Defect engineering on constructing surface active sites in catalysts for environment and energy applications

Abstract

The precise engineering of surface active sites is deemed as an efficient protocol for regulating surfaces and catalytic properties of catalysts. Defect engineering is the most feasible option to modulate the surface active sites of catalysts. Creating specific active sites on the catalyst allows precise modulation of its electronic structure and physicochemical characteristics. Here, we outlined the engineering of several types of defects, including vacancy defects, void defects, dopant-related defects, and defect-based single atomic sites. An overview of progress in fabricating structural defects on catalysts via de novo synthesis or post-synthetic modification was provided. Then, the applications of the well-designed defective catalysts in energy conversion and environmental remediation were carefully elucidated. Finally, current challenges in the precise construction of active defect sites on the catalyst and future perspectives for the development directions of precisely controlled synthesis of defective catalysts were also proposed.

Graphical abstract

Keywords

defect engineering / vacancy / void defects / doping / single atomic sites

Carbon dioxide (CO₂), an anthropogenic greenhouse gas, contributes to global warming and climate change with its rising concentrations in the atmosphere as a result of fossil fuel combustion. CO₂ capture has thus received special attention in the field of environmental science, which can be done by capturing CO₂ from point sources or the air. The captured CO₂ will then be either utilized or stored. The efficient adsorbent materials are necessary for the effective CO₂ capture. So far, a variety of CO₂ adsorbents are available, including carbon-based materials, metal oxides, covalent organic frameworks, metal-organic frameworks, silica, and polymers. A special attention is paid to carbon-based adsorbents due to their cost-effectiveness, stability, and environmental friendliness. Especially, biochar is a fascinating CO₂ adsorbent because its manufacture could cut CO₂ emissions by avoiding the open space combustion of agricultural and domestic wastes, i.e., the sources of biochar. Besides, this leads to the conversion of waste into valuable material (circular economy through sustainable waste management). In line with the life cycle analysis, preparing biochar from waste materials promotes environmental sustainability with a reduced environmental impact. According to the United States Environmental Protection Agency, improper food waste management emits 170 million MT of CO₂-equivalent greenhouse gases each year, which is equivalent to the annual CO₂ emissions of 42 coal-fired power plants [1]. Therefore, preparing biochar from carbonaceous waste and using it as CO₂ adsorbent is advantageous, i.e., getting two mangoes with one stone (carbon abatement and sustainable management).

A wide range of carbon resources (e.g., biomass wastes, municipal wastes, plastic wastes, food wastes, municipal wastes) provides the platform to tune the characteristics and CO₂ adsorption capacity of biochar simply by varying its carbon source. Also, many synthetic methods (hydrothermal carbonization, gasification, pyrolysis, and torrefaction) are available for preparing biochar, which can also have impacts on the properties of biochar [2]. This variety of sources and preparation methods highlights an excellent opportunity to develop a highly efficient CO₂ adsorbent in the coming years.

Biochar has inherent microporosity and specific functional groups (e.g., C=O and –OH), which are required for the physisorption and chemisorption of CO₂, respectively. Biochar’s macropores and mesopores facilitate CO₂ diffusion and transportation but not adsorption (Fig.1). Unlike other adsorbents, biochars can be easily activated by increasing microporosity, surface area, and functional groups to enrich the active sites for enhanced CO₂ adsorption. Biochars are activated either physically (using steam or CO₂) or chemically (using alkali or acid). Zhang et al. [3] made biochar from wood pellets and activated it separately using steam (physical) and KOH (chemical). Chemical treatment improves microporosity in a better way; hence biochar activated by the chemical approach has a higher CO₂ absorption (50.75 mg·g⁻¹) than biochar activated by the physical method (38.30 mg·g⁻¹) under the same conditions. Although yielding biochar with a higher adsorption capacity, the chemical treatment may release secondary contaminants [3]. Zhang et al. [4] used a unique activation approach that involved impregnating bamboo-derived biochar with lignin and then treating it with the microwave. As a result, activated biochar has a better porosity and a CO₂ uptake of 134.46 mg·g⁻¹. Luo et al. [5] also used the microwave to install micropores in biochar made from marine biomass.

Fig.1 Porosity in biochar and mechanism of CO2 adsorption over biochar.

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To achieve maximum CO₂ adsorption, the synergistic interplay of physisorption and chemisorption is essential, underlining the combined presence of active sites for physisorption (microporosity) and chemisorption (functional groups) in biochar. As the functional groups located in the pore walls may block the micropores [6], it is important to have functional groups without interrupting microporosity. Chemisorption dominates at both low and high-pressure conditions whereas physisorption dominates usually at the enhanced pressure. On the contrary, the higher temperature does not favor physisorption, attributing to the desorption of physisorbed CO₂ molecules due to their weak interaction with active sites. Therefore, optimizing adsorption conditions and porosity of biochar is essential to establish a better synergism between physisorption and chemisorption. Like enriching microporosity simply by physical and chemical activation methods, the functional groups, in addition to the inherent groups, can be introduced into biochar by facile methods. Especially, enriching the nitrogen-based functional groups is attractive due to their basicity that facilitates the Lewis acid-base interaction with CO₂ and promotes the adsorption of CO₂ (Fig.1). With proper biomass source selection (e.g., microalgae), the intrinsic nitrogen groups in biochar can be obtained without extra treatment [7]. For example, biochar made from Enteromorpha, a marine biomass, contains basic nitrogen groups (e.g., pyridinic-N, pyrrolic-N, and graphitic-N) that aid in CO₂ adsorption through chemical interactions [5]. Also, nitrogen groups can be added through the co-carbonization of carbon and nitrogen compounds (e.g., urea). Special emphasis is given to amine-modified biochar adsorbents because the amine groups involve strong and selective interaction with CO₂ molecules, forming carbamates [7]. Ji et al. [8] created a biochar-silica hybrid material with amine groups connected to silica rather than biochar, utilizing siloxane linkers with numerous amine groups. A linker molecule comprises three amine sites, which enables the increased CO₂ adsorption.

