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Here, a unique heteroatom-doped spongy carbonaceous material from dwarf banana peel has been synthesized successfully using the one-step hydrothermal method. The discarded banana peel was reused as a carbon source for the formation of heteroatom-doped porous carbon. This biowaste-derived heteroatom-doped porous carbonaceous material (BH-PCM) has plenty of interconnected pores with an acceptable surface area of 213 m2 g−1. Thoroughly characterized BH-PCM has been used as electrode material for supercapacitor using a three-electrode system with an aqueous 1 M H2SO4 solution. The as-synthesized BH-PCM holds an excellent specific capacitance of 137 F g−1 at 0.5 A g−1 and an impressive rate performance with a capacitance enduring 51 F g−1 at 5.0 A g−1. After 10,000 galvanostatic charge–discharge cycles, an initial capacitance of 94% was maintained. To show the practical applicability of the BH-PCM, the symmetrical two-electrode cell was fabricated and delivered the gravimetric specific capacitances of 87 F g−1 at 1 A g−1. The excellent electrochemical performance of BH-PCM towards supercapacitor was due to their high surface area, reasonable heteroatom doping rate, and a suitable degree of graphitization. This study offers a green approach for the development of environmental-friendly potential carbon-based electrode, by converting biowaste to clean/green energy.

The electrolysis of water is considered as a potentially realistic technology for the massive production of hydrogen. The use of graphene composites in electrocatalytic water splitting has been extensively investigated. Graphene-iron oxide composites were prepared via in situ polymerization of 2-(methacryloyloxy)ethyl phosphorylcholine (MPC) and poly (ethylene glycol) monomethacrylate (PEG) on graphene surface (non-oxidative graphite-HOPG/G) in presence of iron oxide nanoparticles (IONPs) and denoted as G-INSCP. Copolymers PMPC-co-PEG (CP) and block copolymer PMPC-b-PEG (BCP) were prepared and their structures were thoroughly characterized. These polymers were used to prepare G-INSCP, G-CP, and G-BCP, their stabilities were compared and their morphologies were studied. HOPG, G-CP, and G-INSCP were used in the hydrogen evolution reaction (HER) as effective platinum catalyst alternatives. G-BCP composite was excluded owing to its very low stability. To evaluate the performance of these electrocatalysts in acidic media, linear sweep voltammetry and electrochemical impedance spectroscopy were employed. Results revealed that, compared with HOPG and G-CP, G-INSCP exhibited a significantly improved catalytic activity with respect to HER in an acidic electrolyte. Additionally, at a current density of 10 mA cm−2, G-INSCP demonstrated a lower overpotential and Tafel slope of 95 mVRHE and 67 mV dec−1, respectively. These observations were attributed to the synergistic effect between the magnetic IONPs and PMPC polymer along with the increase in the electron transfer rate owing to the conductive graphene in the catalyst. Thus G-INSCP catalyst can be a potential candidate for HER and paving the way for the advancement of new and similar catalysts for other applications.

Spherical-shaped graphene oxide-embedded chitosan/gelatin hydrogel particles (CGGO) were prepared by using inverse suspension method from biopolymers chitosan and gelatin with graphene oxide for the adsorption of heavy metal ions (HM). The prepared CGGO particles were characterized by various physicochemical techniques such as field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy analysis, X-ray diffraction, and Fourier transform infrared spectrometry. HM-Pb(II), Cd(II), Hg(II), and Cr(III) adsorption experiments using CGGO showed 55% removal efficiency of Hg(II) in the single metal system. However, in the multiple metal ion system, all metal ions showed removal efficiency > 70%. This suggests that the prepared hydrogel particles can be effectively used for the removal of HM. The preparation method also paves the way for the large-scale production of hydrogel particles as HM adsorbents.

This study aims to explore heavy metal ion adsorbents with excellent removal performance. For this, chitosan and gelatin-based hydrogel beads (Hyb) were prepared and crosslinked with a nanocellulose structure using ammonium zirconium carbonate (AZC) and calcium chloride (Ca). The prepared hybrid aerogels, HybAZC and HybCa, were characterized by using various techniques to investigate their respective morphologies and functional groups for a better understanding of their capacity for heavy metal ion adsorption. Then, we systematically investigated the difference in removal and adsorption capacities of heavy metal ions for single and multiple ion cases using the prepared aerogels-HybAZC and HybCa. The tested heavy metal ions were Hg(II), Pb(II), Cd(II), and Cr(III) ions. For the adsorption systems with single ion (S-HybAZC and S-HybCa) cases, every single metal ionic solution was studied in the presence of the aerogels; but for the multiple ion (M-HybAZC and M-HybCa) adsorption systems, mixed metal ionic solutions with predetermined concentrations of four heavy metal ions were studied. In a single system using S-HybAZC and S-HybCa aerogels, the removal efficiencies of all metal ions except the Cd(II) ion (using S-HybCa) were calculated to be above 65%. In multiple systems, regardless of the quality or quantity of aerogels or metal ions, the removal efficiencies were calculated to be above 85%. Overall, results suggest the prepared aerogels HybAZC and HybCa can be employed as effective adsorbents for single and multiple systems. Thus, hybrid nanocellulose aerogels have great potential for practical applications in the removal of heavy metal ions.

