Heterojunction Type Research Articles

Self-healing wearable self-powered deep ultraviolet photodetectors based on Ga2O3

Gallium oxide (Ga2O3) based flexible heterojunction type deep ultraviolet (UV) photodetectors show excellent solar-blind photoelectric performance, even when not powered, which makes them ideal for use in intelligent wearable devices. However, traditional flexible photodetectors are prone to damage during use due to poor toughness, which reduces the service life of these devices. Self-healing hydrogels have been demonstrated to have the ability to repair damage and their combination with Ga2O3 could potentially improve the lifetime of the flexible photodetectors while maintaining their performance. Herein, a novel self-healing and self-powered flexible photodetector has been constructed onto the hydrogel substrate, which exhibits an excellent responsivity of 0.24 mA/W under 254 nm UV light at zero bias due to the built-in electric field originating from the PEDOT: PSS/Ga2O3 heterojunction. The self-healing of the Ga2O3 based photodetector was enabled by the reversible property of the synthesis of agarose and polyvinyl alcohol double network, which allows the photodetector to recover its original configuration and function after damage. After self-healing, the photocurrent of the photodetector decreases from 1.23 to 1.21 μA, while the dark current rises from 0.95 to 0.97 μA, with a barely unchanged of photoresponse speed. Such a remarkable recovery capability and the photodetector’s superior photoelectric performance not only significantly enhance a device lifespan but also present new possibilities to develop wearable and intelligent electronics in the future.

Constructing Type-II and S-Scheme Heterojunctions of Cu2O@Cu4(SO4)(OH)6·H2O Polyhedra by In Situ Etching Cu2O with Different Exposed Facets for Enhanced Photocatalytic Sterilization and Degradation Performance.

The construction of type-II or S-scheme heterojunctions can effectively accelerate the directional migration of charge carriers and inhibit the recombination of electron-hole pairs to improve the catalytic performance of the composite catalyst; therefore, the construction and formation mechanism of a heterojunction are worth further investigation. Herein, Cu2O@Cu4(SO4)(OH)6·H2O core-shell polyhedral heterojunctions were fabricated via in situ etching Cu2O with octahedral, cuboctahedral, and cubic shapes by sodium thiosulfate (Na2S2O3). Cu2O@Cu4(SO4)(OH)6·H2O polyhedral heterojunctions demonstrated obviously enhanced sterilization and degradation performance than the corresponding single Cu2O polyhedra and Cu4(SO4)(OH)6·H2O. When Cu2O with a different morphology contacts with Cu4(SO4)(OH)6·H2O, a built-in electric field is established at the interface due to the difference in Fermi level (Ef); meanwhile, the direction of band bending and the band alignment are determined. These lead to the different migration pathways of electrons and holes, and thereby, a type-II or S-scheme heterojunction is constructed. The results showed that octahedral o-Cu2O@Cu4(SO4)(OH)6·H2O is an S-scheme heterojunction; however, cuboctahedral co-Cu2O@Cu4(SO4)(OH)6·H2O and cubic c-Cu2O@Cu4(SO4)(OH)6·H2O are type-II heterojunctions. By means of X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), diffuse reflectance spectra (DRS), and Mott-Schottky analyses, the band alignments, Fermi levels, and band offsets (ΔECB, ΔEVB) of Cu2O@Cu4(SO4)(OH)6·H2O polyhedral heterojunctions were estimated; the results indicated that the catalytic ability of the composite catalyst is determined by the type of heterojunction and the sizes of band offsets. Cubic c-Cu2O@Cu4(SO4)(OH)6·H2O has the strongest driving force (namely, biggest band offsets) to accelerate charge migration and effectively separate charge carriers, so it exhibits the strongest catalytic bactericidal and degrading abilities.

Emerging Enhancement and Regulation Strategies for Ferromagnetic 2D Transition Metal Dichalcogenides.

