Xiaoqiong Zhang

Facile and tunable fabrication of Fe3O4/graphene oxide nanocomposites and their application in the magnetic solid-phase extraction of polycyclic aromatic hydrocarbons from environmental water samples

An electrostatic self-assembly approach was employed to prepare Fe(3)O(4)/graphene oxide nanocomposites, and their application in the magnetic solid-phase extraction of polycyclic aromatic hydrocarbons from environmental samples was investigated. With the highly hydrophilic graphene oxide sheets and positively charged surface of the Fe(3)O(4) nanoparticles, the nanocomposites were synthesized through electrostatic interaction in aqueous solution. Simultaneously, the different loading amounts of Fe(3)O(4) onto the graphene oxide were easily controlled by changing the proportion of the initial precursors. The identity of the hybrid materials was confirmed using transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and a vibrating sample magnetometer. Five polycyclic aromatic hydrocarbons were selected as model analytes to validate the extraction performance of the Fe(3)O(4)/GO nanocomposite as a MSPE sorbent. The excellent adsorption property was attributed to the dominant roles of π-π stacking interaction and hydrophobic interaction. After optimizing the conditions, the results indicated that the recoveries of these compounds were in the range of 76.8-103.2%, with relative standard deviations ranging between 1.7% and 11.7%; the limits of detection were in the range of 0.09-0.19 ng mL(-1).

One-step synthesis of magnetic graphene oxide nanocomposite and its application in magnetic solid phase extraction of heavy metal ions from biological samples.

A novel magnetic graphene oxide nanocomposite was synthesized by one-step coprecipitation method and characterized by transmission electron microscopy, X-ray photoelectron spectroscopy and vibrating sample magnetometer. The nanocomposite beard many intriguing properties, including chemical stability, high adsorption capacity, and superparamagnetic. These properties evoked great interest and desire of its exploration in magnetic solid-phase extraction of heavy metal ions from complex samples. Several parameters effecting the analytical performance, such as the sample pH, amounts of adsorbent, sample volumes, elution volumes, and coexisting ions, had been investigated in detail. The adsorbed metal ions were easy eluted by controlling the pH condition and the materials could be reused more than 20 times. Under the optimized conditions, the limits of detection were 0.016, 0.046, 0.395, 0.038, 0.157 μg L(-1) for Co(2+), Ni(2+), Cu(2+), Cd(2+), and Pb(2+), respectively. The intra-day relative standard deviations (n=5) were in the range of 1.8-5.5% at 10 μg L(-1). The proposed method was successfully applied to biological sample analysis and got excellent recoveries in the range of 81-113% even the matrix was complex.

Preparation and retention mechanism study of graphene and graphene oxide bonded silica microspheres as stationary phases for high performance liquid chromatography.

Graphene oxide (GO) bonded stationary phase for high performance liquid chromatography (HPLC) was fabricated by coating GO sheets onto aminosilica microspheres via covalent coupling. Graphene (G) functionalized HPLC stationary phase was then prepared through hydrazine reduction of GO bonded silica (GO@SiO2) composite, which was the first example of using graphene as stationary-phase component for HPLC. Effective separations of the tested neutral and polar compounds on both GO@SiO2 and graphene bonded silica (G@SiO2) columns were achieved under the optimal experimental conditions. Compared with commercial C18 column, the different chromatographic performances of GO and graphene bonded columns were ascribed to their unique retention mechanisms. The polyaromatic scaffold of GO and graphene gives π-π stacking property and hydrophobic effect, and other retention mechanisms, such as π-π electron-donor-acceptor (EDA) interaction for the separation of nitroaromatic compounds and hydrogen bonding for hydroxyl and amino compounds, may also be taken into consideration. Experimental results indicated that the mixed-mode retention mechanism can facilitate the separation of analytes with similar hydrophobicity, which is a unique property compared with C18 column. Additionally, G@SiO2 showed higher affinity to aromatic analytes in contrast with GO@SiO2 and its retention mechanism was not consistent with the typical reversed phase behavior. The separation of aromatic compounds on G@SiO2 column relies primarily on the π-π stacking interaction and then the hydrophobicity, while the two interactions have equal shares on GO@SiO2 column.

One-pot synthesis of UiO-66@SiO2 shell–core microspheres as stationary phase for high performance liquid chromatography

The unusual properties of ultrahigh surface area, adsorption affinity and shape selectivity make metal–organic frameworks (MOFs) a promising candidate as the stationary phase for high performance liquid chromatography (HPLC). However, the problems of high column backpressure and low column efficiency resulting from the direct packing of irregular MOF particles still remain in the HPLC separation. Herein, a facile one-pot synthesis method for the fabrication of MOFs@SiO2 shell–core microspheres was developed with aminosilica as the supporting substrate to grow the MOF shell. The density and particle size of the MOF shell could be easily controlled by adjusting the concentration of reactants, reaction temperature and time. UiO-66 (UiO for University of Oslo) was chosen as a model MOF because of its excellent chemical stability and unique reverse shape selectivity. The selected compounds including xylenes and ethylbenzene were effectively separated on the prepared UiO-66@SiO2 packed column with high resolution, good reproducibility and low column backpressure. The UiO-66@SiO2 packed column showed both reverse shape selectivity and a molecular sieving effect, making it attractive for the separation of structural isomers. Besides, the retention of analytes was also ascribed to the synergic effect of the hydrogen bonding between analytes and the amino groups of aminosilica, the hydrophobic effect and the π–π interaction between analytes and the aromatic rings of the UiO-66 shell.

