Pristine Anatase Research Articles

Manipulating the H2O2 Reactivity on Pristine Anatase TiO2 with Various Surface Features and Implications in Oxidation Reactions.

Anatase TiO2 is commonly used as a catalyst/support in reactions involving H2O2, yet the understanding of interactions between common TiO2 surfaces and H2O2 remains limited. Herein, we synthesized well-defined TiO2 crystallites with (101), (001), and fluorine-modified (001) [F-(001)] surfaces to examine how surface features, including the arrangement of five-coordinated Ti (Ti5c) sites and the presence of fluorine, influence H2O2 activation. Our findings reveal that these surface features significantly affect the physiochemical properties of adsorbed H2O2. Specifically, fluorine on the F-(001) surface introduces an additional hydrogen bond to the Ti5c-peroxo species, altering the electronic structure of H2O2 compared to those with the (101) and (001) surfaces. Using cyclohexene as a probe substrate, we successfully distinguished the reactivities of the Ti5c-peroxo species. The activity of those on the F-(001) surface was significantly higher than the activity of those on the (001) surface, while the (101) surface showed negligible oxidation activity. These insights can guide the design of TiO2-based catalysts for H2O2-related reactions.

Multiphasic titania photoanode: A facile phase assisted approach to enhance the photoelectrochemical and photovoltaic performance

A facile low-temperature method has been proposed and utilized to synthesize pristine and multiphasic titania. Increasing reactant acid content led to the phase transition of titania from pristine anatase to triphasic anatase-rutile-brookite mixed phase; then to biphasic anatase-rutile mixed phase and ultimately pristine rutile. Morphological differences between the samples led to different dye loading on the Dye Sensitized Solar Cell (DSSC) photoanodes, with anatase showing highest loading. However, the Electrochemical Impedance Spectroscopic (EIS) analyses revealed that the triphasic titania photoanode showed superior charge transport ability as evidenced by the lowest charge transfer resistance and highest carrier lifetime. This led to the triphasic DSSC showing a photoconversion efficiency of 4.23 % which is 45 % greater than the reference DP25 DSSC and 72 % better than that of the anatase DSSC despite having a 24 % lower dye loading. These factors suggest that the charge transport properties precede the dye loading capability of the photoanode in determining the DSSC performance. The intimate ternary interfacial junction between the anatase, rutile and brookite phases may be responsible for the enhanced charge transport properties of the triphasic titania. Thus, it is essential to ensure superior photoanode charge transport characteristics to enhance the DSSC performance.

Enhanced As(OH)3 adsorption by anatase TiO2 through facet control and Fe, N dual doping: A DFT+D3 study

Anatase and rutile, two major polymorphs of TiO2, have been used widely for environmental remediation, while anatase is apparently less effective for As(III) pollution management and needs substantial improvement. Herein, DFT calculations show that (001) rather than (101) and (100) facets of anatase are highly selective for As(III) adsorption. Facet control plays critical role during As(III) adsorption over pristine anatase surfaces and remains for mono doping, while diminishes substantially for dual doping. The second doping profoundly enhances As(III) adsorption for anatase facets with low activities and proves to be a viable strategy. Distinct from pristine surfaces where bidentate binuclear complexes prevail, monodentate complexes may become preferred due to doping, especially for dual doping where Fe site promotes adsorption via electronic effects. Doping causes As(III) oxidation when As centers interact directly with surfaces, and for mono doping, electron back-donation re-reduces As(V) to As(IV), while As(IV) occurs less for dual doping due to electron reservoir of Fe site that inhibits As(V) re-reduction. Regulatory mechanisms of facet control and effects of mono and dual doping for As(III) adsorption are further unraveled at molecular level. Results provide significant new insights for As(III) pollution management, and conduce to design As(III) scavengers and manage As-associated pollution.

Noble metals-deposited TiO2 photocatalysts for photoreduction of CO2: Exploration of surface chemistry and a reflection on the importance of wavelength dependence

We report the enhanced photocatalytic performance of CO2 reduction by introducing noble metal-deposited TiO2 photocatalysts (NMD/TiO2) under both visible light irradiation (VLI) and UV. It was found that NMD-TiO2 samples demonstrated an expanded ability for light absorption, resulting in an improved photoefficiency for CO2 reduction and selectivity towards carbon monoxide (CO). The conversion yields of CO2 to CO followed the order: Rh >Ru >Pt and with Rh/TiO2 reached 10.65 μmol/gcat (under visible light) and 7.84 μmol/gcat (under UV), which are ∼3 and 10 times more as compared to pristine anatase TiO2 (0, and 2.43 μmol/gcat). Various factors were addressed including theoretical studies via DFT revealed that the formation of new impurity energy state levels in NMD/TiO2, which act as acceptor levels. Moreover, DRIFTS studies showed that the H-O-C-O and formyl (H2CO) species were the important intermediates towards the hydrogenation of CO2 to CO. Also, a charge transfer mechanism toward CO2 reduction was elucidated.