Graphene is an excellent 2D material that has extraordinary properties such as high surface area, electron mobility, conductivity, and high light transmission. Polymer composites are used in many applications in place of polymers. In recent years, the development of stable graphene dispersions with high graphene concentrations has attracted great attention due to their applications in energy, bio-fields, and so forth. Thus, this review essentially discusses the preparation of stable graphene–polymer composites/dispersions. Discussion on existing methods of preparing graphene is included with their merits and demerits. Among existing methods, mechanical exfoliation is widely used for the preparation of stable graphene dispersion, the theoretical background of this method is discussed briefly. Solvents, surfactants, and polymers that are used for dispersing graphene and the factors to be considered while preparing stable graphene dispersions are discussed in detail. Further, the direct applications of stable graphene dispersions are discussed briefly. Finally, a summary and prospects for the development of stable graphene dispersions are proposed.

The iron-oxide nanoparticles (IONPs) filled multi-walled carbon nanotubes (IONP-MWCNTs hybrid) were directly synthesized via chemical vapour deposition method with acetylene as a carbon source. The bare IONPs were synthesized by hydrothermal method and the prepared bare IONPs were employed as a catalytic-support as well as a filling agent for the synthesis of IONP-MWCNTs hybrid at about 800 °C under atmospheric pressure. The synthesized IONP-MWCNTs hybrid was characterized by various physicochemical techniques including X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, field emission scanning electron microscopy and high-resolution transmission electron microscopy. The results demonstrate that the carbon nanotubes were successfully generated on the IONPs with the high yield because of unique carbon-iron metal interactions. An average diameter of synthesized IONPs and MWCNTs are around 9 and 50 nm, respectively. In addition, the HRTEM images and Raman spectrum confirms the obtained IONP-MWCNTs hybrid is well graphitic without major carbonaceous impurities. The electrochemical activity of the synthesized IONP-MWCNTs hybrid was performed in 2 M KOH using a three-electrode cell setup with a saturated Ag/AgCl as a reference electrode and a platinum plate as a counter-electrode by cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy techniques. This electrode active material (IONP-MWCNTs hybrid) possess excellent supercapacitive behaviour and has excellent cyclic stability, even after 5000 cycles of charge-discharge at 4 A g−1 as current density. Thus, the synthesized IONP-MWCNTs hybrid will be a suitable as well as an economical electrode active material for high-performance supercapacitors.

As an efficient photocatalytic titanium dioxide nanoparticles@nitrogen-doped carbon (TiO2 NPs@C) nanocomposite and bright fluorescent with good biocompatible nitrogen-doped carbon dots (N-CDs) were synthesized at once by an affordable hydrothermal method. Physicochemical properties of the synthesized materials were examined by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, field emission scanning electron microscopy (FESEM) with energy dispersive X-ray (EDX) and elemental mapping analysis, high resolution transmission electron microscopy (HRTEM), atomic force microscopy (AFM), ultraviolet–visible (UV–vis) spectroscopy and fluorescence spectroscopy. The photocatalytic efficiency of synthesized TiO2 NPs@C nanocomposite was evaluated in the degradation of methylene blue (MB) under UV-light irradiation. The degradation efficiency of TiO2 NPs@C nanocomposite is about 90% when extending the irradiation time to 40 min, the rate constant is 5 times higher than that of bare TiO2 NPs. The augmentation of photocatalytic activity of TiO2 NPs@C nanocomposite was attributed to the synergistic effect between TiO2 NPs and graphene-like carbon within the nanocomposite. The recycling studies were conducted and the photodegradation efficiency of TiO2 NPs@C nanocomposite did not show any significant changes up to three cycles, suggesting that the synthesized photocatalyst has good repeatability and the considerable stability. In addition, the carbon derived from a natural green source possesses the hydroxyl and nitrogen-containing functional groups on the surface which resulting TiO2 NPs @C nanocomposite with high photocatalytic activity. Also, the obtained N-CDs displays almost zero toxicity towards the Candida albicans cells even at high concentrations which can be utilized as a powerful in-vitro label-free fluorescent probe for live cell imaging. Based on their bright with stable fluorescence and cellular imaging with good biocompatibility, N-CDs would offer a great potential for a wide range of applications in the biomedical and clinical applications in the near future.

Hexagon-shaped composite made up of iron oxide nanoparticles@carbon (IONP@C-HIOP) was successfully synthesized at 185 °C by a simple hydrothermal method. All the analytical results confirmed the formation of IONP@C-HIOP with a uniform size without apparent aggregation. The IONP@C-HIOP composite exhibits excellent catalytic activity towards hydrogen evolution reaction (HER) with lowest onset-potential (−25 mVRHE) and Tafel slope (45 mV dec−1) in 0.5 M H2SO4 aqueous electrolyte. The high electrocatalytic performance of the composite towards HER attributes to the carbon decorated IONPs, providing a conducting network for fast electron transport from IONPs to electrodes. The composite shows high stability representing a synergistic effect between IONPs and carbon for efficient HER. In addition, the supernatant solution (byproduct) of IONP@C-HIOP showed durable fluorescence activity and was used as a label-free fluorescent probe for live cell imaging applications. This method of synthesis is a simple and economic for multi-diverse applications. Thus, the main product of synthesized IONP@C-HIOP might be an ideal choice for environmental-friendly applications HER and the byproduct for cell imaging.

