Efficient Interfacial Charge Transfer Research Articles

Solid-Solution-Like o-C3N4/Ag2SO4 Nanocomposite as a Direct Z-Scheme Photocatalytic System for Photosynthesis of Active Oxygen Species

Efficient photosynthesis of active oxygen species (e.g., •OH, •O2–, and H2O2) is of cardinal significance for environmental science and biochemistry. We report a system of o-C3N4/Ag2SO4 with solid-solution-like structure synthesized by coordinating the 5s orbit of Ag+ with surface 2p lone electrons of o-C3N4. The as-synthesized o-C3N4/Ag2SO4 demonstrates a unique electronic structure, as illuminated high light absorption, perfect redox potentials, large BET specific area, abundant active sites, and efficient interfacial charge transfer. Electron paramagnetic resonance spectra and Mott–Schottky measurements confirm that o-C3N4/Ag2SO4 photocatalysts demonstrate highly efficient activity for yielding •OH, •O2–, and H2O2 species with the Z-scheme photocatalytic principle. Experimental and DFT calculation reveal that the transferred electrons on the conduction band (CB) made up of Ag 5s were favorably shifted into the valence band (VB) composed of N 2p with the formed coordination under irradiation, greatly pr...

Unsymmetrical and Symmetrical Zn(II) Phthalocyanines as Hole-Transporting Materials for Perovskite Solar Cells

An unsymmetrical zinc phthalocyanine with one carboxyl and three tert-butyl groups (TT1) and a symmetrical zinc phthalocyanine with four tert-butyl groups (TT0) are employed as hole-transporting materials (HTMs) in mixed-ion perovskite [HC(NH2)2]0.1(CH3NH3)0.9PbI3 solar cells. The optical and electrochemical data of TT1 and TT0 exhibit appropriate energy levels for efficient interfacial charge transfer with the perovskite. The perovskite solar cells with TT1 show 16 ± 1 mA/cm2 photocurrent and 0.95 ± 0.07 V open circuit voltage resulting in 13.0 ± 0.7% power conversion efficiency at 1 sun. Under the same conditions, the symmetric phthalocyanine TT0 shows 20.2 mA/cm2 photocurrent and 1.05 V open circuit voltage resulting in 14% power conversion efficiency.

Porphyrin decorated Bi2O2CO3 nanocomposites with efficient difunctional properties of photocatalysis and optical nonlinearity

Considerable attention has been paid to design multifunctional hybrid materials for developing novel optoelectronic systems. Here, a series of novel porphyrin decorated Bi2O2CO3 nanocomposites (BOC/TPP) loaded with different porphyrin contents was prepared by a facile solvothermal technique to maximize the photocatalysis and optical nonlinearity. The photoresponsive range of the BOC/TPP nanocomposites can be extended from UV to visible light, and the band gap can be continuously tuned. The wide absorption of the as-prepared nanocomposites in the visible light region makes them suitable for photocatalytic and nonlinear transmission studies. The associated photocatalysis and optical nonlinearity for the BOC/TPP nanocomposites are shown to be dependent on the contents of porphyrin. Compared to BOC, TPP and other prepared nanocomposites with different TPP loadings, the BOC/0.03TPP nanocomposite with 3 wt% TPP exhibits the highest photocatalytic performance and nonlinear optical absorption effect, due to the efficient interfacial charge transfer and the strong interfacial electronic interactions between TPP and BOC. These findings provide an ideal scientific platform to guide the rational design of difunctional nanomaterials with desired optoelectronic performances.

Efficient interfacial charge transfer through plasmon sensitized Ag@Bi2O3 hierarchical photoanodes for photoelectrocatalytic degradation of chlorinated phenols.

