Yaoguang Wang

Removal of mercury and methylene blue from aqueous solution by xanthate functionalized magnetic graphene oxide: Sorption kinetic and uptake mechanism.

Xanthate functionalized magnetic graphene oxide (Fe3O4-xGO) was successfully synthesized through linking xanthate groups to a kind of graphenes magnetic material (Fe3O4-GS). Fe3O4-xGO was found to be an ideal adsorbent for Hg(II) and methylene blue removal with a higher adsorption capacity. The synthesized adsorbent was characterized by SEM, TEM, FTIR, XRD, and BET respectively. Fe3O4-xGO can be simply recovered from water with magnetic separation at low magnetic field within only 1min. The adsorption capacity was found to be 118.55mg g(-1) for Hg(2+) (contact time for 180min, pH at 7 and temperature at 25°C) and 526.32mg g(-1) for methylene blue (contact time for 120min, pH at 5.5 and temperature at 25°C), respectively. Kinetic data showed good correlation with pseudo-second-order equation and the Langmuir model was found to fit for the isotherm data, which showed the contaminant sorption was accomplished mainly via chelation or ion exchange. The results of thermodynamic studies (ΔG<0, ΔH>0, ΔS>0) illustrate that the adsorption process was endothermic and spontaneous in nature. The experimental results suggest that Fe3O4-xGO has the potential applications in the environmental management.

Using reduced graphene oxide-Ca:CdSe nanocomposite to enhance photoelectrochemical activity of gold nanoparticles functionalized tungsten oxide for highly sensitive prostate specific antigen detection

An ultrasensitive sandwich-type photoelectrochemical (PEC) immunosensor was constructed for the detection of prostate specific antigen (PSA). In this work, Au-nanoparticle-loaded tungsten oxide (WO3-Au) hybrid composites was applied as PEC sensing platform, while Ca ions doped CdSe equipped on the conducting framework of reduced graphene oxide (rGO-Ca:CdSe) nanocomposites were employed as the signal amplification probe. As for WO3-Au, massive Au nanoparticles were formed on the surface of WO3 without any additional reducing agent, providing a novel nanocarriers for anchoring plenty of the primary antibodies due to the large specific surface area and good biocompatibility by chemical bonding between Au nanoparticles and -NH2 of antibodies. Besides, the incorporation of the rGO and the doping of Ca ions could improve the conductivity and hinder the recombination of electron-hole pairs of CdSe nanoparticles effectively, thereby enhancing the photocurrent conversion efficiency. Based on the sandwich immunoreaction, the primary antibody was immobilized onto WO3-Au substrate, after the formed rGO-Ca:CdSe labels were captured onto the electrode surface via the specific antibody-antigen interaction, the photocurrent intensity could be further enhanced due to the sensitization effect. Under the optimal conditions, the proposed PEC immunosensor shows a linear relationship between photocurrent variation and the logarithm of PSA concentration in the wide range of 5pgmL-1 to 50ngmL-1 with a low detection limit of 2.6pgmL-1 (S/N=3). Moreover, it also presented good stability and acceptable specificity, indicating the potential applications in clinical diagnostics.

A novel ECL biosensor for the detection of concanavalin A based on glucose functionalized NiCo2S4 nanoparticles-grown on carboxylic graphene as quenching probe

An electrochemiluminescence (ECL) biosensor was developed for detection of Concanavalin A (Con A). Chitosan/Ru(bpy)32+/silica/Fe3O4 nanomaterials (CRuSi-Fe3O4) were synthesized through W/O microemulsion route. The added Fe3O4 nanoparticles can simplify the prepared process and enhance the conductivity of nanomaterials which can increase the ECL intensity of luminophor CRuSi-Fe3O4. In addition, the layered structure of CRuSi-Fe3O4 can immobilize lots of Con A using glutaraldehyde as the coupling agent which can improve the sensitivity of the biosensor. Then the quenching probe glucose functionalized NiCo2S4 nanoparticles-grown on carboxylic graphene (NiCo2S4-COOH-rGO@Glu) was anchored on the modified-electrode via the specific carbohydrate-Con A interaction. Here, NiCo2S4 was used to quench the ECL of CRuSi-Fe3O4, graphene was used to grow NiCo2S4 nanoparticles as carrier materials and glucose was served as the recognition element for bounding Con A. Therefore, a desirable quenching ECL signal was measured with S2O82- as the coreactant of CRuSi-Fe3O4. Under the optimization of determination conditions, a linear response range for Con A from 0.5pgmL-1 to 100ngmL-1 was obtained, and the detection limit was calculated to be 0.18pgmL-1 (S/N=3).

