Specific Surface Area Of Material Research Articles

Sintering Kinetics of Austenitic Stainless Steel AISI 316L Modified with Nanographite Particles with Highly Developed BET Specific Surface Area.

The subject of this work was the study of processes occurring during sintering of water atomized AISI 316L austenitic stainless steel powder modified by the addition of graphite nanoparticles. The main purpose of the work was to determine the effect of modification of the AISI 316L stainless steel austenitic powder by the addition of graphite nanopowder on the sintering kinetics and oxide reduction mechanism. The phenomena occurring during the sintering process and oxide reduction mechanisms were subjected to detailed characterizations. Mixtures with two types of nanopowder with a high BET (measurement technique of the specific surface area of materials based on Brunauer–Emmett–Teller theory) specific surface area of 350 and 400 m2/g and for comparison with graphite micropowder with a poorly developed BET specific surface area of 15 m2/g were tested. The conducted thermal analysis showed that the samples made of austenitic stainless steel doped with 0.2% and 0.3% by weight graphite nanopowder with a BET specific surface area of 400 m2/g, sintered best the oxide reduction reactions, with a more intensive participation of carbon, for these samples.

Preparation of novel reticulated prickly porous ceramics with mullite whiskers

Porous materials are widely used in heat exchangers, sewage treatment, electromagnetic shielding, thermal insulation, gas adsorption, photocatalytic due to their high specific surface area. The specific surface area of materials plays a pivotal role in them. It can be enhanced by increasing the porosity of the material, but the cost of this improvement is reducing the strength of the material. In order to improve performance, it is necessary to increase its surface area without reducing the strength of the material. In this work, mullite porous ceramics with mullite whisker on the inside and outside surfaces structures, which known as prickly porous ceramics(PPCs). They were fabricated using polyurethane foam coated with slurries as the pore-forming agents, sintered after secondary impregnation with silica sol and ammonium fluoroaluminate. The the sintering temperature as well as slurry composition of secondary impregnation were tuned to tailor the strength and surface structures of the PPCs. In addition, the potential of PPCs as high-temperature catalyst supports was demonstrated. Overall, the PPCs demonstrated large surface areas and high mechanical strength. This study paved the way for the fabrication of high-performance porous ceramics.

1,3,5-Triethynylbenzene and melamine as monomers to synthesize three-dimensional network porous aromatic frameworks based silica/florisil for determination of carbendazim and thiabendazole in spinach.

In this study, the new and efficient three-dimensional network porous aromatic frameworks materials called Silica-PAFs-a, Florisil-PAFs-a, Silica-PAFs-b, and Florisil-PAFs-b were first synthesized. The properties of materials were analyzed by five characterization methods. The materials were used as adsorbents in pipette-tip solid-phase extraction for the effective determination of carbendazim and thiabendazole in spinach sample. Meanwhile, the obtained materials were tested by static adsorption and dynamic adsorption. The result showed that the specific surface area of materials greatly increased after introducing three-dimensional network porous aromatic frameworks. Microstructural modification exposed a large number of amino reactive groups that made them have a better adsorption amount for the two targets. The calibration graphs of carbendazim and thiabendazole in methanol were linear over 0.10-300.0µg/mL, and the limits of detection and quantification were 0.00546 and 0.0182µg/mL, and 0.00741 and 0.0247µg/mL respectively. A reliable analytical method was developed for recognition targets in spinach sample by Silica-PAFs-b with satisfactory extraction recoveries (96.25 and 100.51%). The proposed method using the material was applied for trace analysis of the carbendazim and thiabendazole residue.

Antimicrobial Cellulose Nanofibril Porous Materials Obtained by Supercritical Impregnation of Thymol.

