Removal Of Bisphenol A From Water By Iron-loaded Zeolite Combined With Advanced Oxidation Technology

Bisphenol A(BPA),a typical endocrine disruptor,is widely used in industries such as building materials,plastics and thermal paper production.BPA is difficult to be degraded in the environment and its toxicity persists,which can pose ecotoxicological risks not only to plants and animals in aquatic and soil environments,but also to human health.The advanced oxidation techniques based on peroxynitrite(PDS)and hydrogen(H2O2)peroxide have become a hot research topic,but their practical use is limited by the narrow pH adaptation range and the large amount of iron sludge generation.Therefore,this method has been widely used to activate PDS and H2O2 systems for the degradation of organic pollutants.However,most of the current studies are limited to the use of a single oxidant,and systematic comparison of the two is rare.Although China ranks first in the amount of zeolite,it is only used in the building materials industry such as cement manufacturing.Compared with its use as adsorbent and catalyst in foreign countries,it should be considered how to make full use of zeolite resources and enhance its social benefits.In this paper,iron-loaded zeolites,labeled Z300,Z500,and Z700,were prepared by hydrothermal calcination at calcination temperatures of 300,500,and 700℃,respectively,and zeolite-loaded nano-zero-valent iron,labeled Z-nZVI,was successfully prepared by liquid-phase reduction,using the above four materials as catalysts for the degradation of BPA in water by activated PDS and H2O2 systems.The effect of each factor on the degradation of BPA was investigated to explore its degradation mechanism under the two systems and to provide data for the application of BPA in advanced oxidation.The main findings of the study are as follows:(1)Four catalysts,Z300,Z500,Z700 and Z-nZVI,were successfully prepared by hydrothermal calcination method and liquid phase reduction method.SEM results showed that the slab aggregation phenomenon became more and more obvious with the increase of calcination temperature for the first three catalysts;the loading of nano zero-valent iron made the surface of zeolite more rounded and clearer at the edges.BET results corresponded to this,the specific surface area of Z500 and Z700 The specific surface area of Z500 and Z700 gradually decreased,while the specific surface area of zero-valent iron nanoparticles loaded with zeolite increased.the results of XRD and XPS analysis revealed that iron was successfully loaded into the zeolite,and the main elements of the catalyst were Si,Fe,C and O.(2)When Z300,Z500,Z700 and Z-nZVI were used as catalysts to activate the PDS system for the degradation reaction of BPA,the BPA in the four systems was degraded to 97.74%,80.20%,71.89%and 80.31%,respectively,after 60 min of reaction when 25℃,pH=7,catalyst dosage of 0.5 g/L,PDS concentration of 1 mmol/L and the initial concentration of BPA was 20 mg/L.The catalysts were used in the four systems to degrade BPA to 97.74%,80.20%,71.89%and 80.31%after 60 min of reaction,respectively.The single-factor effect experiments showed that there were inflection points for both catalyst dosage and PDS concentration,and the reasonable selection of both was very important during the experiments;the four systems maintained good treatment effects in the pH range of 3～7,but the degradation of BPA by the reaction showed a decreasing trend with the increase of pH and the initial concentration of BPA;The materials still had good removal effects after recycling three times,which proved the stability.The free radicals of the PDS system were ranked as follows:1O2>·O2->SO4-·>·OH.The activation of PDS by Fe2+produced strong oxidizing radicals and a series of chain reactions to complete the degradation of BPA.(3)BPA removal experiments were conducted with Z300,Z500,Z700 and Z-nZVI as catalysts and activated H2O2 for the removal of BPA from the systems when 25℃,pH=7,catalyst dosage of 1 g/L,H2O2 concentration of 5 mmol/L and initial BPA concentration of 20 mg/L were used,and BPA in the four systems was degraded after 60 min of reaction to The BPA in the four systems was degraded to 100.00%,93.52%,77.69%and 81.28%after 60 min of reaction,respectively.The single-factor effect experiments showed that there were peaks in the catalyst dosage and H2O2 concentration;the system was more ideal for BPA removal in the pH range of 3～7,but the degradation of BPA decreased with the increase of pH and initial concentration of BPA;The materials were recycled three times and still maintained good BPA removal effect,which proved the good stability of the four materials This proved that the four materials have good stability.The free radical detection experiments on the H2O2 system showed that the degradation mechanism of BPA by the four systems was mainly dominated by·OH.It was found that·OH was mainly generated by the activation of H2O2 by Fe2+successfully loaded on the zeolite.1O2 and·O2-played little role in this system,presumably due to the poor activity and slow generation rate of ·O2-in the reaction.(4)Comparing the activation of PDS and H2O2 systems with four materials,it was found that the H2O2 system used twice as much catalyst dosing and five times more oxidant concentration than PDS for the degradation of BPA at 25℃,pH=7,and an initial concentration of 20 mg/L of BPA,which shows that the oxidation capacity of PDS is stronger than that of H2O2.It was found that the catalyst was more effective because it required less energy to activate PDS,produced more types of radicals and had a longer half-life of SO4-·.The results of single-factor experiments such as common anions showed that the degradation of BPA was less affected by anions in the PDS system,and the pH range of the system was wider.