary composites of polyacrylonitrile and polyamic acid

Abstract: High mechanical performance carbon nanofibers are highly required for the carbon nanofiber-reinforced composites, and it is necessary to develop novel precursors for the preparation of carbon nanofibers. In this work, blends of poly(acrylonitrile-butyl acrylate mono-butyl itaconate) (co-PAN) and polyamic acid (PAA) were electrospun into aligned nanofibers and the nanofibers were converted to carbon nanofibers by thermal imidization, pre-oxidation and high-temperature carbonization. FT-IR spectroscopy was applied to monitor the chemical structures of the nanofibers before and after pre-oxidation. Tensile tests were used to characterize the mechanical properties of electrospun carbon nanofibers (ECNFs). The microstructures of ECNFs were investigated by high-resolution TEM and Raman spectroscopy. The results indicated that the ECNFs derived from blend of co-PAN/PAA with molar ratio of 6/4 and with carbonization temperature of 1400 °C possessed the highest tensile strength of 1212 MPa, which could be attributed to the ordered graphitic structures in ECNFs.

3D printing of hydroxyapatite scaffolds with good mechanical and biocompatible properties by digital light processing

Abstract: Hydroxyapatite is a scaffold material widely used in clinical repair of bone defects, but it is difficult for traditional methods to make customized artificial bone implants with complicated shapes. 3D printing biomaterials used as personalized tissue substitutes have the ability to promote and enhance regeneration in areas of defected tissue. The present study aimed at demonstrating the capacity of one 3D printing technique, digital light processing (DLP), to produce HA scaffold. Using HA powder and photopolymer as raw materials, a mixture of HA mass ratio of 30 wt% was prepared by viscosity test. It was used for forming ceramic sample by DLP technology. According to differential scanning calorimetry and thermal gravity analysis, it was revealed that the main temperature range for the decomposition of photopolymer was from 300 to 500 °C. Thus, the two-step sintering process parameters were determined, including sintering temperature range and heating rate. XRD analysis showed that the phase of HA did not change after sintering. SEM results showed that the grain of the sintered ceramic was compact. The compression model was designed by finite element analysis. The mechanical test results showed that the sample had good compression performance. The biological properties of the scaffold were determined by cell culture in vitro. According to the proliferation of cells, it was concluded that the HA scaffold was biocompatible and suitable for cell growth and proliferation. The experimental results show that the DLP technology can be used to form the ceramic scaffold, and the photopolymer in the as-printed sample can be removed by proper high-temperature sintering. The ceramic parts with good compression performance and biocompatibility could be obtained.

Novel nanohybrid biocatalyst: application in the kinetic resolution of secondary alcohols

Abstract: In this work, a nanohybrid material was developed and used for the first time to the kinetic resolution of secondary alcohols as rac-indanol, rac-1-phenylethanol (rac-1), rac-1-(3-bromophenyl)-1-ethanol (rac-2) and rac-1-(3-methylphenyl)-1-ethanol (rac-3). Chiral indanol is used as a precursor intermediate for the synthesis of enantiomeric drugs, such as (+)-Indatraline, Irindalone, Indinavir, (+)-Sertraline and Rasagiline mesylate. Chiral 1-phenylethanol is used as an ophthalmic preservative, a solvatochromic dye and an inhibitor of cholesterol absorption and as a mild floral fragrance. For this purpose, the ultrasound irradiation was used to couple APTES on the superparamagnetic nanoparticles surface. Then, the system was activated with glutaraldehyde and used as a support for immobilization of lipase from Pseudomonas fluorescens. Thermal stability analysis was performed in buffer and hexane, showing an excellent stability in buffer solution at 60 °C, holding 72% of the initial activity, even after 7 h. In hexane (40 °C), the immobilized enzyme retained 100% of activity with 693 min of half-life time at 50 °C. The high thermal stability is mainly related to the covalent bonding between enzymes and support. Immobilized lipase on magnetic support proved to be a robust biocatalyst in the kinetic resolution, leading to (S)-indanol with high selectivity (e.e. > 99%, E > 200) in 1.75 h at 50 °C, being reused five times without significant loss of the activity and selectivity. The kinetic resolution of rac-1, via acetylation reaction, catalyzed by lipase from Pseudomonas fluorescens immobilized on magnetic support, led to (R)-acetate with enantiomeric excess > 99% and to the remaining (S)-alcohol with enantiomeric excess of 94%, conversion of 49% and E > 200, after 48 h of reaction at 40 °C. Under the same reactions conditions, rac-2 and rac-3 were slightly less reactive, since the corresponding (R)-acetates were obtained with conversion values of 44%, but with high enantioselectivity (enantiomeric excesses > 99% and E values > 200). These results correspond to an important step in heterogeneous catalysis due to the ability to obtain important precursors for the synthesis of enantiomerically pure chiral drugs and other bioactive substances.

