A selective and sensitive sensor based on highly dispersed cobalt porphyrin-Co<Subscript>3</Subscript>O<Subscript>4</Subscript>-graphene oxide nanocomposites for the detection of methyl parathion

A new type of graphene-Co₃O₄ functionalized porphyrin was synthesized and used for selective and sensitive detection of methyl parathion (MP). Co₃O₄ nanoparticles were firstly modified onto graphene oxide sheets and the porphyrin/Co₃O₄/graphene nanocomposites were then synthesized by self-assembly decoration of anion porphyrin on Co₃O₄-modified graphene sheets by π–π stacking. By dexterously controlling the electrochemical reduction variables and optimizing the electrode preparation parameters, with the satisfactory conductivity, strong adsorption toward MP, the developed novel sensor fabricated with the as-synthesized nano-assembly for determination of MP shows some satisfactory properties such as a wide linear concentration range (from 4.0?×?10^?7 M to 2.0?×?10^?5 M), low detection limit (1.1?×?10^?8 M), favorable repeatability, long-time storage stability, and satisfactory anti-interference ability. It also had high precision for the real sample analysis, which indicated the good perspective for field application.     

A cationic porphyrin-based self-assembled film for mercury ion detection

A cationic 5,15-(p-(9,9-bis(6-trimethylammoniumhexyl)fluorenylethynyl)phenyl)porphyrin tetrabromide was synthesized and the self-assembled films were used for Hg²⁺ detection in aqueous media. The detection response is based on fluorescence quenching of the porphyrin molecule upon coordination with Hg²⁺. The detection shows high selectivity for Hg²⁺ over Cu²⁺, Zn²⁺, Pb²⁺, Cd²⁺, Mn²⁺, Ni²⁺, Co²⁺ and Ca²⁺. A linear response toward Hg²⁺ in a concentration range of 1 × 10⁻¹⁰-1 × 10⁻⁶ M was observed for the film with a detection limit of 0.1 nM. The cationic porphyrin film shows higher stability and significant improvement in detection sensitivity, as compared to other porphyrin-based sensors. The amphiphilic cationic nature of the porphyrin synthesized also allows for the direct deposition of a porphyrin layer on a bare glass surface through self-assembly.     

Preparing graphene oxide–copper composite material from spent lithium ion batteries and catalytic performance analysis

The wide use of lithium ion batteries (LIBs) has created much waste, which has become a global issue. It is vital to recycle waste LIBs considering their environmental risks and resource characteristics. Anode graphite from spent LIBs still possess a complete layer structure and contain some oxygen-containing groups between layers, which can be reused to prepare high value-added products. Given the intrinsic defect structure of anode graphite, copper foils in LIB anode electrodes, and excellent properties of graphene, graphene oxide–copper composite material was prepared in this work. Anode graphite was firstly purified to remove organic impurities by calcination and remove lithium. Purified graphite was used to prepare graphene oxide–copper composite material after oxidation to graphite oxide, ultrasonic exfoliation to graphene oxide (GO), and Cu²⁺ adsorption. Compared with natural graphite, preparing graphite oxide using anode graphite consumed 40% less concentrated H₂SO₄ and 28.6% less KMnO₄. Cu²⁺ was well adsorbed by 1.0 mg L^?1 stable GO suspension at pH 5.3 for 120 min. Graphene oxide–copper composite material could be successfully obtained after 6 h absorption, 3 h bonding between GO and Cu²⁺ with 3/100 of GO/CuSO₄ mass ratio. Compared to CuO, graphene oxide–copper composite material had better catalytic photodegradation performance on methylene blue, and the electric field further improved the photodegradation efficiency of the composite material.     

