Half-adsorption Time Research Articles

Environmental risk mitigation of lambda-cyhalothrin using tryptophan-modified magnetic nanoparticles: A sustainable emergency response strategy

Lambda-cyhalothrin, a synthetic pyrethroid pesticide extensively used in agriculture, poses significant environmental challenges due to its extensive and long-term application. To remediate pollution caused by such organic contaminants, our study introduces a rapid and convenient one-pot synthesis method for creating amino acid-modified magnetic nano-adsorbents (AA-MNPs). Research found that after modification with tryptophan (Trp), the adsorption effectiveness of MNPs on Lambda-cyhalothrin significantly increases. This modification enhances the carbon content of the magnetic nanoparticles, while minimally affecting the magnetic saturation of the MNPs. Trp-MNP exhibited an approximate particle size of 450 nm and a specific surface area of 52.36 m2 g-1. The isotherm and kinetic experiments were well-fitted to the Liu isotherm model and the pseudo-second-order model, respectively. Thermodynamic assessments suggested that the adsorption process is spontaneous and exothermic. Results indicated that the maximum adsorption capacity 144.34 mg g-1 for Trp-MNPs at 298 K, outperforming adsorbents reported in the literature. The half-adsorption time was reduced to 8 min at 298 K with an initial concentration of 60 mg L-1. This enhancement was likely influenced by the aromatic ring modification and hydrophobicity of Trp-MNPs. The study explored potential removal mechanisms from a tri-phase perspective, investigating the interactions between the adsorbent, adsorbate, and solvent.

Enhancing the affinity and adsorption efficiency of Glochidion ericarpum Champ leave extract to cotton for colouristic and functional properties integrating trimethyl chitosan and ultrasonic technique

Recently, sustainable fabrication of hygiene-related textiles combining bioactive substances and cleaner production technique has been increasingly emphasized. This research introduces an efficient ultrasonic-assisted electrostatic co-deposition strategy for colouristic, antibacterial and ultraviolet (UV) protective cotton fabric with trimethyl chitosan (TMC) – a chitosan derivative, and Glochidion ericarpum Champ leave extract (GECLE). Results reveal that TMC significantly promotes the adsorption of GECLE to cotton by creating additional cationic binding sites. Based on Pesudo first-/second-order kinetic models, chemisorption is verified as the dominant mechanism triggered by the electrostatic interaction between TMC and GECLE. Indicated by adsorption rate constant k, the efficiency under ultrasound is enhanced by 13.5 % (60 °C) and 23.8 % (80 °C). Correspondingly, the half adsorption time (t1/2) is shortened by 29.5 % (60 °C) and 37.9 % (80 °C), which approximately saves 16.66 × 103 kJ (60 °C) and 31.31 × 103 kJ (80 °C) of energy. Through mathematical modelling, the factors that influenced the colour depth occured in the following order of importance: Concentration > pH > Temperature. Under optimal condition (GECLE concentration 9.36 g/L, pH 1.63 and temperature 61.70 °C), a theoretical maximum K/S value of 10.25 is achieved. Integrating the analyses above, a triple interactive scheme among TMC, GECLE and cotton fibre is proposed. GECLE (10 g/L) treated cotton deactivates up to 95% of Escherichia coli with 80% retention after 5 repeated launderings, and also provides an ‘Excellent’ rate of UV shielding performance. In general, the ultrasonic-assisted eco-dyeing and finishing process for cotton is explored in depth from practical and theoretical perspectives, which pushes forward the development of sustainable textile industry.

