Removal of radiocobalt from aqueous solution by oxidized MWCNT

The study was undertaken to evaluate the feasibility of oxidized multiwalled carbon nanotube (oxidized MWCNT) for the removal of radiocobalt (⁶⁰Co) from aqueous solutions. The oxygen functional groups of oxidized MWCNT were characterized by FT-IR and XPS. Batch experiments were performed to study the sorption of cobalt as a function of contact time, solid contents, pH, ionic strength, foreign ions, and temperature. Two kinetic models viz. pseudo-first-order and pseudo-second-order were used to determine kinetic sorption parameters, and the kinetic sorption could be described more favorably by the pseudo-second-order model. The thermodynamic parameters (∆G°, ∆S°, ∆H°) calculated from the temperature-dependent sorption isotherms indicated that the sorption of Co(II) on oxidized MWCNT was an endothermic and spontaneous processes. The results suggest that oxidized MWCNT can be used efficiently in the treatment of industrial effluents containing radioactive and heavy metal ions.     

Removal of radiocobalt ions from aqueous solutions by natural halloysite nanotubes

In this study, natural halloysite nanotubes (HNTs) were applied to remove radiocobalt from wastewaters under various environmental parameters such as contact time, pH, ionic strength, foreign ions and temperature by using batch technique. The results indicated that the sorption of Co(II) on HNTs was dependent on ionic strength at pH < 8.5 and independent of ionic strength at pH > 8.5. Langmuir and Freundlich models were applied to simulate the sorption isotherms of Co(II) at three different temperatures of 293, 313 and 333 K. Langmuir model fitted the sorption isotherms of Co(II) on HNTs better than Freundlich model. The thermodynamic parameters (ΔG ⁰, ΔS ⁰ and ΔH ⁰) calculated from the temperature-dependent sorption isotherms manifested that the sorption of Co(II) on HNTs was an endothermic and spontaneous process. The sorption of Co(II) was dominated by outer-sphere surface complexation or ion exchange at low pH, whereas inner-sphere surface complexation or precipitation was the main sorption mechanism at high pH. The experimental results show that HNTs have good potentialities for cost-effective disposal of cobalt-bearing wastewaters.     

Removal of radiocobalt from aqueous solution by Mg2Al layered double hydroxide

The adsorption behavior of radiocobalt by Mg₂Al layered double hydroxide (Mg₂Al LDH) was studied as a function of contact time, pH, ionic strength, foreign ions, FA and temperature under ambient conditions. The results showed that the kinetic adsorption could be described by a pseudo-second order model very well. The adsorption of Co(II) on Mg₂Al LDH was strongly dependent on pH and ionic strength. The presence of FA enhanced the adsorption of Co(II) on Mg₂Al LDH at low pH, whereas reduced Co(II) adsorption at high pH. The Langmuir model fitted the adsorption isotherms of Co(II) better than the Freundlich and D–R model at three different temperatures of 303, 323 and 343 K. The thermodynamic parameters (ΔH°, ΔS° and ΔG°) calculated from the temperature dependent adsorption isotherms indicated that the adsorption process of Co(II) on Mg₂Al LDH was endothermic and spontaneous. The results show that Mg₂Al LDH is a promising material for the preconcentration and separation of pollutants from large volumes of aqueous solutions.     

苯胺在碳纳米管上的吸附特征

苯胺是一种重要的有机化工原料,能通过皮肤和呼吸道进入人体而引起中毒,还会严重污染环境。目前,国内外处理含苯胺废水的方法主要有氧化法、萃取法、生化法、吸附法等。本文使用碳纳米管进行液相吸附除去苯胺。     

