Controlled Preparation Of Polyaniline@Halloysite Composite Nanotubes And The Properties Of Cr(?)Adsorption/Reduction And Selective Oxidation Of Cyclohexene

Cyclohexene oxidation can produce a variety of important organic synthetic intermediate.Among them,the oxidation product 1,2-cyclohexanediol has been extensively studied owing to its important role in the synthesis of drug intermediates,polyesters,catechol and liquid crystalline polymers.On the other hand,Cr(?)removal with high efficiency are rather attractive for the serious threat to ecosystems and human health because of its high toxicity,potential carcinogenicity and nondegradability.In order to solve the remained issues in cyclohexene catalytic oxidation(including poor selectivity towards target product,harsh synthesis conditions and difficulty in recovery)and Cr(?)removal,it is proposed in this dissertation to one-step synthesis of polyaniline@halloysite composite nanotubes with halloysite nanotube as support at room temperature and study of its performance for selective oxidation of cyclohexene to 1,2-cyclohexanediol and Cr(?)adsorption/reduction.The main conclusions of the study are as follows:1.One-step synthesis of polyaniline@halloysite composite nanotubes(PANI@HA)at room temperature is proposed.By employing the different properties of interior/exterior surface and negatively charged exterior surface of halloysite nanotubes,the PANI can be induced to grow onto the surface of halloysite nanotubes at room temperature.By facilely tuning the dopant acid(HCl,H2SO4,HNO3,H3PO4),acidity and apparent weight proportion for aniline(ANI)and halloysite(HA)nanotubes in the synthesis process,PANI with tuned oxidation state,doping extent,and content are in situ growing on halloysite nanotubes.The results show the PANI@HA fabricated with HCl as dopant acid tuning the acidity at 0.3 M and 1 M and 204%apparent weight proportion for ANI and HA(PH/0.3 M/204%-HCl and PH/1 M/204%-HCl)shows the higher doping degree and the PANI in composite nanotubes is mainly existed in the form of emeraldine salt.2.The selective oxidation of cyclohexene to 1,2-cyclohexanediol by the above synthesized polyaniline@halloysite composite nanotubes is studied.The cyclohexene selective oxidation result shows PANI@HA nanotubes are effective catalysts in solvent-free reaction system with H2O2 as oxidant and their catalytic activity is relied on the doping acid,acidity and ANI/HA weight ratio in the fabrication.Wherein,PANI@HA synthesized with HCl as doping acid to condition the acidity at 1 M and 204%ANI/HA weight ratio(PH/1 M/204%-HCl)demonsrates the highest catalytic activity(98.17%conversion and 99.50%selectivity to 1,2-cyclohexanediol).The cyclohexene selective catalytic activity is with a well match to the PANI doping degree in PANI@HA.And the optimal reaction condition is 20 mg catalyst,2.5 mL H2O2,70 ? and the reaction time is 24 h.Furthermore,PH/1 M/204%-HCl has exhibit superior cycling performance with 99.11%conversion and 96.92%selectivity to 1,2-cyclohexanediol after five cycles.CV of PANI@HA indicates cyclohexene selective oxidation is attributed to reversible redox reaction of PANI in PANI@HA to catalytic decomposition of H2O2.3.The Cr(?)adsorption/reduction properties of the above synthesized polyaniline@halloysite composite nanotubes is studied.The adsorption result shows the fabricated PANI@HA hybrid nanotubes can effectively adsorb Cr(?)and the adsorption ability changes according to the dopant acid,acidity and apparent weight proportion for ANI and HA in the synthesis process.Among them,the PANI@HA fabricated with HCl as dopant acid tuning the acidity at 0.3 M and 204%apparent weight proportion for ANI and HA(PH/0.3 M/204%-HCl)shows the highest adsorption capacity.The adsorption capacity is in accordance well with the doping extent of PANI in PANI@HA.Furthermore,when PH/0.3 M/204%-HCl is redoped with HNO3,H2SO4 and H3PO4,the adsorption capacity declines,implying the dopant acid in the process of redoping exhibit marked effect on Cr(?)adsorption for the PANI@HA hybrid nanotubes.PH/0.3 M/204%-HCl and PH/0.3 M/204%-H3PO4 have demonstrated good regenerability with above 80%removal ratio after four cycles.The adsorption behavior is in good agreement with Langmuir and pseudo second order equations,indicating the adsorption of PANI@HA for Cr(?)is chemical adsorption.FT-IR and XPS of PANI@HA after Cr(?)adsorption indicate that the doped amine/imine group(-NH+/=N-+)groups are the main adsorption sites for the removal of Cr(?)by electrostatic adsorption and reduction of the adsorbed Cr(?)to Cr(?)simultaneously.