Pristine Counterpart Research Articles

Engineering Multifunctionality in MoSe2 Nanostructures Via Strategic Mn Doping for Electrochemical Energy Storage and Photosensing

To achieve advanced functionalities in nanostructured MoSe2 for enhanced electrochemical charge storage and improved photosensing, here we propose an effective strategy, i.e., the substitutional doping of the heteroatom Mn. We achieve a 313% increase in specific capacitance for 6.2% of Mn doping compared to pristine MoSe2 at the scan rate of 5 mV/s in a three-electrode configuration. For a two-electrode arrangement, also superior charge-storage performance is noted. The enhanced electrode performance can be attributed to the increase of electrical conductivity arising due to an increase of electron density for the n-type nature of Mn doping realized via an X-ray photoelectron spectroscopy study and density functional theory calculation. The latter one also unveils that Mn doping introduces catalytically active sites by disrupting homogeneous charge distribution over the topology of the MoSe2 basal plane contributing to better charge-storage performance. Mn doping-induced shift in the Fermi level of MoSe2 toward the conduction band also minimizes the contact barrier height signifying its improved capabilities for a photosensor device. Additionally, Mn doping causes alleviation of the charge-recombination process resulting in increase of photocarrier separation. As a result, we observe a 187% enhancement in the photocurrent and significantly higher responsivity and detectivity for 6.2% Mn-doped MoSe2 than its pristine counterpart. Our proposed doping strategy to modulate charge storage as well as photoresponse properties demonstrates high potential for MoSe2 along with other two-dimensional transition-metal dichalcogenides in developing next-generation energy-storage and optoelectronic devices.

Silver Nanoparticle-Decorated Defective Zr-Based Metal–Organic Frameworks for Efficient Electrocatalytic Carbon Dioxide Reduction with Ultrahigh Mass Activity

Electrochemical reduction is considered to be a fascinating strategy to alleviate CO2 accumulation by converting it into value-added products. In this work, we used silver nanoparticle (Ag NP)-incorporated defective, thiol-functionalized UiO-66 metal–organic frameworks (MOFs) as a catalyst for the electrocatalytic conversion of CO2 to CO. We used a de novo defect engineering technique, coordination modulation, for defect incorporation as well as the functionalization of the MOF, where the introduced thiol moieties act as anchoring sites for the Ag NPs. Ag@UiO-66-SH catalyzed the CO2 reduction reaction to form CO with a Faradaic efficiency (FE) of 74% and a partial current density of 19.5 mA cm–2 at −1.1 V vs a reversible hydrogen electrode. This material showed remarkable catalytic stability, retaining the FE for CO without any significant loss in reduction current over 10 h and an excellent mass-specific activity of 218 A g–1. Density functional theory calculations further establish the enhanced catalytic CO2 reduction reaction (CO2RR) activity of Ag@UiO-66-SH compared to their pristine counterparts based on free energy calculations. This study demonstrates the use of metal NP–MOF composite materials with very less metal loading as an effective catalyst for CO2RR to CO.

Enhanced hydrogen generation via overall water splitting using novel MoS2-BN nanoflowers assembled TiO2 ternary heterostructures

