TiO2 Heterostructure Research Articles

Fabricating structured 2D Ti3AlC2 MAX dispersed TiO2 heterostructure with Ni2P as a cocatalyst for efficient photocatalytic H2 production

Abstract A novel 2D MAX structure of Ti3AlC2 multilayers dispersed with TiO2/Ni2P heterojunction was designed and fabricated through modified sol-gel method for enhanced photocatalytic hydrogen production. Ni2P cocatalyst coupled 2D Ti3AlC2/TiO2 composite showed enhanced visible light absorption with promoted charge carrier separation. The activity of pristine Ti3AlC2 was obviously increased with the growth of TiO2 NPs and by exfoliating 2D MAX structure into multilayers. 2D Ti3AlC2/TiO2/Ni2P composite exhibited highest H2 production of 13000 μmol g−1 which was 1.29, 3.63 and 3.80 times more than the amount generated by TiO2/Ti3AlC2, TiO2/Ni2P and pristine TiO2, respectively. This enhanced activity was obviously due to good dispersion of TiO2/Ni2P over the Ti3AlC2 multilayers with boosted photoinduced charge carrier separation. Among the sacrificial reagents, glycerol-water mixture gave maximum H2 production due to the presence of more α-hydrogen atoms. More importantly, highest CO2 was evolved using a glycerol-water mixture compared to methanol, confirming both photocatalytic water splitting and photoreforming reactions occur simultaneously. The reaction mechanism to understand the role of each component in the composite catalyst is further discussed. The findings of this work would be helpful in commercial applications of Ti3AlC2 MAX based structured catalysts for H2 production and other sustainable energy systems.

Photosynthesis of H2 and its storage on the Bandgap Engineered Mesoporous (Ni2+/Ni3+)O @ TiO2 heterostructure

A noble-metal free and surface defect-induced mesoporous mixed valent NiO decorated TiO2 heterostructure with tuned bandgap has been successfully prepared. Its outstanding visible-light driven hydrogen evolution and its excellent H2 storage ability have been examined and confirmed. The formation of oxygen vacancies by surface defect creates the Ni3+ and Ti3+ on the interface of the heterostructure induce the efficient H2 evolution, bench-marked by 1200% enhancement in catalytic performance. The underlying chemistries include the near-unity occupancy of eg orbital (t2g6 eg1) of Ni3+ which speeds up the electron transfer and significantly promote the excellent electron-hole separation efficiency, establishes the outstanding overall charge-transfer efficiency and long-term photocatalytic activity in the visible light spectrum. Multiple Ti3+ adsorption centers in the structure attract multiple intact H2 molecules per each center via a sigma - pi bonding motif - namely the Kubas interaction - which leads to 480% higher H2 adsorption capability against the performance of the pristine mesoporous TiO2. Not only the significant results, the study also provide an air-stable synthetic method on the basis of low-cost and abundant materials, which are strongly favoured for scaling up production.

Photocatalysis, enhanced anti-bacterial performance and discerning thiourea sensing of Ag2O·SnO2·TiO2 hetero-structure

A novel multifunctional material with high dye degradation efficiency, photoluminescence (PL) and electro-sensing ability was synthesized with a simple co-precipitation method followed by thermal calcination. The dye degradation efficiency was 98% at pH 9 within only 60 min. The material also showed excellent anti-bacterial activity against both Gram positive and Gram negative bacteria in the presence and absence of light. For the electro-sensor application of Ag2O·SnO2·TiO2, glassy carbon electrode (GCE) was modified by the Ag2O·SnO2·TiO2 nanomaterials at room conditions. The resulting Ag2O·SnO2·TiO2/Nafion/GCE sensor assembly was employed to determine Thiourea (TU) by a simple and reliable electrochemical approach at low-potential. Hazardous TU was selected as the target analyte by the selectivity study. In the investigative study, for the TU concentrations of 0.10 nM to 0.10 M, the calibration plot was found linear (r2 = 0.9997). Calculated sensitivity and limit of detection values were obtained as 4.2913 μAμM−1 cm−2 and 2.3 ± 0.1 pM (S/N = 3) respectively.

