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.

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.

NiCo Alloy Nanoparticles on a N/C Dual-Doped Matrix as a Cathode Catalyst for Improved Microbial Fuel Cell Performance.

The cathode material properties of the microbial fuel cell (MFC) have a quite important effect on their power generation capacity. Excellent oxygen reduction reaction (ORR) performance is the key to obtaining the remarkable capability of MFC. In this study, a series of catalysts are successfully prepared by a simple step-by-step hydrothermal, in situ growth, solution polymerization, and pyrolysis procedure. Here, the NiCo nanoparticles loading on nitrogen/carbon dual-doped matrix annealing at 800 °C (NiCo@DNC-800) under Ar shows good ORR activity with a maximum power density of 2325.60 ± 41.96 mW m-2 in the case of the 2 mg cm-2 minimal catalyst loading, and which is about 2.16 times more than that achieved by 20% Pt/C (1074.21 ± 39.36 mW m-2 ). The unique N/C duel-doped matrix provides more graphitic-N and pyridinic-N that can reduce the resistance of electron diffusion and transport, together with the synergistic catalysis of NiCo active sites improving the oxygen reduction reaction performance of MFC greatly. In addition, the NiCo@DNC-800 cathode catalyst demonstrates that composite materials have great application potential in water pollution treatment and new green energy strategies.

Pressure-induced phase transitions and superconductivity in a quasi-1-dimensional topological crystalline insulator α-Bi4Br4.

Great progress has been achieved in the research field of topological states of matter during the past decade. Recently, a quasi-1-dimensional bismuth bromide, Bi4Br4, has been predicted to be a rotational symmetry-protected topological crystalline insulator; it would also exhibit more exotic topological properties under pressure. Here, we report a thorough study of phase transitions and superconductivity in a quasihydrostatically pressurized α-Bi4Br4 crystal by performing detailed measurements of electrical resistance, alternating current magnetic susceptibility, and in situ high-pressure single-crystal X-ray diffraction together with first principles calculations. We find a pressure-induced insulator-metal transition between ∼3.0 and 3.8 GPa where valence and conduction bands cross the Fermi level to form a set of small pockets of holes and electrons. With further increase of pressure, 2 superconductive transitions emerge. One shows a sharp resistance drop to 0 near 6.8 K at 3.8 GPa; the transition temperature gradually lowers with increasing pressure and completely vanishes above 12.0 GPa. Another transition sets in around 9.0 K at 5.5 GPa and persists up to the highest pressure of 45.0 GPa studied in this work. Intriguingly, we find that the first superconducting phase might coexist with a nontrivial rotational symmetry-protected topology in the pressure range of ∼3.8 to 4.3 GPa; the second one is associated with a structural phase transition from monoclinic C2/m to triclinic P-1 symmetry.

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.

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.

Pt/MnO2 Nanoflowers Anchored to Boron Nitride Aerogels for Highly Efficient Enrichment and Catalytic Oxidation of Formaldehyde at Room Temperature.

The catalytic room temperature oxidation of formaldehyde (HCHO) is widely considered as a viable method for the abatement of indoor toxic HCHO pollution. Herein, Pt/MnO2 nanoflowers anchored to boron nitride aerogels (Pt/MnO2 -BN) were fabricated for the catalytic room temperature oxidation of HCHO. The three-dimensional Pt/MnO2 -BN aerogels demonstrated superior catalytic activity as a result of the improved diffusion of the reactant molecules within the porous structure. Furthermore, the porous aerogels displayed excellent HCHO adsorption capacities, which promote a rapid HCHO gas-phase concentration reduction and a subsequent complete oxidation of the adsorbed HCHO. The combined adsorption and oxidation properties of the Pt/MnO2 -BN aerogels enhance the oxidative removal of HCHO. The optimized Pt/MnO2 -BN demonstrated excellent catalytic activity toward HCHO (200 ppm) at room temperature, achieving a 96 % formaldehyde conversion after 50 min.

