| Industrial effluent and domestic sewage containing excessive amounts of toxic and harmful heavy metal ions,such as Pbru,Zn2+ and Cu2+,have discharged into the environment,which not only seriously threatens the natural ecological environment and the health of people,but also has become a huge challenge for China's sustainable economic development.Due to simple operation and short period,adsorption method is one of the effective ways to remove heavy metal ions.The adsorption performance mainly depends on the chemical composition,crystal structure,surface properties and pore structure of the adsorbents.Among them,the high specific surface area favors to enhance adsorption capacity,while the suitable pore size aids to improve not only the adsorption efficiency,but also the utilization efficiency of the specific surface.Therefore,it is of great scientific significance and practical application value to construct novelly green adsorbents with high-performance and suitable pore structure for the removal of toxic and harmful heavy metal ions,which will promote the sustainable development of economy and society in China.Newly porous magnesium silicate adsorbent as a typical two-dimension layered silicate compound,has the advantages of rich sources and environmental friendly.However,the low specific surface area and small pore size directly restrict their adsorption performance and practical applications.In this work,with the aiming of designation and preparation of magnesium silicate adsorbents which can efficiently remove toxic and harmful heavy metal ions,magnesium silicate materials with different morphology and hierarchically porous structure were prepared by controlling chemical composition,surface properties,morphology and pore structure,and breaking through the related key technologies.At the same time,using three typical heavy metal ions such as Pb2+,Zn2+,Cu2+ as the probe,systematically investigated the adsorption behavior and mechanism towards different heavy metal ions and then revealed the adsorption properties of magnesium silicate and the structure-performance relationship.The main contents and results were as follows:(1)Based on the mechanism of nucleation and growth of nanomaterials,a method involving separate nucleation and aging steps was developed to synthesize a series of magnesium silicate adsorption materials with small particle size,high specific surface area,and systematically investigated the adsorption performance for Pb2+,Zn2+ ions by adjusting and optimizing morphology,pore structure and surface charge density.The results showed that compared with the traditional hydrothermal method,the developed method was able effectively prepare magnesium silicate adsorption materials with small size and high specific surface;the average particle size of ca.460 nm was 75.8%of smaller size,and the specific surface area was ca.597 m2·g-1 with 121%of increase;the adsorption performance of Pb2+,Zn2+ ions was significantly improved because of smaller particle size and higher specific surface area,for example,the adsorption capacity for Pb2+ was increased to 142.1 mg·g-1,and that for Zn2+ ion was increased to 46.5 mg·g-1.Also,the adsorption capcity of magnesium silicate for methylene blue was raised 0.36 times by controlling the surface charge.(2)Based on the interface effect of different solvents,a mixed solvothermal method was developed to prepare a series of hierarchically porous magnesium silicate adsorption materials by adjusting the ratio between ethanol and water under the condition of no template,and then investigated the adsorption behavior for Pb2+,Zn2+,Cu2+ and the structure-activity relationship between the adsorption performance and the pore structure in detail.The results showed that the mixed solvothermal method was available to prepare hierarchically porous magnesium silicate adsorption materials with multilevel pore distribution in the range of 0.5?200 nm,especially the abundance of mesoporous and macroporous materials;the maximum specific surface area was up to 708 m2·g-1 and the average pore size was 6.89 nm,which were much higher than the reported value in the literature.With the suitable pore structure,the maximum adsorption capacity of Pb2+,Zn2+ and Cu2+ was 436.7,78.8 and 52.3 mg·g-1,respectively;after being recycled and regenerated by EDTA solution for 3 times,the adsorption capacity of Pb2+ remained more than 85%,which exhibited a certain recycling performance.(3)Based on the structural topology transformation effect,a series of hierarchically porous magnesium silicate(MS)composite films on carbon fiber(CP@MS)were prepared through in-situ phase transformation method.Using carbon fiber(cp)as the substrate and the carbon fiber supported basic magnesium carbonate as the precursor,the in-situ reaction was carried out with sodium silicate,and then the adsorption behavior of Zn2+?Cu2+ and the structure-performance relationship between the adsorption performance and the pore structure were examined in detail.The results showed that:The hierarchically porous magnesium silicate composite films were able to be prepared by solid phase transformation reaction with the pore distribution in the range of 0.8?200 nm;The loading amount of magnesium silicate on carbon fiber was about 27.3 wt%with the highest specific surface area of ca.11 m2·g-1,and the average pore size of 13 nm;The suitable pH range was 4.0?7.0,and the maximum adsorption capacity of Zn2+,Cu2+ was 198.0 and 131.5 mg·g-1,respectively,which followed the quasi-second-order kinetics and Langmuir adsorption model with cation-exchange adsorption mechanism;In a home-made water filtration device,the polluted water was able to be treated to meet the standard of WHO,and the recycling performance was good,which exhibited promisingly practical applications. |
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