Synergistic Removal of Bromate and Ibuprofen by Graphene Oxide and TiO2 Heterostructure Doped with F: Performance and Mechanism

The batch experiments of photocatalytic oxidation-reduction of bromate and ibuprofen (IBP) by graphene oxide (GO) and TiO2 heterostructure doped with F (FGT) particles were conducted. The performance and mechanism of synergistic removal of bromate and IBP by FGT were discussed. The results show that a demonstrable synergistic effect and excellent removal rate of bromate and IBP by FGT were exhibited. When pH is 5.2 and the dosage of FGT is 0.1 g/L, the reaction rate constants of bromate and IBP increased from 0.0584 min-1 and 0.4188 min-1 to 0.1353 min-1 and 0.4504 min-1, respectively, compared with the degradation of bromate or IBP alone. The reaction of photocatalytic synergistic degradation is appropriately fitted through Langmuir-Hinshelwood first-order kinetics. The mechanism of synergistic removal of bromate and IBP by FGT was discussed. And electrons (e-), hydroxyl radical (⋅OH), and superoxide radical (⋅O2-) are the main active species. The electrons play a main role in the bromate reduction, and bromine is the only reduction product, while the oxidation of IBP is the result of ⋅OH and ⋅O2-, and ⋅OH plays a key role. The recombination of electrons and holes is inhibited by simultaneous consumption of bromate and IBP, which makes full use of the redox properties of FGT and plays a synergistic role in the removal of pollutants. The results indicate that photocatalytic oxidation-reduction by FGT is a promising, efficient, and environmental-friendly method for synchronous removal of combined pollution in water.

Nanotube confinement-induced g-C3N4/TiO2 nanorods with rich oxygen vacancies for enhanced photocatalytic water decontamination

Construction of semiconductor heterojunctions is an efficient strategy to improve photo-induced charges separation and thus enhance photocatalytic activities. Herein, g-C3N4/TiO2 heterostructures were prepared via a facile thermal procedure, with TiO2 nanorods as matrix and g-C3N4 as visible-light sensitizer. Heterojunctions formed while precursors cyanamide polymerized to g-C3N4 and protonated titanate nanotube (H-TNTs) dehydrated and shrinked to TiO2 nanorods. Notably, confined polymerization of g-C3N4 occurred at both external surface and internal space of H-TNTs with the assistant of vacuum treatment, while NH3 released from cyanamide decomposition yielded abundant oxygen vacancies (VO) in TiO2 nanorods. Compared with pristine TiO2 nanorods, the heterostructured g-C3N4/TiO2 nanorods possess 1.7 times more active in photocatalytic removal of organic dye Orange II. A mechanism was proposed for heterostructured g-C3N4/TiO2 nanorods, being attributed to synergistic increasing light harvesting by VO and charges separation by heterojunctions.

A Novel Pt–TiO2 Heterostructure with Oxygen‐Deficient Layer as Bilaterally Enhanced Sonosensitizer for Synergistic Chemo‐Sonodynamic Cancer Therapy

AbstractSonodynamic therapy (SDT) activated by ultrasound is attractive as a potential alternative to conventional phototriggered therapies owing to the deeper penetration depth and the absence of phototoxicity. Nevertheless, the low quantum yield of nano‐sonosensitizer and the tumor hypoxia remain significant challenges for SDT. Herein, a novel TiO2‐based nano‐sonosensitizer is reported to bilaterally enhance the quantum yield by simultaneous integration of precious metal Pt nanoparticles (NPs) and an oxygen‐deficient layer. Furthermore, the hollow cavity of TiO2 serves as a reservoir to load doxorubicin, an anticancer drug for chemotherapy as well as a molecular sonosensitizer for SDT. The decorated Pt NPs act as nanozymes to catalyze the decomposition of endogenous hydrogen peroxide for the generation of oxygen to alleviate tumor hypoxia, reduce resistance to chemotherapy, and provide sufficient oxygen source for subsequently facilitating SDT‐induced reactive oxygen species production. The high chemo‐sonodynamic synergistic efficacy is systematically demonstrated both in vitro and in vivo. More importantly, it is believed that the novel design and the new finding in the synthesis of Pt–TiO2 heterostructures can be popularized for the preparation and application of the semiconductor‐based nanoplatforms in many fields.

