Synthesis Of Silicon-based Anionic Porous Organic Polymers And Adsorption Properties For Cationic Dyes

In the second chapter we report a straightforward access to two new anionic porous organic polymers?Si-POPs?,based on hexacoordinate[SiO₆]^2–species and polyimine aromatic linkers,which exhibit an outstanding capability for removal of cationic dyes from contaminated industrial water.These multifunctional materials,stable under air and in water,were synthesized via solvothermal chemistry exploiting Schiff base formation between tri?protocatechuic aldehyde?-silicate and 4,4'-diaminobiphenyl?for Si-POP-1?or 4,4'-diamino-2,2'-stilbenedisulfonic acid?for Si-POP-2?.Charge neutrality of the Si-POPs is achieved by[Et₃NH]⁺cations.Structures were determined by spectroscopic techniques(FT-IR,Solid State ¹³CNMR)while SEM and TEM revealed a micrometer-scale solid sphere morphology for Si-POP-1 and hollow nanometer-sized tubes for Si-POP-2.BET specific surface area determination gave 376 and 234 m²/g for Si-POP-1and Si-POP-2.The unprecedented adsorption ability of these materials for standard cationic dyes like Methylene Blue?MB?,Malachite Green?MG?,Basic Blue 7?BB7?was unveiled looking up system variables such as pH,contact time,temperature and mixed-dye solutions.At 25°C,the maximum adsorption capacity of Si-POP-1 reached 300.3 mg/g,for MB and 378.5 mg/g for MG,while the performance of Si-POP-2 at the same temperature was substantially higher?3516 mg/g for MB and 662 mg/g for MG?.Furthermore,at 35°C the maximum adsorption of MB on Si-POP-2attained 4098 mg/g,overtaking performances of previous adsorbents.It was found that both Si-POP-1 and Si-POP-2 exhibit charge and size selective adsorption.Thermodynamics indicated that adsorptions were spontaneous and endothermic.A minimal loss of adsorptive capacity of Si-POP-2?less than 4%?was observed.In the third chapter,a new family of bakelite-type anionic microporous organic polymers?MOPs?is described,which were assembled by the condensation reaction between anionic unit tri?protocatechuic aldehyde?-silicate and phlorglucinol or resorcinol by reference to the synthetic method of bakelite.The new materials exhibit uniform and solid microspheres,remarkable high BET specific surface area of 1846.5 and 2206.7 m²/g,and narrow pore size distribution around 1nm region.The adsorption capacities of MOP-1 and MOP-2 toward MB and MG run up to 712.2,593.6,233.8 and 324.7 mg/g at 25°C,respectively,but they hardly adsorbed MO and BB7,exhibiting charge and size-selectivity.The adsorption thermodynamics and kinetics were investigated and the pseudo-second-order kinetic model and Langmuir isotherm model were suitable for the adsorption process of MB and MG on MOP-1 and MOP-2.The negative values of the Gibbs free energy and the positive values of enthalpy changes indicated that adsorptions were spontaneous and endothermic.Moreover,the absorbents MOP-1 and MOP-2 can be re-used at least four times in the adsorption of MB and MG with less than 5%loss of adsorption capacity.