Facile synthesis of nanoceria by a molten hydroxide method and its photocatalytic properties

Ceria nanoparticles were facilely synthesized by a molten NaOH-KOH hydroxide flux method with the precursor of Ce(NO3)3·6H2O under different conditions in alumina crucibles or Teflon-lined stainless steel autoclave.The XRD patterns and TEM images show that both the crystal and particle sizes of synthesized nanoceria are around 10 nm.XPS results reveal that the nanoceria obtained in alumina crucible has a Ce3+fraction of 17.1%which is higher than that of ceria synthesized in the Teflon vessel,the FTIR spectra of nanoceria prepared in alumina crucible show a stronger intensity of O-H stretching mode.UV-DRS and PL spectra results show that the nanoceria synthesized in alumina crucible with a calculated band gap of 2.9 eV has a wider responding light wavelength and a lower photogene rated electron-hole recombination rate,due to a higher concentration of oxygen vacancies(Ce^3+%).The photocatalytic results show that the degradation ratio and rate of the Rhodamine B(RhB)solution with the nanoceria synthesized in alumina crucible are 98.39%and 0.02919 min-1,both of which are larger than those of the ceria obtained from Teflon vessel.This method proves to be a simple and scalable way to synthesize nanoceria with rich oxygen vacancies and high photocatalytic activity.

Catalytic action of rare earth oxide(La_(2)O_(3),CeO_(2),Pr_(6)O_(11))on electrochemical oxidation of activated carbon in molten KOH-NaOH

The oxidation of anode carbon fuel directly affects the electrochemical performance of molten hydroxide direct carbon fuel cell(MHDCFC).In general,the anode carbon fuel can be oxidized at high temperature,thus the direct carbon fuel cell(DCFC)can show great electrochemical performance.In this study,rare earth oxides(La_(2)O_(3),CeO_(2),Pr_(6)O_(11))were prepared by the method of precipitation.Activated carbon was prepared by pretreatment of lignite.Rare earth oxides and activated carbon were mixed as anode carbon fuel,and rare earth oxides were used to catalyze the electrochemical oxidation of anode carbon fuel.The results show that CeO_(2)has better electrocatalytic activity compared with La_(2)O_(3)and Pr_(6)O_(11) in the MHDCFC.The electrochemical test results show that the current density(at 0.4 V)increases from 81.02 to 112.90 mA/cm^(2)and the maximum power density increases from 34.78 to 47.05 mW/cm^(2)at 450℃,when the mass fraction of CeO_(2)is increased from 0 to 40%.When the mass fraction of CeO_(2)is 30%,the current density(82.55 mA/cm^(2)at 0.4 V)at 400℃is higher than that(81.02 mA/cm^(2)at 0.4 V)without CeO_(2)at 450℃.The electrochemical oxidation mechanism of CeO_(2)catalyzed anode carbon fuel is discussed.

Thermal defluorination behaviors of PFOS,PFOA and PFBS during regeneration of activated carbon by molten salt

Current study proposes a green regeneration method of activated carbon(AC)laden with Perfluorochemicals(PFCs)from the perspective of environmental safety and resource regeneration.The defluorination efficiencies of AC adsorbed perfluorooctanesulfonate(PFOS),perfluorooctanoic acid(PFOA)and perfluorobutanesulfonate(PFBS)using three molten sodium salts and one molten alkali were compared.Results showed that defluorination efficiencies of molten NaOH for the three PFCs were higher than the other three molten sodium salts at lower temperature.At 700°C,the defluorination efficiencies of PFOS and PFBS using molten NaOH reached to 84.2%and 79.2%,respectively,while the defluorination efficiency of PFOA was 35.3%.In addition,the temperature of molten salt,the holding time and the ratio of salt to carbon were directly proportional to the defluorination efficiency.The low defluorination efficiency of PFOA was due to the low thermal stability of PFOA,which made it difficult to be captured by molten salt.The weight loss range of PFOA was 75°C–125°C,which was much lower than PFOS and PFBS(400°C–500°C).From the perspective of gas production,fluorine-containing gases produced from molten NaOH-treated AC were significantly reduced,which means that environmental risks were significantly reduced.After molten NaOH treatment,the regenerated AC had higher adsorption capacity than that of pre-treated AC.