CuO/Cu2O nanoparticles: A simple and green synthesis, characterization and their electrocatalytic performance toward formaldehyde oxidation

Electrochemical sensing performance of two CuO nanomaterial-modified dual-working electrodes

Two CuO nanostructures, namely, nanospheres (CuONSs) and nanochains (CuONCs) with different shapes but similar diameters, were synthesized and characterized. With these two nanomaterials as electrode modifiers, a systematic comparative study was conducted to examine their electrochemical sensing of catechol (CT) using a dual-working electrode system. The results suggest that for CuONS- and CuONC-modified glassy carbon electrodes, the electrode process for the CT redox is diffusion-controlled, and the modification amount and electrolyte pH have a similar effect on the response. However, the CuONCs showed a higher peak current and lower peak potential, as well as a lower detection limit for the electrochemical oxidation of CT. This is explained by the lower charge transfer impedance and higher electroactive surface area of the CuONCs. Notably, an unexpected peak appeared in the cyclic voltammograms when the pH was <4 for the CuONCs and <3 for the CuONSs. For this phenomenon, UV-Vis spectra, zeta potential, and size distribution experiments demonstrated changes in the two CuO nanostructures at lower pH, illustrating that CuONSs can tolerate a higher pH as compared to CuONCs. The multiple comparisons between the two nanomaterials presented here can provide references for the selection of electrochemical sensing materials.

Real-time, noise and drift resilient formaldehyde sensing at room temperature with aerogel filaments

Formaldehyde, a known human carcinogen, is a common indoor air pollutant. However, its real-time and selective recognition from interfering gases remains challenging, especially for low-power sensors suffering from noise and baseline drift. We report a fully 3D-printed quantum dot/graphene-based aerogel sensor for highly sensitive and real-time recognition of formaldehyde at room temperature. By optimizing the morphology and doping of printed structures, we achieve a record-high and stable response of 15.23% for 1 part per million formaldehyde and an ultralow detection limit of 8.02 parts per billion consuming only ∼130-microwatt power. On the basis of measured dynamic response snapshots, we also develop intelligent computational algorithms for robust and accurate detection in real time despite simulated substantial noise and baseline drift, hitherto unachievable for room temperature sensors. Our framework in combining materials engineering, structural design, and computational algorithm to capture dynamic response offers unprecedented real-time identification capabilities of formaldehyde and other volatile organic compounds at room temperature.

Recent Advances in Electrochemical Sensors for Formaldehyde

Formaldehyde, a ubiquitous indoor air pollutant, plays a significant role in various biological processes, posing both environmental and health challenges. This comprehensive review delves into the latest advancements in electrochemical methods for detecting formaldehyde, a compound of growing concern due to its widespread use and potential health hazards. This review underscores the inherent advantages of electrochemical techniques, such as high sensitivity, selectivity, and capability for real-time analysis, making them highly effective for formaldehyde monitoring. We explore the fundamental principles, mechanisms, and diverse methodologies employed in electrochemical formaldehyde detection, highlighting the role of innovative sensing materials and electrodes. Special attention is given to recent developments in nanotechnology and sensor design, which significantly enhance the sensitivity and selectivity of these detection systems. Moreover, this review identifies current challenges and discusses future research directions. Our aim is to encourage ongoing research and innovation in this field, ultimately leading to the development of advanced, practical solutions for formaldehyde detection in various environmental and biological contexts.

High Selectivity Fuel from Efficient CO2 Conversion by Zn-Modified rGO and Amine-Functionalized CuO as a Photocatalyst

Reduced graphene oxide (rGO) has been used in copper (II) oxide (CuO)-based photocatalysts as an additive material. An application of this CuO-based photocatalyst is in the CO₂ reduction process. The preparation of rGO by a Zn-modified Hummers' method has resulted in a high quality of rGO in terms of excellent crystallinity and morphology. However, implementing Zn-modified rGO in CuO-based photocatalysts for the CO₂ reduction process has yet to be studied. Therefore, this study explores the potential of combining Zn-modified rGO with CuO photocatalysts and performing these rGO/CuO composite photocatalysts to convert CO₂ into valuable chemical products. The rGO was synthesized by using a Zn-modified Hummers' method and covalently grafted with CuO by amine functionalization with three different compositions (1:10, 1:20, and 1:30) of rGO/CuO photocatalyst. XRD, FTIR, and SEM were used to investigate the crystallinity, chemical bonds, and morphology of the prepared rGO and rGO/CuO composites. The performance of rGO/CuO photocatalysts for the CO₂ reduction process was quantitively measured by GC-MS. We found that the rGO showed successful reduction using a Zn reducing agent. The rGO sheet could be grafted with CuO particles and resulted in a good morphology of rGO/CuO, as shown from the XRD, FTIR, and SEM results. The rGO/CuO material showed photocatalytic performance due to the advantages of synergistic components and resulted in methanol, ethanolamine, and aldehyde as fuel with amounts of 37.12, 8730, and 17.1 mmol/g catalyst, respectively. Meanwhile, adding CO₂ flow time increases the resulting quantity of the product. In conclusion, the rGO/CuO composite could have potential for large-scale CO₂ conversion and storage applications.

