Arkamita Bandyopadhyay

Nanocomposites of C3N4 with Layers of MoS2 and Nitrogenated RGO, Obtained by Covalent Cross-Linking: Synthesis, Characterization, and HER Activity

Generation of hydrogen by photochemical, electrochemical, and other means is a vital area of research today, and a variety of materials have been explored as catalysts for this purpose. C3N4, MoS2, and nitrogenated RGO (NRGO) are some of the important catalytic materials investigated for the hydrogen evolution reaction (HER) reaction, but the observed catalytic activities are somewhat marginal. Prompted by preliminary reports that covalent cross-linking of 2D materials to generate heteroassemblies or nanocomposites may have beneficial effect on the catalytic activity, we have synthesized nanocomposites wherein C3N4 is covalently bonded to MoS2 or NRGO nanosheets. The photochemical HER activity of the C3N4-MoS2 nanocomposite is found to be remarkable with an activity of 12778 μmol h-1 g-1 and a turnover frequency of 2.35 h-1. The physical mixture of C3N4 and MoS2, on the other hand, does not exhibit notable catalytic activity. Encouraged by this result, we have studied electrochemical HER activity of these composites as well. C3N4-MoS2 shows superior activity relative to a physical mixture of MoS2 and C3N4. Density functional theory calculations have been carried out to understand the HER activity of the nanocomposites. Charge-transfer between the components and greater planarity of cross-linked layers are important causes of the superior catalytic activity of the nanocomposites. Covalent linking of such 2D materials appears to be a worthwhile strategy for catalysis and other applications.

Highly Luminescent Microporous Organic Polymer with Lewis Acidic Boron Sites on the Pore Surface: Ratiometric Sensing and Capture of F− Ions

Reversible and selective capture/detection of F(-) ions in water is of the utmost importance, as excess intake leads to adverse effects on human health. Highly robust Lewis acidic luminescent porous organic materials have potential for efficient sequestration and detection of F(-) ions. Herein, the rational design and synthesis of a boron-based, Lewis acidic microporous organic polymer (BMOP) derived from tris(4-bromo-2,3,5,6-tetramethylphenyl)boron nodes and diethynylbiphenyl linkers with a pore size of 1.08 nm for selective turn-on sensing and capture of F(-) ion are reported. The presence of a vacant pπ orbital on the boron center of BMOP results in intramolecular charge transfer (ICT) from the linker to boron. BMOP shows selective turn-on blue emission for F(-) ions in aqueous mixtures with a detection limit of 2.6 μM. Strong B-F interactions facilitate rapid sequestration of F(-) by BMOP. The ICT emission of BMOP can be reversibly regenerated by addition of an excess of water, and the polymer can be reused several times.

Doping phosphorene by holes and electrons through molecular charge transfer

An important aspect of phosphorene, the novel two-dimensional semiconductor, is whether holes and electrons can both be doped in this material. Some reports found that only electrons can be preferentially doped into phosphorene. There are some theoretical calculations showing charge-transfer interaction with both tetrathiafulvalene (TTF) and tetracyanoethylene (TCNE). We have carried out an investigation of chemical doping of phosphorene by a variety of electron donor and acceptor molecules, employing both experiment and theory, Raman scattering being a crucial aspect of the study. We find that both electron acceptors and donors interact with phosphorene by charge-transfer, with the acceptors having more marked effects. All the three Raman bands of phosphorene soften and exhibit band broadening on interaction with both donor and acceptor molecules. First-principles calculations establish the occurrence of charge-transfer between phosphorene with donors as well as acceptors. The absence of electron-hole asymmetry is noteworthy.

