Satisfactory Long-term Stability Research Articles

Graphenoxide Cross-Linker Based Potentiometric Biosensor Design for Sarcosine Determination.

Sarcosine, also known as N-methyl glycine, is a natural amino acid that is an intermediate and by product in glycine synthesis and degradation. Recently found in many peptides, sarcosine has been researched as a newly accepted prostate cancer marker. The increased concentration of sarcosine in blood serum and the urine showed that malignancy of measured prostate cancer cells is active. In this article, we aimed to design a potentiometric biosensor for detection of sarcosine with a low detection limit, high selectivity, short response time, wide linear range, and satisfactory long-term stability. In this article, we developed a new Graphene oxide (GFOX) photosensitive cross-linker based potentiometric biosensor based on the AmiNoAcid (monomer) Decorated and Light Underpinning Conjugation Approach (ANADOLUCA) method. The functional groups determined using Raman, FT-IR, XPS analyzes, and surface characterization, the morphology of synthesized GFOX photosensitive cross-linker were determined by TEM and AFM studies. Then, the performance of the GFOX based potentiometric biosensor has been evaluated. When the usage of the developed GFOX doped potentiometric biosensor against sarcosine determination, it was found that 10-4 mM sarcosine was determined in 60 seconds in the solution. In addition, the detection limit of the GFOX doped potentiometric biosensor was found to be 9.45x10-7 mM, and the linear potentiometric biosensor was found to be in the concentration range of 10-1 to 10-5 mM. The selectivity studies of the developed potentiometric biosensor were investigated using glycine solutions, and it was determined that GFOX doped potentiometric biosensor was more selective against sarcosine. Besides this, a reusability test using 10-3 mM sarcosine solution showed that reproducible studies were performed without the loss of potential of designed potentiometric biosensor and no loss of sensitivity. After applying the framework, we get a new potentiometric biosensor for sarcosine determination. GFOX photosensitive cross-linker was used in designing potentiometric biosensors, and this increased the stability and efficiency of the biosensor. Therefore, the developed potentiometric biosensor for sarcosine determination could be easily used for the early diagnosis of prostate cancer.

Colorimetric paper-based sarcosine assay with improved sensitivity.

This manuscript reports on a simple paper-based bienzymatic colorimetric assay for sarcosine as an important urinary biomarker of prostate cancer. All required assay reagents are pre-deposited on hydrophilic filter paper spots surrounded by a hydrophobic barrier. Sarcosine in the sample solution is selectively oxidized in the presence of sarcosine oxidase (SOx), resulting in the formation of hydrogen peroxide, which is subsequently detected through the horseradish peroxidase (HRP)-catalyzed conversion of the colorless indicator 3,3',5,5'-tetramethylbenzidine (TMB) into its blue-colored oxidation product. By the modification of the paper with positively charged poly(allylamine hydrochloride) (PAH), a linear response to sarcosine between 0 and 10μM and a significant lowering of the limit of detection (LOD) (0.6μM) compared to the unmodified paper substrate (12.6μM) has been achieved. The improvement of the LOD was attributed to the fact that the presence of the polymer limits the enzyme-driven colorimetric reaction to the surface of the paper substrate, resulting in stronger color development. In experiments in artificial urine matrix, the bicarbonate anion was identified as an inhibitor of the colorimetric reaction. This inhibition was successfully eliminated through on-device sample pH adjustments with pH-buffer components pre-deposited onto assay devices. The LOD for sarcosine achieved in artificial urine matrix (2.5μM) is below the 5μM threshold value for this urinary biomarker required for diagnostic purposes. Finally, good selectivity over all 20 natural amino acids and satisfactory long-term storage stability of reagent-modified paper substrates at - 20°C for a period of 50days were confirmed.

Expanding the applications of photodynamic therapy-tooth bleaching.

