Solvent-free radiofrequency (RF) nitrogen plasma treatment was applied to incorporate nitrogen atoms in relatively high concentration. Graphene oxide (GO) and two reduced GOs of different O-content were used as target substrates to reveal the influence of the functional groups decorating the graphene lattice on the quantity and quality of nitrogen incorporation. Despite the relatively high oxygen content of the samples no N–O bonds develop but three kinds of different N–C bonds of very similar concentration are formed. Reduction of the GO removed the O-groups but did not heal the vacancies where N doping may occur. After two days the implanted N content drops, the N1 state (sp2 N in pyridine ring, C–N–C) showing the least stability.

Synthesis of zirconium carbide (ZrC) powder was investigated applying a non-conventional atmospheric radiofrequency (RF) thermal plasma process. In one case, zirconium dioxide (ZrO2) was reacted with solid carbon or with methane with varying molar ratio. In the other, zirconium-propoxide (NZP), containing both constituents, was thermally decomposed in the Ar plasma. Temperature-dependent thermodynamic analysis was performed in the 500-5500 K temperature range to estimate the formation of possible equilibrium products for each reaction stoichiometry. Broad temperature range exists for the stability of solid ZrC for each explored reaction system. In accordance with this prediction, X-ray diffraction studies detected the ZrC as the major phase in all the prepared powders. The yield of particular runs ranged from 39 % to 98 %. Practically, full conversion was typical for the case of NZP precursor, however only partial conversion could be detected in ZrO2 reactions. The average particle size of the powders falls between 10 nm and 100 nm depending on the type of the reaction systems (either calculated from the specific surface area or derived from broadening the XRD reflections). The transmission electron micrographs indicated mostly globular shape of the nanosize particles. Quantitative analysis of the surface of the powders by X-ray photoelectron spectroscopy revealed the presence of oxygen and carbon. Evaluating the spectra of the powders prepared from NZP, and taking in the account its spherical shape, a ZrC core covered by a very thin (≈1.0 nm) ZrO2 layer may be accounted for the measured oxygen and a thicker carbonaceous layer.

The solvent-free nitrogen plasma treatment is able to incorporate nitrogen atoms in relatively high concentration. Graphene oxide (GO) and two reduced GOs of different O-content were used as target substrates to reveal the influence of the functional groups decorating the graphene lattice on the quantity and quality of nitrogen incorporation. Despite the relatively high oxygen content of the samples no N―O bonds develop but three kinds of different N―C bonds of very similar concentration are formed. Reduction of the GO removed the O-groups but did not heal the vacancies where N doping may occur. After two days the implanted N content drops, the sp2 N in pyridine ring, C‒N‒C state showing the least stability. Quantum chemical calculations with single N doping on a C88H26 model suggest that N incorporation not only improves the efficiency of the already active zigzag edge in the cathodic oxygen reduction reaction (ORR), but creates new active sites at the armchair edge and in the middle of the graphene sheet. Not only the concentration but also the relative position and the chemical form of nitrogen heteroatoms play an important role in the electrocatalytic process.

The adsorption of the fluorescent dye, Oxazine 1 (OX) was studied on graphene oxide (GO), in the range of low (<= 10(-7) M) OX concentrations, exploiting the high sensitivity of fluorescence spectroscopy. Dry GO was characterized using XRD, TEM, XPS, Raman and IR spectroscopy, while its chemistry in aqueous suspension was examined with potentiometric titration. Adsorption isotherms were measured at pH 6.4 and 10.2 at temperatures 20 and 35 degrees C. All the isotherms were well described by the Langmuir equation. The saturation capacities n(m) were higher at pH 10.2 than at 6.4 at the respective temperature, in accordance with the presence of additional dissociated acidic groups on the GO surface. The n(m) values corresponded to a few percent occupancy of the dissociated acidic groups of GO. The equilibrium constant K-L for OX was substantially higher than the values reported for the adsorption of other cationic dyes from more concentrated solutions, indicating that our results refer to binding to the most active sites. The large negative adsorption enthalpy and the positive adsorption entropy are also indicative of strong binding interactions. In this case, probably the Coulomb interactions between the opposite charges on the adsorbent and adsorbate are dominant in the binding interactions.

