Multi-walled Carbon Nanotubes Dosage Research Articles

Spatial degradation characteristics and numerical prediction for life of MWCNTs-reinforced concrete by salt freezing

Nanotechnology is of great importance towards the multiscale enhancement of mechanical strength, anti-cracking, corrosion and/or abrasion resistance of concrete. To optimize the durability of concrete structure in a frigid and saline environment, the multi-walled carbon nanotubes (MWCNTs) were introduced along with the evaluation of spatial deterioration characteristics and numerical prediction for its service life in this work. The degree and mechanism of salt freeze-thaw damage relief of MWCNTs-reinforced concrete (CNTC) were investigated by establishing relief rate (Rf, RE and Rp) and damage parameters (Df, DE and Dp) in terms of compressive strength, relative dynamic elastic modulus and porosity. Macroscopic results showed that the presence of MWCNTs substantially delayed the evolution of spatial damage of concrete. The optimum dosage of MWCNTs for the degradation mitigation was also determined to be 0.05 wt% from the microscale scanning electron microscopy, mercury intrusion and mesoscale X-CT scanning techniques, which was responsible to the well-dispersed MWCNTs without entanglement. The synergic effects of filling, nucleation and bridging of MWCNTs in hydrating concrete decreased the porosity and effectively inhibited micro-crack propagation of concrete under the salt freezing effects. Besides, the evolutionary relationships between Df, DE and Dp were established, and a three parameters-dependent prediction index D had been established on the basis of the entropy method and grey system theory GM(1,1) model. The experimental results were in good agreement with the prediction model, and further showed that the salt- freeze-thaw damage of CNTC was significantly reduced.

Investigation of hydration kinetics, microstructure and mechanical properties of multiwalled carbon nano tubes (MWCNT) based future emerging ecological economic ultra high-performance concrete (E3 UHPC)

In recent years, attest to the growing prominence of sustainable buildings and the integration of advanced materials like nanomaterials in construction practices. Among these advancements, the strategic application of multi-walled carbon nanotubes (MWCNTs) alongside dispersion techniques such as surfactant agents, functionalization, and ultrasonication is pioneering. These techniques are instrumental in elevating the mechanical strength and durability of cement paste and mortar. The approach involves gradually introducing nanomaterials to create a cementitious composite, allowing for a systematic analysis of their effects on each type and determination of the optimal dosage. The influence of MWCNT with various dosage combination on rheological, mechanical and microstructural properties of ultra high-performance concrete (UHPC) were investigated in this study. According to test results, the UHPC MWCNT 0.06 % mix can be considered as the best UHPC mix due to discussed specifications. The outcomes of the research demonstrate that the optimal dosage of MWCNT enhances various mechanical properties of UHPC significantly. At 28 days of curing, the addition of MWCNT resulted in improvements of 32.97 % in compressive strength, 49.72 % in split tensile strength, 40.41 % in flexural strength, and 9.09 % in dynamic modulus. The observed enhancements in mechanical properties can be attributed to the pore-filling, bridging, and densification effects of MWCNT within the calcium-silicate-hydrate structure of UHPC. Moreover, the incorporation of MWCNT facilitates the development of a more sustainable and environmentally friendly UHPC, thereby supporting sustainable construction practices.

Enhanced photocatalytic properties of MWCNTs-decorated SrTiO3–SrCO3 hierarchical structures achieved by efficient charge transfer

Cr (VI) is a heavy metal ion that cannot be ignored in industrial wastewater and is highly toxic, posing a serious threat to the health and safety of natural organisms. In order to remove Cr (VI) ions in the wastewater, photocatalysis is currently employed and becomes a promising and effective way but the photocatalytic rate still needs further improvement. In this work, multi-walled carbon nanotubes (MWCNTs) modified SrTiO3–SrCO3 microspheres with a three-dimensional porous structure were prepared by a facile solvothermal method. When the dosage of MWCNTs was 0.55 wt%, the obtained sample exhibited the highest photocatalytic efficiency, with approximately 100 % removal of Cr (VI) within 6 min and the photocatalytic rate constant (k) can reach 0.52 min−1 under full-spectrum light irradiation. The enhancement in the photocatalytic performance is probably attributed to the large surface area for more adsorption of Cr (VI) ions on the sample and effectively transfer of photo-generated carriers via the hetero-structures for the reaction of Cr (VI) ions with more carriers. Therefore, this work can provide a facile method for the preparation of photocatalysts with good performance for the removal of Cr (VI) in the wastewater.

