Electrophoretic deposition of hydroxyapatite-chitosan-CNTs nanocomposite coatings

Three component suspensions of hydroxyapatite (HA), chitosan and CNTs were prepared in ethanol base solution (15 vol% water and 0.05 vol% acetic acid). The adsorption of HA nanoparticles on CNTs was investigated by FTIR and SEM analysis. It was found that HA nanoparticles are adsorbed on CNTs via chemical bonding between -NH₂ groups of chitosan (adsorbed on their surface) and -COOH groups of CNTs. Current density as well as kinetics of EPD was studied at 60 V. It was found that current density increases or remains nearly constant during EPD due to the rise in water electrolysis as deposit grows on the substrate. Deposition weight against EPD time showed a linear trend due to the absence of any voltage drop over the deposit during EPD. The incorporation of chitosan and CNTs in the microstructure of coatings was confirmed by TG/DTA and SEM analysis. CNTs exhibited high efficiency in reinforcing the microstructure of coatings and preventing from their cracking. CNTs incorporation in the coatings improved their mechanical properties (adhesion strength, hardness and elastic modulus) and corrosion resistance.     

Adsorption of zinc(II) from water with purified carbon nanotubes

Commercial single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) were purified by sodium hypochlorite solutions and were employed as adsorbents to study the adsorption characteristics of zinc from water. The properties of CNTs such as purity, structure and nature of the surface were greatly improved after purification which made CNTs become more hydrophilic and suitable for adsorption of Zn²⁺. In general, the adsorption capacity of Zn²⁺ onto CNTs increased with the increase of pH in the pH range of 1-8, fluctuated very little and reached maximum in the pH range of 8-11 and decreased at a pH of 12. A comparative study on the adsorption of Zn²⁺ between CNTs and commercial powdered activated carbon (PAC) was also conducted. The maximum adsorption capacities of Zn²⁺ calculated by the Langmuir model are 43.66, 32.68, and with SWCNTs, MWCNTs and PAC, respectively, at an initial Zn²⁺ concentration range of 10-. The short contact time needed to reach equilibrium as well as the high adsorption capacity suggests that SWCNTs and MWCNTs possess highly potential applications for the removal of Zn²⁺ from water.     

Hybrid polyvinyl alcohol/polyvinyl chloride nanocomposites reinforced with graphene-carbon nanotube for acid red environmental treatments

ABSTRACT

Hybrid polyvinyl alcohol and polyvinyl chloride/graphene and carbon nanotube nanocomposites PVA–PVC/Gr–CNTs_a-e were successfully synthesized by a solution-casting method. Mixed Gr–CNTs ratio (50%:50%) was prepared in 2, 5, 10, 15, and 20 wt% and added to the host polymers (PVA/PVC). The characterization tools for the fabricated nanocomposites show homogenous interaction between the fillers and PVA/PVC polymer matrix. A significant improvement in the thermal properties of the (PVA/PVC) matrix was observed by adding mixed fillers, even at low loadings of mixed Gr–CNTs on to the matrix. Scanning electron microscopy and transmission electron microscopy images of the prepared composites show a good dispersion of PVA–PVC and mixed Gr–CNTs and present core-shell morphology. Impressive improvement in the percentage of acid red removal using PVA–PVC/Gr–CNTs_a–e was achieved and improved with time, solution temperature, and composites mass. The process of removing acid red was described kinetically and thermodynamically. The pseudo-second-order kinetic model is the most appropriate kinetic model to describe the adsorption of acid red by PVA–PVC and PVA–PVC/Gr–CNTs_d nanocomposites from an aqueous solution. Our results offer a facile method for the removal of acid red from three types of water: red sea, tap water, and distilled water.     

碳纳米管对水体重金属污染物的吸附/解吸性能研究进展

详细阐述了碳纳米管(CNTs)对水体中和重金属离子的吸附/解吸影响因素和吸附机理,展望了碳纳米管在环境治理方面应用前景。     

Comparison with as-grown and microwave modified carbon nanotubes to removal aqueous bisphenol A

