Kinetic Intraparticle Diffusion Research Articles

Removal of Copper ions from aqueous solutions using polymer derivations of poly (styrene-alt-maleic anhydride)

In this study chelating resins have been considered to be suitable materials for the recovery of Copper (II) ions in water treatments. Furthermore, these modified resins were reacted with 1,2-diaminoethane in the presence of ultrasonic irradiation for the preparation of a tridimensional chelating resin on the Nano scale for the recovery of Copper (II) ions from aqueous solutions. This method which is used for removing and determining Copper (II) ions using copolymers derived resins of poly (styrene-alternative-maleic anhydride) (SMA) and atomic absorption spectroscopy. The method is simple, sensitive, inexpensive and fast. The various parameters such as pH, contact time, concentrations of metal ions, mass of resin, and agitation speed were investigated on adsorption effect. The adsorption behavior of Copper (II) ions were investigated by the synthesis of chelating resins at various pHs. The prepared resins showed a good tendency for removing the selected metal ions from aqueous solution, even at an acidic pH. Also, the prepared resins were examined for the removal of Copper (II) ions from real samples such as industrial wastewater and were shown to be very efficient at adsorption in the cases of Copper (II) ions. The pseudo-first-order, pseudo-second-order, and intra-particle diffusion kinetics equations were used for modeling of adsorption data and it was shown that pseudo-second-order kinetic equation could best describe the adsorption kinetics. The intra-particle diffusion study revealed that external diffusion might be involved in this case. The resins were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, and X-ray diffraction analysis.

Adsorption of different dyes from aqueous solution using Si-MCM-41 having very high surface area

Adsorption characteristics of four different dyes Safranin O (cationic), Neutral Red (neutral), Congo Red (anionic) and Reactive Red 2 (anionic) on Si-MCM-41 material having very high surface area are reported. The surface morphology of Si-MCM-41 material before and after adsorbing dye molecules are characterised by FTIR, HRXRD, nitrogen adsorption–desorption isotherms, FESEM, and HRTEM. The adsorption capacities of Si-MCM-41 for the dyes followed a decreasing order of NR > SF > CR > RR2. The adsorption kinetics, isotherm and thermodynamic parameters are investigated in detail for these dyes using calcined Si-MCM-41. The kinetics and isotherm data showed that both SF and NR adsorb more rapidly than CR and RR2, in accordance with pseudo-second-order kinetics model as well as intraparticle diffusion kinetics model and Langmuir adsorption isotherm model respectively. The thermodynamic data suggest that the dye uptake process is spontaneous. The high adsorption capacities of dyes on Si-MCM-41 (qm = 275.5 mg g−1 for SF, qm = 288.2 mg g−1 for NR) is explained on the basis of electrostatic interactions as well as H-bonding interactions between adsorbent and adsorbate molecules. Good regeneration capacity is another important aspect of the material that makes it potent for the uptake of dyes from aqueous solution.

Synthesis and use of SBA-15 adsorbent for dye-loaded wastewater treatment

Adsorption of four dyes, namely neutral red (NR), safranin O (SF), reactive red 2 (RR2) and congo red (CR), onto SBA-15 (Santa Barbara Amorphous) material was studied in detail not only to investigate the possible effects of interactions between adsorbate molecules and adsorbent but also the potential of this material for the removal of dyes from wastewater. SBA-15 and dye adsorbed SBA-15 were thoroughly characterised using standard analytical tools. High resolution X-ray diffractogram (HR-XRD) of SBA-15 shows four distinct peaks characteristic of highly ordered mesoporous material. Peak intensities of diffractograms of dye adsorbed SBA-15 are less intense. Nitrogen adsorption-desorption isotherm of SBA-15 is type-IV typical of mesoporous material. Such isotherms of dye adsorbed SBA-15 are different from that of SBA-15. Specific surface area, average pore diameter, and total pore volume decreased on adsorption of dyes- clearly indicating that pores have been blocked. High resolution transmission electron microscopic (HR-TEM) analyses of SBA-15 and dye adsorbed SBA-15 show distinct changes in pore morphology. It is observed that the adsorption capacities of SBA-15 towards NR and SF are much greater in comparison to RR2 and CR. The adsorption kinetics and isotherm follow the pseudo-second-order kinetics model, intraparticle diffusion kinetics model and Langmuir adsorption isotherm model respectively. The thermodynamic parameter suggests that the dye uptake process is spontaneous. The high adsorption capacity of SBA-15 (qm=289.86mgg−1 for NR, qm=257.73mg g−1 for SF) is probably due to electrostatic interactions as well as H-bonding interactions between adsorbent and adsorbate molecules.