Effects of Multi-Walled Carbon Nanotube Dosages and Sonication Time on Hydration Heat Evolution in Cementitious Composites.

This study aimed to investigate the heat generated during the hydration process in cementitious composites containing multi-walled carbon nanotubes (MWCNTs). The cumulative heat release and heat flow of these cementitious composites were measured over a period of 168 h using isothermal calorimetry. Three different MWCNT dosages, 0.05 wt%, 0.1 wt%, and 0.2 wt%, along with two different sonication times for the solution, which were 20 min and 60 min, were applied in the experimental program. The results reveal that the incorporation of MWCNTs and the use of a naphthalene-based superplasticizer to disperse the nanotubes generally led to a reduction in heat emission during the early stages of hydration, a lower first peak value in the initial stage of hydration, and a significant delay in the acceleration period compared with the reference sample lacking this superplasticizer. Furthermore, the results demonstrate that both the dosage of multi-walled carbon nanotubes (MWCNTs) and the sonication time have an impact on the heat emission and hydration process since the same amount of superplasticizer was applied to all pastes. An increase in the MWCNT dosage led to a decrease in the rate of hydration heat at the main peak for all pastes. Additionally, longer sonication times resulted in lower values of heat generated, reduced main peak values in the heat rate evolution, and generally extended delays in the occurrence of the main peak.

Cobalt carbonate hydroxide-embedded in multi-layered holey nanoflower cross-linked with carbon nanotube for highly efficient supercapacitors with ultrahigh rate performance

In this work, bimetallic nickel-cobalt based metal organic framework (MOF) is in-situ grown on 2D laminar Co2(OH)2CO3 with multi-walled carbon nanotubes (MWCNTs) aid to form nanoflower-like hierarchical porous heterogeneous structure for advanced supercapacitor application. Benefitting from the low crystal surface energy of Co2(OH)2CO3, its intersection and connection with MOF generate convenient electron path and open channel for ionic transmission, and large contact area. The high aromaticity of MWCNTs slows down destruction for MOF structure from water molecule through providing hydrophobic environment, guaranteeing stable presence of the resulting composite in aqueous electrolyte. The synergistic effect of Ni/Co with high redox activity in bimetallic NiCo-MOF provides rapid and multiple redox reactions for enhanced capacitance. Taking full advantage of promising merits of individual components, the optimized NiCo MOF-Co2(OH)2CO3 nanosheet-MWCNT30 (NCM-NS-CNT30) composite under MWCNT dosage of 30 mg delivers greatly enhanced specific capacitance (1773 F g−1 at 1 A g−1) and obviously improved rate performance (96.5 % retention at 10 A g−1). Based on it, the fabricated hybrid supercapacitor (HSC) NCM-NS-CNT30//AC presents comparatively good energy density (30.625 Wh Kg−1), superior to most recently reported Ni, Co-based supercapacitors.

Development of nanomodified-cementitious composite using phase change material for energy saving applications

In this study, a nanoengineered thermal-energy storing cementitious composite incorporated with a microencapsulated phase change material (m-PCM) and the combination of multi-walled carbon nanotubes (MWCNTs) and silica fume (SF), were developed for energy-saving purposes. m-PCM with a phase-change temperature of 5.5 °C and an enthalpy of 84 J/g was added to create latent heat storage in cement mortar. MWCNTs were added to improve the mechanical and thermal performance of the cementitious composite. m-PCM was incorporated in the cement mortar in proportions of 5%, 10%, and 15% by binder weight. However, the dosage of MWCNTs and SF kept constant at 0.05% and 10% by binder weight, respectively. A uniaxial compression test was performed to analyze the effect of m-PCM on the mechanical properties of the mortar. The compression test results showed a significant decrease in mechanical strength owing to the addition of m-PCMs. However, the addition of SF/MWCNTs significantly enhanced the compressive strength of m-PCM mortars. A thermal-cycling test, assisted by an electrically-controlled–heated wire system, was performed to study the thermal response of nanoengineered m-PCM mortars with respect to varying ambient temperatures. The results revealed that the energy requirement for thermal regulation in m-PCM mortars with MWCNTs was reduced by approximately 60% as compared to the control specimen.

