Papers by Ammar Bin Yousaf
Emergent materials, Mar 11, 2024
Green hydrogen production using solar water splitting and solving water pollution issues are intr... more Green hydrogen production using solar water splitting and solving water pollution issues are intricately intertwined global goals which are hindered by the scarcity of highly active photocatalytic materials. Herein, we have presented a simple strategy to couple two semiconductors (Cu 2 O and ZnCdS) to form a type-I heterojunction with high visible light response. The as-synthesized heterojunction was well characterized by the battery techniques, such as TEM, HAADF-STEM elemental mapping, XRD and XPS. The visible light response was higher for composite than individual components, as was also supported by UV-vis DRS. The Cu 2 O-ZnCdS composite showed a higher visible light-driven photocatalytic H 2 production rate (78.5 µmol g-1 h-1). The catalyst was also active for photocatalytic degradation of a model dye-methylene blue (MB)-with a degradation rate constant of 0.079 min −1. The enhanced performance of the Cu 2 O-loaded ZnCdS catalysts can be ascribed to both factors, such as enhancement of the visible light absorption and the growth of Cu 2 O-ZnCdS heterojunction. The heterojunction formation facilitates efficient charge separation with smaller charge resistance, as evidenced by transient photocurrent response and electrochemical impedance spectroscopy (EIS) studies. This study strongly indicates that the photocatalytic reactions with this catalyst material are kinetically favoured by coupling the two semiconductors.
Oxygen-Deficient TiO<sub>2 – <i>x</i></sub>/Methylene Blue Colloids: Highly Efficient Photoreversible Intelligent Ink
Langmuir, Aug 24, 2016
Oxygen-sensitive photoreversible intelligent ink capable of assessment with the human eye is an o... more Oxygen-sensitive photoreversible intelligent ink capable of assessment with the human eye is an ongoing demand in the modern era. In the food industry, redox-dye-based oxygen indicator films have been proposed, but the leaching of dyes from the film that contaminates the food is one unsolved issue. On the other hand, it is also highly desirable to develop rewritable paper that significantly reduces the pressure on modern society for the production and consumption of paper. Herein, we have developed an oxygen-deficient TiO2 - x/methylene blue (MB) sol without relying on external sacrificial electron donors (SEDs) for photoreversible color switching. Oxygen vacancies in TiO2 - x can work as electron donor to favor the adsorption of the substrate and improve the charge separation that is required for the redox-based color-switching system. The problems of rewriteable paper and food packaging are addressed as two sides of a single coin in this article. We have used hydroxyethyl cellulose (HEC) for rewritable paper that can significantly delay the oxidation of leuco-MB (LMB) through hydrogen bonding and retain the printed information for a long time. The dye leaching from oxygen indicator films is also significantly reduced (only 1.54%) by using furcelleran as the coating polymer that is extracted from edible red seaweed.
Single-phase Mn-Fe interfacial oxides nanocomposites encored on carbon nitride sheets exhibited enhanced performance for electrocatalytic oxygen reduction reactions
Journal of Electroanalytical Chemistry, Dec 1, 2022
Nanostructural synergism as Mn N C channels in manganese (IV) oxide and fluffy g-C3N4 layered composite with exceptional catalytic capabilities
Journal of Colloid and Interface Science, Mar 1, 2022
The avenues of catalysis and material science are always accepted and it is hoped that a state-of... more The avenues of catalysis and material science are always accepted and it is hoped that a state-of-the-art catalyst with exceptional intrinsic redox characteristics would be produced. This study focused on developing a multi-featured catalyst of high economical and commercial standards to meet the multi-directional applications of environmental and energy demands. Manganese (IV) oxide nanosheets made of fluffy-sheet-like g-C3N4 material were successfully synthesized by pyrolysis method. The electron-rich g-C3N4 network and semiconducting metallic oxides of MnO2 nanosheets generated high electron density interfaces within the intra-composite structure. The input of active interfaces along with strong metal-to-support interactions achieved between two parallel nanosheets in MnO2/g-C3N4 catalyst intrinsically boosted up its electrochemical and optical characteristics for it to be used in multi-catalytic fields. Successful trails of catalysts' performance have been made in three major catalytic fields with enhanced activities such as heterogeneous catalysis (reduction of nitrobenzene with rate constant of "K = 0.734 min-1" and hydrogenation of styrene with "100% conversion" efficiency, including negligible change in five consecutive cycles), photocatalysis (degradation of methylene blue dye model within 20 min with negligible change in five consecutive cycles) and electrocatalysis (oxygen reduction reactions having comparable "diffusion-limited-current density" behaviour with that of the commercial Pt/C catalyst). The enhanced performance of catalysts in transforming chemicals, degrading organic pollutant species and producing sustainable energy resources from air oxygen can mitigate the challenges faced in environmental and energy crises, respectively.
