Facile synthesis of porous bimetallic alloyed PdAg nanoflowers supported on reduced graphene oxide for simultaneous detection of ascorbic acid, dopamine, and uric acid.

Porous bimetallic alloyed palladium silver (PdAg) nanoflowers supported on reduced graphene oxide (PdAg NFs/rGO) were prepared via a facile and simple in situ reduction process, with the assistance of cetyltrimethylammonium bromide as a structure directing agent. The as-prepared nanocomposite modified glassy carbon electrode (PdAg NFs/rGO/GCE) showed enhanced catalytic currents and enlarged peak potential separations for the oxidation of ascorbic acid (AA), dopamine (DA), and uric acid (UA) as compared to those of PdAg/GCE, rGO/GCE, commercial Pd/C/GCE, and bare GCE. The as-developed sensor can selectively detect AA, DA, and UA with a good anti-interference ability, wide concentration ranges of 1.0 µM-2.1 mM, 0.4-96.0 µM, and 1.0-150.0 µM, respectively, together with low detection limits of 0.057, 0.048, and 0.081 µM (S/N = 3), respectively. For simultaneous detection of AA, DA, and UA, the linear current-concentration responses were observed from 1.0 µM-4.1 mM, 0.05-112.0 µM, and 3.0-186.0 µM, with the detection limits of 0.185, 0.017, and 0.654 µM (S/N = 3), respectively.

Facile synthesis of water-soluble and biocompatible fluorescent nitrogen-doped carbon dots for cell imaging.

A simple, facile and green hydrothermal method was developed in the synthesis of water-soluble nitrogen-doped carbon dots (N-CDs) from streptomycin. The as-prepared N-CDs displayed bright blue fluorescence under the irradiation of UV light, together with a high quantum yield of 7.6% and good biocompatibility as demonstrated by the cell viability assay. Thus, the N-CDs can be used as fluorescent probes for cell imaging, which have potential applications in bioimaging and related fields. This strategy opens a new way for the preparation of fluorescent carbon nanomaterials using small molecules as carbon sources.

Pollutant removal and membrane fouling in an anaerobic submerged membrane bioreactor for real sewage treatment.

Real sewage was continuously treated by a laboratory-scale anaerobic submerged membrane bioreactor (AnSMBR) for over 160 days. Results showed that around 90% of chemical oxygen demand, and 99% of turbidity and total suspended solids in the sewage could be removed by the AnSMBR system. Membrane flux sustained at 11 L/(m(2) h) was realized with biogas sparging. Small flocs from sludge deflocculation in the early operational period caused a high membrane fouling rate, and the high specific filtration resistance of the cake layer appeared mostly attributable to the osmotic pressure effect. The performance results were also compared with those in the literature for upflow anaerobic sludge blanket reactors and aerobic membrane bioreactors for sewage treatment, demonstrating that AnSMBR could provide a desirable alternative for sewage treatment.

Intranasally administered thermosensitive gel for brain-targeted delivery of rhynchophylline to treat Parkinson's disease.

The aim of this study is to overcome the obstacle of the blood-brain barrier (BBB) in therapeutic drugs of Parkinson's disease (PD), like rhynchophylline (RIN) entry by intranasal administration and to solve the problem of short residence time of drugs in the nasal cavity by the dosage form design of thermosensitive gel. We first conducted a study of the screening of absorption enhancers and 3% hydroxypropyl-ß-cyclodextrin (HP-ß-CD) was effective to improve the nasal mucosal permeability of RIN. By adjusting the ratio of different components in order to make the gel with adhesion and rapid gelation which were determined to be Poloxamer 407 (P407) 20%, Poloxamer 188 (P188) 1%, polyethylene glycol 6000 (PEG-6000) 1% and HP-ß-CD 3%. In addition, the characterization showed that the thermosensitive gel was network cross-linked, rapidly gelation upon entry into the nasal cavity and was stable as semi-solid state with adhesion as well as sustained release properties. Moreover, pharmacokinetic study was performed to evaluate the bioavailability and brain targeting of RIN thermosensitive gel and which were 1.6 times and 2.1 times higher than those of oral administration. We also evaluated the anti-PD effects of RIN thermosensitive gel in-vitro as well as in-vivo. The results showed that RIN thermosensitive gel was effective in repairing the motor function impairment, dysregulated expression levels of oxidative stress factors, and positive neuronal damage within the substantia nigra and dopamine caused by PD. The constructed intranasal drug administration strategy through thermosensitive gel provided a new choice for targeted treatment of PD together with other central nervous system diseases.