The compatibility of biochar with both inorganic and organic materials enables the formation of a synergistic hybrid composite for optimal CO₂ adsorption efficiency. Because of their basicity, alkaline earth metal oxides (e.g., magnesium) are frequently added to biochar, allowing for both physisorption and chemisorption of CO₂. Pu et al. [9] added MgO into walnut shell-derived biochar to improve dynamic CO₂ uptake. Fortunately, many biomass sources contain alkali earth metals in their structure. For example, tamarind bark contains calcium oxalate, which can be used to make biochar with a high calcium content for good CO₂ adsorption [10]. Similarly, organic molecules (e.g., ionic liquids) capable of CO₂ chemisorption are mixed into biochar, resulting in effective composite materials. Arjona-Jaime et al. [11] created a biochar-ionic liquid composite that shows 90% better efficiency and faster kinetics than the bulk ionic liquid. As stated above, physisorption dominates at high pressure.

As known, biochar materials exhibit different CO₂ adsorption capacities depending upon the nature of their biomass sources. Interestingly, the same biochar could also display different CO₂ capacity values according to the conditions like CO₂ concentration, temperature, and competitive adsorbates. The CO₂ concentration usually reveals positive impacts on the CO₂ adsorption capacity of biochar, i.e., the CO₂ adsorption capacity increases with the concentration of CO₂. For instance, Ding and Liu [12] studied the CO₂ adsorption capacity of SCK-800-1 (a biochar prepared using KOH and sargassum with 1:1 weight ratio at 800 °C) under various CO₂ concentrations (3%, 8%, 12%, and 18%) without changing the feed flow rate of total flue gas. As shown in Fig.2(a), the breakthrough times decrease from 6.6 to 5.1 min while increasing CO₂ concentration from 3% to 18%. This is because the higher CO₂ concentration allows more CO₂ molecules to pass via the reactor per unit time, enabling the faster saturation of active sites. Notably, the CO₂ adsorption capacity of SCK-800-1 enhances from 0.23 to 1.08 mmol·g⁻¹, with the increase of CO₂ concentration from 3% to 18%, which is attributed to the increase of CO₂ concentration gradient and the resultant CO₂ mass transfer rate. The authors also studied the variation of CO₂ adsorption capacity with temperature. The adsorption capacity of SCK-800-1 is maximum (1.05 mmol·g⁻¹) at 25 °C. With the increase in temperature, the CO₂ adsorption capacity gradually decreases and reduces to 0.45 mmol·g⁻¹, at 100 °C. This is because the rise in temperature increases the surface energy and the molecular diffusion of CO₂ on the biochar’s surface. As a result, the adsorption force of biochar is reduced for CO₂, increasing the chance of CO₂ desorption at elevated temperatures [12]. Though this seems a common trend in the literature, exceptions cannot be excluded based on the modification or activation carried out on biochar materials [5]. Like CO₂ concentration and temperature, humidity can also have a significant impact on the CO₂ adsorption capacity. Especially, the CO₂ adsorption capacity of hydrophilic biochar (i.e., activated with oxygen-related polar functional groups) gradually loses its CO₂ adsorption capacity with the increase of humidity. As illustrated in Fig.2(b), the increase in humidity levels does not have a significant impact on the CO₂ adsorption capacity of wood-derived raw biochar (BC-Raw), as biochar adsorbs 1.3 and 0.85 mg·g⁻¹ CO₂ at 8.8% and 87.9% relative humidity (RH) levels, respectively. However, for the KOH-activated biochar (BC-KOH1:1) containing more polar functional groups, the impact of humidity is apparent, i.e., the CO₂ adsorption capacity of BC-KOH1:1 decreases from 3.7 to 1.3 mg·g⁻¹ when increasing RH from 8.8% to 87.9%, respectively [3]. This might be due to the strong interaction between the hydrophilic polar groups of biochar and water. Hence, preparing biochar materials with hydrophobic and non-polar properties is important to limit the competitive adsorption of water molecules and realize the practical applications of biochar.

Fig.2 (a) CO2 breakthrough curves of SCK-800-1 at various CO2 inlet concentrations [12]. Reprinted with permission from ref. [12], copyright 2020, Elsevier. (b) 15% CO2 adsorption ability of wood-derived biochar (BC) samples at different relative humidity (RH) levels [3]. Reprinted with permission from ref. [3], copyright 2022, Elsevier. (BC-Raw: wood-derived raw biochar; BC-Steam: steam activated biochar; BC-KOH1:1: KOH activated biochar; BC-KOH-lmp: biochar actirated with KOH by impregnation) (c) Multicomponent breakthrough curves of CO2, NO, and SO2 through LBB20 (a kind of biochar) at 25 °C [4]. Reprinted with permission from ref. [4], copyright 2024, Springer Nature. (d) Unique advantages of biochar materials for CO2 adsorption.

