Comparative Study of TiO2, ZnO, and Nb2O5 Photoanodes for Nitro-Substituted Naphthoquinone Photosensitizer-Based Solar Cells

This research focuses on the first demonstration of NO2Lw (2-hydroxy-3-nitronaphthalene-1,4-dione) as a photosensitizer and TiO2, ZnO, and Nb2O5 as photoanode materials for dye-sensitized solar cells (DSSCs). The metal-free organic photosensitizer (i.e., nitro-group-substituted naphthoquinone, NO2Lw) was synthesized for this purpose. As a photoanode material, metal oxides, such as TiO2, ZnO, and Nb2O5, were selected. The synthesized NO2Lw contains an electron-withdrawing group (-NO2) and anchoring groups (-OH) that exhibit absorption in the visible range. The UV-visible absorbance spectrum of NO2Lw demonstrates the absorption ascribed to ultraviolet and visible region charge transfer. The NO2Lw interacts with the TiO2, ZnO, and Nb2O5 photoanode, as shown by bathochromic shifts in wavelengths in the photosensitizer-loaded TiO2, ZnO, and Nb2O5 photoanodes. FT-IR analysis also studied the bonding interaction between NO2Lw and TiO2, ZnO, and Nb2O5 photoanode material. The TiO2, ZnO, and Nb2O5 photoanodes loaded with NO2Lw exhibit a shift in the wavenumber of the functional groups, indicating that these groups were involved in loading the NO2Lw photosensitizer. The amount of photosensitizer loading was calculated, showing that TiO2 has higher loading than ZnO and Nb2O5 photoanodes; this factor may constitute an increased JSC value of the TiO2 photoanode. The device performance is compared using photocurrent-voltage (J-V) curves; electrochemical impedance spectroscopy (EIS) measurement examines the device's charge transport. The TiO2 photoanode showed higher performance than the ZnO and Nb2O5 photoanodes in terms of photoelectrochemical properties. When compared to ZnO and Nb2O5 photoanodes-based DSSCs, the TiO2 photoanode Bode plot shows a signature frequency peak corresponding to electron recombination rate toward the low-frequency region, showing that TiO2 has a greater electron lifetime than ZnO and Nb2O5 photoanodes based DSSCs.

Naphthoquinoneoxime-Sensitized Titanium Dioxide Photoanodes: Photoelectrochemical Properties

Naphthoquinoneoxime derivatives, viz., LwOx, 3-hydroxy-4-(hydroxyimino)naphthalen-1 (4H)-one; PthOx, 3-hydroxy-4-(hydroxyimino)-2-methylnaphthalen-1(4H)-one; and Cl_LwOx, 2-chloro-3-hydroxy-4-(hydroxyimino)naphthalen-1(4H)-one, are used in fabrication of dye-sensitized solar cells (DSSCs). The photophysical and electrochemical properties of the sensitizers were studied. The HOMO-LUMO energy gaps of the sensitizers (LwOx, PthOx, and Cl_LwOx) calculated by using the intersection of UV-visible and fluorescence spectra are 2.85, 2.71, and 2.87 eV, respectively. The energy band alignment energy level of the sensitizer, that is, the lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO), should match with the energy level of the TiO₂ conduction band and the redox potential of iodine/triiodide electrolyte to allow smooth electron transfer. The electrochemical characterization of sensitizers was done to find the LUMO and HOMO level of the sensitizer. It shows that the LUMO level of (LwOx, PthOx, and Cl_LwOx) is above the conduction band position of TiO₂. Electrochemical impedance spectroscopy was used to study the charge transport resistance and electron lifetime of DSSCs. The charge transport resistance at the TiO₂ |electrolyte|counter electrode interface was reduced in the Cl_LwOx device; thus, the electron lifetime of Cl_LwOx was enhanced compared to LwOx and PthOx sensitizers. The fabricated device was characterized using photocurrent density-voltage (J-V) measurement. It is observed that there was an enhancement in the overall power conversion efficiency (η) of the DSSCs fabricated by using Cl_LwOx sensitizers as compared to LwOx and PthOx sensitizer-loaded photoanodes. Enhancement in power conversion efficiency, that is, photovoltage and photocurrent, is achieved due to the chlorine substituent. Thus, the chlorine substituent naphthoquinoneoxime pushes the electron density, enhancing the pushing nature and facilitating the lone pair present in the N-OH moiety to attach to TiO₂ more strongly.

