β-BiO-BiWO Nanocomposite Ornated with -Tetraphenylporphyrin: Interfacial Electrochemistry and Photoresponsive Detection of Nanomolar Hexavalent Cr.

Hexavalent chromium exposure via inhalation, ingestion, or both has been proven to adversely affect internal organs, induce toxic effects, cause allergies, and contribute to the development of cancer. It requires a substantial and challenging effort to detect several heavy metal ions conveniently, sensitively, and reliably by using materials that are easy to synthesize and have a high yield. The impact of light on the electrocatalytic oxidation/reduction process proves an environmentally friendly methodology with numerous applications in pollution control. The extensive use of photoactive materials in photoelectrochemical (PEC) sensors necessitates the development of stable and highly effective photoactive materials. Hence, the solvothermal synthesis of the organic-inorganic hybrid nanocomposite β-BiO-BiWO/HTPP with varying weight percentages of -tetraphenylporphyrin (HTPP) resulted in a selective electrode for electrocatalytic and photoelectrocatalytic reduction of Cr on fluorine-doped tin oxide (FTO) by an adsorption-reduction mechanism. HTPP increases the active site density and provides an effective surface area for efficient adsorption by providing both pyridinic- and pyrrolic-N atoms to β-BiO-BiWO/HTPP. HTPP could effectively adsorb Cr in the β-BiO-BiWO/HTPP composite system through electrostatic interaction, and the adsorbed Cr ions were reduced to trivalent chromium Cr, resulting in promising Cr sensing. The projected density of states and Bader charge calculations result in the electrostatic attraction among the N-2p orbital of HTPP and the 3d and 4s orbitals of the Cr atom, resulting in the adsorption of the hexavalent Cr atom onto the active center of HTPP. Moreover, the addition of HTPP results in the development of a mesoporous surface that offers strong electrical conductivity, a substantial surface area, improved charge-mass transport, intimate contact between the electrolyte and catalyst, an extended fluorescence lifetime, and increased stability. The role of pH values was thoroughly investigated. All electrochemical and photoelectrochemical studies were carried out on 5 wt % HTPP-ornated β-BiO-BiWO. Nanocomposite β-BiO-BiWO/5 wt % HTPP demonstrated reliable cyclic stability, reproducibility, good sensitivity (8.005 μA mM cm), and a low limit of detection (LOD) (8.0 nM) toward photoelectrocatalytic reduction of Cr. The interference study in the presence of a few inorganic entities exhibited excellent selectivity. This tale amplification approach for developing a β-BiO-BiWO/5 wt % HTPP nanocomposite system suggests a deeper understanding of the application of photoelectrocatalytic reduction of Cr in environmental remediation with real samples under light irradiation.