水热法制备六方柱状ZnO微晶的形貌、结构与光催化性能

发布时间：2018-05-21 15:43

  本文选题：氧化锌微晶 + 水热法　； 参考：《武汉理工大学》2011年硕士论文

【摘要】：ZnO半导体材料作为一种性能优良的光催化剂,在环境治理和保护方面有很大的应用前景,由于ZnO的光催化性能与其尺寸、形貌和表面缺陷等有关,因此,研究ZnO的晶体形貌和结构对ZnO光催化性能的影响是目前研究热点之本文以不同的锌盐和碱液,采用水热法合成了 一。Zn(CHCOO)2·2H2O-NaOH、Zn(NO3)2·6H2O-KOH和Zn(CHCOO)2·2H2O-HMTA三个不同体系的ZnO微晶,系统研究了不同的反应条件对ZnO微晶微观形貌的影响,探讨了不同体系的ZnO微晶的生长机理,并以甲基橙为降解物,通过光催化降解实验,研究了不同ZnO微晶形貌、结晶度、晶面与光催化活性的关系,同时,对结晶优良的六方柱状ZnO进行稀土金属离子的掺杂,以提高其光催化降解活性,研究掺杂离子及掺杂量对ZnO微晶光催化活性的影响。另外,以载玻片为基体,制备了负载型六方柱状ZnO微晶。实验中采用XRD、SEM、UV-Vis和紫外分光光度计等现代测试分析手段对样品的晶相、微观结构、吸收光谱以及光催化降解活性进行了测试分析。 在Zn(CHCOO)2·2H2O-NaOH体系中,采用正交试验,以ZnO微晶形貌作为质量评价因素,通过改变溶液的OH-/Zn2+摩尔浓度比、反应温度和反应时间研究了不同的反应条件对ZnO晶体形貌的影响,确定了影响ZnO微晶形貌的主要因素和最佳制备工艺。结果表明,适宜的反应温度是ZnO微晶形成的必要条件,在较低温度下,ZnO产物中含有未完全分解的碱式碳酸锌,当温度升温至160℃,碱式碳酸锌完全分解形成ZnO, OH-/Zn2+摩尔浓度比是影响ZnO微晶形貌的主要因素,当OH-/Zn2+摩尔浓度比为1：1时,ZnO微晶为柱状ZnO,随着OH-/Zn2+摩尔浓度比的增加, ZnO的长径比明显减小,当OH-/Zn2+摩尔浓度比为3：1时,ZnO为片状。获得最佳ZnO微晶形貌的制备工艺是：OH-/Zn2+浓度比为1：1,反应温度为160℃,反应时间为10h。此体系的反应生长机理可以利用负离子配位生长基团理论模型来解释,醋酸锌溶液与氢氧化钠溶液混合后形成Zn(OH)2,当溶液中达到过饱和程度时,Zn(OH)2水解形成生长基元[Zn(OH)4]2-和ZnO晶核,由于溶液中OH-离子影响生长基元的结构和ZnO晶体的界面性质,使得在不同的OH-/Zn2+摩尔浓度比条件下,生长基元在ZnO晶核上的定向生长不同而形成不同形貌的ZnO微晶。 在Zn(NO3)2·6H2O-KOH体系中,采用正交试验方法分析了影响ZnO微晶结晶性能的主次因素,分别是OH-/Zn2+浓度比反应时间反应温度,并通过极差分析得到获得最优结晶性能样品S10的制备工艺组合为：A3B3C2,即OH-/Zn2+浓度比为1：1,反应时间为15h,反应温度为160℃,样品S10的结晶度为91.2%,高于其他样品。通过样品的SEM形貌分析中可知,OH-/Zn2+浓度比是影响样品形貌的主要因素,当OH-/Zn2+浓度比为1：1时,样品为六方柱状ZnO；当OH-/Zn2+浓度比为2：1时,样品为短柱状ZnO,并且颗粒尺寸减小；当OH-/Zn2+浓度比为3：1时,样品为片状ZnO。此系统反应生长机理从“生长条件—晶体结构—晶体形貌”三个方面来探讨,硝酸锌溶液与氢氧化钾溶液混合后形成前驱体Zn(OH)2, Zn(OH)2在一定的反应条件下溶解形成生长基元[Zn(OH)4]2-,继而成核,在一定反应条件下,ZnO在晶核上沉积吸附生长成形态不同的晶体形貌。 在Zn(CHCOO)2·2H2O-HMTA体系中着重研究了不同的反应条件对ZnO形貌的影响,探讨了六方柱状ZnO的形成机理。结果表明,溶液浓度、pH值、反应温度和反应时间对生成晶体的形貌和晶体质量都会产生影响。制备结晶良好的ZnO的最佳反应条件为：反应液浓度为0.57mol/L, pH值为6.0,反应温度为97℃,反应时间为16h。六方柱状ZnO晶体的形成机理是：在一定的水热条件下,醋酸锌与六次甲基四胺水解后形成晶核,由于(0001)晶面的生长速率大于其他晶面,以及(0001)晶面易俘获原子,使得成核后的ZnO沿(0001)面定向生长,最终形成六方柱状结构。 以甲基橙为降解物,研究不同体系的ZnO样品的光催化性能,结果表明,晶体形貌和显露晶面对ZnO样品的光催化性能影响较大,晶体形貌为片状的ZnO样品的光催化降解率高于其他形貌,同时,由于(0001)晶面具有较高的表面能,当样品中显露(0001)晶面时,光催化活性高于其他晶面显露的样品。其中,显露晶面为(0001)晶面的片状ZnO样品L2在4h的光催化降解率为84.27%,一级动力学常数(k1)为8.1×10-3,另外,结晶度增加、样品表面粗糙有助于提高样品的光催化性能,其机理是片状ZnO样品主要显露(0001)晶面,由于(0001)晶面是Zn-Zn原子密排面,其结构具有不饱和性,氧分子容易吸附在(0001)面而形成具有强氧化性的·O2-,另外,溶液中的OH-离子也容易吸附在(0001)面,促进了同样具有强氧化性·OH的生成,可以将甲基橙分子氧化为H2O和CO2,提高了ZnO微晶的光催化降解率。