【摘要】：當今社會經(jīng)濟迅猛發(fā)展,隨之而來的能源短缺以及生態(tài)環(huán)境問題,已然成為人類關(guān)心的熱點,而對環(huán)境污染控制和凈化的研究也已成為亟待全球科學家攻克的重要難題。光催化技術(shù)是一種綠色的高級氧化技術(shù),在光的照射下,半導體材料能夠活化氧氣分子或水分子,使之產(chǎn)生具有活性的自由基,降解和消除掉各種環(huán)境污染物。光催化技術(shù)不僅能夠有效的利用太陽能,將其轉(zhuǎn)化為氫能等容易為人類所用的能源,從而解決資源短缺等問題;還能夠把有毒、有害的有機、無機環(huán)境污染物降解或者礦化為低毒性甚至無毒性的物質(zhì),降低對環(huán)境造成的污染。然而,以二氧化鈦(Ti02)為代表的傳統(tǒng)半導體氧化物光催化劑,因其本身能帶結(jié)構(gòu)局限,存在對光的響應范圍較窄等問題,導致對太陽能的利用率較低,同時其本身還有穩(wěn)定性較差等缺點,這些因素都限制了其在光催化領(lǐng)域的發(fā)展和應用。因此,如何實現(xiàn)光能的有效轉(zhuǎn)換,尋找和制備具有寬光譜響應范圍、高量子效率且易回收利用等優(yōu)勢的光催化材料是亟待研究者解決的關(guān)鍵科學性問題。目前,以石墨相氮化碳(g-C3N4)為代表的非金屬層狀材料,其特殊的電子結(jié)構(gòu),使之展現(xiàn)出獨特的性能,同時它還具備良好的熱穩(wěn)定性、化學穩(wěn)定性,成為科研工作者研究和關(guān)注的熱點。另外該材料成本低廉,具有合適的能帶結(jié)構(gòu),其禁帶寬度(Eg)約為2.7 eV,是類似于石墨的片層結(jié)構(gòu)材料,可以從多種富含氮元素的天然材料中制得。g-C3N4在可見光照射下即可光解水、光催化降解多種污染物,是一種理想的可見光響應型光催化劑。但光譜吸收范圍窄、比表面積小、光生電子-空穴對復合率高等缺陷影響了其光催化性能的提升。本論文以g-C3N4為研究中心,通過多種修飾改性方法,改善其光催化性能,在對該材料進行微觀結(jié)構(gòu)表征以及光催化性能評價基礎上,對其性能提升的原因及作用機制進行了詳細的分析,主要研究內(nèi)容如下:首先,以多層g-C3N4為基底材料,通過半導體復合的方法來提高其可見光催化性能。采用離子交換法分別制備了銀/氯化銀(Ag/AgCl)和碘化銀(AgI)納米顆粒改性的g-C3N4納米復合材料(Ag/AgCl/g-C3N4和AgI/g-C3N4),一方面擴展了g-C3N4可以利用的可見光范圍;另一方面利用二者之間的協(xié)同效應促進光生電子-空穴對的分離,提升其光催化降解性能。利用多種表征方法分別對Ag/AgCl/g-C3N4和AgI/g-C3N4納米復合材料的微觀結(jié)構(gòu)和形貌進行分析,并深入考察了 Ag/AgCl/g-C3N4和AgI/g-C3N4納米復合光催化劑在可見光照射下降解環(huán)境有機污染物的性能。結(jié)果表明,隨著Ag/AgCl和AgI含量的升高,復合光催化劑在可見光區(qū)的吸收逐漸增強。在可見光的照射下,AgCl/g-C3N4中會有部分Ag單質(zhì)出現(xiàn),形成Ag/AgCl/g-C3N4復合納米材料,Ag單質(zhì)的等離子共振效應以及材料之間構(gòu)建的協(xié)同作用共同提升了光催化性能,然而該體系仍存在穩(wěn)定性較差的問題;相比之下,AgI具有更強的光催化活性,與g-C3N4的復合可增強AgI的穩(wěn)定性,二者之間的協(xié)同作用有助于光生電子-空穴對的遷移和分離,最終使復合材料的光電流強度和光催化活性等均得到顯著提高。其次,與石墨材料相比,二維以及三維結(jié)構(gòu)的石墨烯材料具有更優(yōu)越的光電性質(zhì)和表面特性。而層狀g-C3N4材料與石墨結(jié)構(gòu)相似,層間以范德華力相連,比表面積較小,影響了其光催化性能。借鑒石墨烯的研究思路,以多層g-C3N4材料為基底,通過剝離、自組裝等方式將其制備成二維或者三維結(jié)構(gòu),打破g-C3N4材料層間的范德華力,增大其表面積并提升其光催化性能。采用溶劑剝離法,控制合成了二維類石墨烯型氮化碳(GL-C3N4),該材料具有較高的比表面積、有效的電子-空穴對分離率和優(yōu)越的光電性能,在可見光照射下,GL-C3N4的光電流強度和光催化活性都得到了顯著的提高。另外,在二維GL-C3N4研究的基礎上,進一步在離子液體的輔助下,將體相g-C3N4轉(zhuǎn)變?yōu)榫哂腥S網(wǎng)絡結(jié)構(gòu)的g-C3N4水凝膠。運用多種表征手段結(jié)合理論計算研究了三維網(wǎng)絡結(jié)構(gòu)g-C3N4水凝膠形成的機理,據(jù)此提出了一個將層狀材料剝離轉(zhuǎn)化成穩(wěn)定的三維水凝膠的普適性方法。研究表明,三維網(wǎng)絡結(jié)構(gòu)g-C3N4水凝膠具有特殊的電子結(jié)構(gòu)和光學特性,可拓展g-C3N4在光學等領(lǐng)域的應用,這為后期濕法化學的研究以及納米材料光電特性的調(diào)控提供了新的方法和思路。綜合二維GL-C3N4與三維g-C3N4水凝膠光催化特性的研究可以發(fā)現(xiàn):二維GL-C3N4因具有較大的表面積和優(yōu)異的光生載流子轉(zhuǎn)移和分離效率,而具備更優(yōu)的光催化性能。最后,為進一步提升二維GL-C3N4的光催化性能,而向其中引入具有寬光吸收范圍、高量子效率、強光生載流子遷移能力的新型納米材料,利用復合材料的協(xié)同效應提升其電子-空穴對的分離效率及其對可見光的吸收能力�；诖�,設計制備了 ZnS/GL-C3N4以及GL-MoS2/C3N4復合材料,并將其應用于光催化降解有機污染物。研究結(jié)果顯示,在可見光照射下,不同維度的納米復合材料光催化降解有機污染物的活性優(yōu)于純GL-C3N4材料。隨著復合材料單體間接觸面積的增加,建立了載流子的快速傳輸通道,加速了界面電荷的轉(zhuǎn)移能力,能夠顯著改善GL-C3N4的光電化學性質(zhì)。同時,復合納米材料提高了對可見光的利用率,實現(xiàn)了有機污染物的高效、深度降解。該研究工作展示的獨特策略可以擴展到其他納米復合體系中,也為合理設計和優(yōu)化其他重要的化學和催化反應提供了新的研究思路和實驗手段。
