Shengyang Tao

Multifunctional mesoporous material for detection, adsorption and removal of Hg2+ in aqueous solution

A novel, “all-in-one”, multifunctional microsphere with a fluorescent mesoporous silica shell (Rhodamine B coordinate receptor inside) and a magnetic core (Fe3O4) has been successfully fabricated using a sol–gel method and small molecular (CTAB) surfactants as structure-directing agents. At the same time, they were examined for environmental protection applications to detect, adsorb and remove Hg2+ in aqueous solution. The prepared nanocomposite microspheres were fluorescent, mesoporous, and magnetizable, with a diameter of 300–450 nm, a surface area of 600 m2 g−1, a pore size of 2.5 nm, and a saturation magnetization of 27.5 emu g−1. These multifuctional microspheres showed excellent fluorescence sensitivity and selectivity towards Hg2+ over other metal ions (Na+, Mg2+, Mn2+, Co2+, Ni2+, Zn2+, Cd2+, Ag+, Pb2+ and Cu2+). Upon the addition of Hg2+, an overall emission change of 16-fold was observed, and the detection limit of Hg2+ was as low as 10 ppb. The adsorption process of Hg2+ on the microspheres was well described by the Langmuir equation. The equilibrium can be established within five minutes and the adsorption capacity was 21.05 mg g−1. The concentration of Hg2+ ions can be reduced to less than 0.05 ppm and the used microspheres can be easily separated from the mixture by adding an external magnetic field. These results suggest that these “all-in-one” multifunctional nanocomposites are potentially useful materials for simultaneously rapidly detecting and recovering dangerous pollutants in aqueous solution.

Metalloporphyrins as sensing elements for the rapid detection of trace TNT vapor

A series of porphyrin or metalloporphyrin-doped mesostructured silica films were successfully fabricated using small molecular (CTAB) or macromolecular (F127, P123) surfactants as structure-directing agents, and examined for chemosensor applications to detect trace vapors of explosives such as TNT and DNT. All prepared nanocomposite films show high fluorescence quenching sensitivity towards TNT and DNT vapors, but, their performances are strongly dependent on the formed mesostructure, the pore size and the type of sensing elements (porphyrin units). The cadmium porphyrin film with bicontinuous worm-like mesostructure exhibits the highest quenching efficiency, close to 60% after 10 s of exposure. Besides the superior TNT detecting capability, these hybrid films offer several advantages over other fluorescence-based sensory materials, such as a simple preparation procedure, inexpensive materials as well as the stability of organic sensing elements in an inorganic matrix. These results suggest that these new kinds of mesostructured nanocomposites are potentially useful chemosensory materials for rapidly detecting trace explosives.

Pyridine-functionalized mesoporous silica as an efficient adsorbent for the removal of acid dyestuffs

Pyridine-functionalized mesoporous silica was prepared via direct condensation of tetraethoxysilane (TEOS) and N-(3-(triethoxysilyl)propyl)isonicotinamide using the copolymer P123 as structure-directing agent, and employed as adsorbent for the removal of alizarin red S, reactive brilliant red X-3B and reactive yellow X-RG from waste water. The adsorption measurements showed that, due to the large surface areas and the high affinity of pyridine groups, the prepared adsorbents exhibit a high adsorption capacity and an extremely rapid adsorption rate for acid dyestuffs. Using the linear forms of Langmuir, Freundlich and Redlich–Peterson isotherms, the experimental equilibrium data were analyzed. It is found that the experimental data for the adsorption of alizarin red S and reactive brilliant red X-3B can fit the Langmuir isotherm, while the Freundlich model is very suitable for describing the adsorption behavior of reactive yellow X-RG. On the basis of the Langmuir analysis, the monolayer adsorption capacities were determined to be 143.8, 891.1 and 3369.3 mg of dye per gram of adsorbent for alizarin red S, reactive brilliant red X-3B and reactive yellow X-RG, respectively. Since the pyridine unit is known as a good ligand for various metal ions, a hydrogen-bonding donor as well as an organic base, pyridine-functionalized mesoporous silica should be a promising absorbent not only for acid dyestuffs, but also for other organic and inorganic pollutants.

