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Optimizing the physical-chemical properties of carbon nanotubes (CNT) and graphene nanoplatelets (GNP) on Cu(II) adsorption

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... Several methods, such as, chemical precipitation, ion exchange, adsorption, membrane filtration, coagulation/flocculation, flotation and electrochemical treatment are utilized to remove cobalt (and other heavy metal ions) from aqueous solutions [6] [7] [8] [9]. Among these, adsorption has gained attention due to its inexpensiveness, universal nature and ease of operation [10]. ...
... So, technologies for cobalt removal from aqueous media are essential to avoid the negative impacts, and also, to recover this metal3456. Several methods, such as, chemical precipitation, ion exchange, adsorption, membrane filtration, coagulation/flocculation, flotation and electrochemical treatment are utilized to remove cobalt (and other heavy metal ions) from aqueous solutions6789. Among these, adsorption has gained attention due to its inexpensiveness, universal nature and ease of operation [10]. ...
Article
Ultrasound-assisted (UA) and supercritical CO2 technologies (SCO2) were used to modify the chitin surface and, improve its adsorption characteristics regarding to cobalt. Chitin, before and after the treatments, was characterized by N2 adsorption isotherms (BET), infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and scanning electron microscopy (SEM). Unmodified and surface modified chitins were used as adsorbents to remove cobalt from aqueous solutions. The adsorption study was performed by equilibrium isotherms and kinetic curves. The chitin particle characteristics, such as, surface area, pore volume and porosity were improved by the UA and SCO2 treatments. The crystallinity index decreased after the UA and SCO2 treatments, and also, intense surface modifications were observed. Langmuir and Freundlich models were adequate to represent the adsorption equilibrium. The maximum adsorption capacities were 50.03, 83.94 and 63.08 mg g−1 for unmodified chitin, UA surface modified chitin and SCO2 surface modified chitin. The adsorption kinetic curves were well represented by the pseudo-second order model. UA and SCO2 technologies are alternatives to modify the chitin surface and improve its adsorption characteristics.
... Carbon-based materials (carbon nanotube (CNT), graphite, and graphene oxide (GO)) have attracted attention due to their antimicrobial properties and superior adsorption abilities [1,17]. Rosenzweig et al. reported the graphene nanoplates (GNP) showed poor adsorptive capacity associated to stacked-nanoplatelets, but good colloidal stability due to high functionalized surface [18]. In the literature, there are many studies in which composite adsorbents, which are prepared together with carbon-based materials and alginate, are used for heavy metal removal [19,20]. ...
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Depending on the increase in the world population, the need for consumption and industrial resources is increasing day by day. In the wastewater caused by industrial production, a serious amount of heavy metals and water pollution caused by inorganic dyestuffs occur. In this study, graphene nanoplate/natural zeolite/sodium alginate bio-composite adsorbent was prepared and copper removal from wastewater by adsorption method was investigated. The characterization of the adsorbent was carried out by Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction and Brunauer-Emmett-Teller. In addition to batch adsorption tests, isotherm, kinetic and thermodynamic studies, experimental optimization was carried out with experimental parameters determined by the surface response methodology. Four experimental parameters (adsorbent dosage, metal concentration, solution pH, and contact time) were evaluated in a versatile way to determine the efficiency of heavy metal adsorption. The highest copper removal was obtained as 92.9% and 91.4%, respectively, in the experimental and model study at the adsorbent dosage of 0.5 g, the solution pH of 4.5, and the copper concentration of 20 ppm. The parametric results was meet with the optimization results with an R 2 value of 0.9834. The three most commonly used adsorption isotherms at 25 °C were calculated. The high R 2 value was found to be 0.9834 for the Langmuir isotherm model. It was determined that the adsorption kinetics matched the pseudo-second-order kinetics.
... Adsorption is a well-known separation process and recognized as an effective, efficient and economic method for water decontamination than chemical processes such as precipitation or ionexchange. In recent years, numerous adsorbents have been investigated including polymer-functionalized silica [3], carbon nanotube [4][5][6], mesoporous silica [7], chelating resin [8][9][10], natural inorganic minerals for adsorption of Cu 2? ions from wastewater [11,12], chitosan/silica hybrid microspheres [13,14]. Much attention has been paid to composites with three-dimensional network structure, and having functional groups such as carboxylic acid [15,16], amine [17], hydroxyl [18], and sulfonic acid [19] groups for the removal of Cu 2? ions from aqueous solutions. ...
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To decrease exhaust gas, waste solution, and solid waste accompanied by the synthetic adsorbent procedure and fast separation the adsorbent from large volumes of wastewater. In this paper, large scale SGAP with three-dimensional interpenetrating network structure were prepared in two steps: (1) soluble glass/poly(acryamide) gels were synthesized via free radical polymerization method; (2) soluble glass/poly(acryamide) gels with three-dimensional interpenetrating network structure were foamed at 190 °C for 30 min. The obtained SGAP were used to investigate adsorption of Cu2+ from aqueous solutions. The research results display that the obtained composite has high adsorption capacity at optimum pH = 5. The maximum adsorption capacity was 406.2 mg g−1 within 420 min at 45 °C. The kinetic datum were analyzed using the pseudo first-order and pseudo second-order models and found to fit very well the pseudo second-order kinetic model. Datum of equilibrium experiments were fitted well to Langmuir isotherm. Thermodynamic parameters showed that the adsorption process was spontaneous, endothermic. Energy-dispersive X-ray analyses and Fourier transform infrared spectrophotometry demonstrate the adsorption of Cu2+ onto SGAP.
... High aspect ratio of CNT makes it a possible candidate for water purification. In recent years, great efforts have been made to remove various organic pollutants and metal ions in wastewater by CNT [16,17]. To further improve their adsorption performance, various CNT composites have been synthesized and widely used to remove dye pollutions from wastewater. ...
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Functionalized carbon nanotube/mixed metal oxides (CNT/MMO) nanocomposites composed of CNT and Mg(Al)O nanoparticles have been synthesized by pyrolysis of a terephthalic intercalated layered double hydroxide (LDH) precursor. The chemical composition and morphology of this nanocomposites were investigated by XRD, SEM, and TEM measurements. FTIR characterization shows that the surface of the prepared CNT is functionalized with abundant oxygen-containing groups without further modification. As a novel adsorbent, the as-prepared functionalized CNT/Mg(Al)O nanocomposites exhibit very high performance in the removal of Congo red (CR) dye from aqueous solutions. The initial pH of dye solution and dosage of adsorbent have an important influence on the adsorption property of the CNT/Mg(Al)O nanocomposites. The adsorption isotherm obeys the Langmuir model, with the maximum adsorption capacity greatly enhanced to 1250 mg/g, exhibiting potential applications in wastewater treatment. A adsorption mechanism that involves (i) strong interactions between the functional groups on the surface of CNT and CR molecules and (ii) electrostatic interactions between positively charged reconstructed LDH layer and negatively charged CR molecules, was proposed.