The present work demonstrates an extremely proficient and robust study of efficient interfacial charge transfer through plasmonic Ag decorated Bi2O3 hierarchical photoanodes for the photoelectrochemical treatment of chlorinated phenols. Unique 2D flake-like Bi2O3 hierarchical nanostructures were grown onto a fluorine-doped tin oxide (FTO) substrate by a simple chemical bath deposition method using triethanolamine as complexing agent. The formation of Bi2O3 on FTO was governed by the decomposition of a nucleated bismuth-hydroxyl complex (Bi2O1-x(OH)x) and modification to the electrode was carried out by the deposition of Ag via a chemical reduction method using hydrazine hydrate. Both the fabricated electrodes were well characterized for their photo- and electro-optical properties. Efficient charge separation was observed due to the surface plasmon resonance phenomenon of silver nanoparticles with the favorable intrinsic properties of Bi2O3 under application of a small electric bias of 1 V preventing the recombination of charge carriers and thereby increasing the rate of photoelectrocatalytic degradation of the chlorinated phenols. PEC degradation using the Ag@Bi2O3 photoelectrode followed the trend 4-CP < 2,4-DCP < 2,4,6-TCP < P-CP due to efficient attack at the chlorinated positions by reactive oxygen species with increasing chlorine substitution and also due to the absence of an expected chain reaction of the generated chlorine radicals (Cl˙) during the PEC reaction. The PEC activity of Ag@Bi2O3 was 1.5 times higher than a Bi2O3 nanoflake electrode for 4-CP over 2 h. The fabricated Ag@Bi2O3 proved to be an efficient photoelectrode with synergistic solar-induced photoactivity. A detailed mechanistic study in the presence of scavengers suggests degradation by produced hydroxyl radical species. Thus, physical insights into the degradation of chlorinated phenols were obtained.

Direct Experimental Observation of Facet-Dependent SERS of Cu2 O Polyhedra.

Semiconductor-based surface enhanced Raman scattering (SERS) has attracted great attention due to its excellent spectral reproducibility, high uniformity, and good anti-interference ability. However, its relatively low SERS sensitivity still hinders its further developments in both performance and applications. Since the SERS is a peculiar surface effect, investigating the facet-dependent SERS activity of semiconductor nanostructures is crucial to boost their SERS signals. Although the semiconductor facet-dependent SERS effect is predicted via numerical calculations, convincing experimental evidence is scarce due to complicated and undefined surface conditions. In this work, three facet-defined ({100}, {110}, and {111} facets) Cu2 O microcrystals (MCs) with clear surface atomic configuration are utilized to investigate the facet-dependent SERS effect. The results from the Kelvin probe force microscopy measurements on single Cu2 O polyhedron, demonstrate that the facet-dependent work function plays a crucial role in the interfacial charge transfer process. Comparing with the {110} and {111} facets, the {100} facet possesses the lowest electronic work function, which enables more efficient interfacial charge transfer. The simulation results further confirm that the {100}-facets can transfer the most electrons from Cu2 O MCs to molecules due to its lowest facet work function, resulting in the largest increment of the molecular polarization.

The Development of Functional Mesocrystals for Energy Harvesting, Storage, and Conversion.

Higher-ordered semiconductors have attracted extensive research interest as an adopted engineering for active solar energy harvesting, storage, and conversion. It is well-known that the effective separation and anisotropic migration of photogenerated charges are the basic driven force required for superior efficiency. However, the morphology and stoichiometric variation of these semiconductors play essential roles in their physicochemical properties of bulk and surface, especially for efficient interparticle or interfacial charge transfer. To this point, the strategy of controlling the topotactic transformation toward superstructures with optimized functionality is preferable for a wide range of optoelectronic and catalytic engineering applications. In this Minireview, we provide an overview of the crystal orientation, synthetic engineering, functional applications, and spatial and temporal charge dynamics in TiO2 mesocrystals and others. The viewpoint of in-depth understanding of the structure-related kinetics would offer an opportunity for design of versatile mesocrystal semiconductors sought-after for potential applications.

New Insights into the Electronic Structure and Photoelectrochemical Properties of Nitrogen-Doped HNb3O8 via a Combined in Situ Experimental and DFT Investigation.

