$ZnS / {Ti}_{3} C_{2} T_{x}$ MXene nanocomposites based humidity sensor with improved sensing performance
$ZnS / {Ti}_{3} C_{2} T_{x}$ 基于 MXene 纳米复合材料的湿度传感器，具有更高的传感性能

Yutong Han $^{*, 1}$ , Huina Cao $^{1}$ , Yuzhong Cao ©, Yu Yao ®, Ziyang Yin, Xingyu Huang, Yuanshou Zhu, Zhigang Zhu
韩宇彤 $^{*, 1}$ ，曹 $^{1}$ 慧娜，曹©玉忠，尹®宇，尹紫阳，黄星宇，朱元寿，朱志刚

School of Health Science and Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China
上海理工大学健康科学与工程学院，上海 200093

A R T I C L E I N F O

Keywords: 关键字：

{Ti}_{3} C_{2} T_{x}

Humidity sensor 湿度传感器
Respiratory monitoring 呼吸监测
Non-contact human-machine interaction
非接触式人机交互

Abstract 抽象

Humidity sensors have flourished in human respiratory monitoring, non-contact human-machine interaction (HMI), and environmental humidity monitoring, inseparable from the change to using the fundamental sensitive materials with application-oriented sensing performance. Structural and functional designs of ${Ti}_{3} C_{2} T_{x}$ MXenes are attracting growing attention as sensitive platforms owing to good hydrophilicity and conductivity. Herein, $ZnS / {Ti}_{3} C_{2} T_{x}$ humidity-sensitive material is successfully prepared via a hydrothermal method. The prepared $ZnS /$ ${Ti}_{3} C_{2} T_{x}$ humidity sensors exhibit high responses of $71 %, 392 %$ , and $1010 %$ at $10.9 %, 54.0 %$ , and $92.2 % RH$ , respectively. The response of $ZnS / {Ti}_{3} C_{2} T_{x}$ humidity sensor at $54 % RH$ is 28 folds higher than that of the ${Ti}_{3} C_{2} T_{x}$ humidity sensor. The designed $ZnS / {Ti}_{3} C_{2} T_{x}$ humidity sensor has good repeatability and anti-interference capability, and low hysteresis. These performance characteristics enable the sensor to distinguish different human respiration frequencies, monitor human respiration in real-time and dynamically monitor fingertip humidity.
湿度传感器在人体呼吸监测、非接触式人机交互（HMI）和环境湿度监测方面蓬勃发展，与使用具有面向应用传感性能的基础敏感材料的变化密不可分。MXenes 的结构 ${Ti}_{3} C_{2} T_{x}$ 和功能设计由于具有良好的亲水性和导电性，作为敏感平台越来越受到关注。在此， $ZnS / {Ti}_{3} C_{2} T_{x}$ 通过水热法成功制备了湿度敏感材料。制备 $ZnS /$ ${Ti}_{3} C_{2} T_{x}$ 的湿度传感器分别表现出 $71 %, 392 %$ 、 $1010 %$ 、和 $10.9 %, 54.0 %$ $92.2 % RH$ 的高响应。湿度传感器的 $ZnS / {Ti}_{3} C_{2} T_{x}$ $54 % RH$ 响应比 ${Ti}_{3} C_{2} T_{x}$ 湿度传感器的响应高 28 倍。设计的 $ZnS / {Ti}_{3} C_{2} T_{x}$ 湿度传感器具有良好的重复性和抗干扰能力，并且具有低滞后性。这些性能特征使传感器能够区分不同的人体呼吸频率，实时监测人体呼吸并动态监测指尖湿度。

1. Introduction 1. 引言

With the development and integration of the Internet of Things and Artificial Intelligence, non-contact respiratory monitoring is receiving more and more attention [1]. Human respiration with abundant information can reveal the health of the body, and respiratory rate and breathing pattern can be used as early diagnostic markers for certain respiratory diseases (such as shortness of breath and apnoea syndrome) [2-4]. Furthermore, with the advancement of technology, touchscreens are widely used in different fields, increasing the rate of virus transmission and making cross-infection highly likely [5]. The hygienic and safe non-contact HMI prevents physical contact with the human body and equipment [6].
随着物联网和人工智能的发展和融合，非接触式呼吸监测越来越受到关注 [1]。具有丰富信息的人类呼吸可以揭示身体的健康状况，呼吸频率和呼吸模式可以作为某些呼吸系统疾病（如呼吸急促和呼吸暂停综合征）的早期诊断标志物[2-4]。此外，随着技术的进步，触摸屏被广泛应用于不同领域，增加了病毒传播的速度，使交叉感染的可能性极高 [5]。卫生和安全的非接触式 HMI 可防止与人体和设备发生物理接触 [6]。

