Effect of pore size distribution on tetracycline adsorption using magnetic hypercrosslinked resins

• Larger average pore sizes lead to faster adsorption dynamics.
• The surface area and pore volume of the resins have positive effects on adsorption.
• The fouling caused by humic acid to the resins is weak.
• Tannic acid could seriously foul resins by site competition and pore blockage.
• Q100-3 was proved to be anti-fouling by its unobstructed internal pore structure.

Pore structures are very important factors that influence the adsorption and fouling-resistance properties of adsorbents. This study prepared three magnetic porous resins using different amounts of porogen. The pore volume, average pore size, and specific surface area of the resin improved with increased usage of the solvating porogen toluene. Q100-3, which was obtained at a porogen ratio of 3:1, showed the largest surface area (1322 m2/g) and pore volume (2.8 cm3/g). The increase in average pore diameter improved the adsorption equilibrium of the resins, and the increase in total pore volume and specific surface area enhanced the number of adsorption sites of the adsorbents. Q100-3 showed a larger adsorption capacity for tetracycline (TC) than Q100-1 and Q100-2. Two model compounds of natural organic matter, humic acid (HA) and tannic acid (TA), were chosen to evaluate the fouling-resistance of the resins during TC removal. The resins adsorbed very low amounts of HA (3–13 mg/g); thus, competition between HA and TC was weak. HA molecules, because of their large size, were prevented from transportation into the pores by size exclusion effects, leading to negligible pore blocking. By contrast, because of its small molecular size, TA could be well adsorbed by all three resins. The competitive adsorption experiment demonstrated that the presence of TA had a very important effect on both Q100-1 and Q100-2 in terms of TC adsorption. In particular, the amount of TC adsorbed onto Q100-1 with 200 mg/L TA dropped to only 7.88% of the adsorbed amount of TC on Q100-1 without TA because of serious pore blockage. Adsorbed TA could not cause pore blockage in the magnetic resin Q100-3, which featured an unobstructed internal pore structure. Thus, the decrease in adsorbed amount of TC was controlled to within 3% in this resin.

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