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Hydrogen energy is converted to electricity through fuel cells, aided by nanostructured materials. Fuel cell technology is a promising method for utilizing energy sources, ensuring sustainability, and protecting the environment. However, it still faces drawbacks such as high cost, operability, and durability issues. Nanomaterials can address these drawbacks by enhancing catalysts, electrodes, and fuel cell membranes, which play a crucial role in separating hydrogen into protons and electrons. Proton exchange membrane fuel cells (PEMFCs) have gained significant attention in scientific research. The primary objectives are to reduce greenhouse gas emissions, particularly in the automotive industry, and develop cost-effective methods and materials to enhance PEMFC efficiency. We provide a typical yet inclusive review of various types of proton-conducting membranes. In this review article, special focus is given to the distinctive nature of nanomaterial-filled proton-conducting membranes and their essential characteristics, including their structural, dielectric, proton transport, and thermal properties. We provide an overview of the various reported nanomaterials, such as metal oxide, carbon, and polymeric nanomaterials. Additionally, the synthesis methods in situ polymerization, solution casting, electrospinning, and layer-by-layer assembly for proton-conducting membrane preparation were analyzed. In conclusion, the way to implement the desired energy conversion application, such as a fuel cell, using a nanostructured proton-conducting membrane has been demonstrated.

Preparing electrode materials plays an essential role in the fabrication of high-performance supercapacitors. In general, heteroatom doping in carbon-based electrode materials enhances the electrochemical properties. Herein, nitrogen, oxygen, and sulfur co-doped porous carbon (PC) materials were prepared by direct pyrolysis of Anacardium occidentale (AO) nut-skin waste for high-performance supercapacitor applications. The as-prepared AO-PC material possessed interconnected micropore/mesopore structures and exhibited a high specific surface area of 615 m2 g−1. The Raman spectrum revealed a moderate degree of graphitization of AO-PC materials. These superior properties of the as-prepared AO-PC material help to deliver high specific capacitance. After fabricating the working electrode, the electrochemical performances including cyclic voltammetry, galvanostatic charge–discharge, and electrochemical impedance spectroscopy measurements were conducted in 1 M H2SO4 aqueous solution using a three-electrode configuration for supercapacitor applications. The AO-PC material delivered a high specific capacitance of 193 F g−1 at a current density of 0.5 A g−1. The AO-PC material demonstrated −1. All the above outcomes confirmed that the as-prepared AO-PC from AO nut-skin waste via simple pyrolysis is an ideal electrode material for fabricating high-performance supercapacitors. Moreover, this work provides a cost-effective and environmentally friendly strategy for adding value to biomass waste by a simple pyrolysis route.

Here, a simple one-step hydrothermal-assisted carbonization process was adopted for the preparation of nitrogen/phosphorous-doped carbon dots from a water-soluble polymer, poly 2-(methacryloyloxy)ethyl phosphorylcholine (PMPC). By the free-radical polymerization method, PMPC was synthesized using 2-(methacryloyloxy)ethyl phosphorylcholine (MPC) and 4,4′-azobis (4-cyanovaleric acid). The water-soluble polymers, PMPC, that have nitrogen/phosphorus moieties are used to prepare carbon dots (P-CDs). The resulting P-CDs were thoroughly characterized by various analytical techniques such as field emission-scanning electron microscopy (FESEM) with energy-dispersive X-ray spectroscopy (EDS), high-resolution transmittance electron microscopy (HRTEM), X-ray diffraction (XRD), Raman spectroscopy, attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), Ultraviolet-visible (UV-vis) spectroscopy and fluorescence spectroscopy to determine their structural and optical properties. The synthesized P-CDs displayed bright/durable fluorescence, were stable for long periods, and confirmed the enrichment of functionalities including oxygen, phosphorus, and nitrogen heteroatoms in the carbon matrix. Since the synthesized P-CDs showed bright fluorescence with excellent photostability, excitation-dependent fluorescence emission, and excellent quantum yield (23%), it has been explored as a fluorescent (security) ink for drawing and writing (anti-counterfeiting). Further, cytotoxicity study results advised for biocompatibility and thus were used for cellular multicolor imaging in nematodes. This work not only demonstrated the preparation of CDs from polymers that can be used as advanced fluorescence ink, a bioimaging agent for anti-counterfeiting, and cellular multicolor imaging candidate, but additionally prominently opened a new perspective on the bulk preparation of CDs simply and efficiently for various applications.

