Biotechnological Applications of Nanoencapsulated Essential Oils: A Review.

Essential oils (EOs) are complex mixtures of volatile and semi-volatile organic compounds that originate from different plant tissues, including flowers, buds, leaves and bark. According to their chemical composition, EOs have a characteristic aroma and present a wide spectrum of applications, namely in the food, agricultural, environmental, cosmetic and pharmaceutical sectors. These applications are mainly due to their biological properties. However, EOs are unstable and easily degradable if not protected from external factors such as oxidation, heat and light. Therefore, there is growing interest in the encapsulation of EOs, since polymeric nanocarriers serve as a barrier between the oil and the environment. In this context, nanoencapsulation seems to be an interesting approach as it not only prevents the exposure and degradation of EOs and their bioactive constituents by creating a physical barrier, but it also facilitates their controlled release, thus resulting in greater bioavailability and efficiency. In this review, we focused on selecting recent articles whose objective concerned the nanoencapsulation of essential oils from different plant species and highlighted their chemical constituents and their potential biotechnological applications. We also present the fundamentals of the most commonly used encapsulation methods, and the biopolymer carriers that are suitable for encapsulating EOs.

Rietveld Refinement, Morphology, and Optical and Photoluminescence Properties of a ß-Ag1.94Cu0.06MoO4 Solid Solution.

Corner-truncated cubic ß-Ag1.94Cu0.06MoO4 microcrystals were synthesized using the hydrothermal method. These were investigated by X-ray diffraction, confirming obtention of the spinel structure Fd3̅m. Through Raman spectroscopy are confirmed all modes for the point group of Oh7. The Egap shows a decrease of the band gap from 3.20 to 3.07 eV, with reduction of the conduction band occurring from -0.20 eV (ß-Ag2MoO4) to -0.13 eV (ß-Ag1.94Cu0.06MoO4), suggesting a p-type behavior for the Cu2+ ion. The field-emission scanning electron microscopy images confirm the morphological changes for ß-Ag2MoO4, where potato-like microcrystals were found. Meanwhile, corner-truncated cubic microcrystals for ß-Ag1.94Cu0.06MoO4. The photoluminescence (PL) spectrum confirms the increase in the PL emission for ß-Ag1.94Cu0.06MoO4, with suppression of the deep defects occurring in the structure caused by oxygen and silver atoms. In contrast, the green region is intensified because of distortions of the Ag-O and Mo-O bonds. Therefore, the ß-Ag1.94Cu0.06MoO4 solid solution has PL emission with CCT (4510 K) and CIE coordinates (x = 0.372 and y = 0.433), which could be interesting properties for applications as light-emitting diodes.

Pineapple (Ananás comosus) leaves ash as a solid base catalyst for biodiesel synthesis.

Homogeneous catalysts used for biodiesel synthesis have several limitations, including non-recoverability/reusability, saponification, emulsification, equipment corrosion, and environmental pollution. To overcome these limitations, we synthesized a novel catalyst via calcination of pineapple leaves waste. This catalyst was characterized by X-ray powder diffraction, X-ray fluorescence, Fourier transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy, and soluble alkalinity measurements. The catalyst's activity with regards to soybean oil transesterification was analyzed, and multiple process parameters (temperature, catalyst amount, reaction time, and methanol:oil molar ratio) were examined. A high catalytic activity, probably related to the 85 wt% content of alkali/alkali metals (K, Ca and Mg), was observed after a 30 min reaction time, 60 °C, 4 wt% of catalyst, oil to methanol molar ratio of 1:40, reaching an oil to biodiesel conversion above 98%. We conclude that the novel catalyst presented here is efficient, cost-effective, and sustainable, while simultaneously abundant waste is reduced.

Removal of rhodamine 6G from synthetic effluents using Clitoria fairchildiana pods as low-cost biosorbent.

