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B doped as well as B and N co-doped highly reduced graphene oxide and multiwall carbon nanotubes/Ni oxide and Ni hydroxide nanohybrid layers were synthesized using a one-step laser technique. NiO nanoparticles, graphene oxide platelets, and multiwall carbon nanotubes were used as starting materials for the preparation of the composite layers. H3BO3 was used as B precursor and urea as well as NH3 as N precursors for B and N co-doping of the composite layers. The influence of the nature and concentration of the B and N precursors on the physico-chemical properties of the nanohybrid layers, chemical composition and chemical bonding states, crystalline structure, as well as charge transfer properties was systematically investigated. The relation between the physico-chemical properties and functional characteristics of the nanohybrid layers, photocatalytic removal of water contaminants under simulated sun irradiation conditions was studied, identifying the optimum concentrations of the dopant precursor materials. The mechanism of the photodegradation process was explored, based of the band structure of the composites. The main intermediates, reactive oxygen species implied in the photocatalytic degradation processes of organic molecules, was investigated through the addition of scavengers to the organic dye test solutions. The highest photocatalytic activities were achieved for B and N co-doped samples synthesised using H3BO3 as B and urea as N precursors.

Hybrid layers consisting of Fe oxide, Fe hydroxide, and nitrogen doped graphene-like platelets have been synthesized by an eco-friendly laser-based method for photocatalytic applications. The complex composite layers show high photodecomposition efficiency towards degradation of antibiotic molecules under visible light irradiation. The photodecomposition efficiency was investigated as a function of relative concentrations of base materials, Fe oxide nanoparticles and graphene oxide platelets used for the preparation of target dispersions submitted to laser irradiation. Although reference pure Fe oxide/Fe hydroxide layers have high absorption in the visible spectral region, their photodecomposition efficiency is negligible under the same irradiation conditions. The high photocatalytic decomposition efficiency of the nanohybrid layer, up to 80% of the initial antibiotic molecules was assigned to synergistic effects between the constituent materials, efficient separation of the electron-hole pairs generated by visible light irradiation on the surface of Fe oxide and Fe hydroxide nanoparticles, in the presence of conducting graphene-like platelets. Nitrogen doped graphene-like platelets contribute also to the generation of electron-hole pairs under visible light irradiation, as demonstrated by the photocatalytic activity of pure, reference nitrogen doped graphene-like layers. The results also showed that adsorption processes do not contribute significantly to the removal of antibiotic molecules from the test solutions. The decrease of the antibiotic concentration under visible light irradiation was assigned primarily to photocatalytic decomposition mechanisms.

The development of new synthetic methods is paramount for the versatile production of complex multicomponent electrodes for supercapacitors with enhanced performance. The reactive inverse matrix assisted pulsed laser evaporation (RIMAPLE) technique shows promise for the deposition of complex functional nanocomposites in a facile way. In this work, hybrid supercapacitor electrodes constituted by reduced graphene oxide (rGO) and carbon nanotubes (CNTs) decorated with a myriad of cerium and manganese oxide nanoparticles were obtained by using GO sheets, CNTs, CeO2 nanoparticles and, for the first time, the (NH4)2[Mn2(C6H5O7)2(H2O)2] coordination compound as precursors in the RIMAPLE targets. Compositional and structural characterizations revealed that post-annealing treatments at mild conditions (150-250 °C) induce a further reduction of the rGO and CNTs, besides an oxidation of the Ce oxide phases (Ce3+ to Ce4+) and a reduction of the Mn oxides (Mn3+ to Mn2+). The substantial change of the carbon and metal oxide nanostructures causes an up to 8-fold increase of the capacitance of the electrodes (63 F/cm3 @ 10 mV/s). Finally, the generation of a high quantity of edge defects at 250 °C and long dwell time leads to the drop of the electrode's capacitance.