This study presents the impregnation in supercritical carbon dioxide (scCO2) of nanocellulose-based structures with thymol as a natural antimicrobial molecule to prepare bioactive, biosourced materials. First, cellulose nanofibrils (CNFs) were used to produce four types of materials (nanopapers, cryogels from water or tert-butyl alcohol suspensions, and aerogels) of increasing specific surface area up to 160 m2·g-1, thanks to the use of different processes, namely, vacuum filtration, freeze-drying, and supercritical drying. Second, these CNF-based structures were impregnated with thymol in the scCO2 medium using a relatively low temperature and pressure of 40 °C and 100 bar during 1 h. The amount of impregnated thymol in the different CNF materials was investigated by fluorescence spectroscopy, 13C NMR analysis, and gas chromatography. All three methods consistently showed that the amount of impregnated thymol increases with the specific surface area of the material. The antimicrobial activity of the impregnated CNF-based materials was then measured against three reference strains of microorganisms: the Gram-negative Escherichia coli and Gram-positive Staphylococcus epidermidis bacteria, and the yeast Candida albicans using the disk diffusion test method. The latter revealed the leaching of thymol in sufficient amounts to generate antimicrobial activity against the three strains in the case of the cryogel derived from a tert-butyl alcohol suspension and the aerogel, which are the two materials exhibiting the highest specific surface areas. The proposed strategy, therefore, enabled us to precisely steer the amount of active molecule loading and the related antimicrobial activity by adjusting the specific surface area of the biosourced material impregnated in green supercritical conditions. These results are very promising and confirm that supercritical impregnation of active molecules onto nanocellulose three-dimensional (3D) structures can be an interesting solution for the design of active medical devices such as wound dressings.

A Novel Coated of Mg/Fe Layered Double Hydroxide on Date Palm Stones

Mg/Fe layered double hydroxide coated low cost activated carbon (AC-Mg/Fe) was synthesized to be as a novel material by a co-precipitation method. The using of Scanning electron microscope (SEM), Energy Dispersive Spectroscopy (EDS), X-Ray Diffraction Analysis (XRD) and Specific surface area of materials by Brunauer–Emmett–Teller analysis (BET) were employed for characterize the synthesized coated adsorbent. The XRD and SEM displayed that the particles on the surface of low cost activated carbon are regular and good-defined, and the structure of LDHs is typical lamellar. The crystallite size of the coated adsorbent according to the XRD analysis was to be 96.7 nm. The contents of the Fe and Mg after modification increase noticeably according to the EDS analysis. From BET analysis, it was an increasing in the specific surface area of the adsorbent from 22.57 m2/g (before synthesize) to 81.77 cm/g (after synthesize). This analysis resulted in successfully coated Mg/Fe layered double hydroxide (Mg/Fe-LDH) on activated carbon for preparing of a high capacity adsorbent and magnetic sorbent for easy separation by magnetic field.

Photocatalytic behavior of biochar-modified carbon nitride with enriched visible-light reactivity

Ultra-thin layered structures and modified bandgaps are two efficient strategies to increase the photocatalytic performance of various materials for the semiconductor industry. In the present study, we combined both strategies in one material to form carbon-doped graphitic carbon nitride (g-C3N4) nano-layered structures by the method of melamine thermal condensation, in the presence of different mass ratios of biochar. The characterization showed that the composite with the best ratio retained the g-C3N4 polymeric framework and the bond with g-C3N4. The biochar was established via π-π stacking interactions and ether bond bridges. The π-conjugated electron systems provided from biochar can elevate charge separation efficiency. The ultra-thin structure also curtailed the distance of photogenerated electrons migrating to the surface and enlarge specific surface area of materials. The presence of carbon narrowed the bandgap and increased light absorption at a wider range of wavelengths of g-C3N4. The biochar/melamine ratio of 1:15 presented the best performance, 2.8 and 5 times faster than g-C3N4 degradating Rhodamine and Methyl Orange, respectively. Moreover, the catalyst presented a good stability for 4 cycles. In addition to that, biochar from waste biomass can be considered a sustainable, cost-effective, and efficient option to modify g-C3N4-based photocatalysts.

