Cellulose-based humidity sensors have attracted great research interest due to their hydrophilicity, biodegradability, and low cost. However, they still suffer from relatively low humidity sensitivity. Due to the presence of negatively charged carboxylate groups, 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose nanofibril (CNF) exhibits enhanced hydrophilicity and ion conductivity, which is considered a promising candidate for humidity sensing. In this work, we developed a facile strategy to improve the humidity sensitivity of CNF films by regulating their surface charge density. With the increase in surface charge density, both water uptake and charge carrier densities of the CNF films can be improved, enabling a humidity sensitivity of up to 44.5 % (%RH), higher than that of most polymer-based humidity sensors reported in the literature. Meanwhile, the sensor also showed good linearity (R = 0.998) over the 15–75 % RH at 1 kHz. With these features, the CNF film was further demonstrated for applications in noncontact sensing, such as human respiration, moisture on fingertips, and water leakage, indicating the great potential of CNF film in humidity monitoring.

中文翻译：

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表面电荷操控可改善 TEMPO 氧化纤维素纳米纤丝的湿度传感

基于纤维素的湿度传感器由于其亲水性、可生物降解性和低成本而引起了极大的研究兴趣。然而，它们的湿度敏感性仍然相对较低。由于带负电荷的羧酸根基团的存在，2,2,6,6-四甲基哌啶-1-氧基（TEMPO）氧化纤维素纳米原纤维（CNF）表现出增强的亲水性和离子电导率，被认为是湿度传感的有前途的候选者。在这项工作中，我们开发了一种简单的策略，通过调节 CNF 薄膜的表面电荷密度来提高其湿度敏感性。随着表面电荷密度的增加，CNF 薄膜的吸水率和载流子密度都可以提高，从而使湿度灵敏度高达 44.5% (%RH)，高于大多数基于聚合物的湿度传感器。文学。同时，传感器在 1 kHz、15-75% RH 范围内也表现出良好的线性度 (R = 0.998)。凭借这些特性，CNF薄膜进一步展示了其在人体呼吸、指尖湿气、漏水等非接触传感领域的应用，表明CNF薄膜在湿度监测方面的巨大潜力。