The full knowledge of the charge storage mechanisms occurring in complex composite electrodes is key for the straightforward development of advanced electrochemical capacitors. In this work, hybrid electrodes composed of reduced graphene oxide, multiwall carbon nanotubes and NiO nanostructures were fabricated through reactive inverse matrix assisted pulsed laser evaporation technique. Nitrogen doping of the carbon nanostructures was carried out by introducing ammonia, urea and melamine precursors in the target. The N-doped graphene electrodes exhibited a significant capacitance enhancement as compared to non-doped ones. This fact is commonly ascribed to faradaic mechanisms. However, our structural-compositional studies point to a significant change of the structural configuration of the composites at the nanoscale upon the nitrogen functionalization as the source of the electrodes’ capacitance enhancement. The composites fabricated with urea precursor exhibited the highest capacitance, and this fact was associated with the presence of pyridinic N groups that triggered the formation of a high amount of structural defects (vacancies – boundaries) and microporosity, not observed in the samples synthesized with other precursors that mainly contained pyrrolic-graphitic N.

Major research efforts are being carried out for the technological advancement to an energetically sustainable society. However, for the full commercial integration of electrochemical energy storage devices, not only materials with higher performance should be designed and manufactured but also more competitive production techniques need to be developed. The laser processing technology is well extended at the industrial sector for the versatile and high throughput modification of a wide range of materials. In this work, a method based on laser processing is presented for the fabrication of hybrid electrodes composed of graphene nanowalls (GNWs) coated with different transition-metal oxide nanostructures for electrochemical capacitor (EC) applications. GNW/stainless steel electrodes grown by plasma enhanced chemical vapor deposition were decorated with metal oxide nanostructures by means of their laser surface processing while immersed in aqueous organometallic solutions. The pseudocapacitive nature of the laser-induced crystallized oxide materials prompted an increase of the GNW electrodes’ capacitance by 3 orders of magnitude, up to ca. 28 F/cm3 at 10 mV/s, at both the positive and negative voltages. Finally, asymmetric aqueous and solid-state ECs revealed excellent stability upon tens of thousands of charge–discharge cycles.

Novel composite materials are being investigated for improving the energy storage performance of electrochemical capacitors. For this goal, synergistic effects via the combination of diverse types of materials are crucial. In this work, electrodes composed of reduced graphene oxide, multiwall carbon nanotubes, as well as cerium and manganese oxides were fabricated through reactive inverse matrix-assisted pulsed laser evaporation (RIMAPLE). UV-pulsed laser irradiation of frozen aqueous dispersions containing graphene oxide sheets, carbon nanotubes, and ceria nanoentities, besides manganese acetate precursor, led to the simultaneous chemical transformation and co-deposition of hybrid electrodes onto flexible metallic substrates via photothermal and photochemical processes. Thorough morphological and compositional studies of the electrodes demonstrated the laser-induced reduction of graphene oxide, besides the crystallization of a mixture of cerium and manganese oxide nanostructures decorating the carbon nanoentities during the deposition process. Electrochemical analyses revealed a remarkable improvement of performance with the combination of electrochemical double layer in the porous nanocarbon framework with pseudocapacitance from the oxide nanostructures, obtaining excellent volumetric capacitances of up to 140 F cm−3 at 10 mV s−1 with the combination of all four materials. The attained results are the best ones yet published regarding RIMAPLE of hybrid nanocarbon-based electrodes with micrometric thickness. Finally, symmetric electrochemical capacitors were fabricated using aqueous electrolyte, revealing excellent stability upon tens of thousands of charge–discharge cycles.

Porous multicomponent surface layers consisting of bimetallic oxide nanoparticles, carbon nanomaterials reduced graphene oxide (GO) and multiwall carbon nanotubes (MWCNTs) were prepared by reactive inverse matrix assisted pulsed laser evaporation. The layers were tested as electrodes for supercapacitor devices. Bimetallic oxide nanoparticles were grown through the mixing of simple inorganic oxides and organic compounds in distilled water. A frequency quadrupled Nd:YAG laser was used for the irradiation of the target dispersions consisting of GO platelets, MWCNTs, NiO, and Zn acetate. Besides oxide nanoparticles synthesis, which were present both on the surface of GO platelets and MWCTs and were also encapsulated within the MWCNTs walls, the GO platelets used for the preparation of the target dispersion were reduced under the effect of the laser pulses. An enhancement of the electrochemical performances of the nanohybrid electrodes were obtained as a results of the formation of bimetallic oxide nanoparticles. The electrodes exhibit fast charge–discharge cycling rate and improved storage capacity as compared to compound layer counterparts containing carbon nanomaterials, reduced graphene oxide, carbon nanotubes and simple binary transition metal oxide nanoparticles, 40F/cm3 volumetric capacitance at 10 mV/s scan rate, 1.5 mW/cm3 energy density and 12 W/cm3 power density at 4 mA/cm3 current density.

