Evonik Aeroxide P25 Research Articles

Environmental significance of the interaction between titanium dioxides and soil solutions

Nanotechnology, especially in the field of photocatalysis, has witnessed rapid advancements, with titanium dioxide being one of the most widely used photocatalysts. As the use of products containing photoactive nanomaterials increases, concerns have arisen regarding their potential release into the environment over time. This release can impact soil, groundwater, and surrounding ecosystems, resulting in nanoparticles being dispersed in water and eventually depleted from the system. This study aimed to investigate how different soil solutions affect the structural, textural properties, and photocatalytic activity of titanium dioxide-based, commercial reference Evonik Aeroxide P25. The Regosol soil solution, characterized by acidic pH, low ionic content, and high organic matter content, induced nanoparticle aggregation and bandgap changes. In addition, the acidic pH hindered the adsorption process, potentially affecting the photocatalytic processes. In contrast, the Chernozem soil solution, with slightly alkaline pH, high ionic content, and low organic matter content, did not significantly alter the morphology or structure of the material. However, various organic compounds were absorbed on the surface, reducing the availability of active sites. The study highlights the importance of understanding the influence of soil solutions on nanomaterials, as it impacts their properties and environmental risks. Results show that the material is still activated, i.e., it can exert its photoactive effect on the environment. This sheds light on the challenges posed by nanoparticles in soil, particularly in terms of their toxicity and consequences for the surrounding ecosystems. The study underlines the need for further research in this area to assess potential risks and optimise the use of nanomaterials in environmental remediation.

Easy stabilization of Evonik Aeroxide P25 colloidal suspension by 4-hydroxybenzoic acid functionalization

A new functionalization method was developed with the aim of producing stable TiO2-based colloids starting from commercial Evonik Aeroxide P25 powder. The stability of P25 colloids was efficiently increased by grafting 4-hydroxybenzoic acid (4-HBA) on the P25 surface. Results highlighted that 4-HBA interacted with the surface of P25 through its carboxylic group.The key parameter for an optimized stability is the 4-HBA/P25 ratio. If the amount of 4-HBA is too high compared to the TiO2 available surface, 4-HBA molecules preferentially interact with each other, therefore reducing their adsorption on P25.Eight different amounts of 4-HBA were grafted on P25, producing stable colloids in both ethanol and water medium. In both media, the optimal properties and highest stability were obtained for a 4-HBA/TiO2 mass ratio equal to 0.333.This optimal sample was further tested and compared to pure P25 (used as reference material) for p-nitrophenol (PNP) degradation under UV-visible light without any stirring to highlight the beneficial effect of the powder stability. The photocatalytic results showed that the grafted sample reached a degradation up to 8 times higher than pure P25. This functionalization method is easy to implement and stabilizes colloids starting from any pre-synthesized powder. This versatility widens the field of applications, and opens the door for further developments in areas such as coatings.

Eco-Friendly Colloidal Aqueous Sol-Gel Process for TiO2 Synthesis: The Peptization Method to Obtain Crystalline and Photoactive Materials at Low Temperature

This work reviews an eco-friendly process for producing TiO2 via colloidal aqueous sol–gel synthesis, resulting in crystalline materials without a calcination step. Three types of colloidal aqueous TiO2 are reviewed: the as-synthesized type obtained directly after synthesis, without any specific treatment; the calcined, obtained after a subsequent calcination step; and the hydrothermal, obtained after a specific autoclave treatment. This eco-friendly process is based on the hydrolysis of a Ti precursor in excess of water, followed by the peptization of the precipitated TiO2. Compared to classical TiO2 synthesis, this method results in crystalline TiO2 nanoparticles without any thermal treatment and uses only small amounts of organic chemicals. Depending on the synthesis parameters, the three crystalline phases of TiO2 (anatase, brookite, and rutile) can be obtained. The morphology of the nanoparticles can also be tailored by the synthesis parameters. The most important parameter is the peptizing agent. Indeed, depending on its acidic or basic character and also on its amount, it can modulate the crystallinity and morphology of TiO2. Colloidal aqueous TiO2 photocatalysts are mainly being used in various photocatalytic reactions for organic pollutant degradation. The as-synthesized materials seem to have equivalent photocatalytic efficiency to the photocatalysts post-treated with thermal treatments and the commercial Evonik Aeroxide P25, which is produced by a high-temperature process. Indeed, as-prepared, the TiO2 photocatalysts present a high specific surface area and crystalline phases. Emerging applications are also referenced, such as elaborating catalysts for fuel cells, nanocomposite drug delivery systems, or the inkjet printing of microstructures. Only a few works have explored these new properties, giving a lot of potential avenues for studying this eco-friendly TiO2 synthesis method for innovative implementations.

