Recombination Rate Of Charge Carriers Research Articles

Facile synthesis of 2D nanoflakes and 3D nanosponge-like Ni1−xO via direct calcination of Ni (II) coordination compounds of imidazole and 4-nitrobenzoate: Adsorptive separation kinetics and photocatalytic removal of Amaranth dye contaminated wastewater

This study reports a simple method of direct calcination of Ni (II) coordination compounds with N-donor and O-donor ligands such as imidazole and 4-nitrobenzoate to form 2D and 3D Ni1−xO nanostructures. Controlled calcination of imidazole coordinated compound [Ni(Im)6](4-nba)2.2H2O (I) produced 2D nanoflakes in comparison to 4-nitrobenzoate coordinated compound [Ni(H2O)4(4-nba)2].2H2O which formed Ni1−xO nanosponge. Replacement of four coordinated imidazole ligands in compound I with an equivalent number of 4-nitrobenzoate and water molecules as in [Ni(H2O)2(Im)2(4-nba)2] (II) lead to the collapse of flake-like structure upon combustion with the induction of porosity, confirming the dominant effect of 4-nitrobenzoate ligand to form porous structures of Ni1−xO. Material characterization studies revealed that all Ni1−xO nanostructures exhibit cubic phase wherein increase in surface area, pore-volume, and reduction in particle size from 2D nanoflakes to 3D nanosponge is evident. The adsorptive removal of Amaranth dye as a model pollutant using synthesized Ni1−xO nanostructures exhibited high dye removal efficiency of up to 82.81% in the case of 3D nanosponge. The adsorption process is well explained based on the Sips isotherm model and pseudo-first-order reaction kinetics. Photocatalytic Amaranth dye degradation efficiency of 93.80% in 70 min with highest kapp = 4.04×10−2 min−1 is achieved which is attributed to the high surface area and reduction in charge carrier recombination rate as a result of extensive and robust mesoporous structure.

Layer-by-Layer Titanium (IV) Chloride Treatment of TiO2 Films to Improve Solar Energy Harvesting in Dye-Sensitized Solar Cells

A layer-by-layer titanium (IV) chloride treatment was applied on different layers of TiO2 in dye-sensitized solar cells (DSSCs). The effects were analysed and compared with standard untreated devices. A significant increase in short-circuit current density (JSC) was observed by employing layer-by-layer TiCl4 treatment of TiO2 in DSSCs. This increase of JSC is attributed to the increased inter-particle connectivity and increase in TiO2 nanoparticle size, resulting in better electron transfer and a lower charge carrier recombination rate. The DSSC fabricated with layer-by-layer-treated TiO2 achieved power conversion efficiency of 8.3%, which is significantly higher than the 6.7% achieved for the DSSC fabricated without TiCl4 treatment. Electrochemical impedance spectroscopy (EIS) was performed to assess the better performance of the device fabricated with TiCl4 treatment. Atomic force microscopy and surface roughness were studied to visualize and statistically determine the function of TiCl4 treatment on different layers of TiO2. Transient photocurrent and transient photovoltage measurements were also performed to gain insight into interfacial charge carrier recombination.

Size-dependent effects of ZnO nanoparticles on the photocatalytic degradation of phenol in a water solution

The effect of the ZnO nanoparticles (NPs) size on the photocatalytic degradation of phenol in a water solution under the influence of UV and Vis radiation was discussed. For the first time, research on photocatalytic degradation has used ZnO NPs produced by only one method (microwave solvothermal synthesis without heat treatment or other processes of reduction/oxidisation of the surface of NPs samples). ZnO NPs average size was determined using the Scherrer's formula, Nanopowder XRD Processor Demo web application, by converting the results of the specific surface area-density, and TEM tests. The ZnO NPs (average size between 23 nm and 71 nm) characterise by uniform morphology and narrow size distribution. The photocatalytic performance of ZnO NPs increases with the increase of the particle size and the decrease of the specific surface area. For both UV and Vis radiation, the highest reaction rate for phenol degradation was found for ZnO sample with the average particle size of 71 nm. Low concentrations of resorcine and hydroquinone (co-products of phenol degradation) were found for UV light photocatalytic test. However, high concentrations of hydro- and p-benzoquinone were observed for visible light photoactivity due to the slower decomposition of the main contamination associated with the utilized of other type of radiation. The photocatalytic activity was found to be attributable to the decrease in the charge carrier recombination rate.

