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Iron oxide nanoparticles have tremendous scientific and technological potential in a broad range of technologies, from energy applications to biomedicine. To improve their performance, single‐crystalline and defect‐free nanoparticles have thus far been aspired. However, in several recent studies, defect‐rich nanoparticles outperform their defect‐free counterparts in magnetic hyperthermia and magnetic particle imaging (MPI). Here, an overview on the state‐of‐the‐art of design and characterization of defects and resulting spin disorder in magnetic nanoparticles is presented with a focus on iron oxide nanoparticles. The beneficial impact of defects and disorder on intracellular magnetic hyperthermia performance of magnetic nanoparticles for drug delivery and cancer therapy is emphasized. Defect‐engineering in iron oxide nanoparticles emerges to become an alternative approach to tailor their magnetic properties for biomedicine, as it is already common practice in established systems such as semiconductors and emerging fields including perovskite solar cells. Finally, perspectives and thoughts are given on how to deliberately induce defects in iron oxide nanoparticles and their potential implications for magnetic tracers to monitor cell therapy and immunotherapy by MPI. Recent developments in the emerging research field of defect‐engineering in magnetic nanoparticles and its beneficial impact on magnetic hyperthermia performance of nanoparticles are presented. Different fields of research relevant to magnetic nanoparticles from synthesis to magnetic structure determination and biomedical applications are covered, considering defects and associated magnetic disorder at different length scales.

HighlightsThis review summarizes the decade milestone advancement of defect-engineered g-C3N4 and emphasizes the roles of crystallinity and defect traps toward a more precise defective g-C3N4 “customization” in the future.A critical insight into the defect traps has been discussed in depth, probing the defect-induced states and photocarrier transfer kinetics of g-C3N4.The prospect and outlooking for precise defective g-C3N4 “customization” is proposed.Over the past decade, graphitic carbon nitride (g-C3N4) has emerged as a universal photocatalyst toward various sustainable carbo-neutral technologies. Despite solar applications discrepancy, g-C3N4 is still confronted with a general fatal issue of insufficient supply of thermodynamically active photocarriers due to its inferior solar harvesting ability and sluggish charge transfer dynamics. Fortunately, this could be significantly alleviated by the “all-in-one” defect engineering strategy, which enables a simultaneous amelioration of both textural uniqueness and intrinsic electronic band structures. To this end, we have summarized an unprecedently comprehensive discussion on defect controls including the vacancy/non-metallic dopant creation with optimized electronic band structure and electronic density, metallic doping with ultra-active coordinated environment (M–Nx, M–C2N2, M–O bonding), functional group grafting with optimized band structure, and promoted crystallinity with extended conjugation π system with weakened interlayered van der Waals interaction. Among them, the defect states induced by various defect types such as N vacancy, P/S/halogen dopants, and cyano group in boosting solar harvesting and accelerating photocarrier transfer have also been emphasized. More importantly, the shallow defect traps identified by femtosecond transient absorption spectra (fs-TAS) have also been highlighted. It is believed that this review would pave the way for future readers with a unique insight into a more precise defective g-C3N4 “customization”, motivating more profound thinking and flourishing research outputs on g-C3N4-based photocatalysis.

Photocatalytic water splitting is promising for hydrogen energy production using solar energy and developing highly efficient photocatalysts is challenging. Defect engineering is proved to be a very useful strategy to promote the photocatalytic performance of metal‐based photocatalysts, however, the vital role of defects is still ambiguous. This work comprehensively reviews point defective metal‐based photocatalysts for water splitting, focusing on understanding the defects' disorder effect on optical adsorption, charge separation and migration, and surface reaction. The controllable synthesis and tuning strategies of defective structure to improve the photocatalytic performance are summarized, then the characterization techniques and density functional theory calculations are discussed to unveil the defect structure, and analyze the defects induced electronic structure change of catalysts and its ultimate effect on the photocatalytic activity at the molecular level. Finally, the challenge in developing more efficient defective metal‐based photocatalysts is outlined. This work may help further the understanding of the fundamental role of defect structure in the photocatalytic reaction process and guide the rational design and fabrication of highly efficient and low‐cost photocatalysts. This work summarizes the role of defects in metal‐based materials for photocatalytic water splitting from an experimental and theoretical perspective. The fabrication and characterization methods of defective metal‐based photocatalysts are summarized. Defects induced electronic structure changes of catalysts and how they ultimately affect the reactivity are discussed. The challenges and outlook in developing defective metal‐based catalysts are also given.