Ultra-low Pt-decorated NiCu bimetallic alloys nanoparticles supported on reduced graphene oxide for electro-oxidation of methanol
MRS Communications, Jul 26, 2018
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Modulation of wettability, gradient and adhesion on self-assembled monolayer by counterion exchange and pH
Journal of Colloid and Interface Science, Feb 1, 2018
In this study, two quaternary ammonium salts derived from l-lipoic acid were applied for self-ass... more In this study, two quaternary ammonium salts derived from l-lipoic acid were applied for self-assembled monolayers formation on rough structured gold surface. The derivatives differ in functionality since one possesses simple quaternary ammonium group whereas the other one is carboxybetaine ester containing quaternary ammonium group with pH hydrolysable ester group as a pendant. The response of surface wettability to ion exchange between Cland perfluorooctanoate, kinetics and gradient wettability were examined by water contact angle measurement and confirmed by X-ray photoelectron spectroscopy. Furthermore, adhesion forces related to applied counterion on the entire surface and after hydrolysis were investigated by atomic force microscopy measurement at nanometer scales. A dramatic change in wettability upon counterion exchange from superhydrophilic for Clto very or superhydrophobic for perfluorooctanoate in a repeatable manner was observed for both derivatives. Kinetics of counterion exchanges revealed faster hydration of simple quaternary derivate. The wettability gradient could be designed from superhydrophobic to superhydrophilic either in a reversible manner by simple immersion of the modified surface in a counterion solution modulated by ionic strength or in an irreversible manner for carboxybetaine ester derivate by time-controlled hydrolysis to charge balanced carboxybetaine.
Journal of Electroanalytical Chemistry, Jun 1, 2017
Direct methanol fuel cells (DMFCs) proved to be promising alternative for renewable energy resour... more Direct methanol fuel cells (DMFCs) proved to be promising alternative for renewable energy resources. There are several factors involved for the hindrance of their commercialization. Herein, the alteration in catalyst's chemistry has been mainly focused to improve the performance of DMFCs. Mesoporous carbon supported bimetallic combinations of Pt with metallic oxides such as, Pt/CeO 2-MC, Pt/PrO 2-MC, Pt/NdO 2-MC, and Pt/SmO 2-MC were synthesized and tested as methanol electro-oxidation anode catalysts. These high-surface area anodes were synthesized by impregnation with Pt to form the desired methanol electro-oxidation catalysts. The as-prepared catalysts were characterized using XRD, BET surface area, and EDS. High surface areas of 684-778 m 2 /g were achieved for the CeO 2-MC, PrO 2-MC, NdO 2-MC, and SmO 2-MC, which enabled excellent dispersion of the Pt nanoparticles onto their surfaces. The Pt/CeO 2-MC catalyst showed the highest activity for methanol electro-oxidation, which is about 3.5% more than that of the commercial Pt-Ru/C (E-TEK) catalyst. In addition, the prepared catalysts showed significant stability and durability.
Ceramics International, Aug 1, 2018
In this work, multi-walled carbon nanotubes (MWCNTs), natural graphite (NG) and epoxy (EP) were u... more In this work, multi-walled carbon nanotubes (MWCNTs), natural graphite (NG) and epoxy (EP) were used to fabricate bipolar plates by the compression moulding technique. The mechanical and thermal behaviours of the asdeveloped material were investigated in terms of the effects of temperature on the morphological, mechanical and electrical properties. It was observed that the flexural strength of the MWCNT/NG/EP composite decreased with increasing temperature. The highest flexural strength (27.05 MPa) was recorded at 25 °C. When heated to 200 °C, the flexural strength of the material decreased by up to 2.40 MPa. The shore hardness of the MWCNT/NG/EP composite decreased with increasing temperature. The highest shore hardness (69.7 HD) was recorded at a temperature of 25 °C, while the lowest shore hardness (31.3 HD) was recorded at 200 °C. The temperaturedependent through-plane and in-plane electrical conductivities of the MWCNT/NG/EP composite were also investigated, although its contact, bulk and forward resistivity values were found to decrease. The experimental results revealed that the effect of temperature on the thermal and mechanical properties of the bipolar plate material was different at different temperatures. The synergistic electrical nature of the as-designed material may be ascribed to the phenomenon of electron transfer among the channels of natural graphite and MWCNTs. The enhanced mechanical behaviour was attributed to the presence of EP in the composite material.
