Self-Sensing, Ultralight, and Conductive 3D Graphene/Iron Oxide Aerogel Elastomer Deformable in a Magnetic Field

Activation of peroxymonosulfate by sustainable biomass-based carbon nanotubes for controlling the spread of plant viruses in water environments

With the increasing demand for water in hydroponic systems and agricultural irrigation, viral diseases have seriously affected the yield and quality of crops. By removing plant viruses in water environments, virus transmission can be prevented and agricultural production and ecosystems can be protected. But so far, there have been few reports on the removal of plant viruses in water environments. Herein, in this study, easily recyclable biomass-based carbon nanotubes catalysts were synthesized with varying metal activities to activate peroxymonosulfate (PMS). Among them, the magnetic 0.125Fe@NCNTs-1/PMS system showed the best overall removal performance against pepper mild mottle virus, with a 5.9 log10 removal within 1 min. Notably, the key reactive species in the 0.125Fe@NCNTs-1/PMS system is 1O2, which can maintain good removal effect in real water matrices (river water and tap water). Through RNA fragment analyses and label free analysis, it was found that this system could effectively cleave virus particles, destroy viral proteins and expose their genome. The capsid protein of pepper mild mottle virus was effectively decomposed where serine may be the main attacking sites by 1O2. Long viral RNA fragments (3349 and 1642 nt) were cut into smaller fragments (∼160 nt) and caused their degradation. In summary, this study contributes to controlling the spread of plant viruses in real water environment, which will potentially help protect agricultural production and food safety, and improve the health and sustainability of ecosystems.

3D microprinting of inorganic porous materials by chemical linking-induced solidification of nanocrystals

Three-dimensional (3D) microprinting is considered a next-generation manufacturing process for the production of microscale components; however, the narrow range of suitable materials, which include mainly polymers, is a critical issue that limits the application of this process to functional inorganic materials. Herein, we develop a generalised microscale 3D printing method for the production of purely inorganic nanocrystal-based porous materials. Our process is designed to solidify all-inorganic nanocrystals via immediate dispersibility control and surface linking-induced interconnection in the nonsolvent linker bath and thereby creates multibranched gel networks. The process works with various inorganic materials, including metals, semiconductors, magnets, oxides, and multi-materials, not requiring organic binders or stereolithographic equipment. Filaments with a diameter of sub-10 μm are printed into designed complex 3D microarchitectures, which exhibit full nanocrystal functionality and high specific surface areas as well as hierarchical porous structures. This approach provides the platform technology for designing functional inorganics-based porous materials.

Turning waste avocado stones and montmorillonite into magnetite-supported nanocomposites for the depollution of methylene blue: adsorbent reusability and performance optimization

The existence of methylene blue (MB) in wastewater even as traces is raising environmental concerns. In this regard, the performances of four adsorbents, avocado stone biochar (AVS-BC), montmorillonite (MMT), and their magnetite Fe3O4-derived counterparts, were compared. Results showed the superior performance of Fe3O4@AVS-BC and Fe3O4@MMT nanocomposites with removal percentages (%R) of 95.59% and 88%. The morphological features of AVS-BC as revealed by SEM analysis showed a highly porous surface compared to a plane and smooth surface in the case of MMT. Surface analysis using FT-IR and Raman spectroscopies corroborated the existence of the Fe-O peaks upon loading with magnetite. The XRD analysis confirmed the formation of cubic magnetite nanoparticles. The adsorption process in the batch mode was optimized using central composite design (CCD). Equilibrium and kinetic isotherms showed that the adsorption of MB onto Fe3O4@AVS-BC fitted well with the Langmuir isotherm and the pseudo-second-order (PSO) model. The maximum adsorption capacity (qm) was 118.9 mg/g (Fe3O4@AVS-BC) and 72.39 mg/g (Fe3O4@MMT). The Fe3O4@AVS-BC showed a higher selectivity toward MB compared to other organic contaminants. The MB-laden adsorbent was successfully used for the remediation of Cr (III), Ni (II), and Cd (II) with removal efficiencies hitting 100% following thermal activation.

Flexible Nanocomposite Conductors for Electromagnetic Interference Shielding

HIGHLIGHTS

Convincing candidates of flexible (stretchable/compressible) electromagnetic interference shielding nanocomposites are discussed in detail from the views of fabrication, mechanical elasticity and shielding performance. Detailed summary of the relationship between deformation of materials and electromagnetic shielding performance. The future directions and challenges in developing flexible (particularly elastic) shielding nanocomposites are highlighted. With the extensive use of electronic communication technology in integrated circuit systems and wearable devices, electromagnetic interference (EMI) has increased dramatically. The shortcomings of conventional rigid EMI shielding materials include high brittleness, poor comfort, and unsuitability for conforming and deformable applications. Hitherto, flexible (particularly elastic) nanocomposites have attracted enormous interest due to their excellent deformability. However, the current flexible shielding nanocomposites present low mechanical stability and resilience, relatively poor EMI shielding performance, and limited multifunctionality. Herein, the advances in low-dimensional EMI shielding nanomaterials-based elastomers are outlined and a selection of the most remarkable examples is discussed. And the corresponding modification strategies and deformability performance are summarized. Finally, expectations for this quickly increasing sector are discussed, as well as future challenges.

Recent Advances in Functional Nanomaterials for Diagnostic and Sensing Using Self-Assembled Monolayers

Functional nanomaterials have attracted attention by producing different structures in any field. These materials have several potential applications, including medicine, electronics, and energy, which provide many unique properties. These nanostructures can be synthesized using various methods, including self-assembly, which can be used for the same applications. This unique nanomaterial is increasingly being used for biological detection due to its unique optical, electrical, and mechanical properties, which provide sensitive and specific sensors for detecting biomolecules such as DNA, RNA, and proteins. This review highlights recent advances in the field and discusses the fabrication and characterization of the corresponding materials, which can be further applied in optical, magnetic, electronic, and sensor fields.