Biosorption of methylene blue from aqueous solution by natural Osmanthus fragrans powder

The potential of Osmanthus fragrans powder as a natural biosorbent was investigated for the removal of methylene blue (MB) from aqueous solution. The effects of various experimental conditions including contact time, adsorbent dose, initial MB concentration, solution pH, salt ionic strength, and temperature on the adsorption properties of O. fragrans powder were discussed. The adsorption kinetic data were modeled using pseudo-first-order, pseudo-second-order, and intraparticle diffusion kinetics equations, indicating that the pseudo-second-order and intraparticle diffusion models could better describe the adsorption kinetics. Furthermore, adsorption equilibrium data were analyzed by Langmuir and Freundlich models, suggesting the Langmuir model presented a better correlation with the experimental data. The maximum adsorption capacities (qm) of O. fragrans powder for MB obtained from the Langmuir model were 155.52, 165.02, and 172.71 mg g−1 at different temperatures of 288.15, 298.15, and 308.15 K, respectively. Thermodynamic parameters such as standard free energy changes (ΔG°), standard enthalpy changes (ΔH°), and standard entropy changes (ΔS°) were also calculated. The results showed that the adsorption process was spontaneous and endothermic in nature. In addition, the possible adsorption mechanism of O. fragrans powder as adsorbent was proposed. The present study implies that O. fragrans powder were a promising candidate as novel biosorbents for the removal of MB from aqueous solution.

Adsorption of Pb(II) on raw and organically modified Jordanian bentonite

AbstractA comparative study using bentonite (BT), hexadecyltrimethylammonium-modified bentonite (BT-HDTMA) and phenyl fatty hydroxamic acid-modified bentonite (BT-PFHA) as adsorbents for the removal of Pb(II) has been proposed. These adsorbents were characterized by X-ray diffraction, X-ray fluorescence, Fourier-transform infrared spectroscopy and surface area measurement. Cation exchange capacity was also determined in this study. The adsorbent capabilities for Pb(II) from aqueous solution were investigated, and the optimal experimental conditions including adsorption time, adsorbent dosage, the initial concentration of Pb(II), pH and temperature that might influence the adsorption performance were also investigated. The experimental equilibrium adsorption data were tested by four widely used two-parameter equations, the Langmuir, Freundlich, Dubinin- Radushkevich (D-R) and Temkin isotherms. The monolayer adsorption capacities of BT, BT-HDTMA and BT-PFHA for Pb(II) were 149.3, 227.3 and 256.4 mg/g, respectively. The experimental kinetic data were analysed by pseudo-first order, pseudo-second order and intraparticle diffusion kinetics models. The experimental data fitted very well with the pseudo-second order kinetic model. Determination of the thermodynamic parameters, ΔG, ΔH and ΔS showed the adsorption to be feasible, spontaneous and exothermic.

