TiO2 Heterophase Research Articles

Interface engineering of Ti3C2 MXene assisted anatase/rutile TiO2 with hetero-phase junction for enhancing the photocatalytic activity of tetracycline hydrochloride removal and H2 production

The conventional heterojunction formed by combining two different semiconductors is associated with issues of low compatibility, restricted intimate contact, and limited charge anti-recombination process. To address these issues, a simple strategy was adopted to fabricate a hetero-phase junction flanked with two dissimilar crystal phases of a single semiconducting material. This study employed TiB2 as the initial material to fabricate an anatase/rutile TiO2 hetero-phase junction material (AR-TiO2), followed by its combination with highly conductive monolayer Ti3C2 nanosheets to develop an AR-TiO2/Ti3C2 composite photocatalyst. The photocatalyst displayed a wide range of light absorption and a remarkable capability for separating photogenerated carriers. The closely interconnected hetero-phase junction surface, formed by the rutile and anatase phases of AR-TiO2, combined with the incorporation of highly conductive Ti3C2 nanosheets, synergistically increased the availability of multi-dimensional active sites and increased the efficacy of separating photogenerated electron pairs. The optimized AR-TiO2/Ti3C2 achieved a degradation efficiency of 91.49 % for tetracycline hydrochloride (TCH) within 2 h and produced 1005.81 μmol of hydrogen in 6 h. The impacts of initial pH, co-existing anions, initial TCH concentration, initial temperature, and various pollutant species on the catalytic efficiency were also investigated. pH was shown to have the greatest impact on the photocatalytic performance of AR-TiO2/Ti3C2 for TCH degradation. •O2−, and h+ were identified as the primary reactive species that enabled the photocatalytic performance of AR-TiO2/Ti3C2 through trapping experiments. This study presents a novel method to synthesize hetero-phase junction photocatalysts and suggests that Ti3C2 has potential prospects for use in photocatalysis.

Binary junctions enhance electron storage and potential difference for photo-assisted electrocatalytic CO2 reduction to HCOOH

Photo-assisted electrocatalytic (PAEC) CO2 conversion is a crucial approach for achieving sustainable carbon neutrality. Here, we have developed a binary-junctions photoanode by integrating SrTiO3 and anatase-rutile TiO2 nanotube arrays (STO/A-R TNTAs), which exhibits exceptional activity and selectivity in converting CO2 to HCOOH. The synergetic effects of the SrTiO3/TiO2 heterogeneous junction and the anatase-rutile TiO2 heterophase junction effectively facilitate photoelectron separation and storage, leading to a potential difference between anode and cathode. The establishment of the electron storage strategy, triggered by hetero- junction/phase interfaces, serves as remarkably efficient electron trapping regions with dam-like characteristics. As a result, the STO/A-R TNTAs achieves a generation rate of 68.24 μmol cm−2 h−1 with 92.25% selectivity and 90.70% Faradic efficiency. This performance is approximately 8 times higher compared to the pristine TiO2 nanotube arrays photoanode. The implementation of the electron storage mechanism presents a promising approach to improve CO2 reduction activity and selectivity.

S-doped TiN supported N, P, S-tridoped TiO2 with hetero-phase junctions for fuel cell startup/shutdown durability

A platinum group metal-free S-doped TiN-supported N, P, S-tridoped TiO2 catalyst with anatase/rutile TiO2 hetero-phase junctions is revealed to display a high durability against fuel cell startup/shutdown cycles not to lose its anion dopants.

Heterophase Polymorph of TiO2 (Anatase, Rutile, Brookite, TiO2 (B)) for Efficient Photocatalyst: Fabrication and Activity.

TiO2 exists naturally in three crystalline forms: Anatase, rutile, brookite, and TiO2 (B). These polymorphs exhibit different properties and consequently different photocatalytic performances. This paper aims to clarify the differences between titanium dioxide polymorphs, and the differences in homophase, biphase, and triphase properties in various photocatalytic applications. However, homophase TiO2 has various disadvantages such as high recombination rates and low adsorption capacity. Meanwhile, TiO2 heterophase can effectively stimulate electron transfer from one phase to another causing superior photocatalytic performance. Various studies have reported the biphase of polymorph TiO2 such as anatase/rutile, anatase/brookite, rutile/brookite, and anatase/TiO2 (B). In addition, this paper also presents the triphase of the TiO2 polymorph. This review is mainly focused on information regarding the heterophase of the TiO2 polymorph, fabrication of heterophase synthesis, and its application as a photocatalyst.

