No full-text available
To read the full-text of this research,
you can request a copy directly from the author.
Adsorption of Reactive Dye Onto Carbon Nanotubes: Equilibrium, Kinetics and Thermodynamics
Abstract
The adsorption efficiency of carbon nanotubes for Procion Red MX-5B at various pHs and temperatures was examined. The amount adsorbed increased with the CNTs dosage; however, the adsorption capacity initially increased with the CNTs dosage (<0.25 g/l) and then declined as the CNTs dosage increased further (>0.25 g/l). The linear correlation coefficients and standard deviations of Langmuir and Freundlich isotherms were determined and the results revealed that Langmuir isotherm fitted the experimental results well. Kinetic analyses were conducted using pseudo first- and second-order models and the intraparticle diffusion model. The regression results showed that the adsorption kinetics were more accurately represented by a pseudo second-order model. Changes in the free energy of adsorption (DeltaG degrees ), enthalpy (DeltaH degrees ) and entropy (DeltaS degrees), as well as the activation energy (E(a)) were determined. DeltaH degrees and DeltaS degrees were 31.55 kJ/mol and 216.99J/molK, respectively, at pH 6.5 and 41.47 kJ/mol and 244.64 J/molK at pH 10. The activation energy was 33.35 kJ/mol at pH 6.5. DeltaH degrees, DeltaG degrees and E(a) all suggested that the adsorption of Procion Red MX-5B onto CNTs was by physisorption.
... The application of CNTs as absorbents to highly remove dyes has been shown in many studies. At various pH levels and temperatures, Adsorption of Procion Red MX-5B, a reactive dye, on carbon nanotubes was studied by Wu et al. (2007) [17]. Multi-walled carbon nanotubes were utilized to extract morin and alizarin red S from wastewater, according to Ghaedi et al.'s 2011 research [18]. ...
... The application of CNTs as absorbents to highly remove dyes has been shown in many studies. At various pH levels and temperatures, Adsorption of Procion Red MX-5B, a reactive dye, on carbon nanotubes was studied by Wu et al. (2007) [17]. Multi-walled carbon nanotubes were utilized to extract morin and alizarin red S from wastewater, according to Ghaedi et al.'s 2011 research [18]. ...
In the current investigation, functionalization of the multiwalled carbon nanotubes (MWCNTs-TMD) is conducted to enhance the adsorption potential applications. A ratio of 1:3 of the oxidizing acids (HNO 3 and H 2 SO 4) is used to attach the oxygen functional groups to the surface of MWCNTs and the prepared sample is F-MWCNT. To examine the surface morphology of the functionalized tubes in the prepared samples, transmission electron microscopy and scanning electron microscopy were utilized. Meanwhile, energy dispersive X-ray, and X-ray diffraction analysis were employed to account for the elemental composition and structure, respectively. The data obtained from these investigations revealed a notable decrease in the length and diameter of the func-tionalized tubes. The adsorption efficiency of F-MWCNTs was examined by methylene blue removal from aqueous solutions. The results demonstrated that the removal percentage of F-MWCNTs could reach 80%. Functionalized MWCNTs have greater surface area than the pristine one, which improves the efficiency of MWCNTs-based filters for water purification. The functionalization process provides an effective approach to modify MWCNTs and significantly enhances their adsorption efficiency.
... Approximatively, the total elimination percentage for MB and MO dyes at pH 7 and 25 °C is attained after ~50 and 180 min, respectively. The results showed that the used sample yielded higher values than those previously noted for metal-oxide-based adsorbents [47][48][49][50], demonstrating the effectiveness of the used technique in enhancing the dye removal performance. ...
... Approximatively, the total elimination percentage for MB and MO dyes at pH 7 and 25 • C is attained after~50 and 180 min, respectively. The results showed that the used sample yielded higher values than those previously noted for metal-oxide-based adsorbents [47][48][49][50], demonstrating the effectiveness of the used technique in enhancing the dye removal performance. ...
In this study, anodic aluminum oxide membranes (AAOMs) and Au-coated AAOMs (AAOM/Au) with pore diameters of 55 nm and inter-pore spacing of 100 nm are used to develop ZnO/AAOM and ZnO/ZnAl2O4/Au nanoarrays of different morphologies. The effects of the electrodeposition current, time, barrier layer, and Au coating on the morphology of the resultant nanostructures were investigated using field emission scanning electron microscopy. Energy dispersive X-ray and X-ray diffraction were used to analyze the structural parameters and elemental composition of the ZnO/ZnAl2O4/Au nanoarray, and the Kirkendall effect was confirmed. The developed ZnO/ZnAl2O4/Au electrode was applied to remove organic dyes from aqueous solutions, including methylene blue (MB) and methyl orange (MO). Using a 3 cm2 ZnO/ZnAl2O4/Au sample, the 100% dye removal for 20 ppm MB and MO dyes at pH 7 and 25 °C was achieved after approximately 50 and 180 min, respectively. According to the kinetics analysis, the pseudo-second-order model controls the dye adsorption onto the sample surface. AAOM/Au and ZnO/ZnAl2O4/Au nanoarrays are also used as pH sensor electrodes. The sensing capability of AAOM/Au showed Nernstian behavior with a sensitivity of 65.1 mV/pH (R2 = 0.99) in a wide pH range of 2–9 and a detection limit of pH 12.6, whereas the ZnO/ZnAl2O4/Au electrode showed a slope of 40.1 ± 1.6 mV/pH (R2 = 0.996) in a pH range of 2–6. The electrode’s behavior was more consistent with non-Nernstian behavior over the whole pH range under investigation. The sensitivity equation was given by V(mV) = 482.6 + 372.6 e−0.2095 pH at 25 °C with R2 = 1.0, which could be explained in terms of changes in the surface charge during protonation and deprotonation.
... If a linear plot passing through the origin is obtained, it is presumed that adsorption occurs solely through intraparticle diffusion. If a linear graph is obtained that does not pass through the origin, the process is controlled by two or more steps 59,60 . The graphs obtained in this study show linear relationships that do not intersect at the origin. ...
More than 70% of the potash fertilizer globally is produced by the froth flotation process, in which 4-dodecylmorpholine (DMP) serves as a reverse flotation agent. As the potash fertilizer production rapidly rises, the increased DMP levels in discharged brine pose a threat to the production of high-value chemicals. In this paper, composite particles of basic magnesium sulfate@TiO2 (BMS@TiO2) were prepared using a simple and mild loading method. These particles were utilized for the adsorption and photocatalytic degradation of DMP in brine. Compared with normal powdered materials, the granular BMS@TiO2 in this study can be easily separated from liquid, and the degradation intermediates will not enter the brine without causing secondary pollution. BMS@TiO2 consists of 5·1·7 phase (5Mg(OH)2·MgSO4·7H2O) whisker clusters embedding 2.3% TiO2. The adsorption equilibrium of DMP on BMS@TiO2 particles was achieved through hydrogen bonding and pore interception with the adsorption capacity of approximately 5 mg g⁻¹ after 6 h. The photodegradation efficiency of DMP adsorbed on BMS@TiO2 reached about 92% within 16 h, which is compared with that of pure TiO2 nanoparticles. Additionally, excellent stability and recyclability of BMS@TiO2 were also observed in five cycle tests of adsorption and photocatalytic degradation of DMP, and the possible photocatalytic degradation pathways and mechanism of DMP are proposed following molecular electrostatic potential analysis. This work provides a sustainable and environmentally friendly approach for eliminating organic micropollutants from water environments.
... When the F-ions were either simple to adsorb or there were some challenges, the scale of variation in 1/n, with a value ranging from 0.5 to 0.56, became apparent, accelerating with an increase in reaction temperature. Moreover, a value of 1/n below unity in this study implies the occurrence of the chemisorption process (Wu, 2007). Temkin isotherm model, specifically takes adsorbing speciesadsorbent interactions into account. ...
The study aimed to investigate the defluoridation capacity of nano-hydroxyapatite (HAP) [Ca10(PO4)6(OH)2] and alum-doped hydroxyapatite (AHAP) [Ca8Al(PO4)6.(OH)2] as an environmental friendly adsorbent. The physicochemical characteristics of both the material (HAP and AHAP) were examined using XRD, FE-SEM-EDS, and BET techniques. The batch adsorption study revealed a fluoride removal efficiency of up to 83% (AHAP) and 74% (HAP) under acidic conditions (pH-2). The doping of alum alters the surface chemistry and enhances the affinity of AHAP for fluoride adsorption. The pseudo-second-order kinetic (R²–0.9941) and Langmuir isotherm (R²–0.9425) models best describe the adsorption mechanism and behavior. The thermodynamic analysis indicated the spontaneous and endothermic nature of the adsorption process. The study also tested the applicability of the artificial neural network (ANN) modeling approach using MATLAB R2013a to simulate the simulated absorptive efficiency of AHAP. This study suggests that AHAP proved an effective adsorbent for defluoridation.
... The increase in values of ΔG with the increase in temperature indicates that the adsorption process is more favorable at lower temperature. Moreover, the value of ΔG for physical adsorption lies between 0 and 20 kJ/mol, while the chemical adsorption ranges from 80 to 400 kJ/mol [40,46]. The results obtained indicate a physical adsorption of AS onto synthesized polymeric adsorbents. ...
This article presents styrene–divinylbenzene copolymers that contain aminophosphinic acid groups, used to remove acetylsalicylic acid (AS). The chemically modified copolymers were obtained using phenylphosphinic acid and propylamine (AAP1), benzylamine (AAP2) and, respectively, butylamine (AAP3) by the “one-pot” Kabachnik–Fields synthesis. The obtained adsorbents were characterized by FT-IR spectroscopy, thermogravimetric analysis, SEM/EDX analysis and statistical modeling of the repetitive unit. The weight loss of the samples, when analyzed in a nitrogen atmosphere and at 800 °C, was the following: AAP1: 58.71%; AAP2: 59.52%; and for AAP3: 59.66%. The adsorption process at equilibrium was modeled by the Langmuir, Freundlich, Sips and Redlich–Peterson adsorption isotherms. The maximum adsorption capacity given by the Langmuir isotherm was influenced by the amine used in the synthesis of sorbent. The best results were obtained at 298 K, with a maximum adsorption capacity of 0.236 mmol/g (42.52 mg/g) on the copolymer AAP1. The adsorption process was fast, over 85% of the maximum adsorption capacity being achieved in the first 4 h. The adsorption of AS on the studied adsorbents is an exothermic and thermodynamically favorable process.
