Au-SnS Hetero Nanostructures: Size of Au Matters

In nanoscale, with size variation, Au shows different optical behaviors. For the small size clusters (sub-5 nm), it behaves more like semiconductors having sp and d band electronic energy levels splitting and also do not show the characteristic plasmon. However, for larger size particles (>5 nm), it shows the plasmonic absorption. Considering these two structures of Au⁰, we report here their coupling with a low bandgap semiconductor SnS and study the difference in their formation chemistry and materials’ properties. Following a common synthetic approach in which a smaller size SnS cube and tetrahedron shapes result in Au cluster decorated Au-SnS heterostructures, larger size SnS cubes form coupled Au-SnS nanostructures. Contrastingly, the nonplasmonic Au⁰ cluster-SnS hinders the photocatalytic activity, whereas the plasmonic coupled Au-SnS enhances the catalytic activity toward reduction of organic dye methylene blue. However, both types of heterostructures show enhanced photocurrent as well as photoresponse activities. Details of the chemistry of formation, epitaxy at the junction, and change in the materials’ properties are studied and reported here in this article

Graphene Quantum Dots from a Facile Sono-Fenton Reaction and Its Hybrid with a Polythiophene Graft Copolymer toward Photovoltaic Application

A new and facile approach for synthesizing graphene quantum dots (GQDs) using sono-Fenton reaction in an aqueous dispersion of graphene oxide (GO) is reported. The transmission electron microscopy (TEM) micrographs of GQDs indicate its average diameter as ∼5.6 ± 1.4 nm having a lattice parameter of 0.24 nm. GQDs are used to fabricate composites (PG) with a water-soluble polymer, polythiophene-<i>g</i>-poly­[(diethylene glycol methyl ether methacrylate)-<i>co</i>-poly­(<i>N</i>,<i>N</i>-dimethylaminoethyl methacrylate)] [PT-<i>g</i>-P­(MeO₂MA-<i>co</i>-DMAEMA), P]. TEM micrographs indicate that both P and PG possess distinct core–shell morphology and the average particle size of P (0.16 ± 0.08 μm) increases in PG (0.95 ± 0.45 μm). Fourier transform infrared and X-ray photoelectron spectrometry spectra suggest an interaction between −OH and −COOH groups of GQDs and −NMe₂ groups of P. A decrease of the intensity ratio of Raman D and G bands (<i>I</i>_D/<i>I</i>_G) is noticed during GQD and PG formation. In contrast to GO, GQDs do not exhibit any absorption peak for its smaller-sized sp² domain, and in PG, the π–π* absorption of polythiophene (430 nm) of P disappears. The photoluminescence (PL) peak of GQD shifts from 450 to 580 nm upon a change in excitation from 270 to 540 nm. PL emission of PG at 537 nm is quenched, and it shifts toward lower wavelength (∼430 nm) with increasing aging time for energy transfer from P to GQDs followed by <i>up-converted</i> emission of GQDs. Both P and PG exhibit semiconducting behavior, and PG produces an almost reproducible photocurrent. Dye-sensitized solar cells (DSSCs) fabricated with an indium–titanium oxide/PG/graphite device using the N719 dye exhibit a short-circuit current (<i>J</i>_sc) of 4.36 mA/cm², an open-circuit voltage (<i>V</i>_oc) of 0.78 V, a fill factor of 0.52, and a power conversion efficiency (PCE, η) of 1.76%. Extending the use of GQDs to fabricate DSSCs with polypyrrole, both <i>V</i>_oc and <i>J</i>_sc increase with increasing GQD concentration, showing a maximum PCE of 2.09%. The PG composite exhibits better cell viability than the components

A Co-assembled Gel of a Pyromellitic Dianhydride Derivative and Polyaniline with Optoelectronic and Photovoltaic Properties

5,5′-(1,3,5,7-Tetraoxopyrrolo­[3,4-<i>f</i>]­isoindole-2,6-diyl)­diisophthalic acid (PMDIG) is used to produce a supramolecular hydrogel via acid–base treatment. The field emission scanning electron micrograph and atomic force microscopy micrographs exhibit a fibrillar network structure from intermolecular supramolecular interaction, supported from Fourier transform infrared (FTIR) and UV–vis spectra. The fluorescence intensity of the PMDIG gel is 16 times higher than that of the sodium salt of PMDIG with a 42 nm red shift of the emission peak. Upon addition of an anilinium chloride solution to the PMDIG gel, it transforms into the sol, and when a solid ammonium persulfate is spread over it, a stable hydrogel is produced. The co-assembled PMDIG–polyaniline (PANI) gel exhibits a fibrillar network morphology, and the co-assembly is formed by the supramolecular interaction between the polyaniline (donor) and the PMDIG (acceptor) molecules, which is evident from FTIR spectra and wide angle X-ray scattering results. The UV–vis spectrum of the PMDIG–PANI hydrogel exhibits the characteristic peaks of polaron band transitions of the doped PANI. The PMDIG–PANI co-assembled hydrogel has a 51-fold higher storage modulus, a 52-fold higher elasticity, a 1.4-fold increase in stiffness, and a 5-fold increase of fragility compared to the values of the PMDIG hydrogel. The PMDIG–PANI xerogel exhibits a 4 order of magnitude increase in dc conductivity compared to that of PMDIG, and the <i>I</i>–<i>V</i> characteristic curve exhibits a rectification property under white light illumination showing photocurrent rectification, a new phenomenon reported here for the supramolecular gel systems. A dye-sensitized solar cell fabricated with an ITO/PMDIG–PANI/graphite device shows a power conversion efficiency (η) of 0.1%. A discussion of the mechanism of gel formation and the sol state of the PMDIG–aniline system is included considering the contact angle values of the xerogels