... Each of these methods may have undesirable effects, such as time/energy consumption, excessive loss of CNTs and morphological damage (Hou et al., 2008). Although there are several studies in which MWCNTs, prior to be used as adsorbent, were treated by the aforementioned methods (Lu et al., 2008; Rosenzweig et al., 2014; Yao et al., 2010), to the best of our knowledge, using a multistep procedure consisting of irradiation in a modified domestic microwave followed by sonication in dilute acid has not been studied yet. Therefore, in this study, this combined pretreatment method is applied to achieve the desired functionalization of MWCNTs and minimize some adverse effects of the other intense methods. ...
Article
The main aim of present study was to enhance the adsorption capacity of Reactive Blue 19 (RB19) onto multi-walled carbon nanotubes (MWCNTs), pretreated in a multistep functionalization process. The functionalization procedure consisted of microwave irradiation followed by sonication in dilute H2SO4. The properties of MWCNTs were investigated by X-ray diffraction, scanning electron microscopy, N2 adsorption isotherms (Brunauer-Emmett-Teller surface area analysis), Raman spectroscopy and Fourier transform infrared spectroscopy. The effective addition of desired functional groups resulted in a considerable increase of dye removal efficiency and adsorption capacity. For pristine and functionalized MWCNTs, the maximum adsorption capacities were found to be 53.33 and 211.02 mg/g, respectively. In addition to the main aim of this research, a statistical/mathematical approach - response surface methodology - was utilized to simulate and determine the optimum conditions of RB19 removal by functionalized MWCNTs using three selected parameters (adsorbent dose, initial dye concentration and pH). High R2-value (97.75%) and a good agreement between predicted R2-value (89.11%) and adjusted R2-value (95.72%) demonstrated an acceptable proportion of the experimental and predicted results. For maximum RB19 removal efficiency, eight optimum scenarios were also obtained and validated by further experiments.
... They act by the removal of HOCs (chlorinated and brominated), reduction of nitrogen-containing compounds (including nitrate, azo dye, and nitrobenzene), adsorption, and coprecipitation of heavy metals (Fang et al. 2010;Giasuddin et al. 2007;Singh et al. 2012). Copper is an essential nutrient at a trace level for plants and animals, but at a higher concentration it would be toxic (Rosenzweig et al. 2014). Among different categories of NZVMs, NZVI is of special interest due to its relatively high reactivity, low costs, and low environmental toxicity, which shows a great potential for environmental remediation of contaminants (Dorjee et al. 2014;Gunawardana et al. 2011). ...
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Engineered nanoscale zero-valent metals (NZVMs) representing the forefront of technologies have been considered as promising materials for environmental remediation and antimicrobial effect, due to their high reducibility and strong adsorption capability. This review is focused on the methodology for synthesis of bare NZVMs, supported NZVMs, modified NZVMs, and bimetallic systems with both traditional and green methods. Recent studies have demonstrated that self-assembly methods can play an important role for obtaining ordered, controllable, and tunable NZVMs. In addition to common characterization methods, the state-of-the-art methods have been developed to obtain the properties of NZVMs (e.g., granularity, size distribution, specific surface area, shape, crystal form, and chemical bond) with the resolution down to subnanometer scale. These methods include spherical aberration corrected scanning transmission electron microscopy (Cs-corrected STEM), electron energy-loss spectroscopy (EELS), and near edge X-ray absorption fine structure (NEXAFS). A growing body of experimental data has proven that nanoscale zero-valent iron (NZVI) is highly effective and versatile. This article discusses the applications of NZVMs to treatment of heavy metals, halogenated organic compounds, polycyclic aromatic hydrocarbons, nutrients, radioelements, and microorganisms, using both ex situ and in situ methods. Furthermore, this paper briefly describes the ecotoxicological effects for NZVMs and the research prospects related to their synthesis, modification, characterization, and applications.
... The physical properties of the MWCNTS are listed in table 1 [23][24][25]. The purity of the ENMs and the concentration of the trace inorganics were discussed in our previous study [26,27]. The physical properties of the pollutants selected for this study are listed in table 2. Laser doppler velocimetry in conjunction with phase analysis light scattering (Malvern Zetasizer Nano, Malvern Instruments Ltd) was used to measure the zeta potential of TiO 2 and MWCNTs at selected pH values. ...
Article
As nanomaterials become an increasing part of everyday consumer products, it is imperative to monitor their potential release during production, use and disposal, and to assess their impact on the health of humans and the ecosystem. This necessitates research to better understand how the properties of engineered nanomaterials (ENMs) lead to their accumulation and redistribution in the environment, and to assess whether they could become novel pollutants or if they can affect the mobility and bioavailability of other toxins. This study focuses on understanding the influence of nanostructured-TiO2 and the interaction of multi-walled carbon nanotubes with organic pollutants in water. We studied the adsorption and water phase dispersion of model pollutants with relatively small water solubility (i.e., two- and three-ring polyaromatic hydrocarbons and insecticides) with respect to ENMs. The sorption of pollutants was measured based on water phase analysis, and by separating suspended particles from the water phase and analyzing dried samples using integrated thermal-chromatographic-mass spectroscopic (TGA/GC/MS) techniques. Solid phase analysis using a combination of TGA/GC/MS is a novel technique that can provide real-time quantitative analysis and which helps to understand the interaction of hydrophobic organic pollutants and ENMs. The adsorption of these contaminants to nanomaterials increased the concentration of the contaminants in the aqueous phase as compared to the 'real' partitioning due to the octanol-water partitioning. The study showed that ENMs can significantly influence the adsorption and dispersion of hydrophobic/low water soluble contaminants. The type of ENM, the exposure to light, and the water pH have a significant influence on the partitioning of pollutants.
... As one of the carbon-based nanomaterials with extraordinary properties, graphene has attracted tremendously more attention by researchers since its isolated characterization in 2004 by Novoselov. 1 Owing to its chemical bonding characteristics as a carbon allotrope similar to its conjugates such as carbon nanotubes, it has excellent mechanical, thermal, 2 and electrical properties. 1 For instance, it is branded as the strongest material 3 with 1.06 TPa Young's modulus 4 and 130 6 10 GPa tensile strength. 5 In addition to many other studies focusing on the chemical, physical, and electrical properties of graphene, [6][7][8][9][10][11][12][13][14] its hybrid applications in combination with other materials are also investigated extensively. Majority of those studies are related to graphene nanocomposites with polymeric matrix constituent. ...
Article
In this paper, mechanical characteristics of the aluminum layer coated with graphene are investigated by performing numerical tensile experiments through classical molecular dynamics simulations. Based on the results of the simulations, it is shown that coating with graphene enhances the Young's modulus of aluminum by 88% while changing the tensile behavior of aluminum with hardening-softening mechanisms and significantly increased toughness. Furthermore, the effect of loading rate is examined and a transformation to an amorphous phase is observed in the coated aluminum structure as the loading rate is increased. Even though the dominant component of the coated hybrid structure is the aluminum core in the elastic region, the graphene layer shows its effects majorly in the plastic region by a 60% increase in the ultimate tensile strength. High loading rates at room temperature cause the structure transforms to an amorphous phase, as expected. Thus, effects of loading rate and temperature on amorphization are investigated by performing the same simulations at different strain rates and temperatures (i.e., 0, 300, and 600 K).