Heteroatom functionalization on a graphene surface can endow the physical and structural properties of graphene. Here, a one-step in situ polymerization method was used for the noncovalent functionalization of a graphene surface with poly-N-vinyl-2-pyrrolidone (PNVP) and the exfoliation of graphite into graphene sheets. The obtained graphene/poly-N-vinyl pyrrolidone (GPNVP) composite was thoroughly characterized. The surface morphology of GPNVP was observed using field emission scanning electron microscopy and high-resolution transmission electron microscopy. Raman spectroscopy and X-ray diffraction studies were carried out to check for the exfoliation of graphite into graphene sheets. Thermogravimetric analysis was performed to calculate the amount of PNVP on the graphene surface in the GPNVP composite. The successful formation of the GPNVP composite and functionalization of the graphene surface was confirmed by various studies. The cyclic voltammetry measurement at different scan rates (5–500 mV/s) and electrochemical impedance spectroscopy study of the GPNVP composite were performed in the typical three-electrode system. The GPNVP composite has excellent rate capability with the capacitive property. This study demonstrates the one-pot preparation of exfoliation and functionalization of a graphene surface with the heterocyclic polymer PNVP, the resulting GPNVP composite will be an ideal candidate for various electrochemical applications.

Nitrogen-doped carbon dot decorated zinc oxide nanoparticles (N-CDs@ZnO composite) were successfully fabricated by an economical wet-impregnation method and used as a photocatalyst for the degradation of aqueous methylene blue (MB) dye under UV-light at room temperature. The chemical composition and morphological features of the prepared N-CDs@ZnO composite were characterized by attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and field emission scanning electron microscopy (FESEM). The photodegradation capability of the N-CDs@ZnO composite was compared with that of bare ZnO nanoparticles, under identical experimental conditions. The results show that the N-CDs@ZnO composite exhibits notably higher photocatalytic activity (degradation efficiency over 99%, 60 min) compared to bare ZnO nanoparticles (75%, 60 min) towards the degradation of MB under UV-light irradiation. Besides, the degradation obeyed the pseudo-first-order kinetics model with a photocatalytic rate constant (k) of 0.0557 min-1, which was ∼2.3 times higher than that of bare ZnO nanoparticles (0.0240 min-1). The crucial roles of N-CDs in the enhancement of the photocatalytic activity of the N-CDs@ZnO composite arise because the N-CDs can efficiently absorb UV-light and trap electrons, thus hindering the recombination of the photo-generated electron-hole pairs and also suppressing the photocorrosion of the ZnO nanoparticles in the N-CDs@ZnO composite. The N-CDs@ZnO composite not only showed good photocatalytic activity but also had good stability since the photocatalytic activity did not significantly decrease after three cycling tests. The present study shows that the N-CDs@ZnO composite can be considered as an ideal photocatalyst in the field of dye degradation. Overall, the present approach obeys green chemistry principles with the simple construction of the N-CDs@ZnO composite and the composite holds promise for the development of efficient photocatalytic systems.

Growing global biowaste and its environmental issues challenge the need for converting biowastes into a beneficial product. Among the biowaste, here kiwi fruit (Actinidia Deliciosa) peels are considered for the preparation of carbon dots (CDs). Using a green one-pot hydrothermal-carbonization method, kiwi fruit peels were effectively converted into valuable kiwi fruit peel carbon dots (KFP-CDs). The morphology, physio-chemical and optical properties of as-synthesized KFP-CDs were analyzed using various analytical techniques such as X-ray powder diffraction, Raman spectroscopy, attenuated total reflection-Fourier transform infrared spectroscopy, field emission scanning electron microscopy, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, Ultraviolet–visible, and fluorescence spectroscopy. The KFP-CDs revealed a homogeneous spherical shape, monodispersed with an average size of 5 nm. The characterization confirms that KFP-CDs have functional groups such as –CN, –COOH, and –OH which are responsible for the easy dispersion of KFP-CDs in aqueous media. Without any preprocessing, KFP-CDs exhibit strong fluorescence upon exposure to UV light. Further, KFP-CDs displayed excitation-dependent fluorescence emission with a good quantum yield of about 18%. Thus by considering the excellent properties of KFP-CDs, KFP-CDs were used as fluorescent ink for drawing and writing without any capping/passivation agent. The pictures and words were instantaneously viewed when exposed to UV light. In addition, KFP-CDs tested for cell imaging in four human cell lines (normal and cancer cells) bestowed excellent biocompatibility and low cytotoxicity, which is important for the safe and long-term development of cellular imaging. The findings imply that KFP-CDs can be utilized as a cell labeling agent for mesenchymal stem cells, breast cancer, and thyroid cancer cells in vitro imaging. Thus, these observations revealed that investigating sustainable resource-based CDs can open up new avenues for tackling environmental issues.

