Freundlich Equilibrium Isotherm Research Articles

Adsorption of NMST from acetic acid on coconut activated carbon: Kinetics, isotherms and thermodynamics

ABSTRACT Exploration has been made into 2-nitro-4-methylsulfonyltoluene (NMST) adsorption on coconut activated carbon from acetic acid. The results demonstrate that the adsorption of NMST on activated carbon augments with its concentration in acetic acid. NMST adsorption on activated carbon is also improved with temperature. Though NMST adsorption on per gram of carbon will decrease with carbon dosage, more NMST will be adsorbed. The kinetic study depicts that NMST adsorption on activated carbon is in good agreement with the pseudo-second-order kinetic equation. Both of the Langmuir and Freundlich equilibrium isotherm models are well fit for the experimental results, with R2 = 0.9994 and 0.9979, respectively. The adsorption thermodynamic parameters (ΔH, ΔG, ΔS) calculated with Van’t Hoff equations indicate that NMST adsorption on carbon is spontaneous and endothermic.

Adsorption characteristics of nickel (II) from aqueous solutions by Zeolite Scony Mobile-5 (ZSM-5) incorporated in sodium alginate beads

Nickel, a prevalent metal in the ecosystem, is released into the environment through various anthropogenic activities, leading to adverse effects. This research explored utilizing zeolite scony mobile-5 (ZSM-5) nanoparticles encapsulated in sodium alginate (SA) for nickel (II) removal from aqueous solutions. The adsorption characteristics of SA/ZSM-5 were examined concerning contact duration, initial metal ion concentration, pH level, temperature, and sorbent dosage. The findings revealed that a rising pH reduced Ni (II) uptake by the sorbent while increasing the Ni (II) concentration from 25 to 100 mg L−1 led to a decrease in removal percentage from 91 to 80% under optimal conditions. Furthermore, as sorbent dosage increased from 4 to 16 g L−1, uptake capacity declined from 9.972 to 1.55 mg g−1. Concurrently, SA/ZSM-5 beads' Ni (II) sorption capacity decreased from 96.12 to 59.14% with a temperature increase ranging from 25 to 55 °C. The Ni (II) sorption data on SA/ZSM-5 beads are aptly represented by Langmuir and Freundlich equilibrium isotherm models. Moreover, a second-order kinetic model characterizes the adsorption kinetics of Ni (II) on the SA/ZSM-5 beads. A negative free energy change (ΔG°) demonstrates that the process is both viable and spontaneous. The negative enthalpy values indicate an exothermic nature at the solid–liquid interface while negative entropy values suggest a decrease in randomness. In conclusion, this novel adsorbent exhibits promise for removing nickel from aqueous solutions and could potentially be employed in small-scale industries under similar conditions.

Exploring the potential of magnetic persimmon tannins-based bio-adsorbent for Cd (II) ions removal from water: Experiment and DFT study

Cadmium (Cd (II)) pollution in water and soil is a global problem that poses a serious threat to both human health and the ecological balance of the environment. Therefore, the development of efficient and environmentally friendly bio-adsorbent materials is the key to remediating Cd (II) pollution. Herein, a magnetic persimmon tannins composites bio-adsorbent (Fe3O4/PT, MPT) which is decorated with iron oxide has been successfully prepared by the crosslinking method for investigating its adsorption potential and mechanisms of Cd (II) in aqueous solution. The maximum Cd (II) adsorption capacity of MPT adsorbent is 73.33 mg/g. Further, the adsorption kinetic and isotherm are in line with the pseudo-second-order model and Freundlich equilibrium isotherm model. The thermodynamic study showed that the adsorption process is exothermic and spontaneous. Especially, the density functional theory calculations of geometric configuration and isosurface diagram both confirm the interaction mechanisms between MPT and Cd (II) including chelation reactions and electrostatic interactions, which are consistent with experiment results. All these results indicate that MPT bio-adsorbent can be used as an efficient, environmentally friendly and low-cost bio-adsorbent for the removal of Cd (II) contaminants from aqueous solution.

