Behavior and Mechanisms of Cd(Ⅱ) Adsorption from Water by Niobate-Modified Titanate Nanosheets

Abstract

Niobate-modified titanate nanosheets (Nb-TNS) were synthesized through a hydrothermal method and used to remove Cd(Ⅱ) from water. TEM and SEM characterizations indicated that the new nanocomposites were non-curled nanosheets. XRD showed that the material was composed of sodium tri-titanate and niobate, and titanate was the primary component. Ion exchange between Cd2+ and Na+ in the interlayers of the Nb-TNSs was the dominant mechanism for Cd(Ⅱ) adsorption, leading to good adsorption performance. The material exhibited rapid adsorption kinetics for Cd(Ⅱ), reaching 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 the Langmuir isotherm model, which was larger than that of 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 the adsorption of Cd(Ⅱ) by Nb-TNS owing to the competition for adsorption sites. In addition, a slight inhibition effect on the adsorption in the presence of humic acid (HA) was found. Cd(Ⅱ) was efficiently desorbed from Nb-TNS after HNO3 treatment, and -ONa sites were restored with NaOH treatment. Considering its simple synthesis method, high removal efficiency for heavy metals, and good reusability, Nb-TNS is a promising material for remediation of areas contaminated by heavy metals.