Effects of the nitrogen form ratios on photosynthetic productivity of poplar under condition of phenolic acids.

Phenolic acids can reduce nitrogen utilization rate of poplar, which seriously restrict the productivity of poplar plantation. In this study, three phenolic acid concentrations (T0, T1, and T2) and three ratios of nitrogen forms (NH4+-N to NO3--were 1:3, 1:7, and 1:14) were chosen for orthogonal experiment on poplar (Populus × euramericana "Neva") seedlings to study the effects of the nitrogen form ratios on photosynthetic productivity of poplar under environment of phenolic acids. Results showed that photosynthetic physiology parameters were influenced by both phenolic acid concentration and nitrogen form ratio. The order of net photosynthetic rate (PN) values obtained from 9 treatments were T1-1:3, T0-1:3, T2-1:3, T0-1:7, T1-1:7, T0-1:14, T2-1:7, T1-1:14, and T2-1:14 (from high to low). Under environment of phenolic acids, when poplar were treated with NH4+-N to NO3--N ratio of 1:14, the major limitation factor of photosynthesis was non stomatal factor. When poplar were treated with NH4+-N to NO3-N ratio of 1:3, the major limitation factor of photosynthesis changed to stomatal factor. The leaf nitrogen content and total biomass were obviously positively related with PN (p < 0.05). Phenolic acid inhibited photosynthetic productivity of poplar in a major way and this effect decreased with increase of the content of NH4+-N.

Increasing the ratio of ammonia nitrogen fertilizer in soil can effectively reduce the toxic effect of phenolic acids on poplar and improve the photosynthetic productivity of poplar.

Interfacial Engineering of Hierarchical Transition Metal Oxide Heterostructures for Highly Sensitive Sensing of Hydrogen Peroxide.

Hydrogen peroxide (H2 O2 ) is a major messenger molecule in cellular signal transduction. Direct detection of H2 O2 in complex environments provides the capability to illuminate its various biological functions. With this in mind, a novel electrochemical approach is here proposed by integrating a series of CoO nanostructures on CuO backbone at electrode interfaces. High-resolution transmission electron microscopy (HRTEM), X-ray diffraction, and X-ray photoelectron spectroscopy demonstrate successful formation of core-shell CuO-CoO hetero-nanostructures. Theoretical calculations further confirm energy-favorable adsorption of H2 O2 on surface sites of CuO-CoO heterostructures. Contributing to the efficient electron transfer path and enhanced capture of H2 O2 in the unique leaf-like CuO-CoO hierarchical 3D interface, an optimal biosensor-based CuO-CoO-2.5 h electrode exhibits an ultrahigh sensitivity (6349 µA m m-1 cm-2 ), excellent selectivity, and a wide detection range for H2 O2 , and is capable of monitoring endogenous H2 O2 derived from human lung carcinoma cells A549. The synergistic effects for enhanced H2 O2 adsorption in integrated CuO-CoO nanostructures and performance of the sensor suggest a potential for exploring pathological and physiological roles of reactive oxygen species like H2 O2 in biological systems.

Three-Dimensional Hierarchical Architectures Derived from Surface-Mounted Metal-Organic Framework Membranes for Enhanced Electrocatalysis.

Inspired by the rapid development of metal-organic-framework-derived materials in various applications, a facile synthetic strategy was developed for fabrication of 3D hierarchical nanoarchitectures. A surface-mounted metal-organic framework membrane was pyrolyzed at a range of temperatures to produce catalysts with excellent trifunctional electrocatalytic efficiencies for the oxygen reduction, hydrogen evolution, and oxygen evolution reactions.

The catalytic effect of TiO2 nanosheets on extracellular electron transfer of Shewanella loihica PV-4.

