Deposition of Visible Light-Active C-Doped Titania Films via Magnetron Sputtering Using CO₂ as a Source of Carbon

Evaluation of the impact of alkyl silane entity (APTES) on photocatalyst (TiO2) and their photocatalytic degradation of organic compounds for environmental remediation

Environmental pollution by diverse organic pollutants is a serious issue facing humanity, and the scientific community is working hard to find a solution to climatic change due to pollution. Along the same lines, we have tried to find a material/method which is economical and less laborious for achieving the same desired objectives. In this work, the surface modification of titanium dioxide to be used as a photocatalyst was carried out with different concentrations of alkyl silane agent APTES (3-aminopropyltriethoxysilane) and studied their impact on the degradation of representative compound, i.e., methylene blue. The surface-modified TiO₂-APTES nanoparticles were obtained via the solvothermal process. The APTES in different molar (0.21-0.41 M) concentrations was obtained by dissolving APTES in ethanol. The obtained samples were characterized through Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy, and UV-visible spectroscopy. The photocatalytic activity was inferred from the degradation ability of functionalized nanoparticles for methylene blue and evaluated by UV-visible spectroscopy. Our results demonstrated a significant 70% degradation rate of methylene blue.

In situ engineering of highly conductive TiO2/carbon heterostructure fibers for enhanced electrocatalytic degradation of water pollutants

Rational design of nanocomposite electrode materials with high conductivity, activity, and mechanical strength is critical in electrocatalysis. Herein, freestanding, flexible heteronanocomposites were fabricated in situ by carbonizing electrospun fibers with TiO₂ nanoparticles on the surface for electrocatalytic degradation of water pollutants. The carbonization temperature was observed as a dominant parameter affecting the characteristics of the electrodes. As the carbonization temperature increased to 1000 °C, the conductivity of the electrode was significantly enhanced due to the high degree of graphitization (I_D/I_G ratio 1.10) and the dominant rutile phase. Additionally, the formation of TiO₂ protrusions and the C-Ti heterostructure were observed at 1000 °C, which contributed to increasing the electrocatalytic activity. When 1.5 V (vs. Ag/AgCl) was employed, electrocatalytic experiments using the electrode achieved 90% degradation of crystal violet and 10.9-87.5% for an array of micropollutants. The electrical energy-per-order (EEO) for the removal of crystal violet was 0.7 kWh/m³/order, indicative of low-energy requirement. The efficient electrocatalytic activity can be ascribed to the fast electron transfer and the strong ability to generate hydroxyl radicals. Our findings expand efforts for the design of highly conductive heteronanocomposites in a facile in situ approach, providing a promising perspective for the energy-efficient electrocatalytic degradation of water pollutants.

A post-deposition annealing approach for organic residues control in TiO2 and its impact on Sb2Se3/TiO2 device performance

We report a systematic investigation on the influence of the two-step post-deposition treatments (PDTs) on TiO2 buffer layers deposited by ultrasonic spray pyrolysis (USP) for emerging Sb2Se3 photovoltaics. Air annealing...

Efficient Visible-Light Photocatalysis of TiO2-δ Nanobelts Utilizing Self-Induced Defects and Carbon Doping

Efficient visible-light photocatalysis was realized by exploring self-induced defect states, including the abundant surface states of TiO_2-δ nanobelts synthesized through metal-organic chemical vapor deposition (MOCVD). The TiO_2-δ nanobelts exhibited two strong defect-induced absorption peaks at 2.91 and 1.92 eV, overlapping with the conduction band states so that photoexcited carriers can contribute effectively for the photocatalysis reaction. To further enhance visible-light photocatalytic activity, carbon atoms, the by-product of the MOCVD reaction, were self-doped at the judiciously determined growth conditions. The resulting visible-light photocatalysis suggests that the large surface area and consequent high concentration of the surface states of the TiO_2-δ nanobelts can be effectively utilized in a wide range of photocatalysis applications.

Enhanced optical properties and photocatalytic activity of TiO2 nanotubes by using magnetic activated carbon: evaluating photocatalytic reduction of Cr(VI)

