Enhanced photocatalytic inactivation of bacteria on Fe-containing TiO2 nanoparticles under fluorescent light

Enhanced solar light-driven photocatalysis of norfloxacin using Fe-doped TiO2: RSM optimization, DFT simulations, and toxicity study

This study investigates the photocatalytic degradation of norfloxacin (NFX) utilizing Fe-doped TiO2 nanocomposite under natural sunlight. TiO2-based photocatalysts were synthesized using chemical precipitation varying Fe-dopant concentration and characterized in detail. Theoretical modelling, centred on density functional theory (DFT), elucidated that Fe ions within the TiO2 lattice are effectively confined, thereby narrowing the wide band gap of TiO2. The findings strongly support that Fe3+ ions augmented the photocatalytic activity of TiO2 by facilitating an intermediate interfacial route for electron and hole transfer, particularly up to an optimal dopant concentration of 1.5 M%. Subsequently, a three-level Box-Behnken design (BBD) was developed to determine the initial pH, optimal catalyst concentration, and drug dosage. High-performance liquid chromatography-mass spectrometry (HPLC-MS) was employed to identify reaction intermediates, thereby establishing a potential degradation pathway. Notably, sustained recyclability was achieved, with 82% degradation efficiency maintained over five cycles. Additionally, the toxicity of degradation intermediates was evaluated through bacterial and phytotoxicity tests, affirming the environmental safety of treated water. In vitro toxicity of the nanomaterial was also examined, emphasizing its environmental implications. Scavenger experiments revealed that hole and hydroxyl radicals were the primary active species in Fe-TiO2-based photocatalysis. Furthermore, the antibacterial potential of the synthesized catalyst was assessed using Escherichia coli and Staphylococcus aureus to observe their respective antibacterial responses.

Combination Strategies of Different Antimicrobials: An Efficient and Alternative Tool for Pathogen Inactivation

Despite the discovery and development of an array of antimicrobial agents, multidrug resistance poses a major threat to public health and progressively increases mortality. Recently, several studies have focused on developing promising solutions to overcome these problems. This has led to the development of effective alternative methods of controlling antibiotic-resistant pathogens. The use of antimicrobial agents in combination can produce synergistic effects if each drug invades a different target or signaling pathway with a different mechanism of action. Therefore, drug combinations can achieve a higher probability and selectivity of therapeutic responses than single drugs. In this systematic review, we discuss the combined effects of different antimicrobial agents, such as plant extracts, essential oils, and nanomaterials. Furthermore, we review their synergistic interactions and antimicrobial activities with the mechanism of action, toxicity, and future directions of different antimicrobial agents in combination. Upon combination at an optimum synergistic ratio, two or more drugs can have a significantly enhanced therapeutic effect at lower concentrations. Hence, using drug combinations could be a new, simple, and effective alternative to solve the problem of antibiotic resistance and reduce susceptibility.

Synthesis of new composite based on TiO2 immobilized in glass fibers for photo-catalytic degradation of chlorobenzene in aqueous solutions

In this study photo-catalytic degradation of chlorobenzene from aqueous solutions using CQD decorated Fe-doped TiO₂ immobilized in Glass Fibers (GF) was investigated. Characteristics of the synthesized photo-catalyst were determined by EF-SEM, EDX, BET, XRD, FTIR, and DRS analysis. Additionally, DRS analysis demonstrated adding CQD to the TiO₂-Fe reduced its band gap energy from 2.96 eV to 2.91eV, while that was 3.10 eV for undoped TiO₂. Among that three photo-catalysts, GF/CQD_(4.5 wt%) decorated Fe-TiO₂ composite had performance nearly 100.0%, when pH was 5 and low concentration of chlorobenzene. In addition, GF/CQD_(4.5 wt%) decorated Fe-TiO₂ composite show it could be well applied for five times and with a little reduction on the performance. Also, no detectable Fe found to be released from the composite. Minimum inhibitory concentration (MIC) for E. coli bacteria was 12.2 mg L^-1 of chlorobenzene residual. Our findings show the catalyst was successful for chlorobenzene removal in the wastewater effluent. In conclusion, present hybrid composite could successfully and safely remove chlorobenzene from synthetic aqueous solution.

