Electrostatic Self-assembly Method Research Articles

Facile assembly of BiVO4/protonated g-C3N4/AgI with a novel dual Z-scheme mechanism for visible-light photocatalytic degradation of Rhodamine B

Constructing Z-scheme photocatalyst is an effective strategy to achieve efficient photogenerated electron-holes separation and retain its outstanding redox ability simultaneously. In this work, a novel ternary BiVO4/protonated g-C3N4/AgI photocatalyst with a double Z-scheme mechanism is successfully constructed by electrostatic self-assembly method loading of BiVO4 onto protonated g-C3N4 and subsequently via an in situ precipitation route. Using Rhodamine B (RhB) as the target of elimination, BiVO4/protonated g-C3N4/AgI displays excellent photocatalytic performance with the 94.67% removal after 60-min visible light irradiation. The photodegradation rate constant of RhB is 0.04963 min−1, which faster than pristine BiVO4 (0.0004 min−1), BiVO4/protonated g-C3N4 (0.0209 min−1) and BiVO4/AgI (0.0317 min−1), respectively. Such enhancement in photocatalytic activity is correlated to improved light absorption, faster charge carrier separation and transportation as well as more powerful redox ability originating from the formation of double Z-scheme heterostructure. Also, the as-prepared ternary sample exhibits high stability after four cycles of the photodegradation reaction. Furthermore, the possible photocatalytic mechanism of BiVO4/protonated g-C3N4/AgI is also proposed. Therefore, we believe that this work can provide insights into the understanding the significant role of design and synthesis the double Z-scheme in semiconductor heterostructure system for environmental remediation.

Amorphous MoS3 decoration on 2D functionalized MXene as a bifunctional electrode for stable and robust lithium storage

The development of electrode materials with the synergistic effects of good chemical stability and high electrical conductivity has improved the sluggish ion kinetics and severe capacity degradation of rechargeable lithium batteries. Herein, a multifunctional heterostructure material (MoS3-Ti3C2Tx) comprising a functionalized MXene (Ti3C2Tx) and amorphous MoS3 is prepared by a scalable electrostatic self-assembly method. Remarkably, as lithium-ion battery anodes, the resultant MoS3-Ti3C2Tx not only exhibits increased electrochemical activity, accelerated lithium-ion diffusion and fast charge transfer kinetics but also shows high specific capacity, excellent rate performance and long-term cycling stability. By virtue of these merits, MoS3-Ti3C2Tx offers an excellent reversible capacity of 1043 mAh g−1 at 200 mA g−1 and exhibited a capacity of 568 mAh g−1 at a current density of 2 A g−1 after 1000 cycles. When acting as the cathode for lithium-sulfur batteries, the amorphous MoS3 anchored on MXene demonstrates high capture and catalytic activity towards polysulfide conversion. Accordingly, the optimized electrode exhibits a capacity of 836 mAh g−1 at 0.2C after 100 cycles and a satisfactory rate performance of 463 mAh g−1 at 2C after 400 cycles. Moreover, the associated conversion mechanism is studied by ex situ XPS. These results demonstrate that heterostructure composites constructed by an amorphous sulfide and surface functionalized MXene are feasible electrode materials for both lithium-sulfur batteries and lithium-ion batteries.

Highly Sensitive Room-Temperature NO2 Gas Sensors Based on Three-Dimensional Multiwalled Carbon Nanotube Networks on SiO2 Nanospheres

The electrical conductivity of carbon nanotubes (CNTs) has been demonstrated to be highly sensitive to the change of vapor/gas molecules in the local environment owing to the large specific surface area and quantum size effect, which enable CNTs to be an ideal sensing material for next-generation room-temperature gas sensors. However, the sensing properties of CNT films or networks cannot be maximized because of the inevitable agglomeration during the fabrication process. Herein, three-dimensional (3D) SiO₂@multiwalled CNTs (MWCNTs) core–shell nanospheres have been first used to fabricate room-temperature gas sensors, which were prepared using an electrostatic self-assembly method. The as-fabricated 3D SiO₂@MWCNTs sensor exhibits a recorded sensitivity of 82.61% toward 1 ppm nitrogen dioxide (NO₂) at room temperature, which is 1.97 times higher than that of devices based on random two-dimensional (2D) MWCNTs. Meanwhile, the recovery time of ∼44 s is smaller than that of a 2D MWCNT gas sensor. Such an ultrahigh sensing performance is attributed to an effective utilization of the large specific surface area of MWCNT networks with 3D structures. We believe that our findings will contribute to the further development of high-performance CNT-based sensing devices and also provide a new approach to fabricate the sensing devices using one-dimensional nanomaterials.

