scispace - formally typeset
Search or ask a question
Author

Asif Ali Tahir

Bio: Asif Ali Tahir is an academic researcher from University of Exeter. The author has contributed to research in topics: Thin film & Materials science. The author has an hindex of 34, co-authored 109 publications receiving 4296 citations. Previous affiliations of Asif Ali Tahir include University of Maiduguri & University of Liverpool.


Papers
More filters
Journal ArticleDOI
TL;DR: A waterstable porous porphyrin MOF with a BET surface area of 1400 m g 1 which performs visible-lightdriven hydrogen generation from water and reveals that no aluminium is coordinated within the porphyrsin ring, consistent with the need to use reactive trialkylaluminium reagents for metalation of the p Morphyrin in solution.
Abstract: 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.

614 citations

Journal ArticleDOI
TL;DR: In this article, a thin film photoelectrodes were fabricated by aerosol-assisted chemical vapor deposition (AACVD) using a new hexanuclear iron precursor [Fe6(PhCOO)10(acac)2(O)2 (OH)2]·3C7H8 (1) (where PhCOO = benzoate and acac = 2,4-pentanedionate).
Abstract: α-Fe2O3 thin film photoelectrodes were fabricated by aerosol-assisted chemical vapor deposition (AACVD) using a new hexanuclear iron precursor [Fe6(PhCOO)10(acac)2(O)2(OH)2]·3C7H8 (1) (where PhCOO = benzoate and acac = 2,4-pentanedionate). The precursor (1) designed for AACVD has a low decomposition temperature and sufficient solubility in organic solvents and was synthesized by simple chemical techniques in high yield. It was characterized by melting point, FT-IR, X-ray crystallography, and thermogravimetry (TGA). The TGA analysis proved that complex (1) undergoes facile thermal decomposition at 475 °C to give iron oxide residue. In-house designed AACVD equipment was used to deposit highly crystalline thin films of α-Fe2O3 on fluorine-doped SnO2 coated glass substrates at 475 °C in a single step. The material properties were characterized by XRD, XPS, and Raman spectroscopy, and the results confirmed that films were highly crystalline α-Fe2O3 and free from other phases of iron oxide. Further analysis of ...

321 citations

Journal ArticleDOI
TL;DR: In this paper, the performance of g-C3N4/BiVO4 was investigated in Z-scheme configuration and the experimental observations were counterchecked with density functional theory simulations.
Abstract: BiVO4 is a considerably promising semiconductor for photoelectrochemical water splitting due to its stability, low cost and moderate band gap. In this research, g-C3N4 was proposed in Z-scheme configuration which boosted the performance of BiVO4 up to four times. The experimental observations were counterchecked with Density Functional Theory (DFT) simulations. A TiO2/BiVO4 heterojunction was developed and its performance was compared with that of g-C3N4/BiVO4. The photocurrent for g-C3N4/BiVO4 was 0.42 mAcm−2 at 1.23 V vs. RHE which was the highest among g-C3N4 based Z-scheme heterojunction devices. Lower charge transfer resistance, higher light absorption and more oxygen vacancy sites were observed for the g-C3N4 based heterojunction. The simulated results attested that g-C3N4 and BiVO4 formed a van der Waals type heterojunction, where an internal electric field facilitated the separation of electron/hole pair at g-C3N4/BiVO4 interface which further restrained the carrier recombination. Both the valence and conduction band edge positions of g-C3N4 and BiVO4 changed with the Fermi energy level. The resulted heterojunction had small effective masses of electrons (0.01 me) and holes (0.10 me) with ideal band edge positions where both CBM and VBM were well above and below the redox potential of water.

275 citations

Journal ArticleDOI
TL;DR: 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), indicating the presence of a kinetic bottleneck in the overall process.
Abstract: 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.

