Multichromophores Onto Graphene: Supramolecular Non-Covalent Approaches for Efficient Light Harvesting.

The idea of attaching multiple porphyrins to graphene is explored. A charged porphyrin salt is stabilized onto exfoliated graphene by taking advantage of π-π* interactions and a second porphyrin light harvester is anchored through electrostatic interactions with the former. The interactions are capable of allowing electronic communication of the second, electrostatically attached, porphyrin with graphene, effectively quenching its emission. The graphene-porphyrin-porphyrin triad is examined through optical (UV-Vis, steady state and time resolved photoluminescence) techniques, while electrochemistry is employed to study the thermodynamically favored pathways through which the interaction occurs. The porphyrin that is electrostatically stabilized onto the graphene nanoensemble shows lifetimes one order of magnitude faster than its π-π* stacked analogue suggesting a more efficient pathwa

Chemical Functionalization of Exfoliated Graphene

Graphene is turning out to be the material that will effectively kick-start a new era for nanotechnology. The impressive properties of this atom-thick carbon layer are taking shape and form with early reports of successful applications based on it. The turning point for this material will be its low cost mass production. In this report a chemist’s perspective on the production methods for graphene and the subsequent functionalization processes is discussed

Donor-acceptor graphene-based hybrid materials for managing photoinduced electrontransfer reactions

Graphene research and in particular the topic of chemical functionalization has been exploded in the last decade. The main aim is to induce solubility and thereby enhance processability of the material, which is otherwise insoluble and inapplicable for technological applications when stacked in the form of graphite. In this frame, initially, graphite was oxidized under harsh conditions to yield exfoliated graphene oxide sheets, soluble in aqueous media and amenable to chemical modifications due to the presence of carboxylic acid groups at the edges of the lattice. Some donor-acceptor hybrid materials with photo- and/or electro-active components were prepared and characterized, while their charge-transfer properties were evaluated. However, it was obvious that the highly defected framework of graphene oxide cannot be really utilized in applications that are governed by charge-transfer processes, for example in solar cells. The alternative route for solubilizing and modifying graphene by exfoliating graphite is the current method of choice for the realization of novel hybrid materials and further boost their direct applicability in artificial photosynthesis and the construction of photovoltaic devices. In this review article, the routes for obtaining donor-acceptor graphene-based hybrid materials for managing charge-transfer phenomena, mainly, but not exclusively, with porphyrins and phthalocyanines are presented. Earlier examples and studies performed on graphene oxide modified with organic electron donors are also given

Sulfur-doped carbon nanohorn bifunctional electrocatalyst for water splitting

Sulfur-doped carbon nanohorns (S-CNHs) were prepared by an easy one-pot solvothermal process and were employed as efficient electrocatalysts towards water splitting. Initially, oxidation of CNHs followed by thermal treatment with the Lawesson’s reagent resulted in the formation of S-CNHs with the sulfur content determined as high as 3%. The S-CNHs were thoroughly characterized by spectroscopic, thermal and electron microscopy imaging means and then electrocatalytically screened. Specifically, S-CNHs showed excellent activity and durability for both O2 and H2 evolution reactions, by showing low overpotential at 1.63 and -0.2 V vs. RHE for oxygen and hydrogen evolution reaction, respectively. Additionally, S-CNHs showed significantly lower Tafel slope value and lower current resistance compared to oxidized and pristine CNHs for both electrocatalytic reactions. The outstanding electrocatalytic properties and high conductivity, along with the high S-doping level, render S-CNHs a promising bifunctional electrocatalyst for water splitting

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

Chemical Functionalization of 2D Materials

This Special Issue of Chemistry-A European Journal is dedicated to the Chemical Functionalization of 2D Materials, and features some great contributions from experts in the field of 2D materials. This issue was originally assembled to support the Symposium G "Chemical Functionalization of 2D Materials" at the European Materials Research Society (E-MRS) 2020 Spring Meeting, which was originally scheduled to be held in Strasbourg, France, from May 25th to 29th, 2020. Although the E-MRS 2020 Spring Meeting has been cancelled due to the COVID-19 outbreak, the publication of this Special Issue has proceeded and has become even more important as the contributors discuss diverse and timely research themes related to 2D materials. In this Editorial, a brief overview of the different types of 2D materials is given, together with the chemical functionalization schemes that can be applied to them to achieve new properties as well as enable improved performance in applications. Some of the articles featured in this Special Issue are also highlighted, with the hope that they will inspire readers and further advance the field

