Asif Ali Tahir

A Water‐Stable Porphyrin‐Based Metal–Organic Framework Active for Visible‐Light Photocatalysis

Metal–organic frameworks (MOFs) permit the combination of high internal surface area with chemical and physical functionality conferred by the molecular linker. Porphyrins are versatile functional molecules in catalysis, light harvesting, and molecular sensing. Porphyrins have been used as building blocks for MOFs, affording catalysts, light harvesting and selective sorption in liquid and gas phases. MOFs based on Alcarboxylate coordination chemistry are amongst the most thermally and chemically stable of such systems reported to date. Here we report a waterstable porous porphyrin MOF with a BET surface area of 1400 m g 1 which performs visible-lightdriven hydrogen generation from water. The freebase porphyrin can be metalated within the rigid host structure. The reaction of AlCl3·6 H2O with the free-base meso-tetra(4-carboxyl-phenyl) porphyrin H2TCPP (Figure 1b) in water under hydrothermal conditions at 180 8C followed by washing with dimethyl formamide (DMF) to remove unreacted ligand leads to the formation of the microcrystalline porous red compound H2TCPP[AlOH]2(DMF3(H2O)2) 1 (referred to as Al-PMOF, experimental details are given in section 1.1 in the Supporting Information). The linker consists of four benzoate groups around the central porphyrin core. The analyzed composition reveals that no aluminium is coordinated within the porphyrin ring, consistent with the need to use reactive trialkylaluminium reagents for metalation of the porphyrin in solution. The reaction temperature is required to solubilize the porphyrin linker. The crystal structure of 1 was solved and refined from synchrotron powder Xray diffraction collected at 100 K. Indexing and Pawley refinement revealed an orthorhombic cell (a = 31.978(3) , b = 6.5812(4) , c = 16.862(2) , V= 3548.7(6) ) consistent with the C222, Cmm2, and Cmmm space groups. Each of these candidate space groups was evaluated by simulated annealing using a semi-rigid body to describe the TCPP unit (Figure S1 in the Supporting Information) with eight refined parameters describing distances and angles within the porphyrin. The best results were obtained for the benzoic acid group perpendicular to the central porphyrin ring, which can be best described in Cmmm symmetry, and zero occupancy for Al at the center of the porphyrin. This model was used in the final Rietveld analysis (Figure 1a). Fourier mapping revealed a single guest atom in the channels attributed to oxygen from water, which was included in the final refinement (Figure S2 in the Supporting Information). Each porphyrin linker in 1 is coordinated to eight aluminium centers (Figure 1c–e) through the four carboxylate groups which each bridge two aluminium units. There is Figure 1. a) Final Rietveld refinement of 1 (100 K) showing observed (gray crosses), calculated (line a), and difference (line b) plots (Q = 2p/d). Bragg peak positions are indicated. b) TCPP porphyrinic linker in 1. c–e) Crystal structure of 1 viewed down [001], [100], and [010] directions, respectively.

Kinetics of light-driven oxygen evolution at alpha-Fe2O3 electrodes.

The kinetics of light-driven oxygen evolution at polycrystalline alpha-Fe2O3 layers prepared by aerosol-assisted chemical vapour deposition has been studied using intensity modulated photocurrent spectroscopy (IMPS). Analysis of the frequency-dependent IMPS response gives information about the competition between the 4-electron oxidation of water by photogenerated holes and losses due to electron-hole recombination via surface states. The very slow kinetics of oxygen evolution indicates the presence of a kinetic bottleneck in the overall process. Surface treatment of the alpha-Fe2O3 with dilute cobalt nitrate solution leads to a remarkable improvement in the photocurrent response, but contrary to expectation, the results of this study show that this is not due to catalysis of hole transfer but is instead the consequence of almost complete suppression of surface recombination.

Silver(I) complexes of 9-anthracenecarboxylic acid and imidazoles: synthesis, structure and antimicrobial activity

[Ag(2)(9-aca)(2)] (1) (9-acaH = 9-anthracenecarboxylic acid) reacts with a series of imidazoles to give [Ag(imidH)(2.3)(CH(3)CN)(0.7)](9-aca) (3), [Ag(6)(imidH)(4)(9-aca)(6)(MeOH)(2)] (4), {[Ag(1-Me-imid)(2)](2)[Ag(4)(9-aca)(6)]} (5), {[Ag(1-Bu-imid)(2)](2)[Ag(4)(9-aca)(6)]} (6) and [Ag(apim)](9-aca)·H(2)O (7) (imidH = imidazole; 1-Me-imid = 1-methylimidazole; 1-Bu-imid = 1-butylimidazole; apim = 1-(3-aminopropyl)imidazole). The mononuclear complex 3, hexanuclear 4-6, and polymeric 7, were all characterised using X-ray crystallography. While many of the complexes possess excellent in vitro antifungal and antibacterial activities they are, unanimously, more effective against fungal cells. The insect, Galleria mellonella, can survive high doses of the Ag(i) complexes administered in vivo, and a number of the complexes offer significant protection to larvae infected with a lethal dose of pathogenic Candida albicans cells.