Envisaging headway in the applicability of sustainable H2 energy, the novel report of the fabrication of MoS2-BN/TiO2 (MBT) heterogeneous nanostructures has been proposed via facile in-situ hydrothermal route with an aim to propound the superior substitute of noble metal based conventionally employed catalytic system to surmount their exorbitant cost. We inferred the ascendancy of MoS2-BN nanoflowers over pristine MoS2 counterpart in an establishment of TiO2 based heterostructured catalysis. MBT heterostrucutres were extensively scrutinized with respect to their structural, optoelectronic and computational characteristics. En route to enhanced H2 evolution, we have investigated the significance of interfacial junctions and exposed sites in the MBT heterostructures. In order to achieve broader pertinence in green H2 fuel, the performance of MBT heterostrucutres was ascertained with subject to photochemical, electrochemical and photo-electrochemical (PEC) water splitting. Loaded concentration of MoS2-BN was varied in MBT catalysts and 2.5 wt% MoS2-BN/TiO2 exhibited optimum photocatalytic response with an H2 production rate of 2.6 mmol/g/h with 6.94% AQY and improved photo-current response of 0.99 mA/cm2 towards PEC. Electrochemical investigations further intensified the caliber of MBT as HER catalyst ascribed to the higher cathodic current density of 49.23 mA/cm2 at 1.22 V potential. The advancement in the catalytic efficiency of MBT heterostructures was evidenced by the synergetic relationship between MoS2-BN and TiO2 which stimulated the separation and transfer of photo-charged carriers, and lowered the overpotential values consequently surging the kinetics of H2 evolution.

Ambient temperature NO2 removal by reversible NO2 adsorption on copper-based metal-organic frameworks (MOFs)-derived nanoporous adsorbents

Nitrogen dioxide (NO2) is a potent atmospheric pollutant generated from fossil fuel combustion at power plants, industrial plants, and vehicles, which raises serious health concerns (e.g., respiratory diseases) and contributes to severe environmental pollution issues (e.g., acid rain and ground-level ozone). Adsorption is an efficient approach for ambient temperature NO2 removal, whose efficiency highly depends on the design of the adsorbents. The widely reported activated carbon adsorbents suffer from low and typically irreversible NO2 capacity apart from co-generation of considerable amounts of polluting NO (up to 50% of adsorbed NO2), which is released back into the atmosphere. Herein we report copper-based metal–organic framework (MOF)-derived carbon materials (i.e., Cu@C(CuBTC) and Cu@C(CuBDC)) featuring high NO2 capacity coupled with minimal release of NO and outstanding reusability for NO2 removal under ambient temperature. Both Cu@C(CuBTC) and Cu@C(CuBDC) showed an impressive improvement (up to 13.5 times) in NO2 capacity over their pristine MOFs counterparts, with Cu@C(CuBTC) showing the highest NO2 capacity (4.97 mmol/g) and minimal (<20 % of adsorbed NO2) release of NO in this study. Such a massive improvement in the NO2 capacity of carbonized composites is attributed to highly active and homogenously dispersed Cu nanoclusters, which serve as adsorption sites and play the dominant role in NO2 removal. Further, for the first time, Cu@C(CuBTC) exhibited outstanding reusability for NO2 removal under humid conditions, reflected by stable NO2 capacity in the cyclic adsorption tests (5 cycles), suggesting a great potential for real-world applications. This study provides a general and facile strategy for designing highly dispersed, water-resistant, and stable copper nanoclusters on carbon support for efficient adsorptive removal of various toxic gases under ambient temperature.

Exploring the Sub-nanoscale Structure of Cobalt Molybdenum Sulfide and the Role of a Cobalt Promoter in Catalytic Hydrogen Evolution.

Cobalt-promoted molybdenum sulfide (CoMoS) is known as a promising catalyst for H2 evolution reaction and hydrogen desulfurization reaction. This material exhibits superior catalytic activity as compared to its pristine molybdenum sulfide counterpart. However, revealing the actual structure of cobalt-promoted molybdenum sulfide as well as the plausible contribution of a cobalt promoter is still challenging, especially when the material has an amorphous nature. Herein, we report, for the first time, on the use of positron annihilation spectroscopy (PAS), being a nondestructive nuclear radiation-based method, to visualize the position of a Co promoter within the structure of MoS at the atomic scale, which is inaccessible by conventional characterization tools. It is found that at low concentrations, a Co atom occupies preferably the Mo-vacancies, thus generating the ternary phase CoMoS whose structure is composed of a Co-S-Mo building block. Increasing the Co concentration, e.g., a Co/Mo molar ratio of higher than 1.12/1, leads to the occupation of both Mo-vacancies and S-vacancies by Co. In this case, secondary phases such as MoS and CoS are also produced together with the CoMoS one. Combining the PAS and electrochemical analyses, we highlight the important contribution of a Co promoter to enhancing the catalytic H2 evolution activity. Having more Co promoter in the Mo-vacancies promotes the H2 evolution rate, whereas having Co in the S-vacancies causes a drop in H2 evolution ability. Furthermore, the occupation of Co to the S-vacancies leads also to the destabilization of the CoMoS catalyst, resulting in a rapid degradation of catalytic activity.

