Removal of methylene blue from aqueous solution with silica nano-sheets derived from vermiculite

The adsorption kinetics of a cationic dye, methylene blue (MB), onto the silica nano-sheets derived from vermiculite via acid leaching was investigated in aqueous solution in a batch system with respect to contact time, initial dye concentration, pH, and temperature. Experimental results have shown that increasing initial dye concentration favors the adsorption while the acidic pH and temperature go against the adsorption. Experimental data related to the adsorption of MB on the silica nano-sheets under different conditions were applied to the pseudo-first-order equation, the pseudo-second-order equation and the intraparticle diffusion equation, and the rate constants of first-order adsorption (k(1)), the rate constants of second-order adsorption (k(2)) and intraparticle diffusion rate constants (k(int)) were calculated, respectively. The experimental data fitted very well the pseudo-second-order kinetic model. The activation energy of system (E(a)) was calculated as 3.42 kJ/mol. The thermodynamics parameters of activation such as Gibbs free energy, enthalpy, entropy were also evaluated and found that DeltaG*, DeltaH*, and DeltaS* are 65.95 (71.63, 77.45)kJ/mol, 0.984 (0.776, 0.568)kJ/mol, and -0.222 (-0.223, -0.224)kJ/(Kmol) at 20 (45, 70) degrees C, respectively. The desorption of the dye on the silica nano-sheets using ethanol was also investigated primarily.     

Adsorptive removal of methylene blue by tea waste

The potentiality of tea waste for the adsorptive removal of methylene blue, a cationic dye, from aqueous solution was studied. Batch kinetics and isotherm studies were carried out under varying experimental conditions of contact time, initial methylene blue concentration, adsorbent dosage and pH. The nature of the possible adsorbent and methylene blue interactions was examined by the FTIR technique. The pH(pzc) of the adsorbent was estimated by titration method and a value of 4.3+/-0.2 was obtained. An adsorption-desorption study was carried out resulting the mechanism of adsorption was reversible and ion-exchange. Adsorption equilibrium of tea waste reached within 5h for methylene blue concentrations of 20-50mg/L. The sorption was analyzed using pseudo-first-order and pseudo-second order kinetic models and the sorption kinetics was found to follow a pseudo-second order kinetic model. The extent of the dye removal increased with increasing initial dye concentration. The equilibrium data in aqueous solutions were well represented by the Langmuir isotherm model. The adsorption capacity of methylene blue onto tea waste was found to be as high as 85.16mg/g, which is several folds higher than the adsorption capacity of a number of recently studied in the literature potential adsorbents. Tea waste appears as a very prospective adsorbent for the removal of methylene blue from aqueous solution.     

Scavenging behaviour of meranti sawdust in the removal of methylene blue from aqueous solution

Meranti (Philippine mahogany) sawdust, an inexpensive material, showed strong scavenging behaviour through adsorption for the removal of methylene blue (MB) from aqueous solution. Batch studies were performed to evaluate and optimize the effects of various parameters such as contact time, pH, initial dye concentrations and adsorbent dosage. Langmuir, Freundlich and Temkin isotherms were used to analyze the equilibrium data at different temperatures. The experimental data fitted well with the Langmuir adsorption isotherm, indicating thereby the mono layer adsorption of the dye. The monolayer sorption capacity of meranti sawdust for MB was found to be 120.48, 117.64, 149.25 and 158.73 mg/g at 30, 40, 50 and 60 °C, respectively. Thermodynamic calculations showed that the MB adsorption process is endothermic and spontaneous in nature. Kinetic studies showed that the adsorption followed a pseudo-second-order kinetic model. The results indicated that the meranti sawdust could be an alternative material in place of more costly adsorbents used for dye removal.     

