Enhanced Photosensitization by Carbon Dots Co-adsorbing with Dye on p-Type Semiconductor (Nickel Oxide) Solar Cells

Green Synthesis of Nickel Oxide NPs Incorporating Carbon Dots for Antimicrobial Activities

A biosynthesis composite using the green synthesis of titled metal nanoparticles (nickel oxide nanoparticles, NiO NPs, and carbon dots, C-dots) was produced, characterized, and then applied for antimicrobial activities. NiO NPs were produced using the Croton macrostachyus (Bakkannisa) plant leaf extract and nickel nitrate (III) hexahydrate [Ni(NO3)2·2H2O] as precursors, while C-dots were produced using citric acid and o-phenylenediamine (o-OPD). The distribution of the average particle size of the NiO NPs and NiO NPs@C-dots was 25.34 ± 0.12 and 24.95 ± 0.22 nm, respectively. The antimicrobial effects of the prepared materials were tested against the selected bacterial and fungal strains. Based on the outcomes of the bioassay, it was realized that both the bare and composite materials were effective against all bacterial strains. The composite's high surface area with strong inhibitive effective antimicrobial effects against bacterial and fungal strains were observed. Therefore, strong inhibitive effects of 21-24 and 22-26 mm were observed with NiO NPs and NiO NPs@C-dots, respectively.

Modification of Flexible Electrodes for P-Type (Nickel Oxide) Dye-Sensitized Solar Cell Performance Based on the Cellulose Nanofiber Film

The preparation of flexible electrode, including working electrode (WE) and counter electrode (CE), for dye-sensitized solar cells (DSSCs) utilizing metal oxides using environmentally friendly sustainable TEMPO-oxidized cellulose nanofibers (TOCNFs) is reported in this work. A new type of flexible electrode for the DSSCs, which were made of cellulose nanofiber composites with nickel hydroxide [CNF/Ni(OH)₂] substrate films and cellulose nanofiber composites with polypyrrole (CNF/PPY). Nickel hydroxide, Ni(OH)₂, has been prepared hydrothermally in the presence of TOCNFs, [TOCNF@Ni(OH)₂]. Similarly, the conductive polymer substrate has also been prepared from a composite consisting of TOCNF and PPY, TOCNF@ PPY film, by means of polymerization for the CE. Overall, the prepared electrodes both WE from CNF/Ni(OH)₂ substrates and CE from the TOCNF@PPY substrate film were revealed as the novelty of this work and which no one has introduced previously. Although NiO nanoparticles (NPs) coated on the Ni(OH)₂/TOCNF electrode also produced a good power conversion efficiency, PCE (0.75%); nevertheless, the NiO NP treatment with carbon dots boosted the efficiency up to 1.3%.

Enhancement of Perovskite Solar Cells by TiO2-Carbon Dot Electron Transport Film Layers

The high performance of perovskite solar cells was produced with the help of an electron transport layer (ETL) and hole transport layer. The film ETL (mesoporous (meso)-TiO₂/carbon dot) boosted the efficiency of the perovskite solar cells. A perovskite cell was fabricated by a coating of carbon dot on a meso-TiO₂ ETL. The fabricated meso-TiO₂/carbon dot-based device has decreased the pin-holes of the perovskite film layer compared to the meso-TiO₂-based device, which boosted 3% of the averaged PCE value of the devices. The UV-visible spectroscopy confirmed that the meso-TiO₂/carbon dot ETL showed better absorbance, that is, absorbed more incident light than meso-TiO₂ ETL to generate higher power conversion efficiency. Coating of carbon dot on meso-TiO₂ reduced carrier recombination, and fadeaway of the perovskite film cracks. The X-ray diffraction spectra displayed the removal of the perovskite component after spin-coating of carbon dot to the meso-TiO₂ ETL, indicating that the suppression of non-radiative recombination improves the device performance compared to meso-TiO₂ ETL. The stability after four weeks on the performance of the device was improved to be 92% by depositing carbon dot on meso-TiO₂ ETL compared to the meso-TiO₂ ETL-based device (82%). Thus, the high-quality perovskite cell was fabricated by coating carbon dot on a meso-TiO₂ ETL, because the electron transport between ETL and perovskite film layer was improved by the injection of electrons from carbon dot.

