Effective removal azo dyes from wastewater solution via hollow structure MgCo-LDH adsorbent

Abstract

Azo dyes wastewater caused serious environmental pollution problems due to their extremely stable molecular structure. Hollow structure MgCo-LDH was prepared to purify Congo red (CR) and Acid red 66 (AR66) wastewater. The ZIF-67 was employed as sacrificial template to fabricate the hollow structure MgCo-LDH nanomaterial via Mg²⁺ simultaneous etching and subsequent coprecipitation reactions in magnesium nitrate solution. The MgCo-LDH nanomaterial provided abundant sites to adsorb the azo dyes owing to the nanosheets and hollow structures. The experimental analysis indicated that the optimal adsorption process conditions were MgCo-LDH amount of 50 mg for CR and 70 mg for AR66, adsorption time of 70 min, rotational speed of 340 r·min⁻¹, adsorption temperature of 25 °C, and pH range of 3–9 for 15 mL of 250 mg L⁻¹ azo dyes solution. The hollow structure MgCo-LDH had high saturation adsorption capacities of 1050.28 ± 37.34 mg g⁻¹ for CR and 285.40 ± 5.80 mg g⁻¹ for AR66 at the optimal condition parameters. The removal efficiencies of CR and AR66 were higher than 94.32 ± 2.09 % and 94.95 ± 1.61 %, respectively. The density functional theory calculations revealed that the azo dye molecules were adsorbed onto MgCo-LDH surface through the formation of hydrogen bonds between the hydroxyl groups and sulfonic acid groups. This work provided a potential strategy for harmless treatment of azo dyes wastewater.