Graphical abstract
... Regarding its magnitude, values for ΔH° above 40 kJ mol −1 characterize adsorption of a chemical nature, while values between 0 and 40 kJ mol −1 represent physical adsorption heats. 134 The thermodynamic parameters mentioned above can be obtained from the Van't Hoff model (Eqn 11). The variation Determination of the thermodynamic parameters (ΔG°, ΔH° and ΔS°) is dependent on the thermodynamic equilibrium (K C ). ...
Recently, the development of techniques to produce detoxified biocompounds has attracted much research interest. This study reviews adsorbents for application in the purification and detoxification of biocompounds, aiming to identify the field's knowledge gaps, trends, updates and hotspots. This review focuses on the description of the types of adsorbents (activated carbon, zeolites, clays, clay minerals and biosorbents) and their activation methods (chemical and physical) for laboratory and industrial adsorption. The adsorbents that stand out are activated carbon and chitosan‐based adsorbents. Moreover, there is a research trend toward using adsorbents to purify bioactive compounds, sugars and amino acids. Finally, adsorbents underscore a growing global research interest in exploring effective treatments for removing various combinations.
... Both K id and I values are listed in table 6. Applying this model to our adsorbate-adsorbent systems, the linear plots do not pass through the origin indicating that the Intraparticle diffusion model is not the sole rate controlling step. similar results were also observed in the literature [49]. (14) Where, K c is equilibrium constant, R is gas constant and T is absolute temperature. ...
In the present investigation the adsorption behavior of methylene blue (MB) dye from aqueous solution onto untreated chinar leaves powder (CLP) and chinar leaves biochar (CLB) has been studied. To find out optimum conditions, adsorption process was carried out by varying different parameters such as contact time, adsorbent dose, concentration, temperature, salts, and pH. The equilibrium adsorption data were subjected to different popular isotherms (Langmuir, Freundlich, and Temkin) and kinetic models (pseudo-first order, pseudo-second order and intra-particle diffusion model). The thermodynamic study was also done on the adsorption process. The maximum monolayer adsorption capacities for MB dye onto given adsorbents are 1.53 mg/g (CLP) and 1.02 mg/g (CLB). Also the values of R L and n suggest favourable adsorption process of MB dye onto CLP and CLB adsorbents. The pseudo-second order kinetic model is best obeyed by both the mentioned adsorbents for MB dye adsorption with R 2 value equal to 1. Thermodynamic study reveals that the adsorption process of MB dye is spontaneous, endothermic (CLB) and exothermic (CLP). At an equilibrium time of 20 min the uptake efficiency (> 99%) was recorded for both the low cost adsorbents (CLP and CLB) thus proved them fast and effective adsorbents for the removal of MB dye.
... A study of the effect of temperature, was conducted for the adsorption of the adsorbents under study on the surface of activated carbon, the obtained results were included in tables (11) and at the (pH Natural ), shaking time (60) min, weight of activated carbon samples (0.1) gm, constant speed (90) cycle/min. The results contained in Table ( 11) can be discussed according to the following points: 1-In general, at a fixed concentration, we notice that increasing the temperature of the adsorption medium from (298-338) K leads to a decrease in the adsorption efficiency and adsorption capacity (qe) and regardless of the nature the material the adsorbent, as the increase in temperature leads to an increase in the process of returning particles of the adsorbed substance from the adsorbent surface to the solution (Desorption) [20] ; Because of the breaking of the forces that link the adsorbent and the adsorbent surface, and this indicates that the adsorption process is a heat-emitting process (Exothermic) [21] , which indicates the physical nature of adsorption in the studied system, and this statement applies exactly to Le Chalet's rule [14] , It has been observed that the temperature (298) Kelvin is the best temperature for adsorption, and this is confirmed by previous studies [1,22] . 2-At a constant concentration and a constant temperature, we notice a difference in the efficiency and adsorption capacity of the materials under study. ...
... As a result, the reactions between dye molecules and CNTs are more efficient, resulting in increased interaction across the surface area and an increase in adsorbent performance [214]. The adsorption capabilities of carbon nanotubes for different dyes are shown in Table S1 [215][216][217][218][219][220][221][222][223][224][225][226][227][228][229][230]. Regarding the most used dyes, malachite green and methylene blue, carbon nanotubes adsorbed 13.95 and 188.68 mg/g, respectively, in normal pH conditions [215,217]. ...
The demand for energy has increased tremendously around the whole world due to rapid urbanization and booming industrialization. Energy is the major key to achieving an improved social life, but energy production and utilization processes are the main contributors to environmental pollution and greenhouse gas emissions. Mitigation of the energy crisis and reduction in pollution (water and air) difficulties are the leading research topics nowadays. Carbonaceous materials offer some of the best solutions to minimize these problems in an easy and effective way. It is also advantageous that the sources of carbon-based materials are economical, the synthesis processes are comfortable, and the applications are environmentally friendly. Among carbonaceous materials, activated carbons, graphene, and carbon nanotubes have shown outstanding performance in mitigating the energy crisis and environmental pollution. These three carbonaceous materials exhibit unique adsorption properties for energy storage, water purification, and gas cleansing due to their outstanding electrical conductivity, large specific surface areas, and strong mechanical strength. This paper reviews the synthesis methods for activated carbons, carbon nanotubes, and graphene and their significant applications in energy storage, water treatment, and carbon dioxide gas capture to improve environmental sustainability.
... The plot of thermodynamics study (Experiment conditions: m = 0.06 g, C i = 100 mg.L −1 , pH = 7, t = 60 min, and T = 25-55 ˚C) passes through the origin, then the adsorption process is controlled only by penetration into the particles. If the data show a multi-line plot, two or more steps will be effective in the absorption process (Ai et al., 2011;Kannan & Sundaram, 2001;Rastgordani & Zolgharnein, 2021;Wu, 2007;. According to Fig. 5, by plotting q t versus t 1/2 for IC, a multi-line plot is obtained. ...
Polyethylene glycol-modified hydroxyapatite nanoparticle was employed as a new and effective adsorbent for the removal of indigo carmine dye from an aqueous solution. The synthesized adsorbent was characterized by X-ray diffraction (XRD), Fourier transformation infrared spectroscopy (FTIR), energy-dispersive X-ray spectroscopy (EDX), and field-emission scanning electron microscopy (FESEM). In addition, the effects of factors such as pH, temperature, dye concentration, time, and amount of adsorbent on the removal efficiency or adsorbent capacity were investigated. The pH, temperature, and concentration (C) of dye solution positively affect q while the temperature and adsorbent dosage (m) negatively affects q. For R%, the m and C effects are inverse. With the increase of pH, the amount of electrostatic attraction between the adsorbent surface and dye increases. It will lead to an increase in dye adsorption. The optimum conditions were obtained as t = 60 min, pH = 7, T = 25˚C, m = 0.06 mg, and C = 700 mg˖L⁻¹. To study the equilibrium behavior of adsorbent-adsorbate interaction, Langmuir, Freundlich, Sips, Dubinin-Radushkevich, and Temkin isotherms were considered. Experimental data were well described by Sips with R² = 0.9927. The maximum adsorption capacity (qmax) of the Sips model was 129.3 (mg.g⁻¹). The kinetic experimental data obey the pseudo-second-order model (R² = 0.9989). Based on the negative value of thermodynamic parameters including ∆H°, ∆S°, and ∆G°, the adsorption process is exothermic and spontaneous chemisorption at various temperatures (298, 308, 318, and 328 K). Based on the effect study of the presence of Mg²⁺, Ca²⁺, K⁺, and Na⁺ ions on the removal efficiency of indigo carmine dye, the adsorption capacity decreases with increasing salt concentration, especialy for the + 2 charged ions. Furthermore, the desorption of indigo carmine dye from the modified hydroxyapatite nanoparticles was evaluated with NaOH, HCl, HNO3, and CH3COOH. Also, indigo carmine removal by this adsorbent from tap water was investigated in comparison with laboratory conditions.
... The adsorption rate was higher in the initial phase of the reaction due to the available binding surfaces on the adsorbent. Later, the increase in adsorption rate was less due to the repulsive forces of the dye molecules (Wu 2007, Yao et al. 2011). ...
Herein, we prepared the silica nanoparticles (SiO2 NPs) by a modified Stober's method for methyl orange (MO) removal. The SiO2 NPs were found to be spherical with a zeta size of 152.5 d. nm, a PDI of 0.377, and a zeta potential of -5.59 mV. The effect of different parameters (initial dye concentration, reaction time, temperature, and pH) on the adsorption of MO by SiO2 NPs was determined. The adsorption pattern of SiO2 NPs was highly fitted with the Langmuir, Freundlich, Redlich-Peteroen, and Temkin isotherm models. The highest adsorption rate was recorded at 69.40 mg/g of SiO2 NPs. Furthermore, the toxic effect of before and after removal of MO in aqueous solution was tested in terms of phytotoxicity and acute toxicity. The SiO2 NPs treated MO dye solution were not exhibited significant toxicity to corn seeds and Artemia salina. These results indicated that SiO2 NPs can be used for the adsorption of MO.
... Areas vs. their primary materials CNTseACF composites, CNTseFe 3 O 4 composites, CNTsedolomite composites, CNTsecellulose composites, and CNTsegraphene composites are examples of these composites. Also, by reducing aggregate formation the adsorption capabilities of CNTs can be improved by making them more hydrophilic in character, that results in the highest selectivity for the adsorption of ionic species from aqueous media due to the presence of oxygen-containing groups at the surface [108]. ...
