一锅法光热催化升级转化聚乳酸制备氢气和丙酮酸

One-pot photothermal upcycling of polylactic acid to hydrogen and pyruvic acid

聚乳酸(PLA)是一种生物可降解高分子材料,近年来已广泛用作常规塑料的替代品.然而,其在自然环境中生物降解往往需要较长时间,这不仅延长了降解周期,还导致了碳资源的浪费.光热催化技术不仅可以利用清洁的太阳能资源原位产生活性氧化还原物种,同时通过引入热源改善纯光或纯热催化效率低和产物选择性差等难题,有望在塑料催化升级转化过程中发挥作用.本文通过原位光沉积方法分别在二氧化钛(TiO_(2))、氮化碳纳米片(A-V-PCN)和硫化镉(CdS)半导体载体上制备了一系列铂基光热催化剂,铂纳米粒子的平均粒径约2 nm.对铂基光热催化剂的光热催化乳酸水溶液的析氢反应进行了综合评价和比较.结果表明,铂基光热催化剂的光热催化制氢性能远优于纯光催化和纯热催化.其中,CdS半导体负载的铂基催化剂(Pt/CdS)对聚乳酸光热催化转化表现出最优的催化活性,在150°C时,Pt/CdS催化产氢速率分别是Pt/TiO_(2)和Pt/A-V-PCN的1.2倍和4.8倍.变温光电流密度响应、莫特-肖特基以及荧光光谱测试结果表明,提高温度可以有效地抑制光生载流子的复合,从而大幅度提高光热催化转化效率.对不同光热催化剂的液相产物和能带结构进行分析发现,具有合适带隙的CdS半导体能够高选择性地催化生成丙酮酸.相比之下,TiO_(2)和A-V-PCN半导体上由于形成羟基自由基,导致丙酮酸被进一步氧化分解为乙醛和少量的甲酸.原位电子自旋共振表征和理论计算结果进一步揭示,CdS有助于关键中间体(碳中心自由基)的形成和连续脱氢,从而促进了Pt/CdS高选择性制备丙酮酸,并有效抑制过氧化产物的累积.将Pt/CdS催化剂应用于实际聚乳酸塑料时,其光热催化反应的制氢速率为200±17.5 mmol·gcat^(-1)·gplastic^(-1),丙酮酸在液体产物中的选择性为98.1%,产率达到100±11.5 mmol·gcat^(-1)·gplastic^(-1).循环稳定性实验和反应前后的催化剂表征结果表明,Pt/CdS催化剂在光热反应条件下具有较好的稳定性.综上,本工作实现了一锅法光热催化转化聚乳酸为氢气和高附加值含氧化合物丙酮酸,发展了一种高效高选择性转化塑料废弃物为高附加值化学品的光热催化策略,为废塑料碳资源的绿色循环利用提供了解决思路.

While biodegradable polymers such as polylactic acid(PLA)are widely used as alternatives to non-biodegradable polymers to address the plastic crisis,their biodegradation is difficult to control,and the process emits carbon.Conversion of PLA waste into value-added products via thermal and photocatalytic pathways is a promising solution.Herein,we describe a one-pot photothermal catalytic method that efficiently converts PLA into hydrogen and other valuable chemicals without requiring a concentrated KOH solution.Examining the catalytic properties of Pt/A-V-PCN(atomic-layered g-C3N4),Pt/TiO_(2),and Pt/CdS for the photothermal reforming of lactic acid(LA)indicated superior hydrogen production for all the employed catalysts owing to the promotion effects of external heat on the excitation and utilization of carriers,as characterized by electrochemical impedance spectroscopy Nyquist and transient photocurrent(I-t)tests.We found that the cadmium sulfide(CdS)possesses excellent selectivity for converting LA into pyruvic acid(PyA).Using in situ electrochemical electron spin resonance spectroscopy experiments and density functional theory computations,we found that the high PyA selectivity for LA oxidation on the CdS surface was attributed to the different affinities of the active sites for C-and O-adsorbed species,resulting in enhanced dehydrogenation and hindered C-C cleavage.Furthermore,Pt/CdS demonstrated increased reactivity and achieved 98.1%selectivity for high-value pyruvic acid in liquid products during the one-pot photothermal upcycling of commercial PLA plastics.Hence,this study provides a strategy for developing more efficient catalytic routes for upcycling PLA and other polyesters.