Confinement of Quantum Dots in between Monolayered Graphene Nanosheets for Arousing Boosted Multifarious Photoredox Selective Organic Transformation.

Transition metal chalcogenide quantum dots (TMC QDs) represent promising light-harvesting antennas because of their fascinating physicochemical properties including quantum confinement effect and suitable energy band structures. However, TMC QDs generally suffer from poor photoactivities and photostability due to deficiency of active sites and ultrafast recombination rate of photoinduced charge carriers. Here, we demonstrate how to rationally arouse the charge transfer kinetic of TMC QDs by close monolayered graphene (GR) encapsulation via a ligand-dominated layer-by-layer (LbL) assembly utilizing oppositely charged TMC QDs and GR nanosheets as the building blocks. The assembly units were spontaneously and intimately integrated in an alternate integration mode, thereby resulting in the multilayered three-dimensional (3D) TMC QDs/GR ensembles. It was unveiled that multifarious photoactivities of TMC QDs/GR nanocomposites toward versatile photoredox organic catalysis including photocatalytic aromatic alcohols oxidation to aldehydes and nitroaromatics reduction to amino derivatives under visible light irradiation are conspicuously boosted because of spatially multilayered monolayered GR encapsulation which are superior to those of TMC QDs counterparts. The substantially enhanced photoactivities of TMC QDs/GR nanocomposites arise from reasons including improved light absorption and enhanced charge separation efficacy because of GR encapsulation together with unique stacking mode between TMC QDs and GR endowed by LbL assembly. Our work would provide a promising and efficacious route to smartly accelerate the charge transfer kinetic of TMC QDs for solar energy conversion.

Defect-induced visible-light-driven photocatalytic and photoelectrochemical performance of ZnO–CeO2 nanoheterojunctions

The construction of heterojunctions based on metal oxide semiconductors is an emerging approach for enhancing the charge-carrier dynamics of photocatalysts. The current study focuses on building heterojunctions of Zn and Ce oxides to effectively catalyze photoinduced degradation of organic dyes, such as methylene blue (MB). To obtain a suitable ZnO–CeO2 heterojunction, photocatalysts with different Zn:Ce ratios of 3:1, 1:1, and 1:3 were synthesized using a hydrothermal method. The optimized ZnO–CeO2 heterojunction with a 1:1 ratio exhibited superior photocatalytic performance for MB degradation under solar and visible-light irradiation. This can be ascribed to the formation of oxygen vacancies with suitable trap levels induced by the readily interconvertible Ce3+/Ce4+ ions in CeO2. Owing to its low rate of charge-carrier recombination and enhanced photoinduced charge-carrier lifetime, the rate of MB degradation using the optimized photocatalyst was 6.4 times that using pristine ZnO under visible-light illumination. Moreover, photoelectrochemical analysis demonstrated that the optimized catalyst exhibited a significant visible-light response with a high charge-carrier separation efficiency. Thus, such ZnO–CeO2 heterojunctions with improved visible-light-driven photocatalytic and photoelectrochemical properties can be potentially used for wastewater treatment and other catalytic applications.

High visible light photocatalytic activities obtained by integrating g-C3N4 with ferroelectric PbTiO3

Graphitic carbon nitride (g-C3N4) with the merits of high visible light absorption, proper electronic band structure with high conduction band edge and variable modulation, is viewed as a promising photocatalyst for practical use. To alleviate its high recombination rate of photo-excited charge carriers and maximize the photocatalytic performances, it is paramount to design highly effective transfer channels for photo-excited charge carriers. Ferroelectric materials can have the charge carriers transport in opposite directions owing to the internal spontaneous polarization, which may be suitable for constructing the heterostructure with g-C3N4 for efficient charge separation. Inspired by this concept, herein ferroelectric PbTiO3, which can be the visible-light absorber, is coupled with g-C3N4 to construct PbTiO3/g-C3N4 heterostructure with close contact via Pb–N bond by the facile post thermal treatment. The optimized PbTiO3/g-C3N4 heterostructure exhibited excellent photocatalytic and photoelectrochemical activities under visible light irradiation. Moreover, the simultaneous application of ultrasound-induced mechanical waves can further improve its photocatalytic activities through reinforcing the built-in piezoelectric field. This work proposes a widely applicable strategy for the fabrication of high-performance ferroelectric based photocatalysts and also provides some new ideas for developing the understanding of ferroelectric photocatalysis.