Two-dimensionaltransition metal dichalcogenides (2D TMDs) present promising applications in various fields such as electronics, optoelectronics, memory devices, batteries, superconductors, and hydrogen evolution reactions due to their regulable energy band structures and unique properties. For emerging spintronics applications, materials with excellent room-temperature ferromagnetism are required. Although most transition metal compounds do not possess room-temperature ferromagnetism on their own, they are widely modified by researchers using the emerging strategies to engineer or modulate their intrinsic properties. This paper reviews recent enhancement approaches to induce magnetism in 2D TMDs, mainly using doping, vacancy defects, composite of heterostructures, phase modulation, and adsorption, and also by electron irradiation induction, O plasma treatment, etc. On this basis, the produced effects of these methods for the introduction of magnetism into 2D TMDs are compressively summarized and constructively discussed. For perspective, research on magnetic doping techniques for 2D TMDs materials should be directed toward more reliable and efficient directions, such as exploring advanced design strategies to combine dilute magnetic semiconductors, antiferromagnetic semiconductors, and superconductors to develop new types of heterojunctions; and advancing experimentation strategies to fabricate the designed materials and enable their functionalities with simultaneously pursuing the upscalable growth methods for high-quality monolayers to multilayers.

Light Control-Induced Oxygen Vacancy Generation and In Situ Surface Heterojunction Reconstruction for Boosting CO2 Reduction.

The weak adsorption of CO2 and the fast recombination of photogenerated charges harshly restrain the photocatalytic CO2 reduction efficiency. The simultaneous catalyst design with strong CO2 capture ability and fast charge separation efficiency is challenging. Herein, taking advantage of the metastable characteristic of oxygen vacancy, amorphous defect Bi2O2CO3 (named BOvC) was built on the surface of defect-rich BiOBr (named BOvB) through an in situ surface reconstruction progress, in which the CO32- in solution reacted with the generated Bi(3-x)+ around the oxygen vacancies. The in situ formed BOvC is tightly in contact with the BOvB and can prevent the further destruction of the oxygen vacancy sites essential for CO2 adsorption and visible light utilization. Additionally, the superficial BOvC associated with the internal BOvB forms a typical heterojunction promoting the interface carriers' separation. Finally, the in situ formation of BOvC boosted the BOvB and showed better activity in the photocatalytic reduction of CO2 into CO (three times compared to that of pristine BiOBr). This work provides a comprehensive solution for governing defects chemistry and heterojunction design, as well as gives an in-depth understanding of the function of vacancies in CO2 reduction.

Rationally designed 2D/2D highly reduced graphene oxide modified wide band gap semiconductor photocatalysts for hydrogen production

The wide band gap semiconductor is considered a potential water splitting photocatalyst. However, the wide band gap means that visible light absorption is weak and more energy is required to transfer electrons to the conduction band, which will greatly limit the photocatalytic performance. We design the SiC/RGO heterojunction and GaN/RGO heterojunction, using first-principles hybrid density functional theory to explore whether this shortcoming can be improved. The results prove that both types of heterojunction have effectively reduced the band gap, and the light absorption capacity has been significantly enhanced. However, only the GaN/RGO heterojunction meets the conditions for photocatalytic water splitting, that is, the energy levels of water oxidation and reduction are all within its band range, thus ensuring the occurrence of water splitting. What's more, there is a potential well between the layers, which helps effectively prevent the recombination of photogenerated charge carriers, thereby further enhancing the photocatalytic properties of the GaN/RGO heterojunction. Besides, the oxidation reaction and reduction reaction occur at a relatively synchronous rate in the process of water splitting. This ensures that the overall reaction proceeds at a faster rate, and also improves the efficiency of photocatalysis. What has been found above provides a reliable choice for experimenters to explore new photocatalysts.

