Efficient destruction of pathogenic bacteria with NiO/SrBi2O4 under visible light irradiation

The photocatalytic inactivation of pathogenic bacteria in water was investigated systematically with NiO/SrBi2O4 under visible light (lambda > 420 nm) irradiation. The catalyst was found to be highly effective in killing Escherichia coli, a Gram-negative bacterium, and Staphylococcus aureus, a Gram-positive bacterium. ESR studies revealed that *OH and O2*- were involved as the active species in the photocatalytic reaction. The decomposition process of the cell wall and the cell membrane was directly observed byTEM and further confirmed by the determination of potassium ion (K+) leakage from the killed bacteria. A possible cell damage mechanism by visible-light-driven NiO/SrBi2O4 is proposed. In addition, the effects of pH, methanol, and inorganic ions on bacterial photocatalytic inactivation were investigated. These results indicated that the electrostatic force interaction of bacteria-catalyst is crucial for high bactericidal efficiency.     

Novel approach to enhance photosensitized degradation of rhodamine B under visible light irradiation by the ZnxCd1-xS/TiO2 nanocomposites

In order to exploit efficient photosensitizers with appropriate electronic states to enhance the transfer of electrons, ZnxCd1-xS/TiO2 nanocomposites were first synthesized by a simple hydrothermal method. The samples were characterized by X-ray diffraction, transmission electron microscopy, diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, electron spin resonance, and photoluminescence techniques. The results showed that the composite of the two inorganic semiconductors largely enhanced the photosensitized degradation of rhodamine B (RhB) under visible light irradiation (420 nm<λ<800 nm). These photocatalytic reactions were driven mainly by the light absorption of RhB molecules and to a lesser extent by the excitation of ZnxCd1-xS. They were supposed to arise mainly from the electron transferred from the adsorbed dye in its singlet excited state to the conduction band of ZnxCd1-xS and TiO2. Such a heterogeneous photocatalytic reaction has much significance in the degradation of organic pollutants in ordinary photocatalysis.     

Mesoporous nitrogen-doped TiO2 for the photocatalytic destruction of the cyanobacterial toxin microcystin-LR under visible light irradiation

The presence of the harmful cyanobacterial toxins in water resources worldwide drives the development of an innovative and practical water treatment technology with great urgency. This study deals with two important aspects: the fabrication of mesoporous nitrogen-doped TiO2 (N-TiO2) photocatalysts and their environmental application for the destruction of microcystin-LR (MC-LR) under visible light. In a nanotechnological sol-gel synthesis method, a nitrogen-containing surfactant (dodecylammonium chloride) was introduced as a pore templating material for tailor-designing the structural properties of TiO2 and as a nitrogen dopant for its visible light response. The resulting N-TiO2 exhibited significantly enhanced structural properties including 2-8 nm mesoporous structure (porosity 44%) and high surface area of 150 m2/g. Red shift in light absorbance up to 468 nm, 0.9 eV lower binding energy of electrons in Ti 2p state, and reduced interplanar distance of crystal lattices proved nitrogen doping in the TiO2 lattice. Due to its narrow band gap at 2.65 eV, N-TiO2 efficiently degraded MC-LR under visible spectrum above 420 nm. Acidic condition (pH 3.5) was more favorable for the adsorption and photocatalytic degradation of MC-LR on N-TiO2 due to electrostatic attraction forces between negatively charged MC-LR and +6.5 mV charged N-TiO2. Even under UV light, MC-LR was decomposed 3-4 times faster using N-TiO2 than control TiO2. The degradation pathways and reaction intermediates of MC-LR were not directly related to the energy source for TiO2 activation (UV and visible) and nature of TiO2 (neat and nitrogen-doped). This study implies a strong possibility for the in situ photocatalytic remediation of contaminated water with cyanobacterial toxins and other toxic compounds using solar light, a sustainable source of energy.     

Role of hydroxyl radicals and mechanism of Escherichia coli inactivation on Ag/AgBr/TiO2 nanotube array electrode under visible light irradiation

A ternary Ag/AgBr/TiO(2) nanotube array electrode with enhanced visible-light activity was synthesized by a two-step approach including electrochemical process of anodization and an in situ photoassisted deposition strategy. The dramatically enhanced photoelectrocatalytic activity of the composite electrode was evaluated via the inactivation of Escherichia coli under visible light irradiation (λ>420 nm), whose performance of complete sterilization was much superior to other reference photocatalysts. PL, ESR, and radicals trapping studies revealed hydroxyl radicals were involved as the main active oxygen species in the photoelectrocatalytic reaction. The process of the damage of the cell wall and the cell membrane was directly observed by ESEM, TEM, and FTIR, as well as further confirmed by determination of potassium ion leakage from the killed bacteria. The present results pointed to oxidative attack from the exterior to the interior of the Escherichia coli by OH(?), O(2)(?-), holes and Br(0), causing the cell to die as the primary mechanism of photoelectrocatalytic inactivation.     

