Haiqin Yu

Adsorption of phosphate from aqueous solution by hydroxy-aluminum, hydroxy-iron and hydroxy-iron-aluminum pillared bentonites.

Phosphorus removal is important for the control of eutrophication, and adsorption is an efficient treatment process. In this study, three modified inorganic-bentonites: hydroxy-aluminum pillared bentonite (Al-Bent), hydroxy-iron pillared bentonite (Fe-Bent), and mixed hydroxy-iron-aluminum pillared bentonite (Fe-Al-Bent), were prepared and characterized, and their phosphate adsorption capabilities were evaluated in batch experiments. The results showed a significant increase of interlayer spacing, BET surface area and total pore volume which were all beneficial to phosphate adsorption. Phosphate adsorption capacity followed the order: Al-Bent>Fe-Bent>Fe-Al-Bent. The adsorption rate of phosphate on the adsorbents fits pseudo-second-order kinetic models (R(2)=1.00, 0.99, 1.00, respectively). The Freundlich and Langmuir models both described the adsorption isotherm data well. Thermodynamic studies illustrated that the adsorption process was endothermic and spontaneous in nature. Finally, phosphate adsorption on the inorganic pillared bentonites significantly raised the pH, indicating an anion/OH(-) exchange reaction.

Label-free electrochemical immunosensor based on graphene/methylene blue nanocomposite

For the specificity of prostate cancer markers, prostate specific antigen (PSA) has been widely used in prostate cancer screening, diagnosis, and treatment after monitoring. In normal male serum, PSA can only be detected in traces of 0-4 ng mL(-1). In this paper, we constructed an electrochemical immunosensor for PSA detection using a nanocomposite film of graphene sheets-methylene blue-chitosan (GS-MB-CS) as electrode material. The nanocomposite film showed high binding affinity to the electrode and was used to immobilize the antibody of PSA. The modification procedure was monitored by cyclic voltammetry (CV). An amperometric biosensor was easily developed based on the response of peak current to the capture of PSA induced by specific antigen-antibody reactions. Under optimum conditions, the amperometric signal decreased linearly with PSA concentration (0.05-5.00 ng mL(-1)). A low limit of detection (13 pg mL(-1)) and a high selectivity are obtained. Moreover, the prepared immunosensor was applied for the analysis of PSA in serum samples with satisfactory results. The proposed method may have a promising future in biochemical assays for high selectivity, good reproducibility, and stability.

Kinetic, isotherm and thermodynamic investigations of phosphate adsorption onto core–shell Fe3O4@LDHs composites with easy magnetic separation assistance

In this study, three different magnetic core-shell Fe3O4@LDHs composites, Fe3O4@Zn-Al-, Fe3O4@Mg-Al-, and Fe3O4@Ni-Al-LDH were prepared via a rapid coprecipitation method for phosphate adsorptive removal. The composites were characterized by XRD, FTIR, TEM, VSM and BET analyses. Characterization results proved the successful synthesis of core-shell Fe3O4@LDHs composites with good superparamagnetisms. Batch experiments were conducted to study the adsorption efficiency of phosphate. Optimal conditions for the phosphate adsorption were obtained: 0.05 g of adsorbent, solution pH of 3, and contact time of 60 min. Proposed mechanisms for the removal of phosphate species onto Fe3O4@LDHs composites at different initial solution pH were showed. The kinetic data were described better by the pseudo-second-order kinetic equation and KASRA model. The adsorption isotherm curves showed a three-region behavior in the ARIAN model. It had a good fit with Langmuir model and the maximum adsorption capacity followed the order of Fe3O4@Zn-Al-LDH>Fe3O4@Mg-Al-LDH>Fe3O4@Ni-Al-LDH. Thermodynamic analyses indicated that the phosphate adsorption process was endothermic and spontaneous in nature. The three Fe3O4@LDHs composites could be easily separated from aqueous solution by the external magnetic field in 10s. These novel magnetic core-shell Fe3O4@LDHs adsorbents may offer a simple single step adsorption treatment option to remove phosphate from water without the requirement of pre-/post-treatment for current industrial practice.

