Reactions of Acid Orange 7 with Iron Nanoparticles in Aqueous Solutions

Abstract

The physicochemical properties of two commercial dispersions of iron nanoparticles were studied, together with their behavior in the room-temperature degradation in basic solutions of Acid Orange 7 (AO7), studied by UVÀvis spectroscopy. In one dispersion (bare-RNIP), water was the solvent, and in the other (M-RNIP) a biopolymer (sodium aspartate) was added (RNIP standing for reactive nanoscale iron particles and M for modified). The features of iron nanoparticles (size, morphology, presence of oxidized phases) were studied both in the dispersions as such and in the corresponding dried powders. A protecting role of the biopolymer was observed, as well as changes in the properties with time (aging). With bare-RNIP, the fraction of Fe 3 O 4 (magnetite) steadily increased with time at the expense of Fe 0 , eventually reaching 99%, and with M-RNIP, the Fe 0 content was higher at any time than with bare-RNIP: aging, however, brought about the formation of the Fe 3+ compound FeOOH besides magnetite. As for AO7 degradation, a similar behavior was observed with the two fresh dispersions: with M-RNIP, degradation was complete in a few minutes, and with fresh bare-RNIP, the same process was basically observed, though at a lower rate. In both cases, successive reactions were observed as a minor feature, for which an interpretation is advanced. Aging of M-RNIP does not prevent the degradation reaction: aging in the absence of the polymer, instead, leads, after 6 months, to an entirely different process, consisting in the mere adsorption through the phenol group of AO7 onto the magnetite external layer of bare-RNIP particles. Further aging of bare-RNIP prevents also this phenomenon. The different behavior of the two dispersions relates to the composition of iron nanoparticles. Reaction with water converts Fe 0 into magnetite. When Fe 0 is present and the thickness of the outer magnetite layer is moderate, AO7 degradation occurs. With a thick outer layer, only adsorption is possible, which does not take place on a fully oxidized surface.

Nanomaterials for the Abatement of Pharmaceuticals and Personal Care Products from Wastewater

“…In the last two decades, nanoscale zerovalent iron (NZVI) particles have been considered a promising nanomaterial to remove a wide range of contaminants including heavy metals, pesticides and chlorinated solvents from both groundwater and wastewater [57][58][59].…”

Role of pH in the Aqueous Phase Reactivity of Zerovalent Iron Nanoparticles with Acid Orange 7, a Model Molecule of Azo Dyes

“…In the last decade, much interest has been devoted to Nanoscale Zerovalent Iron (NZVI) [29], acting as a reducing agent for several pollutants, while undergoing oxidation and dissolution [30][31][32][33][34][35][36][37][38]. The use of metallic iron in environmental remediation, indeed, dates back to the midseventies, when it was used as filling reactive material in the Permeable Reactive Barrier technology for reductive dechlorination of halogenated hydrocarbons [39,40].…”

“…The use of metallic iron in environmental remediation, indeed, dates back to the midseventies, when it was used as filling reactive material in the Permeable Reactive Barrier technology for reductive dechlorination of halogenated hydrocarbons [39,40]. This ability has prompted the use of iron particles, ranging from millimetric to nanometric scale, for degradation of other contaminants [41], including pesticides [42,43], nitroaromatics [44], metal ions [31,36,39,45], and dyes [30,[46][47][48][49][50][51][52].…”

“…Whatever its source, NZVI remains, so far, a poorly characterized system, normally consisting of an aqueous slurry featuring a solid phase and, possibly, a stabilizer [30].…”

“…In a previous paper [30], we investigated the degradation of the azo dye Acid Orange 7 (AO7, Scheme 1) by two RNIP suspensions commercialized at pH values around 12. Those experiments were run in slightly basic conditions, as obtained after adding RNIP to a water solution of 0.67 mM AO7 (the latter having a natural pH equal to 6.8, i.e., close to neutrality).…”