Aeroxide P25 Research Articles

Mesoporous pyrophyllite–titania nanocomposites: synthesis and activity in phenol photocatalytic degradation

Pyrophyllite–TiO2 nanocomposite PTi750 was successfully synthesized using a sol–gel method at ambient temperature based on exfoliation of the pyrophyllite layered clay by incorporation of the TiO2 precursor titanium(IV) t-butoxide. PTi750 exhibited higher photocatalytic activity in phenol degradation compared with commercial TiO2 Aeroxide P25. Ag-photodeposited PTi750 was more photoactive than PTi750, exhibiting detoxification, total degradation, and good mineralization of polluted solution and excellent stability after five reuses at optimal conditions in terms of the parameters pH, H2O2 concentration, and photocatalyst amount. The nanocomposites were investigated using several techniques, viz. diffuse-reflectance ultraviolet–visible (UV–Vis) spectrophotometry, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction analysis, X-ray fluorescence spectroscopy, Fourier-transform infrared spectroscopy, and Brunauer–Emmett–Teller (BET) specific surface area measurements.

Ultrathin-Film Titania Photocatalyst on Nanocavity for CO2 Reduction with Boosted Catalytic Efficiencies.

Photocatalytic CO2 reduction with water to hydrocarbons represents a viable and sustainable process toward greenhouse gas reduction and fuel/chemical production. Development of more efficient catalysts is the key to mitigate the limits in photocatalytic processes. Here, a novel ultrathin‐film photocatalytic light absorber (UFPLA) with TiO2 films to design efficient photocatalytic CO2 conversion processes is created. The UFPLA structure conquers the intrinsic trade‐off between optical absorption and charge carrier extraction efficiency, that is, a solar absorber should be thick enough to absorb majority of the light allowable by its bandgap but thin enough to allow charge carrier extraction for reactions. The as‐obtained structures significantly improve TiO2 photocatalytic activity and selectivity to oxygenated hydrocarbons than the benchmark photocatalyst (Aeroxide P25). Remarkably, UFPLAs with 2‐nm‐thick TiO2 films result in hydrocarbon formation rates of 0.967 mmol g−1 h−1, corresponding to 1145 times higher activity than Aeroxide P25. This observation is confirmed by femtosecond transient absorption spectroscopic experiments where longer charge carrier lifetimes are recorded for the thinner films. The current work demonstrates a powerful strategy to control light absorption and catalysis in CO2 conversion and, therefore, creates new and transformative ways of converting solar energy and greenhouse gas to alcohol fuels/chemicals.

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.

Techno-economic evaluation of anatase and p25 TiO2 for treatment basic yellow 28 dye solution through heterogeneous photocatalysis

The photodegradation and mineralization efficiency (technical evaluation) and process economics (economic evaluation) are important in selection of a particular type of TiO2 for large-scale commercial applications involving heterogeneous photocatalysis. In this paper, techno-economic evaluation of indigenous anatase TiO2 (ana-TiO2) and aeroxide p25 TiO2 (p25-TiO2) photocatalyst for heterogeneous photocatalysis of basic yellow 28 (BY28) dye solution is studied. The characterization of photocatalysts was done through X-ray diffraction, Tauc’s plot, and point of zero charge. The important parameters related to heterogeneous photocatalytic process like photocatalyst loading, UV intensity, and A/V (area-to-volume) ratio were studied and optimized as per ability of photocatalyst for the full utilization of light illumination. BY28 dye degradation depicted pseudo-first-order kinetics under UV radiations and solar light. Electric energy per order and collector area per order was also evaluated for the two systems. Finally, economic evaluation of these two types of TiO2 was done in terms of total material and energy cost involved for 90% removal of BY28 dye from 1 m3 solution under UV radiations and solar light. Ana-TiO2 found to be more economical than p25-TiO2 in terms of operating cost involved for photocatalytic degradation of BY28 dye. Alternatively, photocatalytic unit using p25-TiO2 showed higher treatment capacity as compared to ana-TiO2 due to higher photodegradation and mineralization efficiency of the former. Finally, a method for selection of particular type of TiO2 (p25-TiO2 or ana-TiO2) for a photocatalytic unit is suggested by considering volumetric capacity of photocatlytic unit, volume of effluent generated per day by the dyeing unit, photodegradation efficiency of TiO2, and process economics. This study would be useful for the decision making authorities in profitable selection of particular type of TiO2 for treating given volume of effluent.

