Equilibrium,kinetic and thermodynamic studies on the adsorption of phenol onto graphene

Graphene, a new member of carbon family, has been prepared, characterized and used as adsorbent to remove phenol from aqueous solution. The effect parameters including pH, dosage, contact time, and temperature on the adsorption properties of phenol onto graphene were investigated. The results showed that the maximum adsorption capacity can reach 28.26 mg/g at the conditions of initial phenol concentration of 50 mg/L, pH 6.3 and 285 K. Adsorption data were well described by both Freundlich and Langmuir models. The kinetic study illustrated that the adsorption of phenol onto graphene fit the pseudo second-order model. The thermodynamic parameters indicated that the adsorption of phenol onto graphene was endothermic and spontaneous.     

The effect of interfacial interactions on the mechanical properties of polypropylene/natural zeolite composites

The effect of interfacial interactions on the mechanical properties of polypropylene (PP)/natural zeolite composites was investigated under dry and wet conditions. Interfacial interactions were modified to improve filler compatibility and mechanical properties of the composites by surface treatment of natural zeolite with a non-ionic surface modifier; 3 wt% polyethylene glycol (PEG) and three different types of silane coupling agents; 3-aminopropyltriethoxysilane (AMPTES), methyltriethoxysilane (MTES) and 3-mercaptopropyltrimethoxysilane (MPTMS), at four different concentrations (0.5–2 wt%). PP composites containing (2–6 wt%) zeolite were prepared by an extrusion technique. The tensile properties of the composites determined as a function of the filler loading and the concentration of the coupling agents were found to vary with surface treatment of zeolite. Silane treatment indicated significant improvements in the mechanical properties of the composites. According to the dry and wet tensile test results, the maximum improvement in the mechanical properties was obtained for the PP composites containing 1 wt% AMPTES treated zeolite. The improvement in the interfacial interaction was confirmed using a semi-empirical equation developed by Pukanszky. Good agreement was obtained between experimental data and the Pukanszky model prediction. Scanning electron microscopy studies also revealed better dispersion of silane treated filler particles in the PP matrix.     

Effect of soil organic matter chemistry on sorption of trinitrotoluene and 2,4-dinitrotoluene

The sorption of organic contaminants in soil is mainly attributed to the soil organic matter (SOM) content. However, recent studies have highlighted the fact that it is not the total carbon content of the organic matter, but its chemical structure which have a profound effect on the sorption of organic contaminants. In the present study sorption of two nitroaromatic contaminants viz. trinitrotoluene (TNT) and 2,4-dinitrotoluene (2,4-DNT) was studied in different SOM fractions viz. a commercial humic acid, commercial lignin and humic acid and humin extracted from a compost. ¹³C-DP/MAS NMR studies indicated that the structural composition of the organic carbon in different SOM fractions was different. The order of sorption of the nitroaromatics in the different sorbents was: humic acid-commercial > humic acid-compost > humin ～ lignin. Among the aliphatic and aromatic carbon fractions (representing bulk of SOM matrix), adsorption parameter K_f(1/n) for nitroaromatics sorption correlated well with the aliphatic carbon (r = 0.791 for TNT and 0.829 for 2,4-DNT) than the aromatic carbon (r = 0.634 for TNT and r = 0.616 for 2,4-DNT). However, among carbon containing functional groups, carbonyl carbon showed strong positive correlation with sorption of TNT (r = 0.991) and 2,4-DNT (r = 0.967) while O-alkyl carbon showed negative correlation (r = 0.832 for TNT and r = 0.828 for 2,4-DNT). The study indicates that aliphatic domains in the SOM significantly affect the non-specific sorption of both the nitroaromatic contaminants.     

