In-situ growing protective Cr-substituted goethite film on iron shavings (Fe0) as efficient catalytic ozonation catalysts: A comparative study

Abstract

Abstract H2O2-modified iron shavings (HMI) with surface γ-FeOOH film were effective as a catalyst in catalytic ozonation, but the iron leaching and loss of surface component limited its application. In this study, Cr-modified iron shavings (CrMI) was developed by introducing Cr3+ to promote Cr-substituted goethite (α-Fe(Cr3+)OOH) film formation on iron shavings. The variety in stability and catalytic performance between CrMI and HMI were compared. The α-Fe(Cr3+)OOH film was compact while the γ-FeOOH film contained abundant voids and microcracks as observed from SEM. After long-time ozonation, α-Fe(Cr3+)OOH film was thin and homogeneous whereas γ-FeOOH film grew thicker through inner iron layer corrosion as indicated by XPS etching. The α-Fe(Cr3+)OOH film has 63% reduction in corrosion current densities (22.95 μA) and 96% reduction of donor densities (3.40 × 1020 cm−3) as well as 9 times increase in polarization resistance (4399.0 Ω cm2), which verified that it was more stable and less defective. Owing to the protective properties of α-Fe(Cr3+)OOH film, iron leaching of CrMI were reduced for 85% with only 4.1 mg L−1 of total iron concentration detected in solution, and surface loss of CrMI were reduced for 91% with only 5.8 NTU of turbidity left in the solution after catalytic ozonation. Moreover, the addition of CrMI as catalyst in ozonation led to slightly higher mineralization rate of 79% for organic pollutants as the results of higher surface acid sites density and more hydroxyl radicals generation. It also presented excellent reusability based on 20 h successive run with unnoticeable performance decay and metal release. These results revealed that, with excellent stability and high catalytic performance, CrMI was highly competitive for long-term application in wastewater treatment.