Effect of Fe(III)/Citrate Concentrations and Ratio on the Photoproduction of Hydroxyl Radicals: Application on the Degradation of Diphenhydramine

Abstract

Fe(III)-citrate complexes are photoreactive and ubiquitous in natural waters. In this study, the effect of Fe(III)/ citrate concentrations and ratio on the photoproduction of • OH as a function of pH (3−9) was systematically investigated. The • OH formation mechanism was elucidated according to the pH-dependent formation rate of • OH and the speciation distribution analysis of Fe(III) species. At high Fe(III)-to-citrate ratio (10:50), the • OH photoproduction increased with decreasing pH. In contrast, the • OH photoproduction increased in the order of pH 9.0 < 3.0 < 7.0 < 6.0 < 5.0 at low Fe(III)-to-citrate ratios (10:100−10:300). At identical Fe(III)-to-citrate ratio (1:10), high concentration of Fe(III)-citrate complexes rendered a downward trend for • OH production with increasing pH. FeOHcit − is the predominant reactive species responsible for the • OH formation at high pH. The optimal pH for • OH production was governed by the amount of O 2• − and the stability of Fe(II) species in the Fe(III)-cit solution. The Fe(III)-cit-induced photodegradation of diphenhydramine verified the pH-dependent trend for • OH production. By GC-MS and LC-ESI-MS analyses, the photoproducts of diphenhydramine were identified and the degradation pathway was proposed.

Identification of position isomers by energy‐resolved mass spectrometry

“…A similar product was also observed by Feng et al . during their end‐product studies . To explain the identity of this compound, the authors propose a C 10 ‐hydroxyl substituted DPH analogue with the help of limited MS/MS studies.…”

“…This fragment ion allows the assignment of compound D as either the C 10 (an identical structure proposed by Feng et al . ) or C 12 /C 13 hydroxylated derivative of DPH. This assignment is based on the observed instability of the N ‐hydroxymethyl intermediate which leads to a diphenylmethylium ion ( m / z 167) by benzylic dissociation of the precursor ion [ D + H] + (Scheme ).…”

“…In this report, we present an ERMS‐based strategy for the rapid characterization of position isomers derived from the reaction of ● OH with diphenhydramine (DPH), a first‐generation antihistamine and a potential candidate from the group of so‐called ‘emerging organic contaminants’. Destruction of this compound by various AOPs is thoroughly experimented . Very recently, Feng et al .…”

Selecting the best AOP for isoxazolyl penicillins degradation as a function of water characteristics: Effects of pH, chemical nature of additives and pollutant concentration

“…On the contrary, a remarkable enhancement (~80%) was observed when OA was in an equimolar concentration with the substrate. This improvement can be mainly attributed to the formation of two iron-oxalate complexes: (6)) (Feng et al, 2012;Pignatello et al, 2006).…”

Activation of Hydrogen Peroxide by Activated Carbon Fibers Coupled with Fe(Ⅲ)-Citrate for Degradation of Dyes at Neutral pH

“…在这些配体中, EDTA 尽管与铁配位具有较好的稳定性, 但因其可生物 降解性差而受到限制 [9] ; 柠檬酸不仅是一种天然的化合 物, 具有无毒、可生物降解等特性, 而且与铁离子形成 配合物的累积稳定常数(lg β＝12.5)明显高于草酸铁(lg β ＝9.4)和琥珀酸铁(lg β＝7.49) [10] , 这说明柠檬酸铁在催 化过程中具有较好的化学稳定性. 因此, 近年来柠檬酸 铁在类芬顿催化领域特别备受关注 [11,12] . 但是, 柠檬酸 铁在均相反应中往往伴随着不可避免的配体自分解过 程, 这一缺陷不仅使得柠檬酸铁的催化活性逐渐降低, 而且进一步会导致大量氢氧化铁沉淀的产生, 从而带来 二次污染.…”