Edible rice paper-based multifunctional humidity sensor powered by triboelectricity

https://doi.org/10.1016/j.susmat.2023.e00596Get rights and content

Highlights

  • Edible rice paper was used as the functional material/substrate of a humidity sensor

  • Developed sensor was made self-powered by using rice paper as tribopositive layer of TENG

  • Rice paper was used in pristine form without compromising biocompatibility to enhance performance

  • Developed sensor showed significantly high performance compared to other paper-based sensors

  • Obtained results remained highly stable for 3 months

Abstract

Electronic wastes are causing unadorned burden on our environment due to the use of hazardous materials therefore, using naturally available green materials is necessary for sustainable and eco-friendly future. Biowastes can be used as functional materials of advanced electronic devices owing to their biocompatibility, low cost, and abundant availability. In this study, we have explored the multifunctional humidity sensitive response of a cellulose enriched edible rice paper (CERP). Presence of hydrophilic functional groups and highly porous surface of CERP made it a highly suitable sensing material for adsorbing/desorbing water molecules over a full relative humidity (RH) sensing range (0–100 %RH). Fast response/recovery times (5/16 s) were recorded along with a high sensitivity of 97%. CERP was also used as the electropositive layer of a triboelectric nanogenerator (TENG) for harvesting energy, making it a self-powered humidity sensor. High performance results were obtained including output voltage (162 V), output current (2 μA), and power density (3 μW/cm2), respectively. Electrical energy produced by TENG was enough to charge 3 commercial capacitors (1 μF, 4.7 μF, and 10 μF) and light 30 green LEDs. Obtained results were highly stable (1500 s) and repeatable with a long lifetime (3 months).

Introduction

High-level humidity can have adverse effects on human body such as frizzy hair, increased sweating, lethargic mood, fainting, heat stroke, fungus/mold growth, and hyperthermia. Moreover, low-level humidity results in dry air that trigger skin dryness, eyes irritation, dry nasal passage (worsening sinus infection), etc. Therefore, humidity sensors are of significant value to live a healthy life by maintaining ideal moisture content (40–60%) in our surrounding environment. Humidity sensors can also help to monitor and control healthy environment for living organisms and several industrial processes. Application areas of humidity sensors include but are not limited to monitoring respiration rate, weather prediction, skin dryness, noncontact switching, medical diagnosis for various diseases, food processing, pharmaceuticals, packaging, and agriculture [[1], [2], [3]]. Research endeavors should be dedicated to further enhance the quality and features of humidity sensors such as high sensitivity, flexibility, robustness, portability, self-decomposition, biocompatibility, and fast response/recovery time. Fabrication of a humidity sensor with the above-mentioned attributes can be a challenging task due to the complexity of involved technology. Moreover, controlling the synthesis of a laboratory made functional material with micro/nanostructure is not an easy task either and can also involve toxic chemical reagents. Researchers are therefore, striving to develop a humidity sensor with the added features of biocompatibility, low cost, facile fabrication, and easy disposability, without polluting environment but traditional methods/materials involve high temperature, power losses, high energy requirement, and toxic reagents [4,5]. Advanced electronics is searching for green solutions instead of conventional methods to avoid burden on environment and refrain from potential hazards to human life. Exploring green functional materials is a growing research area to offer clean, safe, and ecofriendly alternative to existing hazardous/toxic chemicals. Naturally available materials derived from plant extracts and food products such as potato peel, wood, tomato skin, paper, silk, tomato peel, honey, etc. can be used as potential functional materials/substrates for advanced electronic devices with the added advantage of recyclability [[6], [7], [8], [9], [10]]. Moreover, green electronics can avoid the emission of greenhouse gases during the purification and removal of electronic wastes (E-wastes) hence, reducing global warming because improper disposal of E-waste leads to harmful effects on the environment sustainability. Processing of green materials does not involve any sintering or chemical deposition.

Among green materials, cellulose enriched papers are biodegradable materials that can be used both as the substrate and active material of next generation humidity sensors. Paper has most desirable characteristics for its potential use in electronics and it has already been used in multiple devices successfully including supercapacitors [11], energy harvesters [12], sensors [13], batteries [14], and transistors [15]. Paper is generally used as the substrate of electronic devices instead of functional material because its intrinsic hydrophilic nature can deteriorate the device performance however, this drawback can serve as the key advantage for a humidity sensor because high hydrophilicity of paper can further enhance sensitivity of a humidity sensor. Moreover, surface of a cellulose enriched paper is pliable and porous framework that provides an ideal platform for adsorbing/desorbing water molecules in quick time. Cellulose enriched papers have added features of light weight, abundant availability, and ecofriendly. However, most of the existing fabrication technologies are either expensive or not compatible with paper based electronic devices. Duan et al. [16] paved the way for using paper as the sensitive layer and substrate of an advanced humidity sensor with the major deficiency of slow response/recovery time. Different reports are available in which paper based composites have been used for sensing humidity including polyacrylic acid coated carbon nanotube-paper composites [13,[17], [18], [19]], graphite/paper [20], paper coated with graphene [21], cadmium sulfide nanoparticles coated paper [22], poly(ionic liquid)s/paper [23], graphene oxide/paper [24], glycidyl trimethyl ammonium chloride paper [25], cobalt chloride/filter paper [26], cesium lead bromide coated paper [27]. These modified paper-based sensors exhibited promising sensing characteristics with the major limitations of loss in biocompatibility and lack of biodegradability.