Biosorption of Pb(II), Cu(II), and Ni(II) ions onto novel lowcost P. eldarica leaves-based biosorbent: isotherm, kinetics, and operational parameters investigation

In this study, the novel low-cost Pinus eldarica leaves-based biosorbent (Pe) was introduced to remove heavy metal ions from aqueous media. The Pe ability of Pb(II), Cu(II), and Ni(II) ions biosorption was investigated in aqueous solutions. The maximum sorption capacity was 40, 26, and 33 mg g−1 for Pb(II), Cu(II), and Ni(II), respectively, that was so promising. Experiments were carried out in lab-scale batch reactors as function of initial pH (pH0), initial concentration of heavy metal ions (C0), and contact time (t). The statistical analysis was applied to determine the significant parameters, rank of parameter influences, and type of influences. The adsorption kinetics data were modeled using the pseudo-first, pseudo-second-order, and intraparticle diffusion kinetics equations. The pseudo-first-order and pseudo-second-order kinetics equations described the adsorption kinetics very well. Finally, the equilibrium data were described by 15 isotherm models with different number of parameters from two to five. The results revealed that the Langmuir and Fritz–Schlunder models provided the best correlation of the experimental data.

Design of batch process for preconcentration and recovery of U(VI) from liquid waste by powdered corn cobs

Sorption of uranium(VI) from aqueous solution onto powdered corn cob has been carried out using batch technique. The maximum removal (98.5%) was obtained at pH 5 and contact time 60min. Freundlich, Langmuir, Temkin and Dubinin–Radushkevich (D–R) isotherms are used for describing the sorption process. It is found that the Langmuir isotherm appears to be the best fitting model and pseudo-first order, pseudo-second order, Elovich and intraparticle diffusion kinetics models were studied. The results indicate that the process follows the pseudo-second-order kinetics model. As well as the thermodynamic data indicate that the sorption processes is exothermic. The values of enthalpy (ΔH°), mean free energy (E) and activation energy (Ea) indicate that the sorption process is physical sorption. A single stage of batch adsorber has been designed for various volumes using the Langmuir isotherm.

Biosorption of Cr(VI) ions from aqueous solutions by a newly isolated Bosea sp. strain Zer-1 from soil samples of a refuse processing plant.

The adsorption behavior of Cr(VI) ions from aqueous solution by a chromium-tolerant strain was studied through batch experiments. An isolate designated Zer-1 was identified as a species of Bosea on the basis of 16S rRNA results. It showed a maximum resistance to 550 mg·L(-1) Cr(VI). The effects of 3 important operating parameters, initial solution pH, initial Cr(VI) concentration, and biomass dose, were investigated by central composite design. On the basis of response surface methodology results, maximal removal efficiency of Cr(VI) was achieved under the following conditions: pH, 2.0; initial concentration of metal ions, 55 mg·L(-1); and biomass dose, 2.0 g·L(-1). Under the optimal conditions, the maximum removal efficiency of Cr(VI) ions was found to be nearly 98%. The experimental data exhibited a better fit with the Langmuir model than the Freundlich model. The biosorption mechanisms were investigated with pseudo-first-order, pseudo-second-order, and intraparticle diffusion kinetics models. These results revealed that biosorption of Cr(VI) onto bacterial biomass could be an alternative method for the removal of metal ions from aqueous solution.

Efficient biosorption of lead(II) and cadmium(II) ions from aqueous solutions by functionalized cell with intracellular CaCO3 mineral scaffolds

The functionalized Saccharomyces cerevisiae cell with biogenic intracellular CaCO3 mineral scaffold, synthesized via a simple and environmentally friendly approach, was efficient for removing lead (II) and cadmium (II) ions from aqueous solutions. The CaCO3 mineral scaffold could promote the uptake of the heavy metal ions and increase the biosorption capabilities of the adsorbent. Compared with the Freundlich isotherm, Langmuir model more fitted the equilibrium data. The maximum removal capacity of functionalized cells for Pb(II) and Cd(II) was 116.69 and 42.63mgg−1, respectively. Further investigation showed that the adsorbent had high removal efficiency for trace amount of heavy metal ions. Adsorption data were modeled using the pseudo-first-order, pseudo-second-order and intra-particle diffusion kinetics equations. The results indicated that pseudo-second-order kinetic equation and intra-particle diffusion model could better describe the adsorption kinetics. The heavy metal ions might be removed by functionalized cells via membrane transport of metal ions and precipitation transformation.