Machine learning and materials modelling interpretation of in vivo toxicological response to TiO2 nanoparticles library (UV and non-UV exposure)

Assessing the risks of nanomaterials/nanoparticles (NMs/NPs) under various environmental conditions requires a more systematic approach, including the comparison of effects across many NMs with identified different but related characters/descriptors. Hence, there is an urgent need to provide coherent (eco)toxicological datasets containing comprehensive toxicity information relating to a diverse spectra of NPs characters. These datasets are test benches for developing holistic methodologies with broader applicability. In the present study we assessed the effects of a custom design Fe-doped TiO₂ NPs library, using the soil invertebrate Enchytraeus crypticus (Oligochaeta), via a 5-day pulse via aqueous exposure followed by a 21-days recovery period in soil (survival, reproduction assessment). Obviously, when testing TiO₂, realistic conditions should include UV exposure. The 11 Fe-TiO₂ library contains NPs of size range between 5-27 nm with varying %Fe (enabling the photoactivation of TiO₂ at energy wavelengths in the visible-light range). The NPs were each described by 122 descriptors, being a mixture of measured and atomistic model descriptors. The data were explored using single and univariate statistical methods, combined with machine learning and multiscale modelling techniques. An iterative pruning process was adopted for identifying automatically the most significant descriptors. TiO₂ NPs toxicity decreased when combined with UV. Notably, the short-term water exposure induced lasting biological responses even after longer-term recovery in clean exposure. The correspondence with Fe-content correlated with the band-gap hence the reduction of UV oxidative stress. The inclusion of both measured and modelled materials data benefitted the explanation of the results, when combined with machine learning.

Photo-catalytic degradation of bisphenol-a from aqueous solutions using GF/Fe-TiO2-CQD hybrid composite

In this photocatalytic study, removal of bisphenol-A from aqueous solution was studied using the GF/Fe-TiO2-CQD composite. Due to its health and environmental effects, this compound should be disposed of sources that are mainly industrial wastewater. The phis-chemical properties of the composite were determined by traditional analyzes of EF-SEM, EDX, BET, XRD, FTIR and DRS. In this study, different ratios of CQD in the composite (1.5, 4.5 and 7.5 wt%), pH, and bisphenol-A concentration as variable parameters were investigated. All analyzes, EF-SEM, EDX, BET, XRD, FTIR, show that the GF/Fe-TiO2-CQD composite is well coated on glass fibers (GF) and all the elements in the catalyst are present. On the other hand, DRS analysis showed that CQD reduces the band gap of Fe-TiO2 from 2.96 eV to 2.91 eV, it was 3.10 eV for TiO2. Among different catalysts, GF/Fe-TiO2-CQD4.5wt% has the best performance. The results showed that for GF/Fe-TiO2-CQD4.5wt%, optimum for the process was at pH = 6 in low concentration of bisphenol-A. The first order model for the photocatalytic degradation process were well studied. In addition, GF/Fe-TiO2-CQD4.5wt% showed that it can be used many times with a minimal reduction in performance. As a result, the GF/Fe-TiO2-CQD4.5wt% composite can successfully remove bisphenol-A form in synthetic aqueous solution. However, it is necessary to further studies to applied that for real water source in water and wastewater treatment plants.

Synthesis and Characterization of Fe-TiO2 Nanomaterial: Performance Evaluation for RB5 Decolorization and In Vitro Antibacterial Studies

A photocatalytic system for decolorization of double azo reactive black 5 (RB5) dye and water disinfection of E. coli was developed. Sol gel method was employed for the synthesis of Fe-TiO₂ photocatalysts and were characterized using thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) coupled with energy dispersive X-ray analysis (EDX), transmission electron microscopy (TEM), diffuse reflectance spectroscopy (DRS) and Brunauer–Emmett–Teller (BET) analysis. Results showed that photocatalytic efficiency was greatly influenced by 0.1 weight percent iron loading and 300 °C calcination temperature. The optimized reaction parameters were found to be the ambient temperature, working solution pH 6.2 and 1 mg g⁻¹ dose to completely decolorize RB5. The isotherm studies showed that RB5 adsorption by Fe-TiO₂ followed the Langmuir isotherm with maximum adsorption capacity of 42.7 mg g⁻¹ and K_ads 0.0079 L mg⁻¹. Under illumination, the modified photocatalytic material had higher decolorization efficiency as compared to unmodified photocatalyst. Kinetic studies of the modified material under visible light irradiation indicated the reaction followed the pseudo-first-order kinetics. The illumination reaction followed the Langmuir-Hinshelwood (L-H) model as the rate of dye decolorization increased with an incremental increase in dye concentration. The L-H constant K_c was 1.5542 mg L^–1∙h^–1 while K_ads was found 0.1317 L mg^–1. The best photocatalyst showed prominent percent reduction of E. coli in 120 min. Finally, 0.1Fe-TiO₂-300 could be an efficient photocatalyst and can provide a composite solution for RB5 decolorization and bacterial strain inhibition.