Rational Construction of MnCo2O4.5 Deposited TiO2 Nanotube Array Heterostructures with Enhanced Photocatalytic Degradation of Tetracycline

AbstractA novel type of heterostructured photocatalyst, MnCo2O4.5 deposited TiO2 nanotube arrays (TNAs), was successfully synthesized via a two‐step anodization and chemical bath deposition method. The decoration of MnCo2O4.5 nanoparticles on anatase TNAs significantly enhances its photocatalytic degradation activity of tetracycline (TC). The optimized 140MnCo2O4.5/TiO2 nanotube arrays (140 M/TNA) catalyst exhibited the highest photocatalytic degradation of TC with an efficiency of 93.1 % after 2 h illumination. Meanwhile, the material showed good stability after a 5 cycle test. The mechanism of increased activity is attributed to the MnCo2O4.5/TiO2 heterostructure, which extends the response range to visible light and promotes electron–hole separation. Further radical capture experiment reveals that .O2− is vital as an active species for degrading TC in this system. The photocatalyst obtained via this rational synthesis strategy can effectively remove organic pollutants from waste water under visible light irradiation.

In-situ implantation of plasmonic Ag into metal-organic frameworks for constructing efficient Ag/NH2-MIL-125/TiO2 photoanode

Realizing a highly efficient catalytic activity for photoelectrochemical (PEC) water splitting has been becoming a key challenge for fabricating TiO2 photoanode, due to its weak light-response ability and poor electrical conductivity. For the first time, we prepared the TiO2 nanorods decorated with NH2-MIL-125 film, and subsequently in-situ implanted Ag nanoparticles (Ag NPs) into NH2-MIL-125 film by mild reduction process with the help of amine group. The synergistic effect between NH2-MIL-125 and Ag NPs is aimed at efficiently improving light-response and the overall conductivity of photoanode. The PEC performance of as-prepared Ag/NH2-MIL-125/TiO2 hybrid-photoanode has been systemically investigated. The photocurrent density of optimal Ag/NH2-MIL-125/TiO2 has reached 1.06 mA/cm2 at 1.23 V (vs. RHE) under illumination (100 mW/cm2), which is almost 4.42 times higher than that of pristine TiO2. The incident photon-to-electron conversion efficiency (IPCE) value of Ag/NH2-MIL-125/TiO2 has been increased to 51.0% at 390 nm. Furthermore, the desirable charge injection (ηinjection) of 96.4% and charge separation (ηseparation) efficiency of 33.1% have been achieved. The in-situ introduction of Ag NPs into NH2-MIL-125/TiO2 heterostructure provides a novel model for understanding the synergistic effect between metal and MOF over PEC water splitting.

Study of the Effect of TiO2 Layer on the Adsorption and Photocatalytic Activity of TiO2-MoS2 Heterostructures under Visible-Infrared Light

In the last decade, the urgent need to environmental protection has promoted the development of new materials with potential applications to remediate air and polluted water. In this work, the effect of the TiO2 thin layer over MoS2 material in photocatalytic activity is reported. We prepared different heterostructures, using a combination of electrospinning, solvothermal, and spin-coating techniques. The properties of the samples were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray diffraction (XRD), nitrogen adsorption-desorption isotherms, UV-Vis diffuse reflectance spectroscopy (UV-Vis-DRS), and X-ray photoelectron spectroscopy (XPS). The adsorption and photocatalytic activity were evaluated by discoloration of rhodamine B solution. The TiO2-MoS2/TiO2 heterostructure presented three optical absorption edges at 1.3 eV, 2.28 eV, and 3.23 eV. The high adsorption capacity of MoS2 was eliminated with the addition of TiO2 thin film. The samples show high photocatalytic activity in the visible-IR light spectrum.