Super plasticizer assisted bath ultra sonication for dispersion of multi walled carbon nanotubes in cement composites

This paper presents the observations and findings from an experimental study for dispersion of multiwalled carbon nanotubes (MWCNTs) by bath ultra-sonication in the presence of polycarboxylate ether (PCE) based superplasticizer. Commercial brand of superplasticizer (SP) compatible with cement was adopted for exploring its usage as surfactant during aqueous dispersion of MWCNTs. Cement composite pastes were evaluated for variation in compressive strength and fresh property for a fixed addition percentage of MWCNT. Aqueous dispersion of MWCNTs for incorporation to cement pastes was prepared considering three different sonication process variables; time period of sonication, SP to MWCNT dosage during sonication and temperature of sonication medium. A total of 168 experimental variations were evaluated for compressive strength of resulting cement–carbon nanotubes composite pastes at 7 days age to arrive at an optimal process of bath ultra-sonication with governing variables. Results showed that a sonication time period in the range of 4–5 hours with an SP to MWCNT ratio of 2.5–3 was necessary for satisfactory dispersion of MWCNTs over different temperature ranges of sonication bath medium. Further, the temperature of sonication medium in the range of 35–40°C during aqueous dispersion of MWCNTs was observed to induce noticeable enhancement in strength of composite system indicating improvement in dispersion within an optimal range of sonication medium temperature. Microscopic observations for optimal process variables of dispersion during bath ultra sonication showed evidence of physical changes in MWCNTs from an agglomerated state of particles to separated state.

Self-sensing concrete with recycled coarse aggregates and multi-walled carbon nanotubes: A sustainable and effective method

This study explores the production of self-sensing concrete using recycled coarse aggregates and Multi-walled Carbon Nanotubes (MWCNTs) in varying dosages. The objective is to reduce the usage of natural coarse aggregates and to develop an environmentally friendly and sustainable material for the future generation. The self-sensing concrete was also self-compacting (SCC), which enhances its ability to fill complicated molds without the need for external vibration. The fresh properties of the self-sensing concrete were tested, and the mix proportions with varying dosages of MWCNTs were within the prescribed limit as per European Federation of National Associations Representing for Concrete (EFNARC) code. The mechanical properties of the self-sensing concrete were also evaluated, and it was observed that incorporating MWCNTs into the concrete enhanced its strength. Incorporating MWCNT into concrete increased its strength, seen in higher compressive and split tensile strengths. Adding 0.05%, 0.1%, and 0.15% of MWCNT resulted in compressive strength increases of 1.51%, 3.21%, and 4.72%, respectively. Likewise, the inclusion of 0.05%, 0.1%, and 0.15% of MWCNT led to split tensile strength increases of 1.54%, 3.31%, and 4.82%, respectively. The SEM images of specimens with different MWCNT dosages show a random yet uniform dispersion within the concrete matrix. The initial electrical resistance plot demonstrates the transformation from conventional to self-sensing concrete, with the resistance dropping significantly from 400k-ohms to 37k-ohms. This plot establishes the critical threshold level for self-sensing at 0.10% MWCNTs. Furthermore, the study examined the stress sensing ability and crack detection properties of the self-sensing concrete, and it was found that during cyclic loading, the concrete's stress sensing ability improves with increasing MWCNT dosage. The most favorable similarity plot between stress and FCR is seen at 0.15% MWCNT. However, considering economic reasons, a dosage of 0.1% MWCNT can be considered the best option since it doesn't show a significant difference for both stress and crack detection property.