Effect of oxidation on mechanical properties of copper nanowire: A ReaxFF (reactive force field) molecular dynamics study

Nanostructures with high surface area to volume ratio, such as oxidized and coated Cu nanowires (NWs), exhibit unique mechanical properties due to their size and surface effects. Understanding the complex oxidation process of Cu NWs at nanoscale and quantifying its resulting effects on mechanical behavior and properties are significantly essential for effective usage of Cu NW devices in a wide range of applications in nanoelectronics. Here, we perform molecular dynamics simulations using ReaxFF (reactive force field) to investigate the oxidation process and mechanisms of [001]-oriented cylindrical Cu NWs and its contribution on the mechanical deformation behavior and material properties as a function of NW sizes. The relatively thin oxide CuxOy layer is formed on the surface of Cu NWs in an O2 environment, creating a core/shell (Cu/CuxOy) NW structure that played a key role in governing the overall tensile mechanical deformation behavior and properties of Cu NW. The formation of oxide layer effects, including the resulting interface and defects, leads to a reduction in the initial dislocation nucleation barrier, which facilitates the onset of plasticity and stress relaxation, ultimately resulting in a negative impact on the tensile strength, Young's modulus, yield stress and strain, and flow stress when compared to pristine counterparts. It is worth noting that the tensile mechanical response and properties of the Cu NWs are highly dependent on the pre-existing oxide shell layer associated with the size of NW, determining the overall mechanical performance and properties of Cu NWs.

The impacts of dust aerosol and convective available potential energy on precipitation vertical structure in southeastern China as seen from multisource observations

Abstract. The potential impacts of dust aerosols and atmospheric convective available potential energy (CAPE) on the vertical development of precipitating clouds in southeastern China (20–30∘ N, 110–125∘ E) in June, July, and August from 2000 to 2013 were studied using multisource observations. In southeastern China, heavy-dust conditions are coupled with strong northerly winds that transport air masses containing high concentrations of mineral dust particles, with cold temperatures, and with strong wind shear. This leads to weaker CAPE on dusty days compared with that on pristine days. Based on satellite observations, precipitating drops under dusty conditions grow faster in the middle atmospheric layers (with a temperature of between −5 and +2 ∘C) but slower in the upper and lower layers compared with their pristine counterparts. For a given precipitation top height (PTH), the precipitation rate under dusty conditions is lower in the upper layer but higher in the middle and lower layers. Moreover, the associated latent heating rate released by precipitation in the middle layer is higher. The precipitation top temperature (PTT) shows a fairly good linear relationship with the near-surface rain rate (NSRR): the linear regression slope between the PTT and NSRR is stable under dusty and pristine conditions. However, the PTT0 (the PTT related to rain onset) at the onset of precipitation is highly affected by both the CAPE and aerosol conditions. On pristine days, a stronger CAPE facilitates the vertical development of precipitation and leads to a decrease in PTT0, at a rate of −0.65 ∘C per 100 J kg−1 of CAPE for deep convective precipitation (with a variation of 15 %) and at a rate of −0.41 ∘C per 100 J kg−1 of CAPE for stratiform precipitation (with variation of 12 %). After removing the impacts of CAPE on PTT, dust aerosols led to an increase in PTT0, at a rate of +4.19 ∘C per unit aerosol optical depth (AOD) for deep convective precipitation and at a rate of +0.35 ∘C per unit AOD for stratiform precipitation. This study showed clear evidence that meteorological conditions and aerosol conditions combine to impact the vertical development of precipitation clouds. A quantitative estimation of the sensitivity of PTT to CAPE and dust was also provided.

