P25 TiO2 Research Articles

Elaboration and characterization of the brownmillerite Ca2Fe2O5 synthesized by citrate sol-gel method. Application for photocatalytic H2-Production under visible light over Ca2Fe2O5/ZnO hetero-system

The present work is devoted to the synthesis of the ferrite Ca2Fe2O5 as photocatalyst crystallizing in the brownmillerite structure. The ternary oxide is prepared by sol-gel auto combustion and characterized by physical and electrochemical methods. The thermal analysis (TG/DSC) shows that, the formation of the brownmillerite is observed above 660 °C. The X-ray diffraction and BET analysis show respectively a single phase with an active surface area of ∼6 m2 g−1. The SEM micrographs exhibit an inhomogeneous structure formed by agglomeration of irregular shaped grains, confirmed by the laser granulometry analysis. The forbidden band (∼2.3 eV) determined from the diffuse reflectance, permits to explore ∼ 30% of the sun spectrum into chemical energy. The p-type comportment of Ca2Fe2O5 is demonstrated by the capacitance-potential (C−2 - E) graph with a flat band potential (Efb = 0.93 VSCE), due to oxygen over-stoichiometry. The negative potential of the conduction band (−1.06 VSCE) predicts the feasibility of the H2 generation. Indeed, Ca2Fe2O5 is chemical stable in a wide pH domain and is positively experimented as photocatalyst for the H2-production under visible light. The best performance is obtained in alkaline medium (NaOH, 0.1 M) with a mean evolution rate of 18 μmol g−1 min−1. However, Ca2Fe2O5 coupled to ZnO sol-gel (ZnO-SG) improves the catalytic performance. The H2 evolution rate over (Ca2Fe2O5/ZnO-SG) reached 24 μmol g−1 min−1 after 60 min. It has also been shown that ZnO–P, prepared by precipitation, is more efficient than that synthetized by sol-gel method (ZnO-SG) and TiO2–P25.

Supramolecule self-assembly approach to direct Z-scheme TiO2/g-C3N4 heterojunctions for efficient photocatalytic degradation of emerging phenolic pollutants

To improve the visible-light photocatalytic oxidation activity of anatase TiO2 or graphitic carbon nitride (g-C3N4) towards organic pollutants, the present work develops a supramolecule self-assembly approach combined with thermal polycondensation to construct direct Z-scheme-dictated TiO2/g-C3N4 heterojunctions. This in-situ route not only leads to the TiO2/g-C3N4 with porous sheet-like nanostructures but also establishes hydrogen-bonded intimate interfacial contact between TiO2 and g-C3N4. The TiO2/g-C3N4 heterojunctions demonstrate significantly enhanced visible-light photocatalytic activity in the degradation of emerging phenolic pollutants, acetaminophen and methylparaben, as compared with TiO2, P25 TiO2 and g-C3N4; additionally, TiO2-to-g-C3N4 molar ratio in the heterojunctions influences the activity remarkably. This enhanced photocatalytic oxidation performance is mainly ascribed to the direct Z-scheme-dictated charge carrier transfer mechanism, driven by well-matched energy band structures of TiO2 and g-C3N4 as well as the intimate interfacial contact between TiO2 and g-C3N4. Accordingly, the spatial separation of the photogenerated charge carriers is boosted; simultaneously, strong redox ability of electrons on conduction band of g-C3N4 and holes on valence band of TiO2 is retained. Therefore, abundant reactive oxygen species like •O2− anion radicals and •OH radicals are generated. These reactive oxygen species together with holes are responsible for the elevated photocatalytic oxidation performance of TiO2/g-C3N4 heterojunctions.