Ultrathin 2D Ti3C2 MXene Co-catalyst anchored on porous g-C3N4 for enhanced photocatalytic CO2 reduction under visible-light irradiation

Constructing an efficient photocatalyst is critical for photocatalytic carbon dioxide (CO2) into valuable fuel. Herein, a high-efficiency catalyst was synthesized by a simple one-step electrostatic self-assembly method, in which Ti3C2 (TC) was anchored on porous g-C3N4 (PCN) with rich –NHx via NHx-Ti bond. Such a chemical interaction made the optimized TC/PCN-2 with 2 wt% loading of Ti3C2 possess highest CH4 production (0.99 μmol·h−1·g−1catalyst) under visible light (>420 nm), which was 14 times higher than that of pure PCN (0.07 µmol·h−1·gcatalyst−1) at the same condition. More importantly, the TC/PCN-2 photocatalyst still maintained satisfied activity after four cycles. Besides the formation of NHx-Ti chemical bonding and superior conductivity of Ti3C2 as a co-catalyst, which facilitated interfacial charges separation and migration, the exceptional performance could also attribute to the enhanced CO2 adsorption/activation and improved light-harvesting capability. This work provided a potential application in energy conversion with MXene as an efficient co-catalyst.

In Situ Growth of Mo2C on Cathodes for Efficient Microbial Electrosynthesis of Acetate from CO2

Microbial electrosynthesis (MES) is an electrochemical reduction technique where microorganisms attached to electrodes are used as catalysts for CO2 reduction into chemicals. In situ grown molybdenum carbide (Mo2C) without binder-modified electrodes for MES was constructed in different layer numbers. Results showed that the hydrogen evolution reaction activity of carbon felt (CF) with Mo2C was higher than that of bare CF. The volumetric acetate production rate of MES with in situ grown Mo2C through a single electrostatic self-assembly method was 0.15 ± 0.01 g L–1 day–1, which was 1.8 times that of the control. The final acetate concentration reached 4.56 ± 0.1 g L–1 within 30 days, and the coulomb efficiency was 50 ± 0.3%. In addition, scanning electron microscopy and microbial community analyses showed that Mo2C with a single layer was conducive to the attachment of microorganisms, improved the enrichment of Acetobacterium and Arcobacter, and inhibited the abundance of Sulfurospirillum. In situ grown Mo2C-modified cathode is an effective strategy for improving MES efficiency.

Ti3C2 MXene-bridged Ag/Ag3PO4 hybrids toward enhanced visible-light-driven photocatalytic activity

As a novel transition metal carbides and/or carbonitrides, MXene possess two-dimensional characteristic, abundant surface hydrophilic functional groups, and excellent electrical conductivity that bestow a possibility to building MXene-based photocatalysts. Inspired by this, an emerging Ti3C2 MXene cocatalyst bridged Ag/Ag3PO4 to induce a highly visible-light-driven photocatalytic activity, synthesized by electrostatic self-assembly method and the partial reduction of Ag+ ions to Ag0 in MXene solution is reported. The resultant hybrids reveal a well-defined hybrid structures with Ag/Ag3PO4 anchoring on the layer structured Ti3C2 nanosheets. Benefiting from the unique structural features, the Ag/Ag3PO4/Ti3C2 hybrids present Ti3C2 content-dependent photocatalytic activity toward the methyl orange (MO) degradation and Cr(VI) reduction under visible-light irradiation. Remarkably, the Ag/Ag3PO4/Ti3C2 hybrid with 3 wt% Ti3C2 content achieves the greatest MO degradation efficiency and Cr(VI) reduction efficiency after irradiation for 1 h, which are increased to 1.72 and 1.46 times higher than that obtained on pristine Ag3PO4 nanoparticles, respectively. Such impressive photocatalytic activity is related to the synergeric effects derived from Ag, Ag3PO4, and Ti3C2, which greatly enhance visible light absorption, promote separation and transfer of photo-generated electron-hole pairs. This work highlights that the MXene-based photocatalysts would be desirable candidates for environmental purification of organic pollutants and heavy metal ions.