Phytochemical, spectroscopic and density functional theory study of Diospyrin, and non-bonding interactions of Diospyrin with atmospheric gases.

Density functional theory (DFT) and phytochemical study of a natural product, Diospyrin (DO) have been carried out. A suitable level of theory was developed, based on correlating the experimental and theoretical data. Hybrid DFT method at B3LYP/6-31G (d,p) level of theory is employed for obtaining the electronic, spectroscopic, inter-molecular interaction and thermodynamic properties of DO. The exact structure of DO is confirmed from the nice validation of the theory and experiment. Non-covalent interactions of DO with different atmospheric gases such as NH3, CO2, CO, and H2O were studied to find out its electroactive nature. The experimental and predicted geometrical parameters, IR and UV-vis spectra (B3LYP/6-31+G (d,p) level of theory) show excellent correlation. Inter-molecular non-bonding interaction of DO with atmospheric gases is investigated through geometrical parameters, electronic properties, charge analysis, and thermodynamic parameters. Electronic properties include, ionization potential (I.P.), electron affinities (E.A.), electrostatic potential (ESP), density of states (DOS), HOMO, LUMO, and band gap. All these characterizations have corroborated each other and confirmed the presence of non-covalent nature in DO with the mentioned gases.

The Application of Graphene and Its Derivatives to Energy Conversion, Storage, and Environmental and Biosensing Devices

Graphene (GR) and its derivatives are promising materials on the horizon of nanotechnology and material science and have attracted a tremendous amount of research interest in recent years. The unique atom-thick 2D structure with sp(2) hybridization and large specific surface area, high thermal conductivity, superior electron mobility, and chemical stability have made GR and its derivatives extremely attractive components for composite materials for solar energy conversion, energy storage, environmental purification, and biosensor applications. This review gives a brief introduction of GRs unique structure, band structure engineering, physical and chemical properties, and recent energy-related progress of GR-based materials in the fields of energy conversion (e.g., photocatalysis, photoelectrochemical water splitting, CO2 reduction, dye-sensitized and organic solar cells, and photosensitizers in photovoltaic devices) and energy storage (batteries, fuel cells, and supercapacitors). The vast coverage of advancements in environmental applications of GR-based materials for photocatalytic degradation of organic pollutants, gas sensing, and removal of heavy-metal ions is presented. Additionally, the use of graphene composites in the biosensing field is discussed. We conclude the review with remarks on the challenges, prospects, and further development of GR-based materials in the exciting fields of energy, environment, and bioscience.

Heterobimetallic copper–barium complexes for deposition of composite oxide thin films

Heterobimetallic molecular precursors [Ba(dmap)4Cu4(OAc)6·THF] (1) and [Ba(dmap)4Cu4(TFA)6·THF] (2) [dmap = N,N-dimethylaminopropanolate, OAc = acetate and TFA = trifluoroacetate] for the deposition of barium–copper composite oxide thin films, were prepared by the interaction of Ba(dmap)2 with Cu(OAc)2 for 1 and Cu(TFA)2 for 2, in THF. Both heterobimetallic complexes were characterized by melting point, elemental analysis, FT-IR spectroscopy, mass spectrometry and single crystal X-ray diffraction. X-Ray crystallography shows that complex 1 crystallizes in the orthorhombic space groupP212121 with the cell dimensions a = 11.2621(11) A, b = 18.2768(17) A and c = 24.541(2) A, while complex 2 crystallizes in the monoclinic space groupC2/c with a = 23.9288(14) A, b = 19.8564(12) A, c = 25.5925(15) A and β = 112.4390(10)°. Thermal gravimetric analysis shows that both complexes 1 and 2 undergo controlled thermal decomposition at 450 °C and 400 °C, respectively, to give mixed metal oxide composite thin films. Scanning electron microscopy (SEM), energy dispersive X-ray (EDX) and X-ray powder diffraction (XRD) analyses of the thin films suggest the formation of good quality crystalline thin films of BaCuO2–CuO composites from both 1 and 2, with average grain sizes of 105 to 175 nm and 110 to 205 nm, respectively.

