Gamma-FeOOH based hierarchically porous zeolite monoliths for As(V) removal: Characterisation, adsorption and response surface methodology

Abstract

γ-FeOOH based hierarchical zeolite LTA monoliths as sorbents for As(V) removal were synthesized by modifying hierarchical zeolite LTA monoliths with HCl and FeCl3 solutions. The obtained γ-FeOOH based monoliths (abbreviated as Fe-HZ) maintain the interconnected macropores network structure, which offers a practical solution to the diffusion limitations associated with traditional agglomerated zeolites. Moreover, the self-supported sorbents can be easily recycled after treatment. The derived γ-FeOOH based monolith exhibits higher BET surface area while slightly decreased thermal stability compared with those unmodified sample (labeled as HZ). The sorption performance of HZ and Fe-HZ are evaluated, taking the initial/equilibrium pH, adsorption time and initial concentration into account. Fe-HZ shows an optimal adsorption over the pH range 2–7, and the uptake capacity is 5.11 mg/g at pH of 6 with the equilibrium time of 240 min. Whereas only 0.67 mg/g can be attained for HZ. The dynamic data follows pseudo-second-order model, demonstrating As(V) species chemisorbed on Fe-HZ, and the chemisorption is ascribed to ligand exchange reactions between As(V) species and hydroxyl functional groups. Freundlich and Langmuir isotherms are both acceptable for the equilibrium data of arsenic adsorption on Fe-HZ. In addition, response surface methodology is applied for modeling and optimization monoliths preparation parameters. Results show that the importance of variable factors influencing arsenic adsorption follows the sequence: FeCl3 concentration > PMMA/MK mass ratio > FeCl3 modification time > HCl modification time.