Enhanced fluoride removal from water by non-thermal plasma modified CeO2/Mg–Fe layered double hydroxides

A novel fast and efficient adsorbent based on lamellar compound namely CeO₂/Mg–Fe layered double hydroxide composite has been designed for fluoride removal from water. In order to improve fluoride removal efficiency, non-thermal plasma (NTP) was used to modify the surface state of composites. The prepared composites were characterized by powder X-ray diffraction, thermogravimetric analysis and surface area analyzer. Adsorption equilibrium and kinetics of fluoride on NTP modified composites were investigated. Experimental results indicated that the adsorption capacity was enhanced with NTP surface modification. The maximum adsorption capacity has been found to be 38.7–60.4 mg/g. The kinetic data of adsorption were found to best fit the pseudo-second-order model, while the equilibrium data were found to be well described by Langmuir model. In order to understand the mechanism of adsorption, thermodynamic parameters such as ΔG^θ, ΔS^θ and E_a were calculated. After NTP treatment, the ΔS^θ increased from − 34.7 J/mol·K to − 0.770 J/mol·K, the E_a decreased from 78.8 kJ/mol to 58.9 kJ/mol and the ΔG^θ (25 °C) decreased from − 2.62 kJ/mol to − 3.14 kJ/mol. These values indicate that the fluoride adsorption on NTP modified composites was improved.     

Chitosan-modified palygorskite: Preparation,characterization and reactive dye removal

Chitosan-modified palygorskite (CTS-modified PA) was prepared by surface grafting of PA with chitosan, and the CTS-modified PA was used as an effective adsorbent for the removal of reactive dye. The effects of various experimental parameters such as initial pH, adsorbent dosage, contact time and initial dye concentration on adsorption were investigated. The adsorption behavior of CTS-modified PA showed that the adsorption kinetics and isotherms were in good agreement with the pseudo-second-order equation and the Langmuir equation, and the maximum adsorption capacity of CTS-modified PA calculated by the Langmuir model was 71.38 mg g^− 1, which was much higher than that of the unmodified PA (6.3 mg g^− 1).     

Heavy metals uptake from aqueous solutions and industrial wastewaters by humic acid-immobilized polymer/bentonite composite: Kinetics and equilibrium modeling

This study explored the feasibility of utilizing a novel adsorbent, humic acid-immobilized-amine-modified polyacrylamide/bentonite composite (HA-Am-PAA-B) for the adsorption of Cu(II), Zn(II) and Co(II) ions from aqueous solutions. The FTIR and XRD analyses were done to characterize the adsorbent material. The effects of pH, contact time, initial adsorbate concentration, ionic strength and adsorbent dose on adsorption of metal ions were investigated using batch adsorption experiments. The optimum pH for Cu(II), Zn(II) and Co(II) adsorption was observed at 5.0, 9.0 and 8.0, respectively. The mechanism for the removal of metal ions by HA-Am-PAA-B was based on ion exchange and complexation reactions. Metal removal by HA-Am-PAA-B followed a pseudo-second-order kinetics and equilibrium was achieved within 120 min. The suitability of Langmuir, Freundlich and Dubinin-Radushkevich adsorption models to the equilibrium data was investigated. The adsorption was well described by the Langmuir isotherm model. The maximum monolayer adsorption capacity was 106.2, 96.1 and 52.9 mg g^?1 for Cu(II), Zn(II) and Co(II) ions, respectively, at 30 °C. The efficiency of HA-Am-PAA-B in removing metal ions from different industry wastewaters was tested. Adsorbed metal ions were desorbed effectively (97.7 for Cu(II), 98.5 for Zn(II) and 99.2% for Co(II)) by 0.1 M HCl. The reusability of the HA-Am-PAA-B for several cycles was also demonstrated.     

Effect of particle size,heating rate and CNT addition on densification,microstructure and mechanical properties of B4C ceramics

Monolithic B₄C ceramics and B₄C–CNT composites were prepared by spark plasma sintering (SPS). The influence of particle size, heating rate, and CNT addition on sintering behavior, microstructure and mechanical properties were studied. Two different B₄C powders were used to examine the effect of particle size. The effect of heating rate on monolithic B₄C was investigated by applying three different heating rates (75, 150 and 225 °C/min). Moreover, in order to evaluate the effect of CNT addition, B₄C–CNT (0.5–3 mass%) composites were also produced. Fully dense monolithic B₄C ceramics were obtained by using heating rate of 75 °C/min. Vickers hardness value increased with increasing CNT content, and B₄C–CNT composite with 3 mass% CNTs had the highest hardness value of 32.8 GPa. Addition of CNTs and increase in heating rate had a positive effect on the fracture toughness and the highest fracture toughness value, 5.9 MPa m^1/2, was achieved in composite with 3 mass% CNTs.     

