Removal of trace heavy metal ions puts high demands on designing adsorbents with favorable surfaces.Crystal-plane engineering can provide controllable adsorption energy between surficial planes and adsorbents.Herein,we have creatively synthesized Mg-doped CaCO_(3)nanoarchitectures assembled by layered sheets(Mg-CaCO_(3)LSs)with high-index facets of(441)through a facile wet chemical process.Adsorption tests reveal that the layer-bylayer assembled sample exhibits a maximum Pb(II)adsorption capacity of 1961.9 mg·g^(-1),agreeing with the monolayer-adsorption Langmuir model.At an initial Pb(II)ion concentration of 20 mg·L^(-1),the adsorption can achieve a high removal rate near 99.0%within 1 min,and the adsorption kinetics follows a chemisorption pseudo-second-order model.Interestingly,the Mg-CaCO_(3)LSs show much-improved adsorption properties towards low-concentration Pb(II)ions,which could reduce the concentration from 1 mg·L^(-1)to~2.9μg·L^(-1)in 3 h(within 30 min decrease to less than 10μg·L^(-1),meeting drinking water standard from WHO).For comparison,the commercial CaCO_(3)and collected CaCO_(3)scale show much lower adsorption values with Pb(Ⅱ)ion residual concentration of~935.0 and~944.9μg·L^(-1)in 3 h,respectively.Xray diffraction(XRD),energy dispersive spectroscopy(EDS),and inductively coupled plasma(ICP)characterizations on the Mg-CaCO_(3)LSs before and after adsorbing Pb(Ⅱ)confirm that the high removal performance could be ascribed to fast metal ion exchange and excellent physical adsorption contributed by high-index planes.The density functional theory(DFT)calculations also confirm that the much-enhanced adsorption kinetics benefits from the optimal adsorption of the(441)planes.This work will provide a feasible route to design highefficient low-cost adsorbents through crystal-plane engineering.
The reduced graphene oxide-Fe3O4（rGO-Fe3O4） hybrid nanocomposite was prepared via a one-pot facile hydrothermal method for adsorption of heavy metal ions. The results of compositional and morphological characteri- zations show that the Fe3O4 NPs with an average diameter of 20 nm have been uniformly dispersed in rGO sheets. Due to the higher specific surface area of rGO and the magnetic properties of Fe3O4 nanoparticles, the prepared rGO-Fe3O4 hybrid nanosheets showed good adsorption capacity for the removal of Pb（II） from wastewater by simple magnetic separation. The result of control tests show that the adsorption capacity of rGO-Fe3O4 can be influenced by the ratio of ferric chloride（FeC13） to graphene oxide（GO） during the process of sample preparation and the initial concentration of Pb（II）. A better adsorption capacity was 30.68 mg/g at n（FeCl3）/m（GO） ratio of 1：5（mmol：mg） at pH=7.0 with the initial concentration of Pb（II） ions of 80 mg/L, and the experimental data were well fitted with the Langmuir adsorption model. The composite with absorbed Pb（II） can be easily collected by magnetic separation from wastewater because of the excellent magnetism of Fe3O4 NPs. The rGO-Fe3O4 hybrid nanocomposite provides an ef- fective and environment-friendly absorbent with great application potential in water purification.
Single-crystalline Li-doped Co3O4 truncated octahedra with different doping contents were synthesized by a simple combustion method with the fuel of multi-walled carbon nanotubes(MWCNTs).Controlled experiments showed that the pristine well-defined Co3O4 octahedra were obtained with exposed surfaces of {111} planes without lithium doping.In comparison with the octahedra,the truncated Co3O4 octahedra were composed of original {111} planes and extra {100} planes.It could be attributable to the selective adsorption of lithium ions on the {100} planes,making these planes with higher surface energy coexist with the crystal faces of {111}.Furthermore,the Li-doped truncated octahedra and undoped octahedra were used as catalysts in CO oxidation and as anode materials for Li-ion batteries(LIBs).The measurements exhibited that the Li-doped octahedra with added {100} crystal faces showed improved catalytic activity and electrochemical property because of the exposure of the higher energy faces of {100} and enhanced conductivity by Li doping.
