Zeolites as a Class of Semiconductors for High-Performance Electrically Transduced Sensing

Surface Heterogeneity at the Polymer-Food Interface Influences Ag Migration from Plastic Packaging Incorporating Ag-Exchanged Zeolites

Silver-enabled polymers, with their antimicrobial properties, could prolong the shelf life and maintain quality in packaged foods. However, there is limited understanding about how the Ag form in the polymer, food chemistry, and other factors affect the transfer (migration) of Ag from the polymer to the food under the intended conditions of use. In this study, we investigated the release of Ag from polymer composites (PCs) incorporating two different Ag-exchanged zeolites (Ag-Y), which have been explored as potential scaffolds for loading high concentrations of Ag within common polymers. We manufactured two Ag-Y films based on low-density polyethylene (LDPE): one incorporating ionic Ag (Ag+) and one incorporating nanoparticulate Ag (AgNPs), each with similar initial Ag concentrations. Then, we assessed the migration of Ag out of these PCs into food simulants under accelerated room temperature storage conditions. In all simulants investigated, the Ag+-Y/LDPE film exhibited a higher migration of Ag compared to the AgNP-Y/LDPE film, suggesting a lower fraction of readily releasable Ag in the latter material. Total Ag migration from AgNP-Y/LDPE over 10 days at 40 °C was 11.10 ± 2.05 ng cm-2 of packaging surface area in water, 7.63 ± 1.59 ng cm-2 in a 9 wt % aqueous sucrose solution, and 21.29 ± 1.98 ng cm-2 in a commercial sweetened carbonated beverage (Squirt). In contrast, Ag migration from Ag+-Y/LDPE was measured at 49.61 ± 3.46, 57.48 ± 9.65, and 91.54 ± 5.58 ng cm-2 in water, sucrose solution, and Squirt drink, respectively. Surface characterization techniques, including atomic force microscopy (AFM), scanning electron microscopy (SEM), and conductivity measurements, revealed the presence of exposed zeolite particles at the surface of the films, suggesting that direct interactions between Ag-exchanged zeolites and food components at the simulant-polymer interface play an important role in determining Ag migration from Ag-Y/LDPE PCs.

Reverse Hydrogen Spillover on Metal Oxides for Water-Promoted Catalytic Oxidation Reactions

Understanding the water-involved mechanism on metal oxide surface and the dynamic interaction of water with active sites is crucial in solving water poisoning in catalytic reactions. Herein, this work solves this problem by designing the water-promoted function of metal oxides in the ethanol oxidation reaction. In situ multimodal spectroscopies unveil that the competitive adsorption of water-dissociated *OH species with O2 at Sn active sites results in water poisoning and the sluggish proton transfer in CoO-SnO2 imparts water-resistant effect. Carbon material as electron donor and proton transport channel optimizes the Co active sites and expedites the reverse hydrogen spillover from CoO to SnO2. The water-promoted function arises from spillover protons facilitating O2 activation on the SnO2 surface, leading to crucial *OOH intermediate formation for catalyzing C-H and C-C cleavage. Consequently, the tailored CoO-C-SnO2 showcases a remarkable 60-fold enhancement in ethanol oxidation reaction compared to bare SnO2 under high-humidity conditions.

Imparting Chemiresistor with Humidity-Independent Sensitivity toward Trace-Level Formaldehyde via Substitutional Doping Platinum Single Atom

The modification of metal oxides with noble metals is one of the most effective means of improving gas-sensing performance of chemiresistors, but it is often accompanied by unintended side effects such as sensor resistance increases up to unmeasurable levels. Herein, a carbonization-oxidation method is demonstrated using ultrasonic spray pyrolysis technique to realize platinum (Pt) single atom (SA) substitutional doping into SnO2 (named PtSA-SnO2). The substitutional doping strategy can obviously enhance gas-sensing properties, and meanwhile decrease sensor resistance by two orders of magnitude (decreased from ≈850 to ≈2 MΩ), which are attributed to the tuning of band gap and fermi-level position, efficient single atom catalysis, and the raising of adsorption capability of formaldehyde, as validated by the state-of-the-art characterizations, such as spherical aberration-corrected scanning transmission electron microscopy (Cs-corrected STEM), in situ diffuse reflectance infrared Fourier transformed spectra (in situ DRIFT), CO temperature-programmed reduction (CO-TPR), and theoretical calculations. As a proof of concept, the developed PtSA-SnO2 sensor shows humidity-independent (30-70% relative humidity) gas-sensing performance in the selective detection of formaldehyde with high response, distinguishable selectivity (8< Sformaldehyde/Sinterferant <14), and ultra-low detection limit (10 ppb). This work presents a generalized and facile method to design high-performance metal oxides for chemical sensing of volatile organic compounds (VOCs).

