2020, Vol. 11引用本文 |
| Z-型异质结光催化剂的设计、制备和应用研究进展 |  [PDF全文] |
2. 广东石油化工学院化学工程学院，广东 茂名 525000
2. School of Chemical Engineering, Guangdong University of Petrochemical Technology, Maoming 525000, China
有效解决环境污染和能源短缺问题是国内外科学家研究的热点。光催化技术在能源和环境领域有着广阔的应用前景，引起了广泛的重视[1-5]。其主要研究领域有水体净化[6-11]、空气净化[12-14]、能源转换[15-16]、杀菌消毒[17-19]、自清洁[20-23]等。
常见半导体光催化剂有一元半导体光催化剂和多元半导体光催化剂。对于一元半导体光催化剂来说，由于固定的能带结构，难以同时兼顾宽的光吸收范围及强的氧化还原能力。因为扩大光吸收范围需要较窄的带隙，而强氧化还原能力需要价带电位越正、导带电位越负，这必然导致宽的带隙[24]。同时光生电子和空穴易发生复合，使得光催化反应量子效率低[25]。多元半导体光催化剂的存在可以很好解决不兼容的问题。多元半导体光催化活性的提高可以归因于异质结的形成，不同的半导体材料有不同的能带结构，形成异质结后不仅可以调整带隙宽度还可以改变氧化还原能力，因此可以促进光生载流子的分离和转移，同时扩展对光的吸收范围以及提高光催化剂的稳定性[26-27]。常见的异质结有传统异质结和Z-型异质结，传统异质结由于两种半导体材料能带位置的不同，光生电子会发生迁移，这种电荷迁移方式虽然可以促进光生电子与空穴的分离，但是氧化还原能力却被减弱。在此情况下，Z-型异质结的发现很好地解决了单一光催化剂反应量子效率低和传统异质结氧化还原能力不足的问题。Z-型异质结一般由两种能带交错的半导体材料构成和导电介质构成，由于两种材料与介质间的内部作用使得特定的一部分光生电子与空穴被消耗或发生复合，保留了具有更强氧化还原能力的电子与空穴，因此具有能有效分离电子空穴对、保留强氧化-还原活性位点、扩大光响应范围和提高光催化活性等优点，成为近年来光催化研究的热点[24, 28]。文中简要介绍了Z-型异质结的来源，对比了Z-型异质结与传统异质结的机理区别，总结了目前Z-型异质结的类型以及在产氢、CO2还原、有机物降解以及水中重金属离子去除等方面的应用。
1 Z-型异质结来源在常见的传统异质结中，通常可以根据两个半导体光催化剂的导带和价带位置分为两种类型：typeⅠ和typeⅡ。在typeⅠ中（图 1（a）），光催化剂Ⅱ（PCⅡ）的导带（CB）位高于光催化剂Ⅰ（PCⅠ），而PCⅡ的价带（VB）位低于PCⅠ，在热力学允许的前提下，由于两种半导体间的能带差，光生电子和空穴会从PCⅡ移动到PCⅠ，由于光生电子与空穴聚集在同一半导体上，故这种异质结往往不能改善光催化剂[29-30]。在typeⅡ中（图 1（b）），与PCⅡ相比，PCⅠ具有更高的CB和VB位，更高的费米能级（EF）[31]。光照后，两种半导体材料均受到激发，电子（e-）跃迁到CB上，而PCⅠ中CB位置较PCⅡ中CB高，同样，在热力学允许的条件下，由于两者间的能带差，电子会从PCⅠ的CB转移至PCⅡ的CB上并在此位置上积累，相反，PCⅡ中VB位置较PCⅠ中VB低，因此空穴（h+）会从PCⅠ的VB转移至PCⅡ的VB上并在此位置上积累[32]。电子有还原能力，空穴有氧化能力，当价带电势越正，氧化能力越强；导带电势越负，还原能力越强[33]。因此，这种载流子转移方式存在的弊端是没能保留最强氧化还原电位，对氧化还原能力有所影响[26, 34-35]。还有一种typeⅢ类型的能带结构（图 1（c）），也是其中一种半导体的价带和导带都高于另一种半导体，但PCⅠ的价带位比PCⅡ导带位还要高。这种类型的能带结构通过适当的导电介质可以将其应用于Z-型异质结中[32]。
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| 图 1 异质结机理 Fig. 1 Heterojunction mechanism |