Nanocage-Shaped Co3- x Zrx O4 Solid-Solution Supports Loaded with Pt Nanoparticles as Effective Catalysts for the Enhancement of Toluene Oxidation.

Nanocage-shaped Co3- x Zrx O4 solid-solution supports and the corresponding platinum loaded nanocomposites, yPt/Co3- x Zrx O4 (x =0.27, 0.50, 0.69; y = 0.5, 1.0, 2.0 wt.%), are successfully fabricated via a Cu2 O nanocube hard template method and a glycol reduction method, respectively. The hollow nanocage structures obviously improve surface areas; moreover, the Zr doping forms the Co3- x Zrx O4 solid-solution supports, and the corresponding yPt/Co3- x Zrx O4 catalysts promote the enhancement of catalytic performance. Catalytic activity toward toluene combustion is enhanced for the 2.0 wt% Pt/Co2.73 Zr0.27 O4 catalyst. The catalysts are characterized using multiple techniques. Pt nanoparticles are uniformly dispersed across the Co2.73 Zr0.27 O4 nanocage surface. The 2.0 wt% Pt/Co2.73 Zr0.27 O4 catalyst exhibits the highest catalytic activity among all the samples and demonstrates good stability, with 90% toluene conversion obtained at a temperature of 165 °C. The same catalyst accomplishes full toluene oxidation at 180 °C, at a weight hourly space velocity of 36 000 mL h-1 g-1 . The apparent activation energy (Ea ) over the yPt/Co2.73 Zr0.27 O4 samples are significantly lower than those over the Co3- x Zrx O4 supports, with the 2.0 wt% Pt/Co2.73 Zr0.27 O4 catalyst exhibiting the lowest Ea value. These findings demonstrate the potential of the 2.0 wt% Pt/Co2.73 Zr0.27 O4 catalyst as a promising catalyst toward atmospheric toluene removal.

Construction of Hierarchical Hollow Co9 S8 /ZnIn2 S4 Tubular Heterostructures for Highly Efficient Solar Energy Conversion and Environmental Remediation.

Visible-light-responsive hierarchical Co9 S8 /ZnIn2 S4 tubular heterostructures are fabricated by growing 2D ZnIn2 S4 nanosheets on 1D hollow Co9 S8 nanotubes. This design combines two photoresponsive sulfide semiconductors in a stable heterojunction with a hierarchical hollow tubular structure, improving visible-light absorption, yielding a large surface area, exposing sufficient catalytically active sites, and promoting the separation and migration of photogenerated charges. The hierarchical nanotubes exhibit excellent photocatalytic H2 evolution and CrVI reduction efficiency. Under visible-light illumination, the optimized Co9 S8 /ZnIn2 S4 heterostructure provides a remarkable H2 generation rate of 9039 µmol h-1 g-1 without the use of any co-catalysts and CrVI is completely reduced in 45 min. The Co9 S8 /ZnIn2 S4 heterostructure is stable after multiple photocatalytic cycles.

Surface Engineering of g-C3 N4 by Stacked BiOBr Sheets Rich in Oxygen Vacancies for Boosting Photocatalytic Performance.

BiOBr containing surface oxygen vacancies (OVs) was prepared by a simple solvothermal method and combined with graphitic carbon nitride (g-C3 N4 ) to construct a heterojunction for photocatalytic oxidation of nitric oxide (NO) and reduction of carbon dioxide (CO2 ). The formation of the heterojunction enhanced the transfer and separation efficiency of photogenerated carriers. Furthermore, the surface OVs sufficiently exposed catalytically active sites, and enabled capture of photoexcited electrons at the surface of the catalyst. Internal recombination of photogenerated charges was also limited, which contributed to generation of more active oxygen for NO oxidation. Heterojunction and OVs worked together to form a spatial conductive network framework, which achieved 63 % NO removal, 96 % selectivity for carbonaceous products (that is, CO and CH4 ). The stability of the catalyst was confirmed by cycling experiments and X-ray diffraction and transmission electron microscopy after NO removal.