TiO2 Nanotubes Decorated with Mo2C for Enhanced Photoelectrochemical Water-Splitting Properties.

The presence of Ti3+ in the structure of TiO2 nanotube arrays (NTs) has been shown to enhance the photoelectrochemical (PEC) water-splitting performance of these NTs, leading to improved results compared to pristine anatase TiO2 NTs. To further improve the properties related to PEC performance, we successfully produced TiO2 NTs using a two-step electrochemical anodization technique, followed by annealing at a temperature of 450 °C. Subsequently, Mo2C was decorated onto the NTs by dip coating them with precursors at varying concentrations and times. The presence of anatase TiO2 and Ti3O5 phases within the TiO2 NTs was confirmed through X-ray diffraction (XRD) analysis. The TiO2 NTs that were decorated with Mo2C demonstrated a photocurrent density of approximately 1.4 mA cm-2, a value that is approximately five times greater than the photocurrent density exhibited by the bare TiO2 NTs, which was approximately 0.21 mA cm-2. The observed increase in photocurrent density can be ascribed to the incorporation of Mo2C as a cocatalyst, which significantly enhances the photocatalytic characteristics of the TiO2 NTs. The successful deposition of Mo2C onto the TiO2 NTs was further corroborated by the characterization techniques utilized. The utilization of field emission scanning electron microscopy (FESEM) allowed for the observation of Mo2C particles on the surface of TiO2 NTs. To validate the composition and optical characteristics of the decorated NTs, X-ray photoelectron spectroscopy (XPS) and UV absorbance analysis were performed. This study introduces a potentially effective method for developing efficient photoelectrodes based on TiO2 for environmentally sustainable hydrogen production through the use of photoelectrochemical water-splitting devices. The utilization of Mo2C as a cocatalyst on TiO2 NTs presents opportunities for the advancement of effective and environmentally friendly photoelectrochemical (PEC) systems.

Enhancing Photocatalytic Hydrogen Evolution by Synergistic Benefits of MXene Cocatalysis and Homo-Interface Engineering.

Photocatalytic water splitting holds great promise as a sustainable and cost-effectiveness alternative for the production of hydrogen. Nevertheless, the practical implementation of this strategy is hindered by suboptimal visible light utilization and sluggish charge carrier dynamics, leading to low yield. MXene is a promising cocatalyst due to its high conductivity, abundance of active sites, tunable terminal functional groups, and great specific surface area. Homo-interface has perfect lattice matching and uniform composition, which are more conducive to photogenerated carriers' separation and migration. In this study, a novel ternary heterogeneous photocatalyst, a-TiO2 /H-TiO2 /Ti3 C2 MXene (MXTi), is presented using an electrostatic self-assembly method. Compared to commercial P25, pristine anatase, and rutile TiO2 , as-prepared MXTi exhibit exceptional photocatalytic hydrogen evolution performance, achieving a rate of 0.387mmol h-1 . The significant improvement is attributable to the synergistic effect of homo-interface engineering and Ti3 C2 MXene, which leads to widened light absorption and efficient carrier transportation. The findings highlight the potential of interface engineering and MXene cocatalyst loading as a proactive approach to enhance the performance of photocatalytic water splitting, paving the way for more sustainable and efficient hydrogen production.

