Photo and electrochemical applications of green synthesized ZnO/Ag2O nanocomposites materials under visible light using P. macrosolen L. leaf

Abstract

This study investigates the photo-catalytic and super-capacitive properties of green-synthesized ZnO/Ag₂O nanocomposites using P. macrosolen L. leaf extract. The synthesis was performed in a single step at low temperature with a short reaction time. The synthesized materials were characterized using XRD, SEM, TEM, FTIR, UV-VIS and XPS. The ZnO/Ag₂O nanocomposites exhibited exceptional photo-catalytic efficiency and stability under visible light for the degradation of carbon-based dyes. The degradation rate constants of the optimized ZnO/Ag₂O nanocomposites were 0.054351 min⁻¹ for Methylene Orange (MO) and 0.048751 min⁻¹ for Toluidine Blue (TB), achieving degradation efficiencies of 99.69% and 98.50%, respectively, compared to ZnO (0.0075 min⁻¹). This remarkable improvement in visible-light photo-catalytic performance is attributed to the hetero-junction formation, which enhances charge separation and transfer through the matched crystal lattices and energy bands of Ag₂O and ZnO. The Ag₂O nanoparticles efficiently generate and transfer excited electrons to the ZnO conduction band under visible-light irradiation. Electrochemical studies revealed a significant improvement in specific capacitance, with the ZnO/Ag₂O composite containing 50 wt% AgNO₃ achieving a maximum specific capacitance of 655.0 F/g at a scan rate of 10 mV/s. This superior performance highlights the synergistic effect of ZnO and Ag₂O in improving photo-catalytic and electrochemical properties. These findings demonstrate the potential of ZnO/Ag₂O nanocomposites for industrial dye degradation and super-capacitor applications.

Keywords: Ag2O; Characterizations; Green synthesis; Photocatalysis; Supercapacitor; ZnO.

Fig. 1

Schematic diagram of green synthesis of ZnO/Ag₂O NCMs.

Fig. 2

Shows the XRD patterns of (a) ZA₃, ZA₄, ZA₅, (b) ZA₀, (c) Ag₂O and (d) average crystalline sizes of ZA₃, ZA₄ and ZA₅. The average crystalline sizes were calculated using Debye-Scherer’s equation from XRD data:

Fig. 3

FTIR study of (a) P. macrosolen L. Leaf extracts (b) ZA₅ (c) Ag₂O NPs and (d) ZA₀.

Fig. 4

(a)-(i) Typical SEM image, Particle size distributions, SEM EDS of Ag₂O NPs, ZA₀, ZA₅ respectively.

Fig. 4

(a)-(i) Typical SEM image, Particle size distributions, SEM EDS of Ag₂O NPs, ZA₀, ZA₅ respectively.

Fig. 5

Analysis of ZA₀ (a) HR TEM image, (b) particle size distribution, (c) Elemental mapping and (d) TEM-EDS analysis.

Fig. 6

TEM analysis of Ag₂O NPs (a), HR TEM image of Ag₂O NPs (b), Particle size distributions (c) TEM EDS mapping pattern and (d) Elemental compositions.

Fig. 7

(a)-(b) HRTEM patterns of ZA₅, (c) HRTEM pattern of with particles size distribution, (d) Elemental composition of the materials, (e) SAED of pattern of ZnO/Ag₂O NCMs (f) Elemental mapping of ZA₀, Ag₂O NPs and ZA₅ (g) (i) Full scan survey spectra of pure ZnO and ZA₄ and ZA₅, and high-resolution XPS spectra of the Zn 2p (ii), Ag 3d (iii), and O1s (iv) of the ZA₅.

Fig. 8

(a) and (c) The Tauc plot of optical energy band gaps of ZA₀, ZA₃, ZA₄, ZA₅ and A_g2O NPS respectively, (d) UV-visible absorption spectrums of ZA₀, ZA₅, and Ag₂O NPs.

Fig. 9

Time-dependent absorption of MO dye (a)-(b) with catalyst in 60 min and (c)-(d) without catalyst in 60 min.

Fig. 10

Time-dependent absorption of Toluidine Blue (TB) dye (a)-(b) with catalyst in 60 min and (c)-(d) without catalyst in 60 min.

Fig. 11

Time-dependent absorption of MO dyes (a)-(b) with Ag₂O catalyst at in 60 min and (c)-(d) without catalyst in 60 min.

Fig. 12

Time-dependent absorption of Toluidine Blue (TB) dye (a)-(b) with Ag₄-catalyst at in 60 min and (c)-(d) without catalyst in 60 min.

Fig. 13

(a) Potentio-static charging and discharging, (b) Impedance Nyquist-plots, (c) Current density vrs specific capacitance, and (d) current density vrs power density relations of ZA₅.

Fig. 14

Presents: (a) CV curves of the ZA₅ super capacitor at various scan rates, (b) The corresponding specific capacitance values of the ZA₅ super capacitor, (c) Cycling performance of the ZA₅ electrodes at a current density of 2.5 A/g, with an inset showing the charge-discharge (CD) curves at different current densities, (d) XRD patterns of the ZA₅ electrode before and after testing its energy storage performances, (e) SEM images of ZA₅ before and after usages.

Fig. 15

Possible mechanism of photo catalytic degradation activity of ZnO/Ag₂O NCMs.

Fig. 16

The possible structure of salts and bioactive compound acted as reducing, capping and stabilizing agents in the formations of nanocomposite materials.