金屬助催化劑的制備及其對CdS可見光分解水產(chǎn)氫性能的影響
發(fā)布時間：2018-08-27 05:48
【摘要】：太陽能光解水制氫在解決全球能源和環(huán)境問題中具有重要的研究價值。CdS具有可見光響應(yīng),但單獨作為光催化劑存在產(chǎn)氫速率低及易發(fā)生光腐蝕的缺點。通常采用負載貴金屬來提高產(chǎn)氫效率,但是卻顯著提高了催化劑的成本,限制了太陽能分解水產(chǎn)氫的實際應(yīng)用。本文旨在減少貴金屬Pt的用量并提高CdS光催化體系的產(chǎn)氫活性,主要采用兩種技術(shù)路線：1)采用非貴金屬鎳(Ni)作為助催化劑。通過控制Ni納米粒子的大小和結(jié)晶度提高體系的產(chǎn)氫活性；2)采用鉑基二元金屬助催化劑Pt@M(M=Pd,Ru),考察二元金屬協(xié)同催化作用對體系產(chǎn)氫速率的影響。研究內(nèi)容具體如下：一、Ni助催化劑對CdS可見光產(chǎn)氫活性的影響研究減小Ni的晶粒尺度：以CdS為基礎(chǔ)光催化劑,進行非貴金屬Ni納米顆粒的控制沉積的研究。首先通過化學(xué)還原法制得Ni納米顆粒,然后利用光解水反應(yīng)產(chǎn)生的光生電子將其負載到CdS表面。采用透射電鏡、粉末X射線衍射儀、紫外-可見漫反射光譜儀和熒光光譜儀對制備的光催化劑進行表征。透射電鏡顯示制得的Ni納米顆粒直徑約為3 nm,且均勻地沉積于CdS表面。Ni納米粒子在光解水過程中,選擇性地沉積于CdS的(100),(002)和(101)晶面制得的納米Ni/CdS光催化劑表現(xiàn)出較高的分解水制氫活性。紫外-可見漫發(fā)射圖顯示,Ni的負載增加了CdS對可見光的吸收。在熒光圖譜中,Ni/CdS發(fā)生了熒光淬滅現(xiàn)象,這是由于CdS表面沉積的Ni納米粒子在CdS光催化分解水反應(yīng)中充當了電子捕獲阱的角色。以300 W氙燈為光源,(NH4)2SO3為犧牲試劑,對Ni/CdS進行了可見光分解水產(chǎn)氫性能的測試。結(jié)果表明Ni的最佳負載量為2.5%,產(chǎn)氫速率高達9.050 mmol·h-1·g-1,對應(yīng)于λ=420 nm處的量子效率為9.4%；且Ni/CdS連續(xù)反應(yīng)16.5 h后,催化活性未出現(xiàn)降低現(xiàn)象,顯示了催化劑的穩(wěn)定性。提高Ni的結(jié)晶度：通過化學(xué)還原法制備了高結(jié)晶度的Ni納米顆粒,即在堿性條件下,采用水合肼N2H4·H2O在70℃將NiC12還原。在CdS發(fā)生分解水反應(yīng)的同時,利用光生電子將制得的Ni納米粒子沉積在CdS納米棒表面,即采用光化學(xué)還原的方法將Ni納米顆粒沉積于CdS納米棒表面形成Ni/CdS光催化劑。采用透射電鏡、粉末X射線衍射儀、紫外-可見漫反射光譜儀、比表面積及孔隙率分析儀和熒光光譜儀對光催化劑進行了表征。由XRD圖得知高結(jié)晶度的Ni納米粒子是fcc結(jié)構(gòu),透射電鏡圖顯示Ni納米顆粒的平均直徑為10 nm。在光催化反應(yīng)中,Ni納米粒子選擇性地沉積于CdS納米棒的(100)、(002)和(101)晶面。Ni/CdS的BET比表面積為28.8 m2/g,高于單獨的CdS納米棒,證實了Ni納米晶體沉積在CdS納米棒表面。此外Ni/CdS在可見光區(qū)域的吸收有所增強,且Ni的沉積導(dǎo)致了CdS產(chǎn)生了熒光淬滅現(xiàn)象,說明Ni在光解水反應(yīng)中充當電子捕獲阱的角色,提高了載流子的利用效率。光催化分解水產(chǎn)氫實驗表明負載量為4%時Ni/CdS表現(xiàn)出最高的產(chǎn)氫活性,高達25.848 mmol·h-1·-g-1,對應(yīng)于λ-420 nm處的量子效率為26.8%,且在連續(xù)反應(yīng)20 h后活性仍舊十分穩(wěn)定。高結(jié)晶度的助催化劑Ni納米粒子在提高CdS光催化活性方面很有成效。二、鉑基二元金屬助催化劑Pt@M(M=Pd, Ru)的合成及其對CdS可見光產(chǎn)氫活性的影響研究采用兩步還原法分別制備了Pt@Pd和Pt@Ru二元金屬納米顆粒,并通過光化學(xué)還原法將其沉積在CdS表面,研究了其對CdS可見光分解水產(chǎn)氫性能的影響。采用X射線光電子能譜、透射電鏡、紫外-可見漫反射及時間分辨熒光技術(shù)對光催化劑進行了表征。XPS結(jié)果證實了二元金屬核殼結(jié)構(gòu)的存在,TEM顯示制得的鉑鈀和鉑釕二元金屬納米粒子大小約為10 nm,分別形成了核殼結(jié)構(gòu)的Pt@Pd和Pt@Ru。UV-Vis DRS顯示核殼結(jié)構(gòu)的助催化劑Pt@Pd和Pt@Ru負載到CdS表面,增加了其對可見光的吸收。以300 W氙燈為光源,以(NH4)2SO3為犧牲試劑,分別考察了單一助催化劑Pt、Pd和Ru及二元助催化劑Pt@Pd和Pt@Ru對CdS光分解水產(chǎn)氫性能的影響。實驗表明,二元金屬助催化劑的協(xié)同效應(yīng)導(dǎo)致了光催化活性的提高,其中鉑鈀比為7：3時,產(chǎn)氫速率最高(26.9 mmol·h-1·g-1);鉑釕比為7：3時,產(chǎn)氫速率最高(18.4 mmol·h-1·g1),均高于單一助催化劑的最高產(chǎn)氫活性。TRPL表明二元金屬助催化劑延長了載流子的壽命,提高了光催化活性。
