Photocatalytic Degradation of Acetaldehyde on Mesoporous TiO2: Effects of Surface Area and Crystallinity on the Photocatalytic Activity

Preparation of TiO2-deposited silica-based catalysts for photocatalytic decomposition of chloro-pesticide to environmentally less toxic species

Herein, titanium (IV) oxide (TiO₂) loaded into montmorillonite (MK10) and sand is presented as an efficient heterogeneous catalyst for the degradation of 1,4-dichlorobenzene (DCB) as a model organic pollutant in the aqueous phase. The catalyst was synthesized by incorporating titanium isopropoxide as a precursor into MK10 through a simple solvent impregnation method, followed by direct calcination. The same protocol was applied to a clean quartz matrix. The resulting catalysts were characterized in detail using a variety of techniques. The TiO₂ deposited MK10 and sand exhibited photochemical removal of DCB (>99% of 100 mg L^-1) from the aqueous phase; this process followed a pseudo second-order kinetic model values in the range of Q_e:111-113 mg g^-1 and K₂: 4-5 × 10^-4 g mg^-1 min^-1. The kinetic plots indicate that after 30 min, the intermediates start to decrease and complete degradation occurs in 180 min. The modified materials showed fast DCB degradation kinetics under photochemical reaction conditions and adsorption under dark reaction conditions. The unmodified matrix adsorbed 99.12-99.88% of the DCB under both dark and light reaction conditions. These photocatalysts are stable, reusable, and least amount of titanium leaching. The simple two step synthesis, and high photocatalytic performance (with 10 mg of the catalyst without any oxidants) of our catalysts can be promising in environmental applications to treat similar organic pollutants in wastewater. These catalysts have enhanced activity and durability for environmental catalytic pollutant degradation reactions and can provide insights beyond single metal oxide catalysts for heterogeneous catalysis at diverse operating conditions.

Tunable TiO2-BN-Pd nanofibers by combining electrospinning and atomic layer deposition to enhance photodegradation of acetaminophen

The demand for fresh and clean water sources is increasing globally, and there is a need to develop novel routes to eliminate micropollutants and other harmful species from water. Photocatalysis is a promising alternative green technology that has shown great performance in the degradation of persistent pollutants. Titanium dioxide is the most used catalyst owing to its attractive physico-chemical properties, but this semiconductor presents limitations in the photocatalysis process due to the high band gap and the fast recombination of the photogenerated carriers. Herein, a novel photocatalyst has been developed, based on titanium dioxide nanofibers (TiO2 NFs) synthesized by electrospinning. The TiO2 NFs were coated by atomic layer deposition (ALD) to grow boron nitride (BN) and palladium (Pd) on their surface. The UV-Vis spectroscopy measurements confirmed the increase of the band gap and the extension of the spectral response to the visible range. The obtained TiO2/BN/Pd nanofibers were then tested for photocatalysis, and showed a drastic increase of acetaminophen (ACT) degradation (>90%), compared to only 20% degradation obtained with pure TiO2 after 4 h of visible light irradiation. The high photocatalytic activity was attributed to the good dispersion of Pd NPs on TiO2-BN nanofibers, leading to a higher transfer of photoexcited hole carriers and a decrease of photogenerated electron-charge recombination. To confirm its reusability, recycling tests on the hybrid photocatalyst TiO2/BN/Pd have been performed, showing a good stability over 5 cycles under UV and visible light. In addition, toxicity tests as well as quenching tests were carried out to check the toxicity of the byproducts formed and to determine active species responsible for the degradation. The results presented in this work demonstrate the potential of TiO2/BN/Pd nanomaterials, and open new prospects for the preparation of tunable photocatalysts.

Application of Bi12ZnO20 Sillenite as an Efficient Photocatalyst for Wastewater Treatment: Removal of Both Organic and Inorganic Compounds

