Hydrophobically Associated Hydrogel for High Sensitivity and Resolution of an Interdigital Electrode Pressure Sensor.

Hydrogel-based flexible strain sensors have been known for their excellent ability to convert different motions of humans into electrical signals, thus enabling real-time monitoring of various human health parameters. In this work, a composite hydrogel with hydrophobic association and hybrid cross-linking was fabricated by using polyacrylamide (PAm), surfactant sodium dodecyl sulfate (SDS), lauryl methacrylate (LMA), and polypyrrole (PPy). The dynamic dissociation-conjugation among LMA, SDS, and PPy could dissipate energy to improve the toughness of hydrogels. The SDS/PPy/LMPAm composite hydrogel with a toughness of 1.44 MJ/m3, tensile fracture stress of 345 kPa, tensile strain of 1021%, and electrical conductivity of 0.57 S/m was obtained. Furthermore, an interdigital electrode flexible pressure sensor was designed to replace the bipolar electrode flexible pressure sensor, which greatly improved the sensitivity and resolution of the pressure sensor. The SDS/PPy/LMPAm composite hydrogel-based interdigital electrode flexible pressure sensor showed extraordinary stability and identified different hand gestures as well as monitored the pulse signal of humans. Moreover, the characteristic systolic and diastolic peaks were clearly observed. The pulse frequency (65 times/min) and the radial artery augmentation index (0.57) were calculated, which are very important in evaluating the arterial vessel wall and function of human arteries.

Recent Advances in UV-Cured Encapsulation for Stable and Durable Perovskite Solar Cell Devices.

The stability and durability of perovskite solar cells (PSCs) are two main challenges retarding their industrial commercialization. The encapsulation of PSCs is a critical process that improves the stability of PSC devices for practical applications, and intrinsic stability improvement relies on materials optimization. Among all encapsulation materials, UV-curable resins are promising materials for PSC encapsulation due to their short curing time, low shrinkage, and good adhesion to various substrates. In this review, the requirements for PSC encapsulation materials and the advantages of UV-curable resins are firstly critically assessed based on a discussion of the PSC degradation mechanism. Recent advances in improving the encapsulation performance are reviewed from the perspectives of molecular modification, encapsulation materials, and corresponding architecture design while highlighting excellent representative works. Finally, the concluding remarks summarize promising research directions and remaining challenges for the use of UV-curable resins in encapsulation. Potential solutions to current challenges are proposed to inspire future work devoted to transitioning PSCs from the lab to practical application.

Enhanced plasmonic photocatalytic performance of C doped TiN nanocrystals through ultrathin carbon layers.

Carbon-doped TiN nanoparticles on an ultrathin carbon layer, were successfully used for photocatalytic dye degradation synthesised by a simple calcination process. The resulting catalyst exhibited remarkable plasmonic photocatalytic performance under visible light irradiation. In comparison with benchmark rutile TiO2 and g-C3N4/TiO2 heterostructure catalysts, the first-order reaction rate constant of the developed catalyst improved approximately 34.2 and 6.5 times, respectively. The doping concentration of carbon and the crystal size of TiN nanoparticles, predominantly influenced by the amount of urea and calcination temperature, were identified as crucial factors governing the plasmonic photocatalytic activity. Density functional theory (DFT) calculations indicated that the introduction of carbon-sp bands into the TiN band structure promoted interband excitation of electrons and facilitated the generation of hotter holes, thereby enhancing the degradation of dyes and ultimately contributing to the superior photocatalytic activity observed.

Synergistic Effects of Interfacial Energy Level Regulation and Stress Relaxation via a Buried Interface for Highly Efficient Perovskite Solar Cells.

An electron-transport layer with appropriate energy alignment and enhanced charge transfer is critical for perovskite solar cells (PSCs). In addition, interface stress and lattice distortion are inevitable during the crystallization process of perovskite. Herein, IT-4F is introduced into PSCs at the buried SnO2 and perovskite interface, which assists in releasing the residual stress in the perovskite layer. Meanwhile, the work function of SnO2/IT-4F is lower than that of SnO2, which facilitates charge transfer from perovskite to ETL and consequently leads to a significant improvement in the power conversion efficiency (PCE) to 23.73%. The VOC obtained is as high as 1.17 V, corresponding to a low voltage deficit of 0.38 V for a 1.55 eV bandgap. Consequently, the device based on IT-4F maintains 94% of the initial PCE over 2700 h when stored in N2 and retains 87% of the initial PCE after operation for 1000 h.

Dopant-Free Polymer Hole Transport Materials for Highly Stable and Efficient CsPbI3 Perovskite Solar Cells.

