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Materials, Volume 11, Issue 1 (January 2018)

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Cover Story (view full-size image) Sensing biological and chemical analytes using liquid crystals (LCs) has been successfully [...] Read more.
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Open AccessArticle Fe-Doped Sol-Gel Glasses and Glass-Ceramics for Magnetic Hyperthermia
Materials 2018, 11(1), 173; https://doi.org/10.3390/ma11010173
Received: 24 December 2017 / Revised: 17 January 2018 / Accepted: 19 January 2018 / Published: 22 January 2018
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Abstract
This work deals with the synthesis and characterization of novel Fe-containing sol-gel materials obtained by modifying the composition of a binary SiO2-CaO parent glass with the addition of Fe2O3. The effect of different processing conditions (calcination in
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This work deals with the synthesis and characterization of novel Fe-containing sol-gel materials obtained by modifying the composition of a binary SiO2-CaO parent glass with the addition of Fe2O3. The effect of different processing conditions (calcination in air vs. argon flowing) on the formation of magnetic crystalline phases was investigated. The produced materials were analyzed from thermal (hot-stage microscopy, differential thermal analysis, and differential thermal calorimetry) and microstructural (X-ray diffraction) viewpoints to assess both the behavior upon heating and the development of crystalline phases. N2 adsorption–desorption measurements allowed determining that these materials have high surface area (40–120 m2/g) and mesoporous texture with mesopore size in the range of 18 to 30 nm. It was assessed that the magnetic properties can actually be tailored by controlling the Fe content and the environmental conditions (oxidant vs. inert atmosphere) during calcination. The glasses and glass-ceramics developed in this work show promise for applications in bone tissue healing which require the use of biocompatible magnetic implants able to elicit therapeutic actions, such as hyperthermia for bone cancer treatment. Full article
(This article belongs to the Special Issue Bioactive Glasses 2017)
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Open AccessArticle The Enhanced Catalytic Performance and Stability of Rh/γ-Al2O3 Catalyst Synthesized by Atomic Layer Deposition (ALD) for Methane Dry Reforming
Materials 2018, 11(1), 172; https://doi.org/10.3390/ma11010172
Received: 11 December 2017 / Revised: 5 January 2018 / Accepted: 13 January 2018 / Published: 22 January 2018
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Abstract
Rh/γ-Al2O3 catalysts were synthesized by both incipient wetness impregnation (IWI) and atomic layer deposition (ALD). The TEM images of the two catalysts showed that the catalyst from ALD had smaller particle size, and narrower size distribution. The surface chemical states
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Rh/γ-Al2O3 catalysts were synthesized by both incipient wetness impregnation (IWI) and atomic layer deposition (ALD). The TEM images of the two catalysts showed that the catalyst from ALD had smaller particle size, and narrower size distribution. The surface chemical states of both catalysts were investigated by both XPS and X-ray Absorption Near Edge Structure (XANES), and the catalyst from IWI had higher concentration of Rh3+ than that from ALD. The catalytic performance of both catalysts was tested in the dry reforming of methane reaction. The catalyst from ALD showed a higher conversion and selectivity than that from IWI. The stability testing results indicated that the catalyst from ALD showed similar stability to that from IWI at 500 °C, but higher stability at 800 °C. Full article
(This article belongs to the Section Advanced Nanomaterials)
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Open AccessArticle Electrochemical Behaviour and Galvanic Effects of Titanium Implants Coupled to Metallic Suprastructures in Artificial Saliva
Materials 2018, 11(1), 171; https://doi.org/10.3390/ma11010171
Received: 9 January 2018 / Revised: 9 January 2018 / Accepted: 17 January 2018 / Published: 22 January 2018
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Abstract
The aim of the present study is to analyze the electrochemical behavior of five different dental alloys: two cobalt-chromium alloys (CoCr and CoCr-c), one nickel-chromium-titanium alloy (NiCrTi), one gold-palladium alloy (Au), and one titanium alloy (Ti6Al4V), and the galvanic effect when they are