The Influence of the Ratio of Au and Pt Nanoparticles in Ternary Composites with TiO2

In the present work, ternary composites were synthesized from commercial titanias (Evonik Aeroxide P25, Aldrich anatase—AA and Aldrich rutile—AR) and two noble metals (gold and platinum). This research focuses on the composition of the photocatalysts, especially on the noble metals. The ratio between the noble metals varies from 0.25 to 0.75% in each composite for each noble metal. Transmission electron microscopy (TEM), X-ray diffraction (XRD) and diffuse reflectance spectroscopy (DRS) measurements were carried out to investigate the structural and optical properties. From the TEM, it can be observed that the particle sizes of the noble metals were between 1 and 4 nm, while the (anatase and rutile) crystals of P25 were 20–40 nm. The XRD showed that the semiconductors’ composition remained unchanged during/after the deposition of noble metal nanoparticles. By the DRS measurements, using the Kubelka–Munk equation, it can be concluded that the deposition of the noble metal nanoparticles resulted the decrease of the bandgap energies of the titanias. The photocatalytic activity was investigated under the irradiation of UV light. Oxalic acid and salicylic acid were used as model pollutants. The hydrogen production capacity was investigated as well, where the sacrificial agent was oxalic acid, and UV irradiation was used.

Influence of Thermal Activation of Titania on Photoreactivity of Pt/TiO2 in Hydrogen Production

A series of Pt/TiO2 photocatalysts was prepared by impregnation of fresh and thermal-activated titania (commercial Evonik Aeroxide P25 TiO2) with an aqueous solution of H2PtCl6 followed by reduction in an aqueous solution of NaBH4. The thermal activation was performed by annealing in air. The photocatalytic activity of the Pt/TiO2 catalysts was measured for the hydrogen production from a mixture of glycerol under UV radiation. It was found that the activation at 300–600 °C provides an increase in the photoreactivity of resulting Pt/TiO2 photocatalysts in the production of hydrogen while its structural and textural properties do not change. This effect is due to formation of cationic vacancies that limits fast electron–hole recombination.

Application of TiO2-Cu Composites in Photocatalytic Degradation Different Pollutants and Hydrogen Production

In the present work, copper nanoparticles were deposited onto the surface of two different commercial titanias (Evonik Aeroxide P25 and Aldrich anatase). During the synthesis, the concentration of copper was systematically varied (0.5%, 1.0%, 1.5%, 5.0%, and 10 wt.%) to optimize the composite-composition. The photocatalytic activity was evaluated under UV-light, using methyl orange and Rhodamine B as model and ketoprofen as real pollutant. For the hydrogen production capacity, oxalic acid was used as the sacrificial agent. The morpho-structural properties were investigated by using XRD (X-ray diffraction), TEM (Transmission Electron Microscopy) DRS (Diffuse Reflectance Spectroscopy), XPS (X-ray Photoelectron Spectroscopy), and SEM-EDX methods (Scanning Electron Microscopy-Energy Dispersive X-ray Analysis). Increasing the copper concentration enhanced the photocatalytic activity for methyl orange degradation in the case of Aldrich anatase-based composites. When the P25-based composites were considered, there was no correlation between the Cu concentration and the activity; but, independently of the base photocatalyst, the composites containing 10% Cu were the best performing materials. Contrarily, for the ketoprofen degradation, increasing the copper concentration deteriorated the photoactivity. For both Aldrich anatase and P25, the best photocatalytic activity was shown by the composites containing 0.5% Cu. For the degradation of Rhodamine B solution, 1.5% of copper nanoparticles was the most suitable. When the hydrogen production capacity was evaluated, the P25-based composites showed higher performance (produced more hydrogen) than the Aldrich anatase-based ones. It was found that Cu was present in four different forms, including belloite (Cu(OH)Cl), metallic Cu, and presumably amorphous Cu(I)- and Cu(II)-based compounds, which were easily convertible among themselves during the photocatalytic processes.

The Comparison of the Photocatalytic Performance Shown by TiO₂ and TiO₂/WO₃ Composites- A Parametric and Kinetic Study.

