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Developing highly efficient catalysts for hydrogen evolution reaction (HER) play a significant role in the large-scale application of electrochemical water splitting. Here, we develop an ultrafine ...

The photoelectric properties of pristine, Mn-doped, Fe-doped and Co-doped graphene are investigated by DFT investigation. Doped graphene exhibits interesting tuning of electronic and optical proper...

We build a novel fluorescence resonance energy transfer (FRET) method based on N-doped graphene quantum dots (NGQDs)–MnO2 nanocomposite for rapid, sensitive detection of glutathione (G SH) levels in human serum. In this strategy, MnO2 nanosheets on the NGQDs surface serve as a quencher. NGQDs fluorescence can make a recovery by the addition of GSH, which can reduce MnO2 to Mn2+, and thus the GSH can be monitored. The MnO2 platform affords minimal background and high sensitivity for detecting GSH in this proposed scheme. Meanwhile, relevant fluorescence on–off–on processes were monitored, and the sensing mechanism was explored.

Nitrogen doped graphene quantum dots (N-GQDs) have attracted much attention because of their superior electronic and optical properties. The preparation of N-GQDs can be usually performed via a top...

Development of bifunctional catalysts with low platinum (Pt) content for the ethanol oxidation reaction (EOR) and the oxygen reduction reaction (ORR) is highly desirable, yet challenging. Herein, we present structural engineering of a series of two-dimensional/three-dimensional (2D/3D) hierarchical N-doped graphene-supported nanosized Pt

Nitrogen-doped graphene represents a good alternative and a promising catalytic structure for the oxygen reduction reaction (ORR) in fuel cell applications compared with the more costly Pt-containi...

In this study, we have designed and fabricated a portable electrochemical sensor for direct detection of capsaicin in chili samples at the point-of-testing. The sensor, shaped like a chili pepper a...

Oxygen reduction reaction (ORR) is a crucial cathodic reaction for fuel cells. Due to its sluggish kinetics, various ORR electrocatalysts have been designed and extensively investigated. Traditionally, Pt-based materials serve as efficient ORR catalysts. However, Pt’s low abundance, high cost and poor durability have compelled people to explore other materials. For example, silver (Ag) is comparatively well-stocked and low-cost, which has drawn great attention. Although Ag shows exceptional anti-poisoning property, it is not good as Pt. Recently, enhanced electrochemical behavior of plasmonic nanostructures under illumination has been examined through both theoretical modeling and experimental investigations. As a green and sustainable energy source, solar energy can be efficiently introduced into fuel cells and metal-air batteries. Plasmonic Ag nanoparticles have strong spectral absorption in the ultraviolet and visible light bands due to unique localized surface plasmon resonance effects. Meanwhile, nitrogen-doped graphene (NG) incorporates nitrogen (N) atoms into graphene skeleton through a hydrothermal process, thereby providing active ORR sites. Also, the vacancies and defects generated by the N-doping allow silver nanoparticles to be better dispersed on the graphene as well as maintain silver nanoparticles during the reaction. Herein, plasmonic Ag nanoparticles decorated N-doped graphene (Ag/NG) were synthesized and utilized as ORR catalysts. The ORR performance of Ag/NG greatly exceeded that of pure Ag nanoparticles and NG. For instance, the half-wave potential was 0.86 V, exceeding that of commercial Pt/C (20 wt. %). Under the AM1.5G simulated sunlight, Ag/NG demonstrated photo-enhanced electrocatalytic performance with right shifting of onset potential and enhanced current density. Therefore, the Ag/NG composite provides a potential strategy for the development of solar-enhanced electrocatalysts for fuel cells and metal-air batteries.

