Fabrication Of Iron,Manganese,Cobalt Based Composite Materials For Efficient Pollutant Removal

In recent years,with the rapid economic development,it has inevitably produced a large number of life and industrial wastewater.Among them,eutrophication and arsenic pollution have become the thorny issue,constituting a serious threat to human health and environment.Adsorption has been recognized as one of the promising candidates for phosphate and arsenic remediation.However,conventional adsorbents,e.g.bio-adsorbents,activated carbon and mineral,possess limited adsorption capacity due to their relatively small surface area and thus might not be feasible in the practical restoration of pollution.Accordingly,there is an urgent need for the development of adsorption-based purification technique mainly dependent on the absorbent materials,which can maintain the superior performance and simultaneously ensure facile separation from the solution,benefiting from the increased surface specific area and fully exposed active sites.In addition,the frequent oil spill is becoming a serious world-wide environmental problem,constituting a serious threat to energy shortage and marine ecological balance.In view of the increasing environmental pollution,commonly used technologies for oil spill remediation have been imposed to prevent the potential harm to the ecosystems of oceans and coastlines.Unfortunately,the current technologies for oil spill remediation suffer from more or less severe drawbacks and can not effectively remove oil pollutions.Accordingly,there is an urgent need for the development of high-performance technologies for effective oil-recovery and water remediation.In summary,hierarchical flower-like iron containing γ-MnO₂ hollow microspheres,3D β-FeOOH NRs/CF monolith and 3D Hierarchical Fe₃O₄/GO-CF have been successfully fabricated and their adsorption behavior towards phosphate and arsenic are investigated under various conditions.Similarly,the frequent oil spill is becoming a serious world-wide environmental problem,constituting a serious threat to energy shortage and marine ecological balance.Herein,we have demonstrated a vapor-phase hydrothermal method to prepare Co-MOFs on a free-standing carbon foam substrate for oil-water separation.Furthermore,we also develop a simple pumped device system which can collect the oil spill by a simple way.The main results are listed as follows:（1）The eutrophication of water bodies caused by the excessive release of phosphorus is becoming a serious world-wide environmental trouble.To address this issue,the exploitation of three-dimensional（3D）hierarchical architectures will be an effective strategy for sequestrating phosphate and preventing the occurrence of eutrophication.In this study,3D flower-like hierarchical iron containing MnO₂ hollow microspheres have been successfully fabricated via a facile one-step template-free route for the efficient removal of phosphate.Field-emission scanning electron microscopy（FESEM）and transmission electron microscopy（TEM）studies show that the microspheres obtained consists of numerous intertwining nanosheets.Strikingly,the thickness of these nanosheets can be elaborately modulated ranging from 30 to 2 nm via varying Fe/Mn ratios,accordingly resulting in the difference of the resultant phosphate adsorption performance.The uptake of phosphate onto these hierarchical microspheres show that the obtained hierarchical iron containing MnO₂ hollow microspheres possess the markedly enhanced phosphate removal performance over undoped counterparts regardless of the removal rate or efficiency;meanwhile,the enhanced effect become more obvious with increasing iron amount due to larger specific surface area and abundant active sites.Especially,the hierarchical MnO₂ microspheres with 26 wt%Fe incorporation are capable of removing completely low concentration phosphate（below 10 ppm）at a dosage of 0.5 g/L.In addition,the as-obtained materials exhibit higher sorption selectivity toward phosphate over other coexisting anions at high levels,which can be ascribed to the unique hierarchical structures and strong interaction between Mn/Fe sites and phosphate,as confirmed by Fourier-transform infrared（FT-IR）and X-ray photoelectron spectroscopy（XPS）analyses.Furthermore,the regenerated materials can be repeatedly used for five cycles without obvious degradation of performance,suggesting the sustainability of the absorbents.In virtue of high removal efficiency,fast adsorption kinetics,preferable sorption selectivity,as well as satisfactory recyclability,the obtained hierarchical iron containing MnO₂ hollow microspheres will be promising in eliminating the phosphate pollution from eutrophic waters.