Large Vacancy Research Articles

Effect of Calcination Temperature in Large-Aperture Medium-Entropy Oxide (FeCoCuZnNa)O on CO2 Hydrogenation for Light Olefins

The catalytic hydrogenation of carbon dioxide is not only a way to mitigate the greenhouse effect but also provides high-value chemicals. In this work, a medium-entropy oxide catalyst (FeCoCuZnNa)O was prepared by the sol–gel method for highly active and selective hydrogenation of CO2 to value-added hydrocarbons. When reacted at 290 °C, 2.5 MPa, and 2500 mL·gcat−1·h−1, the CO2 conversion and selectivity of olefin were affected by the calcination temperature of the catalyst, and the best performances were 39% and 41.3%. The large pore size and oxygen vacancies (Ov) formed by (FeCoCuZnNa)O promote the activation of CO2 and promote the C-C coupling reaction of Fe5C2 in a hydrogenation reaction. The promoted C-C coupling reaction was related to the surface enrichment of iron species. The presence of Ov also inhibited the excessive hydrogenation reaction, further improving the selectivity of light olefins. In addition, (FeCoCuZnNa)O did not show significant deactivation within 75 h, indicating that the catalyst has strong industrial potential.

Recent Advances in Barium Cobaltite-Based Perovskite Oxides as Cathodes for Intermediate-Temperature Solid Oxide Fuel Cells.

Solid oxide fuel cells (SOFCs) are considered as advanced energy conversion technologies due to the high efficiency, fuel flexibility, and all-solid structure. Nevertheless, their widespread applications are strongly hindered by the high operational temperatures, limited material selection choices, inferior long-term stability, and relatively high costs. Therefore, reducing operational temperatures of SOFCs to intermediate-temperature (IT, 500-800°C) range can remarkably promote the practical applications by enabling the use of low-cost materials and enhancing the cell stability. Nevertheless, the conventional cathodes for high-temperature SOFCs display inferior electrocatalytic activity for oxygen reduction reaction (ORR) at reduced temperatures. Barium cobaltite (BaCoO3-δ)-based perovskite oxides are regarded as promising cathodes for IT-SOFCs because of the high free lattice volume and large oxygen vacancy content. However, BaCoO3-δ-based perovskite oxides suffer from poor structural stability, inferior thermal compatibility, and insufficient ionic conductivity. Herein, an in-time review about the recent advances in BaCoO3-δ-based cathodes for IT-SOFCs is presented by emphasizing the material design strategies including functional/selectively doping, deficiency control, and (nano)composite construction to enhance the ORR activity/durability and thermal compatibility. Finally, the currently existed challenges and future research trends are presented. This review will provide valuable insights for the development of BaCoO3-δ-based electrocatalysts for various energy conversion/storage technologies.

The CeO2 morphology modulates the density and catalytic performance of dual-active site for enhancing the palmitic acid conversion

Designing active sites with multi-function to meet the complicated reaction is a challenge task. Herein, we find that morphology of cerium oxide (CeO2) shows strong influence on the density and catalytic reactivity of dual-active site formed on it. Nanorods CeO2 (CeO2-NR) has large specific surface area and abundant oxygen vacancy (Ov), making small size of Ni (below 2 nm) highly disperse on it. However, 39.7 nm Ni poorly distributes on CeO2 composed of irregularly stacked particles (CeO2-NP), displaying much smaller specific surface area and fewer Ov compared with those on CeO2-NR. Small size Ni and abundant Ov show better abilities in activation of H2 and palmitic acid, respectively. Moreover, abundant Ov and highly dispersed Ni increase their intimacy on CeO2-NR. These make Ni/CeO2-NR catalyst has high density of Ni-Ov dual-active site, showing better synergetic catalytic performance for conversion of palmitic acid into alkanes than that on Ni/CeO2-NP.

