The increasing coexistence of toxic metals and organic pollutants in water demands multifunctional adsorbents capable of high-capacity, and thermodynamically stable removal. This study advances multifunctional adsorption science by resolving the interplay between composite structure and contaminant-dependent interaction mechanisms, quantitatively integrating kinetic, equilibrium, and thermodynamic descriptors into a unified framework for broad-spectrum water purification. In this study, an Alginate–GO/LDH Functional Composite was developed and evaluated for the adsorption of Pb, As, methylene blue (MB), ibuprofen (Ibu), and naphthalene (Nap), with the objective of elucidating quantitative performance and underlying adsorption mechanisms. Equilibrium isotherm analysis demonstrated an exceptional affinity of the adsorbent toward heavy metals, with Langmuir maximum adsorption capacities of 370.4 mg g−1 for Pb and 384.6 mg g−1 for As. The excellent model fitting (R2 = 0.99 and 0.95) and favorable separation factors (RL = 0.14–0.33) indicate strong monolayer chemisorption. In contrast, the adsorption of methylene blue (MB, R² = 0.98), ibuprofen (Ibu, R2 = 0.97), and naproxen (Nap, R2 = 0.95) was better described by the Freundlich isotherm, suggesting multilayer adsorption on a heterogeneous surface. The corresponding favorable separation factors (RL = 0.43–0.94) further confirm the efficient adsorption behavior of these organic pollutants. Kinetic results demonstrated that adsorption of all contaminants obeyed the pseudo-second-order model (R2 ≥ 0.98), identifying chemisorption as the rate-limiting step. Temperature strongly influenced adsorption: Pb uptake increased from 76.34 to 322.58 mg g−1 (10–60 °C), MB reached an exceptional 1000 mg g−1 at 60 °C, Ibu increased from 30.03 to 50.25 mg g−1, and Nap from 13.62 to 25.71 mg g−1, whereas As adsorption decreased from 121.95 to 66.67 mg g−1, indicating a distinct exothermic mechanism. Thermodynamic analysis revealed that all adsorption processes were spontaneous (ΔG° < 0), while Pb, MB, Ibu, and Nap exhibited endothermic adsorption with positive enthalpy changes (ΔH° = +8.7 to +42.2 kJ mol−1), indicating enhanced adsorption at elevated temperatures, whereas As adsorption was exothermic (ΔH° = −7.01 kJ mol−1), favoring lower temperatures and demonstrating a fundamentally different interaction mechanism. These results establish Alginate–GO/LDH as a robust, high-capacity adsorbent for treating complex multi-contaminant water systems.