Preparation and characterization of titanium dioxide nanoparticles and in vitro investigation of their cytotoxicity and antibacterial activity against Staphylococcus aureus and Escherichia coli

Titanium dioxide nanoparticles (TiO₂ NPs) are photo-active metallic nanoparticles becoming promising agents in modern biomedical applications. Herein, a novel process for the synthesis of TiO₂ NPs with high stability was developed by a sol-gel process and to investigate their cytotoxicity and antibacterial activity. Numerous experiments have been performed to confirm the morphologies, compositions, and physicochemical properties of prepared TiO₂ NPs, such as field emission scanning electron microscopy, dynamic light scattering, Zeta potential, Fourier transform infrared spectroscopy and X-ray diffraction. MTT assay was applied to assess the cytotoxicity of the prepared nanoparticles. The results indicate that the synthesized nanoparticles' diameter is about 68 nm and contains the anatase phase, in the range of 2θ from 25 to 80 °C. The hydrodynamic radius of nanoparticles is about 140.4 nm, and the zeta potential of nanoparticles is about -44.6 mV. The MTT results have not shown any toxicity; the antibacterial inhibitory effect of TiO₂ NPs at 200 mg/mL concentrations exhibited superior antibacterial activity at 15.9 ± 0.1, 14.0 ± 0.1 against Staphylococcus aureus and Escherichia coli, respectively. In conclusion, colloidal solutions with high stability were successfully synthesized, contributing to decreased dimensions and increased antibacterial properties.

Photocatalytic Reactivity of Carbon–Nitrogen–Sulfur-Doped TiO2 Upconversion Phosphor Composites

Sol–gel synthesized N-doped and carbon–nitrogen–sulfur (CNS)-doped TiO2 solutions were deposited on upconversion phosphor using a dip coating method. Scanning electron microscopy (SEM) imaging showed that there was a change in the morphology of TiO2 coated on NaYF4:Yb,Er from spherical to nanorods caused by additional urea and thiourea doping reagents. Fourier transform infrared (FTIR) spectroscopy further verified the existence of nitrate–hyponitrite, carboxylate, and SO42− because of the doping effect. NaYF4:Yb,Er composites coated with N- and CNS-doped TiO2 exhibited a slight shift of UV-Vis spectra towards the visible light region. Photodecomposition of methylene blue (MB) was evaluated under 254 nm germicidal lamps and a 300 W Xe lamp with UV/Vis cut off filters. The photodegradation of toluene was evaluated on TiO2/NaYF4:Yb,Er and CNS-doped TiO2/NaYF4:Yb,Er samples under UV light illumination. The photocatalytic reactivity with CNS-doped TiO2/NaYF4:Yb,Er surpassed that of the undoped TiO2/NaYF4:Yb,Er for the MB solution and toluene. Photocatalytic activity is increased by CNS doping of TiO2, which improves light sensitization as a result of band gap narrowing due to impurity sites.

Nickel-Graphene Nanoplatelet Deposited on Carbon Fiber as Binder-Free Electrode for Electrochemical Supercapacitor Application

A binder-free process for the electrode preparation for supercapacitor application was suggested by drop casting graphene nanoplatelets on a carbon fiber (GnP@CF) followed by electrodeposition of Ni nanoparticles (NPs). The microstructure of the electrode showed that Ni was homogeneously distributed over the surface of the GnP@CF. XRD analysis confirmed the cubic structure of metallic Ni NPs. The Ni-GnP@CF electrode showed excellent pseudocapacitive behavior in alkaline solution by exhibiting a specific capacitance of 480 F/g at 1.0 A/g, while it was 375 F/g for Ni@CF. The low value of series resistance of Ni-GnP@CF (1 Ω) was attributed to the high capacitance. The enhanced capacitance of the electrode could be correlated to the highly nanoporous structure of the composite material, synergetic effect of the electrical double layer charge-storage properties of graphene, and the pseudocapacitive nature of Ni NPs.

Anti-bacterial activity of inorganic nanomaterials and their antimicrobial peptide conjugates against resistant and non-resistant pathogens

This review details the antimicrobial applications of inorganic nanomaterials of mostly metallic form, and the augmentation of activity by surface conjugation of peptide ligands. The review is subdivided into three main sections, of which the first describes the antimicrobial activity of inorganic nanomaterials against gram-positive, gram-negative and multidrug-resistant bacterial strains. The second section highlights the range of antimicrobial peptides and the drug resistance strategies employed by bacterial species to counter lethality. The final part discusses the role of antimicrobial peptide-decorated inorganic nanomaterials in the fight against bacterial strains that show resistance. General strategies for the preparation of antimicrobial peptides and their conjugation to nanomaterials are discussed, emphasizing the use of elemental and metallic oxide nanomaterials. Importantly, the permeation of antimicrobial peptides through the bacterial membrane is shown to aid the delivery of nanomaterials into bacterial cells. By judicious use of targeting ligands, the nanomaterial becomes able to differentiate between bacterial and mammalian cells and, thus, reduce side effects. Moreover, peptide conjugation to the surface of a nanomaterial will alter surface chemistry in ways that lead to reduction in toxicity and improvements in biocompatibility.