Spatial distribution characteristics and microscopic mechanisms for enhancing mechanical properties of MWCNTs in recycled coarse aggregate shotcrete

This study aimed to investigate the spatial distribution characteristics of multi-walled carbon nanotubes (MWCNTs) in recycled coarse aggregate shotcrete (RCAS) and the influence of the dosage of MWCNTs on flow characteristic, mechanical properties and its microscopic mechanism. In this paper, 100% of natural coarse aggregate (NCA) was replaced by recycled coarse aggregate (RCA). Multiple nano-characterization techniques were adopted, and the wet-mix shotcrete technology and a combined device for variable addition of MWCNTs suspension were used. The experimental results showed that with the increase of the dosage of MWCNTs, the flow characteristic of RCAS in fresh state decreased. In terms of mechanical properties, the compressive strength, splitting tensile strength and flexural strength of RCAS all showed a trend of increasing first and then decreasing, when MWCNTs was 0.09 wt%, the flexural strength and splitting strength of RCAS reached the peak value. When the dosage of MWCNTs was 0.03 wt%, 0.06 wt% and 0.09 wt%, the quantity distribution of MWCNTs in the RCAS was average and centered. Appropriate dosage of MWCNTs (0.06 wt% or 0.09 wt%) had a positive effect on improving the compactness of interface transition zone (ITZ) of the RCA, optimizing the internal pore size distribution of RCAS, accelerating the hydration reaction rate and increasing the yield of hydration products.

Modeling of lead (II) ion adsorption on multiwall carbon nanotubes using artificial neural network and Monte Carlo technique

In this study, Pb2+ removal from wastewater using multiwall carbon nanotubes (MWCNTs) was investigated. XRD, SEM-EDX, BET, and FTIR were employed for MWCNT characterization. The effects of various parameters, including the solution pH, adsorbent dosage, initial concentration of Pb2+, and contact time, on the Pb2+ removal from wastewater were investigated experimentally. Furthermore, the nonlinear relationship among the parameters was predicted using an artificial neural network (ANN) approach. The Levenberg–Marquardt training algorithm showed the best training performance, with a mean-square error of 2.200 × 10−5 and an R2 of 0.998. Combining the ANN models and Monte Carlo simulation, Pb2+ removal efficiency of 99.8% was obtained under the optimum conditions (pH of 10, MWCNT dosage of 0.05 g, contact duration of 60 min, and Pb2+ concentration of 100 mg/L). The high removal efficiency can be attributed to the available adsorption sites (active sites). The results of the reusability of MWCNTs showed that the adsorption efficiency was higher than 90%. Thus, MWCNTs have great potential for recycling and managing Pb2+ from wastewater.

Influence of multi-walled carbon nanotubes on the multi-scale performance of internally cured concrete containing pre-wetted lightweight aggregate

Multi-walled carbon nanotubes (MWCNTs) is an effective reinforcing nanomaterial in concrete given its outstanding filling, nucleation and bridging effects. This study evaluates the enhancement of MWCNTs on internally cured concrete (ICC) containing pre-wetted lightweight aggregate (LWA) through mechanical tests, SEM-EDS and XRD evaluations. The variations in the dosages of MWCNTs and LWA and the connection between water-to-binder (w/b) ratios and MWCNT dosages were considered. Results show that adding MWCNTs benefits the mechanical performance of LWA-ICC but at a dosage of less than 0.25 wt%. A richer C–S–H phase can be identified in both the interfacial transition zone and the general matrix with the addition of MWCNTs. The internal curing of LWA presents a positive synergistic effect with MWCNTs and can offset the adverse influence of LWA’s low-strength given a dosage of less than 40 vol%. An increased w/b ratio leads to a porous microstructure with a richer phase in calcium hydroxide, resulting in decreased mechanical performance. However, the negative effect of a high w/b ratio, i.e., 0.55, on concrete performance can be improved given a higher MWCNT dosage of 0.25 wt%.

