Hierarchical Materials Research Articles

Hierarchical porous SAPO-34 decorated with Mo and W oxides for concurrent transesterification-esterifications for efficient biodiesel production from acidic soybean oil

Hierarchical porous materials have gained much attention as promising heterogeneous catalyst supports due to their high efficiency of mass transfer and high exposure of active centers. In this research, the hierarchical porous SAPO-34 support with microporous, mesoporous, and macroporous hierarchical structure was initially prepared by in-situ alkali etching. Then, Mo and W oxides were incorporated into this hierarchical porous support by using the impregnation method to prepare Mo15W15/HSAPO-34/70 catalyst. This developed catalyst was applied to concurrently catalyze the oil transesterification and free fatty acid (FFA) esterification to biodiesel as the low-value oils severed as feedstocks. The textural and physicochemical properties of the nanocatalysts were evaluated by XRD, XPS, SEM, EDS, TEM, UV–vis, NH3-TPD, Py-FTIR, and nitrogen porosimetry measurement. This catalyst had hierarchical porous structure to ameliorate the large oil molecular transfer, and featured dual Brønsted-Lewis acid sites to synergistically boost the catalytic efficiency for the biodiesel production. Over this catalyst, the oil conversion of 90.1 % and full FFA conversion were achieved under optimized operation conditions, therefore imparting to one-pot conversion to biodiesel with low-value oils as feedstocks. In addition, this catalyst not only exhibited superior tolerance to moisture and FFAs, but also retained high activities after five reuse cycles, thus revealing its tremendous potential of being used in durable and efficient biodiesel production. The present work opens a new avenue for synthesizing a robust solid acid catalyst to achieve a one-pot biodiesel production from low-value oils.

Recycling Fe and improving organic pollutant removal via in situ forming magnetic core-shell Fe3O4@CaFe-LDH in Fe(II)-catalyzed oxidative wastewater treatment

Due to its high efficiency, Fe(II)-based catalytic oxidation has been one of the most popular types of technology for treating growing organic pollutants. A lot of chemical Fe sludge along with various refractory pollutants was concomitantly produced, which may cause secondary environmental problems without proper disposal. We here innovatively proposed an effective method of achieving zero Fe sludge, reusing Fe resources (Fe recovery = 100%) and advancing organics removal (final TOC removal > 70%) simultaneously, based on the in situ formation of magnetic Ca-Fe layered double hydroxide (Fe3O4@CaFe-LDH) nano-material. Cations (Ca2+ and Fe3+) concentration (≥ 30 mmol/L) and their molar ratio (Ca:Fe ≥ 1.75) were crucial to the success of the method. Extrinsic nano Fe3O4 was designed to be involved in the Fe(II)-catalytic wastewater treatment process, and was modified by oxidation intermediates/products (especially those with COO− structure), which promoted the co-precipitation of Ca2+ (originated from Ca(OH)2 added after oxidation process) and by-produced Fe3+ cations on its surface to in situ generate core-shell Fe3O4@CaFe-LDH. The oxidation products were further removed during Fe3O4@CaFe-LDH material formation via intercalation and adsorption. This method was applicable to many kinds of organic wastewater, such as bisphenol A, methyl orange, humics, and biogas slurry. The prepared magnetic and hierarchical CaFe-LDH nanocomposite material showed comparable application performance to the recently reported CaFe-LDHs. This work provides a new strategy for efficiently enhancing the efficiency and economy of Fe(II)-catalyzed oxidative wastewater treatment by producing high value-added LDHs materials.

Facile synthesis of three-dimensional MnOX (MnO2, Mn2O3, Mn3O4) hierarchical microflower for removal of phenol through peroxymonosulfate activation

A novel three-dimensional (3D) manganese oxide (MnOX) hierarchical microflowers materials were prepared and applied to activate peroxymonosulfate (PMS) for the removal of phenol. The 3D α-MnO2 material exhibited higher catalytic activity than 3D Mn2O3 and 3D Mn3O4 materials, with 100% phenol removal within 60 min. The quenching experiment and EPR results indicated that 1O2 played a major role in removing phenol, SO4•–, O2•– and •OH ranked second. The kinetic studies indicated that the removal of phenol followed the pseudo-first-order kinetic model, and the reaction activation energy of 3D α-MnO2 material was 25.67 kJ mol−1. Besides, factors of 3D α-MnO2 catalytic performance such as catalyst dosage, PMS dose and reaction temperature were also investigated. This work provided a new approach for synthesizing 3D MnOX catalysts with high-performance and guidance for analyzing the catalytic activity of multivalent metal oxides.