The nitrogen-doping approach has been intensively adopted to improve various properties of metal oxides, especially for adjusting the energy band structure and extending the photoresponse range of oxide photocatalysts. However, the nitrogen doping behavior is still unintelligible and complex due to the diversity of compositions and crystal structures. In this work, new insights into the electronic structure and photoelectrochemical (PEC) properties of nitrogen-doped HNb3O8 were presented. On the one hand, we utilized an in situ experimental strategy to ascertain the effect of nitrogen doping on the energy band and photoelectrochemical (PEC) properties of HNb3O8 and nitrogen-doped HNb3O8 (N-HNb3O8). Their energy band level, donor densities, and interfacial charge transfer properties were studied by Mott-Schottky plots and electrochemical impedance spectroscopy. After nitrogen doping, the conduction band position is unusually descended by 0.23 eV, the valance band position is raised by 0.51 eV, the donor density (Nd) is increased from 3.71 × 1021 to 6.46 × 1021 cm-3, and interfacial charge transfer efficiency is reduced, though. On the other hand, density functional theoretical calculations were also conducted, so as to understand the electronic structures of HNb3O8 and N-HNb3O8. After nitrogen doping, the electronic structure is modified due to the upshift of the valance band edge consisting of hybrid N 2p and O 2p orbitals and the downshift of the conduction band edge consisting of the H 1s and Nb 4d orbitals. Furthermore, these insights into the behavior of nitrogen-doped semiconductors have important guiding significance toward their potential applications.

Effective excitons separation on graphene supported ZrO2[sbnd]TiO2 heterojunction for enhanced H2 production under solar light

A novel photocatalyst comprises of ZrO2TiO2 immobilized on reduced graphene oxide (rGO) – a ternary heterojunction (ZrO2TiO2/rGO) was synthesized by using facile chemical method. The nanocomposite was prepared with a strategy to achieve better utilization of excitons for catalytic reactions by channelizing from metal oxide surfaces to rGO support. TEM and XRD analysis results revealed the heterojunction formed between ZrO2 and single crystalline anatase TiO2. The mesoporous structure of ZrO2TiO2 was confirmed using BET analysis. The red shift in absorption edge position of ZrO2TiO2/rGO photocatalyst was characterized by using diffuse reflectance UV–Visible spectra. ZrO2TiO2/rGO showed greater interfacial charge transfer efficiency than ZrO2TiO2, which was evidenced by well suppressed PL intensity and high photocurrent of ZrO2TiO2/rGO. The suitable band gap of 1.0 wt% ZrO2TiO2/rGO facilitated the utilization of solar light in a wide range by responding to the light of energy equal to as well as greater than 2.95 eV by the additional formation of excited high-energy electrons (HEEs). ZrO2TiO2/rGO showed the enhanced H2 production than TiO2/rGO, which revealed the role of ZrO2 for the effective charge separation at the heterojunction and the solar light response. The optimum loading of 1.0 wt% of ZrO2 and rGO on TiO2 showed the highest photocatalytic performance (7773 μmolh−1gcat−1) for hydrogen (H2) production under direct solar light irradiation.

An insight into titania nanopowders modifying with manganese ions: A promising route for highly efficient and stable photoelectrochemical solar cells

Abstract In this study, we firstly report the synthesis of pure and manganese (Mn) doped titania nanopowders by solution-based chemical process followed by ball-milling and ultra-sonication processes and their usage as photoanode material in dye-sensitized solar cells (DSSCs). Besides examining the properties of physical and charge transfer dynamics, we also made a detailed cost analysis to compare with commercial P25 nanopowders. By incorporating Mn 4+ ions into titania matrix, we have also succeeded not only in lower price but also in significantly enhancing the dye loading capability by increasing specific surface area and the retarding the recombination of electron-hole pairs by forming the discrete interstitial states within the band gap as well as accelerating electron transfer by tailoring in energy gap, leading to better photovoltaic performance. Such that, the cell assembled with 0.4 mol% Mn doped TiO 2 yields an efficiency of 7.33%, which is ∼17% and ∼65% higher than the value obtained for P25 and pure titania-based photoanode, respectively, and shows a fast, stable, and completely reversible photocurrent response accompanying each switch-on/off event. Furthermore, the photoinduced electron transfer (PET) measurements indicate an efficient interfacial charge transfer for 0.4 mol%Mn doped titania (k ET = 0.99 × 10 8 s –1 ) compared to the both synthesized pure TiO 2 (0.74 × 10 8 s –1 ) and commercial P25 (0.94 × 10 8 s –1 ) photoanodes. This work renders the possibility of synthesizing low-cost and easy-preparation Mn-doped titania nanopowders and describes an innovative approach to further boost the efficiency of green technologies such as solar-driven water splitting, photoelectrochemical and perovskite solar cells applications.