Synthesis of a dual-functional terbium doped copper oxide nanoflowers for high-efficiently electrochemical sensing of ofloxacin, pefloxacin and gatifloxacin

The current effort introduces a facile construction of peony-like CuO:Tb³⁺ nanostructure (P-L CuO:Tb³⁺ NS), whose characterization was determined via techniques of X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy. We investigated ofloxacin, pefloxacin and gatifloxacin oxidation electrochemically on P-L CuO:Tb³⁺ NS-modified glassy carbon electrode (P-L CuO:Tb³⁺ NS/GCE), the results of which revealed the irreversible oxidation of drugs through a two-electron oxidation process. An admirable resolution was found for this modified electrode between voltammetric peaks of ofloxacin, pefloxacin and gatifloxacin, suggesting its appropriateness for simultaneous detection of these drugs in pharmaceutical media. In addition, our nanostructure synergistically influenced the electro-catalytic oxidations of these three compounds. Differential pulse voltammetric measurements of ofloxacin, pefloxacin and gatifloxacin through our sensor showed a limit of detection of 1.9, 2.3 and 1.2 nM a as well as a linear dynamic range between 0.01 and 800.0 μM in phosphate buffered solution (0.1 M, pH = 6.0), respectively. Moreover, as-fabricated sensor could successfully co-detect these drugs in real serum and tablets specimens. In addition, since we use animal foods such as milk it is very important to detect their fluoroquinolone residues. For this purpose, the proposed sensor was tested to determine the residues of ofloxacin, pefloxacin and gatifloxacin in milk.

Peroxidase mimicking activity of Saccharum officinarum L. capped gold nanoparticles using o-dianisidine as a substrate

In this study, a biogenic method is reported for the fabrication of gold nanoparticles (Au NPs) using Saccharum officinarum L. (SOL) and studied the peroxidase mimicking activity using o-dianisidine (ODA) as a substrate.

A Novel Cu2O/ZnO@PET Composite Membrane for the Photocatalytic Degradation of Carbendazim

The extremely high levels of water pollution caused by various industrial activities represent one of the most important environmental problems. Efficient techniques and advanced materials have been extensively developed for the removal of highly toxic organic pollutants, including pesticides. This study investigated the photocatalytic degradation of the fungicide carbendazim (Czm) using composite track-etched membranes (TeMs) in an aqueous solution. Copper(I) oxide (Cu₂O) and zinc oxide (ZnO) microtubes (MTs) were prepared using an electroless template deposition technique in porous poly(ethylene terephthalate) (PET) TeMs with nanochannels with a density of 4 × 10⁷ pores/cm⁻² and diameter of 385 ± 9 nm to yield Cu₂O@PET and ZnO@PET composite membranes, respectively. A mixed Cu₂O/ZnO@PET composite was prepared via a two-step deposition process, containing ZnO (87%) and CuZ (13%) as crystalline phases. The structure and composition of all composite membranes were elucidated using scanning electron microscopy (SEM), atomic force microscopy (AFM), energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) techniques. Under UV–visible light irradiation, the Cu₂O/ZnO@PET composite displayed enhanced photocatalytic activity, reaching 98% Czm degradation, higher than Cu₂O@PET and ZnO@PET composites. The maximum Czm degradation efficiency from aqueous solution was obtained at an optimal pH of 6 and contact time of 140 min. The effects of various parameters such as temperature, catalyst dosage and sample exposure time on the photocatalytic degradation process were studied. The degradation reaction of Czm was found to follow the Langmuir–Hinshelwood mechanism and a pseudo-first order kinetic model. The degradation kinetics of Czm accelerated with increasing temperature, and the activation energy (E_a) levels were calculated as 11.9 kJ/mol, 14.22 kJ/mol and 15.82 kJ/mol for Cu₂O/ZnO@PET, ZnO@PET and Cu₂O@PET composite membranes, respectively. The reusability of the Cu₂O/ZnO@PET catalyst was also investigated at different temperatures for 10 consecutive runs, without any activation or regeneration processes. The Cu₂O/ZnO@PET composite exhibited degradation efficiency levels of over 50% at 14 °C and over 30% at 52 °C after 5 consecutive uses.

