Chemically vs Enzymatically Synthesized Polyglycerol-Based Esters: A Comparison between Their Surfactancy.

Polyglycerol fatty acid esters (PGFAEs) are gaining interest in several industrial sectors due to their excellent surfactant properties and their wide range of hydrophilic-lipophilic balance (HLB) values. Moreover, they can be prepared from renewable resources, i.e., fatty acids and glycerol. In this study, polyglycerol-2 stearic acid esters (PG2SAEs) were synthesized by the enzymatic esterification of polyglycerol-2 (PG2) and stearic acid (SA) using the immobilized lipase Novozym 435 as a biocatalyst in a solvent-free system. Reaction conditions, i.e., temperature (80 °C), reactant ratio (1:1.8), and enzyme loading (2.7% w/w), were finely optimized; furthermore, biocatalyst recycling was studied by assessing the residual activity of the lipase after each reaction cycle, up to 20 times. The composition of the enzymatically synthesized products (E) was roughly evaluated by chromatographic methods and mass spectrometry and compared with that of the esters obtained by acid-catalyzed esterification (C). Then, the surfactant properties of the prepared polyglycerol-based surfactants were investigated by interfacial tension studies. Specifically, the emulsifying capacity and stability and the rheological behavior of O/W emulsions prepared in the presence of E were deeply investigated in comparison with those of the chemically synthesized and commercially available product C.

From Lactose to Alkyl Galactoside Fatty Acid Esters as Non-Ionic Biosurfactants: A Two-Step Enzymatic Approach to Cheese Whey Valorization.

A library of alkyl galactosides was synthesized to provide the "polar head" of sugar fatty acid esters to be tested as non-ionic surfactants. The enzymatic transglycosylation of lactose resulted in alkyl ß-D-galactopyranosides, whereas the Fischer glycosylation of galactose afforded isomeric mixtures of α- and ß-galactopyranosides and α- and ß-galactofuranosides. n-Butyl galactosides from either routes were enzymatically esterified with palmitic acid, used as the fatty acid "tail" of the surfactant, giving the corresponding n-butyl 6-O-palmitoyl-galactosides. Measurements of interfacial tension and emulsifying properties of n-butyl 6-O-palmitoyl-galactosides revealed that the esters of galactopyranosides are superior to those of galactofuranosides, and that the enantiopure n-butyl 6-O-palmitoyl-ß-D-galactoside, prepared by the fully enzymatic route, leads to the most stable emulsion. These results pave the way to the use of lactose-rich cheese whey as raw material for the obtainment of bio-based surfactants.

Acetone and Toluene Gas Sensing by WO3: Focusing on the Selectivity from First Principle Calculations.

Sensitivity and selectivity are the two major parameters that should be optimized in chemiresistive devices with boosted performances towards Volatile Organic Compounds (VOCs). Notwithstanding a plethora of metal oxides/VOCs combinations that have been investigated so far, a close inspection based on theoretical models to provide guidelines to enhance sensors features has been scarcely explored. In this work, we measured experimentally the sensor response of a WO3 chemiresistor towards gaseous acetone and toluene, observing a two orders of magnitude higher signal for the former. In order to gain insight on the observed selectivity, Density Functional Theory was then adopted to elucidate how acetone and toluene molecules adsorption may perturb the electronic structure of WO3 due to electrostatic interactions with the surface and hybridization with its electronic structure. The results of acetone adsorption suggest the activation of the carbonyl group for reactions, while an overall lower charge redistribution on the surface and the molecule was observed for toluene. This, combined with acetone's higher binding energy, justifies the difference in the final responses. Notably, the presence of surface oxygen vacancies, characterizing the nanostructure of the oxide, influences the sensing performances.

One-step, highly stable Pickering emulsions stabilized by ZnO: tuning emulsion stability by in situ functionalization.