On the early behavior and microstructure of oil well cement paste incorporating with carbon nanotubes cured at a high temperature

With the rapid development of shale gas/oil exploitation, hostile downhole condition asks for more flexible and ductile oil well cement paste (OWCP). This study is devoted to investigating the influence of multi-walled carbon nanotubes (MWCNTs) on the rheological behavior, early mechanical properties and volume stability of OWCP by means of different experimental methodologies. Multiple microstructural techniques are employed to further understand the reinforcing mechanism of MWCNTs on the performances of OWCP. The results show that the optimal dosage of MWCNTs is 0.6wt.‰. The rheological behavior of MWCNTs/OWCP slurry at low shearing rate is improved after the addition of 0.6wt.‰MWCNTs. The mechanical properties and autogenous shrinkage of MWCNTs/OWCP composites are enhanced after the addition of the optimal dosage of MWCNTs, MWCNTs/OWCP composites with addition of 0.6wt.‰MWCNTs exhibit more flexible and ductile than plain OWCP. The additional nucleation sites provided by MWCNTs, the role of bridging effect and pull-out effect by MWCNTs, and the high curing temperature are all responsible for the enhanced mechanical properties of MWCNTs/OWCP composites. Owing to the addition of MWCNTs, the relationship between the compressive strengths of MWCNTs/OWCP composites and gel/space ratios does not exhibit exponential form. However, the addition of MWCNTs does not alter the Avrami-type exponential relationship between the degree of hydration and curing ages, moreover, it does not alter the linear relationship between the mercury intrusion porosity and gel/space ratio.

Modeling of Congo Red Adsorption onto Multi-walled Carbon Nanotubes Using Response Surface Methodology: Kinetic, Isotherm and Thermodynamic Studies

In this present study, an adsorption process was investigated to removal of Congo Red (CR) dye from aqueous solutions by using multi-walled carbon nanotubes (MWCNTs) as an adsorbent. The physico-chemical properties of MWCNTs were characterized by TEM, SEM, Raman spectroscopy and BET surface area. The response surface methodology, which is including central composite design, was used to investigate the effects of four independent parameters (initial pH of solution (5.5–11.5), initial CR concentration (15–75 mg/L), MWCNTs amount (0.05–0.25 g/L) and contact time (20–60 min)). ANOVA evaluated with Design Expert 10.0 showed that a high value of regression coefficient (R2 = 0.988) a good agreement between experimental and model predicted response in addition to significance of the model. The optimum values of the independent variables giving the maximum removal efficiency (78.36%) of CR dye were obtained at the optimum adsorption conditions of initial solution pH: 5.5; initial CR concentration: 15 mg/L; MWCNTs dosage: 0.25 g/L and contact time: 59.62 min. The kinetic study illustrated that the experimental data are well defined with pseudo-second-order adsorption kinetic model. The maximum adsorption capacity (qmax) increased from 115.8 mg/g to 138.3 mg/g with the increase in temperature from 293 to 323 K. Thermodynamic parameters, ΔH (8.56 kJ/mol), ΔG (− 27.08 and − 30.73 kJ/mol) and ΔS (0.1215 kJ/mol K) were determined for the adsorption process.

Improvement in mechanical properties of enamel via carbon nanotube addition

AbstractEnameled metal equipment exploits the strength of metal materials and the corrosion resistance of enamel; therefore, it is widely used in the chemical industry. However, the mechanical properties of the enamel restrict its service life. Multi‐walled carbon nanotubes (MWCNTs) are one‐dimensional nanomaterials with high‐specific surface area, C–C bond structure, and SP2 hybrid orbital. Herein, the effect of the dosage of MWCNTs on the mechanical properties of enamel is studied by adding MWCNTs to improve the mechanical properties of the enamel. Microscopic observation showed that the toughening mechanism of MWCNTs was mainly manifested in fracture and pull out behaviors. According to three‐point bending test, when 0.4 wt% carbon nanotubes were added, the reinforcing effect of enamel layer reached the best state. These results provide reference for optimizing the formulation of enamel and extending the service life of enamel.