In the present study, we aim to synthesize heteroatom (nitrogen or boron) doped-reduced graphene oxide (N-rGO or B-rGO) as a catalyst for the electro-oxidation of hydroquinones, used as a candidate of fuel (hydrogen carrier molecule) for direct-type fuel cells (DFCs), and evaluate the doping effect on its catalytic activity. N-rGO and B-rGO were prepared from a mixture of graphene oxide (GO) and urea or boron trioxide by pyrolysis method. We characterized the morphology and crystal structure of the prepared materials by transmission electron microscopy, and X-ray diffraction, respectively. Energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy show the loading amount of the heteroatoms, 10.4 wt% N and 2.9 wt% B, as well as their chemical nature. The electrochemical analysis of the prepared materials by rotating disk electrode system reveals high activity of B-rGO, 15 and 85 mV lower overvoltage compared with rGO at the half-wave potential of diffusion-limited current, for the electro-oxidation of hydroquinone and methyl-hydroquinone, respectively, because of its electron-accepting nature. We demonstrate that thus modified carbons exhibit high activity, B-rGO > N-rGO > rGO, for the oxidation of hydroquinone derivatives as non-metallic anodes of DFCs.

Since high capacity small rechargeable ion storage batteries are greatly required due to the increasing development of mobile technologies, search for new types of electrode materials with superior...

Flexible enzymatic biofuel cell (EBFC) has been considered as an alternative power source for wearable devices, in which, the design of the substrate electrode is of significance for its mechanical...

Herein we report the mass-production of Cl-doped graphene nanodots through the implementation of pulsed plasma on graphite rod in CHCl3 medium. The Cl-doped graphene shows the band gap, which is as...

Protecting alkali metals from oxygen crossover is a key unsolved challenge in metal–oxygen batteries. Herein, we report a new “reactive-armor strategy” by using freestanding three-dimensional sulfu...

Pesticides, widely used for pest control and plant growth regulation, have posed a threat to the environment and human health. Conventional methods to analyze pesticide residues are not applied to resource-limited areas because of their high cost, complexity, and requirements for expensive instruments (such as GC/MS and LC/MS). To address these challenges, herein we fabricated colorimetric nanozyme sensor arrays based on heteroatom-doped graphene for detection of aromatic pesticides. The active sites of nanozymes could be differentially masked when different pesticides were adsorbed on the graphene, which in turn resulted in the decrease of their peroxidase-mimicking activities. On the basis of this principle, five pesticides (i.e., lactofen, fluoroxypyr-meptyl, bensulfuron-methyl, fomesafen, and diafenthiuron) from 5 to 500 μM were successfully discriminated by the sensor arrays. In addition, discrimination for different concentrations of each pesticide and different ratios of two mixed pesticides were also demonstrated. The practical application of the sensor arrays was further validated by successfully discriminating the pesticides in soil samples. This work not only provides a facile and cost-effective method to detect pesticides but also makes a positive contribution to food safety and environmental protection.

The energy crisis and the rise of flexible electronics call for a renewable and flexible energy source due to the inconvenience of the traditional power supply. A triboelectric nanogenerator (TENG)...

Covalent organic polymers (COPs) provide an interesting platform for constructing the low-cost and highly efficient multifunctional electrocatalysts in view of their tailorable structures and prope...

Covalent functionalization of two-dimensional materials is a versatile tool to induce deep changes in their initial properties leading to new functionalities. Unfortunately, in the case of graphene its poor chemical reactivity turns this task rather difficult from the practical point of view. In this work, we show how the adsorption of external species can be controlled by substitutional nitrogen atoms properly distributed through the graphene layer. Nitrogen atoms can be experimentally incorporated in the graphene lattice with high precision and tunable concentration and they can be used as active sites to trigger an ordered functionalization. By means of first-principles calculations we study the adsorption of single and multiple oxygen atoms in the vicinity of substitutional N defects, revealing a rich scenario regarding adsorption configurations and electronic properties. In particular, we find a stable structure involving three oxygen atoms that induces a robust magnetic behavior in the graphene layer. The great chemical variability found in the oxygen-decorated N-doped structures presented in this study constitutes a valuable platform for the future development of graphene-based electronic and sensing devices.

In the drive towards energy harvesting, graphene and their derivations are most promising photothermal materials for solar evaporation. Here is a facile approach for constructing gradient vertical-...