[Abstract]:Solar photolysis of water to produce hydrogen has important research value in solving global energy and environmental problems. CdS has visible light response, but as a single photocatalyst, it has the shortcomings of low hydrogen production rate and easy photocorrosion. Usually, noble metals are loaded to improve the hydrogen production efficiency, but the cost of the catalyst is significantly increased and the catalyst is limited too much. In order to reduce the amount of precious metal Pt and improve the hydrogen production activity of CdS photocatalytic system, two technical routes were adopted: 1) using non-precious metal nickel (Ni) as co-catalyst; 2) using platinum-based binary gold to improve the hydrogen production activity of the system by controlling the size and crystallinity of Ni nanoparticles; Pt@M(M=Pd,Ru) is a co-catalyst. The effect of binary metal synergistic catalysis on hydrogen production rate of the system was investigated. The main contents are as follows: 1. The effect of Ni co-catalyst on visible light hydrogen production activity of CdS was studied. The grain size of Ni was reduced. The controlled deposition of non-noble metal Ni nanoparticles was studied based on CdS photocatalyst. Ni nanoparticles were prepared by chemical reduction and then loaded onto CdS surface by photogenerated electrons produced by photolysis of water. The photocatalysts were characterized by TEM, powder X-ray diffraction, UV-Vis diffuse reflectance spectroscopy and fluorescence spectroscopy. The diameter of Ni nanoparticles was about 1. Ni nanoparticles were selectively deposited on the (100), (002) and (101) surfaces of CdS during the photolysis of water. The photocatalytic activity of Ni/CdS prepared on the (100), (002) and (101) surfaces of CdS was high. The UV-Vis diffuse emission spectra showed that the Ni loading increased the absorption of CdS to visible light. Fluorescence quenching occurred because Ni nanoparticles deposited on CdS surface acted as electron trapping traps in CdS photocatalytic water decomposition reaction. Using 300 W xenon lamp as light source, (NH4)2SO3 as sacrificial reagent, the hydrogen production performance of Ni/CdS in visible light aquatic decomposition was tested. The results showed that the optimum loading of Ni was 2.5%, and the hydrogen production rate was high. The quantum efficiency corresponding to lambda=420 nm is 9.4%, and the catalytic activity of Ni/CdS does not decrease after 16.5 hours of continuous reaction, showing the stability of the catalyst. To improve the crystallinity of Ni, high crystallinity Ni nanoparticles were prepared by chemical reduction method, that is, hydrazine hydrate N2H4.H2O was used in alkaline conditions. NiC12 was reduced at 70 C. When CdS was decomposed into water, the Ni nanoparticles were deposited on the surface of CdS nanorods by photoelectrons. The Ni nanoparticles were deposited on the surface of CdS nanorods by photochemical reduction to form Ni/CdS photocatalyst. Transmission electron microscopy, powder X-ray diffraction and