Label-free electrochemical immunosensor for prostate-specific antigen based on silver hybridized mesoporous silica nanoparticles

Due to high sensitivity and good selectivity, electrochemical immunosensor is often used to detect tumor markers. Prostate-specific antigen (PSA) is the most validated tumor marker for prostate cancer. In this work, mesoporous silica nanoparticles (MSNs) were used to increase the fixation capacity of primary antibody, and silver nanoparticles (Ag NPs) were used to enhance the electron transfer rates. Silver hybridized mesoporous silica nanoparticles (Ag@MSNs) were synthesized and used as electrode material. Hydroquinone (HQ) generated a stable electrochemical signal and was used as a mediator. Based on the specific antibody-antigen interaction, a label-free immunosensor was developed for the sensing of PSA. The current method allows us to detect PSA over a wide concentration range from 0.05 to 50.0 ng ml(-1) with a detection limit of 15 pg ml(-1). The proposed immunosensor was used to determine PSA in human serum with satisfactory results.

Nanoporous PtCo-based ultrasensitive enzyme-free immunosensor for zeranoldetection

Nanoporous PtCo alloy was designed as an antibody carrier for preparation of a highly sensitive immunosensor. The immunosensor was constructed by assembling the capture zeranol antibody on thionine decorated graphene nanosheets modified glassy carbon electrode. With an enzyme-free immunosensor mode, the nanoporous PtCo alloy, synthesized by dealloying method, had shown strong electrocatalytic activity toward antigen-antibody reaction. The use of PtCo alloy carrier offered a high amount of antibody on each immunoconjugate, hence amplified the detectable signal from the electro-reaction of dissolved oxygen. Cyclic voltammetry and electrochemical impedance spectroscopy were used to characterize the recognition of zeranol. Due to the poor conductivity of zeranol, a small amount of zeranol immobilized onto the electrode could result in great change in the electron-transfer resistance. Some factors that would affect the performance of the immunosensor were studied, such as concentration of PtCo, pH, and the ratio of TH to GS. With zeranol concentration range (0.05 to 5.0 ng/mL), the immunosensor exhibited a highly sensitive response to zeranol with a detection limit of 13 pg/mL. The immunosensor was evaluated for bovine urine sample, receiving satisfactory results.

Ultrasensitive electrochemical immunosensor for zeranol detection based on signal amplification strategy of nanoporous gold films and nano-montmorillonite as labels

Nano-montmorillonites belong to aluminosilicate clay minerals with innocuity, high specific surface area, ion exchange, and favorable adsorption property. Due to the excellent properties, montmorillonites can be used as labels for the electrochemical immunosensors. In this study, nano-montmorillonites were converted to sodium montmorillonites (Na-Mont) and further utilized for the immobilization of thionine (TH), horseradish peroxidase (HRP) and the secondary anti-zeranol antibody (Ab(2)). The modified particles, Na-Mont-TH-HRP-Ab(2) were used as labels for immunosensors to detect zeranol. This protocol was used to prepare the immunosensor with the primary antibody (Ab(1)) immobilized onto the nanoporous gold films (NPG) modified glassy carbon electrode (GCE) surface. Within zeranol concentration range (0.01-12ng mL(-1)), a linear calibration plot (Y=0.4326+8.713X, r=0.9996) was obtained with a detection limit of 3pg mL(-1) under optimal conditions. The proposed immunosensor showed good reproducibility, selectivity, and stability. This new type of immunosensors with montmorillonites and NPG as labels may provide potential applications for the detection of zeranol.

A reusable naphthalimide-functionalized magnetic fluorescent nanosensor for the simultaneous determination and removal of trace Hg2+ in aqueous solution

On the basis of high selective and sensitive interaction of 1,8-naphthalimide with Hg(2+) and the formation of stable neutral imide-Hg-imide complexes, we designed and synthesized a novel magnetic fluorescent sensor (S1) employed Fe(3)O(4) magnetic nanoparticles and 1,8-naphthalimide fluorescent sensor. Under optimum conditions, S1 exhibits the high selectivity toward Hg(2+) over other metal ions, with the detection limit of 1.03×10(-8)M. We demonstrated that a reliable fluorescence response of S1 toward Hg(2+) over a broad pH range (pH=5.0-9.0) could be reused at least four cycles. The maximum sorption capacity of S1 was about 5.6 mg g(-1). In addition, the removal of Hg(2+) in water was achieved by the aggregation-induced sedimentation (AIS) strategy. Moreover, the suspended magnetic nanoparticles could be removed by external magnetic field, and the secondary pollution was avoided. The above-mentioned results indicate that this approach may serve as a foundation of the preparation of the multifunctional magnetic fluorescent sensor for simple, rapid, and simultaneous determination and removal of trace Hg(2+) and other pollutants in environmental samples.