Effect of electron withdrawing substituent and extended π- conjugation on photophysical properties of Ruthenium polyterpyridine D-P-A complexes and interfacial studies with semiconducting TiO 2 nanoparticle: Experimental and computational evidences

Abstract The necessity of improving the excited state properties for efficient interfacial charge transfer to semiconducting TiO 2 material drag us to design complex 2 [(L2)Ru(L4)]2PF 6 and complex 3 [(L2)Ru(L1)Ru(L3)]4PF 6 based on D-P-A functionalisation (D = Donor, P = Photosensitizer and A = Acceptor). The study involves a comparative account of complexes 1–3, where our previously reported complex 1 considered as a basic motif. We have improved the excited state properties of complex 1 by substituting with an additional electron withdrawing group and extended π-conjugation in mononuclear complex 2 and binuclear complex 3 respectively. Compared to the average excited state lifetime (τ avg ) of 5.54 ns for complex 1, both complexes 2 and 3 show improved excited state lifetime of 10.24 ns and 22.06 ns respectively. Further, the anchoring of complexes on high bandgap TiO 2 semiconductor surface to perform interfacial charge transfer have been shown via Time-Correlated Single Photon Counting (TCSPC) studies, which displayed quenched decay pattern and decreased excited state lifetime in the complex 2/3-TiO 2 system compared to their bare complex solution. Therefore, the obtained average excited state lifetime in complex 2 and 3 is sufficient to perform interfacial charge transfer study in the semiconductiong TiO 2 nanoparticle. This interfacial charge transfer further strengthened by the femtosecond transient absorption spectroscopic studies in colloidal TiO 2 nanoparticle which give the evidence for the presence of cation radical and injected conduction band electron (e − CB) through their characteristic absorption. The Cyclic voltammetry experiment exhibit first reduction potential ( E red 1 ) for complex 2 and 3 at −1.22 V and −1.17 V respectively compared to −1.27 V for complex 1. The higher value of E red 1 in complex 2 and 3 indicate the higher electron affinity of the ligand for reduction due to an additional electron withdrawing group and extended π- conjugation respectively. Also, the TDDFT studies using B3LYP exchange correlations functional and LANL2DZ basis set along with salvation effect in Gaussian 09 programs give an overview of transitions involved in 1 MLCT and are in support with the experimental UV–vis absorption spectra of complexes. The trend of LUMO energy level for complexes obtained from electrochemical studies is also in agreement with the LUMO energy level distribution obtained from DFT analysis.

Morphological tuning of photo-booster g-C3N4 with higher surface area and better charge transfers for enhanced power conversion efficiency of quantum dot sensitized solar cells

Photo-booster effect of g-C3N4 Nanotubes (g-C3N4 NTs) on the photovoltaic properties are investigated using the composites having ZnO Nanorods (ZnO NRs) with different composition ratios, sensitized by CdS quantum dots. Enhanced performance is attributed to the cumulative effects of this composite i.e., (i) a significant decrement of fluorescence intensity in steady state PL, (ii) faster electron lifetime and good electron injection rate from dynamic PL, and (iii) sufficient loading of sensitizer at photoanodic scaffold for better harvesting of solar energy. An increase of 32% in power conversion efficiency (PCE, η) is observed in case of g-C3N4 NTs based device as compare to g-C3N4 Nanoflakes (g-C3N4 NFs). Increased PCE value is mainly due to (i) efficient separation and transportation of the photogenerated charge carriers along a one dimensional (1D) path, resulting in shorter lifetime of charge carriers and (ii) high surface area which provides more active sites for loading of sensitizer particles, results in an improvement of light harvesting ability. Further, electrochemical impedance spectroscopic (EIS) analyses showed an efficient interfacial charge transfer by reducing the recombination processes i.e., the back transferring of photoexcited electron at electrode/electrolyte interface.