Graphene as an efficient sorbent for the SPE of organochlorine pesticides in water samples coupled with GC-MS.

The determination of organochlorine pesticides in water samples, which are harmful to humans, is very important for environmental risk assessment. Based on the excellent adsorption properties of graphene, an SPE coupled with GC-MS method for the monitoring of organochlorines (four hexachlorcyclohexanes and four dichlorodiphenyltrichloroethanes) was developed. Owing to the hydrophobic interaction and π-π stacking interaction between the analytes and graphene, the analytes quantitatively adsorbed onto the graphene-based SPE cartridge were eluted by ethyl acetate for analysis. Several parameters influencing the analytical performance, such as the kind of elution, sample volume, reusability of the cartridge, have been investigated in detail. Under the optimal conditions, detection of limits of 1.95-9.38 ng/L, recoveries of 83.9-107.3% at two spiked concentration levels (0.1 and 10 ng/mL) and RSDs in the range of 2.9-7.4% for real water samples were obtained for all the analytes. This work reveals the great potential of graphene in sample preparation procedures.

Synthesis of highly dispersed mesostructured cellular foam silica sphere and its application in high-performance liquid chromatography

Highly dispersed mesostructured cellular foam silica spheres of relatively uniform micrometer size (3.5-4.5 μm) were successfully prepared using a triblock copolymer EO(20)PO(70)EO(20) as the structure-directing agent accompanied by TMB and K(2)SO(4). Both two additives have effective influence and K(2)SO(4) have better performance than other inorganic salts such as KCl and NaCl. The pore size and surface area were tuned by TMB and NH(4)F. The resultant S-MCFs were modified with C(18) group before being used as the HPLC stationary phase for effective separation of aromatic compounds and phthalic acid esters. The perfect spherical morphology and large pore volume gave rise to low and stable back pressure. High surface area, ultralarge pore size and unique pore structure would permit high flow rates and afford the possibility for fast separation.

Synthesis of large‐pore mesostructured cellular foam silica spheres for the adsorption of biomolecules

Mesostructured cellular foam (MCF) silica spheres with different textual parameters were synthesized using a triblock copolymer as a template. The effects of acid concentration and aging time on the window size and morphology were discussed. Besides, the adsorption performances of lysozyme and bovine serum albumin on the blank MCF with different window size and aminopropyl-modified MCFs were studied. The adsorption capacity and rates were shown to be dependent on the window size and surface chemical properties of the adsorbents. In particular, the MCF with window size of 15.2 nm showed fast adsorption for lysozyme with an adsorption capacity of 500 mg/g in 10 min. Furthermore, it has been shown that MCF spheres are potential materials in the separation of biomolecules because of their chemical tunable surface and molecular sieve properties.

Preparation and retention mechanism exploration of mesostructured cellular foam silica as stationary phase for high performance liquid chromatography.

Siliceous mesostructured cellular foam (MCF) with highly interconnected porous structure, ultralarge pore size and relatively uniform particle size (3-5μm) was prepared to achieve the mixed-mode and efficient separation of intact proteins. And molecular sieving effect for the first time played an important role in protein separation using mesoporous silica materials as HPLC stationary phase. The spherical silica particles were synthesized via hydrothermal method and the pore size was easily regulated by adding NH4F as well as altering the aging time. After aminopropyl derivatization, the chromatographic performance of functionalized mesoporous silica particles was investigated in comparison with those without modification and commercial NH2 column, and their mixed-mode retention mechanisms were investigated in detail. The superior separation performance for the retention of proteins was obtained on our home-made column in comparison with commercial NH2 column. The influences of aminopropyl derivatization and mobile phase composition on the column property were also investigated. Moreover, the home-made column showed similar performance for separation of polar anilines and neutral PAHs with the commercial column, owing to mixed-mode retention mechanisms including p-π stacking, electron interaction, hydrophobic effect, π-π EDA interaction and hydrogen bonding. All these results indicated that the aminopropyl modified MCF would be promising in the mixed-mode and efficient separation of biomolecules in addition with small molecules.

In-syringe solid-phase extraction for on-site sampling of pyrethroids in environmental water samples

On-site sampling is an analytical approach that can ensure the accuracy of monitoring data and enhance the effectiveness of environmental protection measures. In the present work, an in-syringe solid-phase extraction (SPE) device was designed for on-site sampling of trace contaminants in environmental water samples followed by gas chromatography-mass spectrometry (GC-MS) analysis. Template assisted freeze casting followed by hydrazine vapor reduction approach was used to synthesize a hierarchical porous graphene aerogel (HPGA), which was used as the sorbent in the in-syringe SPE device. Environmental degradable pyrethroids were selected as the model analytes. Owing to the large specific surface area and hydrophobicity of HPGA, the target molecules could be completely extracted during one aspirating/dispensing cycle. The analytes were stable on the sorbent for at least 72 h when the device was stored under airtight and light-free conditions, and were not affected by the pH value of sample solution. All results demonstrated that the device could meet the requirements of on-site sampling. For practical application, the limits of detection were found to be in the range of 0.012-0.11 ng mL-1 under the optimized conditions, and satisfactory recoveries in the range of 65.7-105.9% were obtained for the analysis of real samples. The results of this study demonstrate the immense potential of HPGA for the enrichment of trace environmental pollutants, and meanwhile promote the application of the in-syringe SPE technique as a promising candidate for on-site sampling.