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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]

Novel polyamidoamine (PAMAM) dendrimer-functionalized palygorskite (Pal) adsorbents, up to generation 4.0, with high adsorption capacity, were designed and efficiently synthesized by grafting PAMAM onto 3-aminopropyltriethoxysilane-modified palygorskite (NH 2 -Pal) surfaces. This was carried out using a divergent method including the Michael addition of methyl acrylate (MA) and amidation of the resultant ester moieties with ethylenediamine (EDA). The optimal conditions for Michael addition were achieved using 88.8 mmol MA (relative to 4.0 g NH 2 -Pal) at 323 K for 24 h. The optimal conditions for amidation of the resultant esters were achieved using 179.3 mmol EDA (relative to 2.1 g Pal-PAMAM G0.5) at 323 K for 48 h. All of the amino-terminated Pal-PAMAM G( n ) ( n = 0, 1, 2, 3 and 4) adsorbents exhibited very high density amino-terminated groups and adsorption capacities for both Pb 2 + and Reactive Red 3BS, which increased with increasing generation number. The maximum adsorption capacity for Pb 2 + at 293 K was 68.5 ± 3.3, 151.1 ± 5.7, 196.5 ± 6.1, 389.1 ± 9.6 and 694.4 ± 12.9 mg/g for Pal-PAMAM G( n ) ( n = 0, 1, 2, 3 and 4), respectively. The maximum adsorption capacity for Reactive Red 3BS at 293 K was 34.2 ± 2.7, 69.9 ± 4.3, 122.0 ± 6.4, 242.7 ± 7.1 and 322.6 ± 6.9 mg/g for Pal-PAMAM G( n ) ( n = 0, 1, 2, 3 and 4), respectively. [ABSTRACT FROM AUTHOR]

To improve the performance of ceramic membranes and reduce their costs, a new ceramic microfiltration membrane with a separation layer made of attapulgite nanofibers was fabricated by dip-coating on the inner surface of ɑ-alumina tubular supports. The membrane has a separation layer of attapulgite nanofibers without evident defects and exhibits excellent interface properties, showing good adherence to the ɑ-alumina substrate. The nanofiber membrane has an average pore size of 0.250 μm, thickness of approximately 6.7 μm, and a pure water flux of 1540 L/(m 2 h bar). The membrane was able to reject all the calcium carbonate particles in suspension, and showed a steady permeate flux of approximately 980 L/(m 2 h bar). In addition, the membrane can be easily regenerated by backwashing without any damage, and therefore used repeatedly. [ABSTRACT FROM AUTHOR]

Fouling of membranes by proteins is a major problem in membrane filtration operations. To reduce protein-fouling, an easy-clean surface was designed by grafting temperature-sensitive poly (N-isopropylacrylamide) (PNIPAAm) brushes onto the surface of zirconium oxide (ZrO2) membranes via chemical grafting. The grafting density of PNIPAAm brushes and polymer thickness were controlled by changing the NIPAM concentration. The water fluxes of the PNIPAAm-grafted-ZrO2 (PNIPAAm-g-ZrO2) membranes were highly dependent on the solution temperature, and increased at higher solution temperature. An increase in the water fluxes was evident at approximately 32–34°C. Compared with the ZrO2 membranes, the fluxes for the PNIPAAm-g-ZrO2 membrane declined more gradually at both 25°C and 35°C, and a high initial rejection of 89.4%, along with a suitable steady flux of 66.2Lm−2 h−1, were achieved at 25°C. The PNIPAAm-g-ZrO2 membrane exhibited good anti-fouling properties and improved membrane performance during the filtration of bovine serum albumin (BSA). In particular, due to the reversible volume phase transition of PNIPAAm around the lower critical solution temperature (LCST), an environmentally-friendly membrane cleaning method by means of temperature-change water elution around the LCST of the PNIPAAm brushes was proposed. Following the alternate temperature-change (35°C/25°C) cleaning, a flux recovery of about 80% was obtained for the PNIPAAm-g-ZrO2 membrane (the flux recovery of the ZrO2 membrane was only about 14% at 25°C). Moreover, when the experiments were repeated four times, the anti-fouling and easy-cleaning properties were maintained. The hydrophilicity and the rapid stretching of PNIPAAm chains were considered responsible for loosening and shaking off the adsorbed BSA on the graft membrane surface. [ABSTRACT FROM AUTHOR]

