Properties of multifunctional composite materials based on nanomaterials: a review

Optical Phenomena in Molecule-Based Magnetic Materials

Since the last century, we have witnessed the development of molecular magnetism which deals with magnetic materials based on molecular species, i.e., organic radicals and metal complexes. Among them, the broadest attention was devoted to molecule-based ferro-/ferrimagnets, spin transition materials, including those exploring electron transfer, molecular nanomagnets, such as single-molecule magnets (SMMs), molecular qubits, and stimuli-responsive magnetic materials. Their physical properties open the application horizons in sensors, data storage, spintronics, and quantum computation. It was found that various optical phenomena, such as thermochromism, photoswitching of magnetic and optical characteristics, luminescence, nonlinear optical and chiroptical effects, as well as optical responsivity to external stimuli, can be implemented into molecule-based magnetic materials. Moreover, the fruitful interactions of these optical effects with magnetism in molecule-based materials can provide new physical cross-effects and multifunctionality, enriching the applications in optical, electronic, and magnetic devices. This Review aims to show the scope of optical phenomena generated in molecule-based magnetic materials, including the recent advances in such areas as high-temperature photomagnetism, optical thermometry utilizing SMMs, optical addressability of molecular qubits, magneto-chiral dichroism, and opto-magneto-electric multifunctionality. These findings are discussed in the context of the types of optical phenomena accessible for various classes of molecule-based magnetic materials.

Revealing the Adverse Impact of Additive Carbon Material on Microorganisms and Its Implications for Biogas Yields: A Critical Review

Biochar could be a brilliant additive supporting the anaerobic fermentation process. However, it should be taken into account that in some cases it could also be harmful to microorganisms responsible for biogas production. The negative impact of carbon materials could be a result of an overdose of biochar, high biochar pH, increased arsenic mobility in the methane fermentation solution caused by the carbon material, and low porosity of some carbon materials for microorganisms. Moreover, when biochar is affected by an anaerobic digest solution, it could reduce the biodiversity of microorganisms. The purpose of the article is not to reject the idea of biochar additives to increase the efficiency of biogas production, but to draw attention to the properties and ways of adding these materials that could reduce biogas production. These findings have practical relevance for organizations seeking to implement such systems in industrial or local-scale biogas plants and provide valuable insights for future research. Needless to say, this study will also support the implementation of biogas technologies and waste management in implementing the idea of a circular economy, further emphasizing the significance of the research.

Scalable Manufacturing Process and Multifunctional Performance of Cotton Fibre-Reinforced Poly(Lactic Acid) (PLA) Bio-Composites Coated by Graphene Oxide

Natural fibre biopolymer composites with both fibres and matrix being derived from biomaterials are increasingly used in demanding applications, such as sensing, packaging, building, and transport, and require good electrical, thermal, and flame retardant properties. Herein, an investigation of the effectiveness of functionalising nonwoven cotton/poly(lactic acid) (PLA) fibre mats with graphene oxide nanosheets has been reported by using a facile dip-coating method followed by thermal reduction for enhancing the electric, thermal, and abrasion-resistance properties. The manufacturing processes for preparing biocomposites and introducing functionality are readily scalable. Experimental results reveal that with the addition of less than 0.5 wt% graphene nanoplatelets, the biocomposites showed significant improvements in abrasion resistance, electrical conductivity, thermal conductivity, and diffusivity. Furthermore, the composite shows excellent piezo-resistivity to act as strain sensors with a gauge factor of 2.59 at strains up to 1%.

Synthesis and characterization of aramid composites reinforced with silanized graphene platelets