Synthesis and photocatalytic properties of biomimetic morphology silicon carbide

Silicon carbide materials with bionic morphology are prepared by impregnation-calcination method using the template of leaf vein. The microstructure, element composition, and band gap of biomimetic morphology silicon carbide are characterized by scanning electron microscopy (SEM), x-ray diffraction (XRD), ultraviolet-visible light spectrum (UV–vis) and x-ray photoelectron spectroscopy(XPS). Photocatalytic property of biomimetic morphology silicon carbide has been measured by the dye decolorization reaction. The results demonstrate that calcination temperature has the important effect on the formation of silicon carbide. The morphology of silicon carbide can keep the original biomimetic shape of leaf vein template, and there is meosporous structure with a diameter of 2–4 nm on the interior of material. The average gain size of materials is about 16.9 nm and the specific surface area of materials is about 84.7 m2 g−1. After calculation, the band gap of material is 3.02 eV. For performance testing, the degradation rate of silicon carbide is 92.86% for the first time, and after the fourth repetition, the degradation rate decreased to 86.74%.

Thermal behaviors of a porous calcium silicate material prepared from coal-bearing strata kaolinite

The thermal behaviors of a porous calcium silicate (PCS) material prepared from coal-bearing strata kaolinite were investigated by thermogravimetry and derivative thermogravimetry (TG–DTG), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy, and Brunauer–Emmett–Teller method. The XRD results showed that the PCS was determined as calcium silicate hydrates (C–S–H) and a small amount of CaCO3, which transformed to an orderly crystal structure of wollastonite approximately at 700 °C. The TG–DTG results indicated that the dehydration was observed until 300 °C and the dehydroxylation presented at 728 °C. The PCS exhibited a large number of pores with a fibrous flake network structure, which disappeared at 800 °C. The BET data showed that the specific surface area of material decreased as the temperature increased. The high-temperature phase transformation of PCS underwent the following transformation: active calcium silicate → dehydrated calcium silicate → dehydroxylated calcium silicate → wollastonite.

Bioethanol production from bamboo with alkali-catalyzed liquid hot water pretreatment

Altering recalcitrant structures of bamboo is essential to obtain high yield of bioethanol via bioconversion process. With the goal of improving cell wall digestibility, alkaline liquid hot water was used to pretreat N. affinis. The effects of temperature and alkali dosage on structural alterations were determined by chemical composition, Brunauer Emmett Teller (BET) and gel permeation chromatography (GPC). The relationship between these changes and substrate digestibility was addressed by separate enzymatic hydrolysis and fermentation (SHF). The results indicated that pretreatments partly removed and degraded hemicelluloses and lignin, reducing yields of substrates and molecular weights of carbohydrates. With the change of cell wall structure, specific surface area of materials increased after LHW pretreatment but decreased with further removal of lignin and hemicellulosic fractions. Maximum bioconversion was obtained by pretreatment with 0.5% NaOH aqueous at 170 °C and SHF, yielding 4.8 g/L ethanol.

Sustainable N-containing biochars obtained at low temperatures as sorbing materials for environmental application: Municipal biowaste-derived substances and nanosponges case studies

Bio-based substances (BBS) obtained from composted urban biowaste and nanosponges obtained from β-cyclodextrins (βCD) were used as green source to produce biochar via pyrolysis performed under mild conditions. Pyrolysis conditions were optimized by means of TGA analysis, and different temperatures of pyrolysis were investigated. The resulting carbonaceous materials were characterized with several physicochemical techniques (elemental analysis, FTIR spectroscopy, XRD, SEM, surface area analysis, and zeta potential measurements). Additionally, the adsorption capacity of such materials was tested toward the removal of charged dyes from aqueous environment. Isothermal experiments carried out at circumneutral pH indicated an important charge-selectivity, which encourages their use as sustainable alternative materials in wastewater purification treatments. Moreover, the analysis of the adsorption capacity as a function of specific surface area of materials suggests the strategy to obtain carbonaceous solids with enhanced capacity in capture of polar molecules.

Production of Carbon Materials with Specified Porosity

The results of studies on the oxidation of carbon black are represented. It was found that materials with different porosity can be obtained by varying the nature of an activating agent and the conditions of activation. A correlation of the sizes of carbon crystallites in the initial sample, the extent of their boundaries, and the rates of pyrocompaction and oxidation of these samples with the specific surface area of materials obtained upon activation was established.

(Invited) Electroreduction of Oxygen on Nitrogen-Doped Carbide-Derived Carbon Materials in Alkaline Media

The oxygen reduction reaction (ORR) is one of the most important electrochemical reactions, used in metal-air type batteries and different types of fuel cells. The traditionally used catalyst, platinum, is expensive and scarcely available and thus many new catalysts have emerged, among which are heteroatom-doped carbon materials. Various carbon nanostructures have been widely used as base materials for heteroatom doping due to their high electrical conductivity, porosity and stability in electrochemical conditions. Owing to their porous structure, reactants and products are easily transferred to and from the active sites. Among these materials, carbide-derived carbon (CDC), which is a carbon material produced by removing metal atoms from a carbide lattice, stands out as an exceptional way to gain a base material with tunable properties. The specific surface area of CDC materials is typically in the range of 1000–2000 m2 g−1, the pore size is easily tunable via selection of different starting carbides and synthesis temperature with reproducible results in large scales. Previously, we have studied ORR electrocatalysis on undoped CDC materials in alkaline media. These materials catalyzed a 2e‒ reduction of O2.1 In this work, we demonstrate a pyrolysis method to synthesize nitrogen-doped carbide-derived carbon catalysts using titanium carbide as a base material and dicyandiamide (DCDA) as a nitrogen source. The CDC materials are obtained using chlorination to remove the titanium and then pyrolyzed along with DCDA at 800 °C for 2 h in a tube furnace to substitute nitrogen into the carbon lattice.2 The physical characteristics of the catalyst materials were studied using N2 physisorption, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy and scanning electron microscopy, which revealed that the materials had been successfully nitrogen doped, had a very high specific surface area and were highly amorphous. SEM revealed highly porous materials consisting of particles of various sizes (Figure 1a). These catalysts were then tested using the rotating disk electrode (RDE) method in alkaline solution toward the ORR. The mediocre activity of the CDC materials was increased by the nitrogen-doping procedure, which further increased the already high specific surface area of the materials and produced nitrogen-containing groups on the surface of the catalysts. The catalysts produced via the nitrogen doping of carbide-derived carbon are superior to the catalyst synthesized by chlorinating titanium carbonitride, but still not as active as 20% Pt/C (Figure 1b). However, the process for CDC synthesis is already used commercially and adding nitrogen doping to it would be just one more step. The N-doped CDC catalysts also showed excellent stability over 1000 potential cycles, which is an important property for fuel cell applications. Overall, the nitrogen-doped CDC catalysts are promising cathode materials for alkaline membrane fuel cell as they are stable and highly active toward ORR. Work is in progress to test these materials in fuel cell conditions. References I. Kruusenberg, J. Leis, M. Arulepp, and K. Tammeveski, J. Solid State Electrochem., 14, 1269 (2010). S. Ratso, I. Kruusenberg, M. Käärik, M. Kook, R. Saar, M. Pärs, J. Leis, and K. Tammeveski, Carbon, 113, 159 (2017). Figure 1

Utilization of waste expanded perlite as new effective supplementary cementitious material

Expanded perlite is a valuable lightweight material for building materials industry as well as for agriculture, horticulture etc. Unfortunately during both production as well as processing of expanded perlite, some fine grained waste perlite is being formed. Due to its extremely low bulk density waste expanded perlite is difficult to handle, utilize and causes dust formation. Paper presents method of utilization of waste expanded perlite as a valuable, high performance pozzolanic supplementary cementitious material. Waste expanded perlite was ground in ball mill in order to destroy cellular microstructure of waste expanded perlite. It resulted in significant increase in specific surface area of material. Results of strength tests showed, that addition of ground waste expanded perlite may result in strength gain up to 50% (for 35% addition in respect to cement mass). Due to its high activity ground waste expanded perlite can be used as both cement substitute as well as cement additive depending on desired properties of final material. Investigations showed, that ground waste expanded perlite is material of pozzolanic activity. Except strength test, pozzolanic activity was investigated by solubility test according to ASTM C379-65T. Direct measurements of calcium hydroxide content in hydrating alite pastes confirmed that ground expanded perlite reacts with calcium hydroxide what results in reduction of calcium hydroxide content in alite paste. Pozzolanic activity of ground waste expanded perlite was compared with commonly used commercial pozzolanas. Obtained results allow to classify ground waste expanded perlite as material of pozzolanic properties. It can be valuable supplementary cementitous material mainly for special applications due to its high pozzolanic activity and very bright, almost white colour. In addition to that, ground waste expanded perlite used as cement replacement allows to decrease carbon dioxide emission, since Portland cement manufacturing is connected with emission of considerable amount of carbon dioxide.