Influence of carbon-fiber felts on the development of carbon–carbon composites

Oxidized PAN-fiber felt was carbonized to 600, 1000, and 1800 °C, respectively. Different carbon/carbon composites (C/C composites) were prepared from oxidized PAN-fiber felt, the carbonized felts, and resol-type phenol–formaldehyde resin. These composites were then carbonized and graphized at temperatures of between 600 and 2400 °C. The C/C composite made with oxidized PAN-fiber felt showed a strong fiber/matrix bonding, and those developed from the carbonized felt (heat-treatment of 1800 °C) showed a poor fiber/matrix bonding. The graphitized composites reinforced with the oxidized PAN-fiber felt resulted in having a high flexural strength (325 MPa), and the graphitized composites reinforced with the carbonized felt (carbonized at 1800 °C) had a low flexural strength (9 MPa). It was found that the stress-orientation promoted the formation of the anisotropic texture around the fibers as well as between the fibers. This felt may very well be able to provide a low-cost route for producing multidimensional C/C composites.     

Synthesis,characterization and magnetic performance of Co-incorporated ordered mesoporous carbons

Co-incorporated ordered mesoporous carbon (Co-OMC) with magnetic frameworks has been synthesized via a one-pot self-assembly strategy. The effects of cobalt loading on carbon matrix, adsorption properties and magnetic properties of the resultant mesostructured cobalt/carbon composites were investigated by nitrogen sorption, X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TG) and magnetometer measurements. The results show that the mesoporous composites with a high cobalt content (such as 18.0 wt%) possess an ordered and uniform mesoporous structure (5.3 nm), high surface areas (up to 687 m²/g) and high pore volumes (up to 0.54 cm³/g). Cobalt nanoparticles of size 4–9 nm are confined inside the mesopores or walls of the mesoporous carbon. These materials exhibit typical ferromagnetic characteristics. The saturation magnetization strength can be easily adjusted by changing the content of cobalt. The carbonization temperatures have significant effects on the structure and magnetic properties of Co-OMC also.     

The fabrication and wear properties of C/Al and (C + SiC)/Al composites based on wood template

Wood with its rational and magical inner structures was used as a template to fabricate C/Al and (C + SiC)/Al composites in this research. The carbon frame was first pyrolyzed from the wood template. The final composites were then obtained by infiltrating Al alloy and silicone resin into the carbon frame. The microstructures and the wear properties of these products were analyzed. The results show that the structures of the C/Al and (C + SiC)/Al composites are controlled by the natural structures of the wood. Moreover, the carbon in the composites reduced the wear rate of the Al alloy as an efficient lubricant. Compared with the C/Al composite, the (C + SiC)/Al composite shows better wear resistance because of silicon carbide.     

Synthesis and characterization of 13X zeolite from low-grade natural kaolin

In this study, 13X zeolite was successfully synthesized from low-grade natural kaolin via alkali fusion followed by hydrothermal treatment, without extra Si source or dealumination. Fusion with NaOH, followed by hydrothermal reaction, kaolinite, illite and trace of quartz in kaolin sample were converted into zeolite. The effects of various factors during the synthesis process such as NaOH addition amount, crystallization time and temperature on the crystalline products were studied. The optimum synthesis conditions to get purity 13X zeolite were found to be alkali fusion of kaolin with the weight ration of NaOH/kaolin = 2.0 at 200 °C for 4 h, and crystallized at 90 °C for 8 h after homogenization by agitated at 50 °C for 2 h. The product was characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FT-IR) and N₂ adsorption–desorption. The BET surface area of the product was found to be 326 m² g⁻¹. It can be concluded that the study provides the basic data and the process for extensive and efficient utilization of low-grade natural kaolin.     

The effect of structural properties of natural silica precursors in the mesoporogen-free synthesis of hierarchical ZSM-5 below 100 °C

The low-temperature synthesis of zeolite ZSM-5 below 100 °C is gaining new attention. This is due to the fact that such synthesis may simultaneously implement the introduction of mesopores into crystalline microporous zeolite structure. Herein, we report the use of natural silica precursors from rice husks in the mesoporogen-free synthesis of hierarchical ZSM-5 below 100 °C and their structural properties which govern the course of crystallization. Rice husks are agricultural wastes with high silica content, which should be exploited to give a positive impact, i.e. highly value-added materials. In this study, the amorphous silica from rice husks was extracted using sequential base-acid treatment. The extracted silica was similarly reactive as Ludox HS-40, even with the reduced amounts of the organic structure-directing agent (OSDA). The product was highly crystalline ZSM-5 with spherical morphology composed of small crystallites, enabling the presence of intercrystallite mesopores. The subjection of extracted silica into the calcination at 550 °C for 6 h, prior to the low-temperature synthesis, altered the silica structure via hydroxyl condensation. The distinct structural properties affected the occurring crystallization in which the resulted products were ZSM-5–disordered-mesoporous silica composites. The possible mechanisms of these two different results may involve the dual roles of tetrapropylammonium ion (TPA⁺) as zeolite OSDA and non-templating structure directing agent. These insights were based on the spectroscopic (FTIR, Raman, ²⁹Si and ²⁷Al MAS NMR spectroscopy), microscopic (TEM and HRTEM) and physicochemical characterizations (XRD and N₂ adsorption-desorption isotherm).     

