Photocatalytic degradation of methyl orange via supramolecular self-assembly of cucurbit[6]uril and phosphotungstic acid

Heterogeneous photocatalysis caused by solar energy is a promising green strategy for the treatment of organic wastewater contaminants. However, many conventional photocatalysts have limited applications owing to defects such as inability to absorb visible light, fast charge recombination, and poor adsorption capacity. Herein, a new photocatalyst, Q[6]-PTA, was obtained via the supramolecular self-assembly of cucurbit[6]uril (Q[6]) and phosphotungstic acid (PTA) in solution. Structural characterization demonstrates that Q[6] and PTA have their original structures in Q[6]-PTA, and the driving force of their self-assembly is the electrostatic interaction between the positive outer surface of Q[6] and PTA anion. Compared with PTA, Q[6]-PTA has a larger specific surface area and porosity, increased number of active sites, enhanced adsorption properties, and considerably higher photoresponse range (from ultraviolet to visible light), moreover, it can effectively inhibit the charge recombination of PTA. In visible light, Q6-PTA was used as a photocatalyst to degrade methyl orange (MO) in the aqueous solution with a degradation rate of > 99%. Its excellent photocatalytic performance can be attributed to the higher specific surface area and reduction in band gap and reduction in photogenerated electron and hole recombination rate. After repeated use for three times, the Q[6]-PTA catalyst demonstrated high activity for degrading MO. This study demonstrates that the supramolecular self-assembly of cucurbit[n]uril/heteropolyacid is a facile and effective strategy for developing efficient and stable heterogeneous photocatalysts.