P-type Cu2O Nanoparticles Research Articles

Band engineering for building cascading charge transport channels in ternary CdS-based nanorod array photoanode toward efficient photoelectrochemical H2 generation

A novel CdS/CdSe/Cu2O nanorod array (NRA) photoelectrode with cascading charge transport channels was designed for the first time to remarkedly boot photoelectrochemical (PEC) hydrogen generation under visible light illumination with zero bias. This ternary photoelectrode was constructed by modifying CdS nanorod arrays with n-type CdSe and p-type Cu2O nanoparticles, successively. In this novel photoanode, CdSe and Cu2O with small band gap not merely highly heighten the visible light absorption capacity of CdS, but more importantly integrate with CdS to build cascading charge transport channels at the CdS/CdSe and CdSe/Cu2O interfaces, dramatically facilitating the separation and transport efficiency for photoexcited electron and hole pairs. The CdS/CdSe/Cu2O NRA photoelectrode gains an obvious hydrogen generation rate of 193.2 μmol·h−1, 8.2 times higher than that of bare CdS NRA photoelectrode. The remarkably enhanced PEC hydrogen production for the CdS/CdSe/Cu2O NRA photoanode can be ascribed to effective solar energy utilization and charge carrier separation.

Photocatalytic bioheteronanostructures by integrating multicomponent Cu2O–Au nanoparticles into ZnO-coated butterfly wings colored by photonic nanoarchitectures

Complex biological photocatalytic heteronanostructures were produced by the integration of different multicomponent Au–Cu2O nanoparticles (NPs) into the blue-colored photonic nanoarchitectures occurring in the wings of male Polyommatus icarus butterflies. Both bare wings and wings conformally coated by 15-nm ZnO by atomic layer deposition were used as substrates. The NPs were characterized by UV–visible spectroscopy, focus stacking optical microscopy, and electron microscopy. After the deposition of the different NPs, the photocatalytic performance of the samples under visible light illumination was tested by the photodegradation of methyl orange in aqueous solution monitored continuously by an immersion probe. It was found that the components of the biological hetero-nanoarchitecture: ZnO-coated wings and wings without ZnO with deposited NPs exhibited poor catalytic performance. But the combined system: ZnO-coated wings with NPs deposited onto them exhibited sixfold to eightfold increase in their catalytic performance. This increase is attributed to the extension of the ZnO absorption into the visible range and to the formation of the heterojunction between the n-type ZnO and the p-type Cu2O NPs which resulted in the charge transfer of the photogenerated carriers. As the samples exhibited good stability under the continuous magnetic stirring, they can be used in flow-through systems suitable for wastewater remediation. The biological templates for the hetero-nanoarchitectures were produced by the controlled breeding of herbivorous insects, which does not raise any environmental concerns.

A photofuel cell-driven self-powered genosensor with a triple-quenching tag of p-Cu2O/Ti3C2Tx for signal amplification

Herein, an ultrasensitive self-powered genosensor is constructed by modifying a model hairpin capture DNA (cDNA) on a nanostructured n-type CdS modified ITO (n-CdS|ITO) photoanode of a photofuel cell. Then, the modified hairpin cDNA is transformed into a single-stranded DNA (ssDNA) by a target DNA (tDNA) and λ-exonuclease. Afterwards, a triple-quenching tag is specially designed by the in situ growth of p-type Cu2O nanoparticles on ultrathin (a few layers) Ti3C2Tx nanosheets to form a p-Cu2O/Ti3C2Tx composite. This is then introduced onto the photoanode surface via strong chelation between the exposed Ti ions on Ti3C2Tx and the ssDNA on n-CdS|ITO. The introduction of p-Cu2O/Ti3C2Tx dramatically decreases the open-circuit voltage (Eocv) of the genosensor and is based on a p-n type semiconductor quenching strategy. This strategy simplifies the complex and expensive aptamer chain design and modification process for the introduction of p-type semiconductors in other biosensing platforms based on a similar quenching mechanism. Meanwhile, both p-Cu2O and Ti3C2Tx exhibit good peroxidase-like catalytic activity, which results in precipitation and steric hindrance on n-CdS|ITO to further quench the output signals. Furthermore, the large Ti3C2Tx nanosheets partially blocked the light absorption of n-CdS. Due to this triple-quenching effect, a wide linear range (1 fM ∼ 100 pM) and a low detection limit (0.230 fM, S/N = 3) are obtained by the genosensor for detecting the tDNA, in this case a biomarker for chronic myelogenous leukemia.