Humidity sensors can effectively collect humidity information from exhaled gas and skin surfaces, demonstrating good potential for respiratory monitoring and non-contact HMI [7-9]. According to the output signal, humidity sensors can generally be classified as resistive, capacitive, impedance, and other types (such as voltage humidity sensors, quartz crystal microbalances humidity sensors) [10-14]. In particular, resistive humidity sensors have been intensively explored for simple
湿度传感器可以有效地从呼出的气体和皮肤表面收集湿度信息，在呼吸监测和非接触式人机界面方面具有良好的潜力[7-9]。根据输出信号，湿度传感器一般可分为电阻式、电容式、阻抗式和其他类型（如电压湿度传感器、石英晶体微量天平湿度传感器）[10-14]。特别是，电阻式湿度传感器已被深入探索，其目的很简单
manufacturing, low cost, and easy integration [15]. The resistive humidity sensor generally consists of humidity-sensitive materials, electrodes, and substrates [16].
制造、低成本和易于集成 [15]。电阻式湿度传感器通常由湿敏材料、电极和基板组成 [16]。

Hydrophilic materials, including semiconducting metal oxides, polymers, graphene, transition metal sulfides, transition metal carbides and nitrides, have been widely used to detect humidity [10,17-23].

{Ti}_{3} C_{2} T_{x}

MXene, a transition metal carbide and carbon nitride, has received much attention in humidity sensing for its unique accordion-like structure, high electrical conductivity, strong hydrophilicity, abundant surface groups, and high specific surface area (SSA) [24-30]. Further, the abundant surface groups (

- OH, - F, - O

) of

{Ti}_{3} C_{2} T_{x}

MXene present many active sites to adsorb water molecules. When water molecules are inserted into the layers of MXene, the conductivity decreases owing to the low conductivity of water and the increase of the interlayer distance [31-33]. However, the strong van der Waals forces between the MXene layers can easily induce stacking of nanosheets., limiting its hydration and dehydration capacity [33-36].
亲水性材料，包括半导体金属氧化物、聚合物、石墨烯、过渡金属硫化物、过渡金属碳化物和氮化物，已被广泛用于检测湿度 [10,17-23]。

{Ti}_{3} C_{2} T_{x}

MXene 是一种过渡金属碳化物和氮化碳，因其独特的手风琴状结构、高导电性、强亲水性、丰富的表面基团和高比表面积（SSA）而受到湿度传感的广泛关注[24-30]。此外，MXene 丰富的

{Ti}_{3} C_{2} T_{x}

表面基团（

- OH, - F, - O

）呈现了许多吸附水分子的活性位点。当水分子插入 MXene 层时，由于水的低电导率和层间距离的增加，电导率降低[31-33]。然而，MXene 层之间的强范德华力很容易诱导纳米片的堆叠，限制了其水化和脱水能力[33-36]。

Combining MXene with other humidity-sensitive materials is an effective strategy to enhance humidity performance. For instance, Radovic et al. prepared highly stretchable MXene/polyelectrolyte
将 MXene 与其他湿度敏感材料结合使用是提高湿度性能的有效策略。例如，Radovic 等人制备了高度可拉伸的 MXene/聚电解质

multilayer membranes. They assembled them into humidity sensors using the layer-by-layer assembly technique, demonstrating good cyclic stability to humidity changes and fast response/recovery times [37]. Chen et al. prepared

CuO / {Ti}_{3} C_{2} T_{x}

humidity-sensitive materials by the self-assembly method. They prepared

CuO / {Ti}_{3} C_{2} T_{x}

sensors with good repeatability and low hysteresis values, enhancing the response by about 5 times compared to MXene at

97 %

RH [38]. However, despite significant progress in MXene-based humidity sensing technologies, critical challenges persist in meeting the stringent requirements for practical deployment. The operational performance parameters, including response/recovery dynamics, hysteresis effects, signal reproducibility, and long-term stability under continuous operation, remain suboptimal. ZnS is one of the most critical II-VI semiconductors with abundant sulphur vacancies and interstitial sulphur lattice defects, which is considered a good humidity-sensitive material [39-41].
多层膜。他们使用逐层组装技术将它们组装到湿度传感器中，表现出对湿度变化的良好循环稳定性和快速响应/恢复时间 [37]。Chen 等人通过自组装方法制备

CuO / {Ti}_{3} C_{2} T_{x}

了湿敏材料。他们制备

CuO / {Ti}_{3} C_{2} T_{x}

了具有良好可重复性和低磁滞值的传感器，在 RH 时，与 MXene 相比，响应

97 %

提高了约 5 倍 [38]。然而，尽管基于 MXene 的湿度传感技术取得了重大进展，但在满足实际部署的严格要求方面仍然存在关键挑战。作性能参数，包括响应/恢复动力学、磁滞效应、信号再现性和连续运行下的长期稳定性，仍然不是最佳的。ZnS 是最关键的 II-VI 半导体之一，具有丰富的硫空位和间隙硫晶格缺陷，被认为是一种良好的湿敏材料 [39-41]。