Boron-Doped TiO2-CNT Nanocomposites with Improved Photocatalytic Efficiency toward Photodegradation of Toluene Gas and Photo-Inactivation of Escherichia coli

An in-situ sol-gel method was used for the synthesis of boron-doped TiO2-CNT nanocomposites with varied boron concentrations from 1 to 4 mol%. The synthesized nanocomposites were characterized by various techniques, namely XRD, UV-DRS, TEM, PL, and XPS; all results show that 3 mol% B-TiO2-CNT nanocomposites have superior properties to pure TiO2, 3B-TiO2 nanoparticles, and other nanocomposites. TEM images clearly show the B-TiO2 nanoparticles decorated on the CNT surface. Photo-luminescence studies confirm that boron doping of up to 3 mol% in TiO2-CNT nanocomposites reduces the electron-hole pair recombination rate. The photocatalytic performance of the B-TiO2-CNT nanocomposites was tested against the photodegradation of toluene gas and the photocatalytic inactivation of E. coli in the presence of UV and visible light respectively. B-TiO2-CNT (3 mol%) nanocomposites show the highest photocatalytic activity.

Preparation of TiO2 and Fe-TiO2 with an Impinging Stream-Rotating Packed Bed by the Precipitation Method for the Photodegradation of Gaseous Toluene

Nano-TiO₂ has always been one of the most important topics in the research of photocatalysts due to its special activity and stability. However, it has always been difficult to obtain nano-TiO₂ with high dispersion, a small particle size and high photocatalytic activity. In this paper, nano-TiO₂ powder was prepared by combining the high-gravity technique and direct precipitation method in an impinging stream-rotating packed bed (IS-RPB) reactor followed by Fe³⁺ in-situ doping. TiOSO₄ and NH₃·H₂O solutions were cut into very small liquid microelements by high-speed rotating packing, and the mass transfer and microscopic mixing of the nucleation and growth processes of nano-TiO₂ were strengthened in IS-RPB, which was beneficial to the continuous production of high quality nano-TiO₂. Pure TiO₂ and iron-doped nano-TiO₂ (Fe-TiO₂) were obtained in IS-RPB and were investigated by means of X-ray diffraction (XRD), Raman, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), ultraviolet-visible diffuse reflectance spectroscopy (UV-vis DRS) and Brunauer-Emmett-Teller (BET) analysis, which found that pure TiO₂ had a particle size of about 12.5 nm, good dispersibility and a complete anatase crystal at the rotating speed of packing of 800 rpm and calcination temperature of 500 °C. The addition of Fe³⁺ did not change the crystalline structure of TiO₂. Iron was highly dispersed in TiO₂ without the detection of aggregates and was found to exist in a positive trivalent form by XPS. With the increase of iron doping, the photoresponse range of TiO₂ to visible light was broadened from 3.06 eV to 2.26 eV. The degradation efficiency of gaseous toluene by Fe-TiO₂ under ultraviolet light was higher than that of pure TiO₂ and commercial P25 due to Fe³⁺ effectively suppressing the recombination of TiO₂ electrons and holes; the highest efficiency produced by 1.0% Fe-TiO₂ was 95.7%.

Environmental disinfection with photocatalyst as an adjunctive measure to control transmission of methicillin-resistant Staphylococcus aureus: a prospective cohort study in a high-incidence setting

Background

Environmental disinfection with continuously antimicrobial surfaces could offer superior control of surface bioburden. We sought to decide the efficacy of photocatalyst antimicrobial coating in reducing methicillin-resistant Staphylococcus aureus (MRSA) acquisition in high incidence setting.

Methods

We performed prospective cohort study involving patients hospitalized in medical intensive care unit. A titanium dioxide-based photocatalyst was coated on high touch surfaces and walls. Five months of pre-intervention data were compared with five months of post-intervention data. The incidence rates of multidrug-resistant organism acquisition and the rates of hospital-acquired blood stream infection, pneumonia, urinary tract infection, and Clostridium difficile–associated diseases were compared using Cox proportional hazards regression analysis.

