Study On The Fabrication And The Mechanism For Degradation Of Organic Pollutants By 3D Printed Porous Metallic Glasses Fenton-like Catalysts

The adequate access to clean water is vital for the development of human beings.How to deal with the increasingly serious water pollution problem has been attracted worldwide attentions.Metallic glasses（MGs）,with disorder atomic arrangement and the metastable nature,could efficiently degradate organic pollutants,such as azo dyes.However,due to the limitation in the preparation technique of MGs,the currently used MGs catalysts are usually in the form of powders and ribbons,which have small specific surface area and the difficulty in recovery of the catalysts after treatment.3D printing using selective laser melting（SLM）is a promising additive manufacturing technique for fabrication of MGs with complex geometries.In this paper,we attempted to apply the SLM 3D technique to prepare three dimenintianl porous metallic glasses and composite catlysts.The microstructure of the catalysts and the catalytic degradation mechanism have been systematically studied by X-ray diffraction（XRD）,differential scanning calorimetry（DSC）,optical microscopy（OM）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,Brunauer-Emmett-Teller（BET）techique,X-ray photoelectron spectroscopy（XPS）and electrochemical workstation.The contents of the thesis are briefly described as follows:（1）Zr₅₅Cu₃₀Ni₅Al₁₀ metallic glass with three different geometries,i.e.,cubic,hollow and lattice,were prepared by SLM 3D printing.The 3D printed Zr-based MGs are composed of two regions:the molten pools and the heat affected zones（HAZs）.The molten pools maintained an amorphous structure,while the HAZs were partially crystallized.The Zr-based MGs with different geometries exhibited different amorphous contents,among which the hollow one showed the highest amorphous content of⁹0%.The temperature field distribution of both molten pools and HAZs in the printed Zr-based MGs was investigated by finite element method.It was revealed that the cooling rate in molten pools is much higher than that in HAZs,this comprises the reason for the formation of full amorphous stricture in molten pools;whereas partial crystallization ocuured in HAZs due to the annealing effect during repeated laser scanning in SLM process.As compared to 3D printed cubic solid sample,the printed MGs with hollow and latticed structure exhibited a larger size of molten pools,resulting in higher fraction of amorphous phase in the two samples.（2）Based on the 3D printed lattice geometries of Zr₅₅Cu₃₀Ni₅Al₁₀MG,chemical dealloying approach was then used to prepare hierarchical porous structure where the nanoporous Cu distributed on the milli/micro MG networks.It was found that the nanoporous copper was uniform after dealloying treatmemt.Meanwhile,the influence of dealloying parameters（i.e.,dealloying time and HF concentration）on the nanoporous structure was studied.With the increase of dealloying time,the nanopore size was increased.Similarly,the nanopore size also increased with increasing HF concentration.The degradation efficiency of cube and lattice-like 3D hierarchical nanoporous copper catalysts to methyl orange was compared.The catalytic ability of the lattice catalyst was significantly higher than that of the cube one,indicating that network structure is helpful for wastewater degradation due to the accelerated mass transfer in the degradation process.（3）The degradation performance and mechanism of the lattice three-dimensional nanoporous copper（3D NP-Cu）catalysts on methyl orange were studied in detail.The 3D NP-Cu exhibited high degradation efficiency towards methyl orange with a kinetic reaction rate constant of 0.147 min^-1,which was 14 times and 4 times higher than the traditional commercial catalysts Cu²⁺and Cu powder,respectively.In addition,the 3D NP-Cu also had high catalytic degradation activity to the mixed dyes’solution and reduce the chemical oxygen demand,and most importantly fairly good reusability.Our studies revealed that the extraordinary catalytic activities of 3D NP-Cu catalysts originated from their unique 3D hierarchical mill/nano-porous structure with large specific surface area and numerous active atomic steps on Cu ligaments,which generate abundant active species and accelerate the transport of reactants.In addition,the presence of a small amount of Cu₂O active species in as-prepared 3D NP-Cu catalyst also played a critical role in promoting the degradation process,leading to the decomposition of azo dyes even in the absence of H₂O₂.（4）A three-dimensional metallic glass/copper bimetallic catalyst was prepared by 3D printing of Zr-based MG powder and Cu powder.The effect of copper content on the structure and catalytic performance of the bimetallic catalyst was studied.The Cu content was optimized to be 30 wt%,where the bimetallic catalyst（3D MG/Cu）showed the highest catalytic degradation activity for rhodamine B.Then,the catalytic degradation performance and mechanism of the 3D MG/Cu on organic pollutants were studied in detail.The results showed that the 3D MG/Cu could degrade more than 90%of various dye molecules within11 min.Besides,the 3D MG/Cu can also effectively reduce the COD of organic wastewater,and the COD of dye mixture was decreased by nearly 71%after 1.5 h degradation.In addition,the 3D MG/Cu exhibited a good reusability,which can be reused up to 73 times without obvious efficiency decay.The good catalytic activity of the 3D MG/Cu catalyst originated from four aspects:（i）the high intrinsic catalytic activity of MG;（ii）galvanic effect between MG and Cu accelerates charge transfer capacity of the catalyst;（iii）the synergistic effect between Cu and MG accelerates the conversion of Fe³⁺to Fe²⁺,thereby accelerating the catalytic degradation efficiency;and（iv）the unique three-dimensional porous structure that accelerates the mass transfer during degradation,making the reactants more accessible to the active sites.