•Up-to-date evaluation of graphene-based gas sensors.•Hybrids of graphene with noble metals, metal oxides, and conducting polymers.•Systematic comparison of gas-sensing principles graphene-based ...hybrids.•Systematic comparison of gas-sensing properties of graphene-based hybrids.•Presentation of future outlook for graphene-based hybrid gas sensors.
Gas sensors can detect combustible, explosive and toxic gases, and have been widely used in safety monitoring and process control in residential buildings, industries and mines. Recently, graphene-based hybrids were widely investigated as chemiresistive gas sensors with high sensitivity and selectivity. This systematic review is therefore timely and necessary to evaluate the success of graphene-based hybrids in gas detection and to identify their challenges. We review the sensing principles and the synthesis process of the graphene-based hybrids with noble metals, metal oxides and conducting polymers to achieve better understanding and design of novel gas sensors. Our review will assist researchers to understand the evolution and the challenges of graphene-based hybrids, and create interest in development of gas-sensing techniques.
Since the discovery of carbon nanotubes (CNTs), they have drawn considerable research attention and have shown great potential application in many fields due to their unique structural, mechanical, ...and electronic properties. However, their native insolubility severely holds back the process of application. In order to overcome this disadvantage and broaden the scope of their application, chemical functionalization of CNTs has attracted great interest over the past several decades and produced various novel hybrid materials with specific applications. Notably, the rapid development of functionalized CNTs used as electrochemical sensors has been successfully witnessed. In this featured article, the recent progress of electrochemical sensors based on functionalized CNTs is discussed and classified according to modifiers covering organic (oxygen functional groups, small organic molecules, polymers, DNA, protein,
etc.
), inorganic (metal nanoparticles, metal oxide,
etc.
) and organicinorganic hybrids. By employing some representative examples, it will be demonstrated that functionalized CNTs as templates, carriers, immobilizers and transducers are promising for the construction of electrochemical sensors.
Recent progress of electrochemical sensors based on functionalized carbon nanotubes have been discussed and classified according to modifiers.
•Up-to-date assessment of state-of-the-art voltammetric determination of Hg(II).•Quantitative comparison of approaches according to the type of working electrode.•Full cover of modern voltammetric ...determination of Hg(II) with nanomaterials.•Deficiencies identified in present works on voltammetric determination of Hg(II).•Outlook over future trends in voltammetric determination of Hg(II).
Monitoring mercury provides a real challenge in analytical and environmental science, yet solutions are urgently needed due to the adverse effects of mercury on human health and the environment. Electrochemical techniques, more specifically voltammetric techniques, for determination of mercury(II) Hg(II) have inherent advantages. We review the state of the art in voltammetric determination of Hg(II) through quantitatively comparing different approaches classified according to the type of working electrode used. As much modern electroanalysis uses nanomaterials for the design of optimal electrode surfaces, this aspect is covered fully.
•Sensitive electrochemical detection of Pb(II) was realized using porous flower-like NiO/rGO nanocomposite.•Excellent adsorption and surface Ni(II)/Ni(III) cycle of NiO/rGO improve electrochemical ...performance.•Designed electrochemical sensor has high anti-interference ability for the determination of Pb(II).•The proposed method was successfully applied to detect Pb(II) in real wastewater sample.
Herein, combining the good catalysis of NiO with high adsorption and conductivity of reduced graphene oxide (rGO), the electrochemical sensing interface was constructed using the porous flower-like NiO/rGO nanocomposite modified glassy carbon electrode (GCE). The result of Pb(II) detection was obtained with high sensitivity of 92.81 μM μA−1 and low detection limit of 0.01 μM by square wave anodic stripping voltammetry (SWASV). The reasonable sensitive mechanism for enhancing electrochemical performance is that the excellent adsorption capacity and Ni(II)/Ni(III) cycle on surface of NiO/rGO nanocomposite could improve the electrochemical detection signal. Furthermore, the proposed method achieved the high anti-interference on the determination of Pb(II) in the co-existence of Cd(II), Cu(II), Hg(II). The excellent stability and reproducibility were also confirmed by repeatedly test. In addition, the concentration of Pb(II) in real water samples from Taochong wastewater treatment plant in Hefei city were analyzed and calculated accurately. These results indicates that the NiO/rGO nanocomposite as a promising electrode modifier could be potentially applied in electrochemical sensor for detecting Pb(II).
Highly selective adsorption of a polypyrrole/reduced graphene oxide nanocomposite toward Hg(2+) results in electrochemically selective detection of Hg(2+). This interesting finding is of practical ...utility compared to the biotechniques and surface functionalization-based methods.
•A newly designed GO-NH2: Higher adsorption capability than that of activated carbon.•Very quick adsorption property: More than 90% of Co(II) can be removed within 5min.•One of the highest adsorption ...capabilities of today's nanomaterials for Co(II) (116.35mg/g).•GO-NH2 membrane can remove more than 98% Co(II) from the water.
