Photocatalytic Disinfection Performance Research Articles

Enhanced visible-light-driven photocatalytic disinfection using AgBr-modified g-C3N4 composite and its mechanism

In this study, novel AgBr-modified g-C3N4 (AgBr/g-C3N4) photocatalysts were prepared by an adsorption–deposition method and characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Brunauer–Emmett–Teller (BET), and ultraviolet–visible spectroscopy (UV–vis). Furthermore, the photocatalytic disinfection performance on Escherichia coli (ATCC 15597) was investigated. The as-prepared photocatalysts exhibited well crystalline structures and morphologies with C3N4 and exhibited a stronger bacterial inactivation than that of pristine g-C3N4. The disinfection efficiency reached up to 4.80 log under 150 min of visible light irradiation when AgBr-modified g-C3N4 was prepared at a molar ratio of 1:5 (AgBr: g-C3N4), which was a 4.2 log increase compared with that of pristine g-C3N4 under the same experimental conditions. The enhancement of the photocatalytic activity of AgBr/g-C3N4 was attributed to the effective production and transfer of the photo-induced electrons under visible light irradiation, since the AgBr modification reduced the bandgap energy and boarded the visible light area. Furthermore, h+ was found to be the dominant contributor for bacterial inactivation. The h+ and photo-generated reactive oxygen species (ROSs) damaged the cell membranes and destroyed metabolic processes, resulting in leakage of potassium ions and proteins, lipid peroxidation, degradation of intracellular protein, and a reduction of the ATP levels, which finally lead to bacterial death. These results provide a theoretical basis for the development of low-cost, high-efficiency photocatalysts for green/sustainable water disinfection.

Photocatalytic disinfection performance in virus and virus/bacteria system by Cu-TiO2 nanofibers under visible light

The presence of pathogenic microorganisms in water is a great threat to human health, and photocatalysis is promising for disinfection. However, the research on virus inactivation with visible-light photocatalysis is still limited, especially the coexistence of virus and its host bacteria. In this study, bacteriophage f2 and its host E. coil 285 were used as the model microorganisms, and the disinfection performance of prepared Cu-TiO2 nanofibers under visible light was investigated. The result showed that the prepared Cu-TiO2 nanofibers showed a brilliant ability in terms of removing bacteriophage f2 and E. coil 285 under visible light. Series experiments indicated that the initial pH didn't affect the photocatalytic disinfection performance significantly. In the certain range, the removal efficiency of bacteriophage f2 increased with the increase of catalyst dosage, light intensity and temperature, but decreased with the increase of initial virus concentration. In virus/bacteria mixed system, bacteriophage f2 exhibited stronger resistance to photocatalytic oxidation than E. coil 285, and the removal of bacteriophage f2 was obviously affected by being mixed with E. coil 285, while the removal of E. coil 285 almost remained unchanged after being mixed with bacteriophage f2. Further research proved that competitive adsorption in mixed system played a certain role in E. coli 285 inactivation, while the free reactive oxygen species (ROSs) in the bulk phase played a crucial role in phage f2 inactivation.

Enhanced Visible-Light-Driven Photocatalytic Disinfection Performance and Organic Pollutant Degradation Activity of Porous g-C3N4 Nanosheets.

Porous g-C3N4 nanosheet (PCNS) photocatalyst with a thickness of 2.0 nm, pore volume of 0.61 cm3 g-1, and surface area of 190.1 m2 g-1 was prepared by a simple two-step template-free approach without the addition of extra reagents. Compared with the bulk g-C3N4 (BCN), PCNS possesses a greater number of surface reactive sites, improved efficiency of charge transfer, and accelerated separation of photogenerated electron-hole pairs. Accordingly, the visible-light-driven photocatalytic disinfection performance and organic pollutant degradation activity of PCNS are significantly enhanced. Escherichia coli (E. coli) cells can be killed completely by PCNS within 4 h, whereas only 77.1% of E. coli cells can be killed by BCN. The photodegradation rates of PCNS on methylene blue, Acid Red 27, and bisphenol A are almost 6.4, 4.0, and 1.9 times as fast as that of BCN, respectively. The photocurrent intensity of PCNS is about 3.7 times in comparison with that of BCN. Considering the easy preparation and excellent performance, PCNS could be a promising and competitive visible-light-driven photocatalyst in the field of environment remediation.