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The aim of the present study is to analyze the electrochemical behavior of five different dental alloys: two cobalt-chromium alloys (CoCr and CoCr-c), one nickel-chromium-titanium alloy (NiCrTi), one gold-palladium alloy (Au), and one titanium alloy (Ti6Al4V), and the galvanic effect when they are coupled to titanium implants (TiG2). It was carried out by electrochemical techniques (open circuit measurements, potentiodynamic curves and Zero-Resistance Ammetry) in artificial saliva (AS), with and without fluorides in different acidic conditions. The studied alloys are spontaneously passivated, but NiCrTi alloy has a very narrow passive domain and losses its passivity in presence of fluorides, so is not considered as a good option for implant superstructures. Variations of pH from 6.5 to 3 in artificial saliva do not change the electrochemical behavior of Ti, Ti6Al4V, and CoCr alloys, and couples, but when the pH of the artificial saliva is below 3.5 and the fluoride content is 1000 ppm Ti and Ti6Al4V starts actively dissolving, and CoCr-c superstructures coupled to Ti show acceleration of corrosion due to galvanic effects. Thus, NiCrTi is not recommended for implant superstructures because of risk of Ni ion release to the body, and fluorides should be avoided in acidic media because Ti, Ti6Al4V, and CoCr-c superstructures show galvanic corrosion. The best combinations are Ti/Ti6Al4V and Ti/CoCr as alternative of noble gold alloys. Full article
(This article belongs to the Special Issue Dental Implant Materials)
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Open AccessArticle Orientation of Steel Fibers in Magnetically Driven Concrete and Mortar
Materials 2018, 11(1), 170; https://doi.org/10.3390/ma11010170
Received: 13 December 2017 / Revised: 4 January 2018 / Accepted: 16 January 2018 / Published: 22 January 2018
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Abstract
The orientation of steel fibers in magnetically driven concrete and magnetically driven mortar was experimentally studied in this paper using a magnetic method. In the magnetically driven concrete, a steel slag was used to replace the coarse aggregate. In the magnetically driven mortar,
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The orientation of steel fibers in magnetically driven concrete and magnetically driven mortar was experimentally studied in this paper using a magnetic method. In the magnetically driven concrete, a steel slag was used to replace the coarse aggregate. In the magnetically driven mortar, steel slag and iron sand were used to replace the fine aggregate. A device was established to provide the magnetic force. The magnetic force was used to rotate the steel fibers. In addition, the magnetic force was also used to vibrate the concrete and mortar. The effect of magnetic force on the orientation of steel fibers was examined by comparing the direction of fibers before and after vibration. The effect of magnetically driven concrete and mortar on the orientation of steel fibers was also examined by comparing specimens to normal concrete and mortar. It is shown that the fibers could rotate about 90° in magnetically driven concrete. It is also shown that the number of fibers rotated in magnetically driven mortar was much more than in mortar vibrated using a shaking table. A splitting test was performed on concrete specimens to investigate the effect of fiber orientation. In addition, a flexural test was also performed on mortar test specimens. It is shown that the orientation of the steel fibers in magnetically driven concrete and mortar affects the strength of the concrete and mortar specimens. Full article
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Open AccessArticle Effect of Aspect Ratio on the Permittivity of Graphite Fiber in Microwave Heating
Materials 2018, 11(1), 169; https://doi.org/10.3390/ma11010169
Received: 21 November 2017 / Revised: 11 January 2018 / Accepted: 17 January 2018 / Published: 22 January 2018
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Abstract
Microwave (MW) heating has received attention as a new heating source for various industrial processes. Some materials are expected to be a more effective absorber of MW, and graphite is observed as a possible candidate for high-temperature application. We investigated the dependence of
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Microwave (MW) heating has received attention as a new heating source for various industrial processes. Some materials are expected to be a more effective absorber of MW, and graphite is observed as a possible candidate for high-temperature application. We investigated the dependence of the aspect ratio of graphite fibers on both their heating behavior and permittivity under a 2.45 GHz MW electric field. In these experiments, both loss tangent and MW heating behavior indicated that the MW absorption of conductive fibers increases with their aspect ratio. The MW absorption was found to be well accounted for by the application of a spheroidal model for a single fiber. The absorption of graphite fibers decreases with increasing aspect ratio when the long axis of the ellipsoid is perpendicular to the electric field, whereas it increases with the aspect ratio when the long axis is parallel to the electric field. The analytical model indicated that MW heating of the conductive fibers is expected to depend on both the shape and arrangement of the fibers in the electric field. Full article