Facile Synthesis of Modified MnO2/Reduced Graphene Oxide Nanocomposites and their Application in Supercapacitors

Herein, KH-550 was used as surface modifier to prepare modified MnO2/reduced graphene oxide (M-MnO2/rGO) composite electrode materials by utilizing electrostatic interaction at low temperature and normal pressure. X-ray diffraction, scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy were adopted to characterize the material’s phase, morphology, and valence state of elements. The electrochemical properties of the material were measured using a three-electrode system. The results indicate a decrease in the size of the modified MnO2 particles, and that they were uniformly distributed on the rGO sheets. The M-MnO2/rGO composite attained a specific capacitance of 326[Formula: see text]F[Formula: see text]g[Formula: see text] in a solution of 1[Formula: see text]mol[Formula: see text]L[Formula: see text] Na2SO4 at a current density of 0.5[Formula: see text]A[Formula: see text]g[Formula: see text]. The specific capacitance of the material was 92.4% after 1000 cycles. The electrostatic self-assembly method effectively solved the problem of reducing the cycling stability while improving the specific capacitance of the composite materials, and further improved the possibility of applying MnO2/rGO in the field of supercapacitors.

Fabrication of CdS/P2MoxW18-x nanospheres with type II heterostructure for photocatalytic reduction of hexavalent chromium

A serial of CdS/POM (POM denotes polyoxometalate: P2MoxW18-x, x = 3, 9, 15) nanospheres were fabricated through electrostatic self-assembly method. For the first time, the semiconductor properties of the three polyoxometalates were investigated to direct the rational design of the type-II heterojunction photocatalysts. The morphology and semiconducting properties of the as-prepared materials were characterized by using X-ray powder diffraction, scanning electron microscopy, UV–vis diffuse reflectance spectra, Mott-Schottky plots, surface photovoltage spectroscopy and time-resolved photocurrent curves. The band gap of P2Mo3W15, P2Mo9W9 and P2Mo15W3 is taken respectively to be 2.34 eV, 2.26 eV and 2.15 eV. The average diameters of CdS and CdS/P2MoxW18-x (X = 3, 9, 15) nanospheres are all around 80–100 nm, and CdS/P2MoxW18-x (X = 3, 9, 15) nanospheres have better photoelectric performance than pure CdS. The formation of type II heterostructure between CdS and P2MoxW18-x could promote the separation and transfer of photoinduced electron-hole pairs, so the photocatalytic activities of CdS/POM nanospheres for Cr(VI) reduction were improved significantly. Among them, the CdS/P2Mo15W3 photocatalyst exhibited the highest photocatalytic yield of 64% for the Cr(VI) removal. Our study provides new insight into developing novel CdS/P2MoxW18-x nanocomposite photocatalysts for environmental applications.

G-C3N4 nanoparticle@porous g-C3N4 composite photocatalytic materials with significantly enhanced photo-generated carrier separation efficiency

Abstract

Facile synthesis of nano-nanocarriers from chitosan and pectin with improved stability and biocompatibility for anthocyanins delivery: An in vitro and in vivo study

