Cultivation, Purification And Adsorption Of Frustules From Marine Diatoms

The unicellular microorganisms of diatoms are an important part of the marine plankton, which belongs to the producers in the food chain for marine. It is of great significance and provides two fifths of primary productivity. Diatom cell wall, with excellent properties of high surface area, high transmission rate and high toughness., is oddly shaped, constructed wonderful porous structure. Compared with diatomaceous earth, living diatom cells can be purified culture, sustainable production and complete shell structure and other advantages. It has many potential applications in the future development of ultra-fine micro-nano materials and biological materials. In this paper, the cultivation of marine diatoms, purification and adsorption properties of diatom silica shell casing were studied. The main contents and results are as follows:(1) Skeletonema was cultivated. We explored the effects of nitrogen, phosphorus, iron, silicon on the growth of Skeletonema, and found that silicon has most important influence on the growth of Skeletonema, followed by iron, phosphorus,and nitrogen elements. The orthogonal experiment results show that the optimum growth of the algae nutrient ratio:NaNO315mg/L, KH2PO41mg/L, FeSO41mg/L, Na2Si0315mg/L.(2) We have obtained innovative methods for the purification of diatom frustules from diatoms by large-scale culture. The samples were cleaned in an excess of3-5%H2SO4and subsequently heated to600℃for certain time. In our operation, the native frustule morphology was maintained completely, and dry frustules with more than90%SiO2in weight can be obtained. Then using TGA, SEM, EDX, XRD, BET and FTIR on frustules were characterized.(3) T-frustules (Thalassiosira sp. frustules) and diatomite were utilized as adsorbents for the removal of textile dye methylene blue. The pseudo-first-order, pseudo-second-order and intra-particle diffusion models were applied to determine the kinetic data. The experimental data followed a pseudo-second-order rate kinetics. In addition, the linear Langmuir and Freundlich adsorption equations were employed to describe the equilibrium isotherms. Thermodynamic parameters such as enthalpy, free energy and entropy changes were calculated and the results show that the methylene blue adsorption process is favored at low temperatures and occurs spontaneously.