Carboxyl-functionalized Graphene Oxide Research Articles

Self-Assembled AgNP-Containing Nanocomposites Constructed by Electrospinning as Efficient Dye Photocatalyst Materials for Wastewater Treatment.

The design and self-assembly of graphene oxide (GO)-based composite membranes have attracted enormous attention due to their wide application in nanomaterial and environmental fields. In this work, we have successfully developed a strategy to fabricate new composite membranes based on poly(vinyl alcohol)/poly(acrylic acid)/carboxyl-functionalized graphene oxide modified with silver nanoparticles (PVA/PAA/GO-COOH@AgNPs), which were prepared via thermal treatment and the electrospinning technique. Due to the strong π-π forces and strong electrostatic interactions of GO–COOH sheets, the prepared composite membranes and their lager surface areas were modified by scores of AgNPs, which demonstrated that a high-efficiency photocatalyst removed the organic dyes from the aqueous solutions. The prepared PVA/PAA/GO-COOH@AgNPs nanocomposite membranes showed a remarkable photocatalytic capacity in the catalytic degradation of the methylene blue dye solutions. Most importantly, the whole process was easy, mild, and eco-friendly. Additionally, the as-prepared membranes could be repeatedly used after the catalytic reaction.

Femtosecond ytterbium-doped fiber laser mode-locked by carboxyl-functionalized graphene oxide saturable absorber

In contrast with graphene oxide (GO), carboxyl-functionalized graphene oxide (GO-COOH) is more appropriate for fabricating saturable absorbers (SAs) with high modulation depth and low nonsaturable loss because of its higher solubility in water. Here, we present a femtosecond mode-locked ytterbium-doped fiber (YDF) laser based on GO-COOH SA and a nonlinear polarization rotation effect. A mode-locked laser with a center wavelength of 1027 nm, an average output power of 53.5 mW (44.3% conversion efficiency), a fundamental repetition rate of 22 MHz, a pulse duration of 239 fs, and a signal-to-noise ratio of up to 75 dB is obtained.

844-fs mode-locked fiber laser by carboxyl-functionalized graphene oxide

We had proved that a kind of graphene nanomaterial “carboxyl-functionalized graphene oxide (GO-COOH)” possessed nonlinear saturable absorber (SA) property. The modulation depth of a GO-COOH water solution was measured as ∼8%. Moreover, a GO-COOH-based SA device was made and applied in an erbium-doped fiber laser. In this fiber laser, Q-switching pulses and mode-locked pulses were both obtained. With an increase in the pump power, the pulse width of Q-switching pulses decreased from 9.05 to 2.49 μs. The mode-locked pulse width was 844 fs, and the corresponding spectral bandwidth was 3.64 nm. Moreover, polarization adjusting or control was not needed during the whole process of mode locking. It illustrated that the proposed fiber laser incorporating GO-COOH could endure bigger intracavity birefringence. Our results indicated that the GO-COOH nanomaterial was a promising SA for generating high-performance pulse lasers.

Preparation of TiO2 nanoparticles modified electrospun nanocomposite membranes toward efficient dye degradation for wastewater treatment

New poly(vinyl alcohol)/poly(acrylic acid)/carboxyl-functionalized graphene oxide nanocomposite membranes were prepared using electrospinning technique with thermal treatment and modified with TiO2 nanoparticles. The thus prepared composite membranes are composed of polymeric nanofibers with carboxyl-functionalized graphene oxide sheets, which are anchored on the fibers by heat-induced crosslinking reaction. The preparation process of the designed nanocomposites is facile, eco-friendly, and controllable. The TiO2 nanoparticles were deposited uniformly and homogeneously onto the surface of the obtained composite membranes. The as-prepared composite membranes demonstrate efficient photocatalytic capacity toward dye degradation, which is primarily due to the specific surface area of electrospun membranes and the photoactivity of TiO2 nanoparticles. In addition, the composite membranes reported here are easy to regenerate. In comparison with other composite catalysts, the present preparation process is highly eco-friendly and facile to operate and regulate, which demonstrates potential large-scale applications in wastewater treatment and dye removal.