The current tooth bleaching materials are associated with adverse effect. Photodynamic method based on a novel photosensitizer alone, without combining with peroxides, is evaluated for tooth bleaching application. Teeth samples were randomly divided into 3 groups with different treatment schemes, including negative control group (group A, physiological saline), experimental group (group B, ZnPc(Lys)5), and the positive control group (group C, hydrogen peroxide). Tooth color, surface microhardness, and roughness were determined at baseline, right after the first and second phase of bleaching, as well as 1week and 1month post-bleaching. Four samples in each group was randomly selected to evaluate the changes in surface morphology using the scanning electron microscope. The color change values (ΔE) in group B (7.10 ± 1.03) and C (12.22 ± 2.35) were significantly higher than that in group A (0.93 ± 0.30, P < 0.05). Additionally, surface microhardness and roughness were significantly affected in group C, but not in the group A and B. Furthermore, the scanning electron microscope images showed no adverse effect of enamel in the group A and B while the group C demonstrated corrosive changes. ZnPc(Lys)5 had a satisfactory bleaching effect and is promising to be a new type of tooth bleaching agent. The current tooth bleaching materials give a satisfactory clinical outcome and long-term stability, but associated with some adverse reactions. Photosenstizer ZnPc(Lys)5 eliminated the main side effects observed in hydrogen peroxide-based agents on the enamel, and also had a satisfactory bleaching effect and provide a novel selective bleaching scheme for clinical use.

Highly Efficient SO2 Sensing by Light-Assisted Ag/PANI/SnO2 at Room Temperature and the Sensing Mechanism.

Sulfur dioxide (SO2) is one of the most hazardous and common environmental pollutants. However, the development of room-temperature SO2 sensors is seriously lagging behind that of other toxic gas sensors due to their poor recovery properties. In this study, a light-assisted SO2 gas sensor based on polyaniline (PANI) and Ag nanoparticle-comodified tin dioxide nanostructures (Ag/PANI/SnO2) was developed and exhibited remarkable SO2 sensitivity and excellent recovery properties. The response of the Ag/PANI/SnO2 sensor (20.1) to 50 ppm SO2 under 365 nm ultraviolet (UV) light illumination at 20 °C was almost 10 times higher than that of the pure SnO2 sensor. Significantly, the UV-assisted Ag/PANI/SnO2 sensor had a rapid response time (110 s) and recovery time (100 s) to 50 ppm SO2, but in the absence of light, the sensors exhibited poor recovery performance or were even severely and irreversibly deactivated by SO2. The UV-assisted Ag/PANI/SnO2 sensor also exhibited excellent selectivity, superior reproducibility, and satisfactory long-term stability at room temperature. The increased charge carrier density, improved charge-transfer capability, and the higher active surface of the Ag/PANI/SnO2 sensor were revealed by electrochemical measurements and endowed with high SO2 sensitivity. Moreover, the light-induced formation of hot electrons in a high-energy state in Ag/PANI/SnO2 significantly facilitated the recovery of SO2 by the gas sensor.

Iron Phthalocyanine/Two-Dimensional Metal-Organic Framework Composite Nanosheets for Enhanced Alkaline Hydrogen Evolution.

Hydrogen evolution reaction (HER) in alkaline medium is currently under scientific spotlight for generating clean H2 fuel from electrochemical water splitting. However, alkaline HER suffers from sluggish reaction kinetics because of the additional energy required for water dissociation from catalysts in contrast to acidic HER. Herein, we report the development of two-dimensional metal-organic framework (2D MOF) Ni-1,4-benzenedicarboxylic acid-based composite nanosheets for superior performance in HER electrocatalysis. Iron phthalocyanine (FePc) molecules are uniformly anchored on the ultrathin 2D Ni-MOF, showing a substantially increased current density, improved activity, and enhanced durability in alkaline HER. On account of the ultralarge specific surface of Ni-MOF and the coupling effects between FePc and 2D MOFs, the resultant nanosheet catalyst FePc@Ni-MOF exhibits a low overpotential (334 mV) and satisfactory long-term stability (10 h) at a current density of 10 mA·cm-2, which outperform those of pristine FePc, Ni-MOF, and the counterpart FePc@bulk-MOF. This study provides new insights into the synthesis of robust MOF-based nanosheet composites with high performance in catalysis.