Photocatalytic Denitrification of Nitrate Using Fe-TiO2-Coated Clay Filters

In this work, 3D-structured clay filters were prepared and coated with iron-doped titanium dioxide (Fe-TiO2) using 3D printing and sol–gel soaking and calcination techniques. Three-dimensional printing was employed to mold and shape the clay filters before annealing. The coated and uncoated filters were characterized for different properties, i.e., morphology, optical properties, and crystalline structure, using field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), UV/Vis diffused reflectance spectroscopy (DRS), and X-ray diffraction (XRD). The FESEM images show uniform coatings of round-shaped Fe-TiO2 on the tiny pore of the clay filter. The optical energy band gap of the obtained coating was around 2.8 eV, estimated by Tauc’s plot, compared with 3.2 eV of pristine anatase TiO2. The XRD spectra data processed through XRD software revealed the coatings of TiO2 on the filter surface with the obtained phase of anatase. The photocatalytic performance of bare and coated filters was initially tested for the degradation of indigo carmine (IC) dye and the obtained results suggested the photocatalytic degradation of IC dye by the Fe-TiO2 clay filter compared with the bare filter. Afterward, the denitrification of nitrate NO3 at various concentrations was performed using Fe-TiO2-coated clay filters and analyzing the total nitrogen (TN) analysis and reduction of NO3 to nitrite (NO2−), nitrogen monoxide (NO), and nitrogen gas (N2). The TN analysis revealed up to 81% denitrification efficiency of the 30 ppm NO3 solution with the photocatalytic response of the Fe-TiO2-coated filter. The results revealed that the Fe-TiO2-coated clay filter has a high potential for denitrification applications under natural sunlight.

Calcium-doped TiO2 microspheres and near-infrared carbazole-based sensitizer for efficient co-sensitized dye-sensitized solar cell

Here, we synthesized metal-free organic dye (CCPICPB) with two carbazole donor groups and two anchoring groups that exhibit a panchromatic absorption in the near-infrared range of up to 750 nm. To study the photophysical properties of synthesized CCPICPB dye, the UV–Vis and cyclic voltammetric experiments were studied and the obtained results were validated with theoretical simulation studies. After that, the solvothermal approach is used to synthesize pristine anatase and calcium (Ca)-doped TiO2 microspheres with a smooth morphology. These microstructures are examined in depth using XRD, electron microscopy and electrochemical analysis methods. On TiO2 and Ca-doped TiO2 photoanode materials, we first evaluated the performance of CCPICPB dye. Upon our optimized experimental condition, the 3% Ca-TiO2 photoanode-based device exhibits an efficiency of 4.04%, which is greater than that of the pristine TiO2 photoanode-based device (2.93%). Because of the quicker electron transport in the Ca-TiO2 film, the short-circuit current density and efficiency of DSSCs were improved. Moreover, when the CCPICPB dye was used as a co-sensitizer with the common Ru(II) dye (Z907), interestingly it showed the highest efficiency (6.11%) when compared with Z907 alone (5.12%). This improved efficiency of the co-sensitized device resulted from greater VOC conjugated with improved JSC. The JSC was improved because CCPICB dye could compensate for the photocurrent loss caused by redox electrolyte while the VOC was improved because electron recombination was inhibited under the co-sensitization conditions.Graphical abstract

Defective TiO2-Supported Dual-Schottky Heterostructure Boosts Fast Reaction Kinetics for High Performance Lithium-Ion Storage

TiO2, as a potential anode for lithium-ion batteries, suffers from low theoretical capacity and inferior reaction kinetics. Herein, we innovatively designed a unique dual-Schottky regulated ternary defective-TiO2-supported Co-nanodots-anchored N-doped-carbon-coated (defective TiO2@Co@NC) electrode, which was expected to possess advanced electrochemical reaction kinetics and increased Li-ion capacity. Molecular mechanics calculations indicated that the isolated cobalt nanodot can be stably formed in defective TiO2@Co@NC. And such a Co nanodot can not only firmly bridge the defective TiO2 matrix and Co-embedded N-doped carbon coating forming a dual-Schottky heterostructure, which boosts the fast reaction kinetics, but also effectively suppress the irreversibility of Li-ion intercalation. Correspondingly, as-designed binder-free defective TiO2@Co@NC anode was successfully synthesized via carbonization of the 3D hierarchical defective TiO2@Co-MOF precursor. In particular, the defective TiO2 nanotube array was for the first time used as nonreactive template to prepare Co-MOF composites. And TEM characterizations revealed that plentiful isolated cobalt nanodots were factually formed in derivative defective TiO2@Co@NC. As expected, defective TiO2@Co@NC electrodes exhibit remarkably high areal capacity (1191.2 μAh cm–2/490.9 mAh g–1 at 100 μA cm–2/41 mA g–1, 2.8 times of the pristine anatase TiO2 anodes), excellent cyclic stability (a capacity fading rate of 0.026% per cycle, at 500 μA cm–2/206.0 mA g–1 for 600 cycles), and superb rate properties (405.0 μAh cm–2/166.9 mAh g–1 at 1000 μA cm–2/412.0 mA g–1). Furthermore, the realization of in situ growth of uniform Co-MOF coatings with controllable thickness in defective TiO2@Co-MOF precursors facilitates the preparation of defective TiO2@Co@NC derivatives with tailored specific capacities, which paves the way for future research on MOF composites and Li-ion batteries.