Many organic dye pollutants have been identified in rivers and lakes around the world, and concern is growing with them as they cause serious changes in the ecological balance of aquatic environments. One of these dyes is rhodamine R6G, which is very water-soluble and has a high corrosive power. Therefore, Clitoria fairchildiana (CF) pods were used as a biosorbent to remove R6G from synthetic dye effluents. CF was characterized by infrared spectroscopy, thermogravimetric analysis, x-ray diffraction, elemental analysis, Boehm titration, and zero charge point measurements. The influence of various factors, such as solution pH, contact time, adsorbent mass, and concentration of R6G, was studied using batch equilibrium experiments. The optimum contact time to reach equilibrium was found to be 15 min, while the optimum adsorbent dose was 8 g L-1. The maximum adsorption capacity of CF (73.84 mg g-1) was observed at pH 6.4 and 298.15 K. Adsorption kinetics followed a pseudo-second-order law, and the isotherm could be best fitted with a Liu model. The obtained thermodynamic parameters indicate that the adsorption of R6G is spontaneous and enthalpy-driven. We thus conclude that CF is an efficient, green, and readily available biosorbent for dye removal from wastewater.

Antimicrobial properties of α-Ag2WO4 rod-like microcrystals synthesized by sonochemistry and sonochemistry followed by hydrothermal conventional method.

In this study we report the synthesis of silver tungstate microcrystals (α-Ag2WO4) by sonochemistry method (SC) at 65 °C and sonochemistry followed by conventional hydrothermal (SC + HC) for 1, 6 and 12 h, at 140 °C. The structural characterization by XRD confirms the alpha phase of the orthorhombic structure and the space group Pn2n, for all synthesized microcrystals. All the actives modes identified at the Raman spectroscopy were characteristic of alpha phase. The optical band gap by UV-Vis spectroscopy using the diffuse reflectance were 2.98, 3.0, 2.99 and 2.96 eV, for the microcrystals SC, SC + HC-1 h, SC + HC-6 h and SC + HC-12 h, respectively. FE-SEM images show the rod-like microcrystals, however, exhibiting the plane surface (1 0 1) only for the synthesized microcrystals with the assistance of the hydrothermal method (SC + HC-1 h, SC + HC- 6 h and SC + HC-12 h). The antimicrobial potential was confirmed for all α-Ag2WO4 microcrystals synthesized. However, the SC + HC-12 h microcrystals were more susceptible in the bacterial and fungal inhibition, with MIC values for microorganisms C. albicans, T. rubrum, MRSA e EHEC, 0.2-0.5, 4-9, 250 and 31.25 µg mL-1, respectively.

Synthesis of water treatment sludge ash-based geopolymers in an Amazonian context.

Water treatment plants (WTP) in the City of Manaus, Brazil, generate tons of sludge daily, which are then disposed of in landfills and main watercourses, particularly two important Amazonian Rivers: the blackwater Negro River and the pale sandy-colored water Solimões River. Because WTP-based sludges are rich in silicon and aluminum, they have been employed in the synthesis of geopolymers - alkaline activated inorganic polymers consisting of silicate and aluminosilicate chains. This paper reports the results of a geopolymeric synthesis process in which calcined sludge was explored as a source of silica and alumina. In this research, a laboratory testing program was developed to characterize the waste material generated from a water treatment plant in Manaus, whose intake water is influenced by the above referred rivers. Sample preparation involved kiln drying at 110 °C for 8 h, grinding in ball mill for 2 h, and calcination at 750 °C for 6 h. The calcined sludge was used as precursor, and potassium hydroxide added as activating alkali. Two geopolymers, one from each sludge source, were prepared following identical procedures. The chemical, compositional, morphological, thermal and mechanical properties of the fresh and hardened geopolymers were characterized. The geopolymers reached uniaxial compressive strengths of over 50 MPa at 28 days. Calcination conveyed more refined properties to the sludge-based geopolymers, akin to metakaolin-based geopolymers. The results presented herein support the technical feasibility of geopolymer synthesis in the lab scale.