(This article belongs to the Special Issue Electromagnetic Wave Absorbing Structures)
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Open AccessFeature PaperArticle One-Step Preparation of Large Area Films of Oriented MoS2 Nanoparticles on Multilayer Graphene and Its Electrocatalytic Activity for Hydrogen Evolution
Materials 2018, 11(1), 168; https://doi.org/10.3390/ma11010168
Received: 14 December 2017 / Revised: 9 January 2018 / Accepted: 17 January 2018 / Published: 22 January 2018
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Abstract
MoS2 is a promising material to replace Pt-based catalysts for the hydrogen evolution reaction (HER), due to its excellent stability and high activity. In this work, MoS2 nanoparticles supported on graphitic carbon (about 20 nm) with a preferential 002 facet orientation
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MoS2 is a promising material to replace Pt-based catalysts for the hydrogen evolution reaction (HER), due to its excellent stability and high activity. In this work, MoS2 nanoparticles supported on graphitic carbon (about 20 nm) with a preferential 002 facet orientation have been prepared by pyrolysis of alginic acid films on quartz containing adsorbed (NH4)2MoS4 at 900 °C under Ar atmosphere. Although some variation of the electrocatalytic activity has been observed from batch to batch, the MoS2 sample exhibited activity for HER (a potential onset between 0.2 and 0.3 V vs. SCE), depending on the concentrations of (NH4)2MoS4 precursor used in the preparation process. The loading and particle size of MoS2, which correlate with the amount of exposed active sites in the sample, are the main factors influencing the electrocatalytic activity. Full article
(This article belongs to the Special Issue Graphene/Carbon Nanotubes Application in Solar Cells)
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Open AccessArticle Microstructure Evolution and Mechanical Properties of Underwater Dry and Local Dry Cavity Welded Joints of 690 MPa Grade High Strength Steel
Materials 2018, 11(1), 167; https://doi.org/10.3390/ma11010167
Received: 1 December 2017 / Revised: 13 January 2018 / Accepted: 15 January 2018 / Published: 22 January 2018
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Abstract
Q690E high strength low alloy (HSLA) steel plays an important role in offshore structures. In addition, underwater local cavity welding (ULCW) technique was widely used to repair important offshore constructions. However, the high cooling rate of ULCW joints results in bad welding quality
[...] Read more.
Q690E high strength low alloy (HSLA) steel plays an important role in offshore structures. In addition, underwater local cavity welding (ULCW) technique was widely used to repair important offshore constructions. However, the high cooling rate of ULCW joints results in bad welding quality compared with underwater dry welding (UDW) joints. Q690E high strength low alloy steels were welded by multi-pass UDW and ULCW techniques, to study the microstructural evolution and mechanical properties of underwater welded joints. The microstructure and fracture morphology of welded joints were observed by scanning electron microscope and optical microscope. The elemental distribution in the microstructure was determined with an Electron Probe Microanalyzer. The results indicated that the microstructure of both two welded joints was similar. However, martensite and martensite-austenite components were significantly different with different underwater welding methods such that the micro-hardness of the HAZ and FZ in the ULCW specimen was higher than that of the corresponding regions in UDW joint. The yield strength and ultimate tensile strength of the ULCW specimen are 109 MPa lower and 77 MPa lower, respectively, than those of the UDW joint. The impact toughness of the UDW joint was superior to those of the ULCW joint. Full article
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Open AccessFeature PaperReview Advanced Material Strategies for Next-Generation Additive Manufacturing
Materials 2018, 11(1), 166; https://doi.org/10.3390/ma11010166
Received: 29 December 2017 / Revised: 15 January 2018 / Accepted: 17 January 2018 / Published: 22 January 2018
Cited by 2 | PDF Full-text (3625 KB) | HTML Full-text | XML Full-text
Abstract
Additive manufacturing (AM) has drawn tremendous attention in various fields. In recent years, great efforts have been made to develop novel additive manufacturing processes such as micro-/nano-scale 3D printing, bioprinting, and 4D printing for the fabrication of complex 3D structures with high resolution,