Synthesis of new C,N,S,Fe-multidoping nanoparticles with potential photochemical response

New multidoped TiO2 nanomaterials with potential photochemical response were synthesized through an uncomplicated sol–gel process, and their structures and properties were evaluated using X-ray diffraction (XRD), transmission electron microscopy (TEM), UV-visible diffuse reflectance spectroscopy (DRS) and specific surface area (N2 adsorption-desorption). The results showed that the crystallite size of doped TiO2 nanomaterials was smaller than undoped TiO2 P25 and the surface area of these nanomaterials was found to average 800 m2/g for C,N,S-0.3Fe-TiO2. Their optical properties shifted from UV into visible light region and induced visible light absorption between 394 − 918 nm. The photochemical response of these TiO2 doped nanomaterials was followed using methyl orange (MO) dye under visible light irradiation. In fact, doped TiO2 nanomaterials with nitrogen, carbon, iron and/or sulfur exhibited a photochemical response 2 to 3 folds greater than TiO2 P25, and the photocatalytic efficiency depends on the doses and nature of dopants. In addition, the synergetic of S,N,C, and iron has shown significant effects on the crystalline structure, optical properties, pore volume and surface area.

Hydrophobic agents and pH modification as comparative chemical effect on the hydrophobic and photocatalytic properties in SiO2-TiO2 coating

The SiO2-TiO2 composite has been studied through several techniques obtaining different morphologies and specific properties of SiO2 and TiO2. Nevertheless, the modification of the synthesis pH and the addition of different hydrophobic agents, such as hexamethyldisilazane (HDMS) and polydimethylsiloxane (PDMS), have not been thoroughly studied and reported. This work assessed the presence of two different hydrophobic agents and the pH modification. The SiO2-TiO2 coating was synthesized through two vias, basic and acid environment, employing the sol–gel method coupled to the sonochemistry technique. Moreover, the change of pH and use of P25 TiO2 nanoparticles and TiO2-synthesized nanoparticles allows establishing a relationship with the self-cleaning properties. The samples of SiO2-TiO2 composite were analyzed by AFM, indicating a variation in surface morphology and roughness concerning the PDMS and HMDS hydrophobic agent. ATR-FTIR analysis exhibit changes in intensity in vibrations of the Si-O, PDMS, and HMDS bonds. Raman spectroscopy results show the vibrations of the anatase and rutile phases of the TiO2 and the corresponding vibrations to the hydrophobic agents. The evaluation of self-cleaning properties demonstrated changes from the hydrophobic state to the hydrophilic state due to the addition of the nanoparticles of TiO2 to the SiO2. The photocatalytic activity was modified and improved in the HMDS-1 coating due to the hydrophobic agent and type of nanoparticles. To compare the effect of the pH in the PDMS and HMDS coatings, carried out with cyclic voltammograms and Differential Capacitance spectra. Finally, the storage time of SiO2-TiO2 coating was improved using the HMDS hydrophobic agent.

Enhanced CO2 conversion on highly-strained and oxygen-deficient BiVO4 photocatalyst

Bismuth vanadate (BiVO4) has recently received significant attention for photocatalytic CO2 conversion due to its low bandgap and high stability, but low position of the conduction band and high electron-hole recombination rate limit its photocatalytic activity. In this study, to overcome the drawbacks of BiVO4, oxygen vacancies and lattice strain are simultaneously introduced in this oxide using a high-pressure torsion process. The processed material not only shows the low recombination rate and enhanced conduction band level but also exhibits bandgap narrowing. The oxygen-deficient and highly-strained BiVO4 shows a high photocatalytic CO2 conversion rate with an activity comparable to the P25 TiO2 photocatalyst. The enhancement of photocatalytic activity is discussed based on the modification of band structure, enhanced light absorbance, the lifetime of excited electrons, and the role of oxygen vacancies as activation sites for CO2 photoreduction. This work introduces a feasible pathway to develop active photocatalysts for CO2 conversion by lattice strain and defect engineering.

