Linear and nonlinear optical studies of bare and copper doped TiO2 nanoparticles via sol gel technique

Sol-Gel-Derived TiO2 and TiO2/Cu Nanoparticles: Synthesis, Characterization, and Antibacterial Efficacy

This study reports on the antibacterial efficacy of both the TiO2 and TiO2/Cu nanoparticles prepared through the sol-gel method. The materials were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and Brunauer-Emmett-Teller (BET) analysis. The SEM and TEM showed the spherical morphology of the nanoparticles, while EDX and XPS confirmed the incorporation of Cu into the TiO2 nanoparticles. The XRD confirmed the formation of the tetragonal anatase phase of TiO2/Cu while the FTIR revealed the functional groups linked to the doped TiO2 nanoparticles. The thermal stability of TiO2/Cu was found to be lower than pure TiO2. Moreover, TiO2 and the doped TiO2 nanoparticles were notably effective against Bacillus subtilis(B. subtilis) andEscherichia coli(E. coli); however, the addition of Cu to TiO2 did not have any effect on the antibacterial activity probably due to the lower weight content in the composites. Interestingly, the antibacterial efficiency was determined to be 90 and 80% against B. subtilis and E. coli, respectively.

Fabrication and Characterization of Electrospun Cu-Doped TiO2 Nanofibers and Enhancement of Photocatalytic Performance Depending on Cu Content and Electron Beam Irradiation

Titanium dioxide (TiO₂) is a widely studied material with many attractive properties such as its photocatalytic features. However, its commercial use is limited due to issues such as deactivation in the visible spectrum caused by its wide bandgap and the short lifetime of photo-excited charge carriers. To overcome these challenges, various modifications could be considered. In this study, we investigated copper doping and electron beam treatment. As-spun TiO2 nanofibers were fabricated by electrospinning a TiO2 sol, which obtained viscosity through a polyvinylpyrrolidone (PVP) matrix. Cu-doped TiO2 nanofibers with varying dopant concentrations were synthesized by adding copper salts. Then, the as-spun nanofibers were calcined for crystallization. To evaluate photocatalytic performance, a photodegradation test of methylene blue aqueous solution was performed for 6 h. Methylene blue concentration was measured over time using UV-Vis spectroscopy. The results showed that Cu doping at an appropriate concentration and electron-beam irradiation showed improved photocatalytic efficiency compared to bare TiO2 nanofibers. When the molar ratio of Cu/Ti was 0.05%, photodegradation rate was highest, which was 10.39% higher than that of bare TiO2. As a result of additional electron-beam treatment of this sample, photocatalytic efficiency improved up to 8.93% compared to samples without electron-beam treatment.

Enhanced surface second harmonic generation in nanolaminates

Second-harmonic generation (SHG) is a second-order nonlinear optical process that is not allowed in media with inversion symmetry. However, due to the broken symmetry at the surface, surface SHG still occurs, but is generally weak. We experimentally investigate the surface SHG in periodic stacks of alternating, subwavelength dielectric layers, which have a large number of surfaces, thus enhancing surface SHG considerably. To this end, multilayer stacks of SiO₂/TiO₂ were grown by Plasma Enhanced Atomic Layer Deposition (PEALD) on fused silica substrates. With this technique, individual layers of a thickness of less than 2 nm can be fabricated. We experimentally show that under large angles of incidence (> 20 degrees) there is substantial SHG, well beyond the level, which can be observed from simple interfaces. We perform this experiment for samples with different periods and thicknesses of SiO₂/TiO₂ and our results are in agreement with theoretical calculations.