Titania Nanorods Embedded with 2-Bromo-3-(methylamino)naphthalene-1,4-dione for Dye-Sensitized Solar Cells

In a recent study, TiO₂ nanorod electrodes were prepared by the hydrothermal approach followed by calcination at various temperatures from 300 to 600 °C. The effects of calcination temperature on the morphological and structural properties were investigated. The novel analogue of aminonaphthoquinone(2R-(n-alkylamino)-1,4-naphthoquinone) photosensitizer, viz. BrA1, 2-bromo-3-(methylamino)naphthalene-1,4-dione was synthesized from 2,3-dibromonaphthalene-1,4-dione. X-ray crystallographic data collection and refinement confirm that BrA1 crystallizes in the triclinic space group P 1̅. After loading BrA1, the photosensitizer on the annealed TiO₂ nanorod (TiO₂NR) electrodes, the optical properties of the photoanodes showed broadbands in each of the UV and visible regions, which are attributed to the π →π* and n → π* charge-transfer transitions, respectively. The dye-sensitized solar cell (DSSC) system was formed by loading the BrA1 photosensitizer on TiO₂NR. The electrochemical impedance spectroscopy (EIS) analyses confirm that calcination temperature improves the charge transportation by lowering the resistance path during the photovoltaic process in TiO₂NR (400 °C) photoanode-based DSSCs due to the sufficient photosensitizer adsorption and fast electron injection. Due to the effective light harvesting by the BrA1 photosensitizer and charge transport through the TiO₂ nanorod, the power conversion efficiencies (PCE) of the TiO₂NR (400 °C/BrA1-based) DSSCs were improved for 2-bromo-3-(methylamino)naphthalene-1,4-dione.

Green Extraction Strategies for Sea Urchin Waste Valorization

Commonly known as “purple sea urchin,” Paracentrotus lividus occurs in the Mediterranean Sea and the eastern Atlantic Ocean. This species is a highly appreciated food resource and Italy is the main consumer among the European countries. Gonads are the edible part of the animal but they represent only a small fraction (10–30%) of the entire sea urchin mass, therefore, the majority ends up as waste. Recently, an innovative methodology was successfully developed to obtain high-value collagen from sea urchin by-products to be used for tissue engineering. However, tissues used for the collagen extraction are still a small portion of the sea urchin waste (<20%) and the remaining part, mainly the carbonate-rich test and spines, are discarded. Residual cell tissues, tests, and spines contain polyunsaturated fatty acids, carotenoids, and a class of small polyphenols, called polyhydroxynaphthoquinones (PHNQ). PHNQ, due to their polyhydroxylated quinonoid nature, show remarkable pharmacologic effects, and have high economic significance and widespread application in several cosmetic and pharmaceuticals applications. A green extraction strategy aimed to obtain compounds of interest from the wastes of sea urchins was developed. The core strategy was the supercritical CO₂ technique, characterized by low environmental impacts. Fatty acids and carotenoids were successfully and selectively extracted and identified depending on the physical parameters of the supercritical CO₂ extraction. Finally, the exhausted powder was extracted by solvent-based procedures to yield PHNQ. The presence of Spinochrome A and Spinochrome B was confirmed and extracts were characterized by a remarkably high antioxidant activity, measured through the 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) assay. Overall, the selective and successive extraction methods were validated for the valorization of waste from sea urchins, demonstrating the feasibility of the techniques targeting added-value compounds.