Mesoporous single crystal titanium oxide microparticles for enhanced visible light photodegradation

We report a facile one-step fabrication method of mesoporous single crystal ellipsoidal TiO2 (e-TiO2) microparticles with oxygen vacancies. In this method, hydrogen peroxide was used for the oxidation of titanium plate, and ammonia fluoride was used for the microparticle morphology controlling and pore introducing. Characterizations and calculations have proved that our as-synthesized TiO2 microparticles were in anatase phase with meso pores, single crystal structure and Ti (III) component. UV–vis–NIR spectra have also indicated that the bandgap of the e-TiO2 was 2.4 eV, much lower than typical anatase materials (3.2 eV). Rhodamine B and Methylene blue were introduced as dyes for the photodegradation test of the e-TiO2 compared to commercial P25–TiO2. Our e-TiO2 had better adsorption of both dyes and very high efficiency for the photodegradation of Rhodamine B under visible light illumination, whose kinetic constant is four times as much as P25–TiO2. Thus, the one-step synthesized e-TiO2 has high efficiency for visible light dye photodegradation.

Degradation of chemical warfare agents by nickel doped titanium dioxide powders: Enhanced surface activity

Here, Nickel doped anatase TiO 2 samples were prepared and characterized by X-ray diffraction, transmission electron microscope, X-ray photoelectron spectroscopy, specific surface area (BET), porosity determination (BJH) and CO 2 -TPD experiments. DFT calculation was conducted to investigate the oxygen vacancy formation energies and hydroxyl groups activity. The as-prepared Ni 2+ doped TiO 2 samples were used for heterogeneous degradation of chemical warfare agents (CWAs) and a high degradation rate, 92.2% and > 99.5% for sulfur mustard (HD) within 1 h and 12 h, > 99.5% for soman (GD) in less than 30 min, and > 99.5% for VX in less than 5 min was achieved, which were significantly enhanced compared with commercial P25 and anatase TiO 2 nanoparticles under identical conditions. The formation of non-toxic hydrolysis products confirmed the nucleophilic hydrolysis pathway via surface reaction. Integration of experimental and computational methods could well illustrate that surface structure changes of TiO 2 after Ni 2+ doping was the main reason for the superior stoichiometric activity towards CWAs.

Photoreduction of carbon dioxide and photodegradation of organic pollutants using alkali cobalt oxides MCoO2 (M = Li or Na) as catalysts

The recycling of lithium batteries should be prioritized, and the use of discarded alkali metal battery electrode materials as photocatalysts merits research attention. This study synthesized alkali metal cobalt oxide (MCoO2, M = Li or Na) as a photocatalyst for the photoreduction of CO2 and degradation of toxic organic substances. The optimized NaCoO2 and LiCoO2 photocatalysts increased the photocatalytic CO2–CH4 conversion rate to 21.0 and 13.4 μmol g−1 h−1 under ultraviolet light irradiation and to 16.2 and 5.3 μmol g−1 h−1 under visible light irradiation, which is 17 times higher than that achieved by TiO2 P25. The rate constants of the optimized reactions of crystal violet (CV) with LiCoO2 and NaCoO2 were 2.29 × 10−2 and 4.35 × 10−2 h−1, respectively. The quenching effect of the scavengers and electron paramagnetic resonance in CV degradation indicated that active O2•−, 1O2, and h+ play the main role, whereas •OH plays a minor role for LiCoO2. The hyperfine splitting of the DMPO−•OH and DMPO−•CH3 adducts was aN = 1.508 mT, aHβ = 1.478 mT and aN = 1.558 mT, aHβ = 2.267 mT, respectively, whereas the hyperfine splitting of DMPO+• was aN = 1.475 mT. The quenching effect also indicated that active O2•− and h+ play the main role and that •OH and 1O2 play a minor role for NaCoO2. The hyperfine splitting of the DMPO−•OH and DMPO+• adducts was aN = 1.517 mT, aHβ = 1.489 mT and aN = 1.496 mT, respectively. Discarded alkali metal battery electrode materials can be reused as photocatalysts to address environmental pollution.

