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Attapulgite (APT) is widely used in wastewater treatment due to its exceptional adsorption and colloidal properties, as well as its cost-effectiveness and eco-friendliness. However, low-grade APT generally limits its performance. Here, a colloid mill-assisted ultrasonic-fractional centrifugal purification method was developed to refine low-grade APT. This process successfully separated and removed impurity minerals such as quartz and dolomite from the raw ore, resulting in a refined APT purity increase from 16.9% to 60% with a specific surface area of 135.5 m2∙g−1. Further modifying of the refined APT was carried out through the hydrothermal method using varying dosages of cetyltrimethylammonium chloride (CTAC), resulting in the production of four different APT adsorbents denoted as QAPT-n (n = CTAC mole number) ranging from 0.5 to 5 mmol. Using Congo red (CR) as the target pollutant, the QAPT-5 sample exhibited the best adsorption capacity with the maximum quantity of 1652.2 mg∙g−1 in a neutral solution at 30 °C due to the highest surface charge (zeta potential = 8.25 mV). Moreover, the QAPT-5 pellets (~2.0 g adsorbent) shaped by the alginate-assisted molding method removed more than 96% of 200 mL aqueous solution containing 200 mg∙L−1 CR and maintained this efficiency in 10 adsorption–elution cycles, which exhibited the promising practical application. [ABSTRACT FROM AUTHOR]

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Heavy-metal ions are common pollutants in wastewater and are thus attracting considerable attention. Herein, an eco-friendly biodegradable adsorbent, iminodisuccinic acid (IDS) modified attapulgite (ATP) is prepared by graft-polymerization to reduce Cu(II) in water, referred as IDS-ATP. The equilibrium adsorption capacity of IDS-ATP for Cu(II) is increased by 329.5% and 272% compared with raw ATP and non-degradable chelator ethylenediaminetetraacetic acid-modified ATP (EDTA-ATP), respectively. Moreover, the adsorption capacities for Cu(II) in combined system increased by 186% compared with in single system. The structure and surface properties of IDS-ATP are characterized, demonstrating that the IDS moieties are anchored on the surface of ATP without structural damage. In the aqueous Cu(II) (64 mg /L), the best adsorption pH is 5.0, the best dosage is 800 mg/L, and the adsorption equilibrium time is 4 h. The adsorption of IDS-ATP is chemical adsorption and regenerated adsorbent still exhibits high adsorption capacity. The adsorption mechanism includes the coordination of amino groups with Cu(II), the chelation of -COOH on heavy metals (HMs), and the ion exchange. Taking Cu(II) as an example to study the process of IDS-ATP in water, it is beneficial to apply this degradable material to reduce the other HMs. [ABSTRACT FROM AUTHOR]

Magnetite/zirconium-comodified attapulgite (Fe/ZrATP) acting as a novel phosphorus (P) sorbent was synthesized, characterized and applied to control P in an aquatic environment. Batch experiments demonstrated that at an adsorption dose of 0.2 g, 97.8% of the phosphate was rapidly sequestered from aqueous solution within 24 h, and the composite reached a maximal sorption capacity of 3 mg/g. The adsorption performance of the adsorbent Fe/ZrATP was minimally affected by changes in the initial pH (pH = 2–11). In addition, Fe/ZrATP presented excellent selectivity for phosphate when coexisting ions that often occur in water bodies were present; the solution ionic strength exerted little influence on phosphate sorption behavior. Adsorption and desorption experiments indicated that the removal of phosphate was mainly due to adsorption. The Fe/ZrATP adsorption isotherm was fitted to the Freundlich adsorption model. Moreover, the composite demonstrated excellent recyclability performance. The P adsorption mechanism of Fe/ZrATP involves electrostatic interactions, ligand exchange and surface precipitation. Our findings indicated that the separable Fe/ZrATP demonstrated high efficiency and sustainable phosphate removal, which is promising in phosphate removal and recovery applications [ABSTRACT FROM AUTHOR]

Adsorption is one of the effective methods of treating dye wastewater. However, the selection of suitable adsorbent materials is the key to treating dye wastewater. In this paper, GO−ATP was prepared by an intercalation method by inserting graphene oxide (GO) into the interlayer of alabaster attapulgite (ATP), and GO−ATP@CS−PVA aerogel was prepared by co−blending−crosslinking with chitosan (CS) and polyvinyl alcohol (PVA) for the adsorption and removal of crystalline violet dye from the solution. The physicochemical properties of the materials are characterized by various methods. The results showed that the layer spacing of the GO−ATP increased from 1.063 nm to 1.185 nm for the ATP, and the specific surface area was 187.65 m2·g−1, which was 45.7% greater than that of the ATP. The FTIR results further confirmed the success of the GO−ATP intercalation modification. The thermogravimetric analysis (TGA) results show that the aerogel has good thermal stability properties. The results of static adsorption experiments show that at 302 K and pH 9.0, the adsorption capacity of the GO−ATP@CS−PVA aerogel is 136.06 mg·g−1. The mass of the aerogel after adsorption−solution equilibrium is 11.4 times that of the initial mass, with excellent adsorption capacity. The quasi−secondary kinetic, Freundlich, and Temkin isotherm models can better describe the adsorption process of the aerogel. The biobased composite aerogel GO−ATP@CS−PVA has good swelling properties, a large specific surface area, easy collection and a low preparation cost. The good network structure gives it unique resilience. The incorporation of clay as a nano−filler can also improve the mechanical properties of the composite aerogel. [ABSTRACT FROM AUTHOR]

A novel iron-modified Na-based montmorillonite (Fe-MT) or iron-modified Na-based attapulgite (Fe-AT) adsorbent is successfully prepared using ion exchange method and applied to remove tetracycline (TC) in water, and the spent adsorbents saturated with organic pollutants are regenerated under microwave (MW) irradiation. The influences of the ratio of Fe3+ and cation exchange capacity, adsorption time, adsorbent dosage, MW power, and irradiation time are investigated. The possible adsorption and MW regeneration mechanism is also proposed. The results indicate that Fe-MT and Fe-AT have enhanced interlayer spacing and surface area after the Na-based montmorillonite (Na-MT) or Na-based attapulgite (Na-AT) are modified using Fe3+. 97.70 % and 95.04 % adsorption are obtained using Fe-MT and Fe-AT within 30.0 min at 298 K, respectively, while 78.54 % and 61.92 % adsorption are obtained using Na-MT and Na-AT, respectively. Also, the adsorption processes fit well with pseudo-second-order reaction kinetic and Freundlich model, signifying chemical and multilayered adsorption. The adsorption of TC using the above four adsorbents are spontaneous and endothermic. Moreover, MW regeneration can enhance the adsorption capacity of Fe-MT or Fe-AT, and the regeneration ratios can reach 98.82 % and 93.14 % under 800 W MW within 5.0 min, respectively. By comparison, the adsorption capacity, regeneration performance and reusability of Fe-MT with larger interlayer spacing and surface area are superior to that of Fe-AT. Therefore, this work provides new perspectives on the adsorption technique using modified clay minerals as adsorbents for dealing antibiotics in water and wastewater, and the MW regeneration technology for regenerating spent adsorbents saturated with organic pollutants. • A novel Fe-MT or Fe-AT adsorbent is prepared adopting ion exchange method. • Fe3+ increases interlayer spacing and pore structure for enhanced TC adsorption. • Spent adsorbents saturated with pollutants can be regenerated under MW irradiation. • Regeneration performance of Fe-MT and Fe-AT are enhanced using Fe3+ modification. [ABSTRACT FROM AUTHOR]