Assembly of Ni(OH)2 nanoparticle films on aqueous surfaces induced by small amounts of toluene, and the study of their unmediated electrocatalytic oxidation toward some small biomolecules.

A simple strategy for the preparation of a Ni(OH)2 nanoparticle film is described. Ni(OH)2 nanoparticles were synthesized in an aqueous solution of Ni2+ and tert-butylamine in the presence of small amounts of toluene, which induced the nanoparticles to assemble a thin film on the aqueous surface. The obtained Ni(OH)2 nanoparticle film was easily transferred onto the electrode surfaces and exhibited stable electrochemical performance. The electrochemical behavior of various small biomolecules, including cysteine, homocysteine, glutathione, histidine, glycine, cystine, methionine, lysine, aspartic acid, glutamic acid, phenylalanine, ascorbic acid, uric acid and dopamine, were studied at the Ni(OH)2 nanoparticle-film-modified electrode. The Ni(OH)2 nanoparticle film exhibits excellent direct, unmediated electrocatalysis toward the oxidation of cysteine, homocysteine and ascorbic acid in a pH 7.4 buffer solution with a low onset potential and a high oxidation signal. This behavior differs from many reports in which small organic molecules are electrocatalyzed indirectly by the Ni(OH)2/NiOOH redox couple in a strongly alkaline solution.

Mass transfer and reaction simultaneously enhanced airlift microbial electrolytic cell system with high gaseous o-xylene removal capacity.

To overcome the limitation of mass transfer and reaction rate involved in the biodegradation of gaseous o-xylene, the airlift reactor and microbial electrolysis cell were integrated to construct an airlift microbial electrolysis cell (AL-MEC) system for the first time, in which the bioanode was modified by polypyrrole to further improve biofilm attachment. The developed AL-MEC system achieved 95.4% o-xylene removal efficiency at optimized conditions, and maintained around 75% removal efficiency even while the inlet o-xylene load was as high as 684 g m-3 h-1. The existence of O2 exhibited a competition in electrons with the bioanode but a positive effect on ring-opening process in the o-xylene oxidation. The limitation of mass transfer had been overcome as the empty bed resistance time in the range of 20-80 s did not influence the system performance significantly. The microbial community analysis confirmed the o-xylene degradation microbes and electroactive bacteria were the dominant, which could be further enriched at 0.3 V against standard hydrogen electrode. This work revealed the feasibility of the AL-MEC system for the degradation of o-xylene and similar compounds, and provided insights into bioelectrochemical system design with high gaseous pollution removal capacity.

Different fouling propensities of loosely and tightly bound extracellular polymeric substances (EPSs) and the related fouling mechanisms in a membrane bioreactor.

In this study, fouling propensities of loosely bound extracellular polymeric substances (LB-EPSs) and tightly bound EPSs (TB-EPSs) in a membrane bioreactor (MBR) were investigated. It was found that, both the LB-EPSs and TB-EPSs possessed rather high specific filtration resistance (SFR), and LB-EPSs possessed about three times higher SFR but a lower adhesion ability than the TB-EPSs. A series of characterizations demonstrated that LB-EPSs had higher ratio of proteins to polysaccharides (PN/PS ratio), lower CO bonds content, higher hydrophilicity, higher deformation or mixing ability and more abundant high molecular weight (MW) substances than TB-EPSs. Thermodynamic analyzes revealed that the total interaction energy between the TB-EPSs and membrane was always attractive and strengthened, well explaining the higher adhesion ability of the TB-EPSs than the LB-EPSs. Meanwhile, the filtration process was found to be associated with gel layer formation, and the high SFR of EPSs was caused by the chemical potential change in gel layer filtration. According to the Flory-Huggins lattice theory, LB-EPSs tended to form a gel layer with higher cross-linking and/or polymer entanglement level because they contained more abundant high molecular weight (MW) substance, corresponding to higher SFR than that of the TB-EPSs. The proposed thermodynamic mechanisms well interpreted the different fouling propensities of LB-EPSs and TB-EPSs in MBRs.

