CN111659412A - La0.7Sr0.3MnO3/α-Fe2O3制备及其光催化作用 - Google Patents
La0.7Sr0.3MnO3/α-Fe2O3制备及其光催化作用 Download PDFInfo
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Abstract
本发明提供一种磁性复合氧化物La0.7Sr0.3MnO3/α‑Fe2O3，并用荧光光谱，紫外‑可见漫反射光谱，X射线衍射等技术对其进行了表征，结果表明：磁性复合氧化物La0.7Sr0.3MnO3/α‑Fe2O3在紫外及可见光下均有明显吸收，在太阳光下表现了良好的光催化性能，磁性复合氧化物在适宜条件下可使模拟甲基橙废水的降解率达到90%；对生化处理后的焦化废水进行太阳光光催化2h后，焦化废水的可生化性提高，将其继续进行生物处理后，达到了国家焦化废水的排放标准；磁性复合氧化物La0.7Sr0.3MnO3/α‑Fe2O3是一个高效的太阳光驱动的磁性光催化剂，在处理有机废水方面具有广阔的应用前景。
Description
技术领域
本发明涉及p-n异质结磁性复合氧化物La0.7Sr0.3MnO3/α-Fe2O3的制备及其光催化作用。具体来讲，是指具有磁性钙钛矿物氧化物La0.7Sr0.3MnO3与α-Fe2O3形成的p-n异质结磁性复合氧化物光催化剂及其光催化降解有机废水的作用。
背景技术
光催化氧化技术是一种新型高级氧化技术,已逐渐成为生物难降解废水处理的热点。光催化剂的材料众多，包括TiO2、ZnO、Fe2O3、钙钛矿氧化物等，在光催化领域应用广泛。但是单一的光催化剂，由于光生电子与空穴的复合率较高，光催化效果不理想，而且悬浮的微纳米催化剂粉体易团聚，回收困难，还会造成环境的二次污染。经研究发现，设计和制备p-n异质结光催化剂、贵金属沉积、掺杂、负载及半导体复合等方法，均可以有效提高催化剂的光催化性能。
钙钛矿型氧化物光催化剂禁带宽度较窄，太阳光利用率高，尤其在可见光区具有较好的响应，且由于周期表中大部分元素都能形成钙钛矿结构的氧化物，故可通过负载、掺杂及构建p-n异质结光催化剂来提高其光催化性能。已有研究表明：钙钛矿氧化物La1-χSrχMnO3 (0＜χ≤0.5) 具有超顺磁性的特点，对其掺杂可以改变其磁性、光催化活性等。其中La0.7Sr0.3MnO3的磁性最好，为 p型半导体，而α-Fe2O3为n型半导体，所以将两者复合可形成p-n异质结La0.7Sr0.3MnO3/α-Fe2O3复合氧化物。
以模拟甲基橙废水为光催化降解对象，利用本发明设计和合成的p-n异质结复合物La0.7Sr0.3MnO3/α-Fe2O3在太阳光下对其进行光催化降解，结果表明： p-n异质结磁性复合氧化物La0.7Sr0.3MnO3/α-Fe2O3光催化性能远高于它们的构成组分: La0.7Sr0.3MnO3与α-Fe2O3，这是由于p-n异质结复合物La0.7Sr0.3MnO3/α-Fe2O3的具有更高的光生电子和空穴的分离效率，所以具有更好的光催化效率。
对于经过生物处理后仍不能满足排放标准的焦化废水，利用本发明合成的p-n异质结复合物La0.7Sr0.3MnO3/α-Fe2O3在太阳光下对其进行光催化降解，发现焦化废水的可生化性提高，继续生物降解后可以满足到焦化废水排放标准。
发明内容
本发明的目的是提供一种p-n异质结磁性复合氧化物La0.7Sr0.3MnO3/α-Fe2O3催化剂的制备方法及其光催化降解有机废水的作用。本发明实现过程如下：
一、p-n异质结磁性复合氧化物La0.7Sr0.3MnO3/α-Fe2O3 制备