Organic dyes, a class of highly poisonous and carcinogenic chemicals that pose serious health risks to humans and aquatic life, are the most prevalent organic pollutants found in wastewater from sectors such as textiles, rubber, and cosmetics. Organic dyes, a class of highly poisonous and carcinogenic chemicals that pose serious health risks to humans and aquatic life, are the most prevalent organic pollutants found in wastewater from sectors such as textiles, rubber, and cosmetics. This review compares and contrasts several dye removals processes. Adsorption has proved to be a quick and efficient way to get colours out of wastewater. This research focuses on the most recent developments in porous materials for organic dye adsorption. Dyes were used to color food and other industrial items, textiles, plastics, cosmetics, and tannery. Non-ionic dyes, cationic dyes (basic dyes), and acid dyes are the three types of dyes (dispersed dyes). The process of removing dyes from sewage from industry has become increasingly essential from an environmental standpoint. In an aqueous system, cationic dyes have a net positive charge due to their sulphonate groups, while anionic dyes have a net negative charge. To avoid contamination of the aquatic environment, these waste dyes must be handled first. This dye’s aromatic composition offers it increased dura-bility and makes it tough to decompose. Color wastes were removed from waste water via oxida-tion, electrochemistry, coagulation, solvent extraction, photocatalytic degradation, ozonation, and adsorption, among other ways. However, the adsorption process is more advantageous than other ways. As a result of its ease of use, high effectiveness, simple design, easy availability of adsorbents, and most importantly, its low cost. Different porous materials’ properties, functionalization, and modification are also discussed. Also discussed are the adsorption behaviors and mechanisms of these adsorbents in the adsorption of organic dyes. Finally, future research challenges and oppor-tunities in the development of innovative materials for very efficient dye removal are suggested.
... Equation ( K F , n: the freundlich constants being indicators of the adsorption capacity and adsorption intensity, respectively [124]. ...
In this study magnetic nanoparticles were prepared in two forms, the first is Ni1-xCoxFe2O4 and the second is Ni1-xMgxFe2O4 for the x values, (x= 0.0,0.1,0.3,0.5,0.7 ) respectively by chemical co-precipitation thermal method and annealed at temperature of (700 oC ) and pH=11.
The structural properties of the prepared samples were studied by using the energy-dispersive X-ray spectroscopy EDX, the scanning electron microscope, the XRD spectroscopy, and the Fourier transforms Infra-red of the FT-IR infrared spectrometer. The synthetic results showed that the prepared particles possess practical proportions that correspond largely to the theoretical proportions, which means the validity of the proposed structures and all the samples show nearly perfect stoichiometry and high purity. This is what is observed from the EDX measurements. The SEM analysis reveals the increasing proportion of cobalt and magnesium for both compounds, and that the particles had spherical and irregular geometric structures within sizes that were often greater than 100 nm. The powder XRD pattern confirms a single-phase cubic spinel structure and the average particle size calculated via the Scherrer equation ranged between (16.31-29.53) nm. Based on X-ray diffraction, information were very close to those recorded using microscopy SEM, and the FTIR spectra confirmed two peaks (ν1 and ν2) around 400 and 600 cm-1, respectively. These bands are attributed to the stretching vibration of interactions between the oxygen atom and the cations in tetrahedral and octahedral sites. Therefore, bands indicate that the spectral composition of all samples is ferrite.
The magnetic properties of the particles through the VSM test showed that the addition of cobalt and magnesium to the NiFe2O4 was improved the magnetic properties of the main ferrite with a good to high ratio from the narrowness of the hysteria loop give the characteristics of a soft ferrite.
The work presented in this thesis focused on the efficient use of magnetic nanoparticles in water treatment processes. It involves choosing the best two samples of prepared magnetic nanoparticles from each mixture based on their structural and magnetic properties for use in the removal of lead and cadmium ions from aqueous solution under laboratory conditions. The Go- 2(N-morpholino ethanesulfonic acid) was used to prepare novel magnetic adsorbents by mixing with the best four ferrites. Among these four nanoparticles are com.1 (GO- 2(N-morpholinoethansulfonic acid)- Ni0.9Co0.1Fe2O4), com.2 (GO- 2(N-morpholinoethansulfonic acid)- Ni0.5Co0.5Fe2O4), com.3 (GO-2(N-morpholinoethansulfonic acid)- Ni0.7Mg0.3Fe2O4), and Com.4 ( GO-2(N-morpholinoethansulfonic acid)- Ni0.5Mg0.5Fe2O4 ).
After determining the optimal concentration of lead and cadmium, The following optimal conditions were studied: contact time, adsorbent quantity, acidity, and temperature. The optimal concentration was (100 ppm) for all conditions except composite 4, where the removal of lead ions was (250 ppm).
Through the experiments, it was observed that with an increase in the contact time, pH, the dosage, and temperature, the percentage of removal of lead and cadmium ions increased from the aqueous solution. Among the four magnetic nanoparticles, results showed that the (com2) and (com4). Gave the best percentage of removal of lead and cadmium ions from the aqueous solution. The kinetic results of adsorption showed that the adsorption of lead and cadmium ions by the magnetic nanoparticles surfaces followed a pseudo-second order equation based on the values of (R2) and from studying the isotherms of Freundlich, Langmuir, and Temkin models of the four compounds. The results show the Freundlich isotherm is the ruling isotherm in these materials, as it was perfectly suitable for all adsorption cases despite the relatively few differences with the (R2 ) values for the rest of the isotherms. This confirms that the adsorption was of a heterogeneous type. The approaches and treatment methods described in this thesis are simple to use, robust and environmental friendly.
... The slower rate of removal at the later stages can be accredited to the diffusion of the dyes into the inner part of the adsorbent since the external surface has been occupied by the molecules of the dye [2]. Once equilibrium is attained, there was no further increase since the remaining vacant sites are difficult to occupy probably due to the repulsive forces between the molecules on the adsorbents and the bulk phase [23,24] . ...
... The equilibrium distribution of solutes between the liquid and solid phases can best be described by the adsorption isotherms, for which various models such as e.g. B. Langmuir [36], Freundlich [37], Temkin [38], Radke-Prausnitz and Fritzschlunder [39] and compared the obtained data with these generalized and nonlinear isotherm fitting curves studied for the above-mentioned adsorption isotherm models (Fig. 5). The Langmuir model proposes monolayer adsorption with no mutual effects between the adsorbed species. ...
The current study was aimed at elucidation of the adsorption properties of Amberlite IRA-68 resin for vanadium ions in
aqueous media. We investigated the effect of different parameters such as contact time, pH, initial concentration,
temperature, and adsorbent dosage on the uptake rate of vanadium. The findings showed that the equilibrium data were best
fitted by the Freundlich isotherm, and the maximum adsorption capacity of the resin was 211.5 mg g-1 at 50 °C. The best
possible pH for adsorption was 4.5. The first, and second-order reaction models and the Weber-Morris model were applied to
the kinetics data. Among them, the best fitting was obtained by the second-order model. The rate-controlling step at the onset
of the uptake was liquid film resistance, which gradually changed to intraparticle diffusion. Thermodynamic study revealed
that adsorption was endothermic and spontaneous. The Amberlite IRA-68 resin could preserve more than 95% of its capacity
after 8 cycles of adsorption/desorption.
Keywords: Vanadium adsorption, Amberlite IRA-68, Kinetics, Isotherm, Thermodynamic
دراسة اتزان وحركية وثرموداينميكية لامتزاز عدد من المبيدات على سطح الفحم المنشط المحضر والتجاري
Printing and dyeing wastewater, that is discharged after textile printing and dyeing processing, can cause irreversible damage to the aquatic ecosystem and harm the health of human beings. Till now, completely and readily removing dye molecules from industrial wastewater using a single catalyst rather than the combination of several materials remains a significant challenge. Herein, in situ preparation of carbon nanotube membranes (N‐CNTM and N‐TiO 2 ‐CNTM) are reported that are doped using N with/without TiO 2 , respectively. These membranes can simultaneously function as an adsorber, a photo‐catalyst, and an electrocatalyst to efficiently remove dye pollutes from industrial waste water. Further researches reveal that the formation of p‐n type heterojunction inside of the N‐CNTM and N‐TiO 2 ‐CNTM, can improve the hole separation and charge storage abilities, resulting in the efficient removal of dyes in the industrial waste water. This work provides a promising approach for the preparation of functionalized carbon nanotubes derived from waste biomass for the treatment of industrial water, reflecting the concept of treating waste with waste.
Adsorption and photocatalytic decolorization methods were used to remove Reactive Orange 16 dye from textile wastewater by using ethyleneglycoldimethacrylate and 1-vinyl-1,2,4-triazole, m-poly(EGDMA-VTA)-TiO2 polymer composite particles with magnetic synthesized by suspension polymerization. The characterization of the synthesized m-poly(EGDMA-VTA)-TiO2 particules were carried out by using XRD, FTIR, SEM–EDS-elemental mapping, ESR, and BET analyses. Both adsorption and photocatalytic decolorization processes of RO16 dye were applied to the polymer particles. The effects of solution pH, amount of adsorbent, initial dye concentration, temperature, and time on the adsorption capacity were investigated. The removal of R016 dye reached a maximum at pH 3. Dye substance removal decreased due to increasing temperature and adsorbent amount. As a result of experimental studies, the adsorption of RO16 dye was explained by the Langmuir isotherm, while its kinetics was stated by a pseudo-second-order mechanism. Additionally, thermodynamic functions (ΔHo, ΔGo, and ΔSo) have been determined. At the end of adsorption, the decolorization kinetics were elucidated by examining the adsorbent amount, time, and dye concentration parameters for the photocatalytic decolorization of non-adsorbed dyes. It was determined that the photocatalytic activity was highest at low dye concentration and high photocatalyst content. Additionally, it was determined that decolorization kinetics studies were compatible with the Langmuir–Hinshelwood model.
Constructing crystalline covalent organic frameworks (COF) robust 3D reusable macroscopic objects exposing more adsorption sites with high water flux for use as a filter is an unresolved challenge. A simple scalable procedure is shown for making a robust, highly compressible 3D crystalline COF nanowire interconnected porous open‐cell sponge. The compressive strength and Young's modulus (80% strain) of the sponge are 175 and 238 kPa, respectively. The sponge can withstand multiple compression‐release cycles and a load of 2800 times its weight without collapsing. As an exemplary application, the use of a COF sponge in the selective removal and separation of cationic model dye from a mixture of dyes in water by adsorption and filtration with >99% efficiency is shown. Depending on the dye concentration, the dye removal time can be as short as 2 min, and dye adsorption efficiency can be as high as 653 mg g⁻¹ (COF in the sponge). During filtration, the sponges as filters show a high water flux of 2355 L h⁻¹ m⁻² under ambient conditions and maintain their performance for many cycles. The lightweight, reusability, and efficiency make present sponges sustainable materials as adsorbents and filters.
