Search

Er3+/Yb3+ co-doped CdMoO4 phosphors with high upconversion emission intensity and sensitive temperature sensing properties.

In this work, a novel, earth-abundant, and environmentally benign NaFeSi2O6 catalyst is synthesized by a one-step solvothermal method without the introduction of any surfactants.

Selective photocatalysis is a very promising direction to improve the activities of photocatalysts. Combining the technique of molecular imprinting (MIP) with heterogeneous photocatalysis can be an appealing approach to achieve our aim. Herein, using the MIP technique, the monoclinic MIP-BiVO4 was successfully synthesized by the presence of rhodamine B (RhB) during the hydrothermal synthesis. The synthesized MIP-BiVO4 possessed better adsorptive and photocatalytic activities than pristine BiVO4. RhB added in the synthesis process worked as a template and served a crucial role in the formation of the MIP-BiVO4 morphology. The photoelectrochemical analysis verified the superiority of MIP-BiVO4 sample in the transfer and separation of the electron–hole pairs. Holes played the most crucial role in the degradation of the pollutants. The effective approach combining MIP technique in the synthesis of photocatalysts would provide some guidance to selective photocatalysis field for designing and synthesizing highly efficient photocatalysts.

Carbon-molybdenum disulfide (C-MoS2) ultrathin nanosheets were prepared by a hydrothermal process, and then AgI/C-MoS2 were synthesized via an in-situ deposition method. This ternary heterojunction composite exhibited better photocatalytic activity compared with those of one-component (pristine MoS2) and bicomponent (AgI/MoS2 and C-MoS2) materials for the degradation of organic dyes under the visible-light irradiation. In particular, by comparing with AgI/MoS2, the significant role of conductive amorphous carbon in AgI/C-MoS2 in enhancing the charge transfer during the photocatalytic degradation of dyes was first confirmed by photocurrent response and electrochemical impedance spectroscopy (EIS). A possible photocatalytic mechanism was proposed based on the capture experiment results. Furthermore, a straightforward and interesting way had been applied to test the recycled/newly-prepared AgI/C-MoS2 composite for revealing its distinctive self-cleaning performance and recyclability characteristic besides its good photocatalytic activity. This work could provide a reference for the design of other new ternary heterojunction composite materials with special structures and properties.

Herein is developed a ternary heterostructured catalyst, based on a periodic array of 1D TiN nanotubes, with a TiO2 nanoparticulate intermediate layer and a In2O3-x(OH)y nanoparticulate shell for improved performance in the photocatalytic reverse water gas shift reaction. It is demonstrated that the ordering of the three components in the heterostructure sensitively determine its activity in CO2 photocatalysis. Specifically, TiN nanotubes not only provide a photothermal driving force for the photocatalytic reaction, owing to their strong optical absorption properties, but they also serve as a crucial scaffold for minimizing the required quantity of In2O3-x(OH)y nanoparticles, leading to an enhanced CO production rate. Simultaneously, the TiO2 nanoparticle layer supplies photogenerated electrons and holes that are transferred to active sites on In2O3-x(OH)y nanoparticles and participate in the reactions occurring at the catalyst surface.

Open-framework structured materials such as Prussian blue analogues and sodium superionic conductor (NASICON) materials have been regarded as promising electrode candidates for aqueous batteries. These materials exhibit outstanding long cycle stability and high rate capacity retention, due to their high ion diffusive rate in the crystal and the stable structure maintenance in the electrochemical reaction process. Herein, an open-framework structured material [Ni(en)

Nanostructured forms of stoichiometric In2O3 are proving to be efficacious catalysts for the gas-phase hydrogenation of CO2. These conversions can be facilitated using either heat or light; however, until now, the limited optical absorption intensity evidenced by the pale-yellow color of In2O3 has prevented the use of both together. To take advantage of the heat and light content of solar energy, it would be advantageous to make indium oxide black. Herein, we present a synthetic route to tune the color of In2O3 to pitch black by controlling its degree of non-stoichiometry. Black indium oxide comprises amorphous non-stoichiometric domains of In2O3-x on a core of crystalline stoichiometric In2O3, and has 100% selectivity towards the hydrogenation of CO2 to CO with a turnover frequency of 2.44 s−1., The utilization of white-colored, wide-bandgap CO2 hydrogenation photocatalysts has been hindered by their limited light-harvesting ability. By making stoichiometric white indium oxide non-stoichiometric and black, it is transformed from a highly inactive to a highly active photothermal catalyst.

