2D-2D Heterojunction Research Articles

One-Pot Synthesis of 2D-2D WO3 /g-C3 N4 Photocatalyst in Reverse Microemulsion System via Supercritical CO2 for Enhanced Hydrogen Generation.

Construction of Z-scheme photocatalyst is an effective approach for using solar energy to produce hydrogen during water splitting. Herein, 2D/2D WO3 /g-C3 N4 heterojunction photocatalyst was synthesized by a convenient and green method including exfoliation and heterojunction procedures, in the reverse microemulsion system via supercritical carbon dioxide (scCO2 ). The resultant W/CN-10.3 composite exhibited enhanced photocatalytic activities towards the hydrogen evolution during water splitting with a hydrogen evolution rate of 688.51 μmol g-1 h-1 , which was more than 16 times higher than bulk g-C3 N4 with the same loading amount of Pt as cocatalyst. Due to its effective separation of photogenerated carriers and prolonged lifetime, more photoexcited electrons with high reduction ability could contribute to the production of H2 . Possible formation mechanism of 2D-2D WO3 /g-C3 N4 nanosheets via scCO2 in the reverse microemulsion system by the one-pot method has been proposed. This work provides an efficient and green strategy to synthesize 2D-2D heterojunction for the utilization in solar-to-fuel conversion.

TiO2/BiOBr 2D-2D heterostructure via in-situ approach for enhanced visible-light photocatalytic N2 fixation

Two-dimensional (2D)-2D heterojunctions have great potential for solar energy utilization and photocatalytic nitrogen fixation due to their unique electron transport pathways. Herein, TiO2/BiOBr 2D-2D heterojunction photocatalysts with different composite ratios were synthesized. The TiO2/BiOBr heterojunction demonstrated excellent photocatalytic nitrogen fixation activity and good cycling stability during the experiment. The maximum NH3 production rate of the prepared 15% TiO2/BiOBr heterojunction catalyst was 1.43 mmol/g/h, which was more than about 4 times as much as that of pure BiOBr. The high photocatalytic nitrogen fixation performance can be mainly ascribed to the 2D interface between TiO2 and BiOBr nanosheets in the heterojunction. As demonstrated by transient photocurrents, electrochemical impedance spectra and photoluminescence quenching studies, 2D interface can speed up the transfer of photogenerated electrons and provide more electrons to participate in the nitrogen fixation reaction, thus improving the performance of photocatalytic nitrogen fixation. Our results demonstrated that the construction of 2D-2D heterojunctions can be an effective strategy to improve solar energy utilization.

Fabrication of 2D-2D Heterojunction Catalyst with Covalent Organic Framework (COF) and MoS2 for Highly Efficient Photocatalytic Degradation of Organic Pollutants.

In this work, for the first time, we fabricated a novel covalent organic framework (COF)-based 2D-2D heterojunction composite MoS2/COF by a facile hydrothermal method. The results of photocatalytic degradation of TC and RhB under simulated solar light irradiation showed that the as-prepared composite exhibited outstanding catalytic efficiency compared with pristine COFs and MoS2. The significantly enhanced catalytic efficiency can be ascribed to the formation of 2D-2D heterojunction with a well-matched band position between COF and MoS2, which can effectively restrain the recombination of charge carriers and increase the light absorption as well as the specific surface area. Moreover, the fabricated 2D-2D layered structure can effectively increase the contact area with an intimate interface contact, which greatly facilitates the charge mobility and transfer in the interfaces. This study reveals that artful integration of organic (COFs) and inorganic materials into a single hybrid with a 2D-2D interface is an effective strategy to fabricate highly efficient photocatalysts.

Strongly interfacial-coupled 2D-2D TiO2/g-C3N4 heterostructure for enhanced visible-light induced synthesis and conversion

Two-dimensional (2D) nanosheet-based nanocomposites have attracted intensive interest owing to the unique electronic and optical properties from their constituent phases and the synergistic effect from the heterojunctions. In this study, an interfacial coupled TiO2/g-C3N4 2D-2D heterostructure has been prepared via in situ growth of ultrathin 2D-TiO2 on dispersed g-C3N4 nanosheets. This strongly coupled 2D-2D TiO2/g-C3N4, different from the weakly bonded 2D-TiO2/g-C3N4 heterostructures produced by mechanical mixing, has unique electronic structures and chemical states due to strong interlayer charge transfer, confirmed by both experimental and theoretical analyses. Significantly enhanced visible-light responses have been observed, indicating a great potential for visible-light induced photosynthesis and photocatalysis. For benzylamine coupling reactions under visible-light irradiation, 80 % yield rate has been achieved, superior to ∼30 % yield rate when adopting either 2D-TiO2 or g-C3N4 structure. The enhanced photocatalytic activity can be attributed to the adequate separation of photo-generated electrons at the strongly coupled 2D-2D heterojunction interfaces.

