Synthesis and Photocatalytic Activity of Anatase TiO2 Nanoparticles-coated Carbon Nanotubes

A. Ali G. Inhibitory effect of Titanium dioxide (Tio2) nanoparticles and their synergistic activity with antibiotics in some types of bacteria

Titanium dioxide nanoparticles (TiO2 NPs) were studied as antibacterial agents at different concentrations against clinical and environmental bacterial isolates without UV or photocatalytic activation. Five TiO2 NPs concentrations (20µg/ml,50µg/ml, 100µg/ml,500µg/ml and 1000µg/ml) were studied against 15 bacterial species:10 clinical isolates and 5 environmental isolates) compared with antibiotics Amikacin(AK)and Levloxacin(LEV).Only500µg/ml concentration of TiO2 NPs was active against 7 bacterial isolates (3 clinical and 4 environmental), and 1000µg/ml concentration of TiO2 NPs was effective against 9 isolates (6 clinical and 3 environmental ). These concentrations were mixed with the antibiotics Levloxacin LEV and Amikacin AK to investigate the possibility of synergistic activity against studied bacteria. Bacterial isolate's response or sensitivity to the antibiotic and TiO2 NPs mixture was varied; AK plus 500µg/ml TiO2 NPs concentration showed increased inhibitory activity against 7 isolates (3 clinical, 4 environmental) and 1000µg/ml TiO2 NPs mixed with AK showed increased inhibition activity against one environmental bacterial isolates, where Ak mixed with 500 and Ak plus 1000 µg/ml showed the same effect as the antibiotic alone or less.LEV antibiotic shows no difference in the effect on all 9 bacteria (7 clinical and 2 environmental), while LEV mixed with 500 µg/ml have increased inhibition zones on 4 bacteria (2 clinical, 2 environmental) , and LEV mixed with 1000µg/ml have higher effect than the antibiotic alone on three isolates (2 clinical,1 environmental). Keywords: antibiotic; titanium nanoparticles dioxide; antibacterial.

Structural, Optical, and Arsenic Removal Properties of Sol-Gel Synthesized Fe-Doped TiO2 Nanoparticles

Pure and Fe-doped TiO₂ nanoparticles were synthesized by the sol-gel method. The samples were characterized by X-ray diffraction, Raman spectroscopy, BET, UV-vis diffuse reflectance spectroscopy, and scanning electron microscopy. The results show a dependence between the crystallite size and the amount of dopant, which decreases from 13.02 to 12.81 nm. The same behavior was observed in the optical properties, where the band gap decreased from 3.2 to 2.86 eV. The arsenic (V) adsorption was tested in aqueous solution containing 5 mg/L of arsenic and 0.5 g/L of adsorbent at pH 7 and in dark conditions. The results indicate that the TiO₂-B sample shows a higher arsenic removal, reaching 88% arsenic removal from the water at pH 7. Thus, it is also shown that the best performance occurs at pH 5, where it reaches an arsenic removal of 94%. Ion competition studies show that arsenic removal capacity is slightly affected by chloride, carbonate, nitrate, and sulfate ions. According to the results, the synthesized samples are a promising material for treating arsenic-contaminated water.

Size-strain line-broadening analysis of anatase/brookite (TiO2)-based nanocomposites with carbon (C): XRPD and Raman spectroscopic analysis

A size-strain line-broadening analysis of the XRPD patterns and Raman spectra for two anatase/brookite (TiO₂)-based nanocomposites with carbon (C) was carried out and the results compared with those of a similar sample free of carbon. The crystal structures and microstructures of anatase and brookite, as well as their relative abundance ratio, have been refined from XRPD data by the Rietveld method (the low amount of carbon is neglected). The XRPD size-strain analysis resulted in reliable structure and microstructure results for both anatase and brookite. The experimental Raman spectra of all the samples in the region 100-200 cm^-1 are dominated by a strong feature primarily composed of the most intense modes of anatase (E_g) and brookite (A_1g). The anatase crystallite sizes of 14-17 nm, estimated by XRPD, suggest the application of the phonon confinement model (PCM) for the analysis of the anatase E_g mode, whereas the relatively large brookite crystallite size (27-29 nm) does not imply the use of the PCM for the brookite A_1g mode. Superposition of the anatase E_g mode profile, calculated by the PCM, and the Lorentzian shape of the brookite A_1g mode provide an appropriate simulation of the change in the dominant Raman feature in the spectra of TiO₂-based nanocomposites with carbon. Raman spectra measured in the high-frequency range (1000-2000 cm^-1) provide information on carbon in the investigated nanocomposite materials. The results from field-emission scanning electron microscope (SEM), thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy and nitrogen physisorption measurements support the XRPD and Raman results.

