A simple and mild chemical oxidation route to high-purity nano-graphene oxide

Nano-graphene oxide (nGO) is used in a wide range of applications including cellular imaging, drug delivery, desalination and energy storage. Current preparation protocols are similar as for standard graphene oxide (GO) and typically rely on mixtures of sulfuric acid and potassium permanganate. We present a new route to nGO (∼30 nm diameter) using a quite defective arc-discharge carbon source and only 9 M nitric acid as the oxidising agent. The preparation can be scaled up proportionately with current GO protocols with 50 mL of half-concentrated nitric acid able to process one gram of arc-discharge material. The workup is straight forward and involves neutralization with sodium hydroxide which precipitates the sodium salt of nGO from solution. The only by-product of the new procedure is aqueous sodium nitrate which makes this protocol the cleanest route yet to nGO. The presence and quantities of functional groups in our nGO are determined and compared with standard GO. We anticipate that this new route to nGO will foster a range of new applications. The presence of highly reactive carboxylic anhydride groups on our nGO material in particular offers an excellent opportunity for purpose-specific chemical functionalization

Highly efficient heavy-metal extraction from water with carboxylated graphene nanoflakes

Heavy metals such a lead or cadmium have a wide range of detrimental and devastating effects on human health. It is therefore of paramount importance to efficiently remove heavy metals from industrial wastewater streams as well as drinking water. Carbon materials, including graphene and graphene oxide (GO), have recently been advocated as efficient sorption materials for heavy metals. We show that highly carboxylated graphene nanoflakes (cx-GNF) outperform nano-graphene oxide (nGO) as well as traditional GO with respect to extracting Fe 2+ , Cu 2+ , Fe 3+ , Cd 2+ and Pb 2+ cations from water. The sorption capacity for Pb 2+ , for example, is more than six times greater for the cx-GNF compared to GO which is attributed to the efficient formation of lead carboxylates as well as strong cation-π interactions. The large numbers of carboxylic acid groups as well as the intact graphenic regions of the cx-GNF are therefore responsible for the strong binding of the heavy metal cations. Remarkably, the performance of the as-made cx-GNF can easily compete with previously reported carbon materials that have undergone additional chemical-functionalisation procedures for the purpose of heavy-metal extraction. Furthermore, the recyclability of the cx-GNF material with respect to Pb 2+ loading is demonstrated as well as the outstanding performance for Pb 2+ extraction in the presence of excess Ca 2+ or Mg 2+ cations which are often present under environmental conditions. Out of all the graphene materials, the cx-GNF therefore show the greatest potential for future application in heavy-metal extraction processes

Preparation, chemistry and applications of novel carbon nanomaterials

The isolation of graphene in 2004, and subsequent Nobel Prize for Physics being awarded to Andre Geim and Konstantin Novoselov in 2010, has sparked a renewed interest in graphene around the world due to graphene’s remarkable physical properties such as mechanical stability, optical transparency, impermeability and electrical and thermal conductivity. Graphene Oxide (GO), the oxidised analogue of graphene, has also received much attention owing to its hydrophilic nature. This has made GO a very promising material for aqueous processing, giving it a significant advantage over graphene. In this way, GO has been used in many composite materials, involving biological molecules, metal-organic-frameworks (MOFs) and other hybrid systems. Unfortunately, much uncertainty surrounds the chemical nature of GO, and therefore its chemistry, thus creating a lot of controversy in the literature. Similarly, the preparation of GO also results in lengthy procedures and toxic by-products. To address these issues, this thesis describes the preparation of alternative carbon nanomaterials, as a potential substitute to GO, which have well-defined structures and chemistry and/or reduce the toxic waste produced. The chemistry and applications of these new materials are explored and benchmarked against conventional GO, which is prepared via permanganate oxidation (PM-GO). The preparation of three novel carbon materials, carboxylated graphene nanoflakes (cx-GNFs), nano-graphene oxide (nGO) and GO prepared via dichromate oxidation (DC-GO) are initially reported, along with extensive characterisations. The cx-GNFs are a highly soluble (~100 mg mL-1) and well-defined material consisting of carboxyl groups and unoxidised sp2 carbon only. nGO is prepared via an eco-friendly procedure producing nano-sized GO and DC-GO was prepared in order to elucidate its chemical structure which remains uncertain in the literature. The thermal annealing behaviour of the materials are reported next and the cx-GNFs and the nGO are shown to form carboxylic anhydrides in yields up to 81%, which is the first experimental evidence for this functional group at the graphene edge. The existence of carboxylic anhydrides in dynamic equilibrium with carboxylic acids in water was demonstrated at room temperature for the cx-GNFs, and was consequently exploited for room temperature chemical functionalisations with well-known amines such as ethylenediamine and cysteamine. These functionalised materials were then explored in the context of tagging gold nanoparticles and changing the zeta potential of the native cx-GNFs. The application of these novel materials in heavy-metal extraction is also presented and found to greatly exceed the capacity of PM-GO - by up to six times. Collaborations with other research groups in the field of nano-sensors, ice-nucleation and electrochemistry, revealed the cx-GNFs to be a particularly promising material

