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19 pages, 6537 KiB

Open AccessFeature PaperArticle

Microwave Synthesis, Characterization and Perspectives of Wood Pencil-Derived Carbon

by Nikolaos Chalmpes, Georgios Asimakopoulos, Maria Baikousi, Constantinos E. Salmas, Dimitrios Moschovas, Apostolos Avgeropoulos, Athanasios B. Bourlinos, Iosif Tantis, Aristides Bakandritsos, Dimitrios Gournis and Michael A. Karakassides

Appl. Sci. 2022, 12(1), 410; https://doi.org/10.3390/app12010410 - 1 Jan 2022

Cited by 2 | Viewed by 2771

Abstract

More than 14 billion pencils are manufactured and used globally every year. On average, a pencil is discarded after 60% of its original length has been depleted. In the present work we propose a simple and affordable way of converting this non-neglectable amount [...] Read more.

More than 14 billion pencils are manufactured and used globally every year. On average, a pencil is discarded after 60% of its original length has been depleted. In the present work we propose a simple and affordable way of converting this non-neglectable amount of waste into added value carbon product. In particular, we demonstrate the microwave synthesis of carbon from the wood pencil with and without chemical activation. This could be a process stage before the final recycling of the expensive graphite core. In the latter case, irradiation of the wood pencil in a domestic microwave oven heats up the pencil’s graphite core, thus inducing carbonization of its wood casing. The carbonized product consists of amorphous carbon nanosheets having relatively low surface area. However, if the wood pencil is soaked in 50% KOH aqueous solution prior to microwave irradiation, a significantly higher surface area of carbon is obtained, consisting of irregular-shaped porous particles. Consequently, the obtained carbon can easily decolorize a methylene blue aqueous solution, can be used to make pocket warmers or gunpowder, and lastly, serves as an excellent adsorbent towards Cr(VI) removal from water, showing a maximum adsorption capacity of 70–75 mg/g within 24 h at 23 °C, pH = 3. Full article

(This article belongs to the Special Issue Characterization and Application of Nanoporous Materials)

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16 pages, 2414 KiB

Open AccessFeature PaperArticle

Influence of Pore-Size/Porosity on Ion Transport and Static BSA Fouling for TiO₂-Covered Nanoporous Alumina Membranes

by Lourdes Gelde, Ana Laura Cuevas and Juana Benavente

Appl. Sci. 2021, 11(12), 5687; https://doi.org/10.3390/app11125687 - 19 Jun 2021

Cited by 7 | Viewed by 1912

Abstract

The influence of geometrical parameters (pore radii and porosity) on ion transport through two almost ideal nanoporous alumina membranes (NPAMs) coated with a thin TiO₂ layer by the atomic layer deposition technique (Sf-NPAM/TiO₂ and Ox-NPAM/TiO₂ samples) was analyzed by membrane [...] Read more.

The influence of geometrical parameters (pore radii and porosity) on ion transport through two almost ideal nanoporous alumina membranes (NPAMs) coated with a thin TiO₂ layer by the atomic layer deposition technique (Sf-NPAM/TiO₂ and Ox-NPAM/TiO₂ samples) was analyzed by membrane potential and electrochemical impedance spectroscopy measurements. The results showed the significant effect of pore radii (10 nm for Sf-NPAM/TiO₂ and 13 nm for Ox-NPAM/TiO₂) when compared with porosity (9% and 6%, respectively). Both electrochemical techniques were also used for estimation of protein (bovine serum albumin or BSA) static fouling, and the results seem to indicate deposition of a BSA layer on the Sf-NPAM/TiO₂ fouled membrane surface but pore-wall deposition in the case of the fouled Ox-NPAM/TiO₂ sample. Moreover, a typical and simple optical technique such as light transmission/reflection (wavelength ranging between 0 and 2000 nm) was also used for membrane analysis, showing only slight transmittance differences in the visible region when both clean membranes were compared. However, a rather significant transmittance reduction (~18%) was observed for the fouled Sf-NPAM/TiO₂ sample compared to the fouled Ox-NPAM/TiO₂ sample, and was associated with BSA deposition on the membrane surface, thus supporting the electrochemical analysis results. Full article