Enhanced photoelectrochemical water splitting activity of carbon nanotubes@TiO2 nanoribbons in different electrolytes

Hydrogen production from water splitting by a photocatalytic process is one way that can be used to solve global problems related to energy depletion and environmental pollution. This work aims to design and characterize a novel photocatalyst nanohybrid carbon nanotubes@TiO₂ nanoribbons (CNTs@TNRs) for enhanced photoelectrochemical (PEC) water splitting in different electrolytes under visible light irradiance. Here, hydrothermal and chemical vapor deposition (HT-CVD) were combined to grow CNTs @ the nanopits of TNRs producing network of nanohybrid CNTs@TNRs. The structural, morphological, optical, and photocatylatic properties of the TNRs and CNTs@TNRs nanohybrid were characterized by different techniques. The crystallite size is increased from 14.86 nm for TNRs to 21.61 nm for CNTs@TNRs nanohybrid. The CNTs@TNRs nanohybrid has well-resolved nanopits on the surface of the TNRs with an average diameter of 10 nm. The absorption edge of CNTs@TNRs relative to TNRs was strongly shifted to the visible light region. The band gap values are 3.78 and 2.07 eV for TNRs and CNTs@TNRs, respectively. The TNRs and CNTs@TNRs were used for the photocatalytic water splitting under visible light irradiance in Na₂S₂O₃, HCl and KOH electrolytes of different concentrations. The calculated incident photon-to-current conversion efficiency (IPCE) was 97% at 510 nm. These values are higher than those previously reported for different photoelectrodes. The number of hydrogen moles was calculated to be 300 μmol h^-1 cm^-2. Therefore, our work demonstrates a feasible route for efficient PEC water splitting under sunlight irradiation utilizing the novel CNTs@TNRs photocatalyst.

Characterization of Photoactive Fe-TiO2 Lime Coatings for Building Protection: The Role of Iron Content

Iron-doped TiO₂ nanoparticles, ranging in Fe concentrations from 0.05 up to 1.00% w/w, were synthesized through a simple sol-gel method. Fourier-transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), Ultraviolet-Visible (UV-Vis) spectroscopy, nitrogen adsorption−desorption isotherms, X-ray photoelectron spectroscopy (XPS), and X-ray absorption near-edge structure spectroscopy (XANES) were used to characterize the synthesized nanoparticles. The characterization of the Fe-doped TiO₂ nanoparticles revealed the predominant presence of anatase crystalline form, as well as the incorporation of the Fe³⁺ ions into the crystal lattice of TiO₂. The photocatalytic assessment of the Fe-doped TiO₂ nanoparticles indicated that the low iron doping titania (0.05 and 0.10% w/w) have a positive effect on the photocatalytic degradation of Methyl Orange under visible radiation. Moreover, FTIR monitoring of calcium hydroxide pastes enriched with low Fe-doped TiO₂ revealed enhancement of carbonation at both early and later stages. Improved photocatalytic performance and increased lime carbonation, observed in lime coatings with low Fe-doped TiO₂ admixtures, established them as invaluable contributors to the protection of the built environment.

