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.

Synthesis of silver nanoparticles using bio valorization coffee waste extract: photocatalytic flow-rate performance, antibacterial activity, and electrochemical investigation

It is well known that biogenic synthesis, as compared to other processes, has proven to be highly effective in the fabrication of silver nanoparticles (AgNPs). Thus, our current study focused on synthesizing AgNPs using coffee waste extract (CWE). CWE contains many compounds identified by HPLC, which reduce, cap, and stabilize AgNPs in its solution. The as-synthesized AgNPs were produced with a monodispersed small size around 20 nm and exhibited in-plane dipole plasmon resonances of hexagonal nanoplates. AgNPs were characterized by both physical and spectroscopic methods, which confirmed their nanoscale dimensions with a hexagonal shape. The as-prepared AgNPs (12 mg) enabled the photodegradation of phenol compounds (20 mL) with a removal efficiency of ~ 94.6% in a short time in the presence of citric acid. Additionally, the second promising application of AgNPs was the tendency to remove the hazard 2,4 dinitroaniline (2,4 DNA) with a percent more than 97% while using only 7 mg of AgNPs. Moreover, the green synthesized AgNPs are superior in inhibiting bacterial growth and killing most infected microbes such as B. subtilis, P. aeruginosa, S. aureus, and E. coli. The electrochemical characteristics of the AgNPs were evaluated using a three-electrode system. The calculated specific capacitance was 280 F g-1 at 0.56 A g-1. Furthermore, after 1000 cycles at 2.2 A g-1, the AgNPs electrode demonstrates an excellent cycling stability behavior with 94.8% capacitance retention. Based on the previous promising results, it can be concluded that CWE is an environmentally benign extract to prepare AgNPs with low cost, saving and easily used for many great domains in photocatalytic, phenol compound removals, and production of functional nanodevices.

Activated biochar derived from peanut shells as the electrode materials with excellent performance in Zinc-air battery and supercapacitance

The use of activated biochar-based electrode derived from waste biomass in energy technologies, such as metal-air batteries and supercapacitors, is an important strategy for realizing energy and environmental sustainability in the future. Herein, peanut shells (waste biomass) were employed to prepare activated biochar materials by pyrolysis in molten KCl and heat-treatment. The effective dispersion and corrosion effects of molten salt for the pyrolysis products during pyrolysis obviously increase defects and specific surface area of the activated biochar materials. The prepared activated biochar material (PS-800-1000) by pyrolysis in molten KCl at 800 °C and heat-treatment at 1000 °C exhibits excellent catalytic activity with half-wave potential of 0.84 V vs. RHE, comparable to commercial Pt/C for oxygen reduction reaction (ORR) in 0.1 M KOH and outstanding supercapacitance performance in 6 M KOH with high specific capacitance (355 F g^-1 at 0.5 A g^-1), which exceeds all reported biochar derived from peanut shells. The PS-800-1000-based zinc-air battery (ZAB) displays higher peak power density (141 mW cm^-2), specific capacity (767 mAh g_Zn^-1) and cycling stability than Pt/C-based ZAB. The activated biochar prepared by pyrolysis in molten KCl and heat-treatment method from peanut shells can be a promising candidate for replacing precious metals in energy conversion/storage devices.

Enhanced electrochemical performances of peanut shell derived activated carbon and its Fe3O4 nanocomposites for capacitive deionization of Cr(VI) ions

Capacitive deionization (CDI) is one of the most efficient and emerging techniques for the removal of toxic metal ions from aqueous solutions. In this study, mesoporous peanut shell derived activated carbon (PSAC) was prepared by low temperature pyrolysis at 500 °C. Subsequently, a novel iron oxide/PSAC (Fe₃O₄/PSAC) nanocomposite adsorbent was prepared via facile one-pot hydrothermal synthesis method at 180 °C. Nucleation growth mechanism and appropriate characterizations of prepared nanocomposites were investigated. The obtained Fe₃O₄/PSAC possessed a highly mesoporous structure, and a large specific surface area (680 m²/g). The electrochemical analysis showed that the obtained Fe₃O₄/PSAC nanocomposites exhibited higher capacitance (610 F/g at 10 mV/s), good stability and low internal resistance. A batch mode adsorption and CDI based Cr(VI) removal studies were conducted. Effects of solution pH and cycle time on Cr(VI) electrosorption capacity were further investigated. The Fe₃O₄/PSAC based electrodes exhibit a maximum electrosorption capacity of 24.5 mg/g at 1.2 V, which was remarkably larger than other reported materials. The fabricated composite displayed higher electrosorption capacity with rapid time and a favorable reduction of Cr (VI) to Cr(III). Studies indicated that the Fe₃O₄/PSAC based CDI electrode possesses a good potential to be applied for the removal of toxic metal ions from wastewater.