Fluorinated photoreduced graphene oxide with semi-ionic C-F bonds: An effective carbon based photocatalyst for the removal of volatile organic compounds.

There is much interest in developing metal-free halogenated graphene such as fluorinated graphene for various catalytic applications. In this work, a fluorine-doped graphene oxide photocatalyst was investigated for photocatalytic oxidation (PCO) of a volatile organic compound (VOC), namely gaseous methanol. The fluorination process of graphene oxide (GO) was carried out via a novel and facile solution-based photoirradiation method. The fluorine atoms were doped on the surface of the GO in a semi-ionic C-F bond configuration. This presence of the semi-ionic C-F bonds induced a dramatic 7-fold increment of the hole charge carrier density of the photocatalyst. The fluorinated GO photocatalyst exhibited excellent photodegradation up to 93.5% or 0.493 h-1 according pseudo-first order kinetics for methanol. In addition, 91.7% of methanol was mineralized into harmless carbon dioxide (CO2) under UV-A irradiation. Furthermore, the photocatalyst demonstrated good stability in five cycles of methanol PCO. Besides methanol, other VOCs such as acetone and formaldehyde were also photodegraded. This work reveals the potential of fluorination in producing effective graphene-based photocatalyst for VOC removal.

Exposure to polystyrene microplastics impairs hippocampus-dependent learning and memory in mice.

Microplastics (MPs) pollution has become a serious environmental issue worldwide, but its potential effects on health remain unknown. The administration of polystyrene MPs (PS-MPs) to mice for eight weeks impaired learning and memory behavior. PS-MPs were detected in the brain especially in the hippocampus of these mice. Concurrently, the hippocampus had decreased levels of immediate-early genes, aberrantly enhanced synaptic glutamate AMPA receptors, and elevated neuroinflammation, all of which are critical for synaptic plasticity and memory. Interestingly, ablation of the vagus nerve, a modulator of the gut-brain axis, improved the memory function of PS-MPs mice. These results indicate that exposure to PS-MPs in mice alters the expression of neuronal activity-dependent genes and synaptic proteins, and increases neuroinflammation in the hippocampus, subsequently causing behavioral changes through the vagus nerve-dependent pathway. Our findings shed light on the adverse impacts of PS-MPs on the brain and hippocampal learning and memory.

Silver enriched silver phosphate microcubes as an efficient recyclable SERS substrate for the detection of heavy metal ions.

A rapid, cost-effective and accurate detection of heavy metal ions is crucial for human health monitoring and environmental protection. Surface-enhanced Raman spectroscopy (SERS) has become a reliable method due to its outstanding performance for the identification of contaminants. In this paper, silver phosphate microcubes (Ag3PO4) were fabricated using two different precipitation methods for ultrasensitive SERS detection of heavy metal ions. The use of an organic linker (BPy) with Ag3PO4 enabled the immobilization of Hg2+ and Pb2+ ions. The formation of Ag3PO4 was confirmed by XRD, UV-DRS, FESEM coupled with EDX and HRTEM. The analytical enhancement factor (AEF) obtained was 1010 with a detection limit of 10-15 M indicating high sensitivity. Based on these results, the possible SERS mechanism has been proposed and discussed. Moreover, an excellent reusability of Ag3PO4 substrate for at least four cycles was achieved upon the light exposure on heavy metal loaded substrate due to its superior catalytic ability for the degradation of heavy metal ions. The as-prepared substrate demonstrated remarkable stability, selectivity and SERS sensitivity towards real samples. The results conclude that Ag3PO4 microcubes offer a great prospect in recyclable SERS applications.

Rehardening and the Protective Effect of Gamma-Polyglutamic Acid/Nano-Hydroxyapatite Paste on Surface-Etched Enamel.