Dispersed TiO2 hollow spheres were successfully prepared which was obtained via Ostwald ripening under solvothermal conditions without any templates or surfactants. Then, the AgI/TiO2 was synthesized by the deposition-precipitation process. Finally, Ag/AgI/TiO2 was obtained by a photocatalytic reduction way. Their characteristics were analyzed by XRD, SEM, HRTEM, N2 adsorption-desorption measurements and UV-vis absorption spectra. To demonstrate the potential applications of such composites, their antibacterial activity against Escherichia coli (E. coli) was studied by microcalorimetry for the first time, and their photocatalytic performance for degradation of different organic dyes under simulated UV and visible light was discussed. The results indicated that Ag/AgI/TiO2 hollow spheres revealed elevated antibacterial and photocatalytic activity because of their unique morphology, hollow structure and high surface area. The mechanism of the excellent antibacterial and photocatalytic activity of Ag/AgI/TiO2 hollow spheres are discussed which are attributed to the synergetic effect of Ag, AgI and TiO2. It suggested that the new Ag/AgI/TiO2 photocatalyst has broad application prospects in solar cell, sensor, antibacterial, catalysis and nanotechnology.

Ultrathin g-C3N4 nanosheets have been fabricated via a two-step calcination regulated by melamine precursors at a high heating rate (30 °C min−1). The resulting g-C3N4 nanosheets were further employed as carriers for the growth of carbon quantum dots (CQDs) and (110) exposed α-Fe2O3 through the PVP-enabled adsorption effects by a solvothermal process. It was discovered that the so fabricated ternary photocatalyst α-Fe2O3/CQD@g-C3N4 presented a broad-spectrum absorption range (up to 800 nm) and particularly enhanced active sites of photogenerated electrons for highly efficient photocatalytic oxygen reduction toward H2O2 evolution in pure water. A H2O2 production rate of 1.16 μM min−1 could be expected for the developed photocatalyst under visible light irradiation, which is about 19 times faster than that of pure ultrathin g-C3N4. Herein, the loaded Fe2O3 could transform the H2O2 evolution from two-step single-electron reduction into one-step two-electron one, as verified by the various active species experiments and rotating ring-disk electrode tests. This work presents a new perspective in designing ultrathin g-C3N4 through a simple method of precursor-regulated calcination, which features more outstanding advantages than the conventional exfoliation of bulk g-C3N4 towards ultrathin g-C3N4. More importantly, it provides an optimized photocatalytic reaction route of two-electron oxygen reduction for efficient H2O2 production in pure water under visible light irradiation, without the need for noble metals or organic sacrificial agents.

Tailoring the performance of a photocatalyst by design is challenge in the field of renewable synthetic fuels. Herein, polymorphic heterostructures comprised of two indium oxide based photocatalysts, with distinct structures yet continuously adjustable fractions of the same composition, enable optimization of the activity and selectivity of CO2 hydrogenation to CO and CH3OH. The strategy rests on the cubic (c-) to rhombohedral (rh-) indium oxide hydroxide In2O3−x(OH)y phase transition, in which the fraction of the cubic phase that nucleates and grows within the rhombohedral phase is under precise structural and compositional control. Interfaces so-formed between cubic and rhombohedral polymorphs with distinct electronic band structures as well as separate locations of electron trapping oxygen vacancies and hole trapping hydroxyl defects in individual In2O3−x(OH)y components, enable charge generation, separation and lifetimes of photogenerated electron–hole pairs to be finely tuned. This facilitates command over H2 and CO2 surface chemical reactions that are responsible for the activity and selectivity towards products CO and CH3OH. The control over the performance metrics of a CO2 hydrogenation photocatalyst provided by tuneable rh/c-In2O3−x(OH)y polymorphic heterostructures, affords promising opportunities for the future development of renewable synthetic fuels.