Adsorption of roxarsone from aqueous solution by multi-walled carbon nanotubes

Molecularly imprinted particle for bisphenol A (BPA-MIP) was prepared using the surface molecular imprinting technique with a sol-gel process on the surface of silica nanoparticles. The dosages of diethylenetriaminepentaacetic acid (DTPA) as a functional monomer and teraethyl orthosilicate (TEOS) as a cross-linker were optimized, respectively. The prepared BPA-MIP was characterized by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), Fourier transform infrared spectrometer (FTIR), thermogravimetric analysis (TGA), and a standard Brunauer-Emett-Teller (BET) analysis. Moreover, the proper binding and selective recognition ability were also investigated by a single batch binding experiment. The equilibrium data fitted well to the pseudo-second-order kinetic and the Langmuir model for BPA binding onto BPA-MIP, respectively. The saturate binding capacity of BPA-MIP was found to be 30.26 μmol g(-1), which was three times higher than that of BPA non-molecular imprinted particle (BPA-NIP). The satisfactory results demonstrated that the obtained BPA-MIP showed an appreciable binding specificity toward BPA than similar structural compounds in water phase. The BPA-MIP could serve as an efficient selective material for determining or removing BPA from water environment.     

Removal of radiocobalt form aqueous solutions by inorganic exchangers

The sorption of radiocobalt from aqueous as well as organic solvents by natural and treated clays has been investigated. The effect of many factors, such as time, pH, carrier concentration, etc., were studied. In was found that the uptake is maximum in neutral, or slightly alkaline solutions. The rate of sorption depends on the velocity of shaking, which may indicate the operation of the film-diffusion mechanism, in addition to some contribution from particle-diffusion mechanism, but the dependence of the rate on shaking velocity could be attributed to an increase in the surface area of the clays. The conclusion is that natural clays are well suited for the removal of radioactive cobalt with slight, if any modification. These clays may be considered superior to synthetic exchangers for the removal of⁶⁰Co, if the availibility and prices of the former are taken into account.     

Removal of 2,4-dichlorophenol from aqueous solution by static-air-activated carbon fibers

Static-air-activated carbon fibers (ACFs) with lotus-root-like axially porous structure were used to adsorb 2,4-dichlorophenol (2,4-DCP) from aqueous solution. The adsorption isotherm was evaluated in the pH range 3.0-11.0. Results indicated that both Langmuir and Redlich-Peterson adsorption isotherms were appropriate for describing the adsorption characteristics of 2,4-DCP at various pH values and that lower pH values were favorable for adsorption. The adsorption of 2,4-DCP was controlled by the synergetic effects of pi-pi interaction and electrostatic attraction, and the former was dominant. Breakthrough curve results showed that the 2,4-DCP removal efficiency increased with an increase in the empty-bed contact time (EBCT). An EBCT of 0.660 min was sufficient for the adsorption of 2,4-DCP onto ACF, indicating a high adsorption rate. Desorption experiment results revealed that the ACF saturated with 2,4-DCP could be regenerated effectively by a 0.001 M NaOH solution.     

Adsorption of radiocobalt on lead dioxide from aqueous solution

Adsorption of cobalt on lead dioxide from aqueous solutions has been studied in relation to shaking time, amount of adsorbent, pH, and concentration of the adsorbate. The data fitted very well Langmuir, Freundlich, and Dubinin-Radushkevich isotherms and their corresponding constants were calculated. In another set of experiments the influence of different anions and cations on the adsorption of cobalt under the optimum experimental conditions have been determined. EDTA, tartrate, citrate, thiocyanate, oxalate, U(VI), Al(III), Fe(III), Cr(III), and Th(IV), drastically reduced adsorption of cobalt. Therefore these anions and cations should be removed before adsorption of cobalt on lead dioxide. Adsorption of other metal ions on the oxide were measured under identical conditions. TheK _D values indicate that cobalt can be separated successfully from Hg(II), Ag(I), Ta(V), In(III) and Tc(VII).     

