The precise control and monitoring of pH values remain critical for many chemical, physiological and biological processes. Perylene diimide (PDI)-based molecules and materials exhibit excellent thermal, chemical and photochemical stability, unique UV-vis absorption and fluorescent emission properties, low cytotoxicity, as well as intrinsic electron-withdrawing (n-type semiconductor) nature and impressive molecular assembly capability. These features combined enable promising applications of PDIs in chemosensors via optical signal modulations (e.g., fluorescent or colorimetric). One of the typical applications lies in the probing of pH under various conditions, which in turn helps monitor the extracellular (environmental) and intracellular pH change and pH-relying molecular recognition of inorganic or organic ions, as well as biological species, and so on. In this review, we give a special overview of the recent progress in PDI-based optical chemosensors for pH probing in various aqueous and binary water–organic media. Specific emphasis will be given to the key design roles of sensing materials regarding the architectures and the corresponding sensing mechanisms for a sensitive and selective pH response. The molecular design of PDIs and structural optimization of their assemblies in order to be suitable for sensing various pH ranges as applied in diverse scenarios will be discussed in detail. Moreover, the future perspective will be discussed, focusing on the current key challenges of PDI-based chemosensors in pH monitoring and the potential approach of new research, which may help address the challenges.

Hydrogen peroxide (H₂O₂), a common oxidant present in the environment, food, and biological systems, has wide-ranging applications. While H₂O₂ is generally considered non-toxic, prolonged or repeated exposure to high concentrations can be harmful, making its accurate detection crucial in environmental monitoring, food safety, healthcare, and other fields. This review delves into the recent advancements in H₂O₂ detection methods, with a particular focus on chemosensors. We comprehensively summarize the fundamental principles of various chemosensor principles (e.g., colorimetric, fluorescence, chemiluminescence, electrochemical, and chemiresistive approaches), active materials, and diverse applications. Additionally, we discuss the current challenges and future prospects in this field, emphasizing the need for innovative materials and advanced sensing technologies to meet the growing demand for highly sensitive, accurate, reliable, real-time, and cost-effective H₂O₂ detection solutions.

Despite the fact that PEDOT:PSS has been successfully used in the field of flexible electronics, some of its applications in the domain of rigid conductive coating have been limited by the pricey cost and subpar mechanical properties (hardness, adhesion, and moisture absorption) of the commercially available Clevios™ PH 1000, as well as the poor conductivity, film formation, and mechanical properties of the self-made PEDOT:PSS. In the process of investigating the low-cost preparation of PEDOT-based conductive polymer coatings, we discovered that self-made PEDOT:PSS, a waterborne epoxy resin, and a bio-based epoxy curing agent can be blended uniformly to produce good film-forming conductive coatings. Later, the addition of KH560-modified nano-SiO₂ further improved the coating’s hardness while ensuring a modest increase in conductivity. Meanwhile, the inadequacies of the epoxy resin, which are not UV-resistant, were considerably improved by the synergistic action of PEDOT:PSS and the modified SiO₂. The result is a low-cost method designed for creating conductive coatings that are UV-resistant and may be utilized for electromagnetic, electrothermal, and antistatic shielding applications. Such a PEDOT:PSS/epoxy composite system and its design approach will broaden the scope of PEDOT:PSS’s application and will inspire future research in and practical implementations of PEDOT:PSS-based conducting coatings.

Before steel can be utilized, pickling is necessary to remove surface oxidation products. However, as the ferrous ion concentration in the pickling solution increases, the pickling rate significantly diminishes, necessitating the treatment of spent pickling solution (SPS) to mitigate its hazardous effects prior to disposal. Current industrial methods predominantly rely on neutralization and precipitation techniques, which are cost-prohibitive and generate substantial by-products, thus failing to meet environmental protection standards. In this study, a new method, which is based on the formation of FeC₂O₄·2H₂O precipitate in a strong acid solution, is proposed to treat the SPS. Initially, the SPS undergoes a two-step impurity removal process, followed by the controlled addition of oxalic acid dihydrate (H₂C₂O₄·2H₂O) to precipitate iron. The resulting precipitate is filtered, washed, and vacuum-dried, and the regenerated acid is recycled back into the pickling tank. When 1 g/10 mL of H₂C₂O₄·2H₂O is used, the iron removal rate achieves 60%, and the acidity of the regenerated acid increases by 11.3%. X-ray diffraction pattern (XRD) and thermogravimetric–differential scanning calorimetry (TG-DSC) characterization showed that the precipitate was α-FeC₂O₄·2H₂O, with an average particle size of about 3.19 μm and a purity of 95.24%. This process innovatively achieves efficient recycling of acid and iron resources, offering a potential solution to the industrial challenge of difficult SPS treatment in the steel industry and meeting the urgent need for sustainable development.

Poly (3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) stands out as a renowned commercial conducting polymer composite, boasting extensive and promising applications in the realm of film electronics. In this study, we have made a concerted effort to overcome the inherent drawbacks of PEDOT:PSS films (especially, high moisture absorption, mechanical damage vulnerability, insufficient substrate adhesion ability, etc.) by uniformly blending them with polydimethylsiloxane polyurea (PDMS-PUa) and silica (SiO₂) nanoparticles through a feasible mechanical stirring process, which effectively harnesses the intermolecular interactions, as well as the morphological and structural characteristics, among the various components. The Si−O bonds within PDMS-PUa and the −CH₃ groups attached to Si atoms significantly enhance the hydrophobicity of the composite film (as evidenced by a water contact angle of 132.89° under optimized component ratios). Meanwhile, SiO₂ microscopically modifies the surface morphology, resulting in increased surface roughness. This composite film not only maintains high conductivity (1.21 S/cm, in contrast to 0.83 S/cm for the PEDOT:PSS film) but also preserves its hydrophobicity and electrical properties under rigorous conditions, including high-temperature exposure (60–200 °C), ultraviolet (UV) aging (365.0 nm, 1.32 mW/cm²), and abradability testing (2000 CW abrasive paper, drag force of approximately 0.98 N, 40 cycles). Furthermore, the film demonstrates enhanced resistance to both acidic (1 mol/L, 24 h) and alkaline (1 mol/L, 24 h) environments, along with excellent self-cleaning and de-icing capabilities (−6 °C), and satisfactory adhesion (Level 2). Notably, the dried composite film can be re-dispersed into a solution with the aid of isopropanol through simple magnetic stirring, and the sequentially coated films also exhibit good surface hydrophobicity (136.49°), equivalent to that of the pristine film. This research aims to overcome the intrinsic performance drawbacks of PEDOT:PSS-based materials, enabling them to meet the demands of complex application scenarios in the field of organic electronics while endowing them with multifunctionality.

Through the selection of N-type organic semiconductor molecules and the method of supramolecular self-assembly at the solvent phase interface, a perylene tetracarboxylic diimide (PTCDIs) nanofiber film with loose and porous morphology was constructed via in situ deposition on the surface of ITO conductive glass. Then, the P-type organic semiconducting polymer poly(3,4−ethylenedioxythiophene) (PEDOT) was grown in the fiber interweaving network of this film via quantitative electrochemical polymerization, thus preparing a PTCDIs@PEDOT composite film with N−P heterojunction architecture. The composite film has a nanometer-sized N−P heterojunction interpenetrating network structure, which is beneficial for full exposure to and contact of hydrogen peroxide vapor (HPV). The response time is 5.76 min, the recovery time is 5.53 min, and the response to 1.0 ppm concentration of HPV is 1.76. The PTCDIs@PEDOT film has good moisture resistance and improved sensitivity and signal response for gas-phase H₂O₂ detection.