Fluorene oxidation by solar-driven photo-Fenton process: toward mild pH conditions

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are on the list of priority pollutants to be eliminated from the environment due to their carcinogenic and mutagenic action, chemical stability, and resistance to biodegradation. The aim of this study was to evaluate the degradation of fluorene, a well-known PAH, in aqueous solutions (0.03 and 0.08 mg L), by means of a solar-driven conventional (PF) and modified photo-Fenton mediated by ferrioxalate complexes (PFF). Photolysis was also employed for comparison purposes. PF reaction was evaluated at different pH values (2.8, 3.5, and 4.0) and iron concentrations (2, 5, 10, and 20 mg L). On the other hand, PFF studies were conducted at mild pH conditions (4.0, 5.0, and 6.0) and iron content of 2 mg L, keeping initial iron/oxalate molar ratio at 1:3. In both PF and PFF, the initial hydrogen peroxide/iron molar ratio was maintained at 5. In the presence of methanol as cosolvent for fluorene dissolution, the PF reaction was hampered and no consumption of HO was observed during the reaction carried out at constant pH (2.8). This led to low degradation rates, similar to those achieved by photolysis. Under the same pH but using acetonitrile as cosolvent for fluorene dissolution, fluorene degradation was found to be proportional to the iron content used in the PF experiments. On the other hand, at an invariable iron concentration of 5 mg Fe L, the increase in pH was accompanied by a decrease in the molar fraction of the most photoactive iron complex (FeOH) and ferric hydroxides precipitation, leading to a reduction in the fluorene degradation rate. With regard to the PFF tests, similar fluorene degradation performance was achieved at pH 4 and 5, while at pH 6 iron precipitation became relevant and the degradation rate was slightly slower. PFF has shown to be more efficient than the PF under the same pH (4) and iron concentration (2 mg L). Moreover, even at near neutral pH (6), fluorine degradation was shown to be feasible by using ferrioxalate complexes.

Synthesis and Study of an Efficient Metal-Organic Framework Adsorbent (MIL-96(Al)) for Fluoride Removal from Water

“…Excessive fluoride in natural water is predominantly caused by the discharge of fluoride-rich wastewater effluent or surface water washing of fluoridecontaining ore over long periods [1,2]. Excessive fluoride in the human body can mineralize calcium hydroxyphosphate to calcium fluorophosphate, which causes a significant change in the fluoride-phosphorus ratio resulting in spurs, periosteal hyperplasia, osteoporosis, osteosclerosis, and bone deformation [3,4]. Long-term intake of high-fluoride food by children will result in enamel hypoplasia, tooth damage, and fluoride deposition, causing a series of deformities in the bones [5,6].…”