Syed Mujtaba Shah

Development of photocatalysts for selective and efficient organic transformations

One of the main goals of organic chemists is to find easy, environmentally friendly, and cost effective methods for the synthesis of industrially important compounds. Photocatalysts have brought revolution in this regard as they make use of unlimited source of energy (the solar light) to carry out the synthesis of organic compounds having otherwise complex synthetic procedures. However, selectivity of the products has been a major issue since the beginning of photocatalysis. The present article encompasses state of the art accomplishments in harvesting light energy for selective organic transformations using photocatalysts. Several approaches for the development of photocatalysts for selective organic conversions have been critically discussed with the objective of developing efficient, selective, environmental friendly and high yield photocatalytic methodologies.

Evaluation of electrical, dielectric and magnetic characteristics of Al–La doped nickel spinel ferrites

The paper reports the effects of lanthanum and aluminum ions, on the structural, electrical and magnetic properties of NiFe2O4 spinel ferrite nanoparticles. The precursors have been synthesized via a hydrothermal route in the presence of ascorbic acid (AA) using urea as a reducing agent and fuel for maintaining the uniform morphology and equal particle size distribution. In order to find out the optimum temperature (1023 K) for the formation of the spinel phase of the doped nickel ferrite, thermogravimetric analysis (TGA) for the un-annealed samples was performed. The X-ray diffraction patterns show that NiFe2−2xAlxLaxO4 have been well crystallized to spinel ferrite crystal structure with the Fd3m space group. The average crystallite size obtained is in the range of 9–19 nm, a size useful for attaining a suitable signal-to-noise ratio in high-density recording media and in electrical devices. In order to render the synthesized samples for diminishing eddy current losses, we were able to enhance the room temperature resistivity through proper selection of dopant used. The dielectric constant and dielectric loss decreased with applied frequency for all the samples showing normal behavior of ferrites. The calculated magnetic parameters such as saturation magnetization (Ms), remanence (Mr) and coercivity (Hc), showed increased values for some Al–La doped samples.

Photo-sensitization of ZnS nanoparticles with renowned ruthenium dyes N3, N719 and Z907 for application in solid state dye sensitized solar cells: A comparative study.

This article presents a comprehensive relative report on the grafting of ZnS with renowned ruthenium ((Ru) dyes i.e. N3, N719 and Z907) and gives insight into their charge transfer interaction and sensitization mechanism for boosting solar cell efficiency. Influence of dye concentration on cell performance is also reported here. ZnS nanoparticles synthesized by a simple coprecipitation method with an average particle size of 15±2nm were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Elemental dispersive X-ray analysis (EDAX), tunneling electron microscopy (TEM) and UV-Visible (UV-Vis) spectroscopy. UV-Vis, photoluminescence (PL) and Fourier transform infra-red (FT-IR) spectroscopy confirms the successful grafting of these dyes over ZnS nanoparticles surface. Low-energy metal-to-ligand charge-transfer transition (MLCT) bands of dyes are mainly affected on grafting over the nanoparticle surface. Moreover their current voltage (I-V) results confirm the efficiency enhancement in ZnS solid state dye sensitized solar cells (SSDSSCs) owing to effective sensitization of this material with Ru dyes and helps in finding the optimum dye concentration for nanoparticles sensitization. Highest rise in overall solar cell efficiency i.e. 64% of the reference device has been observed for 0.3mM N719-ZnS sample owing to increased open circuit voltage (Voc) and fill factor (FF). Experimental and proposed results were found in good agreement with each other.

Co-grafting of porphyrins and fullerenes on ZnO nanorods: Towards supramolecular donor-acceptor assembly

This work presents the synthesis and physico-chemical characterization of a novel artificial photosynthetic design, using anisotropic semiconducting nanorods as scaffolds to assemble organic donor-acceptor complexes on their surface. These hierarchical hybrid D-A assemblies were obtained by the co-grafting of porphyrins and fullerenes on the ZnO nanorods. Polarity of the solvent and porphyrin to fullerene ratios were investigated to be markedly influencing the donor-acceptor interaction under the co-grafted conditions on ZnO nanorods. Fourier transform infrared spectroscopy, cyclic voltammetry, electronic absorption and fluorescence spectroscopic techniques were used to characterize the formation and investigate the optoelectronic properties of porphyrin-fullerene complexes on the surface of ZnO. To the best of our knowledge, this is the first example of highly interacting porphyrin-fullerene complexes on ZnO nanorods, which may allow generating efficient nanosystems for artificial photosynthesis and harvesting of solar energy.

Flexible, Low Cost, and Platinum-Free Counter Electrode for Efficient Dye-Sensitized Solar Cells

A platinum-free counter electrode composed of surface modified aligned multiwalled carbon nanotubes (MWCNTs) fibers was fabricated for efficient flexible dye-sensitized solar cells (DSSCs). Surface modification of MWCNTs fibers with simple one step hydrothermal deposition of cobalt selenide nanoparticles, confirmed by scanning electron microscopy and X-ray diffraction, provided a significant improvement (∼2-times) in their electrocatalytic activity. Cyclic voltammetry and electrochemical impedance spectroscopy suggest a photoelectric conversion efficiency of 6.42% for our modified fibers, higher than 3.4% and 5.6% efficeincy of pristine MWCNTs fiber and commonly used Pt wire, respectively. Good mechanical and performance stability after repeated bending and high output voltage for in-series connection suggest that our surface modified MWCNTs fiber based DSSCs may find applications as flexible power source in next-generation flexible/wearable electronics.

