Effective photodegradation of organic pollutantsin the presence of mono and bi-metallic complexes under visible-light irradiation

Article abstract of DOI:10.1016/j.jphotochem.2020.112996

The synthesis of new mono and bi-metallic complexes such as Zn (II) and Ag-Zn (II) complexes with organic functional group-based ligand (OFL) presented in the current work along with the exploration of their applicability in the photocatalytic degradation

Full text of DOI:10.1016/j.jphotochem.2020.112996

Journal Pre-proof
Effective Photodegradation of Organic Pollutantsin the Presence of Mono
and Bi-metallic complexes under Visible-Light Irradiation
Mahesh Subburu (Methodology) (Investigation) (Formal analysis)
(Writing - original draft), Ramesh Gade, Venkanna Guguloth,
Prabhakar Chetti, Koteshwar Rao Ravulapelly, Someshwar Pola
(Conceptualization) (Validation) (Formal analysis) (Resources)
(Writing - review and editing) (Supervision) (Project administration)
PII:
S1010-6030(20)30793-0
DOI:
https://doi.org/10.1016/j.jphotochem.2020.112996
JPC 112996
Reference:
To appear in:
Journal of Photochemistry & Photobiology, A: Chemistry
Received Date:
Revised Date:
Accepted Date:
1 June 2020
19 October 2020
22 October 2020
Please cite this article as: Subburu M, Gade R, Guguloth V, Chetti P, Ravulapelly KR, Pola S,
Effective Photodegradation of Organic Pollutantsin the Presence of Mono and Bi-metallic
complexes under Visible-Light Irradiation, Journal of Photochemistry and amp; Photobiology,
A: Chemistry (2020), doi: https://doi.org/10.1016/j.jphotochem.2020.112996

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Effective Photodegradation of Organic Pollutantsin the Presence of Mono and
Bi-metallic complexes under Visible-Light Irradiation
Mahesh Subburu,a Ramesh Gade,aVenkanna Guguloth,a Prabhakar Chetti,b Koteshwar Rao
Ravulapelly,aand Someshwar Polaa*
aDepartment of Chemistry, Osmania University, Hyderabad, India.
bDepartment of Chemistry, National Institute of Technology, Kurukshetra, India.
*Corresponding author: E-mail address: somesh.pola@gmail.com Tel: + 919959972288
Graphical Abstract
[Ag-Zn(DCMPPT)(H2O)(OAc)] complex act as photocatalyst for degradation of organic dye
pollutants and industrial wastewater under visible light irradiation due to Ag nanoparticles are
insitu generation from bi-metallic complex then which helps to holes stability in HOMO of
complex.
Highlights
 Synthesis of new Zn (II) complex and Ag-Zn bi-metallic complex using organic
functional group-based ligand which consists of N and S donor atoms for
complexation.
 Several spectroscopic techniques are used for characterization new complexes.

 New complexes act as photocatalysts for degradation of organic dye pollutants and
industrial wastewater under visible light irradiation.
 Identification of active species for the degradation of degradation of organic dye
pollutants and industrial wastewater is hydroxy radicals from scavengers study.
Abstract
The synthesis of new mono and bi-metallic complexes such as Zn (II) and Ag-Zn (II) complexes
with organic functional group-based ligand (OFL)presented in the current work along with the
exploration of their applicability in the photocatalytic degradation of organic dyes under visible-
light irradiation. The Zn (II) complex obtained from organic functional group-based ligands,
complexed with the donor atoms such as S and N under solvothermal conditions and Ag-Zn (II)
complex formed through Ag ions complexed with pyridine ring nitrogen atom. These Zn(II)-
complexes were systematically analyzed using the physicochemical studies and other
spectroscopictechniques. From these facts, it is clarified that the complexes show square planar
geometry with organic functional group-based ligands coordination via mercapto and azomethine
groups. The reported complexes were used for the photodegradation of standard organic dye
pollutants used in various textile and food processing industries. The complex [Ag-
Zn(DCMPPT)(H2O)(OAc)] shows higher photocatalytic activity than [Zn(DCMPPT)(H2O)]
because of the high surface area, low bandgap energy and further visible-light available for the
●
initiation of OH radicals To identify the active species in the photocatalytic process, the
mechanism process also reported for the fast photodegradation of organic dye pollutants in the
existence of some radical quenchers.
Keywords:Ag(I)-Zn(II) bi-metallic complex, Ag nanoparticles, Wastewater,Photodegradation
Introduction
Most of the organic dye pollutants are toxic and produce very serious ecological pollution
by discharging harmful materials into the marine system and are not easy to degrade in water.
Purification of industrial wastewater is a big taskor mission for environmental scientists to
regulate a few kinds of chemicals by several procedures such as physico-chemical, microbial,
and photodegradation methods [1-3]. Still, these methods are not reached the purposeful

