Superhydrophobic Photocatalytic Self‐Cleaning Nanocellulose‐Based Strain Sensor for Full‐Range Human Motion Monitoring

Nanocellulose‐based strain sensor (NBSS) have been a subject of growing interest for wearable electronics. However, these electronic devices are susceptible to damage when they come into contact with water and organic contaminants. Recently, researchers have developed a superhydrophobic NBSS. Unfortunately, it does not treat organic pollutants in water when used in an underwater environment. In this paper, a new solution: a superhydrophobic photocatalytic self‐cleaning NBSS created through scrape coating and dip coating methods is proposed. This new method shows outstanding self‐cleaning capabilities against water and organic contaminants due to the synergistic effects of the superhydrophobicity and photocatalysis of MnO2 nanoparticles. Furthermore, the superhydrophobic photocatalytic self‐cleaning NBSS has an exceptional response time of 0.66 s, a fast recovery time of 0.81 s, a sensitivity ≈66.53 at a strain of 0.5%. It is expect that the superhydrophobic photocatalytic self‐cleaning NBSS can monitor human movements, including finger twists, wrist movements, elbow bends, and knee movements. Not only is the fabrication method cost‐effective and scalable, but the new NBSS holds great promise in a wide range of fields, including human‐machine interactive systems, smart systems, and human‐body monitoring. Overall, the study provides significant guidance for future designs for wearable strain sensors.


Introduction
With the rapid development of the materials industry and modern processing technologies, flexible materials have been developed for a wide range of applications. [1,2]The nanocellulosebased strain sensor (NBSS) shows excellent potential in novel DOI: 10.1002/admi.202300350[5][6] However, the hydrophilic nature of the NBSS restricts its use in water-based environments. [7]esearchers have endeavored to address this limitation by developing flexible sensors with superhydrophobic characteristics.For example, Xia et al. [8] presented a microcracked carbonized paperbased superhydrophobic strain sensor, demonstrating the potential of superhydrophobic wearable electronics.Similarly, Lee et al. [9] successfully developed a superhydrophobic NBSS with outstanding strain sensing performance.Collectively, these results demonstrate tremendous potential for the development of superhydrophobic wearable electronics.
[12] In practical applications, however, organic grease pollutants tend to adhere to the NBSS surface, causing damage to the superhydrophobic coating.15] Thus, superhydrophobic NBSSs that exhibit photocatalytic activity can repel liquids and also degrade organic pollutants.[18] The combination of superhydrophobicity and photocatalytic activity of MnO 2 nanoparticles displays excellent synergistic behavior, resulting in better self-cleaning properties.Unfortunately, there is a lack of research on superhydrophobic NBSS with both physical and chemical self-cleaning properties.Moreover, the current fabrication process of superhydrophobic NBSSs is somewhat complex and time-consuming, thereby hindering its large-scale application.
This study utilized cost-effective and scalable scrape coating and dip coating methods to manufacture the superhydrophobic photocatalytic self-cleaning NBSS, which is capable of monitoring full-range human motion.A conductive NBSS was formed by applying a thin layer of graphene to the nanocellulose surface.Next, an in situ generated mixture of stearic acid (STA) and MnO 2 was coated onto the conductive NBSS's surface, resulting in a superhydrophobic photocatalytic self-cleaning NBSS with a high water contact angle of 161°.The NBSS demonstrated exceptional self-cleaning capabilities toward water and organic contaminants, due to the synergetic function of superhydrophobicity and MnO 2 nanoparticles' photocatalytic activity.This is not possible with some conventional superhydrophobic Ag (Octadecanoic Acid/Ag Nanoparticle-Decorated Rubber Composites [19] ) and reduced graphene oxide based sensors (RGO nylon/PU fabric [20] ).Furthermore, it is feasible to assemble the superhydrophobic photocatalytic self-cleaning NBSS into electronic skin.Due to their notable sensitivity (≈66.53 at 0.5% strain and a stretch speed of 113.1 m min −1 ) and fast response time (0.66 s response time and 0.81 s recovery time), the assembled skin has the potential to detect various body movements, including those of fingers, wrists, elbows, and knees.There is considerable potential for the fabricated superhydrophobic photocatalytic self-cleaning NBSS in a variety of fields, including human-machine interactive systems, smart systems, smart robotics, and human-body monitoring.Overall, this research provides valuable insights, contributing to the design of the next generation of wearable strain sensors.