A newly designed amination graphene oxide (GO-NH2), a superior adsorption capability to that of activated carbon, was fabricated by graphene oxide (GO) combining with aromatic diazonium salt. The resultant GO-NH2 maintained a high surface area of 320m2/g. When used as an adsorbent, the GO-NH2 demonstrated a very quick adsorption property for the removal of Co(II) ions, more than 90% of Co(II) ions could be removed within 5min for dilute solutions at 0.3g/L adsorbent dose. The adsorption capability approaches 116.35mg/g, which is one of the highest capabilities of today's materials. The thermodynamic parameters calculated from temperature-dependent adsorption isotherms suggested that the Co(II) ions adsorption on GO-NH2 was a spontaneous process. Considering the superior adsorption capability, the GO-NH2 filter membrane was fabricated for the removal of Co(II) ions. Membrane filtration experiments revealed that the removal capabilities of the materials for cobalt ions depended on the membrane's thickness, flow rate and initial concentration of Co(II) ions. The highest percentage removal of Co(II) exceeds 98%, indicating that the GO-NH2 is one of the very suitable membrane materials in environmental pollution management.
Heavy metal ions (HMIs) are one of the major environmental pollution problems currently faced. To monitor and control HMIs, rapid and reliable detection is required. Electrochemical analysis is one ...of the promising methods for on‐site detection and monitoring due to high sensitivity, short response time, etc. Recently, nanometal oxides with special surface physicochemical properties have been widely used as electrode modifiers to enhance sensitivity and selectivity for HMIs detection. In this work, recent advances in the electrochemical detection of HMIs using nanometal oxides, which are attributed to specific crystal facets and phases, surficial defects and vacancies, and oxidation state cycle, are comprehensively summarized and discussed in aspects of synthesis, characterization, electroanalysis application, and mechanism. Moreover, the challenges and opportunities for the development and application of nanometal oxides with functional surface physicochemical properties in electrochemical determination of HMIs are presented.
This work systematically summarizes and discusses the synthesis and application of nanometal oxides with special surface physicochemical properties, including crystal facets and crystal phases, defects and oxygen vacancies, and oxidation states cycle in electrochemical detection of heavy metal ions. The sensitive mechanism for enhancing electrochemical signals by these nanometal oxides is highlighted.
•The CeO2–ZrO2 hollow nanospheres had strong affinity and selectivity to arsenic.•The adsorbent showed excellent ability to remove arsenic at low concentrations.•The adsorption mechanism was ...investigated by FTIR and XPS.•The adsorbent showed potential application for drinking water treatment.
Arsenic contaminated natural water is commonly used as drinking water source in some districts of Asia. To meet the increasingly strict drinking water standards, exploration of efficient arsenic removal methods is highly desired. In this study, hierarchically porous CeO2–ZrO2 nanospheres were synthesized, and their suitability as arsenic sorbents was examined. The CeO2–ZrO2 hollow nanospheres showed an adsorption capacity of 27.1 and 9.2mgg−1 for As(V) and As(III), respectively, at an equilibrium arsenic concentration of 0.01mgL−1 (the standard for drinking water) under neutral conditions, indicating a high arsenic removal performance of the adsorbent at low arsenic concentrations. Such a great arsenic adsorption capacity was attributed to the high surface hydroxyl density and presence of hierarchically porous network in the hollow nanospheres. The analysis of Fourier transformed infrared spectra and X-ray photoelectron spectroscopy demonstrated that the adsorption of arsenic on the CeO2–ZrO2 nanospheres was completed through the formation of a surface complex by substituting hydroxyl with arsenic species. In addition, the CeO2–ZrO2 nanospheres were able to remove over 97% arsenic in real underground water with initial arsenic concentration of 0.376mgL−1 to meet the guideline limit of arsenic in drinking water regulated by the World Health Organization without any pre-treatment and/or pH adjustment.
In recent decades, electrochemical detection of arsenic(III) has been undergoing revolutionary developments with higher sensitivity and lower detection limit. Despite great success, electrochemical ...detection of As(III) still depends heavily on noble metals (predominantly Au) in a strong acid condition, thus increasing the cost and hampering the widespread application. Here, we report a disposable platform completely free from noble metals for electrochemical detection of As(III) in drinking water under nearly neutral condition by square wave anodic stripping voltammetry. By combining the high adsorptivity of Fe3O4 microspheres toward As(III) and the advantages of room temperature ionic liquid (RTIL), the Fe3O4-RTIL composite modified screen-printed carbon electrode (SPCE) showed even better electrochemical performance than commonly used noble metals. Several ionic liquids with different viscosities and surface tensions were found to have a different effect on the voltammetric behavior toward As(III). Under the optimized conditions, the Fe3O4-RTIL composites offered direct detection of As(III) within the desirable range (10 ppb) in drinking water as specified by the World Health Organization (WHO), with a detection limit (3σ method) of 8 × 10–4 ppb. The obtained sensitivity was 4.91 μA ppb–1, which is the highest as far as we know. In addition, a possible mechanism for As(III) preconcentration based on adsorption has been proposed and supported by designed experiments. Finally, this platform was successfully applied to analyzing a real sample collected from Inner Mongolia, China.
This article provides a comprehensive review of current research activities that concentrate on chemical sensors based on nanotubes, nanorods, nanobelts, and nanowires. We devote the most attention ...on the experimental principle, design of sensing devices, sensing mechanism, and some important conclusions. We elaborate on development of chemical sensors based on nanostructured materials in the following four sections: (1) nanotube sensors; (2) nanorod sensors; (3) nanobelt sensors; (4) nanowire sensors. We conclude this review with personal perspectives on the directions towards which future research on nanostructured sensors might be directed.