Graphene-based photocatalytic layers were prepared by reactive matrix assisted pulsed laser evaporation technique. Binary, nitrogen doped reduced graphene oxide (RGO)/TiO2 and ternary RGO/TiO2/graphitic carbon nitride (g-C3N4) compounds were synthesized and simultaneously deposited onto solid substrates. Aqueous dispersions of commercial graphene oxide platelets and TiO2 nanoparticles were prepared. NH3 or melamine powder was added to the dispersions to achieve enhanced nitrogen doping and synthesis of g-C3N4 during laser irradiation. The photocatalytic efficiency of the layers towards degradation of antibiotic, chloramphenicol and organic dye molecules was systematically investigated and correlated with structural, compositional, and morphological features. This study provides new insights into the importance of TiO2 crystal facets and the synergistic effects between TiO2 nanocrystals and the other constituents, nitrogen doped RGO and g-C3N4 of the hybrid layers. As a result of combined effect of constituent materials, TiO2, RGO, and g-C3N4 as well as N doping of RGO, through the generation of quaternary and pyrrolic N functionalities, the composite layers showed high photocatalytic efficiency for degradation of organic molecules. Stability and reusability experiments indicated that the composite layers maintain their high photodegradation efficiency towards organic molecules during consecutive degradation cycles. Active radical scavenging experiments were also carried out in order to determine the role of the main active species involved in the photocatalytic degradation process.

Carbon nanotube – highly reduced graphene oxide – transition metal oxide (ZnO) nanohybrid layers were synthesized using a one-step laser technique. Commercial multiwall carbon nanotubes (MWCNTs), graphene oxide (GO) platelets and ZnO nanoparticles were used as starting materials. We discuss the influence of carbon/metal oxide ratio on the physico-chemical properties of the nanohybrid layers, geometrical characteristics, shape and dimensions of constituent nanoentities, chemical composition and chemical bonding states, optical properties, UV–visible absorption, band gap values, as well as charge transfer properties. In the followings the relation between these properties and functional characteristics, removal of water contaminants, antibiotic molecules, and charge storage performances of the ternary, MWCNTs/reduced GO/ZnO layers are presented, identifying the optimum relative concentrations of the constituting nanomaterials. The high photocatalytic efficiencies both under UV and visible light irradiations, even after several consecutive degradation cycles, were attributed to effective separation of photogenerated charge carriers by carbon nanomaterials as well as formation of oxygen deficient ZnOx−1 nanocrystals. The enhanced charge storage capacity of ternary nanohybrid electrodes is based on combined electrochemical double layer capacitance and pseudocapacitance implying redox reactions on the surface and subsurface of the layers in contact with the electrolyte. Both functional properties are strongly influenced by the relative concentrations of the nanomaterials constituting the ternary layers.

Metal–organic frameworks (MOFs) capable of mobility and manipulation are attractive materials for potential applications in targeted drug delivery, catalysis, and small‐scale machines. One way of rendering MOFs navigable is incorporating magnetically responsive nanostructures, which usually involve at least two preparation steps: the growth of the magnetic nanomaterial and its incorporation during the synthesis of the MOF crystals. Now, by using optimal combinations of salts and ligands, zeolitic imidazolate framework composite structures with ferrimagnetic behavior can be readily obtained via a one‐step synthetic procedure, that is, without the incorporation of extrinsic magnetic components. The ferrimagnetism of the composite originates from binary oxides of iron and transition metals such as cobalt. This approach exhibits similarities to the natural mineralization of iron oxide species, as is observed in ores and in biomineralization.