Synthesis and characterization of β-TCP/CNT nanocomposite: Morphology,microstructure and in vitro bioactivity

In this study, β-TCP/CNT nanocomposite has been synthesized by solution precipitation method. Then, the effects of the different percentage of CNT (CNT1β-TCP, CNT3β-TCP, CNT5β-TCP) and surfactant (CNT1β-TCP1SDBS, CNT1β-TCP2SDBS, CNT1β-TCP3SDBS) on β-TCP/CNT nanocomposite powder were studied. The X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and Transmission electron microscopy (TEM) analyses were used to characterize the samples. The observations revealed that the microstructure of 1 wt% CNT could provide dispersion without agglomeration in nanocomposite powder; however, a higher concentration of CNT powder in the nanocomposite resulted in the formation of Ca₂PO₇ phase. Implementing 2 wt% of SDBS as a surfactant modified the shape, size, and distribution of CNT particles on nanocomposites. Finally, the nanocomposite sample was immersed in simulated body fluid (SBF) to evaluate the in vitro bioactivity. It obviously showed an apatite layer on the surface after 7 days of immersion in SBF. Taken together, this nanocomposite might be potentially to be used as bone repair biomaterial.     

Fabrication and toughening behavior of carbon nanotube (CNT) scaffold reinforced SiBCN ceramic composites with high CNT loading

Uniform dispersion, high loading and three-dimensional (3D) continuous network of carbon nanotube (CNT) are desired for high-performance nanocomposites to fully utilize the superior strength and toughness of CNTs. In this work, monolithic CNTs/SiBCN composites with high CNT loading (10 wt% and 20 wt%) were prepared from 3D scaffold-like CNT cottons and a liquid polyborosilazane (PBSZ) precursor through precursor infiltration and pyrolysis process. The 3D CNT scaffold in the nanocomposite can function as passive filler and gas path to ensure formation of monolithic bulks. Moreover, direct infiltration of PBSZ into the pores among CNT cotton can hinder agglomeration of CNTs and localize CNTs at the original sites, guarantee good alignment and high CNT concentration in the final nanocomposite. This highly concentrated 3D CNT reinforcement in the nanocomposite shows unique resistance to cracking under external stress related to the complex fracture behavior of CNT bundles during the cracking formation and extension process (including CNT bridging, aligning, pulling out and then breaking), which more favors for absorbing energies and enhance toughness of the ceramic composites.     

The performance of CNT as catalyst support on CO oxidation at low temperature

A carbon nanotube (CNT) was used as catalyst support impregnated with transition metal cobalt for CO oxidation at low temperature. Catalyst properties were analyzed by X-ray powder diffractometer (XRD), X-ray photoelectron spectrometer (XPS), and transmission electron microscope (TEM). Analytical results for TEM and XRD demonstrated that cobalt particles were highly dispersed on the carbon nanotube (20–30 nm) with nanosized cobalt particles (10–15 nm). These investigations indicated that Co/CNT generates about 99% of the high activity for CO conversion at 250 °C and thermally stability that is superior to Co/activated carbon (AC). The optimum reaction conditions for CO conversion were O₂ concentration 3%, operation temperature 250 °C, CO concentration 5000 ppm, and space velocity 156,000 h⁻¹. At 250 °C, CO may act as a reductant for NO reduction over Co/CNT in the presence of oxygen, whereas CO/NO = 2.5 showed that maximum NO reduction was 30%. Under H₂ rich conditions, the optimum reaction temperature for CO conversion was under 300 °C, and performance of CO₂ selectivity was better at 200 °C than 250 °C as the oxygen concentration increased.     

Thermodynamics and regeneration studies of CO2 adsorption on multiwalled carbon nanotubes

Multiwalled carbon nanotubes (CNTs) were fabricated and modified by 3-aminopropyl-triethoxysilane (APTS) solutions to study thermodynamics and regeneration of CO₂ adsorption from gas streams. The CO₂ adsorption capacities of CNTs and CNT(APTS) decreased with temperature indicating the exothermic nature of adsorption process while the thermodynamic analysis gave low isosteric heats of adsorption, which are typical for physical adsorption. The cyclic CO₂ adsorption on CNT(APTS) showed that the adsorbed CO₂ could be effectively desorbed via thermal treatment at 120 °C for 25 min while the adsorbed CO₂ due to physical interaction could be effectively desorbed via vacuum suction at 0.145 atm for 30 min. If a combination of thermal and vacuum desorption was conducted at 120 °C and 0.145 atm, the time for effectively desorbing CO₂ could be further shortened to 5 min. The adsorption capacities and the physicochemical properties of CNT(APTS) were preserved during 20 cycles of adsorption and regeneration. These results suggest that the CNT(APTS) can be stably employed in prolonged cyclic operation and they are thus possibly cost-effective sorbents for CO₂ capture from flue gases.     