Carboxyl-functionalized graphene oxide polyamide nanofiltration membrane for desalination of dye solutions containing monovalent salt

Novel carboxyl-functionalized graphene oxide (CFGO)/polyamide (PA) nanofiltration (NF) membranes were prepared via interfacial polymerization (IP) of piperazine (PIP) and trimesoyl chloride (TMC). CFGO was fabricated by a chemical modification (ring opening followed by esterification) to the epoxide ring of GO. CFGO was then introduced in the PIP aqueous phase as an additive in the IP reaction. Compared with a pristine PA reference membrane, both the GO/PA and CFGO/PA membrane have an enhanced permeability (the optimum concentration of GO and CFGO in the membrane was 0.05% and 0.07%, and the corresponding water flux is 96.5 and 112.1L/m2/h, respectively),with a slight decrease of the salt rejection. In dye desalination experiment, the permeation flux of 0.05%GO/PA membrane is only 75.5L/m2/h, with 98.1% rejection of New Coccine (a dye with negative charge) and 28.7% retention for NaCl. For 0.07%CFGO/PA membrane, it can cut off 25.0% NaCl and 95.1% New Coccine, and its permeation flux can reach 110.4L/m2/h, which shows that the CFGO/PA membrane could be potentially applied to the dye desalination and concentration process. The CFGO/PA membrane shows better performances in permeability and dye desalination than GO/PA membrane, due to the significantly increased hydrophilicity and enhanced surface charge density.

Optical Limiting of Carboxyl–Graphene Oxide

Using the Z-scan method, the nonlinear optical absorption property of carboxyl-functionalized graphene oxide (GO) was researched for the first time. The strong optical limiting (OL) effect was found in carboxyl-GO, which can be attributed to the two-photon absorption (2PA). At 532-nm excitation condition, the threshold of OL behavior is only 8% of that at 1064 nm excitation, and the saturable intensity $I_{s}$ as well as the 2PA coefficient β2 are 1.31 GW/cm2 and 0.17 cm/GW, respectively. It indicates that carboxyl-GO is an excellent nanomaterial for OL application, especially in short wavelength scope.

Enhanced desalination performance of carboxyl functionalized graphene oxide nanofiltration membranes

The desalting performance of graphene oxide (GO) membranes was further optimized using one-step carboxylation via nucleophilic substitution reactions between epoxy groups of graphene oxide (GO) and amino groups of glycine. GO and GO-COOH membranes with highly ordered structure were prepared by pressure-assisted self-assembly technique. The performance of GO and GO-COOH membranes was investigated and compared. The results showed that GO-COOH membranes exhibited not only higher permeability but also better salt rejections compared with pristine GO membranes. The surface physicochemical properties of GO-COOH membrane including negativity and hydrophilicity were improved as well. The transport mechanism revealed that the improvement of desalting properties was attributed to enhanced electrostatic repulsion by inducing effective negative charge. The higher permeability of GO-COOH membranes resulted from increased water nanochannels and improved surface hydrophilicity. Overall, GO-COOH membranes show great potential in the separation field due to prominent permeation performance and desirable separation property.

Carboxyl-functionalized graphene oxide composites as SPR biosensors with enhanced sensitivity for immunoaffinity detection

This work demonstrates the excellent potential of carboxyl-functionalized graphene oxide (GO–COOH) composites to form biocompatible surfaces on sensing films for use in surface plasmon resonance (SPR)-based immunoaffinity biosensors. Carboxyl-functionalization of graphene carbon can modulate its visible spectrum, and can therefore be used to improve and control the plasmonic coupling mechanism. The binding properties of the molecules between a sensing film and a protein were elucidated at various flow rates of those molecules. The bio-specific binding interaction among the molecules was investigated by performing an antigen and antibody affinity immunoassay. The results thus obtained revealed that the overall affinity binding value, KA, of the Au/GO–COOH chip can be significantly enhanced by up to ∼5.15 times that of the Au/GO chip. With respect to the shifts of the SPR angles of the chips, the affinity immunoassay interaction at a BSA concentration of 1μg/ml for an Au/GO-COOH chip, an Au/GO chip and a traditional SPR chip are 35.5m°, 9.128m° and 8.816m°, respectively. The enhancement of the antigen-antibody interaction of the Au/GO–COOH chip cause this chip to become four times as sensitive to the SPR angle shift and to have the lowest antibody detection limit of 0.01pg/ml. These results indicate the potential of the chip in detecting specific proteins, and the development of real-time in vivo blood analysis and diagnosis based on cancer tumor markers.

