Metal‐free, luminescent, carbogenic nanomaterials (LCNMs) constitute a novel class of optical materials with low environmental impact. LCNMs, e.g., carbon dots (CDs), graphitic carbon nitride (g‐C3N4), and carbonized polymer microspheres (CPM) show strong blue/cyan emissions, but rather weak yellow/red emission. This has been a serious drawback in applying them to light‐emitting and bio‐imaging applications. Here, by integrating single‐component LCNMs in photonic microcavities, the study spectroscopically engineers the coupling between photonic modes in these microcavities and optical transitions to “reconfigure” the emission spectra of these luminescent materials. Resonant photons are confined in the microcavity, which allows selective re‐excitation of phosphors to effectively emit down‐converted photons. The down‐converted photons re‐excite the phosphors and are multiply recycled, leading to …

Colloidal carbon dots (CDs) have garnered much attention as metal‐free photoluminescent nanomaterials, yet creation of solid‐state fluorescent (SSF) materials emitting in the deep red (DR) to near‐infrared (NIR) range poses a significant challenge with practical implications. To address this challenge and to engineer photonic functionalities, a micro‐resonator architecture is developed using carbonized polymer microspheres (CPMs), evolved from conventional colloidal nanodots. Gram‐scale production of CPMs utilizes controlled microscopic phase separation facilitated by natural peptide cross‐linking during hydrothermal processing. The resulting microstructure effectively suppresses aggregation‐induced quenching (AIQ), enabling strong solid‐state light emission. Both experimental and theoretical analysis support a role for extended π‐conjugated polycyclic aromatic hydrocarbons (PAHs) trapped within

Carbonized polymer dots (CPDs) are versatile nanomaterials with remarkable optical properties that enable their use in a wide range of photonics applications. CPDs exhibit excitation‐wavelength‐dependent tunable emissions that span the visible to near‐infrared (NIR) spectrum. In this study, whispering‐gallery‐mode (WGM) emission achieved using CPDs‐coated monodisperse polystyrene (CPDs@PS) microbeads is used to develop wavelength‐adaptable photonic barcodes by leveraging the excitation‐dependent photoluminescence of CPDs. Each resonant emission peak acts as a unique fingerprint of photonics barcodes related to the corresponding microresonator caused by WGM emission. These photonic barcodes can be easily disguised and then authenticated by varying the excitation wavelength. WGM‐based barcodes can exhibit a large number of encoding capacities by adjusting the resonator

Light-element-based fluorescent materials, colloidal graphene quantum dots, and carbon dots (CDs) have sparked an immense amount of scientific interest in the past decade. However, a significant challenge in practical applications has emerged concerning the development of solid-state fluorescence (SSF) materials. This study addresses this knowledge gap by exploring the unexplored photonic facets of C-based solid-state microphotonic emitters. The proposed synthesis approach focuses on carbonized polymer microspheres (CPMs) instead of conventional nanodots. These microspheres exhibit remarkable SSF spanning the entire visible spectrum from blue to red. The highly spherical shape of CPMs imparts built-in photonic properties in addition to its intrinsic CD-based attributes. Leveraging their excitation-dependent photoluminescence property, these microspheres exhibit amplified spontaneous emission

The proliferation of green technologies to combat the energy crisis has fostered the demand for efficient electrocatalysts towards the hydrogen evolution reaction (HER). It is a challenge to realize electrocatalysts with high activity and stability. Herein, we report a combinatorial design strategy by coupling Ru and CrN to boost the HER performance and durability, surpassing pristine Ru/NC, CrN/NC, and even commercial Pt/C. An in situ Ru–CrN decoration over N-doped carbon (Ru–CrN/NC) is achieved via one-step pyrolysis. CrN induces an electronic modulation in the hybrid that allows facile electron transfer to improve the HER activity. A drastic drop in the η10 for Ru–CrN/NC to 7 and 2 times relative to CrN/NC and Ru/NC, respectively, is observed in alkaline media. Similar observations have been made in acidic media as well. Ru–CrN/NC shows high durability in both the reaction media after 24 h of operation