Journal of The Electrochemical Society, 2019
Perfluoroctylsilane grafted Ti3C2X-based hydrogel liquid marble for controlled movement, self-assembly, light-induced release, and water evaporation system
Materials today communications, Jun 1, 2023
Electrochemical surface activation of commercial tungsten carbide for enhanced electrocatalytic hydrogen evolution and methanol oxidation reactions
Journal of Electroanalytical Chemistry, Aug 1, 2022
Engineering at Subatomic Scale: Achieving Selective Catalytic Pathways via Tuning of the Oxidation States in Functionalized Single‐Atom Quantum Catalysts
Small, Jul 27, 2022
Regulating the catalytic pathways of single‐atom sites in single atom catalysts (SACs) is an exci... more Regulating the catalytic pathways of single‐atom sites in single atom catalysts (SACs) is an exciting debate at the moment, which has redirected the research towards understanding and modifying the single‐atom catalytic sites through various strategies including altering the coordination environment of single atom for desirable outcomes as well as increasing their number. One useful aspect concerning the tunability of the catalytic pathways of SACs, which has been overlooked, is the oxidation state dynamics of the single atoms. In this study, iron single‐atoms (FeSA) with variable oxidation states, dependent on the precursors, are harnessed inside a nitrogen‐rich functionalized carbon quantum dots (CQDs) matrix via a facile one‐step and low‐temperature synthesis process. Dynamic electronic properties are imparted to the FeSAs by the simpler carbon dots matrix of CQDs in order to achieve the desired catalytic pathways of reactive oxygen species (ROS) generation in different environments, which are explored experimentally and theoretically for an in‐depth understanding of the redox chemistry that drives the alternative catalytic pathways in FeSA@CQDs. These alternative and oxidation state‐dependent catalytic pathways are employed for specific as well as cascade‐like activities simulating natural enzymes as well as biomarkers for the detection of cancerous cells.
Electrochimica Acta, Jul 1, 2017
Rotating disc electrodes are preferred devices to analyze electrochemical reactions in electroche... more Rotating disc electrodes are preferred devices to analyze electrochemical reactions in electrochemical cellsand various rotating machinery such as fans, turbines, and centrifugal pumps. This model contains system of fully coupled and highly non-linear equations. This manuscript outlines the steady state solution of rotating disc flow coupled through the fluid viscosity, to the mass-concentration field of chemical species and heat transfer of power-law fluid over rotating disk. Furthermore, a simple analytical expression (Padé approximation) of velocity component/ self-similar velocity profiles is derived from the short and long distance expression. Our analytical results for all distance are compared with previous small and long distance and numerical solutions (Runge-Kutta method), which are in satisfactory agreement.
A precious-metal-free Fe-intercalated carbon nitride porous-network with enhanced activity for the oxygen reduction reaction and methanol-tolerant oxygen reduction reaction
Sustainable Energy and Fuels, 2020
The economical cost of the catalyst material has remained a challenging task in traditional fuel ... more The economical cost of the catalyst material has remained a challenging task in traditional fuel cells (FCs) and in direct methanol fuel cells (DMFCs).
