| Bisphenol A (BPA) is an extensively used chemical commonly found in a wide variety of consumer products, including polycarbonate plastics and epoxy resins. Due to the ubiquity of BPA and its endocrine-disrupting properties associated with various adverse health effects, the exploration of BPA elimination methods has been greatly inspired. The low cost, abundance, and environmentally friendly nature make environmental minerals as catalysts in advanced oxidation processes (AOPs) highly prospective. In the present study, the feasibility of using tourmaline as a heterogeneous Fenton-like catalyst was explored in view of the effects of operational parameters on the BPA degradation and the catalytic mechanism proposed. Furthermore, tourmaline-supported TiO2as catalysts were prepared and their photocatalytic performance and mechanism towards BPA degradation in aqueous solution were evaluated and speculated, respectively. Several conclusions were obtained as follows:(1) Tourmaline was utilized as a heterogeneous catalyst for the oxidation of BPA with synergetic H2O2-catalytic ability and ultrasonic irradiation. A higher tourmaline dose, an appropriate H2O2concentration and a lower pH favored BPA degradation. Concomitant with complete BPA removal, approximately84%of total organic carbon (TOC) was mineralized after5h reaction under the following optimized reaction conditions:sonication (40kHz,500W), tourmaline loading5.0g L-1, H2O250mM and pH2.0. This high BPA removal was attributed to the synergistic function of heterogeneous and homogeneous catalysis, based on the data of iron leaching and H2O2conversion at different pHs. A retarded first-order kinetic model was employed to describe BPA degradation.(2) BPA removal using ultrasonic combined with tourmaline-catalyzed Fenton-like oxidation was mainly caused by the attack of hydroxyl radicals. In view of the X-ray photoelectron spectroscopy (XPS) results during the reaction, a possible mechanism involving accelerated transfer in the Fe(III)/Fe(II) cycle on the tourmaline surface was proposed. Moreover, eight intermediates were observed by GC-MS and LC-MS/MS, and a possible reaction scheme of BPA degradation involving oxidative skeletal rearrangement, hydroxylation, demethylation and dehydration was also proposed.(3) Tourmaline/TiO2catalysts were prepared with different contents of tourmaline as the TiO2supports through a sol-gel method, and were characterized using SEM, XRD and N2adsorption/desorption analyses. The results indicated the synthesized catalysts were coated tightly with small TiO2nanoparticles or aggregates which exhibited all the characteristic reflections of anatase phase, and no rutile phase existed in all samples. The crystallite sizes of TiO2were estimated to be about8-12nm by applying the Scherrer equation. The prepared catalysts had pronounced mesoporosity of narrow pore size distribution mainly centered in the range of2-6nm. In general, the addition of tourmaline led to reduced specific surface areas, pore volumes and pore diameters.(4) The optimum photocatalyst was observed to be that containing20wt.%of tourmaline as the TiO2support—T(20%)-TiO2catalyst, which exhibited much higher removal rate (100%) than pure TiO2(78.9%) and the mixture of TiO2and tourmaline with the same mass ratio in T(20%)-TiO2catalyst (88.2%) towards BPA degradation after UV irradiation time of2h.(5) Neutral, slightly alkaline and strong acidic media favored BPA removal. HCO3-stimulated BPA degradation to some extent, while Cl-slightly inhibited it, as well as K+, Na+, possibly resulting from the effect of Cl-coexisting. SO42-, NO3-, Ca2+, Mg2+exhibited a negligible influence, and the photocatalytic activity was impeded with addition of Cu2+and humic acid. Due to the competitive absorbance of light with catalyst and photoinduced production of·OH, Fe3+and H2O2showed complicated effects on BPA degradation depending on their concentration.(6) BPA degradation was dominated by the·OH oxidation, and a high mineralization of BPA was achieved. The enhanced photocatalytic activity due to the introduction of tourmaline was related to the effective seperation of electron-hole pairs resulting from its strong electrostatic field. |
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