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聚酰亚胺基复合光催化剂的制备及用于降解水中有机染料性能研究
论文作者:童鞋论文网  论文来源:www.txlunwenw.com  发布时间:2019/9/11 8:27:55  

摘要:晶态聚酰亚铵 (PI) 是一种新型的半导体光催化纳米材料,其带隙大约为2.7 eV,属于N型半导体的范畴。它在可见光下有较强的吸收响应,能够吸收较多的可见光,对提高光催化剂对自然光的利用率提供了保证,其物化性质与石墨相氮化碳(g-C3N4)相类似,耐高温,稳定性好,微观结构呈现出典型的片层状形貌,可以作为其他半导体材料的载体。一般采用固体煅烧的方法进行制备,制备简单,原料易得,在整个反应过程中无任何有害物质产出,具备绿色无毒,价格低廉,可控性高等优点。但是,PI在可见光下的光催化效率较低,主要原因是在催化的过程中电子和空穴易发生耦合现象,降低了电子和空穴与目标污染物接触的机率。银系光催化材料(Ag2O, AgI, Ag3PO4)等在太阳光下有优良的光催化行能,能够对有机染料进行有效降解,但是因其是颗粒状,易发生团聚,同样存在电子和空穴易结合的问题,影响了它的光催化性能。将PI和银系光催化材料进行复合,能够解决电子和空学结合的问题,同时避免了催化剂分子的团聚的发生,对提高光催化活性大有帮助。

本文采用原位沉淀的方法,将PI和银系光催化材料进行复合,成功制备出一系列复合光催化剂,并借助XRD, FT-IR, SEM, TEM, PL, TOC等常规技术手段对其进行表征说明,探究了复合光催化剂在可见光下降解罗丹明B (RhB)的性能,并进行了稳定性和反应机理的研究。主要内容如下:

(1)利用原位生长的原理,制备出PI-AgI纳米复合半导体材料,AgI可以分散在PI上,避免了颗粒的团聚,在可见光的条件下,对RhB染料的降解具有显著的效果。究其原因,是PI和AgI之间能够形成异质结,有效避免了空穴和电子结合,加速了反应的速率。

(2)将片状的PI和颗粒状的Ag3PO4复合,制备出PI-Ag3PO4光催化材料,平均粒径为20 nm的Ag3PO4依附于PI纳米片上。在可见光的照射下,PI-Ag3PO4降解10mg/L的RhB溶液的速率相比纯样的Ag3PO4提高了4倍多,表现出了优异的光催化性能。异质结的形成,加速了电子和空穴的转移速率,同时,循环实验,也表明此种复合材料具备良好的稳定性。

(3)将PI超声振荡分散在蒸馏水中,分别加入适当的Ag离子和铬酸根离子,制备了PI-Ag2CrO4复合光催化材料,在可见光的范围下,降解RhB取得了良好的效果。复合后的光催化剂对可见光有强烈的吸收,通过活性物种实验,可以证明在整个催化过程中起主要作用的是空穴。

(4)颗粒状的Ag3VO4极易发生团聚,以PI为基底,可以发挥PI材料拥有较大比表积的优势,一定程度上阻止Ag3VO4的团聚,从而增大光催化剂与降解有机物的接触面积,加快反应速率。Ag3VO4的加入,拓宽了PI在可见光下的响应范围,增加了可见光的吸收强度,同时,避免了空穴和电子的结合,促进了光催化速率的提升。

(5)以制备好的PI作为载体,用原位生长的方法,将n型半导体PI和p型半导体Ag2O复合。Ag2O颗粒分散在PI的表面,分散后的Ag2O的颗粒大小下降许多。在可见光的照射下,用PI-Ag2O复合光催化剂降解10 mg/L的罗丹明B(RhB),发现其光催化效果比纯的PI和氧化银提高了不少,当Ag2O:PI=2:1时,PI-Ag2O的降解效果最佳,120分钟内可以达到98%的降解率。

Crystalline polyimide (PI) is a new type ofsemiconductor photocatalytic nanomaterials. Its bandgap is about 2.7 eV, whichbelongs to the category of n-type semiconductor. It has strong absorptionresponse under visible light and can absorb more visible light. It can improvethe utilization of natural light by photocatalyst. Its physical and chemicalproperties are similar to graphite phase carbon nitride (g-C3N4). It has hightemperature resistance, good stability and typical lamellar morphology. It canbe used as a carrier for other semiconductor materials. In general, solidcalcination method is used for preparation. The preparation is simple, rawmaterials are easy to obtain, and no harmful substances are produced in thewhole reaction process. It has the advantages of green, non-toxic, low priceand high controllability. However, the photocatalytic efficiency of PI undervisible light is low. The main reason is that electrons and holes are easilycoupled in the process of catalysis, which reduces the probability of contactbetween electrons and holes and target pollutants. Silver photocatalyticmaterials (Ag2O, AgI, Ag3PO4) have excellent photocatalytic activity undersunlight and can effectively degrade organic dyes. However, because of theirgranular shape, they are prone to agglomeration, and there are also problems ofeasy combination of electrons and holes, which affect their photocatalyticperformance. The combination of PI and photocatalytic materials can solve theproblem of the combination of electronics and space science, and avoid theagglomeration of catalyst molecules. It is helpful to improve thephotocatalytic activity.

In this paper, PI and silver photocatalystswere synthesized by in-situ precipitation, and a series of compositephotocatalysts were successfully prepared. The photocatalysts werecharacterized by XRD, FT-IR, SEM, TEM, PL, TOC and other conventionaltechniques. The properties of composite photocatalysts for the degradation ofrhodamine B (RhB) under visible light were investigated, and the stability andreaction mechanism were studied. The main contents are as follows:

(1) PI-AgI nanocomposite semiconductormaterials were prepared by in-situ growth. AgI can be dispersed on PI and avoidagglomeration of particles. Under visible light conditions, it has significanteffect on the degradation of RhB dyes. The reason is that heterojunctions canbe formed between PI and AgI, which can effectively avoid the combination ofholes and electrons and accelerate the reaction rate.

(2) PI-Ag3PO4 photocatalytic materials wereprepared by compounding sheet PI and granular Ag3PO4. The average particle sizeof the photocatalytic materials was 20 nm, and Ag3PO4 was attached to the PInanosheets. Under visible light irradiation, the degradation rate of 10 mg/LRhB solution by PI-Ag3PO4 was more than four times higher than that of pureAg3PO4, showing excellent photocatalytic performance. The formation ofheterojunction accelerates the transfer rate of electron and hole. At the sametime, cyclic experiments also show that the composite has good stability.

(3) PI-Ag2CrO4 composite photocatalyticmaterials were prepared by dispersing PI ultrasonic oscillation in distilledwater and adding appropriate Ag ions and chromium ions respectively. In thevisible light range, the degradation of RhB achieved good results. Thecomposite photocatalyst has a strong absorption of visible light. Through theexperiments of active species, it can be proved that holes play a major role inthe whole catalytic process.

(4) Particle Ag3VO4 is easy to agglomerate.PI as the base material can exert the advantage of larger specific surface areaof PI material, prevent Ag3VO4 agglomeration to a certain extent, increase thecontact area between photocatalyst and degradation organic matter, andaccelerate the reaction rate. The addition of Ag3VO4 broadens the responserange of PI under visible light, increases the absorption.

关键词:聚酰亚铵;氧化银;碘化银;铬酸银;光催化剂

PI; Ag2O; AgI; Ag2CrO4; Photocatalyst

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