| Alizarin red（AR）,as a typical anthraquinone dye,is widely used in the textile printing and dyeing industry.However,due to the presence of aromatic rings in its chemical structure,alizarin red has high physicochemical stability and photothermal stability,which is difficult to degrade naturally.The untreated AR wastewater that directly discharged into aquatic environments such as lakes,streams and ponds can induce serious threats to aquatic ecosystems and human health.At present,there are two main methods for the removal of AR wastewater.One of them is physical treatment methods,such as adsorption,membrane filtration,ion exchange,etc.This method exhibits high efficiency and large processing capacity,but this only transfers AR from water to somewhere else,which is easy to cause secondary pollution.The second approach is chemical treatment methods,such as chemical reagent oxidation,electrochemical anodic oxidation,photocatalytic degradation,etc.This method can degrade AR into non-toxic or mineralized substances,but the efficiency is unsatisfying and only low concentrations of AR wastewater can be treated.In order to overcome the limitations of a single treatment method,scientists have proposed the adsorption-photocatalytic technology,that is,to endow the adsorbent photocatalytic properties at the same time,so that the adsorbed pollutants can be degraded into non-toxic or mineralized substances in situ through photocatalysis.Therefore,the capability of the wastewater treatment of the adsorbent can be further improved.However,few people have employed the adsorptionphotocatalytic technology to treat AR wastewater.Polyaniline（PANI）is one of the most investigated adsorbents due to its easy availability of raw materials,facile synthesis,high controllability,good physicochemical properties,mechanical flexibility and environmental stability.However,pure polyaniline has poor adsorption performance and poor photocatalytic degradation performance.Based on the above fact,in this thesis,PANI was composited with graphene oxide（GO）and carbon nanotubes（CNTs）to study its adsorption and photocatalytic degradation properties for AR dyes.（1）PANI nanofibers,PANI/GO composites,and PANI/CNTs composites were synthesized by chemical oxidation,blending,and in-situ polymerization,respectively.The morphology and structure of the materials were characterized by scanning electron microscopy,infrared spectroscopy,X-ray diffraction,Raman spectroscopy,X-ray photoelectron spectroscopy and thermogravimetric analysis.The specific surface area and pore size of the material were characterized by nitrogen adsorption-desorption.The PANI composite materials were demonstrated to be featured with mesopores,and their pore volume and pore size are improved.The optoelectronic properties of the material were characterized by UV-vis diffuse reflection and electrochemical impedance.The PANI composite materials show absorption under visible light,and the related impedance is smaller,which improves the transfer ability of photogenerated electrons.（2）The effects of adsorbent amount,initial pH value,adsorption temperature,adsorption time and initial AR concentration on the adsorption performance were systematically studied in the system of AR adsorption by PANI and its composites.The adsorption mechanism study showed that the adsorption process of AR conformed to the pseudo-second-order kinetics and the Freundlich isotherm model.The adsorption capacities of PANI,PANI/GO and PANI/CNTs for AR were 258.329 and 447 mg/g,respectively.In addition,the removal rate of AR by PANI/CNTs is over 90%,and it has high selectivity for AR.Moreover,the recycling experiments indicated that the PANI/CNTs can be reused.（3）In the photocatalytic degradation of AR by PANI and its composites,the effects of adsorbent amount,initial pH value,photocatalytic time and initial AR concentration on the photocatalytic degradation performance were systematically studied.The results showed that the photocatalytic degradation of AR by PANI and its composites conforms to the L-H kinetic model.After photocatalytic degradation,the removal rate of AR by PANI/GO was increased from 47.3%to 67.1%,and the removal rate of AR by PANI/CNTs was increased from 87.5%to 91.0%.The combination with carbon nanomaterials GO or CNTs delays the recombination of electron-hole pairs generated by PANI,thereby effectively enhancing the photocatalytic degradation performance of PANI and the related removal efficiency for AR. |