Nitrogen-Doped Graphene Quantum Dots as Possible Substrates to Stabilize Planar Conformer of Au20 over Its Tetrahedral Conformer: A Systematic DFT Study

Utilizing the strengths of nitrogen-doped graphene quantum dot (N-GQD) as a substrate, herein, we have shown that one can stabilize the catalytically more active planar Au20 (P-Au20) compared with the thermodynamically more stable tetrahedral structure (T-Au20) on an N-GQD. Clearly, this simple route avoids the usage of traditional transition-metal oxide substrates, which have been suggested and used for stabilizing the planar structure for a long time. Considering the experimental success in the synthesis of N-GQDs and in the stabilization of Au nanoparticles on N-doped graphene, we expect our proposed method to stabilize planar structure will be realized experimentally and will be useful for industrial level applications.

Tuning the opto-electronic properties of MoS2 layer using charge transfer interactions: effect of different donor molecules

We have performed density functional theory calculations to study the effect of adsorption of a set of organic electron donor molecules on single layer MoS2 to find the optimum condition to tune the charge transfer, as well as to find how it changes the electronic properties of single layer MoS2. We have performed our calculations for three sets of organic Lewis bases. We have found that all the molecules are physisorbed on MoS2. Our calculations show that the charge transfer from the molecules to the MoS2 layer is highly dependent upon the inductive effect and HOMO–LUMO gap of the molecules. Furthermore, we show that the charge transfer interaction tunes the electronic and optical property of MoS2 to a significant amount: for example, the band-gap of the system can be changed from 1.8 eV to even a low value of 0.2 eV, making it interesting for different optoelectronic device applications.

Shining Light on New-Generation Two-Dimensional Materials from a Computational Viewpoint

Energy- and sensing-related applications using two-dimensional (2D) materials with tunable optoelectronic properties have been a hot topic of research. The genres of 2D materials grow every day, leading to new possibilities in optoelectronic devices. In this Perspective, we have discussed in a nutshell several impacts of light-matter interactions in new-generation 2D materials. Using reliable computational approaches, in-depth understanding about the fundamental optical absorption and emission character as well as further prediction of the potential applications for these materials in the field of photovoltaics and sensing have been explored. Various modifications of the parent 2D materials by computational designing with enhanced performance have been investigated to guide the experimental efforts. The major computational challenges and their probable solutions for 2D-material-based optoelectronic research have also been briefly outlined.

Redox-active and semi-conducting donor–acceptor conjugated microporous polymers as metal-free ORR catalysts

Metal-free pristine conjugated microporous polymers (CMPs) catalyzing electrochemical oxygen reduction reaction (ORR) are still rare. We therefore put forward a design strategy to fabricate electrochemically active CMPs by linking donor nodes and acceptor spacers. The two new CMPs have been structurally well characterized and show semi-conduction and redox-activity. As a proof of concept, we show that both the CMPs have appreciable ORR activity and catalytic stability over time. Further, DFT calculations reveal the origin of the semi-conducting property and also the mode of oxygen binding to the catalytic centres. This work shows the potential application of pristine metal-free CMPs in energy conversion processes.

Solvent-Modulated Emission Properties in a Superhydrophobic Oligo(p-phenyleneethynylene)-Based 3D Porous Supramolecular Framework

A chromophoric oligo( p-phenyleneethynylene) (OPE) bola-amphiphile with dioxyoctyl side chains (H2OPE-C8) has been self-assembled with CdII to form a 1D coordination polymer, {Cd(OPE-C8)(DMF)2(H2O)} (1), which is further interdigitated to form a 2D network. Such 2D networks are further interwoven to form a 3D supramolecular framework with surface-projected alkyl chains. The desolvated framework showed permanent porosity, as realized from the CO2 adsorption profile. 1 showed high water contact angles, portraying its superhydrophobic nature. 1 also showed a linker-based cyan luminescence. Solvent removal led to a bathochromic shift in emission into the green region. Resolvation with N, N-dimethylformamide brought back the original cyan emission, whereas for tetrahydrofuran, ethanol, and methanol, it persisted at an intermediate state. Density functional theory calculations unraveled that, twisting of the OPE phenyl rings generated the red shift in emission.