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A. A. Baba et al.
Introduction
Today, various clay minerals such as talc, halloysite, and kaolin have been utilized
in the development of various nanomaterials [1]. Among these nanomaterials, mesoporous materials preparation, characterization with possible industrial applications
have been the most popular. This among others, is majorly attributed to its wide
and diverse applications in catalysis, adsorption, drug delivery, reinforcement of
elastomer products and so on [2, 3]. Thus, efforts in meeting the high demands for
mesostructured materials has led to the development of varieties of starting materials
as well as low energy consuming preparation techniques. Consequently, kaolinite
with a layered tetrahedral structure of silica and octahedral alumina, high surface
area, non-toxic and small particle size was proposed for the preparation of mesoporous silica and alumina [4]. In obtaining the aforementioned industrial raw materials, various processing techniques have been utilized to fabricate porous materials
including sol–gel technique or micro-emulsion and pillaring. But the techniques to
prepare this material need expensive organic raw materials, a large amount of organic
liquid, expensive precursors and rigorous reaction conditions; so, it is very difficult
to be widely applied. The selective leaching method involving different lixiviants
(acids/bases and their salts) are often used to extract silica in the form of either
silicic acid or alkali metal silicate solutions. This causes exchangeable cations to be
replaced by H
+ ions, while the SiO 4 groups are largely intact in the acid environment,
as Al
3+ escape out of octahedral sites [3, 4]. Consequently, this study was carried
out using hydrochloric acid to produce mesostructured silica with improved specific
surface area for defined industrial uses at optimized conditions. Also, the effects of
hydrochloric acid concentration, reaction temperature and solid–liquid ratio on the
rate of pore formation were evaluated. The aforementioned reaction parameters will
help to broaden our understanding of dissolution kinetics in the scale-up process for
low energy mesoporous silica production from the local kaolinite ore.
Materials and Methods
Materials
Kaolinite sample sourced from Share area of Kwara State, Nigeria was thermally
activated at 850 °C to produce metakaolin (MK) which was used as the starting material for the preparation of the porous materials. The starting material and synthesized
products were accordingly characterized by using the MINI PAL 4 EDXRF spectrometer, EMPYREAN X-ray diffractometer, the FEI Nova NanoSEM 230 TEM
and Nitrogen adsorption/desorption isotherms at 77 K using a Micromeritics BET,
Tristar II 3020. The measurements were performed after degassing overnight at
90 °C. Concentrated hydrochloric acid (HCl) of analytical BDH grade was used in
this study. Deionized water was used for the preparation of all aqueous solutions in
this study.
A. A. Baba et al.
Introduction
Today, various clay minerals such as talc, halloysite, and kaolin have been utilized
in the development of various nanomaterials [1]. Among these nanomaterials, mesoporous materials preparation, characterization with possible industrial applications
have been the most popular. This among others, is majorly attributed to its wide
and diverse applications in catalysis, adsorption, drug delivery, reinforcement of
elastomer products and so on [2, 3]. Thus, efforts in meeting the high demands for
mesostructured materials has led to the development of varieties of starting materials
as well as low energy consuming preparation techniques. Consequently, kaolinite
with a layered tetrahedral structure of silica and octahedral alumina, high surface
area, non-toxic and small particle size was proposed for the preparation of mesoporous silica and alumina [4]. In obtaining the aforementioned industrial raw materials, various processing techniques have been utilized to fabricate porous materials
including sol–gel technique or micro-emulsion and pillaring. But the techniques to
prepare this material need expensive organic raw materials, a large amount of organic
liquid, expensive precursors and rigorous reaction conditions; so, it is very difficult
to be widely applied. The selective leaching method involving different lixiviants
(acids/bases and their salts) are often used to extract silica in the form of either
silicic acid or alkali metal silicate solutions. This causes exchangeable cations to be
replaced by H
+ ions, while the SiO 4 groups are largely intact in the acid environment,
as Al
3+ escape out of octahedral sites [3, 4]. Consequently, this study was carried
out using hydrochloric acid to produce mesostructured silica with improved specific
surface area for defined industrial uses at optimized conditions. Also, the effects of
hydrochloric acid concentration, reaction temperature and solid–liquid ratio on the
rate of pore formation were evaluated. The aforementioned reaction parameters will
help to broaden our understanding of dissolution kinetics in the scale-up process for
low energy mesoporous silica production from the local kaolinite ore.
Materials and Methods
Materials
Kaolinite sample sourced from Share area of Kwara State, Nigeria was thermally
activated at 850 °C to produce metakaolin (MK) which was used as the starting material for the preparation of the porous materials. The starting material and synthesized
products were accordingly characterized by using the MINI PAL 4 EDXRF spectrometer, EMPYREAN X-ray diffractometer, the FEI Nova NanoSEM 230 TEM
and Nitrogen adsorption/desorption isotherms at 77 K using a Micromeritics BET,
Tristar II 3020. The measurements were performed after degassing overnight at
90 °C. Concentrated hydrochloric acid (HCl) of analytical BDH grade was used in
this study. Deionized water was used for the preparation of all aqueous solutions in
this study.