Adsorption Mechanism of Lead on Wood/Nano-Manganese Oxide Composite

Discharge of untreated industrial wastewater containing heavy metals such as Pb2+ is hazardous to the environment due to their high toxicity. This study reports on the adsorption, desorption, and kinetic study on Pb2+ removal from aqueous solutions using wood/Nano-manganese oxide composite (WB-NMO). The optimum pH, contact time and temperature for adsorption were found to be 5.0, 4 h and 333 K, respectively. Pseudo-second-order kinetics best described the adsorption process with an initial sorption rate of 4.0 mg g min-1, and a half-adsorption time t1/2 of 31.6 min. Best fit for adsorption isotherm was obtained with the Brunauer-Emmett-Teller (BET) model with a maximum adsorption capacity of 213 mg/g for an initial metal concentration of 60 mg/L. Both intra-particle diffusion and film diffusion contribute to the rate-determining step. Desorption experiments with 0.5 mol/L HCl, inferred the reusability of the composite. Adsorption experiment of Pb2+ from industrial wastewater confirmed that the prepared WB-NMO is a promising candidate for wastewater treatment. The WB-NMO demonstrated high Pb2+ removal efficiency and is considered as a promising alternative and reusable composite for lead removal from contaminated effluents.

A comparative adsorption study: 17β-estradiol onto aerobic granular sludge and activated sludge

Adsorption plays a significant role in removing hydrophobic 17β-estradiol (E2) from wastewater. Batch experiments were conducted to compare the adsorption of E2 onto activated aerobic granular sludge (AGS) and activated sludge (AS), and features evaluated included the adsorption kinetics, thermodynamics, and influence of other environmental factors. By using a non-chemical wet-heat technique, both AGS and AS were treated to inactivated status. Then, after loading E2, the adsorption equilibrium capacity of the AGS was found to be greater than that of the AS at the same initial concentration of E2. Moreover, both the adsorption processes corresponded to a pseudo-second-order kinetic model; the adsorption rate constant of AGS was found to be higher and the half-adsorption time was shorter than that of AS. Next, evaluations of adsorption isotherms and thermodynamics indicated that the adsorption process was mainly a physical process. Lower temperatures facilitated a higher equilibrium adsorption capacity. However, the adsorption binding sites of AGS were distributed more uniformly at higher temperature, in contrast to the distribution found for AS. Finally, acidic conditions and an appropriate ionic strength (0.4 mol/L) were found to be particularly conducive to the adsorption process. Overall, the results showed that AGS has the potential to adsorb E2 with significant efficiency, thereby offering a new and more efficient means of treating E2 and trace oestrogens in wastewater.

Particle-Assisted Ion-Imprinted Cryogels for Selective CdIIIon Removal

Herein, we have reported particle-assisted ion-imprinted cryogels, which were synthesized by embedding finely crushed functional particles into cryogel structure under semifrozen conditions. These cryogels showed high adsorption efficiency and affinity against CdII ions. CdII adsorption performances were evaluated by varying some effective factors. In order to analyze the data, we applied Langmuir and Freundlich adsorption isotherms while using three different kinetic models, pseudo-first-order, pseudo-second-order, and Weber–Morris as well. Also, the dimensionless equilibrium parameter (RL), initial adsorption rate, and half-adsorption time were calculated. The results revealed that ion-imprinted-polymer (IIP) cryogels have homogeneously distributed cavities, which were formed by a particle-assisted imprinting process, and the theoretical maximum adsorption capacity (Qmax, 35.97 μg/g) was very close to the experimental value (Qeq, 32.15 μg/g). In addition, RL values for both IIP and nonimprinted-polymer cryogels showed favorability of the adsorption process, while kinetic models indicated that there were no diffusion limitations during the adsorption process, which means that the rate-limiting step was chemosorption of heavy-metal ions on binding sites (imprinted cavities or functional groups) with a high initial adsorption rate and a low half-adsorption time. Desorption, reusability, and selectivity studies were also conducted to state the performance of the cryogels. In conclusion, this promising approach provides a novel methodology for selective CdII removal from water sources.