Preparation of a novel iron oxychloride (FeOCl) auxiliary electrode in promoting electrokinetic remediation of Cr(VI) contaminated soil: An experimental and DFT calculation analysis

The utilization of auxiliary electrode can improve substantially the electrokinetic remediation efficiency of heavy metal contaminated soil. The increase in the auxiliary electrode performance is the key to further promote the electrokinetic remediation efficiency. In this study, two kinds of auxiliary electrodes, pure FeOCl and doped FeOCl with W and S, were prepared and used in the electrokinetic remediation of Cr(VI) contaminated soil. The system equipped with the auxiliary electrode doped FeOCl brought more stable system current (202 mA) and more uniform electric field than blank group (130 mA). The reduction rate of Cr(VI) was increased by 50% due to the presence of Fe²⁺ and S^2-. The accelerating migration of ions by auxiliary electrode was responsible for the improvement in electrokinetic remediation efficiency. Density functional theory (DFT) calculation showed that Cl vacancy formation energies of pure FeOCl, S-doped FeOCl (S/FeOCl) and W-doped FeOCl (W/FeOCl) were 1.29, 1.15 and 1.49 eV respectively, and the ion diffusion barriers were 0.093, 0.099 and 0.148 eV respectively. Calculation results indicated that the doping of S was conducive to the diffusion of Cl ions, and the bonding of W-Cl was stronger than Fe-Cl. The charging and discharging process of auxiliary electrode became easier due to the formation of lower vacancy in S-doped FeOCl, which could bring a higher current for the electrokinetic remediation system. The electrochemical performance of FeOCl doped with W and S was improved obviously. This study provided a further explanation for the positive role of auxiliary electrode in electrokinetic remediation system.

Application of graphene aerogels in oil spill recovery: A review

Oil spills have long been a serious threat to marine environment. Physical recovery is the safest and most efficient method in the emergency disposal of offshore oil spill. Graphene aerogel (GA) has a wide application prospect in offshore oil spill emergency recovery and disposal given its unique structural characteristics. In this article, the preparation methods of GA adsorbent are summarized. On this basis, in the background of the application of offshore oil spill recovery, the related properties and targeted modification schemes of GA, such as adsorption, mechanical, and magnetic properties, as well as photothermal conversion properties for disposal of oil spills with high viscosity, are discussed. The Joule heating/photothermal conversion scheme can improve the recovery efficiency of offshore high viscosity oil spills, and adding metal composite materials can increase the magnetic performance and surface roughness of GA and facilitate positioning and recovery after offshore oil spills disposal. The challenges and prospects of modification research are also highlighted, and guidance for further optimizing the performance of GA in offshore oil spill recovery is provided.

Steady release-activation of hydrogen peroxide and molecular oxygen towards the removal of ciprofloxacin in the FeOCl/CaO2 system

Difficult storage of hydrogen peroxide (H₂O₂), low production of reactive oxygen species (ROS), and inefficient Fe(II)/Fe(III) recycling limit the application of the Fenton-like process. Calcium peroxide (CaO₂) based iron oxychloride (FeOCl) system was developed for solving these deficiencies, and ciprofloxacin (CIP) was effectively degraded within 20 min treatment. 0.33 mmol/L H₂O₂ and 2.4 mg/L dissolved oxygen (DO) were produced via CaO₂. Quenching experiments and electron paramagnetic resonance results confirmed that hydroxyl radicals (·OH) and superoxide anion (·O₂^-) worked as the main ROS. Density functional theory (DFT) calculations and experimental results suggested that H atoms of H₂O₂ adsorbed on FeOCl favored the activation of H₂O₂ into ·OH and DO into ·O₂^-, and electrophilic Cl and O coordination in FeOCl contributed to the cycle of Fe(II)/Fe(III). ·OH and·O₂^- were responsible for CIP degradation, and toxicity assessments demonstrated that the developed system reduced the hazard of treated solution. Clarity of FeOCl/CaO₂ system triple roles, including H₂O₂ and O₂ production, activation into ROS, and Fe(II)/Fe(III) recycling, facilitates the efficient utilization of O₂ in Fenton-like system.

Superelastic 3D Assembled Clay/Graphene Aerogels for Continuous Solar Desalination and Oil/Organic Solvent Absorption

Superelastic, arbitrary-shaped, and 3D assembled clay/graphene aerogels (CGAs) are fabricated using commercial foam as sacrificial skeleton. The CGAs possess superelasticity under compressive strain of 95% and compressive stress of 0.09-0.23 MPa. The use of clay as skeletal support significantly reduces the use of graphene by 50%. The hydrophobic CGAs show high solvent absorption capacity of 186-519 times its own weight. Moreover, both the compression and combustion methods can be adopted for reusing the CGAs. In particular, it is demonstrated a design of 3D assembled hydrophilic CGA equipped with salt collection system for continuous solar desalination. Due to energy recovery and brine transport management promoted by this design, the 3D assembled CGA system exhibits an extremely high evaporation rate of 4.11 kg m-2  h-1 and excellent salt-resistant property without salt precipitation even in 20 wt% brine for continuous 36 h illumination (1 kW m-2 ), which is the best reported result from the solar desalination devices. More importantly, salts can be collected conveniently by squeezing and drying the solution out of the salt collection system. The work provides new insights into the design of 3D assembled CGAs and advances their applications in continuous solar desalination and efficient oil/organic solvent adsorption.