Removal of Direct Red 23 from aqueous solution using corn stalks: Isotherms, kinetics and thermodynamic studies

The objective of this study was to assess the suitability and efficiency of corn stalk (CS) for the removal of diazo dye Direct Red 23 (DR23) from aqueous solutions. The effect of different variables in the batch method as a function of solution pH, contact time, initial dye concentration, CS amount, temperature, and so forth by the optimization method has been investigated. The color reduction was monitored by spectrophotometry at 503nm before and after DR23 adsorption on the CS, and the removal percentage was calculated using the difference in absorbance. The sorption processes followed the pseudo second order in addition to intraparticle diffusion kinetics models with a good correlation coefficient with the overall entire adsorption of DR23 on adsorbent. The experimental equilibrium data were tested by four widely used isotherm models namely, Langmuir, Freundlich, Tempkin and Dubinin–Radushkevich (D–R). It was found that adsorption of DR23 on CS well with the Freindlich isotherm model, implying monolayer coverage of dye molecules onto the surface of the adsorbent. More than 99% removal efficiency was obtained within 10min at adsorbent dose of 0.2g for initial dye concentration of 10–90mgL−1 at pH 3. Various thermodynamic parameters, such as Gibbs free energy, entropy, and enthalpy, of the ongoing adsorption process have been calculated. Judgment based on the obtained results of thermodynamic values shows the spontaneous and endothermic nature adsorption processes on adsorbent.

Synthesis and ultraviolet‐visible spectroscopic and electrochemical analyses of dyes derived from 2‐aminobenzothiazole, and study of their adsorption on titanium dioxide

A series of Schiff bases with hydroxyl anchoring group/s in various positions were synthesised. Their visible light absorption and electrochemical and physicochemical adsorption properties were investigated. Results show that the studied compounds have adequate highest-occupied-molecular-orbital and lowest-unoccupied-molecular-orbital levels that match with the conduction band of titanium dioxide and the redox potential of the electrolyte. Adsorption of azomethine compounds with hydroxyl group/s on titanium dioxide was studied. Experimental data show that the introduction of two β-hydroxyethyl groups can greatly enhance the adsorption efficiency of the studied Schiff base on titanium dioxide. Sorption kinetics was measured for di-(β-hydroxyethyl)aminobenzyliden-2-aminobenzothiazol. Results show rapid initial sorption (<30 min), followed by a slower rate of increasing uptake between 0.5 and 6 h. Kinetic data were modelled using pseudo-first-order, pseudo-second-order, and intraparticle diffusion kinetics equations. These results indicate that the pseudo-second-order equation and intraparticle diffusion model can better describe the adsorption kinetics of di-(β-hydroxyethyl)aminobenzyliden-2-aminobenzothiazol onto titanium dioxide.

Adsorption of Ni(II), Cu(II) and Cd(II) from aqueous solutions by amino modified nanostructured microfibrillated cellulose

The aim of the present study was to investigate the adsorption properties of aminopropyltriethoxysilane (APS) modified microfibrillated cellulose (MFC) in aqueous solutions containing Ni(II), Cu(II) and Cd(II) ions. The modified adsorbents were characterized using elemental analysis, Fourier transform infrared spectroscopy, SEM and zeta potential analysis. The adsorption and regeneration studies were conducted in batch mode using various different pH values and contact times. The maximum removal capacities of the APS/MFC adsorbent for Ni(II), Cu(II), and Cd(II) ions were 2.734, 3.150 and 4.195 mmol/g, respectively. The Langmuir, Sips and Dubinin-Radushkevich models were representative to simulate adsorption isotherms. The adsorption kinetics of Ni(II) Cu(II), and Cd(II) adsorption by APS/MFC data were modeled using the pseudo-first-order, pseudo-second-order and intra-particle diffusion kinetics equations. The results indicate that the pseudo-second-order kinetic equation and intra-particle diffusion model were adequate to describe the adsorption kinetics.

