Highly Anion-Conductive Viologen-based Two-Dimensional Polymer Membranes as Nanopower Generators.

Two-dimensional polymers (2DPs) and their layer-stacked 2D covalent organic frameworks (2D COFs) membranes hold great potential for harvesting sustainable osmotic energy. The nascent research has yet to simultaneously achieve high ionic flux and selectivity, primarily due to inefficient ion transport dynamics. This is directly related to ultrasmall pore size (<3 nm), much smaller than the duple Debye length in the diluted electrolyte (6~20 nm), as well as low charge density (<4.5 mC m-2). Here, we introduce a π-conjugated viologen-based 2DP (V2DP) membrane possessing a large pore size of 4.5 nm, strategically enhancing the overlapping of the electric double layer, coupled with an exceptional positive surface charge density (~6 mC m-2). These characteristics enable the membrane to facilitate high anion flux while maintaining ideal selectivity. Notably, V2DP membranes realize an impressive current density of 5.5×103 A m-2, surpassing  previously nanofluidic membranes. In practical application scenario involving the mixing of artificial seawater and river water, the V2DP membranes exhibit a considerable ion transference number of 0.70 towards Cl-, contributing to an outstanding power density of ~55 W m-2. Theoretical calculations reveal that the large quantity of anion transport sites act as binding sites evenly located in the positively charged N-containing pyridine rings.

Bioinspired 2D nanofluidic membranes for energy applications.

Bioinspired two-dimensional (2D) nanofluidic membranes have been explored for the creation of high-performance ion transport systems that can mimic the delicate transport functions of living organisms. Advanced energy devices made from these membranes show excellent energy storage and conversion capabilities. Further research and development in this area are essential to unlock the full potential of energy devices and facilitate the development of high-performance equipment toward real-world applications and a sustainable future. However, there has been minimal review and summarization of 2D nanofluidic membranes in recent years. Thus, it is necessary to carry out an extensive review to provide a survey library for researchers in related fields. In this review, the classification and the raw materials that are used to construct 2D nanofluidic membranes are first presented. Second, the top-down and bottom-up methods for constructing 2D membranes are introduced. Next, the applications of bioinspired 2D membranes in osmotic energy, hydraulic energy, mechanical energy, photoelectric conversion, lithium batteries, and flow batteries are discussed in detail. Finally, the opportunities and challenges that 2D nanofluidic membranes are likely to face in the future are envisioned. This review aims to provide a broad knowledge base for constructing high-performance bioinspired 2D nanofluidic membranes for advanced energy applications.

Application of 3D printing technology for green synthesis of Fe2O3 using ABS/TPU/chlorella skeletons for methyl orange removal.

Photocatalysis is widely acknowledged as an efficient and environmentally friendly method for treating dye-contaminated wastewater. However, the utilization of powdered photocatalysts presents significant challenges, including issues related to recyclability and the potential for secondary pollution. Herein, a novel technique based on 3D printing for the synthesizing of iron oxide (Fe2O3) involving chlorella was presented. Initially, chlorella powders were immobilized within acrylonitrile butadiene styrene (ABS) and thermoplastic polyurethane (TPU) substrate plastics using melt extrusion technology. Subsequently, these composite materials were transformed into ABS/TPU/chlorella skeletons (ATCh40), through fused deposition molding (FDM) technology. The integration of Fe2O3 onto the ATCh40 (ATCh40-Fe2O3) skeletons was accomplished by subjecting them to controlled heating in an oil bath. A comprehensive characterization of the synthesized materials confirms the successful growth of Fe2O3 on the surface of 3D skeletons. This strategy effectively addresses the immobilization challenges associated with powdered photocatalysts. In photocatalytic degradation experiments targeting methyl orange (MO), the ATCh40-Fe2O3 skeletons exhibited a remarkable MO removal rate of 91% within 240 min. Under conditions where the pH of MO solution was maintained at 3, and the ATCh40-Fe2O3 skeletons were subjected to a heat treatment in a 150 °C blast drying oven for 2 hours, the degradation rate of MO remained substantial, achieving 90% removal after 6 cycles. In contrast, when the same synthetic procedure was applied to ABS/TPU (AT) skeletons, the resulting product was identified as α-FeOOH. The MO removal rate by the AT-α-FeOOH skeletons was considerably lower, reaching only 49% after 240 min. This research provided a practical approach for the construction of photocatalytic devices through the use of 3D printing technology.