Densification during hot-pressing of carbon nanotube–metal–magnesium aluminate spinel nanocomposites

The densification by hot-pressing of ceramic–matrix composites containing a dispersion of carbon nanotubes (CNT), mostly single-walled, is studied for the first time. Fifteen different CNT–Co/Mo–MgAl₂O₄ composite powders containing between 1.2 and 16.7 vol.% CNT were prepared by catalytic chemical vapour deposition. The in situ growth of CNT within the oxide powder made it possible to obtain a highly homogeneous distribution of CNT. Low contents of CNT (up to 5 vol.%) are beneficial for the first shrinkage step (up to 1100 °C), dominated by the rearrangement process, while higher contents are detrimental. At higher temperatures (1100–1300 °C), CNT clearly inhibit the shrinkage, and this detrimental effect regularly increases with the CNT content. Several explanations are proposed, in relation with the particular mechanical properties of CNT and their highly connected web-like distribution within the material.     

Palladium,silver, and zinc oxide nanoparticles loaded on activated carbon as adsorbent for removal of bromophenol red from aqueous solution

The adsorption of bromophenol red (BPR) onto three adsorbents including palladium, silver and zinc oxide nanoparticles loaded on activated carbon (Pd-NP-AC, Ag-NP-AC and ZnO-NP-AC) in a batch system has been studied and the influence of various parameters has been optimized. The influence of time on removal of BPR on all adsorbent was investigated and experimental data were analyzed by four kinetic models including pseudo first and second-order, Elovich and the intraparticle diffusion equations. Following fitting the experimental data to these models, the respective parameters of each model such as rate constants, equilibrium adsorption capacities and correlation coefficients for each model were investigated and based on well known criterion their applicability was judged. It was seen that the adsorption of BPR onto all adsorbents sufficiently described by the pseudo second-order equation in addition to interparticle diffusion model. The adsorption of BPR on all adsorbent was investigated at various concentration of dye and the experimental equilibrium data were analyzed and fitted to the Langmuir, Freundlich, Tempkin, Dubinin, and Radushkevich equations. A single stage in batch process was efficient and suitable for all adsorbents using the Langmuir isotherm with maximum adsorption of 143 mg g^?1 for Pd-NP-AC, 250 mg g^?1 for Ag-NP-AC and 200 mg g^?1 for ZnO-NR-AC. Thermodynamic parameters such as ΔG°, ΔH°, and ΔS° for Pd-NP-AC adsorbent were calculated.     

Thermal fatigue and hypothermal atomic oxygen exposure behavior of carbon nanotube wire

In low earth orbit (LEO), components of space systems are exposed to damaging hypothermal atomic oxygen and thermal fatigue. Carbon nanotube (CNT) wires are candidate materials for different applications in space systems. Thirty-yarn CNT wire’s behavior was evaluated when exposed to hypothermal atomic oxygen and thermal fatigue. CNT wire specimens were exposed to a nominal fluence of hypothermal atomic oxygen of 2 × 10²⁰ atoms/cm². The erosion rate due to hypothermal collision between atomic oxygen and CNT wires was calculated to be 2.64 × 10⁻²⁵ cm³/atom, which is comparable to highly ordered pyrolytic graphite. The tensile strength of CNT wire was not affected by this exposure, and a minor reduction of electrical conductivity (2.5%) was found. Scanning electron microscopy (SEM) and Energy Dispersive X-ray spectroscopy analysis showed erosion of surface layer with depleted carbon and increased oxygen. Thermal fatigue excursion of 5000 cycles from 70 to −50 °C at a rate of 55 °C/min showed no loss in tensile strength; however a large decrease in conductivity (18%) was seen. SEM analysis showed that the thermal fatigue created buckling of yarn and fracture of individual CNTs bundles. These reduced the effective area and electrical conductivity of CNT wire.     

