Recent progress in applications of graphene oxide for gas sensing: A review

This paper is a review of the recent progress on gas sensors using graphene oxide (GO). GO is not a new material but its unique features have recently been of interest for gas sensing applications, and not just as an intermediate for reduced graphene oxide (RGO). Graphene and RGO have been well known gas-sensing materials, but GO is also an attractive sensing material that has been well studied these last few years. The functional groups on GO nanosheets play important roles in adsorbing gas molecules, and the electric or optical properties of GO materials change with exposure to certain gases. Addition of metal nanoparticles and metal oxide nanocomposites is an effective way to make GO materials selective and sensitive to analyte gases. In this paper, several applications of GO based sensors are summarized for detection of water vapor, NO₂, H₂, NH₃, H₂S, and organic vapors. Also binding energies of gas molecules onto graphene and the oxygenous functional groups are summarized, and problems and possible solutions are discussed for the GO-based gas sensors.     

Gold Nanoparticles Decorated Graphene as a High Performance Sensor for Determination of Trace Hydrazine Levels in Water

Electrochemical sensors provide a selective, sensitive and an easy approach to detect hazardous substances such as hydrazine. Herein, we investigate a facile route for the fabrication of a nanostructured composite based on Au nanoparticles (AuNPs) decorated graphene and present its sensing performance towards hydrazine. Our strategy involves electrophoretic deposition (EPD) of graphene oxide (GO) on Au substrate to obtain a uniform layer EPD‐GO, followed by electrochemical reduction of GO to yield high quality graphene ERGO and electrodeposition of monodispersed AuNPs on ERGO (AuNPs/ERGO/Au). The modified AuNPs/ERGO/Au electrode was characterized using scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT‐IR) techniques. The sensor exhibited an improved catalytic activity with a peak potential of +87 mV (vs. Ag/AgCl) for hydrazine oxidation. The high performance of this hybrid electrode is due to the presence of a synergistic effect between AuNPs and ERGO at their interface. Insights into the mechanism and kinetics of hydrazine oxidation are withdrawn from varying the voltage scan rate as the reaction is fully irreversible and diffusion‐controlled. The proposed hydrazine sensor showed suitability for nanomolar detection (detection limit of 74 nM), high selectivity in the presence of common ions and efficiency for application in water samples.     

Graphene Oxide-Based Stimuli-Responsive Platforms for Biomedical Applications

Graphene is a two-dimensional sp² hybridized carbon material that has attracted tremendous attention for its stimuli-responsive applications, owing to its high surface area and excellent electrical, optical, thermal, and mechanical properties. The physicochemical properties of graphene can be tuned by surface functionalization. The biomedical field pays special attention to stimuli-responsive materials due to their responsive abilities under different conditions. Stimuli-responsive materials exhibit great potential in changing their behavior upon exposure to external or internal factors, such as pH, light, electric field, magnetic field, and temperature. Graphene-based materials, particularly graphene oxide (GO), have been widely used in stimuli-responsive applications due to their superior biocompatibility compared to other forms of graphene. GO has been commonly utilized in tissue engineering, bioimaging, biosensing, cancer therapy, and drug delivery. GO-based stimuli-responsive platforms for wound healing applications have not yet been fully explored. This review describes the effects of different stimuli-responsive factors, such as pH, light, temperature, and magnetic and electric fields on GO-based materials and their applications. The wound healing applications of GO-based materials is extensively discussed with cancer therapy and drug delivery.     

Graphene oxide-based two-dimensional molecular brush for efficient removal of lead and copper ions from water media

In this study, graphene oxide (GO)-based two-dimensional molecular brush was fabricated by grafting polyacrylamide onto GO nanosheets for efficient removal of Pb²⁺ and Cu²⁺ from water media. Owing to the rich oxygen and nitrogen functional groups in the composites, the synthetic GO two-dimensional molecular brush can get the maximum adsorption capacity of 268.4 mg/g for Pb²⁺ and 127.2 mg/g for Cu²⁺, respectively. Moreover, the interspaces between the stacked two-dimensional molecular brushes provide fast pathways for the diffusion of heavy metal ions. As a result, GO-based two-dimensional molecular brush can reach the adsorption equilibrium within 60 min. These results indicated that the synthetic GO-based two-dimensional molecular brush is a promising adsorbent to separate heavy metal ions from water media.     