investigation for the removal of toxic pollutants and the processes are also very expensive. To
this observation, enormous research efforts have been made on the photodegradation of
industrial wastewater using pure semiconductor oxides. Semiconductor oxides show
photodegradation of organic pollutants due to their high stability, non-toxicity, but these are also
having high manufacturing cost [4]. However, semiconductor oxides show lower catalytic
performance because of the large bandgap energy, the particles size is not equal and very high
recombination energy [5]. Another new technique is an advanced oxidation process (AOPs) [6-
8], which is one of the paths to produce ●OH, but it is also a highly expensive method.
OFLs based metal complexes are an important class of molecules due to different
oxidation states, monitoring the fulfillment of metals in anenormous diversity of suitable
catalytic conversions. Meanwhile, in the last few decades, magnetic properties, structural
arrangements and spectroscopic information of Schiff’s base complexes have been examined [9-
11]. The metal complexes of the OFLs receiving a widerange of applications such as
photocatalytic, analytical, biological and industrial due to their significant performance in
catalysis for new organic transformations [12-16]. The metal complex of OFLs also acts as
photocatalysts for photodegradation of organic pollutants [17]. Hence, OFL ligand-based metal
complexes are crucial for the photocatalytic degradation of organic dye pollutants under visible
light conditions.
Recently, photodegradation of organic dye pollutants by using Ti (IV) Schiff’s base
complexes have been reported for the degradation of methylene blue [18] and also reported Ag-
dopedPd(II) complex for degradation of azo-dyes under visible light irradiation [19]. Kadiiska
●
●
and co-workers described that a series of radical ions or radicals with HO2 /O2●–and OH were
stimulated in the photocatalytic process [20]. Further, Singh et al. described that [Fe(III)-salen]Cl
complex has been used for the degradation of organic-dye contaminants [21].It is observed from
the literature that in several numbers of photodegradation methods, hydrogen peroxide (H2O2) is
●
playing a significant role in the generation of highly active radicalspecies such as OH radicals
and is reacts with toxic molecules for the photomineralization method [21]. However, usage of a
larger quantity of H2O2 is unsafe and affectsthe health conditions of humans. Recently, some
types of Ni(II)-complexes obtained from Schiff’s bases were utilized for the degradation of
rhodamine-B (RhB)and methylene blue (MB) dyes without using of H2O2, as photocatalysts
usedunder visible-light conditions [16,22]. The zeolite captured Ni(II) and Cu(II) Schiff’s base

complexes used for oxidation of benzhydrol and photodegradation of RhB dye under visible-
light and time taken for degradation was 3 to 4 hours [23]. The majority of the studies on
Schiff’s base metal complexes are pH-sensitive, if the pH of the solution is greater than 9, the
metal complexes are less stable [24]. Also, most of the known metal-organic frameworks act as
photocatalysts are not having much variation in the structures and their structure-activity
relationship and it is still unclear [25].
Metal complexes used for several organic transformations [26], but there are few gaps
found in the field of photocatalysis like degradation of organic dye pollutants. For this reason,
OFL based complexes are focused on the development of visible light sensitive photocatalysts
with some significant features such as photostability, less recombination energy, high surface
area, recyclable, and reasonable synthetic methodology. Photocatalysts are using OFL based
complexes underneath visiblelight has motivating significant consideration due to its prospective
properties in biodegradable remediation by parting the organic dye pollutants to very harmless
products.
Scheme 1 Structures of various dyes used for photodegradation
In one such study, the new Schiff’s base Zn(II) and Ag-Zn(II) complex synthesis from N,
S-donor based tridentate OFLs are reported. The newly synthesized [Zn(DCMPPT)H2O] and

[Ag-Zn(DCMPPT)(H2O)(OAc)] complexes are used for photodegradation of selected organic
dye toxic molecules under visiblelight irradiation (selected organic dyes are shown in Scheme 1).
EXPERIMENTAL SECTION
Materials and Methods
All starting materials purchased from Alfa Aesar and listed as Ag(OAc), Zn(OAc)2,various dyes,
phenylglyoxylic acid, ammonium tetrathiocyanodiammonochromate (Reinecke salt from Sigma-
Aldrich) directly used for complexation and photodegradation process. Preparation of organic
functional
ligand
(E)-3-(((4,5-dichloro-2-mercaptophenyl)imino)methyl)pyridine-2-thiol
(DCMPPT)” was carried out as per earlier reported method [18].
Synthesis of complexes
Preparation of the Zn((E)-3-(((4,5-dichloro-2-mercaptophenyl)imino)methyl)pyridine-2-thiol)
[Zn(DCMPPT)(H2O)]
A 20 ml ethanol solution of DCMPPT ligand (1.00 mmol) and one equivalent amount of
Zn(OAc)2 was added in the reaction flask with continuous stirring at room temperature
conditions for 30 min. and shown in Scheme 2.The reaction mass was refluxed for a further four
hours at 80 - 90oC. Then the reaction mixture cooled to room temperature, the precipitated
complex product was filtered to get solid crude complex.The obtained crude product was washed
with various solvents such as acetone, methanol,and diethyl ether to obtained pure pale-yellow
compound with a 74% yield.
Rf 0.28 (9:1 ratio of CHCl3/MeOH); Molecular formulae: C12H8Cl2N2OS2Zn; CHN
analysis expt. (calcd): C% 36.29 (36.34), H% 2.01 (2.03),Cl% 17.84 (17.88), N% 7.01 (7.06),
1
S% 16.14 (16.17) and Zn% 16.43 (16.43); H NMR (400MHz, d6-DMSO ) δ (ppm) = 8.28 (m,
13
1H), 7.82 (m, 1H), 7.62 (s, 1H), 7.48(m, 1H), 7. 13 (s, 1H), 6.92 (s, 1H) and 3.52 (br, 2H); C
NMR (100 MHzCDCl3) δ (ppm) = 162.842, 147.305, 143.242, 142.842, 139.197, 132.008,
130.875,130.528, 130.446, 129.725, 128.403, 127.671, 127.574, 126.868, 125.890, 113.744, and
109.790; MS (EI): 375.8639 (M-(H2O))+; UV-Vis: 291.12, and 405.02 nm.
Preparation
of
the
bi-metallic
complex
[Ag-Zn((E)-3-(((4,5-dichloro-2-
mercaptophenyl)imino)methyl)pyridine-2-thiol)(H2O)(OAc)]([Ag-Zn(DCMPPT)(H2O))(OAc)]):
Silver acetate (1.00 mmol) was placedin10 ml solution of [Zn(DCMPPT)(H2O)](1.00
mmol, in DMF and ethanol (2:8)) with continuous stirring at ambient conditions. Then the