This work aims to synthesize and characterize a material that can be used as an effective catalyst for photocatalytic application to remove both organic and inorganic compounds from wastewater. In this context, sillenite Bi12ZnO20 (BZO) in a pure phase was synthesized using the sol-gel method. Before calcination, differential scanning calorimetry (DSC) analysis was done to determine the temperature of the formation of the sillenite phase, which was found to be 800 °C. After calcination, the phase was identified by X-ray diffraction (XRD) and then refined using the Rietveld refinement technique. The results prove that BZO crystals have a cubic symmetry with the space group I23 (N°197); the lattice parameters of the structure were also determined. From the crystalline size, the surface area was estimated using the Brunauer-Emmett-Teller (BET) method, which was found to be 11.22 m2/g. The formation of sillenite was also checked using the Raman technique. The morphology of the crystals was visualized using electron scanning microscope (SEM) analysis. After that, the optical properties of BZO were investigated by diffuse reflectance spectroscopy (DRS) and photoluminescence (PL); an optical gap of 2.9 eV was found. In the final step, the photocatalytic activity of the BZO crystals was evaluated for the removal of inorganic and organic pollutants, namely hexavalent chromium Cr(VI) and Cefixime (CFX). An efficient removal rate was achieved for both contaminants within only 3 h, with a 94.34% degradation rate for CFX and a 77.19% reduction rate for Cr(VI). Additionally, a kinetic study was carried out using a first-order model, and the results showed that the kinetic properties are compatible with this model. According to these findings, we can conclude that the sillenite BZO can be used as an efficient photocatalyst for wastewater treatment by eliminating both organic and inorganic compounds.

Indoor gas phase photoactivity of yttrium modified titanate films for fast acetaldehyde oxidation

Photoactive materials hold structural and catalytic features that make them particularly suitable for environmental applications and in the present work, protonated H₃Ti₃O₇-Y nanofiber-like materials were prepared via the microwave assisted hydrothermal technique. The as-prepared nanofibers exhibited high surface area with titanate structure. The nanofibers, before and after yttrium incorporation, were well-distributed and the fibrous morphology could be observed clearly; as the yttrium loading increased, ribbons and the anatase phase were formed. Practical films of these nanofibers confirmed their likely UV-photoactive properties with 200 ppm of acetaldehyde degradation within 25 min in the presence of 50% of humidity. Activity retention was achieved, keeping stability for 2 consecutive cycles at room temperature. Nowadays, the increase in home office work sets human health at risk, for the exposure to toxic volatile organic compounds and microorganisms such as viruses and bacteria is more frequent indoors. In this context, the synthesized photoactive yttrium-titanate films stand as upcoming practical UV-driven materials for cleaning pollution that concentrated urban activity and indoor environments.

Photocatalytic Decomposition of Acetaldehyde on Different TiO2-Based Materials: A Review

Purification of air from the organic contaminants by the photocatalytic process has been confirmed to be very perspective. Although many various photocatalysts have been prepared and studied so far, TiO2 is still the most commonly used, because of its advantageous properties such as non-toxicity, relatively low cost and high stability. Surface modifications of TiO2 were extensively proceeded in order to increase photocatalytic activity of the photocatalyst under both UV and visible light activations. The intention of this review paper was to summarize the scientific achievements devoted to developing of TiO2-based materials considered as photocatalysts for the photocatalytic degradation of acetaldehyde in air. Influence of the preparation and modification methods on the parameters of the resultant photocatalyst is reviewed and discussed in this work. Affinity of the photocatalyst surfaces towards adsorption of acetaldehyde will be described by taking into account its physicochemical parameters. Impact of the contact time of a pollutant with the photocatalyst surface is analyzed and discussed with respect to both the degradation rate and mineralization degree of the contaminant. Influence of the photocatalyst properties on the mechanism and yield of the photocatalytic reactions is discussed. New data related to the acetaldehyde decomposition on commercial TiO2 were added, which indicated the different mechanisms occurring on the anatase and rutile structures. Finally, possible applications of the materials revealing photocatalytic activity are presented with a special attention paid to the photocatalytic purification of air from Volatile Organic Compounds (VOCs).

Modified Nano-TiO2 Based Composites for Environmental Photocatalytic Applications

TiO2 probably plays the most important role in photocatalysis due to its excellent chemical and physical properties. However, the band gap of TiO2 corresponds to the Ultraviolet (UV) region, which is inactive under visible irradiation. At present, TiO2 has become activated in the visible light region by metal and nonmetal doping and the fabrication of composites. Recently, nano-TiO2 has attracted much attention due to its characteristics of larger specific surface area and more exposed surface active sites. nano-TiO2 has been obtained in many morphologies such as ultrathin nanosheets, nanotubes, and hollow nanospheres. This work focuses on the application of nano-TiO2 in efficient environmental photocatalysis such as hydrogen production, dye degradation, CO2 degradation, and nitrogen fixation, and discusses the methods to improve the activity of nano-TiO2 in the future.

