Sorption Characteristics Of Pharmaceutically Active Compounds To Biochar Studied Using Pp-LFERs

Biochar is a cheap,green and highly efficient adsorbent.It is a promising sorbent to treat pharmaceutically active compounds(PhACs)in water and soil environment.In this study,Fourier transform infrared spectroscopy,BET and scanning electron microscope were used to characterize the properties of biochar.Sorption batch experiments and polyparameter linear free energy relationships(pp-LFERs)model were adopted to predict the sorption coefficients and to elucidate the sorption mechanisms.14 pharmaceutically active compounds(PhACs)with diverse functional groups(carboxyl,hydroxyl and nitrogenous heterocyclic)were selected as sorbates.The characteristics of PhACs sorption to commercial rice straws biochar(carbonization temperature: 400~500 ?,200 mesh)were studied based on different intermolecular interactions.The main conclusions were as follows:(1)The results showed that 14 PhACs sorption to biochar included two stages,i.e.,the fast sorption in the beginning and the slow sorption in the following period.In the first stage,outside surface sorption and sorbate diffusion into macro and mesopores are the main mechanisms.In the second stage,inner surface sorption and sorbate diffusion into micropores dominated the sorption process.(2)Sorption mechanisms of 3 molecular hydroxyl PhACs to biochar include partition and adsorption(i.e.,van der Waals interactions and hydrogen bonding).Among 6 nitrogenous heterocyclic PhACs,the sorption mechanisms of molecules of antipyrine,aminopyrine and carbamazepine to biochar were partition,van der Waals and hydrogen bonding.The sorption of cationic mirtazapine,atenolol,lidocaine to biochar was driven by van der Waals force,hydrogen bonding and electrostatic interaction.(3)The sorption of 5 anionic hydroxyl PhACs to biochar was driven by various forces,including hydrogen bonding,?-? electron donor acceptor interactions,van der Waals and electrostatic interaction.The maximum sorption capacity was observed at the solution pH range of pKa±1.0 for five hydroxyl PhACs.For different forms(with different pH)of sorbate,the difference in the point of formation of hydrogen bonds is the main factor causing the sorption difference.(4)The pp-LFERs model of various activity(Cw/Sw)PhACs sorption to biochar was established by multiple linear regression method: lg Kd,activity(L/g)=(0.191-0.149 lg ai)E +(-0.433-0.106 lg ai)S +(0.261-0.124 lg ai)A +(-2.486-0.169 lg ai)B +(1.472-0.095 lg ai)V +(-0.945+0.101 lg ai)(N=228,R2=0.93,SE=0.23,F=268).The results of multiple correlation coefficient(R2=0.93),standard error(SE=0.23),F-statistic(F=268),leave-one-out cross validation(Q2LOO=0.90)and external cross validation correlation coefficient(Q2EXT=0.92)indicated that the model was stable and of high predictive ability.The pp-LFERs model could be used to predict the biochar-water sorption coefficients of PhACs.(5)The pp-LFERs model was used to quantify the contribution of different intermolecular forces in sorption of PhACs to biochar.Electron donation basicity(bB)and cavity formation energy(vV)were the main driven forces.