Preparing of Cellulose Nanofibers (CNFs)
To obtain powdered cellulose nanofibers (CNFs), CFs (4 g) were suspended in water (500 mL) containing PEG (0.04 g).An oxida-tion reaction was initiated by adding 5 mmol L −1 NaClO solution to the mixture, which was then maintained at a pH of 10 for 3 h at room temperature.In an ice bath, 3 mg mL −1 oxidized cellulose/water slurries were sonicated for 10 min using an ultrasonic generator equipped with a 13 cm-diameter probe tip and an output power of 400 W (WS-FB02, Weisi (Xiamen) Technology Co., Ltd., China).The unpurified cellulose was removed by centrifuging the cellulose nanofiber dispersions at 10,000 rpm for 10 min to obtain the powdered CNFs.

Preparing of the Superhydrophobic Photocatalytic Self-Cleaning NBSS
A glass rod was used to dissolve lignocellulosic fiber pulp (1.0 g) completely in 50 ml of ethanol.Then, PEO (500 mg) was added to the solution and vacuum-compressed at 55 °C for 3 h to flocculate the cellulose.The nanocellulose-based substrate (NBSS) was then fabricated.Next, the graphene slurry was applied evenly onto the NBSS surface and sintered at 90 °C for 2 h to ensure appropriate conductivity.The fiber was used as a binder to improve interfacial interaction between the graphene and the NBSS, and the hydrophilic functional groups on the surface delivered homogeneity and stability.The conductive NBSS was then dipped into 0-1.1 mol L −1 manganese sulfate solution for 5 min, followed by 0.5 mol L −1 sodium hydroxide for 2 s, to form conductive NBSS+MnO 2 .In the final step, the conductive NBSS+MnO 2 was modified with a 10 g L −1 stearic acid solution for 1 min and then heated at 60 °C for 5 h to obtain the superhydrophobic photocatalytic self-cleaning NBSS.The fabrication process of the superhydrophobic photocatalytic self-cleaning NBSS was depicted schematically in Figure 1.

Characterization
The characterization of the sample was performed using various analytical techniques: SEM was used to observe its morphology, FTIR was used to detect its molecular structure and chemical bonds, XRD was used to analyze its crystal structure.The contact angle was measured by dropping 4 μL of water onto the sample, and the average value was calculated at least five different locations for each specimen.

Physcial/Chemical/Mechanical Stability Tests
The chemical, thermal and mechanical stability of the superhydrophobic photocatalytic self-cleaning NBSS were investigated.The chemical stability was assessed by immersing the sample in various corrosion environments for a specific duration.Thermal stability was analyzed by subjecting the sample to different high temperatures for 2 h.To conduct mechanical stability testing, a weight of 50 g was placed on the top of the superhydrophobic photocatalytic self-cleaning NBSS surface, with 1000-mesh sandpaper underneath the NBSS surface to evaluate its abrasion resistance.Additionally, the sample was subjected to UV irradiation and mechanical bending to test its overall stability.