The influence of acidic edge groups on the electrochemical performance of graphene nanoflakes

Graphene nanoflakes (GNF) with lateral dimensions of ca. 30 nm and edge-terminated with carboxylic acid functionalities have been characterised and the influence of acidic functionalities on the [Fe(CN)6]3−/4− redox couple studied using cyclic voltammetry and spectroelectrochemical methods. The presence of the COOH-terminated GNF in solution as well as immobilised onto an electrode surface was found to inhibit the redox reaction, supporting the conclusion that GNF promote instability of [Fe(CN)6]3−/4− in solution. The redox reaction was also much less influenced by the presence of GNF in D2O, highlighting the role played by readily available protons in destabilising the [Fe(CN)6]3−/4− redox couple. In the presence of GNF in solution, an additional, very intense cyanide stretch IR band was observed that was attributed to the formation of a new, non-soluble species. When D2O was used as the solvent, the IR spectrum showed no evidence of a new cyano species

Electrochemical characterisation of graphene nanoflakes with functionalised edges

Graphene nanoflakes (GNF) of diameter ca. 30 nm and edge-terminated with carboxylic acid (COOH) or amide functionalities were characterised electrochemically after drop-coating onto a boron-doped diamond (BDD) electrode. In the presence of the outer-sphere redox probe ferrocenemethanol there was no discernible difference in electrochemical response between the clean BDD and GNF-modified electrodes. When ferricyanide or hydroquinone were used as redox probes there was a marked difference in response at the electrode modified with COOH-terminated GNF in comparison to the unmodified BDD and amide-terminated GNF electrode. The response of the COOH-terminated GNF electrode was highly pH dependent, with the most dramatic differences in response noted at pH < 8. This pH range coincides with partial protonation of the carboxylic acid groups as determined by titration. The acid edge groups occupy a range of bonding environments and are observed to undergo deprotonation over a pH range ca. 3.7 to 8.3. The protonation state of the GNF influences the oxidation mechanism of hydroquinone and in particular the number of solution protons involved in the reaction mechanism. The voltammetric response of ferricyanide is very inhibited by the presence of COOH-terminated GNF at pH < 8, especially in low ionic strength solution. While the protonation state of the GNF is clearly a major factor in the observed response, the exact role of the acid group in the redox process has not been firmly established. It may be that the ferricyanide species is unstable in the solution environment surrounding the GNF, where dynamic protonation equilibria are at play, perhaps through disruption to ion pairing

Multi-functionalised graphene nanoflakes as tumour-targeting theranostic drug-delivery vehicles

Graphene nanoflakes (GNFs) consist of a graphene sheet approximately 30 nm in diameter with a pristine aromatic system and an edge terminated with carboxylic acid groups. Their high water solubility and relative ease of functionalisation using carboxylate chemistry means that GNFs are potential scaffolds for the synthesis of theranostic agents. In this work, GNFs were multi-functionalised with derivatives of (i) a peptide-based Glu-NH-C(O)-NH-Lys ligand that binds prostate-specific membrane antigen (PSMA), (ii) a potent anti-mitotic drug (R)-ispinesib, (iii) the chelate desferrioxamine B (DFO), and (iv) an albumin-binding tag reported to extend pharmacokinetic half-life in vivo. Subsequent 68Ga radiochemistry and experiments in vitro and in vivo were used to evaluate the performance of GNFs in theranostic drug design. Efficient 68Ga-radiolabelling was achieved and the particle-loading of (R)-ispinesib and Glu-NH-C(O)-NH-Lys was confirmed using cellular assays. Using dose–response curves and FACS analysis it was shown that GNFs loaded with (R)-ispinesib inhibited the kinesin spindle protein (KSP) and induced G2/M-phase cell cycle arrest. Cellular uptake and blocking experiments demonstrated that GNFs functionalised with the Glu-NH-C(O)-NH-Lys ligand showed specificity toward PSMA expressing cells (LNCaP). The distribution profile and excretion rates of 68Ga-radiolabelled GNFs in athymic nude mice was evaluated using time–activity curves derived from dynamic positron-emission tomography (PET). Image analysis indicated that GNFs have low accumulation and retention in background tissue, with rapid renal clearance. In summary, our study shows that GNFs are suitable candidates for use in theranostic drug design

