Liquid-liquid reaction of hydrogen peroxide and sodium hypochlorite for the production of singlet oxygen in a centrifugal flow singlet oxygen generator

An attempt is made to produce gas-phase singlet oxygen O2(a1Δg) in a liquid-liquid reaction between acidic hydrogen peroxide (AHP) and sodium hypochlorite (NaOCl). The attempt arises from the fact that basic hydrogen peroxide (BHP) has long been the prime source for producing singlet delta oxygen through its reaction with chlorine. However, BHP suffers from the defect of being unstable during storage. Exploratory experiments were performed in a centrifugal flow singlet oxygen generator (CF-SOG) with two streams of solutions, AHP and NaOCl, mixed in a slit nozzle and then injected into the arc-shaped concavity in the CF-SOG to form a rotating liquid flow with a remarkable centrifugal force. With the help of this centrifugal force, the product of the O2(1Δ) reaction was quickly separated from the liquid phase. The gas-phase O2(1Δ) was detected via the spectrum of O2(1Δ) cooperative dimolecular emission with a CCD spectrograph. Experimental results show that it is feasible to produce gas-phase O2(1Δ) from the AHP + NaOCl reaction, and the stronger the acidity, the more efficient the O2(1Δ) production. However, since in the AHP + NaOCl reaction, Cl2 unavoidably appears as a byproduct, its catalytic action on the decomposition of H2O2 into ground-state O2 remains a major obstacle to utilising the AHP + NaOCl reaction in producing gas-phase O2(1Δ). Qualitative interpretation shows that the AHP + NaOCl reaction is virtually the reaction of interaction of molecular H2O2 with molecular HOCl, its mechanism being analogous to that of reaction of BHP with Cl2, where HOOCl is the key intermediate. It is difficult to form the intermediate HOOCl via the H2O2 + NaOCl reaction in a basic medium, thus gas-phase O2(1Δ) cannot be obtained in appreciable quantities.