An Experimental and Theoretical Study of Dye Properties of Thiophenyl Derivatives of 2-Hydroxy-1,4-naphthoquinone (Lawsone)

A prospective study of the dye properties of non-toxic lawsone thiophenyl derivatives, obtained using a green synthetic methodology allowed for the description of their bathochromic shifts in comparison to those of lawsone, a well-known natural pigment used as a colorant that recently also has aroused interest in dye-sensitized solar cells (DSSCs). These compounds exhibited colors close to red, with absorption bands in visible and UV wavelength range. The colorimetric study showed that these compounds exhibited a darker color than that of lawsone within a range of colors depending on the substituent in the phenyl ring. Computational calculations employing Density Functional Theory (DFT) and Time-Dependent Density Functional Theory (TD-DFT), showed that the derivatives have lower excitation energies than lawsone, while the alignment of their frontier orbitals regarding the conduction bands of TiO₂ and ZnO and the redox potential of the electrolyte I^-/I₃^- suggests that they could be employed as sensitizers. The study of the interactions of the lawsone and a derivative with a TiO₂ surface model by different anchoring modes, showed that the adsorption is thermodynamically favored. Natural bond orbital (NBO) analysis indicates a two-center bonding (BD) O-Ti as the main interaction of the dyes with TiO₂.

Safety and bioactivity assessment of aqueous extract of Thai Henna (Lawsonia inermis Linn.) Leaf

The worldwide demand for a natural dye by the cosmetic and food industry has recently gained interest. To provide scientific data supporting the usage of Thai henna leaf as a natural colorant, the phytochemical constituents, safety, and bioactivity of aqueous extract of the henna leaf by autoclave (HAE) and hot water (HHE) were determined. HAE contained a higher amount of total phenolic and flavonoid contents than HHE. The major constituents in both extracts were ferulic acid, gallic acid, and luteolin. The extracts displayed no marked mutagenic activity both in vitro and in vivo mammalian-like biotransformation. HAE and HHE also exhibited non-cytotoxicity to human immortalized keratinocyte cells (HaCaT), peripheral blood mononuclear cells (PBMCs), and murine macrophage RAW 264.7 cell line with IC₂₀ and IC₅₀ > 200 μg/ml. The extracts exhibited antioxidant and anti-inflammatory activity as evidenced by significant scavenging of ABTS and DPPH radicals and decreasing NO levels in LPS-induced RAW 264.7 cells. The antioxidant and anti-inflammatory properties of the extracts might be attributed to their phenolic and flavonoid contents. In conclusion, the traditional use of henna as a natural dye appears not to exert toxic effects and seems biosecure. Regarding safety, antioxidant, and anti-inflammatory properties, the aqueous extract of Thai henna leaf might thus serve as a readily available source for utilization in commercial health industries.

Light-Assisted Rechargeable Lithium Batteries: Organic Molecules for Simultaneous Energy Harvesting and Storage

Lithium batteries that could be charged on exposure to sunlight will bring exciting new energy storage technologies. Here, we report a photorechargeable lithium battery employing nature-derived organic molecules as a photoactive and lithium storage electrode material. By absorbing sunlight of a desired frequency, lithiated tetrakislawsone electrodes generate electron-hole pairs. The holes oxidize the lithiated tetrakislawsone to tetrakislawsone while the generated electrons flow from the tetrakislawsone cathode to the Li metal anode. During electrochemical operation, the observed rise in charging current, specific capacity, and Coulombic efficiency under light irradiation in contrast to the absence of light indicates that the quinone-based organic electrode is acting as both photoactive and lithium storage material. Careful selection of electrode materials with optimal bandgap to absorb the intended frequency of sunlight and functional groups to accept Li-ions reversibly is a key to the progress of solar rechargeable batteries.