Kinetic and mechanistic related approaches for mostly titania were intensively studied in the literature. However, combined modelling and kinetic studies are few. Therefore, the present work focuses on modelling the dependence of the degradation kinetics of two model compounds (salicylic acid-SA and methyl orange-MO) on Evonik Aeroxide P25, hydrothermally prepared hierarchical TiO₂ and P25/WO₃ nanostars, obtained also by hydrothermal crystallization. The obtained individual semiconductors and the composites were characterized using XRD, DRS, SEM, while the photocatalytic degradation of the model pollutants were carried out varying the catalyst load, the initial pollutant concentration and incident light intensity. It was found that the degradation kinetics were independent from the hierarchical nature of the material, while significant dependencies of the degradation efficiency was found from the previously mentioned investigation parameters. All these parametric interdependences were successfully studied and a kinetic model was proposed for both bare TiO₂ and TiO₂/WO₃ composite systems.

Detailed Investigation of Phenol Degradation on Au/TiO₂ Composite Materials.

Photocatalytic applicability of different TiO₂-based nanomaterials is a current hot topic. Therefore, our interest for the present research was to elucidate the formation of primary and secondary intermediates during the phenol degradation by photocatalysis, in the presence of Au/TiO₂ nanocomposites. The composites consisted of differently shaped gold nanoparticles and commercial titania (Evonik Aeroxide P25). The obtained composites and the noble metal nanoparticles' morphology was investigated by Transmission Electron Microscopy (TEM), their optical properties were explored using Diffuse Reflectance Spectroscopy (DRS), while the crystal structure was characterized by X-ray diffraction (XRD). The photocatalytic activity was investigated by photodegradation of phenol and methyl orange. In case of phenol it was shown that, the formation of degradation intermediates, was dependent on the Au nanoparticles' shape, leading to high amounts of different intermediates as follows: hydroquinone for composites with spherical Au nanoparticles, 1,2,4-trihydroxy-benzene for triangle shaped nanoparticles, and pyrocatechol for TiO₂.

Detailed Spectroscopic and Structural Analysis of TiO2/WO3 Composite Semiconductors

WO3-TiO2 composite materials were obtained using commercial titania (Evonik Aeroxide P25) and hydrothermally crystallized WO3. Different ratios of TiO2/WO3 were investigated, starting at 1 wt.% of WO3 to 50 wt.%. The morphology of WO3 was of the star-like type, and its structure is basically composed of monoclinic crystalline phase. All spectroscopic characteristics of the composites and their derived data (band-gap energy value, light absorption threshold, and IR specific bands) directly varied with the increase of the WO3 content. However, the oxalic acid photodegradation achieved under UV light reached the highest yield for 24 wt.% WO3 content, a result that was attributed to the charge separation efficiency and the surface hydrophilicity. The latter mentioned reason points out the crucial importance of the surface quality of the investigated structure in photocatalytic tests.

Mapping the Photocatalytic Activity and Ecotoxicology of Au, Pt/TiO2 Composite Photocatalysts

In the present research gold and platinum nanoparticles were deposited simultaneously on three different commercial titania photocatalysts (Evonik Aeroxide P25, Aldrich rutile, and Aldrich anatase). For the synthesis of the composites two noble metal reduction methods (in situ and impregnation) and three noble metal deposition routes (i.e., by changing their deposition order, Au/Pt, Pt/Au, and Au–Pt simultaneously) were used. The photocatalytic performances of the nanocomposites were evaluated under UV irradiation, through degradation of oxalic acid and photocatalytic hydrogen production. The best performing photocatalyst was obtained by sequential noble metal deposition (first Au followed by Pt) on Evonik Aeroxide P25. The morphological and structural properties were studied/investigated by using DRS, TEM, HRTEM, EDX, and XRD. The gold and platinum nanoparticles formed clusters in most of the cases. Furthermore, the ecotoxicity of the composites was investigated using Lemna minor growth inhibition tests using static “lake” approach completed by DLS and ROS indirect measurements. The toxic effect of the composites which showed the highest photocatalytic activity did not differ from that of their commercial counterparts, showing that these nanoparticles were eco-friendly. This result shows the great capacity of these materials to be used in the next future in photocatalytic applications.