The synthesis and characterization of aramid composites reinforced with graphene platelets are reported. Hydroxy-functionalised graphene platelets were modified with two sol-gel binders (aminopropyl- or aminophenyl-trialkoxysilanes) and then chemically linked with aramid chains. The effect of the two sol-gel binders on the physiochemical and mechanical properties was evaluated. Chemical changes during the sol-gel reaction and subsequent amidation process in the nano-composite preparation were evaluated by the XPS and FTIR analyses. Thin films of these composites with different proportions of graphene were prepared. Morphology of the hybrids prepared was studied by the SEM technique. Properties of the composite films were studied by dynamical mechanical thermal (DMT) analysis to measure their glass transition temperature (T g) and storage modulus. These properties have been compared with previously reported values using pristine graphene (Gr) as a filler. The increase in thermal mechanical properties on addition of silanized graphene (SiGr) showed a large shift in the T g and more increase in storage modulus by chemically binding SiGr sheets on the aramid chains. Aminophenyl-trialkoxysilane was found to give better results due to the presence of phenyl groups which were more rigid than propyl groups present in aminopropyl-trialkoxysilane. The effect of chemical bonding and the possible π-π secondary bond interactions between the matrix and graphene platelets on the properties of the resulting hybrids are discussed.

Effect of Fe(III) Modification on the Phosphorus Removal Behavior of Ce(III) Carbonate Adsorbents

Excessive phosphorus (P) in water is the main reason for eutrophication, which has been a global problem for many years. For the adsorption treatment of phosphorus-containing wastewater, adsorbents are key research topics. In this study, we develop the synthesis of a series of Ce/Fe adsorbents by modifying the commercial cerium carbonate with Fe₂(SO₄)₃. By conducting comprehensive analysis with XRD, FTIR, and SEM, we find that the amorphous granular structure and large chunky structure created by the high and low Fe content, respectively, both had a negative effect on the adsorption capacity of phosphate. Among different adsorbents, Ce/Fe-15/3, with Ce loading of 28.33 wt % and Fe loading of 5.66 wt %, exhibits high P adsorption capacity of 58 mg P/g (in pH = 7, 30 mg P/L solution). It also demonstrates excellent selectivity toward phosphate adsorption in Cl^-, SO₄ ^2-, and NO₃ ^- solution (up to 20 times of the phosphate molarity) and good adsorption stability in acidic environments (pH = 3-6). The adsorption behavior of Ce/Fe-15/3 can be modeled well by the Langmuir model and pseudo-second-order (PSO) model. By conducting the XPS analysis, we conclude that the adsorption mechanism is a combination effect of Ce/PO₄ ^3- and Fe/PO₄ ^3- chemical interactions.

Relationship between the Formation of Magnetic Clusters and Hexagonal Phase of Gold Matrix in AuxFe1-x Nanophase Thin Films

AuxFe1-x nanophase thin films of different compositions and thicknesses were prepared by co-deposition magnetron sputtering. Complex morpho-structural and magnetic investigations of the films were performed by X-ray Diffraction, cross-section Transmission Electron Microscopy, Selected Area Electron Diffraction, Magneto Optical Kerr Effect, Superconducting Quantum Interference Device magnetometry and Conversion Electron Mössbauer Spectroscopy. It was proven that depending on the preparation conditions, different configurations of defect α-Fe magnetic clusters, i.e., randomly distributed or auto-assembled in lamellar or filiform configurations, can be formed in the Au matrix. A close relationship between the Fe clustering process and the type of the crystalline structure of the Au matrix was underlined, with the stabilization of a hexagonal phase at a composition close to 70 at. % of Au and at optimal thickness. Due to different types of inter-cluster magnetic interactions and spin anisotropies, different types of magnetic order from 2D Ising type to 3D Heisenberg type, as well as superparamagnetic behavior of non-interacting Fe clusters of similar average size, were evidenced.

Smart Infrastructure Monitoring through Self-Sensing Composite Sensors and Systems: A Study on Smart Concrete Sensors with Varying Carbon-Based Filler

Structural Health Monitoring allows an automated performance assessment of buildings and infrastructures, both during their service lives and after critical events, such as earthquakes or landslides. The strength of this technology is in the diffuse nature of the sensing outputs that can be achieved for a full-scale structure. Traditional sensors adopted for monitoring purposes possess peculiar drawbacks related to placement and maintenance issues. Smart construction materials, which are able to monitor their states of strain and stress, represent a possible solution to these issues, increasing the durability and reliability of the monitoring system through embedding or the bulk fabrication of smart structures. The potentialities of such novel sensors and systems are based on their reliability and flexibility. Indeed, due to their peculiar characteristics, they can combine mechanical and sensing properties. We present a study on the optimization and the characterization of construction materials doped with different types of fillers for developing a novel class of sensors able to correlate variations of external strains to variations of electrical signals. This paper presents the results of an experimental investigation of composite samples at small and medium scales, made of cementitious materials with carbon-based inclusions. Different from a previous work by the authors, different carbon-based filler composite sensors are first compared at a small cubic sample scale and then tailored for larger plate specimens. Possible applications are in the strain/stress monitoring, damage detection, and load monitoring of concrete buildings and infrastructures.

