Biochar from olive tree twigs and spent malt rootlets as electrodes in Zn-air batteries.

Biochars, i.e. porous carbons obtained by pyrolysis of biomass, can act as electrocatalysts for oxygen evolution and oxygen reduction reaction. In the present work, two biochars have been prepared by using materials of completely different biomass origin: olive-tree twigs and spent malt rootlets (brewery wastes). Both biomass species were subjected to pyrolysis under limited oxygen supply and then they were activated by mixing with KOH and pyrolysis again. The obtained biochars were characterized by several techniques in order to determine their structural characteristics and the composition of their active components. Despite their different origin, the two biochars demonstrated similar structural and compositional characteristics thus highlighting the importance of the pyrolysis and activation procedure. Both biochars were used as electrocatalysts in the operation of rechargeable Zn-air batteries, where they also demonstrated similar electrocatalytic capacities with only a small advantage gained by olive-tree-twigs biochar. Compared to bare nanoparticulate carbon (carbon black), both biochars demonstrated a marked advantage towards oxygen evolution reaction.

Two-Birds-with-One-Stone Synthesis of Hydrophilic and Hydrophobic Fluorescent Carbon Nanodots from Dunaliella salina Biomass as 4-Nitrophenol Nanoprobes Based on Inner Filter Effect and First Derivative Redshift of Emission Band.

4-Nitrophenol (4-NP) has been listed as a priority pollutant and has also been reported as a human urinary metabolite used as a marker to evaluate exposure to certain pesticides. In the work herein, a solvothermal approach is applied to the one-pot synthesis of both hydrophilic and hydrophobic fluorescent carbon nanodots (CNDs), utilizing the halophilic microalgae Dunaliella salina as a biomass precursor. Both kinds of the produced CNDs showed appreciable optical properties and quantum yields, good photostability and they were capable of probing 4-NP by quenching their fluorescence through the inner filter effect. Interestingly, a prominent 4-NP concentration-dependent redshift of the corresponding emission band of the hydrophilic CNDs was noticed, which was further exploited, for the first time, as an analytical platform. Capitalizing on these properties, analytical methods were developed and applied to a variety of matrixes, such as tap water, treated municipal wastewater and human urine. The method based on the hydrophilic CNDs (λex/λem: 330/420 nm) was linear in the range of 0.80-45.0 µM and showed acceptable recoveries (from 102.2 to 113.7%) with relative standard deviations of 2.1% (intra-day) and 2.8% (inter-day) for the quenching-based detection mode and 2.9% (intra-day) and 3.5% (inter-day) for the redshift one. The method based on the hydrophobic CNDs (λex/λem: 380/465 nm) was linear in the range of 1.4-23.0 µM, with recoveries laying within the range of 98.2-104.5% and relative standard deviations of 3.3% and 4.0% for intra-day and inter-day assays, respectively.

Construction of Pd-Co-Doped CdS Heterojunctions as Efficient Platforms in Photocatalysis.

In this work, we present the structural, optical and photocatalytic properties of CdS semiconducting nanostructures, doped with palladium- and cobalt-based species. XRD analysis, corroborated by Raman and XPS, demonstrated the growth of CdS crystallites in the hexagonal structure, whereas solvothermal conversion of neat precursor metal salts resulted in the formation of metallic Pd and cobalt oxide, respectively. Scanning electron microscopy imaging certified the dendritic structure of hybrids, especially in the case where CdS was grown in the presence of either palladium- or cobalt-based nanoparticles. XPS surface analysis revealed that a major fraction of metallic Pd nanoparticles was converted to PdO during the in situ growth of CdS nanoparticles. The oxidation of Pd nanoparticles could be ascribed to chemisorption of oxygen phases onto the metal surface. The presence of cocatalyst nanoparticles resulted in an appreciable shift of the absorption edge of the ternary hybrids by about 50 nm. The optimized hybrid was found to photodegrade Orange G dye almost quantitatively within 2 h, by simulated solar light irradiation. Scavenging experiments revealed that hydroxy radicals were the main transient intermediate, leading to the oxidative degradation of the dye.

Highly Efficient Simulated Solar Light-Driven Photocatalytic Degradation of 4-Nitrophenol over CdS/Carbon/MoSx Hybrids.