In this work, the dual functionality of cellulose enriched edible rice paper (CERP) was studied by using it as the active layer/substrate of a humidity sensor and as the electropositive layer of a triboelectric nanogenerator (TENG) for self-powering humidity sensor. Highly porous structure and excessive hydrophilic functional groups present inside the rice paper made it an ideal candidate for sensing humidity. Humidity was sensed in the full operating range (0–100 %RH) with a high sensitivity (97%), and low hysteresis (1.4%) between adsorption/desorption curves. Furthermore, this biocompatible humidity sensor exhibited fast response/recovery time (5/16 s) as depicted from its dynamic response. Reports on other paper (printing paper, filter paper, parchment paper, tissue paper, tracing paper, etc.) based humidity sensors are available but those paper-based humidity sensors were functionalized with different hazardous/toxic chemicals/reagents to enhance their performance hence, compromising on the biocompatibility of device. Furthermore, paper was mainly used as the substrate only in earlier reported devices. We have used rice paper both as the sensitive material and substrate of humidity sensor in its pure form without compromising on its biocompatibility. CERP-humidity sensor (CERP-HS) was efficiently used for multifunctional applications including real time environment monitoring, touchless sensing, skin dryness, and examining breath rate. Furthermore, the motivation behind using CERP as the tribopositive layer of a TENG to self-power humidity sensor was derived from the fact that rice paper is made of mixed rice flour and potato flour containing polysaccharides, starch, and cellulose that are sensitive triboactive materials. Rice paper is a biodegradable material with the added feature of easy recyclability. Additional feature of CERP as a tribopositive layer made our humidity sensor portable, battery free, cost effective, and easy to fabricate. Maximum output voltage achieved by CERP-TENG was 162 V with output current of 2 μA and the peak power density of 3 μW/cm2 at the load resistance of 100 MΩ. Multiple commercially available capacitors were charged (1 μF, 4.7 μF, and 10 μF), and low power electronic devices (LEDs and LCD) were also powered successfully by using CERP-TENG. Self-powered humidity sensing was tested with different relative humidity conditions (30–80 %RH). Facile fabrication, low cost, and ecofriendly nature of CERP makes this work distinguished contribution towards large scale production of biocompatible, flexible, portable, and self-powered humidity sensors.

Section snippets

Materials

Commercially available CERP was purchased from a local market of Jeju Island, South Korea. Commercially available silver (Ag) ink pen with a low resistivity of 0.05–0.2 Ω/sq./mil was used for patterning IDEs (Circuit Scribe, USA). Transparent and adhesive silicon tape was used for enhancing durability of TENG (Rorentech, Seoul, South Korea). Copper foil tape with a low electrical resistivity of 1.673 μΩ and dual conductivity was used as the electrode of TENG (LoviMag, USA).

Fabrication of humidity sensor

Commercially

Topographical and cross-sectional results

Surface roughness (Ra = 1.63 μm) of CERP was determined by using 3D nanoprofiler. Cross-sectional FESEM images were used to determine the thickness of various layers in humidity sensor and TENG. Humidity sensor was composed of two layers including Ag IDE and rice paper whose thickness were ∼ 31.8 μm and ∼ 109 μm respectively, as shown in Fig. 1(a). Electronegative tribolayer consisted of adhesive silicon tape and FTO coated PET with thickness of ∼449 μm and ∼ 143 μm, respectively as shown in

Conclusion

A green solution for sensing humidity was propose din this study by using CERP as the functional layer. Added features of portability and self-powered electronic device were achieved by using same rice paper for harvesting electrical energy from mechanical energy. The obtained results of biocompatible humidity sensor showed that that rice paper is a highly suitable material for sensing humidity variations in its environment that changes its intrinsic resistance with varying relative humidity

Authorship statement

Conception and design of study: H.M.M ur Rehman, A.P.S. Prasanna, M.M. Rehman.

Acquisition of data: H.M.M ur Rehman, A.P.S. Prasanna, M. Khan.

Analysis and/or interpretation of data: M.M. Rehman, W.Y. Kim, S.J. Kim.

Drafting the manuscript: H.M.M ur Rehman, A.P.S. Prasanna, M.M. Rehman, M. Khan.

Revising the manuscript critically for important intellectual content: M.M. Rehman, A.P.S. Prasanna, W.Y. Kim, S.J. Kim.

Approval of the version of the manuscript to be published: Hafiz Mohammad Mutee ur

Declaration of Competing Interest

Authors declare no conflict of interest.

Acknowledgement

This research was funded by [National Research Foundation of Korea (NRF)- Korea Government (Ministry of Science and ICT)] grant number (NRF- 2020H1D3A1A04081545, 2021R1A4A2000934, 2021R1F1A1062800). This research has also been supported as Project Open Innovation R&D (21-DC-004) and supported by K-water.

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