A series of flexible, lightweight, and highly conductive cellulose nanopapers were fabricated through in situ polymerization of aniline monomer on to cellulose nanofibers with a rationale for ...attenuating electromagnetic radiations within 8.2–12.4 GHz (X band). The demonstrated paper exhibits good conductivity due to the formation of a continuous coating of polyaniline (PANI) over the cellulose nanofibers (CNF) during in situ polymerization, which is evident from scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction analysis. The free hydroxyl groups on the surface of nanocellulose fibers promptly form intermolecular hydrogen bonding with PANI, which plays a vital role in shielding electromagnetic radiations and makes the cellulose nanopapers even more robust. These composite nanopapers exhibited an average shielding effectiveness of ca. −23 dB (>99% attenuation) at 8.2 GHz with 1 mm paper thickness. The fabricated papers exhibited an effective attenuation of electromagnetic waves by a predominant absorption mechanism (ca. 87%) rather than reflection (ca. 13%), which is highly desirable for the present-day telecommunication sector. Unlike metal-based shields, these demonstrated PANI/CNF papers have given a new platform for designing green microwave attenuators via an absorption mechanism. The prime novelty of the present study is that these robust PANI/CNF nanopapers have the ability to attenuate incoming microwave radiations to an extent that is 360% higher than the shielding effectiveness value reported in the previous literature. This makes them suitable for use in commercial electronic gadgets. This demonstrated work also opens up new avenues for using cellulose nanofibers as an effective substrate for fabricating conductive flexible papers using polyaniline. The direct current conductivity value of PANI/CNF nanopaper was 0.314 S/cm, which is one of the key requisites for the fabrication of efficient electromagnetic shields. Nevertheless, such nanopapers also open up an arena of applications such as electrodes for supercapacitors, separators for Li–S, Li–polymer batteries, and other freestanding flexible paper-based devices.
An array of highly conductive, lightweight and flexible cellulose nanopapers as effective attenuators of electromagnetic radiations within 8.2–12.4 GHz (X band) were formulated via in situ ...polymerization of pyrrole monomers on to cellulose nanofibers (CNFs). It is quite obvious that the free hydroxyl groups on the surface of CNFs facilitate the formation of intense intermolecular hydrogen bonding with PPy which is envisaged for its excellent electromagnetic shielding performance with an average shielding effectiveness of ca. –22 dB (>99% attenuation) at 8.2 GHz for a paper having 1 mm thickness. The fabricated papers displayed a predominant absorption mechanism (ca. 89%) rather than reflection (ca. 11%) for efficiently attenuating electromagnetic radiations, which has a considerable importance in the modern telecommunication sector. Thus, the designed PPy/CNF papers would replace the conventional metal‐based shields and pave way for the development of green microwave attenuators functioning via a strong absorption mechanism. The PPy/CNF nanopapers exhibited a DC conductivity of 0.21 S/cm, a prime requisite for the development of highly efficient electromagnetic shields. Undoubtedly, such nanopapers can be employed in wide range of applications such as electrodes for supercapacitors and other freestanding flexible paper‐based devices.
Heterogeneous catalysis for biodiesel production via esterification has emerged as a preferred route as it permits to overcome the disadvantages associated to homogeneous catalysis, which presents ...serious drawbacks that affect biodiesel production and increase its costs such as corrosivity, difficult removal, and non-reuse of the catalyst. This study evaluated the esterification of oleic acid (OA) using CoFe
2
O
4
and MnFe
2
O
4
ferrite magnetic nanoparticles (MNPs) coated with sulfonated lignin (SL). SL was synthesized from sugarcane bagasse lignin employing acetyl sulfate (sulfonating agent). Two different proportions of reactants were adopted, obtaining the solids SL5 and SL7.5—posteriorly incorporated into the MNPs. Reaction parameters evaluated were as follows: time (4 and 6 h) and temperature (80 and 100 °C), with other parameters fixed. The catalysts were characterized by XRD, BET method, SEM, TGA, and elemental analysis. The sulfonic group contents were determined by acid–base titration. The conversion of OA into methyl esters was determined by GC–MS and FTIR. Elemental analysis showed that SL5 and SL7.5 have 2.68% of sulfur content by mass and the following minimal molecular formulas C
9
H
10,52
O
5,62
(SO
3
H)
0,18
and C
9
H
10,52
O
5,62
(SO
3
H)
0,17
. XRD and TGA data evidenced that coated MNPs exhibit incorporation percentage of SL higher than 50%, with the best results for CoFe
2
O
4
-SL5 (79.5%) and CoFe
2
O
4
-SL7.5 (78.5%). GC–MS and FTIR data revealed that the highest OA conversions were achieved under 6 h and 100 °C. In addition, CoFe
2
O
4
-SL5 and MnFe
2
O
4
-SL7.5 exhibited the best catalytic performances in the esterification reactions with conversions of OA into fatty acid methyl esters of approximately 80%.
