Intraparticle Surface Diffusion Research Articles

Development of a magnetic calcium-alginate hydrogel-sphere encapsulated with Fe–Mn–Zr ternary metal composite for heavy metal adsorption

Heavy metal contamination has become one of the greatest global environmental problems. In this study, a magnetic calcium-alginate hydrogel-sphere encapsulated with Fe–Mn–Zr ternary-metal composite (MCHETC) was prepared through a combined co-precipitation and extrusion approach and used for the adsorption of heavy metals in aqueous solutions. The active sites were dispersed in the MCHETC, which can be separated by the magnetic force for the ease in operation. Above 80% of ultimate adsorption was completed at a contact time of 5 h. The copper uptake history was well described by the intraparticle surface diffusion model, suggesting a multi-step process for the adsorption. The optimum pH for adsorption was 4; the maximum adsorption capacity was 103.1 mg-Cu/g. The adsorption capability well remained after the 5 adsorption–desorption cycles and the copper could be recovered. Furthermore, the adsorbent performed well in the nature water spiked with copper ions. The mechanism studies illustrated that the adsorption was mainly controlled by the ion-exchange reaction. This study demonstrated that the MCHETC adsorption technology may be used for heavy metal removal and recovery with higher efficacy.

Gadolinium(III) terephthalate metal-organic framework for rapid sequestration of phosphate in 10 min: Material development and adsorption study

Phosphorus with concentration above a few ppm in waters can easily cause eutrophication and poor water quality (e.g. algal blooming). In this study, we synthesized a non-porous gadolinium terephthalic acid (Gd-PTA) metal-organic framework (MOF) for efficient and rapid removal of phosphorus. Gd-PTA was prepared with gadolinium as the core metal center and terephthalic acid as the organic ligand, by which a well defined structure of new MOF was established. The adsorption isotherm and kinetics were well described by Langmuir isotherm equation and the intraparticle surface diffusion model, respectively. The maximum adsorption capacity was as high as 206.13- PO43− mg/g, which outperforms many reported and/or commercially available adsorbents (normmaly 5–150 PO43− mg/g). The adsorption was completed at the end of 10-min contact time, much faster than many reported adsorbents for uptake of anions (normmaly hours to days). The MOF performed very well in the uptake in phosphate containing solution with initial pH 3 to 9 and ionic strength (NaNO3) of 0–1 M, and in the presences of competiting sulphate, nitrate, carbonate and humic acid (each with 30, 50, and 100 mg/L). The absorption of phosphate was mainly controlled by ion exchange between phosphate and organic ligand of MOF as well as the interaction between unsaturated metal center of coordination and phosphate. This study demonstrates that the newly developed MOF reported here is a promising adsorbent for cost-effective treatment of phosphorus in water and wastewater.

Cost-effective phosphorus removal from aqueous solution by a chitosan/lanthanum hydrogel bead: Material development, characterization of uptake process and investigation of mechanisms

Excessive phosphorus is one of the main reasons leading to eutrophication that causes severe ecosystem imbalance and negative human health impacts. In this study, several chitosan (CS)/lanthanum (La) hydrogel beads were first synthesized and tested for phosphorus removal. The stable cross-linked CS/La hydrogel bead prepared with the optimized conditions of 10 wt% La/CS and 1.5 mL of 5% glutaraldehyde demonstrated exceptional performance in the removal. It removed phosphate effectively from an aqueous solution in the pH range from 2 to 7. The complete phosphate uptake was achieved at contact time of 6 h under the completely mixing batch condition. The experimental maximum adsorption capacity of 107.7 mg g−1 was observed at solution pH 4. The phosphate adsorption was well described by the Freundlich isotherm and the intraparticle surface diffusion model. Furthermore, the adsorbent was effectively regenerated and reused in a five-cycle adsorption-desorption operation. The removal of phosphate can be attributed to electrostatic attraction and ion exchange. Moreover, the bead was capable of removing heavy metals: copper, zinc and lead. This adsorbent may be served as a cost-effective material for the treatment of phosphorus-contaminated water so as to minimize the occurrence of eutrophication.

