Nickel Complexes and Carbon Dots for Efficient Light‐Driven Hydrogen Production

Abstract

Nitrogen‐doped carbon dots were used as photosensitizers for H2 evolution in the presence of a series of mononuclear thiosemicarbazone nickel complexes. The catalysts were designed to display different substituents at the para position of the phenyl rings. These chemical modifications tune the electron‐donating abilities of the complexes and influence their capability to reduce protons into hydrogen. All photocatalytic experiments were performed in aqueous solution, using as sacrificial electron donor TCEP/Asc (1 : 1), 0.1 M each, at pH=5. The complex bearing the most electron‐donating ligand with the dimethylamino (N(CH3)2) substituent behaves as the best catalyst in our series of photocatalytic systems with TONCAT=148, under white led radiation for 30 h. Therefore, this noble metal‐free system can effectively produce hydrogen in water and further chemical modification of the ligand will likely improve its production.

Light-induced hydrogen production from water using nickel(ii) catalysts and N-doped carbon-dot photosensitizers: catalytic efficiency enhancement by increase of catalyst nuclearity

“…A series of experiments were carried out using varying concentrations of the two complexes and a fixed amount of NCDs and calculating their respective TONs. Keeping the amount of NCDs fixed at 10 mg in 3 mL of H 2 O (the optimum amount for NCDs found in our previous studies 49,50 ), the highest TONs were obtained for 50 nmol of 2 and 8, giving TONs of 272 and 290, respectively, in 24 h, while using the complexes at higher amounts, lower TONs were obtained (180 and 215 for 150 nmol of 2 and 8, respectively). When the amount of NCDs was varied, in the presence of 50 nmol of 2 or 8, lower TONs were obtained, validating our choice for the PS concentration.…”

“…NCDs were prepared as described in our recently published work. 49,50 In particular, citric acid was hydrothermally treated in the presence of ethylenediamine, at 180 °C for 8 h. The product was purified using a dialysis membrane bag of 1 kDa and freeze-dried, to obtain NCDs as powder. The synthesized NCDs were studied and characterized by several spectroscopic techniques as previously reported.…”

“…The presence of N atoms in these materials allows modification of their photoluminescence properties, while it also facilitates the occurrence of charge separation and electron transfer processes, rendering them ideal choices as low-cost, versatile, and effective PS's for the development of environmentally benign photocatalytic systems for H 2 production. 49,50 Herein, we present a "green" photocatalytic system for the effective photoreduction of aqueous protons to H 2 , which employs Ni(II) heterocyclic thioamidato (L N S − ) complexes as CATs. The potential of this class of complexes to catalyze the particular transformation (firstly studied in combination with organic molecular PS's by Eisenberg 51,52 ) originates from the versatile nature of the thioamidato ligands.…”

How Metal Nuclearity Impacts Electrocatalytic H2 Production in Thiocarbohydrazone-Based Complexes

“…Such complexes have been found to possess a rather low overpotential requirement, with the ligand playing an active role in HER, and being highly customizable [16,27]. Recently, we have characterized and studied a set of mononuclear nickel-thiosemicarbazone (NiL) complexes, with chemically tuned para substituents in phenyl groups present in the ligand [24,28]. To lower the potential of the redox-active ligand, we attempted to increase the delocalization of the electronic density.…”

Rethinking Electronic Effects in Photochemical Hydrogen Evolution Using CuInS2@ZnS Quantum Dots Sensitizers

“…However, the toxicity of cadmium strongly prevents application in the green chemistry context. In order to tackle this issue, only recently have cadmium-free QDs been successfully applied in energy conversion schemes [ 22 , 23 , 24 , 25 ]. Of remarkable interest, core-shell CuInS 2 @ZnS nanocrystals proved to be extremely active and durable for the production of hydrogen under irradiation in the presence of a molecular cobalt tetrazamacrocyclic complex as the HEC and ascorbate as the sacrificial electron donor [ 26 ].…”