TiO2 water-bell photoreactor for wastewater treatment

In spite of the intense academic research that has been conducted on the possibility of mineralization of a vast range of water pollutants using TiO2 photocatalysis, the scale up to industrial scale and commercialization of TiO2 photocatalysis treatment systems is still very limited. The design of a photocatalytic reactor that is simple, energy efficient, less expensive to build and operate is crucial for the development and widespread of TiO2 photocatalysis.A solar photocatalytic reactor is designed and constructed. The reactor is based on generating a thin water film to allow for solar light penetration and continuous oxygenation. Recirculating the reaction solution at a high flow rate ensure good mixing and avoid dead zones in the photoreactor. Reactor performance for degradation of phenol, as a model compound, was evaluated using aeroxide P25. Factors affecting the degradation efficiency were studied including catalyst loading, light intensity, initial pollutant concentration, oxidant addition and exposure time. Dissolved oxygen levels, temperature and pH were monitored through all the conducted tests. The water-bell photoreactor performance was compared with other photoreactors using benchmarks: the degradation rate constant and the reactor throughput. The photoreactor is promising for scale-up and commercialization owing to its modular design, an integrated storage, simple and cheap components that are not susceptible to breakage and optical losses.

Effect of the Co-deposition of Pd and Pt on $$\hbox {TiO}_{2}$$ TiO 2 Photoactivity

$$\hbox {TiO}_{2}$$ was obtained by a simple sol–gel synthesis and subsequently modified by the addition of Pt and/or Pd particles on the surface by photodeposition. These photocatalysts were characterised by X-ray diffraction analysis, UV–Vis diffuse reflectance spectra, Brunauer–Emmett–Teller measurements, Fourier transform infrared spectroscopy, transmission electron microscopy, electron dispersive spectroscopy and X-ray photoelectron spectroscopy. Their photocatalytic activity was studied by following the degradation, mineralisation and detoxification of solutions of phenol, propanil and methylene blue. For comparison purposes, different commercial $$\hbox {TiO}_{2}$$ catalysts were also tested: Kronos vlp7000, Millenium PC100, Aeroxide P90 and Aeroxide P25. This latter catalyst was also modified with Pt and/or Pd. The degradation kinetics of all the pollutants in aqueous solutions satisfactorily followed the pseudo-first order according to the Langmuir–Hinshelwood model in conditions of low concentration values. It was found that the simultaneous photodeposition of Pt and Pd contributed to enhancing photoactivity more than the individual deposition of either Pt or Pd.

On the role of BmimPF6 and P/F- containing additives in the sol-gel synthesis of TiO2 photocatalysts with enhanced activity in the gas phase degradation of methyl ethyl ketone