Facile green synthesis of fingernails derived carbon quantum dots for Cu2+ sensing and photodegradation of 2,4-dichlorophenol

The present study reports a facile method to prepare carbon quantum dots (CQDs) via hydrothermal treatment using human fingernails as a green precursor. Fingernails derived CQDs (FN-CQDs) could selectively detect copper ions (Cu2+) at the concentration as low as 1 nM. Different weightage of FN-CQDs (30 wt%, 40 wt% and 50 wt%) were coupled with pure graphitic carbon nitride (g-C3N4) to remove 2,4-dicholorophenol (2,4-DCP) under sunlight irradiation. The composite loaded with 50 wt% of FN-CQD removed 100 % of 2,4-DCP in 75 min, which was almost 2 times higher than g-C3N4. The photocatalytic performance was in agreement with ultraviolet–visible diffuse reflectance spectra (UV–vis DRS) in which the photosensitizing effect was significantly exerted by 50 wt% of CQDs. In the presence of FN-CQDs, g-C3N4 was sensitized by sunlight with an average light intensity of ∼ 937 × 100 lx to donate more electrons for the generation of oxidizing radicals. Excessive loading of FN-CQDs (up to 50 wt%) created trap state that decreased the charge carrier transport in FN-CQDs/g-C3N4(50). Such drawbacks did not affect the overall performance of FN-CQDs/g-C3N4(50). The higher loading of FN-CQDs exerted stronger photosensitizing effects to overcome the limitation of high recombination rate of charge carriers and lower surface area. FN-CQDs could act as photosensitizer to increase the light absorption range to generate more electron and holes. It also served as electron reservoir for the reduction of oxygen molecule to produce superoxide anion radical (O2−). Scavenging tests identified that O2− was the most active radical in the photodegradation of 2,4-DCP.

Modulation of 2D GaS/BTe vdW heterostructure as an efficient HER catalyst under external electric field influence

Modeling the 2D Van der Waals (vdW) heterostructure photocatalysts is an effective way to take advantage of solar energy and suppressing the fast recombination rate of photo-generated charge carriers. In the present work, we have systematically investigated the electronic, optical and photocatalytic properties of the GaS/BTe vdW heterostructure under an applied external electric field using first-principles calculations. Our results reveal that the GaS/BTe vdW heterostructure has an indirect band gap of 1.06/1.59 eV with PBE/HSE06 functional without electric field. The results also imply that electrons are likely to transfer from GaS to BTe monolayer due to the deeper potential of BTe monolayer. The GaS/BTe vdW system forms a type-II band alignment and established a large electric field at the interface, controlling to effective separation of the electron–hole pairs. Also, the transverse external electric considerably changes the band gap and transform from type-II to type-I and type-III band alignments. The GaS/BTe vdW heterostructure, also enhanced the optical absorption as compared to pristine GaS and BTe monolayer. Furthermore, the (−)ve electric field significantly increases the optical absorption spectrum in infrared (IR) to visible region, while the (+)ve electric field enhances the optical absorption coefficients in visible to ultraviolet (UV) region. The external transverse electric field enhances the hydrogen evolution reaction (HER) activity on the 2D vdW heterostructure. These obtained results predict that the 2D GaS/BTe vdW heterostructures carry potential applications to enhancing the photocatalytic performance under visible light irradiation.