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Both flue gas and open air are a mixture of multiple gases, including CO₂. Therefore, to realize the practical applications, biochar materials should achieve the selective adsorption of CO₂. In the literature, the CO₂ adsorption selectivity of biochar is studied in the presence of various gases like N₂, NO_x, SO_x, etc. In general, the typical flue gas from coal-fired power plants possesses 10%–16% CO₂, and small traces of NO_x, and SO_x. So, Zhang et al. [4] prepared a gas mixture (CO₂-12 vol %, NO-0.4 vol %, and SO₂-0.4 vol %) for a multicomponent competitive adsorption experiment using a biochar (LBB₂₀). During the individual gas adsorption experiments, LBB₂₀ adsorbs 28.50 mg·g⁻¹ CO₂, 0.24 mg·g⁻¹ NO, and 50.10 mg·g⁻¹ SO₂ under identical conditions. While using the prepared multicomponent gaseous mixture, the adsorption capacity of LBB₂₀ is invariably declined for CO₂ (23.70 mg·g⁻¹), NO (0.14 mg·g⁻¹), and SO₂ (45.06 mg·g⁻¹). Owing to its small size and dynamic diameter, NO quickly passes the column. Both CO₂ and SO₂ slowly reach the active site and replace weakly adsorbed NO molecules, as supported by the increasing outlet concentration of NO. Unlike NO, SO₂ demonstrates an adverse effect on CO₂ adsorption because both SO₂ and CO₂ display an acidic nature and involve competitive adsorption. However, the faster movement of CO₂ could allow the reduction of CO₂ adsorption capacity only by 16.8% even in the presence of SO₂ (Fig.2(c)) [4]. This might be assigned to the lignin impregnation of biochar at a suitable quantity which selectively enhances the mobility of CO₂ inside the pore channels. Therefore, a higher selectivity for CO₂ adsorption is possible by modifying raw biochar using suitable methods. The selective adsorption of CO₂ from N₂ is equally important for the post-combustion CO₂ capture and direct air capture. At low pressures, the biochar materials achieve a higher CO₂ adsorption selectivity due to the dominant role of their functional groups and non-reactive adsorption of N₂. Differently, while increasing the pressure, the CO₂ adsorption selectivity is gradually decreased owing to the dominant role of pore filling and eventually reaches the stable selectivity [13]. During the competitive adsorption between CO₂ and CO over biochar materials, achieving a maximum CO₂ adsorption selectivity is not difficult due to the easy and complete removal of weakly adsorbed CO molecules by CO₂ molecules even with 50% CO concentration [14]. These reports suggest that biochar selection, biochar modification, and adsorption conditions can control the CO₂ adsorption selectivity. However, attaining the maximum CO₂ adsorption selectivity using biochars remains a big challenge because it demands many optimization experiments, especially, in real conditions. To help with this problem, Yuan et al. [15] attempted an active learning strategy for preparing a high-performance engineered biochar by recommending optimal synthesis parameters and feedstocks.

In summary, the following unique characteristics (Fig.2(d)) make biochar an interesting CO₂ adsorbent than other adsorbents: (1) low cost, thermal stability, and environmental friendliness; (2) preparation promoting carbon abatement and sustainable management; (3) availability of various precursors; (4) availability of simple preparation methods; (5) ease of activation to enrich microporosity and functionalization; (6) physisorption and chemisorption in synergy; (7) compatibility with organic and inorganic compounds, resulting in highly efficient hybrid adsorbents. Despite these advantages, a few issues must be solved before proposing biochar as a commercial CO₂ adsorbent. Biochar regeneration, or CO₂ desorption, must take place at a lower temperature, even for nitrogen-rich biochar materials. There have been very few CO₂ adsorption experiments with biochar under practical conditions. The real environment comprises complicated gas combinations. Therefore, acidic gases such as SO_x and NO_x can occupy the basic nitrogen groups of biochar, preventing CO₂ adsorption. Humidity, temperature, and pressure are the variables in the environment; hence the CO₂ adsorption behavior of biochar materials must be studied under fluctuating humidity, pressure, and temperature conditions, but such studies are rare. Hope these issues will be addressed by rationally designing biochar materials and studying their CO₂ adsorption capacity under practical conditions.

References

[1] Beller M , Centi G . Catalysis and sustainable development: the marriage for innovation. ChemSusChem, 2009, 2(6): 459–460

[2] Linares N , Silvestre-Albero A M , Serrano E , Silvestre-Albero J , García-Martínez J . Mesoporous materials for clean energy technologies. Chemical Society Reviews, 2014, 43(22): 7681–7717

[3] Roduner E . Understanding catalysis. Chemical Society Reviews, 2014, 43(24): 8226–8239

[4] Vogt C , Weckhuysen B M . The concept of active site in heterogeneous catalysis. Nature Reviews Chemistry, 2022, 6(2): 89–111

[5] Wang Y , Chen L , Cao H , Chi Z , Chen C , Duan X , Xie Y , Qi F , Song W , Liu J . . Role of oxygen vacancies and Mn sites in hierarchical Mn₂O₃/LaMnO_3–δ perovskite composites for aqueous organic pollutants decontamination. Applied Catalysis B: Environmental, 2019, 245: 546–554

[6] Hattori H . Solid base catalysts: generation of basic sites and application to organic synthesis. Applied Catalysis A, General, 2001, 222(1-2): 247–259

[7] Wachs I E , Roberts C A . Monitoring surface metal oxide catalytic active sites with Raman spectroscopy. Chemical Society Reviews, 2010, 39(12): 5002–5017

[8] Du Y , Sheng H , Astruc D , Zhu M . Atomically precise noble metal nanoclusters as efficient catalysts: a bridge between structure and properties. Chemical Reviews, 2020, 120(2): 526–622

[9] Kröger F . Defect chemistry in crystalline solids. Annual Review of Materials Science, 1977, 7(1): 449–475

[10] Tang T , Wang Z , Guan J . A review of defect engineering in two-dimensional materials for electrocatalytic hydrogen evolution reaction. Chinese Journal of Catalysis, 2022, 43(3): 636–678

[11] Thomas J M , Raja R , Lewis D W . Single-site heterogeneous catalysts. Angewandte Chemie International Edition, 2005, 44(40): 6456–6482

[12] Liu L , Corma A . Structural transformations of solid electrocatalysts and photocatalysts. Nature Reviews Chemistry, 2021, 5(4): 256–276

[13] Zambelli T , Wintterlin J , Trost J , Ertl G . Identification of the “active sites” of a surface-catalyzed reaction. Science, 1996, 273(5282): 1688–1690

[14] Sun Y , Gao S , Lei F , Xie Y . Atomically-thin two-dimensional sheets for understanding active sites in catalysis. Chemical Society Reviews, 2015, 44(3): 623–636

[15] Yan D , Li Y , Huo J , Chen R , Dai L , Wang S . Defect chemistry of nonprecious-metal electrocatalysts for oxygen reactions. Advanced Materials, 2017, 29(48): 1606459

[16] Xie C , Yan D , Li H , Du S , Chen W , Wang Y , Zou Y , Chen R , Wang S . Defect chemistry in heterogeneous catalysis: recognition, understanding, and utilization. ACS Catalysis, 2020, 10(19): 11082–11098

[17] Lannoo M , Bourgoin J . Atomic configuration of point defects. In: Point Defects in Semiconductors I. Springer Series in Solid-State Sciences. Berlin, Heidelberg: Springer-Verlag, 1981, 22: 1–35

[18] Leonardi A , Scardi P . Dislocation effects on the diffraction line profiles from nanocrystalline domains. Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science, 2016, 47(12): 5722–5732

