Synthesis Of FeTiO₃ Particles As Fenton-Like Catalysts For Catalytic Degradation Of Organic Pollutants

As one of the most abundant minerals in China,ilmenite（FeTiO₃）is an antiferromagnetic semiconductor with a wide bandgap（2.58–2.90 e V）and high electric capacity and conductivity,and used to produce titania or as electrode materials and photocatalysts.Iron and titanium ions in FeTiO₃ generally exist in mixed valence states(Fe²⁺/Fe³⁺and Ti⁴⁺/Ti³⁺)due to the electron transfer in the form of Fe²⁺+Ti⁴⁺（?）Fe³⁺+Ti³⁺.Rich ferrous ions(Fe²⁺)in FeTiO₃ can serve as active species to active H2O2 just like in conventional Fenton reaction for degradation of organic pollutants.Therefore,FeTiO₃ is a potential low-cost and green heterogeneous Fenton-like catalyst for environmental remediation,which has been less reported so far and deserves more investigation.In this thesis,FeTiO₃ particles were prepared by different methods and applied to activate H2O2 to degrade various organic pollutants with improved catalytic performances.The main research works in this thesis are summarized as follows:1.FeTiO₃ particles were prepared by sol-gel method with hexadecyltrimethyl ammonium bromide（CTAB）as an additive.It was found that the FeTiO₃ sample made with 10 wt%of CTAB（denoted as FTO-N1）had the best catalytic performance.SEM revealed that FTO-N1 with the BET specific surface area（SBET）of 159.0 m²/g mainly consisted of spherical particles with a large amount of interparticle pores.XPS confirmed the presence of mixed valence states of Fe and Ti species on the surface of FTO-N1.FTO-N1 effectively activated H2O2 to degrade 25 mg/L of various organic pollutants（including orange G（OG）,rhodamine B（Rh B）,metronidazole（MNZ）,methylene blue（MB）,paracetamol（APAP）,tetracycline（TC））at p H～3,indicating that FTO-N1 had a wide applicability.The degradation process of different pollutants on FTO-N1 generally conformed to the pseudo-first-order kinetic model.The corresponding first-order kinetic rate constants,k1s,of OG,MB,APAP,Rh B,MNZ,and TC were 0.1951,0.0734,0.0435,0.0368,0.0142 and 0.0100 min^-1,respectively.FTO-N1 could be reused for five times for degradation of OG or Rh B with high activity（the 3-h degradation rate in each run was>90%of 25 mg/L of OG,or>75%of 25 mg/L of Rh B,with the COD removal rates of up to64%）.The quenching and trapping experiments of active species found that·OH was the main active species with some contribution of O2^·-during the degradation of Rh B with H2O2 on FTO-N1.2.FeTiO₃ particles were prepared by direct solution calcination method.The calcination temperature was optimized to be 600 ^oC to obtain highly crystalline and pure FeTiO₃ particles（denoted as FTO-R1）.FTO-R1 was characterized by XRD,N2physisorption,SEM,TEM,XPS,BET and isoelectric point measurement.SEM images exhibited that FTO-R1 with SBET of 44.7 m²/g was mainly composed of thin flakes and blocks.XPS found some carbonaceous intermediates adsorbed on FTO-R1 after the TC degradation.FTO-R1 exhibited a better catalytic performance than FTO-N1 during degrading TC（25 mg/L）for 180 min at neutral p H.The catalytic activity of FTO-R1 in the TC degradation remained unchanged after five cycles（>90%of TC（25 mg/L）degraded with>58%of COD removal rate each time）.However,the degradation rate of TC（25mg/L）on FTO-N1 was only 50%after the second use.The degradation process of 25 mg/L of various organic pollutants（TC,APAP and ciprofloxacin（CIP））on FTO-R1 was in accordance with the first-order kinetic model.The k1s values of TC、APAP and CIP were respectively 0.0233、0.0030和0.0042 min^-1.The activation energy for the TC degradation with H2O2 on FTO-R1 was 26.25 k J/mol.It was found that the main active species during the degradation of TC with H₂O₂on FTO-R1 might not be·OH,¹O₂ or O₂^·-by quenching and trapping experiments of active species.More investigation was needed about the degradation mechanism of TC with H2O2 on FTO-R1.3.FeTiO₃ particles with high activity were synthesized by using tetraethyl orthosilicate（TEOS）as silicon source,which in-situ formed Si O2 as an auxiliary agent during calcination.Effects of the TEOS amount and calcination temperature on the catalytic degradation performance of the resulting FeTiO₃ samples were investigated.The synthesis conditions were optimized as follows:20 wt%of TEOS and calcination temperature of 700 ^oC（the corresponding sample was named FTO-M1）.The folded sheet structure of FTO-M1 was observed by TEM.FTO-M1 activated H2O2 to completely degrade 25 mg/L of CIP within 60 min.For comparison,the degradation rates of 25 mg/L of CIP on FTO-N1 and FTO-R1 after 180 min were respectively 73%and 52%.FTO-M1could be recycled for at least five times（>95%of 25 mg/L CIP degraded each time）.The activation energy for degradation of CIP with H2O2 on FTO-M1 was only 19.40 k J/mol.In addition,FTO-M1 could also activate H2O2 to effectively degrade 25 mg/L of Rh B,TC or CIP with more than 94%of degradation rates in 180 min,but only 30%of 25 mg/L of MNZ degraded under the same reaction conditions.Both quenching and trapping experiments of active species confirmed that·OH was the main active species for degradation of CIP with H2O2 on FTO-M1.