Enhancing the quantum yield of singlet oxygen: photocatalytic degradation of mustard gas simulant 2-chloroethyl ethyl sulfide catalyzed by a hybrid of polyhydroxyl aluminum cations and porphyrin anions

By combining the anionic salt meso-tetra(4-carboxyphenyl)porphyrin (TCPP4−) and the Keggin polyoxometalate cation cluster [Al13O4(OH)24(H2O)12]7+ via a simple ion-exchange method, a hybrid (C48H26N4O8)[Al13O4(OH)24(H2O)12]2(OH)10·18H2O (Al13–TCPP) was prepared and thoroughly characterized as a prototype of polyoxometalate–porphyrin hybrids for the photocatalytic degradation of the mustard gas simulant 2-chloroethyl ethyl sulfide (CEES). The experimental results showed that the catalytic degradation rate of CEES in the presence of Al13–TCPP reached 96.16 and 99.01% in 180 and 90 min in methanol and methanol–water solvent mixture (v/v = 1 : 1), respectively. The reaction followed first-order reaction kinetics, and the half-life and kinetic constant in methanol and solvent mixture were 39.8 min, −0.017 min−1 and 14.7 min, −0.047 min−1. Mechanism analysis indicated that under visible light irradiation in air, CEES was degraded through a combination of oxidation and alcoholysis/hydrolysis in methanol and the methanol–water solvent mixture. The superoxide radical (O2˙−) and singlet molecular oxygen (1O2) generated by Al13–TCPP selectively oxidized CEES into a non-toxic sulfoxide. The singlet oxygen capture experiments showed that Al13–TCPP (Φ = 0.236) had a higher quantum yield of singlet oxygen generation than H4TCPP (Φ = 0.135) under visible light irradiation in air. The material Al13–TCPP has good reusability, and the degradation rate of CEES can still reach 98.37% after being recycled five times.