Nylon Fabric/GO Based Self-Powered Humidity Sensor Based on the Galvanic Cell Principle with High Air Permeability and Rapid-Response.

Flexible humidity sensors have received more and more attention in people's lives, and the problems of gas permeability and power supply issues of the device have long been areas in need of improvement. In this work, inspired by the high air permeability of daily wear clothing and galvanic batteries, a self-powered humidity sensor with high air permeability and fast response is designed. A nylon fabric/GO net (as a humidity sensitive layer and solid electrolyte) is obtained by spraying technique. This structure enables the sensor to have fast response/recovery (0.78 s/0.93 s, calculated at 90% of the final value), ultra-high response (0.83 V) and excellent stability (over 150 cycles) at 35 °C. Such sensors are useful for health monitoring, such as non-contact monitoring of human respiratory rate before and after exercise, and monitoring a level of humidity in the palms, arms, and fingers. This research provides an idea for developing a flexible wearable humidity sensor that is both breathable and self-powered and can also be mass-produced similar to wearable clothing.

Pressure-Regulated Nanoconfined Channels for Highly Effective Mechanical-Electrical Conversion in Proton Battery-Type Self-Powered Pressure Sensor.

Battery-sensing-based all-in-one pressure sensors are generally successfully constructed by mimicking the information transfer of living organisms and the sensing behavior of human skin, possessing features such as low energy consumption and detection of low/high-frequency mechanical signals. To design high-performance all-in-one pressure sensors, a deeper understanding of the intrinsic mechanisms of such sensors is required. Here, a mechanical-electrical conversion mechanism based on pressure-modulated nanoconfined channels is proposed. Then, the mechanism of ion accelerated transport in graphene oxide (GO) nanoconfined channels under pressure is revealed by density functional theory (DFT) calculation. Based on this mechanism, a proton battery-type self-powered pressure sensor MoO3 /GO[CNF/Ca] /activated carbon (AC) is designed with an open-circuit voltage stabilization of 0.648 V, an ultrafast response/recovery time of 86.0 ms/93.0 ms, pressure detection ranges of up to 60.0 kPa, and excellent static/dynamic pressure response. In addition, the one-piece device design enables self-supply, miniaturization, and charge/discharge reuse, showing application potential in wearable electronics, health monitoring, and other fields.

Insights into the Acid-Induced Gelation of Original Pectin from Potato Cell Walls by Gluconic Acid-δ-Lactone.

The acid-induced gelation of pectin in potato cell walls has been gradually recognized to be related to the improvement in the cell wall integrity after heat processing. The aim of this study was to characterize the acid-induced gelation of original pectin from a potato cell wall (OPP). Rheological analyses showed a typical solution-sol-gel transition process of OPP with different additions of gluconic acid-δ-lactone (GDL). The gelation time (Gt) of OPP was significantly shortened from 7424 s to 2286 s. The complex viscosity (η*) of OPP gradually increased after 4000 s when the pH was lower than 3.13 and increased from 0.15 to a range of 0.20~6.3 Pa·s at 9000 s. The increase in shear rate caused a decrease in η, indicating that OPP belongs to a typical non-Newtonian fluid. Furthermore, a decrease in ζ-potential (from -21.5 mV to -11.3 mV) and an increase in particle size distribution (from a nano to micro scale) was observed in OPP after gelation, as well as a more complex (fractal dimension increased from 1.78 to 1.86) and compact (cores observed by cryo-SEM became smaller and denser) structure. The crystallinity of OPP also increased from 8.61% to 26.44%~38.11% with the addition of GDL. The above results call for an investigation of the role of acid-induced OPP gelation on potato cell walls after heat processing.

A Zinc-Ion Battery-Type Self-Powered Pressure Sensor with Long Service Life.

