Preparation And Adsorption Properties Of Micro-nano Structured Adsorbents Toward Heavy Metal Ions

Food safety issues are related to human health and economic development,which make an effect on the well-organized proceed of overall healthy society.Heavy metal pollution in food is a kind of ubiquitous and harmful food safety problem,which is one of the inevitable hidden dangers that threaten the field of food safety.Heavy metal ions are easily being accumulated and difficult to degrade,which can induce great damage to human health along with the transfer of food chain.Therefore,the food safety control of heavy metal pollution does not only limited on controlling the content of heavy metal elements in food matrix,but also required for comprehensive monitoring and effective management from food resource to food processing.According to the food safety control idea of"from farmland to table",this article serves adsorption technology as the technological process to develop and design a series of heavy metal adsorbents with micro-nano structure.This article contains the construction of adsorption platform within liquid particles adsorption,membrane adsorption and solid phase extraction systems,and the relevant adsorption performance,adsorption mechanism and utilization value were also investigated.The main research contents and results of this paper are shown as follows:1.Preparation of sulfur and nitrogen co-doped porous biochar and study of its heavy metal adsorption performance.Heavy metal contaminant in water resources is a primary research topic for food safety control.In this study,biowaste defatted soybean residues were mixed with potassium oxalate(activator)and calcium sulfate(hard template)then were carbonized with one-step pyrolysis method.According to scanning electron microscope,X-ray photoelectron spectroscopy and Raman characterizations,the results proved that the as-prepared biochar adsorbent exhibits a hierarchical porous microstructure,co-doping of sulfur and nitrogen elements,and functionalized with abundant acitve sites on its surface,which displays excellent adsorption capacities and high adsorption affinity towards Pb²⁺,Cu²⁺and Ni²⁺.The results elucidate that the selective adsorption property was ascribed to the co-doped sulfur and nitrogen,and revealed the adsorption process is a chemical monolayer adsorption,which the maximum adsorption capacities of Pb²⁺,Cu²⁺and Ni²⁺are 619.23 mg g^-1 and 1250.21 mg g^-1 and 1356.62mg g^-1,respectively.In addition,due to the co-doping of sulfur and nitrogen and the in-situ reduction of metal nanoparticles,the used biochar can be converted into a catalyst with excellent catalytic activity,which can be further used for the catalytic decomposition of organic pollutants and the toxic degradation of chromium.The prepared porous biochars converted from food biowaste have shown great potential in efficient water purification and sustainable utilization in homogeneous catalysis,which provide a research foundation for ensuring food safety control and pave the way for effectively utilization of food waste.2.Preparation of hydrotalcite/sodium alginate-based hydrogel as solid-phase extraction column for heavy metal separation.Aiming at the difficult of selective heavy metals separation in food analysis,a hydrotalcite/sodium alginate composite hydrogel was prepared and utilized for solid phase extraction column packing,which realized effective enrichment and separation of lead ions during food samples pretreatment.This solid phase extraction column combines with hydrotalcite nanosheets which were prepared by a simple hydrothermal synthesis method.According to the Lewis soft and hard acid-base theory,the intercalated sulfide anions endow the nanosheets with high selectivity towards Pb²⁺and exhibit high anti-interference property;the hydrotalcite/sodium alginate-based hydrogel can realize simple,time-saving and highly selective enrichment and extraction towards lead ions and were successfully utilized in a variety of food samples.Ascribed to the good adsorption performance and high enrichment effect,the solid phase extraction platform provides an efficient platform which was suitable for food sample pretreatment,while ensuring effective analysis and exhibiting great potential for practical utilization.3.Preparation of hierarchical adsorptive membrane based on hydrotalcite and study of the adsorption performance for heavy metal ions.In response to the potential threats caused by trace heavy metal pollution in food processing,the microflower-like hierarchical adsorptive membrane based on the above-mentioned hydrotalcite nanosheets were constructed through a one-pot hydrothermal method.The research results reveal that the microflower-like hierarchical membrane exhibited higher adsorption capacity compared with lamellar structured one.The dynamic adsorption results proved that the microstructure of adsorptive membrane has a great impact on the corresponding adsorption efficiency;further fluid dynamic simulations show that the fluid flow at the membrane interface were changed from laminar to turbulent flow correspondingly.This hydrodynamic transformation can cause the change of mass transfer behavior from molecular diffusion to eddy diffusion,which undergoes a more intricate contact interplay and highlight the importance of geometry-induced effects to overcome the diffusion constraints at the solid-liquid interfaces.This change effectively increases the removal efficiency for 78.3%.Under simulated drinking water conditions,the hierarchical structured membrane can effectively reduce the concentration of Pb²⁺and Cu²⁺under the drinking water standard level of the World Health Organization.This research provides technically inspiration on exploring novel adsorptive membranes for heavy metal control in food processing.4.Preparation of biomimetic neuron adsorptive networks for heavy metal adsorption and electrochemical-induced selective desorption.In view of the tedious regeneration process and limited regeneration capacity of traditional adsorbents,a kind of neuron-like adsorbent of polyaniline/ZIF-67/potassium manganese nanowire composite was constructed to achieve high adsorption efficiency of heavy metal ions and electrochemical-induced desorption,which can be a smart adsorbent platform for heavy metal ions with a reversible adsorption-desorption cycle.The results show that the neuron structured adsorbent can ensure the improvement of the heavy metals adsorption capacities toward lead and chromium,which can achieve high adsorption capacities of 526.31 mg g^-1 and 525.01 mg g^-1,respectively.The electrochemical-induced redox on the surface of adsorbent can change the state of adsorption sites,thereby causing the adsorbed heavy metal to be desorbed from the surface,avoiding complicated chemical treatment for regeneration.The research uses a biomimetic strategy to design smart heavy metal adsorbents and was expected to serve as a smart adsorbent platform to achieve a water-food-energy nexus cycling.