Mechanical properties of hierarchical lattice via strain gradient homogenization approach

With the advancement of 3D printing technology, manufacturing metamaterials with extreme mechanical properties is becoming more feasible. Hierarchical lattices appear to be ideal candidates for obtaining desirable lightweight, high specific stiffness, and enhanced specific energy absorption. They can be constructed by architected substructures at multiple length scales. The interpretations of the underlying deformation mechanisms are necessary in order to manipulate with expected mechanical properties. In this paper, experiments were conducted to examine the effective mechanical behaviors of hierarchical lattice metamaterials. A strain gradient homogenization approach has been employed to correlate their morphological characteristics to the resulting material properties. The effective stiffness tensors are identified including the fourth-, fifth-, and sixth-order stiffness tensors. The higher-order inertial parameters are determined by a fitting procedure. Comparisons between direct finite element analyses and the homogenized strain gradient continua have been made for hierarchical lattice materials under static and dynamic loads. It is found that strain gradient homogenization approach can be an accurate, efficient and reliable way of predicting the mechanical behaviors of hierarchical lattice. A systematic analysis of geometrical parameters was conducted to uncover the underlying mechanisms responsible for the enhancement of effective properties. This work offers a novel approach for designing the mechanical properties of hierarchical metamaterials through precise control of secondary structure types and distributions.

Modified Solid Electrolyte Interphases with Alkali Chloride Additives for Aluminum-Sulfur Batteries with Enhanced Cyclability

Al-S batteries are promising energy storage devices, employing high-capacity and low-cost Al (2980 mA h g-1, 8050 mAh cm-3) and sulfur (1672 mAh g-1) as the anode and cathode, respectively. However, Al-S batteries suffer from the notorious shuttle effect of polysulfides as other intensively investigated metal-sulfur batteries. Up to now, several strategies have been proposed to improve the poor reversibility and lifespan of Al-S batteries. At the cathode side, materials that can adsorb polysulfides have been employed as the host material of sulfur to reduce the dissolution of polysulfides,1,2 e.g., heteroatom-functionalized and/or hierarchical porous carbonaceous materials, metal-organic frameworks (MOFs), boron nitrides, and Mxenes.3,4 Nonetheless, AMAs, which also play an important role in the shuttle process, have received little attention up to now. Suitable engineering of electrolytes enabling an electronically insulating solid electrolyte interphase (SEI) on AMAs may suppress the deposition of low-solubility Al2S3 and/or short-chain polysulfides further promoting the cell cycling performance.Herein, alkali chlorides are, for the first time, proposed as electrolyte additives to modify the SEI on AMAs and suppress the polysulfide shuttle in Al-S batteries.5 It is demonstrated that adding NaCl to the conventional [AlCl3]1.3[EmimCl]1 electrolyte can enhance the cyclability of Al-S batteries by forming a thicker, NaxAlyO2-containing SEI layer on AMAs. In addition to NaCl, LiCl and KCl as electrolyte additives also lead to improvement of Al-S batteries’ lifespan. These findings provide a new path to suppress the detrimental polysulfides shuttle effect in Al-S batteries, resulting in their improved cycle performance. References (1) Smajic, J.; Wee, S.; Simoes, F. R. F.; Hedhili, M. N.; Wehbe, N.; Abou-Hamad, E.; Costa, P. M. F. J. Capacity Retention Analysis in Aluminum-Sulfur Batteries. ACS Appl. Energy Mater. 2020, 3 (7), 6805–6814.(2) Zhang, Y.; Ma, L.; Tang, R.; Zheng, X.; Wang, X.; Dong, Y.; Kong, G.; Zhao, F.; Wei, L. The Host Hollow Carbon Nanospheres as Cathode Material for Nonaqueous Room-Temperature Al–S Batteries. Int. J. Hydrogen Energy 2021, 46 (7), 4936–4946.(3) Guo, Y.; Jin, H.; Qi, Z.; Hu, Z.; Ji, H.; Wan, L. J. Carbonized-MOF as a Sulfur Host for Aluminum–Sulfur Batteries with Enhanced Capacity and Cycling Life. Adv. Funct. Mater. 2019, 29 (7), 1–6.(4) Wang, Z.; Zheng, X.; Chen, A.; Han, Y.; Wei, L.; Li, J. Unraveling the Anchoring Effect of MXene-Supported Single Atoms as Cathodes for Aluminum−Sulfur Batteries. ACS Mater. Lett. 2022, 4, 8, 1436-1445.(5) Xu, C.; Diemant, T.; Liu, X.; Passerini, S. Modified Solid Electrolyte Interphases with Alkali Chloride Additives for Aluminum–Sulfur Batteries with Enhanced Cyclability. Adv. Funct. Mater. 2023. 2214405.