Advances in magnetic field-assisted electrolyte's physicochemical properties and electrokinetic parameters: A case study on the response ability of chloramphenicol on Fe3O4@carbon spheres-based electrochemical nanosensor

Despite the utilization of external magnetic field (MF) in promoting the intrinsic unique features of magnetic nanomaterials in many different applications has been reported, however the origin of MF-dependent electrochemical behaviors as well as the electrochemical response of analytes at the electrode in sensor applications is still not clear. In this report, the influence of MF on the electrolyte's physicochemical properties (polarization, mass transport, charge/electron transfer) and electrode's properties (conductivity, morphology, surface area, interaction, adsorption capability, electrocatalytic ability) was thoroughly investigated. Herein, the working electrode surface was modified with carbon spheres (CSs), magnetic nanoparticles (Fe₃O₄NPs), and their nanocomposites (Fe₃O₄@CSs), respectively. Then, they were directly used to enhance the electrochemical characteristics and response-ability of chloramphenicol (CAP). More interestingly, a series of various kinetic parameters related to the diffusion-controlled process of K₃[Fe(CN)₆]/K₄[Fe(CN)₆)] and the adsorption-controlled process of CAP were calculated at the bare electrode and the modified electrodes with and without the presence of MF. These parameters not only exhibit the crucial role of the modification of electrode surface with the proposed materials but also show positive impacts of the presence of external MF. Besides, the mechanism and hypothesis for the enhancements were proposed and discussed in detail, further demonstrating the development potential of using Fe₃O₄@CS nanocomposites with MF assistant for advanced energy, environmental, and sensor related-applications.

In situ preparation of BiOCl0.75I0.25/g-C3N4-Cl in reduced graphene hydrogel photoanode for simultaneous removal of tetracycline hydrochloride and hexavalent chromium with efficient electricity generation

A novel three-dimensional porous photoanode of BiOCl_0.75I_0.25/g-C₃N₄-Cl/reduced graphene hydrogel (BOCI/CNCl/rGH) was successfully fabricated by a combined in-situ growth and re-dispersion strategy. It was verified that BOCI/CNCl composite exhibited photocatalytic efficiency, and the introduced rGH not only provided superior conductivity which was favorable for charge transfer, but also increased the specific surface area and reactive sites than the fluorine-doped tin oxide (FTO) coated glass. On the basis of these advantages, the short-circuit current and maximum power density were increased by 5.1 and 1.2 times, and the respective removal efficiency of tetracycline hydrochloride (TCH) and hexavalent chromium (Cr(VI)) was increased by 29% and 32% in BOCI/CNCl/rGH, comparing with BOCI/CNCl/FTO. Notably, the removal efficiencies could reach 87% and 85% in TCH and Cr(VI) coexistence system, which were higher than those in TCH or Cr(VI) alone system. This study provides a novel strategy for designing highly efficient photoanode for multiple pollutants removal and electricity generation.

Recent advances in engineering iron oxide nanoparticles for effective magnetic resonance imaging

Iron oxide nanoparticle (IONP) with unique magnetic property and high biocompatibility have been widely used as magnetic resonance imaging (MRI) contrast agent (CA) for long time. However, a review which comprehensively summarizes the recent development of IONP as traditional T₂ CA and its new application for different modality of MRI, such as T₁ imaging, simultaneous T₂/T₁ or MRI/other imaging modality, and as environment responsive CA is rare. This review starts with an investigation of direction on the development of high-performance MRI CA in both T₂ and T₁ modal based on quantum mechanical outer sphere and Solomon–Bloembergen–Morgan (SBM) theory. Recent rational attempts to increase the MRI contrast of IONP by adjusting the key parameters, including magnetization, size, effective radius, inhomogeneity of surrounding generated magnetic field, crystal phase, coordination number of water, electronic relaxation time, and surface modification are summarized. Besides the strategies to improve r₂ or r₁ values, strategies to increase the in vivo contrast efficiency of IONP have been reviewed from three different aspects, those are introducing second imaging modality to increase the imaging accuracy, endowing IONP with environment response capacity to elevate the signal difference between lesion and normal tissue, and optimizing the interface structure to improve the accumulation amount of IONP in lesion. This detailed review provides a deep understanding of recent researches on the development of high-performance IONP based MRI CAs. It is hoped to trigger deep thinking for design of next generation MRI CAs for early and accurate diagnosis.

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T₂ contrast capacity of iron oxide nanoparticles (IONPs) could be improved based on quantum mechanical outer sphere theory.

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IONPs could be expand to be used as effective T₁ CAs by improving q value, extending τ_s, and optimizing interface structure.

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Environment responsive MRI CAs have been developed to improve the diagnosis accuracy.

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Introducing other imaging contrast moiety into IONPs could increase the contrast efficiency.

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Optimizing in vivo behavior of IONPs have been proved to enlarge the signal difference between normal tissue and lesion.

A Highly Compressible and Stretchable Carbon Spring for Smart Vibration and Magnetism Sensors

Porous carbon materials demonstrate extensive applications for their attractive characteristics. Mechanical flexibility is an essential property guaranteeing their durability. After decades of research efforts, compressive brittleness of porous carbon materials is well resolved. However, reversible stretchability remains challenging to achieve due to the intrinsically weak connections and fragile joints of the porous carbon networks. Herein, it is presented that a porous all-carbon material achieving both elastic compressibility and stretchability at large strain from -80% to 80% can be obtained when a unique long-range lamellar multi-arch microstructure is introduced. Impressively, the porous all-carbon material can maintain reliable structural robustness and durability under loading condition of cyclic compressing-stretching process, similar to a real metallic spring. The unique performance renders it as a promising platform for making smart vibration and magnetism sensors, even capable of operating at extreme temperatures. Furthermore, this study provides valuable insights for creating highly stretchable and compressible porous materials from other neat inorganic components for diverse applications in future.

