Toward Eco-Friendly Dye-Sensitized Solar Cells (DSSCs): Natural Dyes and Aqueous Electrolytes

Due to their low cost, facile fabrication, and high-power conversion efficiency (PCE), dye-sensitized solar cells (DSSCs) have attracted much attention. Ruthenium (Ru) complex dyes and organic solvent-based electrolytes are typically used in high-efficiency DSSCs. However, Ru dyes are expensive and require a complex synthesis process. Organic solvents are toxic, environmentally hazardous, and explosive, and can cause leakage problems due to their low surface tension. This review summarizes and discusses previous works to replace them with natural dyes and water-based electrolytes to fabricate low-cost, safe, biocompatible, and environmentally friendly DSSCs. Although the performance of “eco-friendly DSSCs” remains less than 1%, continuous efforts to improve the PCE can accelerate the development of more practical devices, such as designing novel redox couples and photosensitizers, interfacial engineering of photoanodes and electrolytes, and biomimetic approaches inspired by natural systems.

A Highly Durable, Self-Photosensitized Mononuclear Ruthenium Catalyst for CO2 Reduction

A novel mononuclear ruthenium (Ru) complex bearing a PNNP-type tetradentate ligand is introduced here as a self-photosensitized catalyst for the reduction of carbon dioxide (CO2). When the pre-activation of the Ru complex by reaction with a base was carried out, an induction period of catalyst almost disappeared and the catalyst turnover numbers (TONs) over a reaction time of 144 h reached 307 and 489 for carbon monoxide (CO) and for formic acid (HCO2H), respectively. The complex has a long lifespan as a dual photosensitizer and reduction catalyst, due to the sterically bulky and structurally robust (PNNP)Ru framework. Isotope labeling experiments under 13CO2 atmosphere indicate that CO and HCO2H were both produced from CO2.

Fabrication of Covalently Linked Ruthenium Complex Onto Carbon Nitride Nanotubes For The Photocatalytic Degradation of Tetracycline Antibiotic

Due to the problem of direct disposal of effluents contains antibiotics to the environment and the emergence of resistant bacterial pathogens, the wastewater treatment of pharmaceutical industry has known as an importance research background. In this study, the refinement and photodegradation ability of one of the most widely used antibiotics, “tetracycline” was investigated by ruthenium complex immobilized on the modified graphitic carbon nitride nanotubes. For this purpose, graphitic carbon nitride nanotubes (g-C3N4 NTs) were successfully synthesized by the hydrothermal method and functionalized with 1,10-Phenantroline-5,6-dione ligand during another step. Then, the functionalized g-C3N4 NTs were reinforced with immobilization of dichloro(p-cymene)ruthenium(II) dimer. The structure and morphology of the prepared photocatalyst was studied by X-ray diffraction (XRD), fourier transform infrared (FT-IR), scanning, and transmission electron microscopy (SEM & TEM) analyses. In the following, the photocatalyst's ability to optically degrade the tetracycline antibiotics was performed in a suspension reactor equipped with a LED lamp (60 W) and effective parameters such as the amount of catalyst, irradiation time, temperature, and pH were optimized. The results showed that the immobilization of Ru complex onto functionalized g-C3N4 NTs improved the photocatalytic activity and increased the degradation efficiencies to amount 43%. Furthermore, COD analysis was used for the determination of the amount of mineralization and results showed that the mineralization of 10 mg/L tetracycline solution of about 90% can be performed using 20 mg of Ru (II) complex/ g-C3N4 NTs at pH=7 after 480 min without any additive oxidant.

Bulky PNP Ligands Blocking Metal-Ligand Cooperation Allow for Isolation of Ru(0), and Lead to Catalytically Active Ru Complexes in Acceptorless Alcohol Dehydrogenation

We synthesized two 4Me-PNP ligands which block metal-ligand cooperation (MLC) with the Ru center and compared their Ru complex chemistry to their two traditional analogues used in acceptorless alcohol dehydrogenation catalysis. The corresponding 4Me-PNP complexes, which do not undergo dearomatization upon addition of base, allowed us to obtain rare, albeit unstable, 16 electron mono CO Ru(0) complexes. Reactivity with CO and H₂ allows for stabilization and extensive characterization of bis CO Ru(0) 18 electron and Ru(II) cis and trans dihydride species that were also shown to be capable of C(sp²)-H activation. Reactivity and catalysis are contrasted to non-methylated Ru(II) species, showing that an MLC pathway is not necessary, with dramatic differences in outcomes during catalysis between ⁱPr and ^tBu PNP complexes within each of the 4Me and non-methylated backbone PNP series being observed. Unusual intermediates are characterized in one of the new and one of the traditional complexes, and a common catalysis deactivation pathway was identified.

Bulky PNP Ligands Blocking Metal-Ligand Cooperation Allow for Isolation of Ru(0), and Lead to Catalytically Active Ru Complexes in Acceptorless Alcohol Dehydrogenation

We synthesized two 4Me-PNP ligands which block metal-ligand cooperation (MLC) with the Ru center and compared their Ru complex chemistry to their two traditional analogues used in acceptorless alcohol dehydrogenation catalysis. The corresponding 4Me-PNP complexes, which do not undergo dearomatization upon addition of base, allowed us to obtain rare, albeit unstable, 16 electron mono CO Ru(0) complexes. Reactivity with CO and H₂ allows for stabilization and extensive characterization of bis CO Ru(0) 18 electron and Ru(II) cis and trans dihydride species that were also shown to be capable of C(sp²)-H activation. Reactivity and catalysis are contrasted to non-methylated Ru(II) species, showing that an MLC pathway is not necessary, with dramatic differences in outcomes during catalysis between ⁱPr and ^tBu PNP complexes within each of the 4Me and non-methylated backbone PNP series being observed. Unusual intermediates are characterized in one of the new and one of the traditional complexes, and a common catalysis deactivation pathway was identified.