Accurate and continuous pressure signal detection without external power supply is a key technology to realize the miniaturization of wearable electronic equipment, the internet of things, and artificial intelligence. However, it is difficult to be achieved by using current sensor technologies. Here, a new one-body strategy, i.e., zinc-ion battery pressure (ZIB-P) sensor technology, which designs the rechargeable solid-state ZIB itself as a flexible pressure sensor is reported. In the device, an isolation layer is introduced into the sandwich configuration solid-state battery to realize the change of device internal resistance by pressure during the transformation of the mechanical signal to the electrical signal. This battery pressure sensor possesses good flexibility, fast response/recovery time (76.0/88.0 ms), stable long-term response, excellent cycle stability (100 000 times), and wide pressure detection range (2.0 to 3.68 × 105  Pa). Especially, the excellent charge-discharge performance in the ZIB-P sensor endows it with the real-time detection ability of human vital signs (pulse, limb movement, etc.) and ultrahigh stability without degradation even under 100 000 times pressure stimulation. The ZIB-P sensor strategy provides a new solution for the future development of miniaturized wearable electronic devices.

Flexible MXene/Bacterial Cellulose Film Sound Detector Based on Piezoresistive Sensing Mechanism.

Flexible pressure sensors have aroused extensive attention in health monitoring, human-computer interaction, soft robotics, and more, as a staple member of wearable electronics. However, a majority of traditional research focuses solely on foundational mechanical sensing tests and ordinary human-motion monitoring, ignoring its other applications in daily life. In this work, a paper-based pressure sensor is prepared by using MXene/bacterial cellulose film with three-dimensional isolation layer structure, and its sensing capability as a wearable sound detector has also been studied. The as-prepared device exhibits great comprehensive mechanical sensing performance as well as accurate detection of human physiological signals. As a sound detector, not only can it recognize different voice signals and sound attributes by monitoring movement of throat muscles, but also it will distinguish a variety of natural sounds through air pressure waves caused by sound transmission (also called sound waves), like the eardrum. Besides, it plays an important role in sound visualization technology because of the ability for capturing and presenting music signals. Moreover, millimeter-scale thickness, lightweight, and degradable raw materials make the sensor convenient and easy to carry, meeting requirements of environmental protection as well.

Studying Plasmon Dispersion of MXene for Enhanced Electromagnetic Absorption.

2D metal carbides and nitrides (MXene) are promising candidates for electromagnetic (EM) shielding, saturable absorption, thermal therapy, and photocatalysis owing to their excellent EM absorption. The plasmon resonances in metallic MXene micro/nanostructures may play an important role in enhancing the EM absorption; however, their contribution has not been determined due to the lack of a precise understanding of its plasmon behavior. Here, the use of high-spatial-resolution electron energy-loss spectroscopy to measure the plasmon dispersion of MXene films with different thicknesses is reported, enabling accurate analysis of the EM absorption of complex MXene structures in a wide frequency range via a theoretical model. The EM absorption of MXene can be excited at the desired frequency by controlling the momentum (e.g., the sizes of the nanoflakes for EM excitation) as the strength can be enhanced by increasing the layer number and the interlayer distance in MXene. For example, a 3 nm interlayer distance can nearly double the plasmon-enhanced EM absorption in MXene nanostructures. These findings can guide the design of advanced ultrathin EM absorption materials for a broad range of applications.

Selective Decomposition of Waste Rubber from the Shoe Industry by the Combination of Thermal Process and Mechanical Grinding.

A major challenge in waste rubber (WR) industry is achieving a high sol fraction and high molecular weight of recycled rubber at the same time. Herein, the WR from the shoe industry was thermo-mechanically ground via the torque rheometer. The effect of grinding temperature and filling rate were systematically investigated. The particle size distribution, structure evolution, and morphology of the recycled rubber were explored by laser particle size analyzer, Fourier transform infrared spectroscopy (FTIR), sol fraction analysis, gel permeation chromatography (GPC), differential scanning calorimeter (DSC), and scanning electron microscope (SEM). The results indicate that the thermo-mechanical method could reduce the particle size of WR. Moreover, the particle size distribution of WR after being ground can be described by Rosin's equation. The oxidation reaction occurs during thermal-mechanical grinding. With the increase of the grinding temperature and filling rate, the sol fraction of the recycled WR increases. It is also found that a high sol fraction (43.7%) and high molecular weight (35,284 g/mol) of reclaimed rubber could be achieved at 80 °C with a filling rate of 85%. Moreover, the obtained recycled rubber compound with SBR show a similar vulcanization characteristics to pure SBR. Our selective decomposition of waste rubber strategy opens up a new way for upgrading WR in shoe industry.

