A novel electrochemical sensor for the determination of cadmium ions based on nitrogen-enriched carbon modified electrode

In the present work, nitrogen-doped carbon was synthesized starting from a chitosan/urea mixture and immobilized at the surface of a bare glassy carbon electrode to detect Cd(II) ions using differential pulse-anodic stripping voltammetry method (DP-ASV). The synthesized nitrogen-doped carbon showed a significant potential for determining Cd(II) ions. Doping carbon with nitrogen atoms gives a structure with increased valence band energy, leading to acceleration of the electron transfer by creating an interaction of nitrogen's free electrons with Cd(II), which subsequently increases the peak current value. After the characterization of nitrogen-doped carbon by various methods, cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were used to study the prepared sensor's electrochemical behavior. Under optimal conditions, the proposed sensor has a linear response of 3.0 to 150 nM and its detection limit is 2.0 nM. This sensor can analyze Cd(II) in tap and river water as real samples.

The Facile Production of p-Chloroaniline Facilitated by an Efficient and Chemoselective Metal-Free N/S Co-Doped Carbon Catalyst

The catalytic hydrogenation of the toxic and harmful p-chloronitrobenzene to produce the value-added p-chloroaniline is an essential reaction for the sustainable chemical industry. Nevertheless, ensuring satisfactory control of its chemoselectivity is a great challenge. In this work, a N/S co-doped metal-free carbon catalyst has been fabricated by using cysteine as a source of C, N, and S. The presence of calcium citrate (porogen agent) in the mixture subjected to pyrolysis provided the carbon with porosity, which permitted us to overcome the issues associated with the loss of heteroatoms during an otherwise necessary activation thermal treatment. Full characterization was carried out and the catalytic performance of the metal-free carbon material was tested in the hydrogenation reaction of p-chloronitrobenzene to selectively produce p-chloroaniline. Full selectivity was obtained but conversion was highly dependent on the introduction of S due to the synergetic effect of S and N heteroatoms. The N/S co-doped carbon (CYSCIT) exhibits a mesoporous architecture which favors mass transfer and a higher doping level, with more exposed N and S doping atoms which act as catalytic sites for the hydrogenation of p-chloronitrobenzene, resulting in enhanced catalytic performance when compared to the N-doped carbon obtained from melamine and calcium citrate (MELCIT) used as a reference.

Glutaraldehyde and terephthaldehyde-crosslinked chitosan for cationic and anionic dyes removal from aqueous solutions: Experimental, DFT, kinetic and thermodynamic studies

Novel chitosan polymers were synthesized using two cross-linkers, Glutaraldehyde and Terephthaldehyde, to enhance stability and efficiency. Characterization techniques (XRD, FTIR, FE-SEM, TGA, DTG, BJH, and BET) confirmed successful synthesis. These polymers were employed as adsorbents for removing Malachite Green (MG) and Congo Red (CR) dyes from water. Batch experiments and DFT calculations investigated the adsorption process, thermodynamics, and kinetics. Results showed the CSGT-III polymer achieved the highest removal efficiency. For initial dye concentrations ([CR]o = 50 mg/L, [MG]o = 20 mg/L) and adsorbent doses (0.8 g/L for CR, 0.4 g/L for MG), removal efficiencies were 96.99 % for CR and 99.07 % for MG. Thermodynamic analysis confirmed the spontaneous nature of adsorption, and the process was endothermic for both dyes. The Langmuir model fitted adsorption isotherms well, indicating a homogeneous surface. Kinetic analysis revealed a pseudo-second-order model for both dyes.

High energy density storage, antifungal activity and enhanced bioimaging by green self-doped heteroatom carbon dots