All-inorganic perovskite CsPbI3 contains no volatile organic components and is a thermally stable photoactive material for wide-bandgap perovskite solar cells (PSCs); however, CsPbI3 readily undergoes undesirable phase transitions due to the hygroscopic nature of the ionic dopants used in commonly used hole transport materials. In the current study, the popular donor material PM6 in organic solar cells is used as a hole transport layer (HTL). The benzodithiophene-based backbone-conjugated polymer requires no dopant and leads to a higher power conversion efficiency (PCE) than 2,2',7,7'-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'-spirobifluorene (Spiro-OMeTAD). Moreover, PM6 also shows priorities in hole mobility, hydrophobicity, cascade energy level alignment, and even defect passivation of perovskite films. With PM6 as the dopant-free HTL, the PSCs achieve a champion PCE of 18.27% with a competitive fill factor of 82.8%. Notably, the present PCE is based on the dopant-free HTL in CsPbI3 PSCs reported thus far. The PSCs with PM6 as the HTL retain over 90% of the initial PCE stored in a glovebox filled with N2 for 3000 h. In contrast, the PSCs with Spiro-OMeTAD as the HTL maintain ≈80% of the initial PCE under the same conditions.

A Ratiometric Probe Based on Carbon Dots and Calcein & Eu3+ for the Fluorescent Detection of Sodium Tripolyphosphate.

Sodium tripolyphosphate, a food additive, is applied broadly in food industry. However, excessive accumulation of sodium tripolyphosphate can result in electrolyte abnormality of the body. Therefore, it is of great importance to investigate an effective method for the detection of sodium tripolyphosphate. In this work, nitrogen-doped carbon dots (NCDs) with constant fluorescence were fabricated using a domestic microwave oven. A ratiometric fluorescent probe was constructed in which NCDs were as internal standard, calcein & Eu3+ were as the detection signal. The fluorescence of calcein at 515 nm was quenched by Eu3+, whereas the emission peak of NCDs at 446 nm was almost unchanged. Additionally, the fluorescence of calcein was recovered because of the strong interaction of sodium tripolyphosphate and Eu3+. The linear range for sodium tripolyphosphate was 0.5-6 µmol/L with detection limit of 0.12 µmol/L. Furthermore, the ratiometric fluorescent probe was applied for sodium tripolyphosphate detection in real milk samples.

Fabrication of sodium alginate-melamine@ZIF-67 composite hydrogel and its adsorption application for Pb(II) in wastewater.

A low-cost and environmental-friendly sodium alginate-melamine@zeolitic imidazolate framework-67 (SA-ME@ZIF-67) adsorbent was fabricated by chemical grafting and in situ growth for the removal of lead ions in wastewater. Firstly, melamine (ME) was grafted onto sodium alginate (SA) by amide reaction, and then SA-ME was dropped into a solution of calcium chloride to form hydrogel bead, and ZIF-67 was grown on the SA-ME hydrogel bead by the in situ growth method. The SA-ME@ZIF-67 adsorbent was characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. The SA-ME@ZIF-67 adsorbent was used to effectively adsorb Pb(II) from aqueous solutions. The initial concentrations of lead ions, adsorbent dose, initial pH of lead ion solution, temperature, and adsorption time for the material were optimized. The adsorption isotherms and kinetics fitted to Langmuir isotherm model (R2 = 0.9281, 0.9420, and 0.9623 at the temperatures of 288.15 K, 298.15 K, and 308.15 K, respectively) and pseudo-second-order kinetic model (R2 = 0.9901) respectively. According to the Langmuir model at 308.15 K, the maximum adsorption capacity of the adsorbent for Pb(II) was 634.99 mg/g. The recycling application of the adsorbent was possible as it was easily collected and reused after five adsorption-regeneration cycles. In addition, the Pb(II) in real wastewater samples has been efficiently removed using the fabricated hydrogel. The results showed that the SA-ME@ZIF-67 adsorbent had high adsorption capacity, removal efficiency, and easy recyclability for Pb(II).

Highly Elastic, Sensitive, Stretchable, and Skin-Inspired Conductive Sodium Alginate/Polyacrylamide/Gallium Composite Hydrogel with Toughness as a Flexible Strain Sensor.

