Hierarchical Surface Structures Research Articles

Highly selective detection of ethanol based on hierarchical three-dimensional SnO2: Combining experiment with first-principles calculation

Improving gas sensing characteristics through the microstructure has attracted more and more attention in recent years. A hierarchical SnO2 nanostructure and its high ethanol selectivity were developed in this work. The hierarchical SnO2 nanostructure was obtained by a facile annealing process using SnS2 nanoflowers as precursor. The SEM and TEM results show that a flower-like SnO2 structure composed of nanoplates forms a hierarchical structure. The hierarchical SnO2 demonstrated excellent response time and high selectivity to ethanol at 200℃. The response/recovery time to 20 ppm ethanol vapor is about 0.75 s and 50 s, respectively. The enhanced sensing properties benefit from its unique structure, including the flower-like hierarchical structure and abundant surface defects, providing more gas active centers and diffusion paths. In order to understand the high selectivity, the first-principles calculations were carried out on the adsorption behavior between SnO2 and various gases. The result demonstrated that SnO2 was theoretically more selective in ethanol than other gases based on the adsorption energy. Humidity test and cycle test effectively prove that the sensor based on SnO2 nanoflower has great prospects for the detection of ethanol.

Hierarchical composite membrane with multiscale roughness structures for water-in-oil emulsion separation

A hierarchical structure composite membrane, which consisted of a polyvinylidene fluoride (PVDF) nanofiber selective layer, a polymethyl methacrylate (PMMA) microspheres layer, and a polyacrylonitrile (PAN) nanofiber support layer, was successfully fabricated by electrospinning. The morphology, mechanical property, wettability and the water-in-oil (W/O) emulsion separation performance of the electrospun PAN-PMMA-PVDF membranes were investigated. The mechanism of W/O emulsion separation was clarified. The results indicated that surface roughness of the composite membrane can be manipulated by changing the concentration of PMMA spinning solution (8-14 wt%). The PAN-PMMA(12)-PVDF membrane was determined to be a suitable material based on the separation performance for W/O emulsion. Furthermore, the membrane with the water contact angles of 131°, showed a good tensile strength and flexibility, fast oil permeability, and high hydrophobicity. More importantly, this membrane had high porosity (85.1%), which exhibited high flux (2408 L·m−2·h−1) and good separation efficiency (92%) for methylbenzene, as well as the good reusability. Overall, this study provides a way to fabricate nanofibrous mats with hierarchical structure and multiscale surface roughness. The proposed membranes are viable alternatives for W/O emulsion separation with high efficiency.

Enhanced triethylamine-sensing properties of hierarchical molybdenum trioxide nanostructures derived by oxidizing molybdenum disulfide nanosheets

A 3D α-MoO3 nanostructure for high-performance triethylamine (TEA) detection was synthesized via the facial oxidation of MoS2 nanoflowers (NFs) obtained by a hydrothermal process. The influence of the time of hydrothermal process in growing MoS2 on the morphologies of the final MoO3 obtained after calcination was investigated. As-obtained MoO3 and their precursors were systematically characterized by various techniques, such as X-ray diffraction, Raman, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and N2 adsorption–desorption isotherms. Results showed that MoO3 with a hierarchical layered nanostructure was successfully obtained. After hydrothermal treatment of the MoS2 precursor for 20 h, the typical MoO3-based sensor (called M20) exhibited a high response of 2.42 at a very low TEA concentration of only 0.1 ppm at 240 °C. The M20 sensor response to 50 ppm TEA was as high as 125 with a fast response/recovery time of 14/22 s. Moreover, the sensor had a high stability and reproducibility as well as a high selectivity against other interfering VOCs or gases. Due to the tendency of TEA to adsorb to active oxygen sites of MoO3, the enhanced sensing properties of MoO3 can be ascribed to the remarkable hierarchical structure and large surface area. MoO3 obtained after calcination of hydrothermally grown MoS2 is thus a promising sensing material for enhanced TEA gas detection.