Herein, the

ZnS / {Ti}_{3} C_{2} T_{x}

nanocomposites have been successfully prepared by hydrothermal method, and the humidity sensing performance is investigated at room temperature. The fabricated humidity sensors exhibit remarkable repeatability with low hysteresis (

2.4 %

), good immunity to interference, high humidity response (the responses at

10.9 %, 54.0 %

, and

92.2 % RH

were

71 %, 392 %

, and

1010 %

, respectively), and a wide detection range. The

ZnS / {Ti}_{3} C_{2} T_{x}

sensors show a 28 -fold higher response than

{Ti}_{3} C_{2} T_{x}

MXene, significantly enhancing the humidity-sensitive performance.
本文通过水热法成功制备了

ZnS / {Ti}_{3} C_{2} T_{x}

纳米复合材料，并在室温下研究了湿度传感性能。制造的湿度传感器表现出卓越的可重复性、低滞后（

2.4 %

）、良好的抗干扰性、高湿度响应（分别为

10.9 %, 54.0 %

、和

92.2 % RH

WERE

71 %, 392 %

和

1010 %

的响应）和较宽的检测范围。传感器

ZnS / {Ti}_{3} C_{2} T_{x}

的响应速度比

{Ti}_{3} C_{2} T_{x}

MXene 高 28 倍，显著提高了湿敏性能。

2. Experimental section 2. 实验部分

2.1. Materials 2.1. 材料

{Ti}_{3} {AlC}_{2}

MAX phase was supplied from Jilin 11th Technology Co., Ltd. Sodium fluoride ( NaF ) was obtained from Shanghai Titan Technology Co., Ltd. Thioacetamide (TAA), hydrochloric acid (HCl), anhydrous ethanol

({CH}_{3} {CH}_{2} OH)

and zinc nitrate hexahydrate ( Zn

{({NO}_{3})}_{2} \cdot 6 H_{2} O

) were obtained from Sinopharm Chemical Reagent Co., Ltd. Polyvinylpyrrolidone (PVP) was obtained from Sigma-Aldrich Co., Ltd.

{Ti}_{3} {AlC}_{2}

MAX 固定相由吉林第十一科技有限公司提供氟化钠（NaF）由上海泰坦科技有限公司获得硫代乙酰胺（TAA）、盐酸（HCl）、无水乙醇

({CH}_{3} {CH}_{2} OH)

和六水硝酸锌（Zn

{({NO}_{3})}_{2} \cdot 6 H_{2} O

）由国药集团化学试剂有限公司提供聚乙烯基吡咯烷酮（PVP）由 Sigma-Aldrich Co.， Ltd.获得。

2.2. Synthesis of $T i_{3} C_{2} T_{x}$ and $ZnS / T i_{3} C_{2} T_{x}$ composites
2.2. $T i_{3} C_{2} T_{x}$ 合成和 $ZnS / T i_{3} C_{2} T_{x}$ 复合材料

Fig. 1a depicts the experimental procedure.

{Ti}_{3} C_{2} T_{x}

was prepared similarly to previous work [42]. Briefly,

NaF (2.0 g)

was dissolved in 40 mL of

HCl (6 M)

with magnetic stirring.

Next, {Ti}_{3} {AlC}_{2} (2.0 g)

was added gradually and stirred at

60^{\circ} C

for 48 h . Then, the product was washed until the pH of the supernatant reached 6 . Finally, the material was dried to get multilayer

{Ti}_{3} C_{2} T_{x}

MXene powder.
图 1a 描述了实验过程。

{Ti}_{3} C_{2} T_{x}

的制备方法与以前的工作类似 [42]。简而言之，

NaF (2.0 g)

在磁力搅拌下溶解在 40 mL 中

HCl (6 M)

。

Next, {Ti}_{3} {AlC}_{2} (2.0 g)

逐渐加入并搅拌

60^{\circ} C

48 小时。然后，洗涤产品至上清液的 pH 值达到 6 。最后，将材料干燥得到多层

{Ti}_{3} C_{2} T_{x}

MXene 粉末。

ZnS / {Ti}_{3} C_{2} T_{x}

composites were obtained by a hydrothermal method. First,

{Ti}_{3} C_{2} T_{x} (20 mg)

was dispersed in 30 mL deionized water (DI), mixed well and then

Zn {({NO}_{3})}_{2} \cdot 6 H_{2} O (38.7 mg)

was added and stirred at room temperature for 30 min , referred to as solution A. TAA ( 9.8 mg ) was added in 30 mL DI, stirred well and then PVP ( 6.5 mg ) was added and referred to as solution