In this paper, Co9S8/Ni3S2 nanoflakes (NFs) with sulfur deficiencies were grown in-situ on N-doped graphene nanotubes (N-GNTs). They were successfully prepared through electrodeposition followed by hydrogenation treatment, which is able to act as a self-supported electrode for asymmetric supercapacitors (ASCs). Combining the defect-rich active materials with highly conductive skeletons, the hybrid electrode N-GNTs@sd-Co9S8/Ni3S2 NFs show ultrahigh specific capacity of ∼304 mA h g−1 and prominent rate capability (capacity retention ratio of ∼85% even at 100 A g−1), and deliver a long cycling lifespan of ~1.9% capacitance loss after 10000 cycles. In addition, an ASC was constructed using the as-synthesized composite electrode as the positive electrode and active carbon (AC) as the negative electrode. The fabricated device shows a high energy density of ~45.1 Wh kg−1 at ~3.4 kW kg−1 and superior cycling stability. This work substantiates a smart strategy to fabricate novel composite electrode materials for next-generation supercapacitors by incorporating riched deficiencies into nanostructures.

In this work, we demonstrate a simple, facile, and efficient one-pot synthesis of polymer–quantum dot nanocomposite films where nitrogen-doped graphene quantum dots (N-GQDs) were homogeneously disp...

The oxygen reduction reaction (ORR) strictly determines the performance of a variety of energy storage and conversion devices, and platinum (Pt) has been commonly used as the efficient catalyst for...

We performed density function theory calculations to study the effect of strain on electronic properties of pristine and doped graphene. A dramatic change in density of states (DOS) and band struct...

Carbon plays a significant role in the development of electrode materials used in, for example, catalysis, energy storage and sensing. Graphene-based coatings and carbon nanotubes have expanded that role through nanostructuring of hybrids or the formation of composites. In particular, the formation of hybrids of nanocarbons with iridium oxide yield nanostructured materials through direct anodic deposition, which have substantially improved charge capacities vs. pure IrOx. Modification of the possible redox sites, new structuring of the hybrids and increased charge capacities are expected as a result. This work shows that nitrogen (N)-doped graphenes, as part of an IrOx hybrid, offer a new redox chemistry on graphene oxide through electrochemical modulation of the redox states of nitrogen in graphene, and yield stable nitro groups bound to carbon, which have, so far, the largest oxidation state reported in N-doped graphene. The hybrid materials are obtained in the form of coatings thanks to spontaneous adhesion of iridium oxo species on N-doped graphenes and further anodic electrodeposition of the mixture. While the oxidizing synthesis process already involves modification of the oxidation state of nitrogen, further electrochemical cycling evidences the electrochemical processes for both the IrOx and N groups attached to the graphene oxide. All the hybrids obtained present a wide range of nitrogen-based groups that include the nitro group, and a significant charge capacity that remains large upon electrochemical cycling and that involves all the faradaic processes from the iridium and graphene components. One hybrid, in particular, which includes the highest starting oxidation state, reaches a significantly higher charge capacity, higher even than the graphene oxide hybrid, and with 70% retention upon cycling. Although nitrogen doping of graphene is considered to be a reducing process, this study shows that an oxidizing range of nitrogen doping is also possible. IrOx, and the reversible redox processes that iridium offers, are thought to be essential in stabilizing an unusual nitro-carbon-oxide system and allowing a sustained high charge storage capacity that is twice that of pristine graphene or graphene oxide hybrids., The authors acknowledge financing from the Ministry of Science, Innovation and Universities, through MAT2015-65192-R, MAT2017-86616-R, RTI2018-097753-B-I00, Fundació Marató TV3 (110130/31) and Severo Ochoa Program (SEV-2015-0496).

The first examples of heterogeneous Fe-catalysed cyclopropanation reactions are presented. Pyrolysis of in situ-generated iron/phenanthroline complexes in the presence of a carbonaceous material leads to specific supported nanosized iron particles, which are effective catalysts for carbene transfer reactions. Using olefins as substrates, cyclopropanes are obtained in high yields and moderate diastereoselectivities. The developed protocol is scalable and the activity of the recycled catalyst after deactivation can be effectively restored using an oxidative reactivation protocol under mild conditions.

