Numerical Model to Simulate Electrochemical Charging of Nanocrystal Films

Electrochemical charging of nanocrystal films opens up new possibilities for designing quantum dot-based device structures, but a solid theoretical framework of this process and its limitations is lacking. In this work, drift-diffusion simulations are employed to model the charging of nanocrystal films and gain insight into the electrochemical doping process. Through steady state simulations it is shown that the Fermi level and doping density in the nanocrystal film depend on the concentration of the electrolyte in addition to the value of the applied potential. Time-resolved simulations reveal that charging is often limited by transport of electrolyte ions. However, ion transport in the film is dominated by drift, rather than diffusion, and the concentration profile of ions differs substantially from concentration profiles of diffusing redox species at flat electrodes. Classical electrochemical theory cannot be used to model this type of mass transport limited behavior in films of nanocrystals, so a new model is developed. We show that the Randles-Ševčík equation, which is derived for electrochemical species diffusing in solution, but is often applied to films as well, results in a significant underestimation of the diffusion coefficients of the charge compensating electrolyte ions.

Photocatalytic degradation of methylene blue under UV and visible light by brookite–rutile bi-crystalline phase of TiO2

Brookite–rutile bi-crystalline phase of TiO₂ were synthesized and applied for the degradation of methylene blue under UV and visible light irradiation by photocatalytic reaction.

Rapid photocatalytic degradation of cationic organic dyes using Li-doped Ni/NiO nanocomposites and their electrochemical performance

This work reports novel bi-functional Li-doped Ni/NiO nanocomposites as potential candidates for energy storage and water treatment applications.

Nitrogen-doped TiO2(B) nanobelts enabling enhancement of electronic conductivity and efficiency of lithium-ion storage

To enhance the intrinsic electrical conductivities of TiO₂(B) nanobelts, nitrogen(N)-doped TiO₂(B) nanobelts (N-TNB) were prepared in this study by a facile and cost-effective hydrothermal method using urea as the nitrogen source with TiO₂ (P25) nanoparticles. x-ray photoelectron spectroscopy confirmed that the N-atoms preferentially occupied up to ∼0.516 atom% in the interstitial sites of the N-TNB and the maximum concentration of substituted-N bonds in the N-TNB was ∼0.154 atom%, thereby the total concentration of doped nitrogen elements of ∼0.67 atom% improved the high intrinsic electrical conductivity and ionic diffusivity of the TiO₂(B) nanobelts. The as-prepared N-TNB electrode delivered the highest specific capacity of 133.9 mAh g^-1 in the first cycle, with an exceptional cyclic capacity retention at an ultrafast current rate of 1000 mA g^-1; this is not less than 51% after 500 cycles and represents an excellent rate capability of ∼37 mAh g^-1 at an ultra-high rate of 40 C. These values are among the best ever reported on comparison of the delivered highest discharge capacity of N-TNB at 1000 mA g^-1 and high-rate capabilities of its Li⁺ ion storage with the literature data for N-TNB (∼231.5 mAh g^-1 at a very low current density of 16.75 mA g^-1, ∼0.1 C) of similar materials used in sodium-ion batteries. This implies the potential feasibility of these N-TNB as high-capacity anode materials for next-generation, high-energy-density, electrochemical energy-storage devices.

Conversion Reaction Mechanism of Ultrafine Bimetallic Co-Fe Selenides Embedded in Hollow Mesoporous Carbon Nanospheres and Their Excellent K-Ion Storage Performance