Activated carbon/graphene composites with high-rate performance as electrode materials for electrochemical capacitors

Glucose-derived activated carbon (GAC)/reduced graphene oxide (RGO) composites are prepared by pre-carbonization of the precursors (aqueous mixture of glucose and graphene oxide) and KOH activation of the pyrolysis products. The effect of the mass ratio of graphene oxide (GO) in the precursor on the electrochemical performance of GAC/RGO composites as electrode materials for electrochemical capacitors is investigated. It is found that the thermally reduced graphene oxide sheets serves as a wrinkled carrier to support the activated carbon particles after activation. The pore size distribution and surface area are depended on the mass ratio of GO. Besides, the rate capability of GAC is improved by the introduction of GO in the precursor. The highest specific capacitance of 334 F g^?1 is achieved for the GAC/RGO composite prepared from the precursor with a GO mass ratio of 3 %.     

Al3+/graphene composites for electrochemical detection of DNA cleavage

Herein, we present the electrochemical co-deposition of Al3+/graphene composites directly from an aqueous mixture containing graphene oxide (GO) and Al3+. The obtained Al3+/graphene composites with good electrochemical activity were regarded as an appropriate immobilization platform for double-stranded DNA (dsDNA). The nontoxic redox probe xanthurenic acid (XA) was successfully applied to recognize single-stranded DNA and dsDNA. We illustrated that the scission of dsDNA caused by GO combining with some metal ions could be detected by monitoring the electrochemical signals of XA.     

Interaction and photodynamic activity of cationic porphyrin derivatives bearing different patterns of charge distribution with GMP and DNA

The interaction of amphiphilic cationic porphyrins, containing different patterns of meso-substitution by 4-(3-N,N,N-trimethylammoniumpropoxy)phenyl (A) and 4-(trifluoromethyl)phenyl (B) groups, with guanosine 5′-monophosphate (GMP) and calf thymus DNA have been studied by optical methods in phosphate buffer solution. The properties of these synthetic porphyrins were compared with those of representative standard of anionic 5,10,15,20-tetra(4-sulphonatophenyl)porphyrin (TPPS₄⁴⁻) and cationic 5,10,15,20-tetra(4-N,N,N-trimethylammonium phenyl)porphyrin (TMAP⁴⁺). Stable complexes with GMP were found for cationic porphyrins, except for monocationic AB₃⁺. The binding constant (K_GMP  10⁴ M⁻¹) follows the order: A₃B³⁺  ABAB²⁺ > A₄⁴⁺  TMAP⁴⁺. Also, interaction with DNA was observed for all evaluated cationic porphyrins. For these related cationic porphyrins, the binding constant (K_DNA  10⁵ M⁻¹) increases with the number of cationic charges. On the other hand, the photodynamic activity of porphyrins was analyzed in solution of GMP and DNA. Monocationic AB₃⁺ is a less effective sensitizer to oxidize GMP in comparison with the other cationic porphyrins, in agreement with the lack of detected interaction with this nucleotide. The electrophoretic analysis of DNA indicates that photocleavage takes place when the samples are exposed to photoexcited tricationic and tetracationic porphyrins. In the presence of sodium azide the DNA decomposition was diminished. Also, reduction in the DNA photocleavage was observed under anoxic condition, indicating that oxygen is essential for DNA photocleavage sensitized by these cationic porphyrins. In addition, an increase in DNA degradation was not observed in deuteriated water. Therefore, an important contribution of type I photoreaction processes could be occurring in the DNA photodamage sensitized by these cationic porphyrins. These results provide a better understanding of the characteristics needed for sensitizers to produce efficient DNA photocleavage.     

Stripping Voltammetric Analysis of Mercury at Base-treated Graphene Oxide Electrodes