Results

In total, 621 patients were included. There was significant decrease in MRSA acquisition rate after photocatalyst coating (hazard ratio, 0.37; 95% confidence interval, 0.14–0.99; p = 0.04). However, clinical identification of vancomycin-resistant Enterococcus spp. and multidrug-resistant Acinetobacter baumannii did not decrease significantly. The hazard of contracting hospital-acquired pneumonia during the intervention period compared to baseline period was 0.46 (95% confidence interval, 0.23–0.94; p = 0.03).

Conclusions

In conclusion, MRSA rate was significantly reduced after photocatalyst coating. We provide evidence that photocatalyst disinfection can be an adjunctive measure to control MRSA acquisition in high-incidence settings.

Trial registration

ISRCTN Registry (ISRCTN31972004). Registered retrospectively on November 19, 2018.

Electronic supplementary material

The online version of this article (10.1186/s12879-018-3555-1) contains supplementary material, which is available to authorized users.

Critical evaluation of mechanism responsible for biomass abatement during electrochemical coagulation (EC) process: A critical review

This is a first review paper that delineates fundamental disinfection mechanism undergoes during the simple electrochemical coagulation (EC) process. The elucidation of detailed mechanistic phenomenon of EC process involved would help to enhance the disinfection efficiency. In this context, the biomass (bacteria, virus and algae) abatement mechanism by EC is critically reviewed and rationalized based on the experimental demonstration performed from the recent decade. Whereas, the effect of most significant abiotic operating parameters, dissolved contents and bacteria cell wall composition on biomass reduction are explored in detail. From these analyses, physical removal and chemical inactivation routes are identified for bacteria abatement mechanism during the EC process using sacrificial electrodes. Which includes (i) enmeshment of microbial contaminants by EC flocs, (ii) sweeping flocculation is preferentially for destabilization of negatively charged biomass, and (iii) inactivation/attenuation of micro-organism cell walls by electrochemically induced reactive oxygen species (ROS) or direct interaction of electric field. Perhaps, the overall abatement mechanism attributes due to the aforementioned phenomenon endures independently and/or synergistically during the EC process. Nonetheless, to obtain better understanding of virus and algae abatement mechanism, we require more experimental investigation on algae and virus removal. Eventually, more intensive research efforts on biomass attenuation by EC are most important to reinforce this claim.

Visible Light Photocatalytic Activity of NaYF4:(Yb,Er)-CuO/TiO2 Composite

TiO2 photocatalysts are limited to ultraviolet light photo-activation, however, by coupling with NaYF4:(Yb,Er) they can utilize visible light activation, but with low efficiencies. In order to enhance visible light photo-activity, CuO nanoparticles were coupled with NaYF4:(Yb,Er) by mechanical ball-milling and coated with TiO2-sol. The coupling of CuO nanoparticles with NaYF4:(Yb,Er)/TiO2 caused the formation of a NaYF4:(Yb,Er)-CuO/TiO2 composite capable of visible absorption with a remarkably reduced band gap of ~2.5 eV. The NaYF4:(Yb,Er)-CuO/TiO2 composite in H2O2 showed the most efficient methylene blue (MB) degradation efficiency of more than 99.5% after exposure to visible light.

Photoinactivation of bacteria by using Fe-doped TiO2-MWCNTs nanocomposites

In this study, nanocomposites of Fe-doped TiO₂ with multi-walled carbon nanotubes (0.1- 0.5 wt. %) were prepared by using sol-gel method. The structural and morphological analysis were carried out with using X-ray diffraction pattern and transmission electron microscopy, which confirm the presence of pure anatase phase and particle sizes in the range 15-20 nm. X-ray photoelectron spectroscopy was used to determine the surface compositions of the nanocomposites. UV-vis diffuse reflectance spectra confirm redshift in the optical absorption edge of nanocomposites with increasing amount of multi-walled carbon nanotubes. Nanocomposites show photoinactivation against gram-positive Bacillus subtilis as well as gram-negative Pseudomonas aeruginosa. Fe-TiO₂-multi-walled carbon nanotubes (0.5 wt. %) nanocomposites show higher photoinactivation capability as compared with other nanocomposites. The photoluminescence study reveals that the Fe-TiO₂-multi-walled carbon nanotubes nanocomposites are capable to generate higher rate of reactive oxygen species species than that of other nanocomposites. Our experimental results demonstrated that the Fe-TiO₂-multi-walled carbon nanotubes nanocomposites act as efficient antibacterial agents against a wide range of microorganisms to prevent and control the persistence and spreading of bacterial infections.