El consentimiento del uso de la voz como medio probatorio, en un proceso judicial

Nuestra investigación lleva como título “El Consentimiento del Uso de la Voz como Medio Probatorio, en el Proceso Judicial”, tuvo como propósito de investigación establecer la manera en que se viene protegiendo el uso de la voz, a través de los medios probatorios en el proceso judicial. La metodología utilizada fue de tipo básica, el mismo que buscó interpretar y plantear probables soluciones. También, el tipo de investigación, coadyuvó a venideras investigaciones, siendo que, el mismo se amplió mediante el análisis de teorías, y que su intención no es fue de una inmediata aplicación. El enfoque de tesis correspondió al Cualitativo, el cual utilizó la recolección de datos sin medición numérica para descubrir o afinar preguntas de investigación en el proceso de interpretación. Los resultados obtenidos mostraron que está acreditado que, existe deficiencias en la protección de la voz través de los medios probatorios en un proceso judicial determinado; que el uso de la grabación de la voz de una persona, si vulnera su dignidad, por cuanto de su uso se puede dañar su imagen, trayectoria y trascendencia; existen casos de presentación de una grabación de voz ante procesos judiciales determinados

Ausentismo, presentismo y rendimiento académico en estudiantes de universidades peruanas

The objective of this research was to determine the effect of absenteeism and presenteeism on the academic performance of undergraduate students from the Business and Engineering Schools in Peruvian Universities. The study is based on a self-report survey of 8,203 students from the business and engineering schools of Peruvian universities. Scales were used to analyze absenteeism, presenteeism and academic performance that showed suitable psychometric properties. The results showed that presenteeism has a higher impact on the academic performance of students (β = 0.628) compared toabsenteeism (β = 0.101). Absenteeism has a greater effect on courses and disapproved terms (Beta = 0.163) and presenteeism, on the evolution of academic performance (β = -0.145). Finally, by means of a model of structural equations, the causal structure of the academic performance decrease from absenteeism and presenteeism is proven.El objetivo de la presente investigación fue determinar el efecto del ausentismo y presentismo sobre el rendimiento académico en los estudiantes de pregrado de las Escuelas de Negocios e Ingenierías en las Universidades Peruanas. El estudio se sustenta en una encuesta de autoreporte a 8,203 estudiantes de las escuelas de negocios e ingenierías de las universidades peruanas. Se emplearon escalas para analizar el ausentismo, presentismo y rendimiento académico que mostraron adecuadas propiedades psicométricas. Los resultados evidenciaron que el presentismo tiene un mayor impacto sobre el rendimiento académico disminuido de los estudiantes (β = 0.628) en comparación al ausentismo (β = 0.101). El ausentismo tiene un mayor efecto sobre los cursos y ciclos desaprobados (β = 0.163) y el presentismo sobre la evolución del rendimiento académico (β = -0.145).  Finalmente, mediante un modelo de ecuaciones estructurales se demuestra la estructura causal de la disminución del rendimiento académico a partir del ausentismo y presentismo.El objetivo de la presente investigación fue determinar el efecto del ausentismo y presentismo sobre el rendimiento académico en los estudiantes de pregrado de las Escuelas de Negocios e Ingenierías en las Universidades Peruanas. El estudio se sustenta en una encuesta de autoreporte a 8,203 estudiantes de las escuelas de negocios e ingenierías de las universidades peruanas. Se emplearon escalas para analizar el ausentismo, presentismo y rendimiento académico que mostraron adecuadas propiedades psicométricas. Los resultados evidenciaron que el presentismo tiene un mayor impacto sobre el rendimiento académico disminuido de los estudiantes (β = 0.628) en comparación al ausentismo (β = 0.101). El ausentismo tiene un mayor efecto sobre los cursos y ciclos desaprobados (β = 0.163) y el presentismo sobre la evolución del rendimiento académico (β = -0.145).  Finalmente, mediante un modelo de ecuaciones estructurales se demuestra la estructura causal de la disminución del rendimiento académico a partir del ausentismo y presentismo