Coincident Site Epitaxy at the Junction of Au–Cu₂ZnSnS₄ Heteronanostructures

Considering the chemistry of the formation and physics at interfaces, we report on the heterostructure of a promising new energy material, Au–Cu₂ZnSnS₄ (Au-CZTS), and investigate the impact of coupling on Au on improving both the photostability and the photoresponse behavior. We focus primarily on the fundamental issues involved in bringing together two dissimilar materials having different chemical and physical properties in a single building block where one is a multinary semiconductor nanomaterial and the other is a plasmonic noble metal. The formation of heteroepitaxy at the junction of Au and CZTS was investigated for two different phases of CZTS. Considering epitaxy formation along the {111} planes of Au, it was observed that the wurtzite and tetragonal phases of CZTS exhibit coincident site epitaxy with different periodic intervals. A detailed study of this epitaxy formation with Au in both phases of CZTS has been carried out and reported. Because Au-CZTS is a promising new material, we have further investigated its photocurrent and photoresponse behavior and compared them with the properties and behavior of pure CZTS. We believe that these findings will help the energy-materials community, providing guidelines for investigating new functional materials and their applications

Succinato-bridged Cd(II)-nicotinylhydrazone 3D coordination polymer: structure, photoconductivity and computational studies

Strategies for clean energy are important components of the United Nation’s Sustainable Development Goals (SDGs). To this end, we have studied the conductivity of a Cd(II)-based 3D coordination polymer, [Cd(succ)(pcih)(H2O)]n (1) (H2succ = succinic acid; pcih = pyridine-4-carboxaldehyde iso-nicotinoyl hydrazone). Compound 1 was structurally characterized by single-crystal X-ray diffraction. The bridging groups, succ2− and pcih, self-assembled via H-bonding and π∙∙∙π interactions. The optical band gap calculated from a Tauc’s plot was determined to be 3.71 eV which is consistent with semiconducting behavior. The experimental barrier height, 0.71 eV (dark phase); 0.49 eV (light phase) and series resistance, 358.48 Ω (dark); 133.73 Ω (light), also support the photoinduced enhancement of conductivity. The non-ohmic relation, I α V2, showed an enhancement of conductivity by 2.5 times upon light irradiation [3.36 × 10−6 S m−1 (dark) and 8.37 × 10−6 S m−1 (light)]. DFT computations employing the crystallographic parameters of 1 indicated a HOMO/LUMO energy gap of 4.06 eV, within the range of semiconducting materials. The optical stability of 1 was examined by fluorescence measurements and lifetime data.</p

Conductive MoS₂ Quantum Dot/Polyaniline Aerogel for Enhanced Electrocatalytic Hydrogen Evolution and Photoresponse Properties

The low conductivity and poor active sites of MoS₂ sheet present a huge barrier for it is exploitation of catalytic applications in the hydrogen evolution reaction (HER). To alleviate this difficulty, we have synthesized MoS₂ quantum dots (QDs) having greater quantity of catalytic edge sites by breaking up the bulk MoS₂ sheet using the solvent exfoliation technique. The synthesized MoS₂ QDs are embedded into polyaniline (PANI)–<i>N</i>,<i>N</i>′-dibenzoyl-l-cystine (DBC) hydrogel matrix by in situ polymerization of aniline where DBC acts as a gelator, dopant, and cross-linker. The hybrid conducting aerogels (DBC-MoS₂-PANI) thus produced act as an efficient electrocatalyst showing lower HER overpotential in comparison to MoS₂ QDs. It exhibits an optimum overpotential value of 196 mV at 10 mA cm^–2, a favorable Tafel slope of 58 mV/dec, and an excellent cyclic stability. Also, DBC-MoS₂-PANI aerogel is used in photoresponding devices. The DBC-MoS₂-PANI hybrid aerogel exhibits a better photoresponse compared to the DBC-PANI aerogel and MoS₂ QDs upon white light illumination of 1 sun. The hybrid aerogel exhibits a maximum enhancement of photocurrent to the value of 3.95 mA at 2 V bias, and the time-dependent photoillumination shows much faster rise and decay of photocurrent compared to those of DBC-PANI aerogel and MoS₂ QDs