Preparation and characterization of MnIn-layered double hydroxides (LDHs), extension of the synthesis to fabricate MnM(III)-LDHs (M = Al, Sc, Cr, Fe, Ga), and the comparison of their photocatalytic and catalytic activities in the oxidation of hydroquinone

The preparation of a new member of the hydrotalcite supergroup, i.e., MnIn-LDHs with Mn:In molar ratios from 5:2 to 8:2 was developed for the first time, by using the co-precipitation technique. The effect of the presence of air, N2 or H2 was systematically tested. The physico-chemical properties of the solids were characterized in detail. The application of reductive atmosphere proved to be vital for achieving phase-pure products. While the thermal behavior of the LDHs with different Mn:In molar ratios were largely similar, the increasing Mn:In ratio resulted in decreasing direct optical band gaps from 4.06 to 3.14 eV. By using the optimized conditions found for MnIn-LDHs, Mn4M(III)-LDHs were also prepared with M = Al, Sc, Cr, Fe, Ga. The catalytic performance of the various Mn(II)-based LDHs were tested under dark and UV–Vis-illuminated conditions for the transformation of hydroquinone in acetonitrile medium. The photocatalytic mechanism over MnIn-LDHs was studied by radical trapping tests, indicating the photogenerated holes play an important role in the decomposition of hydroquinone and even benzoquinone. The incorporation of Sc(III), Cr(III) and Fe(III) resulted in catalysts with outstanding performance both with and without illumination; under these conditions several metal oxides/semiconductors (like BiVO4, Bi2WO6, SrTiO3, Bi2O3, SnO2, WO3, In2O3, ZnO and Degussa P25 TiO2) and even the nonmetallic g-C3N4 proved to be inactive. The largest photocatalytic contributions were measured for the Mn4Cr- and Mn4In-LDHs. The selectivity and yield of the benzoquinone formation was found to be the largest in the case of the Mn4Al-, Mn4Fe- and Mn4In-LDHs using UV–Vis light source.

Fe2O3 Incorporated Anatase/Brookite Biphasic TiO2 for degradation of Phenol under Simulated Solar Light

This work describes the synthesis of Fe-doped mesoporous anatase and brookite polymorphs of TiO2 in the occurrence of P-123 surfactant at varying Fe3+ ions contents (0.5–2%). The photocatalytic performance of the newly synthesized Fe–TiO2 was evaluated for phenol degradation compared to the parent TiO2, commercial P25 and 2%Fe–P25 under the solar simulator. XRD and TEM results illustrated that the construction of TiO2 NPs with brookite and anatase phases and the diameter of 10 nm was achieved. The surface area of 2%Fe–TiO2 NPs (100 m2/g) revealed a large two times compared to that of P25 (50 m2/g). Interestingly, the optimum 2%Fe–TiO2 photocatalyst exhibited complete degradation phenol within 40 min, and it was two times greater than that bare TiO2 and commercial P25 under simulated solar light. The rate constant for degradation of phenol over 2% Fe–TiO2 was enhanced 5.5 and 2.93 folds than that P25 and bare TiO2 NPs. The photocatalytic enhancement performance of Fe–TiO2 photocatalyst was supposedly created from the got better utilization of the visible light range. This is because Fe3+ ions can serve as a transient capturing site for photoinduced hole-electron, which suppressed the charge carriers' recombination and extended their lifetime. Photoelectrochemical measurements such as electrochemical impedance spectroscopy, chronoamperometry and cyclic voltammetry were conducted to verify and confirm the photocatalytic performance of the newly synthesized photocatalysts.

Surface sulfate modified TiO2 visible light active photocatalyst for complex wastewater purification: Preparation, characterization and photocatalytic activity

One of the major concerns of today's society is the rapid deterioration of our environment. Wastewater purification via catalysts could be a solution for a part of this situation. Related to this topic. Related to this topic here we report the facile preparation of surface-modified TiO2 photocatalyst performed by simply grinding and calcination process, using elemental sulfur originated from the desulfurization of petroleum.Visible light active (Eg = 2.91 eV) sulfur modified TiO2 were prepared with low surface charge (-62.2 ± 0.7 mV). The improved photocatalytic activity of sulfated samples was proved via benzoic acid photodegradation tests under visible light and compared to the reference P25. According to the results, the sulfated TiO2 degraded 41% of the initial benzoic acid, while TiO2 degraded only 27%. Next mechanically stable photoreactive composite layers were prepared using the ST-benzene catalyst and it was presented that the thin film can successfully degrade the model water. In the complex sample, the ST-benzene containing photocatalyst layer's efficiency was 25.3% for phenol, 20.3% for niacin, 30.0% for paracetamol, 10.6% for caffeine and 28.8% for imidacloprid respectively. In addition, it is also presented that the sulfated photocatalyst is able to generate more hydroxyl radicals (which depends on the reaction rate constant of 7-hydroxycoumarin formation, kST-benzene = 6.682×10−5 µmol×L−1 × s−1) than the initial P25 TiO2, which makes it a promising photocatalyst for water purification.