Structure and properties of cotton fabrics treated with functionalized dialdehyde chitosan

In this research, modified cotton fabrics were prepared by pad-dry-cure technique from the aldehyde chitosan solution containing 3-aminopropyltriethoxysilane (APTES) and 1,2-ethanediamine (EDA) respectively. The structural characterization of the modified cotton fabrics was performed by attenuated total reflection ATR, scanning electron microscopy (SEM) and thermogravimetry (TG) analysis and physical mechanical properties were measured. The adsorption kinetics of modified cotton fabrics were also investigated by using the pseudo first-order and pseudo second-order kinetic model. The dyeing rate constant k1, k2 and half adsorption time t1/2 were calculated, respectively. The results show that the mechanical properties of different modified cotton fabrics were improved, and the surface color depth values (K/S), UV index UPF and anti-wrinkle properties were better than those of untreated cotton. Dyeing kinetics data at different temperatures indicate that Direct Pink 12B up-take on the modified cotton fabrics fitted to pseudo second-order kinetic model.

Magnetically modified coffee silverskin for the removal of xenobiotics from wastewater

Coffee silverskin (CS), a solid waste from the coffee industry, was magnetically modified by contact with an aqueous ferrofluid containing magnetite nanoparticles. The resulting material was characterized by SEM-EDX analysis and X-ray diffraction. To assess the suitability of the magnetically modified CS for the removal of pollutants from wastewaters, both equilibrium and kinetic adsorption experiments were performed. Methylene blue was used as a model contaminant. Equilibrium and kinetic data were fitted by the Langmuir equation and the pseudo-secondorder model. A maximum adsorption capacity of 556 mg g –1 and a half-adsorption time ranging from 12.8 to 35.3 min were determined. The magnetically modified adsorbent was regenerated by washing with 0.01 N HCl and recovered from the aqueous solution by a permanent magnet. Overall, the results obtained strongly support the use of the magnetic material developed as a new lowcost adsorbent for the large-scale removal of pollutants from wastewater.

Removal of Methylene Blue from Aqueous Solution by Adsorption on Low-Grade Green Coffee Beans

Low-grade coffee beans (LCBs), a waste produced in large quantities by the coffee industry, was investigated as a potential low-cost adsorbent for the removal of methylene blue (MB) from wastewater. The waste was characterized by SEM analysis and FTIR spectroscopy. Equilibrium and kinetic experiments were performed to study the adsorption process. The equilibrium data were found to be well described by the Langmuir model, from which a maximum adsorption capacity of 476.2 mg g1was derived. A half-adsorption time ranging from 12.5 to 96.2 min was estimated by fitting the experimental kinetic data to the pseudo-second-order model.

Removal of cationic dye methylene blue (MB) from aqueous solution by ground raw and base modified pine cone powder

The adsorption capacity of raw and sodium hydroxide-treated pine cone powder in the removal of methylene blue (MB) from aqueous solution was investigated in a batch system. It was found that the base modified pine cone exhibits large adsorption capacity compared with raw pine cone. The extent of adsorption capacity was increased with the increase in NaOH concentration. Overall, the extent of MB dye adsorption increased with increase in initial dye concentration, contact time, and solution pH but decreased with increase in salt concentration and temperature for both the systems. Surface characteristics of pine cone and base modified pine cone were investigated using Fourier transform infrared spectrophotometer and scanning electron microscope. Equilibrium data were best described by both Langmuir isotherm and Freundlich adsorption isotherm. The maximum monolayer adsorption capacity was found to be 129.87 mg g−1 at solution pH of 9.02 for an initial dye concentration of 10 ppm by raw pine cone. The base modified pine cone showed the higher monolayer adsorption capacity of 142.25 mg g−1 compared with raw pine cone biomass. The value of separation factor, R L, from Langmuir equation and Freundlich constant, n, both give an indication of favourable adsorption. The various kinetic models, such as pseudo-first-order model, pseudo-second-order model, intraparticle diffusion model, double-exponential model, and liquid film diffusion model, were used to describe the kinetic and mechanism of adsorption process. Overall, kinetic studies showed that the dye adsorption process followed pseudo-second-order kinetics based on other models. The different kinetic parameters, including rate constant, half-adsorption time and diffusion coefficient, were determined at different physicochemical conditions. A single-stage bath adsorber design for the MB adsorption onto pine cone and modified pine cone has been presented based on the Langmuir isotherm model equation. Thermodynamic parameters, such as standard Gibbs free energy (ΔG 0), standard enthalpy (ΔH 0) and standard entropy (ΔS 0), were also calculated.

