CN113731462A - 一种基于La2Ce2O7与g-C3N4的光催化复合材料的制备方法与应用 - Google Patents
一种基于La2Ce2O7与g-C3N4的光催化复合材料的制备方法与应用 Download PDFInfo
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Abstract
本发明公开了一种基于La2Ce2O7与g‑C3N4的光催化复合材料的制备方法与应用。称取La(NO3)3·6H2O和Ce(NO3)3·6H2O溶于去离子水中,再加入柠檬酸磁力搅拌,调节pH值后,继续磁力搅至水分蒸发形成胶体,再将胶体烘干后在350℃下保温,最后于800℃下空气氛围煅烧,冷却后将混磨粉末与三聚氰胺及熔盐混磨,进行熔盐法得光催化复合材料。本发明成本低、效率高、环境友好,所得的g‑C3N4复合的La2Ce2O7材料是典型复合异质结结构,具有较多表面光催化活性区域和可见光响应,光催化性能稳定,因此在制备新型光催化剂上具有重大的潜在应用价值。
Description
技术领域
本发明涉及光催化技术领域,具体涉及一种基于La2Ce2O7与g-C3N4的光催化复合材料的制备方法与应用。
背景技术
随着工业的不断发展,人类面对着环境污染和能源短缺这两项重大挑战。而由于工业上对于染料的高需求,有机染料成为水资源污染的重要原因。工业上最常用的染料是罗丹明B(RhB),用于生产塑料、纺织品、纸张印刷和皮革等方面,但RhB会对生物和环境稳定性造成严重威胁,于是,去除工业废水中的有机染料成为一项重要任务。近年来,随着科学技术的进步,许多传统方法被用来解决水污染的问题,包括物理吸附法、电化学法、臭氧氧化法和光催化降解法。在各种先进的废水处理方法中,半导体光催化降解法由于其绿色、高效、低成本和无二次污染等优点,被认为是一种很有前途的废水处理方法。
CeO2是一种N型半导体金属光催化材料,其带隙为3.2 ev,其中含有丰富的氧空位缺陷,具有很高的储氧能力,并能通过Ce3+和Ce4+之间的转化来吸收和释放氧,因此,CeO2被广泛应用于催化剂、氧传感器、紫外阻挡材料、发光材料和固体氧化物燃料电池。然而,由于CeO2禁带宽度大和太阳能利用率低等缺点,使得其在废水处理中的应用受到了限制,为了扩大其应用的范围,研究者采取了不同的改性策略来改善CeO2的光催化性能,主要包括贵金属负载,半导体复合和元素掺杂。根据报道掺杂La3+取代Ce4+会产生电荷不平衡,从而引入氧空位缺陷,而不会扭曲它们的萤石结构,这些氧空位可以增强材料的磁性和光催化性能。于是,作为与La掺杂的CeO2具有相似萤石结构的一种稀土铈酸盐,La2Ce2O7因其出色的电学、催化和机械性能引起了研究者们逐渐的关注,这种材料被广泛应用于固体氧化物燃料电池、传感器、催化剂、发光材料和热障涂层等,目前La2Ce2O7材料在光催化领域研究鲜见报道。
目前,为提高La2Ce2O7在光催化领域性能,主要集中在两个方面:一是对La2Ce2O7单元改性,通过控制形貌结构和元素掺杂改性,提高光催化性能;二是通过寻求有机或无机化合物与La2Ce2O7形成二元或多元复合异质结,提高光催化性能。在这些策略中,复合异质结半导体材料,被认为是由于电荷分离的增加而提高光催化活性的常用有效方法。
溶胶-凝胶法因其产物颗粒均匀、尺寸小和产物纯度高等优点被广泛应用于微材料的合成。特别是与固相反应相比,化学反应将容易进行,而且仅需要较低的合成温度,由于溶胶-凝胶体系中组分的扩散在纳米范围内,而固相反应时组分扩散是在微米范围内,因此反应容易进行,温度较低。