Heavy metal ions have become a major problem that seriously affects the environment, ecology, and human health with the development of industrialization. Herein, the amino-grafted attapulgite/graphene oxide (A-ATP/GO) nanocomposites were synthesized for Pb(II) removal. The influencing factors including the ratio of the components, pH value, adsorption time, initial concentration of Pb(II) solution, and adsorbent amount were investigated to achieve the optimal adsorption performance. The as-prepared A-ATP/GO were used in Pb(II) solution (150 mg/L, 30 mL, pH = 5) for Pb(II) adsorption, which exhibited a great adsorption ability of 146.97 mg/g for Pb(II). The adsorption kinetic model and isotherms model were applied to investigate the adsorption mechanism of Pb(II) on A-ATP/GO. The A-ATP/GO composite could still maintain an original adsorption of 79.85% after 5 consecutive times, exhibiting the good reproducibility. It was believed that our results could shed light on the design and fabrication of low-cost graphene-based composite adsorbents for high-efficient Pb(II) removal. [ABSTRACT FROM AUTHOR]

This work focused on using attapulgite and chitosan as raw materials to improve the adsorption capacity of Cd2+ from the aqueous phase by optimizing the preparation experimental parameters. The modification parameters (attapulgite-chitosan mass ratio, calcination temperature, and time) were specifically studied and optimized. The results indicated that the mass ratio of attapulgite to chitosan was 1:4, the calcination temperature was 300 °C, and the calcination time was 1 h. Both raw and functionalized attapulgite samples were characterized by nitrogen adsorption-desorption isotherms at 77 K, X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and zeta potential analysis. A series of adsorption experiments showed that the pseudo-second-order kinetic model and Langmuir adsorption isotherm better corresponded with the adsorption characteristics of the newly prepared adsorbent, and the maximum adsorption amount of Cd2+ was 109.30 mg/g. Moreover, the effects of the pH value and coexisting cations on the Cd2+ adsorption in aqueous solution were investigated. Adsorption mechanism of Cd2+ on adsorbent might attribute to complexation, ion exchange reaction, and self-polarization. [ABSTRACT FROM AUTHOR]

This study investigates the performance of support vector machine (SVM), multivariate adaptive regression spline (MARS), and random forest (RF) models for predicting the lead (Pb) adsorption by attapulgite clay. Models are constructed using batch stochastic data of heavy metal (HM) concentrations under different physicochemical conditions. Implementation of auto-hyper-parameter tuning using grid-search approach and comparative analysis is performed against the benchmark artificial intelligence (AI) models. Models are constructed based on Pb concentration (IC), the dosage of attapulgite clay (dose), contact time (CT), pH, and NaNO3 (SN). Principle component analysis (PCA) and correlation analysis (CA) methods are integrated to assess the importance of the applied predictors and their relationship with the target. Research findings approved the potential of the grid-RF model as a marginal superior predictive model against the grid-SVM in terms of MAE, i.e., 3.29 and 3.34, respectively; moreover, the md scored the same, i.e., 0.93, which reveals the potential predictability for both. Nonetheless, grid-MARS and standalone MARS models remained likewise in their predictability. IC parameter demonstrated the highest influential among all the predictors with the highest value of importance in the case of all three evaluators. The solution pH and dose stands together with marginal differences in case of PCA method; however, solution pH and CT appeared with similarity impact using the PCA method. [ABSTRACT FROM AUTHOR]

Pollution from heavy‐metal ions has become a major challenge to the global fight against environmental pollution. Given the availability of various low‐cost and environmentally friendly adsorbents, adsorption has become the most efficient technology for the removal of heavy metals from water. In this study, attapulgite (ATP) was directly functionalized by coupling with an aminosilane agent. Analysis showed this maneuver provided a suitable adsorbent for the removal of lead ion (Pb2+) from an aqueous solution. The effects of several parameters including solution pH, contacting time, adsorbent dosage, and initial Pb2+ ion concentration were investigated. Batch sorption results showed that the adsorption process was rapid and over 98% of Pb2+ was removed within 30 min at the optimal pH 4.0. The maximum adsorption capacity at 25°C, calculated by the Langmuir isotherm, was 82.17, 78.80, 61.13, and 28.56 mg/g for γ‐divinyltriaminepropyl‐methyldimethoxylsilane‐grafted attapulgite (KH‐103‐ATP), γ‐aminopropyl‐methyldiethoxysilane‐grafted attapulgite (KH‐912‐ATP), N‐(β‐aminoethyl‐γ‐aminopropyl)‐methyl‐dimethoxysilane‐grafted attapulgite (KH‐602‐ATP), and ATP, respectively. Moreover, molecular dynamics simulations of adsorption behaviors of heavy‐metal ions at attapulgite surfaces (010) modified by aminosilane agents were carried out. Both the PMF value and diffusion coefficient of metal ions suggest that KH‐103‐ATP owns the highest rate constant and capacity compared with the other two. And the analysis of free energy and results of XPS characterization revealed that Pb2+ formed covalent bonds with the nitrogen atom of aminosilane agents. [ABSTRACT FROM AUTHOR]

In this study, KH550 modified acid-activated attapulgites (KH550-HATP) were prepared and assessed for their capacity to remove Cu(II) ion from aqueous solution. The obtained adsorption behavior using different KH550-content KH550-HATP revealed that Cu(II) adsorption onto KH550-HATP followed pseudo-first-order kinetics and was mainly controlled by film diffusion mechanism. And there is a considerable contribution of the intraparticle diffusion effects for low KH550-content KH550-HATP. In addition, adsorption isotherms indicate that the adsorption pattern on KH550- HATP fit well with the Langmuir isotherm, and the maximum monolayer adsorption capacity for Cu(II) at temperatures of 283, 293, 303, and 313 K were 3.33, 5.92, 9.75, 13.85 mg g-1, respectively, where the characteristic parameters for each adsorption isotherm were also determined. The adsorption process confirmed endothermic reactions in the range from 283 to 313 K. X-ray diffraction, X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy patterns of KH550-HATP before and after Cu(II) adsorption manifest both interlayer ion exchange and surface complication play important roles. Results of competitive adsorption of several different metal ions show that KH550-HATP has adsorption capacity on Cu2+, Cd2+ and Ca2+, among which Cu2+ is chelated by KH550 selectively. These findings indicate that KH550-HATP could be an effective and environmentally friendly selective adsorbent for removing Cu(II) from wastewater. [ABSTRACT FROM AUTHOR]

Antimony (Sb) is a potentially carcinogenic metalloid and is listed as a high priority pollutant by the World Health Organization. We used FeCl3-modified attapulgite (ATP) incorporating sodium alginate (SA) to synthesize an Fe-ATP bead for Sb(III) removal from the aquatic environment. The parameters of the adsorption process, including pH, temperature, and initial contaminant loading, were systematically optimized. The results indicated that the optimum solution pH range was 1.0-11.0, and the adsorption capacity was up to 39.24 mg g-1. The value of ΔH° (2.973 kJ mol-1) and ΔG° (-2.6668 kJ mol-1 (303.15 K), -2.8558 kJ mol-1 (313.15 K), -3.0364 kJ mol-1 (323.15 K)) showed that the Sb(III) adsorption onto Fe-ATP beads was a spontaneous endothermic process and the adsorption efficiency increases with temperature. The adsorption generally reached equilibrium after 20 min. The Sb(III) adsorption efficiency onto Fe-ATP beads remained greater than 80% after 5 regeneration cycles. In view of the broad applicable pH and high adsorption capacity, Fe-ATP bead is a potential adsorbent for Sb(III) recovered from polluted water. [ABSTRACT FROM AUTHOR]

