Porous Templates Research Articles

Macroscale Fabrication of Lightweight and Strong Porous Carbon Foams through Template-Coating Pair Design.

Manufacturing of low-density-high-strength carbon foams can benefit the construction, transportation, and packaging industries. One successful route to lightweight and mechanically strong carbon foams involves pyrolysis of polymeric architectures, which is inevitably accompanied by drastic volumetric shrinkage (usually >98%). As such, a challenge of these materials lies in maintaining bulk dimensions of building struts that span orders of magnitude difference in length scale from centimeters to nanometers. This work demonstrates fabrication of macroscale low-density-high-strength carbon foams that feature exceptional dimensional stability through pyrolysis of robust template-coating pairs. The template serves as the architectural blueprint and contains strength-imparting properties (e.g., high node density and small strut dimensions); it is composed of a low char-yielding porous polystyrene backbone with a high carbonization-onset temperature. The coating serves to imprint and transcribe the template architecture into pyrolytic carbon; it is composed of a high char-yielding conjugated polymer with a relatively low carbonization-onset temperature. The designed carbonization mismatch enables structural inheritance, while the decomposition mismatch affords hollow struts, minimizing density. The carbons synthesized through this new framework exhibit remarkable dimensional stability (≈80% dimension retention; ≈50% volume retention) and some of the highest specific strengths (≈0.13GPa g-1 cm3 ) among reported carbon foams derived from porous polymer templates.

Salt-template-assisted melt-processed porous poly (vinylidene fluoride) nanocomposites for highly efficient all-day passive radiative cooling

• Porous PVDF composite sheet (PPCS) was fabricate by scalable melt-processing using cheap micron-scale table salts as pore templates and nano-alumina as fillers. • PPCS exhibits high solar reflectivity of 91.8% and high infrared emittance of 94.3%, enabling sub-ambient daytime/nighttime radiative cooling of 8.3 °C/12.0 ℃. • PPCS has satisfied strength, hydrophobic self-cleaning, and flame retardance for practical application. • This work provides a low-cost, organic-solvent-free strategy to fabricate thick PDRC materials. Passive daytime radiative cooling (PDRC) has recently attracted tremendous attention as one promising thermal management strategy. However, a large amount of hazardous organic solvent is usually used for fabricating most PDRC materials, increasing the manufacturing cost and posing serious environmental problems. Here, a scalable melt-processed approach was adopted to fabricate porous poly (vinylidene fluoride) composite sheet (PPCS) using cheap micron-scale table salts as pore templates and nano-alumina as fillers. The obtained PPCS exhibits a high solar reflectivity (91.8 %) and high infrared emittance (94.3 %), enables an efficient sub-ambient daytime radiative cooling of 8.3 °C with a cooling power of 61.7 W·m -2 and nighttime cooling of 12.0 ℃ with a cooling power of 148.3 W·m -2 . In addition, PPCS has satisfied strength, hydrophobic self-cleaning, and flame retardance for practical application. This work provides a scalable, low-cost, organic-solvent-free approach to fabricate PDRC materials with varying thickness from micron scale to centimeter scale.

A REVIEW OF THE DEVELOPMENT OF THE GEL CASTING METHOD FOR POROUS CERAMIC FABRICATION

The objective of this paper is to present an overview of the development of gel casting methods on synthesis techniques and the characteristics of gel casting porous ceramics and its applications. The gel casting method is a colloidal ceramic synthesis method that requires a short period for the ceramic body to develop. This review provides the latest developments in the gel casting process of synthesizing porous ceramics. At the beginning of the gel casting method development, the acrylamide (AM) system was the most commonly utilized system. Over time, the use of the AM system began to be minimized because of its toxicity. Researchers began to develop natural polymers as pore templates and natural minerals as raw materials in the gel casting method. In addition to polymers and raw materials, the gel casting process also requires additives such as gelling agents and dispersants. At the end of this review, a mapping of how to select the additives in the gel casting process, for AM systems and non-AM systems for the fabrication of porous ceramics is presented. The characteristic of porous ceramics produced by AM and non-AM systems are almost similar. Porous ceramic applications have been used as bone tissue supports, energy storage, filters, and catalyst support. This review will be a reference for future research related to the process of fabrication of advanced porous ceramics using the environmentally friendly gel casting method.