Emerging contaminant (Triclosan) removal by adsorption and oxidation process: comparative study

Triclosan is an antibacterial and antifungal agent present in a wide range of personal care products, including toothpaste, soaps, detergents, and surgical and surface cleaning agents. Many studies have been conducted to investigate the toxic potential of Triclosan (TCS) on human health, plants, and the environment, and it has been reported to be an endocrine disruptor. This study addresses the removal efficiency of TCS using nano-zerovalent iron (nZVI), multi-walled carbon nanotubes (MWCNTs), and carbon filter. Wherein, nZVI is synthesized by an environmentally benign method, i.e., using Camellia Sinensis (Tea) extract used as a reducing agent and carbon filter is prepared by coating MWCNTs onto the cotton cloth. Removal efficiency has been studied for TCS at different operational parameters such as concentrations of TCS from (5 to 20 ppm), dosages of nZVI and dosage of MWCNTs (0.05–0.3 g/l) and pH (3–11). Results of this study indicate that, till a concentration of 5 ppm, 0.1 g/lit dosage of nZVI and MWCNTs has shown a removal efficiency of 97.07 and 100% at reaction time of 40 and 20 min, respectively. An incorporation carbon filter has been proven an efficient than dispersing MWCNTs in aqueous solutions.

Rheological Properties and Flow Behaviour of Cement-Based Materials Modified by Carbon Nanotubes and Plasticising Admixtures

In this study, the rheological properties of cement paste modified by a suspension containing both multi-walled carbon nanotubes (MWCNT) and carboxymethyl cellulose (CMC) (MWCNT/CMC suspension) with different types of plasticising admixtures (Pl), such as lignosulphonate (LS), sulfonated naphthalene formaldehyde condensate (NF), and polycarboxylate ether (PCE) were evaluated. The increase in yield stress and plastic viscosity up to 20% was established in the case of the modification of cement-based mixtures by MWCNT in the dosage up to 0.24% by weight of cement (bwoc) without Pl and with LS and NF. The complex modification of cement paste by MWCNT and PCE increases the yield stress and plastic viscosity from the MWCNT dosage of 0.06% and 0.015% bwoc, respectively. The yield stress and plastic viscosity of cement paste with PCE enhanced by 265% and 107%, respectively, in a MWCNT dosage of 0.12% bwoc. MWCNT do not have a significant influence on the flow behaviour index of cement paste; however, in the case of usage of PCE, the shear thickening effect decreased from a MWCNT dosage of 0.03% bwoc. The significant reduction in the volume coefficient of water bleeding by 99, 100, and 83% was obtained with LS, NF, and PCE, respectively, with an increase in MWCNT dosage up to 0.24% bwoc.

Effects of hydroxyl, carboxyl, and amino functionalized carbon nanotubes on the functional diversity of microbial community in riverine sediment

Nowadays, more and more attention is focused on the environmental harm brought by the wide production and use of carbon nanotubes. In this study, the metabolic function of sediment microbial community was investigated after unfunctionalized or functionalized multi-walled carbon nanotubes (MWCNTs) were incorporated. The surface functional groups on the studied functionalized MWCNTs in this work were hydroxyl, carboxyl, and amino, respectively. The metabolic functional diversity was determined by Biolog EcoPlates after one-month exposure to MWCNTs. Incorporating 0.5 wt% amino functionalized MWCNTs significantly decreased the microbial activity and diversity, and all types of MWCNTs caused great inhibition on the microbial metabolism at the dosage of 2.0 wt%. The sediment microbes preferred polymers and amino acids. Principal component and similarity analysis indicated that the microbial carbon metabolism was more affected by the MWCNT dosage compared with the functionalization, and 2.0 wt% amino functionalized MWCNTs made the greatest difference in metabolic function of sediment microbial community. These consequences may help to assess the environmental risks of MWCNTs from the aspect of ecological relevance of sediment microbial community.

Effect of the dosage of MWCNT's on deterioration resistant of concrete subjected to combined freeze–thaw cycles and sulfate attack

AbstractIn this study, the deterioration resistant of concrete with and without multi‐walled carbon nanotubes (MWCNTs) against combined freeze–thaw cycles and sulfate attack was studied, and concretes incorporating MWCNTs (i.e., 0.05, 0.10, and 0.15 wt%) as partial replacement of Portland cement were exposed to 5% sodium sulfate solution under freeze–thaw cycles. The performance, including compressive strength, relative dynamic elastic modulus, mass loss, microstructure, deterioration resistant coefficient of concretes were evaluated. Results show that when exposed to 5% sodium sulfate solution, MWCNTs could enhance the mechanical and durability properties of concrete subjected to combined freeze–thaw cycles and sulfate attack, regardless of the dosage of MWCNTs. The deterioration resistant of MWCNTs concrete was not increase with the increase dosage of MWCNTs. And the best resistance performance was obtained in concrete containing lower dosage of MWCNTs. In addition, MWCNTs could promote formation of hydration and corrosion products, and delay deterioration of concrete was demonstrated by SEM and thermogravimetric analysis.