Removal of o‐nitrobenzoic acid by adsorption on to a new organoclay: montmorillonite modified with HDTMA microemulsion

A new organoclay, consisting of montmorillonite modified by a hexadecyl trimethyl ammonium (HDTMA) microemulsion, was synthesized, characterized and used as an adsorbent for the removal of o‐nitrobenzoic acid from aqueous solution. Adsorption kinetics, isotherms and effects of operating variables, such as adsorbent dosage, ionic strength and initial solution pH, were also investigated. The results of Fourier transform infrared spectroscopy (FTIR), X‐ray diffraction (XRD) analysis and BET surface area determination indicated that HDTMA molecules had entered into the interlayer of the montmorillonite. The optimized experimental conditions for the adsorption of o‐nitrobenzoic acid by montmorillonite modified by HDTMA microemulsion were 0.5 g adsorbent dosage, 0.4 mL of 0.1 mol·lbL−1 CaCl2 solution, initial solution pH of 6.0 and contact time of 6 h. The adsorption isotherms of o‐nitrobenzoic acid fitted the Langmuir model well (R 2 = 0.9880). The adsorption kinetics data fitted the pseudo‐second‐order equation (R 2 = 0.9999). These above results indicate that montmorillonite modified by an HDTMA microemulsion can be used as adsorbent for o‐nitrobenzoic acid because of its high adsorption capacity and low cost.

Removal of basic dyes (malachite green) from aqueous medium by adsorption onto amino functionalized graphenes in batch mode

AbstractIn this paper, graphene oxides and amino functionalized graphenes (NH2-G) were prepared and employed as adsorbent for the removal of a basic dye, malachite green (MG). The effect of several parameters (pH, dye concentration, adsorption time, and temperature) of the adsorption process was investigated for NH2-G. Four different adsorption isotherms were used to analyze the equilibrium of the adsorption system. The adsorption mechanism was investigated by adsorption thermodynamics and adsorption kinetics. The results indicated that NH2-G showed a high efficiency for the removal of the basic dye MG with the maximum adsorption capacity of 91.48 mg g−1. According to the obtained thermodynamic data, the adsorption of MG onto NH2-G was an endothermic process with a large adsorption enthalpy. The kinetic study showed that the whole adsorption process fit the pseudo-second-order kinetics model well.

Calcined ZnAl- and Fe3O4/ZnAl–layered double hydroxides for efficient removal of Cr(VI) from aqueous solution

Calcined ZnAl- and Fe3O4/ZnAl–layered double hydroxides (ZnAl–CLDH and Fe3O4/ZnAl–CLDH) were used as adsorbents to evaluate the uptake properties for Cr(VI) removal from aqueous solution by batch equilibrium experiments. The XRD, FTIR and TEM results showed that the calcined ZnAl–LDH and Fe3O4/ZnAl–LDH recovered layered structures according to the memory effect of hydrotalcite. Optimized conditions of Cr(VI) adsorption were obtained: 2.0 g L−1 adsorbent, initial solution pH of 3.0 and contact time of 60 min. The kinetic data was described better by a pseudo-second-order kinetic equation. The adsorption isotherms had a good fit with Langmuir and Freundlich models. Thermodynamic analyses indicated that the adsorption process was endothermic and spontaneous in nature. The adsorption mechanisms involved the reconstruction of LDHs, surface complexation, anion exchange and physical adsorption. The higher adsorption capacities of the calcined products suggested that the ZnAl–CLDH and Fe3O4/ZnAl–CLDH were potential adsorbents for Cr(VI) removal from water and wastewater. Moreover, the magnetic Fe3O4/ZnAl–CLDH can be easily separated using a magnet after the adsorption process.