Electronic properties of rutile and anatase TiO2 and their effect on CO2 adsorption: A comparison of first principle approaches

• The choice of suitable functional is dependent on the desired property. • A high U value or hybrid functional is required for credible electronic properties. • Grimme D3 is needed for adsorptions, but not for electronic and optical properties. • Activated CO 2 displays strong adsorption, bending and charge transfer. Photocatalysis is a promising technique for utilizing solar light in chemical synthesis. Among several effective photocatalysts, TiO 2 remains the archetypal representative. Using density functional theory calculations, we characterized the geometric, mechanical, electronic and optical properties of rutile and anatase TiO 2 . We show that a proper choice of the functional and corrections is of paramount importance. While the geometric and mechanical properties are well reproduced with conventional GGA functionals, electronic properties require at least a Hubbard approach. Despite being revered as superior, hybrid functionals do not necessarily perform better and a prudent choice is required. On the contrary, a lower Hubbard correction is desirable for a proper description of interactions, defects and structures. Lastly, CO 2 adsorption was studied on several surfaces. Pristine anatase and rutile surfaces poorly activate CO 2 , with the exception of rutile (0 0 1), which binds CO 2 strongly in a bent form, showing considerable charge transfer and activation.

Laser-assisted rapid synthesis of anatase/rutile TiO2 heterojunction with Function-specified micro-zones for the effective photo-oxidation of sulfamethoxazole

A solid-state laser scanning treatment (SLST) was adopted to synthesize anatase/rutile TiO2 heterojunction with effective charge carrier separation and high surface adsorption performances for the photodegradation of sulfamethoxazole (SMX). The 1064 nm pulsed fiber laser could in-situ generate rutile zones on the pristine sheet-like anatase crystal enclosed by (001) facets, which could form the well-defined anatase/rutile interface to promote the formation of dominating active species (h+ and ∙OH) on the anatase zones. X-ray absorption fine structure (XAFS) measurements, low temperature electron paramagnetic resonance (LT-EPR) as well as the density functional theory (DFT) simulation proved that the oxygen vacancies (VO) could both introduce defective energy states to promote the light absorption and enhance the SMX adsorption on anatase zones. Based on the delicately designed micro-zones, the photodegradation efficiency of the optimized catalyst could reach 99.3 %, which demonstrated ∼7 times higher performance than that of pristine TiO2 and exhibited robust stability under environmental conditions. Gaussian and Vienna Ab Initio Package (VASP) programs were used to provide detailed degradation pathways and mechanism for SMX. This SLST could be potentially employed to create function-specified zones on various catalysts for different applicational aims.

Modified HSE06 functional applied to anatase TiO2: influence of exchange fraction on the quasiparticle electronic structure and optical response

The influence of non-interacting Kohn–Sham Hamiltonian on the non-self consistent GW(G 0 W 0) quasiparticle gap and Bethe–Salpeter-equation (BSE) optical spectra of anatase TiO2 is systematically evaluated. G 0 W 0 and BSE calculations are carried out starting with HSE06 (Heyd–Scuseria–Ernzerhof) type functionals containing 20%, 25% and 30% exact Hartree–Fock exchange. The results are also compared against G 0 W 0 + BSE calculations starting from semi-local (PBE) functionals. Our results indicate that the G 0 W 0 and BSE calculations of anatase TiO2 depend critically on the mean-field starting point, wherein its dependence is mainly introduced through the dielectric screening evaluated at the intermediate G 0 W 0. We find that the band dispersion, density of states, and consequently the oscillator strengths of optical excitation and spatial localization of excitons are insensitive to the starting points while the quasiparticle gap, optical gap and exciton binding energies are strongly affected. G 0 W 0 quasiparticle gap of anatase TiO2 computed over hybrid functional starting points is typically overestimated compared to measured values. However, by varying the amount of exact exchange, the dielectric screening can be tuned, and thus the quasiparticle gap. Exciton binding energy is shown to increase in proportion to the increase of the amount of exact exchange. A simple extrapolation of the calculated data leads to the exact match with the recently measured value with 13% of the exact exchange. Systematic analysis of G 0 W 0 + BSE calculation starting from screened hybrid functionals provided in this study forms a reference for all such future calculations of pristine anatase TiO2 and its derivatives.