Langmuir, Aug 22, 2018
A procedure for the preparation of copolymers bearing sulfobetaine and carboxybetaine methacrylic... more A procedure for the preparation of copolymers bearing sulfobetaine and carboxybetaine methacrylic-based monomers by free-radical polymerisation is described and discussed. A combination of monomers affects the upper critical solution temperature (UCST) in water and in the presence of a simple NaCl electrolyte while retaining the zwitterionic character. In addition, hydrogel samples were prepared and showed tuneable water structure and mechanical properties. The total non-freezable water content decreases with the amount of carboxybetaine segment in the hydrogel feed and the compression moduli were in a range of 0.7-1.6 MPa. Responses to external conditions such as temperature and ion strength were investigated and a potential application such as modulated thermal detection is proposed. The presence of the carboxylate group in the carboxybetaine segment enables a small fluorescence probe and peptide bearing RDG motif to be attached to polymer and hydrogel samples, respectively. The hydrogel samples functionalized with the
International Journal of Electrochemical Science, Dec 1, 2015
Palladium Nanocubes based tri-metallic nanocomposite has been synthesized by electrochemical code... more Palladium Nanocubes based tri-metallic nanocomposite has been synthesized by electrochemical codeposition of PtRu on Pd-NCs. Structural and morphological characterizations of PtRu@Pd-NCs nanocomposite material were performed using X-ray diffraction, X-ray photoelectron spectroscopy analysis and transmission electron microscopy. The electrocatalytic activity for methanol oxidation reaction (MOR) is studied in HClO 4 aqueous solution. A significant improvement in the MOR activity is observed by increasing the atomic ratio of Pt in PtRu co-deposition on Pd-NCs up to an optimum value. Among all prepared catalysts, Pt 3 Ru@Pd-NCs has shown highest mass activity (ca.10500 mA mg-1 Pd and 75mA mg-1 Pt) and specific activity (ca. 7.85 mA cm-2) for MOR at lower peak potential ca. 0.70V. The as-developed catalyst has also shown lower onset potential with enhanced durability and stability towards MOR. The results can be attributed to the collective effect of PtRu nanoparticles and the enhanced electron transfer of Pd-NCs in tri-metallic nanocomposite material.
Chinese Journal of Chemical Physics, Oct 27, 2014
Methanol oxidation reaction (MOR) at Pt and Pt electrode surface deposited with various amounts o... more Methanol oxidation reaction (MOR) at Pt and Pt electrode surface deposited with various amounts of Ru (denoted as Pt x Ru y , nominal coverage y is 0.17, 0.27, and 0.44 ML) in 0.1 mol/L HClO 4 +0.5 mol/L MeOH has been studied under potentiostatic conditions by in situ FTIR spectroscopy in attenuated-total-reflection configuration and differential electrochemical mass spectrometry under controlled flow conditions. Results reveal that (i) CO is the only methanol-related adsorbate observed by IR spectroscopy at all the Pt and PtRu electrodes examined at potentials from 0.3 V to 0.6 V (vs. RHE); (ii) at Pt 0.56 Ru 0.44 , two IR bands, one from CO adsorbed at Ru islands and the other from CO L at Pt substrate are detected, while at other electrodes, only a single band for CO L adsorbed at Pt is observed; (iii) MOR activity decreases in the order of Pt 0.73 Ru 0.27 >Pt 0.56 Ru 0.44 >Pt 0.83 Ru 0.17 >Pt; (iv) at 0.5 V, MOR at Pt 0.73 Ru 0.27 reaches a current efficiency of 50% for CO 2 production, the turnover frequency from CH 3 OH to CO 2 is ca. 0.1 molecule/(site•sec). Suggestions for further improving of PtRu catalysts for MOR are provided.
Enhancement of visible light-driven hydrogen production over zinc cadmium sulfide nanoparticles anchored on BiVO4 nanorods
International Journal of Hydrogen Energy, Feb 1, 2022
Journal of materials chemistry. A, Materials for energy and sustainability, 2017
International Journal of Hydrogen Energy, Mar 1, 2018
Depletion of fossil fuels and associated environmental issues has drawn attention of researchers ... more Depletion of fossil fuels and associated environmental issues has drawn attention of researchers to renewable energy resources and photocatalytic hydrogen production is considered to be safe and applicable method to meet future energy demand. Herein, we have used a-Bi 2 O 3 nanorods for loading CZS (Cd 0.5 Zn 0.5 S) to form a heterostructure for photocatalytic H 2 production. The a-Bi 2 O 3 /CZS heterostructure was characterized through TEM, Elemental Mapping, XRD and XPS analysis. The a-Bi 2 O 3 /CZS heterostructure shows photocatalytic H 2 production rate of 254.1 mmol h À1 with apparent quantum yield of 6.8% (l ¼ 420 nm). The enhanced photocatalytic performance was supported by transient photocurrent response curves and electrochemical impedance spectroscopy (EIS) results which suggest the efficient charge separation and electron mobility in a-Bi 2 O 3 /CZS heterostructure. The intimate contact formed between a-Bi 2 O 3 nanorods and CZS nanoparticles responsible for the efficient flow of electrons following a Z-scheme pattern resulting in higher photocatalytic H 2 production. Moreover, the as-synthesized a-Bi 2 O 3 /CZS heterostructure shows negligible loss of activity after 4 consecutive recycling cycles. Our findings open new possibilities for the design of heterostructure based photocatalysts.
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Papers by Ammar Bin Yousaf