熔盐法有着适用范围广、产物形貌和尺寸易于调控和产物粒度均匀等优点。由于在液态的熔盐中可以加快物质的传递速度,使得反应温度降低且反应时间缩短,同时熔盐分布于整个反应体系中,贯穿于反应形成的粒子之间,有效避免了颗粒间发生团聚现象,故使用熔盐法制备的样品粒度通常分布较为均匀等。
综上所述,目前在La2Ce2O7制备方面,未有采用溶胶-凝胶法制备,并选取g-C3N4与La2Ce2O7进行复合材料制备的报道,同时在材料改性方面也未有研究。
发明内容
针对现有技术的不足,本发明提供一种基于La2Ce2O7与g-C3N4的光催化复合材料的制备方法与应用,通过创新地选择三聚氰胺与La2Ce2O7混合,再加入熔盐混合,通过一定温度条件下,制备出具有较高活性的可见光响应的La2Ce2O7/g-C3N4光催化复合材料,具有较强的太阳光响应的催化降解活性,另外该方法制备工艺简单,能耗低,所制的材料催化效率高,拓宽其在光催化领域上的应用。
为解决现有技术问题,本发明采取的技术方案为:
一种基于La2Ce2O7与g-C3N4的光催化复合材料的制备方法,包括以下步骤:
步骤1,用溶胶凝胶法制备La2Ce2O7
按化学计量称取La(NO3)3·6H2O和Ce(NO3)3· 6H2O溶于去离子水中得混合溶液A,向混合溶液A中加入柠檬酸并磁力搅拌30min形成溶胶,再滴加10μL/s氨水调节pH至8-10后,置于70℃加热磁力搅拌器搅拌,至水分蒸发形成粘稠状(不出现明显水溶液现象)得到凝胶;再将凝胶转移至烘箱中100℃干燥10小时,再在350℃下保温1小时去除有机物,最后在马弗炉中空气氛围下煅烧,所得样品La2Ce2O7,记为LCO;所述柠檬酸与混合溶液A中金属阳离子的摩尔比为1.5:1;
称La2Ce2O7与三聚氰胺进行精细研磨1h,再加入NaCl和KCl研磨3h,并将研磨后的混合物放入马弗炉中以500℃保温3小时,待冷却至室温后,用无水乙醇水溶液反复在离心机中离心洗涤3-5次,烘干过夜,即得La2Ce2O7/g-C3N4光催化复合材料,记为LCO/CN-x,其中x为不同质量的三聚氰胺数值,且x为0.5~4。
作为改进的是,步骤1中马弗炉中煅烧参数为800℃、3小时。
作为改进的是,步骤2中La2Ce2O7与三聚氰胺混合时, x即为2。作为改进的是,步骤2中NaCl和KCl的混合物总质量为La2Ce2O7和g-C3N4总质量的20倍,且质量比为1:1。
作为改进的是,步骤2中马弗炉的升温速度为5-10℃/min,离心的速率为4000r/min。
作为改进的是,步骤2中无水乙醇水溶液按照乙醇与水按照等体积混合;烘干过夜的温度为80℃。
上述制备的La2Ce2O7/g-C3N4光催化复合材料在降解RhB溶液上的应用。
工作原理:一方面,La2Ce2O7和g-C3N4本身特殊的能带结构,具备一定的可见光响应能力;另一方面,形成复合异质结改性后形成界面内接电场,可以有利于的光生电子-空穴对的快速分离,从而提高量子产率,因此在在可见光响应范围内,也提高光催化降解性能。
有益效果:
与现有技术相比,本发明一种基于La2Ce2O7与g-C3N4的光催化复合材料的制备方法与应用,成本低、效率高、环境友好、安全便利,过程简单等优点,所得的La2Ce2O7/g-C3N4光催化复合材料具有较多的表面活性区域,具有可见光响应,光催化性能稳定,对RhB具有优异的降解效果。
附图说明
图1为本发明不同实施例制备La2Ce2O7/g-C3N4光催化复合材料的XRD图谱;
图2为本发明实施例5中LCO/CN-2不同元素的XPS光谱图;
图3为不同物质的相关图像, (a) 为LCO的SEM图像,(b)为CN的SEM图像,(c) LCO/CN-2的SEM图像,(d)为LCO/CN-2的TEM图像,(e)为Ce元素分布图, (f) LCO/CN-2的HRTEM图像,(g)为La元素分布图,(h)为C元素分布图,(i)为N元素分布图,(j)为O元素分布图;
