Heterogeneous catalysis of FeOOH in-situ loaded biochar for reactive red X-3B: Catalytic mechanism based on Fenton-like system

Fenton reaction is one of the effective methods applying in the industrial wastewater treatment. However, the iron ions (Fe3+) used in conventional Fenton reaction are difficult to recover, which will convert into Fe(OH)3 and produce a large amount of excess sludge. Biochar with rich porous structure is an excellent adsorbent, but it is challenging to reuse after adsorption. Considering these facts, the FeOOH was in-situ loaded onto carboxylated biochars, and the recyclable heterogeneous catalysts (FeOOH@CBC) were fabricated. The cyclic adsorption-photocatalytic processes of FeOOH@CBC with different crystal structures (amorphous FeOOH, α-FeOOH and β-FeOOH) for reactive red X-3B were explored. Under the simulated solar irradiation, the α-FeOOH@CBC shown outstanding catalytic activity for reactive red X-3B (1000 mg·L−1) with a decolorization rate of 99.9% in 90 min, and the released Fe3+ concentration was below the detection range (0.1 mM) of potassium thiocyanate colorimetry method. After the 10th cycle, the COD removal rate of α-FeOOH@CBC for reactive red X-3B still reached 95% (14,550 mg·g−1). The excellent reusability of α-FeOOH@CBC and minimal iron ion release can decrease the solid waste pollution from adsorbed biochar, which may promote the large-scale application of biochar in industrial wastewater treatment.