Magnetic field-assisted SPR biosensor based on carboxyl-functionalized graphene oxide sensing film and Fe3O4-hollow gold nanohybrids probe

A novel surface plasmon resonance (SPR) biosensor, coupled with the magnetic bioseparation technique, was constructed and used to the determination of human IgG. Carboxyl-functionalized graphene oxide (cGO) sheet was employed as the sensing film for the efficient immobilization of capture antibody (Ab1). Nanoconjugates (FHAb2), obtained by binding detection antibody (Ab2) to the nanohybrids containing Fe3O4 nanoparticles (Fe3O4 NPs) and hollow gold sphere nanoparticles (HGNPs), were used to specifically collect the target analytes from sample solutions and serve as labels. Owing to the notable plasmonic fields spreading over inner and outer surfaces, HGNPs played key roles in amplifying the SPR response signals originating from the dielectric changes on the sensing films during the binding of Ab1 and human IgG-Ab2FH complexes. In addition, FHAb2 were also used as “vehicles” for the rapid delivery of the separated and enriched target analytes from sample solutions to the sensor surface via an external magnet. In the present method, taking advantages of the magnetic field-driven mass transfer and the significant signal amplification effect of FHAb2, the separation and analysis of human IgG in serum samples are quite effective and sensitive. The limit of detection was 1.88ngmL−1, which is about 260-fold lower than that obtained by routine SPR biosensors with sandwich assay.

Gold nanostar-enhanced surface plasmon resonance biosensor based on carboxyl-functionalized graphene oxide

A new high-sensitivity surface plasmon resonance (SPR) biosensor based on biofunctional gold nanostars (AuNSs) and carboxyl-functionalized graphene oxide (cGO) sheets was described. Compared with spherical gold nanoparticles (AuNPs), the anisotropic structure of AuNSs, which concentrates the electric charge density on its sharp tips, could enhance the local electromagnetic field and the electronic coupling effect significantly. cGO was obtained by a diazonium reaction of graphene oxide (GO) with 4-aminobenzoic acid. Compared with GO, cGO could immobilize more antibodies due to the abundant carboxylic groups on its surface. Testing results show that there are fairly large improvements in the analytical performance of the SPR biosensor using cGO/AuNSs-antigen conjugate, and the detection limit of the proposed biosensor is 0.0375 μg mL−1, which is 32 times lower than that of graphene oxide-based biosensor.

Carboxyl-functionalized graphene oxide-modified electrode for the electrochemical determination of nonsteroidal anti-inflammatory drug diclofenac

A simple and sensitive electrochemical method was proposed for the quantitative determination of nonsteroidal anti-inflammatory drug diclofenac (DCF). For the first time, carboxyl-functionalized graphene oxide (GO-COOH)-modified glassy carbon electrode (GCE) was employed for the determination of DCF by cyclic voltammetry (CV) and linear sweep voltammetric (LSV) techniques. The proposed modified electrode showed strong electrocatalytic activity toward DCF with higher anodic peak enhancement than that of the unmodified electrode. The practicality of the proposed electrode for the detection of DCF in human urine and blood serum samples was successfully demonstrated using LSV techniques. The obtained results were satisfactory. The detection limit and sensitivity of the proposed method were of 0.09 μM and 0.532 μA μM−1 cm−2, respectively (by LSV). Applicability of the proposed method was verified with commercially available pharmaceutical tablets, and the obtained results were in good agreement with the claimed label amounts of the tablets. In addition, this method could be used for the accurate detection of DCF in clinical and pharmaceutical industries in the future.

Copper-doped titanium dioxide nanoparticles as dual-functional labels for fabrication of electrochemical immunosensors

Constructions of versatile electroactive labels are key issues in the development of electrochemical immunosensors. In this study, copper-doped titanium dioxide nanoparticle (Cu@TiO2) was synthesized and used as labels for fabrication of sandwich-type electrochemical immunosensors on glassy carbon electrode (GCE). Due to the presence of copper ions, Cu@TiO2 shows a strong response current when coupled to an electrode. The prepared nanocomposite also shows high electrocatalytic activity towards reduction of hydrogen peroxide (H2O2). The dual functionality of Cu@TiO2 enables the fabrication of immunosensor using different detection modes, that is, square wave voltammetry (SWV) or chronoamperometry (CA). While Cu@TiO2 was used as labels of secondary antibodies (Ab2), carboxyl functionalized graphene oxide (CFGO) was used as electrode materials to immobilize primary antibodies (Ab1). Using human immunoglobulin G (IgG) as a model analyte, the immunosensor shows high sensitivity, acceptable stability and good reproducibility for both detection modes. Under optimal conditions, a linear range from 0.1pg/mL to 100ng/mL with a detection limit of 0.052pg/mL was obtained for SWV analysis. For CA analysis, a wider linear range from 0.01pg/mL to 100ng/mL and a lower detection limit of 0.0043pg/mL were obtained. The proposed metal ion-based enzyme-free and noble metal-free immunosensor may have promising applications in clinical diagnoses and many other fields.

