A review of functionalized carbon nanotubes and graphene for heavy metal adsorption from water: Preparation, application, and mechanism.

Nanoporous adsorbents of ZnO/ZnFe2O4/C were synthesized by using a metal organic framework (Fe(III)-modified MOF-5) as both the precursor and the self-sacrificing template. The adsorption properties of ZnO/ZnFe2O4/C toward Pb(ii) ions were investigated, including the pH effect, adsorption equilibrium and adsorption kinetics. The adsorption isotherms and kinetics were well described by using the Langmuir isotherm model and pseudo-second-order model, respectively. The MOF-derived inorganic adsorbents exhibited high absorption performance with a maximum adsorption capacity of 344.83 mg g(-1). X-ray powder diffraction and high-resolution X-ray photoelectron spectroscopy suggest that Zn(ii) was substituted by a significant portion of Pb(ii) on the surface of ZnO nanocrystals. Microscopic observations also demonstrate the effect of Pb(ii) ions on ZnO crystals as reflected by the considerably reduced average particle size and defective outer layer. Quantitative measurement of the released Zn(ii) ions and the adsorbed Pb(ii) ions indicated a nearly linear relationship (R(2) = 0.977). Moreover, Pb-containing ZnO/ZnFe2O4/C adsorbents are strongly magnetic allowing their separation from the water environment by an external magnet.

Ion exchange induced removal of Pb(ii) by MOF-derived magnetic inorganic sorbents.

Among the heavy metal ions, copper(ii) can cause eye and liver damage at high uptake. The existence of copper ions (Cu(2+)) even with an ultralow concentration of less than 0.1 μg g(-1) can be toxic to living organisms. Thus, it is highly desirable to develop efficient adsorbents to remove Cu(2+) from aqueous solutions. In this work, without any surface functionalization or pretreatment, a water-stable zeolitic imidazolate framework (ZIF-8) synthesized at room temperature is directly used as a highly efficient adsorbent for removal of copper ions from aqueous solutions. To experimentally unveil the adsorption mechanism of Cu(2+) by using ZIF-8, we explore various effects from a series of important factors, such as pH value, contact time, temperature and initial Cu(2+) concentration. As a result, ZIF-8 nanocrystals demonstrate an unexpected high adsorption capacity of Cu(2+) and high removal efficiency for both high and low concentrations of Cu(2+) from water. Moreover, ZIF-8 nanocrystals possess fast kinetics for removing Cu(2+) with the adsorption time of less than 30 min. In addition, the pH of the solution ranging from 3 to 6 shows little effect on the adsorption of Cu(2+) by ZIF-8. The adsorption mechanism is proposed for the first time and systematically verified by various characterization techniques, such as TEM, FTIR, XPS, XRD and SEM.

Unveiling the adsorption mechanism of zeolitic imidazolate framework-8 with high efficiency for removal of copper ions from aqueous solutions

Synergistic coagulation of GO and secondary adsorption of heavy metal ions on Ca/Al layered double hydroxides

Magnetic porous polymers (MPPs) were successfully fabricated by a facile strategy of the high internal phase emulsions (HIPEs) technique. The microstructure, chemical composition, and magnetic properties of the MPPs were characterized. Impregnated with poly(styrene-divinylbenzene), stabilized by the amine-functionalized Fe3O4 nanoparticles (Fe3O4–NH2), the as-prepared MPPs with rich pore hierarchy were employed to removal Pb2+ and Cd2+ from aqueous solution. The MPPs display outstanding removal capacities toward Pb2+ (257 mg/g) and Cd2+ (129 mg/g) within 15 min, and the encapsulated Fe3O4–NH2 nanoparticles endow the MPPs with the ability of magnetic separation (30.15 emu/g). Additionally, the results indicate that the adsorptions of Pb2+ and Cd2+ are strongly dependent on pH and ionic strength, demonstrating that the interactions of Pb2+ and Cd2+ were mainly dominated by outer-sphere surface complexation and electrostatic attraction. The adsorption process is revealed by thermodynamic parameters to be spo...

Magnetic Porous Polymers Prepared via High Internal Phase Emulsions for Efficient Removal of Pb2+ and Cd2+

Nano-titanium oxide (nano-TiO2) was synthesized and characterized by using XRD, TEM, XPS and FTIR. The effect of contact time, solid content, pH, foreign anions, ionic strength, humic acid (HA) and temperature on the removal of Pb(II) by nano-TiO2 were investigated using a batch technique. The batch results showed that the adsorption of Pb(II) on nano-TiO2 significantly decreased with increasing ionic strength at low pH conditions, whereas the ionic strength-independent adsorption was observed at high pH, indicating that the ion exchange and inner-sphere surface complexation dominated the adsorption of Pb(II) at low and high pH, respectively. The further evidences were provided by the effect of foreign anions and HA. The maximum adsorption capacity of Pb(II) on nano-TiO2 calculated from a Langmuir model at pH 5.0 and 293 K was 30.8 mg g−1, which was significantly higher than commercial P25 TiO2 (15.0 mg g−1). The thermodynamic parameters showed that the adsorption of Pb(II) on nano-TiO2 was an endothermic and spontaneous process. The hydroxyl groups of nano-TiO2 were responsible for the highly effective adsorption of Pb(II) by XPS analyses. Based on surface complexation modeling, a diffuse layer model gave excellent fitting for the pH-edge adsorption data. The results indicated that the nano-TiO2 could be used as a suitable adsorbent for the removal of heavy metals from large volumes of aqueous solutions in environmental cleanup.

Huiyi Gao

Papers

Removal of Pb(II) by nano-titanium oxide investigated by batch, XPS and model techniques