Mechanism And Research Of Removal Of Heavy Metals In Water By Modified Titanate Nanomaterials

Modern industry society is developing rapidly,at the same time it is destroying humanity’s livelihood environment at the unprecedented speed.As an important environmental factor,water body has been polluted by various substances discharged by human beings in different degrees.Heavy metals,as one of the pollutants,have caused incalculable damage to the environment due to their general characteristics such as high toxicity,difficult degradation and easy enrichment.Titanate nanotubes（TNTs）show great potential applications in wastewater treatment area due to their uniform,composition and property.In recent years,modified titanate nanomaterials have also become a hot topic.In this study,niobate modified titanate nanosheets（Nb-TNS）were synthesized through a hydrothermal method and used to remove Cd（Ⅱ）from water and FeS modified titanate nanotubes（FeS@TNTs）were synthesized through a two-step water–ethanol hydrothermal method and used to remove Cr（Ⅵ）from water.The specific research results are as follows:（1）The new nanocomposites（Nb-TNS）were non-curled nanosheets.Ion-exchange between Cd²⁺and Na⁺in the interlayers of Nb-TNS was the dominant mechanism for Cd（Ⅱ）adsorption,leading to good adsorption performance.The material exhibited rapid adsorption kinetics for Cd（Ⅱ）,which could reach equilibrium within 60 min,and the data fit well with the pseudo-second order model（R²=1）.The maximum adsorption capacity of Cd（Ⅱ）was 287.9 mg·g^-1 according to Langmuir isotherm model,which was larger than most of traditional adsorbents.Higher pH promoted adsorption because the negatively charged material could capture Cd（Ⅱ）cations more easily.Co-existing inorganic ions(Na⁺and Ca²⁺)were unfavorable to adsorption of Cd（Ⅱ）by Nb-TNS due to competition of adsorption sites.In addition,slight inhibition effect on adsorption in the presence of humic acid（HA）was found.Cd（Ⅱ）could be efficiently desorbed from Nb-TNS after HNO₃ treatment,and-ONa sites restored upon NaOH treatment.Considering the simple synthesis method,high removal efficiency for heavy metals and good reusability,Nb-TNS should be a promising material in heavy metal contaminated water remediation area.（2）The adsorption rate of Nb-TNs series materials on Cd（Ⅱ）was extremely fast,and the adsorption equilibrium was achieved within 60 min.The dominant mechanism for Cd（Ⅱ）adsorption was ion-exchange between Cd²⁺and Na⁺in the interlayers of Nb-TNs.Nb-TNs-12h,Nb-TNs-24h,Nb-TNs-48h and Nb-TNs-72h had the maximum adsorption capacity of 244.142 mg·g^-1,251.654mg·g^-1,316.685 mg·g^-1 and 287.900 mg·g^-1,with the highest adsorption capacity of Nb-TNs-48h on Cd（Ⅱ）.（3）The new nanocomposites（FeS@TNTs）were nanotubes.Cr（Ⅵ）was removed more than 90%by FeS@TNTs in the first 60 min and then the reaction reached equilibrium within 240 min.The effects of reaction time,pH value,coexisting anions and humic acid on the removal of Cr（Ⅵ）by FeS@TNTs were investigated.The removal of Cr（Ⅵ）by FeS@TNTs was greatly affected by pH value.In acidic environment,the removal rate of Cr（Ⅵ）gradually increased with the increase of pH value.When the pH value was 4⁶,the adsorption amount reached the maximum value(24.647 mg·g^-1).In alkaline environment,the removal rate of Cr（Ⅵ）gradually decreased with the increase of pH value.The coexisting anions(NO₃^-,SO₄^2-and Cl^-)almost had no effect on the removal of Cr（Ⅵ）,but PO₄^3-inhibited the removel of Cr（Ⅵ）by FeS@TNTs.There was a obvious suppression effect in the presence of humic acid（HA）.The dominant removal mechanism of Cr（Ⅵ）by FeS@TNTs was that Cr（Ⅵ）was reduced to Cr（III）by Fe²⁺,and Cr（III）migrated to the surface of FeS@TNTs by electrostatic interaction,and then ion-exchange between Cr（III）and Na⁺in the interlayers of FeS@TNTs.