Engineering of defects in semiconductors provides an effective protocol for improving photocatalytic N 2 conversion efficiency. This review focuses on the state-of-the-art progress in defect engineering of photocatalysts for the N 2 reduction toward ammonia. The basic principles and mechanisms of thermal catalyzed and photon-induced N 2 reduction are first concisely recapped, including relevant properties of the N 2 molecule, reaction pathways, and NH 3 quantification methods. Subsequently, defect classification, synthesis strategies, and identification techniques are compendiously summarized. Advances of in situ characterization techniques for monitoring defect state during the N 2 reduction process are also described. Especially, various surface defect strategies and their critical roles in improving the N 2 photoreduction performance are highlighted, including surface vacancies (i.e., anionic vacancies and cationic vacancies), heteroatom doping (i.e., metal element doping and nonmetal element doping), and atomically defined surface sites. Finally, future opportunities and challenges as well as perspectives on further development of defect-engineered photocatalysts for the nitrogen reduction to ammonia are presented. It is expected that this review can provide a profound guidance for more specialized design of defect-engineered catalysts with high activity and stability for nitrogen photochemical fixation.

HighlightsTwo-dimensional materials including TMDCs, hBN, graphene, non-layered compounds, black phosphorous, Xenes and other emerging materials with large lateral dimensions exceeding a hundred micrometres are summarised detailing their synthetic strategies.Crystal quality optimisations and defect engineering are discussed for large-area two-dimensional materials synthesis.Electronics and optoelectronics applications enabled by large-area two-dimensional materials are explored..Large-area and high-quality two-dimensional crystals are the basis for the development of the next-generation electronic and optical devices. The synthesis of two-dimensional materials in wafer scales is the first critical step for future technology uptake by the industries; however, currently presented as a significant challenge. Substantial efforts have been devoted to producing atomically thin two-dimensional materials with large lateral dimensions, controllable and uniform thicknesses, large crystal domains and minimum defects. In this review, recent advances in synthetic routes to obtain high-quality two-dimensional crystals with lateral sizes exceeding a hundred micrometres are outlined. Applications of the achieved large-area two-dimensional crystals in electronics and optoelectronics are summarised, and advantages and disadvantages of each approach considering ease of the synthesis, defects, grain sizes and uniformity are discussed.

The introduction of vacancy defects in semiconductors has been proven to be a highly effective approach to improve their photocatalytic activity owing to their advantages of promoting light absorption, facilitating photogenerated carrier separation, optimizing electronic structure, and enabling the production of reactive radicals. Herein, we outline the state‐of‐the‐art vacancy‐engineered photocatalysts in various applications and reveal how the vacancies influence photocatalytic performance. Specifically, the types of vacancy defects, the methods for tailoring vacancies, the advanced characterization techniques, the categories of photocatalysts with vacancy defects, and the corresponding photocatalytic behaviors are presented. Meanwhile, the methods of vacancies creation and the related photocatalytic performance are correlated, which can be very useful to guide the readers to quickly obtain in‐depth knowledge and to have a good idea about the selection of defect engineering methods. The precise characterization of vacancy defects is highly challenging. This review describes the accurate use of a series of characterization techniques with detailed comments and suggestions. This represents the uniqueness of this comprehensive review. The challenges and development prospects in engineering photocatalysts with vacancy defects for practical applications are discussed to provide a promising research direction in this field. The state‐of‐the‐art vacancy‐engineered photocatalysts in various applications and the effects of vacancies on photocatalytic performance have been outlined. The types of vacancy defects, the methods for tailoring vacancies, the advanced characterization techniques, the categories of photocatalysts with vacancy defects, and the corresponding photocatalytic behaviors are presented.

Defect engineering is an effective approach to manipulate electromagnetic (EM) parameters and enhance absorption ability, but defect induced dielectric loss dominant mechanism has not been completely clarified. Here the defect induced dielectric loss dominant mechanism in virtue of multi‐shelled spinel hollow sphere for the first time is demonstrated. The unique but identical morphology design as well as suitable composition modulation for serial spinels can exclude the disturbance of EM wave dissipation from dipolar/interfacial polarization and conduction loss. In temperature‐regulated defect in NiCo2O4 serial materials, two kinds of defects, defect in spinel structure and oxygen vacancy are detected. Defect in spinel structure played more profound role on determining materials’ EM wave dissipation than that of oxygen vacancy. When evaluated serial Co‐based materials as absorbers, defect induced polarization loss is responsible for the superior absorption performance of NiCo2O4‐based material due to its more defect sites in spinel structure. It is discovered that electron spin resonance test may be adopted as a novel approach to directly probe EM wave absorption capacities of materials. This work not only provides a strategy to prepare lightweight, efficient EM wave absorber but also illustrates the importance of defect engineering on regulation of materials’ dielectric loss capacity. The importance of defect induced polarization loss in electromagnetic wave absorption is revealed by engineering defect in serial Co‐based multi‐shelled spinel hollow spheres. For the first time, defect in spinel structure and its induced loss mechanism is found to play dominate role over other loss mechanisms. This unique hollow structure also affords lightweight spinel electromagnetic wave absorbing materials.