A 2D-2D heterojunction Bi2WO6/WS2-x as a broad-spectrum bactericide: Sulfur vacancies mediate the interface interactions between biology and nanomaterials

We report a heterojunction Bi2WO6/WS2-x with sulfur vacancies as a broad-spectrum bactericide to efficiently kill Gram-positive and Gram-negative bacteria in vitro and in vivo under visible-light irradiation. Sulfur vacancies in single-layer WS2 make the surface electron-rich. Integration of Bi2WO6 with WS2 enhances the photoelectric activity under visible-light irradiation. Sulfur vacancies promote the generation of radicals and the extraction of membrane phospholipids from bacterial cells. Density functional theory verifies that S vacancies strengthen the interactions between the Bi2WO6/WS2-x surface and H2O, enhancing the generation of ·OH. Two-dimensional correlation spectroscopy analysis reveals that perturbation of β-sheet proteins and formation of outer-sphere surface complexes contribute to the high antibacterial capacity. Bi2WO6/WS2-x accelerates the re-epithelialization and healing of infected wounds in an animal model. Uncommonly, Bi2WO6/WS2-x does not exhibit drug resistance and is biocompatible with human cells. Our results indicate that vacancy-functionalized heterojunctions are potentially promising antibacterial agents by regulating the interface interaction between biology and nanomaterials.

From One to Two: In Situ Construction of an Ultrathin 2D-2D Closely Bonded Heterojunction from a Single-Phase Monolayer Nanosheet.

Despite the many attempts to build ultrathin 2D-2D heterojunctions via wet chemical methods, the resulting composite materials reported to date suffer from poor interfacial bonding and/or complexity of the synthetic protocols. Encouraged by the structural compatibility of Bi2WO6 and Bi2O2S, both of which are 2D semiconductors sharing a rather similar structural unit of a [Bi2O2]2+ slice in their crystal structures, we have successfully fabricated an ultrathin nanosheet with a tightly bonded 2D-2D heterojunction between the two components by facilely joining the [Bi2O2]2+ and [S]2- slices using a simple two-step hydrothermal method. Such a Bi2WO6-Bi2O2S 2D-2D heterojunction has a five-alternating-layer (Bi2O2S-Bi2WO6-Bi2O2S-Bi2WO6-Bi2O2S) sandwich structure and a thickness down to ca. 5 nm and was obtained by simply growing the Bi2O2S layer in situ on the surface of monolayer Bi2WO6 nanosheets. The judicious combination of Bi2WO6 and Bi2O2S through a 2D-2D heterojunction not only extended light absorption in the visible range but also significantly enhanced photo(electro)chemical water splitting efficiencies in comparison to the bare Bi2WO6 nanosheets alone due to the close-bonding-promoted interfacial charge separation. Our findings provide a viable methodology to build a host of nanomaterials with closely bonded 2D nanosheets, which can be used as photocatalysts and electrocatalysts, among others.

Engineering the Dimensional Interface of BiVO4-2D Reduced Graphene Oxide (RGO) Nanocomposite for Enhanced Visible Light Photocatalytic Performance.

Graphene as a two-dimensional (2D) nanoplatform is beneficial for assembling a 2D heterojunction photocatalytic system to promote electron transfer in semiconductor composites. Here a BiVO4 nanosheets/reduced graphene oxide (RGO) based 2D-2D heterojunction photocatalytic system as well as 0D-2D BiVO4 nanoparticles/RGO and 1D-2D BiVO4 nanotubes/RGO nanocomposites are fabricated by a feasible solvothermal process. During the synthesis; the growth of BiVO4 and the intimate interfacial contact between BiVO4 and RGO occur simultaneously. Compared to 0D-2D and 1D-2D heterojunctions, the resulting 2D-2D BiVO4 nanosheets/RGO composites yield superior chemical coupling; leading to exhibit higher photocatalytic activity toward the degradation of acetaminophen under visible light irradiation. Photoluminescence (PL) and photocurrent experiments revealed that the apparent electron transfer rate in 2D-2D BiVO4 nanosheets/RGO composites is faster than that in 0D-2D BiVO4 nanoparticles/RGO composites. The experimental findings presented here clearly demonstrate that the 2D-2D heterojunction interface can highlight the optoelectronic coupling between nanomaterials and promote the electron–hole separation. This study will motivate new developments in dimensionality factors on designing the heterojunction photocatalysts and promote their photodegradation photocatalytic application in environmental issues.

