Application of carbocatalysts in water/wastewaterpractices: removal of endocrine disrupting compound bisphenol a

Environmental contaminant has now major regulatory implications toward theecosystem health. Endocrine disrupting compounds (EDCs) have become a subjectof particular concern to researchers in recent years because they act as hormones andhave an impact on living life, which in turn causes many diseases. EDCs can effectreproductive function in males and females. Increased incidence of breast cancer,abnormal growth patterns and neurodevelopmental delays in children, as well aschanges in immune function. (EDCs) are mostly man-made, found in variousmaterials such as pesticides, additives or contaminants in food, and personal careproducts. These chemicals can interfere with endocrine or hormone systems atcertain doses. Human exposure to these chemicals via ingestion of food, dust andwater, via inhalation of gases and particles in the air, and through the skin. Achievingefficient treatment of highly complex structured EDCs has become important inprotecting terrestrial and aquatic environments from the ecotoxicological effectscaused by these priority pollutants. The list of such xenobiotic compounds is broadlyfor example alkylphenols (AP), phthalates, bisphenol A (BPA),polybromodiphenylethers and natural and synthetic estrogens. Extensive research isunderway to develop appropriate and effective methods for the complete removal ofEDCs, conversion to harmless degradation products, or removal of endocrineactivities. Advanced oxidation processes (AOP) based on the production of reactivefree radicals play a very important role in the removal of many organic pollutantswith different chemical structures, either alone or in combination with classicaltechnologies. In recent years, research has been focused on the removal of difficult,even inert and / or toxic contaminants via the sulfate radical-based AOP.Bisphenol A (BPA, 4,4'-(propane-2,2-diyl) diphenol) is an organic syntheticcompound. Chemical formula (CH ) C(C H OH) belonging to the group of₃ ₂ ₆ ₄ ₂diphenylmethane derivatives and bisphenols, with two hydroxyphenyl groups.Mainly found in polycarbonate plastics and epoxy resins. Polycarbonate plastics areoften used in containers that store food and beverages, compact disk, motorcyclehelmets, medical devices. They may also be used in other consumer goods. Unlike polycarbonate plastics, epoxy resins are used to coat the inside of metal products,such as food cans, bottle tops and water supply lines, some dental sealants andcomposites. Some research shown that BPA has adversly affects the endocrine system, the centralnervous system and can also be transferred from the pregnant woman to thedeveloping fetus or child through the placenta and breast milk. Because of theadverse effect of these chemical numerous validated studies have been conducted to determine what happens to BPA in the environment. Due to the fact that biotreatmentrequires long retention times and cannot degrade BPAs completely, rapid andefficient treatment process including advanced oxidation process (AOPs) havesuccessfully been developed to the efficient treatment of BPAs. Most methods of application are not effective in the treatment of many contaminantssuch as phenols, insecticides, solvents, household chemicals and medicines, whereasdifferent AOPs are recommended when wastewater components have a highchemical stability and/or low biodegradability. AOPs represent a collection ofvarious technologies based on the use of different oxides that can provide the fullmineralization of many organic chemicals (conversion to CO2). AOPs based on theproduction of reactive free radicals (such as hydroxyl, HO and sulfate, SO4-radicals) play a very important role in the treatment of many organic pollutants withdifferent chemical structures, either alone or in combination with conventionaltechnologies. In recent years, research on the removal of difficult-to-treat, even inertand/or toxic pollutants by SO4- -based AOPs has come to the forefront. SO4- candestruct variety of organic contaminants. Genarally, persulfate (PS) andperoxymonosulfate (PMS) can be used to generate SO4- by either homogeneous orheterogeneous activation. To activate PS or PMS we can use homogeneous catalysiswhich applies heat, alkaline, UV or metal ions. Heterogeneous catalysis employssolid materials, such as cobalt or manganese based catalysts to activate the sulfateperoxide salts. Because of the physical and chemical properties nanocarbons such as graphene,fullerene, and carbon nanotubes with fascinating, have availed themselves for metal-free environmental catalysis. Firstly, discovered reduced graphene oxide (rGO) andsurface tuned carbon nanotubes can efficiently activate PMS and PS to generatereactive species for catalytic oxidation of organic pollutants. It was further reportedthat the catalytic performance of the carbocatalysts can be significantly improved. rGO exhibits a capacity to degrade organic pollutants. rGO/oxidant treatmentsystems showed high oxidation capacity due to the high activation capacity of rGOover a wider pH range and leads to generation of HO and SO4- by an electrontransfer mechanism from rGO to oxidant. The presence of an oxidant in the mediumincreases the number of radicals formed, which leads to faster oxidation.In the present study, the performance of reduced graphen oxide (rGO) wasinvestigated as an activator for PS and PMS to degrade Bisphenol A (BPA), one ofthe most common known EDCs, from different aqueous matrices namely distilledwater (DW) and municipal wastewater treatment plant effluent (TWW). Themorphology, textural property and structure of the prepared rGO before theactivation of oxidants were thoroughly characterized by various techniques andradical scavenging experiments were employed in order to deliver an insight into thegeneration and evolution of reactive radicals on the metal-free rGO catalyst.Furthermore, the stability and reusability of the rGO was also questioned within thescope of this experimental study.The effect of oxidant (PS and PMS) and catalyst (rGO) concentrations on BPAdegradation rates in DW and TWW samples was examined. Complete BPAdegradation occurred in DW and TWW with the PS/rGO treatment system after 10 min and 30 min, respectively, whereas 94% (DW) and 83% (TWW) BPA removalswere obtained with PMS/rGO for the same treatment period (BPA=2mg/L;rGO=0.02g/L; PS=0.25mM; PMS=0.5mM). The radical quenching experimentsdemonstrated that the SO4- predominated in the activation of PS and PMS with rGOfor BPA removal, however, HO contributed to the catalytic oxidation process but toa lower extend. The reusability test results, where the catalyst was deactivatedseriously just after second cycle, highlighted the need for further studies to enhancethe stability of rGO. This study represented an environmentally benign and efficientoxidative treatment of BPA along with insights into the rGO activated PS or PMS processes.