Font Size: a A A

In Situ Bio-electrocatalyzed Hydrogen Peroxide Oxidation For Azo Dye Degradation

Posted on:2016-09-16Degree:DoctorType:Dissertation
Country:ChinaCandidate:G E YuanFull Text:PDF
GTID:1221330461977707Subject:Environmental Engineering
Abstract/Summary:PDF Full Text Request
Dye wastewater is regarded as one of the industrial wastewaters difficult to deal with due to its deep colority, high toxicity, complicated composition and poor biodegradability. As a vitally important kind of electrochemical advanced oxidation technology, electro-Fenton has been attracting ever more attention in the respect of refractory pollutant processing, but high energy consumption, low pH value and large amount of iron sludge production limit its application. Microbial fuel cell (MFC) is a hot topic in the fields of wastewater treatment because of its peculiar capacity of converting chemical energy of organic matter in domestic wastewater directly into electricity. Electro-Fenton reaction driven by MFC in the cathode chamber can not only significantly reduce the energy consumption but also recover part of electric energy, revealing a good prospect of application. However, MFC driven electro-Fenton system still has some problems, such as high oxygen reduction overpotential, low hydrogen peroxide (H2O2) yield, iron sludge production, and low utilization efficiency of hydroxyl radicals (·OH).To solve the above problems, studies were conducted from two aspects of cathode materials and peroxidation catalyst in this text. Firstly, anthraquinone monosulfonate (AQS)/reduced graphene oxide (RGO) composites were utilized as the MFC cathode to reduce oxygen reduction overpotential and thus improve the ability of H2O2 production. Secondly, an organic metal chelate, iron phthalocyanine (FePc), replaced free ferrous ions (Fe2+) to react with H2O2 to form high-valent active species (O=FeⅣPc), making the catalytic oxidation in the cathode more selective, and simultaneously extending the pH range of catholyte and avoiding iron sludge production. A new type bio-electrocatalyzed hydrogen peroxide oxidation system was constructed by using AQS/RGO as cathode materials and FePc as peroxidation catalyst to degrade a typical azo dye, Congo red (CR). Main content and results are as follows:(1) AQS was noncovalently immobilized onto the basal plane of RGO by π-π stacking interaction via a chemical reduction-adsorption method to form AQS/RGO composites. The adsorption of AQS was in favour of the dispersion of RGO in aqueous solution, and the concentration of AQS on the surface of RGO was estimated to be 1.72×10-12 mol/cm2. Electrochemical tests showed that RGO facilitated the electron transfer between AQS and the surface of carbon electrode when potassium ferricyanide was used as a redox probe. Compared with AQS and RGO, AQS/RGO modified electrode exhibited better electrocatalytic activity towards oxygen reduction reaction in neutral phosphate buffered solution. Rotating disk electrode data demonstrated that the products of oxygen reduction on AQS/RGO modified electrode were mainly H2O2 at the cathodic potential above-1.0 V and H2O below-1.0 V, re spectively. Thus, AQS/RGO composites can be used as efficient electrocatalysts to synthesize H2O2 at low overpotential.(2) The as-prepared AQS/RGO composites were used as the cathode catalyst of MFC to produce H2O2, and simultaneously remove chemical oxygen demand (COD) of wastewater in the anode chamber and output a certain amount of electric energy. Compared with control experiments, the MFC with AQS/RGO modified cathode showed better performance in power output, COD removal and H2O2 production. Its maximum output power density got up to 750.3 mW/m3, and the corresponding COD removal rate in the anode chamber and H2O2 concentration generated in the cathode chamber in one cycle at an external resistance of 1000 Ω were 74.3% and 24.5 mg/L, respectively. The value of external resistance had great influence on the performance of MFC, and operating MFC with a smaller external resistance could improve COD removal and H2O2 production. The MFC with AQS/RGO modified cathode was operated for eight successive cycles at an external resistance of 1000 Ω, and the amounts of H2O2 generated in its cathode chamber were considerably stable.(3) In order to improve the catalytic performance of FePc, FePc/exfoliated graphite (EG) composites were prepared using low-cost EG as supports. The results of scanning electron microscope (SEM) showed that FePc was uniformly dispersed on the surface of EG in the form of nanorods. The catalytic oxidation activities of FePc/EG were tested with CR as the target pollutant in the presence of H2O2. Experimental results showed that FePc/EG-H2O2 system exhibited excellent oxidative activity towards CR degradation and 94.4% CR of 100 uM was removed within 150 min in neutral solution. This outstanding performance could be attributed to the synergistic effect between the hydrophobic FePc nanorods and the hydrophilic EG flakes, which not only improved the adsorption capacity of FePc/EG but also promoted the oxidative degradation of CR. lower pH was beneficial to CR degradation, but higher initial concentration of CR would reduce its decolorization efficiency. Experimental results using fert-butanol as a radical scavenger indicated that the catalytic oxidation process involved the homolytic cleavage of O-O bonds of HOOFe111Pc, forming active O=FeⅣPc and 昈H afterwards. The degradation pathway of CR was revealed by using liquid chromatography-mass spectrometry (LC-MS) analysis technology. Both the azo bonds and the C-C bonds of aromatic cycle of CR were effectively disrupted, and the intermediate products were mainly lower molecular organic acids, such as maleic acid, and malonic acid.(4) A granular bed catalytic oxidation reactor (COR) was constructed with FePc/EG catalyst and then connected with MFC cathode chamber in series to form a new bio-electrocatalyzed hydrogen peroxide oxidation (MFC-COR) system. The MFC-COR system could use glucose-simulated wastewater as the energy source to degrade CR in the cathode chamber. Experimental results manifested that both H2O2 generated at the MFC cathode and residual dissolved oxygen could be utilized as oxidants in the COR reactor for CR degradation. Over 90% of CR (100 μM) was degraded within 72 h in neutral solution, and the degradation products were mainly less toxic and easy biodegradable organics. The open-circuit potential and maximum power density of the MFC reactor were measured as 0.615 V and 808.3 mW/m3, respectively. External resistance and the catholyte pH had great effects on the removal rate of CR. The removal rate of CR decreased by 19.3% after 33 cycles of operation, which was mainly attributed to partial inactivation of the FePc/EG catalyst.
Keywords/Search Tags:Azo Dye, Oxygen Reduction Reaction, Microbial Fuel Cell, CatalyticOxidation, Iron Phthalocyanine
PDF Full Text Request
Related items