Preparation of zeolite-A/chitosan hybrid composites and their bioactivities and antimicrobial activities

Zeolite-A/chitosan hybrid composites with zeolite contents of 20–55 wt.% were prepared by in situ transformation of silica/chitosan mixtures in a sodium aluminate alkaline solution through impregnation–gelation–hydrothermal synthesis. The products were characterized by X-ray diffraction, diffuse reflectance infrared Fourier transform spectroscopy, scanning electron microscopy, thermogravimetric analysis, and mercury penetration porosimetry. Their in vitro bioactivities were examined using as-synthesized and Ca^2 +-exchanged hybrid composites in simulated body fluid (SBF) for hydroxyapatite (HAP) growth. Their antimicrobial activities for Escherichia coli (E. coli) in trypticase soy broth (TSB) were evaluated using Ag⁺-exchanged hybrid composites. The zeolite-A/chitosan hybrid composites could be prepared as various shapes, including cylinders, plates and thin films. They possessed macropores with pore sizes ranging from 100 to 300 μm and showed compressive mechanical strength as high as 3.2 MPa when the zeolite content was 35 wt.%. Fast growth on the Ca^2 +-exchanged hybrid composites was observed with the highest weight gain of 51.4% in 30 days. The 35 wt.% Ag⁺-exchanged hybrid composite showed the highest antimicrobial activity, which could reduce the 9 × 10⁶ CFU mL^? 1 E. coli concentration to zero within 4 h of incubation time with the Ag⁺-exchanged hybrid composite amount of 0.4 g L^? 1. The bioactivity and antimicrobial activity could be combined by ion-exchanging the composites first with Ca^2 + and then with Ag⁺. These zeolite-A/chitosan hybrid composites have potential applications on tissue engineering and antimicrobial food packaging.     

Near infrared and mid infrared investigations of adsorbed phenol on HDTMAB organoclays

X-ray diffraction patterns (XRD), infrared Spectroscopy (IR) and near infrared spectroscopy (NIR) have been used to measure the adsorption of phenol on untreated montmorillonite and on hexadecyltrimethylammonium bromide (HDTMAB) modified montmorillonite. The mid infrared spectra indicate that both the surfactant molecule and phenol enter the interlayer of organoclays, replacing the interlayer cations. The higher concentration surfactant leads to a decrease in wavenumber of the bands of organoclays and to increase in intensity. The near infrared spectra (9000–4000 cm^?1) show a prominent band 8260 cm^?1, assigned to the combination result of the CH stretching vibrations of high concentration surfactant and absorbed phenol. The main band observed at 7090 cm^?1 is assigned to the first fundamental overtone of the OH stretching vibrations at 3415 cm^?1 for organoclay. The organoclays are characterised by prominent bands situated between 5900 and 5700 cm^?1. Both the higher concentration of organic molecules and adsorbed phenol causing the near infrared spectra of organic clays to be more complex for spectra in the region from 4700 to 5500 cm^?1. The main band of 4535 cm^?1 for montmorillonite shifts towards the lower wavenumber sites for higher concentration organoclay. The intensity of near infrared spectra generally rises with the value of surfactant concentration increasing, showing certain regularity. It is concluded that phenol is adsorbed to significantly greater amounts on the higher concentration organoclays.     