HYPOTHESIS: Oxide-stabilized emulsions generally require a surface functionalization step to tune the oxide wettability, often involving hazardous hydrophobizing agents. Here, we propose the in situ functionalization of ZnO in vegetable oils without the addition of any modifier, resulting in the one-step formation of highly stable Pickering emulsions. EXPERIMENTS: The role of ZnO surface features was studied by modifying the particles' wettability through surface functionalization and by comparing different oil phases. The emulsion stability was assessed through aging tests, multiple hot-and-cold cycles, centrifugation, and addition of multiple electrolytes. FINDINGS: While the wetting features of the functionalized oxide play a crucial role when the oil phase is methyl octanoate, emulsions based on vegetable oils form also using hydrophilic ZnO. During the emulsification, an in situ functionalization of bare ZnO particles takes place due to the fatty acids present in vegetable oil. These in situ-generated systems lead to stable emulsions showing < 2 µm-diameter oil droplets. The resulting emulsions display excellent stability over time (over seven months) and against temperature variations, mechanical stress and increased ionic strength. Finally, we demonstrate that this approach can be extended to a variety of vegetable oils and oxides with different morphologies.

Calcitic-based stones protection by a low-fluorine modified methacrylic coating.

Atmospheric pollutants, such as NOx, SO2, and particulate matter, together with water percolation inside the stone pores, represent the main causes of cultural heritage decay. In order to avoid these undesired phenomena, the application of protective coatings represents a reliable solution. In this context, the present study focused on the synthesis of low-fluorine content methacrylic-based (MMA) polymeric resins characterized by seven F atoms (namely F7 monomer) in the lateral chains. Four different percentages (1.0, 2.5, 5.0, and 10.0%) of the present monomer were adopted to obtain a final polymeric structure showing the desired hydrophobicity, processability, and structural and thermal stability (even after accelerated UV aging tests). MMA_F7(1.0) seemed to be the optimal one; therefore, it was further applied onto Candoglia marble. Specifically, the treated substrates showed good surface hydrophobicity, water repellency, and water vapor transpirability. No color variation was observed even after a 1.5-year exposure in a real polluted environment (Monza Cathedral). Interestingly, the application of this coating hindered the atmospheric nitrates penetration inside the stones and, at the same time, it limited the sulfates (gypsum) formation, thus revealing a very promising marbles protection resin.

Design of New Polyacrylate Microcapsules to Modify the Water-Soluble Active Substances Release.

Despite the poor photochemical stability of capsules walls, polyacrylate is one of the most successful polymers for microencapsulation. To improve polyacrylate performance, the combined use of different acrylate-based polymers could be exploited. Herein butyl methacrylate (BUMA)-based lattices were obtained via free radical polymerization in water by adding (i) methacrylic acid (MA)/methyl methacrylate (MMA) and (ii) methacrylamide (MAC) respectively, as an aqueous phase in Pickering emulsions, thanks to both the excellent polymer shells' stability and the high encapsulation efficiency. A series of BUMA_MA_MMA terpolymers with complex macromolecular structures and BUMA_MAC linear copolymers were synthesized and used as dispersing media of an active material. Rate and yield of encapsulation, active substance adsorption onto the polymer wall, capsule morphology, shelf-life and controlled release were investigated. The effectiveness of the prepared BUMA-based microcapsules was demonstrated: BUMA-based terpolymers together with the modified ones (BUMA_MAC) led to slow (within ca. 60 h) and fast (in around 10 h) releasing microcapsules, respectively.

Stable Coloured Micrometric Films from Highly Concentrated Nano-Silver Sols: The Role of the Stabilizing Agents.

The synthesis of highly concentrated aqueous silver nanoparticles (NPs), exploiting different types of polymeric stabilizing agents, has been extensively investigated, especially for the stabilization of spherical yellow nanoparticles. In this context, here, a successful and easy wet chemical method was adopted to synthesize concentrated primary colored (yellow, red, blue and green) sols. The influence of polyvinylpyrrolidone (PVP) and polyvinyl alcohol (PVA) in affecting the final stability was finely investigating via UV/Vis spectroscopy, dynamic light scattering, TEM and colorimetric analysis. The next step consisted on the deposition of obtained sols onto a crown-treated polyethylene terephthalate (PET) support to obtain transparent colored micrometric homogeneous films. The fabricated PVP-based Ag films were revealed to be outstandingly UV-stable, contrarily to PVA-based films, probably due to the degradation of the polymer itself. Indeed, after UV aging tests, the PVA macromolecules could be broken and chemically modified (demonstrated by FT-IR analyses). This resulted in there being insufficient macromolecules to efficiently cover the surface of the nanoparticles, meaning that the nanoparticles tended to aggregate with each other, destabilizing the system itself. Hence, the obtained colored films described herein could represent a promising tool for different applications, from color shifting to optoelectronic devices.