Water treatment is crucial in solving the rising people's appetite for water and global water shortages. Carbon nanotubes (CNTs) have considerable promise for water treatment because of their adjustable and distinctive arbitrary, physical, as well as chemical characteristics. This illustrates the benefits and risks of integrating CNT into the traditional water treatment resource. Due to their outstanding adsorbent ability and chemical and mechanical properties, CNTs have gained global consideration in environmental applications. The desalination and extraction capability of CNT were improved due to chemical or physical modifications in pure CNTs by various functional groups. The CNT-based composites have many benefits, such as antifouling performance, high selectivity, and increased water permeability. Nevertheless, their full-scale implementations are still constrained by their high costs. Functionalized CNTs and their promising nanocomposites to eliminate contaminants are advised for marketing and extensive water/wastewater treatment.
Water is the most critical component of the earth's ecosystem because it is fundamental to the survival of plants and animals. However, our water supply is continuously polluting. Removing contaminants from water is a crucial part of addressing water scarcity and maintaining a healthy ecosystem for all. This review focuses on adsorption and the CNTs/AC family nano adsorbents and their contribution to the removal of fluoride and other contaminants. Many types of wastewater treatment methods have been employed, including precipitation, ion-exchange, adsorption, membrane filtration, etc. A water technology with great efficiency and low cost, without requiring costly infrastructure, is the most preferred option due to adsorption. Recently, the application of carbon family nanomaterials as adsorbents has been prevalent due to their phenomenal surface properties, simple customization, immense specific surface area, numerous variations in structural type, chemical stability, porosity, low density, ease of regeneration, and the ability to be reused. Hazardous contaminants, such as fluoride, generate major public health risks. Water contamination by heavy metals provides a significant health concern, including an increased chance of getting diseases like cancer, anaemia, carcinogenic effects, and acute effects in children. The increased presence of fluoride in water could cause fluorosis, joint pain, severe anaemia, and other problems. The following review focuses on current findings regarding the utilisation of CNTs and AC nanoparticles in the elimination of harmful contaminants and fluoride.
Cellulose nanocrystals (CNC) were obtained by series of chemical treatments on dried and grounded sugarcane bagasse. Particle size analysis and X-ray diffraction (XRD) studies were done which confirmed the crystalline behavior of prepared nanocellulose. Nanocomposite adsorbent was prepared by using CNC as filler, chitosan as a binder, and N, N-methylenebisacrylamide (MBA) as cross-linker in different ratios. Field emission scanning electron microscope (FESEM) showed the porous structure of the composite. Fourier transform infrared spectroscopy (FTIR) confirmed crosslinking between CNC and chitosan, contact angle results showed hydrophilic behavior of nanocomposite, and tensile strength testing confirmed good strength of prepared nanocomposite. Malachite green (MG) dye adsorption capacity of nanocomposite adsorbent for different initial dye concentrations was studied and results depicted a maximum removal rate in the first 30 min which reached equilibrium in 90 m. The highest removal rate was observed with 5.0% CNCs content in the nanocomposite. The experimental data showed the best-fitted correlation with Freundlich isotherm (R² = 0.99) and follow a pseudo 2nd order reaction (R² = 0.93) by enabling the chemisorption adsorption phenomenon. The regeneration capacity of the nanocomposite was also analyzed, and it was observed that about 90% of the dye was removed from the pre-adsorbed nanocomposite material.
The sorption kinetics of two of the most frequently used antibiotics onto recycled (weathered) polyvinyl chloride (PVC) was investigated, using Freundlich and Langmuir isotherm models. Various experimental conditions were set, including pH, contact time, rotational speed, temperature, and initial concentration. The batch experimental results indicated that Freundlich model was better fitted than Langmuir (R2: 98.7 and 84.7, for CIP and CLA respectively). Maximum adsorption capacity is 45.9 mg/g and 22.0 mg/g for CIP and CLA, respectively. Enthalpy (ΔH), and entropy (ΔS) values were negative for CIP, indicating that the reaction was exothermic and spontaneous, respectively. It was vice versa for CLA. Field emission scanning electron microscope (FESEM) and Fourier transform infrared spectrometer (FT-IR) analysis confirmed the physical adsorption mechanism. The results demonstrated that the recycled PVC microplastic has a good capacity for adsorption for both antibiotics.
Over the past century, the scarcity of pure drinking water has increased worldwide, and due to the overwhelming rise in demand the situation could be exacerbated in coming days. To alleviate this global issue, several technologies for purifying water have been developed which are limited by certain factors. Therefore, research interests in nanomaterials-based water purification technologies are growing to tackle water scarcity. Among the various proposed methods and nanomaterials, carbon nanotubes (CNTs) and functionalized CNTs are superior to water purification and treatment processes due to configurable properties such as high surface area, high reactivity, lower cost, and less adverse effects on the environment. This review introduces most of the CNTs and functionalized CNTs-based water purification and treatment technologies and the challenges associated with these applications. The comparative studies among these methods are also be discussed to help researchers bring novel CNTs-based efficient technologies in the near future for a sustainable world.
Water quality is deteriorating continuously as increasing levels of toxic inorganic and organic contaminants mostly discharging into the aquatic environment. Removal of such pollutants from the water system is an emerging research area. During the past few years use of biodegradable and biocompatible natural additives has attracted considerable attention to alleviate pollutants from wastewater. The chitosan and its composites emerged as a promising adsorbents due to their low price, abundance, amino, and hydroxyl groups, as well as their potential to remove various toxins from wastewater. However, a few challenges associated with its practical use include lack of selectivity, low mechanical strength, and solubility in acidic medium. Therefore, several approaches for modification have been explored to improve the physicochemical properties of chitosan for wastewater treatment. Chitosan nanocomposites found effective for the removal of metals, pharmaceuticals, pesticides, microplastics from the wastewaters. Nanoparticle doped with chitosan in the form of nano-biocomposites has recently gained much attention and proven a successful tool for water purification. Hence, applying chitosan-based adsorbents with numerous modifications is a cutting-edge approach to eliminating toxic pollutants from aquatic systems with the global aim of making potable water available worldwide. This review presents an overview of distinct materials and methods for developing novel chitosan-based nanocomposites for wastewater treatment.
H1.6Mn1.6O4 lithium-ion sieve with spinel structure was successfully prepared by hydrothermal, high-temperature calcination and ion exchange reaction. XRD, SEM, TEM, N2 ad/desorption and FTIR methods were employed to characterize the microstructure and morphology of the synthesized materials in detail. The experimental results show that H1.6Mn1.6O4 has the characteristics of mesoporous structure and nanotube morphology with length of ∼ 10 μm and diameter of 500–700 nm, and the spiny structure was grown on the surface of the nanotube uniformly. The effect of Al³⁺ doping on the structure and morphology of H1.6Mn1.6O4 was studied. The results show that Al³⁺ doping does not change the microstructure and morphology of H1.6Mn1.6O4, but the specific surface area and pore volume are increased to a certain extent. H1.6Mn1.6O4 and H1.6Mn1.6−xAlxO4 were used as lithium-ion adsorbents to study the adsorption properties of Li⁺ in solution. The adsorption experiment results show that the adsorption capacity of H1.6Mn1.6O4 increased with increasing solution pH value, indicating that the strong alkaline solution with higher pH value is more favorable for Li⁺ adsorption. The adsorption isotherm results show that Li⁺ adsorption process was fitted well by Langmuir model, indicating that Li⁺ maybe adsorbed on the surface of manganese oxides lithium-ion sieves via a monolayer adsorption. The theoretical maximum adsorption capacity of H1.6Mn1.6O4 and H1.6Mn1.6−xAlxO4 can reach 39.54 mg/g and 40.54 mg/g, respectively. The results of adsorption kinetics show that the adsorption rate of both H1.6Mn1.6O4 and H1.6Mn1.6−xAlxO4 is fast, and the adsorption capacity of H1.6Mn1.6−xAlxO4 (24.65 mg/g) is slightly better than H1.6Mn1.6O4 (24.33 mg/g). Li⁺ adsorption process can be well described by the pseudo-second-order model, suggesting adsorption behavior is mainly controlled by chemical sorption. Additionally, the free energy change (ΔGΘ) was determined by Van't Hoff equation is negative, which confirms the adsorption process is spontaneous and feasible. The positive value of ΔSΘ of adsorption reaction reflects there is a certain of affinity between manganese oxides lithium-ion sieves and Li⁺ in solution.
Graphical Abstract
The regular spiny structure on the surface of H1.6Mn1.6O4 nanotube lithium-ion sieve was synthesized. This special morphology not only keeps the nanotube pore structure to increase the adsorption ability and also increases the outer surface area to accelerate the Li⁺ diffusion speed without any substrate.
Manganese dioxide nanomaterials with high crystallinity and purity was prepared quickly by a simple hydrothermal reaction, and the effect of hexadecyl trimethyl ammonium chloride (CTAC) on crystal form, morphology and pore structure of manganese dioxide was investigated. Removal of methylene blue from aqueous solution by adsorption onto two manganese dioxide adsorbents was studied. The material characterization results showed that manganese dioxides have (2×2) tunnel structure and nanowires morphology. BET surface area and pore volume of ɑ‐MnO2 (CTAC) was 58.99 m²/g and 0.2081 cm³/g, respectively. The adsorption results showed that pH value had a certain effect on the removal of methylene blue. The adsorption kinetics results indicated that the adsorption rate of ɑ‐MnO2 and ɑ‐MnO2 (CTAC) to methylene blue was very fast, most adsorption was completed within 5 minutes, and the adsorption equilibrium was reached after 2 hours. The removal efficiency of ɑ‐MnO2 and ɑ‐MnO2 (CTAC) was 71.27 % and 78.92 %, respectively. Pseudo‐second‐order kinetic model was better fitted with adsorption data than pseudo‐first‐order model, suggesting adsorption behavior is controlled by chemical processes. Additionally, the free energy change (ΔGΘ) was determined by Van′t Hoff equation is negative, which confirms the adsorption process is spontaneous and feasible. The adsorption mechanism involves a complex process of electrostatic attraction, charge‐independent adsorption, physical adsorption, hydrogen bonding and redox.
