1. Introduction
Facing
the excessive use of fossil energy and the increasingly serious
environmental pollution problem, the use of infinite solar energy is a
possible and promising solution [1, 2]. Since Fujishima and Honda’s
research on the photoelectrochemical hydrogen production of titanium
dioxide (TiO2) photoanode in 1972, semiconductor-based
photocatalysts have received widespread attention worldwide [3]. And
many photocatalysts have been developed, such as TiO2[4], CdS [5, 6], Zn0.5Cd0.5S
[7, 8], BiVO4 [9],
g-C3N4 [10, 11], MOFs and their
derivatives [12]. However, the light conversion efficiency and
photocatalytic performance have not improved significantly. In order to
synthesize advanced high-efficiency photocatalytic materials, the
research interest of semiconductor materials based on MOFs and its
derivatives is increasing.
As an kind of emerging material, metal organic frameworks (MOFs) are
important and potential materials in heterogeneous catalytic reactions
due to its rich pore structure, large specific surface, high structural
diversity, adjustable chemical properties, and highly dispersed metal
sites [13, 14]. MOFs are used as precursors for the synthesis of
MOF-based hybrid structures, which will provide more opportunities for
the comprehensive conversion and application of MOFs and develop more
unique potentials about MOFs. Low-temperature phosphating of different
kinds of MOFs can lead to excellent performance of transition metal
phosphides, such as Ni2P [15, 16], CoP [17], FeP
[18, 19] and NiCoP [20]. These phosphides, as n-type
semiconductors, are favorable for accepting photo-generated electrons.
In previous research reports, transition metal phosphides were mainly
used as co-catalysts to enhance the photocatalytic H2release to improve the separation and transport efficiency of
electron-hole pairs [21, 22, 23]. In fact, the transition metal
phosphide alone exhibits better photocatalytic performance under dye
sensitization conditions, mainly due to its narrow band gap structure
and strong light absorption capacity [24, 25].
A promising approach to enhance the catalytic performance of MOFs and
their derivatives is to change MOFs into a core-shell structure
[26]. Here, we have developed a novel in-situ growth scheme that
combines the advantages of ZIF-9 and
Cu3(BTC)2, and uses Cu-MOFs@ZIF-9(Co)
core-shell material as a precursor to derive Cu3P@CoP
composite catalyst. Since Cu3P is a p-type semiconductor
and CoP is a n-type semiconductor, the Cu3P@CoP
composite catalyst obtained from Cu-MOFs@ZIF-9(Co) core-shell material
not only has a layered structure, but also builds a p-n heterogeneity at
the interface. In order to understand this phosphation more deeply, we
control the degree of phosphation of Cu-MOFs@ZIF-9(Co) material on the
one hand, and adjust the ratio of Cu to Co by changing the content of
Cu-MOFs to explore its reasons and rules for the formation of
photocatalytic activity. The unique structure and composition of
Cu3P@CoP can promote charge separation and migration,
provide large surface area and rich active sites to drive water
photolysis. The results show that the optimized Cu-Co-2P-2 photocatalyst
exhibits generation activity of 469.95 μmol H2 and has
high stability. Our work will provide a new strategy for the rational
design of efficient catalysts for MOFs derivatives.