Adsorption of Diethylenetriamine from Water by Activated Carbon: Kinetics, Isotherms and Thermodynamics

ABSTRACT The discharge of diethylenetriamine (DETA) into aqueous environment poses a threat to public health and environment. Therefore, it is imperative to take effective measures to remove DETA from water. The elimination of DETA from water may be realized via the way of adsorption with activated carbon. In this paper, the adsorption of DETA from water by activated carbon originated from coconut shell has been explored in batchwise operation. The effects of stirring speed, temperature, pH, DETA concentration, carbon dosage and particle size on DETA adsorption have been determined by experiment. The adsorption results exhibit that the DETA adsorption rate increases with its concentration in the aqueous solution and temperature. However, the amount of DETA adsorbed on the carbon at equilibrium decreases slightly with temperature. The DETA adsorbed increases with pH changing from 8 to 11 and remains constant if pH rising over 11. The kinetic study shows that DETA adsorption on the activated carbon is in good agreement with the pseudo-second-order kinetic model with a correlation coefficient of 0.999. The DETA removal from the solution increases with the carbon dosage. The Langmuir equilibrium isotherm model has been found to provide a better fitting of the adsorption data than the Freundlich equilibrium isotherm model with a maximum adsorption of 90.50 mg g−1. The thermodynamic parameters evaluated from the experiments are ΔS 14.49 J∙mol−1∙K−1, ΔH −11.32 kJ mol−1 and ΔG changing from −15.71 from −16.15 kJ mol−1with the temperature rising from 30°C to 60°C. The thermodynamic study suggests the exothermic and spontaneous natures of DETA sorption on activated carbon.

Design and Preparation of Magnetically-Oriented Poly(styr-co-MMA)-3MPS Capped Fe(ZnO) Hybrid Microspheres for Ion Exchange Removal of Toxic Pollutants from Wastewater

In this work, polymeric microspheres derived from polystyrene-co-methyl methacrylate embedded with magnetic ZnO nanoparticles (poly(styrene-co-MMA)-3MPS-Fe (ZnO)) were synthesized using the suspension polymerization method. The surfaces of polymeric Fe(ZnO) microspheres were improved by functionalization with amino and sulphonate groups. The physicochemical analysis indicated a large number of positively charged (anion exchange) groups (91 mmol/g) on the amine-modified polymeric microsphere (MFZPI) and a large number of negatively charged (cation exchange) groups (90 mmol/g) on the sulphonate-modified polymeric microsphere (SMFZPI)—revealing ambivalent character of obtained sorbent. The characterization of the synthesized compounds using various analytical techniques such as TGA, FTIR, XRD, SEM/EDX, UV-VIS and VSM indicated that synthesized microspheres were thermally stable, semi-crystalline in structure with hollow irregular morphology, optically active in UV region and slightly magnetic in nature. Due to the introduction of groups having ion exchange properties, these modified poly(styrene-co-MMA)-3MPS-Fe(ZnO) microspheres were used for the ion exchange sorptive removal of Cr(III) and fluorescein from aqueous matrix. The equilibrium sorption capacity of Cr(III) was 16.79 mg/g whereas of fluorescein was 12.03 mg/g under optimized conditions. Therefore, SMFZPI was found to be a promising sorbent for both cationic heavy metals and anionic dyes due to the presence of both acidic and basic groups. The mathematical modelling revealed that the sorption phenomenon followed pseudo-second-order kinetics with Freundlich equilibrium isotherm, indicating multilayer chemisorption of the pollutants on the synthesized ion exchange sorbents. This work establishes the utilization of polymeric magnetic ZnO-based ion exchange sorbents to effectively remove harmful toxins from wastewater.

