Facilitating the Fe( <scp>iii</scp> )/Fe( <scp>ii</scp> ) redox cycle with organic pollutants to enhance the heterogeneous Fenton-like catalytic performance of iron-containing catalysts

The heterogeneous Fenton-like reaction is a promissing technology for removing organic pollutants in water. The reduction of Fe(iii) to Fe(ii), as the rate-limiting step for generating ˙OH, is crucial in heterogeneous Fenton-like reactions and may be improved using organic pollutants with lower redox potential than that of Fe(iii)/Fe(ii). In this work, the rapid reduction of Fe(iii) to Fe(ii) on the MIL-100-Fe catalyst was achieved by degrading methylene blue (MB, <i>E</i> ₀ = 0.01 V), which has the desired lower redox potential than that of MIL-100-Fe(iii)/Fe(ii) (<i>E</i> ₀ = 0.76 V). By contrast, organic pollutants with higher redox potentials than that of MIL-100-Fe, such as phenol (<i>E</i> ₀ = 0.97 V) and <i>p</i>-nitrophenol (<i>E</i> ₀ = 1.23 V), were incapable of reducing Fe(iii) to Fe(ii). As a result, the degradation rate constant of MB was one order of magnitude higher than those of phenol and <i>p</i>-nitrophenol. Notably, MB could also promote the reduction of Fe(iii) to Fe(ii) in the presence of phenol or <i>p</i>-nitrophenol; thus, the degradation rate constants of phenol and <i>p</i>-nitrophenol were significantly enhanced by 50 and 30 times, respectively. The results revealed that organic pollutants with lower redox potential than that of Fe(iii)/Fe(ii) could facilitate the reduction of Fe(iii) to Fe(ii), which is beneficial for producing more ˙OH, thus improving the heterogeneous Fenton-like catalytic performance.