Facet tailoring and Cu doping promoted photo-assisted peroxymonosulfate activation by oxygen-deficient α-MnO2 for efficient mineralization of bisphenol a

Revealing the synergistic mechanism between facets and metal doping during catalytic processes is an efficient approach to improve the catalytic performance. Herein, the synergetic effects between Cu doping and crystal facets over α-MnO2 on the peroxymonosulfate (PMS) activation towards bisphenol A (BPA) degradation under full-spectrum light irradiation were studied in details for the first time. The Cu-doped α-MnO2 with (100), (110), and (310) facets were synthesized by hydrothermal method. The Cu-doped (110)/PMS/Light system presented the highest BPA removal efficiency with high 1O2 generation and selectivity, being superior over the Cu-doped (100), Cu-doped (310) and pristine (110) counterparts. The corresponding mechanism showed that Cu doping for α-MnO2 enhanced the absorption of light, the formation of oxygen vacancies and electronic conductivity as well as PMS activation, especially for the (110) facet, as compared to the (100) and (310) facets. In addition, density functional theory (DFT) calculations and characterizations indicated that the synergetic effect between facet and oxygen vacancies played an important role in 1O2 generation. Moreover, oxygen vacancies accelerated the complexation of PMS with surface Mn(IV) and improved the generation of 1O2, different to that due to Mn(III). Toxicity assessment showed that BPA was partially decomposed into highly toxic intermediates during the degradation process. However, Cu doping and light synergistically improved the mineralization rate of pollutants, removing 95% of the total organic carbon (TOC) and reducing the toxicity of the intermediates. The ultrahigh TOC removal was attributed to the joint effect of 1O2, O2− and electron transfer. This work therefore provides an efficient and highly selective PMS catalyst for 1O2 generation, and reveals the synergistic mechanism between metal doping and crystal facets of the catalyst in advanced oxidation processes.

Reprocessable and Chemically Recyclable Hard Vitrimers Based on Liquid-Crystalline Epoxides.

The rapid increase in demand for recyclable and reusable thermosets has necessitated the development of materials with chemical structures that exhibit these features. Thus, functional mesogenic epoxide monomers bearing both ester and imine groups that can be vitrimerized and recycled are reported herein. The compounds show mesophase characteristics at 100-200°C and can be converted into hard epoxides by a common curing reaction. The obtained hard epoxides have high isotropic thermal conductivity (≈0.64 W m-1 K-1 ), which is derived from their highly ordered microstructures. The cured products can be easily reprocessed through imine metathesis and transesterification, and decomposed products can be obtained through imine hydrolysis under acidic or basic conditions and subsequently be re-cured. Surprisingly, recycled materials can be repeatedly reprocessed or chemically decomposed. The reprocessed materials retain the properties of their pristine counterparts, and the recycled products preserve the advantages of the hard thermosets without alteration to any of their unique properties. A dehydration reaction occurs between the residual hydroxyl groups during the re-hardening, which dramatically increases the glass transition temperature by ≈60°C. These reprocessable and recyclable vitrimers demonstrate the effectiveness and environmental friendliness of the molecular design strategy reported herein.

Efficient Solar Light Photocatalyst Made of Ag3PO4 Coated TiO2-SiO2 Microspheres.

