Optimization of tannase production by Aspergillus glaucus in solid-state fermentation of black tea waste.

Tannases are valuable industrial enzymes used in food, pharmaceutical, cosmetic, leather manufacture and in environmental biotechnology. In this study, 15 fungal isolates were obtained from Egyptian cultivated soil and marine samples. The isolated fungi were qualitatively and quantitatively screened for their abilities to produce tannase. The selected fungal isolate NRC8 giving highest tannase activity was identified by molecular technique (18S rRNA) as Aspergillus glaucus. Among different tannin-containing wastes tested, the black tea waste was the best substrate for tannase production by Aspergillus glaucus in solid-state fermentation (SSF). Optimization of the different process parameters required for maximum enzyme production was carried out to design a suitable SSF process. Maximal tannase production was achieved with moisture content of 75%, an inoculums size of 6 × 108 spore/ml and sodium nitrate 0.2% (pH of 5.0) at 30 °C after 5 days of incubation. Box-Behnken experiment was designed to get a quadratic model for further optimization studies. Four-factor response-surface method with 27 runs was prepared using independent parameters including (moisture content %, initial pH, substrate concentration (g) and sodium nitrate concentration (g) for tannase model. The F- and P-values of the model were 4.30 and 0.002, respectively, which implied that the model is significant. In addition, the lack-of-fit was 1040.37 which indicates the same significance relative to the pure error. A. glaucus tannase was evaluated by the efficiency of conversion of tannic acid to gallic acid. Moreover, production of gallic acid from SSF process of A. glaucus using black tea waste was found to be 38.27 mg/ml. The best bioconversion efficiency was achieved at 40 °C with tannic acid concentration up to 200 g/L.

Cylindrical C96 Fullertubes: A Highly Active Metal-Free O2 -Reduction Electrocatalyst.

A new isolation protocol was recently reported for highly purified metallic Fullertubes D5h -C90 , D3d -C96 , and D5d -C100, which exhibit unique electronic features. Here, we report the oxygen reduction electrocatalytic behavior of C60 , C70 (spheroidal fullerenes), and C90 , C96 , and C100 (tubular fullerenes) using a combination of experimental and theoretical approaches. C96 (a metal-free catalyst) displayed remarkable oxygen reduction reaction (ORR) activity, with an onset potential of 0.85 V and a halfway potential of 0.75 V, which are close to the state-of-the-art Pt/C benchmark catalyst values. We achieved an excellent power density of 0.75 W cm-2 using C96 as a modified cathode in a proton-exchange membrane fuel cell, comparable to other recently reported efficient metal-free catalysts. Combined band structure (experimentally calculated) and free-energy (DFT) investigations show that both favorable energy-level alignment active catalytic sites on the carbon cage are responsible for the superior activity of C96 .

Towards Cs-ion supercapacitors: Cs intercalation in polymorph MoS2 as a model 2D electrode material.

Intercalation of alkali metals has proved to be an effective approach for the enhancement of the energy storage performance in layered-2D materials. However, the research so far has been limited to Li and Na ion intercalation with K ions being recently investigated. Although cesium (Cs) salts are highly soluble in water, Cs+ intercalation has been addressed neither in batteries nor in supercapacitors so far. Herein, we demonstrate the exceptional effect of Cs+ intercalation in MoS2 as a model 2D material to boost its performance as a potential supercapacitor electrode. Cs+ intercalation was found to stabilize the metastable 1T phase and increase the conductivity of the 2H and 3R phases. Cs+-Intercalated 1T MoS2 showed higher quantum capacitance (CQ) than doped graphene.

Comparison between Benzothiadizole-Thiophene- and Benzothiadizole-Furan-Based D-A-π-A Dyes Applied in Dye-Sensitized Solar Cells: Experimental and Theoretical Insights.