Optimization of Bulk Heterojunction Photovoltaic Structures with Heterocyclic Derivatives

Photovoltaic structures of the bulk heterojunction type were fabricated, in which derivatives of N,N-diethylamine-3-Methyl-1-Phenyl-1H-pyrazolo[3,4-b]quinoxalines were used as the active layer. The compounds differed in the position of the electron-donating substituent in the carbocyclic ring. Four isomers were subjected to UV-Vis spectrophotometric measurements in solvents of different polarities. The absorption characteristics were experimentally determined for the tested derivatives. The values of HOMO-LUMO levels were determined by means of quantum chemical calculations using the HyperChem software. The current–voltage and dispersion characteristics of the produced OPV were determined. The spectral characteristics of the refractive indices and extinction coefficients of the active layers were determined using the spectroscopic ellipsometry method. These results were used in the analysis and optimization of photovoltaic structures. It was shown that the location of the N,N-diethylamine substituent affects the photophysical properties of the structure and the photovoltaic properties. The optimization of the OPV_2 photovoltaic structure using the coherent model and the 2 × 2 matrix method can be successfully used in modeling optical multilayer structures, including photovoltaic structures.

Advanced Functional Carbon Nitride by Implanting Semi-Isolated VO2 Active Sites for Photocatalytic H2 Production and Organic Pollutant Degradation.

It is critical to facilitate surface interaction for liquid-solid two-phase photocatalytic reactions. This study demonstrates more advanced, efficient, and rich molecular-level active sites to extend the performance of carbon nitride (CN). To achieve this, semi-isolated vanadium dioxide is obtained by controlling the growth of non-crystalline VO2 anchored into sixfold cavities of the CN lattice. As a proof-of-concept, the experimental and computational results solidly corroborate that this atomic-level design has potentially taken full advantage of two worlds. The photocatalyst comprises the highest dispersion of catalytic sites with the lowest aggregation, like single-atom catalysts. It also demonstrates accelerated charge transfer with the boosted electron-hole pairs, mimicking heterojunction photocatalysts. Density functional theory calculations show that single-site VO2 anchored into the sixfold cavities significantly elevates the Fermi level, compared with the typical heterojunction. The unique features of semi-isolated sites result in a high visible-light photocatalytic H2 production of 645µmol h-1 g-1 with only 1wt% Pt. They also represent an excellent photocatalytic degradation for rhodamine B as well as tetracycline, surpassing the activities obtained from many conventional heterojunctions. This study presents exciting opportunities for the design of new heterogeneous metal oxide for a variety of reactions.

Covalent Organic Framework-Semiconductor-Based Heterostructures for Photocatalytic Applications.

Photocatalysis is a promising and sustainable technology in the fields of energy conversion/storage and environment purification; however, the utilization of individual component as photocatalyst is generally restricted due to the low catalytic activity deriving from the rapid recombination of photogenerated electrons/holes. Covalent organic framework (COF)-semiconductor-based composite photocatalysts with synergistic effects provide a feasible route to achieve high-performance photocatalytic reactions with more active sites, strong light utilization ability, and high stability. In recent years, significant progress has been made in the rational design and preparation of the COF-semiconductors-based heterostructures for photocatalytic water splitting, carbon dioxide (CO2 ) reduction, and dye/pollutant degradation. In this Review, the synthetic strategies of COF-semiconductor-based heterostructures are first introduced, which includes the rational design of the morphology, connection modes, and type of heterojunctions. The performance of COF-semiconductor-based heterostructures in different photocatalytic reactions are comprehensively reviewed. The structure-activity relationship and the synergistic effects within the heterostructures are discussed, and the photocatalytic mechanism and the role of COFs during the photocatalytic process are also presented. Finally, an outlook and challenges of realizing COF-semiconductor-based heterostructures with simple synthesis methods, diverse functions, high performance, and well-defined reaction mechanisms are provided.

Construction of 1D/2D core-shell structured K6Nb10.8O30@Zn2In2S5 as S-scheme photocatalysts for cocatalyst-free hydrogen production