Quantification of interfacial energies associated with membrane fouling in a membrane bioreactor by using BP and GRNN artificial neural networks.

Interfacial energy between sludge foulants and rough membrane surface critically determines adhesive fouling in membrane bioreactors (MBRs). As a current available method, the advanced extensive Derjaguin-Landau-Verwey-Overbeek (XDLVO) approach cannot efficiently quantify the interfacial energy. In this study, novel methods including back propagation (BP) artificial neural network (ANN) and generalized regression neural network (GRNN) were proposed to quantify the interfacial energy associated with the membrane fouling in an MBR. Different levels of 5 apparent input factors and the resulted interfacial energies were used as training and testing databases for establishment of ANN models. The established BP ANN and GRNN models exhibited high regression coefficients and accuracies, suggesting the high capacity of ANN models to capture the complicated non-linear mapping relations between interfacial energy and various factors. As compared with the advanced XDLVO approach, both BP ANN and GRNN showed remarkably improved quantification efficiency. Meanwhile, BP ANN showed better prediction performance than GRNN model. Case study further demonstrated the robustness and feasibility of BP ANN for interfacial energy quantification. This study provided a new approach to quantify interfacial energy associated with membrane fouling.

Effects of molecular weight distribution of soluble microbial products (SMPs) on membrane fouling in a membrane bioreactor (MBR): Novel mechanistic insights.

While molecular weight distribution (MWD) is one of the most important properties of soluble microbial products (SMPs), mechanisms underlying effects of MWD of SMPs on membrane fouling have not well unveiled. In this study, it was found that, the supernatant of sludge suspension in a membrane bioreactor (MBR) for wastewater treatment can be fractionated into a series of SMPs samples with different molecular weight (MW) fraction. The real gel sample mainly formed by the rejected SMPs on membrane surface had a high specific filtration resistance (SFR) of 1.21 × 1016 m-1 kg-1. The SFR of SMPs samples and the model foulants of polyethylene glycol (PEG) increased with their MW. The change trend of SFR with MW cannot be sufficiently explained by three-dimensional excitation-emission matrix (EMM) and chemical compositions. Tyndall effect analysis indicated that gelating ability of SMPs and PEG in the solution increased with their MW. Scanning electron microscope (SEM) confirmed gel structure changes with the PEG MW. Accordingly, mechanisms based on Carman-Kozeny equation and Flory-Huggins lattice theory were proposed to interpret SFR of SMPs with low and high MW, respectively. Simulating these two mechanistic models on PEG samples resulted in the comparable SFR data to the experimental ones, indicating the correctness and feasibility of the proposed mechanisms. The proposed mechanisms provided in-depth understanding of membrane fouling regarding MW, facilitating to develop effective membrane fouling mitigation strategies.

Correlation Analysis of Lignin Accumulation and Expression of Key Genes Involved in Lignin Biosynthesis of Ramie (Boehmeria nivea).

The phloem of the stem of ramie (Boehmeria nivea) is an important source of natural fiber for the textile industry. However, the lignin content in the phloem affects the quality of ramie phloem fiber. In this study, the lignin content and related key gene expression levels were analyzed in the phloem and xylem at different developmental periods. The results showed that the relative expression levels of lignin synthesis-related key genes in the xylem and phloem of the stem gradually decreased from the fast-growing period to the late maturation period, but the corresponding lignin content increased significantly. However, the relative expression levels of a few genes were the highest during the maturation period. During all three periods, the lignin content in ramie stems was positively correlated with the expression of genes, including PAL, C4H and 4CL1 in the phenylpropanoid pathway, F5H and CCoAOMT in the lignin-specific synthetic pathway, and CAD in the downstream pathway of lignin synthesis, but the lignin content was negatively correlated with the expression of genes including 4CL3 in the phenylpropanoid pathway and UDP-GT in the shunt pathway of lignin monomer synthesis. The ramie 4CL3 recombinant protein prefers cinnamic acid as a substrate during catalysis, and it negatively regulates lignin synthesis. It is speculated that ramie 4CL3 is mainly involved in the synthesis of ramie flavonoid compounds, and that 4CL1 is mainly involved in lignin synthesis.