Two-Dimensional Restructuring of Cu2O Can Improve the Performance of Nanosized n-TiO2/p-Cu2O Photoelectrodes under UV-Visible Light.

p-Cu2O/n-TiO2 photoanodes were produced by electrodeposition of octahedral p-type Cu2O nanoparticles over n-type TiO2 nanotubes. The photoresponse of the composite p–n photoanodes was evaluated in photoelectrochemical cells operating at “zero-bias” conditions under either visible or UV–vis irradiation. In both operating conditions, the produced electrodes invariably followed the p–n-based photoanode operations but exhibited lower photoelectrochemical performance as compared to the bare n-TiO2 photoanode under UV–vis light. The reported experimental analysis evidenced that such decreased photoactivity is mainly induced by the scarce efficiency of the nanosized p–n interfaces upon irradiation. To overcome such limitation, a restructuring of the originally electrodeposited p-Cu2O was promoted, following a photoelectrochemical post-treatment strategy. p-Cu2O, restructured in a 2D leaf-like morphology, allowed reaching an improved photoelectrochemical performance for the p–n-based photoanode under UV–vis light. As compared to the bare n-TiO2 behavior, such improvement consisted of photoanodic currents up to three times larger. An analysis of the mechanisms driving the transition from compact (∼100 nm) octahedral p-Cu2O to wider (∼1 μm) 2D leaf-like structures was performed, which highlighted the pivotal role played by the irradiated n-TiO2 NTs.

All-electrochemical fabrication of α-Fe2O3 nanotube array/Cu2O composites toward visible-light-responsive photocatalysis

Composites of anodized hematite (α-Fe2O3) nanotube (FNT) arrays and Cu2O nanoparticles (CNPs) were fabricated using all-electrochemical processes. Two-step anodized iron foils with ethylene-glycol-based electrolyte containing ammonium fluoride show hematite-rich phase after post-annealing in oxygen atmosphere. P-type CNPs with an average diameter of 200 nm were deposited uniformly onto the FNT surface by pulse electrodeposition. The enhancement of hydroxyl radical formation in water for the FNT/CNP composite under visible light (VIS) irradiation was verified by photoluminescence technique using terephthalic acid, suggesting that co-catalyst CNPs on FNT arrays may promote photo-generated hole–electron separation and successive water oxidation on FNT surfaces. Furthermore, hydrogen generation from gas phase photocatalytic decomposition of water/methanol mixture over FNT/CNP was clearly confirmed under VIS irradiation, while H2 was not detected with only FNT and only CNP. This study indicates that electrodeposited CNPs can work as noble-metal-free co-catalysts for VIS responsive photocatalysis based on anodized FNT arrays.

Fabrication and optical properties of InP/Cu2O nanojunctions

The InP/Cu2O nanojunction hybrid materials are fabricated by a facile method via electrodeposition of CU2O nanoparticles on the ordered one dimensional InP nanopore arrays. The morphology and element composition of the InP/Cu2O heterostructures are characterized. Experimental results indicate p-type Cu2O nanoparticles homogenously covered on the surface of n-type InP nanopore arrays and formed efficient heterogeneous structure. Compared to the pristine InP nanopore arrays, the InP/Cu2O nanoheterojunction structure have advantageous of the separation of photogenerated electron-hole pairs.

Enhanced charge separation by oriented growth of Ta3N5-Cu2O n-p array heterojunction

Tantalum nitride (Ta3N5) is one of the most promising photoresponsive semiconductor materials for efficient solar energy conversion, but its fast carrier recombination has hindered research progress severely. Fabricating a heterojunction structure is an effective strategy to promote the charge separation efficiency and thus enhance solar conversion efficiency. Herein, we designed a p-n heterojunction photoanode consisting of n-type Ta3N5 nanorod arrays (NRAs) that grew along the a-axis (light electron effective mass) and p-type Cu2O nanoparticles. This NRA heterojunction shortens the hole diffusion distance, transfers electrons along the a-axis effectively, and enlarges the space charge region. The heterojunction improves the charge separation efficiency of Ta3N5 NRAs significantly, and Ta3N5-Cu2O exhibits a photocurrent density of 9.19 mA cm−2 at 1.6 V vs normal hydrogen electrode (VNHE, pH = 0), an onset potential of 0.326 VNHE, and a maximum incident photon to current efficiency of 60% at 380 nm. Our results demonstrated a potential crystal oriented growth strategy of nanostructured heterojunctions for overcoming the short carrier diffusion distance and fast carrier recombination.