The uptake of phenol using kaolin and fuller's earth and the comparison of their effects with bentonite are investigated in this study. In addition, X-ray fluorescent, X-ray diffraction, and thermogravimetric analyzes were carried out to examine the characteristics of the three adsorbents. Adsorption of phenol as a function of pH level was also investigated. The points of zero charge for kaolin, fuller's earth, and bentonite were determined to be 5.9, 8, and 7.7, respectively. To study the adsorption kinetics and mechanisms, various kinetic models were explored. Two-parameter and three-parameter isotherm models were employed for equilibrium studies. The results showed that decreasing the pH value led to an increase in phenol uptake. The maximum removal efficiencies were 34.35%, 23%, and 42.63% for kaolin, fuller's earth, and bentonite, respectively, for 0.5 g of adsorbent and pH = 4.5. Phenol uptake on the three adsorbents can be expressed by pseudo-second order kinetics. Whereas the Freundlich isotherm suits the experimental data for adsorption onto bentonite and fuller's earth, the Temkin isotherm well suits the experimental data for uptake onto kaolin. The Fourier transform infrared and scanning electron microscope were used in the analysis of the adsorbents surface prior to and after the process of adsorption. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Higher adsorption performance of MATP toward Cd is obtained than ATP. • The –SH groups rather than the S–S are the main active adsorption sites for Cd. • High adsorption affinity of MATP is due to high adsorption energy and bond order. • Bidentate complexes dominate due to higher stable configurations than monodentate. Abstract Mercapto-functionalized attapulgite (MATP) could efficiently adsorb Cd from aqueous solution, achieving adsorption equilibrium within 30 min with the maximum adsorption capacity of 120 mg g−1 at pH 6.7, 7.89-fold higher than that of ATP. Density functional theory (DFT) calculations revealed that the formed S–Cd–S and Cd–S bonds on MATP had lower adsorption energy (−3.75 and −2.84 eV) and higher bond order (1.14 and 0.39) than the corresponding values of Cd–O (−1.02 eV and 0.26) on ATP, which resulted in higher adsorption affinity of MATP toward Cd than ATP. The adsorption capacity increased by 7 times with the increasing of pH from 2.0 to 6.7. The positive-charged surface and protonation of MATP inhibited its adsorption for Cd at strong acid condition (pH < 2.4). However, complexation reactions of the mercapto groups on MATP with Cd at weak acidic and neutral conditions significantly facilitated its adsorption capacity. Mulliken net charge analysis showed that the terminal mercapto groups (–SH) rather than the disulfide (S–S) on MATP were the main active adsorption sites for Cd, which acted as the electron donors and transferred electrons to Cd form the surface complexes. Surface complexation models (SCM) modeling showed that the bidentate complexes predominated across the pH range of 2–7 due to their higher stable configurations than the monodentate. MATP was proved to be an efficient adsorbent for the removal of Cd from water bodies. [ABSTRACT FROM AUTHOR]

Attapulgite clay also known as palygorskite is a mineral clay which possess good adsorption properties based on its adsorption capacity, porous structure and moderate cation exchange properties. The study investigated the effectiveness of naturally occurring and hydrochloric acid modified attapulgite as adsorbents for Cr (VI) remediation in wastewater. The physical properties of the clay were characterized using a range of techniques. X-ray diffraction confirmed the purity of the clay while BET analysis indicated an increase in surface area from 131.4 to 183.2 m2/g after acid modification. The modified attapulgite was predicted to have an adsorption capacity of 75 mg/g compared to 2.1 mg/g for the naturally occurring attapulgite. The increase in adsorption capacity was attributed to a change in surface area as well as changes in the surface chemistry of the clay. The adsorption isotherms were best described by the Langmuir mono-layer adsorption model while the kinetics fit the Langren first order kinetics model. [ABSTRACT FROM AUTHOR]

To improve the adsorption and separation efficiency of lead-containing wastewater by graphene oxide (GO), attapulgite (ATP) was used through a simple hydrothermal reaction. The prepared GO was characterized by SEM, TEM, FTIR, and XPS. The adsorption properties of the prepared GO were investigated. The maximum adsorption capacity of Pb2+ on as-prepared GO at pH 5 and 25 °C was 450.9 mg/g. It is concluded that the as-prepared GO can be used as a high-efficiency adsorbent for lead-containing wastewater. [ABSTRACT FROM AUTHOR]

Abstract This research focused on developing a series of (G1.0, G2.0, G3.0 and G4.0) PAMAM dendrimers modified attapulgite (ATP) sorbents (G1.0-G4.0 PAMAM-ATP) to remove Hg(II) from aqueous solution. The effects of several parameters including solution pH, contacting time, temperature and initial Hg(II) ion concentration were studied. Batch sorption results showed that the adsorption process was rapid and over 90% of Hg(II) was removed within 80 min at optimal pH 5.0. The adsorption capacity of PAMAM-ATP adsorbents followed the order of G2.0 > G1.0 > G3.0 > G4.0 and the maximum adsorption capacities significantly increased from 5 mg/g (raw ATP), 90 mg/g (amine modified ATP, M-ATP), 192.5 mg/g (polyacrylamine modified ATP, PAM-ATP) by previous similar studies to 200.8 mg/g (G2.0-PAMAM-ATP). Kinetics of adsorption was suitable for pseudo-second-order and controlled by chemical adsorption over a whole sorption range. The adsorption capacities increased as temperature rise from 283 to 303 K and the thermodynamics properties implied that the adsorption processes was spontaneous and endothermic. Thus, the adsorption capacities decreased when the temperature was above 303 K. The isotherm adsorption was described by Langmuir model well with monolayer behavior. A specific coordination between Hg(II) and the N, O atoms on the functional groups of PAMAM-ATP surface was determined by XPS analysis. Furthermore, the maximum adsorption capacity of the regenerated G2.0-PAMAM-ATP sorbents could still be higher than 90% after five cycles by acid treatment. The favorable adsorption capacity compared with other adsorbents exhibited that G2.0-PAMAM-ATP was an excellent renewable sorbent for Hg(II) removal. Highlights • Novel method for the preparation of a novel set of PAMAM dendrimers modified attapulgite (G1.0-G4.0 PAMAM-ATP). • High adsorption capacity of the PAMAM-ATP sorbents on Hg(II). • The adsorption kinetics and isotherm models of G1.0-G4.0 PAMAM-ATP for Hg(II) were established. • XPS analyses were used to explain adsorption mechanism. • The adsorbent can be regenerated and reused, five cycles were carried out and the adsorption capacity was maintained >90%. [ABSTRACT FROM AUTHOR]

Zr-based MOFs hybridized by attapulgite (APT) were successfully prepared by simple reflux method and characterized by FTIR, BET, XRD, TGA and XPS. Both cationic and anionic dyes were efficiently, quickly and simultaneously adsorbed by UiO-66, 1%APT/UiO-66 and 5%APT/UiO-66 in 5 min. In anionic dyes (Congo red and alizarin yellow GG) and cationic dye methylene blue, adsorption capacities of UiO-66, 1%APT/UiO-66 and 5%APT/UiO-66 for Congo red were higher, 304.07, 585.00 and 394.63 mg/g, respectively. Capillary effect was adopted to explain characteristic trend of adsorption kinetic curves (first decrease and then increase of adsorption capacity in the second stage). Pseudosecond-order kinetic model and Langmuir isotherm was the best-fit model to evaluate adsorption behaviors of UiO-66, 1%APT/UiO-66 and 5%APT/UiO-66 for adsorption of Congo red. It was more favorable and effective for prepared materials to removal Congo red from solutions containing inorganic salts. When concentration of NaCl was 0.09 mol/L, adsorption capacities of 1%APT/UiO-66 were increased to 589.77, 724.56 and 635.59 mg/g, accordingly. UiO-66, 1%APT/UiO-66 and 5%APT/UiO-66 exhibited good stability and reusability. Main adsorption driving forces were hydrogen bonding interactions, π-π conjugations, electrostatic interactions and sieving effects, and adsorption driving forces of 1%APT/UiO-66 were largest. Above results indicated that UiO-66 hybridized by APT could simultaneous and ultrafast removal of anionic and cationic dyes in aqueous solution, and were potential adsorbents in practical application. [Display omitted] • UiO-66 hybridized by attapulgite were fabricated by simple refluxing method. • Capillary effect was applied to explain characteristic trend of adsorption kinetic. • 1%APT/UiO-66 could simultaneous and ultrafast remove anionic and cationic dyes. • Adsorption forces were hydrogen bonding, π-π, electrostatic and sieving effects. • The presence of salt ions was beneficial to increase of adsorption capacity. [ABSTRACT FROM AUTHOR]