MOF-derived high-entropy oxides (YTbDyErYb)2O3 for boosted non-contact physiological humidity monitoring induced by oxygen vacancy modulation

In recent years, high-entropy oxides (HEOs) have gained significant attention due to their unique structure, yet the usage of HEOs in gas/humidity sensing is still a vast expanse of land worthy of vigorous cultivation. Here, HEOs were designed via high-entropy metal-organic frameworks (HE-MOFs) as sacrificial templates and then calcined at different temperatures to obtain (YTbDyErYb)2O3 (named as HEO-600, HEO-700 and HEO-800). After material characterization, as-synthesized HEOs were explored as humidity sensing materials for the first time at a relative humidity (RH) range of 11%-97%. The HEO-700 sensor exhibits the optimized properties featured in a response of three orders of magnitude (2.8 × 103) and extremely short response time (2 s). The excellent humidity sensing performance of HEO-700 can be attributed to the large surface area (39.6 m2/g) and abundant oxygen vacancies (53.1%). In addition, the HEO-700 sensor demonstrates great potential in real-time human physiological moisture detection, such as finger, breath, and non-contact switch. It is believed that this contribution provides attracting humidity sensing candidate for practical applications, and moreover, will provide inspiration for design of new HEOs in this emerging field of solid-state sensory devices.

Ternary electrochemiluminescence biosensor based on Ce2Sn2O7@MSN luminophore and Au@NiO-CeO2 as a co-reaction accelerator for the detection of prostate specific antigen

A ternary ECL system was constructed with Ce2Sn2O7@MSN composite as luminophore, potassium persulfate as co-reactant and Au@NiO-CeO2 as co-reaction accelerator to realize ultra-sensitive biosensing detection of prostate specific antigen (PSA). The abundant oxygen vacancies in Ce2Sn2O7 endow it with powerful electrochemical redox ability, accelerate energy transfer, and ensure Ce2Sn2O7 excellent electrochemical luminescence performance as a luminophore. Furthermore, to optimize the luminescence energy, enhance stability, and reduce the background signal to improve its signal-to-noise ratio, a highly selective Ce2Sn2O7@MSN biological probe was obtained by coating cerium stannate (Ce2Sn2O7) with mesoporous silica nanospheres (MSN). Au@NiO-CeO2 with a large specific surface area and high oxygen vacancy activity was synthesized as the co-reaction accelerator, which promoted the generation of SO4•− through the rapid reversible oxidation and reduction of Ce4+/Ce3+, thereby the ECL signal amplified effectively. Under optimal conditions, the linear detection range of PSA spans from 100fg mL−1 to 100 ng mL−1, with a remarkable lowest detection limit of 0.037pg mL−1, showcasing significant application potential. This study provides a valuable reference for pyrochlore to be used as luminophore in the detection of various biomarkers by ECL biosensing.

Enhancement of electrochemical stability by molecular cation vacancies of the electrode material CH3NH3NiCl3 for lithium-ion batteries

At present, efforts are being made to find new low-cost materials for photovoltaic, optoelectronic and energy storage applications. In this regard, compounds of the halide perovskite type have been increasingly studied over the past few years. The incorporation of small cations in these compounds and their possible use in rechargeable batteries can be achieved by the electrochemical reversibility technique, where perovskites with large cations are used to obtain a new isostructural compound with smaller cations and large interstitial space or free vacancies for ionic transport. The present work studied the electrochemical reversibility of lithium-ion into CH3NH3NiCl3 (MANiCl3) active material, after the formation of MA+ vacancies or interstitial spaces, taking both experimental and theoretical approaches. The material displayed an anodic behavior and an initial capacity of discharge of ca. 170 mAhg−1 at 0.2C (0.1 mA), a full capacity retention up to the first 25 cycles of charge–discharge, and even reached a retention of up to 80 % of initial capacity at the 80th cycle. First-principles density functional theory calculations show that the shape of the crystal lattice and volume changes of all the different phases involved in the electrochemical process are tiny, at about 3 Å3 per cell. In addition, there are no appreciable elastic contributions to the energy variation during the de-lithiation/lithiation process, indicating that memory effects are not an issue. The calculated formation energies of the lithiated structures and the open circuit voltages are −2.91 eV and 1.33 V for LinMA1-nNiCl3 and −1.41 eV and 2.91 V for Li2nMA1-nNiCl3, respectively. These findings suggest that incorporating one or, at most, to two lithium atoms is favorable for the overall stability and electrochemical performance.