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: 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: Surface modification of palygorskite is one of the important ways to enlarge its application field. This study adopts palygorskite modified by 3-aminopropyl triethoxysilane (APTES) as adsorbent of three reactive dyes. The surface modification of palygorskite was characterized by Fourier transform infrared spectroscopy and X-ray diffraction. Batch studies were carried out to investigate various experimental parameters such as adsorbent dosage, contact time, initial dye concentration and initial pH. The kinetics of the adsorption followed the pseudo-second-order model. Adsorption equilibrium data were fitted by the Langmuir isotherm. The adsorption of the three dyes by palygorskite was low but was strongly increased by the silylated palygorskite. The maximum adsorption capacity calculated by the Langmuir model was 34, 38, 60mg/g for Reactive Red 3BS, Reactive Blue KE-R and Reactive Black GR, respectively. [Copyright &y& Elsevier]

Abstract: TMC-incorporated carbon nitride (CN) with hexagonal and quadrangle honeycomb-like structure and having periodic lattice defects linked by -CONH- bond was synthesized through combining the high calcination with the chemical condensation of melamine and 1,3,5-benzenetricarbonyl trichloride. The obtained CN has a tri-s-triazine ring and benzene ring skeleton, which makes it have excellent mechanical and thermal stability. The BET specific surface area was enhanced to about 125.6 m2/g, and the mean pore size is about 3.43 nm. This CN exhibited an excellent adsorption-enhanced photocatalytic performance.Graphical abstract: [ABSTRACT FROM AUTHOR]

Attapulgite (ATP) hollow fiber membranes with a mesh-like structure layer were prepared via a combined phase-inversion and one-step sintering method. A finger/sponge mixed structure in the membrane cross-section was obtained. The change of ATP chemical structure enhanced the membrane mechanical strength and had few effects on the general physical morphology. High permeate fluxes indicated that the ATP hollow fiber membrane is an attractive alternative as a liquid microfiltration membrane. [ABSTRACT FROM AUTHOR]

Graphitic carbon nitride (g-C 3 N 4) with a layered lamellar structure was successively used to fabricate highly water-selective membranes via hybrid or free-standing methods. Molecular dynamics (MD) simulations were carried out to study the diffusion behaviors of water and ethanol molecules through pristine g-C 3 N 4 (Pri-g-C 3 N 4) and benzene ring-doped g-C 3 N 4 (Ben-g-C 3 N 4) membranes. MD results indicated that hydrogen bonds formed between water molecules and Pri-g-C 3 N 4 or Ben-g-C 3 N 4 nanosheets affected the permeation of water across these nanosheets. Interestingly, the simulation analysis showed that the lamellar structures of Pri-g-C 3 N 4 nanosheets played a significant role in the separation of ethanol and water. The diffusion coefficients of water and ethanol through Pri-g-C 3 N 4 lamellae were 2.24 × 10−5 cm2 s−1 and 1.04 × 10−5 cm2 s−1, respectively. Besides, the movement behaviors of water and ethanol molecules between lamellae of the sheet-shaped g-C 3 N 4 (pristine g-C 3 N 4 , Pri-g-C 3 N 4) and distorted-type carbon nitride g-C 3 N 4 , i.e., benzene ring-doped into g-C 3 N 4 (Ben-g-C 3 N 4) were studied in detail. For the different configurations of g-C 3 N 4 , pure water flow was slower in Pri-g-C 3 N 4 confinement compared to Ben-g-C 3 N 4 , as the lifetime of hydrogen bonds between water molecules in Ben-g-C 3 N 4 was shorter than that in Pri-g-C 3 N 4. Importantly, for ethanol/water binary mixtures, both Pri-g-C 3 N 4 and Ben-g-C 3 N 4 surfaces preferentially adsorb ethanol, where the hydroxyl group of ethanol is closer to the membrane surface. The observed interesting feature suggested that the lamellar structures of Pri-g-C 3 N 4 (or Ben-g-C 3 N 4) nanosheets were efficient in the separation of ethanol and water. Image 1 • Hydrogen bonds between water and g-C 3 N 4 hinder H 2 O across g-C 3 N 4 nanosheets. • Lamellar structures of g-C 3 N 4 play a major role in the separation of ethanol and H 2 O. • The water flux of Ben-g-C 3 N 4 membranes is larger than that of Pri-g-C 3 N 4. • Both Pri-g-C 3 N 4 and Ben-g-C 3 N 4 are efficient in the separation of ethanol and H 2 O. [ABSTRACT FROM AUTHOR]

