Mesoporous TiO2/TiC@C Composite Membranes with Stable TiO2-C Interface for Robust Lithium Storage

Dual-Functional Super-Assembled Mesoporous Carbon-Titania/AAO Hetero-Channels for Bidirectionally Photo-Regulated Ion Transport

Photo-regulated nanofluidic devices have attracted great attention in recent years due to their adjustable ion transport in real time. However, most of the photo-responsive nanofluidic devices can only adjust the ionic current unidirectionally, and cannot simultaneously increase or decrease the current signal intelligently by one device. Herein, a mesoporous carbon-titania/ anodized aluminum hetero-channels (MCT/AAO) is constructed by super-assembly strategy, which exhibits dual-function of cation selectivity and photo response. The polymer and TiO2 nanocrystals jointly build the MCT framework. Polymer framework with abundant negatively charged sites endows MCT/AAO with excellent cation selectivity, and TiO2 nanocrystals are responsible for the photo-regulated ion transport. High photo current densities of 1.8 mA m-2 (increase) and 1.2 mA m-2 (decrease) are realized by MCT/AAO benefiting from the ordered hetero-channels. Significantly, MCT/AAO can also achieve the bidirectionally adjustable osmotic energy by alternating the configurations of concentration gradient. Theoretical and experimental results reveal that the superior photo-generated potential is responsible for the bidirectionally adjustable ion transport. Consequently, MCT/AAO performs the function of harvesting ionic energy from the equilibrium electrolyte solution, which greatly expands its practical application field. This work provides a new strategy in constructing dual-functional hetero-channels toward bidirectionally photo-regulated ionic transport and energy harvesting.

Three-in-one oxygen-deficient titanium dioxide in a pomegranate-inspired design for improved lithium storage

Defects engineering has played an ever-increasing important role in electrochemistry, especially secondary lithium batteries. TiO₂ is regarded as a promising anode due to its attractive cycling stability, low volume strain and great abundance, while challenges of intrinsic poor electrical and ionic conductivity remain to be addressed. Herein, we report a three-in-one oxygen vacancy (V_O)-involved pomegranate design for TiO_2-x/C composite anode, which provides highly improved electrical conduction, shortened Li⁺ pathway and promoted Li⁺ redox. N-doped mesoporous carbon acts as a robust scaffold to support the whole structure, electron highway and efficient reductant to generate V_O on TiO₂ nanoparticles during crystallization. Theoretical calculations reveal the crucial role of surface V_O on TiO₂ in Li electrochemistry. Resultantly, the optimal TiO_2-x/C anode achieves significantly enhanced cycling performance (203 mAh/g retained after 2000 cycles at 1 A/g). Postmortem analysis reveals the robustness of V_O and reasonable structure stability upon cycles for improved battery performance.

Polylactic acid/tapioca starch/banana peel-based material for colorimetric and electrochemical biosensing applications

The rapidly growing electronic and plastic waste has become a global environmental concern. Developing advanced and environmentally safe agro-based materials is an emerging field with an enormous potential for applications in sensors and devices. Here, an agro-based material as membrane has been developed by incorporating tapioca starch and banana peel powder in polylactic acid, with uniform dispersibility and amorphous nature. The material was used for the development of electrochemical sensor for S-gene of SARS-CoV-2. Further, the membrane was used for the development of a non-invasive, colorimetric skin patch for the detection of glucose and a sensor for the assessment of fruit juice quality. Using OECD-recommended model systems, the developed membrane was found to be non-toxic towards aquatic and terrestrial non-target organisms. The developed conductive material opens new avenues in various electrochemical, analytical, and biological applications.

Investigation on In Situ Carbon-Coated ZnFe2O4 as Advanced Anode Material for Li-Ion Batteries

ZnFe₂O₄ as an anode that is believed to attractive. Due to its large theoretical capacity, this electrode is ideal for Lithium-ion batteries. However, the performance of ZnFe₂O₄ while charging and discharging is limited by its volume growth. In the present study, carbon-coated ZnFe₂O₄ is synthesized by the sol–gel method. Carbon is coated on the spherical surface of ZnFe₂O₄ by in situ coating. In situ carbon coating alleviates volume expansion during electrochemical performance and Lithium-ion mobility is accelerated, and electron transit is accelerated; thus, carbon-coated ZnFe₂O₄ show good electrochemical performance. After 50 cycles at a current density of 0.1 A·g⁻¹, the battery had a discharge capacity of 1312 mAh·g⁻¹ and a capacity of roughly 1220 mAh·g⁻¹. The performance of carbon-coated ZnFe₂O₄ as an improved anode is electrochemically used for Li-ion energy storage applications.