Chemiluminescence biosensors for DNA detection using graphene oxide and a horseradish peroxidase-mimicking DNAzyme

In this communication, we demonstrate that graphene oxide (GO) greatly inhibits the peroxidatic activity of a horseradish peroxidase-mimicking DNAzyme. Combining this observation with the unique DNA/GO interactions, an ultrasensitive GO-based chemiluminescence DNA biosensing platform is developed.     

A Review on Graphene Oxide Two-dimensional Macromolecules: from Single Molecules to Macro-assembly

Graphene oxide(GO), which consists of two-dimensional(2 D) sp² carbon hexagonal networks and oxygen-contained functional groups, has laid the foundation of mass production and applications of graphene materials. Made by chemical oxidation of graphite, GO is highly dispersible or even solubilized in water and polar organic solvents, which resolves the hard problem of graphene processing and opens a door to wet-processing of graphene. Despite its defects, GO is easy to functionalize, dope, punch holes, cut into pieces, conduct chemical reduction, form lyotropic liquid crystal, and assemble into macroscopic materials with tunable structures and properties as a living building block. GO sheet has been viewed as a single molecule, a particle, as well as a soft polymer material. An overview on GO as a 2 D macromolecule is essential for studying its intrinsic properties and guiding the development of relevant subjects. This review mainly focuses on recent advances of GO sheets, from single macromolecular behavior to macro-assembled graphene material properties. The first part of this review offers a brief introduction to the synthesis of GO molecules. Then the chemical structure and physical properties of GO are presented, as well as its polarity in solvent and rheology behavior. Several key parameters governing the ultimate stability of GO colloidal behavior, including size, p H and the presence of cation in aqueous dispersions, are highlighted. Furthermore, the discovery of GO liquid crystal and functionalization of GO molecules have built solid new foundations of preparing highly ordered, architecture-tunable, macro-assembled graphene materials, including 1 D graphene fibers, 2 D graphene films, and 3 D graphene architectures. The GO-based composites are also viewed and the interactions between these target materials and GO are carefully discussed. Finally, an outlook is provided in this field, where GO is regarded as macromolecules, pointing out the challenges and opportunities that exist in the field. We hope that this review will be beneficial to the understanding of GO in terms of chemical structure,molecular properties, macro-assembly and potential applications, and encourage further development to extend its investigations from basic research to practical applications.     

Biological and chemical sensors based on graphene materials

Owing to their extraordinary electrical, chemical, optical, mechanical and structural properties, graphene and its derivatives have stimulated exploding interests in their sensor applications ever since the first isolation of free-standing graphene sheets in year 2004. This article critically and comprehensively reviews the emerging graphene-based electrochemical sensors, electronic sensors, optical sensors, and nanopore sensors for biological or chemical detection. We emphasize on the underlying detection (or signal transduction) mechanisms, the unique roles and advantages of the used graphene materials. Properties and preparations of different graphene materials, their functionalizations are also comparatively discussed in view of sensor development. Finally, the perspective and current challenges of graphene sensors are outlined (312 references).     

石墨烯负载的空心银钯纳米粒子的制备及其在过氧化氢检测中的应用

制备了在石墨烯上修饰的AgPd合金纳米粒子,并将其应用于对过氧化氢(H2O2)的电化学检测。通过两步合成得到此纳米复合物:利用柠檬酸钠作为保护剂和还原剂,合成石墨烯负载的Ag纳米粒子(Ag/GO);在100℃下,通过Ag与Pd2+之间的置换反应得到石墨烯负载的具有空心结构的AgPd合金纳米粒子(AgPd/GO)。用紫外-可见光谱(UV-vis),电子显微镜(TEM)等对此纳米复合物的结构及其吸收光谱和形貌进行了表征。电化学循环伏安法(CV)和计时安培法(i-t)的研究结果表明,修饰在石墨烯上的空心AgPd合金纳米粒子对H2O2还原具有显著的催化活性,对H2O2检测的线性范围为0.01～1.4 mmol/L(R=0.990);检出限为1.4μmol/L。     

Robust Superhydrophobic/Superoleophilic Wrinkled Microspherical MOF@rGO Composites for Efficient Oil–Water Separation

