(Figs. 7 and 8)
To investigate the photocatalytic activity of nano-sized CP 1 under UV light irradiation, we selected methylene blue (MB) as the model dye contaminant due to the chemical stability and poor biodegradation. The detailed photocatalytic experiment procedures are depicted in ESI. The degradation of MB was monitored by the characteristic UMI-77 cost at approximately 664nm. As shown in Fig. 9, the absorption peak of MB significantly reduced along with the reaction time. In addition, the control experiment was studied under the uniform conditions without any photocatalyst. Fig. S6 illustrates that no noteworthy decrease of the characteristic absorption was found in the control experiment. The changes in the C/C0 plot of the MB solution against irradiation time are depicted in Fig. 10 (wherein C0 is the initial concentration of the MB solution and C is the concentration of the MB at any given time t). It can be seen that the photocatalytic efficiency reached approximately 90.2% in the presence of nano-sized CP 1 after 120min under UV light irradiation. However, only 11.9% of MB were decomposed without any catalyst. The increased photocatalytic degradation efficiency indicates that nano-sized CP 1 is an excellent candidate as photocatalysts in decomposing MB under UV light irradiation. Furthermore, when nano-sized CP 1 was placed into an aqueous solution of the MB in a dark environment for half an hour, there is no obvious decrease in the absorbance value, which may avoid the possibility of adsorbing such a dye molecule into the frameworks.
In order to study the reproducible ability of nano-sized CP 1, the repeated photocatalytic experiment was also performed. The photocatalytic efficiency of nano-sized CP 1 in the repeated experiment did not significantly change after three cycles, indicating that the crystal materials were stable and reproducible for the degradation of MB (Fig. 11). The XRD patterns of nano-sized CP 1 were almost identical to those of the original CPs after the reactions (Fig. S2).
To detect the possible photocatalytic reaction mechanism of nano-sized CP 1, isopropanol, benzoquinone and ammonium oxalate were added into the photocatalytic experiment as the scavenger for OH, O2− and (h+) radicals, respectively [53,54]. Fig. 12 illustrates that no obvious decrease of the photocatalytic efficiency was observed in the presence of benzoquinone or ammonium oxalate, proving that O2− and (h+) radicals are not the main reactive species. However, isopropanol can greatly suppress the photodegradation of MB solution, which suggests that the photodegradation process of MB is mainly caused by OH radicals. The possible photocatalytic reaction mechanism for the above degradation reactions is proposed as follows (Scheme S1). Under the high-pressure mercury lamp irradiation, the electrons (e−) of nano-sized CP 1 could be excited from the valence band (VB) to the conduction band (CB), resulting in the equal amount of positive vacancies left in the VB (holes, h+). Then the electrons combined with O2 absorbed on the surface of photocatalysts to produce oxygen radicals (O2), which will transform into hydroxyl redicals (OH). At the same time, the hydroxyl (OH−) absorbed on the surface of photocatalysts reacts with the holes (h+) to yield hydroxyl radicals (OH). Finally, hydroxyl radicals (OH) can effectively degradate the MB.
A new nano-sized Co(II) coordination polymer, [Co(Hbibp)(nbta)] (1), was synthesized by sonochemical irradiation. The crystal structure of CP 1 consists of a 1D chain with the SP 1-periodic net (4,4)(0,2) topology, then the chain can further expand into a 2D supramolecular sheet with the SP 2-periodic net (6,3)Ia structure by the N−H⋯O hydrogen bond interactions. Effects of the sonication time and ultrasonic power on the morphology and size of nanoparticles were also studied. The results demonstrate that the size of nanoparticles increased with the increasing sonication time and the higher ultrasonic power led to the decrease in nanoparticles size. Moreover, nano-sized CP 1 can be considered as heterogeneous photocatalysts for the degradation of methylene blue (MB) under UV light irradiation.
(Figs. 7 and 8)