Heteroatom-doped porous carbon material (H-PCM) was synthesized using Anacardium occidentale (cashew) nut’s skin by a simple pyrolysis route. The resulting H-PCM was thoroughly characterized by various analytical techniques such as field emission scanning electron microscopy (FE-SEM) with energy-dispersive X-ray (EDX) spectroscopy, high-resolution transmittance electron microscopy (HRTEM), X-ray diffraction (XRD), Raman spectroscopy, nitrogen adsorption–desorption isotherms, X-ray photoelectron spectroscopy (XPS), and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. The obtained results strongly demonstrated that the synthesized H-PCM exhibited a porous nature, continuous sponge-like and sheet-like smooth morphology, and a moderate degree of graphitization/crystallinity with oxygen-, nitrogen-, and sulfur-containing functionalities in the carbon matrix. After the structural confirmation, as-prepared H-PCM has used a sustainable electrocatalyst for hydrogen evolution reaction (HER) because the metal-free carbonaceous catalysts are one of the most promising candidates. The H-PCM showed excellent HER activities with a lowest Tafel slope of 75 mV dec−1 and durable stability in 0.5 M H2SO4 aqueous solution. Moreover, this work provides a versatile and effective strategy for designing excellent metal-free electrocatalysts from the cheapest biowaste/biomass for large-scale production of hydrogen gas through electrochemical water splitting.

In this study, Anacardium occidentale (A. occidentale) nut skin waste (cashew nut skin waste) was used as a raw material to synthesize functionalized carbon nanodots (F-CNDs). A. occidentale biomass-derived F-CNDs were synthesized at a low temperature (200 °C) using a facile, economical hydrothermal method and subjected to XRD, FESEM, TEM, HRTEM, XPS, Raman Spectroscopy, ATR-FTIR, and Ultraviolet-visible (UV–vis) absorption and fluorescence spectroscopy to determine their structures, chemical compositions, and optical properties. The analysis revealed that dispersed, hydrophilic F-CNDs had a mean diameter of 2.5 nm. XPS and ATR-FTIR showed F-CNDs had a crystalline core and an amorphous surface decorated with –NH2, –COOH, and C=O. In addition, F-CNDs had a quantum yield of 15.5% and exhibited fluorescence with maximum emission at 406 nm when excited at 340 nm. Human colon cancer (HCT-116) cell assays showed that F-CNDs readily penetrated into the cells, had outstanding biocompatibility, high photostability, and minimal toxicity. An MTT assay showed that the viability of HCT-116 cells incubated for 24 h in the presence of F-CNDs (200 μg mL–1) exceeded 95%. Furthermore, when stimulated by filters of three different wavelengths (405, 488, and 555 nm) under a laser scanning confocal microscope, HCT-116 cells containing F-CNDs emitted blue, red, and green, respectively, which suggests F-CNDs might be useful in the biomedical field. Thus, we describe the production of a fluorescent nanoprobe from cashew nut waste potentially suitable for bioimaging applications.

Chebulic Myrobalan is the main ingredient in the Ayurvedic formulation Triphala, which is used for kidney and liver dysfunctions. Herein, natural nitrogen-doped carbon dots (NN-CDs) were prepared from the hydrothermal carbonization of Chebulic Myrobalan and were demonstrated to sense heavy metal ions in an aqueous medium. Briefly, the NN-CDs were developed from Chebulic Myrobalan by a single-step hydrothermal carbonization approach under a mild temperature (200 °C) without any capping and passivation agents. They were then thoroughly characterized to confirm their structural and optical properties. The resulting NN-CDs had small particles (average diameter: 2.5 ± 0.5 nm) with a narrow size distribution (1–4 nm) and a relatable degree of graphitization. They possessed bright and durable fluorescence with excitation-dependent emission behaviors. Further, the as-synthesized NN-CDs were a good fluorometric sensor for the detection of heavy metal ions in an aqueous medium. The NN-CDs showed sensitive and selective sensing platforms for Fe3+ ions; the detection limit was calculated to be 0.86 μM in the dynamic range of 5–25 μM of the ferric (Fe3+) ion concentration. Moreover, these NN-CDs could expand their application as a potential candidate for biomedical applications and offer a new method of hydrothermally carbonizing waste biomass.