Anthocyanins is a type of natural pigment with a variety of physiological activities, are unstable and prone to degradation. In order to improve the stability of anthocyanin, in this study, the nanocarriers were constructed through electrostatic self-assembly method using chitosan and pectin as raw materials for bilberry anthocyanins delivery. Atomic force microscope and scanning electron microscope analyses showed that the nanocarriers were well dispersed spheres with diameters around 100–300 nm when the mass ratio of chitosan/pectin/anthocyanin was 1:1:3. Fourier transform infrared spectroscopy and ultraviolet–visible absorption spectroscopy results revealed that the anthocyanins were successfully doped into the nanocarriers. The encapsulation efficiency of anthocyanins was 66.68%. Moreover, the anthocyanin nanocarriers exhibited increased storage stability under light and dark conditions. In vitro digestion experiments showed that the doped anthocyanins could escape from the interference of stomach acid environment and released slowly in small intestinal fluid, suggesting the controlled delivery of anthocyanins in the gastrointestinal tract. In vitro NRK cell model demonstrated that the nanocarriers could protect against acrylamide-induced damage by viability and cell apoptosis assay. In vivo Caenorhabditis elegans model further showed that the nanocarriers could protect from anthocyanin damage caused by various harmful conditions such as acrylamide, oxidative stress, heat shock and UV light. Furthermore, Caenorhabditis elegans treated with nanocarriers showed longer lifespan, stronger reproductive capability, more flexible locomotion behavior, and less autofluorescent lipofuscin particles. Together, these results suggest that chitosan-pectin nanoparticles can be used as delivery vehicles to improve the stability and bioavailability of the functional factor anthocyanin.

Porous Ni5P4 as a promising cocatalyst for boosting the photocatalytic hydrogen evolution reaction performance

Nonmetallic cocatalysts have demonstrated unprecedented potential for accelerating photocatalytic hydrogen evolution reaction (HER). In this study, a nickel phosphide compound, namely Ni5P4, with porous carnation-like superstructure has been target-synthesized and then employed as HER cocatalyst to in-situ build a hybrid with protonated g-C3N4 nanosheets via an electrostatic self-assembly method. Owing to the synergistic advantages of the excellent metallic conductivity and porous carnation-like superstructure of Ni5P4, the as-obtained HCN/Ni5P4 Schottky-junction with abundant active sites, low H* atom adsorption energy and efficient charge carrier transport channel, affords the photocatalytic H2 production rate of 1157.5 μmol g−1 h−1 when exposed to visible light (λ > 420 nm). This photocatalytic H2 production rate was much higher than those of the corresponding reference cocatalysts, namely Ni2P and NiS2 (169.1 and 593.1 μmol g−1 h−1, respectively), both of which were derived from the same Ni(OH)2 precursor. This study provides a new idea for the design of highly active noble-metal-free materials for the photocatalytic HER.

Osteogenic growth peptide-loaded 3D-printed PCL scaffolds for the promotion of osteogenesis through the ERK pathway

This study aims to improve the osteogenic differentiation in vitro and bone formation in vivo through polycaprolactone (PCL) scaffolds modified with the osteogenic growth peptide (OGP). Three-dimensional (3D)-printed PCL scaffolds were designed with computer-aided design (CAD) software and fabricated by 3D layer-by-layer fused deposition. After the scaffold surfaces were modified by surface amination, the OGP was successfully loaded onto the scaffolds using a electrostatic self-assembly method. The effects of these scaffolds on the biocompatibility and osteogenic differentiation of rat bone marrow-derived stem cells (BMSCs) were studied in vitro. The modification did not influence the adhesion or proliferation, but had a notable osteogenic effect in vitro. This may be attributed to the activation of the mitogen-activated protein kinase/extracellular regulated protein kinase (MAPK/ERK) signalling pathway. Based on the results obtained after implantation into a rat cranial defect model, the PCL/OGP scaffolds notably promoted bone formation and accelerated mineralisation. The innovative modification method introduced in this work, will improve the application of PCL scaffolds in tissue engineering.

Tailoring sensing properties of smart cementitious composites based on excluded volume theory and electrostatic self-assembly

The excluded volume effect is the reduction in free volume of a matrix filled by secondary fillers, which can enhance the conductive network of carbon nanotubes (CNTs) composites and work effectively with microscale secondary fillers. Besides, the electrostatic self-assembly method has been proved effective for dispersing CNTs. Therefore, this study aims to assemble microscale TiO2 with CNTs to develop smart cementitious composites, in an effort to tailor the sensing properties based on the excluded volume theory and electrostatic self-assembly method. The results show the composites with CNT/TiO2 have a high sensitivity, a wide stress/strain monitoring range, and acceptable mechanical properties. In elastic state, the strain sensitivity of cementitious composites can reach 317. The composite can monitor the compressive stress from 0 to 80.7 MPa, with the maximum fractional change in resistivity as high as 84.09%. Furthermore, due to its low water absorption property, the CNT/TiO2 filler exhibits little negative effect on the mechanical properties of cementitious materials with best piezoelectric performance.