Membrane technology can realize wastewater recycling in industry, but its efficiency is threatened by fouling. In this study, magnetic palygorskite (m-Pal) nanofibers were obtained by anchoring Fe 3 O 4 nanoparticles onto the surface of palygorskite. Then, composite membranes composed of poly(vinylidene fluoride) (PVDF) and m-Pal were prepared during a magnetic field assisted phase inversion process. The m-Pal can be elevated to the membrane surface due to magnetic force, thus adjusting membrane performance. The PVDF/m-Pal composite membrane prepared with magnetic field displayed higher water flux and better hydrophilicity than that of pristine PVDF membrane. The water flux can be increased to 343.2 L·m−2·h−1·bar−1, and water contact angle decreases to 71.8° with the addition of 7% m-Pal. Moreover, the anti-fouling and easy-cleaning performance of the composite membrane was demonstrated in bovine serum albumin (BSA) solution separation, with BSA flux and flux recovery ratio increased by 41.3% and 155.4%, respectively, compared with the control PVDF membrane. [Display omitted] • Magnetic palygorskite (m-Pal) was prepared by anchoring nano-Fe 3 O 4 on Pal nanofibers. • Composite membrane was obtained by blending m-Pal with PVDF. • m-Pal was elevated to membrane surface by a magnetic field during preparation. • The anti-fouling and easy-cleaning performance of membrane was improved with m-Pal. [ABSTRACT FROM AUTHOR]

Abstract: New poly(N-isopropylacrylamide) brushes grafted with ZrO2 (PNIPAAm-g-ZrO2) composite membranes, which had been prepared in our laboratory, were used for humic acid (HA) removal. We found that the fluxes associated with such membranes, when compared to those obtained from unmodified ZrO2 membranes, declined slightly at both 25 °C and 35 °C. The PNIPAAm-g-ZrO2 membrane achieved a high rejection, of 98.0%, at a suitable steady flux of 111.9 L m−2 h−1 at 25 °C. This membrane exhibited good anti-fouling properties as well as improved membrane performance during filtration of HA. The important role of pH and Ca2+ concentration in HA removal was also investigated. Lower adsorption fouling and a higher rejection were obtained at higher pH levels. The Ca2+ ions reduced the electrostatic exclusion and played a cross-linking role between HA and the PNIPAAm-g-ZrO2 membrane surface. Fouling was severe in the presence of Ca2+. These tests led to the development of an environment-friendly membrane cleaning method, by means of temperature-change water elution around LCST of PNIPAAm-brushes. After the alternate temperature-change (25 °C/35 °C) cleaning, a flux recovery of 98.2% was obtained for the PNIPAAm-g-ZrO2 membrane. Moreover, after four repeated experiments, the anti-fouling and easy-cleaning properties were still maintained. It is implied that PNIPAAm-brushes were firmly “stuck” to the membrane surface, and could not easily be removed by water cleaning or HA filtration. The PNIPAAm-g-ZrO2 membranes exhibited good stability and great potential for HA removal [Copyright &y& Elsevier]

