Chlorophyll(a)/Carbon Quantum Dot Bio-Nanocomposite Activated Nano-Structured Silicon as an Efficient Photocathode for Photoelectrochemical Water Splitting

Functionalized Phytochemicals-Embedded Carbon Dots Derived from Medicinal Plant for Bioimaging Application

Precise visualization of biological processes necessitates reliable coloring technologies, and fluorescence imaging has emerged as a powerful method for capturing dynamic cellular events. Low emission intensity and solubility of intrinsic fluorescence are still challenging, hindering their application in the biomedical field. The nanostructurization and functionalization of the insoluble phytochemicals, such as chlorophyll and curcumin, into carbon dots (CDs) were conducted to address these challenges. Due to their unique fluorescence characteristics and biocompatibility, CDs derived from medicinal plants hold promise as bioimaging agents. Further, the nitrogen in situ functionalization of the as-synthesized CDs offered tunable optical properties and enhanced solubility. The surface modification aims to achieve a more positive zeta potential, facilitating penetration through biological membranes. This work provides valuable insights into utilizing functionalized phytochemical-embedded carbon dots for bioimaging applications. The doping of nitrogen by adding urea showed an alteration of surface charge, which is more positive based on zeta potential measurement. The more positive CD particles showed that Andrographis paniculata-urea-based CDs were the best particles to penetrate cells than others related to the alteration of the surface charge and the functional group of the CDs, with the optimum dose of 12.5 μg/mL for 3 h of treatment for bioimaging assay.

Near-Infrared-Induced NO-Releasing Photothermal Adhesive Hydrogel with Enhanced Antibacterial Properties

Bacterial infection and the development of antibiotic-resistant bacteria have decreased the effectiveness of traditional antibiotic treatments for wound healing. The design of a multifunctional adhesive hydrogel with antibacterial activity, self-healing properties, and on-demand removability to promote wound healing is highly desirable. In this work, a photothermal cyclodextrin with a NO-releasing moiety has been incorporated within an oxidized sodium alginate conjugated polyacrylamide (OS@PA) hydrogel to get a photothermal NO-releasing GSNOCD-OS@PA hydrogel. Such a multifunctional hydrogel has the unique feature of combined antibacterial activity as a result of a controlled photothermal effect and NO gas release under an 808 near-infrared laser. Because of oxidized sodium alginate (OSA), the hydrogel matrix easily adheres to the skin under twisted and bent states. In vitro cytotoxicity analysis against 3T3 cells showed that the hydrogels OS@PA and GSNOCD-OS@PA are noncytotoxic under laser exposure. The temperature-induced NO release by GSNOCD-OS@PA reached 31.7 mg/L when irradiated with an 808 nm laser for 10 min. The combined photothermal therapy and NO release from GSNOCD-OS@PA effectively reduced viability of both Staphylococcus aureus (Gram-positive) and Escherichia coli (Gram-negative) to 3 and 5%, respectively. Importantly, the phototherapeutic NO-releasing platform displayed effective fibroblast proliferation in a cell scratch assay.

Two-Pronged Approach: Synergistic Tuning of the Surface and Carbon Core to Achieve Yellow Emission in Lignin-Based Carbon Dots

In this study, yellow emissive lignin-based carbon dots (Y-CDs) were successfully prepared through a synergistic approach to adjust its surface and carbon core states. The lignin was initially effectively oxidized and carboxymethylated to impart abundant -COOH onto the precursor, which eventually adjusts the surface state of the CDs. Subsequently, α-naphthol was employed during the solvothermal treatment of lignin with the aim of elevating the sp2 domain content in the CDs and, thus, adjusting its carbon core state. The obtained Y-CDs possessed abundant carboxyl groups and nanoscale spherical shape with an average diameter of 5.21 nm. Meanwhile, the energy gap of Y-CDs was 2.46 eV and the optimal emission wavelength was 561 nm under the excitation wavelength of 410 nm. Synergistic adjusting carbon core and surface of the Y-CDs would alter the surface charge distribution and promote the delocalization of π electrons, and thus lead to a red shifting with the emission wavelength of 154 nm. Furthermore, a shape memory film with excellent recovery performance and fluorescent properties was designed by embedding the Y-CDs into polyvinyl alcohol (PVA) polymer. The incorporation of Y-CDs could impart the film with considerable high-value applications in the fields of intelligent sensing, biomedicine, and tissue engineering.

