Publications by authors named "Aftab Ahmad Khan"

8 Publications

  • Page 1 of 1

Investigation of 9000 hours multi-stress aging effects on High-Temperature Vulcanized Silicone Rubber with silica (nano/micro) filler hybrid composite insulator.

PLoS One 2021 28;16(7):e0253372. Epub 2021 Jul 28.

Manchester Metropolitan University, Manchester, United Kingdom.

Degradation in the polymeric insulators is caused due to the environmental stresses. The main aim of this paper is to explore the improved aging characteristics of hybrid samples by adding nano/micro silica in High Temperature Vulcanized Silicone Rubber (HTV-SiR) under long term accelerated aging conditions for 9000 hours. As HTV-SiR is unable to sustain environmental stresses for a long time, thus a long term accelerated aging behavior is an important phenomenon to be considered for field application. The aging characteristics of nano/micro filled HTV-SiR are analyzed by using techniques such as Scanning Electron Microscopy (SEM), Leakage Current (LC), Fourier Transform Infrared Microscopy (FTIR), Hydrophobicity Classification (HC), and breakdown strength for the aging time of 9000 hours. FTIR and leakage currents are measured after every cycle. All the co-filled samples revealed escalated aging characteristics as compared to the neat sample except the SN8 sample (8% nano-silica+20% micro-silica) after 9000 hours of aging. The highest loading of 6% and 8% nano-silica with 20% micro-silica do not contribute to the improved performance when compared with the neat and hybrid samples. However, from the critical experimental analysis, it is deduced that SN2 sample (2% nano-silica+20% micro-silica) is highly resistant to the long term accelerated aging conditions. SN2 has no cracks, lower loss percentages in the important FTIR absorption peaks, higher breakdown strength and superior HC after aging as compared to the unfilled and hybrid samples.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0253372PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8318273PMC
July 2021

Metal oxide and carbon nanomaterial based membranes for reverse osmosis and membrane distillation: A comparative review.

Environ Res 2021 Jul 19;202:111716. Epub 2021 Jul 19.

Department of Civil and Environmental Engineering, Hanyang University, Seoul, 04763, South Korea. Electronic address:

Commercial membranes typically suffer from fouling and wetting during membrane distillation (MD). In contrast, reverse osmosis (RO) can be subject to the fouling issue if applied for highly saline feed solutions containing foulants (e.g., organics, oils, and surfactants). Among the diverse treatment options, the nanomaterial-based membranes have recently gained great interest due to their advantageous properties (e.g., enhanced flux and roughness, better pore size distribution, and higher conductivity). This review focuses on recent advances in the mechanical properties, anti-fouling capabilities, salt rejection, and economic viability of metal oxide (SiO, TiO, and ZnO) and carbon nanomaterial (graphene oxide/carbon nanotube)-based membranes. Current challenges in applying nanomaterial-based membranes are also discussed. The study further describes the preparation methods, mechanisms, commercial applications, and economical feasibility of metal oxide- and carbon nanomaterial-based membrane technologies.
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http://dx.doi.org/10.1016/j.envres.2021.111716DOI Listing
July 2021

Fluorinated silica-modified anti-oil-fouling omniphobic [email protected] robust membrane for multiple foulants feed in membrane distillation.

Chemosphere 2021 Jan 27;263:128140. Epub 2020 Aug 27.

Department of Civil and Environmental Engineering, Hanyang University 222 Wangsimni-ro, Seongdong-gu, Seoul, 04763, Republic of Korea. Electronic address:

Direct-contact membrane distillation (DCMD) can be eminent solution for oily wastewater treatment if the membrane provided is slippery and tolerant to low surface tension complex solutions. This study describes preparation of an anti-oil-fouling omniphobic polyethersulfone membrane using fluorinated silica nanoparticles ([email protected]) combined with perfluorodecyl triethoxysilane and polydimethylsiloxane for application against oil-In-water (o/w) emulsions. Feed solutions consist of different concentrations of oil (hexadecane), different charge surfactants (anionic sodium dodecyl benzenesulfonate, non-ionic Tween 20, and cationic hexadecyltrimethylammonium bromide, and salt (NaCl). The hierarchical re-entrant micro structured surface of the omniphobic [email protected] membrane and functional groups are confirmed by atomic force microscopy, scanning electron microscopy, and Fourier-transform infrared spectroscopy. The anti-oil-fouling and anti-wetting performance of omniphobic [email protected] membranes are investigated using contact-angle, sliding angles, DCMD tests with multiple foulants of surfactants. Omniphobic [email protected] membrane exhibited effective anti-oil-fouling and anti-wetting performance against emulsions as no severe fouling and a conductivity rises were evident regardless of surfactant charge and the concentration of components. Flux reduction and rejection rates for the omniphobic [email protected] membranes are in a range of 5-15% (only) and >99%, respectively, for various combinations of feed solution components.
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http://dx.doi.org/10.1016/j.chemosphere.2020.128140DOI Listing
January 2021

Synthesis of diindolylmethane (DIM) bearing thiadiazole derivatives as a potent urease inhibitor.

Sci Rep 2020 05 14;10(1):7969. Epub 2020 May 14.

Department of Biomedical Science, Faculty of Medicine and Health Sciences, Universiti Putra Malaysia, 43400, Serdang, Selangor, Malaysia.

The current study describes synthesis of diindolylmethane (DIM) derivatives based-thiadiazole as a new class of urease inhibitors. Diindolylmethane is natural product alkaloid reported to use in medicinal chemistry extensively. Diindolylmethane-based-thiadiazole analogs (1-18) were synthesized and characterized by various spectroscopic techniques HNMR, C-NMR, EI-MS and evaluated for urease (jack bean urease) inhibitory potential. All compounds showed excellent to moderate inhibitory potential having IC value within the range of 0.50 ± 0.01 to 33.20 ± 1.20 µM compared with the standard thiourea (21.60 ± 0.70 µM). Compound 8 (IC = 0.50 ± 0.01 µM) was the most potent inhibitor amongst all derivatives. Structure-activity relationships have been established for all compounds. The key binding interactions of most active compounds with enzyme were confirmed through molecular docking studies.
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http://dx.doi.org/10.1038/s41598-020-64729-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7224224PMC
May 2020

New triazinoindole bearing thiazole/oxazole analogues: Synthesis, α-amylase inhibitory potential and molecular docking study.

Bioorg Chem 2019 11 17;92:103284. Epub 2019 Sep 17.

Atta-ur-Rahman Institute for Natural Products Discovery (AuRIns), Universiti Teknologi MARA Cawangan Selangor Kampus Puncak Alam, 42300 Bandar Puncak Alam, Selangor D.E., Malaysia; Faculty of Pharmacy, Universiti Teknologi MARA Cawangan Selangor Kampus Puncak Alam, 42300 Bandar Puncak Alam, Selangor D.E., Malaysia.

New triazinoindole bearing thiazole/oxazole analogues (1-21) were synthesized and characterized through spectroscopic techniques such as HREI-MS, H and C NMR. The configuration of compound 2i and 2k was confirmed through NOESY. All analogues were evaluated against α-amylase inhibitory potential. Among the synthesized analogues, compound 1h, 1i, 1j, 2a and 2f having IC values 1.80 ± 0.20, 1.90 ± 0.30, 1.2 ± 0.30, 1.2 ± 0.01 and 1.30 ± 0.20 μM respectively, showed excellent α-amylase inhibitory potential when compared with acarbose as standard (IC = 0.91 ± 0.20 µM). All other analogues showed good to moderate inhibitory potential. Structural activity relationship (SAR) has been established and binding interactions were confirmed through docking studies.
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http://dx.doi.org/10.1016/j.bioorg.2019.103284DOI Listing
November 2019

Optimization of membrane modification using SiO for robust anti-fouling performance with calcium-humic acid feed in membrane distillation.

Environ Res 2019 03 18;170:374-382. Epub 2018 Dec 18.