Polymeric carbon dots (PCDs) are an astonishing class of fluorescent materials with distinctive structures, properties, and applications. However, the internal structures of PCDs are still unclear and are the subject of considerable debate due to their complexity. Herein, a new type of pure blue light-emitting PCDs was synthesized hydrothermally from ε-poly-l-lysine and citric acid. PCDs were observed by using scanning transmission electron microscopy coupled with electron energy loss spectroscopy (STEM-EELS) on an atomically thin graphene surface to determine the internal structure and compositional gradients combined with other spectroscopic analyses. These methods revealed that PCDs have a spongy, porous structure with uniform element distribution, reflecting organic polymeric frameworks that embrace fluorescent aromatic moieties devoid of graphitic, inorganic carbon. The polymeric framework acts as …

Multicolor emissions from carbon dots (CDs) are vital for light-emitting diodes (LEDs), particularly for direct, white-light emission (WLE), which enables a replacement of rare earth (RE)-doped phosphors. However, the difficulty of synthesizing single-component WLE CDs with full-spectrum emission severely hinders further investigation of their emission mechanisms and practical applications. Here, we demonstrate rational design and synthesis of chromatically tunable CDs with cyan-, orange-, and white-light emission, precisely tunable along the blackbody Planckian locus by controlling the ratio of different nitrogen dopant sites. We adopted 15N solid-state nuclear magnetic resonance (NMR) spectroscopy and X-ray photoelectron spectroscopy (XPS) to identify and quantify N-dopants in different sites and environments, and we explain their influence on emission properties of these CDs. This study provides guiding …

The solid-state hard encapsulation of carbon dots (CDs) can introduce an additional dimension for the tuning of their optical properties and effective promotion of multifunctional applications as well. In this study, simple hydrothermal and soft-sintering processes have been demonstrated to obtain silicon oxynitride-encapsulated N-doped carbon dots (SiON@NCDs) as well as organosilane-functionalized NCDs (OSi-NCDs). The surface-decorating long alkyl chains on NCDs help to prevent luminescence quenching in solid state and emit blue to orange color while forming a smooth film coating on the substrate. Interestingly, these OSi-NCDs can be readily converted into SiON-encapsulated NCDs (SiON@NCDs) and form a smooth, hard, and visible light transparent coating on a glass surface after soft sintering. This hard coating has the ability to emit white light and 100% block all types of toxic UV light (UV-A, B, and …

Transparent Hard Coatings with SiON-Encapsulated N-Doped Carbon Dots for Complete UV Blocking and White Light Emission

With synergy of structural stability and availability of plenty of active sites with open structure for better reactant/product accessibility, dendritic nanostructures stand alone. However, the complexities/difficulties in their design have largely hindered their wide-scale adoption in catalysis. Herein, with this work we report a green and new protocol for the synthesis of unsupported as well as reduced graphene oxide (rGO)-reinforced dendritic Ru nanostructures (Ru@rGO) via controlled galvanic replacement reaction with Mg as the sacrificial metal. Interestingly, experimental findings elucidate Ru@rGO as a promising electrocatalyst for hydrogen evolution reaction (HER) in a wide range of pH with nearly zero onset potential and superior current density as compared with the state-of-art Pt/C catalyst in alkaline as well as acidic media. It requires only 32 and 68 mV overpotential (η) to achieve a current density of 10 mA cm−2 …

Rechargeable aqueous Zn-ion batteries (ZIBs) and Zn–air batteries (ZABs) are emerging as possible alternatives to Li-based batteries due to their high safety, low cost, and environmental friendliness. The development of high-performance Zn-based energy storage devices requires highly durable, efficient, and earth-abundant cathode catalysts. We demonstrate the synthesis of a three-dimensional (3D) hybrid heterostructure based on MnO-Co and graphitic carbon and its bifunctional energy storage performance toward an ZIB and ZAB for the first time. The 3D nanoarchitecture of N-doped graphitic carbon (NC)-encapsulated MnO-Co heterostructure (MnO-Co@NC) supported on onion-like graphitic carbon (OLC) is obtained from a manganese- and cobalt-based multi-metal complex Mn3[Co(CN)6]2. The NC outer shell is strongly coupled with the inner MnO-Co heterostructure and integrated with OLC. An ZIB …