Removal of methylene blue from aqueous solution by a solvothermal-synthesized graphene/magnetite composite

In this study, we have demonstrated a facile one-step solvothermal method for the synthesis of the graphene nanosheet (GNS)/magnetite (Fe(3)O(4)) composite. During the solvothermal treatment, in situ conversion of FeCl(3) to Fe(3)O(4) and simultaneous reduction of graphene oxide (GO) into graphene in ethylene glycol solution were achieved. Electron microscopy study suggests the Fe(3)O(4) spheres with a size of about 200 nm are uniformly distributed and firmly anchored on the wrinkled graphene layers with a high density. The resulting GNS/Fe(3)O(4) composite shows extraordinary adsorption capacity and fast adsorption rates for removal of organic dye, methylene blue (MB), in water. The adsorption kinetics, isotherms and thermodynamics were investigated in detail to reveal that the kinetics and equilibrium adsorptions are well-described by pseudo-second-order kinetic and Langmuir isotherm model, respectively. The thermodynamic parameters reveal that the adsorption process is spontaneous and endothermic in nature. This study shows that the as-prepared GNS/Fe(3)O(4) composite could be utilized as an efficient, magnetically separable adsorbent for the environmental cleanup.     

Removal of methylene blue from aqueous solution by adsorption onto pineapple leaf powder

The ability of an unconventional bio-adsorbent, pineapple leaf powder (PLP) for the adsorption of methylene blue (MB) from aqueous solution was studied. It was observed that intra-particle diffusion was involved in the adsorption process and that the kinetic data fitted well with a pseudo-second-order equation. Fitting parameters revealed that the rate of adsorption increased with decrease in dye concentration and decrease in ionic strength while the mixing speed did not have a significant effect on adsorption. The adsorption was favorable at higher pH and lower temperature, and the equilibrium data were well fitted by the Langmuir isotherm. The maximum adsorption capacity varied from 4.68 × 10⁻⁴ to 9.28 × 10⁻⁴ mol/g when pH increases from 3.5 to 9.5. Thermodynamic parameters suggest that the adsorption is a typical physical process, spontaneous, and exothermic in nature. The results revealed that this agricultural waste has potential to be used as an economical adsorbent for the removal of methylene blue from aqueous solution.     

Na0.5Li0.5CoO2 nanopowders: Facile synthesis,characterization and their application for the removal of methylene blue dye from aqueous solution

In this paper, delafossite-type Na_0.5Li_0.5CoO₂ nanoparticles (NPs) with an average particle size of 50 nm were successfully synthesized by sol–gel method. Prepared NPs were characterized by differential thermal analysis, powder X-ray diffraction, transmission electron microscopy, scanning electron microscopy, and scanning tunneling microscopy. The nanoparticles showed the excellent adsorption properties towards methylene blue dye (MBD) as a reactive dye. The kinetics of removal of MBD in aqueous solutions was studied in a series of experiments which were varied in the amount of NPs, contact time, pH, and temperature. The experimental data were fitted very well in the pseudo-second order kinetic model and the Freundlich adsorption isotherm model. 92% of dye was successfully removed in 10 min using 0.02 g Na_0.5Li_0.5CoO₂ NPs in a pH = 11. Thermodynamic study indicates that the adsorption of MBD is feasible, and spontaneous in nature.     

Removal of methylene blue from aqueous solution by chaff in batch mode

A new adsorbent system for removing methylene blue (MB) from aqueous solutions has been investigated. This new adsorbent is cereal chaff, an agriculture product in middle-west region in China. Variables of the system, including biosorption time, chaff dose, pH, salt concentration and initial MB concentration, were adopted to study their effects on MB removal. The results showed that as the dose of chaff increased, the percentage of MB sorption increased accordingly. There was no significant difference in the dye concentration remaining when the pH was increased from 4.0 to 11.0. The salt concentration has negative effect on MB removal. At the experimental range of MB concentration, the amount of MB adsorbed onto per unit mass of chaff (q(e)) is direct ratio to MB initial concentration (c(0)). The equilibrium data were analyzed using five equilibrium models, the Langmuir, the Freundlich, the Redlich-Peterson, the Koble-Corrigan and the Temkin isotherms. The results of non-linear regressive analysis are that the isotherms of Langmuir, Redlich-Peterson and Koble-Corrigan are better fit than the isotherms of Freundlich and Temkin at different temperatures according to the values of determined coefficients (R(2)) and Chi-square statistic (chi(2)). The maximum equilibrium capacities of chaff from Langmuir models are 20.3, 25.3 and 26.3 mg g(-1) at 298, 318 and 333K, respectively. Using the equilibrium concentration constants obtained at different temperatures, various thermodynamic parameters, such as DeltaG(0), DeltaH(0) and DeltaS(0), have been calculated. The thermodynamics parameters of MB/chaff system indicate spontaneous and endothermic process. It was concluded that an increase in temperature results in a bigger MB loading per unit weight of the chaff.     

