Generation Of Vacancies Research Articles

Investigation of Nonmetal F‐doped Co3O4 as Catalyst for N2O Catalytic Decomposition

AbstractAn effective nonmetal F‐doped Co3O4 (F‐Co3O4) catalyst was prepared using co‐precipitation method, and its catalytic performance was investigated for N2O decomposition comparing with pure Co3O4 catalyst. The catalytic activity test indicates that F‐Co3O4 catalyst exhibits better activity with 100% N2O conversion at a reaction temperature of 380 °C, which is 80 °C lower than that of pure Co3O4. The characterization results show that F is successfully doped into the lattice of Co3O4 and replaces part of O sites, which enlarges the surface area, enhances the surface basicity, and leads to higher basic sites density on the surface of Co3O4. Moreover, F doping promotes the electron donation capacity of Co2+, weakening of Co─O bond and generation of more oxygen vacancies. The synergy of the above factors results in reduction of activation energy over F‐Co3O4 catalyst, thus F‐Co3O4 catalyst exhibits better catalytic performance than pure Co3O4 for N2O decomposition, even in the existence of O2 or H2O as impurity gas. Meanwhile, F‐Co3O4 catalyst also exhibits better stability than pure Co3O4. This work will provide practical reference for constructing efficient nonmetal‐doped Co3O4 catalysts for N2O decomposition.

Synchronous inverse valence modulation of Ni3+/Co2+ over metal/metal-oxide heterojunction catalyst to promote hydrodeoxygenation performance of lignin derivatives

The proper design of catalyst structure is crucial for highly selective hydrodeoxygenation. Here, a strategy of in-situ topological transformation was proposed to prepare a MOF/LDH composite self-sacrificial template mediated by NiCo-MOF template, and a metal-monomer/metal-oxide composite heterojunction catalyst was synthesized. The result indicated that the formation of Ni3+ species on the surface of t-NiCo-60 catalyst was generated through this unique structural transformation, which promoted the charge movement between Ni-Co and caused more Co2+ to be formed, and this simultaneous reverse valence modulation between Ni3+/Co2+ facilitated the generation of oxygen vacancies, which improved the hydrogen heterocleavage activation on the catalyst and enabled the t-NiCo-60 catalyst to remove oxygen-containing groups from lignin derivatives with high selectivity. Achieved complete conversion of lignin derivatives in a short duration of time and highly selective generation of the target products (92.5% selectivity for cyclohexanol and 99.9% selectivity for 2-methoxy-4-methylphenol). This research provides a new approach for the efficient upgrading of lignin derivatives.

Transparent Zinc Oxide Memristor Structures: Magnetron Sputtering of Thin Films, Resistive Switching Investigation, and Crossbar Array Fabrication

This paper presents the results of experimental studies of the influence of high-frequency magnetron sputtering power on the structural and electrophysical properties of nanocrystalline ZnO films. It is shown that at a magnetron sputtering power of 75 W in an argon atmosphere at room temperature, ZnO films have a relatively smooth surface and a uniform nanocrystalline structure. Based on the results obtained, the formation and study of resistive switching of transparent ITO/ZnO/ITO memristor structures as well as a crossbar array based on them were performed. It is demonstrated that memristor structures based on ZnO films obtained at a magnetron sputtering power of 75 W exhibit stable resistive switching for 1000 cycles between high resistance states (HRS = 537.4 ± 26.7 Ω) and low resistance states (LRS = 291.4 ± 38.5 Ω), while the resistance ratio in HRS/LRS is ~1.8. On the basis of the experimental findings, we carried out mathematical modeling of the resistive switching of this structure, and it demonstrated that the regions with an increase in the electric field strength along the edge of the upper electrode become the main sources of oxygen vacancy generation in ZnO film. A crossbar array of 16 transparent ITO/ZnO/ITO memristor structures was also fabricated, demonstrating 20,000 resistive switching cycles between LRS = 13.8 ± 1.4 kΩ and HRS = 34.8 ± 2.6 kΩ for all devices, with a resistance ratio of HRS/LRS of ~2.5. The obtained results can be used in the development of technological processes for the manufacturing of transparent memristor crossbars for neuromorphic structures of machine vision, robotics, and artificial intelligence systems.

