Vol.9 No.3 2017

Research paper : Development of HASClay® as a high-performance adsorption material (M. Suzuki et al.)−159−Synthesiology - English edition Vol.9 No.3 (2017) used where the heating temperature is less than 100 ºC.(3) The method shall be one where synthesis can be accomplished at one cycle per day.(4) The synthesis efciency (yield) shall be adjusted so the concentration at heating will produce 100 g or more of solid weight after dehydration of 1L of the solution.The number of parameters to be investigated decreased by setting the binding condition as in (1)–(4), and we set the most important parameter as Si/Al molar ratio.After setting such conditions, we attempted the synthesis of materials that showed adsorption volume of more than 30 wt% at relative humidity of 60 %, and had a linear adsorption isothermal curve. As a result, we succeeded in synthesizing an excellent water vapor adsorbent called HASClay®.[13]The name HASClay® is derived from the fact that in its x-ray diffraction pattern, although there was no peak or layer structure of amorphous hydroxyl aluminum silicate (HAS), there was a peak for clay sheet. Also, the product was not a mixture of two substances but was one substance, and this was deemed the composite of HAS and clay, hence the name HASClay. The performance of HASClay was about 45 wt%, which greatly surpassed the initial target value of 30 wt% at relative humidity of 60 %. Considering the prospect of this future adsorbent we trademarked the product.3.3 Study of the structure of HASClay and categorization by performanceAlong period of two years was required for us to reach HASClay®. First, we were able to synthesize the material that was the primary substance of HASClay® (HASClay grade III or HASClay GIII). However, in ordinary analysis such as powder X-ray diffraction, we were unable to determine the difference between allophane and a Si/Al amorphous substance, and the difference could be seen only by solid NMR.To clarify the structure of this substance, we temporarily suspended the conditions we set in Subchapter 3.2, and shifted to the identication of the substances. In the synthesis procedure, we conducted the removal of salts such as sodium chloride and sodium sulfate by centrifugation that was mandatory in high-concentration synthesis of imogolite, and the synthesis temperature of 98 ºC or less was raised to 110 ºC or more. As a result, by desalination, the water vapor adsorption capacity increased (HASClay grade II or HASClay GII). By further removing the salts and heating for 4 h at 200 ºC, we discovered a substance that could be clearly identied by X-ray powder diffraction, and this was called the highest performing HASClay® (HASClay grade I or HASClay GI) that was the composite of amorphous aluminum silicate and low-crystalline clay. The HASClay GII and GIII became HASClay GI when it was heated for 40 days at 98 ºC, and they were called HASClay precursors.The X-ray powder diffraction patterns for HASClay GI and HASClay GIII are shown in Fig. 8,[13] the 29Si-NMR spectra in Fig. 9,[14][15] and their TEM photographs are shown in Fig. 10.[14][16]In X-ray powder diffraction, HASClay GI had two types of peaks: one was a broad peak corresponding to the reection of layered clay minerals (hk0) at around 2θ = 21º and 35º, and the other was a broad peak characteristic to amorphous aluminum silicate at around 2θ = 26º and 40º. In contrast, HASClay GIII had only one broad peak that was characteristic to amorphous aluminum silicate at around 2θ = 26º and 40º.In the 29Si-NMR spectrum, HASClay GI had a sharp peak at −78 ppm and a broad peak at −86 ppm and −110 ppm. The sharp peak of −78 ppm was caused by the structure similar to allophane and imogolite, and the remaining −86 ppm peak corresponded to the structure of layered aluminum silicate such as vermiculite, while the −110 ppm peak appeared in the area of peaks caused by a structure where all sides of Si tetrahedron had the Si-O-Si bonds. HASClay GIII showed a sharp peak at −78 ppm that arose from the structure similar to allophane and imogolite in the 29Si-NMR spectrum, and Fig. 7 Conditions necessary for the synthesis of new adsorbentsFig. 8 Powder x-ray diffraction pattern of HASClayGeneral synthesis method(2) Synthesis at less than 100 ºC (does not use autoclaves, etc.)(3) Synthesis at one cycle per day(4) Yield is 100 g/L or more(1) Inexpensive raw materialProductSynthesisRaw material(a) HASClay GI(b) HASClay GIIIIntensity2θ (Cu, Kα)706050403020100

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