Unraveling the Role of Interface in Photogenerated Charge Separation at the Anatase/Rutile Heterophase Junction

Heterophase junctions have emerged as an effective strategy for spatial charge separation in photocatalysis. However, the photogenerated charge separation pathway at the junction region remains in doubt, and how the interfacial structure affects charge separation is unclear. Herein, we fabricate well-defined TiO2 heterophase junctions between rutile and anatase and employ in situ photochemical probing reactions to track the interfacial charges distribution by means of spherical aberration correction transmission electron microscope (CS aberration TEM). The photoreduction deposition of platinum (Pt) nanoclusters and photo-oxidation deposition of metal oxide nanoparticles demonstrate that the photogenerated electrons smoothly migrate across the interfacial phase junction from rutile to anatase phases and the photogenerated holes move in an opposite direction, which provides direct evidence on the spatial charge separation at the heterophase junction. Moreover, the atomic interfacial structure of anatase/rutile TiO2 heterophase junction formed is conducive for photogenerated charges moving from one phase to the other. This study revises the photogenerated charge separation at the anatase/rutile heterophase junction and demonstrates the important role of the interfacial structure on spatial charge separation.

Unraveling the Lattice Matching Effect in Surface Phase Junctions for Interfacial Charge Separation

Exquisite control over the interface structure is highly desired for the successful fabrication of a semiconductor heterojunction, which has been confirmed to effectively promote charge separation and transfer. However, the influences of the interface microstructure in the heterojunction on the charge separation and transfer efficiency are still unclear. Herein, taking the TiO2 heterophase junction (A/R) between anatase and rutile phases and the TiO2 homophase junction (Rs/R) between large rutile rodlike particles and small rutile nanoparticles (∼20 nm) as a prototypical model, it is found that the lattice match at the interface is a key factor determining the charge separation and transfer efficiency and the photocatalytic activity. As compared with A/R, the atomically smooth interface with a highly matched lattice in Rs/R leads to a less-defective and abrupt interface and provides a smooth interfacial charge separation and transfer path, leading to improved charge separation and transfer efficiency and a great enhancement in photocatalytic activity. This study provides a novel insight into optimizing the heterojunction structure by designing a highly matched lattice interface between two components.

Engineering of anatase/rutile TiO2 heterophase junction via in-situ phase transformation for enhanced photocatalytic hydrogen evolution

Constructing effective interphase boundary is one of the efficient approaches for improving photocatalytic performances of semiconductor materials. In this work, an anatase/rutile-TiO2 (AR-TiO2) heterophase junction with appropriate carbon content was successfully fabricated via an in-situ phase transformation process. The phase transformation started from the inner core of the nanoparticles and the area of phase interface between anatase and rutile was carefully controlled by regulating the activation temperature. The well-established type-II band alignment between two TiO2 phases with residual carbon as additional charge transfer intermediary which significantly improved the light-harvesting and photoinduced electron-hole pair separation. As a result, the optimal AR-TiO2-550 catalyst (without adding commonly used Pt as co-catalyst) remarkably enhanced photocatalytic H2 generation (201 μmol h−1 g−1), which was about 12-fold to that of P25. The AR-TiO2-550 heterophase junction also showed long-term stability under simulated solar light irradiation. This research provides a new phase engineering route for developing high-efficient photocatalysts.