Optimising Crystallisation during Rapid Prototyping of Fe3O4-PA6 Polymer Nanocomposite Component

Polymer components capable of self-healing can rapidly be manufactured by injecting the monomer (ε-caprolactam), activator and catalyst mixed with a small amount of magnetic nanoparticles into a steel mould. The anionic polymerisation of the monomer produces a polymer component capturing magnetic nanoparticles in a dispersed state. Any microcracks developed in this nanocomposite component can be healed by exposing it to an external alternating magnetic field. Due to the magnetocaloric effect, the nanoparticles locally melt the polymer in response to the magnetic field and fill the cracks, but the nanoparticles require establishing a network within the matrix of the polymer through effective dispersion for functional and uniform melting. The dispersed nanoparticles, however, affect the degree of crystallinity of the polymer depending on the radius of gyration of the polymer chain and the diameter of the magnetic nanoparticle agglomerates. The variation in the degree of crystallinity and crystallite size induced by nanoparticles can affect the melting temperature as well as its mechanical strength after testing for applications, such as stimuli-based self-healing. In the case of in situ synthesis of the polyamide-6 (PA6) magnetic nanocomposite (PMC), there is an opportunity to alter the degree of crystallinity and crystallite size by optimising the catalyst and activator concentration in the monomer. This optimisation method offers an opportunity to tune the crystallinity and, thus, the properties of PMC, which otherwise can be affected by the addition of nanoparticles. To study the effect of the concentration of the catalyst and activator on thermal properties, the degree of crystallinity and the crystallite size of the component (PMC), the ratio of activator and catalyst is varied during the anionic polymerisation of ε-caprolactam, but the concentration of Fe3O4 nanoparticles is kept constant at 1 wt%. Differential Scanning Calorimetry (DSC), Fourier-transform infrared spectroscopy (FTIR), XRD (X-ray diffraction) and Thermogravimetric analysis (TGA) were used to find the required concentration of the activator and catalyst for optimum properties. It was observed that the sample with 30% N-acetyl caprolactam (NACL) (with 50% EtMgBr) among all of the samples was most suitable to Rapid Prototype the PMC dog-bone sample with the desired degree of crystallinity and required formability.

In Situ Manipulation and Micromechanical Characterization of Diatom Frustule Constituents Using Focused Ion Beam Scanning Electron Microscopy

Biocomposite structures are difficult to characterize by bulk approaches due to their morphological complexity and compositional heterogeneity. Therefore, a versatile method is required to assess, for example, the mechanical properties of geometrically simple parts of biocomposites at the relevant length scales. Here, it is demonstrated how a combination of Focused Ion Beam Scanning Electron Microscopy (FIB-SEM) and micromanipulators can be used to isolate, transfer, and determine the mechanical properties of frustule constituents of diatom Thalassiosira pseudonana (T.p.). Specifically, two parts of the diatom frustule, girdle bands and valves, are separated by FIB milling and manipulated using a sharp tungsten tip without compromising their physical or chemical integrity. In situ mechanical studies on isolated girdle bands combined with Finite Element Method (FEM) simulations, enables the quantitative assessment of the Young's modulus of this biosilica; E = 40.0 GPa. In addition, the mechanical strength of isolated valves could be measured by transferring and mounting them on top of premilled holes in the sample support. This approach may be extended to any hierarchical biocomposite material, regardless of its chemical composition, to isolate, transfer, and investigate the mechanical properties of selected constituents or specific regions.

