High efficiency selective and reversible capture of lactulose using new boronic acid-functionalized porous polymeric monoliths

Boronate affinity materials have been widely used for the enrichment and molecular recognition of cis-diol-compounds. Herein, new boronic acid-functionalized porous polymeric monoliths were rationally fabricated through a facile bulk polymerization method. The synthesized adsorbent (M2) with uniform elements distribution, highly porous structures, large specific surface area (308 m2/g), and abundant mesopores (9.24 nm) was found favorable for achieving high adsorption efficiency. Notably, through typical pH-responsive adsorption (pH = 10.0), M2 exhibits fast adsorption rate (<15 min), superior adsorption selectivity towards lactulose and a much higher adsorption capacity for lactulose (qe-Lu = 114.52 ± 4.56 mg/g) than lactose (qe-La < 2.5 mg/g). Meanwhile, pH-driven desorption (pH = 2.0) was almost instantaneous (<5 min) complete. Kinetic study shows the adsorption follows the pseudo-second-order model (R2 = 0.997) and the Langmuir model is more qualified (R2 = 0.983–0.987) to explicate the adsorption isotherms, indicating a monolayer chemical adsorption between lactulose and M2. Thermodynamic studies demonstrated the uptake of lactulose was spontaneous and feasible in nature. The purity of lactulose through selective adsorption and desorption can be effectively improved to PuLu-D > 95%, regardless of the ratio of lactulose to lactose within a practical range (≥1:5). A possible adsorption mechanism involving the hydrophobic/hydrophilic properties, sugar specificity, and pH-responsive effect was proposed to account for the highly efficient capture of lactulose. Remarkably, M2 can be simply regenerated by pH switch and efficiently reused multiple times without significant drop in recycle efficiency (Re > 95%), well proving its feasibility in sustainable industrial applications. The obtained quite encouraging results demonstrated that the newly developed adsorbents hold high potential in lactulose purification.