Removal of Zn(II) from aqueous solution by natural halloysite nanotubes

Clay minerals have been widely used in wastewater disposal due to their strong sorption and complexation ability towards various environmental pollutants. In this study, the removal of Zn(II) from aqueous solution by natural halloysite nanotubes (HNTs) was studied as a function of various solution chemistry conditions such as contact time, pH, ionic strength, coexisting electrolyte ions and temperature under ambient conditions. The results indicated that the removal of Zn(II) by HNTs was strongly dependent on pH and ionic strength. Langmuir and Freundlich models were used to simulate the sorption isotherms of Zn(II) at three different temperatures of 293, 313 and 333 K. The thermodynamic parameters (ΔH ⁰, ΔS ⁰ and ΔG ⁰) calculated from the temperature dependent sorption isotherms indicated that the removal process of Zn(II) by HNTs was endothermic and spontaneous. At low pH, the removal of Zn(II) was dominated by outer-sphere surface complexation and/or cation exchange with Na⁺/H⁺ on HNT surfaces, whereas inner-sphere surface complexation was the main removal mechanism at high pH. From the experimental results, one can conclude that HNTs may have a good potentiality for the disposal of Zn(II)-bearing wastewaters.     

Removal of thorium from aqueous solution by ordered mesoporous carbon CMK-3

The ability of ordered mesoporous carbon CMK-3 has been explored for the removal and recovery of thorium from aqueous solutions. The textural properties of CMK-3 were characterized using small-angle X-ray diffraction and N₂ adsorption–desorption, and the BET specific surface area, pore volume and the pore size were 1143.7 m²/g, 1.10 cm³/g and 3.4 nm. The influences of different experimental parameters such as solution pH, initial concentration, contact time, ionic strength and temperature on adsorption were investigated. The CMK-3 showed the highest thorium sorption capacity at initial pH of 3.0 and contact time of 175 min. Adsorption kinetics was better described by the pseudo-second-order model and adsorption process could be well defined by the Langmuir isotherm. The thermodynamic parameters, △G°(298 K), △H° and △S° were determined to be -0.74 kJ·mol^?1, 9.17 kJ·mol^?1 and 33.24 J·mol^?1·K^?1, respectively, which demonstrated the sorption process of CMK-3 towards Th(IV) was feasible, spontaneous and endothermic in nature. The adsorbed CMK-3 could be effectively regenerated by 0.02 mol/L HCl solution for the removal and recovery of Th(IV).     

Amino-functionalized multi-walled carbon nanotubes for removal of cesium from aqueous solution

Journal of Radioanalytical and Nuclear Chemistry - Amino-functionalized multi-walled carbon nanotubes (MWCNTs) were synthesized by a simple, cost-effective method using 3-aminopropyltriethoxysilane...     

Diglycolamide functionalized multi-walled carbon nanotubes for removal of uranium from aqueous solution by adsorption

Diglycolamide functionalized multi-walled carbon nanotubes (DGA-MWCNTs) were synthesized by sequential chemical reactions for removal of uranium from aqueous solution. Characterization studies were carried out using FT-IR spectroscopy, XRD and SEM analysis. Adsorption of uranium from aqueous solution on this material was studied as a function of nitric acid concentration, adsorbent dose and initial uranium concentration. The uranium adsorption data on DGA-MWCNTs followed the Langmuir and Freundlich adsorption isotherms. The adsorption capacity of DGA-MWCNTs as well as adsorption isotherms and the effect of temperature on uranium ion adsorption were investigated. The standard enthalpy, entropy, and free energy of adsorption of the uranium with DGA-MWCNTs were calculated to be 6.09 kJ mole⁻¹, 0.106 kJ mole⁻¹ K⁻¹ and −25.51 kJ mole⁻¹ respectively at 298K. The results suggest that DGA-MWCNTs can be used as efficient adsorbent for uranium ion removal.     

