Iron Oxide Nanomaterials Research Articles

Multifunctional Porous Iron Oxide Nanoagents for MRI and Photothermal/Chemo Synergistic Therapy.

Nanoagents of integrating multiple imaging and therapeutic modalities have attracted tremendous attention for biomedical applications. Herein, we synthesize porous hollow Fe3O4 as a theranostic agent for MRI and combined photothermal/chemo cancer therapy. The as-prepared porous iron oxide nanoagents allow for T2-weighted MR imaging. Interestingly, we demonstrate that the porous structure endows the nanoagents an outstanding photothermal property for cancer cell killing, in comparison with other types of iron oxide nanomaterials. Under the exposure of an NIR laser, the heat produced by porous Fe3O4 can accelerate the release of the loaded drug (e.g., DOX) to enhance chemotherapeutic efficacy, promoting the ablation of cancer cells with synergistic photothermal/chemotherapy.

Application of Iron Oxide Nanoparticles in Contemporary Experimental Physiology and Cell Biology Research

Abstract Recent findings have suggested that iron oxide nanoparticles (IONPs) have some exceptional chemical characteristics which make them useful in both experimental physiology and cell biology research. These nanoparticles might be applied as drug delivery systems for anti-cancer and other medications. Also, IONPs might be a valuable part of many novel bioassays in various fundamental medical fields. In recent years, several studies have indicated that IONPs may have certain cytotoxic and genotoxic potential in living systems. During in vitro conditions, IONPs might induce generation of reactive oxygen species and cause oxidative stress in some cell populations. The toxicity of IONPs is not yet fully understood, and additional research is needed to confirm if IONPs have detrimental effects on human health. This short article focuses on the recent developments and trends in the fields of nanomedicine and nanobiology regarding iron oxide nanomaterials and their application in fundamental medical disciplines such as experimental physiology. We discuss our previously published works on structural effects of IONPs and other metallic nanoparticles on cell nucleus in in vitro conditions. We also describe our recent findings regarding the impact of IONPs on certain biophysical properties of subcellular components.

Iron-oxide-based twin nanoplates with strong T2 relaxation shortening for contrast-enhanced magnetic resonance imaging.

Iron oxide nanomaterials have been intensively investigated over the past few decades as magnetic resonance imaging (MRI) contrast agents (CAs) due to their favorable magnetism and excellent biocompatibility. However, commercial iron-oxide-nanoparticle-based CAs suffer from low T2 relaxivity, which significantly limits their applications in the biomedical field. Herein, we report a new type of iron oxide nanoplate (IOP) with an interesting twinning plane, which is fabricated via seed growth. Compared with the conventional iron oxide (IO) spherical nanoparticles, iron oxide twin nanoplates (IOP-13) have a larger effective radius, higher saturation magnetization, and greater anisotropy, resulting in their superior T2 relaxivity of 571.21 mM-1 s-1 at 0.5 T, which is about six times higher than that of commercial IO nanoparticles. In vivo MR imaging demonstrated that IOP-13 could be used for liver imaging and liver tumor diagnosis with high sensitivity and accuracy, revealing the great potential of IOP-13 as a next-generation CA. This work provides a novel strategy of structure tuning to devise high-performance T2 contrast agents, which expands the applications of iron oxide nanoparticles in biology and materials.

电化学处理酸洗废液制备氧化铁的研究

酸洗废液是制约金属建材行业发展的一大阻碍，酸洗废液的处理问题因此成为我国近几年来的热点研究问题之一。本文采用自制电化学装置对Fe2+浓度为1 g/L模拟酸洗废液的处理过程及实验产物进行分析，外加电源为12 V。对实验过程中的铁离子浓度在阴阳两极出水实时变化趋势进行定量分析，得出结论：实验设备可使Fe2+向Fe3+转化，最终向沉淀转化。对实验产物进行定性分析，通过XRD表征可知产物成分为氧化铁，通过SEM表征对氧化铁产物形貌进行分析，可知产物晶体为片状，粒径为纳米，分布较为均匀。并对实验接下来的方向提出要求，制备形貌可控的氧化铁纳米材料，以及再生酸液可达到回用标准。 Waste pickling is a major obstacle to the development of metal building materials industry, and the treatment of waste pickling has become one of the hot topics in recent years in China. In this paper, the treatment process and the experimental samples of simulated waste pickling with Fe2+ concentration of 1 g/L were analyzed by the self-made electrochemical device, and the external power supply was 12 V. The quantitative analysis of the real-time variation trend of ferric ion concentration in cathode and anode during the experiment was carried out. The conclusion is that the experimental equipment can transform Fe2+ to Fe3+ and finally to the precipitation. The quali-tative analysis of the experimental products showed that the samples were iron oxide by XRD, and the pattern of iron oxide was analyzed by SEM. It was found that the crystal samples was flaky, the particle size was nanometer, and well-distributed. In addition, the requirements of the following experiments were proposed to prepare the iron oxide nano-materials with controllable pattern, and the regenerated acid could be reused.

