Fenton reaction is one of the effective methods applying in the industrial wastewater treatment . However, the iron ions (Fe 3+ ) 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 Fe 3+ 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.
This study investigated the inhibition effects of sulfate on ferrous ion-activated persulfate oxidation of azo dye reactive brilliant red X-3B. The experimental results showed that the degradation efficiency of reactive brilliant red X-3B decreased from 100% to 63% in 60 min when the initial concentration of sulfate increased from 0 to 3 g/L. The ferrous/persulfate molar ratio had remarkable influence on persulfate oxidation capability in presence of sulfate. SO42−could coordinate with Fe2+and Fe3+in generating FeSO4ion pairs as well as FeSO4+or Fe(SO4)2−complexes, which were difficult to activate persulfate and reduced the regeneration of Fe2+. Radicals quenching and electron paramagnetic resonance experiments showed that ·OH and SO4·−were responsible for the oxidation of reactive brilliant red X-3B; however, the addition of sulfate significantly inhibited the generation of SO4·−, and then the generation of ·OH. Moreover, the corresponding Nernst equation indicated that high concentration of sulfate reduced the oxidation potential of SO4·−/SO42−. Experimental results proved that the adverse effects of sulfate on the persulfate oxidation could be counteracted either by batch addition of ferrous or by adding Ba2+to remove SO42−in the system.Keywords:persulfate;sulfate;sulfate radicals;reactive brilliant red X-3B
Zinc titanate-quartz composite microspheres were synthesized via a sol-gel route, and polyethylene glycol was used to reduce ZnTiO 3 crystal aggregation and to promote the photocatalytic activity of the ZnTiO 3 (n)-SiO 2 composites. The crystallite size of ZnTiO 3 was found to decrease from 37.8 nm (ZnTiO 3 (0)-SiO 2 ) to 27.2 nm (ZnTiO 3 (2.5)-SiO 2 ) with increasing polyethylene glycol amount. Many free fine ZnTiO 3 particles were obtained in the composites after the removal of polyethylene glycol during calcination . The bandgap energies of ZnTiO 3 (0)-SiO 2 , ZnTiO 3 (0.5)-SiO 2 , ZnTiO 3 (1.5)-SiO 2 and ZnTiO 3 (2.5)-SiO 2 were measured as 3.49, 3.71, 3.89 and 3.54 eV, respectively. Both the pore volumes and the surface areas of ZnTiO 3 (0.5)-SiO 2 and ZnTiO 3 (1.5)-SiO 2 were found to be enlarged compared to those of ZnTiO 3 (0)-SiO 2 . Polyethylene glycol can significantly enhance the photocatalytic activity of ZnTiO 3 (n)-SiO 2 composites. In terms of hydroxyl radical production, the composites follow the sequence ZnTiO 3 (1.5)-SiO 2 , ZnTiO 3 (0.5)-SiO 2 , ZnTiO 3 (2.5)-SiO 2 and ZnTiO 3 (0)-SiO 2 . The RBR X–3B degradation rate constants for ZnTiO 3 (1.5)-SiO 2 , ZnTiO 3 (0.5)-SiO 2 and ZnTiO 3 (0)-SiO 2 were calculated as 0.02474, 0.02201 and 0.01777 min −1 , respectively. A total of 89.5% of RBR X–3B molecules were degraded on ZnTiO 3 (1.5)-SiO 2 after 80 min of reaction, leading to the decomposition of major organic groups in the dye.
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