Fabrication of centimeter-sized Sb2S3/SiO2 monolithic mimosa pudica nanoflowers for remediation of hazardous pollutants from industrial wastewater

Photocatalysis using ‘easy-to-separate’ metal-oxide/sulfide monoliths is a promising method to tackle the grievous issue of water pollution. Here, ‘mimosa pudica’ flower-like Sb2S3/SiO2 monoliths were prepared by impregnation of antimony chloride solution in silica monoliths followed by treatment with potassium thiocyanate, refluxing and calcination. The nanoflower-like morphology of the synthesized monoliths was verified using field emission scanning electron microscope images. The Brunauer–Emmett–Teller model for surface area analysis showed that monoliths had a high surface area of 83 m2/g with mesopore diameter of 13.61 nm. The purity/crystallinity and the elemental state of the sulfide were confirmed using X-ray diffraction analysis and X-ray photon spectroscopy whereas energy dispersive spectroscopy verified the homogeneous elemental distribution of the catalyst. The diffuse reflectance spectroscopy and photoluminescence spectroscopy confirmed that Sb2S3/SiO2 monoliths had a narrow band gap (∼1.57 eV) and low recombination rate of photoinduced charge carriers. Thermal stability of the materials was also investigated by thermogravimetric analysis. The photocatalytic performance of monoliths was examined by photodegradation of model pollutants methylene blue (MB) and thiamethoxam (TM). At optimum pH and catalyst-concentration, monoliths exhibited best efficiency (with high rate-constant) in sunlight for degradation of MB (96%; 0.018 min−1) and in UV light for degradation of TM (70%; 0.0057 min−1). The catalyst was reused for four cycles for degrading MB (∼71% efficiency). A comparative study with reported literature data confirmed the superiority of the monoliths for MB degradation. The trapping experiments indicated that superoxide anion radicals and holes had a dominant role in the MB and TM degradation, respectively. MB was mineralized almost completely exhibiting ∼99.7% removal of total organic carbon (TOC). The photocatalytic treatment of industrial wastewater revealed ∼97% TOC- removal besides ∼92% removal of chemical oxygen demand. It validated that this photocatalyst is better than physicochemical treatment done by industries. This monolithic catalyst can indeed be advantageous for the remediation of perilous contaminants from a practical viewpoint.

RETRACTED: Atomic layer deposition of Cu2O on NH2-MIL-101(Fe) for enhanced photocatalytic performance and decreased electron/hole recombination

Coupling appropriate semiconductor nanoparticles with massive surface-area support has become a promising but challenging strategy to photocatalyst design for enhanced photocatalytic activity in environmental cleaning applications, owing to the severe aggregation issues of nanoparticles. Herein, the atomic layer deposition (ALD) approach was applied to uniformly disperse ultrafine Cu 2 O nanoparticles (5–10 nm) on metal-organic frameworks without aggregation, forming NH 2 -MIL-101(Fe)/Cu 2 O nanocomposite photocatalysts. The Cu 2 O mass within the nanocomposites can be well controlled by merely adjusting the ALD cycles. The optimal NH 2 -MIL-101(Fe)/Cu 2 O displays a high photodegradation efficiency of 92% for RhB and excellent stability under visible light. The reaction kinetics and photocurrent response experimental results reveal that the optimal NH 2 -MIL-101(Fe)/Cu 2 O photocatalyst exhibits effective charge separation/transfer and suppressed recombination rate of charge carriers, which will significantly increase the solar light utilization efficiency and photocatalytic activity. We believe the presented photocatalyst synthesis strategy here can be generalized to construct other photocatalysts for various photocatalytic applications.

Synergetic catalytic behavior of dual metal-organic framework coated hematite photoanode for photoelectrochemical water splitting performance

The performance of oxide photoanodes constructed with hematite (Fe2O3) nanostructures is among the best for low-cost photoelectrochemical water-splitting cells. However, due to limited light absorption capacity, a high photogenerated charge carrier recombination rate, and sluggish surface oxygen evolution reaction (OER) kinetic on the surface, the photocurrent density generated by bare hematite is lower than the theoretical value. To overcome these limitations, we fabricate hematite photoanodes with a dual metal–organic framework (MIL-88B@ZIF-67) coating, which greatly enhances light harvesting efficiency and the intrinsic charge carrier transport rate. Owing to these spectacular advantages, the optimized Fe2O3/MIL-88B@ZIF-67 photoanode affords a stable photocurrent density of 2.52 mA∙cm−2 at 1.23 V vs. a reversible hydrogen electrode (RHE) under one sun irradiation. The photocurrent density is significantly higher than that achieved with a bare Fe2O3 photoanode (0.27 mA∙cm−2). Most importantly, the cathodic shift of the Fe2O3/MIL-88B@ZIF-67 photoanode (119 mV) is larger than that of pristine Fe2O3. The measured incident photon-to-electron conversion efficiency of the Fe2O3/MIL-88B@ZIF-67 photoanode reaches 30.85% at 330 nm. A photocurrent decay of only 5% over 20 h indicates that the photoanode is also extraordinarily stable. We find that it is crucial to precisely control the number of MIL-88B@ZIF-67 coating layers to reduce the charge carrier recombination rate. We expect that our approach will be effective for the design of efficient and stable photoanodes for PEC water splitting.