The role of phosphate and fluoride ions brought by the BmimPF6 ionic liquid via hydrolysis during the sol gel synthesis of TiO2 has been investigated by replacing BmimPF6 with phosphorous- and fluorine-containing additives, phosphoric acid (PA) and sodium fluoride (NaF), respectively. Correlation between the physico-chemical properties and the photocatalytic behavior of the synthesized TiO2 materials was established. High crystallinity anatase TiO2 photocatalysts with controlled crystallite size and shape resulting from P/F-induced modifications displayed strongly improved photocatalytic activity and mineralization yield under UV-A illumination in the degradation of methyl ethyl ketone (MEK) taken as model Volatile Organic Compound (VOC), compared to the TiO2 Aeroxide P25 reference and sol-gel TiO2 counterpart synthesized in absence of any BmimPF6. We showed that the BmimPF6 ionic liquid could be efficiently substituted by cheap PA and NaF additives in an adequate ratio in the sol-gel synthesis for synthesizing TiO2 photocatalysts without altering the main physico-chemical properties and the photocatalytic activity. We proposed a similar synthesis mechanism in both ionic liquid- and P/F-assisted sol-gel syntheses of TiO2, involving a combined role of phosphate and fluoride ions. The reaction of phosphates with titanium hydroxide network in the early stage of the sol-gel synthesis resulted in a size control of TiO2 crystallites and thus in higher specific surface area, in favor of a higher MEK conversion rate, while the fluoride ions were hypothesized to cause an anisotropic TiO2 crystal growth during the aging step of the sol gel synthesis, in favor of a higher selectivity to CO2 through a favored adsorption of intermediate products of MEK degradation on the exposed TiO2 {001} facets.

Vasomotor function in rat arteries after ex vivo and intragastric exposure to food-grade titanium dioxide and vegetable carbon particles

BackgroundHumans are continuously exposed to particles in the gastrointestinal tract. Exposure may occur directly through ingestion of particles via food or indirectly by removal of inhaled material from the airways by the mucociliary clearance system. We examined the effects of food-grade particle exposure on vasomotor function and systemic oxidative stress in an ex vivo study and intragastrically exposed rats.MethodsIn an ex vivo study, aorta rings from naïve Sprague-Dawley rats were exposed for 30 min to food-grade TiO2 (E171), benchmark TiO2 (Aeroxide P25), food-grade vegetable carbon (E153) or benchmark carbon black (Printex 90). Subsequently, the vasomotor function was assessed in wire myographs. In an in vivo study, lean Zucker rats were exposed intragastrically once a week for 10 weeks to vehicle, E171 or E153. Doses were comparable to human daily intake. Vasomotor function in the coronary arteries and aorta was assessed using wire myographs. Tetrahydrobiopterin, ascorbate, malondialdehyde and asymmetric dimethylarginine were measured in blood as markers of oxidative stress and vascular function.ResultsDirect exposure of E171 to aorta rings ex vivo increased the acetylcholine-induced vasorelaxation and 5-hydroxytryptamine-induced vasocontraction. E153 only increased acetylcholine-induced vasorelaxation, and Printex 90 increased the 5-hydroxytryptamine-induced vasocontraction, whereas Aeroxide P25 did not affect the vasomotor function. In vivo exposure showed similar results as ex vivo exposure; increased acetylcholine-induced vasorelaxation in coronary artery segments of E153 and E171 exposed rats, whereas E171 exposure altered 5-hydroxytryptamine-induced vasocontraction in distal coronary artery segments. Plasma levels of markers of oxidative stress and vascular function showed no differences between groups.ConclusionGastrointestinal tract exposure to E171 and E153 was associated with modest albeit statistically significant alterations in the vasocontraction and vasorelaxation responses. Direct particle exposure to aorta rings elicited a similar type of response. The vasomotor responses were not related to biomarkers of systemic oxidative stress.

Removal of Waterborne Pathogen by Nanomaterial-Membrane Coupling System.

The waterborne pathogenic viruses threaten human health. And the nanomaterial-membrane coupling system is promising in virus removal. In this study, phage MS2 was selected as the model virus to investigate the removal of virus with the coupling system. Results revealed that commercial nano TiO2 (Degussa Aeroxide P25) showed both of excellent adsorption and photocatalysis performance for virus removal compared with nano ZnO, nano Fe3O4, carbon nanotube, graphene, nano Ni and Nano TiO2 (anatase). In P25 photocatalysis process, the removal efficiency of phage MS2 increased with the increase of P25 concentration (0~1000 mg L-1), virus initial concentration (102~106 PFU mL-1), UV irradiation doses (5~120 mJ cm-2) and UV light intensity (0.126~0.742 mW cm-2). However, when the P25 concentration increased to over 1000 mg L-1, the virus removal efficiency would remain stable with the increase of P25 concentration. The nanomaterial-membrane coupling system showed excellent performance for virus removal, which was mainly attributed to the adsorption and photocatalysis of P25, and the intercept of membrane. When the P25 concentration was 100 mg L-1, UV irradiation dose was 20 mJ cm-2 and transmembrane pressure was 20 kPa, the phage MS2 removal efficiency could be up to 100%.