Bio-mimicked guided tissue regeneration/guided bone regeneration membranes with hierarchical structured surfaces replicated from teak leaf exhibits enhanced bioactivity.

Bio-mimicked GTR/GBR membranes with hierarchical structured surfaces were developed by direct and indirect replication of teak leaf surface. The membranes were fabricated using solvent casting method with customized templates. The surfaces obtained were those with micro-trichomes (MTS) and micro-depression (MDS) that resembled a whorling pattern. Structural details of the fabricated membrane surfaces were studied under stereomicroscope and scanning electron microscopy. Surface roughness, water wetting angle, water uptake, and degradation properties of the membranes were examined. The effects of the micro-patterned hierarchical structure on in vitro bioactivities of human osteoblast-like cells (MG63) and human gingival fibroblast cells HGF1-RT1 were studied. In vivo study carried out on rat skulls to assess the response of surrounding tissues for 4 weeks showed that the bio-mimicked MTS and MDS membrane surfaces enhanced the cell proliferation. The proliferation significantly increased with increasing surface roughness and decreasing contact angle. There was also an evidence of rapid new bone maturation with membranes with MTS. It is thus suggested that the teak leaf mimicked whorling patterned hierarchical structured surface is an important design for enhancing bioactivity.

Light absorption and hydrophobicity of a polystyrene/multiwall carbon nanotube composite with surface nanostructures

This paper describes an investigation into how combined carbon nanotube doping and surface nanostructuring affects the surface properties of polystyrene. Multiwall carbon nanotubes (MWCNTs) have unique anisotropic electrical properties that can be utilized for light absorption, electromagnetic shielding and nanoscale electostatic forces. Polystyrene was doped with 5 wt% MWCNTs and the resulting composite was wetted onto a porous anodic alumina template to form a nanostructure surface of nanotubes. Scanning electron microscopy revealed a hierarchical surface structure with the composite nanotubes bundled together as the MWCNTs increased the attractive forces between the composite nanotubes. Water droplet testing revealed that this hierarchical surface structure was superhydrophobic. Though the presence of the MWCNTs caused a direct increase in absorption, the hierarchical surface structure increased reflection. The addition of 5 wt% of the anionic surfactant Sodium Dodecyl Benzene Sulfonate to ensure MWCNT dispersal did not significantly change hydrophobicity or light absorption despite the hierarchical surface structure becoming finer. The created composite has potential use as a surface layer on an organic surface cell as it provides reduced cleaning needs and electrical disturbance but further work is required to reduce the reflection.

Multiple Wetting-Dewetting States of a Water Droplet on Dual-Scale Hierarchical Structured Surfaces.

Surfaces with microscale roughness can entail dual-scale hierarchical structures such as the recently reported nano/microstructured surfaces produced in the laboratory (Wang et al. Nature2020, 582, 55−5732494077). However, how the dual-scale hierarchical structured surface affects the apparent wetting/dewetting states of a water droplet, and the transitions between the states are still largely unexplored. Here, we report a systematic large-scale molecular dynamics (MD) simulation study on the wetting/dewetting states of water droplets on various dual-scale nano/near-submicrometer structured surfaces. To this end, we devise slab-water/slab-substrate model systems with a variety of dual-scale surface structures and with different degrees of intrinsic wettability (as measured based on the counterpart smooth surface). The dual-scale hierarchical structure can be described as “nanotexture-on-near-submicrometer-hill”. Depending on three prototypical nanotextures, our MD simulations reveal five possible wetting/dewetting states for a water droplet: (i) Cassie state; (ii) infiltrated upper-valley state; (iii) immersed nanotexture-on-hill state; (iv) infiltrated valley state; and (v) Wenzel state. The transitions between these wetting/dewetting states are strongly dependent on the intrinsic wettability (Ein), the initial location of the water droplet, the height of the nanotextures (H1), and the spacing between nanotextures (W1). Notably, Ein–H1 and Ein–W1 diagrams show that regions of rich wetting/dewetting states can be identified, including regions where between one to five states can coexist.