Cobalt oxide nanoparticles@nitrogen-doped reduced graphene oxide (Co3O4@N-rGO) composite and nitrogen-doped graphene dots (N-GDs) were synthesized by a one-pot simple hydrothermal method. The average sizes of the synthesized bare cobalt oxide nanoparticles (Co3O4 NPs) and Co3O4 NPs in the Co3O4@N-rGO composite were around 22 and 24 nm, respectively with an interlayer distance of 0.21 nm, as calculated using the XRD patterns. The Co3O4@N-rGO electrode exhibits superior capacitive performance with a high capability of about 450 F g−1 at a current density of 1 A g−1 and has excellent cyclic stability, even after 1000 cycles of GCD at a current density of 4 A g−1. The obtained N-GDs exhibited high sensitivity and selectivity towards Fe2+ and Fe3+, the limit of detection was as low as 1.1 and 1.0 μM, respectively, representing high sensitivity to Fe2+ and Fe3+. Besides, the N-GDs was applied for bio-imaging. We found that N-GDs were suitable candidates for differential staining applications in yeast cells with good cell permeability and localization with negligible cytotoxicity. Hence, N-GDs may find dual utility as probes for the detection of cellular pools of metal ions (Fe3+/Fe2+) and also for early detection of opportunistic yeast infections in biological samples.

Herein, Sargassum coreanum (marine algae)-mediated silver nanoparticles (AgNPs) were successfully synthesized by a simple reduction method. The synthesized AgNPs were characterized using ultraviolet-visible spectroscopy, attenuated total reflection Fourier transformed infrared spectroscopy, X-ray diffractometry, field emission scanning electron microscopy (FESEM) with energy-dispersive X-ray (EDX) spectroscopy, and high-resolution transmission electron microscopy (HR-TEM) analysis. The acquired colloidal AgNPs were strongly absorbed around 420 nm and displayed brown color under visible light. The XRD pattern of AgNPs exposed their face-centered cubic geometry along with crystalline nature. The HRTEM images of synthesized AgNPs confirmed the mean particle size of 19 nm with a distorted spherical shape, and the calculated interlayer distance (d-spacing value) was about 0.24 nm. Further, the catalytic degradation of methylene blue using sodium borohydride and AgNPs was monitored using UV–vis spectroscopy. The result revealed that AgNPs performed as a superior catalyst, which completely degraded MB in 20 min. The rate constant for MB degradation was calculated to be 0.106 min−1, demonstrating that the marine algae-mediated AgNPs had outstanding catalytic activity. This approach is easy and environmentally benign, which can be applied for environmental-based applications such as dye degradation and pollutant detoxification.

This paper’s emphasis is on the development of a fluorescent chemosensor for Fe3+ ions in an aqueous solution, using hydrophilic carbon dots (O-CDs). A simple, cost-effective, and environmentally friendly one-step hydrothermal synthesis method was used to synthesize fluorescent hydrophilic O-CDs from Oxalis corniculata (Family; Oxalidaceae). The graphitic structure and size distribution of the O-CDs was verified by X-ray diffraction, Raman spectroscopy, and high-resolution transmission electron microscopy studies. The resulting O-CDs had a near-spherical shape and an adequate degree of graphitization at the core, with an average diameter of 4.5 nm. X-ray photoelectron and Fourier transform infrared spectroscopy methods revealed the presence of several hydrophilic groups (carbonyl, amine, carboxyl, and hydroxyl, along with nitrogen and oxygen-rich molecules) on the surface of O-CDs. The synthesized hydrophilic O-CDs with excitation wavelength-dependent emission fluorescence characteristics showed a high quantum yield of about 20%. Besides this, the hydrophilic O-CDs exhibited a bright and controllable fluorescence with prolonged stability and photo-stability. These fluorescent hydrophilic O-CDs were used as a nanoprobe for the fluorometric identification of Fe3+ ions in an aqueous solution, with high sensitivity and selectivity. By quenching the blue emission fluorescence of this nanosensor, a highly sensitive Fe3+ ion in the range of 10–50 µM with a minimum detection limit of 0.73 µM was achieved. In addition, the developed nanosensor can be used to sense intracellular Fe3+ ions with high biocompatibility and cellular imaging capacity, and it has a lot of potential in biomedical applications.

Deep eutectic solvents (DES) are considered as a green non-toxic electrolyte for the replacement of cyanide based toxic electrolytes towards the electrodeposition of noble metal and alloy nanoparticles on conducting surfaces. In this work, ruthenium nanoparticles (RuNPs) are electrochemically synthesized over cathodically treated stainless-steel mesh (CSS) by applying the cathodic current of −15 mA/cm2 using ruthenium chloride and deep eutectic mixture consists of choline chloride/urea as electrolyte. The resulting material is abbreviated as RuNPs@CSS and are characterized by surface analytical tools such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning elctron microscopy with energy dispersive spectrum (FE-SEM with EDS). Further, the electrocatalytic hydrogen evolution reaction (HER) activity of RuNPs@CSS is accessed and compared with state of art Pt electrode using open circuit potential (OCP), linear sweep voltammetry (LSV), Tafel plot and electrochemical impedance spectroscopy (EIS) measurements in 0.5 M H2SO4. The calculated HER's onset potential and over potential @ −10 mA/cm2 of RuNPs@CSS are about −0.0273 and −0.0657 V vs. RHE, which are very close to the bare Pt values. The EIS results suggested that, RuNPs@CSS possess excellent conductivity, which decrease the charge transfer resistance and enhances the HER. This study proved that the electrodeposited RuNPs@SS is better replacement for Pt based electrocatalysts towards acidic HER.