Fe-Oxide Nanomaterial: Synthesis, Characterization and Lead Removal

Organic solvent free iron oxide nanomaterial used for lead removal was synthesized by co-precipitation method. Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopic with energy dispersive X-ray analysis (SEM-EDX), X-ray diffraction (XRD) and thermo gravimetric-differential thermal (TG-DTA) analysis were used to determine the surface characteristics and analysis of iron oxide. Optimization of solution pH, adsorbent dosage, contact time, agitation speed and initial lead ion concentration were conducted for further adsorption isotherm, kinetics, thermodynamics and desorption study. Langmuir sorption isotherm model fits the adsorption data better than Freundlich, Dubinin-Radushkevich (D-RK) and Flory-Huggins (FH) models. The mean adsorption energy and free energy obtained from D-RK and FH models guides that the mechanism was under control of physical adsorption and actuality of spontaneous reaction, respectively. From kinetics of adsorption pseudo second (PSO) model fits well than pseudo first (PFO) and Elovich adsorption-reaction models. And to test whether the reaction is under control of adsorption-diffusion or not the intra particle diffusion (IPD) model was tested, but it fails to pass through the origin. This indicates that the reaction mechanism only under control of adsorption-reaction. The maximum adsorption capacity (qmax) of the adsorbent was 70.422 mg/g.

Using porous magnetic iron oxide nanomaterials as a facile photoporation nanoplatform for macromolecular delivery.

The intracellular delivery of exogenous macromolecules such as functional proteins, antibodies, polysaccharides and nucleic acids into living cells for biomedical applications is of great interest. Even though great efforts have been devoted to this task, universal delivery systems that provide excellent intracellular delivery performance combined with easy cell recovery are urgently needed. Magnetic iron oxide nanoparticles show promising potential for various biomedical applications because of their advantages such as high biocompatibility and cost-effectiveness. Herein, a new facile platform for macromolecular delivery was developed based on the photothermal properties of porous magnetic iron oxide nanoparticles (P-MNPs). The near-infrared radiation (NIR) absorption behavior of P-MNPs remarkably facilitates the delivery of macromolecules into cells while maintaining high cell viability. Furthermore, the assistance of polycationic polyethylenimine improves the efficiency of DNA delivery. Most importantly, the cells could be easily recovered after macromolecular delivery by trypsinization, which is of great significance for further practical application of the delivery system. The facile and cost-effective platform proposed in this work provides a new avenue for the utilization of P-MNPs in macromolecular delivery.

Thin films containing oxalate-capped iron oxide nanomaterials deposited on glass substrate for fast Fenton degradation of some micropollutants

The main goal of the study was to evaluate the catalytic activity of two hybrid nanocatalysts consisting in Fe3O4 nanoparticles modified with either chitosan (CS) or polyethylene glycol (PEG)/ferrous oxalate (FO), and further deposited on solid substrate as thin films. X-ray powder diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, and scanning electron microscopy (SEM) were employed for the structural and morphological characterizations of the heterogeneous catalysts. The degradation kinetic studies of two reactive azo dye (Reactive Black 5 (RB5) and Reactive Yellow 84 (RY84)) as well as Bisphenol A (BPA) solutions were carried out using Fenton-like oxidation, in the presence of different concentrations of H2O2, at initial near-neutral pH and room temperature. The results indicated that a low amount of catalytic material (0.15g/L), deposited as thin film, was able to efficiently trigger dye degradation in solution in the presence of 6.5mmol/L H2O2 for RB5 and of only 1.6mmol/L H2O2 in the case of BPA and RY84. In the presence of complex matrices such as WWTP waters, the removal of BPA was low (only 24% for effluent samples). Our findings recommend the studied immobilized nanocatalysts as promising economical tools for the pre-treatment of wastewaters using advanced oxidation processes (AOPs).