[Abstract]:Nowadays, with the rapid development of society and economy, energy shortage and ecological environment problems have become the focus of human concern, and the study of environmental pollution control and purification has become an important problem to be solved by scientists all over the world. Materials can activate oxygen molecules or water molecules to produce active free radicals, degrade and eliminate various environmental pollutants. Photocatalytic technology can not only effectively utilize solar energy, convert it into hydrogen energy and other easily used energy for mankind, thereby solving the shortage of resources and other problems; but also can poisonous, harmful organic, inorganic. Degradation or mineralization of environmental pollutants into low toxic or even non-toxic substances can reduce environmental pollution. However, traditional semiconductor oxide photocatalysts, represented by titanium dioxide (Ti02), have a narrow range of response to light due to their limited energy band structure, resulting in low utilization of solar energy, and at the same time, their photocatalytic activities are limited. These factors limit its development and application in the field of photocatalysis. Therefore, how to realize the effective conversion of light energy, find and prepare photocatalytic materials with broad spectral response range, high quantum efficiency and easy recycling are the key scientific problems to be solved by researchers. Previously, graphite-phase carbon nitride (g-C3N4) as a representative of non-metallic layered materials, its special electronic structure, so that it shows a unique performance, while it also has good thermal stability, chemical stability, has become a research focus of researchers. In addition, the material is low-cost, with appropriate band structure, its band gap width (Eg) (2.7 eV) is a kind of lamellar structure material similar to graphite, which can be prepared from a variety of natural materials rich in nitrogen. g-C3N4 can photolyse water under visible light and photocatalytic degradation of a variety of pollutants. It is an ideal visible light-responsive photocatalyst. However, it has a narrow spectral absorption range, small specific surface area and photogenerated electron-hole pairing. In this paper, g-C3N4 was modified by various modification methods to improve its photocatalytic performance. Based on the microstructure characterization and photocatalytic performance evaluation of the material, the reasons and mechanism of its performance improvement were analyzed in detail. The main contents are as follows: Firstly, the visible photocatalytic properties of the multilayer g-C3N4 were improved by the semiconductor composite method. The Ag/AgCl and AgI nanoparticles modified g-C3N4 nanocomposites (Ag/AgCl/g-C3N4 and AgI/g-C3N4) were prepared by ion exchange method, respectively. On the other hand, the synergistic effect between them was used to promote the separation of photogenerated electron-hole pairs and enhance their photocatalytic degradation performance. The microstructure and morphology of Ag/AgCl/g-C3N4 and AgI/g-C3N4 nanocomposites were analyzed by various characterization methods, and Ag/AgCl/g-C3N4 and AgI/g-C3N4 and AgI/g-C3N were investigated in depth. The results show that the absorption of Ag/AgCl and AgI increases with the increase of Ag/AgCl and AgI content. Under the visible light irradiation, some Ag elements appear in AgCl/g-C3N4 and form Ag/AgCl/g-C3N4 composite nanomaterials, Ag elements. Plasma resonance effect and the synergistic effect between the materials enhance the photocatalytic