(Invited) Tailor-Made Hierarchical Nested-Network Nanoporous Metals By Dealloying

Structural hierarchy is known to optimize functional and mechanical behaviors in deliberately designed structures and natural materials. The benefits of hierarchy implementing the high strength and the high surface-to-volume of nanoscale objects into hierarchical structures would lead to even more interesting mechanical characteristics and more opportunities for interface- or surface-controlled functional applications. This talk focuses on nested network random nanomaterials "hierarchical nanoporous gold" made by two-stage self-organization dealloying processes, which processes allow for large samples contained over trillions of struts to be synthesized. Both the strut size and porosity at each hierarchy level are tuned independently. The strut size can be controlled from 10 nm to 300 nm, and the porosity from 80% to 90%. Compression tests on these hierarchical nanoporous gold materials demonstrated that the structural hierarchy brings enhanced mechanics for truly nanoscale network materials. The experiments are well supported by our proposed scaling laws for the stiffness and strength for nested network with different numbers of hierarchy levels [1].[1] S. Shi, Y. Li, B.-N. Ngo-Dinh, J. Markmann and J. Weissmüller, Scaling behavior of stiffness and strength of hierarchical network nanomaterials, Science 371 (6533), 2021.

Alkylation of Toluene to Mono‐benzylated Toluene over Micro‐mesoporous Zeolite: Effect of Post‐synthetic Treatment and Catalytic Application

AbstractPost‐synthetic modification using acid (HNO3) and base (NaOH) are utilised to synthesize hierarchical micro‐mesoporous zeolites with different pore structure. To investigate structural change in materials, X‐ray diffraction (XRD), Scanning electron microscope (SEM), Inductive coupled plasma‐optical emission spectrometry (ICP‐OES), 29Si and 27Al MAS NMR, and N2 adsorption‐desorption isotherms techniques were employed. Acid base titration, and ammonia‐temperature programmed desorption (NH3‐TPD) was performed to evaluate acidic characteristics of materials. As revealed by characterisation, the structure was well preserved after the modification. Hierarchical materials along with parent materials have been evaluated in the toluene alkylation with benzyl alcohol producing mono‐benzylated toluene. All zeolite samples were proved to be catalytically active by their result in the alkylation reaction. Acid treated samples were compared with base treated and parent samples. The results indicate that, base modification significantly increases the mesoporous pore volume in all zeolite as compared to acid modification. Moreover, the highest benzyl alcohol conversion was found to be 98 % in the base modified Beta, with the highest mono‐benzylated toluene selectivity (69 %). Reaction optimization was also studied by altering reaction duration, temperature, and catalyst amount. The reaction products were analysed using Gas Chromatography (GC) and confirmed using Gas chromatography mass spectrometry (GC‐MS).

Three-Dimensional Printing of Cellulose/Covalent Organic Frameworks (CelloCOFs) for CO2 Adsorption and Water Treatment.