Many revolutionary approaches are on the way pertaining to the high occurrence of tooth decay, which is an enduring challenge in the field of preventive dentistry. However, an ideal dental care material has yet to be fully developed. With this aim, this research reports a dramatic enhancement in the rehardening potential of surface-etched enamels through a plausible synergistic effect of the novel combination of γ-polyglutamic acid (γ-PGA) and nano-hydroxyapatite (nano-HAp) paste, within the limitations of the study. The percentage of recovery of the surface microhardness (SMHR%) and the surface parameters for 9 wt% γ-PGA/nano-HAp paste on acid-etched enamel were investigated with a Vickers microhardness tester and an atomic force microscope, respectively. This in vitro study demonstrates that γ-PGA/nano-HAp treatment could increase the SMHR% of etched enamel to 39.59 ± 6.69% in 30 min. To test the hypothesis of the rehardening mechanism and the preventive effect of the γ-PGA/nano-HAp paste, the surface parameters of mean peak spacing (Rsm) and mean arithmetic surface roughness (Ra) were both measured and compared to the specimens subjected to demineralization and/or remineralization. After the treatment of γ-PGA/nano-HAp on the etched surface, the reduction in Rsm from 999 ± 120 nm to 700 ± 80 nm suggests the possible mechanism of void-filling within a short treatment time of 10 min. Furthermore, ΔRa-I, the roughness change due to etching before remineralization, was 23.15 ± 3.23 nm, while ΔRa-II, the roughness change after remineralization, was 11.99 ± 3.90 nm. This statistically significant reduction in roughness change (p < 0.05) implies a protective effect against the demineralization process. The as-developed novel γ-PGA/nano-HAp paste possesses a high efficacy towards tooth microhardness rehardening, and a protective effect against acid etching.

Random lasers from photonic crystal wings of butterfly and moth for speckle-free imaging.

Several biological membranes have been served as scattering materials of random lasers, but few of them include natural photonic crystals. Here, we propose and demonstrate a facile approach to fabricating high-performance biological photonic crystal random lasers, which is cost-effective and reproducible for mass production. As a benchmark, optical and lasing properties of dye-coated Lepidoptera wings, including Papilio ulysses butterfly and Chrysiridia rhipheus moth, are characterized and show a stable laser emission with a superior threshold of 0.016 mJ/cm2, as compared to previous studies. To deploy the proposed devices in practical implementation, we have applied the as-fabricated biological devices to bright speckle-free imaging applications, which is a more sustainable and more accessible imaging strategy.

Ultrasound-assisted sequentially precipitated nickel-silica catalysts and its application in the partial hydrogenation of edible oil.

Sequentially precipitated Mg-promoted nickel-silica catalysts with ageing performed under various ultrasonic intensities were employed to study the catalyst performance in the partial hydrogenation of sunflower oil. Results from various characterisation studies showed that increasing ultrasonic intensity caused a higher degree of hydroxycarbonate erosion and suppressed the formation of Ni silicates and silica support, which improved Ni dispersion, BET surface area and catalyst reducibility. Growth of silica clusters on the catalyst aggregates were observed in the absence of ultrasonication, which explained the higher silica and nickel silicate content on the outer surface of the catalyst particle. Application of ultrasound also altered the electron density of the Ni species, which led to higher activity and enhanced product selectivity for sonicated catalysts. The catalyst synthesised with ultrasonic intensity of 20.78 Wcm-2 achieved 22.6% increase in hydrogenation activity, along with 28.5% decrease in trans-C18:1 yield at IV = 70, thus supporting the feasibility of such technique.

Study of laser actions by bird's feathers with photonic crystals.

Random lasers had been made by some biomaterials as light scattering materials, but natural photonic crystals have been rarely reported as scattering materials. Here we demonstrate the ability of natural photonic crystals to drive laser actions by sandwiched the feathers of the Turquoise-Fronted Amazon parrot and dye between two plastic films. Parrot feathers comprise abundant photonic crystals, and different color feathers compose of different ratios of the photonic crystal, which directly affect the feather reflectance. In this study, the multi-reflection scattering that occurred at the interface between the photonic crystal and gain media efficiently reduce the threshold; therefore, the more photonic crystal constitutes in the feathers; the lower threshold can be obtained. The random lasers can be easily made by the integration of bird feather photonic crystals and dye with a simple and sustainable manufacturing approach.

