1,721,045 research outputs found
MXene-Based Nanozymes: Current Challenges and Future Prospects
Full text linkMXene-based nanozymes (recently called MXenzymes) have emerged as promising candidates for environmental remediation, biomedical, (bio-)catalytic, and sensing technologies due to their surface tunability, tailored electronic properties, remarkable electrical conductivity, and high surface area. These materials offer significant advantages over traditional enzymes, such as enhanced stability, tunable catalytic activity, and multifunctionality. However, despite the increasing number of studies in this field, critical challenges remain, including the long-term stability, the lack of studies on structure-activity relationships to better understand the catalytic mechanisms, and the scalability required for real-world applications. This mini-review provides a comprehensive overview of the most recent advancements in MXenzymes, focusing on the types of MXenes used, the reported enzyme-like activity, and the role of the photothermal effects in enhancing their catalytic performance. Moreover, key limitations such as oxidation susceptibility, biocompatibility concerns, and the scarce in-depth mechanistic studies are critically examined. Lastly, the necessary steps to transition from proof-of-concept studies to real-world applications are discussed. By addressing the listed fundamental challenges, MXenzymes could represent a valuable and effective alternative to natural enzymes used in catalysis, medicine, and environmental science
Tailored MnO2 Nanorods as Highly Efficient Materials for Methyl Orange Adsorption/Degradation
No full textNowadays, organic dyes are used in various industries and so they are one of the main water pollutants with severe environmental impact1. Particularly, Methyl Orange (MO) is an azo-dye widely recognized as potential carcinogen1. Therefore, the treatment of wastewater, prior to disposal, is becoming more and more urgent2. Many technologies have been exploited to remove/degrade aqueous MO and among them, adsorption is one of the most effective methods2. In this context, we investigated the adsorption capacities of four different MnO2 nanopowders (prepared by tailoring the synthetic route), which showed very promising and novel results in terms of MO adsorption/degradation.
EXPERIMENTAL
Synthesis of MnO2 nanoparticles
We adopted a one-pot hydrothermal procedure already optimized in our laboratory3, by using stoichiometric MnSO4 ́H2O or MnCl2 ́4H2O as the salt precursors, and (NH4)2S2O8, KMnO4 or KBrO3 as the oxidizing agents. Samples were labeled as MX_Y according to either the salt precursor (X = S for MnSO4 ́H2O or Cl for MnCl2 ́4H2O) or the oxidant (Y = N for (NH4)2S2O8, K for KMnO4 or Br for KBrO3) used.
Sample characterizations
X-Ray Powder Diffraction (XRPD) analyses were performed on a Philips PW 3710 Bragg-Brentano goniometer, with graphite-monochromated Cu Kα radiation, between 20° and 90° (0.1° step). Transmission Electron Microscope (TEM) analyses were performed on LIBRA 200 EFTEM (Zeiss) instrument operated at 200 kV accelerating voltage. The BET surface area and total pore volume was determined by a multipoint BET-BJH method (Coulter SA3100 apparatus).
Methyl Orange removal tests
The MO adsorption/removal capability was achieved by mixing 150 mL of MO aqueous solution (100 mg L-1) and 75 mg of MnO2 nanopowders. All the experiments were carried out at spontaneous pH (~3), under vigorous stirring. The kinetics were monitored for 2 h by UV/Vis spectroscopy (MO peak at 465 nm, Shimadzu UV/Vis spectrophotometer UV-2600). The amount of MO adsorbed during time (qt, mg g-1) was calculated using the following equation: qt = V(c0 – ct) , where c0 and ct (in mg L-1) at the initial and certain time t, respectively; V (in L) is the volume of the solution and W (g) is the mass of the adsorbent used. Furthermore, to investigate the MO degradation mechanism, aliquots of MO eluate (after 2 h) were examined by using HPLC-MS technique (HPLC Agilent Technologies 1200 series instrument coupled with a Thermo Scientific LTQ Orbitrap XL analyzer), and the used powders were investigated by Fourier Transformed Infrared (FTIR) spectroscopy.
