Carboxyl-functionalized Graphene Research Articles

Cationically Modified Nanocrystalline Cellulose/Carboxyl-Functionalized Graphene Quantum Dots Nanocomposite Thin Film: Characterization and Potential Sensing Application

In this study, highly functional cationically modified nanocrystalline cellulose (NCC)/carboxyl-functionalized graphene quantum dots (CGQD) has been described. The surface of NCC was first modified with hexadecyltrimethylammonium bromide (CTA) before combining with CGQD. The CGQD, CTA-NCC and CTA-NCC/CGQD nanocomposites thin films were prepared using spin coating technique. The obtained nanocomposite thin films were then characterized by using the Fourier transform infrared spectroscopy (FTIR) which confirmed the existence of hydroxyl groups, carboxyl groups and alkyl groups in CTA-NCC/CGQD. The optical properties of the thin films were characterized using UV–Vis spectroscopy. The absorption of CTA-NCC/CGQD was high with an optical band gap of 4.127 eV. On the other hand, the CTA-NCC/CGQD nanocomposite thin film showed positive responses towards glucose solution of different concentration using an optical method based on surface plasmon resonance phenomenon. This work suggests that the novel nanocomposite thin film has potential for a sensing application in glucose detection.

A Novel Method for the Removal of Uranium by Using Carboxyl Functionalized Graphene Oxide

Graphene oxide (GO) and functionalized carboxylic graphene oxide (COOH-GO) were successfully synthesized by modified Hummer’s technique. The prepared GO and COOH-GO was characterized successfully by UV-Visible Spectroscopy, Fourier transforms infrared spectroscopy (FTIR), X-ray diffraction, Raman spectroscopy, Scanning electron microscopy (SEM)& Zeta potential. The removal of U(VI) heavy metal comparative study was done by using Graphite, GO & COOH-GO and the removal were confirmed by using LED fluorimeter. The effect of pH of medium, contact time, adsorbent dose, initial concentration of U(VI) were examined for the removal of U(VI). The extent of U(VI) removal has been found to be in the order of COOH-GO >GO> graphite. The U(VI) removal maximum efficiency was observed ~96% observed at pH 4.5. The higher removal efficiency is attributed to the higher negative surface charge of COOH-GO (zeta potential:-39.9 mV) in comparison to zeta potential of GO (-28.9 mV) &graphite (-21.6 mV).

Carboxyl-Functionalized Graphene for Highly Efficient H<sub>2</sub>-Evolution Activity of TiO<sub>2</sub> Photocatalyst

Carboxyl-Functionalized Graphene for Highly Efficient H<sub>2</sub>-Evolution Activity of TiO<sub>2</sub> Photocatalyst

Characterization of immobilized α-amylase on functionalized graphene oxide surface

Carboxyl-functionalized graphene oxide (GO-COOH) and amino-functionalized graphene oxide (GO-NH2) were prepared for use as carriers for α-amylase immobilization with 2-3% glutaraldehyde as a coupling agent. The α-amylase immobilized onto modified GO exhibited shifts in both working optimum pH and temperature with an increase from pH 6.0 to pH 7.0, and increased optimum temperature by 5-10℃ compared with the free enzyme. The loading capacity of the carriers is 786.8 mg/g (GO-COOH) and 437 mg/g (GO-NH2), respectively. The immobilized α-amylase exhibited a comparable stability activity in comparison with the free enzyme. The FT-IR spectra, UV-visible spectra as well as SEM analysis proved the presence of amine groups and carboxyl groups in the GO, and also covalent immobilization of α-amylase on the modified carrier. The constant values, the Km was 3.541 mg•mL1, 4.072 mg•mL1 and 8.004 mg•mL1 for free enzymes, GO-COOH-E, and GO-NH2-E, respectively, and their Vmax were 7.341 mg•mL1•min1, 4.968 mg•mL1•min1 and 6.655 mg•mL1•min1, respectively. Furthermore, above 54% of the original activity of the immobilized enzyme was retained after 7 reaction cycles, indicating excellent reusability.