Exploration of Reactive Black 5 Dye Desorption from Composite Hydrogel Beads—Adsorbent Reusability, Kinetic and Equilibrium Isotherms

A low-cost adsorbent was prepared by using cherry stones powder and chitosan and used to retain Reactive Black 5 dye from aqueous solution. Then, the spent material was submitted to a regeneration process. Five different eluents (water, sodium hydroxide, hydrochloric acid, sodium chloride and ethanol) were tested. Among them, sodium hydroxide was selected for an advanced investigation. Values of three working conditions, namely the eluent volume, its concentration and the desorption temperature, were optimized by Response Surface Methodology-Box-Behnken Design. In the established settings (NaOH volume: 30 mL, NaOH concentration: 1.5 M, working temperature: 40 °C), three successive cycles of adsorption/desorption were conducted. The analysis performed by Scanning Electron Microscopy and by Fourier Transform Infrared Spectroscopy revealed the evolution of the adsorbent throughout the dye elution from the material. Pseudo-second-order kinetic model and Freundlich equilibrium isotherm were able to accurately describe the desorption process. Based on the acquired results, our outcomes sustain the suitability of the synthesized material as dye adsorbent and the possibility of efficaciously recycling and reusing it.

Treatment of Industrial Saline Wastewater Using Eco-Friendly Adsorbents

The wastewater generated from the oil and gas sector is one of the major environmental issues. Varieties of techniques are employed for the treatment of generated wastewater. In this work, an attempt has been made to treat industrial saline wastewater from the oil and gas industry using a combination of synthesized biopolymer, chitosan, with graphene. Chitosan has been synthesized from a bioresource using marine spent. Chitosan was characterized using field emission scanning electron microscopy (FE-SEM), Fourier transform infrared (FT-IR) spectroscopy, energy dispersive X-ray (EDX) spectroscopy, and thermogravimetric analysis (TGA). Batch experiments were conducted by varying the composition of graphene viz 1, 2, 3, 4, and 5 w/w with respect to a fixed amount of chitosan. The percentage removal efficiency of chemical oxygen demand (COD), total dissolved solids (TDS), total suspended solids (TSS), turbidity, and oil and grease were evaluated. A combination of chitosan and graphene has effectively removed the pollutants present in oil produced water (OPW) compared to chitosan alone. The maximum percentage removal efficiencies of COD (84%), TDS (91%), TSS (80%), turbidity (95%), and oil and grease (99.9%) were obtained for a mixture of chitosan (0.5 g/100 mL) and 5 wt% graphenes. The Freundlich equilibrium isotherm model suited the adsorption data well.

Computational and Experimental Investigation of the Selective Adsorption of Indium/Iron Ions by the Epigallocatechin Gallate Monomer.

Selective recovery of indium has been widely studied to improve the resource efficiency of critical metals. However, the interaction and selective adsorption mechanism of indium/iron ions with tannin-based adsorbents is still unclear and hinders further optimization of their selective adsorption performance. In this study, the epigallocatechin gallate (EGCG) monomer, which is the key functional unit of persimmon tannin, was chosen to explore the ability and mechanism of selective separation/extraction of indium from indium-iron mixture solutions. The density functional theory calculation results indicated that the deprotonated EGCG was easier to combine with indium/iron cations than those of un-deprotonated EGCG. Moreover, the interaction of the EGCG-Fe(III) complex was dominated by chelation and electrostatic interaction, while that of the EGCG-In(III) complex was controlled by electrostatic interactions and aromatic ring stacking effects. Furthermore, the calculation of binding energy verified that EGCG exhibited a stronger affinity for Fe(III) than that for In(III) and preferentially adsorbed iron ions in acidic or neutral solutions. Further experimental results were consistent with the theoretical study, which showed that the Freundlich equilibrium isotherm fit the In(III) and Fe(III) adsorption behavior very well, and the Fe(III) adsorption processes followed a pseudo-second-order model. Thermodynamics data revealed that the adsorption of In(III) and Fe(III) onto EGCG was feasible, spontaneous, and endothermic. The adsorption rate of the EGCG monomer for Fe(III) in neutral solution (1:1 mixed solution, pH = 3.0) was 45.7%, 4.3 times that of In(III) (10.7%). This study provides an in-depth understanding of the relationship between the structure of EGCG and the selective adsorption capacity at the molecular level and provides theoretical guidance for further optimization of the selective adsorption performance of structurally similar tannin-based adsorbents.

