Adsorption of tetracycline in wastewater by copper-based nitrogen-carbon microspheres
Three copper-based nitrogen-carbon microspheres Cu-x/NC(x=1,2,3)were successfully synthesized by a one-step hydrothermal method using water-soluble low relative molecular mass chitosan(0.1000 g)as carbon and nitrogen sources,copper nitrate trihydrate(0.2174,0.2899,0.6522 g)as copper sources,characterized by SEM,FTIR,XRD,Raman spectroscopy and BET,and then evaluated via static adsorption experiments for their tetracycline hydrochloride(TC)adsorption performance,of which the adsorption kinetics,adsorption isotherms and thermodynamic parameters as well as the resistance to ion interference,pH stability and cyclic adsorption performance were further analyzed.The results showed that Cu-x/NC exhibited a regular spherical structure with oxygen-containing and nitrogen-containing groups on the surface and a uniform distribution of Cu elements.Cu-2/NC(5 mg)exhibited the maximum adsorption capacity for TC(1993.42 mg/g)at 25 ℃ for 24 h,and followed the Langmuir isotherm model and pseudo-second-order kinetic model,with a spontaneous and endothermic adsorption process.The presence of NaCl in TC solution didn't reduce the equilibrium adsorption capacity of Cu-2/NC toward TC,and TC solution at pH=5.5 was most favorable for adsorption.In the 7-cycle adsorption tests,Cu-2/NC showed a relatively stable removal rate to TC(95.84%~86.67%).The main driving force for TC adsorption by Cu-2/NC was attributed to hydrogen bond,Cu cation bonding bridge,electron donor-acceptor interaction and electrostatic interactions.