Structured aluminium surfaces with tunable wettability fabricated by a green approach

In present article, we have fabricated micro/nano hierarchical structured aluminium surfaces with a vivid range of wettability and controllable adhesion using a facile and environment-friendly approach. The micropatterned surfaces show hydrophobicity with high adhesion due to impregnated wetting state, analogous to rose petal effect. Interestingly, the micro/nano hierarchical structured surfaces become superhydrophilic due to formation of aluminium oxide and hydroxide nanoflakes. After fluorination, these surfaces become superhydrophobic with a very low contact angle hysteresis. They also exhibit a very high chemical and thermal stability along with excellent self-cleaning capability.

Fe-based metal organic framework derivative with enhanced Lewis acidity and hierarchical pores for excellent adsorption of oxygenated volatile organic compounds

A series of Fe-based metal organic framework derived materials were prepared by thermal treating MIL-100(Fe) in nitrogen atmosphere for adsorption removal of oxygenated volatile organic compounds (OVOCs) such as methanol, formaldehyde and acetone under dynamic conditions. The experimental results showed that the partially carbonized M-350 material obtained by calcining MIL-100(Fe) at 350 °C exhibited the best adsorption performance and high stability. The breakthrough adsorption capacity of M-350 for methanol was 61.5% higher than that of pure MIL-100 (Fe), and it was 24.7, 6.5 and 2.6 times higher than that of commercial activated carbon, ZSM-5 and SAPO-34 adsorbents, respectively. The excellent adsorption performance was attributed to the exposure of abundant coordinatively unsaturated iron metal sites acting as Lewis acid sites through high temperature calcination, which had a strong affinity for OVOCs. Meanwhile, a hierarchical porous structure and high specific surface area further promoted the adsorption. This work provides new insights into the further development of metal organic frameworks based functional materials for VOCs removal and purification.

Polydopamine Nanocluster Embedded Nanofibrous Membrane via Blow Spinning for Separation of Oil/Water Emulsions.

Developing a porous separation membrane that can efficiently separate oil–water emulsions still represents a challenge. In this study, nanofiber membranes with polydopamine clusters polymerized and embedded on the surface were successfully constructed using a solution blow-spinning process. The hierarchical surface structure enhanced the selective wettability, superhydrophilicity in air (≈0°), and underwater oleophobicity (≈160.2°) of the membrane. This membrane can effectively separate oil–water emulsions, achieving an excellent permeation flux (1552 Lm−2 h−1) and high separation efficiency (~99.86%) while operating only under the force of gravity. When the external driving pressure was increased to 20 kPa, the separation efficiency hardly changed (99.81%). However, the permeation flux significantly increased to 5894 Lm−2 h−1. These results show that the as-prepared polydopamine nanocluster-embedded nanofiber membrane has an excellent potential for oily wastewater treatment applications.

Hazardous Petroleum Sludge-Derived Nitrogen and Oxygen Co-Doped Carbon Material with Hierarchical Porous Structure for High-Performance All-Solid-State Supercapacitors.

Rational design and sustainable preparation of high-performance carbonaceous electrode materials are important to the practical application of supercapacitors. In this work, a cost-effective synthesis strategy for nitrogen and oxygen co-doped porous carbon (NOC) from petroleum sludge waste was developed. The hierarchical porous structure and ultra-high surface area (2514.7 m2 g−1) of NOC electrode materials could provide an efficient transport path and capacitance active site for electrolyte ions. The uniform co-doping of N and O heteroatoms brought enhanced wettability, electrical conductivity and probably additional pseudo-capacitance. The as-obtained NOC electrodes exhibited a high specific capacitance (441.2 F g−1 at 0.5 A g−1), outstanding rate capability, and cycling performance with inconspicuous capacitance loss after 10,000 cycles. Further, the assembled all-solid-state MnO2/NOC asymmetrical supercapacitor device (ASC) could deliver an excellent capacitance of 119.3 F g−1 at 0.2 A g−1 under a wide potential operation window of 0–1.8 V with flexible mechanical stability. This ASC device yielded a superior energy density of 53.7 W h kg−1 at a power density of 180 W kg−1 and a reasonable cycling life. Overall, this sustainable, low-cost and waste-derived porous carbon electrode material might be widely used in the field of energy storage, now and into the foreseeable future.