在Zn(CHCOO)2·2H2O-HMTA体系中,由于样品的颗粒尺寸较大,并且表面光滑,对甲基橙分子吸附较少,样品的光催化活性较低,其中晶体形貌最佳的样品H2光催化降解率仅为24.29%,一级动力学常数(k1)为1.1×10-3。获得最佳光催化降解效率的光催化环境为：ZnO的添加量为0.1g/100mL,甲基橙的初始浓度为15mg/L,甲基橙溶液的pH值为10.0。 为了提高晶体形貌最佳的样品H2的光催化活性,对样品H2进行稀土离子的掺杂,研究了La3+和Yb3+掺杂量对光催化活性的影响,结果表明,不同的掺杂量对光催化活性的影响不同,当Yb3+掺杂量为0.2mol%时,样品D5的光催化活性最高,4h的降解率为51.41%,一级动力学常数(k1)为2.9×10-3,掺杂后样品的光催化降解率提高了27.21%,其机理是Yb3+掺杂后的样品D5不仅拓展了ZnO晶体的吸收范围,而且缩小了ZnO晶体的禁带宽度,使得电子从价带跃迁到导带所需要的能量变小,在紫外光照的情况下,更易形成光生-空穴对。另外,样品D5中ZnO微晶表面比较粗糙,可以吸附更多的甲基橙分子进行光催化降解,ZnO样品的光催化活性提高。 通过水热法,以二水醋酸锌和六次甲基四胺为原料在载玻片上生长ZnO微米棒,分析了其生长机制,结果表明,ZnO纳米棒生长时,反应条件的不同影响着晶核的形成和晶体的生长,从而导致结晶形态有所不同。其中,反应液浓度和pH值对ZnO纳米棒的形貌影响显著。其生长机制是：HMTA水解生成的NH3与溶液中Zn2+发生络合反应,生成锌胺络合离子[Zn(NH3)4]2+,在一定的反应条件下,锌胺络合离子逐渐转化为ZnO。由于ZnO的晶核和晶体之间存在竞争,当反应液的浓度较高时,醋酸根离子吸附在ZnO微晶的(0001)晶面,从而减慢了(0001)晶面的生长速率,ZnO的长径比减小。当采用氨水调节溶液的pH值时,氨水不仅参与反应生成前驱物Zn(NH3)4(OH)2,水热条件下脱水产生ZnO；而且反应液中的NH4+可以吸附在ZnO晶核的表面,影响着ZnO微晶生长体系的界面能,对ZnO晶体的定向生长具有导向作用,所以ZnO微晶容易自组装取向连接,形成“孪生”棒状晶体。
[Abstract]:As a good photocatalyst with excellent performance, ZnO semiconductor materials have great potential in environmental protection and protection. The photocatalytic properties of ZnO are related to their size, morphology and surface defects. Therefore, the study of the influence of the crystal morphology and structure of ZnO on the photocatalytic properties of ZnO is a hot topic at present with different zinc Salt and lye are synthesized by hydrothermal method
.Zn (CHCOO) 2. 2H2O-NaOH, Zn (NO3) 2. 6H2O-KOH and Zn (CHCOO) 2. 2H2O-HMTA three different ZnO microcrystals. The effect of different reaction conditions on the micromorphology of ZnO microcrystals was systematically investigated. The growth mechanism of the ZnO microcrystals in different systems was discussed. The relationship between the morphology, crystallinity, crystal surface and photocatalytic activity, and the doping of rare earth metal ions to the fine six square columnar ZnO in order to improve the photocatalytic degradation activity and study the effect of doping ions and doping amount on the photocatalytic activity of ZnO microcrystals. In addition, the loaded six square columnar ZnO microcrystals were prepared by the glass substrate. XRD, SEM, UV-Vis and UV spectrophotometer are used to test and analyze the crystal phase, microstructure, absorption spectrum and photocatalytic degradation activity of the sample.