Recently, carbon dots (CDs) have received increasing attention, and several reports have indicated that CDs are promising fluorescent carbon-based materials. CDs present outstanding physical and chemical properties because of their excellent properties, CDs are used in a wide range of applications, such as bioimaging, sensing, drug delivery, and nanoelectronics. Numerous approaches can be used to prepare CDs, such as arc discharge, laser ablation, electrochemical exfoliation, chemical oxidation, ultrasonic passivation, combustion, microwave pyrolysis, the template method, and the hydrothermal method. In addition, basic techniques used for the separation of CDs are included and discussed shortly. In this short review, the synthesis and characterization of CDs from plant sources using the eco-friendly hydrothermal method is described. Further, the importance of hydrothermally synthesized CDs is discussed briefly. The applications and advantages of CDs in bioimaging, fluorescent inks, and detections or sensing are also reported herein. Finally, we summarize the importance, challenges, and future direction towards the research of CDs.

Recently, the use of natural products for the synthesis of carbon dots (CDs) has received much attention. Herein, leftover kiwi (Actinidia Deliciosa) fruit peels were successfully turned into beneficial fluorescent carbon dots (KN-CDs) via the hydrothermal-carbonization route. KN-CDs 1 and KN-CDs 2 were prepared without and with ammonium hydroxide, respectively. KN-CDs 1 and KN-CDs 2 were systematically characterized by various analytical techniques. Synthesized KN-CDs showed spherical-shaped morphology with narrow size distribution and excellent optical properties with excitation-independent behaviors. The quantum yields of KN-CDs 1 and KN-CDs 2 were calculated as 14 and 19%, respectively. Additionally, the KN-CDs possess excellent prolonging and photostability. Because of the excellent optical properties of KN-CDs, they were utilized as fluorescent sensors. The strong fluorescence of the KN-CDs was selectively quenched by Fe3+ ion, and quenching behavior showed a linear correlation with the concentrations of Fe3+ ion. KN-CDs 1 and KN-CDs 2 showed the detection of Fe3+ ions within the concentration range of 5–25 µM with the detection limit of 0.95 and 0.85 µM, respectively. Based on the turn-off sensing by the detection of Fe3+ ions, KN-CDs would be a promising candidate as a selective and sensitive fluorescent sensor.

Anchoring electrocatalyst nanoparticles on carbon materials is a promising strategy to establish a hybrid electrocatalyst with unique structure and properties. Deriving carbon support from waste materials is an environmentally green approach. In the present study, the pyrolysis of the heterogeneous mixture containing synthetic disposal material and nickel salt yields N-doped carbon fibers-supported nickel oxide (NiO@CFs) hybrid electrocatalyst. The NiO nanoparticles are well incorporated on the porous carbon base, which has densely packed sharp-edge carbon fibers (CFs). The unique carbon structure incorporated with the NiO nanoparticles that facilitates the adsorption of electrolyte ions, rushes the transfer of electrolyte ions, and thus enhances the electrochemical activity. The as-derived carbon support maximized the electrocatalyst active sites while utilizing low electrocatalyst mass loading. Specifically, the synthetic disposable material-derived-carbon fibers supported NiO (NiO@CFs) hybrid electrocatalyst exhibited remarkably higher surface area and lower charge transfer resistance when compared to that of bare NiO. Intriguingly, the NiO@CFs hybrid electrocatalyst exhibited desirable oxygen evolution reaction (OER) performance (η = 280 mV at 10 mA cm−2) and consistent durability for a 24 h continuous run. This study emphasizes that the utilization of synthetic disposal materials for deriving carbon support is an environmentally effective methodology to incorporate/hybridize electrochemically active materials for the various electrochemical applications.

In this work, we have demonstrated a prompt anodic electrochemical exfoliation of graphite into graphene sheets (GS) in aqueous media. For the synthesis of GS, a constant potential of +10 V has been applied between two identical graphite sheets in 0.1 M aqueous ammonium sulfate. The exfoliated GS were characterized via standard analytical tools such as Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Raman, X-ray photoelectron spectroscopy (XPS), and field emission scanning electron microscopy with energy dispersive spectrum (FE-SEM with EDS). Further, the electrochemical performance of GS coated Ni foam (GS/Ni foam) was assessed by cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS) techniques in 2 M KOH. The quasi-rectangular shaped voltammograms and triangular shaped GCD curves in a three-electrode system was evidenced the double-layer capacitance of GS/Ni foam, which exhibited maximum specific capacitance of 84.82 and 40. 83 F/g at 2 mV/s, and 0.1 A/g of current density, respectively. Moreover, the symmetric two-electrode performance of GS/Ni foam was also examined, which showed good energy density (3.03 Wh/kg) and power density (562.5 W/kg). This study proves that the anodically exfoliated GS can act as a good symmetric supercapacitor in KOH.