Abstract MgO decked few layer Graphene Coated Fullers' Earth (MgO-FLG-FE) is prepared by microwave irradiation and tested as adsorbent to remove Acid Blue 9 (AB9) and Safranin O (SO) dye from aqueous solutions. MgO-FLG-FE was characterized by FTIR, XRD, FESEM, HRTEM, RAMAN, and BET. The adsorbent dose required for the maximum removal of AB9 and SO dyes are 1.0 g and 0.08 g which is in very low quantity compared with FE. The contact time to achieve equilibrium is 120 min in both the dyes. Langmuir, Freundlich and Dubinin-Radushkevich adsorption isotherms are applied to understand the adsorption mechanism for both the dyes in aqueous solutions. The uptake of AB9 and SO dye by MgO-FLG-FE is best explained by Langmuir adsorption isotherm. The adsorption capacities of MgO-FLG-FE for AB9 and SO are 37.7 mg/g and 201.1 mg/g respectively when compared with Fuller's Earth (36.7 mg/g and 131.19 mg/g). The adsorbent capacity of FE was enhanced by coating with very small amount of MgO decked FLG. The Pseudo-second order equation is best explained through the adsorption kinetics in this study. Graphical abstract Image 1 Highlights • Novelty of decorating MgO-decked FLG on Fuller's Earth. • Understanding morphological features of MgO-FLG-FE is also interesting. • FEA capacity is increased by decorating with MgO-decked few layer graphene. • MgO-FLG-FE acts as an excellent adsorbent to remove Safranin O & Acid blue 9 dyes. • Chemisorption is the major mode of adsorption of SO and AB9 dyes onto MgO-FLG-FE. [ABSTRACT FROM AUTHOR]

A polyethyleneimine (PEI)-modified attapulgite was employed as a new adsorbent for solid-phase extraction (SPE) of chlorophenols (CPs) from environmental water samples. Key factors pivotal to extraction efficiency, such as organic additive, pH, salt, sample loading volume, elution volume, and sample loading flow rate, were investigated. The maximum adsorption capacity of CPs reached 38 mg/g, and the adsorption behavior could be described with the Langmuir isotherm model. The developed SPE procedure was then tested on river water samples. Of this cartridge, 0.4 g could be used to treat up to 100 mL of the water sample, with high recoveries achieved. The limit of detection (S/N = 3) and the limit of quantification (S/N = 10) were in range of 0.08-0.56 and 0.27-1.88 ng/mL, respectively. The mean recoveries of CPs spiked in river water samples ranged from 84.4 to 96.8% with relative standard deviations for the intra-day and inter-day less than 6.30%. The developed SPE method exhibited high sensitivity, high selectivity, excellent accuracy, and good repeatability to the analysis of trace CPs in complicated aqueous matrices.ᅟ [ABSTRACT FROM AUTHOR]

Herein, we presented a simple synthetic strategy for fabricating magnetic nanoparticles uniformly dispersed on the surface of attapulgite (ATP), namely the impregnation and pyrolysis method. Subsequently, using magnetic attapulgite as supported core through chemical modification, a novel surface molecularly imprinted nanomaterial (named as MATP/MIPs) was prepared via precipitation polymerization. The obtained MATP/MIPs showed excellent properties by a variety of characterizations including FT-IR, SEM, TEM, VSM, XRD and TGA. Moreover, the adsorption experiments were carried out in aqueous medium at different temperatures, to study the adsorption isotherm, adsorption kinetics and selective recognition ability of MATP/MIPs toward sulfamethazine (SMZ). The experimental data were fitted to the Freundlich isotherm model better than to the Langmuir model. The equilibrium adsorption capacity for SMZ onto MATP/MIPs is higher than onto MATP/NIPs, demonstrating the existence of imprinted cavities. Due to the advantage of coated nanoshell, the adsorption equilibrium was achieved quickly within 45min, and the data were well-described by the pseudo-second-order kinetic mode. Compared with other antibiotics, the MATP/MIPs exhibited excellent selectivity for SMZ. In addition, the imprinted material still showed good regeneration ability after 10 cycles which make it possible for practical application in the recognition and separation of antibiotics. A novel magnetic surface molecularly imprinted nanomaterial based onto attapulgite nanorod (MATP/MIPs) has been successfully prepared by precipitation polymerization, which exhibited fast adsorption kinetics and selective recognition ability toward targeted sulfamethazine (SMZ) from water, as well as good regeneration ability, making it possible for practical application in the recognition and separation of antibiotics. [ABSTRACT FROM AUTHOR]

Phenanthrene (Phe), a typical polycyclic aromatic hydrocarbon (PAH) pollutant, poses an enormous safety risk to rice-crab coculture (RC) paddy ecosystems. In this study, humic acid-modified purified attapulgite (HA-ATP) with a composite structure was successfully fabricated to adsorb PAHs released from paddy soil to overlying water in RC paddy ecosystems in Northeast China. The maximum crab bioturbation intensities for dissolved Phe and particulate Phe were 64.83nullng/L·(cm2·d) and 214.29nullng/L·(cm2·d), respectively. The highest concentration of dissolved Phe released from paddy soil to overlying water due to crab bioturbation reached 80.89nullng/L, while the corresponding concentration of particulate Phe reached 267.36nullng/L. The dissolved organic carbon (DOC) and total suspended solid (TSS) concentrations in overlying water increased correspondingly and were strongly correlated with dissolved Phe and particulate Phe concentrations, respectively (P < 0.05). When 6% HA-ATP was added to the surface layer of paddy soil, the efficiency of the adsorption of Phe release was 24.00%–36.38% for particulate Phe and 89.99%–91.91% for dissolved Phe. Because HA-ATP has a large adsorption pore size (11.33 nm) and surface area (82.41nullm2/g) as well as many HA functional groups, it provided multiple hydrophobic adsorption sites for dissolved Phe, which was conducive to competitive adsorption with DOC in the overlying water. In contrast to that adsorbed by DOC, the average proportion of dissolved Phe adsorbed by HA-ATP reached 90.55%, which reduced the dissolved Phe concentration in the overlying water. Furthermore, even though the particulate Phe was resuspended by crab bioturbation, HA-ATP immobilized particulate Phe due to its capacity to inhibit desorption, which achieved the goal of reducing the Phe concentration in the overlying water. This result was confirmed by research on the adsorption-desorption characteristics of HA-ATP. This research provides an environmentally friendly in situ remediation method for reducing agricultural environmental risks and improving rice crop quality. [Display omitted] • Modified attapulgite was prepared by hot acid modification with humic acid. • Crab bioturbation disrupted the Phe distribution balance between paddy soil and overlying water. • The adsorption efficiency of released dissolved and particulate Phe reached 91.91% and 36.38%. • HA-ATP and DOC competitively adsorbed dissolved Phe in overlying water. • HA-ATP immobilized particulate Phe in overlying water during resuspension. [ABSTRACT FROM AUTHOR]