Immobilization laccase on heterophase TiO2 microsphere as a photo-enzyme integrated catalyst for emerging contaminants degradation under visible light

The successful combination of enzymes and photocatalysts in one pot is an elegant approach for the reactions with high efficiency. This combination usually requires both enzymes and photocatalysts with reasonable activity under the same condition. Herein, a photo-enzyme integrated catalyst by immobilizing laccase on clustered porous TiO2 heterophase junction (HPJs) microsphere (denoted as mTiO2-CVs) is synthesized for the first time. The TiO2 microsphere with ordered regular radial structure and controllable heterophase junction (anatase/rutile) composition is prepared by a pressure-driven hydrothermal assembly method. The ratio of rutile and anatase phase of mTiO2-CVs can be controlled by adjusting the amount of hydrochloric acid in the preparing process. The characterization results of mTiO2-CVs prove that the mTiO2-CVs has regular morphology, uniform mesoporous structure, larger specific surface area and narrower band gap, and can realize the effective utilization of visible light. After immobilizing laccase on mTiO2-CVs by adsorption method, the integrated catalyst (mTiO2-CVs2.5@lac) can be obtained. Compared with free laccase, mTiO2-CVs2.5, and commercial P25, mTiO2-CVs2.5@lac shows higher catalytic efficiency in the emerging contaminants degradation under visible light. Therefore, the photo-enzyme integrated catalyst presented in this study provides a promising platform for emerging organic pollutants degradation by combining the enzymes with photocatalysts

Preparation of carbon-coated brookite@anatase TiO2 heterophase junction nanocables with enhanced photocatalytic performance.

One-dimensional TiO2@C nanocables with a heterophase junction have been successfully prepared by coating brookite@anatase TiO2 with a thin layer of hydrothermal carbon (HTC). Compared with anatase TiO2, the biphase brookite@anatase structure can reduce the recombination rate of the excited electron/hole pairs of TiO2. The HTC coating not only enhances the adsorption capability of the TiO2 catalyst for organic pollutants but also facilitates photogenerated electron transfer to further increase its photocatalytic activity. Therefore, compared with anatase TiO2, brookite@anatase TiO2, and TiO2@C, the brookite@anatase TiO2@C shows the highest photocatalytic activity for the photodegradation of tetracycline (TC) under the irradiation of UV-visible light. Moreover, ˙O2 has been proved to be the predominant active species for the photodegradation of TC, and the photocatalytic mechanism of brookite@anatase TiO2@C nanocables has also been proposed.

Synergistic Design of Anatase–Rutile TiO2 Nanostructured Heterophase Junctions toward Efficient Photoelectrochemical Water Oxidation

Synergistically designing porous nanostructures and appropriate band alignment for TiO2 heterophase junctions is key to efficient charge transfer, which is crucial in enhancing photoelectrochemical (PEC) water splitting for hydrogen production. Here, we investigate the efficiency of PEC water oxidation in anatase–rutile TiO2 nanostructured heterophase junctions that present the type-II band alignment. We specifically prove the importance of a phase alignment in heterophase junction for effective charge separation. The TiO2 heterophase junctions were prepared by transferring TiO2 nanotube (TNT) arrays onto FTO substrate with the help of a TiO2 nanoparticle (TNP) glue layer. The PEC characterization reveals that the rutile (R)-TNT/anatase (A)-TNP heterophase junction has a higher photocurrent density than those of A-TNT/R-TNP junction and anatase or rutile single phase, corresponding to twofold enhanced efficiency. This type-II band alignment of R-TNT/A-TNP for water oxidation, in which photogenerated electrons (holes) will flow from rutile (anatase) to anatase (rutile), enables to facilitate efficient electron-hole separation as well as lower the effective bandgap of heterophase junctions. This work provides insight into the functional role of heterophase junction for boosting the PEC performances of TiO2 nanostructures.

Construction of a triple sequential junction for efficient separation of photogenerated charges in photocatalysis.

A triple sequential junction by rationally combining anatase/rutile nanoparticle TiO2 heterophase (Ans/R) and rutile/rutile TiO2 homophase (Rns/R) junctions was fabricated as a proof of concept. Such a continuous charge separation and transfer channel resulted in a remarkable enhancement in the separation of photogenerated carriers and the photocatalytic activity.