Polymer nanoparticles (PNPs) are generally formed by the spontaneous self-assembly of polymers that vary size from 1 to 1000 nm [...]

The scientific community is being forced to consider alternative renewable fuels such as biodiesel as a result of the sharp increases in the price of petroleum and the increased demand for petroleum-derived products. Transesterification is a technique used to create biodiesel where a variety of edible oils, non-edible oils, and animal fats are used. For this, either a homogeneous or heterogeneous catalyst is utilized. An appropriate catalyst is chosen based on the quantity of free fatty acid content in the oil. The main distinction between homogeneous and heterogeneous catalysts is that compared to the heterogeneous catalyst, the homogeneous catalyst is not affected by the quantity of free fatty acids in the oil. Early methods of producing biodiesel relied on homogeneous catalysts, which have drawbacks such as high flammability, toxicity, corrosion, byproducts such as soap and glycerol, and high wastewater output. The majority of these issues are solved by heterogeneous catalysts. Recent innovations use novel heterogeneous catalysts that are obtained from biomass and biowaste resources. Numerous researchers have documented the use of biomass-derived heterogeneous catalysts in the production of high-quality, pure biodiesel as a potentially greener manufacturing method. The catalysts were significantly altered through conventional physical processes that were both cost- and energy-effective. The present review is intended to analyze catalysts from biowaste for making biodiesel at a minimal cost. The most recent methods for creating diverse kinds of catalysts—including acidic, basic, bifunctional, and nanocatalysts—from various chemicals and biomass are highlighted in this review. Additionally, the effects of various catalyst preparation methods on biodiesel yield are thoroughly explored.

In this study, sustainable, low-cost, and environmentally friendly biomass (Terminalia chebula) was employed as a precursor for the formation of nitrogen-doped carbon dots (N-CDs). The hydrothermally assisted Terminalia chebula fruit-derived N-CDs (TC-CDs) emitted different bright fluorescent colors under various excitation wavelengths. The prepared TC-CDs showed a spherical morphology with a narrow size distribution and excellent water dispensability due to their abundant functionalities, such as oxygen- and nitrogen-bearing molecules on the surfaces of the TC-CDs. Additionally, these TC-CDs exhibited high photostability, good biocompatibility, very low toxicity, and excellent cell permeability against HCT-116 human colon carcinoma cells. The cell viability of HCT-116 human colon carcinoma cells in the presence of TC-CDs aqueous solution was calculated by MTT assay, and cell viability was higher than 95%, even at a higher concentration of 200 μg mL−1 after 24 h incubation time. Finally, the uptake of TC-CDs by HCT-116 human colon carcinoma cells displayed distinguished blue, green, and red colors during in vitro imaging when excited by three filters with different wavelengths under a laser scanning confocal microscope. Thus, TC-CDs could be used as a potential candidate for various biomedical applications. Moreover, the conversion of low-cost/waste natural biomass into products of value promotes the sustainable development of the economy and human society.

Research on the synthesis of water-soluble polymers has accelerated in recent years, as they are employed in many bio-applications. Herein, the synthesis of poly[2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide (PSB) by free radical polymerization in a sonication bath is described. PSB and iron oxide nanoparticles (IONPs) were simultaneously stabilized on the graphene surface. Graphene surfaces with PSB (GPSB) and graphene surfaces with PSB and IONPs (GPSBI) were prepared. Since PSB is a water-soluble polymer, the hydrophobic nature of graphene surfaces converts to hydrophilic nature. Subsequently, the prepared graphene composites, GPSB and GPSBI, were well-dispersed in water. The preparation of GPSB and GPSBI was confirmed by X-ray diffraction, Raman spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and thermogravimetric analysis. The impacts of PSB and IONPs on the graphene surfaces were studied systematically.

