Breakthroughs in the Design of Novel Carbon-Based Metal Oxides Nanocomposites for VOCs Gas Sensing

Nowadays, the detection of volatile organic compounds (VOCs) at trace levels (down to ppb) is feasible by exploiting ultra-sensitive and highly selective chemoresistors, especially in the field of medical diagnosis. By coupling metal oxide semiconductors (MOS e.g., SnO2, ZnO, WO3, CuO, TiO2 and Fe2O3) with innovative carbon-based materials (graphene, graphene oxide, reduced graphene oxide, single-wall and multi-wall carbon nanotubes), outstanding performances in terms of sensitivity, selectivity, limits of detection, response and recovery times towards specific gaseous targets (such as ethanol, acetone, formaldehyde and aromatic compounds) can be easily achieved. Notably, carbonaceous species, highly interconnected to MOS nanoparticles, enhance the sensor responses by (i) increasing the surface area and the pore content, (ii) favoring the electron migration, the transfer efficiency (spillover effect) and gas diffusion rate, (iii) promoting the active sites concomitantly limiting the nanopowders agglomeration; and (iv) forming nano-heterojunctions. Herein, the aim of the present review is to highlight the above-mentioned hybrid features in order to engineer novel flexible, miniaturized and low working temperature sensors, able to detect specific VOC biomarkers of a human’s disease.

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Design and Synthesis of Novel 2D Porous Zinc Oxide-Nickel Oxide Composite Nanosheets for Detecting Ethanol Vapor

Nanomaterials ◽

10.3390/nano10101989 ◽

2020 ◽

Vol 10 (10) ◽

pp. 1989

Author(s):

Yuan-Chang Liang ◽

Yen-Cheng Chang ◽

Wei-Cheng Zhao

Keyword(s):

Zinc Oxide ◽

Nickel Oxide ◽

Active Sites ◽

Gas Sensing ◽

Ethanol Vapor ◽

Gas Diffusion ◽

High Specific Surface Area ◽

Sputtering Deposition ◽

Vapor Sensing ◽

Sensing Performance

The porous zinc oxide-nickel oxide (ZnO-NiO) composite nanosheets were synthesized via sputtering deposition of NiO thin film on the porous ZnO nanosheet templates. Various NiO film coverage sizes on porous ZnO nanosheet templates were achieved by changing NiO sputtering duration in this study. The microstructures of the porous ZnO-NiO composite nanosheets were investigated herein. The rugged surface feature of the porous ZnO-NiO composite nanosheets were formed and thicker NiO coverage layer narrowed the pore size on the ZnO nanosheet template. The gas sensors based on the porous ZnO-NiO composite nanosheets displayed higher sensing responses to ethanol vapor in comparison with the pristine ZnO template at the given target gas concentrations. Furthermore, the porous ZnO-NiO composite nanosheets with the suitable NiO coverage content demonstrated superior gas-sensing performance towards 50–750 ppm ethanol vapor. The observed ethanol vapor-sensing performance might be attributed to suitable ZnO/NiO heterojunction numbers and unique porous nanosheet structure with a high specific surface area, providing abundant active sites on the surface and numerous gas diffusion channels for the ethanol vapor molecules. This study demonstrated that coating of NiO on the porous ZnO nanosheet template with a suitable coverage size via sputtering deposition is a promising route to fabricate porous ZnO-NiO composite nanosheets with a high ethanol vapor sensing ability.

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Pd-Functionalized SnO2 Nanofibers Prepared by Shaddock Peels as Bio-Templates for High Gas Sensing Performance toward Butane

Nanomaterials ◽

10.3390/nano9010013 ◽

2018 ◽

Vol 9 (1) ◽

pp. 13 ◽

Cited By ~ 2

Author(s):

Rongjun Zhao ◽

Zhezhe Wang ◽

Yue Yang ◽

Xinxin Xing ◽

Tong Zou ◽

...

Keyword(s):