Strong re-entrant cellular structures with negative Poisson’s ratio

Abstract: In this paper, two new 2D re-entrant topologies with negative Poisson’s ratio are presented and their mechanical properties (Poisson’s ratio and energy absorption capacity) are studied using finite element method as a function of geometric parameters. The first topology (model 1) was constructed by adding two sinusoidal-shaped ribs into the classical re-entrant topology, while the second topology (model 2) was made by introducing extra vertical ribs to reinforce the sinusoidal-shaped ribs. Simulation results show that model 1 and model 2 topologies can reach a minimum value in Poisson’s ratio of − 1.12 and − 0.58 with an appropriate geometric aspect ratio, respectively. The energy absorption capacities of model 1, model 2 and classical re-entrant model were studied at various compression velocities. Enhanced energy absorption capacities were observed in the two new re-entrant topologies compared with the classical re-entrant topology. Model 2 exhibited the highest energy absorption capacity and a highest plateau stress. The plateau stress of model 1 was about half that of model 2, and when the compression velocity is more than 20 m/s, the plateau stress of model 1 became lower than that of the classical re-entrant model.

Stabilizers for nitrate ester-based energetic materials and their mechanism of action: a state-of-the-art review

Abstract: Aliphatic nitrate esters are currently the most widely used energetic ingredients in single-, double-, and triple-base propellants. These nitrate esters are unstable at ambient conditions, and stabilizing agents should be incorporated into the energetic compositions to inhibit and slow down the decomposition reactions that can occur. However, the currently used stabilizers present a number of environmental and human health issues. To overcome these shortcomings, many stabilizers have been appeared in the past few decades and continue to be developed. Furthermore, several analytical techniques have been introduced to monitor the stability of nitrate ester-based energetic materials as well, since the existing ones could not be efficiently applied. Therefore, this review paper discusses and summarizes the current and emergent stabilizers as well as their mechanisms of action. A critical and analytical examination of their advantages and drawbacks is made.

Adsorption and removal of organophosphorus pesticides from environmental water and soil samples by using magnetic multi-walled carbon nanotubes @ organic framework ZIF-8

Abstract: In this study, the functional adsorbent metal–organic framework ZIF-8/magnetic multi-walled carbon nanotubes (M-M-ZIF-8) was successfully prepared for removal of eight organophosphorus pesticides from environmental water and soil samples. The M-M-ZIF-8 was characterized and their adsorption capacity was evaluated based on their isothermal adsorption curves. The results suggest that ZIF-8 particles are deposited on the surface of the magnetic MWCNTs via coordination–polymerization strategy. In addition, M-M-ZIF-8 has high static adsorption capacities for organophosphorus pesticides because of its high specific surface area and porous structure. The static adsorption data fit the Freundlich adsorption model better than the Langmuir model. Under the optimized conditions, M-M-ZIF-8 was successfully applied to remove the eight organophosphorus pesticides from environmental water and soil samples. A possible mechanism is valence-electron-driven adsorption by sharing or exchanging of electrons between the organophosphorus pesticide molecules and the vacant active sites of M-M-ZIF-8. Therefore, M-M-ZIF-8 is a promising hybrid adsorbent for adsorption and removal of organic pollutions from the environment.

