CuSiF₆(4,4′-bipyridine)₂, a Crystalline Complex with Excellent Adsorptivity for Thiophenic Sulfur Compounds in Model Oil

CuSiF₆(4,4′-bipyridine)₂ (SIFSIX-1-Cu) is a crystalline complex of CuSiF₆ and 4,4′-bipyridine with rich microporosity, high specific area (∼1100 m²·g^–1), and negligible hydroscopicity. Furthermore, this complex can be synthesized and dried under much milder conditions compared with conventional MOFs. In this paper, three complexes, SIFSIX-1-Cu(1), SIFSIX-1-Cu(2), and SIFSIX-1-Cu(3), were prepared using Cu­(BF₄)₂, Cu­(NO₃)₂, and CuSO₄, respectively, as the copper sources, and their structure was characterized by SEM, XPS, XRD, and N₂-adsorption desorption measurements. The adsorptivity of these compounds for dibenzothiophene (DBT) in model oil follows the order of SIFSIX-1-Cu(1) > SIFSIX-1-Cu(2) > SIFSIX-1-Cu(3), which is consistent with the order of their crystallinity and specific areas. The adsorption amount of SIFSIX-1-Cu(1) is 49.5 mg-S·g^–1 for DBT model oil at an equilibrium sulfur concentration of 700 ppm and 303.15 K, and follows the order of DBT > benzothiophene (BT) > 3-methylthiophene (3-MT) for other sulfur compounds. The adsorptive desulfurization performance of SIFSIX-1-Cu is one of competitive sorbents among MOFs. The used sorbent can be regenerated easily by methanol washing and can be reused with an approximately 11% loss of adsorption capacity after five cycles. This study reveals the potential application of microporous crystal complexes for fuel desulfurization.