Electrostatic Self-assembly Process Research Articles

Boosted charge separation in direct Z-scheme heterojunctions of CsPbBr3/Ultrathin carbon nitride for improved photocatalytic CO2reduction

A direct Z-scheme 2D/2D heterojunction of CsPbBr3/g-C3N4was fabricatedviaa simple electrostatic self-assembly process, which exhibited a remarkably photocatalytic performance for converting CO2and H2O to CH4.

Core-Shell Structured SiO2@NiFe LDH Composite for Broadband Electromagnetic Wave Absorption.

In this work, a novel core-shell structure material, NiFe layered double hydroxide (NiFe LDH) loaded on SiO2 microspheres (SiO2@NiFe LDH), was synthesized by a one-step hydrothermal method, and the spontaneous electrostatic self-assembly process. The morphology, structure, and microwave absorption properties of SiO2@NiFe LDH nanocomposites with different NiFe element ratios were systematically investigated. The results show that the sample of SiO2@NiFe LDH-3 nanocomposite has excellent microwave absorption properties. It exhibits broadband effective absorption bandwidth (RL < -10 dB) of 8.24 GHz (from 9.76 GHz to 18.0 GHz) and the reflection loss is -53.78 dB at the matched thickness of 6.95 mm. It is expected that this SiO2@NiFe-LDH core-shell structural material can be used as a promising non-precious, metal-based material microwave absorber to eliminate electromagnetic wave contamination.

Highly sensitive, flexible and transparent TiO2/nanocellulose humidity sensor for respiration and skin monitoring

Because of its biodegradability, biocompatibility, strong hydrophilicity, and high specific surface area, nanocellulose has been considered as a potential material for flexible humidity sensors. Herein, we developed a TiO2/CNC humidity sensor with good flexibility based on the nanocellulose (CNC) prepared by the enzymatic method. Nano TiO2 with a positive charge was adsorbed on the surface of CNC with a negative charge, and conductive fibers were obtained by an electrostatic self-assembly process. The TiO2/CNC composite exhibits high optical transmittance (84.5% at 600 nm), flexibility (the tensile elongation reaches 57.82%), and robust mechanical property (the tensile strength reaches 44.66 MPa). The obtained TiO2/CNC humidity sensor achieved high humidity response (R0/R = 450.9), rapid response/recovery speed (22/13 s), folding durability (20 times), and long-term stability (40 days). TiO2/CNC had outstanding performance in actual respiratory rate detection, and the assembled TiO2/CNC skin moisture detector with flexibility and transparency could monitor human body moisture in real-time, showing its potential as a smart wearable device.

Graphene oxide/Cu(OH)2 composites as efficient multifunctional hosts for lithium-sulfur batteries

Lithium-sulfur batteries are advanced energy storage system with high theoretical specific capacity and low cost but suffer from poor cyclic performance. To overcome the shortcomings, this study synthesized graphene oxide (GO)/Cu(OH)2 composites using the modified Hummers method and electrostatic self-assembly process. The sulfur was anchored in the GO/Cu(OH)2 composites using the melting method. The oxygen-containing function groups of GO are helpful for achieving good ion/electron accessibility, and the interlayers of GO have many active sites for polysulfide conversion. The polar hydrophilic hydroxyl group of Cu(OH)2 particles have strong chemisorption for polysulfides during the electrochemical process. Therefore, the synergistic effect of GO and Cu(OH)2 in the composites as sulfur hosts can inhibit the dissolution and shuttling of polysulfides. The lithium-sulfur batteries with GO/Cu(OH)2 composites as hosts have high capacity of 1427 mAh g−1 at 0.1 C, 1222 mAh g−1 at 0.5 C, and excellent cyclic performance for 250 cycles with a retained capacity of 929 mAh g−1 (0.5 C).

