Effect of Oxyfluorination of PFA-Coated Metal Mesh with Superhydrophobic Properties on the Filtration Performance of SiO2 Microparticles.

Recently, semiconductor wastewater treatment has received much attention due to the emergence of environmental issues. Acid-resistant coatings are essential for metal prefilters used in semiconductor wastewater treatment. Perfluoroalkoxy alkane is mainly used as an acid-resistant coating agent, since PFA has inherent superhydrophobicity, water permeability is lowered. To solve this problem, the surface of the PFA-coated metal mesh was treated via an oxyfluorination method in which an injected mixed gas of fluorine and oxygen reacted with the surface functional groups. Surface analysis, water contact angle measurement, and water permeability tests were performed on the surface-treated PFA-coated mesh. Consequently, the superhydrophobic surface was effectively converted to a hydrophobic surface as the PFA coating layer was surface-modified with C-O-OH functional groups via the oxyfluorination reaction. As a result of using simulation solutions that float silica particles of various sizes, the permeability and particle removal rate of the surface-modified PFA-coated stainless-steel mesh were improved compared to those before surface modification. Therefore, the oxyfluorination treatment used in this study was suitable for improving the filtration performance of SiO2 microparticles in the PFA-coated stainless-steel mesh.

A Comprehensive Review of Gas Sensors Using Carbon Materials.

In recent years, interest in carbon materials for use in gas sensors has increased. Carbon materials have unique electrical, optical and mechanical properties, making these materials very interesting. In this review, the properties of carbon materials are first introduced. Surface modification for carbon materials, fabrication for gas sensors, and the gas-sensing conditions and mechanisms according to the different types of carbon materials are chiefly described. In particular, this review focuses on the enhancement of the gas-sensing properties of carbon materials depending on the modification methods used and its mechanism.

Preparation and Characterization of Cobalt/Graphene Composites Using Liquid Phase Plasma System.

Liquid phase plasma (LPP) method was applied, for the first time, to the impregnation of cabalt nanoparticles onto graphene. Nanoparticles were dispersed uniformly on the surface of the two-dimensional graphene sheet. The electron miocroscopy observation showed approximately 2-7 nm sized spherical nanoparticles deposited on the surface of graphene sheets. The XPS and EDX analyses revealed that both metal Co and CoO were present in the Co/graphene composites synthesized by the LPP method.

Investigation on Sized-Regulated Iron Nanoparticles Prepared by Liquid Phase Plasma Reduction Process.

The liquid-phase plasma reduction method has been applied to prepare iron nanoparticles from iron chloride solution using a bipolar pulsed electrical discharge system. The excited states of atomic iron, hydrogen, and oxygen as well as the molecular bands of hydroxyl radicals were detected in the emission spectra. The iron nanoclusters formed at the initial stage convert to dispersion of small iron nanoparticles, which then grows slowly to form anisotropic, tetragonal shape. The cationic surfactant of CTAB was shown to exhibit a large influence on the particle generation procedure.

SiO/Carbon complex produced by carbothermal reduction for the anode materials of high-performance lithium ion battery.

SiO/carbon complexes were prepared by electrospinning and carbothermal reduction to improve the rate performance at a high C rate, and their electrochemical properties were investigated for use as an anode material in a lithium ion battery. The SiO/carbon complexes that were prepared by electrospinning had a fibrous structure with considerable beads. The crystal structure, composition, and surface chemical composition of the SiO/carbon complexes changed based on the carbothermal reduction temperature. The SiO/carbon complexes were a mixture of SiO2, PAN-based carbon, and beta-SiC. SiC crystal structures and C--Si--O or Si--C bonds formed from the reaction of SiO2 and PAN in the SiO2/PAN complex during carbothermal reduction above 1,500 degrees C. The charge-discharge profiles of these SiO/carbon complexes were similar to those observed for disordered carbon. The second discharge capacities and rate capabilities of the SiO/carbon complexes were higher than those of graphite. These results were based on reversible lithium insertion into and extraction from a silicon material, such as amorphous SiO2 or Cx--Si--Oy.

Effects of pore structure on the high-performance capacitive deionization using chemically activated carbon nanofibers.