Roles of MXene in Pressure Sensing: Preparation, Composite Structure Design, and Mechanism.

Flexible pressure sensors are one of the most important components in the fields of electronic skin (e-skin), robotics, and health monitoring. However, the application of pressure sensors in practice is still difficult and expensive due to the limited sensing properties and complex manufacturing process. The emergence of MXene, a red-hot member of the 2D nanomaterials, has brought a brand-new breakthrough for pressure sensing. Ti3 C2 Tx is the most popular studied MXene in the field of pressure sensing and shows good mechanical, electrical properties, excellent hydrophilicity, and extensive modifiability. It will ameliorate the properties of the sensitive layer and electrode layer of the pressure sensor, and further apply pressure sensing to many fields, such as e-skin flexibility. Herein, the preparation technologies, antioxidant methods, and properties of MXene are summarized. The design of MXene-based microstructures is introduced, including hydrogels, aerogels, foam, fabrics, and composite nanofibers. The mechanisms of MXene pressure sensors are further broached, including piezoresistive, capacitive, piezoelectric, triboelectric, and potentiometric transduction mechanism. Moreover, the integration of multiple devices is reviewed. Finally, the chance and challenge of pressure sensors improved by MXene smart materials in future e-skin and the Internet of Things are prospected.

Antibiotic residue and toxicity assessment of wastewater during the pharmaceutical production processes.

Various pollutants are released during pharmaceutical production processes, which is of great concern. Most studies have focused on the terminal treatment results of mixed pharmaceutical wastewater, and further research on wastewater from the production processes is required. This study investigated the wastewater quality indicators, residual antibiotics, and biological toxicity of the wastewater during the production process in a large pharmaceutical producing factory in Northern China. The wastewater contained numerous organic pollutants, with the chemical oxygen demand (COD) values ranging from 2.0 × 103 to 2.6 × 105 mg L-1 and the total nitrogen (TN) values ranging from 1.3 × 103 to 2.0 × 104 mg L-1. High concentrations of cephalexin and cefradine remained in the wastewater of the production workshop, with the highest concentration of cefradine reaching 1328 mg L-1. The wastewater from the oxidation and solvent recovery workshops was more toxic to Vibrio fischeri and Daphnia magna than that of other workshops. Moreover, the biological acute toxicity of wastewater was significantly correlated with the concentration of COD and TN (p < 0.01). This study provides new insights into the treatment of antibiotic production wastewater, illuminating the incomplete extraction of products and the significant risk posed by pharmaceutical wastewater to the environment.

Residual ß-lactam antibiotics and ecotoxicity to Vibrio fischeri, Daphnia magna of pharmaceutical wastewater in the treatment process.

The discharge of pharmaceutical wastewater introduces numerous pollutants into the environment, and their pollution level reduction has aroused extensive concern. This study investigated the variation in residual antibiotics and ecotoxicity to two nutritional-level model organisms in the pharmaceutical wastewater treatment process (PWTP). The wastewater in the equalization tank contained massive organic matters (2.9-18.7 times higher than the permissible values in GB21903-2008) and antibiotics (310.88 µg/L), posing extremely toxic effects to Vibrio fischeri (V. fischeri) and Daphnia magna (D. magna). The biological anaerobic/aerobic treatment units contributed the most to the reduction of antibiotics and the ecotoxicity to both organisms, with the removal rates of 72% and > 90%, respectively. The ecotoxicity of pharmaceutical wastewater was strongly and positively correlated with the residual antibiotics, amoxicillin, cephalexin, ammonia nitrogen, and total phosphorus (P < 0.05). However, the detected amounts of amoxicillin and cephalexin were approximately 105 times lower than the predicted no-effect concentrations of amoxicillin and cephalexin to V. fischeri and D. magna in freshwater, which implied the joint ecotoxicity posed by multicomponent mixtures, such as the residual antibiotics and organic toxic substances, rather than the specific residual antibiotics. This study provides a better understanding of the variations and residual levels of pollutants in PWTPs, including their ecotoxicity risk to the aquatic environment, highlighting the need to optimize pharmaceutical wastewater treatment technologies.