[19] Hemesath E R , Schreiber D K , Gulsoy E B , Kisielowski C F , Petford-Long A K , Voorhees P W , Lauhon L J . Catalyst incorporation at defects during nanowire growth. Nano Letters, 2012, 12(1): 167–171

[20] Rudolph P . Fundamentals and engineering of defects. Progress in Crystal Growth and Characterization of Materials, 2016, 62(2): 89–110

[21] Murakami Y . Material defects as the basis of fatigue design. International Journal of Fatigue, 2012, 41: 2–10

[22] Schlögl R . Heterogeneous catalysis. Angewandte Chemie International Edition, 2015, 54(11): 3465–3520

[23] Zhang Y , Gao F , You H , Li Z , Zou B , Du Y . Recent advances in one-dimensional noble-metal-based catalysts with multiple structures for efficient fuel-cell electrocatalysis. Coordination Chemistry Reviews, 2022, 450: 214244

[24] Wang B , Liu J , Yao S , Liu F , Li Y , He J , Lin Z , Huang F , Liu C , Wang M . Vacancy engineering in nanostructured semiconductors for enhancing photocatalysis. Journal of Materials Chemistry. A, Materials for Energy and Sustainability, 2021, 9(32): 17143–17172

[25] Sun Y , Wang H , Xing Q , Cui W , Li J , Wu S , Sun L . The pivotal effects of oxygen vacancy on Bi₂MoO₆: promoted visible light photocatalytic activity and reaction mechanism. Chinese Journal of Catalysis, 2019, 40(5): 647–655

[26] Guan S , Wang L , Xu S , Yang D , Waterhouse G I N , Qu X , Zhou S . Vacancy-enhanced generation of singlet oxygen for photodynamic therapy. Chemical Science, 2019, 10(8): 2336–2341

[27] Zheng X , Li Y , Zhang L , Shen L , Xiao Y , Zhang Y , Au C , Jiang L . Insight into the effect of morphology on catalytic performance of porous CeO₂ nanocrystals for H₂S selective oxidation. Applied Catalysis B: Environmental, 2019, 252: 98–110

[28] Zhou S , Jin W , Ding Y , Shao B , Wang B , Hu X , Kong Y . In-situ intercalation of Au nanoparticles and magnetic γ-Fe₂O₃ in the walls of MCM-41 with abundant void defects for highly efficient reduction of 4-nitrophenol and organic dyes. Dalton Transactions, 2018, 47(47): 16862–16875

[29] Tang Q , Ma Y , Wang J . The active sites engineering of catalysts for CO₂ activation and conversion. Solar RRL, 2021, 5(2): 2000443

[30] Connell G , Dumesic J A . The generation of Brønsted and Lewis acid sites on the surface of silica by addition of dopant cations. Journal of Catalysis, 1987, 105(2): 285–298

[31] Lee J , Kumar A , Kim M G , Yang T , Shao X , Liu X , Liu Y , Hong Y , Jadhav A R , Liang M . . Single-metal-atom dopants increase the Lewis acidity of metal oxides and promote nitrogen fixation. ACS Energy Letters, 2021, 6(12): 4299–4308

[32] Zhang Y , Guo L , Tao L , Lu Y , Wang S . Defect-based single-atom electrocatalysts. Small Methods, 2019, 3(9): 1800406

[33] Xue Q , Xie Y , Wu S , Wu T , Soo Y , Day S , Tang C C , Man H W , Yuen S T , Wong K . . A rational study on the geometric and electronic properties of single-atom catalysts for enhanced catalytic performance. Nanoscale, 2020, 12(45): 23206–23212

[34] Xi J , Jung H S , Xu Y , Xiao F , Bae J W , Wang S . Synthesis strategies, catalytic applications, and performance regulation of single-atom catalysts. Advanced Functional Materials, 2021, 31(12): 2008318

[35] Liu D , He Q , Ding S , Song L . Structural regulation and support coupling effect of single-atom catalysts for heterogeneous catalysis. Advanced Energy Materials, 2020, 10(32): 2001482

[36] Lang R , Du X , Huang Y , Jiang X , Zhang Q , Guo Y , Liu K , Qiao B , Wang A , Zhang T . Single-atom catalysts based on the metal-oxide interaction. Chemical Reviews, 2020, 120(21): 11986–12043

[37] Bai S , Zhang N , Gao C , Xiong Y . Defect engineering in photocatalytic materials. Nano Energy, 2018, 53: 296–336

[38] Zhuang G , Yan J , Wen Y , Zhuang Z , Yu Y . Two-dimensional transition metal oxides and chalcogenides for advanced photocatalysis: progress, challenges, and opportunities. Solar RRL, 2021, 5(6): 2000403

[39] Zhou Y , Wang F , Zhou J , Dong B , Dong Y , Liu X , Liu B , Yu J , Chai Y . Triple captured iron by defect abundant NiO for efficient water oxidation. Inorganic Chemistry Frontiers, 2022, 9(6): 1281–1292

[40] Gao W , Chi J , Wang Z , Lin J , Liu D , Zeng J , Yu J , Wang L , Chai Y , Dong B . Optimized bimetallic nickel-iron phosphides with rich defects as enhanced electrocatalysts for oxygen evolution reaction. Journal of Colloid and Interface Science, 2019, 537: 11–19

[41] Ye G , Wan L , Zhang Q , Liu H , Zhou J , Wu L , Zeng X , Wang H , Chen X , Wang J . Boosting catalytic performance of MOF-808(Zr) by direct generation of rich defective Zr nodes via a solvent-free approach. Inorganic Chemistry, 2023, 62(10): 4248–4259

[42] Fang Z , Bueken B , De Vos D E , Fischer R A . Defect-engineered metal-organic frameworks. Angewandte Chemie International Edition, 2015, 54(25): 7234–7254

[43] ShollD SLivelyR P. Defects in metal-organic frameworks: challenge or opportunity? Journal of Physical Chemistry Letters, 2015, 6(17): 3437–3444

