Preparation Of Porous Spinel Monoliths And Its Adsorption Performance Towards Organic Dyes

The contamination caused by the release of industrial wastewater containing varies of organic dyes into the water source environment,ecological systems as well as food,has brought a serious threat to the gloable nature and human health.Adsorption-based method using green adsorbent materials has been considered as one of the promising method for the management of wastewater,owing to its high removal efficiency,adsorption capacity,low cost and easy to operate.Furthermore,it should be highlighted that the adsorbents plays a key point in the adsorption field.Based on the review of the water treatment technology and the research status of adsorbents,spinel-type porous monoliths materials have been proposed to be untilized as adsorbents for the treatment of wastewater containing organic dyes,which three porous spinel-type double metal oxides,ZnAl2O4?MgAl2O4 and CuAl2O4 spinel have been synthesized as adsorbents via the sol-gel route accompanished by phase separation.Epoxide is used to accelerate the sol-gel transmition and the control the synergic effects with the polymers,thus to contribute to the construction of co-continuous skeletons and the inter-connected macroporous channels.The pore characterictics of these three spinel-type porous monoliths materials and their adsorption performance as well as selective adsorption ability towards anionic dyes and cationic dyes are studied in detail.The effects of some factors such as adsorbents dosage,solution pH,dye concentration and adsorption time on the adsorption properties of monolithic adsorbents were also discussed.We also analysize the adsorption isotherms and the adsorption kinetics,a prbable adsorption mechanism is proposed for explaining the adsorption performance,thus to provide a theoretival basis for the development and the application of porous spinel materials in the adsorption filed of wastewater treatment.The main conclusions are shown as follows:(1)Metal salt ZnCl2 and AlCl3 6H2O were used as precursors,the mixture of deionized water(H2O)and ethanol(EtOH)was used as solvents,propylene oxide(PO)was used as gel accelerator and polyethylene oxide(PEO)was used as phase separation inducer,to synthesize porous ZnAl2O4 spinel monoliths materials,using the sol-gel route accompanished with phase separation.Results indicate:when the amount of PEO is 0.14g,the ratio of H2O and EtOH is 3.5mL/1.5mL,the volume of PO is 3.4mL,porous ZnAl2O4 spinel monoliths with well-defined interconnected macroporous channels and co-continuous skeleton can be prepared.The macropore size is at 0.7 ?m,the porosity is 65%.Crystillined ZnAl2O4 spinel was ontained after heat-treatment above 600? without spoiling the macroporous structures.After heat-treatment,the macropore size was reduced to 0.5?m,the porosity increased to 75%and the specific surface area increased to 109 m2·g-1.The maximum adsorption capacity of sample before and after heat-treatment(ZA1 and ZA2)for the anionic dyes Congo Red(CR)were 2348.3 and 1574.4 mg g-1,and the maximum adsorption capacity for Methyl Orange(MO)were 1013.5 and 1015.1 mg g-1,respectively.Furthermore,the adsorption process was found to fit the Langmuir isothermal model and pseudo-second order model.(2)Metal salt MgCl2 and AlCl3 6H2O were used as precursors,the mixture of deionized water(H2O)and ethanol(EtOH)was used as solvents,propylene oxide(PO)was used as gel accelerator and polyethylene oxide(PEO)was used as phase separation inducer,to synthesize porous MgAl2O4 spinel monoliths materials,using the sol-gel route accompanished with phase separation.Results indicate:when the amount of PEO is 0.08g,porous MgAl2O4 spinel monoliths with well-defined interconnected macroporous channels and co-continuous skeleton can be prepared.The macropore size is at 1.9 ?m,the porosity is 53.5%,and the specific surface area is 12.7m2 g-1.Crystillined MgAl2O4 spinel is ontained after heat-treatment above 700 ?without spoiling the macroporous structures.After heat-treatment,the macropore size was distributed in the range of 0.7-1.0?m,the porosity increased to 65-75%and the specific surface area increased to 10-90 m2 g-1.The porous MgAl2O4 spinel shows high affinity and adsorption rate towards anionic dyes such as Methyl Orange(MO),Congo Red(CR)and Methyl Blue(MB),but exclude cationic dyes Rhodamine B(RhB)and Methylene Blue(MeB).The adsorption process was found to fit the Langmuir isothermal model and pseudo-second order model.According to the Langmuir model,the maximum adsorption capacity of porous MgAl2O4 spinel is 2721.6 mg g-1 for CR,2469.7 mg g-1 for MO and 6771.9 mg g-1 for MB.(3)Metal salt CuCl2·242O and AlC13·6H20 were used as precursors,the mixture of deionized water(H2O)and ethanol(EtOH)was used as solvents,propylene oxide(PO)was used as gel accelerator and polyethylene oxide(PEO)was used as phase separation inducer,to synthesize porous CuAl2O4 spinel monoliths materials,using the sol-gel route accompanished with phase separation.Results indicate:when the amount of PEO is 0.06g,porous CuAl2O4 spinel monoliths with well-defined interconnected macroporous channels and co-continuous skeleton can be prepared.The macropore size is at 2.1?m,the porosity is 57%,and the specific surface area is 46.6m2·g-1.Crystillined CuAl2O4 spinel was ontained after heat-treatment above 500?without spoiling the macroporous structures.After heat-treatment,the macropore size was distributed in the range of 0.5-1.0?m,the porosity increased to 65-70%and the specific surface area increased to 10-70 m2 g-1.The porous CuAl2O4 spinel shows high affinity and adsorption rate towards anionic dyes such as Methyl Orange(MO),Congo Red(CR)and Methyl Blue(MB),but exclude cationic dyes Rhodamine B(RhB)and Methylene Blue(MeB).The adsorption process was found to fit the Langmuir isothermal model and pseudo-second order model.According to the Langmuir model,the maximum adsorption capacity of porous CuAl2O4 spinel is 1789.9 mg g-1 for CR,1184.2 mg g-1 for MO and 1579.3 mg g-1 for MB.