RESULTS AND DISCUSSION
By varying the starting salt precursors/oxidizing agents, we succeeded in tailoring MnO2 structural, morphological and surface features. Particularly, novel MnO nanorods (from manganese sulphate and potassium bromate, namely MS_Br, inset of Fig. 1) showed the highest MO adsorption efficiency, probably due to both i) its polymorphic composition, i.e. b-ramsdellite enhances the adsorption capability and ii) its highest percentage of pores with diameter under 20 nm, i.e. smaller pores promote the entrapment of the small MO molecules, avoiding any adsorption/desorption equilibria.
Moreover, by means of HPLC-MS and infrared spectroscopy analyses, we also observed the MO degradation by MS_Br. Thus, we hypothesized a novel pathway, based on: i) the loss of one/two methyl groups from the nitrogen atom; ii) the addition of –OH groups to the phenyl ring; iii) the cleavage of the azo-bond; and iv) the removal of the amine group from the p-sulfanilic acid (Fig. 1). No other species characterized by lower m/z values have been detected.
CONCLUSION
Herein, we successfully prepared tailor-made MnO2 nanorods with ad hoc physico-chemical features, to be applied as MO adsorbents. Due to its peculiar properties, novel MS_Br sample showed the most performing MO adsorption/degradation behaviour.
REFERENCES
1. T. Dang et. al, J. Phys. Chem. Solids 98, 50 (2016) 2. D. Zhao et. al, Procedia Environ. Sci. 18, 890 (2013) 3. E. Pargoletti et. al, J. Power Sources 325, 116 (2016
Chemoenzymatic Synthesis of Alkyl Glycoside Fatty Acid Esters and Investigation of their Emulsifying Properties
No full textSugar fatty acid esters (SFAEs) are non-ionic surfactants that are characterized by excellent surface and interfacial tension reduction capability, low toxicity, and biodegradability. These features make SFAEs extremely promising for industrial applications as emulsifiers in the cosmetic and food sectors.[1] Interestingly, SFAEs can be obtained from renewable resources (from industrial waste and biomass) by enzymatic and/or chemoenzymatic approaches, thus answering the need for evermore sustainable and circular chemistry.[2,3]
6-O-Lauroyl-, 6-O-palmitoyl- and 6-O-stearoyl-1-O-butyl glucopyranosides were enzymatically synthesized by reacting n-butyl glucoside with molten fatty acids in an easily scalable solvent-free system. Derivatization of glucose as an alkyl glucoside before the esterification reaction played a key role to circumvent the striking different solubility of glucose and fatty acids. The physico-chemical properties of these tensides, such as interfacial tension features, W/O emulsification capability and W/O stability over time were deeply investigated.[4]
References
1. N.S. Neta, J.A. Teixeira, L.R. Rodrigues, Crit. Rev. Food Sci. Nutr. 2015, 5, 595.
2. A.R. Alcántara, P. Domínguez de María, J.A. Littlechild, M. Schürmann, R.A. Sheldon, R. Wohlgemuth, ChemSusChem 2022, e202102709.