Cascade Förster Resonance Energy Transfer Studies for Enhancement of Light Harvesting on Dye-Sensitized Solar Cells

This work reports cascade Förster resonance energy transfer (FRET)-based n-type (ZnO) and p-type (NiO) dye-sensitized solar cells (DSSCs), discussing approaches to enhance their overall performance. Although DSSCs suffer from poorer performance than other solar cells, the use of composites with carbon dot (Cdot) can enhance the power conversion efficiency (PCE) of DSSCs. However, further improvements are demanded through molecular design to stimulate DSSCs. Here, a photosensitized system based on a cascade FRET was induced alongside the conventional photosensitizer dye (N719). To N719 in a DSSC is transferred the energy cascaded through donor fluorescence materials (pyrene, 3-acetyl-7-N,N-diethyl-coumarin or coumarin and acridine orange), and this process enhances the light-harvesting properties of the sensitizers in the DSSC across a broad region of the solar spectrum. PCE values of 10.7 and 11.3% were achieved for ZnO/Cdot and NiO/Cdot DSSCs, respectively. These high PCE values result from the energy transfer among multi-photosensitizers (cascade FRET fluorophores, N719, and Cdot). Moreover, Cdot can play a role in intensifying the adsorption of dyes and discouraging charge recombination on the semiconductor. The present results raise expectations that a significant improvement in photovoltaic performance can be attained of DSSCs exploiting the cascade FRET photonics phenomenon.

Complexation Nanoarchitectonics of Carbon Dots with Doxorubicin toward Photodynamic Anti-Cancer Therapy

Carbon dots (Cdots) are known as photosensitizers in which the nitrogen doping is able to improve the oxygen-photosensitization performance and singlet-oxygen generation. Herein, the characteristics of nanoconjugates of nitrogen-doped Cdots and doxorubicin were compared with the property of nitrogen-doped Cdots alone. The investigation was performed for the evaluation of pH-dependent zeta potential, quantum yield, photosensitization efficiency and singlet-oxygen generation, besides spectroscopy (UV-visible absorption and fluorescence spectra) and cytotoxicity on cancer model (HeLa cells). Encapsulation efficiency, drug loading, and drug release without and with light irradiation were also carried out. These investigations were always pursued under the comparison among different nitrogen amounts (ethylenediamine/citric acid = 1-5) in Cdots, and some characteristics strongly depended on nitrogen amounts in Cdots. For instance, surface charge, UV-visible absorbance, emission intensity, quantum yield, photosensitization efficiency and singlet-oxygen generation were most effective at ethylenediamine/citric acid = 4. Moreover, strong conjugation of DOX to Cdots via π-π stacking and electrostatic interactions resulted in a high carrier efficiency and an effective drug loading and release. The results suggested that nitrogen-doped Cdots can be considered promising candidates to be used in a combination therapy involving photodynamic and anticancer strategies under the mutual effect with DOX.

Cobalt Incorporated Graphitic Carbon Nitride as a Bifunctional Catalyst for Electrochemical Water-Splitting Reactions in Acidic Media

Non-noble metal-based bifunctional electrocatalysts may be a promising new resource for electrocatalytic water-splitting devices. In this work, transition metal (cobalt)-incorporated graphitic carbon nitride was synthesized and fabricated in electrodes for use as bifunctional catalysts. The optimum catalytic activity of this bifunctional material for the hydrogen evolution reaction (HER), which benefitted at a cobalt content of 10.6 wt%, was promoted by the highest surface area and conductivity. The activity achieved a minimum overpotential of ~85 mV at 10 mA/cm² and a Tafel slope of 44.2 mV/dec in an acidic electrolyte. These values of the HER were close to those of a benchmark catalyst (platinum on carbon paper electrode). Moreover, the kinetics evaluation at the optimum catalyst ensured the catalyst flows (Volmer-Heyrovsky mechanism), indicating that the adsorption step is rate-determining for the HER. The activity for the oxygen evolution reaction (OER) indicated an overpotential of ~530 mV at 10 mAcm^-2 and a Tafel slope of 193.3 mV/dec, which were slightly less or nearly the same as those of the benchmark catalyst. Stability tests using long-term potential cycles confirmed the high durability of the catalyst for both HER and OER. Moreover, the optimal bifunctional catalyst achieved a current density of 10 mAcm^-2 at a cell voltage of 1.84 V, which was slightly less than that of the benchmark catalyst (1.98 V). Thus, this research reveals that the present bifunctional, non-noble metallic electrocatalyst is adequate for use as a water-splitting technology in acidic media.