图4为本发明实施例5中紫外-可见吸收光谱,其中图4(a)为LCO、CN和LCO/CN-2的紫外-可见漫反射吸收光谱图4(b)为(αhυ)1/2对光子能量(hυ)作图计算LCO和CN的带隙能;
图5(a)为不同样品在模拟太阳光下降解RhB速率;
图5(b)为不同样品光催化降解RhB溶液的反应动力学常数曲线;
图5 (c) 为不同CN含量的LCO/CN反应动力学常数的变化;
图5(d) 为模拟太阳光下LCO/CN-2降解RhB循环试验。
具体实例方式
为使本发明实施例的目的、技术方案和优点更加清楚,下面将对本发明实施例中的技术方案进行清楚、完成地描述。实施例中未注明具体条件者,按照常规条件或制造商建议的条件进行。所用试剂或仪器未注明生产厂商者,均为可以通过市售购买获得的常规产品。
本发明所有实施例所用的La2Ce2O7通过溶胶凝胶法制备,具体步骤如:按化学计量称取La(NO3)3·6H2O和Ce(NO3)3·6H2O溶于去离子水中得混合溶液A,向混合溶液A中加入柠檬酸并磁力搅拌30min形成溶胶,再滴加10μL/s氨水调节pH至8-10后,置于70℃加热磁力搅拌器搅拌,至水分蒸发形成粘稠状(不出现明显水溶液现象)得到凝胶;再将凝胶转移至烘箱中100℃干燥10小时,再在350℃下保温1小时去除有机物,最后在马弗炉中空气氛围下800℃下煅烧3h,所得样品La2Ce2O7,记为LCO;所述柠檬酸与混合溶液A中金属阳离子的摩尔比为1.5:1。
实施例1
(1)称取1.0000g La2Ce2O7和0.5000g的三聚氰胺进行精细研磨1h,再与NaCl和KCl混合,进行熔盐混磨3h得混合粉末;
(2)再将混磨粉末置于氧化铝坩埚中,再放入马弗炉中升到500℃保温3h,自然冷却至环境温度,得半成品;
(3)取出半成品,并用无水乙醇水溶液(按照乙醇与水按照等体积混合)反复洗涤,洗涤用转速为4000r/min ,并将洗涤后的半成品粉体置于80 ℃烘箱中过夜烘干,(缩写为LCO/CN-0.5)。
实施例 2
(1)称取1.0000 gLa2Ce2O7和1.0000g的三聚氰胺进行精细研磨1h,再与NaCl和KCl混合,进行熔盐混磨3h得混合粉末;
(2)再将混磨粉末置于氧化铝坩埚中,再放入马弗炉中升到500℃保温3h,自然冷却至环境温度,得半成品;
(3)取出半成品,并用无水乙醇水溶液(按照乙醇与水按照等体积混合)反复洗涤,洗涤用转速为4000r/min ,并将洗涤后的半成品粉体置于80 ℃烘箱中过夜烘干,(缩写为LCO/CN-1)。
实施例 3
(1)称取1.0000 g La2Ce2O7和2.0000 g的三聚氰胺进行精细研磨1h,再与NaCl和KCl混合,进行熔盐混磨3h得混合粉末;
(2)再将混磨粉末置于氧化铝坩埚中,再放入马弗炉中升到500℃保温3h,自然冷却至环境温度,得半成品;
(3)取出半成品,取出半成品,并用无水乙醇水溶液(按照乙醇与水按照等体积混合)反复洗涤,洗涤用转速为4000r/min ,并将洗涤后的半成品粉体置于80 ℃烘箱中过夜烘干,(缩写为LCO/CN-2)。
实施例 4
(1)称取1.0000 g La2Ce2O7和3.0000 g的三聚氰胺进行精细研磨1h,再与NaCl和KCl混合,进行熔盐混磨3h得混合粉末;
(2)再将混磨粉末置于氧化铝坩埚中,再放入马弗炉中升到500℃保温3h,自然冷却至环境温度,得半成品;
(3)取出半成品,并用无水乙醇水溶液(按照乙醇与水按照等体积混合)反复洗涤,洗涤用转速为4000r/min ,并将洗涤后的半成品粉体置于80 ℃烘箱中过夜烘干,(缩写为LCO/CN-3)。