在自然界中，绿色植物通过光合作用将H2O和CO2转化为O2和碳链，这是由电子传递链串联两个不同的光系统来实现的。光照后，光系统Ⅱ（PSⅡ）吸收能量，发生光解水产生质子、电子和氧气，电子从PSⅡ流出，通过质体醌、细胞色素复合体等物质传递至光系统Ⅰ（PSⅠ），再经由铁氧蛋白等物质的传递最终形成还原性辅酶Ⅱ（NADPH）用于暗反应中CO2固定，而光解水产生的质子与传递过程中发生反应产生的质子用于转化为ATP[36]。这个串联光系统的电子传递链像字母“Z”，因此，也被称为Z-型系统[30, 37]。Z-异质结体系模仿绿色植物自然光合作用，构建两个“光系统”―PCⅠ和PCⅡ，通过导电介质使内部电荷迁移，形成Z-型异质结，能有效分离电子与空穴，且具有较强的氧化还原能力[38]。
传统异质结是以电荷转移的方式达到电子与空穴分离的目的，且这种迁移方式往往不具有最强氧化还原能力；而Z-型异质结是通过在内部搭建导电介质或形成内部电场来消耗部分光生电子与空穴，使具有最强氧化还原能力的电子与空穴得到分离并用于光催化反应。以直接Z-型异质结为例，在Z-型异质结中（图 1（d）），光照后，两种半导体材料均受到激发，电子跃迁到CB上，由于界面间的相互作用形成内部电场，在电场的作用下，PCⅡCB位置上的电子会与PCⅠVB位置上的空穴发生复合被消耗，同时抑制其他电荷迁移方式的复合，从而使具有强还原能力的PCⅠCB上的电子与具有强氧化能力的PCⅡVB上的空穴参与光催化反应[39-40]。经过此迁移过程，不仅促进电子-空穴的分离，减小有效电子空穴对的复合概率，更具有很强的氧化还原能力来驱动光催化反应，拓宽光响应范围。
2 Z-型异质结分类常见Z-型异质结主要由两种能带交错的半导体材料及导电介质构成，人们根据异质结间介质形态的不同，可将其大概分为：以游离的氧化还原离子对为介质的液相Z-型异质结；以电子导体为介质的全固态Z-型异质结；无介质、直接接触的直接Z-型异质结以及新型的由三元半导体材料根据直接Z-型异质结构建出来的双Z-型异质结[24, 41-42]。
2.1 液相Z-型异质结1979年由Bard首次提出液相Z-型异质结光催化剂[43]，它是由带有游离的氧化还原离子对（如Fe3+/Fe2+，IO3-/I-等）的两种半导体连接而成，其中游离的氧化还原离子对作为电子的受体和供体形成D-A反应。如图 2（a）所示，在光照下，两种半导体PCⅠ和PCⅡ均被激发产生电子和空穴，分别位于价带和导带。PCⅡ价带上的空穴会与反应物发生氧化反应，而其导带上的电子与游离的氧化还原离子对发生反应被消耗；同理，PCⅠ导带上的电子会与反应物发生还原反应，而其价带上的空穴会与游离的氧化还原离子对发生反应被消耗。
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| 图 2 Z-型异质结机理 Fig. 2 Z-scheme heterojunction mechanism diagrams |
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除了常用Fe3+/Fe2+，IO3-/I-作为游离氧化还原离子对外，还有以NO3-/NO2-为氧化还原离子对光解水产氢产氧[44]，甚至以络合物[Co（bpy）3]3+/2+/[Co（phen）3]3+/2+为氧化还原离子对的Z-型异质结光催化剂[45]。
然而，液相Z-型异质结光催化剂还存在诸多缺点。氧化还原介质诱导的反应在热力学上是可行的，而且很容易发生，但是，逆反应、光屏蔽效应、离子对扩散限制的电荷载体转移速度慢等因素也导致液相Z-型异质结光催化剂的应用受到限制[46-48]。此外，大多数氧化还原介质不稳定，容易失活，导致反应速率下降，且氧化还原介质容易与PCⅡVB上空穴发生氧化反应、与PCⅠCB上电子发生还原反应形成副反应。
2.2 全固态Z-型异质结第二代Z-型异质结是以电子导体为介质的全固态Z-型。如图 2（b）所示，在光照下，两种半导体PCⅠ和PCⅡ均被激发产生电子和空穴，分别位于价带和导带。PCⅠ价带上的空穴与PCⅡ导带上的电子会通过中间的电子导体进行迁移，在电子导体上湮灭[49-50]。这样就使得PCⅠ导带上的电子与PCⅡ价带上的空穴发生有效分离，并减小其复合概率，同时，PC I和PC II界面的电子传递介质可以降低电子的传递阻抗，从而提高界面间的电子传递速率[51]。固态电子介质的关键在于在介质的供电子能力和接受电子能力之间实现动态平衡，使其在反应过程中保持相对不变[52]。其中常用的电子导体有Ag、Au、Pt等贵金属，或者石墨烯、碳纳米纤维等导电材料[53-54]。