Solar light active photocatalyst was prepared as silver phosphate (Ag3PO4) coating on titania-silica (TiO2-SiO2) microspheres. Titania-silica microsphere was obtained by spray drying TiO2-SiO2 colloidal solutions, whereas Ag3PO4 was applied by wet impregnation. XRD on the granules and SEM analysis show that the silver phosphate particles cover the surface of the titania-silica microspheres, and UV-visible diffuse reflectance analysis highlights that Ag3PO4/TiO2-SiO2 composites can absorb the entire visible light spectrum. BET measurements show higher specific surface area of the composite samples compared to bare Ag3PO4. Photocatalytic activity was evaluated by dye degradation tests under solar light irradiation. The prepared catalysts follow a pseudo-first-order rate law for dye degradation tests under solar light irradiation. The composite catalysts with an Ag3PO4/TiO2-SiO2 ratio of 1:1.6 wt% show better catalytic activity towards both rhodamine B and methylene blue degradation and compared with the results with uncoated TiO2-SiO2 microspheres and the benchmark commercial TiO2 (Evonik-P25) as a reference. The composite photocatalyst showed exceptional efficiency compared to its pristine counterparts and reference material. This is explained as having a higher surface area with optimum light absorption capacity.

Thermoelectric enhancement of p-type Si 80Ge 20 alloy via co-compositing of dual oxides: Respective regulation for power factor and thermal conductivity by β-Ga 2O 3 and SiO 2 aerogel powders

Si-based thermoelectric (TE) materials are exhibiting remarkable perspectives in self-energized applications with their special advantages. However, the relatively high total thermal conductivity (<i>κ</i>) prevents their TE enhancement. Here, a strategy of co-compositing dual oxides was implemented for enhancing the TE properties of p-type Si₈₀Ge₂₀ bulks. Composited Ga₂O₃ was demonstrated to enhance the power factor (<i>PF</i>) due to the crystallization-induced effect of produced Ga by decomposition on SiGe matrix. Associating with compositing SiO₂ aerogel (a-SiO₂) powder, not only introduced the fine amorphous inclusions and decreased the grain size of host matrix, but also various nano morphologies were formed, i.e., nano inclusions, precipitations, twin boundaries (TBs), and faults. Combining with the eutectic Ge, hierarchical scattering centers impeded the phonon transport comprehensively (decreasing the phonon group velocity (<inline-formula> <math display="inline" id="MA1"><mrow><msub><mi>v</mi><mtext>a</mtext></msub></mrow></math></inline-formula>) and relaxation time) for reducing the lattice-induced thermal conductivity (<inline-formula> <math display="inline" id="MA2"><mrow><msub><mi>κ</mi><mtext>l</mtext></msub><mo stretchy="false">)</mo></mrow></math></inline-formula>. As a result, a minimum <inline-formula> <math display="inline" id="MA3"><mi>κ</mi></math></inline-formula> of 2.38 W·m⁻¹·K⁻¹ was achieved, which is significantly dropped by 32.6% in contrast with that of the pristine counterpart. Ultimately, a maximal dimensionless figure of merit (<i>ZT</i>) of 0.9 was achieved at 600 ℃, which is better than those of most corresponding oxide-composited Si-based bulks.

A BiVO4Photoanode with a VOxLayer Bearing Oxygen Vacancies Offers Improved Charge Transfer and Oxygen Evolution Kinetics in Photoelectrochemical Water Splitting

AbstractSluggish oxygen evolution kinetics are one of the key limitations of bismuth vanadate (BiVO4) photoanodes for efficient photoelectrochemical (PEC) water splitting. To address this issue, we report a vanadium oxide (VOx) with enriched oxygen vacancies conformally grown on BiVO4photoanodes by a simple photo‐assisted electrodeposition process. The optimized BiVO4/VOxphotoanode exhibits a photocurrent density of 6.29 mA cm−2at 1.23 V versus the reversible hydrogen electrode under AM 1.5 G illumination, which is ca. 385 % as high as that of its pristine counterpart. A high charge‐transfer efficiency of 96 % is achieved and stable PEC water splitting is realized, with a photocurrent retention rate of 88.3 % upon 40 h of testing. The excellent PEC performance is attributed to the presence of oxygen vacancies in VOxthat forms undercoordinated sites, which strengthen the adsorption of water molecules onto the active sites and promote charge transfer during the oxygen evolution reaction. This work demonstrates the potential of vanadium‐based catalysts for PEC water oxidation.