In recent years, photocatalytic reduction of Cr(VI) to Cr(III) by TiO₂ nanostructures, as a potent environmental technology has attracted a lot of attention. However, several defects including the large band gap energy of TiO₂, fast photogenerated charge recombination and re-oxidation of Cr(III) restrict their practical application. In this work, the incorporation of TiO₂ nanotubes (TNTs) with magnetic activated carbon (MAC) and photoreduction in the presence of a hole scavenger were studied as a preferable approach. The results revealed that coupling TNTs with 2 wt% MAC can boost the surface area from 89.54 to 307.87 m² g^-1 as well as decrease the band gap energy from 3.1 to 2.7 eV. As a consequence of the enhancement in textural features and optical properties, TNTs/MAC (2%) led to improvement of photoreduction efficiency (from 47% to 66%) in comparison with the TNTs. Meanwhile, the experiments demonstrated that using 0.2 g TNTs/MAC as an optimal dosage in acidic solution increases the photoreduction efficiency up to 81%. The hole scavenger investigation had a marvellous result. It was found that in the presence of oxalic acid, TNTs/MAC (2%) could reduce 97% of Cr(VI) which it was due to trapping oxidative species and charge-transfer-complex-mediated process. Furthermore, the kinetic study affirmed that the photoreduction follow first-order kinetics and the reaction rate constants by TNTs/MAC (2%) are 1.5 times as great as those of TNTs. Moreover, the reusability tests illustrated TNTs/MAC (2%) has good stability and is active even up to the six runs.

Spin Coating Immobilisation of C-N-TiO2 Co-Doped Nano Catalyst on Glass and Application for Photocatalysis or as Electron Transporting Layer for Perovskite Solar Cells

Producing active thin films coated on supports resolves many issues of powder-based photo catalysis and energy harvesting. In this study, thin films of C-N-TiO2 were prepared by dynamic spin coating of C-N-TiO2 sol-gel on glass support. The effect of spin speed and sol gel precursor to solvent volume ratio on the film thickness was investigated. The C-N-TiO2-coated glass was annealed at 350 °C at a ramping rate of 10 °C/min with a holding time of 2 hours under a continuous flow of dry N2. The C-N-TiO2 films were characterised by profilometry analysis, light microscopy (LM), and scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS). The outcomes of this study proved that a spin coating technique followed by an annealing process to stabilise the layer could be used for immobilisation of the photo catalyst on glass. The exposure of C-N-TiO2 films to UV radiation induced photocatalytic decolouration of orange II (O.II) dye. The prepared C-N-TiO2 films showed a reasonable power conversion efficiency average (PCE of 9%) with respect to the reference device (15%). The study offers a feasible route for the engineering of C-N-TiO2 films applicable to wastewater remediation processes and energy harvesting in solar cell technologies.

Studies on interstitial carbon doping from a Ti precursor in a hierarchical TiO2 nanostructured photoanode by a single step hydrothermal route

Carbon doping from a Ti precursor in TiO₂ synthesized by a hydrothermal method was studied. The structural, optical and morphological study of the deposited material was carried out using X-ray diffraction, UV-vis spectroscopy and scanning electron microscopy characterization techniques. The elemental composition of the TiO₂ deposited with different precursor concentrations was studied using X-ray photoelectron spectroscopy and electron dispersive X-ray spectroscopy. The amount of elemental carbon in the TiO₂ matrix is found to be increased as the Ti precursor concentration is increased, which strengthens the proposed idea of carbon doping via a Ti precursor.

Interstitial carbon doping is possible directly from a Ti precursor (titanium(iv) isopropoxide) without using any other carbon source.

Energetics and optical properties of carbon impurities in rutile TiO2

Titanium dioxide is one of the most promising materials for many applications such as photovoltaics and photocatalysis. Non-metal doping of TiO2 is widely used to improve the photoconversion efficiency by shifting the absorption edge from the UV to visible-light region. Here, we employ hybrid density-functional calculations to investigate the energetics and optical properties of carbon (C) impurities in rutile TiO2. The predominant configurations of the C impurities are identified through the calculated formation energies under O-poor and O-rich growth conditions. Under the O-poor condition, we find that C occupying the oxygen site (CO) is energetically favorable for Fermi-level values near the conduction band minimum (n-type TiO2), and acts as a double acceptor. Under the O-rich condition, the Ci-VTi complex is energetically favorable, and is exclusively stable in the neutral charge state. We also find that interstitial hydrogen (Hi) can bind to CO, forming a CO-Hi complex. Our results suggest that CO and CO-Hi are a cause of visible-light absorption under oxygen deficient growth conditions.

Micro-Patterning of Magnetron Sputtered Titanium Dioxide Coatings and Their Efficiency for Photocatalytic Applications

Titanium dioxide thin films were deposited onto sola-lime glass substrates by reactive magnetron sputtering. Fine stainless steel mesh sheets with different aperture sizes were applied as masks over glass substrates to allow the deposition of the coatings with micro-patterned structures and, therefore, enhanced surface area. Non-patterned titania films were deposited for comparison purposes. The titanium dioxide films were post-deposition annealed at 873 K for crystallinity development and then extensively analysed by a number of analytical techniques, including scanning electron microscopy (SEM)/energy-dispersive X-ray spectroscopy (EDX), optical and stylus profilometry, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and UV-Vis spectroscopy. The photocatalytic activity of non-patterned and micro-patterned titania films was assessed under UV light irradiation by three different methods; namely methylene blue, stearic acid, and oleic acid degradation. The results revealed that the micro-patterned coatings significantly outperformed non-patterned titania in all types of photocatalytic tests, due to their higher values of surface area. Increasing the aperture of the stainless steel mesh resulted in lower photocatalytic activity and lower surface area values, compared to the coatings deposited through a smaller aperture mesh.

