Adsorption of a non-steroidal anti-inflammatory drug onto MgAl/LDH-activated carbon composite – Experimental investigation and statistical physics modeling

Abstract

A Layered Double Hydroxides (LDH) with Mg and Al composite (MgAl/LDH-biochar) was synthesised by the co-precipitation method, using bovine bone activated carbon as support structure for the LDH particles. The adsorbent was applied for diclofenac sodium (DS) removal from synthetic water. Batch experiments provided a DS removal of almost 80 % under optimized conditions. The performances of the MgAl/LDH-biochar composite (i.e. adsorption capacity as much as 5.96 mg/g) result significantly better when compared to the raw biochar (2.35 mg/g) at first 15 min. Despites the equilibrium data provided good adjustments for all tested models, Redlich-Peterson model showed the highest values of R2 and lower values of average relative error (ARE) and Akaike’s information criterion (AIC). The kinetic data of DS adsorption was best represented by the pseudo-second order model. The regenerability of MgAl/LDH-biochar was also evaluated through six adsorption/desorption cycles using either methanol or sodium chloride (0.5 mol/L) as desorbing agents, showing that the material can be reused until the third cycle maintaining a good adsorption capacity. The thermodynamic studies suggested that the adsorption process was spontaneous and exothermic, since the adsorption capacity decreased when the temperature increased. Finally, for a deeper insight in the DS adsorption mechanism, monolayer model formulated via statistical physics was adopted to describe the adsorption geometry of this relvant water pollutant and also to further characterize the interactions between DS and the tested adsorbent.