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(a¹Δ_g) 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.