Graphite/h-BN van der Waals heterostructure as a gate stack for HgTe quantum wells.

Two-dimensional topological insulators have attracted much interest due to their potential applications in spintronics and quantum computing. To access the exotic physical phenomena, a gate electric field is required to tune the Fermi level into the bulk band gap. Hexagonal boron nitride (h-BN) is a promising alternative gate dielectric due to its unique advantages such as flat and charge-free surface. Here we present a h-BN/graphite van der Waals heterostructure as a top gate on HgTe heterostructure-based Hall bar devices. We compare our results to devices with h-BN/Ti/Au and HfO2/Ti/Au gates. Devices with a h-BN/graphite gate show no charge carrier density shift compared to as-grown structures, in contrast to a significant n-type carrier density increase for HfO2/Ti/Au. We attribute this observation mainly to the comparable work function of HgTe and graphite. In addition, devices with h-BN gate dielectric show slightly higher electron mobility compared to HfO2-based devices. Our results demonstrate the compatibility between layered materials transfer and wet-etched structures and provide a strategy to solve the issue of significant shifts of the carrier density in gated HgTe heterostructures.

Triazine-based conjugated polymers with regulation of D-A configuration for enhanced photocatalytic activity.

Photocatalysis is a green and environmentally friendly method for degrading dangerous and nonbiodegradable pollutants. In this study, a sequence of metal-free triazine-based electronic donor-acceptor (D-A) conjugated polymers Tr-X (X = Th, BT, BTh) were prepared by D-A configuration regulation between triazine (Tr) and monomers containing N and S, such as thiophene (Th), bithiophene (BTh) and benzothiadiazole (BT) units, for the photocatalytic degradation of bisphenol A (BPA) and benzene contaminants in water under visible light. Among these, Tr-BTh exhibited complete photocatalytic degradation owing to its excellent D-A configuration. Moreover, the N and S atoms, which are rich in triazine and thiophene units, serve as highly dispersed reactive sites. The separation and transfer of photogenerated carriers can be further improved by expanding the light-absorption range of polymers. In addition, the polymers showed good adsorption for BPA and other aromatic organic pollutants through π-π interaction and surface hydrogen bonding, which provides a facile strategy for efficient polymer-based photocatalysts for water purification.

Ternary heterojunction of cross-linked benzene Polymer/Bi2MoO6-Graphene oxide catalysts promote efficient adsorption and photocatalytic removal of oxytetracycline.

Antibiotics are refractory degradable organic pollutants that present a significant hazard to water environments. In this work, a ternary composite (KB/BMO-GO) comprising of graphene oxide (GO), Bi2MoO6 (BMO), and a cross-linked benzene polymer (KB) was synthesized and applied to promote the synergistic adsorption-photocatalytic degradation of the refractory pollutant, oxytetracycline (OTC). The inclusion of GO and KB in the composite enhanced the OTC adsorption performance of the catalysts, and the construction of Z-scheme heterojunction promoted the photogenerated charge separation efficiency and broadened the range of light absorption, thereby enhancing the photocatalytic performance. Moreover, we compared the performance of catalysts loaded with different mass ratios of KB (x% KB/BMO-GO). Among them, the 15 % KB/BMO-GO catalyst sample had the best OTC degradation performance. Specifically, 15 % KB/BMO-GO could adsorb 69.7 % of OTC in 30 min, reaching an OTC degradation rate of 93.3 % under visible light irradiation. h+ and 1O2 are the main active substances in the photocatalytic process. In addition, the catalysts are acid-alkali and salt-resistant, as well as good reusability. This study provides a valuable reference for the preparation of highly efficient photocatalysts for synergistic adsorption-photodegradation processes.

Interfacial Self-Assembly-Induced Lattice Distortion in Ti3C2 for Enhanced Piezocatalytic Activity.