Biofunctionalized CdS Quantum Dots: A Case Study on Nanomaterial Toxicity in the Photocatalytic Wastewater Treatment Process

The toxic nature of inorganic nanostructured materials as photocatalysts is often not accounted for in traditional wastewater treatment reactions. Particularly, some inorganic nanomaterials employed as photocatalysts may release secondary pollutants in the form of ionic species that leach out due to photocorrosion. In this context, this work is a proof-of-concept study for exploring the environmental toxicity effect of extremely small-sized nanoparticles (<10 nm) like quantum dots (QDs) that are employed as photocatalysts, and in this study, cadmium sulfide (CdS) QDs are chosen. Typically, CdS is an excellent semiconductor with suitable bandgap and band-edge positions that is attractive for applications in solar cells, photocatalysis, and bioimaging. However, the leaching of toxic cadmium (Cd²⁺) metal ions due to the poor photocorrosion stability of CdS is a matter of serious concern. Therefore, in this report, a cost-effective strategy is devised for biofunctionalizing the active surface of CdS QDs by employing tea leaf extract, which is expected to hinder photocorrosion and prevent the leaching of toxic Cd²⁺ ions. The coating of tea leaf moieties (chlorophyll and polyphenol) over the CdS QDs (referred to hereafter as G-CdS QDs) was confirmed through structural, morphological, and chemical analysis. Moreover, the enhanced visible-light absorption and emission intensity of G-CdS QDs in comparison to that of C-CdS QDs synthesized through a conventional chemical synthesis approach confirmed the presence of chlorophyll/polyphenol coating. Interestingly, the polyphenol/chlorophyll molecules formed a heterojunction with CdS QDs and enabled the G-CdS QDs to exhibit enhanced photocatalytic activity in the degradation of methylene blue dye molecules over C-CdS QDs while effectively preventing photocorrosion as confirmed from cyclic photodegradation studies. Furthermore, detailed toxicity studies were conducted by exposing zebrafish embryos to the as-synthesized CdS QDs for 72 h. Surprisingly, the survival rate of the zebrafish embryos exposed to G-CdS QDs was equal to that of the control, indicating a significant reduction in the leaching of Cd²⁺ ions from G-CdS QDs in comparison to C-CdS QDs. The chemical environment of C-CdS and G-CdS before and after the photocatalysis reaction was examined by X-ray photoelectron spectroscopy. These experimental findings prove that biocompatibility and toxicity could be controlled by simply adding tea leaf extract during the synthesis of nanostructured materials, and revisiting green synthesis techniques can be beneficial. Furthermore, repurposing the discarded tea leaves may not only facilitate the control of toxicity of inorganic nanostructured materials but can also help in enhancing global environmental sustainability.

A smartphone-assisted ultrasensitive detection of acrylamide in thermally processed snacks using CQD@Au NP integrated FRET sensor

Selective, sensitive, and accurate detection of acrylamide (AA) in thermally processed food is a great challenge for food safety. This paper describes a "turn-on" fluorescence strategy to detect AA in real samples. Herein, the fluorescence intensity of glutathione-modified carbon quantum dots (GSHCQDs) was quenched initially upon the addition of gold nanoparticles (Au NPs) via fluorescence resonance electron transfer (FRET) to form a quenched GSHCQD-Au nanoprobe. When AA was introduced to the quenched GSHCQD-Au nanoprobe, the strong thiol-ene Michael addition (M-A) reaction among the -SH group of GSHCQD and AA occurred which releases GSHCQD to the medium and FL intensity at 520 nm is regained. The GSHCQD-Au nanoprobe can detect the AA in a normal aqueous solution (pH 7) selectively over a short response time of 5 min. Under the optimized conditions, the detection limit of AA was obtained to be 0.12 pM, over a wide linear range of 0-200 nM. Especially, this FRET-based sensing method was utilized successfully for the sensitive detection of AA using an RGB app installed on a smartphone, opening a new approach for the smart sensing of food contaminants.