Herein, the BiFeO3 was modified by substituting varying manganese (Mn) concentration to improve the efficacy of eliminating methyl orange (MO), a water-soluble carcinogenic azo dye was presented. To examine the structure, morphology and band gap characteristics of the as-synthesised Mn-BiFeO3 nanocatalyst were characterised using various techniques including XRD, FESEM with EDX, FTIR, UV-vis DRS, and BET. Subsequently, parameters affecting the removal performance, such as adsorbent dosage (0.02–0.10 g), initial dye concentrations (10–60 mg/L), initial pH (1–13), percentage mol of manganese substitution (0–30%), and reusability of the adsorbent, were examined in detail. The specific surface area increases with doping from 6.829 to 13.063 m²/g, leading to enhanced adsorption capacity of manganese-substituted BiFeO3 as opposed to pristine BiFeO3. Adsorption kinetics was found to follow the pseudo-second-order kinetic model, while the adsorption equilibrium data obeyed the Freundlich isotherm model with a maximum adsorption capacity of 25.2 mg/g at 298 K. Interestingly, the catalyst showed more than 95% adsorption even after three consecutive cycles and therefore could be a good candidate for wastewater remediation.
In this article, we reported the micron sized particles of poly (methacrylic acid) (p [MAA]) microgel and explored their applications as anionic adsorbents. The micron sized particles of poly (methacrylic acid) microgel were prepared by a simple inverse suspension polymerization method. The adsorptive elimination of adsorbates of cationic nature including malachite green (MG) and methylene blue (MB) from the aqueous medium was studied systematically. The adsorption tests were carried out using various initial concentrations of dyes and with different amounts of adsorbents. The adsorption equilibrium was established in 60 min. The adsorption capacity of the p (MAA) microgel was found as high as 351 mg/g for MG and 65 mg/g for MB. The maximum removal percentage for MG and MB was recorded as 88 and 68%, respectively. The adsorption data was computed with adsorption isotherm models including Langmuir, Freundlich, and Temkin. The Langmuir model was observed to be more applicable for the adsorption of MG while the adsorption of MB was best matched with Temkin model. The adsorption data was also treated with pseudo first order and pseudo second order kinetic models along with intraparticle diffusion and Elovich models. The pseudo second order kinetic model was most suitable with adsorption of both the MG and MB.
Introduction
Owing to the restoration of hydroxyl groups, cellulose acetate fibers can be dyed with direct dyes. There are some drawbacks in the conventional deacetylation process of cellulose acetate from environmental point of view.
Methods
This process involves high temperature, alkalinity and large volume of effluent. The goal of this work is to improve the dyeing properties of cellulose acetate fabric using an eco-friendly treatment process. In this paper, cellulose acetate fabric was treated with ultraviolet light (UVB) at an air pressure of 1 atm to improve dyeability. Then, the untreated and UV treated fabrics were dyed with direct and disperse dyes. UV treated cellulose acetate fabric showed higher dye adsorption compare to that of untreated cellulose acetate fabric. Five adsorption isotherm models including sold solution, Langmuir, Freundlich, Temkin and BET were applied to determine the adsorption behavior. At all temperatures studied, experimental data were better fitted with the Freundlich and Nernst models for direct and disperse dyes respectively. Thermodynamic parameters such as change in free energy (ΔG0), the enthalpy (ΔH0), and the entropy (ΔS0) were also evaluated.
Results
The calculated thermodynamic values showed that the adsorption of these dyes onto the cellulose acetate fabric was a physical adsorption process and endothermic in nature. These data also implied that the adsorption of direct dye onto cellulose acetate fabric was spontaneous at the experimental temperature range and adsorption of disperse dyes can be spontaneous at higher temperatures. Moreover, the ΔG0 values for the adsorption of disperse dyes onto the UV-treated fabrics were less than those for untreated fabrics suggesting that UV treated fabrics require less external energy.
Conclusion
Among the kinetic models studied, it was found that the pseudo second-order kinetic model was the best model to describe the dye sorption process on the UV treated and untreated cellulose acetate fabrics. The UV treatment led to an improvement in the boundary layer diffusion effect.
In this study, the potential of two adsorbents prepared from Port Jackson (PJ) plant for the removal of Janus Green (JG) and Victoria Blue (VB) dyes from wastewater was investigated. One of the adsorbents was prepared from Port Jackson by employing the plant's leaves in their natural form after washing while the second one was obtained by treating the leaves with concentrated sulphuric acid. The adsorbents were characterized using Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM). Batch adsorption experiments were conducted with different initial concentrations of dyes, adsorbents doses, temperatures and contact times to determine their effects on the process efficiency. Equilibrium isotherm, kinetics and thermodynamics of the processes were also evaluated. The percentage removal of the dyes by the two adsorbents increased with increasing contact time and adsorbent dosage but decreased with increasing temperature. The kinetics parameters obtained were found to follow pseudo-second order model, suggesting that the rate limiting step may be chemisorption. Thermodynamic studies reveal that the adsorption processes were spontaneous and exothermic in nature as evident from the negative values of Gibbs free energy (G 0) and enthalpy (H 0) obtained. The processes were accompanied with decreased randomness as shown in the negative change in entropy (S 0). It can be concluded that the two adsorbents have good potentials for remediating JG and VB dye-contaminated wastewater
Graphene oxide (GO) was a promising adsorbent for the contaminants removal in the wastewater. However, the nanoscale GO with the properties of easy agglomeration and difficult to separate in the solution severely restricted its widespread practical application. Therefore, a monolithic and structured GO bulk was prepared by a 3D printing method and used as adsorbent for the removal of Cu²⁺ ions. The rheological property and printability of the ink, as well as the mechanical property and adsorption capacity of the printed GO bulk were investigated. It was found that the optimal ratio of GO: sodium alginate was 1.5:2.0 with the compressive strength was 6.23 MPa. Batch experiments exhibited that the Cu²⁺ sorption was an endothermic reaction and the maximum adsorption capacity calculated by Langmuir model was 179.32 mg/g at 303.15 K. Kinetics, FTIR and XPS analysis revealed that the mechanism of Cu²⁺ adsorption was mainly a chemical dominated process involving the oxygen functional groups contained in GO and sodium alginate. The desorption and regeneration test results indicated that the printed GO bulk was an ideal adsorbent for heavy metals removal in real applications due to its excellent adsorption capacity and convenient recycling performance.
INTRODUCTION
Deacetylation of cellulose acetate restores hydroxyl groups on the surface of fibers and improves hydrophilicity. From an environmental point of view, the conventional deacetylation process involves alkalinity and large effluent volume. The goal of this work is to introduce a new eco-friendly bio-treatment process.
METHOD
In this study, cellulose acetate fabrics were bio-treated with laccase enzyme. Then, the untreated and bio-treated fabrics were dyed with direct and dispersed dyes. Laccase pretreatment improved color strength (16%) and crocking durability. After bio-treatment, the bending rigidity decreased for the warp (17.8) and weft (10.8) directions. The Freundlich model was the best model to describe the adsorption of direct dye onto the untreated fabric. In contrast, the Langmuir model better described the adsorption behavior of bio-treated fabric.
RESULT
Nernst model was suitable for dispersed dye adsorption. The partition coefficient was increased after laccase treatment. Thermodynamic analysis showed that the dye sorption was endothermic and nonspontaneous.
CONCLUSION
It was also found that bio-treated fabrics require less external energy. All performed experiments approved the efficiency of the deacetylation process, which led to an improvement in dyeing properties.
Abstract
The adsorption of Acid Blue 193 (AB193) onto dodecylethyldimethylammonium (DEDMA)-sepiolite was investigated in aqueous solution in a batch system with respect to contact time, pH and temperature. The surface modification of DEDMA-sepiolite was examined by the FT-IR technique. The pseudo-first-order, pseudo-second-order kinetic models and the intraparticle diffusion model were used to describe the kinetic data and the rate constants were evaluated. The experimental data fitted very well with the pseudo-second-order kinetic model and also followed the simple external diffusion model up to initial 10 min and then by intraparticle diffusion model up to 75 min, whereas diffusion is not only the rate-controlling step. The adsorption capacities of natural sepiolite and DEDMA-sepiolite at pH 1.5 and 20 °C were (1.19 and 2.57) × 10−4 mol g−1, respectively. The above results indicate that DEDMA-sepiolite has around two times higher adsorption capacity than natural sepiolite. The Langmuir and Freundlich adsorption models were applied to describe the equilibrium isotherms and the isotherm constants were also determined. The Freundlich model agrees with experimental data well. The activation energy, change of Gibbs free energy, enthalpy and entropy of adsorption were also evaluated for the adsorption of AB193 onto DEDMA-sepiolite.
Laboratory investigations show that rates of adsorption of persistent organic compounds on granular carbon are quite low. Intraparticle diffusion of solute appears to control the rate of uptake, thus the rate is partially a function of the pore size distribution of the adsorbent, of the molecular size and configuration of the solute, and of the relative electrokinetic properties of adsorbate and adsorbent. Systemic factors such as temperature and pH will influence the rates of adsorption; rates increase with increasing temperature and decrease with increasing pH. The effect of initial concentration of solute is of considerable significance, the rate of uptake being a linear function of the square-root of concentration within the range of experimentation. Relative reaction rates also vary reciprocally with the square of the diameter of individual carbon particle for a given weight of carbon. Based on the findings of the research, fluidized-bed operation is suggested as an efficient means of using adsorption for treatment of waters and waste waters.