According to the Rourke's model, graphene oxide(GO) synthesized from the oxidation of graphite actually consisted of partly oxidized graphene sheets and highly oxidized debris(OD). The OD was strongly adhered to the surface of graphene sheets, while they could be facilely removed by a base-washing procedure. The existence and removal by base-washing of OD were characterized by means of thermogravimetric analysis(TGA), FTIR spectroscopy, X-ray photoelectron spectroscopy(XPS), transmission electron microscopy(TEM) and Raman spectroscopy. The adsorption of OD not only made a great difference to the physical and chemical properties of GO, but also affected its electrochemical behavior when it was employed as an electrode material. In this article, we demonstrated that the electrochemical deposition and the subsequent voltammetric stripping analysis of mercury were significantly influenced by the presence of OD. The consequence suggests that the presence of OD on the sheets of GO restricts the electrochemical deposition behavior of mercury and further lowers the sensitivity of the voltammetric stripping responses. The sensitivity was observed as 0.78 A·L·mol^-1 at base-washed(bw)-GO/GC(glassy carbon) better than that at as-prepared GO(a-GO)/GC for 0.28 A·L·mol^-1. The limit of detection was calculated as 2.95 and 0.83 μmol/L before and after removing the OD, respectively. The availability of both electrodes was evaluated by detecting Hg²⁺ in lake water specimens using standard samples recovery.     

Synthesis and characterization of polypyrrole/graphite oxide composite by in situ emulsion polymerization

This work demonstrates a feasible route to synthesize the layered polypyrrole/graphite oxide (PPy/GO) composite by in situ emulsion polymerization in the presence of cationic surfactant cetyltrimethylammonium bromide (CTAB) as emulsifier. AFM and XRD results reveal that the GO can be delaminated into nanosheets and well dispersed in aqueous solution in the presence of CTAB. The PPy nanowires are formed due to the presence of the lamellar mesostructured (CTA)₂S₂O₈ as a template. The results of the PPy/GO composite indicate the PPy insert successfully into GO interlayers, and the nanofiber‐like PPy are deposited onto the GO surface. Owing to π–π electron stacking effect between the pyrrole ring of PPy and the unoxided domain of GO sheets, the electrical conductivity of PPy/GO composite (5 S/cm) significantly improves in comparison with pure PPy nanowires (0.94 S/cm) and pristine GO (1 × 10^?6 S/cm). © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1329–1335, 2010     

Removal of Th4+ ions from aqueous solutions by graphene oxide

The removal of Th⁴⁺ ions from aqueous solutions was investigated using single-layer graphene oxide (GO) as a sorbent which was prepared by the modified Hummers’ method through batch adsorption experiments at room temperature. Structural characterizations of the sorbent were also investigated. The influences of the pH value of solution, contact time, sorbent dose, ionic strength, the initial metal ion concentration and temperature on the adsorption of Th⁴⁺ were also investigated. These results indicated that the adsorption of Th⁴⁺ was dependent on the pH and independent on the ionic strength. The sorbent provided significant Th⁴⁺ removal (>98.7 %) at pH 3.0 and the adsorption equilibrium was achieved after only 10 min. The Langmuir adsorption isotherm fit the absorption profile very closely, and indicated that a maximum adsorption capacity of 1.77 mmol g^?1 of GO (411 mg g^?1) after 2 h. The thermodynamic parameters showed that this adsorption process was endothermic and spontaneous. Moreover, the desorption level of Th⁴⁺ from GO, by using 0.1 mol L^?1 H₂SO₄ as a stripping agent, was 84.2 ± 1.2 %, and that of 0.5 mol L^?1 HNO₃ as a stripping agent, was 79.8 ± 3.0 %.     

Synthesis and characterization of graphene oxide/modified poly(<Emphasis Type="Italic">N</Emphasis>-isopropylacrylamide) nanocomposite

In this study, the graphene oxide/poly(N-isopropylacrylamide) nanocomposite modified with 2-mercaptoethanol (GO/MPNIPAM) was synthesized in three stages. N-Isopropylacrylamide polymerization was firstly performed in the presence of azobisisobutyronitrile as an initiator, which was discovered by Homer, and 2-mercaptoethanol as a modifier. Then, the graphene oxide/modified polymer nanocomposite was synthesized by the covalent interactions between carboxylic acids of the graphene oxide and hydroxyl groups of the modified polymer during the esterification reaction. The GO/MPNIPAM nanocomposite includes some percentage of the polymer that improves solubility and stability of the GO sheets in physiological applications; due to the interaction between the MPNIPAM and the modified GO polymer, a bridge-like connection is formed between the GO sheets and the process that leads to remove a large number of hydrophilic groups on the GO nanocomposite and therefore, the GO/MPNIPAM is well dissolved in organic solvents. This property is beneficial for anti-cancer drug delivery as well as π–π interactions between the nanocomposite and aromatic drugs. The nanocomposite is not a toxic material for human body at all and has high capacity for drug delivery. Structure and morphology of the nanocomposite were studied by FTIR, SEM, XRD, UV, TGA and Raman analysis. The analysis done by X-ray diffraction pattern confirmed the presence of graphene oxide in nanocomposites and improved crystalline polymer in nanocomposites.     

