Controlled Preparation Of Diatomite-based Composite Materials For Treatment Of Organic Wastewater

In recent years,the research and utilization of diatomite has gradually become a hot spot in the field of micro and nano-technology,thanks to their unique shapes and ordered porous structures at the micro-and nanoscale,high specific surface area,favorable thermal stability and cost-effectiveness advantages.However,diatomite-based nanocomposites have been impeded due to the poor uniformity and dispersity,low amount of active substance load,less effective pore along with poor pore utilization,which are not fully utilized.To solve these problems,controllable fabrication methods were used to prepare Surface modified diatomite with excellent performance of the three-dimensional porous material.The functional composites are achieved by controllable deposition of functional materials on diatomite surface.This composite material maintaining the pore structure of diatomite and high specific surface area provides a large number of active sites for functional materials,and significantly improves the performance of diatomite-based composite materials as a photo Fenton catalyst,a Fenton catalyst,an adsorbent material and a reduction catalyst.The results expand the application range of diatomite composite materials in the environmental field.The main results include:?1?On the basis of MnO2@diatomite,iron oxide-coated diatomites were prepared through hydrothermal synthesis and sacrificial template redox etching reaction.The microstructure characterization results revealed that the Fe2O3 nanorods were uniformly distributed on the surface of diatomite.The effects of diverse synthetic parameters on morphology of as-synthesized Fe2O3@diatomite were investigated.Two different crystal phases of Fe2O3@diatomite were obtained from the FeOOH@diatomite samples calcined under different atmospheres.The catalytic activity of?-Fe₂O₃@diatomite was evaluated by the heterogeneous photo Fenton-like system through degradation of methylene blue(MB,10⁴0 mg L^-1)in the presence of hydrogen peroxide?H2O2,9 mM¹20 mM?under UV light irradiation.It was found that?-Fe2O3@diatomite composites showed very excellent degradation efficiency,which was about 99%within120 min under UV irradiation.This catalyst extended the range of pH values of homogeneous Fenton reaction,in which the MB removal rate was maintained over80.8%.Moreover,the?-Fe₂O₃@diatomite catalyst still showed sound reusability after 5rounds of degradation of MB dye.In principles,a possible photo-catalytic mechanism was proposed to testify metal oxides composites for heterogeneous photo Fenton-like reaction.?2?On the basis of the preparation of FeOOH@diatomite composite by sacrificial template method in the second chapter,the Fe2O3 nanosheets with double-shell hollow structure were prepared by replica molding from diatomite framework.Pure Fe2O3nanosheets were successfully obtained.The double-shell Fe2O3 hollow structure achieved via the NaOH etching silica method was observed.The Fe2O3 nanosheets possessed uniformly distributed porous nanosheets.Such structural features enlarged the specific surface area of Fe2O3 nanosheets and led to more catalytic active sites.In the heterogeneous photo-Fenton reaction,the double-shell Fe2O3 hollow morphology exhibited excellent catalytic capability for the degradation of Malachite green?MG?at circumneutral pH condition.Under optimum condition,MG solution was almost completely decolorized in 60 minutes?99.9%?.The Fe2O3 nanosheets also showed good stability and recyclability,demonstrating great potential as a promising photo-Fenton catalyst for the effective degradation of MG dye in wastewater.?3?Using diatomite as a carrier,under the neutral condition,the fabrication of the complex three dimensional?3D?diatomite/manganese silicate nanosheets composite?DMSNs?were achieved.The manganese silicate nanosheets are uniformly grown on the inner and outer surface of diatomite with controllable morphology using a hydrothermal method.Such structural features enlarged the specific surface area,resulting in more catalytic active sites.In the heterogeneous Fenton-like reaction,the DMSNs exhibited excellent catalytic capability for the degradation of malachite green?MG?.Under optimum condition,500 mg/L MG solution was nearly 93%decolorized at70 minutes in the reaction.The presented results show an enhanced catalytic behavior of the DMSNs prepared by the low-cost natural diatomite material and simple controllable process,which indicates their potential for environmental remediation applications.?4?On the basis of diatomite,magnesium silicate nanosheets were grown on diatomite by one-step hydrothermal method,which increased the specific surface area of diatomite-based materials.The surface of the DE/MgSi material was uniform and presented.It is distributed on the inner and outer surfaces of diatomite.Using the prepared DE/MgSi as template,the PANI layers were loaded on the surface of DE/MgSi by in-situ oxidative polymerization.The HCl acid-doped DE/MgSi/PANI composite was prepared and used for the adsorption experiment of MO in solution.The DE/MgSi/PANI-2 composite can quickly reach the adsorption equilibrium of MO in 60 min.The adsorption kinetics accords with the PSO kinetic model.The adsorption process is affected by both intragranular diffusion and liquid film diffusion.The adsorption isotherm conforms to the Redlich-Peterson isotherm adsorption model.The adsorption process includes chemical adsorption and physical adsorption,but mainly chemical adsorption.The maximum saturated adsorption capacity of the Langmuir adsorption isotherm model was 412.52 mg/g.The DE/MgSi/PANI-2 has good cycle regeneration performance,and the adsorption amount remains at about 70%of the initial adsorption amount after 6 adsorption-desorption cycles.The adsorption of MO by DE/MgSi/PANI-2 is mainly based on chemical adsorption such as electrostatic interaction or complexation,and physics such as?-?bond and intermolecular force on DE/MgSi/PANI-2.The combined effect of adsorption.?5?Firstly,diatomite is used as the silicon source,and the porous structure of diatomite soil is used as the carrier.By in-situ growth of nickel silicate nanosheets,the specific surface area of the composite increased,and the distribution of nickel silicate is uniform.On this basis,the PANI polymer was uniformly loaded with a large specific surface area of the composite material,and the nickel silicate nanosheet was reduced to a nickel element by utilizing the carbon reduction ability of PANI under high temperature cracking.The in-situ reduction of nickel material is realized in DE/Ni/N-C-800 material,and polyaniline is decomposed to form a nitrogen-doped carbon layer structure supported on the surface of DE/NiSi.The reduced nickel metal nano-particles has very good dispersibility.The DE/Ni/N-C-800 material exhibits superparamagnetism resulting in easily recyclable in homodisperse solution.The prepared DE/Ni/N-C-800 material was used to catalytically degrade 4-nitrophenol.The DE/Ni/N-C nanocatalyst exhibits excellent catalytic performance,and the catalytic process conforms to the pseudo first-order kinetic equation.The maximum catalytic rate is 0.035 s^-1.After 10 cycles of DE/Ni/N-C-800,the catalytic performance is still higher than 95%,showing high stability.Through the above research,the stability and uniformity of diatomite-based mono-,binary and multi-component composites are realized by the precise regulation of diatomite-based composites.The internal relation between the composite materials information and wastewater treatment performance will beestablished.It not only provides theoretical guidance for the preparation of high-performance diatomite-based materials,but also for reducing the transitional mining of diatomite minerals,keeping green mountains and green hills,and practicing sustainable development.