Phase and Defect Engineering of MoSe2 Nanosheets for Enhanced NIR-II Photothermal Immunotherapy.

Inducing immunogenic cell death (ICD) during photothermal therapy (PTT) has the potential to effectively trigger photothermal immunotherapy (PTI). However, ICD induced by PTT alone is often limited by inefficient PTT, low immunogenicity of tumor cells, and a dysregulated redox microenvironment. Herein, we develop MoSe2 nanosheets with high-percentage metallic 1T phase and rich exposed active Mo centers through phase and defect engineering of MoSe2 as an effective nanoagent for PTI. The metallic 1T phase in MoSe2 nanosheets endows them with strong PTT performance, and the abundant exposed active Mo centers endow them with high activity for glutathione (GSH) depletion. The MoSe2-mediated high-performance PTT synergizing with efficient GSH depletion facilitates the release of tumor-associated antigens to induce robust ICD, thus significantly enhancing checkpoint blockade immunotherapy and activating systemic immune response in mouse models of colorectal cancer and triple-negative metastatic breast cancer.

Laser-Induced Controllable Porosity in Additive Manufacturing Boosts Efficiency of Electrocatalytic Water Splitting.

In laser-based additive manufacturing (AM), porosity and unmelted metal powder are typically considered undesirable and harmful. Nevertheless in this work, precisely controlling laser parameters during printing can intentionally introduce controllable porosity, yielding a porous electrode with enhanced catalytic activity for the oxygen evolution reaction (OER). This study demonstrates that deliberate introduction of porosity, typically considered a defect, leads to improved gas molecule desorption, enhanced mass transfer, and increased catalytically active sites. The optimized P-93% electrode displays superior OER performance with an overpotential of 270 mV at 20 mA cm-2. Furthermore, it exhibits remarkable long-term stability, operating continuously for over 1000 h at 10 mA cm-2 and more than 500 h at 500 mA cm-2. This study not only provides a straightforward and mass-producible method for efficient, binder-free OER catalysts but also, if optimized, underscores the potential of laser-based AM driven defect engineering as a promising strategy for industrial water splitting.

Strain-Mediated Defect Engineering toward Rapid Atomic Migration in Fe-Al Diffusion Couples.

In the pursuit of rapid atomic migration in lightweight Fe-Al diffusion couples, rationally designing short-circuit diffusion paths has become paramount. Herein, a strain-mediated defect engineering strategy was proposed for reducing the vacancy activation energy and enhancing diffusion behaviors along dislocations (DLs) and grain boundaries (GBs). Combining the modified Arrhenius-type relationship, an interfacial apparent activation energy of 139 kJ mol-1 was acquired utilizing defect engineering, which was decreased by about 49%. This was closely related to high-density vacancies, DLs, and GBs formed in strained Fe and Al materials, which provided more low activation energy paths for atomic migration. First-principles calculations indicated that the lattice diffusion barrier mediated by monovacancy was reduced with strain incorporation, attributed to the weakened atom-vacancy bond as a consequence of less electron transport. The synergistic effect of abnormal electron-charge distribution in the bulk and strong attraction force at the Al/Fe interface radically resulted in rapid atomic migration, collectively regulating the "breaking-forming bond" process.

Spontaneous Atomic-Scale Polar Skyrmions and Merons on a SrTiO3 (001) Surface: Defect Engineering for Emerging Topological Orders.

The emergence of nontrivial topological order in condensed matter has been attracting a great deal of attention owing to its promising technological applications in novel functional nanodevices. In ferroelectrics, the realization of polar topological order at an ultimately small scale is extremely challenging due to the lack of chiral interaction and the critical size of the ferroelectricity. Here, we break through these limitations and demonstrate that the ultimate atomic-scale polar skyrmion and meron (∼2 nm) can be induced by engineering oxygen vacancies on the SrTiO3 (001) surface based on first-principles calculations. The paraelectric-to-antiferrodistortive phase transition leads to a novel topological transition from skyrmion to meron, indicating phase-topology correlations. We also discuss accumulating and driving polar skyrmions based on the oxygen divacancy model; these results and the recent discovery of defect engineering techniques suggest the possibility of arithmetic operations on topological numbers through the natural self-organization and diffusion features of oxygen vacancies.