Strain Sensing Test
The experimental protocol was approved by the Office of Research Ethics at Nanchang Hangkong University.Prior to any data collection, written informed consent was obtained from all participants.A high resistance measuring instrument (Changzhou Tonghui Electronics Co. Ltd.TH2684A, China) was used to evaluate the strain sensing performance of the 40×10×0.12mm 3 superhydrophobic photocatalytic self-cleaning NBSS.To achieve full-range body motion monitoring, two copper wires were attached to the two opposing ends of the superhydrophobic photocatalytic self-cleaning NBSS with conductive silver paste, and connected to a resistance meter, which measured the sensor's resistance in real-time throughout the strain sensing test.The strain sensor was applied to human skin for demonstrating full range body motion monitoring, and the resistance variation was recorded once the movement was detected.The gauge factor (GF) was generally used to assess the strain sensitivity of the sensor, which determines the relative change in strain resistance per unit strain.The GF can be calculated using Equation ( 1) and ( 2). [21] = ΔR R 0  (1) Where ∆R was the relative resistance change, R 0 was the initial resistance of the strain sensor,  was the bending strain applied to the strain sensor, r was the bending radius, and h was the thickness of the composite film.

Superhydrophobic Physical Self-Cleaning
One piece of the superhydrophobic photocatalytic self-cleaning NBSS was secured at an angle of 30°using double-sided tape.
The surface was then covered with methylene orange (MO) and methylene blue (MB) particles to evaluate the self-cleaning ability of the superhydrophobic photocatalytic self-cleaning NBSS.The effectiveness of the self-cleaning ability was tested by rinsing the surface with water to remove MO and MB particles.

Photocatalytic Chemical Self-Cleaning
The efficiency of a photocatalytic system was measured by the rate constant of the photocatalytic degradation process, making the study of photocatalytic reaction kinetics crucial.The Langmuir-Hinshelwood kinetic equation (L-H equation) was typically used to describe the photocatalytic degradation process.According to this equation, the reaction rate was dependent on the substrate concentration, and can be expressed mathematically: [22] When the concentration of substrate was very low (C 0 <<1), integrating Equation (3) gives the first-order reaction kinetic equation where r 0 represents the rate of the reaction at the beginning, k r was the rate constant of the reaction, k a was the adsorption equilibrium constant, K was the apparent rate constant, and A was the integration constant used in calculations.C 0 was the initial solution concentration and C represents the instantaneous concentration of the reactants.
The photodegradation ability of the superhydrophobic photocatalytic self-cleaning NBSS was evaluated by using methylene blue (MB), a water-soluble pollutant.The superhydrophobic photocatalytic self-cleaning NBSS was then exposed to UV light (320 nm, 100 mW cm −2 ) for different periods at room temperature.Meanwhile, the dual-beam UV-vis spectrometer (UV755B, Yoke, China) was used to measure the light absorption of MB in water.The degradation rate was determined by Equation ( 5):