Development of morphology tuned SnS hierarchical structures for enhanced photosensitive photodiode fabrication

Hierarchical structure transformation and surface modification of solvothermal method synthesized SnS with oleic acid in ethylene glycol solvent were discussed in detail. The structural, optical, and morphology of as prepared SnS samples were examined by X-ray diffraction (XRD), Raman Spectroscopy, and Field Emission Scanning Electron Microscopy (FE-SEM). XRD verifies the orthorhombic crystal structure of the SnS phase for all synthesized samples. Single-phase nature of synthesized particles was confirmed with Raman characterization. Morphology evolution of SnS from regular to hierarchical structures upon adding oleic acid is performed through FE-SEM analysis. Junction diodes p-SnS/n-Si fabricated with different oleic acid concentrations (0.5, 1.5, and 2.5 mL) synthesized SnS particles show better photo-response, which can be used in photodiode applications.

Surface engineering of biomaterials in orthopedic and dental implants: Strategies to improve osteointegration, bacteriostatic and bactericidal activities

The success of biomedical implants in orthopedic and dental applications is usually limited due to insufficient bone-implant integration, and implant-related infections. Biointerfaces are critical in regulating their interactions and the desirable performance of biomaterials in biological environment. Surface engineering has been widely studied to realize better control of the interface interaction to further enhance the desired behavior of biomaterials. This review aims to investigate surface coating strategies in hard tissue applications to address insufficient osteointegration and implant-related infection problems. We first focused on surface coatings to enhance the osteointegration and biocompatibility of implants by emphasizing calcium phosphate-related, nanoscale TiO2 -related, bioactive tantalum-based and biomolecules incorporated coatings. Different coating strategies such as plasma spraying, biomimetic deposition, electrochemical anodization and LENS are discussed. We then discussed techniques to construct anti-adhesive and bactericidal surface while emphasizing multifunctional surface coating techniques that combine potential osteointegration and antibacterial activities. The effects of nanotopography via TiO2 coatings on antibacterial performance are interesting and included. A smart bacteria-responsive titanium dioxide nanotubes coating is also attractive and elaborated. Developing multifunctional surface coatings combining osteogenesis and antimicrobial activity is the current trend. Surface engineering methods are usually combined to obtain hierarchical multiscale surface structures with better biofunctionalization outcomes.

Spreading and Drying Dynamics of Water Drop on Hot Surface of Superwicking Ti-6Al-4V Alloy Material Fabricated by Femtosecond Laser.

A superwicking Ti-6Al-4V alloy material with a hierarchical capillary surface structure was fabricated using femtosecond laser. The basic capillary surface structure is an array of micropillars/microholes. For enhancing its capillary action, the surface of the micropillars/microholes is additionally structured by regular fine microgrooves using a technique of laser-induced periodic surface structures (LIPSS), providing an extremely strong capillary action in a temperature range between 23 °C and 80 °C. Due to strong capillary action, a water drop quickly spreads in the wicking surface structure and forms a thin film over a large surface area, resulting in fast evaporation. The maximum water flow velocity after the acceleration stage is found to be 225–250 mm/s. In contrast to other metallic materials with surface capillarity produced by laser processing, the wicking performance of which quickly degrades with time, the wicking functionality of the material created here is long-lasting. Strong and long-lasting wicking properties make the created material suitable for a large variety of practical applications based on liquid-vapor phase change. Potential significant energy savings in air-conditioning and cooling data centers due to application of the material created here can contribute to mitigation of global warming.