Direct growth of Pt@Ag nanochains on tailorable graphene oxide with a green, in situ, template-free method and its biosensing application

In this work, we have investigated the in situ growth of Ag nanochains (AgNCs) on carboxyl-functionalized graphene oxide based on enzymatic metalization for the first time. The merit of this method is that the AgNCs could be generated directly on carboxyl-functionalized graphene oxide in a natural, environmentally friendly and sustainable way with high productivity. Furthermore, the Pt nanoparticles were wrapped around the AgNCs (Pt@AgNCs) which manifested some superior functions, such as excellent electrical conductivity and well-defined electrochemical redox activity. With Pt@AgNCs as the electrochemical redox probe, we developed a label-free electrochemical aptasensor for highly sensitive detection of platelet-derived growth factor. A linear response was obtained over a wide range from 6 pM to 40 nM with a detection limit of 1.97 pM.

Iron(II) phthalocyanine covalently functionalized graphene as a highly efficient non-precious-metal catalyst for the oxygen reduction reaction in alkaline media

A novel iron(II) phthalocyanine covalently modified graphene (FePc-Gr) was synthesized by reduction of the product obtained through an amidation reaction between carboxyl-functionalized graphene oxide (CFGO) and iron(II) tetra-aminophthalocyanine (FeTAPc). The FePc-Gr hybird was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy (RS) and X-ray photoelectron spectroscopy (XPS), respectively. The electrocatalytic properties of FePc-Gr toward the oxygen reduction reaction (ORR) were evaluated using cyclic voltammetry (CV) and linear sweep voltammetry methods. The peak potential of the ORR on the FePc-Gr catalyst was found to be about −0.12V vs. SCE in 0.1M NaOH solution, which was 180 and 360mV more positive than that on FeTAPc and bare GCE, respectively. The rotating disk electrode (RDE) and rotating ring disk electrode (RRDE) measurements revealed that the ORR mechanism was nearly via a direct four-electron pathway to water on FePc-Gr. The current still remained 83.5% of its initial after chronoamperometric test for 10,000s. Nevertheless, Pt/C catalyst only retained 40.5% of its initial current. The peak potential and peak current changed slightly when 3M methanol was introduced. So the FePc-Gr composite catalyst for ORR exhibited high activity, good stability and methanol-tolerance, which could be used as a promising Pt-free catalyst for ORR in alkaline direct methanol fuel cell (DMFC).

Enzyme Immobilization on Carboxyl-Functionalized Graphene Oxide for Catalysis in Organic Solvent

Carboxyl-functionalized graphene oxide (GO–COOH) was utilized to immobilize lipase. Fourier transform infrared (FTIR), UV–visible, and X-ray photoelectron (XPS) spectra were measured to characterize lipase immobilization. At the optimal temperature of 40 °C, the immobilized lipase retains 80% of the hydrolytic activity of the native lipase. For catalyzing the enantioselective reaction in the organic solvent heptane, at 50 °C (optimal), the catalysis efficiency of the immobilized lipase is 1.6 times that of native lipase, and the immobilized lipase retains the selectivity of the native lipase. This work demonstrates that graphene oxide is a suitable support for immobilization of lipase for catalysis in organic solvent.

Application of carboxyl functionalized graphene oxide as mimetic peroxidase for sensitive voltammetric detection of H2O2 with 3,3′,5,5′-tetramethylbenzidine

A sensitive electrochemical method for H2O2 determination was proposed with carboxyl functionalized graphene oxide (GO-COOH) as mimetic peroxidase and 3,3′,5,5′-tetramethylbenzidine (TMB) as substrate. GO-COOH exhibited intrinsic peroxidase-like activity that could catalyze the oxidation of TMB with H2O2. The generated product exhibited a sensitive second order derivative linear sweep voltammetric reduction peak at −0.93V (vs. Ag/AgCl) in Britton–Robinson buffer. Under the optimal conditions the reduction peak current was proportional to H2O2 concentration in the linear range from 0.006 to 0.8μmolL−1 with the detection limit of 1.0nmolL−1 (3σ). This proposed method was further applied to determine H2O2 content in fresh milk samples with satisfactory results.