reaction mixture was heated for four hours and continued for a further one hour at 100oC
(Scheme 2). After five hours, the reaction mixture cooled to room temperature to get adark-
colored crude product.The crude material was filtered and washed with double distilled water,
acetone, cold methanol, and diethyl ether to found pure dark-grey with shiny solid [Ag-
Zn(DCMPPT)(H2O)(OAc)]material with 48 % yield. Furthermore, to check the complexation of
Ag ions in the complex formation process, the rest of the solution was titrated with0.1 M KCl
solution ensuing no formation of a solid precipitate of AgCl, this shows a calculable quantity of
Ag complexed and obtained purebi-metallic complex.
Rf 0.22 (8:2 ratio of CHCl3/MeOH); Molecular formulae: C15H13AgCl2N2O3S2Zn; CHN
analysis expt. (calcd): C% 31.15 (31.19), H% 2.24 (2.27), Cl% 12.24 (12.28), N% 4.83 (4.85),
Ag% 18.64 (18.68), S% 11.07 (11.10) and Zn% 11.26 (11.32); 1H NMR (400MHz, d6-DMSO ) δ
(ppm) = 8.23 (m, 1H), 7.83 (m, 1H), 7.59 (s, 1H), 7.48 (m, 1H), 7.18 (s, 1H), 6.92 (s, 1H), 3.68
(br, 2H), and 2.36 (s, 3H);13C NMR (100 MHz CDCl3) δ (ppm) = 204.933, 166.859, 140.860,
138.328, 130.695, 130.353, 130.207, 130.148, 129.522, 129.215, 129.070, 128.989, 128.931,
128.873, 128.822, 128.654, 128.267, 127.953, 127.838, 127.422, 127.262, 126.859 and 26.859;
MS (EI): 560.7929 (M+1)+; UV-Vis: 293.46 and 408.06 nm.
Scheme 2 Synthesis of new [Zn(DCMPPT)(H2O)] and [Ag-Zn(DCMPPT)(H2O)](OAc)
complexes
Estimation of surface area
BET surface areas were determined by N2 adsorption at liquid nitrogen temperature using
a BELSORP-mini II instrument (BEL JAPAN, INC.). Prior to the measurement, the samples
were degassed at 200 oC for 2 h.
Photodegradation reactions
Photodegradation of various organic dyes
The photocatalyst (25 mg) was addedto a dye pollutant 50 mL solution (5 x 10-5 M) in an
80 mL quartz glass cylinder type tubular photoreactor. The degradation of various the dyes was

kept in the occurrence of visible-light (50 Watts LED light with photon flux is 8.92 x 1013
Einstein/s and wavelength 380-840 nm), as observed by using the chemical actinometric
technique with Reinecke salt [5] for 60 min. Adsorption-desorption equilibrium procedure for
the individual dye was achieved in the absence of light for 20 min then the light is allowed to fall
on the reaction mixture. Once the light is turned on then each 10 min of time interval sample was
taken for analysis, photocatalyst was separated by filtration and examined usinga UV-visible
spectrophotometer at dye λmax
.
Photodegradation of Industrial Wastewater (IWW)
The photocatalyst (complexes) (50 mg) was dispersed in 200 mL of industrial wastewater
(IWW) in a 500 mL cylindrical quartz glass reactor. The photodegradation of IWW was carried
out under visible light (50 Watts LED light) for 240 min. Adsorption-desorption pre-equilibrium
of the dye was attained in the dark for 60 min. before irradiation and sampling. Samples were
collected every 30 min. for analysis and filtered through a Millipore filter (MF-Millipore
Membrane Filter, 0.22 µm pore size)to remove the catalyst particles and then examined by UV-
Vis spectrophotometer at respective λmax value.
Controlled photoreaction for identification of in-situ formed Ag NPs
The photocatalyst (50 mg) was dispersed in 50 mL of double distilled water in an 80 mL
cylindrical quartz glass reactor. The photoreaction of water was carried out under visible light
(400 Watts Tungsten light) for 60 min. For every 10 min of time samples were collected for
analysis and filtered through a Millipore filter(MF-Millipore Membrane Filter, 0.22 µm pore
size) to remove the catalyst particles and then examined by UV-Vis spectrophotometer at
respective λmax value.
Results and Discussion
Methods used forthe characterization of complexes with various spectroscopic techniques and
their details are described in the supplementary information.
Characterization of photocatalysts
The Zn (II) and bi-metallic complexes are non-hydroscopic and are very stable at ambient
conditions.Complexesare completely soluble in DMF, and DMSO, but very less soluble in
acetone,chloroform, methanoland ethanol. The EDX information of both complexes is revealed
in Figure 1. The EDX spectrum shows that Ag, Zn, S, N, Cl, and O atoms are existing in the