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Additive manufacturing (AM) has drawn tremendous attention in various fields. In recent years, great efforts have been made to develop novel additive manufacturing processes such as micro-/nano-scale 3D printing, bioprinting, and 4D printing for the fabrication of complex 3D structures with high resolution, living components, and multimaterials. The development of advanced functional materials is important for the implementation of these novel additive manufacturing processes. Here, a state-of-the-art review on advanced material strategies for novel additive manufacturing processes is provided, mainly including conductive materials, biomaterials, and smart materials. The advantages, limitations, and future perspectives of these materials for additive manufacturing are discussed. It is believed that the innovations of material strategies in parallel with the evolution of additive manufacturing processes will provide numerous possibilities for the fabrication of complex smart constructs with multiple functions, which will significantly widen the application fields of next-generation additive manufacturing. Full article
(This article belongs to the Special Issue NextGen Materials for 3D Printing)
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Open AccessArticle Poly(hydroxyalkanoate)s-Based Hydrophobic Coatings for the Protection of Stone in Cultural Heritage
Materials 2018, 11(1), 165; https://doi.org/10.3390/ma11010165
Received: 4 December 2017 / Revised: 11 January 2018 / Accepted: 17 January 2018 / Published: 20 January 2018
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Abstract
Reversibility is a mandatory requirement for materials used in heritage conservation, including hydrophobic protectives. Nevertheless, current protectives for stone are not actually reversible as they remain on the surfaces for a long time after their hydrophobicity is lost and can hardly be removed.
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Reversibility is a mandatory requirement for materials used in heritage conservation, including hydrophobic protectives. Nevertheless, current protectives for stone are not actually reversible as they remain on the surfaces for a long time after their hydrophobicity is lost and can hardly be removed. Ineffective and aged coatings may jeopardise the stone re-treatability and further conservation interventions. This paper aims at investigating the performance of PHAs-based coatings for stone protection, their main potential being the ‘reversibility by biodegradation’ once water repellency ended. The biopolymer coatings were applied to three different kinds of stone, representative of lithotypes used in historic architecture: sandstone, limestone and marble. Spray, poultice and dip-coating were tested as coating techniques. The effectiveness and compatibility of the protectives were evaluated in terms of capillary water absorption, static and dynamic contact angles, water vapour diffusion, colour alteration and surface morphology. The stones’ wettability after application of two commercial protectives was investigated too, for comparison. Finally, samples were subjected to artificial ageing to investigate their solar light stability. Promising results in terms of efficacy and compatibility were obtained, although the PHAs-based formulations developed here still need improvement for increased durability and on-site applicability. Full article
(This article belongs to the Special Issue Recent Advances in Smart Materials for the Built Environment)
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Open AccessArticle Preparation of 1D Hierarchical Material Mesosilica/Pal Composite and Its Performance in the Adsorption of Methyl Orange
Materials 2018, 11(1), 164; https://doi.org/10.3390/ma11010164
Received: 25 December 2017 / Revised: 16 January 2018 / Accepted: 17 January 2018 / Published: 20 January 2018
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Abstract
This paper highlights the synthesis of a one-dimensional (1D) hierarchical material mesosilica/palygorskite (Pal) composite and evaluates its adsorption performance for anionic dye methyl orange (MO) in comparison with Pal and Mobile crystalline material-41 (MCM-41). The Mesosilica/Pal composite is consisted of mesosilica coated Pal
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This paper highlights the synthesis of a one-dimensional (1D) hierarchical material mesosilica/palygorskite (Pal) composite and evaluates its adsorption performance for anionic dye methyl orange (MO) in comparison with Pal and Mobile crystalline material-41 (MCM-41). The Mesosilica/Pal composite is consisted of mesosilica coated Pal nanorods and prepared through a dual template approach using cetyltrimethyl ammonium bromide (CTAB) and Pal as soft and hard templates, respectively. The composition and structure of the resultant material was characterized by a scanning electron microscope (SEM), transmissionelectron microscopy (TEM), N2 adsorption-desorption analysis, small-angle X-Ray powder diffraction (XRD), and zeta potential measurement. Adsorption experiments were carried out with different absorbents at different contact times and pH levels. Compared with Pal and MCM-41, the mesosilica/Pal composite exhibited the best efficiency for MO adsorption. Its adsorption ratio is as high as 70.4%. Its adsorption equilibrium time is as short as 30 min. Results testify that the MO retention is promoted for the micro-mesoporous hierarchical structure and positive surface charge electrostatic interactions of the mesosilica/Pal composite. The regenerability of the mesosilica/Pal composite absorbent was also assessed. 1D morphology makes it facile to separate from aqueous solutions. It can be effortlessly recovered and reused for up to nine cycles. Full article