实施例5
(1)称取1.0000 g La2Ce2O7和4.0000 g的三聚氰胺进行精细研磨1h,再与NaCl和KCl混合,进行熔盐混磨3h得混合粉末;
(2)再将混磨粉末置于氧化铝坩埚中,再放入马弗炉中以升到500℃保温3h,自然冷却至环境温度,得半成品;
(3)取出半成品,并用无水乙醇水溶液(按照乙醇与水按照等体积混合)反复洗涤,洗涤用转速为4000r/min ,并将洗涤后的半成品粉体置于80 ℃烘箱中过夜烘干,(缩写为LCO/CN-4)。
对比例
为便于实验比较,称取5g三聚氰胺,按上述实验条件合成g-C3N4,所得样品记为CN。
性能测试
为了对本发明实施例中得到的La2Ce2O7/g-C3N4光催化复合材料的自身品质和催化性能进行验证和分析,本试验例对实施例1-5所得的La2Ce2O7/g-C3N4光催化剂,以及单一La2Ce2O7和g-C3N4进行了试验,测试分析结果表现均较好,具体测试方法如下:
催化剂的表征:样品的XRD分析采用日本的Shimadzu XRD-6000型X射线衍射仪进行,Cu靶(λ=0.1541 nm),配有石墨单色镜,管压为40 KV,管流为30mA,扫描速度:2 °/min,扫描角度范围为10-80°。样品的形貌表征通过QUANTA200型扫描电镜(SEM)(美国FEI公司)和JEM-2100型透射电镜(TEM)(日本JEOL公司)。样品XPS分析通过ESCALAB250Xi 型X射线电子能谱仪进行检测,其电子能量分析器:分析面积为0.02~8 mm连续可调。
光催化性能测试:通过模拟太阳光条件下对罗丹明B(RhB)溶液进行降解,以测试光催化性能。其中光源为氙灯(300W),距离液面高度20cm,取0.1000g催化剂均匀分散在100.00ml浓度为10 mg/L的RhB溶液中,采用循环冷却的方式保持反应器室温。光照前,将混合悬浮液搅拌暗吸附45分钟,以实现暗吸附平衡,再光催化反应,每15min,取样一次(样品的体积4 mL),离心去沉淀物,进行吸光度分析。
具体地说明:
首先,本发明对所测成品进行了鉴定,分别对光催化剂进行X射线粉末衍射分析测试,其结果如图1所示为La2Ce2O7、g-C3N4和LCO/CN的XRD图谱,由于没有检测到与纯La2O3和CeO2有关的任何衍射,这证明在高温煅烧过程中,前驱体之间的固相反应非常完全,生成的催化剂具有纯的La2Ce2O7相,这与文献报道相一致。值得注意的是在2θ= 30-45°范围内只出现一个衍射峰,故所获得的La2Ce2O7被认为是萤石相。对于纯g-C3N4,可以明显看到位于2θ=13.0°和27.4°存在两个衍射峰,他们分别对应于四方晶相g-C3N4的(100)和(002)晶面(JCPDS 87-1526)。而对于复合材料LCO-CN系列,在g-C3N4 含量较低时,(002)面衍射峰消失,这可以认为是被LCO强衍射峰覆盖。甚至,在复合材料中(100)晶面消失,这是因为g-C3N4被剥离成薄层纳米结构。
为进一步确认复合后的表面化学组成和化学态,图2为LCO/CN-2的XPS图谱。如图2(b)所示,图2(b)中显示了Ce 3d5/2和Ce 3d3/2的特征峰,Ce 3d轨道可拟合为以上8个峰,其中位于917.0 eV,907.5 eV,902.6 eV,900.7 eV的结合能归因于Ce 3d5/2,位于898.2 eV,888.4 eV,884.2 eV,882.4 eV属于Ce 3d3/2,此外917.0 eV,907.5eV,900.7 eV,898.2 eV四个结合能的峰属于Ce3+,902.6eV,888.4 eV,884.1 eV,882.4 eV四个结合能的峰属于Ce4 +。