[44] Gao P , Chen Z , Gong Y , Zhang R , Liu H , Tang P , Chen X , Passerini S , Liu J . The role of cation vacancies in electrode materials for enhanced electrochemical energy storage: synthesis, advanced characterization, and fundamentals. Advanced Energy Materials, 2020, 10(14): 1903780

[45] Pang Q , Yang L , Li Q . Vacancies in metal-organic frameworks: formation, arrangement, and functions. Small Structures, 2022, 3(5): 2100203

[46] Wu Y , Li Y , Gao J , Zhang Q . Recent advances in vacancy engineering of metal-organic frameworks and their derivatives for electrocatalysis. SusMat, 2021, 1(1): 66–87

[47] Ren J , Ledwaba M , Musyoka N M , Langmi H W , Mathe M , Liao S , Pang W . Structural defects in metal-organic frameworks (MOFs): formation, detection and control towards practices of interests. Coordination Chemistry Reviews, 2017, 349: 169–197

[48] Cirujano F G , Martin N , Wee L H . Design of hierarchical architectures in metal-oganic frameworks for catalysis and adsorption. Chemistry of Materials, 2020, 32(24): 10268–10295

[49] Lázaro I A , Szalad H , Valiente P , Albero J , García H , Martí-Gastaldo C . Tuning the photocatalytic activity of Ti-based metal-organic frameworks through modulator defect-engineered functionalization. ACS Applied Materials & Interfaces, 2022, 14(18): 21007–21017

[50] Wei R , Gaggioli C A , Li G , Islamoglu T , Zhang Z , Yu P , Farha O K , Cramer C J , Gagliardi L , Yang D . . Tuning the properties of Zr₆O₈ nodes in the metal organic framework UiO-66 by selection of node-bound ligands and linkers. Chemistry of Materials, 2019, 31(5): 1655–1663

[51] Barin G , Krungleviciute V , Gutov O , Hupp J T , Yildirim T , Farha O K . Defect creation by linker fragmentation in metal-organic frameworks and its effects on gas uptake properties. Inorganic Chemistry, 2014, 53(13): 6914–6919

[52] El-Gamel N E . Generation of defect-modulated metal-organic frameworks by fragmented-linker co-assembly of CPO-27(M) frameworks. European Journal of Inorganic Chemistry, 2015, 2015(8): 1351–1358

[53] Fan Z , Wang J , Wang W , Burger S , Wang Z , Wang Y , Wöll C , Cokoja M , Fischer R A . Defect engineering of copper paddlewheel-based metal-organic frameworks of type NOTT-100: implementing truncated linkers and its effect on catalytic properties. ACS Applied Materials & Interfaces, 2020, 12(34): 37993–38002

[54] Lei L , Huang D , Cheng M , Deng R , Chen S , Chen Y , Wang W . Defects engineering of bimetallic Ni-based catalysts for electrochemical energy conversion. Coordination Chemistry Reviews, 2020, 418: 213372

[55] Zhang X , Zhang Z , Huang H , Wang Y , Tong N , Lin J , Liu D , Wang X . Oxygen vacancy modulation of two-dimensional γ-Ga₂O₃ nanosheets as efficient catalysts for photocatalytic hydrogen evolution. Nanoscale, 2018, 10(45): 21509–21517

[56] Chen S , Huang H , Zhao D , Zhou J , Yu J , Qu B , Liu Q , Sun H , Zhao J . Direct growth of polycrystalline GaN porous layer with rich nitrogen vacancies: application to catalyst-free electrochemical detection. ACS Applied Materials & Interfaces, 2020, 12(48): 53807–53815

[57] Wang J , Lin S , Tian N , Ma T , Zhang Y , Huang H . Nanostructured metal sulfides: classification, modification strategy, and solar-driven CO₂ reduction application. Advanced Functional Materials, 2021, 31(9): 2008008

[58] Jing X , Lu N , Huang J , Zhang P , Zhang Z . One-step hydrothermal synthesis of S-defect-controlled ZnIn₂S₄ microflowers with improved kinetics process of charge-carriers for photocatalytic H₂ evolution. Journal of Energy Chemistry, 2021, 58: 397–407

[59] Li K , Yang J , Gu J . Hierarchically porous MOFs synthesized by soft-template strategies. Accounts of Chemical Research, 2022, 55(16): 2235–2247

[60] Cai G , Jiang H L . A modulator-induced defect-formation strategy to hierarchically porous metal-organic frameworks with high stability. Angewandte Chemie International Edition, 2017, 56(2): 563–567

[61] Yuan D , Zhao D , Sun D , Zhou H . An isoreticular series of metal-organic frameworks with dendritic hexacarboxylate ligands and exceptionally high gas-uptake capacity. Angewandte Chemie, 2010, 122(31): 5485–5489

[62] Zhao D , Yuan D , Sun D , Zhou H . Stabilization of metal-organic frameworks with high surface areas by the incorporation of mesocavities with microwindows. Journal of the American Chemical Society, 2009, 131(26): 9186–9188

[63] Farha O K , Yazaydın A Ö , Eryazici I , Malliakas C D , Hauser B G , Kanatzidis M G , Nguyen S T , Snurr R Q , Hupp J T . De novo synthesis of a metal-organic framework material featuring ultrahigh surface area and gas storage capacities. Nature Chemistry, 2010, 2(11): 944–948

[64] Furukawa H , Ko N , Go Y B , Aratani N , Choi S B , Choi E , Yazaydin A Ö , Snurr R Q , O’Keeffe M , Kim J . . Ultrahigh porosity in metal-organic frameworks. Science, 2010, 329(5990): 424–428

[65] Li M , Liu Y , Li F , Shen C , Kaneti Y V , Yamauchi Y , Yuliarto B , Chen B , Wang C . Defect-rich hierarchical porous UiO-66(Zr) for tunable phosphate removal. Environmental Science & Technology, 2021, 55(19): 13209–13218

[66] Tang C , Wang H , Chen X , Li B , Hou T , Zhang B , Zhang Q , Titirici M , Wei F . Topological defects in metal-free nanocarbon for oxygen electrocatalysis. Advanced Materials, 2016, 28(32): 6845–6851

