Enhanced Direct Photolysis of Organic Micropollutants by Far-UVC Light at 222 nm from KrCl* Excilamps

Abstract

Krypton chloride (KrCl*) excilamps emitting at far-UVC 222 nm represent a promising technology for microbial disinfection and advanced oxidation of organic micropollutants (OMPs) in water treatment. However, direct photolysis rates and photochemical properties at 222 nm are largely unknown for common OMPs. In this study, we evaluated photolysis for 46 OMPs by a KrCl* excilamp and compared it with a low-pressure mercury UV lamp. Generally, OMP photolysis was greatly enhanced at 222 nm with fluence rate-normalized rate constants of 0.2–21.6 cm2·μEinstein–1, regardless of whether they feature higher or lower absorbance at 222 nm than at 254 nm. The photolysis rate constants and quantum yields were 10–100 and 1.1–47 times higher, respectively, than those at 254 nm for most OMPs. The enhanced photolysis at 222 nm was mainly caused by strong light absorbance for non-nitrogenous, aniline-like, and triazine OMPs, while notably higher quantum yield (4–47 times of that at 254 nm) occurred for nitrogenous OMPs. At 222 nm, humic acid can inhibit OMP photolysis by light screening and potentially by quenching intermediates, while nitrate/nitrite may contribute more than others to screen light. Overall, KrCl* excilamps are promising in achieving effective OMP photolysis and merit further research.

Far-UVC Photolysis of Peroxydisulfate for Micropollutant Degradation in Water

“…Radical production rate ( k ) by UV photolysis of PDS can be described by eq , where Φ inn is the innate quantum yield of PDS photolysis and E PDS is UV light absorbed by PDS (see details of E PDS calculation in Text S7). k = Φ inn E PDS …”

“…As shown in Figure , k predicted / E 0 of 16 micropollutants by the UV 222 /PDS AOP range from 8.68 × 10 –3 to 4.79 × 10 –2 cm 2 mJ –1 (corresponding to a degradation percentage of 37.62–92.60%) in surface water at an initial PDS dosage of 100 μM and a UV fluence of 54.4 mJ cm –2 . For micropollutants that have high molar absorption coefficients (ε > 8000 M –1 cm –1 ) and/or quantum yield (Φ > 0.3 mol Einstein –1 ), including diclofenac, naproxen, clofibric acid, atrazine, sulfamethoxazole, sulfadiazine, ciprofloxacine, and ibuprofen, >20% of their degradation is contributed by direct UV 222 photolysis (Figure ). Micropollutants including atenolol, carbamazepine, caffeine, phenol, N , N -diethyl-meta-toluamide, bisphenol A, aniline, and sulfadimethoxine are predominantly degraded by radicals (HO • , SO 4 •– , and Cl • ) generated in the UV 222 /PDS AOP (Figure ).…”

“…The incident fluence-based rate constants ( k predicted / E 0 ) of 16 micropollutants by the UV 222 /PDS AOP in real surface water are predicted and compared with the UV 254 /PDS AOP. These micropollutants were selected because 1) they have higher risk potential compared to other micropollutants; and 2) the molar absorption coefficients and quantum yields of these micropollutants at 222 and 254 nm (Table S8), as well as the second-order rate constants of these micropollutants toward radicals (HO • , Cl • , and SO 4 •– ) and PDS are available in the literature for calculation and prediction (Table S9). The contributions of direct UV photolysis, PDS oxidation, and radical attack are calculated accordingly, with calculation details and results shown in Text S13 and Table S10, respectively.…”

“…Excimer lamps (e.g., krypton chloride) emitting Far-UVC light at a peak emission wavelength at around 222 nm (UV 222 ) have emerged as promising alternatives to UV 254 for driving UV-AOPs. , Oxidant precursors (e.g., H 2 O 2 , chlorine, and nitrate) have been reported to have much higher molar absorption coefficients or quantum yields at 222 nm than 254 nm, and give higher radical yields in the UV 222 -driven AOPs than the UV 254 -driven AOPs. PDS also has a 8.8-time higher molar absorption coefficient at 222 nm (146.9 M –1 cm –1 ) than at 254 nm (16.6 M –1 cm –1 ). , The quantum yield of PDS at 222 nm might also be higher than 254 nm because the photon energy at 222 nm (539 kJ einstein –1 ) is 1.14 times higher than at 254 nm (471 kJ einstein –1 ). , Thus, we hypothesized that the radical yields would be higher in the UV 222 /PDS AOP than the UV 254 /PDS AOP. Several studies have reported the degradation of few contaminants (two dyes, thiocyanate, bisphenol A, atrazine, and ceftriaxone) in deionized water by AOPs that involve the use of UV 222 and PDS. − Some showed enhanced performance of the UV/PDS AOP by switching the wavelength from 254 to 222 nm. , However, the performance enhancement was not explained because the fundamentals, the radical yields, that lead to the enhancement were not explored.…”

Accelerated mineralization of textile wastewater under 222 nm irradiation from Kr/Cl2 excilamp: an environmentally friendly and energy efficient approach

“…Li et al 26 examine the efficiency of Kr/Cl 2 excilamp for the disinfection of waterborne pathogens. Kr/Cl 2 excilamp developed by them provides an intensity of 0.03-0.3 mW/cm 2 by utilizing the power from 15 to 60 W. Xu et al 8 reported the degradation of 46 organic micropollutants under direct photolysis by Kr/Cl 2 excilamps and concluded that nitrate/nitrites present in the water matrix improves the degradation of non-nitrogenous, aniline and trizine OMP, while higher quantum yield occurs for nitrogenous OMPs. So, the degradation of different organic pollutant depends upon the molar absorption coefficients and the quantum yield at the wavelength used.…”