Direct printing synthesis of self-organized copper oxide hollow spheres on a substrate using copper(II) complex ink: gas sensing and photoelectrochemical properties

A Comprehensive Review on Printed Electronics: A Technology Drift towards a Sustainable Future

Printable electronics is emerging as one of the fast-growing engineering fields with a higher degree of customization and reliability. Ironically, sustainable printing technology is essential because of the minimal waste to the environment. To move forward, we need to harness the fabrication technology with the potential to support traditional process. In this review, we have systematically discussed in detail the various manufacturing materials and processing technologies. The selection criteria for the assessment are conducted systematically on the manuscript published in the last 10 years (2012-2022) in peer-reviewed journals. We have discussed the various kinds of printable ink which are used for fabrication based on nanoparticles, nanosheets, nanowires, molecular formulation, and resin. The printing methods and technologies used for printing for each technology are also reviewed in detail. Despite the major development in printing technology some critical challenges needed to be addressed and critically assessed. One such challenge is the coffee ring effect, the possible methods to reduce the effect on modulating the ink environmental condition are also indicated. Finally, a summary of printable electronics for various applications across the diverse industrial manufacturing sector is presented.

A Promising Three-Step Heat Treatment Process for Preparing CuO Films for Photocatalytic Hydrogen Evolution from Water

Copper (II) oxide (CuO) nanostructures were prepared on fluorine-doped tin oxide (FTO) using a three-step heat treatment process in a sol-gel dip-coating method. The precursor used for the dip-coating process was prepared using copper acetate, propan-2-ol, diethanolamine, and polyethylene glycol 400. Dip-coated films in layers of 2, 4, 6, 8, and 10 were prepared by drying each layer at 110 and 250 °C for 10 and 5 min, respectively, followed by calcination at 550 °C for 1 h. The films were applied toward photocatalytic hydrogen evolution from water. The X-ray diffraction (XRD) pattern of the films confirmed the tenorite phase of pure CuO. Raman spectroscopy revealed the 1Ag and 2Bg phonon modes of CuO, confirming the high purity of the films produced. The CuO films absorb significant photons in the visible spectrum due to their low optical band gap of 1.25-1.33 eV. The highest photocurrent of -2.0 mA/cm2 at 0.45 V vs reversible hydrogen electrode (RHE) was recorded for CuO films consisting of six layers under 1 sun illumination. A more porous surface, low charge transfer resistance, and high double-layer capacitance at the CuO/electrolyte interface observed for the films consisting of six layers contributed to the high photocurrent density attained by the films. CuO films consisting of six layers prepared using the conventional two-step heat treatment process for comparative purposes yielded 65.0% less photocurrent at 0.45 V vs RHE compared to similar films fabricated via the three-step heating method. The photocurrent response of the CuO nanostructures prepared using the three-step heat treatment process is promising and can be employed for making CuO for photovoltaic and optoelectronic applications.

Opposite Sensing Response of Heterojunction Gas Sensors Based on SnO2-Cr2O3 Nanocomposites to H2 against CO and Its Selectivity Mechanism

Metal oxide semiconductor (MOS) gas sensors show poor selectivity when exposed to mixed gases. This is a challenge in gas sensors and limits their wide applications. There is no efficient way to detect a specific gas when two homogeneous gases are concurrently exposed to sensing materials. The p-n nanojunction of xSnO₂-yCr₂O₃ nanocomposites (NCs) are prepared and used as sensing materials (x/y shows the Sn/Cr molar ratio in the SnO₂-Cr₂O₃ composite and is marked as Sn_xCr_y for simplicity). The gas sensing properties, crystal structure, morphology, and chemical states are characterized by employing an electrochemical workstation, an X-ray diffractometer, a transmission electron microscope, and an X-ray photoelectron spectrometer, respectively. The gas sensing results indicate that Sn_xCr_y NCs with x/y greater than 0.07 demonstrate a p-type behavior to both CO and H₂, whereas the Sn_xCr_y NCs with x/y < 0.07 illustrate an n-type behavior to the aforementioned reduced gases. Interestingly, the Sn_xCr_y NCs with x/y = 0.07 show an n-type behavior to H₂ but a p-type to CO. The effect of the operating temperature on the opposite sensing response of the fabricated sensors has been investigated. Most importantly, the mechanism of selectivity opposite sensing response is proposed using the aforementioned characterization techniques. This paper proposes a promising strategy to overcome the drawback of low selectivity of this type of sensor.

In Situ Assembly of Ordered Hierarchical CuO Microhemisphere Nanowire Arrays for High-Performance Bifunctional Sensing Applications

Seeking a facile approach to directly assemble bridged metal oxide nanowires on substrates with predefined electrodes without the need for complex postsynthesis alignment and/or device procedures will bridge the gap between fundamental research and practical applications for diverse biochemical sensing, electronic, optoelectronic, and energy storage devices. Herein, regularly bridged CuO microhemisphere nanowire arrays (RB-MNAs) are rationally designed on indium tin oxide electrodes via thermal oxidation of ordered Cu microhemisphere arrays obtained by solid-state dewetting of patterned Ag/Cu/Ag films. Both the position and spacing of CuO microhemisphere nanowires can be well controlled by as-used shadow mask and the thickness of Cu film, which allows homogeneous manipulation of the bridging of adjacent nanowires grown from neighboring CuO hemispheres, and thus benefits highly sensitive trimethylamine (TMA) sensors and broad band (UV-visible to infrared) photodetectors. The electrical response of 3.62 toward 100 ppm TMA is comparable to that of state-of-the-art CuO-based sensors. Together with the feasibility of in situ assembly of RB-MNAs device arrays via common lithographic technologies, this work promises commercial device applications of CuO nanowires.