The growth of industry fulfills our necessity and promotes economic development. However, pollutants from such industries pollute water bodies which pose a high risk for living organisms. Thus, researchers have been urged to develop an efficient method to remove toxic heavy metal ions from water bodies. The adsorption method shows promising results for the removal of heavy metal ions and is easy to operate on a large scale, thus can be applied to practical applications. Numerous adsorbents were developed and reported, among them hydrogels, which attract great attention because of the reusability, ease of preparation, and handling. Hydrogels are generally prepared by the cross-linking of polymers that result in a three-dimensional structure, showing high porosity and high functionality. They are hydrophilic in nature because of the functional groups, and are non-toxic. Thus, this review provides various methods of hydrogel adsorbents preparation and summarizes recent progress in the use of hydrogel adsorbents for the removal of heavy metal ions. Further, the mechanism involved in the removal of heavy metal ions is briefly discussed. The most recent studies about the adsorption method for the treatment of heavy metal ions contaminated water are presented.

This article describes a comprehensive study for the preparation of graphene dispersions by liquid-phase exfoliation using amphiphilic diblock copolymers; poly(ethylene oxide)-block-poly(styrene) (PEO-b-PS), poly(ethylene oxide)-block-poly(4-vinylpyridine) (PEO-b-PVP), and poly(ethylene oxide)-block-poly(pyrenemethyl methacrylate) (PEO-b-PPy) with similar block lengths. Block copolymers were prepared from PEO using the Steglich coupling reaction followed by reversible addition-fragmentation chain transfer (RAFT) polymerization. Graphite platelets (G) and reduced graphene oxide (rGO) were used as graphene sources. The dispersion stability of graphene in ethanol was comparatively investigated by on-line turbidity, and the graphene concentration in the dispersions was determined gravimetrically. Our results revealed that the graphene dispersions with PEO-b-PVP were much more stable and included graphene with fewer defects than that with PEO-b-PS or PEO-b-PPy, as confirmed by turbidity and Raman analyses. Gravimetry confirmed that graphene concentrations up to 1.7 and 1.8mg/mL could be obtained from G and rGO dispersions, respectively, using PEO-b-PVP after one week. Distinctions in adhesion forces of PS, VP, PPy block units with graphene surface and the variation in solubility of the block copolymers in ethanol medium significantly affected the stability of the graphene dispersion.

Synthesis of an eco-friendly and efficient antibacterial and antifouling coatings is presented by exploiting urushiol, a natural varnishing material. Since urushiol has inherent outstanding surface-protecting and antimicrobial properties, a series of poly (methyl methacrylate)-urushiol polymer compositions were prepared and fabricated into films. The prepared films were subjected to antimicrobial and antifouling studies. The polymer systems were characterized by various physico-spectroscopic techniques such as 1H NMR, Fourier transform infrared spectroscopy, differential scanning calorimetry, atomic force microscopy, and thermal gravimetric analysis. The confocal laser scanning micrographs, obtained for Pseudomonas aeruginosa biofilm formation, demonstrated an excellent antimicrobial response of the urushiol-incorporated polymers against this bacterial strain. We also demonstrated an inhibitory attachment effect against Navicula incerta, a fouling microalgal strain.

Banana peel is a common solid biowaste. This paper reports a sustainable synthesis of carbon quantum dots (CQDs) from banana peel waste by a simple hydrothermal method. The resulting CQDs have a narrow size distribution, and the average particle size was measured as 5 nm. The nitrogen-containing and oxygen-containing functionalities on/in the surface of carbon structure were observed in the resulting CQDs. CQDs emit intense blue fluorescence under the excitation of UV-light (365 nm) with a good quantum yield of 20% without any surface passivation chemicals. Besides, CQDs exhibit excellent water solubility and excitation-dependent emission performance. Furthermore, the banana peel waste-derived CQDs had almost no photobleaching under UV-light irradiation for a long-time, suggesting that they have high photostability. Since no chemical reagent was involved in the synthesis of CQDs, the synthesized CQDs were confirmed to have lower toxicity for nematodes even at a high concentration of 200 μg mL−1. Because of the intense fluorescence with excellent fluorescence stability and biocompatibility, CQDs can be used for bioimaging in nematodes. The CQDs efficiently stained into the whole body of the nematodes and brightly illuminated the multicolor by varying the excitation wavelength. Therefore, fluorescent CQDs would be a great potential candidate for bioimaging applications.

Hollow carbon nanospheres (HCNSs) supported on monodisperse iron oxide nanoparticles (IONPs) were synthesized by a carbonization route using sucrose as the carbon precursor. The resulting product of the obtained HCNSs possessed a narrow size distribution of 15 nm and an interlayer distance of 0.35 nm. The intensity of the D to G value was less than 1, which confirms the obtained HCNSs with graphitization. This study is expected to pave the way for the application of HCNSs in nanoelectronics.

The graphenated carbon nanotubes (G-CNTs) were synthesized on monodisperse spherical iron oxide nanoparticles (IONPs) using acetylene as carbon precursor by simple chemical vapor deposition method. The reaction parameters such as temperature and flow of carbon source were optimized in order to achieve G-CNTs with excellent quality and quantity. Transmission electron microscopy (TEM) clearly illustrated that the graphene flakes are forming along the whole length on CNTs. The degree of graphitization was revealed by X-ray diffraction (XRD) analysis and Raman spectroscopic techniques. The intensity of D to G value was less than one which confirms the obtained G-CNTs have high degree of graphitization. The optimum reaction temperature for the IONPs to form metallic clusters which in turn lead to the formation of G-CNTs with high carbon deposition yield is at 900 °C. The TEM shows the CNTs diameter is 50 nm with foiled graphene flakes of diameter around 70 nm. Our results advocate for IONPs as a promising catalytic template for quantitative and qualitative productivity of nanohybrid G-CNTs. The produced G-CNTs with high degree of graphitization might be an ideal candidate for nanoelectronic application like super capacitors and so on.