B

. Then solution

B

was mixed with solution

A

ZnS / {Ti}_{3} C_{2} T_{x}

通过水热法获得复合材料。首先，

{Ti}_{3} C_{2} T_{x} (20 mg)

分散在 30 mL 去离子水（DI）中，充分混合，然后

Zn {({NO}_{3})}_{2} \cdot 6 H_{2} O (38.7 mg)

加入并在室温下搅拌 30 min，称为溶液 A，将 TAA （ 9.8 mg ）加入 30 mL 去离子水（DI）中，充分搅拌，然后加入 PVP （ 6.5 mg ），称为溶液

B

。然后将溶液

B

与溶液

A

混合

Fig. 1. Schematic illustration of (a) the preparation process of

{Ti}_{3} C_{2} T_{x}

and

ZnS / {Ti}_{3} C_{2} T_{x}

, (b) the preparation process of the humidity sensor, and © the dynamic measurement system.
图 1.（a）

{Ti}_{3} C_{2} T_{x}

湿度

ZnS / {Ti}_{3} C_{2} T_{x}

传感器的制备过程，（© b）湿度传感器和动态测量系统的制备过程的示意图。
and the mixture was moved to an autoclave at

130^{\circ} C

for 6 h . The reaction product was washed with ethanol and DI several times and then dried in a vacuum oven at

60^{\circ} C

to obtain

ZnS / {Ti}_{3} C_{2} T_{x} . ZnS / {Ti}_{3} C_{2} T_{x}

composites with various amounts of ZnS nanoparticles could be obtained by changing the amount of

Zn {({NO}_{3})}_{2} \cdot 6 H_{2} O

(26.8, 38.7, and 50.6 mg ) and the corresponding TAA (

6.8, 9.8

, and 12.8 mg ), which were designated ZM-1, ZM-2, and ZM-3, respectively. The pure

{Ti}_{3} C_{2} T_{x}

was labeled as ZM-0.
并将混合物移至高压灭菌

130^{\circ} C

器中 6 小时。将反应产物用乙醇和 DI 洗涤数次，然后在真空烘箱中干燥

60^{\circ} C

，通过改变

Zn {({NO}_{3})}_{2} \cdot 6 H_{2} O

（26.8、38.7 和 50.6 mg）和相应的 TAA （

6.8, 9.8

和 12.8 mg）的量，可以

ZnS / {Ti}_{3} C_{2} T_{x} . ZnS / {Ti}_{3} C_{2} T_{x}

获得具有不同量 ZnS 纳米颗粒的复合材料，分别命名为 ZM-1、ZM-2 和 ZM-3。纯

{Ti}_{3} C_{2} T_{x}

品标记为 ZM-0。

2.3. Characterizations 2.3. 特征

The microstructure and morphology of

{Ti}_{3} C_{2} T_{x}

and

ZnS / {Ti}_{3} C_{2} T_{x}

composites were characterized using scanning electron microscopy (SEM, Ultra Plus, Carl Zeiss ULTRA plus) and transmission electron microscopy (TEM, FEI Talos F200X G2). The crystalline phase information was characterized using an X-ray diffractometer (XRD, Bruker D2 Phaser) with

Cu K α 1

radiation (wavelength (

λ = 1.5406 Å

). Fourier transform infrared spectra (FTIR) were obtained using a PerkinElmer Spectrum 3. Raman spectra were measured using a Thermo Scientific DXR

^{TM}

2xi (laser wavelength: 532 nm ). Nitrogen adsorption-desorption isotherms were characterized on a Micromeritics ASAP 2460 nitrogen adsorbent apparatus and were used to measure the specific surface area of the materials. X-ray photoelectron spectroscopy (XPS, Thermo Scientific K-Alpha) was performed.
使用扫描电子显微镜（SEM， Ultra Plus， Carl Zeiss ULTRA plus）和透射电子显微镜（TEM， FEI Talos F200X G2）对

ZnS / {Ti}_{3} C_{2} T_{x}

复合材料的

{Ti}_{3} C_{2} T_{x}

微观结构和形貌进行表征。使用 X 射线衍射仪（XRD，Bruker D2 Phaser）和

Cu K α 1

辐射（波长（））对晶体相位信息进行表征

λ = 1.5406 Å

。使用 PerkinElmer Spectrum 3 获得傅里叶变换红外光谱（FTIR）。使用 Thermo Scientific DXR

^{TM}

2xi（激光波长：532 nm）测量拉曼光谱。在 Micromeritics ASAP 2460 氮吸附仪上对氮气吸附-脱附等温线进行了表征，并用于测量材料的比表面积。进行 X 射线光电子能谱（XPS， Thermo Scientific K-Alpha）。

