Heterojunction Nanostructures Research Articles

Metal‐Free Modification Overcomes the Photocatalytic Limitations of Graphitic Carbon Nitride: Efficient Production and In Situ Application of Hydrogen Peroxide

AbstractGraphitic carbon nitride (g‐C3N4) assisted photocatalytic production of hydrogen peroxide (H2O2 has already attracted the interest of many researchers due to its environmental sustainability. Nevertheless, the inherent drawbacks of g‐C3N4 limit its progress. Metal‐free modification strategies, including nanostructure design, defect introduction, doping, and heterojunction construction, have been developed to improve the efficiency of g‐C3N4 photocatalytic H2O2 production. Compared to metal modification, metal‐free strategies avoid the use of precious metals and the leaching of heavy metal ions, which have the advantages of good stability and environmental friendliness. However, a comprehensive review of H2O2 production from g‐C3N4 modified by metal‐free strategies is still lacking. This review first recaps the mechanism of photocatalytic H2O2 production by g‐C3N4, including photoexcitation, carrier separation and redox reactions. Then, the perspective advances in metal‐free modified g‐C3N4 photocatalysts are presented, with the special focus on the kernel connection between different strategies and mechanism based on the pivotal stages of H2O2 production. Subsequently, recent applications of g‐C3N4‐based photocatalysts for in situ generated H2O2, mainly including water purification and organic synthesis, are briefly discussed. Finally, the prospects of g‐C3N4‐based photocatalysts are envisioned with the hope that it will have “something to do” in the field of H2O2 production.

An efficient NiS-ReS2/CdS nanoparticles with dual cocatalysts for photocatalytic hydrogen production

The construction of heterojunctions is one of efficacious ways to improve the charge transfer and suppress the recombination of photoexcited electron-hole pairs for enhancing reactive activities of photocatalysts. Ternary NiS-ReS2/CdS composites are synthesized via a one-step hydrothermal method and the heterojunction nanostructures are achieved. The NiS-ReS2/CdS photocatalyst exhibits the superior photocatalytic activity with a hydrogen production rate up to 139 mmol g−1 h−1, which is much higher than binary composites and pure CdS. The contributions of the dual cocatalysts NiS and ReS2 are verified to narrower bandgaps, lower resistances and increase photocurrent density of NiS-ReS2/CdS, promoting the absorption of visible light and the migration of photoinduced electrons. The NiS-ReS2/CdS heterostructures provide a possible dual Z-scheme path for the rapid transfer of electrons. The tailoring of the dual cocatalysts is effective to improve the photocatalytic hydrogen production.

Fabrication of chrysanthemums like TiO2@In2S3 S-scheme heterojunction nanostructures for the degradation of methylene blue dye present in aqueous solution

Removal of contaminants from water and wastewater has drawn interest from all over the world because of its enormous impact on the environment as well as the potential threat to human and other biological existence. As a result, the primary objective for humans is to have consistent access to upgraded and clean water sources. In this study, thioacetamide, titanium dioxide, and Indium (III) nitrate n-hydrate were used in the hydrothermal process to produce TiO2@In2S3 hybrid material. The high purity of the TiO2@In2S3 hybrid materials was shown by XRD analysis, UV-DRS has been utilized to study the optical properties of TiO2@In2S3 hybrid materials and the In2S3 sample which reveals that they have a band gap between 1.71 and 1.88 eV. The stoichiometry of the hybrid materials TiO2@In2S3 was confirmed by EDX analysis. Additionally, SEM examination displayed the TiO2@In2S3 hybrid materials’ chrysanthemums morphology. The produced TiO2@In2S3 hybrid materials exhibit complete degradation of MB dye pollutants within 60 min under an LED lamp. The photocatalytic decomposition of MB dye with TiO2, β-In2S3 and TiO2@In2S3 follows a pseudo-first-order process with rate constants of 2.88 × 10−3, 4.67 × 10−3, and 7.73 × 10−2 min−1, respectively. TiO2 and β-In2S3 composites had a synergistic impact, and an appropriate S-scheme charge carrier mechanism was suggested, validating the composite as an economical and effective catalyst for environmental remediation.