Electronically regulated Mn-N site-loaded MXenes for highly efficient and selective singlet oxygen generation via PMS activation

In this study, a novel catalyst featuring dual-reactive sites of transition metal and nonmetal is presented, which modifies electronic polarization to enhance the selective generation of singlet oxygen (1O2), resulting in effective degradation of antibiotics. Using MXenes as a substrate, a structurally stable Mn-N@MXenes catalyst with controllable reactive sites was synthesized via a hydrothermal method by adjusting the content of the Mn-N precursor. The study revealed that the loading of Mn-N active sites changes the electronic structure and polarization of MXenes, resulting in asymmetric electronic structures and the generation of numerous oxygen vacancies. These characteristics enable the Mn-N@MXenes/PMS system to selectively generate 1O2 and superoxide radicals (O2∙-), with a synergistic index of 5.77. Compared to the MXenes/PMS system, the Mn-N@MXenes/PMS system significantly boosts the degradation efficiency of ofloxacin (OFL) from 71.32% to 96.07% under optimal conditions. The results demonstrate that during PMS activation, the catalyst maintains a nearly constant degradation rate after four cycles, exhibiting excellent stability and recyclability. Furthermore, the system shows superior performance and environmental adaptability in degrading actual water matrices and other pollutants. This study reveals electronic regulation mechanisms in catalyst design that facilitate pollutant degradation via both radical and non-radical pathways, offering new strategies for efficient degradation.

Insights into the relationship between regulation of oxygen vacancy and singlet oxygen generation in peracetic acid activation

Peracetic acid (PAA) has shown good potential in advanced oxidation techniques, but the mechanism regulating the generation of non-radical species in peracetic acid has not been clarified. Herein, Ov-Co3O4/C-x was prepared by pyrolysis of ZIF-L precursors at different temperatures to achieve the regulation of oxygen vacancy concentration and used for the degradation of sulfamethazine (SMT) by activated PAA. When x = 350 °C, the prepared Ov-Co3O4/C-350 with the highest oxygen vacancy content had the highest SMT removal efficiency and the highest rate constant(kobs), which degraded SMT by 99.6 % within 30 min. The role of oxygen vacancies(OVs) on the surface of Ov-Co3O4/C-350 was investigated using quenching experiments, Electron Paramagnetic Resonance (EPR) and X-ray Photoelectron Spectroscopy (XPS) techniques. The results showed that oxygen vacancy on the metal oxide surface can be converted into more reactive oxygen(O*), and surface OVs of Ov-Co3O4/C-350 enable efficient capture of PAA, thus generating 1O2 and R-O•. The higher the content of oxygen vacancies is, the more 1O2 is produced, while concentration of R-O• was not significantly correlated with oxygen vacancy content. Furthermore, the degradation pathway of SMT was predicted through density functional theory (DFT) calculations and identifications of intermediates, indicating that electron-rich sites such as aromatic rings and S-N bonds in the SMT molecule are more easily oxidized by reactive species. Besides, due to the low biotoxicity of the degradation products of the Ov-Co3O4/C-350/PAA system, the reaction can effectively reduce the biotoxicity and developmental toxicity. This study provides a controllable surface property strategy for a new idea in PAA-based AOP.

Oxygen reservoir effect of Tungsten trioxide electrode on endurance performance of ferroelectric capacitors for FeRAM applications

The effect of W and WO3 electrodes on the ferroelectric characteristics of HZO (Zr-doped HfO2)-based MFM (metal-ferroelectric-metal) capacitors was investigated. During the deposition of tungsten, the W electrode was formed using only Ar gas, while the WO3 electrode was formed using a mixture of Ar and O2 gases. The W-based MFM capacitors exhibited superior remnant polarization (2Pr of 107.9 µC/cm2 at 700 oC) compared to the WO3-based capacitors; however, their endurance performance was degraded. In contrast, the WO3-based capacitors showed endurance performance enhanced by three orders of magnitude due to the oxygen-rich reservoir effect. The oxygen introduced during the deposition of WO3 prevented the oxygen scavenging effect of tungsten. Consequently, excessive generation of oxygen vacancies in the HZO layer was suppressed, resulting in improved endurance performance. These results were quantitatively confirmed through TEM, XPS, and XRD analyses.