Composite hydrophobic attapulgite fiber silica aerogels (AF-SAs) were prepared by modifying aerogels with AF. AF-SA composites with various fiber contents were prepared using a sol–gel method. The composite containing 0.30 g of added fiber was a typical nanoporous material; it had a specific surface area of 594.08 m2/g, a porosity of 75.00%, a pore volume of 2.15 cm3/g, and an average pore diameter of 84.74 nm. The kinetics of total petroleum hydrocarbon (TPH) adsorption onto AF-SAs was second order, and the isothermal adsorption of TPH conformed to the Langmuir adsorption model. The TPH adsorption capacity of an AF-SA, calculated using the Langmuir equation, was 5.00 g/g. Alkanes and aromatic hydrocarbons were both strongly adsorbed. The main adsorption mechanisms involved physical and chemical processes. The physical processes involved monolayer and multilayer adsorptions. Chemical adsorption occurred mainly after adsorption of TPH onto the AF-SA. The adsorption process was additionally assessed by monitoring the positions and areas of the Fourier-transform infrared absorptions of the main components (silicate, attapulgite, and functional groups of the surface-modification agent) of the composite materials. [ABSTRACT FROM PUBLISHER]

Nanocomposite particle used for adsorption has attracted continuous attention because of large specific surface area and adjustable properties from nanocomponent. Herein nanocomposite particle with cellulose core and attapulgite nanofibers shell was prepared. The size of cellulose core was about 2 mm and the thickness of nanofibers shell is about 300 μm. Adsorption capacity of nanocomposite particle to methylene blue can reach up to 11.07 mg L−1 and the best adsorption effect occurs at pH = 8; pseudo-first-order equation and the Langmuir equation best describe the adsorption kinetic and isotherm, respectively; repeated adsorption-desorption experimental results show that 94.64% of the original adsorption capacity can be retained after being reused three times. [ABSTRACT FROM AUTHOR]

A new type of Zn2+ion-imprinted polymer (Zn2+-IIP) was synthesized on the surface of attapulgite, displaying high affinity and selectivity to Zn2+. Fourier transform infrared spectra (FTIR) revealed Zn2+-IIP to be an organic–inorganic hybrid polymer, with Zn2+imprinted cavities formed by CTS groups and connected to the surface of the attapulgite by A-187 cross-linked network. The adsorption kinetic investigation showed that the adsorption of Zn2+on Zn2+-IIP was a pseudo-second-order process. The maximum adsorption capacities of Zn2+were 0.536, 0.665, 0.715, and 0.722 meq/g at 288, 298, 308, and 318 K, respectively, where the activation energy,Ea, was evaluated as 23.8 kJ/mol. By thermodynamic study, ΔH° and ΔS° of the adsorption were determined as 30.862 kJ/mol and 108.664 J/mol K, respectively, while the negative ΔG° decreased with rising temperatures, indicating that the adsorption process was feasible and spontaneous. The adsorption selectivity of the Zn2+-IIP was also investigated via competitive adsorption of Zn2+, Cd2+, Cs+, Co2+, Ba2+, Sr2+, and Pb2+from a mixture, demonstrating that Zn2+-IIP had the capability of recognizing Zn2+with high affinity and selectivity. The study of multi adsorption–desorption cycles showed that the Zn2+-IIP can be reused many times without a significant decrease in the adsorption capacity. [ABSTRACT FROM PUBLISHER]

Fuller’s earth immobilized nanoscale zerovalent iron (F-nZVI 1–8 ) were synthesized by borohydride reduction method. The iron loading of fuller’s earth immobilized nZVI was varied from 5 to 50% (w/w) in these F-nZVI 1–8. The F-nZVI 1–8 were characterized by FE-SEM–EDX, FTIR, BET, XRD and TGA. The FE-SEM analysis showed an increase in agglomeration of nZVI on the immobilized material with increase in the loading of Fe 0 . F-nZVI 1–8 were studied for adsorptive removal of As(III) and As(V) from aqueous solution, with an emphasis on the effect of Fe 0 loading of adsorbent on arsenic remediation. Iron loading has a significant role in adsorption of As(III) and As(V) on F-nZVI, with increase in adsorption with optimum iron loading of 20% (w/w) on fuller’s earth (F-nZVI-4). However, increase in loading above 20%, resulted in no significant increase in As(III) and As(V) adsorption. The adsorption results fitted well with Langmuir and Freundlich isotherm models and the maximum adsorption capacity of F-nZVI-4 for As(III) and As(V) were observed to be 50.08 and 91.42 mg/g, respectively. The adsorption isotherm and kinetic studies indicate a rapid removal of As(III) and As(V) from the aqueous solution in the presence of F-nZVI 1-8, with an substantially high rate of removal for arsenic with F-nZVI-4. [ABSTRACT FROM AUTHOR]

Due to its low cost and easy availability, the natural clay, attapulgite (ATP), is a promising substitute of relatively expensive zeolites for adsorption and catalysis. However, the narrow porous network of ATP hinders its practical applications severely. In the present study, a tandem demetalization–desilication strategy was developed to enhance porosity of ATP by adding NH 4 F followed the HCl treatment, for the first time. The HCl treatment leaches out the cations (including Mg, Ca, Al, and Fe) in octahedral sheets and generates silicon products, which block the pores of ATP. The subsequent addition of NH 4 F leads to the formation of a buffer solution, which is efficient in the removal of silicon products. As a result, abundant secondary porosity is created, which induces an obvious increase of surface area from 128 to 232 m 2 g −1 and pore volume from 0.38 to 0.77 cm 3 g −1 . The preliminary applications of the obtained material in adsorption and catalysis were also tested. The material exhibits obviously better performance in the selective adsorption of CO 2 from CH 4 and N 2 than pristine ATP, and the adsorption amount of CO 2 increases sharply from 23.5 to 57.5 mg g −1 . In the Friedel–Crafts alkylation reaction of benzyl bromide with toluene, the obtained material can catalyze the conversion of 99.2% of benzyl bromide, which is 3.3 times as high as that catalyzed by pristine ATP. These properties make the obtained material highly promising in substituting zeolites for various applications. [ABSTRACT FROM AUTHOR]

Low concentrations of ammonium are difficult to remove from surface water through traditional adsorption, air stripping, and biological techniques. Hence, we flocculate attapulgite-graft-polyacrylamide (ATP-g-PAM) and immobilize cells in this study to purify low-ammonia surface water. ATP-g-PAM was synthesized by grafting the polymerization reaction of ATP and acrylamide (AM). In this process, FeSO4and NaHSO3acted as initiators. The optimum reaction conditions were as follows: 15% AM monomer, 2% ATP, 10.5 × 10−4 mol/mol AM initiator concentration with a 1:5 molar ratio of FeSO4to NaHSO3, and 5 h reaction time. The ATP-g-PAM structure was characterized further by Fourier transform infrared spectra, thermogravimetric analysis, scanning electron microscopy, and transmission electron microscopy. Results indicated that AM monomers were successfully grafted onto the ATP surface. Pellets of ATP-g-PAM-bound nitrifying bacteria were manufactured for surface water treatment. The ammonia-nitrogen removal rate ranged from 14.9 to 33.9% for adsorption and flocculation, and from 69.4 to 82.6% under cell immobilization. Post-treatment, ammonia-nitrogen was less than 0.8 mg/L. Therefore, ATP-g-PAM can be an ideal carrier material of microbial fixations in water and wastewater treatment because the double-action of adsorption and flocculation induced by ATP-g-PAM can supplement the removal of pollutants. [ABSTRACT FROM AUTHOR]