Sandwich template derived porous ZnO@gCN heterostructure nanocomposites and the enhanced photocatalytic efficiency in oxidative coupling of amines

Abstract The construction of heterostructure composites is an efficient way to widen the spectral response range and reduce the photogenerated electrons-holes recombination, but it is still a challenge to realize the maximizing the photocatalytic performance of different photoresponsive material, especially at low temperature. In this work, we construct a series of ZnO@gCN-UA/MA composites by first designing a series of UA@ZIF-8@MA sandwich templates and then calcining these sandwich templates at high temperature. During the pyrolysis process, ZIF-8 and melamine precursors would convert into ZnO and gCN structure so as to form the ZnO@gCN composite at high temperature, while urea molecular would decompose to release ammonia molecules which rush out from the interior of ZIF-8 to make the ZnO@gCN-UA/MA composites become fluffy and porous. Detailed characterization results reveal that the ZnO@gCN-UA/MA composites exhibit enhanced spectral response range and the lower charge-carrier recombination rates. When being used in photocatalytic oxidative coupling of amines at low temperature under air condition, the optimal ZnO(0.1)@gCN-UA/MA catalyst exhibits excellent activity, affording the imine product with 96% yield. Moreover, the catalysts also exhibit a wide substrate compatibility and recyclability.

Physicochemical and electrochemical characterization of CdO/g-C3N4 nanocomposite for the photoreforming of petrochemical wastewater

Abstract Current research involved fabrication of cadmium oxide-graphitic carbon nitride (CdO/g-C3N4) nanocomposite and evaluation of their photocatalytic properties by physical and electrochemical analysis techniques. The X-ray diffraction (XRD) test demonstrated that the nanocomposite consists of graphite and monteponite phases. UV–Vis absorption and photoluminescence (PL) analysis clearly pointed out both the band gap reduction and inhibition in recombination rate of charge carriers. Based on the photoelectrochemical (PEC) analysis, linear sweep voltammetry (LSV) data demonstrated that CdO/g-C3N4 nanocomposite shows higher anodic current (0.57 mA/cm2) under light emission as compared to dark environment (0.02 mA/cm2). This study was also deliberated with proposed mechanism on photoreforming of wastewater reaction scheme.

Surface Plasmon response of Pd deposited ZnO/CuO nanostructures with enhanced photocatalytic efficacy towards the degradation of organic pollutants

Herein, we have synthesized novel noble metal Pd deposited ZnO/CuO (8:1) nano-composites using simple single step deposition method with different weight percentage. The morphological, structural, elemental and optical characteristics of synthesized materials were uncovered by using different techniques such as FESEM, TEM, XRD, XPS and UVDRS. The synthesized materials are highly crystalline in nature. To evaluate the degradation efficacy of synthesized nano-composite materials, two organic pollutants; rhodamine B and triclopyr, are taken into account. The complete degradation of RhB and TCP is observed in 20 and 60 min. The nano-composite with 2% Pd shows highest efficacy towards the photodegradation of pollutants. The better photodegradation efficacy of synthesized nano-composite materials is attributed to appropriate amount of Pd deposition which helps in shifting the absorption towards NIR region and efficiently reduces the recombination rate of charge carriers.