High-efficiency degradation of p-arsanilic acid and arsenic immobilization with iron encapsulated B/N-doped carbon nanotubes at natural solution pH

p-arsanilic acid (p-ASA) is still widely applied as feed additive in many countries. Accompanied with chemical reactions in the environment, p-ASA will release more toxic inorganic arsenic. In order to safely and efficiently treat p-ASA flow washing into the environment, iron encapsulated B/N-doped carbon nanotubes (Fe@C-NB) were fabricated and used as the catalyst for the degradation of p-ASA. The calcination temperature and the dose of the iron salt have significant effects on the structure and properties of the catalysts. We have produced a series of catalysts of the same type to facilitate the degradation of p-ASA. Under optimal conditions of material (Fe@C-NB) syntheses, both 95% degradation of p-ASA and 86% total arsenic immobilization can be obtained with oxidant (Peroxymonosulfate, PMS) and catalyst (Fe@C-NB) treatment after 60 min. The effects of oxidant types (peroxydisulfate (PDS), PMS, hydrogen peroxide (H₂O₂)), amount, initial solution pH, inorganic anion, and other reaction conditions were studied in the p-ASA removal. In this Fenton-like reaction, the Fe@C-NB exhibits high efficiency and excellent stability without complex preparation methods; besides, the advantages of short reaction time and natural reaction conditions in Fe@C-NB/PMS system will promote the practical application of Fenton-like.

Study of non-uniform axial magnetic field induced deformation of a soft cylindrical magneto-active actuator

Magneto-active polymers (MAPs) can undergo rapid and noticeable deformation through external wireless magnetic stimulation, offering a possibility to develop potential applications such as in actuators, flexible micro-grippers, soft robots, etc. In this paper, a theoretical model is presented to depict the relationship between nonlinear deformation and the external mechanical load applied on cylindrical samples in the presence of magnetic fields generated by an electromagnet. The geometrical and electromagnetic properties of the electromagnet are explicitly modeled in COMSOL Multiphysics based on the measured data. Furthermore, a finite element model is constructed to obtain detailed information (such as strain field), which cannot be obtained in experiments. The theoretical and simulation results fit quite well with the experimental results, showing the accuracy of the model construction. The proposed designing approach and model provide guidelines for researchers to enrich the applications of MAPs.

Progress in modifications of 3D graphene-based adsorbents for environmental applications

3D graphene-based materials are promising adsorbents for environmental applications. Furthermore, increasing attention has been paid to the improvement of 3D graphene adsorbents for removing pollutants. In this article, the progress in the modification of 3D graphene materials and their performance for removing pollutants were reviewed. The modification strategies, which were classified as (1) the activation with CO₂ (steam and other oxidants) and (2) the surface functionalization with polymers (metals, and metal oxides), were evaluated. The performances of modified 3D graphene materials were assessed for the removal of waste gases (such as CO₂), refractory organics, and heavy metals. The challenges and future research directions were discussed for the environmental applications of 3D graphene materials.

Sorption as a rapidly response for oil spill accidents: A material and mechanistic approach

Accidents involving oil transportation has increase due to directly connection with the elevation of global energy demand. The environmental losses are tremendous and brings huge economic issues to remediate the spilled oil. This report presents an up-to-date review on an overall aspects of oil spill remediation techniques, the fundamentals and advantages of sorption, the most applied materials through diverse types of oil spill sites and oils with variety features, highlight to natural materials and future prospective. As the environment preservation progressively becomes a major social concern issue, the achievement of a worldwide distribution process aligned with environmental legislation and economic viability is crucial to the oil industry. For this, a specific preparation considering several scenarios must be carried out regarding minimization of oil spillages. Since the sorbent materials are decisive for sorption, it was approached the main sorbents: natural, graphenic, nano, polymeric and waste materials, and future trends.

Selective adsorption of cesium (I) from water by Prussian blue analogues anchored on 3D reduced graphene oxide aerogel

In this paper, Prussian blue analogues (PBAs) anchored on 3D reduced graphene aerogel (denoted as 3D rGO/PBAs) was prepared, characterized and applied for adsorption of Cs(I) from aqueous solution. The results showed that 3D rGO/PBAs had high specific surface and good hydrophilic property, which was beneficial to the exposure of adsorptive sites and the transfer of adsorbates. The composite exhibited excellent adsorption performance towards Cs(I), and the maximum adsorption capacity was up to 204.9 mg/g, higher than most of reported values. The pseudo second-order kinetic model (R² = 0.999) and the Langmuir isotherm model (R² = 0.997) could fit the adsorption process well, suggesting the nature of homogeneous monolayer chemisorption. High distribution coefficients (k_d) (2.8 × 10⁴ to 5.8 × 10⁴ mL/g), revealed that the composite had good selectivity. Ion-exchange, ion trapping and the complexation interaction might be involved in the process of cesium adsorption, in which ion-exchange may be dominant by characterization results.

Flexible pressure sensors with high pressure sensitivity and low detection limit using a unique honeycomb-designed polyimide/reduced graphene oxide composite aerogel

It is still a challenge to fabricate flexible pressure sensors that possess high sensitivity, ultralow detection limit, wide sensing range, and fast response for intelligent electronic devices. We here demonstrate superelastic and highly pressure-sensitive polyimide (PI)/reduced graphene oxide (rGO) aerogel sensors with unique honeycomb structure, which were designed and fabricated using a bidirectional freezing technique. This unique honeycomb structure with large aspect ratio is composed of aligned thin lamellar layers and interconnected bridges. The combination of the aligned lamellar layers and the bridges endows the aerogel sensors with high pressure sensitivity (1.33 kPa^-1), ultralow detection limit (3 Pa), broad detection range (80% strain, 59 kPa), fast response time (60 ms), and excellent stability during cycling (over 1000 cycles). Remarkably, the aerogel sensors maintain stable piezoresistive performance at -50 °C, 100 °C, and 200 °C in air, indicating promising potential applications in harsh environments. Owing to the high sensitivity and wide sensing range, the aerogel sensors have been used to detect a full-range of human motion including small-scale motion monitoring (wrist pulse, blowing, puffing) and large-scale movement monitoring (finger bending, elbow bending, walking, running). These advantages make the composite aerogels attractive for high-performance flexible pressure sensors and wearable electronic devices.