One-Step Fast Synthesis of Nanoparticles for MRI: Coating Chemistry as the Key Variable Determining Positive or Negative Contrast.

Iron oxide nanomaterial is a typical example of a magnetic resonance imaging probe for negative contrast. It has also been shown how this nanomaterial can be synthesized for positive contrast by modification of the composition and size of the core. However, the role of the organic coating in the relaxometric properties is largely unexplored. Here, maghemite nanoparticles with either excellent positive or very good negative contrast performance are obtained by modifying coating thickness while the core is kept unchanged. Different nanoparticles with tailored features as contrast agent according to the coating layer thickness have been obtained in a single-step microwave-driven synthesis by heating at different temperatures. A comprehensive analysis is conducted of how the composition and structure of the coating affects the final magnetic, relaxometric, and imaging performance. These results show how the organic coating plays a fundamental role in the intrinsic relaxometric parameters of iron oxide-based contrast media.

Synthesis of Distinct Iron Oxide Nanomaterial Shapes Using Lyotropic Liquid Crystal Solvents.

A room temperature reduction-hydrolysis of Fe(III) precursors such as FeCl3 or Fe(acac)3 in various lyotropic liquid crystal phases (lamellar, hexagonal columnar, or micellar) formed by a range of ionic or neutral surfactants in H2O is shown to be an effective and mild approach for the preparation of iron oxide (IO) nanomaterials with several morphologies (shapes and dimensions), such as extended thin nanosheets with lateral dimensions of several hundred nanometers as well as smaller nanoflakes and nanodiscs in the tens of nanometers size regime. We will discuss the role of the used surfactants and lyotropic liquid crystal phases as well as the shape and size differences depending upon when and how the resulting nanomaterials were isolated from the reaction mixture. The presented synthetic methodology using lyotropic liquid crystal solvents should be widely applicable to several other transition metal oxides for which the described reduction-hydrolysis reaction sequence is a suitable pathway to obtain nanoscale particles.

Thermally induced phase transformation in multi-phase iron oxide nanoparticles on vacuum annealing

The evolution of magnetic phases in multi-phase iron oxide nanoparticles, synthesized via the transferred arc plasma induced gas phase condensation method, was investigated by X-ray diffraction, vibrating sample magnetometry and 57Fe Mössbauer spectroscopy. The particles are proposed to be consisting of three different iron oxide phases: α-Fe2O3, γ-Fe2O3 and Fe3O4. These nanoparticles were exposed to high temperature (∼935K) under vacuum (10−3mbar He pressure), and the thermally induced phase transformations were investigated. The Rietveld refinement of the X-ray diffraction data corroborates the least-squares fitting of the transmission Mössbauer spectra in confirming the presence of Fe3O4, γ-Fe2O3 and α-Fe2O3 phases before the thermal treatment, while only Fe3O4 and α-Fe2O3 phases exist after thermal treatment. On thermal annealing in vacuum, conversion from γ-Fe2O3 to Fe3O4 and α-Fe2O3 was observed. Interestingly, we have observed a phase transformation occurring in the temperature range ∼498K–538K, which is strikingly lower than the phase transformation temperature of γ-Fe2O3 to α-Fe2O3 (573–623K) in air. Combining the results of Rietveld refinement of X-ray diffraction patterns and Mössbauer spectroscopy, we have attributed this phase transformation to the phase conversion of a metastable “defected and strained” d-Fe3O4 phase, present in the as-prepared sample, to the α-Fe2O3 phase. Stabilization of the phases by controlling the phase transformations during the use of different iron-oxide nanoparticles is the key factor to select them for a particular application. Our investigation provides insight into the effect of temperature and chemical nature of the environment, which are the primary factors governing the phase stability, suitability and longevity of the iron oxide nanomaterials prepared by the gas-phase condensation method for various applications.

Janus plasmonic-magnetic gold-iron oxide nanoparticles as contrast agents for multimodal imaging.

