Anti-inflammatory drug diclofenac removal by a synthesized MgAl layered double hydroxide

Abstract

Layered double hydroxides (LDHs) containing Mg:Al (molar ratio 3:1) were synthesized by coprecipitation from nitrate salts under alkaline conditions. Their further characterisation by different techniques allowed the determination of their structural, nanotextural and chemical properties. XRD measurements confirmed the high crystallisation with the presence of two metal cations (Mg2+ and Al3+). The use of these materials as eco-friendly adsorbents was analysed to remove diclofenac from wastewater. Under optimal conditions (0.4 g L 1, 30 ppm initial pollutant concentration, pH 8.5), around 65% diclofenac removal was achieved after 60 min of treatment. The pseudo-second kinetic order model and Freundlich isotherm accurately described the experimental data, suggesting chemisorption process on the heterogeneous LDH surface. After diclofenac adsorption, XRD analysis revealed an increase in interlayer spacing followed by contraction of adjacent layers, so that anion exchange between layer was considered to be the main mechanism for diclofenac adsorption. Thermodynamic studies indicate diclofenac adsorption occurs spontaneously, endothermically, and also, with increasing randomness at the solid/solution surface. Batch test revealed limitations in terms of long-term stability of the material. Therefore, a post-synthesis strategy, calcination, was required to increase the degree of resistance. For this purpose, the effect of calcination temperature was examined in the range 200–300 C. Although, the kinetic rate constant decreased slightly after calcination, the improvement of its structural properties allowed to operate under continuous system.