A general perspective of Fe–Mn–Al–C steels

Abstract: During the last years, the scientific and industrial community has focused on the astonishing properties of Fe–Mn–Al–C steels. These high advanced steels allow high-density reductions about ~ 18% lighter than conventional steels, high corrosion resistance, high strength (ultimate tensile strength ~ 1 Gpa), and at the same time ductility above 60%. The increase in the tensile or yield strength and the ductility at the same time is almost a special feature of this kind of new steels, which makes them so interesting for many applications such as in the automotive, armor, and mining industry. The control of these properties depends on a complex relationship between the chemical composition of the steel, the test temperature, the external loads, and the processing parameters of the steel. This review has been conceived to elucidate these complex relations and gather the most important aspects of Fe–Mn–Al–C steels developed so far.

Effects of octadecylamine functionalization of carbon nanotubes on dispersion, polarity, and mechanical properties of CNT/HDPE nanocomposites

Abstract: Homogeneous dispersion of carbon nanotubes (CNTs) in polymers has significantly improved their processing and application as nanomaterials. Generally, CNTs tend to agglomerate due to their high aspect ratios and strong van der Waals interaction. Surface functionalization appears to be a solution to this problem. This study presents a controlled dispersion of carbon nanotubes in polyethylene through surface modification using a mixture of concentrated acid and octadecylamine (ODA). CNTs were characterized by Fourier transform infrared, Raman and X-ray photoelectron spectroscopy, and transmission electron microscopy. The results confirmed that carboxyl and alkane groups were successfully introduced on CNT surfaces. The acid- and amine-functionalized carbon nanotubes were dispersed in four solvents with different polarities (water, ethanol, acetone, and xylene) to correlate the degree of dispersion of CNT with their polarity. The results showed that CNT dispersion stability strongly depends on solvent and carbon nanotube polarities after the functionalization step. The nanohardness and tensile tests showed that the addition of CNTs, especially the functionalized with ODA, leaded the polymer harder, increasing its Young’s modulus and tensile strength. However, its toughness and deformation capacity were reduced. The potential applications of CNT-based polymer nanocomposites broaden considerably due to the surface engineering of carbon nanotubes.

Factors affecting the hygroexpansion of paper

Abstract: Paper is a widely used packaging material and is nowadays regaining importance, e.g., as bio-based and biodegradable material. Moreover, new technologies such as polymer–fiber composites, printed electronics and the deep drawing of paper are developing. The process stability and also the resulting quality of paper converting processes such as coating, metallization, printing, and the printing of electronics are highly affected by the hygroexpansion of paper. In order to reduce production instability and to choose and develop paper substrates with ideal characteristics, critical parameters need to be known. This paper offers an extensive overview of those parameters, starting at a molecular and microscopic level with the effect of the constituents and morphology of single fibers, before moving on to paper contents, chemical modifications and additives and finally concluding with paper production and fiber network modification. It was found that the major influences are single fiber sorption, inter-fiber contacts, microfibril angle, fiber morphology (length, width, curliness) and fiber orientation. This review gives new ideas and insights for technologists working in research, development and production optimization of paper-based products.