Effect of the Titanium Isopropoxide:Acetylacetone Molar Ratio on the Photocatalytic Activity of TiO2 Thin Films

TiO₂ thin films with different titanium isopropoxide (TTIP):acetylacetone (AcacH) molar ratios in solution were prepared by the chemical spray pyrolysis method. The TTIP:AcacH molar ratio in spray solution varied from 1:3 to 1:20. TiO₂ films were deposited onto the glass substrates at 350 °C and heat-treated at 500 °C. The morphology, structure, surface chemical composition, and photocatalytic activity of the obtained TiO₂ films were investigated. TiO₂ films showed a transparency of ca 80% in the visible spectral region and a band gap of ca 3.4 eV irrespective of the TTIP:AcacH molar ratio in the spray solution. TiO₂ films consist of the anatase crystalline phase with a mean crystallite size in the range of 30-40 nm. Self-cleaning properties of the films were estimated using the stearic acid (SA) test. A thin layer of 8.8-mM SA solution was spin-coated onto the TiO₂ film. The degradation rate of SA as a function of irradiation time was monitored by Fourier-transform infrared spectroscopy (FTIR). An increase in the TTIP:AcacH molar ratio from 1:4 to 1:8 resulted in a ten-fold increase in the photodegradation reaction rate constant (from 0.02 to the 0.2 min^-1) under ultraviolet light and in a four-fold increase under visible light.

Pure Anatase Phase Titanium Dioxide Films Prepared by Mist Chemical Vapor Deposition

In this research, pure anatase phase titanium dioxide thin films were successfully fabricated for the first time using the mist chemical vapor deposition method, and optional values for deposition temperature and concentration of titanium tetraisopropoxide were established. It was found that the crystallinity of the titanium dioxide film was significantly improved by increasing the deposition temperature. The best crystallinity of titanium dioxide film was obtained at 400 °C. It was confirmed that pure anatase phase titanium dioxide films could be obtained using different concentrations of titanium tetraisopropoxide. The lower concentration of titanium tetraisopropoxide produced better crystallinity in the resultant titanium dioxide film. The morphologies of the titanium dioxide thin films were also significantly influenced by the concentration of titanium tetraisopropoxide in the precursor solution.

Facet-Dependent Cuprous Oxide Nanocrystals Decorated with Graphene as Durable Photocatalysts under Visible Light

Three morphologies (octahedral, hierarchical and rhombic dodecahedral) of crystal Cu₂O with different facets ({111}, {111}/{110}, and {110}) incorporating graphene sheets (denoted as o-Cu₂O-G, h-Cu₂O-G and r-Cu₂O-G, respectively) have been fabricated by using simple solution-phase techniques. Among these photocatalysts, the r-Cu₂O-G possesses the best photocatalytic performance of 98% removal efficiency of methyl orange (MO) with outstanding kinetics for 120 min of visible light irradiation. This enhancement is mainly due to the dangling “Cu” atoms in the highly active {110} facets, resulting in the increased adsorption of negatively charged MO. More importantly, the unique interfacial structures of Cu₂O rhombic dodecahedra connected to graphene nanosheets can not only decrease the recombination of electron-hole pairs but also stabilize the crystal structure of Cu₂O, as verified by a series of spectroscopic analyses (e.g., X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM)). The effective photocatalysts developed in this work could be applied to the efficient decolorization of negatively charged organic dyes by employing solar energy.

Controllable Charge Transfer in Ag-TiO₂ Composite Structure for SERS Application

The nanocaps array of TiO₂/Ag bilayer with different Ag thicknesses and co-sputtering TiO₂-Ag monolayer with different TiO₂ contents were fabricated on a two-dimensional colloidal array substrate for the investigation of Surface enhanced Raman scattering (SERS) properties. For the TiO₂/Ag bilayer, when the Ag thickness increased, SERS intensity decreased. Meanwhile, a significant enhancement was observed when the sublayer Ag was 10 nm compared to the pure Ag monolayer, which was ascribed to the metal-semiconductor synergistic effect that electromagnetic mechanism (EM) provided by roughness surface and charge-transfer (CT) enhancement mechanism from TiO₂-Ag composite components. In comparison to the TiO₂/Ag bilayer, the co-sputtered TiO₂-Ag monolayer decreased the aggregation of Ag particles and led to the formation of small Ag particles, which showed that TiO₂ could effectively inhibit the aggregation and growth of Ag nanoparticles.