Papers by Khairiraihanna Johari
The removal process of Hg(II) and MeHg(II) from aqueous solution by surface modified agrowaste bi... more The removal process of Hg(II) and MeHg(II) from aqueous solution by surface modified agrowaste biomass (AWB) was studied. The surface modifications were carried out by methods of mercerization, oxidative delignification, acid treatment, and biological treatment using laccase. The modifications promoted disruption of AWB structural surfaces and thus changed their physical and chemical properties as well as Hg(II) and MeHg(II) adsorption performances. The adsorption efficiency of Hg(II) was higher than MeHg(II) for all AWB adsorbents. The adsorption capacity of Hg(II) and MeHg(II) for AWB-Pure was 0.97 and 0.17 mmol/g, respectively. The highest adsorption capacity of Hg(II) and MeHg(II) was respectively observed for the AWB-Laccase (0.98 ± 0.04 mmol/ g) and AWB-NaOCl/NaOH (0.40 ± 0.07 mmol/g). The adsorption selectivity of modified AWB adsorbents towards Hg(II) and MeHg(II) studied using oilfield produced water and natural gas condensate samples was found to be lower as compared to AWB-Pure, but higher selec-tivity was observed for other metals. The renewability studies show that the pure and modified AWB adsorbents had similar adsorption performance characteristics. The high Hg(II) adsorption efficiency (g [ 90 %) was observed up to the third adsorption cycle, while for the MeHg(II), it decreased after each adsorption–desorption cycle.
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A B S T R A C T This study was conducted to investigate the high efficiency of coconut pith (CP) ... more A B S T R A C T This study was conducted to investigate the high efficiency of coconut pith (CP) adsorbent in removing Hg(II) and MeHg(II) ions from aqueous solution. The CP adsorbent was characterized using a scanning electron microscope (SEM), nitrogen adsorption-desorption (NAD) analysis, determination of pH at zero point charge (pH pzc), Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). Adsorption performance of the CP adsorbent at various parameters was conducted by varying the initial pH of solution, adsorbent dosage, initial pH, temperature, and contact time. It was found that adsorption capacity, adsorption rate and enthalpy of the Hg(II) adsorption were higher compared to the MeHg(II). The adsorption capacity of Hg(II) was 2.60 mmol/g, which was five times higher than MeHg(II). The adsorption isotherm analysis showed that the Hg(II) and MeHg(II) adsorption data fitted to the Langmuir and Freundlich models, respectively. The overall mechanism of both mercury adsorptions is a combination of physical and chemical processes in which the film diffusion was the rate controlling-step. The adsorbent regenerability study results showed that the Hg(II) adsorption remained stable up to five adsorption cycles, which was better than MeHg(II). The selectivity studies reveal the potential application of the CP adsorbent for the treatment of oilfield produced water (OPW) and natural gas condensate (NGC) that are rich in mercury ions as well as other cations.
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Industrial & Engineering Chemistry Research, 2013
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Environmental Progress & Sustainable Energy, 2015
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Microporous and Mesoporous Materials, 2014
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Environmental Technology (United Kingdom), 2014
In this study, elemental mercury (EM) adsorbents were synthesized using tetraethyl orthosilicate ... more In this study, elemental mercury (EM) adsorbents were synthesized using tetraethyl orthosilicate (TEOS) and 3-mercaptopropyl trimethoxysilane as silica precursors. The synthesized silica gel (SG)-TEOS was further functionalized through impregnation with elemental sulphur and carbon disulphide (CS2). The SG adsorbents were then characterized by using scanning electron microscope, Fourier transform infra-red spectrophotometer, nitrogen adsorption/desorption, and energy-dispersive X-ray diffractometer. The EM adsorption of the SG adsorbents was determined using fabricated fixed-bed adsorber. The EM adsorption results showed that the sulphur-functionalized SG adsorbents had a greater Hgo breakthrough adsorption capacity, confirming that the presence of sulphur in silica matrices can improve Hgo adsorption performance due to their high affinity towards mercury. The highest Hgo adsorption capacity was observed for SG-TEOS(CS2) (82.62 microg/g), which was approximately 2.9 times higher than SG-TEOS (28.47 microg/g). The rate of Hgo adsorption was observed higher for sulphur-impregnated adsorbents, and decreased with the increase in the bed temperatures.
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Journal of Environmental Science and Technology, 2015
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Waste Management & Research, 2014
The preparation of chars and activated carbon as low-cost elemental mercury adsorbents was carrie... more The preparation of chars and activated carbon as low-cost elemental mercury adsorbents was carried out through the carbonisation of coconut husk (pith and fibre) and the activation of chars with potassium hydroxide (KOH), respectively. The synthesised adsorbents were characterised by using scanning electron microscopy, Fourier transform infrared spectroscopy and nitrogen adsorption/desorption analysis. The elemental mercury removal performance was measured using a conventional flow type packed-bed adsorber. The physical and chemical properties of the adsorbents changed as a result of the carbonisation and activation process, hence affecting on the extent of elemental mercury adsorption. The highest elemental mercury (Hg°) adsorption capacity was obtained for the CP-CHAR (3142.57 µg g(-1)), which significantly outperformed the pristine and activated carbon adsorbents, as well as higher than some adsorbents reported in the literature.
