Plant-protein-enabled biodegradable triboelectric nanogenerator for sustainable agriculture

Abstract

As the use of triboelectric nanogenerators (TENGs) increases, the generation of related electronic waste has been a major challenge. Therefore, the development of environmentally friendly, biodegradable, and low-cost TENGs must be prioritized. Having discovered that plant proteins, by-products of grain processing, possess excellent triboelectric properties, we explore these properties by evaluating the protein structure. The proteins are recycled to fabricate triboelectric layers, and the triboelectric series according to electrical properties is determined for the first time. Using a special structure design, we construct a plant-protein-enabled biodegradable TENG by integrating a polylactic acid film, which is used as a new type of mulch film to construct a growth-promoting system that generates space electric fields for agriculture. Thus, from the plant protein to the crop, a sustainable recycling loop is implemented. Using bean seedlings as a model to confirm the feasibility of the mulch film, we further use it in the cultivation of greenhouse vegetables. Experimental results demonstrate the applicability of the proposed plant-protein-enabled biodegradable TENG in sustainable agriculture.

Keywords: Biodegradable; Energy harvesting; Nanodevice; Plant protein; Sustainability; Triboelectric nanogenerator.

Graphical abstract

Fig. 1

Triboelectric charging behaviors and output current signal. (a) Fabrication of plant-protein-film-enabled bio-TENG. (b) Photographs of RP, PPI, SPI, WG, and zein films. The plant protein films have some level of transparency. (c) Schematic diagram showing triboelectric charging behavior of plant protein film (using Al as conductive electrode and PDMS as triboelectric negative layer). (d) Output current signal and its magnified view over one cycle.

Fig. 2

Triboelectric charging behavior of various plant protein films (CA, cellulose acetate). Output current signals of TENGs with (a) RP, (b) PPI, (c) SPI, (d) WG, and (e) zein as triboelectric materials and surface roughness of the corresponding plant protein films. (f) Charging of plant protein films upon contact with another film. (g) Open-circuit voltage and (h) short-circuit current of plant-protein-PLA-enabled bio-TENGs (plant protein film as triboelectric positive layer and PLA as triboelectric negative layer).

Fig. 3

ATR-FTIR analysis of five plant protein films. ATR-FTIR spectra of plant protein films in (a) 4000–500 cm⁻¹ and (b) 3600–2700 cm⁻¹. (c) ATR-FTIR spectra in 1800–1000 cm⁻¹. (d) Gaussian-curve-fit inverted second-derivative amide I spectra of RP film.

Fig. 4

The influence of the chemical structure on the bio-TENG. AFM-IR map of RP film at (a) 1210, (b) 1462, (c) 1546, and (d) 1670 cm⁻¹. (e) RGB overlay of regions at 1462, 1546, and 1670 cm⁻¹ representing δ(CH₂), amide II, and amide I, respectively. Stick model and molecular formula of amino acids including (f) nitrogen-containing and (g) carboxyl groups on the side chain and a normalized number of nitrogen-containing groups and carboxyl groups calculated by amino acid analysis of five plant protein films. (Arg, arginine; His, histidine; Lys, lysine; Asp, aspartic acid; Glu, glutamic acid)

Fig. 5

Bio-TENG as a biodegradable mulch film to construct a growth-promoting system that generates space electric fields. (a) Schematic diagram of the electric field experiment. (b) Percentage of weight gain (left) and elongation (right) in control (without electric field) and test (with electric field) groups after 48 h of growth. Whiskers indicate mean ± standard deviation for n = 24 bean seeds per group. Two-sample t-test; ****p < 0.0001. (c) Typical photographs of beans with (test) and without (control) electric field application before and after 48 h of growth. (d) Plant-protein-enabled bio-TENG used as biodegradable mulch film to construct the growth-promoting system that generates a space electric field for agriculture.

Fig. 6

Bio-TENG as a biodegradable mulch film to construct the growth-promoting system that generates a space electric field for bok choi crops. Data are expressed as mean ± standard deviation for n = 20 bok choi seedlings per group analyzed by one-way ANOVA (analysis of variance); *p < 0.05; **p < 0.01; ***p < 0.001; ****p < 0.0001. (a) Plant height of four bok choi groups over time and (b) difference in plant height between groups in different periods. (c) Crown diameter over time of four bok choi groups and (d) difference in crown diameter between groups in different periods. (e) Number of leaves over time of four bok choi groups and (f) difference in the number of leaves between groups in different periods.