A BiVO4 Photoanode with a VOx Layer Bearing Oxygen Vacancies Offers Improved Charge Transfer and Oxygen Evolution Kinetics in Photoelectrochemical Water Splitting.

Sluggish oxygen evolution kinetics are one of the key limitations of bismuth vanadate (BiVO4 ) photoanodes for efficient photoelectrochemical (PEC) water splitting. To address this issue, we report a vanadium oxide (VOx ) with enriched oxygen vacancies conformally grown on BiVO4 photoanodes by a simple photo-assisted electrodeposition process. The optimized BiVO4 /VOx photoanode exhibits a photocurrent density of 6.29 mA cm-2 at 1.23 V versus the reversible hydrogen electrode under AM 1.5 G illumination, which is ca. 385 % as high as that of its pristine counterpart. A high charge-transfer efficiency of 96 % is achieved and stable PEC water splitting is realized, with a photocurrent retention rate of 88.3 % upon 40 h of testing. The excellent PEC performance is attributed to the presence of oxygen vacancies in VOx that forms undercoordinated sites, which strengthen the adsorption of water molecules onto the active sites and promote charge transfer during the oxygen evolution reaction. This work demonstrates the potential of vanadium-based catalysts for PEC water oxidation.

Bandgap and defects regulation of La2−xAxNi1−yByO4+δ (A = K, Sr, B = Co, Mn) Ruddlesden-Popper type perovskites for efficient photocatalytic hydrogen evolution

The doping of certain exotic metal ions in photocatalysts may produce surface defects (such as oxygen vacancies) as well as bandgap changes, which may play an important role for their photocatalytic performance. In this work, bandgap modulation by precise control of defect concentration and transition metal oxidation state mainly owning to A-site doping and the B-site cations were achieved for the Ruddlesden-Popper structure (La2NiO4). The effects of K+, Sr2+, Co2+, Mn2+ single-mental doping and co-doping on the photocatalytic activity of La2NiO4 photocatalysts were investigated. It was found that the co-doping samples had a significant synergistic effect on the optical properties and photocatalytic activity of La2NiO4 photocatalysts. All the single-metal-doped La2NiO4 photocatalysts exhibited higher photocatalytic activity than their pristine counterpart. Moreover, the Sr2+, Co2+ co-doped La2NiO4 exhibited the best optical properties, photocatalytic activity and a the hydrogen production rate of La1.9Sr0.1Ni0.8Co0.2O4+δ more than 29 times of pure La2NiO4, has been achieved. Further analysis indicates that the surface oxygen vacancies as active sites promote efficient separation and migration of photogenerated carriers. The co-doped photocatalyst not only has a narrower bandgap, but also owns a more favorable conduction band position for photoinduced electron reduction. Overall, this work provides a simple method for introducing oxygen defects and bandgap modulation in Ruddlesden-Popper structure through metal ion doping. It is also expected to enlarge the understanding of the structure-dependence of the photocatalytic performance of perovskite materials.

Interfacial Solid-State Mediator-Based Z-Scheme Heterojunction TiO2@Ti3C2/MgIn2S4 Microflower for Efficient Photocatalytic Pharmaceutical Micropollutant Degradation and Hydrogen Generation: Stability, Kinetics, and Mechanistic Insights