Evolution of glassy carbon under heat treatment: correlation structure–mechanical properties

Abstract: In order to accommodate an increasing demand for glassy carbon products with tailored characteristics, one has to understand the origin of their structure-related properties. In this work, through the use of high-resolution transmission electron microscopy, Raman spectroscopy, and electron energy loss spectroscopy it has been demonstrated that the structure of glassy carbon at different stages of the carbonization process resembles the curvature observed in fragments of nanotubes, fullerenes, or nanoonions. The measured nanoindentation hardness and reduced Young’s modulus change as a function of the pyrolysis temperature from the range of 600–2500 °C and reach maximum values for carbon pyrolyzed at around 1000 °C. Essentially, the highest values of the mechanical parameters for glassy carbon manufactured at that temperature can be related to the greatest amount of non-planar sp 2 -hybridized carbon atoms involved in the formation of curved graphene-like layers. Such complex labyrinth-like structure with sp 2 -type bonding would be rigid and hard to break that explains the glassy carbon high strength and hardness.

Manufacturing and 3D printing of continuous carbon fiber prepreg filament

Abstract: The current research proposes a novel method for printing continuous carbon fiber composite parts. At first, continuous carbon fiber prepreg filament for Fused Deposition Modeling 3D printing was manufactured, followed by modification of extruder head of 3D printers to print the filament. Thereafter, three-point flexural test and Response Surface Methodology were adopted to study the mechanical properties of the composite parts printed with the filament. After testing, a mathematical model was developed to describe and analyze the relationship between the printing parameters (printing temperature, printing speed, and layer thickness) and the flexural strength of printed composite parts. We discovered that the flexural strength and flexural modulus of printed composites significantly improved with the proposed method with specified printing parameters, and while of all the parameters, the layer thickness had the greatest contribution towards the final flexural strength. The results indicate that the discussed method could be a promising approach to print CCF composites.

A review of non-destructive techniques used for mechanical damage assessment in polymer composites

Abstract: Polymer composite materials are being increasingly used in primary load-bearing structures in several advanced industrial fields such as aerospace vessels, railway wagons and mega-scaled wind turbines where detection of subcritical damage initiation can significantly reduce safety issues and maintenance costs. It is therefore crucial to inspect these composite structures in order to assess their structural health and to ensure their integrity. Non-destructive testing techniques (NDT) are used for this purpose, making it possible to monitor mechanical damage of composite materials under in situ or ex situ service conditions. This paper reviews the capabilities of the most common NDT techniques used to inspect the integrity of composite materials. Each technique has a detection potential and cannot allow a full diagnosis of the mechanical damage state of the material. Thus, depending on the occurring damage mechanism and the conditions of use, one technique will be preferred over another, or several techniques should be combined to improve the diagnosis of the damage state of the structures.

Synthesis and sintering of (Mg, Co, Ni, Cu, Zn)O entropy-stabilized oxides obtained by wet chemical methods

Abstract: Entropy-stabilized oxides represent a novel family of advanced ceramic materials with attractive functional properties. In this work, entropy-stabilized oxides, in the system (Mg, Co, Ni, Cu, Zn)O, were produced by co-precipitation and hydrothermal synthesis. Although TG/DTA and XRD analyses of as-synthetized powders point out complex thermal evolution, in both cases the desired single-phase rock salt solid solution was obtained after a proper thermal treatment. The dilatometric analysis points out the excellent sinterability of the obtained powders, which were successfully consolidated for the first time reaching nearly full density (~ 97%) at relatively low temperature (1050 °C).

Review: nanoparticles and nanostructured materials in papermaking

Abstract: The introduction of nanoparticles (NPs) and nanostructured materials (NSMs) in papermaking originally emerged from the perspective of improving processing operations and reducing material consumption. However, a very broad range of nanomaterials (NMs) can be incorporated into the paper structure and allows creating paper products with novel properties. This review is of interdisciplinary nature, addressing the emerging area of nanotechnology in papermaking focusing on resources, chemical synthesis and processing, colloidal properties, and deposition methods. An overview of different NMs used in papermaking together with their intrinsic properties and a link to possible applications is presented from a chemical point of view. After a brief introduction on NMs classification and papermaking, their role as additives or pigments in the paper structure is described. The different compositions and morphologies of NMs and NSMs are included, based on wood components, inorganic, organic, carbon-based, and composite NPs. In a first approach, nanopaper substrates are made from fibrillary NPs, including cellulose-based or carbon-based NMs. In a second approach, the NPs can be added to a regular wood pulp as nanofillers or used in coating compositions as nanopigments. The most important processing steps for NMs in papermaking are illustrated including the internal filling of fiber lumen, LbL deposition or fiber wall modification, with important advances in the field on the in situ deposition of NPs on the paper fibers. Usually, the manufacture of products with advanced functionality is associated with complex processes and hazardous materials. A key to success is in understanding how the NMs, cellulose matrix, functional additives, and processes all interact to provide the intended paper functionality while reducing materials waste and keeping the processes simple and energy efficient.