Graphene oxide-CuFe2O4 nanohybrid material as an adsorbent of Congo red dye

This work evaluates the performance of graphene oxide (GO) - copper ferrite (CuFe2O4) nanohybrid in the removal of Congo Red (CR) dye from aqueous solutions. The adsorbent was prepared via a three-step method. Firstly, GO was produced via a modified Hummers method, using graphite powder as starting material. Following this, GO surface was treated with ionic surfactants, cetyltrimethylammonium bromide (CTAB) and poly(sodium-4-styrenesulfonate) (PSS). Subsequently, the functionalized GO was decorated with magnetic CuFe2O4 nanoparticles via an electrostatic self-assembly process using a solvothermal treatment. The as-synthesized CuFe2O4-GO nanohybrid was characterized by X-Ray Diffraction (XRD) Analysis, Fourier Transform Infrared (FT-IR) Spectroscopy, micro-Raman Spectroscopy, Thermogravimetric Analysis (TGA), Field Emission Scanning Electron Microscopy (FE-SEM), High-Resolution Transition Electron Microscopy (HR-TEM) with Energy Dispersive Spectroscopy (EDS) mapping, as well as, N2 Adsorption/Desorption measurements. We investigated the CR adsorption of the GO-CuFe2O4 nanohybrid at various initial CR concentrations and contact times. Both Langmuir and Freundlich models were employed to describe the adsorption isotherms, while the adsorption kinetics of CR by GO-CuFe2O4 were found to be pseudo-second order. Our results demonstrate that GO-CuFe2O4 is an attractive adsorbent for the efficient removal of CR dye from wastewater.

Preparation of fly ash-based cobalt-iron silicate as supercapacitor electrode material

Based on the high-calcium fly ash of an actual coal-fired power plant, the crystalline silica is successfully transformed into cobalt-iron silicate, and then CNFs/FA-CoFeSiSx with good energy storage performance is obtained by modifying the cobalt-iron silicate as the electrode material of supercapacitor. The crystalline silica is successfully converted to silicate (Ca2SiO4) by high-temperature calcination with NaHCO3 and fly ash. Meanwhile, a 3D porous structure of fly ash is obtained by etching. Ion exchange is successfully carried out by the one-step hydrothermal method, which realizes the transition of Ca2SiO4 to Co2SiO4 and Fe2SiO4. The further modification through electrostatic self-assembly and sulfurization process significantly increases the electron migration rates. The situation that fly ash is difficult to be used in energy storage is ameliorated by the coordinated regulation of various strategies. The final product CNFs/FA-CoFeSiSx exhibited a high specific capacitance (493.33 F·g−1 at 0.5 A·g−1), high Coulombic efficiency (about 100% at 10 A·g−1), and good cycle performance (79.50% capacitance retention after 1800 cycles). Finally, a solid-state asymmetric supercapacitor is assembled based on CNFs/FA-CoFeSiSx as the positive electrode and commercial active carbon as the negative electrode, which performs the maximum energy density of 25.43 Wh·kg−1 and power density of 359.07 W·kg−1. Considering the good energy storage characteristics of fly ash electrode materials, this work provides a low-cost preparation method for electrochemical energy storage and realizes the high-value utilization of fly ash.

Self-assembly synthesis of 3D graphene/nano-Fe3O4 hybrid aerogels with improved mechanical and thermal properties

Graphene aerogel and graphene-magnetite hybrid aerogel were prepared using hydrothermal method followed by a freeze-drying process. Magnetite nanoparticles were encapsulated by graphene sheets in an electrostatic self-assembly process. The morphology and properties of aerogels were characterized by several techniques including UV-Vis spectroscopy, Raman spectroscopy, FESEM, TEM and XRD. The mechanical and thermal behavior of the aerogels were evaluated at different concentration levels of Fe3O4 nanoparticles (0, 10, 20 and 30 wt%). The compressive strengths of the hybrid aerogels at the strain of 80% for graphene aerogels containing 0, 10, 20 and 30 wt% Fe3O4 nanoparticles were determined to be 5.93, 12.96, 6.85, and 6.15 kPa, respectively. The highest mechanical properties were achieved for the sample containing 10 wt% Fe3O4 nanoparticles (FGA10). Thermal analysis revealed that FGA10 sample had a 15% less weight loss when heated up to 600 °C compared with that for the bare graphene aerogel, indicating the formation of a more thermally stable structure. Furthermore, adding Fe3O4 nanoparticles improved the thermal insulation performance of the graphene aerogel, since the dynamic heat transfer rate and heat dissipation rate of FGA10 were lower than those for the bare graphene aerogel.