Graphene/MOF‐based composite materials in three‐dimensional (3D) architectures are promising for the treatment of oil‐containing wastewater by absorption owing to their intrinsic properties of graphene and metal‐organic frameworks (MOFs), such as high porosity, ultralow density, and facilely tailored superwettability. In this study, novel wrinkled 3D microspherical MOF@rGO composites with both superhydrophobic and superoleophilic properties were developed by embedding MOF nanoparticles between graphene oxide (GO) nanosheets, followed by high‐temperature reduction self‐assembly. The microspherical composites feature a unique micro/nano hierarchy consisting of crumpled reduced GO (rGO) nanosheets intercalated with well‐dispersed MOF nanoparticles. Combined with the superwettability and abundant meso/microporosity, the peculiar architectures of wrinkled ZIF‐8@rGO microspheres show very fast absorption rates and high sorption selectivity for organic solvents and oils from water.     

Graphene and graphene oxide: two ideal choices for the enrichment and ionization of long-chain fatty acids free from matrix-assisted laser desorption/ionization matrix interference

In this work, graphene (G) and graphene oxide (GO) were utilized to enrich and ionize long-chain fatty acids. All together five long-chain fatty acids were selected as models here, n-dodecanoic acid (C12), n-tetradecanoic acid (C14), n-hexadecanoic acid (C16), n-octadecanoic acid (C18), and n-eicosanoic acid (C20). Due to the large surface area and strong interaction force of G or GO, all the five long-chain fatty models were effectively enriched by G or GO. On the other hand, the excellent electronic, thermal, and mechanical properties enable G and GO to be prefect energy receptacles for laser radiation, which make the ionization steps more effective. Eventually, the promoted G and GO methodology can sensitively detect the five long-chain fatty acid models from real biological samples even at low concentrations. Meanwhile, by adopting our promoted methodology, the detection of long-chain fatty acids by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) was demonstrated to be simple, sensitive, fast, cost effective and high throughput, which is meaningful as to practical usage.     

Fabrication of macroporous polystyrene/graphene oxide composite monolith and its adsorption property for tetracycline

Macroporous polystyrene microsphere/graphene oxide(PS/GO) composite monolith was first prepared using Pickering emulsion droplets as the soft template. The Pickering emulsion was stabilized by PS/GO composite particles in-situ formed in an acidic water phase. With the evaporation of water and the oil phase(octane), the Pickering emulsion droplets agglomerated and combined with each other, forming a three-dimensional macroporous PS/GO composite matrix with excellent mechanical strength. The size of the macrospores ranged from 4 mm to 20 mm. The macroporous PS/GO composite monolith exhibited high adsorption capacity for tetracycline(TC) in an aqueous solution at p H 4–6. The maximum adsorption capacity reached 197.9 mg g 1at p H 6. The adsorption behaviour of TC fitted well with the Langmuir model and pseudo-second-order kinetic model. This work offers a simple and efficient approach to fabricate macroporous GO-based monolith with high strength and adsorption ability for organic pollutants.     

Toehold-mediated nonenzymatic amplification circuit on graphene oxide fluorescence switching platform for sensitive and homogeneous microRNA detection

A novel graphene oxide (GO) fluorescence switch-based homogenous system has been developed to solve two problems that are commonly encountered in conventional GO-based biosensors. First, with the assistance of toehold-mediated nonenzymatic amplification (TMNA), the sensitivity of this system greatly surpasses that of previously described GO-based biosensors, which are always limited to the nM range due to the lack of efficient signal amplification. Second, without enzymatic participation in amplification, the unreliability of detection resulting from nonspecific desorption of DNA probes on the GO surface by enzymatic protein can be avoided. Moreover, the interaction mechanism of the double-stranded TMNA products contains several single-stranded toeholds at two ends and GO has also been explored with combinations of atomic force microscopy imaging, zeta potential detection, and fluorescence assays. It has been shown that the hybrids can be anchored to the surface of GO through the end with more unpaired bases, and that the other end, which has weaker interaction with GO, can escape GO adsorption due to the robustness of the central dsDNA structures. We verified this GO fluorescence switch-based detection system by detecting microRNA 21, an overexpressed non-encoding gene in a variety of malignant cells. Rational design of the probes allowed the isothermal nonenzymatic reaction to achieve more than 100-fold amplification efficiency. The detection results showed that our strategy has a detection limit of 10 pM and a detection range of four orders of magnitude.     

