Polymeric micelle assembly for the direct synthesis of platinum-decorated mesoporous TiO(2) toward highly selective sensing of acetaldehyde

Enhancing the Hydrogen-Sensing Performance of p-Type PdO by Modulating the Conduction Model

The implementation of the p-type metal oxide semiconductor (MOS) in modern sensing systems requires a strategy to effectively enhance its inherent low response. However, for p-type MOS sensors, conventional methods such as catalyst nanoparticle (NP) decoration and grain size regulation do not work as effectively as they do for n-type MOS sensors, which is basically due to the fact that the p-type MOS adopts an unfavorable parallel conduction model. Herein, taking Au@PdO as an example, we demonstrate that the conduction model of the p-type MOS can be manipulated into the series conduction model by inserting a high-conductive metallic core into less-conductive p-type MOS NPs. This unique series conduction model makes the sensor response of Au@PdO nanoparticle arrays (NAs) very sensitive to the catalyst NP decoration as well as the change of structural parameters. For example, Au@PdO NAs demonstrate an ∼9000 times increase in sensor response when decorated with Pd NPs, whereas there is only ∼100 times increase for PdO NAs. This greatly improved response value outperforms all previously reported PdO-based (and most other p-type semiconductor-based) H2 sensors, which helps the obtained sensor to achieve an ultralow detection limit of ∼0.1 ppm at room temperature. Additionally, Au@PdO NAs inherit the high surface reactivity and gas adsorption property of p-type PdO. As a result, the as-prepared sensor exhibits high humidity-resistive property and excellent selectivity. This work provides a new strategy to significantly enhance the sensing performance of p-type gas sensors by manipulating their conduction model.

Phenyl-Modified Carbon Nitride Quantum Nanoflakes for Ultra-Highly Selective Sensing of Formic Acid: A Combined Experimental by QCM and Density Functional Theory Study

Formic acid (HCOOH) is an important intermediate in chemical synthesis, pharmaceuticals, the food industry, and leather tanning and is considered to be an effective hydrogen storage molecule. Direct contact with its vapor and its inhalation lead to burns, nerve injury, and dermatosis. Thus, it is critical to establish efficient sensing materials and devices for the rapid detection of HCOOH. In the present study, we introduce a chemical sensor based on a quartz crystal microbalance (QCM) sensor capable of detecting trace amounts of HCOOH. This sensor is composed of colloidal phenyl-terminated carbon nitride (Ph-g-C₃N₄) quantum nanoflakes prepared using a facile solid-state method involving the supramolecular preorganization technology. In contrast to other synthetic methods of modified carbon nitride materials, this approach requires no hard templates, hazardous chemicals, or hydrothermal treatments. Comprehensive characterization and density functional theory (DFT) calculations revealed that the QCM sensor designed and prepared here exhibits enhanced detection sensitivity and selectivity for volatile HCOOH, which originates from chemical and hydrogen-bonding interactions between HCOOH and the surface of Ph-g-C₃N₄. According to DFT results, HCOOH is located close to the cavity of the Ph-g-C₃N₄ unit, with bonding to graphitic carbon and pyridinic nitrogen atoms of the nanoflake. The sensitivity of the Ph-g-C₃N₄-nanoflake-based QCM sensor was found to be the highest (128.99 Hz ppm^-1) of the substances studied, with a limit of detection (LOD) of HCOOH down to a sub-ppm level of 80 ppb. This sensing technology based on phenyl-terminated attached-g-C₃N₄ nanoflakes establishes a simple, low-cost solution to improve the performance of QCM sensors for the effective discrimination of HCOOH, HCHO, and CH₃COOH vapors using smart electronic noses.

Porous Tungsten Oxide: Recent Advances in Design, Synthesis, and Applications

Tungsten oxide (WO₃ ) has received ever more attention and has been highly researched over the last decade due to its being a low-cost transition metal semiconductor with tunable, yet widely stable, band gaps. This minireview briefly highlights the challenges in the design and synthesis of porous WO₃ including methods, precursors, solvent effects, crystal phases, and surface activities of the porous WO₃ base material. These topics are explored while also drawing a connection of how the morphology and crystal phase affect the band gap. The shifts in band gap not only impact the optical properties of tungsten but also allow tuning to operate on different energy levels, which makes WO₃ highly desirable in many applications such as supercapacitors, batteries, solar cells, catalysts, sensors, smart windows, and bioapplications.