Exposure to NaCl enhances Cd2＋ biosorption potential of Sesuvium portulacastrum (L.)

Cadmium (Cd2＋) is a major heavy metal pollutant and it causes many serious effects on the environment. The established Cd2＋ removal methods are expensive and produce secondary waste, while biosorption is a potential alternative. In view of this, Sesuvium portulacastrum (L.) is explored, which is a facultative halophyte and is known to survive under both salt and heavy metal stress conditions. Using the dried powder of Sesuvium biomass, two independent biosorbents were prepared including ConB (grown under control condition) and NaClB (grown under 200 mM NaCl) and their Fourier-transform infrared spectroscopy (FTIR) indicated significant alteration in peak position of various functional groups. The Cd2＋ biosorption capacity in NaClB (306 mg g−1) was found higher than ConB (203 mg g−1). The kinetic and equilibrium studies revealed the contribution of intraparticle diffusion in the biosorption process of both the biosorbents. Further, the higher intraparticle diffusion rate constant indicated the faster biosorption process in NaClB. The experimental data correlated better with Freundlich equilibrium isotherm (r2=0.96 for ConB and r2=0.99 for NaClB) than Langmuir, indicating multilayer biosorption and heterogeneity within the biosorbents. Scanning electron microscope (SEM) imaging indicated that the rough surface of ConB changed to smooth after Cd2＋ biosorption, with lesser number of pores. In case of NaClB, Cd2＋ biosorption narrowed the vertical channels. EDX (Energy Dispersive X-ray) spectrum validated the Cd2＋ binding in both ConB and NaClB. Taken together, the study highlighted NaCl-treated Sesuvium as an eco-friendly green biosorbent for Cd2＋ removal from aqueous solutions.

Production of polyacrylonitrile nanofibres modified with Cyanex 272 for recovery of gallium from solution

ABSTRACT The objectives of this work were to develop polyacrylonitrile nanofibres modified with the commercial Cyanex 272 extractor and apply them for the recovery of gallium present in aqueous solution. The nanofibres were produced using the centrifugation technique, employing Forcespinning® equipment. The average nanofibre diameter ranged from 530 to 840 nm. The highest adsorption of gallium was achieved at pH 2.5, with a pseudo-second order kinetic model and the Freundlich equilibrium isotherm model providing the best fits of the experimental data. The thermodynamic parameters showed that the adsorption was spontaneous, favourable, and endothermic. The maximum capacity of the PAN/Cyanex 272 nanofibres for the recovery of gallium was 38.93 mg g−1. In successive reuse cycles, the nanofibres showed a small decrease of the adsorption capacity for the metal after the first cycle, while the efficiency remained constant in the subsequent cycles. The desorption efficiency remained constant throughout the cycles, with values in the range 80%–90%. The findings demonstrated that PAN/Cyanex 272 nanofibres have excellent potential for use as adsorbents, providing good capacity for the recovery of gallium and satisfactory stability during reuse in several cycles.

Phytoremediation of azo dye methyl red by macroalgae Chara vulgaris L.: kinetic and equilibrium studies.