ORR in Non-Aqueous Solvent for Li-Air Batteries: The Influence of Doped MnO2-Nanoelectrocatalyst.

One of the major drawbacks in Lithium-air batteries is the sluggish kinetics of the oxygen reduction reaction (ORR). In this context, better performances can be achieved by adopting a suitable electrocatalyst, such as MnO2. Herein, we tried to design nano-MnO2 tuning the final ORR electroactivity by tailoring the doping agent (Co or Fe) and its content (2% or 5% molar ratios). Staircase-linear sweep voltammetries (S-LSV) were performed to investigate the nanopowders electrocatalytic behavior in organic solvent (propylene carbonate, PC and 0.15 M LiNO3 as electrolyte). Two percent Co-doped MnO2 revealed to be the best-performing sample in terms of ORR onset shift (of ~130 mV with respect to bare glassy carbon electrode), due to its great lattice defectivity and presence of the highly electroactive γ polymorph (by X-ray diffraction analyses, XRPD and infrared spectroscopy, FTIR). 5% Co together with 2% Fe could also be promising, since they exhibited fewer diffusive limitations, mainly due to their peculiar pore distribution (by Brunauer-Emmett-Teller, BET) that disfavored the cathode clogging. Particularly, a too-high Fe content led to iron segregation (by energy dispersive X-ray spectroscopy, EDX, X-ray photoelectron spectroscopy, XPS and FTIR) provoking a decrease of the electroactive sites, with negative consequences for the ORR.

Breakthroughs in the Design of Novel Carbon-Based Metal Oxides Nanocomposites for VOCs Gas Sensing.

Nowadays, the detection of volatile organic compounds (VOCs) at trace levels (down to ppb) is feasible by exploiting ultra-sensitive and highly selective chemoresistors, especially in the field of medical diagnosis. By coupling metal oxide semiconductors (MOS e.g., SnO2, ZnO, WO3, CuO, TiO2 and Fe2O3) with innovative carbon-based materials (graphene, graphene oxide, reduced graphene oxide, single-wall and multi-wall carbon nanotubes), outstanding performances in terms of sensitivity, selectivity, limits of detection, response and recovery times towards specific gaseous targets (such as ethanol, acetone, formaldehyde and aromatic compounds) can be easily achieved. Notably, carbonaceous species, highly interconnected to MOS nanoparticles, enhance the sensor responses by (i) increasing the surface area and the pore content, (ii) favoring the electron migration, the transfer efficiency (spillover effect) and gas diffusion rate, (iii) promoting the active sites concomitantly limiting the nanopowders agglomeration; and (iv) forming nano-heterojunctions. Herein, the aim of the present review is to highlight the above-mentioned hybrid features in order to engineer novel flexible, miniaturized and low working temperature sensors, able to detect specific VOC biomarkers of a human's disease.

Engineering of SnO2-Graphene Oxide Nanoheterojunctions for Selective Room-Temperature Chemical Sensing and Optoelectronic Devices.

The development of high-performing sensing materials, able to detect ppb-trace concentrations of volatile organic compounds (VOCs) at low temperatures, is required for the development of next-generation miniaturized wireless sensors. Here, we present the engineering of selective room-temperature (RT) chemical sensors, comprising highly porous tin dioxide (SnO2)-graphene oxide (GO) nanoheterojunction layouts. The optoelectronic and chemical properties of these highly porous (>90%) p-n heterojunctions were systematically investigated in terms of composition and morphologies. Optimized SnO2-GO layouts demonstrate significant potential as both visible-blind photodetectors and selective RT chemical sensors. Notably, a low GO content results in an excellent UV light responsivity (400 A W-1), with short rise and decay times, and RT high chemical sensitivity with selective detection of VOCs such as ethanol down to 100 ppb. In contrast, a high concentration of GO drastically decreases the RT response to ethanol and results in good selectivity to ethylbenzene. The feasibility of tuning the chemical selectivity of sensor response by engineering the relative amount of GO and SnO2 is a promising feature that may guide the future development of miniaturized solid-state gas sensors. Furthermore, the excellent optoelectronic properties of these SnO2-GO nanoheterojunctions may find applications in various other areas such as optoelectronic devices and (photo)electrocatalysis.