ZnO/CuO/CdS Heterojunction Nanostructures as N-P-N for Optoelectronic Applications Effectiveness of Optoelectronic Devices

ZnO/CuO/CdS Heterojunction Nanostructures as N-P-N for Optoelectronic Applications Effectiveness of Optoelectronic Devices

Interfacial Electronic Interactions Between Ultrathin NiFe-MOF Nanosheets and Ir Nanoparticles Heterojunctions Leading to Efficient Overall Water Splitting.

Creating specific noble metal/metal-organic framework (MOF) heterojunction nanostructures represents an effective strategy to promote water electrolysis but remains rather challenging. Herein, a heterojunction electrocatalyst is developed by growing Ir nanoparticles on ultrathin NiFe-MOF nanosheets supported by nickel foam (NF) via a readily accessible solvothermal approach and subsequent redox strategy. Because of the electronic interactions between Ir nanoparticles and NiFe-MOF nanosheets, the optimized Ir@NiFe-MOF/NF catalyst exhibits exceptional bifunctional performance for the hydrogen evolution reaction (HER) (η10 = 15mV, η denotes the overpotential) and oxygen evolution reaction (OER) (η10 = 213mV) in 1.0m KOH solution, superior to commercial and recently reported electrocatalysts. Density functional theory calculations are used to further investigate the electronic interactions between Ir nanoparticles and NiFe-MOF nanosheets, shedding light on the mechanisms behind the enhanced HER and OER performance. This work details a promising approach for the design and development of efficient electrocatalysts for overall water splitting.

Investigations on the microwave-assisted growth of ZnO nanorods and the performance of nanostructured heterojunction UV photodetector

Vertically aligned ZnO nanorods have been grown using the microwave-assisted technique. The current approach offers a potential environment for achieving the ultra-fast (3–7 min) growth of ZnO nanorods compared to the conventional aqueous solution method, where the growth proceeds over a longer time in hours. ZnO nanorods have been grown by altering the molarity, microwave power, and growth time. Increasing the molarity and microwave power resulted in increasing dimensions of the nanorods. The growth of the ZnO nanorods began around 3 min, and it was noticed that the length of the nanorods increased as the growth period progressed. The nanorods grown using this technique have been effectively used to fabricate CuI/ZnO nanorods heterojunction.

Enhanced solar light-induced performance of a step-scheme heterojunction nanostructure (C3N4/ZrO2) for mixed dye degradation and methanol oxidation

This study focuses on the high demand for innovative nanostructured materials with boosted photocatalytic performance for the degradation of organic pollutants and oxidation of organic compounds. A nanostructure consisting of graphitic carbon nitride (C3N4) and zirconium oxide (ZrO2) denoted as C3N4/ZrO was synthesized via direct thermal pyrolysis. A comprehensive array of characterization techniques (XRD, FESEM, HRTEM and UV-DRs analysis) was utilized for a detailed analysis of the prepared photocatalysts. The photoactivity of the C3N4/ZrO nanostructure was explored by the photocatalytic degradation of a mixture of dyes (Rh B + CV), and methanol oxidation reaction and compared with those of pristine C3N4 and ZrO2. The photoactivity of C3N4/ZrO for degrading the mixed dye under simulated solar light was 97% higher than those of pristine C3N4 (88%) and ZrO2 (31%). The C3N4/ZrO nanostructure, functioning as a step-scheme heterojunction, demonstrated superior photocatalytic performance due to enhanced charge transport facilitated by robust interfacial contact between C3N4 and ZrO2. This enhanced photodegradation efficiency, reaching 97%, establishes a foundation for the development of heterojunction catalysts with exceptional photocatalytic activities. Furthermore, the methanol oxidation activity of the C3N4/ZrO nanostructure was exceptionally high, yielding a 138.25 mA/cm2 current density at a 2 M methanol. The proposed material has a high application potential for mitigating pollution and energy issues.

