Visible Light Driven Hydrogen Evolution with a Noble Metal Free CuGa2_{2}In3_{3}S8_{8} Nanoparticle System in Water

CuGa$_{2}$In$_{3}$S$_{8}$ (CGIS) nanoparticles were synthesised by a hot-injection method and rendered water dispersible by modification with the hydrophilic ligand 3-mercaptopropionic acid (MPA). The CGIS nanoparticles were characterised by X-ray diffraction, transmission electron microscopy, X-ray photoelectron, diffuse reflectance and infrared spectroscopy as well as inductively coupled plasma optical emission spectroscopy. Photocatalytic H$_{2}$ production using the MPA modified CGIS nanoparticles and a nickel salt under visible light irradiation was achieved from acidic solution (pH 2.6) with ascorbic acid as a sacrificial electron donor. Previously, CGIS required the presence of a precious metal co-catalyst and sulfide ions as a sacrificial reagent in alkaline solution to display photocatalytic activity for H$_{2}$ generation. In the reported system, visible light irradiation of the MPA modified CGIS nanoparticles with a Ni salt displayed even superior sacrificial H$_{2}$ evolution activity than when employing the precious metals Pt, Rh and Ru. An external quantum efficiency of more than 12% was achieved at λ = 540 nm, which is almost twice that previously reported for CGIS nanoparticles in the presence of a noble metal co-catalyst and sulfide ions as an electron donor.T.A.K. thanks the Science and Technology Development Fund (STDF) of the Arab Republic of Egypt and the British Council at Cairo for financially supporting his visit to the University of Cambridge, UK. G.A.M.H. was supported by a Cambridge Trust / Australia Poynton PhD scholarship.This is the author accepted manuscript. The final version is available from the Royal Society of Chemistry at http://dx.doi.org/10.1039/C6CY01103A

Solar hydrogen production using carbon quantum dots and a molecular nickel catalyst.

Carbon quantum dots (CQDs) are established as excellent photosensitizers in combination with a molecular catalyst for solar light driven hydrogen production in aqueous solution. The inexpensive CQDs can be prepared by straightforward thermolysis of citric acid in a simple one-pot, multigram synthesis and are therefore scalable. The CQDs produced reducing equivalents under solar irradiation in a homogeneous photocatalytic system with a Ni-bis(diphosphine) catalyst, giving an activity of 398 μmolH2 (gCQD)(-1) h(-1) and a "per Ni catalyst" turnover frequency of 41 h(-1). The CQDs displayed activity in the visible region beyond λ > 455 nm and maintained their full photocatalytic activity for at least 1 day under full solar spectrum irradiation. A high quantum efficiency of 1.4% was recorded for the noble- and toxic-metal free photocatalytic system. Thus, CQDs are shown to be a highly sustainable light-absorbing material for photocatalytic schemes, which are not limited by cost, toxicity, or lack of scalability. The photocatalytic hybrid system was limited by the lifetime of the molecular catalyst, and intriguingly, no photocatalytic activity was observed using the CQDs and 3d transition metal salts or platinum precursors. This observation highlights the advantage of using a molecular catalyst over commonly used heterogeneous catalysts in this photocatalytic system.This work was supported by an Oppenheimer PhD scholarship (to B.C.M.M.), a Poynton PhD scholarship (to G.A.M.H.), a Marie Curie postdoctoral fellowship (GAN 624997 to C.C.), an EPSRC Career Acceleration Fellowship (EP/H00338X/2 to E.R.), the Christian Doppler Research Association (Austrian Federal Ministry of Science, Research, and Economy and the National Foundation for Research, Technology and Development), and the OMV Group.This is the final version of the article. It first appeared from ACS via http://dx.doi.org/10.1021/jacs.5b01650