Bubble-induced self-assembly synthesis of defective hierarchical boehmite with ultra-high removal efficiency towards Congo red: Preparation and adsorption mechanism

To cope with the increasingly urgent environmental issue and provide promising alternative adsorbents, the synergistic preparation route of dissolution and bubble-induced self-assembly was firstly exploited to guide the reconstruction process of a defective hierarchical porous boehmite-microspheres (BMS) adsorbent in a favorable direction to improve the CR adsorption capacity using aluminium hydroxide industrial waste as raw materials. Multiple non-in-situ physicochemical characterization instruments demonstrate that BMS-4 adsorbent possesses abundant coordinatively unsaturated Al–species, large specific surface area, high porosity, oxygen vacancies and oxygen-containing groups, which promote the maximum adsorption capacities for CR up to 6805.08 ± 5.4 mg g−1. Moreover, the Pseudo-second order model and the Langmuir model are more suitable for describing the behavior of CR adsorption, which proves it is more inclined to be monolayer adsorption and there is no chemical reaction between CR and adsorbent. More importantly, it can be practiced in eight cycles of adsorption tests, achieving ultra-high stability for over 94.46 % of the original adsorption capacity. Combined with density-functional theory (DFT) calculations and experimental results, it is illustrated that the amino protonation is responsible for the additional enhancement of CR adsorption, in addition, oxygen vacancy capture and BMS-4/CR–SO3+–NH3 mechanism for enhanced adsorption of dyes is proposed, both of which show that bubble-induced self-assembly provides a promising route for the preparation of high-performance adsorbents.

Oxygen vacancy migration and impact on high voltage DC polarization in 0.8BaTiO3–0.2BiZn0.5Ti0.5O3

AbstractElectrical polarization and defect transport are examined in 0.8BaTiO3–0.2BiZn0.5Ti0.5O3, an attractive capacitor material for high power electronics. Oxygen vacancies are suggested to be the majority charge carrier at or below 250°C with a grain conduction hopping activation energy of 0.97 eV and 0.92 eV for thermally stimulated depolarization current (TSDC) and impedance spectroscopy measurements, respectively. At higher temperature, thermally generated electronic conduction with an activation energy of 1.6 eV is dominant. Significant oxygen vacancy concentration is indicated (up to ∼1%) due to cation vacancy formation (i.e., acceptor defects) from observed Bi (and likely Zn) volatility. Oxygen vacancy diffusivity is estimated to be 10−12.8 cm2/s at 250°C. Low diffusivity and high activation energies are indicative of significant defect interactions. Dipolar oxygen vacancy defects are also indicated, with an activation energy of 0.59 eV from TSDC measurements. The large oxygen vacancy content leads to a short lifetime during high voltage (30 kV/cm), high temperature (250°C) direct current (DC) electrical measurements.

Preparation of Heterogeneous Fenton Catalysts Cu-Doped MnO2 for Enhanced Degradation of Dyes in Wastewater.