Double core-shell structure stabilized porous Si@graphene@TiO2 microsphere anode with excellent cyclability and high coulombic efficiency

The vast volume expansion of Si anode during lithiation process leads to poor cyclability and low initial coulombic efficiency (ICE), and thus seriously hampers its applications in lithium-ion batteries (LIBs). To overcome these obstacles, in this study, a double core-shell structure stabilized hierarchical porous Si (p-Si) microsphere was synthesized through a graphene-involved electrostatic self-assembly process coupled with a solvent-confined TiO2 (sc-TiO2) monomicelle assembly strategy. The advanced solvent-confined monomicelle assembly process enables the uniform deposition of ultra-thin TiO2 layer on p-Si@graphene (p-Si@G) microsphere. The G/sc-TiO2 hybrid double shell layer can significantly consolidate porous structure of p-Si microsphere and simultaneously improve the ICE value of p-Si@G@sc-TiO2 microsphere. The resulting p-Si@G@sc-TiO2 composite shows a high capacity value of 2597.9 mAh g−1 at 0.2 A g−1 with a high ICE value of 80.59%. The p-Si@G@sc-TiO2 composite also demonstrates excellent rate capability with capacity of 802.53 mAh g−1 at 8 A g−1 and outstanding cyclability with capacity retention of 68% (1005.1 mAh g−1) after 300 cycles at 2 A g−1, superior to that of p-Si, p-Si@G as well as p-Si@G@TiO2 microsphere preparing by traditional sol-gel TiO2 coating method, suggesting its promising applications in LIBs.

Direct Z-scheme 0D/2D heterojunction of CuO quantum Dots/ultrathin CoAl-LDH for boosting charge separation and photocatalytic CO2 reduction

A direct Z-scheme 0D/2D heterojunction of CuO Quantum dots/ultrathin CoAl-LDH (CuO/CoAl-u) was fabricated by a simple electrostatic self-assembly process for photocatalytic CO2 reduction. An intimate interaction is formed between CuO and CoAl-u, which enables an effective Z-scheme interfacial charge transfer and thus boosts the charge separation as evidenced by various characterization technologies. Notably, the 4.5 %CuO/CoAl-u heterojunction achieves superior photocatalytic performance with a CH3OH yield of 283.26 μmol·g−1·h−1, which is higher than the pristine CoAl-u. Such the enhanced photocatalytic performance turns out to originate from prominent optical absorption property, effective separation of photo-induced carriers in CuO/CoAl-u and preserved higher reduction ability of CoAl-u. XPS measurements together with density functional theory calculations provide a clear description of the charge separation pathways and thus a possible mechanism for photocatalytic CO2 reduction is proposed. This work would provide a novel opportunity for the development of LDH-based photocatalysts with the enhanced activities in solar energy conversion.

Self-assembled homogeneous SiOC@C/graphene with three-dimensional lamellar structure enabling improved capacity and rate performances for lithium ion storage

SiOC as an alternative silicon-based material possesses great potential in lithium ion batteries due to its high reversible capacity, tunable chemical component and various synthetic route. However, large-scale production of SiOC powders grinded from SiOC bulks is restricted in commercial application because of the poor electrical conductivity. Herein, three dimensional (3D) lamellar SiOC@C/rGO composite is fabricated through hydrothermal reaction and electrostatic self-assembly process, in which SiOC powders encapsulated by amorphous carbon layers are homogeneously dispersed in graphene sheets. Cfree nanoclusters in SiOC, carbon layers on SiOC surface and graphene supporters in the composite establish the multidimensional interconnected conductive architecture and possess favorable interfacial adhesion. Therefore, SiOC@C/rGO exhibits high specific capacity (676 mAh g−1 at 200 mA g−1) and remarkable rate capability (306.4 mAh g−1 at 4000 mA g−1). The full cell assembled with this anode and LiFePO4 cathode also demonstrates stable voltage platform and good performance for 200 cycles. The excellent performance of SiOC@C/rGO profits from the synergistic effect of robust construction, multidimensional conductive architecture and chemical. CompositionThe proposed strategy can also be developed to prepare other materials with graphene layer to enhance their electrical conductivity for commercial application.