Photocatalytic degradation of 2,4-dichlorophenol on ZrO2–TiO2: influence of crystal size, surface area, and energetic states

ZrO2–TiO2 heterostructure with 5 mol% of ZrO2 was synthesized by the sol–gel method and calcined at different temperatures (300–600 °C). The photocatalysts were characterized by thermal analysis, X-ray diffraction, physisorption of N2, diffuse reflectance spectroscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy. The photocatalytic activity was tested for the removal of 2,4-dichlorophenol under ultraviolet irradiation, being the materials exhibiting the best performance those calcined at 400 °C and 500 °C with 99% and 98% of degradation, respectively, after 150 min under irradiation. This behavior was related to a smaller crystallite size, higher surface area, and significant hydroxyl radicals produced. The (photo)electrochemical study showed that temperatures of 400 °C and 500 °C also generated an optimum amount of energetic states that act as electron traps and decrease the electron–hole pair recombination, favoring the oxidation of 2,4-dichlorophenol. However, at 300 °C and 600 °C, these energetic states act as an energy barrier that reduces the effective charge transfer and therefore decreases the photocatalytic activity of the materials.

Enhanced Photoelectrochemical Performance of g-C3N4/tiO2 Heterostructure by the Cooperation of Oxygen Vacancy and Protonation Treatment

A g-C3N4/TiO2 (CN/TiO2) nanocomposite was fabricated by depositing proton-functionalized g-C3N4 nanosheets onto the TiO2 nanotube array films with oxygen vacancies. Proton-functionalized g-C3N4 (p-CN) nanosheets was prepared by sonication-exfoliation of bulk g-C3N4 in the presence of hydrochloric acid. Protonation pretreatment of g-C3N4 reduce the size of g-C3N4 and increase the interfacial contact area of g-C3N4 nanosheets with TiO2 nanotube arrays. TiO2 nanotube arrays containing oxygen vacancy (OV-TiO2) was obtained by NaBH4 reduction, which results in the enhanced visible light absorption. As a result, the best photocurrent density of p-CN/OV-TiO2 nanocomposite is 5.3 times higher than that of CN/TiO2 samples. As further confirmed by photocatalytic degradation of methyl orange (MO), p-CN/OV-TiO2 heterostructure exhibit the highest photocatalytic activity among all the prepared samples. This improved photoelectrochemical (PEC) and photocatalytic performance can be attributed to the formation of a direct Z-Scheme heterostructure between protonated g-C3N4 and TiO2 containing oxygen vacancy.

Design of iso-material heterostructures of TiO2via seed mediated growth and arrested phase transitions.

Stabilization of different morphologies of iso-material native/non-native heterostructures is important for electron-hole separation in the context of photo-electrochemical and opto-electronic devices. In this regard, we explore the stabilities of different morphologies of rutile ("native", ground state phase) and anatase ("non-native" phase) TiO2 heterostructures through (1) seed-mediated growth and (2) a thermally induced arrested phase transition synthesis protocol. Furthermore, the experimental results are analyzed through a combination of Density Functional Tight Binding (DFTB) and Finite Element Model (FEM) methods. During the seed-mediated growth, anatase is grown over a polydispersed and polycrystalline rutile core through thermal treatment yielding core-shell, Janus and yolk-shell iso-material heterostructures as observed from HRTEM. The arrested phase transition of anatase to rutile at different annealing temperatures yields rutile crystals in the subsurface region of the anatase and rutile/core-thin anatase/shell heterostructures but does not yield a Janus structure. Small particles that can be modeled via DFTB computations suggest that: (1) a heterostructure of the rutile/core-anatase/shell is energetically more stable than the anatase/core-rutile/shell or any other Janus configuration, (2) the off-centered rutile/core-anatase shell is more favorable to the mid-centered rutile/core-anatase shell and (3) Janus heterostructures can be stabilized when the mass ratio of the rutile seed to anatase overgrowth is high. FEM simulations, performed to evaluate the importance of stress relaxation in bicrystalline materials without defects, suggest that Janus structures can be stabilized in larger particles. The present studies add to the heuristics available for synthesizing iso-material heterostructures.