Constructing heterostructures is an effective strategy to achieve efficient photocatalysis. The determination of the heterojunction types depends on the photo-induced charge carrier transfer path. Therefore, understanding the charge carrier transfer mechanism of heterojunctions plays an irreplaceable role in guiding the construction of rational heterojunctions. However, it is challenging due to the microscopic nature of charge carrier transfer. Herein, an S-scheme K6Nb10.8O30@Zn2In2S5 (KNbO@ZIS) heterojunction with 1D/2D core-shell structure is designed for improving photocatalytic hydrogen production. KNbO@ZIS exhibits a greatly improved cocatalyst-free hydrogen generation activity (12.35 mmol h−1 g−1) compared to K6Nb10.8O30 (KNbO) and Zn2In2S5 (ZIS) under UV–visible illumination. The improvement of photocatalytic performance is mainly attributed to the suppressed recombination of photogenerated charge carriers by the S-scheme heterojunction. The 1D/2D core-shell structure further accelerates the charge carrier transfer in the photocatalysts. S-scheme heterojunction mechanism is also demonstrated by ex/in situ irradiated X-ray photoelectron spectroscopy and Kelvin probe force microscopy measurements as well as work function calculations. This work provides a powerful strategy for designing novel heterojunction composites.

Recent advances in designing ZnIn2S4-based heterostructured photocatalysts for hydrogen evolution

• This review mainly introduced various ZnIn 2 S 4 -based heterojunctions and their PHE application. • In-depth discussion on the mechanisms of various ZnIn 2 S 4 -based heterojunction systems for boosting PHE efficiency is provided. • We expressly introduced overall water splitting, dual-functional and photothermal effect-assisted PHE systems. • Some identification methods are presented for confirming heterojunction types. • The current states, challenges and perspectives of ZnIn 2 S 4 -based heterostructured photocatalysts for PHE are discussed. Water and solar energy are inexhaustible on Earth, and thus hydrogen evolution through photocatalytic water splitting taking sunlight as the input energy is an ideal green energy generation technology. As a typical visible-light-responsive photocatalyst, ZnIn 2 S 4 attracted worldwide research attention because of its many advantages for photocatalytic hydrogen evolution (PHE), such as layered structure, simple syntheses, structural stability, environmental friendliness, and suitable electronic band structure. In recent years, constructing ZnIn 2 S 4 -based heterostructured photocatalysts has become a research focus for their significantly improved spatial charge carrier separation efficiency and PHE performances. According to the charge carrier transfer/separation mechanisms, heterostructured ZnIn 2 S 4 -based photocatalysts are divided into five categories, conventional heterojunctions (type-I and type-II), p-n heterojunction, Z-scheme heterojunction, S-scheme (or Step-scheme) heterojunction, and co-catalyst deposition based heterojunction systems. This article reviews the recent advances in ZnIn 2 S 4 -based heterostructured photocatalysts for PHE. Firstly, the central part of this review introduced various ZnIn 2 S 4 -based heterojunctions and their PHE application. Secondly, apart from common half-reaction of water-splitting, we expressly introduced overall water splitting, dual-functional and photothermal effect-assisted PHE systems. Then, we briefly presented some identification methods for confirming heterojunction types. Finally, the current states, challenges and perspectives of ZnIn 2 S 4 -based heterostructured photocatalysts for PHE are also discussed. This review aims to explore the advantages of diverse ZnIn 2 S 4 -based heterostructures, and can provide an insight into designing high-efficiency heterostructured photocatalysts for PHE application.

High-Performance Carbon Nanodots/Graphene Heterojunction Solar-Blind Ultraviolet Photodetector via Vertical Structure

The vertical-structure heterojunction has been highlighted as a promising candidate for the solar-blind ultraviolet (UV) photodetector (PD) due to the control of its channel length and the strong electric field-induced high carrier mobility. Meanwhile, carbon nanodot (CND) has drawn great attention to be playing an essential role in absorbing solar-blind UV waves as the active layer of the PD. However, CND prepared for solar-blind UV PDs, independent of sophisticated manufacturing method and extreme process conditions, has yet to be well developed. Herein, for the very first time, a vertical structure CNDs/graphene heterojunction type solar-blind UV PD is introduced, where the CND and the graphene are used as the photosensitive layer and the transparent electrode, respectively. Particularly, the CND is fabricated with a low-cost and one-step electrochemical strategy. The device realizes an optimized performance tradeoff, presenting responsivity of 76.01 mA/W, normalized detectivity of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4.17\times 10^{{10}}$ </tex-math></inline-formula> Jones, and rise/decay time of 0.54/0.27 s under the illumination of 1.47 mW/cm2 at 254-nm wavelength, along with the bias voltage of −5 V and the substrate voltage of 10 V applied. The results show that this work has unlocked the critical bottleneck of developing a graphene-based solar-blind UV PD with higher responsivity, greater detectivity, and shorter response time, unveiling the potential for missile warning, flame detection, and other areas of interest.