Phytoremediation is an innovative, eco-friendly, and solar-driven technique, which becomes a well-known alternative solution for remediation of hazardous dyes from wastewater. In present research work, potential of a submerged fresh water macroalgae Chara vulgaris L. (C. vulgaris) examined for removal of acidic azo dye methyl red (MR) in its solution form. A series of experiments were done with C. vulgaris to predict the effects of different parameters viz. contact time, initial dye concentration, amount of macroalgae, and pH. The increase in initial dye concentration directly impacts on the potential of macroalgae. The decolorization percentage declined with increase in initial dye concentration. The equilibrium condition was found to achieve after contact time of approximately 48h. The decolorization of MR dye was found to be favorable at pH5. The macroalgae was successfully utilized repeatedly with MR for eight cycles in batch experiments. The kinetics of phytoremediation of MR dye was studied with help of pseudo-first-order, pseudo-second-order, and Elovich kinetic models and the results were well suited to pseudo-second-order kinetic model with the correlation value R2 ≥ 0.99. In addition, the experimental data was also assessed by using Langmuir and Freundlich adsorption equilibrium isotherms. The results of phytoremediation data was found to be in favor of Freundlich equilibrium isotherm which having the correlation value R2 ≥ 0.977. The intraparticle diffusion model also studied to interpret the macroalgae phytoremediation mechanism for phytoremediation of MR. The surface interactions of C. vulgaris were investigated before and after the removal of dye with Fourier transform-infrared spectroscopy (FTIR) technique. On the basis of these studies, a hypothetical mechanism has also been proposed to depict the phytoremediation of acidic azo dye by C. vulgaris.

Performance of Immobilized Chlorella Algae for Removing pb(II) Ions from Aqueous Solution

This study aims to show the effectiveness of immobilization of Chlorella green algae biomass in the form of bead for the removal of lead ions from synthetic polluted water at various operational parameters such as pH (2–6), biosorbent dosage (0.5–20 g/L) and initial concentration (10–100 mg/L). More than 90 % removal efficiency was achieved. FTIR and SEM-EDX analysis of the biosorbent before and after sorption show differences in the functional groups on the adsorbent surface. Langmuir and Freundlich equilibrium isotherm, pseudo-first-order and pseudo-second-order kinetic models were applied to the experimental and results and show good conformity with Langmuir isotherm model and pseudo-second-order kinetic model with correlation coefficient (0.994) and (0.998) respectively.

Efficient adsorption of methylene blue from aqueous solution by graphene oxide modified persimmon tannins.

With the rapid development of dye and textile industry, the pollution of dye wastewater has aroused widespread public concern due to the potential risk to human health. Therefore, it is of significance for the removal of dye pollutants from wastewater. In this work, a green and efficient bio-adsorbent, graphene oxide modified persimmon tannin (PT-GO), has been fabricated through glutaraldehyde crosslinking method for efficient adsorption of methylene blue (MB) from aqueous solutions. The prepared PT-GO bio-adsorbent was analyzed by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, x-ray photoelectron spectra (XPS) and Brunauer-Emmett-Teller (BET) analysis. The adsorption behavior of the PT-GO bio-adsorbent towards MB dye in a batch adsorption process was investigated. The maximum MB adsorption capacity achieved 256.58 mg g-1 with MB concentration of 35 mg L-1 at 323 K. The Freundlich equilibrium isotherm and the pseudo-second order model fit the adsorption behavior very well. Thermodynamics data revealed that the adsorption of MB onto PT-GO bio-adsorbent was feasible, spontaneous and endothermic. Redox reactions, electrostatic interactions and π-π interactions dominated the adsorption of MB onto PT-GO bio-adsorbent. In addition, the regeneration of the PT-GO was efficiently achieved and MB removal efficiency remained high (88.3%) after fifth cycles. All these results indicated that PT-GO bio-adsorbent could be a promising biomass adsorbent for the removal of organic dye contaminants with non-toxic, efficient and low cost.

Landfill leachate treatment using activated carbon obtained from coffee waste

ABSTRACT A set of experiments were carried out in order to establish and evaluate the potential of activated carbon, produced from coffee waste in adsorption process, in the depuration of landfill leachate. Different reagents were studied in the activation of carbon: HCl, HCl + H2O2, H3PO4, H3PO4 + H2O2, all with an impregnation rate of 1:1. The activated carbon that showed the best global results was activated with H3PO4, obtaining a 51.0, 32.8, 66.0, 81.0 and 97.1% elimination of chemical oxygen demand, ammonia, total chlorine, bromine and copper, respectively. This activated carbon has a total pore area of 4.85 m2/g and a median pore diameter of 65.32 micrometers. When different loads of this carbon were placed in a stirrer system in contact with landfill leachate, with the aim of evaluating the effect of the adsorption load and contact time, the concentration of ammonia decreased from the beginning of the adsorption process to the end of it, and the removal of ammonia increased with the increase in the adsorbent load. However, the trend of the amount adsorbed per unit mass decreased with increased dosage. The model Freundlich equilibrium isotherm fits experimental data adequately, giving R2 values of 0.95, 1/n of 0.5183, and a K value of 7.08*10-5 L/g, being favourable for adsorption process.