Selective removal of organic and inorganic air pollutants by adjusting the g-C3N4/TiO2 ratio

During the recent years, g-C3N4/TiO2 composites have been regarded as efficient photocatalysts for the removal of air pollutants. The combination of these materials gives excellent photocatalytic performances, as each ones advantage covers the disadvantages of the other. In the present study, g-C3N4/TiO2 heterostructures were synthesized by mixing chemically exfoliated g-C3N4 with commercial TiO2 P25 in different ratios and were examined for the removal of NOx and acetaldehyde under visible-light irradiation. The results of photocatalytic tests in correlation with the EPR experiments revealed that heterostructures containing higher amount of TiO2 are efficient in systems where the attack of hydroxyl radicals prevails (acetaldehyde), while dominant g-C3N4 content provides effectiveness in systems where superoxide radical anions play the key role (NOx). This outcome is directly coupled with the energy positions of conduction- and valence-band edges of each material.

A bipolar modified separator using TiO2 nanosheets anchored on N-doped carbon scaffold for high-performance Li–S batteries

Lithium-sulfur batteries hold promise for next generation batteries due to their high theoretical energy density and low cost. However, the rapid capacity fading caused by the shuttle of polysulfide between two electrodes severely hinders the practical application of Li–S batteries. To address the issue, we reported a three-dimensional heterostructured TiO2 nanosheets/N-doped carbon (TO/NC), which is coated on a commercial polypropylene (PP) separator, as an efficient barrier for Li–S batteries. The TO/NC coating layer provides a bipolar chemical adsorption of lithium polysulfides (LiPSs) via TiO2 nanosheets with exposed (001) facets and N-doped carbon, showing high trapping capacity and remarkable electrocatalytic activity for LiPSs. The slurry-bladed carbon black/sulfur cathode with 64 wt% sulfur offers outstanding performance with an initial capacity of 1314 mA h g−1 at 0.2 C. Over 900 cycles, the cell still maintains the capacity of 448 mA h g−1 at a 1 C rate with a degradation rate of only 0.055% per cycle. The separator reported in this work holds great promise for the development of high-energy Li–S batteries.

MoS2 supported on hydrogenated TiO2 heterostructure film as photocathode for photoelectrochemical hydrogen production

The substitution of noble metal platinum catalyst is one of the important research contents for sustainable development and is also the key to the practical application of photoelectrochemical (PEC) hydrogen production. In this work, we loaded the 1T-2H mixed phase MoS2 on the hydrogenated anatase/rutile heterophase TiO2 (A-H-RTNA) by hydrothermal method to prepare a new MoS2/A-H-RTNA electrode material. The prepared material exhibited higher carrier density, lower PL intensity and higher conductivity than Pt/A-H-RTNA because 1T-MoS2 has more active sites and lower charge transfer resistance than Pt. With the bias voltage of −0.4 V, the optimized 16MoS2/A-H-RTNA as photocathode shows the largest PEC hydrogen production rate of 1840 mmol m−2 h−1, which is 2.9 and 2.2 times higher than those of A-H-RTNA (625 mmol m−2 h−1) and Pt/A-H-RTNA (848 mmol m−2 h−1), respectively. We innovatively used the prepared 16MoS2/A-H-RTNA film as counter electrode instead of Pt electrode to construct a PEC system without any noble-metal. The result demonstrates that the noble-metal-free MoS2 loaded on TiO2 electrode as counter electrode has 75% PEC activity of noble metal Pt electrode. This study develops a PEC method for hydrogen evolution, which no longer depends on precious metal platinum as cathode.

On the Role of Plasmonic Nanoparticles on the Photocatalytic of TiO2 Nanoparticles for Visible-Light Photoreduction of Bicarbonate

The potential application of anatase titanium dioxide (TiO2) nanoparticles for solar fuel generation has been recently attracting many attentions due to its excellent chemical stability. Nevertheless, the fast charge recombination during photoexcitation process may often reduce the photocatalytic activity. This work presents the role of plasmonic Au nanoparticles on enhancing the photocatalytic activity of TiO2 nanoparticles for a visible-light-driven conversion of bicarbonate to formate. Here, two types of nano-sized Au and TiO2 heterostructures, i.e., Au-TiO2 Janus nanostructures and core-shell Au@TiO2 nanostructures were successfully prepared and characterized using UV-Vis and HR-TEM. Results demonstrated that Au-TiO2 Janus nanostructures had a superior photocatalytic activity compared to TiO2 nanoparticles and core-shell Au@TiO2 nanostructures. This photocatalytic enhancement is believed due to the presence of surface plasmon resonance (SPR) phenomenon in Au nanoparticles that provides a Fermi energy level, which could prevent the charge recombination process during photoexcitation.