Fabrication of porous ZrO2 hollow sphere and its adsorption performance to Congo red in water

Hollow and solid ZrO2 microspheres with mesoporous structures were prepared by a hydrothermal method using zirconium oxychloride and urea as precursors. The as-prepared samples were characterized by X-ray diffraction, scanning and transmission electron microscopy and nitrogen adsorption–desorption isotherms. Adsorption performance of the as-prepared samples toward Congo red (CR) aqueous solutions was investigated and discussed. The pore structure analyses indicated that the prepared ZrO2 hollow and solid microspheres contained bimodal porous organization: small mesopores (ca. 2nm) and large mesopores and macropores (ca. 40–70nm). The CR equilibrium adsorption data of the as-prepared samples were fitted using Langmuir and Freundlich equations, indicating that the Langmuir equation exhibited the better correlation of the experimental data. The CR adsorption capacities were determined by the Langmuir equation and found to be 59.5, 21.4 and 4.8mgg−1 for the ZrO2 hollow, solid microsphere and reagent samples, respectively. Adsorption data were further modeled by the pseudo-first-order, pseudo-second-order and intra-particle diffusion kinetics equations. The results suggested that pseudo-second-order kinetic and intra-particle diffusion equations could better describe the kinetics of CR adsorption. The prepared ZrO2 hollow microsphere was found to be good adsorbent for the CR removal from water due to its high specific surface areas and bimodal porous structures.

Metal-impregnated carbon applied as adsorbent for removal of sulphur compounds using fixed-bed column technology

Metal-impregnated carbons (Cu–AC; Ag–AC and Pd–AC) were studied as adsorbents for the desulphurization of liquid fuels. A real gasoline was examined for sulphur compounds. Textural characteristics of adsorbents were determined by nitrogen adsorption/desorption isotherms at 77 K. The adsorption isotherms were obtained by frontal analysis in a single fixed bed at 30°C and 45°C. Breakthrough curves were simulated according to a mathematical model that assumed axially dispersed flow and mass transfer described by a linear driving force approximation and nonlinear adsorption equilibrium reached instantaneously on the external surface of the adsorbents particles. The model was solved numerically by orthogonal collocation in finite elements, using the commercial solver gPROMS. The proposed model matched experimental data reasonably well. Resistance to mass transfer was significant and thought to be due to intraparticle diffusion kinetics. The results confirmed the efficiency of the use of activated carbon (AC) in the adsorption of sulphur compounds, especially when its surface is modified with metals. Comparing adsorption capacities of sulphur compounds from real gasoline, AC–Pd material appeared more selective than other materials, even presenting a behaviour of rapid saturation explained by the presence of other components competing for adsorption sites, reducing their effectiveness in removing sulphur compounds. Both pristine AC and Pd–AC showed good regenerability. The regenerated Pd–AC sorbent can recover about 85% of the desulphurization capacity.

Adsorption of Arsenite by Six Submerged Plants from Nansi Lake, China

Nansi Lake is the largest and the most important freshwater lake in north China for the South-North Water Transfer Project. Due to long-time and large-scale fish farming of history, the excess fish food and excretion usually release pentavalent arsenic, which is converted into trivalent arsenic (As (III)) in the lake sediment and released into lake water. Adsorption of arsenite using six submerged plants (Mimulicalyx rosulatus,Potamogeton maackianus,Hydrilla,Watermifoil,Pteris vittata, andPotamogeton crispus) as adsorbing materials was investigated. The experimental data obtained have been analyzed using Langmuir, Freundlich, and Dubinin-Radushkevich isotherm models and the pseudo-first-order, pseudo-second-order, and intraparticle diffusion kinetics models. According to the results, the As (III) equilibrium data agreed well with the Freundlich isotherm model. The adsorption capacity of the plants was in the following order:Potamogeton crispus&gt;Pteris vittata&gt;Potamogeton maackianus&gt;Mimulicalyx rosulatus&gt;Hydrilla&gt;Watermifoil. The sorption system with the six submerged plants was better described by pseudo-second-order than by first-order kinetics. Moreover, the adsorption withPotamogeton crispuscould follow intraparticle diffusion (IPD) model. The initial adsorption and rate of IPD usingPotamogeton crispusandPteris vittatawere higher than those using other plants studied.