Structure and properties of the stable two-dimensional conducting polymer Mg5C60

We present a study on the structural, spectroscopic, conducting, and magnetic properties of Mg5C60, which is a two-dimensional (2D) fulleride polymer. The polymer phase is stable up to the exceptionally high temperature of 823 K. The infrared and Raman studies suggest the formation of single bonds between the fulleride ions and possibly Mg-C-60 covalent bonds. Mg5C60 is a metal at ambient temperature, as shown by electron spin resonance and microwave conductivity measurements. The smooth transition from a metallic to a paramagnetic insulator state below 200 K is attributed to Anderson localization driven by structural disorder

One-step covalent hydrophobic/hydrophilic functionalization of chemically exfoliated molybdenum disulfide nanosheets with RAFT derived polymers

The covalent functionalization of chemically exfoliated molybdenum disulfide (ce-MoS2) with hydrophobic poly(methyl methacrylate) and hydrophilic poly(acrylic acid) polymers, in a single-step without additives, is presented. The nature of chemical modification and the impact on the structure of ce-MoS2 were spectroscopically investigated. Complexation of Eu3+ was accomplished on grafted polycarboxylate chains on MoS2

Oligothiophene/graphene supramolecular ensembles managing light induced processes: Preparation, characterization, and femtosecond transient absorption studies leading to charge‐separation

Advances  in  organic  synthetic  chemistry  combined  with  the  exceptional  electronic  properties  of  carbon  allotropes,  particularly graphene, is the basis to design and fabricate novel electron donor-­‐acceptor ensembles with desired properties for technological applications. Thiophene-­‐based materials, mainly thiophene-­‐containing polymers, are known for  their  notable  electronic  properties.  In  this  frame  moving  from  polymer  to  oligomer  forms,  new  fundamental  information would help to the better understanding of their electrochemical and photophysical properties. Furthermore, a successful  combination  of  their  electronic  properties  with  those  of  graphene  is  a  challenging  goal.  In  this  work  two  oligothiophene compounds consists of three and nine thiophene-­‐rings, abbreviated as 3T and 9T, respectively, were synthesized and noncovalently associated with liquid phase exfoliated few-­‐layered graphene sheets (abbreviated as eG), forming donor-­‐acceptor 3T/eG and 9T/eG nanoensembes. Markedly, intra-­‐ensemble electronic interactions between the two  components  in  the  ground  and  excited  states  were  evaluated  with  the  aid  of  UV-­‐Vis  and  photoluminescence  spectroscopy. Furthermore, redox assays revealed an one-­‐electron oxidation of 3T accompanied by one-­‐electron reduction due  to  eG  in  3T/eG,  while  two  reversible  one-­‐electron  oxidations  of  9T  accompanied  by  one-­‐electron  reduction  of  eG  9T/eG. The electrochemical band gap for 3T/eG and 9T/eG ensembles were calculated and verified that the negative free-­‐energy change for the charge-­‐separated state of 3T/eG and 9T/eG via the singlet excited state of 3T and 9T respectively, were  thermodynamically  favorable.  Finally,  results  of  transient  pump-­‐probe  spectroscopic  studies  at  the  femtosecond  time scale were supportive of charge transfer type interactions in the 3T/eG and 9T/eG ensembles. The estimated rates for intra-­‐ensemble charge separation were found to be 9.52 x 109 s-­‐1 and 2.2 x 1011 s-­‐1, respectively, for 3T/eG and 9T/eG in THF, revealing moderate to ultrafast photoinduced events in the oligothiophene/graphene supramolecular ensemble

Graphene exfoliation in organic solvents and switching solubility in aqueous media with the aid of amphiphilic block copolymers.

The successful exfoliation of graphite to graphene sheets in liquid phase via tip sonication was achieved. A number of solvents were examined for several time periods and it was found that o-dichlorobenzene (o-DCB) and N-methyl-1,2-pyrolidone (NMP) are ideal solvents to exfoliate graphite and produce stable 10 dispersions of graphene. The exfoliated graphene dispersions were characterized by complementary techniques including AFM, DLS, TGA and Raman. Furthermore, treatment of stable dispersions of exfoliated graphene sheets in NMP with poly[styrene-b-(2-vinylpyridine)] block copolymer, under acidic conditions, resulted on aqueous solubilization of graphene. Similar results were obtained, i.e. transfer of graphene from the organic to the aqueous phase, when poly(isoprene-b-acrylic acid) block copolymer was 15 added on exfoliated graphene in NMP