Adsorption of methylene blue onto spinel magnesium aluminate nanoparticles: Adsorption isotherms, kinetic and thermodynamic studies

Magnesium aluminate spinel has been synthesized at nanoscale by coprecipitation method. The synthesized material was characterized for the phase composition, quantitative description, surface morphology, surface area, pore volume and pore diameter. X-ray diffraction analysis confirmed the formation of the cubic spinel phase with no peaks corresponding to the impurity phases. The Scherrer crystallite size calculated from line broadening is 20nm. The pore surface area was found to be 343m2/g by N2 vapor adsorption experiments and material was characterized as mesoporous on the basis of pore diameter analysis. The scanning electron micrograph shows the agglomeration of particles while the nanosize is confirmed by the transmission electron micrograph. The porous nature of the material was then explored for carrying out the adsorption of methylene blue solutions onto the surface. Adsorption studies were carried out with 0.1g of the material and the effect of pH and shaking times were studied and both were found to influence the adsorption. Adsorption data was also fitted to Temkin, Freundlich and the Langmuir adsorption models in order to study the mechanism of adsorption by interpreting the calculated parameters like, heat of adsorption (BT), binding energy (KT), degree of adsorption (KF), heterogeneous factor (n), and energy of adsorption (KL), binding forces (aL), and the separation factor (RL). The pseudo-second order rate constant (Kp−2), initial sorption rate (Srate) and the half adsorption time (t1/2) were also calculated and explained to clarify the mechanism of adsorption onto MgAl2O4 surface. Gibbs free energy was also calculated from the adsorption data at room temperature.

Removal of anionic surfactant sodium dodecyl sulphate from aqueous solution by adsorption onto pine cone biomass of Pinus Radiate: equilibrium, thermodynamic, kinetics, mechanism and process design

Abstract This study was undertaken to evaluate the adsorption potential of a natural, low-cost agricultural by-product adsorbent, Pine cone (Pinus Radiate), to remove sodium dodecylsulfate (SDS) from aqueous solution. It was found that the extent of SDS adsorption by pine cone biomass increased with initial surfactant concentration and contact time but decreased with increasing solution pH, amount of adsorbent, and temperature of the system. These studies also suggested that the electrostatic forces and surfactant self-assembly are dominant mechanisms governing this pH dependent adsorption process. Overall, kinetic studies showed that the surfactant adsorption process followed pseudo-second-order kinetics based on pseudo-first-order and intraparticle diffusion models. The different kinetic parameters including rate constant, half adsorption time, and diffusion coefficient were determined at different physicochemical conditions. Equilibrium data were fitted by both the Langmuir isotherm and Freundlich adsorption isotherm. The maximum monolayer adsorption capacity of pine cone biomass was 95.75 mg g−1 at 20°C. The value of separation factor, R L from Langmuir equation and “n” from Freundlich also indicated favourable adsorption. Thermodynamic parameters such as ΔG 0, ΔH 0, and ΔS 0 were calculated. A single-stage batch absorber design for the SDS adsorption onto pine cone biomass also presented based on the Freundlich isotherm model equation.

Investigating the adsorption performance of nanoscale pigment on cationized cotton substrate

In this research, a nanoscale suspension of phthalocyanine blue pigment was prepared with the assistance of a polymeric dispersant using a micro-jet milling method. The analysis of particle size distribution indicates that the pigment has a.80nm particle size in suspension. The zeta potential measurement shows that the polymeric dispersant can offer zeta potentials over -30mv on the pigment surface, which can ensure the pigment suspension in good stability. The adsorption properties of this nanoscale pigment on cationized cotton fabrics were investigated, and factors affecting the pigment adsorption such as bath pH, salt concentration and time were studied. The kinetics of pigment adsorption was studied by using the pseudo first-order kinetic model, and the adsorption rate constant k1, half adsorption time t1/2 and adsorption activation energy Ea were calculated, respectively.