The design of compact nanoprobes for multimodal bioimaging is a current challenge and may have a major impact on diagnostics and therapeutics. Multicomponent gold-iron oxide nanoparticles have shown high potential as contrast agents in numerous imaging techniques due to the complementary features of iron oxide and gold nanomaterials. In this paper we describe novel gold-iron oxide Janus magnetic-plasmonic nanoparticles as versatile nanoprobes for multimodal imaging. The nanoparticles are characterized as contrast agents for different imaging techniques, including X-ray computed tomography (CT), T2-weighted nuclear magnetic resonance imaging (MRI), photoacoustic imaging (PA), dark-field and bright-field optical microscopy, transmission electron microscopy (TEM), and surface enhanced Raman spectroscopy (SERS). We discuss the effect of particle size and morphology on their performance as contrast agents and show the advantage of a Janus configuration. Additionally, the uptake of nanoparticles by cells can be simultaneously visualized in dark- and bright-field optical microscopy, SERS mapping, and electron microscopy. These complementary techniques allow a complete view of cell uptake in an artifact-free manner, with multiplexing capabilities, and with extra information regarding the nanoparticles' fate inside the cells. Altogether, the results obtained with these non-invasive techniques show the high versatility of these nanoparticles, the advantages of a Janus configuration, and their high potential in multipurpose biomedical applications.

Synthesis of high saturation magnetic iron oxide nanomaterials via low temperature hydrothermal method

Iron oxide nanoparticles (IONPs) were synthesized through a simple low temperature hydrothermal approach to obtain with high saturation magnetization properties. Two series of iron precursors (sulfates and chlorides) were used in synthesis process by varying the reaction temperature at a constant pH. The X-ray diffraction pattern indicates the inverse spinel structure of the synthesized IONPs. The Field emission scanning electron microscopy and high resolution transmission electron microscopy studies revealed that the particles prepared using iron sulfate were consisting a mixer of spherical (16–40nm) and rod (diameter ~20–25nm, length <100nm) morphologies that synthesized at 130°C, while the IONPs synthesized by iron chlorides are found to be well distributed spherical shapes with size range 5–20nm. On other hand, the IONPs synthesized at reaction temperature of 190°C has spherical (16–46nm) morphology in both series. The band gap values of IONPs were calculated from the obtained optical absorption spectra of the samples. The IONPs synthesized using iron sulfate at temperature of 130°C exhibited high saturation magnetization (MS) of 103.017emu/g and low remanant magnetization (Mr) of 0.22emu/g with coercivity (Hc) of 70.9Oe, which may be attributed to the smaller magnetic domains (dm) and dead magnetic layer thickness (t).

Effect of phosphate and oleic acid capping on structure, magnetic properties and thermal stability of iron oxide nanoparticles

The thermal stability and magnetic properties of iron oxide nanomaterials under different environmental conditions are important for technological applications. Herein, we report the influence of dynamic capping of iron oxide nanoparticles with phosphate and oleic acid, on their structure, magnetic properties and thermal stability and compare the results with that of uncoated nanoparticles. The composition, structure, morphology, quality of capping, thermal stability and magnetic properties of prepared magnetite nanoparticles are evaluated by using X-Ray Diffractometer (XRD), Small angle X-ray scattering (SAXS), High resolution transmission electron microscopy (HRTEM), Energy dispersive X-ray (EDX) analysis, Fourier transform infrared (FTIR) spectrometer, Thermo gravimetric analyzer (TGA), Differential scanning calorimetry (DSC) and Vibrating Sample Magnetometer (VSM). Our results suggest that the rapid adsorption of phosphate ions onto specific crystal planes of nucleated magnetite enabled the growth of magnetite core into nearly cubic shape while the oleic acid capping enabled a homogeneous growth of magnetite core along all the crystallographic directions, enabling the formation of nearly spherical particles with narrow size distribution. On the contrary, the phosphate adsorbs as multilayer islands on nanoparticles, leading to a broader size distribution, identical to the uncoated particles. The HRTEM analysis showed dark areas with asymmetric contrast in uncoated nanoparticles, which was not observed in phosphate and oleic acid capped magnetite. The FTIR study on phosphate coated magnetite particles confirms that the surface capping is a mixture of mono and non-protonated monodentate phosphate complexes. The DSC studies confirm a 100 °C enhancement in the magnetic phase thermal stability in phosphate-coated particles, as compared to uncoated and oleic acid coated magnetite. The temperature dependant magnetization results showed a lower blocking temperature for phosphate capped nanoparticles due to the denser multilayer islands of phosphate over magnetite as compared to a uniform close packed monolayer coverage of oleic acid. These results are useful for tailoring stable superparamagnetic nanoparticles for technological applications.