Defect-Induced All-Solid-State Frustrated Lewis Pair on Metal-Organic Monolayer Accelerating Photocatalytic CO2 Reduction with H2O Vapor.

Understanding the structure-performance relationships of a frustrated Lewis pair (FLP) at the atomic level is key to yielding high efficiency in activating chemically "inert" molecules into value-added products. A sound strategy was developed herein through incorporating oxygen defects into a Zr-based metal-organic layer (Zr-MOL-D) and employing Lewis basic proximal surface hydroxyls for the in situ formation of solid heterogeneous FLP (Zr4-δ-VO-Zr-OH). Zr-MOL-D exhibits a superior CO2 to CO conversion rate of 49.4 µmol g-1 h-1 in water vapor without any sacrificing agent or photosensitizer, which is about 12 times higher than that of pure MOL (Zr-MOL-P), with extreme stability even after being placed for half a year. Theoretical and experimental results reveal that the introduction of FLP converts the process of the crucial intermediate COOH* from an endothermic reaction to an exothermic spontaneous reaction. This work is expected to provide new prospects for developing efficient MOL-based photocatalysts in FLP chemistry through a sound defect-engineering strategy.

Atomic Defects Engineering Boosts Urea Synthesis toward Carbon Dioxide and Nitrate Coelectroreduction.

The atomic defect engineering could feasibly decorate the chemical behaviors of reaction intermediates to regulate catalytic performance. Herein, we created oxygen vacancies on the surface of In(OH)3 nanobelts for efficient urea electrosynthesis. When the oxygen vacancies were constructed on the surface of the In(OH)3 nanobelts, the faradaic efficiency for urea reached 80.1%, which is 2.9 times higher than that (20.7%) of the pristine In(OH)3 nanobelts. At -0.8 V versus reversible hydrogen electrode, In(OH)3 nanobelts with abundant oxygen vacancies exhibited partial current density for urea of -18.8 mA cm-2. Such a value represents the highest activity for urea electrosynthesis among recent reports. Density functional theory calculations suggested that the unsaturated In sites adjacent to oxygen defects helped to optimize the adsorbed configurations of key intermediates, promoting both the C-N coupling and the activation of the adsorbed CO2NH2 intermediate. In-situ spectroscopy measurements further validated the promotional effect of the oxygen vacancies on urea electrosynthesis.

Offcut Substrate-Induced Defect Trapping at Step Edges.

We report step edge-induced localized defects suppressing subsequent antiphase boundary formation in the bulk structure of a trilayer oxide heterostructure. The heterostructure encompasses a layer of La0.66Sr0.34MnO3 sandwiched between a superconducting La1.84Sr0.16CuO4 bottom layer and an insulating La2CuO4 top layer. The combination of a minor a-axis mismatch (0.11 Å) and a pronounced c-axis mismatch (2.73 Å) at the step edges leads to the emergence of localized defects exclusively forming at the step edge. Employing atomically resolved electron energy-loss spectroscopy maps, we discern the electronic state of those structures in the second La0.66Sr0.34MnO3 unit cell near the step edge. In particular, a reduction in the pre-edge region of the O-K edge indicates the formation of oxygen vacancies induced by the strained step edge. This study underscores our capability to control defects at the nanoscale.

Electronic Structure Modulation of Oxygen-Enriched Defective CdS for Efficient Photocatalytic H2O2 Production.

Artificial photosynthesis for hydrogen peroxide (H2O2) presents a sustainable and environmentally friendly approach to generate clean fuel and chemicals. However, the catalytic activity is hindered by challenges such as severe charge recombination, insufficient active sites, and poor selectivity. Here, a robust strategy is proposed to regulate the electronic structure of catalyst by the collaborative effect of defect engineering and dopant. The well designed oxygen-doped CdS nanorods with S2- defects and Cd2+ 4d10 electron configuration (CdS-O,Sv) is successfully synthesized, and the Cd2+ active sites around S defects or oxygen atoms exhibit rapid charge separation, suppressed carrier recombination, and enhanced charge utilization. Consequently, a remarkable H2O2 production rate of 1.62 mmol g-1 h-1 under air conditions is acquired, with an apparent quantum yield (AQY) of 9.96% at a single wavelength of 450 nm. This work provides valuable insights into the synergistic effect between defect and doping on catalytic activity.