Waste and low-cost lignocellulosic biomasses are well studied and widely used as raw materials for porous carbon adsorbents. Much less attention is given to the exploration of the potential of marine biomasses, though these materials contain also nitrogen, which—if preserved during the processing—has a beneficial influence on the sorption properties of the porous carbon obtained. Here, we report a multi-technique investigation into the conversion of crab shell to porous carbon adsorbent. Thermogravimetry and pyrolysis-GC/MS studies were used to reveal the thermal degradation of this natural polymer and follow the decomposition process through the identification of the products. Almost 40 various volatile degradation products were distinguished released at 500 °C pyrolysis temperature. Based on the TGA/DTG results, two temperatures, 350 and 500 °C, were selected to obtain pyrolytic samples in macroscopic quantities in order to characterize the morphology and surface chemistry of the solid fraction. More than 50% of the nitrogen atoms were still in the carbonaceous matrix after the 500 °C pyrolysis in the C–N=C, C–NH and 3C–N-type bonds. The ash content < 1% included hydroxylapatite-type crystalline matter. Based on these results, we may conclude that crab shells have a high potential as precursor of nitrogen-containing biochar.

The facile preparation of dynamic interfaces is presented based on the combination of photoisomerizable azobenzenes and polydopamine (PDA)/Au nanoparticle composite materials. Azobenzenes with different spacer lengths (C3 , C6 ) and surface-binding groups (SH, NH2 ) were synthesized. The polymer layer on macroscopic quartz surface was prepared by the facile aerobic autopolymerisation of dopamine hydrochloride under basic conditions. The presence of redox-active catechol moieties meant that gold nanoparticles were formed on the polymer surface. The obtained UV-Vis spectroscopic results confirmed that following their successful assembly, the switching of azobenzenes on PDA/Au was not affected by the surface binding group and the spacer length of the azobenzene molecules under the measurement conditions. Furthermore, facilitated by the curved nature of the Au particles, the surface-bound azobenzene layer could be reconstructed by ligand-exchange processes, and the photochemical characterization of the mixed layer was performed.

Carbon quantum dots (CQDs) are a novel family of fluorescent materials that could be employed as non-toxic alternatives to molecular fluorescent dyes in biological research and also in medicine. Four different preparation approaches, including microwave assisted heating and solvent refluxing, were explored. In addition to the widely used microwave assisted methods, a simple convenient new procedure is presented here for the particle synthesis. A detailed X-ray photoelectron spectroscopic (XPS) analysis was employed to characterize the composition, and more importantly, the chemical structure of the CQD samples and the interrelation of the characteristic surface chemical groups with the fluorescence properties and with surface polarity was unambiguously established. In vitro cellular internalization experiments documented their applicability as fluorescence labels while non-toxic properties were also approved. It was demonstrated that the adequate water-dispersibility of the particles plays a crucial role in their biological application. The synthetized CQD samples turned to be promising for cellular imaging applications both in laser illuminated flow cytometric measurements and in fluorescence microscopy.

Graphene oxide (GO) containing resorcinol – formaldehyde and resorcinol – formaldehyde – melamine polymer aerogels were converted to carbon aerogels in order to study the cooperative effect of the reduced GO and nitrogen functionalities on the electrochemical behavior of carbon aerogels. The morphology of the carbon gel was characterized by scanning and transmission electron microscopy, and low temperature nitrogen adsorption/desorption. X-ray photoelectron spectroscopy was used to study their surface chemistry. The thermal behavior was investigated by thermogravimetric analysis. The electrochemical performance was tested with cyclic- and linear sweep voltammetry (CV and LSV, respectively). The final N content was ca 1 atomic%. The nitrogen atoms are in a C=N-C type chemical environment or replace a carbon atom in the graphene-like layer. Either N or the reduced GO enhance the activity in oxygen reduction reaction. When both are present in the matrix the dominant reduction pathway changes from the slow 2e− to the more efficient 4e− route. It is also probable that the in-situ formed H2O2 improves the wettability of the basically hydrophobic carbon surface and increases the electrochemically active surface.