The Process Parameters and Morphology of the As-Prepared Sample
Figure 2a,b display the cross-sectional morphology of nonconductive bacterial cellulose (NBSS) and conductive NBSS.The NBSS is mainly crossed by a backbone of cellulose, while the conductive NBSS displays a bilayer structure, with graphene embedded in the NBSS and forming an ≈36 μm thick conductive layer.Figure 2c,d display the surface morphology of the conductive NBSS and the superhydrophobic and photocatalytic self-cleaning NBSS. Figure 2c shows that the surface of the conductive NBSS has a macromolecular arrangement of cellulose and a flat layer of graphene firmly attached to it.Manganese dioxide (MnO 2 ) nanoparticles cover the conductive NBSS surface, resulting in a superhydrophobic surface.Figure 3 shows the energy-dispersive X-ray spectroscopy (EDX) and corresponding element mapping of the superhydrophobic and photocatalytic self-cleaning NBSS.SEM-EDX discovered the presence of manganese (Mn) on the surface.Carbon (C), oxygen (O), Mn, and sulfur (S) elements were visible on the surface, with Mn and S deriving from manganese (II) sulfate.Figure S1a (Supporting Information) shows the influence of the sintering time on the prepared sample's surface conductivity.The NBSS became electrically conductive after 0.1 h of sintering, with a conductivity of 0.127 S m −1 , attributed to the formation of an effective conductive network.The conductivity steadily increased with sintering time to 41.8 S m −1 , indicating a stable conductive network.MnO 2 and STA particles were then deposited onto the conductive NBSS surface to obtain the conductive NBSS.
Figure S1b (Supporting Information) shows the influence of the in situ growth time on the contact angle and sliding angle of the conductive NBSS.As the in situ growth time increased from 0 to 120 s, the contact angle increased from 89.2°to 158°, resulting in a superhydrophobic surface.The sliding angle dropped from 8.7°to 4.6°at 120 s, indicating low adhesion.However, as the in situ growth time increased beyond 120 s, the contact angle decreased, and the sliding angle increased due to particle agglomeration.This demonstrated that 120 s was the optimal in situ growth time to achieve a stable micro-nano structure and the superhydrophobic property.The deposition of MnO 2 particles on conductive NBSS surfaces has little effect on their conductivity, as reported by Zhao et al. [23] for graphene/MnO 2 composite materials.Therefore, MnO 2 has a better effect on conductivity than on superhydrophobicity.
Figure 4a shows the crystallographic structure of the prepared samples using powder X-ray diffraction (XRD).The original conductive NBSS showed a dominant diffraction peak at 2 = 26.6°corresponding to graphene's (002) crystalline planes, [24] and a distinctive peak at 2 = 21.6°corresponding to STA's (311) crystalline planes.After depositing MnO 2 and STA particles, the two typical peaks weakened, and a new broad peak at 2 = 60.2°corresponding to MnO 2 's (521) planes appeared, indicating the successful introduction of MnO 2 and interfacial interaction. [25]Figure 4b shows the FT-IR spectra of the conductive NBSS, conductive NBSS+STA, conductive NBSS+MnO 2 , and superhydrophobic photocatalytic selfcleaning NBSS.The NBSS was mainly composed of cellulose, with stretching vibrations of -OH at 3734 cm −1 and 3471 cm −1 , and bending and stretching vibrations of C─H bonds at 2920 and 2848 cm −1 , respectively.Peaks at 2360 cm −1 corresponded to the absorption vibration peaks of CO 2 , and 1100 cm −1 peaks resulted from C-O stretching vibration peaks of asymmetric bridges. [26]he conductive NBSS+STA exhibited a -COOH stretching vibration peak at 1703 cm −1 , indicating STA incorporation in the superhydrophobic photocatalytic self-cleaning NBSS.The conductive NBSS+MnO 2 and superhydrophobic photocatalytic self-cleaning NBSS showed an asymmetric stretching vibration peak of Mn-O at 626 cm −1 , indicating the incorporation of MnO 2 micro-nanoparticles in the material structure. [27]These data suggest that STA and MnO 2 are wrapped around the conductive NBSS.

Stability Performance
Exposure to extreme conditions can diminish both the material surface's conductivity and superhydrophobicity.Hence, it is crucial to evaluate the stability of the superhydrophobic photocatalytic self-cleaning NBSS, as depicted in Figure 5.The prolonged use of the superhydrophobic photocatalytic self-cleaning NBSS poses a significant challenge in terms of mechanical stability.After 140 bending cycles, the water contact angle of the superhydrophobic photocatalytic self-cleaning NBSS decreased by 15°compared to the initial angle of 170°, while the rolling angle increased from 4°to 10°. Figure 5a indicates that the superhydrophobic photocatalytic self-cleaning NBSS surface developed minute cracks after 140 bending cycles, causing a decrease in conductivity from 3.8 × 10 −3 s to 0.1 × 10 −3 s.Comparable results in Figure 5b present a decrease in both surface conductivity and water contact angle of the superhydrophobic photocatalytic self-cleaning NBSS with increasing wear distance, whereas the rolling angle exhibits an opposite trend.Figure 5c demonstrates the thermal stability of the superhydrophobic photocatalytic self-cleaning NBSS, with the water contact angle consistently above 160°and the rolling angle remaining below 10°as the temperature increases from 30 °C to 90 °C.However, as the temperature exceeded 90 °C, the water contact angle decreased, the rolling angle increased, and the conductivity rose due to the breakage of the STA molecular chain.Figure 5d reveals the excellent UV resistance of the superhydrophobic coating on the surface of the photocatalytic self-cleaning NBSS.The water contact angle remained above 160°, while the rolling angle stayed below 10°, and the surface conductivity remained stable, as illustrated in Figure 5d.However, when subjected to acidic solutions with pH values of 4 or 6, the superhydrophobic photocatalytic selfcleaning NBSS failed, leading to a substantial reduction in the contact angle, as depicted in Figure 5e.The primary cause of this failure is the detrimental effect of H + ions in the acidic solution on the coated surface.Figure 5f demonstrates the maintained stability of the conductivity in the superhydrophobic photocatalytic self-cleaning NBSS when exposed to acidic or alkaline solutions.The superhydrophobic photocatalytic self-cleaning NBSS investigated in this study exhibits outstanding physical, chemical, and mechanical stability.