Herein, a series of heterogeneous Fenton catalysts, Cu doped MnO2 (CDM), with different Cu/Mn molar ratios were prepared via a hydrothermal reaction. Meanwhile, detailed characterizations were used to study the structures of CDM, and it is amazing that the morphology of CDM changed from nanowires to nanoflowers with an increasing amount of Cu doped. Apart from this, both the specific surface area and oxygen vacancy increased obviously with the increasing Cu/Mn molar ratio. Then, the degradation of different dyes was utilized to evaluate the catalytic activity of different CDM with H2O2 used as the oxidizing agent, and the 50%-CDM with the highest content of Cu doped displayed the best catalytic activity. Herein, the degradation efficiency (D%) of Congo red (CR) solution with low concentration (60 mg/L) reached 100% in 3 min, while the D% of CR solution with a high concentration (300 mg/L) reached 99.4% after 5 min with a higher dosage of H2O2. Additionally, the 50%-CDM also displayed excellent reusability, for which the D% values were still higher than 90% after the 14th cycles. Based on the structure characteristics and mechanism analysis, the excellent catalytic capacity of 50%-CDM was due to the combined influence of large specific surface area and abundant oxygen vacancy. Thus, a promising heterogeneous Fenton catalyst was developed in this study, which proved the treatment efficiency of actual dye wastewater.

Machine-Learning driven STM images prediction of doped/defective graphene: Towards optimized tools for 2D nanomaterials characterization

Scanning tunneling microscopy (STM) is a key characterization technique that allows for visualization of specific features at nanostructures, given its ability to reveal changes in local charge densities in doping or defective sites. Besides the experimental acquisition of STM data from real samples, there is the theoretical route, which allows for STM images simulation from ab-initio calculations on defined nanostructures. This work presents an alternative route for theoretical STM image prediction by means of Machine Learning (ML) methods, based on the training of deep convolutional neural networks using simulated STM data. The ML-based STM predictions for defective, B- and N-doped graphene quantum dots are compared to ab-initio STM simulations, in terms of accuracy of structural rearrangements, charge density localizations, and computational resources requirements. The results demonstrate that STM images predicted by ML-methods are accurate at doping sites, whereas they show good similarity to simulations of large structural vacancies. This work represents a novel alternative for the use of ML methods in image-based characterization routines of doped/defective graphene, and potentially, for other 2-dimensional nanomaterials.

Influence of the distance of a collisional cascade to an edge dipole in [formula omitted]-Fe on dislocation mobility and defect production

In this work we studied the effects of 20 keV collision cascades in alpha iron with a 1/2〈111〉{110} edge dipole using molecular dynamics. We analysed three different cases: a) the primary knock-on atom (PKA) is centred between both dislocations, b) the PKA is closer to one of the dislocations, and c) the PKA is on top of one of the dislocations and directed towards it. Our calculations show enhanced formation of vacancy clusters in the bulk for intermediate distances due to the absorption of self-interstitials by the dislocation during the collision cascade reducing the recombination between vacancies and self-interstitials. This effect results in the formation of jogs at the dislocation and the consequent climb due to the absorption of the self-interstitials. As a result, there is an unbalance between vacancies and self-interstitials produced by the collision cascade, with a significantly larger number of vacancies than self-interstitials in the bulk and the formation of large vacancy clusters. When the collision cascade develops directly on top of the dislocation, jogs are formed due to both the absorption of vacancies and self-interstitials, inducing climb and with the total dislocation length increasing up to several nanometers.

Hybrid density functional theory simulation of sodium impurity and impurity–vacancy defect complexes in germanium: perspectives of defect engineering for activation of shallow donors

At present, germanium (Ge) as a high-mobility material is considered as a possible replacement for Si in microelectronics. The main obstacle in the method is the large vacancy concentration obtained after the implantation of shallow donors. This prevents the formation of n+ regions and has a negative impact on device performance. One way to eliminate the detrimental effects of such defects is through the codoping approach. In this study, the behavior of Na impurities in germanium together with the formation of defect complexes with vacancies, divacancies and shallow donors (P and As) were investigated using hybrid density functional theory calculations. The site preference, diffusion barriers, charge states and binding energies of various complexes, as well as the activation of donor–vacancy complexes with both F and Na codoping were investigated. For this purpose, two extreme cases were considered. Firstly, we calculate the concentrations of substitutional and interstitial Na together with monovacancies in the case of quasi-equilibrium conditions realized for doping from melt. Another extreme case is Na codoping during ion implantation. Our calculations show that Na passivates vacancies, divacancies and donor–vacancy complexes (E-centers) with a large energy gain, which prevents rapid donor diffusion similar to the case of doping with fluorine. We have shown that the passivation of E-centers with both F and Na impurities leads to the back transformation of such complexes into shallow donors. This means that codoping with Na may neutralize the harmful effects of vacancies and is a perspective for defect engineering.

