| In this paper, a new-type Fenton-like technology based on the catalytic materials has been built in order to solve the technical problem of refractory organic pollutants. On account of the rational design and basic scientific issue of Fenton-like catalyst, graphene-based composite catalysts (Mn3O4-rGO, Co-rGOand Co(OH)2)/PMS system has been established. It is well-known that the generation rate of active free radicals is an important optimizing index for Fenton-like system. The new type of graphene-based catalysts were designed and prepared for the catalytic test. Through a series of studies, the growth mechanism and the structure control approach of the as-prepared catalysts have been revealed, the reaction mechanism of organic pollutants mineralization has been verified and the structure activity relationship of composition-structure-surface/interfacial property-catalytic performance has been explained. All of the results show that our investgations have gained satisfying achievements in basic theories and applications of novel Fenton-like system. The major contents are described as follows:(1) Graphene oxide (GO), prepared from purified natural graphite by the modified Hummers method, was used as the presoma for the fabrication process. Mn3o4-rGO hybrids were successfully synthesized by the in-situ method in water and the as-prepared Mn3O4-rGO hybrids as heterogenous catalysts of PMS activition for the degradation of Orange Ⅱ was investigated. The surface morphology and structure of the Mn3O4-rGO hybrids were characterized by field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), powder X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA). The result showed that the Mn3O4 nanoparticles at a size of approximately 29.2 nm was supported on graphene sheets successfully. The catalytic performance test indicated that 30 mg/L of Orange Ⅱ could be completely oxidized in 120 min at 25℃ and 0.05 g/L of Mn3O4-rGO hybrids. Furthermore, The efficiency of Orange Ⅱ decomposition increased with increasing temperature (25-55℃), pH (4.0-11.0), and PMS dosage (0.25-1.5 g/L), but it decreased with increasing initial Orange Ⅱ concentration (30-90 mg/L). Meantime, after 4 rounds of regeneration of the catalyst, the catalyst exhibited stable performance, because the reaction still can be finished within 60 min.(2) Cobalt nanoparticles (NPs) supported on reduced graphene oxide (rGO) was synthesized by a two-step in situ co-reduction method and an innovative advcanced oxidation system of Co-rGO/PMS was constructed. It was found that the combination of Co and graphene produces a synergistic effect in catalytic activity. Co-rGO hybrids showed stronger catalytic activity for the heterogeneous activation of PMS and the degradation of organic pollutants than Co. With the addition of 0.05 g/L of catalysts and 0.2 g/L of PMS, the Co-rGO hybrid produced fast and full degradation of Orang Ⅱ (60 mg/L) with the apparent rate constant of 0.0747 min-1, being 2.1 folds of that (0.042 min-1) over nano-Co NPs.(3) a-Co(OH)2-rGO hybrids were synthesized by a one-pot hydrothermal method using glucose as a reducing agent for graphene oxide (GO) reduction and the as-prepared a-Co(OH)2-rGO hybrids as heterogenous catalysts of PMS activation for the degradation of Orange Ⅱ were investigated. The characterization results showed that the a-Co(OH)2 nanoflakes were dispersed on the basal planes of graphene irregularly. The catalytic performance study found that the added phenol (30 mg/L) was almost completely removed (with a removal of 99%) in 60 min by using 0.1 g/L a-Co(OH)2-rGO and 0.5 g/L PMS. With higher addition of catalyst (0.1 g/L), phenol degradation could be achieved in 10 min. Finally, based on the HPLC analysis of the degradation intermediates in the a-Co(OH)2-rGO/PMS system, a detail mechanism for phenol degradation was proposed. |
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