2.4. Fabrication and measurement of humidity sensors
2.4. 湿度传感器的制造和测量

The fabrication process of sensors is shown in Fig. 1b. Polyethylene terephthalate (PET) is selected as flexible substrates due to the impressive mechanical characteristics across a wide temperature range. First, the PET was rinsed repeatedly and dried in an oven. A mask was placed on the surface of the PET substrate, and a scribing machine was used to create a pattern of interdigitated electrodes (width and gap:

300 μ m

) on the PET substrate. A gold film was deposited onto the PET substrate using a plasma sputter to form the gold-interdigitated electrode. The geometry and real image of the interdigitated electrode are shown in Fig. S1. Subsequently, 10 mg of

ZnS / {Ti}_{3} C_{2} T_{x}

powder was dispersed in

200 μ L

of a mixture of DI water and anhydrous ethanol (1:1). Then,

7 μ L

of dispersion was drop-coated on the electrode to fabricate the humidity sensor. Three sets of humidity sensors were prepared using different batches of sensitive materials and the performance was systematically tested and analyzed.
传感器的制造过程如图 1b 所示。聚对苯二甲酸乙二醇酯（PET）因其在较宽的温度范围内具有令人印象深刻的机械特性而被选为柔性基材。首先，PET 被反复冲洗并在烘箱中干燥。在 PET 基材表面放置掩模，并使用划线机在 PET 基材上创建叉指电极（宽度和间隙：

300 μ m

）的图案。使用等离子溅射将金膜沉积到 PET 基材上，以形成金叉指电极。叉指电极的几何形状和真实图像如图 S1 所示。随后，将 10 mg

ZnS / {Ti}_{3} C_{2} T_{x}

粉末分散在去离子水和无水乙醇（1：1）的混合物中

200 μ L

。然后，

7 μ L

将分散液滴涂在电极上以制造湿度传感器。使用不同批次的敏感材料制备了三套湿度传感器，并对其性能进行了系统测试和分析。

The humidity-sensitive performance of the sensors is measured using a home-built dynamic test system, as illustrated in Fig. 1c. Dry air (

N_{2}

79 \pm 1 %, O_{2} : 21 \pm 1 %

) is used as a background gas, and humidity is obtained by bubbling air through a glass bottle with water. Different RH conditions (10.9-92.2 % RH) are obtained by accurately controlling the mass flow ratio of wet and dry air through two mass flow controllers (MFC1 and MFC2) at room temperature (total flow rate:

300 mL / \min

). The actual RH is calibrated using a commercial hygrometer (Testo 625), and the room temperature of

25^{\circ} C

is controlled by an air conditioner. Resistance signals are captured using a Keithley 2450 source meter (measurement voltage: 1 V ). The response is defined as

(R - R_{0}) /

R_{0} \times 100 %

, where

R_{0}

is the resistance in dry air, and

R

is the resistance at a specific relative humidity. All tests are performed at room temperature

(25^{\circ} C)

.
传感器的湿敏性能是使用自制的动态测试系统测量的，如图 1c 所示。干燥空气（

N_{2}

：

79 \pm 1 %, O_{2} : 21 \pm 1 %

）用作背景气体，通过盛有水的玻璃瓶中鼓泡空气来获得湿度。在室温下，通过两个质量流量控制器（MFC1 和 MFC2）精确控制湿空气和干空气的质量流量比（总流量：

300 mL / \min

），获得不同的 RH 条件（10.9-92.2 % RH）。实际的相对湿度是使用商用湿度计（Testo 625）校准的，室温

25^{\circ} C

由空调控制。使用 Keithley 2450 源表（测量电压：1 V）捕获电阻信号。响应定义为

(R - R_{0}) /

R_{0} \times 100 %

，其中

R_{0}

是干燥空气中的电阻，是

R

特定相对湿度下的电阻。所有测试均在室温

(25^{\circ} C)

下进行。

The resistance signal is collected using the CGS-8 Intelligent Analysis System (Elite Technology Co., Ltd, Beijing, China) to evaluate the effects of common gases (triethylamine, acetone, ammonia, formaldehyde, and ethanol) on the humidity sensor. Specific concentration of ammonia is obtained by diluting highly concentrated ammonia gas. The amount of gas added can be calculated using Equation of

V = y_{2} V_{2} / y_{1}

, where

V_{2}

is the volume of the test chamber of the CGS- 8 device ( 20 L ),

y_{1}

is the concentration of the

{NH}_{3}

to be diluted (

10.10 %

), and

y_{2}

is the target concentration of the gas. The concentration of the other gas molecules is obtained by heating and evaporating organic liquid on a quartz plate
使用 CGS-8 智能分析系统（Elite Technology Co.， Ltd，中国北京）收集电阻信号，以评估常见气体（三乙胺、丙酮、氨、甲醛和乙醇）对湿度传感器的影响。通过稀释高浓度氨气获得比浓度的氨。添加的气体量可以使用方程