Electron transfer kinetics of Shewanella loihica PV-4 at the up-growing TiO2 nanosheet (TiO2-NS) modified carbon paper (CP) electrode was investigated. The effect of TiO2-NSs, which speeds up the interfacial electron transfer of outer membrane c-type cytochromes (OMCs), was revealed for the first time. TiO2-NSs with a polar surface modified hydrophobic CP into super-hydrophilic TiO2-NS/CP. The favorable interaction between PV-4 and TiO2-NSs not only enhanced microbial adhesion, but also altered the redox nature of OMCs. The mid-point potential of OMCs at TiO2-NS/CP was shifted to a more negative potential, indicating a higher thermodynamic driving force for the protein to release electrons. Moreover, electron transfer from OMCs to TiO2-NSs was also benefited from the positive shift of flat-band potential Vfb owing to reduced pH at the electrode/microorganism interface, as well as good electrical conductivity of TiO2-NSs. As a result, the electron transfer rate constant ket of OMCs at the TiO2-NS/CP anode was about three times faster than that at the CP anode. The accelerated electron transfer kinetics as well as 15% increase of biomass together accounted for a 97% increase of the maximum output power density in the MFC. The result expanded our knowledge about the role of a designed TiO2 nanostructure in microbial electron transfer that can be applied in other bio-electrochemical systems.

Tailoring colloidal photonic crystals with wide viewing angles.

Photonic crystal materials are developed from colloidal crystal fibers or beads. As the fibers have cylindrical symmetry, the fiber-composed PhCs show anisotropic angle independence. By contrast, the bead-composed PhCs display angle-independent structural colors because of the spherical symmetry of their bead elements.

Photonic crystal beads from gravity-driven microfluidics.

This Letter reports a simple method for the mass production of 3D colloidal photonic crystal beads (PCBs) by using a gravity-driven microfluidic device and online droplet drying method. Compared to traditional methods, the droplet templates of the PCBs are generated by using the ultrastable gravity as the driving force for the microfluidics, thus the PCBs are formed with minimal polydispersity. Moreover, drying of the droplet templates is integrated into the production process, and the nanoparticles in the droplets self-assemble online. Overall, this process results in PCBs with good morphology, low polydispersity, brilliant structural colors, and narrow stop bands. PCBs could be bulk generated by this process for many practical applications, such as multiplex-encoded assays and the construction of novel optical materials.

Synthesis and enhanced visible-light responsive of C,N,S-tridoped TiO2 hollow spheres.

C,N,S-tridoped TiO2 hollow spheres (labeled as C,N,S-THs) were synthesized using carbon spheres as template and C,N,S-tridoped TiO2 nanoparticles as building blocks. The structure and physicochemical properties of the catalysts were characterized by Xray diffraction (XRD), scanning electron microscopy (SEM), UV-Vis diffuse reflectance spectrum (DRS), N2 adsorption-desorption isotherms, X-ray photoelectron spectroscopy (XPS) and Photoluminescence emission spectroscopy (PL). The results showed that the hollow spheres had average diameter of about 200 nm and the shell thickness was about 20 nm. The tridoped TiO2 hollow spheres exhibited strong absorption in the visible-light region. C,N,S-tridoped could narrow the band gap of the THs by mixing the orbit O 2p with C 2p, N 2p and S 3p orbits and shift its optical response from ultraviolet (UV) to the visible-light region. PL analysis indicated that the electron-hole recombination rate of TiO2 hollow spheres had been effectively inhibited when doped with C, N and S elements. The photocatalytic activities of the samples were evaluated for the degradation of X-3B (Reactive Brilliant Red dye, C.I. Reactive Red 2) aqueous solution under visible-light (lambda > 420 nm) irradiation. It was found that the C,N,S-tridoped TiO2 hollow spheres indicated higher photocatalytic activity than commercial P25 and the undoped counterpart photocatalyst.

Fabrication of ringlike and disclike nano-structures with surface-enhanced Raman scattering activity.

Functional gold nanoparticles with tunable surface ligands were used to assemble ringlike and disclike nano-structures. The adjustable formation mechanism was deduced, and important assembling processes happened such as evaporation, cooling, Marangoni flow and drying. With its hydrophobic nature, butanethiol monolayer-protected gold nanoparticles were arranged to form ringlike nano-assemblies. Well-defined disclike nano-structures were obtained as a result of the change of hydrophilic-hydrophobic property and the aggregation of carboxyl group functionalized gold nanoparticles induced by tris(2-aminoethyl)amine. Surface-enhanced Raman spectroscopy (SERS) activities of nano-assemblies were examined. These nano-assemblies showed strong SERS enhancement occurred with the increase of localized surface plasmon resonance. The efficient technique will open a new avenue for fabricating organized nanoparticle structures in a convenient manner. It may be potentially applied for the biosensor due to SERS activities of those structures.

The role of bromides upon electrochemical mineralization of bisphenol A with boron-doped diamond anode.