UV-Vis diffuse reflection were used. The photocatalysts were characterized by spectroscope, specific surface area and porosity analyzer and fluorescence spectrometer. XRD showed that the highly crystalline Ni nanoparticles were FCC structure. TEM showed that the average diameter of Ni nanoparticles was 10 nm. In photocatalytic reaction, Ni nanoparticles were selectively deposited on (100), (002) and (101) CdS nanorods. The BET specific surface area of Ni/CdS is 28.8 m2/g, which is higher than that of CdS nanorods alone. It is confirmed that Ni nanocrystals are deposited on the surface of CdS nanorods. In addition, the absorption of Ni/CdS in the visible region is enhanced, and the deposition of Ni results in the fluorescence quenching of CdS, indicating that Ni acts as an electron trap in the photolysis of water reaction and enhances the absorption of Ni/CdS nanocrystals. The photocatalytic decomposition of water for hydrogen production showed that Ni/CdS exhibited the highest hydrogen production activity at 4% loading, up to 25.848 mmol H-1 g-1 and 26.8% quantum efficiency corresponding to lambda-420 nm. The activity remained very stable after 20 h of continuous reaction. Pt@Pd and Pt@Ru binary metal nanoparticles were prepared by two-step reduction method and deposited on CdS surface by photochemical reduction method. Their effects on CdS visible light decomposition aquatic products were studied. The photocatalyst was characterized by X-ray photoelectron spectroscopy, transmission electron microscopy, ultraviolet-visible diffuse reflectance and time-resolved fluorescence spectroscopy. XPS results confirmed the existence of binary metal core-shell structure. TEM showed that the prepared Pt-Pd and Pt-Ru binary metal nanoparticles were about 10 nm in size, forming core-shell structure P, respectively. T@Pd and Pt@Ru.UV-Vis DRS showed that the core-shell structure of the promoters Pt@Pd and Pt@Ru were loaded on the surface of CdS to increase their visible light absorption. The effects of single promoter Pt, Pd and Ru as well as binary promoters Pt@Pd and Pt@Ru on the photodecomposition of aquatic hydrogen by CdS were investigated using 300 W xenon lamp as light source and (NH4)2SO3 as sacrificial reagent, respectively. The results show that the synergistic effect of binary metal promoters leads to the enhancement of photocatalytic activity, in which the highest hydrogen production rate (26.9 mmol H 1 g 1) occurs when the Pt Pd ratio is 7:3, and the highest hydrogen production rate (18.4 mmol H 1 g 1) occurs when Pt Ru ratio is 7:3, which is higher than the highest hydrogen production activity of a single The lifetime of carriers increases the photocatalytic activity.