Graphical abstract
The antimicrobial and cytotoxic activities of the leaf or flower ethanol extracts from Senna and Cassia species.
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•Species belonging to the genera Senna or Cassia are widely used in ...Brazilian traditional medicine.•The antimicrobial and cytotoxic activities of the leaf or flower ethanol extracts from Senna and Cassia species were evaluated.•S. macranthera flower ethanol extract exerted significant antifungal activity that was correlated with a series of phenolic compounds.
In Brazilian traditional medicine, botanical species belonging to the genera Senna and Cassia are widely used as laxative, analgesic, and antifungal agents to treat ringworm and other fungal skin infections. This has motivated us to select and to screen ten species of these genera for their antibacterial, antifungal, and cytotoxic activities. The leaf or flower ethanol extracts were investigated against aerobic and anaerobic oral bacteria and Candida spp.; the microdilution broth method was employed. Cytotoxicity was determined against Vero cells. Among the plant extracts evaluated herein, four extracts at 200.0–400.0 μg mL–1 presented moderate activities against at least two bacterial strains. Concerning the antifungal action, the S. macranthera flower ethanol extract exerted significant antifungal effect with MIC values ranging from 5.9 to 23.4 μg mL–1. This extract was submitted to liquid-liquid extraction, and the resulting fractions were tested. The ethyl acetate fraction showed better antifungal activity (MIC values of 5.9 μg mL–1 for C. glabrata and 23.4 μg mL–1 for C. albicans and C. tropicalis) as compared with amphotericin B (0.1–0.2 μg mL–1), used as positive control. The bioactive metabolites of this fraction were identified by UHPLC–ESI/HRMS/MSn, which revealed the presence of eighteen compounds, including one organic acid (1), two flavan-3-ol (2 and 3), one flavone (4), two glycosylated flavonols (5 and 6), five proanthocyanidin dimers (7–11b), and seven proanthocyanidin trimers (12–18). The antimicrobial activities of some Senna or Cassia species studied here have been reported for the first time. The present results show that S. macranthera flowers are an interesting source of new antifungal agents.
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•Antioxidant activity of the extract and fractions from leaves of Cassia bakeriana.•Inhibition of α-amylase activity of the ethanolic extract.•Inhibition of glycation of the ...dichloromethane and ethyl acetate fractions.•Identification of compounds by liquid chromatography coupled to mass spectrometry.•Extracts and fractions showed low cytotoxicity against Vero cells.