Layer-to-tunnel manganese oxides transformation triggered by pyrogenic carbon and trace metals: Key role of reducing and oxidizing components cooperation

Manganese oxide (MnOx) plays crucial roles in shaping various environmental and geochemistry processes, with their reactivity largely dependent on the structure of MnOx. Tunnel MnOx effectively hosts a substantial quantity of soil elements within its tunnel structure, exerting significant control over element turnover and pertinent geochemical processes, while the precise determinants regarding the layer-to-tunnel transformation of MnOx with electron transfer remain unclear. In this study, we delved into the transformation of layer-structured MnOx during the interaction with coexisting soil redox components (pyrogenic carbon and Tl with differing redox reactivity). Our findings revealed that the transformation from layer to tunnel structure only occurred in the presence of reductive pyrogenic carbon and oxidative Tl(III) rather than sole reductants/oxidants within a short incubation period of 6 weeks. The macro reducing environment created by the pyrogenic carbon and the micro oxidizing environment related to the Tl(III) chelation was pivotal in the cyclic valence change of Mn, resulting in the generation of Mn(III) and vacancies in the Mn structure, the prerequisite for the layer-to-tunnel transformation. Anchoring of oxidative Tl(III) on the surface or inside the tunnel structure of MnOx through Tl–O–Mn bonding was the key to building a micro oxidative environment under bulk-reducing conditions. During the transformation, Tl was integrated into the tunnel of high-crystallinity MnOx, and prolonged incubation resulted in the deeper embedding of Tl and the formation of atomic clusters. The embedding of Tl inside of the tunnel MnOx led to lower solubility and bioaccessibility, with only 0.05–0.26 mg Kg−1 being extracted with soil organic acids through reductive dissolution and 8.7–8.9 % by in vitro physiologically based extraction test. This study underscores the significant role of electron-donating and electron-accepting components in triggering interconnected geochemical processes with MnOx, carbon, and trace elements.

Low‐Intensity Ultrasound‐Activated Cavitation Effect Triggers Piezoelectric Catalysis Coordinating Respiratory Chain Interference Tactics Against Bacterial Infection

AbstractPiezocatalytic therapy has aroused considerable attention in the treatment of bacterial infection due to its noninvasive and deep tissue penetration capabilities. The catalytic efficiency, however, is significantly constrained by the insufficient piezoresponse of sonosensitizers at low‐intensity ultrasound (LIU) accompanied poor separation efficiency of charges, resulting in unsatisfactory sterilization. To address the dilemma, a piezocatalytic bio‐heterojunction (P‐bioHJ) consisting of BiOI and few‐layered Mxene is constructed for rapid antibacterial. The engineered P‐bioHJ not merely possesses a relatively narrow‐bandgap for responding to the sonoluminescence emitted by the sonocavitation effect, but rather induces the interfacial polarization and the generation of oxygen vacancies to facilitate the effective separation of carriers, leading to a burst of radicals for rapid sterilization. Transcriptomic analysis reveals that P‐bioHJ instigates sterilization by interfering with bacterial electron transport chain, disrupting both metabolism and energy synthesis. In vitro experiments indicate excellent cytocompatibility of P‐bioHJ. Furthermore, in vivo assays demonstrate that P‐bioHJ exhibits outstanding antimicrobial properties in a cutaneous infection model with LIU, and promotes angiogenesis and osteogenesis in an infectious bone defect model by decorating with naringin. As envisaged, this work offers valuable insight to augment piezocatalytic therapy by harnessing sonocavitation effect, advancing the remediation of infected tissue regeneration.

Construction of a MoOx/MoS2 Heterojunction via the Surface Sulfurization of the Oxide and Its Photocurrent-Switching Characteristics in the Range of the Broadband Light Spectrum.