[67] Zoller F , Häringer S , Böhm D , Luxa J , Sofer Z , Fattakhova-Rohlfing D . Carbonaceous oxygen evolution reaction catalysts: from defect and doping-induced activity over hybrid compounds to ordered framework structures. Small, 2021, 17(48): 2007484

[68] Zhang A , Liang Y , Zhang H , Geng Z , Zeng J . Doping regulation in transition metal compounds for electrocatalysis. Chemical Society Reviews, 2021, 50(17): 9817–9844

[69] Karakitsou K E , Verykios X E . Effects of altervalent cation doping of titania on its performance as a photocatalyst for water cleavage. Journal of Physical Chemistry, 1993, 97(6): 1184–1189

[70] Shen Z , Jin X , Tian J , Li M , Yuan Y , Zhang S , Fang S , Fan X , Xu W , Lu H . . Cation-doped ZnS catalysts for polysulfide conversion in lithium-sulfur batteries. Nature Catalysis, 2022, 5(6): 555–563

[71] Xie J , Lü Q , Qiao W , Bu C , Zhang Y , Zhai X , Lü R , Chai Y , Dong B . Enhancing cobalt-oxygen bond to stabilize defective Co₂MnO₄ in acidic oxygen evolution. Acta Physico-Chimica Sinica, 2024, 40(3): 2305021

[72] Sun Y , Xu K , Wei Z , Li H , Zhang T , Li X , Cai W , Ma J , Fan H J , Li Y . Strong electronic interaction in dual-cation-incorporated NiSe₂ nanosheets with lattice distortion for highly efficient overall water splitting. Advanced Materials, 2018, 30(35): 1802121

[73] Patnaik S , Sahoo D P , Parida K . Recent advances in anion doped g-C₃N₄ photocatalysts: a review. Carbon, 2021, 172: 682–711

[74] Jiang L , Yuan X , Pan Y , Liang J , Zeng G , Wu Z , Wang H . Doping of graphitic carbon nitride for photocatalysis: a reveiw. Applied Catalysis B: Environmental, 2017, 217: 388–406

[75] Lu C , Zhang P , Jiang S , Wu X , Song S , Zhu M , Lou Z , Li Z , Liu F , Liu Y . . Photocatalytic reduction elimination of UO₂²⁺ pollutant under visible light with metal-free sulfur doped g-C₃N₄ photocatalyst. Applied Catalysis B: Environmental, 2017, 200: 378–385

[76] Xu H , Zhang T , Wang D , Cai D , Chen S , Wang H , Shu S , Zhu Y . Degradation of tetracycline using persulfate activated by a honeycomb structured S-doped g-C₃N₄/biochar under visible light. Separation and Purification Technology, 2022, 300: 121833

[77] Hasija V , Singh P , Thakur S , Stando K , Nguyen V , Van Le Q , Alshehri S M , Ahamad T , Wu K C , Raizada P . Oxygen doping facilitated N-vacancies in g-C₃N₄ regulates electronic band gap structure for trimethoprim and Cr(VI) mitigation: simulation studies and photocatalytic degradation pathways. Applied Materials Today, 2022, 29: 101676

[78] Zhang X , Li F , Fan R , Zhao J , Dong B , Wang F , Liu H , Yu J , Liu C , Chai Y F . P double-doped Fe₃O₄ with abundant defect sites for efficient hydrogen evolution at high current density. Journal of Materials Chemistry. A, Materials for Energy and Sustainability, 2021, 9(28): 15836–15845

[79] Rong H , Zhan T , Sun Y , Wen Y , Liu X , Teng H . ZIF-8 derived nitrogen, phosphorus and sulfur tri-doped mesoporous carbon for boosting electrocatalysis to oxygen reduction in universal pH range. Electrochimica Acta, 2019, 318: 783–793

[80] Tian L , Pang X , Xu H , Liu D , Lu X , Li J , Wang J , Li Z . Cation-anion dual doping modifying electronic structure of hollow CoP nanoboxes for enhanced water oxidation electrocatalysis. Inorganic Chemistry, 2022, 61(42): 16944–16951

[81] Yuan C , Xu T , Guo M , Zhang T , Yu X . Cation/anion-doping induced electronic structure regulation strategy to boost the catalytic hydrogen evolution from ammonia borane hydrolysis. Applied Catalysis B: Environmental, 2023, 321: 122044

[82] Wang P , Ma X , Hao X , Tang B , Abudula A , Guan G . Oxygen vacancy defect engineering to promote catalytic activity toward the oxidation of VOCs: a critical review. Catalysis Reviews, 2022, 66(2): 586–639

[83] Huang Y , Yu Y , Yu Y , Zhang B . Oxygen vacancy engineering in photocatalysis. Solar RRL, 2020, 4(8): 2000037

[84] Fu L , Chen H , Wang K , Wang X . Oxygen-vacancy generation in MgFe₂O₄ by high temperature calcination and its improved photocatalytic activity for CO₂ reduction. Journal of Alloys and Compounds, 2022, 891: 161925

[85] Su L , Zhang Y , Zhan X , Zhang L , Zhao Y , Zhu X , Wu H , Chen H , Shen C , Wang L . Pr₆O₁₁: temperature-dependent oxygen vacancy regulation and catalytic performance for lithium-oxygen batteries. ACS Applied Materials & Interfaces, 2022, 14(36): 40975–40984

[86] Li Z , Yan Q , Jiang Q , Gao Y , Xue T , Li R , Liu Y , Wang Q . Oxygen vacancy mediated Cu_yCo_3–yFe₁O_x mixed oxide as highly active and stable toluene oxidation catalyst by multiple phase interfaces formation and metal doping effect. Applied Catalysis B: Environmental, 2020, 269: 118827

[87] Xie Q , Wang M , Xu Y , Li X , Zhou X , Hong L , Jiang L , Lin W . S vacancy modulated Zn_xCd_1–xS/CoP quantum dots for efficient H₂ evolution from water splitting under visible light. Journal of Energy Chemistry, 2021, 61: 210–218

[88] Zhang R , Ning X , Wang Z , Zhao H , He Y , Han Z , Du P , Lu X . Significantly promoting the photogenerated charge separation by introducing an oxygen vacancy regulation strategy on the FeNiOOH co-catalyst. Small, 2022, 18(20): 2107938