Fabrication of Single-Phase Manganese Oxide Films by Metal-Organic Decomposition

Here, single-phase Mn2O3 and Mn3O4 films are successfully fabricated by a facile solution process based on metal-organic decomposition (MOD), for the first time. A formulated manganese 2-ethylhexanoate solution was used as an MOD precursor for the preparation of manganese oxide films. The difference in thermal decomposition behavior of precursor solution in air and inert atmospheres was observed, indicating that the calcination atmosphere is the main factor for controlling the valence of manganese oxide films. Significantly, the solution-coated films on substrates are found to be transformed into single-phase Mn2O3 and Mn3O4 films when they are calcinated under air and inert atmosphere, respectively. The film crystallinity was improved with increasing calcination temperature for both Mn2O3 and Mn3O4 films. In particular, it is noted that the grains of Mn2O3 film were somewhat linearly grown in air, while those of Mn3O4 film exhibited the drastic growth in Ar with an increase of calcination temperature.

Gas Sensors Based on Copper Oxide Nanomaterials: A Review

Metal oxide semiconductors have found widespread applications in chemical sensors based on electrical transduction principles, in particular for the detection of a large variety of gaseous analytes, including environmental pollutants and hazardous gases. This review recapitulates the progress in copper oxide nanomaterial-based devices, while discussing decisive factors influencing gas sensing properties and performance. Literature reports on the highly sensitive detection of several target molecules, including volatile organic compounds, hydrogen sulfide, carbon monoxide, carbon dioxide, hydrogen and nitrogen oxide from parts-per-million down to parts-per-billion concentrations are compared. Physico-chemical mechanisms for sensing and transduction are summarized and prospects for future developments are outlined.

CuBi2O4 Prepared by the Polymerized Complex Method for Gas-Sensing Applications

Multicomponent oxides can be extensively explored as alternative gas-sensing materials to binary oxides with their structural and compositional versatilities. In this work, the gas-sensing properties of CuBi₂O₄ have been investigated toward various reducing gases (C₂H₅OH, NH₃, H₂, CO, and H₂S) and oxidizing gas (NO₂) for the first time. For this, the powder synthesis has been developed using the polymerized complex method (Pechini method) to obtain a single-phase polycrystalline CuBi₂O₄. The defect, optical, and electronic properties in the prepared CuBi₂O₄ powder were modulated by varying the calcination temperature from 500 to 700 °C. Noticeably, a high concentration of Cu⁺-oxygen vacancy ([Formula: see text]) defect complexes and isolated Cu²⁺ ion clusters was found in the 500 °C-calcined CuBi₂O₄, where they were removed through air calcination at higher temperatures (up to 700 °C) while making the compound more stoichiometric. The change in the intrinsic defect concentration with the calcination temperature led to the variation of the electronic band gap energy and hole concentration in CuBi₂O₄ with the polaronic hopping conduction (activation energy = 0.43 eV). The CuBi₂O₄ sensor with 500 °C-calcined powder showed the highest gas responses (specifically, 10.4 toward 1000 ppm C₂H₅OH at the operating temperature of 400 °C) with the highest defect concentration. As a result, the gas-sensing characteristics of CuBi₂O₄ are found to be dominantly affected by the intrinsic defect concentration, which is controlled by the calcination temperature. Toward reducing H₂S and oxidizing NO₂ gases, the multiple reactions arising simultaneously on the surface of the CuBi₂O₄ sensor govern its response behavior, depending on the gas concentration and the operating temperature. We believe that this work can be a cornerstone for understanding the effect of chemical defect on the gas-sensing characteristics in multicomponent oxides.

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.

Synthesis and applications of porous non-silica metal oxide submicrospheres

A variety of metal oxide particles of spherical morphology from nano to micrometer size have been reviewed with a special emphasis on the appraisal of synthetic strategies and applications in biomedical, environmental and energy-related areas.

Recent developments and directions in printed nanomaterials

In this review, we survey several recent developments in printing of nanomaterials for contacts, transistors, sensors of various kinds, light-emitting diodes, solar cells, memory devices, and bone and organ implants. The commonly used nanomaterials are classified according to whether they are conductive, semiconducting/insulating or biological in nature. While many printing processes are covered, special attention is paid to inkjet printing and roll-to-roll printing in light of their complexity and popularity. In conclusion, we present our view of the future development of this field.

Ultrasmall Cu2O nanocrystals: facile synthesis, controllable assembly and photocatalytic properties

2D or 3D Cu₂O superstructures are successfully achieved from ideal Cu₂O building blocks.

EG-Assisted hand-in-hand growth of prism-like Cu2O nanorods with high aspect ratios and their thermal conductive performance

EG acts as a “bridge” that controls the “hand-in-hand” growth and transforms the Cu₂O wires into prism-like nanorods.