本文選題：氧化鋅微晶 + 水熱法��； 參考：《武漢理工大學(xué)》2011年碩士論文

【摘要】：ZnO半導(dǎo)體材料作為一種性能優(yōu)良的光催化劑,在環(huán)境治理和保護(hù)方面有很大的應(yīng)用前景,由于ZnO的光催化性能與其尺寸、形貌和表面缺陷等有關(guān),因此,研究ZnO的晶體形貌和結(jié)構(gòu)對(duì)ZnO光催化性能的影響是目前研究熱點(diǎn)之本文以不同的鋅鹽和堿液,采用水熱法合成了 一。Zn(CHCOO)2·2H2O-NaOH、Zn(NO3)2·6H2O-KOH和Zn(CHCOO)2·2H2O-HMTA三個(gè)不同體系的ZnO微晶,系統(tǒng)研究了不同的反應(yīng)條件對(duì)ZnO微晶微觀形貌的影響,探討了不同體系的ZnO微晶的生長(zhǎng)機(jī)理,并以甲基橙為降解物,通過光催化降解實(shí)驗(yàn),研究了不同ZnO微晶形貌、結(jié)晶度、晶面與光催化活性的關(guān)系,同時(shí),對(duì)結(jié)晶優(yōu)良的六方柱狀ZnO進(jìn)行稀土金屬離子的摻雜,以提高其光催化降解活性,研究摻雜離子及摻雜量對(duì)ZnO微晶光催化活性的影響。另外,以載玻片為基體,制備了負(fù)載型六方柱狀ZnO微晶。實(shí)驗(yàn)中采用XRD、SEM、UV-Vis和紫外分光光度計(jì)等現(xiàn)代測(cè)試分析手段對(duì)樣品的晶相、微觀結(jié)構(gòu)、吸收光譜以及光催化降解活性進(jìn)行了測(cè)試分析。 在Zn(CHCOO)2·2H2O-NaOH體系中,采用正交試驗(yàn),以ZnO微晶形貌作為質(zhì)量評(píng)價(jià)因素,通過改變?nèi)芤旱腛H-/Zn2+摩爾濃度比、反應(yīng)溫度和反應(yīng)時(shí)間研究了不同的反應(yīng)條件對(duì)ZnO晶體形貌的影響,確定了影響ZnO微晶形貌的主要因素和最佳制備工藝。結(jié)果表明,適宜的反應(yīng)溫度是ZnO微晶形成的必要條件,在較低溫度下,ZnO產(chǎn)物中含有未完全分解的堿式碳酸鋅,當(dāng)溫度升溫至160℃,堿式碳酸鋅完全分解形成ZnO, OH-/Zn2+摩爾濃度比是影響ZnO微晶形貌的主要因素,當(dāng)OH-/Zn2+摩爾濃度比為1：1時(shí),ZnO微晶為柱狀ZnO,隨著OH-/Zn2+摩爾濃度比的增加, ZnO的長(zhǎng)徑比明顯減小,當(dāng)OH-/Zn2+摩爾濃度比為3：1時(shí),ZnO為片狀。獲得最佳ZnO微晶形貌的制備工藝是：OH-/Zn2+濃度比為1：1,反應(yīng)溫度為160℃,反應(yīng)時(shí)間為10h。此體系的反應(yīng)生長(zhǎng)機(jī)理可以利用負(fù)離子配位生長(zhǎng)基團(tuán)理論模型來解釋,醋酸鋅溶液與氫氧化鈉溶液混合后形成Zn(OH)2,當(dāng)溶液中達(dá)到過飽和程度時(shí),Zn(OH)2水解形成生長(zhǎng)基元[Zn(OH)4]2-和ZnO晶核,由于溶液中OH-離子影響生長(zhǎng)基元的結(jié)構(gòu)和ZnO晶體的界面性質(zhì),使得在不同的OH-/Zn2+摩爾濃度比條件下,生長(zhǎng)基元在ZnO晶核上的定向生長(zhǎng)不同而形成不同形貌的ZnO微晶。 在Zn(NO3)2·6H2O-KOH體系中,采用正交試驗(yàn)方法分析了影響ZnO微晶結(jié)晶性能的主次因素,分別是OH-/Zn2+濃度比反應(yīng)時(shí)間反應(yīng)溫度,并通過極差分析得到獲得最優(yōu)結(jié)晶性能樣品S10的制備工藝組合為：A3B3C2,即OH-/Zn2+濃度比為1：1,反應(yīng)時(shí)間為15h,反應(yīng)溫度為160℃,樣品S10的結(jié)晶度為91.2%,高于其他樣品。通過樣品的SEM形貌分析中可知,OH-/Zn2+濃度比是影響樣品形貌的主要因素,當(dāng)OH-/Zn2+濃度比為1：1時(shí),樣品為六方柱狀ZnO；當(dāng)OH-/Zn2+濃度比為2：1時(shí),樣品為短柱狀ZnO,并且顆粒尺寸減小；當(dāng)OH-/Zn2+濃度比為3：1時(shí),樣品為片狀ZnO。此系統(tǒng)反應(yīng)生長(zhǎng)機(jī)理從“生長(zhǎng)條件—晶體結(jié)構(gòu)—晶體形貌”三個(gè)方面來探討,硝酸鋅溶液與氫氧化鉀溶液混合后形成前驅(qū)體Zn(OH)2, Zn(OH)2在一定的反應(yīng)條件下溶解形成生長(zhǎng)基元[Zn(OH)4]2-,繼而成核,在一定反應(yīng)條件下,ZnO在晶核上沉積吸附生長(zhǎng)成形態(tài)不同的晶體形貌。 在Zn(CHCOO)2·2H2O-HMTA體系中著重研究了不同的反應(yīng)條件對(duì)ZnO形貌的影響,探討了六方柱狀ZnO的形成機(jī)理。結(jié)果表明,溶液濃度、pH值、反應(yīng)溫度和反應(yīng)時(shí)間對(duì)生成晶體的形貌和晶體質(zhì)量都會(huì)產(chǎn)生影響。