A portable gas sensor based on In2O3@CuO P-N heterojunction connected via Wi-Fi to a smartphone for real-time carbon monoxide determination

This research presents a compact portable electronic gas sensor that can be monitored through a smartphone application. The smart sensor utilizes three state-of-the-art sensors. The sensors integrate an ESP8266 microcontroller within the same device. This facilitates their integration with the electronics and enhances their performance. Herein, primarily focuses on utilizing the sensor to detect carbon monoxide. This article outlines the fabrication process of a gas sensor utilizing a P-N heterojunction, eliminating the need for a binder. The sensor consists of CuO/copper foam nanowires and hierarchical In2O3. In order to verify the system's functionality, it underwent testing with various levels of CO concentrations (10-900 ppm), including particular tests designed to examine the device's performance in different humidity and temperature circumstances. A mobile application for the provision of monitoring services has been developed at last. To process the information obtained from the gas sensor, an algorithm has been constructed, trained, and integrated into a smartphone for this purpose. This research demonstrated that a smartphone-coupled gas sensor is a viable system for real-time monitoring and the detection of CO gas.

Green Synthesis of Copper Nanoparticles Using Sargassum spp. for Electrochemical Reduction of CO2

This study presents a green method of producing copper nanoparticles (CuNPs) using aqueous extracts from Sargassum spp. as reducing, stabilizing, and capping agents. The CuNPs created using this algae-based method are not hazardous, they are eco-friendly, and less toxic than their chemically synthesized counterparts. The XRD characterization of the CuNPs revealed the presence of Cu and CuO, with a crystallite size ranging from 13 to 17 nm. Following this, the CuNPs were supported onto a carbon substrate, also derived from Sargassum spp. (biochar CSKPH). The CuNPs in biochar (CuNPs-CSKPH) did not appear in the XRD diffractograms, but the SEM-EDS results showed that they accounted for 36 % of the copper weight. The voltamperometric study of CuNps-CSKPH in acid media validated the presence of Cu and the amount was determined to be 2.58 μg. The catalytic activity of CuNPs-CSKPH was analyzed for the electrochemical reduction of CO2. The use of Sargassum spp. has great potential to tackle two environmental problems simultaneously, by using it as raw material for the synthesis of activated biochar as support, as well as the synthesis of CuNPs, and secondly, by using it as a sustainable material for the electrochemical conversion of CO2.

Voltammetric Detection of Glucose-The Electrochemical Behavior of the Copper Oxide Materials with Well-Defined Facets

Cu₂O nanomaterials with well-defined facets and uniform size were synthesized by a wet-chemical method. Regardless of the additive composition, powders crystallize mostly in cuprite form. To compare their electrochemical behavior, the obtained materials were deposited on carbon glassy electrodes. The response to glucose from the materials with different exposed facets was recorded with a delay at the anodic curve. The chronoamperometric analyses (AMP) exhibited a lower signal in contrast to the cyclic voltammetry data (CV), indicating that the number of active sites involved in glucose oxidation processes resulting from the structure of the material is insufficient. For samples with dominant (100) or (111) planes, a typical characteristic was observed, however, with an additional peak at the anodic curve. The location of the peaks is approximately the same and no significant differences from the AMP and CV analysis were observed. The sample enclosed by the (111) facets exhibited higher activity; however, as a result of the redox reaction with glucose molecules, the surface state is changing. Cu₂O materials enclosed by (100) planes exhibited optimal sensitivity as well as a large detective range. Samples with differential facet exposition present various current-potential profiles, as the effect of binder-particle interaction with Nafion.