The development of porous organic polymers, specifically covalent organic frameworks (COFs), has facilitated the advancement of numerous applications. Nevertheless, the limited availability of COFs solely in powder form imposes constraints on their potential applications. Furthermore, it is worth noting that COFs tend to undergo aggregation, leading to a decrease in the number of active sites available within the material. This work presents a comprehensive methodology for the transformation of a COF into three-dimensional (3D) scaffolds using the technique of 3D printing. As part of the 3D printing process, a composite material called CelloCOF was created by combining cellulose nanofibrils (CNF), sodium alginate, and COF materials (i.e., COF-1 and COF-2). The intervention successfully mitigated the agglomeration of the COF nanoparticles, resulting in the creation of abundant active sites that can be effectively utilized for adsorption purposes. The method of 3D printing can be described as a simple and basic procedure that can be adapted to accommodate hierarchical porous materials with distinct micro- and macropore regimes. This technology demonstrates versatility in its use across a range of COF materials. The adsorption capacities of 3D CelloCOF materials were evaluated for three different adsorbates: carbon dioxide (CO2), heavy metal ions, and perfluorooctanesulfonic acid (PFOS). The results showed that the materials exhibited adsorption capabilities of 19.9, 7.4-34, and 118.5-410.8 mg/g for CO2, PFOS, and heavy metals, respectively. The adsorption properties of the material were found to be outstanding, exhibiting a high degree of recyclability and exceptional selectivity. Based on our research findings, it is conceivable that the utilization of custom-designed composites based on COFs could present new opportunities in the realm of water and air purification.

3D printing and freeze casting hierarchical mxene pressure sensor

Although MXene sheets are highly conductive, it is still challenging to prepare MXene complex functional materials for flexible electronics by simple and effective methods. In 3D printing, especially direct ink writing (DIW), different materials are used to create complex 3D shapes by formulating inks with controlled rheological properties. Herein, a printable MXene ink is developed, exhibiting good rheological properties, to print different complex shapes, and potentially manufacture electronic devices such as sensors. Then, we fabricated a highly sensitive hierarchical structure MXene composite materials composed of two layers of bionic micro-spine microstructure and network structure, formed by 3D printing and freeze casting. The obtained MXene composite materials exhibit good pressuring sensing properties with a sensitivity of 17.5 kPa−1, a fast response time (<100 ms), and excellent cycle stability exceeding 10,000 cycles. The sensing mechanism suggesting that the hierarchical structure can effectively improve the sensitivity and response time. It also has good potential application in the monitoring of human health activities, including the detection of human joint activities, walking, pressure distribution, and other sports.

Hierarchical macroporous polymer structures fabricated by coassembly of polymersomes and polymer brushes

Synthesis of hierarchical macroporous structures has aroused great interest due to the potential applications and unique properties of the materials. In this research, polymersomes and polymer brush-grafted silica particles are used as building blocks for the fabrication of hierarchical macroporous polymer particles. In order to investigate the mechanism of the self-assembly and synthesize hierarchical materials, two-component self-assembly of poly(2-(dimethylamino)ethyl methacrylate)-block-polystyrene (PDMAEMA55-b-PS316) and PS343, and three-component self-assembly of PDMAEMA55-b-PS316, PS343 and PS brushes on silica particles (SiO2-PS343) in THF/methanol mixtures were performed. In the coassembly of PDMAEMA55-b-PS316 and PS343, with an increase in PS343 content the morphology of the self-assembled structures changes from spherical micelles, to polymersomes, and to aggregated polymersomes. In the coassembly of PDMAEMA55-b-PS316, PS343 and SiO2-PS343, aggregated polymersomes and silica particles are formed. After etching silica particles with HF acid, macroporous polymer structures are produced. After quaternization of PDMAEMA blocks with methyl iodide, hierarchical macroporous structures with hydrophilic quaternized PDMAEMA blocks at the coronae and hydrophobic PS domains inside the structures are produced in aqueous solution. Toluene, used as a model compound, is able to diffuse into the hydrophobic domains of the structures, and at high toluene content a transition from the hierarchical macroporous structures to hollow structures is observed.

Auricularia-shaped MoS2 nanosheet arrays coated hierarchical multilayer MoS2/PPy/rGO composites for efficient microwave absorption

The rapid development of electronic technology has exacerbated electromagnetic pollution. It's crucial to develop efficient microwave-absorbing (MA) materials for blocking electromagnetic damage to electronic instruments and human health. However, simple structure MA materials usually have limited microwave absorption capacities and cannot simultaneously meet requirements for lightweight, wide bandwidth, and high loss. Constructing hierarchical structure composites and thereby introducing multiple absorption mechanisms is an effective way to improve the MA performance. In this study, we synthesized an auricularia-shaped MoS2 nanosheet array coated hierarchical multilayer MoS2/PPy/rGO (MPG) composite by a facile hydrothermal method. In the preparation process, using PPy to modify the rGO surface plays a key role, which effectively avoids rGO agglomeration and provides substrates for MoS2 nanosheets to grow on. The thicket of MoS2 nanosheets creates numerous nanoscale interfaces, promoting interface polarization and improving impedance matching. The multilayer heterogeneous structure facilitates multiple reflections and scattering, further attenuating electromagnetic waves. By optimizing the addition of PPy, the material's microstructure and microwave absorption performance were improved. The MPG-10 sample achieved the best reflection loss of −53.5 dB (2.07 mm thickness) and an effective absorption bandwidth of 5.36 GHz (1.82 mm thickness). This work contributes a new idea for the structural design of graphene-based hierarchical heterogeneous microwave absorption materials.