Ausentismo, presentismo y rendimiento académico en estudiantes de universidades peruanas

The objective of this research was to determine the effect of absenteeism and presenteeism on the academic performance of undergraduate students from the Business and Engineering Schools in Peruvian Universities. The study is based on a self-report survey of 8,203 students from the business and engineering schools of Peruvian universities. Scales were used to analyze absenteeism, presenteeism and academic performance that showed suitable psychometric properties. The results showed that presenteeism has a higher impact on the academic performance of students (β = 0.628) compared toabsenteeism (β = 0.101). Absenteeism has a greater effect on courses and disapproved terms (Beta = 0.163) and presenteeism, on the evolution of academic performance (β = -0.145). Finally, by means of a model of structural equations, the causal structure of the academic performance decrease from absenteeism and presenteeism is proven.El objetivo de la presente investigación fue determinar el efecto del ausentismo y presentismo sobre el rendimiento académico en los estudiantes de pregrado de las Escuelas de Negocios e Ingenierías en las Universidades Peruanas. El estudio se sustenta en una encuesta de autoreporte a 8,203 estudiantes de las escuelas de negocios e ingenierías de las universidades peruanas. Se emplearon escalas para analizar el ausentismo, presentismo y rendimiento académico que mostraron adecuadas propiedades psicométricas. Los resultados evidenciaron que el presentismo tiene un mayor impacto sobre el rendimiento académico disminuido de los estudiantes (β = 0.628) en comparación al ausentismo (β = 0.101). El ausentismo tiene un mayor efecto sobre los cursos y ciclos desaprobados (β = 0.163) y el presentismo sobre la evolución del rendimiento académico (β = -0.145).  Finalmente, mediante un modelo de ecuaciones estructurales se demuestra la estructura causal de la disminución del rendimiento académico a partir del ausentismo y presentismo.El objetivo de la presente investigación fue determinar el efecto del ausentismo y presentismo sobre el rendimiento académico en los estudiantes de pregrado de las Escuelas de Negocios e Ingenierías en las Universidades Peruanas. El estudio se sustenta en una encuesta de autoreporte a 8,203 estudiantes de las escuelas de negocios e ingenierías de las universidades peruanas. Se emplearon escalas para analizar el ausentismo, presentismo y rendimiento académico que mostraron adecuadas propiedades psicométricas. Los resultados evidenciaron que el presentismo tiene un mayor impacto sobre el rendimiento académico disminuido de los estudiantes (β = 0.628) en comparación al ausentismo (β = 0.101). El ausentismo tiene un mayor efecto sobre los cursos y ciclos desaprobados (β = 0.163) y el presentismo sobre la evolución del rendimiento académico (β = -0.145).  Finalmente, mediante un modelo de ecuaciones estructurales se demuestra la estructura causal de la disminución del rendimiento académico a partir del ausentismo y presentismo

Surface redox chemistry and mechanochemistry of insulating polystyrene nanospheres

Cyclic voltammetry (CV) of polystyrene nanospheres was carried out after immobilisation onto boron-doped diamond electrodes. Although the polystyrene is insulating, a voltammetric response was obtained. This was attributed to the high surface area of the nanospheres, allowing the redox chemistry of the polystyrene surface to be probed despite the non-conducting nature of the bulk. The polystyrene redox response was found to be strongly dependent on prior mechanical agitation. Centrifuged, sonicated and vortexed polystyrene nanospheres all exhibited significantly higher oxidation currents than the non-agitated polystyrene. Mechanical treatment by sonication and centrifugation was found to bring about changes to surface chemistry of the polystyrene spheres, in particular the introduction of oxygen functionalities. For these samples the CV response is attributed to the presence of surface phenol functionalities. On the non-agitated and vortex treated polystyrene surfaces X-ray photoelectron spectroscopy revealed an absence of oxygen functionalities that could explain the redox response. Repetition of the CV experiment in the presence of a solution spin trap suggests that radical species play a role in the observed response. For the vortexed sample the increased oxidation currents were attributed to significant surface roughening and deformation, as revealed by Transmission Electron Microscopy