Potassium-ion batteries (KIBs) are considered as promising alternatives to lithium-ion batteries owing to the abundance and affordability of potassium. However, the development of suitable electrode materials that can stably store large-sized K ions remains a challenge. This study proposes a facile impregnation method for synthesizing ultrafine cobalt-iron bimetallic selenides embedded in hollow mesoporous carbon nanospheres (HMCSs) as superior anodes for KIBs. This involves loading metal precursors into HMCS templates using a repeated "drop and drying" process followed by selenization at various temperatures, facilitating not only the preparation of bimetallic selenide/carbon composites but also controlling their structures. HMCSs serve as structural skeletons, conductive templates, and vehicles to restrain the overgrowth of bimetallic selenide particles during thermal treatment. Various analysis strategies are employed to investigate the charge-discharge mechanism of the new bimetallic selenide anodes. This unique-structured composite exhibits a high discharge capacity (485 mA h g^-1 at 0.1 A g^-1 after 200 cycles) and enhanced rate capability (272 mA h g^-1 at 2.0 A g^-1 ) as a promising anode material for KIBs. Furthermore, the electrochemical properties of various nanostructures, from hollow to frog egg-like structures, obtained by adjusting the selenization temperature, are compared.

Resistive switching and synaptic learning performance of a TiO2 thin film based device prepared by sol-gel and spin coating techniques

A resistance random access memory device based on TiO₂ thin films was fabricated using a sol-gel spin and coating techniques. The composition, surface morphology, and microstructure of the TiO₂ films were characterized using x-ray diffraction, Raman spectroscopy, scanning electronic microscopy, and transmission electron microscopy, respectively. The fabricated Al/TiO₂ film/fluorine-doped tin oxide device exhibited electroforming-free bipolar resistive switching characteristics with a stable ON/OFF ratio higher than 300. The performance of the endurance cycling was still good after 100 direct sweeping cycles. A retention time of no less than 10⁴ s was confirmed. A switching mechanism is systematically discussed based on the test results, and space-charge-limited current was found to be responsible for the switching behavior. Multilevel memory performance was realized in the as-fabricated devices. The synaptic performance was investigated by applying consecutive positive (0-2 V) and negative (0 to -1.6 V) voltage sweeps. The fabricated devices were found to exhibit 'learning-experience' behavior.

Morphology- and Crystalline Composition-Governed Activity of Titania-Based Photocatalysts: Overview and Perspective

Titania photocatalysts have been intensively examined for both mechanism study and possible commercial applications for more than 30 years. Although various reports have already been published on titania, including comprehensive review papers, the morphology-governed activity, especially for novel nanostructures, has not been reviewed recently. Therefore, this paper presents novel, attractive, and prospective titania photocatalysts, including zero-, one-, two-, and three-dimensional titania structures. The 1D, 2D, and 3D titania structures have been mainly designed for possible applications, e.g., (i) continuous use without the necessity of particulate titania separation, (ii) efficient light harvesting (e.g., inverse opals), (iii) enhanced activity (fast charge carriers’ separation, e.g., 1D nanoplates and 2D nanotubes). It should be pointed out that these structures might be also useful for mechanism investigation, e.g., (i) 3D titania aerogels with gold either incorporated inside the 3D network or supported in the porosity, and (ii) titania mesocrystals with gold deposited either on basal or lateral surfaces, for the clarification of plasmonic photocatalysis. Moreover, 0D nanostructures of special composition and morphology, e.g., magnetic(core)–titania(shell), mixed-phase titania (anatase/rutile/brookite), and faceted titania NPs have been presented, due to their exceptional properties, including easy separation in the magnetic field, high activity, and mechanism clarification, respectively. Although anatase has been usually thought as the most active phase of titania, the co-existence of other crystalline phases accelerates the photocatalytic activity significantly, and thus mixed-phase titania (e.g., famous P25) exhibits high photocatalytic activity for both oxidation and reduction reactions. It is believed that this review might be useful for the architecture design of novel nanomaterials for broad and diverse applications, including environmental purification, energy conversion, synthesis and preparation of “intelligent” surfaces with self-cleaning, antifogging, and antiseptic properties.