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Open AccessArticle Glass Polarization Induced Drift of a Closed-Loop Micro-Accelerometer
Materials 2018, 11(1), 163; https://doi.org/10.3390/ma11010163
Received: 8 December 2017 / Revised: 15 January 2018 / Accepted: 19 January 2018 / Published: 20 January 2018
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Abstract
The glass polarization effects were introduced in this paper to study the main cause of turn-on drift phenomenon of closed-loop micro-accelerometers. The glass substrate underneath the sensitive silicon structure underwent a polarizing process when the DC bias voltage was applied. The slow polarizing
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The glass polarization effects were introduced in this paper to study the main cause of turn-on drift phenomenon of closed-loop micro-accelerometers. The glass substrate underneath the sensitive silicon structure underwent a polarizing process when the DC bias voltage was applied. The slow polarizing process induced an additional electrostatic field to continually drag the movable mass block from one position to another so that the sensing capacitance was changed, which led to an output drift of micro-accelerometers. This drift was indirectly tested by experiments and could be sharply reduced by a shielding layer deposited on the glass substrate because the extra electrical filed was prohibited from generating extra electrostatic forces on the movable fingers of the mass block. The experimental results indicate the average magnitude of drift decreased about 73%, from 3.69 to 0.99 mV. The conclusions proposed in this paper showed a meaningful guideline to improve the stability of micro-devices based on silicon-on-glass structures. Full article
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Open AccessArticle Influence of Magnesium Ions in the Seawater Environment on the Improvement of the Corrosion Resistance of Low-Chromium-Alloy Steel
Materials 2018, 11(1), 162; https://doi.org/10.3390/ma11010162
Received: 1 December 2017 / Revised: 11 January 2018 / Accepted: 18 January 2018 / Published: 20 January 2018
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Abstract
This study examined the synergic effect of alloying the element Cr and the environmental element Mg2+ ions on the corrosion property of a low-alloy steel in seawater at 60 °C, by means of electrochemical impedance spectroscopy (EIS), linear polarization resistance (LPR) tests
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This study examined the synergic effect of alloying the element Cr and the environmental element Mg2+ ions on the corrosion property of a low-alloy steel in seawater at 60 °C, by means of electrochemical impedance spectroscopy (EIS), linear polarization resistance (LPR) tests and weight-loss tests. The Mg2+ ions in seawater played an important role in lowering the electron transfer of the rust layer in the Cr-containing steel. The corrosion resistance of the Cr-containing steel is superior to that of blank steel in Mg2+ ions containing seawater. XPS and XRD results indicated that the formation of MgFe2O4 and a mixed layer (Cr oxide + FeCr2O4 + MgCr2O4) improved the corrosion resistance of the low-alloy steel in the seawater. Full article
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Open AccessArticle Blood Vessel Formation and Bone Regeneration Potential of the Stromal Vascular Fraction Seeded on a Calcium Phosphate Scaffold in the Human Maxillary Sinus Floor Elevation Model
Materials 2018, 11(1), 161; https://doi.org/10.3390/ma11010161
Received: 15 December 2017 / Revised: 12 January 2018 / Accepted: 18 January 2018 / Published: 20 January 2018
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Abstract
Bone substitutes are used as alternatives for autologous bone grafts in patients undergoing maxillary sinus floor elevation (MSFE) for dental implant placement. However, bone substitutes lack osteoinductive and angiogenic potential. Addition of adipose stem cells (ASCs) may stimulate osteogenesis and osteoinduction, as well