V = y_{2} V_{2} / y_{1}

计算，其中

V_{2}

是 CGS-8 设备测试室的体积（ 20 L ），

y_{1}

是要稀释的

{NH}_{3}

浓度（

10.10 %

），

y_{2}

是气体的目标浓度。其他气体分子的浓度是通过在石英板上加热和蒸发有机液体来获得的
(possible to heat) inside the test chamber. The amount of organic liquid added was calculated using Equation of

V_{1} = V_{2} C M / (22.4 d ρ) \times 10^{- 3}

, where

V_{1}

is the volume of the liquid to be added

(μ L); V_{2}

is the volume of the test chamber (L);

C

is the concentration of the gas to be prepared (ppm);

M

is the molecular weight of the substance (

g / mol

);

d

is the purity of the liquid;

ρ

is the density of the liquid

(g / {cm}^{3})

; The response of reducing and oxidizing gases is defined as

| R_{g} - R_{a} | / R_{a} \times 100 %

, where

R_{a}

and

R_{g}

represent the resistances when the sensor is exposed to the air and the target gas. All gas sensing tests are performed at

25^{\circ} C

and

21 %

RH.
（可加热）在测试室内。使用方程计算

V_{1} = V_{2} C M / (22.4 d ρ) \times 10^{- 3}

添加的有机液体的量，其中

V_{1}

是要添加

(μ L); V_{2}

的液体的体积是测试室的体积（L）;

C

是要制备的气体的浓度（ppm）;

M

是物质的分子量（

g / mol

）;

d

是液体的纯度;

ρ

是液体

(g / {cm}^{3})

的密度;还原性气体和氧化性气体的响应定义为

| R_{g} - R_{a} | / R_{a} \times 100 %

，其中

R_{a}

和表示

R_{g}

传感器暴露于空气和目标气体时的电阻。所有气体传感测试均在 RH 和

21 %

RH 下

25^{\circ} C

进行。

3. Results and discussion
3. 结果和讨论

3.1. Characterization 3.1. 特征

The material morphologies and surface microstructures are studied using SEM and TEM. SEM images of the

{Ti}_{3} {AlC}_{2}

and

{Ti}_{3} C_{2} T_{x}

are presented in Fig. 2a and b. The Al atomic layer of

{Ti}_{3} {AlC}_{2}

is etched using the mixed solution of HCl and NaF , and producing

{Ti}_{3} C_{2} T_{x}

has an accordionlike multilayer structure. The SEM images of the

ZnS / {Ti}_{3} C_{2} T_{x}

composites in Fig. 2c reveal that ZnS nanoparticles are well-distributed on the surfaces and interlayers of

{Ti}_{3} C_{2} T_{x}

. EDS mapping images of

ZnS / {Ti}_{3} C_{2} T_{x}

(Fig. S2) further demonstrate the uniform dispersion of

C, Ti, Zn

, and S . TEM of the

ZnS / {Ti}_{3} C_{2} T_{x}

in Fig. 2d shows that ZnS nanoparticles grew closely on the

{Ti}_{3} C_{2} T_{x}

surface. Fig. 2(e-f) displays HRTEM images of

ZnS / {Ti}_{3} C_{2} T_{x}

, the lattice spacings of

0.23, 0.16

, and 0.32 nm correspond to the (105) and (110) planes of

{Ti}_{3} C_{2} T_{x}

and the (111) crystal plane of ZnS , respectively.
使用 SEM 和 TEM 研究了材料形貌和表面微观结构。

{Ti}_{3} {AlC}_{2}

和

{Ti}_{3} C_{2} T_{x}

的 SEM 图像如图 2a 和 b 所示。的 Al 原子层

{Ti}_{3} {AlC}_{2}

是使用 HCl 和 NaF 的混合溶液蚀刻的，并产生

{Ti}_{3} C_{2} T_{x}

具有手风琴状的多层结构。图 2c 中

ZnS / {Ti}_{3} C_{2} T_{x}

复合材料的 SEM 图像显示，ZnS 纳米颗粒在

{Ti}_{3} C_{2} T_{x}

.（图 S2）的

ZnS / {Ti}_{3} C_{2} T_{x}

EDS 映射图像进一步证明了和 S 的

C, Ti, Zn

均匀色散。图 2d

ZnS / {Ti}_{3} C_{2} T_{x}

中的 TEM 显示 ZnS 纳米颗粒在

{Ti}_{3} C_{2} T_{x}

表面上紧密生长。图 2（e-f）显示了的 HRTEM 图像

ZnS / {Ti}_{3} C_{2} T_{x}

，晶格间距

0.23, 0.16

和 0.32 nm 分别对应于 ZnS 的（105）和（110）晶面

{Ti}_{3} C_{2} T_{x}

以及（111）晶面。

XRD patterns of

{Ti}_{3} {AlC}_{2}, {Ti}_{3} C_{2} T_{x}

, and

ZnS / {Ti}_{3} C_{2} T_{x}

are performed to explore the crystal structure of the materials further. Fig. 3a shows the (104) characteristic peak of