Interface engineering is a vital concern to achieve high efficiency in heterojunction photocatalysts. The judicious design of efficient interfacial electron mediators to accelerate the charge transfer efficiency in Z-scheme heterojunctions with interfacial contact for enhancing the performance of photocatalysts is essential and has been considered an immense challenge. Inspired by nature, multivariate all-solid-state Z-scheme TiO2@Ti3C2/MIS heterojunction composites were fabricated via a simple two-step oxidation strategy for highly promoted multiple photocatalytic applications. The morphological analysis of TiO2@Ti3C2/MIS composites demonstrated that MgIn2S4 (MIS) microflowers were accumulated on the surface of Ti3C2@TiO2 nanosheets, providing dense active sites to the MIS microflowers for efficient photocatalytic applications. The HRTEM and XPS characterization distinctly clarified the close interfacial interaction between MIS with Ti3C2 and TiO2. The optimized TiO2@Ti3C2/MIS-15 photocatalysts exhibited the highest photocatalytic ciprofloxacin degradation (92%) and hydrogen evolution (520.3 μmol h–1) as compared to those of their pristine counterparts. From the mechanistic insights, the charge migration pathway was observed between MIS and TiO2, where Ti3C2 nanosheets served as an electron bridge in constructing the Z-scheme and thus extended the lifetime of the charge carriers photoinduced by MIS and TiO2. The significant participation of •O2– and •OH radicals during photocatalytic CIP degradation was verified by active species trapping experiments, EPR, and liquid chromatography–mass spectrometry (LC-MS) analysis. The current study provides a strategy to design mediator-based Z-scheme heterojunction interfaces for improving the catalytic activity of MXene-derived photocatalysts.

Effects of Missing Linker Defects on the Elastic Properties and Mechanical Stability of the Metal–Organic Framework HKUST-1

The defects can naturally exist or be artificially designed in metal–organic frameworks (MOFs), which could significantly affect their mechanical properties. In this paper, the elastic properties of HKUST-1 with randomly distributed missing linker defects are investigated by reactive molecular dynamics simulations together with the strain-fluctuation method. Although all elastic constants of HKUST-1 are found to reduce due to the linker missing, the cubic symmetry is retained in the defective HKUST-1, indicating that the simplified Born stability criterion is still applicable in determining its mechanical stability. On the basis of the simplified Born stability criterion together with direct compression simulations, the critical pressure of instability of HKUST-1 with randomly distributed defects is found to almost linearly decrease as the defect concentration grows. The mechanical instability is similarly attributed to the compression mode in both pristine and defective HKUST-1. Moreover, the direct compression simulations indicate an obvious intermediate transition process existing during the structural collapse of the defective HKUST-1, which is absent in its pristine counterpart. Overall, this work is expected to provide a more precise understanding of the mechanical properties of realistic MOFs.

NiFe-Layered Double Hydroxides/Lead-free Cs2AgBiBr6 Perovskite 2D/2D Heterojunction for Photocatalytic CO2 Conversion

Designing of heterojunction photocatalysts with appropriate interfacial contact plays crucial roles in enhancing the interfacial charge transfer/separation. A two-dimensional (2D)/2D face-to-face heterojunction is an ideal option since this architecture with a large contact area can provide abundant reactive centers and promote the interfacial charge transfer/separation between layers. Herein, a novel 2D/2D heterojunction of NiFe-layered double hydroxides (NiFe-LDH)/Cs2AgBiBr6 (CABB) was fabricated by electrostatic self-assembly of NiFe-LDH and CABB nanosheets. This unique 2D/2D architecture endowed NiFe-LDH/CABB with a large contact area and a short charge transport distance, assuring remarkable interfacial charge transfer/separation rates. As a result, the 2D/2D NiFe-LDH/CABB heterojunction exhibited significant improvement in photocatalytic CO2 reduction under visible light than the pristine counterparts. Based on density functional theory calculations and various characterizations, a step scheme charge-transfer mechanism was proposed. This investigation sheds light on the designing and manufacturing of highly efficient 2D/2D heterostructure photocatalysts for artificial photosynthesis.