Exploring SnxTi1-xO2 Solid Solutions Grown onto Graphene Oxide (GO) as Selective Toluene Gas Sensors.

The major drawback of oxide-based sensors is the lack of selectivity. In this context, SnxTi1-xO2/graphene oxide (GO)-based materials were synthesized via a simple hydrothermal route, varying the titanium content in the tin dioxide matrix. Then, toluene and acetone gas sensing performances of the as-prepared sensors were systematically investigated. Specifically, by using 32:1 SnO2/GO and 32:1 TiO2/GO, a greater selectivity towards acetone analyte, also at room temperature, was obtained even at ppb level. However, solid solutions possessing a higher content of tin relative to titanium (as 32:1 Sn0.55Ti0.45O2/GO) exhibited higher selectivity towards bigger and non-polar molecules (such as toluene) at 350 °C, rather than acetone. A deep experimental investigation of structural (XRPD and Raman), morphological (SEM, TEM, BET surface area and pores volume) and surface (XPS analyses) properties allowed us to give a feasible explanation of the different selectivity. Moreover, by exploiting the UV light, the lowest operating temperature to obtain a significant and reliable signal was 250 °C, keeping the greater selectivity to the toluene analyte. Hence, the feasibility of tuning the chemical selectivity by engineering the relative amount of SnO2 and TiO2 is a promising feature that may guide the future development of miniaturized chemoresistors.

Room-temperature photodetectors and VOC sensors based on graphene oxide-ZnO nano-heterojunctions.

The rapid development of smart wearable electronics is driving the engineering of novel miniaturized sensing materials that can rapidly respond to very small changes in the concentration of biomarkers at room temperature. Carbon-based nanomaterials offer numerous attractive properties such as low resistivity, good mechanical robustness and integration potential, but lack a strong detection and transduction mechanism for the measurement of chemical molecules or photons. Here, we present a three-dimensional nanostructured architecture comprising optimally integrated graphene oxide (GO)-ZnO heterojunctions for the room temperature sensing of volatile biomarkers. We show that this layout also provides excellent response to UV light showcasing its applicability as a visible-blind photodetector. Notably, the optimal integration of well-dispersed GO nanodomains in a 3D ZnO network significantly enhances the room-temperature chemical sensitivity and light responsivity, while higher GO contents drastically worsen the material performance. This is attributed to the different roles of GO at low and high contents. Small amounts of GO lead to the formation of electron depleted nano-heterojunctions with excellent electron-hole separation efficiency. In contrast, large amounts of GO form a percolating electrical network that inhibits the light and chemical-sensing properties of the ZnO nanoparticles. Our optimal GO-ZnO demonstrates 33 A W-1 responsivity to UV light as well as the room temperature detection of volatile organic compounds down to 100 ppb. We believe that these findings provide guidelines for the future engineering of hybrid carbon-metal oxide devices for applications extending from optoelectronics to chemical sensing and electrocatalysis.

Towards Novel Fluorinated Methacrylic Coatings for Cultural Heritage: A Combined Polymers and Surfaces Chemistry Study.

In this work, new co- and ter-polymers of methyl methacrylate (MMA), ethyl methacrylate (EMA), and N-butyl methacrylate (nBuMA), containing just 1% mol × mol-1 of a fluorinated co-monomer, 3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluoro-octyl methacrylate (POMA), were synthesized. After an UV accelerated aging test, the photo-chemical stability of the polymers prepared was determined by 1H NMR and FT-IR spectroscopy, size exclusion chromatography, differential scanning calorimetry and wettability measurements. The polymers were applied to Botticino tiles to achieve better performances in terms of water repellency and consequently deterioration resistance. One-year prolonged exposure to a real environment was conducted and the properties of the coated materials and their performances were studied using different surface techniques such as water contact angle (WCA) and colorimetric measurements (CIELaB), capillary absorption, permeability (RVP) tests and soluble salts determination. The effectiveness of the fluorinated methacrylic coatings was clearly demonstrated; among all the resins, the co-polymer MMA_POMA seems to be the most performing one. Furthermore, both the UV photo-chemical resistance and the easiness of removal was successfully studied.