3. T. Keijer, Nat. Chem. 2019, 11, 190.
4. S. Sangiorgio, E. Pargoletti, M. Rabuffetti, M.S. Robescu, R. Semproli, D. Ubiali, G. Cappelletti, G. Speranza, under review
This work was financially supported by Cariplo Foundation (Italy) (call: “Circular Economy for a sustainable future 2020”, project BioSurf, ID 2020-1094)
Tailored MnO2 Nanoparticles as Electrocatalysts for Metal-Air Batteries
Full text linkIn next-generation electronics, electrified transportation and energy storage, metal-air batteries represent one class of promising power sources thanks to their remarkably high theoretical energy and light weight [1]. The main feature of metal-air batteries is the combination of a metal anode with high energy density and an air electrode with open structure that facilitates the drawing of cathode active materials (i.e. oxygen) from air [1]. In these types of devices, Gas Diffusion Electrodes (GDEs) are widely used as cathodes [2]. However, one of the main drawbacks related to the cathodic reaction (ORR) is the overpotential loss (about 0.3-0.4 V) under operative conditions. Thus, lots of efforts were spent to inhibit the voltage loss requiring an effective ORR catalyst [1,3]. One of the most promising materials, in terms of both performances and costs, seems to be MnOx. According to the recent literature, MnO2 would ensure capacities comparable to those of platinum, letting higher capacity retention to be reached in non-aqueous electrolytes to prevent Li decomposition [1].
In the present work, the electrochemical performances of either bare or Fe/Co-doped MnO2 nano-electrocatalysts are evaluated by Linear Sweep Voltammetries (LSVs). The crystal structure and the surface properties are examined by means of XRPD, BET-BJH, TEM, SEM/EDX and XPS analyses. Correlations between their physico-chemical features and the final electrocatalytic performances are drawn. Experimental results reveal that the as-synthesized powders have excellent electrochemical properties in organic electrolytes (0.15 M LiNO3 in propylene carbonate, PC) showing a shift of the onset potential of about 150 mV with 2% Co-doped MnO2, thus resulting very promising candidates to be used in lithium-air batteries [4]
Low temperature/uv-assisted composites as gas sensors for medical applications
Full text linkThe sensing of gas molecules is of fundamental importance for environmental monitoring, control of chemical processes, medical applications, and so on [1]. Furthermore, recent success in non-invasive medical diagnostics, based on human breath analysis, is pushing forward the development of extremely sensitive gas sensors for ppb detection of specific analytes (e.g. acetone) in a complex gas mixture [1,2]. In recent years, graphene-based gas sensors have attracted much attention and different structures have been developed showing high sensing performances and room temperature working conditions [2]. However, they still suffer from several problems, which could be overcome by covering the graphene surface with metal oxide semiconductors. Furthermore, studies regarding the detection of Volatile Organic Compounds (VOCs) are still at the beginning [3].
Hence, the present work will be aimed at: i) optimizing the synthetic routes of ad hoc composite VOCs sensing materials (based on graphene oxide/SnO2 hybrids); ii) engineering the gas sensor device; and iii) evaluating the sensing performances at both high and mild temperatures (also exploiting the UV light) towards gaseous ethanol, acetone and ethylbenzene. Starting from pure graphite, graphene oxide (GO) powder was synthesized by adopting the Hummer’s modified method, in which the synthetic route was deeply investigated, and several parameters (such as H2O2 concentration) were modulated. Once optimized this step, SnO2 were grown on its surface by hydrothermal method, varying the starting salt precursor/GO weight ratio between 4 and 32. For comparison, pure commercial and home-made SnO2 were also tested. Several physico-chemical analyses were performed to characterize all the as-prepared nanopowders. Subsequently, a homogeneous film was deposited by spraying technique onto Pt-Interdigitated Electrodes (Pt-IDEs). Then, gaseous ethanol (Figure 1) and acetone were sensed, obtaining very promising results for both pure and hybrid materials at 350°C, and at lower temperatures (150°C to 30°C, by exploiting the UV light) for the graphene-based samples
The hydrophobicity modulation of glass and marble materials by different Si-based coatings
