J. Ahemed et al.
Journal of Photochemistry & Photobiology, A: Chemistry 419 (2021) 113455
2
.3. Photo-fragmentation of various organic dye pollutants (ODPs)
were studied to find out their relative thermal stability and decompo-
sition characteristics [24]. The TGA data of all the complexes were
◦
The catalyst (new Zn (II) complexes) (50 mg) was placed in an
achieved under N
2
atmosphere between 50 and 1000 C at a heating rate
aqueous solution of ODP (10-4 M, 50 mL) in an 80 mL cylindrical quartz
glass reactor. The photo-fragmentation of ODP was studied under visible
of 10 C min and shown in the Fig. 1. The thermograms of all three Zn-
complexes exhibit decomposition in a single stage due to coordinated
ligand part and chloride ions. In the decomposition stage, ligand part
◦
-1
8
light (300 Watts Tungsten lamp with photon flux of 6.42 × 10 Einstein/
◦
s) for 180 min. Before irradiation and sampling, adsorption–desorption
was lost in the temperature range of 350–550 C. After decomposition,
pre-equilibrium of the dye was accomplished in the dark for a period of
the residue left in the crucible is confirmed as nano particle of ZnO [25].
The obtained residue of ZnO powder was tested with the Powder X-ray
diffraction (P-XRD) and shown in Fig. S7. The P-XRD peaks are matched
with JCPDS data (Card No: 36–1415) [26].
6
0 min. Samples were collected at every 30 min interval and the sus-
pended catalyst particles were separated through a Millipore filter and
then estimated by UV–Vis spectrophotometer at respective λmax
.
The bonding mode of the ligand was elucidated by comparing the IR
spectra of ligands PPMHT or PTMHT or MIMHPT and its Zn (II) com-
plexes, shown in Fig. S8. For the ligands, narrow strong bands appeared
2
.4. Photo decomposition of food industrial wastewater (FIWW)
The Zn (II) complex (photocatalyst) (100 mg) was distributed in 500
ꢀ 1
in the IR spectra at 2862 – 2968 cm , and is assigned as symmetric and
H) stretching modes of the alkyl group. The strong
asymmetric
ν
(C
–
mL of FIWW in a 1000 mL cylindrical quartz glass photoreactor. The
ꢀ 1
photo decomposition of FIWW was supported out under visible light
band observed at 1682 cm in the spectrum of PPMHT are attributed to
8
–
–
–
C
the stretching vibration of the imine nitrogen (Ar–
N
) [29]. The
(
300 Watts Tungsten lamp with photon flux of 6.42 × 10 Einstein/s) for
1
80 min. The FIWW solution kept dark under 60 min. for achieving of
band due to the imine nitrogen also shifted to lower in the frequencies
ꢀ 1
adsorption–desorption equilibrium. After removal of the photocatalyst
particles through a Millipore Membrane filter (0.24 µm pore size), every
(1632–1626 cm ) in all the complexes indicating its coordination with
imine nitrogen. Similarly, coordinated water peaks were identified and
also imine peaks were moved to lower frequencies in Zn (II) complexes
of PTMHT and MIMHPT ligands. The two new vibrionic modes in the
3
0 min. of time interval, collected the sample and characterized through
UV–vis and LC-MS spectra.
ꢀ 1
far-IR spectra of complexes, one around 434 cm and the other around
ꢀ 1
3
12 cm are also observed and are due to
ν
(Zn-N) and (Zn-Cl) [22,27]
ν
2
.5. Photo-oxidation of methyl arenes
respectively. These vibrational modes in the infrared spectra of com-
plexes indicating that the Zn (II) ion is coordinated to the PPMHT/
PTMHT/MIMHPT ligands through aromatic ring nitrogen, imine nitro-
gen atoms and one hydroxyl group. The IR spectral absorptions of Zn (II)
2
5 mg of photo-catalyst was placed in 10 mmol of methyl arene in a
1
0 mL cylindrical quartz glass reactor. Then 25 mg of superoxide or
hydroxyl radical scavengers(benzoquinone (BQ) / t-butyl alcohol (TB))
was added [22]. The photo-oxidation experiments were carried out
under visible light (300 Watts Tungsten lamp) for 8 h [13]. The reaction
mixture was monitored with TLC. After completion of reaction, the
photo-catalyst was filtered and washed with distilled water and
extracted by using ethyl acetate. The crude products were purified by
simple filter column to yield pure aldehydes (Scheme 2) with 70 to 85%
yields.