{Ti}_{3} {AlC}_{2}

at around

38^{\circ}

disappeared, which indicates the Al layers in

{Ti}_{3} {AlC}_{2}

are successfully removed. Meanwhile, the (002) peaks of

{Ti}_{3} {AlC}_{2}, {Ti}_{3} C_{2} T_{x}

and

ZnS / {Ti}_{3} C_{2} T_{x}

are

{8.5}^{\circ}, {7.3}^{\circ}

, and

{6.1}^{\circ}

, respectively. The d-spacing of the materials can be calculated by Bragg’s law using the equation of

n λ = 2 d \sin θ

, where

n

is the diffraction technique level (

n = 1

λ

is the wavelength of incident X-rays (

λ =

1.5406 Å

d

is the lattice spacing (layer spacing), and

θ

is the diffraction angle. Thus, the

{Ti}_{3} {AlC}_{2}, {Ti}_{3} C_{2} T_{x}

and

ZnS / {Ti}_{3} C_{2} T_{x} d

-spacing is calculated to be

10.39, 12.09

, and

14.48 Å

, respectively, suggesting a gradual increase in layer spacing [43,44]. The peaks at

{28.7}^{\circ}, {47.8}^{\circ}

, and

{56.6}^{\circ}

correspond to the (111), (220), and (311) facets of ZnS (JCPDS 05-0566), respectively. A small amount of Ti is oxidized during the synthesis, as indicated by the diffraction peak of

ZnS / {Ti}_{3} C_{2} T_{x}

{25.3}^{\circ}

, corresponding to the (101) facet of

{TiO}_{2}

(JCPDS 73-1764) [45]. Fig. 3b shows the FTIR spectra of

{Ti}_{3} C_{2} T_{x}

and

ZnS / {Ti}_{3} C_{2} T_{x}

. The 1350 and

3439 {cm}^{- 1}

bands are the O-H stretching vibrational modes of liganded and atmospherically adsorbed water, respectively, and the

1640 {cm}^{- 1}

corresponds to the

C = O

stretching vibration peak. The Raman spectra of

{Ti}_{3} C_{2} T_{x}

and

ZnS / {Ti}_{3} C_{2} T_{x}

are characterized (Fig. 3c). A peak appears around

160 {cm}^{- 1}

, corresponding to the in-plane (

E_{g}

) vibrations of Ti and C atoms. The

E_{g}

peak of

ZnS / {Ti}_{3} C_{2} T_{x}

is shifted to lower wavenumbers than

{Ti}_{3} C_{2} T_{x}

. The red shift indicates effective charge transfer between ZnS and

{Ti}_{3} C_{2} T_{x}

, suggesting the formation of the heterojunctions [46, 47]. Fig. 3d displays the SSA of

{Ti}_{3} C_{2} T_{x}

and

ZnS / {Ti}_{3} C_{2} T_{x}

is 6.1 and

15.7 m^{2} / g

, respectively. The increased SSA may enhance the adsorption of water molecules.
的 XRD 图谱