Anodic oxidation with boron-doped diamond (BDD) has been regarded as outstanding option for wastewater treatment. However, in the presence of halide, the extreme promise of the technology may be hampered by the formation of toxic halogenated by-products. While the behaviors of chloride are relatively understood, little is currently known about the role of bromide and its effect on the generation of brominated transformation by-products (BTPs). Herein, we reported for the first time the bromide-mediated electrochemical mineralization of bisphenol A with BDD anodes. Firstly, we employed statistical methodology to determine the impacts of the main operating variables on the mineralization performance, and the novel and peculiar roles of bromides during the electrolytic oxidations were identified. Next, LC/MS analysis was used to identify the reaction intermediates, and plenty of BTPs (including oligomers of complex structures) were thus detected. Detailed transformation mechanisms responsible for the BTPs were also proposed. Lastly, we used ECOSAR program to determine the ecological toxicity of all detected by-products, and the structure-toxicity relation involved was discussed. Overall, the above results are of particular interest to understand BTPs formation mechanism in electrochemical oxidation processes, which as well provide guidelines to minimize potential risks of BDD technology for phenolic wastewater treatment.

Rethinking electrochemical oxidation of bisphenol A in chloride medium: Formation of toxic chlorinated oligomers.

Using boron-doped diamond (BDD) anodes to degrade bisphenol A (BPA) had been an active area of research interest within the past 20 years. A major concern about the process lie in the formation of toxic chlorinated aromatic by-products when chloride electrolytes were present in the reaction system. In this contribution, we highlighted the formation of complex poly-chlorinated oligomer by-products in electrochemical oxidation processes, which had often been overlooked in previous studies. Moreover, the distribution and complexity of the chlorinated oligomers were found to be strongly linked to the adopted initial chloride concentration. Formation of simple chlorinated by-products was ascribed to the electrophilic substitution reactions mediated by active chlorine species, while the oligomer by-products (including chlorinated dimers, trimers and tetramers) were generated through the coupling reactions between various chlorinated phenoxy radicals. The possible mechanisms describing the formation of these by-products were also proposed. The obtained results shed light on the possible risk of BDD technology in the treatment of phenolic wastewater containing chloride electrolytes.

Fabrication and enhanced visible light photocatalytic activity of fluorine doped TiO2 by loaded with Ag.

F-doped TiO2 loaded with Ag (Ag/F-TiO2) was prepared by sol-gel process combined with photoreduction method. The physical and chemical properties of the prepared samples were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), high-resolution transmission electron microscope (HRTEM), UV-Vis diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL). XPS analysis indicated Ag species existed as Ag0 in the structure of Ag/F-TiO2 samples. UV-Vis diffuse reflectance spectra showed that the light absorption of Ag/F-TiO2 in the visible region had a significant enhancement compared with the F-doped TiO2 (F-TiO2). PL analysis indicated that the electron-hole recombination rate had been effectively inhibited when Ag loaded on the surface of F-TiO2. The photocatalytic activities of the samples were evaluated for the degradation of X-3B (Reactive Brilliant Red dye, C.I. reactive red 2) under visible light (lambda > 420 nm) irradiation. Compared with F-TiO2, the sample of 0.50 Ag/F-TiO2 showed the highest photocatalytic activity. The interaction between F species and metallic Ag was responsible for improving the visible light photocatalytic activity.

Controllable assembly of dimers and trimers of gold Nanoparticle bridged by Tris(2-aminoethyl)amine.

In this paper, dimer and trimer assemblies were prepared through covalent coupling of the monomer, i.e., carboxyl monofuntional gold nanoparticles using Tris(2-aminoethyl)amine (Tren) as a bridging ligand. TEM examination showed that the dimer structures could be obtained with an increased yield using Tren instead of ethylenediamine (EDA) as a bridging molecule without N,N'-Diisopropylcarbodiimide (DIC) in reaction solution. Comparatively, the main trimer structures were obtained when DIC was added into reaction solution. The absorption spectra showed the red shift of the surface plasmon resonance (SPR) from monomer to trimer due to dipole-dipole interaction between proximate particles.

Reversible pH manipulation of the fluorescence emission from sectorial poly(amido amine) dendrimers.

