Photocatalytic applications with CdS•block copolymer/exfoliated graphene nanoensembles: Hydrogen generation and degradation of Rhodamine B

Amphiphilic block copolymer poly (isoprene-b-acrylic acid) (PI-b-PAA) stabilized exfoliated graphene in water and allowed the immobilization of semiconductor CdS nanoparticles forming CdS•PI-b-PAA/graphene. Characterization with HR-TEM and EDX justified the success of preparation and revealed the presence of spherical CdS. Moreover, UV-Vis and photoluminescence assays suggested that electronic interactions within CdS•PI-b-PAA/graphene exist as evidenced by the significant quenching of the characteristic emission of CdS by exfoliated graphene. Photoillumination of CdS•PI-b-PAA/graphene, in the presence of ammonium formate as quencher for the photogenerated holes, resulted on the generation of hydrogen by water splitting, monitored by the reduction of 4-nitroaniline to benzene-1,4-diamine (> 80±4% at 20 min; 100% at 24 min), much faster and efficient as compared when reference CdS•PI-b-PAA was used as photocatalyst (< 30±3% at 20 min; 100% at 240 min). Moreover, Rhodamine B was photocatalytically degraded by CdS•PI-b-PAA/graphene, with fast kinetics under visible light illumination in the presence of air. The enhancement of both photocatalytic processes by CdS•PI-b-PAA/graphene was rationalized in terms of effective separation of holes–electrons, contrary to reference CdS•PI-b-PAA, in which rapid recombination of the hole–electron pair is inevitable due to the absence of exfoliated graphene as suitable electron acceptor

Tuning the Catalytic Activity of Graphene Nanosheets for Oxygen Reduction Reaction via Size and Thickness Reduction

Currently, the fundamental factors that control the oxygen reduction reaction (ORR) activity of graphene itself, in particular the dependence of the ORR activity on the number of exposed edge sites remain elusive, mainly due to limited synthesis routes of achieving small size graphene. In this work, the synthesis of low oxygen content (< 2.5 +/-0.2 at %), few layer graphene nanosheets with lateral dimensions smaller than a few hundred nm was achieved using a combination of ionic liquid assisted grinding of high purity graphite coupled with sequential centrifugation. We show for the first time, that the graphene nanosheets possessing a plethora of edges exhibited considerably higher electron transfer numbers compared to the thicker graphene nanoplatelets. This enhanced ORR activity was accomplished by successfully exploiting the plethora of edges of the nanosized graphene as well as the efficient electron communication between the active edge sites and the electrode substrate. The graphene nanosheets were characterized by an onset potential of -0.13 V vs. Ag/AgCl and a current density of -3.85 mA/cm2 at -1 V, which represent the best ORR performance ever achieved from an undoped carbon based catalyst. This work demonstrates how low oxygen content nanosized graphene synthesized by a simple route can considerably impact the ORR catalytic activity and hence it is of significance in designing and optimizing advanced metal-free ORR electrocatalysts.Comment: corresponding author: [email protected], ACS Applied Materials and Interfaces 201

A real-time flood forecasting technique

A simple hydrologic technique is presented which is applied to short-term forecasting of floodflows at the outlet of a river basin by using rainfall information and water levels of the flood events at an upstream index station of the basin. The time of occurrence of the forecasted floodflow is also estimated. The applicability to real-time forecasting, the lack of any requirements for automatic network or for in-field computer facilities, the simplicity and the accuracy of the forecasting technique are its basic advantages—especially in a country such as Greece with a conventional hydrometeorological network and limited financial resources—in solving specific engineering problems. The flood forecasting technique is successfully being applied to the middle course of the Kalamas river in Northwestern Greece at a dam site during construction of the river&apos;s diversion for protecting lives of workers and equipment. It should be noted that, where resources permit, the average basin rainfall between the upstream index station and the outlet of the basin could be better represented using more than one rainfall station. For some regions it is possible that the nomograms used for forecasting may need to be developed on a seasonal basis. © Elsevier Sequoia/Printed in The Netherlands

Combining Dithienosilole-Based Organic Dyes with a Brookite/Platinum Photocatalyst toward Enhanced Visible-Light-Driven Hydrogen Production

Dye-sensitized photocatalytic hydrogen generation is emerging as a promising process to produce fuels using a clean and abundant energy source such as sunlight. In the first part of this work, three organic dyes featuring a dithieno[3,2-b:2\u2032,3\u2032-d]silole heterocyclic unit (OB1\u2013OB3), bearing different substituents on various parts of the molecular scaffold, were synthesized, characterized, and used as sensitizers for the commercially available benchmark TiO2 (P25), first in dye-sensitized solar cells and then for the photocatalyzed production of hydrogen with triethanolamine as a sacrificial electron donor. In the second part of the study, aiming to improve the efficiency of the photocatalytic system, P25 was replaced with the less investigated brookite TiO2 polymorph. The photocatalyst obtained upon sensitization with the best performing dye, OB2, still in the presence of Pt as co-catalyst, displayed an enhanced performance in hydrogen production compared to that based on P25 at a lower dye loading. Extended time experiments confirmed that the catalyst was still significantly active after 1 week under continuous illumination, providing a maximum TON of 4201. The higher efficiency of the brookite-based catalytic system and its prolonged stability are especially significant in the perspective of the practical application of the dye-sensitized photocatalytic H2 production technology

Nitrogen implantation of suspended graphene flakes: Annealing effects and selectivity of sp² nitrogen species

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