A hierarchical porous N-doped carbon material as catalyst derived from the folic acid-Zn/KBr hydrogel: Reaction network and kinetics and mechanism for the oxidation of furfural to maleic acid

A novel hydrogel (named FA-Zn/KBr) was prepared, by taking advantage of the hydrogen-bonding and π-π stacking interactions between the pterin heterocycles of the folic acid (FA) molecules. The hydrogel is composed of highly dispersed KBr, coordinated zinc ions, and stacked arrays of folate tetramers. Due to the presence of KBr, a hierarchical porous nitrogen-doped carbon (PNC-800) material with a specific surface area 2807.9 m2/g can be formed through the calcination of the FA-Zn/KBr xerogel under N2. PNC-800 is used to catalyze the oxidation of furfural to maleic acid in the presence of H2O2. Representative nine reactions constitute the reaction network. The reaction rate constants and apparent activation energy were obtained for each reaction. Based on the kinetics parameters, the simulated results are in good agreement with the experimental data. The mechanism of the reaction catalyzed by PNC-800 is proposed based on ample experimental evidence. The graphitic nitrogen species in PNC-800 are the active sites. PNC-800 catalyzes the decomposition of hydrogen peroxide to generate hydroxyl radical (HȮ), which oxidizes furfural to furfural radical, and the furfural radical is subsequently converted to 5-hydroxy-furan-2(5H)-one (HFONE). The conversion of furfural to maleic acid via the formation of HFONE is the main reaction pathway. In addition, the hierarchical porous structure with a high specific surface area facilitates the interaction of reactant with the active sites. PNC-800 has been shown an excellent catalytic activity for the production of maleic acid from furfural. For the oxidation of 1000 mM furfural using 50 mg PNC-800 at 80 °C within 9 h, the conversion of furfural is 100 % with a maleic acid yield 67.5 %.

High-Performance Supercapacitors Using Hierarchical And Sulfur-Doped Trimetallic NiCo/NiMn Layered Double Hydroxides.

A supercapacitor features high power density and long cycling life. However, its energy density is low. To ensemble a supercapacitor with high power- and energy-densities, the applied capacitor electrodes play the key roles. Herein, a high-performance capacitive electrode is designed and grown on a flexible carbon cloth (CC) substrate via a hydrothermal reaction and a subsequent ion exchange sulfuration process. It has a 3D heterostructure, consisting of sulfur-doped NiMn-layered double hydroxide (LDH) nanosheets (NMLS) and sulfur-doped NiCo-LDH nanowires (NCLS). The electrode with sheet-shaped NMLS and wire-shaped NCLS on their top (NMLS@NCLS/CC) increases the available surface area, providing more pseudocapacitive sites. It exhibits a gravimetric capacity of 555.2 C g-1 at a current density of 1 A g-1 , the retention rate of 75.1% when the current density reaches up to 20 A g-1 , as well as superior cyclic stability. The assembled asymmetric supercapacitor that is composed of a NMLS@NCLS/CC positive electrode and a sulfurized activated carbon negative electrode presents a maximum energy density of 24.2Wh kg-1 and a maximum power density of 16000W kg-1 . In this study, a facile strategy for designing hierarchical LDH materials is demonstrated as well as their applications in advanced energy storage systems.