[89] Chang Y , Huang H , Yang T , Wang L , Zhu H , Zhong C . Simultaneous introduction of oxygen vacancies and hierarchical pores into titanium-based metal-organic framework for enhanced photocatalytic performance. Journal of Colloid and Interface Science, 2021, 599: 785–794

[90] Gao W , Li S , He H , Li X , Cheng Z , Yang Y , Wang J , Shen Q , Wang X , Xiong Y . . Vacancy-defect modulated pathway of photoreduction of CO₂ on single atomically thin AgInP₂S₆ sheets into olefiant gas. Nature Communications, 2021, 12(1): 4747

[91] Yi L , Chen L , Lu C , Ni Y , Xu Z . Effects of oxygen defects on structure and properties of Sm_0.5Sr_0.5CoO_3–δ annealed in different atmospheres. Journal of Rare Earths, 2013, 31(12): 1183–1190

[92] Wang K , Chang Y , Lv L , Long Y . Effect of annealing temperature on oxygen vacancy concentrations of nanocrystalline CeO₂ film. Applied Surface Science, 2015, 351: 164–168

[93] Li Q , Zhu X , Yang J , Yu Q , Zhu X , Chu J , Du Y , Wang C , Hua Y , Li H . . Plasma treated Bi₂WO₆ ultrathin nanosheets with oxygen vacancies for improved photocatalytic CO₂ reduction. Inorganic Chemistry Frontiers, 2020, 7(3): 597–602

[94] Li X , Zhang J , Zhou F , Zhang H , Bai J , Wang Y , Wang H . Preparation of N-vacancy-doped g-C₃N₄ with outstanding photocatalytic H₂O₂ production ability by dielectric barrier discharge plasma treatment. Chinese Journal of Catalysis, 2018, 39(6): 1090–1098

[95] Wu L , Li Y , Fu Z , Su B . Hierarchically structured porous materials: synthesis strategies and applications in energy storage. National Science Review, 2020, 7(11): 1667–1701

[96] Huang H , Li J , Wang K , Han T , Tong M , Li L , Xie Y , Yang Q , Liu D , Zhong C . An in situ self-assembly template strategy for the preparation of hierarchical-pore metal-organic frameworks. Nature Communications, 2015, 6(1): 8847

[97] Kirchon A , Li J , Xia F , Day G S , Becker B , Chen W , Sue H , Fang Y , Zhou H . Modulation versus templating: fine-tuning of hierarchally porous PCN-250 using fatty acids to engineer guest adsorption. Angewandte Chemie International Edition, 2019, 58(36): 12425–12430

[98] Hu M , Ju Y , Liang K , Suma T , Cui J , Caruso F . Void engineering in metal-organic frameworks via synergistic etching and surface functionalization. Advanced Functional Materials, 2016, 26(32): 5827–5834

[99] Liang X , Fu N , Yao S , Li Z , Li Y . The progress and outlook of metal single-atom-site catalysis. Journal of the American Chemical Society, 2022, 144(40): 18155–18174

[100] Pan Y , Zhang C , Liu Z , Chen C , Li Y . Structural regulation with atomic-level precision: from single-atomic site to diatomic and atomic interface catalysis. Matter, 2020, 2(1): 78–110

[101] Rong X , Wang H , Lu X , Si R , Lu T . Controlled synthesis of a vacancy-defect single-atom catalyst for boosting CO₂ electroreduction. Angewandte Chemie, 2020, 132(5): 1977–1981

[102] Ji S , Chen Y , Wang X , Zhang Z , Wang D , Li Y . Chemical synthesis of single atomic site catalysts. Chemical Reviews, 2020, 120(21): 11900–11955

[103] Yuan L , Tang T , Hu J , Wan L . Confinement strategies for precise synthesis of efficient electrocatalysts from the macroscopic to the atomic level. Accounts of Materials Research, 2021, 2(10): 907–919

[104] Chen Y , Ji S , Chen C , Peng Q , Wang D , Li Y . Single-atom catalysts: synthetic strategies and electrochemical applications. Joule, 2018, 2(7): 1242–1264

[105] Liang S , Zou L , Zheng L , Li L , Wang X , Song L , Xu J . Highly stable Co single atom confined in hierarchical carbon molecular sieve as efficient electrocatalysts in metal-air batteries. Advanced Energy Materials, 2022, 12(11): 2103097

[106] Cheng X , Wang J , Zhao K , Bi Y . Spatially confined iron single-atom and potassium ion in carbon nitride toward efficient CO₂ reduction. Applied Catalysis B: Environmental, 2022, 316: 121643

[107] Mo Q , Zhang L , Li S , Song H , Fan Y , Su C . Engineering single-atom sites into pore-confined nanospaces of porphyrinic metal-organic frameworks for the highly efficient photocatalytic hydrogen evolution reaction. Journal of the American Chemical Society, 2022, 144(49): 22747–22758

[108] Wang Y , Wang D , Li Y . Rational design of single-atom site electrocatalysts: from theoretical understandings to practical applications. Advanced Materials, 2021, 33(34): 2008151

[109] Wan J , Chen W , Jia C , Zheng L , Dong J , Zheng X , Wang Y , Yan W , Chen C , Peng Q . . Defect effects on TiO₂ nanosheets: stabilizing single atomic site Au and promoting catalytic properties. Advanced Materials, 2018, 30(11): 1705369

[110] Jin J , Han X , Fang Y , Zhang Z , Li Y , Zhang T , Han A , Liu J . Microenvironment engineering of Ru single-atom catalysts by regulating the cation vacancies in NiFe-layered double hydroxides. Advanced Functional Materials, 2022, 32(8): 2109218

[111] Chen Z , Li X , Zhao J , Zhang S , Wang J , Zhang H , Zhang J , Dong Q , Zhang W , Hu W . . Stabilizing Pt single atoms through Pt-Se electron bridges on vacancy-enriched nickel selenide for efficient electrocatalytic hydrogen evolution. Angewandte Chemie International Edition, 2023, 62(39): e202308686