Wafer-Scale Fabrication of Silicon Nanocones via Controlling Catalyst Evolution in All-Wet Metal-Assisted Chemical Etching

All-wet metal-assisted chemical etching (MACE) is a simple and low-cost method to fabricate one-dimensional Si nanostructures. However, it remains a challenge to fabricate Si nanocones (SiNCs) with this method. Here, we achieved wafer-scale fabrication of SiNC arrays through an all-wet MACE process. The key to fabricate SiNCs is to control the catalyst evolution from deposition to etching stages. Different from conventional MACE processes, large-size Ag particles by solution deposition are obtained through increasing AgNO₃ concentration or extending the reaction time in the seed solution. Then, the large-size Ag particles are simultaneously etched during the Si etching process in an etching solution with a high H₂O₂ concentration due to the accelerated cathode process and inhibited anode process in Ag/Si microscopic galvanic cells. The successive decrease of Ag particle sizes causes the proportionate increase of diameters of the etched Si nanostructures, forming SiNC arrays. The SiNC arrays exhibit a stronger light-trapping ability and better photoelectrochemical performance compared with Si nanowire arrays. SiNCs were fabricated by using n-type 1-10 Ω cm Si(100) wafers in this work. Though the specific experimental conditions for preparing SiNCs may differ when using different Si wafers, the summarized diagram will still provide valuable guidance for morphology control of Si nanostructures in MACE processes.

Fabrication of an amorphous metal oxide/p-BiVO4 photocathode: understanding the role of entropy for reducing nitrate to ammonia

Entropy regulation makes an amorphous metal oxide/p-BiVO4 heterostructure a desirable catalyst for the NO3− reduction reaction in a photoelectrochemical system.

Direct Z-scheme SiNWs@Co3O4 photocathode with a cocatalyst of sludge-derived carbon quantum dots for efficient photoelectrochemical hydrogen production

Solar driven photoelectrochemical (PEC) hydrogen production has attracted considerable attention, but the design of highly efficient, robust and low-cost photocathode still remains a significant challenge. Herein, we report a novel SiNWs@Co₃O₄Z-scheme heterojunction photocathode with carbon quantum dots eco-friendly derived from sludge (SCQDs) as the co-catalyst. The photocathode not only leads to effective separation of electron-hole pair, lower transmission resistance, and longer lifetime of charge carriers, but also elevates the stability by preventing direct contact between the SiNWs and the electrolyte as well as the self-oxidation. Simultaneously, the excellent electron transport properties of the SCQDs further improved the PEC performance. Correspondingly, a maximum current density of 14.88 mA·cm^-2 was obtained at -0.67 V with the applied bias photon-to-current efficiency (ABPE) achieving 8.4% under visible light irradiations at pH = 7. This work provides a promising scheme for Si-based photocathodes for PEC hydrogen production with a high performance, reliable stability, and low-cost.

Mesoporous Ultrathin In2O3 Nanosheet Cocatalysts on a Silicon Nanowire Photoanode for Efficient Photoelectrochemical Water Splitting