The first to fourth generation (G1-G4) of sectorial poly(amido amine) (PAMAM) dendrimers with ethanolamine core and amino terminals are synthesized by a divergent route. Blue fluorescence emission from these dendrimers is observed. It is found that there is a remarkable difference in the fluorescence behavior for these different generations of dendrimers. The emission intensity of these dendrimers is almost linearly enhanced along with the increase of their concentrations. A significant pH-dependent profile of the fluorescence intensity is also observed. As the pH value decreases from 8 to 3, the fluorescence intensity increases almost linearly. Furthermore, the fluorescence intensity of the dendrimers shows a reversible behavior depending on pH value within the pH range from 3 to 11. This property enables the reversible manipulation of the fluorescence of these dendrimers by adjusting the pH values, which contributes to a potential application of these materials in fluorescent pH sensors.

Synergistic improvement of Shewanella loihica PV-4 extracellular electron transfer using a TiO2@TiN nanocomposite.

Extracellular electron transfer (EET) allows microorganisms to perform anaerobic respiration using insoluble electron acceptors, including minerals and electrodes. EET-based applications require efficient electron transfer between living and non-living systems. To improve EET efficiency, the TiO2@TiN nanocomposite was used to form hybrid biofilms with Shewanella loihica PV-4 (PV-4). Chronoamperometry showed that peak current was increased 4.6-fold via the addition of the TiO2@TiN nanocomposite. Different biofilms were further tested in a dual-chamber microbial fuel cell. The PV-4 biofilm resulted a maximum power density of 33.4 mW/m2, while the hybrid biofilm of the TiO2@TiN nanocomposite with PV-4 yielded a 92.8% increase of power density. Electrochemical impedance spectroscopy analyses showed a lower electron-transfer resistance in the hybrid biofilm. Biological measurements revealed that both flavin secretion and cytochrome c expression were increased when the TiO2@TiN nanocomposite presented. These results demonstrated that the TiO2@TiN nanocomposite could synergistically enhance the EET of PV-4 through altering its metabolism. Our findings provide a new strategy for optimizing biotic-abiotic interactions in bioelectrochemical systems.

Application of the blending of PNIPAM-co-PS nanofibers with functionalized Au nanoparticles for the high-sensitive diagnosis of cancer cells.

The blending of poly(N-isopropylacrylamide)-co-polystyrene nanofibers with functionalized gold nanoparticles was explored to form the new nanocomposites to facilitate the accumulation of daunorubicin inside leukemia cells and potentially enhance the cure efficiency. The synergistic enhancement effect of the nanocomposites on the drug uptake of daunorubicin in drug resistant leukemia K562 cells has been observed by using electrochemical and confocal fluorescence microscopy studies. The results suggest that these nanocomposites could be utilized to facilitate the drug delivery and realization of the early diagnosis of the respective cancer cells, suggesting the potential valuable application in the relative biomedical and bioanalysis areas.

Transformation of bisphenol A by electrochemical oxidation in the presence of nitrite and formation of nitrated aromatic by-products.

In this contribution, the electrocatalytic abatement of bisphenol A (BPA) with boron-doped diamond (BDD) anode had been conducted in NaNO2 electrolytes. Central composite design was used as statistical multivariate method to optimize the operating parameters adopted (applied current density, flow rate, concentration of NaNO2 and initial pH). The results from response surface analysis indicated that pH was the most influential factor for TOC decay, and a maximum TOC decay of 63.7% was achieved under the optimized operating conditions (9.04 mA cm-2 of applied current density, 400 mL min-1 of flow rate, 10 mM of NaNO2, 4.0 of initial pH and 60 min of electrolysis time). Besides, LC/MS technique was applied to identify the main reaction intermediates, and plenty of nitrated oligomers were detected at the end of the degradation. These by-products were generated via the coaction of coupling reaction of nitrated phenol and electrophilic substitution mediated by nitrogen dioxide radicals. Moreover, our results showed that the degree of nitration depended heavily on the employed initial nitrite concentration. This was one of the very few investigations dealing with nitrophenolic by-products in nitrite medium, and thus the findings exhibited important implications for electrochemical degradation of BPA and its related phenolic pollutants.

The role of nitrite in electrocatalytic oxidation of phenol: An unexpected nitration process relevant to groundwater remediation with boron-doped diamond electrode.