A trace ppb-level electrochemical H2S sensor based on ultrathin Pt nanotubes

An amperometric sensor has been developed with high sensitivity for real-time measurement of H2S gas at room temperature (25 °C ± 2 °C). In order to enhance the utilization of platinum and improve its catalytic performance, an ultrathin and one-dimensional (1D) Pt nanotubes (Pt NTs, ~3.5 nm in wall thickness) were designed and used as sensing electrode materials. Different concentrations of H2S gas were tested to evaluate the sensitivity of the sensor and to obtain the relationship between the electricity response signal and H2S gas concentration. At room temperature, the sensor based on Pt NTs shows better sensing performance than that based on Pt nanoparticles, which is mainly attributed to two factors, namely, the inherent characteristic of the hollow 1D Pt NTs. The Pt NTs-based sensor shows a detection limit as low as 0.025 ppb, which are the lowest among H2S gas sensors reported in the literatures. The response and recovery times are 0.75 s and 0.86 s for 0.8 ppb H2S, respectively. In addition, the sensor shows a wide range (100 ppm-0.025 ppb), high selectivity compared to other gases (including CO, NH3, CH2O, NO and NO2), good reproducibility, and satisfactory long-term stability. Thus, the ultrathin Pt NTs-based gas sensor would be a great potential to the real-time and online monitoring of the trace ppb-level H2S gas at room temperature.

Ultraflexible Reedlike Carbon Nanofiber Membranes Decorated with Ni–Co–S Nanosheets and Fe2O3–C Core–Shell Nanoneedle Arrays as Electrodes of Flexible Quasi-Solid-State Asymmetric Supercapacitors

Flexible and lightweight supercapacitors with satisfactory energy density and long-term stability are urgently required to provide power for flexible, foldable, and wearable electronic devices. Her...

Hierarchical structure TiNb2O7 microspheres derived from titanate for high-performance lithium-ion batteries

Hierarchical structure TiNb2O7 microspheres derived from titanate displayed satisfactory long-term cycling stability and prominent rate capability for lithium-ion batteries.

Deep eutectic solvent for curing of phthalonitrile resin: Lower the curing temperature but improve the properties of thermosetting

Long curing duration and high curing temperature are commonly known to restrict the application of the phthalonitrile resin. In this study, a deep eutectic solvent (DES) containing ZnCl2 and urea has been developed to improve the curing process of the resorcinol-based phthalonitrile resin (DPPh) without sacrificing the useful properties of the resin. For the molar ratio of ZnCl2 and urea as 1:1 (ZnCl2-urea (1–1)), the initial curing temperature and apparent activation energy of the system were recorded as 179.5°C and 90.1 kJ/mol, respectively, indicating a reduction of 31.2% and 39.0% as compared to the pristine ZnCl2 system. More importantly, with curing time of 6 h and post-curing temperature of 300°C, the temperature at 5% weight loss as well as glass transition temperature of the resin with DES as the curing agent were 523.1°C and 370.2°C, respectively, demonstrating a significant improvement as compared to the resin cured with ZnCl2. In addition, the satisfactory long-term oxidation stability of the resin could also be obtained by employing the new curing agent. The findings from this study open a functional pathway for facile preparation of the high-performance curing agent for the phthalonitrile resin.

Bioinspired modification of molybdenum disulfide nanosheets to prepare a loose nanofiltration membrane for wastewater treatment

Loose nanofiltration membrane (NFM) is suitable for wastewater treatment especially for dye solution desalination due to its high rejection of dyes and high permeance of salts. In this study, MoS2@PDA was prepared by modifying molybdenum disulfide (MoS2) nanosheets with polydopamine (PDA). Then, the loose nanofiltration membrane was prepared by the deposition of MoS2@PDA on hydrolyzed polyacrylonitrile (HPAN) ultrafiltration membrane with pressure-assisted self-assembly. The morphology and properties of MoS2@PDA and MoS2@PDA NFMs were analyzed by SEM, TEM, TGA, FT-IR, AFM, WCA, XRD, and ζ-potentials. The PDA nanoaggregates on the surface of MoS2 nanosheets interfered with the regular stacking of MoS2 nanosheets parallel to the membrane surface, so the resultant membranes showed irregular loose structure which could provide transmembrane channels along with the impermeable nanosheet surface for molecule diffusion. When the MoS2 loading was 0.116 mg/cm2 and the PDA modification time was 5 h, the pure water flux of MoS2@PDA NFM could reach 204.05 LMH/bar, the rejection of methylene blue was 99 %, and rejection of salts (NaCl, Na2SO4, MgCl2, MgSO4) were less than 12 %. And MoS2@PDA NFM exhibited satisfactory long-term operational stability. This study provides a new strategy for the design of loose nanofiltration membrane with high performance.