Self-heteroatom-doped N-carbon dots (N-CDs) with a 2.35 eV energy gap and a 65.5% fluorescence quantum yield were created using a one-step, efficient, inexpensive, and environmentally friendly microwave irradiation method. FE-SEM, EDX, FT-IR, XRD, UV-VIS spectroscopy, FL spectroscopy, and CV electrochemical analysis were used to characterise the produced heteroatom-doped N-CDs. The graphitic carbon dot surface is doped with heteroatom functional groups such (S, P, K, Mg, Zn) = 1%, in addition to the additional passivating agent (N), according to the EDX surface morphology and the spontaneous heteroatom doping was caused by the heterogeneous chemical composition of pumpkin seeds. These spontaneous heteroatom-doped N-CDs possess quasispherical amorphous graphitic structure with an average size of less than 10 nm and the interplaner distance of 0.334 nm. Calculations utilising cyclic voltammetry showed that the heteroatom-doped N-CDs placed on nickel electrodes had a high specific capacitance value of 1044 F/g at a scan rate of 10 mV/s in 3 M of KOH electrolyte solution. Furthermore, it demonstrated a high energy and power density of 28.50 Wh/kg and 3350 W/kg, respectively. The higher value of specific capacitance and energy density were attributed to the fact that the Ni/CDs electrode material possesses both EDLC and PC properties due to the sufficient surface area and the multiple active sites of the prepared N-CDs. Furthermore, the heteroatom N-CDs revealed the antifungal action and bioimaging of the "Cladosporium cladosporioides" mould, which is mostly accountable for economic losses in agricultural products. The functional groups of nitrogen, sulphur, phosphorus, and zinc on the surface of the CDs have strong antibacterial and antifungal properties as well as fluorescence enhanced bioimaging.

SARS-CoV-2 external structures interacting with nanospheres using docking and molecular dynamics

Coronavirus is caused by the SARS-CoV-2 virus has shown rapid proliferation and scarcity of treatments with proven effectiveness. In this way, we simulated the hospitalization of carbon nanospheres, with external active sites of the SARS-CoV-2 virus (M-Pro, S-Gly and E-Pro), which can be adsorbed or inactivated when interacting with the nanospheres. The computational procedures performed in this work were developed with the SwissDock server for molecular docking and the GROMACS software for molecular dynamics, making it possible to extract relevant data on affinity energy, distance between molecules, free Gibbs energy and mean square deviation of atomic positions, surface area accessible to solvents. Molecular docking indicates that all ligands have an affinity for the receptor's active sites. The nanospheres interact favorably with all proteins, showing promising results, especially C60, which presented the best affinity energy and RMSD values ​​for all protein macromolecules investigated. The C60 with E-Pro exhibited the highest affinity energy of -9.361 kcal/mol, demonstrating stability in both molecular docking and molecular dynamics simulations. Our RMSD calculations indicated that the nanospheres remained predominantly stable, fluctuating within a range of 2 to 3 Å. Additionally, the analysis of other structures yielded promising results that hold potential for application in other proteases.Communicated by Ramaswamy H. Sarma.

Novel and sustainable green sulfur-doped carbon nanospheres via hydrothermal process for Cd (II) ion removal

Herein, the synthesis, characterization, and adsorption performance of a novel green sulfur-doped carbon nanosphere (S-CNs) is studied to eliminate Cd (II) ions from water effectively. S-CNs were characterized using different techniques including Raman spectroscopy, powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDX), , Brunauer-Emmett-Teller (BET) specific surface area analysis and Fourier transform infrared spectrophotometry (FT-IR), were performed. The efficient adsorption of the Cd (II) ions onto S-CNs strongly depended on pH, initial concentration of Cd (II) ions, S-CNs dosage, and temperature. Four isotherm models (Langmuir, Freundlich, Temkin & Redlich Peterson) were tested for modeling. Out of four, Langmuir showed more applicability than the other three models, with a Q_max value of 242.72 mg/g. Kinetic modeling studies suggest a superior fit of the obtained experimental data with the Elovich equation (linear) and pseudo-second-order (non-linear) rather than other linear and non-linear models. Data obtained from thermodynamic modeling indicates that using S-CNs for Cd (II) ions adsorption is a spontaneous and endothermic . The current work recommends using better and recyclable S-CNs to uptake excess Cd (II) ions.

Charge separation effect in the nanocomposites of Co3O4-QDs: visible light photocatalytic dye degradation in aqueous solutions