Integration of Quantitative Trait Loci Mapping and Expression Profiling Analysis to Identify Genes Potentially Involved in Ramie Fiber Lignin Biosynthesis.

Ramie fibers, one of the most important natural fibers in China, are mainly composed of lignin, cellulose, and hemicellulose. As the high lignin content in the fibers results in a prickly texture, the lignin content is deemed to be an important trait of the fiber quality. In this study, the genetic basis of the fiber lignin content was evaluated, resulting in the identification of five quantitative trait loci (QTLs). Three genes, whole_GLEAN_10021050, whole_GLEAN_10026962, and whole_GLEAN_10009464 that were identified on the QTL regions of qLC7, qLC10, and qLC13, respectively, were found to be homologs of the Arabidopsis lignin biosynthetic genes. Moreover, all three genes displayed differential expression in the barks located in the top and middle parts of the stem, where lignin was not being synthesized and where it was being biosynthesized, respectively. Sequence comparison found that these three genes had wide variations in their coding sequences (CDSs) and putative promoter regions between the two parents, especially the MYB gene whole_GLEAN_10021050, whose protein had insertions/deletions of five amino acids and substitutions of two amino acids in the conserved domain. This evidence indicates that these three genes are potentially involved in lignin biosynthesis in ramie fibers. The QTLs identified from this study provide a basis for the improvement of lignin content and fiber quality in ramie breeding. The characterization of the three candidate genes here will be helpful for the future clarification of their functions in ramie.

A unified thermodynamic mechanism underlying fouling behaviors of soluble microbial products (SMPs) in a membrane bioreactor.

Soluble microbial products (SMPs) are the predominate foulants determining fouling extent in membrane bioreactors (MBRs). However, exact mechanism underlying their typical fouling behaviors remains unrevealed. In this study, the typical fouling behaviors of SMPs during initial operational period of a MBR were characterized. It was found that, although being low content, SMPs rather than sludge particulates preferentially adhered to membrane surface to accumulate a gel layer, and moreover, specific filtration resistance (SFR) of SMPs was approximately 700 times larger than that of the sludge particulates at operational day 3. According to energy balance principle, a unified thermodynamic mechanism underlying these fouling behaviors of SMPs was proposed. Thermodynamic analyses demonstrated that, the attractive interaction energy strength in contact between SMPs and membrane was larger by around 3700 times than that between sludge particulates and membrane, well explaining the extremely high adhesive ability of SMPs over sludge particlulates. Meanwhile, filtration through a SMPs layer was modelled and simulated as a thermodynamic process. Simulation on an agar gel showed that, about 92.6% of SFR was originated from mixing free energy change during filtration. Such a result satisfactorily interpreted the extremely high SFR of SMPs layer over sludge cake layer. The revealed thermodynamic mechanism underlying SMPs fouling behaviors significantly deepened understanding of fouling, and facilitated to development of effective fouling control strategies.

Self-assembly of graphene oxide/PEDOT:PSS nanocomposite as a novel adsorbent for uranium immobilization from wastewater.

In recent years, water pollution caused by radionuclides has become a rising concern, among which uranium is a representative class of actinide element. Since hexavalent uranium, i.e. U(VI), is biologically hazardous with high migration, it's essential to develop efficient adsorbents to minimize the impact on the environment. Towards this end, we have synthesized a novel material (GO/PEDOT:PSS) by direct assembling graphene oxide (GO) and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) through a facile ball milling method, which shows impressing performance for the immobilization of U(VI). On the basis of the batch experiments, GO/PEDOT:PSS exhibits ionic strength-independent sorption edges and temperature-promoted sorption isotherms, revealing an inner-sphere complexation with endothermic nature. The sorption kinetics can be illustrated by the pseudo-second-order model, yielding a rate constant of 1.09. × 10-2 g mg-1∙min-1, while the sorption isotherms are in coincidence with the Langmuir model, according to which the maximum sorption capacity is measured to be 384.51 mg g-1 at pH 4.5 under 298 K, indicating a monolayer sorption mechanism. In the light of the FT-IR and XPS investigations, the surface carboxyl/sulfonate group is responsible to the chelation of U(VI), indicating that the enhanced sorption capacity may be ascribed to the PSS moiety. These findings can greatly contribute to the design strategy for developing highly efficient adsorbents in the field of radioactive wastewater treatment.