Herein, self-assembled monolayers (SAMs) are constructed on the surface of Ti3C2 MXene to improve its environmental stability and piezocatalytic activity. Ti3C2/SAMs-X (X = H, Cl, and NH2) was prepared to enhance the piezocatalytic degradation of bisphenol A (BPA) and hydrogen production. Surface-treated Ti3C2 exhibits different lattice parameters and symmetry, thus leading to an increased polarization. The presence of polar functional groups in SAMs remarkably increases the surface potential of Ti3C2, thereby promoting the migration of piezoelectric electrons. Ti3C2/SAMs-NH2 exhibits the highest piezocatalytic performance, thus improving BPA removal and H2 generation by 7 and 1.8 times, respectively. In addition, Ti3C2/SAMs-NH2 remained stable under 100% relative humidity for 15 days. Therefore, it provides a facile strategy for modulating piezocatalytic properties through interfacial self-assembly-induced lattice distortion.

Improving the Sulfurophobicity of the NiS-Doping CoS Electrocatalyst Boosts the Low-Energy-Consumption Sulfide Oxidation Reaction Process.

Producing sulfur from a sulfide oxidation reaction (SOR)-based technique using sulfide aqueous solution has attracted considerable attention due to its ecofriendliness. This study demonstrates that NiS-doped cobalt sulfide NiS-CoS-supported NiCo alloy foam can deliver the SOR with superior electrocatalytic activity and robust stability compared to reported non-noble metal-based catalysts. Only 0.34 V vs RHE is required to drive a current density of 100 mA cm-2 for the SOR. According to the experiment, the catalyst exhibits a unique sulfurophobicity feature because of the weak interaction between sulfur and the transition metal sulfide (low affinity for elemental sulfur), preventing electrode corrosion during the SOR process. More impressively, the chain-growth mechanism of the SOR from short- to long-chain polysulfides was revealed by combining electrochemical and spectroscopic in situ methods, such as in situ ultraviolet-visible and Raman. It is also demonstrated that electrons can transfer straight from the sulfion (S2-) to the active site on the anode surface during the low-energy-consumption SOR process. This work provides new insight into simultaneous energy-saving hydrogen production and high-value-added S recovery from sulfide-containing wastewater.

Vibration-driven Reduction of CO2 to Acetate with 100 % Selectivity by SnS Nanobelt Piezocatalysts.

Converting CO2 into high-value C2 chemicals such as acetate with high selectivity and efficiency is a critical issue in renewable energy storage. Herein, for the first time we present a vibration-driven piezocatalysis with tin(II) monosulfide (SnS) nanobelts for conversion of CO2 to acetate with 100 % selectivity, and the highest production rate (2.21 mM h-1 ) compared with reported catalysts. Mechanism analysis reveal that the polarized charges triggered by periodic mechanical vibration promote the adsorption and activation of CO2 . The electron transfer can be facilitated due to built-in electric field, decreased band gap and work function of SnS under stress. Remarkably, reduced distance between active sites leads to charge enrichment on Sn sites, promoting the C-C coupling, reducing the energy barriers of the rate determining step. It puts forward a bran-new strategy for converting CO2 into high-value C2 products with efficient, low-cost and environment-friendly piezocatalysis utilizing mechanical energy.

Built-in electric field and oxygen absorption synergistically optimized an organic/inorganic heterojunction for high-efficiency photocatalytic hydrogen peroxide production.

The production of hydrogen peroxide (H2O2) from oxygen and water is an attractive route for converting solar energy into chemical energy. In order to achieve high solar-to-H2O2 conversion efficiency, floral inorganic/organic (CdS/TpBpy) composite with strong oxygen absorption and S-scheme heterojunction was synthesized by simple solvothermal-hydrothermal methods. The unique flower-like structure increased the active sites and oxygen absorption. The existence of S-scheme heterojuntion facilitated the charge transfer across the built-in electric field. Without sacrificial reagents or stabilizers, the optimal CdS/TpBpy had a higher H2O2 production (3600 µmol g-1 h-1), which was 2.4 and 25.6 times than those of TpBpy and CdS, respectively. Meanwhile, CdS/TpBpy inhibited the H2O2 decomposition, thus increasing the overall output. Furthermore, a series of experiments and calculations were carried out to verify the photocatalytic mechanism. This work demonstrates a modification method to improve the photocatalytic activity of hybrid composites, and shows potential applications in energy conversion.