Novel Pb2+ Ion Imprinted Polymers Based on Ionic Interaction via Synergy of Dual Functional Monomers for Selective Solid-Phase Extraction of Pb2+ in Water Samples

A novel kind of Pb(2+) ion imprinted polymers (IIPs) was prepared based on ionic interactions via the synergy of dual functional monomers of methacrylic acid and vinyl pyridine for selective solid-phase extraction (SPE) of Pb(2+) in water samples. Suspension polymerization was employed for the formation of template Pb(2+)/monomer complex by self-assembly in the presence of ethylene glycol dimethacrylate cross-linker. The resulted Pb(2+) IIPs showed fast kinetics, high binding capacity, and the adsorption processes obeyed intraparticle diffusion kinetics and Langmuir isotherm models. The IIPs displayed excellent selectivity toward Pb(2+) over other metal ions such as Cu(2+), Cd(2+), Zn(2+), and Mn(2+) with selective coefficients above 30, as well as high anti-interference ability for Pb(2+) confronting with common coexisting various ions. Through 10 adsorption-desorption cycles, the reusable IIPs exhibited a good recoverability with the standard error within 5%. These features suggested the IIPs were ideal candidates for extraction and removal of Pb(2+) ions. Consequently, the IIPs were utilized as SPE sorbents and related parameters were optimized. An excellent linearity was presented in the range of 0.2-50 μg L(-1) (R(2) = 0.9998), as well as the limits of detection and quantification were achieved of 0.06 and 0.19 μg L(-1), respectively. A good repeatability was obtained with the relative standard deviation of 2.8%. Furthermore, real water samples were successfully analyzed and satisfactory recoveries varying from 95.5 to 104.6% were attained. The IIPs-SPE demonstrated potential application perspectives for rapid and high-effective cleanup and enrichment of trace Pb(2+) ions in complicated matrices.

Direct concurrent multi-scale CFD modeling: The effect of intraparticle transfer on the flow field in a MTO FBR

In this study, a coupled model based on a direct concurrent multi-scale approach incorporating a single particle model and a two-phase CFD model was developed to predict the effects of intraparticle transfer on the flow field and main composition distributions of a catalytic reaction to convert methanol to olefins (MTO) in a fluidized bed reactor (FBR). A single particle model was first constructed to describe the individual intraparticle molecular diffusion and reaction kinetics, while a CFD model characterized the gas–solid flow field in the FBR. Because the grid cells generated in the CFD model were too small compared with the size of the FBR, no distributions were considered in a single grid. In this case, all catalyst particles inside each small computational cell for the CFD model experienced the same external conditions, thus ensuring the effective coupling of the two models. This was validated by comparing the above assumption with simulation results and with experiment results. On the basis of the coupled model, the intraparticle transfer limitation and the flow field in the FBR were predicted numerically. The simulated results indicated that the intraparticle transfer limitation did exist and had significant effects on the reactor flow field. This model is expected to be useful in predicting the intraparticle transfer limitation in FBRs.