Preferred catalysis distinctly determined by metals doped with nitrogen in three-dimensionally ordered porous carbon materials.

Three-dimensionally ordered nanoporous structures were generated in carbon materials doped with metals and nitrogen as catalytically active sites for electrochemical reactions. Free-base and metal phthalocyanines with a strategically designed molecular structure were used as carbon sources to obtain an ordered porous structure via homogeneous self-assembly with Fe3O4 nanoparticles as the pore template and the prevention of melting away during carbonization. The doping of Fe and nitrogen was achieved by a reaction between the free-base phthalocyanine and Fe3O4 through carbonization at 550 °C, while Co and Ni were doped using the corresponding metal phthalocyanines. The preference of these three types of ordered porous carbon materials for catalytic reactions was distinctly determined by the doped metals. Fe-N-doped carbon showed the highest activity for O2 reduction. Additional heat treatment at 800 °C enhanced this activity. CO2 reduction and H2 evolution were preferred by the Ni- and Co-N-doped carbon materials, respectively. A change in the template particle size was capable of controlling the pore size to enhance mass transfer and improve performance. The technique presented in this study enabled systematic metal doping and pore size control in the ordered porous structures of carbonaceous catalysts.

Influence of junction resistance on spatiotemporal dynamics and reservoir computing performance arising from an SWNT/POM 3D network formed via a scaffold template technique.

For scientists in numerous fields, creating a physical device that can function like the human brain is an aspiration. It is believed that we may achieve brain-like spatiotemporal information processing by fabricating an in materio reservoir computing (RC) device because of a complex random network topology with nonlinear dynamics. One of the significant drawbacks of a two-dimensional physical reservoir system is the difficulty in controlling the network density. This work reports the use of a 3D porous template as a scaffold to fabricate a three-dimensional network of a single-walled carbon nanotube polyoxometalate nanocomposite. Although the three-dimensional system exhibits better nonlinear dynamics and spatiotemporal dynamics, and higher harmonics generation than a two-dimensional system, the results suggest a correlation between a higher number of resistive junctions and reservoir performance. We show that by increasing the spatial dimension of the device, the memory capacity improves, while the scale-free network exponent (γ) remains nearly unchanged. The three-dimensional device also displays improved performance in the well-known RC benchmark task of waveform generation. This study demonstrates the impact of an additional spatial dimension, network distribution and network density on in materio RC device performance and tries to shed some light on the reason behind such behavior.

Fe3O4-SiO2 Mesoporous Core/Shell Nanoparticles for Magnetic Field-Induced Ibuprofen-Controlled Release.

Hybrid magnetic nanoparticles made up of an iron oxide, Fe3O4, core and a mesoporous SiO2 shell with high magnetization and a large surface area were proposed as an efficient drug delivery platform. The core/shell structure was synthesized by two seed-mediated growth steps combining solvothermal and sol-gel approaches and using organic molecules as a porous scaffolding template. The system presents a mean particle diameter of 30(5) nm (9 nm magnetic core diameter and 10 nm silica shell thickness) with superparamagnetic behavior, saturation magnetization of 32 emu/g, and a significant AC magnetic-field-induced heating response (SAR = 63 W/gFe3O4, measured at an amplitude of 400 Oe and a frequency of 307 kHz). Using ibuprofen as a model drug, the specific surface area (231 m2/g) of the porous structure exhibits a high molecule loading capacity (10 wt %), and controlled drug release efficiency (67%) can be achieved using the external AC magnetic field for short time periods (5 min), showing faster and higher drug desorption compared to that of similar stimulus-responsive iron oxide-based nanocarriers. In addition, it is demonstrated that the magnetic field-induced drug release shows higher efficiency compared to that of the sustained release at fixed temperatures (47 and 53% for 37 and 42 °C, respectively), considering that the maximum temperature reached during the exposure to the magnetic field is well below (31 °C). Therefore, it can be hypothesized that short periods of exposure to the oscillating field induce much greater heating within the nanoparticles than in the external solution.