Dimensional matched ultrathin BiVO4/Ti3C2Tx heterosystem for efficient photocatalytic conversion of CO2 to methanol

Dimensional matched ultrathin BiVO4/Ti3C2Tx MXene 2D/2D heterosystem is developed via a facile electrostatic self-assembly process. The composite shows an increased CO2 uptake capacity than that of the bare BiVO4 nanosheets. Besides, the well collaborated 2D/2D heterogeneous structure efficiently promotes the photoexcited charge transfer and separation. As a result, the photocatalytic CH3OH production rate of the BiVO4/Ti3C2Tx hydrid can reach 20.13 μmol g−1h−1, which is 4.1 times of the pristine BiVO4.

Embedding 1D WO3 Nanotubes into 2D Ultrathin Porous g-C3N4 to Improve the Stability and Efficiency of Photocatalytic Hydrogen Production

Recently, two-dimensional (2D) g-C3N4 has attracted great interest for visible-light-driven H2 production. Thinning, doping, and reticulation have been demonstrated as effective strategies to improve the efficiency of photocatalysis, but are a challenge for structural stability. Herein, a targeted method was implemented by embedding the one-dimensional (1D) WO3 nanotubes matrix into the frameworks of 2D porous g-C3N4 to form a porous P-doped g-C3N4 nanosheets/WO3 nanotubes (PCNS/WNT) by a flexible electrostatic self-assembly process. As a visible-light-sensitive photocatalyst, the as-prepared hybrids exhibited impressive performance for hydrogen generation, which was attributed to the advantages of synergetic mechanism owing to a higher specific surface area, more reaction active sites, enhanced light absorption, and a better photogenerated carrier separation. Interestingly, the insertion of 1D WO3 nanotubes not only accelerates electrons transfer along the 1D channel but also provides robust support for 2D porous g-C3N4 architecture. As a result, the maximum photocatalytic H2 evolution rate of PCNW-50 is 547 μmol g–1 h–1, which is about four times higher than that of pure PCNS, and there is no significant reduction of H2 production after five cycles. Moreover, this 2D/1D PCNS/WNT hybrid was first reported in the area of photocatalytic hydrogen evolution and provides ideas for designing novel stable architecture of photocatalyst.

Effect of amination of titanium dioxide in the TiO2/rGO composite on the efficient photocatalytic removal of gaseous formaldehyde at room temperature

Abstract In order to obtain the advanced photocatalyst with high performance for removing the gaseous formaldehyde, a new strategy with amination of titanium dioxide (TiO2) and combination with reduced graphene oxide (rGO) is proposed in this work. TiO2 was first aminated into amino-TiO2 and then combined with rGO by an electrostatic self-assembly process to form the amino-TiO2/rGO photocatalysts. The structure and morphology were characterized by XRD, FTIR, and SEM, respectively. Physicochemical properties were measured by EIS, XPS, ESR, PL, and photocurrent measurements. The mechanism of the photocatalytic reaction was studied. Optimal amino-TiO2/rGO catalyst exhibits high catalytic activity and recyclability. The reaction rate constant of HCHO over this catalyst is approximately 9.8 × 10−3 L mol−1 ·min−1, which is 10.5 times higher than that of the commercial Degussa P25 TiO2. The analysis results from XPS and ESR indicates that the high catalytic activity could be mainly attributed to the imine formed by chemisorption of amino and HCHO. The reaction speed of formaldehyde photolysis increases as the concentration of HCHO on the photocatalyst surface increased. In addition, the introduction of graphene enhances carrier separation efficiency so that leads to more reactive radicals such as hydroxyl radicals (·OH) and superoxide radicals (·O2−), leading to improved performance on formaldehyde photolysis. This could provide a useful method for highly efficient formaldehyde photocatalysis.