Insight into the mechanisms for hexavalent chromium reduction and sulfisoxazole degradation catalyzed by graphitic carbon nitride: The Yin and Yang in the photo-assisted processes.

As robust polymeric catalysts, graphitic carbon nitride (g-C3N4) has been known to have great application potential in environmental remediation. However, the mechanisms in the photo-assisted catalytic processes during the reduction or oxidation of pollutants are still difficult to discern and therefore not well studied. In this work, visible-assisted catalytic reduction of hexavalent chromium (Cr(VI)) or oxidation of sulfisoxazole (SIZ) by g-C3N4 with the addition of formic acid (FA) or potassium peroxydisulfate (PS) were systematically investigated. Effects of operation parameters such as g-C3N4 dosage, FA concentration, Cr(VI) concentration, solution pH, PS concentration were studied. The results showed g-C3N4 can be effective and robust catalyst for both the reduction (Yin) and oxidation (Yang) reactions in the environmental remediation. Mechanisms were studied by using electron spin resonance (ESR) spectroscopy. The results revealed the CO 2- is the predominant radical for Cr(VI) reduction in the g-C3N4/FA/Vis system and the SO4- and OH are all the main radicals for the oxidation of SIZ in the g-C3N4/PS/Vis system. The photo-generated carriers by g-C3N4, act as radical initiator, were responsible for the production of the reactive radical species in aqueous solution. This work not only shed a new light on the application of semiconductor polymers for the removal of micropollutants and also will expand the applicability of the polymeric photocatalysts for environmental remediation.

A novel strategy to develop antifouling and antibacterial conductive Cu/polydopamine/polyvinylidene fluoride membranes for water treatment.

Membrane fouling problem impedes widespread application of polyvinylidene fluoride (PVDF) membrane for water treatment. This study proposed a novel strategy to endow hydrophobic PVDF ultrafiltration (UF) membrane with good antifouling and antibacterial activity. The novel strategy includes 3 steps: polydopamine (PDA) modification, Ag catalytic activation and electroless Cu plating. Via this strategy, copper nanoparticles (CuNPs) were in situ immobilized on PVDF membrane. The adhesive PDA layer not only facilitated to firm attachment of CuNPs, but also increased surface hydrophilicity. Scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) analyses confirmed successful immobilization of CuNPs, which improved surface hydrophilicity and absolution value of negative zeta potential as compared with the pristine PVDF membrane. Meanwhile, the modified Cu/PDA/PVDF membrane had relatively high conductivity, significantly improving antifouling performance when 0.30 V cm-1 of external electrical field was applied. Antibacterial tests revealed that the modified membrane possessed significantly enhanced antibacterial activity against live E. coli. The novel modification strategy in this study gave important implications for membrane fabrication, and the modified membrane possessed attractive potential in water treatment.

Mechanistic insights into alginate fouling caused by calcium ions based on terahertz time-domain spectra analyses and DFT calculations.

Fouling mechanisms underlying the filtration behaviors of alginate solution caused by calcium addition were investigated by Terahertz time-domain spectroscopy (THz-TDS) and density functional theory (DFT) techniques. Filtration tests showed that specific filtration resistance (SFR) of alginate solution (0.75 g L-1) monotonously increased with calcium addition at a relatively low range of calcium concentration (0-1.0 mM), and SFR (2.61 × 1015 m kg-1) of alginate solution with 1.0 mM calcium addition was extremely high as compared with sludge suspension. Characterizations by X-ray photoelectric spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and Thermogravimetric analysis (TGA) showed that the composition of functional groups, elements and thermal stability of alginate was not apparently affected by calcium concentration. Howbeit, THz-TDS spectra showed that calcium addition caused structural variation of alginate polymer in solution. DTF calculation results showed that initial binding of alginate chains induced by calcium ions preferentially occurred in intermolecular other than intramolecular, and moreover, the two alginate chains bridged by a calcium atom tend to stretch in a tetrahedron structure (cross to each other) other than parallel to each other. According to these results, "chemical potential gap" depicted by Flory-Huggins theory was suggested to be responsible for the filtration behaviors of alginate solution caused by calcium addition. This study provided the mechanistic insights into membrane fouling.