Amino-functionalized magnetic bacterial cellulose/activated carbon composite for Pb2+ and methyl orange sorption from aqueous solution

A new nanostructured amino-functionalized magnetic bacterial cellulose/activated carbon(BC/AC)composite bioadsorbent(AMBCAC)was prepared for removal of Pb~(2+)and methyl orange(MO)from aqueous solution.The results demonstrated that the equilibrium adsorption capacity(q_e)for Pb~(2+)obviously increases by 2.14 times after introduction of amino groups,the optimum p H for Pb~(2+)and MO adsorption was 5.0 and 3.0,respectively,and the q_eof AMBCAC was 161.78 mg g~(-1)for Pb~(2+)and 83.26 mg g~(-1)for MO under the optimal conditions in this investigation.The kinetics and adsorption isotherm data of the sorption process were well fitted by pseudo-second-order kinetic model and Langmuir isotherm respectively.The thermodynamic results(the Gibbs free energy change G0,the enthalpy change H0,the entropy change S0)implied that the adsorption process of Pb~(2+)and MO was feasible,endothermic and spontaneous in nature.These results support that the AMBCAC composite developed in this work can provide a cheap and efficient way for easy removal of both Pb~(2+)and MO as a promising adsorbent candidate for wastewater treatment.     

ZnCo2O4 nanorods as a novel class of high-performance adsorbent for removal of methyl blue

Spinel ZnCo₂O₄ nanorods were synthesized by a simple template-free hydrothermal method in the presence of zinc chloride, cobalt chloride, glucose, and urea. The phase structure, morphology and chemical composition have been characterized by X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and the corresponding selected area electron diffraction (SAED). The results showed that the typically porous and poly-crystalline structure was successfully grown on the surface of ZnCo₂O₄ nanorods. The ZnCo₂O₄ nanorods were further applied to remove methyl blue (MB), which was used as a model of organic pollutants in aqueous solution. In particular, the maximum equilibrium adsorption capacity of MB in ZnCo₂O₄ nanorods reaches up to 2400?mg/g, which is higher than that of most adsorbents. The adsorption isotherms and kinetics followed standard Langmuir and pseudo-second-order models, respectively. MB adsorption decreased with increasing solution pH at pH?>?7 implying that MB adsorption on ZnCo₂O₄ nanorods may via chemisorption between negatively charged MB molecular and positively charged adsorption sites on the surface of ZnCo₂O₄ nanorods. This study provides great promise of using ZnCo₂O₄ nanorods as adsorbent for removal of pollutant dyes.     

Adsorptive removal of fluoride from aqueous solution using orange waste loaded with multi-valent metal ions

Adsorption gels for fluoride ion were prepared from orange waste by saponification followed by metal loading. The pectin compounds contained in orange waste creates ligand exchange sites once it is loaded with multi-valent metal ions such as Al³⁺, La³⁺, Ce³⁺, Ti⁴⁺, Sn⁴⁺, and V⁴⁺ to be used for fluoride removal from aqueous solution. The optimum pH for fluoride removal depends on the type of loaded metal ions. The isotherm experiments showed the Langmuir type monolayer adsorption. Among all kinds of metal loaded gels tested, Al loaded gel appeared to exhibit the most favorable adsorption behavior. The adsorption kinetics of fluoride on loaded gel demonstrated fast adsorption process. The presence of NO₃⁻, Cl⁻ and Na⁺ ions has negligible effect on fluoride removal whereas SO₄²⁻ and HCO₃⁻ retarded the fluoride removal capacity in some extent. Fluoride removal at different adsorbent doses showed that fluoride concentration can be successfully lowered down to the acceptable level of environmental standard. The fluoride adsorption mechanism was interpreted in terms of ligand exchange mechanism. The complete elution of adsorbed fluoride from the gel was successfully achieved using NaOH solution.     

