Methylene blue degradation by the VUV/UV/persulfate process: Effect of pH on the roles of photolysis and oxidation

Abstract

Graphical Abstract Highlights  VUV/UV/persulfate (VUV/UV/PS) process obviously enhanced methylene blue degradation. VUV UV HO • other SO 4 •-J o u r n a l P r e -p r o o f  Degradation and mineralization of methylene blue exhibited different trends with pH. HO • and SO4 •were proved to be the principal reactive oxygen species. The application potential of VUV/UV/PS process was demonstrated in real waters. Solution pH notably affected photon absorption distributions and reaction mechanism. AbstractThis study investigated methylene blue (MB) degradation by the vacuumultraviolet/ultraviolet/persulfate (VUV/UV/PS) process using a mini-fluidic VUV/UV photoreaction system. Results show that MB degradation by the VUV/UV/PS process was significantly higher than that of the conventional UV/PS process, as the VUV photolysis of H2O and PS generated more reactive oxygen species (ROSs). HO • and SO4 •-, identified as the main ROSs, were mostly consumed by dissolved organic carbon and Clin real waters, respectively. Additionally, the impacts of solution pH and the concentrations of PS, humic acid, and inorganic ions (HCO3 -, Cl -, NO3 -, SO4 2-, Fe(II), and Fe(III)) were systematically evaluated. The solution pH significantly affected the photon absorption distributions, as well as the contributions of photolysis and oxidation to MB degradation, resulting in different variations in the degradation rate constant and total organic carbon removal ratio with increasing solution pH. At all tested pH levels (3.0-11.0), particularly under acidic conditions, HO • and SO4 •were two predominant contributors to MB degradation, while VUV and UV photolysis contributed more when the solution pH increased. This study provides a highly efficient process for organic J o u r n a l P r e -p r o o f pollutant removal, which could be applied in water treatment. S O 2 SO ( 1.4) hv        (1) Low-pressure (LP) mercury lamps are a highly efficient UV light source for water treatment, with a photon-energy efficiency of approximately 36% [12]. By using J o u r n a l P r e -p r o o f

Stability of the Photocatalytic Activity of TiO2 Deposited by Reactive Sputtering

“…It is possible to note that the degradation of the methylene blue solution is faster in the TiO 2 samples than in the control solution (Table 2), however, because the methylene blue solution also presents photodegradative characteristics probably mediated by photolysis [31][32][33] , after a long time of exposure to irradiation, they tend to present similar final results, as shown in Figure 2a. Figure 2b displays the degradation and concentration of methylene blue of the three samples deposited on different substrates, standardized to the percentage of degradation at 1 cm 2 of the sample area.…”

“…As the lamp has a main peak at 254 nm, such an effect is possible because there is enough energy for it to occur. During photolysis, water molecules that are irradiated by UV lamps undergo the breaking process, for example, in hydroxyl radicals that are highly oxidative and can react with methylene blue molecules, degrading them [31][32][33] .…”

Study on UV Ferrous Activated Persulfate Degradation Conditions of Thiacloprid Pesticide Residues in Environmental Water

“…After the Fe2+ concentration is increased, the sulfate in the solution is greatly activated in a short period of time to produce a large amount of SO4•-. However, when SO4•-is excessive, in addition to degrading the target pollutant thiacloprid, it will have a redox reaction with Fe 2+ [16], resulting in a decrease in Fe 2+ concentration, which affects the improvement of the degradation rate of thiacloprid. Therefore, it can be preliminarily determined that the optimal Fe2+ concentration is 0.3mmol/L.…”

“…3 that the degradation rate increases significantly with the increase of UV power, reaches the maximum when the UV power is 45W and then is basically unchanged with the increase of UV power. This is because increasing the UV power can increase the input activation energy, which is conducive to the rate of persulfate activation to SO4•- [16]. At the same time, more abundant oxidants can be provided by increasing the concentration of persulfate.…”

P=O Functionalized Black Phosphorus/1T-WS2 Nanocomposite High Efficiency Hybrid Photocatalyst for Air/Water Pollutant Degradation

“…Over the past decades, many researchers have tried to find various systems and technologies to remove these dyes from industrial wastewater. Typically, adsorption [ 3 , 4 , 5 ], coagulation [ 6 ], ultraviolet decomposition [ 7 ], oxidation and reduction treatments are used to remove dyes [ 8 , 9 , 10 ]. However, many of these technologies are expensive and pose secondary risks, including toxic and hazardous chemicals.…”