Design of Perovskite Oxides as Anion-Intercalation-Type Electrodes for Supercapacitors: Cation Leaching Effect.

Oxygen ions can be exploited as a charge carrier to effectively realize a new type of anion-intercalation supercapacitor. In this study, to get some useful guidelines for future materials development, we comparatively studied SrCoO3-δ (SC), Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF), and Co3O4 as electrodes in supercapacitors with aqueous alkaline electrolyte. The effect of interaction between the electrode materials with the alkaline solution was focused on the structure and specific surface area of the electrode material, and ultimately the electrochemical performance was emphasized. Both BSCF and SC were found to experience cation leaching in alkaline solution, resulting in an increase in the specific surface area of the material, but overleaching caused the damage of perovskite structure of BSCF. Barium leaching was more serious than strontium, and the cation leaching was component dependent. Although high initial capacitance was achieved for BSCF, it was not a good candidate as intercalation-type electrode for supercapacitor because of poor cycling stability from serious Ba(2+) and Sr(2+) leaching. Instead, SC was a favorable electrode candidate for practical use in supercapacitors due to its high capacity and proper cation leaching capacity, which brought beneficial effect on cycling stability. It is suggested that cation leaching effect should be seriously considered in the development of new perovskite materials as electrodes for supercapacitors.

Preparation, characterization, and photocatalytic activity evaluation of Fe–N-codoped TiO2/fly ash cenospheres floating photocatalyst

Nitrogen-doped titanium dioxide (TiO2) and Fe-N-codoped TiO2 layers on fly ash cenospheres (FAC) as floating photocatalyst were successfully prepared through sol-gel method. Photocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), ultraviolet (UV)-Vis diffuse reflectance spectroscopy (DRS), and nitrogen adsorption analyses for Brunauer-Emmett-Teller (BET) specific surface area. Photocatalytic efficiency of the prepared catalyst was evaluated through using the decomposition of Rhodamine B (RhB) as a model compound under visible light irradiation. Photocatalytic activity and kinetics of catalyst under visible light were detected in details from different Fe/Ti mole ratios by detecting photodegradation of RhB. Experimental results show that when the calcination temperature was 550°C, the dosage of FAC was 3.0g, and the mole ratio of Fe/Ti was 0.71%; the synthesized Fe-N-TiO2/FAC photocatalyst presented as anatase phase and that N and Fe ions were doped into TiO2 lattice. The material's specific surface area was 34.027m2/g, and UV-Vis diffuse reflectance spectroscopy shows that the edge of the photon absorption has been red shifted up to 400-500nm. Fe-N-codoped titanium dioxide on FAC had excellent photocatalytic activity during the process of photodegradation of RhB under visible light irradiation.

A new ZnO/rGO/polyaniline ternary nanocomposite as photocatalyst with improved photocatalytic activity

ZnO as a promising photocatalyst has gained much attention for the removal of organic pollutants from water. However, the main drawbacks of the relatively low photocatalytic activity and high recombination rate of photoexcited electron-hole pairs restrict its potential applications. Herein, a ternary ZnO/reduced graphene oxide (rGO)/polyanline (PANI) nanocomposite has been synthesized and used as the photocatalyst, characterized by TEM, SEM, X-Ray diffraction, FTIR and Raman. The ZnO/rGO(7wt.%)/PANI(10wt.%) photocatalyst shows an enhanced photocatalytic performance for the photodegradation of methyl orange with a maximum degradation efficiency of almost 100% within 60min under UV light irradiation compared to pure ZnO (15%). This improvement is attributed to the rGO which effectively improves the ability to transfer the photoexcited electrons and the specific surface area of material, the PANI which increases the absorption of light and adsorption of dyes, and the synergistic effect among ZnO, rGO and PANI.