Hierarchical Nano/Micro-Structured Surfaces With High Surface Area/Volume Ratios

Abstract Recently, many studies have investigated additive manufacturing (AM) of hierarchical surfaces with high surface area/volume (SA/V) ratios, and their performance has been characterized for applications in next-generation functional devices. Despite recent advances, it remains challenging to design and manufacture high SA/V ratio structures with desired functionalities. In this study, we established the complex correlations among the SA/V ratio, surface structure geometry, functionality, and manufacturability in the two-photon polymerization (TPP) process. Inspired by numerous natural structures, we proposed a 3-level hierarchical structure design along with the mathematical modeling of the SA/V ratio. Geometric and manufacturing constraints were modeled to create well-defined three-dimensional hierarchically structured surfaces with a high accuracy. A process flowchart was developed to design the proposed surface structures to achieve the target functionality, SA/V ratio, and geometric accuracy. Surfaces with varied SA/V ratios and hierarchy levels were designed and printed. The wettability and antireflection properties of the fabricated surfaces were characterized. It was observed that the wetting and antireflection properties of the 3-level design could be easily tailored by adjusting the design parameter settings and hierarchy levels. Furthermore, the proposed surface structure could change a naturally hydrophilic surface to near-superhydrophobic. Geometrical light trapping effects were enabled and the antireflection property could be significantly enhanced (> 80% less reflection) by the proposed hierarchical surface structures. Experimental results implied the great potential of the proposed surface structures for various applications such as microfluidics, optics, energy, and interfaces.

N, P-codoped porous carbon derived from chitosan with hierarchical N-enriched structure and ultra-high specific surface Area toward high-performance supercapacitors

In this work, a facile “carbonization-activation” strategy is developed to synthesize N, P-codoped hierarchical porous carbon. Phosphoric acid is innovatively introduced during the hydrothermal process to achieve in-situ P doping as well as create abundant pores, and the employment of sodamide is of vital importance to simultaneously serve as activating agent and N-source to succeed a high-level N doping. Thus, the obtained samples exhibit a unique three-dimensional hierarchical structure with an ultra-high specific surface area (3646 m2 g−1) and ultra-high N-doping level (9.81 at.%). Computational analyses confirm that N, P co-doping and higher N content can enhance active sites and widen potential differences of carbon materials to improve their capacitance. The as-prepared carbon materials demonstrate superior electrochemical performances, such as an ultra-high capacitance of 586 F g−1 at 1 A g−1, a superior rate capability of 409 F g−1 at 20 A g−1, and excellent long-term stability of 97 % capacitance retention after 10,000 cycles in 6 M KOH. Moreover, an assembled symmetric supercapacitor delivers a high energy density of 28.1 Wh kg−1 at the power density of 450 W kg−1 in 1 M Na2SO4, demonstrating a great potential for applications in supercapacitors.

A SUPERHYDROPHOBIC COATING ON TITANIUM ALLOYS BY SIMPLE CHEMICAL ETCHING

In the present study, a scalable-manufactured and environmental-friendly method was proposed to fabricate the superhydrophobic coating on titanium alloy. The hierarchical binary surface structures were obtained by hydrothermal treatment of titanium alloy with oxalic acid and sodium hydroxide solutions successively. The hierarchical structure surfaces after fluoroalkyl-silane modification possessed a maximum contact angle of 158.7∘ and a sliding angle of 4.3∘. The low contact angle hysteresis surface can lead to efficient self-cleaning performance, which was confirmed by the bounce and roll off of water droplet on the surface. Furthermore, the anticorrosion behaviors of the superhydrophobic coating in 3.5[Formula: see text]wt.% NaCl solution was evaluated by the electrochemical impedance spectroscopy (EIS). It was found that the superhydrophobic coating can maintain its superhydrophobic state (150∘) within 48 h, thereby effectively preventing the corrosive medium from penetrating into the coating. This simple yet fast anti-corrosion/self-cleaning superhydrophobic coating manufacturing strategy will enlighten its potential application in the engineering fields.