Carbon spheres/activated carbon composite materials with high Cr(VI) adsorption capacity prepared by a hydrothermal method

Glucose and commercial activated carbon (AC) were used as starting materials to hydrothermally synthesize carbon spheres on the surface of AC, producing new carbon sphere–AC hybrid carbon materials. It was found that micrometer-sized carbon spheres, rich in oxygen-containing functional groups, can be effectively anchored to, and well-dispersed on, the surface and at the entrance to the macropores of AC. As the glucose concentration increased, the size and dispersion of carbon spheres changed, the porosity of the AC decreased, the number of oxygen-containing functional groups increased, and COH gradually became the dominant functional group. The carbon composites that were obtained exhibited a remarkably enhanced adsorption capacity for Cr(VI) per unit mass and per unit surface area. The highest adsorption capacity per unit mass achieved was 0.4834 mmol g^?1, about 4 times that of unmodified AC. The abundant surface oxygen-containing functional groups and relatively well-developed pore structure were the main causes of the high specific adsorption capacity of the carbon sphere/AC composites.     

Gas sensitive vapor grown carbon nanofiber/polystyrene sensors

A new class of conductive composites with good gas sensitivity was fabricated by filling polystyrene with vapor grown carbon nanofibers (VGCNF). A solution mixing/solvent removal procedure was used. VGCNFs form conductive networks at fiber loadings above the percolation limit within the matrix. Greatly improved conductivity is achieved relative to the same volume fraction of carbon black addition when these fibers are distributed to give reasonably uniform dispersions in the matrix. The high aspect ratios of these fibers (∼70–250 nm diameters and 5–75 μm lengths) assist in forming low wt.% percolation thresholds (below 1 wt.% fiber). Excellent gas sensitivity with 10⁴–10⁵ times higher than the original resistance value in many saturated organic vapors and a maximum resistance response of about 1.1 × 10⁵ times exposure to saturated THF vapor at 6.25 wt.% of VGCNF in the polystyrene matrix was observed. The maximum resistance response declined from about 2.0 × 10⁵ times at 15 °C to about 3.4 × 10⁴ times at 55 °C. These composites exhibited stable and reusable gas sensitivity to THF vapor. Carbon black/polystyrene composites exhibit a negative vapor coefficient (NVC) upon swelling caused by filler redistribution. In contrast, VGCNF/polystyrene composites are more stable, with much smaller NVC values due to their high aspect ratios and reinforcing effects which stabilize electrical percolation pathways. Thus, VGCNF/organic polymer composites are good gas sensor candidates for detecting organic vapors.     

Physical,mechanical and morphological properties of polymer composites manufactured from carbon nanotubes and wood flour

The objective of this investigation was to evaluate physical, mechanical and morphological properties of experimental polymer type panels made from single-wall carbon nanotube (SWCNT) and wood flour. The composites with different SWCNTs (0, 1, 2, 3 phc) and maleic anhydride grafted polyethylene (MAPE) (0 and 3 phc) contents were mixed by melt compounding in an internal mixer and then the composites manufactured by injection molding method. The mass ratio of the wood flour to LDPE was 50/50 (w/w) in all compounds. Water absorption, thickness swelling, bending characteristics, impact strength and morphological properties of the manufactured composites were evaluated. Based on the findings in this work the water absorption and thickness swelling of the nanocomposites decreased with increasing with amount of the SWCNTs (from 1 to 3 phc) and MAPE (3 phc) in the panels. The mechanical properties of LDPE/wood-flour composites could be significantly enhanced with increased percentage of MAPE and SWCNTs content. Panels having 2 phc SWCNTs and 3 phc MAPE exhibited the highest impact strength value. Also Scanning Electron Microscope (SEM) micrographs showed that carbon nanotubes can fill the voids of wood plastic composites as well as addition of MAPE and SWCNTs enhanced interaction between the components.     