In the study, bagasse fly ash (BFA) (generated as waste material from sugar mill), was used as an adsorbent for the removal of Orange-G (OG), and Methyl Violet (MV), from aqueous solution. Batch studies were performed to address various experimental parameters like pH, contact time, adsorbent dose and initial concentration for the removal of these dyes. Effective pH for OG and MV removal were 4 and 9, respectively. Greater percentage of dye was removed with decrease in the initial concentration of dyes, and increase in amount of adsorbent used. Kinetic study showed that the adsorption of dyes on BFA was a gradual process. Quasi-equilibrium reached in 4h. Pseudo-first-order, pseudo-second-order, Bangham and intra-particle particle diffusion models were used to fit the experimental data. Pseudo-second-order rate equation was able to provide realistic description of adsorption kinetics. Equilibrium isotherms were analysed by Freundlich, Langmuir, Redlich–Peterson, Dubnin–Radushkevich, and Tempkin isotherm equations using correlation coefficients and five different error functions. Freundlich equation is found to best represent the equilibrium data for OG-BFA system while Redlich–Peterson equation better fits the data for MV-BFA system. Thermodynamic study showed that adsorption of MV on BFA (with a more negative Gibbs free energy value) is more favoured among the dyes studied. BFA which was used without any pretreatment showed high surface area, pore volume and pore size exhibiting its potential to be used as an adsorbent for the removal of OG and MV.
One kind of adsorbents with high adsorption capacity of anionic dyes was prepared using ionically and chemically cross-linked chitosan beads. A batch system was applied to study the adsorption of four reactive dyes (RB2, RR2, RY2, RY86), three acid dyes (AO12, AR14, AO7) and one direct dye (DR81) from aqueous solutions by the cross-linked chitosan beads. The adsorption capacities had very large values of 1911–2498 (g/kg) at pH 3–4, 30 °C, which were 3.4–15.0 and 2.7–27.4 times those of the commercial activated carbon and chitin, respectively. The Langmuir and Freundlich adsorption models were applied to describe the equilibrium isotherms. The Langmuir model agreed very well with experimental data (R2 > 0.9893). The kinetics of adsorption, the ADMI color value and decolorization efficiency for different initial dye concentrations were evaluated by the pseudo first-order and second-order models. The data agreed very well with the pseudo second-order kinetic model. The adsorption capacity increased largely with decreasing solution pH and adsorbent dosage. The free energy changes ΔG0 for adsorption of anionic dyes in acidic solutions at 30 °C were evaluated. The negative values of ΔG0 indicate overall adsorption processes are spontaneous.
The synthesis and adsorption capacity of carbon nanotubes (CNTs)-iron oxides magnetic composites were investigated. The sample composites exhibited good adsorption capacity for Pb(II) and Cu(II) from aqueous solution. The magnetic composites were synthesized from a suspension of 1.0 g oxidized CNTs in a 300 ml solution of 0.585 g FeCl3 · 6H2O and 0.390 g FeSO4 · 6H2O. at 70 °C under N 2 atmosphere. The powder XRD characterization of the sample composites showed that the magnetic phase formed was maghemite or magnetite. The adsorption of the sample composites was found to be pH dependent.
Activated carbon and chitosan were investigated for the sorption of several dyes. While the sorption on activated carbon was largely independent of the pH, the sorption of dyes on chitosan was controlled by the acidity of the solution. Anionic dye sorption onto chitosan occurred through electrostatic attraction on protonated amine groups. Sorption experiments were focused on dilute solutions and sorption capacities ranged between 200 and 2000 mumol g(-1) for chitosan and between 50 and 900 mumol g(-1) for activated carbon. Since, in most cases, equilibrium was reached within the first 12 hours of contact, sorption kinetics are relatively fast. However, both sorption capacities (sorption isotherms) and kinetics depended on the type of dyes. The attempt to correlate sorption performance to the structure of the dye failed. Sorption kinetics are strongly influenced not only by intraparticle diffusion resistance but also by the affinity of the dye for the sorbent.
Ni-Zn ferrite powders were synthesized by self-propagating high temperature synthesis (SHS) method. X-ray diffraction, TEM
and vibrating sample magnetometry (VSM) were used to characterize the phase composition, microstructure and magnetic properties
of the combustion products. The effect of the combustion temperature (T
c), the major parameter of the SHS process, on particle size, phase composition and magnetic properties of the products was
also studied. The results showed that particle size grew with the increasing combustion temperature. The maximum saturation
magnetization,M
s, increased with combustion temperature indicating the growth of grain size and high degree of ferritization, while residual
magnetization,M
r, and coercive force,H
c, decreased. Compared with other methods, Ni0.35Zn0.65Fe2O4 ferrite powders with improved magnetic properties can be obtained by SHS at 1000°C.
In the present study, natural sepiolite was used as an adsorbent for the investigation of the adsorption kinetics, isotherms and thermodynamic parameters of an acid dye (Acid Blue 193, AB193) from aqueous solution at various pHs, temperatures and concentrations. Two simplified kinetic models, first-order and pseudo-second-order, were used to predict the adsorption rate constants. It was found that the kinetics of the adsorption of AB193 onto natural sepiolite at different operating conditions was the best described by the pseudo-second-order model. The rate parameters of the intraparticle diffusion model for adsorption were also evaluated and compared to identify the adsorption mechanisms. Adsorption isotherms and equilibrium adsorption capacities were determined by the fittings of the experimental data to three well-known isotherm models including Langmuir, Freundlich and Dubinin-Radushkevich (D-R). The results showed that the D-R model appears to fit the adsorption better than other adsorption models for the adsorption of AB193 onto natural sepiolite. The equilibrium constants were used to calculate thermodynamic parameters, such as the change of free energy, enthalpy and entropy.
The effect of carbon nanotubes (CNTs) on the adsorption and the photocatalytic properties of TiO2 (P25) for the treatment of azo dyes, including one monoazo dye Procion Red MX-5B, and two diazo dyes Procion Yellow HE4R and Procion Red HE3B, are investigated by Brunauer–Emmett–Teller (BET) measurement, spectrophotometer, total organic carbon (TOC), high proficiency liquid chromatography (HPLC), Raman spectroscopy (Raman), photoluminescence (PL), electron paramagnetic resonance (EPR) and transmission electron microscopy (TEM) analyses. The results show that compared with activated carbon (AC), CNTs can comparatively better improve the adsorption of the dyes onto P25 due to the strong interaction between P25 and CNTs. Residual TOC in the solutions and the amount of cyanuric acid evolved after degradation both confirm that the adsorption ability of P25 is enhanced by CNTs. CNTs also facilitate the photocatalytic activity of P25 in the degradation of the three azo dyes more efficiently than AC. With PL and EPR analysis, the mechanism of the enhancement of the photocatalytic activity of P25 by CNTs is proposed. The excited e− in conduction band of TiO2 may migrate into CNTs, of which have special structure and the ability for e− transport. Thus, the possibility of the recombination of e−/h+ pairs decreases. Meanwhile, O2 adsorbed on the surface of CNTs may accept e− and form O2−, which also leads to the formation of OH in the system. Therefore, there are more radicals in the system, resulting in the quicker degradation of the dyes.
Carbon nanotubes (CTNs) show exceptional adsorption capability and high adsorption efficiency for lead removal from water. The adsorption is significantly influenced by the pH value of the solution and the nanotube surface status, which can be controlled by their treatment processing. The adsorption isotherms are well described by both Langmuir and Freundlich models. Our results suggest that CNTs can be good Pb2+ adsorbers and have great potential applications in environmental protection.
The kinetics and mechanism of methylene blue adsorption on commercial activated carbon (CAC) and indigenously prepared activated carbons from bamboo dust, coconut shell, groundnut shell, rice husk, and straw, have been studied. The effects of various experimental parameters have been investigated using a batch adsorption technique to obtain information on treating effluents from the dye industry. The extent of dye removal increased with decrease in the initial concentration of the dye and particle size of the adsorbent and also increased with increase in contact time, amount of adsorbent used and the initial pH of the solution. Adsorption data were modeled using the Freundlich and Langmuir adsorption isotherms and first order kinetic equations. The kinetics of adsorption were found to be first order with regard to intra-particle diffusion rate. The adsorption capacities of indigenous activated carbons have been compared with that of the commercial activated carbon. The results indicate that such carbons could be employed as low cost alternatives to commercial activated carbon in wastewater treatment for the removal of colour and dyes.
Titanium dioxide/carbon nanotubes (TiO2/CNTs) composites were prepared with the aid of ultrasonic irradiation. Products of different TiO2:CNTs molar ratio were characterized by X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) adsorption analysis, thermogravimetric and differential thermal analysis (TGA–DSC), photoluminescence (PL) and UV–vis spectroscopy measurements (UV–vis). The photocatalytic activity was evaluated by the degradation of acetone and by the detection of the hydroxyl radical (·OH) signals using electron paramagnetic resonance (EPR). It is found that the crystalline TiO2 is composed of both anatase and brookite phases. The agglomerated morphology and the particle size of TiO2 in the composites change in the presence of CNTs. The CNTs in the composites are virtually all covered by TiO2. Other than an increase of the surface area, the addition of CNTs does not affect the mesoporous nature of the TiO2. Meanwhile, more hydroxyl groups are available on the surface of the composite than in the case of the pure TiO2. The higher the content of CNTs, there is more effective in the suppression of the recombination of photo-generated e−/h+ pairs. However, excessive CNTs also shield the TiO2 from absorbing UV light. The optimal amount of TiO2 and CNTs is in the range of 1:0.1 and 1:0.2 (feedstock molar ratio). These samples have much more highly photocatalytic activity than P25 and TiO2/activated carbon (AC) composite. The mechanism for the enhanced photocatalytic activity of TiO2 by CNTs is proposed.
A novel adsorbent, ceria supported on carbon nanotubes (CeO2-CNTs), was developed for the removal of arsenate from water. The experiments show that CeO2-CNTs is an effective adsorbent for arsenate, and the adsorption is pH-dependent. Ca2+ and Mg2+ significantly enhanced its adsorption capacity, which suggests that it is a promising adsorbent for drinking water purification. Under natural pH conditions, an increase from 0 to 10 mg/L in the concentration of Ca2+ and Mg2+ results in an increase from 10 to 81.9 and 78.8 mg/g in the amount of As(V) adsorbed, respectively. The loaded adsorbent can be efficiently regenerated by diluted NaOH, and a regeneration efficiency of 94% was achieved using 0.1 mol/L NaOH. The adsorption mechanism was also suggested.