Mesoporous titanium dioxide@ zinc oxide–graphene oxide nanocarriers for colon-specific drug delivery

Abstract: In this project, TiO2@ZnO nanoparticles core–shell nanostructured and titanium dioxide@ mesoporous zinc oxide–graphene oxide (TiO2@ZnO–GO) hybrid nanocomposites as controlled targeted drug delivery systems were synthesized by a facile sono-chemical method. We prepared a novel mesoporous and core–shell structure as a drug nanocarrier (NCs) for the loading and pH-responsive characteristics of the chemotherapeutic curcumin. The structure, surface charge, and surface morphology of NCs were studied using with X-ray diffraction, Fourier transform infrared spectroscopy, dynamic light scattering, brunauer–emmett–teller, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The SEM and TEM images of NCs show the uniform hexagonal mesoporous morphology with average grain size of about ∼ 190 nm. The drug loading was very high about 16 and 19 for TiO2@ZnO and TiO2@ZnO–GO, respectively. The NCs showed pH-dependent drug release behavior. Drug release from TiO2@ZnO–GO in neutral pH were higher than in acidic medium, due to anionic charge of GO nanosheet. MTT assay results showed that the curcumin-loaded NCs showed significant toxicity due to which cell viability reduced to below 50% at 140 μg/mL concentration, thereby confirming its anticancer effects. The goal of this study is the application of water-dispersed TiO2@ZnO–GO with pH-dependent release properties for design a new drug delivery carrier.

Enhancing the reactivity of aluminosilicate materials toward geopolymer synthesis

Abstract: Geopolymers are alternative materials to portland cement, obtained by alkaline activation of aluminosilicates. They exhibit excellent properties and a wide range of potential applications in the field of civil engineering. Several natural aluminosilicates and industrial by-products can be used for geopolymer synthesis, but a lot of starting materials have the disadvantage of poor reactivity and low strength development. This paper presents a comprehensive review of the main methods used to alter the reactivity of aluminosilicate materials for geopolymer synthesis, as reported recently in the literature. The methods consist of mechanical, thermal, physical separation and chemical activation, of which mechanical activation is the most commonly employed technique. The reactivity of the activated aluminosilicate materials is mainly related to the activation method and the treatment parameters. Chemical activation by alkaline fusion is a promising method allowing preparation of one-part geopolymer materials, an alternative class of geopolymeric binders. However, the resulting alkaline-fused geopolymer products are vulnerable to attack by excessive alkalis.

Grain growth during spark plasma and flash sintering of ceramic nanoparticles: a review

Abstract: Spark plasma and flash sintering process characteristics together with their corresponding sintering and densification mechanisms and field effects were briefly reviewed. The enhanced and inhibited grain growth obtained using these field-assisted densification techniques were reported for different ceramic nanoparticle systems and related to their respective densification mechanisms. When the densification is aided by plastic deformation, the kinetics of grain growth depends on the particles’ rotation/sliding rate and is controlled by lattice and pipe diffusion. When the densification is aided by spark, plasma, and the particles’ surface softening, grain growth kinetics is controlled by viscous diffusion and interface reactions. Grain growth in both cases is hierarchical by grain rotation, grain cluster formation and sliding, as long as the plastic deformation proceeds or as long as plasma exists. Densification by diffusion in a solid state via defects leads to normal grain growth, which takes over at the final stage of sintering. Various field effects, as well as the effect of external pressure on the grain growth behaviour were also addressed.