The mechanical property and microscopic deformation mechanism of nanoparticle-contained graphene foam materials under uniaxial compression

Nanoparticle-contained graphene foams have found more and more practical applications in recent years, which desperately requires a deep understanding on basic mechanics of this hybrid material. In this paper, the microscopic deformation mechanism and mechanical properties of such a hybrid material under uniaxial compression, that are inevitably encountered in applications and further affect its functions, are systematically studied by the coarse-grained molecular dynamics simulation method. Two major factors of the size and volume fraction of nanoparticles are considered. It is found that the constitutive relation of nanoparticle filled graphene foam materials consists of three parts: the elastic deformation stage, deformation with inner re-organization and the final compaction stage, which is much similar to the experimental measurement of pristine graphene foam materials. Interestingly, both the initial and intermediate modulus of such a hybrid material is significantly affected by the size and volume fraction of nanoparticles, due to their influences on the microstructural evolution. The experimentally observed 'spacer effect' of such a hybrid material is well re-produced and further found to be particle-size sensitive. With the increase of nanoparticle size, the micro deformation mechanism will change from nanoparticles trapped in the graphene sheet, slipping on the graphene sheet, to aggregation outside the graphene sheet. Beyond a critical relative particle size 0.26, the graphene-sheet-dominated deformation mode changes to be a nanoparticle-dominated one. The final microstructure after compression of the hybrid system converges to two stable configurations of the 'sandwiched' and 'randomly-stacked' one. The results should be helpful not only to understand the micro mechanism of such a hybrid material in different applications, but also to the design of advanced composites and devices based on porous materials mixed with particles.

In situ reduced graphene-based aerogels embedded with gold nanoparticles for real-time humidity sensing and toxic dyes elimination

Hybrid aerogels are promising candidates for energy storage, biosensing, and medical applications, but the conventional fabrication methods, being time-consuming and complex, limit their widespread utilization. The critical issues affecting their functionality include the un-controllable particle dispersity, loading of active materials, and the porosity. We report a simple and efficient method to synthesize in situ reduced Au nanoparticles@graphene (Au@graphene) hybrid aerogel using near-infrared radiation (NIR), resulting the uniform loading of well-dispersed Au nanoparticles (Au-NPs) as well as in situ reduction of graphene oxide (GO) with enhanced conductivity. The concentration of iso-propylacrylamide and GO can be adjusted to control the aerogel pore size during the freeze-drying process. Reduction of HAuCl₄ and GO to high extent under NIR light was confirmed with advanced characterization techniques. Density functional theory based calculations with generalized gradient-corrected functional (GGA/PW91) in the hybrid aerogel system, and dnd basis sets are used for the confirmation of possible interactions between the GO, Au-NPs, and the polymer. The as-designed highly porous and conductive aerogel shows an excellent humidity response (30-97%) and successfully removes the methylene blue pollutant from the aqueous solution to a high extent (90%). Therefore, Au@graphene hybrid aerogel is potentially an exciting candidate for a wide range of applications in the humidity sensing and biomedical disease detection.

Multifunctional magnetic soft composites: a review

Magnetically responsive soft materials are soft composites where magnetic fillers are embedded into soft polymeric matrices. These active materials have attracted extensive research and industrial interest due to their ability to realize fast and programmable shape changes through remote and untethered control under the application of magnetic fields. They would have many high-impact potential applications in soft robotics/devices, metamaterials, and biomedical devices. With a broad range of functional magnetic fillers, polymeric matrices, and advanced fabrication techniques, the material properties can be programmed for integrated functions, including programmable shape morphing, dynamic shape deformation-based locomotion, object manipulation and assembly, remote heat generation, as well as reconfigurable electronics. In this review, an overview of state-of-the-art developments and future perspectives in the multifunctional magnetically responsive soft materials is presented.

Natural-based Hydrogels: A Journey from Simple to Smart Networks for Medical Examination

Natural hydrogels, due to their unique biological properties, have been used extensively for various medical and clinical examinations that are performed to investigate the signs of disease. Recently, complex-crosslinking strategies improved the mechanical properties and advanced approaches have resulted in the introduction of naturally derived hydrogels that exhibit high biocompatibility, with shape memory and self-healing characteristics. Moreover, the creation of self-assembled natural hydrogels under physiological conditions has provided the opportunity to engineer fine-tuning properties. To highlight recent studies of natural-based hydrogels and their applications for medical investigation, a critical review was undertaken using published papers from the Science Direct database. This review presents different natural-based hydrogels (natural, natural-synthetic hybrid and complex-crosslinked hydrogels), their historical evolution, and recent studies of medical examination applications. The application of natural-based hydrogels in the design and fabrication of biosensors, catheters and medical electrodes, detection of cancer, targeted delivery of imaging compounds (bioimaging) and fabrication of fluorescent bioprobes is summarised here. Without doubt, in future, more useful and practical concepts will be derived to identify natural-based hydrogels for a wide range of clinical examination applications.

3D-printed graphene/polymer structures for electron-tunneling based devices

Designing 3D printed micro-architectures using electronic materials with well-understood electronic transport within such structures will potentially lead to accessible device fabrication for 'on-demand' applications. Here we show controlled nozzle-extrusion based 3D printing of a commercially available nano-composite of graphene/polylactic acid, enabling the fabrication of a tensile gauge functioning via the readjustment of the electron-tunneling barrier width between conductive graphene-centers. The electronic transport in the graphene/polymer 3D printed structure exhibited the Fowler Nordheim mechanism with a tunneling width of 0.79-0.95 nm and graphene centers having a carrier concentration of 2.66 × 10¹²/cm². Furthermore, a mechanical strain that increases the electron-tunneling width between graphene nanostructures (~ 38 nm) by only 0.19 Ǻ reduces the electron flux by 1e/s/nm² (from 18.51 to 19.51 e/s/nm²) through the polylactic acid junctions in the 3D-printed heterostructure. This corresponds to a sensitivity of 2.59 Ω/Ω%, which compares well with other tensile gauges. We envision that the proposed electron-tunneling model for conductive 3D-printed structures with thermal expansion and external strain will lead to an evolution in the design of next-generation of 'on-demand' printed electronic and electromechanical devices.

