Degradation Of Dye Rhodamine B In Aqueous Solution By Homogeneous Catalyst Co²⁺ And Heterogeneous Catalyst SBA-15Supported Co And Fe With Oxone

Sulfate radical-based advanced oxidation technologies are attractingconsiderable attention due to the high oxidizing ability of sulfate radicals.Homogeneous and heterogeneous Co（Ⅱ）-oxone systems were investigated fordegradation of refractory dye Rhodamine B （RhB） in aqueous solution.For homogeneous Co（Ⅱ）-oxone system, the degradation of RhB wasinvestigated by using Co²⁺as catalyst for activation oxone to generate sulfateradicals attacking the RhB molecules. The optimum operation conditions wereselected by orthogonal design test and the effects of Co²⁺concentration, oxonedosage and reactants concentration on the degradation rate and efficiency of RhBwere investigated with the RhB degradation kinetics and mechanism explored. In thecase of heterogeneous Co（Ⅱ）-oxone system, the RhB degradation was studied usingthe prepared Co/SBA-15or CoFe/SBA-15as catalyst for activation oxone. A powdercatalyst Co/SBA-15was first synthesized through an incipient wetness impregnationtechnique using SBA-15as the support, Co（NO₃）₂·6H₂O as the precursor. The effectsof Co/SBA-15dosage, oxone dosage and reactants concentration on the degradationrate and efficiency of RhB were investigated with the kinetics of RhB degradationestablished. The Co/SBA-15recycle was also studied and the degradation pathwayof RhB was proposed with UV-vis spectrophotometry. A powder catalystCoFe/SBA-15was prepared through an incipient wetness impregnation techniqueusing SBA-15as the support, Co（NO₃）₂·6H₂O and Fe（NO₃）₃·9H₂O as the precursor.The samples synthesized were characterized by X-ray diffraction （XRD）, N₂adsorption-desorption, vibrating sample magnetometer （VSM） and scanning electronmicroscopy （SEM） techniques. The effects of Co and Fe loading and calcinationtemperature on the performance of the CoFe/SBA-15catalyst and the CoFe/SBA-15recycle were investigated. The effects of CoFe/SBA-15dosage, oxone dosage andreactants concentration on the degradation rate and efficiency of RhB and the degradation pathway were also investigated with the kinetics of RhB degradationestablished. A powder Fe/SBA-15catalyst for the activation of oxone and thesubsequent degradation of RhB was also prepared through an incipient wetnessimpregnation technique using SBA-15as the support, Fe（NO₃）₃·9H₂O as theprecursor. The samples synthesized were characterized by XRD, N₂adsorption-desorption and SEM. Effects of Fe/SBA-15dosage, oxone dosage, initialRhB concentration and reaction temperature on the degradation rate and efficiencyof RhB were investigated with the kinetics of RhB degradation established and thedegradation pathway proposed.The results show that the optimum operation conditions for Co²⁺-oxone-RhBsystem are Co²⁺concentration at400μg/L, the molar ratio of oxone to RhB at30:1and the initial RhB concentration at10mg/L, under which99%RhB degradationefficiency was achieved. The degradation rate and efficiency of RhB were increasedwith increasing of Co²⁺concentration, oxone dosage and reaction temperature. Thedegradation efficiency of RhB did not change obviously with increasing of reactantsconcentration, but the degradation rate did decrease. The RhB degradation followedthe first-order kinetics and the dominant radicals were identified as SO₄^·－. InCo/SBA-15-oxone-RhB system, the increase of Co/SBA-15and oxone dosages andthe decrease of reactants concentration had the positive effect on the RhBdegradation efficiency and rate. A tea bag-like catalyst prepared using thehydrophilic polytetrafluoroethylene （PTFE） membranes facilitated the recycle of thepowdered catalysts. During16runs of recycling tests, the catalyst always maintainedhigh catalytic activity with the RhB removal more than85%in2hours and Coleaching less than61μg/L. The magnetization of CoFe/SBA-15was measured to be8.3emu/g and CoFe2O4was the predominant species present both inside and outsidethe support. The CoFe/SBA-15with10wt%Co loading and9.5wt%Fe loading bythe calcination at700°C had the best performance. The adsorption isotherm of RhBonto CoFe/SBA-15matched Freundlich model well. In CoFe/SBA-15-oxone-RhB system, the increase of CoFe/SBA-15and oxone dosages and the decrease ofreactants concentration had the positive effect on the RhB degradation rate and thedegradation followed the first-order kinetics. During10runs of recycling tests, thecatalyst always maintained high catalytic activity with the RhB removal more than84%in2hours and Co leaching less than73μg/L. As to Fe/SBA-15, α-Fe₂O₃wasidentified to be the main oxide present both inside and outside the support. Theadsorption of RhB on Fe/SBA-15agreed well with the Langmuir adsorption modelwith maximum adsorption capacity of125mg/g. In Fe/SBA-15-oxone-RhB system,the increase of Fe/SBA-15and oxone dosages and the decrease of initial RhBconcentration had the positive effect on the RhB degradation rate, and thedegradation followed the first-order kinetics. Interestingly, the primary radicals inthe Fe/SBA-15-oxone-RhB system were identified as OH·instead of SO₄^·－, whichmay be responsible for the much lower RhB degradation rate than that forCo/SBA-15-oxone-RhB system. Moreover, higher reaction temperature canaccelerate the RhB degradation and the apparent activation energy was calculated tobe28.86KJ/mol. And the Fe/SBA-15catalyst always kept high activity during5runs with Fe leaching of less than0.17mg/L. Fe/SBA-15has the advantage ofavoiding the hazards from the Co leaching over Co supported heterogeneous catalystand a bright prospect for practical application.