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Nisar, Jawad
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Publications (10 of 20) Show all publications
Wang, B., Nisar, J., Almeida, C. G., Santos Mascarenhas, A. J., Silva, L. A., Francis David, D. G., . . . da Silva, A. F. (2014). Optical and electronic properties of nanosized BiTaO4 and BiNbO4 photocatalysts: Experiment and theory. Physica status solidi. B, Basic research, 251(5), 1034-1039
Open this publication in new window or tab >>Optical and electronic properties of nanosized BiTaO4 and BiNbO4 photocatalysts: Experiment and theory
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2014 (English)In: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 251, no 5, p. 1034-1039Article in journal (Refereed) Published
Abstract [en]

Nanosized BiTaO4 and BiNbO4 were prepared by the citrate method. The electronic and optical properties of BiTaO4 and BiNbO4 have been investigated by means of photo-acoustic spectroscopy (PAS), X-ray photo-electron spectroscopy (XPS), and first-principles calculations based on density functional theory. The measured valence band (from XPS) of both materials agreed well with the theoretical findings. It was also found that the calculated optical properties such as dynamical dielectric function and optical absorption spectra are in good agreement with the experimental findings. According to the absorption spectra, the absorption edges of BiNbO4 and BiTaO4 are located at 370 and 330nm, respectively. Both phases have the ability to harvest UV light and relatively high surface area to volume ratio and can be used as UV/visible light-driven photocatalysts.

Keywords
electronic structure, niobates, optical absorption, photocatalysis, tantalates, water splitting
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-227876 (URN)10.1002/pssb.201350265 (DOI)000335983000017 ()
Available from: 2014-07-02 Created: 2014-07-01 Last updated: 2017-12-05Bibliographically approved
Liu, P., Nisar, J., Sa, B., Pathak, B. & Ahuja, R. (2013). Anion-Anion Mediated Coupling in Layered Perovskite La2Ti2O7 for Visible Light Photocatalysis. The Journal of Physical Chemistry C, 117(27), 13845-13852
Open this publication in new window or tab >>Anion-Anion Mediated Coupling in Layered Perovskite La2Ti2O7 for Visible Light Photocatalysis
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2013 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, no 27, p. 13845-13852Article in journal (Refereed) Published
Abstract [en]

Anionic-anionic (N-N, P-P, N-P, and C-S) mediated coupling can be introduced in the layered perovskite La2Ti2O7 structure for visible light photocatalysis. The anionic-anionic codoped La2Ti2O7 systems lower the band gap much more than their respective monodoping systems. Moreover, the electronic band positions of the doped systems with respect to the water oxidation/reduction potentials show that codoped (N-N, N-P, and C-S) systems are more promising candidates for visible-light photocatalysis. The calculated defect formation energy shows that the codoped systems are more stable than their respective monodoped systems.

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-207648 (URN)10.1021/jp402971b (DOI)000321883600010 ()
Available from: 2013-09-17 Created: 2013-09-17 Last updated: 2017-12-06Bibliographically approved
Wang, B., Kanhere, P. D., Chen, Z., Nisar, J., Pathak, B. & Ahuja, R. (2013). Anion-Doped NaTaO3 for Visible Light Photocatalysis. The Journal of Physical Chemistry C, 117(44), 22518-22524
Open this publication in new window or tab >>Anion-Doped NaTaO3 for Visible Light Photocatalysis
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2013 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, no 44, p. 22518-22524Article in journal (Refereed) Published
Abstract [en]

In this paper, we have employed DFT and HSE06 methods to study the doping effects on the NaTaO3 photocatalyst. N, S, C, and P monodoping and N-N, C-S, P-P, and N-P codoping have been studied. The redopants' formation energies have been calculated, and we find S monodoping is energetically more favorable than any other elemental doping. The mechanism of anion doping on the electronic properties of NaTaO3 is discussed. We find the band gap reduces significantly if we dope with anionic elements whose p orbital energy is higher than the O 2p orbitals. N and S can shift the valence band edge upward without losing the ability to split water into H-2 and O-2. Double-hole-mediated codoping can decrease the band gap significantly. On the basis of our calculations, codoping with N-N, C-S, and P-P could absorb visible light. However, they can only decompose water into H-2 when the valence band edge is above the water oxidation level.