Nano zero-valent iron (nZVI) modified attapulgite composite (nZVI@ATP) was prepared by liquid phase reduction method for Cd2+ removal from aqueous solution. A series of characterization methods confirmed that nZVI particles with a particle size of 50–100 nm were evenly distributes on the surface of attapulgite after pickling, which greatly overcomes the agglomeration of nZVI. Composite material had the optimum removal rate of Cd2+ when the ratio of iron to attapulgite was 1: 2. More than 98% of Cd2+ was removed from aqueous solution using nZVI@ATP at an initial condition of 100 mg/LCd2+ under the conditions of 1 g/L of nZVI@ATP, pH 5.0 and a temperature of 25 ℃, much higher than that of attapulgite. Kinetic studies revealed that Cd2+ adsorption process followed the pseudo-second-order model, and basically reached the adsorption equilibrium after 2 h, indicating that chemisorption was the dominant adsorption mechanism. Adsorption thermodynamics showed that the adsorption process was a spontaneous endothermic reaction, accompanied by the increase in entropy. The Freundlich adsorption isotherm model could well fit the adsorption process. The presence of Na+, Ca2+ and Mg2+ in the solution strongly inhibited the removal of Cd2+. The mechanism of Cd2+ removal by nZVI@ATP involved multiple processes, mainly including surface-complexation adsorption and precipitation/co-precipitation. The results exhibited that nZVI@ATP has excellent potential as an adsorbent for the removal of Cd2+ from the contaminated water. [Display omitted] • Spherical nZVI particles were uniformly dispersed on the surface of ATP, and the agglomeration phenomenon is weakened. • Cd2+ removal was mailly attributed to complex with the iron oxides on the surface of nZVI. • nZVI@ATP(1:2) exhibited excellent efficiency for Cd2+ removal. • The removal of Cd2+ by nZVI@ATP follows the pseudo-second-order kinetic adsorption model. [ABSTRACT FROM AUTHOR]

Attapulgite (ATP) clay was modified with different silane coupling agents [3-triethoxysilylpropylamine (KH550), γ-glycidoxypropyltrimethoxysilane (KH560) and γ-methacryloxypropyltrimethoxysilane (KH570)] and used as a decolourizer for bleaching of refined palm oil. The effects of different silane coupling agents on the structure, surface charges and pore structure of ATP were investigated by Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, Zeta potential and nitrogen adsorption-desorption isotherm techniques, and the decolourization efficiency of the modified ATP was evaluated by UV-Vis absorbance and Lovibond colour. The results show that the KH550-modified ATP exhibits the best decolourization performance, which can decrease the red-yellow value of refined palm oil by 31.96% and the phosphorus content by 77.69% after bleaching; while the unmodified ATP can only decrease these values by 17.30% and 62.31%, respectively. [ABSTRACT FROM AUTHOR]

A series of polyurethane-attapulgite porous (HATT/PU) materials were prepared from polyether polyol (NJ-330), toluene diisocyanate (TDI), acid activated attapulgite (HATT), sodium bicarbonate as foaming agent, dibutylbis (lauroyloxy) tin (DBLT) as catalyst and silicon oil as stabilizer by foaming technique. The materials were characterized by FTIR, XRD and SEM. The polyurethane-attapulgite porous material as adsorbent was applied to malachite green (MG) dye wastewater treatment. Effects of attapulgite content, time, temperature, pH, and adsorbent dosage have been studied. The experimental results show that the maximum adsorption efficiency occurred at an attapulgite content of 6.0%, a time of 2.5 h, a temperature of 35°C, a pH >5 and a HATT/PU dosage of 40 mg/mL. Equilibrium isotherms for the adsorption of the dye have been measured experimentally. Results were analyzed by the Freundlich and Langmuir equation and the characteristics parameters for each adsorption isotherm were determined: Gibb's free energy (Δ G°), change in enthalpy (Δ H°) and change in entropy (Δ S°) have been calculated. The results indicated that the adsorption process was spontaneously an endothermic reaction and kinetically proceeded according to the pseudo-second-order model. The experimental results suggest that the prepared polyurethane-attapulgite porous materials have potential application for the wastewater treatment containing MG dye. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013 [ABSTRACT FROM AUTHOR]

A novel Ni(II) ion-imprinted polymer [Ni(II)-IIP] was prepared by surface-imprinting technique using aniline as the functional monomer and 3-methacryloxypropyltrimethoxysilane (MPS)-modified attapulgite as the support material. The prepared sorbents were characterized by Fourier transmission infrared spectra, BET and scanning electron microscopy. The adsorption experiments carried out using Ni(II)-IIPs were optimized by changing the length of the polymer, contact time, solution pH, the concentration of template ion and the amount of cross-linking agent, etc. In addition, batch experiments were performed to evaluate adsorption kinetics and adsorption isotherms. The study results revealed that Ni(II)-IIPs had higher adsorption capacity and higher recognizing ability for Ni2+ compared with non-imprinted polymers. The experimental data fitted well with both the pseudo-second-order kinetic model and the Langmuir model. The maximum theoretical adsorption capacity for Ni2+ ions is 123.61 mg/g. The relative selectivity factor values of Ni(II)-IIPs for adsorbing Ni2+/Cu2+, Ni2+/Hg2+ and Ni2+/Cr2O72- are 80.94, 31.68 and 5.29, respectively. In addition, the decrease in the adsorption capacity of Ni(II)-IIPs is negligible after reusing several times. [ABSTRACT FROM AUTHOR]

Attapulgite modified with iron was used as an adsorbent for fluoride removal from aqueous solutions. The pristine attapulgite and the iron-modified attapulgite composite were characterized by X-ray powder diffraction (XRD), Fourier transform infrared (FT-IR) tech-niques, and the pH point of zero charge measurement. The XRD analysis indicates the existence of iron oxide hydroxide (FeO[OH]) in the iron-modified attapulgite composite. The FT-IR spectra of the iron-modified attapulgite composite before and after adsorption indicate that the involvement of the hydroxide radical in the fluoride adsorption. The effects of pH, contact time, initial concentration, and temperature on fluoride adsorption by the adsorbent were studied in a batch system. Kinetics studies show that the fluoride adsorption kinetics over the adsorbent is well-described by the pseudo-second-order kinetic model. The fluoride adsorption isotherm is well-fitted by the Langmuir model. Desorption studies show that the iron-modified attapulgite adsorbent can be easily regenerated at pH 12.5. The adsorption mechanism is discussed in detail. [ABSTRACT FROM AUTHOR]

Abstract: Natural attapulgite (ATP) was modified with an amino-terminated organosilicon (3-aminopropyltriethoxysilane, APTES) in order to develop an effective adsorbent for aqueous Hg(II) removal. The surface area of the modified ATP (M-ATP) was calculated using the Brunauer–Emmett–Teller method. The adsorbent was characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray fluorescence (XRF), Fourier transform infrared spectroscopy (FT-IR) and electrophoretic mobility. Due to complexation between mercury and the amine functional groups on the M-ATP, the adsorption capacities significantly increased from 5mg/g (raw ATP) to 90mg/g (M-ATP). Batch adsorption results showed that the adsorption process was rapid and over 90% of aqueous Hg(II) was removed within 1h. The efficiency of the adsorbent was found to remain almost constant over a wide pH range (3–11). Adsorption of Hg(II) by M-ATP was proposed as the complexation between mercury and the amine functional groups on the M-ATP surface. Ionic strength and co-existing ions had a slight influence on the adsorption capacity. Hg(II) adsorbed onto M-ATP could be effectively desorbed in 1:1 (m/m) chlorohydric acid/thiourea solution. Our results suggest that the M-ATP may be used as renewable adsorbents for fast removal of Hg(II) from aqueous solutions. [Copyright &y& Elsevier]