[112] Hejazi S , Mehdi-pour H , Otieno C O , Müller J , Pour-Ali S , Shahsanaei M , Tafreshi S S , Butz B , Killian M S , Mohajernia S . Room-temperature defect-engineered titania: an efficient platform for Pt single atom decoration for photocatalytic H₂ evolution. International Journal of Hydrogen Energy, 2024, 51: 222–233

[113] Geng L , Zhang Q , Wang X , Han H , Zhang Y , Li C , Li Z , Zhang D , Zhang X , Abdukayum A . . Electronic modulation induced by oxygen vacancy creating in copper oxides toward accelerated hydrogenation kinetics of nitroaromatics. Applied Catalysis B: Environmental, 2024, 343: 123575

[114] Huang H , Cho A , Kim S , Jun H , Lee A , Han J W , Lee J . Structural design of amorphous CoMoP_x with abundant active sites and synergistic catalysis effect for effective water splitting. Advanced Functional Materials, 2020, 30(43): 2003889

[115] Liu W , Luo C , Zhang S , Zhang B , Ma J , Wang X , Liu W , Li Z , Yang Q , Lv W . Cobalt-doping of molybdenum disulfide for enhanced catalytic polysulfide conversion in lithium-sulfur batteries. ACS Nano, 2021, 15(4): 7491–7499

[116] Zhong X , Yi W , Qu Y , Zhang L , Bai H , Zhu Y , Wan J , Chen S , Yang M , Huang L . . Co single-atom anchored on Co₃O₄ and nitrogen-doped active carbon toward bifunctional catalyst for zinc-air batteries. Applied Catalysis B: Environmental, 2020, 260: 118188

[117] Yang H , Liu X , Hao M , Xie Y , Wang X , Tian H , Waterhouse G I N , Kruger P E , Telfer S G , Ma S . Functionalized iron-nitrogen-carbon electrocatalyst provides a reversible electron transfer platform for efficient uranium extraction from seawater. Advanced Materials, 2021, 33(51): 2106621

[118] Yang H , Liu Y , Liu X , Wang X , Tian H , Waterhouse G I N , Kruger P E , Telfer S G , Ma S . Large-scale synthesis of N-doped carbon capsules supporting atomically dispersed iron for efficient oxygen reduction reaction electrocatalysis. eScience, 2022, 2(2): 227–234

[119] Liu X , Xie Y , Hao M , Chen Z , Yang H , Waterhouse G I N , Ma S , Wang X . Highly efficient electrocatalytic uranium extraction from seawater over an amidoxime-functionalized In-N-C catalyst. Advanced Science (Weinheim, Baden-Wurttemberg, Germany), 2022, 9(23): 2201735

[120] Liu X , Xie Y , Li Y , Hao M , Chen Z , Yang H , Waterhouse G I N , Ma S , Wang X . Functional carbon capsules supporting ruthenium nanoclusters for efficient electrocatalytic ⁹⁹TcO₄-/ReO₄- removal from acidic and alkaline nuclear wastes. Advanced Science, 2023, 10(30): 2303536

[121] Gao W , Yang M , Chi J , Zhang X , Xie J , Guo B , Wang L , Chai Y , Dong B . In situ construction of surface defects of carbon-doped ternary cobalt-nickel-iron phosphide nanocubes for efficient overall water splitting. Science China Materials, 2019, 62: 1285–1296

[122] Zhao G , Busser G M , Froese C , Hu B , Bonke S A , Schnegg A , Ai Y , Wei D , Wang X , Peng B . . Anaerobic alcohol conversion to carbonyl compounds over nanoscaled Rh-doped SrTiO₃ under visible light. Journal of Physical Chemistry Letters, 2019, 10(9): 2075–2080

[123] Hu Y , Zhao G , Pan Q , Wang H , Shen Z , Peng B , Busser G W , Wang X , Muhler M . Highly selective anaerobic oxidation of alcohols over Fe‐doped SrTiO₃ under visible light. ChemCatChem, 2019, 11(20): 5139–5144

[124] Li B , Hong J , Ai Y , Hu Y , Shen Z , Li S , Zou Y , Zhang S , Wang X , Zhao G . . Visible-near-infrared-light-driven selective oxidation of alcohols over nanostructured Cu doped SrTiO₃ in water under mild condition. Journal of Catalysis, 2021, 399: 142–149

[125] Shen Z , Hu Y , Pan Q , Huang C , Zhu B , Xia W , Wang H , Yue J , Muhler M , Zhao G . . Oxygen vacancies-enriched Ta-doped Bi₂WO₆ with Pt as cocatalyst for boosting the dehydrogenation of benzyl alcohol in water. Applied Surface Science, 2022, 571: 151370

[126] Zou Y , Hu Y , Uhrich A , Shen Z , Peng B , Ji Z , Muhler M , Zhao G , Wang X , Xu X . Steering accessible oxygen vacancies for alcohol oxidation over defective Nb₂O₅ under visible light illumination. Applied Catalysis B: Environmental, 2021, 298: 120584

[127] Zhang S , Liu Y , Gu P , Ma R , Wen T , Zhao G , Li L , Ai Y , Hu C , Wang X . Enhanced photodegradation of toxic organic pollutants using dual-oxygen-doped porous g-C₃N₄: mechanism exploration from both experimental and DFT studies. Applied Catalysis B: Environmental, 2019, 248: 1–10

[128] Zhang S , Liu Y , Ma R , Jia D , Wen T , Ai Y , Zhao G , Fang F , Hu B , Wang X . Molybdenum(VI)-oxo clusters incorporation activates g-C₃N₄ with simultaneously regulating charge transfer and reaction centers for boosting photocatalytic performance. Advanced Functional Materials, 2022, 32(38): 2204175

[129] Li C , Guo Y , Tang D , Guo Y , Wang G , Jiang H , Li J . Optimizing electron structure of Zn-doped AgFeO₂ with abundant oxygen vacancies to boost photocatalytic activity for Cr(VI) reduction and organic pollutants decomposition: DFT insights and experimental. Chemical Engineering Journal, 2021, 411: 128515

Competing interests

The authors declare that they have no competing interests.

Acknowledgements

We gratefully acknowledge funding support from the National Science Foundation of China (Grant No. 22306124), the Beijing Outstanding Young Scientist Program.

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