Synthesis of interstratified graphene/montmorillonite composite material through organics-pillared,delamination and co-stacking and its application in hexavalent chromium removal from aqueous solution

Layers from two different delaminated dispersions of 3-aminopropyltriethoxysilane (APTES)-intercalated montmorillonite (Mts) and octylamine (OA)-intercalated graphene oxide (GO) could be co-stacked to obtain APTES-intercalated Mts (Mts-APTES)/OA-intercalated GO (GO-OA) interstratified composites (MAGO). The synthesized composites were characterized by XRD, FTIR, BET, TGA, TEM and XPS, which showed that MAGO had been prepared successfully. The optimal concentration of APTES was 8% in anhydrous toluene which avoided self-polymerization of APTES while facilitating the nucleophilic attack of APTES amine groups and the protic character of ethanol to compete with silane for the intimal hydroxyl groups by H-bonding. The MAGO demonstrated an extremely fast Cr(VI) removal from aqueous solution with a high removal efficiency at low pH. Data from batch studies of the adsorption process followed pseudo-second-order kinetics. The results fit a Langmuir model of adsorption, with maximum adsorption capacities of MAGO composites at pH 3.0 being 44.25 mg g^?1, 47.46 mg g^?1, 49.58 mg g^?1 under 30 °C, 40 °C, 50 °C, respectively, which were much higher than capacities of some conventional adsorbents. The reusability of the MAGO composite was also determined through adsorption-desorption studies, providing evidence for the potential use of MAGO composite in the removal of Cr(VI) from acidic wastewater.     

Preparation and characterization of poly(3-octylthiophene)/carbon fiber thermoelectric composite materials

Poly(3-alkylthiophene) (P3AT) with a high Seebeck coefficient has recently been reported. However, P3AT/inorganic conductive composites exhibit relatively poor thermoelectric performance because of their low electrical conductivity. In this work, carbon fiber sheets with a high electrical conductivity were chosen as the inorganic phase, and poly(3-octylthiophene)(P3OT)/carbon fiber composites were prepared by casting P3OT solution onto the carbon fiber sheets. The carbon fiber sheets incorporated into the composites can provide good electrical conductivity, and P3OT can provide a high Seebeck coefficient. The highest power factor of 7.05 μW m⁻¹ K⁻² was obtained for the composite with 50 wt% P3OT. This work suggests a promising method for preparing large-scale thermoelectric composites with excellent properties.     

Lightweight carbon-bonded carbon fiber composites with quasi-layered and network structure

Lightweight carbon-bonded carbon fiber (CBCF) composites were fabricated with chopped carbon fibers and dilute phenolic resin solution by pressure filtration, followed by carbonization at 1000 °C in argon. The as-prepared CBCF composites had a homogenous fiber network distribution in xy direction and quasi-layered structure in z direction. The pyrolytic carbon derived from phenolic resin was mainly accumulated at the intersections and surfaces of chopped carbon fibers. The composites possessed compressive strengths ranged from 0.93–6.63 MPa in xy direction to 0.30–2.01 MPa in z direction with a density of 0.162–0.381 g cm^− 3. The thermal conductivity increased from 0.314–0.505 to 0.139–0.368 Wm^− 1 K^− 1 in xy and z directions, respectively. The experimental results indicate that the CBCF composites prepared by this technique can significantly contribute to improve the thermal insulation and mechanical properties at high temperature.     

Preparation and characterization of carbon/montmorillonite composites and nanocomposites from waste bleaching sodium montmorillonite clay

Waste bleaching sodium montmorillonite clay was used to prepare carbon/clay nanocomposites and composites by calcination in a reducing atmosphere. The main purpose of this study was to determine the influence of the calcination temperature and solvent washing in the material structure and its adsorption properties. X-ray diffraction patterns detected the nanocomposite formation only in the samples calcinated at 350 °C, whose structures were also described by Fourier transform infrared spectra. SEM images showed that all the samples were composed of various agglutinated grains and the non-washed sample calcinated at 350 °C presented the highest carbon recovery as its surface was the smoothest one, as confirmed by thermogravimetry curve. As a result of this higher carbon content, its methylene blue and gasoline adsorption capacities were the highest, albeit a bit lower in comparison to activated carbon due to the hydrocarbon formation onto sample surface. Finally, BET and BJH studies showed that porosity should also be improved in order to achieve higher adsorption values.     

