Microalgae-derived carbon quantum dots mediated formation of metal sulfide nano-adsorbents with exceptional cadmium removal performance

Abstract

Metal sulfides are regarded as efficient scavengers for heavy metals. However, the heavy metal adsorption capacity of metal sulfides is far from its theoretical values due to the insufficient exposure of adsorption sites. Surface modification of metal sulfides is considered one of the most effective strategies for improving heavy metal removal performance. Here, microalgae-derived carbon quantum dots (CQDs) were used as a green modifier for mediating nano-MnS/FeS formation to enhance Cd²⁺ removal. With the addition of 1 wt% CQDs, the Cd²⁺ adsorption capacity of 1 %CQDs-MnS reached 481 mg/g at 25 °C and 648.6 mg/g at 45 °C, which surpassed most of the previously reported metal sulfides. Furthermore, the CQDs-modified MnS displayed a better Cd²⁺ removal capacity than the commercial modifier sodium alginate. The mechanism analysis suggested that decreasing the particle size to expose more adsorption sites and providing additional chelating sites derived from the CQDs are two main reasons why CQDs enhance the Cd²⁺ adsorption capacity of metal sulfides. This study presents an exceptional cadmium nano-adsorbent of 1 %CQDs-MnS and provides a new perspective on the enhancement of heavy metal removal by using CQDs as a promising and universal green modifier that mediates the formation of metal sulfides.

Keywords: Adsorption of heavy metals; Carbon quantum dots; FeS; MnS; Surface modification.