Ultrathin NiV Layered Double Hydroxide for Methanol Electrooxidation: Understanding the Proton Detachment Kinetics and Methanol Dehydrogenation Oxidation.

Electrochemical methanol oxidation reaction (MOR) is regarded as a promising pathway to obtain value-added chemicals and drive cathodic H2 production, while the rational design of catalyst and in-depth understanding of the structure-activity relationship remains challenging. Herein, the ultrathin NiV-LDH (u-NiV-LDH) with abundant defects is successfully synthesized, and the defect-enriched structure is finely determined by X-ray adsorption fine structure etc. When applied for MOR, the as-prepared u-NiV-LDH presents a low potential of 1.41 V versus RHE at 100 mA cm-2, which is much lower than that of bulk NiV-LDH (1.75 V vs RHE) at the same current density. The yield of H2 and formate is 98.2% and 88.1% as its initial over five cycles and the ultrathin structure of u-NiV-LDH can be well maintained. Various operando experiments and theoretical calculations prove that the few-layer stacking structure makes u-NiV-LDH free from the interlayer hydrogen diffusion process and the hydrogen can be directly detached from LDH laminate. Moreover, the abundant surface defects upshift the d-band center of u-NiV-LDH and endow a higher local methanol concentration, resulting in an accelerated dehydrogenation kinetics on u-NiV-LDH. The synergy of the proton detachment from the laminate and the methanol dehydrogenation oxidation contributes to the excellent MOR performance of u-NiV-LDH.

Advances in Defect Engineering of Metal Oxides for Photocatalytic CO2 Reduction.

Photocatalytic CO2 reduction technology, capable of converting low-density solar energy into high-density chemical energy, stands as a promising approach to alleviate the energy crisis and achieve carbon neutrality. Semiconductor metal oxides, characterized by their abundant reserves, good stability, and easily tunable structures, have found extensive applications in the field of photocatalysis. However, the wide bandgap inherent in metal oxides contributes to their poor efficiency in photocatalytic CO2 reduction. Defect engineering presents an effective strategy to address these challenges. This paper reviews the research progress in defect engineering to enhance the photocatalytic CO2 reduction performance of metal oxides, summarizing defect classifications, preparation methods, and characterization techniques. The focus is on defect engineering, represented by vacancies and doping, for improving the performance of metal oxide photocatalysts. This includes advancements in expanding the photoresponse range, enhancing photogenerated charge separation, and promoting CO2 molecule activation. Finally, the paper provides a summary of the current issues and challenges faced by defect engineering, along with a prospective outlook on the future development of photocatalytic CO2 reduction technology.

Defect Engineering Centrosymmetric 2D Material Flexocatalysts.

In this study, the flexoelectric characteristics of 2D TiO2 nanosheets are examined. The theoretical calculations and experimental results reveal an excellent strain-induced flexoelectric potential (flexopotential) by an effective defect engineering strategy, which suppresses the recombination of electron-hole pairs, thus substantially improving the catalytic activity of the TiO2 nanosheets in the degradation of Rhodamine B dye and the hydrogen evolution reaction in a dark environment. The results indicate that strain-induced bandgap reduction enhances the catalytic activity of the TiO2 nanosheets. In addition, the TiO2 nanosheets degraded Rhodamine B, with kobs being ≈1.5 × 10-2 min-1 in dark, while TiO2 nanoparticles show only an adsorption effect. 2D TiO2 nanosheets achieve a hydrogen production rate of 137.9 µmol g-1 h-1 under a dark environment, 197% higher than those of TiO2 nanoparticles (70.1 µmol g-1 h-1). The flexopotential of the TiO2 nanosheets is enhanced by increasing the bending moment, with excellent flexopotential along the y-axis. Density functional theory is used to identify the stress-induced bandgap reduction and oxygen vacancy formation, which results in the self-dissociation of H2O on the surface of the TiO in the dark. The present findings provide novel insights into the role of TiO2 flexocatalysis in electrochemical reactions.

