Hole Charge Carriers Research Articles

(Invited) Polaronic Transport in Iron Oxides from Density Functional Theory

Iron oxides such as hematite (α-Fe2O3) play an important role in diverse fields ranging from biogeochemistry to photocatalysis. In the majority of these cases their electrical properties are key because they facilitate electron transfer reactions occurring at their interfaces. The iron oxides tend to be wide band gap semiconductors with a narrow d band. Consequently, electron and hole charge carriers localize by self-trapping to form polarons, carriers whose mobilities are tied to the lattice distortions they create. Site-to-site polaron transport is thermally activated and the rate depends on the energy to reorganize the local structure into a suitable transition state, as well as the strength of the electronic coupling in that transient configuration. In turn, these depend on factors that determine the atomic and electronic structure, including crystallographic direction.Because the structure of polarons, the reorganization energy, and the electronic coupling matrix element are not readily experimentally accessible, quantum mechanical calculations have been extraordinarily useful. However, this also means that the accuracy of predicting polaronic charge carrier mobilities depends strongly on the computational method used. In the ~20 years since the first application of ab initio cluster model computations to this topic for hematite, both the methodological rigor and the supporting computational power have greatly advanced. After a brief historical overview, this talk will highlight current findings obtained with gap-optimized hybrid density functional theory with periodic boundary conditions performed on massively parallel supercomputers. Comparisons will be made to the original calculations for hematite published in 2003. The DFT-based predictions for other iron oxide phases will also be discussed.Specifically, we will present calculations of both the electron and hole polaron structures and associated reorganization energies for the bulk of hematite, lepidocrocite (γ-FeOOH), goethite (α-FeOOH) and white rust (Fe(OH)2).1 Through the use of gap-optimized hybrid functionals and large supercells under periodic boundary conditions, we remove some of the complications and uncertainties present in earlier cluster model calculations. It is found that while the hole polaron in these materials generally localizes onto a single iron site, the electron polaron delocalizes across two iron sites of the same spin layer as a consequence of the lower reorganization energy for electrons compared to holes. An exception to these trends is the hole of goethite, which according to our calculations does not form a localized polaron.For hematite,2 we find that upon ionization the hole relaxes from a delocalized band state to a polaron localized on a single iron atom with localization induced by tetragonal distortion of the six surrounding iron-oxygen bonds. This distortion is responsible for sluggish hopping transport in the Fe-bilayer, characterized by an activation energy of 70 meV and a hole mobility of 0.031 cm2/(V s). By contrast, the excess electron induces a smaller distortion of the iron-oxygen bonds resulting in delocalization over two neighboring Fe units. We find that 2-site delocalization is advantageous for charge transport due to the larger spatial displacements per transfer step. As a result, the electron mobility is predicted to be a factor of three higher than the hole mobility, 0.098 cm2/(V s), in qualitative agreement with experimental observations.The advances made on the theory and simulation front have provided increasing insight into the nature of polaronic transport in the iron oxides, and the methods have been widely duplicated successfully to a variety of materials. However, there is tremendous room for expansion of the work to treat the more challenging aspects governing iron oxide behavior in natural systems and in device application, including the role of interfaces, surface potential, and defects to name a few. Theoretical computations seem poised now more than ever to help unlock the fundamental insight into charge carrier transport in polaronic materials needed to understand and adapt their electrical transport properties. References Ahart C.S., Blumberger J., Rosso K.M. (2020) Polaronic structure of excess electrons and holes for a series of bulk iron oxides. Physical Chemistry Chemical Physics, 22, 10699-10709.Ahart C.S., Rosso K.M., Blumberger J. (2022) Electron and hole mobilities in bulk hematite from spin-constrained density functional theory. Journal of the American Chemical Society, 144, 4623-4632.