Orientador: Abner de Siervo Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin Resumo: Apresentamos uma investigaçao sistemática da síntese de nanoestruturas de carbono e de grafeno dopado (Gr) por meio de métodos de crescimentos bottom-up. Utilizamos microscopia de tunelamento em varredura e espectroscopia de tunelamento de eletrons (STM/STS) para explorar a morfologia das amostras durante a síntese e suas propriedades eletrônicas locais, enquanto a espectroscopia de fotoelétrons de raios-X (XPS) foi empregada para estudar o estado químico da amostra. Cálculos da teoria do funcional da densidade (DFT) foram realizados para suportar nossos resultados experimentais. Em primeiro lugar, apresentamos o crescimento de monocamadas de boro-nitrogênio-carbono (h-BNC) na hexagonais a partir de um único e novo precursor molecular (hexametil borazina - C6H18B3N3) superfície de Ir(111). A partir de imagens de STM combinadas com c'alculo DFT, demonstramos que o h-BNC e' formado pela dopagem de Gr com (BN)8 unidades dispostas em conformação de seis anéis, localizadas nas regiões tipo fcc e hcp do padrão moiré do Gr na superfície do Ir(111). Isso limita sua densidade em Gr e minimiza a segregação. Experimentos adicionais foram realizados em Rh(111), os resultados mostram que a síntese de h-BNC ou heteroestruturas laterais Gr-hBN a partir de um único precursor molecular não ocorre nesta superfície, devido a interdifusão dos átomos de carbono no cristal de Rh na temperatura de crescimento de h-BN. No entanto, em Rh(111) uma monocamada de h-BN de alta qualidade foi sintetizada. Em segundo lugar, investigamos a síntese de redes quadradas porosas organometálicas de porfirinas Br4TPP sobre a superfície Ag(100) empregando a síntese química assistida por superfícies. Diferentes motivos organometalicos foram formados à temperatura ambiente (RT). Estudamos o papel crítico da temperatura do substrato durante a deposição do precursor. Os resultados mostram que o crescimento das redes quadradas é favorecido a 450K. Combinado resultados de STM e cálculos de DFT, identificamos a conformação de adsorção molecular como saddle shape e a periodicidade de rede como sendo de (1, 90 ± 0, 03)nm. Os cálculos sugerem que, uma vez formada a rede TPP com os átomos de Ag, a remoção desses átomos é um processo altamente energético; portanto, o sistema fica cineticamente aprisionado. Portanto, promover a ligação C-C por tratamento térmico sem destruir a rede não é possível. Foram observadas cadeias de moléculas ao longo da direção ?530? em Ag(100) para temperaturas de deposição acima da RT. As moléculas estão em estrutura totalmente invertida, a conformação típica de adsorção relatada em Cu(111). Finalmente, mediante o método de reação de acoplamento de Ullmann, foram sintetizadas nanofitas (GNRs) porosas de grafeno dopadas com nitrogênio sobre a superfície Ag(100) e Cu(111). Para cada superfície, investigamos a influência da temperatura do substrato durante a deposição molecular na seletividade das vias de reação, encontrando o parâmetro apropriado para o crescimento das cadeias, o que permite controlar a sí?ntese pela temperatura do substrato. A partir de imagens de STM, observamos a coexistência de cadeias organometálicas com extremidades covalentes e GNRs constituídos por cerca de seis unidades. As influências do substrato sâo claramente percebidas pela orientação das cadeias metálicas e das estruturas covalentes Abstract: In this thesis, we present the systematic investigation of the synthesis of carbon nanostructures and doped graphene (Gr) via bottom-up methods, using a comprehensive multi-technique approach. By scanning tunneling microscopy/spectroscopy (STM/ STS) the morphology of the sample during the hierarchy synthesis and their local electronic properties were explored, while X-ray photoelectron spectroscopy (XPS) probed the chemical state of the sample. Density functional theory (DFT) calculations support our experimental results. Firstly, we present the successful growth of hexagonal boron-nitrogen-carbon monolayer (h-BNC) from a novel single molecular precursor (hexamethyl borazine - C6H18B3N3) by chemical vapor deposition (CVD) on Ir(111). From STM images combined with DFT calculation, we have demonstrated that h-BNC is formed by doping Gr with small BN nanoclusters. The dopant was identified as (BN)8 units arranged in six-fold BN rings conformation, preferably sitting in the fcc- and hcp-type regions of the Gr moire' pattern on Ir(111). This behavior limits its density on Gr and minimizes the segregation between Gr and h-NB domanis. In addition, for a BN concentration of about 17%, a band gap between 1.4 and 1.6 eV was determined, showing the material's semiconductor behavior. Additional experiments were performed on Rh(111), the results show that the synthesis of h-BNC or lateral heterostructures Gr-hBN from a single molecular precursor does not take place on the surface due to the carbon atoms strongly dissolving into the Rh bulk at h-BN growth temperature. However, on Rh(111), a high-quality h-BN monolayer was synthesized. Secondly, we investigated the on-surface synthesis of organometallic square pore network from Br4TPP porphyrin on Ag(100). Due to the substrate reactivity and low debromination barrier, different motif coordinated by Ag adatoms were already formed at room temperature (RT). We studied the critical role of substrate temperature during the deposition of the precursor. The results show that square motif growth is favored at 450K. We identified the molecular adsorption conformation as saddle shape and the lattice periodicity as (1.90 ± 0.03)nm. The calculations suggest that once the TPP network with Ag adatoms is formed, removing these atoms is a highly energetic process; hence the system becomes kinetically trapped. Therefore promoting C-C bonding by thermal annealing without destroying the network it is not possible. Moreover, chains of molecules sit along ?530? direction on Ag(100) were observed for deposition above RT. The molecules are in fully inverted structure. From our best knowledge, this is the first time that porphyrins are observed in an inverted structure and saddle shape on Ag(100). Finally, by surface-assisted Ullmann coupling reaction, nitrogen-doped porous graphene nanoribbons (GNRs) were synthesized on Ag(100) and Cu(111). For each surface, we investigated the influence of the substrate temperature during molecular deposition on the selectivity of reaction pathways, finding the appropriate parameters for growing the chains, which allows controlling the synthesis by the substrate temperature. From the STM data, we observed the coexistence organometallic chains with covalent ends and GNRs constituted by about six units. The substrate's influences are clearly noticed by the orientation of the metalled chains and the covalent structures Doutorado Física Doutora em Ciências CNPQ 140721/2019-3

