Tannin as a natural biomass has been extracted from oak gall and was immobilized on hexagonal mesoporous silicate (HMS) in order to remove direct yellow 86 (DY86) from aque- ous solution. The characteristics of the oak gall tannin-HMS adsorbent were substantiated by different techniques such as FTIR, TEM, TGA, BET, and XRD. From the BET analysis, a decline of 75.61% for the surface area of HMS nanoparticles was observed and indicates the proper coating through tannin. In order to analyze the adsorption data, five different isotherms were utilized and nonlinear regression scheme was employed using MATLAB soft- ware. It was concluded from the Langmuir isotherm that the maximum monolayer adsorption capacity was 435.5 mg g−1 . The thermodynamic analysis of this study also revealed that the adsorption was feasible, since the process was spontaneous and endothermic. The findings also indicate that the adsorption of DY86 follows the pseudo-second-order kinetic model.

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