Biosynthesis of TiO2 nanoparticles and their application for treatment of brain injury-An in-vitro toxicity study towards central nervous system

In the current study, a facile green synthesis of TiO₂ nanoparticles (NPs) utilizing the leaf extract of Lippia citriodora as a stabilizing and reducing agent was reported. The prepared TiO₂ NPs were studied using XRD, UV, HRTEM, FTIR, Raman and EDS analysis. TEM analysis confirmed that the nanoparticles size is in 20-40 nm range. FTIR and UV-Visible spectra represented the TiO₂ NPs formation. Similarly, the analysis of XRD and EDS validated the crystalline rutile structure of TiO₂NPs formed. In addition, this investigation was shown to examine the TiO₂NPs toxicity on the CNS central nervous system in vitro. In the extracted cell cultures from the rats ECB embryonic cortical brain, substantial decline in the neuroblasts has been noticed once after incubating with TiO₂NPs for 24 h to 96 h (5 to 20 μg/ml). This study also demonstrates the decline of neuroblast proliferation. In the conclusion, our investigation illustrated evidently the TiO₂NPs toxic effect on the neuronal cells and rat brain also mentioned about toxicity effects of TiO₂ which were not yet described, for example the decline in vitro neuroblast proliferation.

New Insights into the Electron-Collection Efficiency Improvement of CdS-Sensitized TiO2 Nanorod Photoelectrodes by Interfacial Seed-Layer Mediation

Titanium dioxide (TiO₂) nanorods (NRs) are widely used as photoanodes in photoelectrochemical (PEC) solar fuel production because of their remarkable photoactivity and stability. In addition, TiO₂ NR electrode materials can be decorated with active CdS quantum dots (QDs) to expand the sunlight photon capture. The overall photoelectric conversion efficiency for TiO₂ NR or QD-sensitized TiO₂ NR electrode materials in PEC is typically dominated by their interfacial electron transfer (ET) properties. To understand the key factors affecting the ET, the anatase TiO₂ seed layer was added into the interface between the rutile TiO₂ NRs and fluorine-doped tin oxide (FTO) substrate. This seed layer enhanced the photocatalytic performance of both the TiO₂ NR and CdS QD-sensitized TiO₂ NR photoanodes in PEC. Time-resolved photoluminescence spectroscopy and PEC analyses, including Mott-Schottky, electrochemical impedance spectroscopy, and photovoltage ( V_ph) measurements, were used to study the charge-carrier dynamics at the interfaces between the FTO, TiO₂, and CdS QD. Analysis of the results showed that band alignment at the anatase/rutile junction between the TiO₂ and FTO promoted electron-collection efficiency ( e_EC) at the FTO/TiO₂ interface and ET rate constant ( k_ET) at the TiO₂/CdS QD interface. Furthermore, 34% enhancement of the efficiency in hydrogen (H₂) generation demonstrated the potential of the TiO₂ seed-layer-mediated TiO₂/CdS QD NR photoanode in the application of PEC solar fuel production. The current work represents new insights into the mechanism of ET in TiO₂ and TiO₂/CdS QD NR, which is very useful for the development of photoelectrode materials in solar energy conversions.

The Role of Dopant Ions on Charge Injection and Transport in Electrochemically Doped Quantum Dot Films

Control over the charge density is very important for implementation of colloidal semiconductor nanocrystals into various optoelectronic applications. A promising approach to dope nanocrystal assemblies is charge injection by electrochemistry, in which the charge compensating electrolyte ions can be regarded as external dopant ions. To gain insight into the doping mechanism and the role of the external dopant ions, we investigate charge injection in ZnO nanocrystal assemblies for a large series of charge compensating electrolyte ions with spectroelectrochemical and electrochemical transistor measurements. We show that charge injection is limited by the diffusion of cations in the nanocrystal films as their diffusion coefficient are found to be ∼7 orders of magnitude lower than those of electrons. We further show that the rate of charge injection depends strongly on the cation size and cation concentration. Strikingly, the onset of electron injection varies up to 0.4 V, depending on the size of the electrolyte cation. For the small ions Li⁺ and Na⁺ the onset is at significantly less negative potentials. For larger ions (K⁺, quaternary ammonium ions) the onset is always at the same, more negative potential, suggesting that intercalation may take place for Li⁺ and Na⁺. Finally, we show that the nature of the charge compensating cation does not affect the source-drain electronic conductivity and mobility, indicating that shallow donor levels from intercalating ions fully hybridize with the quantum confined energy levels and that the reorganization energy due to intercalating ions does not strongly affect electron transport in these nanocrystal assemblies.