Metal oxide/activated carbon composites for the reactive adsorption and catalytic oxidation of formaldehyde and toluene in air

The synergistic effect of ‘reactive adsorption and catalytic oxidation (RACO)’ has been investigated to develop an efficient method to remove volatile organic compounds (VOCs: formaldehyde (FA) + toluene) using an amorphous-manganese dioxide-activated carbon (Am-MnO2-AC) composite. The RACO of FA and toluene onto Am-MnO2-AC was examined individually and as a mixture at multiple-isothermal conditions from room temperature (RT) to 300 °C. At RT, the values for 10% adsorption breakthrough volume (BTV10%) of single FA and toluene by Am-MnO2-AC were 45.9 and 152 L g−1, respectively, approx. 1.3-fold higher than those for their mixture. The BTV10% values for FA measured in single and mixture were 270–280 times higher than their pristine AC counterparts. The RACO performance of Am-MnO2-AC was investigated more intensively against a dual component system in reference to its crystalline forms (e.g., δ-MnO2) and two other metal-doped forms (i.e., cobalt and silver). Accordingly, Am-MnO2-AC exhibited the highest catalytic reactivity so as to achieve the complete oxidation of FA and toluene (as individual components) into carbon dioxide (CO2) at 100 and 275 °C, respectively. The thermal catalytic oxidation of FA and toluene onto Am-MnO2-AC was suggested to follow the Langmuir-Hinshelwood mechanism. The enhanced RACO performance of Am-MnO2-AC was ascribed to its higher surface porosity and higher concentration of oxygen vacancies (e.g., Mn3+/Mn4+ of 0.707 and adsorbed oxygen (OA)/lattice oxygen (OL) of 1.79). The present study is expected to provide deep insights into the practical application of metal oxide/AC composites for cleaner indoor air quality.

Non-metal doping induced dual p-n charge properties in a single ZnIn2S4 crystal structure provoking charge transfer behaviors and boosting photocatalytic hydrogen generation

Construction of heterojunction is conventionally regarded as the prevailing technique to render effective solar-driven photocatalytic water splitting. Nonetheless, realization of p-n homojunction emerges to be an appealing scheme attributed to the non-defective layer coupling and minor charge transfer impedance. Herein, nitrogen-doped ZnIn2S4 (N-ZIS) with dual p-n charge properties was facilely synthesized via one-step in-situ solvothermal method. Systematic investigations unveil that the substituting phenomenon of hosting S by extrinsic N atom with dissimilar electronegativity and valence electron, which eventually ameliorates charge transfer rate and inhibits electron-hole pairs recombination. First-principle density functional theory calculations affirm the p-nature induced by N-doping imparting favorable charge redistribution in the ZIS framework and diminishing hydrogen (H2) evolution reaction kinetic barrier at the surface-active sites. Therein, optimal N-ZIS generated 1575.71 μmol∙g−1 of H2 under 6-hour visible-light irradiation (with an apparent quantum yield of 6.59 % at 420 nm monochromatic light irradiation), which is 6.35-fold than the pristine counterpart.

Toward a blind image quality evaluator in the wild by learning beyond human opinion scores

Nowadays, most existing blind image quality assessment (BIQA) models inthewild heavily rely on human ratings, which are extraordinarily labor-expensive to collect. Here, we propose an opinion−free BIQA method that learns from multiple annotators to assess the perceptual quality of images captured in the wild. Specifically, we first synthesize distorted images based on the pristine counterparts. We then randomly assemble a set of image pairs from the synthetic images, and use a group of IQA models to assign pseudo-binary labels for each pair indicating which image has higher quality as the supervisory signal. Based on the newly established pseudo-labeled dataset, we train a deep neural network (DNN)-based BIQA model to rank the perceptual quality, optimized for consistency with the binary rank labels. Since there exists domain shift, e.g., distortion shift and content shift, between the synthetic and in-the-wild images, we leverage two ways to alleviate this issue. First, the simulated distortions should be similar to authentic distortions as much as possible. Second, an unsupervised domain adaptation (UDA) module is further applied to encourage learning domain-invariant features between two domains. Extensive experiments demonstrate the effectiveness of our proposed opinion−free BIQA model, yielding SOTA performance in terms of correlation with human opinion scores, as well as gMAD competition. Our code is available at: https://github.com/wangzhihua520/OF_BIQA.