The Preparation of Compressible and Fire‐Resistant Sponge‐Supported Reduced Graphene Oxide Aerogel for Electromagnetic Interference Shielding

We here report a facile method to fabricate a sponge‐supported reduced graphene oxide aerogel (S‐RGOA) using a commercial melamine sponge and graphene oxide (GO). Firstly, GO sheets were self‐assembled within the melamine sponge by the assistance of a chemical cross‐linking agent; and then, freeze‐drying and thermal treatment were adopted to prepare S‐RGOA, in which continuous porous reduced graphene oxide (RGO) network formed between the skeleton. The resulting S‐RGOA exhibited a high electromagnetic interference shielding effectiveness (EMI SE) of 20.4‐27.3 dB in 8–12 GHz and the specific EMI SE could reach 1437 dB?cm³g^?1. The mechanical test suggests that the lightweight S‐RGOA is compressible and possesses low energy dissipation. Burning and TGA measurements indicate that S‐RGOA is fire‐resistant and has excellent thermal stability. Our work provides an economical and environmentally‐friendly method to fabricate RGO aerogels for using as electromagnetic interference materials.     

Dynamic dispersion stability of graphene oxide with metal ions

Graphene oxide(GO),an important chemical precursor of graphene,can stably disperse in aqueous surrounding and undergo aggregation as metal cations introduced.The usual instability of GO with ions is caused by the shielding effect of ions and crosslinking between GO and ions.However,the dynamic stability of GO under ions exchange still remains unclear.Here,we investigated the dynamic dispersion stability of GO with metal ions and observed a redispersion behavior in concentrated Fe~(3+) solution,other than permanent aggregation.The exchange with Fe~(3+) ions drives the reversion of zeta(ζ) potential and enables the redispersion to individual GO-Fe~(3+) complex sheets,following a dynamic electric double layer(EDL) mechanism.It is found that the specifically strong electrostatic shielding effect and coordination attraction between Fe~(3+) and functional oxygen groups allows the selective redispersion of GO in concentrated Fe~(3+) solution.The revealed dynamic dispersion stability complements our understanding on the dispersive stability of GO and can be utilized to fabricate graphene-metal hybrids for rich applications.     

Synthesis and Characterization of a Series of Cationic Porphyrins Having Different Steric Effects

Abstract

A series of cationic porphyrins having only different steric effects and their cobalt complexes were synthesized. The cations of these porphyrins are meso-tetrakis(4-N-propylpyridyl)porphyrin (TPPyP⁴⁺), meso-tetrakis(4-N-ethylpyridyl)porphyrin (TEPyP⁴⁺) and meso-tetrakis(4-N-methylpyridyl)porphyrin (TMPyP⁴⁺), respectively. The anions are I^? (water soluble porphyrins) and ClO₄ ^? (organic solvent soluble porphyrins), respectively. The synthetic cationic porphyrins were characterized by elemental analysis, UV-visible absorption spectra, FTIR, MALDI-TOF-MS and ¹H-NMR spectra.     

Scalable Template Synthesis of Resorcinol–Formaldehyde/Graphene Oxide Composite Aerogels with Tunable Densities and Mechanical Properties

Resorcinol–formaldehyde (RF) and graphene oxide (GO) aerogels have found a variety of applications owing to their excellent properties and remarkable flexibility. However, the macroscopic and controllable synthesis of their composite gels is still a great challenge. By using GO sheets as template skeletons and metal ions (Co²⁺, Ni²⁺, or Ca²⁺) as catalysts and linkers, the first low‐temperature scalable strategy for the synthesis of a new kind of RF–GO composite gel with tunable densities and mechanical properties was developed. The aerogels can tolerate a strain as high as 80 % and quickly recover their original morphology after the compression has been released. Owing to their high compressibility, the gels might find applications in various areas, for example, as adsorbents for the removal of dye pollutants and in oil‐spill cleanup.     