Using boron-doped diamond (BDD) to mineralize recalcitrant organics has been one of the hottest areas of research interest in the field of water treatment. Here we report for the first time that, in the presence of nitrite ions (NO2-), the anodic oxidation of phenol with BDD electrode will lead to the formation of nitrated by-products of phenol. These by-products include 2-nitrophenol, 4-nitrophenol, 2,4-dinitrophenol, 2,6-dinitrophenol, 2,4,6-trinitrophenol, 2,3,4,6-tetranitrophenol, 2,3,4,5,6-pentanitrophenol, as well as a large number of dimers and trimers of nitrophenols. Increasing the concentration of NO2- will not only greatly affects the degradation and mineralization of phenol, but also enhances the formation of nitrophenols. The nitrated by-products are mainly generated via electrophilic substitution reactions mediated by nitrogen dioxide radicals and hydroxyl radicals, as well as via coupling reactions of phenol. In addition, it is found that several simple nitrophenols may also be formed in nitrate media. As a whole, formation of nitrated by-products is a novel phenomenon in anodic oxidation processes. Since nitrated aromatics are well known for their persistence in the environment, their formations in BDD anode cells should be carefully scrutinized before such technology is applied to groundwater remediation.

Electrochemical mineralization of uric acid with boron-doped diamond electrode: Factor analysis and degradation mechanism.

In the present study, the mineralization performance and pathway of uric acid (UA) on boron-doped diamond (BDD) anodes were investigated. The oxidation behavior of UA on BDD surface was firstly tested through cyclic voltammetry measurements. The individual and joint effects of four quantitative parameters (applied current density, NaHCO3 concentration, NaCl concentration and flow rate) on UA mineralization were then examined with Doehlert experimental design. The results acquired by statistical analysis revealed that NaCl concentration and applied current density displayed the most dominant roles on UA degradation, while the influences of NaHCO3 concentration and flow rate were statistically insignificant. As a result, the following optimal conditions were reached: applied current density of 7.80 mA cm-2, NaHCO3 concentration of 6.0 mM, NaCl concentration of 9.0 mM and flow rate of 600 mL min-1, which gave a TOC decay of 89.4%, a specific energy consumption of 125.36 KWh kg-1 TOC, a combustion current efficiency of 15.0% and an electrical energy per order of 35.79 KWh m-3 order-1 within 30 min of electrolysis. Further results from LC/MS analysis confirmed the ring rupture of UA during the electrolysis, due to the attack of hydroxyl radicals and active chlorine species. Accordingly, two plausible degradation pathways of UA in bicarbonate and chloride media on BDD anode were proposed respectively.

Flavin-mediated extracellular electron transfer in Gram-positive bacteria Bacillus cereus DIF1 and Rhodococcus ruber DIF2.

Flavin-mediated extracellular electron transfer was studied in two Gram-positive bacteria: Bacillus cereus strain DIF1 and Rhodococcus ruber strain DIF2. The electrochemical activities of these strains were confirmed using amperometric I-t curves and cyclic voltammetry (CV). Spent anodes with biofilms in fresh anolytes showed no redox peaks, while new anodes in the spent broth showed relative redox peaks using CV measurements, indicating the presence of a redox electron mediator secreted by bacteria. Adding riboflavins (RF) and flavin mononucleotide (FMN) improved the electron transfer of the microbial fuel cells inoculated with the two strains. The redox peaks indicated that flavins existed in the anolyte, and HPLC analysis showed that RF and FMN were secreted by the two bacterial strains. The concentration of RF increased until the bacteria grew to the log phase in microbial fuel cells. The concentration of RF decreased and that of FMN increased after the log phase. The two strains secreted FMN only in the microbial fuel cell. These results confirmed that the electrochemical activity mediated by flavins and FMN is essential in the extracellular electron transfer process in the strains DIF1 and DIF2.

Magnetically separable composite photocatalyst with enhanced photocatalytic activity.

A novel magnetically separable composite photocatalyst, anatase titania-coated magnetic activated carbon (TMAC), was prepared in this article. In the synthesis, magnetic activated carbon (MAC) was firstly obtained by adsorbing magnetic Fe3O4 nanoparticles onto the activated carbon (AC), and then the obtained MAC was directly coated by anatase titania nanoparticles prepared at low temperature (i.e. 75 degrees C). The prepared samples were characterized by XRD, SEM and vibrating sample magnetometer (VSM). The composite photocatalyst can be easily separated from solution by a magnet, its photocatalytic activity in degradation of phenol in aqueous solution also has dramatic enhancement compared to that of the neat titania.