Band alignment type I, II transformations in Hf2CO2/MoS2 heterostructures using biaxial strain, external electric field, and interlayer coupling: a first principal investigation.

The transition to neuromorphic devices is relevant to the development of materials capable of providing electronic switching in response to external stimuli. In the present work, the Hf2CO2/MoS2 heterostructure under biaxial strain, interlayer coupling, and an electric field was investigated by first-principles calculations based on density functional theory. We have shown that the influence of lateral deformation as well as the perpendicular external electric field is more significant compared to the influence of external vertical pressure on changes in the heterojunction type of heterostructure. The lateral stretching leads to a type-I and lateral compression results in a type-II heterojunction, and an external electric field also has an effect on heterojunction type. The combination of these impacts can tune the Hf2CO2/MoS2 heterostructure. The current work suggests a compelling way to make type-I and type-II heterostructure types consisting of Hf2CO2 and MoS2 monolayers for new nanodevices in fields like photonics, electronics, optoelectronic and neuromorphic applications.

The NH2-UiO-66/3,4,9,10-perylenetetracarboxylicdiimide for Cr(VI) reduction: DFT calculation, performance, and mechanism

The composite molecular structure model of NH2-UiO-66/PDINH (UiOxPDy) constructed from NH2-UiO-66 and PDINH (3,4,9,10-perylenetetracarboxylicdiimide) was built to conduct density functional theory (DFT) calculations for predicting the heterojunction type and corresponding Cr(VI) reduction reaction mechanism. The results of DFT calculations illustrated that Z-scheme heterojunction interface was inclined to form between NH2-UiO-66 and PDINH via automatically matching the dominant crystal plane, which was in consistent with the results of X-ray photoelectron spectroscopy. Subsequently, the Z-scheme heterojunction UiOxPDy composites (x, y represented the mass of NH2-UiO-66 and PDINH, respectively) were fabricated via ball-milling treatment, which were used to accomplish effective photocatalytic Cr(VI) reduction under low power LED visible light. The as-prepared optimal UiO125PD75 composite demonstrated good stability and reuse performance in the five runs’ successive operations. The corresponding Cr(VI) reduction mechanism over UiO125PD75 was verified with the aid of electrochemical test, radical scavenging experiments and electron spin resonance.

Rationally engineered avtive sites for efficient and durable hydrogen production over γ-graphyne assembly CuMoO4 S-scheme heterojunction

The introduction of novel materials is crucial to broaden the development of the field of artificial photosynthesis. The high recombination rate of photogenerated carriers remains one of the fundamental reasons that hinder the development of photocatalysis. In view of this, we coupled γ-GY containing alkyne bonds with CuMoO4 to form interfacial S-scheme heterojunctions. The formation of S-scheme heterojunctions accelerates the electron transfer and improves the separation efficiency of photogenerated carriers, while enhancing the photoreduction ability of the composite catalysts and allowing more electrons to participate in the reduction reaction of H+ under light conditions. The heterojunction type between γ-GY and CuMoO4 was determined as S-scheme heterojunction as well as the electron migration path between the catalysts base on in situ radiation XPS spectroscopy and Density Functional Theory (DFT) as the theoretical guidance. This work provides a basis for the structural optimization of γ-GY based on in situ and theoretical calculations, and expands the application of mechanical preparation of γ-GY in photocatalysis.