Waste cigarette butts-templated synthesis of in-situ graphitic carbon-doped ZnO fibers boosting dual-selectivity NO2/butanone at different temperatures

How to build a dual-selective ZnO-based gas sensor remains challenging due to the fact that the great majority of reported gas sensors were designed to monitor only a single given harmful gas. Herein, discarded cigarette butts were chose as template, and dipped in zinc nitrate solution. Then, the obtained precursors were calcined to synthesize two types of ZnO-based fibers with V-shaped grooves. Among, the fiber component (GC/ZnO, GC being graphitic carbon) calcined at 400 °C composes of 7.02 wt% GC and small nanoparticles, which possesses multistage mesopores, large specific surface area and abundant oxygen vacancies. These factors not only optimize the percentage and state of oxygen species adsorbed in sensing layer, but also expose more active sites and facilitate surface chemical reactions, thereby providing a dual-selective platform for different gases. The GC/ZnO sensor shows high response of 624 for 10 ppm NO2 at 92 °C, and good response of 22.5 for 100 ppm butanone at 170 °C. Also, it has reversible response-recovery, low detection limit, as well as satisfactory stability and humidity resistance. This is the first report on a conductometric sensor that achieves the rapid and accurate detection of above harmful gases. In addition, its temperature-controlled dual-functional sensing mechanism was also analyzed.

Efficient electroreduction of carbon dioxide to formate enabled by bismuth nanosheets enriched dual [formula omitted] vacancy

The electrocatalytic reduction of carbon dioxide (CO2ER) into formate presents a compelling solution for mitigating dependence on fossil energy and green utilization of CO2. Bismuth (Bi) has been gaining recognition as a promising catalyst material for the CO2ER to formate. The performance of Bi catalysts (named as Bi-V) can be significantly improved when they possess single metal atom vacancy. However, creating larger-sized metal atom vacancies within Bi catalysts remains a significant challenge. In this work, Bi nanosheets with dual VBi0 vacancy (Bi-DV) were synthesized utilizing in situ electrochemical transformation, using BiOBr nanosheets with triple vacancy associates (VBi″′VO··VBi″′, VBi″′ and VO·· denote the Bi3+ and O2− vacancy, respectively) as a template. The obtained Bi-DV achieved higher CO2ER activity than Bi-V, showing Faradaic efficiency for formate production of >92% from -0.9 to -1.2 VRHE in an H-type cell, and the partial current density of formate reached up to 755 mA/cm2 in a flow cell. The comprehensive characterizations coupled with density functional theory calculations demonstrate that the dual VBi0 vacancy on the surface of Bi-DV expedite the reaction kinetics toward CO2ER, by reducing the thermodynamic barrier of *OCHO intermediate formation. This research provides critical insights into the potential of large atom vacancies to enhance electrocatalysis performance.

Ultra-stable aqueous nickel-ion storage achieved by iron-ion pre-introduction assisted hydrated vanadium oxide cathode