In the Zn (CHCOO) 2 / 2H2O-NaOH system, orthogonal test was used to use ZnO microcrystalline morphology as a quality evaluation factor. The influence of different reaction conditions on the morphology of ZnO crystal was studied by changing the molar concentration ratio of OH-/Zn2+, reaction temperature and reaction time, and the main factors affecting the morphology of ZnO microcrystals and the optimum preparation process were determined. It is shown that the suitable reaction temperature is a necessary condition for the formation of ZnO microcrystals. In the lower temperature, the ZnO product contains alkaline zinc carbonate, which is not completely decomposed. When the temperature rises to 160, the alkaline zinc carbonate is completely decomposed to ZnO, and the molar concentration ratio of OH-/Zn2+ is the main factor affecting the morphology of ZnO microcrystalline, when the molar concentration ratio of OH-/Zn2+ is 1:1, Zn O microcrystal is columnar ZnO. With the increase of molar concentration ratio of OH-/Zn2+, the ratio of length to diameter of ZnO decreases obviously. When OH-/Zn2+ molar concentration is 3:1, ZnO is flaky. The preparation process of optimum ZnO microcrystal morphology is: OH-/Zn2+ concentration ratio is 1:1, reaction temperature is 160 C, reaction time is 10h., the reaction growth mechanism can be used negative. The theoretical model of ion coordination growth group explains that zinc acetate solution is mixed with sodium hydroxide solution to form Zn (OH) 2. When the solution reaches the degree of supersaturation, Zn (OH) 2 hydrolysate to form the growth element [Zn (OH) 4]2- and ZnO nucleus. Because the OH- ions in the solution influence the structure of the growth element and the interfacial properties of the ZnO crystal, it is in the different OH-/Z. Under the molar concentration ratio of n2+, the orientation growth of growth units on ZnO nuclei is different, and ZnO microcrystals with different morphologies are formed.
In the Zn (NO3) 2 / 6H2O-KOH system, the main and secondary factors affecting the crystallization properties of ZnO microcrystals are analyzed by orthogonal test. The reaction temperature of OH-/Zn2+ concentration is compared with the reaction time, respectively. The preparation process of the optimum crystallization performance sample S10 is obtained by the extreme difference analysis. A3B3C2, OH-/Zn2+ concentration ratio is 1:1, and the reaction time is 15h. The temperature of the reaction is 160, and the crystallinity of the sample S10 is 91.2%, which is higher than that of the other samples. By the SEM morphology analysis, the concentration ratio of OH-/Zn2+ is the main factor affecting the sample morphology. When the OH-/Zn2+ concentration ratio is 1:1, the sample is six square columnar ZnO; when the OH-/Zn2+ concentration ratio is 2:1, the sample is a short columnar ZnO, and the particle size is the size of the sample. When the concentration ratio of OH-/Zn2+ is 3:1, the sample is flaky ZnO.. The growth mechanism of the system is discussed from three aspects of "growth condition crystal structure crystal morphology", and zinc nitrate solution is mixed with potassium hydroxide solution to form precursor Zn (OH) 2, Zn (OH) 2 dissolves to form growth element [Zn (OH) 4]2- under a fixed reaction condition. Then nucleation, under certain reaction conditions, ZnO is deposited on the nucleus and grown into different morphologies.
In the Zn (CHCOO) 2 / 2H2O-HMTA system, the effect of different reaction conditions on the morphology of ZnO was studied. The formation mechanism of the six square columnar ZnO was discussed. The results showed that the solution concentration, pH value, reaction temperature and reaction time had an effect on the morphology and crystal quality of the crystal. The optimum reaction conditions for preparing the well crystallized ZnO were as follows: The reaction liquid concentration is 0.57mol/L, the pH value is 6, the reaction temperature is 97 C, the reaction time is 16h. six square columnar ZnO crystal formation mechanism is: under certain hydrothermal condition, zinc acetate and six times methyl four amine hydrolyze to form the nucleation, because (0001) the growth rate is larger than the other crystal surface, and (0001) the crystal surface is easy to capture the atom, making the formation. The ZnO after nucleation grows along the (0001) plane and finally forms a six column structure.