Nanoarchitectured porous carbons derived from ZIFs toward highly sensitive and selective QCM sensor for hazardous aromatic vapors

Metal-organic frameworks (MOFs) are a versatile source of carbon nanoarchitectures in gas sensing applications (Torad et al., 2019). Herein, several types of nanoporous carbons (NPCs) have been prepared by in-situ carbothermal treatment of zeolitic imidazolate frameworks (ZIFs) under different inert atmospheres to achieve a highly sensitive discrimination of vaporized aromatic compounds. In this study, we demonstrate how different carbonization conditions under the flow of N₂ or H₂ gases affect the surface area and the degree of graphitization of the resulting NPCs polyhedrons, and their consequent effect on the sensing performance in terms of sensitivity and selectivity toward toxic volatile hydrocarbons. A growth of carbon nanotubes (CNTs) is observed on the surface of polyhedral NPCs after careful carbonization of ZIF crystals under H₂ atmosphere. The fabricated quartz crystal microbalance (QCM) sensor with CNT-containing NPCs demonstrates increased sensitivity and selectivity towards toxic volatile aromatic hydrocarbons over the aliphatic analogues, suggesting the rich growth of hairy graphitic-like CNTs on the surface of carbon framework act as highly selective sensing antennae for vapor molecular discrimination of toxic aromatic hydrocarbons. Despite of increased selectivity towards volatile aromatic compounds, however, the surface area of CNT-rich NPCs derived from hybrid ZIFs and ZIF-67 is greatly sacrificed as compared to CNT-free NPCs from ZIF-8 polyhedron. In the case of Co-containing ZIF-67, the rich growth of hair-like CNTs, which is induced by the presence of Co, is observed during carbothermal reduction under a flow of H₂ gas, thus allowing ultra-selective detection of aromatic hydrocarbons in the vapor phase, such as benzene (C₆H₆) and toluene (C₆H₅CH₃) over their aliphatic analogue, c-hexane (c-C₆H₁₂) of same molecular mass, size and vapor pressure.

Metal-incorporated mesoporous oxides: Synthesis and applications

Mesoporous oxides are outstanding metal nanoparticle catalyst supports owing to their well-defined porous structures. Such mesoporous architectures not only prevent the aggregation of metal nanoparticles but also enhance their catalytic performance. Metal/metal oxide heterojunctions exhibit unique chemical and physical properties because of the surface reconstruction around the junction and electron transfer/interaction across the interface. This article reviews the methods used for synthesizing metal-supported hybrid nanostructures and their applications as catalysts for environmental remediation and sensors for detecting hazardous materials.

Rational Design of Nanoporous MoS2 /VS2 Heteroarchitecture for Ultrahigh Performance Ammonia Sensors

2D transition metal dichalcogenides (TMDs) have received widespread interest by virtue of their excellent electrical, optical, and electrochemical characteristics. Recent studies on TMDs have revealed their versatile utilization as electrocatalysts, supercapacitors, battery materials, and sensors, etc. In this study, MoS₂ nanosheets are successfully assembled on the porous VS₂ (P-VS₂ ) scaffold to form a MoS₂ /VS₂ heterostructure. Their gas-sensing features, such as sensitivity and selectivity, are investigated by using a quartz crystal microbalance (QCM) technique. The QCM results and density functional theory (DFT) calculations reveal the impressive affinity of the MoS₂ /VS₂ heterostructure sensor toward ammonia with a higher adsorption uptake than the pristine MoS₂ or P-VS₂ sensor. Furthermore, the adsorption kinetics of the MoS₂ /VS₂ heterostructure sensor toward ammonia follow the pseudo-first-order kinetics model. The excellent sensing features of the MoS₂ /VS₂ heterostructure render it attractive for high-performance ammonia sensors in diverse applications.