Energy and environmental applications of Sn4+/Ti4+ doped α-Fe2O3@Cu2O/CuO photoanode under optimized photoelectrochemical conditions

The most promising technique for directly converting solar energy into clean fuels and environmental remediation by organic dye degradation is photoelectrochemical (PEC) process. We introduced Sn⁴⁺/Ti⁴⁺ doped α-Fe₂O₃@Cu_xO heterojunction photoanode with complete optimization for PEC hydrogen (H₂) generation and organic dye degradation. Improvement of photocurrent photo and reducing overpotentials under optimized conditions lead to enhancing PEC performances, degradation efficiency of organic compounds, and H₂ generation generation rate. The optimized heterojunction photoanode (5TiFe@Cu_xO-D) showed IPCE exceeding 42% compared with pristine hematite (Fe_0.01-800_6h) nanostructures (28%). Additionally, all the optimized photoanodes showed higher PEC stability for 10 h. Time-resolved PL spectra confirm the improved average lifetime for heterojunction photoanodes, supporting the enhanced PEC performance. Optimized 5TiFe@Cu_xO-D material achieved PEC H₂ generation of ∼300 μL h^-1.cm^-2 which is two times higher than pristine hematite's activity (150 μL h^-1.cm^-2) and almost 99% degradation efficiency within 120 min of irradiation time. Therefore, a state-of-the-art study has been explored for hematite-based heterojunction photoanodes reflecting the superior PEC performance and hydrogen, methyl orange (MO) dye degradation activities. The improved results were reported because of stable morphology and better crystallinity acquired through systematic investigation of thermal effects and hydrothermal duration, improved electrical properties by Sn/Ti doping into the lattice of α-Fe₂O₃ and optimization of Cu_xO deposition methods. The formation of well-defined heterojunction minimizes the recombination of the charge carrier and leads to effective transportation of excited electrons for the enhanced PEC performance.

Investigation of copper nanoscale electro-crystallization under directed and non-directed electrodeposition from dilute electrolytes

In situ and ex situ atomic force microscopy was used to investigate crystal growth in copper electro-crystallization localized and directed by a moving nanoelectrode in close proximity to a gold substrate in a highly dilute electrolyte.

Surface engraving engineering of polyhedral photocatalysts

Surface engraving engineering of polyhedral photocatalysts is overviewed based on synthetic strategies and engraved surface-related photocatalytic mechanisms. Some challenges and perspectives are also proposed.

The solid-state in situ construction of Cu2O/CuO heterostructures with adjustable phase compositions to promote CO oxidation activity

Cu₂O/CuO heterojunctions were fabricated via in situ solid-state technology. Tuning the ratio of reactants enables optimization of the components of the Cu₂O/CuO heterostructures and their catalytic activities for CO oxidation.

Surface-Controlled Photocatalysis and Chemical Sensing of TiO2, α-Fe2O3, and Cu2O Nanocrystals

A relatively new approach to the design of photocatalytic and gas sensing materials is to use the shape-controlled nanocrystals with well-defined facets exposed to light or gas molecules. An abrupt increase in a number of papers on the synthesis and characterization of metal oxide semiconductors such as a TiO2, α-Fe2O3, Cu2O of low-dimensionality, applied to surface-controlled photocatalysis and gas sensing, has been recently observed. The aim of this paper is to review the work performed in this field of research. Here, the focus is on the mechanism and processes that affect the growth of nanocrystals, their morphological, electrical, and optical properties and finally their photocatalytic as well as gas sensing performance.

Small-Scale Biological and Artificial Multidimensional Sensors for 3D Sensing

A vast majority of existing sub-millimeter-scale sensors have a planar, 2D geometry as a result of conventional top-down lithographic procedures. However, 2D sensors often suffer from restricted sensing capability, allowing only partial measurements of 3D quantities. Here, nano/microscale sensors with different geometric (1D, 2D, and 3D) configurations are reviewed to introduce their advantages and limitations when sensing changes in quantities in 3D space. This Review categorizes sensors based on their geometric configuration and sensing capabilities. Among the sensors reviewed here, the 3D configuration sensors defined on polyhedral structures are especially advantageous when sensing spatially distributed 3D quantities. The nano- and microscale vertex configuration forming polyhedral structures enable full 3D spatial sensing due to orthogonally aligned sensing elements. Particularly, the cubic configuration leveraged in 3D sensors offers an array of diverse applications in the field of biosensing for micro-organisms and proteins, optical metamaterials for invisibility cloaking, 3D imaging, and low-power remote sensing of position and angular momentum for use in microbots. Here, various 3D sensors are compared to assess the advantages of their geometry and its impact on sensing mechanisms. 3D biosensors in nature are also explored to provide vital clues for the development of novel 3D sensors.