Dual-phase metal nitrides as highly efficient co-catalysts for photocatalytic hydrogen evolution

Low solar-to-fuel conversion in conventional semiconductor-based photocatalysts limits their commercial applications. Searching for highly efficient cost-effective co-catalysts is desirable for the development of artificial photosynthesis systems. In this work, we report a simple yet efficient electrostatic self-assembly process to synthesize one-dimensional Co4N-WNx-CdS composites for visible light-driven hydrogen evolution in pure water. Biphasic transition metal nitrides Co4N-WNx with high conductivity and enriched active sites leads to multi-level electrons transfer and lower over-potential for hydrogen production. Co4N-WNx-CdS composite, with optimized wt%, exhibits the highest rate of photocatalytic hydrogen evolution (14.42 mmol g−1h−1) under vacuum condition. This rate is ~ 8 times higher than that of the Pt-CdS composite (1.78 mmol g−1h−1).

2D ultrathin NiMOF decorated by Ti3C2 MXene for highly improved photocatalytic performance

Two-dimensional (2D) nanomaterials, especially 2D ultrathin layered nanomaterials, have been under increasing demand for solar energy usage and conversion owing to their unique characteristics such as large surface area, easily accessible catalytic sites and high electron transfer efficiency. In this work, layered Ti3C2 was used as the noble-metal-free cocatalyst to design 2D/2D composite by a simple electrostatic self-assembly process, which was based on the ultrathin nickel metal organic framework (UNiMOF) nanosheets. Thanks to the similar layered structures, a conductive and intimate interface formed between Ti3C2 and UNiMOF, which could promote the charge transfer and accelerate the separation of photoexcited electrons and holes. Thus, the obtained 2D/2D UNiMOF/Ti3C2 hybrids exhibited higher activity for photocatalytic degradation of methylene blue (MB) than bare UNiMOF under UV–vis light irradiation, and the activity was boosted by almost 4.0 times when loaded with 1.5 wt% Ti3C2. Moreover, the as-synthesized UNiMOF/Ti3C2 composites showed excellent stability. The possible mechanism for photocatalytic degradation of MB was also explored.

Fabrication of HRP/Bi2WO6 photoenzyme-coupled artificial catalytic system for efficiently degrading bisphenol A

A novel photoenzyme-coupled artificial catalytic system is fabricated by immobilizing horseradish peroxidase (HRP) on the Bi2WO6 hollow nanospheres via a facile electrostatic self-assembly process. The obtained Bi2WO6/HRP sample not only improves the visible light harvest ability but also promotes the high-efficiency separation of charge carriers. More importantly, the photogenerated electrons and produced H2O2 on Bi2WO6 directly take part in redox cycle reactions of HRP to induce photoenzyme synergic catalytic effect. In consequence, the degradation activity of Bi2WO6/HRP is significantly improved relative to Bi2WO6 and HRP for removing bisphenol A (BPA) under the visible light irradiation. This work launches a feasible design strategy for exploiting photoenzyme-coupled artificial catalytic system with special structure to degrade organic pollutants in water efficiently.

Understanding the high-performance Fe(OH)3@GO nanoarchitecture as effective sulfur hosts for the high capacity of lithium-sulfur batteries

Although the lithium-sulfur battery has received widespread attention for its promising future in the energy-storage practical application areas, it still faces some obstacles that hinder commercial and practical utilizations. Here, a Fe(OH)3@GO nanocomposite, 10–20 nm particles anchored on GO surface, as a novel sulfur host has been developed for Li-S batteries, where the construction of Fe(OH)3@GO nanoarchitecture proceeds via electrostatic self-assembly process between the negatively charged GO sheets and the positively charged Fe(OH)3 colloid particles. The wealthy hydroxyl groups of Fe(OH)3 would appeal to intermediate polysulfides more strongly than Fe2O3, resulting in the surface chemical bonds between Fe(OH)3 and polysulfides. On the other hand, GO often contains different functional groups capable of entrapping polysulfides via forming chemical interactions. These advantages of both Fe(OH)3 and GO give the S/Fe(OH)3@GO cathode high specific capacity (1569.8 mA h g−1 at 0.5 C), good rate performance up to 5 C, and long cycling stability over 500 cycles under high sulfur loading. Compared to Fe2O3@GO nanocomposites, the enhanced electrochemical performance for the Fe(OH)3@GO nanocomposite could be attributed to both sufficient surface binding interaction and fast charge-transfer kinetics.