(This article belongs to the Special Issue Characterization and Application of Nanoporous Materials)

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20 pages, 3092 KiB

Open AccessArticle

Nanoporous Activated Carbon Derived via Pyrolysis Process of Spent Coffee: Structural Characterization. Investigation of Its Use for Hexavalent Chromium Removal

by Georgios Asimakopoulos, Maria Baikousi, Vasilis Kostas, Marios Papantoniou, Athanasios B. Bourlinos, Radek Zbořil, Michael A. Karakassides and Constantinos E. Salmas

Appl. Sci. 2020, 10(24), 8812; https://doi.org/10.3390/app10248812 - 9 Dec 2020

Cited by 16 | Viewed by 3221

Abstract

Hexavalent chromium (Cr(VI)) is a heavy metal that is highly soluble and exhibits toxic effects on biological systems. Nevertheless, it is used in many industrial applications. The adsorption process of Cr(VI), using activated carbon (AC), is under investigation globally. On the other hand, [...] Read more.

Hexavalent chromium (Cr(VI)) is a heavy metal that is highly soluble and exhibits toxic effects on biological systems. Nevertheless, it is used in many industrial applications. The adsorption process of Cr(VI), using activated carbon (AC), is under investigation globally. On the other hand, around six million tons of spent coffee is sent to landfill annually. In the spirit of cyclic economy, this research investigated the production of AC from spent coffee for the removal of Cr(VI) from wastewater. The AC was produced via pyrolysis process under a nitrogen atmosphere. Chemical activation using potassium hydroxide (KOH) occurred simultaneously with the pyrolysis process. The produced AC was tested as an absorber of Cr(VI). The best fitted kinetic model was the diffusion–chemisorption model. A 24-h adsorption experiment was carried out using a solution with a pH of 3 and an initial Cr(VI) concentration of 54.14 ppm. This resulted in an experimental maximum capacity of 109 mg/g, while the theoretical prediction was 137 mg/g. It also resulted in an initial adsorption rate (r_i) of 110 (mg/(g h)). The Brunauer–Emmett–Teller surface area (S_gBET) was 1372 m²/g, the Langmuir surface area (S_gLang.) was 1875 m²/g, and the corrugated pore structure model surface area (S_gCPSM) was 1869 m²/g. The micropore volume was 84.6%, exhibiting micropores at D_micro1 = 1.28 and D_micro2 = 1.6 nm. The tortuosity factor (τ) was 4.65. Full article

(This article belongs to the Special Issue Characterization and Application of Nanoporous Materials)

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10 pages, 1632 KiB

Open AccessArticle

Theoretical Study of a New Porous 2D Silicon-Filled Composite Based on Graphene and Single-Walled Carbon Nanotubes for Lithium-Ion Batteries

by Dmitry A. Kolosov and Olga E. Glukhova

Appl. Sci. 2020, 10(17), 5786; https://doi.org/10.3390/app10175786 - 21 Aug 2020

Cited by 3 | Viewed by 2546

Abstract

The incorporation of Si16 nanoclusters into the pores of pillared graphene on the base of single-walled carbon nanotubes (SWCNTs) significantly improved its properties as anode material of Li-ion batteries. Quantum-chemical calculation of the silicon-filled pillared graphene efficiency found (I) the optimal mass fraction [...] Read more.

The incorporation of Si16 nanoclusters into the pores of pillared graphene on the base of single-walled carbon nanotubes (SWCNTs) significantly improved its properties as anode material of Li-ion batteries. Quantum-chemical calculation of the silicon-filled pillared graphene efficiency found (I) the optimal mass fraction of silicon (Si)providing maximum anode capacity; (II) the optimal Li: C and Li: Si ratios, when a smaller number of C and Si atoms captured more amount of Li ions; and (III) the conditions of the most energetically favorable delithiation process. For 2D-pillared graphene with a sheet spacing of 2–3 nm and SWCNTs distance of ~5 nm the best silicon concentration in pores was ~13–18 wt.%. In this case the value of achieved capacity exceeded the graphite anode one by 400%. Increasing of silicon mass fraction to 35–44% or more leads to a decrease in the anode capacity and to a risk of pillared graphene destruction. It is predicted that this study will provide useful information for the design of hybrid silicon-carbon anodes for efficient next-generation Li-ion batteries. Full article