A new role for Fe3+ in TiO2 hydrosol: accelerated photodegradation of dyes under visible light

The effect of Fe3+ on the photocatalytic activity of TiO2 hydrosol prepared through a low-temperature route has been investigated under visible light irradiation. The total reactive oxygen species (ROS) level and the accumulation of Fe2+ during the photodegradation process were detected to examine the role of Fe3+. In contrastto an aqueous TiO2 dispersion where Fe3+ strongly inhibited the photoactivity of TiO2 via suppressing the reduction of O2 and decreasing the production of ROS, Fe3+ accelerated the photodegradation of all dyes examined in the hydrosol through increasing the yield of oxidative ROS. The influence of the prebound hydroxyl groups on the surface of TiO2 was compared to that of free alcohols in aqueous solution, which revealed the cooperative function of the surface hydroxyl groups. The thoroughly contrary effect of Fe3+ on the photocatalysis of TiO2 hydrosol and TiO2 powder, which are all anatase nanocrystallites but are synthesized with different procedures, was ascribed to the complexation of the hydroxyl groups bound to TiO2 surface with Fe3+. The formation of such complexes has resulted in an altered electron-transfer pathway of the dye-sensitized photocatalysis under visible light irradiation.     

Highly enhanced photoreductive degradation of perchlorinated compounds on dye-sensitized metal/TiO2 under visible light

This study reports an example of visible-light photocatalyst based on TiO2 modified by ruthenium-complex sensitizers and noble metal deposits. The photodegradation of trichloroacetate (TCA) and carbon tetrachloride was used as a probe reaction for evaluating the visible light activity of the photocatalyst under the illumination of lambda > 420 nm. Photodeposition of platinum nanoparticles on dye-sensitized TiO2 (Pt/TiO2/Ru(II)L3) drastically enhanced the degradation rate of TCA and CCl4. The visible light reactivity of Pt/TiO2/Ru(II)L3 was optimal with [Ru(II)L3] = 10 microM, [TiO2] = 0.5 g/L, and Pt loading of about 0.2 wt %. Although no electron donors to regenerate the oxidized Ru-sensitizers were added in the aqueous suspension, the photoreductive dechlorination of perchlorinated compounds proceeded far beyond the stoichiometric limit of the initial sensitizer concentration. Water acted as an electron donor to regenerate the sensitizer with a concurrent production of dioxygen. On the other hand, Pt/TiO2/Ru(II)L3 was completely inactive in the presence of dissolved oxygen and the in-situ generated dioxygen gradually decelerated the dechlorination rate. Conduction band electrons transferred to O2 in preference to CCl4 and TCA on Pt deposits. Other noble metals (Ag, Au, and Pd) deposited on TiO2 showed a better oxygen-tolerance but less visible-light reactivity than PtTiO2/Ru(II)L3. Effects of metal loading on the visible light activity and its implications for the efficientvisible-light photocatalyst development are discussed.     

Migration of titanium dioxide from PET/TiO2 composite film for polymer-laminated steel

PET/TiO₂ composite film is the most widely used film for polymer-laminated steel, and the migration of TiO₂ is very important for the safety evaluation of its packaged food. Microwave digestion, wet digestion and dry ashing were used for pretreatment of composite film to determine the content of TiO₂ in composite film. Migration tests were carried out at 40°C, 60°C and 80°C 4% using acetic acid and 50% ethanol as the acid and ester food simulants. The migration amount of TiO₂ was determined by inductively coupled plasma optical emission spectrometry (ICP-OES). With increasing temperature and time, the migration of TiO₂ increased. In 4% acetic acid, the migration amount of TiO₂ at 40°C for 10 days was 1.88 mg kg^?1 and the migration amount at 80°C for 8 h was 3.32 mg kg^?1, indicating that the effect of temperature on migration was more obvious. Under the same conditions, the migration amount of TiO₂ in 4% acetic acid was greater than in 50% ethanol. X-ray diffraction (XRD), scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimeter (DSC) were used to analyse the crystal structure, morphology, chemical groups and thermal properties of the film before and after the migration tests. The results showed that filmTiO₂ had a stable rutile type crystal structure and it was almost uniformly distributed. PET and TiO₂ were combined with strong chemical bonds. After TiO₂ migration, the crystallinity and the glass transition temperature (Tg) of the film decreased, but the change of melting temperature (Tm) was not obvious.     

