Modulation Of Pore Structure In Diatomite And Its Adsorptive Property

Diatomite has many advantages,such as highly porous structure,large surface area,excellent absorbability,good chemical stability,strong biological safety,widely distributed resources,and so on,which make diatomite suitable for the utilizations as high-quality adsorption materials.Diatomite-based products such as diatom mud have being come into people's daily life,but the diatomite products on the market greatly varies in quality,partially due to the imperfect of evaluation methods to determine the humidity controlling performance and formaldehyde removal capacity.On the other hand,the adsorption mechanism of such guest substances onto diatomite surface is still not entirely clarified,suggesting that the properties of diatomite-based products have still some potential to being improved.In this work,low grade diatomite was employed as the raw material for a process of high-temperature calcination to adjust the pore structural parameter of diatomite,in which the influence of calcinated temperature and holding time upon the pore structure of diatomite was investigated in details.Static adsorption method and saturated adsorption method were used to determine the humidity controlling properties of diatomite,in which acetylacetone-assisted spectrophotometric method was found to be effective in the measurements of actual formaldehyde adsorption capacity.Thereafter,a process of hydrothermal solidification was proposed to prepare diatomite-based building board with reasonable mechanical strength and outstanding performance in moisture adsorption/desorption and formaldehyde removal.Microstructural characterization revealed a specific surface area of 66.64m2·g-1 in the crude diatomite,and a feasible calcination being operated at 500 ? upgraded the surface area of diatomite 68.81m2·g-1,but further increase of calcination temperature or prolonged holding time were not favorite for the improvement of such diatomite,since the specific surface area suddenly decreased to 27.25m2·g-1 at 800?.By making use of a static adsorptive method to determine the moisture adsorption/desorption capacity of diatomite,it is found that the moisture adsorption capacity decreased,when the holding time was constant,with the increasing of calcination temperature,but the moisture desorption amount of calcinated diatomitewas higher than that of crude diatomite.,revealing that the calcination treatment has obvious ability of improvement to the moisture desorption performance of diatomite.On the other hand,when the calcination temperature was the same,the moisture adsorption/desorption amount of diatomite decreased evidently with the increasing of holding time,because of the collapse of diatomite surface pore structure at high temperature,namely the specific surface area diminished and the moisture adsorption-desorption amount decreased simultaneously.Under the conditions of saturated adsorption method,a detectable difference was found from the comparison of humidity controlling process with the nitrogen cryo-sorption process,because the measured adsorption of moisture must involved physical adsorption and chemical adsorption at same time,evidently supported by the experimental results that the moisture adsorption/desorption curves did not coincide with each other under the humidity lower than 10%RH.Typical adsorption kinetics and thermodynamics models were adopted to analyze the progress of moisture adsorption onto diatomite.The results display that the diatomite adsorption process answered well with a pseudo-second-order model,along with a fitting coefficient(R2)as high as 0.991 to 0.999,and the fitting results very close to the experimental adsorption value;it is also found that the experimental value matched with the Langmuir model.The crude diatomite and calcined diatomite were also employed in the determination of formaldehyde removal by a static adsorption test.Adsorption of formaldehyde is closely connected with the specific surface area of diatomite,and as a result,the calcination at 500?effectively reduced the diatomite impurities and consequently increased the adsorption amount,but the increasing of calcination temperature or holding time is not proposed,since such treatment lead to the damage of diatomite pore structure,which resulted in the decrease of specific surface area.In the process of hydrothermal solidification,diatomite was mixed with calcium hydroxide and water according to certain proportion,which made the powdered diatomite to produce building board.The pore structure of diatomite was found to be improved effectively after the calcinations,along with an enhanced mechanical strength.Some feasible ways were proposed to upgrade the humidity controlling property of hydrothermally solidified diatomite,such as increasing the diatomite content or appropriately reduce the molding pressure,despite that the mechanical strength is decline.It is shown that diatomite has a natural advantage in moisture adsorption and formaldehyde removal,but appropriate calcination is still proposed to activate diatomite by adjusting the pore structure,which may contributes to improve the diatomite pore structure.Hydrothermally solidified diatomite has great potential application in the field of green building materials.