Yanmei Zheng

Plant-mediated synthesis of platinum nanoparticles and its bioreductive mechanism.

Pt nanoparticles (PtNPs) were biologically synthesized by reducing Na2PtCl4 with Cacumen Platycladi Extract (CPE). The effects of reaction temperature, initial Pt(II) concentration, and CPE percentage on Pt(II) conversion and the size distribution of the PtNPs were studied. The results showed that the Pt(II) conversion rate reached 95.9% and that PtNPs measuring 2.4±0.8nm were obtained under the following conditions: reaction temperature, 90°C; CPE percentage, 70%; initial Pt(II) concentration, 0.5mM; reaction time, 25h. In addition, the bioreduction of Pt(II) was attributed to reducing sugars and flavonoids rather than proteins. The elucidation of bioreductive mechanism of Pt(II) ions was achieved by investigating the changes that occurred in the reducing sugar, flavonoid and protein concentrations in the plant extract, leading to a good insight into the formation mechanism of such biosynthesized PtNPs.

Biogenic flower-shaped Au–Pd nanoparticles: synthesis, SERS detection and catalysis towards benzyl alcohol oxidation

∼40 nm flower-shaped Au–Pd bimetallic nanoparticles were prepared in a facile and eco-friendly way based on the simultaneous bioreduction of HAuCl4 and Na2PdCl4 with ascorbic acid and Cacumen Platycladi leaf extract at room temperature. Characterization techniques, such as transmission electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction, were employed to confirm that the as-synthesized nanoparticles were alloys. The obtained flower-shaped Au–Pd alloy nanoparticles exhibited an excellent surface enhanced Raman spectroscopic activity with rhodamine 6G and efficient catalytic ability for the oxidation of benzyl alcohol to benzaldehyde.

Fabrication of Au/Pd alloy nanoparticle/Pichia pastoris composites: a microorganism-mediated approach

Synthesis of metal nanoparticles (NPs) is in the limelight in modern nanotechnology. In this present study, bimetallic Au/Pd NP/Pichia pastoris composites were successfully fabricated through a one-pot microbial reduction of aqueous HAuCl4 and PdCl2 in the presence of H2 as an electron donor. Interestingly, flower-like alloy Au/Pd NP/Pichia pastoris composites were obtained under the following conditions, NaCl concentration 0.9% (w/v), molar ratio of Au/Pd (1:2) and the time for pre-adsorption of Au(III) and Pd(II) ions 15 min, through fresh yeast reduction. The mapping results from scanning transmission electron microscopy (STEM) with a high-angle annular dark field detector confirmed that the Au/Pd NPs on the surface of the yeast were indeed alloy. Furthermore, the energy dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS) measurements showed that the composition of the bimetallic NPs were consistent with the initial molar ratio of the precursors.

Nitrogen and phosphorus removal coupled with carbohydrate production by five microalgae cultures cultivated in biogas slurry.

In this study, five microalgae strains were cultured for their ability to survive in biogas slurry, remove nitrogen resources and accumulate carbohydrates. It was proved that five microalgae strains adapted in biogas slurry well without ammonia inhibition. Among them, Chlorella vulgaris ESP-6 showed the best performance on carbohydrate accumulation, giving the highest carbohydrate content of 61.5% in biogas slurry and the highest ammonia removal efficiency and rate of 96.3% and 91.7mg/L/d respectively in biogas slurry with phosphorus and magnesium added. Additionally, the absence of phosphorus and magnesium that can be adverse for biomass accumulation resulted in earlier timing of carbohydrate accumulation and magnesium was firstly recognized and proved as the influence factor for carbohydrate accumulation. Microalgae that cultured in biogas slurry accumulated more carbohydrate in cell, making biogas slurry more suitable medium for the improvement of carbohydrate content, thus can be regarded as a new strategy to accumulate carbohydrate.

Effectiveness and mechanisms of ammonium adsorption on biochars derived from biogas residues

The solid by-product of anaerobic digestion derived biochar has been used as an adsorbent for the liquid by-product and is a viable and environmental friendly way to control waste. In this study, two biochars (BC-PM, BC-ST) from pig manure biogas residue (BR-PM) and straw biogas residue (BR-ST) were assessed for ammonium adsorption. The ammonium adsorption on both BC-PM and BC-ST followed the Elovich kinetic model and fit well with the Langmuir isotherm, whereas BC-PM was better than BC-ST at absorbing ammonium. In addition, the adsorption mechanism was elucidated by analysing the physicochemical properties of the biochars. The Brunauer–Emmett–Teller (BET) surface area, pore structure and micromorphology, which are mainly related to the carbon in the biochars, had no direct correlation with the ammonium adsorption capacity. However, the ash in the biochars played an important role in ammonium adsorption. The metal elements in biochar ash significantly decreased after adsorption, especially potassium, which nearly disappeared as a result of ion exchange with ammonium. However, the quartz and carbonate mineral in biochar ash also functioned as ammonium adsorption sites according to Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) analysis. This study revealed the irreplaceable role of ash in biochars for ammonium adsorption, which will guide the preparation of biochars from different types of feedstocks for ammonium adsorption.

Facile morphology control of 3D porous CeO2 for CO oxidation

3D porous CeO2 with various morphologies was successfully synthesized via a facile precipitation using glycine as the soft bio-template. During the synthesis, it was demonstrated that the morphology of CeO2 depended on the molar ratio of reactants. Furthermore, the catalytic performance towards CO oxidation of the as-synthesized CeO2 with different morphologies was investigated. CeO2 with a bowknot shape showed excellent catalytic performance, giving complete CO conversion at 370 °C, due to its properties of much higher oxygen vacancies, loosely packed pore structure and larger specific surface area.

Separation of biosynthesized gold nanoparticles by density gradient centrifugation

ABSTRACT The electronic, optical, magnetic, and catalytic properties of noble metal nanoparticles (NPs) strongly depend on their size. The size control of the noble metal NPs is one of the significant issues in the field of nanotechnology. We demonstrate both theoretically and experimentally that gold NPs can be separated by density gradient centrifugation (DGC) according to their size. By analyzing the force balance in a centrifuge with a horizontal rotor, a model was developed that relates the sedimentation shift to the centrifugation time and can be used to predict the effect of separation by the shift of particles within a specific period of time. The influences of centrifugation time and centrifugal force on the separation effect of DGC were evaluated.