Removal of anionic dye Congo red from aqueous solution by raw pine and acid-treated pine cone powder as adsorbent: Equilibrium, thermodynamic, kinetics, mechanism and process design

Pine cone a natural, low-cost agricultural by-product in Australia has been studied for its potential application as an adsorbent in its raw and hydrochloric acid modified form. Surface study of pine cone and treated pine cone was investigated using Fourier transform infrared (FTIR) and scanning electron microscopy (SEM). The modification process leads to increases in the specific surface area and decreases mean particle sizes of acid-treated pine cone when compared to raw pine cone biomass. Batch adsorption experiments were performed to remove anionic dye Congo red from aqueous solution. It was found that the extent of Congo red adsorption by both raw pine cone biomass and acid-treated biomass increased with initial dye concentration, contact time, temperature but decreased with increasing solution pH and amount of adsorbent of the system. Overall, kinetic studies showed that the dye adsorption process followed pseudo-second-order kinetics based on pseudo-first-order and intra-particle diffusion models. The different kinetic parameters including rate constant, half-adsorption time, and diffusion coefficient were determined at different physico-chemical conditions. Equilibrium data were best represented by Freundlich isotherm model among Langmuir and Freundlich adsorption isotherm models. It was observed that the adsorption was pH dependent and the maximum adsorption of 32.65mg/g occurred at pH of 3.55 for an initial dye concentration of 20ppm by raw pine cone, whereas for acid-treated pine cone the maximum adsorption of 40.19mg/g for the same experimental conditions. Freundlich constant ‘n’ also indicated favourable adsorption. Thermodynamic parameters such as ∆G0, ∆H0, and ∆S0 were calculated. A single-stage batch absorber design for the Congo red adsorption onto pine cone biomass also presented based on the Freundlich isotherm model equation.

Performance of rattle-type magnetic mesoporous silica spheres in the adsorption of single and binary antibiotics

The rattle-type γ-Fe 2O 3/mesoporous silica spheres (γ-Fe 2O 3/mSiO 2 spheres) were synthesized with a facial and selectively etching strategy. The prepared particles were characterized by FT-IR, XRD, TEM, SEM, VSM, Raman spectroscopy and nitrogen adsorption–desorption analysis, and the results indicated that γ-Fe 2O 3/mSiO 2 spheres exhibited magnetic property ( M s = 14.43 emu g −1) and composed of mesoporous silica (mean diameter, thickness and pore size was 660 nm, 60 nm, and 2.29 nm, respectively). Then the γ-Fe 2O 3/mSiO 2 spheres were employed as sorbents to remove tetracycline (TC) and sulfamethazine (SMZ) in both single and binary aqueous solutions. The adsorption kinetics of γ-Fe 2O 3/mSiO 2 spheres were well-described by the pseudo-second-order equation, initial adsorption rate, and half-adsorption time. The Langmuir isotherm model was fitted to the equilibrium data better than that for Freundlich model, and the monolayer adsorption capacity of γ-Fe 2O 3/mSiO 2 spheres for TC and SMZ were 0.0791 mmol g −1 and 0.0342 mmol g −1 at 298 K, respectively. In binary systems, SMZ adsorption onto γ-Fe 2O 3/mSiO 2 spheres was more affected by the simultaneous presence of competitive antibiotics than that for TC. In addition, the reusability of the material without obviously deterioration in performance was observed at least four repealed cycles.