The as-grown CNTs and graphitized CNTs were used as adsorbents to remove 1,2-dichlorobenzene from water. The experiments demonstrate that it takes only 40 min for CNTs to attain equilibrium and the adsorption capacity of as-grown and graphitized CNTs is 30.8 and 28.7 mg/g, respectively, from a 20 mg/l solution. CNTs can be used as adsorbents in a wide pH range of 3–10. Thermodynamic calculations indicate that the adsorption reaction is spontaneous with a high affinity and the adsorption is an endothermic reaction.
Aligned carbon nanotubes (ACNTs), a new type of carbon material, were prepared by catalytic decomposition of xylene using ferrocene as catalyst. The kinetics experiment of ACNTs shows that fluoride adsorption rate is fast in the first 60 min and the adsorption capacity reaches 3.0 mg/g rapidly, then it decreases and adsorption achieves equilibrium gradually in about 180 min. The fluoride adsorption of ACNTs depends slightly on the solution pH value. The highest adsorption capacity of ACNTs occurs at pH 7 and reaches 4.5 mg/g at equilibrium fluoride concentration of 15 mg/l. The experimental results indicate that ACNTs are promising candidate materials for fluoride removal.
Carbon nanotubes (CNTs) were oxidized with H2O2, KMnO4 and HNO3. Their physicochemical properties were investigated by BET N2 adsorption, laser particle examination, Boehm’s titration, zeta potential measurement and cadmium(II) adsorption. The experimental results suggest that cadmium(II) adsorption capacities for three kinds of oxidized CNTs increase due to the functional groups introduced by oxidation compared with the as-grown CNTs. The cadmium(II) adsorption capacity of the as-grown CNTs is only 1.1 mg g−1, while it reaches 2.6, 5.1 and 11.0 mg g−1 for the H2O2, HNO3 and KMnO4 oxidized CNTs, respectively, at the cadmium(II) equilibrium concentration of 4 mg l−1. Adsorption of cadmium(II) by CNTs was strongly pH-dependent and the increase of adsorption capacities for HNO3 and KMnO4 oxidized CNTs is more obvious than that of the as-grown and H2O2 oxidized CNTs at lower pH regions. The experiments of CNT dosage effect on the cadmium(II) adsorption show that the adsorption capacity for KMnO4 oxidized CNTs has a sharper increase at the CNT dosage from 0.03 to 0.08 g per 100 ml than the as-grown, H2O2 and HNO3 oxidized CNTs and its removal efficiency almost reaches 100% at CNT dosage of 0.08 g per 100 ml. Analysis revealed that the KMnO4 oxidized CNTs hosted manganese residuals, and these surely contributed to cadmium sorption to a yet-undefined extent.
Commercial single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) were purified by sodium hypochlorite solutions and were employed as adsorbents to study the adsorption characteristics of zinc from water. The properties of CNTs such as purity, structure and nature of the surface were greatly improved after purification which made CNTs become more hydrophilic and suitable for adsorption of Zn2+. In general, the adsorption capacity of Zn2+ onto CNTs increased with the increase of pH in the pH range of 1–8, fluctuated very little and reached maximum in the pH range of 8–11 and decreased at a pH of 12. A comparative study on the adsorption of Zn2+ between CNTs and commercial powdered activated carbon (PAC) was also conducted. The maximum adsorption capacities of Zn2+ calculated by the Langmuir model are 43.66, 32.68, and with SWCNTs, MWCNTs and PAC, respectively, at an initial Zn2+ concentration range of 10–. The short contact time needed to reach equilibrium as well as the high adsorption capacity suggests that SWCNTs and MWCNTs possess highly potential applications for the removal of Zn2+ from water.
The sorption of two dyes, namely, Basic Blue 69 and Acid Blue 25 onto peat has been studied in terms of pseudo-second order and first order mechanisms for chemical sorption as well as an intraparticle diffusion mechanism process. The batch sorption process, based on the assumption of a pseudo-second order mechanism, has been developed to predict the rate constant of sorption. the equilibrium capacity and initial sorption rate with the effect of agitation, initial dye concentration and temperature. An activation energy of sorption has also been evaluated with the pseudo-second order rate constants. A comparison of the equilibrium sorption capacity evaluated has been made from pseudo-second order model and Langmuir isotherm.
Four kinds of CNTs with different morphologies were produced by chemical vapour deposition method. After oxidation with nitric acid, their specific surface area, particle size distribution and functional groups on the surfaces were characterized. Adsorption isothermal experiment shows that the CNTs with more defects, which can be easily introduced more functional groups on their surfaces prepared at 650 °C, have higher lead adsorption capability from aqueous solution and are promising adsorbents in wastewater treatment.
The dye, Methylene Blue, was adsorbed on an adsorbent prepared from mature leaves of the Neem tree (Azadirachta indica). A batch adsorption study was carried out with variable adsorbate concentration, adsorbent amount, pH, and temperature. Ninety-three percent of the dye could be removed by 2 g of the Neem leaf powder from 1 L of an aqueous solution containing 25 mg of the dye at 300 K. The adsorption followed pseudo first order kinetics with a mean rate constant of 3.73 × 10−3 min−1 and an intra-particle diffusion rate constant of 6.36 × 10−2 mg g−1 min−0.5. A possible mechanism of adsorption was suggested on the basis of concurrently operating surface adsorption and pore diffusion. The experimental data yielded excellent fits with Langmuir and Freundlich isotherm equations. The Langmuir monolayer capacity had a mean value of 8.76 mg g−1. The adsorption of the dye was endothermic in nature (ΔH: 4.62–16.74 kJ mol−1) and was accompanied by an increase in entropy (ΔS: 54.22–90.23 J mol−1 K−1) and a decrease in Gibbs energy (ΔG: −10.33 to −13.62 kJ mol−1 in the temperature range of 300–330 K). The results indicated that the dye, Methylene Blue, strongly interacts with a biomass-based adsorbent, the Neem leaf powder.
The adsorption of Acid Blue 193 (AB193) onto benzyltrimethylammonium (BTMA)-bentonite was investigated in aqueous solution in a batch system with respect to contact time, pH and temperature. The surface modification of BTMA-bentonite was examined using the FTIR technique. The pseudo-first-order, pseudo-second-order kinetic models and the intraparticle diffusion model were used to describe the kinetic data and the rate constants were evaluated. The experimental data fitted very well the pseudo-second-order kinetic model and also followed the intraparticle diffusion model up to 60 min, whereas diffusion is not only the rate controlling step. The Langmuir, Freundlich and Dubinin–Radushkevich (D–R) adsorption models were applied to describe the equilibrium isotherms and the isotherm constants were also determined. The Langmuir, Freundlich and D–R models agree with experimental data well. The change of free energy, enthalpy and entropy of adsorption were also evaluated for the adsorption of AB193 onto BTMA-bentonite. The results show that BTMA-bentonite could be employed as low-cost material for the removal of acid dyes from effluents.
This study concerns with the development of modified montmorillonites as adsorbents for water treatment. Polymeric aluminium and iron intercalated forms of montmorillonites have been prepared in the absence and presence of an alkylammonium cationic surfactant (Hexdecyl-trimethyl-ammonium bromide, HDTMA). Montmorillonites intercalated with polymeric Al, Fe, Fe/Al (2:1 Fe to Al ratio in solution), possess large N2 Brunauer-Emmett-Teller (BET) surface areas. XRD data also shows trace amounts of illite and plagioclase within the clay materials. Montmorillonites intercalated with HDTMA, polymeric Fe/HDTMA, polymeric Al/HDTMA and polymeric Fe/Al/HDTMA (1:1 metal to surfactant molar ratio in solution) undergo some losses of N2 BET surface areas. Preliminary adsorption studies on phenol have shown that polymeric Al/HDTMA- and HDTMA-only-modified montmorillonites possess a good affinity for phenol, whereas the polymeric Al/Fe modified- and starting montmorillonites have little affinity for phenol adsorption.
Adsorption of Co(II) ions from aqueous sepiolite suspensions has been systematically investigated as a function of several variables including activation conditions, solid to liquid ratio, pH and temperature. The results are analyzed to identify the mechanism of cobalt uptake by sepiolite. Both abstraction and real adsorption isotherms were constructed to isolate the precipitation of cobalt from the real adsorption. Also, for the first time a plausible correlation between the released Mg(II) ions from sepiolite matrix and those adsorbed Co(II) ions is made. A one to one ion exchange mechanism is found to describe the results. The data obtained from adsorption isotherms at different temperatures were fitted to various adsorption models to calculate thermodynamic quantities such as the free energy of adsorption, heat of adsorption and entropy of adsorption. The thermodynamic data indicate that Co(II) adsorption onto sepiolite is entropically driven and characterized by physical adsorption.
The capacity and mechanism of metal hydroxide sludge in removing azo reactive dyes from aqueous solution was investigated with different parameters, such as charge amount of dyes, system pH, adsorbent particle size, and adsorbent dosage. The three anionic dyes used were CI Reactive Red 2, CI Reactive Red 120, and CI Reactive Red 141, increasing in number of sulfonic groups, respectively. Only 0.2% (w/v) of powdered sludge (<75microm) achieved color removal from 30 mg l(-1) reactive dye solutions within 5 min without pH adjustment. The larger the charge amount of the dyes, the greater the adsorption (>90%) on the metal hydroxide sludge. The system pH played a significant role in the adsorption on metal hydroxides and formation of dye-metal complexes. The optimum system pH for dye adsorption was 8-9 which was close to the pH(zpc) of the sludge while the precipitation of dye-metal complexes occurred at system pH 2. The maximum adsorption capacity (Q degrees ) of the sludge for the reactive dyes was 48-62 mg dye g(-1) adsorbent. The Langmuir and Freundlich models showed that the higher charged dyes had a higher affinity of adsorption. The smaller particle size and the greater amount of adsorbent showed the faster process, due to an increase in surface area of adsorbent. Desorption studies elucidated that metal hydroxide sludge had a tendency for ion exchange adsorption of sulfonated azo reactive dyes. Leaching data showed that the treated water was nontoxic at a system pH above 5 or a solution pH above 2.