Great enhancement in phosphate uptake onto lanthanum carbonate grafted microfibrous composite under a low-voltage electrostatic field

Removal of phosphorus from water via cost-effective measures becomes important for water industry mainly due to eutrophication in waterbody. In our lab, a novel lanthanum carbonate-microfibrous composite (LC-MC) with good performance was previously synthesized for the removal of phosphorus. In this study, we further improved our technology by applying the electrostatic field (direct current, DC) to the adsorption system. It was showed that the applied DC can greatly improve the adsorption of phosphate in particular the adsorption capacity. Better removal was seen in the pH range of 5–9 at a higher temperature. The maximum adsorption capacity of 47.57 mg-PO43− g−1 was achieved, which was 1.4 times of that operated in the absence of applied DC. The adsorption equilibrium was established at the contact time of 240 min; the adsorption history was well described by the intraparticle surface diffusion model. The negative effect from oxygen-containing anions on the phosphate uptake followed the decreasing sequence of: humic acid > carbonate > nitrate > sulfate; on the other hand, the halogen anions had almost no influence on it. Finally, the mechanism study by XPS, XRD, and IR demonstrated that the ligand exchange played an important role in the electro-assisted phosphate uptake process.

Mathematical modeling of arsenic(V) adsorption onto iron oxyhydroxides in an adsorption-submerged membrane hybrid system

The adsorption of arsenic (V), As(V), on two porous iron oxyhydroxide-based adsorbents, namely, micro-sized tetravalent manganese feroxyhyte (μTMF) and granular ferric hydroxide (μGFH), applied in a submerged microfiltration membrane hybrid system has been investigated and modeled. Batch adsorption tests were carried out to determine adsorption equilibrium and kinetics parameters of As(V) in a bench-scale slurry reactor setup. A mathematical model has been developed to describe the kinetic data as well as to predict the As(V) breakthrough curves in the hybrid system based on the homogeneous surface diffusion model (HSDM) and the corresponding solute mass balance equation. The kinetic parameters describing the mass transfer resistance due to intraparticle surface diffusion (Ds) involved in the HSDM was determined. The fitted Ds values for the smaller (1–63 μm) and larger (1–250 μm) diameter particles of μGFH and μTMF were estimated to be 1.09 × 10−18 m2/s and 1.53 × 10-16 m2/s, and 2.26 × 10−18 m2/s and 1.01 × 10-16 m2/s, respectively. The estimated values of mass transfer coefficient/ kinetic parameters are then applied in the developed model to predict the As(V) concentration profiles in the effluent of the hybrid membrane system. The predicted results were compared with experimental data for As(V) removal and showed an excellent agreement. After validation at varying adsorbent doses and membrane fluxes, the developed mathematical model was used to predict the influence of different operation conditions on As(V) effluent concentration profile. The model simulations also exhibit that the hybrid system benefits from increasing the amount of adsorbent initially dosed and from decreasing the membrane flux (increasing the contact time).

Removal of iodide from water using silver nanoparticles-impregnated synthetic zeolites

Synthetic zeolite-based Ag-nanocomposites were synthesized, characterized and used to remove iodide from aqueous solutions. The results showed high removal efficiency (up to 94.85%) and the formation silver iodide which is stable into the material. The maximum achieved adsorption capacity of the nanocomposites was between 19.54 and 20.44mg/g. The removal mechanism was meticulously studied by taking into account both water chemistry and surface interactions backed by multiple characterization techniques, such as XRD, XRF, SEM/EDX, TEM and BET. The qualitative and quantitative examination of pre- and post-adsorption of nanocomposite samples proved that the anchored silver iodide was formed via oxidation of initial silver nanoparticles followed by reaction with iodide to form a stable crystalline precipitate on the surface of the materials. A diffusion-based adsorption model indicated that the controlling mechanism is a slow intraparticle surface diffusion with diffusion coefficients in the range of 0.37–1.72×10−13cm2/s. The investigation of competing and co-existing anions (Cl−, Br−, CO32−, and CrO42−) on the removal efficiency of iodide demonstrated a negligible effect showing a kinetically favorable precipitation reaction of iodide over other anions.