ZIF-67-Derived 3D Hollow Mesoporous Crystalline Co3 O4 Wrapped by 2D g-C3 N4 Nanosheets for Photocatalytic Removal of Nitric Oxide.

ZIF-67-derived 3D hollow mesoporous crystalline Co3 O4 wrapped by 2D graphitic carbon nitride (g-C3 N4 ) nanosheets are prepared by low temperature annealing, and are used for the photocatalytic oxidation of nitric oxide (NO) at a concentration of 600 ppb. The p-n heterojunction between Co3 O4 and g-C3 N4 forms a spatial conductive network frame and results in a broad visible light response range. The hollow mesoporous structure of Co3 O4 contributes to the circulation and adsorption of NO, and the large specific surface area exposes abundant active sites for the reaction of active species. A maximum NO degradation efficiency of 57% is achieved by adjusting the mass of the Co3 O4 precursor. Cycling tests and X-ray diffraction indicate the high stability and recyclability of the composite, making it promising in environmental purification applications.

3D Gold-Modified Cerium and Cobalt Oxide Catalyst on a Graphene Aerogel for Highly Efficient Catalytic Formaldehyde Oxidation.

A hard template method is used to prepare porous gold-doped cerium and cobalt oxide (Au-Cex Coy ) materials. A series of 3D Au-Ce x Coy /graphene aerogel (GA) composites is then fabricated by a facile heating method. The obtained catalysts possess a well-defined structure of ordered arrays of nanotubes and good performance in formaldehyde (HCHO) oxidation. The composition and surface elemental valence states of the catalysts are modulated by the Ce/Co molar ratio. The Au-Cex Coy catalyst and graphene oxide sheets are well compounded within 60 s through a diamine cross-linker to form 3D Au-Cex Coy /GA composites. In addition, the resulting catalyst of 3 wt% Au-Ce3 Co/GA achieves ≈55% conversion at room temperature and 100% conversion when the reaction temperature is raised at 60 °C. The synergistic effect between CeO2 and Co3 O4 promotes the migration of oxygen species and the activation of Au, which facilitates HCHO oxidation. The method used to prepare the 3D catalyst could be used to produce other catalytic materials with good replication of the template. In addition, these findings provide a simple method for rapid fabrication of catalyst/GA composites. The superior activity and stability of the 3D Au-Ce3 Co/GA catalyst make it potentially applicable in HCHO removal.

Detection of NO2 Down to One ppb Using Ion-in-Conjugation-Inspired Polymer.

Nitrogen dioxide (NO2 ) emission has severe impact on human health and the ecological environment and effective monitoring of NO2 requires the detection limit (limit of detection) of several parts-per-billion (ppb). All organic semiconductor-based NO2 sensors fail to reach such a level. In this work, using an ion-in-conjugation inspired-polymer (poly(3,3'-diaminobenzidine-squarine, noted as PDBS) as the sensory material, NO2 can be detected as low as 1 ppb, which is the lowest among all reported organic NO2 sensors. In addition, the sensor has high sensitivity, good reversibility, and long-time stability with a period longer than 120 d. Theoretical calculations reveal that PDBS offers unreacted amine and zwitterionic groups, which can offer both the H-bonding and ion-dipole interaction to NO2 . The moderate binding energies (≈0.6 eV) offer high sensitivity, selectivity as well as good reversibility. The results demonstrate that the ion-in-conjugation can be employed to greatly improve sensitivity and selectivity in organic gas sensors by inducing both H-bonding and ion-dipole attraction.

Environmentally Robust Memristor Enabled by Lead-Free Double Perovskite for High-Performance Information Storage.