... XPS can thus provide a measure of the number of defects through the O/C ratio, quantify the different types of carbon functionalities present, indicate the formation of chemical bonds, and evaluate the physisorption of molecules [11,12]. The importance of this quantification is crucial in order to correlate chemical properties of GRMs with their performance, for example, in permeability [5], water purification [13] or bio-sensing [14]. ...
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Article
A simple, fast and general protocol for quantitative analysis of X-ray photoelectron spectroscopy (XPS) data provides accurate estimations of chemical species in graphene and related materials (GRMs). XPS data are commonly used to estimate the quality of and defects in graphene and graphene oxide (GO), by comparing carbon and oxygen 1s XPS peaks, obtaining an O/C ratio. This approach, however, cannot be used in the presence of extraneous oxygen contamination. The protocol, based on quantitative line-shape analysis of C 1s signals, uses asymmetric pseudo-Voigt line-shapes (APV), in contrast to Gaussian-based approaches conventionally used in fitting XPS spectra, thus allowing better accuracy in quantifying C 1s contributions from graphitic carbon (sp2), defects (sp3 carbon), carbons bonded to hydroxyl and epoxy groups, and from carbonyl and carboxyl groups. The APV protocol was evaluated on GRMs with O/C ratios ranging from 0.02 to 0.30 with film thicknesses from monolayers to bulk-like (>30 nm) layers and also applied to previously published data, showing better results compared to those from conventional XPS fitting protocols. Based uniquely on C 1s data, the APV protocol can quantify O/C ratio and the presence of specific functional groups in GRMs even on SiOx, substrates, or in samples containing water.
... Compared to traditional materials, the utilisation of nanoparticles with an extensive surface area and unique structure happens to be most efficacious in water treatment. Among a few kinds of nanoparticles examined as adsorbents; carbonaceous nano-fillers, for example, graphite, diamond, fullerenes and carbon nanotubes (CNTs) have captured attention because of their tunable pore size, large surface area and magnificent combination with discrete materials [2][3][4][5][6]. The evolution of potential composites consolidating carbon nanotubes is an exciting concept. ...
Article
The distinctive and tuneable physical, chemical and configurational properties of carbon nanotubes (CNTs), has prompted their combination with metal oxides to contrive carbon composites showing entrancing adsorption property with incredible potential in water treatment. MWCNT/Alumina (RMAC) nodules with effective adsorption capacity were synthesized following aqueous sol-gel route. Batch sorption experiments examined the efficiency of removal of dyes and heavy metal ions from an aqueous solution on RMAC nodules. The factors affecting adsorption were studied for adsorption of methylene blue dye (MB) and hexavalent chromium by altering the MWCNT concentration from 1 wt.% to 5 wt.%. The adsorption experiment demonstrated an adsorption capacity of 187.5 and 597 mg g ⁻¹ at 25 °C for MB and Cr (VI) respectively. Various characterization techniques such as XRD, BET, TEM, Raman, FTIR, TPD and CHN were employed to study the initial development of the material. Multiple adsorption interaction mechanisms (electrostatic interactions, hydrogen bonding, π−π electron-donor-acceptor interactions) may be credited for the remarkable adsorption capacity of these nodules. Results of this work are of great significance for environmental applications of Alumina/MWCNT composite as a promising adsorbent nanomaterial for organic pollutants from aqueous solutions. Apart from high sorption ability, these nodules offer ease of separation with splendid regeneration ability.
... Carbon nanotube (CNT), a significant material, has gained considerable attention in water purification, because of its great specific surface area, small size, large aspect ratio, fast water transport, as well as ease of functionalization (Dasgupta et al., 2017;Ersan et al., 2017). Over the years, great endeavors have been made to remove various organic and inorganic pollutants from water/ wastewater by virtue of CNT (Rosenzweig et al., 2014;Yu et al., 2011). Nevertheless, the adsorption saturation is still the pivotal factor that restricts the further application of adsorption in water/ wastewater treatment, without exception for CNT (Fiyadh et al., 2019;Zhang et al., 2015). ...
... However, there is the scarce literature on the optimization of process parameters for MLG synthesis by CVD using Co-Ni/Al 2 O 3 . The aim of the present study is to analyze the effects of three growth variables using the response surface methodology (RSM) optimization technique, which uses a suitable polynomial equation for the experimental data [25,26]. The second-ordered central composite design (CCD) provides an essential and precise statistical model to evaluate the significance of these variables and their interaction effect in the synthesis of MLG by CVD. ...
Article
This study investigates the optimization of multilayer graphene (MLG) growth on Co–Ni/Al2O3 substrate. The MLG synthesized by chemical vapor deposition technique (CVD) was characterized using various instrument techniques. The surface area and pore volume of the MLG were estimated as ~ 642 m2/g and ~ 2.7 cm3/g, respectively. The Raman spectrometric analysis showed evidence of MLG. The effects of parameters such as temperature, Co–Ni composition and ethanol flow rate were investigated using response surface methodology (RSM) and central composite design. The maximum MLG yield of 77% was attained at optimum conditions of 800 °C, Co–Ni composition of 0.3/0.7 and ethanol flow rate of 11 ml/min. The analysis of variance (ANOVA) results showed that the RSM quadratic model is significant with a p value < 0.0001. The coefficient of determination (R2) values of 0.9694 revealed the reliability of the RSM model. The potential of CVD as a technique to synthesize MLG growth of a highly ordered crystallinity structure has been demonstrated in this study. The resulting MLG films are promising materials for the use in improving graphene-based electronics, sensing and energy devices.
... The desorption hysteresis could be explained by two hypotheses: one was caused by the capillary concentration of molecules in the mesoporous and macroporous materials; the other was caused by the deformation of the pore structure [64,65]. Some researchers believed that it was caused by the rearrangement or agglomeration of the adsorbents [66]. From Figure 9a-c, there were different degrees of desorption hysteresis phenomena on the three BP-based materials. ...
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Dye effluent has attracted considerable attention from worldwide researchers due to its harm and toxicity in recent years; as a result, the treatment for dye has become one of the focuses in the environmental field. Adsorption has been widely applied in water treatment owing to its various advantages. However, the adsorption behaviors of the new materials, such as the 2D black phosphorus (BP), for pollution were urgently revealed and improved. In this work, BP, black phosphorene (BPR), and sulfonated BPR (BPRS) were prepared by the vapor phase deposition method, liquid-phase exfoliating method, and modification with sulfonation, respectively. The three BP-based materials were characterized and used as adsorbents for the removal of methylene blue (MB) in water. The results showed that the specific surface areas (SSAs) of BP, BPR, and BPRS were only 6.78, 6.92, and 7.72 m2·g−1, respectively. However, the maximum adsorption capacities of BP, BPR, and BPRS for MB could reach up to 84.03, 91.74, and 140.85 mg·g−1, which were higher than other reported materials with large SSAs such as graphene (GP), nanosheet/magnetite, and reduced graphene oxide (rGO). In the process of BP adsorbing MB, wrinkles were generated, and the wrinkles would further induce adsorption. BPR had fewer layers (3–5), more wrinkles, and stronger adsorption capacity (91.74 mg·g−1). The interactions between the BP-based materials and MB might cause the BP-based materials to deform, i.e., to form wrinkles, thereby creating new adsorption sites between layers, and then further inducing adsorption. Although the wrinkles had a certain promotion effect, the adsorption capacity was limited, so the sulfonic acid functional group was introduced to modify BPR to increase its adsorption sites and promote the adsorption effect. These findings could provide a new viewpoint and insight on the adsorption behavior and potential application of the BP-based materials.