Active Sites ◽

Gas Sensing ◽

Spillover Effect ◽

Internal Surface ◽

Pd Nanoparticles ◽

Sno2 Nanostructures ◽

Pure Sno2 ◽

Internal Surface Area ◽

One Dimensional ◽

Practical Applications

Pd-functionalized one-dimensional (1D) SnO2 nanostructures were synthesized via a facile hydrothermal method and shaddock peels were used as bio-templates to induce a 1D-fiber-like morphology into the gas sensing materials. The gas-sensing performances of sensors based on different ratios of Pd-functionalized SnO2 composites were measured. All results indicate that the sensor based on 5 mol % Pd-functionalized SnO2 composites exhibited significantly enhanced gas-sensing performances toward butane. With regard to pure SnO2, enhanced levels of gas response and selectivity were observed. With 5 mol % Pd-functionalized SnO2 composites, detection limits as low as 10 ppm with responses of 1.38 ± 0.26 were attained. Additionally, the sensor exhibited rapid response/recovery times (3.20/6.28 s) at 3000 ppm butane, good repeatability and long-term stability, demonstrating their potential in practical applications. The excellent gas-sensing performances are attributed to the unique one-dimensional morphology and the large internal surface area of sensing materials afforded using bio-templates, which provide more active sites for the reaction between butane molecules and adsorbed oxygen ions. The catalysis and “spillover effect” of Pd nanoparticles also play an important role in the sensing of butane gas as further discussed in the paper.

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Zinc Oxide/Reduced Graphene Oxide Nanocomposites for Rapid Detection of Toluene Gas at Room Temperature

Sensor Letters ◽

10.1166/sl.2020.4288 ◽

2020 ◽

Vol 18 (10) ◽

pp. 745-749

Author(s):

Chih-Chia Wang ◽

Chiu-Hung Liu ◽

Hsuan-Hua Hsieh ◽

Chih-Wei Tang ◽

Chen-Bin Wang

Keyword(s):

Zinc Oxide ◽

Graphene Oxide ◽

Reduced Graphene Oxide ◽

Room Temperature ◽

Gas Sensing ◽

Fast Response ◽

Reduced Graphene ◽

New Strategy ◽

Recovery Times ◽

Response And Recovery

In this study, a nanostructured zinc oxide/reduced graphene oxide (ZnO/rGO) composite was deposited on a quartz crystal microbalance (QCM) as a toluene gas sensor at room temperature. A series of ZnO, rGO and ZnO/rGO sensing materials was fabricated and characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and Raman spectroscopy. There was significant efficiency of the ZnO/rGO composite on the sensing performance for toluene. For specific gas fluxes, the nanostructured ZnO/rGO offered sufficient paths and region for vapor diffusion and adsorption. The sensing test results illustrated that the nanostructured ZnO/rGO composite showed significant enhancement in the frequency shifts (△f) for toluene comparing to pure ZnO and rGO. Also, the ZnO/rGO-coated QCM sensor displayed a fast response (both the response and recovery times < 30 s) and reproducibility for sensing toluene gas at room temperature. We believe that the novel insights on ambient temperature gas sensing on nanostructured ZnO/rGO composite could provide a new strategy for preparing a highly efficient sensing materials.

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Efficient Production of Biodiesel Catalyzed by Acidic Nanoporous Carbon Materials：A Review

Current Nanoscience ◽

10.2174/1573413716666200319131508 ◽

2020 ◽

Vol 16 ◽

Author(s):

Anping Wang ◽

Heng Zhang ◽

Hu Li ◽

Song Yang

Keyword(s):

Pore Structure ◽

Active Sites ◽

Catalytic Performance ◽

Nanoporous Carbon ◽

Biodiesel Production ◽

Efficient Production ◽

Fossil Energy ◽

Catalytic Materials ◽

High Acid ◽

Carbon Based

Background: With the gradual decrease of fossil energy, the development of alternatives to fossil energy has attracted more and more attention. Biodiesel is considered to be the most potent alternative to fossil energy, mainly due to its green, renewable and biodegradable advantages. The stable, efficient and reusable catalysts are undoubtedly the most critical in the preparation of biodiesel. Among them, nanoporous carbon-based acidic materials are very important biodiesel catalysts. Objective: The latest advances of acidic nanoporous carbon catalysts in biodiesel production was reviewed. Methods: Biodiesel is mainly synthesized by esterification and transesterification. Due to the important role of nanoporous carbon-based acidic materials in the catalytic preparation of biodiesel, we focused on the synthesis, physical and chemical properties, catalytic performance and reusability. Results: Acidic catalytic materials have a good catalytic performance for high acid value feedstocks. However, the preparation of biodiesel with acid catalyst requires relatively strict reaction conditions. The application of nanoporous acidic carbon-based materials, due to the support of carbon-based framework, makes the catalyst have good stability and unique pore structure, accelerates the reaction mass transfer speed and accelerates the reaction. Conclusion: Nanoporous carbon-based acidic catalysts have the advantages of suitable pore structure, high active sites, and high stability. In order to make these catalytic processes more efficient, environmentally friendly and low cost, it is an important research direction for the future biodiesel catalysts to develop new catalytic materials with high specific surface area, suitable pore size, high acid density, and excellent performance.

