Fig. 6 H2 evolution amount of (a) pure
NiSe2, MCS with different weight loading ratios of
NiSe2; (b) AQE of MCNS-10 in the 400-600 nm
wavelength range. (c) The stability test of hydrogen production
cycle of MCNS-10; (d) XRD of MCNS-10 composite catalyst after
hydrogen production.
3.7 The PL and TRPL spectra
In order to study the crucial role of NiSe2 cocatalyst
in the boosting the processes of charge separation, transfer and
recombination in the composite material MCSN system, the all samples
were tested by PL and TRPL spectra.Fig.
7a shown PL spectra of all as-synthesized catalysts with an excitation
and emission wavelength of 390 and 533 nm, respectively. The no
fluorescence peak was detected in
NiSe2, indicating
that NiSe2 could not excited by irradiation. The
composite catalyst MCNS-10 exhibited the lowest PL intensity compared
with other binary composites, indicating that higher separation
efficiency of electron-hole pair.
The fluorescence lifetime generally refer to the average time required
for an electron to transfer from an excited state to a ground state.
The TRPL spectra shown inFig. 7b further indicated that the charge carriers lifetime of
MCNS-10 (2.21 ns) was significantly lower than that of MCS (2.46 ns),
MCNS-3 (2.4 ns), MCNS-5 (2.3 ns), MCNS-15 (2.25 ns), MCNS-20 (2.38 ns).
Generally, the electron lifetime was negatively correlated with electron
transfer rate. The consequences show that the electron transit time of
MCNS-10 composite is short [47], this was because
NiSe2 could provide additional decay channel to the
excited states of the MCNS [43]. We further studied the catalyst
performance from two aspects values of electron transfer rate constant
(KET) and the electron injection
efficiency (ηinj).
The parameters of emission decay of the samples as the shownTable 2 . It was clearly observed that KET and
ηinj value of MCNS-10 were larger than that MCS and
other composite catalysts, indicating that NiSe2 acted
as electron traps can effectively capture electrons attached on the
surface of MCS [6,45,46]. Further, three dimensional topography of
NiSe2 exposed more active sites and improved the
separation efficiency of electrons and hole pairs. These analyses
together shown that the NiSe2 play an important role in
hydrogen production experiments [25].