Role of the growth step on the structural, optical and surface features of TiO2/SnO2 composites.

TiO2/SnO2 composites have attracted considerable attention for their application in photocatalysis, fuel cells and sensors. Structural, morphological, optical and surface features play a pivotal role in photoelectrochemical applications and are critically related to the synthetic route. Most of the reported synthetic procedures require high-temperature treatments in order to tailor the sample crystallinity, usually at the expense of surface hydroxylation and morphology. In this work, we investigate the role of a treatment in an autoclave at a low temperature (100°C) on the sample properties and photocatalytic performance. With respect to samples calcined at 400°C, the milder crystallization treatment promotes anatase phase, mesoporosity and water chemi/physisorption, while reducing the incorporation of heteroatoms within the TiO2 lattice. The role of Sn content was also investigated, showing a marked influence, especially on the structural properties. Notably, at a high content, Sn favours the formation of rutile TiO2 at very low reaction temperatures (100°C), thanks to the structural compatibility with cassiterite SnO2. Selected samples were tested towards the photocatalytic degradation of tetracycline in water under UV light. Overall, the low-temperature treatment enables to tune the TiO2 phase composition while maintaining its surface hydrophilicity and gives rise to well-dispersed SnO2 at the TiO2 surface.

Nano-MnO2 Decoration of TiO2 Microparticles to Promote Gaseous Ethanol Visible Photoremoval.

TiO2-based photocatalysis under visible light is an attractive way to abate air pollutants. Moreover, developing photocatalytic materials on a large-scale requires safe and low-cost precursors. Both high-performance TiO2 nanopowders and visible-light active noble metals do not match these requirements. Here, we report the design of novel Mn-decorated micrometric TiO2 particles. Pigmentary TiO2 replaced unsafe nano-TiO2 and firmly supported MnOx particles. Mn replaced noble metals such as Au or Ag, opening the way for the development of lower cost catalysts. Varying Mn loading or pH during the impregnation affected the final activity, thus giving important information to optimize the synthesis. Photocatalytic activity screening occurred on the gas-phase degradation of ethanol as a reference molecule, both under ultraviolet (UV) (6 h) and Light Emitting Diode (LED) (24 h) irradiation. Mn-doped TiO2 reached a maximum ethanol degradation of 35% under visible light after 24 h for the sample containing 20% of Mn. Also, we found that an acidic pH increased both ethanol degradation and mineralization to CO2, while an alkaline pH drastically slowed down the reaction. A strict correlation between photocatalytic results and physico-chemical characterizations of the synthesized powders were drawn.

A Nanostructured Matrices Assessment to Study Drug Distribution in Solid Tumor Tissues by Mass Spectrometry Imaging.

The imaging of drugs inside tissues is pivotal in oncology to assess whether a drug reaches all cells in an adequate enough concentration to eradicate the tumor. Matrix-Assisted Laser Desorption Ionization Mass Spectrometry Imaging (MALDI-MSI) is one of the most promising imaging techniques that enables the simultaneous visualization of multiple compounds inside tissues. The choice of a suitable matrix constitutes a critical aspect during the development of a MALDI-MSI protocol since the matrix ionization efficiency changes depending on the analyte structure and its physico-chemical properties. The objective of this study is the improvement of the MALDI-MSI technique in the field of pharmacology; developing specifically designed nanostructured surfaces that allow the imaging of different drugs with high sensitivity and reproducibility. Among several nanomaterials, we tested the behavior of gold and titanium nanoparticles, and halloysites and carbon nanotubes as possible matrices. All nanomaterials were firstly screened by co-spotting them with drugs on a MALDI plate, evaluating the drug signal intensity and the signal-to-noise ratio. The best performing matrices were tested on control tumor slices, and were spotted with drugs to check the ion suppression effect of the biological matrix. Finally; the best nanomaterials were employed in a preliminary drug distribution study inside tumors from treated mice.