Photocatalytic reduction of chromium (VI) using combustion synthesized TiO2

Advanced oxidation processes, such as photocatalysis, have shown a great potential for removing the toxic chemical pollutants. In the current work, photocatalytic reduction of Chromium (VI) is studied using combustion synthesized TiO2. The activity of combustion synthesized TiO2 was compared with the activity of TiO2 synthesized using sol-gel method, and with commercially available Aeroxide P25 catalyst. Effect of different parameters, namely, catalyst loading, initial concentration of Cr (VI), pH and various fuels in combustion synthesis on the photocatalytic activity were investigated. Maximum reduction was observed for TiO2 synthesized using glycine as a fuel at a catalyst loading of 0.5g/L and an acidic pH of 4. The combustion synthesized TiO2 was significantly active for the reduction of Cr (VI) than other catalysts used in the study.

Removal of antibiotics, antibiotic-resistant bacteria and their associated genes by graphene-based TiO2 composite photocatalysts under solar radiation in urban wastewaters

The present work investigated: (i) the removal of the antibiotics sulfamethoxazole (SMX), erythromycin (ERY) and clarithromycin (CLA); (ii) the inactivation of the total and antibiotic-resistant E. coli along with their regrowth potential after treatment; (iii) the removal of the total genomic DNA content; and (iv) the removal of selected antibiotic resistance genes (ARGs), namely sul1, ampC, ermB, mecA, as well as species-specific sequences, namely ecfX for Pseudomonas aeruginosa and enterococci-specific 23S rRNA, by graphene-based TiO2 composite photocatalysts under solar radiation, in real urban wastewaters. TiO2-reduced graphene oxide (TiO2-rGO) composite photocatalysts were synthesized by two ex-situ synthesis methods, namely hydrothermal (HD) treatment and photocatalytic (PH) treatment, starting from graphene oxide and Aeroxide P25 TiO2, and were characterized with various techniques, such as XRD, FT-IR, Raman, XPS, SEM and surface area (BET) analyses. The potential of the synthesized TiO2-rGO composites for the removal of the abovementioned antibiotic-related microcontaminants was compared to the efficiency shown by pristine Aeroxide P25 TiO2 under simulated solar radiation, in real urban wastewater effluents treated by a membrane bioreactor. The results showed that TiO2-rGO-PH was more efficient in the photocatalytic degradation of ERY (84±2%) and CLA (86±5%), while degradation of SMX (87±4%) was found to be slightly higher with Aeroxide P25 TiO2. It was also demonstrated that more than 180min of treatment were satisfactory for the complete inactivation and complete absence of post-treatment regrowth of E. coli bacteria (<LOD) even 24h after the end of the treatment, for all examined photocatalytic materials. The least amount of regrowth at all experimental times was observed in the presence of TiO2-rGO-HD. Moreover, the synthesized graphene-based photocatalysts successfully removed ampC and significantly reduced ecfX abundance of Pseudomonas aeruginosa, but sul1, ermB and 23S rRNA for enterococci sequences were found to be persistent throughout treatment with all catalyst types. Finally, the total DNA concentration remained stable throughout the photocatalytic treatment (4.2–4.8ngμL−1), indicating the high total genomic DNA stability in treated wastewater and its resistance to photocatalytic treatment.