In order to utilize the longer wavelength light, the surface sulfurization of MoO3 was carried out. The photocurrent responses to typical 650, 808, 980, and 1064 nm light sources with Au gap electrodes were investigated. The results showed that the surface S-O exchange of MoO3 improved the interfacial charge transfer in the range of the broadband light spectrum. The S and O can be exchanged on the surface of MoO3 nanosheets under the hydrothermal condition, leading to the formation of a surface MoOx/MoS2 heterojunction. The interfacial interaction between the MoO3 nanosheets and MoS2 easily generated free electrons and holes, and it effectively avoided the recombination of photogenerated carriers. Meanwhile, the surface S-doping of MoO3 also resulted in the generation of an oxygen vacancy and sulfur vacancy on MoO3-xS2-y. The plasmonic characteristics of MoO3-x contributed to the enhancement of the interfacial charge transfer by photoexcitation. Otherwise, even with zero bias applied, a good photoelectric signal was still obtained with polyimide film substrates and carbon electrodes. This indicates that the formation of the heterojunction generates a strong built-in electric field that drives the photogenerated carrier transport, which can be self-powered. This study provides a simple and low-cost method for the surface functionalization of some metal oxides with a wide bandgap.

Mixed atomic-scale electronic configuration as a strategy to avoid cocatalyst utilization in photocatalysis by high-entropy oxides

To enhance the activity of photocatalysts for hydrogen production and CO2 conversion, noble metal cocatalysts as electron traps and/or acceptors such as platinum or gold are usually utilized. This study hypothesizes that mixing elements with heterogeneous electronic configurations and diverse electronegativities can provide both acceptor and donor sites of electrons to avoid using cocatalysts. This hypothesis was examined in high-entropy oxides (HEOs), which show high flexibility for atomic-scale compositional changes by keeping their single- or dual-phase structure. A new high-entropy oxide was designed and synthesized by mixing elements with an empty d orbital (titanium, zirconium, niobium and tantalum) and a fully occupied d orbital (gallium). The oxide, synthesized by high-pressure torsion followed by calcination, had two phases (88 wt% orthorhombic (Pbcn) and 12 wt% monoclinic (I2/m)) with an overall composition of TiZrNbTaGaO10.5. It exhibited UV and visible light absorbance with a low bandgap of 2.5 eV, low radiative electron-hole recombination and oxygen vacancy generation due to mixed valences of cations. It successfully acted as a photocatalyst for CO and CH4 production from CO2 conversion and hydrogen production from water splitting without cocatalyst addition. These findings confirm that introducing heterogeneous electronic configurations and electronegativities can be considered as a design criterion to avoid the need to use cocatalysts.

Uv-activated Ni ions as electron donors for in-situ generation of tunable oxygen vacancies on the surface of Bi2O2CO3 with improving photocatalytic activity for sulfadiazine degradation

In this study, a simple UV-mediated method for creating oxygen vacancies in Bi2O2CO3 is explored. Traditional methods have drawbacks like stringent conditions and difficulty in control. Here, Ni ions embedded in the layers of Bi2O2CO3 act as electron donors, generating oxygen vacancies in situ at room temperature and atmospheric pressure without additional reducing agents. Characterization via ESR, XPS, and other techniques shows a positive correlation between oxygen vacancy concentration and UV irradiation duration. The mechanism of in situ generation under Ni ion doping and UV irradiation is discussed. Additionally, the ability of BOC/Ni-X (Bi2O2CO3 with X minutes of irradiation) catalysts to degrade sulfadiazine under visible light is investigated. Results indicate that controlling irradiation time allows fabrication of Bi2O2CO3 with suitable band gaps, enhancing its ability to degrade sulfadiazine. The initial Bi2O2CO3 material could only remove 5 % of sulfadiazine after 60 min of degradation, while the best modified material with 50 min of light exposure had a removal rate of 90 % for sulfadiazine. This study offers a new approach for constructing oxygen vacancies in metal oxide nanomaterials at room temperature and atmospheric pressure.