Emerging pollutant mixture mineralization by TiO2 photocatalysts. The role of the water medium.

Pharmaceutics and personal care products (PPCPs) are raising growing concern due to their widespread usage and resistance to conventional remediation techniques. Several of them raise significant health and environmental concerns, especially when present in complex mixtures. Due to their chemical resistance, Advanced Oxidation Processes (AOPs) are needed for their complete removal from surface and wastewaters. In the present work, photocatalysis by titanium dioxide (TiO2) under UV and simulated solar irradiation was adopted to degrade tetracycline hydrochloride, paracetamol, caffeine and atenolol, both as single pollutants and in mixtures. All molecules showed high removal and mineralization degrees. Moreover, no interference effects decreased the efficiency of the processes in the case of pollutant mixtures, achieving 60% of mineralization after 6 h. An immobilized TiO2 system was also developed by depositing titania on titanium meshes. A 50% mineralization degree of the pollutant mixture was obtained after 6 h, revealing a suitable efficiency for field applications. Eventually, the impact of the matrix composition on the photocatalytic efficiency was investigated by studying the reaction both in simulated drinking water and in commercial bottled mineral water. The scavenger role played by HCO3- species appears to be dominant in inhibiting the mineralization.

Photo-renewable electroanalytical sensor for neurotransmitters detection in body fluid mimics.

A composite electrode with a sandwich structure combining the properties of silver nanoparticles and a titania photoactive layer was used for the electroanalytical detection, by differential pulse voltammetry, of three neurotransmitters: dopamine, norepinephrine, and serotonin. The three analytes were determined at low detection limits (around 0.03 µM) also in the presence of conventional interferents, such as uric and ascorbic acids. The fouling of the electrode surface was overcome by irradiating the device with UVA light, restoring the initial sensor sensitivity. Dopamine, norepinephrine, and serotonin were determined also in simulated biological matrices: liquor (artificially reproduced cerebrospinal fluid) and serum. Moreover, the contemporaneous detection of dopamine and norepinephrine in simulated human urine solutions was also demonstrated, representing the first step towards clinical applications of the proposed methodology. Graphical abstract The photo-renewable electroanalytical sensor.

The Influence of Carbonaceous Matrices and Electrocatalytic MnO2 Nanopowders on Lithium-Air Battery Performances.

Here, we report new gas diffusion electrodes (GDEs) prepared by mixing two different pore size carbonaceous matrices and pure and silver-doped manganese dioxide nanopowders, used as electrode supports and electrocatalytic materials, respectively. MnO2 nanoparticles are finely characterized in terms of structural (X-ray powder diffraction (XRPD), energy dispersive X-ray (EDX)), morphological (SEM, high-angle annular dark field (HAADF)-scanning transmission electron microscopy (STEM)/TEM), surface (Brunauer Emmet Teller (BET)-Barrett Joyner Halenda (BJH) method) and electrochemical properties. Two mesoporous carbons, showing diverse surface areas and pore volume distributions, have been employed. The GDE performances are evaluated by chronopotentiometric measurements to highlight the effects induced by the adopted materials. The best combination, hollow core mesoporous shell carbon (HCMSC) with 1.0% Ag-doped hydrothermal MnO2 (M_hydro_1.0%Ag) allows reaching very high specific capacity close to 1400 mAh·g-1. Considerably high charge retention through cycles is also observed, due to the presence of silver as a dopant for the electrocatalytic MnO2 nanoparticles.

Self-cleaning properties in engineered sensors for dopamine electroanalytical detection.

Fouling and passivation are the major drawbacks for a wide applicability of electroanalytical sensors based on nanomaterials, especially in biomedical and environmental fields. The production of highly engineered devices, designed ad hoc for specific applications, is the key factor in the direction of overcoming the problem and accessing effective sensors. Here, the fine-tuning of the system, composed of a highly ordered distribution of silver nanoparticles between a bottom silica and a top titania layer, confers multifunctional properties to the device for a biomedical complex challenge: dopamine detection. The crucial importance of each component towards a robust and efficient electroanalytical system is studied. The total recovery of the electrode performance after a simple UV-A cleaning step (self-cleaning), due to the photoactive interface and the aging resistance, is deeply investigated.