In this work, we performed plasma treatment of thin layers of graphene oxide samples in various nitrogen containing gases (mainly NH3 and N2). Experiments were performed in the preparation chamber of the X‐ray photoelectron spectrometer, allowing “in situ” characterization of the treated surface. Introduction of nitrogen into the top surface was intensified by applying negative voltage on the sample between 0 and 300 V accelerating the positive plasma ions towards the sample.Significant amount of nitrogen (≈10 atomic %) was built into the top atomic layers of the graphene oxide samples at application of the 2 types of plasma gases for 10‐minute reaction time. When comparing the NH3 and N2 plasma treatments, more complete reduction and closely similar amount of nitrogen was found at applying NH3 plasma.When increasing the bias, the N‐content increased, together with decrease of the O content. The high‐resolution C1s, O1s, and N1s spectra are broad, representing different chemical states. The peak envelopes of the O1s and N1s lines could be decomposed essentially to 3, while the C1s spectrum to 5 different, well‐separated peaks, being identical for all samples.The component peaks were assigned to specific chemical bonding states (N1s: 398.3 eV sp2 pyridine N, 399.7 eV sp2 pyrrole, diazine or triazine N, 401.0 eV N in graphite plane; O1s: 530.8 eV carbonyl, 532.2 eV ether, epoxy, alcohol, ester C═O, 533.6 eV ester C―O―C, carboxyl OH). The relative amounts of C―O and C―N bonding states changed significantly with advancement of the treatment performed at increasing biases.

Titanate nanotubes offer certain benefits like high specific surface area, anisotropic mesoporous structure and ease of synthesis over other nanostructured titania forms. However, their application in visible light driven photocatalysis is hindered by their wide band-gap, which can be remedied by, e.g., anionic doping. Here we report on a systematic study to insert nitrogen into lattice positions in titanate nanotubes. The efficiency of N2+ bombardment, N2 plasma and NH3 plasma treatment is compared to that of NH3 gas synthesized in situ by the thermal decomposition of urea or NH4F. N2+ bombarded single crystalline rutile TiO2 was used as a doping benchmark (16 at.% N incorporated). Surface species were identified by diffuse reflectance infrared spectroscopy, structural features were characterized by scanning electron microscopy and powder X-ray diffraction measurements. The local chemical environment of nitrogen built into the nanotube samples was probed by X-ray photoelectron spectroscopy. Positively charged NH3 plasma treatment offered the best doping performance. This process succeeded in inserting 20 at.% N into nanotube lattice positions by replacing oxygen and forming Ti–N bonds. Remarkably, the nanotubular morphology and titanate crystal structure were both fully conserved during the process. Since plasma treatment is a readily scalable technology, the suggested method could be utilized in developing efficient visible light driven photocatalysts based on N-doped titanate nanotubes.

The application of Pd-polydopamine and magnetic Fe3O4@ Pd-polydopamine catalysts in catalytic transfer hydrogenation reactions and the Heck arylation is reported. The reduction of a wide range of aromatic nitro-compounds bearing both electron- donating and -withdrawing substituents to the corresponding anilines could be efficiently performed, although the reduction of carbonyl compounds was found to be less general. In the latter case, only aromatic ketones could be reduced to the corresponding alcohols, whereas aldehyde substrates were unaffected, which may be owing to their reaction with the catalyst support leading to catalyst deactivation. By using magnetic Fe3O4@ Pd-polydopamine system, facilitated catalyst recovery and reuse for five consecutive cycles without considerable loss of activity in nitro-group reduction. The efficiency of the catalyst in Heck reactions was comparable to that in transfer hydrogenation, however, no catalytic activity was observed upon reuse in this case, likely as a result of metal leaching. We also explored tandem Heck reaction/catalytic transfer hydrogenation sequences, however, the two reactions showed limited compatibility under the applied conditions.

Graphene oxide foams with a wide range of poly (vinyl alcohol) contents were synthesized by freeze casting, and then thermally reduced at 300ºC in argon atmosphere. Their thermal stability, microstructure, composition and chemical states of constituents, mechanical and electrical properties were investigated by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, thermogravimetry, compressive testing and electrochemical analysis. The results indicated that the PVA content highly influenced the crystallinity and microstructure, resulting in different mechanical properties. After thermal reduction, not only graphene oxide was reduced to graphene, but also PVA was subjected to partial pyrolysis. With the increase of the PVA content, the intensity of the sp2 C-C bond decreased while the sp3 C-C bond increased. Although the mechanical properties decreased after thermal reduction, the composite foams still showed high cyclic structure stability up to 18 % compression strain. Meanwhile, the reduced foams exhibited high electrical conductivity. Applying as anodes in lithium ion battery, the initial discharge capacity for the foams can reach 1822 mA h g-1 and it remained more than 330 mA h g-1 after 50 cycles.