Octahedral-Like CuO/In2O3 Mesocages with Double-Shell Architectures: Rational Preparation and Application in Hydrogen Sulfide Detection

This contribution describes a facile strategy for constructing octahedral-like CuO/In₂O₃ mesocages with double-shell architectures. The synthetic method included first preparation of unifrom Cu₂O as an ideal self-sacrificial template and then decoration by a In₂O₃ outer layer through room-temperature Cu₂O-engaged redox etching reaction combined with subsequent annealing process. Various characterization techniques manifested that In₂O₃ nanoparticles were uniformly grown on the surface of CuO mesocages, resulting in a well-defined double-shelled heterostructure. When evaluated as a novel sensing material for hydrogen sulfide (H₂S) detection, the resultant octahedral-like CuO/In₂O₃ heterostructures exhibited obviously enhanced sensing response, lower operating temperature as well as faster response/recover speed during the dynamic measurement compared to the pristine CuO particles, which is likely related to the high-level of adsorbed oxygen concentration, resistance modulation effect, and unique microstructure of as-prepared CuO/In₂O₃ heterostructure.

Topological Transformations of Core-Shell Precursors to Hierarchically Hollow Assemblages of Copper Silicate Nanotubes

Functional hollow materials have attracted extensive research attention due to their promising prospects for catalysis. Herein, we report an alternative synthesis of hierarchically hollow structured materials directly from core-shell structured templates, based on confined chemical reactions between the solid matter of a core and shell under hydrothermal conditions. More specifically, we have developed a novel and facile strategy to transform core-shell structured Cu₂O@mSiO₂ (m = mesoporous) to tubular copper silicate assemblages (TCSA). Depending on the original shapes of Cu₂O, TCSA can be tailored as spherical or cubic assemblages with stacking copper silicate nanotubes (inner diameter: 4.5 nm, thickness: 0.8 nm, length: ca. 96 nm) in the shell. Moreover, by utilizing the residual reductive Cu(I) (ca. 10 at% of total surface copper) on TCSA support, in situ generations of Pd nanoparticles (∼4.5 nm) and Au nanoparticles (∼5.8 nm) were successfully achieved based on the spontaneous galvanic replacement reactions. Two integrated nanocatalysts (viz., Pd/TCSA and Au/TCSA) have been prepared with this approach. As an example, Pd/TCSA exhibits excellent activity and recyclability for Suzuki-Miyaura cross-coupling reactions.

Stoichiometry, Morphology, and Size-Controlled Electrochemical Fabrication of CuxO (x = 1, 2) at Underpotential

A new one-step electrochemical approach has been developed for the morphology, size, and stoichiometry-controlled synthesis of Cu₂O, CuO, and Cu₂O/CuO composite structures at room temperature without using surfactants, capping agents, or any other additives. The electrochemical deposition of a Cu monolayer using underpotential deposition (UPD) and the flow rate of oxygen gas bubbled through the deposition solution used for oxidation of the Cu layer are the key parameters for controlling the stoichiometry of the Cu_xO (x = 1, 2) structures. The morphologies, crystallinity, stoichiometries, optical properties, and photoelectrochemical properties of the as-electrodeposited Cu₂O and CuO materials were analyzed using scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy dispersive spectroscopy (EDS), UV-vis absorption, and photoelectrochemical (PEC) techniques. The results indicated that the Cu₂O and CuO materials electrodeposited on both indium tin oxide coated (ITO) quartz and gold electrodes using this new electrochemical technique exhibit high-quality single crystalline structures and high photoactivity with rapid photoelectrical response to light irradiation.