Photocatalytic activity of graphene oxide-TiO2 thin films sensitized by natural dyes extracted from Bactris guineensis

This study synthesized and characterized composites of graphene oxide and TiO2 (GO-TiO2). GO-TiO2 thin films were deposited using the doctor blade technique. Subsequently, the thin films were sensitized with a natural dye extracted from a Colombian source (Bactris guineensis). Thermogravimetric analysis, X-ray diffraction, Raman spectroscopy, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and diffuse reflectance measurements were used for physico-chemical characterization. All the samples were polycrystalline in nature, and the diffraction signals corresponded to the TiO2 anatase crystalline phase. Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR) verified the synthesis of composite thin films, and the SEM analysis confirmed the TiO2 films morphological modification after the process of GO incorporation and sensitization. XPS results suggested a possibility of appearance of titanium (III) through the formation of oxygen vacancies (Ov). Furthermore, the optical results indicated that the presence of the natural sensitizer and GO improved the optical properties of TiO2 in the visible range. Finally, the photocatalytic degradation of methylene blue was studied under visible irradiation in aqueous solution, and pseudo-first-order model was used to obtain kinetic information about photocatalytic degradation. These results indicated that the presence of GO has an important synergistic effect in conjunction with the natural sensitizer, reaching a photocatalytic yield of 33%.

Novel Antimicrobial Titanium Dioxide Nanotubes Obtained through a Combination of Atomic Layer Deposition and Electrospinning Technologies

The search for new antimicrobial substances has increased in recent years. Antimicrobial nanostructures are one of the most promising alternatives. In this work, titanium dioxide nanotubes were obtained by an atomic layer deposition (ALD) process over electrospun polyvinyl alcohol nanofibers (PVN) at different temperatures with the purpose of obtaining antimicrobial nanostructures with a high specific area. Electrospinning and ALD parameters were studied in order to obtain PVN with smallest diameter and highest deposition rate, respectively. Chamber temperature was a key factor during ALD process and an appropriate titanium dioxide deposition performance was achieved at 200 °C. Subsequently, thermal and morphological analysis by SEM and TEM microscopies revealed hollow nanotubes were obtained after calcination process at 600 °C. This temperature allowed complete polymer removal and influenced the resulting anatase crystallographic structure of titanium dioxide that positively affected their antimicrobial activities. X-ray analysis confirmed the change of titanium dioxide crystallographic structure from amorphous phase of deposited PVN to anatase crystalline structure of nanotubes. These new nanostructures with very large surface areas resulted in interesting antimicrobial properties against Gram-positive and Gram-negative bacteria. Titanium dioxide nanotubes presented the highest activity against Escherichia coli with 5 log cycles reduction at 200 μg/mL concentration.

Degradation of organic pollutants by bio-inspired rectangular and hexagonal titanium dioxide nanostructures

Dyes are used in textile, printing, leather, pharmaceutical, food and cosmetic industries. Dyes add color and pattern to materials. The presence of even very low concentration of dyes/dyes degradation products in effluent is highly toxic to humans and aquatic organisms. It is important to remove these dye degradation pollutants from the industrial effluents before their disposal. In recent years nanoparticles have been used for the removal of dyes from industrial waste water. Titanium dioxide nanostructures (TiO₂ NS) were synthesized via a one-step facile green process. The formation of TiO₂ NS was confirmed by Fourier transform infrared (FTIR) and Raman spectroscopy. Anatase (~76%) and rutile (~24%) phases were present, as determined by X-ray diffraction (XRD) analysis. X-ray photoelectron spectroscopy (XPS) was used to study the surface oxidation states of the TiO₂ NS. High resolution transmission electron microscopy (HR-TEM) images revealed that the samples had hexagonal and rectangular morphologies, with diameters of ~24-32nm. The TiO₂ NS were used to evaluate the photocatalytic activities of methylene blue (MB) and malachite green (MG) dyes under UV light and in dark conditions. After 60min of UV irradiation, nearly 71% of the MB and 78% of the MG was decolorized in the presence of as-synthesized TiO₂ NPs.

Benefits of tubular morphologies on electron transfer properties in CNT/TiNT nanohybrid photocatalyst for enhanced H2 production

Beneficial effects of tubular morphologies on electron transfer properties in CNT/TiNT nanohybrid photocatalysts for enhanced H₂ production as both co-catalyst and sensitizer are shown schematically here.

