An innovative approach for the synthesis of 4Tris@Porphyrin and anderson polyoxometalate based covalent organic framework to reveal its potential for photocatalytic properties

Abstract

Herein, a polyhydroxy containing metallo porphyrin linked through amide functional group with Anderson polyoxometalate (POM) was used to form TPMnA-COF. Structure and applications have been unlocked thoroughly by means of FT-IR, UV–visible, ¹HNMR, PXRD, SEM and cyclic voltammetric (CV) spectral analysis. The TPMnA-COF was tested as catalyst to explore the photocurrent and photodegradation properties. ITO electrode was fabricated to study optical activity, absorption study and photocurrent generation. The adsorption study of TPMnA-COF has been studied using Langmuir and Freundlich model with calculated Langmuir constants q_m, K_L, R_L and R² values of about 12.42 mg/g, 0.33 M^-1, 0.30 and 0.98 respectively. The 1/n, K_f and R² values obtained from Freundlich adsorption isotherm were 0.70, 3.16 M^-1 and 0.96 respectively. The band gap value evaluated via absorption edge of UV–visible spectra in DMSO solution was 2.75 eV while the band gap value calculated for ultra-thin film was 1.95 eV. The calculated real, imaginary dielectric constants, Urbach edge, refractive index and the electrical conductivity values for ultra-thin film of TPMnA-COF were 518.8, 2.9 × 10⁻¹¹-8.1 × 10⁻¹¹, −3.802 meV, 22.8–22.6 and 8.3 × 10⁴−3.4 × 10⁴ S/m), respectively. Responsivity for film was also tested using purple, blue, green, yellow, orange and red colourlights and the observed responsivity for different lower light intensities were 3.05, 2.9, 1.6, 1.55, 1.5 and 1.4 mA/W respectively. Furthermore, photodegradation activity of TPMnA-COF in Methylene-Blue (MB) and Rhodamine B(Rh–B) dyes under 3 W light. The results showed higher photocatalytic efficiency for Rh–B than that for MB with obtained degradation efficiency of 81 % and 60.4 %, respectively after 660 min. The scavengers such as ammonium oxalate (AO, h⁺), isopropanol (ISOP, ^•OH), catalase (CAT, H₂O₂) and superoxide dismutase (SODM, O₂^−●) were used to find out the effectiveness of each reactive specie to degrade the dyes solution in the mechanism of degradation. It was observed that AO (h⁺) and ISOP(^•OH) were more active species in the photodegradation mechanism than CAT(H₂O₂) and SODM(O₂^−●).