Synthesis of Poly (-isopropylacrylamide)--(acrylic Acid) Microgel-entrapped CdS Quantum Dots and Their Photocatalytic Degradation of an Organic Dye

CdS quantum dots (CdSQDs) were generated inside the network structure of poly (-isopropylacrylamide)--(acrylic acid) (pNIPAm--AAc) microgels and their ability to photocatalytically degrade organic dyes was evaluated using rhodamine B (RhB). The microgel-stabilized CdSQDs were generated by first enriching the microgels with Cd followed by their reaction with NaS. The resultant microgels were characterized, and the CdSQDs were found to be distributed throughout the microgels. We went on to show that the hybrid microgels exhibited photocatalytic properties by exposing them to a solution of RhB followed by exposure to UV irradiation. We found that the hybrid microgels were able to degrade the RhB, while native microgels without CdSQDs present were not capable of the same behavior. Due to the thermo- and pH-responsivity of pNIPAm--AAc-based microgels their ability to degrade RhB was also evaluated as a function of environmental temperature and solution pH. We showed that the removal efficiency was highest when the microgels were in their swollen state, which we attribute to more effective mass transfer of the RhB inside the microgels when their porous structure is expanded. Finally, we show that the hybrid microgels can be reused multiple times, although their photocatalytic degradation ability decreases the more they are used, which may be a result of the aggregation and decomposition of the CdSQDs. We conclude that this approach is an effective means of removing RhB from water, which may be modified to photodegrade a variety of other organic compounds.