complex. Which designated that the Zn2+ ions are complexed to tridentate ligand unit and
Ag+also complexed through pyridine rings.
Mass Spectral data, molar conductance and FESEM morphological studies
The mass spectral data of complexes reveals that the base peaks are matching with
[Zn(DCMPPT)]+and [Ag-Zn(DCMPPT)H2O(OAc)] [19] (Figure S1 and S2). In mass spectra of
[Zn(DCMPPT)(H2O)], showed two peaks with two different m/z values such as 394.8751 and
376.8648 respectively. These peaks indicated that [M+1]+molecular ion and [(M+1)-H2O]+
fragmented ion peak respectively. Similarly, in the case of [Ag-Zn(DCMPPT)(H2O)(OAc)]
complex exhibited that three significant peaks with m/z values such as 560.7934 ([M+1])+,
501.7801 ([M+1]-OAc)+and 376.8647 (([M+1]-OAc)-(Ag++H2O)]+ions respectively.
Ionic or covalent nature of the new Zn(II) complexes identified through molar
conductance studies. The low molar conductance values revealed that both the complexes in
DMF solvent indicated that these complexes are covalent due to the presence of water molecule
and acetate ions in inside the coordination sphere ([Zn(DCMPPT)H2O] and [Ag-
Zn(DCMPPT))H2O)(OAc)] [18,27] and the corresponding data presented Table 1.The
morphological studies of Zn(II) complexes have completely reformed in its shape and size when
associated with the ligand DCMPPT compared to the morphology of ligand alone. The FESEM
imageries of Zn(II) complexes exhibited that the particles form nanoflakes, subsequently re-
complexed with Ag ions and the total morphology transformed into nanocubes [28]. Comparison
of nanosheet type [Zn(DCMPPT)(H2O)] with ligands is shown in Figure 2.
Table 1. Physico-chemical, % of elements and molar conductivity data of ligand and
complexes
%
aM.P/D.
%H
(calc
d)
Λm ohm-1
mol-1 cm2
(DMF)
---
%C
(calcd)
%Cl
%N
%S
%M
Compound
Yield P. (oC)
(calcd) (calcd) (calcd) (calcd)
*L
78
74
186
254
45.68
(45.72)
36.31
2.54
22.51
8.85
20.31
(20.34)
16.15
(16.17) (16.48)
(Zn)
--
C12H8Cl2N2S2
[Zn(L)H2O]
C12H8Cl2N2OS2Zn
(2.56) (22.49) (8.89)
2.02 17.85 6.99
(2.03) (17.88) (7.02)
16.46
10.68
14.78
(36.34)
[Ag-Zn(L)H2O](OAc) 48
C14H11AgCl2N2O3S2Zn
306
29.79
1.95
12.54
4.94
11.34
19.12
(29.84)
(1.97) (12.58) (4.97)
(11.38) (19.14)
(Ag)
11.58
(11.60)
(Zn)
*L = DCMPPT

Thermogravimetric and XPS studies
The thermograms (Figure 3) of the Zn (II) complexes exhibit two stages percentage
weightloss, significant in the temperature range of 200 – 450 oC which indicates that coordinated
water molecules and ligand part. Therefore, two-step decomposition specified that complexes are
associated with one water and ligandmolecule and formed square planar complexes[29-31]. The
obtained residues were examined by using XPS. The data found that the binding energies of
various elements present in residues are N, O, S and Zn in [Zn(DCMPPT)(H2O)] and Ag, N, O,
S and Zn in [Ag-Zn(DCMPPT)(H2O)(OAc)] respectively, and are shown in Figure 4.
Powder XRD (P-XRD) pattern of ligand and complexes
The P-XRD peaks of the DCMPPT OFL exhibited 2θ values that exist in between 5 and
50 with high-intensity 2θ peak at 5.82o(111). Nevertheless, [Zn(DCMPPT)(H2O)] complex peaks
were altered when related to the DCMPPT. Hence, Zn2+ ion has been complexed with the N, and
S donor atoms and H2O molecule of the OFL. A peak showed in DCMPPT at 2θ = 9.68o(111)
was increased after coordination with Zn2+ ions, and one more maximum peaks at 2θ = 21.53o
(100) and 25.09o (220)was shifted to higher 2θ value side.Also, in the bi-metallic complex, all
the peaks shifted to higher 2θ value side which designated that the development of a
characteristic Ag-Zn based framework, especially a broad peak around 2θ = 25.12° (220),
recognized to the interlayer distance in [Ag-Zn(DCMPPT)(H2O)(OAc)]. In the complexes, two
sulphur and one N-atoms and one water molecule are coordinated with Zn and geometrically
arranged as square planar complex and Ag nanoparticles are occupied in between two Zn-
complexes and form a layered type MOFs with acetate ions placed inside the coordination
sphere. All the peaks werebroadened and a reference peak was shownat 44o (200) [32],which
indicated that presence Ag ions in between the layers of the [Zn(DCMPPT)(H2O)] complex as
shown Figure 5. The unit cell parameters of DCMPPT, [Zn(DCMPPT)(H2O)], and [Ag-
Zn(DCMPPT)(H2O)(OAc)] materials are obtained by least-square fitting using POWD software.
The
unit
cell
parameters
of
DCMPPT,
[Zn(DCMPPT)(H2O)],
and
[Ag-
Zn(DCMPPT)(H2O)(OAc)] (DCMPPT: monoclinic lattice, a = 10.432 Å, b = 4.912 Å, c = 9.452
Å, and β = 103.64°, P21/c space group; [Zn(DCMPPT)(H2O)]: orthorhombic lattice, a = 9.517
Å, b = 13.412 Å, c = 33.140 Å , and α = β = γ = 90°, Pna2(1) space group; [Ag-
Zn(DCMPPT)(H2O)(OAc)]: triclinic lattice, a = 13.823 Å, b = 14.283 Å, c = 14.453 Å , and α =
82.55o, β = 78.34o γ = 72.69°, P1 space group) are given as input parameters for least-square