Electromagnetic Interference Shielding of Graphene Aerogel with Layered Microstructure Fabricated via Mechanical Compression

Graphene aerogel is a promising electromagnetic interference (EMI) shielding material because of its light weight, excellent electrical conductivity, uniform three-dimensional (3D) microporous structure, and good mechanical strength. The graphene aerogel with high EMI shielding performance is attracting considerable critical attention. In this study, a novel procedure to fabricate high EMI shielding graphene aerogel was presented, inspired by the irreversible deformation of hydrogels under mechanical pressure. The procedure involved a mechanical compression step on graphene hydrogels for the purpose of altering microstructures followed by freeze-drying and thermal annealing at 900 °C to generate the final products. Because of the flow of internal liquid caused by mechanical compression, the microstructures of hydrogels changed from a cellular configuration to a layered configuration. After a high degree of compression, GAs can be endowed with homogeneous layered structure and high density, which plays a leading role in electromagnetic wave dissipation. Consequently, the aerogels with excellent electrical conductivity (181.8 S/m) and EMI shielding properties (43.29 dB) could be obtained. Besides, the compression process enabled us to form complex hydrogel shapes via different molds. This method enhances the formability of graphene aerogels and provides a robust way to control the microstructure.

Rapid Synthesis of Porous Graphene Microspheres through a Three-Dimensionally Printed Inkjet Nozzle for Selective Pollutant Removal from Water

Graphene microspheres are fabricated through a 3D-printed inkjet nozzle based on the gas-liquid microfluidic method. This method realizes rapid and controllable fabrication of uniform graphene microspheres with up to 800 μL min^-1 (ca. 1 L d^-1) of yields, which is 2 orders of magnitude higher than those of the conventional microfluidic method. The diameter of the graphene microspheres could be flexibly controlled from 0.5 to 3.5 mm by adjusting the gas pressure. The porous graphene microspheres show great dye decoloration performance. The maximum adsorption capacity of methylene blue is 596 mg/g, which is the highest adsorption capacity among that of the reduced graphene-oxide absorbents. A performance improvement of 21% is obtained by applying sodium alginate into graphene as a curing agent. The adsorption behavior follows a Langmuir isotherm and pseudo-second-order kinetic model. Besides, the graphene microspheres exhibit great selective adsorption and could separate cationic dye methylene blue (MB) and anionic dye methyl orange (MO).

Flexible Ferrofluids: Design and Applications

Ferrofluids, also known as ferromagnetic particle suspensions, are materials with an excellent magnetic response, which have attracted increasing interest in both industrial production and scientific research areas. Because of their outstanding features, such as rapid magnetic reaction, flexible flowability, as well as tunable optical and thermal properties, ferrofluids have found applications in various fields, including material science, physics, chemistry, biology, medicine, and engineering. Here, a comprehensive, in-depth insight into the diverse applications of ferrofluids from material fabrication, droplet manipulation, and biomedicine to energy and machinery is provided. Design of ferrofluid-related devices, recent developments, as well as present challenges and future prospects are also outlined.

An advanced sol-gel strategy for enhancing interfacial reactivity of iron oxide nanoparticles on rosin biochar substrate to remove Cr(VI)

The application of iron oxide nanoparticles (IONs) is often limited by agglomeration and low loading. Here, we presented a facile phase change material (PCM) -based sol-gel strategy for the fabrication of α-Fe₂O₃ nanoparticles. Rosin was used as the PCM in the sol-gel process and the carbon-based substrate of α-Fe₂O₃ nanoparticles in the thermal process. The α-Fe₂O₃ nanoparticle embedded rosin-derived biochar(α-Fe₂O₃@HrBc)were highly dispersed. The dispersity of α-Fe₂O₃ nanoparticle could be regulated by the weight ratios of rosin to FeCl₃·6H₂O during the preparation, as evidenced by the scanning electron microscope (SEM) spectrum and the sorption capacity results. Among a series of α-Fe₂O₃@HrBc nanocomposites, the one with the weight ratios of 1/1.5 rosin/FeCl₃·6H₂O had the highest capacity for hexavalent chromium (Cr(VI)) sorption. This phenomenon can be ascribed to a remarkably enhanced interfacial reactivity due to an increase in the dispersity of α-Fe₂O₃ nanoparticle. In addition, SEM showed that the majority of α-Fe₂O₃ nanoparticles was dispersed on and inside the biochar substrate. Batch adsorption experiments revealed that the α-Fe₂O₃@HrBc adsorbed 90% Cr(VI) within one minute, and the maximum capacity was up to 166 mg·g^-1 based on the Langmuir model. The FTIR and XPS spectra revealed that the adsorbed Cr(VI) species were partially reduced to less toxic Cr(III). Considering that α-Fe₂O₃ nanoparticles provided important sorption sites, the newly formed Cr(III) and the remaining Cr(VI) ions could be adsorbed on α-Fe₂O₃@HrBc via the formation of FeCr coprecipitation.

Versatile Aerogels for Sensors

Aerogels are unique solid-state materials composed of interconnected 3D solid networks and a large number of air-filled pores. They extend the structural characteristics as well as physicochemical properties of nanoscale building blocks to macroscale, and integrate typical characteristics of aerogels, such as high porosity, large surface area, and low density, with specific properties of the various constituents. These features endow aerogels with high sensitivity, high selectivity, and fast response and recovery for sensing materials in sensors such as gas sensors, biosensors and strain and pressure sensors, among others. Considerable research efforts in recent years have been devoted to the development of aerogel-based sensors and encouraging accomplishments have been achieved. Herein, groundbreaking advances in the preparation, classification, and physicochemical properties of aerogels and their sensing applications are presented. Moreover, the current challenges and some perspectives for the development of high-performance aerogel-based sensors are summarized.