Department of Civil and Environmental Engineering, Hanyang University, 222 Wangsimni-ro, Seongdong-gu, Seoul 04763, Republic of Korea. Electronic address:

The goal of this study was to prepare a robust anti-wetting and anti-fouling polyethersulfone (PES) membrane for the rejection of a highly saline (NaCl and CaCl·2HO) feed solution containing humic acid (HA) in direct contact membrane distillation (DCMD). Response surface methodology (RSM) was used to determine the optimum formulation of the used materials. The variable factors selected were polydimethyl siloxane (PDMS) and silica (SiO); liquid entry pressure (LEP) and contact angle (CA) were selected as responses. Scanning electron microscopy (SEM) analysis confirmed the SiO deposition and Fourier-transform infrared spectroscopy (FTIR) test evidenced the new functional groups i.e., Si-OH, siloxane, and C-F bond vibrations at 3446, 1099 cm, and 1150-1240 cm respectively on the membrane surface. The average roughness (Ra) was increased four times for the coated membranes (0.202-0.242 µm) as compared to that for pristine PES membrane (0.053 µm). The optimum PES-13 membrane exhibited consistent flux of 12 LMH and salt rejection (> 99%) with anti-fouling characteristic in DCMD using the feed solution of 3.5 wt% NaCl + 10 mM CaCl·2HO + 10 mg L HA. The PES-13 membrane may therefore be a key membrane for application in DCMD against CaCl·2HO-containing salty solutions with HA.
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http://dx.doi.org/10.1016/j.envres.2018.12.036DOI Listing
March 2019

Throughput Measurement of a Dual-Band MIMO Rectangular Dielectric Resonator Antenna for LTE Applications.

Sensors (Basel) 2017 Jan 13;17(1). Epub 2017 Jan 13.

Department of Electrical Engineering, COMSATS Institute of Information Technology, 22060 Abbottabad, Pakistan.

An L-shaped dual-band multiple-input multiple-output (MIMO) rectangular dielectric resonator antenna (RDRA) for long term evolution (LTE) applications is proposed. The presented antenna can transmit and receive information independently using fundamental TE and higher order TE modes of the DRA. TE degenerate mode covers LTE band 2 (1.85-1.99 GHz), 3 (1.71-1.88 GHz), and 9 (1.7499-1.7849 GHz) at GHz whereas TE covers LTE band 7 (2.5-2.69 GHz) at GHz, respectively. An efficient design method has been used to reduce mutual coupling between ports by changing the effective permittivity values of DRA by introducing a cylindrical air-gap at an optimal position in the dielectric resonator. This air-gap along with matching strips at the corners of the dielectric resonator keeps the isolation at a value more than 17 dB at both the bands. The diversity performance has also been evaluated by calculating the envelope correlation coefficient, diversity gain, and mean effective gain of the proposed design. MIMO performance has been evaluated by measuring the throughput of the proposed MIMO antenna. Experimental results successfully validate the presented design methodology in this work.
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http://dx.doi.org/10.3390/s17010148DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5298721PMC
January 2017

Synthesis of 4-thiazolidinone analogs as potent in vitro anti-urease agents.

Bioorg Chem 2015 Dec 23;63:123-31. Epub 2015 Oct 23.

HEJ, Research Institute of Chemistry, ICCBS, University of Karachi, Karachi 75270, Pakistan.

4-Thiazolidinone analogs 1-20 were synthesized, characterized by (1)H NMR and EI-MS and investigated for urease inhibitory activity. All twenty (20) analogs exhibited varied degree of urease inhibitory potential with IC50 values 1.73-69.65μM, if compared with standard thiourea having IC50 value of 21.25±0.15μM. Among the series, eight derivatives 3, 6, 8, 10, 15, 17, 19, and 20 showed outstanding urease inhibitory potential with IC50 values of 9.34±0.02, 14.62±0.03, 8.43±0.01, 7.3±0.04, 2.31±0.002, 5.75±0.003, 8.81±0.005, and 1.73±0.001μM, respectively, which is better than the standard thiourea. The remaining analogs showed good to excellent urease inhibition. The binding interactions of these compounds were confirmed through molecular docking studies.
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http://dx.doi.org/10.1016/j.bioorg.2015.10.005DOI Listing
December 2015
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