Abstract: The present study investigated the feasibility of using modified attapulgites for the sorptive removal of β-blocker propranolol. The attapulgites were modified by different reagents including hydrochloric acid, silane coupling agent and chotosan. And the modified attapulgites were characterized by N2 sorption–desorption, Fourier transform infrared spectroscopy, zeta potential measurements, and X-ray diffraction technique. The as-made attapulgites were applied to removing propranolol from aqueous solution, and the effects of pH, ionic strength, sorbent dosage, and humic acid on sorption were investigated by batch experiments. The sorption capacity of the as-made attapulgites was compared with that of natural attapulgite, powdered activated carbon and other reported sorbent. The results suggested that the acid-activated attapulgite had a higher sorption capacity for propranolol than the other sorbents involved. The sorption kinetics and equilibrium isotherms of propranolol onto acid-activated attapulgite were also studied. The sorption process followed the pseudo-second order equation and the sorption data were fitted well with the Langmuir isotherm equations. Both physisorption and chemisorption played important roles for propranolol sorption onto acid-activated ATP. Owing to its high sorption capacity and low cost, acid-activated attapulgite has potential value in the removal of propranolol from sewage and natural waters in engineering application. [Copyright &y& Elsevier]

Abstract: The amine moiety has an important function in many applications, including, adsorption, catalysis, electrochemistry, chromatography, and nanocomposite materials. We developed an effective adsorbent for aqueous reactive dye removal by modifying attapulgite with an amino-terminated organosilicon (3-aminopropyltriethoxysilane, APTES). Surface properties of the APTES-modified attapulgite were characterized by the Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and nitrogen adsorption–desorption. We evaluated the impact of solvent, APTES concentration, water volume, reaction time, and temperature on the surface modification. NH2–attapulgite was used to remove reactive dyes in aqueous solution and showed very high adsorption rates of 99.32%, 99.67%, and 96.42% for Reactive Red 3BS, Reactive Blue KE-R and Reactive Black GR, respectively. These powerful dye removal effects were attributed to strong electrostatic interactions between reactive dyes and the grafted NH2 groups. [Copyright &y& Elsevier]

Abstract: Via encapsulation of attapulgite/Fe3O4 magnetic particles (ATP/Fe3O4), 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 16nm), and exhibited magnetic property (M s =5.67emug−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 145.79mgg−1 at 298K. 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. [Copyright &y& Elsevier]

Abstract: A novel spherical composite of polyvinyl alcohol (PVA) and attapulgite (ATP) with macroreticular structure, i.e. MR-PVA/ATP composites, was prepared as an adsorbent for some contaminations from aqueous environment, which would hold the advantages of PVA and ATP in the same time. The resulting adsorbents hold uniform and rich aperture with good mass transfer property, processing properties and stability. It has been proved with easy separation and excellent adsorption for methylene blue and lead in aqueous solution, and the adsorption rate will be accelerated when increasing porogen in its preparation. The adsorption process of methylene blue and lead on it includes both chemo-adsorption and physical adsorption. The adsorption process all fits the pseudo second order kinetics very well with rapid initial adsorption rate. The addition of attapulgite increased the adsorption capacity of lead ions significantly. By further graft functional groups on the ATP, it has potential to prepare various adsorbents to satisfy specific requirements. Such kind of adsorption material will perform a wide application prospect in the purification treatment for wastewater. [Copyright &y& Elsevier]

Recently, magnetic sorbents have received considerable attention because of their excellent segregative features and sorption capacities. Herein, attapulgite/iron oxide magnetic (ATP/IOM) composites were prepared and characterized. The sorption results indicated that ATP/IOM composites were superior to ATP and iron oxides individually for the removal of U(VI) from aqueous solution. Based on X-ray photoelectron spectroscopy (XPS) analysis and surface complexation model, the main sorption species of U(VI) on ATP were ᆖX2UO20 below pH 4.0 and ᆖSsOUO2+, ᆖSwOUO2CO3−, and ᆖSwOUO2(CO3)23− above pH 5.0. However the prevalent species on ATP/IOM composites were ᆖSsOUO2+ and ᆖSwOUO2(CO3)23− over the observed pH range. ATP/IOM composites are a promising candidate for pre-concentration and immobilization of radionuclides from large volumes of aqueous solutions, as required for remediation purposes. [ABSTRACT FROM AUTHOR]

A simple and reliable approach using surface imprinting technique combined with chitosan incorporated sol-gel process was established to synthesise a novel Co(II)-imprinted polymer (Co-IIP) with attapulgite as the support material. Then the prepared polymer was characterised by using fourier tranmission infrared spectra (FT-IR) and scanning electron microscopy (SEM), and the imprinting mechanism of Co-IIP was proposed. Batch experiments studies were performed to evaluate the adsorption kinetics, selective recognition, adsorption isotherm, desorption and regeneration characters of Co-IIP. Results showed that Co-IIP offered fast kinetics for the adsorption and desortion Co2+ under the optimum conditions. The adsorption and selective recognition Co2+ were both followed the order Co-IIP > attapulgite > NIP. Moreover, Langmuir adsorption isotherm fitted well for the experimental equilibrium data of Co-IIP, and the maximum adsorption capacity of Co-IIP was 31.5 mg g-1. Furthermore, Co-IIP could be reused four times with only about 13.42 ∼ 16.17% regeneration loss, and the enrichment factor was more than 10.0. The developed method was also successfully applied to the determination of trace Co2+ in river sediments with satisfactory results. The relative standard deviation of the method (RSD) and the detection limit (3σ) were 1.35% and 0.0263, respectively. [ABSTRACT FROM AUTHOR]

Abstract: Polyaniline/attapulgite composite (ATP–PANI) was prepared by in situ chemical oxidation and characterized by FITR, XRD, and TEM. Characterized results showed that polyaniline (PANI) was successfully encapsulated on the surface of attapulgite (ATP). Humic acid (HA) adsorption onto ATP–PANI was investigated by batch experiments and adsorption kinetic tests. In contrast with the low HA adsorption amount on ATP, substantially enhanced HA adsorption onto ATP–PANI was observed. Adsorption isotherms of HA can be well described by Langmuir model and the maximum adsorption amounts were found to be 43.01, 52.91, 61.35mg/g at 15, 25, and 35°C, respectively. HA adsorption increased with rise in temperature indicating of an endothermic process of HA adsorption onto ATP–PANI. Pseudo-second order kinetic equation can fit HA adsorption very well and the adsorption rate decreased with increasing initial HA concentration. HA adsorption decreased monotonously with increasing solution pH. Co-existed cations (Na+, K+, Ca2+) in aqueous solution improved HA adsorption amount on ATP–PANI, and the augment of HA adsorption amount was order as Ca2+ >K+ >Na+. Results of HA adsorption onto ATP–PANI showed that the electrostatic interaction between amine and imine groups of the adsorbents and HA molecules in solution may account for the enhanced HA adsorption. The HA molecules adsorbed on ATP–PANI can be effectively desorbed in 2M NaOH solution, and regenerated adsorbent can be repeatedly used in the subsequently four adsorption-regeneration cycles with little loss of HA adsorption amount. [Copyright &y& Elsevier]

Sorption of U(VI) from aqueous solution to Na-attapulgite was investigated at different experimental chemistry conditions by using batch technique. The attapulgite sample was characterized by FTIR and XRD. Sorption of U(VI) on attapulgite was strongly dependent on pH and ionic strength. The sorption of U(VI) on attapulgite increased quickly with rising pH at pH < 6, and decreased with increasing pH at pH > 7. The presence of humic acid (HA) enhanced the sorption of U(VI) on attapulgite obviously at low pH because of the strong complexation of surface adsorbed HA with U(VI) on attapulgite surface. Sorption of U(VI) on attapulgite was mainly dominated by ion exchange and/or outer-sphere surface complexation at low pH values, whereas the sorption was attributed to the inner-sphere surface complexation or precipitation at high pH values. The sorption increased with increasing temperature and the thermodynamic parameters calculated from the temperature dependent sorption isotherms suggested that the sorption of U(VI) on attapulgite was a spontaneous and endothermic process. The results indicate that attapulgite is a very suitable material for the preconcentration of U(VI) ions from large volumes of aqueous solutions. [ABSTRACT FROM AUTHOR]