Grass waste: A novel sorbent for the removal of basic dye from aqueous solution

The aim of the present work was to investigate the feasibility of grass waste (GW) for methylene blue (MB) adsorption. The adsorption of MB on GW material was studied as a function of GW dose (0.05–1.20 g), solution pH 3–10, contact time and initial concentration (70–380 mg/L). The influence of these parameters on the adsorption capacity was studied using the batch process. The experimental data were analyzed by the Langmuir and Freundlich isotherms. The adsorption isotherm was found to follow the Langmuir model. The monolayer adsorption capacity was found to be 457.640 mg/g. The kinetic data were fitted to the pseudo-first-order and pseudo-second-order models, and were found to follow closely the pseudo-second-order kinetic model. The results revealed that GW adsorbent is potentially low-cost adsorbent for adsorption of MB.     

Electrochemical removal of indium ions from aqueous solution using iron electrodes

The removal of indium ions from aqueous solution was carried out by electrocoagulation in batch mode using an iron electrode. Various operating parameters that could potentially affect the removal efficiency were investigated, including the current density, pH variation, supporting electrolyte, initial concentration, and temperature. The optimum current density, supporting electrolyte concentration, and temperature were found to be 6.4 mA/cm², 0.003N NaCl, and 298 K, respectively. When the pH values lower than 6.1, the removal efficiencies of indium ions via electrocoagulation were up to 5 times greater than those by adding sodium hydroxide. The indium ion removal efficiency decreased with an increase in the initial concentration. Results for the indium ion removal kinetics at various current densities show that the kinetic rates conformed to the pseudo-second-order kinetic model with good correlation. The experimental data were also tested against different adsorption isotherm models for describing the electrocoagulation process. The adsorption of indium ions preferably fitting the Langmuir adsorption isotherm suggests monolayer coverage of adsorbed molecules.     

Improved photodynamic efficiency for methylene blue from silica-methylene blue@tannic acid-Fe(III) ions complexes in aqueous solutions

To avoid multidrug resistance and tumour recurrence, photodynamic therapy (PDT) was emerging as an alternative therapy and its efficiency was related to photosensitizer (PS) efficiency, oxygen concentration and light characteristic. Methylene blue (MB) molecules as PSs were loaded in silica (silica-MB) and followed by encapsulation by coordination complexes of tannic acid (TA) and Fe(III) ions. In comparison with those of silica-MB, decreased condensation of Si-O-Si, shifted infrared absorbance frequencies of chemical bands, delayed thermal degradation and modulated release behavior of MB were observed for silica-MB@TA with a core–shell structure. Although MB dimers were dominantly released from silica-MB, release of MB monomers from silica-MB@TA was significantly promoted, which was described by the Higuchi model. The promotion of release of MB monomers from silica-MB@TA indicated the well control of aggregate states of MB by the encapsulation of TA and Fe(III) ions complexes. Through monitoring the oxidation of uric acid, generation efficiency of singlet oxygen (¹O₂) by MB released from silica-MB@TA was fairly higher than that from silica-MB. A facile method to encapsulate silica-MB with complexes of TA and Fe(III) ions was herein demonstrated to raise the generation efficiency of singlet oxygen.     