Co-exposure to titanium dioxide nanoparticles does not affect cadmium toxicity in radish seeds (Raphanus sativus)

Recent developments on environmental fate models indicate that as nano waste, engineered nanomaterials (ENMs) could reach terrestrial ecosystems thus potentially affecting environmental and human health. Plants can be therefore exposed to ENMs but controversial data in terms of fate and toxicity are currently available. Furthermore, there is a current lack of information on complex interactions/transformations to which ENMs undergo in the natural environment as for instance interacting with existing toxic compounds. The aim of the present study was to assess the behavior and biological effects of titanium dioxide nanoparticles (n-TiO2) (Aeroxide P25, Degussa Evonik) and its interaction with cadmium (CdCl2) in plants using radish seeds (Raphanus sativus L. Parvus) as model species. Radish seeds were exposed to n-TiO2 (1–1000mg/L) and CdCl2 (1–250mg/L) alone and in combination using a seed germination and seedling growth toxicity test OECD 208. Percentage of seed germination, germination index (GI) and root elongation were calculated. Cell morphology and oxidative stress parameters as glutathione-S-transferase (GST) and catalase activities (CAT) were measured in radish seeds after 5 days of exposure. Z-Average, PdI and Z-potential of n-TiO2 in Milli-Q water as exposure medium were also determined. DLS analysis showed small aggregates of n-TiO2, negative Z-potential and stable PdI in seed's exposure media. Germination percentage, GI and root length resulted affected by n-TiO2 exposure compared to controls. In particular, n-TiO2 at 1mg/L and 100mg/L did not affect radish seeds germination (100%) while at concentration of 10mg/L, 200mg/L, 500mg/L, and 1000mg/L a slight but not significant decrease of germination % was observed. Similarly root length and GI resulted significantly higher in seeds exposed to 10mg/L and 200mg/L compared to 1mg/L, 100mg/L, 500mg/L, 1000mg/L and control (p < 0.05). On the opposite, CdCl2 significantly abolished germination % and GI compared to control seeds and a concentration dependent decrease on root elongation was observed against controls (p < 0.05). As well, significant decrease of germination %, GI and root elongation was observed in seeds co-exposed to n-TiO2 and CdCl2 at the highest concentrations (1000mg/L n-TiO2 and 250mg/L CdCl2) compared to co-exposed seeds at low concentration (1mg/L n-TiO2 and 1mg/L CdCl2) and controls (p < 0.05). Root elongation significantly increase compared to control at the lowest co-exposure concentration (p < 0.05). Similarly at intermediate concentrations of 10 and 100mg/L in co-exposure conditions, n-TiO2 did not affect CdCl2 toxicity. Concerning antioxidant enzymes, a significant increase of CAT activity in seeds exposed to single high n-TiO2 concentration (1000mg/L) was observed while n-TiO2 (1mg/L), CdCl2 (1 and 250mg/L) and co-exposure resulted significantly decreased compared to controls (p < 0.05). Regarding GST activity, a slight increase in seeds exposed to 1000mg/L n-TiO2 but no significantly was observed, however both n-TiO2 and CdCl2 alone (1 and 250mg/L, respectively) or in combinations caused a significant decrease in GST activity (p < 0.05). Therefore, overall data support the hypothesis that the presence of n-TiO2 do not affect the toxicity of CdCl2 at least at the highest concentration (100 and 250mg/L) in radish seeds. Morphological alterations in nuclei, vacuoles and shape of radish root cells were observed upon single Cd exposure and not abolished in the presence of n-TiO2. Nevertheless, although n-TiO2 seems not to reduce Cd toxicity at high concentration (up to 250mg/L), interactions cannot be excluded based on obtained results.

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.