Aqueous Nickel-ion batteries (ANIBs) are attracting growing attention for next-generation energy storage devices, but their development is hindered by deficient satisfactory cathode materials and undefined reaction mechanisms. Herein, a novel layered vanadium oxide with Fe3+-ions pillars (Fe0.29V2O5·0.57H2O, FVO) is developed and innovatively used for effective Ni2+ ion storage. The large interlayer spacing and abundant oxide vacancies of FVO can provide broad ion migration channels and rich ion storage sites. The pre-intercalated Fe3+-ions can firmly support the integrity of the layered structure by Fe-O bonds to achieve excellent cycle stability. RGO is further introduced to construct the FVO@G composite can improve the conductivity and stability of the FVO electrode. As a result, the FVO@G electrode exhibits exceptional Ni2+ storage performance of 169.8 mAh g−1 at 0.5C and ultrahigh capacity retention of 91.9% after 320 cycles at 10C. The Ni2+ storage mechanism in FVO@G is clarified by in-situ XRD and ex-situ Raman, ex-situ XPS techniques, the results show that FVO@G undergoes a phase transition accompanied by an expansion of the interlayer spacing upon the first charging, and the electrodes display a high degree of structural reversibility and a negligible volume expansion during the subsequent cycles. Furthermore, density functional theory (DFT) calculations show that FVO provides efficient diffusion paths along the b-axis with ultrafast transport kinetics. This work is a significant step in ANIBs research and provides valuable insights for the design of high-performance ANIBs cathode material.

Magnetically separable and visible light-driven photocatalytic activity of graphene oxide based α-Fe2O3 nanocomposite

This work investigates the impact of graphene oxide (GO) on the structural, morphological, optical, and photocatalytic investigations of Fe2O3, an excellent photocatalyst for industrial wastewater treatment. Using the straightforward and inexpensive sol-gel auto-combustion, hummer's method and sonication method, Fe2O3 nanoparticle (NPs), GO nanosheet, and GO-based Fe2O3 (GO/Fe2O3) nanocomposite have been synthesized, respectively. The XRD patterns, Raman spectra, and FTIR spectroscopy were used for the structural analysis, which verifies the single phase hexagonal geometry of Fe2O3 NPs. The average size of the crystallites is seen to have reduced from 50 nm to 44 nm for Fe2O3 and GO/Fe2O3. The SEM along with EDS were applied to investigate the surface morphology and confirm the existence of the elements Fe and O in pure Fe2O3, and C, Fe and O in GO/Fe2O3. From UV–vis absorbance spectra, the decrease in optical band gap (2.5 eV–1.9 eV) caused by GO incorporation has been inferred, as clearly displayed in the Tauc plots. X-ray photoelectron spectroscopy (XPS) confirms the presence of Fe2+/Fe+3 ionic states and large oxygen vacancies in the GO/Fe2O3 nanocomposite. The photocatalytic properties of both materials for the toxic MB (methylene blue) dye photodegradation in an aqueous solution was evaluated while being exposed to sunlight. It makes an excellent choice for wastewater treatment due to the high photocatalytic activity of magnetically separable GO/Fe2O3 nanocomposite for decomposing the MB dye.

Steering in-situ low-voltage phase transition from spinel to layered cathode for high-performance zinc-ion batteries

ZnV2O4, as a ternary transition metal oxides (TOMs), has garnered significant attention as a high-performance cathode for zinc-ion batteries (ZIBs) primarily due to its high theoretical capacity and abundance. However, its densely-packed lattice structure and strong coulomb interactions with the guest Zn2+ severely restrict the exposure of active sites and impede the diffusion kinetics. Herein, we propose an innovative in-situ low-voltage phase transition strategy and successfully trigger thorough phase transition of spinel-structured ZnV2O4 to layered-structured Zn3(OH)2V2O7⋅2H2O (ZnVOHNSs). In-depth mechanism analysis reveals that a thorough and efficient transition reaction necessitates meticulous control of the external driving force, reaction kinetics, and the reactant. The activated ZnVOHNSs with large lattice spacing and abundant oxygen vacancies provides an unobstructed pathway for accelerated ion diffusion and abundant exposed active sites for ions storage. Moreover, the inherent structure stability of ZnVOHNSs ensures exceptional reaction stability and reversibility during the Zn2+ intercalation/deintercalation process. Benefiting from these merits, the activated ZnVOHNSs cathode exhibits high reversible capacity and extraordinary rate capability (achieving 369 and 233 mAh g−1 at 0.1 and 20 A g−1, respectively), which exceeds most reported cathode materials in ZIBs. This work unveils the critical phase transition mechanism and offers insight into electrode design for advanced batteries.

