Visible light induced oxygenation of alkenes with water sensitized by silicon-porphyrins with the second most earth-abundant element

Numerical simulation study of high-efficiency silicon-based cell destined for photoelectrochemical wastewater treatment

Photoelectrochemical setups based on semiconductor photoelectrodes are known for their effectiveness in wastewater treatment, powered by solar energy, which is a renewable and sustainable source. These systems require semiconductor photocatalysts with excellent light-absorbing properties and high stability in aqueous environments. In this regard, silicon is highly investigated in solar cells thanks to its narrow bandgap, making it a potential solar harvester. Metal oxides stand as promising semiconductors, which are non-toxic and thermodynamically stable. In this work, two high-efficiency silicon-based cells have been investigated via Solar Cell Capacitance Simulator (SCAPS-1D) software. Thickness and doping concentration, of each layer, have been scrutinized for multiple buffer propositions to investigate the physical feasibility and optimal values allowing maximal light harvesting. It was found that the overall cell performance is influenced by extremely high doping concentrations for some layers. The effect of temperature was investigated as well at temperatures ranging from 300 to 350 K; it was discovered that the cell demonstrates great performance at the ambient temperature. A maximum solar efficiency of about 25.44% was calculated. Our findings build the path towards fabricating highly efficient Si-based solar cells for photoelectrochemical wastewater treatment.

Molecular Characteristics of Water-Insoluble Tin-Porphyrins for Designing the One-Photon-Induced Two-Electron Oxidation of Water in Artificial Photosynthesis

Faced with the new stage of water oxidation by molecular catalysts (MCs) in artificial photosynthesis to overcome the bottle neck issue, the "Photon-flux density problem of sunlight," a two-electron oxidation process forming H₂O₂ in place of the conventional four-electron oxidation evolving O₂ has attracted much attention. The molecular characteristics of tin(IV)-tetrapyridylporphyrin (SnTPyP), as one of the most promising MCs for the two-electron water oxidation, has been studied in detail. The protolytic equilibria among nine species of SnTPyP, with eight pK_a values on the axial ligands' water molecules and peripheral pyridyl nitrogen atoms in both the ground and excited states, have been clarified through the measurements of UV-vis, fluorescence, ¹H NMR, and dynamic fluorescence decay behaviour. The oxidation potentials in the Pourbaix diagram and spin densities by DFT calculation of the one-electron oxidized form of each nine species have predicted that the fully deprotonated species ([SnTPyP(O^-)₂]^2-) and the singly deprotonated one ([SnTPyP(OH)(O^-)]^-) serve as the most favourable MCs for visible light-induced two-electron water oxidation when they are adsorbed on TiO₂ for H₂ formation or SnO₂ for Z-scheme CO₂ reduction in the molecular catalyst sensitized system of artificial photosynthesis.

Amplification of Radiation-Induced Signal of LED Strip by Increasing Number of LED Chips and Using Amplifier Board

Transducers, such as photodiodes, phototransistors, and photovoltaic cells are promising radiation detectors. However, for accurate radiation detection and dosimetry, signals that emanate from these devices have to be sufficient to facilitate accurate calibrations, i.e., assigning a quantity of radiation dose to a specific magnitude of the signal. More so, purposely fabricated for luminescence, LEDs produce significantly low signals during radiation detection applications. Therefore, this paper investigates the enhancement and augmentation of photovoltaic signals that were generated when LED strips were being exposed to diagnostic X-rays. Initially, signal amplification was achieved through increasing the effective LED active area (from 60 to 120 chips); by successively connecting LED strips. Further, signal amplification was undertaken by injecting the raw LED strip signal into an amplifier board with adjustable gains. In both the signal amplification techniques, the tube voltage (kVp), tube current-time product (mAs), and source-to-detector distance (SDD) were varied. The principal findings show that effective active area-based signal amplifications produced an overall average of 91.16% signal enhancement throughout all of the X-ray parameter variations. On the other hand, the amplifier board produced an average of 36.48% signal enhancement for the signals that were injected into it. Chip number increment-based signal amplifications had a 0.687% less coefficient of variation than amplifier board signal amplifications. The amplifier board signal amplifications were impaired by factors, such as dark currents, amplifier board maximum operational output voltage, and saturation. Therefore, future electronic signal amplification could use amplifier boards having low dark currents and high operational voltage headroom. The low-cost and simplicity that are associated with active-area amplification could be further exploited in a hybrid amplification technique with electronic amplification and scintillators.