Memristors are emerging as a rising star of new computing and information storage techniques. However, the practical applications are severely challenged by their instability toward harsh conditions, including high moisture, high temperatures, fire, ionizing irradiation, and mechanical bending. In this work, for the first time, lead-free double perovskite Cs2 AgBiBr6 is utilized for environmentally robust memristors, enabling highly efficient information storage. The memory performance of the typical indium-tin-oxide/Cs2 AgBiBr6 /Au sandwich-like memristors is retained after 1000 switching cycles, 105 s of reading, and 104 times of mechanical bending, comparable to other halide perovskite memristors. Most importantly, the memristive behavior remains robust in harsh environments, including humidity up to 80%, temperatures as high as 453 K, an alcohol burner flame for 10 s, and 60 Co γ-ray irradiation for a dosage of 5 × 105 rad (SI), which is not achieved by any other memristors and commercial flash memory techniques. The realization of an environmentally robust memristor from Cs2 AgBiBr6 with a high memory performance will inspire further development of robust electronics using lead-free double perovskites.

Platinum-Supported Zirconia Nanotube Arrays Supported on Graphene Aerogels Modified with Metal-Organic Frameworks: Adsorption and Oxidation of Formaldehyde at Room Temperature.

Precious-metal catalysts (e.g., Au, Rh, Ag, Ru, Pt, and Pd) supported on transition-metal oxides (e.g., Al2 O3 , Fe2 O3 , CeO2 , ZrO2 , Co3 O4 , MnO2 , TiO2 , and NiO) can effectively oxidize volatile organic compounds. In this study, porous platinum-supported zirconia materials have been prepared by a "surface-casting" method. The synthesized catalysts present an ordered nanotube structure and exhibited excellent performance toward the catalytic oxidation of formaldehyde. A facile method, utilizing a boiling water bath, was used to fabricate graphene aerogel (GA), and the macroscopic 3D Pt/ZrO2 -GA was modified by introducing an adjustable MOF coating by a surface step-by-step method. The unblocked mesoporous structure of the graphene aerogel facilitates the ingress and egress of reactants and product molecules. The selected 7 wt.% Pt/ZrO2 -GA-MOF-5 composite demonstrated excellent performance for HCHO adsorption. Additionally, this catalyst achieved around 90 % conversion when subjected to a reaction temperature of 70 °C (T90 % =70 °C). The Pt/ZrO2 -GA-MOF-5 composite induces a catalytic cycle, increasing the conversion by simultaneously adsorbing and oxidizing HCHO. This work provides a simple approach to increasing reactant concentration on the catalyst to increase the rate of reaction.

Self-Healing Graphene-Reinforced Composite for Highly Efficient Oil/Water Separation.

One of the most pervasive environmental problems is oily sewage; emerging materials are needed that could effectively solve this global challenge. Special wetting materials typically combine micro/nanoscale hierarchical structures with a low surface energy, which could produce superhydrophobic performance and these superhydrophobic materials are very important for a wide variety of applications, including self-cleaning and antiadhesives. However, the majority of these manmade materials still suffer from poor durability, which seriously hinders their practical applications. A better choice is that use of supramolecular materials with self-healing ability, which could provide an efficient method to solve materials poor durability problem. However, lightweight materials with special wettbility and self-healing still remain a challenge. In this work, we confine polyborosiloxane (PBS) in an ultralight graphene network to form a robust, special function graphene foam that has the ability to self-repair. Hydroxyl terminated poly(dimethylsiloxane) and boric acid as the as raw material were used to synthesis PBS at room temperature. The as-prepared composite network could be compressed and their properties fully restored without an external stimulus after being subjected to repeated damage. In addition, the prepared composite foam retains the porosity of the original graphene foam. The present work suggests encouraging applications of the self-healing graphene/PBS foam in water/organic solvent separations.

Enhancement of organic pollutants bio-decontamination from aqueous solution using newly-designed Pseudomonas putida-GA/MIL-100(Fe) bio-nanocomposites.