Functional design and understanding of effective additives for achieving high-quality perovskite films and passivating surface defects

Achieving high-quality perovskite films without surface defects is regarded as a crucial target for the development of durable high-performance perovskite solar cells. Additive engineering is commonly employed to simultaneously control the growth of perovskite crystals and passivate defects. Here, 4-(trifluoromethyl)benzoic anhydride (4-TBA) composed of benzene rings functionalized with carbonyl and trifluoromethyl groups was used as an example additive to study the characteristics of additives used for producing high-quality perovskites and controlling their surface properties. The interaction between 4-TBA and perovskite precursor materials was investigated using density functional theory (DFT) simulations. The electron-rich carbonyl group efficiently passivated the under-coordinated lead-ion defects. Additionally, hydrogen bonding between trifluoromethyl and organic cations prevents the generation of cation vacancies. Because of its intrinsic hydrophobicity, the trifluoromethyl group simultaneously improves the moisture and heat stability of the film. 4-TBA serves as a universal modifier for various perovskite compositions. The power conversion efficiency (PCE) of inverted perovskite solar cells (PSCs) based on methylammonium (MA) with 4-TBA was improved from 16.15% to 19.28%. Similarly, the PCE of inverted PSCs based on a cesium formamidinium MA (CsFAMA) perovskite film increased from 20.72% to 23.58%, upon addition of 4-TBA. Furthermore, the moisture and thermal stability of 4-TBA-treated films and devices was significantly enhanced, along with prolonged device performance. Our work provides guidance on selecting the structure and functional groups that are essential for surface defect passivation and the production of high-quality perovskites.

Rapid charge transfer via anion bridge strategy for enhanced deep photocatalytic NO oxidation

Surface defect engineering and interfacial heterojunction construction can provide a promising strategy to achieving efficient reactant molecular activation and rapid charge transfer. However, traditional surface defect and interfacial heterojunction could often suffer from the potential space barrier, sluggish electron transfer, and weak reactant adsorption/activation, resulting in unsatisfactory pollutant removal effect. Herein, the anions (WO42−) bridged AgBr/Bi4O5Br2 heterojunction, involves the in situ growth of AgBr onto Bi4O5Br2 with the generation of bromine vacancies (BVs), is designed and synthesized by using a chemical deposition method. By establishing an electron-bridge into the interface of AgBr and Bi4O5Br2, a rapid charge carrier transfer channel is created, efficiently promoting the transport of photogenerated electrons from AgBr to Bi4O5Br2. Importantly, these spatially separated electrons of AgBr-WO42−-Bi4O5Br2 are captured by the active sites (BVs) in Bi4O5Br2to promote reactant activation, resulting in highly stable photocatalytic NO removal (67.7 %) and efficient inhibition of toxic NO2 formation (417.9 ppb → 30.6 ppb). The effective removal of NO2 by other anions, such as PO43-, demonstrates the broad applicability of this approach. This work introduces a synergistic mechanism of electron bridge, built-in electric field and vacancy engineering to create rapid charge carrier transfer channel and molecular activation strategy in designing highly efficient photocatalysts for deep photocatalytic NO oxidation.

Revealing the essence of anion ligands in regulating amorphous MnOx to activate peracetic acid for micropollutant removal

How the anion ligands of manganese precursors affect the catalytic activity of amorphous manganese oxides (MnOx) in Fenton-like process is poorly understood. Here, five amorphous MnOx synthesized by Mn(II) precursors with different ligands were characterized and adopted to activate peracetic acid (PAA) for bisphenol A (BPA) degradation. Although > 90 % BPA removal was achieved in the five MnOx/PAA processes via both adsorption and oxidation, the oxidation kobs greatly differentiates by the ligands types with the order of MnOx-N > MnOx-S > MnOx-Cl > MnOx-AA > MnOx-OA. Ligands types would affect the specific surface area of MnOx and their ability to adsorb BPA, however which is not the decisive factor in determining the contaminant oxidation efficiency. Multiple experimental results indicate that the generation of oxygen vacancies induced by the ligands alters the Mn(III)/Mn(IV) ratio, ultimately contributing to the different efficiency of BPA oxidation driven by the direct electron transfer mechanism. Moreover, amorphous MnOx holds the promise of practical applications in catalytic PAA of various micropollutants with good stability. This study advances the fundamental understanding of ligand-regulated amorphous MnOx-catalyzed PAA process.

