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Kian Ping Loh – One of the best experts on this subject based on the ideXlab platform.

  • Self-assembly and selected area growth of zinc oxide nanorods on any surface promoted by an Aluminum precoat
    Journal of Physical Chemistry B, 2004
    Co-Authors: Yee Wee Koh, Ming Lin, Chow Kim Tan, Yong Lim Foo, Kian Ping Loh

    Abstract:

    We demonstrate a simple method to direct the self-assembly of ZnO nanorods on flat and curved surfaces in hydrothermal synthesis by precoating the substrate with a thin film of Aluminum (Al). The Al was transformed in the alkali hydrothermal environment into hydrotalcite-like zinc Aluminum Carbonate sheets, which provide a lattice-matched substrate for the self-assembly of ZnO nanorods. Selective growth of ZnO nanorods on the Al-patterned substrate as well as the high-density coating of carbon nanotubes by ZnO nanorods along the tangential and radial walls has been demonstrated using hydrothermal synthesis. The interfacial chemistry involved in the growth of ZnO and hydrotalcite-like zinc Aluminum Carbonate sheets is also discussed.

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Mazhar Mehmood – One of the best experts on this subject based on the ideXlab platform.

  • Formation of porous α-alumina from ammonium Aluminum Carbonate hydroxide whiskers
    Ceramics International, 2019
    Co-Authors: Jamil Ahmad, Muhammad Ismail Tariq, Rizwan Ahmad, Syed Mujtaba Ul-hassan, Mazhar Mehmood, Abdul Faheem Khan, Shabana Waseem, Shoaib Mehboob, Muhammad Tauseef Tanvir

    Abstract:

    Abstract Ammonium Aluminum Carbonate hydroxide (AACH) whiskers prepared by hydrothermal technique were employed as precursor material for development of porous alumina. After compaction of AACH whiskers at 8 bars, calcination was performed at 650 °C followed by sintering at different temperatures. The sintered samples were characterized by XRD, FTIR, SEM and mercury intrusion porosimetry. Mechanical strength was determined by compression testing. At sintering temperatures of 1200 °C to 1400 °C, the % age porosity was around 80%. At 1500 °C, the percentage porosity decreased to 71%. The as-prepared AACH consisted of bundles of whiskers with diameters as thick as 0.7 µm, while an individual whisker had a diameter of about 100 nm with an aspect ratio of about 33. A two-phase mixture consisting of θ- and α-alumina was obtained at 1100 °C, while at 1200 °C and above, single phase α-alumina was formed. θ-alumina retained the bundle-like morphology. However, transformation to α-alumina was accompanied by formation of bead-like morphology. These beads were joined together through necks/stems within the whiskers as well as across the parallel-lying whiskers. These necks grew at 1300 °C to form aggregates with smooth surfaces. At 1400 °C, these aggregates started joining with each other by neck formation and at 1500 °C, a three-dimensional network was formed. For sintering temperatures of up to 1400 °C, pores with sizes around 260 nm were very stable. At 1500 °C, significant pore growth took place along with an overall densification. Therefore, number of pores with sizes of around 260 nm decreased and those with sizes around 10 µm, 1 µm and 5 nm increased. The compression strength of samples sintered at 1100 °C to 1300 °C was in the range of 3.4–4.3 MPa. At 1400 °C, the strength increased to 5.2 MPa, while at 1500 °C, it jumped to 10.8 MPa due to the formation of three-dimensional network.

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  • Terahertz time domain spectroscopy of hydrothermally synthesized boehmite and ammonium dawsonite nanostructures
    Infrared Physics & Technology, 2016
    Co-Authors: Shoaib Mehboob, Jamil Ahmad, Muhammad Tauseef Tanvir, Mazhar Mehmood, Mushtaq Ahmed, Izhar Ahmad

    Abstract:

    Abstract The frequency dependent optical and dielectric properties of boehmite (AlOOH) and ammonium Aluminum Carbonate hydroxide (AACH) nanostructures, prepared at different temperatures via hydrothermal synthesis, were studied by using terahertz time domain spectroscopy (THz-TDS). The complex refractive indices, absorption coefficients and complex dielectric constants were determined and compared for different synthesis temperatures. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) were also performed to confirm the formation of boehmite and AACH. Scanning electron microscopy (SEM) was performed to study the morphology of nanostructures. The study reveals the formation of AACH at higher temperatures and decrease in refractive index with increasing synthesis temperature. The higher absorption coefficient and lower refractive index and dielectric constant were observed for AACH than for boehmite.