Among the various organic pollutants and industrial chemicals, 4-nitrophenol has been one of the most monitored substances in aqueous environments, due to its enhanced solubility in such systems. This research reports for the first time the microwave-assisted synthesis of CdS/carbon/MoSx hybrids and the subsequent utilization of such systems as photocatalysts for 4-nitrophenol degradation. The hybrids demonstrated a variable photocatalytic activity, by using a variety of organic substances as precursors for the solvothermal carbonization step. By using ascorbic acid as precursor, the corresponding ternary composite exhibited excellent photocatalytic activity, with the 4-nitrophenol concentration been almost quantitatively decayed within 45 min of irradiation. This could be ascribed due to the generation of a high population of heterojunctions as well as the chemical speciation of Mo-based nanostructures. Such ternary hybrids may be utilized as potential photocatalytic systems in processes, where removal of toxic water-soluble substances is the key issue.

Rapid Microwave-Assisted Synthesis of CdS/Graphene/MoSx Tunable Heterojunctions and Their Application in Photocatalysis.

Nanoscale two-dimensional nanostructures have shown great potential as functional components in photocatalysis. Here, investigations on the synthesis of heterostructured hybrids, comprised of 0D CdS nanoparticles as semiconductor and 2D/2D graphene/MoSx as co-catalyst, are reported. The approach involves a rapid microwave-assisted reaction in autoclave conditions, by adopting either a one-step or a two-step protocol. The chemical speciation of the nanocomposites was found to depend strongly on the compounding conditions of the precursor substances. The photocatalytic activity was assessed by monitoring the photodegradation rate of 4-nitrophenol in solution using simulated solar light irradiation. The photocatalytic activity of the hybrids may be attributed to a combination of beneficial characteristics, strongly related to the chemical speciation of the composite components. Moreover, intimate contacts of the latter result in efficient heterojunctions. Overall, the present study provides valuable insight into the development of functional heterostructured photocatalysts comprised of two-dimensional nanomaterials.

Highly fluorescent N-doped carbon nanodots as an effective multi-probe quenching system for the determination of nitrite, nitrate and ferric ions in food matrices.

Tris-(hydroxymethyl)-aminomethane and urea were used as low-cost precursor compounds to synthesize highly fluorescent N-doped carbon nanodots (CNDs), in an environmentally-friendly, inexpensive process. The as-prepared CNDs exhibit blue fluorescence, excellent photostability under various conditions, water dispersibility and stability over several parameters, such as a wide range of pH. The N-doped CNDs were applied as a multi-probe fluorescence quenching system to the sensitive detection of nitrite (NO2-), nitrate (NO3-) and ferric (Fe3+) ions in food matrices. The recoveries from spiked food samples were fairly acceptable without significant interferences despite the complexity of the tested matrices. The decrease in fluorescence intensity is in linear relationship with the concentrations of NO2-, NO3- and Fe3+, in the ranges of 0.015-1.11 mM, 0.072-0.60 mM and 2.9-176 µΜ, respectively. The as-synthesized carbon dots were used for the detection of NO2-, NO3- and Fe3+ in food matrices after proper pretreatment, concluding that the multi-probe fluorescence system may potentially be implemented in food control. The FRET mechanism is able to describe the quenching of the CNDs-NO2- system, while the proportional temperature-dependent relationship with the slopes of calibration plots hint at a dynamic quenching mechanism. In the case of the CNDs-Fe3+ system, the slopes exhibit an inverse temperature dependence, indicating a static mechanism while there is no indication of a FRET mechanism.

Graphene: A new activator of sodium persulfate for the advanced oxidation of parabens in water.

