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 (TCPP(4−)) and the Keggin polyoxometalate cation cluster [Al(13)O(4)(OH)(24)(H(2)O)(12)](7+)via a simple ion-exchange method, a hybrid (C(48)H(26)N(4)O(8))[Al(13)O(4)(OH)(24)(H(2)O)(12)](2)(OH)(10)·18H(2)O (Al(13)–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 Al(13)–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 (O(2)˙(−)) and singlet molecular oxygen ((1)O(2)) generated by Al(13)–TCPP selectively oxidized CEES into a non-toxic sulfoxide. The singlet oxygen capture experiments showed that Al(13)–TCPP (Φ = 0.236) had a higher quantum yield of singlet oxygen generation than H(4)TCPP (Φ = 0.135) under visible light irradiation in air. The material Al(13)–TCPP has good reusability, and the degradation rate of CEES can still reach 98.37% after being recycled five times.