Intercalation of diclofenac in modified Zn/Al hydrotalcite-like preparation

The intercalation of a pharmaceutically active material diclofenac into modified Zn/Al Hydrotalcite-like (Zn/Al HTlc) preparation has been investigated by the coprecipitation and ion exchange method, respectively. The synthetic materials were characterized using X- Ray Diffraction (XRD); Fourier transforms infrared spectroscopy (FTIR); Scanning Electron Microscope (SEM); X-Ray Fluorescence (XRF) and surface area analyzer. The results show that the basal spacing of the product was expanded to 11.03 A for direct synthesis and 10.68 A for indirect synthesis, suggesting that diclofenac anion was intercalated into Zn/Al HTlc and arranged in a tilted bilayer fashion and the specific surface area of material increased after the intercalation of diclofenac.

Synthesis Process and Properties of V5+-Doped LiFePO4/C

Olivine structure LiFe1−xVxPO4/C (x = 0.02, 0.04, 0.06) composite materials as the cathode for lithium ion batteries were synthesized by carbon-thermal reduction method, using Fe(NO3)3 · 9H2O, LiH2PO4, NH4VO3, and C6H12O6 (glucose) as raw materials. The X-ray diffraction (XRD), scanning electronic microscope (SEM) laser particle size analysis, specific surface area tester, and electrochemical performance testing were used to study its structure, morphology, and electrochemical properties. The results showed that the diffraction peaks of the prepared materials correspond to the single phase of LiFePO4/C and can be indexed as the olivine structure. Particle diameter of LiFe1−xVxPO4/C (x = 0.04) was uniform. Specific surface areas of materials are all increased. An electrochemical test showed that LiFe1−xVxPO4/C (x = 0.04) demonstrated a better electrochemical capacity of 141.065 mAh · g−1 at 0.1C rate, and which had an increase of 10.77% than the un-doped sample. After 20 cycles, charge and discharge specific capacity almost had no attenuation.

Catalytic performances of Ni–CaO–mayenite in CO2 sorption enhanced steam methane reforming

Ni–CaO–mayenite (Ca12Al14O33) catalysts for the CO2 Sorption Enhanced Steam Methane Reforming (SE-SMR) have been developed using the microwave assisted self-combustion method of preparation. The sorption of CO2 by CaO shifts the steam reforming and the Water Gas Shift reaction (WGS) towards H2 production and favors the heat balance of the global reaction.The CO2 sorption has been studied on materials with different CaO/Ca12Al14O33 ratios and for different types of preparation. The specific surface area of materials, the temperature of Ni phases' reducibility and CO2 sorption are all essential for material efficiency. The Ni–CA75MM catalyst was the most active and stable in methane steam reforming with CO2 sorption, even at an unusually low temperature (650°C).

Calcination removing soft template cetyl trimethyl ammonium bromide and its effects on capacitance performance of supercapacitor electrode MnO2

It is the first time to use calcination methods to remove the residual surfactant Cetyl Trimethyl Ammonium Bromide (CTAB) acting as soft template or structure directing agent for supercapacitor MnO2 electrodes. MnO2 was synthesized by liquid co-precipitation in the presence of CTAB. The as-prepared oxides heated at different heat treatment temperature are characterized systematically by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), N2 physical adsorption, cyclic voltammetry (CV) and galvanostatic charge/discharge tests. Results indicate that CTAB can be removed completely with the increase of heat treatment temperature, but the temperature also has great influences on the performance of MnO2. The free water, physical adsorption water and crystalline water lose successively, and the crystalline changes from amorphous α-MnO2⋅nH2O, first to crystalline MnO2, then to α-Mn2O3 and α-Mn3O4 accompanying with the oxygen loss process. Simultaneously, the specific capacitance and specific surface area of material exhibit similar variation trends being increase at first and then decrease as the heat calcination temperature increases. Sample MO-200 treated at 200°C has the largest Brunauer–Emmett–Teller (BET) specific surface area (276.2m2g−1) and specific capacitance (240.1Fg−1) at 500mAg−1. Therefore, in view of improving the capacitance performance, the relative low heat treatment temperature is suitable for MnO2 materials.