Preparation Of FeO_x/SiO₂ Composites And Their Performance Of Purifying Dye Contaminated Wastewater

FeO_x/SiO₂ composites can be used in the fields including organic synthesis,and denitrification wastewater treatment,etc.FeO_x/SiO₂ composites with large specific surface area and high Fenton catalytic activity are widely used in the treatment of dye contaminated wastewater.However,they are mainly in powder form.If they are made in bulk form,it will facilitate their recovery and reutilization.In the experiment,ceramic technology was used to prepare FeO_x/SiO₂ composites.First,the iron organic salt or iron oxide was mixed with porous SiO₂ gel by ball milling.Bulk samples were pressed by moulding,following by calcinatin to form FeO_x/SiO₂ composite adsorbent and catalysts.The effects of Fe/SiO₂ molar ratio（0,0.01,0.02,0.05,0.1）and calcination on the textrual properties and iron state of the bulk FeO_x/SiO₂ composites were investigated by thermogravimetry,infrared spectroscopy,N₂ isothermal adsorption,SEM,XPS and DR UV-vis technique.The results show that the SiO₂ gel powder was bonded with iron species during ball milling,which is conducive to the uniform distribution of Fe in the gel matrix.At the same time,the specific surface area of the composites increased with the addition of iron species.When the molar ratio of Fe/SiO₂ was 0.05,the sample had the largest surface area of 580 m²/g.XPS results confirm the coexistence of Fe²⁺/Fe³⁺in the samples.When the molar ratio of Fe/SiO₂ is 0.05,Fe²⁺and Fe³⁺accounted for 39.1% and 60.9%respectively.DR UV-vis analysis showed that Fe²⁺mainly exists in nano-oxide particles in the products.The results show that the bulk FeO_x/SiO₂ composites and the added hydrogen peroxide solution constituted a Fenton-like catalyst system,which first adsorbed methylene blue（MB）molecules in simulated wastewater and then degraded them.TOC,EA and GC-MS analysis confirmed that MB was degraded into small molecules,water and CO₂.The ability of bulk FeO_x/SiO₂ composites to adsorb and degrade MB was related to the molar ratios of Fe/SiO₂,the dosages of materials,the amount of hydrogen peroxide solution,the initial concentration of MB,contact time and temperature.The composite which had the Fe/SiO₂ molar ratio of 0.05 had the best dye degradation performance.The removal efficiency of the sample toward 1000 mg/L MB solution reached 99.94% in 72 h,which was equivalent to 100 mg MB per gram of the sample.After five application of recycling,the composite still maintained high catalytic activity.The leaching amount of iron into the treated solution was very small,with an average leaching of 0.023%.Instead of using Fe（acac）₃,cheap Fe₂O₃ powder was also used to prepare bulky FeO_x/SiO₂ catalyst by compositing with the SiO₂ xerogels.The effects of calcination atmosphere,C/Fe molar ratio on the textural properties,the state of iron and the adsorption and degradation of MB were investigated.When the C/Fe ratio was 2,the specific surface area of the sample reached 492 m²/g.XRD results showed that with the increase of C/Fe molar ratios,γ-Fe₂O₃ phase increased,while that ofα-Fe₂O₃ phase decreased.In addition Fe₃O₄ phase appeared and increased with the C/Fe molar ratios,which indicated that the addition of carbon black and the calcination in nitrogen atmosphere promoted the reduction of Fe³⁺ to Fe²⁺.The degradation of 20mg/L MB solution by the composites showed that the MB removal efficiency of sample calcined in N₂ atmosphere was 50% higher than that of samples calcined in air atmosphere.At the same time,the former was close to equilibrium in 5 hours with MB removal efficiency of 93.8%,while the degradation of MB by the latter increased with time,till 24 hour with MB removal efficiency of 82.6%.When the molar ratio of C/Fe was 2,the sample had a removal efficiency toward MB of 89.5%,TOC 74.6%,which was 9% lower than that of the composite prepared with Fe（acac）₃ as iron source under the same conditions.