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Bone substitutes are used as alternatives for autologous bone grafts in patients undergoing maxillary sinus floor elevation (MSFE) for dental implant placement. However, bone substitutes lack osteoinductive and angiogenic potential. Addition of adipose stem cells (ASCs) may stimulate osteogenesis and osteoinduction, as well as angiogenesis. We aimed to evaluate the vascularization in relation to bone formation potential of the ASC-containing stromal vascular fraction (SVF) of adipose tissue, seeded on two types of calcium phosphate carriers, within the human MSFE model, in a phase I study. Autologous SVF was obtained from ten patients and seeded on β-tricalcium phosphate (n = 5) or biphasic calcium phosphate carriers (n = 5), and used for MSFE in a one-step surgical procedure. After six months, biopsies were obtained during dental implant placement, and the quantification of the number of blood vessels was performed using histomorphometric analysis and immunohistochemical stainings for blood vessel markers, i.e., CD34 and alpha-smooth muscle actin. Bone percentages seemed to correlate with blood vessel formation and were higher in study versus control biopsies in the cranial area, in particular in β-tricalcium phosphate-treated patients. This study shows the safety, feasibility, and efficiency of the use of ASCs in the human MSFE, and indicates a pro-angiogenic effect of SVF. Full article
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Open AccessArticle Quadrilateral Micro-Hole Array Machining on Invar Thin Film: Wet Etching and Electrochemical Fusion Machining
Materials 2018, 11(1), 160; https://doi.org/10.3390/ma11010160
Received: 11 December 2017 / Revised: 3 January 2018 / Accepted: 17 January 2018 / Published: 19 January 2018
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Abstract
Ultra-precision products which contain a micro-hole array have recently shown remarkable demand growth in many fields, especially in the semiconductor and display industries. Photoresist etching and electrochemical machining are widely known as precision methods for machining micro-holes with no residual stress and lower
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Ultra-precision products which contain a micro-hole array have recently shown remarkable demand growth in many fields, especially in the semiconductor and display industries. Photoresist etching and electrochemical machining are widely known as precision methods for machining micro-holes with no residual stress and lower surface roughness on the fabricated products. The Invar shadow masks used for organic light-emitting diodes (OLEDs) contain numerous micro-holes and are currently machined by a photoresist etching method. However, this method has several problems, such as uncontrollable hole machining accuracy, non-etched areas, and overcutting. To solve these problems, a machining method that combines photoresist etching and electrochemical machining can be applied. In this study, negative photoresist with a quadrilateral hole array pattern was dry coated onto 30-µm-thick Invar thin film, and then exposure and development were carried out. After that, photoresist single-side wet etching and a fusion method of wet etching-electrochemical machining were used to machine micro-holes on the Invar. The hole machining geometry, surface quality, and overcutting characteristics of the methods were studied. Wet etching and electrochemical fusion machining can improve the accuracy and surface quality. The overcutting phenomenon can also be controlled by the fusion machining. Experimental results show that the proposed method is promising for the fabrication of Invar film shadow masks. Full article
(This article belongs to the Section Manufacturing Processes and Systems)
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Open AccessArticle Nitrogen-Containing Functional Groups-Facilitated Acetone Adsorption by ZIF-8-Derived Porous Carbon
Materials 2018, 11(1), 159; https://doi.org/10.3390/ma11010159
Received: 19 December 2017 / Revised: 17 January 2018 / Accepted: 18 January 2018 / Published: 19 January 2018
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Abstract
Nitrogen-doped porous carbon (ZC) is prepared by modification with ammonia for increasing the specific surface area and surface polarity after carbonization of zeolite imidazole framework-8 (ZIF-8). The structure and properties of these ZCs were characterized by Transmission electron microscopy, X-ray diffraction, N2
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Nitrogen-doped porous carbon (ZC) is prepared by modification with ammonia for increasing the specific surface area and surface polarity after carbonization of zeolite imidazole framework-8 (ZIF-8). The structure and properties of these ZCs were characterized by Transmission electron microscopy, X-ray diffraction, N2 sorption, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. Through static adsorption tests of these carbons, the sample obtained at 600 °C was selected as an excellent adsorbent, which exhibited an excellent acetone capacity of 417.2 mg g−1 (25 °C) with a very large surface area and high-level nitrogen doping (13.55%). The microporosity, surface area and N-containing groups of the materials, pyrrolic-N, pyridinic-N, and oxidized-N groups in particular, were found to be the determining factors for acetone adsorption by means of molecular simulation with density functional theory. These findings indicate that N-doped microporous carbon materials are potential promising adsorbents for acetone. Full article
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