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1,4-Dihydroxyanthraquinone (1,4-DHAQ, a fluorophore) doped carbon nanotubes@cellulose (1,4-DHAQ-doped CNTs@CL) nanofibrous membranes have been prepared via electrospining and subsequent deacetylating in this work. It has been successfully applied for highly sensitive detection of Cu2+ in aqueous solution. The surface area per unit mass (S/M) ratio of the nanofibrous membrane was enhanced by incorporating the CNTs into cellulose. Moreover, the excellent metal ions sorption capability of CNTs improved the sensitivity of the sensing materials. Both of the two points mentioned above significantly improved the lower detection limit of fluorescence sensing as expected. As the resultant byproduct of Cu2+-contaminated 1,4-DHAQ-doped CNTs@CL nanofibrous membranes showing recovered fluorescence by extra addition of Cr3+ in solution, 1,4-DHAQ and Cu2+ co-doped CNTs@CL (denoted as 1,4-DHAQ/Cu2+ co-doped CNTs@CL) mircoporous nanofibrous membranes have been further fabricated for fluorescence enhancement detection of Cr3+ in aqueous solution. It was found that the fluorescence intensity of the 1,4-DHAQ-doped CNTs@CL nanofibrous membranes linearly decreased with Cu2+ concentration in the range of 0―2.2×10―8 M, while that of the 1,4-DHAQ/Cu2+ co-doped CNTs@CL nanofibrous membranes linearly increased with Cr3+ concentration in the range of 0―2.4×10―8 M. The excellent fluorescence sensing property of the 1,4-DHAQ-doped CNTs@CL and 1,4-DHAQ/Cu2+ co-doped CNTs@CL nanofibrous membranes for Cu2+ and Cr3+ were further demonstrated by using polluted lake waters, proving their potential applications in environmental monitoring areas. The design concept mentioned in this work might also open a door to the design of other effective fluorescence probes with high sensitivity.
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Cellulose beads loaded with graphene nanoplatelets (GNP) were prepared by a physical gelation method, which was feasible under mild conditions. The phases spontaneously separate when the cellulosic solution is dropped into an acid solution, maintaining semi-spherical shapes with diameter between 3.4 and 3.9 mm, which is desirable for continuous-flow systems. Beads were tested for the removal of Congo red dye using a differential column batch reactor. Langmuir isotherm described the adsorption equilibrium, with maximum adsorption capacities of 98.1 and 139.6 mg/g for cellulose and cellulose-GNP beads. GNP increased the number of binding sites in the adsorbent. Removal efficiencies were higher than 90% within a broad range of initial concentration and sorbent loading. Static batch experiments evidenced slow kinetics for both sorbents, reaching equilibrium after 400 min. Hence, mass transfer was enhanced using a differential column batch reactor. The mass transfer coefficient, kL increased from 3.16 ×10⁻⁴ to 6.94 ×10⁻⁴ L/mg min, reaching equilibrium in half of the static adsorption time. External mass transfer resistance was minimized as turbulent flow is developed around the sorbent particles, allowing to obtain adsorption efficiencies close to 100% in a reasonably low time of 100 min. GNP promoted faster kinetics, as kL was 7.58 ×10⁻⁴ L/mg min. A model was developed to describe the adsorption dynamics based on the equilibrium. Although desorption was not favorable, cellulose-GNP beads’ direct disposal is attractive due to the sorbent’s hydrogel-like nature. A future work perspective is to evaluate these adsorbents under continuous fixed-bed operation.
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In this study, the reduced graphene oxide was modified by grafting thymine on its surface. The resultant reduced graphene oxide-thymine composite (rGO-Thy) exhibits a higher Hg(II) adsorption capacity and selectivity compared with rGO as the functional group of thymine shows a strong affinity toward Hg(II) and form thymine-Hg(II)-thymine complex. The relative selectivity coefficients of rGO-Thy for Hg(II)/Pb(II), Hg (II)/Ni(II), Hg (II)/Co(II), Hg (II)/Cu(II) and Hg(II)/Cd(II) are 21.72, 7.08, 5.37, 4.37 and 10.51, respectively. This is mainly attributed to thymine specific binding with Hg(II). In the addition, the adsorption capacity of rGO-Thy for Hg(II) is almost two times higher than reduced graphene oxide (rGO). Kinetics studies indicate that the adsorption process fits well with the pseudo-second-order model, and the adsorption kinetic constant is 0.02 g•mg−1•min−1. Moreover, the practical application of rGO-Thy achieves almost 100% removal efficiency and the treatment volumes of actual industrial wastewater using a fixed bed column are as high as 390 BV for Hg(II), which indicate that rGO-Thy has great potential in advanced wastewater treatment.
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The chemical functionalization of carbon nanotubes (CNTs) using sodium persulfate (SPS) oxidation was designed to improve their dispersion stability in water. The test results indicated that base activated SPS oxidation of CNTs (BSPS/CNTs) adds a significant amount of oxygen functional groups to the surface of CNTs. The BSPS/CNTs dispersion is dependent on a solution within the pH range of 5-12. Experimental results obtained by Fourier Transform Infrared Spectroscopy and X-ray Photoelectron Spectroscopy demonstrated that CNTs were successfully modified and the carboxylic functional groups (e.g., –COO-Na+ or –COO-H+) were created. The BSPS/CNTs, which carry negative charges, enhance the dispersion characteristics of CNTs. The BSPS/CNTs adsorption capacities of inorganic ions (e.g., copper ion) and organic compounds (e.g., benzene) were higher than those obtained by raw CNTs mainly due to enhanced CNTs dispersion. Furthermore, Langmuir and Freundlich adsorption models were applied to examine both raw CNTs and BSPS/CNTs adsorption behaviors. Copper and benzene sorption onto BSPS/CNTs fit the Freundlich isotherm model well, while raw CNTs adsorption did not fit any model. The findings of this study are of great significance for the base activated persulfate oxidation process, indicating that the functionalization of CNTs enhances CNTs dispersivity in water.