Bisphenol S degradation via persulfate activation under UV-LED using mixed catalysts: Synergistic effect of Cu-TiO2 and Zn-TiO2 for catalysis

A photocatalyst composed of Zn-TiO₂ and Cu-TiO₂ through simple physical mixing was used to activate persulfate(PS) for Bisphenol S (BPS) degradation. Zn-TiO₂ and Cu-TiO₂ were prepared with a sol gel method and were characterized by X-ray diffraction (XRD), Raman, Transmission electron microscope (TEM), Fourier-transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The two catalysts have shown an obvious synergistic effect in the photocatalytic degradation process. When 5 mM persulfate and 0.3 g/L catalyst were used, the removal rate of mixed catalyst (0.2 g/L Zn-TiO₂ and 0.1 g/L Cu-TiO₂) is 100 % in 18 min, which is significantly better than that of 0.3 g/L Zn-TiO₂(58 %) and 0.3 g/L Cu-TiO₂(90 %). Typically, the effects of various operation parameters, including the ratio of Cu-TiO₂/Zn-TiO₂, catalyst dosage, persulfate dosage, initial concentration of BPS, and initial solution pH, were examined. Reactive oxygen species (ROS) in the UV/mixed catalyst/PS process was identified by scavenger and electron paramagnetic resonance (EPR) tests. The superoxide radicals generated by both Zn-TiO₂ and the hydrolysis of persulfate in the system could accelerate the Cu (II)/Cu(I) redox cycles and results in the synergistic effect. This study proposed a new and effective way to improve the reaction by simply combining two catalysts, and unraveled the mechanism behind the synergistic effect, which could provide new ideas to use the catalyst more effectively for wastewater treatment or other areas.

Nitrogen and Carbon Nitride-Doped TiO2 for Multiple Catalysis and Its Antimicrobial Activity

Nitrogen (N) and carbon nitride (C3N4)-doped TiO2 nanostructures were prepared using co-precipitation route. Fixed amount of N and various concentrations (0.1, 0.2, 0.3 wt%) of C3N4 were doped in TiO2 lattice. Through multiple techniques, structural, chemical, optical and morphological properties of samples were thoroughly investigated. XRD results verified anatase TiO2 presence along the substitutional doping of N, while higher degree of crystallinity as well as increased crystallite size were noticed after doping. HR-TEM study revealed formation of nanostructures incorporated on two dimensional (2D) C3N4 nanosheet surface. Elemental composition was checked out using EDS technique which confirmed the presence of dopant in product. Optical characteristics were evaluated with UV-vis spectroscopy which depicted representative redshift in absorption spectra resulted in a reduction in bandgap energy in N/C3N4-doped TiO2 samples. The formation of Ti-O-Ti bonds and different molecular vibrations were disclosed by FTIR. Trap sites and charge carrier's migration in the materials were evaluated with PL spectroscopy. Multiple catalytic activities (photo, sono and photo-sono) were undertaken to evaluate the dye degradation performance of prepared specimen against methylene blue and ciprofloxacin. Further, antimicrobial activity was analyzed against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) bacteria.

Influence of terbium (III) ions on the photocatalytic activity of TiO2 and CeO2 for the degradation of methylene blue in industrial effluents

This study reports the preparation of TiO₂ and CeO₂ doped with different quantities of terbium and discusses the influence of this dopant on the photocatalytic activity of the semiconductors, with respect to the degradation of methylene blue, under ultraviolet and solar radiations. The oxides obtained were characterized by X-ray diffraction, infrared vibrational spectroscopy, diffuse reflectance spectroscopy, scanning electron microscopy, and dispersive energy spectroscopy. The results indicate that the presence of the dopant in TiO₂ favored the formation of the anatase crystalline phase to the detriment of rutile, increased the band gap energy, and decreased the size of the nanoparticles. Doping CeO₂ with Tb resulted in a fluorite-type crystalline structure, reduced band gap, and smaller particle size. The photocatalytic activity decreases as the concentration of terbium increases regardless of the radiation source and nature of the oxide. Furthermore, a better performance was observed for all semiconductors excited by solar radiation in comparison to ultraviolet light. The samples of pure TiO₂ and TiO₂ doped with 0.5 and 1% terbium showed total removal of the dye after less than 120 min of reaction, while the samples of pure CeO₂ and CeO₂ doped with 0.5% terbium showed approximately 80% and 57% of dye removal after 120 min, suggesting that these materials can be promising for the treatment of industrial effluents.