Photo-treatment of water is a promising environmentally friendly process that provides clean water and makes wastewater reusable in industry. Thus, efforts toward finding highly efficient photocatalysts have gained a huge attention to remove the organic contaminants in water. Quantum dots (QDs) are extensively utilized for photocatalytic remediation regarding their prominent optical, electrical, and chemical properties. Herein, we report the highly efficient and environmentally friendly synthesis of Co₃O₄-QDs-based graphene quantum dots (GQDs) and infinite coordination polymer comprising Zn nodes (Zn-ICP) nanocomposites as active and robust photocatalysts for photo-assisted water treatment. The pristine Co₃O₄-QDs, GQDs, and Zn-ICP showed lower activity under visible light. However, after functionalization of GQDs and Zn-ICP with Co₃O₄-QDs, the activity increased, and more photocatalytic efficiency was achieved. For instance, Zn-ICP, GQDs, Co₃O₄-QDs, Co₃O₄-QDs/Zn-ICP, and Co₃O₄-QDs/GQD degraded 21, 19, 52, 73, and 83% of rhodamine B (RhB) and 34, 46, 50, 73, and 76% of methylene blue (MB) after 60 min. The high photocatalytic efficiency was ascribed to the conjugation of Co₃O₄-QDs with GQDs and Zn-ICP which causes efficient absorption of visible light. The existence of Co₃O₄-QDs was found to be essential not only for effective charge separation but also widening the region of light absorption followed by increase in photocatalytic performances. Charge separation in photocatalytic reactions, energy levels of nanocomposites, and mechanism of the photocatalytic process were investigated by photoluminescence spectra (PL), Mott-Schottky, electrochemical impedance (EIS), and diffuse reflectance UV-Vis spectroscopy (DRS).

Corrigendum to “Green Synthesis of S- and N-Codoped Carbon Nanospheres and Application as Adsorbent of Pb (II) from Aqueous Solution”

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An ultra-low-cost and adjustable in-house electrospinning machine to produce PVA nanofiber

Electrospinning is a method that uses a high-voltage electric field to fabricate nanofiber by charging and ejecting a polymer solution through a syringe. Compared to other methods, it produces nanofiber using simple and easy techniques. The widespread usage of the commercial electrospinning machines (Spinboxsystems)-BASIC KIT type for beginners is limited due to its price of over USD15,595. Additionally, the Original Equipment Manufacturer (OEM) spare parts are expensive to replace, which increases the production cost of Polyvinyl Alcohol (PVA) polymer nanofiber and hinders its application in various fields. This led to the successful design and development of an in-house built electrospinning machine at a total cost below USD2,000. The new machine is easy and simple to operate while also producing PVA nanofiber with excellent properties.

Recent Advances and Mechanistic Insights into Antibacterial Activity, Antibiofilm Activity, and Cytotoxicity of Silver Nanoparticles

The substantial increase in multidrug-resistant (MDR) pathogenic bacteria is a major threat to global health. Recently, the Centers for Disease Control and Prevention reported possibilities of greater deaths due to bacterial infections than cancer. Nanomaterials, especially small-sized (size ≤10 nm) silver nanoparticles (AgNPs), can be employed to combat these deadly bacterial diseases. However, high reactivity, instability, susceptibility to fast oxidation, and cytotoxicity remain crucial shortcomings for their uptake and clinical application. In this review, we discuss various AgNPs-based approaches to eradicate bacterial infections and provide comprehensive mechanistic insights and recent advances in antibacterial activity, antibiofilm activity, and cytotoxicity (both in vitro and in vivo) of AgNPs. The mechanistic of antimicrobial activity involves four steps: (i) adhesion of AgNPs to cell wall/membrane and its disruption; (ii) intracellular penetration and damage; (iii) oxidative stress; and (iv) modulation of signal transduction pathways. Numerous factors affecting the bactericidal activity of AgNPs such as shape, size, crystallinity, pH, and surface coating/charge have also been described in detail. The review also sheds light on antimicrobial photodynamic therapy and the role of AgNPs versus Ag⁺ ions release in bactericidal activities. In addition, different methods of synthesis of AgNPs have been discussed in brief.

Carbon dots conjugated nanocomposite for the enhanced electrochemical performance of supercapacitor electrodes