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Fe3O4/carboxylate-rich carbon composite (Fe3O4/CRC) have been synthesized via a facile one-step low temperature carbonization method from simple precursors, the single iron source FeSO4.7H2O and sodium gluconate. Carboxylate groups of sodium gluconate can coordinate with Fe(Ⅱ) and form the ferricarboxylate complexes. During the low temperature carbonization process, Fe3O4 can be obtained through the thermal decomposition of ferricarboxylate complexes. In addition, sodium gluconate can serve as the source of carboxylate functional group of Fe3O4/CRC. Due to the lower temperature of carbonization process (300 °C), abundant carboxylate group can be remained in amorphous carbon and serve as the metal-binding functional group to enhance the adsorption affinity between Fe3O4/CRC and Cu (Ⅱ). Fe3O4/CRC was found to be an ideal adsorbent for Cu (Ⅱ) removal with a higher adsorption capacity. We investigated how the contact time, temperature, pH, and initial concentration of Cu (Ⅱ) can affect the adsorption of Cu (Ⅱ) on Fe3O4/CRC. In addition, we also did some theoretical simulation about the Cu (Ⅱ) adsorption model. Among the various kinetics models, the pseudo-second-order is the most suitable kinetics model for adsorption of Cu (Ⅱ) onto Fe3O4/CRC. Adsorption of the heavy metals to Fe3O4/CRC reached equilibrium in less than 5 min, and agreed well to the Langmuir adsorption model with maximum adsorption capacities 66.67 mg g-1 at 25 °C. The adsorption-desorption studies indicated that Fe3O4/CRC possesses good stability and good reusability.
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Graphene oxide (GO) has an attracting and ever-growing interest in various research fields for its fascinating nanostructures. In this study, bacterial cellulose (BC) was used as a matrix to synthesize GO-based materials by a mechanical mixing method. The modification of GO with PEI significantly improved the bonding force between GO nanofillers and BC matrix. The morphology of the nanocomposites had a significant effect on the mechanical properties, hydrophilic properties as well as the antibacterial activity. After the modification, the GO-PEI/BC showed a strong antimicrobial effect on Saccharomyces cerevisiae due to the effective direct contacts between the nanofillers of the composites and the cell surfaces. This study demonstrates that the morphology of the nanocomposites has a great effect on physiochemical properties and the interactions between the microorganism and the nanocomposites.
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Take full advantage of the high adsorption capability of tartaric acid (TA) and high stability of multi-walled carbon nanotubes (MWCNTs) in organic/inorganic solvents, TA modified MWCNT (MWCNT-TA) was prepared and its adsorption properties for bivalent copper ion [Cu(II)] were studied. The MWCNT-TA composites were confirmed by Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, and high-resolution transmission electron microscopy (HRTEM). And the surface area of MWCNT-TA was determined by the Brunauer–Emmett–Teller (BET) method. The removal capacity of MWCNT-TA for Cu(II) was further investigated. In order to optimize the adsorption conditions, batch adsorption experiments were performed, and some factors that affecting the adsorption process including initial Cu(II) concentration, pH, contact time, and temperature were investigated. The adsorption kinetics could be better described by the pseudo second-order model, and the adsorption matches with the Langmuir isotherm. The results indicated that MWCNT-TA possessed higher adsorption capability for Cu(II) than pristine MWCNTs and TA. Additionally, MWCNT-TA can be facilely separated from aqueous solution by centrifugation and filtration after adsorption of Cu(II). Therefore, MWCNT-TA would find its potential application in wastewater treatment in the future.
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The objective of this study was to investigate the effect of chloride ions (Cl−) on Cu2+ adsorption to carbon nanotubes (CNT). The isotherms showed a significant decrease in adsorption capacity on F-400, pristine, and acid-functionalized CNT in the presence of Cl−, but had little effect on alcohol-functionalized CNT. Several inductively coupled plasma (ICP) analyses measured the impurities concentration of (1) aqueous-phase isotherm solute, (2) as-received, and (3) acid-washed CNT solutions. Chemical-equilibrium-modeling software MINEQL+ calculations were applied to compare ICP results to complexes formation. The model suggested that some solid-phase residual-catalytic metals, such as Cr2+, after released in water from as-received CNT, formed aqueous-phase complexes and were readsorbed. The 18-metal ICP results were more than two orders of magnitude lower ( 5.1, when less Cu2+ ions are present in solution. scanning electron microscopy–energy dispersive X-ray spectroscopy analysis showed impurities on as-received F-400 and positively charged surface at pH 5.1 (pHpzc 7.1) explaining possible electrostatic attraction of Cl− ions, blocking adsorptive sites, reducing its adsorptive capacity for Cu2+.
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In this study, multiwall carbon nanotubes (MWNTs) were modified with nitric acid chemically and by dielectric barrier discharge (DBD) plasma in an oxygen-based atmosphere. Used carbon nanotubes (CNTs) were prepared by chemical vapour deposition (CVD) floating catalyst method. For removing amorphous carbon and metal catalyst, MWNTs were exposed to dry air and washed with hydrochloric acid. Heating purified CNTs under helium atmosphere caused elimination of acidic functional groups. Fourier transformed infrared spectroscopy (FTIR) shows formation of oxygen containing groups such as C=O and COOH. Brunauer, Emmett, Teller (BET) analysis revealed that functionalization causes generation of defects on the sidewalls and opening of the ends of CNTs. Results of temperature-programmed desorption (TPD) and gas chromatography(GC) indicate that nitric acid treatment create more acidic groups than plasma treatment. Keywords—Carbon nanotubes (CNTs), chemical treatment, functionalization, plasma.
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The author observe sixfold enhancement in the near band gap emission of ZnO nanorods by employing surface plasmon of Au nanoparticles, while the defect-related emission is completely suppressed. Time-resolved photoluminescence indicates that the decay process becomes much faster by Au capping. The remarkable enhancement of the ultraviolet emission intensities and transition rates is ascribed to the charge transfer and efficient coupling between ZnO nanorods and Au surface plasmons. The suppression of the green emission might be due to a combined effect of Au surface plasmon and passivation of the ZnO nanorod surface traps.
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Microwave excited Ar / H <sub>2</sub> O surface-wave plasma was used to treat multiwall carbon nanotubes (MWCNTs) to modify their surface characteristics and thus improve their dispersion capability in water. Changes in the atom composition and structure properties of MWCNTs were analyzed using x-ray photoelectron spectroscopy and Raman spectroscopy, and the surface morphology of MWCNTs was observed by field emission scanning electron microscopy and scanning transmission electron microscopy. The results indicated that Ar / H <sub>2</sub> O plasma treatment greatly enhanced the content of oxygen, and modified surface microstructure properties. The integrity of nanotube patterns, however, was not damaged.
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Multi-walled carbon nanotubes (MWCNTs) have been functionalized by a dielectric barrier discharge plasma in air and compared to those functionalized in HNO3. The MWCNTs were prepared by chemical vapor deposition of xylene using ferrocene as a catalyst at 850 °C. Air oxidation followed by acid treatment was used to purify the MWCNTs, which were then annealed in helium. The MWCNTs were functionalized in air in a plasma reactor at room temperature. Quantitative analyses of gases evolved during the temperature programmed desorption of the functionalized nanotubes were carried out using Fourier transform infrared spectroscopy and gas chromatography. The influence of plasma parameters, including power in the range of 8–90 W and treatment time in the range of 1–9 min, on the number of the functional groups was investigated. It is shown that the extent of functionalization increases with increasing discharge power, provided that the exposure time of the MWCNTs in the plasma atmosphere does not exceed a certain period of time. Compared to acid treatment, plasma functionalization offers the advantages of much shorter treatment time, and produces less damage.