Synthesis and characterization of CuxO/Bi2O3 oxides for removal of HCHO under visible light irradiation

Cu_xO/Bi₂O₃ oxides grown on nickel foam were synthesized via an electrodeposition method to degrade indoor HCHO under visible light irradiation and fully characterized by XRD, SEM, FT-IR, and UV-Vis technologies. The characterization results showed that the Cu_xO/Bi₂O₃ oxides were successfully loaded on nickel foam and the visible light response spectrum was expanded to 740 nm. Plackett-Burman design combined with central composite design has been used to optimize factors that affect HCHO removal performance. The results demonstrated that bismuth nitrate content, polyethylene glycol 600 content, sintering time, and lactic acid concentration were the four most important factors affecting the HCHO removal performance over Cu_xO/Bi₂O₃ sample. The optimum Cu_xO/Bi₂O₃ sample could degrade 88.796% of HCHO in 300 min at the conditions of 4.28 mol/L lactic acid, 4.86% polyethylene glycol 600, 194.03 min sintering time, and 45.83 g bismuth nitrate, and the HCHO removal rate remained 82.3% after five cycles. A plausible mechanism for the degradation of HCHO under visible light irradiation was proposed. This work provides a feasible solution for removing indoor formaldehyde in the field of photocatalysis.

Metal- and metal/oxide-based engineered nanoparticles and nanostructures: a review on the applications, nanotoxicological effects, and risk control strategies

The production and demand of nanoparticles in the manufacturing sector and personal care products, release a large number of engineered nanoparticles (ENPs) into the atmosphere, aquatic ecosystems, and terrestrial environments. The intentional or involuntary incorporation of ENPs into the environment is carried out through different processes. The ENPs are combined with other compounds and release into the atmosphere, settling on the ground due to the water cycle or other atmospheric phenomena. In the case of aquatic ecosystems, the ENPs undergo hetero-aggregation and sedimentation, reaching different living organisms and flora, as well as groundwater. Accordingly, the high mobility of ENPs in diverse ecosystems is strongly related to physical, chemical, and biological processes. Recent studies have been focused on the toxicological effects of a wide variety of ENPs using different validated biological models. This literature review emphasizes the study of toxicological effects related to using the most common ENPs, specifically metal and metal/oxides-based nanoparticles, addressing different synthesis methodologies, applications, and toxicological evaluations. The results suggest negative impacts on biological models, such as oxidative stress, metabolic and locomotive toxicity, DNA replication dysfunction, and bioaccumulation. Finally, it was consulted the protocols for the control of risks, following the assessment and management process, as well as the classification system for technological alternatives and risk management measures of ENPs, which are useful for the transfer of technology and nanoparticles commercialization.

Algae-mediated route to biogenic cuprous oxide nanoparticles and spindle-like CaCO3: a comparative study, facile synthesis, and biological properties

Biocompatible syntheses of Cu2O nanoparticles are relatively low compared to some other reported metal oxides due to their low stability and requiring more carefully controlled synthetic conditions. In the present study, the efficiency of three brown algae (Cystoseira myrica, Sargassum latifolium and Padina australis) extracts collected from the Persian Gulf was evaluated in the biosynthesis of Cu2O nanoparticles. A fast and simplified synthesis of Cu2O nanoparticles with average size between 12 and 26 nm was successfully achieved through an eco-friendly method using the aqueous extracts of Sargassum latifolium and Cystoseira myrica. Whereas, under the same reaction conditions using Padina australis extract no Cu2O nanoparticles were produced, and unexpectedly, the results approved the formation of spindle shaped CaCO3 with average sizes of 1-2 μm in length and 300-500 nm in width. Structure, morphology and composition of the as-prepared products were characterized by XRD, FT-IR, UV-vis, TEM and FESEM analysis. This work confirms that the biomolecules present in algae have the ability to affect particle size, morphology, composition, and physicochemical properties of the synthesized particles. The Cu2O nanoparticles prepared in this study were stable and exhibited efficient antibacterial and anticancer activity. This biosynthesis technique can be valuable in environmental, biotechnological, pharmaceutical and medical applications.

Application of biosynthesized metal nanoparticles in electrochemical sensors

Recently, the development of eco-friendly, cost-effective and reliable methods for synthesis of metal nanoparticles has drawn a considerable attention. The so-called green synthesis, using mild reaction conditions and natural resources as plant extracts and microorganisms, has established as a convenient, sustainable, cheap and environmentally safe approach for synthesis of a wide range of nanomaterials. Over the past decade, biosynthesis is regarded as an important tool for reducing the harmful effects of traditional nanoparticle synthesis methods commonly used in laboratories and industry. This review emphasizes the significance of biosynthesized metal nanoparticles in the field of electrochemical sensing. There is increasing evidence that green synthesis of nanoparticles provides a new direction in designing of cost-effective, highly sensitive and selective electrode-catalysts applicable in food, clinical and environmental analysis. The article is based on 157 references and provided a detailed overview on the main approaches for green synthesis of metal nanoparticles and their applications in designing of electrochemical sensor devices. Important operational characteristics including sensitivity, dynamic range, limit of detection, as well as data on stability and reproducibility of sensors have also been covered.