261 citations

Journal ArticleDOI
TL;DR: In this article, thin films were deposited from solutions of either chloroform, dichloromethane, or a 1:1 mixture of chloromethanes and toluene at temperature between 350 to 450 °C and characterized by X-ray diffraction (XRD), UV−vis spectroscopy, field emission gun scanning electron microscopy (FEGSEM), and energy dispersive Xray (EDX) analysis.
Abstract: Bi2S3 nanotubes and nanoparticle in the form of thin films were deposited on fluorine doped SnO2 (FTO) coated conducting glass substrates by Aerosol Assisted Chemical Vapor Deposition (AACVD) using tris-(N,N-diethyldithiocarbamato)bismuth(III), [Bi(S2CN(C2H5)2)3]2 (1) as a precursor. Thin films were deposited from solutions of (1) in either chloroform, dichloromethane, or a 1:1 mixture of chloroform and toluene at temperature between 350 to 450 °C and characterized by X-ray diffraction (XRD), UV−vis spectroscopy, field emission gun scanning electron microscopy (FEGSEM), and energy dispersive X-ray (EDX) analysis. FEGSEM images of films deposited from chloroform or dichloromethane exhibit well-defined and evenly distributed nanotubes with an average internal diameter of 40 nm. Films deposited from chloroform/toluene, on the other hand, have compact nanostuctured morphology. Bandgaps of 1.85 and 1.8 eV were estimated for nanotubes and nanoparticles, respectively, by extrapolating the linear part of the Tauc...

205 citations


Cited by
More filters
Journal ArticleDOI
TL;DR: This paper presents a meta-analyses of the chiral stationary phase transition of Na6(CO3)(SO4)2, Na2SO4, and Na2CO3 of the Na2O/Na2O 2 mixture at the stationary phase and shows clear patterns in the response of these two materials to each other.
Abstract: Jenny Schneider,*,† Masaya Matsuoka,‡ Masato Takeuchi,‡ Jinlong Zhang, Yu Horiuchi,‡ Masakazu Anpo,‡ and Detlef W. Bahnemann*,† †Institut fur Technische Chemie, Leibniz Universitaẗ Hannover, Callinstrasse 3, D-30167 Hannover, Germany ‡Faculty of Engineering, Osaka Prefecture University, 1 Gakuen-cho, Sakai Osaka 599-8531, Japan Key Lab for Advanced Materials and Institute of Fine Chemicals, East China University of Science and Technology, Shanghai 200237, China

4,353 citations

Journal ArticleDOI
TL;DR: This review discusses various nanomaterials that have been explored to mimic different kinds of enzymes and covers their kinetics, mechanisms and applications in numerous fields, from biosensing and immunoassays, to stem cell growth and pollutant removal.
Abstract: Over the past few decades, researchers have established artificial enzymes as highly stable and low-cost alternatives to natural enzymes in a wide range of applications. A variety of materials including cyclodextrins, metal complexes, porphyrins, polymers, dendrimers and biomolecules have been extensively explored to mimic the structures and functions of naturally occurring enzymes. Recently, some nanomaterials have been found to exhibit unexpected enzyme-like activities, and great advances have been made in this area due to the tremendous progress in nano-research and the unique characteristics of nanomaterials. To highlight the progress in the field of nanomaterial-based artificial enzymes (nanozymes), this review discusses various nanomaterials that have been explored to mimic different kinds of enzymes. We cover their kinetics, mechanisms and applications in numerous fields, from biosensing and immunoassays, to stem cell growth and pollutant removal. We also summarize several approaches to tune the activities of nanozymes. Finally, we make comparisons between nanozymes and other catalytic materials (other artificial enzymes, natural enzymes, organic catalysts and nanomaterial-based catalysts) and address the current challenges and future directions (302 references).

2,951 citations

Journal ArticleDOI
28 Feb 2014-Science
TL;DR: It is demonstrated that a nanoporous morphology effectively suppresses bulk carrier recombination without additional doping, manifesting an electron-hole separation yield of 0.90 at 1.23 volts (V) versus the reversible hydrogen electrode (RHE).
Abstract: Bismuth vanadate (BiVO4) has a band structure that is well-suited for potential use as a photoanode in solar water splitting, but it suffers from poor electron-hole separation. Here, we demonstrate that a nanoporous morphology (specific surface area of 31.8 square meters per gram) effectively suppresses bulk carrier recombination without additional doping, manifesting an electron-hole separation yield of 0.90 at 1.23 volts (V) versus the reversible hydrogen electrode (RHE). We enhanced the propensity for surface-reaching holes to instigate water-splitting chemistry by serially applying two different oxygen evolution catalyst (OEC) layers, FeOOH and NiOOH, which reduces interface recombination at the BiVO4/OEC junction while creating a more favorable Helmholtz layer potential drop at the OEC/electrolyte junction. The resulting BiVO4/FeOOH/NiOOH photoanode achieves a photocurrent density of 2.73 milliamps per square centimenter at a potential as low as 0.6 V versus RHE.

2,361 citations