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Of the variety of adsorbents available for the removal of heavy and toxic metals, activated carbon has been the most popular. A number of minerals, clays and waste materials have been regularly used for the removal of metallic pollutants from water and industrial effluents. Recently there has been emphasis on the application of nanoparticles and nanostructured materials as efficient and viable alternatives to activated carbon. Carbon nanotubes also have been proved effective alternatives for the removal of metallic pollutants from aqueous solutions. Because of their importance from an environmental viewpoint, special emphasis has been given to the removal of the metals Cr, Cd, Hg, Zn, As, and Cu. Separation of the used nanoparticles from aqueous solutions and the health aspects of the separated nanoparticles have also been discussed. A significant number of the latest articles have been critically scanned for the present review to give a vivid picture of these exotic materials for water remediation.
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Grafting oxygen-containing functional groups onto carbon nanotubes (CNTs) by acid treatment improves their dispersion in aqueous solutions, but there is a lack of quantitative information on the colloidal properties of oxidized CNTs. We have studied the influence that pH and electrolytes have in determining the colloidal stability of oxidized multiwalled carbon nanotubes (O-MWCNTs), prepared by refluxing pristine MWCNTs in nitric acid. The acid-treated MWCNTs contained oxygen predominantly in the form of carboxyl groups. Colloidal suspensions of O-MWCNTs were prepared by low-power sonication and contained negatively charged, individual MWCNTs with an average length of approximately 650 nm. Time-resolved dynamic light scattering revealed that the aggregation rate of O-MWCNTs exhibited both reaction and mass-transport limited regimes in the presence of different electrolytes and as a function of pH. Particle stability profiles constructed from aggregation rate data allowed for the determination of critical coagulation concentrations (CCC), a metric of colloidal stability. The CCC values of O-MWCNTs varied with counterion concentration and valence in a manner consistentwith DLVO theory. Potentiometric measurements of surface charge correlated well with the observed pH-dependent variations in the O-MWCNT's colloidal stability. Electrophoretic mobility was also a diagnostic of particle stability, but only in neutral and acidic conditions.
Chapter
Carbon nanotubes, first discovered in the 1990s, have become one of the most eye-catching materials and have attracted great attention in the nanoscience community, because of their unique structure and truly remarkable electronic and mechanical properties. More importantly, these theoretically predicted properties have been subsequently evidenced by various experimental investigations. In this chapter, we present an overview of atomic and geometric structures of carbon nanotubes and their related properties, typically electronic, mechanical, and thermal properties.
Article
The phenomena involved in the possible applications of carbon nanotubes (CNT) for nanofluidics and nanofiltration has been investigated. Researchers focus on molecular dynamics simulations of water confined to single-walled CNT of various sizes and compare their entropy, enthalpy, and free energy to determine the factors behind spontaneous filling at 300 K. Postdoctoral researcher Tod A. Pascal and colleagues calculated that entropy is the key to filling nanotubes with water. The water molecules near the walls inside the CNT are constrained by few hydrogen bonds and the water in the nanotubes is disordered and has higher entropy compared with the bulk fluid. The entropic gain dominates any enthalpic loss due to broken hydrogen bonding. Pascal emphasizes that the modeled behavior is entirely dependent on the unique hydrogen-bonding nature of liquid water. Another group of researchers found that the melting point of water in CNT decreases with the increase in diameter.
Article
By introducing the sp3s* tight-binding model, the band structure and electronic density of states of single-walled carbon nanotubes are calculated. It is found that “metallic” zigzag single-walled carbon nanotubes open gaps about 7 meV-0.2 eV near Fermi level. In addition, the changes of diameter and chiral angles plays important roles in electronic properties of carbon nanotubes, especially of small-diameters tubes.
Conference Paper
This paper reviews our works about the development of thin composite film based on aligned carbon nanotubes (CNT) forest, embedded in epoxy or PMMA polymer matrix, in order to fabricate membranes dedicated to water purification issue. Indeed, the small internal radius of nanotubes, the smoothness of their inner core and the hydrophobic properties of its interna surface induce remarkable flowing properties for water molecules. In this article, thinnin technology process is investigated to obtain composite film with opened CNT. Different etching techniques as grinding, Chemical Mechanical Polishing (CMP) and isotropic plasma O2ar investigated in term of etching rate and membrane roughness, using AFM and SEM characterizations. Results show CMP process in lapping configuration permits to obtain agreement between high etching rate and membrane roughness. Moreover, to improve water flowing through membrane, O2plasma treatment is used to remove polymer residue spread over CNT. Joint use of lapping and plasma treatment permits to obtain 35μm-thick nanoporous membrane with well-opened protruding nanotubes.
Article
Potential sources of error in evaluating the adsorptive capacity of granular activated carbon (GAC) are identified and discussed, with special attention given to carbon sampling and preparation, preparation of test solutions, and selection of GAC dosages, adsórbate concentration, and equilibration time. Adsorptive capacity can vary with particle size, but data are presented to show that this may not always occur. Heterogeneous solutions require careful selection of GAC dosages and adsorbate concentration, and the data for such solutions require careful interpretation. Model simulations are used to illustrate the importance of closely approaching equilibrium and to estimate the time required to approach equilibrium under various conditions. For large GAC particles and slowly diffusing adsorbates, several years may be required to reach equilibrium. Failure to reach equilibrium can result in a significant underestimation of adsorptive capacity. Pulverizing GAC greatly reduces the time required to reach equilibrium, thus reducing the possibility of biodegradation of the adsorbate.
Article
Six commonly used wet chemical oxidants (HNO3, KMnO4, H2SO4/HNO3, (NH4)2S2O8, H2O2, and O3) were evaluated in terms of their effects on the surface chemistry and structure of MWCNTs using a combination of analytical techniques. X-ray photoelectron spectroscopy (XPS) and energy dispersive spectroscopy (EDX) were used to characterize the extent of surface oxidation, while chemical derivatization techniques used in conjunction with XPS allowed the concentration of carboxyl, carbonyl, and hydroxyl groups at the surface to be quantified for each MWCNT sample. Our results indicate that the distribution of oxygen-containing functional groups was insensitive to the reaction conditions (e.g., w/w% of oxidant), but was sensitive to the identity of the oxidant. MWCNTs treated with (NH4)2S2O8, H2O2, and O3 yielded higher concentrations of carbonyl and hydroxyl functional groups, while more aggressive oxidants (e.g., HNO3, KMnO4) formed higher fractional concentrations of carboxyl groups. IR spectroscopy was unable to identify oxygen-containing functional groups present on MWCNTs, while Raman spectra highlighted the frequently ambiguous nature of this technique for measuring CNT structural integrity. TEM was able to provide detailed structural information on oxidized MWCNT, including the extent of sidewall damage for different oxidative treatments.
Article
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 pHiep 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 29.92kJ/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.
Article
Water-dispersible graphene nanosheets were achieved by a simple three-step process. First, pristine graphite was oxidized and exfoliated to obtain graphene oxide, which was further acylated with thionyl chloride to introduce acyl chloride groups on the surfaces. Second, graphene oxide was covalently functionalized with an environment-friendly reagent, namely, adenosine. Subsequently, adenosine-functionalized graphene oxide was reduced to obtain graphene nanosheets by using NaBH4 as a reducing agent. This approach facilitates graphene nanosheets that have a combination of stable aqueous dispersions and an electrical conductivity that are much better in comparison to graphene oxide, offering a great flexibility for further applications.
