Application of vacuum-ultraviolet (VUV) for phenolic homologues removal in humic acid solution: Efficiency, pathway and DFT calculation

Superiority of UV222 radiation by in situ aquatic electrode KrCl excimer in disinfecting waterborne pathogens: Mechanism and efficacy

Microbial safety in water has always been the focus of attention, especially during the COVID-19 pandemic. Development of green, efficient and safe disinfection technology is the key to control the spread of pathogenic microorganisms. Here, an in situ aquatic electrode KrCl excimer radiation with main emission wavelength 222 nm (UV222) was designed and used to disinfect model waterborne virus and bacteria, i.e. phage MS2, E. coli and S. aureus. High inactivation efficacy and diversity of inactivation mechanisms of UV222 were proved by comparision with those of commercial UV254. UV222 could totally inactivate MS2, E. coli and S. aureus with initial concentrations of ∼10⁷ PFU or CFU mL^-1 within 20, 15, and 36 mJ/cm², respectively. The UV dose required by UV254 to inactivate the same logarithmic pathogenic microorganism is at least twice that of UV222. The protein, genomic and cell membrane irreparable damage contributed to the microbial inactivation by UV222, but UV254 only act on nucleic acid of the target microorganisms. We found that UV222 damage nucleic acid with almost the same or even higher efficacy with UV254. In addition, free base damage of UV222 in similar ways with UV254(dimer and hydrate). But due to the quantum yield of free base degradation of UV222 was greater than UV254, the photolysis rates of UV222 to A, G, C and U four bases were 11.5, 1.2, 3.2 and 1 times as those of UV254, respectively. Excellent disinfection performance in UV222 irradiation was also achieved in real water matrices (WWTP and Lake). In addition, it was proved that coexisting HCO₃^- or HPO₄^{2 -} in real and synthetic water matrices can produce • OH to promote UV222 disinfection. This study provided novel insight into the UV222 disinfection process and demonstrated its possibility to take place of the conventional ultraviolet mercury lamp in water purification.

Adsorption-enhanced catalytic oxidation for long-lasting dynamic degradation of organic dyes by porous manganese-based biopolymeric catalyst

Improving the adsorption kinetics of metal-oxide catalysts is critical for the enhancement of catalytic performance in heterogeneous catalytic oxidation reactions. Herein, based on the biopolymer pomelo peels (PP) and metal-oxide catalyst manganese oxide (MnO_x), an adsorption-enhanced catalyst (MnO_x-PP) was constructed for catalytic organic dyes oxidative-degradation. MnO_x-PP shows excellent methylene blue (MB) and total carbon content (TOC) removal efficiency of 99.5 % and 66.31 % respectively, and keeps the long-lasting stable dynamic degradation efficiency during 72 h based on the self-built continuous single-pass MB purification device. The chemical structure similarity and negative-charge polarity sites of the biopolymer PP improve the adsorption kinetics of organic macromolecule MB, and construct the adsorption-enhanced catalytic oxidation microenvironment. Meanwhile, the adsorption-enhanced catalyst MnO_x-PP obtains lower ionization potential and O₂ adsorption energy to promote the continuous generation of active substance (O₂*, OH*) for the further catalytic oxidation of adsorbed MB molecules. This work explored the adsorption-enhanced catalytic oxidation mechanism for the degradation of organic pollutants, and provided a feasible technical idea for designing adsorption-enhanced catalysts for the long-lasting efficient removal of organic dyes.

Degradation mechanism of BPA under VUV irradiation: efficiency contribution and DFT calculations

Bisphenol A (BPA) is regarded as a hazardous pollutant that exists widely in aquatic environments, posing a severe threat to human health. In this study, a vacuum ultraviolet (VUV) lamp emitting a hybrid of 254 nm and 185 nm light was used to degrade BPA. Results indicated that photolysis via 254 nm wavelength accounted for 24.93% for BPA decay, while indirect oxidation was responsible for 52.27% of decay. Results confirmed that the degradation of BPA under VUV illumination mainly occurred via photo-excited degradation and ·OH electrophilic addition reactions based on average local ionization energy (ALIE) calculation and density functional theory (DFT) calculations. Therefore, only light with a wavelength of 254 nm was able to induce the first three excited states of BPA, forming the electron transition type of n → π* from O atom to a single benzene ring and π → π* in the single benzene ring. Indirect oxidation by ·OH occurred as it preferentially attacked the C6 atom in BPA ring A. Moreover, the energy required for photo-excited degradation was about twofold than that of ·OH electrophilic addition reactions.

Non-Stacked γ-Fe2O3/C@TiO2 Double-Layer Hollow Nanoparticles for Enhanced Photocatalytic Applications under Visible Light

Herein, a non-stacked γ-Fe₂O₃/C@TiO₂ double-layer hollow nano photocatalyst has been developed with ultrathin nanosheets-assembled double shells for photodegradation phenol. High catalytic performance was found that the phenol could be completely degraded in 135 min under visible light, due to the moderate band edge position (VB at 0.59 eV and CB at −0.66 eV) of the non-stacked γ-Fe₂O₃/C@TiO₂, which can expand the excitation wavelength range into the visible light region and produce a high concentration of free radicals (such as ·OH, ·O²⁻, holes). Furthermore, the interior of the hollow composite γ-Fe₂O₃ is responsible for charge generation, and the carbon matrix facilitates charge transfer to the external TiO₂ shell. This overlap improved the selection/utilization efficiency, while the unique non-stacked double-layered structure inhibited initial charge recombination over the photocatalysts. This work provides new approaches for photocatalytic applications with γ-Fe₂O₃/C-based materials.