TiO2/BiVO4 composite from preformed nanoparticles for heterogeneous photocatalysis

Heteroaggregation of preformed nanocrystals used as building blocks is an interesting approach for the synthesis of heterostructures since it is possible to retain the main surface characteristics of the materials. In this paper, we studied the synthesis of a heterostructure consisting of monoclinic BiVO4 and anatase TiO2 phase for photocatalytic application. The heterostructures were synthesized using the building blocks technique with different TiO2/BiVO4 molar ratios under hydrothermal treatment. The effectiveness of heteroaggregations formation results in more photoactive catalysts due to the possibility of electron transfer between the materials. Methylene Blue (MB) solutions were decolorized under ultraviolet and visible radiation to evaluate the samples' photocatalytic activity. As a result, the as-synthesized samples presented higher photocatalytic efficiency than pristine anatase TiO2 and m-BiVO4 precursors. The increase of the photocatalytic properties is mainly attributed to the separation of the photogenerated charges, which is the central feature of heterostructures formed due to the collision of the particles during hydrothermal treatment.

Tailoring of structural, optical and electrical properties of anatase TiO2 via doping of cobalt and nitrogen ions

Pure (pristine) anatase and mono–doped and co–doped derivatives of TiO2 having nitrogen (N) and cobalt (Co) as dopants with respective fixed doping concentrations of 0.7 mol.% and 1.0 mol.% were synthesized using auto–combustion sol–gel technique. The doping effects at corresponding non–metal and transition metal sites of TiO2 on the basis of the structural, optical and electrical properties have been investigated. X–ray diffraction (XRD) measurement confirms the formation of pure anatase phase of TiO2 for all samples having I41/amd space group of tetragonal structure which has been also verified by the Raman spectroscopy measurement. Various crystallographic parameters have been calculated by performing Rietveld refinement of XRD data including average crystallite size that has been observed in the range of 10–15 nm. Pure anatase phase indicates the incorporation of Co2+ into TiO2 lattice which assists the substitution of N in place of oxygen in co–doped TiO2. The band gap tuning towards the visible region from 3.2 to 2.1 eV has been achieved with mono–doping and co–doping of the N and Co in TiO2 lattice. This can be described in terms of the formation of localized levels of N–2p and Co–3d states in mono–doping and an isolated intermediate band formation in co–doping case. Electrical properties have been investigated in details and explained as the synergetic effects of structural and inherent ionic characters of various dopants. The observed band gaps of all doped samples lie within the visible region which makes them pertinent as the solar energy harnessing materials for photocatalytic and photovoltaic applications.

Effect of temperature on the action spectra of pristine and Cu-grafted titania

The dependence of action spectra for pristine and Cu-grafted anatase TiO2 on temperature for photocatalytic acetone vapor oxidation at 40, 100 and 140 °C is described. The results obtained demonstrate the thermal inhibition of activity under UV irradiation for pristine titania at 140 °C, while for TiO2 grafted with copper species this inhibition is suppressed. Photonic efficiency of visible radiation energy utilization by Cu-grafted titania increases with temperature and exceeds the corresponding value for pure anatase in the investigated temperature range.

Structure and Stability of Pristine and Carboxylate-Covered Anatase TiO2(001) in Aqueous Environment

Structure and Stability of Pristine and Carboxylate-Covered Anatase TiO₂(001) in Aqueous Environment

Oriented titania nanotube biphase junction arrays on water splitting

Photocatalyst with phase junction is of great importance to achieve high charge separation and transfer efficiency on solar energy utilization. Herein, an oriented anatase/rutile biphase junction based on TiO2 nanotube arrays are facile prepared by novel oriented thermal annealing method. Its phase distribution and proportion can be tuned by adjusting heat radiation direction and time, respectively. Light absorption spectroscopy and photoelectrochemical measurements reveal that the oriented phase junction is crucial for charge transfer and separation. The sample containing with 34.4% rutile phase has the highest incident photon-to-current efficiency and charge separation efficiency, and achieves ca. 2.2 and 4.7 folds photocurrent density enhancement compared to pristine anatase and rutile phase TiO2 arrays, respectively. The photocurrent density of oriented biphase junction arrays (0.458 mA·cm−2 at 1.23 V vs RHE) is also significantly higher than random phase junction sample or previous reported result. This work demonstrates that the great potential of oriented biphase junction arrays can be applied in efficient charge separation and transfer on solar energy conversion.

