Spremljanje produktov elektrokemijske razgradnje benzotriazola

Korenčič, Eva (author), Prosen, Helena (mentor)

Benzotriazoli predstavljajo eno izmed skupin novih onesnaževal. Polarne spojine iz te skupine zaradi protikorozivnih lastnosti uporabljamo kot dodatke k različnim industrijskim tekočinam, pa tudi k detergentom za strojno pomivanje posode, ki jih uporabljamo v gospodinjstvu. Njihov glavni vir vnosa v okolje je odpadna voda iz čistilnih naprav, kjer se nepopolno odstranijo. Relativno stabilni so tudi v okolju, ker pa so vodotopni, nazadnje pritečejo iz naših pip. V okolju se nahajajo v koncentracijah reda velikosti od ng/L do μg/L. Toksični so predvsem za vodne organizme, predstavljajo pa tudi potencialne karcinogene spojine za človeka. Razvijanje terciarnih metod za njihovo odstranjevanje je zato zelo pomembno. Ena od metod za obdelavo odpadnih vod je elektrooksidacija (EO), ki pa je za razliko od te študije v literaturi preizkušena predvsem v kombinaciji z drugimi tehnikami. Spremljala sem razgradnjo 1H-benzotriazola (BTA) v vzorcih sintetičnih odpadnih vod z EO. Pomemben del priprave tovrstnih vzorcev je ekstrakcija na trdno fazo (SPE), ki sem jo tudi sama uporabljala. Prav zato sem raziskala tudi, kako na izkoristek ekstrakcije BTA iz vzorcev vplivajo različni parametri. pH sam po sebi ni vplival na izkoristek ekstrakcije, vendar pa so se razlike med izkoristki ekstrakcij pri različnih pH vrednostih pokazale ob prisotnosti pomožnih elektrolitov. Preizkusili smo štiri različne elektrolite: NaCl, H2SO4, Na2SO4 in Na2CO3. Vrsta pomožnega elektrolita je pomembno vplivala na izkoristek ekstrakcije, ki je segal od 59 % pri Na2SO4 do 86 % pri Na2CO3. Ugotovila sem še, da se izkoristki ekstrakcij znatno znižajo pri koncentracijah BTA, višjih od 20 mg/L. Pri monitoringu razgradnje BTA sem opazovala vpliv anodnega materiala, pomožnega elektrolita in gostote toka na EO ter primerjala hitrost razgradnje pri visokih in nizkih koncentracijah BTA. Razgradnja je bila hitrejša pri višjih gostotah toka in nižjih koncentracijah BTA. Med anodnimi materiali smo preizkusili elektrodo iz mešanih kovinskih oksidov (MMO) in iz z borom dopiranega diamanta (BDD), pri čemer je bila razgradnja z BDD anodo hitrejša in je povzročila manj pretvorbenih produktov. Razgradnje so bile pri vseh pomožnih elektrolitih psevdo prvega reda. Produkte razgradnje sem spremljala z LC-MS/MS in jih opazila pri uporabi NaCl, ki je povzročil nastanek toksičnih kloriranih organskih spojin, ter H2SO4, ki je povzročila nastanek različnih hidroksiliranih benzotriazolov. Razgradnja je bila najhitrejša z uporabo H2SO4 – po 2,5 h se je od približno 1 mM začetne koncentracije razgradilo 97 % BTA.

• Language: Slovenian
• Keywords: benzotriazol, elektrooksidacija, ekstrakcija na trdno fazo, produkti razgradnje, odpadne vode
• Work type: Master's thesis/paper
• Typology: 2.09 - Master's Thesis
• Organization: FKKT - Faculty of Chemistry and Chemical Technology
• Year: 2021
• PID: 20.500.12556/RUL-128186
• COBISS.SI-ID: 71719683
• Publication date in RUL: 05.07.2021

Secondary language

• Language: English
• Title: Monitoring of products of electrochemical degradation of benzotriazole

Abstract

Benzotriazoles are a group of emerging organic pollutants. Due to their anticorrosive properties, the polar ones are used as additives in various industrial liquids, as well as in dishwashing detergents that we use in our households. Their main source of entry into the environment is wastewater from wastewater treatment plants, where they are insufficiently removed. They are also relatively stable in the environment and in the end, due to their water solubility, travel to our faucets. In the environment, they are found in concentrations ranging from ng/L to μg/L. They are toxic for aquatic organisms but are also suspected human carcinogens. Development of tertiary methods for their removal is hence of great importance. One of the methods of wastewater treatment is electrooxidation (EO) which is, in contrast to the present study, mainly tested in combination with other techniques. I monitored the degradation of 1H-benzotriazole (BTA) in synthetic wastewater samples with EO. An important part of analysis is sample preparation by solid-phase extraction (SPE) which I also used within my work. Hence, I also researched the influence of different parameters on BTA recovery via SPE. pH value of samples did not directly influence the recoveries, however, differences among recoveries at different pH values arose when supporting electrolytes were present. We tested four different electrolytes: NaCl, H2SO4, Na2SO4 and Na2CO3. The type of electrolyte had a great influence on SPE recoveries which ranged from 59% with Na2SO4 to 86% with Na2CO3. I also found that SPE recoveries lowered notably at BTA concentrations higher than 20 mg/L. During BTA degradation monitoring, I observed the influence of anodic material, supporting electrolyte and current density on EO and compared the rate of degradation at high and low BTA concentrations. The rate of degradation was higher at higher current densities and lower BTA concentrations. Among anodic materials we tested mixed metal oxide (MMO) and boron-doped diamond (BDD) electrodes and found that the rate of degradation was higher and accompanied by fewer transformation products at BDD electrode. Degradations with all tested electrolytes gave pseudo-first order kinetics. Transformation products were monitored by LC-MS/MS and were noticed mainly with the use of NaCl, which caused the emergence of toxic chlorinated organic compounds, and with the use of H2SO4, which caused the emergence of various hydroxylated benzotriazoles. The degradation rate was the highest when H2SO4 was used – after 2.5 h, 97% BTA was degraded from approximately 1 mM initial concentration.

• Keywords: benzotriazole, electrooxidation, solid-phase extraction, products of degradation, wastewater