Superhydrophobic Physical Self-Cleaning
The new composite material achieved its self-cleaning ability through two mechanisms.First, by removing impurities through water, due to its low surface adhesion and superhydrophobicity.Second, by utilizing the photocatalytic activity of MnO 2 to catalyze organic pollutant degradation.Figure 6a shows that when a single water droplet touched the material and was pushed against it, the water kept its spherical shape and did not stick.As shown in Figure 6b, a 5-liter water droplet sliding on a slanted material had no visible adherence to water.Further examination of the self-cleaning capability was done in Figure 6c and Movie S1 (Supporting Information), demonstrating the antifouling and self-cleaning properties of the material tested against methylene orange (MO) powder as contaminants.When the MO solution was put directly over the material's surface, the MO powder flowed down immediately to the bottom, with the material surface remaining clean and dry.These results are due to the unique rough structure of the superhydrophobic surface and the surface's modification by low surface energy substances that result in lower forces between the microparticles and the surface, thus removing contaminants from the material.

Photocatalytic Chemical Self-Cleaning
The photocatalytic efficiency of the superhydrophobic photocatalytic self-cleaning NBSS is investigated in this study.The MB solution was subjected to breakdown by the superhydrophobic photocatalytic self-cleaning NBSS under both UV irradiation and dark conditions, as demonstrated in Figure 7. Figure 7a shows that the absorption spectral amplitude of the MB solution dropped after 3 h of UV irradiation.In contrast, Figure 7b reveals that the absorption spectral amplitude of the MB solution remained consistent in dark conditions.The degradation ability (C/C 0 ) versus time was plotted for both UV and dark settings in Figure 7c.The results indicate that the degradation ability under UV settings was substantially stronger than that of dark settings.The photocatalysis of MnO 2 nanoparticles is the primary contributor to the superhydrophobic photocatalytic self-cleaning NBSS's high degradation efficiency, while its physical absorption potential is insignificant.Linear curves derived from Equations ( 3) and (4) were used to determine the degradation rates of 0.269 and 0.034 h −1 under UV and dark settings, respectively.The rate constants obtained from the linear regression analysis in Figure 7b are consistent with Equation (4).These findings demonstrate that the photocatalytic degradation of MB in superhydrophobic photocatalytic coatings follows the Langmuir-Hinshelwood first-order kinetic equation.Figure 7d illustrates the percentage of photocatalytic degradation efficiency of the superhydrophobic photocatalytic self-cleaning NBSS on MB dye solutions of different periods under UV and dark settings.Under UV irradiation, the photocatalytic degradation efficiency of the superhydrophobic photocatalytic self-cleaning NBSS was ≈80.8%, whereas, after 3 h in the dark, the efficiency was 10.18%.
MnO 2 nanoparticles produced on the superhydrophobic photocatalytic self-cleaning NBSS can act as effective photocatalysts for pollutant degradation, surpassing conventional superhydrophobic materials.Under UV light exposure, electrons in MnO 2 's valence band are stimulated and transferred to its conduction band.This process leads to the generation of photoelectrons (e − ) and photoholes (h + ) in the CB and VB, respectively.Photogenerated photoelectrons (e − ) and photoholes (h + ) can interact with nearby oxygen and water molecules transforming into superoxide radicals (•O 2− ) and hydroxyl radicals (•OH − ).These radical species are highly effective in fragmenting various organic compounds [28,29] and thus facilitating organic pollutant degradation.

