Drinking water pollution with heavy metals is a global problem with dire public health consequences. Existing water purification methods are unable to the rapid and concurrent removal of toxic metals to trace levels. Here, we introduce the new 2D hybrid LDH–[Sn2S6] as an unprecedented sorbent that shows highly efficient and concurrent removal of Cu2+, Ag+, Cd2+, Pb2+, and Hg2+ from ppm (mg/L) to ppb (µg/L) level. In mixed-ion states of Zn2+, Co2+, Ni2+, Ag+, Cu2+, Hg 2+, Pb2+, and Cd2+ (10 ppm each, 80 ppm in total), LDH–[Sn2S6] shows simultaneous removal of &gt; 99.9 % of Cu2+, Ag+, Cd2+, Pb2+ , and Hg2+ enabling the final concentrations below 5 ppb. At this mixed-ion states, the selectivity order was obtained as Zn2+, Co2+, Ni2+ &lt;&lt; Ag+, Cu2+ &lt; Hg 2+ &lt; Pb2+, Cd2+. Remarkably, LDH–[Sn2S6] removes over 99.0 % of Cu2+, Ag+, Cd2+, Pb2+, and Hg2+ at pH ~ 2 to 9 preserving high distribution constant (Kd) ~ 105 to 107 mL/g in the entire pH range. LDH–[Sn2S6] shows enormous sorption capacities (qm) of 378, 978, 332, 579 and 666 mg/g for Cu2+, Ag+, Cd2+, Pb2+, and Hg 2+, respectively. Strikingly, in the mixed-ion sate of Zn2+, Co2+, Ni2+, Ag+, Cu2+, Hg 2+, Pb2+, and Cd2+ in potable water (1 ppm each; ~8 ppm in total), the adsorption of Ag+, Cu2+, Hg 2+, Pb2+, and Cd2+ is extremely rapid. LDH–[Sn2S6] can simultaneously remove noxious Ag+, Hg 2+, Pb2+, and Cd2+ down to 5 ppb just in seconds, yielding the World Health Organization (WHO) defined drinkable levels. LDH–[Sn2S6] shows the sorption kinetics that follows a pseudo-second-order model, suggesting that chemisorption adsorption mechanisms involve through M-S bonding. Altogether, the LDH–[Sn2S6] becomes an exceptional material that shows ultrahigh removal, unprecedented selectivity, extremely rapid adsorption kinetics, a wide range of pH stability, and a massive adsorption capacity. The integration of such exceptional features places LDH–[Sn2S6] at the top of all adsorbents known to date. Thus, this cost-effective material could be used for wastewater purifications.

Highly efficient, rapid, and concurrent removal of a wide range of heavy metals by the novel 2D hybrid LDH–[Sn2S6]

ACS Fall 2021

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