Current density-induced emergence of soft and hard magnetic phases in Fe nanowire arrays

The capability of generating magnetically soft and hard phases in a material is important in many aspects, ranging from basic science to applications. Here, the emergence of soft and hard magnetic phases is reported in Fe nanowire (NW) arrays with a diameter of 35 nm fabricated by using a pulsed electrochemical deposition method in porous aluminum oxide templates under different current density (C d ) values in the range of 25–100 mA cm−2. The variation of C d influences the grain size, crystallinity, electrodeposition efficiency and length of the Fe NWs, as characterized by x-ray diffraction, high-resolution transmission electron microscopy, vibrating sample magnetometry and field-emission scanning electron microscopy. Increasing C d from 25 to 80 mA cm−2 results in a significant decrease in coercivity and squareness from 1590 to 900 Oe and 0.9 to 0.5, respectively, inducing the soft and hard phases along the length of Fe NWs. Further increasing the C d leads to the separation of the phases, as evidenced by first-order reversal curve analysis. From a theoretical aspect, the emergence of the soft phase may lead to the occurrence of the fanning reversal mode in the NWs, for which there is no precedent in previous experimental investigations.

Small-sized Ag nanoparticle stacked films promoted by sustainedly released surfactants for plasmonic broadband super absorption

Large-area, highly absorptive films stacked of uniform Ag nanoparticles (AgNPs) with sub-20 nm size were fabricated by magnetron sputtering at the presence of adhesive tape, during which O-containing compounds were sustainedly released from the adhesive glue that acted as gaseous surfactants to promote the nucleation and simultaneously suppress the coalescence of the AgNPs. Plasmonic absorbers of metal-insulator-metal (MIM) configuration with a gradient-thickness insulator layer were constructed by conformally depositing such small-sized AgNP stacked films (S-AgSFs) on alumina templates with V-shaped nanopores. The broadband optical impedance matching of this novel MIM structure enables broadband light absorption from ultraviolet to near-infrared region, by working together with the large absorption cross-section, strong interparticle plasmon coupling of closely stacking small-sized AgNPs, and the light-trapping effect of the porous template. The average absorbance reaches 96.8 % in the visible region and 86.7 % in the 200–1600 nm range, respectively, showing the great potential of this absorber for applications in antireflection, solar energy harvesting and utilizing, etc. This adhesive-tape-assisted physical vapor deposition approach is simple, cost-effective, and can be applied to various types of substrates, which will enrich the fabrication strategy of metal nanostructures with effectively controlled geometries and optical properties.

Electrodeposited PPy@TiO2 and PEDOT@TiO2 Counter Electrodes for [Co(bpy)3]2+/3+ Redox Mediator-Based Dye-Sensitized Solar Cells

The main goal of this work is to enhance the catalytic performance of PPy and PEDOT films toward the Co2+/Co3+ redox couple. PPy and PEDOT films were electrodeposited separately on a porous TiO2 template to assess their suitability as alternative catalysts in dye-sensitized solar cells (DSSC) based on the [Co(bpy)3]2+/3+ redox shuttle. The obtained PPy@TiO2 and PEDOT@TiO2 counter electrodes displayed much rougher surfaces. Electrochemical studies indicate the superior catalytic activity of both the electrodeposited electrodes toward Co3+ reduction, as indicated by lower charge transfer resistance than that of pristine films and even that of Pt electrodes. Therefore, the fabricated DSSC devices with these counter electrodes achieved higher power conversion efficiencies compared to cells with pristine PPy and PEDOT counter electrodes, or even with a Pt counter electrode. Interestingly, the assembled DSSC device with a PEDOT@TiO2 counter electrode displayed the highest performance among all with a power conversion efficiency of 6.62%, which is better than that obtained by the device with a Pt electrode (6.07%).

Vertically Oriented Porous PET as Template to Integrated Metal Halide for High-Performance Large-Area and Ultra-Flexible X-Ray Detector.

High-performance X-ray detectors have immense potential in medical and security inspections. However, the current X-ray detectors are limited in flexible, high-spatial-resolution large-scale detection, and integration for imaging. Here, nuclear track-etched porous polyethylene terephthalate (PET) is developed as the template for preparing uniform, large-area (≥105 cm2 ), and flexible metal halide (MH)-based X-ray detectors. Adjustable high-density vertically oriented porous PET with adjustable thickness can provide proper physical support for flexible thick absorption film, thus improving X-ray absorption ability with excellent bending stability. Moreover, vertical channels can block the ion migration, lateral charge diffusion, and water/oxygen attacks, increasing activation energy for ionic transport, charge collection rate of electrodes, and environmental stability. Hence, the related detectors eventually obtain large sensitivity (6722 µC Gyair -1 cm-2 ), low detection limit (1.87 nGyair s-1 ), and high spatial resolution (5.17 lp mm-1 ) compared to the detectors without porous PET template. Meanwhile, the device shows no degradation after storage or working under various thermal attacks. MH-filled-PET is also monolithically integrated on the bottom circuit with different MHs and it is applied to single-pixel mode and fast linear-array imaging in a broad range of X-rays photon energy (20 to 160keV).