fitting the powder data of DCMPPT, [Zn(DCMPPT)(H2O)], and [Ag-Zn(DCMPPT)(H2O)(OAc)]
materials [33-36].
IR and NMR studies
The IR bands of Zn and bi-metallic complexes provide a shred of evidence about the
coordination with Zn2+ ions with ligand and also, Ag+ ions re-complexed with Zn-complex. All
the peaks of complexes are compared with ligands and are shifted its wavenumber by 15- 25 cm-
1 due to complexation between Zn and ligand through azomethine and -SH groups [18]. Some
new peaks were also found at 860, 432, and 387 cm-1, which belongs to the coordinated water
molecule, and ν(Zn-S) and ν(Zn-N) of azomethine groups respectively, and are shown in Figure
S3. 1H-NMR spectra of complexes such as [Zn(DCMPPT)(H2O)] and [Ag-
Zn(DCMPPT)(H2O)(OAc)] were analyzed in d6-DMSO and CDCl3. The significant peaks of
ligand were disappeared as compared to complex spectra and azomethine proton was deshielded,
and also attached aromatic hydrogen atoms are slightly deshielded, which indicated that Zn (II)
complex was formed through N, S donor atoms of ligand [37]. However, one more important
broad peak at 3.58 ppm was also observed, which belongs to the coordinated water molecule of
the [Zn(DCMPPT)(H2O)] complex. Whereas, in case of [Ag-Zn(DCMPPT)(H2O)(OAc)]
complex, spectrum presented some significant variations compared with the
[Zn(DCMPPT)(H2O)] complex, a new peak at 2.36 ppm of acetyl group protons with a singlet
and aromatic protons are moved to the up-field side as revealed in Figure S4 and S5. Hence, it is
specified that Ag ions existing and coordinated with pyridine ring N atom, in [Ag-
Zn(DCMPPT)(H2O)(OAc)] complex. Also, in13C-NMR spectra of the [Zn(DCMPPT)(H2O)]
peaks were changed compared with the DCMPPT ligand spectrum (Figure S6 and S7). Hence,
complexes are extremely stable and Zn (II) ions are fit into tridentate ligand and complexing
through N and S atoms of the ligand. Finally, established on bases of spectral data the
[Zn(DCMPPT)(H2O)] and [Ag-Zn(DCMPPT)(H2O)(OAc)] complexes are coordinated through S
and N atoms and as shown in Figure 6.
Electronic spectral and surface area studies
The
electronic
properties
of
the
[Zn(DCMPPT)(H2O)]
and
[Ag-
Zn(DCMPPT)(H2O)(OAc)] in DMF were examined. Figure 7a reveals the UV-vis spectra of the
[Zn(DCMPPT)(H2O)] and [Ag-Zn(DCMPPT)(H2O)(OAc)] in solution. The Zn(II) complexes
show a significant band, and this band is spin-allowed transition due to squareplanar geometry

and the bandis assigned as T2g →T1u [38]. From absorption spectra, the bandgap values are
estimated from the onset λ value of spectra. A strengthening of the UV-Vis Light Diffuse
Reflectance spectra of DCMPPT, [Zn(DCMPPT)(H2O)] and [Ag-Zn(DCMPPT)(H2O)(OAc)]
samples described in Figure 7b, it reveals that the existence of an extensive surface plasmonic
resonance (SPR) band between 340 and 550 nm well-matched to the SPR of Ag ions and are
complexed with [Zn(DCMPPT)(H2O)]. The bandgap energy values attained from UV-vis-DRS
solid state are shown in Table 2.
From the UV-vis-DRS spectra OFL and Zn-complexes bandgap values (Eg) are evaluated
by using the Kubelka-Munk method using the following equations 1 and 2 [39]:
2equation 1
(
)
1−푅
( )
퐹 푅 =
2푅
2
(
)
ℎ푣퐹 ~ (ℎ푣 − 퐸푔) equation 2
Where R is the reflectance, F is the Kubelka-Munk function, Eg is the bandgap and hν is
1/2
the photon energy. By plotting between (hvF) and hν, the Eg of the DCMPPT,
[Zn(DCMPPT)(H2O)] and [Ag/Zn(DCMPPT)(H2O)(OAc)] was attained.
Surface area of the [Ag-Zn(DCMPPT)(H2O)(OAc)] complex exhibited higher than
[Zn(DCMPPT)(H2O)]. However, the ligand surface area is much lower than both the complexes
and as shown in Table-2 and isotherm shown in Figure S8.
Table 2. Bandgap energies (solid phases) and Surface area of DCMPPT and Zn(II)-
complexes
Compound
Surface area Bandgap energy (eV)
(m2/g)
14
(solid-phase)
2.84
DCMPPT
[Zn(DCMPPT)](H2O)]
[Ag-Zn(DCMPPT)](H2O)(OAc)]
94
156
2.52
2.42
Electrochemical studies
The redox properties of [Zn(DCMPPT)(H2O)] and [Ag-Zn(DCMPPT)(H2O)(OAc)]
complexes are studied by applying cyclic voltammetry in CH3CN/CHCl3(1:1 ratio,0.1 mol ·L–1
n-Bu4NPF6). As revealed in Figure 8, single-electron oxidation waves are observed in the

