Degradation Of Tetrabromobisphenol A By Granular Sponge Iron/silver Bimetallic Particles Under The Ultrasound Irradiation

Tetrabromobisphenol A (TBBPA) is widely used as flame retardant in numerousproducts such as electrical apparatus, electronic product, Plasties, textiles, transportationpackaging，construction materials and other fire prevention materials. They inevitablycontaminate the environment and TBBPA has been frequently detected in variousenvironmental matrices, including atmosphere、water and soil. With the increasing of TBBPAin the environment, the research of removal technology of TBBPA has become increasinglyimportant. In this study, we investigated the reductive degradation of TBBPA using granularsponge iron/silver (SPI/Ag) bimetallic particles under ultrasonic radiation (US) with the hopeof providing some meaningful advices for the real engineering application.Using scanning electron microscope (SEM)，X-ray diffraction (XRD), X-ray-photo-electron spectrograph (XPS) to observe the specific surface area, morphology, particle shape,crystal structure and surface elemental composition.The characterization results revealed thatthe displacement plating produced a non-uniform overlayer of Ag additive on iron; XRDpatterns of the SPI/Ag bimetallic particles indicate that Fe is crystalline. XPS results indicatethat the particles surface have been oxided at a certain extent in the preparation or cleaningprocess.Batch experiments demonstrated that under ultrasonic radiation (US) the SPI/Agbimetallic particles could effectively debrominate TBBPA with the debromination efficiencyreached92%in120min. It indicated that both the deposition of Ag and US played importantrole in the reduction of TBBPA.The degradations of TBBPA by SPI/Ag and sponge iron (SPI)followed pseudo-first-order kinetics equations. The reaction rate constant (K) of thedegradation TBBPA by SPI/Ag was0.0193min-1which is about six times higher than thatof by granular sponge iron (SPI).The effects of Ag loading, SPI/Ag dosage, initial solution pH,and TBBPA concentration on degradation efficiency were studied. The results showed that ahigher dosage of SPI/Ag, a lower initial concentration of solution, and slightly acidicconditions were beneficial to the catalytic debromination of TBBPA.Reaction conditions weredetermined selectively as Ag loading of3%, metal addition of30g/L, initial TBBPAconcentration of2mg/L, pH=6.0±0.5, T=30℃.Study on the debromination kinetics showed that the degradation of TBBPA fit thepseudo-first-order reactions. with increasing of SPI/Ag dosage, the degradation rates increase.As the initial TBBPA concentration increased, the kobsdecreased, suggesting saturation ofSPI/Ag bimetallic particles surface reactive sites. correlation between the pseudo-first-orderrate constant (kobs) and Ag loading showed that the rate constants were up to0.0212, when Ag loading ranged from0.5%to3%, whereas as the Ag loading increased, the kobsreached0.014at10%Ag loading, indicating that excessive Ag deposition decreased the SPI/Ag bimetallicparticle reaction rate. Like the relationship between the reaction rate constant(kobs) and pH,the optimal pH value for TBBPA degradation using SPI/Ag bimetallic particles was6.0(0.341min-1, R2=0.998). Moreover, major reduction products of TBBPA was identified byLC-MS/MS. TBBPA was transformed to tri-BBPA，di-BBPA，mono-BBPA and BPA.Thedegradation possibly proceeds through stepwise debromination from n-bromo-to (n-l)-bromo-BPA, with bromine being sequentially substituted by hydrogen.In addition, luminescent bacteria test showed that the acute toxicity of the SPI/Agreduction treated solution was evidently lower than that of original solution (before reduction).In degradation process，the trend of the acute bio-toxicity for the reaction solutions wasdecreased at fist, subsequently increased, and then decresed untill the reaction end. At the endof reaction, the acute bio-toxicity was much lower than the begining.