Plasmonic enhancement of betanin-lawsone co-sensitized solar cells via tailored bimodal size distribution of silver nanoparticles

Natural pigment-based photosensitizers are an attractive pathway for realizing low cost and environmentally friendly solar cells. Here, broadband light-harvesting is achieved using two natural pigments, betanin and lawsone, absorbing in the green and blue region of the solar spectrum respectively. The use of bimodal size distribution of AgNPs tailored for each of the pigments to further increase their efficiency is the key feature of this work. This study demonstrates a significant enhancement in current-density, voltage, and efficiency by 20.1%, 5.5%, and 28.6% respectively, in a betanin-lawsone co-sensitized solar cell, via plasmonic enhancement using silver nanoparticles (AgNPs). The optimum sizes of the nanoparticles have been calculated by studying their optical response and electric field profiles using Finite Difference Time Domain (FDTD) simulations, aimed at matching their resonant wavelengths with the absorption bands of the dyes. Simulations show that AgNPs of diameters 20 nm and 60 nm are optimum for enhanced absorption by lawsone and betanin respectively. The FDTD simulations of the plasmonic photoelectrodes demonstrated 30% and 15% enhancement in the power absorption by betanin and lawsone at the LSPR peaks of the 60 nm and 20 nm AgNPs respectively. An optimum overall concentration of 2% (v/v) and a ratio of 4:1 (20 nm:60 nm) of the bimodal distribution of the AgNPs, was determined for incorporation in the photoanodes. An average efficiency of 1.02 ± 0.006% was achieved by the betanin-lawsone co-sensitized solar cell with the bimodal distribution of AgNPs, compared to 0.793 ± 0.006% achieved by the non-plasmonic solar cell of otherwise identical configuration. Electrochemical impedance spectroscopy confirmed that the incorporation of the bimodal distribution of AgNPs in the solar cells also enabled enhanced electron lifetime and reduced recombination compared to the non-plasmonic counterpart, thereby improving the charge transfer. The plasmonic enhancement methodology presented here can be applied to further improve the efficiency of other natural dye-sensitized solar cells.

Performance Enhancement of Betanin Solar Cells Co-Sensitized with Indigo and Lawsone: A Comparative Study

Co-sensitization is an important strategy toward efficiency enhancement of solar cells by enabling better light harvesting across the solar spectrum. Betanin is a natural dye which absorbs light in the major portion of the incident solar spectrum (green region) and is the most efficient natural pigment used in dye-sensitized solar cells. This study investigates the performance enhancement of a betanin solar cell by co-sensitizing it with two natural pigments which show complementary light absorption, i.e., indigo and lawsone, absorbing in the red and blue regions of the solar spectrum, respectively. The calculated highest occupied molecular orbital and lowest unoccupied molecular orbital energies of the pigment molecules, derived from density functional theory (DFT) simulations, confirmed their optimal alignment with respect to the conduction band energy of the TiO₂ semiconductor and reduction potential energy level of the I^-/I₃ ^- electrolyte, a necessary requirement for optimal device performance. Lawsone solar cells displayed better performance, showing average efficiencies of 0.311 ± 0.034%, compared to indigo solar cells showing efficiencies of 0.060 ± 0.004%. Betanin was co-sensitized with indigo and lawsone, and the performances of the co-sensitized solar cells were compared. The betanin/lawsone co-sensitized solar cell showed a higher average efficiency of 0.793 ± 0.021% compared to 0.655 ± 0.019% obtained for the betanin/indigo co-sensitized solar cell. An 11.7% enhancement in efficiency (with respect to betanin) was observed for the betanin/indigo solar cell, whereas a higher enhancement of 25.5% was observed for the betanin/lawsone solar cell. Electrochemical impedance spectroscopy studies confirmed that the higher efficiency can be attributed to the higher electron lifetime of 313.8 ms in the betanin/lawsone co-sensitized solar cell compared to 291.4 ms in the betanin/indigo solar cell. This is due to the energy levels being more optimally aligned in lawsone compared to that of indigo, as observed in the DFT studies, and the lack of dipole moment in indigo, resulting in more efficient charge separation and charge transfer in lawsone.