Application of the Superhydrophobic Photocatalytic Self-Cleaning NBSS for Full Range Human Motion Monitoring
As discussed earlier, the superhydrophobic photocatalytic selfcleaning NBSS exhibits exceptional superhydrophobic stability and surface conductivity.The remarkable superhydrophobicity of NBSS ensures excellent resistance to water, making it ideal for use in different wet conditions.Upon water droplets contact, the current in the conductive NBSS reduced substantially from 76 mA initially to 63 mA on complete wetting, as seen in Figure 8a-c and Movie S2 (Supporting Informaation).This resulted from changes in the coating resistance after complete wetting.Conversely, as illustrated in Figure 8d-f, the current remained constant, at 66 ± 0.2 mA, as water droplets came in contact with the superhydrophobic photocatalytic self-cleaning NBSS.The study findings demonstrate that the superhydrophobic photocatalytic self-cleaning NBSS has exceptional water resistance because of its superhydrophobicity, which prevents water from harming internal coating and hence the electrical conductivity.
The superior water resistance of the superhydrophobic photocatalytic self-cleaning NBSS accounts for its steady resistance.Wearable tests were carried out to evaluate the sensing performance of the superhydrophobic photocatalytic self-cleaning NBSS based on repeatability and fatigue resistance.The relative resistance (ΔR/R 0 = (R-R 0 )/R 0 ) was measured, with R 0 representing the initial resistance of the superhydrophobic photocatalytic self-cleaning NBSS, and R indicating the transient resistance at a specific strain.At a strain of 0.5% and a stretch speed of 113.1 m min −1 , the superhydrophobic photocatalytic self-cleaning NBSS exhibited a 0.66s response time and 0.81s recovery time, as indicated in Figure 9a.In Figure S2 and Movie S3 (Supporting Information), the experimental procedure and equipment are shown.This quick response and recovery time guarantee the ability to monitor fast and continuous motion in real-time.The superhydrophobic photocatalytic self-cleaning NBSS bending process sensitivity is ≈66.534, as per Equations ( 1) and ( 2), a crucial metric in evaluating wearable device flexibility.Detailed comparisons of various sensing devices, [29][30][31][32][33][34] including the superhydrophobic photocatalytic self-cleaning NBSS, are   Although other devices may be more sensitive, they may have a complex fabrication process, which could limit their potential applications. [35]In contrast, the superhydrophobic photocatalytic self-cleaning NBSS can be readily utilized through simple and effective coating procedures, and it has the additional advantage of superhydrophobicity in practical contexts.
The wearable electronic device used to monitor human activities is based on resistance sensitivity of the superhydrophobic photocatalytic self-cleaning NBSS.This device was applied to the volunteers' skin throughout the human motion monitoring procedure.The resistance changes of the laminated film were mea-sured using a real-time LCR meter.Figure 9c illustrates the curve representing the monitoring of finger-bending motion.The experimental results indicated stable resistance signals with a pulse rate of ≈25 times per minute, which aligns with typical body parameters.As the angle of finger-bending increased from 0 to 90°, the relative change in resistance (ΔR/R 0 ) increased from 0 to ≈0.25.However, upon returning the fingers to their original position, ΔR/R 0 reverted to its normal value.Furthermore, we utilized the superhydrophobic photocatalytic self-cleaning NBSS to monitor the elbow, wrist, and knee joints of the participants, even during activities involving sweating.The resistance signals remained consistent and repeatable, as demonstrated in Figure 9d-g.Thus, the study's results strongly support the potential application of the superhydrophobic photocatalytic selfcleaning NBSS for comprehensive human motion monitoring.