【學(xué)位授予單位】：河南大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：O643.36;TQ116.2
本文編號：2206283
[Abstract]:Solar photolysis of water to produce hydrogen has important research value in solving global energy and environmental problems. CdS has visible light response, but as a single photocatalyst, it has the shortcomings of low hydrogen production rate and easy photocorrosion. Usually, noble metals are loaded to improve the hydrogen production efficiency, but the cost of the catalyst is significantly increased and the catalyst is limited too much. In order to reduce the amount of precious metal Pt and improve the hydrogen production activity of CdS photocatalytic system, two technical routes were adopted: 1) using non-precious metal nickel (Ni) as co-catalyst; 2) using platinum-based binary gold to improve the hydrogen production activity of the system by controlling the size and crystallinity of Ni nanoparticles; Pt@M(M=Pd,Ru) is a co-catalyst. The effect of binary metal synergistic catalysis on hydrogen production rate of the system was investigated. The main contents are as follows: 1. The effect of Ni co-catalyst on visible light hydrogen production activity of CdS was studied. The grain size of Ni was reduced. The controlled deposition of non-noble metal Ni nanoparticles was studied based on CdS photocatalyst. Ni nanoparticles were prepared by chemical reduction and then loaded onto CdS surface by photogenerated electrons produced by photolysis of water. The photocatalysts were characterized by TEM, powder X-ray diffraction, UV-Vis diffuse reflectance spectroscopy and fluorescence spectroscopy. The diameter of Ni nanoparticles was about 1. Ni nanoparticles were selectively deposited on the (100), (002) and (101) surfaces of CdS during the photolysis of water. The photocatalytic activity of Ni/CdS prepared on the (100), (002) and (101) surfaces of CdS was high. The UV-Vis diffuse emission spectra showed that the Ni loading increased the absorption of CdS to visible light. Fluorescence quenching occurred because Ni nanoparticles deposited on CdS surface acted as electron trapping traps in CdS photocatalytic water decomposition reaction. Using 300 W xenon lamp as light source, (NH4)2SO3 as sacrificial reagent, the hydrogen production performance of Ni/CdS in visible light aquatic decomposition was tested. The results showed that the optimum loading of Ni was 2.5%, and the hydrogen production rate was high. The quantum efficiency corresponding to lambda=420 nm is 9.4%, and the catalytic activity of Ni/CdS does not decrease after 16.5 hours of continuous reaction, showing the stability of the catalyst. To improve the crystallinity of Ni, high crystallinity Ni nanoparticles were prepared by chemical reduction method, that is, hydrazine hydrate N2H4.H2O was used in alkaline conditions. NiC12 was reduced at 70 C. When CdS was decomposed into water, the Ni nanoparticles were deposited on the surface of CdS nanorods by photoelectrons. The Ni nanoparticles were deposited on the surface of CdS nanorods by photochemical reduction to form Ni/CdS photocatalyst. Transmission electron microscopy, powder X-ray diffraction and UV-Vis diffuse reflection were used. The photocatalysts were characterized by spectroscope, specific surface area and porosity analyzer and fluorescence spectrometer. XRD showed that the highly crystalline Ni nanoparticles were FCC structure. TEM showed that the average diameter of Ni nanoparticles was 10 nm. In photocatalytic reaction, Ni nanoparticles were selectively deposited on (100), (002) and (101) CdS nanorods. The BET specific surface area of Ni/CdS is 28.8 m2/g, which is higher than that of CdS nanorods alone. It is confirmed that Ni nanocrystals are deposited on the surface of CdS nanorods. In addition, the absorption of Ni/CdS in the visible region is enhanced, and the deposition of Ni results in the fluorescence quenching of CdS, indicating that Ni acts as an electron trap in the photolysis of water reaction and enhances the absorption of Ni/CdS nanocrystals. The photocatalytic decomposition of water for hydrogen production showed that Ni/CdS exhibited the highest hydrogen production activity at 4% loading, up to 25.848 mmol H-1 g-1 and 26.8% quantum efficiency corresponding to lambda-420 nm. The activity remained very stable after 20 h of continuous reaction. Pt@Pd and Pt@Ru binary metal nanoparticles were prepared by two-step reduction method and deposited on CdS surface by photochemical reduction method. Their effects on CdS visible light decomposition aquatic products were studied. The photocatalyst was characterized by X-ray photoelectron spectroscopy, transmission electron microscopy, ultraviolet-visible diffuse reflectance and time-resolved fluorescence spectroscopy. XPS results confirmed the existence of binary metal core-shell structure. TEM showed that the prepared Pt-Pd and Pt-Ru binary metal nanoparticles were about 10 nm in size, forming core-shell structure P, respectively. T@Pd and Pt@Ru.UV-Vis DRS showed that the core-shell structure of the promoters Pt@Pd and Pt@Ru were loaded on the surface of CdS to increase their visible light absorption. The effects of single promoter Pt, Pd and Ru as well as binary promoters Pt@Pd and Pt@Ru on the photodecomposition of aquatic hydrogen by CdS were investigated using 300 W xenon lamp as light source and (NH4)2SO3 as sacrificial reagent, respectively. The results show that the synergistic effect of binary metal promoters leads to the enhancement of photocatalytic activity, in which the highest hydrogen production rate (26.9 mmol H 1 g 1) occurs when the Pt Pd ratio is 7:3, and the highest hydrogen production rate (18.4 mmol H 1 g 1) occurs when Pt Ru ratio is 7:3, which is higher than the highest hydrogen production activity of a single The lifetime of carriers increases the photocatalytic activity.
【學(xué)位授予單位】：河南大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：O643.36;TQ116.2
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