Adsorptive removal of heavy metals from aqueous solution by treated sawdust (Acacia arabica)

The removal of Cr(VI), Pb(II), Hg(II) and Cu(II), by treated sawdust has been found to be concentration, pH, contact time, adsorbent dose and temperature dependent. The adsorption parameters were determined using both Langmuir and Freundlich isotherm models. Adsorption capacity for treated sawdust, i.e. Cr(VI) (111.61 mg/g), Pb(II) (52.38 mg/g), Hg(II) (20.62 mg/g), and Cu(II) (5.64 mg/g), respectively. Surface complexation and ion exchange are the major removal mechanisms involved. The adsorption isotherm studies clearly indicated that the adsorptive behaviour of metal ions on treated sawdust satisfies not only the Langmuir assumptions but also the Freundlich assumptions. The applicability of Lagergren kinetic model has also been investigated. The adsorption follows first-order kinetics. Thermodynamic constant (k_ad), standard free energy (ΔG°), enthalpy (ΔH°) and entropy (ΔS°) were calculated for predicting the nature of adsorption. The percentage adsorption increases with pH to attain a maximum at pH 6 and thereafter it decreases with further increase in pH. The results indicate the potential application of this method for effluent treatment in industries and also provide strong evidence to support the adsorption mechanism proposed.     

NaP1 zeolite synthesized via effective extraction of Si and Al from red mud for methylene blue adsorption

NaP1 zeolite, using red mud (RM) as raw material, was successfully prepared via alkali fusion and hydrothermal method. NaP1 zeolite, which was a mesoporous material, had specific surface area and pore diameter of 79.3 m²·g⁻¹ and 7.26 nm, respectively. NaP1 zeolite had excellent adsorption properties. Under the optimum adsorption conditions, methylene blue (MB) was adsorbed through NaP1 zeolite, the adsorption capacity was 48.7 mg·g⁻¹ and the removal efficiency was 97.1%. The adsorbent was regenerated with sodium chloride as eluent. The adsorption capacity of the adsorbent regenerated three times still was satisfactory 34.53 mg·g⁻¹, which showed the excellent stability performance from NaP1 zeolite. The adsorption conformed to the pseudo second order kinetic and Freundlich isotherm model. Moreover, MB molecules were adsorbed by diffusion on the outer surface, diffusion on the inner surface, and adsorption on the inner surface of NaP1 zeolite. And, during the external diffusion, electrostatic attraction and hydrogen bonding created. Al and Si were extracted from RM to prepare NaP1 zeolite with excellent adsorption properties. This result provides an important example for the development of the potential value of RM.     

Fabrication of graphene oxide/bentonite composites with excellent adsorption performances for toluidine blue removal from aqueous solution

The graphene oxide/bentonite (BG) composites are prepared through graphene oxide (GO) nanosheets successfully intercalated into acid-treated bentonite interlayer and deposited onto external surface. The BG composites exhibit a higher uptake capacity of toluidine blue (TB) dye from water solutions than normal bentonite owing to the synergistic effect between bentonite and GO. The as-prepared composites are characterized by scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and N₂-sorption analysis. The process parameters affecting the adsorption behaviors such as initial pH, temperature, contact time and initial concentration of dye are systematically investigated. The Langmuir isotherm model fit well with the equilibrium adsorption isotherm data and the maximum adsorption capacity is 458.7?mg·g^?1 at pH 8 for BG composites modified using 1% GO. The pseudo-second-order kinetic model well describes the adsorption process of TB onto BG composites. The TB adsorption on BG composites is mainly attributed to ion exchange, electrostatic interaction and intermolecular interactions. The outstanding adsorption performances of composites for the removal of TB dye from water demonstrate its significant potential for environmental applications.     

Adsorption of methylene blue onto hazelnut shell: Kinetics, mechanism and activation parameters

The adsorption kinetics of methylene blue (MB) on the hazelnut shell with respect to the initial dye concentration, pH, ionic strength, particle size and temperature were investigated. The rate and the transport/kinetic processes of MB adsorption were described by applying the first-order Lagergren, the pseudo-second-order, mass transfer coefficient and the intraparticle diffusion models. Kinetic studies showed that the kinetic data were well described by the pseudo-second-order kinetic model. Significant increases in initial adsorption rate were observed with the increase in temperature followed by pH and initial MB concentration. The intraparticle diffusion was found to be the rate-limiting step in the adsorption process. Adsorption activation energy was calculated to be 45.6kJmol(-1). The values of activation parameters such as free energy (DeltaG(*)), enthalpy (DeltaH(*)) and entropy (DeltaS(*)) were also determined as 83.4kJmol(-1), 42.9kJmol(-1) and -133.5Jmol(-1)K(-1), respectively.     