Tungsten Catalysts for Visible Light Driven Ofloxacin Photocatalytic Degradation and Hydrogen Production

Some tungsten catalysts of interest that are synthesized are bismuth tungstate (BT) and Tetrabutylammonium decatungstate (TBADT), using two consolidated procedures. BT is used as a photo-catalyst for the simulated solar light degradation of ofloxacin (OFL) antibiotic under relevant real conditions (µg L−1, fresh water) with the limit of 0.05 g L−1 of catalyst. A quantitative drug decomposition occurred following a bi-exponential first-order law, with an efficiency comparable with the most used P25 TiO2 catalyst. The photocatalytic profiles of OFL at µg L−1 and mg L−1 were monitored by high-pressure liquid chromatography (HPLC) coupled with fluorescence (FD) and ultraviolet (UV) detectors. Additionally, the main photoproducts were identified by high-pressure liquid chromatography coupled to electrospray ionization in tandem with mass spectrometry (HPLC-ESI-MS/MS). The catalyst Tetrabutylammonium decatungstate (TBADT) was used as a catalyst to produce hydrogen from glucose and 2-propanol in aqueous solution, providing hydrogen gas evolution up to 10 µmol g−1 h−1.

Mixed-Phase TiO2 with Oxygen Vacancies for Enhanced Visible Light Photocatalysis Performance

Because of the decrease in the band gap and the carrier recombination rate, the visible light photocatalysis performance of the mixed-phase TiO2 with oxygen vacancies is better than that of the pure-phase TiO2. In this study, two different acids were separately applied in the hydrothermal synthesis of TiO2 nanoparticles without any post-heat treatment. The reaction was carried out at a relatively low temperature not exceeding 140∘C. Both kinds of crystallized TiO2 powders show much more band gap reduction than that of commercial Degussa P25 TiO2 nanoparticles, which can be attributed to the oxygen vacancies. Under the visible light illumination-assisted photocatalytic degradation of methyl orange in water, the two mixed-phase TiO2 powders exhibited a steady photocatalytic activity upon increasing to five cycles. The highest photocatalytic efficiency of the two powders is 2.7 times than that of the P25 powder, which is regarded as an excellent photocatalyst for water purification.

Could Iron-Nitrogen Doping Modulate the Cytotoxicity of TiO2 Nanoparticles?

Titanium dioxide nanoparticles (TiO2 NPs) are found in several products on the market that include paints, smart textiles, cosmetics and food products. Besides these, TiO2 NPs are intensively researched for their use in biomedicine, agriculture or installations to produce energy. Taking into account that several risks have been associated with the use of TiO2 NPs, our aim was to provide TiO2 NPs with improved qualities and lower toxicity to humans and the environment. Pure TiO2 P25 NPs and the same NPs co-doped with iron (1%) and nitrogen atoms (P25-Fe(1%)-N NPs) by hydrothermal treatment to increase the photocatalytic activity in the visible light spectrum were in vitro evaluated in the presence of human lung cells. After 24 and 72 h of incubation, the oxidative stress was initiated in a time- and dose-dependent manner with major differences between pure P25 and P25-Fe(1%)-N NPs as revealed by malondialdehyde and reactive oxygen species levels. Additionally, a lower dynamic of autophagic vacuoles formation was observed in cells exposed to Fe-N-doped P25 NPs compared to the pure ones. Therefore, our results suggest that Fe-N doping of TiO2 NPs can represent a valuable alternative to the conventional P25 Degussa particles in industrial and medical applications.

