全有机S型异质结PDI-Ala/S-C_(3)N_(4)光催化剂增强光催化性能

All Organic S-Scheme Heterojunction PDI-Ala/S-C_(3)N_(4) Photocatalyst with Enhanced Photocatalytic Performance

有机光催化剂以其适宜的氧化还原能带、低成本、高化学稳定性、分子结构和电子结构的可调控性而备受关注。PDI-Ala(N,N’-二(丙酸)-苝-3,4,9,10-四羧酸二亚胺)是一种新型的有机光催化剂,具有较强的可见光响应、低价带位置、强氧化能力等特点。然而,低的光生电荷转移速率和高的载流子复合率限制了它的应用。由于g-C_(3)N_(4)存在芳香杂环结构且PDI-Ala的刚性平面结构存在着离域大π键,g-C_(3)N_(4)和PDI-Ala可以通过π–π相互作用和N―C键紧密结合。通过硫掺杂g-C_(3)N_(4)合成了S-C_(3)N_(4),其能带结构相比于g-C_(3)N_(4)更能与PDI-Ala相匹配。电子离域效应、内建电场和新形成的界面化学键共同促进了PDI-Ala与S-C_(3)N_(4)之间光生载流子的分离与迁移。因此,采用原位自组装的方法制备了一种由有机半导体PDI-Ala和S-C_(3)N_(4)组成的S型(阶梯型)异质结光催化剂。在制备过程中,PDI-Ala通过横向氢键和纵向π–π堆积自组装成超分子。采用X射线衍射(XRD)、透射电子显微镜(TEM)、能谱仪(EDS)、X射线光电子能谱(XPS)、紫外可见漫反射光谱(UVVis-DRS)、电化学阻抗谱(EIS)、Mott-Schottky曲线(MS)等多种表征方法,对PDI-Ala/S-C_(3)N_(4)光催化剂的晶体结构、形貌、价态、光学性能、稳定性和能带结构进行了系统的分析和研究;利用密度泛函理论(DFT)计算了材料的功函数和界面耦合特性。研究了合成的光催化剂在H2O2生产中的光催化活性以及在可见光照射下对四环素(TC)和对硝基苯酚(PNP)的降解作用。该S型异质结具有能带匹配和紧密的界面结合,加速了分子间的电子转移,拓宽了异质结的可见光响应范围。此外,在PDI-Ala/S-C_(3)N_(4)光催化降解反应过程中,产生并积累了多种活性物种(h^(+)、·O^(-)_(2)和H_(2)O_(2))。因此,PDI-Ala/SC_(3)N_(4)异质结在降解TC、PNP和H_(2)O_(2)生产方面表现出更强的光催化性能。在可见光照射下,30%PDI-Ala/S-C_(3)N_(4)样品在90 min内去除了90%的TC,H_(2)O_(2)的产率为28.3μmol·h^(-1)·g^(-1),分别是PDI-Ala的2.9倍和S-C_(3)N_(4)的1.6倍。结果表明,由苝二酰亚胺(PDIs)基超分子和S-C_(3)N_(4)组成的全有机光催化剂可有效地用于降解有机污染物和生产H_(2)O_(2)。本研究不仅为全有机S型异质结的设计提供了一种新的策略,而且为理解具有有效界面键合的异质结构催化剂的构效关系提供了新的见解和参考。

Organic photocatalysts have attracted attention owing to their suitable redox band positions,low cost,high chemical stability,and good tunability of their framework and electronic structure.As a novel organic photocatalyst,PDI-Ala(N,N’-bis(propionic acid)-perylene-3,4,9,10-tetracarboxylic diimide)has strong visible-light response,low valence band position,and strong oxidation ability.However,the low photogenerated charge transfer rate and high carrier recombination rate limit its application.Due to the aromatic heterocyclic structure of g-C_(3)N_(4) and large delocalizedπbond in the planar structure of PDI-Ala,g-C_(3)N_(4) and PDI-Ala can be tightly combined throughπ–πinteractions and N―C bond.The band structure of sulfur-doped g-C_(3)N_(4)(S-C_(3)N_(4))matched well with PDI-Ala than that with g-C_(3)N_(4).The electron delocalization effect,internal electric field,and newly formed chemical bond jointly promote the separation and migration of photogenerated carriers between PDI-Ala and S-C_(3)N_(4).To this end,a novel step-scheme(Sscheme)heterojunction photocatalyst comprising organic semiconductor PDI-Ala and S-C_(3)N_(4) was prepared by an in situ self-assembly strategy.Meanwhile,PDI-Ala was self-assembled by transverse hydrogen bonding and longitudinalπ–πstacking.The crystal structure,morphology,valency,optical properties,stability,and energy band structure of the PDIAla/S-C_(3)N_(4) photocatalysts were systematically analyzed and studied by various characterization methods such as X-ray diffraction,transmission electron microscopy,energy dispersive X-ray spectrometry,X-ray photoelectron spectroscopy,ultraviolet visible diffuse reflectance spectroscopy,electrochemical impedance spectroscopy,and Mott-Schottky curve.The work functions and interface coupling characteristics were determined using density functional theory.The photocatalytic activities of the synthesized photocatalyst for H_(2)O_(2) production and the degradation of tetracycline(TC)and p-nitrophenol(PNP)under visible-light irradiation are discussed.The PDI-Ala/S-C_(3)N_(4) S-scheme heterojunction with band matching and tight interface bonding accelerates the intermolecular electron transfer and broadens the visible-light response range of the heterojunction.In addition,in the processes of the PDI-Ala/S-C_(3)N_(4) photocatalytic degradation reaction,a variety of active species(h^(+),·O^(-)_(2),and H_(2)O_(2))were produced and accumulated.Therefore,the PDI-Ala/S-C_(3)N_(4) heterojunction exhibited enhanced photocatalytic performance in the degradation of TC,PNP,and H_(2)O_(2) production.Under visible-light irradiation,the optimum 30%PDI-Ala/S-C_(3)N_(4) removed 90%of TC within 90 min.In addition,30%PDI-Ala/S-C_(3)N_(4) displayed the highest H_(2)O_(2) evolution rate of 28.3μmol·h^(-1)·g^(-1),which was 2.9 and 1.6 times higher than those of PDI-Ala and S-C_(3)N_(4),respectively.These results reveal that the all organic photocatalyst comprising PDI-based supramolecular and S-C_(3)N_(4) can be efficiently applied for the degradation of organic pollutants and production of H_(2)O_(2).This work not only provides a novel strategy for the design of all organic S-scheme heterojunctions but also provides a new insight and reference for understanding the structure–activity relationship of heterostructure catalysts with effective interface bonding.