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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]

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: 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]

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]