Hypochlorous acid decomposition in the pH 5-8 region

Adam, Luke C.; Fábián, István; Suzuki, Kazunori; Gordon, Gilbert

doi:10.1021/ic00043a011

Cited by 150 publications

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“…At pH 7.6, this rate constant will be even lower. 27 Therefore, the decay rate of HOCl was enhanced about 10 8 times at pH 7.6 in the presence of 0.2 g L −1 CuO. Figure 1B shows significant chlorate formation, except at pH 9.6, indicating that chlorate can be formed via a CuO-catalyzed disproportionation reaction.…”

Section: ■ Results and Discussionmentioning

confidence: 90%

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Enhanced Bromate Formation during Chlorination of Bromide-Containing Waters in the Presence of CuO: Catalytic Disproportionation of Hypobromous Acid

Liu

Gunten

Croué

2012

Environ. Sci. Technol.

109

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Bromate (BrO 3 − ) in drinking water is traditionally seen as an ozonation byproduct from the oxidation of bromide (Br − ), and its formation during chlorination is usually not significant. This study shows enhanced bromate formation during chlorination of bromide-containing waters in the presence of cupric oxide (CuO). CuO was effective to catalyze hypochlorous acid (HOCl) or hypobromous acid (HOBr) decay (e.g., at least 10 4 times enhancement for HOBr at pH 8.6 by 0.2 g L −1 CuO). Significant halate concentrations were formed from a CuO-catalyzed hypohalite disproportionation pathway. For example, the chlorate concentration was 2.7 ± 0.2 μM (225.5 ± 16.7 μg L −1 ) after 90 min for HOCl (C o = 37 μM, 2.6 mg L −1 Cl 2 ) in the presence of 0.2 g L −1 CuO at pH 7.6, and the bromate concentration was 6.6 ± 0.5 μM (844.8 ± 64 μg L −1 ) after 180 min for HOBr (C o = 35 μM) in the presence of 0.2 g L −1 CuO at pH 8.6. The maximum halate formation was at pHs 7.6 and 8.6 for HOCl or HOBr, respectively, which are close to their corresponding pK a values. In a HOCl−Br − −CuO system, BrO 3 − formation increases with increasing CuO doses and initial HOCl and Br − concentrations. A molar conversion (Br − to BrO 3 − ) of up to (90 ± 1)% could be achieved in the HOCl−Br − −CuO system because of recycling of Br − to HOBr by HOCl, whereas the maximum BrO 3 − yield in HOBr−CuO is only 26%. Bromate formation is initiated by the formation of a complex between CuO and HOBr/ OBr − , which then reacts with HOBr to generate bromite. Bromite is further oxidized to BrO 3 − by a second CuO-catalyzed process. These novel findings may have implications for bromate formation during chlorination of bromide-containing drinking waters in copper pipes. ■ INTRODUCTIONThe formation of bromate during the ozonation of bromidecontaining waters has been intensively studied. 1−5 In the presence of ozone, bromate is produced from the reactions of ozone and ·OH radicals with bromide (Br − ), via several intermediates including hypobromite (BrO − ) and bromite (BrO 2 − ). 5 Because bromate is potentially carcinogenic, it is regulated in potable water at a maximum contaminant level (MCL) of 10 μg L −1 in many countries. 6−8 Moreover, bromate is stable, and there is currently no economically feasible technology to remove it once it is formed. 9 Therefore, the treatment conditions have to be optimized in some cases to mitigate bromate formation while disinfection is still guaranteed (e.g., ammonia addition and lowering the pH 9 ).

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Section: ■ Results and Discussionmentioning

confidence: 90%

“…In the absence of metal oxides, the depletion of HOCl mainly occurs through slow disproportionation (eq 7), 27 and oxygen generation (eq 8) is minor (less than 10%). 22 …”

Section: ■ Results and Discussionmentioning

confidence: 99%

Enhanced Bromate Formation during Chlorination of Bromide-Containing Waters in the Presence of CuO: Catalytic Disproportionation of Hypobromous Acid

Liu

Gunten

Croué

2012

Environ. Sci. Technol.