Abstract: The first study on the high efficiency of triocarbohydrazide modified attapulgite as solid-phase extractant for preconcentration of trace Au(III) prior to the measurement by inductively coupled plasma optical emission spectrometry (ICP-OES) has been reported. Experimental conditions for effective adsorption of trace levels of Au(III) were optimized with respect to different experimental parameters using batch and column procedures in detail. At pH 3, Au(III) could be quantitatively adsorbed on the new sorbent, and the adsorbed Au(III) could be completely eluted from the sorbent surface by 2.0mL 1.0molL−1 of HCl+2% CS(NH2)2 solution. An enrichment factor of 150 was accomplished. Moreover, common interfering ions did not interfere in both separation and determination. The maximum adsorption capacity of the sorbent for Au(III) was found to be 66.7mgg−1. The detection limit (3σ) of this method was 0.32μgL−1 and the relative standard deviation (RSD) was 3.3% (n =8). The method, with high selectivity, sensitivity and reproducibility, was validated using certified reference materials, and had been applied for the determination of trace Au(III) with satisfactory results. [Copyright &y& Elsevier]

Sorption of radionickel on attapulgite is studied as a function of contact time, ionic strength, pH and temperature. The results indicate that the sorption of Ni(II) on attapulgite is strongly ionic strength-dependent at pH <8, and independent of ionic strength at pH >8. Outer-sphere surface complexation or ion exchange contributes to Ni(II) sorption on attapulgite at pH <8, whereas the sorption of Ni(II) is mainly dominated by inner-sphere surface complexation at pH >8. The sorption of Ni(II) on attapulgite increases with increasing temperature, and the thermodynamic parameters (Δ H, Δ G and Δ S) calculated from the temperature dependent sorption isotherms suggest that the sorption of Ni(II) on attapulgite is a spontaneous and endothermic process. The high sorption capacity of attapulgite suggests that attapulgite is a suitable material for the preconcentration and solidification of radionickel from large volumes of aqueous solutions. [ABSTRACT FROM AUTHOR]

Abstract: In the present study, the competitive adsorption characteristics of binary and ternary heavy metal ions Hg2+, Pb2+ and Co2+ on polyacrylamide/attapulgite (PAM/ATP) were investigated in batch systems. PAM/ATP was prepared by the solution polymerization of acrylamide (AM) onto γ-methacryloxypropyl trimethoxy silane (KH-570) modified attapulgite (ATP) and characterized by the technique of X-ray photoelectron spectroscopy (XPS). Equilibrium and kinetic adsorption data showed that PAM/ATP displays a high selectivity towards one metal in a two-component or a three-component system with an affinity order of Hg2+ > Pb2+ > Co2+. The equilibrium behaviors of heavy metal species with stronger affinity toward PAM/ATP can be described by the Langmuir equation while the adsorption kinetics of the metals can be well fitted to a pseudo-second-order kinetic model. Desorption was performed using hot acetic acid, and the regenerated adsorbents could be reused with little loss of adsorption capacity. [Copyright &y& Elsevier]

Abstract: Adsorption of Cr(III) and Fe(III) onto chitosan/attapulgite composites (CTS/ATP) was investigated with respect to pH, temperature, initial concentration and binary solution. Equilibrium data, at various temperatures, were described by the Langmuir, Freundlich isotherm models. The Freundlich isotherm model was fitted to the experimental data significantly better than the Langmuir isotherm. In a binary solution, the combined effect of adsorbing one metal ion in the presence of the other metal ion reduced the adsorption capacity of either metal ion. The kinetic data was well fitted to the intraparticle diffusion equation, which indicated that the three adsorption steps belonged to the pseudo-second-order adsorption process. Intraparticle diffusion increased with the increase in adsorbate concentration while film and pore diffusion decreased. The thermodynamics parameters (positive values of ΔH°, ΔS° and negative values of ΔG°) indicated the binding systems between CTS/ATP and adsorbate were endothermic, entropy gained and spontaneous in nature. [Copyright &y& Elsevier]

Abstract: Batch adsorption experiments were carried out for the removal of methylene blue (MB) cationic dye from aqueous solution using chitosan-g-poly (acrylic acid)/attapulgite composites (CTS-g-PAA/APT) as adsorbent. The effects of attapulgite (APT) content, initial pH value of the dye solution and temperature on adsorption were investigated. Results showed that APT content of composites had some influence on adsorption capacities, and introducing a small amount of APT could improve adsorption capacity of chitosan-g-poly (acrylic acid) (CTS-g-PAA) to a certain extent. Results from kinetic experimental data showed that the adsorption rate of MB on CTS-g-PAA and CTS-g-PAA/APT with 30% of APT was fast, and more than 90% of the maximum adsorption capacities for MB were achieved within the initial 15min. The adsorption behaviors of CTS-g-PAA and CTS-g-PAA/APT showed that the adsorption kinetics and isotherms were in good agreement with a pseudo-second-order equation and the Langmuir equation, and the maximum adsorption capacities reached 1873 and 1848mg/g for CTS-g-PAA and CTS-g-PAA/APT, respectively. The discussion results of the desorption studies implied that CTS-g-PAA and CTS-g-PAA/APT can be used as promising adsorbents for the removal of MB from wastewater. [ABSTRACT FROM AUTHOR]

Abstract: β-Cyclodextrin/attapulgite (β-CD/ATP) composites were prepared for the adsorption of 2,4-didichlorophenol (2,4-DCP) and 2,6-didichlorophenol (2,6-DCP) from aqueous solution. β-CD/ATP composites mainly possessed mesopores, high surface area and big pore volume which were benefit for the adsorption capacity. The batch mode adsorption experiments with respect to pH, temperature, initial concentration, contact time and binary dichlorophenol solution were investigated. Equilibrium data, at various temperatures, were described by the Langmuir, Freundlich and Dubinin–Radushkevich isotherm models. The Langmuir isotherm model was fitted to the experimental data significantly better than the other models. The kinetic data were well fitted to the intraparticle diffusion equation, which indicated that three steps belonged to the pseudo-second-order adsorption process. Intraparticle diffusion increased with the increase of adsorbate concentrations while film and pore diffusion decreased. The initial adsorption factor, R i, showed that initial adsorption for 2,4-DCP was intermediate while was strong for 2,6-DCP. The thermodynamics parameters (positive values of ΔH° and ΔS°, negative values of ΔG°) indicated that binding systems between β-CD/ATP composites and adsorbates (2,4-DCP and 2,6-DCP) were endothermic, entropy gained and spontaneous in nature. [Copyright &y& Elsevier]

Abstract: Ion beam bombardment, as a unique and facile technique, was found and developed to fabricate nano-networks from rigid nano-rods. To study the differences of their characteristics, attapulgite (ATP) was chosen as a model. The results of methylene blue adsorption performance investigation demonstrated that attapulgite nano-networks (ATP-N) have better adsorption capability than the attapulgite nano-rods (ATP-R). The mechanism proposed that, compared with nano-rods, nano-networks exhibited larger interspace, better separation, higher pore-size and porosity and higher BET specific surface area due to the microstructure of complex three-dimensional networks caused by physical crosslinking, through a series of analysis of the scanning electron microscopy, BET surface area and X-ray powder diffraction. [Copyright &y& Elsevier]