Kinetics and thermodynamic study of aniline adsorption by multi-walled carbon nanotubes from aqueous solution

Multi-walled carbon nanotubes (MWCNTs) were used in the adsorptive removal of aniline, an organic pollutant, from an aqueous solution. It was found that carbon nanotubes with a higher specific surface area adsorbed and removed more aniline from an aqueous solution. The adsorption was dependent on factors, such as MWCNTs dosage, contact time, aniline concentration, solution pH and temperature. The adsorption study was analyzed kinetically, and the results revealed that the adsorption followed pseudo-second order kinetics with good correlation coefficients. In addition, it was found that the adsorption of aniline occurred in two consecutive steps, including the slow intra-particle diffusion of aniline molecules through the nanotubes. Various thermodynamic parameters, including the Gibbs free energy change (ΔG°), enthalpy change (ΔH°) and entropy change (ΔS°), were calculated. The results indicated that the spontaneity of the adsorption, exothermic nature of the adsorption and the decrease in the randomness reported as ΔG°, ΔH° and ΔS°, respectively, were all negative.     

Removal of uranium(VI) from aqueous solution by apricot shell activated carbon

Uranium is a toxic and radioactive heavy metal found in nuclear effluents and should be treated based on environmental considerations. The adsorption of uranyl cations (UO₂ ²⁺) by apricot shell activated carbon (ASAC) was investigated in a batch system. The effects of pH, contact time, temperature, adsorbent dosage on the adsorption kinetics and equilibrium adsorption isotherms of U(VI) were examined. The U(VI) uptake was fast within the first 60 min and reached an equilibrium state at 120 min. The adsorption process was highly pH dependent and the maximum adsorption was obtained at an initial solution pH of 6.0. Temperature over the range 25–45 °C had little effect on the U(VI) adsorption. The U(VI) removal efficiency increased concurrently with increasing ASAC dosage, whereas the U(VI) adsorption capacity decreased with increasing ASAC dosage. The adsorption process followed both Langmuir and Freundlich isotherms. On the basis of Langmuir model, the maximum adsorption capacity was found to be 59.17 mg U(VI)/g adsorbent. The adsorption kinetics can be very well defined by the pseudo-first-order rate model. The present results suggest that ASAC could be used as an adsorbent for an efficient removal of U(VI) from aqueous solution.     

Removal,recovery and enrichment of metals from aqueous solutions using carbon nanotubes

Environmental pollution caused by toxic metals (heavy metals, radioactive metals, etc.) is one of the major global issues, thus removal of toxic metals from contaminated water seems to be particularly important. On the other hand, the recovery and enrichment of metals, especially noble metals, from waste water is also crucial. To address these issues, nanotechnology plays an essential role in environmental monitoring and pollution control. To remove metals from contaminated water, or enrich metals from waste water, carbon nanotubes (CNTs) and their composites have attracted great attention due to their excellent adsorption performance. The removal efficiency for metal ions by CNTs was observed aroud 10–80 %, which could be improved to approach 100 % by selectively functionalizing CNTs with organic ligands. Herein, we review the applications of CNTs in treatment of toxic metal-containing wastewater for environmental monitoring and metals recovery. Due to their higher sensitivity and selectivity towards the enrichment of metals or detection of toxic metal pollution of the environment, and the latest research progress of using CNT composites for metal treatment is also discussed.     

Removal of methyl violet from aqueous solution by perlite

The use of perlite for the removal of methyl violet from aqueous solutions at different concentration, pH, and temperature has been investigated. Adsorption equilibrium is reached within 1 h. The capacity of perlite samples for the adsorption of methyl violet was found to increase with increasing pH and temperature and decrease with expansion and increasing acid-activation. The adsorption isotherms are described by means of the Langmuir and Freundlich isotherms. The adsorption isotherm was measured experimentally at different conditions and the experimental data were correlated reasonably well by the adsorption isotherm of Langmuir. The order of heat of adsorption corresponds to a physical reaction. It is concluded that the methyl violet is physically adsorbed onto the perlite. The removal efficiency (P) and dimensionless separation factor (R) have shown that perlite can be used for removal of methyl violet from aqueous solutions, but unexpanded perlite is more effective.     

