Fe ₂ O ₃ -loaded activated carbon fiber/polymer materials and their photocatalytic activity for methylene blue mineralization by combined heterogeneous-homogeneous photocatalytic processes

Fe ₂ O ₃ -supported activated carbon felts (Fe-ACFTs) were prepared by impregnating the felts consisted of activated carbon fibers (ACFs) with either polyester fibers (PS-A20) or polyethylene pulp (PE-W15) in Fe(III) nitrate solution and calcination at 250 °C for 1 h. The prepared Fe-ACFTs with 31–35 wt% Fe were characterized by N ₂ -adsorption, scanning electron microscopy, and X-ray diffraction. The Fe-ACFT(PS-A20) samples with 5–31 wt% Fe were microporous with specific surface areas (S _BET ) ranging from 750 to 150 m ² /g, whereas the Fe-ACFT(PE-W15) samples with 2–35 wt% Fe were mesoporous with S _BET ranging from 830 to 320 m ² /g. The deposition of iron oxide resulted in a decrease in the S _BET and methylene blue (MB) adsorption capacity while increasing the photodegradation of MB. The optimum MB degradation conditions included 0.98 mM oxalic acid, pH = 3, 0.02–0.05 mM MB, and 100 mg/L photocatalyst. The negative impact of MB desorption during the photodegradation reaction was more pronounced for mesoporous PE-W15 samples and can be neglected by adding oxalic acid in cyclic experiments. Almost complete and simultaneous mineralization of oxalate and MB was achieved by the combined heterogeneous-homogeneous photocatalytic processes. The leached Fe ions in aqueous solution [Fe ³⁺ ] _f were measured after 60 min for every cycle and found to be about 2 ppm in all four successive cycles. The developed photocatalytic materials have shown good performance even at low content of iron oxide (2–5 wt% Fe-ACFT). Moreover, it is easy to re-impregnate the ACF when the content of iron oxide is reduced during the cyclic process. Thus, low leaching of Fe ions and possibility of cyclic usage are the advantages of the photocatalytic materials developed in this study.