Photocatalytic performance of electrospun CNT/TiO2 nanofibers in a simulated air purifier under visible light irradiation

The photocatalytic treatment of gaseous benzene under visible light irradiation was developed using electrospun carbon nanotube/titanium dioxide (CNT/TiO₂) nanofibers as visible light active photocatalysts. The CNT/TiO₂ nanofibers were fabricated by electrospinning CNT/poly(vinyl pyrrolidone) (PVP) solution followed by the removal of PVP by calcination at 450 °C. The molar ratio of CNT/TiO₂ was fixed at 0.05:1 by weight, and the quantity of CNT/TiO₂ loaded in PVP solution varied between 30 and 60 % wt. CNT/TiO₂ nanofibers have high specific surface area (116 m²/g), significantly higher than that of TiO₂ nanofibers (44 m²/g). The photocatalytic performance of the CNT/TiO₂ nanofibers was investigated by decolorization of 1 × 10^-5 M methylene blue (MB) dye (in water solution) and degradation of 100 ppm gaseous benzene under visible light irradiation. The 50-CNT/TiO₂ nanofibers (calcined CNT/TiO₂ nanofibers fabricated from a spinning solution of 50 % wt CNT/TiO₂ based on PVP) had higher MB degradation efficiency (58 %) than did other CNT/TiO₂ nanofibers and pristine TiO₂ nanofibers (15 %) under visible light irradiation. The photocatalytic degradation of gaseous benzene under visible light irradiation on filters made of 50-CNT/TiO₂ nanofibers was carried out in a simulated air purifier system. Similar to MB results, the degradation efficiency of gaseous benzene by 50-CNT/TiO₂ nanofibers (52 %) was higher than by other CNT/TiO₂ nanofibers and pristine TiO₂ nanofibers (18 %). The synergistic effects of the larger surface area and lower band gap energy of CNT/TiO₂ nanofibers were presented as strong adsorption ability and greater visible light adsorption. The CNT/TiO₂ nanofiber prepared in this study has potential for use in air purifiers to improve air treatment efficiency with less energy.

In situ production of titanium dioxide nanoparticles in molten salt phase for thermal energy storage and heat-transfer fluid applications

In this study, TiO₂ nanoparticles (average particle size 16 nm) were successfully produced in molten salt phase and were showed to significantly enhance the specific heat capacity of a binary eutectic mixture of sodium and potassium nitrate (60/40) by 5.4 % at 390 °C and 7.5 % at 445 °C for 3.0 wt% of precursors used. The objective of this research was to develop a cost-effective alternate method of production which is potentially scalable, as current techniques utilized are not economically viable for large quantities. Enhancing the specific heat capacity of molten salt would promote more competitive pricing for electricity production by concentrating solar power plant. Here, a simple precursor (TiOSO₄) was added to a binary eutectic mixture of potassium and sodium nitrate, heated to 450 °C, and cooled to witness the production of nanoparticles.

Fabrication of ordered arrays of CNT/TiO2 nanotubes and their photocatalytic properties

In this work, fabrication and characterization of ordered arrays of CNT/TiO₂ nanotubes imbedded in porous anodic aluminum oxide (AAO) membranes were reported.

MALDI mass spectrometry for probing the anti- staphylococcal capability of TiO2nanoparticles via near-UV and laser irradiation

We report the use of MALDI-MS as an effective tool in investigating the anti-staphylococcal property of TiO₂nanoparticles under near-UV and for the first time also under laser irradiation.

