Open-layered MBenes: Comparisons of different wet etching techniques and electrochemical detection of heavy metal ions with high sensitivity & selectivity

Despite significant progress in MBenes preparation and application in electrochemistry, achieving perfect layered structures and high purity under different etching conditions remains challenging. Additionally, their potential for electrochemical detection of heavy metal ions is underexplored. This study compares non-fluoride etchants for synthesizing MBene MoB from MoAlB and explores new applications in heavy metal ions detection. Ammonium persulfate (APS) etchant achieves a high Al etching rate of ∼71 %, resulting in restacked accordion-like MBene, but high temperatures lead to stable, insoluble AlxO. CuCl₂ has a lower etching rate of ∼54 %, producing flake structures with copper impurities. Acid etching yields a perfect layered structure but a lower etching rate, while alkali etching provides similar rate to APS with the highest purity. Complete Al removal at higher temperatures causes loss of the layered structure. Our research demonstrates that some maintaining Al during hydrothermal etching maintains the layered structure, with subsequent room-temperature etching producing fluffy open-layered MoB (OL-MBene). Electrochemical studies showed OL-MBene-modified GCE performs excellently in detecting Cd²⁺, Pb²⁺, Cu²⁺, and Hg²⁺, with high sensitivity and selectivity, especially for Cu²⁺ and Pb²⁺. Pb²⁺ shows the highest sensitivity due to its lowest adsorption energy on the MBene surface. Competitive adsorption studies indicate Pb²⁺ competes with Hg²⁺ for adsorption sites but minimally impacts Cd²⁺ and Cu²⁺ adsorption. This research enhances understanding of MBene synthesis and introduces a new method for sensitive electrochemical sensors.