Ultrathin CoOOH/Co(OH)2 hybrid nanosheets for high-performance anodes of lithium-ion batteries

CoOOH and Co(OH)2 have great potential in lithium-ion battery anodes due to their high theoretical specific capacities. But they suffer from large volume change during the cycle and hence display fast capacity fading. Carbon coated ultrathin two-dimensional porous nanostructure engineering can be conducive to improving cycling stability of both CoOOH and Co(OH)2, but it is a huge challenge. Herein, a tetraethyl orthosilicate (TEOS) assisted synthesis of carbon coated ultrathin porous CoOOH/Co(OH)2 hybrid nanosheets (COH@C NSs) has been proposed and achieved successfully. This original idea using the TEOS as the reactant not only constructs the ultrathin two-dimensional nanosheets as a structure directing reagent but also forms a porous structure as a precursor of SiO2 pore templates. As a result, the COH@C NSs integrate the advantages of ultrathin two-dimensional nanosheets, porous structure and carbon coating, and hence have significantly improved structural stability and electrochemical kinetics during the cycle, delivering 845.3 mA h g−1 in 350th cycle at 200 mA g−1 and 696.2 mA h g−1 in 400th cycle at 1000 mA g−1. This work gives a unique insight for engineering ultrathin two-dimensional porous nanostructure of high-capacity CoOOH/Co(OH)2 hybrid electrode.

Temperature dependence of magnetic anisotropy in a cylindrical Fe65Pd35 nanowire array

Fe65Pd35 cylindrical nanowires (NWs) were synthesized in commercial anodic alumina porous templates via potentiostatic electrodeposition. The morphology, composition, and crystalline structure were analyzed by scanning and transmission electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction. The NWs obtained are (10 ± 2) μm long and (200 ± 20) nm in diameter, with a polycrystalline microstructure. Magnetic properties were investigated by measuring the Zero Field Cooling-Field Cooling magnetization curves and hysteresis loops in the temperature range 10 K to 350 K. The magnetization easy axis is determined to be along the NWs axis, indicating strong anisotropy in this direction, which cannot be accounted for by only considering shape anisotropy. The hysteresis loops were fitted using the law of approach to saturation, obtaining the effective anisotropy field HA and the effective anisotropy constant Keff value for different temperatures. The blocking temperature TB dependence on the magnetic field H was also analyzed, indicating that a blocked magnetic contribution is present, arising from the smaller grains in the NWs. The observed enhancement in the effective magnetic anisotropy of the array throughout the studied temperature range is explained by considering magnetic interactions among these nanograins.

Growth of Highly-Ordered Metal Nanoparticle Arrays in the Dimpled Pores of an Anodic Aluminum Oxide Template.

A reliable, scalable, and inexpensive technology for the fabrication of ordered arrays of metal nanoparticles with large areal coverage on various substrates is presented. The nanoparticle arrays were formed on aluminum substrates using a two-step anodization process. By varying the anodization potential, the pore diameter, inter-pore spacing, and pore ordering in the anodic aluminum oxide (AAO) template were tuned. Following a chemical etch, the height of the pores in the AAO membrane were reduced to create a dimpled membrane surface. Periodic arrays of metal nanoparticles were subsequently created by evaporating metal on to the dimpled surface, allowing for individual nanoparticles to form within the dimples by a solid state de-wetting process induced by annealing. The ordered nanoparticle array could then be transferred to a substrate of choice using a polymer lift-off method. Following optimization of the experimental parameters, it was possible to obtain cm2 coverage of metal nanoparticles, like gold and indium, on silicon, quartz and sapphire substrates, with average sizes in the range of 50-90 nm. The de-wetting process was investigated for a specific geometry of the dimpled surface and the results explained for two different film thicknesses. Using a simple model, the experimental results were interpreted and supported by numerical estimations.