Microporous silica membranes promote plasmonic nanoparticle stability for SERS detection of uranyl

Silica membrane stabilized gold coated silver (Ag@Au) (i.e., internally etched silica coated Ag@Au (IE Ag@Au@SiO2)) nanoparticles promote surface-enhanced Raman scattering (SERS) activity and detection of uranium(vi) oxide (uranyl) under harsh solution phase conditions including at pH 3-7, with ionic strengths up to 150 mM, and temperatures up to 37 °C for at least 10 hours. These materials overcome traditional solution-phase plasmonic nanomaterial limitations including signal variability and/or degradation arising from nanoparticle aggregation, dissolution, and/or surface chemistry changes. Quantitative uranyl detection occurs via coordination to 3-mercaptopropionate (MPA), a result confirmed through changes in correlated SERS intensities for uranyl and COOH/COO- vibrational modes. Quantification is demonstrated down to 110 nM, a concentration below toxic levels. As pH varies from 3 to 7, the plasmonic properties of the nanoparticles are unchanged, and the uranyl signal depends on both the protonation state of MPA as well as uranyl solubility. High ionic strengths (up to 150 mM) and incubation at 37 °C for at least 10 hours do not impact the SERS activity of uranyl even though slight silica dissolution is observed during thermal treatment. All in all, microporous silica membranes effectively protect the nanoparticles against variations in solution conditions thus illustrating robust tunability for uranyl detection using SERS.

Efficient Laser-Induced Construction of Oxygen-Vacancy Abundant Nano-ZnCo2 O4 /Porous Reduced Graphene Oxide Hybrids toward Exceptional Capacitive Lithium Storage

Recently, binary ZnCo₂ O₄ has drawn enormous attention for lithium-ion batteries (LIBs) as attractive anode owing to its large theoretical capacity and good environmental benignity. However, the modest electrical conductivity and serious volumetric effect/particle agglomeration over cycling hinder its extensive applications. To address the concerns, herein, a rapid laser-irradiation methodology is firstly devised toward efficient synthesis of oxygen-vacancy abundant nano-ZnCo₂ O₄ /porous reduced graphene oxide (rGO) hybrids as anodes for LIBs. The synergistic contributions from nano-dimensional ZnCo₂ O₄ with rich oxygen vacancies and flexible rGO guarantee abundant active sites, fast electron/ion transport, and robust structural stability, and inhibit the agglomeration of nanoscale ZnCo₂ O₄ , favoring for superb electrochemical lithium-storage performance. More encouragingly, the optimal L-ZCO@rGO-30 anode exhibits a large reversible capacity of ≈1053 mAh g^-1 at 0.05 A g^-1 , excellent cycling stability (≈746 mAh g^-1 at 1.0 A g^-1 after 250 cycles), and preeminent rate capability (≈686 mAh g^-1 at 3.2 A g^-1 ). Further kinetic analysis corroborates that the capacitive-controlled process dominates the involved electrochemical reactions of hybrid anodes. More significantly, this rational design holds the promise of being extended for smart fabrication of other oxygen-vacancy abundant metal oxide/porous rGO hybrids toward advanced LIBs and beyond.

Unprecedented and highly stable lithium storage capacity of (001) faceted nanosheet-constructed hierarchically porous TiO2/rGO hybrid architecture for high-performance Li-ion batteries

Active crystal facets can generate special properties for various applications. Herein, we report a (001) faceted nanosheet-constructed hierarchically porous TiO₂/rGO hybrid architecture with unprecedented and highly stable lithium storage performance. Density functional theory calculations show that the (001) faceted TiO₂ nanosheets enable enhanced reaction kinetics by reinforcing their contact with the electrolyte and shortening the path length of Li⁺ diffusion and insertion-extraction. The reduced graphene oxide (rGO) nanosheets in this TiO₂/rGO hybrid largely improve charge transport, while the porous hierarchy at different length scales favors continuous electrolyte permeation and accommodates volume change. This hierarchically porous TiO₂/rGO hybrid anode material demonstrates an excellent reversible capacity of 250 mAh g^–1 at 1 C (1 C = 335 mA g^–1) at a voltage window of 1.0–3.0 V. Even after 1000 cycles at 5 C and 500 cycles at 10 C, the anode retains exceptional and stable capacities of 176 and 160 mAh g^–1, respectively. Moreover, the formed Li₂Ti₂O₄ nanodots facilitate reversed Li⁺ insertion-extraction during the cycling process. The above results indicate the best performance of TiO₂-based materials as anodes for lithium-ion batteries reported in the literature.

