Study On Selective Removal Of Salicylic Acid By Molecularly Imprinted TiO₂

Salicylic acid is a pollutant with low concentration,high toxicity and biodegradation,which can cause certain harm to the atmosphere and water.The conventional water treatment process is inefficient in treating wastewater including salicylic acid and it is difficult to achieve effluent standard at one time.Molecularly imprinted polymers synthesized by molecular imprinting method can selectively remove salicylic acid.After the removal of salicylic acid,the cost of conventional water treatment was significantly reduced.In the experiment,molecularly imprinted TiO2 was prepared by two methods,and the two kind of molecularly imprinted TiO2 were loaded with graphene.In the first method,the molecularly imprinted TiO2(MIP-TiO2)was prepared by chemical oxidation where salicylic acid was utilized as a template molecule,TiO2 was utilized as a functional monomer,p-phenylenediamine was utilized as crosslinking agent and ammonium peroxydisulfate was utilized as oxidant.The experimental results showed that the mass ratio of template molecules to functional monomers was 1:25.The removal efficiency of salicylic acid was the highest when the catalyst was polymerized for 4 hours in acidic condition of p H=1.5.In the second method,MIP-TiO2 was prepared by sol-gel method where salicylic acid was utilized as template molecule and TiO2 was utilized as functional monomer.The experimental results showed that the highest removal efficiency of salicylic acid was achieved by calcining the gel prepared at 1:5 molar ratio of salicylic acid and tetra butyl titanate at550 degrees Celsius for 120 min.Two kinds of G/MIP-TiO2 were prepared by two catalysts loaded with graphene.The photocatalytic degradation of 50 ml of salicylic acid solution(0.01g/L)was carried out with 0.05 g catalyst.The removal rate of MIP-TiO2 by chemical oxidation was 82.9% in 180 min.Being loaded with graphene reduced the removalefficiency of MIP-TiO2 and the decolorization rate of salicylic acid in 180 min decreased to 60.9%.The removal rate of MIP-TiO2 by using sol-gel method was88.7% in 180 min,and the removal efficiency of MIP-TiO2 was increased by being loaded with graphene.The decolorization rate increased to 97% in 180 min.Photocatalytic experiments were carried out in 50 ml mixture(0.01 g/L)consist of benzoic acid and salicylic acid in which 0.05 g catalyst was added.The rate constant for salicylic acid removal of MIP-TiO2 prepared by chemical oxidation was 0.00551min-1,and the selection factor was 2.46.Graphene reduced the selectivity of MIP-TiO2,and the selection factor decreased to 1.10.The rate constant of MIP-TiO2 prepared by sol-gel method was 0.00595 min-1,and the selection factor was 2.66.Graphene retained the selectivity of MIP-TiO2,and the selection factor after being loaded with graphene was 2.41.Based on the data above,the characterization of the catalyst tested by XRD,BET,SEM,TEM and UV-Vis were analyzed.Molecularly imprinted method could significantly improve the adsorption and selectivity of TiO2,and thus to increase the removal rate and the selectivity.The modification of graphene significantly improved the photocatalytic activity of molecularly imprinted polymers prepared by sol-gel method and it did not affect the selectivity of the catalyst at the same time.