Development of potentıometrıc bıosensor for dıagnosıs of prostate cancer

Prostate cancer is an important public health problem in the world with its burden of disease, increase in fatality and incidence rates. Recently, naturally occurring amino acid sarcosine has been investigated as a recognized marker of prostate cancer. The aim of the study for the early detection of prostate cancer is to develop a method of high sensitivity, low cost and low concentration in the determination of sarcosine. High sensitive nano anti-sarcosine-antibody and nano anti-sarcosine antibody-GFOX polymer have been prepared for the potentiometric detection of sarcosine and its reusability as biosensors have investigated. Nano anti-sarcosine antibody and nano anti-sarcosine antibody-GFOX potentiometric biosensor have shown excellent detection performance. Nano anti-sarcosine antibody potentiometric biosensor and nano anti-sarcosine antibody-GFOX potentiometric biosensor have low detection limit (4.75 × 10−9 mM and 3.34 × 10−9mM, respectively), high selectivity, short response time, wide linear range, and satisfactory long-term stability (3–4 months) for sarcosine detection.

Fabrication and Characterization of Controlled-Morphology Self-Supported Fe/Co Layered Double Hydroxides as Catalysts for the Oxygen Evolution Reaction

Electrochemical water splitting is a promising method of hydrogen production that involves two half reactions, namely the fast hydrogen evolution reaction and the slow oxygen evolution reaction (OER). The latter reaction can be accelerated by electrocatalysts, which reduce its overpotential to improve energy conversion efficiency. Herein, Fe-doped Co layered double hydroxides on 3D Ni foam (CoxFey-LDH/NF) with different Co/Fe molar ratios were hydrothermally synthesized in a single step and evaluated as OER catalysts. Structural and electrochemical characterizations provided insights into the origin of the synergistic effect of Fe and Co on OER performance enhancement and indicated that catalyst composition, crystal/electronic structure, and surface morphology are strongly related to Fe content. The best-performing catalyst, Co3Fe1-LDH/NF, exhibited a nanoneedle morphology, an overpotential of 201 mV at a current density of 10 mA cm−2, a small Tafel slope of 47.9 mV dec−1, and satisfactory long-term electrochemical stability in 1.0 M KOH. Thus, this work emphasizes the significance of effective structure design via precise control of catalyst morphology for the development of non-precious metal electrocatalysts.

Metal-free amino acid glycine-derived nitrogen-doped carbon aerogel with superhigh surface area for highly efficient Zn-Air batteries

Development of high-efficiency non-noble metal materials to substitute Pt-based catalysts for oxygen reduction reactions is crucial in the commercial viability of Zn-air batteries technology. Nitrogen doped carbons (NDCs) are highly appealing as promising candidates. This study reports a facile molten salt (MS) method to synthesize aerogel-like nitrogen doped carbon (NDC-MS). The eutectic mixture acting as combined solvent and porogen leads to the obtained porous materials with extremely large surface area (1548.6 m2 g−1) and relatively high pore volume. The unique aerogel-like structure with hierarchical structure, increased catalytic active sits, extended surface area and large pore volume is beneficial for enhancing oxygen reduction reaction (ORR) performance. The resultant NDC-MS displays a superb ORR catalytic activity with high half-wave potential of 0.88 V, which is one of the most effective figures in previous literature of metal-free catalysts. The superb ORR performance can also be evaluated by Zn–air batteries with satisfactory power density and long-term operation stability. Therefore, such an efficient and green synthetic strategy can open up a new avenue for a wide range of commercial application of heteroatom doped carbon materials in advanced energy technologies.