We report the synthesis of a transparent plastic material with very high performance ultraviolet (UV)-blocking and blue-light (440 nm) emission. Polyvinyl alcohol (PVA) was employed as a transparent plastic matrix that disperses N-doped carbon dots (N-CDs) prepared via hydrothermal treatment of citric acid, ethylene diamine, and HCl solution. Luminescence of these N-CDs is excitation-independent and the quantum yield (QY) is maximal at an excitation wavelength range of 350–370 nm, in the UV-A radiation segment of the solar spectrum. By encapsulating N-CDs in a polyvinyl alcohol (PVA) matrix, the absolute QY achieves 91%, which is higher than in aqueous solution. As the particle concentration increases in PVA matrix or in solution, UV absorbance increases and QY decreases. On the other hand, UV absorbance of the film is proportional to thickness with no appreciable deterioration in QY, a quality that is …

The synthesis is described of a pH-universal hydrogen evolution electrocatalyst based on N and P co-doped graphitic carbon encapsulated OsP2 (OsP2@NPC) nanoparticles of 1.8 nm size for the electrocatalytic hydrogen evolution reaction (HER). Our OsP2-based catalyst is catalytically active at all pH values and delivers the benchmark current density of 10 mA cm−2 at an overpotential of 46, 90 and 144 mV in acidic, alkaline and neutral pH, respectively.

Here, Pd-coated Ru nanocrystals supported on N-doped graphene (Pd–Ru@NG) are obtained via electroless deposition of Pd on Ru nanocrystals. We have demonstrated that Pd boosts the electrocatalytic performance of Pd–Ru@NG towards the hydrogen evolution reaction (HER) and alcohol tolerant oxygen reduction reaction (ORR) as compared to Pt/C.

Development of significantly active and stable bifunctional catalysts toward hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) remains a challenge. It is also challenging to find a suitable support for the catalysts. Though the N-doped graphene tube (NGT) has many advantages over others due to its excellent electrical conductivity, high surface area, easy synthesis, and low cost, it shows very poor HER and ORR activity. Here, we report the in situ decoration of Ru nanocrystals (Ru NCs) on NGT (Ru@NGT) and their applications as efficient bifunctional electrocatalyst toward ORR and HER. The coordinated Ru complex (ruthenium acetylacetonate) is a unique precursor which directly converted to ultrafine (∼2 nm) and highly dispersed Ru NCs on NGT surface at low temperature without any treatment of the NGT surface. Because of strong coupling with the Ru on NGT, the hydrogen evolution …

Pt is known to be a state-of-the-art catalyst for oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER), while it can also be used for the hydrogenation of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). The quest is ongoing to find a suitable catalyst to circumvent the problems associated with the precious metal Pt. Here, we report a facile and green strategy to fabricate CoFe nanoalloys encapsulated in N-doped graphene layers (CoxFe1–x@N-G) by pyrolysis and their catalytic activity toward ORR, HER, and hydrogenation of 4-NP. Intensive studies have been carried out to elucidate the roles of alloying and N-doping. The catalytic activity is found to improve with increasing amounts of Co in the CoFe core and N-doping in the graphene layers. A similar onset potential with better current density as compared to the state-of-the-art Pt/C catalyst in alkaline medium has been achieved for CoxFe1–x@N-G …

Developing an efficient and cost-effective electrocatalyst for the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) is of paramount importance for designing metal–air batteries and water electrolyzers. Herein, we present an economical approach for the synthesis of a bifunctional electrocatalyst consisting of cobalt–chromium nanostructures entrapped in a graphene tube doped with nitrogen (CoCr@NGT). The graphene tube is of a large size (cross-sectional diameter ∼ 100 nm) with a wall thickness of more than 10 graphene layers. The Cr alloying with the entrapped Co in the NGT drastically enhanced both the HER and OER performance with a low overpotential (η) and better current density along with long-term durability. Hence, CoCr@NGT can be used as a total alkaline water electrolyzer as both an anode and cathode catalyst delivering a current density of 10 mA/cm2 at around 1.58 …

