Atomistic Explanation for Interlayer Charge Transfer in Metal–Semiconductor Nanocomposites: The Case of Silver and Anatase

Abstract

A concerted theoretical and experimental investigation of the silver/anatase hybrid nanocomposite, a very promising material for advanced sensing applications, is presented. We measure its exceptional electrochemical virtues in terms of current densities and reproducibility, providing their explanation at the atomic-scale level and demonstrating how and why silver acts as a positive electrode. Using periodic plane-wave DFT calculations, we estimate the overall amount of electron transfer toward the semiconductor side of the interface at equilibrium. Suitably designed (photo)electrochemical experiments strictly agree, both qualitatively and quantitatively, with the theoretical charge transfer estimates. The unique permanent charge separation occurring in the device is possible because of the favorable synergy of Ag and TiO2, which exploits in a favorable band alignment, while the electron–hole recombination rate and carrier mobility decrease when electrons cross the metal–semiconductor interface. Finally, the hybrid material is proven to be extremely robust against aging, showing complete regeneration, even after 1 year.

Room-temperature photodetectors and VOC sensors based on graphene oxide–ZnO nano-heterojunctions

“…A constant phase element (CPE) was used instead of a real capacitance, due to the presence of defects and impurities that introduce inhomogeneities in the electrical properties of the investigated materials. The charge transfer resistance (R DL ) at the solid-liquid interface (the parameters that changes more when the probe reacts), showed similar values for the 32:1 ZnO/GO (0.05 kΩ cm -2 ) and GO (0.03 kΩ cm -2 ), and it is two orders of magnitude smaller with respect to the ZnO one (ca 3.50 Ω cm -2 ; Table 3), which was in line with the literaure [75][76][77] . The ZnO+GO, on the contrary, exhibited a behavior close to the ZnO, with a charge transfer resistance of about 1.10 kΩ cm -2 .…”

“…This indicates an intimate interaction between GO and ZnO, further suggesting the formation of p-n heterojunctions between GO and ZnO. To further confirm the formation of nanoscale heterojunctions, electrochemical impedance measurements were performed in line with previous analysis of similar heterojunctions 75,76 . Figure 6c shows the Bode plots relative to 32:1 ZnO/GO, mechanically mixed ZnO-GO, pristine ZnO, GO and glassy carbon electrode.…”

“…Interestingly, the 32:1 ZnO/GO showed an intermediate behavior with a capacitance of ca 5 mF cm -2 s -1 , which is greater than that of the ZnO+GO one of ca 2 mF cm -2 s -1 . The EIS technique has been previously used to provide information about the actual presence of a p-n heterojunction, modelling it as a parallel combination of a resistance (R HJ ), accounting for the leakage and recombination paths through the p/n-type MOS interface, and a constant phase element (CPE HJ ), due to the non-ideal capacitance resulting from the depletion region of the p-n junction [75][76][77] . Notably, 32:1 ZnO/GO plot fitted well this model, while the other investigated materials could be not modelled with the above describe heterojunction circuit.…”

Charge Carriers Cascade in a Ternary TiO2/TiO2/ZnS Heterojunction: A DFT Study

“…Several examples of these composites were presented recently, also including titania-based materials. [24][25][26][27] More specifically, titania can be combined with a metal, [28][29][30][31][32][33] graphene, [34,35] or another oxide. [19,20,36,37] Composites can be also created by interfacing two different polymorphs of TiO 2 , [38][39][40][41][42][43] or even two different faces of the same polymorph.…”

A detailed investigation of MnO2 nanorods to be grown onto activated carbon. High efficiency towards aqueous methyl orange adsorption/degradation

“…However, manganese oxides suffer from the low electron transfer performance and the small surface area [30]; hence, in order to overcome these issues, a MnO 2 growth onto Activated Carbon (AC) support could be performed, achieving composites characterized by enlarged surface area and great adsorption capabilities [31][32][33]. Indeed, the possibility to combine different materials to produce innovative composite with enhanced performances with respect to the precursors has brought important results in many research fields [34][35][36].…”