This study examines adsorption kinetics and activation parameters of methyl violet on perlite. The effect of process parameters like contact time, concentration of dye, temperature and pH on the extent of methyl violet adsorption from solution has been investigated. Results of the kinetic studies show that the adsorption reaction is first order with respect to dye solution concentration with activation energy of 13.2 kJ mol(-1). This low activation energy value indicates that the adsorption reaction is diffusion controlled. The activation parameters using Arrhenius and Eyring equations have been calculated. Adsorption increases with increase of variables such as contact time, initial dye concentration, temperature and pH.
The sorptive removal of hexavalent chromium from aqueous solutions by calcined Mg-Al-CO(3) hydrotalcite was investigated in a batch mode. The influence of agitation speed, solution pH, initial chromium concentration, sorbent concentration and temperature has been tested in kinetic runs. Three kinetic models have been evaluated to fit the experimental data: the pseudo-first order, the modified-second order and the Elovich equation. It was shown that the first-order model could best describe the sorption kinetics. A Freundlich isotherm was used to fit equilibrium experiments. Hydrotalcite presents a sorption capacity of approximately 120 mg Cr/g, under the investigated experimental conditions. The calculated activation energy for process studied was around 40 kJ/mol.
Liquids and sludges containing polychlorinated biphenyls (PCBs) can be treated to concentrate the PCBs in a solid residue. The latter can then be handled to destroy the PCBs. A study on sorption kinetics of PCBs on fly ash was conducted in controlled batch systems. TCB and HeCB are removed at 25 degrees C by adsorption on fly ash up to 97% at pH 7, with an adsorbent dose of 5 g/l. An examination of the thermodynamic parameters shows that the adsorption of TCB and HeCB by fly ash is a process occurring spontaneously at ambient conditions. Activation energies for the sorption process ranged between 5.6 and 49.1 kJ/mol. It was observed that the rate at which TCB and HeCB are adsorbed onto fly ash showed a diffusion limitation. The uptake rate of TCB and HeCB increases with increasing initial concentration and gradually tends to a constant value. A decrease in the adsorption of TCB and HeCB was observed when interfering ions and other PCB congeners were present. Changing the pH in the aqueous solution from 2 to 10 had no effect on the adsorption process. Overall, fly ash can be used for an efficient removal of PCBs from several aqueous solutions.
Dodecyltrimethylammonium bromide-modified bentonite (DTMA-bentonite) was prepared and tested as an adsorbent for an acid dye (Acid Blue 193, AB193) removal from aqueous solution in comparison with Na-bentonite. The effect of various experimental parameters was investigated using a batch adsorption technique. In this manner, the adsorption isotherms, adsorption kinetics, and temperature and pH effects upon Acid Blue 193 adsorption on Na-bentonite and DTMA-bentonite were thoroughly examined. Results show that a pH value of 1.5 is favorable for the adsorption of Acid Blue 193. The isothermal data could be well described by the Freundlich equation. The dynamical data fit well with the pseudo-second-order kinetic model. The adsorption capacity of DTMA-bentonite (740.5 mg g(-1)) was found to be around 11 times higher than that of Na-bentonite (67.1 mg g(-1)) at 20 degrees C. Thermodynamic parameters such as activation energy (E(a)) and change in the free energy (DeltaG(0)), the enthalpy (DeltaH(0)), and the entropy (DeltaS(0)) were also evaluated. The overall adsorption process was exothermic but it is only spontaneous at 20 degrees C. The results indicate that Na-bentonite and DTMA-bentonite could be employed as low-cost alternatives to activated carbon in wastewater treatment for the removal of color which comes from textile dyes.
Adsorption thermodynamics of Pb2+ on carbon nanotubes has been studied at various temperatures of 280, 298 and 321 K and the thermodynamic parameters, such as equilibrium constant (K0), standard free energy changes (DeltaG0), standard enthalpy change (DeltaH0) and standard entropy change (DeltaS0), have been obtained. A pseudo-second-order rate model has been employed to describe the kinetic adsorption processes. Desorption studies reveal that Pb2+ can be easily removed from carbon nanotubes by altering the pH values of the solution using both HCl and HNO3, indicating that carbon nanotubes are a promising absorbent for wastewater treatment.
Commercial carbon nanotubes (CNTs) were purified by acid solution and were employed as adsorbents to study adsorption of trihalomethanes (THMs) from water. The properties of CNTs such as purity, structure and nature of the surface were greatly improved after acid treatment which made CNTs become more hydrophilic and suitable for adsorption of low molecular weight and relatively polar THM molecules. The adsorption of THMs onto CNTs fluctuates very little in the pH range 3-7, but decreases with pH value as pH exceeds 7. A comparative study between CNTs and powdered activated carbon (PAC) for adsorption of THMs from water was also conducted. The short time needed to reach equilibrium as well as the high adsorption capacity of CHCl3, which accounts for a significant portion of THMs in the chlorinated drinking water, suggests that CNTs possess highly potential applications for THMs removal from water.
The adsorption of Acid Red 57 (AR57) onto surfactant-modified sepiolite was investigated in aqueous solution in a batch system with respect to contact time, pH and temperature. The surface modification of surfactant-modified sepiolite was controlled using the FTIR technique. The pseudo-first-order, pseudo-second-order kinetic models and the intraparticle diffusion model were used to describe the kinetic data and the rate constants were evaluated. The experimental data fitted very well the pseudo-second-order kinetic model and also followed the intraparticle diffusion model up to 90 min, whereas diffusion is not only the rate controlling step. The Langmuir and Freundlich adsorption models were applied to describe the equilibrium isotherms and the isotherm constants were also determined. The Freundlich model agrees with experimental data well. The activation energy, change of free energy, enthalpy and entropy of adsorption were also evaluated for the adsorption of AR57 onto surfactant-modified sepiolite. The results indicate that surfactant-modified sepiolite could be employed as low-cost material for the removal of textile dyes from effluents.
The macroalga Caulerpa lentillifera was found to have adsorption capacity for a basic dye, Astrazon Blue FGRL. For the whole range of concentrations employed in this work (20-1280 mgl(-1)), the adsorption reached equilibrium within the first hour. The kinetic data corresponded well with the pseudo second-order kinetic model where the rate constants decreased as initial dye concentrations increased. At low dye concentrations (20-80 mgl(-1)), an increase in the adsorbent dosage resulted in a higher removal percentage of the dye, but a lower amount of dye adsorbed per unit mass (q). The adsorption isotherm followed both the Langmuir and Freundlich models within the temperature range employed in this work (18-70 degrees C). The highest maximum adsorption capacity (q(m)) was obtained at 50 degrees C. The enthalpy of adsorption was estimated at 14.87 kJmol(-1) suggesting a chemical adsorption mechanism.
The adsorption and the kinetics of the cation exchange of rhodamine-6G (Rh-6G) with Na(+)-montmorillonite (Na(+)-MMT) have been studied. The binding parameters of Rh-6G have been determined by applying Freundlich and D-R isotherms. The enthalpy and the entropy of adsorption have been determined. The isosteric heat of adsorption has also been determined and decreases with increasing the concentration of Rh-6G. Increasing the concentration of Rh-6G led to a decrease in the adsorption capacity, which attributed to the formation of Rh-6G aggregates. Kinetic measurements of the cation exchange were followed up using a stopped-flow electrical conductivity detection unit. The cation-exchange process exhibited first-order kinetics with respect to the dye concentration and inversely proportional to the clay concentration. The measurements were accomplished at different temperatures and the activation parameters were determined. Increasing the Na(+)-MMT concentration led to a decrease in the rate constant. The latter is also affected by changing the exchangeable cation.
Ceria nanoparticles supported on aligned carbon nanotubes (CeO(2)/ACNTs), a novel adsorbent for Cr(VI) from drinking water, were prepared by chemical reaction of CeCl(3) with NaOH in aligned carbon nanotube solution and subsequent heat treatment. The best Cr(VI) adsorption effect of CeO(2)/ACNTs occurs at a pH range of 3.0-7.4. The largest adsorption capacity of CeO(2)/ACNTs reaches 30.2 mg g(-1) at an equilibrium Cr(VI) concentration of 35.3 mg l(-1) at pH 7.0. The experiment results suggest that CeO(2)/ACNTs have great potential applications in environmental protection.
Comparisonofthesorptionofanionic dyesonactivatedcarbonandchitosanderivativesfromdilutesolutions
- E Guibal
- P Mccarrick
- J M Tobin
E.Guibal,P.McCarrick,J.M.Tobin,Comparisonofthesorptionofanionic dyesonactivatedcarbonandchitosanderivativesfromdilutesolutions,Sep. Sci. Technol. 38 (2003) 3049–3073.
Kinetics, isotherm and thermodynamic studiesofadsorptionofAcidBlue193fromaqueoussolutionsontonatural sepiolite, Colloid Surf
- A Ozcan
- E M Oncu
- A S Ozcan
A. Ozcan, E.M. Oncu, A.S. Ozcan, Kinetics, isotherm and thermodynamic studiesofadsorptionofAcidBlue193fromaqueoussolutionsontonatural sepiolite, Colloid Surf. A 277 (2006) 90–97.
- M J Jaycock
- G D Parfitt
M.J. Jaycock, G.D. Parfitt, Chemistry of Interfaces, Ellis Horwood Ltd.,
Onichester, 1981, pp. 12–13.
- Y H Li
- S G Wang
- J Q Wei
- X F Zhang
- C L Xu
- Z K Luan
- D H Wu
- B Q Wei
Y.H. Li, S.G. Wang, J.Q. Wei, X.F. Zhang, C.L. Xu, Z.K. Luan, D.H. Wu,
B.Q. Wei, Lead adsorption on carbon nanotubes, Chem. Phys. Lett. 357
(2002) 263–266.
- Y Yu
- J C Yu
- J G Yu
- Y C Kwok
- Y K Che
- J C Zhao
- L Ding
- W K Ge
- P K Wong
Y. Yu, J.C. Yu, J.G. Yu, Y.C. Kwok, Y.K. Che, J.C. Zhao, L. Ding, W.K. Ge,
P.K. Wong, Enhancement of photocatalytic activity of mesoporous TiO 2
by using carbon nanotubes, Appl. Catal. A: Gen. 289 (2005) 186–196.