As a classic flexible material, hydrogels show great potential in wearable electronic devices. The application of strain sensors prepared using them in human health monitoring and humanoid robotics is developing rapidly. However, it is still a challenge to fabricate a high-toughness, large-tensile-deformation, strain-sensitive. and human-skin-fit hydrogel with the integration of excellent mechanical properties and high electrical conductivity. In this study, a flexible sensor using a highly strain-sensitive skin-like hydrogel with acrylamide and sodium alginate was designed using liquid metallic gallium as a "reactive" conductive filler. The sensor had a low elastic modulus (30 kPa) similar to that of skin, a high-toughness (2.25 MJ m-3), self-stiffness, a large tensile deformation (1400%), recoverability, and excellent fatigue resistance. Moreover, the addition of gallium might enhance the electrical conductivity (1.9 S m-1) of the hydrogel while maintaining high transparency, and the flexible sensor device constructed from it showed high sensitivity to strain (gauge factor = 4.08) and pressure (gauge factor = 0.455 kPa-1). As a result, the hydrogel sensor could monitor various human motions, including large-scale joint bending and tiny facial expression, breathing, voice recognition, and handwriting. Furthermore, it might even be used for human-computer communication.

Fabrication of in situ ZIF-67 grown on alginate hydrogels and its application for enhancing Cu (II) adsorption from aqueous solutions.

Synthesizing high uniform metal-organic frameworks grown on natural biomass such as sodium alginate (ALG), which can efficiently remove metal ions from aqueous solution, is a challenging project. A simple and eco-friendly method of preparing ALG@ZIF-67 hydrogels by in situ synthesis of ZIF-67 onto ALG hydrogels was established. Combining the virtues of ALG with abundant hydroxyl and carboxyl groups and ZIF-67 with excellent porous structure, the obtained ALG@ZIF-67 hydrogels have excellent adsorption for Cu2+ (153.63 mg/g), which was much higher than that of pure ALG hydrogels (111.79 mg/g). The methodology showed that the adsorption process was in accord with the Langmuir isotherm adsorption model (R2 = 0.9972) and pseudo-second-order kinetic model (R2 = 0.9822). The thermodynamic experiments demonstrated that Cu (II) was absorbed by hydrogel with an endothermic and spontaneous process. The competitive adsorption experiment results of ALG@ZIF-67 hydrogel indicated that the absorption capacity of Cu (II) was higher than that of Cd (II), Ni (II), Zn (II) and Mn (II). Moreover, the ALG@ZIF-67 hydrogels still had excellent reusability after five adsorption-desorption cycles. The results indicated that the ALG@ZIF-67 hydrogels had the advantages of low cost, easy preparation, and environment friendly.

In situ synthesis of fluorescent polydopamine polymer dots based on Fenton reaction for a multi-sensing platform.

The development of fluorescent nanosensors has attracted extensive research interest owing to their superior optoelectronic properties. However, current fluorescent nanoprobes generally involve complicated synthesis processes, background signal disturbance, and limited analyte detection. In this work, a facile and time-saving synthetic strategy for the preparation of green emitting polydopamine polymer dots (PDA-PDs) from dopamine via Fenton reaction at room temperature was proposed for the first time. The obtained PDA-PDs possessed excellent luminescence properties, with a long-wavelength emission of 522 nm, a large Stokes shift of 142 nm, and good photostability against ionic strength and UV irradiation. The formation mechanism of fluorescent PDA-PDs is as follows: in the presence of Fe2+ and H2O2, dopamine could rapidly undergo oxidation to its quinone derivatives and further polymerize to synthesize the fluorescent PDA-PDs with the acceleration of hydroxyl radicals produced from the Fenton reaction. Thus, a versatile turn-on fluorescence sensing method was developed for the detection of multi-analytes (including Fe2+, dopamine, H2O2, and glucose) based on monitoring the intrinsic fluorescence signal of the in situ formation of PDA-PDs. This sensing method could be efficiently applied for the detection of Fe2+, dopamine, and glucose in real human serum samples. Moreover, a three-input AND molecular logic gate based on this sensing platform was designed with the fluorescence signal of PDA-PDs as the gate. Finally, the proposed PDA-PDs could have immense broad prospects in nanomaterials and biosensors.

A biomimetic "polysoap" for single-walled carbon nanotube dispersion.

As-synthesized single-walled carbon nanotubes (SWNTs) are bundled mixtures of different species. The current challenge in the field of carbon nanotube research lies in the processing and separation of SWNTs, which first require efficient dispersion of individual SWNTs in solvents. We report DNA-mimicking polysoap surfactants that disperse SWNTs in aqueous solutions more effectively than DNA. The polysoaps are synthesized by functionalizing the side chain of poly(styrene-alt-maleic acid) with aminopyrene. The synthetic nature of the polysoap opens a new approach to further optimization of not only SWNT dispersion efficiency but also multi-functional SWNT dispersing surfactant.