Catalytic and photocatalytic ozonation with activated carbon as technologies in the removal of aqueous micropollutants

Clopyralid degradation by different treatment processes combining olive stone activated carbon (OSAC), ozone and Solar-Simulated Radiation (SSR) were studied. Firstly, a detailed study of clopyralid adsorption onto OSAC was carried out. The fitted experimental data suggest pseudo-first order kinetics and Freundlich equilibrium isotherm models to describe the process. Secondly, the application of catalytic ozonation was explored. The combination of ozone and OSAC significantly improved the generation of hydroxyl radicals. Moreover, the catalyst showed higher stability and kept efficiency in reuse cycles, if compared to adsorption. Thirdly, the combination of O3, OSAC, and SSR was applied, and different systems were compared, focusing on pH as the main variable. At basic pH (pH = 9), the best removal rate was achieved by O3/OSAC/SSR. Finally, all systems were applied for the treatment of the target compound in an urban wastewater matrix, focusing on the effect of inorganic carbon. The presence of carbonates inhibited only the mineralization rate, not affecting the compound removal.

An multifunction Zn0.3Mn0.4O4 nanospheres for carbon dioxide reduction to methane via photocatalysis and reused after five cycles for phosphate adsorption

The Zn0.3Mn0.4O4 Nanospheres (ZnMnONs) were synthesized for the photocatalytic reduction of CO2 to CH4. The average particle size was 70.1 nm and having composition of Zn, Mn and O are about 18.93, 21.30 and 59.77 wt% respectively. The catalysts were characterized by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), IR spectra and UV–vis spectrophotometer. Zn0.3Mn0.4O4 is used for efficient photocatalytic CO2 to methane which is an important component in a future sustainable post carbon energy system. It was reached to 2.65 μmol/g of CH4 yield, and the photocatalyst presented a potential for reducing CO2 emission. The recovered nanospheres sample from methane production is further used for phosphate adsorption for exploring its multifunction application. The maximum% adsorption observed at 200 mg of adsorbent concentration at 40 min of agitation time. The adsorption study follows the first order of kinetics, Langmuir isotherm graph deduced the qmax value at 125 mg/g & Freundlich equilibrium isotherm also shows the linear plot. The essential features of the Langmuir isotherm can be expressed in terms of a dimensionless constant called separation factor. The value of RL indicates the shape of the isotherms to be either unfavorable (RL > 1), linear (RL = 1), favorable (0 < RL < 1) or irreversible (RL = 0). It was observed that the value of RL was in the range of 0–1 and finally the Thermodynamic parameter related to the adsorption process ΔG shows the value at −4587.24 J mol−1.

Experimental Investigation and Modeling of Nickel Removal from Wastewater Using Modified Rice Husk in Continuous Reactor by Response Surface Methodology

In this paper, we investigate the adsorption efficiency of modified rice husk for continuous removal of Ni(II) ions by evaluating the breakthrough curves obtained at different bed heights, initial Ni(II) concentrations, and flow rates. We use response surface methodology to investigate the individual as well as cumulative effect of these process variables optimizing the process conditions for the maximum removal of Ni(II) from aqueous solution. We statistically evaluate our obtained quadratic model through analysis of variance, student’s t test, and residual test. According to our results, height of adsorbent is the most effective parameter on continuous Ni(II) removal efficiency with a positive effect, while initial Ni(II) concentration has negative effect on adsorption efficiency, and flow rate is negligible. Our predicted values of Ni(II) removal obtained by using the response functions match perfectly with our experimental data. Under the optimum condition, the removal efficiency of Ni(II) ions is 63.57%. According to our batch experiments, the adsorption process can be well described by both Langmuir and Freundlich equilibrium isotherm models resulting in a maximum adsorption capacity for Ni(II) ions by modified rice husk as 26.6 mg/g.