A new route for degradation of volatile organic compounds under visible light: using the bifunctional photocatalyst Pt/TiO2-xNx in H2-O2 atmosphere

The bifunctional photocatalyst Pt/TiO2-xNx has been successfully prepared by wet impregnation. The properties of Pt/ TiO2-xNx have been investigated by diffuse reflectance spectra, X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, a photoluminescence technique with terephthalic acid, and electric field induced surface photovoltage spectra. The photocatalytic activity of the sample was evaluated by the decomposition of volatile organic pollutants (VOCs) in a H2-O2 atmosphere under visible light irradiation. The results demonstrated that nitrogen-doped and platinum-modified TiO2 in a H2-O2 atmosphere could enormously increase the quantum efficiency of the photocatalytic system with excellent photocatalytic activity and high catalytic stability. The increased quantum efficiency can be explained by enhanced separation efficiency of photogenerated electron-hole pairs, higher interface electron transfer rate, and an increased number of surface hydroxyl radicals in the photocatalytic process. A mechanism was proposed to elucidate the degradation of VOCs over PtTiO(2-x)Nx in a H2-O2 atmosphere under visible light irradiation.     

Photoelectrocatalytic degradation of triazine-containing azo dyes at gamma-Bi2MoO6 film electrode under visible light irradiation (lamda > 420 nm)

Triazine-containing azo dyes, anionic reactive brilliant red K-2G, reactive brilliant Red X-3B, and reactive yellow KD-3G were degraded in the electrooxidation, photocatalysis and combined electrooxidation and phtocatalysis process at the gamma-Bi2MoO6 film electrode under visible light irradiation. Furthermore, in the combined process, synergetic degradation of the dyes was observed by the analysis of degradation kinetics and total organic carbon variation. The synergetic mechanism was studied using X-ray photoelectron spectra and electrochemical impedance spectra as well as analysis of variation of current vs time in various processes. It is suggested that application of bias potential with a lower value than the redox potential of the targeted dyes efficiently increases the photocatalysis rate of the dyes by prohibiting recombination of electrons and holes. At the bias greater than the redox potential of the dyes, the degradation of the dyes was efficiently improved bythe combined electrooxidation and photocatalysis process. The main active oxygen species involved in the dyes degradation was hydroxyl radicals as confirmed via DMPO spin-trapping electron spin resonance measurements and the effect of radical scavengers. Intermediates mainly including organic aromatic and aliphatic carboxylic acids were detected.     

Enhanced photocatalytic degradation of dye pollutants under visible irradiation on Al(III)-modified TiO2: structure, interaction, and interfacial electron transfer

Aluminum(III)-modified TiO2 was prepared by sol-gel process via a sudden gelating method. The structure of the modified material and the local environment of aluminum were investigated using X-ray diffraction, HRTEM, XPS, 27Al MAS NMR, and xi-potential measurements. The effect of the aluminum modification on interaction between the dye and photocatalyst, the interfacial electron transfer process, and thereby the degradation of dye pollutants under visible irradiation were also examined by FTIR spectra and UV-vis diffuse reflectance spectra. It was found that, rather than incorporating into the crystal lattice of TiO2, the aluminum forms an overlayer of Al2O3 on the surface of TiO2, interfaced with Ti-O-Al bonds. It is interesting that the carboxylate-containing dyes such as Rhodamine B (RhB) adsorb preferentially on the Al2O3, rather than the Ti(IV) sites on the surface of TiO2. The photodegradation rate observed for RhB is nearly 5-fold faster than that obtained in the pristine TiO2 system. The photodegradation of dyes on the aluminum(III)-modified photocatalyst is of great dependence on the structure and anchoring group of the dyes. Structure with carboxylate as anchoring group and amino group as electron donor is favorable for degradation. The mechanistic details are discussed on the basis of experimental results.     

