A critical study of interactive fluoride adsorption by raw marine organisms and a synthetic organic 2-amino-3-cyano-4(4-nitrophenyl)-6-phenylpyridine as adsorbent tools.

Defluoridation process using raw marine organisms and synthetic organic adsorbents was accurately studied. The marine adsorbents (algae, bivalves, sea star, brittle star, and coral reef) were collected from the Egyptian Mediterranean Sea and Red Sea. The organic adsorbent of 2-amino-3-cyano-4(4-nitrophenyl)-6-phenylpyridine was synthesized. The influence of pH, shaking time, effect of temperature and adsorbent's weight was studied. A complete fluoride removal by marine adsorbents was gained within 15-20 min. Fluoride removal procedure was evaluated by some adsorption isotherm models of linear two-parameter ((Freundlich, Tempkin, Langmuir, Flory-Huggins, Dubinin-Radushkevich, Non-ideal competitive adsorption (NICA), Brunauer-Emmett-Teller (BET), and Generalized)), nonlinear two-parameter (Langmuir and Freundlich), and nonlinear three-parameter (Redlich-Peterson, Khan, Generalized, and Toth). The most appropriate models were evaluated by error functions and statistical tests like coefficient (R2) and chi-square (χ2). Additionally, the kinetic and thermodynamic variables were calculated at variable temperatures. The results indicated that the pseudo-second-order model fitted better than the pseudo-first-order one. The negative ΔG° values confirmed that the adsorption process was favorable and spontaneous. Interestingly, this study indicated the great removal capacity of the raw organisms.