The improved photocatalytic activity of highly expanded MoS2 under visible light emitting diodes.

Photocatalytic degradation is a promising method to remove organic pollutants from water. Photocatalysts based on two-dimensional (2D) transition metal dichalcogenides (TMDs) such as MoS2 nanomaterials have gained tremendous popularity. This is due to their narrow band gap and high visible light absorption. Herein, a MoS2 photocatalyst with highly expanded interlayer spaces of 1.51 nm was synthesized in the presence of Pluronic F-127 as a template by a facile one-pot hydrothermal method. This expanded MoS2 (MF-1) managed to photodegrade 98% (2.62 × 10-2 min-1) of methylene blue (MB) dye under irradiation of 1 W visible light-emitting diode (LED) white light. The dominant performance of MF-1 is attributed to the highly expanded interlayer spacing, which exposed more active edge sites. Moreover, the formation of surface defects such as surface cracks and sulfur vacancies (Sv) facilitates the adsorption capacity and in situ generation of reactive oxygen species (ROS). The dominant ROS responsible for the photodegradation of MB is superoxide radical (˙O2 -). The photocatalyst shows good recyclability without deterioration even after five consecutive cycles.

Engineering S. oneidensis for Performance Improvement of Microbial Fuel Cell-a Mini Review.

Microbial fuel cell (MFC) is a promising technology that utilizes exoelectrogens cultivated in the form of biofilm to generate power from various types of sources supplied. A metal-reducing pathway is utilized by these organisms to transfer electrons obtained from the metabolism of substrate from anaerobic respiration extracellularly. A widely established model organism that is capable of extracellular electron transfer (EET) is Shewanella oneidensis. This review highlights the strategies used in the transformation of S. oneidensis and the recent development of MFC in terms of intervention through genetic modifications. S. oneidensis was genetically engineered for several aims including the study on the underlying mechanisms of EET, and the enhancement of power generation and wastewater treating potential when used in an MFC. Through engineering S. oneidensis, genes responsible for EET are identified and strategies on enhancing the EET efficiency are studied. Overexpressing genes related to EET to enhance biofilm formation, mediator biosynthesis, and respiration appears as one of the common approaches.

Biomass-Derived Porous Carbons Derived from Soybean Residues for High Performance Solid State Supercapacitors.

A series of heteroatom-containing porous carbons with high surface area and hierarchical porosity were successfully prepared by hydrothermal, chemical activation, and carbonization processes from soybean residues. The initial concentration of soybean residues has a significant impact on the textural and surface functional properties of the obtained biomass-derived porous carbons (BDPCs). SRAC5 sample with a BET surface area of 1945 m2 g-1 and a wide micro/mesopore size distribution, nitrogen content of 3.8 at %, and oxygen content of 15.8 at % presents the best electrochemical performance, reaching 489 F g-1 at 1 A g-1 in 6 M LiNO3 aqueous solution. A solid-state symmetric supercapacitor (SSC) device delivers a specific capacitance of 123 F g-1 at 1 A g-1 and a high energy density of 68.2 Wh kg-1 at a power density of 1 kW kg-1 with a wide voltage window of 2.0 V and maintains good cycling stability of 89.9% capacitance retention at 2A g-1 (over 5000 cycles). The outstanding electrochemical performances are ascribed to the synergistic effects of the high specific surface area, appropriate pore distribution, favorable heteroatom functional groups, and suitable electrolyte, which facilitates electrical double-layer and pseudocapacitive mechanisms for power and energy storage, respectively.

Hydrothermal Effect on Mechanical Properties of Nephila pilipes Spidroin.