Please note that technical editing may introduce minor changes to the text and/or graphics, which may alter content. The journal’s standard Terms & Conditions and the Ethical guidelines still apply. In no event shall the Royal Society of Chemistry be held responsible for any errors or omissions in this Accepted Manuscript or any consequences arising from the use of any information it contains. Accepted Manuscript Journal of Materials Chemistry B

Silica@zirconia@poly(malic acid) nanocarriers of 110 nm mean diameter were designed, synthesized and characterized for the targeted delivery of diagnostic and therapeutic 99mTc to folate-overexpressing tumors. An important achievement was that a multifunctional l-(-)-malic-acid-based copolymer was formed in situ at the surface of the inorganic cores in a single synthetic step incorporating l-(-)-malic acid, β-cyclodextrin rings, folic acid moieties, and polyethylene glycol chains. Morphological and in-depth structural analysis of the particles proved their core@shell structure. Stability experiments in aqueous media evidenced that stable suspensions can be obtained from the lyophilized powder in 10 mM phosphate buffer at pH 7.4. During 14-day degradation experiments, the nanoparticles were found to be slowly dissolving (including inorganic core) in saline and also in total cell medium. An in vitro toxicity assay on hepatocytes showed a concentration-dependent decrease of cell viability down to 63 ± 1% at the highest applied concentration (0.5 mg ml-1). Proof of concept experiments of technetium-99m radiolabelling and in vivo labelling stability are presented.

We performed glow discharge N2 or Ar plasma treatments of thin layers of graphene oxide (GO) deposited from slurry in alcohol onto stainless steel substrates. The treatment was performed in the preparation chamber of the x‐ray photoelectron spectrometer, allowing reliable in situ characterization of the treated surface by quantitative x‐ray photoelectron spectroscopy. For the treatment, 10 min plasma exposure was selected, based on preliminary experiments. Intensity of the treatment was enhanced by applying a negative bias between 0–300 V on the sample. Approximately 10 at% nitrogen was incorporated into the graphene oxide samples from N2 plasma within this short reaction time. When increasing the bias, the N‐content increased from 10 to 13 at%, together with the decrease of the O content from the starting value of 29 to ~15 at%. The reducing effect of Ar plasma was less pronounced, decreasing the oxygen content to ~21 at% only. The high resolution C1s, O1s, and N1s spectra show several different chemical states. The peak envelopes of the O1s and N1s lines could be decomposed to three while the C1s spectrum to five different peaks of identical position for all samples. The component peaks were tentatively assigned to specific chemical bonding states. The relative amounts of C–O and C–N bonding states changed slightly with advancement of the treatment performed at increasing biases. It was established that the carboxyl‐type and the carbonyl‐type C–O clusters were more affected by both plasma treatments as their amount was selectively eliminated. Copyright © 2016 John Wiley & Sons, Ltd.

In this work, in addition to the conventional thermal process, two non-conventional ways, the plasma and ion beam activations are described for preparing gold nanoparticles from microcrystalline AuCN precursor. The phase formation at plasma and ion beam treatments was compared with that at thermal treatments and the products and transformations were characterized by thermogravimetry-mass-spectrometry (TG-MS), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). TG-MS measurements in Ar atmosphere revealed that AuCN decomposition starts at 400°C and completes at ≈700°C with evolution of gaseous (CN)2. XPS and TEM show that in heat treatment at 450°C for 1h in Ar, loss of nitrogen and carbon occurs and small, 5–30nm gold particles forms. Heating at 450°C for 10h in sealed ampoule, much larger, 60–200nm size and well faceted Au particles develop together with a fibrous (CN)n polymer phase, and the Au crystallites are covered by a 3–5nm thick polymer shell. Low pressure Ar plasma treatment at 300eV energy results in 4–20nm size Au particles and removes most of the nitrogen and part of carbon. During Ar+ ion bombardment with 2500eV energy, 5–30nm size Au crystallites form already in 10min, with preferential loss of nitrogen and with increased amount of carbon residue. The results suggest that plasma and ion beam activation, acting similarly to thermal treatment, may be used to prepare Au nanoparticles from AuCN on selected surface areas either by depositing AuCN precursors on selected regions or by focusing the applied ionized radiation. Thus they may offer alternative ways for preparing tailor-made catalysts, electronic devices and sensors for different applications.