Hexanuclear copper–nickel and copper–cobalt complexes for thin film deposition of ceramic oxide composites

Heterobimetallic molecular Cu–Ni and Cu–Co complexes [Cu2Ni4(acac)2(dmae)2(dmaeH)2(OH)(TFA)6] (1) and [Cu2Co4(acac)2(dmae)2(dmaeH)2(OH)(TFA)6] (2) [dmae = N,N-dimethylaminoethanol, TFA = trifluoroacetic acid and acac = 2,4-pentanedionate] were prepared and tested as precursors for the deposition of mixed metal oxide composite thin films. The complexes were synthesized by reaction of the tetrameric copper(II) complex [Cu(dmae)(TFA)]4 with M(acac)2·xH2O [M = Ni, x = 2; Co, x = 1] in THF and were characterized by melting point, elemental analysis, FT-IR spectroscopy, TG/DTG and single-crystal X-ray diffraction. The complexes are isomorphous and crystallize in the triclinic centrosymmetric space group P. Aerosol assisted chemical vapour deposition (AACVD) studies carried out on (1) and (2) showed that they are promising precursors for the deposition of thin films of crystalline CuO–NiO and Cu2O–CoO composites, respectively. The size, shape, surface morphology, microstructure, chemical composition and crystallinity of the resulting mixed-metal oxide composite thin films were analysed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The analysis proved that the thin films are crystalline, uniform, smooth and tightly adherent to the substrates.

Fluoro Substituted Monomeric and Uni-Dimensional Polymeric Organotin(IV) Esters of (E)-4-oxo-4-((3-trifluoromethyl)phenyl)amino)but-2-enoic acid; Synthesis, Characterization and Their In vitro Inhibitory Studies

Inhibition effects of novel organotin(IV) esters of (E)-4-oxo-4-((3-trifluoromethyl)phenyl)amino)but-2-enoic acid have been studied against bacterial, fungal, tumoral and insecticidal strains. The complexes have shown potency against all these strains and is attributed to the multiple interactive sites of the ligand that not only change the environment around tin but also can make interactions with DNA. The synthesized complexes were characterized by physical, spectral, analytical and multinuclear nmr (1H, 13C, 119Sn) data. The X-ray structure analysis of the complex is reported.

Unbiased Spontaneous Solar Fuel Production using Stable LaFeO3 Photoelectrode

Photoelectrochemical (PEC) water splitting to produce solar fuel (hydrogen) has long been considered as the Holy Grail to a carbon-free hydrogen economy. The PEC concept to produce solar fuel is to emulate the natural photosynthesis using man made materials. The bottle-neck in realising the concept practically has been the difficulty in identifying stable low-cost semiconductors that meet the thermodynamic and kinetic criteria for photoelectrolysis. We have fabricated a novel p-type LaFeO3 photoelectrode using an inexpensive and scalable spray pyrolysis method. Our nanostructured LaFeO3 photoelectrode results in spontaneous hydrogen evolution from water without any external bias applied. Moreover, the photoelectrode has a faradaic efficiency of 30% and showed excellent stability over 21 hours. From optical and impedance data, the constructed band diagram showed that LaFeO3 can straddle the water redox potential with the conduction band at −1.11 V above the reduction potential of hydrogen. We have fabricated a low cost LaFeO3 photoelectrode that can spontaneously produce hydrogen from water using sunlight, making it a strong future candidate for renewable hydrogen generation.

Temperature-controlled Deposition of Copper(I) Oxide and Metallic Copper Nanostructures from Single-source Molecular Precursor

A simple method of depositing morphology- and phase-tailored thin films of copper(i) oxide and metallic copper from [Cu(dmae)(TFA)]4·CH2Cl2 (1), where dmae is N,N-dimethylaminoethanolato and TFA is trifluoroacetato, on glass substrates by aerosol-assisted chemical vapour deposition is demonstrated. The tetrameric precursor 1 was synthesized and its structure was determined by single-crystal X-ray crystallography. Precursor 1 was applied for the deposition of nanostructured thin films of copper(i) oxide and copper nanowires at 250 and 375°C respectively. The deposited thin films were characterized by powder X-ray diffraction, field emission scanning electron microscopy, energy-dispersive X-ray diffraction, and ultraviolet–visible spectroscopy. The results indicate that the phase and morphology of the deposited material are strongly dependent on deposition temperature. UV-vis studies reveal that copper(i) oxide films with a band gap of 2.48 eV may find possible applications in tandem photoelectrochemical devices as light-absorbing material.