Removal Of P-arsanilic Acid By Magnetic Microporous Biochar Derived From Hazelnut Shell

Arsenic exposures is a vital threat of global environment,especially related with the groundwater that is a significant part of drinking water.Arsenic exposures are usually divided into two parts artificially.The one is associated with inorganic arsenic classified in Group 1 by IARC including arsenate and arsenite,while the other is associated with less toxic organic arsenic compounds represented by 4-aminophenylarsonic acid(p-ASA,p-arsanilic acid).pASA,as one of paramount antibacterial organoarsenic compounds,has been widely used as feed additives in swine and poultry industry for coccidiosis control as well as growth promotion in the past several decades.However,p-ASA resulting from poultry excretion is released into soil,subsequently leached into groundwater downward,and finally maybe converted to the arsenate and arsenite in the process of biodegradation,resulting in a significantly increasing biotoxicity and metabolism to threaten the safety of drinking water severely.Hence,there is an urgent need for removal of p-ASA to avoid this potential threat.Especially,the concentration of p-ASA in the aquaculture wastewater is relatively low,at the mg/L level.Compared with other strategies,the adsorption method is more suitable strategy for the treatment of lowconcentration pollutants,so it is regarded as one of the most promising methods.It is well known that biochar is an important type of environmentally friendly adsorbent.Hazel groves are widely distributed in Northeast China,North China and other regions.Thus,hazelnut shells,an agricultural waste to be urgently addressed,becomes a promising candidate of precursor.This paper pyrolyzed natural biomass,hazelnut shells,into magnetic microporous biochar(MMHC)through synchronous carbonization magnetization method.In addition,the original hazelnut shell biochar(HC)with direct carbonization and the porous hazelnut shell charcoal(MHC)only activated without an iron source were synthesized as control samples.SEM and TEM images showed that the addition of ZnCl2 produced more irregular pores into the material,while the introduction of iron sources converted the irregular pores of the material to more regular pores,which is in agreement with the nitrogen adsorption and desorption test result.The introduction of porogen increased the specific surface area,while the introduction of iron source did not reduce the specific surface area significantly.XRD and XPS analysis confirmed that added iron source was successfully converted to ferric tetroxide after pyrolysis.Raman analysis confirmed that the introduction of ZnCl2 reduces the degree of graphitization,which changed the carbon matrix in the material from nanocrystalline graphite to amorphous carbon.Two kind of elemental analysis methods have shown that the introduction of ZnCl2 and iron sources increases the oxygen content in the carbon matrix,which may be due to the increase in the amount of organic oxygen-containing functional groups on the surface.The adsorption results showed that the adsorption capacity of MMHC for p-ASA is as high as 218.2 mg/g,and the removal rate is 87.3%,which wasmuch higher than that of HC and MHC.The optimum pH of the adsorption process is 4,the adsorption kinetics follows a quasi-secondorder adsorption model,and the adsorption isotherms conform to the Langmuir model and Freundlich model.Infrared spectra before and after adsorption indicated that characteristic peaks of Fe-O-As groups appear after adsorption,revealing complexation interaction during the adsorption process.The C1s spectrum in XPS shows that there is no obvious C=O on the surface of the MMHC material,indicating that there is no significant π-π interaction in the adsorption process,while the O1s peak indicates that the hydrogen bond content is reduced after adsorption,indicating that the adsorption process involved H-bond interactions.