The protein mediated approach is a common method for the synthesis of photoluminescent gold quantum clusters (GQCs), where proteins, acting as reducing and stabilizing agents, react with gold salts through cysteine residues. For the better understanding of the phenomenon, the aqueous phase reaction of HAuCl4 and L-cysteine has been investigated at the supramolecular level by various experimental techniques and molecular mechanics simulations. We have observed the formation of a novel photoluminescent product, (AuCys)(n)(beta), which shows emission in the orange region of the spectrum. Small- and wide-angle X-ray scattering (SWAXS) measurements have revealed the presence of nanosized lamellae, which have an internal multilayer superlattice structure with a characteristic periodic distance of 1.3 nm. Based on the results, the layers are built up by zigzag shaped (AuCys)(n), polymer chains connected through aurophilic bonds. The aurophilic network is stabilized via salt bridges and hydrogen bonds, which are also responsible for the interlayer interactions. Here, the evolution of the multilayer structure has been monitored by the combined application of photoluminescence spectroscopy and time-resolved SAXS. It has been concluded that there is a strong correlation between the emission and the scattering intensity, which suggests that the two- and three-dimensional aggregation of the building blocks to form sheets and multilayers are simultaneous processes. Furthermore, we have revealed that the formation and behavior of (AuCys)(n)(beta) show significant differences to that of Au-L-glutathione compounds described earlier despite the similarity of L-cysteine and L-glutathione. These results evidence that L-cysteine and gold species form building blocks that can be applied expansively in supramolecular and cluster chemistry. (C) 2015 Elsevier B.V. All rights reserved.

Well-ordered nano-carbon materials, like multiwall carbon nanotubes, graphene oxide, graphene due to their unique physical and chemical properties, are candidates for promising applications.In this work thin multilayered graphene, single layer graphene oxide layers and highly oriented pyrolytic graphite (HOPG) surface were treated by RF activated N-2 gas plasma at nominally room temperature. Negative bias in the 0-200 V range and treatment time of 10 min was applied. Surface chemical alterations were followed by X-ray photoelectron spectroscopy (XPS). The applied treatments resulted in a significant build-up of nitrogen in the surface of these nano-carbon materials. The amount of nitrogen varied between 4 and 10 atomic %, depending on type of carbon and on biasing conditions. Evaluating the high-resolution N1s XP spectral region, typically three different chemical bonding states of the nitrogen were delineated. Peak component at 398.3 eV is assigned to C=N-C type, at 399.7 eV to sp(2) N in melamine-type ring structure and at 400.9 eV to N substituting carbon in a graphite-like environment. Identical chemical bonding of the nitrogen was detected on the surface of HOPG treated in the same way for comparison.

In this chapter, corrosion protection performance of hybrid zinc-rich paints (ZRPs) formulated with zinc at 70 and 80 wt.%, and nano-size particulates at 3.21 and 1.75 wt.% contents is analyzed. The nano-size filler phase was composed of polypyrrole supported with either alumina or alumina/multiwalled carbon nanotubes. Durability of the coatings was tested with immersion and salt-spray chamber propagations. Protection mechanism of the hybrid ZRPs is discussed regarding structural and electrical properties of the particles and paint dispersions. Hybrid ZRPs indicate firm barrier nature, moderate inhibition, and restrained active galvanic function to steel substrates. Hindered mass transport and limited water uptake through the low porosity hybrid coatings combined with three-dimensional arrangement of nano-size particles at the statistical and kinetic percolation thresholds are key factors to provide well-balanced and highly efficient combined, complex protection to low carbon steel substrates. Nevertheless, incorporation of inhibitor particles results in completely different fundamental properties from those typical of traditional ZRPs.