2
+
complexes are shown in Fig. S8. Therefore, the complexation of Zn ion
with ligand PPMHT or PTMHT or MIMHPT through the nitrogen of
thiazole via tautomerism, heterocyclic ring and imine along with one
chloride ion directly bonded to Zn2 ion. Which is supported by low
conductance value of the complexes, which reveal that the anion chlo-
ride is coordinated with the metal ion.
+
1
The H NMR spectra of diamagnetic Zn-complexes were recorded in
d -DMSO at room temperature. The resonance signals (δ ppm) of
6
different types of protons in the Zn (II) complexes and representative
spectra are shown in Figs. S9 to S14. The azomethine proton resonance
signal observed at 8.72 ppm in the spectrum of ligand PPMHT and it is
shifted to down field side by 0.15–0.20 ppm in its Zn(II) complex, which
indicates that the nitrogen atoms are coordinated to Zn(II) metal ion
3
. Results and discussion
The physicochemical and analytical data of all the metal (II) com-
plexes with new ligands PPMHT, PTMHT and MIMHPT are given in
Table 1. The experimental results of elements C, H, N and metal are in
good agreement with the values calculated for the formulae [Zn
[
22]. Similarly, 1H NMR spectra of other two Zn (II) complexes with
respective ligand clearly shifted the peaks which indicated that Zn (II)
ions were strongly complexed with ligand and highly stable. Based on
above analysis the tentative structures of the Zn (II) complexes are
shown in Fig. S15.
(
PPMHT)(Cl)], [Zn(PTMHT)Cl)] and [Zn(MIMHPT)Cl]. The mass
spectra of both the ligands and Zn (II) complexes (Figs. S1-S6) were
confirmed by using maldi (TOF) technique and the high mass peak was
assigned as [ZnL(Cl)] (L = PPMHT, PTMHT and MIMHPT). The molar
The solution phase UV–vis spectra of ligands and Zn (II) complexes
are shown in Fig. 2a and b. In Zn (II) complexes all the absorption bands
shifted to higher wavelength side as compared to ligands (PPMHT,
PTMHT and MIMHPT), given in Table 2. In the reported complexes, the
heteroatoms have the additional non-bonding electrons, which assists
more active delocalized electrons in heterocyclic systems of the thiazole
derivatives and hence the λmax values of thiazole-based Zn (II) com-
plexes are moved to a higher wavelength region than ligands. Therefore,
bandgap energy is decreased due to intramolecular metal–ligand charge
transfer within entire complex [28]. The bandgap energy values are also
presented in the Table 2.
conductance values of all the complexes were specific in N, N-dime-
-
3
thylformamide at 10 M concentration and the results are presented in
Table1. The molar conductance values between 10.99, 11.43 and 12.36
-
1
2
ꢀ 1
O cm mol indicative of that all the complexes were non-electrolytes
23]. The conductance values are unaffected even after 48 h, confirmed
[
that, there is no perceptible ionization and strong interactions between
the metal ion, PPMHT or PTMHT or MIMHPT ligand and the chloride
ions. Therefore, the mass spectral data, analytical data and molar
conductance confirms the formulae of the complexes as [Zn(PPMHT)Cl],
[
Zn(PTMHT)Cl)] and [Zn(MIMHPT)Cl] [22].
The thermal decomposition and stabilities of all the Zn-complexes
Solid state UV–vis-DRS spectra of ligands and complexes were
examined and given in Table 2 and shown in Fig. 2c and d. The ab-
sorption bands are shifted towards higher wavelength region by 50 to
7
0 nm, due to strong overlapping of orbitals in solid phase than solution
phase.
The HOMO-LUMO gap energies of ligands and complexes in solution
DMF) and solid phases were almost equal which indicated the metal-
ligands charge transfer (MLCT) was same.
(
Scheme 2. Photooxidation of methyl arenes in the presence of Zn (II) com-
plexes under visible light irradiation.
3