{Ti}_{3} {AlC}_{2}, {Ti}_{3} C_{2} T_{x}

和

ZnS / {Ti}_{3} C_{2} T_{x}

的执行是为了进一步探索材料的晶体结构。图 3a 显示了

{Ti}_{3} {AlC}_{2}

at 附近的

38^{\circ}

（104）特征峰消失，这表明中的

{Ti}_{3} {AlC}_{2}

Al 层已成功去除。同时，

{Ti}_{3} {AlC}_{2}, {Ti}_{3} C_{2} T_{x}

和的

ZnS / {Ti}_{3} C_{2} T_{x}

（002）峰值分别为

{8.5}^{\circ}, {7.3}^{\circ}

和、和

{6.1}^{\circ}

。材料的 d 间距可以通过布拉格定律使用方程

n λ = 2 d \sin θ

计算，其中

n

是衍射技术能级（

n = 1

），

λ

是入射 X 射线的波长（

λ =

1.5406 Å

），

d

是晶格间距（层间距），

θ

是衍射角。因此，计算出

{Ti}_{3} {AlC}_{2}, {Ti}_{3} C_{2} T_{x}

和

ZnS / {Ti}_{3} C_{2} T_{x} d

-spacing 分别为

10.39, 12.09

和

14.48 Å

，表明层间距逐渐增加 [43,44]。和处

{28.7}^{\circ}, {47.8}^{\circ}

的峰分别

{56.6}^{\circ}

对应于 ZnS （JCPDS 05-0566）的（111）、（220）和（311）个面。在合成过程中，少量的 Ti 被氧化，如

ZnS / {Ti}_{3} C_{2} T_{x}

{25.3}^{\circ}

的衍射峰所示，对应于

{TiO}_{2}

（JCPDS 73-1764）的（101）面[45]。图 3b 显示了

{Ti}_{3} C_{2} T_{x}

和的

ZnS / {Ti}_{3} C_{2} T_{x}

FTIR 光谱。1350 和

3439 {cm}^{- 1}

波段分别是配体水和大气吸附水的 O-H 拉伸振动模式，对应于

1640 {cm}^{- 1}

C = O

拉伸振动峰值。的

{Ti}_{3} C_{2} T_{x}

和

ZnS / {Ti}_{3} C_{2} T_{x}

的拉曼光谱被表征（图 3c）。在

160 {cm}^{- 1}

周围出现一个峰值，对应于 Ti 和 C 原子的面内（

E_{g}

）振动。的

E_{g}

ZnS / {Ti}_{3} C_{2} T_{x}

峰值被移动到比更低的波数

{Ti}_{3} C_{2} T_{x}

。红移表示 ZnS 和

{Ti}_{3} C_{2} T_{x}

之间的有效电荷转移，表明异质结的形成 [46， 47]。Fig. 3d 分别显示

{Ti}_{3} C_{2} T_{x}

和的 SSA 为

ZnS / {Ti}_{3} C_{2} T_{x}

6.1 和

15.7 m^{2} / g

。增加的 SSA 可能会增强水分子的吸附。

The chemical state of the material is further analyzed using XPS, with the results presented in Fig. 4. Fig. 4a displays the Ti 2p spectra of

{Ti}_{3} C_{2} T_{x}

showing fitted peaks near 455.08, 461.12, 456.31, and 462.45 eV , which correspond to

{Ti}^{2 +} 2 p_{3 / 2}, T_{i}^{2 +} 2 p_{1 / 2}, {Ti}^{3 +} 2 p_{3 / 2}

, and

{Ti}^{3 +} 2 p_{1 / 2}

, respectively [48]. The 459.02 and 464.63 eV peaks correspond to the Ti atomic oxidation state

({TiO}_{2})

. Fig. 4 b indicates that the C 1 s spectra can be fitted to C-C and C-Ti bonds at 284.80 and 281.68 eV , respectively. Fig. 4c shows the Zn 2 p spectra of

ZnS / {Ti}_{3} C_{2} T_{x}

, with two significant peaks at 1021.55 and 1044.48 eV , respectively, correlating to

Zn 2 p_{3 / 2}

and

Zn 2 p_{1 / 2}

. Fig. 4d presents the S 2 p XPS spectrum, with
使用 XPS 进一步分析材料的化学状态，结果如图 4 所示。图 4a 显示了 Ti 2p 光谱，

{Ti}_{3} C_{2} T_{x}

显示了 455.08、461.12、456.31 和 462.45 eV 附近的拟合峰，分别对应于

{Ti}^{2 +} 2 p_{3 / 2}, T_{i}^{2 +} 2 p_{1 / 2}, {Ti}^{3 +} 2 p_{3 / 2}

和

{Ti}^{3 +} 2 p_{1 / 2}

[48]。459.02 和 464.63 eV 峰对应于 Ti 原子氧化态

({TiO}_{2})

。图 4 b 表明 C 1 s 光谱可以分别在 284.80 和 281.68 eV 下拟合到 C-C 和 C-Ti 键上。图 4c 显示了的

ZnS / {Ti}_{3} C_{2} T_{x}

Zn 2 p 光谱，在 1021.55 和 1044.48 eV 处有两个显著的峰值，分别与

Zn 2 p_{3 / 2}

和

Zn 2 p_{1 / 2}

相关。图 4d 显示了 S 2 p XPS 光谱，其中

- Corresponding authors. 通讯作者。
E-mail addresses: yutonghan@usst.edu.cn (Y. Han), zhigang_zhu259@163.com (Z. Zhu).
电子邮件地址：yutonghan@usst.edu.cn （Y. Han）、zhigang_zhu259@163.com （Z. Zhu）。
$^{1}$ These authors contributed equally to this work.
$^{1}$ 这些作者对这项工作做出了同样的贡献。

A R T I C L E I N F O

Keywords: 关键字：

Abstract 抽象

1. Introduction 1. 引言

2. Experimental section 2. 实验部分

2.1. Materials 2.1. 材料

2.3. Characterizations 2.3. 特征

2.4. Fabrication and measurement of humidity sensors2.4. 湿度传感器的制造和测量

3. Results and discussion3. 结果和讨论

3.1. Characterization 3.1. 特征

2.4. Fabrication and measurement of humidity sensors
2.4. 湿度传感器的制造和测量

3. Results and discussion
3. 结果和讨论