Thermal-evaporation-deposited CsCu2I3 films with self-trapped excitons for electrically driven yellow light-emitting diodes

Ternary copper halide CsCu2I3 has shown tremendous potentials in addressing the lead toxicity and instability issues of lead-based perovskites light-emitting diodes (LEDs) toward practical applications. However, the development of CsCu2I3-based LEDs still faces great challenges due to the difficulties in fabricating high-quality CsCu2I3 films and designing well-matched device configurations caused by the inherent wide bandgap. Herein, a thermal evaporation technique conjunction with post-annealing treatment was employed to fabricate high-quality CsCu2I3 films, which show a dense and smooth morphology, an excellent heat/ultraviolet light/moisture/oxygen stability, and a bright broadband yellow emission centered at 550 nm. Temperature-dependent photoluminescence and femtosecond transient absorption spectroscopy measurements indicate that the broadband emission with large Stokes shifts of CsCu2I3 films originates from self-trapped excitons-related recombination. Furthermore, a stepwise “energy ladder” hole transport layer of PEDOT:PSS/Poly-TPD/PVK was applied in CsCu2I3-based LEDs to improve the hole injection and charge carrier recombination, leading to an increased device performances. By collaborative optimization, a yellow LED emitting at 550 nm with a peak luminance of 219.6 cd/m2, an external quantum efficiency of 0.49 %, and a half-lifetime of 48.5 min is realized, providing a new idea for the development of environmental-friendly LEDs based on copper halide systems.

Ferroelectricity modulates polaronic coupling at multiferroic interfaces

Physics of the multiferroic interfaces is currently understood mostly within a phenomenological framework based on screening of the polarization field and depolarizing charges. Additional effects still unexplored are the band dependence of the interfacial charge modulation and the associated changes of the electron-phonon interaction, coupling the charge and lattice degrees of freedom. Here, multiferroic heterostructures of the colossal-magnetoresistance manganite La1-xSrxMnO3 buried under ferroelectric BaTiO3 and PbZrxTi1-xO3 are investigated using soft-X-ray angle-resolved photoemission. The experimental band dispersions from the buried La1-xSrxMnO3 identify coexisting two-dimensional hole and three-dimensional electron charge carriers. The ferroelectric polarization modulates their charge density, affecting the coupling of the 2D holes and 3D electrons with the lattice which forms large Fröhlich polarons inherently reducing mobility of the charge carriers. Our k-resolved results on the orbital occupancy, band filling and electron-lattice interaction in multiferroic oxide heterostructures modulated by the ferroelectric polarization disclose most fundamental physics of these systems needed for further progress of beyond-CMOS ferro-functional electronics.

The Hall current effect of magnetic-optical-elastic-thermal-diffusive semiconductor model during electrons-holes excitation processes

In this work, a theoretical electrons and holes interaction model in semiconductors is studied. This mathematical-physical model is described during an optical-elastic-thermal-diffusion (OETD) process when the medium is excited by photo-energy due to high temperatures. The effect of the Hall current associated with the fall of a strong magnetic field on the outer surface of the semiconductor medium is studied. The density of magnetic flux due to the magnetic field causes a Hall effect. The governing equations are taken into one dimensional (1D) in the context of electronics-thermal-elastic deformation. To illustrate that the Laplace transform with initial conditions of the dimensionless main physical fields is used. The general linear solutions for the charge carrier holes and electrons, strain, and thermal distributions are obtained mathematically in the Laplace domain. Some thermal, mechanical, and optical conditions are taken at the free surface of the semiconductor with the Laplace inverse approximate technique numerically to obtain the complete solutions of the main physical fields in the time domain. The Hall current effect and influence of thermal relaxation times according to photo-thermoelasticity theory are presented graphically and discussed for silicon material.