Towards understanding the mechanism of titanium suppressing vacancy clustering/void nucleation in vanadium alloy

The energetics and dynamics of vacancy/vacancyn (Vacn) clusters in presence of Ti in vanadium alloy were systemically investigated by first-principles calculations to elucidate the mechanism of Ti suppressing vacancy clustering/void nucleation. Energetically, Ti can reduce vacancy formation energy and stabilize vacancy/Vacn cluster, and the TimVacn clusters are more stable than alone Vacn over 30 % with m, n = 5, corresponding to the smaller saturated size. Kinetically, mono-/di-vacancy diffusion and vacancy clustering near Ti are predicted by the CI-NEB methods and empirical formula. Vacancy diffusing towards Ti shows a lower barrier of 0.04 eV than 0.39 eV in vanadium and the energy barriers of vacancy migrating towards Ti-Vac complexes decrease gradually and are even close to zero during vacancy clustering. The migration barriers of vacancy dissociating from Ti-Vac complexes are relatively higher, and Ti changes the migration mechanism of di-vacancy from one-step to two-step. Ti significantly reduces vacancy effective diffusivity, and the effective diffusivity decreases with Ti concentration. The present results show that Ti additions provide more nucleation sites of vacancies, forming large numbers of stable small-size complexes and hindering vacancy diffusion, and eventually suppress the formation and growth of large vacancy clusters/voids.

In-situ sodium chloride template synthesis of γ-WO3 hollow cubes for high-sensing and dual-selective hydrazine/dibutylamine detection at different temperatures

The fabrication of a chemiresistive sensor with dual-selectivity to highly toxic and explosive N2H4/dibutylamine (DBA) remains challenging due to no report. To this aim, we synthesized uniform (NH4)0.33WO3 cuboid precursors through optimized solvothermal reaction and in-situ formed NaCl template. Subsequently, the precursors were calcined in air to transform into γ-WO3 hollow cubes (WO3-HC) assembled from near-spherical nanoparticles, and the effect of calcination temperature on microstructures and gas-sensing properties was investigated. Among, WO3-HC-5 obtained by calcining precursor at 500 °C has broad pore channels, large specific surface area and abundant oxygen vacancy defects. Under the catalytic synergy of surface W6+ Lewis acid with dangling bonds, WO3-HC-5 sensor realizes the bifunctional monitoring of N2H4 and DBA. It presents large response value (S = 606.6) to 100 ppm N2H4 at 50 °C and a good response (S = 76.7) to the same concentration of DBA at 217 °C, and has fast response rate, low practical detection limit, satisfactory stability and humidity resistance. WO3-HC-5 represents the first metal oxide-based sensor with dual-selectivity towards aforementioned harmful gases at different operating temperatures. Moreover, the bifunctional mechanism has been characterized and analyzed in detail.

High-Pressure Torsion for Highly-Strained and High-Entropy Photocatalysts

Nowadays, the environmental crisis caused by using fossil fuels and CO2 emissions has become a universal concern in people’s life. Photocatalysis is a promising clean technology to produce hydrogen fuel, convert harmful components such as CO2, and degrade pollutants like dyes in water. There are various strategies to improve the efficiency of photocatalysis so that it can be used instead of conventional methods; however, the low efficiency of the process has remained a big drawback. In recent years, high-pressure torsion (HPT), as a severe plastic deformation (SPD) method, has shown extremely high potential as an effective strategy to improve the activity of conventional photocatalysts and synthesize new and highly efficient photocatalysts. This method can successfully improve the activity by increasing the light absorbance, narrowing the bandgap, aligning the band structure, decreasing the electron-hole recombination, and accelerating the electron-hole separation by introducing large lattice strain, oxygen vacancies, nitrogen vacancies, high-pressure phases, heterojunctions, and high-entropy ceramics. This study reviews the recent findings on the improvement of the efficiency of photocatalysts by HPT processing and discusses the parameters that lead to these improvements.