Graphene oxide-based supramolecular hydrogels for making nanohybrid systems with Au nanoparticles

In the presence of a small amount of a proteinous amino acid (arginine/tryptophan/histidine) or a nucleoside (adenosine/guanosine/cytidine), graphene oxide (GO) forms supramolecular stable hydrogels. These hydrogels have been characterized by field-emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), X-ray diffraction (XRD) analysis, Raman spectroscopy, and rheology. The morphology of the hydrogel reveals the presence of nanofibers and nanosheets. This suggests the supramolecular aggregation of GO in the presence of an amino acid/nucleoside. Rheological studies of arginine containing a GO-based hydrogel show a very high G' value (6.058 × 10(4) Pa), indicating the rigid, solid-like behavior of this gel. One of these hydrogels (GO-tryptophan) has been successfully utilized for the in situ synthesis and stabilization of Au nanoparticles (Au NPs) within the hydrogel matrix without the presence of any other external reducing and stabilizing agents to make Au NPs containing the GO-based nanohybrid material. The Au NPs containing the hybrid hydrogel has been characterized by using UV/vis spectroscopy, X-ray diffraction (XRD), and transmission electron microscopy (TEM). In this study, gold salt (Au(3+)) has been bioreduced by the tryptophan within the hydrogel. This is a facile "green chemical" method of preparing the GO-based nanohybrid material within the hydrogel matrix. The significance of this method is the in situ reduction of gold salt within the gel phase, and this helps to decorate the nascently formed Au NPs almost homogeneously and uniformly on the surface of the GO nanosheets within the gel matrix.     

Porous reduced graphene oxide for ultrasensitive detection of nitrogen dioxide

The defect engineering in graphene plays a significant role for the application of gas sensors. In this work, we proposed an efficient method to prepare ultrasensitive gas sensors based on the porous reduced graphene oxide (PRGO). Photo-Fenton etching was carried out on GO nanosheets in a controlled manner to enrich their vacancy defects. The resulting porous graphene oxide (PGO) was then drop-coated on interdigital electrodes and hydrothermal reduced at 180 °C. Controllable reduction was achieved by varying the water amount. The gas sensor based on PRGO-5 min-6 h exhibited superior sensing and selective performance toward nitrogen dioxide (NO₂), with an exceptional high sensitivity up to 12 ppm^?1. The theoretical limit of detection is down to 0.66 ppb. The excellent performance could be mainly attributed to the typical vacancy defects of PRGO. Some residue carboxylic groups on the edges could also facilitate the adsorption of polar molecules. The process has a great potential for scalable fabrication of high-performance NO₂ gas sensors.     

Fluorescence chemical sensor based on water‐soluble poly(p‐phenylene ethynylene)–graphene oxide composite for Cu2+

A chemical sensor for metal ions was fabricated based on a water‐soluble conjugated polymer–graphene oxide (GO) composite. Water‐soluble poly(p‐phenylene ethynylene) (PPE) with sulfonic acid side chain groups was used to prepare a very stable water‐soluble PPE–GO composite with strong π–π interactions in water. The relationship between the optical properties and metal ion sensing capability of the PPE–GO composite in aqueous solution was investigated. Addition of metal ions enhanced the fluorescence intensity of the composite, and, in particular, the composite enabled the fluorescence detection of Cu²⁺ in aqueous solutions with high selectivity and sensitivity. Therefore, this conjugated polymer–GO composite sensor system was found to be an effective turn‐on type chemical sensor for metal ions. Copyright © 2015 John Wiley & Sons, Ltd.     

Understanding Self-assembly,Colloidal Behavior and Rheological Properties of Graphene Derivatives for High-performance Supercapacitor Fabrication

Graphene derivatives, such as graphene oxide(GO) and reduced graphene oxide(RGO), have been widely used as promising twodimensional nanoscale building blocks due to their fascinating properties, cost-effective production, and good processability. Understanding the intrinsic self-assembling, colloidal, and rheological features of graphene derivatives is of critical importance to establish the formation-structureproperty relationship of graphene-based materials. This article reviews recent progresses in our studies of these interesting properties of graphene derivatives for developing high performance supercapacitors. The content is organized to include characteristics of the dispersions of graphene derivatives, self-assembly of nanosheets from liquid medium, colloidal behavior, rheological properties of the dispersions, processing methods based on the properties, and performance of the fabricated supercapacitors. GO and RGO nanosheets are proved to form different types of assembled structures with unique morphologies, such as ultrathin layer-by-layer films, porous aggregates, and nanoscrolls. The unique rheological properties of GO dispersions and hydrogels, feasible for both the traditional wet-processing and newly-developed technology like three-dimensional printing, are highlighted for their potential in structural manipulation and scalable fabrication of graphene-based devices. The research devoted to up-grading the performance of supercapacitors is presented in some details, which could be applicable for fabricating other graphene-based energy storage devices. Some challenges and perspectives in our point of view are given in the last part of this feature article.     