Natural Source-Based Graphene as Sensitising Agents for Air Quality Monitoring

Natural carbon powder has been used as a precursor to prepare two main types of sensitising agents of nitrogen-doped carbon nanoparticles (N-CNPs) and nitrogen-doped graphene quantum dots coupled to nanosheets (N-GQDs-NSs) by using simple treatments of chemical oxidation and centrifugation separation. Characterization based on FTIR, XPS, XRD, Raman spectroscopy, FE-SEM, HR-TEM, AFM, UV-Vis and FL, revealed successful doping carbon nanoparticle with nitrogen with an average plane dimension of 50 nm and relatively smooth surface. The versatility of the prepared samples as sensitising agents was developed and established by exploiting its ability for detection of volatile organic compounds via simple optical fibre based sensing configuration. The comparative experimental studies on the proposed sensor performance indicate fast response achieved at a few tens of seconds and excellent repeatability in exposure to the methanol vapour. The low limit of detection of 4.3, 4.9 and 10.5 ppm was obtained in exposure to the methanol, ethanol and propanol vapours, respectively, in the atmosphere condition. This study gives insights into the chemical/physical mechanism of an enhanced economic optical fibre based gas sensor and illustrates it for diverse sensing applications, especially for chemical vapour remote detection and future air quality monitoring.

TiO₂-Based Nanoheterostructures for Promoting Gas Sensitivity Performance: Designs, Developments, and Prospects

Gas sensors based on titanium dioxide (TiO₂) have attracted much public attention during the past decades due to their excellent potential for applications in environmental pollution remediation, transportation industries, personal safety, biology, and medicine. Numerous efforts have therefore been devoted to improving the sensing performance of TiO₂. In those effects, the construct of nanoheterostructures is a promising tactic in gas sensing modification, which shows superior sensing performance to that of the single component-based sensors. In this review, we briefly summarize and highlight the development of TiO₂-based heterostructure gas sensing materials with diverse models, including semiconductor/semiconductor nanoheterostructures, noble metal/semiconductor nanoheterostructures, carbon-group-materials/semiconductor nano- heterostructures, and organic/inorganic nanoheterostructures, which have been investigated for effective enhancement of gas sensing properties through the increase of sensitivity, selectivity, and stability, decrease of optimal work temperature and response/recovery time, and minimization of detectable levels.

Ordered lamellar supermicroporous titania templating by rosin-derived quaternary ammonium salt

By using dehydroabietyltrimethyl ammonium bromine (DTAB), a novel rosin-derived quaternary ammonium salt, as template and peroxotitanium acid as precursor, ordered lamellar supermicroporous titania has been synthesized via a hydrothermal process. The template agent:titanium source molar ratio in the synthesis system and the hydrothermal temperature have great impact on the microstructure characteristics of the samples. The increase of DTAB:TiO₂ molar ratio from 0.04:1 to 0.10:1 is favorable to the increase of regularity of pore structures, but has no significant effects on the crystalline structures. The increase of the hydrothermal temperature from 343 to 393 K can induce an increase in crystallinity of the samples. However, the exorbitant hydrothermal temperature will reduce the regularity of pore structures. When the mole ratio of DTAB:TiO₂ is 0.10:1 and the hydrothermal temperature is 373 K, the as-synthesized sample possesses pore structure with the highest level of long-range order, as well as pore wall with semicrystallized anatase phase. The pore size and the pore wall thickness are about 2.0 nm and 1.0 nm, respectively.

Highly Efficient Elimination of Carbon Monoxide with Binary Copper-Manganese Oxide Contained Ordered Nanoporous Silicas

Ordered nanoporous silicas containing various binary copper-manganese oxides were prepared as catalytic systems for effective carbon monoxide elimination. The carbon monoxide elimination efficiency was demonstrated as a function of the [Mn]/[Cu] ratio and reaction time. The prepared catalysts were characterized by Brunauer-Emmett-Teller (BET) method, small- and wide-angle X-ray diffraction (XRD), and high-resolution transmission electron microscopy (HR-TEM) for structural analysis. Moreover, quantitative analysis of the binary metal oxides within the nanoporous silica was achieved by inductively coupled plasma (ICP). The binary metal oxide-loaded nanoporous silica showed high room temperature catalytic efficiency with over 98 % elimination of carbon monoxide at higher concentration ratio of [Mn]/[Cu].

Hierarchical mesoporous silicas templated by PE-b-PEO-b-PLA triblock copolymer for fluorescent drug delivery

Hierarchical mesoporous silicas for fluorescent drug-delivery molecule templated by PE-b-PEO-b-PLA triblock copolymer.

Multi-Stimuli-Responsive Polymeric Materials

Stimuli-responsive materials are of immense importance because of their ability to undergo alteration of their properties in response to their environment. The properties of such materials can be tuned by subtle adjustments in temperature, pH, light, and so forth. Among such smart materials, multi-stimuli-responsive polymeric materials are of pronounced significance as they offer a wide range of applications and their properties can be tuned through several mechanisms. Here, we aim to highlight some recent studies showcasing the multi-stimuli-responsive character of these polymers, which are still relatively little known compared to their single-stimuli-responsive counterpart.