UVA LEDs and solar light photocatalytic oxidation/ozonation as a tertiary treatment using supported TiO2: With an eye on the photochemical properties of the secondary effluent

Photocatalytic oxidation/ozonation of a mixture of eight pharmaceuticals added to a secondary effluent, SE, of an urban wastewater treatment plant has been studied using TiO2 supported on commercial Al2O3/SiO2 ceramic foams. As radiation source UVA LEDs (365 nm) or solar radiation was used. Pharmaceuticals were added at high (1 mg L−1 each) or relatively low (50 μg L−1 each) concentration, contributing 25% and 1.5% to the initial TOC, respectively. Under both types of radiation, the photolysis of SE generated reactive species capable of degrading the contaminants (indirect photolysis), this effect being greater at lower initial concentration of pollutants. Lower concentration of contaminants also favoured their degradation and the SE mineralization by photocatalytic oxidation, whereas its effect on ozonation was low. The best results were obtained by photocatalytic ozonation, especially in terms of COD removal, without observing any synergism or antagonism between O3/Radiation and TiO2/Radiation systems. In SE, the performance of the supported catalyst resulted much better than that of suspended TiO2 P25, which showed almost no activity in this matrix. Through different cycles of reuse, the stability of the supported catalyst was confirmed.

A mechanistic study on photocatalytic activity of hydrothermally synthesized titanium dioxide nanowires decorated by silver phosphate

Heterostructure semiconductors have attracted increasing attention in the energy, environment, and catalysis domains. This study employed the hydrothermal method to synthesize titanium dioxide nanowires (TNWs) from TiO2–P25 nanoparticles. An effective strategy was used for coupling TNWs with a proper semiconductor with a narrow bandgap (Ag3PO4) for the purpose of enhancing absorption capacity in the visible light area and preventing the recombination of the photo-generated electrons and holes. The Ag3PO4/TNWs heterostructures consisted of Ag3PO4 nanoparticles firmly attached to the TNWs surfaces in varying ratios. The synthesized nanostructures were investigated by the Transmission Electron Microscopy (TEM), BET-BJH, and UV–Vis Diffusion Reflectance Spectra (DRS) techniques, as well as the X-ray diffractometer instrument. The photocatalytic degradation of RhB showed that the Ag3PO4/TNWs heterostructures manifested better photocatalytic performance than the pure TNWs and Ag3PO4. Likewise, the Ag3PO4/TNWs heterostructure photocatalyst reduced the loading of the noble Ag metal and thus decreased the practical application costs of the Ag3PO4 photocatalyst. A detailed mechanism study revealed the effective roles of holes and anion radical superoxides in the photocatalytic activity of the Ag3PO4/TNWs heterostructures.

Simple Fabrication of a Continuous-Flow Photocatalytic Reactor Using Dopamine-Assisted Immobilization onto a Fluoropolymer Tubing

A flow reactor has been found to be advantageous for a photocatalytic reaction due to enhanced transport phenomena and photon transfer. A fluoropolymer is a promising material for fabricating a photocatalytic flow reactor because it is transparent, commercially available, and inexpensive. However, its high hydrophobicity and chemically inert nature makes it difficult to coat photocatalysts. In this work, we successfully developed a protocol to immobilize photocatalysts (TiO2–P25) onto the wall of a perfluoroalkoxy alkane tubing. The immobilization was enabled by the initial depositions of polydopamine and polyethyleneimine (PEI) layers. Then, through an ionic interaction, P25 was immobilized onto the PEI layer. A layer-by-layer PEI–P25 assembly yielded a high photocatalyst loading, which in turn enhanced the photocatalytic activity significantly. A continuous-flow operation of the photocatalytic methylene blue decolorization was demonstrated with negligible leaching of the photocatalysts and minimal loss in activity over time. A transport phenomenon inside the tubular reactor was modeled to elucidate the effect of the process parameters on kinetic and adsorption parameters. This simply fabricated flow reactor shows a great potential for photocatalytic applications.