PVDF/PLA electrospun fiber membrane impregnated with metal nanoparticles for emulsion separation, surface antimicrobial, and antifouling activities.

Although many superwetting materials have been designed for the treatment of oil-containing wastewater, separation strategies for oil-in-water systems containing bacteria have rarely been reported. Herein, poly(vinylidene difluoride)- and poly(lactic acid)-blended fibrous membranes loaded with silver and copper oxide nanoparticles were successfully prepared by a two-step method of electrostatic spinning and liquid-phase synthesis. The product membrane showed excellent super-oleophilic properties in air and hydrophobicity under oil. It could separate water-in-oil emulsion systems containing surfactants with an efficiency above 90%. More importantly, the nanoparticle-loaded fibers were characterized by material degradability and slowly released ions. The fibers exhibited excellent antibacterial activities against both gram-positive and -negative bacteria. This work provides a feasible strategy for water-in-oil emulsion separation and bacterial treatment of wastewater.

Optical bulk-boundary dichotomy in a quantum spin Hall insulator.

The bulk-boundary correspondence is a critical concept in topological quantum materials. For instance, a quantum spin Hall insulator features a bulk insulating gap with gapless helical boundary states protected by the underlying Z2 topology. However, the bulk-boundary dichotomy and distinction are rarely explored in optical experiments, which can provide unique information about topological charge carriers beyond transport and electronic spectroscopy techniques. Here, we utilize mid-infrared absorption micro-spectroscopy and pump-probe micro-spectroscopy to elucidate the bulk-boundary optical responses of Bi4Br4, a recently discovered room-temperature quantum spin Hall insulator. Benefiting from the low energy of infrared photons and the high spatial resolution, we unambiguously resolve a strong absorption from the boundary states while the bulk absorption is suppressed by its insulating gap. Moreover, the boundary absorption exhibits strong polarization anisotropy, consistent with the one-dimensional nature of the topological boundary states. Our infrared pump-probe microscopy further measures a substantially increased carrier lifetime for the boundary states, which reaches one nanosecond scale. The nanosecond lifetime is about one to two orders longer than that of most topological materials and can be attributed to the linear dispersion nature of the helical boundary states. Our findings demonstrate the optical bulk-boundary dichotomy in a topological material and provide a proof-of-principal methodology for studying topological optoelectronics.

Efficient photocatalytic hydrogen peroxide production induced by the strong internal electric field of all-organic S-scheme heterojunction.

Light-driven reaction of oxygen and water to hydrogen peroxide (H2O2) is an environmental protection method, which can convert solar energy into green products. In this work, perylene-3, 4, 9, 10-tetracarboxylic diimide (PDINH) could be recrystallized in situ on the surface of porous carbon nitride (PCN), to obtain an all-organic S-scheme heterojunction (PDINH/PCN). The design of the hierarchical porous photocatalyst improved the mass transfer, enhanced the light absorption and increased specific surface area. Moreover, the construction of the S-scheme heterojunction at the interface of PDINH and PCN exhibited suitable band, which facilitated the separation and transfer of carriers. The H2O2 production rate was up to 922.4 µmol g-1h-1, which was 2.6 and 53.3 times higher than that of PCN and PDINH. Therefore, the all-organic S-scheme heterojunction provides an insight for improving the photocatalytic H2O2 production.

Low quantity of Pt loaded onto CeCoOx nanoboxes: Surface-rich reactive oxygen species for catalytic oxidation of toluene.