Storage Stability of Kinnow Fruit (Citrus reticulata) as Affected by CMC and Guar Gum-Based Silver Nanoparticle Coatings

The influence of carboxy methyl cellulose (CMC) and guargum-based coatings containing silver nanoparticles was studied on the postharvest storage stability of the kinnow mandarin (Citrus reticulata cv. Blanco) for a period of 120 days (85%–90% relative humidity) at 4 °C and 10 °C. Physicochemical and microbiological qualities were monitored after every 15 days of storage. Overall results revealed an increase in total soluble solid (TSS), total sugars, reducing sugars and weight loss but this increase was comparatively less significant in coated fruits stored at 4 °C. Ascorbic acid, total phenolics, and antioxidant activity was significantly enhanced in coated fruits stored at 4 °C. Titratable acidity significantly decreased during storage except for coated kinnow stored at 4 °C. In control samples stored at 10 °C, high intensity of fruit rotting and no chilling injury was observed. Total aerobic psychrotrophic bacteria and yeast and molds were noticed in all treatments during storage but the growth was not significant in coated fruits at 4 °C. Kinnow fruit can be kept in good quality after coating for four months at 4 °C and for 2 months at 10 °C.

Adsorption of porphyrin and carminic acid on TiO2 nanoparticles: A photo-active nano-hybrid material for hybrid bulk heterojunction solar cells

A photo-active nano-hybrid material consisting of titania nanoparticles, carminic acid, and sulphonic acid functionalized porphyrin is reported here. In an attempt to extend the absorption spectrum of titania to visible region by co-adsorbing carminic acid and sulphonic acid functionalized porphyrin on its surface. Interesting changes in the UV-visible and fluorescence spectra were noticed. The adsorption of carminic acid resulted in the formation of charge transfer complex with titania nanoparticles. This was confirmed by the electronic absorption and fluorescence emission spectroscopies. Chemisorption of porphyrin on the carminic acid functionalized titania further boosted the charge transfer effect. This was noticed by the increase in intensity and width of the charge transfer absorption and emission bands. Energy level diagram showed that the interaction among the constituents of the nano-hybrid assembly permitted the flow of electron in a cascade manner from carminic acid to TiO2.This also allowed direct flow of electrons either from carminic acid or porphyrin toward titania. The material was used as an active blend in hybrid bulk heterojunction solar cells. Co-functionalized TiO2-based devices were found 3.5 times more efficient than the reference device but morphology of the device proved a major setback.

Photoswitching in azobenzene self-assembled monolayers capped on zinc oxide: Nanodots vs nanorods

We report the synthesis and spectroscopic characterization of nanohybrid structures consisting of an azobenzene compound grafted on the surface of zinc oxide nanoparticles. Characteristic bathochromic shifts indicate that the azobenzene photochromic molecules self-assemble onto the surface of the nanocrystals. The extent of packing is dependent on the shape of the nanoparticle. ZnO nanorods, with flat facets, enable a tighter organization of the molecules in the self-assembled monolayer than in the case of nanodots that display a more curvated shape. Consistently, the efficiency of photochromic switching of the self-assembled monolayer on ZnO nanoparticles is also shown to be strongly affected by nanoparticle shape.

Synthesis and characterization of multi-responsive poly (NIPAm-co-AAc) microgels

Two samples of multi-responsive copolymer microgels, poly(N-isopropylacrylamide-co-acrylic acid) [P(NIPAm-co-AAc)], were synthesized by emulsion polymerization using different amounts of emulsifier. The unreacted monomers and surfactant were removed from the microgels by dialysis. Dynamic Laser Light Scattering (DLS) was used to determine the diffusion coefficient and hydrodynamic radius (Rh) of the microgels at different pH values and temperatures. At pH 7 the microgel showed rapid response to temperature and underwent volume phase transition (VPT) as the temperature was raised. At lower temperature the microgels were in the hydrated or swollen state but beyond 38oC, the size was abruptly decreased. Under different conditions of pH and NaCl concentrations, variations in VPTT values were noticed. By increasing pH the VPTT was increased but the addition of salt had an inverse effect. The weight average molar mass (Mw) and radius of gyration (Rg) were measured by Static Laser Light Scattering (SLS). FTIR spectroscopy was used to confirm the chemical structures of microgels

Metal-free polymer/MWCNT composite fiber as an efficient counter electrode in fiber shape dye-sensitized solar cells.

UNLABELLED Highly aligned multiwall carbon nanotubes (MWCNT) as fiber were modified with a conducting polymer via a simple dip coating method. Modified MWCNT exhibited admirable improvement in electrocatalytic activity for the reduction of tri-iodide in dye sensitized solar cells. Scanning electron microscopy images confirm the successful deposition of polymer on MWCNT. Cyclic voltammetry, square wave voltammetry and electrochemical impedance spectroscopy studies were carried out to investigate the inner mechanism for the charge transfer behaviour. Results from bare and modified electrodes revealed that the MWCNT/(poly (3,4-ethylene dioxythiophene):poly(styrene sulfonate) ( PEDOT PSS) composite electrode is much better at catalysing the [Formula: see text] redox couple compared to the pristine fiber electrode. The photoelectric conversion efficiency of 5.03% for the modified MWCNT electrodes was comparable with that of the conventional Pt-based electrode. The scientific results of this study reveal that MWCNT/PEDOT:PSS may be a better choice for the replacement of cost intensive electrode materials such as platinum. Good performance even after bending up to 90° and in-series connection to enhance the output voltage were also successfully achieved, highlighting the practical application of this novel device.