1.1 La0.7Sr0.3MnO3制备：准确称量醋酸镧、醋酸锶、醋酸锰，使其摩尔比为0.7:0.3:1，将称量的反应物溶解在是其5-6倍的去离子水中，待完全溶解后，在60-100℃温度下水解，随着溶剂水的蒸发至糊状时加无水乙醇脱水蒸干后，放置在逐步升温至700-800℃马弗炉中煅烧1.5-3h后，得到La0.7Sr0.3MnO3粉体；
1.2 p-n异质结La0.7Sr0.3MnO3/α-Fe2O3的制备：取2.0 mmol的Fe(NO3)3.9H2O 溶于20.0ml无水乙醇得硝酸铁溶液A，搅拌1h；在A溶液中加入一定量的La0.7Sr0.3MnO3粉体，并将另外10.0 ml溶有2.0-5.0mg聚乙二醇的无水乙醇溶液边搅拌边滴加到硝酸铁溶液A中，α-Fe2O3负载量为10-30%，然后将所得溶液在60-100℃温度下继续反应，待溶剂挥发所得产物干燥后研磨，随后在300-400℃ 煅烧2h得到不同α-Fe2O3负载量的p-n异质结磁性复合氧化物La0.7Sr0.3MnO3/α-Fe2O3。
上述各反应物的摩尔比、实验温度控制、煅烧温度及反应时间等实验条件的确定均是在大量实验基础上得出的,其条件并不对本发明做任何限制。
二、p-n异质结磁性复合氧化物La0.7Sr0.3MnO3/α-Fe2O3 光催化作用
本发明还提供了p-n异质结La0.7Sr0.3MnO3/α-Fe2O3对生物难降解有机物如甲基橙废水及生化处理后无法达标排放的焦化废水的光催化降解作用。太原5月，选择晴天，早上8:30至下午4:00进行光催化实验，选择La0.7Sr0.3MnO3/α-Fe2O3作为光催化剂，探讨其光催化作用。结果表明：所合成的p-n异质结磁性复合氧化物La0.7Sr0.3MnO3/α-Fe2O3在太阳光下，对甲基橙模拟废水的光催化作用明显高于其构成组分La0.7Sr0.3MnO3与α-Fe2O3的光催化作用；对来自某焦化公司生物处理后的焦化废水为降解对象，在太阳光下用La0.7Sr0.3MnO3/α-Fe2O3对其进行光催化降解后，明显提高了其可生物降解性，在继续经过生物处理后，其水质符合焦化废水排放标准。
本发明具有以下的优点及效果：
1）p-n异质结复合氧化物La0.7Sr0.3MnO3/α-Fe2O3具有近超顺磁性特性。纳微米的La0.7Sr0.3MnO3与α-Fe2O3都具有磁性，两者复合其饱和磁化强度达为39.3 emu/g，饱和磁化强度高，其近超顺磁性特性使悬浮的纳微米催化剂有不易团聚的特点，克服了没有磁性的普通悬浆型光催化剂如二氧化钛难以分离的弊端，光催化剂可在外加磁场下实现简单分离。2）催化剂既可吸收紫外光，也可吸收可见光，所合成p-n异质结复合氧化物La0.7Sr0.3MnO3/α-Fe2O3是一个能充分利用太阳光的磁性光催化剂，可极大的降低企业的废水处理成本。3）p-n异质结复合氧化物La0.7Sr0.3MnO3/α-Fe2O3由于可降低光生电子和空穴的复合率，所以具有高的光催化性能。4）本发明所涉及的p-n异质结La0.7Sr0.3MnO3/α-Fe2O3复合氧化物的制备方法简单，条件温和，原料环保且易得，具有广阔的市场应用前景。
附图说明
图1 XRD谱图：p-n异质结La0.7Sr0.3MnO3/α-Fe2O3,La0.7Sr0.3MnO3-δ及α-Fe2O3；
图2 UV-Vis漫反射图： α-Fe2O3，La0.7Sr0.3MnO3和p-n异质结La0.7Sr0.3MnO3/α-Fe2O3 ；
图3磁性能图谱： α-Fe2O3，La0.7Sr0.3MnO3和p-n异质结La0.7Sr0.3MnO3/α-Fe2O3；
图4 荧光光谱：α-Fe2O3，La0.7Sr0.3MnO3和系列不同氧化铁负载量p-n异质结La0.7Sr0.3MnO3/α-Fe2O3；
图5 透射电镜图： (a) La0.7Sr0.3MnO3/α-Fe2O3, (b)附有晶格条纹的高倍透射电镜图，(c) 电子衍射图 (SAED；).
