Reductive degradation of chlorinated organophosphate esters by nanoscale zerovalent iron/cetyltrimethylammonium bromide composites: Reactivity, mechanism and new pathways. (1st January 2021)

• Record Type: Journal Article
• Authors: Li, Dan; Zhong, Yin; Zhu, Xifen; Wang, Heli; Yang, Weiqiang; Deng, Yirong; Huang, Weilin; Peng, Ping'an
• Is Part Of: Water research. Volume 188(2021)
• Publication Date: 2021-01-01
• Subjects: TCEP -- S-nZVI/CTAB -- O, O-di-(2-chloroethyl)O-ethyl phosphate -- ethane -- hydrophobic adsorption; Water -- Pollution -- Research -- Periodicals; 363.7394
• DOI: 10.1016/j.watres.2020.116447
• Languages: English
• ISSNs: 0043-1354

Abstract

Highlights: The degradation rate of Cl-OPEs is in the decreasing order of TDCPP > TCPP > TCEP. The reactivity of S-nZVI or nZVI towards Cl-OPEs is enhanced by CTAB. CTAB enhances the hydrophobic attraction between Cl-OPEs and particle surfaces. The S-nZVI/CTAB composite exhibits a better performance than nZVI/CTAB composite. DCEEP and C2 H6 are reported as degradation products of TCEP for the first time. Abstract: Chlorinated organophosphate esters (Cl-OPEs), e.g., tris(2-chloroethyl) phosphate (TCEP), tris(2-chloro-2-propyl) phosphate (TCPP) and tris(1, 3-dichloro-2-propyl) phosphate (TDCPP), are widely used as additive flame retardants in commercial and building products. They have potential persistent organic pollutant properties and are frequently detected in various waters, especially in wastewaters. Nanoscale zerovalent iron (nZVI)-based method is an efficient reductive technology for treating waters polluted by halogenated organic pollutants (HOCs). Cetyltrimethylammonium bromide (CTAB) is a ubiquitous surfactant in wastewaters and can favorably affect the interaction between HOCs and nZVI. However, its effect on the Cl-OPEs removal by nZVI-based materials still remains unknown. Herein, the adsorption and degradation efficiencies of Cl-OPEs by nZVI and sulfidated nZVI (S-nZVI) in the presence or absence of CTAB were quantified based on the decreasing concentrations of Cl-OPEs in reaction systems. Our results showed that TDCPP and TCPP were adsorbed onto the nZVI or S-nZVI surface and subsequently degraded. In contrast, TCEP was just adsorbed onto the particle surface without further degradation. The addition of CTAB significantly enhanced the hydrophobic adsorption between Cl-OPEs and nZVI or S-nZVI, leading to increased degradation of Cl-OPEs (especially TCEP). CTAB adsorption isotherms indicated that S-nZVI had a higher adsorption capacity for CTAB than nZVI. The S-nZVI/CTAB composite exhibited a better performance than nZVI/CTAB composite. When S-nZVI was combined with 100.0 mg L −1 CTAB, 100% of TDCPP, TCPP and TCEP was degraded within 3 hours, 5 and 14 days, respectively. As the concentration of CTAB was increased up to 335.0 mg L −1, TCEP could be completely degraded within 3 days by S-nZVI. Five degradation products of TCEP were identified, of which O, O-di-(2-chloroethyl) O-ethyl phosphate (DCEEP) and ethane were reported for the first time. We propose that TCEP is dechlorinated by nZVI or S-nZVI through the electron attack at the ethyl-chlorine group to form bis(2-chloroethyl) phosphate, DCEEP, chloride, ethene and ethane, representing previously unknown degradation pathways. Graphical abstract: Image, graphical abstract