Amid global efforts toward carbon neutrality, nanoconfined catalysis has emerged as a transformative strategy to address energy transition challenges through precise regulation of catalytic microenvironments. This review systematically examines recent advancements in nanoconfined catalytic systems for carbon-based energy conversion (CO2, CH4, etc.), highlighting their unique capability to modulate electronic structures and reaction pathways via quantum confinement and interfacial effects. By categorizing their architectures into dimension-oriented frameworks (1D nanotube channels, 2D layered interfaces, 3D core-shell structures, and heterointerfaces), we reveal how geometric constraints synergize with mass/electron transfer dynamics to enhance selectivity and stability. Critical optimization strategies—including heteroatom doping to optimize active site coordination, defect engineering to lower energy barriers, and surface modification to tailor local microenvironments—are analyzed to elucidate their roles in stabilizing metastable intermediates and suppressing catalyst deactivation. We further emphasize the integration of machine learning, in situ characterization, and modular design as essential pathways to establish structure–activity correlations and accelerate industrial implementation. This work provides a multidimensional perspective bridging fundamental mechanisms with practical applications to advance carbon-neutral energy systems.

Defect engineering in photocatalytic materials has garnered significant interest due to the considerable impact of defects on light absorption, charge separation, and surface reaction dynamics. However, a limited understanding of how these defects influence photocatalytic properties remains a persistent challenge. This review comprehensively analyzes the vital role of defect engineering for enhancing the photocatalytic performance, highlighting its significant influence on material properties and efficiency. It systematically classifies defect types, including vacancy defects (oxygen and metal vacancies), doping defects (anion and cation), interstitial defects, surface defects (step edges, terraces, kinks, and disordered layers), antisite defects, and interfacial defects in the core–shell structures and heterostructure borders. The impact of complex defect groups and manifold defects on improved photocatalytic performance is also examined. The review emphasizes the principal benefits of defect engineering, including the enhancement of light adsorption, reduction of band gaps, improved charge separation and movements, and suppression of charge recombination. These enhancements lead to a boost in catalytic active sites, optimization of electronic structures, tailored band alignments, and the development of mid‐gap states, leading to improved structural stability, photocorrosion resistance, and better reaction selectivity. Furthermore, the most recent improvements, such as oxygen vacancies, nitrogen and sulfur doping, surface defect engineering, and innovations in heterostructures, defect‐rich metal–organic frameworks, and defective nanostructures, are examined comprehensively. This study offers essential insights into modern techniques and approaches in defect engineering, highlighting its significance in addressing challenges in photocatalytic materials and promoting the advancement of effective and adaptable platforms for renewable energy and environmental uses. Different types of defects were comprehensively studied. Heterojunction and interface defects were deeply highlighted. Advantages of defect engineering have been discussed in detail. Defect engineering presents new opportunities for cost‐effective photocatalysts.

Two‐dimensional (2D) materials as tungsten disulphide (WS2) are rising as the ideal platform for the next generation of nanoscale devices due to the excellent electric‐transport and optical properties. However, the presence of defects in the as grown samples represents one of the main limiting factors for commercial applications. At the same time, WS2 properties are frequently tailored by introducing impurities at specific sites. Aim of this review paper is to present a complete description and discussion of the effects of both intentional and unintentional defects in WS2, by an in depth analysis of the recent experimental and theoretical investigations reported in the literature. First, the most frequent intrinsic defects in WS2 are presented and their effects in the readily synthetized material are discussed. Possible solutions to remove and heal unintentional defects are also analyzed. Following, different doping schemes are reported, including the traditional substitution approach and innovative techniques based on the surface charge transfer with adsorbed atoms or molecules. The plethora of WS2 monolayer modifications presented in this review and the systematic analysis of the corresponding optical and electronic properties, represent strategic degrees of freedom the researchers may exploit to tailor WS2 optical and electronic properties for specific device applications. Controlling the electric and optical properties of WS2 monolayers via intentional defect inclusion is an effective way to mitigate the intrinsic defect issue and tailor the material properties. This work provides a systematic analysis of defects in WS2, considering both intrinsic defects and different, innovative doping schemes, reporting a combination of theoretical and experimental evidence.