Notable in situ surface transformation of Cu2O nanomaterials leads to dramatic activity enhancement for CO oxidation

Irrespective of the initial states, the pure Cu(i) surface of Cu₂O would in situ transform into a stable Cu(i)–Cu(ii) composite surface during the first catalytic run of CO oxidation, resulting in dramatic activity enhancement.

Hollow CuxO (x = 2, 1) micro/nanostructures: synthesis, fundamental properties and applications

In this review, we comprehensively summarize the important advances in hollow Cu_xO micro/nanostructures, including the universal synthesis strategies, the interfacial Cu–O atomic structures as well as the intrinsic properties, and potential applications. Remarks on emerging issues and promising research directions are also discussed.

Facile fabrication of CuO/Cu2O composites with high catalytic performances

CuO/Cu₂O composites having good catalytic properties for the reduction of 4-nitrophenol have been prepared facilely for wastewater treatment.

Highly sensitive and selective CO gas sensor based on a hydrophobic SnO2/CuO bilayer

CO gas sensing mechanism of SnO₂/CuO bilayer sensor.

Facet-Controlled Synthetic Strategy of Cu2O-Based Crystals for Catalysis and Sensing

Shape-dependent catalysis and sensing behaviours are primarily focused on nanocrystals enclosed by low-index facets, especially the three basic facets ({100}, {111}, and {110}). Several novel strategies have recently exploded by tailoring the original nanocrystals to greatly improve the catalysis and sensing performances. In this Review, we firstly introduce the synthesis of a variety of Cu₂O nanocrystals, including the three basic Cu₂O nanocrystals (cubes, octahedra and rhombic dodecahedra, enclosed by the {100}, {111}, and {110} facets, respectively), and Cu₂O nanocrystals enclosed by high-index planes. We then discuss in detail the three main facet-controlled synthetic strategies (deposition, etching and templating) to fabricate Cu₂O-based nanocrystals with heterogeneous, etched, or hollow structures, including a number of important concepts involved in those facet-controlled routes, such as the selective adsorption of capping agents for protecting special facets, and the impacts of surface energy and active sites on reaction activity trends. Finally, we highlight the facet-dependent properties of the Cu₂O and Cu₂O-based nanocrystals for applications in photocatalysis, gas catalysis, organocatalysis and sensing, as well as the relationship between their structures and properties. We also summarize and comment upon future facet-related directions.

Recent advances in hybrid Cu2O-based heterogeneous nanostructures

Hybrid Cu2O-based heterogeneous nanostructures possess novel synergistic properties that arise from the integrated interaction between the disparate components, thereby showing promising potential for various important applications including solar cells, carbon monoxide oxidation, photocatalysts, field emission, sensors, templates and so on. With the rapid progress in nanomaterials science and nanotechnology, hybrid Cu2O-based heterogeneous nanostructures with well-controlled compositions, shapes and sizes have been rationally designed and synthesized. This review attempts to summarize the important advances in the development of different types of hybrid Cu2O-based heterogeneous nanostructures, such as hybrid Cu2O-metal nanostructures, hybrid Cu2O-metal oxide nanostructures and hybrid Cu2O-carbon nanostructures. The correlations between the improved performances and interfacial structures of the hybrid Cu2O-based heterogeneous nanostructures are discussed based on some important and representative examples. Several key scientific issues and perspective research directions in this field are also given.

Morphology-controllable synthesis of novel Bi25VO40 microcubes: optical properties and catalytic activities for the reduction of aromatic nitro compounds

Novel Bi₂₅VO₄₀ microcubes were successfully prepared via a facile hydrothermal synthesis route and they exhibited excellent optical and catalytic properties.

Plate-like p-n heterogeneous NiO/WO₃ nanocomposites for high performance room temperature NO₂ sensors

Plate-like heterogeneous NiO/WO₃ nanocomposites have been successfully prepared by annealing Ni(OH)₂ and H₂WO₄ in air. These NiO/WO₃ nanocomposites have shown excellent sensitivity towards NO₂ and ultrafast response at room temperature due to their p-n heterogeneous characteristics.