Herein, a simple, cost-effective, and in-situ environmentally friendly approach was adopted to synthesize carbon dot-adorned silver nanoparticles (CDs@AgNPs) from yellow myrobalan (Terminalia chebula) fruit using a hydrothermal treatment without any additional reducing and or stabilizing agents. The as-synthesized CDs@AgNP composite was systematically characterized using multiple analytical techniques: FESEM, TEM, XRD, Raman, ATR-FTIR, XPS, and UV-vis spectroscopy. All the results of the characterization techniques strongly support the idea that the CDs were successfully made to adorn the AgNPs. This effectively synthesized CDs@AgNP composite was applied as a catalyst for the degradation of organic dyes, including methylene blue (MB) and methyl orange (MO). The degradation results revealed that CDs@AgNPs exhibit a superior catalytic activity in the degradation of MB and MO in the presence of NaBH4 (SB) under ambient temperatures. In total, 99.5 and 99.0% rates of degradation of MB and MO were observed using CDs@AgNP composite with SB, respectively. A plausible mechanism for the reductive degradation of MB and MO is discussed in detail. Moreover, the CDs@AgNP composite has great potential for wastewater treatment applications.

In recent years, fuel cell (FC) technology has seen a promising increase in its proportion in stationary power production. Several pilot projects are in operation across the world, with the number of running hours steadily rising, either as stand-alone units or as part of integrated gas turbine–electric energy plants. FCs are a potential energy source with great efficiency and zero emissions. To ensure the best performance, they normally function within a confined temperature and humidity range; nevertheless, this makes the system difficult to regulate, resulting in defects and hastened deterioration. For diagnosis, there are two primary approaches: restricted input information, which gives an unobtrusive, rapid yet restricted examination, and advanced characterization, which provides a more accurate diagnosis but frequently necessitates invasive or delayed tests. Artificial Intelligence (AI) algorithms have shown considerable promise in providing accurate diagnoses with quick data collecting. This work focuses on software models that allow the user to evaluate many different possibilities in the shortest amount of time and is a vital method for proper and dynamic analysis of such entities. The artificial neural network, genetic algorithm, particle swarm optimization, random forest, support vector machine, and extreme learning machine are common AI approaches discussed in this review. This article examines the modern practice and provides recommendations for future machine learning methodologies in fuel cell diagnostic applications. In this study, these six AI tools are specifically explained with results for a better understanding of the fuel cell diagnosis. The conclusion suggests that these approaches are not only a popular and beneficial tool for simulating the nature of an FC system, but they are also appropriate for optimizing the operational parameters necessary for an ideal FC device. Finally, observations and ideas for future research, enhancements, and investigations are offered.

In this study, calcium carbonate nanoparticles (CCNPs) and calcium oxide nanoparticles (CONPs) are synthesized by the carbonization/calcination of calcium oleate. CONPs are an essential inorganic material, and they are used as catalysts and as effective chemisorbents for toxic gases. CCNPs are widely used in plastics, printing ink, and medicines. Here, calcium oleate is used as a starting material for the preparation of CCNPs and CONPs. This calcium oleate is prepared from calcium hydroxide and oleic acid in ethanol under mild reflux conditions. The effect of the calcination temperature of calcium oleate is examined during the synthesis of CCNPs and CONPs. By simple carbonization/calcination, calcite-type CCNPs and CONPs are prepared at 600 °C, respectively. The synthesized nanomaterials are analyzed by various physicochemical characterization techniques such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy, thermogravimetric analysis (TGA) with derivative thermogravimetry (DTG), and scanning electron microscopy (SEM) with energy dispersive X-ray analysis. An X-ray diffractometer and the Scherrer formula are used to analyze the crystalline phase and crystallite size of prepared nanoparticles. TGA techniques confirm the thermal stability of the calcium oleate, CCNPs, and CONPs. The SEM analysis illustrates the dispersive behavior and cubic/spherical morphologies of CCNPs/CONPs. Furthermore, the obtained results are compared to the CCNP and CONP samples prepared using calcium hydroxide. As a result, the carbonization/calcination of calcium oleate produces monodispersed CONPs, which are then compared to the CONPs from calcium hydroxide. Additionally, from calcium oleate, CONPs can be prepared on a large scale in a cheap, convenient way, using simple equipment which can be applied in various applications.