Several technological routes are being investigated for improving the energy storage capability and power delivery of electrochemical capacitors. In this work, ternary hybrid electrodes composed of conducting graphene/reduced graphene oxide (rGO), which store charge mainly through electric double-layer mechanisms, covered by NiO nanostructures, for adding pseudocapacitance, were fabricated through a matrix assisted pulsed laser evaporation technique. The incorporation of multiwall carbon nanotubes (MWCNTs) provokes an increase of the porosity and thus, a substantial enhancement of the electrodes’ capacitance (from 4 to 20 F cm−3 at 10 mV s−1). Volumetric capacitances of 34 F cm−3 were also obtained with electrodes containing just carbon nanotubes coated with NiO nanostructures. Moreover, the use of nitrogen containing precursors (ammonia, urea) for laser-induced N-doping of the nanocarbons also provokes a notable increase of the capacitance. Remarkably, N-containing groups in rGO–MWCNTs mainly add electric double layer charge storage, pointing to an increase of electrode porosity, whereas redox reactions contribute with a minor diffusion fraction. It was also observed that the loading of carbon nanotubes leads to an increase of diffusion-controlled charge storage mechanisms versus capacitive ones in rGO-based electrodes, the opposite effect being observed in graphene electrodes.

Electrodes constituted by nitrogen-doped reduced graphene oxide (NrGO) in combination with NiO nanostructures were fabricated by means of reactive inverse matrix assisted pulsed laser evaporation technique. The structure-composition of the electrode composites was tailored by laser-inducing chemical reactions of graphene oxide (GO) flakes with different precursor molecules (citric acid, ascorbic acid and imidazole) during GO deposition. Structural characterizations reveal the formation of wrinkles and nanoholes in the NrGO sheets, besides their coating with NiO nanostructures. Compositional studies disclose that imidazole precursor promotes the synthesis of NrGO with the largest degree of reduction and nitrogen doping (mainly with graphitic and pyridinic N). Electrochemical analyses of the obtained electrodes reveal that NiO nanostructures increase surface charge storage processes (double layer – pseudocapacitive) over diffusive ones, being the imidazole-based electrodes the ones exhibiting the best performance (up to 114 F cm−3 at 10 mV s−1). Symmetric and asymmetric electrochemical capacitors were also fabricated showing excellent robustness over 10,000 charge-discharge cycles at high specific currents.

The synthesis of metal-free graphene-based photocatalysts has received great attention recently due to their expected contributions to the development of solar-based hydrogen generation via water-splitting in a low cost and ecological manner. In this work, a new method for the generation of nitrogen-doped graphene-based powder employing an alternative solution to commonly used toxic and hazardous organic solvents is presented. The procedure involves ultraviolet pulsed laser irradiation of graphene oxide (GO) flakes dispersed in 1-butyl-3-methylimidazolium [bmim]-based ionic liquids using both chloride and acetate anions. The structural and compositional analysis using transmission electron microscopy, X-ray photoelectron and infrared spectroscopy indicate that the irradiated GO becomes partially reduced and doped with graphitic, pyrrolic and pyridinic nitrogen species. Interestingly, the relative content of the nitrogen functionalities is controlled by the anion in the ionic liquid and its concentration, with the obtained graphene-based powders showing higher photocatalytic activity than GO. Furthermore, a remarkable synergistic effect is observed for GO-[bmim]-acetate powder (acting as co-catalyst) in combination with anatase TiO2 nanoparticles. The presented method opens new research avenues for the cost-effective mass production of graphene-based photocatalysts for water splitting applications.