109

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“…Thus, the null hypothesis tested in the study had to be rejected as differences could be detected in antibacterial efficacy results among all the examined solutions. Nonetheless, surfactants may modify the stability of the chlorine level of NaOCl solutions (13,25). Chlorine has a strong tendency to acquire electrons in order to achieve greater stability, and this translates into chlorine's oxidizing activity (23).…”

Section: Discussionmentioning

confidence: 99%

Antibacterial Power of Sodium Hypochlorite Combined with Surfactants and Acetic Acid

et al. 2014

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The aim of this ex vivo study was to compare the antibacterial power of 1% NaOCl with 1% acetic acid, 5.25% NaOCl and two commercially available NaOCl modified with surfactants in bovine root dentin. A total of 120 dentin tubes prepared from intact bovine incisors were infected for 21 days with Enterococcus faecalis and randomly divided into six groups as follows: 5.25%NaOCl; Hypoclean; Chlor-Xtra; 1% NaOCl with 1% acetic acid; infected dentin tubes (positive control); and sterile dentin tubes (negative control). At experimental times of 0, 7, 14, 21 and 28 days, dentin chips were collected using sequential round burs with increasing diameters in separate test tubes containing 3 mL of freshly prepared BHI. Statistical analysis were performed using parametric methods (one-way ANOVA, and Bonferroni's multiple comparisons test, α=0.01). After culturing, the number of colony-forming units (CFU) was counted. All the NaOCl solutions showed small number of CFU over 28 days. ChlorXtra and Hypoclean had the smallest number of CFU at all times with greater antimicrobial efficacy than 5.25% NaOCl and 1% NaOCl solution with 1% acetic acid. Antibacterial Power of Sodium H y p o c h l o r i t e C o m b i n e d w i t h S u r f a c t a n t s a n d Ac e t i c Ac i d

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“…The solubility of Cl2 (aq) in water is very low and therefore Cl2 (aq) readily escapes from the solution. Also, in the neutral pH region (6.5 to 7.5), undissociated HOCl tends to be decomposed at a relatively high rate (Adam et al, 1992) and its concentration decreases gradually during the storage period. On the other hand, dissociated -OCl is more stable in alkaline water, especially at pHs above 10, and AC concentration is almost constant even after a 6-month storage (Siqueira, 2000).…”

Section: Membrane Permeability and Germicidal Activitymentioning

confidence: 99%

Mechanisms of Actions of Sodium Hypochlorite in Cleaning and Disinfection Processes

2006

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Sodium hypochlorite (NaOCI) is the most widely used disinfectant in the food industry despite the increasing availability of other disinfectants.Sodium hypochlorite fulfills many requirements as the ideal disinfectant and furthermore it has an excellent cleaning action. The effectiveness of sodium hypochlorite in the cleaning and disinfection processes depends on the concentration of available chlorine and the pH of the solution. Hypochlorous acid (HOCI) is a weak acid and dissociates to the hypochlorite ion (-OCI) and proton (H+) depending on the solution pH. It is generally believed that HOCI is the active species in the germicidal action, whereas the concentration of -OCI is a key factor determining the cleaning efficiency. This implies that the optimal pH region of the germicidal activity of sodium hypochlorite differs from that of its cleaning activity. This paper describes the theory and practice of the cleaning and disinfecting operations based on the use of sodium hypochlorite solution.

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Hypochlorous acid decomposition in the pH 5-8 region

Cited by 150 publications

References 0 publications

Enhanced Bromate Formation during Chlorination of Bromide-Containing Waters in the Presence of CuO: Catalytic Disproportionation of Hypobromous Acid

Enhanced Bromate Formation during Chlorination of Bromide-Containing Waters in the Presence of CuO: Catalytic Disproportionation of Hypobromous Acid

Antibacterial Power of Sodium Hypochlorite Combined with Surfactants and Acetic Acid

Mechanisms of Actions of Sodium Hypochlorite in Cleaning and Disinfection Processes

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