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A new type of carbonized polymer dot was prepared by the one-step hydrothermal method of triethoxylsilane (TEOS) and citric acid (CA). The sensor made from carbonized polymer dots (CPDs) showed superior gas sensing performance toward ammonia at room temperature. The Si, O-codoped CPDs exhibited superior ammonia sensing performance at room temperature, including a low practical limit of detection (pLOD) of 1 ppm ( R a : 1.10, 1 ppm), short response/recovery time (30/36 s, 1 ppm), high humidity resistance (less than 5% undulation when changing relative humidity to 80 from 30%), high stability (less than 5% initial response undulation after 120 days), reliable repeatability, and high selectivity against other interferential gases. The gas sensing mechanism was investigated through control experiments and in situ FTIR, indicating that Si, O-codoping essentially improves the electron transfer capability of CPDs and synergistically dominates the superior ammonia sensing properties of the CPDs. This work presents a facile strategy for constructing novel high-performance, single-component carbonized polymer dots for gas sensing.R g : 1.10, 1 ppm), short response/recovery time (30/36 s, 1 ppm), high humidity resistance (less than 5% undulation when changing relative humidity to 80 from 30%), high stability (less than 5% initial response undulation after 120 days), reliable repeatability, and high selectivity against other interferential gases. The gas sensing mechanism was investigated through control experiments and in situ FTIR, indicating that Si, O-codoping essentially improves the electron transfer capability of CPDs and synergistically dominates the superior ammonia sensing properties of the CPDs. This work presents a facile strategy for constructing novel high-performance, single-component carbonized polymer dots for gas sensing.

In this study, colorimetric indicator films (CIFs) were developed by integrating neutral red covalently immobilized onto TEMPO-oxidized cellulose nanofibrils (NR@TOCNFs) and poly(acrylic acid) (PAA) inside a poly(vinyl alcohol) (PVA) matrix. The successful covalent immobilization of NR onto the TOCNFs was confirmed using attenuated total reflection-Fourier transform infrared, X-ray photoelectron spectroscopy, and thermogravimetric analyses. The CIFs had a visible color change from red to yellow as the pH changed from 2.0 to 10.0. The colorimetric response of CIFs improved as the NR@TOCNF content increased, while it decreased as the PAA level increased. The critical pH ranges for the color change of CIFs were 6-7, 7-8, and 8-9 for 3 %, 5 %, and 7 % PAA, respectively, at 0.3 % NR@TOCNF. The best ammonia sensitivity was found in the indicator films containing 3 % PAA and 0.3 % NR@TOCNF. These results showed that the CIFs could be applied for freshness detection in food packaging., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Ltd. All rights reserved.)