Modulating chelation with pH sensitivity for controlled structural defects and enhanced electrochemical and photocatalytic activities of LDH films

Abstract

The convergence of organic compounds and their incorporation into inorganic layers paves the way for pioneering organic–inorganic hybrid materials with finely tuned, precise functional properties, promising a new era of advanced applications that push the boundaries of current technology. This study employs a pH-responsive chelation approach to control defects in MgAl-LDH, aiming to enhance its electrochemical and photocatalytic properties. This involves the synthesis of MgAl-LDH on plasma-assisted oxidized substrates, followed by the sequential introduction of [EDTA]⁴⁻ and [Zn(EDTA)]²⁻ anions into the LDH galleries via an anion exchange route. The chelation of EDTA with the metallic ions is pH-dependent, where a higher pH value encourages the inclusion of [EDTA]⁴⁻ anions, supported by the stability of LDH flakes, while a lower pH value facilitates the introduction of [Zn(EDTA)]²⁻ anions. The results show that the integration of [Zn(EDTA)]²⁻ anions leads to a more compact structure and a reduction in the size of LDH flakes, effectively sealing existing defects within the hybrid material. When exposed to a 3.5% NaCl solution, the LDH–EDTA–Zn sample exhibited superior electrochemical stability, characterized by a lower corrosion current density (2.12 × 10⁻⁹ A cm⁻²) and higher total polarization resistance (2.73 × 10⁷ Ω cm²). Moreover, the LDH–EDTA–Zn sample demonstrated exceptional photocatalytic efficiency, effectively decomposing rhodamine dye in an aqueous solution, attaining an impressive photocatalytic efficiency of 99.7% within just 25 minutes, while maintaining stability throughout five consecutive cycles, surpassing the performance of previously reported LDH-based catalysts. The interaction mechanism between the chelated anions and the LDH surface was elucidated by applying density functional theory. This research presents a promising approach for developing advanced organic–inorganic hybrid materials with exceptional electrochemical and photocatalytic performance.