Settleable engineered titanium dioxide nanomaterials for the removal of natural organic matter from drinking water

Four linear engineered TiO2 nanomaterials (LENs) were synthesized and evaluated in terms of settlability and their ability to remove natural organic matter (NOM) from river water. The size, surface characteristics, and crystallinity of the LENs were manipulated by varying the temperatures used during the synthesis procedure. All four LENs settled out of purified water more effectively than standard Degussa Evonik Aeroxide P25 nanoparticles. The settling behaviour of the nanomaterials was impacted by surface charge effects and interactions with NOM and ionic species in the river water matrix. The reduction of two disinfection byproduct precursor surrogate parameters, DOC and UV254, by the LENs via adsorption (no irradiation) and photocatalytic degradation under UVA LED irradiation was compared to that by P25 nanoparticles. After 60 min of irradiation DOC removal by the LENs ranged from 20 to 50% and UV254 reduction ranged from 65 to 90%. Two of the most promising LENs were reused multiple times and although both materials experienced decreases in treatment efficacy over successive reuse cycles, the reusability of both LENs was equal to or superior to that of P25 nanoparticles. The electrical energy per order required to remove DOC and UV254 from the water ranged from 8 to 36 times higher than that required for UV/H2O2 treatment but comparable to results reported by other researchers using UV/TiO2 for NOM removal. A subset of the nanomaterials evaluated in this study may prove to be a viable alternative to standard TiO2 nanoparticles for the removal of DBP precursors from drinking water, but the characteristics of the water matrix have important effects on settling efficiency and will require site-specific evaluation.

Anatase and rutile in evonik aeroxide P25: Heterojunctioned or individual nanoparticles?

Evonik Aeroxide P25 (formerly Degussa P25) is a flame-made multiphasic TiO2 nanoparticles containing anatase and rutile, as well as a small amount of amorphous TiO2. The past decades have witnessed the wide applications of P25 as a benchmark material for studying photocatalytic mechanism, materials and process. However, controversy remains regarding the microstructure of anatase and rutile: do they interwoven forming heterojunction structure or exist individually? To clarify it, we selected a medium alkaline, LiOH to erode bare P25 under a mild hydrothermal condition. Since rutile presents much higher resistances towards dissolution by LiOH than anatase, it is reasonable to find during hydrothermal reaction that the ratio of anatase to rutile (A/R) gradually decrease if they exist individually. Reversely, the A/R value gradually increases at the beginning of the hydrothermal reaction, implying that rutile shows high activity towards dissolution and phase transformation to lithium titanate. As calculated, around 15% rutile nanoparticles more likely exist on the surface of anatase with the formation of a heterojunction structure, although isolated nanoparticles with sole rutile phase coexist. In addition to XRD analysis, TEM measurement shows that the Moiré fringes frequently present, which further manifests that some anatase particles are covered with rutile clusters or thin overlayers.

The investigation of the photocatalytic efficiency of spherical gold nanocages/TiO 2 and silver nanospheres/TiO 2 composites

Abstract The paper presents the influence of spherical Ag, Au nanoparticles (AgNS) and Au spherical nanocages (AuIND) on the photocatalytic properties (degradation of organic compounds and H 2 production) of commercial TiO 2 (Evonik Aeroxide P25, Aldrich anatase – AA and Aldrich rutile – AR). The resulted TiO 2 -based composites were characterized by different techniques, such as XRD (X-ray Diffraction), TEM (Transmission Electron Microscopy), DRS (Diffuse Reflectance Spectroscopy) and X-ray Fluorescence (XRF). For the synthesis of composites in situ (IS) and impregnation (IMP) procedures based on the chemical reduction method were used. The degradation of well-known model pollutants (oxalic acid and phenol) was carried out to find correlation between the applied synthesis procedure and the obtained photocatalytic activities. In all the cases oxalic acid was degraded efficiently by nearly all the composite materials (and showed superior activity compared to the base photocatalysts), while in the case of phenol the noble metal containing nanostructures were less efficient then the corresponding commercial TiO 2 . Furthermore, it was concluded that in the case of oxalic acid degradation, the nature of the used noble metals did not influence significantly the activity. From the chosen synthesis approaches IS method resulted the most efficient composites. When phenol was degraded, the formation of hydroxylated intermediates was favored instead of the phenol degradation. Under these circumstances, AA and AR based composites were the best when considering simultaneously both the intermediate formation and degradation efficiency values. For photocatalytic H 2 production the most efficient photocatalyst was the AuIND_P25_IS, which points out the effectiveness of the IS method.