Article
We studied the adsorption of single atoms on a semiconducting and metallic single-wall carbon nanotube from first principles for a large number of foreign atoms. The stable adsorption sites, binding energy, and the resulting electronic properties are analyzed. The character of the bonding and associated physical properties exhibit dramatic variations depending on the type of the adsorbed atom. While the atoms of good conducting metals, such as Cu and Au, form very weak bonding, atoms such as Ti, Sc, Nb, and Ta are adsorbed with relatively high binding energy. Most of the adsorbed transition-metal atoms excluding Ni, Pd, and Pt have a magnetic ground state with a significant magnetic moment. Our results suggest that carbon nanotubes can be functionalized in different ways by their coverage with different atoms, showing interesting applications such as one-dimensional nanomagnets or nanoconductors and conducting connects, etc.
Article
The adsorptive capacity of multiwall CNTs for copper species in water depends on the type of functional group present on their surface. The alcohol (OH) and acid (COOH) network forces formed by van der Waals bonds within the CNT bundles can define their aggregate state and available sites for copper adsorption. Copper is attracted to different oxygen radicals on the surface and within the bundles of CNTs. The effect of initial concentration shown on isotherm curves was investigated as an impact of different network forces and the presence of impurities leached from as-received CNTs. Deprotonation of CNTs reduced the COOH network forces, improved adsorption capacity and removed the effect of initial concentration. Impurities leached from CNTs under the effect of pH were less than 1mgg(-1) for each metal, which was insignificant compared to copper in solution. Pristine CNTs were acid washed and purified (Ox-CNTs), improving their adsorption capacity, but the effect of initial concentration was still present. Adsorption of copper is stronger for OH-functionalized CNTs, followed by deprotonated COOH-functionalized CNTs, as-received COOH-functionalized CNT, Ox-CNTs and finally pristine CNTs. FTIR, XPS and zeta potential measurements were used to identify and quantify the different surface functional groups present on CNTs.
Article
Visualization of embedded carbon nanotubes (CNTs) in polymer using a scanning electron microscope (SEM) has been established as a convenient technique to evaluate CNT dispersion. This technique is known as voltage contrast imaging and is different from material contrast and topographic contrast imaging. By investigating CNT/epoxy composites the voltage contrast imaging theory is further understood. Trapping of electrons at the CNT/epoxy interface induces a local potential difference which enhances the image contrast. By coating the composite with a polymer film of different thicknesses the imaging depth (i.e. from how deep the CNTs can be seen) is determined to be up to 250 nm, and is a function of the accelerating voltage of the SEM. Visibility of CNTs is found to be sensitive to the CNT dispersion and concentration, as well as to the accelerating voltage.
Article
Due to the enormous difference in the scales involved in correlating the macroscopic properties with the micro- and nano-physical mechanisms of carbon nanotube-reinforced composites, multiscale mechanics analysis is of considerable interest. A hybrid atomistic/continuum mechanics method is established in the present paper to study the deformation and fracture behaviors of carbon nanotubes (CNTs) in composites. The unit cell containing a CNT embedded in a matrix is divided in three regions, which are simulated by the atomic-potential method, the continuum method based on the modified Cauchy–Born rule, and the classical continuum mechanics, respectively. The effect of CNT interaction is taken into account via the Mori–Tanaka effective field method of micromechanics. This method not only can predict the formation of Stone–Wales (5-7-7-5) defects, but also simulate the subsequent deformation and fracture process of CNTs. It is found that the critical strain of defect nucleation in a CNT is sensitive to its chiral angle but not to its diameter. The critical strain of Stone–Wales defect formation of zigzag CNTs is nearly twice that of armchair CNTs. Due to the constraint effect of matrix, the CNTs embedded in a composite are easier to fracture in comparison with those not embedded. With the increase in the Young’s modulus of the matrix, the critical breaking strain of CNTs decreases.
Article
Modified multiwalled carbon nanotubes (MWCNTs) were used as a packing material for flow injection on-line microcolumn preconcentration of trace amounts of the metal ions of Cu, Zn, Mn and Pb, and subsequent flame atomic absorption spectrometry (FAAS) in one run after desorbing the ions with hydrochloric acid and injecting them into the nebulizer of an FAAS. Parameters such as loading time, flow rate, pH, eluent concentration, and flow rate were optimized. Enrichment factors are 20.3, 14.2, 20.6 and 15.4 respectively, and the sample throughput is 25h−1. The limits of detection (three times the standard deviation of the blank) are 0.59, 0.62, 0.28 and 1.00µgL−1, respectively, and standard deviations range from 2.6 to 4.6% (n = 7). The method was applied to the analysis of these ions in vegetables, and accuracy assessed via recovery experiments.
Article
In this article, the technical feasibility of various kinds of raw and surface oxidized carbon nanotubes (CNTs) for sorption of divalent metal ions (Cd2+, Cu2+, Ni2+, Pb2+, Zn2+) from aqueous solution is reviewed. The sorption mechanisms appear mainly attributable to chemical interactions between the metal ions and the surface functional groups of the CNTs. The sorption capacities of CNTs remarkably increased after oxidized by NaOCl, HNO3 and KMnO4 solutions and such surface oxidized CNTs show great potential as superior sorbents for environmental protection applications. Effects of process parameters, such as CNT characterizations (surface area, pore size distribution, sorbent mass, and surface total acidity), solution properties (ionic strength, pH, initial sorbate concentration and temperature) and competition for sorption sites by multiple metal ions, on the performance of CNTs are addressed in some detail. The recovery of metal ions and the regeneration of CNTs can be achieved using acid elution with little effect on the CNT performance. The utilization of CNTs for the treatment of water and wastewater containing divalent metal ions is gaining more attention as a simple and effective means of pollution control. Future research works on developing a cost-effective way of CNT production and testing the toxicity of CNTs and CNT-related materials are recommended.
Article
This paper describes a novel technique for fabrication of micro- and nanofluidic device that consists of a carbon nanotube (CNT) and a polydimethylsiloxane (PDMS) microchannel. Single CNT was placed at desired locations using dielectrophoresis (DEP) and PDMS microchannel was constructed on the aligned CNT via photolithography and soft lithography techniques. This technique enables a CNT to be seamlessly embedded in a PDMS microchannel. Moreover, controlling the PDMS curing condition enables the construction of the device with or without a CNT (the device without CNT has a trace nanochannel in PDMS). Preliminary flow tests such as capillary effect and pressure-driven flow were performed with the fabricated devices. In the capillary effect tests, the flow stopped at the nanochannel in both devices. In the pressure-driven flow lower flow resistance was observed in the device with a CNT.