Capacitive deionization (CDI) electrodes were constructed from activated carbon fibers prepared using electrospinning and chemical activation. The CDI efficiencies of these electrodes were studied as a function of their specific surface areas, pore volumes and pore sizes via salt ion adsorption. The specific surface areas increased approximately 90 fold and the pore volume also increased approximately 26 fold with the use of greater amounts of the chemical activation agent. There was a relative increase in the mesopore fraction with higher porosity. A NaCI solution was passed through a prepared CDI system, and the salt removal efficiency of the CDI system was determined by the separation of the Na+ and Cl- ions toward the anode and cathode. The CDI efficiency increased with greater specific surface areas and pore volumes. In addition, the efficiency per unit pore volume increased with a reduction in the micropore fraction, resulting in the suppressed overlapping effect. In conclusion, the obtained improvements in CDI efficiency were mainly attributed to mesopores, but the micropores also played an important role in the high-performance CDI under conditions of high applied potential and high ion concentrations.

Electrical resistance behavior of oxyfluorinated graphene under oxidizing and reducing gas exposure.

The electrical resistance behavior of graphene was studied under oxidizing and reducing gas exposure. The graphene surface was modified via oxyfluorination to obtain a specific surface area and oxygen functional groups. Fluorine radicals provided improved pore structure and introduction of an oxygen functional group. A high-performance gas sensor was obtained based on enlarged target gas adsorption sites and an enhanced electron charge transfer between the target gas and carbon surface via improved pore structure and the introduction of oxygen functional groups, respectively.

Highly visible-light-active sulfur and carbon co-doped TiO2 (SC-TiO2) heterogeneous photocatalysts prepared by underwater discharge plasma.

To promptly and simply create highly crystalline S/C co-doped TiO2 (SC-TiO2) photocatalysts at room temperature and atmospheric pressure, we suggest a novel plasma-assisted sol-gel synthesis method. This method is a simultaneous synthetic process, in which an underwater plasma undergoes continuous reactions to generate high-energy atomic and molecular species that enable TiO2 to achieve crystallinity, a large surface area, and a heterogeneous structure within a few minutes. In particular, it was demonstrated that the heterogeneously structured TiO2 was formed by doping that sulfur and carbon replace O or Ti atoms in the TiO2 lattice depending on the composition of the synthesis solution during underwater plasma treatment. The resultant SC-TiO2 photocatalysts had narrowed bandgap energies and extended optical absorption scope into the visible range by inducing the intermediate states within bandgap due to generation of oxygen vacancies on the surface of TiO2 through synthesis, crystallization, and doping. Correspondingly, SC-TiO2 showed a significant degradation efficiency ([k] = 6.91 h-1) of tetracycline (TC, antibiotics) under solar light irradiation, up to approximately 4 times higher compared to commercial TiO2 ([k] = 1.68 h-1), resulting in great water purification. Therefore, we anticipate that this underwater discharge plasma system will prove to be an advantageous technique for producing heterostructural TiO2 photocatalysts with superior photocatalytic efficiency for environmental applications.

Optimization of Pore Characteristics of Graphite-Based Anode for Li-Ion Batteries by Control of the Particle Size Distribution.

We investigate the reassembly techniques for utilizing fine graphite particles, smaller than 5 µm, as high-efficiency, high-rate anode materials for lithium-ion batteries. Fine graphite particles of two sizes (0.4-1.2 µm and 5 µm) are utilized, and the mixing ratio of the two particles is varied to control the porosity of the assembled graphite. The packing characteristics of the assembled graphite change based on the mixing ratio of the two types of fine graphite particles, forming assembled graphite with varying porosities. The open porosity of the manufactured assembled graphite samples ranges from 0.94% to 3.55%, while the closed porosity ranges from 21.41% to 26.51%. All the assembled graphite shows improved electrochemical characteristics properties compared with anodes composed solely of fine graphite particles without granulation. The sample assembled by mixing 1.2 µm and 5 µm graphite at a 60:40 ratio exhibits the lowest total porosity (27.45%). Moreover, it exhibits a 92.3% initial Coulombic efficiency (a 4.7% improvement over fine graphite particles) and a capacity of 163.4 mAh/g at a 5C-rate (a 1.9-fold improvement over fine graphite particles).