Intercalation of Carbon Nanosheet into Layered TiO2 Grain for Highly Interfacial Lithium Storage

Interfacial energy storage contributes a new mechanism to the emergence of energy storage devices with not only a high-energy density of batteries but also a high-power density of capacitors. In this study, success was achieved in preparing a highly ordered two-dimensional (2D) carbon/TiO₂ (C/TiO₂) nanosheet composite using commercially available organic molecules with multifunctional groups and taking advantage of the wedge effects, oxidative polymerization, and carbonization. An experiment was conducted to validate the excellent performance of this 2D composite with respect to interfacial energy storage. The coin cell with 2D C/TiO₂ nanosheet composite demonstrates a specific capacity of as high as 510 mAh g^-1 and a high specific energy of 390.9 Wh kg^-1 at a specific power of 75.9 W kg^-1 with a current density of 0.1 A g^-1, and it also remains 39.0 Wh kg^-1 at a specific power of 8.2 kW kg^-1 with a high current density of 12.8 A g^-1. The excellent electrochemical performance can be attributed to the superior artificial interface capacitive Li⁺ storage capability, which would bridge the energy and power density gap between batteries and capacitors. Meanwhile, there are two varieties of carbon derivatives, 2D carbon nanosheet stacks and exfoliated carbon nanosheets, which can be obtained by wet-chemical etching and mechanical peeling. The experimental route is simple from commercially available raw materials, and it could be scalable at a low cost and large scale, which makes it suitable for application in various fields such as energy storage, nanocatalysis, sensors, and so on.

Recent advances in the synthesis of hierarchically mesoporous TiO2 materials for energy and environmental applications

Because of their low cost, natural abundance, environmental benignity, plentiful polymorphs, good chemical stability and excellent optical properties, TiO₂ materials are of great importance in the areas of physics, chemistry and material science. Much effort has been devoted to the synthesis of TiO₂ nanomaterials for various applications. Among them, mesoporous TiO₂ materials, especially with hierarchically porous structures, show great potential owing to their extraordinarily high surface areas, large pore volumes, tunable pore structures and morphologies, and nanoscale effects. This review aims to provide an overview of the synthesis and applications of hierarchically mesoporous TiO₂ materials. In the first section, the general synthetic strategies for hierarchically mesoporous TiO₂ materials are reviewed. After that, we summarize the architectures of hierarchically mesoporous TiO₂ materials, including nanofibers, nanosheets, microparticles, films, spheres, core-shell and multi-level structures. At the same time, the corresponding mechanisms and the key factors for the controllable synthesis are highlighted. Following this, the applications of hierarchically mesoporous TiO₂ materials in terms of energy storage and environmental protection, including photocatalytic degradation of pollutants, photocatalytic fuel generation, photoelectrochemical water splitting, catalyst support, lithium-ion batteries and sodium-ion batteries, are discussed. Finally, we outline the challenges and future directions of research and development in this area.

Facile Synthesis of Flower-Like MnCo2 O4 @PANi-rGO: A High-Performance Anode Material for Lithium-Ion Batteries

Flower-like MnCo₂ O₄ was prepared in a self-assembly process and used in the formation of MnCo₂ O₄ @polyaniline (MnCo₂ O₄ @PANi) that proceeds by a simple in situ polymerization. The MnCo₂ O₄ @PANi-reduced graphite oxide (MnCo₂ O₄ @PANi-rGO) composite was then synthesized by introducing rGO into MnCo₂ O₄ @PANi. This modification improves the overall electronic conductivity of the MnCo₂ O₄ @PANi-rGO because of the dual conductive functions of rGO and PANi; it also provides a buffer for the changes in electrode volume during cycling, thus improving the lithium-storage performance of MnCo₂ O₄ @PANi-rGO. The electrochemical performance of the samples was evaluated by charge/discharge cycling testing, cyclic voltammetry, and electrochemical impedance spectroscopy. MnCo₂ O₄ @PANi-rGO delivers a discharge capacity of 745 mAh g^-1 and a Coulombic efficiency of 100 % after 1050 cycles at a current density of 500 mA g^-1 , and is a promising anode material for lithium-ion batteries.

Bio-derived yellow porous TiO2: the lithiation induced activation of an oxygen-vacancy dominated TiO2 lattice evoking a large boost in lithium storage performance

Oxygen deficient TiO₂ has attracted extensive attention owning to its narrow bandgap and high electrical conductivity. In this work, novel yellow TiO₂ with hierarchically porous architecture is fabricated by a facile pyrolysis method in air via a biomass template. The obtained yellow TiO₂ exhibits interesting lithiation induced activation during cycling, which gives rise to a phase change from poorly crystallized TiO₂ to an amorphous phase, accompanied by a colour change from yellow to black. In contrast to the intercalation mechanism reported in most of the literature on the TiO₂ anode of LIBs, notably, the reversible redox reaction between Ti³⁺ and metal Ti can be verified in this case, demonstrating the novel conversion reaction mechanism of the TiO₂ electrode. Based on this, the yellow porous TiO₂ delivers enhanced electrochemical performance as an anode for LIBs with a superior capacity of 480 mA h g^-1 at 5 A g^-1 and a high capacity of 206 mA h g^-1 at 10 A g^-1 after 8000 cycles.