2006年首次发现的CdS和TiO2就是以Au作为电荷转移介质[55]，研究发现，CdS-Au-TiO2之间形成牢固的空间结构，Au作为电荷转移介质，加速载流子迁移，提高光催化活性。对于全固态Z-型异质结光催化剂，电子导体是最重要的一部分，因为它不仅可以提高载流子的转移效率还可以增强光催化稳定性[40]。相比于液相Z-型异质结，全固态Z-型异质结不仅很好地避免了逆反应，有利于光催化剂的回收，而且可以应用于液相和气相反应中[56]。但是，全固态Z-型光催化中所使用的电子导体通常价格较昂贵，因此应用受限。
Wang等[57]在2009年制备了无电子导体、由两种紧密接触的半导体构成Z-型异质结光催化剂，通过延长载流子寿命的方法提高产氢效率。此理论的提出为直接Z-型异质结光催化剂奠定了基础，开展了无电子媒介、直接接触构成Z-型体系的研究。
2.3 直接Z-型异质结第三代Z-型异质结为直接Z-型。直接Z-型异质结于2013年由Yu等[58]提出，不同于之前两种Z-型异质结光催化剂需要载流子转移介质，它是由两个半导体直接接触形成的（图 2（c））[59-60]。由于两种半导体光催化剂具有交错能带结构、不同的费米能级，因此当两种半导体光催化剂相互接触后，它们之间的功函数差会诱导自由电子发生迁移（图 3（a）），接触部位的能带发生弯曲、电荷重新分布使得费米能级达到平衡，因而形成独特的内部电场（图 3（b））。内部电场的形成对光生电荷载流子的分离和转移过程有重要影响[61-62]。内部电场的作用是：第一，促进PCⅡCB上电子与PCⅠVB上的空穴发生复合（图 3（c））[50]；第二，抑制PCⅠCB上的电子向PCⅡCB迁移、PCⅡVB上的空穴向PCⅠVB迁移（图 3（d））；同时还可以抑制PCⅠCB上的电子与PCⅡVB上的空穴发生复合（图 3（e））[56]。在直接Z-型异质结中，两半导体材料之间紧密接触形成较强的相互作用，这有利于减小载流子转移的阻力。
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| 图 3 交错能带构型的半导体示意[56] Fig. 3 Semiconductor schematic diagram of staggered energy band configurations[56] |
2.4 双Z-型异质结
上述电荷转移机制均按二元Z-型异质结阐明，除常见的由二元材料构成Z-型异质结光催化剂之外，还有由三元材料构成双Z-型异质结[63-64]。此类异质结通常无其他介质来转移多余电子空穴，是由3种材料直接接触，在直接Z-型异质结的基础上再增加一步内部电荷转移消耗，进一步提升电子与空穴的分离效率，其机理依然遵循上面所述。常见三元双Z-型异质结机理有2种形式，如图 4所示。
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| 图 4 双Z-型异质结机理 Fig. 4 Mechanism diagram of double Z-scheme heterojunction |
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| 图 5 Zn3（VO4）2·2H2O相变构建三元异质相结模型 Fig. 5 Ternary heterojunction model constructed by Zn3(VO4)2·2H2O phase transition |
3 Z-型异质结的制备 3.1 Z-型异质结构建理论
常见Z-型异质结一般由两种半导体构成，以此为例，为成功构建Z-型异质结光催化剂，所选的两种半导体材料应具有能带交错的结构，即满足其中一种半导体材料的CB和VB位置较高、费米能级较高的要求。其次，要求一种半导体作为氧化型，即其VB电位低于反应所需氧化电位；另一种半导体作为还原型，即其CB电位高于反应所需还原电位。同样，三元Z-型异质结也遵循上述规律。构建异质结的目的在于扩大光响应范围、提高光捕获效率、促进载流子的分离和迁移、扩大比表面积以容纳更多的活性位点、促进反应分子的扩散和高结晶度以便获得更高的光催化活性[56]。由于每一种半导体光催化剂都具有独特的晶体结构和能带结构，这使得其具有独特的物理化学性质，在与另一种半导体光催化剂耦合后会表现出不同的物理及化学性质。因此，在构建Z-型异质结时应考虑晶体的形态形貌、能带结构、晶体结构等特性。