Effective 1D/2D nanostructured S-scheme W18O49/g-C3N4 heterojunction photocatalyst fabrication for improved photocatalytic nitrogen fixation performance

The fundamental insights into the reaction mechanism, especially the electron transfer mechanism, are highly promising yet challenging for W18O49/g-C3N4 heterojunction catalysts during photocatalytic nitrogen fixation. Herein, the 1D/2D nanostructured S-scheme heterojunctions were designed by in situ growth of 1D W18O49 nanowires on 2D g-C3N4 nanosheets through solvothermal method using methanol as solvent. In situ XPS analysis revealed that electrons in the conduction band of W18O49 recombine with holes in the valence band of g-C3N4 under the conduction effect of internal electric field, band bending, and Coulombic attraction in the W18O49/g-C3N4 heterojunction. The photogenerated electrons are retained in g-C3N4, where the negative reduction potential of its conduction band enhances the activation of N2. As a result, the ammonia generation rate employing the optimal W18O49/g-C3N4 heterojunction is 64.8 μmol gcat−1 h−1, approximately double that of W18O49 alone and 2.3 times higher than that of g-C3N4. The enhanced activity and facile methodology make the current material exceedingly appealing for implementation in photocatalytic nitrogen fixation for the synthesis of ammonia.

Mesoporous and Encapsulated In2O3/Ti3C2Tx Schottky Heterojunctions for Rapid and ppb-Level NO2 Detection at Room Temperature.

Rapid and ultrasensitive detection of toxic gases at room temperature is highly desired in health protection but presents grand challenges in the sensing materials reported so far. Here, we present a gas sensor based on novel zero dimensional (0D)/two dimensional (2D) indium oxide (In2O3)/titanium carbide (Ti3C2Tx) Schottky heterostructures with a high surface area and rich oxygen vacancies for parts per billion (ppb) level nitrogen dioxide (NO2) detection at room temperature. The In2O3/Ti3C2Tx gas sensor exhibits a fast response time (4 s), good response (193.45% to 250 ppb NO2), high selectivity, and excellent cycling stability. The rich surface oxygen vacancies play the role of active sites for the adsorption of NO2 molecules, and the Schottky junctions effectively adjust the charge-transfer behavior through the conduction tunnel in the sensing material. Furthermore, In2O3 nanoparticles almost fully cover the Ti3C2Tx nanosheets which can avoid the oxidation of Ti3C2Tx, thus contributing to the good cycling stability of the sensing materials. This work sheds light on the sensing mechanism of heterojunction nanostructures and provides an efficient pathway to construct high-performance gas sensors through the rational design of active sites.

In2O3-SnO2 Hedgehog-Like nanostructured heterojunction for acetone detection

The In2O3-SnO2 heterojunction nanostructures resembling hedgehogs were synthesized through hydrothermal method and physical stirring for acetone detection. SEM and TEM characterization showed that the composites were SnO2 nanosheets (NSs) assembled into a flower-like morphology with In2O3 particles grown in situ on the NSs. The In2O3-SnO2 sensor has excellent vapor sensitivity compared to pure SnO2. At an optimal temperature of 260 ℃, the In2O3-SnO2 sensor achieves a response value of 19.4 for acetone vapors at a concentration of 100 ppm. The composites still exhibit excellent gas-sensitized performance at low concentration (100 ppb). The improved gas-sensitized performance of In2O3-SnO2 composites is attributed to the sea urchin-like nanoflower morphology enriched with oxygen vacancies and the formation of n-n heterojunctions. To further substantiate its enhancing mechanism, the adsorption behavior of acetone molecules on the fabricated composite material was investigated through the utilization of density functional theory (DFT). This study confirms the enhanced gas sensing performance of In2O3-SnO2 heterojunction composites towards acetone and elucidates the enhancement mechanism by DFT calculations.

A novel multifunctional SERS microfluidic sensor based on ZnO/Ag nanoflower arrays for label-free ultrasensitive detection of bacteria.