Powders to Thin Films: Advances in Conjugated Microporous Polymer Chemical Sensors

Chemical sensing of harmful species released either from natural or anthropogenic activities is critical to ensuring human safety and health. Over the last decade, conjugated microporous polymers (CMPs) have been proven to be potential sensor materials with the possibility of realizing sensing devices for practical applications. CMPs found to be unique among other porous materials such as metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) due to their high chemical/thermal stability, high surface area, microporosity, efficient host-guest interactions with the analyte, efficient exciton migration along the π-conjugated chains, and tailorable structure to target specific analytes. Several CMP-based optical, electrochemical, colorimetric, and ratiometric sensors with excellent selectivity and sensing performance were reported. This review comprehensively discusses the advances in CMP chemical sensors (powders and thin films) in the detection of nitroaromatic explosives, chemical warfare agents, anions, metal ions, biomolecules, iodine, and volatile organic compounds (VOCs), with simultaneous delineation of design strategy principles guiding the selectivity and sensitivity of CMP. Preceding this, various photophysical mechanisms responsible for chemical sensing are discussed in detail for convenience. Finally, future challenges to be addressed in the field of CMP chemical sensors are discussed.

Essential role of lattice oxygen in hydrogen sensing reaction

Understanding the sensing mechanism of metal oxide semiconductors is imperative to the development of high-performance sensors. The traditional sensing mechanism only recognizes the effect of surface chemisorbed oxygen from the air but ignores surface lattice oxygen. Herein, using in-situ characterizations, we provide direct experimental evidence that the surface chemisorbed oxygen participated in the sensing process can come from lattice oxygen of the oxides. Further density functional theory (DFT) calculations prove that the p-band center of O serves as a state of art for regulating the participation of lattice oxygen in gas-sensing reactions. Based on our experimental data and theoretical calculations, we discuss mechanisms that are fundamentally different from the conventional mechanism and show that the easily participation of lattice oxygen is helpful for the high response value of the materials.

Nanoarchitectonics of a Smectite with 4,4'-Diammonium-α-truxillic Acid and Its Methyl Ester for the Removal of o-Phenylphenol and Biphenyl from Water

Adsorbents with hydrophilic and hydrophobic natures were designed by intercalating a bioderived molecule; 4,4'-diammonium-α-truxillic acid (4ATA) and 4,4'-diammonium-α-truxillic acid dimethyl ester (E4ATA), which both are bioderived molecules, into a smectite (purified bentonite) to concentrate o-phenylphenol and biphenyl, respectively, from water. The adsorption isotherm showed high affinity between the 4ATA-smectite hybrid and o-phenylphenol with a high Langmuir constant (0.98 L mg-1). Meanwhile, the E4ATA-smectite hybrid adsorbed biphenyl with a high Langmuir constant (3.61 L mg-1). The adsorption properties of 4ATA- and E4ATA-smectite hybrid were contributed by the chemical characteristics of 4ATA and E4ATA in the interlayer space of the smectite.

Design of a SnO2/Zeolite Gas Sensor to Enhance Formaldehyde Sensing Properties: From the Strategy of the Band Gap-Tunable Zeolite

ZSM-5 zeolite is usually used in gas sensors as an auxiliary material to improve the gas-sensitive properties of other semiconductor materials, such as its molecular sieve properties and surface adsorption properties. Here, the gas-sensitive mechanism analysis of SnO2/zeolite gas sensors is studied for the first time based on the perspective of zeolite as a band gap-tunable semiconductor that was reported recently. The gas-sensing mechanism of the zeolite/semiconductor has been modeled based on the surface charge theory, and the work function of the ZSM-5 zeolite has been revealed for the first time. A heterostructure of Ag and ZSM-5 was designed and compounded to tune the band gap of the ZSM-5 zeolite by the ammonia pool effect method. The band gap width of the zeolite decreases from 4.51 to 3.61 eV. A series of characterization techniques were used to analyze the distribution and morphology of silver nanoparticles in zeolites and the variation of the ZSM-5 band gap. Then, SnO2/Ag@ZSM-5 sensors were fabricated, and the gas-sensing performances were measured. The gas-sensing results show that the SnO2/Ag@ZSM-5 sensor has an improved response to formaldehyde in particular compared to the SnO2 sensor. The response value of the SnO2/Ag@ZSM-5 sensor to 70 ppm formaldehyde reached 29.4, which is a 528% improvement compared to the SnO2 sensor. Additionally, the selectivity was greatly enhanced. This study provides a strategy for designing and developing higher-performance gas sensors.

The role of 13X molecular sieves in photocatalytic nitrogen fixation

To overcome the weak adsorption and difficult activation of N2 on catalysts in the photocatalytic nitrogen reduction reaction (NRR), we put forward that the introduction of molecular sieve 13X may realize the enrichment and activation of N2. 13X and the photoactive substrate BiOBr were assembled electrostatically to construct composite catalysts. In the presence of 13X, they are rich in nitrogen adsorption and activation sites, and the highest ammonia yield can reach 360.5 μmol h-1 gcat-1. It is surprising to find that 13X is able to optimize the photoelectric properties. This work extends the function of molecular sieves in the NRR and offers guidance to design catalysts with high photocatalytic activity.