Amine-functionalized disordered hierarchical porous silica derived from blast furnace slag with high adsorption capability and cyclic stability for CO2 adsorption

This study proposes a novel solution to the challenge of achieving high cycle stability in CO2 adsorbents prepared through impregnation with organic amines. Specifically, industrial waste blast furnace slag was used to prepare a support material called BHF, which possesses three pore structures: micropores, mesopores, and macropores. This unique structure facilitates high loading of organic amines and improves CO2 adsorption effectiveness. To counteract agglomeration effects caused by loading large amounts of organic amines, the morphology and skeleton of the carrier material were analyzed in detail. The results showed that the rough “hive” morphology, disordered cell-like skeleton structure and abundant pores of BHF allows for uniform dispersion of polyethyleneimine (PEHA), an organic amine, and provides advantageous transportation of CO2 molecules within the adsorbent. Based on the study of kinetics, activation energy, and isosteric heat of adsorption, the adsorption mechanism of 70PEHA-BHF was determined to be a chemical-physical binding adsorption. The adsorption-diffusion mechanism suggests that the rate-limiting step is film diffusion. Furthermore, the 70PEHA-BHF adsorbent achieves a balance between CO2 adsorption capacity and cycle stability. At 80 °C and 15 vol.% CO2, the CO2 adsorption capacity of 70PEHA-BHF is 6.27 mmol/g, with only a 1.43 % CO2 loss after 10 cycles of testing. It anticipates that this newly developed 70PEHA-BHF adsorbent will provide additional possibilities for the application of hierarchical porous materials in CO2 adsorption research.

One-Step Synthesis of Nitrogen-Doped Porous Carbon Derived from Biomass for Lithium-Ion Battery

Bamboo shoot is renewable biomass rich in carbon and nitrogen. To take advantage of its sources of carbon and nitrogen, hierarchical porous nitrogen-doped carbon materials derived from bamboo shoot were acquired via a one-step method in this study. The obtained carbons were characterized by using XRD, Raman, N2 sorption, SEM, TEM, XPS, etc. The carbon calcinated at 700 °C with KHCO3 treatment (BSC) displays a large surface area (1475.5 m2 g−1) and typically porous structure from micro- to macropores, a self-nitrogen content, and many defects, which could offer transport channels and active sites for lithium ions while used as carbon anode. Based on the above features and the synergistic effects among them, BSC exhibits the typical electrochemical performance of a carbon-based anode material, with a specific capacity as high as 611.3 mA h g−1 (a Coulombic efficiency of 98.7%) after 100 cycles at a current density of 0.1 A g−1. Meanwhile, it also has a good rate performance and excellent cycling properties (436.1 mA h g−1 after 300 cycles at 0.1 A g−1) compared with NBSC (carbon directly carbonized at 700 °C). Thus, it is promising for further improvements made to porous carbon derived from biomass and used as anode in the application of energy storage, and could be a guideline for the preparation of high-value-added carbon materials derived from biomass.

Exploring the Potential of Hierarchical Zeolite-Templated Carbon Materials for High-Performance Li-O2 Batteries: Insights from Molecular Simulations.

The commercialization of ultrahigh capacity lithium-oxygen (Li-O2) batteries is highly dependent on the cathode architecture, and a better understanding of its role in species transport and solid discharge product (i.e., Li2O2) formation is critical to improving the discharge capacity. Tailoring the pore size distribution in the cathode structure can enhance the ion mobility and increase the number of reaction sites to improve the formation of solid Li2O2. In this work, the potential of hierarchical zeolite-templated carbon (ZTC) structures as novel electrodes for Li-O2 batteries was investigated by using reactive force field molecular dynamics simulation (reaxFF-MD). Initially, 47 microporous zeolite-templated carbon morphologies were screened based on microporosity and specific area. Among them, four structures (i.e., RHO-, BEA-, MFI-, and FAU-ZTCs) were selected for further investigation including hierarchical features in their structures. Discharge product cluster analysis, self-diffusivities, and density number profiles of Li+, O2, and dimethyl sulfoxide (DMSO) electrolyte were obtained to find that the RHO-type ZTC exhibited enhanced mass transfer compared to conventional microporous ZTC (approximately 31% for O2, 44% for Li+, and 91% for DMSO) electrodes. This is due to the promoted formation of small-sized product clusters, creating more accessible sites for oxygen reduction reaction and mass transport. These findings indicate how hierarchical ZTC electrodes with micro- and mesopores can enhance the discharge performance of aprotic Li-O2 batteries, providing molecular insights into the underlying phenomena.

