Journal Pre-proof Investigation of the efficiency of BiOI/BiOCl composite photocatalysts using UV, cool and warm white LED light sources - photon efficiency, toxicity, reusability, matrix effect, and energy consumption

BiOI, BiOCl, and their composites (BiOI:BiOCl) with molar ratios from 95:5 to 5:95 were 17 synthesized and tested in the transformation of methyl orange (MO) and 18 sulfamethoxypyridazine (SMP) antibiotic, using three various LED light sources: UV LEDs 19 (398 nm), cool and warm white LEDs (400 - 700 nm). The 80:20 BiOI:BiOCl photocatalyst 20 showed the best adsorption capacity for MO and enhanced activity compared to BiOI and 21 BiOCl. The apparent quantum yield (  app ) of the MO and SMP transformation for cool and 22 warm white light was slightly lower than for 398 nm UV radiation. The effect of methanol 23 and 1,4-benzoquinone proved that the transformation is initiated mainly via direct charge 24 transfer, resulting in the demethylation of MO and SO 2 extrusion from SMP. The change of 25 photocatalytic efficiency was followed during three cycles. After the first one, the 26 transformation rates decreased, but there was no significant difference between the second 27 and third cycles. The decreased efficiency is most probably caused by the intermediates, 28 whose continuous accumulation was observed during the cycles. Ecotoxicity confirmed that no toxic substances were leached from the catalyst, but the transformation of 30 both MO and SMP results in toxic intermediates. Using 80:20 BiOI:BiOCl and LED light 31 source, the energy requirement of the removal is about half of the value determined using 32 TiO 2 and a mercury vapor lamp. The effect of some components of wastewater (Cl − , HCO 3− 33 and humic acids), pH, and two matrices on the composite photocatalysts' efficiency and 34 stability were also investigated. 35 The present study aims to prepare composites BiOCl/BiOI photocatalyst with different ratios, to determine their absorption properties and photocatalytic activity, and to compare the apparent quantum yields using different LED light sources (398 nm UV, cool and warm white light). For evaluation of the photocatalytic performance of the pure BiOI, BiOCl, and the composites, the methyl orange (MO) dye and sulfamethoxypyridazine (SMP) antibiotic degradation was chosen. Toxicity measurements have also been performed to investigate the potential risk of using these photocatalysts. studies of the effects of water biologically treated provide information on the practical applicability best

molar ratios, to determine their absorption properties and photocatalytic activity, and to 96 compare the apparent quantum yields using different LED light sources (398 nm UV, cool 97 and warm white light). For evaluation of the photocatalytic performance of the pure BiOI, 98 BiOCl, and the composites, the methyl orange (MO) dye and sulfamethoxypyridazine (SMP) 99 antibiotic degradation was chosen. Toxicity measurements have also been performed to 100 investigate the potential risk of using these photocatalysts. Also, studies of the effects of Cl − , 101 HCO 3 − , humic acid, pH and two matrices (river water and biologically treated domestic purification. When the effect of additives was studied, NaCl (VWR, 99%), sodium-humate 112 (Sigma Aldrich, tech. grade), methanol (VWR, 99.9 %), and 1,4-benzoquinone (Acros 'cool white' (LEDmaster, λ emission =400-650 nm, 390 lumens, 4.6 W), and 'warm white' 145 (LEDmaster, λ emission =400-700 nm, 600 lumens, 4.6 W). 1.0 m of LED tape (60 LED/meter) 146 was fixed on the inside of the aluminum, double-walled reactor having 66 mm inner diameter.

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The reactors were equipped with a water cooling system to ensure the LEDs' constant light 148 output. The electrical power required to operate the LEDs was the same (4.6 W) in all cases; 149 thus, the efficiency of the photocatalysts was determined at the same electrical energy input.

Analytical methods
ions is performed by complexation with 1,10-phenanthroline. Within the range of 365 -514 171 nm, the quantum yield of the Fe 2+ formation changes from 1.2 to 0.93 (Kuhn et al., 2004). 172 The photocatalysts adsorb well the MO dye. NaF solution (0.5 cm 3 , 0.5 M) was added    containing 0.5 g dm -3 catalyst was 29 % and 11 % for BiOI and BiOCl, respectively. This can 281 be partly explained by the difference between the specific surface area (Table 1)  significantly (from 6.5 to 6.2) during the transformation.

315
For MO, significantly increased activity was determined for the composite catalysts 316 having more than 50% BiOCl content. The discoloration rate reached the maximum value in 317 the range of 70-95% BiOCl content (Fig. 2b). Adsorption capacity and transformation 318 efficiency are correlated (Fig. 2).

319
In the spectrophotometric measurements, the characteristic change of the shape of the 320 MO spectrum and the shift of its maximum to the lower wavelengths indicates the formation 321 of products having significant absorption around 400-450 nm (Fig. S6). Therefore, the HPLC-  (Fig. 3). For both organic substances, the transformation rate was significantly 343 higher using 398 nm irradiation than visible light, similarly, the product formation was 344 markedly faster ( Fig S5). Both BiOI and the composite catalyst proved better activity than  In the case of MO using 398 nm light, the value of Φ app was much higher for BiOI than 367 for BiOCl, while for SMP there was no significant difference between them. In the case of 368 MO transformation, the Φ app measured for the composite was nearly double than the Φ app of 369 BiOI, regardless of the light source (Fig 3), and the Φ app for cool and warm white light was     Table   467 S1 shows the chemical parameters of the matrices. The pH of the solution was adjusted to 9.2 and 4.0 with NaOH and H 2 SO 4 solutions, 476 respectively. The addition of BiOI:BiOCl catalyst restored the pH of the suspension to around 477 6.5. The protonation-deprotonation process of MO (pKa = 3.46) could not affect its 478 adsorption. Nevertheless, the relative amount of adsorbed MO (from 36% to 21% and 27%) 479 and the conversion rate (to 45% and 53%) was significantly reduced (Fig 7). The ionic photocatalyst and substrate, thereby affect the photodegradation. NaCl decreased the 482 adsorption of MO (to 16%) and its conversion rate (to 49%), but increased the transformation 483 rate of SMP (by 46%). A significant change was observed when 525 mg dm -3 NaHCO 3 was 484 added to the suspension. The transformation rate of MO was completely and of SMP partly 485 (to 58%) inhibited. MO practically did not adsorb in this case. Spectrophotometric 486 measurements show that the concentration of Iin the solution did not change due to the 487 addition of NaOH, but H 2 SO 4 and NaCl, and even NaHCO 3 increased that, suggesting a 488 change in the surface of the catalyst (Fig 7). The relative high Iconcentration in the The humic acids and humates often compete for adsorption sites with the pollutants.

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As our results show, humate decreased the transformation of MO and SMP to a similar extent.

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The authors declare that they have no known competing financial interests or personal 590 relationships that could have influenced the work reported in this paper.

Declaration of interests
☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: