Study On Boron Removal Capability Of Novel Chelating Group-modified Mesoporous Molecular Sieve Materials

With the increasing shortage of freshwater resources,and demand for safe drinking water,irrigation water,industrial water,it has gradually become a trend to obtain clean water through desalination or treatment of high salty wastewater,even contaminated surface water.Within this case,the problem of removing boron from aqueous solutions has puzzled researchers for decades.On the other hand,the environmental problems,caused by a large amount of boron-containing wastewater from industrial and agricultural production and people's daily life,are also becoming more and more prominent.Therefore,it is vital to develop a safe,reliable and efficient boron removal technology.In this dissertation,two classes of novel pyrocatechol-modified mesoporous molecular sieves(CL-MCM-41,NCL-MCM-41,CL-SBA-15 and NCL-SBA-15)were synthesized as the adsorptive materials to remove boron in aqueous solution.Different adsorption times,initial concentrations of boric acid,temperature and pH were studied to learn about boron adsorption properties of new adsorbents.The experiments showed that boron adsorption capacity of the novel chelating adsorbents is better than commercial boron specific resin IRA 743 and the same chelating group-modified resin material.It was found that when the pH was about 9 and the initial concentration of boric acid was 0.5 M,the boron adsorption capacities were 52.1 mg/g for CL-MCM-41,and as high as 82.0 mg/g for NCL-MCM-41.Taking CL-MCM-41 as the research focus,three synthetic routes had been tried to synthesize the pyrocatechol-modified MCM-41.One way was proved to be able to afford grafted molecular sieve material,which was characterized by XRD,TEM,EA,BET,etc.The results of boron adsorption experiments indicated that the equilibrium time of adsorption is about 5 h;and the adsorption capacity of adsorbent will increase with the increasing initial concentration of boric acid;low temperature and basic conditions would be beneficial to the adsorption process.The adsorption kinetic and isothermal models showed that the adsorption process of CLMCM-41 fits pseudo-second-order kinetic model and Langmuir isotherm model well;and thermodynamic calculations showed that it is an exothermic and spontaneous process.Recycle regeneration experiments showed that CL-MCM-41 can be regenerated by mild conditions of 15% acetic acid solution.Finally,the adsorption capacities of six adsorbents were compared,which illustrated that for materials with the same class of functional groups,the one with a chelating group of larger conductive value change(?)will have a better adsorption capacity;and pyrocatechol-modified adsorbents have a better capacity than glucamine-modified adsorbents.To sum up,the novel chelating boron adsorption materials synthesized by this work will offer a variety of practical applications owing to their outstanding boron removal capacity,good hydrothermal stability and excellent regeneration ability.