As a wide-bandgap semiconductor (3.37 eV), zinc oxide (ZnO) has become an ideal substrate material for photoelectrochemical (PEC) sensors, thanks to its advantages of high electron mobility (210 cm2V?1s?1) and isoelectric point (pI ≈ 9.5). Its hexagonal wurtzite structure provides stable electron transport channels, but it has two core drawbacks:
Spectral Response Limitation: The intrinsic absorption edge only reaches 387 nm (ultraviolet region), with a visible light utilization rate of < 5%.
High Carrier Recombination Rate: The bulk electron-hole pair lifetime is < 100 ps, and the quantum efficiency is only 12-15%.
Zinc vacancy (V_Zn?) → Donor level (Ec - 0.3 eV)
Oxygen interstitial (O_i2?) → Acceptor level (Ev + 0.5 eV)
Carrier recombination rate caused by self-compensation effect: 2.8 × 1012 s?1cm?3
1D Nanowire Arrays: Directional electron transport increases mobility to 340 cm2V?1s?1.
2D Nanosheet Networks: Specific surface area > 200 m2/g, with active site density reaching 101? sites/cm2.
3D Hierarchical Structures: Light path length increased by 3.7 times, and visible light harvesting efficiency increased to 31%.
Polarization charges induced by mechanical stress establish a built-in electric field:
P?? = 0.62 C/m2 (piezoelectric coefficient)
V_piezo = (e??/ε) × σ × L
When a stress of 10 kPa is applied, the internal electric field strength of ZnO nanowires reaches 0.35 V/μm, increasing the carrier separation efficiency by 58%.
Nitrogen Doping: Introduces N?? acceptor levels, narrowing the bandgap to 2.91 eV.
Oxygen Vacancy Regulation: Vo?? defect states redshift the absorption edge to 520 nm.
Zinc Vacancy Synergy: V_Zn?-Vo?? composite defects extend the carrier lifetime to 1.8 ns.
Noble metal nanoparticles induce localized surface plasmon resonance (LSPR):
Enhancement factor |E/E?| = [ε_(tái)m/(ε_(tái)m + 2ε_(tái)d)]2 (Mie theory)
The Au@ZnO system exhibits a 12-fold enhancement in light absorption at 550 nm.
ZnO(e?) → BiOI(CB)
BiOI(h?) → ZnO(VB)
The interfacial built-in electric field increases the electron migration rate to 4.5 × 10? cm/s, which is 3 orders of magnitude higher than that of single-phase materials.
ZnO(e?) + SnIn?S?(h?) → Recombination and annihilation
Retains the high redox capability of ZnO(h?)/SnIn?S?(e?)
This mechanism reduces the detection limit of Cr(VI) to 0.08 ppb (sensitivity: 5.7 μA/ppb).
The MXene/ZnO/Ag?S structure achieves full-spectrum response:
MXene layer: Contributes to hot electron injection through infrared absorption (> 800 nm).
Ag?S quantum dots: Generate excitons via visible light excitation.
ZnO framework: Directionally transports carriers.
The ternary synergy results in a photocurrent density of 18.7 mA/cm2 (under AM 1.5G illumination).
Long-term Stability: Zn2? leaching in physiological environments causes signal drift (> 17% attenuation over 72 h).
Interfacial Charge Traps: The interfacial state density at heterojunction interfaces is > 1013 cm?2eV?1.
Flexibility Adaptability: The conductive network breaks when the bending radius is < 5 mm.