Full text linkHydrophobic polymers applied on hydroxylated surfaces increase their durability against undesired weathering processes. The achievement of a certain degree of surface hydrophobicity (reducing the water permeation) constitutes one of the main research focuses. Herein, two commercial Si-based resins (e.g. Alpha®SI30 and Bluesil®BP9710), directly applied on both glass and Carrara marble substrates, and a silanization process by using trichloromethylsilane (TCMS) were adopted. Contact angle measurements together with hysteresis determination and Surface Free Energy (SFE) were carried out to evaluate the hydrophobic features. Hence, since only in the case of TCMS a good hydrophobicity was achieved ( around 150°), two commercial polysiloxane-based additives (e.g. TegoPhobe 1500N and TegoPhobe 1650) were added respectively to Alpha®SI30 and Bluesil®BP9710, according to their chemical compatibility. These auxiliary substances allowed to decrease the wettability features of either glass or marble. Furthermore, since all the investigated coatings could be used as stone materials protective agents, water capillary absorption and vapor permeability tests were performed. Also in this case, TCMS revealed to be the most performing one among the adopted silane-based resins, thanks to the drastic reduction of absorbed water and the decrease of vapor permeability within the threshold value of 50%. Finally, the coatings stability was evaluated by accelerated ageing tests
A novel optimized mold release oil-in-water emulsion for polyurethane foams production
Full text linkRelease agents are compounds usually sprayed on the molds surface, forming a thin film that can act as a barrier preventing the sticking. Herein, both physical and chemical optimization of a wax-based O/W emulsion for polyurethane (PU) foams is reported. E_N1.8Cet1.2Ac2.5 sample (where N, Cet and Ac stand for the percentages of linear amine, cetyl alcohol and acetic acid), emulsified by the inversion point method, turned out to have the optimal composition, in terms of smaller oil droplets size (by Dynamic Light Scattering analysis and optical measurements), long-term stability (by Abbe refractometer and backscattering tests), good spreading (contact angle and surface tension measurements) and low corrosion phenomena (by potentiodynamic polarization tests, Scanning Electron Microscopy analysis). Principal Component Analysis helped to find the best correlations among all the investigated variables and to have some predictions on the role of the different raw materials in affecting the final stability of the emulsions
Bare and titanium-doped manganese dioxide nanoparticles : their pivotal role in energetic and sensoristic applications
No full textThe most prominent feature of metal-air batteries is the combination of a metal anode and an air electrode with open structure to draw cathode active materials from air. Oxygen reduction is the main cathodic process, but unfortunately it is affected by overpotential loss under operation conditions. Thus, an effective catalyst is required. Owing to their structural flexibility and versatility, manganese oxides have been widely applied in several research fields. Since MnO2 possesses quite a lot polymorphic phases, its controlled synthesis is pivotal. Hence, this Thesis work was focused on i) the hydrothermal synthesis of bare and novel Ti-doped MnO2 nanopowders, ii) their deep physico-chemical characterization and iii) their application as electrocatalysts for the Oxygen Reduction Reaction (ORR). In the synthetic route, the oxidizing agent was varied (i.e. (NH4)2S2O8 for samples labelled as MH_N and KMnO4 for MH_K ones) to study the correlation between the physico-chemical properties and the electrochemical performances of the nanopowders. Indeed, it has been possible to observe that both the oxidants cations and Ti-dopant ions play a pivotal role in modifying the nanopowders structural, morphological and surface properties. For the electrochemical tests, Linear Sweep Voltammetries (LSVs) have been carried out in KOH (-1.0 – 0.0 V vs SCE). Gas Diffusion Electrodes (GDEs), prepared by adding the synthesized uncalcined MnO2 to the air-cathode slurry, have performed explicitly better than GDEs made of only carbonaceous matrixes, proving synthesized MnO2 to be good electrocatalysts for the ORR (4). Furthermore, GDE(MH_K) seems to have less diffusive limitations probably due to the much higher O2 permeability, which is connected to the greater MH_K pore volume (confirmed by BET analyses). On the kinetic point of view (Tafel elaborations), high values of exchange current densities have been determined for GDEs with Ti-doped nanopowders. In particular, the presence of 5% Ti-doped MH_N has led to an increase of almost six orders of magnitude. Parallel to the above investigation, a preliminary forefront study about the use of MH_K sample (chosen for its highest BET surface area) for CHCl3 detection was developed. Thus, Glassy Carbon Electrodes (GCEs) were modified by drop casting of a suspension of the adopted MnO2 in DMF (20 μL, 0.5 g cm-3). Contrary to the response obtained with only GCE (no peaks evidence), the presence of MnO2 (at neutral pH) has caused the appearance of two peaks in the Cyclic Voltammetry (CV) anodic scan (ascribable to two characteristic reactions of MnO2) and a further broad peak in the cathodic scan (at -0.5 V vs SCE) that can be due to the reduction of O2. The presence of chloroform has led to a linear decreasing of the specific CV peaks currents, because of the adsorption of the pollutant molecules onto the electrode surface (indirect detection method).