As a natural adsorption material, graphene has become a hot research topic in water treatment due to its unique framework, large surface area, low cost, and simple preparation. Here, a series of composite material aerogels (GA/MIL-100(Fe)) consisting of Fe metal-organic frameworks (MIL-100 (Fe)) and graphene-based aerogel (GA) were prepared through a hydrothermal and step-by-step strategy and used for the adsorption of an azo dye in wastewater, scilicet acid orange 10 (AO10). The adsorption equilibrium of AO10 solutions with concentrations of 50 and 100 mg/L was reached within 45 min but the dye could not be fully removed. Besides, the synthesized composite material (GA/MIL-100(Fe)) was a good carrier for immobilized Pseudomonas putida cells due to its good biocompatibility and non-toxicity. A new, environmentally friendly adsorption and biodegradation process has been exploited here, which was to immobilize bacterial cells to the surface of GA/MIL-100(Fe) by a covalent bonding method to form a novel biocomposite material. The material could be used to completely remove AO10 dyes in 14 and 26 h from solutions with initial AO10 concentrations of 50 and 100 mg/L, respectively. This way of combining biological and physical adsorption has a higher processing efficiency and shows huge potential for the treatment of industrial wastewater.

Z-Scheme 2D/2D Heterojunction of Black Phosphorus/Monolayer Bi2 WO6 Nanosheets with Enhanced Photocatalytic Activities.

Black phosphorus (BP), a star-shaped two-dimensional material, has attracted considerable attention owing to its unique chemical and physical properties. BP shows great potential in photocatalysis area because of its excellent optical properties; however, its applications in this field have been limited to date. Now, a Z-scheme heterojunction of 2D/2D BP/monolayer Bi2 WO6 (MBWO) is fabricated by a simple and effective method. The BP/MBWO heterojunction exhibits enhanced photocatalytic performance in photocatalytic water splitting to produce H2 and NO removal to purify air; the highest H2 evolution rate of BP/MBWO is 21042 µmol g-1 , is 9.15 times that of pristine MBWO and the NO removal ratio was as high as 67 %. A Z-scheme photocatalytic mechanism is proposed based on monitoring of . O2 - , . OH, NO2 , and NO3 - species in the reaction. This work broadens applications of BP and highlights its promise in the treatment of environmental pollution and renewable energy issues.

Eye-Readable Detection and Oxidation of CO with a Platinum-Based Catalyst and a Binuclear Rhodium Complex.

Toxic gases that are colorless and odorless, such as CO, are a major environmental concern and require early detection to prevent serious toxicological effects. In this study, a unique system (Pt/HMSs-BRC) was fabricated by combining a catalyst (Pt/hollow mesoporous silica spheres, Pt/HMSs) with a silica gel containing an adsorbed chromogenic probe (binuclear rhodium complex, BRC). The process is a simple method to prepare well-dispersed and uniform Pt nanoparticles. The Pt/HMSs-BRC materials demonstrated early CO detection and excellent catalytic performance for CO oxidation. The probe exhibited remarkable color modulation from gray-violet to light-yellow when exposed to CO concentration levels above 50 ppm, and the color of the chromogenic probe was fully recoverable. By a kinetics-assisted discrimination method and DFT calculations, it was found that the corner Pt sites are the dominant active sites for CO oxidation.

3D Aerogel of Graphitic Carbon Nitride Modified with Perylene Imide and Graphene Oxide for Highly Efficient Nitric Oxide Removal under Visible Light.

3D materials are considered promising for photocatalytic applications in air purification because of their large surface areas, controllability, and recyclability. Here, a series of aerogels consisting of graphitic-carbon nitride (g-C3 N4 ) modified with a perylene imide (PI) and graphene oxide (GO) are prepared for nitric oxide (NO) removal under visible-light irradiation. All of the photocatalysts exhibit excellent activity in NO removal because of the strong light absorption and good planarity of PI-g-C3 N4 coupled with the favorable charge transport properties of GO, which slow the recombination of electron-hole pairs. The aerogel containing thiophene displays the most efficient NO removal of the aerogel series, with a removal ratio of up to 66%. Density functional theory calculations are conducted to explain this result and recycling experiments are carried out to verify the stability and recyclability of these photocatalysts.