Graphene Aerogel Broken to Fragments for a Piezoresistive Pressure Sensor with a Higher Sensitivity

The porous and elastic reduced graphene aerogel (rGA) is a promising active material for piezoresistive pressure sensors (PRSs) to realize an electronic skin. Due to the specific working mechanism and the limitation of the rGA's monolithic conductive network, the PRSs based on rGA suffer from a limited change of resistance with mechanical deformation, so they show poor sensitivity and cannot detect low pressures. Here we aim to improve the sensitivity of the PRS and make it suitable for a low-pressure system (0.5-8 kPa) through an effective method. The monolithic rGA is broken into small pieces by cutting (named as CGA). The sensitivity of the PRS based on CGA can be improved by 10 times that of the uncut rGA (named as UCGA). The resistance variation ratio of CGA (0.96) is 1.45 times of the resistance variation ratio of the UCGA (0.66). By using a package of elastic polypropylene thin films (PP), the cycle stability performance of CGA remains stable after 4200 cycles. The CGA can detect the pulse of a human being with sensitivity higher than the UCGA and the ordinary sensors. This method is simple, effective, and universal to improve the sensitivity of PRS based on porous and elastic materials.

3D Printing of Ultralight Biomimetic Hierarchical Graphene Materials with Exceptional Stiffness and Resilience

Biological materials with hierarchical architectures (e.g., a macroscopic hollow structure and a microscopic cellular structure) offer unique inspiration for designing and manufacturing advanced biomimetic materials with outstanding mechanical performance and low density. Most conventional biomimetic materials only benefit from bioinspired architecture at a single length scale (e.g., microscopic material structure), which largely limits the mechanical performance of the resulting materials. There exists great potential to maxime the mechanical performance of biomimetic materials by leveraging a bioinspired hierarchical structure. An ink-based three-dimensional (3D) printing strategy to manufacture an ultralight biomimetic hierarchical graphene material (BHGMs) with exceptionally high stiffness and resilience is demonstrated. By simultaneously engineering 3D-printed macroscopic hollow structures and constructing an ice-crystal-induced cellular microstructure, BHGMs can achieve ultrahigh elasticity and stability at compressive strains up to 95%. Multiscale finite element analyses indicate that the hierarchical structures of BHGMs effectively reduce the macroscopic strain and transform the microscopic compressive deformation into the rotation and bending of the interconnected graphene flakes. This 3D printing strategy demonstrates the great potential that exists for the assembly of other functional materials into hierarchical cellular structures for various applications where high stiffness and resilience at low density are simultaneously required.

Biochar-supported magnetic noble metallic nanoparticles for the fast recovery of excessive reductant during pollutant reduction

The catalytic reduction of diverse pollutants by noble metal catalysts in the presence of reductants is a highly effective and widely used method. However, the considerable cost of noble metal catalysts impedes the practical application of this method, and the recovery of excessive reductants has not been reported previously. In this work, we prepared inexpensive biochar-supported magnetic noble metallic nanoparticles (NPs) and efficiently recovered the excessive reductants in the form of H₂. The as-synthesized biochar-supported noble metallic NPs exhibited high H₂ recovery during the 4-nitrophenol reduction reaction. Results showed that the catalysts with low noble metallic content have higher H₂ recovery rate than commercial Pd/C, Ag/C, and Pt/C. The catalytic mechanism of magnetic biochar-supported noble metallic NPs was demonstrated to be a "synergetic effect", where biochar and Fe₃O₄ acted as accelerants that enable noble metallic NPs to produce active hydrogen for the reduction reaction, and the excess active hydrogen atoms combined to form H₂.

Large-area superelastic graphene aerogels based on a room-temperature reduction self-assembly strategy for sensing and particulate matter (PM2.5 and PM10) capture

Graphene aerogels are emerging low density and superelasticity macroscopic porous materials with various applications. However, it still remains a challenge to develop a versatile strategy under ambient conditions for fabricating large-area, high-performance graphene aerogels, which is crucial for their practical applications. Here, we report a novel room-temperature reduction self-assembly (RTRS) strategy to fabricate large-area graphene aerogels under ambient conditions. The strategy is based on using unique hydrazine hydrates as reducing agents to generate stable microbubbles beneficial for the formation of macroporous graphene hydrogels. Interestingly, the resultant hydrogel followed by a simple pre-freeze treatment can be naturally dried into graphene aerogels without noticeable volume shrinkage or structure cracking. Benefiting from the mild conditions, a large-area graphene aerogel with a diameter of up to 27 cm was prepared as an example. The as-formed aerogels exhibit a stable honeycomb-like coarse-pores structure, a low density of 3.6 mg cm-3 and superelasticity (rapidly recoverable from 95% compression) which are suitable for pressure/strain sensors. Moreover, the aerogel exhibits superior particulate matter adsorption efficiency (PM2.5: 93.7%, PM10: 96.2%) and good recycling ability. Importantly, the preparation process is cost-effective and easily scalable without the need for any special drying techniques and heating processes, which provides an ideal platform for mass production of graphene aerogels toward practical applications.

Multifunctional Photo- and Magnetoresponsive Graphene Oxide-Fe3O4 Nanocomposite-Alginate Hydrogel Platform for Ice Recrystallization Inhibition

Tuning ice recrystallization (IR) has attracted tremendous interest in fundamental research and a variety of practical applications, including food and pharmaceutical engineering, fabrication of anti-icing coating and porous materials, and cryopreservation of biological cells and tissues. Although great efforts have been devoted to modulation of IR for better microstructure control of various materials, it still remains a challenge, especially in cryopreservation, where insufficient suppression of IR during warming is fatal to the cells. Herein, we report an all-in-one platform, combining the external physical fields and the functional materials for both active and passive suppression of IR, where the photo- and magnetothermal dual-modal heating of GO-Fe₃O₄ nanocomposites (NCs) can be used to suppress IR with both enhanced global warming and microscale thermal disturbance. Moreover, the materials alginate hydrogels and GO-Fe₃O₄ NCs can act as IR inhibitors for further suppression of the IR effect. As a typical application, we show that this GO-Fe₃O₄ nanocomposite-alginate hydrogel platform can successfully enable low-cryoprotectant, high-quality vitrification of stem cell-laden hydrogels. We believe that the versatile ice recrystallization inhibition platform will have a profound influence on cryopreservation and tremendously facilitate stem cell-based medicine to meet its ever-increasing demand in clinical settings.