Additively manufactured BaTiO3 composite scaffolds: A novel strategy for load bearing bone tissue engineering applications

Piezoelectric ceramics, such as BaTiO₃, have gained considerable attention in bone tissue engineering applications thanks to their biocompatibility, ability to sustain a charged surface as well as improve bone cells' adhesion and proliferation. However, the poor processability and brittleness of these materials hinder the fabrication of three-dimensional scaffolds for load bearing tissue engineering applications. For the first time, this study focused on the fabrication and characterisation of BaTiO₃ composite scaffolds by using a multi-material 3D printing technology. Polycaprolactone (PCL) was selected and used as dispersion phase for its low melting point, easy processability and wide adoption in bone tissue engineering. The proposed single-step extrusion-based strategy enabled a faster and solvent-free process, where raw materials in powder forms were mechanically mixed and subsequently fed into the 3D printing system for further processing. PCL, PCL/hydroxyapatite and PCL/BaTiO₃ composite scaffolds were successfully produced with high level of consistency and an inner architecture made of seamlessly integrated layers. The inclusion of BaTiO₃ ceramic particles (10% wt.) significantly improved the mechanical performance of the scaffolds (54 ± 0.5 MPa) compared to PCL/hydroxyapatite scaffolds (40.4 ± 0.1 MPa); moreover, the presence of BaTiO₃ increased the dielectric permittivity over the entire frequency spectrum and tested temperatures. Human osteoblasts Saos-2 were seeded on scaffolds and cellular adhesion, proliferation, differentiation and deposition of bone-like extracellular matrix were evaluated. All tested scaffolds (PCL, PCL/hydroxyapatite and PCL/BaTiO₃) supported cell growth and viability, preserving the characteristic cellular osteoblastic phenotype morphology, with PCL/BaTiO₃ composite scaffolds exhibiting higher mineralisation (ALP activity) and deposited bone-like extracellular matrix (osteocalcin and collagen I). The single-step multi-material additive manufacturing technology used for the fabrication of electroactive PCL/BaTiO₃ composite scaffolds holds great promise for sustainability (reduced material waste and manufacturing costs) and it importantly suggests PCL/BaTiO₃ scaffolds as promising candidates for load bearing bone tissue engineering applications to solve unmet clinical needs.

Distinguished Contributions in the Fields of Biomedical and Environmental Applications Incorporating Nanostructured Materials and Composites in Journal Molecules

During the last two years, over 10,000 papers (articles, reviews, communications etc.) were published in Molecules [...].

Synthesis and Characterization of Polymer-Based Coatings Modified with Bioactive Ceramic and Bovine Serum Albumin

This study involves the synthesis of hydroxyapatite and describes the preparation and characterization of polymer coatings based on poly(ethylene glycol) diacrylate and poly(ethylene glycol) and modified with bovine serum albumin and hydroxyapatite. Hydroxyapatite was obtained by wet chemical synthesis and characterized by X-ray diffraction and FTIR spectroscopy, and its Ca/P molar ratio was determined (1.69 ± 0.08). The ceramic and bovine serum albumin were used in the preparation of composite materials with the polymeric matrix. The chemical composition of coatings was characterized with FTIR spectroscopy, and their morphology was recorded with SEM imaging. Moreover, the measurements of surface roughness parameters and stereometric research were performed. The prepared coatings were subjected to in vitro studies in simulated body fluid and artificial saliva. Changes in chemical composition and morphology after immersion were examined with FTIR spectroscopy and SEM imaging. Based on the conducted research, it can be stated that applied modifiers promote the biomineralization process. The roughness analysis confirmed prepared materials were characterized by the micrometer-scale topography. The materials morphology and roughness, and the morphology of the newly formed apatite deposit, were dependent on the type of the used modifier, and the artificial fluid used in in vitro studies.

Zero Valent Iron Nanoparticle-Loaded Nanobentonite Intercalated Carboxymethyl Chitosan for Efficient Removal of Both Anionic and Cationic Dyes

A zero valent iron-loaded nano-bentonite intercalated carboxymethyl chitosan (nZVI@nBent-CMC) composite was fabricated and characterized by FT-IR, TEM, TEM-EDX, XRD, BET surface area, and zeta potential measurements. The as-fabricated nZVI@nBent-CMC composite exhibited excellent removal efficiency for both anionic Congo red (CR) dye and cationic crystal violet (CV) dye. The maximum uptake capacities of CR and CV onto the nZVI@nBent-CMC composite were found to be 884.95 and 505.05 mg/g, respectively. The adsorption process of both dyes well fitted with the Langmuir isotherm model and pseudo-second order kinetic model. Thermodynamic data clarified that the adsorptions of both CR and CV onto the nZVI@nBent-CMC composite are spontaneous processes. Moreover, the adsorption of CR onto the nZVI@nBent-CMC composite was found to be an exothermic process while that of CV is an endothermic process. The nZVI@nBent-CMC composite also exhibited excellent reusability for both studied dyes without noticeable loss in the removal efficiency, suggesting its validity to remove both anionic and cationic dyes from wastewater.