On-Surface Synthesis of Nonmetal Porphyrins

We report the on-surface synthesis of a nonmetal porphyrin, namely, silicon tetraphenylporphyrin (Si-TPP), by the deposition of atomic silicon onto a free-base TPP layer on a Ag(100) surface under ultrahigh vacuum (UHV) conditions. Scanning tunneling microscopy provides insights into the self-assembly of the TPP molecules before and after Si insertion. Silicon coordinates with all four nitrogen atoms of the TPP macrocycle and interacts with a silver atom of the substrate as confirmed by scanning tunneling spectroscopy, X-ray photoelectron spectroscopy, and complementary density functional theory calculations. The Si-TPP complex presents a saddle-shaped conformation that is stable under STM manipulation. Our study shows how protocols established for the on-surface metalation of tetrapyrroles can be adopted to achieve nonmetal porphyrins. Complementary experiments yielding Si-TPP and Ge-TPP on Ag(111) highlight the applicability to different main group elements and supports. The success of our nonmetal porphyrin synthesis procedure is further corroborated by a temperature-programmed desorption experiment, revealing the desorption of Ge-TPP. This extension of interfacial complex formation beyond metal elements opens promising prospects for new tetrapyrrole architectures with distinct properties and functionalities.

Silicon-coordinated nitrogen-doped graphene as a promising metal-free catalyst for N2O reduction by CO: a theoretical study

Metal-free catalysts for the transformation of N₂O and CO into green products under mild conditions have long been expected. The present work proposes using silicon-coordinated nitrogen-doped graphene (SiN₄G) as a catalyst for N₂O reduction and CO oxidation based on periodic DFT calculations. The reaction proceeds via two steps, which are N₂O reduction at the Si reaction center, producing Si–O*, which subsequently oxidizes CO to CO₂. The N₂O reduction occurs with an activation energy barrier of 0.34 eV, while the CO oxidation step requires an energy of 0.66 eV. The overall reaction is highly exothermic, with a reaction energy of −3.41 eV, mostly due to the N₂ generation step. Compared to other metal-free catalysts, SiN₄G shows the higher selectivity because it not only strongly prefers to adsorb N₂O over CO, but the produced N₂ and CO₂ are easily desorbed, which prevents the poisoning of the active catalytic sites. These results demonstrate that SiN₄G is a promising metal-free catalyst for N₂O reduction and CO oxidation under mild conditions, as the reaction is both thermodynamically and kinetically favorable.

Mechanistic insight into the N₂O reduction and CO oxidation on SiN₄G is reported in this theoretical study. The high reactive and selective SiN₄ center leads this metal-free catalyst as a promising catalyst for this reaction under mild conditions.

Synthesis of water-soluble silicon-porphyrin: protolytic behaviour of axially coordinated hydroxy groups

A new water-soluble silicon(IV)-tetra(4-carboxyphenyl)porphyrin (SiTCPP) with silicon(iv), the second most abundant element on Earth, in the center of porphyrin was synthesized. Fundamental properties including protolytic behaviour of axially coordinating hydroxy groups, and electrochemical behaviour were characterized. The properties were compared with those of silicon(IV)-tetra(2,4,6-trimethylphenyl)porphyrin (SiTMP) and silicon(IV)-tetra(4-trifluoromethylphenyl)porphyrin (SiTFMPP) and discussed in respect to the electron donating/withdrawing effect of the substituents. Two axially coordinating hydroxy groups of SiTCPP exhibit a four-step protolytic behaviour under the acidic conditions along with a single step protolysis of peripheral carboxyl groups. Though SiTCPP and SiTFMPP did not show any reactivity in the photochemical oxygenation of a substrate with K2PtCl6 as a sacrificial electron acceptor, the first oxidation wave in the electrochemical process of SiTCPP and SiTFMPP showed catalytic behaviour in aqueous acetonitrile solution at any pH condition, in contrast to SiTMP which has only a reversible oxidation wave under neutral and weakly acidic conditions. The criteria for the electrochemical oxidative activation of water and the photooxygenation of the substrate were obtained. The higher oxidation wave of Si-porphyrins than ∼0.86 volt vs. SHE is required for the electrochemical oxidation of water, while suitable protecting groups such as a methyl substituent is a requisite for the photochemical oxygenation with K2PtCl6 as a sacrificial electron acceptor.