Engineered nanoscale schwertmannites as Fenton–like catalysts for highly efficient degradation of nitrophenols

The Fenton process has been considered as one of the most promising advanced oxidation processes (AOPs) for the treatment of persistent organic pollutants (POPs). Herein, engineered nanoscale schwertmannite (nano–SCH) were fabricated from a PVP (polyvinylpyrrolidone) assisted room–temperature synthesis. The as–prepared well–dispersed nano–SCH materials were further studied as Fenton–like catalysts for 4–nitrophenol (4–NP) degradation in the presence of H2O2. Results showed that the optimized nano–SCH–0.125 was able to degrade 91.0% of 4–NP in 60 min at 298 K, thanks to the nanoscale and hierarchical surface structures that provided abundant reactive sites at solid/solution interfaces. Moreover, mechanism study indicated that •OH radicals were the main reactive species responsible for the excellent 4–NP degradation performances during the Fenton–like processes. This work thus provides a viable pathway to engineer nanoscale materials with enhanced catalytic properties in oxidative degradation of environmental pollutants.

Linoleic Acid-Derived Carbon Microspheres with Hierarchical Porous Structure and Controllable Surface Groups toward Application in Supercapacitors

Hierarchical porous carbons (HPCs) with optimized porosity and enriched surface functional groups are a promising carbon material for supercapacitor development. However, it is a challenge to reali...

Hierarchical porous N-doped carbon xerogels for high performance CO2 capture and supercapacitor

Novel microporous carbon xerogels (CX-HMTAs) with different morphologies and well-developed porosity were successfully fabricated. The hierarchical pore, surface structure, and nitrogen content could be easily controlled by adjusting the amount of hexamethylenetetramine (HMTA). The samples as-obtained exhibited high micropore volume and large specific surface area, which were applied as supercapacitor electrodes and CO2 capture materials. The CX-HMTA4 with a moderate concentration of HMTA (0.72 %) afforded the highest CO2 adsorption capability with 4.21 mmol g−1 at 273 K and 1 bar, and excellent ideal adsorption solution theory (IAST) selectivity with 70 for CO2/N2 capture at 298 K. Moreover, the CX-HMTA4 were simultaneously conducted as a supercapacitor electrode, and gave a maximum specific capacitance of 161 F g-1 and high stability (retained 99.4 % capacity after 1000 cycles) in 6 M KOH electrolyte at 1 A g-1, showed a great advance when compared with most reported benchmark carbon materials. The multifunctional porous carbon materials presented herein were facilely prepared without any activation, exhibiting considerable potentials for large-scale gas adsorption/separation and electrochemical energy storage.

Adsorptive removal of aflatoxin B1 from vegetable oils via novel adsorbents derived from a metal-organic framework

Vegetable oils are essential daily diet, but they are simply contaminated with aflatoxin B1 (AFB1), a serious toxic compound to human health. Adsorption method due to the easy operation, high efficiency and low costing is set to become a main detoxification technique for AFB1. Unfortunately, previous reported adsorbents were rarely used for detoxification in food industry since they cannot meet the criteria of large-scale production of edible oils. Metal-organic frameworks (MOFs) with unique textural properties could be favorable precursors for synthesis of advanced materials. In this research, three kinds of Cu-BTC MOF-derived porous materials were prepared by different carbonization temperature and characterized by XRD, SEM, FT-IR, and nitrogen adsorption-desorption techniques. Isotherm and kinetic studies on the adsorption behaviour of AFB1 onto the three porous carbonaceous materials have been systematically conducted. The results revealed that the porous carbonaceous materials could act as the excellent adsorbents that were of enough adsorption sites for AFB1, mainly due to the hierarchical porous structure and large surface areas for the enhancement of adsorption capacity. Notably, the porous carbonaceous materials could not only remove more than 90% of AFB1 from real vegetable oils within 30 min, but also remain the treated oils at low cytotoxicity. Meanwhile, the detoxification process could little affect the quality of oils. Thus, the Cu-BTC MOF-derived porous carbonaceous materials with high efficiency, safe, practical and economic characteristics could be novel potential adsorbents used in the application of AFB1 removal from contaminated vegetable oils.