Khairiraihanna Johari

Surface chemistry modifications of rice husk toward enhancement of Hg(II) adsorption from aqueous solution

The modified rice husks were characterized in terms of morphology (scanning electron microscopy), functional groups (Fourier transform infrared spectroscopy), surface charge (pHpzc), and elemental composition which indicate the treatments that led to significant changes to its surface chemistry. Batch adsorption studies showed that the highest adsorption capacity of Hg(II) was 89 and 118xa0mg/g obtained by sulfur-functionalized rice husk (RH-CS) and organosilane-grafted rice husk (RH-GM), respectively. The reusability of raw rice husk (RH-Raw) and alkali-treated rice husk (RH-NaOH) was superior to RH-CS and RH-GM; even though their adsorption capacities were slightly lower. However, their selectivity was comparable to that of the RH-CS and RH-GM. In addition, the results demonstrated the potential application of rice husk-based adsorbents for treating Hg(II) containing wastewaters such as produced water from oil and gas exploration activities.

Adsorption enhancement of elemental mercury onto sulphur-functionalized silica gel adsorbents

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 Hg° breakthrough adsorption capacity, confirming that the presence of sulphur in silica matrices can improve Hg° adsorption performance due to their high affinity towards mercury. The highest Hg° adsorption capacity was observed for SG-TEOS(CS2) (82.62 μg/g), which was approximately 2.9 times higher than SG-TEOS (28.47 μg/g). The rate of Hg° adsorption was observed higher for sulphur-impregnated adsorbents, and decreased with the increase in the bed temperatures.

STUDY OF HG(II) REMOVAL FROM AQUEOUS SOLUTION USING LIGNOCELLULOSIC COCONUT FIBER BIOSORBENTS: EQUILIBRIUM AND KINETIC EVALUATION

Lignocellulosic coconut wastes such as pith and fiber, which are abundantly available and cheap, have the potential of being used as low-cost biosorbents for heavy metal ion removal. In this study, pristine (CF-Pristine) and NaOH-treated (CF-NaOH) coconut fibers were used as a biosorbent for Hg(II) removal from an aqueous solution. The coconut fiber biosorbent (CFB) was characterized by scanning electron microscopy (SEM) and Fourier transform-infrared (FTIR) spectroscopy. The Hg(II) sorption capacities obtained for CF-Pristine and CF-NaOH were 144.4 and 135.0 mg/g, respectively. Both the equilibrium and kinetic data of Hg(II) sorption onto CFB followed the Langmuir isotherm model and a pseudo-second-order kinetic model, respectively. A further analysis of the kinetic data suggested that the Hg(II) sorption process was governed by both intraparticle and external mass transfer processes, in which film diffusion was the rate-limiting step. These results demonstrated that both pristine- and alkali-treated coconut wastes could be potential low-cost biosorbent alternatives for the removal of Hg(II) from aqueous solutions, such as water containing Hg(II) produced in the oil and gas industry.

Synthesis and Characterization of Novel Sulfur-Functionalized Silica Gels as Mercury Adsorbents

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 47.83xa0mg/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.

Removal performance of elemental mercury by low-cost adsorbents prepared through facile methods of carbonisation and activation of coconut husk.

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 (3142.57u2009µgu2009g−1), which significantly outperformed the pristine and activated carbon adsorbents, as well as higher than some adsorbents reported in the literature.

Removal of elemental mercury from gas stream using sulfur-functionalized silica microspheres (S-SMs)

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 50xa0°C, the adsorption capacity and rate of adsorbents (SMs, S8-SMs and CS2-SMs) were (5.71, 37.24, and 83.41xa0µg/g) and (0.319, 0.749, and 1.922xa0µgxa0Hg°/gxa0min), 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.

Silver Adsorption Enhancement from Aqueous and Photographic Waste Solutions by Mercerized Coconut Fiber

The mercerized coconut fiber (CF-NaOH) was prepared by treating the pristine coconut fiber (CF-Pure) with NaOH solution. The morphology and chemical composition of CF-Pure changed after mercerization process. The maximum Ag(I) adsorption capacity of the CF-Pure and CF-NaOH was 0.502 and 0.612 mmol/g, in which the equilibrium data fitted to the Freundlich and Langmuir isotherm models, respectively. The Ag(I) adsorption rate also increased by using CF-NaOH and the kinetic data of both CF-Pure and CF-NaOH obeyed the pseudo-second order kinetic model. The enhancement of Ag(I) adsorption selectivity from photographic waste solution was also observed for the CF-NaOH.

Silver Ion Adsorption using Alkali and Organosilane Modified Coconut Pith Biosorbents

The coconut pith biosorbents were prepared by modifying coconut pith (CP) with sodium hydroxide and bis(triethoxysilylpropyl) tetrasulfide to enhance its sorption capacity and selectivity toward silver ion [Ag(I)]. It was found that the Ag(I) sorption capacity of pure CP, CP modified with sodium hydroxide, and CP modified with bis(triethoxysilylpropyl) tetrasulfide was 0.50, 0.48, and 0.62 mmol/g, respectively. The Ag(I) equilibrium data were best fitted to the Langmuir isotherm model, whereas the kinetic data obeyed the pseudo-second-order kinetic model with the anticipation of the film diffusion as the rate-limiting step. The sorption process was generally governed by a combination of physical and chemical sorption mechanisms. The Ag(I) sorption capacity and selectivity of coconut pith biosorbents were low as compared with other metal ions.