A new carbon molecular sieve for propylene/propane separations

A new carbon molecular sieve (CMS) with a propylene/propane separation factor of approximately 27 was synthesized by a facile pyrolysis process from a gel-type strong acid cation exchange resin. The micropore shrinkage process during pyrolysis was investigated using a new high throughput adsorption technique with 48 parallel cells. This significantly reduced the characterization time. The ratio of propylene/propane adsorption rate in the CMS adsorbent changes from 1 to more than 150 when the final pyrolysis temperature changes from 550 to 1000 °C. The best performing CMS pyrolyzed at 850 °C was further characterized using a gravimetric adsorption method. The propylene and propane diffusivities are 1.0 × 10⁻⁹ and 1.1 × 10⁻¹¹ cm² s⁻¹ at 100 kPa and 90 °C. The high propylene/propane diffusivity ratio of 90 is similar to that in zeolite 4A, while the propylene diffusivity was more than 30 times higher than that in zeolite 4A. An effluent of 90 mol% propylene was obtained from a feed of 25 mol% propylene during adsorption/desorption tests using the CMS adsorbent pyrolyzed at 850 °C in a fixed-bed configuration. The new CMS adsorbent is a promising candidate for industrial scale propylene/propane separations.     

Design and synthesis of three-dimensional needle-like CoNi2S4/CNT/graphene nanocomposite with improved electrochemical properties

In this paper, we described a simple two–step method for preparing needle-like CoNi₂S₄/CNT/graphene nanocomposite with robust connection among its ternary components. The prepared CoNi₂S₄/CNT/graphene nanocomposite has been thoroughly characterized by spectroscopic (Fourier-transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy), X-ray diffraction and thermogravimetric analysis. Microscopy techniques (scanning electron microscopy–energy dispersive spectroscopy and transmission electron microscopy) were employed to probe the morphological structures. The electrochemical properties of the as-prepared 3D architectures were investigated with three and two-electrode systems. In addition to its high specific capacitance (710 F g⁻¹ at 20 A g⁻¹), after charging–discharging for 2000 cycles, the electrode still maintained the capacity retention of about 82%. When used as the active electrode material for supercapacitors, the fabricated CoNi₂S₄–g–CNT nanostructure exhibited excellent specific capacitance and good rate capability, making it a promising candidate for next-generation supercapacitors.     

Adsorption of Pb(II) from aqueous solution to Ni-doped bamboo charcoal

Bamboo charcoal (BC) obtained by pyrolysis of Makino bamboo in the absence of oxygen was used as support for the preparation of Ni-doped adsorbent (Ni-BC). The low-cost composite was characterized and used as an adsorbent for Pb(II) removal from water. The results showed that both BET surface area and total pore volume of Ni-BC increased. The adsorption of Pb(II) strongly depended on solution pH, temperature and ionic strength. The adsorption isotherms followed Langmuir isotherm model well, and the maximum adsorption capacities of Pb(II) at 298 K were 25.0 and 142.7 mg/g for BC and Ni-BC, respectively. The adsorption processes were well fitted by pseudo-second-order kinetic model. Thermodynamic parameters showed that the adsorptions of Pb(II) onto both adsorbents were feasible, spontaneous, and exothermic under the studied conditions. The spent Ni-BC could be readily regenerated for reuse.     

Processing and properties of sol gel derived alumina–carbon nano tube composites

High purity alumina–carbon nano tube (CNT) composites were prepared by an aqueous sol–gel processing route. CNTs were dispersed in alumina sol containing appropriate amount of MgO precursor. Aqueous slurry of alumina was seeded into the sol followed by gelation, drying and calcination at 1000 °C for 1 h. The calcined powder consisting of alumina-coated CNTs and alumina was milled, sieved, dried, pressed and pressureless sintered at 1400–1600 °C for 1 h in nitrogen atmosphere. Sintered samples were further isostatically hot pressed at 1300 °C and the properties were compared with the pressureless sintered samples. Phase formation was followed by XRD study, CNT retention was confirmed by Raman studies and the samples were further characterized for mechanical and microstructural properties.     

The growth of carbon nanotubes in aluminum powders by the catalytic pyrolysis of polyethylene glycol

A simple approach based on the catalytic pyrolysis of polyethylene glycol (PEG) was developed to grow a uniform dispersion of carbon nanotubes (CNTs) in Al powders and thus supply raw material for the powder metallurgy fabrication of CNT/Al composites. Al nanoflake powders with quite a large surface area were used to adsorb a homogeneous PEG and citric acid film, and then were impregnated with a cobalt nitrate solution to anchor Co(II) by complexation with citric acid. Then the Al nanoflake powders were heated to 230 °C to form Co oxide nanoparticles, and then to 570 °C to induce the thermal decomposition of PEG. The pyrolytic products of PEG not only served as the reducing agent to reduce Co oxide to Co nanoparticle catalyst, but also as the carbon source for CNT growth. As a result, 2.13 wt.% graphitic CNTs, with diameters of 10–20 nm and length ranging from sub-micron to a few micrometers, were homogeneously grown in 500 nm thick Al nanoflakes. And the as-obtained CNT/Al composites fabricated by hot-pressing exhibited enhanced strength, which was almost two times that of the matrix.     