Conclusion
This study successfully fabricated superhydrophobic photocatalytic self-cleaning NBSS by utilizing a combination of scape coating and dip-coating methods.A graphene layer was applied on the nanocellulose surface to form conductive channels, while an in situ MnO 2 /stearic acid mixture was generated to create superhydrophobicity.The NBSS surface, exhibiting excellent selfcleaning performance toward water and organic contaminants, was achieved by the synergistic effect of the superhydrophobicity and photocatalysis of MnO 2 nanoparticles.Furthermore, the superhydrophobic photocatalytic self-cleaning NBSS displayed great sensitivity and a fast response, making it an ideal candidate for assembling electronic skin.The electronic skin demonstrated the ability to detect deformation during human body movements accurately.Additionally, the constructed NBSS can be valuable in various applications, such as man-machine interactive systems, smart robots, and human body monitoring.Hence, this study provides essential insight for the development of the nextgeneration wearable strain sensor.

Figure 1 .
Figure 1.a) Fabrication process of cellulose nanofiber.b) Fabrication process of the superhydrophobic photocatalytic self-cleaning NBSS.

Figure 3 .
Figure 3. a) SEM images of the superhydrophobic photocatalytic self-cleaning NBSS.b) EDS spectrum of the superhydrophobic photocatalytic selfcleaning NBSS.c) Mapping elements of C element.d) Mapping elements of O element.e) Mapping elements of Mn element.f) Mapping elements of S element.

Figure 4 .
Figure 4. a) XRD patterns of the as-prepared samples.b) FTIR spectra of the as-prepared samples.

Figure 5 .
Figure 5.The surface conductivity, water contact angle and rolling angle of the superhydrophobic photocatalytic self-cleaning NBSS: a) Blending test; b) Wearing test; c) Thermal stability test; d) UV irradiation test.e) Water contact angle test of the superhydrophobic photocatalytic self-cleaning NBSS during different pH environment.f) Surface conductivity test of the superhydrophobic photocatalytic self-cleaning NBSS during different pH environment.

Figure 6 .
Figure 6.a) The total move process of one drop on the superhydrophobic photocatalytic self-cleaning NBSS surface.b) A series of digital photos of a 5 L water droplet moving over a slightly inclined the superhydrophobic photocatalytic self-cleaning NBSS surface over time.c) The superwetting characteristic of the superhydrophobic photocatalytic self-cleaning NBSS surface for MO powder pollutants.

Figure 7 .
Figure 7.Under a) UV irradiation and b) dark environment, MB dye solution was photodegraded by the superhydrophobic photocatalytic self-cleaning NBSS.c) C/C 0 -time diagram of degradation ability under dark settings and UV settings.d) Percentage of degradation ability by the superhydrophobic photocatalytic self-cleaning NBSS under dark settings and UV settings.

Figure 8 .
Figure 8. Real-time current monitoring of the LED series circuit after continuous water dripping on the conductive NBSS surface with a) 0, b) 5, and c) 10 ml.Real-time current monitoring of LED series circuit after continuous dripping on the surface of the superhydrophobic photocatalytic self-cleaning NBSS with d) 0, e) 5, and f) 10 ml.

Figure 9 .
Figure 9. a) Response time and recovery time of the superhydrophobic photocatalytic self-cleaning NBSS at a stretch rate of 113.1 m/min at 0.05% strain.b) Comparison of the sensitivity of the superhydrophobic photocatalytic self-cleaning NBSS with other reported strain sensors at small strains.real-time resistive signal of the sensor to the body movement of the tester, including c) bending the fingers, d) bending the elbow, e) bending the wrist, and f) bending the knee.g) Real time resistance signal of the sensor bending under sweat at pH 6.4.