Phosphotungstic Acid: An Efficient Catalyst for the Aqueous Phase Synthesis of Bis-(4-hydroxycoumarin-3-yl)methanes

In this present work, we report that phosphotungstic acid provides a simple, efficient and environmentally benign route is a two-component one-pot domino Knoevenagel-type condensation/Michael reaction between 4-coumarin derivative and an aldehyde in water as a solvent in shorter duration with high yields.      

Recycling of Bakery Waste as an Alternative Carbon Source for Rhamnolipid Biosurfactant Production

Production of a rhamnolipid biosurfactant (RBS) using discarded mixed bakery waste (BW) employing bacterial strain Pseudomonas aeruginosa strain PG1 (identified by 16 s rDNA sequencing) was investigated for bioconversion of the food waste. Dry and powder form BW was supplemented with mineral salt media (MSM) as a sole carbon source for production of RBS. RBS production was measured based on the drop collapse assay and surface tension (ST) reduction of the culture media. Production of RBS in the culture media was enhanced by optimizing the carbon source (BW) concentration and the proper nitrogen source along with the pH of the MSM. Under optimized culture conditions, 11.56 g L⁻¹ day⁻¹ crude biosurfactant (BS) was achieved. The RBS had the ability to reduce the ST of the optimized MSM from 72.0 to 25.8 mN m⁻¹ during culture, where the critical micelle concentration (CMC) of the biosurfactant was found to be 100 mg L⁻¹. Liquid Chromatography Mass Spectroscopy (LC-MS), Fourier Transform Infrared spectroscopy (FTIR), and scanning electron microscopy (SEM)–energy dispersive X-ray spectroscopy (EDS) analyses of the purified BS confirmed that it is of rhamnolipid in nature and it is made up of both monorhamnolipid and dirhamnolipid congeners. Furthermore, the RBS did not express any cytotoxic effect on the cell line of mouse L292 fibroblastic cell indicating the biosafety nature of the high-value biomolecule.     

Structural,magnetic, and textural properties of iron oxide-reduced graphene oxide hybrids and their use for the electrochemical detection of chromium

Superparamagnetic Fe₃O₄ nanoparticles were anchored on reduced graphene oxide (RGO) nanosheets by co-precipitation of iron salts in the presence of different amounts of graphene oxide (GO). A pH dependent zeta potential and good aqueous dispersions were observed for the three hybrids of Fe₃O₄ and RGO. The structure, morphology and microstructure of the hybrids were examined by X-ray diffraction, transmission electron microscopy (TEM), Fourier transform infrared spectroscopy, Raman and X-ray photoelectron spectroscopy. TEM images reveal lattice fringes (d₃₁₁ = 0.26 nm) of Fe₃O₄ nanoparticles with clear stacked layers of RGO nanosheets. The textural properties including the pore size distribution and loading of Fe₃O₄ nanoparticles to form Fe₃O₄–RGO hybrids have been controlled by changing the concentration of GO. An observed maximum (～10 nm) in pore size distribution for the sample with 0.25 mg ml^?1 of GO is different from that prepared using 1.0 mg ml^?1 GO. The superparamagnetic behavior is also lost in the latter and it exhibits a ferrimagnetic nature. The electrochemical behavior of the hybrids towards chromium ion was assessed and a novel electrode system using cyclic voltammetry for the preparation of an electrochemical sensor platform is proposed. The textural properties seem to influence the electrochemical and magnetic behavior of the hybrids.     

Pretreatment processes assisted subcritical water hydrolysis for valorisation of spent coffee grounds

This study investigated the effect of sequential extraction techniques and pretreatment methods in enhancing the recovery of high-value products from spent coffee ground. Supercritical carbon dioxide (SC-CO₂) deoiling was performed to recover non-polar lipids, and subcritical water (SCW) hydrolysis of deoiled spent coffee ground (SCG) was conducted involving pretreatment with ultrasound (US-SCG), and sample particle size reduction (PS-SCG). SCW temperature, solid/liquid mixing ratio, constant pressure and residence time were studied for their effect on extracting reducing sugars (RS), total phenolic content (TPC), total flavonoid content (TFC), 5-HMF, and furfural. Temperature increase enhanced hydrolysis efficiency and promoted RS dehydration into 5-HMF and furfural. At 180 °C and 40 mg/600 mL, TPC, TFC and RS values increased significantly with ultrasound pretreatment correlating with improved antioxidant activities by DPPH and ABTS assays. Highest amount of 5-HMF and furfural was obtained at 210°C (highest temperature studied) with 44.71 and 2.36 mg/100 g. Chlorogenic acid recovery was the highest in the non-deoiled SCG (15.07 mg/100 g), with no significant difference observed in PS-SCG, suggesting an increase due to its reduced particle size. The results of this study provide comprehensive knowledge on the combined effects of integrated engineering systems to boost the valorisation of SCGs into high-value products.     