Application of Thermally Fluorinated Multi-Wall Carbon Nanotubes as an Additive to an Li4Ti5O12 Lithium Ion Battery.

In this study, multi-walled carbon nanotubes (MWCNTs) were modified by thermal fluorination to improve dispersibility between MWCNTs and Li4Ti5O12 (LTO) and were used as additives to compensate for the disadvantages of LTO anode materials with low electronic conductivity. The degree of fluorination of the MWCNTs was controlled by modifying the reaction time at constant fluorination temperature; the clear structure and surface functional group changes in the MWCNTs due to the degree of fluorination were determined. In addition, the homogeneous dispersion in the LTO was improved due to the strong electronegativity of fluorine. The F-MWCNT conductive additive was shown to exhibit an excellent electrochemical performance as an anode for lithium ion batteries (LIBs). In particular, the optimized LTO with added fluorinated MWCNTs not only exhibited a high specific capacity of 104.8 mAh g-1 at 15.0 C but also maintained a capacity of ~116.8 mAh g-1 at a high rate of 10.0 C, showing a capacity almost 1.4 times higher than that of LTO with the addition of pristine MWCNTs and an improvement in the electrical conductivity. These results can be ascribed to the fact that the semi-ionic C-F bond of the fluorinated MWCNTs reacts with the Li metal during the charge/discharge process to form LiF, and the fluorinated MWCNTs are converted into MWCNTs to increase the conductivity due to the bridge effect of the conductive additive, carbon black, with LTO.

Control of cyclic stability and volume expansion on graphite-SiO x -C hierarchical structure for Li-ion battery anodes.

To increase the energy density of today's batteries, studies on adding Si-based materials to graphite have been widely conducted. However, adding a Si-based material in the slurry mixing step suffers from low distribution due to the self-aggregation property of the Si-based material. Herein, a hierarchical structure is proposed to increase the integrity by using APS to provide a bonding effect between graphite and SiO x . Additionally, to endow a protection layer, carbon is coated on the surface using the CVD method. The designed structure demonstrates enhanced integrity based on electrochemical performance. The MSG (methane decomposed SiO x @G) electrode demonstrates a high ICE of 85.6% with 429.8 mA h g-1 initial discharge capacity. In addition, the MSG anode has superior capacity retention (89.3%) after 100 cycles, with enhanced volumetric expansion (12.7%) after 50 cycles. We believe that the excellent electrochemical performance of MSG is attributed to increased integrity by using APS (3-aminopropyltrimethoxysilane) with a CVD carbon coating.

Self-Cleaning Polyester Fabric Prepared with TiOF2 and Hexadecyltrimethoxysilane.

In this study, self-cleaning polyester (PET) fabrics were prepared using TiOF2 and hexadecyltrimethoxysilane(HDS) treatment. TiOF2 was synthesized via direct fluorination of a precursor TiO2 at various reaction temperatures. The prepared PET fabrics had superior photocatalytic self-cleaning properties compared with anatase TiO2/HDS-treated PET fabrics under UV and sunlight with 98% decomposition of methylene blue. TiOF2/HDS-treated PET fabrics also had superior superhydrophobic self-cleaning properties compared with anatase TiO2/HDS-treated PET fabrics with a 161° water contact angle and 6° roll-off angle. After the self-cleaning tests of the non-dyed TiOF2/HDS-treated PET fabrics, we prepared dyed TiOF2/HDS-treated PET fabrics to test practical aspects of the treatment method. These PET fabrics were barely stained by tomato ketchup; even when stained, they could be self-cleaned within 4 h. These results suggest that practical self-cleaning PET fabrics with superhydrophobicity and photocatalytic degradation could be prepared using TiOF2/HDS-treatment.

Photocatalytic degradation of procion blue dye in aqueous solution by a TiO2-carbon nano-composite.