Thermally reduced graphene oxide: synthesis, studies and characterization

Abstract: The main purpose of this study is to synthesize reduced graphene oxide (rGO) using graphite (GR) as a starting material. This paper explains didactic step-by-step of the synthesis, the role of each reagent, showing pictures of the entire process and including a well-explained characterization study. The rGO was prepared using modified Hummer’s method, followed by thermal reduction. The materials were characterized from the starting material (GR), through the intermediate material (GO) and finally the material of interest (rGO). Various techniques and procedures were used to characterize the materials such as X-ray diffraction, infrared and Raman spectroscopy, scanning electron microscopy, electrochemical characterization and dispersion analysis. Morphological and structural characterization of the obtained materials suggests that the synthesis and reduction to obtain rGO were effective. The obtained materials were electrochemically evaluated using ferri/ferrocyanide redox probe. The association of chemical oxidation of GR with KMnO4 in the presence of H2SO4 with further thermal reduction makes possible to produce rGO in large scale and with quality as noticed by outstanding electrochemical behavior toward the redox couple [Fe(CN)6]3−/[Fe(CN)6]4− probe.

Synthesis of novel PVA–starch formulation-supported Cu–Zn nanoparticle carrying carbon nanofibers as a nanofertilizer: controlled release of micronutrients

Abstract: Recent applications of nanotechnology in agriculture have successfully demonstrated the utility of nanomaterials as a potential plant-growth regulator. Practical application of nanomaterial-based fertilizers in agricultural lands requires a suitable substrate to effectively disperse the nanomaterials. In this study, a polymeric formulation of PVA–starch was synthesized as a substrate for the slow release of the Cu–Zn micronutrient carrying carbon nanofibers (CNFs). The Cu–Zn/CNFs were in situ dispersed in the PVA–starch blend during a polymerization step. The effectiveness of the prepared nanofertilizer was demonstrated using chickpea as a model plant and different doses, viz. 0.25, 0.50, 1.0, 2.0 and 4.0 g of PBMC per kg of soil (garden) up to 30 days. The dissolution of PBMC increased with increasing amounts of starch in the PBMC matrix, indicating the biodegradability of PVA in the blend. Scanning electron microscopy and elemental analysis confirmed the translocation of the Cu–Zn/CNFs from roots to shoots of the plant. The PBMC(1-1)-grown plants were measured to be the tallest (~ 33 cm), whereas the control plants reached a length of ~ 18 cm only, indicating the effectiveness of the prepared micronutrient in sustaining the plant growth. The superoxide anion radicals and hydrogen peroxide in the control plants were measured to be 207 ± 3.15 and 272 ± 5.74 nmol/g of the plant, whereas PBMC(1-1)-grown plants contained 129 ± 3.25 and 194 ± 6.47 nmol/g of the reactive oxygen species, respectively, indicating that the Zn nanoparticles were effective in scavenging the reactive species. The metal release profiles of PBMC indicated the Cu and Zn concentrations to be 5.3 ± 0.05 and 2.8 ± 0.1 mg/g-CNF, respectively, which were significantly lower from Cu–Zn/CNF, attributed to the slow release of the metals from the prepared polymeric formulation. The proposed integration of the biodegradable polymeric formulation with the micronutrient carrying CNFs opens a new perspective on the application of nanotechnology in agricultural practices.