Black liquor, an industrial waste product of papermaking, is primarily used as a low-grade combustible energy source. Despite its high lignin content, the potential utility of black liquor as a feedstock in products manufacturing, remains to be exploited. Demonstrated here in is the use of black liquor as a primary feed-stock for synthesizing graphene quantum dots that exhibit both up-conversion and photoluminescence when excited using visible/near-infrared radiation, thereby enabling the photosensitization of ultraviolet-absorbing TiO2 nanosheets. In addition, these graphene quantum dots can trap photo-generated electrons to realize the effective separation of electron-hole pairs. Together, these two processes facilitate the solar-powered generation of H2 from H2 O, and CO from H2 O-CO2 , using broadband solar radiation.

Surface frustrated Lewis pairs (SFLPs) have been implicated in the gas-phase heterogeneous (photo)catalytic hydrogenation of CO2 to CO and CH3 OH by In2 O3-x (OH)y . A key step in the reaction pathway is envisioned to be the heterolysis of H2 on a proximal Lewis acid-Lewis base pair, the SFLP, the chemistry of which is described as In⋅⋅⋅In-OH + H2 → In-OH2 + ⋅⋅⋅In-H- . The product of the heterolysis, thought to be a protonated hydroxide Lewis base In-OH2 + and a hydride coordinated Lewis acid In-H- , can react with CO2 to form either CO or CH3 OH. While the experimental and theoretical evidence is compelling for heterolysis of H2 on the SFLP, all conclusions derive from indirect proof, and direct observation remains lacking. Unexpectedly, we have discovered rhombohedral In2 O3-x (OH)y can enable dissociation of H2 at room temperature, which allows its direct observation by several analytical techniques. The collected analytical results lean towards the heterolysis rather than the homolysis reaction pathway.

Titanium dioxide is the only known material that can enable gas-phase CO2 photocatalysis in its anatase and rutile polymorphic forms. Materials engineering of polymorphism provides a useful strategy for optimizing the performance metrics of a photocatalyst. In this paper, it is shown that the less well known rhombohedral polymorph of indium sesquioxide, like its well-documented cubic polymorph, is a CO2 hydrogenation photocatalyst for the production of CH3OH and CO. Significantly, the rhombohedral polymorph exhibits higher activity, superior stability and improved selectivity towards CH3OH over CO. These gains in catalyst performance originate in the enhanced acidity and basicity of surface frustrated Lewis pairs in the rhombohedral form., Polymorphs, compounds with identical chemical stoichiometries yet different atomic configurations, expand the range of potential chemical properties and new applications. Here, authors show rhombohedral indium oxides to be highly active and selective for photocatalytic CO2 hydrogenation.

Sodium ferric silicate nanosheets with ultrathin 2D structure were firstly synthesized by hydrothermal method using ferric nitrate and sodium silicate as precursors. The as-prepared nanosheets were characterized by SEM, TEM, AFM, XRD, XPS and N2-physisorption. Adsorption of ten dyes (including 5 cationic dyes and 5 anionic dyes) from aqueous solutions was investigated and discussed. The nanosheets were found to be amorphous and had a thickness of 0.85 nm. The ultrathin nanosheets displayed remarkable selective adsorption capacity toward cationic dyes due to the features of high specific surface area, negative charged surface and good mass transportation property. In particular, such ultrathin nanosheets showed a maximum adsorption capacity of 1.77 mg m−2 per unit surface area for methylene blue (MB), which is the highest value among the reported silicates adsorbents. The equilibrium adsorption data of MB suggested that the Langmuir model was much more suitable for the experimental data, and the pseudo-second-order kinetic equation could well describe the adsorption kinetics. Moreover, the sodium ferric silicate nanosheets could be regenerated by simple calcination and used repeatedly in dyes removal, demonstrating the potential application in wastewater purification and treatment.

Well dispersive CdS quantum dots (QDs) were successfully in-situ grown on cadmium hydroxyapatite (Cd5(PO4)3OH, Cd-Hap) assembled rods through a self-sacrificing hydrothermal method. No any nocuous organic ligands were used in such self-sacrificing route, allowing for a green approach to prepare CdS QDs with clean surfaces and enough active sites. The deposition of CdS QDs onto Cd-Hap surfaces led to a dramatically enhanced performance in H2 production under visible light irradiation as compared to bulk CdS nanoparticles. The optimal CdS QDs/Cd-Hap composite displayed a H2 evolution rate of 14.1 μmol h−1 without using any noble metal cocatalyst, which was about 4.2 times higher than that of pristine CdS. The apparent quantum efficiency for CdS QDs/Cd-Hap composite was up to 18%. It was also found that CdS QDs/Cd-Hap composite can continuously generate H2 from water in the presence of electron donors for more than 125 h. The enhanced photocatalytic performance of CdS QDs/Cd-Hap composites could be attributed to the high charge separation efficiency resulting from the efficient capture of photoinduced electrons by oxygen vacancies in Cd-Hap rods and the quantum confinement effect of CdS QDs with strong redox capacity as well as the increased active sites.