Treatment of methylene blue containing wastewater by a cost-effective micro-scale biochar/polysulfone mixed matrix hollow fiber membrane: Performance and mechanism studies

Dye containing wastewater has increasingly become an important contamination due to operation of various industries such as textile industry. In this study, a micro-scale biochar particles/polysulfone mixed matrix hollow fiber membrane (MMM) was applied for the removal of methylene blue from water. The static and dynamic adsorption performance was investigated. We found that the MMM exhibited a high removal efficiency of methylene blue under a wide pH range of 4–10. The adsorption process on biochar and MMM obeyed the intraparticle surface diffusion model and Langmuir isotherm model. At neutral pH, the maximum adsorption capacity was 544.459 mg/g for biochar and 165.808 mg/g for MMM. Better regeneration with a desorption rate above 92% was achieved by 1-M NaCl in 90% ethanol aqueous solution. Furthermore, the MMM displayed good performance in treating methylene blue containing wastewater through a continuous filtration mode. More importantly, the MMM showed an excellent reusability for methylene blue removal; it was able to achieve 81% of the permeate yield of the fresh MMM after three regeneration cycles. Finally, the adsorption mechanism studies indicated that the removal of methylene blue was associated with electrostatic interaction, hydrogen bonding and hydrophobic interaction.

Load-dependent surface diffusion model for analyzing the kinetics of protein adsorption onto mesoporous materials

The adsorption of cytochrome c in water onto organic and carbon xerogels with narrow pore size distributions has been studied by carrying out transient and equilibrium batch adsorption experiments. It was found that equilibrium adsorption exhibits a quasi-Langmuirian behavior (a g coefficient in the Redlich-Peterson isotherms of over 0.95) involving the formation of a monolayer of cyt c with a depth of ∼4nm on the surface of all xerogels for a packing density of the protein inside the pores of 0.29gcm–3. A load-dependent surface diffusion model (LDSDM) has been developed and numerically solved to fit the experimental kinetic adsorption curves. The results of the LDSDM show better fittings than the standard homogeneous surface diffusion model. The value of the external mass transfer coefficient obtained by numerical optimization confirms that the process is controlled by the intraparticle surface diffusion of cyt c. The surface diffusion coefficients decrease with increasing protein load down to zero for the maximum possible load. The decrease is steeper in the case of the xerogels with the smallest average pore diameter (∼15nm), the limit at which the zero-load diffusion coefficient of cyt c also begins to be negatively affected by interactions with the opposite wall of the pore.

Development of a novel biochar/PSF mixed matrix membrane and study of key parameters in treatment of copper and lead contaminated water

Mixed matrix membrane (MMM) has attracted increasing attentions in various applications, such as water treatment. In this study, an innovative biochar/polysulfone (PSF) mixed matrix hollow fiber membrane was fabricated by incorporating micro-sized biochar particles in the PSF matrix. It was demonstrated that the membrane was more hydrophilic than the pure PSF membrane. Higher water flux was obtained. The adsorption of copper and lead on the MMM increased as the pH was increased with the maximum adsorption capacity observed at pH > 4.5. The adsorption equilibrium was established in 7 and 12 h for lead and copper, respectively. The adsorption kinetics and isotherm followed the intraparticle surface diffusion model and Freundlich isotherm, respectively. The presence of humic acid (HA) had a little effect on the adsorption, while the ionic strength showed an adverse effect on the removal. In addition, the feed concentration and cross flow rate significantly affected the removal efficiency in a continuous filtration mode. The increase in feed concentration and cross flow rate resulted in a reduction in the volume of treated permeate that had the copper/lead concentrations below the regulated levels for drinking water. The MMM exhibited an excellent regeneration-reuse performance in the removal of both copper and lead. Finally, our mechanism studies indicated that the uptake of heavy metals was controlled by a combination of key reactions of complexation, ion-exchange and precipitation. This study indicated that the MMM can be applied as an effective and eco-friendly material for the treatment of heavy metals contaminated water.