When solid graphene oxide (GO) is treated with microwave, it generates a huge amount of heat followed by reduction and exfoliation. This can be used as a high temperature reactor for ultrafast and in situ synthesis of reduced graphene oxide (rGO) based hybrids within 60 s in an open atmosphere. rGO based hybrids such as Fe3C-G@rGO, Co-Fe3C-G@rGO, Fe-Fe3C-NG@rGO, CoO@rGO, and Pt@rGO (G represents graphene, and NG represents N-doped graphene) have been synthesized by simply mixing appropriate precursors with GO and treating with microwave. The experiments require neither any external high temperature reactors/furnaces nor any chemical reagents or solvents. Then, rGO based hybrids have been exploited for oxygen evolution reaction (OER), oxygen reduction reaction (ORR), and methanol oxidation activity. CoO@rGO and Co-Fe3C-G@rGO show outstanding OER performances with …

A free-standing 3D MoS2/Mo electrode was prepared via a facile, one-step hydrothermal method wherein the Mo foil itself acted as the Mo source and thio-urea as the S source. When directly used as a hydrogen evolution reaction (HER) electrode, the as-prepared MoS2/Mo exhibited a low onset potential of 120 mV, requiring an overpotential of only 334 mV to reach a current density of 100 mA cm−2 while maintaining its catalytic activity for over 20 h. The activation energy of the reaction was determined to be ∼120 meV by temperature-dependent HER studies. In addition, we have also shown that MoS2 structures can be repetitively grown on Mo foil for subsequent HER application by etching MoS2 with H2O2. The HER performance was enhanced further by incorporating reduced graphene oxide (rGO) into the 3D MoS2/Mo electrode, which facilitated better electron transfer through rGO. The onset potential of the …

Since hydrogen is a clean and renewable energy source, the design of efficient and new catalysts for hydrogen evolution reaction (HER) has attracted significant attention. Ultrafine (∼2 nm) monodispersed Ru nanocrystals on N-doped graphene (Ru@NG) show Pt-like catalytic activity towards HER in both alkaline and acidic media with zero onset potential and better current density as compared to Pt/C. The HER performance strongly depends on the nanosize effect of Ru nanocrystals and their dispersion on NG. Transfer of electrons from Ru to carbon results in an electron-deficient metal centre and greatly enhances the HER activity. This new 4-d transition metal electrocatalyst has the potential to serve as an alternative to the Pt benchmark catalyst, which is more costly than Ru.

Here, we demonstrate a green and environment-friendly pyrolysis route for the synthesis of metal-rich sulphide embedded in an N-doped carbon (NC) framework in the absence of sulphide ions (S2−). The metal–chelate complex (tris(ethylenediamine) metal(II) sulfate) serves as a new and single source precursor for the synthesis of earth abundant and non-precious hybrid structures such as metal-rich sulphides Co9S8@NC and Ni3S2@NC when MII = Co2+ and Ni2+ and counter sulphate (SO42−) ions are the source of S. Both the hybrids show superior OER activity as compared to commercial RuO2.

We report a unique, single source precursor Prussian blue (iron(III) ferrocyanide (FeIII4[FeII(CN)6]3)) for the synthesis of Fe/Fe3C nanoparticle encapsulated N-doped graphitic layers and bamboo-like graphitic nanotubes. Hollow N-doped graphite (N-HG) nanostructures are obtained when the encapsulated nanostructures are treated with an acid. Both the encapsulated nanostructures and N-HG are shown to be applicable as bi-functional electrocatalysts for oxygen reduction (ORR) and oxygen evolution reactions (OER). The ORR activity is shown to be improved for N-HG and is comparable to commercial Pt/C. On the other hand, encapsulated nanostructures exhibit OER activity with long-term stability comparable to commercial RuO2.