Photocatalytic degradation activity of goji berry extract synthesized silver-loaded mesoporous zinc oxide (Ag@ZnO) nanocomposites under simulated solar light irradiation

Different approaches have been developed for the synthesis of various nanostructured materials with unique morphologies. This study demonstrated the photocatalytic and antimicrobial abilities of silver-loaded zinc oxide nanocomposites (Ag@ZnO NCs). Initially, ZnO with a unique mesoporous ellipsoidal morphology in the size range of 0.59 ± 0.11 × 0.33 ± 0.09 µm (length × width) was synthesized using aqueous precipitation in a mild hydrothermal condition (80 °C) with the aqueous fruit extract of goji berry (GB) (as an additive) and calcined in air at 200 °C/2 h and 250 °C/3 h. Powder X-ray diffraction (XRD) revealed the formation of a hexagonal phase of the wurtzite (WZ) structure. The average crystallite size of ZnO was 23.74 ± 4.9 nm as calculated using Debye–Scherrer’s equation. It also possesses higher thermal stability with the surface area, pore volume, and pore size of 11.77 m2/g, 0.027 cm3/g, and 9.52 nm, respectively. Furthermore, different mesoporous Ag@ZnO NCs loaded with face-centered cubic (fcc) silver nanoparticles (Ag NPs) in the range of 90–160 nm were synthesized by GB extract as a reducing and capping agent on the surface of ZnO after calcination in air. The immobilization of Ag NPs was confirmed by XRD, X-ray photoelectron spectroscopy (XPS), field-emission scanning electron microscopy (FE-SEM), FE-transmission electron microscopy (FE-TEM), and energy-dispersive X-ray spectroscopy (EDS). It was found that Ag0.2@ZnO NC (0.2 wt% of Ag) showed excellent photocatalytic degradation of both methylene blue (MB) (cationic) and congo red (CR) (anionic) dyes under simulated solar irradiation. The photocatalytic degradation of 99.3 ± 0.35% MB and 98.5 ± 1.3% CR occurred in 90 and 55 min, respectively, at room temperature by Ag0.2@ZnO NC. Besides, these NCs also showed broad-spectrum antibacterial activity against both Gram-positive and Gram-negative bacteria. The mechanistic concept of generating reactive oxygen species (ROS) by electron and hole charge (e‾/h+) carriers seems to be responsible for the photocatalytic degradation of commercial dyes and antibacterial activities by Ag@ZnO NCs. Thus, these silver-loaded mesoporous ellipsoidal ZnO NCs are promising candidates as photocatalysts for industrial/wastewater treatment as well as in antimicrobial therapeutics.

Investigation on transport property of heterostructure in Bi/Bi2Sr2CaCu2O8+δ composite film

The heterostructure of bismuth (Bi) and Bi2Sr2CaCu2O8+δ (Bi2212) is considered as a potential type of quantum material. The strain-engineering controls the band structure in the composite films, which is applied in the high-temperature quantum spin Hall materials. In this work, Bi/Bi2212 composite film is synthesized using a two-step method to reduce the fabrication cost. The microstructure and transport properties of the composite films are characterized and analyzed. Experimental results demonstrate that the Bi/Bi2212 composite film obtains the high-quality crystallinity and excellent connectivity. The transport property measurement results show that the band structure changes due to the coupled effects of the strain and electric field. The origin is the compensation between the electron and hole charge carriers. The above band gap change leads to a shift in the metal-semiconductor transition temperature. Functionally coupled composite films exhibit new properties in magnetoresistance devices.

A brief review of nanoparticles-doped PEDOT:PSS nanocomposite for OLED and OPV

Abstract In recent years, several strategies have been proposed and demonstrated to enhance the efficiency of organic light-emitting diodes (OLEDs) and organic photovoltaics (OPVs). In both types of devices, poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is commonly used to enhance hole injection. The layer is further designed by incorporating metallic-based, carbon-based, organic, inorganic, and hybrid nanoparticles with the aim of improving the performance and hence the efficiency through the improvement of light out-coupling in OLEDs and enhancement in light absorption generation of hole-charge carriers in OPVs. This review elucidates the use of different types of nanoparticles that are doped into PEDOT:PSS and their effects on OLEDs or OPVs. The effects include surface plasmon resonance (SPR), scattering, better charge transport, improvement in surface morphology and electrical properties of PEDOT:PSS. Promising results have been obtained and can potentially lead to low cost, large-area manufacturing process.