TiO2-Graphene Quantum Dots Nanocomposites for Photocatalysis in Energy and Biomedical Applications

The focus of current research in material science has shifted from “less efficient” single-component nanomaterials to the superior-performance, next-generation, multifunctional nanocomposites. TiO2 is a widely used benchmark photocatalyst with unique physicochemical properties. However, the large bandgap and massive recombination of photogenerated charge carriers limit its overall photocatalytic efficiency. When TiO2 nanoparticles are modified with graphene quantum dots (GQDs), some significant improvements can be achieved in terms of (i) broadening the light absorption wavelengths, (ii) design of active reaction sites, and (iii) control of the electron-hole (e−-h+) recombination. Accordingly, TiO2-GQDs nanocomposites exhibit promising multifunctionalities in a wide range of fields including, but not limited to, energy, biomedical aids, electronics, and flexible wearable sensors. This review presents some important aspects of TiO2-GQDs nanocomposites as photocatalysts in energy and biomedical applications. These include: (1) structural formulations and synthesis methods of TiO2-GQDs nanocomposites; (2) discourse about the mechanism behind the overall higher photoactivities of these nanocomposites; (3) various characterization techniques which can be used to judge the photocatalytic performance of these nanocomposites, and (4) the application of these nanocomposites in biomedical and energy conversion devices. Although some objectives have been achieved, new challenges still exist and hinder the widespread application of these nanocomposites. These challenges are briefly discussed in the Future Scope section of this review.

Thermoset Polymer Matrix Composites of Epoxy, Unsaturated Polyester, and Novolac Resin Embedding Construction and Demolition Wastes powder: A Comparative Study

Composite materials that consisted of a polymer resin as matrix (PMCs), filled using construction and demolition (C&D) wastes powder of different grain sizing in micro-scale were manufactured and studied. Three different kinds of resins were used as the matrix for the purposes of this study. More specifically, composites made of epoxy and unsaturated polyester resins purchased from the market and phenolic resin (novolac) laboratory synthesized, were produced. The morphological and elemental analysis of these materials was performed through scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD). Additionally, mechanical performance and thermal insulating efficiency of these materials were examined through bending and shear strength tests according to the three-point method and via determination of the thermal conductivity coefficient λ. C&D wastes have undergone the appropriate processing in order to prepare filling products of the required granular size in pulverized form. In this research study, construction and demolition waste-based thermosetting polymer composites were produced with flexural strength in the range 20-60 MPa, shear strength in between 1-8 MPa, and thermal conductivity coefficients in the range of 0.27-1.20 W/ m K. The developed materials embedded 30-50% w/w C&D wastes, depending on the resin used as the matrix.

Polymer-Based Composites: An Indispensable Material for Present and Future Applications

Right from the early days, polymer materials have been discovered as being beneficial for various applications but a poor understanding of these materials greatly handicapped their usage. However, with a change in this trend, polymer materials have gradually displaced other materials in most applications. In recent times, due to improved research and knowledge, polymer-based materials are the first choice materials for several applications and are now replacing other materials rapidly. More advanced materials from polymers are being developed daily as a substitute for other materials even in areas where polymers are considered not to be suitable in the time past. More recently, polymers have replaced metals and ceramics in applications like constructions, aerospace, automobiles, and medical. It is no doubt that this trend will continue due to the inherent properties of polymers and sustainability potential. Today, most of the limitations of polymers are being taken care of in the formulation of composite materials. Besides, the adaptation to positive environmental influence is being handled by scientists and researchers. Hence, this review reveals core areas of application of polymer-based composites and the significance of these materials to the advancement of humanity.