The development of polymer-based conductive inks has gained increasing interest in the areas of printed and molded electronics. Graphene-based materials are explored in this scope, reduced graphene oxide (rGO) being among the most used conductive filler components of the inks. Herein, rGO is doped with nitrogen to obtain N-rGO; the replacement of oxygen atoms by nitrogen ones increases the electrical conductivity of graphene. Polymer-based conductive inks reinforced with graphene are developed based on polyvinylpyrrolidone (PVP) as polymer binder and dihydrolevoglucosenone (Cyrene) as solvent, leading thus to environmentally friendly conductive inks. Screen-printable inks are optimized in terms of viscosity and adhesion properties, leading to printed films with sheet resistance close to Rs=1ksq1, the graphene:PVP inks being also biocompatible and nontoxic., This work was supported by the Portuguese Foundation for Science and Technology (FCT): projects UID/FIS/04650/2021, UIDB/05256/2020, UIDP/05256/2020, PTDC/FIS-MAC/28157/2017, and PTDC/BTM-MAT/28237/2017, grants SFRH/BPD/110914/2015 (P.C.) and SFRH/BD/145741/2019 (M.F.), and Stimulus of Scientific Employments 2020.04028.CEECIND (C.M.C.) and 2020.04163.CEECIND (C.R.). The authors thank Basque Government Industry Department under the ELKARTEK program and European Union’s Horizon 2020 Programme, ICT-02-2018, Flexible and Wearable Electronics, grant agreement no. 825339, WEARPLEX, wearable multiplexed biomedical electrodes.

11 figures.-- Supplementary information available., Bifunctional oxygen electrocatalysts are essential in the development of low-temperature unitized regenerative fuel cells (URFCs), as a promising alternative for storing energy via hydrogen. TiO2, as a semiconductor material, is commonly not established as an active electrocatalyst for oxygen reduction and oxygen evolution due to its poor electrical conductivity and low reactivity. Here, we demonstrated that composites composed of TiO2 and N-doped graphene can be active in oxygen reduction and evolution reactions in an alkaline environment. Combination factors such anatase/rutile interaction, N-doping graphene, and the presence of Ti3+/Ti–N species raise the active sites and improve the electrochemical activity. Our results may afford an opportunity to develop a non-noble and promising electrocatalyst in energy storage technology., This research was funded by the Ministry of Science, Innovation and Universities and FEDER, grant number ENE2017-83976-C2-1-R