Photocatalytic properties of iodometallates with in situ-generated organic bases as countercations

Abstract

Herein, the in situ N-alkylation between tripyridine molecules and C₂H₅OH was employed to obtain four iodometallates (Mⁿ⁺ = Pb²⁺, Cu⁺ and Ag⁺). Among them, the alkylation degree of the tripyridine molecules is different, and the in situ-generated tripyridine derivatives showed different configurations. This is not only related to the structure of the inorganic anions but also related to the tripyridine molecule itself. The two moieties were actually templates for each other. The Pb²⁺ compound 1 was found to effectively catalyze the degradation of Rhodamine B (RhB), with its degradation efficiency reaching 94% in 70 min. In contrast, the degradation efficiency for the Cu⁺ and Ag⁺ compounds 2–4 did not exceed 50%. The free radical trapping test indicated that with the Pb²⁺ compound as the photocatalyst, both superoxide ion radicals (˙O₂⁻) and holes (h⁺) played a key role. Alternatively, with compound 3 or 4 as the photocatalyst, only ˙O₂⁻ played a role. The differences should be related to the band gap of the materials, where the Pb²⁺ compound has a slightly wider band gap, leading to a higher exciton separation efficiency. Due to the involvement of more free radicals, the usual intermediates did not appear in the catalytic process of 1, while the colored species appeared in the catalytic process of 3 and 4. The cyclic test verified that compound 1 still had high catalytic activity after recycling five times. Also, we investigated the catalytic capacity of 1 for the degradation of 5-times the quantity of RhB. The degradation rate reached 99% in 5.5 hours, indicating that 1 has a good photocatalytic performance for degrading a high concentration of RhB. However, given that the amount of catalyst and dye used in each study was different, it was difficult to compare the results. Thus, herein, we introduced for the first time the method of calculating the TOF value to better evaluate the photodegradation performance of each hybrid material.