High-Efficiency and Stable Perovskite Photodetectors with an F4-TCNQ-Modified Interface of NiOx and Perovskite Layers.

Nickel oxide (NiOx), a typical p-type semiconductor, is emerging as the most promising hole transport layer material. However, the inferior interfacial contact of the NiOx/perovskite interface has limited the improvement of the performance of photodetectors (PDs). In this work, 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ) is introduced to modify the NiOx/perovskite interface to prepare high-performance PDs. This study shows that the F4-TCNQ layer interacts with the NiOx/perovskite layers. It can increase the Ni3+/Ni2+ ratio and then enhance the hole extraction and charge carrier mobility; on the contrary, it can form a new Lewis adduct and passivate the undercoordinated Pb2+ ions. Furthermore, with the F4-TCNQ modification, the perovskite film exhibits good thermal stability and photostability. The PDs demonstrate excellent photoelectric properties and long-term stability in the atmosphere. This finding provides a simple and efficient way to further develop the NiOx/perovskite interface.

Crystallization Regulation and Morphological Evolution for HTM‐free Tin‐Lead (1.28eV) Alloyed Perovskite Solar Cells

There have been huge achievements of all‐perovskite tandem solar cells, which recently realized the highest power conversion efficiency of 24.8%. However, the complex device structure and complicated manufacture processes severely restrict the further development of all‐perovskite tandem solar cells. In this work, we successfully fabricated high‐efficiency hole transport material‐free (HTM‐free) Sn−Pb alloyed narrow bandgap perovskite solar cells (PSCs) by introducing guanidinium thiocyanate (GASCN) and hydroiodic acid (HI) into the perovskite precursor solution. GASCN and HI play a positive synergy effect during perovskite crystallization process resulting in larger grain size, fewer surface defects, and lower trap density to suppress the Sn2+ oxidation degradation. Furthermore, they could effectively adjust the energy level of perovskite materials, reduce the energy level difference between perovskite and ITO resulting in more efficiently transport of free hole charge carriers. As a result, with adding GASCN and HI, the achieved highest power conversion efficiency of HTM‐free devices increased from 12.58% to 17.85%, which is one of the highest PCEs among all values reported to date for the HTM‐free narrow‐bandgap (1.2–1.4 eV) Sn−Pb binary PSCs. Moreover, the optimized device shows improved environmental stability. Our additive strategy manifests a remarkable step towards the facile, cost‐efficient fabrication of HTM‐free perovskite‐based tandem solar cells with both high efficiency and simple fabrication process.

An unreported peak of the electroluminescence turn-on transience from OLEDs with electron or hole potential well

An unreported peak was discovered at the transient electroluminescence (TEL) rising edge from pure emission layer (EML) based OLEDs with an energy potential well for electron or hole charge carriers. A series of control experiments indicated that the formation mechanism of this peak is completely different from the already-reported peak originated from exciton interactions such as singlet-triplet and triplet-triplet annihilations. Herein, the peak at the TEL rising edge is generated by the radiative recombination of injected carriers with pre-stored charges in the energy potential well. Surprisingly, for the pure EML-based OLEDs with simultaneous electron and hole potential wells, the peak at the TEL rising edge disappeared, and contrarily, a super-high spike was observed at the TEL falling edge. Such an already-reported spike at the TEL falling edge was considered to only appear in doped-EML systems. This contradiction leads to the reconsideration for the formation mechanisms of the spike at the TEL falling edge. Accordingly, this work not only deepens the physical understanding of the unprecedented peak at the TEL rising edge and the already-reported spike at the TEL falling edge, but also reveals the effects of the energy potential well on the carrier recombination process in OLEDs.