Maltol‐Functionalized Fe3O4 Nanoparticles as T2 Magnetic Resonance Imaging Contrast Agents

AbstractWe present the use of maltol (3‐hydroxy‐2‐methyl‐4H‐pyran‐4‐one) as a capping ligand for iron oxide nanomaterials. Water‐soluble maltol‐coated Fe3O4 nanoparticles were synthesized by a reductive one‐pot synthesis. The nanoparticles were found to be stable in water, and their superparamagnetic properties enabled their application as ultrahigh field T2 magnetic resonance imaging (MRI) contrast agents. High r2 relaxivity and r2/r1 ratios were determined at clinical (B0 = 3 T) and ultrahigh (B0 = 9.4 T) fields, making them on par or superior to current iron‐oxide based commercial MRI contrast agents. A low cytotoxic response in three distinct cell types (HUVEC, KB, U343) indicate maltol‐coated Fe3O4 nanoparticles are promising T2 MRI contrast agents.

Green synthesis of magnetic iron nanoparticles coated by olive oil and verifying its efficiency in extraction of nickel from environmental samples via UV–vis spectrophotometry

In this research, we report the synthesis and functionalization of magnetic iron nanoparticles using green chemistry (olive oil) for application of dispersive solid–liquid phase microextraction (DSLME) as a novel method for preconcentration and determination of nickel ions in soil, potato, red tea, white tea, mushroom, lettuce, cabbage, apple, urban water, purified drinking water through household water treatment device. Nickel is a dangerous toxic metal that can cause serious damage to the environment and then its removal is necessary. Recently, iron oxide nano materials have gained much attention due to their properties, such as extremely small, non-toxic, excellent magnetic properties, high surface area, great biocompatibility and high level of reactivity with metal which makes them worthwhile in the removal of these metals. For optimizing the important parameters affecting the extraction procedure, analyte concentration, pH, type of disperser solvent, absorption time, ionic strength effect, type of desorption solvent and desorption time investigated. SEM and FT-IR spectrum used for characterization of the synthesized magnetic nanoparticles. The measurements were done under the optimized conditions. Matrices effect and accuracy were examined by the determination of the relative recovery (RR%) of the real samples. Linear range, detection limit and relative standard deviation (RSD) are 1–5000ng/ml, 0.821ng/ml and 0.196%, respectively.

Evaluating magnetic nano-ferrofluid as a novel coagulant for surface water treatment

In the area of environmental remediation, nanomaterials offer the potential for the efficient removal of pollutants and biological contaminants. With the rapid development of nanotechnology, nano-ferrofluid or magnetic fluids are currently being widely studied in water treatment field. The utilization of iron oxide nanomaterials or magnetic nanoparticles (MNs) has received great attention due to their unique properties, such as biocompatibility, small size, high surface area to volume ratio, and easy separation from solution using an external magnetic field. However, a few works have been conducted on coagulant and enhancing coagulation process using simple nano-ferrofluid without any modification. In the present study, at first, we synthesized nano-ferrofluid; then, after characterizations, we use the magnetic fluid for water treatment. For this purpose, we choose Karun River in the southwest of Iran as a model and water samples are collected. Then, they are treated with a small amount of magnetic fluid. In this process, the effect of this nanomaterial on turbidity, hardness, alkalinity, removal of some important heavy metal cations, and important anions like phosphate, population of coliform bacteria and fecal coliform bacteria, and amount of chemical oxygen demand (COD) is investigated separately. Also, the effect of some important parameters such as time and rate of mixing steps, pH, temperature, and reusability of these nanomagnetic particles as a coagulant is investigated and the interesting and applicable results are obtained. In general, the combination of removing important hazardous ions with 1μgmL−1 such as Cd2+, Co2+, Mn2+, Fe2+, Pb2+, Zn2+, Ni2+, and Cu2+ cations (more than 90%), great ability in decreasing turbidity (about 90%), excellent antibacterial efficiency (98% of fecal coliform bacteria and 97% of coliform bacteria were removed), decreasing COD (about 60%), green and cheap preparation, ease of use, and decreased time of separating those with external magnetic field compared to available commercial coagulants. To the best of our knowledge, most of available coagulants can only decrease turbidity. Notably, in decreasing turbidity, MNs have the same efficiency over the pH range (4.0–8.0) and temperature range (15–45°C) in real samples. Meanwhile the most coagulants do not have these properties simultaneously.