The prevalence of diabetes has increased rapidly in the world. Chronic hyperglycemia is associated with the complications of diabetes and is a major problem for medicine. The present study aimed to explore the antidiabetic potential of the leaves of Cassia bakeriana Craib (family Leguminosae) by evaluating the antioxidant activity and inhibition of α-amylase, α-glucosidase, lipase and glycation activities, in addition to determining the chemical constituents of the most active fractions. Therefore, the n-hexane extract (HE) and the ethanolic extract (EE) of the leaves were prepared by maceration, and the fractions were obtained by liquid-liquid extraction. The EE of C. bakeriana and its fractions showed high antioxidant activity in the oxygen radical absorbance capacity (ORAC) assay, being superior to the positive control (ascorbic acid). In the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay, the n-butanol fraction (BF) and ethyl acetate fraction (EAF) presented the best results. The EE showed higher inhibition of α-amylase activity (IC50 = 5.00 ± 0.85 μg mL−1) followed by EAF and BF. DF was the most active in the inhibition of α-glucosidase activity (IC50 = 359.55 ± 2.90 μg mL−1). The HE showed high inhibition of pancreatic lipase activity (IC50 = 25.27 ± 8.78 μg mL−1) and dichloromethane fraction (DF) and EAF were the most active inhibitors of glycation (IC50 = 37.85 ± 0.49 and 53.25 ± 11.24 μg mL−1, respectively). The fractionation of DF by semi-preparative HPLC-DAD led to the isolation of flavonoids: kaempferol-3-O-rhamnoside (I) and kaempferol (II), which were characterized by NMR and HPLC-ESI-MS. These compounds showed antioxidant activity in the ORAC method, but only compound II was active in the DPPH method. The isolated kaempferol (II) showed inhibitory activity against α-amylase (IC50 = 1.5 ± 0.14 μg mL−1). The compounds I and II showed inhibition of glycation (IC50 = 84.27 ± 11.38 and 64.16 ± 1.53 μg mL−1, respectively). Through the HPLC-ESI-MS analysis of the EE, DF and EAF, it was possible to propose the identification of some compounds such as acid phenolics, flavonoids, megastigmane, fatty acids and derivatives, sphingolipids, proanthocyanidins, cyanidin and anthraquinone.
Spiders are part of the soil biodiversity, considered fundamental to the food chain hierarchy, directly and indirectly influencing several services in agricultural and forest ecosystems. The present ...study aimed to evaluate the biodiversity of soil spider families and identify which soil properties influence their presence, as well as proposing families as potential bioindicators. Native forest (NF) and reforested sites (RF) with Araucaria angustifolia (Bertol.) Kuntze were evaluated in three regions of the state São Paulo, both in the winter and summer. Fifteen soil samples were collected from each forest to evaluate the biological (spiders and microbiological), chemical and physical soil properties, in addition to properties of the litter (dry matter and C, N and S contents). For soil spiders, two sampling methods were used: pitfall traps and soil monoliths. In total, 591 individuals were collected, and distributed in 30 families, of which 306 individuals (22 families) came from pitfall traps and 285 individuals (26 families) from monoliths. Only samples obtained by the monolith method revealed seasonal differences in the mean density and richness of spiders between NF and RF. Canonical discriminant analysis showed the separation of these forests of Araucaria. Principal Component Analysis demonstrated the correlation of a number of spider families with certain soil properties (organic carbon, basal respiration, metabolic quotient, litter carbon, total porosity, bulk density and soil moisture). We identified 10 families (Anapidae, Corinnidae, Dipluridae, Hahniidae, Linyphiidae, Lycosidae, Nemesiidae, Palpimanidae, Salticidae, Scytodidae) that contributed most to separating native forest from the replanted forest, indicating the possibility of the spiders being used as bioindicators.
•Cellulose nanocrystals (CNs) with different polymorphs (I and II) were obtained.•CNs with different sizes and shapes (cilindrical and circular) were obtained.•CNs composed of cellulose II had lower ...DP values than CNs composed of cellulose I.•CNs extracted using H2SO4 were less thermally stable than those extracted using HCl.•The type of polymorph and acid employed affected the thermal degradation kinetics.
Cellulose nanocrystals (CNs) were extracted from different sources by acid hydrolysis using H2SO4 and HCl. The thermal decomposition of resulting CNs was studied by thermogravimetric analysis (TGA). The kinetic parameters were determined using the Flynn–Wall–Ozawa (FWO) and Kissinger methods. CNs were also characterized by X-ray diffraction (XRD), Atomic Force Microscopy (AFM), elemental analysis (EA), Zeta Potential (ZP) and degree of polymerization (DP). The results of the XRD analysis showed different profiles, making it possible to differentiate cellulose I from cellulose II. The results obtained by the FWO method showed that cellulose II CNs had an increased activation energy (Ea) with conversion (α), while in CNs of cellulose I the Ea remained constant or decreased slightly. This difference between Ea values for the thermal decomposition of CNs was mainly attributed to different crystalline arrangements of cellulose I and cellulose II, and to the type of acid employed.