Naturally, a combination of metal oxides and carbon materials enhances the electrochemical performance of supercapacitor (SC) electrodes. We report on two different materials with highly conductive carbon dots (CDs) and a Co0.5Ni0.5Fe2O4/SiO2/TiO2 nanocomposite with a high power density, a high specific surface area, and a nanoporous structure to improve power and energy density in energy storage devices. A simple and low-cost process for synthesizing the hybrid SC electrode material Co0.5Ni0.5Fe2O4/SiO2/TiO2/CDs, known as CDs-nanocomposite, was performed via a layer-by-layer method; then, the CDs-nanocomposite was loaded on a nickel foam substrate for SC electrochemical measurements. A comparative study of the surface and morphology of CDs, the Co0.5Ni0.5Fe2O4/SiO2/TiO2 nanocomposite and CDs-nanocomposite was carried out using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), BET surface area, and Raman spectroscopy. The synthesized CDs-nanocomposite electrode material displayed enhanced electrochemical performance, having a high specific capacitance of 913.7 F g-1 at a scan rate of 5 mV s-1 and capacitance retention of 72.2%, as well as remarkable long-life cyclic stability over 3000 cycles in the three-electrode setup and 1 M KOH electrolyte. It also demonstrated a superior energy density of 130.7 W h kg-1. The improved electrochemical behavior of the CDs-nanocomposite for SC electrodes, together with its fast and simple synthesis method, provides a suitable point of reference. Other kinds of metal oxide nanocomposites can be synthesized for use in energy storage devices.

Facile sonochemical method for preparation of Cs2HgI4 nanostructures as a promising visible-light photocatalyst

Attempts are continuing to discover novel and efficient solutions to promote water grade and industrial sewage treatment. For the first time, we present a novel Cs₂HgI₄ photocatalyst functional below visible radiation. Cs₂HgI₄ nano photocatalyst has been prepared via an accelerated sonochemical approach to examine its photocatalytic progression. Several construction circumstances, including variations of power and time of sonication and performance of different surfactant types, were conducted to produce fine particles with uniform morphology. FESEM images attested that the presence of surfactant had an adverse and destructive effect on the morphology of products. The bandgap for Cs₂HgI₄ nanostructures was determined to be approximately 2.3 eV, making these nanostructures desirable for photocatalytic applications. The photocatalytic data confirmed that Cs₂HgI₄ could destroy acidic coloring agents greater than basic ones. The highest photodegradation was observed for methyl orange with 76.8%.

A new phase transfer nanocatalyst NiFe2O4-PEG for removal of dibenzothiophene by an ultrasound assisted oxidative process: kinetics, thermodynamic study and experimental design

In this study, NiFe₂O₄–PEG, an effective nanocatalyst was synthesized via a hydrothermal method using different PEG concentrations and synthesis times. The synthesized nanocatalyst was used in the ultrasound assisted oxidative desulfurization (UAOD) of model fuels (e.g. n-hexane and dibenzothiophene (DBT)) for the first time. The nanocatalyst was then characterized by XRD, FTIR, BET, SEM, VSM and TEM analyses. In addition, central composite design was used to evaluate the effective variables on the UAOD process. The optimal values of effective factors such as catalyst dose, oxidant amount, irradiation time and ultrasonic power to maximize of the percentage of sulfur removal were 0.149 g, 15 mL, 11.96 min, and 70 MHz, respectively. Moreover, the kinetic aspects of the oxidation reaction of DBT in the UAOD process were investigated using a pseudo-first-order model. Furthermore, using the Arrhenius equation, an activation energy of 35.86 kJ mol⁻¹ was obtained. Additionally, thermodynamic analysis showed that the oxidation reaction of DBT was endothermic with a positive Gibbs free of energy, indicating the non-spontaneity of oxidation of DBT in the UAOD process. Moreover, the conversion rate of DBT has increased from 57% at 35 °C to 85% at 65 °C.

In this study, NiFe₂O₄–PEG, an effective nanocatalyst was synthesized via a hydrothermal method using different PEG concentrations and synthesis times.

Facile preparation and characterization of a novel visible-light-responsive Rb2HgI4 nanostructure photocatalyst

Visible photocatalytic procedures exhibit encouraging potential in water purification by increasing the photocatalytic performance. Therefore, the improvement of low-cost and efficient photocatalysts for environmental remediation is an increasing demand, and photocatalysts based on semiconductors have gained considerable attention due to their superior stability and activity. In the current study, novel Rb₂HgI₄ nanostructures were prepared via a simple, low-cost, and low-temperature solid-state method. The effects of different parameters such as type of surfactants, reaction temperature, and reaction time were studied on the structure, crystallinity, particle size, and shape of nanostructures. This new compound has a suitable band gap (2.6 eV) in the visible region. The photocatalytic performance of Rb₂HgI₄ was examined for the removal of coloring agents under visible light irradiation and it was found that this compound could degrade and eliminate acid black 1 by about 72.1%.