Thermodynamic insights into membrane fouling in a membrane bioreactor: Evaluating thermodynamic interactions with Gaussian membrane surface.

While membrane bioreactor (MBR) technology is generally considered as one of the most promising technologies for wastewater treatment and recovery, membrane fouling remains the major obstacle limiting its applications. Interfacial interactions, which critically determine adhesion process and membrane fouling, were investigated in this study. It was found that, natural membrane surface was of a Gaussian surface obeying Gaussian distribution. A Gaussian approach integrating Fourier transform technique, Gaussian distribution and spectrum method was deduced to simulate rough surface topography of membrane. Thereafter, surface element integral (SEI) method, together with composite Simpson rule and triangulation of Gaussian surface was proposed to calculate interfacial interactions. By using the unified method, quantification of interfacial interactions with a Gaussian membrane surface was realized for the first time to date. It was further found that, membrane surface topography had profound impacts on interfacial interactions and adhesive fouling in the MBR. The deduced method can be used to address impacts of various factors on interfacial interactions and adhesive fouling, posing in-depth thermodynamic insights into membrane fouling and pointing towards its widespread potential in fouling research in MBRs.

Membrane fouling in a submerged membrane bioreactor: An unified approach to construct topography and to evaluate interaction energy between two randomly rough surfaces.

Quantitatively evaluating interaction energy between two randomly rough surfaces is the prerequisite to quantitatively understand and control membrane fouling in membrane bioreactors (MBRs). In this study, a new unified approach to construct rough topographies and to quantify interaction energy between a randomly rough particle and a randomly rough membrane was proposed. It was found that, natural rough topographies of both foulants and membrane could be well constructed by a modified two-variable Weierstrass-Mandelbrot (WM) function included in fractal theory. Spatial differential relationships between two constructed surfaces were accordingly established. Thereafter, a new approach combining these relationships, surface element integration (SEI) approach and composite Simpson's rule was deduced to calculate the interaction energy between two randomly rough surfaces in a submerged MBR. The obtained results indicate the profound effects of surface morphology on interaction energy and membrane fouling. This study provided a basic approach to investigate membrane fouling and interface behaviors.

Simple synthesis of hierarchical AuPt alloy nanochains for construction of highly sensitive hydrazine and nitrite sensors.

Herein, a single-step co-reduction aqueous route was designed for preparation of hierarchical AuPt alloy nanochains, firstly using amprolium hydrochloride as a new stabilizing agent and structure-director. The morphology, structure, composition, and size of the products were characterized by a series of technique. The growth mechanism of AuPt nanochains was discussed in details. The AuPt nanochains modified glassy carbon electrode showed the improved analytical performances for determination of nitrite and hydrazine. The linear ranges of nitrite are 0.5-366.4µM and 466.4-2666.4µM for the two segments, and the detection limit is 0.03µM (S/N=3). The linear ranges of hydrazine are 5.0-116.4µM and 166.4-2666.4µM for the two segments, along with the low detection limit of 0.26µM (S/N=3). The performances of AuPt nanochains were superior to those of individual Pt and Au nanoparticles. It is ascribed to the specific hierarchical structures and synergistic effects of the bimetals.

Physicochemical correlations between membrane surface hydrophilicity and adhesive fouling in membrane bioreactors.

36 membrane material cases used in membrane bioreactors (MBRs) covering wide range of hydrophilicity/hydrophobicity were used to calculate thermodynamic interactions between membranes and foulants. It was found that adhesive fouling can be represented by the total interaction energy at minimum separation distance (h0). No functional relationship between membrane hydrophilicity and adhesive fouling can be deduced. However, membrane hydrophilicity, in terms of water contact angle or interaction energy between two identical surfaces at h0 in water (ΔGsws), had high statistical correlations with adhesive fouling. This statistical correlations should be attributed to the major role of acid-base interaction in total interaction associated with adhesion in most of membrane cases. Moreover, the statistical correlations were independent of the changes in membrane surface roughness or hydrophilicity/hydrophobicity of foulants. These findings satisfactorily explained the inconsistent conclusions in the literature regarding effects of membrane hydrophilicity on adhesive fouling, giving implications for membrane fouling mitigation.