The superlative mechanical properties of spider silk and its conspicuous variations have instigated significant interest over the past few years. However, current attempts to synthetically spin spider silk fibers often yield an inferior physical performance, owing to the improper molecular interactions of silk proteins. Considering this, herein, a post-treatment process to reorganize molecular structures and improve the physical strength of spider silk is reported. The major ampullate dragline silk from Nephila pilipes with a high ß-sheet content and an adequate tensile strength was utilized as the study material, while that from Cyrtophora moluccensis was regarded as a reference. Our results indicated that the hydrothermal post-treatment (50-70 °C) of natural spider silk could effectively induce the alternation of secondary structures (random coil to ß-sheet) and increase the overall tensile strength of the silk. Such advantageous post-treatment strategy when applied to regenerated spider silk also leads to an increment in the strength by ~2.5-3.0 folds, recapitulating ~90% of the strength of native spider silk. Overall, this study provides a facile and effective post-spinning means for enhancing the molecular structures and mechanical properties of as-spun silk threads, both natural and regenerated.

Effective photoreduction of graphene oxide for photodegradation of volatile organic compounds.

Nowadays, humans spend most of their time indoors and are frequently exposed to volatile organic compounds (VOCs) from various sources. The photocatalytic oxidation (PCO) method is a relatively more efficient method than the adsorption method for removing VOCs from the environment. In this work, graphene oxide (GO) was partially reduced via photoreduction under ultraviolet light (UV-A) irradiation and then used as a photocatalyst to degrade VOCs. After photoreduction, the band gap of the partially reduced graphene oxide (PRGO) decreased from 3.5-4.5 eV to 3.1-4.0 eV. Methanol vapour, which acts as a model VOC, was photodegraded using the PRGO. The effectiveness of the PRGO was mainly due to the removal of oxygen functional groups and restoration of the sp2 domain. This lowered the band gap and slowed down the electron recombination rate, which resulted in a higher photocatalytic activity. The photocatalytic activity of PRGO followed pseudo-first order kinetics, with a rate constant of 0.0025 min-1, and it could be reused for five cycles without any significant loss in the photocatalytic activity. This study demonstrates the potential of PRGO as a versatile and stable metal-free photocatalyst to remove indoor pollutants.

Adsorptive decontamination of diclofenac by three-dimensional graphene-based adsorbent: Response surface methodology, adsorption equilibrium, kinetic and thermodynamic studies.

Pharmaceutical residues are emerging pollutants in the aquatic environment and their removal by conventional wastewater treatment methods has proven to be ineffective. This research aimed to develop a three-dimensional reduced graphene oxide aerogel (rGOA) for the removal of diclofenac in aqueous solution. The preparation of rGOA involved facile self-assembly of graphene oxide under a reductive environment of L-ascorbic acid. Characterisation of rGOA was performed by Fourier transform infrared, scanning electron microscope, transmission electron microscopy, nitrogen adsorption-desorption, Raman spectroscopy and X-ray diffraction. The developed rGOA had a measured density of 20.39 ±â€¯5.28 mg/cm3, specific surface area of 132.19 m2/g, cumulative pore volume of 0.5388 cm3/g and point of zero charge of 6.3. A study on the simultaneous interactions of independent factors by response surface methodology suggested dosage and initial concentration as the dominant parameters influencing the adsorption of diclofenac. The highest diclofenac adsorption capacity (596.71 mg/g) was achieved at the optimum conditions of 0.25 g/L dosage, 325 mg/L initial concentration, 200 rpm shaking speed and 30 °C temperature. The adsorption equilibrium data were best fitted to the Freundlich model with correlation coefficient (R2) varying from 0.9500 to 0.9802. The adsorption kinetic data were best correlated to the pseudo-first-order model with R2 ranging from 0.8467 to 0.9621. Thermodynamic analysis showed that the process was spontaneous (∆G = - 7.19 to - 0.48 kJ/mol) and exothermic (∆H = - 12.82 to - 2.17 kJ/mol). This research concluded that rGOA is a very promising adsorbent for the remediation of water polluted by diclofenac.

A Facile Measurement for Monitoring Dragline Silk Dope Concentration in Nephila pilipes upon Spinning.

