ß-Bi2O3-Bi2WO6 Nanocomposite Ornated with meso-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 ß-Bi2O3-Bi2WO6/H2TPP with varying weight percentages of meso-tetraphenylporphyrin (H2TPP) resulted in a selective electrode for electrocatalytic and photoelectrocatalytic reduction of Cr6+ on fluorine-doped tin oxide (FTO) by an adsorption-reduction mechanism. H2TPP increases the active site density and provides an effective surface area for efficient adsorption by providing both pyridinic- and pyrrolic-N atoms to ß-Bi2O3-Bi2WO6/H2TPP. H2TPP could effectively adsorb Cr6+ in the ß-Bi2O3-Bi2WO6/H2TPP composite system through electrostatic interaction, and the adsorbed Cr6+ ions were reduced to trivalent chromium Cr3+, resulting in promising Cr6+ sensing. The projected density of states and Bader charge calculations result in the electrostatic attraction among the N-2p orbital of H2TPP and the 3d and 4s orbitals of the Cr atom, resulting in the adsorption of the hexavalent Cr atom onto the active center of H2TPP. Moreover, the addition of H2TPP 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 % H2TPP-ornated ß-Bi2O3-Bi2WO6. Nanocomposite ß-Bi2O3-Bi2WO6/5 wt % H2TPP demonstrated reliable cyclic stability, reproducibility, good sensitivity (8.005 µA mM cm-2), and a low limit of detection (LOD) (8.0 nM) toward photoelectrocatalytic reduction of Cr6+. The interference study in the presence of a few inorganic entities exhibited excellent selectivity. This tale amplification approach for developing a ß-Bi2O3-Bi2WO6/5 wt % H2TPP nanocomposite system suggests a deeper understanding of the application of photoelectrocatalytic reduction of Cr6+ in environmental remediation with real samples under light irradiation.

Anab initiostudy of catechol sensing in pristine and transition metal decoratedγ-graphyne.

Catechol is a toxic biomolecule due to its low degradability to the ecosystem and unpredictable impact on human health. In this work, we have investigated the catechol sensing properties of pristine and transition metal (Ag, Au, Pd, and Ti) decoratedγ-graphyne (GY) systems by employing the density functional theory and first-principles molecular dynamics approach. Simulation results revealed that Pd and Ti atom is more suitable than Ag and Au atom for the decoration of the GY structure with a large charge transfer of 0.29e and 1.54e from valence d-orbitals of the Pd/Ti atom to the carbon-2p orbitals of GY. The GY + Ti system offers excellent electrochemical sensing towards catechol with charge donation of 0.14e from catechol O-p orbitals to Ti-d orbitals, while the catechol molecule is physisorbed to pristine GY with only 0.04e of charge transfer. There exists an energy barrier of 5.19 eV for the diffusion of the Ti atom, which prevents the system from metal-metal clustering. To verify the thermal stability of the sensing material, we have conducted the molecular dynamics simulations at 300 K. We have reported feasible recovery times of 2.05 × 10-5s and 4.7 × 102s for sensing substrate GY + Pd and GY + Ti, respectively, at 500 K of UV light.

Prediction of a novel 2D porous boron nitride material with excellent electronic, optical and catalytic properties.

Holey graphyne (HGY) is a recently synthesized two-dimensional semiconducting allotrope of carbon composed of a regular pattern of six- and eight-vertex carbon rings. In this study, based on first-principles density functional theory and molecular dynamics simulations, we predict a similar stable porous boron nitride holey graphyne-like structure that we call BN-holey-graphyne (BN-HGY). The dynamical and thermal stability of the structure at room temperature is confirmed by performing calculations of the phonon dispersion relations, and also ab initio molecular dynamics simulations. The BN-HGY structure has a wide direct band gap of 5.18 eV, which can be controllably tuned by substituting carbon, aluminum, silicon, and phosphorus atoms in place of sp and sp2 hybridized boron and nitrogen atoms of BN-HGY. We have also calculated the optical properties of the HGY and BN-HGY structures for the first time and found that the optical absorption spectra of these structures span the full visible region and a wide range of the ultraviolet region. We found that the Gibbs free energy of the BN-HGY structure for the hydrogen adsorption process is very close to zero (-0.04 eV) and, therefore, the BN-HGY structure can be utilized as a potential catalyst for the HER. Therefore, we propose that the boron nitride analog of holey graphyne can be synthesized, and it has a wide range of applications in nanoelectronics, optoelectronics, spintronics, ultraviolet lasers, and solar cell devices.

Benchmarking Gaussian Basis Sets in Quantum-Chemical Calculations of Photoabsorption Spectra of Light Atomic Clusters.

The choice of Gaussian basis functions for computing the ground-state properties of molecules and clusters, employing wave function-based electron-correlated approaches, is a well-studied subject. However, the same cannot be said when it comes to the excited-state properties of such systems, in general, and optical properties, in particular. The aim of the present study is to understand how the choice of basis functions affects the calculations of linear optical absorption in clusters, qualitatively and quantitatively. For this purpose, we have calculated linear optical absorption spectra of several small charged and neutral clusters, namely, Li2, Li3, Li4, B2 +, B3 +, Be2 +, and Be3 +, using a variety of Gaussian basis sets. The calculations were performed within the frozen-core approximation, and a rigorous account of electron correlation effects in the valence sector was taken by employing various levels of configuration interaction (CI) approach both for the ground and excited states. Our results on the peak locations in the absorption spectra of Li3 and Li4 are in very good agreement with the experiments. Our general recommendation is that for excited-state calculations, it is very important to utilize those basis sets which contain augmented functions. Relatively smaller aug-cc-pVDZ basis sets also yield high-quality results for photoabsorption spectra and are recommended for such calculations if the computational resources are limited.