Application of nanostructured aluminium titanate (Al2TiO5) photocatalyst for removal of organic pollutants from water: Influencing factors and kinetic study

In this study, aluminum titanate (Al2TiO5)-based nanostructure with the outstanding photocatalytic performance was prepared via the simple citrate sol-gel method. The effects of thee operational variables such as pH, temperature, catalyst dosage, and initial dye concentration on the photodegradation efficiency of methylene blue (MB) were explored in some details. The results showed that compared to TiO2, AT benefits a superior photocatalytic activity due to its narrow band gap (2.88 eV) and low recombination rate of charge carriers. Increasing the wastewater temperature from 25 to 60 °C can improve the degradation percent from 22.15 to 52%. Based on the thermokinetic calculations, the Arrhenius activation energy, ΔH, and ΔS values were also estimated as +24.69 kJ mol−1, 21.78 J mol−1, and 222.48 J K−1.mole−1, respectively. According to the Langmuir-Hinshelwood kinetic model, the photocatalyst follows a first-order equation in a wide range of temperatures. In addition, escalating the pH value from 4 to 9.5 may noticeably enhance the photodegradation efficiency from 7.1 to 46.6%. The enhanced photocatalytic activity at alkaline media was mainly attributed to the excessive generation of hydroxyl ions, improved adsorption of cationic dye on the catalyst surfaces, and effective separation of involved charge carriers. The maximum performance was obtained for the AT dosage of 20 mg/lit and MB concentration of 2.5 mg/lit. Finally, the recycling experiments after 6 runs verified the high stability of the photocatalyst.

Sunlight-driven photocatalytic degradation of rhodamine B dye by Ag/FeWO4/g-C3N4 composites

A wide range of processes have been adopted for environmental remediation; among them, photocatalysis appeared as an appealing strategy for degradation of organic pollutants. Heterogeneous photocatalysis efficiently dissociates the charge carriers and helps in reducing the rapid recombination rate of charge carriers resulting in enhanced photocatalytic degradation. A semiconductor photocatalyst graphitic carbon nitride (g-C3N4), when doped with metals or non-metals, showed increased degradation abilities. Hence, a ternary photocatalyst was synthesized by thermal condensation of urea coupled with ferric tungstate (FeWO4) and doped with a noble metal (Ag) resulting in visible light susceptive semiconductor photocatalyst Ag/FeWO4/g-C3N4. The characterization of the fabricated composite was done by Fourier transform infrared, scanning electron microscopy energy-dispersive X-ray, and X-ray diffraction. The Ag/FWO/GCN was used to degrade the rhodamine B (RhB) dye. Under sunlight, Ag/FeWO4/g-C3N4 showed enhanced photocatalytic degradation of rhodamine B dye, which was ascribed to the change in bandgap and reduced charge recombination. The parameters used for the optimization of the photocatalyst were pH, catalyst dose, oxidant dose, and irradiation time. The composite (Ag/FeWO4/g-C3N4) showed ~ 98% degradation of RhB dye under optimized conditions (i.e., pH = 8, catalyst dose = 50 mg/100 ml, oxidant dose = 9 mM, irradiation time = 120 min and RhB conc. 50 ppm).

Robust water splitting on staggered gap heterojunctions based on WO3∖WS2–MoS2 nanostructures

Abstract The high charge carrier recombination rate and weak oxygen evolution kinetics have impeded the efficiency of WO3 photoelectrodes for water splitting. We present a novel type II heterojunction semiconductor based on mixed WS2 and MoS2 nanosheets on WO3 nanoflakes hydrothermally grown on highly porous W skeletons. The chemically exfoliated transition metal dichalcogenide (TMD) sheets with submicrometric lateral sizes were deposited on the surface of WO3 nanoflakes by the electrophoretic technique to fabricate a staggered gap heterojunction. The photoanode exhibited an impressive current density of 14.9 mA cm−2 at 1.23 VRHE which comprised ∼1.7 mA cm−2 photocurrent under 100 mW cm−2 simulated sunlight. Co-deposition of MoS2 and WS2 sheets on WO3 nanoflakes improved the current density of porous W∖WO3 electrodes by about 340%, while only about 36% improvement is achieved by deposition of single TMD (WO3∖MoS2 or WO3∖WS2) demonstrating the synergetic effects of TMDs. The high stability of the photoanode in highly acidic media is shown. The synergetic effects of TMDs on active sites, charge transfer resistance, and charge transport properties are elaborated by electrochemical impedance spectroscopy and Mott-Schottky analyses. The composite electrode has a great potential to be used for diverse electrochemical applications including water splitting.