Effect of catalyst calcination temperature in the visible light photocatalytic oxidation of gaseous formaldehyde by multi-element doped titanium dioxide

The present study investigates the influence of calcination temperature on the properties and photoactivity of multi-element doped TiO₂. The photocatalysts were prepared by incorporating silver (Ag), fluorine (F), nitrogen (N), and tungsten (W) into the TiO₂ structure via the sol-gel method. Spectroscopic techniques were used to elucidate the correlation between the structural and optical properties of the doped photocatalyst and its photoactivity. XRD results showed that the mean crystallite size increased for undoped photocatalysts and decreased for the doped photocatalysts when calcination was done at higher temperatures. UV-Vis spectra showed that the absorption cut-off wavelength shifted towards the visible light region for the as-synthesized photocatalysts and band gap narrowing was attributed to multi-element doping and calcination. FTIR spectra results showed the shifting of OH-bending absorption bands towards increasing wave numbers. The activity of the photocatalysts was evaluated in terms of gaseous formaldehyde removal under visible light irradiation. The highest photocatalytic removal of gaseous formaldehyde was found at 88%. The study confirms the effectiveness of multi-element doped TiO₂ to remove gaseous formaldehyde in air by visible light photocatalysis and the results have a lot of potential to extend the application to other organic air contaminants.

One-step formation of TiO2 hollow spheres via a facile microwave-assisted process for photocatalytic activity

Mesoporous TiO₂ hollow spherical nanostructures with high surface areas were successfully prepared using a microwave method. The prepared hollow spheres had a size range between 200 and 500 nm. The spheres consisted of numerous smaller TiO₂ nanoparticles with an average diameter of 8 nm. The particles had an essentially mesoporous structure, with a pore size in the range of 2-50 nm. The results confirmed that the synthesised of anatase TiO₂ nanoparticles with specific surface area approximately 172.3 m² g^-1. The effect of ultraviolet and visible light irradiation and catalyst dosage on the TiO₂ photocatalytic activity was studied by measuring the degradation rate of methylene blue. The maximum dye degradation performances with low catalyst loading (30 mg) were 99% and 63.4% using the same duration of ultraviolet and visible light irradiation, respectively (120 min).

Shape Evolution of Hierarchical W18O49 Nanostructures: A Systematic Investigation of the Growth Mechanism, Properties and Morphology-Dependent Photocatalytic Activities

Hierarchical tungsten oxide assemblies such as spindle-like structures, flowers with sharp petals, nanowires and regular hexagonal structures are successfully synthesized via a solvothermal reduction method by simply adjusting the reaction conditions. On the basis of the experimental results, it is determined that the reaction time significantly influences the phase transition, microstructure and photocatalytic activity of the prepared samples. The possible mechanisms for the morphology evolution process have been systematically proposed. Moreover, the as-prepared products exhibit significant morphology-dependent photocatalytic activity. The flower-like W₁₈O₄₉ prepared at 6 h possesses a large specific surface area (150.1 m²∙g⁻¹), improved separation efficiency of electron-hole pairs and decreased electron-transfer resistance according to the photoelectrochemical measurements. As a result, the flower-like W₁₈O₄₉ prepared at 6 h exhibits the highest photocatalytic activity for the degradation of Methyl orange aqueous solution. The radical trap experiments showed that the degradation of MO was driven mainly by the participation of h⁺ and •O₂⁻ radicals.

Versatility of Evaporation-Induced Self-Assembly (EISA) Method for Preparation of Mesoporous TiO₂ for Energy and Environmental Applications

Evaporation-Induced Self-Assembly (EISA) method for the preparation of mesoporous titanium dioxide materials is reviewed. The versatility of EISA method for the rapid and facile synthesis of TiO₂ thin films and powders is highlighted. Non-ionic surfactants such as Pluronic P123, F127 and cationic surfactants such as cetyltrimethylammonium bromide have been extensively employed for the preparation of mesoporous TiO₂. In particular, EISA method allows for fabrication of highly uniform, robust, crack-free films with controllable thickness. Eleven characterization techniques for elucidating the structure of the EISA prepared mesoporous TiO₂ are discussed in this paper. These many characterization methods provide a holistic picture of the structure of mesoporous TiO₂. Mesoporous titanium dioxide materials have been employed in several applications that include Dye Sensitized Solar Cells (DSSCs), photocatalytic degradation of organics and splitting of water, and batteries.