This study proposes a microfluidic platform for rapid enrichment and ultrasensitive SERS detection of bacteria. The platform comprises ZnO nanoflower arrays decorated with silver nanoparticles to enhance the SERS sensitivity. The ZnO nanoflower array substrate with a 3D reticular columnar structure is prepared using the hydrothermal method. SEM analysis depicts the 3.05 μm gap distribution of the substrate array to intercept the most bacteria in the particle sizes range of 0.5 to 3 μm. Then, silver nanoparticles are deposited on the ZnO nano-array surface by liquid evaporation self-assembly. TEM and SEM analysis indicate nanosize of Ag particles, evenly distributed on the substrate, enhancing the SERS efficiency and improving sensing reproducibility. The probe molecules (R6G) are tested to demonstrate the high SERS activity of the proposed microfluidic sensor. Then, Escherichia coli, Staphylococcus aureus, Enterococcus faecalis, and Bacillus subtilis are selected, demonstrating the sensor's excellent bacterial capture and sensitive recognition capabilities, with a detection limit as low as 102 CFU mL-1. Additionally, the antibacterial properties of ZnO/Ag heterojunction nanostructures are studied, suggesting their ability to inactivate bacteria. Compared with the traditional Au-enhanced chip, the sensor preparation is easy, safe, reliable, and low-cost. Moreover, the ZnO nano-array exhibits a large specific surface area, high interception ability, stronger and uniform SERS performance, and effective and reliable detection of trace pathogens. This work provides potential future ZnO/Ag microfluidic SERS sensor applications for rapid, unlabeled, and trace pathogens detection in clinical and environmental applications, potentially achieving breakthroughs in early detection, prevention, and treatment.

Phase transformation and heterojunction nanostructures of bismuth iron oxide

The construction of an efficient bismuth iron oxide shows great potential in excellent crystal structure properties and visible light photocatalysis. However, it is challenging to synthesize nanostructures with the desired morphologies. For the first time, the bismuth iron oxide is fabricated using sol–gel synthesis method, exhibiting the desired crystallite size and tuning the types of heterojunction nanostructures by regulating the concentration of Fe3+ and calcination temperature. As a result, the feeding ratios of bismuth ferrite materials Bi2Fe4O9, BiFeO3/Bi2Fe4O9, BiFeO3, BiFeO3/Bi25FeO40, and Bi25FeO40 are 2:1, 1.5:1, 1:1, 0.75:1, 0.5:1, and 0.04:1, respectively. Besides, the calcination temperature not only influences the granularity of bismuth iron oxide but also promotes the phase transformation from BiFeO3 to Bi2Fe4O9. Moreover, BiFeO3/Bi2Fe4O9 and BiFeO3/Bi25FeO40 heterojunction nanostructures display strong interactions between BiFeO3–Bi2Fe4O9 and Bi25FeO40. Besides, BiFeO3/Bi25FeO40 heterojunction nanostructures exhibit obvious grain boundary with the smallest bandgap. This study presents far-reaching implications and provides pathways to prepare BiFeO3/Bi2Fe4O9 and BiFeO3/Bi25FeO40 heterojunction nanostructures.

MoS2/Au heterojunction nanostructures for electrochemical detection of trace Hg(II) in wastewater samples

In this study, a highly sensitive electrochemical sensor was developed for the detection of mercury ions in wastewater samples. The sensor was constructed using MoS2/Au heterojunction nanostructures, which involved depositing plasmonic Au nanoparticles onto MoS2 nanosheets on screen-printed carbon electrodes. The MoS2/Au-SPCE sensor demonstrated outstanding electrochemical sensing capabilities, attributed to the emergence of a mid-gap state across the Fermi level. This state arises from the interaction between the Au 5d (Au, +1 charge state) and Mo 3d (MoS2, +4 charge state) orbitals. This performance was superior to that of single Au nanoparticles and MoS2. The sensor showed high sensitivity in detecting Hg(II) ions with a wide linear range from 0.02 ppm to 0.0004 ppb and a LOD of 0.0004 ppb. The developed sensor was effectively applied for the detection of Hg(II) ions in factory wastewater and other samples. The MoS2/Au-SPCE sensor was successfully used to detect low concentrations of 565.0 ppb and 92.0 ppb Hg(II) in the investigated samples. This study introduces a new electrochemical sensor, leveraging the MoS2/Au heterostructures, meticulously crafted for the intricate sensing of Hg(II) ions

Enhanced photoresponsivity in Bi2Se3 decorated GaN nanowall network-based photodetectors