Self-powered and improved photoresponsive broadband photodetecting sensors using Au/NiFe2O4/p-Si heterojunction architecture

Recently, heterojunctions-based photodetectors (PDs) with outstanding photosensitivity and fast switching time received substantial attention due to their broadband (BB) photoresponse in various regimes of the electromagnetic spectrum. Still, there is an increasing demand to accomplish BB PDs operating at photovoltaic (self-driven) mode for serving the today's societal energy efficient needs. In this work, Au and NiFe2O4 thin films were deposited onto p-Si substrates to accomplish interdigitated Au/NiFe2O4/p-Si heterojunction type BB PDs operated in self-powered mode. The structural, optical, morphological and magnetic parameters of the prepared NiFe2O4 thin films as a function of annealing process were studied using XRD, UV–Vis, AFM and XAS/XMCD techniques. Tauc's plot fitted from the UV–Vis absorption data for the as-deposited, 700 °C and 800 °C NiFe2O4 thin films were 4.85, 3.42 and 2.85 eV, respectively. The photodetection parameters of the fabricated interdigitated Au/NiFe2O4/p-Si BB PDs were analyzed with I–V, photoresponsivity and response (rise/fall) times as a function of annealing process. All the fabricated Au/NiFe2O4/p-Si BB PD devices with/without annealing process operated in photovoltaic mode (at 0 V). The PD device annealed at 800 °C unveiled better photoresponsivity (12.35 A/W @1060 nm), detectivity (5.9 × 1014 Jones @1060 nm) and rise/fall times (89 ms/185 ms @900 nm) compared to the as-prepared/700 °C annealed PD devices. The reason for this was attributable to the accomplished improvement in crystallinity (XRD), surface morphology (AFM), reduction of bandgap (UV–Vis) and variation of spin/orbital magnetic moments (XAS/XMCD). In this work, we suggest one of the alternative and cost-effective electron beam evaporation method to grow the desired epitaxial NiFe2O4 thin films compared to the other physical vapor deposition approaches such as PLD and ALD to fit the future necessities of optoelectronic field.

Plasma Ag-loaded bandgap variational Zn1-xMgxO-enhanced charge separation for photoelectrochemical water oxidation of CuWO4 photoanodes

The recombination of photogenerated carriers and sluggish surface oxidation kinetics severely inhibited the development of copper tungstate (CuWO4) photoanode photoelectrochemical (PEC) water oxidation. Herein, the Zn1-xMgxO-modified CuWO4 photoanode ameliorated the vital matter of easy recombination of electron-hole pairs, where the transformation of the heterojunction type (type I to type II) between Zn1-xMgxO and CuWO4 played a crucial role in the extraction of carriers. Further, the effective charge separation was obtained utilizing the local surface plasmon resonance (LSPR) of plasma metal (Ag), which facilitated the PEC water oxidation reaction. Besides, the surface states trapped/stored holes and reduced charge transfer resistance, thus facilitating charge transfer. The overlap of the fillable surface states with filled redox coupled states ensured the enhancement of the water oxidation kinetics, which further promoted the charge transfer. As a result, the optimized CuWO4/Zn0.7Mg0.3O/Ag photoanode showed significant advancement in photocurrent density (1.71 mA/cm2 at 1.23 V vs. RHE), electrochemical impedance and stability. This work emphasized the interfacial structure modulation of two strategies that potentially provide more ideas and options for the design of other efficient photoanodes.

Efficient Visible-Light Driven Photocatalytic Hydrogen Production by Z-Scheme ZnWO4/Mn0.5Cd0.5S Nanocomposite without Precious Metal Cocatalyst

How to restrain the recombination of photogenerated electrons and holes is still very important for photocatalytic hydrogen production. Herein, Z-scheme ZnWO4/Mn0.5Cd0.5S (ZWMCS) nanocomposites are prepared and are applied as visible-light driven precious metal cocatalyst free photocatalyst for hydrogen generation. The ZnWO4/Mn0.5Cd0.5S nanocomposites with 30 wt% ZnWO4 (ZWMCS-2) can reach a photocatalytic hydrogen evolution rate of 3.36 mmol g−1 h−1, which is much higher than that of single ZnWO4 (trace) and Mn0.5Cd0.5S (1.96 mmol g−1 h−1). Cycling test reveals that the ZMWCS-2 nanocomposite can maintain stable photocatalytic hydrogen evolution for seven cycles (21 h). The type of heterojunction in the ZWMCS-2 nanocomposite can be identified as Z-scheme heterojunction. The Z-scheme heterojunction can effectively separate the electrons and holes, so that the hydrogen generation activity and stability of the ZWMCS-2 nanocomposite can be enhanced. This work provides a highly efficient and stable Z-scheme heterojunction photocatalyst for hydrogen generation.

