Mesoporous Silica-Confined MOF-525 for Stable Adsorption of Tetracycline over a Wide pH Application Range

SBA-15@MOF-525 composites were constructed by in situ self-assembly of a metal–organic framework (MOF-525) with mesoporous SBA-15 silica. MOF-525 crystals were confined inside the mesopores as well as grown on the outside surface of SBA-15, under the impact of the structure-directing role of SBA-15, and the composites exhibited both microporous and mesoporous characteristics. In general, the adsorption of tetracycline (TC) on MOF-525 was affected by pH. The adsorption capacity of MOF-525 decreased rapidly, especially in an alkaline environment, due to the collapse of the MOF-525 skeleton. By contrast, incorporating MOF-525 into SBA-15 improved the stability of MOF-525. The adsorption of TC on SBA-15@MOF-525 was almost unaffected by pH. High and stable adsorption capacity over a wide pH range was maintained under acidic, neutral, and alkaline environments. The composites were used effectively for TC adsorption. The maximum adsorption capacity of TC on SBA-15@MOF-525 was 690 mg/g, which is higher than that of most of the reported adsorbents. The great potential of SBA-15@MOF-525 in practical applications was demonstrated by investigating the adsorption of TC in lake water samples.