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Investigation of Gas Diffusion Electrode Systems for the Electrochemical CO2 Conversion

Catalysts ◽

10.3390/catal11040482 ◽

2021 ◽

Vol 11 (4) ◽

pp. 482

Author(s):

Hilmar Guzmán ◽

Federica Zammillo ◽

Daniela Roldán ◽

Camilla Galletti ◽

Nunzio Russo ◽

...

Keyword(s):

Carbon Capture ◽

Active Sites ◽

Co2 Reduction ◽

Gas Diffusion ◽

Gas Diffusion Electrode ◽

Catalyst Loading ◽

Co2 Conversion ◽

Atmospheric Conditions ◽

Electrochemical Co2 Reduction ◽

Liquid Products

Electrochemical CO2 reduction is a promising carbon capture and utilisation technology. Herein, a continuous flow gas diffusion electrode (GDE)-cell configuration has been studied to convert CO2 via electrochemical reduction under atmospheric conditions. To this purpose, Cu-based electrocatalysts immobilised on a porous and conductive GDE have been tested. Many system variables have been evaluated to find the most promising conditions able to lead to increased production of CO2 reduction liquid products, specifically: applied potentials, catalyst loading, Nafion content, KHCO3 electrolyte concentration, and the presence of metal oxides, like ZnO or/and Al2O3. In particular, the CO productivity increased at the lowest Nafion content of 15%, leading to syngas with an H2/CO ratio of ~1. Meanwhile, at the highest Nafion content (45%), C2+ products formation has been increased, and the CO selectivity has been decreased by 80%. The reported results revealed that the liquid crossover through the GDE highly impacts CO2 diffusion to the catalyst active sites, thus reducing the CO2 conversion efficiency. Through mathematical modelling, it has been confirmed that the increase of the local pH, coupled to the electrode-wetting, promotes the formation of bicarbonate species that deactivate the catalysts surface, hindering the mechanisms for the C2+ liquid products generation. These results want to shine the spotlight on kinetics and transport limitations, shifting the focus from catalytic activity of materials to other involved factors.

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Electrokinetic and in situ spectroscopic investigations of CO electrochemical reduction on copper

Nature Communications ◽

10.1038/s41467-021-23582-2 ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Jing Li ◽

Xiaoxia Chang ◽

Haochen Zhang ◽

Arnav S. Malkani ◽

Mu-jeng Cheng ◽

...

Keyword(s):

Mass Transport ◽

Active Sites ◽

Gas Diffusion ◽

Reduction Reaction ◽

Adsorbed Hydrogen ◽

Diffusion Type ◽

Proton Coupled Electron Transfer ◽

Alkaline Electrolytes ◽

Reaction Orders

AbstractRigorous electrokinetic results are key to understanding the reaction mechanisms in the electrochemical CO reduction reaction (CORR), however, most reported results are compromised by the CO mass transport limitation. In this work, we determined mass transport-free CORR kinetics by employing a gas-diffusion type electrode and identified dependence of catalyst surface speciation on the electrolyte pH using in-situ surface enhanced vibrational spectroscopies. Based on the measured Tafel slopes and reaction orders, we demonstrate that the formation rates of C2+ products are most likely limited by the dimerization of CO adsorbate. CH4 production is limited by the CO hydrogenation step via a proton coupled electron transfer and a chemical hydrogenation step of CO by adsorbed hydrogen atom in weakly (7 < pH < 11) and strongly (pH > 11) alkaline electrolytes, respectively. Further, CH4 and C2+ products are likely formed on distinct types of active sites.

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Enhanced gas sensing and photocatalytic activity of reduced graphene oxide loaded TiO2 nanoparticles

Chemical Physics Letters ◽

10.1016/j.cplett.2021.138897 ◽

2021 ◽

pp. 138897

Author(s):

Suresh Sagadevan ◽

J. Anita Lett ◽

Getu Kassegn Weldegebrieal ◽

Md Rokon ud Dowla Biswas ◽

Won Chun Oh ◽

...

Keyword(s):

Photocatalytic Activity ◽

Graphene Oxide ◽

Tio2 Nanoparticles ◽

Reduced Graphene Oxide ◽

Gas Sensing ◽

Reduced Graphene

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Co3Fe7 nanoparticles encapsulated in porous nitrogen-doped carbon nanofiber as bifunctional electrocatalysts for rechargeable zinc-air battery

Materials Chemistry Frontiers ◽

10.1039/d1qm00707f ◽

2021 ◽

Author(s):

Miaomiao Liu ◽

Yulong He ◽

Jintao Zhang

Keyword(s):

Oxygen Reduction ◽

Active Sites ◽

Carbon Nanofiber ◽

Nitrogen Doped ◽

Bifunctional Electrocatalysts ◽

Air Battery ◽

Nitrogen Doped Carbon ◽

Carbon Based

Exploration of inexpensitive and high perfomance carbon-based electrocatalyst with abundant active sites for oxygen reduction and evolution reactions is vital for enhancing the performance of zinc air battery. Herein, the...

