| With the rapid development of the industrial economy,the generation of a large number of industrial pollutants has caused serious pollution to China's water environment.Heavy metals have become one of the major pollutants.Due to their high toxicity and biodegradability,they have caused inestimable harm to the aquatic environment and humans.Titanate nanotubes(TNTs)have a uniform structure,large specific surface area,special physical and chemical properties,etc.,and have good application prospects in the field of treating water and heavy metal pollution.In recent years,the use of precious metals or other materials to modify titanate nanotubes and their application in the treatment of heavy metal pollution in water has gradually become a research hotspot.In this paper,the advantages of titanate and niobate materials for the removal of heavy metal ions are combined,and the niobate modified titanate nanoflakes(Nb/TiNFs)are synthesized by a one-step hydrothermal method.Their structural characteristics are analyzed and applied to heavy metals in water.The adsorption and removal of ionic Pb(?),on this basis,explore the competitive adsorption mechanism of Pb(?),Cu(?),Cd(?)in the composite system.the result shows:(1)The results of XRD,TEM and SEM confirmed that the newly synthesized Nb/TiNFs had a nano-sheet structure,with trititanate as the main crystal phase.Nb/TiNFs showed rapid adsorption kinetics for Pb(?),which reached the adsorption equilibrium within 5 minutes and conformed to the quasi-second-order kinetic model(R2>0.99).The adsorption isotherms were better simulated by Langmuir model(R2>0.99),the theoretical maximum adsorption capacity of Pb(?)is 488.323 mg·g-1.This indicates that the adsorption of Nb/TiNFs to Pb(?)is dominated by monolayer adsorption and chemical adsorption.The adsorption mechanism is mainly the ion exchange of Na+/H+between Pb(?)and Nb/TiNFs.Nb/TiNFs has a good adsorption effect on the heavy metal Pb(?)in a wide pH range,it will inhibit the adsorption of Pb(?)under acidic conditions,and the adsorption effect is the best when pH=5.The coexistence of Na+has little effect on the adsorption of Pb(?),and Ca2+ion has a slight inhibitory effect on the adsorption of Pb(?).The main mechanism is that Na+and Ca2+compete with Pb(?)for the adsorption sites,and the reason for the ineffective inhibition It is the strong affinity of Nb/TiNFs for Pb(?).Soluble humic acid(HA)moderately inhibited the adsorption of Pb(?)on Nb/TiNFs.Adsorbent concentration has a greater effect on adsorption,and high adsorbent concentration is beneficial to the removal of Pb(?).Nb/TiNFs,as a permeable reaction wall medium,can effectively remove groundwater Pb(?)pollution,prevent its migration in groundwater,and provide an alternative way for in-situ remediation of groundwater.(2)Nb/TiNFs have fast adsorption kinetics and high adsorption capaci ty for Pb(?),Cu(?),Cd(?),the specific mechanism is the ion exchange between metal cation and interlayer Na+/H+.The adsorption isotherm is co nsistent with the Langmuir model,and the theoreti-cal maximum adsorptio n capacity Pb(?)(2.441 mmol·g1)>Cu(?)(1.850 mmol·g-1)>Cd(?)(1.704 mm ol·g-1).Competitive adsorption results show that under the composite syste m,there is competitive adsorption between metal ions.In the binary syste m,the presence of Pb(?)greatly affects the adsorption of Cu(?)and Cd(?),and Nb/TiNFs adsorbs Cu(?)has the same affinity as Cd(?),and io ns with concentration advantages have adsorption advantages.In the tern-a ry system(concentration ratio is 1:1:1),the competitiveness is Pb(?)>Cu(I I)>Cd(?),the main mechanism is that Pb(?)has the largest electronegati-vity and is easily attracted to Ion exchange is performed on the surface of Nb/TiNFs.Because Nb/TiNFs has the advantages of simple synthesis method and efficient removal of metal cations in the sewage of complex systems,it can provide an alternative way for the treatment of many kinds of heavy metal polluted wastewater. |
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