Characterization of P-nitrophenol adsorption kinetic properties in batch and fixed bed adsorbers

P-nitrophenol (PNP) adsorption in batch and fixed bed adsorbers was studied. The homogeneous surface diffusion model (HSDM) based on external mass transfer and intraparticle surface diffusion was used to describe the adsorption kinetics for PNP in stirred batch adsorber at various initial concentrations and activated carbon dosages. The fixed bed model considering both external and internal mass transfer resistances as well as axial dispersion with non-linear isotherm was utilized to predict the fixed bed breakthrough curves for PNP adsorption under the conditions of different flow rates and inlet concentrations. The equilibrium parameters and surface diffusivity (D s ) were obtained from separate experiments in batch adsorber. The obtained value of D s is 4.187×1012 m2/s. The external film mass transfer coefficient (k f ) and axial dispersion coefficient (D L ) were estimated by the correlations of Goeuret and Wike-Chang. The Biot number determined by HSDM indicated that the adsorption rate of PNP onto activated carbon in stirred batch was controlled by intraparticle diffusion and film mass transfer. A sensitivity analysis was carried out and showed that the fixed bed model calculations were sensitive to D s and k f , but insensitive to D L . The sensitivity analysis and Biot number both confirm that intraparticle diffusion and film mass transfer are the controlling mass transfer mechanism in fixed bed adsorption system.

A zirconium-based nanoparticle: Essential factors for sustainable application in treatment of fluoride containing water

Excessive intake of fluoride can cause a severe threat on human beings. In this study, a zirconium-based nano-particles (NPs) was synthesized for effective defluoridation from aqueous solution. The pH effect, adsorption kinetics, adsorption isotherms, and effect of co-existing substances on the fluoride uptake were investigated. The results showed that the sorbent had a high adsorption capacity for fluoride within a wide pH ranging from 3 to 10. The optimal pH for the adsorption was around 4. The study of adsorption kinetics revealed that most uptake of fluoride occurred in the first 1h, and the adsorption equilibrium was established within 4h. Langmuir equation well described the adsorption isotherm data; the maximum adsorption capacities of 97.48 and 78.56mg/g were found at optimal pH and neutral pH, respectively. The presence of PO43-, NO3- and natural organic matters did not significantly inhibit the fluoride removal. However, both HCO3- and SiO23- retarded the removal. The regeneration revealed that the sorbent possessed a high reusability for defluoridation. The intraparticle surface diffusion model well described the adsorption kinetics. The FTIR and XPS analysis demonstrated that the adsorption of fluoride was mainly associated with the ion-exchange between sulfate and fluoride ions.

Adsorption behaviour of methylene blue on carbon nanoparticles

Nanoadsorbents have been regarded as promising materials for water treatment. The adsorption behaviour determines the applications of nanoadsorbents. In this reported work, the authors studied the adsorption behaviour of methylene blue on oxidised carbon nanoparticles (O-CNPs) in batch experiments. The adsorption data were fitted by the Freundlich model, rather than the Langmuir model. The kinetics studies indicated that it followed the pseudo-second-order model. The intraparticle diffusion model fitting suggested that the adsorption involved both intraparticle diffusion and surface diffusion. The adsorption was more effective at higher pH and lower ionic strength. The implication for the applications of O-CNPs in water treatment is discussed.

Kinetics of acrylonitrile adsorption from an aqueous solution using Dowex Optipore L-493

Adsorption is widely applied in water treatment and activated carbon is the most common adsorbent. Slow intraparticle mass transfer and incomplete regeneration of the activated carbon form drawbacks in adsorption processes. Recently the use of polymeric sorbents as an alternative for activated carbon has been increasing. In this study the kinetics of the adsorption of acrylonitrile from an aqueous solution onto Dowex Optipore L-493, a polymeric sorbent, is examined using zero-length columns. The adsorption equilibrium was found by use of batch experiments and it could be described by a Langmuir isotherm. The external mass transfer was estimated by use of correlations. The intraparticle surface diffusion coefficient was found to be 2.0 × 10 −10 m 2/s. The fast intraparticle mass transfer allows running adsorption columns with a high superficial velocity which is desirable for industrial processes.

Design and fabrication of an innovative and environmental friendly adsorbent for boron removal

Boron can pose adverse effects on human beings and plants species. It exists in various water environments and is difficult to be removed by conventional technologies. In this study, an efficient and environmental friendly sorbent was fabricated by the functionalization of a natural biopolymer, chitosan, with N-methylglucamine through atom transfer radical polymerization. The SEM and BET studies revealed that the sorbent had a rougher surface and a more porous structure than the chitosan. At the optimum neutral pH, the maximum sorption capacity was as high as 3.25 mmol/g, much higher than the commercial boron selective resins (e.g., Amberlite IRA-743) and many other synthesized sorbents. Almost 90% of boron sorption occurred within 8 h and the equilibrium was established in 12 h, which was well described by an intraparticle surface diffusion model. The presence of sodium chloride and sodium nitrate had no effect on the boron removal. The boron concentration in seawater could be reduced to less than 0.5 mg/L from 4.8 mg/L when a sorbent dosage of 1.2 g/L was used. It was therefore concluded that the sorption technology from this study could be promising for boron removal from aqueous solutions.