Chromophoric Ion Receptor-Decorated Porous Monolithic Polymer for the Solid-State Naked Eye Sensing of Hg(II): An Experimental and Theoretical Approach.

The current work presents a perspective to obliterate toxic Hg(II) from an aqueous environment, a strategic environmental remediation and decontamination measure. We report a simple, efficient, and reusable solid-state visual sensing strategy for the selective detection and quantitative recovery of ultratrace Hg(II). The capture of Hg(II) ions was effectuated using a macro-/mesoporous polymer monolith uniformly decorated with an azo-based chromophoric ion receptor, i.e., 7-((1H-benzo[d]imidazol-2-yl)diazenyl)quinolin-8-ol (BIDQ). The porous polymer template was synthesized through free radical polymerization of gylcidylmethacrylate and ethylene glycol dimethacrylate, leading to distinct structural and surface properties that offer exclusive solid-state colorimetric selectivity for Hg(II) upon restricted spatial dispersion of the ion receptor. The sensor provides a broad linear response range of 1-200 μg/L, with an outstanding detection limit of 0.2 μg/L for Hg(II) ions, thus effectuating reliable and reproducible sensing. Optimizing analytical parameters such as solution pH, receptor concentration, sensor quantity, kinetics, temperature, and matrix interference proved to be promising for the real-time monitoring of toxic mercury ions from aqueous/industrial systems, with maximum response in the pH range of 7.5-8.0, with a response time of ≤80 s. Density functional theory (DFT) calculations were employed to study the electronic structure of BIDQ upon chelating with Hg(II) ions, using 6-311G and LAND2Z basis sets.

On the influence of protein aggregate sizes for the formation of solid and hollow protein microparticles

Microparticles can function as carriers of e.g. pharmaceuticals and food ingredients. Hollow microparticles can enhance the capacitance due to their large interior void. For preparing microparticles, polymers have been assembled into spherical structures through the use of porous CaCO3 templates, followed by polymer cross-linking and selective template removal. However, this often results in the formation of microparticles with a solid core. Here we use proteins with different aggregate size distributions (<10 nm or >100 nm) to either form solid or hollow microparticles. Proteins were mixed with CaCl2 and Na2CO3 solutions, which from CaCO3 microcrystals (with 20–60 nm pores) with encapsulated proteins. Here it will be shown that small protein aggregates uniformly distributed into the CaCO3 templates. However, larger protein aggregates accumulated at the template edges. Au3+ ions were then added, which oxidize and cross-link proteins and are reduced to form gold nanoparticles (AuNPs). After removal of the templates, the small proteins formed solid microparticles and the larger protein aggregates hollow microparticles. This method of fabrication of solid and hollow protein microparticles, with embedded AuNPs, could be used for generating biomaterials with a broader range of applications, such as hosting molecules and multimodal imaging due to the presence of the AuNPs.

Self-templated synthesis of boron-doped porous carbon by chemical interaction of 2LiBH4·CO2 with CO2

The realization of heteroatom doping can enable carbon functional materials to have superior physiochemical properties via tailoring electron and ion distribution. However, the facile synthesis of heteroatom-doped carbon materials without CO2 emission from precursor is a major challenge for low-carbon utilization of carbon materials. Herein, we report a facile self–templated method to synthesize boron–doped porous carbon derived from CO2 based on the new reactions of 2LiBH4·CO2 with CO2. Boron–doped porous carbon is produced via a consecutive reaction between 2LiBH4·CO2 and CO2. The solid intermediate products with porous structure are formed at the first-step reaction. The newly developed porous solid products serve as the template for the chemical vapor deposition of gaseous intermediate products at the second-step reactions. The self-templated mechanism is demonstrated to form porous templates at initial stage for depositing carbon and boron sources on templates to produce boron-doped porous carbon. As a lithium storage material, it delivers a reversible capacity as high as ∼ 1660 mAh/g at 0.2 A/g and ∼ 890 mAh/g at 1.0 A/g after 1200 cycles. This finding opens a low-carbon and self-templated strategy to synthesize heteroatom–doped carbon functional materials from CO2.