Wavelength-Controlled Photoconductance Polarity Switching via Harnessing Defects in Doped PdSe2 for Artificial Synaptic Features.

Optoelectronic synapses are currently drawing significant attention as fundamental building blocks of neuromorphic computing to mimic brain functions. In this study, a two-terminal synaptic device based on a doped PdSe2 flake is proposed to imitate the key neural functions in an optical pathway. Due to the wavelength-dependent desorption of oxygen clusters near the intrinsic selenide vacancy defects, the doped PdSe2 photodetector achieves a high negative photoresponsivity of -7.8 × 103 A W-1 at 473 nm and a positive photoresponsivity of 181 A W-1 at 1064 nm. This wavelength-selective bi-direction photoresponse endows an all-optical pathway to imitate the fundamental functions of artificial synapses on a device level, such as psychological learning and forgetting capability, as well as dynamic logic functions. The underpinning photoresponse is further demonstrated on a flexible platform, providing a viable technology for neuromorphic computing in wearable electronics. Furthermore, the p-type doping results in an effective increase of the channel's electrical conductivity and a significant reduction in power consumption. Such low-power-consuming optical synapses with simple device architecture and low-dimensional features demonstrate tremendous promise for building multifunctional artificial neuromorphic systems in the future.

2D Atomic Layers for CO2 Photoreduction.

Artificial photosynthesis can convert carbon dioxide into high value-added chemicals. However, due to the poor charge separation efficiency and CO2 activation ability, the conversion efficiency of photocatalytic CO2 reduction is greatly restricted. Ultrathin 2D photocatalyst emerges as an alternative to realize the higher CO2 reduction performance. In this review, the basic principle of CO2 photoreduction is introduced, and the types, advantages, and advances of 2D photocatalysts are reviewed in detail including metal oxides, metal chalcogenides, bismuth-based materials, MXene, metal-organic framework, and metal-free materials. Subsequently, the tactics for improving the performance of 2D photocatalysts are introduced in detail via the surface atomic configuration and electronic state tuning such as component tuning, crystal facet control, defect engineering, element doping, cocatalyst modification, polarization, and strain engineering. Finally, the concluding remarks and future development of 2D photocatalysts in CO2 reduction are prospected.

Tuning Main Group Element-based Metal-Organic Framework to Boost Electrocatalytic Nitrogen Reduction Under Ambient Conditions.

Main group element-based materials are emerging catalysts for ammonia (NH3 ) production via a sustainable electrochemical nitrogen reduction reaction (N2 RR) pathway under ambient conditions. However, their N2 RR performances are less explored due to the limited active behavior and unclear mechanism. Here, an aluminum-based defective metal-organic framework (MOF), aluminum-fumarate (Al-Fum), is investigated. As a proof of concept, the pristine Al-Fum MOF is synthesized by the solvothermal reaction process, and the defect engineering method namely solvent-assisted linker exchange, is applied to create the defective Al sites. The defective Al sites play an important role in ensuring the N2 RR activity for defective Al-Fum. It is found that only the defective Al-Fum enables stable and effective electrochemical N2 RR, in terms of the highest production rate of 53.9 µg(NH3 ) h-1 mgcat -1 (in 0.4 m K2 SO4 ) and the Faradaic efficiency of 73.8% (in 0.1 m K2 SO4 ) at -0.15 V vs reversible hydrogen electrode) under ambient conditions. Density functional theory calculations confirm that the N2 activation can be achieved on the defective Al sites. Such sites also allow the subsequent protonation process via the alternating associative mechanism. This defect characteristic gives the main group Al-based MOFs the ability to serve as promising electrocatalysts for N2 RR and other attractive applications.

Quantum-Sized Co Nanoparticles with Rich Vacancies Enabled the Uniform Deposition of Lithium Metal and Fast Polysulfide Conversion.