A versatile method based on the matrix assisted pulsed laser evaporation (MAPLE) technique was used for the fabrication of graphene-based electrodes for application in supercapacitors. The simultaneous deposition and chemical transformation of graphene oxide (GO) and GO–NiO nanoparticles was attained by including nitrogen-containing chemically reactive compounds (ammonia, urea and melamine) in aqueous MAPLE targets. Morphological analyses reveal the formation of hundreds of nanometres to tens of micrometres thick porous films on both plastic and metallic flexible substrates. Structural and compositional studies, carried out by transmission electron microscopy, and Raman and X-ray photoelectron spectroscopies, disclose significant deoxidation and nitrogen doping of the GO material. The electrodes reveal remarkable electrochemical performance, showing a maximum volumetric capacitance of 350 F cm 3 (9 mF cm 2 areal capacitance) in aqueous electrolyte. Symmetric supercapacitors fabricated with these electrodes reveal excellent long-term stability at high specific intensities. From the obtained results, it can be asserted that the reactive inverse MAPLE method stands out as a promising technology not only for the adaptable fabrication of flexible graphene-based composite electrodes but also for a wide variety of advanced functional materials for diverse applications.

Graphene oxide (GO) and reduced GO films with different amounts of silver nanoparticles (Ag NPs) have been deposited on quartz and silicon substrates by matrix assisted pulsed laser evaporation (MAPLE). The morphology, structure, chemical composition, and optical and electrochemical properties were evaluated by scanning electron microscopy, X-ray photoelectron spectroscopy, ultraviolet–visible spectrophotometry, and cyclic voltammetry measurements. The properties of the films obtained with two types of GO precursors have been compared. A reduction of the amount of oxygen containing groups is observed with the increase of the Ag concentration, which leads to a decrease of the optical band gap. Moreover, the deposition in nitrogen gas ambience leads to the N-doping of rGO material. The films obtained with the highest amount of Ag and with nitrogen doping show potential to be used in energy storage electrodes.

Electrically conductive and highly hydrophobic surface layers are attractive for many practical applications. In this work the functional, wetting and electrical properties of titanium dioxide (TiO2), TiO2/silver (Ag), and TiO2/reduced graphene oxide (rGO)/Ag nanocomposite coatings layers are reported. The functional properties of the layers were correlated with their chemical composition and bonding states between the constituent elements, determined in turn by the synthesis and immobilization process parameters. The nanocomposite coatings were obtained by matrix assisted pulsed laser evaporation, a laser-based environmental friendly thin film deposition technique. The synthesized ternary TiO2/rGO/Ag coatings has optimum performances, highly hydrophobic character and low electrical resistance, attributed to the presence of Ag nanoparticles and to the reduction of the oxygen containing functional groups of the GO platelets during laser irradiation and transfer processes leading to the formation of graphene-like material.

Laser-induced chemical conversion of graphene oxide (GO) is an effective way to modify its properties and expand its potential use for numerous applications. In this work, a mechanically stable and flexible free-standing GO membrane is synthesized and further processed by ultraviolet laser radiation in gas and liquid ammonia-rich environments. Electron and atomic force microscopy, as well as X-ray photoelectron spectroscopy analysis, reveal that laser irradiation in gas leads to a large defect-induced morphology modification and high deoxygenation process, accompanied by the slight incorporation of nitrogen functionality to the reduced GO structure. Conversely, irradiation in liquid provokes significant integration of nitrogen groups, essentially amines, into a partially reduced GO structure, without evident modification of the morphology. Electrical measurements on the macro- and nano-scale point to a complex contribution of morphology and oxidized regions to the overall resistance of the rGO.

© 2015 Elsevier Ltd. All rights reserved. Ultraviolet laser irradiation of films composed of graphene oxide (GO) and GO-magnetite (Fe3O4) nanoparticles deposited on polydimethylsiloxane substrates is carried out. The irradiations are performed in vacuum and ammonia-rich gas environments. Electron and scanning probe microscopies reveal a rippling process in GO sheets as the accumulation of laser pulses proceeds, being the effect more pronounced with the increase of laser fluence. X-ray photoelectron spectroscopy analyses point to laser-induced chemical reaction pathways in GO completely different depending on the environment and the presence or absence of Fe3O4 nanoparticles. It is demonstrated that GO-based films with diverse type of oxygen- and nitrogen-containing chemical groups can be obtained by means of laser irradiation processes. The sheet resistance of these materials is also correlated to their structure and composition.