In this work, three composites with different contents (5, 10, and 15% w/w) of kraft pulp fibre were produced as reinforcing elements for natural latex matrix and the mechanical properties were ...evaluated. In order to improve the interfacial adhesion between the matrix and the reinforcing element, chemical modifications were carried out on the surface of the fibres using octanoyl and benzoyl chlorides as modifying agents. The extension of chemical modification of the fibres was visualized by the presence of absorption bands in the spectroscopy analyzes of the modified fibre in relation to the crude fibre (ester carbonyl 1700–1740 cm
−1
); in addition, the hydroxyl band was preserved, which indicates a modification of surface character. The modified fibres became more hydrophobic due to the decrease in surface energy and the change in the dispersive and polar components. An increase in the storage modulus was observed for the composites with surface-modified fibres, which agrees with the improved dispersion between the surface-modified fibres and the matrix verified by means of scanning electron microscopy images. The incorporation of fibres did not cause changes in the thermal properties of the composites.
•Biodiesel from sunflower oil was successfully purified with natural adsorbents.•Starch from different sources and cellulose fibers were used as adsorbents.•Dry washing has removed more impurities ...than the wet washing.•Was reduced the acidity index, alkalinity, free glycerine and turbidity of biodiesel.
This work describes a study of the purification of biodiesel produced from sunflower oil by dry cold washing using natural adsorbents as cellulose and starch from different sources (corn, potato, cassava and rice), and the comparison with dry cold washing with a commercial adsorbent Select 450® and with the conventional wet washing with hot water. The purification by dry washing was carried out by varying the amount of adsorbents in 1%, 2%, 5% and 10% (w/v) at 25°C for 10min. For the purification by wet washing, the biodiesel was successively washed with acidified water and pure water at 85°C until neutralisation. The efficiency of the processes for the removal of biodiesel impurities was evaluated by determining the acidity index, combined alkalinity, free glycerine and turbidity of the biodiesel. All adsorbents studied presented good efficiency in the removal of the impurities and showed similar behaviour independent of the kind or amount of adsorbent employed. The use of natural adsorbents for the purification of biodiesel have been shown to be a promissory process to be applied as an industrial stage of the purification of biodiesel during their production.
The work presented here aims to study and compare the performance of a polyvinylidene fluoride (PVDF) electrospun membrane, unmodified cellulose nanofiber (CNF) based PVDF membrane, and Meldrum’s ...acid (2,2-dimethyl-1,3-dioxane-4,6-dione) modified CNF-based PVDF membranes against the Fe2O3 nanoparticle filtration and crystal violet (CV) dye adsorption. Herein, we introduced a facile method to produce a unique green adsorbent material from cellulose nanofibers (CNFs) via a nonsolvent assisted procedure using Meldrum’s acid as an esterification agent to enhance the adsorption toward positively charged crystal violet dyes. Most of the surface modifications of cellulose nanofibers have been done using toxic organic solvents like pyridine, dimethyl acetate, (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO), etc. So far, this is the first report on the surface modification of cellulose nanofibers via a nonsolvent assisted procedure. Both CNF-based PVDF membranes were prepared by successive coating of modified and unmodified CNFs on to the surface of a PVDF electrospun membrane. All the demonstrated membranes showed high filtration capacity against the Fe2O3 nanoparticles. With the 10 mg/L of crystal violet (CV) aqueous solution, CV adsorption of PVDF electrospun membrane, and unmodified CNF-based PVDF membrane was around 1.368 and 2.948 mg/g of the membrane respectively, whereas it was 3.984 mg/g of the membrane by Meldrum’s acid CNF-based PVDF membrane. The demonstrated Meldrum’s acid modified CNF-based PVDF membrane was proven to be the efficient media that can concurrently eliminate the Fe2O3 nanoparticles and CV dyes from the water. The investigation into the surface chemistries of cellulose nanofibers beyond the adoption of toxic solvents can enhance the economic usefulness of the process and also yield a new ecofriendly adsorbent material that is agreeable to adsorbing various toxic pollutants.
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