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Defect-Rich Heterogeneous MoS2/rGO/NiS Nanocomposite for Efficient pH-Universal Hydrogen Evolution

Nanomaterials ◽

10.3390/nano11030662 ◽

2021 ◽

Vol 11 (3) ◽

pp. 662 ◽

Cited By ~ 1

Author(s):

Guangsheng Liu ◽

Kunyapat Thummavichai ◽

Xuefeng Lv ◽

Wenting Chen ◽

Tingjun Lin ◽

...

Keyword(s):

Graphene Oxide ◽

Hydrogen Evolution ◽

Hydrogen Evolution Reaction ◽

Active Sites ◽

Reduced Graphene ◽

Heterogeneous Interfaces ◽

Wide Ph Range ◽

Ph Range ◽

A Current ◽

Poor Stability

Molybdenum disulfide (MoS2) has been universally demonstrated to be an effective electrocatalytic catalyst for hydrogen evolution reaction (HER). However, the low conductivity, few active sites and poor stability of MoS2-based electrocatalysts hinder its hydrogen evolution performance in a wide pH range. The introduction of other metal phases and carbon materials can create rich interfaces and defects to enhance the activity and stability of the catalyst. Herein, a new defect-rich heterogeneous ternary nanocomposite consisted of MoS2, NiS and reduced graphene oxide (rGO) are synthesized using ultrathin αNi(OH)2 nanowires as the nickel source. The MoS2/rGO/NiS-5 of optimal formulation in 0.5 M H2SO4, 1.0 M KOH and 1.0 M PBS only requires 152, 169 and 209 mV of overpotential to achieve a current density of 10 mA cm−2 (denoted as η10), respectively. The excellent HER performance of the MoS2/rGO/NiS-5 electrocatalyst can be ascribed to the synergistic effect of abundant heterogeneous interfaces in MoS2/rGO/NiS, expanded interlayer spacings, and the addition of high conductivity graphene oxide. The method reported here can provide a new idea for catalyst with Ni-Mo heterojunction, pH-universal and inexpensive hydrogen evolution reaction electrocatalyst.

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ZnO/RGO Heterojunction Based near Room Temperature Alcohol SENSOR with Improved Efficiency

Engineering Proceedings ◽

10.3390/i3s2021dresden-10073 ◽

2021 ◽

Vol 6 (1) ◽

pp. 25

Author(s):

Sanghamitra Ghosal ◽

Partha Bhattacharyya

Keyword(s):

Active Sites ◽

Room Temperature ◽

Surface Engineering ◽

Gas Sensing ◽

Energy Band Diagram ◽

Future Generation ◽

High Yield ◽

Synthesis Process ◽

Ethanol Sensor ◽

Vapor Sensing

The systematic optimization of surface engineering (dimensionality) indeed plays a crucial role in achieving efficient vapor-sensing performance. Among various semiconducting metal oxides, owing to some of its unique features and advantages, ZnO has attracted researchers on a global scale due to its application in various fields, including chemical sensors. The concomitant optimization of the surface attributes (varying different dimensions) of ZnO have become a sensation for the entire research community. Moreover, the small thickness and extremely large surface of exfoliated 2D nanosheets render the gas sensing material an ideal candidate for achieving strong coupling with different gas molecules. However, temperature is a crucial factor in the field of chemical sensing. Recently, graphene-based gas sensors have attracted attention due to their variety of structures, unique sensing performances and room temperature working conditions. In this work, a highly sensitive and fast responsive low temperature (60 °C)-based ethanol sensor, based on RGO/2D ZnO nanosheets hybrid structure, is reported. After detailed characterizations, the vapor sensing potentiality of this sensor was tested for the detection of ethanol. The ethanol sensor offered the response magnitude of 89% (100 ppm concentration) with response and recovery time of 12 s/29 s, respectively. Due to excessively high number of active sites for VOC interaction, with high yield synthesis process and appreciably high carrier mobility, this has paved the way for developing future generation, miniaturized and flexible (wearable) vapor sensor devices, meeting the multidimensional requirements for traditional and upcoming (health/medical sector) applications. The underlying mechanistic framework for vapor sensing, using this hybrid junction, is explained with the Energy Band Diagram.

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