（2）The resulting iron containing MnO₂ hollow microspheres exhibit a noticeable enhanced performance for As（III）removal in aqueous phase compared to that of the undoped counterparts,accompanied by 102.84 mg/g of the saturated removal capacity towards As（III）.The excellent performance for the arsenic removal may be attributed to the unique structural characteristics of highly accessible surface and fully exposed active sites inherited from the hierarchical iron containing γ-MnO₂ samples.The co-existence of oxidation and adsorption is another key factor for the improvement of As（Ⅲ）removal efficiency,in which manganese dioxide is mainly responsible for oxidizing As（Ⅲ）to As（Ⅴ）and ferrous species may serve to the adsorption of the generated As（Ⅴ）,as evidenced by XPS analysis.Importantly,the composites exhibit an excellent regenerative ability over three cycles without a significant decrease in its removal efficiency towards As（Ⅲ）.Furthermore,the relatively large micrometer-scale particles can be easily separated by filtration,accompanied by fewer secondary contaminants risks than nanoparticles.Therefore,the fabricated hierarchical Fe-containing γ-MnO₂ hollow spheres in the present study will be an excellent candidate for the arsenic transformation and removal from the contaminated water based on the synergistic effects of effective oxidizing and adsorptive performance,good regeneration performance together with the convenient separation.（3）Arsenic pollution in waters has become a worldwide thorny issue,constituting a serious hazard to the whole ecosystem and public health worldwide.Accordingly,it is highly desirable to devise high-performance adsorbents for arsenic decontamination.Herein,a simple and cost-effective strategy is developed for the in-situ growth ofβ-FeOOH nanorods（NRs）on three dimensional（3D）carbon foam（CF）skeletons via a simple calcination process and subsequent hydrothermal treatment.The as-fabricated 3D β-FeOOH NRs/CF monolith can be innovatively utilized for the arsenic remediation from contaminated aqueous systems,accompanied by remarkably high adsorption capacity of 103.4 mg·g-1 for arsenite and 172.9 mg·g-1 for arsenate.The excellent performance for arsenic removal may be attributed to the unique structural characteristics,such as highly accessible surface,fully exposed active sites and efficient mass transfer associated with interconnected hierarchical porous networks.Simultaneously,the existence of abundant hydroxyl functional groups is another key factor for the improvement of arsenic removal.In addition,the as-obtained materials exhibit exceptional sorption selectivity toward arsenic over other coexisting anions at high levels,which can be ascribed to strong affinity between active sites and arsenic.More importantly,the free-standing 3D porous monolith not only makes it easy for separation and collection after treatment but also efficiently prevents the undesirable potential release of nanoparticles into aquatic environments while maintaining the outstanding properties of nanometer scale building blocks.Furthermore,the regenerated materials can be repeatedly used for five cycles without obvious degradation of performance,suggesting the sustainability of the monolith absorbents.In view of extremely high adsorption capacities,preferable sorption selectivity and satisfactory recyclability,as well as facile separation nature,the obtained 3D β-FeOOH NRs/CF monolith will be an ideal candidate for arsenic decontamination in practical application.（4）The 3D Hierarchical Fe₃O₄/GO-CF with abundant active sites has been successfully fabricated via coating GO on the surface of Fe₃O₄ nanoparctiles which firmly attachs on the skelton of 3D porous carbonized polymer foam for efficient As（Ⅲ）removal.The Fe₃O₄/GO-CF shows an enhanced As（Ⅲ）removal performance,in which Fe₃O₄ nanoparctiles act as the adsorption active center,the CF and GO constitute the bearing surface which allow the Fe₃O₄ nanoparctiles for uniform deposition,which greatly increases the active sites exposed.The saturated adsorption capacity of Fe₃O₄/GO-CF is as large as 111 mg/g for As（Ⅲ）calculated by the Langmuir isotherm model,exceeding largely other Fe-containing composite materials.The excellent performance for the arsenic removal may be attributed to the unique structural characteristics and fully exposed active sites inherited from the Fe₃O₄.Furthermore,the regenerated materials can be repeatedly used for five cycles without obvious degradation of performance,suggesting the sustainability of the adsorbents.More importantly,the light weight,micrometer-scale monolith can be easily separated from aqueous solution via a magnet.Thus,the low-cost Fe₃O₄/GO-CF adsorbents could be an ideal candidate for arsenic decontamination in practical application.（5）The frequent oil spill is becoming a serious world-wide environmental problem,constituting a serious threat to energy shortage and marine ecological balance;accordingly,there is an urgent need for the development of high-performance technologies for effective oil-recovery.Here,we have developed a vapor-phase hydrothermal method to prepare Co-MOFs on a free-standing carbon foam substrate for oil-water separation.The carbonized Co-MOFs/CF shows an excellent performance for oil adsorption because of the large water contact angle and hierarchical structure,which can provide numerous macroporous channels for the liquid transportation.Furthermore,a simple pumped device based on oil sorbents has been developed for in situ collection of oil spills from the water surface with high speed and efficiency.The results mentioned above indicate that the pumped device will be a promising method in eliminating the oils and organic pollutants from water.