Adsorption, antibacterial and molecular dynamic studies of bentonite clay–gemini (Bt–16-4-16) hybrid material

Abstract

This work reports the preparation of a novel hybrid material, integrating a gemini surfactant, butane-1,4-bis(hexadecyldimethylammonium) dibromide, 16-4-16, into bentonite clay (raw Bt), which possessed the ability to remove tartrazine dye (TD) from aqueous solutions. The Bt-16-4-16 hybrid material was characterized through FT-IR, XRD, SEM, EDX, and BET. The results were further compared with previously reported Bt–16-3-16 hybrid material (prepared using propane-1,3-bis(hexadecyldimethylammonium) dibromide, 16-3-16, gemini surfactant). The Bt-16-4-16 and Bt–16-3-16 demonstrated around 97–98 % removal efficiency towards TD under specific experimental conditions examined ([TD] = 10 mg L⁻¹, [adsorbent] = 2 g L⁻¹, pH = 3, equilibrium time = 60 min, temperature = 298.15 K). With the rise in [TD] (from 1 to 100 mg L⁻¹), the hybrid materials showed a prominent rise in adsorption capacity from 0.51 to 44.36 mg g⁻¹ for Bt-16-4-16 and 0.50 to 42.61 mg g⁻¹ for Bt-16-3-16. The efficiency of Bt–16-4-16 and Bt-16-3-16 in the removal of TD was not influenced much by the presence of various cations (Mg²⁺, Ca²⁺, Ni²⁺, Cu²⁺) and anions (EDTA, sulphate, HCO₃¯and SO₄²⁻). The presence of 0.1 M NaCl caused a 0.05 % and 1.43 % decrease in the removal efficiency of Bt-16-4-16 and Bt-16-3-16, respectively. The results followed pseudo-second-order adsorption kinetics and agreed with the Freundlich isotherm. The Bt-16-4-16 and Bt-16-3-16 achieved maximum adsorption capacities of 128.7 and 117.8 mg g⁻¹ against TD. The adsorption thermodynamics revealed that the process at the adsorbent's solid-liquid interfaces is entropy-driven, spontaneous, and endothermic. Both Bt-16-4-16 and Bt-16-3-16 were found to be reusable even after the 5^th cycle. The Bt–16-4-16 showed a strong affinity towards TD and quickly reached maximum adsorption capacity at a relatively low fugacity of ≤15 kPa. Further, the antibacterial property of Bt-16-4-16 and Bt-16-3-16 was also tested.