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-212868 (URN)10.1021/jp407025r (DOI)000326845400007 ()
Available from: 2013-12-17 Created: 2013-12-16 Last updated: 2017-12-06Bibliographically approved
Liu, P., Nisar, J., Pathak, B. & Ahuja, R. (2013). Cationic-anionic mediated charge compensation on La2Ti2O7 for visible light photocatalysis. Physical Chemistry, Chemical Physics - PCCP, 15(40), 17150-17157
Open this publication in new window or tab >>Cationic-anionic mediated charge compensation on La2Ti2O7 for visible light photocatalysis
2013 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 15, no 40, p. 17150-17157Article in journal (Refereed) Published
Abstract [en]

The cationic-anionic mediated charge compensation effect was studied in the layered perovskite La2Ti2O7 for the visible light photocatalysis. Our screened hybrid density functional study shows that the electronic structure of La2Ti2O7 can be tuned by the cationic (V, Nb, Ta)/anionic (N) mono-and co-doping. Such mono-doping creates impurity states in the band gap which helps the electron-hole recombination. But if the charge compensation is made by the cationic-anionic mediated co-doping then such impurity states can be removed and can be a promising strategy for visible light photocatalysis. The absolute band edge position of the doped La2Ti2O7 has been aligned with respect to the water oxidation/reduction potential. The calculated defect formation energy shows the stability of the co-doping system is improved due to the coulomb interactions and charge compensations effect.

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-210763 (URN)10.1039/c3cp52269e (DOI)000325398500017 ()
Available from: 2013-11-14 Created: 2013-11-14 Last updated: 2017-12-06Bibliographically approved
Yilmaz, S., Nisar, J., Atasoy, Y., McGlynn, E., Ahuja, R., Parlak, M. & Bacaksiz, E. (2013). Defect-induced room temperature ferromagnetism in B-doped ZnO. Ceramics International, 39(4), 4609-4617
Open this publication in new window or tab >>Defect-induced room temperature ferromagnetism in B-doped ZnO
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2013 (English)In: Ceramics International, ISSN 0272-8842, E-ISSN 1873-3956, Vol. 39, no 4, p. 4609-4617Article in journal (Refereed) Published
Abstract [en]

ZnO microrods were grown on glass substrates by the spray pyrolysis method and boron was doped into the ZnO microrods by diffusion. X-ray diffraction results confirmed that the incorporation of B leads to a slight reduction in the deposit texture. Scanning electron microscopy measurements showed that the morphology of the ZnO samples changed from a microrod to nanocrystalline structure with B-doping. Photoluminescence data indicate that B-doping leads to a relative increase of the unstructured green band intensity. Magnetic measurements revealed that B-doped ZnO samples exhibited room temperature ferromagnetism related to defects, in agreement with first principles theoretical calculations. 

Keywords
ZnO:B, Photoluminescence, Ferromagnetism, First-principle calculation
National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-201235 (URN)10.1016/j.ceramint.2012.11.060 (DOI)000318129100144 ()
Available from: 2013-06-10 Created: 2013-06-10 Last updated: 2017-12-06Bibliographically approved
Jiang, X., Nisar, J., Pathak, B., Zhao, J. & Ahuja, R. (2013). Graphene oxide as a chemically tunable 2-D material for visible-light photocatalyst applications. Journal of Catalysis, 299, 204-209
Open this publication in new window or tab >>Graphene oxide as a chemically tunable 2-D material for visible-light photocatalyst applications
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2013 (English)In: Journal of Catalysis, ISSN 0021-9517, E-ISSN 1090-2694, Vol. 299, p. 204-209Article in journal (Refereed) Published
Abstract [en]

To elucidate the usage of graphene oxide (GO) as a photocatalysis material, we have studied the effect of epoxy and hydroxyl functionalization on the electronic structure, work function, CBM/VBM position, and optical absorption spectra of GO using density functional theory calculations. By varying the coverage and relative ratio of the surface epoxy (-O-) and hydroxyl (-OH) groups, both band gap and work function of the GO materials can be tuned to meet the requirement of photocatalyst. Interestingly, the electronic structures of GO materials with 40-50% (33-67%) coverage and OH:O ratio of 2:1(1:1) are suitable for both reduction and oxidation reactions for water splitting. Among of these systems, the GO composition with 50% coverage and OH:O (1:1) ratio can be very promising materials for visible-light-driven photocatalyst. Our results not only explain the recent experimental observations about 2-D graphene oxide as promising visible-light-driven photocatalyst materials but can also be very helpful in designing the optimal composition for higher performance.