Photodecolorisation of melanoidins in vinasse with illuminated TiO2-ZnO/activated carbon composite

ABSTRACTA hybrid photo-catalyst, TiO2-ZnO, was synthesized by immobilizing ZnO on commercial TiO2 (aeroxide P25). Activated carbon (AC) was subsequently used to support the hybrid, thus forming a TiO2-ZnO/AC composite catalyst. Fourier transform infrared (FTIR) analysis and scanning electron microscopy integrated with energy-dispersive X-ray spectroscopy (SEM-EDX) investigations revealed successful catalyst synthesis. Optical properties of the hybrid determined from photoluminescence (PL) and Ultraviolet-visible (UV-vis) spectroscopy confirmed a restrained recombination of electron-hole pairs and reduced energy band gap due to a successful heterojunction formation. The prepared catalysts were used to photodecolorise vinasse in a 12-W UVC batch photoreactor. TiO2-ZnO had improved photocatalytic activity compared with TiO2 and ZnO separately. On supporting the hybrid onto AC, both adsorption and photocatalytic activities were further enhanced with improved overall color removal of 86% from 68%. Photodecolorisation followed the pseudo-first-order reaction model with the rate constant () observed decreasing from 0.0701 to 0.0436 min−1 on increasing the initial concentration from 5,000 to 14,000 ppm. The UV process was found to be 33-fold less energy intensive for color reduction as compared to total organic carbon (TOC) reduction. Formation of nitrates during the photodecolorisation process was attributed to the mineralization of nitrogen heteroatoms in the color-causing melanoidin compounds.

Photocatalytic degradation of 2-(4-methylphenoxy)ethanol over TiO2 spheres

The photocatalytic TiO2-assisted decomposition of 2-(4-methylphenoxy)ethanol (MPET) in aqueous solution has been studied for the first time. The intermediate compounds of MPET photodegradation have been also determined. A toxic p-cresol is formed in significant quantities during the photocatalytic reaction. A solvent-exchange approach for a template-free preparation of spherical TiO2 particles has been described, which is based solely on precipitation of hydrous titania from aqueous titanium peroxo complex by using organic solvents. The proposed method favours the formation of spherical titania particles with a mean size varying from 50 to 260nm depending on the choice of solvent. The procedure for converting nonporous titania spheres into mesoporous material maintaining the same spherical morphology has been developed. The synthesized TiO2 spheres demonstrate a degree of MPET photo-degradation close to that of the commercial titania Aeroxide P25, besides being successfully recovered and reused for four reaction cycles without loss of photocatalytic activity. The effectiveness of the commercial Aeroxide P25 in MPET photodegradation, on the other hand, suffers 10-time drop during the third reaction cycle, which is attributed to its poor recoverability because the photocatalyst is composed of small particles of 20nm size.

Photocatalytic activity of titanium dioxide nanoparticles produced by methods of high-energy physical dispersion

Photocatalytic activity of titanium dioxide nanoparticle samples under study is almost uncorrelated with their phase composition and, in particular, with the content of the anatase phase. The photocatalytic activity depends on the annealing temperature of the nanoparticles. The photocatalytic activity is positively affected by an ultrasonic radiation of the nanoparticles. The highest photocatalytic activity, comparable with that of the AEROXIDE P25 reference nanopowders, is observed for nanoparticles produced by a method of electrical explosion of wires.

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.

Synthesis of nanocrystalline TiO2 nanorods via hydrothermal method: An efficient photoanode material for dye sensitized solar cells

Nanocrystalline TiO2 nanorods (NRs) were successfully grown via hydrothermal process. The powder X-ray diffraction (PXRD) pattern shows larger fraction of anatase phase with good crystallinity. Surface morphology of the grown NRs and its dimensions were identified with high resolution transmission electron microscopy (HRTEM) analysis. The crystalline nature of the NRs was also identified with bright spots obtained from selected area electron diffraction (SAED) analysis. The specific surface area and average pore width of the material are 34.84m2/g and 3.1nm respectively. Based on the surface morphology, crystalline and mesoporous properties of the NRs, nanocrystalline dye sensitized solar cells (DSSCs) were made and their performances were compared with commercially available Aeroxide P25 nanoparticles. The performance of the NRs shows high short circuit current density (Jsc=15.45mA/cm2) and high conversion efficiency of 6.5% in DSSCs. From the electrochemical impedance measurement, lower charge transfer resistance (Rct) has been observed for NRs based DSSC device in the interfaces.