An optimized oxygen activity of catalysts can facilitate oxidation of volatile organic compounds. This work shows the first construction of Ce-Co oxide thin-walled nanoboxes. Bulk-phase lattice oxygen is activated by metal-metal interactions. The subsequent uniform dispersion of low loaded Pt nanoparticles further enhances the surface-adsorbed oxygen content, and creates an oxygen-rich reaction interface. Competitive adsorption of water vapor was also inhibited, and complete catalytic oxidation of toluene was achieved at low temperature (T90 =140 °C). A diffuse reflectance infrared Fourier-transform spectroscopy probe was used to investigate the adsorption-catalytic process and the possible synergistic catalytic mechanism (Langmuir-Hinshelwood and Mars-van Krevelen). This work provides a strategy for improving the catalyt Crystal structure ic oxidation performance of nanocatalysts for volatile organic compounds by increasing the catalytic oxygen activity.

Sulfonate-modified calixarene-based porous organic polymers for electrostatic enhancement and efficient rapid removal of cationic dyes in water.

Developing of fast and efficient adsorbents for removal of low concentration refractory organics in water is significant. Herein, a novel calix[4]arene-based porous organic polymer CaPy is constructed through Sonogashira-Hagihara cross-coupling polycondensation. The strong polar sulfonate is further anchored onto the polymer skeleton of CaPy and three sulfonate-modified anionic polymers CaPy-S1, CaPy-S2, and CaPy-S3 were obtained and fully characterized. The adsorption isotherms showed that the maximum adsorption capacities of CaPy, CaPy-S1, CaPy-S2, and CaPy-S3 toward methylene blue (MB) were 270, 1454, 558 and 1381 mg g-1, whereas those for Rhodamine B (RhB) were 183, 2653, 1132, and 1796 mg g-1, respectively. The maximum adsorption capacity toward RhB was the highest reported vale among the currently used synthetic adsorbents. In addition, the pseudo-second-order rate constants of CaPy, CaPy-S1, CaPy-S2, and CaPy-S3 toward MB were 0.00572, 0.488, 2.24, and 0.192 g mg-1 min-1, respectively, and those toward RhB were 0.000234, 0.138, 0.0819, and 0.203 g mg-1 min-1, respectively. The pseudo-second-order rate constant of CaPy-S2 toward MB was 2.24 g mg-1 min-1 indicating one of the highest adsorption speeds. The activation energy of CaPy-S1 for RhB and MB were 121 and 109 kJ mol-1, respectively, demonstrating that the adsorption of both dyes on CaPy-S1 was chemisorption process. Further, the obtained values of Gibbs free energy were negative, revealing that the adsorption process was spontaneous. This work provides an effective approach for improving adsorption performance via post-modification.

Construction of Perylene-based Amphiphilic Micelle and Its Efficient Adsorption and In Situ Photodegradation of Bisphenol A in Aqueous Solution.

Low mass-transfer efficiency and reaction-driving force make it difficult to realize thorough purification in traditional low-concentration pollutant treatments. Herein, we propose an "adsorption/catalysis in situ" perylene based bifunctional micelle for efficient, accurate and rapid adsorption and catalytic degradation of low-concentration bisphenol A (BPA). They show super-fast (within 10 s), high capacity (448 mg g-1 ) and selectivity for BPA adsorption, due to π-π, hydrophobic interactions and hydrogen bonding. The BPA degradation efficiency improves by up to 8 times after forming micelles compared with simple perylene nanorods, which is primarily due to the superior mass-transfer from adsorption. Moreover, self-assembly can optimize the stacking of the perylene moieties and facilitate charge transfer in micelle, and the regular π-π stacking of inside perylene units enhances the response to visible light, resulting in high catalytic capacity and good cycling stability.

NH2-MIL-125(Ti) modified graphitic carbon nitride with carbon vacancy for efficient photocatalytic NO removal.