The notorious polysulfide shuttling and uncontrollable Li-dendrite growth are the main obstacles to the marketization of Li-S batteries. Herein, a dual-functional material consisting of vacancy-rich quantum-sized Co nanodots anchored on a mesoporous carbon layer (v-Co/meso-C) is proposed. This material exposes more active sites to improve its reaction performance and simultaneously realizes excellent lithiophilicity and sulfiphilicity characteristics in Li-S electrochemistry. As Li metal deposition hosts, v-Co/meso-C shows small nucleation overpotential, low polarization, and ultra-long cycling stability in both half and symmetric cells, as confirmed by experimental studies. On the S cathode side, experimental and theoretical calculations demonstrate that v-Co/meso-C enhances the adsorption of polysulfides and boosts their catalytic conversion rate. This, in turn, suppresses the shuttle effect of polysulfides and improves sulfur utilization efficiency. Finally, a shuttle-free and dendrite-free v-Co/meso-C@Li//v-Co/meso-C@S full cell is fabricated, exhibiting excellent rate performance (739 mAh g-1 at 5.0 C) and good cyclability (capacity decay rate is 0.033% and 0.035% per cycle at 2.0 and 5.0 C, respectively). Even a pouch cell with high sulfur loading (5.5 mg cm-2) and lean electrolyte/sulfur (4.8 µL mg-1) can still work 50 cycles with 80% capacity retention rate. This study shows far-reaching implications in the design of dendrite-free, shuttle-free Li-S batteries.

Atomic Basal Defect-Rich MoS2 by One-Step Synthesis and Mechanism Exploration.

Two-dimensional molybdenum disulfide (2D MoS2) shows great promise as a surface-enhanced Raman scattering (SERS) substrate due to its strong exciton resonance. However, the inert basal plane limits the performance of SERS. In this work, a strategy is proposed for the one-step synthesis of atomically basal defect-rich MoS2. The study first reveals that NaCl plays a two-stage role in the growth process, where NaCl initially promotes the rapid growth of large MoS2 as previously reported, and then promotes the formation of atomic basal defects dominated by single sulfur vacancies. Additionally, spectral changes induced by modulation of experimental parameters and density function theory calculation show that defect generation occurs during cooling. Meanwhile, the ratio of E 2 g 1 ${\mathrm{E}}_{{\mathrm{2g}}}^{\mathrm{1}}$ to A1g in defect-rich MoS2 exhibits different variation trends compared with pristine MoS2 in power-dependent Raman, and the ratio increases with increasing basal defects. In SERS tests, the limit of detection for rhodamine 6G reached 10-9 m, which is comparable to the performance of conventional noble metal SERS substrate. The activation strategy of the inert basal plane is applicable to other 2D transition metal dichalcogenides, and further has the potential to enhance performance in other domains, such as SERS and hydrogen evolution reactions.

Hollow Cu/CoS2 Nanozyme with Defect-Induced Enzymatic Catalytic Sites and Binding Pockets for Highly Sensitive Fluorescence Detection of Alkaline Phosphatase.

Along with an ever-deepening understanding of the catalytic principle of natural enzymes, the rational design of high-activity biomimetic nanozymes has become a hot topic in current research. Inspired by the active centers of natural enzymes consisting of catalytic sites and binding pockets, a Cu-doped CoS2 hollow nanocube (Cu/CoS2 HNCs) nanozyme integrating substitution defects and vacancies is developed through a defect engineering strategy. It is shown that the vacancies and substitution defects in the developed Cu/CoS2 HNC nanozymes serve as binding pockets and catalytic sites, respectively. The construction of this key active center and the accelerated electron transfer from the Co/Cu redox cycle significantly improve the substrate affinity and catalytic efficiency of the Cu/CoS2 HNCs nanozymes, which results in the excellent catalytic performance of the Cu/CoS2 HNC nanozymes. Using the superior enzymatic activity of Cu/CoS2 HNCs, a fluorescence detection platform for alkaline phosphatase (ALP) is established, which is a wider detection range and lower limit of detection (LOD) than previous work. This work broadens the family of nanozymes and provide a new idea for the development of novel nanozymes with high enzyme activity, as well as a guideline for the construction of highly sensitive fluorescent sensors.

