Activated Carbon Fiber-supported Metallo-porphyrin For Degradation Of Organic Pollutants

Biomimetic catalytic decomposition of organic pollutants has attracted increasing attentionover the past few decades. Among the various strategies, metalloporphyrin is currentlyconsidered as the potential biomimetic catalysts for the purification of water. However, the directapplication of metalloporphyrin as an oxidation catalyst in aqueous solution is usuallychallenging due to the disadvantages associated with bare metalloporphyrin, such as low activity,poor pH tolerance and stability, difficulties in separatity and reuse. Therefore, the development ofmetalloporphyrin catalysts with improved activity, pH tolerance and stability has been an activeand challenging research project. In this study, we evaluated a novel heterogeneous catalyst,hemin-ACF, based on activated carbon fiber (ACF) supported hemin. Environmental-friendlyH2O2and reactive red195were used as oxidant and target pollutant to investigate the catalyticdegradation performance of hemin-ACF. Experimenal results showed that compared with barehemin, the introduction of ACF significantly enhanced the ability of hemin for the activation ofhydrogen peroxide, and greatly improved its pH-tolerance, stability and separability. Meanwhile,we found that the introduction of ascorbic acid (AA) to the hemin-ACF/H2O2system drasticallyenhanced the catalytic degradation of organic pollutants. This dissertation not only offers newinsights into the widespread application of metalloporphyrin as a biomimetic catalyst fordecomposition of organic pollutants, but also endows fibers new connotation of biomimeticcatalysis. Importantly, it has important academic and practical value to solve more and moreserious water contamination. The main contnents are as follows:Hemin-ACF was obtained by immobilizing hemin on ACF covalently, characterized byXPS and UV-Vis. The reactive red195(RR195) was catalytically degraded by hemin-ACF/H2O2system. Effects of solution pH and temperature on the catalytic oxidation as well as the sustainedcatalytic stability of hemin-ACF were investigated. The experimental results showed thathemin-ACF possessed high activity, being an order of magnitude greater than that over barehemin (pH=6.98, T=50°C, kobs(hemin-ACF)=0.0871min–1kobs(hemin)=0.0084min–1).After10times of cyclic utilizations, no obvious decrease of catalytic activity was observed,indicating that hemin-ACF had excellent catalytic and reuse performance. Various scavengersand probe compounds (isopropanol, benzoquinone and sodium azide) combined with electron paramagnetic resonance (EPR) spectroscopy and UV-vis spectroscopy have been used to identifythe active species involved in the catalytic system. Based on the above analysis, the enhancedmechanism in the hemin-ACF/H2O2system was discussed.In order to establish a more efficient catalytic oxidation system, AA was introduced to thehemin-ACF/H2O2system to construct the hemin-ACF/AA/H2O2system. Compared withhemin/H2O2and hemin-ACF/H2O2, this system can greatly increase the degradation of dyes. Weanalyzed the reason for this enhanced phenomenon and found that in the hemin-ACF/H2O2system, the free electrons of hemin-ACF decreased with the reaction time (i.e.“discharging”)companying with enhanced OH and Fe(IV)=O, suggesting that an electron transfer from theACF to H2O2and hemin, thereby accelerating the catalytic cycle of hemin, generating enhanced OH and Fe(IV)=O. When AAwas introduced to the hemin-ACF/H2O2system, the free electronscontent of hemin-ACF firstly increased, indicating that AA can supply electron to ACF, and thendecreased more obviously, suggesting ACF transferred electron to hemin faster, thus furthergenerating more greatly enhanced OH and Fe(IV)=O.