A review of performance, mechanism, and challenges of layered double hydroxide-based biocomposites for the adsorptive removal of dye contaminants from water and wastewater

Layered double hydroxides (LDHs) are promising materials owing to their unique properties and environmental compatibility. Integrating biosorbents like biochar, starch, alginate , and chitosan with LDHs enhances physicochemical characteristics such as surface area (0.043 to 1273 m 2 /g), ion exchange capabilities, surface functionalities (−OH, −COOH, C−O−C, C O, C C, CO 3 2− , NO 3 − etc.), and stability, and biocompatibility. The review evaluates synthesis methods and indicates that coprecipitation and hydrothermal are widely adopted for various LDH-biocomposites. The dye removal performance at different adsorption conditions, kinetic and isotherm modelling and parametric optimization, including analysis of variance and response surface methodology of LDH-biocomposites, are discussed. The LDH-biocomposites demonstrated excellent adsorption performance for various dyes and the maximum adsorption capacities were reported as 653.59 mg/g for methylene blue, 1555 mg/g for methyl orange, 1112 mg/g for Congo red, 496.55 mg/g for crystal violet, 876.2 mg/g for Eriochrome black T, 666.4 mg/g for malachite green, 625 mg/g for indigo carmine, 483 mg/g for reactive blue 4, 4272 mg/g for reactive yellow 2, and 400 mg/g for sunset yellow. The interaction mechanism of various dyes with LDH-biocomposites is examined, showing that the presence of functional groups on the adsorbent's surface determined the existence of electrostatic interactions , hydrogen bonding , anion exchange and pi-pi interactions. The regeneration performance illustrated that the LDH biocomposites have retained approximately 80–95 % of dye removal performance after multiple cycles. Finally, the challenges and future perspectives are proposed for the application of LDH-biocomposites as green biosorbents for the efficient treatment of dye-contaminated wastewater.