图6 太阳光下对模拟甲基橙废水光催化降解作用。
具体实施方式
本发明是通过以下实施例实现的，但实施中所述条件和结果对发明的内容和权利不构成限制。
一、p-n异质结磁性复合氧化物La0.7Sr0.3MnO3/α-Fe2O3 制备
1.1 La0.7Sr0.3MnO3-δ制备：准确称量醋酸镧、醋酸锶、醋酸锰，使其摩尔比0.7:0.3:1，将称量的反应物溶解在是其5倍的水中，待完全溶解后，在80℃温度下水解，随着溶剂水的蒸发至糊状时加无水乙醇脱水蒸干后，放置于马弗炉，将其逐步升温至800℃后煅烧1.5h，得到La0.7Sr0.3MnO3-δ粉体；
1.2 p-n异质结La0.7Sr0.3MnO3/α-Fe2O3的制备：取2.0 mmol的Fe(NO3)3.9H2O 溶于20.0ml无水乙醇得硝酸铁溶液A，搅拌1h；随后在A溶液中加入一定量的La0.7Sr0.3MnO3粉体，边搅拌边逐滴加入10.0 ml溶有3mg聚乙二醇的无水乙醇溶液，然后在70℃反应，待溶剂挥发所得产物干燥研磨后，在300℃ 煅烧2h得到20% α-Fe2O3负载量的p-n异质结磁性复合氧化物La0.7Sr0.3MnO3/α-Fe2O3。
二、p-n异质结La0.7Sr0.3MnO3/α-Fe2O3复合氧化物的表征
2.1 p-n异质结La0.7Sr0.3MnO3/α-Fe2O3的XRD图 ：由图1可见：每个XRD峰都分裂成可分辫的峰，可知所得的钙钛矿氧化物的结构为斜方六面体。图1中没有氧化铁的主峰出现，可能是由于负载量小，XRD无法检出所致。对p-n异质结La0.7Sr0.3MnO3/α-Fe2O3复合氧化物进行的光电子能谱测试及高分辨透射电镜（图5）均说明：p-n异质结复合氧化物La0.7Sr0.3MnO3/α-Fe2O3明显存在铁元素，说明本发明可制备出p-n异质结La0.7Sr0.3MnO3/α-Fe2O3复合的氧化物。
2.2 p-n异质结La0.7Sr0.3MnO3/α-Fe2O3的紫外可见漫反射光谱：由图2可知： p-n异质结La0.7Sr0.3MnO3/α-Fe2O3无论对紫外和可见光吸收都比其构成组分La0.7Sr0.3MnO3和α-Fe2O3两者的吸收强度大，说明本发明方法制备的p-n异质结复合氧化物La0.7Sr0.3MnO3/α-Fe2O3是一个能充分利用太阳光的磁性光催化剂。
2.3 p-n异质结La0.7Sr0.3MnO3/α-Fe2O3 的磁性能: 由图3的磁滞回线可知：La0.7Sr0.3MnO3和α-Fe2O3都有近超顺磁特点，两者形成的p-n异质结La0.7Sr0.3MnO3/α-Fe2O3的饱和磁为39.3emu/g，完全可以被外加磁场进行分离。
2.4 p-n异质结La0.7Sr0.3MnO3/α-Fe2O3荧光光谱：一般条件下，荧光越强意味着光生载流子复合机会越大，无法有效分离，故光催化活性低。由图4可见，负载20% α-Fe2O3 p-n异质结La0.7Sr0.3MnO3/α-Fe2O3与La0.7Sr0.3MnO3-δ和α-Fe2O3相比，荧光强度最低，说明其光生载流子复合机会越小，光催化活性高， p-n异质结复合氧化物La0.7Sr0.3MnO3/α-Fe2O3 是性能优越的磁性太阳光活性的光催化剂。