Competitive adsorption of metal ions onto goethite–humic acid-modified kaolinite clay

A binary mixture of humic acid and geothite was prepared and used to modify kaolinite to produce geothite–humic acid (GHA)-modified kaolinite adsorbent useful for the adsorption of Pb2+, Cd2+, Zn2+, Ni2+ and Cu2+ from Single and Quinary (5) metal ion systems. The cation exchange capacity (CEC) and specific surface area of GHA-modified kaolinite clay adsorbent were found to be 40 meq/100 g and 13 m2/g, respectively, with the CEC being five times that of raw kaolinite clay (7.81 meq/100 g). The Langmuir–Freundlich equilibrium isotherm model gave better fit to experimental data as compared with other isotherm models. In Quinary metal ion system, the presence of Zn2+ and Cu2+ appears to have an antagonistic effect on the adsorption of Pb2+, Cd2+ and Ni2+, while the presence of Pb2+, Cd2+ and Ni2+ shows a synergistic effect on the adsorption of Zn2+ and Cu2+. The GHA-modified kaolinite showed strong preference for the adsorption of Pb2+ in both metal ion systems. Brouers–Weron–Sotolongo (BWS) kinetic model gave better fit to kinetic data compared with other kinetic models used. Data from BWS kinetic model indicate that adsorption of metal ions onto GHA-modified adsorbent in both metal ion systems followed strictly, diffusion-controlled mechanism with adsorption reaction proceeding to 50 % equilibrium in <2 min in the Single metal ion system and <1 min in the Quinary metal ion system. Adsorption of metal ions onto GHA-modified kaolinite is fairly spontaneous and endothermic in nature in both metal ion systems although the rate of metal ion uptake and spontaneity of reaction are reduced in the Quinary metal ion system.

Preparation, structure and adsorption properties of synthesized multiwall carbon nanotubes for highly effective removal of maxilon blue dye

Multiwall carbon nanotubes (MWCNTs) have been hydrothermally prepared using polyethylene glycol as the carbon source. Herein, new MWCNTs composites with high adsorption capacity were prepared and applied as efficient adsorbents for adsorption of maxilon blue dye (GRL) from aqueous solution. The morphologies of the MWCNTs were characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform-infrared (FT-IR) spectroscopy. The adsorption property of maxilon blue (GRL) from aqueous solution onto MWCNTs was studied as a function of mass dosage, pH of solution, initial dye concentration and temperature. The adsorption of GRL depends on the initial pH of the solution with maximum uptake occurring at about pH 10. The maximum adsorption capacity of prepared MWCNTs was 260.7mg/g. Langmuir, Freundlich and Temkin isotherms were applied to fit the experimental data. The Freundlich equilibrium isotherm fitted well the experimental data indicating the homogeneity of the adsorbent surface sites. Thermodynamics parameters were studied the changes in free energy (ΔG0), enthalpy (ΔH0) and entropy (ΔS0) during adsorption. It is noticeable that the adsorption of GRL dye onto MWCNTs was a spontaneous and endothermic process and indicates that the adsorption is favored at high temperature.

Perspectives on the use of equilibrium isotherm equations to elucidate coagulation–flocculation mechanisms in plant-based coagulants

Viewpoints on the applicability of the equilibrium isotherm equations in coagulation–flocculation (CF) process are presented herein to stem the tide of the misuse. The two widely used equilibrium isotherm equations (Langmuir and Freundlich equilibrium isotherm equations) have been erroneously used to elucidate the CF mechanism, using plant-based coagulants, without a tenable theoretical basis. This erroneous use of equilibrium isotherm equations in CF process was based on the assumption that adsorption process is the rate determining step in the mechanism of CF process, using plant-based coagulants. This is in contrary to the fact that the rate determining step is a kinetic process, which is different from the equilibrium state.