Lawsone isomers, lawsone ether and bilawsone for dye-sensitized solar cells applications: DFT and UV-Vis studies

Structural and optoelectronic properties of lawsone (L), lawsone ether (LE) and bilawsone (BL) were studied theoretically using the DFT and time-dependent DFT methods with hybrid functional B3LYP5 and 6-311G (2d,p) basis set. For the monomer lawsone molecule, isomerization reaction between two rotational isomers was analyzed based on a thermodynamic approach. The electronic spectra of the dyes molecules in a vacuum and solvents (DMSO and CH₂Cl₂) were computed. The maximum wavelengths were found at 355-408 nm for the LE and 350-448 nm for BL that indicated bands shift to visible range compared to L (340 nm). The UV-Vis spectra of the L and BL were measured experimentally in DMSO solution. For the BL, a broad and intensive band was observed in a visible region at 452 nm that apparently would favour sensitizing ability of the dye. The optoelectronic properties of the LE and BL showed them as more promising candidates for DSSCs applications compared to the individual lawsone dye.

Structure and Photoelectrical Properties of Natural Photoactive Dyes for Solar Cells

A series of natural photoactive dyes, named as D1–D6 were successfully extracted from six kinds of plant leaves for solar cells. The photoelectrical properties of dyes were measured via UV-Vis absorption spectra, cyclic voltammetry as well as photovoltaic measurement. To theoretically reveal the experimental phenomena, the chlorophyll was selected as the reference dye, where the ground and excited state properties of chlorophyll were calculated via density functional theory (DFT) and time-dependent density functional theory (TD-DFT). The experimental results show that the absorption peaks of those dyes are mainly distributed in the visible light regions of 400–420 nm and 650–700 nm, which are consistent with the absorption spectrum of chlorophyll. The photoelectrical conversion efficiencies of the solar cells sensitized by the six kinds of natural dyes are in the order of D1 > D4 > D2 > D5 > D6 > D3. The dye D1 performance exhibits the highest photoelectrical conversion efficiency of 1.08% among the investigated six natural dyes, with an open circuit voltage of 0.58 V, a short-circuit current density of 2.64 mA cm−2 and a fill factor of 0.70.

In vitro and in vivo antifungal efficacy of plant based lawsone against Fusarium oxysporum species complex

Fusarium oxysporum is an ascomycete facultative fungus which generally affects to plants. However, it is recently known as a serious emerging opportunistic pathogen of human and other animals. F. oxysporum shows broad resistance to commonly used antifungal agents and therefore development of alternative therapeutic agents is required. In this study, we investigated the antifungal efficacy of plant based natural lawsone against pathogenic F. oxysporum. Antifungal susceptibility test determined the concentration dependent growth inhibition of lawsone against F. oxysporum with minimum inhibitory concentration (MIC) at 100μg/mL. Ultra-structural analysis indicates the prominent damage on cell wall of the mycelium after lawsone treatment, and suggests that it could increase the membrane permeability and disintegration of cells leading to cellular death. Propidium iodide (PI) uptake assay results showed the higher level of cell death in lawsone treated F. oxysporum which further confirms the loss of plasma membrane integrity. Also, detection of reactive oxygen species (ROS) using DCFH-DA has clearly indicated that lawsone (100μg/mL) can induce the ROS level in the filaments of F. oxysporum. MTT assay results showed the loss of viability and germination capacity of F. oxysporum spores by lawsone in concentration dependent manner. Moreover, lawsone treatment induced the mRNA expression of two autophagy related genes (ATG1 and ATG8) indicating that lawsone may activate the autophagy related pathways in F. oxysporum due to the oxidative stress generated by ROS. F. oxysporum infected zebrafish has recovered after lawsone therapy as a topical treatment suggesting that lawsone is a potential natural antifusariosis agent.