Label-free Electrochemiluminescent Immunosensor for Detection of Prostate Specific Antigen based on Aminated Graphene Quantum Dots and Carboxyl Graphene Quantum Dots

Prostate-specific antigen (PSA) was used as the model, an ultrasensitive label-free electrochemiluminescent immunosensor was developed based on graphene quantum dots. Au/Ag-rGO was sythsized and used as electrode material to load a great deal of graphene quantum dots due to the large surface area and excellent electron conductivity. After aminated graphene quantum dots and acarboxyl graphene quantum dots were modified onto the electrode, the ECL intensity was much high using K2S2O8 as coreactant. Then, antibody of PSA was immobilized on the surface of modified electrode surface through the adsorption of Au/Ag toward proteins, leading to the decrease of the ECL intensity. As proven by ECL spectra test and electrochemical impedance spectroscopy (EIS) analysis, the fabrication process of the immunosensor is successful. Under the optimal conditions, the ECL intensity decreased linearly with the logarithm of PSA concentration in the range of 1 pg/mL ~ 10 ng/mL. The detection limit achieved is 0.29 pg/mL. The immunosensor results were validated through the detection of PSA in serum samples with satisfactory results. Due to excellent stability, high sensitivity, acceptable repeatability and selectivity, the immunosensor has promising applications in disease and drug analysis.

Mechanism of Pb(II) and methylene blue adsorption onto magnetic carbonate hydroxyapatite/graphene oxide

Magnetic carbonate hydroxyapatite/graphene oxide (M-CHAP/GO) was successfully prepared by loading magnetic carbonate hydroxyapatite (M-CHAP) onto graphene oxide sheets and was found to be an ideal adsorbent for heavy metal (Pb(II)) and dye (methylene blue). The obtained adsorbent was characterized by SEM, FTIR, XRD, BET, TGA, XPS and zeta potential, respectively. M-CHAP/GO nano-particles possessed a favorable and stable morphology. Moreover, the good magnetic properties of M-CHAP/GO made it simple to recover from water with magnetic separation. The equilibrium adsorption capacity was 277.7 mg g−1 for Pb(II) and 546.4 mg g−1 for methylene blue under the optimal conditions. The pseudo-second-order equation and the Langmuir model showed good correlation with the experimental data and explained well the mechanism of adsorption. It was found that the adsorption process was accomplished mainly via chelation and ion exchange. Thermodynamic studies (ΔG 0, ΔS > 0) implied that the adsorption process was endothermic and spontaneous in nature. The other adsorption mechanisms are further researched in this article. All the experimental results show that M-CHAP/GO nano-particles have potential application in the future of environmental management.

The removal of lead ions from aqueous solution by using magnetic hydroxypropyl chitosan/oxidized multiwalled carbon nanotubes composites.

Magnetic hydroxypropyl chitosan/oxidized multiwalled carbon nanotubes (MHC/OMCNTs) composites were fabricated and applied as the adsorbent to study the adsorption characteristic of lead ions in aqueous solution. The results of Fourier transform infrared spectrum (FTIR), X-ray powder diffraction (XRD) and scanning electron microscope (SEM) showed that the MHC/OMCNTs composites were synthesized successfully. The effects of the solution pH and the contact time were investigated, indicating that the optimal pH and contact time were pH 5.0 and 120min, respectively. The removal of lead ions was rather quick and the kinetic adsorption can be well described by pseudo-second-order model. The experimental results showed that the Sips model is more suitable than Langmuir, Freundlich and Dubinin-Radushkevich models. Furthermore, the parameters of the adsorption thermodynamic calculated in this research such as free energy (ΔG, -2.304 to -5.078kJmol(-1)), enthalpy (ΔH, 39.03kJmol(-1)) and entropy (ΔS, 138.7Jmol(-1)K(-1)) indicated that the adsorption process was endothermic and spontaneous. Therefore, the results in this research suggest that the MHC/OMCNTs composites are ideal adsorbent for the removal of lead ions in aqueous solution.