A review on catalytic applications of Au/TiO2 nanoparticles in the removal of water pollutant

Nanomaterials are showing great potential for the improvement of water treatment technologies. In recent years, catalysis and photocatalysis processes using gold nanoparticles (Au-NPs) have received great attention due to their effectiveness in degrading and mineralizing organic compounds. This paper aims to review and summarize the recently published works and R & D progress in the field of photocatalytic oxidation of various water pollutants such as toxic organic compounds (i.e. azo dyes and phenols) by Au-NPs/TiO2 under solar, visible and UV irradiation. Extensive research which has focused on the enhancement of photocatalysis by modification of TiO2 employing Au-NPs is also reviewed. Moreover, the effects of various operating parameters on the photocatalytic activity of these catalysts, such as size and loading amount of Au-NPs, pH and calcination, are discussed. The support type, loading amount and particle size of deposited Au-NPs are the most important parameters for Au/TiO2 catalytic activity. Our study showed in particular that the modification of TiO2, including semiconductor coupling, can increase the photoactivity of Au/TiO2. In contrast, doping large gold NPs can mask or block the TiO2 active sites, reducing photocatalytic activity. The optimized loading amount of Au-NP varied for each experimental condition. Finally, research trends and prospects for the future are briefly discussed.

Photocatalytic reduction of CO2 on TiO2 and other semiconductors

Rising atmospheric levels of carbon dioxide and the depletion of fossil fuel reserves raise serious concerns about the ensuing effects on the global climate and future energy supply. Utilizing the abundant solar energy to convert CO2 into fuels such as methane or methanol could address both problems simultaneously as well as provide a convenient means of energy storage. In this Review, current approaches for the heterogeneous photocatalytic reduction of CO2 on TiO2 and other metal oxide, oxynitride, sulfide, and phosphide semiconductors are presented. Research in this field is focused primarily on the development of novel nanostructured photocatalytic materials and on the investigation of the mechanism of the process, from light absorption through charge separation and transport to CO2 reduction pathways. The measures used to quantify the efficiency of the process are also discussed in detail.

Laundering durability of photocatalyzed self-cleaning cotton fabric with TiO₂ nanoparticles covalently immobilized

Photocatalyzed self-cleaning cotton fabrics with TiO2 nanoparticles covalently immobilized are obtained by cograft polymerization of 2-hydroxyethyl acrylate (HEA) together with the surface functionalized TiO2 nanoparticles under γ-ray irradiation. The covalent bonds between the TiO2 nanoparticles and cotton fabrics bridged by poly(2-hydroxyethyl acrylate) (PHEA) graft chains is strong enough to survive 30 accelerated laundering circles, equivalent to 150 commercial or domestic launderings.

Self-standing crystalline TiO2 nanotubes/CNTs heterojunction membrane: synthesis and characterization

In the present study, we report for the first time synthesis of TiO(2) nanotubes/CNTs heterojunction membrane. Chemical vapor deposition (CVD) of CNTs at 650 °C in a mixture of H(2)/He atmosphere led to in situ detachment of the anodically fabricated TiO(2) nanotube layers from the Ti substrate underneath. Morphological and structural evolution of TiO(2) nanotubes after CNTs deposition were investigated by field- emission scanning electron microscopy (FESEM), glancing angle X-ray diffraction (GAXRD), and X-ray photoelectron spectroscopy (XPS) analyses.

The fabrication of CNTs/TiO(2) photoanodes for sensitive determination of organic compounds

Titanium dioxide (TiO(2)) and carbon nanotubes (CNTs) are the two most popular functional materials in recent years. In this study, CNTs/TiO(2) composite and TiO(2) photoanodes were fabricated by a dip-coating technique, followed by subsequent calcination. The resultant photoanodes were characterized by scanning electron microscopy (SEM), x-ray diffraction (XRD), and UV-visible spectroscopy (UV-vis). The results suggest that the carbon nanotubes were successfully incorporated with the TiO(2) nanoparticulates without damage and that the resultant TiO(2) nanoparticles consisted of anatase and rutile. The CNTs/TiO(2) photoanodes were capable of oxidizing various types of organic compounds (e.g. glucose, potassium hydrogen phthalate, and phenol) in aqueous solutions in a photoelectrochemical bulk cell. In comparison with the pure TiO(2) photoanode, the sensitivity of the photoanode for the detection of organic compounds has been improved by 64%, while the background current was reduced by 80% due to the introduction of the CNTs. These advantages can be ascribed to the improved adsorptivity to organic compounds, increased absorption of UV light and enhanced electron transport at the CNTs/TiO(2) photoanode due to the introduction of the CNTs.