Gecko-inspired hierarchically rough surface used as a reprintable paper

While paper continues to remain one of the most widely used materials for writing and printing, and while its demand continues to grow, the environmental cost of using paper is rather huge. Paper is made by extracting the cellulose fibres from wood, and to meet the demand for it, large numbers of trees are felled. Making paper requires huge quantity of water, energy, and also toxic chemicals. In fact, paper is considered the 3rd largest industrial polluter of air, water, and soil. Yet a viable alternative to paper doesn't exist. Inspired by the inherent ability of many natural surfaces to keep themselves clean, we have made a reprintable paper which can be used over 50 cycles. It is prepared by casting crosslinkable silicone on a porous template, leading to hierarchical random surface features having dimensions ranging from tens of nano-meter to hundreds of micrometers. On this surface, ink particles of wide-ranging sizes and surface chemical characteristics adhere via intermolecular interactions. However, unlike conventional papers, in which particles get mechanically trapped inside the porous network of the cellulose fibres, here the ink particles remain accessible for cleaning via gentle scrubbing with a rough surface, soaked with a suitable liquid. Thus, this paper continues to remain both cleanable and printable.

The Calcination Effect on the Crystallinity, Nitrogen Content, and Pore Structure of Nitrogen-Doped Titanium Dioxide

Mesoporous nitrogen-doped titanium dioxide nanomaterials have been synthesized through a one-step sol gel process with dodecylamine as the pore template as well as the nitrogen source. The calcination process plays an important role in the crystallization process, determination of doped nitrogen, and pore formation. The effect of calcination temperature on the material structure was studied by calcination treatment of the as-synthesized material at several temperature variations. The resulting materials were characterized using FTIR, XRD, XPS, and N2 gassorption analysis. The results showed that the anatase TiO2 crystal structure began to form with calcination at 400 °C. The higher calcination temperature tends to cause the transformation of anatase crystal phase into rutile. The higher calcination temperature also affects the doped nitrogen content, where the pore-templating molecules begin to disappear at a calcination temperature and leaving a number of dopants on TiO2. All dopants are released from TiO2 at a calcination temperature of 600 °C. The optimum calcination temperature to form mesoporous structure was 450 °C, and the sintering occurs at a calcination temperature higher than optimum temperature indicated by the collapse of the pore structure.

Electrochemical Deposition of Ferromagnetic Ni Nanoparticles in InP Nanotemplates Fabricated by Anodic Etching Using Environmentally Friendly Electrolyte.

Porous InP templates possessing a thickness of up to 100 µm and uniformly distributed porosity were prepared by anodic etching of InP substrates exhibiting different electrical conductivities, involving an environmentally friendly electrolyte. Ni nanoparticles were successfully directly deposited by pulsed electroplating into prefabricated InP templates without any additional deposition of intermediary layers. The parameters of electrodeposition, including the pulse amplitude, pulse width and interval between pulses, were optimized to reach a uniform metal deposition covering the inner surface of the nanopores. The electrochemical dissolution of n-InP single crystals was investigated by measuring the current-voltage dependences, while the Ni-decorated n-InP templates have been characterized by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). The proposed technology is expected to be of interest for sensing and photocatalytic applications, as well as for the exploration of their plasmonic and magnetic properties.

Natural Hollow Fiber-Derived Carbon Microtube with Broadband Microwave Attenuation Capacity.

Constructing hierarchical structures is indispensable to tuning the electromagnetic properties of carbon-based materials. Here, carbon microtubes with nanometer wall thickness and micrometer diameter were fabricated by a feasible approach with economical and sustainable kapok fiber. The carbonized kapok fiber (CKF) exhibits microscale pores from the inherent porous templates as well as pyrolysis-induced nanopores inside the wall, affording the hierarchical carbon microtube with excellent microwave absorbing performance over broad frequency. Particularly, CKF-650 exhibits an optimized reflection loss (RL) of -62.46 dB (10.32 GHz, 2.2 mm), while CKF-600 demonstrates an effective absorption bandwidth (RL &lt; -10 dB) of 6.80 GHz (11.20-18.00 GHz, 2.8 mm). Moreover, more than 90% of the incident electromagnetic wave ranging from 2.88 GHz to 18.00 GHz can be dissipated by simply controlling the carbonization temperature of KF and/or the thickness of the carbon-microtube-based absorber. These encouraging findings provide a facile alternative route to fabricate microwave absorbers with broadband attenuation capacity by utilizing sustainable biomass.