| How to effectively remediate textile wastewater attracts more attention in the treatment of wastewater. Peroxydisulfate (PS) and hydrogen peroxide (H2O2) are available green oxidants, but always need to be activated by catalysts due to their relatively stable properties. In the recent years, heterogeneous catalysts used for the activation of PS and H2O2 to generate SO4·- and OH· oxidative radicals show a promising future in the degradation of recalcitrant organics. In this work, the kinetics and mechanisms of the oxidative degradation of phenol by PS and H2O2 catalyzed by different heterogeneous catalysts will be investigated.One of the intrinsic drawbacks in the Fenton and Fenton-like systems is the strict pH control (always pH 2.0-4.0), which limits their practical applications in the treatment of alkaline wastewater. The heterogeneous Ni/PS system was firstly used for the remediation of alkaline phenolic wastewater in this study. Our results indicate that β-Ni(OH)2/PS and β-NiOOH/PS systems exhibit high removal efficiencies in the removal of phenol under alkaline conditions. A complete removal of 100 mg L-1 phenol can be achieved within 5 min at initial pH 11.0,1.0 g L-1 PS and 0.2 g L-1 β-Ni(OH)2. Ni(III) in β-NiOOH plays an important role in the removal of phenol via a rapid adsorption of phenol on β-NiOOH. After that, Ni(III) with a strong oxidizing ability further oxidizes the adsorbed phenol to intermediate products with a reduction of Ni(III) to Ni(II). Besides phenol, organic contaminants such as methylene blue, methyl orange, bisphenol A, chlorobenzene and aniline can also be effectively removed, suggesting the wide applicability of P-Ni(OH)2/PS in the treatment of other organic contaminants. The insignificant effect of inorganic anions such as Cl-, NO3-and SO42- on the catalytic activities indicates a promising application of this catalyst in the treatment of wastewater with a high salinity. Besides, P-Ni(OH)2/PS system shows a high stability and reusability.The catalytic activities of a-Ni(OH)2, γ-MOOH and NiO were also investigated in this study. Our results show that the catalytic activity of a-Ni(OH)2 is higher than that of P-Ni(OH)2, and a complete removal of 100 mg L-1 phenol can be achieved within 1 min at initial pH 11.0,0.2 g L-1 a-Ni(OH)2 and 1.0 g L-1 PS. This is because that α-Ni(OH)2 is oxidized to y-NiOOH, a stronger oxidant than β-NiOOH due to the presence of Ni(III)/Ni(IV) in γ-NiOOH. NiO shows a relatively mild activity in the removal of phenol, and NiO-450 shows a better performance than NiO-600 because more Ni(III) in NiO-450 was involved in the removal of phenol.In order to obtain more nickel-based heterogeneous catalysts with low costs and high performances, the abundant manganese and iron minerals are chosen as the available matrix to immobilize Ni(II). Birnessite shows the highest adsorption capacity to Ni(II) among the nine synthetic minerals, and the Mn vacancies on birnessite are the main adsorption sites. The Ni(II)-adsorbed birnessite system also exhibits a good efficiency in heterogeneously activating PS to remove phenol. Ni(III), OH· and SO4·-can all effectively remove phenol. On the other hand, Ni(II) structurally-incorpotated birnessite shows negligible improvement on the removal of phenol.The presence of organic compounds with different functional groups such as-OH,-NH3 and -COOH may affect the physical properties (such as crystalline) of heterogeneous catalysts, which further affect their catalytic activities. Wastewater containing Ni(II) is a renewable resource, and in order to improve the utilization of nickel from wastewater, we investigate the influence of phenol, aniline and benzoic acid on the physical properties and catalytic activities of the heterogeneous catalysts. Aniline caused a decrease in the crystallinity of P-Ni(OH)2, and the inhibition of catalytic activities follows the order of aniline> phenol> benzoic acid. The presence of 1.06 mM aniline decreases the kinetic constants from 0.583 to 0.229 min-1 in the removal of phenol. Although the presence of organics reduces the activities of β-Ni(OH)2, it is feasible to use wastewater conaining Ni(II) to treat organic wastewater.The new Mo-Sch/H2O2 Fenton-like system is also firstly investigated in this study to degrade phenol under acidic conditions. Our results indicate the oxidation mechanism involved in Mo-SCh/H2O2 system is dependent on the amount of Moimm on Sch. Phenol oxidation is predominantly mediated by OH· at low Moimm, whereas ·OOH and 1O2 play important roles at high Moimm-Modiss exhibits inhibitory effects on the Fe(III) system due to the significant reduction of the utilization efficiency of H2O2. The Modiss/H2O2 system can also oxidize phenol by formation of dimeric Mo2O3(O2)42-and ·OOH.This work systematically investigates the kinetics and mechanisms involved in the oxidative degradation of phenol by PS catalyzed by nickel (oxyhydr)oxides under alkaline conditions and by H2O2 catalyzed by Mo-Sch under acidic conditions. This work provides additional choices for efficient AOPs catalysts to treat organic wastewater under alkaline conditions, and enriches our understanding on the different mechanisms of H2O2 activation under acid conditions.In this regard, this study provides theoretical supports to broaden the applications and deepen our understanding on the catalytic mechanisms of AOPs.
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