This study utilized carbon nanotubes (CNTs) to remove bisphenol A (BPA) from aqueous solution. The surfaces of CNTs were modified by SOCl₂/NH₄OH under microwave irradiation. The surface characteristics of as-grown and modified CNTs were analyzed by measuring zeta potential, and using a scanning electron microscope, a surface area analyzer and a Fourier transform infrared spectroscope. The specific surface area of modified CNTs exceeded that of as-grown CNTs. The pH_iep values of as-grown CNTs and modified CNTs were determined to be 4.3 and 6.5, respectively. Some amine functionalities were formed on the surface of modified CNTs; therefore, the surface of the modified CNTs contained more positive charges than that of the as-grown CNTs. The adsorption kinetics were examined using pseudo first- and second-order models, intraparticle diffusion and Bangham's models. The equilibrium data were simulated using Langmuir, Freundlich, Dubinin and Radushkevich (D-R) and Temkin isotherms. The results reveal that the pseudo second-order model and Langmuir isotherm fit the kinetics and equilibrium data, respectively. The adsorption capacity of BPA on the surface of CNTs fluctuates very little with pH in the range of 3-9, suggesting the high stability of CNTs as an adsorbent for BPA over a rather wide pH range. The values of ΔH⁰ and ΔS⁰ were calculated to be − 11.7 kJ/mol and 46.1 J/mol, respectively. The isotherm and thermodynamic simulations indicate that the adsorption of BPA onto as-grown CNTs proceeds by physisorption process.     

Adsorption of chromium (VI) on functionalized and non-functionalized carbon nanotubes

We did a comparative study on the adsorption capacity of Cr (VI) between functionalized carbon nanotubes (CNTs) and non-functionalized CNTs. The statistical analysis reveals that the optimum conditions for the highest removal of Cr (VI) are at pH 9, with dosage 0.1 gram, agitation speed and time of 120 rpm and 120 minutes, respectively. For the initial concentration of 1.0 mg/l, the removal efficiency of Cr (VI) using functionalized CNTs was 87.6% and 83% of non-functionalized CNTs. The maximum adsorption capacities of functionalized and non-functionalized CNTs were 2.517 and 2.49 mg/g, respectively. Langmuir and Freundlich models were adopted to study the adsorption isotherm, which provided a K _L and K _F value of 1.217 L/mg and 18.14 mg^1?n L ⁿ /g functionalized CNT, while 2.365 L/mg and 2.307 mg^1?n L ⁿ /g for non-functionalized CNTs. This result proves that functionalized CNTs are a better adsorbent with a higher adsorption capacity compared with the non-functionalized CNTs.     

Water purification of removal aqueous copper (II) by as-grown and modified multi-walled carbon nanotubes

This study compares aqueous copper (II) adsorbed onto as-grown and modified carbon nanotubes (CNTs), using H₂SO₄ and H₂SO₄/KMnO₄ processes. H₂SO₄ and H₂SO₄/KMnO₄ modifications reduced pH_iep and Fourier Transform Infrared Spectroscopy (FTIR) analysis revealed that some functional groups were formed on modified CNTs. The adsorption capacity of copper (II) onto modified CNTs was greater than that of as-grown CNTs, especially at pH 6. The results demonstrate that the modified processes increased the adsorption capacity because the functional groups were generated on the modified surfaces of the CNTs. Additionally, the adsorption capacity of copper (II) onto as-grown and modified CNTs both increased with temperature, and the results indicated that the Langmuir isotherm fitted the experimental data well. Simulation results indicated that the ΔH⁰ values of as-grown, H₂SO₄-modified CNTs and H₂SO₄/KMnO₄-modified CNTs were 4.83, 14.37 and 29.92 kJ/mol, respectively. Based on ΔH⁰, the adsorption of Cu²⁺ onto H₂SO₄/KMnO₄-modified CNTs is suggested to proceed simultaneously by physisorption and chemisorption but that onto as-grown and H₂SO₄-modified CNTs may proceed only by physisorption.     

Competitive adsorption of Pb, Cu and Cd ions from aqueous solutions by multiwalled carbon nanotubes

The individual and competitive adsorption capacities of Pb²⁺, Cu²⁺ and Cd²⁺ by nitric acid treated multiwalled carbon nanotubes (CNTs) were studied. The maximum sorption capacities calculated by applying the Langmuir equation to single ion adsorption isotherms were 97.08 mg/g for Pb²⁺, 24.49 mg/g for Cu²⁺ and 10.86 mg/g for Cd²⁺ at an equilibrium concentration of 10 mg/l. The competitive adsorption studies showed that the affinity order of three metal ions adsorbed by CNTs is Pb²⁺>Cu²⁺>Cd²⁺. The Langmuir adsorption model can represent experimental data of Pb²⁺ and Cu²⁺ well, but does not provide a good fit for Cd²⁺ adsorption data. The effects of solution pH, ionic strength and CNT dosage on the competitive adsorption of Pb²⁺, Cu²⁺ and Cd²⁺ ions were investigated. The comparison of CNTs with other adsorbents suggests that CNTs have great potential applications in environmental protection regardless of their higher cost at present.     

