Optimized Synthesis of Molecularly Imprinted Hybrid Polymer by Factorial Design for Selective Caffeine Extraction in Surface Water

A hybrid imprinted polymer (HMIP) was synthetized via sol-gel technique in aqueous solution for caffeine separation from environmental waters samples. The optimal conditions of synthesis were stablished by application of a 2³ full factorial experimental design with three factors: ratio of functional monomer and cross-linker reagent, and acid or basic catalyst (HCl or NH₄OH). The HMIP obtained with the factorial designs was 22.5 times more selective for caffeine than control polymer, with an adsorption mechanism of pseudo-second order with two sorption sites. The maximum equilibrium adsorption capacity was 1.91 mg g⁻¹ that was maintained until ten cycles of reuse, indicating their excellent stability. The material was 21 times more selective for caffeine than for its analogous molecules (theophylline and theobromine). HMIP was applied in solid phase extraction (SPE) procedure and caffeine extraction of surface water had good recoveries (93.0%). These results demonstrated that the factorial experimental design resulted in an efficient and selective sorbent for caffeine with a reduction of number of synthesis and problems of trial-and-error protocol as well as reagents consumption decrease.

Keywords:
molecularly imprinted polymer; factorial experimental design; hybrid synthesis; caffeine; water