The thermophysical properties and the stability of nanofluids containing carboxyl-functionalized graphene nano-platelets and multi-walled carbon nanotubes

Two structures of carbon-based materials with sp2-hybridized are carbon nanotubes and graphene arrayed in the concentric tube and two-dimensional sheet, respectively. The most important problems of graphene and carbon nanotube for use in various applications are insufficient dispersibility and their inadequate stability in different organic and aqueous solvents. The low interaction with other materials is second category problems of carbon nanostructures. Functionalization, a common method suggested by numerous researchers, can be employed to enhance this property. In this regard, the nanofluids containing graphene nanoplatelets and carboxylated multi-walled carbon nanotube were synthesized and dispersed in deionized water to prepare homogeneous samples of 0.1 and 0.2 wt%. The stability dependency of samples was investigated, for the first time, on ultrasonic time and microwave irradiation. Thermophysical properties including shear stress, viscosity, surface tension, density and stability were also measured and reported.

Highly efficient electrochemical detection of lead ion using metal-organic framework and graphene as platform based on DNAzyme

Abstract Based on the electrode modified by the carboxyl-functionalized graphene, a highly sensitive electrochemical sensor for Pb2+ detection was proposed by using 8–17 DNAzyme as the recognition element and the reaction of H2O2 catalyzed by Fe-MIL-101 as the signal probe. Due to the high selectivity of the 8–17 DNAzyme to Pb2+, the excellent catalytic ability of Fe-MIL-101 and the advantages of graphene, the proposed electrochemical sensor exhibited an excellent sensing performance with a wide linear range of 10−13 to10−7 mol·L−1, a lower detection limit of 1.74 × 10−14 mol·L−1 and high selectivity to Pb2+. Tap water and river water were analyzed by the developed sensor with satisfying recoveries and RSD, demonstrating a promising practicability for the determination of Pb2+ in the real sample analysis. Furthermore, the proposed strategy could be extended to the determination of other metal ions just by changing the specific DNAzymes.

Graphene quantum dots modification of yolk-shell Co3O4@CuO microspheres for boosted lithium storage performance

In this report, we present the synthesis of yolk-shell Co3O4@CuO microspheres followed with the surface modification of carboxyl-functionalized graphene quantum dots (donated as Co3O4@CuO@GQDs) and investigate their lithium storage properties. Derived from metal-organic frameworks (MOFs), the obtained yolk-shell Co3O4@CuO microspheres exhibit well-defined microstructure and high porosities. The yolk-shell Co3O4@CuO structure is designed to adapt the stepwise lithium insertion mechanism (first in CuO shell and then in Co3O4 core). In addition, the GQDs decorated on the surface of Co3O4@CuO microspheres not only provides larger specific surface area, more active sites and enhanced electronic conductivity, but also works as a buffer to alleviate the volume expansion and a reservoir for electrolyte molecules to improve the ionic conductivity. Furthermore, the –COOH groups from GQDs exhibits good hydrophilicity which is supposed to be useful for the combination of GQDs with Co3O4@CuO and also shows strong affinity to Li+. Based on the above merits from the structural and compositional design, the Co3O4@CuO@GQDs anode displays enhanced cyclability and superior lithium storage performance. Specifically, compared to the bald Co3O4@CuO microspheres without GQDs which suffer from a severe capacity decline with an inferior capacity of 414 mAh g−1 after 200 cycles, the Co3O4@CuO@GQDs anode displays an initial specific capacity of 816 mAh g−1 and a high reversible charge capacity of 1054 mAh g−1 after 200 cycles at 0.1 A g−1.

Carboxyl-functionalized graphene SGFET: pH sensing mechanism and reliability of anodization

In this work, we fabricated graphene solution-gate field-effect transistor (SGFET) to investigate the pH sensitivity of carboxyl functional groups. The functionalization of graphene with carboxyl was achieved through anodization by applying a sequential potential scan from 0.6 V to 1.3 V in 0.1 V steps. Raman spectroscopy was used to determine the defect density of the graphene caused by the anodization. The sequential anodization in Carmody buffer solution at pH 7 had low defective effect on graphene structure and shows that the original structure of graphene was conserved. Furthermore, we measured pH sensitivity of the carboxyl-functionalized graphene at pH 2 to pH 12. The pH sensitivity was 32.6 mV/pH at low pH region and pH sensitivity measurement was saturated at high pH (basic region). The negatively charged surface of carboxyl-functionalized graphene caused weak pH detection in the basic region. The pH sensing mechanism of carboxyl functionalized graphene in the low and high pH region is discussed in detail. The reliability of the carboxyl-functionalized graphene SGFET device was evaluated by measuring pH sensitivity repetitively after anodization at different potential scans of 0.9 V, 1.3 V, 1.5 V, 1.7 V and 1.9 V which demonstrated in all cases that, the pH sensitivity of carboxyl functionalization on graphene SGFET shows a similar trend. This functionalization method allows the modification of the graphene surface for further uses in biosensing.