TiO2 anatase nanorods with non-equilibrium crystallographic {001} facets and their coatings exhibiting high photo-oxidation of NO gas

ABSTRACTDevelopment of highly active photocatalysts is mandatory for more widespread application of this alternative environmental technology. Synthesis of photocatalysts, such as anatase TiO2, with more reactive, non-equilibrium, crystallographic facets is theoretically justified by a more efficient interfacial charge transfer to reactive adsorbed species, increasing quantum efficiency of photocatalyst. Air and vacuum calcinations of protonated trititanate nanotubes lead to their transformation to anatase nanorods. The nanorods synthesized by air calcination demonstrate photo-oxidation of NO gas more than three times superior to the one presented by the benchmark P-25 photocatalyst. This performance has been explained in terms of 50% higher specific surface area and, more importantly, through the predominance of more reactive, non-equilibrium, {001} crystallographic facets of the anatase nanorods. These facets present a high density of undercoordinated Ti cations, which favors adsorption of reactant species, and strained Ti–O–Ti bonds, leading to more efficient photo-oxidation reactions. Reduced Ti species, such as Ti3+, were not observed in the as-obtained nanorods, while reactive adsorbed molecules are scarce on the nanorods obtained through vacuum calcination. Dip-coating of TiO2 anatase nanorods (air calcined) over soda-lime glass plates was used to prepare visible light transparent, superhydrophilic and highly adherent photocatalytic coatings with homogenously distributed nanopores.

A hybrid of CdS/HCa2Nb3O10 ultrathin nanosheets for promoting photocatalytic hydrogen evolution.

A hybrid of CdS/HCa2Nb3O10 ultrathin nanosheets was synthesized successfully through a multistep approach. The structures, constitutions, morphologies and specific surface areas of the obtained CdS/HCa2Nb3O10 were characterized well by XRD, XPS, TEM/HRTEM and BET, respectively. The TEM and BET results demonstrated that the unique structural features of CdS/HCa2Nb3O10 restrained the aggregation of CdS nanoparticles as well as the restacking of nanosheets effectively. HRTEM showed that CdS nanocrystals of about 25-30 nm were firmly anchored on HCa2Nb3O10 nanosheets and a tough heterointerface between CdS and the nanosheets was formed. Efficient interfacial charge transfer from CdS to HCa2Nb3O10 nanosheets was also confirmed by EPR and photocurrent responses. The photocatalytic activity tests (λ > 400 nm) showed that the optimal hydrogen evolution activity of CdS/HCa2Nb3O10 was about 4 times that of the bare CdS, because of the efficient separation of photo-generated carriers.

Polyaniline decorated Bi2MoO6 nanosheets with effective interfacial charge transfer as photocatalysts and optical limiters.

Polyaniline (PANI)-decorated Bi2MoO6 nanosheets (BMO/PANI) were prepared by a facile solvothermal method. Different characterization techniques, including X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, diffuse reflectance ultraviolet-visible spectroscopy, photoluminescence spectroscopy, electrochemical impedance spectroscopy, photocurrent spectroscopy, and nanosecond time-resolved emission studies, have been employed to investigate the structure, optical and electrical properties of the BMO/PANI composites. The wide absorption of the samples in the visible light region makes them suitable for nonlinear transmission and photocatalytic activity studies. The associated photocatalytic activity and optical nonlinearities for the BMO/PANI composites are shown to be dependent on the PANI loadings. The rational mechanisms responsible for deteriorating pollutants and improving optical nonlinearities were also proposed, which could be mainly attributed to the efficient interfacial charge transfer and the interfacial electronic interactions between PANI and Bi2MoO6. The photoluminescence spectroscopy, electrochemical impedance spectroscopy, and photocurrent spectroscopy studies confirmed that the interface charge separation efficiency was greatly improved by coupling Bi2MoO6 with PANI. The tuning of photocatalysis and nonlinear optical behaviors with variation in the content of PANI provides an easy way to attain tunable properties, which are exceedingly required in optoelectronics applications.

