Two New Methods of Synthesis for the Perbromate Ion: Chemistry and Determination by LC-MS/MS

Bromate Oxidation of Ammonium Salts: In Situ Acid Formation for Reservoir Stimulation

A redox chemistry approach has been employed to synthesize an assortment of acids in the subterranean environment for the purpose of enhancing productivity from hydrocarbon-bearing rock formations. Experimental studies revealed that bromate selectively oxidizes a series of ammonium salts NH₄X where X = F^-, Cl^-, Br^-, SO₄^2-, and CF₃CO₂^- to produce 5-17 wt % HX. Importantly, the in situ method allows strategic placement of the acid in the zone of interest where the fluid is heated, and the reaction is triggered. Ammonium counteranions are shown to influence the kinetics of the bromate-ammonium reaction, and the conditions are tailored to promote oxidation of ammonium at reservoir temperatures. The reaction is observed to be acid-catalyzed, where the formation of bromous acid (HBrO₂) is involved in the rate-limiting step. As a result, an induction period that scales with the p K_a of the acid being formed is followed by rapid formation of the reaction products.

Comparative analysis of the photocatalytic reduction of drinking water oxoanions using titanium dioxide

Regulated oxidized pollutants in drinking water can have significant health effects, resulting in the need for ancillary treatment processes. Oxoanions (e.g., nitrate) are one important class of oxidized inorganic ions. Ion exchange and reverse osmosis are often used treatment processes for oxoanions, but these separation processes leave behind a concentrated waste product that still requires treatment or disposal. Photocatalysis has emerged as a sustainable treatment technology capable of catalytically reducing oxoanions directly to innocuous byproducts. Compared with the large volume of knowledge available for photocatalytic oxidation, very little knowledge exists regarding photocatalytic reduction of oxoanion pollutants. This study investigates the reduction of various oxoanions of concern in drinking water (nitrate, nitrite, bromate, perchlorate, chlorate, chlorite, chromate) using a commercial titanium dioxide photocatalyst and a polychromatic light source. Results showed that oxoanions were readily reduced under acidic conditions in the presence of formate, which served as a hole scavenger, with the first-order rate decreasing as follows: bromate > nitrite > chlorate > nitrate > dichromate > perchlorate, corresponding to rate constants of 0.33, 0.080, 0.052, 0.0074, 0.0041, and 0 cm²/photons × 10¹⁸, respectively. Only bromate and nitrite were reduced at neutral pH, with substantially lower rate constants of 0.034 and 0.0021 cm²/photons × 10¹⁸, respectively. No direct relationship between oxoanion physicochemical properties, including electronegativity of central atom, internal bond strength, and polarizability was discovered. However, observations presented herein suggest the presence of kinetic barriers unique to each oxoanion and provides a framework for investigating photocatalytic reduction mechanisms of oxoanions in order to design better photocatalysts and optimize treatment.