Double-layer electromagnetic wave absorber based on barium titanate/carbon nanotube nanocomposites

The electromagnetic wave absorption properties of double-layer barium titanate/carbon nanotube (BTO/CNT) nanocomposites were evaluated. The BTO/CNT nanomaterials were characterized using X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, and field emission scanning electron microscopy. The reflection loss (R.L.) of the samples was calculated based on the measured complex permittivity and permeability. The minimum R.L. of single-layer BTO/CNT 30 wt% nanocomposites sample with a thickness of 1.1 mm reached ~−30.3 dB (over 99.9% absorption) at 13.8 GHz, and the bandwidth of the reflection loss less than −10 dB (over 90% absorption) was 1.5 GHz. The double-layer composites consist of BTO/CNT 30 wt% (absorption layer) with thickness of 1.0 mm and BTO 30 wt% (matching layer) with thickness of 0.3 mm showed a minimum R.L. of ~−63.7 dB (over 99.9999% absorption) at 13.7 GHz, and the bandwidth of the reflection loss less than −10 dB was 1.7 GHz. Wider response bandwidth, >1.7 GHz also can be achieved with different designs of double-layer absorbers. The R.L. significantly improved and wider response bandwidth can be obtained with double-layer composites. The capability to modulate the absorption and bandwidth of these samples to suit various applications in different frequency bands indicates that these nanocomposites could be an excellent electromagnetic wave absorber.     

Adsorption of Reactive Blue 114 dye by using a new adsorbent: Pomelo peel

This paper describes the removal of Reactive Blue 114 dye from aqueous solutions by using pomelo (Citrus grandis) peel. Pomelo peel can be described as a new, low cost, abundantly available adsorbent. The optimum adsorbent mass, dye concentration, contact time and pH were determined in this study. The parameters of Langmuir, Freundlich and Temkin adsorption isotherms were also obtained using concentrations of the dyes ranging from 1.0 to 200 mg/L. Maximum adsorption capacity was obtained as 16 mg/g at pH 2 and 303 K solution temperature. The adsorption process was observed to be reaching equilibrium after about 90 min.     

Simultaneous preconcentration of Cd(II), Cu(II) and Pb(II) on Nano-TiO2 modified with 2-mercaptobenzothiazole prior to flame atomic absorption spectrometric determination

Nano-TiO₂ modified with 2-mercaptobenzothiazole (MBT) was investigated as a new adsorbent for preconcentration of Cd(II), Cu(II) and Pb(II). The metal ions are adsorbed onto nano-TiO₂-MBT, eluted by nitric acid and determined by flame atomic absorption spectrometry. The parameters affecting the adsorption were investigated. Under optimized conditions, the calibration curves were linear in the range of 0.2–25.0, 0.2–20.0, and 3.0–70.0 ng mL⁻¹ for cadmium, copper and lead, respectively. The limits of detection for Cd(II), Cu(II) and Pb(II) were 0.12, 0.15 and 1.38 ng mL⁻¹, respectively. The method was applied to determination of Cd(II), Cu(II) and Pb(II) in water and ore samples.     

Removal of Reactive Blue 21 onto magnetic chitosan microparticles functionalized with polyamidoamine dendrimers

Chitosan/poly(amidoamine) (MCS/PAMAM) microparticles were prepared as magnetic adsorbents for removal of Reactive Blue 21 (RB 21) dye from aqueous solution. Characterization of these particles was carried out using scanning electron microscopy, Fourier transform-infrared spectroscopy, X-ray diffractometry and vibrating sample magnetometry. The results indicate that the magnetic chitosan microparticles (MCS) were functionalized with PAMAM dendrimers and maintained its intrinsic magnetic properties. The effects of initial pH, adsorbent dose, initial concentration, contact time and temperature on adsorption were investigated. Kinetic studies showed that the dye adsorption process followed a pseudo-second-order kinetic model but that the adsorption rate was also influenced by intraparticle diffusion. Equilibrium adsorption isotherm data indicated a good fit to the Langmuir isotherm. The maximum adsorption capacities obtained from the Langmuir model were 555.56, 588.24, 625.00 and 666.67 mg g⁻¹ at 303, 313, 323 and 333 K, respectively. The thermodynamic parameters revealed the feasibility, spontaneity and endothermic nature of the adsorption. Recycling experiments confirmed the relative reusability of the adsorbent.