One-pot hydrothermal preparation of PbO-decorated brookite/anatase TiO2 composites with remarkably enhanced CO2 photoreduction activity

Converting CO2 into solar fuels can deliver dual benefits to reducing the atmospheric CO2 levels and mitigating the energy shortage. Herein, PbO-decorated TiO2 composites (PbO/TiO2) are synthesized by a one-pot hydrothermal method. It is found that Pb2+ ions cause the product transforming from brookite TiO2quasi nanocubes (pristine TiO2) into heterophase junctions composed by brookite nanorods and anatase nanoparticles. By using as photocatalyst, 1.0% PbO/TiO2 delivers the best CH4/CO production activities of 53.21/5.99 μmol g−1 h−1 with an overall photoactivity of 437.7 μmol g−1 h−1. It is 33.2 times of the pristine TiO2 with an overall photoactivity of 13.2 μmol g−1 h−1. Further investigations demonstrate that the heterophase junctions can effectively retard the charge recombination, and the PbO promotes the CO2 adsorption/activation processes, and therefore causing the remarkably enhanced activity. The present work opens up an ideal synthetic route for metal oxide-assistant TiO2 heterophase junctions with highly photoactive CO2 conversion.

Remarkably enhanced H2 response and detection range in Nb doped rutile/anatase heterophase junction TiO2 thin film hydrogen sensors

Hydrogen sensors combining wide detection range and high response, that can operate at room temperature, are urgently demanded for monitoring different concentrations of hydrogen on a single device. Here, a novel one-step hydrothermal method is reported to construct Nb doped rutile/anatase TiO2 heterophase junctions for a highly sensitive H2 sensor. The Nb concentration in the solvent plays an important role for the heterophase juncton self-assemble, and the reaction time determines the surface morphology giving either a rutile TiO2 nanorod decorated anatase form, or a Nb doped rutile/anatase TiO2 bi-layer structure. An inverse dependence of the detectivity on H2 concentration is obtained as theoretically predicted but previously not experimentally verified for the high concentration region at low temperatures. The H2 concentration detection range is remarkably expanded, extending from 1 ppm to 12000 ppm for nanorod decorated film. The H2 response at 1 ppm is significantly enhanced to 22.5%, and reaches 98.9% in 8000 ppm H2 for the bilayer structure. The remarkablely extended detection range is the result of the massive accumulation of reactive pre-absorbed O2− on the surface due to the Nb doping, and the significantly enhanced response at room temperature results from the joint contributions of pre-absorbed O2−, film compactness and the heterophase junction. Moreover, Nb doped rutile/anatase TiO2 heterophase juncton films show high stability and humidity resistance for hydrogen sensing.

More efficiently enhancing photocatalytic activity by embedding Pt within anatase–rutile TiO2 heterophase junction than exposing Pt on the outside surface

Loading noble metal on the surface has been widely used to improve photocatalytic activity of semiconductor photocatalyst. Here, Pt-embedded anatase (A)-rutile (R) TiO2 junction photocatalyst (A/Pt/R) was found to show much more efficient photocatalytic H2 evolution activity than the other TiO2 photocatalysts loading Pt on the outside surface (such as Pt/A/R, Pt/A, Pt/R and Pt/P25), although the as-embedded Pt is unreachable to reactants. The A/Pt/R sample shows a photocatalytic H2 evolution rate as high as 17.9 mmol⋅gcat−1⋅h−1, which is 27.2 and 2.5 times higher than the common A/R and Pt/A/R samples, respectively. The traditional theory fails to explain the unexpected high photoactivity. The reverse tandem Schottky junction is suggested to be possibly responsible for the high photoactivity of A/Pt/R, which allows the photogenerated electrons to transfer more swimmingly from rutile to anatase than the common A/R phasejunction. This finding provides a new strategy for further promoting photocatalytic activity of Pt/TiO2 and other heterophase or heterojunction photocatalysts.

SrCO3-modified brookite/anatase TiO2 heterophase junctions with enhanced activity and selectivity of CO2 photoreduction to CH4