Ultrasensitive flexible NH3 gas sensor based on polyaniline/SrGe4O9 nanocomposite with ppt-level detection ability at room temperature

Detection limit as an important parameter of gas sensors, much effort has been devoted to developing high-performance gas sensors with low detection limit. However, the development of gas sensors with ppt-level detection limit still faces enormous challenges. In this work, a flexible and ultra-highly sensitive ammonia (NH3) sensor based on polyaniline/SrGe4O9 nanocomposites (PSN) was successfully fabricated via a facile in situ chemical oxidation polymerization method. When exposed to 0.2–10 ppm NH3 at 25 °C in 60% relative humidity (RH), the PSN sensor showed larger sensitivity (20.59% ppm−1) than that of PANI sensor (9.82% ppm−1). The response of the PSN sensor (16%) was two-fold higher than that of the PANI one (8%) to 0.2 ppm NH3 at room temperature. Meanwhile, the response time of the PSN sensor (24 s) was reduced to up to a third of that of the PANI sensor (64 s) for 800 ppb NH3. Additionally, the flexible PSN sensor exhibited good reproducibility, satisfactory long-term stability, excellent selectivity and outstanding flexibility to NH3 at room temperature. Significantly, the PSN sensor presented the ultra-low detection limit of 250 ppt toward NH3. Such outstanding gas-sensing properties were attributed to the unique hierarchical architecture with abundant mesoporous and the formation of p-n heterojunction at the interface between p-type PANI and n-type SrGe4O9. This research provides new strategies for developing high-performance NH3 sensors with supersensitive and ultra-low detection limit.

Development and characterization of composite carbon nanofibers surface-coated with ZnO/Ag nanoparticle arrays for ammonia sensor application

This research intended to develop an ultra-fast sensor for detecting ammonia blended with water at room temperature, based on nonwoven carbon nanowires (CNWs). Indicated to individual characterizations of fabricated CNWs loaded by silver nanoparticles (AgNPs) and zinc oxide nanorods (ZnONr), the output resistance of nanowires sensors has a proportional relation with ammonia concentrations. The carbon nanowire sensor based on AgNPs and ZnONr possessed an ammonia sensing response with a concentration of 0.01 to 1 M when blended with deionized water. Meanwhile, the fabricated nanowire sensor also had a fast response to recovery time 8-10 s for ammonia solutions, which was the excellent assign to satisfactory selectivity, long-term stability, and quick response. The results not only provided an effective technique for the in-situ loading of the AgNPs and ZnONr into the fabricated carbon nanofibers (CNF) but also significantly broaden the applicability of designed sensor nanowires for ammonia sensing at the room temperature with excellent selectivity and fast response/recovery time.

The Room Temperature Gas Sensor Based on Polyaniline/SrGe4O9 Nanocomposites for Ppt-Level NH3 Detection

