Research On Preparation Of Nitrogen Doped Carbon Nanotubes By Modified Ferric Phosphate And Its Application

Phosphate slag,as a byproduct of the phosphating process on the surface of metal parts,could bring serious environmental and healthy damages to human,and soil and water environment due to its strong acidity,high phosphorus and some heavy metal ion.Many scholars study a lot on how to deal with and dispose of phosphate slag both at home and abroad.However,there are still some shortcomings in the large-scale phosphate slag treatment and recycling.Ferric phosphate(Fe PO4),as the main component of phosphate slag,can be effectively purified during hydrothermal crystallization process and can be applied in many fields such as,catalysis,water purification and electrochemical performance.However,ferric phosphate has many limits in practical applications due to its small specific surface area.Therefore,this study not only showed that phosphate residue can be effectively recovered,but also demonstrated that a promising catalyst can be fabricated for the removal of organic pollutants.Nitrogen-doped carbon nanotubes have been extensively studied for their high specific surface area and abundant active sites.However,the agglomeration of nitrogen-doped carbon nanotubes,caused by high surface activity,limits its application on the practical production process.Inspired by the above aspects,we explored an effective method to recover Fe PO4 from phosphate residue and further synthesize nitrogen-doped carbon nanotubes by the chemical vapor deposition method.To the best of our knowledge,such an approach has not been reported in any previous publications.The synthesized NCNTs-Fe PO4 composite has shown strong catalytic capability to remove organic dye in aqueous solution.This study not only showed that phosphate residue can be effectively recovered but also demonstrated that a promising catalyst can be fabricated for organic pollutant removal.In this paper,the phosphating slag as raw material was used to produce iron phosphate.And the surface of Fe PO4 was modified by sodium bicarbonate dilute solution,resulting in iron oxide on the surface of Fe PO4.The nitrogen-doped carbon nanotubes were prepared by chemical vapor deposition using Fe2O3/Fe PO4 as a catalyst.Finally,the product was labeled as NCNTs/Fe PO4.Moreover,the different reaction conditions were investigated,such as temperature and nitrogen source,to reveal morphology formation of the product.The results revealed that when the temperature reaches 850? and diethylamine is used as carbon source,the nitrogen-doped carbon nanotubes are uniformly distributed at a diameter of 100 ~ 200 nm on the surface of Fe PO4.It was also found that NCNTs/Fe PO4 has an excellent Fenton-like catalytic performance on Rh B degradation together with UV and H2O2.The kinetic studies indicated that the initial dye concentration,catalyst dosage,H2O2 dosage,and p H have a great influence on Rh B oxidative degradation.With the increase of initial concentration of rhodamine B solution,the photocatalytic degradation efficiency of NCNTs/Fe PO4 decreased gradually.As for increasing the amount of catalyst,the degradation efficiency of rhodamine B gradually increased.However,the photodegradation efficiency slightly decreased when the catalyst exceed to 2.0 g/L;With the increase of oxidant dosage,the degradation efficiency of rhodamine B gradually increased,but when the oxidant dosage was higher than 10mmol/L,the photodegradation efficiency decreased;NCNTs/Fe PO4 catalyst showed good catalytic activity at a wide p H value.The NCNTs/Fe PO4 also presented good recycling performance after 6 cycles,which still remained 50% Rh B removal.The XPS and CV analysis provied a mechanism that the electron transfer between Fe(III)and NCNTs promoted Fe(II)production to accelerating H2O2 production from H2O2.Further analysis of NCNTs/Fe PO4 by UV diffuse reflectance spectroscopy showed that the catalyst has good absorption peak under visible light.Therefore,the xenon lamp simulated sunlight was used as light source and PDS was used as oxidant to investigate visible light catalytic performance on methyl orange degradation.The catalyst dosage,the oxidant dosage and p H value on the photocatalytic activity were also discussed.The results showed that the Vis-NCNTs/Fe PO4-K2S2O8 system showed the highest photocatalytic degradation activity.In the series experiments,the degradation efficiency of methyl orange gradually increases with the catalyst increasing,but it would decrease when the system added to some degree.The degradation efficiency of methyl orange decreased with the increase of potassium persulfate concentration when the amount was higher than 4.0 g / L.Recycle performance tests revealed that the efficiency of methyl orange removal remained 40% after 5 cycles,which indicated that the NCNTs/Fe PO4 catalyst possess a good visible light catalytic performance.