Controllable synthesis of hierarchical MnOx/TiO2 composite nanofibers for complete oxidation of low-concentration acetone

A novel hierarchical MnO_x/TiO₂ composite nanofiber was fabricated by combining the electrospinning technique and hydrothermal growth method. The synthesized nanomaterial, which comprised primary TiO₂ nanofibers and secondary MnO_x nanoneedles, was further investigated for complete catalytic oxidation of volatile organic compounds for the first time, and this presented high-oxidation performance on low-concentration acetone. The morphological, structural, physicochemical characterization, and catalytic performance analyses demonstrated that the highest catalytic activity was achieved from the obtained MnO_x/TiO₂ nanofiber catalyst with 30wt.% manganese loading. This finding can be ascribed to the synergistic effect of the specific hierarchical nanofibrous morphology, the abundant surface-adsorbed oxygen, the superior redox property, and the sufficient specific surface.

Mesoporous Titania Microspheres with Highly Tunable Pores as an Anode Material for Lithium Ion Batteries

Mesoporous titania microspheres (MTMs) have been employed in many applications, including (photo)catalysis as well as energy conversion and storage. Their morphology offers a hierarchical structural design motif that lends itself to being incorporated into established large-scale fabrication processes. Despite the fact that device performance hinges on the precise morphological characteristics of these materials, control over the detailed mesopore structure and the tunability of the pore size remains a challenge. Especially the accessibility of a wide range of mesopore sizes by the same synthesis method is desirable, as this would allow for a comparative study of the relationship between structural features and performance. Here, we report a method that combines sol-gel chemistry with polymer micro- and macrophase separation to synthesize porous titania spheres with diameters in the micrometer range. The as-prepared MTMs exhibit well-defined, accessible porosities with mesopore sizes adjustable by the choice of the polymers. When applied as an anode material in lithium ion batteries (LIBs), the MTMs demonstrate excellent performance. The influence of the pore size and an in situ carbon coating on charge transport and storage is examined, providing important insights for the optimization of structured titania anodes in LIBs. Our synthesis strategy presents a facile one-pot approach that can be applied to different structure-directing agents and inorganic materials, thus further extending its scope of application.

Nanostructured Silica-Titania Hybrid using Dendritic Fibrous Nanosilica as a Photocatalyst

A new method has been developed to fabricate active TiO₂ photocatalysts by tuning the morphology of the catalyst support. A sustainable solution-phase TiO₂ deposition on dendritic fibrous nanosilica (DFNS) protocol is developed, which is better than the complex and expensive atomic layer deposition technique. In general, catalytic activity decreases with an increased TiO₂ loading on conventional mesoporous silica because of the loss of the surface area caused by the blocking of pores. Notably, in the case of the dendritic fibrous nanosilica KCC-1 as a support, because of its open fibrous morphology, even at the highest TiO₂ loading, a relatively large amount of surface area remained intact. This improved the accessibility of active sites, which increased the catalytic performance of the KCC-1/TiO₂ photocatalyst. KCC-1-supported TiO₂ is a superior photocatalyst in terms of H₂ generation (26.4 mmol gTiO2 ^-1  h^-1 ) under UV light. This study may provide a new direction for photocatalyst development through the morphology control of the support.

Applications of hierarchically structured porous materials from energy storage and conversion, catalysis, photocatalysis, adsorption, separation, and sensing to biomedicine

A comprehensive review of the recent progress in the applications of hierarchically structured porous materials is given.