Adsorption of cadmium(II) from aqueous solution by surface oxidized carbon nanotubes

Carbon nanotubes (CNTs) were oxidized with H₂O₂, KMnO₄ and HNO₃. Their physicochemical properties were investigated by BET N₂ adsorption, laser particle examination, Boehm’s titration, zeta potential measurement and cadmium(II) adsorption. The experimental results suggest that cadmium(II) adsorption capacities for three kinds of oxidized CNTs increase due to the functional groups introduced by oxidation compared with the as-grown CNTs. The cadmium(II) adsorption capacity of the as-grown CNTs is only 1.1 mg g⁻¹, while it reaches 2.6, 5.1 and 11.0 mg g⁻¹ for the H₂O₂, HNO₃ and KMnO₄ oxidized CNTs, respectively, at the cadmium(II) equilibrium concentration of 4 mg l⁻¹. Adsorption of cadmium(II) by CNTs was strongly pH-dependent and the increase of adsorption capacities for HNO₃ and KMnO₄ oxidized CNTs is more obvious than that of the as-grown and H₂O₂ oxidized CNTs at lower pH regions. The experiments of CNT dosage effect on the cadmium(II) adsorption show that the adsorption capacity for KMnO₄ oxidized CNTs has a sharper increase at the CNT dosage from 0.03 to 0.08 g per 100 ml than the as-grown, H₂O₂ and HNO₃ oxidized CNTs and its removal efficiency almost reaches 100% at CNT dosage of 0.08 g per 100 ml. Analysis revealed that the KMnO₄ oxidized CNTs hosted manganese residuals, and these surely contributed to cadmium sorption to a yet-undefined extent.     

A first-principles study of nitrogen- and boron-assisted platinum adsorption on carbon nanotubes

We have performed first-principles calculations to investigate the origin of adsorption of platinum on nitrogen- and boron-doped carbon nanotubes (CNTs). Our calculation results reveal that both nitrogen- and boron-doped CNTs can assist the reactivity of platinum adsorption on the CNT surface, although the detailed mechanisms are very different. For nitrogen-doped CNTs, the enhanced adsorption results from activation of the nitrogen-neighboring carbon atoms due to the large electron affinity of nitrogen. In this case, the nitrogen atoms mediate the platinum adsorption enhancement on the CNT surface. In contrast, the enhanced platinum adsorption in boron-doped CNTs can be attributed to the strong hybridization between the platinum d orbital and boron p orbital. Our results explain the experimentally observed enhanced adsorption of platinum on nitrogen-doped CNTs and also suggest that boron-doped CNTs may be a better candidate for fuel cell applications.     

The Development of Filter Media Using Plant and Marine Waste for Virus Removal from Drinking Water

Abstract:

Two natural wastes, palm leaves and shrimp shells, were purified and tested for their efficiency in adsorbing enteroviruses from drinking water. The chemical modification of marine waste was evaluated to prepare carboxymethyl chitin, while O-carboxymethyl chitosan was prepared by deacetylation of the carboxymethyl chitin to improve the adsorption of viruses from drinking water. The role of the reaction parameters such as temperature, time, concentration of alkali and etherified agent, and the material-to-liquor ratio were examined. Also, the effect of pH on the adsorption efficiency of enteroviruses in modified waste was evaluated. The results showed that raw palm leaves and O-carboxymethyl chitosan prepared as filter matrix exhibited a better adsorption efficiency in a wide range of pH levels. They can be used to adsorb viruses directly from tap water at ambient pH values without having multivalent-containing salts or adjusting the pH of tap water.     

Oxidized carbon nanotubes for simultaneous removal of endrin and Cd(Π) from water and their separation from water

BACKGROUND: Previous investigation has shown that carbon nanotubes (CNTs) are effective for the removal of organic pollutants and oxidized carbon nanotubes (OCNTs) are effective for the removal of heavy metals. In this investigation, OCNTs were used for simultaneous removal of endrin and Cd(Π) from water. Separation of OCNTs from water was also investigated. RESULTS: The removal efficiencies of endrin and Cd(Π) by OCNTs were 89–97% and 96–100%, respectively. Endrin removal capacity of OCNTs is approximately the same as that of powdered activated carbon (PAC) and as‐prepared CNTs. Cd(Π) removal capacity of OCNTs is much higher than that of PAC and as‐prepared CNTs. OCNTs can be separated efficiently from water using AlCl₃. CONCLUSION: OCNTs are effective for the simultaneous removal of endrin and Cd(Π) and after adsorption, OCNTs can be separated from water by dosing AlCl₃. Copyright © 2008 Society of Chemical Industry     