(This article belongs to the Special Issue Characterization and Application of Nanoporous Materials)

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17 pages, 3841 KiB

Open AccessFeature PaperArticle

Optical and Electrochemical Characterization of Nanoporous Alumina Structures: Pore Size, Porosity, and Structure Effect

by Ana Laura Cuevas, A. Silvia González, Víctor Vega, Víctor M. Prida and Juana Benavente

Appl. Sci. 2020, 10(14), 4864; https://doi.org/10.3390/app10144864 - 15 Jul 2020

Cited by 8 | Viewed by 2223

Abstract

Three nanoporous alumina structures (NPASs) obtained by the two-step anodization method were optically and electrochemically characterized. Two of the structures were symmetric (NPAS-Sf and NPAS-Ph) and one was asymmetric (NPAS-And); pore size ranged from 10 nm to 100 nm and porosity was 12% [...] Read more.

Three nanoporous alumina structures (NPASs) obtained by the two-step anodization method were optically and electrochemically characterized. Two of the structures were symmetric (NPAS-Sf and NPAS-Ph) and one was asymmetric (NPAS-And); pore size ranged from 10 nm to 100 nm and porosity was 12% in the case of the symmetrical NPAS and 23% and 30% for each surface of the asymmetric structure NPAS-And(A) and (B), respectively. Optical parameters of the studied samples (refraction index and extinction coefficient) were obtained from ellypsometric spectroscopy measurements carried out for wavelengths ranging between 250 nm and 1700 nm (visible and near infrared regions), with the total average refraction indices being 1.54, 1.52, 1.14, and 1.05 for NPAS-Sf, NPAS-Ph, NPAS-And(A), and NPAS-And(B), respectively, which indicates porosity control of refraction index values. Electrochemical characterizations (concentration potential and impedance spectroscopy measurements) were performed with NaCl solutions, and they allowed us to estimate samples of effective fixed charge concentration (1.22 × 10⁻² M, 1.13 × 10⁻³ M, and 1.15 × 10⁻³ M), ion transport numbers, permselectivity (33.0%, 3.1%, and 9.6%), and the electrical resistance of each solution/sample system as well as the interfacial effects associated to solution concentration–polarization, which seems to be mainly controlled by pore size and sample symmetry. Full article

(This article belongs to the Special Issue Characterization and Application of Nanoporous Materials)

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9 pages, 2772 KiB

Open AccessArticle

One-Pot Synthesis and Characterization of VO₂(B) with a Large Voltage Window Electrochemical Performance in Aqueous Solution

by Xiaoyu Liu, Jiqi Zheng, Xuyang Jing, Yan Cheng and Changgong Meng

Appl. Sci. 2020, 10(8), 2742; https://doi.org/10.3390/app10082742 - 16 Apr 2020

Cited by 4 | Viewed by 2717

Abstract

B-type vanadium dioxide (defined as VO₂(B)) nanobelts were synthesized through using commercial ammonium metavanadate, oxalic acid via one-step hydrothermal technique. The structure of VO₂(B) was characterized using different instruments. N₂ adsorption-desorption isotherms revealed that the VO₂(B) [...] Read more.

B-type vanadium dioxide (defined as VO₂(B)) nanobelts were synthesized through using commercial ammonium metavanadate, oxalic acid via one-step hydrothermal technique. The structure of VO₂(B) was characterized using different instruments. N₂ adsorption-desorption isotherms revealed that the VO₂(B) nanobelts were porous structures where BET surface area was 10.4 m²·g⁻¹, the pore volume was 0.0687 cm³/g, and the average pore size was 42.7 nm. Furthermore, the VO₂(B) nanobelts as supercapacitors electrode exhibited a large voltage window (−0.8~1.0 V). The measured capacitance was based on the pseudocapacitance. When the discharge current density is 0.5, 1, and 10 A·g⁻¹, the VO₂(B) shows the specific capacitance of 287, 246, and 222 F·g⁻¹, respectively. Full article