Removal of Hg(II) from aqueous solution by resin loaded magnetic β-cyclodextrin bead and graphene oxide sheet: Synthesis, adsorption mechanism and separation properties

Resin loaded magnetic β-cyclodextrin bead and graphene oxide sheet (MCD-GO-R) was synthesized successfully and found to be an excellent adsorbent for Hg(II) removal. The as-prepared adsorbent was characterized by SEM, FTIR, BET, magnetization curve and zeta potential analysis respectively. Good magnetic performance made MCD-GO-R simply recover from aqueous solution at low magnetic field within 30s. And also, the rich functional groups and outstanding dispersity play an important role in the adsorption process. The maximum adsorption capacity was 88.43 mg g(-1) at 323 K and pH 7.1. The as-prepared adsorbent could perform well in a wide pH range from 4.0 to 10.0. Static adsorption experimental data showed good correlation with pseudo-second-order model and Freundlich isotherm models. It was found that the contaminant adsorption was accomplished mainly via chelation or ion exchange and come to equilibrium in only 30 min. All experimental results, especially the excellent reproducibility and resistance to ion interference, suggest that MCD-GO-R has promising applications in water treatment.

An ultrasensitive electrochemical immunosensor for CEA using MWCNT-NH2 supported PdPt nanocages as labels for signal amplification

The excellent catalytic activity of a novel nanomaterial was introduced to ultrasensitive sandwich-type electrochemical immunosensor applications for detection of carcinoembryonic antigen (CEA). Amino-functionalized multi-walled carbon nanotube (MWCNT-NH2) supported PdPt nanocages were used as catalytic labels of secondary anti-CEA. PdPt nanocages with hollow interiors and porous walls could efficiently enhance electrocatalysis for reduction of H2O2. Meanwhile, with good dispersion, large specific surface area and amino groups, MWCNT-NH2 can immobilize a large amount of PdPt nanocages to improve the sensitivity and amplify the signal of the immunosensor. For the immobilization of primary antibodies, 3-aminopropyltriethoxysilane functionalized graphene sheets were used as transducing materials to modify glassy carbon electrodes and to enhance the electron transfer efficiently. Under the optimal conditions, the electrochemical immunosensor exhibited a wide linear range of 0.001-20 ng mL-1 with a low detection limit of 0.2 pg mL-1 for CEA. The proposed sensing strategy enriches electrochemical immunoassays and may have a promising application in bioassay analysis.

Ultrasensitive electrochemical aptasensor for the detection of thrombin based on dual signal amplification strategy of Au@GS and DNA-CoPd NPs conjugates.

In this work, an ultrasensitive electrochemical aptasensor for the detection of thrombin was developed based on Au nanoparticles decorated graphene sheet (Au@GS) and CoPd binary nanoparticles (CoPd NPs). A sulfydryl-labeled thrombin capture probe (Apt1) and a biotin-labeled thrombin reporter probe (Apt2) were designed to achieve a sandwich-type strategy. Au@GS was used as a sensing platform for the facile immobilization of Apt1 through Au-S bond, forming a sensing interface for thrombin. The specific recognition of thrombin induced the attachment of Apt2-CoPd NPs to the electrode. The labeled CoPd NPs showed good catalytic properties toward the reduction of H2O2, resulting in an amperometric signal. The amperometric response was correlated to the thrombin concentration in sample solutions. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) confirmed the successful fabrication of the aptasensor. A linear response to thrombin in the range of 0.01-2.00 ng mL(-1) with a low detection limit (5 pg mL(-1)) was achieved. The proposed aptasensor showed good selectivity, good reproducibility and acceptable stability. This proposed strategy may find many potential applications in the detection of other biomolecules.

Removal of Pb(II) and methylene blue from aqueous solution by magnetic hydroxyapatite-immobilized oxidized multi-walled carbon nanotubes

Magnetic hydroxyapatite-immobilized oxidized multi-walled carbon nanotubes (mHAP-oMWCNTs), an excellent adsorbent for Pb(II) and methylene blue (MB) removal, was synthesized in the present work. It was characterized by SEM, XRD, FTIR, BET, TGA and zeta potential analysis. mHAP-oMWCNTs displayed better adsorption performance than mHAP, mMWCNTs and HAP-oMWCNTs. The adsorption of Pb(II) and MB mainly depend on the ion-exchange property of HAP and the abundant oxygenic functional groups on oMWCNTs surface. Besides, good magnetic performance of mHAP-oMWCNTs makes it easy to achieve the solid-liquid separation. The adsorption kinetic data described well with the pseudo-second-order model and the equilibrium data fitted well with Frendlich and Langmuir isotherms for Pb(II) and MB, respectively. The maximum adsorption capacity was 698.4mgg-1 for Pb(II) and 328.4mgg-1 for MB from Langmuir isotherm. Thermodynamic studies (ΔG<0, ΔH>0, ΔS>0) implied the both adsorption was endothermic and spontaneous process. Furthermore, the excellent reusability of mHAP-oMWCNTs was confirmed by the desorption experiments. All the results showed mHAP-oMWCNTs has a promising application in water treatment.