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A novel adsorbent (AC/Fe 3 O 4 @SiO 2 –NH 2 ) was synthesized via a co-condensation process for the enhanced removal of Pb(II) from aqueous solutions. Characterization analyses including SEM, TEM, BET and XRD confirmed the successful integration of magnetic nanoparticles and amino groups with carbon matrix. Results demonstrated that AC/Fe 3 O 4 @SiO 2 –NH 2 (mass ratio of AC to Fe 3 O 4 was 1:0.25) with specific surface area (48.9 m 2 /g) showed higher adsorption capacity for Pb(II) as compared to other mass ratios. Kinetics study revealed that the adsorption reach equilibrium within 20 h and the maximum adsorption capacity of 104.2 mg/g was achieved with increasing the initial concentration from 20 to 250 mg/L using AC/Fe 3 O 4 @SiO 2 –NH 2 . Maximum removal efficiency was recorded at pH 5.2 and the removal capacities toward four divalent metal ions calculated by the Langmuir model were found to be in the order of Pb(II) > Cu(II) > Ni(II) > Cd(II). Furthermore, Δ G 0 decreased from –1.6 to −3.1 kJ/mol with increase in temperature from 293 to 333 K illustrating that the adsorption was spontaneous and an endothermic process. Complexation adsorption mechanism was found prominent in FTIR and XPS analyses between Pb(II) and AC/Fe 3 O 4 @SiO 2 –NH 2 due to the presence of amino groups. [ABSTRACT FROM AUTHOR]

A novel amino-functionalized multiwalled carbon nanotube (MWCNTs @SiO 2 -NH 2 ) was prepared via co-condensation using etraethyl orthosilicate and 3-aminopropyl trimethoxysilane for effective removal of Pb(II) from water. The Pb (II) adsorption efficiencies of MWCNTs and MWCNTs@SiO 2 -NH 2 were compared and the change of morphology features was assessed in batch adsorption experiments. The characterization analysis like XRD, FITR and XPS revealed that amino groups were successfully grafted on the MWCNTs. Adsorption results demonstrated that the best TEOS/APTMS loading ratio was about 10:3 based on their solution volume ratio. Compared to the poor Pb(II) adsorption capacity of pristine MWCNTs, the maximum adsorption capacity of MWCNTs@SiO 2 -NH 2 was greatly improved to 147 mg/g after amination treatment. Pb(II) adsorption onto MWCNTs@SiO 2 -NH 2 was strongly pH-dependent and the optimal aqueous pH was about 5. Moreover, the pseudo-second-order kinetics model and Langmuir isotherm model could well describe the Pb(II) adsorption process by MWCNTs@SiO 2 -NH 2 . Thermodynamics analysis illustrated that the Pb(II) adsorption was spontaneous and endothermic. FTIR and XPS analysis of MWCNTs@SiO 2 -NH 2 after adsorption demonstrated the complexation between amino groups and Pb(II) played a vital role in the adsorption mechanism. Findings from the present study suggested that successful Pb(II) removal could be achieved using such novel adsorbent composite with optimized process. [ABSTRACT FROM AUTHOR]

Nanoscale zero-valent iron (nZVI) has high removal efficiency and strong reductive ability to organic and inorganic contaminants, but concerns over its stability and dispersity limit its application. In this study, nZVI was modified with sulfide to enhance Cd(II) removal from aqueous solutions. TEM and SEM analyses showed that sulfide-modified nZVI (S-nZVI) had a core-shell structure of nano-sized spherical particles, and BET results proved that sulfide modification doubled the specific surface area from 26.04 to 50.34 m 2  g −1 and inhibited the aggregation of nZVI. Mechanism analysis indicated that Cd(II) was immobilized through complexation and precipitation. Cd(II) removal rate on nZVI was only 32% in 2 h, while complete immobilization could be achieved in 15 min on S-nZVI, and S-nZVI with an optimal S/Fe molar ratio of 0.3 offered a cadmium removal capacity of about 150 mg g −1 at pH 7 and 303 K. The process of Cd(II) immobilization on S-nZVI was fitted well with pseudo-second-order kinetic model, and the increase of temperature favored Cd(II) immobilization, suggesting an endothermic process. The presence of Mg 2+ and Ca 2+ hindered Cd(II) removal while Cu 2+ did the opposite, which led to the order as Cu 2+  > control > Mg 2+  > Ca 2+ . The removal rate of 20 mg L −1 Cd(II) maintained a high level with the fluctuation of environmental conditions such as pH, ion strength and presence of HA. This study demonstrated that S-nZVI could be a promising adsorbent for Cd(II) immobilization from cadmium-contaminated water. [ABSTRACT FROM AUTHOR]

In this study, SiO 2 -EDTA was prepared by silanization reaction between N-(trimethoxysilylpropyl) ethylenediamine triacetic acid, trisodium salt (EDTA-silane) and hydroxyl groups for enhanced removal of Pb(II), Pb(II)-Cit (the clathrate generated by Pb(II) and trisodium citrate dehydrate(Cit)) and Pb(II)-EDTA(20%) from aqueous solutions. SiO 2 -EDTA composites were characterized using SEM, TEM, EDX-mapping, FTIR, XPS and TGA analyses. The influence of solution pH, initial concentration, contact time and co-existing interferents were also studied. Results demonstrated that the composite successfully adsorbed 147.52, 107.65 and 124.18 mg g −1 of Pb(II), Pb(II)-Cit, and Pb(II)-EDTA (20%), respectively with the initial Pb(II) concentration of 100 mg L −1 . Kinetics study revealed that the adsorption rate was significantly high at the beginning and then reached to equilibrium within 1.0 h. Moreover, Pb(II) adsorption capacities were found to considerably affected by co-existing cations and not inhibited by natural organic matter (NOM). Characterization analyses confirmed that EDTA was successfully assembled on SiO 2 which had been used as a supporting matrix due to its huge specific surface area. Findings from this study suggested that the present composite could be considered as a promising adsorbent for large scale treatment of wastewater containing elevated Pb(II) concentration. [ABSTRACT FROM AUTHOR]