碳基量子点荧光传感器在环境检测中的应用研究

由于碳基量子点优越的光学性能、良好的水溶性及良好的生物相容性，其在荧光传感器方面的应用引起了越来越多人的关注，特别是其对金属离子卓越的检测性能使其广泛应用于环境检测。为了更好的了解到碳基量子点的应用，从碳量子点、石墨烯量子点、氧化石墨烯量子点的合成和近十年来关于其在环境检测中的应用做了总结，并对碳基量子点荧光传感器的应用做了展望。     

Smart nano-architectures as potential sensing tools for detecting heavy metal ions in aqueous matrices

The discharge of heavy metal ions into water resources as a result of human activities has become a global issue. Contamination with heavy metal ions poses a major threat to the environment and human health. Therefore, there is a dire need to probe the presence of heavy metal ions in a more selective, facile, quick, cost-effective and sensitive way. Conventional sensors are being utilized to sense heavy metal ions; however, various challenges and limitations like interference, overlapping of oxidation potential, selectivity and sensitivity are associated with them that limit their in-field applicability. Hence, nanomaterial based chemical sensors have emerged as an alternative substitute and are extensively employed for the detection of heavy metal ions as a potent analytical tool. The incorporation of nanomaterials in sensors increases their sensitivity, selectivity, portability, on-site detection capability and device performance. Nanomaterial based electrodes exhibit enhanced performance because surface of electrode at nano-scale level offers high catalytic potential, large active surface area and high conductivity. Therefore, this review addresses the recent progress on chemical sensors based on different nanomaterials such as carbon nanotubes (CNTs), metal nanoparticles, graphene, carbon quantum dots and nanocomposites for sensing heavy metals ions using different sensing approaches. Furthermore, various types of optical sensors such as fluorescence, luminescence and colorimetry sensors have been presented in detail.     

水溶液体系中氧化石墨烯的γ射线辐射还原

石墨烯是一种碳原子以二维蜂窝状晶格结构构成的单片层材料,由于其具有优异的电传导性、力学性能和热传导性近年来受到广泛关注.本文采用γ射线辐射技术分别处理水溶液和对苯二胺(PPD)水溶液中的氧化石墨烯(GO),得到辐照还原氧化石墨烯(RGO)和胺基化修饰的还原氧化石墨烯(RGON).通过傅里叶变换红外(FTIR)光谱、X射线光电子能谱(XPS)、拉曼(Raman)光谱、X射线衍射(XRD)和热失重分析(TGA)等表征分析产物的化学结构和元素组成;通过四探针测试仪和接触角测量仪研究产物的导电性能和亲水性.实验结果表明,在水溶液及PPD水溶液中γ射线辐射均可高效还原GO,还原后得到的RGO和RGON电导率均显著增大.PPD的胺基在辐射还原过程中还可以修饰到石墨烯的表面,因此RGON的亲水性比RGO好,但胺基的存在会干扰石墨烯表面π电子的传导,导致其电导率下降.     

Comparative study of different types of graphenes as electrocatalysts for ascorbic acid

A comparative study regarding the electrocatalytic activity of graphene oxide (GO), chemically-reduced graphene oxide (crGO) and graphene produced by direct liquid exfoliation (dG) is presented. Sensors were developed by modifying glassy carbon (GC) electrodes with GO, crGO and dG and ascorbic acid was used as a pilot analyte. GC/GO electrodes offer substantially lower oxidation overpotential, up to 350 mV, compared with GC/crGO, GC/dG and unmodified GC electrodes. In addition, the different carbon-to-oxygen atomic ratios in GO, as it occurs depending on the synthetic route, were found to have a remarkable effect on the performance of the sensors. Reduction of GO was achieved by immersing the modified electrodes into a stirred solution of NaBH₄ for 10 min at room temperature. This process was used alternatively of the time consuming and laborious process of hydrazine, and its effectiveness was confirmed by cyclic voltammetry and electrochemical impedance spectroscopy. Analytical utility of the sensors is demonstrated.