Improvement of metal adsorption onto chitosan/ Sargassum sp. composite sorbent by an innovative ion-imprint technology

Technology for immobilization of biomass has attracted a great interest due to the high sorption capacity of biomass for sequestration of toxic metals from industrial effluents. However, the currently practiced immobilization methods normally reduce the metal sorption capacities. In this study, an innovative ion-imprint technology was developed to overcome the drawback. Copper ion was first imprinted onto the functional groups of chitosan that formed a pellet-typed sorbent through the granulation with Sargassum sp.; the imprinted copper ion was chemically detached from the sorbent, leading to the formation of a novel copper ion-imprinted chitosan/ Sargassum sp. (CICS) composite adsorbent. The copper sorption on CICS was found to be highly pH-dependent and the maximum uptake capacity was achieved at pH 4.7–5.5. The adsorption isotherm study showed the maximum sorption capacity of CICS of 1.08 mmol/g, much higher than the non-imprinted chitosan/ Sargassum sp. sorbent (NICS) (0.49 mmol/g). The used sorbent was reusable after being regenerated through desorption. The FTIR and XPS studies revealed that the greater sorption of heavy metal was attributed to the large number of primary amine groups available on the surfaces of the ion-imprinted chitosan and the abundant carboxyl groups on Sargassum sp. Finally, an intraparticle surface diffusion controlled model well described the sorption history of the sorbents.

Surface complexation of Pb(II) on amorphous iron oxide and manganese oxide: Spectroscopic and time studies

Hydrous Fe and Mn oxides (HFO and HMO) are important sinks for heavy metals and Pb(II) is one of the more prevalent metal contaminants in the environment. In this work, Pb(II) sorption to HFO (Fe 2O 3⋅ nH 2O, n = 1 – 3 ) and HMO (MnO 2) surfaces has been studied with EXAFS: mononuclear bidentate surface complexes were observed on FeO 6 (MnO 6) octahedra with Pb O distance of 2.25–2.35 Å and Pb Fe(Mn) distances of 3.29–3.36 (3.65–3.76) Å. These surface complexes were invariant of pH 5 and 6, ionic strength 2.8 × 10 −3 to 1.5 × 10 −2 , loading 2.03 × 10 −4 to 9.1 × 10 −3 mol Pb / g , and reaction time up to 21 months. EXAFS data at the Fe K-edge revealed that freshly precipitated HFO exhibits short-range order; the sorbed Pb(II) ions do not substitute for Fe but may inhibit crystallization of HFO. Pb(II) sorbed to HFO through a rapid initial uptake (∼77%) followed by a slow intraparticle diffusion step (∼23%) resulting in a surface diffusivity of 2.5 × 10 −15 cm 2 / s . Results from this study suggest that mechanistic investigations provide a solid basis for successful adsorption modeling and that inclusion of intraparticle surface diffusion may lead to improved geochemical transport depiction.

The impact of Mn oxide coatings on Zn distribution

Zinc sorption to hydrous manganese oxide (HMO)-coated clay was investigated macroscopically, kinetically, and spectroscopically. Adsorption edges and isotherms revealed that the affinity and capacity of the HMO-coated montmorillonite was greater than that of montmorillonite, and when normalized to the oxide present, the coatings behaved similarly to the discrete Mn oxide. Over two pH conditions, 5 and 6, a linear relationship was observed for the isotherms; further analysis with X-ray absorption spectroscopy (XAS) resulted in one type of sorption configuration as a function of loading and ionic strength at pH 5. However, at a surface loading of 10 −3 mol Zn g HMO - coated clay −1 when the pH increased from 5 to 7, the first shell distance decreased slightly, while the atoms and coordination numbers remained the same; this change may be attributed to an increase in electrostatic interactions. After a contact time of 4 months where an additional 60% of the sites become occupied, the slower sorption process was modeled as intraparticle surface diffusion. Best fit diffusivities ranged from 10 −18 to 10 −17 cm 2 / s , where a slower process was observed for the coated surface as compared to the discrete oxide. Interestingly, the porosity of the Mn oxide coating appears to be influenced by the substrate during its growth, as its increase and shift to a smaller pore size distribution resulted in a diffusivity between that observed for discrete HMO and montmorillonite.