Vertical Si nanowire (NW) arrays are a promising photoanode material in the photoelectrochemical (PEC) water splitting field because of their highly efficient light absorption capability and large surface areas for PEC reactions. However, Si NW arrays always suffer from high overpotential, low photocurrent density, and low applied bias photon-to-current efficiency (ABPE) due to their low surface catalytic activity and intense charge recombination. Here, we report an efficient oxygen evolution cocatalyst of optically transparent, mesoporous ultrathin (2.47 nm thick) In2O3 nanosheets, which are coupled on the top of Si NW arrays. Combined with a conformal TiO2 thin film as an intermediate protective layer, this Si NW/TiO2/In2O3 (2.47 nm) heterostructured photoanode exhibited an extremely low onset potential of 0.6 V vs reversible hydrogen electrode (RHE). The Si NW/TiO2/In2O3 (2.47 nm) photoanode also showed a high photocurrent density of 27 mA cm-2 at 1.23 V vs RHE, more than 1 order of magnitude higher than that of the Si NW/TiO2 photoanodes. This improvement in solar water splitting performance was attributed to the significantly promoted charge injection efficiency as a result of the In2O3 nanosheet coupling. This work presents a promising pathway for developing efficient Si-based photoanodes by coupling ultrathin 2D cocatalysts.

Improved hydrogen evolution with SnS2 quantum dot-incorporated black Si photocathode

Black silicon (bSi), possessing appealing light-trapping properties and large specific surface area, ranks high among many other photocathode materials. However, the insufficient dynamics towards HER seriously bother black Si. Herein, a novel photoelectrode with ultrasmall size tin sulfide quantum dot (SnS₂ QD) incorporated black silicon was employed. Nanosized SnS₂ possesses numerous active sites for electrochemical reactions. Impressively, benefiting from SnS₂ QDs, the downward band bending of the Si Fermi level at the interface of electrolyte becomes higher, which remarkably suppresses the recombination of photo-generated carriers, thereby facilitating the participation of photo-generated electrons in PEC-HER. As a result, the thus-designed SnS₂/bSi reveals an exceptional PEC-HER activity with a positive onset potential of 0.235 V vs. reversible hydrogen electrode (RHE), a high photocurrent of 1.23 mA cm^-2 at 0 V vs. RHE, and long-term stability. Besides, the saturated photocurrent of ∼41 mA cm^-2 is achieved at about -0.51 V vs. RHE.

Solvothermal phase change induced morphology transformation in CdS/CoFe2O4@Fe2O3 hierarchical nanosphere arrays as ternary heterojunction photoanodes for solar water splitting

The design of efficient heterojunction photoanodes with appropriate band alignment and ease of charge separation has been one of the most highly focused research areas in photoelectrodes.

Superior light absorbing CdS/vanadium sulphide nanowalls@TiO2 nanorod ternary heterojunction photoanodes for solar water splitting

Vanadium sulphide is an emerging infrared active photocatalyst that has not been utilized to its maximum potential.

Amorphous MnCO3/C Double Layers Decorated on BiVO4 Photoelectrodes to Boost Nitrogen Reduction

NH₃ is mainly obtained by the Haber-Bosch method in the process of industrial production, which is not only accompanied by huge energy consumption but also environmental pollution. The reduction of N₂ to NH₃ under mild conditions is an important breakthrough to solve the current energy and environmental problems, so the preparation of catalysts that can effectively promote the reduction of N₂ is a crucial step. In this work, BiVO₄ decorated with amorphous MnCO₃/C double layers has been successfully synthesized by a one-step method for the first time. The C and MnCO₃ have been formed as ultrathin film, which enables the establishment of a uniform and tight interface with BiVO₄. The temperature-programmed desorption of N₂ (N₂-TPD) spectra confirmed that the MnCO₃/C could endow BiVO₄ with a drastic enhancement of the chemical absorption ability of a N₂ molecule compared with the pristine BiVO₄. Meanwhile, the method of isotope labeling proved that the catalyst exhibited excellent selectivity for the photocatalytic nitrogen reduction reaction (NRR). The production rate of NH₃ up to 2.426 mmol m^-2 h^-1 has been achieved over the BiVO₄/MnCO₃/C, which is almost 8 times that of pristine BiVO₄. The promoted production rate of NH₃ over BiVO₄/MnCO₃/C could be mainly attributed to the cooperative process between MnCO₃ and C amorphous layers. Therefore, this work could provide an alternative insight to understand the NRR process based on the model of a hierarchical amorphous structure.