Abstract: Polyacrylamide/attapulgite (PAM/ATP) was prepared by the solution polymerization of acrylamide (AM) onto γ-methacryloxypropyl trimethoxy silane (KH-570)-modified attapulgite (ATP). PAM/ATP was characterized using Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS). The effects of contact time, adsorbent dosage, and pH of the initial solution on the adsorption capacities for Hg2+ were investigated. The adsorption process was rapid; 88% of adsorption occurred within 5min and equilibrium was achieved at around 40min. The equilibrium data fitted the Langmuir sorption isotherms well, and the maximum adsorption capacity of Hg2+ onto PAM/ATP was found to be 192.5mgg−1. The adsorption kinetics of PAM/ATP fitted a pseudo-second-order kinetic model. Our results suggest that chemisorption processes could be the rate-limiting steps in the process of Hg2+ adsorption. Hg2+ adsorbed onto PAM/ATP could be effectively desorbed in hot acetic acid solution, and the adsorption capacity of the regenerated adsorbents could still be maintained at 95% by the sixth cycle. [Copyright &y& Elsevier]

The natural hydrophilic nanofiber-like palygorskite (Pal) particles were incorporated into the quaternary ammonium functionalized polysulfone (QPSf) to prepare high performance anion exchange membranes. Due to the mutual compatibility between quaternary ammonium groups in quaternized polysulfone and hydrophilic Pal particles, a hydrophilic domain could aggregate, thereby forming a hydrophilic-hydrophobic microphase separation structure. Meanwhile, the small-angle X-ray scattering (SAXS) was utilized to characterize the hydrophilic ionic cluster domain in the composite membrane. The results showed that the corresponding average inter-domain spacing of the QPSf/Pal-0.5 membrane was about 30 nm. Then, the new composite membrane had not only highly efficient hydrophilic ion transport channels but also adjustable hydrophilic-hydrophobic microphase separation structures. Compared with original quaternized polysulfone membranes, the hydroxide conductivity of the QPSf/Pal-0.5 membrane reached 93.0 mS·cm−1 at 80 °C, increasing by 48%, while the methanol permeability was kept between 4.2 × 10−7 and 5.8 × 10−7 cm2·s−1. Quaternary ammonium functional groups were grafted on the polysulfone side chain by chloromethylation and Menshutkin reaction. The hydrophilic palygorskite and quaternary ammonium functionalized polysulfone were mixed and self-assembled to form hydrophilic-hydrophobic microphase separation structure, which is conducive to rapid transport of hydroxide ions. Unlabelled Image • AEMs with high-efficiency ion channels were prepared by incorporating Pal into QPSf. • Ion transport channels can be precisely regulated by controlling the addition of Pal. • The composite AEMs exhibited high hydroxide ion conductivity. • The composite AEMs exhibited excellent mechanical properties. [ABSTRACT FROM AUTHOR]

Palygorskite (PGS) was incorporated into a polyvinylidene fluoride (PVDF) matrix and PVDF/PGS nanocomposite UF membranes were prepared successfully via a combination of non-solvent-induced phase separation (NIPS) and thermally-induced phase separation (TIPS) processes. The influence of the size of the PGS particles (PGS-L, 450 nm and PGS-S, 302 nm) on the membrane pore structure, morphology, mechanical strength, filtration performance and antifouling property were investigated. The results showed that the PVDF/PGS-S composite membranes had higher porosity and lower overall membrane thickness and skin layer thickness. This directly resulted in better PWF, BSA flux, BSA rejection and FRR for the membranes loaded with PGS-S, when compared with the characteristics of PVDF/PGS-L membranes. Thus, the physical structures are dominant factors in determining the separation performance of PVDF/PGS composite membranes. However, the surface roughness and thermal stability of PVDF/PGS-L membranes were greater than those of PVDF/PGS-S membranes and their surface was also more hydrophilic. Moreover, they exhibited higher mechanical strength owing to stronger binding forces and lower porosity. Thus, the composite properties of PVDF/PGS UF membranes could be adjusted by controlling the scale of the inorganic filler. Unlabelled Image • Effects of PGS particle scale on membrane structure and properties were studied. • PVDF/PGS-S membranes had higher porosities and lower overall membrane thicknesses. • PVDF/PGS-L membranes had better thermal stabilities and mechanical strengths. • PVDF/PGS-S membranes displayed better separation and antifouling performances. [ABSTRACT FROM AUTHOR]