Shaping the Assembly of Superparamagnetic Nanoparticles

Superparamagnetism exists only in nanocrystals, and to endow micro/macro-materials with superparamagnetism, superparamagnetic nanoparticles have to be assembled into complex materials. Most techniques currently used to produce such assemblies are inefficient in terms of time and material. Herein, we used evaporation-guided assembly to produce superparamagnetic supraparticles by drying ferrofluid droplets on a superamphiphobic substrate in the presence of an external magnetic field. By tuning the concentration of ferrofluid droplets and controlling the magnetic field, barrel-like, cone-like, and two-tower-like supraparticles were obtained. These assembled supraparticles preserved the superparamagnetism of the original nanoparticles. Moreover, other colloids can easily be integrated into the ferrofluid suspension to produce, by co-assembly, anisotropic binary supraparticles with additional functions. Additionally, the magnetic and anisotropic nature of the resulting supraparticles was harnessed to prepare magnetically actuable microswimmers.

Preparation of Graphene Aerogel with High Mechanical Stability and Microwave Absorption Ability via Combining Surface Support of Metallic-CNTs and Interfacial Cross-Linking by Magnetic Nanoparticles

The preparation of graphene aerogel by hydrothermal or chemical reduction has been one of the hot topics of research. But in the process of assembly, the random weak connection of GO flakes leads to irreversible deformation under compression, and the mechanical stability of aerogel based on graphene is one of its drawbacks that is hard to overcome. Here, a novel method to prepare graphene aerogel with high mechanical stability was proposed via combining surface support brought by metallic-CNT networks and interfacial cross-linking of GO sheets achieved by nanoparticle selective absorption. Thoroughly dispersed metallic-CNTs absorbed on the basal plane of GO flakes formed continuous network structures, which not only improve the mechanical performance of flakes but also provide steric effects to impel the adsorption of metallic oxide magnetic nanoparticles concentrated on the edge of GO flakes, thereby guaranteeing the interfacial connection of adjacent rGO flakes by nanoparticle cross-linking. Meanwhile, the surface and interface reinforce approach can greatly improve the electrical conductivity and mechanical stability of composites. Owing to the light weight, abundant interface, high electrical conductivity, combined with the superparamagnetic properties brought by the magnetic nanoparticles, composite aerogel with high mechanical stability and excellent microwave absorption was achieved, of which the effective absorption bandwidth of the aerogel is 4.4-18 GHz and the maximum value can reach -49 dB. This approach could not only be used to prepare microwave absorption materials with light weight and high performance but also be meaningful to enlarge the construction and application of carbon-based materials.

Tuning Pb(II) Adsorption from Aqueous Solutions on Ultrathin Iron Oxychloride (FeOCl) Nanosheets

Structural tunability and surface functionality of layered two-dimensional (2-D) iron oxychloride (FeOCl) nanosheets are critical for attaining exceptional adsorption properties. In this study, we combine computational and experimental tools to elucidate the distinct adsorption nature of Pb(II) on 2-D FeOCl nanosheets. After finding promising Pb(II) adsorption characteristics by bulk FeOCl sheets (B-FeOCl), we applied computational quantum mechanical modeling to mechanistically explore Pb(II) adsorption on representative FeOCl facets. Results indicate that increasing the exposure of FeOCl oxygen and chlorine sites significantly enhances Pb(II) adsorption. The (110) and (010) facets of FeOCl possess distinct orientations of oxygen and chlorine, resulting in different Pb(II) adsorption energies. Consequently, the (110) facet was found to be more selective toward Pb(II) adsorption than the (010) facet. To exploit this insight, we exfoliated B-FeOCl to obtain ultrathin FeOCl nanosheets (U-FeOCl) possessing unique chlorine- and oxygen-enriched surfaces. As we surmised, U-FeOCl nanosheets achieved excellent Pb(II) adsorption capacity (709 mg g^-1 or 3.24 mmol g^-1). Moreover, U-FeOCl demonstrated rapid adsorption kinetics, shortening adsorption equilibration time to one-third of the time for B-FeOCl. Extensive characterization of FeOCl-Pb adsorption complexes corroborated the simulation results, illustrating that increasing the number of Pb-O and Pb-Cl interaction sites led to the improved Pb(II) adsorption capacity of U-FeOCl.

Highly conductive, mechanically strong graphene monolith assembled by three-dimensional printing of large graphene oxide

The manufacturing of three-dimensional (3D) graphene monolith with high mechanical and electrical performance has become an urgent issue in view of their potential applications in energy and electronics fields. Due to the structure rigidity and poor liquid-phase processing capability of graphene sheets, it is challenging to fabricate 3D graphene monolith with high mechanical performance, including strength, toughness and resiliency. Graphene oxide (GO) shows an improved dispersibility and reduction-restorable conductivity, which enables it to effectively balance the processing and comprehensive performances of graphene monolith. Here, we demonstrate a strategy to fabricate high-performance, shape-designable 3D graphene monolith through a 3D printing method based on large-sized graphene oxide (LGO) fluid ink. The concentration of the LGO ink for printing is as low as 20 mg/mL. The resulting monolith exhibits low density (12.8 mg/cm³), high electrical conductivity (41.1 S/m), high specific strength (10.7 × 10³ N·m/Kg) and compressibility (up to 80% compressive strain). Such a 3D printing technique enables plenty of complicated monolith structures and broadens the application range of graphene.