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  • Single step hydrothermal synthesis of 3D urchin like structures of AACH and Aluminum oxide with thin nano-spikes
    Ceramics International, 2012
    Co-Authors: Muhammad Abdullah, Mazhar Mehmood, Jamil Ahmad

    Abstract:

    Abstract 3D urchins like ammonium Aluminum Carbonate hydroxide (AACH) nanostructures with nano-spikes of dia. 20–30 nm were synthesized by a simple, single step hydrothermal technique by using Aluminum nitrate and urea as precursor materials. It was found that morphology of the produced structure strongly depends upon the urea concentration. With increasing the amount of urea, the AACH particles having embedded rods like surface features transformed into 3D urchins. The added urea decomposed during hydrothermal treatment and increased the pH of the solution, which affected the morphology of the produced nanostructures. SEM, XRD, FTIR and TGA were employed to characterize the produced structures. On heating, the volatile ingredients of AACH were removed, leaving behind the alumina urchins.

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Chenguang Liu – One of the best experts on this subject based on the ideXlab platform.

  • Preparation of NiMo/γ-Al2O3 catalysts with large pore size for vacuum residue hydrotreatment
    Materials Research Bulletin, 2013
    Co-Authors: Zhe Tang, Liu Yunqi, Chenguang Liu

    Abstract:

    gamma-Al2O3 supports with large pore size were prepared by using rod-like ammonium Aluminum Carbonate hydroxide (AACH) as precursors. The textural properties of supports are dependent on the different crystallinity of the as-prepared AACH. For investigating their catalytic performance, NiMo/gamma-Al2O3 hydrotreating catalysts were prepared by loading NiMo oxides on the supports and tested by using vacuum residue as reactant, and the results show that both pore structure and surface acid property of catalysts have significant influences on the catalytic activities for the hydrogenation and the removal of heteroatoms. (C) 2013 Elsevier Ltd. All rights reserved.

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  • Fabrication of high-surface-area γ-alumina by thermal decomposition of AACH precursor using low-temperature solid-state reaction
    Materials Research Bulletin, 2012
    Co-Authors: Yun Qi Liu, Zhe Tang, Ruiyu Zhao, Chenguang Liu

    Abstract:

    Abstract In this paper, systematical investigation has been made for the new simple synthesis pathway of catalytic alumina with high surface area through thermal decomposition of ammonium Aluminum Carbonate hydroxide (AACH), which has been prepared by a low-temperature solid-state reaction in non-aqueous system. The results indicate that the molar ratios of NH 4 HCO 3 /Al influence crystallinities and the morphologies of AACH. Well-crystallized AACH with nanorod morphology and low-crystallized AACH with cluster structure can be obtained with different molar ratios NH 4 HCO 3 /Al. The γ-Al 2 O 3 product with high surface area (511 m 2 /g) can be obtained from the calcination of AACH at 500 °C. Moreover, the results also indicate that crystallinities and morphologies of AACH affect their thermal decomposition behaviors. In addition, the formation of high-surface-area is possibly attributed to intracrystalline porosity of as-prepared γ-Al 2 O 3 .

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  • Facile Synthesis of Ammonium Aluminum Carbonate Hydroxide Multilayered Nanofiber by Using Solid State Reaction
    Advanced Materials Research, 2011
    Co-Authors: Yun Qi Liu, Chenguang Liu

    Abstract:

    In this paper, we make systematical investigation for the new synthesis pathway of AACH multilayered nanofiber, which has been prepared by a low-temperature solid-state reaction. The phase transformation sequence of AACH on heating is found that the precursor converts into γ-Al2O3 at 700-900°C and elevated temperature results in the θ-Al2O3 and α- Al2O3 crystal phase formation at 1000°C. With a higher calcination temperature at 1100°C, α- Al2O3 pattern appears. The specific surface area (SBET) of Aluminum oxide specie calcined at 500°C for 4h is still in 420.2m2/g. Meanwhile, it suggests a partial change in particle sizes and morphology of sample calcined at 500°C for 4h.

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