Na2b4o7 10h2o

Actinometry using KI/KIO₃ was performed to measure the fluence delivered by the UVC-LED reactor to the water. The protocol was adapted from [88 (link),89 (link),90 (link),91 (link)] and is shown in greater detail in the Supplementary Materials [68 (link)]. A similar but simpler, laboratory-scale skid was set up to perform actinometry experiments; details are given in the supplemental information Figure S3 and Table S3 [68 (link)]. The setup used consisted of a water bath, a pump, a flowmeter, a pressure sensor and a needle valve. To perform the actinometry experiments, a 0.6 M KI (Merck, Darmstadt, Germany), 0.1 M KIO₃ (VWR, Darmstadt, Germany) and 0.01 M Na₂B4O₇ 10 H₂O (Sigma-Aldrich, Taufkirchen, Germany) solution was prepared [89 (link)]. The pH of the finished solution was 9–9.2. The solution was adjusted to 23.5 °C in a temperature-controlled water bath, the temperature in the cabinet was set to 15 °C and UVC-LED reactor was turned on for at least 15 min to allow a warm-up period. Within an actinometry experiment, several flow steps were tested, ranging from approximately 1 to 6 L∙h⁻¹ leading to hydraulic retention times in the reactor of 0.7 to 6 s. Samples and blank were taken in triplicates and the absorbance at 352 nm was determined using the DR6000 UV-Vis spectrophotometer (HACH, Düsseldorf, Germany).

Millipore^® Direct UV-Q water was used to prepare all the solutions in this study. GLY of 99.7% purity, AMPA of 99% purity and 9-flourenylmethlylchloroformate chloride (FMOC) of 97% purity were purchased from Sigma Aldrich^® (Seelze, Germany), while acetonitrile was purchased from QREC^®, Malaysia. Stock solutions (500 mg L⁻¹) of GLY and AMPA were prepared by quantitatively dissolving their appropriate quantities into Millipore^® Direct UV-Q water, while 0.02 M FMOC was prepared in acetonitrile. Analytical reagent grade CaCl₂ and KH₂PO₄ were purchased from Emsure^® (Germany) while HgCl₂ and Na₂B₄O₇.10H₂O were purchased from Sigma Aldrich^® (India).