potential region of -2.0 to + 2.0 V (vs Ag/AgCl). This is associated with the OFL DCMPPT,
which upon coordination with a metal ion. The first oxidation potential is moved towards more
negative potential, which is equally as [Zn(DCMPPT)(H2O)]. Moreover, a change in [Ag-
Zn(DCMPPT)(H2O)(OAc)] complex is also observed [40-42], due to the Ag ions coordinated
with the N of pyridine and exists between two molecules/ layers of Zn(II) complexes. This shift
can be described by the electronic interactions between the DCMPPT unit and the Zn2+ ions
produced by the shorter distance among them [43].
Emission spectra
Emission spectra of ligand and complexes were verified in the solid phase and the
materials were excited at 380 nm, 400 nm and 420 for DCMPPT, [Zn(DCMPPT((H2O)] and
[Ag-Zn(DCMPPT((H2O)(OAc)] respectively by using slit width of 5 nm. Emission spectra
provided important evidence about the recombination rate of holes and electrons. From these
facts, it is noticed that the efficiency of the transfer of carriers or trapping of charge to examine
the probability of generation of electron-hole pair from [Ag-Zn(DCMPPT)(H2O)(OAc)] [44]. As
the emission initiates from the recombination of excited holes and electrons, greater emission
strength specifies a greater rate of recombination of charge carriers and vice versa. The emission
strength of [Ag-Zn(DCMPPT)(H2O)(OAc)] was declined almost completely when related to the
complex [Zn(DCMPPT)(H2O)], as exhibited in Figure 9. The lower emission strength of the
[Ag-Zn(DCMPPT)(H2O)(OAc)] complex designates that a low recombination rate, which
suggests that [Ag-Zn(DCMPPT)(H2O)(OAc)] can worthily accelerate up the unraveling of
electrons and holes and exhibit high photodegradation rate ability.
Photocatalysis
Photodegradation of dye pollutants
In the presence of metal complexes, photodegradation of organic dye toxins follows two
methods which are i) mineralization (char) and ii) conversion of small fragments of the
pollutants withstable biodegradable nature [45]. Acid violet 7 (AV7) [46], acid blue 1 (AB1) [47]
and Reactive Red 120 (RR 120) [48,49] are the maximum toxic dyes usually used for the dyeing
procedure in the manufacturing of clothes. B. Subash et.al., studied photodegradation of AB
1/AV 7/RR 120dyes by usingZnO-Ag-ZnS under UV light irradiation [46], however, UV light is
not suitable for industrial purpose.Hence, to overcome this drawback, here the degradation of
AV 7, AB 1, and RR 120 with/without the presence of Zn(II) complexes, in absence and

presence of the visible light were examined and the outcomes are revealed in Figure 10.
Initially, the photodegradation of AV 7, AB 1 and RR 120 dyes are carried out in dark for 20
min. After 20 min, the samples were collected and examined by UV-vis absorption spectroscopy
and found that there is no considerable change in the absorption of toxins even in the occurrence
of a Zn(II) complexes (hardly less than 1%). In the presence of visible light alone, the dye's
photodegradation was noticed was too small (up to 1%), it isdue to the lack of a photocatalyst.
Later on, as soon as the Zn(II) complex was applied under visible light, the photodegradation
proceeded at a controlled rate, depends on the complex applied as photocatalyst. In the presence
of [Ag-Zn(DCMPPT)(H2O)(OAc)], 80%, 65% and 74% of the concentration ofrespective
pollutants were noticed in electronic spectra after 40minutes, and 98 % photomineralization was
also noted after 60minutes. However, in the case of, [Zn(DCMPPT)(H2O)], gave 50 %
photodegradation after 40 min and 70 % after 60 min. Thus,[Ag-Zn(DCMPPT)(H2O)(OAc)] is
the most effective catalyst among the two complexes. The technique of degradation was also
checkedby mass spectrometry, the fragmented process of dye molecules was examined and
presented in Table S1. After 50 min, [Ag-Zn(DCMPPT)(H2O)(OAc)] sample was studied and it
exhibited a peak at 108 m/z (Figures S9-S11). It is evident from these observed peaks that the
catalyst capably causes the breaking of dye molecules in a quick duration of time. The peak is
shown in mass spectra identified as benzoquinone, which is the first product of dye-pollutant
photodegradation as revealed in Figure S11. Subsequently, benzoquinone peak is disappeared
after 60 min, which is evedent for further photomineralization. In the case of,
[Zn(DCMPPT)(H2O)], still, m/z 108 base peak (benzoquinone) was existing after 60 min of
visible light (LED) illumination.
The photoreactivity of a MOF turns on several factors, such as surface area, surface
structure, bandgap energy, the absorptivity of the pollutant, the geometry of the material,and rate
of recombination of holes and electrons. The presence of Ag and Zn metals has a valued effect
on photoreactivity because of the tridentate OFL system. The enhanced rate of photodegradation
under visible light irradiation may be because of (i) the low Eg value falls into the visible light
domain for [Ag-Zn(DCMPPT)(H2O)(OAc)], (ii) Ag ions highly photosensitive in nature,
whichhelps inthe separation of hole-electron pair in the presence of visible light irradiation. [Ag-
Zn(DCMPPT)(H2O)(OAc)] complex band moved towards the higher wavelength (reduced
bandgap) sidedue to the occurrence of Ag ions compared with [Zn(DCMPPT)(H2O)] complex.