Adsorption of methyl tert-butyl ether (MTBE) from aqueous solution by porous polymeric adsorbents

MTBE has emerged as an important water pollutant because of its high mobility, persistence, and toxicity. In this study, a postcrosslinked polymeric adsorbent was prepared by postcrosslinking of a commercial chloromethylated polymer, and a nonpolar porous polymer with comparable surface area and micropore volume to the postcrosslinked polymer was prepared by suspended polymerization. The postcrosslinked polymer, nonpolar porous polymer and chloromethylated polymer were characterized by N2 adsorption, FTIR and XPS analysis. Results showed that postcrosslinking reaction led to the generation of a microporous postcrosslinked polymer with BET surface area 782m2g(-1), average pore width 3.0nm and micropore volume 0.33cm3g(-1). FTIR and XPS analysis indicated the formation of surface oxygen-containing groups on the postcrosslinked polymer. The three polymers were used as adsorbents to remove aqueous methyl tert-butyl ether (MTBE). Adsorption of MTBE over the postcrosslinked polymeric adsorbent was found to follow the linear adsorption isotherm, whereas MTBE adsorption onto the nonpolar porous polymer and chloromethylated polymer followed Langmuir adsorption model. Comparison of adsorption capacities of the postcrosslinked polymer, chloromethylated polymer and nonpolar porous polymer revealed that the adsorption of MTBE from aqueous solution is dependent on both pore structure and surface chemistry of polymeric adsorbents, and the high adsorption efficiency of the postcrosslinked polymer towards MTBE is attributed to its high surface area, large micropore volume and moderate hydrophility. The process of MTBE adsorption onto the adsorbents can be well described by pseudo-second-order kinetics, and the rate of adsorption decreased at higher MTBE initial concentration.     

Adsorptive removal of chlorophenols from aqueous solution by low cost adsorbent--Kinetics and isotherm analysis

Adsorptive removal of parachlorophenol (PCP) and 2,4,6-trichlorophenol (TCP) from aqueous solutions by activated carbon prepared from coconut shell was studied and compared with activated carbon of commercial grade (CAC). Various chemical agents in different concentrations were used (KOH, NaOH, CaCO(3), H(3)PO(4) and ZnCl(2)) for the preparation of coconut shell activated carbon. The coconut shell activated carbon (CSAC) prepared using KOH as chemical agent showed high surface area and best adsorption capacity and was chosen for further studies. Batch adsorption studies were conducted to evaluate the effect of various parameters such as pH, adsorbent dose, contact time and initial PCP and TCP concentration. Adsorption equilibrium reached earlier for CSAC than CAC for both PCP and TCP concentrations. Under optimized conditions the prepared activated carbon showed 99.9% and 99.8% removal efficiency for PCP and TCP, respectively, where as the commercially activated carbon had 97.7% and 95.5% removal for PCP and TCP, respectively, for a solution concentration of 50mg/L. Adsorption followed pseudo-second-order kinetics. The equilibrium adsorption data were analysed by Langmuir, Freundlich, Redlich-Peterson and Sips model using non-linear regression technique. Freundlich isotherms best fitted the data for adsorption equilibrium for both the compounds (PCP and TCP). Similarly, acidic pH was favorable for the adsorption of both PCP and TCP. Studies on pH effect and desorption revealed that chemisorption was involved in the adsorption process. The efficiency of the activated carbon prepared was also tested with real pulp and paper mill effluent. The removal efficiency using both the carbons were found highly satisfactory and was about 98.7% and 96.9% as phenol removal and 97.9% and 93.5% as AOX using CSAC and CAC, respectively.