Enhanced removal of reactive navy blue dye using powdered orange waste

The aim of the present research was to evaluate the suitability of low-cost, ecofriendly and freely available orange waste (OW) biosorbent for the removal of reactive navy blue dye. The biosorption potential of OW was investigated using synthetic solutions of textile dye (reactive navy blue) at different parameters, e.g. biosorbent dose, initial concentrations of solution, contact time, pH and particle size in a batch system. The optimum conditions were identified as contact time of 160min, pH 2, biosorbent dose of 4gL−1, agitation speed of 80rpm and initial dye concentration of 100ppm. The biosorbent was analyzed by surface area analyzer (SAA), Fourier transform infra-red spectroscopy (FT-IR) and scanning electron microscopy (SEM) for its physical and chemical characterization. The FT-IR spectra indicated that hydroxyl and carboxyl groups were major active sites for biosorption, while the results of SEM showed obvious changes in surface morphology after biosorption. Experimental data were fitted in Langmuir and Freundlich equilibrium isotherms and found to follow the Langmuir equation. Adsorption capacity was 30.28mgg−1 with the dye removal efficiency of 82%. The application of pseudo-first order equation, pseudo-second order kinetics, Elovich sorption model and intraparticle diffusion kinetics revealed that pseudo-second order kinetic model best explained the experimental process. The results indicated that orange waste is a cost-effective and eco-friendly biosorbent and competitive to the current wastewater treatment technologies.

Spent green tea leaves for decolourisation of raw textile industry wastewater

True colour measurements of wastewater samples, in terms of American Dye Manufacturers' Institute values, were used to evaluate the effectiveness of decolourisation of textile wastewater using spent green tea leaf powder waste. Raw wastewater samples with a true colour of 868 ADMI were used in the batch adsorption experiments. Results revealed that the true colour removal efficiency of the raw textile wastewater was high in acidic solution and at high temperature, indicating an endothermic nature of the system. The major functional groups of the green tea leaf powder waste involved in adsorption were identified by Fourier Transform‐infrared spectroscopy analysis. Adsorption kinetic data were modelled using the modified Freundlich and intraparticle diffusion kinetics equations. Fitting results of the Langmuir adsorption isotherm showed that the adsorption capacity of the green tea leaf powder waste was 775 ADMI g−1, which is higher than that of powder activated carbon (526 ADMI g−1). The low activation energy values (13.9 kJ mol−1) suggested that adsorption was governed by a diffusion process and the reaction involved a physisorption mechanism. From the perspectives of waste utilisation, remarkable colour adsorption capacity and inexpensive and abundant availability, green tea leaf waste is an attractive alternative for decolourisaton of textile wastewater. Because high temperature favours colour removal, green tea leaf powder can be directly applied in raw textile wastewater treatment.

Chromium(VI) removal by maghemite nanoparticles

Abstract Maghemite nanoparticles were prepared by a co-precipitation method and characterized by Fourier transform infrared spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, nitrogen adsorption and desorption isotherms. The Brunauer–Emmett–Teller surface area, average particle size, pore volume and porosity of maghemite were 73.8 m 2 g −1 , 17.2 ± 4.4 nm, 0.246 cm 3 g −1 , and 56.3%, respectively. Removal of Cr(VI) by the maghemite nanoparticles follows a pseudo-second-order kinetic process. Intraparticle diffusion kinetics implies the adsorption of Cr(VI) onto the maghemite occurs via two distinct phases: the diffusion controlled by external surface followed by an intra-particle diffusion. The equilibrium data was nicely fit to the Langmuir and Langmuir–Freundlich (L–F) models and indicates the adsorption of Cr(VI) is spontaneous and highly favorable. The heterogeneity index, 0.55, implies heterogeneous monolayer adsorption. The adsorption Cr(VI) is favorable under acidic and neutral conditions with maximum removal observed at pH 4. The adsorption of Cr(VI) is modestly inhibited by the presence of ⩾5 ppm humic acid. In summary, the adsorption of Cr(VI) by maghemite nanoparticles is rapid, can be accurately modeled, and is effective under a variety of conditions. Our results indicate these magnetic materials have promising potential to cleanup Cr(VI) contaminated waters to acceptable drinking water standards.