Here, the controlled formation of platinum nanoparticles (PtNPs) and silver nanoparticles (AgNPs) using amine-functionalized multivalent ligands are reported. The effects of reaction temperature and ligand multivalency on the growth kinetics, size, and shape of PtNPs and AgNPs were systematically studied by performing a stepwise and a one-step process. PtNPs and AgNPs were prepared in the presence of amine ligands using platinum (II) acetylacetonate and silver (I) acetylacetonate, respectively. The effects of ligands and temperature on the formation of PtNPs were studied using a transmission electron microscope (TEM). For the characterization of AgNPs, additionally, ultraviolet-visible (UV-Vis) absorption was employed. The TEM measurements revealed that PtNPs prepared at different temperatures (160–200 °C, in a stepwise process) are monodispersed and of spherical shape regardless of the ligand multivalency or reaction temperature. In the preparation of PtNPs by the one-step process, ligands affect the shape of the PtNPs, which can be explained by the affinity of the ligands. The TEM and UV-Vis absorption studies on the formation of AgNPs with mono-, di-, and trivalent ligands showed narrower size distributions, while increasing the temperature from 80 °C to 120 °C and with a trivalent ligand in a one-step process.

Self-assembly of amphiphilic polymers with hydrophilic and hydrophobic units results in micelles (polymeric nanoparticles), where polymer concentrations are above critical micelle concentrations (CMCs). Recently, micelles with metal nanoparticles (MNPs) have been utilized in many bio-applications because of their excellent biocompatibility, pharmacokinetics, adhesion to biosurfaces, targetability, and longevity. The size of the micelles is in the range of 10 to 100 nm, and different shapes of micelles have been developed for applications. Micelles have been focused recently on bio-applications because of their unique properties, size, shape, and biocompatibility, which enhance drug loading and target release in a controlled manner. This review focused on how CMC has been calculated using various techniques. Further, micelle importance is explained briefly, different types and shapes of micelles are discussed, and further extensions for the application of micelles are addressed. In the summary and outlook, points that need focus in future research on micelles are discussed. This will help researchers in the development of micelles for different applications.

It is absolutely essential to convert biomass waste into usable energy in a rational manner. This investigation proposes the economical synthesis of heteroatom (N and S)-doped carbon (ATC) from Aesculus turbinata seed as a natural precursor by carbonization at 800 °C. The final product obtained was characterized using field emission scanning electron microscopy with energy-dispersive X-ray spectroscopy, high-resolution transmittance electron microscopy, X-ray diffraction, Raman spectroscopy, nitrogen adsorption-desorption isotherms, attenuated total reflectance Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy in order to investigate its structural property and chemical composition. The porous carbon achieved by this method contained oxygen, nitrogen, and sulfur from Aesculus turbinata seed and had pores rich in micropores and mesopores. Crystalline ATC obtained with a high surface area (560 m2 g−1) and pore size (3.8 nm) were exploited as electrode material for the supercapacitor. The electrochemical studies revealed a specific capacitance of 142 F g−1 at a current density of 0.5 A g−1 using 1 M H2SO4 as an electrolyte. ATC had exceptional cycling stability, and the capacitance retention was 95% even after 10,000 charge-discharge cycles. The findings show that ATC derived from biomass proved to be a potential energy storage material by converting waste biomass into a high-value-added item, a supercapacitor.

Wireless chemical sensors have been developed as a result of advances in chemical sensing and wireless communication technology. Because of their mobility and widespread availability, smartphones have been extensively combined with sensors such as hand-held detectors, sensor chips, and test strips for biochemical detection. Smartphones are frequently used as controllers, analyzers, and displayers for quick, authentic, and point-of-care monitoring, which may considerably streamline the design and lower the cost of sensing systems. This study looks at the most recent wireless and smartphone-supported chemical sensors. The review is divided into four different topics that emphasize the basic types of wireless smartphone-operated chemical sensors. According to a study of 114 original research publications published during recent years, market opportunities for wireless and smartphone-supported chemical sensor systems include environmental monitoring, healthcare and medicine, food quality, sport, and fitness. The issues and illustrations for each of the primary chemical sensors relevant to many application areas are covered. In terms of performance, the advancement of technologies related to chemical sensors will result in smaller and more lightweight, cost-effective, versatile, and durable devices. Given the limitations, we suggest that wireless and smartphone-supported chemical sensor systems play a significant role in the sensor Internet of Things.

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.

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.

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 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.

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.

Despite the superior properties of graphene, the strong π–π 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.