Graphene was successfully employed as a catalyst for the activation of sodium persulfate, towards the effective degradation of propylparaben, an emerging micro-pollutant, representative of the parabens family. A novel process is proposed which utilizes a commercial graphene nano-powder as the catalyst and sodium persulfate as the oxidizing agent. It was found that over 95% of micro-pollutant degradation occurs within 15 min of reaction time. The effects of catalyst loading (75 mg/L to 1 g/L), sodium persulfate (SPS) concentration (10 mg/L to 1 g/L), initial solution pH (3-9) and initial paraben concentration (0.5 mg/L to 5 mg/L) were examined. Experiments were carried out in different aqueous conditions, including ultrapure water, bottled water and wastewater in order to investigate their effect on the degradation rate. The efficiency of the process was lower at complex water matrices signifying the role of organic matter as scavenger of the oxidant species. The role of radical scavengers was also investigated through the addition of methanol and tert-butanol in several concentrations, which was found to be important only in relatively high values. An experiment in which propylparaben was substituted by methylparaben was conducted and similar results were obtained. The consumption of SPS was found to be high in all pH conditions tested, surpassing 80% in near neutral environment. However, the results indicate that the sulfate radicals formed react with water in alkaline conditions, which are the optimal for the reaction, producing hydroxyl radicals which appear to be the dominant species leading to the rapid degradation of propylparaben. To the best of our knowledge, this is the first time pristine graphene has been implemented as an activator of sodium persulfate for the effective oxidation of micro-pollutants.

Two of a kind but different: Luminescent carbon quantum dots from Citrus peels for iron and tartrazine sensing and cell imaging.

Citrus sinensis and Citrus limon peels were used to synthesize two different kinds of carbon quantum dots (CQDs) via an unsophisticated and inexpensive carbonization procedure. The proposed synthesis is straightforward and adheres to the principles of green chemistry since no organic solvents are used and no toxic by-products are formed, while the residual resources employed facilitate the large scale synthesis of dots. The Citrus sinensis and Citrus limon peels are proved to be excellent precursors for the synthesis of CQDs with highly practical applications. The CQDs display strong excitation-independent, blue fluorescence, which is stable over time. Splendid water dispersibility, photostability and stability over a wide range of pH are some of the main advantages of the CQDs, which enable them to be used as a fluorescent probes. Although many of their features are alike, our findings demonstrate that each kind of the CQDs lend itself to quite distinct analytical applications. The developed fluorescent probes possess high potential for sensitive and selective detection of Fe3+ (Citrus sinensis CQDs) and tartrazine (Citrus limon CQDs) via a quenching mechanism. The decrease in fluorescence intensity is in linear relationship with the concentrations of Fe3+ and tartrazine in the ranges of 0.01-1.0µM and 0.6-23.5µΜ, respectively. Moreover, their low cytotoxicity reinforces their applicability towards cell bioimaging and intracellular detection of Fe3+, which were further studied.

Evaluation of mesoporous carbon aerogels as carriers of the non-steroidal anti-inflammatory drug ibuprofen.

Towards the development of novel drug carriers for oral delivery of poorly soluble drugs mesoporous aerogel carbons (CAs), namely CA10 and CA20 with different pore sizes (10 and 20nm, respectively), were evaluated. The non-steroidal anti-inflammatory lipophilic compound ibuprofen was incorporated via passive loading. The drug loaded carbon aerogels were systemically investigated by means of High-Resolution Transmission Electron Microscopy (HR-TEM), Nitrogen physisorption studies, X-ray diffraction (XRD), Differential Scanning Calorimetry (DSC), X-ray photon electron spectroscopy (XPS) and ζ-potential studies. In vitro release studies were performed in simulated intestinal fluids reflecting both fasted (FaSSIF) and fed (FeSSIF) state conditions. Cytotoxicity studies were conducted with human intestinal cells (Caco-2). Drug was in an amorphous state in the pores of the carbon carrier as shown from the physicochemical characterization studies. The results showed marked differences in the release profiles for ibuprofen from the two aerogels in the media tested whereas in vitro toxicity profiles appear to be compatible with potential therapeutic applications at low concentrations.

PLGA/DPPC/trimethylchitosan spray-dried microparticles for the nasal delivery of ropinirole hydrochloride: in vitro, ex vivo and cytocompatibility assessment.