Carbon dots sensitized 2D-2D heterojunction of BiVO4/Bi3TaO7 for visible light photocatalytic removal towards the broad-spectrum antibiotics.

Focused on the removal of the complicated residual antibiotic in aqueous environment, in this work, a novel carbon dots (C-dots) sensitized 2D-2D heterojunction of BiVO4/Bi3TaO7 were assembled through a simple hydrothermal process. The characteristic by TEM, SEM, and XPS confirmed C-dots evenly anchored on the surface of BiVO4/Bi3TaO7 heterojunction. The as-prepared C-dots/BiVO4/Bi3TaO7 showed superior performance for the degradation of the various antibiotics under visible light illumination. When the concentration of C-dots in the composite is 3 wt.%, the photodegraded rates are obtained to be 91.7%, 89.3%, 87.1%, for tetracycline (TC), amoxicillin (AMX) and ciprofloxacin (CIP), respectively, without significant deactivation during consecutive ten recycle experiments. Furthermore, by assessing the antibiotics mixture solution of TC, AMX and CIP, it is proposed that the prepared samples are potentially effective for the wastewater effluents. A probable mechanism was reasonably proposed. The improved photocatalytic activities could be attributed to the unique construction of the C-dots mediated heterojunction, which could expedite electron migration, improve light harvesting capacity and enhance charge separation efficiency. The present investigation may provide a new perspective to design C-dots mediated heterojunction which could be a potential visible-light-driven photocatalysts for the better practical applications in remediation of broad-spectrum antibiotic residues.

Mediator-free direct dual-Z-scheme Bi2S3/BiVO4/MgIn2S4 composite photocatalysts with enhanced visible-light-driven performance towards carbamazepine degradation

The development of visible-light-driven photocatalysts with high photocatalytic performance is a desired research direction of scholars for energy crisis mitigation and environment restoration. In this study, a series of highly active mediator-free direct dual-Z-scheme Bi2S3/BiVO4/MgIn2S4 hybrid photocatalysts were controllably synthesized by a in-situ growth method for the first time. XRD manifested the coexistence of MgIn2S4, BiVO4 and Bi2S3 in the as-prepared nanocomposites. The intimate 2D-2D hetero-junction interfaces between BiVO4 and MgIn2S4 as well as BiVO4 and Bi2S3 in the hybrid photocatalysts were verified by TEM and HRTEM. The photocatalytic performance of as-fabricated catalysts was estimated by the degradation of carbamazepine (CBZ) under visible light illumination. The results demonstrated that the as-constructed Bi2S3/BiVO4/MgIn2S4 composites displayed significantly improved photocatalytic activity for CBZ degradation by factors of 44.9 and 423.1 compared to MgIn2S4 and BiVO4, respectively. The enhanced photocatalytic performance of Bi2S3/BiVO4/MgIn2S4 composites was actually ascribed to the direct dual-Z-scheme migration mechanism, which was proved by XPS analysis, trapping experiments and ESR results. The formation of direct dual-Z-scheme efficiently enhanced the separation of charge carriers. Furthermore, according to DRS, the expanded light absorption in visible wavelength region also contributed to the boosted photocatalytic activity of Bi2S3/BiVO4/MgIn2S4 composites. The photocatalytic degradation products of CBZ were detected and a tentative degradation pathway was proposed.

An in-situ growth approach to 2D MoS2-2D PbS heterojunction composites with improved photocatalytic activity

The advantage of 2D-2D heterojunction over 2D-0D and 2D-1D heterojunction is that it has larger interface area, which results in the shorter migration distance of photo-induced charge carriers, and can therefore separate the electron-hole pairs more effectively. In this work, to form 2D-2D heterojunction, PbS nanosheets were grown in situ on 2D MoS2 layers via. solvothermal process. The formation of 2D MoS2-2D PbS composites has been confirmed by XRD, Raman, TEM, and EDS analysis. The area of PbS nanosheets attached on MoS2 can be controlled by changing the concentration of PbS precursor in reaction solution. Compared with pristine MoS2, MoS2-PbS composites showed improved light absorption property and enhanced photocatalytic ability using methylene blue as the target of degradation. The optimized composite displayed a photocurrent 5 times higher than that of pristine MoS2.