Electrostatic self-assembly enabled flexible paper-based humidity sensor with high sensitivity and superior durability

Humidity sensors have been widely used for humidity monitoring in industrial fields. However, the application of conventional sensors is limited due to the structural rigidity, high cost, and time-consuming integration process. Owing to the good hydrophilicity, biodegradability, and low cost of cellulose, the sensors built on cellulose bulk materials are considered a feasible method to overcome these drawbacks while providing reasonable performance. Herein, we design a flexible paper-based humidity sensor based on conductive 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose fibers/carbon nanotubes (TOCFs/CNTs) conformal fibers network. The CNTs are dispersed by cationic cetyl trimethyl ammonium bromide (CTAB), which introduces positive charges on the CNTs surface. The conductive fibers are achieved by an electrostatic self-assembly process that positively charged CNTs are adsorbed to the surface of negatively charged TOCFs. The vast number of hydrophilic hydroxyl groups on the surface of TOCFs provide more water molecules adsorption sites and facilitate the electron transfer from water molecules to CNTs, endowing the sensor with an excellent humidity responsive property. Besides, the swelling of the TOCFs greatly damages the conductive CNTs network and further promotes the humidity sensitive performance of the sensor. Benefiting from the unique structure, the obtained sensor exhibits a maximum response value of 87.0% (ΔI/I0, and the response limit is 100%), outstanding linearity (R2 = 0.995) between 11 and 95% relative humidity (RH), superior bending (with a curvature of 2.1 cm−1) and folding (up to 50 times) durability, and good long-time stability (more than 3 months). Finally, as a proof of concept, the sensor demonstrates an excellent responsive property to human breath, fingertip humidity, and the change of air humidity, indicating a great potential towards practical applications.

Incorporation of quaternary ammonium chitooligosaccharides on ZnO/palygorskite nanocomposites for enhancing antibacterial activities

Quaternary ammonium chitooligosaccharides (QACOS) was incorporated onto the ZnO/palygorskite (ZnO/PAL) nanocomposite by a simple electrostatic self-assembly process to produce a new organic-inorganic nanocomposite (QACOS/ZnO/PAL) with excellent antibacterial activity. After loading QACOS, the Zeta potential of ZnO/PAL was changed from -26.7 to +30.3 mV, which facilitates to improve the targeting behavior of ZnO/PAL towards bacteria and its contact with bacteria, resulting in a significant improvement of antibacterial capability. The MIC values of QACOS/ZnO/PAL for inhibiting bacteria (0.5 mg/mL for E. coli and 1 mg/L for S. aureus) were superior to ZnO/PAL and QACOS, demonstrated an expected synergistic antibacterial effect between QACOS and ZnO/PAL. The improved contact and interface interaction between QACOS/ZnO/PAL and bacteria makes it easier to destroy the structural integrity of bacteria. As a whole, the incorporation of polysaccharide as regulators of surface charge opens up a new way to further enhance the antibacterial activity of inorganic antibacterial materials.

Multifunctional closed-pore silica/titania composite antireflective coatings based on self-assembly process

This paper reports multifunctional closed-pore silica/titania composite antireflective coatings (ARCs) prepared through combining with emulsion polymerization, sol-gel chemistry, electrostatic self-assembly, and calcination process. The ARCs show high transmittance, with maximum transmission of 98.1% at wavelength of 519 nm and the average transmittance in visible light region (400–700 nm) of 97.1%, a 7.0% increase compared with that of bare glass. Anatase nano titania decorated ARCs are obtained via controlling calcination temperature at 600 °C for 5 min and proved by XRD results. The ARCs exhibit excellent self-cleaning properties, illustrated by accelerating organic decomposition under UV and sunlight. Furthermore, the ARCs possess outstanding superhydrophilic and antifogging properties. In addition, water is the only solvent used in the whole process. These features make the method have specific advantages in the ARCs field.