Herein is developed a ternary heterostructured catalyst, based on a periodic array of 1D TiN nanotubes, with a TiO

Nanoscale titanium nitride TiN is a metallic material that can effectively harvest sunlight over a broad spectral range and produce high local temperatures via the photothermal effect. Nanoscale indium oxide-hydroxide, In

The novel BiVO4 nanofibers were firstly obtained by two-step synthesis method. Characterized by X-ray diffractometer (XRD) and scanning electron microscopy (SEM), the samples were shown to be nanofibers with monoclinic phase. The ethylene glycol (EG) and NaOH solution played an important role on their formation. Taking rhodamine B (RhB) as the removal object, the nanofibers exhibited the enhanced adsorptive activity compared with other samples. It may be due to the increase of the specific surface area, the acidic surface property of the BiVO4 nanofibers and the nature of the RhB dye. The formation mechanism of the special morphology was investigated and proposed. It is expected to provide some guidance for designing and preparing other materials for removal of organic pollutants.

Phosphate ( PO 4 3 - ) modification of semiconductor photocatalysts such as TiO2, C3N4, BiVO4, and etc. has been shown positive effect on the enhancement of photocatalytic performance. In the present study, we demonstrate a novel one-pot surface modification route on Ag3PO4 photocatalyst by ammonium phosphate [(NH4)3PO4], which combines PO 4 3 - modification with ammonium ( NH 4 + ) etching to show multiple effects on the structural variation of Ag3PO4 samples. The modified Ag3PO4 photocatalysts exhibit much higher photocatalytic performance than bare Ag3PO4 for the degradation of organic dye solutions under visible light irradiation. It is indicated that the NH 4 + etching favors the surface transition from Ag3PO4 to metallic Ag nanoparticles, resulting in the fast capture of photogenerated electrons and the followed generation of O 2 · - radicals. The strongly adsorbed PO 4 3 - on the Ag3PO4 surfaces can further provide more negative electrostatic field, which improves the separation of photogenerated electron-hole pairs by inducing the holes to directly flow to the surface and then enhances the formation of reactive ·OH radicals. Furthermore, the photocatalytic performance of the modified Ag3PO4 photocatalysts can be optimized by monitoring the concentration of (NH4)3PO4 that is 1 mM.

Zn2SiO4 nanocrystallines were synthesized by a low-temperature hydrothermal method, in which the composition and morphology were tailored by changing the hydrothermal temperature and pH value. Zn2SiO4 was applied as novel photocatalyst to degrade various organic pollutants and it exhibited excellent photocatalytic activity and stability as compared to traditional ZnO. The better photocatalytic performance of Zn2SiO4 than ZnO can be attributed to the more generated charge carries, the stronger oxidation ability of h+ and the higher concentration of active O2− radicals.

Herein, based on single organic ligand as bridging linker and metal trimer as structural nodes, one new pillared-layer metal–organic framework (MOF), Zn3(TDC)4·2DMA (TDC = 2,5-Thiophenedicarboxylic acid, DMA = dimethylamine), has been synthesized and structurally characterized. The pillared-layer architecture is formed by Zn3(TDC)2 layer and pillared TDC ligand where TDC ligand acts as a bifunctional linker. Porous structure of MOF was investigated with potential applications in gas molecule adsorption and metal ion fluorescence sensor.