Hybridization of Nickel Oxide Nanoparticle with Carbon Dots and its Application for Antibacterial Activities

Nickel oxide nanoparticles (NiO NPs), composite with carbon dots (C-dots), (NiO NPs@C-dots) were synthesized, characterized and then its antibacterial activity was evaluated. NiO NPs was prepared using Buddleja polystachya Fresen leaf extract and Ni (NO₃ )₂ .6H₂ O as precursors. The C-dots were synthesized from benzene-1-4-diammine and citric acid. The cubic in phase of NiO NPs and NiO NPs@C-dots with their average particle sizes distributions of 21.47+0.56 and 21.61+0.34 nm were shown, respectively. The surface morphology of NiO NPs@C-dots by FE-SEM also revealed a large surface area, which is advantageous for the titled application. The XRD result indicated cubic face wurtzite structure and crystalline nature of NiO NPs. The carbon-doped compounds have no influence on crystal structure of NiO compound and no new peaks were observed. The antibacterial activity of a composite made up of NiO NPs@C-dots was tested, as well as the antibacterial activities of produced compounds, against human photogenic bacterial strains. Both NiO NPs and NiO NPs@C-dots are found to be powerful against all bacterial strains, according to the bioassay results. NiO nanoparticles and NiO@C-dots appeared to display strong to inhibitory effect (14-20 mm) and (17-23mm), respectively.

Carbon dot/inorganic nanomaterial composites

The preparation methods, formation mechanism, properties and applications of carbon dot/inorganic nanohybrid materials are reported.

Capacitance enhancement of nitrogen-doped graphene oxide/magnetite with polyaniline or carbon dots under external magnetic field: Supported by theoretical estimation

The effect of conductive materials (polyaniline (PA) or carbon dots (Cdots)) added to supercapacitor consisting of nitrogen-doped graphene oxide (NG) and magnetic nanoparticles (magnetite, Fe₃O₄) was assessed. Small amounts (4 wt%) of Cdots in composites of NG and Fe₃O₄ nanoparticles have shown better supercapacitor performance than the addition of PA. When the external stimulating force (magnetic field, 8.98 mT) was coupled with the electrochemical system, the specific capacitance was highest (2213 F/g at a scan rate of 5 mV/s) and the cyclic retention was 91% after 5000 cycles for the NG/Cdots/Fe₃O₄ composite electrode. These reports show that the adequate ternary composite materials effectively enhance the specific capacitance, increase the specific energy density and maintain the durability of supercapacitors under the magnet. The increase in the specific capacitance under the uniform magnetic field was proportional to the 3/5 power of bulk electrolyte concentration, although the power value was different from the theoretical estimation. The complex capacitance was almost double under the magnetic field due to the convection induced by the Lorentz force. It was also confirmed in comparison with the theoretical estimation that the Lorentz effect was responsible for the reduction of the charge transfer resistance, the increase of the relaxation time constant, the facilitation of the ion diffusion, and hence the increase of the double-layer capacitance. The present results will open a new window for the enhancement mechanisms on the capacitance efficiency under the magnetic field.

A nanocellulose-based platform towards targeted chemo-photodynamic/photothermal cancer therapy

Cellulose nanocrystals (CNCs) have advantages as drug delivery carriers because of their biocompatibility and the presence of hydroxyl groups which favor chemical modification and drug binding. The present study describes the development of novel multifunctional rod-like CNCs-based carriers as therapeutic platforms: CNCs were hybridized with folic acid for actively targeting tumor cells, carbon dots (Cdots) for both imaging and photodynamic/photothermal treatments and doxorubicin (DOX) as an anticancer drug. Hybridized carriers displayed excellent drug-loading capacity. Moreover, Cdots-containing hybrids showed fluorescence and photosensitized singlet oxygen generation and photothermal behavior. Carriers exhibited pH-sensitive drug release because of changing interactions with DOX, and this release proved to be effective against in vitro cervical cancer cells, as evidenced by dose-dependent reduced cellular viabilities. Additionally, DOX release was promoted by light irradiation and the photodynamic behavior by reactive oxygen species was confirmed. These results demonstrate the potential of multifunctional CNCs-based carriers as platforms for multimodal photodynamic/photothermal-chemotherapy.