Photographing impact of molten molybdenum particles in a plasma spray

Plasma-sprayed molten molybdenum particles (∼40 μm in diameter) were photographed impinging at high velocity (∼140 m/s) on a glass substrate at room temperature. An optical sensor detected thermal radiation emitted by a droplet as it approached the substrate and activated a time delay unit. After a selected time interval, an Nd:YAG laser was triggered, emitting a 5 ns pulse that provided illumination for a charge-coupled device (CCD) camera to photograph the impacting droplet through a long-range microscope. By varying the delay before pulsing the laser, different stages of droplet deformation were recorded. Impacting droplets spread into a thin circular film that ruptured and broke into small fragments. An optical detector recording thermal radiation from the impacting droplet gave a signal that increased as the droplet spread out, reached a maximum when the liquid film began to rupture, and decreased as portions of the droplet recoiled because of surface tension and then flew out of view of the photodetector.     

Experimental determination of NH<Subscript>4</Subscript>NO<Subscript>3</Subscript>-KNO<Subscript>3</Subscript> binary phase diagram

The solid-state phase transitions in ammonium nitrate (AN)-potassium nitrate (KN) system, and the equilibrium AN-KN phase diagram have been determined by using differential scanning calorimetry and high-temperature in situ x-ray diffractometry. Sample preparation was performed in a special “dry room” with very low humidity. A single phase region (AN III) with no phase transitions to 373 K was observed in the composition range 5 to 20% KN; this is critical for use in air bag gas generators. The high-temperature KN phase (KN I) has a wide range of stability from 20 to 100 wt.% KN. There are one eutectic, two eutectoid, three peritectoid, and one congruent transformations in this phase diagram. Two new nonstoichiometric phases were found at lower temperatures in the mid-composition range between the AN and KN terminal solid solutions. Details of the phase equilibria are presented.     

Photocatalytic,magnetic, and electrochemical properties of La doped BiFeO3 nanoparticles

We successfully prepared La_1?xBi_xFeO₃ (L_xB_1?xFO, x?=?0.01–0.1) nanoparticles using a sol-gel technique, and studied their photocatalytic, magnetic, and electrochemical properties. Structural refinement studies of the prepared nanoparticles revealed a gradual structural transition from rhombohedral to orthorhombic. The average grain size was observed to decrease with increasing the concentration of La. The photocatalytic degradation of Rhodamine B (RhB) in the presence of the prepared nanoparticles was studied under visible light irradiation. The L_0.06B_0.94FO nanoparticles showed higher degradation efficiency compared to pure BiFeO₃ (BFO) nanoparticles. Magnetic studies showed that La doping improved the magnetization of BFO due to the reduction in grain size and destruction of cycloid coupling of spins. Higher specific capacitance values were obtained for La doped BFO (LBFO) nanoparticles compared to BFO nanoparticles. A maximum specific capacitance of 219?F?g^?1 was obtained at a current density of 1?A?g^?1 for LBFO nanoparticles.     

Effect of Porosity on Structure,Young's Modulus,and Thermal Conductivity of SiC Foams by Direct Foaming and Gelcasting

The study demonstrates the aqueous processing of solid‐state‐sintered SiC foams by gelcasting technique. Aside from increasing strength of green bodies, gelcasting monomers were the source of carbon additive which helped in sintering of SiC foams. Sintered foams with the relative density (RD) between 0.44 and 0.11 were processed by direct foaming of SiC slurries followed by gelcasting and sintering. Structural analysis by X‐ray tomography showed the presence of spherical pores with bimodal pore size distribution and the proportion of large size cell and their interconnectivity increased in low RD foams. SEM study revealed that decreased RD resulted in gradual changes in the strut microstructure from the grains with faceted interface to smooth interfaced grains. The analysis of changes in Young's modulus and thermal conductivity with RD were in agreement with the Ashby model for open cell foams.     

Synthesis of Nanocrystalline Lanthanum Strontium Manganite Powder by the Urea–Formaldehyde Polymer Gel Combustion Route

Nanocrystalline lanthanum strontium manganite (LSM) powder has been synthesized by combustion of a transparent gel obtained by the polymerization of methylol urea and urea in a solution containing La³⁺, Sr²⁺, and Mn²⁺ (LSM ions). Chemistry of the transparent urea–formaldehyde (UF) polymer gel formation and structure of the gel have been proposed such that the LSM ions act in between the growing UF polymer chains by interacting through NH, OH, and CO groups by co-ordination and prevent polymer self-assembly through inter-chain hydrogen bonding as evidenced from infrared spectrum. Thermally stable structures formed by the decomposition of UF polymer below 300°C undergo combustion in the presence of nitrate oxidant in a temperature range from 350°–450°C. A perovskite LSM phase has been formed by self-sustained combustion of the dried gel initiated with little kerosene. The powder obtained after deagglomeration and calcination at 600°C for 2 h has a D ₅₀ value of 0.19 μm, and the particles are aggregates of crystallites 10–25 nm in size.