Preferential Adsorption of Anionic Dyes onto a Starch-Modified Layered Double Hydroxide: Kinetic, Isotherm, and Thermodynamic Studies

Abstract

In this study, nickel aluminum layered double hydroxide (Ni/Al LDH) is synthesized and then modified with starch to form S-Ni/Al LDH based on a simple co-precipitation method. The adsorption potential of S-Ni/Al LDH is evaluated for the adsorption of anionic azo and cationic dyes, with key variables controlled (e.g., temperature, adsorbent quantity, pH, and contact duration). The adsorption process is determined to be exothermic and spontaneous while being governed dominantly by monolayer chemisorption processes in line with a Langmuir isotherm and pseudo-second-order kinetic model. The maximum adsorption capacity values for S-Ni/Al LDH composite, when assessed in terms of Langmuir isotherm, are 329, 160, and 68.4 mg/g against Congo Red, Sunset Yellow, and Orange G, respectively (with the corresponding partition coefficients of 378, 146, and 7.42 mg g−1 μM−1). Further, S-Ni/Al LDH is readily regenerated up to four cycles with slight reduction in adsorption capacity using an aqueous Na<inf>2</inf>CO<inf>3</inf> solution. As such, the practical utility of the starch-modified LDH for wastewater treatment applications is demonstrated for applications toward wastewater treatment.