Photo–elasto–thermodiffusion waves of semiconductor with ramp-type heating for electrons–holes-coupled model with initial stress

This article introduces mathematical, theoretical physics model when the interaction between the electrons and holes for the semiconductor medium is investigated. The model is studied in the generalized elasto-thermodiffusion (ETD) theory with the initial stress impact during the photothermal (PT) excitation. The governing equations give a detailed account of a one-dimensional (1D) thermoelastic (TD) and electronic(ED) deformation. The basic equations are obtained for the elastic medium without dispersion in a non-dimensional case. The hole charge carrier, displacement, thermal and plasma waves are coupled due to photo-thermal excitation. The Laplace transform method has been applied to solve the coupled principle governing equations. The boundary conditions are applied according to ramp-type heating to obtain the principle fields analytically in Laplace domain. Laplace transform inversion is used numerically to obtain the complete solutions in time domain for the basic fields. The effects of relaxation times according to the photo-thermoelasticity theories and the impact of initial stress are obtained graphically (2D and 3D plots) and discussed with comparing between silicon and germanium semiconductor materials.

Columnar Liquid Crystalline Corannulenes: Synthesis, Assembly and Charge‐Carrier Transport Properties

Main observation and conclusionTwo discotic liquid crystalline (LC) molecules consisting of a bowl‐shaped corannulene core and five‐fold photoactive azobenzene branches with different paraffinic side chains were developed. Their self‐assembly, photo‐responsive behavior and charge‐carrier transport properties were investigated in detail. A wider mesophase temperature range was achieved when utilizing longer and furcal flexible side chain substitution. 2D XRD measurements revealed the π‐packed corannulene‐centered 1b (i.e., with furcal side alkoxyl chains) exhibited helical columnar LC phase. This packing structure also led to a higher hole charge carrier mobility of 7.07 x 10–2 cm2·V–1·s–1 compared to that of the counterpart 1a with linear side chain substitutions.

Theoretical Insight into High‐Efficiency Triple‐Junction Tandem Solar Cells via the Band Engineering of Antimony Chalcogenides

Antimony chalcogenides have become a family of promising photoelectric materials for high‐efficiency solar cells. To date, single‐junction solar cells based on individual antimony selenide or sulfide are dominant and show limited photoelectric conversion efficiency. Therefore, great gaps remain for the multiple junction solar cells. Herein, triple‐junction antimony chalcogenides‐based solar cells are designed and optimized with a theoretical efficiency of 32.98% through band engineering strategies with Sb2S3/Sb2(S0.7Se0.3)3/Sb2Se3 stacking. The optimum Se content of the mid‐cell should be maintained low, i.e., 30% for achieving a low defect density in an absorber layer. Therefore, Sb2(S0.7Se0.3)3‐based mid solar cells have contributed to elevate the external quantum efficiency in triple‐junction devices by the full utilization of the solar spectrum. In a single‐junction solar cell, the bandgap gradient is regulated through the Se content gradient along the depth profile of Sb2(S1−xSex)3. Besides, an increasing Se content profile provides an additional built‐in electric field for boosting hole charge carrier collection. Thus, the high charge carrier generation rate leads to a 17.96% improvement in the conversion efficiency compared with a conventional cell. This work may pave the way to boost the conversion efficiency of antimony chalcogenides‐based solar cells to their theoretical limits.

Efficient and Stable Co3O4/ZnO Nanocomposite for Photochemical Water Splitting

In this study, an efficient Co3O4/ZnO based composite was prepared by the low temperature aqueous chemical growth method for photoelectrochemical water splitting. Both ZnO and Co3O4 constituents are identified in the composite sample through X-ray diffraction technique. Scanning electron microscopy has shown the nanorod like morphology of ZnO with etched top surface. The energy dispersive spectroscopy has shown the presence of cobalt, oxygen and zinc as the main elements in the composite samples. The Co3O4/ZnO composite (with low content of cobalt chloride hexahydrate) shows a significant increase in the photocurrent density (3 mA/cm2 at 0.5 V vs Ag/AgCl, which is 10 times higher than the pristine ZnO). Importantly, a fast and stable photocurrent response is found at an illumination of 1 Sun of light. The superior performance of the Co3O4/ZnO composite system is attributed to the facile promotion of electron–hole charge carrier separation and favourable charge transport. Furthermore, the electrochemical impedance spectroscopy showed a small charge transfer resistance of 259.30 Ohms for the composite material and consequently a robust water splitting is obtained. The prepared composite is earth abundant, inexpensive and scalable, therefore it can be used for diverse applications.

