High efficient hydrogen evolution over self-reproducible platinum photocatalyst
Graphical abstract
Introduction
In the context of global problems in energy and climate, artificial photo-driven energy and chemical production have drawn increasing attention [[1], [2], [3]]. On this, large advancements have been achieved recently in searching and constructing photocatalyst systems [4,5]. However, the progress seems face bottleneck challenge, new concepts and technologies are urgently needed to break through it. Intrinsically, an effective photocatalyst system should be photoactive for light harvest, catalytically-active for molecule activation, and stable for sustainable running [5,6]. Many semiconductor materials (TiO2, ZnO, CdS, C3N4, etc [[7], [8], [9], [10]] and dye molecules [[11], [12], [13]] have proper band structures or molecular energy levels for light harvest but are inert kinetically for target redox reactions, with high overpotentials. Oppositely, many metals, metal oxides, metal complexes (Pt, Pd, Cu, RuO2, IrO2, MnO2, Co3O4, etc [14,15]) are catalytically active to reduce the overpotentials but less photoactive. The current strategy in photocatalyst design is mostly based on physically assembling a photoactive matter and a catalytically-active matter together to create a donor-acceptor system so as to drive a molecular reaction. Such an assembly is indeed effective for the realization of photocatalytic molecule reactions, but the molecular photoactive substances often lose their activity totally within a few hours [16]. This problem has become a harder obstacle, globally blocking technical advance and often disturbing the routine examination to the intrinsic ability of photoactive substance.
On the other hand, in the natural photosynthesis system, all of the photoactive substances (such as chlorophyll, accessory pigments and manganese cluster) are synthesized natively and can be self-reproduced continuously, which ensures the system running efficiently and sustainably, as one of the greatest wonders [17,18]. However, this basic tactics has been rarely applied in the artificial phootocatalysis systems. In the present report, we demonstrate that platinum nanoparticles (PtNPs), normally used as a cocatalyst in photocatalysis [19,20], can exhibit excellent hydrogen evolution rate in the presence of isopropanol, without any light sensitive substances imported externally. They work actually through a native synthesis of photoactive acetonyl-platinum complexes on PtNP surfaces, as shown in Scheme 1. Although the photoactive species are damaged during the reaction, their synthesis is reproducible via continuous isopropanol oxidation and thus allows the system running sustainably.
Section snippets
Preparation of Pt Nanoparticles, denoted as PtNPprep
A mixture of 5 ml of 6.0 mM H2PtCl6 aqueous solution (30 μmol of Pt), 27 ml of water, and 18 ml of methanol containing the 133 mg of PVP was refluxed in a 100 ml flask for 3 h under air to synthesize the PVP-protected Pt nanoparticles (denoted as PtNPprep) [21].
Preparation of Pt Nanoparticles, denoted as PtNPinsitu
The surface-unprotected platinum nanoparticles (denoted as PtNPinsitu) was prepared by an in-situ photo-reduction of H2PtCl6 with aqueous isopropanol solution, without using any protection reagent. Shortly, 0.02 ml of H2PtCl6.6H2O
Results and discussion
This finding was observed initially when we examined the catalytic effect of PtNP on the photochemistry of alcohols in aqueous solution. In the studies, the platinum nanoparticles were initially prepared from the reduction of H2PtCl6 with methanol under a thermal refluxing condition [16], in the presence of surface protection reagent, polyvinyl pyrrolidone (PVP).
The obtained Pt nanoparticles (denoted as PtNPprep) exhibit a narrow size distribution of 2–4 nm and a cubic structure crystalline
Conclusions
Summarily, we demonstrate that in a light-irradiated aqueous isopropanol solution, which photolysis to produce acetone and consume photoelectron in time and be oxidized to form acetone. And then the platinum nanoparticles are able to create a unique self-reproducible photocatalysis system on their surfaces and display sustainable powerful ability for water splitting. Since various metals and organic matters are involved in photocatalysis studies (inc. water splitting and organic synthesis),
Acknowledgements
This work was supported by The Project of the Key Laboratory of Scientific Research in Shaanxi Province Department of Education (no.17JS035), and Natural Science Foundation of Shaanxi Provincial Department of Education (no.17JS035), and Natural Science Foundation of Shaanxi Province (no. 2018JQ2071).
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