Introduction It is an urgent requirement to development of ammonia sensors with low detection limits for environmental monitoring and disease detection [1]. In recent years, much effort has been devoted to developing high performance gas sensors with low detection limit and room temperature detection. However, the development of gas sensors with ppt-level detection limit still faces enormous challenges.PANI-based material has a good selective NH3 response at room temperature. However, the applications of PANI-based sensors have been limited by their slow response speed and high detection limit [2]. To address such limitations, Sensors based on the PANI-based nanocomposite materials have been demonstrated to be effective method for low detection limit to NH3 at room temperature. SrGe4O9 is one of the wide-bandgap metal oxide semiconductors and have the best sensing performance to NH3 among alkaline earth metal germanate. In addition, the morphology of SrGe4O9 can be regulated by various synthetic means. Hence, a flexible NH3 sensor based on PANI/SrGe4O9 nanocomposites thin film was proposed for ultra-low level NH3 detection. Method SrGe4O9 nanowires were synthesized by a facile one-step hydrothermal synthesis, particular steps are described as fellows: 4mmol Sr(CH3COO)2 and 16mmol CeO2 dispersed in 60mL deionized water, then transferred to a 100 mL Teflon-lined stainless autoclave. The solution was stirred for 40 min and heated at 180℃ for 24h, the reaction product washed 3 times alternately with deionized water and dried at 50 ° C for 24 h. To fabricate the PANI-SrGe4O9 flexible gas sensor, the interdigital electrode was first soaked in PDDA solution (1%) and PSS solution (2 mg/ml, PH≈1, adjusted by HCl). After that, the thin sensor was fabricated by in-situ self-assembly method at ~10℃. Specifically ,100 μL Aniline (C6H5NH2) and 5 mg SrGe4O9 nanowires was dissolved in 20ml HCl (2 M). Subsequently, 10 ml APS ((NH4)2S2O8) was gradually added to the mixture within 120 s. The flexible interdigital electrode was immersed into the mixture when the color of solution turn to pale blue. After 15 min the substrate with PANI-SrGe4O9 nanocomposite thin film was removed and washed with HCl (2 M). Finally, the sensor was dried at room temperature for one day. For comparison, pure PANI thin film was also fabricated by the same method. Results and Conclusions In this work, a flexible and ultra-highly sensitive NH3 sensor based on polyaniline/SrGe4O9 nanowires nanocomposites was successfully fabricated via a combined route of facile hydrothermal method and in situ chemical oxidation polymerization method to load the gas sensing material on flexible polyimide (PI) substrate. XRD pattern revealed that polyaniline and SrGe4O9 phases coexisted in the as-prepared nanocomposites. Morphology results indicated polyaniline nanoparticles anchored on the SrGe4O9 nanowires with an average diameter of 100 nm and a length of 2–5 mm. In addition, The NH3 sensing properties of the as-fabricated sensors were evaluated at room temperature (∼25℃) and results indicated that the PANI/SrGe4O9 sensor exhibited higher response value of 344% to 50 ppm NH3, which was greatly superior to the pure PANI. Furthermore, the present sensor also showed fast response speed (37.3s), satisfactory long-term stability, good bending resistance and excellent selectivity towards 50 ppm NH3 at room temperature. The response of the PANI/SrGe4O9 sensor increased with the increasing relative humidity, which can further expand the practical application of the PANI/SrGe4O9 sensor. What's more, the sensor demonstrated an ultra-low detection limit of 50 ppt NH3 at room temperature in 60%RH, which was reported for the first time. Such dramatically enhanced gas-sensing properties of PANI/SrGe4O9 nanofilm might be owing to the synergism effects, the formation of p-n heterojunction at the interface between the n-type SrGe4O9 and p-type PANI, and high surface area of PANI/SrGe4O9 nanocomposite. This research offers new strategies for developing supersensitive gas NH3 sensor and the PANI/SrGe4O9 sensor points its promising applications in ultrasensitive environmental detection and human disease detection.

P doped CoMoO4/RGO as an efficient hybrid catalyst for hydrogen evolution

Transition metal oxides, as newly earth-abundant and low-cost catalysts, have been regarded as promising materials for electrocatalytic oxygen evolution. However, they are rarely used as an electrocatalyst in hydrogen evolution reaction (HER) due to the poor HER activity. Herein, we present a facile two-step method to synthesize P doped CoMoO4/RGO (P-CoMoO4/RGO) with different atomic ratios of Co2+/Co3+ through a simple phosphorization strategy by changing the mass of NaH2PO2. The effective P-doping into CoMoO4/RGO can modify the electronic properties and modulate the atomic ratio of Co2+/Co3+, which promotes the electron transfer and creates more activity sites. Therefore, the optimized P-CoMoO4/RGO with a relatively larger atomic ratio of Co2+/Co3+ shows superior HER performances in alkaline media, which affords a current density of 10 mA cm−2 at a small overpotential of 90 mV and a low Tafel slope of 62 mV dec−1 along with having satisfactory long-term stability. This work provides a valuable route to enhance the HER activity of transition metal oxides.