3.2 Z-型异质结制备方法根据构建Z-型异质结理论，选择合适的半导体材料，通过常规的合成方法进行合成。如沉积-沉淀法、水热-溶剂热法、离子交换法、固态合成法、静电纺丝法、自组装法、机械搅拌法等。表 1所列为各个方法的介绍及特点。
| 表 1 Z-型异质结构建方法 Table 1 Construction method of Z-scheme heterojunction |
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Yu等[65]提出通过相变构建三元双Z-型异质结光催化剂。发现以微波水热合成的前驱体Zn3（OH）2V2O7·2H2O，其相变构建三元异质相结模型见图 5。通过对焙烧温度和时间的精确控制，可以获得具有双Z-型光催化机制的Zn3（VO4）2/Zn2V2O7/ZnO三元高效异质结光催化剂。前驱体Zn3（VO4）2·2H2O在600~800 ℃区间进行相变温度和时间的调控，通过相变反应：Zn3（OH）2V2O7·2H2O→Zn3（VO4）2→Zn2V2O7+ZnO，可以获得Zn3（VO4）2/Zn2V2O7/ZnO三元复合材料。DFT计算及多种光电测试表明，在这种双Z-型模型中，ZnO和Zn2V2O7中的光生电子和Zn3（VO4）2中的空穴复合而消耗掉，保留了ZnO和Zn2V2O7中具有强氧化性的空穴，从而使该催化剂具有极强氧化降解酚类污染物的能力（光电流密度增加30~60倍，氧化活性提高6倍）。
采用溶剂热法制备TiO2/SrTiO3复合材料[66]。分两步进行，首先以乙醇为溶剂使用溶剂热法制备Ti-Gly混合物，再以不同比例的乙醇和水为溶剂以溶剂热的方法制备Ti-Gly-Sr前驱液，在气氛条件下经煅烧得氢化TiO2/SrTiO3复合材料。通过改变反应溶剂中水和乙醇的比例，可以选择性地获得球形、花状或不规则的本体形貌。
此外，在合成Z-型异质结中也可以使用两种甚至两种以上不同的方法共同合成。如采用静电-自组装法合成g-C3N4/ZnO[67]，简单地利用相互间的表面电荷形成静电黏附力，使得g-C3N4在ZnO表面分布均匀，合成紧密且具有层状的微球结构，界面间较强的相互作用，使得接触面发生弯曲，利于内部无用电荷重组，有效分离电子与空穴，拓宽光吸收范围，且微球结构具有比表面积大、光捕获性效率高等优点[68]。
4 应用Z-型异质结光催化剂由于其独特的结构和载流子转移路线，具有较高的载流子分离效率、较强的氧化还原能力等特点，在光解水产氢[69-70]、CO2还原、有机物降解、水中重金属离子还原等方面获得广泛应用。
4.1 光解水产氢图 6所示为Z-型异质结光解水产氢产氧机理图。PCⅡCB上的电子与PCⅠVB上的空穴被转移消耗后，PCⅡVB上的空穴会将H2O氧化为O2；PCⅠCB上的电子会将H2O/H+还原为H2。光解水产氢产氧要满足最基本的氧化还原电位要求，即PCⅠCB要比H+还原电势更负（相对于氢电极，pH=7）；PCⅡVB要比H2O氧化电势更正（相对于氢电极，pH=7）。因此，所制备的光催化剂氧化还原电位差至少为1.23 eV。
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| 图 6 Z-型异质结光催化产氢机理 Fig. 6 Mechanism diagram of photocatalytic hydrogen production of Z-scheme heterojunction |
在BiVO4-Ru/SrTiO3:Rh为光催化剂进行光解水制氢机理揭示[52]，PRGO（光还原氧化石墨烯）会接受来自BiVO4的光生电子，进而转移至Ru/SrTiO3:Rh中与其VB上的空穴结合。而PRGO的存在克服了在粒子间转移电子和空穴的限制，从而大大提高了光催化活性。此异质结消耗了几乎所有无用的电子与空穴，大大提升了所需电子空穴的分离，并减小其重组，使得制氢效率较纯物质大幅提升。