Electrochemical deoxyribonucleic acid biosensor based on carboxyl functionalized graphene oxide and poly-l-lysine modified electrode for the detection of tlh gene sequence related to vibrio parahaemolyticus

A carboxyl functionalized graphene oxide (GO-COOH) and electropolymerized ploy-l-lysine (PLLy) modified glassy carbon electrode (GCE) was fabricated and used for the construction of an electrochemical deoxyribonucleic acid (DNA) biosensor. The NH2 modified probe ssDNA sequences were immobilized on the surface of GO-COOH/PLLy/GCE by covalent linking with the formation of amide bonds, which was stable and furthur hybridized with the target ssDNA sequence. Differential pulse voltammetry (DPV) was used to monitor the hybridization events with methylene blue as electrochemical indicator, which gave a sensitive reduction peak at −0.287V (vs. SCE). Under the optimal conditions the reduction peak current was proportional to the concentration of tlh gene sequence in the range from 1.0×10−12 to 1.0×10−6molL−1 with a detection limit as 1.69×10−13molL−1 (3σ). The polymerase chain reaction products of tlh gene from oyster samples were detected with satisfactory results, indicating the potential application of this electrochemical DNA sensor.

In situ enzymatic silver enhancement based on functionalized graphene oxide and layer-by-layer assembled gold nanoparticles for ultrasensitive detection of thrombin

A highly specific in situ amplification strategy was designed for ultrasensitive detection of thrombin by combining the layer-by-layer (LBL) assembled amplification with alkaline phosphatase (ALP) and gold nanoparticles (Au) mediated silver deposition. High-density carboxyl functionalized graphene oxide (FGO) was introduced as a nanocarrier for LBL assembling of alkaline phosphatase decorated gold nanoparticles (ALP-Au), which was further adopted to label thrombin aptamer II. After sandwich-type reaction, numerous ALP were captured onto the aptasensor surface and catalyzed the hydrolysis of ascorbic acid 2-phosphate (AAP), which in situ generated ascorbic acid (AA), reducing Ag+ to Ag nanoparticles (AgNPs) for electrochemical readout. Inspiringly, the in situ amplification strategy with ethanolamine as an effective blocking agent showed remarkable amplification efficiency, very little nonspecific adsorption, and low background signal, which was favorable to enhance the sensitivity of aptasensor. Our novel dramatic signal amplification strategy, with a detection limit of 2.7fM, showed about 2–3 orders of magnitude improvement in the sensitivity for thrombin detection compared to other universal enzyme-based electrochemical assay.

Functionalized graphene oxide-based carbon paste electrode for potentiometric detection of copper ion(ii)

For the first time, a novel copper ion(II) carbon paste electrode (CPE) based on high-density carboxyl functionalized graphene oxide (GO) is reported. A new hybrid material, 2-amino-5-mercapto-1,3,4-thiiodiazole grafted onto nanoscale graphene oxide (AMT-g-NGO), was introduced as a neutral carrier. The electrode exhibits an excellent Nernstian response to copper ion(II) ranging from 1.0 × 10−7 M to 1.0 × 10−1 M with a slope of 26.2 mV dec−1. Meanwhile, the proposed electrode shows fairly good selectivity and a long life time (2 months). Moreover, the excellent performance on low detection limit (4.0 × 10−8 M), wide applicable pH range (3.0–7.0) and fast response time (15 s), reveal the superiority of the electrode. The response mechanism of the electrode was investigated using AC impedance technique and UV-vis spectroscopy. The sensor can be used as indicator electrode for potentiometric titration of Cu2+ ion with EDTA and successfully applied to the determination of Cu2+ ion in different real samples.

Carboxyl-functionalized graphene oxide–polyaniline composite as a promising supercapacitor material

We report a novel and facile synthesis of a high-quality graphene oxide (GO)–polyaniline (PANI) composite by in situ polymerization suitable for supercapacitor application. Unlike the use of the edged carboxyl groups of graphene sheets as linkers, the current work makes the most of the ample oxygenated groups on the basal plane of graphene sheets to combine with the amine nitrogens of the PANI chain. This is tactically realized by a carboxyl-functionalized process of GO with oxalic acid treatment prior to the combination. The as-constructed carboxyl-functionalized graphene oxide–polyaniline (CFGO–PANI) composite was roundly characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier-transformed infrared spectrometry (FTIR), Raman spectrometry, and thermogravimetric analysis (TGA), and a stable, highly efficient charge-transfer configuration was disclosed and confirmed. The fabricated electrode composed of this CFGO–PANI material showed an excellent electrochemical capacitance performance with aqueous H2SO4 electrolytes.