The enhanced photoactivity of hydrogenated TiO<sub>2</sub>@reduced graphene oxide with p–n junctions

Zhang, Xiaoying; Chen, Zhuoyuan

doi:10.1039/c4ra15819a

Cited by 17 publications

(11 citation statements)

References 39 publications

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“…A half wave potential E 1/2 can be defined as the potential required for reaching a half of the maximum photocurrent density j ph . The E 1/2 values are listed in Table 2 The increase in halfwave potential and photocurrent implies improved charge separation and, once more, suggests the formation of a p-n junction, as also described in the literature for similar TiO 2 /rGO systems [22,49]. In these systems, photoelectrons remain in TiO 2 , while photoholes move to rGO (ECrGO in our case).…”

Section: Dark Voltammogramssupporting

confidence: 75%

Photoactivity improvement of TiO2 electrodes by thin hole transport layers of reduced graphene oxide

Hernández‐Ferrer

Ansón‐Casaos

Víctor-Román

et al. 2019

Electrochimica Acta

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Nanostructured TiO 2 and graphene-based materials constitute components of actual interest in devices related to solar energy conversion and storage. In this work, we show that a thin layer of electrochemically reduced graphene oxide (ECrGO), covering nanostructured TiO 2 photoelectrodes, can significantly improve the photoactivity. In order to understand the working principle, ECrGO/TiO 2 photoelectrodes with different ECrGO thicknesses were prepared and studied by a set of photoelectrochemical measurements. Methanol in alkaline conditions was employed as effective hole acceptor probe to elucidate the electronic phenomena in the electrode layers and interfaces.These studies underline the hole accepting properties of ECrGO and reveal the formation of a p-n junction at the interface between ECrGO and TiO 2 . It is shown forthe first time that the resulting space charge region of about 10 nm defines the operational functionality of the ECrGO layer. Films thinner than the space charge region act as hole transport layer (HTL), which efficiently transfers holes to the liquid interface thus leading to enhanced photoactivity. Thicker films however act as hole blocking layer (HBL), resulting in a systematic decrease of the photoactivity. The finding of a thickness dependent threshold value for the operation of ECrGO as HTL and HBL is of general interest for the fabrication of optoelectronic devices with improved performance.Photoelectrochemistry is a powerful tool to elucidate the performance and working mechanism of materials and interface components used in layered optoelectronic devices, such as thin film solar cells. The resulting data reveal critical information about electronic properties such as conduction and valence band limits, as well as trapping, distribution, separation, recombination and transport of charges [1,2]. Using a simple electrochemical three-electrode configuration, photoelectrochemical measurements enable the elucidation of processes occurring at the working electrode, covering phenomena in bulk materials, across solid-solid interfaces for layered systems, as well as across the solid-liquid interface. Importantly, the acquired information provides valuable feedback for interface engineering towards optoelectronic device structures with improved performance.Materials of great current interest for solar energy conversion and storage are metal oxides such as ZnO [3] or TiO 2 [2], as well as carbon nanomaterials (graphene-based materials and carbon nanotubes) [4]. Employed as photoelectrodes [5], electron transport layers (ETLs) [6] or hole transport layers (HTLs) [7], they constitute important components in optoelectronic devices. Especially TiO 2 , graphene, and their hybrid materials are widely studied for this purpose [2,[8][9][10][11][12]. In dye-sensitized solar cells, TiO 2 is often used as the active layer, working as a photoanode [13,14]. In the case of perovskite [15] and organic solar cells [6], TiO 2 can constitute ETL [16, 17], enabling the transfer of photogenerated electrons from the ...

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Section: Dark Voltammogramssupporting

confidence: 75%

Photoactivity improvement of TiO2 electrodes by thin hole transport layers of reduced graphene oxide

Hernández‐Ferrer

Ansón‐Casaos

Víctor-Román

et al. 2019

Electrochimica Acta

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“…The formation of p-n heterojunction was suggested, building the inner electric fields at the interfaces between RGO and TiO 2 , significantly increasing the charge separation efficiency. 48 Briefly, the semiconductor behavior of the composites had a crossover from p-type to n-type when the hydrogenation temperature increased from 450 °C to 550 °C. There is no doubt that, herein, hydrogenated reduced graphene at 500 °C not only displays the semiconductor behavior but also different interesting properties due to the presence of additional turbostratic carbon.…”

Section: Photocatalytic H 2 and O 2 Evolution Measurementsmentioning

confidence: 99%

“…Much higher reversible discharge capacity at a current rate of 5 C (up to 166.3 mA h g -1 ), remarkable rate capability and outstanding cycling stability (2.4% capacity loss after 100 cycles) are attributed to the greatly improved electronic conductivity derived from hydrogenated TiO 2 (H-TiO 2 ), enhanced electron transport due to the role of reduced graphene as a conductive substrate, and the good contact between the zero-dimensional HTiO 2 nanoparticles with two-dimensional (2D) RGO nanosheets. Very recently, Zhang and Chen 48 reported the influence of hydrogenation temperature for GO-TiO 2 composites on the photocatalytic degradation of Rhodamine B. The highest photocatalytic activity was obtained by the hybrid material prepared at 450 °C due to the formation of p-n junctions and appropriate charge mobility.…”

Section: Introductionmentioning

confidence: 99%

Striving Toward Noble-Metal-Free Photocatalytic Water Splitting: The Hydrogenated-Graphene–TiO₂ Prototype

Nguyen‐Phan¹,

Luo

Liu

et al. 2015

Chem. Mater.

