Efficiency And Mechanism Of Phenol Degradation In Cu²⁺-Enhanced Fe²⁺-Activated Persulfate System

Persufate（PDS） and/or peroxymonosulfate（PMS）, as oxidizing agents, present the advantage in stableness, easy storage, cheapness, safety, and no secondary pollution to the environment. The oxidation capacity of PMS and PDS is not strong, and hence a certain activation method is required in practice to produce highly active oxidizing species. Metal ion activation is the most common activation method. As an environmentally friendly transition metal ions, Fe²⁺ is a promising matter to active PMS and PDS and degrade the organic pollutants in water. Fe²⁺ activation system is simple, reliable, easy to operate, strong in oxidation and environmentally, but at the same time, the system also has its inherent flaws, e.g. narrowed operating p H range, iron mud easily formed from ferric iron during the reaction. Therefore, many water treatments focused on how to further improve the efficiency of Fe²⁺ activation method and resolve its inherent drawbacks, e.g. adding light, microwave, ultrasound or some complexants to prevent the precipitation of ferric iron, and so on. Indeed, a simple way is highly required to achieve high generation efficiency of active species in Fe2 + activating PMS and PDS system and subsequently to promote the degradation of organic pollutants.Based on the degradation of common dyes in transition metal activated PMS or PDS system, a spectrophotometry method was conducted. PMS was determined by Co²⁺-PMSdyes（MB, MV, AO7 and Rh B） spectrophotometry, the optimal determination condition and standard curves for PMS have been developed. PDS was determined by Fe²⁺-PDSMO spectrophotometry, the determination condition has been optimized and the standard curve has been developed. Experiment results have shown that the ions in water have no significant influence during both PMS and PDS determination. F test showed that the new method has no significant difference compared with the traditional method（i.e., idometric method）. Thus, due to the facility and efficiency, this method was applied in the following experiments.The influences of transition metal ions(i.e., Cu²⁺ and Mn²⁺) phenol degradation in Fe²⁺/PMS and Fe²⁺/PDS system have been investigated. In both cases, phenol degradation can be divided into two phases, that is, a rapid phase followed by a slow phase, due to a limitation on PMS（PDS） activation by Fe³⁺, which was formed during the PMS and PDS activation by Fe²⁺. At p H 3.0 and 4.0, the addition of Cu²⁺ can enhance the degradation of phenol. The degradation efficiency of phenol increased with Cu²⁺ and oxidants（PMS or PDS） concentration increasing, especially in the slow phase. Kinetic analysis shows that the apparent rate constants of the two phase increased with Cu²⁺ and oxidants（PMS or PDS） concentration increasing. In the rapid phase, the enhancement have no relation to Cu²⁺ concentration. In addition, the presence of Mn²⁺, Ce³⁺ and Ni²⁺ have no significant influence on phenol degradation in Fe²⁺/PMS and Fe²⁺/PDS system. The comparison experiments shows Cu²⁺ can enhance the phenol degradation in Fe²⁺/PMS, Fe²⁺/PDS and Fenton system, and phenol degradation efficiency follow the order: Cu²⁺/Fenton > Cu²⁺/Fe²⁺/PMS > Cu²⁺/Fe²⁺/PDS. Mn²⁺ and Ce³⁺ can only enhance the degradation in Fe³⁺/H₂O₂ system, and the enhancement was attribute to the quinone-like intermediates and H₂O₂? formed in the system, accelerating the reduction of Fe³⁺ to Fe²⁺, facilitating the formation of ?OH, thus, enhancing the degradation of phenol.The reactive species formed during phenol degradation in Cu²⁺/Fe²⁺/PMS and Cu²⁺/Fe²⁺/PDS system are identified, and sulfate radical has been proved to be the main reactive species by scavenging experiments. Furthermore, the products of AO7 was identified using LC-ESI-triple TOF-MS, interestingly, only sulfate adducts has been found in Cu²⁺/Fe²⁺/PMS and Cu²⁺/Fe²⁺/PDS system, thus the sulfate radical has been ensured to be the reactive species in Cu²⁺/Fe²⁺/PMS and Cu²⁺/Fe²⁺/PDS system. The mechanism of Cu²⁺ enhancement in both Fe²⁺/PMS and Fe²⁺/PDS was discussed, and the enhancement can be explained by the Cu+ formed by the reduction of Cu²⁺ by peroxylmonosulfate radical and peroxyldisulfate radical, that can i) reduce Fe³⁺ to Fe²⁺ and ii) activate PMS and PDS, thus, improve the degradation of phenol in Fe²⁺/PMS and Fe²⁺/PDS system. Additionally, the AO7 degradation in Cu²⁺/HA/PMS and Cu²⁺/HA/PDS system has shown the capability of Cu+ in activating PMS and PDS.