Rates of Hydroxyl Radical Generation and Organic Compound Oxidation in Mineral-Catalyzed Fenton-like Systems

Abstract

The iron oxide-catalyzed production of hydroxyl radical (*OH) from hydrogen peroxide (H2O2) has been used to oxidize organic contaminants in soils and groundwater. The goals of this study are to determine which factors control the generation rate of *OH (VOH) and to show that if VOH and the rate constants of the reactions of *OH with the system's constituents are known, the oxidation rate of a dissolved organic compound can be predicted. Using 14C-labeled formic acid as a probe, we measured VOH in pH 4 slurries of H2O2 and either synthesized ferrihydrite, goethite, or hematite or a natural iron oxide-coated quartzitic aquifer sand. In all of our experiments, VOH was proportional to the product of the concentrations of surface area of the iron oxide and H2O2, although different solids produced *OH at different rates. We used these results to develop a model of the decomposition rate of formic acid as a function of the initial formic acid and hydrogen peroxide concentrations and of the type and quantity of iron oxide. Our model successfully predicted the VOH and organic compound oxidation rates observed in our aquifer sand experiment and in a number of other studies but overpredicted VOH and oxidation rates in other cases, possibly indicating that unknown reactants are either interfering with *OH production or consuming *OH in these systems.

Influence of the operating conditions on highly oxidative radicals generation in Fenton's systems

“…The slurry-phase experiments were carried out with a quartz sand typically used as filter media in drinking water microfiltration processes. Before its use, the sand was sieved (2 mm) to obtain a homogeneous media, autoclaved at 120 • C for 2 min, allowing either sterilization and also the reduction of enzymatic activity [8]. Then, the sand was further characterized in terms of metal content, i.e.…”

“…The chemistry of the Fenton's process is based upon the reaction of hydrogen peroxide (E 0 = 1.80 and 0.87 V at pH 0 and 14 respectively) with a proper catalyst, leading to the generation of a pool of radicals [1], capable of non-selectively oxidizing a wide range of biorefractory organic pollutants such as chlorinated aliphatics, halogenated phenols, PAHs and PCBs. The radical produced in the Fenton's initiation Reaction (I) is the hydroxyl radical, whose formation can be achieved by adding an homogeneous catalyst, such as a transition metal salt [3,4], by generating the metal catalyst electrochemically by means of sacrificial steel electrodes or by using the metals naturally occurring in the environment as heterogeneous catalyst [5][6][7][8][9][10][11][12] The hydroxyl radicals generated through Reaction (I) react with hydrogen peroxide and begin a series of propagation reactions [2] …”

Synthesis of akageneite (beta-FeOOH)/reduced graphene oxide nanocomposites for oxidative decomposition of 2-chlorophenol by Fenton-like reaction

“…The mechanisms involved in the Fenton-like oxidation of organic compounds could be explained by considering both the reactions in solution and at the beta-FeOOH surface. As reported by other researchers [33,37], the first step in the heterogeneous reaction is the surface complexation of H 2 O 2 to Fe(III) forming Fe III H 2 O 2 , leading to the formation of • OH radicals in solution (Eqs. (1)-(4)), which degrades 2-CP (Eq.…”

“…8b). Particularly, only 33% 2-CP was removed for beta-FeOOH because the release iron and OH radical could be decreased [33]. However, Ak-20 and Ak-40 showed a little change in 2-CP removal, because of the rGO content.…”

“…10. Many researchers [33] observe that OH radical is proportional to H 2 O 2 . Compared with Ak, H 2 O 2 degradation on Ak-40 increased significantly whether initial pH as 4.0 or 9.0.…”