2.5 高分辫透射电镜图：图5展示的是La0.7Sr0.3MnO3/α-Fe2O3（20 wt%）的透射电镜图及附有晶格条纹的电子衍射图SAED。通过DigitalMicrograph软件测量，发现两个晶面间距为0.381nm和0.251nm，分别对应La0.7Sr0.3MnO3的012晶面和α-Fe2O3的110晶面。进一步证实了La0.7Sr0.3MnO3和α-Fe2O3之间形成了p-n异质结结构。从图5(a)中可明显看出，La0.7Sr0.3MnO3/α-Fe2O3（20 wt%）颗粒均匀，而图5(b)中可发现二相之间明显地结合形成一个整体，说明两者形成了p-n异质结结构的光催化剂。由于p-n异质结结构的光催化剂可以抑制光生电子与空穴的复合，从而具有更高的光催化活性。
三、p-n异质结复合氧化物La0.7Sr0.3MnO3/α-Fe2O3的光催化活性
3.1 以模拟甲基橙废水为研究对象
以10.0 mg/L的甲基橙(MO)为降解目标对象，p-n异质结La0.7Sr0.3MnO3/α-Fe2O3用量0.75g/L、初始甲基橙溶液的pH值为3.0、光照时间为35min时，太阳光下，（12：00-14：00，平均光照强度95klux），甲基橙(MO)溶液降解率达到90%以上。图6表明：p-n异质结复合氧化物La0.7Sr0.3MnO3/α-Fe2O3(20%)与α-Fe2O3，La0.7Sr0.3MnO3相比，光催化性能最好。
3.2 以生化处理后的实际焦化废水为降解对象
在pH=1、催化剂用量为1.0g/L、光催化时间为2h的适宜条件下，使用La0.7Sr0.3MnO3/α-Fe2O3光催化剂在太阳光下对某公司经过生物处理后的焦化废水进行光催化处理2h后，与原废水相比，焦化废水生化性提高，将其继续进行生物处理后，测得COD为56.0 mg/L，BOD为20.4mg/L，氨氮浓度为5.4mg/L，总磷浓度为1.2mg/L，达到了国家焦化废水排放标准。
总之， p-n异质结磁性复合物La0.7Sr0.3MnO3/α-Fe2O3是太阳光活性的光催化剂，预期在废水处理领域具有广阔的应用前景。
Claims (2)
1.La0.7Sr0.3MnO3/α-Fe2O3的制备方法, 其特征在于，包括以下步骤：
1.1 La0.7Sr0.3MnO3制备：准确称量醋酸镧、醋酸锶、醋酸锰，使其摩尔比为0.7:0.3:1，将称量的反应物溶解在是其5-6倍的去离子水中，待完全溶解后，在60-100℃温度下水解，随着溶剂水的蒸发至糊状时加无水乙醇脱水蒸干后，放置马弗炉中并逐步升温至700-800℃后，煅烧1.5-3h，得到La0.7Sr0.3MnO3粉体；
1.2 p-n异质结La0.7Sr0.3MnO3/α-Fe2O3的制备：取2.0 mmol的Fe(NO3)3•9H2O 溶于20.0ml无水乙醇得硝酸铁溶液A，搅拌1h；在A溶液中加入一定量的La0.7Sr0.3MnO3粉体，并将另外10.0 ml溶有2.0-5.0mg聚乙二醇的无水乙醇溶液边搅拌边滴加到硝酸铁溶液A中，α-Fe2O3负载量为10-30%，然后将所得溶液在60-100℃温度下继续反应，待溶剂挥发所得产物干燥后研磨，随后在300-400℃ 煅烧2h得到不同α-Fe2O3负载量的p-n异质结磁性复合氧化物La0.7Sr0.3MnO3/α-Fe2O3。
2.权利要求1所述的La0.7Sr0.3MnO3/α-Fe2O3制备方法，其特征在于，所述p-n异质结磁性复合光催化剂La0.7Sr0.3MnO3/α-Fe2O3对甲基橙模拟废水及生化处理后仍未达到排放标准焦化废水具有光催化降解作用。
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