Pore characterization of 3D-printed gypsum rocks: a comprehensive approach

Abstract: With advancements in additive manufacturing, now 3D-printed core plugs can be duplicated in order to replace natural rock samples. This can help us to control their parameters to be used in different types of experiments for model verifications. However, prior to such substitutions, we should ensure they can represent natural rock samples through characterizing their physical properties. In this paper, synthetic samples made up of gypsum powder are 3D-printed and then characterized for essential pores properties. The analysis included structures of the pores, quantitative porosity evaluation, pore size distribution, pore surface area, pore shape distribution, and corresponding anisotropy. Mercury injection porosimetry (MIP) and helium porosimetry (HP) combined with X-ray micro-computed tomography were performed to provide us with detailed information about the pores. Porosity was measured 32.66% from micro-CT based on watershed thresholding, which was found comparable with MIP and HP results, 27.90 and 28.86%, respectively. Most of the pores lay in the range from 4 to 10 μm in diameter with relative frequency of 92.04%. The pore shape distribution indicates that 3D-printed gypsum rocks host more spherical pores and fewer blade-shaped pores. In addition, pore anisotropy of the sample that was analyzed by collecting pore orientation in orthogonal axes represented the vertical transverse isotropy.

Ultrafast room-temperature synthesis of hierarchically porous metal–organic frameworks by a versatile cooperative template strategy

Abstract: Hierarchically porous MOFs (HP-MOFs) are commonly prepared by means of hydrothermal synthesis. Nonetheless, its relatively long crystallization time and harsh synthesis conditions have strongly obstructed the enhancement of HP-MOFs space–time yields (STYs) and the decrease in energy consumption. Herein, a simple and versatile method for preparing various HP-MOFs at room temperature was demonstrated, which had introduced surfactant as the template, whereas zinc oxide (ZnO) has been used as an accelerant. The resulting HP-MOFs showed multimodal hierarchical porous structures and excellent thermal stability. More importantly, the synthesis time was reduced dramatically to 11 min, with a maximal HP-MOFs STY of as high as 2575 kg m−3 d−1. Furthermore, the rapid formation process of HP-MOFs was examined through quantum chemistry calculation, and a feasible synthesis mechanism was also proposed. Notably, our synthesis strategy had shown a versatility, since other surfactants could also be used as the templates for the rapid room-temperature fabrication of diverse stable HP-MOFs. Importantly, the porosity of the HP-MOFs could be readily tuned through controlling the type of template. Moreover, gas adsorption measurement of HP-MOFs revealed high CH4 uptake capacity at 298 K due to the increase in surface area and pore volume. Our findings suggest that such method is applicable for the rapid synthesis of a wide variety of HP-MOFs on an industrial scale.

Adsorption behaviors of cationic and anionic dyes from aqueous solution on nanocomposite polypyrrole/SBA-15

Abstract: The present research focuses on the synthesis and the modification of mesoporous silica SBA-15 using in situ polymerization of pyrrole The structural/textural and morphological features of adsorbents were investigated through X-ray diffraction, nitrogen sorption at 77 K, thermogravimetric analysis, Fourier transform infrared spectroscopy, zeta potential measurements and scanning electronic microscopy Several nanocomposites containing different percentages of polypyrrole were tested for the adsorption of both anionic and cationic dyes The effect of adsorbent nature, pH, contact time, adsorbent dose and initial dye concentration were investigated and discussed in terms of adsorption efficiency The adsorption efficiency of MO dye increased in the following sequence: SBA-15 < PPy/SBA-15(1%) < PPy/SBA-15(10%) < PPy/SBA-15(30%) < PPy/SBA-15(50%) The adsorption of MB dye is preferably carried out by parent material SBA-15 and nanocomposite PPy/SBA-15(1%) The experimental data were verified by the Langmuir and Freundlich isotherms, and the kinetic data were fitted by pseudo-first-order and pseudo-second-order models The obtained results showed that the adsorption of the both dye by nanocomposite PPy/SBA-15 followed Langmuir adsorption isotherm models and pseudo-second-order kinetics The adsorbed amounts recorded for MO and MB dyes are 4166 and 5882 mg/g, respectively