Structure and Surface Transformations of Humic-Adsorbed Synthetic Hydrotalcite-Like Materials
Source abstract
Abstract
Hydrotalcite-like material of Mg–Al-carbonate system (MACH) was prepared and its heat-treated product (MACHT) was obtained by calcination at 500°C, for 3 hours at atmospheric condition. The resulting materials were used as adsorbents for removal of humic substance (HS) from synthetic peat water (SPW) and natural peat water (NPW). Batch kinetic study showed that MACH or MACHT adsorb the humic substance with maximum adsorption capacities of around 15 mg of humic substance per g of adsorbent, when SPW was used compared to 78 mg/g when NPW was used. The humic substance uptake on MACH and MACHT from SPW and NPW followed the Langmuir model of adsorption. X-ray diffractograms showed that the layered structure of MACH collapsed when it was heated at 500°C and a new “amorphous-like” phase was observed. Due to the “memory effect” property of hydrotalcite, the regeneration of MACH from MACHT was observed when MACHT was treated with humic substance from SPW or NPW, and the basal spacing of around 7.9 A was restored. The BET surface area increased by about a factor of 3, from 68.0 in MACH to 201.9 m2/g in MACHT, but the micropore surface area decreased by about 20%, from 12.3 in the former to 9.9 m2/g in the latter. Expulsion of water molecules and carbon dioxide from carbonate in the interlayer together with the formation of an “amorphous-like” phase was thought to be the reason for the increase of the BET surface area. The decrease in the micropore area is possibly due to collapse of the layered structure of MACH. The BET surface area for MACH and MACH-humic substance-adsorbed from SPW or NPW is similar. On the other hand, a high reduction in surface area was observed for MACHT-adsorbed humic substance from SPW or NPW, by about 80% in the latter compared to about 90% in the former when compared to MACHT. The regeneration of MACH from MACHT together with the adsorption of humic substances presumably contributed to a high reduction in surface area of humic substance-adsorbed MACHT samples
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Research context
OpenAlex topics: Layered Double Hydroxides Synthesis and Applications · Magnesium Oxide Properties and Applications · Microwave Dielectric Ceramics Synthesis
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