CO_(2)/C_(3)H_(6)O在金属氧化物耦合吡咯氮生物炭表面的共/竞吸附机理研究

Study on co/competitive adsorption mechanism of CO_(2)/C_(3)H_(6)O on the surface of metal oxide-coupled pyrrole nitrogen biochar

本研究采用密度泛函理论,通过比较吸附量、吸附能以及态密度和电荷差分密度的分析,探究了不同金属氧化物耦合吡咯氮生物炭(CN5@MOx,MOx=ZnO、CaO、Na2O)表面CO_(2)与C_(3)H_(6)O(CO_(2)&C_(3)H_(6)O)的吸附机理。首先从CO_(2)/C_(3)H_(6)O单组分方面计算了其在CN5@MOx表面吸附量和吸附能,计算结果表明,在333 K、100 kPa时CN5@Na2O表面对CO_(2)/C_(3)H_(6)O单组分吸附量分别为3.65、15.34 mmol/g,吸附能分别为-145.86、-132.47 kJ/mol,均高于CO_(2)/C_(3)H_(6)O单组分在CN5@CaO及CN5@ZnO表面吸附。得出Na2O掺杂吡咯氮生物炭对CO_(2)/C_(3)H_(6)O单组分吸附效果最优。进一步研究了CO_(2)&C_(3)H_(6)O在CN5@MOx表面共/竞吸附及机理。计算结果表明,CO_(2)&C_(3)H_(6)O在CN5@Na2O、CN5@CaO、CN5@ZnO表面吸附存在临界温度(分别为333、353、393 K),超过临界温度以后CO_(2)&C_(3)H_(6)O共存体系在CN5@MOx表面吸附量较CO_(2)/C_(3)H_(6)O单组分有所提高。CO_(2)&C_(3)H_(6)O在CN5@Na2O、 CN5@CaO、 CN5@ZnO表面吸附能分别比CO_(2)或C_(3)H_(6)O单组分吸附时至少高141.59、112.77、31.75 kJ/mol,CN5@MOx表面对CO_(2)和C_(3)H_(6)O的吸附表现为协同促进作用,且CN5@Na2O对CO_(2)&C_(3)H_(6)O共同吸附效果最佳。采用电荷差分密度和态密度分析CO_(2)&C_(3)H_(6)O在CN5@MOx表面协同吸附作用机理,得出CO_(2)的吸附作用力是通过C_(3)H_(6)O与CO_(2)的间接相互作用产生的,Na2O中Na与C_(3)H_(6)O电子云重叠,发生电荷转移,增强了两者间相互作用力,CN5@Na2O表面C_(3)H_(6)O与CN5在p轨道主要共振峰结合能较CN5@ZnO低了3.43 eV,使得C_(3)H_(6)O在CN5@Na2O表面吸附最稳定。

Biomass has a wide range of sources and is porous,and it is a raw material for the preparation of adsorbents with high application value.The adsorption effect of metal oxide-modified biochar on CO_(2) and acetone can be significantly improved,but the together/competitive relationship and adsorption mechanism of metal oxide-modified biomass-based adsorbent for simultaneous adsorption of multiple components are not clear.Based on this,the co-adsorption relationship between CO_(2) and C_(3)H_(6)O on the surface of metal oxide-doped nitrogen-rich biochar was carried out,which is of great significance for the multi-component synergistic adsorption and removal of biomass-based adsorbents.In this study,the adsorption mechanism of CO_(2) and C_(3)H_(6)O(CO_(2)&C_(3)H_(6)O)on the surface of different metal oxide-coupled pyrrole biochar(CN5@MOx,MOx=ZnO,CaO,Na2O)was explored by comparing the adsorption capacity,adsorption energy,state density and charge differential density analysis.Firstly,the adsorption capacity and adsorption energy of CO_(2)/C_(3)H_(6)O single component were calculated from the CN5@MOx surface,and the calculation results show that at 333 K and 100 kPa,the adsorption capacity of CO_(2)/C_(3)H_(6)O on the surface of the CN5@Na2O is 3.65 and 15.34 mmol/g,and the adsorption energy is−145.86 and−132.47 kJ/mol,respectively,which are higher than that of CO_(2)/C_(3)H_(6)O on the surface of CN5@CaO and CN5@ZnO.It was concluded that Na2O-doped pyrrole-nitrogen biochar had the best adsorption effect on CO_(2)/C_(3)H_(6)O one-component adsorption.The common/competitive adsorption of CO_(2)&C_(3)H_(6)O on the CN5@MOx surface was further studied.The calculation results show that there are critical temperatures for the adsorption of CO_(2)&C_(3)H_(6)O on the surface of CN5@Na2O, CN5@CaO and CN5@ZnO (333, 353 and 393 K, respectively), and the adsorption capacity of CO_(2)&C_(3)H_(6)O coexistence system on the CN5@MOx surface is higher than that of CO_(2)/C_(3)H_(6)O single component after the critical temperature. The adsorption energy of CO_(2)&C_(3)H_(6)O on the surface of CN5@Na2O, CN5@CaO and CN5@ZnO was at least 141.59, 112.77 and 31.75 kJ/mol higher than that of CO_(2) or C_(3)H_(6)O single-component adsorption, respectively, and the adsorption of CO_(2) and C_(3)H_(6)O on the CN5@MOx surface showed a synergistic promotion effect, and the CN5@Na2O had the best co-adsorption effect on CO_(2)&C_(3)H_(6)O. Finally, the electron density difference and density of state were used to analyze the mechanism of synergistic adsorption of CO_(2)&C_(3)H_(6)O on the CN5@MOx surface, and it was concluded that the adsorption force of CO_(2) was generated by the indirect interaction between C_(3)H_(6)O and CO_(2), and the electron cloud of Na and C_(3)H_(6)O in Na2O overlapped, and charge transfer occurred, which enhanced the interaction force between the two. The binding energy of the main formant of C_(3)H_(6)O and CN5 in the p orbital on the CN5@Na2O surface is 3.43 eV lower than that of CN5@ZnO, making the most stable adsorption of C_(3)H_(6)O on the CN5@Na2O surface.