Preparation and adsorption behavior of dodecyltrimethylammonium bromide modified carrageenan hydrogel beads with remarkable removal efficiency and thermostability in water

In this study, water‐soluble polymer carrageenan (CAR) was cross‐linked by dodecyltrimethylammonium bromide (DTAB) in an aqueous solution for the preparation of gel beads, which can be used for removal of methylene blue (MB). The combination of DTAB and CAR was validated by Fourier transform infrared (FTIR) spectroscopy, while the folded surface was characterized by scanning electron microscope. DTAB can be used as a modifier of CAR for promoting the hydrophobicity and stability of hydrogel beads, which even withstood 70°C in water for 24 h without dissociation. The best removal efficiency was achieved 99.6% in 100 mg L −1 MB aqueous solution by CAR‐0.5DTAB, and the maximum adsorption capacity of CAR‐1.5DTAB at 30°C reached 38.6 mg g −1 by wet weight (weight of gel beads in wet condition) in 2000 mg L −1 MB aqueous solution. The CAR‐DTAB adsorption behavior was best fitted with pseudo‐first‐order and Langmuir equations, respectively. The exothermic nature and spontaneity of adsorption process were proved by thermodynamic experiment. Reusability studies revealed that the adsorption performance displayed almost no change after 10 cycles of adsorption/desorption process. The properties of CAR‐DTAB in this research proposed a facile way to prepare stable CAR composite by cross‐linking with quaternary ammonium surfactant.