In conclusion, the present Thesis work focused on the deep investigation of bare and Ti-doped MnO2 electrocatalytic nanoparticles showing novel and promising results
Photocatalytic removal of gaseous ethanol, acetaldehyde and acetic acid: from a fundamental approach to real cases
No full textThe photocatalytic oxidation of volatile organic compounds (VOCs) has been extensively investigated. With respect to water treatment, photocatalytic degradation of air pollutants is still less understood, but this has not prevented photocatalytic building materials and air purifiers to reach the market. Here, we provide a selective overview of the current understanding on VOC photocatalytic oxidation, focusing on ethanol, acetaldehyde, and acetic acid. Among the main indoor pollutants, these molecules are also oxidation intermediates of numerous VOCs. Their adsorption at the photocatalyst surface is first presented, based on theoretical and experimental evidence. Reaction intermediates are discussed, comparing proposed reaction mechanisms. The role of the photocatalyst features in directing adsorption and oxidation phenomena is highlighted, encompassing both TiO2 and emerging photocatalysts. We then critically discuss gaps in our knowledge, such as the effect of air humidity, multi-pollutant interactions and deactivation pathways. Finally, attempts to model VOC degradation in realistic conditions are reviewed
Low Temperature Composite Sensors for Environmental and Medical Applications
Full text linkThe sensing of gas molecules is of fundamental importance for environmental monitoring, control of chemical processes, medical applications, and so on [1]. In recent years, graphene-based gas sensors have attracted much attention due to enhanced graphene thermo-electric conductivity, surface area and mechanical strength. Thus, different structures have been developed and high sensing performances and room temperature working conditions were achieved [2]. However, they still suffer from several problems, which could be overcome by covering the graphene surface with metal oxide nanoparticles. Furthermore, studies regarding the detection of Volatile Organic Compounds (VOCs) are still at the beginning [3]. Hence, the present work will be aimed at: i) optimizing the synthetic routes of ad hoc composite VOCs sensing materials (based on graphene oxide/SnO2 or ZnO hybrids); ii) engineering the gas sensor device; and iii) evaluating the sensing performances at both high and mild temperatures (also exploiting the UV light) towards gaseous ethanol, acetone and ethylbenzene.
Starting from pure graphite, graphene oxide (GO) powder was synthesized by adopting the Hummer’s modified method. The synthetic route was deeply investigated by modulating both the starting carbon material (powder or flakes graphite) and the concentration of the H2O2 (i.e. the quenching/oxidizing agent), thus tailoring the final GO surface/structural properties. Once optimized this step, SnO2 or ZnO were grown on its surface by hydrothermal method, varying the starting salt precursor/GO weight ratio between 4 and 32. For comparison, pure SnO2 and ZnO (both commercial and home-made) were also tested. Several physico-chemical techniques have been used to characterize all the as-prepared nanopowders. Subsequently, a homogeneous layer was deposited by spraying technique onto Pt-Interdigitated Electrodes (Pt-IDEs) starting from an ethanol suspension of each sample (2.5 mg mL-1, Figure 1). Then, gaseous ethanol, acetone and ethylbenzene were sensed, obtaining very promising results (in terms of both response/recovery time and sensibility down to ppb levels) for either pure and hybrid materials at 350°C, and at lower temperatures (150°C to 30°C) for the graphene-based samples
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