Chemical bath deposition synthesis of TiO2/Cu2O core/shell nanowire arrays with enhanced photoelectrochemical water splitting for H2 evolution and photostability

In this study, we have developed a facile chemical bath deposition (CBD) method to grow p-type Cu2O nanoparticles on n-type TiO2 nanowire arrays (TiO2 NWAs) to fabricate TiO2/Cu2O core/shell heterojunction nanowire arrays (TiO2/Cu2O core/shell NWAs). When used as photoelectrode, the fabricated TiO2/Cu2O core/shell NWAs show improved photoelectrochemical (PEC) water splitting activity to pure TiO2 NWAs. The effects of the CBD cycle times on the PEC activities have been studied. The TiO2/Cu2O core/shell heterojunction nanowire array photoelectrode prepared by cycling 5 times in the CBD process achieves the highest photocurrent of 2.5 mA cm−2, which is 2.5 times higher than that of pure TiO2 NWAs. In addition, the H2 generation rate of this photoelectrode reaches to 32 μmol h−1 cm−2, 1.7 times higher than that of pure TiO2 NWAs. Furthermore, the TiO2/Cu2O core/shell heterojunction nanowire array photoelectrode shows excellent photostability and achieves a stable photocurrent of over 2.3 mA cm−2 during long light illumination time of 5 h. The enhanced photocatalytic activity of TiO2/Cu2O core/shell heterojunction nanowire array photoelectrode is attributed to the synergistic actions of TiO2 and Cu2O for improving visible light harvesting, and efficient transfer and separation of photogenerated electrons and holes.

Preparation and Photochemical Properties of Layered MoS2/Cu2o Heterojunction Nanocomposites

In recent years, environmental problems induced by organic pollutants have become an important problem for our society. Semiconductor photochemical treatment is a potential technology for solving the environmental issues. Therefore, lots of efforts have been devoted to develop high-efficiency visible light assisted semiconductor photocatalysts. Cu2O nanoparticle is a well-known p-type semiconductor with a direct band gap of 2.17eV, which endows it a reasonable alternative for photocatalytic applications [1-3]. However, high recombination rate of the electron-hole pairs excited from Cu2O nanoparticles seriously hinders its practical application. Coupling p-type Cu2O nanoparticles with n-type semiconductor to form a P-N heterojunction for carrier separation and produce appropriate energy level difference for charge transfer from one semiconductor to another is a potential approach to decrease recombination rate for high-efficiency degradation. Graphene-like n-type semiconductor MoS2 multilayered nanoplates are the reasonable alternative due to its tunable bandgap with different layers and large amounts of unsaturated active sites [4-5]. In this work, two-dimensional (2D) MoS2 nanoplates with different multilayer thickness were prepared by liquid exfoliation and gradient centrifugation. Then, the MoS2 nanoplates were utilized to match the energy level of Cu2O nanoparticles to form MoS2/Cu2O nanocomposites, which have been achieved by the method of hydrothermal synthesis. Scanning Electrom Microscope images and X-ray diffraction (XRD) pattern of nanoparticles Cu2O and MoS2/Cu2O nanocomposites are shown in Fig.1. It can be seen that the morphology of Cu2O nanoparticles are truncated octahedron structure and closely attached on MoS2 nanosheets with different thickness, which was obtained at the centrifugation speed of 2000 rpm, 4000 rpm, 6000 rpm and 8000 rpm. The photochemical behaviors of Cu2O nanoparticles and different MoS2/Cu2O nanocomposites are characterized through the degradation behaviors of methyl orange (MO) under visible light irradiation (Fig.2). The experimental results show that the degradation efficiency of MoS2/Cu2O nanocomposites can be improved by optimizing the thickness of MoS2 nanoplates from few layers to bulk. The degradation ratios of MO after 3 h are 57.9%, 61.1%, 92.2%, 95.3%, 93.1%, and correspond respectively to the MoS2/Cu2O nanocomposites in which the MoS2 nanosheets were obtained at the centrifugation speed of 0 rpm, 2000 rpm, 4000 rpm, 6000 rpm and 8000 rpm. The possible reason is that the increasing surface area and bandgap of MoS2 may provide large reaction area and produce appropriate energy level difference, which is beneficial for accelerating the degradation process of methyl orange. In summary, the different MoS2/Cu2O heterojunction nanocomposites were prepared through adjusting the thickness of multilayered MoS2 nanoplates. The results show that the optimized degradation ratio of MO can be greatly improved from 57.9% up to 95.3% after 3h using MoS2/Cu2O nanocomposites in comparison with Cu2O nanoparticles.

Aerosol-assisted CVD-grown WO₃ nanoneedles decorated with copper oxide nanoparticles for the selective and humidity-resilient detection of H₂S.

A gas-sensitive hybrid material consisting of Cu2O nanoparticle-decorated WO3 nanoneedles is successfully grown for the first time in a single step via aerosol-assisted chemical vapor deposition. Morphological, structural, and composition analyses show that our method is effective for growing single-crystalline, n-type WO3 nanoneedles decorated with p-type Cu2O nanoparticles at moderate temperatures (i.e., 380 °C), with cost effectiveness and short fabrication times, directly onto microhot plate transducer arrays with the view of obtaining gas sensors. The gas-sensing studies performed show that this hybrid nanomaterial has excellent sensitivity and selectivity to hydrogen sulfide (7-fold increase in response compared with that of pristine WO3 nanoneedles) and a low detection limit (below 300 ppb of H2S), together with unprecedented fast response times (2 s) and high immunity to changes in the background humidity. These superior properties arise because of the multiple p-n heterojunctions created at the nanoscale in our hybrid nanomaterial.