Peroxo group enhanced nanorutile as visible light active photocatalyst

Hydrogen peroxide was applied during the synthesis to enhance the visible light excitability of nanosized (<10nm), pure rutile phase titanium dioxides synthesized by a facile, sol-gel method at low temperature. Different amounts of hydrogen peroxide were used during the synthesis to form peroxo groups on the surface of TiO2-s. As-prepared photocatalysts were characterized by X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), infrared spectroscopy (IR), and X-ray photoelectron spectroscopy (XPS). The photocatalytic activity of the catalysts were investigated by phenol, Rhodamine B dye and coumarin degradation under visible light irradiation. Evonik Aeroxide P25 TiO2 and commercial rutile phase titanium dioxide were used as reference photocatalysts. First order derivative of DRS spectra showed enhanced visible light excitability in the case of Ti:H2O2=1:2 ratio (applied during the synthesis). XPS measurements confirmed the formation of peroxo groups in this specific TiO2. Photocatalytic measurements pointed out that this TiO2 had by far the best photocatalytic performance, exceeding the photocatalytic activity of Aeroxide P25 and commercial rutile as well. This activity gain was attributed to the presence of peroxo groups on the surface.

Differently Shaped Au Nanoparticles: A Case Study on the Enhancement of the Photocatalytic Activity of Commercial TiO₂.

In the present work, the influence of a gold nanoparticle’s shape was investigated on the commercially available Evonik Aeroxide P25. By the variation of specific synthesis parameters, three differently shaped Au nanoparticles were synthetized and deposited on the surface of the chosen commercial titania. The nanoparticles and their composites’ morphological and structural details were evaluated, applying different techniques such as Diffuse Reflectance Spectroscopy (DRS), X-ray Diffraction (XRD), and Transmission Electron Microscopy (TEM). The influence of the Au nanoparticles’ shape was discussed by evaluating their photocatalytic efficiency on phenol and oxalic acid degradation and by investigating the H2 production efficacy of the selected composites. Major differences in their photocatalytic performance depending on the shape of the deposited noble metal were evidenced.

TiO2/WO3/Au/MWCNT composite materials for photocatalytic hydrogen production: Advantages and draw‐backs

AbstractTiO2/WO3/Au/MWCNT composite materials were obtained using different commercial titanias (Aldrich Anatase, Aldrich Rutile, and Evonik Aeroxide P25) and Aldrich WO3. The gold nanoparticles were deposited on the semiconductor oxides' surface by chemical reduction using sodium borohydride, and the MWCNT's were combined with the composite (in different concentrations 0.1–10 wt%) by applying an ultrasonication method. The obtained nanocomposites were successfully characterized by means of X‐ray diffraction, transmission electron microscopy, etc. The aim of the present work was to find the optimal composition (i.e. carbon nanotube content) of the composite for photocatalytic hydrogen production using oxalic acid as a sacrificial agent.

New insights regarding the calcination as a critical parameter in the synthesis of sol–gel made titania powders

The number of studies regarding sol–gel made titania powders is quite high, and nearly all of them use the calcination as the crystallization process. However, several papers are not providing crucial information regarding the calcination parameters, such as, heat treatment atmosphere, heating rate or heat treatment time. Furthermore, nearly no investigations were done regarding short calcination times and fast heating rates. The present paper points out the missing or under-evaluated aspects in the literature and demonstrates their importance throughout simple experiments. First of all, the influence of the calcination atmosphere and the applied flow rate (in tubular furnaces) was proven by demonstrating the inhomogeneity of the obtained samples. Secondly, the major influence of the chosen calcination time and rate was proven by obtaining fast heat treated titania powders. Their activity varied significantly with the applied calcination time, achieving two activity maxima. Also, the obtained activity trend shows that by varying the calcination time highly active titanias can be obtained (more active than Evonik Aeroxide P25).

Ultrasound assisted preparation of stable water-based nanocrystalline TiO 2 suspensions for photocatalytic applications of inkjet-printed films

The use of titania photocatalytic materials in industrial applications is strongly dependent on the stability, nanoparticle size distribution, ease of deposition and cost of the relevant titania precursor solutions or suspensions. The present contribution presents the preparation of inkjet-printed titania films, derived from stable water-based suspensions. The suspensions were synthesized by applying a “top-down” synthetic strategy, namely the ultrasonication of commercially available titania powder (Evonik Aeroxide P25). Crucial parameters, such as suspension stability, energy input requirements, particle size distribution, surface characteristics, compatibility with industrially proven inkjet systems and photocatalytic performance were investigated. The developed synthetic procedure proves environmentally friendly, low cost and most suitable for large scale production of titania thin films, by inkjet printing commercially available ceramic tiles.