Recently, highly responsive photodetectors which are capable of photodetection in a wide range of wavelength spectra are in great demand. To fulfil this, photodetectors formed using heterojunctions of multiple semiconducting materials gain a lot of interest as they cover a broad range of photodetection, and the built-in electric field developed at their interface helps to enhance photoresponse. Here, we have demonstrated a fascinating broadband metal-semiconductor-metal type photodetector (PD) by integrating sputtered Bi2Se3 with the laser molecular beam epitaxy (LMBE) grown GaN film and porous nanowall network on sapphire (0001) substrates. The fabricated photodetectors using a hybrid Bi2Se3/LMBE-GaN nanowall structure exhibit broadband characteristics with a high responsivity of 51.4 and 1.46 A/W when illuminating with the laser of wavelength 355 nm (UV) and 1064 nm (NIR), respectively. The enhanced UV responsivity and good response in the NIR region using Bi2Se3/GaN heterojunction nanostructures suggest futuristic application in dual-wavelength detector devices.

TeO2 doped ZnO nanostructure for the enhanced NO2 gas sensing on MEMS sensor device

Severe health issues occur when human beings are exposed to NO2 gas, which is formed from combustion processes and reactions facilitated by sunlight. In order for safety measurements, NO2 gas sensors are highly needed at low concentration gas detections. ZnO gas sensor with the doping of TeO2 is developed using co-sputtering technique. ZnO/TeO2 heterojunction nanostructure is analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and energy dispersive spectroscopy (EDS) for structural study. Gas sensing properties were tested with Micro electro mechanical system (MEMS) devices, on which ZnO/TeO2 nanostructure is developed. This study focused on doping of 4 different variations of TeO2 with ZnO such as 0%, 2%, 4% and 8% atomic weight percentage (at.w%) of TeO2. Upon testing, 4% ZnO/TeO2 transpired to be best possible parameter for NO2 gas sensing. With maximum NO2 gas concentration of 1 ppm, 4% ZnO/TeO2 sensor exhibited 80% sensing response and with 200 ppb of minimum gas concentration, sensor had 42% response at optimal temperature of 100 oC. TeO2 doped ZnO sensor exhibits superior performance over pure ZnO sensor and has good selectivity over NO2 gas.

Silicon-Based Nanoelectronic Semiconductor Material and Its Surface-Enhanced Raman Image Signals

One-dimensional Zinc Oxide (ZnO) nanomaterials have important applications in devices, such as solar energy, sensors, and piezoelectric materials due to surface effects and quantum size effects. As a semiconductor material, Si has good thermal conductivity and low resistivity. A layer of n-type ZnO nanowires is grown on P-type monocrystalline silicon by transferring the Anodic Aluminum Oxide (AAO) template. The enhanced Raman effect on the surface is attempted by preparing n-type ZnO-P-type Si heterojunction nanostructures. This paper uses Si-based AAO as a template and uses electrochemical deposition method to prepare silicon-based nano-electronic semiconductor material ZnO/AAO/Si. According to SEM analysis, there are uniform pores on the surface of the material, and the cross-section shows that ZnO nanowires have been assembled into the AAO/Si structure. XRD analysis shows that ZnOn nanowires have a hexagonal wurtzite structure. In optoelectronic testing, through PL spectral analysis, the semiconductor material ZnO/AAO/Si has a strong yellow green emission peak near 574 nm. Field emission analysis shows that the β value of the ZnO field enhancement factor in the ZnO/AAO/Si structure is relatively high. The Surface-Enhanced Raman Spectroscopy (SERS) image signal experiment shows that the silicon-based nano-electronic semiconductor material prepared by electrochemical deposition method has good SERS characteristics. The SERS spectral intensity increases with the increase of the concentration of the detected substance and can be used as a SERS substrate to achieve Raman spectral image signal detection of chemical substances with low concentration.