Application of graphene for preconcentration and highly sensitive stripping voltammetric analysis of organophosphate pesticide.

Electrochemical reduced β-cyclodextrin dispersed graphene (β-CD-graphene) was developed as a sorbent for the preconcentration and electrochemical sensing of methyl parathion (MP), a representative nitroaromatic organophosphate pesticide with good redox activity. Benefited from the ultra-large surface area, large delocalized π-electron system and the superconductivity of β-CD-graphene, large amount of MP could be extracted on β-CD-graphene modified electrode via strong π-π interaction and exhibited fast accumulation and electron transfer rate. Combined with differential pulse voltammetric analysis, the sensor shows ultra-high sensitivity, good selectivity and fast response. The limit of detection of 0.05 ppb is more than 10 times lower than those obtained from other sorbent based sensors. The method may open up a new possibility for the widespread use of electrochemical sensors for monitoring of ultra-trace OPs.

Superwetting monolithic SiO2 with hierarchical structure for oil removal

Monolithic silica with macroporous skeleton and well-defined mesopores was prepared via sol–gel method by using triblock polymer P123 as the structure directing agent and tetramethoxysilane (TMOS) as the silicon source. The large macroporous channels (3 μm in diameter), formed by phase separation and sol–gel transition, ensure the substances diffuse in the bulk easily. Appropriate specific area (nearly 400 cm2 g−1) and mesopores (17.67 nm in diameter and 1.99 cm3 g−1 in volume) supply enough space for storing the molecules absorbed. After grafting organic groups on their surface, hydrophobic monolithic hierarchically porous silica (MHS) could be prepared with high capability to adsorb oils and organic contaminants on the surface of water without coadsorption. In order to explore the factors impacting the ability of adsorption, a series of properties are characterized including the BET surface, porous size and water contact angle by changing the type and dosage of modifying agents. The maximum absorptive ability can reach 8 times the monoliths weight, and materials could be recycled more than 20 times by an easy treatment. Good selectivity, better thermal stability, easy removing and excellent recyclability for oil removal give the material potential applications.

High performance adsorbents based on hierarchically porous silica for purifying multicomponent wastewater

Hybrid hierarchically porous silica adsorbents were simply fabricated by the sol–gel method and modified with thiol or sulfonic groups. These materials with pores on both micrometre and nanometre scales exhibit a satisfactorily adsorptive property to various pollutants in water, including heavy metal ions (Hg2+, Cd2+, Pb2+, Cu2+, Ag+ and CrO42−) and organic compounds (dyes, biogenic amines, pesticides and amino acids). The thiol functionalized hierarchically porous silica micro-foam (SH-HSM), which has a low thiol content (0.66 mmol g−1), shows significantly high adsorption capability to Hg2+ (140.1 mg g−1) in particular. Then sulfonic acid-functionalized adsorbent (SO3H-HSM) was obtained through direct oxidization of SH-HSM by H2O2 without destruction of the hierarchical structure. It was found that SO3H-HSM could effectively remove organic compounds with positive charge in solution through electrostatic interactions. The adsorption capability of SO3H-HSM for some basic dyes, such as fuchsin basic, could reach approximately 1145.2 mg g−1. The mixture of SH-HSM and SO3H-HSM showed good purifying capacity to simulate multicomponent wastewater, containing different inorganic and organic chemicals. The removal rate for any of the pollutants was more than 90%, and could even reach 100% for metal ions and dyes. The strong adsorption ability of these porous adsorbents may be due to the interwoven meso- and macroporous structures which can increase mass transport and easier accessibility for pollutants to the active sites.

A reverse membrane emulsification process based on a hierarchically porous monolith for high efficiency water–oil separation

A hierarchically porous monolith with macro- and meso-pores was synthesized via a sol–gel and phase separation process. Due to the surface modification by organic silanes, the wettability of the silica material was effectively controlled. A series of hydrophobic porous silica monoliths (HPSM) were obtained. Using a “reverse membrane emulsification” process, the HPSM not only cleared oil away from water, but also broke the micro-emulsion efficiently, even when emulsion stabilizer was in the system. As the filtration layer, 1.0 g of HPSM could treat 944 mL of oil containing water or 667 mL of surfactant-stabilized micro-emulsion. HPSM materials could remove at maximum 96.5% of the oil in water and 100% surfactant in the micro-emulsion. In addition, the material could be reused through a simple treatment. The excellent separating effect was kept even after 8 times of regeneration. Special selectivity, easy operation and excellent recyclability make the material have great potential for practical application.

