Delamination of CuMgAl layered double hydroxides by non-thermal plasma treatment for photocatalytic degradation of Congo Red dye

Effectively removing pollutants from wastewater remains a significant challenge to achieving a sustainable future. Dyes are a class of pollutants that exhibit chemical stability, are not biodegradable, and have the potential to convert into dangerous substances. Layered double hydroxides (LDHs) have emerged as a promising adsorbent for addressing this problem due to their ion-exchange properties and high surface area. Recent studies indicate that the effectiveness of the LDHs can be further improved by delamination into nano sheets.

In this manuscript we explore the use of argon dielectric barrier discharge (DBD) plasma, a type of non-thermal plasma, as an innovative, greener and milder method to delaminate CuMgAl-LDH turning it into nanosheets. Congo Red (CR) dye was selected as the model pollutant in this study. The resulting plasma treated CuMgAl-LDH (P-CuMgAl-LDH) exhibits a better CR dye adsorption rate. The photodegradation of CR at a concentration of 500 mg L⁻¹ was achieved using 1.0 mg mL⁻¹ of P-CuMgAl-LDH and irradiating with a 370 nm LED. It was found that P-CuMgAl-LDH has significantly higher performance, showing a full discoloration of CR within 1 h and up to 80 % of mineralisation within 1.5 h of irradiation compared to only 16.1 % for CuMgAl-LDH. The photodegradation mechanism studies reveals highly efficient formation of superoxide radical anions (O₂^-•) that further confirm the presence of oxygen vacancies on the P-CuMgAl-LDH. Thus, we conclude that Argon DBD plasma is a valuable tool to efficiently delaminate CuMgAl-LDH under mild conditions and improve its adsorption and photocatalytic properties without the addition of other chemicals.