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Separation Science and Technology, 2015
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Journal of Materials Engineering and Performance, 2014
This paper describes the synthesis, functionalization, and characterization of silica gels as mer... more This paper describes the synthesis, functionalization, and characterization of silica gels as mercury adsorbents. The synthesis was carried out according to the modified Stöber method using tetraethyl orthosilicate [TEOS], 3-mercaptopropyl trimethoxysilane [MPTMS] and bis(triethoxysilylpropyl) tetrasulfide [BTEPST] as precursors. The functionalization was carried out via co-condensation and impregnation methods using MPTMS, BTESPT, elemental sulfur [ES], and carbon disulfide [CS2] as sulfur ligands. The choice of the sulfur ligands as precursors and functionalization agents was due to the existence of sulfur active groups in their molecular structures which were expected to have high affinity toward Hg(II) ions. The synthesized adsorbents were characterized by using scanning electron microscope, fourier transform infrared spectrophotometer, nitrogen adsorption/desorption, and energy dispersive X-ray diffractometer. The batch Hg(II) adsorption experiments were employed to evaluate the Hg(II) adsorption performances of the synthesized adsorbents under different pH values. The results revealed that the highest Hg(II) adsorption capacity was obtained for the SG-MPTMS(10) which was 47.83 mg/g at pH 8.5. In general, the existence of sulfur functional groups, especially MPTMS in the silica matrices, gave a significant enhancement of Hg(II) adsorption capacity and the sulfur functionalization via co-condensation method, which is potential as a superior approach in the mercury adsorbent synthesis.
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Industrial & Engineering Chemistry Research, 2013
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Industrial & Engineering Chemistry Research, 2014
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Industrial & Engineering Chemistry Research, 2013
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Clean Technologies and Environmental Policy, 2014
Silica microspheres (SMs) was synthesized and modified through impregnation with elemental sulfur... more Silica microspheres (SMs) was synthesized and modified through impregnation with elemental sulfur (S8) and carbon disulfide (CS2) to produce sulfur-functionalized silica microspheres (S-SMs). The morphology of SMs did not change after modification, however, its pore characteristics and sulfur content as expected did change significantly. The elemental mercury adsorption rate and capacity from synthetic gas stream increased with the presence of sulfur compounds in the SMs. For instance, at bed temperature of 50 °C, the adsorption capacity and rate of adsorbents (SMs, S8-SMs and CS2-SMs) were (5.71, 37.24, and 83.41 µg/g) and (0.319, 0.749, and 1.922 µg Hg°/g min), respectively. It was observed that the adsorption rate and the capacity increased with bed temperature only for the SMs, while decreasing for the S-SMs. This might be due to different governing adsorption mechanisms for both types of adsorbents.
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The Canadian Journal of Chemical Engineering, 2014
This paper presents a comparative evaluation of mercury(II) adsorption equilibrium and kinetics o... more This paper presents a comparative evaluation of mercury(II) adsorption equilibrium and kinetics onto silica gel and sulfur-functionalised silica gel adsorbents. The silica gel was synthesised using tetraethyl orthosilicate (TEOS) as a precursor, while the sulfur-functionalised silica gel adsorbents were prepared through a co-condensation method using TEOS as a precursor with bis(triethoxysilylpropyl)tetrasulfide (BTESPT) and 3-mercaptopropyl trimethoxysilane (MPTMS) as sulfur ligands. The synthesised adsorbents were characterized by using SEM, FTIR, nitrogen adsorption/desorption (NAD), and EDX. A batch adsorption experiment was employed to evaluate the removal of Hg(II) by using the adsorbents. The study revealed that the Hg(II) adsorption capacity was found to be dependent on the initial Hg(II) concentration, agitation time, and pH of the solution. The Hg(II) adsorption capacities obtained for the SG-TEOS, SG-BTESPT and SG-MPTMS were 40.95, 93.32 and 102.37 mg/g, respectively. The Hg(II) adsorption was well fitted to the Langmuir isotherm models (R2 > 0.935) and obeyed the pseudo-second order kinetics model (R2 > 0.991). A further analysis of the kinetics suggested that the Hg(II) adsorption process was governed by both intra-particle and external mass transfer processes, in which film diffusion was the rate-limiting step.
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Process Safety and Environmental Protection, 2015
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Papers by Khairiraihanna Johari