Advances in advanced solution‐synthesis‐based structural materials for tactile sensors and their intelligent applications

AbstractIntelligent applications, with tactile sensors at their core, represent significant advancement in the field of artificial intelligence. However, achieving perception abilities in tactile sensors that match or exceed human skin remains a formidable challenge. Consequently, the design and implementation of hierarchical structural materials are considered the optimal solution to this challenge. In contrast to conventional methods, such as complicated lithography and three‐dimensional printing, the cost‐effective and scalable nature of advanced solution‐synthesis methods makes them ideal for preparing diverse tactile sensors with hierarchical structural materials. However, the process and applicability of advanced solution synthesis methods have yet to form a seamless system. Accordingly, the development and intellectualization of tactile sensors based on advanced solution synthesis methods are still in their early stages, and require a comprehensive and systematic review to usher in progress. This study delves into the advantages and disadvantages of various advanced solution synthesis methods, providing detailed insights. Furthermore, the positive effects of hierarchical structural materials constructed using these methods in tactile sensors and their intelligent applications are also discussed in depth. Finally, the challenges and future opportunities faced by this emerging field are summarized.image

A silver nanoparticles-polylactic acid microspheres/polylactic acid-thermoplastic polyurethane nanofibers hierarchical antibacterial film

Silver nanoparticles (AgNPs) are commonly incorporated in food packaging to enhance the shelf life of fruits and vegetables. In this work, three microstructures (spherical, hematocyte-like, and pie micromorphology) of AgNPs-polylactic acid (PLA) materials were fabricated on electrospun PLA-thermoplastic polyurethane (TPU) nanofiber film by electrospraying to reduce the safety risks and the cost of food packaging materials brought by AgNPs. Among them, the spherical AgNPs-PLA microsphere/PLA-thermoplastic polyurethane (TPU) hierarchical antibacterial film had good mechanical properties, a low AgNPs content of 0.6 wt%, the highest water contact angle of 140.1°, the highest bacteriostatic rate of 99% ± 1%, and the least bacterial adhesion. The test of this composite film in strawberry packaging successfully extended the shelf life to over 7 days. The hierarchical PLA material shows promising prospects in food packaging, and the preparation method may be a potential candidate for reducing the amount of antimicrobial agent required in antibacterial materials.

Hierarchical-heterostructured porous intermetallics in nickel-cobalt-aluminum alloys as efficient electrocatalysts for hydrogen evolution

Extensive researches have unequivocally revealed the remarkable potential of hierarchical porous intermetallic materials within the realms of electrocatalysis and energy materials. Nevertheless, the efficient and cost-effective synthesis of such electrocatalysts remains a challenging task, and the atomic-level mechanisms underlying hydrogen evolutions at active catalytic sites are still insufficiently comprehended. Herein, we report a novel synthesis technique for the hierarchical-heterostructured non-noble Ni-Co-Al intermetallics using spark plasma sintering followed by a selective dealloying process. This approach maximizes the electrochemical active surface area, thereby facilitating highly efficient hydrogen evolution reactions with an impressively low overpotential of only 75 mV at a current density of 10 mA cm−2 and a Tafel slope of 54 mV dec−1. Through operando X-ray absorption fine structure and theoretical calculations, the dynamic evolution process during the hydrogen evolution reaction procedure is investigated and the atomic Ni and Co sites are identified as synergistic catalytic sites. These characteristics render this hierarchical-heterostructured porous intermetallics appealing contenders for electrocatalysts utilized in high-performance large-scale hydrogen generation applications.

Achieving carbonized minitablet-shaped structures from lignin – The importance of heating rate on shape

Shape-anisotropic building blocks are vital in the creation of hierarchical materials in nature, as it enables directional alignment, property anisotropy and overall functionality improvement in biological materials. Likewise, the performance of carbonized superstructures could potentially be more precisely designed by using anisotropic building blocks. Lignin represents an important and sustainable alternative in the production of carbonized materials, which is due to its abundance and high carbon content (∼60%). However, to expand its utility, for producing carbonized shape-anisotropic materials, adequate synthesis and pyrolysis-protocols are essential. Here, a fractionated and acetylated Kraft lignin was used to successfully self-assemble shape-anisotropic microcapsules. Then a carbonization procedure (slow heating at 0.6 °C min−1), that retained the original shape-anisotropy after carbonization, was developed. The formation mechanism was discussed as a function of the heating rate. The overall strategy was template-free and the attained shape-anisotropies were well-defined and narrow in size distribution. This is a scalable route for achieving shape-anisotropic carbonized building blocks from lignin.