采用浸渍法合成BaZrO3-BaTaO2N固溶体，在I-/IO3-、Fe2+/Fe3+氧化还原离子对存在下与PtOx/WO3、金红石相TiO2相结合构成液相Z-型异质结光催化剂上的产氢和产氧研究表明[82]：在Pt、Ru、Rh、Pd、Ir、Au等助催化剂的作用下，只有在Pt才能同时产氢产氧；在I-/IO3-作为介质时，Pt/BaZrO3-BaTaO2N只有与PtOx/WO3结合才能产氢和产氧；在Fe2+/Fe3+作为介质时，Pt/BaZrO3-BaTaO2N只有与金红石相TiO2结合才能产氢产氧。表 2总结了近期用于产氢和产氧的典型Z-型异质结光催化剂。
| 表 2 用于光解水产氢产氧的Z-型异质结光催化剂 Table 2 Hydrogen and oxygen production over Z-scheme heterojunction photocatalysts |
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4.2 CO2还原
将CO2转化成燃料或化学品，理论上可减少化石燃料的消耗，并缓解温室效应[83-84]。图 7（a）为Z-型异质结CO2还原机理图，两种半导体材料经光激发后产生电子与空穴，PCⅠVB上的空穴与PCⅡCB上的电子被转移消耗；在PCⅡVB上发生氧化反应（一般为H2O氧化产氧）；在PCⅠCB上发生CO2还原。同样，对氧化还原电位的要求是还原电势要比CO2还原电势更负，可以根据CO2还原为不同产物所需的电势调整光催化剂的还原电位来得到不同还原产物。表 3所列为常见CO2还原产物的反应式及电势电位。
| 表 3 CO2还原产物及电势 Table 3 CO2 reduction products and potential |
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LI等[85]报道了在室温、常压可见光驱动下，铁基光催化剂可高效催化CO2还原制CH4。研究团队利用三甲基铵基团功能化的铁四苯基卟啉络合物，采用两步还原法，先将CO2还原成CO，然后将CO还原成CH4。总选择性高达82%，量子产率为0.18%。
图 7（b）为Ag3PO4/g-C3N4全固态Z-型异质结机理图[86]，根据电势电位可以看出，此光催化剂可以将CO2还原为CH3OH、CH4以及CO。结果显示，最优Ag3PO4/g-C3N4光催化剂CO2转化率达57.5 μmol/g/h。
采用简单的混合搅拌的方法制备Ag/TaON-RuBLRu′直接Z-型异质结光催化剂[87]，反应机理如图 7（c）。其中Ru（II）双核络合物（RuBLRu）作用于还原CO2，将其吸附到Ag负载的TaON（Ag/TaON）上进行甲醇氧化。通过同位素实验发现，CH3OH被氧化为HCHO，而CO2和部分HCHO被还原为HCOOH。
图 7（d）为采用水热法制备g-C3N4/SnS2直接Z-型异质结光催化剂机理图[88]。研究发现，电子从g-C3N4转移到SnS2，导致两种半导体在平衡状态下形成界面内电场（IEF），加快电子与空穴的迁移速率。而红外光谱显示在CO2转化过程中有HCOOH作为中间产物出现。制备的样品在可见光照射下生成CH3OH，随着CH3OH的产量不断增加，照射3 h后CH4开始作为另一种产物出现。此研究发现在CO2还原过程中出现产物的转化，随着还原的进行，中间产物也被还原为最终产物。表 4总结了CO2还原的全固态Z-型异质光催化剂。
| 表 4 用于CO2还原的Z-型异质结光催化剂 Table 4 Reduction of CO2 over Z-scheme heterojunction photocatalysts |
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4.3 有机物降解
近年来，Z-型异质结光催化剂因其优良的化学性能被广泛应用于可见光下对水体中染料[94-95]、芳香族化合物[96]、类抗生素[97]等有害污染物的分解。
在g-C3N4/Ag/MoS2全固态Z-型异质结光催化剂中[98]，由于其较大的比表面积为反应提供更多的活性位点，在降解罗丹明B时，降解率是Ag/MoS2的9.43倍、g-C3N4/MoS2的3.56倍。