Adsorptive removal of thorium from aqueous solution using diglycolamide functionalized multi-walled carbon nanotubes

Multi-walled carbon nanotubes (MWCNTs) were functionalized with diglycolamide (DGA) through chemical covalent route. The adsorption behavior of the DGA-functionalized-MWCNTs (DGA-MWCNTs) towards thorium from aqueous solution was studied under varying operating conditions of pH, concentration of thorium, DGA-MWCNTs dosages, contact time, and temperature. The effective range of pH for the removal of Th(IV) is 3.0–4.0. Kinetic data followed a pseudo-second-order model. The equilibrium data were correlated with the Langmuir, Freundlich, Dubinin-Radushkevich and Temkin models. The equilibrium data are best fitted with Langmuir model. The equilibrium Th(IV) sorption capacity was estimated to be 10.58 mg g^?1 at 298 K. The standard enthalpy, entropy, and free energy of adsorption of the thorium with DGA-MWCNTs were calculated to be 8.952 kJ mol^?1, 0.093 kJ mol^?1 K^?1 and -18.521 kJ mol^?1 respectively at 298 K. The determined value of sticking probability (0.072) and observed kinetic and isotherm models reveal the chemical adsorption of thorium on DGA-MWCNTs.     

Dispergation and modification of multi-walled carbon nanotubes in aqueous solution

Multi-walled carbon nanotubes (MWCNTs) are widely applied in development of composite materials. However, their properties are directly influenced by the degree of uniformity of dispersion of MWCNTs in the material’s matrix. In this paper, the dispersing of raw MWCNTs (R-MWCNTs) and decorated MWCNTs (D-MWCNTs) was studied in aqueous solution. The D-MWCNTs were obtained by chemical modification method by treatment of initial MWCNTs with the mixture of concentrated nitric and sulfuric acids (3: 1 vol/vol). To achieve a good dispersion of the MWCNTs, a method utilizing ultrasonic processing and surfactant (polyvinylpyrrolidone, PVP) was employed. MWCNTs were characterized by Fourier transform infrared spectroscopy (FT–IR) and X-ray diffraction (XRD). The prepared MWCNTs suspensions were investigated by UV spectroscopy, zeta potential measurements, surface tension and transmission electron microscopy (TEM). The D-MWCNTs have better dispersibility in aqueous solution; this attributed to the functional groups formed on their surface during chemical modification. The PVP surfactant in a certain concentration of 0.6 g/L has the maximum dispersing effect on MWCNTs in aqueous solution, the optimum concentration ratio of PVP and MWCNTs was 3: 1.     

Purification and dispersibility of multi-walled carbon nanotubes in aqueous solution

In this paper, the pristine multi-walled carbon nanotubes (P-MWCNTs) were purified either by the high temperature treatment (HT-MWCNTs) or by concentrated acid treatment (CA-MWCNTs). The HT-MWCNTs were prepared by heating at 500°C, while the CA-MWCNTs were treated by the mixture of concentrated nitric and sulfuric acids taken in a volume ratio of 3: 1. Ultrasonic processing and surfactants were utilized to achieve homogenous MWCNTs suspensions. The HT-MWCNTs and CA-MWCNTs were characterized by thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FT-IR). Among these three MWCNTs, the prepared homogeneously dispersed MWCNTs suspensions were characterized by UV–Vis absorbency and transmission electron microscopy (TEM). Finally, the dispersion mechanism was discussed. The results showed that both high temperature treatment and concentrated acid treatment can be used for purification of the P-MWCNTs, removing the amorphous carbon and other impurities. In these suspensions, the purified MWCNTs showed a better dispersibility in aqueous solution. The high temperature treatment was a kind of physical purification treatment method and it just burned the amorphous carbon away and strengthened the structure of MWCNTs, while the concentrated acid treatment was a chemical purification treatment method and this chemical treatment method grafted more effective groups to improve the dispersibility of MWCNTs.