In spite of all the efforts towards deciphering the silk spinning process of spiders, the underlying mechanism is yet to be fully revealed. In this research, we designed a novel approach that allowed us to quantitatively evaluate the concentration change of silk dope during the liquid-to-solid spinning process of the orb-weaver Nephila pilipes. As a prior characterization of the optimal silking conditions, we first gauged the influence of silking-rate, ranging from 1.5 to 8.0 m/min, on dragline silk diameters and silk tensile strengths obtained from the spiders. Next, to evaluate the liquid content of the silk dope, the major ampullate gland was dissected and the concentration of the sac portion was measured by thermogravimetric analysis (TGA). The solid content of the dragline fibers leaving the spinneret was investigated by calculating the ratio of collected dried silk to the weight loss of the spider recorded in situ upon spinning. As the results indicate, the tensile strength and diameter of the spun dragline fibers were 800⁻1100 MPa and 8⁻11 µm, respectively. The liquid content of silk stored in the major ampullate sac (50.0 wt%) was significantly lower than that of silk leaving the spinnerets (80.9⁻96.1 wt%), indicating that a liquid supplying mechanism might be involved during the spinning process. This reveals, for the first time, quantitative evidence in support of the lubricative hypothesis proposed formerly, namely that a liquid coating layer is supplemented to compensate for silking resistance during the spinning process of a spider. The spigot, at the exit of the spinneret, is speculated to serve as a valve-like controller that regulates the lubrication process along with fiber formation. Taken together, these findings provide understanding of the physiological functions in the spider spinning process and could further shed some light on the future biomimetic development of silk material fabrication.

Parametric Studies of Titania-Supported Gold-Catalyzed Oxidation of Carbon Monoxide.

This paper remarks the general correlations of the shape and crystallinity of titanium dioxide (TiO2) support on gold deposition and carbon monoxide (CO) oxidation. It was found that due to the larger rutile TiO2 particles and thus the pore volume, the deposited gold particles tended to agglomerate, resulting in smaller catalyst surface area and limited gold loading, whilst anatase TiO2 enabled better gold deposition. Those properties directly related to gold particle size and thus the number of low coordinated atoms play dominant roles in enhancing CO oxidation activity. Gold deposited on anatase spheroidal TiO2 at photo-deposition wavelength of 410 nm for 5 min resulted in the highest CO oxidation activity of 0.0617 mmol CO/s.gAu (89.5% conversion) due to the comparatively highest catalyst surface area (114.4 m²/g), smallest gold particle size (2.8 nm), highest gold loading (7.2%), and highest Au° content (68 mg/g catalyst). CO oxidation activity was also found to be directly proportional to the Au° content. Based on diffuse reflectance infrared Fourier transform spectroscopy, we postulate that anatase TiO2-supported Au undergoes rapid direct oxidation whilst CO oxidation on rutile TiO2-supported Au could be inhibited by co-adsorption of oxygen.

Crystallized nano-sized alpha-tricalcium phosphate from amorphous calcium phosphate: microstructure, cementation and cell response.

New insight on the conversion of amorphous calcium phosphate (ACP) to nano-sized alpha tricalcium phosphate (α-TCP) provides a faster pathway to calcium phosphate bone cements. In this work, synthesized ACP powders were treated with either water or ethanol, dried, crystallized between 700 and 800 °C, and then cooled at different cooling rates. Particle size was measured in a scanning electron microscope, but crystallite size calculated by Rietveld analysis. Phase composition and bonding in the crystallized powder was assessed by x-ray diffraction and Fourier-transform infrared spectroscopy. Results showed that 50 nm sized α-TCP formed after crystallization of lyophilized powders. Water treated ACP retained an unstable state that may allow ordering to nanoapatite, and further transition to ß-TCP after crystallization and subsequent decomposition. Powders treated with ethanol, favoured the formation of pure α-TCP. Faster cooling limited the growth of ß-TCP. Both the initial contact with water and the cooling rate after crystallization dictated ß-TCP formation. Nano-sized α-TCP reacted faster with water to an apatite bone cement than conventionally prepared α-TCP. Water treated and freeze-dried powders showed faster apatite cement formation compared to ethanol treated powders. Good biocompatibility was found in pure α-TCP nanoparticles made from ethanol treatment and with a larger crystallite size. This is the first report of pure α-TCP nanoparticles with a reactivity that has not required additional milling to cause cementation.