Degradation efficiencies of 2,4,6-TCP by Fe0-based advanced oxidation processes (AOPs) with common peroxides

Degradation of 2,4,6-trichlorophenol (2,4,6-TCP) by zero-valent iron (ZVI) activating three common peroxides (peroxymonosulfate (PMS), hydrogen peroxide (H2O2), and peroxydisulfate (PS)) was investigated. The effects of ZVI dosage, peroxides concentration, initial pH, and Cl- concentration were examined. The 2,4,6-TCP degradation efficiencies by Fe0/peroxides (PMS, H2O2, PS) were compared. Results showed that the order for degradation efficiency was H2O2≥PMS>PS. The degradation efficiency of 2,4,6-TCP in ZVI/peroxides systems were optimal at c(Ox) = 1 mmol•L-1; c(Fe0) = 0.1 g/L; initial pH = 3.2. Additionally, pH had a vital effect on 2,4,6-TCP degradation. At pH<3.2, ferrous play a vital role in all reaction, and accelerate the reaction rate rapidly. The existence of NaCl showed different results in the four systems. Chloride had little effect on 2,4,6-TCP degradation when chloride concentration at 5 mM, whereas the presence of 300 mM chloride significantly accelerated the degradation of 2,4,6-TCP from 72.7% to 95.2% in ZVI-PMS system. Notably, the other three systems showed opposite results. In contrast, the AOX (Absorbable Organic Halogen) values were highest in ZVI-PMS-Cl- system, due to the formation of lots of refractory chlorinated phenols as identified by GC-MS. These findings are good for choosing the most suitable technology for chlorophenol wastewater treatment.

Halogen Derivatives in Pyrolyzed Plastics

The article deals with the issue of waste plastics pyrolysis leading to the industrially applicable liquid and gaseous products. The problem of thermally labile halogenated compounds, present in the feedstock, is discussed. The introductory part focuses mainly on halogenated flame retardants and their toxicological and environmental risks. In comparison with the standard recycling of waste plastics, pyrolysis with subsequent material utilization of the liquid product is mentioned as a promising method capable to solve the problem with the presence of halogen derivatives. The following second part of the article summarizes studies searching suitable methods for removing inorganically and organically bound chlorine and bromine from pyrolysis organic condensates - i.e. pyrolysis oils. Dehalogenation processes are divided into several categories according to the nature of the process and also according to the method of application of the respective reagent, catalyst or sorbent. Within each group, the results published in the available literature are briefly summarized. When commenting on them, the main emphasis is placed on the applicability of the obtained pyrolysis oils as raw materials for refinery processing and new polymers production. At the end of the article, a plan of experiments is outlined, which will be carried out during the research of the issue by the authors team. The space is mainly dedicated to the construction of two laboratory apparatuses that has been developed for this purpose.The first batch apparatus working with a vertical retort allows studying of gaseous, liquid and solid pyrolysis products at various temperatures. The second, continuously operating apparatus, is designed to test the efficiency of hydrogen halides adsorption from gaseous mix-tures at high temperatures. The third apparatus designed for the research purposes is a catalytic continuous system enabling to study the decomposition of organic halogen derivatives. The results of the experiments will be published continuously after their verification with sufficient reproducibility.

Chloramination of iopamidol- and bromide-spiked waters containing natural organic matter

Iopamidol (an iodinated x-ray contrast media) and bromide are precursors in the formation of halogenated disinfection byproducts (DBPs). The interactions of these precursors are vital to elucidate the formation of halogenated DBPs during chloramination. This work investigated the formation of total organic halogen and select individual DBPs in two laboratory-chloraminated source waters (SWs) containing iopamidol and bromide. Experiments were carried out in batch reactors containing Barberton SW (BSW) and Cleveland SW (CSW), spiked with iopamidol (5 μM), bromide (15 μM), and 100 μM monochloramine. Total organic iodine concentrations were approximately equal regardless of SW since they are mostly unreacted iopamidol and iopamidol DBPs. Almost equal amount of total organic chlorine (3–4 nM) was produced in the SWs but higher quantities of total organic bromine were formed in BSW than CSW. Substantial quantities of regulated trihalomethanes (THMs) and haloacetic acids (HAAs) were formed in the SWs, along with appreciable concentrations of iodinated trihalomethanes (CHBrClI, CHCl2I, and CHBr2I). Low concentrations of iodo-HAAs were detected, especially at low pH. Overall, bromide concentrations appeared to suppress iodo-DBP formation during chloramination of iopamidol in the presence of natural organic matter. A good correlation (R2 = 0.801) between the yields of regulated DBPs and iodo-DBPs was observed.

Cobaloximes as Building Blocks in Halogen-Bonded Cocrystals

In this work, we explore the halogen-bonded cocrystallization potential of cobaloxime complexes in the synthesis of cocrystals with perhalogenated benzenes. We demonstrate a strategy for synthesizing halogen-bonded metal–organic cocrystals by utilizing cobaloximes whose pendant bromide group and oxime oxygen enable halogen bonding. By combining three well-known halogen bond donor molecules differing in binding geometry and composition with three cobaloxime units, we obtained a total of four previously unreported cocrystals. Single crystal X-ray diffraction experiments showed that the majority of obtained cocrystals exhibited the formation of the targeted I···O and I···Br motives. These results illustrate the potential of cobaloximes as halogen bond acceptors and indicate that this type of halogen bond acceptors may offer a novel route to metal–organic halogen-bonded cocrystals.