Correction to: Synergistic enhancement of electrochemical performance in reversible solid oxide cells via deficiency-induced oxygen vacancy and nanoparticle generation

Correction to: Synergistic enhancement of electrochemical performance in reversible solid oxide cells via deficiency-induced oxygen vacancy and nanoparticle generation

Spectroscopic Analysis of Electrical Phenomena and Oxygen Vacancy Generation for Self-Aligned Fully Solution-Processed Oxide Thin-Film Transistors.

This work unveils critical insights through spectroscopic analysis highlighting electrical phenomena and oxygen vacancy generation in self-aligned fully solution-processed oxide thin-film transistors (TFTs). Ar inductively coupled plasma treatment was conducted to fabricate an amorphous indium zinc oxide (a-InZnO) TFT in a self-aligned process. Results showed that the Ar plasma-activated a-InZnO regions became conductive, which means that a homogeneous layer can act as both channel and electrode in the device. Several techniques were employed to probe specific aspects of the source-drain-channel interface in the fully solution-processed TFTs. X-ray absorption near-edge structure and Extended X-ray absorption fine structure were conducted to investigate the existence of oxygen vacancies, which is the main driving factor in inducing a conductive region. X-ray photoelectron spectroscopy was also used to explain the oxygen refilling mechanism. Ultraviolet Photoelectron Spectroscopy was conducted to analyze the valence band maximum and work function. Integration of these results facilitated the construction of the energy band diagram at the interface, wherein a Schottky barrier height of ∼0.37 eV was observed. By leveraging these techniques, insights into the electronic properties and performance of next-generation transistors are gained, enabling their future widespread adoption.

Rate theory coupling multi-phase-field simulation for neutron irradiation nanophase and vacancy evolution

Radiation damage is a critical problem for the alloys serving under irradiation circumstances where the numerous defects is induced by the cascade collision of radiation particles, the microstructure and mechanical properties will be damaged by the irradiation. By combination of rate theory (RT) and multi-phase-field (MPF) model, the influences of neutron irradiation dose rate (DR) and irradiation temperature are studied on the radiation-enhanced precipitation, vacancies and interstitial atoms in Fe-35Cr-10Al (at%) alloy. The RT coupled with phase-field simulations capture the radiation induced nanoscale precipitates, clustering of vacancies and interstitial atoms. With the increase of DR, the diffusion of solute atoms is accelerated for the generation of vacancies and interstitial atoms, and the growth and coarsening rate of α′ phase is quickened. The DR affects the distribution of elements between α/α′ phases, high DR promotes the Fe and Al to partition into α phase, Cr into α′ phase in the formation of α′ phase. Therefore, in the steady-state coarsening stage, the high DR leads to the α′ phase to reach the equilibrium composition earlier. As the increase of neutron irradiation temperature, the separation and coarsening rate of α′ phase are accelerated. The simulation morphology and quantitative characteristics are consistent with the experimental results. The coupling of RT and MPF simulation in alloys with point defects and nanophase under neutron irradiation put forward the study tactics and theory understanding for radiation-enhanced multiple microstructure evolutions.