The formation of alpha-FeOOH onto hydrothermal biochar through H2O2 and its photocatalytic disinfection

Effect of H2O2 levels on the formation of alpha-FeOOH (goethite) on the modified hydrothermal biochar and its photocatalytic disinfection performance were investigated in this study. Chemical composition analysis indicated that goethite formed successfully on biochars using hydrothermal carbonization (HTC) with H2O2 modification. The investigation for the relationship of oxygen-rich functional groups with H2O2 levels and Fe (III) mass balance during goethite formation implied that carboxylic group on biochars increased obviously with the increase of H2O2 levels, while both hydroxyl and lactone groups increased firstly and then decreased with increase of H2O2 levels. Fe (III) could approximately meet mass balance during the second HTC. Goethite level on goethite coated biochar (GCB) by 20% H2O2 modification was higher than the one for 30% H2O2 modification due to the potential phase transformation. The application of GCB in photocatalytic disinfection systems showed that Escherichia coli inactivation by GCB photocatalysis (solar or UVA irradiation) was evidently greater than the one by the control. The inactivation of E. coli by GCB4 (20% H2O2 modification) photocatalytic disinfection was the best with close to 4.5 log reduction for solar irradiation and about 4 log reduction for UVA irradiation, which had little changes after five cycle experiments, suggesting that the application of GCB4 photocatalysis with solar or UVA to inactivate E. coli was feasible and desirable in this study.

PdO loaded TiO2 hollow sphere composite photocatalyst with a high photocatalytic disinfection efficiency on bacteria

PdO loaded TiO2 hollow spheres were synthesized via first reducing Pd2+ to Pd in ethanol onto TiO2 hollow spheres by refluxing and then oxidizing Pd to PdO through calcination in air. PdO nanoparticles were distributed relatively uniformly both on the surface and in the shell/interior of these TiO2 hollow spheres, to act as potential electron/hole pair separation centers. These PdO loaded TiO2 hollow spheres demonstrated a superior photocatalytic disinfection performance on Eschetichia coil bacteria, compared with the unloaded samples or P25 TiO2 nanoparticles. Their largely enhanced photocatalytic disinfection performance could be attributed to both their unique hollow structure and the electron trapping capability of loaded PdO nanoparticles. Samples with a series of PdO loading ratios were synthesized and tested to determine the optimum PdO loading ratio, which was found to be similar to 0.4 wt.%. Below the optimum PdO loading, the photocatalytic disinfection performance increased with the increase of PdO loading ratio, while further increase of the PdO loading over 0.4% resulted in a deleterious influence on the PdO enhancement effect. The photocatalytic performance differences between Pd and PdO modified samples were also investigated. Samples with 0.4% PdO modification demonstrated a better photocatalytic disinfection effect on E. coli bacteria than samples with 0.4% Pd modification, which could be attributed to their different work functions. (C) 2014 Elsevier B.V. All rights reserved.

Enhanced photocatalytic disinfection of E. coli 8099 using Ag/BiOI composite under visible light irradiation

In this study, an effective photocatalytic disinfection of E. coli 8099 using Ag/BiOI composites under visible light irradiation (λ>420nm) was studied. The nanostructured Ag/BiOI composites were synthesized in the presence of ethylene glycol by a solvothermal process and subsequent photodeposition method. The prepared Ag/BiOI photocatalysts were characterized by X-ray diffraction (XRD), scanning electronic microscopy (SEM), energy dispersive spectrometer (EDS), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and UV–vis diffuse reflectance spectra (DRS) measurement. The experimental results showed that the photocatalytic disinfection efficiency of E. coli (∼5×107cfumL−1) using 2.09%Ag/BiOI was almost 99.99% within 10min irradiation, and significantly higher than that of BiOI. The determination of cell structure destruction by TEM microscopy and the measurement of released K+ further confirmed that the cell membranes of E. coli were ruptured in the photocatalytic disinfection. It was found that the deposited Ag can facilitate the surface-adsorbed O2 to scavenge the photogenerated electrons. The main active species OH for the photocatalytic disinfection performance of E. coli was produced by two pathways, that is, hvb+ oxidized water molecules to form OH (oxidative pathway), and O2 captured the photogenerated electron to generate O2- and subsequently produce OH (reductive pathway).