Keywords
Ab initio calculation, Photolysis, Energy conversion, Renewable resource, Water splitting
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-198930 (URN)10.1016/j.jcat.2012.12.022 (DOI)000316774900021 ()
Available from: 2013-04-29 Created: 2013-04-29 Last updated: 2017-12-06Bibliographically approved
Liu, P., Nisar, J., Ahuja, R. & Pathak, B. (2013). Layered Perovskite Sr2Ta2O7 for Visible Light Photocatalysis: A First Principles Study. The Journal of Physical Chemistry C, 117(10), 5043-5050
Open this publication in new window or tab >>Layered Perovskite Sr2Ta2O7 for Visible Light Photocatalysis: A First Principles Study
2013 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, no 10, p. 5043-5050Article in journal (Refereed) Published
Abstract [en]

The layered perovskite Sr2Ta2O7 has been investigated for efficient visible light photocatalysis using the first principles study. The electronic structure of Sr2Ta2O7 is tuned by the anionic (N)/cationic (Mo, W) mono- and co-doping. Such doping creates impurity states in the band gap and therefore reduces the band gap significantly. The absolute band edge position of the doped Sr2Ta2O7 with respect to the water oxidation/reduction potential depends a lot on the p/d-orbital's energies of anionic/cationic dopants, respectively. The stability of the co-doped system is governed by the Coulomb interactions and charge compensation effects.

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-198384 (URN)10.1021/jp310945e (DOI)000316308400018 ()
Available from: 2013-04-15 Created: 2013-04-15 Last updated: 2017-12-06Bibliographically approved
Dera, P., Nisar, J., Ahuja, R., Tkachev, S. & Prakapenka, V. B. (2013). New type of possible high-pressure polymorphism in NiAs minerals in planetary cores. Physics and chemistry of minerals, 40(2), 183-193
Open this publication in new window or tab >>New type of possible high-pressure polymorphism in NiAs minerals in planetary cores
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2013 (English)In: Physics and chemistry of minerals, ISSN 0342-1791, E-ISSN 1432-2021, Vol. 40, no 2, p. 183-193Article in journal (Refereed) Published
Abstract [en]

The nickel arsenide (B8(1)) and related crystal structures are among the most important crystallographic arrangements assumed by Fe and Ni compounds with light elements such as Si, O, S, and P, expected to be present in planetary cores. Despite the simple structure, some of these materials like troilite (FeS) exhibit complex phase diagrams and rich polymorphism, involving significant changes in interatomic bonding and physical properties. NiP (oP16) represents one of the two principal structure distortions found in the nickel arsenide family and is characterized by P-P bonding interactions that lead to the formation of P-2 dimers. In the current study, the single-crystal synchrotron X-ray diffraction technique, aided by first principles density functional theory (DFT) calculations, has been applied to examine the compression behavior of NiP up to 30 GPa. Two new reversible displacive phase transitions leading to orthorhombic high-pressure phases with Pearson symbols oP40 and oC24 were found to occur at approximately 8.5 and 25.0 GPa, respectively. The oP40 phase has the primitive Pnma space group with unit cell a = 4.7729(5) , b = 16.6619(12) , and c = 5.8071(8) at 16.3(1) GPa and is a superstructure of the ambient oP16 phase with multiplicity of 2.5. The oC24 phase has the acentric Cmc2(1) space group with unit cell a = 9.695(6) , b = 5.7101(9) , and c = 4.7438(6) at 28.5(1) GPa and is a superstructure of the oP16 phase with multiplicity of 1.5. DFT calculations fully support the observed sequence of phase transitions. The two new phases constitute logical next stages of P sublattice polymerization, in which the dilution of the P-3 units, introduced in the first high-pressure phase, decreases, leading to compositions of Ni-20(P-3)(4)(P-2)(4) and Ni-12(P-3)(4), and provide important clues to understanding of phase relations and transformation pathways in the NiAs family.

Keywords
Planetary cores, Nickel arsenide structure, NiP, High pressure, Phase transitions, Polymorphism, Bonding
National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-196035 (URN)10.1007/s00269-012-0560-6 (DOI)000314274200009 ()
Available from: 2013-03-04 Created: 2013-03-04 Last updated: 2017-12-06Bibliographically approved
Nisar, J., Topalian, Z., De Sarkar, A., Österlund, L. & Ahuja, R. (2013). TiO2‑Based Gas Sensor: A Possible Application to SO2. ACS Applied Materials and Interfaces, 5(17), 8516-8522
Open this publication in new window or tab >>TiO2‑Based Gas Sensor: A Possible Application to SO2
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2013 (English)In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 5, no 17, p. 8516-8522Article in journal (Refereed) Published
Abstract [en]