Red blood cell membrane camouflaged magnetic nanoclusters for imaging-guided photothermal therapy

Along with intrinsic magnetic resonance imaging (MRI) advantages, iron oxide nanomaterials capable of photothermal conversion have been reported very recently and have again raised great interest in their designs among biomedical researchers. However, like other inorganic nanomaterials, high macrophage uptake, short blood retention time and unfavorable biodistributions have strongly hampered their applications in vivo. To solve these problems, a rational design of red blood cell (RBC) membrane camouflaged iron oxide magnetic clusters (MNC@RBCs) is presented in this paper. Our data show that by simply introducing an “ultra-stealth” biomimetic coating to iron oxide magnetic nanoclusters (MNCs), MNC@RBCs maintain the imaging and photothermal functionalities inherited from MNCs cores while achieving much lower nonspecific macrophage uptake and dramatically altered fate in vivo. MNC@RBCs with superior prolonged blood retention time, preferred high tumor accumulation and relatively lowered liver biodistribution are demonstrated when injected intravenously in mice, leading to greatly enhanced photothermal therapeutic efficacy by a single treatment without further magnetic force manipulation. Our study illustrates a well prepared integration of MNCs and RBCs, exploiting advantages of both functionalities within a single unit and suggests a promising future for iron-based nanomaterials application in vivo.

Construction of ferrocene-containing nanomaterials via self-assembly of ferrocenyl hyperbranched polyethylene

Self-assembly of ferrocene-containing copolymers has been proved to be a convenient way to construct various functional nanomaterials. Thus, (hyperbranched polyethylene)-grafted-(poly(2-(methacryloyloxy)-ethyl ferrocenecarboxylate)) (HBPE-g-PFcEMA) was synthesized. It's self-assembly properties in the THF/n-hexane solvent mixture and n-hexane were explored. In the THF/n-hexane solvent mixture, spherical micelles were obtained at low concentration of HBPE-g-PFcEMA. However, at higher concentration, only irregular nanoparticles were observed. In contrast, the HBPE-g-PFcEMA micelles prepared in n-hexane by solvent diffusion method were with well-defined structures whether at low or high concentration of HBPE-g-PFcEMA. Furthermore, the nanostructures of these assemblies in n-hexane could be controlled to be sheet, hollow or patchy sphere simply by adjusting the concentration of HBPE-g-PFcEMA. Therefore, a novel and convenient way was provided to construct ferrocene-containing nanomaterials with various nanostructures from the same ferrocenyl hyperbranched copolymer by controlling its concentration. These ferrocene-containing nanomaterials might find their application as precursor in preparing functional iron oxide nanomaterials.

Novel synthesis of an iron oxalate capped iron oxide nanomaterial: a unique soil conditioner and slow release eco-friendly source of iron sustenance in plants

Iron (Fe) is a vital plant-derived micronutrient in the human diet.

Recent Advances in Synthesis, Properties and Applications of Magnetic Oxide Nanomaterials

Oxide nanomaterials are in great demand due to their unique physical, chemical and structural properties. The nanostructured materials with desired magnetic properties are the future of power electronics. Unique magnetic properties and excellent biocompatibility of these materials found applications in pharmaceutical field also. For these applications, the synthesis of magnetic oxide nanomaterials with required properties is highly desirable. Till now, various techniques have been evolved for the synthesis of oxide nanomaterials with full control over their shape, size, morphology and magnetic properties. In nanoscale, the magnetic properties are totally different from their bulk counterparts. In this range, each nanoparticle acts as a single magnetic domain and shows fast response to applied magnetic field. This review article discusses the synthesis techniques, properties and the applications of magnetic oxide nanomaterials. Various characterization techniques for magnetic materials have been discussed along with the literature of iron oxide, nickel oxide, and cobalt oxide nanomaterials. The challenges for further development of these materials have also been presented to broaden their rapidly emerging applications.