Tensible and flexible high-sensitive spandex fiber strain sensor enhanced by carbon nanotubes/Ag nanoparticles.

Although the wearable strain sensors have received extensive research interest in recent years, it remains a huge challenge conforming the requirements in both of ultrahigh stretchability and high strain coefficient (gauge factor). Herein, a stretchable and flexible spandex fiber strain sensor coupled with carbon nanotubes (CNTs)/Ag nanoparticles (Ag NPs) that assembled through an efficient and large-scale layer-by layer self-assembly is presented. To ensure CNTs and Ag NPs can attach well to the spandex fiber without falling off, achieving high sensitivity under large tensile, sodium dodecyl benzene sulfonate, polyvinyl alcohol, and polystyrene sulfonic acid are introduced to improve the adhesion via the molecular entanglement and other interactions between them. Consequently, the strain sensor exhibits remarkable performance, such as an ultrahigh gauge factor of 58.5 in the low-strain range from 0% to 20%, a wide strain range (0%-200%), a fast response time of 42 ms and good working stability (>5000 stretching-releasing cycles). Subsequently, detailed mechanism of the sensor and its use in full range of human motion monitoring are further studied. It is worth noting that with the distinctive mechanism and structure, the special spandex fiber sensor is able to monitor minimum strain as low as 0.053%, showing tremendous prospect for the field of smart fabrics and wearable health care devices.

MOF-derived zirconia-supported Keggin heteropoly acid nanoporous hybrids as a reusable catalyst for methyl oleate production.

In this study, a series of nanoporous HSiW@ZrO2 hybrids were synthesized using a zirconium metal-organic framework UiO-66 as a precursor towards biodiesel production. The structural and morphological properties of the obtained hybrids were characterized by the wide-angle XRD, FTIR, SEM, TEM, N2 adsorption/desorption, and NH3-TPD methods. Moreover, their catalytic activity in terms of calcination temperature during preparation was investigated, and the HSiW@ZrO2 hybrids calcinated at 300 °C exhibited the highest activity and the oleic acid (OA) conversion of 94.0% owing to the presence of the relatively high surface area, appropriate pore size and strong acidity. It was also revealed that the hybrids maintained as high as 82.0% even after nine cycles. Intriguingly, the nanoporous catalysts were found to exhibit excellent catalytic activity towards the esterification of the high acid value of Jatropha curcas oil.

Efficient Production of Biodiesel from Esterification of Lauric Acid Catalyzed by Ammonium and Silver Co-Doped Phosphotungstic Acid Embedded in a Zirconium Metal-Organic Framework Nanocomposite.

A novel solid acid nanocatalyst (Ag1(NH4)2PW12O40/UiO-66) comprising ammonium and silver co-doped H3PW12O40 and zirconium-based metal-organic frameworks (UiO-66) was synthesized and characterized by Fourier transform infrared spectroscopy, N2 adsorption/desorption, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, and ammonia temperature-programmed desorption. The catalytic activity was evaluated for the synthesis of biodiesel via esterification of lauric acid and methanol. The effect of the operating parameters including the molar ratio of lauric acid to methanol, catalyst amount, and reaction temperature and time on the lauric acid conversion was also investigated to obtain optimum reaction conditions. Also, the composite (Ag1(NH4)2PW12O40/UiO-66) was recyclable and reused up to six cycles. Kinetics of the lauric acid esterification has been assumed to be of a pseudo-first order, and the results showed that the activation energy for the esterification process was found to be 35.2 kJ/mol.

Corrigendum: Green and Facile Synthesis of Metal-Organic Framework Cu-BTC-Supported Sn (II)-Substituted Keggin Heteropoly Composites as an Esterification Nanocatalyst for Biodiesel Production.

[This corrects the article DOI: 10.3389/fchem.2020.00129.].

Green and Facile Synthesis of Metal-Organic Framework Cu-BTC-Supported Sn (II)-Substituted Keggin Heteropoly Composites as an Esterification Nanocatalyst for Biodiesel Production.