Sb2S3 grown by ultrasonic spray pyrolysis and its application in a hybrid solar cell

Chemical spray pyrolysis (CSP) is a fast wet-chemical deposition method in which an aerosol is guided by carrier gas onto a hot substrate where the decomposition of the precursor chemicals occurs. The aerosol is produced using an ultrasonic oscillator in a bath of precursor solution and guided by compressed air. The use of the ultrasonic CSP resulted in the growth of homogeneous and well-adhered layers that consist of submicron crystals of single-phase Sb₂S₃ with a bandgap of 1.6 eV if an abundance of sulfur source is present in the precursor solution (SbCl₃/SC(NH₂)₂ = 1:6) sprayed onto the substrate at 250 °C in air. Solar cells with glass-ITO-TiO₂-Sb₂S₃-P3HT-Au structure and an active area of 1 cm² had an open circuit voltage of 630 mV, short circuit current density of 5 mA/cm², a fill factor of 42% and a conversion efficiency of 1.3%. Conversion efficiencies up to 1.9% were obtained from solar cells with smaller areas.

Phases Hybriding and Hierarchical Structuring of Mesoporous TiO2 Nanowire Bundles for High-Rate and High-Capacity Lithium Batteries

A hierarchical mesoporous TiO₂ nanowire bundles (HM-TiO₂-NB) superstructure with amorphous surface and straight nanochannels has been designed and synthesized through a templating method at a low temperature under acidic and wet conditions. The obtained HM-TiO₂-NB superstructure demonstrates high reversible capacity, excellent cycling performance, and superior rate capability. Most importantly, a self-improving phenomenon of Li⁺ insertion capability based on two simultaneous effects, the crystallization of amorphous TiO₂ and the formation of Li₂Ti₂O₄ crystalline dots on the surface of TiO₂ nanowires, has been clearly revealed through ex situ transmission electron microcopy (TEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Raman, and X-ray photoelectron spectroscopy (XPS) techniques during the Li⁺ insertion process. When discharged for 100 cycles at 1 C, the HM-TiO₂-NB exhibits a reversible capacity of 174 mA h g^-1. Even when the current density is increased to 50 C, a very stable and extraordinarily high reversible capacity of 96 mA h g^-1 can be delivered after 50 cycles. Compared to the previously reported results, both the lithium storage capacity and rate capability of our pure TiO₂ material without any additives are among the highest values reported. The advanced electrochemical performance of these HM-TiO₂-NB superstructures is the result of the synergistic effect of hybriding of amorphous and crystalline (anatase/rutile) phases and hierarchically structuring of TiO₂ nanowire bundles. Our material could be a very promising anodic material for lithium-ion batteries.

Bio-ingredient assisted formation of porous TiO2 for Li-ion battery electrodes

Macroporous anatase TiO₂ with mesopores was generated using instant yeast and glucose as the templates. The oxide functioned as the electrode material for Li-ion battery with excellent capacity and cycling stability.

Controllable synthesis of novel hierarchical V2O5/TiO2 nanofibers with improved acetone oxidation performance

A controllable strategy to fabricate novel hierarchical V₂O₅/TiO₂ nanofiber catalysts was proposed. The catalysts were found to present high oxidation performance for acetone. The reaction mechanism of catalytic oxidation was also investigated.

Rapid microwave assisted hydrothermal synthesis of porous α-Fe2O3 nanostructures as stable and high capacity negative electrode for lithium and sodium ion batteries

Porous α-Fe₂O₃ nanostructures were developed in the presence of a base catalyst by a rapid microwave assisted hydrothermal method.

Topochemical synthesis of Bi2O3 microribbons derived from a bismuth oxalate precursor as high-performance lithium-ion batteries

A one-dimensional inorganic arrangement in the bismuth oxalate hydroxide Bi(C₂O₄)OH was directly transformed into bismuth oxide Bi₂O₃via a simple thermal decomposition without a morphology change.

Introduction of ‘lattice-voids’ in high tap density TiO2-B nanowires for enhanced high-rate and high volumetric capacity lithium storage

Enhanced high-rate performance of TiO₂-B nanowires can be achieved by introducing “lattice voids” to produce a partially disordered structure. The obtained TiO₂-B nanowires can show the same excellent rate capability as TiO₂-B nanotubes, but a much higher volumetric capacity and better capacity retention.