Waste Adsorbent Valorization of Biopolymer‐Modified Zn–Fe Layered Double Hydroxides for Crystal Violet Removal and Enhanced Nonenzymatic Urea Detection

Finding suitable and inexpensive bifunctional materials that can act as adsorbents for crystal violet (CV) removal and as electrocatalysts for the electrochemical detection of urea remains one of the contemporary challenges. Waste valorization of spent wastewater nanoadsorbents is a promising route toward achieving circular economy guidelines. In this study, Zn–Fe layered double hydroxides (Zn–Fe LDHs) were synthesized and modified with three natural carbohydrate polymers chitosan, carrageenan, and cellulose using the coprecipitation method. The modified Zn–Fe LDHs were utilized as adsorbents for CV removal. Moreover, the biopolymer‐modified Zn–Fe LDHs both before and after CV adsorption were employed as electrocatalysts for the electrochemical detection of urea in an alkaline medium. The results showed that Zn–Fe LDH/chitosan exhibited the highest current density of 118.3 mA·cm ⁻² for urea detection. Furthermore, after CV adsorption, the catalytic current density of the urea adsorption enhanced to 137.2 mA·cm ⁻² with a stability of 96%. Additionally, the density functional theory (DFT) calculations revealed that the Zn–Fe LDH/chitosan/CV showed the lowest binding energy (Δ E _bind ) values in both gas phase (−18.12 kcal·mol ⁻¹ ) and water phase (−15.67 kcal·mol ⁻¹ ), indicating stronger interactions and suggesting that chitosan functionalization significantly enhances the adsorption capacity of LDH.