- A+
Fig. 1. (a-d) SEM images, (e) element mapping and (f-k) HRTEM images of the NiZn@N-G-900.
如Fig. 1所示,SEM、HRTEM和EDS-mapping结果表明所制备催化剂是由N掺杂石墨包覆Ni金属和Ni3ZnC0.7合金纳米颗粒组成的。
Fig. 2. XPS spectra of the Fresh, Used and Re-calcined NiZn@N-G-900: (a) the N 1s core level and (b) the Ni 2p core level.
XPS结果(Fig. 2)表明,N元素的改变可能对所致被催化剂的性能产生影响。而反应前后并没有检测到Ni元素的价态变化。
Fig. 3. (a)CO2-TPD and (b) NH3-TPD profiles of the Fresh NiZn@N-G-900. (c) Tafel scans of the Fresh NiZn@N-G-900, Used NiZn@N-G-900, Re-calcined NiZn@N-G-900, Ni0 powder and the Zn@N-C-900.
如图Fig. 3(a)所示,所制备NiZn@N-G-900催化剂表面同时存在酸性位点和碱性位点。通常,酸性位点容易与亲核物质(如NH3和HSO5-)结合,而碱性位点容易与亲电物质(如CO2)结合。因此,表面酸性位点有利于PMS的吸附与活化。Tafel曲线表明,所制备NiZn@N-G-900催化剂具有优良的电荷传输性能(Fig. 3(b))。
Fig. 4. (a) A series of results for DFT calculations,including adsorption models (top view, side view), electrostatic potentialdistributions (ESP, Isosurface contour is 0.01 e/bohr3),adsorption energy (Eads), peroxide O-O bond length (lO-O)and electron gain and loss of the adsorbed PMS (Q). (b) The chargedifference distribution of different PMS adsorption models. (Isosurface contouris 0.002 e/bohr3. The light green and light yellow denote theelectron depletion and electron accumulation, respectively.). (c) The workfunction (Ф) of each slab model.
DFT计算结果表明(Fig. 4),在纳米金属颗粒表面包覆石墨或N掺杂石墨,不仅可以降低催化剂表面的功函数(Ф),增强催化剂与吸附质之间的电子转移,而且可以有效地控制表面电荷分布(ESP),为PMS的吸附和活化创造更多的场所。同时,石墨或N掺杂石墨对纳米金属颗粒的包覆程度不同,也会导致PMS与催化剂之间吸附能的变化。通常,适当的吸附能有利于PMS与催化剂之间的电荷转移。PMS吸附模型都表明PMS具有获得电子的趋势。这种趋势会使PMS中O-O过氧键键变长,进而有利于PMS的活化。根据DFT计算结果,提出了PMS的活化机理:当PMS吸附在活性位点上时,一些电子倾向于向PMS转移,从而使O-O过氧键的长度变长。随后,吸附在催化剂表面的、具有较长过氧键的PMS与相邻PMS相互碰撞进而转化为ROS。
Fig. 5. (a) Degradation efficiency of BPA in the NiZn-N-G-900/PMS system under different quenching conditions. (b) Premixed experiments in the NiZn-N-G-900/PMS system. (c) The change of PMS residual in the presence of different scavengers. (d) Effect of β-carotene on BPA degradation in anhydrous methanol. (e) EPR spectra in the NiZn-N-G-900/PMS system. (f) Degradation of BPA in D2O. (Conditions: 20 mg·L−1 BPA, 200 mg·L−1 catalyst, 0.244 mM PMS, pH= 6.5 and temperature = 30 oC).
根据无水甲醇中β-胡萝卜素淬灭实验、重水中BPA降解实验预混合实验和EPR结果得出NiZn@N-G-900/PMS体系属于典型的1O2主导的非自由基体系。同时,体系中1O2大量产生的主要原因归因于催化剂对PMS自分解反应的催化作用。
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