金红石相TiO2-石墨烯复合材料的制备及其光催化性能

以鳞片石墨为原料, 用改进的Hummers法制备氧化石墨烯(GO), 以异丙醇钛为钛源经一步水热法制备得到金红石相TiO₂-石墨烯复合材料(rGO-TiO₂), 考察了氧化石墨烯用量对复合材料光催化性能的影响. 采用X射线衍射(XRD), 比表面积(BET), 透射电镜(TEM), 扫描电镜(SEM), 拉曼光谱, 紫外-可见(UV-Vis)吸收光谱和荧光光谱(PL)等测试手段对复合材料进行表征. 结果表明: 复合材料中TiO₂为针簇状结构的金红石相, 与石墨烯能够均匀复合; 与纯金红石相TiO₂相比, 复合材料具有较大的比表面积. 研究了该复合材料在紫外光下对罗丹明B 以及可见光下对甲基橙光降解效果. 当氧化石墨烯浓度为0.5 mg·mL^-1时, 制备得到的复合材料rGO-TiO₂具有较好的光催化效果.     

氮掺杂石墨烯的制备及其超级电容性能

以氧化石墨烯(GO)为原料, 尿素为还原剂和氮掺杂剂, 采用水热法合成了氮掺杂石墨烯. 利用扫描电子显微镜(SEM)、透射电子显微镜(TEM)、傅里叶变换红外(FTIR)光谱、X 射线衍射(XRD)、X 射线光电子能谱(XPS)、氮气吸脱附分析、电导率和电化学测试对样品的形貌、结构、组成以及电化学性质进行表征. 结果表明:水热条件下尿素能有效地化学还原GO并对其进行氮掺杂; 通过调节原料与掺杂剂的质量比, 可以得到不同氮掺杂含量的石墨烯, 氮元素含量范围为5.47%-7.56% (原子分数); 在6 mol·L^-1的KOH电解液中, 氮元素含量为7.50%的掺杂石墨烯的超级电容性能最优, 即在3 A·g^-1电流密度下首次恒流充放电比电容可达184.5 F·g^-1, 经1200次循环后的比电容为161.7 F·g^-1, 电容保持率为87.6%.     

Date Fruits-Assisted Synthesis and Biocompatibility Assessment of Nickel Oxide Nanoparticles Anchored onto Graphene Sheets for Biomedical Applications

Nanographene- and graphene-based nanohybrids have garnered attention in the biomedical community owing to their biocompatibility, excellent aqueous processability, ease of cellular uptake, facile surface functionalization, and thermal and electrical conductivities. NiO nanoparticle-graphene nanohybrid (G-NiO) was synthesized by first depositing Ni(OH)₂ onto the surface of graphene oxide (GO) sheets. The Ni(OH)₂-GO hybrids were then reduced to G-NiO using date palm syrup at 85 °C. The prepared G-NiO nanohybrids were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy, and energy-dispersive X-ray spectroscopy (EDX). The NiO nanoparticles, with a diameter of approximately 20–30 nm, were uniformly dispersed over the surface of the graphene sheets. The G-NiO hybrids exhibit biocompatibility in human mesenchymal stem cells (hMSCs) up to 100 μg/mL. The nanohybrids do not cause any significant changes in cellular and nuclear morphologies in hMSCs. The as-synthesized nanohybrids show excellent biocompatibility and could be a promising material for biomedical applications.     

