Adsorption characteristics of arsenate on colloidal nanosheets of layered double hydroxide: Fid-Bau Portal

Adsorption characteristics of arsenate on colloidal nanosheets of layered double hydroxide

Koilraj, Paulmanickam / Takaki, Yu / Sasaki, Keiko

Abstract Nanomaterials have gained much interest in water remediation and pollution control in recent years. However, the toxicity associated with nanoparticles remaining in solution after remediation has high impact on the environment. The present study examined the synthesis and characterization of colloidal Mg2Al-NO3 layered double hydroxide (Mg2Al-UD-LDH) nanosheets and their application as adsorbent toward arsenate immobilization. Colloidal LDH nanosheets featured the absence of nanoparticles release in the environment differently from other nanomaterials. The adsorption studies conducted in batch method, revealed that colloidal Mg2Al-UD-LDH nanosheets (obtained by ultrasonic treatment of Mg2Al-NO3-LDH suspension) achieved a higher arsenate adsorption density of 1.21mmol/g than parent Mg2Al-NO3-LDH (1.16mmol/g) at a solid-to-solution dosage of 0.78g LDH/L. The adsorption mechanism of arsenate onto colloidal Mg2Al-UD-LDH nanosheets proceeded through restacking of the nanosheets, besides ion-exchange onto Mg2Al-NO3-LDH and surface adsorption onto Mg2Al-CO3-LDH. Kinetics of arsenate adsorption onto colloidal Mg2Al-UD-LDH nanosheets was rapid, reaching equilibrium within 5min, whereas equilibrium was reached within 120min in the presence of Mg2Al-NO3-LDH. The colloidal LDH nanosheets stacking effect was restricted at higher LDH/As ratios owing to electrostatic repulsion among the nanosheets, as determined by zeta potential measurements. Semi-pilot scale static model systems for arsenate adsorption were examined to further investigate the adsorption performance of colloidal Mg2Al-UD-LDH nanosheets in natural water systems such as river, pond, or lake. Arsenate adsorption was rapid onto colloidal Mg2Al-UD-LDH nanosheets owing to their high dispersibility; specifically, 100% adsorption efficiency was achieved within 5min. Thus, the high adsorption capacity, dispersibility, and fast kinetics of arsenate removal onto colloidal Mg2Al-UD-LDH nanosheets promising for use as an efficient adsorbent for water remediation.

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Highlights • Colloidal MgAl LDH nanosheets were prepared by ultrasonication. • Adsorbed arsenate onto colloidal nanosheets was greater than powdery one. • Colloidal nanosheets showed the faster sorption rate of arsenate than powdery one. • Arsenate adsorption onto colloidal nanosheets proceeds through restacking. • Higher dispersibility of nanosheets promising their use as an efficient adsorbent.