performance, but the stability of the system is still poor; in contrast, AgI has stronger photocatalytic activity, and the combination of AgI and g-C3N4 can enhance the stability of AgI. The synergistic effect between AgI and g-C3N4 can facilitate the photogenerated electron-hole pair migration. Secondly, compared with graphite materials, two-dimensional and three-dimensional graphene materials have superior photoelectric properties and surface properties, while the layered g-C3N4 materials have similar structure to graphite, and the layers are connected by van der Waals force, and the specific surface area is larger. Using graphene as a reference, multi-layer g-C3N4 materials were prepared into two-dimensional or three-dimensional structures by peeling and self-assembly, breaking the van der Waals force between the layers of g-C3N4 materials, increasing its surface area and improving its photocatalytic performance. The two-dimensional class was synthesized by solvent peeling method. Graphene-type carbon nitride (GL-C3N4) has high specific surface area, effective electron-hole separation rate and excellent photoelectric properties. Under visible light irradiation, the photocurrent intensity and photocatalytic activity of GL-C3N4 have been significantly improved. In addition, on the basis of two-dimensional GL-C3N4 research, further assisted by ionic liquids, The bulk g-C3N4 was transformed into g-C3N4 hydrogel with three-dimensional network structure. The formation mechanism of the three-dimensional network structure g-C3N4 hydrogel was studied by using a variety of characterization methods and theoretical calculations. A general method was proposed to transform layered materials into stable three-dimensional network structure g-C3N4 hydrogel. Hydrogels have special electronic structure and optical properties, which can expand the application of g-C3N4 in optics and other fields. This provides new methods and ideas for the later study of wet chemistry and the regulation of photoelectric properties of nanomaterials. Finally, in order to further enhance the photocatalytic performance of two-dimensional GL-C3N4, new nano-materials with wide optical absorption range, high quantum efficiency and strong photo-induced carrier migration ability were introduced into the GL-C3N4 photocatalyst. Based on this, ZnS/GL-C3N4 and GL-MoS2/C3N4 composites were designed and fabricated and applied to photocatalytic degradation of organic pollutants. With the increase of the contact area between the composite monomers, a fast carrier transport channel was established, which accelerated the transfer of interfacial charges and significantly improved the photoelectrochemical properties of GL-C3N4. At the same time, the utilization of visible light was enhanced and the organic pollutants were increased. The unique strategies demonstrated in this work can be extended to other nanocomposite systems and provide new research ideas and experimental means for the rational design and optimization of other important chemical and catalytic reactions.
【學位授予單位】：江蘇大學
【學位級別】：博士
【學位授予年份】：2017
【分類號】：O643.36;X50

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本文編號：2193748