In the present study we investigated polymer-lipid microparticles loaded with ropinirole hydrochloride (RH) for nasal delivery. RH microparticles were further evaluated by means of scanning electron microscopy (SEM), ζ-potential measurements, Fourier-transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and x-ray diffraction (XRD). In vitro release studies were performed in simulated nasal electrolyte solution (SNES) pH5.5 at 35°C. Ex vivo permeation studies were conducted across sheep nasal mucosa. Cytocompatibility was tested in cultured human airway epithelial cells (Calu-3). SEM studies revealed spheroid microparticles in the range of 2.09µm to 2.41µm. The presence of trimethylchitosan (TMC) induced a slight shift towards less negative ζ-potential values. Surface chemistry (XPS) revealed the presence of dipalmitoylphospatidylcholine (DPPC) and poly(lactic-co-glycolic acid) (PLGA) onto microparticles' surface, further corroborating the FT-IR and XRD findings. In vitro release studies showed that the microparticle composition can partly modulate the release of RH. Ex vivo studies demonstrated a 2.35-folded enhancement of RH permeation when RH was co-formulated with TMC of low molecular weight, compared to the control. All formulations tested were found to be non-toxic to cells. The results suggest that polymer-lipid microparticles may be a promising carrier for the nasal delivery of RH.

Facile, substrate-scale growth of mono- and few-layer homogeneous MoS2 films on Mo foils with enhanced catalytic activity as counter electrodes in DSSCs.

The growth of MoS2 films by sulfurization of Mo foils at atmospheric pressure is reported. The growth procedure provides, in a controlled way, mono- and few-layer thick MoS2 films with substrate-scale uniformity across square-centimeter area on commercial foils without any pre- or post-treatment. The prepared few-layer MoS2 films are investigated as counter electrodes for dye-sensitized solar cells (DSSCs) by assessing their ability to catalyse the reduction of I3(-) to I(-) in triiodide redox shuttles. The dependence of the MoS2 catalytic activity on the number of monolayers is explored down to the bilayer thickness, showing performance similar to that of, and stability against corrosion better than, Pt-based nanostructured film. The DSSC with the MoS2-Mo counter electrode yields a photovoltaic energy conversion efficiency of 8.4%, very close to that of the Pt-FTO-based DSSC, i.e. 8.7%. The current results disclose a facile, cost-effective and green method for the fabrication of mechanically robust and chemically stable, few-layer MoS2 on flexible Mo substrates and further demonstrate that efficient counter electrodes for DSSCs can be prepared at thicknesses down to the 1-2 nm scale.

Controlled release of 5-fluorouracil from microporous zeolites.

Zeolite particles with different pore diameter and particle size were loaded with the model anticancer drug 5-fluorouracil. The loaded zeolites were characterized by means of SEM, XRD, DSC, XPS, N2 physisorption and FT-IR. Higher loading of 5-FU was observed for NaX-FAU than BEA. Release studies were carried out in HCl 0.1N. Release of 5-FU from NaX-FAU showed exponential-type behaviour with the drug fully released within 10 min. In the case of BEA, the kinetics of 5-FU shows a multi-step profile with prolonged release over time. Molecular dynamics simulations showed that diffusion of the drug molecule through the BEA framework is lower than for NaX-FAU due to increased van der Waals interaction between the drug and the framework. The effect of zeolitic particles on the viability of Caco-2 monolayers showed that the NaX-FAU particles cause a reduction of cell viability in a more pronounced way compared with the BEA particles. FROM THE CLINICAL EDITOR: This article describes zeolite-based nanoparticles in generating time-controlled release of 5-FU from zeolite preparations for anti-cancer therapy.

Sirolimus encapsulated liposomes for cancer therapy: physicochemical and mechanical characterization of sirolimus distribution within liposome bilayers.

Sirolimus has recently been introduced as a therapeutic agent for breast and prostate cancer. In the current study, conventional and Stealth liposomes were used as carriers for the encapsulation of sirolimus. The physicochemical characteristics of the sirolimus liposome nanoparticles were investigated including the particle size, zeta potential, stability and membrane integrity. In addition atomic force microscopy was used to study the morphology, surface roughness and mechanical properties such as elastic modulus deformation and deformation. Sirolimus encapsulation in Stealth liposomes showed a high degree of deformation and lower packing density especially for dipalmitoyl-phosphatidylcholine (DPPC) Stealth liposomes compared to unloaded. Similar results were obtained by differential scanning calorimetry (DSC) studies; sirolimus loaded liposomes were found to result in a distorted state of the bilayer. X-ray photon electron (XPS) analysis revealed a uniform distribution of sirolimus in multilamellar DPPC Stealth liposomes compared to a nonuniform, greater outer layer lamellar distribution in distearoylphosphatidylcholine (DSPC) Stealth liposomes.