Graphene Quantum Dots Enhanced Photocatalytic Activity of Sb2WO6 Under Ultraviolet‐ and Visible‐Light Irradiation

A novel composite of graphene quantum dots functionalized Sb2WO6 (GQDs/Sb2WO6) was prepared by an electrostatic self‐assembly method and used as a photocatalyst for the degradation of an organic pollutant. The resulting GQDs/Sb2WO6 was characterized by electron microscopy and optical measurements. The photocatalytic activity of GQDs/Sb2WO6 was investigated by degrading methyl orange (MO) under UV‐light and visible‐light irradiation. Compared with pure Sb2WO6, enhancement of the photocatalytic performance of GQDs/Sb2WO6 was achieved, and the degradation efficiency for MO was almost 100% within 3 h under UV‐light irradiation and 71.4% within 3 h under visible‐light irradiation. The photocatalytic degradation mechanism of GQDs/Sb2WO6 was illustrated by free radical and hole scavenging experiments, and the main active species were confirmed to be holes (h+) and superoxide anion radicals (O2·−). Moreover, the GQDs/Sb2WO6 composites exhibited high recyclability and stability and had potential application for decomposing other organic contaminants in water.

Tunable radio-frequency negative permittivity of Carbon/CaCu3Ti4O12 metacomposites

Abstract In this paper, metacomposites of carbon nanotubes/CaCu3Ti4O12 (CNTs/CCTO), carbon blacks/CaCu3Ti4O12 (CBs/CCTO), and CNTs-CBs/CCTO were fabricated by low-temperature sintering process. The CNTs-CBs building blocks were fabricated by one-step electrostatic self-assembly method. In carbon/CCTO metacomposites, magnitude of negative permittivity ranged from 103 to 100 while its band-width ranged from 300 MHz to 1 GHz. An electrical percolation phenomenon was verified in ac conductivity spectra, suggesting the transition of conductive mechanism. Negative permittivity was ascribed to low-frequency plasma oscillation in carbon networks, corresponding to inductive character. The pendulum-like simple harmonic motion (SHM) model was applied to clarify the negative permittivity behavior. Accumulating of carbon clusters or networks in composites resulted in colossal dielectric loss (10−1

TiO2 with exposed (001) facets/Bi4O5Br2 nanosheets heterojunction with enhanced photocatalytic for NO removal

A TiO2 with exposed (001) facets/Bi4O5Br2 nanosheets heterojunction (TNS/BOB) was fabricated via a hydrothermal and electrostatic self-assembly method. The photocatalytic activity for NO removal was evaluated under simulated solar light irradiation. Through optimizing the content of TNS nanosheets, the photo-oxidative NO removal rate of 15% TNS/BOB was increased by up to 54.3%. This value is much higher than that of the individual components TNS (31.1%) and BOB (37.7%). Through capturing experiments and electron spin resonance (ESR) measurements, the main active species in the photocatalytic process were identified as · and ·OH. Discrete Fourier transform computation results and ESR tests revealed that the photo-induced electrons in TNS should recombine with the holes in BOB, leading to effectively promoted charge separation at the TNS/BOB interface through the Z-type charge transfer. This work showed that with appropriate facet control and heterojunction design TiO2 can be used as an effective visible-light photocatalyst material.

Rationally constructing of a novel dual Z-scheme composite photocatalyst with significantly enhanced performance for neonicotinoid degradation under visible light irradiation

A novel dual Z-scheme g-C3N4/WO3/AgI photocatalyst was rationally constructed via a two-step method (electrostatic self-assembly plus selective deposition). Firstly, binary g-C3N4/WO3 system was fabricated by electrostatic self-assembly method. Then, Ag ions were selectively adsorbed on the surface of negatively charged WO3 and reacted with I ions to form AgI nanoparticles. Compared with pure g-C3N4, WO3, AgI and their binary composites, the ternary composites showed significantly enhanced photocatalytic performance for nitenpyram (NTP) degradation under visible light. The enhanced performance can be ascribed to the increased charge transferring/separation efficiency and remaining high reduction/oxidation ability of the photo-generated electrons/holes in the dual Z-scheme system. Furthermore, the possible degradation pathway of NTP was deduced based on the results of high-performance liquid chromatography mass spectrometry (HPLC-MS). This work would broaden insight into the rationally construction of highly efficient Z-scheme composite photocatalysts.