Carboxyl graphene oxide solution saturable absorber for femtosecond mode-locked erbium-doped fiber laser**Project supported by the Central University Special Fund Basic Research and Operating Expenses, China (Grant No. GK201702005), the Natural Science Foundation of Shaanxi Province, China (Grant No. 2017JM6091), the National Natural Science Foundation of China (Grant No. 61705183), and the Fundamental Research Funds for the Central Universities, China (Grant

The carboxyl-functionalized graphene oxide (GO-COOH) is a kind of unique two-dimensional (2D) material and possesses excellent nonlinear saturable absorption property and high water-solubility. In this paper, we prepare saturable absorber (SA) device by depositing GO-COOH nanosheets aqueous solution on a D-shaped fiber. The modulation depth (MD) and saturable intensity of the SA are measured to be 9.6% and 19 MW/cm2, respectively. By inserting the SA into the erbium-doped fiber (EDF) laser, a passively mode-locked EDF laser has been achieved with the spectrum center wavelength of 1562.76 nm. The pulse duration, repetition rate, and the signal-to-noise ratio (SNR) are 500 fs, 14.79 MHz, and 80 dB, respectively. The maximum average output power is measured to be 3.85 mW. These results indicate that the GO-COOH nanosheets SA can be used as a promising mode locker for the generation of ultrashort pulses.

A rapid and sensitive electrochemical sensor for hydroxyl free radicals based on self-assembled monolayers of carboxyl functionalized graphene

In this work, carboxyl-functionalized graphene (CFG) was immobilized on glassy carbon electrode (GCE) by self-assembled monolayers (SAMs) based on covalent interaction with ethylenediamine as an arm linker. The obtained (CFG-NHCH2CH2NH)/GCE can be used as rapid and sensitive electrochemical sensor for hydroxyl free radicals (•OH). In the process of determination, the concentration of •OH was acquired not directly but through the only captured product 3,4-dihydroxybenzoic acid (3,4-DHBA), which is adopting 4-hydroxybenzoic acid (4-HBA) as the •OH trap. The glassy carbon electrode modified with carboxyl-functionalized graphene exhibits well conductivity and electron transfer ability, and also displays good electrocatalytic activity towards the electrochemical redox of 3,4-DHBA. The proposed sensor displays a good linear range from 1.0 to 450.0 μM for 3,4-DHBA with a low detection limit of 0.17 μM (S/N = 3). More importantly, the sensing platform can be successfully applied for •OH detection with the 4-HBA as the •OH trap.

Antimicrobial and antifouling properties of versatile PPSU/carboxylated GO nanocomposite membrane against Gram-positive and Gram-negative bacteria and protein.

Biofouling is a serious issue in membrane-based water and wastewater treatment as it critically compromises the efficacy of the water treatment processes. This investigation demonstrates the antimicrobial and antifouling properties of a nanocomposite membrane system composed of carboxyl-functionalized graphene oxide (COOH-GO) and polyphenylsulfone (PPSU). The PPSU/COOH-GO nanocomposite membrane exhibited excellent antimicrobial properties, achieving maximum bacteriostasis rates of 74.2% and 81.1% against the representative Gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa, respectively) and 41.9% against the representative Gram-positive bacterium (Staphylococcus aureus). The PPSU/COOH-GO nanocomposite membrane inhibited the attachment, colonization, and the biofilm formation of three species. Antifouling was assessed through filtration experiments using a model foulant bovine serum albumin (BSA). The fouling mechanisms were investigated by Hermia's models (complete blocking, intermediate blocking, standard blocking, and cake formation), and the analysis involved fitting the volumetric flux decline experimental data to models. The fouling study revealed a less irreversible fouling and increased flux recovery ratio for the PPSU/COOH-GO nanocomposite membrane. Complete blocking of pores and cake formation were the major fouling mechanisms for the membrane.

Graphene Materials Strengthen Aqueous Polyurethane Adhesives.