Decolourization of Acid Orange 74 Aqueous Solutions in Presence of Multi-Walled Carbon Nanotubes under Ultrasound Irradiation

Few researches focused on the combination of ultrasound and multi-walled carbon nanotubes (MWCNT) in wastewater treatment. In this study, it was found that the combination of ultrasound and MWCNT was more effective in the removal of Acid orange 74 (AO 74) in comparison to single method. And there was a remarkable synergistic effect in the ultrasound/MWCNT combined system. The adsorption behaviour of AO 74 by the combination of ultrasound and multi-walled carbon nanotubes (MWCNT) was investigated under various experimental conditions. The adsorption performance was slightly inhibited with increasing temperature. This fact showed that the adsorption process was exothermic. The removal ratio was improved with increase in MWCNT dosage, which could be attributed to the increased adsorption sites and increased surface area. The dye removal decreasedfrom 96.0 to 41.5% with an increase in the initial concentration of dye from 15 to 100 mg/L. Lower removal ratios at higher dye concentrations were due to the saturation of adsorption, though the adsorption capacity increased from 14 to 41.5 mg/g. It may be due to the high concentration of dye which can provide a high driving force of concentration gradient to overcome all mass transfer resistance. With the increase in pH, removal ratios of AO 74 decreased gradually from pH 3 to 11. At low pH values, the surface of the adsorbent solids was positively charged and easily adsorbed the AO 74 ions having negative charges. But at high pH values, the surface charge of MWCNT got negatively charged, which did not favour the adsorption of negatively charged dye anions. Experimental isotherm data were represented with Langmuir and Freundlich adsorption models. Langmuir isotherm equation fitted better than Freundlich isotherm equation for this system, which meant adsorption of dye onto MWCNT was monolayer adsorption with a finite number of identical sites. The adsorption of AO 74 followed pseudo second-order kinetics. Kinetics analysis suggested lower temperature was favourable for AO 74 adsorption on MWCNT under ultrasound and justified the exothermic adsorption process.

Adsorption onto MWCNTs Coupled with Cloud Point Extraction for Dye Removal from Aqueous Solutions: Optimization by Experimental Design.

The main aim of the study was to examine the feasibility and benefits of adsorption onto multi-walled carbon nanotubes (MWCNTs) coupled with cloud point extraction (CPE) for the removal of Rhodamine B (RB) from aqueous solutions. MWCNTs offer the particular features of the ideal adsorbents for the organic dyes such as hollow tubular structure and specific surface area. Nevertheless, they suffer from the drawbacks of low dispersion in the aqueous solutions and separation inconvenience from the media. Cloud point extraction, combined with the adsorption onto MWCNTs can be a promising method to overcome the problems. In the study, adsorption onto MWCNTs coupled with CPE was applied for RB removal from aqueous solutions. The process was optimized by the response surface modeling method. Moreover, the applicability of the proposed method in the real sample analyses was investigated. MWCNTs were used as adsorbent and Triton X-100 (TX-100) as the nonionic surfactant for CPE process. The experiments were carried out based on a Box-Behnken design (BBD) with the input variables of MWCNTs dosage (0.6-1.2 mg), solution pH (3-9), clouding time (20-40 min) and TX-100 concentration (10-20 v/v%) using 5 mg L-1 RB solutions. Regression analyses resulted in a statistically significant quadratic model (R2=0.9718, F=24.96, p<0.0001) by which the optimum levels of the variables were predicted as: MWCNTs dosage of 0.7 mg, pH=3, clouding time of 39.9 minutes and TX-100 concentration of 19.91% (v/v). The predicted conditions were experimentally validated by achieving an RB removal of 94.24%. Based on the results, the combination of the environmentally friendly technique of CPE with adsorption onto MWCNTs allows the efficient removal of RB from water samples and the method can be effectively optimized by the response surface modeling.