Batch microfabrication of highly integrated silicon-based electrochemical sensor and performance evaluation via nitrite water contaminant determination

Electrochemical sensors play a key role in the monitoring of pollutants in water due to their high-sensitivity and short-response-time etc. However, the stability for long-term sensing testing and hard to mass production of electrochemical sensors always is a challenge issue. In this paper, a novel silicon-based electrochemical sensor that can be mass-produced via the microfabrication technique/MEMS is proposed. By fabricating a liquid conjunct Ag/AgCl reference electrode, employing relatively electrochemical stable Au as the working electrode/counter electrode and verified the effectiveness of as-fabricated sensor by nitrite detection, the micro-fabricated electrochemical sensor demonstrates acceptable limit of detection, desirable linearity and good resistance to other interference substances. Particularly, satisfactory long-term stability was witnessed for the proposed sensor. After continuously operated for 19 days, the sensor still kept 94% response signal when compared with that of the value obtained at its initial state. What’s more, by employing the mass-production technique, favorable response consistency and high reproducibility was witnessed, offering the opportunity of mass-producing the proposed sensor in future. And the high consistency and satisfactory long-term stability of as-proposed sensor indicated that the study on mass production electrochemical sensor fabricating by MEMS was a successful attempt. It is anticipated that the proposed sensor configuration will provide an alternative strategy to design future low power and reliable mini-sensor for water contaminants monitoring.

Novel monolithic catalysts derived from in-situ decoration of Co3O4 and hierarchical Co3O4@MnOx on Ni foam for VOC oxidation

Monolithic Co3O4 and Co3O4@MnOx catalysts have been successfully prepared by in-situ growth. The morphology control and formation mechanism of Co3O4 on Ni foam was investigated in detail. Among the different samples, bamboo leaf-like Co3O4-NF-10 presented good catalytic activity for acetone oxidation (T50 = 179 °C, T90 = 193 °C), which was attributed to its low temperature reducibility, abundant Co3+ and surface adsorbed oxygen species (Oads). Therefore, Co3O4@MnOx-NF was further prepared to obtain abundant Co3+ and Oads species due to the redox reaction between MnO4− and Co2+. As expected, the Co3O4@MnOx-NF catalyst presented significantly improved activity for not only acetone but ethyl acetate and toluene oxidation compared to the Co3O4-NF-10. The high catalytic performance of Co3O4@MnOx-NF was ascribed to its good low-temperature reducibility, abundant Co3+ and Oads species. In addition, Co3O4@MnOx-NF presented a satisfactory cycle and long-term stability. This work shed light on the design of monolithic catalysts in VOC oxidation.

General approach to MOF-derived core-shell bimetallic oxide nanowires for fast response to glucose oxidation

One new type of electrochemical sensors for the effective glucose detection is fabricated based on the use of CuOx@Co3O4 core-shell nanowires on Cu foam as electrocatalysts, which is synthesized through the stepwise process, including anodized nano-sized Cu(OH)2 wires, Metal-organic frameworks (MOFs)-wrapped Cu(OH)2 nanowires, and the following calcination. These as-made hierarchical composites exhibit the structural characteristics of CuOx nanowires core and Co3O4 nanoparticles shell calcinated from the terminally attached microporous ZIF-67. This type of glucose sensor compared to pure individual metal oxides exhibits higher sensitivity (27778 μA mM−1 cm-2 in the range from 0.1–1300.0 μM), lower detection limit (36 nM (S/N = 3)) and faster response time (∼1 s), also displays satisfactory selectivity, reproducibility, and long-term storage stability. Meanwhile, it achieves well-pleasing results in the detection of glucose in real human blood serum compared to commercial sensors. In addition, other four types of self-supporting MOF-derived bimetallic oxides core-shell nanowire arrays on Cu foam are also prepared by adopting the similar three-step procedure, including CuOx@Fe2O3, CuOx@NiO, CuOx@CuOx and CuOx@ZnO core-shell nanowires, demonstrating the versatility of this method. These results confirm that our as-made MOF-derived bimetallic oxide based sensor of CuOx@Co3O4 has a great potential application in the development of enzyme-free sensors for monitoring glucose.