Vacuum UV pre-treatment coupled with self-generated peroxide stimulation of biomass: An innovative hybrid system for detoxification and mineralization of toxic compounds

The degradation of p-nitrophenol (pNP) was investigated in the chemical-less UVC/VUV process (Advanced Oxidation/Reduction Process, AORP), the packed bed bioreactor (PBR), and the hybrid of AORP/PBR system. The control UVC/VUV process degraded and mineralized pNP with rate constants of 0.098 and 0.032 min^-1, respectively, at neutral initial pH. Operating the UVC/VUV process in a fluidized bed reactor improved the rate of pNP degradation by 21 % at a packing ratio of 0.5 %. The fluidized bed AORP was operated under continuous-flow mode, where 79 % degradation and 28 % mineralization of pNP were obtained along a significant improvement in the biodegradability (41 %) at a hydraulic retention time of 20 min. The oxidation with HO and reduction with e_aq^- simultaneously contributed to the degradation of pNP in the UVC/VUV process. In comparison, degradation and mineralization of pNP in a single PBR process (without pretreatment) was found to be 84.7 % and 47.2 %, respectively, during 30 h biotreatment. Coupling the fluidized bed UVC/VUV with the PBR attained complete biodegradation of the residual pNP within 1 h and over 89 % of TOC reduction during 3 h post treatment in the PBR. Accordingly, the hybrid, fluidized bed UVC/VUV reactor coupled with the PBR is an efficient and promising technology for treating toxic environmental contaminants.

Novel VUV/g-C3N4 system with high adaptability to varied environmental conditions and outstanding degradation capacity for chlorophenols

Given the limitations of conventional vacuum ultraviolet (VUV) systems, a novel vacuum ultraviolet/graphite carbon nitride (VUV/g-C₃N₄) system with high adaptability to varying environmental conditions was developed. Compared with conventional VUV and UV/g-C₃N₄ systems, the VUV/g-C₃N₄ system demonstrates a much higher ability for the efficient degradation of chlorophenols (CPs). In particular, the VUV/g-C₃N₄ system exhibits outstanding performance even at low pH and high concentrations of humic acid and SO₄^2-. Alkaline conditions and the presence of HCO₃^- can further promote CP removal. In addition, the feasibility of the VUV/g-C₃N₄ system was verified by its stable operation in both river water and tap water. Unlike conventional photochemical systems relying on •OH, the dominant reactive species for CP degradation by the VUV/g-C₃N₄ system was identified to be •O₂^-. This study conclusively provided a novel system for the efficient photocatalytic treatment of pollutants.

Photocatalytic degradation of unsymmetrical dimethylhydrazine on TiO2/SBA-15 under 185/254 nm vacuum-ultraviolet

In this work, TiO₂/SBA-15 was synthesized via an in situ hydrothermal method and was used for vacuum-ultraviolet (VUV) photocatalytic degradation of unsymmetrical dimethylhydrazine (UDMH) for the first time. Compared with photocatalysis under UV irradiation, VUV photocatalysis exhibited higher photodegradation efficiency due to the synergetic effect of direct photolysis, indirect photooxidation and photocatalytic oxidation. The synthesized TiO₂/SBA-15 catalysts exhibited ordered mesoporous structure and anatase phase TiO₂. Titanium content, initial pH and substrate concentration impacted degradation efficiency of UDMH in the VUV photocatalysis process. Among the prepared catalysts, TiO₂/SBA-15 with the molar ratio of Ti/Si = 1 : 3 (TS-2) showed the best photocatalytic activity under VUV light, with the rate constant of 0.02511 min⁻¹, which is 1.91 times that with VUV/P25. The superior photocatalytic activity of TS-2 is mainly related to the good balance between the specific surface area and TiO₂ contents. The photodegradation efficiency decreases with the increase in the initial UDMH concentration and the maximum degradation rate was obtained at pH 9.0. In the VUV/TS-2 process, ˙OH played a more important role in the degradation of UDMH than ˙O₂⁻ and the degradation pathways contained bond breaking, amidation, isomerisation and oxidation reactions. The TS-2 also showed good reusability with the rate constant maintained at above 90% after five cycles and exhibited satisfactory degradation efficiency in tap water.

Mesoporous TiO₂/SBA-15 under VUV irradiation: enhanced photocatalytic oxidation for UDMH degradation.

Enhanced vacuum UV-based process (VUV/H2O2/PMS) for the effective removal of ammonia from water: Engineering configuration and mechanistic considerations

In this work, the VUV, VUV/H₂O₂, VUV/PMS, and VUV/H₂O₂/PMS processes were compared with the corresponding UVC-based AOPs under identical experimental conditions for the ammonia removal. Among the examined AOPs, the VUV/H₂O₂/PMS demonstrated the highest performance in converting NH₄⁺ to N₂. A 82.7 % removal of 100 mg/L NH₄⁺, with N₂ selectivity over 99 % was obtained in the VUV/H₂O₂/PMS process within 60 min, operated under near neutral pH. Under these operation conditions, [NO₃^-] was around 0.5 mg-N/L with [NO₂^-] remaining below detection. The VUV-mediated generation of SO₄^•-and HO^• with NH₄⁺ had a relative contribution of 37.9 and 62.1 %, respectively. The VUV/H₂O₂/PMS process operated under a flow-through mode achieved efficient removal of 100 mg/L NH₄⁺ (80.5 %) in a hydraulic retention time (HRT) of 40 min. The continuous-flow VUV/H₂O₂/PMS process efficiently treated a real ammonia-laden groundwater and the concentration of NH₄⁺ decreased from 30 mg/L to around 1 mg/L within 60 min HRT. In summary, the VUV/H₂O₂/PMS process was effective from the technical and energetical point of view, hence is a viable and promising technique for treating effluent containing high concentrations of ammonia.