Dual promotional effect of Cu x O clusters grown with atomic layer deposition on TiO2 for photocatalytic hydrogen production.

The promotional effects on photocatalytic hydrogen production of CuxO clusters deposited using atomic layer deposition (ALD) on P25 TiO2 are presented. The structural and surface chemistry study of CuxO/TiO2 samples, along with first principles density functional theory simulations, reveal the strong interaction of ALD deposited CuxO with TiO2, leading to the stabilization of CuxO clusters on the surface; it also demonstrated substantial reduction of Ti4+ to Ti3+ on the surface of CuxO/TiO2 samples after CuxO ALD. The CuxO/TiO2 photocatalysts showed remarkable improvement in hydrogen productivity, with 11 times greater hydrogen production for the optimum sample compared to unmodified P25. With the combination of the hydrogen production data and characterization of CuxO/TiO2 photocatalysts, we inferred that ALD deposited CuxO clusters have a dual promotional effect: increased charge carrier separation and improved light absorption, consistent with known copper promoted TiO2 photocatalysts and generation of a substantial amount of surface Ti3+ which results in self-doping of TiO2 and improves its photo-activity for hydrogen production. The obtained data were also employed to modify the previously proposed expanding photocatalytic area and overlap model to describe the effect of cocatalyst size and weight loading on photocatalyst activity. Comparing the trend of surface Ti3+ content increase and the photocatalytically promoted area, calculated with our model, suggests that the depletion zone formed around the heterojunction of CuxO–TiO2 is the main active area for hydrogen production, and the hydrogen productivity of the photocatalyst depends on the surface coverage by this active area. However, the overlap of these areas suppresses the activity of the photocatalyst.

A Simple Method for Low-temperature Sintering of Titania

A low-temperature sintering process was used to produce pellets at different temperatures using TiO2 anatase (Vetec) and P25 (Evonik) commercial powders. The initial powder was mixed with 75% acetic acid aqueous solution and pressed under 375 MPa. The temperature was applied after the pelletization in a conventional furnace for 4 hours. The best sintering temperature for anatase was 800°C, which is higher than typical cold sintering temperatures but below conventional ones. However, the optimal temperature was 450 °C for P25 due to its density and SEM results. The sintered pellets' maximum densities were 70% (anatase, 800oC) and 66% (P25, 450oC). It was not possible to measure the anatase pellets treated under 800oC because they disintegrated in water. This work studied the effects of the applied pressure, solvent concentration, particle size, and sintering temperature on the properties of sintered pellets, such as integrity, density, and presence of porous. It also evaluated the electrochemical activity measured by cyclic voltammetry (CV), which indicated that the sintered TiO2 pellets are porous with a partial capacitive response.

Synthesis of 2D anatase TiO2 with highly reactive facets by fluorine-free topochemical conversion of 1T-TiS2 nanosheets.

Two-dimensional (2D) anatase titanium dioxide (TiO2) is expected to exhibit different properties as compared to anatase nanocrystallites, due to its highly reactive exposed facets. However, access to 2D anatase TiO2 is limited by the non-layered nature of the bulk crystal, which does not allow use of top-down chemical exfoliation. Large efforts have been dedicated to the growth of 2D anatase TiO2 with high reactive facets by bottom-up approaches, which relies on the use of harmful chemical reagents. Here, we demonstrate a novel fluorine-free strategy based on topochemical conversion of 2D 1T-TiS2 for the production of single crystalline 2D anatase TiO2, exposing the {001} facet on the top and bottom and {100} at the sides of the nanosheet. The exposure of these faces, with no additional defects or doping, gives rise to a significant activity enhancement in the hydrogen evolution reaction, as compared to commercially available Degussa P25 TiO2 nanoparticles. Because of the strong potential of TiO2 in many energy-based applications, our topochemical approach offers a low cost, green and mass scalable route for production of highly crystalline anatase TiO2 with well controlled and highly reactive exposed facets.