Micro-nanostructured Mn2O3@CNTs materials have been successfully synthesized via a carbonate precursor route: MnCO3 ellipsoids precursor were first prepared via a facile hydrothermal approach, and treated by KMnO4 and HCl solutions, then a mesoporous intermediate obtained, followed by heat-decomposition at 500 or 700 °C. After mixed with a small amount of carbon nanotubes, Mn2O3@CNTs materials were used as anodes for lithium ion batteries. The sample annealed at 700 °C exhibits a micro-nanostructured architecture which shows superior electrochemical performance, ex., 802 mA h g−1 after 200 cycles at a current density of 200 and 486 mA h g−1 after 1000 cycles at 1000 mA g−1. This long-term cycling performance depends on the micro-nanoscaled structure that mixed excellent with carbon nanotubes which powers electrolyte penetration and Li+ transport.

A series of Ag 2 S/Ag 3 PO 4 composites with well-defined core/shell structures were synthesized via an in-situ anion-exchange reaction between Ag 3 PO 4 dodecahedrons and Na 2 S solutions. The obtained samples were characterized by XRD, BET, AFS, SEM, TEM, EDX, XPS, DRS and PL. The Ag 2 S/Ag 3 PO 4 composites exhibited excellent photocatalytic activity towards the degradation of MO under both visible and NIR light irradiation. The optimal composite Ag 2 S-5%/Ag 3 PO 4 exhibited the highest visible-light-driven activity, which could degrade almost all MO within 120 min. Under NIR light irradiation, the Ag 2 S-50%/Ag 3 PO 4 composite showed the best photocatalytic activity and decomposed more than 30% of MO after 240 min of irradiation. Recycling experiments confirmed that the Ag 2 S/Ag 3 PO 4 composites had superior cycle performance and stability. The photocatalytic activity was highly dependent on the Ag 2 S content and the well-defined core/shell structure. The enhancement in photocatalytic activity of Ag 2 S/Ag 3 PO 4 composites could be mainly ascribed to the efficient separation of photogenerated charge carriers between the intimate interface of Ag 2 S shell and Ag 3 PO 4 core. The in-situ formed Ag nanoparticles at surfaces of Ag 3 PO 4 and Ag 2 S during photocatalytic process acted as charge transmission bridges and electron trapping centers, respectively, resulting in the stable Ag 2 S/Ag/Ag 3 PO 4 Z-scheme system and Ag/Ag 2 S/Ag 3 PO 4 ternary system. Based on the experimental results, the possible photocatalytic mechanisms for MO degradation over Ag 2 S/Ag 3 PO 4 composites under both visible and NIR light irradiation were proposed.

Ag3PO4/In2S3 composite photocatalysts with ultra–low loading of Ag3PO4 (0.017 ∼ 4.89 wt %) were prepared by a facile precipitate method and characterized by XRD, SEM, TEM, HRTEM, BET, DRS and XPS techniques. The as–obtained composites were employed to degrade different kinds of organic pollutants (dyes and colorless pollutants) in aqueous solution under visible light irradiation. The Ag3PO4/In2S3 composites exhibited excellent adsorption capacity and photocatalytic activity. The optimal composite with 0.086 wt % Ag3PO4 content exhibited the highest photocatalytic activity, which could degrade almost all dyes (MO, MB and RhB) within 7 min of light irradiation and more than 50% of phenol and salicylic acid after 3 h of irradiation. Recycling experiments confirmed that the Ag3PO4/In2S3 catalysts had superior cycle performance and structural stability. The photocatalytic activity enhancement of Ag3PO4/In2S3 composites could be mainly attributed to the efficient separation of photogenerated charge carriers through a Z–scheme system composed of Ag3PO4, Ag and In2S3, in which Ag nanoparticles acted as the charge transmission bridge. The high photocatalytic stability was ascribed to the successful inhibition of the photocorrsion of both In2S3 and Ag3PO4 by transferring the photogenerated holes and electrons from them to Ag, respectively. This study indicated the application of Ag–Ag3PO4 as cocatalyst and provided a new way to design and prepare high–efficiency and stable photocatalysts for photocatalytic decontamination of organic pollutants.

