(Invited) empowering Triboelectric Nanogenerator with Functional Polymers for Environment Monitoring

Abstract

Triboelectric nanogenerator (TENG) proves useful as self-powered sensor. Integration of TENG with functional polymers empowers TENG to exhibit new functionalities and stimuli responsiveness. This study describes the evaluation of spiropyran-functionalized polymer (P1) and guanidinium-functionalized polymers (2 Gdm.) as new materials for TENG, which both show tunable triboelectric output voltage in response to various environmental cues including UV irradiation, humidity change, metal ions and the presence of bacteria. Spiropyran isomerizes to merocyanine upon UV irradiation for 100s (6-8W), resulting in a decrease in output voltage from 100 V to 65 V. In addition, the output voltage is inversely proportional to the irradiation time. Noting high humidity (RH) generally limits the performance of conventional TENGs, such that the output voltage decreases as RH increases. The output voltage of P1 decreases by 48% (from 100V to 52V) and the output voltage of 2 Gdm. decreases by 85% (from 100V to 15V) as the RH changes from 25% to 88%, which is a common behavior of TENG under high humidity. In contrast, the output voltage of the UV irradiated P1 TENG increases by 30% (from 65V to 80V). Because merocyanine is capable of chelating with metal ions to form metal complexes, we also evaluate the effect of metal chelation on triboelectric voltage output. Chelation with copper(II) ions result in restoration of output voltage to ~100V, suggesting the relative position in triboelectric series can be modulated by metal complexation. For guanidinium-functionalized polymers, 2Gdm., the inherent antimicrobial properties of guanidinium side groups enables TENG to be sensitive to both gram-positive and gram-negative bacteria at a concentration of 105 CFU/mL, resulting in decreasing output voltage as bacteria concentration increases. These results demonstrate that the functionalized polymers can be used as a responsive motif to realize smart TENG systems, which exhibits sensitivity to UV irradiation, changes in humidity, and the presence of metal ions or bacteria.