The Ag ions are showed dual nature as existence under visible light which is confirmed through
UV-visible spectral studies and spectra revealed that i) Ag nanoparticles formed [50] on the
surface ii) which boosted the photocatalytic performance of [Zn(DCMPPT)(H2O)]and as shown
in Figure 11. After completion of photoreaction, visible light turned off and [Ag-
Zn(DCMPPT)(H2O)(OAc)] complex was separated and washed with acetone and dried and
measured the UV-vis spectra as shown in the Figure S12. The purity and structural stability of
[Ag-Zn(DCMPPT)(H2O)(OAc)] complex verified with NMR spectra and obtained spectral data
compared with pure complex (before photocatalysis) as shown in Figure S13.The NMR spectra
provides an important information that after visible light turn-off,it is found the original complex
re-generation. Hence, [Ag-Zn(DCMPPT)(H2O)(OAc)] complex used for reusable and stability
studies.
Further organic dye pollutants commonly used for the dying process in the manufacturing
of clothes such as AB 1 and RR 120 were also studied for the degradation process with these
photocatalysts. As shown in Figure 10b and 10c, analogous effects were noted, i-e., [Ag-
Zn(DCMPPT)(H2O)(OAc)]
photodegradation process than Zn(DCMPPT)(H2O).
Degradation of industrial wastewater (sample collected from Food processing Units)
afforded
a
well-organized
photocatalytic
systemfor
The industrial wastewater (IWW) samples are tested with LC-MS technique and data
revealed a wide range of peaks with different m/z values as shown in Figure S14 & S15. From
this information, some important peaks are identified and matched with pesticide molecular
weight and the rest of the peaks are unknown pollutants that were formed through the food
processing methods. After initial analysis, the IWW samples are exposed to visible light
irradiation in the presence of [Ag-Zn(DCMPPT)(H2O)(OAc)] photocatalyst. Then, the tested
sample solutions are taken with regular time intervals and measured the concentration of the
sample by UV-visible spectra. The data revealed that the concentration of pollutants was
gradually decreased and finally, after 240 minutes completely degraded the pesticides and
unknown pollutants present in the IWW samples as shown in Figure 12. The sample solution
was remeasured with LC-MS maximum peaks are disappeared as compared with initial data
(Figure S12). Therefore, [Ag-Zn(DCMPPT)(H2O)(OAc)] complex performance towards the
photocatalytic degradation of IWW is higher than [Zn(DCMMPT)(H2O)] complex. Lastly, the
photodegraded IWW attained was examined for chemical oxygen demand (COD) experiment

with K2Cr2O7 as the oxidizing agent. The COD value recorded for photo-mineralized
wastewater sample is 205 mg/L, as compared with 992 mg/L for the initial IWW sample. With a
typical value of 250 mg/L, the photo-mineralization of contaminants existing in TPE generated
water can be reusable [5].
Kinetic Studies
Moreover, as revealed in Figure S16, the reaction kinetics plots mechanically reveal the
catalytic efficiency modifications under the two photocatalysts enlightened above. Subsequently,
the photomineralization performance of AV 1 dye solution follows the first-order reaction, the
reaction kinetic plot was deduced from the formulae between ln(C/C0) and time (t)
⁄
ln(퐶 퐶표) = −푘푡
(1)
The rate constant
k
of photocatalysis with [Zn(DCMMPT)(H2O)] and [Ag-
Zn(DCMPPT)(H2O)(OAc)] complexes were 0.04205, and 0.14098 min-1 respectively. The k
value of [Ag-Zn(DCMPPT)(H2O)(OAc)] complex photocatalysis process was 3.35 times faster
than simple [Zn(DCMMPT)(H2O)] complex.
Identification of active species
Generally, the photodegradation reaction depends on four kinds of active species like
superoxide radical (O2●─), electron (e-), hole (h+) and hydroxyl radical (●OH) [51-54] in the
existence of photocatalyst. In order to identify the active species involved in photodegradation of
dye pollutants, few types of foragers (t-butanol, benzoquinone, EDTA and K2S2O8, same
quantity with respective photocatalyst) used in the photodegradation process. As revealed in
Figure 13, photodegradation of AV 7 over [Ag-Zn(DCMPPT)(H2O)(OAc)] was delayed with
the occurrence of t-butanol (TBA), benzoquinone (BQ), ethylene diamine tetra acetic acid
(EDTA) and potassium peroxydisulphate (K2S2O8). The outcomes specified that hydroxy
radicals (•OH), and holes are the highly active species involved in the photomineralization of AV
7. However, •OH was more dominant in photomineralization of AV 7 as compared to hole
species. In presence of TBS and K2S2O8 are responsible for the reducing in the mineralization of
AV 7 due to the presence of •OH and hole scavengers (figure 14). The presence of BQ had very
•-
less effect on the mineralization rate, signifying that AV 7 was almost not degraded by O2 .
●
Therefore, the entire photodegradation reactions depend on the OH and hole scavengers, which
are the most important species for photomineralization.
Reusable studies of the photocatalyst