Na-doped cobalt spinel electrocatalysts prepared by programmed electrostatic spraying for improving OER activity and durability in acidic media

The daunting challenge to establish a trade-off among the activity, durability, and cost of electrocatalysts for oxygen evolution reaction (OER) with sluggish reaction kinetics impedes the practical green energy conversion. Hereby, a non-noble metal-based electrocatalyst (i.e., Na-doped Co3O4) was in-situ prepared by programmed electrostatic spraying as an advanced alternative to the costly and scarce state-of-the-art IrO2 and RuO2-based electrocatalysts. The utilization of this sprayer facilitates intimate contact with the substrate electrode and provides short ion diffusion paths, facilitating efficient electron transport. Additionally, the doping of Na ions into the Co3O4 structure results in structural distortion and charge redistribution, leading to the generation of oxygen vacancies (OVs). These OVs enhance the activity of lattice oxygen atoms, thus enabling rapid and durable oxygen evolution in an acidic media (0.5 M H2SO4). The optimal Na-Co3O4 (AA) exhibits a notably low overpotential of 360 mV@10 mA·cm−2 and at least 200 h stability. In addition, density functional theory (DFT) calculations confirm that the incorporation of Na ions significantly elevates electrical conductivity by decreasing the energy band gap and reduces the free energy barrier for the conversion of *O to *OOH, thereby improving the intrinsic OER activity. Finally, by implanting the catalyst in a single-cell proton exchange membrane water electrolyzer (PEMWE), the current density of 100 mA·cm−2 is achieved at a voltage of 1.62 V. This innovative non-noble metal catalyst holds great potential for scalable PEMWE anodes.

Electronic interaction between d electron-poor and d electron-rich transition metal ions promoted the CO2 capture performance of calcium-based adsorbent

The investigation of intrinsic principles for the more precise design CaO adsorbent with excellent CO2 capture performance by doping metal oxides is of great significance, but has not yet been explored. Herein, we address the critical challenge by systematical evaluation on a series of magnetic bimetallic oxides doped calcium-based adsorbents from the perspective of electronic interaction between d electron-poor and d electron-rich transition metal ions promoting the CO2 capture performance. The Mn, Co, Mo and Ni metal ions with varied d-electron numbers are doped into calcium-based adsorbent, and the results show that the introduction of magnetic bimetallic oxides with d electron-poor and d electron-rich transition metal ions into CaO at the same time can significantly promote the stability of CO2 capture. Taking the (Mn-Co)-codoped samples as an example, the relationship of d electron-poor and d electron-rich transition metal ions synergistic interaction and promoted CO2 adsorption performance is elucidated. The loose flake nanostructures favor the diffusion of CO2 inside the particles, and the uniform distribution of each component effectively ensures the double-exchange interactions. The generation of more oxygen vacancies significantly improves the CO2 affinity for the calcium-based sample. Furthermore, the results of kinetic analysis reveal that the synergistic interaction can reduce the apparent activation energy of carbonation reaction. These insights into the systematical regulation of the double-exchange interaction are expected to provide guidance for the relatively more precise design of the calcium-based adsorbent with high performance of CO2 adsorption.

Piezoelectric photocatalytic degradation of formaldehyde based on BFO@OCN heterojunctions

Piezoelectric photocatalysts represent a new class of environment-cleaning materials containing a self-electricity nanogenerator. Wind is one of the common energy sources in the natural environment. The piezoelectric field generated by the action of wind on piezoelectric materials can promote the adsorption of organic pollutants and also facilitate the transfer and separation of photogenerated carriers, thereby improving the efficiency of photocatalytic degradation of formaldehyde. This work developed a BFO@OCN heterojunction composite combing BiFeO3 nanocubes (BFO) and g-C3N4 nanosheets with oxygen vacancies (OCN). This piezoelectric photocatalyst exhibited high activity in degradation of formaldehyde in gas under light irradiation. Within 90 min, the formaldehyde concentration reduced from 1.50 ppm to 0.68 ppm, almost 2 times higher than the pure CN. This enhanced catalytic performance can be attributed to the synergistic interplay between the wind-induced piezoelectric field generated by BFO nanocubes in wind and the heterojunction with oxygen vacancies from g-C3N4 nanosheets. The piezoelectric field promoted the transfer of photoelectrons and holes in opposite directions, which could inhibit their recombination. Meanwhile, it also induced the generation of oxygen vacancies from g-C3N4 nanosheets. Our research findings provided a feasible strategy for developing high-efficiency piezoelectric photocatalysts, which could be decorated on the car outer-surface for self-cleaning and air purification under sunlight irradiation.