Adsorption of fulvic acids from aqueous solutions by carbon nanotubes

Carbon nanotubes (CNTs) were used as adsorbent to remove fulvic acids (FA) from aqueous solutions. The adsorption capacity of CNTs for FA can reach 24 mg g^?1 at 5 °C and equilibrium concentration of 18 mg dm^?3. The kinetic and thermodynamic parameters, such as rate of adsorption, standard free energy changes (ΔG⁰), standard enthalpy change (ΔH⁰) and standard entropy change (ΔS⁰), have been obtained. Acidic conditions (pH = 2–5) favor FA removal. An increase in the ionic strength or the addition of divalent cations increase the adsorption of FA dramatically (FA = 60 mg dm^?3). An increase in the maximum adsorbed amount of FA was observed when treating FA in synthetic seawater. Desorption studies reveal that FA can be easily and quickly removed from CNTs by altering the pH values of the solution. Good adsorption capacity and quick desorption indicate that CNTs are a promising adsorbent to remove FA from aqueous solutions. Copyright © 2007 Society of Chemical Industry     

Krypton adsorption as a suitable tool for surface characterization of multi-walled CNTs

Multi-walled carbon nanotubes (CNTs), pristine and subjected to treatments, are comparatively characterized from N₂ and Kr (77 K) adsorption measurements. The CNTs are lab-synthesized by in situ chemical vapour deposition of an iron-based organometallic compound at 895 °C. The treatments applied to the CNTs include low temperature gas-phase oxidation, mild temperature annealing and ultrasonic dispersion in ethanol, in an attempt to examine possible changes in adsorption characteristics. N₂ and Kr adsorption measurements give rise to steadily increasing and stepped isotherms, respectively. The former are representative of a multilayer adsorption phenomenon, while the latter indicate successive monolayer condensation. The treatments affect differently gas adsorption capacities of the CNTs. Oxidation leads to CNTs with higher BET specific surface area and increased adsorption capacity, though the effect is more pronounced for Kr adsorption. Ultrasonic dispersion of the CNT brings about a significant reduction only in N₂ adsorption capacity. Modifications in the characteristic steps in Kr adsorption isotherms of the CNTs subjected to annealing can be appreciated, although no remarkable changes are observed in N₂ adsorption isotherms. Present results demonstrate that determination of Kr adsorption isotherms represents a more suitable tool to obtain a more reliable textural characterization of CNTs than does N₂ adsorption.     

碳纳米管吸附去除水中大肠杆菌研究

选取常见细菌大肠杆菌E.coil作为对象,研究了碳纳米管(CNTs)对水中微生物的吸附去除效果,探讨了CNTs投加量、溶液pH和温度对吸附过程的影响。结果表明,CNTs对E.coil具有强的吸附能力,在初始1.0 h内保持较高的吸附速率,CNTs投加量为1.0 g.L-1时,吸附去除率高达99.99%。当溶液pH=7.0时,CNTs具有最大吸附去除率;低温有利于CNTs吸附过程的进行。CNTs对E.coil的吸附符合Freundlich和Langmuir等温吸附方程。     

碳纳米管改性对Au/CeO2催化剂乙醇部分氧化制氢的影响

采用沉积沉淀法制备了一系列碳纳米管改性的Au/CeO₂催化剂,以乙醇部分氧化制氢为探针反应,研究了碳纳米管对Au/CeO₂催化剂乙醇部分氧化性能的影响,并运用XRD、TPR、BET等方法对催化剂进行了表征。结果表明,碳纳米管的添加提高了Au/CeO₂催化剂的比表面积、孔容和吸氧量,催化剂的氢气选择性先随碳纳米管添加量的增加而大幅增加,碳纳米管的添加量达6%～10%时,氢气选择性达到43%。进一步提高碳纳米管的含量,氢气选择性增加幅度不大。碳纳米管的添加可以有效抑制副产物CO的产生。     

Preparation, Characterization and Adsorption Performance of Cetyl Pyridine Bromide Modified Bentonites