This paper reports the application of NH2-MIL-125(Ti) modified carbon nitride Cv-C3N4 with carbon vacancies in the removal of NO. We performed a series of characterizations of the complex and compared various ratios with the individual components. The results of UV spectrum analysis show that the composite's range of light absorption expanded due to the modification of Ti metal-organic framework. Furthermore, the results of photocurrent and electrical impedance indicate the compound has a better ability to generate and transfer electrons. The increase in the compound's NO removal efficiency (up to 63%) indicates that MOF has a positive effect on Cv-C3N4 modification-a good method for photocatalysis. Moreover, the compound can promote photocatalysis in a favorable direction.

Metal-organic frameworks-derived manganese trioxide with uniformly loaded ultrasmall platinum nanoparticles boosting benzene combustion.

Four morphologies of metal-organic frameworks derived Mn2O3 were prepared by calcination of metal-organic frameworks self-assembled from metal ions and organic ligands and loaded with platinum. The catalyst showed excellent catalytic performance for benzene (T90% = 131 °C). ESR (electron spin resonance) test showed that due to the strong electron metal support interaction between Pt and Mn2O3, there were a large number of oxygen vacancies on the surface of the catalyst as active sites to promote the oxidation of benzene. The presence of a large number of Lewis acid sites on the catalyst surface was confirmed by Py-IP (Pyridine adsorption infrared spectroscopy) test. The intermediates of benzene catalytic oxidation are ethyl acetate, carboxylic acids and aldehydes, which can be verified by in-situ DRIFTS. In summary, the catalysts synthesized in this work provide a novel perspective for combining metal-organic frameworks-derived oxides and precious metals for the catalytic oxidation of volatile organic compounds.

SuFEx-Enabled Elastic Polysulfates for Efficient Removal of Radioactive Iodomethane and Polar Aprotic Organics through Weak Intermolecular Forces.

Capturing radioactive iodomethane and its vapors is a major challenge due to its low adsorption capacity. Herein, we have developed for the first time a pyridine-entrapped elastic crosslinked polysulfate gel (pyridine/TPC-cPS) as an efficient absorbent for iodomethane capture. Each pyridine-encased TPC-cPS network cell acts as a mini-reactor for salt formation between pyridine and iodomethane. The yield reaches up to 96.65 % and traps saturated iodomethane vapor of 1.573 g gpyridine/TPC-cPS -1 (equivalent to 18.103 g gTPC-cPS -1 ), which is the highest capacity reported to date. Both experiments and molecular dynamics simulations reveal that the unusual adsorption of polysulfate for polar aprotic organics can be attributed to the fact that the electrostatic interactions between the polar group (O=S=O) in the polymer backbone and the polar groups in the organic molecules fixed the solvent in the polymer matrix, while the van der Waals forces between the nonpolar groups in the polymer and molecules induced swelling.

Ni-Co Bimetallic Hydroxide Nanosheet Arrays Anchored on Graphene for Adsorption-Induced Enhanced Photocatalytic CO2 Reduction.

Photocatalytic CO2 reduction can be implemented to use CO2 , a greenhouse gas, as a resource in an energy-saving and environmentally friendly way, in which suitable catalytic materials are required to achieve high-efficiency catalysis. Insufficient accessible active sites on the catalyst surface and inhibited electron transfer severely limit the photocatalytic performance. Therefore, porous aerogels are constructed from composites comprising different ratios of Ni-Co bimetallic hydroxide (Nix Coy ) grown on reduced graphene oxide (GR) into a hierarchical nanosheet-array structure using a facile in situ growth method. Detailed characterization shows that this structure exposes numerous active sites for enhanced adsorption-induced photocatalytic CO2 reduction. Moreover, under the synergistic effect of Ni-Co bimetallic hydroxide, the CO2 adsorption capacity as well as charge-carrier separation and transfer are excellent. As a result, the Ni7 Co3 -GR catalyst exhibits highly improved catalytic performance when compared with recently reported values, with a high CO release rate of 941.5 µmol h-1  g-1 and a selectivity of 96.3% during the photocatalytic reduction of CO2 . This work demonstrates a new strategy for designing nanocomposites with abundant active sites structures.