Magnetic molecularly imprinted polymers based on attapulgite/Fe 3O 4 particles for the selective recognition of 2,4-dichlorophenol

Via encapsulation of attapulgite/Fe 3O 4 magnetic particles (ATP/Fe 3O 4), the magnetic molecularly imprinted polymers (MMIPs) were synthesized for the selective recognition of 2,4-dichlorophenol (2,4-DCP). MMIPs were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) analysis, thermogravimetric analysis (TGA), vibrating sample magnetometer (VSM), transmission electron microscopy (TEM), nitrogen adsorption–desorption analysis and Raman spectroscopy. MMIPs were demonstrated claviform shape with an imprinted polymer film (thickness of about 16 nm), and exhibited magnetic property ( M s = 5.67 emu g −1) and thermal stability. Batch mode adsorption studies were carried out to investigate the specific binding capacity, binding kinetics and recognition specificity. The Langmuir isotherm model was fitted to the equilibrium data better than the other models, and the monolayer adsorption capacity of MMIPs were 145.79 mg g −1 at 298 K. The kinetic properties of MMIPs were well described by the pseudo-second-order equation, initial adsorption rate and half-adsorption time. The selective recognition experiments demonstrated high affinity and selectivity towards 2,4-DCP over structurally related phenolic compounds. In addition, MMIPs could be regenerated, and their adsorption capacity in the fifth use was about 7.53% loss in 2,4-DCP solution. The MMIPs as-prepared were successfully applied to the separation of 2,4-DCP from environmental water samples.

Selective recognition of 4‐nitrophenol from aqueous solution by molecularly imprinted polymers with functionalized tetratitanate whisker composites as support

Three kinds of molecularly imprinted polymers (MIPs) were obtained with surface molecular imprinting technique on functionalized potassium tetratitanate whisker (F-PTW). The results of adsorption experiments indicated that MIP prepared using PTW modified with N-(2-aminoethyl)-3-(trimethoxysilyl)propylamine (AAPTS) (F-PTW A) as support [MIP(1)] was superior to the other two polymers, then MIP(1) was selected to analyze the 4-nitrophenol (4-NP) adsorption process from aqueous solution in this study. AAPTS offered hydrophilic exterior that allowed to self-assemble with the template 4-NP through intermolecular interaction rather than based on the interactions between the functional monomers and template. Equilibrium adsorption data were analyzed by the Langmuir and Freundlich isotherm models at various temperatures. Kinetic properties were successfully investigated by pseudo-first-order model, pseudo-second-order model, intraparticle diffusion equation, initial adsorption rate, half-adsorption time. A diffusion-controlled process as the essential adsorption rate-controlling step was also proposed. The performance of such imprinted polymer was further demonstrated by high-performance liquid chromatography, and the results showed that the selectivity of MIP(1) exhibited higher affinity for template 4-NP over competitive phenolic compounds than that of non-imprinted polymer NIP(1). MIP(1) could be reused four times without significant loss in the adsorption capacity.

Adsorption Characteristics of Polyvinyl Alcohols in Solution on Expanded Graphite

Expanded graphite (EG) adsorbent was prepared with 50 mesh graphite as raw materials, potassium permanganate as oxidant, and vitriol as intercalation compound. Three kinds of polyvinyl alcohol (PVA) with different degree of polymerization (DP) in aqueous solution were used as adsorbates. We have studied the influence of initial PVA concentration, temperature and ionic strength on adsorption capacity. Langmuir constants and Gibbs free energy change (⊿G°) were calculated according to experimental data respectively. Thermodynamic analysis indicates the equilibrium adsorbance of PVA on EG increase with the rise of SO42– concentration. Adsorption isotherms of PVA with different degree of polymerization are all types and we deduce PVA molecules lie flat on EG surface. Adsorption processes are all spontaneous. Kinetic studies show that the kinetic data can be described by pseudo second‐order kinetic model. Second‐order rate constants and the initial adsorption rate rise with the increasing of temperature and half‐adsorption time decreases with the increasing of temperature. The adsorption activation energy of each PVA is less than 20 kJ•mol−1, physical adsorption is the major mode of the overall adsorption process.