In the present study, metal-organic framework Cu-BTC-supported Sn (II)-substituted Keggin heteropoly nanocomposite (Sn1.5PW/Cu-BTC) was successfully prepared by a simple impregnation method and applied as a novel nanocatalyst for producing biodiesel from oleic acid (OA) through esterification. The nanocatalyst was characterized by Fourier transform infrared spectrometry (FTIR), wide-angle X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen adsorption-desorption, thermogravimetrics (TG), and NH3-temperature-programmed desorption (NH3-TPD). Accordingly, the synthesized nanocatalyst with a Sn1.5PW/Cu-BTC weight ratio of 1 exhibited a relatively large specific surface area, appropriate pore size, and high acidity. Moreover, an OA conversion of 87.7% was achieved under optimum reaction conditions. The nanocatalyst was reused seven times, and the OA conversion remained at more than 80% after three uses. Kinetic study showed that the esterification reaction followed first-order kinetics, and the activation energy (E a ) was calculated to be 38.3 kJ/mol.

Efficient biodiesel production from oleic acid using metal-organic framework encapsulated Zr-doped polyoxometalate nano-hybrids.

According to the need of sustainable development, solid catalysts are critical materials for green biodiesel production. In this study, a hydrothermal method was used to develop a reusable and highly active Fe-BTC and UiO-66 metal-organic framework encapsulated Zr-doped polyoxometalate nano-hybrid catalysts (ZrSiW/Fe-BTC and ZrSiW/UiO-66) for the acid-catalyzed esterification of oleic acid with methanol. The structural and compositional characterization of the synthesized catalysts were characterized using various techniques such as Fourier transform infrared spectrometry (FT-IR), X-ray diffraction (XRD), nitrogen adsorption-desorption, scanning electron microscopy (SEM), and thermogravimetric (TG) and temperature programmed desorption (NH3-TPD) analysis. The as-prepared ZrSiW/UiO-66 had excellent catalytic activity in the esterification of oleic acid with methanol, higher than that of ZrSiW/Fe-BTC catalyst, owing to the fact that ZrSiW/UiO-66 nano-hybrids have high acidity, large specific surface area and pore volumes, and relatively large average pore sizes. Furthermore, the reusability and stability of nano-hybrids were also evaluated, and it was found that the stability of ZrSiW/UiO-66 catalyst was better.

[Distribution Characteristics of Sulfonamide Antibiotic Resistance Genes in a Drinking Water Source in East China].

Antibiotic resistance genes (ARGs) in drinking water sources have attracted widespread attention due to the threat they pose to water security and human health. This study mainly focused on the distribution of sulfonamide ARGs (sul 1, sul 2) and one integrase gene (intI 1) in water and sediment using qualitative and fluorescent quantitative PCR, based on previous work on the characteristics of 13 kinds of sulfonamides in a drinking water source in East China. Results showed that the three target genes were all detected in water and sediment. The sul 1 gene was the sulfonamide ARG with highest concentration, with 1.5×104-6.4×105 copies·mL-1 in source water and maximum concentration of 1.6×108 copies·g-1 in sediment. Concentration of sul 1 was 0.6-2.2, 0.5-1.9 order of magnitudes higher than sul 2 and intI 1 genes, respectively. There was no significant difference between the absolute concentrations of sul 1, sul 2, and intI 1 in inflow and outflow. However, in the case of sediment, absolute abundances of sul 1, sul 2, and intI 1 in outflow were higher than those in inflow. The maximum concentration of sul 1 was detected in outflow in summer (6.4×105 copies·mL-1). The concentration of intI 1 was higher in winter compared to other seasons. There was a positive correlation between sul 1 and 13 sulfonamides (r=0.69, P<0.05), and the relative concentration of sul 1 and amount of sulfamethoxazole were significantly positively related (r=0.79, P<0.01). There were also positive correlations between the relative concentrations of intI 1 and sul 1, sul 2 (r:0.80 and 0.73, P<0.05), respectively, suggesting that intI 1 played an important role in horizontal gene transfer of sulfonamide ARGs in this drinking water source. This study provides basic data for monitoring pollution of ARGs, as well as a basis for controlling ARG pollution in the drinking water environment and making management decisions.