Hierarchical Branched Mesoporous TiO2-SnO2 Nanocomposites with Well-Defined n-n Heterojunctions for Highly Efficient Ethanol Sensing

The direct assembly of functional nanoparticles into a highly crystalline mesoporous semiconductor with oriented configurations is challenging but of significance. Herein, an evaporation induced oriented co-assembly strategy is reported to incorporate SnO2 nanocrystals (NCs) into a 3D branched mesoporous TiO2 framework by using poly(ethylene oxide)-block-polystyrene (PEO-b-PS) as the template, SnO2 NCs as the direct tin source, and titanium butoxide (TBOT) as the titania precursor. Owing to the combined properties of ultrasmall particle size (3-5 nm), excellent dispersibility and presence of abundant hydroxyl groups, SnO2 NCs can easily interact with PEO block of the template through hydrogen bonding and co-assemble with hydrolyzed TBOT to form a novel hierarchical branched mesoporous structure (SHMT). After calcination, the obtained composites exhibit a unique 3D flower-like structure, which consists of numerous mesoporous rutile TiO2 branches with uniform cylindrical mesopores (≈9 nm). More importantly, the SnO2 NCs are homogeneously distributed in the mesoporous TiO2 matrix, forming numerous n-n heterojunctions. Due to the unique textual structures, the SHMT-based gas sensors show excellent gas sensing performance with fast response/recovery dynamics, high sensitivity, and selectivity toward ethanol.

Synthesis of uniform ordered mesoporous TiO2 microspheres with controllable phase junctions for efficient solar water splitting

As a benchmark photocatalyst, commercial P25-TiO2 has been widely used for various photocatalytic applications. However, the low surface area and poorly porous structure greatly limit its performance. Herein, uniform ordered mesoporous TiO2 microspheres (denoted as Meso-TiO2-X; X represents the rutile percentage in the resultant microspheres) with controllable anatase/rutile phase junctions and radially oriented mesochannels are synthesized by a coordination-mediated self-assembly approach. The anatase/rutile ratio in the resultant microspheres can be facilely adjusted as desired (rutile percentage: 0-100) by changing the concentration of hydrochloric acid. As a typical one, the as-prepared Meso-TiO2-25 microspheres have a similar anatase/rutile ratio to commercial P25. But the surface area (78.6 m2 g-1) and pore volume (0.39 cm3 g-1) of the resultant microspheres are larger than those of commercial P25. When used as the photocatalyst for H2 generation, the Meso-TiO2-25 delivers high solar-driven H2 evolution rates under air mass 1.5 global (AM 1.5 G) and visible-light (λ > 400 nm), respectively, which are significantly larger than those of commercial P25. This coordination-mediated self-assembly method paves a new way toward the design and synthesis of high performance mesoporous photocatalysts.

Ternary Heterostructural Pt/CNx/Ni as a Supercatalyst for Oxygen Reduction

We report here a supercatalyst for oxygen reduction of Pt/CNx/Ni in a unique ternary heterostructure, in which the Pt and the underlying Ni nanoparticles are separated by two to three layers of nitrogen-doped carbon (CNx), which mediates the transfer of electrons from the inner Ni to the outer Pt and protects the Ni against corrosion at the same time. The well-engineered low-Pt catalyst shows ∼780% enhanced specific mass activity or 490% enhanced specific surface activity compared with a commercial Pt/C catalyst toward oxygen reduction. More importantly, the exceptionally strong tune on the Pt by the unique structure makes the catalyst superbly stable, and its mass activity of 0.72 A/mgPt at 0.90 V (well above the US Department of Energy's 2020 target of 0.44 A/mgPt at 0.90 V) after 50,000 cyclic voltammetry cycles under acidic conditions is still better than that of the fresh commercial catalyst.

Enhanced reversible capability of a macroporous ZnMn2O4/C microsphere anode with a water-soluble binder for long-life and high-rate lithium-ion storage

ZnMn₂O₄ and carbon are mixed uniformly to form macroporous ZnMn₂O₄/C microspheres consisting of many tiny nanoparticles. The macroporous ZnMn₂O₄/C microsphere anode with a CMC binder shows superior cycle performance in lithium-ion batteries.