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Graphane, graphone and hydrogenated graphene (HG) have been extensively studied in recent years due to their interesting properties and potential use in commercial and industrial applications. The present study reports investigation of hydrogenated graphene/TiO 2-x (HGT) nanocomposites as photocatalysts for H 2 and O 2 production from water without the assistance of a noble metal co-catalyst. By combination of several techniques, the morphologies, bulk/atomic structure and electronic properties of all the powders were exhaustively interrogated. Hydrogenation treatment efficiently reduces TiO 2 nanoparticles, while the graphene oxide sheets undergo the topotactic transformation from a graphene-like structure to a mixture of graphitic and turbostratic carbon (amorphous/disordered) upon altering the calcination atmosphere from a mildly reducing to a H 2 -abundant environment. Remarkably, the hydrogenated graphene-TiO 2-x composite that results upon H 2 -rich reduction exhibits the highest photocatalytic H 2 evolution performance equivalent to low loading of Pt (~0.12 wt%), whereas the addition of HG suppresses the O 2 production. We propose that such an enhancement can be attributed to a combination of factors including the introduction of oxygen vacancies and Ti 3+ states, retarding the recombination of charge carriers and thus, facilitating the charge transfer from TiO 2-x to the carbonaceous sheet.

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“…both cell membranes and cellular processes. [7,8] Compared with in vivo synthesis, the cell-free systems enable the advantages of "plug-and-play" cascade assembly, diverse reaction conditions, as well as easy detection, separation, and purification of the products. [9] Cell-free biosynthesis utilizes in vitro networks comprising enzymes and cofactors, and facilitates inclusion of the separately produced enzymes into an optimal cascade.…”

Section: Doi: 101002/smll201902927mentioning

confidence: 99%

Hierarchical Micro‐ and Mesoporous Zn‐Based Metal–Organic Frameworks Templated by Hydrogels: Their Use for Enzyme Immobilization and Catalysis of Knoevenagel Reaction

Cheng

Švec

et al. 2019

Small

121

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Encapsulation of enzymes in metal–organic frameworks (MOFs) is often obstructed by the small size of the orifices typical of most reported MOFs, which prevent the passage of larger‐size enzymes. Here, the preparation of hierarchical micro‐ and mesoporous Zn‐based MOFs via the templated emulsification method using hydrogels as a template is presented. Zinc‐based hydrogels featuring a 3D interconnecting network are first produced via the formation of hydrogen bonds between melamine and salicylic acid in which zinc ions are well distributed. Further coordination with organic linkers followed by the removal of the hydrogel template produces hierarchical Zn‐based MOFs containing both micropores and mesopores. These new MOFs are used for the encapsulation of glucose oxidase and horseradish peroxidase to prove the concept. The immobilized enzymes exhibit a remarkably enhanced increased operational stability and enzymatic activity with a kcat/km value of 85.68 mm s–1. This value is 7.7‐fold higher compared to that found for the free enzymes in solution, and 2.7‐fold higher than enzymes adsorbed on conventional microporous MOFs. The much higher catalytic activity of the mesoporous conjugate for Knoevenagel reactions is demonstrated, since the large pores enable easier access to the active sites, and compared with that observed for catalysis using microporous MOFs.

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The enhanced photoactivity of hydrogenated TiO₂@reduced graphene oxide with p–n junctions

Cited by 17 publications

References 39 publications

Photoactivity improvement of TiO2 electrodes by thin hole transport layers of reduced graphene oxide

Photoactivity improvement of TiO2 electrodes by thin hole transport layers of reduced graphene oxide

Striving Toward Noble-Metal-Free Photocatalytic Water Splitting: The Hydrogenated-Graphene–TiO₂ Prototype

Hierarchical Micro‐ and Mesoporous Zn‐Based Metal–Organic Frameworks Templated by Hydrogels: Their Use for Enzyme Immobilization and Catalysis of Knoevenagel Reaction

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The enhanced photoactivity of hydrogenated TiO2@reduced graphene oxide with p–n junctions

Cited by 17 publications

References 39 publications

Photoactivity improvement of TiO2 electrodes by thin hole transport layers of reduced graphene oxide

Photoactivity improvement of TiO2 electrodes by thin hole transport layers of reduced graphene oxide

Striving Toward Noble-Metal-Free Photocatalytic Water Splitting: The Hydrogenated-Graphene–TiO2 Prototype

Hierarchical Micro‐ and Mesoporous Zn‐Based Metal–Organic Frameworks Templated by Hydrogels: Their Use for Enzyme Immobilization and Catalysis of Knoevenagel Reaction

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The enhanced photoactivity of hydrogenated TiO₂@reduced graphene oxide with p–n junctions

Striving Toward Noble-Metal-Free Photocatalytic Water Splitting: The Hydrogenated-Graphene–TiO₂ Prototype