Mn/MgO was prepared by wet impregnation method and was used as a catalytic template for the growth of graphitic mesoporous carbon (GMC) using acetylene gas as carbon precursor at 900 °C by CVD method. The deposited carbon nanostructured material was separated from the catalytic template by the acid treatment, and was investigated by various physico-chemical techniques such as XRD, BET, SEM, TEM, and Raman spectroscopy. The BET surface area of GMC is ca. 200 m 2 g −1 . The XRD pattern and Raman spectroscopic techniques revealed the crystallinity and the degree of graphitization of mesoporous carbon. The interlayer distance of graphene sheet in GMC is around 0.34 nm. All the analytical results strongly support that the prepared mesoporous carbon to be highly ordered and well in graphitic nature. Further, the results demonstrate that the GMC synthesized by using a Mn/MgO might be a promising contender for the large-scale synthesis.

Hydrophilic nitrogen-doped carbon dots (HN-CDs) were produced by a simple hydrothermal method from biowaste, dwarf banana peel. XRD, Raman spectroscopy, and HRTEM analyses confirmed the graphitic structure and narrow size distribution of the HN-CDs. Nitrogen-doping to the carbon structure/framework and owing rich hydrophilic groups on HN-CDs surface were confirmed by XPS and ATR-FTIR spectroscopy techniques. HN-CDs emitted strong and tunable fluorescence (FL) and possessed a good quantum yield (23%). Thus this novel HN-CDs applied as a nanoprobe for the detection of metal ion (Fe3+ ion) in aqueous solution by the fluorometric method. Excessive or lesser amounts of Fe3+ ion in human bodies lead to diverse diseases. Additionally, the accumulation of Fe3+ ion in the environment will escort to a great threat. The prepared HN-CDs selectively and sensitively detect Fe3+ ions by the FL quenching of HN-CDs with a limit of detection of 0.66 μM in the range of 5–25 μM. Further, the HN-CDs employed as a biocompatible probe for the multicolor bioimaging in rat liver cells. Also, HN-CDs used as fluorescent ink for drawing and writing. Thus, the biowaste/biomass successfully turned to a useful nanoprobe for environmental protection and health care.

The Malus floribunda fruit extract and aqueous ammonia have been employed as carbon and nitrogen resource material, respectively to synthesize nitrogen-doped carbon dots (N-CDs) by a facile one-step hydrothermal method. The N-CDs exhibit excellent lattice fringes with a d-spacing of 0.21 nm. The N-CDs have tunable fluorescence emission with redshift from 390 to 501 nm as the excitation wavelength increased from 300 to 460 nm. Finally, N-CDs have been used as a fluorescent probe to image Caenorhabditis elegans (nematode) in vivo model. It showed low cytotoxicity and remarkable performance due to its good fluorescence quantum yield (19%). Moreover, the obtained N-CDs are potential candidates for biomedicine-related studies.

In this study, we propose a dye–monomer interaction force measurement technique based on atomic force microscopy (AFM) to predict the performance of polymeric dispersants. Cantilevers modified with functional monomers such as styrene, N-butyl acrylate (BA), and 2-(N-phthalimido)ethyl methacrylate (PEMA) were used to characterize the interaction force between these functional monomers and a target dye (Disperse Blue 359). The interaction forces of each monomer—styrene, BA, and PEMA—with Disperse Blue 359 were measured as 10.75 nN, 7.06 nN, and 21.31 nN, respectively, and their trend was consistent with dipole-moment values obtained from density function theory (DFT) calculations (μ(styrene) = 0.0001, μ(PEMA) = 2.3158, μ(Disperse Blue 359) = 3.0368). We synthesized a series of model polymers containing specific functional monomers (CoPS10, CoBA, CoPPEMAs) with similar molecular weights, molecular-weight distributions, and acid contents and compared their actual performance with that predicted from interaction force measurement data. The results were well correlated with the interaction force measurement data. The effect of the PEMA content on dye dispersion stability was also investigated; the results indicated that both the PEMA content and the type of dye-interacting group greatly influenced the characteristics of the dispersion.

An innovative, facile, low-cost and one-pot hydrothermal carbonization method was developed for the synthesis of bright fluorescence nitrogen-doped carbon dots (NCDs) using Piper betle (Betel) leaf as a carbon and nitrogen precursor. Various advanced physicochemical characterization techniques have been performed to confirm the structural and optical properties of the resulting Betel-derived NCDs (B-NCDs). The as-synthesized B-NCDs exhibited unique excitation-dependent fluorescence behavior, high fluorescence/photochemical stability, exceptional solubility in hydrophilic solvents like water, and good biocompatibility. On the basis of the astounding optical behavior of B-NCDs, they were utilized as a nanoprobe for determination of Fe3+ ion by the fluorometric method. Notably, this nanoprobe was performed by a linear relationship between the fluorescence intensity and the concentration of Fe3+ ion ranging from 5 to 30 μM with a detection limit as 0.43 μM. Highly selective and sensitive determination of Fe3+ ion was carried out through the fluorescence quenching of B-NCDs due to the resonance energy/electron transfer (RET) mechanism. Besides, the resulting B-NCDs employed as a biocompatible probe in multicolor imaging applications of HCT-116 human colon cancer cells. B-NCDs is not only efficient nanosensor for the determination of Fe3+ ion and biocompatible probe for the multicolor imaging. It also would be a substantial alternative for the traditional fluorescent inks due to its extraordinary fluorescence stability, biocompatibility, pollution-free, and easily washable. In this report for the first time, Betel leaf as carbon and nitrogen source was used to synthesize B-NCDs without adding any chemical reagent. Thus it was applied for diverse analysis field.

