Preparation Of Different Modified Hydrochars And Their Adsorption Behavior Of Pb(?) In Aqueous Solution

Lead is a soft and ductile heavy metal which is widely used in the manufacturing,construction,and military industries.However,due to unreasonable application and discharge of wastewater,lead can cause pollution in the environment.Lead is degradable and easy to migrate and accumulate in living organisms,and it cannot be biologically.It posing a great threat to environmental safety and human health.Due to its excellent physical and chemical properties,hydrochar can be used as an inexpensive and environmentally friendly adsorbent.However,the original hydrochar has limited removal efficiency of heavy metal pollutants,it needs to be modified to improve its adsorption performance for pollutants.China has a large area of corn planting,and a large amount of straw produced every year.Corn straw has not be used in resources nowadays,instead,it causes waste and brings environmental pollution problems.In this paper,hydrothermal and pyrolysis combined,phosphoric acid modification and polyethyleneimine?PEI?modification were used to modify corn straw-based hydrochar?HC?,and the adsorption properties and mechanism of Pb?II?in aqueous solution were explored.The main contents and results of this research are divided into the following three aspects.?1?The corn stover was as raw material,hydrothermal-hydrothermal pyrolysis,phosphoric acid modification and polyethyleneimine modification were carried out to prepare HPx?HP300,HP500 and HP700?,phosphoric acid modified hydrochar?H₃PO₄-HC?and polyethyleneimine modified hydrochar?PEI-HC?.Scanning electron microscopy?SEM?,Xray diffraction?XRD?,Raman spectroscopy?Raman?,Fourier transform infrared spectroscopy?FT-IR?,X-ray photoelectron spectroscopy?XPS?were carried out to characterize the samples.The results show that HC retains the natural structure of corn stover,and has a large number of carbon microspheres of different sizes on the surface,and contains a large number of oxygen-containing functional groups.Hydro-pyrochar prepared at 300,500,700 °C,the products were named as HP300,HP500,HP700,respectively.With the increase of pyrolysis temperature,the functional groups on the surface of HPx decreased.During the modified process,the original structure of corn stover was destroyed,and the relatively large carbon microspheres on the surface were reduced.As the pyrolysis temperature increased,the micropore structure was formed on the surface of the carbon sphere,making the specific surface area of HPx increased,and the specific surface areas of HP300,HP500 and HP700 were 29.17,47.76 and 362.9 m2 g-1,respectively.SEM observation showed that,similar to HC,there were also a large number of carbon microspheres on the surface of H₃PO₄-HC.The presence of phosphoric acid can promote the degradation of cellulose.The cellulose degradation of phosphoric acid modified hydrothermal carbon is complete,and there are a large number of oxygen-containing functional groups on its surface,and most of them are hydrophilic functional groups.The surface of PEI-HC is covered by PEI,which is rough and uneven.Only a small amount of the carbon microspheres were existed.The surface of HC were covered by PEI which indicated that the introduction of N-containing functional groups were successful on the surface.Due to limitations of the temperature of the hydrothermal preparation of HC,the carbonization degree of PEI-HC was incomplete.?2?The adsorption performance of HC,HP300,HP500 and HP700 on Pb?II?in aqueous solution were determined.HP500 had the best adsorption effect on Pb?II?in aqueous solution,and the maximum adsorption capacity was 43.47 mg g-1.After kinetic and adsorption isotherm model fitting,the experimental data accords with Langmuir model and pseudosecond kinetic model.The results show that the adsorption of monolayers on Pb?II?in aqueous solution on HP500 is monolayer adsorption.Combing with XPS and FT-IR analysis,the adsorption mechanism of HP500 is the chemical adsorption between Pb?II?and C=Ocontaining groups and the physical adsorption by microporous structure on the surface.?3?The adsorption properties of H₃PO₄-HC and PEI-HC on Pb?II?in aqueous solution were determined.The maximum adsorption capacities of H₃PO₄-HC and PEI-HC to Pb?II?were 372.85 mg g-1 and 246.23 mg g-1,respectively.The results of mechanism analysis indicated that the adsorption mechanism of Pb?II?on H₃PO₄-HC was ion exchange and surface complexation,while the adsorption mechanism of PEI-HC included not only ion exchange and surface complexation,but also static electricity adsorption caused by the formation of-NH³⁺.