Carboxyl-functionalized graphene platelets (GP) and graphene oxide (GO) sheets were added to a commercial aqueous adhesive dispersion of thermoplastic polyurethane (TP) (Idrotex 200 from FacGB s.r.l.). For both additives, the weight percentage was of industrial interest, 0.01 and 0.1 wt %. The addition of GP/GO was carried out in a simple and scalable-up process that can be applied to other materials and additives. Mechanical, peel tests were applied on polyurethane strips (75 mm long, 15 mm wide, and 1.5 mm thick) prepared cutting extruded sheets obtained using Estane 58091, a 70D aromatic polyester-based TP. The tests with 0.01 wt % of GP showed statistically significant higher forces at first failure and maximum forces with respect to the pristine adhesive. Sample characterization was carried out with scanning electron microscopy, infrared spectroscopy, X-ray diffraction, and thermal analysis. A mechanism is suggested for the improved performance of the low-dose GP adhesive.

Simultaneous determination of dopamine and uric acid in the presence of ascorbic acid using a gold electrode modified with carboxylated graphene and silver nanocube functionalized polydopamine nanospheres.

A voltammetric sensor is presented for the simultaneous determination of dopamine (DA) and uric acid (UA) in the presence of ascorbic acid (AA). It is based on a gold electrode (GE) modified with carboxyl-functionalized graphene (CFG) and silver nanocube functionalized DA nanospheres (AgNC@PDA-NS). The AgNC@PDA-NS nanocomposite was characterized by scanning electron microscopy and UV-Vis spectroscopy. The electrochemical behavior of the modified electrode was evaluated by electrochemical impedance spectroscopy, cyclic voltammetry and differential pulse voltammetry. The modified electrode displays good electrocatalytic activity towards DA (typically at 0.14V vs. Ag/AgCl) and UA (typically at 0.29V vs. Ag/AgCl) even in the presence of ascorbic acid. Response to DA is linear in the concentration range of 2.5 to 130μM with a detection limit of 0.25μM. Response to UA is linear in the concentration range of 10 to 130μM with a detection limit of 1.9μM. In addition, the sensitivity for DA and UA is 0.538 and 0.156μAμM-1cm-2, respectively. The modified electrode also displays good stability, selectivity and reproducibility. Graphical abstract The gold electrode modified with polydopamine nanospheres functionalized with silver nanocube and carboxylated graphene is used for simultaneous determination of DA and UA in the presence of AA, with wide linear range and low detection limit.

Morphology-control synthesis of a Cu-based metal–organic framework directed by carboxyl-functionalized graphene

Compared to the octahedral metal–organic framework CuBTC (also called HKUST-1), an interesting hexagonal prism shaped CuBTC/carboxyl-functionalized graphene composite was synthesized through a precursor-resolvothermal method. Based on structural characterization results of the composite, the mechanism of crystal morphology-control was proposed that carboxyl-functionalized graphene plays a dual role of structure-directing nucleation sites and framework linkers in the process of CuBTC crystal growth. The precursor-resolvothermal method provides an effective way to transform the morphology of metal–organic frameworks, and the results also demonstrate the possibility of using functionalized graphene to synthesize a wide range of structural motifs in metal–organic frameworks with adjustable metrics. On the basis of maintaining thermal stability, the composite exhibited about a 6% increase in CO2 capacity (from 6.39 mmol·g−1 of CuBTC to 6.77 mmol·g−1 at 273 K and 1 atm).

Highly sensitive carboxyl-graphene oxide-based surface plasmon resonance immunosensor for the detection of lung cancer for cytokeratin 19 biomarker in human plasma

Functionalized graphene oxide is a novel type of highly efficient biosensing material. In this study, we present a carboxyl-functionalized graphene oxide (GO-COOH)-based surface plasmon resonance (SPR) chip for the rapid and quantitative detection of non-small cell lung carcinoma (NSCLC) via the cytolerayin 19 (CK19) protein biomarker in spiked human plasma. We demonstrated the binding specificity of kinetic analysis of interactions between GO-COOH and anti-CK19 and CK19 protein. We also calculated the relationship between the SPR angle and refractive index of GO-COOH, and demonstrated that COOH modified GO sheets on Au film can enhance the field energy propagation intensity of an SPR sensor, resulting in a higher sensitivity for the detection of CK19 protein compared to a conventional Au-based SPR chip. The immunosensor was constructed and engineered by immobilizing a low concentration (10 μg/mL) of CK19 antibody on an SPR chip. The lowest detectable concentration was as low as 1 fg/mL. A spiked 10% human plasma CK19 detection limit of 0.05 pg/mL was achieved, well below the normal physiological level of serum protein (3.3 ng/mL). Therefore, a carboxyl-GO based SPR biosensor appears to have high sensitivity and specificity for the detection of clinical whole plasma biomarkers and possible application in diagnosing diseases.

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.