图2(c)可以观察到峰值能量为838.4 eV和卫星能量为885.7 eV所组成的双峰结构,卫星的高结合能可归因于与O 2p向La 4f的电荷转移有关的振动过程。图2(d)中位于528.8 eV和531.7 eV两个结合能的峰表明在复合材料中至少存在两个氧物种,分别归因于晶格氧和表面化学吸附的氧(·OH)。图2(e)中位于284.6 eV和288.0 eV两个结合能的峰,位于284.6eV的峰归因于C-N的sp2杂化,位于288.0 eV的峰归因于g-C3N4芳香环上N-C=N的sp2键合碳。图2(f)图中可拟合为三个峰,第一个位于398.4 eV的主峰归因于三嗪环的sp2氮的典型信号和骨架上的N-(C)3基团,第二个位于399.8 eV的峰归因于-NH2或者=NH基团,第三个位于404.2 eV的峰归因于电荷效应或者杂环中的正电荷定位
为了进一步证明上述关于物质鉴定的部分推测和进一步地分析研究LCO、CN和LCO/CN-2光催化材料的微观形貌特征,如图3(a)所示为溶胶-凝胶法制备的LCO粉体,从图中可以看出LCO呈现珊瑚状,厚度在5 nm左右,从图3(b)可以观察到CN呈现明显的层状结构,大量CN纳米片重叠在一起。LCO/CN-2复合材料的形貌如图3(c)所示,片状的LCO分散在CN纳米片上,形成的异质结结构有利于光生载流子的分离。通过投射电镜研究了异质结复合材料的界面,在图3(d)上可以明显看到LCO的形态,其中LCO和CN紧密结合,在图3(f)上显示了LCO的晶格条纹和无晶格条纹的CN,并可以观察到LCO和CN间的紧密接触界面。元素分布如图3(e),(g),(h),(i),(j)所示,结合TEM和XRD图像表明,所研究LCO/ CN异质结构中含有Ce,O,La,C和N,且元素在复合材料中均布。
用紫外-可见吸收光谱法对其光学吸收性能进行了评价。如图4(a)所示,与LCO样品相比,LCO与 CN复合后的吸收边发生了红移,意味着LCO/CN-2光吸收扩展到可见光区域,提高了光吸收的范围,增加了太阳光的利用率。通过(αhv)1/2做纵坐标,hv做横坐标作图,得出LCO和CN的带隙值分别为2.52 eV和2.44 eV。图4(b) 分别显示了从LCO和CN的莫特-肖特基曲线,通过将莫特-肖特基曲线线性部分外推至横坐标轴,可得到其平带电位分别为-0.62 V和-0.45 V。由于交点均为负值,两种样品均具有p型半导体特性,其交点值近似等于其CB边缘电位,通过能斯特方程计算可以得到LCO和CN的CB电位分别为-0.42 V Vs NHE和-0.25 V Vs NHE(VNHE=VAg/AgCl+0.197 V)
进一步地,为了验证LCO、CN和LCO/CN-x可见光催化剂的降解能力。本实验对所制备的样品进行了全面的可见光催化降解RhB实验,使用100 mg催化剂对10mg/L的RhB进行了光降解。如图5(a)所示模拟太阳光照射下降解RhB分子,研究了各组分的光催化性能,其中LCO/CN-2的光降解效率高于其他组分,达到了91.4%,且随着复合材料中CN含量的增加,光降解效率呈现先升高后降低的趋势。随着LCO和CN的结合,各组分的光催化活性均得到了增强,这说明两者间形成了促进光生载流子转移的异质结界面,从而提高了光催化活性,但是过量的CN可能将LCO覆盖,阻碍了光捕获,减少了复合界面有效活性点位,导致光催化活性降低。为了定量评价催化剂的光催化活性,对上述样品进行了RhB降解动力学研究,动力学曲线如图5(b)所示,在RhB水溶液中,光催化分解反应近似服从一级动力学,光催化反应可用dC/dt=kC描述,其中C为RhB的浓度,k为总降解速率常数。光催化活性定义为降解速率常数。通过线性回归绘制作为时间函数的-ln(C0/Ct),从直线斜率获得每个样品的速率常数k(单位:min-1),根据图5(c),速率常数k(单位:min-1)随CN含量变化同样符合先升高后降低的趋势,LCO/CN-2的速率常数k(0.02701min-1)明显高于LCO(0.00054min-1)和CN(0.01109min-1)。如图5(d)所示,对LCO/CN-2进行了循环实验,实验表明重复使用4次后,RhB的去除率依然可以达到90%以上,说明该复合材料在降解污染物方面具有良好的稳定性。