Self-supported MoO2-MoO3/Ni2P hybrids as a bifunctional electrocatalyst for energy-saving hydrogen generation via urea-water electrolysis.

The electronic modulation and morphology control of electrocatalysts are effective strategies to improve their catalytic performance. Herein, MoO2-MoO3/Ni2P nanoflowers were fabricated on the skeleton of conductive nickel foam as an electrocatalyst with enhanced performance via a universal hydrothermal and phosphating method. The introduction of P and Mo into the nickel-based catalyst through the co-doping strategy effectively adjusted the electronic structure of the Ni active sites, thereby significantly improving the performance of the catalyst. Particularly, the introduction of Mo allowed adjusting the morphology of the material, thereby increasing the electrochemical active area and promoting the exposure of more active sites. This strategy for improving the electrocatalyst's performance in urea-assisted water splitting will provide a new concept for the simultaneous mitigation of the energy crisis and environmental contamination.

High-Performance and Stable Two-Dimensional MXene-Polyethyleneimine Composite Lamellar Membranes for Molecular Separation.

Two-dimensional (2D) materials are candidates for use in advanced molecular separation and water treatment. Among them, MXenes are cutting-edge two-dimensional (2D) materials with favorable properties such as high hydrophilicity, adjustable interlayer spacing, high mechanical strength, and structural stability. Therefore, they can be used to construct advanced lamellar membranes to ensure enhanced separation performance of modified membranes. Here, we prepared novel stable lamellar membranes through electrostatic attraction between polycation polyethyleneimine (PEI) and a negatively charged MXene, with hydrogen bond formation between their functional groups. By changing the pH of the suspension, the interlayer d-spacing of the prepared membrane could be altered to achieve precise molecular separation and ultrahigh organic solvent penetration. Furthermore, inserting PEI into the interlayer d-spacing of the membrane did not hinder the passage of water molecules. The prepared pH = 2-MXene-PEI membrane for dyes larger than 1.5 nm exhibited a rejection rate of greater than 96%, and the pH = 10-MXene-PEI membrane had a rejection rate of greater than 96% for dyes larger than 1.6 nm. In addition, the optimized MXene-PEI membranes showed channel stability. In this work, high-performance, stable, 2D MXene-PEI membranes with tunable nanochannels were developed. These membranes have great potential for use in precise molecular separation applications.

Catalytic oxidation of VOCs over 3D@2D Pd/CoMn2O4 nanosheets supported on hollow Al2O3 microspheres.

Catalytic oxidation is a promising method for removing harmful volatile organic compounds (VOCs). Therefore, exploring high-efficiency catalysts for catalyzing VOCs is of great significance to the realization of an environment-friendly and sustainable society. Here, a series of 3D@2D constructed Al2O3@CoMn2O4 microspheres with a hollow hierarchical structure supporting Pd nanoparticles was successfully synthesized. The introduction of hollow Al2O3 for the in situ vertical growth of 2D CMO spinel materials constructs a well-defined core - shell hollow hierarchical structure, leading to larger specific surface area, more accessible active sites and promoted catalytic activity of support material. Additionally, theoretical calculations also indicate that the addition of Al2O3 as the support material strengthens the adsorption of toluene and oxygen on CoMn2O4, which promotes their activation. The dispersion of Pd further strengthens the low-temperature reducibility along with more active surface oxygen species and lower apparent activation energy. The optimum 1 wt% Pd/h-Al@4CMO catalyst possesses the lowest apparent activation energy for toluene of 77.4 kJ mol-1, showing the relatively best catalytic activity for VOC oxidation, reaching 100% toluene, benzene, and ethyl acetate conversion at 165, 160, and 155 °C, respectively. Meanwhile, the 1 wt% Pd/h-Al@4CMO sample possesses excellent catalytic stability, outstanding selectivity, and good moisture tolerance, which is an effective candidate for eliminating VOCs contaminants.