| Carbon footprint is an indicator that widely measures the impact of climate change,and is also an important influencing factor for“carbon peaking”and“carbon neutrality”.Energy is the main focus of carbon footprint assessment,and the development of clean,low-carbon,safe and efficient energy harvesting technology has become an inevitable trend.In the past decades,sustainable energy harvesting technology has developed rapidly.Triboelectric nanogenerator(TENG)technology is one of the typical representatives,which can effectively convert raindrop energy,wind energy,vibration energy,etc.into electrical energy.In particular,biomaterials-enabled biological triboelectric nanogenerator(bio-TENG)technology is an effective solution to reduce carbon footprint in recent years.As one of the most important and common biomaterials,proteins havewide source,abundant surface groups,structural diversity,and designability.They are the most promising candidate materials to replace chemical polymers to construct bio-TENG.However,protein-based bio-TENG still has some issues to be solved,i.e.low output power,unclear working mechanism,and unclear influence mechanism between structure and triboelectric behavior.To remedy this,we select the plant protein as the research object,from regulating and improving the performance of protein-based triboelectric layer,to reveal the intrinsic relationship between protein structure and triboelectric behavior.On basis of the triboelectric behavior of proteins,researches were carried out from three aspects:the construction of the research platform and the analysis of related theories,as well as the influence mechanism of different protein structures(primary structure and secondary structure)on the triboelectric behavior.On this basis,an agricultural biodegradable power generation mulch film based on high-performance bio-TENG was designed,and its feasibility for using in a space electric field growth-promoting system was evaluated.The main research contents and results are as follows:(1)In order to meet the needs of studying the triboelectric behavior of protein based bio-TENG,this subject designed and built a preparation,characterization,and testing platform of bio-TENG,which lays a solid foundation for further research on the mechanism between protein structure and triboelectric behavior.In addition,starting from the working principle of the TENG,influencing factors of the contact electrification(CE)process of TENG,the existing CE model,and the group-dominated CE behavior are introduced.The general methods of protein structure modification are also discussed and the potential effects of different protein structures on the triboelectric behavior are analyzed.The above research platform and theoretical analysis provide an effective way for studying the triboelectric behavior of plant protein-based biological interface and exploring the molecular structure of protein to regulate its triboelectric properties.(2)In order to explore the effect of protein primary structure on its triboelectric behavior,five plant protein films with similar secondary structures and different primary structures were prepared.By comparing with the representative materials in the triboelectric series,it was found that all the prepared plant protein films had excellent electron donating ability,and followed the sequence:(+)rice protein,peanut protein isolate,wheat gluten,soybean protein isolate,and zein(–)(Wheat gluten and soy protein isolate have similar triboelectron donating abilities).Among them,the TENG constructed by the rice protein film-PDMS can produce a peak-to-peak voltage of～20 V when the effective contact area is 4 cm~2 and the applied force parameters follow the oscillation power of 15 W and the frequency of 10 Hz.On this basis,the reasons for the difference in the triboelectric behavior of different plant protein films were explored.First,the vibration of chemical bonds in plant protein films was analyzed using Attenuated total reflection-Fourier-transform infrared spectroscopy(ATR-FTIR),it was found that the number of NH in the plant protein film was related to its triboelectric behavior.Next,atomic force microscopy-based infrared spectroscopy(AFM-IR)was used to analyze the surface group distribution of plant protein films,and it was found that the content of nitrogen-containing groups was highly correlated with the triboelectric series of plant protein.Finally,the nitrogen-containing groups and carboxyl group contents of the five proteins were counted by amino acid analysis,and it was found that the plant protein film with more nitrogen-containing groups and fewer carboxyl groups has more excellent electron donating ability.These results indicate that the triboelectric behavior of the protein film is mainly determined by the nitrogen-containing groups and carboxyl groups in its primary structure,wherein the nitrogen-containing groups promote its triboelectric electron-donating ability,while the carboxyl groups show a weakening effect.(3)In order to explore the influence mechanism of protein secondary structure on its triboelectric behavior,two types of rice glutenin(RG)with different secondary structures were prepared under alkaline and neutral conditions,respectively,namely RG(p H 12)and RG(p H-cycle)film.The study showed that the triboelectric output voltage(～68 V)of the RG(p H-cycle)film was 4.8 times of the RG(p H 12)film(～14 V).Circular dichroism(CD)and ATR-FTIR were used to explore the structural changes during RG film formation and the results showed thatβ-sheet,β-turn,andα-helix contributed to the orderly arrangement of amide bonds(CO-NH)and their exposure on the surface of protein film.Such abundant electron donating groups can effectively improve the triboelectric electron donating properties of protein film.On this basis,an ultrasonic-assisted p H-cycle technique was invented to regulate the secondary structure of RG films,and RG films with different secondary structure contents such asβ-sheet andα-helice were prepared.The study found that the moreβ-sheet andα-helix,the more amide bonds on the surface of the RG film,and the better the triboelectric output performance.The above experiments not only verified the proposed theory of the mechanism of protein secondary structure affecting its triboelectric behavior,that is,the special arrangement ofβ-sheet andα-helice helps to expose more amide bonds and improves the triboelectric output performance,and the precise regulation of the triboelectric behavior of the protein film was realized(the triboelectric output voltage alters from～12 V to～200 V).(4)In response to the demand for increasing crop yeild,based on the previous theoretical study,a fully degradable power generation mulch film based on plant protein-based bio-TENG was designed and developed to build a space electric field growth-promoting system for crops.First,a fully degradable protein-based bio-TENG was designed and fabricated.This novel bio-TENG utilizes a biodegradable polylactic acid(PLA)film as the triboelectric pair of the plant protein film,and combines the PEDOT:PSS(Poly[3,4-ethylenedioxythiophene]polystyrene sulfonate)coated on the surface of the PLA film.sulfonate,PEDOT:PSS)as the induction electrode.Subsequently,by optimizing the plant protein film thickness(51μm)and the relative humidity(40%RH)in which the bio-TENG works,the highest triboelectric output voltage of～180 V(peak-to-peak voltage,the effective contact area is 28.26 cm~2)was obtained.The prepared plant protein-based bio-TENG was used as a new type of mulch film for the growth of soybean seedlings.Compared with the control group,the weight gain rate of soybean seedlings treated with the space electric field generated by the mulch film increased from 19.1%to 24.3%,and the elongation rate increased from 132.4%to 223.8%.The results of mung bean germination experiments showed that electric field treatment could increase the water absorption of mung bean and indirectly improve seed germination.Further,the mulch film was applied to the actual growth of pakchoi,and the results showed that the bio-TENG based mulch film had a significant promoting effect on the growth of pakchoi(After 11 days of growth,in contrast with the control group,the growth rate of plant height of pakchoi cultivated with mulch film increased from 94.8%to 133.8%,the crown width increased from 65.0%to 107.0%,and the number of leaves increased from 67.2%to 104.4%).The pakchoi closer to the mulch film(closer to the electric field generated by the mulch film)shows a more obvious growth promoting effect.The above growth experiments of soybean,mung bean and pakchoi verified the feasibility of the fully degradable plant protein-based bio-TENG as a new generation of mulch film for the construction of agricultural growth-promoting system,which is a new and environmentally friendly new technology for improving crop yield. |
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