Synthesis Of Modified Mesoporous Molecular Sieve And Study Of Arsenic Removal Performance

Since high arsenic concentrations in water cause great damage to environment and human body, it is essential that there are technologies for controlling the concentrations of arsenic in aqueous emissions. One effective and economic approach is to use alternative adsorbents. For its large surface area, abundant pore structure, adjustable pore diameter, selective adsorption and great performance, mesoporous molecular sieve has been obtaining increasing scientific attention, possesses a hexagonal array of uniform mesopores. The mesoporous molecular sieve were synthesized using cetyltrimethylammonium bromide (CTAB) as structure template, tetraethyl orthosilicate (TEOS) as silica source by sol gel process.The mesoporous molecular sieve was chemical modified by 3-aminopropyl triethoxysilane (APTES), and then the modified mesoporous molecular sieve was acquired. Based on the physical and chemistry properties of the modified mesoporous molecular sieve, the static adsorption, desorption-regeneration and dynamic adsorption properties have been mainly studied.By static adsorption experiments, the quality of adsorbent depend on the removal rate of arsenic at adsorption equilibrium. The synthetic conditions of modified mesoporous molecular sieve adsorbent were investigated by single factor experiments and orthogonal test. The types of factors and experimental areas, such as calcination temperature, calcination time, modified time, the amount of CTAB, TEOS and APTES were studied. The results indicated that the optimal preparative conditions of modified mesoporous molecular sieve adsorbent:baking temperature 550℃, baking time 6 h, CTAB 0.070 mol/L, TEOS 0.348 mol/L, APTES 0.119 mol/L and modified time 5 h. The order of factors were the amount of TEOS, modified time, the amount of APTES, the amount of CTAB.The structure of the samples were characterized by FT-IR, XRD, BET, SEM, EDX, TEM and TG-DTA. The results indicated that the mesoporous molecular sieve were modified successfully. The samples remains the ordered mesoporous structure. The particle size and morphology of adsorbent did not change much, but the degree of order decreased and lattice constant larger than unmodified adsorbent. The product gets a narrow pore size distribution by the silane modification, the minimum pore diameter was 3.08 nm, the maximum pore diameter is 31.98 nm, the most probable pore diameter was 12.93 nm, the pore volume is 0.875 cm3/g, the surface area was 663.6 m2/g.The adsorption rate of arsenic was determined by time of contact, pH and temperature. The equilibrium time of contact was 180 min, the optimum pH of adsorption is 3.0, and the best temperature was 25℃. The static saturated adsorption capacity of arsenic was 8.500 mg/g at the optimum condition, and the dynamic adsorption capacity of arsenic is 8.701 mg/g. The result of XRD and BET showed that the characteristic absorption peak broadened after the adsorbent regenerated three times, and the surface area decreased to 187.9 m2/g.