High Specific Capacity Thermal Battery Cathodes LiCu2O2 and LiCu3O3 Prepared by a Simple Solid Phase Sintering

The thermal battery has been designed to be active at high temperature to satisfy storage life and large capacity for storage and emergency power. The development of thermal battery with high specific energy requires that the cathode has high thermal stability and excellent conductivity. Here, the semiconductor material Li-Cu-O compounds LiCu₂O₂ and LiCu₃O₃ are synthesized by a simple solid-phase sintering technique, which is simpler than the traditional synthesis process. The thermal decomposition temperatures are 680°C and above 900°C, respectively. This work first applies the Li-Cu-O compounds to the thermal battery. With a cutoff voltage of 1.5 V, the specific capacities of LiCu₂O₂ and LiCu₃O₃ are 423 and 332 mA h g^-1. Both the decomposition temperature and specific capacity are higher than in the commercial FeS₂ and CoS₂, especially LiCu₂O₂. This work affords an alternative of the cathode materials for high specific capacity thermal battery.

Green-Synthesized Rice-Shaped Copper Oxide Nanoparticles Using Caesalpinia bonducella Seed Extract and Their Applications

Copper oxide nanoparticles (CuO Nps) were synthesized using Caesalpinia bonducella seed extract via a green synthetic pathway and were evaluated for electrocatalytic properties by carrying out electrochemical detection of riboflavin [vitamin B2 (VB2)]. The seeds of C. bonducella are known to have strong antioxidant properties arising due to the presence of various components, including citrulline, phytosterinin, β-carotene, and flavonoids, which serve as reducing, stabilizing, and capping agents. The synthesized CuO Nps were characterized using UV-visible spectroscopy, Fourier transform infrared spectroscopy, thermogravimetrc analysis-differential thermal analysis, X-ray diffraction spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy and further used as a modifier for a graphite electrode surface. The modified electrode was electrochemically characterized by cyclic voltammetry, square-wave voltammetry, and chronoamperometry techniques and then assessed for electrocatalysis by carrying out the detection of VB2. The electrochemical sensor could be used for nanomolar detection of VB2 with an observed linear range of 3.13-56.3 nM with a limit of detection of 1.04 nM. The electrode showed good stability and reproducibility over a period of 120 days. The CuO Nps were further analyzed for antibacterial effect with Gram-positive and Gram-negative bacteria, and in both cases, high antibacterial activity was clearly observed. The newly synthesized nanoparticles, thus, proved to be an interesting material for electrochemical and biological studies.

Low-temperature phyto-synthesis of copper oxide nanosheets: Its catalytic effect and application for colorimetric sensing

The last decade has seen a remarkable detonation in modifying chemical processes for nanomaterial synthesis to make them 'green'. Owing to the unique properties of nanomaterial and with regard to environmental issues, in this study, a new alternative and fast eco-friendly approach for the synthesis of copper oxide nanosheets (CuO-NSs) using Terminalia catappa (Indian almond) leaf extract as a renewable and non-toxic reducing agent and efficient stabilizer was reported. It is noteworthy to mention that the present fabrication process can open up the possibility of fast, low cost and high efficiency synthesis of CuO nanostructures with an interesting morphology of nanosheets at ambient temperature and pressure. Optimization of important factors such as pH, the quantity of leaf extract, copper precursor concentration, incubation time and temperature on the formation of CuO-NSs were investigated. The formation of bioreduced CuO-NSs was certified by UV-Vis spectroscopy, XRD, TEM analysis and FT-IR spectroscopy. Due to good stability, and excellent catalytic activity of the synthesized CuO-NSs, they are exerted to degrade of MB dye in water as a model color pollutant in the presence of NaBH₄ at room temperature. Furthermore, color properties of CuO nanostructures aid us to apply these biosynthesized nanomaterials in the design of optical sensors for detection of Fe²⁺ and Fe³⁺ ions. In view of many advantages of the current optical sensors based on CuO-NSs, such as eco-friendly, cost-effective, and straightforward design, the sensing system presents a potential application in environmental science.

The Use of Copper Oxide Thin Films in Gas-Sensing Applications

In this work, the latest achievements in the field of copper oxide thin film gas sensors are presented and discussed. Several methods and deposition techniques are shown with their advantages and disadvantages for commercial applications. Recently, CuO thin film gas sensors have been studied to detect various compounds, such as: nitrogen oxides, carbon oxides, hydrogen sulfide, ammonia, as well as several volatile organic compounds in many different applications, e.g., agriculture. The CuO thin film gas sensors exhibited high 3-S parameters (sensitivity, selectivity, and stability). Furthermore, the possibility to function at room temperature with long-term stability was proven as well, which makes this material very attractive in gas-sensing applications, including exhaled breath analysis.