Heterogeneous Cobalt Catalysts For Dye Degradation Based On PMS Activation

The development of highly efficient and environmentally friendly oxidation processes has been one of the most important and greatly challenging goals in environmental catalysis field. Among various oxidation processes, peroxymonosulfate（PMS） activation to generate sulfate radicals with high reduction potential for effectively degradation of organic pollutants has received considerable attention. Cobalt catalysts are considered as the promising approach to activate PMS due to their high efficiency. In this study, we combined the catalytic properties of cobalt catalysts and huge adsorption capacity, excellent chemical stability of the activated carbon fibers（ACFs） together to develop heterogeneous Co catalytic fibers. Using PMS as the oxidant, dyes as the probe compounds, we investigated the catalytic performance of the catalytic fibers. The obtained catalytic fibers possessed high efficiency, great stability, facile recycling performance and no secondary pollution. This study not only offers new insights into the development of a new generation of functional fibers, but also provides a new practical method for the application in industrial wastewater treatment. Significantly, it has important academic and practical value for the solution to the more and more serious environmental pollution. The main research contents are as follows:Cobalt ion(Co²⁺) were supported onto ACFs to develop a novel heterogeneous catalytic fiber（Co@ACFs）. The structure of the catalytic fiber was characterized by atomic absorption spectrum, X-ray photoelectron spectroscopy, nitrogen adsorption and desorption isotherm, etc. With reactive brilliant red X-3B（RR X-3B） as the probe compound and PMS as the oxidant, the catalytic activity and reusability of Co@ACFs for PMS activation were investigated. Moreover, the role of ACFs in the catalytic degradation was studied. Importantly, we focused on the mechanism investigation by the various radical scavengers such as tert-butyl alcohol, methanol, potassium iodide and electron paramagnetic resonance（EPR）. The experimental results showed that the coordination between ACFs and Co²⁺ did occur in Co@ACFs, and Co@ACFs still exhibited an excellent adsorption capacity after immobilization of Co²⁺. The dyes with different structure including RR X-3B, acid orange 7（AO7）, acid red 1（AR1）, methylene blue（MB） could be efficiently degraded by Co@ACFs/PMS system and the degradation rate was almost 100% in 35 min. Co@ACFs exhibited similar catalytic activity during seven runs. Moreover, no detectable Co²⁺ was observed, suggesting that the catalyst possessed good reusability and stability. ACFs played a significant role in the catalytic degradation: high adsorption capacity in favor of the enhanced catalytic activity; ACFs as an electron donor to accelerate Co²⁺/Co3+ cycle thereby speeding up the degradation. Both hyroxyl and sulfate radicals（?OH, SO4?-） were responsible for the dyes degradation, while ?OH was the dominant radical.In order to develop more stable catalytic oxidation process, cobalt phthalocyanine（CoPc）, which had excellent stability and high catalytic activity, was chosen as the active sites and immobilized on activated carbon fibers（ACFs） by covalent bond to construct heterogeneous catalyst, ACFs-CoPc. The obtained catalyst was characterized by X-ray photoelectron spectroscopy. With acid red 1（AR1） as the target compound, we investigated the catalytic performance of ACFs-CoPc for PMS activation. The reusability and stability of ACFs-CoPc were systematically studied. A hybrid method that combined electron paramagnetic resonance（EPR） technology with different radical scavengers such as ascorbic acid, tert-butyl alcohol, methanol, potassium iodide was employed for the investigation of active species during the catalytic reaction. The results indicated that ACFs-CoPc could effectively activate PMS to degrade 100% of AR1 in 50 min. The oxidation products were small molecular biodegradable compounds. The degradation rate was higher than 98% after 10 successive runs. Moreover, there was no detectable cobalt leaching during the catalytic process, and the structure of CoPc in ACFs-CoPc was not destructed, suggesting that ACFs-CoPc was a stable catalyst with excellent reusability. During the catalytic reaction, dyes were firstly adsorbed to the surface of ACFs-CoPc, and degraded in situ by the generated ?OH, SO4?-, while SO4?- was speculated to serve as the dominant active species in the AR1 degradation.