Adsorption And Catalytic Performance Of Metal-loaded Molecularly Imprinted Catalysts For P-nitrobenzyl Alcohol

As an important fine chemical intermediate,p-nitrobenzyl alcohol(p-NBA)is widely used in many areas.However,there are many analogues of p-NBA,and the emission can cause serious environmental pollution.Hence,how to effectively identify and adsorb has attracted many attentions.In addition,p-nitrobenzaldehyde,the oxidation product of p-NBA,is widely used in modern chemical production,so the research on the catalytic oxidation performance of p-NBA has great significance.In the traditional p-NBA catalytic oxidation process,dilute nitric acid is mostly used as catalyst,which can cause seriously environmental pollution and equipment corrosion.Therefore,it is important to design and synthesize a new environmentally friendly catalyst.To effectively adsorb and catalyze p-NBA,the molecularly imprinted polymer adsorbents and metal-loaded molecularly imprinted catalysts were designed and synthesized,which could provide some ideas for the development of new efficient adsorbents and catalysts.By molecular imprinting technology,the molecularly imprinted polymer adsorbent(p-NBA-MIP)was firstly prepared with p-NBA as template molecule and the blank polymer adsorbent(AA-NIP)without template molecule was prepared for comparison experiments.The p-NBA-MIP and AA-NIP were characterized by pore structure characterization,FT-IR and SEM.The adsorption properties of p-NBA-MIP and AA-NIP for o-nitrobenzyl alcohol(o-NBA),m-nitrobenzyl alcohol(m-NBA)and p-NBA were investigated.Then the adsorption thermodynamics and kinetics were conducted.The results show that the specific surface area and pore volume of p-NBA-MIP are 152.6 m~2/g and 63.1 L/g,respectively,which are higher than those of AA-NIP with values of 50.3 m~2/g and 20.2 L/g,respectively.It provides a spatial possibility for p-NBA-MIP to have better adsorption performance.Compared with AA-NIP,p-NBA-MIP has higher swelling ratio of 44.57%,which is significantly higher than 4.04%of NIP.At 298 K,with initial concentration of 150 mg/L,the equilibrium adsorption capacities of p-NBA-MIP for p-NBA,o-NBA and m-NBA are36.4 mg/g,14 mg/g and 16 mg/g,respectively.The adsorption capacities of AA-NIP for the three adsorbates have slight difference and are less than those of p-NBA-MIP.The adsorption isotherms of p-NBA-MIP and AA-NIP for the three adsorbates can be fitted by the Langmuir and Freundlich equations.The K_b and K_f values of p-NBA-MIP for p-NBA are higher than those for other two adsorbates,which indicates that the adsorption capacity of p-NBA-MIP for p-NBA is greater than that for other two adsorbates.However,the K_b and K_f values of AA-NIP for the three adsorbates are similar,indicating that the adsorption capacity has slight difference.The adsorption thermodynamics results show that when the specific adsorption amount is 10 mg/g with p-NBA-MIP adsorbent for adsorbate of p-NBA,the free energy changes at 298 K,308K and 318 K are-3.523 kJ/mol?-3.288 kJ/mol and-3.008 kJ/mol,respectively.The absolute value of free energy change is decreased with the increasing of temperature,which indicates that the high temperature is not conducive to adsorption.The kinetic results show that Lagergren first order rate equation is more suitable for describing the adsorption of p-NBA,o-NBA and m-NBA by p-NBA-MIP and AA-NIP,and the liquid membrane diffusion rates of p-NBA,o-NBA and m-NBA are similar.The p-NBA-MIP has matching sites for p-NBA molecule perfectly,which shows high adsorption capacity and specific selection recognition performance.By bulk polymerization,the metal-supported molecularly imprinted catalyst(Ni-MIP)was prepared with nickel ion as template molecule and acrylamide(AM)as functional monomer,and non-molecularly imprinted polymer(Ni-NIP)without p-NBA and blank polymer without template molecule(NIP)were also prepared for comparison experiments.The prepared Ni-MIP,Ni-NIP and NIP were characterized by SEM,TEM,FT-IR and UV-Vis and the catalytic properties of Ni-MIP,Ni-NIP and NIP for o-NBA,m-NBA and p-NBA were investigated.The results show that the specific surface areas of Ni-MIP,Ni-NIP and NIP are 161.6 m~2/g,133.2 m~2/g and 51.2m~2/g,respectively,and the corresponding pore volumes are respective 71.1?L/g,62.7?L/g and 12.7?L/g.The specific surface area and pore volume of Ni-MIP are obviously larger than those of Ni-NIP or NIP,indicating that the specific surface area and pore volume of Ni-MIP,Ni-NIP and NIP are affected by the combination of p-NBA template and Ni nanoparticles.FT-IR analyses show that Ni-MIP,Ni-NIP and NIP catalysts have been successfully synthesized.SEM characterization indicates that the rough surface of Ni-MIP is beneficial to adsorption and the pore structure is formed with specific binding to template molecule.TEM characterization illuminates that Ni nanoparticles are successfully loaded into Ni-MIP and Ni-NIP polymer catalysts.The catalytic effects of Ni-MIP are significantly higher than those of Ni-NIP and NIP.For 1 h,the conversion rates of Ni-MIP,Ni-NIP and NIP to p-NBA are 72%,64%and 9%,respectively.The above results show that due to the existence of nickel nanoparticles and holes completely matching p-NBA molecules in Ni-MIP,Ni-MIP exhibits specific selective catalysis and high catalytic activity in the oxidation reaction of p-NBA to p-nitrobenzaldehyde.