Intraparticle diffusion and adsorption of arsenate onto granular ferric hydroxide (GFH).

Porous iron oxides are being evaluated and selected for arsenic removal in potable water systems. Granular ferric hydroxide, a typical porous iron adsorbent, is commercially available and frequently considered in evaluation of arsenic removal methods. GFH is a highly porous (micropore volume approximately 0.0394+/-0.0056 cm(3)g(-1), mesopore volume approximately 0.0995+/-0.0096 cm(3)g(-1)) adsorbent with a BET surface area of 235+/-8 m(2)g(-1). The purpose of this paper is to quantify arsenate adsorption kinetics on GFH and to determine if intraparticle diffusion is a rate-limiting step for arsenic removal in packed-bed treatment systems. Data from bottle-point isotherm and differential column batch reactor (DCBR) experiments were used to estimate Freundlich isotherm parameters (K and 1/n) as well as kinetic parameters describing mass transfer resistances due to film diffusion (k(f)) and intraparticle surface diffusion (D(s)). The pseudo-equilibrium (18 days of contact time) arsenate adsorption density at pH 7 was 8 microg As/mg dry GFH at a liquid phase arsenate concentration of 10 microg As/L. The homogeneous surface diffusion model (HSDM) was used to describe the DCBR data. A non-linear relationship (D(S)=3.0(-9) x R(p)(1.4)) was observed between D(s) and GFH particle radius (R(P)) with D(s) values ranging from 2.98 x 10(-12) cm(2)s(-1) for the smallest GFH mesh size (100 x 140) to 64 x 10(-11) cm(2)s(-1) for the largest GFH mesh size (10 x 30). The rate-limiting process of intraparticle surface diffusion for arsenate adsorption by porous iron oxides appears analogous to organic compound adsorption by activated carbon despite differences in adsorption mechanisms (inner-sphere complexes for As versus hydrophobic interactions for organic contaminants). The findings are discussed in the context of intraparticle surface diffusion affecting packed-bed treatment system design and application of rapid small-scale column tests (RSSCTs) to simulate the performance of pilot- or full-scale systems at the bench-scale.

Importance of Surface Diffusivities in Pesticide Adsorption Kinetics onto Granular Versus Powdered Activated Carbon: Experimental Determination and Modeling

Three pesticides (atrazine, bromoxynil and diuron) and two granular activated carbons are involved in equilibrium and kinetic adsorption experiments. Equilibrium is represented by Freundlich isotherm law and kinetic is described by the Homogeneous Surface Diffusion Model, based on external mass transfer and intraparticle surface diffusion. Equilibrium and long-term experiments are conducted to compare Powdered Activated Carbon and Granular Activated Carbon. These first investigations show that crushing GAC into PAC improves the accessibility of the adsorption sites without increasing the number of these sites. In a second part, kinetics experiments are carried out using a Differential Column Batch Reactor. Thanks to this experimental device, the external mass transfer coefficient kf is calculated from empirical correlation and the effect of external mass transfer on adsorption is likely to be minimized. In order to obtain the intraparticle surface diffusion coefficient Ds for these pesticides, comparisons between experimental kinetic data and simulations are conducted and the best agreement leads to the Ds coefficient. This procedure appears to be an efficient way to acquire surface diffusion coefficients for the adsorption of pesticides onto GAC. Finally it points out the role of surface diffusivity in the adsorption rate. As a matter of fact, even if the amount of the target-compound that could be potentially adsorbed is really important, its surface diffusion coefficient may be small, so that its adsorption may not have enough contact time to be totally achieved.

Effect of adsorbent shape on adsorption dynamics in a batch adsorber

This note compares adsorption dynamic processes in a batch adsorber for three shapes of adsorbents: spherical, planar and cylindrical (fibrous), with concentration-dependent surface diffusivities and involving both intraparticle surface diffusion and film mass transfer resistance.