Fabrication of heterostructure photocatalysts to improve photocatalytic performance is always a hot topic in the photocatalytic field. In this paper, In2S3/In(OH)3 heterostructure photocatalysts were synthesized via a simple combination of an in situ anion exchange reaction and the hydrothermal process. The obtained heterostructures were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-vis diffuse reflectance spectra (UV-vis DRS) and photocurrent experiment. The photocatalytic activity of the as-formed samples was evaluated by the degradation of methyl orange (MO), salicylic acid and 4-chlorophenol aqueous solution under simulated solar light irradiation (200 nm < λ < 800 nm). The results showed that the photocatalytic activities of In2S3/In(OH)3 heterostructures were greatly improved as compared to single phase In(OH)3 and In2S3. The enhancement in their photocatalytic activity could be attributed to the efficient charge transfer in In2S3/In(OH)3 heterostructures, the improved light absorbance capacity and the increased surface area. As compared, In2S3/In(OH)3 displayed higher photocatalytic activity than In2S3/In2O3 at the same In2S3 content. The excellent activity of In2S3/In(OH)3 with respect to In2S3/In2O3 was mainly due to the high concentrations of ˙O2− radicals and the strong oxidation capacity (h+). The current research provides a new insight into the construction of a narrow-band-gap with a wide-band-gap to form heterostructures as promising and efficient photocatalysts for the removal of harmful organic compounds in aqueous solution.

In this work, a simple thermal annealing route has been developed to improve the photocatalytic performance of silver orthophosphate (Ag3PO4) photocatalyst toward organic pollutants degradation under visible light irradiation. The experimental results indicated that thermal treatment of Ag3PO4 led to an obvious lattice shift towards right and significantly narrowed band gap energies due to the formation of Ag vacancies and metallic Ag during Ag3PO4 decomposition. These structural variations notably affected the photocatalytic performance of Ag3PO4 photocatalysts. The activity of the annealed samples was found to be significantly enhanced toward the degradation of MO dye. The highest activity was observed over the sample annealed at 400 °C, which exceeded that of pristine Ag3PO4 by a factor of about 21 times. By means of photoluminescence spectroscopy and photoelectrochemical measurements, we propose that the enormous enhancement in activity was mainly attributed to the efficient separation of photogenerated electrons and holes driven by the synergistic effect of Ag vacancies and metallic Ag. The strong interaction between annealed particles also inhibited the dissolution of Ag+ from Ag3PO4 into aqueous solution, contributing to an improved photocatalytic stability. The strategy presented here provides an ideal platform for the design of other highly efficient and stable Ag-based photocatalysts for broad applications in the field of photocatalysis.

Visible-light-induced dendritic BiVO4/TiO2 photocatalysts have been successfully synthesized via a composite hydrothermal and sol-gel method. Evaluated by the degradation of methylene blue (MB) under visible-light irradiation (420 nm

Visible-light-induced BiVO4 microspheres with different crystalline phases have been successfully synthesized via simple thermal treatment methods. The photocatalytic activities of the samples were evaluated by the degradation of methylene blue (MB) under visible-light irradiation (420 nm < λ < 800 nm). The results indicated that the BiVO4 sample prepared at 400 °C, which was composed of mixed crystalline phases (tetragonal and monoclinic BiVO4), exhibited the best activity. Through the detection of the degradation mechanism, it was found that the mixed phases availed the transfer of electrons and led to the generation of more kinds and amount of active species in the degradation process. The active species enhanced the photocatalytic activity. These results would be useful to develop highly efficient photocatalysts and helpful to reveal the degradation mechanism clearly.

Ag3PO4 dodecahedrons were post-treated by chemical etching with ammonia solution. The etched samples were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 sorption, UV–vis diffuse reflectance spectra (UV–vis DRS), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma (ICP), photoluminescence (PL) and photocurrent experiments. The SEM results showed that upon ammonia etching, the well-defined Ag3PO4 dodecahedrons changed to hollow polyhedrons with increasing etchant dosage. From the XRD, TEM, DRS and XPS results, it could be inferred that ammonia etching of Ag3PO4 led to an obvious lattice shift and significantly narrowed band gap energies due to the formation of Ag vacancies and metallic Ag. These microstructural variations notably affected the photocatalytic performance of Ag3PO4 photocatalysts. The activity of the etched samples was found to be significantly enhanced toward the degradation of methyl orange (MO) dye under visible light irradiation. The highest activity was observed over the sample etched by 0.15 M ammonia solution, which exceeded that of bare Ag3PO4 by a factor of about 6.2 times. The reasons for the improvement of photocatalytic performance of etched samples may be that the newly formed Ag vacancies and metallic Ag improved the separation efficiency of photogenerated electrons and holes.