综上所述,本发明采用溶胶-凝胶法法制备了纯La2Ce2O7,同时使用熔盐法制备了La2Ce2O7/g-C3N4光催化复合材料。本发明成本低、效率高、环境友好、安全便利,过程简单等优点,所得的La2Ce2O7/g-C3N4光催化复合材料具有较多的表面活性区域,具有可见光响应,光催化性能稳定,对RhB具有优异的降解效果,从而本发明提供的La2Ce2O7/g-C3N4光催化复合材料可广泛应用于光催化降解有机污水领域。
以上所述的实施例是本发明一部分实施例,而不是全部的实施例。本发明的实施例的详细叙述并非旨在限制要求保护的本发明的范围内,仅仅表示本发明的选定实施例。基于本发明中的实施例,本领域普通技术人员在没有作出创造性劳动前提下所获得的所有其他实施例,都属于本发明保护范围。
Claims (7)
1.一种基于La2Ce2O7与g-C3N4的光催化复合材料的制备方法,其特征在于,包括以下步骤:
步骤1,采用溶胶凝胶法制备La2Ce2O7
按化学计量称取La(NO3)3·6H2O和Ce(NO3)3· 6H2O溶于去离子水中得混合溶液A,向混合溶液A中加入柠檬酸并磁力搅拌30min形成溶胶,再滴加10μL/s氨水调节pH至8-10后,置于70℃加热磁力搅拌器搅拌,至水分蒸发形成粘稠状得到凝胶;再将凝胶转移至烘箱中100℃干燥10小时后,于350℃下保温1小时去除有机物,最后在马弗炉中空气氛围下煅烧,所得样品La2Ce2O7,记为LCO;所述柠檬酸与混合溶液A中金属阳离子的摩尔比为1.5:1;
步骤2,称样品La2Ce2O7与三聚氰胺进行精细研磨1h,再加入NaCl和KCl的混合物研磨3h,并将研磨后的混合物放入马弗炉中升温到500℃保温3小时,待冷却至室温后,用无水乙醇水溶液反复在离心机中离心洗涤3-5次,烘干过夜,即得La2Ce2O7/g-C3N4光催化复合材料,记为LCO/CN-x,其中x为不同质量的三聚氰胺数值,且x为0.5-4。
2.根据权利要求1所述的一种基于La2Ce2O7与g-C3N4的光催化复合材料的制备方法,其特征在于,步骤1中马弗炉中煅烧参数为800℃、3小时。
3.根据权利要求1所述的一种基于La2Ce2O7与g-C3N4的光催化复合材料的制备方法,其特征在于,步骤2中La2Ce2O7与三聚氰胺混合时,x即为2。
4.根据权利要求1所述的一种基于La2Ce2O7与g-C3N4的光催化复合材料的制备方法,其特征在于,步骤2中NaCl和KCl的混合物总质量为La2Ce2O7与g-C3N4总质量的20倍,且质量比为1:1。
5.根据权利要求1所述的一种基于La2Ce2O7与g-C3N4的光催化复合材料的制备方法,其特征在于,步骤2中马弗炉的升温速度为5-10℃/min,离心的速率为4000r/min。
6.根据权利要求1所述的一种基于La2Ce2O7与g-C3N4的光催化复合材料的制备方法,其特征在于,步骤2中无水乙醇水溶液按照乙醇与水按照等体积混合;烘干过夜的温度为80℃。
7.基于权利要求1制备的La2Ce2O7/g-C3N4光催化复合材料在降解RhB溶液上的应用。
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