Revealing the Optimization Route of Piezoelectric Sonosensitizers: From Mechanism to Engineering Methods.

Piezoelectric catalysis is a novel catalytic technology that has developed rapidly in recent years and has attracted extensive interest among researchers in the field of tumor therapy for its acoustic-sensitizing properties. Nevertheless, researchers are still controversial about the key technical difficulties in the modulation of piezoelectric sonosensitizers for tumor therapy applications, which is undoubtedly a major obstacle to the performance modulation of piezoelectric sonosensitizers. Clarification of this challenge will be beneficial to the design and optimization of piezoelectric sonosensitizers in the future. Here, the authors start from the mechanism of piezoelectric catalysis and elaborate the mechanism and methods of defect engineering and phase engineering for the performance modulation of piezoelectric sonosensitizers based on the energy band theory. The combined therapeutic strategy of piezoelectric sonosensitizers with enzyme catalysis and immunotherapy is introduced. Finally, the challenges and prospects of piezoelectric sonosensitizers are highlighted. Hopefully, the explorations can guide researchers toward the optimization of piezoelectric sonosensitizers and can be applied in their own research.

Tuning Electrons Migration of Dual S Defects Mediated MoS2-x/ZnIn2S4-x Toward Highly Efficient Photocatalytic Hydrogen Production.

Photocatalytic hydrogen production is a prevalent method for hydrogen synthesis. However, high recombination rate of photogenerated carriers and high activation energy barrier of H remain persistent challenge. Here, the two-step hydrothermal method is utilized to prepare dual S-defect mediated catalyst molybdenum sulfide/zinc indium sulfide (MSv/ZISv), which has high hydrogen production rate of 8.83 mmol g-1h-1 under simulated sunlight. The achieved rate is 21.91 times higher than pure ZnIn2S4 substrate. Defects in ZIS within MSv/ZISv modify the primitive electronic structure by creating defect state that retaining good reducing power, leading to the rapid separation of electron-hole pairs and the generation of additional photogenerated carriers. The internal electric field further enhances the migration toward to cocatalyst. Simultaneously, the defects introduced on the MoS2 cause electron rearrangement, leading to electron clustering on both S vacancies and edge S. Thereby MSv/ZISv exhibits the lowest activation energy barrier and |ΔGH*|. This work explores the division of synergies between different types of S defects, providing new insights into the coupling of defect engineering.

Hydrogen-Bonded Organic Framework Derived 2D N, O Co-Doped Carbon Nanobelt with Tunable Pseudocapacitive Contribution for Efficient Capacitive Deionization.

Defect engineering is recognized as an attractive method for modulating the electronic structure and physicochemical characteristics of carbon materials. Exploiting heteroatom-doped porous carbon with copious active sites has attracted great attention for capacitive deionization (CDI). However, traditional methods often rely on the utilization of additional heteroatom sources and strong corrosive activators, suffering from low doping efficiency, insufficient doping level, and potential biotoxicity. Herein, hydrogen-bonded organic frameworks (HOFs) are employed as precursors to synthesize N, O co-doped porous carbon via a simple and green reverse defect engineering strategy, achieving controllable heavy doping of heteroatoms. The N, O co-doping triggers significant pseudocapacitive contribution and the surface pore structure supports the formation of the electric double layer. Therefore, when HOF-derived N, O co-doped carbon is used as CDI electrodes, a superior salt adsorption capacity of 32.29 ± 1.42 mg g-1 and an outstanding maximum salt adsorption rate of 10.58 ± 0.46 mg g-1 min-1 at 1.6 V in 500 mg L-1 NaCl solution are achieved, which are comparable to those of state-of-the-art carbonaceous electrodes. This work exemplifies the effectiveness of the reverse nitrogen-heavy doping strategy on improving the carbon structure, shedding light on the further development of rational designed electrode materials for CDI.