The photocatalytic properties of ZnO samples of different systems were studied with methyl orange as degradation products. The results showed that the crystal morphology and the exposed crystal had great influence on the photocatalytic properties of ZnO samples. The photocatalytic degradation rate of ZnO samples with crystal morphology was higher than that of other morphologies. At the same time, the high surface energy of (0001) crystal surface was revealed in the sample. 0001) on the crystal surface, the photocatalytic activity is higher than that of other crystal surfaces. The photocatalytic degradation rate of L2 in 4H is 84.27%, the first order kinetic constant (K1) is 8.1 x 10-3, and the crystallinity of the sample is increased. The surface roughness of the sample is helpful to improve the photocatalytic performance of the sample, and the mechanism is the sheet like ZnO sample. The product mainly exposing (0001) crystal surface, because (0001) crystal surface is Zn-Zn atomic dense surface, its structure is unsaturated, oxygen molecules easily adsorb on (0001) surface and form a strong oxidizing. O2-. In addition, the OH- ions in the solution are also easily adsorbed on (0001) surface, promoting the same strong oxidation. OH formation, the methyl orange molecular oxygen can be used. The photocatalytic degradation rate of ZnO microcrystals is increased by H2O and CO2. In the Zn (CHCOO) 2 / 2H2O-HMTA system, the sample has a larger particle size and smooth surface, less adsorption of methyl orange and low photocatalytic activity of the sample. The photocatalytic degradation rate of the sample with the best crystal morphology is only 24.29%, and the first-order kinetic constant (K1) is the same. The photocatalytic environment for obtaining the best photocatalytic degradation efficiency of 1.1 x 10-3. is that the addition of ZnO is 0.1g/100mL, the initial concentration of methyl orange is 15mg/L, and the pH value of methyl orange solution is 10.0.
In order to improve the photocatalytic activity of the sample H2 with the best crystal morphology, the sample H2 was doped with rare earth ions. The effect of the amount of La3+ and Yb3+ doping on the photocatalytic activity was studied. The results showed that the effect of different doping amount on the photocatalytic activity was different. When the amount of Yb3+ was 0.2mol%, the photocatalytic activity of the sample D5 was the highest and the degradation rate of 4H. For 51.41%, the first order kinetic constant (K1) is 2.9 x 10-3. The photocatalytic degradation rate of the sample after doping is increased by 27.21%. The mechanism is that the sample D5 after Yb3+ doping not only expands the absorption range of the ZnO crystal, but also reduces the band gap of the ZnO crystal, which makes the electrons from the valence band to the guide band less energy and in the ultraviolet light condition. In addition, the surface of ZnO microcrystals in the sample D5 is relatively rough, and more methyl orange can be adsorbed for photocatalytic degradation, and the photocatalytic activity of ZnO samples is improved.
The growth mechanism of ZnO microns with two water zinc acetate and six times methyl four amine as raw materials was analyzed by hydrothermal method. The results showed that the formation of crystal nuclei and the growth of crystal were affected by different reaction conditions when ZnO nanorods were grown, and the concentration and pH value of the reaction liquid were different to ZnO nanorods. The growth mechanism of the rice rod is remarkable. Its growth mechanism is that the NH3 formed by HMTA hydrolysis with Zn2+ in the solution produces zinc amine complex ion [Zn (NH3) 4]2+. Under certain reaction conditions, zine amine complex ions are gradually converted to ZnO. because of the competition between the nucleation and crystal of ZnO, and when the concentration of the reaction liquid is high, the acetic acid root is isolated. The seed is adsorbed on the (0001) crystal surface of ZnO microcrystal, thus slowing down the growth rate of (0001) crystal surface and decreasing the length diameter ratio of ZnO. When ammonia water is used to regulate the pH value of the solution, the ammonia water not only participates in the reaction to generate the precursor Zn (NH3) 4 (OH) 2, and dehydrates the ZnO under the hydrothermal condition, but the NH4+ in the reaction liquid can be adsorbed on the surface of the ZnO crystal nucleus and affects ZnO. The interface energy of the microcrystalline growth system has a guiding effect on the directional growth of ZnO crystals, so ZnO microcrystals are easily self assembled and connected to form a "twin" bar like crystal.
【学位授予单位】：武汉理工大学
【学位级别】：硕士
【学位授予年份】：2011
【分类号】：O614.241

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