Fixation of SO2 molecules on anatase TiO2 surfaceswith defects have been investigated by first-principles densityfunctional theory (DFT) calculations and in situ Fourier transforminfrared (FTIR) surface spectroscopy on porous TiO2 films. Intrinsicoxygen-vacancy defects, which are formed on TiO2(001) andTiO2(101) surfaces by ultraviolet (UV) light irradiation and atelevated temperatures, are found to be most effective in anchoringthe SO2 gas molecules to the TiO2 surfaces. Both TiO2(101) andTiO2(001) surfaces with oxygen vacancies are found to exhibit higherSO2 adsorption energies in the DFT calculations. The adsorptionmechanism of SO2 is explained on the basis of electronic structure,charge transfer between the molecule and the surface, and the oxidation state of the adsorbed molecule. The theoretical findingsare corroborated by FTIR experiments. Moreover, the (001) surface with oxygen vacancies is found to bind SO2 gas moleculesmore strongly, as compared to the (101) surface. Higher concentration of oxygen vacancies on the TiO2 surfaces is found tosignificantly increase the adsorption energy. The results shed new insight into the sensing properties of TiO2-based gas sensors

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2013
Keywords
SO2 fixation, anatase TiO2 surfaces, gas sensors
National Category
Natural Sciences Engineering and Technology
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics; Engineering Science with specialization in Solid State Physics
Identifiers
urn:nbn:se:uu:diva-212075 (URN)10.1021/am4018835 (DOI)000330017100036 ()23915321 (PubMedID)
Funder
EU, FP7, Seventh Framework ProgrammeSwedish Research CouncilThe Wenner-Gren FoundationSwedish Research Council FormasSwedish Energy Agency
Available from: 2013-12-05 Created: 2013-12-05 Last updated: 2017-12-06Bibliographically approved
Nisar, J. (2012). Atomic Scale Design of Clean Energy Materials: Efficient Solar Energy Conversion and Gas Sensing. (Doctoral dissertation). Uppsala: Acta Universitatis Upsaliensis
Open this publication in new window or tab >>Atomic Scale Design of Clean Energy Materials: Efficient Solar Energy Conversion and Gas Sensing
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The focus of this doctoral thesis is the atomic level design of photocatalysts and gas sensing materials. The band gap narrowing in the metal oxides for the visible-light driven photocatalyst as well as the interaction of water and gas molecules on the reactive surfaces of metal oxides and the electronic structure of kaolinite has been studied by the state-of-art calculations. Present thesis is organized into three sections.

The first section discusses the possibility of converting UV active photocatalysts (such as Sr2Nb2O7, NaTaO3, SrTiO3, BiTaO4 and BiNbO4) into a visible active photocatalysts by their band gap engineering. Foreign elements doping in wide band gap semiconductors is an important strategy to reduce their band gap. Therefore, we have investigated the importance of mono- and co-anionic/cationic doping on UV active photocatalysts. The semiconductor's band edge position is calculated with respect to the water oxidation/reduction potential for various doping. Moreover, the tuning of valence and conduction band edge position is discussed on the basis of dopant's p/d orbital energy.

In the second section of thesis the energetic, electronic and optical properties of TiO2, NiO and β-Si3N4 have been discussed to describe the adsorption mechanism of gas molecules at the surfaces. The dissociation of water into H+ or OH- occurs on the O-vacancy site of the (001)-surface of rutile TiO2 nanowire, which is due to the charge transfer from Ti atom to water molecule. The dissociation of water into OH- and imino (NH) groups is also observed on the β-Si3N4 (0001)-surface due to the dangling bonds of the lower coordinated N and Si surface atoms. Fixation of the SO2 molecules on the anatase TiO2 surfaces with O-deficiency have been investigated by Density Functional Theory (DFT) simulation and Fourier Transform Infrared (FTIR) spectroscopy. DFT calculations have been employed to explore the gas-sensing mechanism of NiO (100)-surface on the basis of energetic and electronic properties.

In the final section the focus is to describe the optical band gap of pristine kaolinite using the hybrid functional method and GW approach. Different possible intrinsic defects in the kaolinite (001) basal surface have been studied and their effect on the electronic structure has been explained. The detailed electronic structure of natural kaolinite has been determined by the combined efforts of first principles calculations and Near Edge X-ray Absorption Fine Structure (NEXAFS).

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2012. p. 68
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 958
Keywords
Photocatalysts, Band gap narrowing, Water dissociation, Density functional theory, Gas sensing, Kaolinite
National Category
Condensed Matter Physics Nano Technology Atom and Molecular Physics and Optics
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-179372 (URN)978-91-554-8436-1 (ISBN)
Public defence
2012-09-28, Häggsalen, Ångström Laboratory, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2012-09-06 Created: 2012-08-14 Last updated: 2013-01-22
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