Plasma- assisted liquid-based growth of g-C3N4/Mn2O3 p-n heterojunction with tunable valence band for photoelectrochemical application

The practical application of graphitic carbon nitride (g-C3N4, CN) is restricted by its low photocatalytic activity and difficult recycling. Herein, we report a CN/Mn2O3 p-n heterojunction grown by a plasma-assisted liquid-based method using a special precursor complex of melamine-cyanuric acid supramolecular on fluorine-doped tin oxide (FTO) substrate. The as-grown CN/Mn2O3/FTO p-n heterojunction exhibits a significantly enhanced photoelectrochemical performance with a photocurrent density of 25 μA/cm2 compared with its powder form (0.9 μA/cm2) formed by common drop coating method，and a tunable valence band (VB) with excellent mechanical strength which is benefit for photocatalytic oxidation reaction and recovery. The formation of CN/Mn2O3/FTO p-n heterojunction can promote the transfer of photoelectrons due to an internal electric field at the interface of p-n junction, leading to the accumulation of electrons and holes in the VB of CN and conduction band (CB) of Mn2O3. The results have shed a light on promoting the practical application of CN, and the developed plasma-assisted liquid-based growth method can be extended to the preparation of other type of functional heterojunctions.

Type II Heterojunction Formed between {010} or {012} Facets Dominated Bismuth Vanadium Oxide and Carbon Nitride to Enhance the Photocatalytic Degradation of Tetracycline.

Both type II and Z schemes can explain the charge transfer behavior of the heterojunction structure well, but the type of heterojunction structure formed between bismuth vanadium oxide and carbon nitride still has not been clarified. Herein, we rationally prepared bismuth vanadium oxide with {010} and {012} facets predominantly and carbon nitride as a decoration to construct a core-shell structure with bismuth vanadium oxide wrapped in carbon nitride to ensure the same photocatalytic reaction interface. Through energy band establishment and radical species investigation, both {010} and {012} facets dominated bismuth vanadium oxide/carbon nitride composites exhibit the type II heterojunction structures rather than the Z-scheme heterojunctions. Furthermore, to investigate the effect of type II heterojunction, the photocatalytic tetracycline degradations were performed, finding that {010} facets dominated bismuth vanadium oxide/carbon nitride composite demonstrated the higher degradation efficiency than that of {012} facets, due to the higher conduction band energy. Additionally, through the free radical trapping experiments and intermediate detection of degradation products, the superoxide radical was proven to be the main active radical to decompose the tetracycline molecules. Therein, the tetracycline molecules were degraded to water and carbon dioxide by dihydroxylation-demethylation-ring opening reactions. This work investigates the effect of crystal planes on heterojunction types through two different exposed crystal planes of bismuth vanadate oxide, which can provide some basic research and theoretical support for the progressive and controlled synthesis of photocatalysts with heterojunction structures.

Two-dimensional heterostructures for photocatalytic CO2 reduction

The photocatalysis conversion of CO2 into fuels has become an encouraging method to address climate and energy issues as a long-term solution. Single material suffers poor yield due to low light energy utilization and high recombination rate of photoinduced electron-hole pairs. It is an efficient approach to construct heterojunction through two or three materials to improve the photocatalytic performance. Recently, 2D-based heterojunction is getting popular for outstanding properties, such as special light collecting structure to enhance light harvest, intimate interface to facilitate charge transfer and separation, and large specific surface area to provide abundant reactive sites. Recently, some new 2D-based heterostructures materials (both structure and composition) have been developed with excellent performance. 2D materials exert structural and functional advantages in these fine composite photocatalysts. In this review, the literatures about the photocatalytic conversion of CO2 are mainly summarized based on overall structure, interface type and material type of 2D-based heterojunction, with special attention given to the preparation, characterization, structural advantages and reaction mechanism of novel 2D-based heterojunction. This work is in hope of offering a basis for designing improved composite photocatalyst for CO2 photoreduction.