Enhanced visible-light photoelectrochemical behaviour of heterojunction composite with Cu2O nanoparticles-decorated TiO2nanotube arrays

Heterojunction composites based on n-type TiO2 nanotubes arrays (TNAs) coupled with p-type Cu2O nanoparticles were synthesized using a square wave voltammetry deposition method for in situ deposition of Cu2O nanoparticles onto the inner surfaces and interfaces of TNAs. The prepared samples were characterized by field-emission scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and UV-vis spectroscopy. When compared with pure TNAs, the Cu2O–TNAs heterojunction composites exhibit considerably higher photocurrent density under visible-light irradiation and enhanced photocatalytic activity for the visible-light-driven photodegradation of methyl orange. Moreover, the photocurrent densities and photocatalytic activity of the Cu2O–TNAs heterostructures largely depend on the deposition potential which determines the content of the Cu2O nanoparticles. The Cu2O–TNAs prepared by the deposition potential of −1.0 V showed the highest photocurrent density (0.91 mA cm−2) and the largest photodegradation rate of methyl orange (88.8%) at the applied potential of 0.5 V under visible light irradiation. The enhanced photoelectrocatalytic activity can be attributed to reducing the recombination rate of the photoexcited electron–hole pairs in TNAs when coupled with Cu2O nanoparticles.

Preparation of p–n junction Cu2O/BiVO4 heterogeneous nanostructures with enhanced visible-light photocatalytic activity

p–n junction Cu2O/BiVO4 heterogeneous nanostructures for enhancement of visible-light photocatalytic properties of BiVO4 nanocrystals have been successfully prepared through coupling a hydrothermal process with polyol strategy. The assembly of p-type Cu2O nanoparticles produces a large number of nano p–n junction heterostructures on the surface of the BiVO4 nanocrystals, where Cu2O and BiVO4 form p- and n-type semiconductors, respectively. The experimental results reveal that these p–n junction Cu2O/BiVO4 heterogeneous nanostructures exhibit much higher visible-light photocatalytic activities than the individual BiVO4 nanocrystals for the degradation of model dyes methylene blue and colorless organic phenol under visible light irradiation. The enhanced photocatalytic efficiencies are attributed to the charge transfer from n-type BiVO4 to the attached p-type Cu2O nanoparticles, which effectively reduces the recombination of electrons and holes, leading to the enhancement of the photocatalytic properties of the heterostructure nanostructures. These new p–n junction heteronanostructures are expected to show considerable potential applications in solar-driven wastewater treatment.

P–n Heterojunction photoelectrodes composed of Cu2O-loaded TiO2 nanotube arrays with enhanced photoelectrochemical and photoelectrocatalytic activities

Cu2O/TiO2 p–n heterojunction photoelectrodes were prepared by depositing different amounts of p-type Cu2O nanoparticles on n-type TiO2 nanotube arrays (i.e., forming Cu2O/TiO2 composite nanotubes) via an ultrasonication-assisted sequential chemical bath deposition. The success of deposition of Cu2O nanoparticles was corroborated by structural and composition characterizations. The enhanced absorption in the visible light region was observed in Cu2O/TiO2 composite nanotubes. The largely improved separation of photogenerated electrons and holes was revealed by photocurrent measurements. Consequently, Cu2O/TiO2 heterojunction photoelectrodes exhibited a more effective photoconversion capability than TiO2 nanotubes alone in photoelectrochemical measurements. Furthermore, Cu2O/TiO2 composite photoelectrodes also possessed superior photoelectrocatalytic activity and stability in the degradation of Rhodamine B. Intriguingly, by selecting an appropriate bias potential, a synergistic effect between electricity and visible light irradiation can be achieved.

Controlled synthesis of coaxial core–shell TiO2/Cu2O heterostructures by electrochemical method and their photoelectrochemical properties

Coaxial heterostructures based on n-type TiO2 nanotubes (TNTs) arrays enclosed with p-type Cu2O nanoparticles were prepared through a combination of anodic oxidation and subsequent electrodeposition. Cu2O nanoparticles were electrodeposited into the inter-tubular space of TNTs to form the coaxial core–shell TNTs@Cu2O heterostructures. The Cu2O nanoparticles were preferentially deposited on the ribs of TNTs arrays, and the amount of thiourea added during electrodeposition of Cu2O played an important role in formation of coaxial core–shell TNTs@Cu2O heterostructures. The heterostructures exhibited excellent photoelectrochemical performance under visible light. Such heterostructures would serve as a promising candidate for solar energy conversion.