Preparation of an Anti-Aggregation Silica/Zinc/Graphene Oxide Nanocomposite with Enhanced Adsorption Capacity

Nanomaterials play a significant role in adsorption treatment of dye wastewater, but irreversible aggregation of nanoparticles poses a significant problem. In this work, nanomesoporous zinc-doped silicate (NMSZ) was prepared by an in situ method. To prevent agglomeration, NMSZ was covalently bonded to graphene oxide (GO) sheets to form a nano-silica/zinc/graphene oxide composite (GO-NMSZ), aimed at removal of cationic dye methylene blue (MB). For comparison, undoped mesoporous silica (MS) was also synthesized and modified to obtain a silica/graphene oxide composite (GO-MS). The materials were characterized by powder XRD, SEM, FTIR spectroscopy, TEM, nitrogen sorption, and X-ray photoelectron spectroscopy (XPS). Preservation of the oxygen-containing groups of GO in the composites led to higher adsorption capacities. The best GO-NMSZ composite exhibited an enhanced adsorption capacity of 100.4 mg g⁻¹ for MB compared to those of undoped GO-MS (80.1 mg g⁻¹) and nongrafted NMSZ (55.7 mg g⁻¹). The nonselective character of GO-NMSZ is demonstrated by effective adsorption of anionic dye Congo red (127.4 mg g⁻¹) and neutral dye isatin (289.0 mg g⁻¹). The adsorption kinetics, adsorption isotherms, and a thermodynamic study suggested that MB adsorption occurs by chemisorption and is endothermic in nature.     

A dynamic light scattering study of photochemically reduced colloidal graphene oxide

Evolution of the hydrodynamic size d _HD of colloidal graphene oxide (GO) sheets in water induced by the photochemical GO reduction by UV light was studied by the dynamic light scattering spectroscopy. An increase of d _HD at an initial stage of the photoreduction is caused by partial photoelimination of the functional groups of GO and breaking of the hydrogen bonds between the fragments of the GO particles resulting in the sheets' unfolding. At deeper photoreduction, a decrease of d _HD is observed as a result of ππ stacking interaction between the aromatic areas of GO particles and crumpling of the GO sheets. Variations of pH affect strongly the d _HD of the photoreduced GO. At pH lowering from 6–7 to 2–3, a drastic growth of d _HD and the sheets' aggregation are observed, caused by the protonation of the carboxyl groups. At pH elevation to 11–12, on the contrary, a decrease of d _HD is observed, which is more pronounced the longer the photochemical GO reduction. The observation reflects crumpling/scrolling of the the GO sheets to minimize the contact area between the aromatic components of the photoreduced GO particles and the dispersive medium. The changes of the photoreduced GO particle size in basic media were found to be reversible.     

Superior Lithium‐Ion Storage Properties of Si‐Based Composite Powders with Unique Si@Carbon@Void@Graphene Configuration

Composite powders of the configuration Si@carbon@void@graphene were prepared by a one‐step spray pyrolysis process, by adding polyvinylpyrrolidone (PVP) to a precursor solution containing graphene oxide (GO) sheets and silicon nanoparticles (NPs). Morphological analysis indicates that the individual Si NPs are coated with amorphous carbon and encapsulated in a micrometer‐sized graphene ball structure that offers a large amount of buffer space. The addition of PVP improves the stability of the colloidal spray solution containing the GO sheets and the Si NPs. Consequently, the prepared Si@C@void@graphene composite powders have a relatively more uniform morphology than the Si@void@graphene composite powders prepared from the spray solution without PVP. The first charge and discharge capacities of the Si@C@void@graphene electrode measured at 0.1 A g^?1 are as high as 3102 and 2215 mA h g^?1, respectively. With an increase in the current rate from 0.5 to 11 A g^?1, 46 % of the original capacity (i.e., 2134 mA h g^?1) is maintained. After 500 cycles at a high rate of 7 A g^?1, the Si@C@void@graphene electrode shows 84 % capacity retention and 99.8 % of the average Coulombic efficiency. The superior cycling and rate capabilities of the prepared Si@C@void@graphene electrode could be attributed to the uniform carbon coating of the Si NPs and the graphene ball structure, which facilitates efficient diffusion of Li ions and prevents the penetration of electrolyte into graphene ball during cycling.