Equilibrium, Kinetics and Mechanism of Removal of Methylene Blue from Aqueous Solution by Adsorption onto Pine Cone Biomass of Pinus radiata

The kinetics and mechanism of methylene blue adsorption onto raw pine cone biomass (Pinus radiata) was investigated under various physicochemical parameters. The extent of the methylene blue dye adsorption increased with increases in initial dye concentration, contact time and solution pH but decreases with the amount of adsorbent, salt concentration and temperature of the system. Overall the kinetic studies showed that the methylene blue adsorption process followed pseudo-second-order kinetics among various kinetic models tested. The different kinetic parameters including rate constant, half-adsorption time and diffusion coefficient are determined at different physicochemical conditions. Equilibrium data were best represented by Langmuir isotherm among Langmuir and Freundlich adsorption isotherm. The maximum monolayer adsorption capacity of pine cone biomass was 109.89 mg/g at 30°C. The value of separation factor, R L, from Langmuir equation and Freundlich constant, n, both give an indication of favourable adsorption. Thermodynamic parameters such as standard Gibbs free energy (∆G 0), standard enthalpy (∆H 0), standard entropy (∆S 0) and the activation energy (A) were calculated. A single-stage batch absorber design for the methylene blue adsorption onto pine cone biomass has been presented based on the Langmuir isotherm model equation.

Adsorption of zinc (Zn 2+) from aqueous solution on natural bentonite

The adsorptive properties of natural bentonite in the removal of zinc (Zn 2+) from aqueous solution were studied. The results show that the amount of adsorption of zinc metal ion increases with initial metal ion concentration, contact time, and solution pH but decreases with the amount of adsorbent and temperature of the system. Kinetic experiments clearly indicate that adsorption of zinc metal ion (Zn 2+) on bentonite is a two step process: a very rapid adsorption of zinc metal ion to the external surface is followed by possible slow decreasing intraparticle diffusion in the interior of the adsorbent which has also been confirmed by intraparticle diffusion model. Overall the kinetic studies showed that the zinc adsorption process followed pseudo-second-order kinetic model. The different kinetic parameters including rate constant, half adsorption time, and diffusion coefficient are determined at different physicochemical conditions. The equilibrium adsorption results are fitted better with Langmuir isotherm compared to Freundlich models. The value of separation factor, R L from Langmuir equation and Freundlich constant, n both give an indication of favorable adsorption. Finally in thermodynamic studies, it has been found that the adsorption process is exothermic due to negative ∆ H 0 accompanied by a decrease in entropy change and Gibbs free energy change (∆ G 0).

Selective recognition of 2,4-dichlorophenol from aqueous solution by uniformly sized molecularly imprinted microspheres with β-cyclodextrin/attapulgite composites as support

In this study, uniformly sized molecularly imprinted microspheres (MIP) using β-cyclodextrin/attapulgite composites as support were prepared for recognitive adsorption of 2,4-dichlorophenol (2,4-DCP) from aqueous solution. Characterization of MIP were achieved by FT-IR spectra, SEM micrographs, nitrogen adsorption–desorption analysis, EDX measurement and elemental analysis. Equilibrium data, at various temperatures, were described by the Langmuir, Freundlich and Dubinin–Radushkevich isotherm models. The thermodynamics parameters (positive values of Δ H° and Δ S°, negative values of Δ G°) indicated that binding system for MIP was endothermic, entropy gained and spontaneous. Kinetic properties were successfully investigated by pseudo-first-order model, pseudo-second-order model, intraparticle diffusion equation, initial adsorption rate, half-adsorption time and activation energy. A diffusion-controlled process as the essential adsorption rate-controlling step was also proposed. MIP could be reused four times without significant loss in adsorption capacity. The selectivity of MIP also demonstrated higher affinity for target 2,4-DCP over competitive phenolic compounds than that of non-imprinted polymers (NIP).