Article
The adsorption of Cu(II) on multiwalled carbon nanotubes (MWCNTs) as a function of pH and ionic strength in the absence and presence of humic acid (HA) or fulvic acid (FA) was studied using batch technique. The results indicated that the adsorption is strongly dependent on pH but independent of ionic strength. A positive effect of HA/FA on Cu(II) adsorption was found at pH <7.5, whereas a negative effect was observed at pH >7.5. The adsorption isotherms can be described better by the Freundlich model than by the Langmuir model in the absence and presence of HA/FA. Adsorption isotherms of Cu(II) at higher initial HA/FA concentrations are higher than those of Cu(II) at lower FA/HA concentrations. The thermodynamic data calculated from temperature-dependent adsorption isotherms suggested that the adsorption was spontaneous and enhanced at higher temperature. Results of this work suggest that MWCNTs may be a promising candidate for the removal of heavy metal ions from aqueous solutions.
Article
We investigate the functionalization of functional groups to graphene nanoribbons with zigzag and armchair edges using first principles calculations. We find that the formation energy for the configuration of the functional groups functionalized to the zigzag edge is ~0.2 eV per functional group lower than that to the armchair edge. The formation energy difference arises from a structural deformation on the armchair edge by the functionalization whereas there is no structural deformation on the zigzag edge. Selective functionalization on the zigzag edge takes place at a condition of the temperature and the pressure of ~25 oC and 10-5 atm. Our findings show that the selective functionalization can offer the opportunity for an approach to the separation of zigzag graphene nanoribbons with their solubility change.
Article
A widely soluble graphene sheet/Congo red (GSCR) composite was synthesized and applied to prepare GSCR/Au hybrid materials. UV-vis absorption, Fourier transform infrared, Raman, and X-ray photoelectron spectra revealed that Congo red (CR) is successfully coupled on graphene sheets. The morphology of GSCR was studied by transmission electron microscopy, scanning electron microscopy, and atomic force microscopy. The dispersion behavior of the GSCR composite was also studied in 18 different solvents, and the digital images indicate that it is soluble both in water and in a variety of organic solvents. The GSCR nanosheets are still single layers or bilayers in water and individual from one to another after 100 days of storage. Furthermore, the mechanism of GSCR's good solubility was successfully explained by the Hansen solubility parameters. The four standard probe result shows that the GSCR films have a bulk conductivity of approximately 6850 S m(-1). The wide solubility and long lifetime of GSCR solutions are absolutely necessary for further treatment. As an example, Au nanoparticles densely decorated CR-functionalized graphene sheets through electrostatic interaction.
Article
Carbon nanotube (CNT) adsorption technology has the potential to support point of use (POU) based treatment approach for removal of bacterial pathogens, natural organic matter (NOM), and cyanobacterial toxins from water systems. Unlike many microporous adsorbents, CNTs possess fibrous shape with high aspect ratio, large accessible external surface area, and well developed mesopores, all contribute to the superior removal capacities of these macromolecular biomolecules and microorganisms. This article provides a comprehensive review on application of CNTs as adsorbent media to concentrate and remove pathogens, NOM, and cyanobacterial (microcystin derivatives) toxins from water systems. The paper also surveys on consideration of CNT based adsorption filters for removal of these contaminants from cost, operational and safety standpoint. Based on the studied literature it appears that POU based CNT technology looks promising, that can possibly avoid difficulties of treating biological contaminants in conventional water treatment plants, and thereby remove the burden of maintaining the biostability of treated water in the distribution systems.
Article
Adsorption of nickel, copper, zinc and cadmium from aqueous solutions on carbon nanotubes oxidized with concentrated nitric acid was carried out in single, binary, ternary and quaternary systems. TEM and adsorption of nitrogen were used to determine texture and structural parameters, respectively. The surface chemistry was evaluated using the pH at the point of zero charge, FTIR spectroscopy and XPS analysis. The experimental results showed that all isotherms for Cu(2+)(aq) fit to Langmuir model in each system. On the other hand, the isotherms for Ni(2+)(aq), Cd(2+)(aq) and Zn(2+)(aq) in multi-component systems reveal the effect of competition for adsorption sites seen as a decrease in the amount adsorbed. The uptakes at the equilibrium concentration of 0-0.04 mmol L(-1) in single system and 0-0.15 mmol L(-1) in binary system are in the order Cu(2+)(aq)>Ni(2+)(aq)>Cd(2+)(aq)>Zn(2+)(aq) while for the ternary and quaternary, the order is Cu(2+)(aq)>Cd(2+)(aq)>Zn(2+)(aq)>Ni(2+)(aq). The results indicate that the mechanism of adsorption is governed by the surface features, ion exchange process and electrochemical potential. The latter plays a significant role in multi-component adsorption where redox reactions, not only on the adsorbent surface but also between the adsorbates, are likely to occur.
Article
Diabetes is a set of diseases characterized by defects in insulin utilization, either through autoimmune destruction of insulin-producing cells (Type I) or insulin resistance (Type II). Treatment options can include regular injections of insulin, which can be painful and inconvenient, often leading to low patient compliance. To overcome this problem, novel formulations of insulin are being investigated, such as inhaled aerosols. Sufficient deposition of powder in the peripheral lung to maximize systemic absorption requires precise control over particle size and density, with particles between 1 and 5 microm in aerodynamic diameter being within the respirable range. Insulin nanoparticles were produced by titrating insulin dissolved at low pH up to the pI of the native protein, and were then further processed into microparticles using solvent displacement. Particle size, crystallinity, dissolution properties, structural stability, and bulk powder density were characterized. We have demonstrated that pure drug insulin microparticles can be produced from nanosuspensions with minimal processing steps without excipients, and with suitable properties for deposition in the peripheral lung.
Article
A qualitative description of the electronic structure of single-wall carbon nanotubes from a chemical perspective is presented using real-space orbital representations and traditional concepts of aromaticity, orbital symmetry and frontier orbitals. This unusual view of carbon nanotubes allows us to merge the solid-state physics description of band structures with the molecular orbitals framework of reaction mechanisms used in organic chemistry and to predict intriguing chemical selectivity based on electronic structure.
Article
Carbon nanotubes have attracted great interest in multidisciplinary study since their discovery. Herein, radionuclide 243Am(III) sorption to uncapped multiwall carbon nanotubes (MWCNTs) was carried out at 20+/-2 degrees C in 0.01 and 0.1 M NaClO4 solutions. Effects of 243Am(III) solution concentration, ionic strength, and pH on 243Am(III) sorption to MWCNTs were also investigated. The sorption is strongly dependent on pH values and weakly dependent on the ionic strength in the experimental conditions. The results show that MWCNTs can adsorb 243Am(III) with extraordinarily high efficiency by forming very stable complexes. Chemisorption or chemicomplexation is the main mechanism of 243Am(III) sorption on the surface of MWCNTs. MWCNTs can be a promising candidate for the preconcentration and solidification of 243Am(III) or its analogue lanthanides and actinides from large volumes of aqueous solution, as required for remediation purposes, and perhaps also as a sorbent for the removal of heavy metal ions from the industry wastewater.
Article
This paper examines the influence of relative income position on individuals' attitudes by analyzing ISSP 1998 microdata from 25 countries along four different dimensions. Our results provide evidence for a sizeable relative income effect while also suggesting that absolute income level may be relevant. Changing the income reference group from regional to national does not significantly alter the results.
Multiwalled carbon nanotube films: fabrication techniques and applications
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