Interface-confined precise processing of Ag nanowire into AgPd-nanoparticle-sealed AgAu nanotroughs for boosting ethanol electrooxidation

The functions of nanomaterials are closely linked with their fine structures and compositions. Precisely processing nanoparticles into morphology- and composition-varied nanostructures can a cutting-edge technology for producing complex nanostructures. Herein, we develop an interface-confined precise processing strategy towards toluene/water-interfacial Ag nanowires. Interfacial Ag nanowires are transformed into AgPd-nanoparticle-sealed AgAu nanotroughs with abundant AgPd/AgAu hetero-junctions (i.e., AgPdAu hetero-junction nanostructures). By adjusting the reaction conditions, composition-varied AgPdAu hetero-junction nanostructures can be obtained. The formation of AgPdAu hetero-junction nanostructures can be attributed to interface-confined precise etching towards Ag nanowires separately from the two subphases of the water and the toluene. Composition-optimized Ag13Pd67Au20 hetero-junction nanostructure shows satisfactory catalytic performance towards ethanol electrooxidation: ∼4 and 2 times in electrochemical-activity-surface-area-normalized activities; ∼6 and 5 times in mass-normalized activities higher than commercial Pd/C and Pt/C, respectively. The outstanding catalytic capability of Ag13Pd67Au20 may be attributed to optimized composition, porous nanostructures as well as abundant AgPd/AgAu hetero-junctions. This work demonstrates the feasibility of precisely processing interfacial nanoparticles, opening the way for creating morphology-well-defined composition-varied complex nanostructures.

Boosted photoelectrocatalytic removal of bisphenol A in a wide spectral range on 3D BiVO4/TiO2 nanoforest

Nanostructure construction and heterojunction engineering are effective strategies for designing highly efficient photoelectrodes. Herein, we report a BiVO4 quantum dots (BQDs)/TiO2 nanoforest photoanode with 3D configuration that exhibited improved light harvesting and charge transfer efficiency. Enhanced and directional charge separation were attributed to the synergetic effect of TiO2 facet heterojunction and BiVO4/TiO2 type-II heterojunction, which were confirmed by in-situ XPS and KPFM technology. Finally, a boosted photoelectrocatalytic (PEC) bisphenol A (BPA) removal for 97.28 % in 30 min under a wide spectral range was achieved. This work offers insight into the rational design of nanostructure and heterojunction of photoelectrode.

AgVO3/Ag6Si2O7 nanocomposites with enhancing visible-light driven photocatalysis performance

The AgVO3/Ag6Si2O7 nanocomposite was developed via the coprecipitation method. After being composited, these two nanostructures developed a heterojunction form. The DRS spectra suggested that these nanocomposites with different ratios possessed suitable bandgap, therefore could strongly absorb visible light. The EIS and Mott−Schottky plot curves show that the AgVO3 structure was n-type conductivity semiconductor, while the Ag6Si2O7 structure was p-type conductivity, and these two semiconductors could form the p-n heterojunction nanostructure. The AgVO3/Ag6Si2O7 nanocomposite possess higher photogenerated carrier transfer efficiency and stability of the photogenerated carriers. The organic dye photodegradation activity studies suggested that the AgSV-12 exhibited the best photocatalysis effectivity, and showed good photodegradation activity to other organic dyes. The ESR and reactive species quenchers study suggested that the reactive species that oxidized the organic dyes were photogenerated holes, •O2− and •OH, and the photogenerated holes played the essential factor. Finally, the photocatalysis mechanism and process were presumed as the p-n heterojunction mechanism.

Optoelectronics characteristics of chemically synthesized Cu(In1-xGax)Se2 based Schottky and heterojunctions

CIGS is an important photovoltaic material in recent years. In this work, we have performed a comparative analysis of various conduction mechanism in CIGSe2 based Schottky and hetero junction nanostructures. Cu(In1-xGax)Se2 nanostructure dispersed in PVP matrix has been synthesized through chemical bath deposition method at a compositional variation x = 0-1. The structural and optical characterization are done and correlated with the In/Ga fraction ratio. The conduction mechanism for both Schottky and hetero structures has been analyses and systematically co-related with compositional variation of In/Ga. By using the thermionic theory, the diode parameters ideality factor, saturation current, barrier height is determined in hetero junction device and co related with composition of Cu(In1-xGax)Se2. Richardson-Schottky(RS) mechanism is found to be dominant in Schottky type junction whereas both Pool-Frenkel(PF) and Richardson-Schottky(RS) mechanism is involved in hetero junction at different range of bias. Our findings points to Cu(In1-xGax)Se2 nanostructures synthesized at x = 0, 0.3,0.5 as promising candidate for solar cell because of their optimum diode parameters and band gap for absorption of maximum solar radiation.