Asymmetric block copolymers for supramolecular templating of inorganic nanospace materials

This review focuses on polymeric micelles consisting of asymmetric block copolymers as designed templates for several inorganic nanospace materials with a wide variety of compositions. The presence of chemically distinct domains of asymmetric triblock and diblock copolymers provide self-assemblies with more diverse morphological and functional features than those constructed by EOn POm EOn type symmetric triblock copolymers, thereby affording well-designed nanospace materials. This strategy can produce unprecedented nanospace materials, which are very difficult to prepare through other conventional organic templating approaches. Here, the recent development on the synthesis of inorganic nanospace materials are mainly focused on, such as hollow spheres, tubes, and porous oxides, using asymmetric triblock copolymers.

Self-assembly of gridlike zinc oxide lamellae for chemical-sensing applications

Hexagonal gridlike ZnO lamellae (GZL) with uniform thickness are synthesized by the o-phthalic acid-assisted hydrothermal method. Here, a systematic study of the assembly behaviors of gridlike ZnO lamellae obtained by the synergistic effect of urea and o-phthalic acid is presented. The morphology evolution and formation mechanism of GZL are also discussed in detail. The as-synthesized samples were characterized by powder X-ray diffraction, scanning electron microscopy, and transmission electron microscopy and electron diffraction spectroscopy. The results show that 2D ZnO lamellae are composed of nanotablets, which are jointed to form grids. The length and width of ZnO lamellae are about 1000 and 500 nm, respectively, and the thickness is about 30 nm. GZL morphology evolves from hexagonal ZnO nanotablets to lamellae with grids. The gas-sensing properties indicate that sensors fabricated from different materials present very different responses to volatile organic compounds. A GZL-based sensor has good response to acetaldehyde, and the response and recovery times are 1 and 6 s, respectively, when it was exposed to 1 ppm of acetaldehyde gas. The possibility of tuning the gas-sensing properties by adjusting the morphology makes GZL a novel candidate for more effective detection of a toxic, volatile gas with low concentration.

Controlling mesopore size and processability of transparent enzyme-loaded silica films for biosensing applications

Silica-based nanoporous thin films including large mesopores are relevant as enzyme supports for applications in biosensing. The diffusion and immobilization of large biomolecules such as enzymes in such porous films require the presence of large mesopores. Creating such morphologies based on a bottom-up synthesis using colloidal templates is a challenge in view of the combination of desired material properties and the robustness of the casting process for the fabrication of thin films. Here a strategy to reproducibly synthesize transparent porous silica thin films with submicrometer thickness and homogeneously distributed porosity is presented. For this purpose, polystyrene-poly-2-vinylpyridine (PS-P2VP) amphiphilic block copolymers are used as porogenic templates. Low-chain alcohols are employed as both selective solvents for the P2VP blocks and reaction media for silica synthesis. Rheology measurements reveal a strong influence of the block copolymer length on the behavior of PS-P2VP micelles in suspension. The pore distribution and accessibility into the film are controlled by adjusting the silica to block copolymer weight ratio. The solvent choice is shown to control not only the micelle size and the generated pore morphology but also the structural homogeneity of the films. Finally, the suitability of the synthesized films as supports for enzymes is tested using a model enzyme, horseradish peroxidase EC 1.11.1.7. Our approach is innovative, robust, and reproducible and provides a convenient alternative to synthesize large mesopores up to small macropores (20-100 nm) in nanostructured thin films with applications in biosensing and functional coatings.

Mesoporous TiO2/Zn2Ti3O8 hybrid films synthesized by polymeric micelle assembly

A hybrid mesoporous TiO₂/Zn₂Ti₃O₈ film synthesized by a polymeric micelle assembly approach.

Polymeric micelle assembly for the direct synthesis of functionalized mesoporous silica with fully accessible Pt nanoparticles toward an improved CO oxidation reaction

Pt-decorated mesoporous silica is directly prepared through a polymeric micelles assembly approach using an asymmetric triblock copolymer.

Direct synthesis of a mesoporous TiO2–RuO2 composite through evaporation-induced polymeric micelle assembly

Evaporation-induced assembly of spherical micelles made of an asymmetric triblock copolymer enables the fabrication of a mesoporous TiO₂–RuO₂ composite with a uniform pore size.