制備結(jié)晶良好的ZnO的最佳反應(yīng)條件為：反應(yīng)液濃度為0.57mol/L, pH值為6.0,反應(yīng)溫度為97℃,反應(yīng)時(shí)間為16h。六方柱狀ZnO晶體的形成機(jī)理是：在一定的水熱條件下,醋酸鋅與六次甲基四胺水解后形成晶核,由于(0001)晶面的生長(zhǎng)速率大于其他晶面,以及(0001)晶面易俘獲原子,使得成核后的ZnO沿(0001)面定向生長(zhǎng),最終形成六方柱狀結(jié)構(gòu)。 以甲基橙為降解物,研究不同體系的ZnO樣品的光催化性能,結(jié)果表明,晶體形貌和顯露晶面對(duì)ZnO樣品的光催化性能影響較大,晶體形貌為片狀的ZnO樣品的光催化降解率高于其他形貌,同時(shí),由于(0001)晶面具有較高的表面能,當(dāng)樣品中顯露(0001)晶面時(shí),光催化活性高于其他晶面顯露的樣品。其中,顯露晶面為(0001)晶面的片狀ZnO樣品L2在4h的光催化降解率為84.27%,一級(jí)動(dòng)力學(xué)常數(shù)(k1)為8.1×10-3,另外,結(jié)晶度增加、樣品表面粗糙有助于提高樣品的光催化性能,其機(jī)理是片狀ZnO樣品主要顯露(0001)晶面,由于(0001)晶面是Zn-Zn原子密排面,其結(jié)構(gòu)具有不飽和性,氧分子容易吸附在(0001)面而形成具有強(qiáng)氧化性的·O2-,另外,溶液中的OH-離子也容易吸附在(0001)面,促進(jìn)了同樣具有強(qiáng)氧化性·OH的生成,可以將甲基橙分子氧化為H2O和CO2,提高了ZnO微晶的光催化降解率。在Zn(CHCOO)2·2H2O-HMTA體系中,由于樣品的顆粒尺寸較大,并且表面光滑,對(duì)甲基橙分子吸附較少,樣品的光催化活性較低,其中晶體形貌最佳的樣品H2光催化降解率僅為24.29%,一級(jí)動(dòng)力學(xué)常數(shù)(k1)為1.1×10-3。獲得最佳光催化降解效率的光催化環(huán)境為：ZnO的添加量為0.1g/100mL,甲基橙的初始濃度為15mg/L,甲基橙溶液的pH值為10.0。 為了提高晶體形貌最佳的樣品H2的光催化活性,對(duì)樣品H2進(jìn)行稀土離子的摻雜,研究了La3+和Yb3+摻雜量對(duì)光催化活性的影響,結(jié)果表明,不同的摻雜量對(duì)光催化活性的影響不同,當(dāng)Yb3+摻雜量為0.2mol%時(shí),樣品D5的光催化活性最高,4h的降解率為51.41%,一級(jí)動(dòng)力學(xué)常數(shù)(k1)為2.9×10-3,摻雜后樣品的光催化降解率提高了27.21%,其機(jī)理是Yb3+摻雜后的樣品D5不僅拓展了ZnO晶體的吸收范圍,而且縮小了ZnO晶體的禁帶寬度,使得電子從價(jià)帶躍遷到導(dǎo)帶所需要的能量變小,在紫外光照的情況下,更易形成光生-空穴對(duì)。另外,樣品D5中ZnO微晶表面比較粗糙,可以吸附更多的甲基橙分子進(jìn)行光催化降解,ZnO樣品的光催化活性提高。 通過水熱法,以二水醋酸鋅和六次甲基四胺為原料在載玻片上生長(zhǎng)ZnO微米棒,分析了其生長(zhǎng)機(jī)制,結(jié)果表明,ZnO納米棒生長(zhǎng)時(shí),反應(yīng)條件的不同影響著晶核的形成和晶體的生長(zhǎng),從而導(dǎo)致結(jié)晶形態(tài)有所不同。其中,反應(yīng)液濃度和pH值對(duì)ZnO納米棒的形貌影響顯著。其生長(zhǎng)機(jī)制是：HMTA水解生成的NH3與溶液中Zn2+發(fā)生絡(luò)合反應(yīng),生成鋅胺絡(luò)合離子[Zn(NH3)4]2+,在一定的反應(yīng)條件下,鋅胺絡(luò)合離子逐漸轉(zhuǎn)化為ZnO。由于ZnO的晶核和晶體之間存在競(jìng)爭(zhēng),當(dāng)反應(yīng)液的濃度較高時(shí),醋酸根離子吸附在ZnO微晶的(0001)晶面,從而減慢了(0001)晶面的生長(zhǎng)速率,ZnO的長(zhǎng)徑比減小。當(dāng)采用氨水調(diào)節(jié)溶液的pH值時(shí),氨水不僅參與反應(yīng)生成前驅(qū)物Zn(NH3)4(OH)2,水熱條件下脫水產(chǎn)生ZnO；而且反應(yīng)液中的NH4+可以吸附在ZnO晶核的表面,影響著ZnO微晶生長(zhǎng)體系的界面能,對(duì)ZnO晶體的定向生長(zhǎng)具有導(dǎo)向作用,所以ZnO微晶容易自組裝取向連接,形成“孿生”棒狀晶體。
[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.
【學(xué)位授予單位】：武漢理工大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2011
【分類號(hào)】：O614.241

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本文編號(hào)：1919806