FeCl3/NaNO2: an efficient photocatalyst for the degradation of aquatic steroid estrogens under natural light irradiation

Assistance and acceleration of the environment's self-remediation of pollutants represent an important and long-standing goal for environmental chemistry communities. Here, a degradation route using a combination of a nitrite and a ferric salt as the photocatalyst is presented for catalytically removing 17beta-estradiol (E2), estriol (E3), and 17alpha-ethynylestradiol (EE2) in water under mimicked natural environmental conditions, i.e., in the phytotron. After a 1 day reaction, 86.6% of the estrogen E2 was degraded. Extending the incubation time to 30 days, more than 99.9% E2 was removed and a very small quantity of malonic acid observed as the residual organic compound, and estrogenic activity was determined. The results showed that the estrogenic activities of the intermediate products are negligible and that there is no secondary risk associated with increased the estrogenic activity. The degradation system demonstrated that FeCl3/NaN02 is an efficient photocatalyst which is active on natural light irradiation. This work highlights a promising development for in situ treatment of pollutants in natural-environment conditions.     

Environmental remediation by an integrated microwave/UV illumination technique. 3. A microwave-powered plasma light source and photoreactor to degrade pollutants in aqueous dispersions of TiO2 illuminated by the emitted UV/visible radiation

The characteristic features of a novel double-quartz cylindrical plasma photoreactor (DQCPP) were assessed by examining the photodegradation of rhodamine-B dye (RhB+) in aqueous TiO2 dispersions irradiated simultaneously by both microwave radiation and UV/visible radiation emitted from a microwave-powered (MW, 2.45 GHz) electrodeless mercury lamp. The features of the DQCPP lamp are given and discussed in terms of the experimental output UV energy in the wavelength ranges 210-300 and 310-400 nm for applied MW powers from 74 to 621 W. The DQCPP and a water-cooled DQCPP reactor absorbed more than 50% MW radiation (50-88 and 50-75%, respectively). The emitted light irradiance scaled sublinearly with applied MW power. Relative to the DQCPP lamp, loss of irradiance by the water-cooled DQCPP lamp was approximately 28-46% at 250 nm and approximately 41-58% at 360 nm in the range of MW power used. The smallest loss occurred at 178.9 W at which the degradation of RhB+ was subsequently examined by UV/visible spectroscopy and by total organic carbon analyses. Highly intense mercury lines were seen at 365, 404, 435, 546, and 579 nm (those below 365 nm were more than 10 times weaker). About 80% of the RhB+ solution was photomineralized after 60 min of irradiation of the aqueous RhB+/TiO2 dispersion with the DQCPP lamp; no UV/ visible spectral features of RhB+ were evident at wavelengths below 250 nm after 30 min. Possible effects of microwave radiation and temperature on the degradative process are described.     

Organo-mineral fertilisers from glass-matrix and organic biomasses: a new way to release nutrients. A novel approach to fertilisation based on plant demand

BACKGROUND: A glass‐matrix fertiliser (GMF), a by‐product from ceramic industries, releases nutrients only in the presence of complexing solutions, similar to those exuded by plant roots. This ensures a slow release of nutrients over time, limiting the risk of their loss in the environment. With the aim to improve fertiliser performance, GMF was mixed with vine vinasse (DVV), pastazzo (a by‐product of the citrus processing industry, PAS) or green compost (COMP) and nutrient release was evaluated by citric and chloridric acid extraction, at different concentrations. RESULTS: Theoretical and actual nutrients release were compared to evaluate possible synergistic effects due to the organic component added to the mineral fertiliser: phosphorus (+7.1%), K (+4.8%), Fe (+8.5%) and Zn (+5.5%) were released more efficiently by 2% citric acid from GMF + DVV, while Ca availability was increased (+5.3%) by 2% citric acid from GMF + PAS mixture. Both DVV and COMP increased by 12–18% the Fe release from GFM matrix. CONCLUSION: Organic biomasses added to GMF increased the release of some macro and micronutrients through an ‘activation effect’, which suggests the employment of these organo‐mineral fertilisers also in short‐cycle crops production. Moreover, the re‐use of some agro‐industrial organic residues gives another ‘adding value’ to this novel organo‐mineral fertilfertilisers. Copyright © 2011 Society of Chemical Industry     

Environmental remediation by an integrated microwave/UV illumination technique. 8. Fate of carboxylic acids, aldehydes, alkoxycarbonyl and phenolic substrates in a microwave radiation field in the presence of TiO2 particles under UV irradiation