Utilization of natural zeolite in aerated concrete production

In this study, natural zeolite (clinoptilolite) was used as an aggregate and bubble-generating agent in autoclaved aerated concrete (AAC) production. The crushed and grinded samples were classified into two different particle sizes: 100 μm (fine-ZF) and 0.5–1 mm (coarse-ZC) before using in AAC mixtures. The effects of particle size, replacement amount (25%, 50%, 75% and 100% against quartz) and curing time on the AAC properties were experimentally investigated. It was found that usage of natural zeolite, especially with a coarser particle size, has beneficial effect on the physical and mechanical properties of AAC. The optimum replacement amount was determined as 50% and at this rate the compressive strength, unit weight and thermal conductivity of AAC were measured as 3.25 MPa, 0.553 kg/dm³ and 0.1913 W/mK, respectively. Scanning electron microscopy analysis also confirmed the above findings. Denser C–S–H structures were obtained up to a replacement amount of 50%. Finally, the test results demonstrated that calcined zeolite acts as both an aggregate and a bubble-generating agent, and that AAC with a compressive strength of 4.6 MPa and unit weight of 0.930 kg/dm³ can be produced without aluminum powder usage.     

Tribological characteristics of innovative Al6061–carbon fiber rod metal matrix composites

Rods made of continuous carbon fibers are being extensively used as structural materials in light weight micro-air vehicles owing to their excellent specific modulus and strength. Further, they possess excellent tribological characteristics – low friction and wear coupled with high conductivity making them an ideal reinforcement in developing light weight, high strength aluminum based metal matrix composites. In the last three decades, researchers have focused mainly on the study of mechanical and tribological behavior of discontinuous carbon fiber reinforced metal matrix composites. However, no information is available regarding the tribological behavior of carbon fibers rod reinforced metal matrix composites, although it is interesting and will result in expanding the applications of metal matrix composites (MMC) where tribological failures are expected.In the light of the above, the present work focuses on development of innovative Al6061–carbon fiber rods composites by casting route and assessing their tribological characteristics. Carbon fiber rods of 4 mm and 6 mm diameters were surface sensitized to achieve electro less nickel coating. Copper plating on the electro less nickel coated carbon fiber rods were carried out. The copper plated carbon fiber rods were arranged in cylindrical array in the metallic mold to which molten Al6061 alloy after degassing was poured at a temperature of 700 °C. The developed innovative composites were subjected to density tests, microstructure studies, hardness, friction and wear tests. A pin on disk configuration was used with hardened steel as the counter face. Load was varied from 20 N to 60 N while the sliding velocity was varied between 0.12 m/s and 0.62 m/s. Scanning electron microscopy (SEM) studies on worn surfaces and wear debris have been carried out to validate the wear mechanism. The developed innovative composites (11 Vol.% & 25 Vol.%) have exhibited lower coefficient of friction and wear rates when compared with matrix alloy.     

In-situ synthesis of TiC/Fe alloy composites with high strength and hardness by reactive sintering

Fe alloy composites reinforced with in-situ titanium carbide(Ti C) particles were fabricated by reactive sintering using different reactant C/Ti ratios of 0.8,0.9,1 and 1.1 to investigate the microstructure and mechanical properties of in-situ Ti C/Fe alloy composites.The microstructure showed that the in-situ synthesized Ti C particles were spherical with a size of 1–3 μm,irrespective of C/Ti ratio.The stoichiometry of in-situ Ti C increased from 0.85 to 0.88 with increasing C/Ti ratio from 0.8 to 0.9,but remained almost unchanged for C/Ti ratios between 0.9 and 1.1 due to the same driving force for carbon diffusion in Ti Cxat the common sintering temperature.The in-situ Ti C/Fe alloy composite with C/Ti = 0.9 showed improved mechanical properties compared with other C/Ti ratios because the presence of excess carbon(C/Ti = 1 and 1.1) resulted in unreacted carbon within the Fe alloy matrix,while insufficient carbon(C/Ti = 0.8)caused the depletion of carbon from the Fe alloy matrix,leading to a significant decrease in hardness.This study presents that the maximized hardness and superior strength of in-situ Ti C/Fe alloy composites can be achieved by microstructure control and stoichiometric analysis of the in-situ synthesized Ti C particles,while maintaining the ductility of the composites,compared to those of the unreinforced Fe alloy.Therefore,we anticipate that the in-situ synthesized Ti C/Fe alloy composites with enhanced mechanical properties have great potential in cutting tool,mold and roller material applications.