Immobilization of well-dispersed Ag nanoparticles on calcium niobate nanosheets as highly active catalyst towards reduction of 4-nitrophenol

Ag nanoparticles were successfully deposited onto calcium niobate nanosheets using the electrostatic self-assembly method, followed by UV irradiation photoreduction. Various characterization techniques including XRD, SEM, HRTEM, BET and XPS have been utilized to study the material crystalline structure, microstructure, pore size and surface properties. Silver nanoparticles in the size range of 2–8 nm are well dispersed on the surface of the calcium niobate nanosheets. The as-synthesized Ag-Ca2Nb3O10 was a mesoporous material with a broad pore size distribution. Ag-Ca2Nb3O10 exhibited remarkable catalytic activity for the reduction of 4-nitrophenol (4-NP) by NaBH4 solution under ambient conditions, and no obvious activity degradation was observed after 5 cycles of durability test. The reduction has a pseudo-first-order rate constant of 18.01 × 10−3s − 1 and an activity parameter of 6.00 s − 1g − 1. The activation energy (Ea) of the reduction reaction was calculated as 59.63 kJ mol−1. The catalyst was recycled several times without any significant catalytic activity loss. This work provides a facile route to synthesize a highly efficient catalyst for the reduction of organic pollutants.

Introduction of amino and rGO into PP nonwoven surface for removal of gaseous aromatic pollutants and particulate matter from air

Gaseous aromatic pollutants such as benzene, toluene or xylene and particulate matter (PM) from an individual’s living environment potentially cause serious and life-threatening health problems. A new bifunctional individual protection material was prepared by grafting polymerization and electrostatic self-assembly method. The individual protection material has a dual function layer consisting of an amino-functionalized nonwoven grafted with dimethylaminoethyl methacrylate (DMAEMA) and a gaseous aromatic pollutant adsorption layer made up of reduced graphene oxide (rGO). The surface composition and structure of materials were obtained by a series of characterization methods. Adsorption and filtration performance for each function layer and double function layer Polypropylene (PP) nonwoven were intensively studied. As indicated by the experiments, the adsorption efficiency of PP-g-DMAEMA/rGO increased with the decreasing oxygen content of GO and increasing the initial concentration of toluene, filter performance and aperture parameters data showed that the surface Zeta potential and pore size had great influence on filtration efficiency of the filter material, the resulting PP nonwoven exhibited prominent multifunctional performance, including a higher adsorption amount (39.1 mg/g) and filter efficiency (72.2%). Consequently, it is expected that the bifunctional PP nonwoven will have potential applications in air purification for the removal of gaseous aromatic pollutants and PM.

Metal-free 2D/2D heterojunction of covalent triazine-based frameworks/graphitic carbon nitride with enhanced interfacial charge separation for highly efficient photocatalytic elimination of antibiotic pollutants

A novel polymer-based 2D/2D heterojunction photocatalysts of covalent triazine-based frameworks/graphitic carbon nitride nanosheets (CTFNS/CNNS) heterojunction are successfully obtained by an electrostatic self-assembly method using amine-functionalized CNNS and carboxyl-rich CTFNS. Such large contact surface and appropriate interfacial contact between CNNS and CTFNS plays a critical role in transfer and separation of charge-carriers. The resulting CTFNS/CNNS heterojunction showed significantly enhanced photocatalytic activity under the irradiation of simulated solar light, which could decompose 10 ppm sulfamethazine (SMT) within 180 min with a high degradation efficiency of 95.8 %. Chloride ions can greatly promote the photocatalytic degradation of SMT due to the production of more radical species. O2− is the dominant active species for SMT decomposition over CTFNS/CNNS heterojunction. Moreover, the degradation intermediates of SMT were identified using high performance liquid chromatography-mass spectrometer and the degradation pathway was proposed. This study provides a new insight into the design of 2D/2D heterojunctions using carbon-based nanomaterials, which exhibits great potential in the degradation of sulfonamide antibiotics in wastewaters.