Dye degradation performance, bactericidal behavior and molecular docking analysis of Cu-doped TiO2 nanoparticles

Copper-doped TiO2 was prepared with a sol-gel chemical method. Various concentrations (3, 6, and 9 wt%) of Cu dopant were employed. Several techniques were implemented to assess the structural, optical, morphological and chemical properties of the synthesized samples. Evaluation of elemental composition using SEM-EDS and XRF techniques showed the presence of dopant element in the prepared samples. XRD analysis confirmed the presence of anatase (TiO2) phase with interstitial doping. Incorporation of dopant was observed to enhance the crystallinity and increase the crystallite size of the synthesized products. SAED profiles revealed a high degree of crystallinity in the prepared specimens, which was also evident in the XRD spectra. Optical properties studied using UV-vis spectroscopy depicted a shift of the maximum absorption to the visible region (redshift) that signified a reduction in the band gap energy of Cu-doped TiO2 samples. Examination of morphological features with scanning and high-resolution transmission electron microscopes revealed the formation of spherical nanoparticles with a tendency to agglomerate with increasing dopant concentration. Molecular vibrations and the formation of Ti-O-Ti bonds were revealed through FTIR spectra. PL spectroscopy recorded the trapping efficiency and migration of charge carriers, which exhibited electron-hole recombination behavior. Doped nanostructures showed enhanced bactericidal performance and synergism against S. aureus and E. coli. In summary, Cu-doped TiO2 nanostructures were observed to impede bacteria effectively, which is deemed beneficial in overcoming ailments caused by pathogens such as microbial etiologies. Furthermore, molecular docking analysis was conducted to study the interaction of Cu-doped TiO2 nanoparticles with multiple proteins namely β-lactamase (binding score: -4.91 kcal mol-1), ddlB (binding score: -5.67 kcal mol-1) and FabI (binding score: -6.13 kcal mol-1) as possible targets with active site residues. Dye degradation/reduction of control and Cu-doped samples were studied through absorption spectroscopy. The obtained outcomes of the performed experiment indicated that the photocatalytic activity of Cu-TiO2 enhanced with increasing dopant concentration, which is thought to be due to a decreased rate of electron-hole pair recombination. Consequently, it is suggested that Cu-TiO2 can be exploited as an effective candidate for antibacterial and dye degradation applications.

Highly Crystalline Ordered Cu-dopedTiO2Nanostructure by Paper Templated Method: Hydrogen Production and Dye Degradation under Natural Sunlight

A highly crystalline ordered Cu-TiO2 nanostructure was synthesized using a simple paper template method using cupric nitrate and titanium isopropoxide as precursors. The structural study by XRD confirmed the formation of highly crystalline anatase phase of Cu-TiO2. The broad diffraction peaks of Cu-TiO2 exhibit the nanocrystalline nature of the product. The optical study by UV-DRS indicated the red shift in absorption wavelength with an increase in Cu doping, i.e., towards the visible region. The FE-SEM and FE-TEM study validated the formation of spherical shaped nanoparticles of Cu-TiO2 having sizes in the range of 20–30 nm. Considering the absorption in the visible region, the photocatalytic study was performed for water splitting and rhodamine-B (RhB) dye degradation under natural sunlight. The 2% Cu-doped TiO2 showed the highest photocatalytic hydrogen evolution, i.e., 1400 µmol·g−1·h−1 from water, among the prepared compositions. The photocatalytic performance of Cu-TiO2 conferred complete degradation of RhB dye within 40 min. The higher activity in both cases was attributed to the formation of highly crystalline ordered nanostructure of Cu-doped TiO2. This synthesis approach has potential to prepare other highly crystalline ordered nanostructured semiconductors for different applications.