Controlled immobilization of acetylcholinesterase on improved hydrophobic gold nanoparticle/Prussian blue modified surface for ultra-trace organophosphate pesticide detection

An ultrasensitive amperometric acetylcholinesterase (AChE) biosensor was fabricated by controlled immobilization of AChE on gold nanoparticles/poly(dimethyldiallylammonium chloride) protected Prussian blue (Au-PDDA-PB) nanocomposite modified electrode surface for the detection of organophorous pesticide. The Au-PDDA-PB membrane served as an excellent matrix for the immobilization of enzyme, which not only enhanced electron transfer but also possessed a relatively large surface area. In addition, the surface hydrophilicity of the Au-PDDA-PB nanocomposite was finely controlled in the static water contact angle range of 25.6-78.1° by adjusting the ratio of gold nanoparticles to PDDA-PB. On an optimized hydrophobic surface, the AChE adopts an orientation with both good activity and stability, which has been proven by electrochemical methods. Benefit from the advantages of the Au-PDDA-PB nanocomposite and the good activity and stability of AChE, the biosensor shows significantly improved sensitivity to monocrotophos, a typical highly toxic organophorous pesticide, with wide linear range (1.0-1000 pg/mL and 1.0-10 ng/mL) and an ultra-low detection limit of 0.8 pg/mL. The biosensor exhibits accuracy, good reproducibility and stability. This strategy may therefore provide useful information for the controlled immobilization of protein and the design of highly sensitive biosensors.

Ultra-sensitive biosensor based on mesocellular silica foam for organophosphorous pesticide detection.

A sensitive amperometric acetylcholinesterase (AChE) biosensor was fabricated based on mesocellular silica foam (MSF), which functioned as both an enzyme immobilization matrix and a solid phase extraction (SPE) material for the preconcentration of target molecules. The hydrophilic interface, the good mechanical/chemical stability, and the suitable pore dimension of MSF provided the entrapped AChE a good environment to well maintain its bioactivity at basic condition. The AChE immobilized in MSF showed improved catalytic ability for the hydrolysis of acetylthiocholine, as evidenced by the increasing of the oxidation current of thiocholine, the enzymatic catalytic hydrolysis production of acetylthiocholine. In addition, the MSF with large surface area showed a modest adsorption capacity for monocrotophos, a model organophosphate used in this study, via the hydrogen bond or physical adsorption interaction. The combination of the SPE and the good enzyme immobilization ability in MSF significantly promoted the sensitivity of the biosensor, and the limit of detection has lowered to 0.05 ng/mL. The biosensor exhibited accuracy, good reproducibility, and acceptable stability when used for garlic samples analysis. The strategy may provide a new method to fabricate highly sensitive biosensors for the detection of ultra-trace organophosphorous pesticide infield.

Magnetic loading of tyrosinase-Fe3O4/mesoporous silica core/shell microspheres for high sensitive electrochemical biosensing.

A new protocol is proposed for magnetic loading and sensitive electrochemical detection of phenol via the tyrosinase cross-linked mesoporous magnetic core/shell microspheres. The mesoporous magnetic microspheres, characterized by transmission electron microscopy, N(2) adsorption/desorption isotherms, and magnetic curve displays high capacity for enzyme immobilization and strong magnetism to adhere to the magnetic electrode surface without any additional adhesive reagent. The biosensor exhibits a wide linear response to phenol ranging from 1.0×10(-9) to 1.0×10(-5) M, a high sensitivity of 78 μA mM(-1), a low detection limit of 1 nM, and a fast response rate (less than 5s). The proposed method is simple, rapid, inexpensive and convenient in electrode renewal, which is recommended as a promising experimental platform for wider applications in biosensing.