Response surface methodology and inductively coupled plasma-optical emission spectroscopy were used to analyze the silicon (Si) and aluminum (Al) ion concentrations extracted from microwave-assisted hydrothermal fusion reactions between coal fly ash (CFA) and sodium hydroxide solution. The extracts containing Si and Al ions were successfully converted to zeolites by hydrothermal treatment at 95 • C for 72 h. Fifteen experimental conditions for the extraction process were obtained using Box-Behnken design through the manipulation of three independent variables. These variables include NaOH concentration (2, 4 and 6 M), power level of microwave irradiation (10, 50 and 100 W)+++ and exposure time (1, 3.5 and 6 min). The statistical analysis result indicated a significant interaction effect with a p value of 0.001. Increasing the values of all the three variables led to an increase in the concentration of Si and Al ions in the CFA extract. The optimized combinations of the three variables within the experimental range for Si and Al extraction were 5.6 M for NaOH concentration, 5.5 min time of exposure to microwave irradiation and 100 W of microwave power level. Based on the extracted concentration values of Si and Al, three products were isolated; zeolite Na-A, sodalite octahydrate and gibbsite which were characterized by their XRD images. Plots of percent yield of the final products versus [Si 4+ ] and [Al 3+ ] revealed a trend of the types of product for various ranges of concentrations of the ions in the extracts prior to hydrothermal treatment at 95 • C.
Layered organic-inorganic hybrid nanocomposite was prepared by inserting the pamoate anion (PA) between Zn and Al layered double hydroxide (LDH) using co-precipitation method. The ageing process was done by two different methods; conventional oil bath and microwaveassisted method at various ageing times, from 15 to 60 min. As a result of successful intercalation of PA anion into Zn-Al LDH lamella, the expansion of the interlayer spacing from 8.9 to 18.1 Å was observed in the powder X-ray diffractogram of the (ZAP) nanocomposite. Percentage of PA intercalated between the LDH was higher in the nanocomposite material aged using microwave irradiation (ZAPM) compared to conventional oil bath method (ZAP). The BET surface areas of ZAPM15 and ZAPM30 were in the range of 100-106 m 2 /g, which were higher compared to ZAP, 90 m 2 /g. In general, the microwave-assisted method has improved the physico-chemical properties of the nanocomposite material with shorter ageing time of 30 min compared to 18 h ageing time by conventional oil bath method.Keywords: pamoate anion; microwave-assisted; layered double hydroxide
IntroductionAt present, the interest in the chemistry of the layered double hydroxides (LDHs or the socalled anionic clays) still attracts attention. The LDHs are layered compounds with well-defined structures consisting of positively charge layers alternately interspersed with change balancing sheets of anions. The positively charged layers of M II and M III cations are octahedrally coordinated by six oxygen anions as hydroxides [1]. Various organic anions can be intercalated into the layer of double hydroxide to form a hybrid of organic-inorganic nanocomposite materials. This material has attracted considerable attention recently, owing to its anion exchange ability as well as its application as selective sorbents and potential catalysts [2][3][4][5][6][7].Conventionally, this type of material can be directly synthesised by co-precipitation technique in which the guest species is included in the reaction solution, followed by ageing process at elevated temperature for 18 h to form nanocomposite. Alternatively, microwave-assisted synthesis can be used to speed up the ageing process from 18 h for conventional method to 15-60 min. Microwave method offered several advantages such as shorter reaction time and new physicochemical properties of the resulting materials. For example, microwave-assisted synthesis of Al-intercalated clays showed a higher surface area and shorter synthesis time compared to the one synthesised by conventional method [8].
The layered double hydroxides (LDHs) with different divalent transition metal groups and nitrate as a counter anion were investigated. Three d-block divalent metals namely cobalt (Co), nickel (Ni) and copper (Cu) were selected. The cobalt/aluminium (CoAN)-, nickel/aluminium (NiAN)- and copper/aluminium (CuAN)-layered double hydroxides were successfully synthesized via co-precipitation method. All the obtained LDHs were characterized by PXRD, FT-IR, ICP-OES, CHNS and TGA/DTG analysis. Interestingly, behavior of the LDHs was dependent on the size of divalent cations. PXRD showed the basal spacing decrease in the order NiAN (0.88nm)> CuAN (0.87nm) > CoAN (0.74nm), and in a linear correlation with the increasing radii of the divalent cations. Similar trend is observed for the weight loss of LDHs, where NiAN has the highest weight loss (53%), followed by CuAN (43%) and CoAN (34%). Further elemental analysis showed the content of trivalent metal cations, nitrate anions and water molecules in the LDHs decrease with the increasing radii.
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