Iron-Manganese-Rich Pelagic Clays For Fenton Catalysis/Micromotors And Hydrogenation Catalysis

Pelagic clays were marine sediments whose main components were clays,often rich in iron and manganese,and most of the iron and manganese presented as colloidal mineral components,i.e.,amorphous（hydrogen）oxides,they also existed in the clay lattice.The clay components in pelagic clays were characterized by poor crystallinity,resulting in high structural activity.In this thesis,we take advantage of the high Fe-Mn content and various forms of them in pelagic clays to use the clays without any modification as catalysts for the purification of wastewater such as dyeing wastewater and nitrophenol wastewater,and the high structural activity of clays made it easy to show high catalytic activity in these heterogeneous reactions.The iron-manganese-rich pelagic clays used in this paper were sampled from the Indian Ocean,and the catalytic processes for degradation of rhodamine B（Rh B）and reduction of 4-nitrophenol（4-NP）were specifically investigated.The main mineral composition of the pelagic clays was tested to be illite/montmorillonite（I/M）and amorphous ferromanganese nodules,containing impurities such as quartz and feldspar.Among them,I/M was very poorly crystalline,with loose structure and high activity.The test results showed that the iron content（calculated as Fe₂O₃）of pelagic clays was21.68%,mostly in Fe（III）valence state,while the manganese content（calculated as Mn O）was 6.17%,mainly in Mn（IV）and Mn（III）valence states.The iron and manganese elements were evenly distributed in the clay sediments,and they existed in the form of amorphous oxides as well as structural ions,and these characteristics gave the pelagic clays good catalytic performance.For Rh B,Fenton-catalyzed degradation with self-propelled micro/nanomotors synergistic strategy has been favored in recent years.Self-propelled micro/nanomotors were capable of self-motion in the fuel solution system,enhancing the performance of Fenton catalysts and enabling mechanical stirring in heterogeneous reactions,which can be used for catalytic reactions in restricted domains.The conventional Fenton catalysts were iron-based materials,while self-propelled motors were often made of precious metals such as Pt.Despite their excellent performance,they still had disadvantages such as high cost,complicated preparation process and material design.Based on this,the H₂O₂ solution system was chosen to provide the oxidant and micromotor fuel for the reaction,so that the iron species in the pelagic clays could act as Fenton catalyst and the ferromanganese nodules could act as self-propelled micromotors.A high average velocity of 183μm s^-1 for nodules was observed in 10.0wt.%H₂O₂ solution,demonstrating the good self-propelled ability of pelagic clay micromotors.Under acidic conditions,Fenton catalysis as well as the adsorption properties of the clay itself made the main contribution to the degradation of Rh B,and the complete removal of Rh B was achieved within 60 min.While under alkaline conditions,the adsorptive bubble separation mechanism（ABS）induced by the micromotors resulted in 94.6%degradation of Rh B within 60 min.Compared with montmorillonite and other terrestrial clays without self-propelled characteristics,the experimental results showed that the removal of Rh B was almost achieved by clay adsorption with adsorption contribution of 55.2%～78.5%,thus showing the excellence of pelagic clays as self-propelled Fenton catalyst for Rh B degradation.For 4-NP,Na BH₄ was commonly used as the reducing agent,and precious metals such as Au and Pt were used as catalysts to convert 4-NP to the low-toxicity 4-aminophenol（4-AP）,which also had the disadvantages of expensive cost and complicated material design and preparation.In this paper,iron-manganese-rich pelagic clays were directly used as hydrogenation catalysts,and the high content of Fe-Mn elements and high structural activity of the clays showed excellent catalytic activity for the reduction of 4-NP.At the beginning of the reaction,some of the high-valent Fe（III）,Mn（IV）and Mn（III）were first reduced to the low-valent Fe（II）and Mn（II）by Na BH₄,resulting in an induction period of the reaction,while the subsequent rapid reduction of4-NP catalyzed by these Fe and Mn elements occurred,the conversion from 4-NP to 4-AP was completed in 7.8 min,and meanwhile the pelagic clays acquired magnetic property.In the cycling experiments,if the pelagic clays maintained its magnetic property,there was no initial induction period and a shortening of the reaction time to5.2 min occurred within a few cycles.In contrast,terrestrial clays such as montmorillonite with very low or even no Fe-Mn content,and synthetic Fe₃O₄ with good crystallinity failed to show catalytic activity for 4-NP reduction,showing the unique advantage of iron-manganese-rich pelagic clays in hydrogenation catalysis.Therefore,the research content of this paper provided new optional materials for water purification catalysts and a new direction for the development and utilization of pelagic resources.