Benzoic acid removal is important for the water treatment and adsorption is an effective treatment process. Cetyl pyridine bromide-modified bentonites (CPB-Bent) and hydroxy-aluminum-pillared bentonites (Al(OH)-Bent) were prepared and characterized by XRD, FTIR and BET. Adsorption experiments were conducted on the adsorption of benzoic acid onto natural bentonites, sodium bentonites (Na-Bent), Al(OH)-Bent and CPB-Bent in batch experiments. Benzoic acid removal onto CPB-Bent is pH dependent and the optimum adsorption is observed at pH ~3.5. The adsorption rate was fast and equilibrium was established within 90-min. The adsorption rate of benzoic acid on CPB-Bent fit a pseudo-second order kinetics model well (R ² = 0.999). The results were analyzed according to the Henry, Langmuir, Freundlich, and Dubinin-Radushkevich isotherm model equations. The adsorption data is well interpreted by the Langmuir isotherm model. Benzoic acid solution at a concentration of 0.5 mmol/L was adsorbed by CPB-Bent; and, the final adsorption efficiency was greater than 90%. The results show that benzoic acid adsorption capability of CPB-Bent is high with the maximum adsorption capability of 94.34 mg/g, which suggests that CPB-Bent is an excellent adsorbent for effective benzoic acid removal from water.     

p-Sulphonatocalix[8]arene functionalized silica resin for the enhanced removal of methylene blue from wastewater: equilibrium and kinetic study

ABSTRACT

The present investigation represents the synthesis of new p-sulphonatocalix[8]arene-based silica resin, p-SC8SR (5) and its application for the enhanced removal of methylene blue (MB) dye from contaminated water. The new p-SC8SR (5) resin was characterized by FT-IR, SEM, and EDX spectroscopy. The adsorption of MB on p-SC8SR (5) was investigated systematically by evaluating the effects of adsorbent dosage, initial pH, contact time, dye concentration, and ionic strength. Excellent adsorption (94%) of MB on p-SC8SR (5) was achieved at pH 9.5, contact time 10 min by using 0.2 mol L^?1 ionic strength and 2 × 10^?5 M initial MB dye concentration. Kinetic behavior of MB dye adsorption process on the newly synthesized p-SC8SR (5) adsorbent follows the pseudo-second-order rate model (R² = 0.998 and 0.999 for 2 × 10^?5 M and 1 × 10^?4 M, respectively). Adsorption isotherms were fitted well by the Freundlich model with excellent value of coefficient of determination (R²) = 0.995 which demonstrated that the adsorption of MB follows multilayer mechanism. Wastewater samples contaminated with MB were used to assess efficiency of the p-SC8SR (5) adsorbent. Results indicated that newly synthesized p-SC8SR (5) was found to be efficient adsorbent. During the removal process, the role of different functional groups’ cyclic structure was scrutinized and found that the ionic property as well as π–π interaction of host molecules played imperative role in the extent of adsorption.     

Synthesis and Photocatalytic Activity of Anatase TiO2 Nanoparticles-coated Carbon Nanotubes

A simple and straightforward approach to prepare TiO₂-coated carbon nanotubes (CNTs) is presented. Anatase TiO₂ nanoparticles (NPs) with the average size ~8 nm were coated on CNTs from peroxo titanic acid (PTA) precursor even at low temperature of 100 °C. We demonstrate the effects of CNTs/TiO₂ molar ratio on the adsorption capability and photocatalytic efficiency under UV–visible irradiation. The samples showed not only good optical absorption in visible range, but also great adsorption capacity for methyl orange (MO) dye molecules. These properties facilitated the great enhancement of photocatalytic activity of TiO₂ NPs-coated CNTs photocatalysts. The TiO₂ NPs-coated CNTs exhibited 2.45 times higher photocatalytic activity for MO degradation than that of pure TiO₂.     

Assessment of adequate sodium hypochlorite concentration for pre‐oxidization of multi‐walled carbon nanotubes

BACKGROUND: Inadequate surface oxidization can potentially destroy the structure and chemical characteristics of the carbon nanotubes (CNTs) and result in loss of sorption capacity and weight. It is necessary to carefully oxidize CNTs using an adequate NaOCl concentration before using it as a sorbent. RESULTS: FE‐SEM images showed that the structure of CNTs oxidized with 7% NaOCl concentration was significantly destroyed and agglomerated as larger carbon particles instead of nanotubes. The surface acidities of CNTs oxidized with 3% and 5% NaOCl concentration were almost the same, with maximum values 6.20 and 6.25 mmol g^?1, respectively, in all studied cases. Conversely, increasing NaOCl concentration to 7% decreased the acidity from 6.25 to 5.0 mmol g^?1, indicating that 7% NaOCl concentration is not suitable for oxidization of CNTs. Assessing the factors (CNTs mass, contact time, pH, and ionic strength), that influence adsorption performance showed that CNTs oxidized with 5% NaOCl concentration performed better than those with 1%, 3% and 7% concentrations. CONCLUSION: Considering simultaneously the percentage recovery, adsorption performance and isotherms of CNTs oxidized by NaOCl solutions at four different concentrations, an optimum NaOCl concentration of 5% is suggested by this study. Copyright © 2010 Society of Chemical Industry