Variable range hopping and modulus relaxation in NiFe2O4 ceramics

Nickel ferrite ceramics prepared from combustion derived powders have been investigated using dielectric, impedance, and modulus spectroscopy over a wide frequency (0.1 Hz–1 MHz) and temperature range (173–473 K). Step-like dielectric response ε'T,f is related to the surface barrier layer capacitor (SBLC) effect. Dielectric relaxation peaks in ε″(f) masked by the huge dielectric loss are revealed by εder″(f) derived from the ε′(f) data following Kramers – Kronig transformations. Multiple relaxations are evidenced from the asymmetric nature of εder″(f) peaks. Impedance Cole-Cole analysis reveals two relaxation processes corresponding to grain and grain-boundary effects. A maximum in the grain capacitance (Cg) at 293 K is attributed to the collective influence of electron and hole charge carriers on dielectric polarization. The modulus analysis reveals distinctly three relaxations occurring at temperatures T ≥ 323 K, and only two relaxations for T < 323 K. The variation of modulus relaxation frequencies ln(fmax) with (1/T) suggests different conduction mechanisms for temperature above and below 323 K. The two relaxations observed in the entire temperature range originate due to hopping of holes and electrons at equivalent B-sites of NiFe2O4, while the third relaxation seen only at temperatures T > 323 K is attributed to defect hopping. The present analysis based on modulus relaxation, dc conductivity, and power law exponent sT indicates two different conduction mechanisms for Nickel ferrite NiFe2O4 with variable range hopping dominating at lower temperatures, and thermally activated hopping at higher temperatures.

Studying the Effect of Halogen Atoms and the Cyano Groups on Optical, Electronic and Charge Transfer Properties of Hexasene Molecule: Molecular Design Methods, Structure-Property Relationship

Bu çalışmada, π-konjugasyon yapısına sahip hekzasen molekülü, farklı halojen atomlar (Flor, Klor, Brom) ve molekülde farklı konumlandırılmış siyano grupları ile dizayn edilmiş, elektronik, optik ve yük transfer özellikleri zamana bağlı ve zamandan bağımsız Yoğunluk Fonksiyon Teorisi (YFT) ile incelenmiştir. Dizayn edilen beş hekzasen türevinin yapı ve özellik arasındaki ilişkiyi kurabilmek için, moleküler geometri, reorganizasyon enerji, HOMO-LUMO orbital enerjileri, iyonizasyon potansiyeli (IP), elektron afinitesi (EA), geometriden dolayı nötr ve yüklü durumlara bağlı olarak bağ uzunluğu değişimi (BUD) üzerine substitüe etkisi incelenmiş ve etkiyi daha iyi anlayabilmek için sonuçlar hekzasen ve antrasen moleküllerin sonuçlarıyla karşılaştırılmıştır. Moleküllerin, elektron enjeksiyon bariyerinin hekzasen molekülünden daha düşük olduğu ve iyi bir boşluk taşıyıcısı olarak bilinen antrasenle kıyaslanabilir derecede etkili boşluk yük transfer oranına sahip olduğu belirtilmiştir. Dizayn edilen hekzasen türevlerinin, optoelektronik alanda potansiyel uygulamalar için ilgi çekebileceğini ve malzeme biliminde umut vaad edeceğini umuyorum.