A nano-composite consisting of TiO2-CNT was prepared via the sol-gel technique by using titanium n-butoxide along with carbon nano-tubes (CNTs) followed by calcination at 450 degrees C. Spectral analysis reveals that the TiO2 formed was present on the carbon in anatase form. The effect of adsorption was investigated in an aqueous solution of procion blue dye in a darkroom and the photochemical reaction in aqueous suspensions of titania composite under UV illumination. The reaction was studied by monitoring the discoloration of dye via employing a UV-Visible spectrophotometeric technique as a function of irradiation time. The composite catalyst was found to be efficient in the photodegradation of the dye.

Influence of Fluorine Doping of Activated Carbon Fibers on Their Water Vapor Adsorption Characteristics.

The characterization of fluorinated carbon fibers by water sorption has been broadly investigated in this work. In brief, a pitch-based activated carbon fiber (ACF) was submitted to a fluorination process under different conditions of partial pressure (F2:N2 ratio) and temperature. This led to samples with varied fluorine content and C-F type bonding. The effect of the fluorination treatment on the textural properties of the ACF was studied by means of nitrogen and carbon dioxide adsorption at -196 and 0°C, respectively, while the changes induced in the surface chemistry of the materials were analyzed by XPS. Also, the affinity and stability of the materials toward water was evaluated by single and cycling isotherms. The obtained results show that a mild fluorination not only can preserve most of the textural properties of the parent ACF, but enhance the water uptake at the first stages of the water sorption process, together with a shift in the upswing of the water isotherms toward lower relative humidities. This indicates that fluorination under certain conditions can actually enhance the surface hydrophilicity of carbon materials with specific properties. On the contrary, higher partial pressures led to highly fluorinated fibers with lower porosity and more hydrophobic character. Moreover, they presented a lower chemical stability as demonstrated by a change in the shape of the water isotherms after two consecutive measurements. The kinetics of water sorption in the ACFs provided further insights into the different sorption phenomena involved. Hence, water sorption can definitely help to tailor the water affinity, stability and performance of fluorinated porous carbon materials under humid conditions.

Activated carbon fibers for toxic gas removal based on electrical investigation: Mechanistic study of p-type/n-type junction structures.

In this study, we evaluated the potential use of CuO-ZnO combination structures with activated carbon fibers (ACFs) for the adsorption (by ACFs) and electrochemical detection (by CuO-ZnO) by of SO2 gas. The gas adsorptivity was concluded to improve as a result of the synergetic effects of physical adsorption by the micropores and mesopores, the specific surface area developed by chemical activation and the chemical adsorption reaction between SO2 and the transition metals introduced in the CuO-ZnO combination structures. From comparison of the SO2 sensing properties, the CuO-ZnO combination structures with ACFs exhibited the fastest sensing capability. This result can be attributed to the larger specific surface area of the semiconductor, which extended its depletion layer by forming p-type CuO/n-type ZnO junctions. This phenomenon led to good SO2 detection through a decrease in the resistance; thus, the contributions of the sensing responses of p-type CuO and n-type ZnO represent a predominant characteristic of the sensor. These types of mechanisms were proven through various physicochemical and electrical characterization methods, especially through evaluation of the SO2 sensing capability of the CuO-ZnO combination structures with ACFs. The reversible sensing capability indicates that the p-n junction structure changed the electrical properties of the ACFs, leading to an intriguing sensing mechanism.

Preparation of platinum-decorated porous graphite nanofibers, and their hydrogen storage behaviors.

In this work, the hydrogen storage behaviors of porous graphite nanofibers (GNFs) decorated by Pt nanoparticles were investigated. The Pt nanoparticles were introduced onto the GNF surfaces using a well-known chemical reduction method. We investigated the hydrogen storage capacity of the Pt-doped GNFs for the platinum content range of 1.3-7.5 mass%. The microstructure of the Pt/porous GNFs was characterized by X-ray diffraction and transmission electron microscopy. The hydrogen storage behaviors of the Pt/GNFs were studied using a PCT apparatus at 298 K and 10 MPa. It was found that amount of hydrogen stored increased with increasing Pt content to 3.4 mass%, and then decreased. This result indicates that the hydrogen storage capacity of porous carbons is based on both their metal content and dispersion rate.

The study of controlling pore size on electrospun carbon nanofibers for hydrogen adsorption.