Photocatalytic and bactericidal properties and molecular docking analysis of TiO2 nanoparticles conjugated with Zr for environmental remediation

Despite implementing several methodologies including a combination of physical, chemical and biological techniques, aquatic and microbial pollution remains a challenge to this day. Recently, nanomaterials have attracted considerable attention due to their extraordinary prospective for utilization toward environmental remediation. Among several probable candidates, TiO₂ stands out due to its potential for use in multifaceted applications. One way to improve the catalytic and antimicrobial potential of TiO₂ is to dope it with certain elements. In this study, Zr-doped TiO₂ was synthesized through a sol–gel chemical method using various dopant concentrations (2, 4, 6, and 8 wt%). Surface morphological, microstructural and elemental analysis was carried out using FESEM and HR-TEM along with EDS to confirm the formation of Zr–TiO₂. XRD spectra showed a linear shift of the (101) anatase peak to lower diffraction angles (from 25.4° to 25.08°) with increasing Zr⁴⁺ concentration. Functional groups were examined via FTIR, an ample absorption band appearing between 400 and 700 cm⁻¹ in the acquired spectrum was attributed to the vibration modes of the Ti–O–Ti linkage present within TiO₂ nanoparticles, which denotes the formation of TiO₂. Experimental results indicated that with increasing dopant concentrations, photocatalytic potential was enhanced significantly. In this respect, TiO₂ doped with 8 wt% Zr (sample 0.08 : 1) exhibited outstanding performance by realizing 98% elimination of synthetic MB in 100 minutes. This is thought to be due to a decreased rate of electron–hole pair recombination that transpires upon doping. Therefore, it is proposed that Zr-doped TiO₂ can be used as an effective photocatalyst material for various environmental and wastewater treatment applications. The good docking scores and binding confirmation of Zr-doped TiO₂ suggested doped nanoparticles as a potential inhibitor against selected targets of both E. coli and S. aureus. Hence, enzyme inhibition studies of Zr-doped TiO₂ NPs are suggested for further confirmation of these in silico predictions.

Despite implementing several methodologies including a combination of physical, chemical and biological techniques, aquatic and microbial pollution remains a challenge to this day.

Structural, optical and photocatalytic properties of Fe and (Co, Fe) co-doped copper oxide spin coated films

Copper oxide films with composition Cu1-x-yFexCoyO (where x⩽0.06 and y⩽0.03 in a molar ratio) and thickness of about 2 μm were spin coated onto ultrasonically cleaned glass substrates. These films were annealed at 500 °C in the air. XRD results show that films are CuO of polycrystalline and monoclinic structures without the detection of any Fe or Co traces. The average crystallite size of pure CuO is 20.44 nm reduced to 18.72 nm after Fe doping, then increased to 26.82 nm due to the co-doping with Co atoms. The optical band gap blue-shifted from 2.15 eV to 2.3 eV followed by red-shift to 2.15 eV after the Co incorporation. The influence of Fe doping and Co co-doping on the optical constants of CuO films as well as the photocatalytic removal of methylene blue (MB) dye is reported. The correlations between the structural modifications and the resultant optical properties are discussed. The obtained results of the fabricated system are compared with those of similar materials.

Sol-gel synthesis and characterization of pure and manganese doped TiO2 nanoparticles--a new NLO active material

Pure and Manganese (4%, 8%, 12% and 16%) doped titanium di-oxide (Mn-TiO2) nanoparticles were synthesized by sol-gel technique. The preparation of pure and Mn doped TiO2 nanoparticles were achieved by tetra-isopropyl orthotitanate and 2-propanol as common starting materials and the products were annealed at 450°C and 750°C to get anatase and rutile phases, respectively. The prepared materials were characterized by X-ray diffraction analysis (XRD), Fourier transform infra-red spectroscopy (FT-IR), UV-VIS-Diffuse reflectance spectroscopy (DRS), Photoluminescence (PL) spectroscopy, Scanning electron microscopy (SEM) with Energy dispersive X-ray analysis (EDX) and Kurtz powder second harmonic generation (SHG) test. XRD patterns confirmed the crystalline nature and tetragonal structure of synthesized materials. The functional groups present in the samples were identified by FTIR study. The allowed direct and indirect band gap energies, as well as the crystallite sizes of obtained nanoparticles were calculated from DRS analysis. Microstructures and elemental identification were done by SEM with EDX analysis. The existence of SHG signals was observed using Nd: YAG laser with fundamental wavelength of 1064 nm. The products were found to be transparent in the entire visible region with cut-off wavelengths within the UV region confirms its suitability for device fabrications.