Exploring the mechanism of Ta3N5/KTaO3 photocatalyst for overall water splitting by first-principles calculations

Abstract The rational fabrication of heterostructures is one of efficient strategies for improving photocatalytic performance of semiconductor photocatalysts. Very recently, Domen and co-workers found that Ta3N5 single crystals grown on the surface of KTaO3 can accomplish photocatalytic overall water splitting for the first time. In order to comprehend the underlying mechanism of this photocatalytic system, we have performed a systematic study based on density functional theory first-principles calculations. Ta3N5(010)/KTaO3(110) slab models have been built according to experimental observations by considering two common terminations of KTaO3(110) surface, named as Ta3N5/O2 and Ta3N5/KTaO. The formations of interfacial bonds are thermodynamically stable, showing a covalent interaction between two components of a heterostructure. Ta3N5/O2 has a higher mobility of photogenerated charge carriers and lower recombination rate of charge carriers than Ta3N5/KTaO. The light absorption of heterostructures displays the feature of KTaO3 in the short wavelength region and the characteristic of Ta3N5 in the long wavelength region. The calculated band offsets show that Ta3N5/O2 and Ta3N5/KTaO have distinct Type-II band alignments, with Ta3N5 as the accumulator of photoinduced electrons in the former and the collector of photogenerated holes in the latter, respectively. The difference in charge density and electrostatic potential between two components acts as a driving force to promote the transfer of electrons and holes to different domains of the interface, which is beneficial to extend the lifetime of photoinduced carriers. Our results demonstrate that the function of Ta3N5 in Ta3N5/KTaO3 photocatalytic system is determined by the termination property of KTaO3(110) surface, which provides a likely reason of the observed photocatalytic activity of overall water splitting achieved by Ta3N5 synthesized by using KTaO3 as a precursor for the nitridation reaction.

The Measurement of Charge Carrier Lifetime in SIGaAs: Cr and EL2-GaAs by Pump-Probe Terahertz Spectroscopy

In the present work, the temporal dynamics of relaxation of a nonequilibrium concentration of charge carriers in SI-GaAs:Cr and EL2-GaAs semiconductor crystals has been studied using pump-probe terahertz spectroscopy. The obtained experimental data were analyzed taking into account the mechanisms of surface and bulk Shockley–Reed–Hall recombination, radiative recombination, interband and trap assisted Auger recombination. It was found that at injection levels arising upon excitation of samples by laser radiation with a pulse duration of 35 fs and an energy of 0.1 mJ per pulse at a central wavelength of 791 nm, Auger recombination mechanisms have a significant effect. Auger recombination mechanisms make a dominant contribution to the recombination rate of nonequilibrium charge carriers at injection levels above 2·1018 cm–3 for SI-GaAs:Cr and above 1018 cm–3 for EL2-GaAs. At lower injection levels, the bulk and surface Shockley-Reed-Hall recombination are the dominant recombination mechanisms.

Influence of SnO2 concentration on electrical response of α-Fe2O3 sintered with different thermal history conditions

Hematite (α-Fe2O3) has been investigated as a promising material for the development of renewable energy technologies. However, intrinsic poor electrical conductivity and fast charge–carrier recombination rate of α-Fe2O3 are the limiting factors for such applications. A suitable approach to overcome these limitations is the insertion of electron-donor species into the α-Fe2O3 structure. This study describes the effects of incorporating SnO2 with different thermal histories on the electrical properties of α-Fe2O3. The sintering temperature at 1300 °C was responsible for a significant increase in the average grain sizes compared to the samples sintered at 1100 °C. Lower resistivity values were observed in samples obtained at 1100 °C with 2.0 wt% SnO2. As such, SnO2 was found to be an excellent modifying agent to favor the overall α-Fe2O3 electrical conductivity. Solid-state impedance spectroscopy was adopted as a versatile tool to analyze the occurrence of preferential grain boundaries for electrical current flow.