Z-scheme visible-light-driven Ag3PO4 nanoparticle@MoS2 quantum dot/few-layered MoS2 nanosheet heterostructures with high efficiency and stability for photocatalytic selective oxidation

A novel MoS2 quantum dots/few-layered MoS2 nanosheets (MQD/FL-MNS)-coated Ag3PO4 nanoparticles (ANP) core@shell heterostructure with high photocatalytic activity and stability under visible light irradiation was fabricated by a simple stirring–ultrasonic exfoliation method and an organic phase in situ growth strategy. TEM, AFM, and Raman characterizations verified the successful preparation and the high quality of the two-dimensional MQD/FL-MNS exfoliated from bulk MoS2. An appreciable direct bandgap of 1.93eV for MQD/FL-MNS is observed, which is favorable for its photocatalytic application. The obtained ANP@MQD/FL-MNS nanocomposites exhibited significantly enhanced performance for photodegradation of organic pollutants (RhB) and photocatalytic selective oxidation of benzyl alcohols (BA) to benzaldehyde compared with pure Ag3PO4, and the ANP@MQD/FL-MNS-6 nanocomposite exhibited the highest photocatalytic activity. The energy band structure and the quenching effects of different scavengers demonstrated that the electrons of MoS2 and the holes of Ag3PO4 with higher oxidability and reducibility are the real participants in photocatalytic reactions. The superior photocatalytic activity of the novel catalyst originates from the particular Z-scheme charge carrier migration mechanism and core@shell heterostructures with an intimate and large contact interface, resulting in highly efficient interfacial charge transfer and the separation of photogenerated electrons and holes. In addition, the introduction of MQD/FL-MNS could boost light harvesting, provide more active adsorption sites, facilitate dissolved O2 activation, and protect the Ag3PO4 from dissolution and photocorrosion during the photocatalytic oxidation reaction

Simultaneous Optimization of Colloidal Stability and Interfacial Charge Transfer Efficiency in Photocatalytic Pt/CdS Nanocrystals.

Colloidal stability and efficient interfacial charge transfer in semiconductor nanocrystals are of great importance for photocatalytic applications in aqueous solution since they provide long-term functionality and high photocatalytic activity, respectively. However, colloidal stability and interfacial charge transfer efficiency are difficult to optimize simultaneously since the ligand layer often acts as both a shell stabilizing the nanocrystals in colloidal suspension and a barrier reducing the efficiency of interfacial charge transfer. Here, we show that, for cysteine-coated, Pt-decorated CdS nanocrystals and Na2SO3 as hole scavenger, triethanolamine (TEOA) replaces the original cysteine ligands in situ and prolongs the highly efficient and steady H2 evolution period by more than a factor of 10. It is shown that Na2SO3 is consumed during H2 generation while TEOA makes no significant contribution to the H2 generation. An apparent quantum yield of 31.5%, a turnover frequency of 0.11 H2/Pt/s, and an interfacial charge transfer rate faster than 0.3 ps were achieved in the TEOA stabilized system. The short length, branched structure and weak binding of TEOA to CdS as well as sufficient free TEOA in the solution are the keys to enhancing colloidal stability and maintaining efficient interfacial charge transfer at the same time. Additionally, TEOA is commercially available and cheap, and we anticipate that this approach can be widely applied in many photocatalytic applications involving colloidal nanocrystals.

Graphitic-C3N4 hybridized N-doped La2Ti2O7 two-dimensional layered composites as efficient visible-light-driven photocatalyst

