Study On Preparation And Application Of Functionalized Mesoporous Materials Based Fly Ash

Fly ash is a major solid waste from coal-fired power plants,with annual emissions could reach up to 5 million tons.However,at present the comprehensive utilization rate of fly ash was only 70%,and the rest of fly ash could be capable of causing serious pollution to water body and soil.Therefore,the rational utilization of fly ash resources has become urgent need.Mesoporous silica was considered as an excellent adsorbent due to its superior characteristics of larger specific area,uniform pore distribution and abundant surface functional groups,which often used to adsorb organic dyes in printing and dyeing wastewater and heavy metal ions in industrial wastewater.However,due to the high price of silicon source,the industrial production of mesoporous silica has not been realized.Thus,it is very critical to find a low-cost silicon source to prepare mesoporous material In this paper,fly ash was employed as the raw material to prepare high-efficient adsorbent which was applied to the removal of organic dyes and heavy metal ions in wastewater to achieve the purpose of "treating waste with waste".In this paper,a high-efficient and economy-environmental resource utilization method was put forward using fly ash as the research object by studying the composition,structure and physical-chemical characteristics.The high added value mesoporous materials were prepared from fly ash with abundant silicon content,and fly ash-based mesoporous molecular sieve was characterized and analyzed via XRD,BET,F-SEM,FT-IR,TEM and other characterization methods.In addition,molecular sieve was functionally modified and investigated the effect of removing pollutants in wastewater under different conditions.The major research contents are as follows:1.Fly ash was employed as raw material and acid-washed with hydrochloric acid to remove impurity.The optimal acidification time of 2 h and acidification concentration of 3 mol/L were determined by XRD,XRF and SEM and so on,and the effects of acidification time and acidification concentration on the purify of fly ash were investigated Subsequently,the desilication process was carried out using acid washing fly ash as raw material and Use sodium hydroxide solution as desiliconization solution by simple alkali solution method,and the structure and composition was analyzed by XRD,XRF,SEM.The optimal desilication alkali concentration of 2 mol/L and temperature of 90? were determined by XRD,XRF and SEM and so on.The effects of desilication alkali concentration and desilication temperature on the desilication rate of fly ash were investigated.The desilication rate can be up to 47.3%under the optimal reaction conditions.2.Mesoporous molecular sieve Al-SBA-15 was prepared via hydrothermal method using P123 as template,fly ash desilication solution as precursor,and the effects of the dosage of template,crystallization temperature and crystallization time on the structure of mesoporous molecular sieve were studied.The results indicated that the optimal reaction condition were Si:P123=1:0.017,crystallization temperature of 100? and crystallization time of 48 h,and the specific surface area and pore volume of the synthesized mesoporous molecular sieve were 788 m2/g,0.95 cm3/g,and the average adsorption pore size was 4.36 nm.In addition,mesoporous molecular sieve was amino-functionally modified by silane coupling agent to obtain NH2-Al-SBA-15,and the structure and composition of NH2-Al-SBA-15 was analyzed by some characterization methods to determine that the amino group has been successfully grafted on the mesoporous molecular sieve.NH2-Al-SBA-15 was used to remove methylene blue in wastewater,and the effects of reaction time,temperature and pH on the removal rate of methylene blue were studied.It manifested that the adsorption amount of methylene blue by NH2-Al-SBA-15 could reach 305.24 mg/g under the optimal circumstance of reaction time 120 min,reaction temperature 25? and reaction pH of 10.3.Al-MCM-41 mesoporous molecular sieve was prepared using CTAB as template and fly ash desilication solution as precursor,and the effects of initial pH of solution,crystallization temperature and crystallization time on the structure of Al-MCM-41 were investigated.The results demonstrated that the specific surface area and pore volume of Al-MCM-41 were 938 m2/g,0.85 cm3/g,and the average adsorption pore size was 5.64 nm when the initial solution pH was 9,crystallization temperature was 110? and crystallization time was 48 h.Furthermore,Al-MCM-41 was modified by amino functionalization,and PVP was grafted onto mesolorous molecular sieve by Schiff base reaction to obtain PVP-Al-MCM-41 The structure and composition of PVP-Al-MCM-41 were characterized to confirm that PVP has been successfully grafted onto Al-MCM-41.PVP-Al-MCM-41 was employed to remove lead ions in industrial wastewater,and the effects of adsorbent dosage,adsorption time and initial solution pH on the removal rate of lead ion were investigated.It presented that the removal rate of lead ion can reach up to 99.56%at the adsorbent amount of 1.5 mg/L,adsorbent time of 90 min and initial solution pH of 5.0.