Polyacrylonitrile (PAN)-based carbon nanofibers (CNFs) were prepared by using electrospinning method and heat treatment to get the media for hydrogen adsorption storage. Potassium hydroxide and zinc chloride activations were conducted to increase specific surface area and pore volume of CNFs. To investigate the relation between pore structure and the capacity of hydrogen adsorption, textural properties of activated CNFs were studied with micropore size distribution, specific surface area, and total pore volume by using BET (Brunauer-Emmett-Teller) surface analyzer apparatus and the capacity of hydrogen adsorption was evaluated by PCT (pressure-composition-temperature) hydrogen adsorption analyzer apparatus with volumetric method. The surface morphology of activated CNFs was observed by SEM (scanning electron microscope) images to investigate the surface change through activation. Even though specific surface area and total pore volume were important factors for increasing the capacity of hydrogen adsorption, the pore volume which has pore width (0.6-0.7 nm) was a much more effective factor than specific surface area and pore volume in PAN-based electrospun activated CNFs.

Chemically Grafted Aminated Carbon Nanotubes and l-Lysine in Ultramodified Conditions for Carbon Dioxide Storage.

The study reported CO2 storage properties of single-walled carbon nanotubes (CNTs) modified by introducing amino groups onto CNT surfaces via a chemical process. Two different approaches were used to produce amino-functionalized nanotubes by adding lithium amide and l-lysine amino acid. Lithium amide was introduced on CNT surfaces, and then, it was further modified by adding amino-moiety (l-lysine amino acid) to obtain multiamino sites on the CNT surface for CO2 storage. The aminated CNT were followed by CO2 adsorption experiments, and amino group interactions with CO2 have helped CNT to achieve higher adsorption capacity. The successful modification of CNTs showed ameliorated CO2 storage capacity as compared to pristine CNT. The modified CNT possessed free amine groups on the surface, which led to an enhanced CO2 adsorption capacity. The modified CNT samples were analyzed by X-ray photoelectron spectroscopy, infrared spectroscopy, and X-ray diffraction techniques.

Hierarchically three-dimensional (3D) nanotubular sea urchin-shaped iron oxide and its application in heavy metal removal and solar-induced photocatalytic degradation.

In this study, hierarchically three-dimensional (3D) nanotubular sea urchin-shaped iron oxide nanostructures (3D-Fe2O3) were synthesized by a facile and rapid ultrasound irradiation method. Additives, templates, inert gas atmosphere, pH regulation, and other complicated procedures were not required. Dense 3D-Fe2O3 with a relatively large Brunauer-Emmett-Teller (BET) surface area of 129.4 m2/g was synthesized within 23 min, and the BET surface area was further improved to 282.7 m2/g by a post heat-treatment process. In addition, this post processing led to phase changes from maghemite (γ phase) to hematite (α phase) Fe2O3. Subsequent characterization suggested that the growth mechanism of the 3D-Fe2O3 follows self-assembly and oriented attachment. The prepared 3D-Fe2O3 was applied to wastewater purification. Ultrasound-irradiated 3D-Fe2O3 can eliminate a As(V) and Cr(VI) from water with 25 times faster removal rate by using a one third smaller amount than commercial α-Fe2O3. This was attributed to the inter-particle pores and relatively positively charged surface of the nanostructure. In addition, post heat treatment on ultrasound-irradiated 3D-Fe2O3 significantly influenced the photocatalytic degradation of methylene blue and phenol, with a 25 times higher removal efficiency than that of commercial α-Fe2O3, because of both high BET surface area and good crystallization of the prepared samples.

Preparation and characteristics of electrospun activated carbon materials having meso- and macropores.

Mesoporous activated carbon samples were prepared from electrospun PAN-based carbon fibers using physical activation with silica. Textural characterization was performed using nitrogen adsorption at 77 K. The BET specific surface area and pore size distribution of silica activated carbon materials were investigated. According to the increment of silica, BET specific surface area was increased about thirty times and it was found that silica activated carbon materials were highly mesoporous by studying pore surface distribution and pore volume distribution. Surface morphology of silica activated carbon materials were observed by SEM images. The spherical typed carbon materials were investigated. The diameter of spherical typed carbon materials was increased in proportional of the increment of silica.