Perovskite-type La2Ti2O7 (LTO), having a layered structure and the separated H2 and O2 evolution sites, is attractive as an efficient photocatalyst. However, the photocatalytic activity is often limited by the poor electron mobility. This problem can be conquered by hybridization with materials having efficient properties for the visible light absorption and charge carrier transport. Here, we report a two-dimensional (2D) layered composite hybridized by approximately 2nm thick graphitic C3N4 nanosheets (g-C3N4) and 7nm thick nitrogen doped LTO nanosheets (NLTO) (g-C3N4/NLTO), in which g-C3N4 and NLTO act as hole receptor and electron conductor, respectively. g-C3N4/NLTO exhibited high photocatalytic activities for H2 production via water splitting and dye degradation under the UV and visible light irradiation, due to the interfacial charge transfer between g-C3N4 and NLTO. The electrochemical measurement showed the type II band alignment with favorable charge transfer from g-C3N4 to NLTO. The 2D architecture with a maximized interfacial area allows efficient charge separation with a short interfacial distance. This efficient interfacial charge transfer is further elucidated from monitoring of charge separation and trapping processes using the femtosecond time-resolved diffused reflectance (TDR) measurement.

CuO@ZnO core-shell nanocomposites: Novel hydrothermal synthesis and enhancement in photocatalytic property

The efficient charge separation and interfacial charge transfer in the semiconductors are of great significance to photocatalytic performance. Herein, we report a facile and cost-effective synthesis of the CuO@ZnO core-shell nanocomposites with the aim to enhance the catalytic activity of ZnO in photodegradation of methylene blue (MB) under UV irradiation. Using a simple two-step hydrothermal method, CuO nanostructures with different thicknesses are grown on ZnO nanoparticles (0.4, 2, 10 and 50% with respect to the ratio of initial molar concentrations of copper to zinc). Significant improvement in the photocatalytic efficiency was observed with utilizing 0.4 and 2%CuO@ZnO nanocomposites compared to the pristine ZnO nanoparticles. The structural and optical properties of the as-prepared samples were investigated by XRD and DRS analysis, respectively. Further, the morphology of the as-synthesized nanostructures was studied by FESEM and TEM imaging, and the high purity and the characteristic functional groups of the final products were also explored using EDX and FTIR spectroscopies, respectively.

Embedding Metal in the Interface of a p-n Heterojunction with a Stack Design for Superior Z-Scheme Photocatalytic Hydrogen Evolution.

The construction of a p-n heterojunction is an efficient strategy to resolve the limited light absorption and serious charge-carrier recombination in semiconductors and enhance the photocatalytic activity. However, the promotion effect is greatly limited by poor interfacial charge transfer efficiency as well as reduced redox ability of charge carriers. In this work, we demonstrate that the embedding of metal Pd into the interface between n-type C3N4 and p-type Cu2O can further enhance the interfacial charge transfer and increase the redox ability of charge carriers through the design of the C3N4-Pd-Cu2O stack nanostructure. The embedded Pd nanocubes in the stack structure not only trap the charge carriers from the semiconductors in promoting the electron-hole separation but also act as a Z-scheme "bridge" in keeping the strong reduction/oxidation ability of the electrons/holes for surface reactions. Furthermore, Pd nanocubes also increase the bonding strength between the two semiconductors. Enabled by this unique design, the hydrogen evolution achieved is dramatically higher than that of its counterpart C3N4-Cu2O structure without Pd embedding. The apparent quantum efficiency (AQE) is 0.9% at 420 nm for the designed C3N4-Pd-Cu2O. This work highlights the rational interfacial design of heterojunctions for enhanced photocatalytic performance.

Enhanced Solar Hydrogen Generation by a Heterojunction of Perovskite-type La2 Ti2 O7 Nanosheets Doped with CdS Quantum Dots.

A heterojunction of a perovskite-type La2 Ti2 O7 (LTO)/CdS quantum dot (QD) nanocomposite was prepared by the chemical bath deposition method. The solar-light-driven H2 generation results show that this CdS QDs/LTO heterojunction exhibits great improvement in the photocatalytic H2 production and its photoelectrochemical properties in comparison with pure CdS QDs and LTO nanosheets. A possible enhanced mechanism of photoinduced interfacial charge transfer between CdS and LTO is proposed for the heterojunction. The shift of the CdS conduction band (CB) edge can enlarge the CB potential difference between CdS QDs and LTO, enhancing transferred driven force of the interfacial electrons and finally improving the two components' separation activity of photogenerated carriers. This study provides a promising method for constructing an efficient photoinduced interfacial charge transfer over LTO and CdS QD heterojunctions for photocatalytic hydrogen production.