Here, we report the clean and facile synthesis of Pt and Pd nanoparticles decorated on reduced graphene oxide (rGO) by the simultaneous reduction of graphene oxide (GO) and the metal ions in Mg/acid medium. As-generated Pt and Pd nanoparticles serve as a heterogeneous catalyst for the further reduction of the rGO by the hydrogen spill-over process. The C/O ratio is much higher as compared to the rGO obtained by the reduction of GO by only Mg/acid. Overall, the process is rapid, facile and green that does not require any toxic chemical agent or any rigorous chemical reactions. We perform the catalytic reduction of 4-nitophenol (4-NP) to 4-aminophenol (4-AP) at room temperature by Pd@rGO and Pt@rGO. The reduction is complete within 35 s for Pd@rGO and 60 s for Pt@rGO when 50 μg of hybrid catalyst is used for 0.5 ml of 1 mM of 4-NP. In case of ethanol oxidation, the current density for Pd@rGO is comparable to commercial Pt/C but is doubled for Pt@rGO. Overall, both structures show highly stable catalytic activity compared to commercial Pt/C.

Here, we demonstrate an uninterrupted galvanic replacement reaction (GRR) for the synthesis of metallic (Ag, Cu and Sn) and bimetallic (Cu–M, M[double bond, length as m-dash]Ag, Au, Pt and Pd) sponges/dendrites by sacrificing the low reduction potential metals (Mg in our case) in acidic medium. The acidic medium prevents the oxide formation on Mg surface and facilitates the uninterrupted reaction. The morphology of dendritic/spongy structures is controlled by the volume of acid used for this reaction. The growth mechanism of the spongy/dendritic microstructures is explained by diffusion-limited aggregate model (DLA), which is also largely affected by the volume of acid. The significance of this method is that the yield can be easily predicted, which is a major challenge for the commercialization of the products. Furthermore, the synthesis is complete in 1–2 minutes at room temperature. We show that the sponges/dendrites efficiently act as catalysts to reduce 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) using NaBH4–a widely studied conversion process.

Here, we demonstrate a Si-mediated environmentally friendly reduction of graphene oxide (GO) and the fabrication of its hybrids with multiwall carbon nanotubes and nanofibers. The reduction of GO is facilitated by nascent hydrogen generated by the reaction between Si and KOH at ∼60 °C. The overall process takes 5 to 7 minutes and 10 to 15 μm of Si is consumed each time. We show that Si can be used multiple times and the rGO based hybrids can be used for electrode materials.

We report a one-pot hydrothermal synthesis of nitrogen doped reduced graphene oxide (N-rGO) and Ag nanoparticle decorated N-rGO hybrid nanostructures from graphene oxide (GO), metal ions and hexamethylenetetramine (HMT). HMT not only reduces GO and metal ions simultaneously but also acts as the source for the nitrogen (N) dopant. We show that the N-rGO can be used as a metal-free surface enhanced Raman spectroscopy (SERS) substrate, while the Ag nanoparticles decorated N-rGO can be used as an effective SERS substrate as well as a template for decorating various other nanostructures on N-rGO.

We report a new protocol for the synthesis of M@rGO (M = Au, Pt, Pd, Ag and rGO = reduced graphene oxide) hybrid nanostructures at room temperature in Zn–acid medium. The roles of Zn–acid are to reduce the GO by generated hydrogen and the deposition of metal nanoparticles on rGO by galvanic replacement reaction between Zn and Mn+.

We report the room temperature cell performance of alkaline direct methanol fuel cells (ADMFCs) with nitrogen-doped carbon nanotubes (NCNTs) as cathode materials. NCNTs show excellent oxygen reduction reaction activity and methanol tolerance in alkaline medium. The open-circuit-voltage (OCV) as well as the power density of ADMFCs first increases and then saturates with NCNT loading. Similarly, the OCV initially increases and reaches saturation with the increase in the concentration of methanol feed stock. Overall, NCNTs exhibit excellent catalytic activity and stability with respect to Pt based cathodes.

We report an environment friendly and green approach to obtain few-layer graphene by the almost instantaneous reduction of graphene oxide using Mg ribbons in acidic solution with a hydrogen spillover mechanism. The typical time is 1–5 min, which is much faster than the reduction by other metal catalysts.