In this work, an ultra-sensing photoelectrochemical (PEC) glucose biosensor has been constructed from the bio-derived nitrogen-doped carbon sheets (NDC) wrapped titanium dioxide nanoparticles (NDC-TiO2 NPs) followed by the covalent immobilization of glucose oxidase (GODx) on them (designated as a GODx/NDC-TiO2NPs/ITO biosensor). Initially, the TiO2 NPs was synthesized by sol-gel method and then NDC-TiO2 NPs was synthesized utilizing a green source of Prunus persica (peach fruit) through a simple hydrothermal process. The synthesized NDC-TiO2 NPs composite was characterized by FESEM, HRTEM, Raman spectroscopy, XRD, ATR-FTIR spectroscopy and XPS to determine composition and phase purity. These fabricated GODx/NDC-TiO2NPs/ITO biosensor exhibited a good charge separation, highly enhanced and stable photocurrent responses with switching PEC behavior under the light (λ > 400 nm). As a result, GODx/NDC-TiO2NPs/ITO PEC glucose sensor exhibits a good photocurrent response to detection of glucose concentrations (0.05–10 μM) with an ultra-low detection limit of 13 nM under optimized PEC experimental conditions. Also, the PEC glucose sensor revealed a high selectivity, good stability, long time durability, and capability to analyze the glucose levels in real human serum. Also, the further development of this work may provide new insights into preparing other bio-derived carbon nanostructure-based photocatalysts for PEC applications.

Graphitic carbon nanosheets (GCNS) were synthesized using mesoporous Ti-MCM-41 molecular sieves as catalytic template and acetylene as carbon precursor following chemical vapor deposition method, under atmospheric pressure. The mesoporous Ti-MCM-41 molecular sieves with various Si/Ti ratios were synthesized by direct hydrothermal method. The materials so obtained were characterized by various physico-chemical techniques such as X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM) and Raman spectroscopy. The analytical results indicated that the obtained GCNS possess high thermal stability and good graphitization with an inter layer distance of around 3.45 A. The influence of reaction parameters such as temperature and catalytic templates was studied to improve the quality and quantity of GCNS. The excellent graphitized GCNS material on a large scale was achieved from Ti-MCM-41 at moderate reaction temperature. This work proposes a way for the large scale synthesis of GCNS with applications suitable for nanoelectronics, nanocomposites and so on.

Zinc oxide nanoparticles decorated graphene oxide (ZnO@GO) composite was synthesized by simple solvothermal method where zinc oxide (ZnO) nanoparticles and graphene oxide (GO) were synthesized via simple thermal oxidation and Hummers method, respectively. The obtained materials were thoroughly characterized by various physico-chemical techniques such as X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Raman spectrum shows the intensity of D to G value was close to one which confirms the obtained GO and ZnO@GO composite possesses moderate graphitization. TEM images shows the ZnO nanoparticles mean size of 15±5nm were dispersed over the wrinkled graphene layers. The photocatalytic performance of ZnO@GO composite on degradation of methylene blue (MB) is investigated and the results show that the GO plays an important role in the enhancement of photocatalytic performance. The synthesized ZnO@GO composite achieves a maximum degradation efficiency of 98.5% in a neutral solution under UV-light irradiation for 15min as compared with pure ZnO (degradation efficiency is 49% after 60min of irradiation) due to the increased light absorption, the reduced charge recombination with the introduction of GO. Moreover, the resulting ZnO@GO composite possesses excellent degradation efficiency as compared to ZnO nanoparticles alone on MB.

Despite the superior properties of graphene, the strong pi-pi interactions among pristine graphenes yielding massive aggregation impede industrial applications. For non-covalent functionalization of highly-ordered pyrolytic graphite (HOPG), poly(2,2,2-trifluoroethyl methacrylate)-block-poly(4-vinyl pyridine) (PTFEMA-b-PVP) block copolymers were prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization and used as polymeric dispersants in liquid phase exfoliation assisted by ultrasonication. The HOPG graphene concentrations were found to be 0.260-0.385 mg/mL in methanolic graphene dispersions stabilized with 10 wt % (relative to HOPG) PTFEMA-b-PVP block copolymers after one week. Raman and atomic force microscopy (AFM) analyses revealed that HOPG could not be completely exfoliated during the sonication. However, on-line turbidity results confirmed that the dispersion stability of HOPG in the presence of the block copolymer lasted for one week and that longer PTFEMA and PVP blocks led to better graphene dispersibility. Force-distance (F-d) analyses of AFM showed that PVP block is a good graphene-philic block while PTFEMA is methanol-philic.