Transport Properties of Ag‐doped ZnSb

The intermetallic compound ZnSb is a (II‐V) narrow gap semiconductor with interesting thermoelectric properties. Electrical resistivity, Hall coefficient, thermopower and thermal conductivity were measured up to 400 K on Ag‐doped samples with concentrations 0.2, 0.5, 1, 2, and 3 at.%, which were consolidated to densities in excess of 99.5 % by spark plasma sintering. The work confirms a huge improvement of the thermoelectric Figure‐of‐merit, ZT, upon Ag doping. The optimum doping level is near 0.5 at.% Ag and results in ZT values around 1.05 at 390 K. The improvement stems from a largely decreased resistivity, which in turn relates to an increase of the hole charge carrier concentration by two orders of magnitude. It is argued that Ag can replace minute concentrations of Zn (on the order of 0.2 at.%) in the crystal structure which enhances the intrinsic impurity band of ZnSb. Excess Ag was found to segregate in grain boundaries. So the best performing material may be considered as a composite Zn~0.998Ag~0.002Sb/Ag~0.003.

Evincing Structural, Electronic, and Magnetic Attributes of LaFe0.5A0.5O3 (A = Co, Cr, and Ti): DFT‐GGA Recapitulation

AbstractIn this article, density functional theory studies are being performed on LaFe0.5A0.5O3 (A = Co, Cr, and Ti) (LFAO). The structural stability of LFAO is inspected using ground state optimization, and enthalpy of formation. The results unveil that LFAO is a ferromagnetic half metallic compound. The calculated magnetic moments, Curie temperature, and electronic band gap are found to change with substitution atoms. All these attributes are explained in detail using DOS and Fermi surface analysis. The results match well with the available literature. The Seebeck coefficient, electrical and thermal conductivity with respect to a time constant are computed using BoltzTrap code. The present dopant compounds show p‐type character with a hole charge carrier. It is expected that studied compounds can be useful for novel spintronic and thermoelectric applications.

Photocatalytic degradation of imidacloprid using semiconductor hybrid nano-catalyst: kinetics, surface reactions and degradation pathways

The presence of imidacloprid in surface waters has raised major environmental concern worldwide. Herein, for degradation and mineralization of imidacloprid, hybrid nano-catalysts g-C3N4/ZnO (< 20 nm) with different compositions were synthesized and characterized. Under UV-C light intensity of 15 W/m2 and at pH 7, degradation was observed to be highest (95.6%) for g-C3N4/ZnO (20:80) in comparison to bare ZnO (80.6%) and g-C3N4 (84.1%) nano-catalysts in just 35 min. The remarkable increase in photocatalytic activity was due to improved surface area (42.87 m2g−1), lower bandgap (2.76 eV) and lower photoluminescence intensity which resulted in lowering the recombination rate of electron–hole charge carriers. Further, higher zeta potential (+28 mV) at pH 7 might have increased intimacy in positively charged catalyst and high electron rich aromatic ring of imidacloprid which enhanced the degradation. The study was extended to analyze the reaction intermediates using LC–MS. The degradation mechanism revealed the formation of by-products such as ethylenediamine, nitroamine, acrolein, CO2 and H2O. Overall, g-C3N4/ZnO (20:80) was found to be a promising catalyst for the degradation of imidacloprid at neutral pH.

Length-dependent photo-electrochemical performance of vertically aligned hematite nanorods

Photo-electrochemical (PEC) cells have been widely studied as an eco-friendly method of producing hydrogen fuel. Among the various materials, hematite (α-Fe2O3) is one of the most promising candidates for PEC applications due to its chemical stability and visible-range bandgap. However, despite the aforementioned advantages, hematite-based PEC cells have suffered from an extremely short hole diffusion length and charge carrier lifetime, resulting in a solar-to-hydrogen efficiency far lower than the theoretical maximum. To overcome these drawbacks, we controlled the length of vertically aligned hematite nanorod (NRs) arrays on a fluorine-doped tin oxide substrate by adjusting the chemical concentrations of the precursor solutions. We confirmed that the PEC performance of the hematite NRs was strongly dependent on their length and showed an approximately inverse proportionality between the length of the hematite NRs and their photoactivity. In addition, the hematite NRs array, with an optimized length, was further modified by cobalt phosphate (Co-Pi) cocatalysts to enhance the water oxidation kinetics and showed 1.54 mA cm−2 of photocurrent at 1.23 V vs. RHE.