(This article belongs to the Special Issue Characterization and Application of Nanoporous Materials)

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20 pages, 4517 KiB

Open AccessArticle

Improving and Optimizing Sound Absorption Performance of Polyurethane Foam by Prepositive Microperforated Polymethyl Methacrylate Panel

by Xiaocui Yang, Xinmin Shen, Haiqin Duan, Fei Yang, Xiaonan Zhang, Ming Pan and Qin Yin

Appl. Sci. 2020, 10(6), 2103; https://doi.org/10.3390/app10062103 - 20 Mar 2020

Cited by 13 | Viewed by 3265

Abstract

Sound absorption performance of polyurethane foam could be improved by adding a prepositive microperforated polymethyl methacrylate panel to form a composite sound-absorbing structure. A theoretical sound absorption model of polyurethane foam and that of the composite structure were constructed by the transfer matrix [...] Read more.

Sound absorption performance of polyurethane foam could be improved by adding a prepositive microperforated polymethyl methacrylate panel to form a composite sound-absorbing structure. A theoretical sound absorption model of polyurethane foam and that of the composite structure were constructed by the transfer matrix method based on the Johnson–Champoux–Allard model and Maa’s theory. Acoustic parameter identification of the polyurethane foam and structural parameter optimization of the composite structures were obtained by the cuckoo search algorithm. The identified porosity and static flow resistivity were 0.958 and 13078 Pa·s/m² respectively, and their accuracies were proved by the experimental validation. Sound absorption characteristics of the composite structures were verified by finite element simulation in virtual acoustic laboratory and validated through standing wave tube measurement in AWA6128A detector. Consistencies among the theoretical data, simulation data, and experimental data of sound absorption coefficients of the composite structures proved the effectiveness of the theoretical sound absorption model, cuckoo search algorithm, and finite element simulation method. Comparisons of actual average sound absorption coefficients of the optimal composite structure with those of the original polyurethane foam proved the practicability of this identification and optimization method, which was propitious to promote its practical application in noise reduction. Full article

(This article belongs to the Special Issue Characterization and Application of Nanoporous Materials)

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Review

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16 pages, 2726 KiB

Open AccessReview

Review of Hygroscopic Coating on Aluminum Fin Surface of Air Conditioning Heat Exchanger

by Song He, Wang Chen, Wansheng Yang and Xudong Zhao

Appl. Sci. 2021, 11(11), 5193; https://doi.org/10.3390/app11115193 - 3 Jun 2021

Cited by 4 | Viewed by 3426

Abstract

Air conditioning energy consumption accounts for most building energy consumption, indoor dehumidification is the main cause of air conditioning energy consumption. Optimize the dehumidification methods of air conditioning systems have great significance to the development of green buildings and people’s pursuit of comfort. [...] Read more.

Air conditioning energy consumption accounts for most building energy consumption, indoor dehumidification is the main cause of air conditioning energy consumption. Optimize the dehumidification methods of air conditioning systems have great significance to the development of green buildings and people’s pursuit of comfort. Improvement of fins on air conditioning heat exchangers is a hot topic of current research and has achieved considerable results in terms of indoor dehumidification and energy saving compared to traditional air conditioners. This paper reviews two kinds of heat exchangers modified by coating, including desiccant-coated heat exchangers and hydrophobic/hydrophilic coated heat exchangers. For desiccant-coated heat exchangers, the preparation methods of advanced desiccant materials and the possibilities of using this material to achieve excellent energy efficiencies were presented, and the operating parameters that affect thermal performance and dehumidification are determined, including airflow temperature, air velocity, inlet air relative humidity, and regeneration temperature. For hydrophobic/hydrophilic coated heat exchangers, different kinds of hybrid hydrophobic-hydrophilic surfaces are highlighted for they are a high water droplet nucleation rate and surface heat transfer efficiency. In addition, the challenges and future works are explained at last. This paper will provide a valuable reference for the follow-up research, which will be helpful for indoor humidity control and reducing the energy consumption of air conditioning. Full article

(This article belongs to the Special Issue Characterization and Application of Nanoporous Materials)

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