Surface engineering of mesoporous anatase titanium dioxide nanotubes for rapid spatial charge separation on horizontal-vertical dimensions and efficient solar-driven photocatalytic hydrogen evolution

The low charge separation efficiency and sunlight utilisation of traditional titanium dioxide (TiO2) nanoparticle photocatalysts greatly limit their applications. Herein, one-dimensional (1D) mesoporous anatase TiO2 nanotubes with engineered surface defects are fabricated using a combination of simple solvothermal synthesis and high-temperature surface hydrogenation strategy. The obtained mesoporous anatase TiO2 nanotubes with mesopores in the nanotube walls and a specific surface area of 110 m2 g−1 decrease the bandgap from 3.18 to 2.98 eV, enhancing the photoresponse to the visible-light region of the solar spectrum. The defective mesoporous anatase TiO2 nanotubes exhibited an excellent photocatalytic hydrogen evolution rate of 9.8 mmol h−1 g−1, which is approximately 2.5 times higher than that of the pristine anatase TiO2 nanotubes. This can be ascribed to the engineered surface defects and 1D mesoporous nanotube structure favouring efficient spatial charge separation on the horizontal–vertical dimensions, enabling visible-light absorption and exposing abundant surface active sites. This study provides a facile and feasible strategy for the fabrication of high-performance 1D mesostructured semiconductor oxide photocatalysts for efficient solar energy conversion.

Sonocatalytic degradation of EDTA in the presence of Ti and Ti@TiO2 nanoparticles

The sonocatalytic degradation of EDTA (C0 = 5 10−3 M) in aqueous solutions was studied under 345 kHz (Pac = 0.25 W mL−1) ultrasound at 22–51 °C, Ar/20%O2, Ar or air, and in the presence of metallic titanium (Ti0) or core-shell Ti@TiO2 nanoparticles (NPs). Ti@TiO2 NPs have been obtained using simultaneous action of hydrothermal conditions (100–214 °C, autogenic pressure P = 1.0–19.0 bar) and 20 kHz ultrasound, called sonohydrothermal (SHT) treatment, on Ti0 NPs in pure water. Ti0 is composed of quasi-spherical particles (30–150 nm) of metallic titanium coated with a metastable titanium suboxide Ti3O. SHT treatment at 150–214 °C leads to the oxidation of Ti3O and partial oxidation of Ti0 and formation of nanocrystalline shell (10–20 nm) composed of TiO2 anatase. It was found that Ti0 NPs do not exhibit catalytic activity in the absence of ultrasound. Moreover, Ti0 NPs remain inactive under ultrasound in the absence of oxygen. However, significant acceleration of EDTA degradation was achieved during sonication in the presence of Ti0 NPs and Ar/20%O2 gas mixture. Coating of Ti0 with TiO2 nanocrystalline shell reduces sonocatalytic activity. Pristine TiO2 anatase nanoparticles do not show a sonocatalytic activity in studied system. Suggested mechanism of EDTA sonocatalytic degradation involves two reaction pathways: (i) sonochemical oxidation of EDTA by OH/HO2 radicals in solution and (ii) EDTA oxidation at the surface of Ti0 NPs in the presence of oxygen activated by cavitation event. Ultrasonic activation most probably occurs due to the local heating of Ti0/O2 species at cavitation bubble/solution interface.

Long‐Living Holes in Grey Anatase TiO2 Enable Noble‐Metal‐Free and Sacrificial‐Agent‐Free Water Splitting

Titanium dioxide has been the benchmark semiconductor in photocatalysis for more than 40 years. Full water splitting, that is, decomposing water into H2 and O2 in stoichiometric amounts and with an acceptable activity, still remains a challenge, even when TiO2‐based photocatalysts are used in combination with noble‐metal co‐catalysts. The bottleneck of anatase‐type TiO2 remains the water oxidation, that is, the hole transfer reaction from pristine anatase to the aqueous environment. In this work, we report that “grey” (defect engineered) anatase can provide a drastically enhanced lifetime of photogenerated holes, which, in turn, enables an efficient oxidation reaction of water to peroxide via a two‐electron pathway. As a result, a Ni@grey anatase TiO2 catalyst can be constructed with an impressive performance in terms of photocatalytic splitting of neutral water into H2 and a stoichiometric amount of H2O2 without the need of any noble metals or sacrificial agents. The finding of long hole lifetimes in grey anatase opens up a wide spectrum of further photocatalytic applications of this material.