Thermal and nonthermal effects originating when a system is subjected to a microwave radiation field in the TiO2-photocatalyzed transformation of model substances containing various functional groups (e.g., benzoic acid, phthalic acid, o-formylbenzoic acid, phthalaldehyde, succinic acid, dimethyl phthalate, diethyl phthalate, and phenol) have been examined under simultaneous irradiation by ultraviolet (UV) and microwave (MW) radiations. Characteristics of the microwave effects and the fate of each substrate during the microwave-assisted photocatalytic process were monitored by UV absorption spectroscopy, HPLC methods, total organic carbon assays, and identification of intermediates using electrospray mass spectral techniques. Microwave thermal and nonthermal effects were delineated by comparing results from MW-generated internal heat versus conventional external heating, and at constant ambient temperature under a microwave field. Factors involved in the nonthermal component of the microwave radiation were inferred for the initial adsorption of the substrate and its subsequent degradation occurring on the surface of TiO2 particles. Microwave effects bear on the mechanism through which a model substrate undergoes oxidative degradation. A characteristic feature of these effects was briefly examined by considering the behavior of polar (dipole moments) substrates in a microwave radiation field.     

Efficient degradation of TCE in groundwater using Pd and electro-generated H2 and O2: a shift in pathway from hydrodechlorination to oxidation in the presence of ferrous ions

Degradation of trichloroethylene (TCE) in simulated groundwater by Pd and electro-generated H(2) and O(2) is investigated in the absence and presence of Fe(II). In the absence of Fe(II), hydrodechlorination dominates TCE degradation, with accumulation of H(2)O(2) up to 17 mg/L. Under weak acidity, low concentrations of oxidizing ?OH radicals are detected due to decomposition of H(2)O(2), slightly contributing to TCE degradation via oxidation. In the presence of Fe(II), the degradation efficiency of TCE at 396 μM improves to 94.9% within 80 min. The product distribution proves that the degradation pathway shifts from 79% hydrodechlorination in the absence of Fe(II) to 84% ?OH oxidation in the presence of Fe(II). TCE degradation follows zeroth-order kinetics with rate constants increasing from 2.0 to 4.6 μM/min with increasing initial Fe(II) concentration from 0 to 27.3 mg/L at pH 4. A good correlation between TCE degradation rate constants and ?OH generation rate constants confirms that ?OH is the predominant reactive species for TCE oxidation. Presence of 10 mM Na(2)SO(4), NaCl, NaNO(3), NaHCO(3), K(2)SO(4), CaSO(4), and MgSO(4) does not significantly influence degradation, but sulfite and sulfide greatly enhance and slightly suppress degradation, respectively. A novel Pd-based electrochemical process is proposed for groundwater remediation.     

Susceptibility of Escherichia coli isolated from uteri of postpartum dairy cows to antibiotic and environmental bacteriophages. Part II: In vitro antimicrobial activity evaluation of a bacteriophage cocktail and several antibiotics

The use of pathogenic-specific antimicrobials, as proposed by bacteriophage therapy, is expected to reduce the incidence of resistance development. Eighty Escherichia coli isolated from uteri of Holstein dairy cows were phenotypically characterized for antimicrobial resistance to ampicillin, ceftiofur, chloramphenicol, florfenicol, spectinomycin, streptomycin, and tetracycline by broth microdilution method. The lytic activity of a bacteriophage cocktail against all isolates was performed by a similar method. Additionally, the effect of different concentrations of antimicrobials and multiplicities of infections (MOI) of the bacteriophage cocktail on E. coli growth curve was measured. Isolates exhibited resistance to ampicillin (33.7%), ceftiofur (1.2%), chloramphenicol (100%), and florfenicol (100%). All strains were resistant to at least 2 of the antimicrobial agents tested; multidrug resistance (≥3 of 7 antimicrobials tested) was observed in 35% of E. coli isolates. The major multidrug resistance profile was found for ampicillin-chloramphenicol-florfenicol, which was observed in more than 96.4% of the multidrug-resistant isolates. The bacteriophage cocktail preparation showed strong antimicrobial activity against multidrug-resistant E. coli. Multiplicity of infection as low as 10⁻⁴ affected the growth of the E. coli isolates. The ratio of 10 bacteriophage particles per bacterial cell (MOI = 10¹) was efficient in inhibiting at least 50% of all isolates. Higher MOI should be tested in future in vitro studies to establish ratios that completely inhibit bacterial growth during longer periods. All isolates resistant to florfenicol were resistant to chloramphenicol and, because florfenicol was recently introduced into veterinary clinics, this finding suggests that the selection pressure of chloramphenicol, as well as other antimicrobials, may still play a relevant role in the emergence and dissemination of florfenicol resistance in E. coli. The bacteriophage cocktail had a notable capacity to inhibit the in vitro growth of E. coli isolates, and it may be an attractive alternative to conventional treatment of metritis by reducing E. coli in uteri of postpartum dairy cows.