Three novel donor-acceptor-π-acceptor-type compounds (WS5, WS6, and WS7) were synthesized and investigated in dye-sensitized solar cells (DSSCs) exploring the effect of conjugated linkers on device performance. The new dyes showed strong light-harvesting ability in the visible region with relatively high molar absorption coefficients (>21 800 M-1 cm-1). This can be attributed to their intrinsic charge transfer (CT) from the arylamine to the acceptor group. Density functional theory (DFT) calculations revealed a favorable lowest unoccupied molecular orbital (LUMO) energy level, allowing efficient injection into the semiconductor conduction band after excitation. Upon application in DSSC devices, the WS5 dye containing 4,7-di(furan-2-yl)benzo[c][1,2,5]thiadiazole as conjugated linker mediated the highest device power conversion efficiency (PCE) amounting to 5.5%. This is higher than that of the WS6-containing dye based on the 4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole linker (3.5%) and the WS7 dye based on the 4-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole linker (4.3%) under AM 1.5 G illumination. The present results show furan-based dye linker systems to have a significant potential for improving DSSC efficiencies.

Correction: Fullerene C76 as a novel electrocatalyst for VO2+/VO2+ and chlorine evolution inhibitor in all-vanadium redox flow batteries.

Correction for 'Fullerene C76 as a novel electrocatalyst for VO2+/VO2+ and chlorine evolution inhibitor in all-vanadium redox flow batteries' by Farah A. El Diwany et al., Chem. Commun., 2020, 56, 7569-7572, DOI: 10.1039/D0CC03544K.

Fullerene C76 as a novel electrocatalyst for VO2+/VO2+ and chlorine evolution inhibitor in all-vanadium redox flow batteries.

We report, for the first time, the superior electrocatalytic activity of fullerene C76 towards VO2+/VO2+ in all-vanadium redox flow batteries. Results show a 99.5% and 97% decrease in charge transfer resistance, compared to treated and untreated carbon cloth. Suppression of chlorine evolution and good stability after 100 cycles are achieved.

Silkworms as a factory of functional wearable energy storage fabrics.

Feeding Bombyx mori larvae with chemically-modified diets affects the structure and properties of the resulted silk. Herein, we provide a road map for the use of silkworms as a factory to produce semiconducting/metallic natural silk that can be used in many technological applications such as supercapacitor electrodes. The silkworms were fed with four different types of chemicals; carbon material (graphite), sulfide (MoS2), oxide (TiO2 nanotubes), and a mixture of reactive chemicals (KMnO4/MnCl2). All the fed materials were successfully integrated into the resulted silk. The capacitive performance of the resulted silk was evaluated as self-standing fabric electrodes as well as on glassy carbon substrates. The self-standing silk and the silk@glassy carbon substrate showed a great enhancement in the capacitive performance over that of the unmodified counterparts. The specific capacitance of the self-standing blank silk negative and positive electrodes was enhanced 4 and 5 folds at 10 mV/s, respectively upon the modification with KMnO4/MnCl2 compared to that of the plain silk electrodes.

Untapped Potential of Polymorph MoS2: Tuned Cationic Intercalation for High-Performance Symmetric Supercapacitors.

Supercapacitors have been the key target as energy storage devices for modern technology that need fast charging. Although supercapacitors have large power density, modifications should be done to manufacture electrodes with high energy density, longer stability, and simple device structure. The polymorph MoS2 has been one of the targeted materials for supercapacitor electrodes. However, it was hard to tune its phase and stability to achieve the maximum possible efficiency. Herein, we demonstrate the effect of the three main phases of MoS2 (the stable semiconductor 2H, the metastable semiconductor 3R, and the metastable metallic 1T) on the capacitance performance. The effect of the cation intercalation on the capacitance performance was also studied in Li2SO4, Na2SO4, and K2SO4 electrolytes. The performance of the electrode containing the metallic 1T outperforms those of the 2H and 3R phases in all electrolytes, with the order 1T > 3R > 2H. The 1T/2H phase showed a maximum performance in the K2SO4 electrolyte with a specific capacitance of 590 F g-1 at a scan rate of 5 mV s-1. MoS2 showed a good performance in both positive and negative potential windows allowing the fabrication of symmetric supercapacitor devices. The 1T MoS2 symmetric device showed a power density of 225 W/kg with an energy density of 4.19 Wh/kg. The capacitance retention was 82% after 1000 cycles, which is an outstanding performance for the metastable 1T-containing electrode.