图 8所示为全固态Z-型Ag3PO4/Ag2MoO4降解染料图[99]，Ag3PO4吸收光子产生光生电子和空穴，金属Ag的表面由于等离子体共振效应和偶极性质，因此也能吸收可见光产生电子与空穴。等离子体诱导的Ag纳米粒子中的电子被运送到Ag2MoO4的CB与O2发生反应，形成·O2-活性物质，进一步氧化有机污染物，而空穴则留在Ag纳米粒子中，Ag3PO4中CB上的光生电子转移到Ag纳米颗粒上，与Ag纳米颗粒中的空穴重新结合，而Ag3PO4的光生空穴停留在VB上，直接氧化染料分子。这有效地形成了Ag3PO4/ Ag2MoO4/Ag全固态Z-型异质结，促进了光生电子与空穴的分离，降低其复合概率，从而提高了光催化剂的活性和稳定性。表 5所列为其他Z-型异质结光催化剂用于有机污染物降解。
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| 图 8 Ag3PO4 / Ag2MoO4 /Ag电荷分离转移示意[99] Fig. 8 Charge separation and transfer diagram of Ag3PO4 / Ag2MoO4 /Ag[99] |
| 表 5 用于降解有机污染物的Z-型异质结光催化剂 Table 5 Degradation of organic pollutants over Z-scheme heterojunction photocatalysts |
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4.4 水中重金属Cr（Ⅵ）还原
在Z-型异质结光催化去除水中重金属离子研究中，几乎都是对Cr（Ⅵ）还原去除的研究[115-116]。
例如Nb3.49N4.56O0.44/（GaxZn1-x）（NxO1-x）直接Z-型异质结光催化剂在模拟阳光照射下30 min内完全还原Cr（VI）[117]。Nb3.49N4.56O0.44是一种n型半导体，其费米能级相对负，比大多数其他（氧）氮化物的费米能级都要负。与另一种半导体复合后往往会发生能带弯曲，在有效分离光生载流子的同时，保留了最强氧化还原电位，这也符合Z-型结构的特点。
Chen等[118]采用静电自组装的方法，在还原氧化石墨烯（rGO）薄片上构建了一个BiOI/Bi2S全固态Z-型异质结，同时进行去除水中的Cr（VI）和苯酚。结果表明，在可见光照射下，由于Cr（VI）和苯酚之间的协同效应，使得Cr（VI）还原和苯酚氧化的效率较高，最佳还原和氧化效率分别达到73%和95%。
采用水热法和光还原法合成Ag/AgBr/BiVO4全固态Z-型光催化剂，同时去除水中Cr（VI）和抗生素研究中发现[119]：所形成的Z型异质结扩大光响应范围、促进电子空穴的分离并加速电子空穴向催化剂表面迁移，同时光氧化抗生素与光还原Cr（VI）相互促进，达到协同作用，更有效地利用电子与空穴。
Yu等[120]提出通过相变构建ZnTiO3/Zn2Ti3O8/ZnO三元Z-型异质结。发现采用溶剂热法制备ZnTiO3前驱体，再通过对煅烧温度及时间的控制，使前驱体ZnTiO3在600~800 ℃发生部分相变：ZnTiO3→Zn2Ti3O8+ZnO，形成以ZnTiO3为主要相的ZnTiO3/Zn2Ti3O8/ZnO三元Z-型异质结。研究表明：高温煅烧下相变产生了空位，提高光响应范围，载流子数量增多；三相之间紧密接触，有利于电荷在体系中转移；Z-型异质结独特的电荷转移方式使光生电子-空穴发生有效分离。以上优点使得在Cr（VI）还原中表现出优异的光催化活性，ZnTiO3/Zn2Ti3O8/ZnO还原Cr（VI）最佳还原率达40%，而纯ZnTiO3还原率为3%，还原效果明显提升。
5 结语Z-型异质结的研究已经取得了很大的进展，然而，光催化反应是一个复杂的过程。Z-型异质结还有如下几个方面需要进一步的研究与解决。①对Z-型异质结光催化剂机理进一步了解，从根本上理解界面上载流子的分离和运输，理解光催化反应的反应途径；②解决液相Z-型异质结中逆反应、光屏蔽、副反应等问题；③开发新的导电介质，降低全固态Z-型异质结的应用成本；④目前Z-型异质结光催化剂已在光解水产氢、有机污染物的降解等方面有着诸多且较深入的研究，但是对于CO2的还原、水中其他重金属离子的去除、选择性有机合成等方面的应用还需深入研究；⑤探索简单有效的Z-型异质结的构建方法是需要发展的方向。将实验研究与理论模拟相结合，可望助推Z-型异质结光催化剂的设计和应用研究。
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