Room temperature humidity sensors based on rGO/MoS2 hybrid composites synthesized by hydrothermal method

Abstract Recently, two-dimensional (2D) materials have attracted attention for gas sensor fields due to their unique properties such as high surface to volume ratio and numerous active sites. In particular, reduced graphene oxide (rGO) and MoS2 are one of the most promising materials for humidity sensor due to the oxygen containing functional groups on the surface of rGO and dangling bonds at the edge site of MoS2. Herein, we present 2D rGO/2D MoS2 hybrid composites (MS-GOs) synthesized by hydrothermal method. rGO and MoS2 are mixed with different molar ratios and drop-casted on SiO2 substrate with Pt interdigitated electrode. At an optimized molar ratio of rGO/MoS2, the sensor device exhibits high sensitivity, good selectivity, rapid response and recovery, and good linearity for humidity sensing. The enhanced sensing properties are attributed to the p-n junction between rGO and MoS2. Our work provides an efficient way for realizing high-performance and fast responding humidity sensors utilizing 2D-2D heterojunction materials based chemoresistive humidity sensors for use in diverse applications.

Dual visible-light active components containing self-doped Bi2O2CO3/g-C3N4 2D-2D heterojunction with enhanced visible-light-driven photocatalytic activity

The (CO3)2− self-doped Bi2O2CO3/g-C3N4 (C-BOC/g-C3N4) unique 2D-2D heterostructure has been developed via a mixed-calcination method. This heterostructure is confirmed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), SEM-mapping, and diffuse reflection spectroscopy (DRS). Due to the charge interaction, it is interesting to observe that C-BOC nanosheets are assembled on g-C3N4 in a surface–surface coupling way, which enables an intimate interfacial interaction between the two components. The photocatalytic activity is evaluated by photodegradation of Rhodamine B (RhB) under visible light (λ>420nm). It is found that all the C-BOC/g-C3N4 composites showed highly enhanced photocatalytic activity. Electrochemical impedance spectra (EIS) measurement revealed that the largely promoted charge transfer derived from the well matchable band structure and intimate interfacial interactions between the two visible-light active components is responsible for the photoactivity enhancement. Besides, the active species trapping and O2− quantitation experiments are conducted to disclose the photocatalytic mechanism.

Perovskite oxide ultrathin nanosheets/g-C3N4 2D-2D heterojunction photocatalysts with significantly enhanced photocatalytic activity towards the photodegradation of tetracycline

Novel visible-light-driven 2D-2D heterojunction photocatalysts was constructed based on 2D g-C3N4 and exfoliated ultrathin K+Ca2Nb3O10− nanosheets, which is derived from Dion-Jacobson phase layer perovskites. The photocatalytic performance of the 2D-2D g-C3N4/K+Ca2Nb3O10− nanosheet heterojunctions was evaluated by the degradation of tetracycline hydrochloride under visible light irradiation. Compared with bare K+Ca2Nb3O10− and g-C3N4, the g-C3N4/K+Ca2Nb3O10− nanosheet heterojunctions exhibited considerably enhanced photocatalytic activity towards the degradation of tetracycline hydrochloride, which is about 6.6 and 1.8 times higher than that of pure K+Ca2Nb3O10− and g-C3N4, respectively. This enhanced activity can be mainly attributed to the synergistic effect of g-C3N4/K+Ca2Nb3O10− nanosheet heterojunctions with strong interfacial interaction and abundant 2D coupling interfaces, which could efficiently promote the photo-induced charge separation. The results of work demonstrated that construction of 2D-2D heterojunctions is an effective strategy to obtain the enhanced photocatalytic activity towards the degradation of tetracycline hydrochloride.

Two-Dimensional Interface Engineering of a Titania–Graphene Nanosheet Composite for Improved Photocatalytic Activity

A graphene-based two-dimensional (2D) nanoplatform provides new opportunities for fabricating 2D heterojunction interfaces to fortify charge transfer in semiconductor assemblies. In this report, TiO2 nanosheet/graphene composite based 2D-2D heterojunctions were fabricated by a solvothermal process. Microscopic and spectroscopic characterization revealed a homogeneous sheetlike morphology with intimate interfacial contact between the TiO2 nanosheet and graphene due to chemical interactions. Compared with 0D-2D Degussa P25 (TiO2)/graphene and 1D-2D TiO2 nanotube/graphene composites, the 2D-2D TiO2 nanosheet/graphene hybrid demonstrated higher photocatalytic activity toward the degradation of rhodamine B and 2,4-dichlorophenol under UV irradiation. Radical trapping and ESR experiments revealed the enhanced generation of ·OH and O2(•-) in the 2D-2D heterojunction system. By analyzing TiO2 excited state deactivation lifetime, the interfacial electron transfer rates determined for 0D-2D, 1D-2D, and 2D-2D TiO2/graphene composites were 1.15 × 10(8) s(-1), 3.47 × 10(8) s(-1), and 1.06 × 10(9) s(-1), respectively. It was therefore proposed that the fast charge separation in the TiO2 nanosheet/graphene photocatalyst promoted the generation of reactive oxygen species and enhanced the photodegradation reactions. The results underscore the key role of nanomaterial dimensionality in interfacial charge transfer processes.