Photo‐Assisted Barrier Effect for Improving the Sensing Performance to Copper Ions

Abstract

complex operation, and not suitable for online detection. By contrast, electrochemical method has the simple, fast and sensitive advantages. [11,12] However, its sensing mechanism often relies on redox reactions, it is easily interfered by substances with similar properties. [13] It is desired to create a new electrochemical sensing mode to resist seawater interference.It is well known that heterojunctions coupling by two semiconductors can exhibit specific functions in catalysis, sensor, energy storage, and conversion. [14][15][16] For example, the ZnO/Co 3 O 4 heterojunction modified by polydopamine has high selectivity and active catalytic performance for CO 2 . [17] CuO/Cu 2 O heterojunction has excellent contribution to improve the detection performance of l-cysteine. [18] At heterojunction interface, semiconductors with different work functions can build a barrier by spontaneous flow of electrons and band bending. Since barrier blocks electron transport, its change can affect electrochemical impedance during electrochemical sensing process. [19,20] Therefore, the barrier mechanism can be used as a valuable tuning factor in electrochemical detection. Different heterojunctions can form different types of barrier, such as Schottky barrier, p-n junction barrier and n-n junction barrier. Among them, n-n junction is formed by the contact of two n-type semiconductors with different work functions. Since most carriers of n-type semiconductor are electrons, it is expected to achieve better electronic regulation ability.As a wide-gap (3.2 eV) n-type semiconductor, TiO 2 has good light response and band regulation ability. [21,22] In 2 O 3 is an indirect band gap (2.8 eV) n-type semiconductor with excellent electrical conductivity and photoelectric chemical stability. [23,24] The appropriate band structure and work functions make them form n-n junction barrier. Since both TiO 2 and In 2 O 3 have good photoelectric characteristics, it is expected to realize good light regulation. Chitosan (CS), as a functional polymer with strong adhesiveness and film-forming property, can selectively absorb Cu 2+ through NH 2 chelation. [25,26] In addition, CS has light transmittance and does not affect the photoexcitation of semiconductor.In this work, the Ti/TiO 2 /In 2 O 3 /CS wire was fabricated by assembling Ti wire for electrochemical detection of Cu 2+ . The photo-assisted adjusting effect of n-n junction barrier on electrochemical response was studied. It is found that barrier can be used as an electrochemical driver to generateCopper ions (Cu 2+ ) pollution poses a serious threat to Marine ecology and fisheries, but the online detection is difficult due to seawater interference. Herein, photo-assisted barrier effect is introduced into electrochemical detection as a driver to generate electrochemical response. The n-n junction barrier exhibits excellent adjusting effect on electrochemical response under photoexcitation and could effectively drive electrochemical response by Cu 2+ adsorption. The prepared Ti/TiO 2 /In 2 O 3 /C...