Utilizing the abundant solar energy to chemically convert CO2 into high-energy chemical fuels such as CO, CH4 or CH3OH offers a way to address the serious concerns about the increasing atmospheric CO2 levels and the depletion of fossil fuels. Herein, a series of SrCO3-modified TiO2 composites have been synthesized by adding SrCl2 into a TiCl4 hydrothermal reaction solution. It is found that brookite TiO2quasi nanocubes with high phase purity (denoted as pristine TiO2) can be derived from the TiCl4 reaction solution, and the additive Sr2+ ions lead to the formation of SrCO3-modified TiO2 heterophase junctions (HPJs) containing brookite nanorods and anatase nanoparticles. When used the SrCO3-modified TiO2 HPJs (hereafter denoted as SrCO3/HPJs) as photocatalyst for CO2 photoreduction, significantly enhanced activity and selectivity for CO2 photoreduction to CH4 can be achieved as compared to the pristine TiO2. Especially, 1.0% SrCO3/HPJs composite shows CH4/CO production activities of 19.66/2.64 μmol g−1 h−1 with an overall photoactivity of 162.6 μmol g−1 h−1, which is 12.3 times of the pristine TiO2 that shows an overall photoactivity of 13.2 μmol g−1 h−1 with CH4/CO production activities of 0.79/3.46 μmol g−1 h−1. The brookite/anatase TiO2 HPJs can effectively promote the photogenerated charge separation and restrain the interfacial charge recombination, and the SrCO3 species on the TiO2 HPJs can act as an efficient synergistic catalyst to improve the CO2 adsorption and activation abilities, and thus cause the enhanced activity and selectivity for CO2 photoreduction to CH4. This work represents the first example of coupling TiO2 HPJs with alkaline earth metal carbonates for efficient CO2 photoreduction.

Low-Temperature-Processed Brookite-Based TiO2 Heterophase Junction Enhances Performance of Planar Perovskite Solar Cells.

In the design of electron-transport layers (ETLs) to enhance the efficiency of planar perovskite solar cells (PSCs), facile electron extraction and transport are important features. Here, we consider the effects of different titanium oxide (TiO2) polymorphs, anatase and brookite. We design and fabricate high-phase-purity, single-crystalline, highly conductive, and low-temperature (<180 °C)-processed brookite-based TiO2 heterophase junctions on fluorine-doped tin oxide (FTO) as the substrate. We test and compare single-phase anatase (A) and brookite (B) and heterophase anatase-brookite (AB) and brookite-anatase (BA) as ETLs in PSCs. The power-conversion efficiencies (PCEs) of PSCs with low-temperature-processed single-layer FTO-B as the ETL were as high as 14.92%, which is the highest reported efficiency of FTO-B-based single-layer PSC. This implies that FTO-B serves as an active phase and can be a potential candidate as an n-type ETL scaffold in planar PSCs. Moreover, the surface of highly crystalline brookite TiO2 exhibits a tendency toward interparticle necking, leading to the formation of compact scaffolds. Furthermore, PSCs with heterophase junction FTO-AB ETLs exhibited PCEs as high as 16.82%, which is superior to those of PSCs with single-phase anatase (FTO-A) and brookite (FTO-B) as the ETLs (13.86% and 14.92%, respectively). In addition, the PSCs with FTO-AB exhibited improved efficiency and decreased hysteresis compared with those with FTO-BA (13.45%) due to the suitable band alignment with the perovskite layer, which resulted in superior photogenerated charge-carrier extraction and reduced charge accumulation at the interface between the heterophase junction and perovskite. Thus, the present work presents an effective strategy by which to develop heterophase junction ETLs and manipulate the interfacial energy band to further improve the performance of planar PSCs and enable the clean and eco-friendly fabrication of low-cost mass production.

Novel Highly Active Anatase/Rutile TiO2 Photocatalyst with Hydrogenated Heterophase Interface Structures for Photoelectrochemical Water Splitting into Hydrogen

In the past few years, anatase/rutile TiO2 heterophase junction structures with highly efficient photocatalytic performance have been explored widely, while their activities are still unsatisfactory in solar-to-hydrogen energy conversion. In this study, a novel anatase/rutile TiO2 photoelectrode with hydrogenated heterophase interface structures (A-H-RTNA) was successfully designed and synthesized for the first time via hydrothermal synthesis–hydrogenation–branching growth. Structure characterization indicated that the hydrogenated interfaces between anatase–branches and rutile–TiO2–nanorod hold appropriate oxygen vacancies and Ti3+ and inferred that new energy levels of oxygen vacancy and Ti–OH lie below the band edge positions of conduction band and valence band of rutile TiO2 nanorod, respectively. The matching energy levels between anatase–branches and hydrogenated rutile–nanorod obviously reduce the recombination of the photogenerated carriers, resulting in a superior photoelectrochemical (PEC) perfo...