A first-principles roadmap and limits to design efficient supercapacitor electrode materials.

Our life is turning into an electronic world where we need our devices charged all the time. Although batteries have been doing the job so far, we need devices that charge way faster with longer cycling stability. The answer could be supercapacitors; however, electrode materials that maintain both high energy density and high power density are yet to be discovered. Currently, researchers base their work on guess and check methods to modify electrode materials with limited organized work that targets the prediction of the properties of materials at an earlier stage. To this end, density functional theory (DFT) could be a realistic tool for early prediction of the properties of supercapacitor electrode materials. The targeted supercapacitor electrodes should exhibit multiple properties, which can be calculated using different DFT routes. Herein, a roadmap to predict the desired supercapacitive properties of materials using different levels of DFT is presented. Our target is to let researchers decide which property of the material they wish to predict or develop and choose the appropriate DFT route to do so.

Recent advances in the use of TiO2 nanotube powder in biological, environmental, and energy applications.

The use of titanium dioxide nanotubes in the powder form (TNTP) has been a hot topic for the past few decades in many applications. The high quality of the fabricated TNTP by various synthetic routes may meet the required threshold of performance in a plethora of fields such as drug delivery, sensors, supercapacitors, and photocatalytic applications. This review briefly discusses the synthesis techniques of TNTP, their use in various applications, and future perspectives to expand their use in more applications.

Unveiling the Effect of the Structure of Carbon Material on the Charge Storage Mechanism in MoS2-Based Supercapacitors.

MoS2 is a 2D material that has been widely used in supercapacitor applications because of its layered structure that provides a large surface area and allows for high electric double-layer charge storage. To enhance the cycling stability and capacitance of MoS2, it is usually mixed with carbon materials. However, the dependence of the charge storage mechanism on the structure of the carbon material is still unclear in literature. Herein, the effect of the structure of the carbon material on the charge storage mechanism in 2H flower-shaped MoS2 is investigated in detail. Specifically, 2H MoS2 was mixed with either 8 nm-diameter carbon nanotubes (CNTs) or graphene nanoflakes (GNFs) in different weight ratios. Also, a composite of MoS2, CNTs, and GNFs (1:1:1) was also studied. The charge storage mechanism was found to depend on the structure and content of the carbon material. Insights into the possible storage mechanism(s) were discussed. The MoS2/CNT/GNF composite showed a predominant pseudocapacitive charge storage mechanism where the diffusion current was ∼89%, with 88.31% of the resulted capacitance being due to faradic processes.

Propping the optical and electronic properties of potential photo-sensitizers with different π-spacers: TD-DFT insights.

We report density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations on the widely used N3 dye (cis-[Ru(2,2'-bipyridine-4,4'-dicarboxylic acid)2(NCS)2] and its trans isomer with different π-spacers. The study compared the sensitization properties of the two isomers in terms of their electronic properties such as light harvesting efficiency (LHE), absorbed wavelength (λMax) and molecular orbital distribution. Also, charge transfer descriptors, such as the charge transfer distance (DCT), dipole moment (µCT), and the amount of charge transferred (qCT) were investigated. Upon replacing the two "2,2'-bipyridine-4,4'-dicarboxylic acid" ligands of the N3 dye with extended π-spacers of "1,4-benzene and 2,5-thiophene" for both the cis and trans isomers, the LHE of the trans isomer was increased by 70% compared to the cis counterpart. The complexes with thiophene spacers showed the highest LHE. The trans isomers showed wider absorbance range of wavelengths and equal wide distribution of charge density in the excited state along the organic ligands. These findings highlight the importance of using π-spacers between the organic ligands and the carboxylate groups to boost the LHE of DSSCs. Also, our study showed that the trans isomer is superior in its optical and electronic properties than the cis counterpart. However, the trans isomer is yet to be tested experimentally in DSSCs.