Two-step alcohothermal synthesis and characterization of enhanced visible-light-active WO3-coated TiO2 heterostructure

A new kind of WO3-coated TiO2 heterostructure with higher photocatalytic activity was prepared via a novel two-step alcohothermal synthesis process. The effects of the WO3 addition on the TiO2/WO3 products were systematically studied, including analysis of the phases, observation of the morphologies and calculation of the band gaps. Under illumination, the conduction band electrons of TiO2 are excited and accompanied by the generation of positive holes. In this heterostructure, the conduction band electrons of WO3 occupy the nearest valence band of TiO2 and then combine with the internal holes, inhibiting the flow of the electrons transferred from the conduction band of TiO2. Compared with anatase TiO2, the WO3-coated TiO2 heterostructure (weight ratio of WO3:TiO2 = 1:2) with a finer grain size exhibits excellent photocatalytic performance.

In-situ synthesis of CdS@TiO2 Nanoparticles-nanobelt Heterojunctions with high photocatalytic property

In this study, CdS nanoparticles were in-situ deposited on the surface of TiO2 nanorods through the liquid phase synthesis method, and the CdS@TiO2 Nanoparticles-nanobelt heterojunctions were obtained. The nanobelts are 50-200nm in width and several tens of micrometers in length, while the size of CdS nanoparticles is about 10 nm. The photocatalytic properties of the products were also studied and the results showed that the photocatalytic activity of CdS@ TiO2 heterostructure is improved greatly compared with that of the common nanobelts. This is attributed to the different band energy structure of the two semiconductors, facilitating efficient charge separation and migration.

Preparation of coral-like Ag2MoO4–TiO2 heterostructure and its photocatalytic properties

In this work, TiO2 nanofibers were prepared by combining electrospinning with an impregnation calcination technique. Ag2MoO4 nanoparticles at various concentrations were successfully deposited onto the surface of the nanofibers by hydrothermal synthesis method. Photocatalytic activities of samples for methyl orange degradation were investigated. The results indicate that Ag2MoO4–TiO2 nanofibers could efficiently degrade methyl orange upon the irradiation with UV-light, showing a greater photocatalytic activity than the pure titanium dioxide.

Synthesis of MoS₂/TiO₂ Nanophotocatalyst and Its Enhanced Visible Light Driven Photocatalytic Performance.

Molybdenum disulfide (MoS₂), as a typical layered transition metal sulfide, has been widely used in photocatalysis. Here, we report layered MoS₂ nanosheet-coated TiO₂ heterostructures that were prepared using a simple photo-assisted deposition method. The as-prepared samples were investigated in detail by using X-ray diffraction, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. Results demonstrated that the MoS₂ nanosheets uniformly covered the outer surface of TiO₂. The visible light-sensitive photocatalytic activity was evaluated by the removal of methylene blue (MB) and 2-chlorophenol (2-CP) in aqueous solution. Thus, the MoS₂/TiO₂ heterostructures exhibited improved photocatalytic degradation activity under visible light compared with the pure TiO₂. Under visible light irradiation for 90 min, the degradation efficiencies of MB and 2-CP over the MoS₂/TiO₂ sample (sunlight irradiation time: 30 min) are as high as 93.6% and 70.6%, respectively. Furthermore, the corresponding mechanism of enhanced photocatalytic activity is proposed on the basis of the comprehensively investigated results from the radical trapping experiments, photoluminescence spectroscopy, and electron spin resonance analysis. The hole oxidation, hydroxyl radicals, and superoxide anion radicals act as the active species simultaneously in the photodegradation of the dye molecules. However, of these species, hole oxidation played the most important roles in the photocatalytic reaction.