The stability and reusability of photocatalyst are examined, by using catalyst separated
from tested solution through the centrifuged method.It was noticed that the photocatalyst
sustained as same dark gray color, signifying that organic dye pollutants were not deposited on
the surface of the photocatalyst and the total pollutants are photomineralized, which is confirmed
from elemental analysis of the complex as matched with pure complex data. Continuous reuse of
bimetallic complex after four runs of photodegradation of organic dye pollutants, the [Ag-
1
Zn(DCMPPT)(H2O)(OAc)] complex was separated and recorded H-NMR spectra. From the
spectra it is confirmed that the bimetallic complex is stable up to four cycles (shown Figure S13).
1
However, after fifth cycle H-NMR spectral data shows mixture of both the complexes such as
[Zn(DCMPPT)(H2O)] and [Ag-Zn(DCMPPT)(H2O)(OAc)] in the ratio of 15:85 as represented in
Figure S17, which indicates that [Ag-Zn(DCMPPT)(H2O)(OAc)] complex stability is decreased
after four runs of photodegradation of organic pollutants. As shown in Figure 14, the
performance of the photocatalysts is with not much changes in photodegradation of pollutants
after sequential turns (four cycles).
The performance of the catalyst slowly declines due to Ag ions are converted into Ag2O
[55,56] and separated from [Zn(DCMPPT(H2O)] which is further characterized by powder XRD
(the PXRD pattern based on the POWD computed software) and shown in Figure 15.The
photodegradation was carried out for five runs (60 min. each) and the yields are 97, 95, 94, 93
and 90% (tye gradual decrease in the yields for five continuous runs are due to formation of
Ag2O, shown in figure 16), which shows the reusability of catalyst. The results reveal that the
photocatalytic activity of [Ag-Zn(DCMPPT)(H2O)(OAc)] could be repeated without a
substantial drop in the catalyst efficiency.
Conclusion
Zn((E)-3-(((4,5-dichloro-2-mercaptophenyl)imino)methyl)pyridine-2-thiol)(H2O)
and
[Ag-Zn((E)-3-(((4,5-dichloro-2-mercaptophenyl)imino)methyl)pyridine-2-thiol)(H2O)(OAc)]
were synthesized and confirmedthrough various spectroscopic methods. The dual nature of Ag
ions under visible light was confirmed by UV-visible spectra. The catalytic property of new Zn
(II) based complexes for various organic dye pollutants was studied under visible-light-driven.
The photocatalytic performance of [Ag-Zn(DCMPPT)(H2O)(OAc)] complex is greaterthan
[Zn(DCMPPT)(H2O)] complex and is highly stable even after five cycles. Moreover,
photodegradation investigationsproposedthat the bimetallic complex with betterphotocatalytic

performance will be a possible candidate for reusable wastewatercleansingunder visible-light-
driven.
Credit author statement
Methodology, Investigation, Formal analysis and Writing – original draft by Mahesh Subburu.
Photochemical reactions performance by Ramesh Gade.
Characterization of Mass spectral data by Venkanna Guguloth.
Koteshwar Rao Ravulapelly provide Thermogravimetric and XPS analysis of complexes
UV-visible DRS and PL spectral data provided by Dr. Prabhakar Chetti.
Conceptualization, Validation, Formal analysis, Resources, Writing – review and editing,
Supervision and Project administration by Dr. Someshwar Pola.
Someshwar Pola
Conflict of Interest and Authorship Conformation Form
Please check the following as appropriate:
o
All authors have participated in (a) conception and design, or analysis and interpretation of
the data; (b) drafting the article or revising it critically for important intellectual content; and
(c) approval of the final version.
o
o
o
This manuscript has not been submitted to, nor is under review at, another journal or other
publishing venue.
The authors have no affiliation with any organization with a direct or indirect financial
interest in the subject matter discussed in the manuscript
The following authors have affiliations with organizations with direct or indirect financial
interest in the subject matter discussed in the manuscript:

Author’s name
Affiliation
Mahesh Subburu
Osmania University
Ramesh Gade
Osmania University
Osmania University
Osmania University
NIT, Kurukshetra, India
Osmania University
Venkanna Guguloth
Koteshwar Rao Ravelapelly
Prabhakar Chetti
Someshwar Pola
Acknowledgment
Authors would like to thank DST - FIST schemes and UGC, New Delhi. Mahesh Subburuthanks
University Grants Commission (UGC), New Delhi for the award of Junior Research
Fellowshipand SP for financial support under SERB (EMR//2014/000452), UGC-UPE-FAR and
DST-PURSE, New Delhi, India.
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Fig. 1 EDX images of a) [Zn(DCMPPT)(H2O)] and b) [Ag/Zn(DCMPPT)(H2O)(OAc)]
complexes.
Fig. 2 FESEM metaphors of a) DCMPPT, b) [Zn(DCMPPT)(H2O)] and c) [Ag-
Zn(DCMPPT)(H2O)(OAc)].
Fig. 3 Thermograms of [Zn(DCMPPT)(H2O)] and [Ag/Zn(DCMPPT)(H2O)(OAc)] complexes.
Fig. 4 XPS spectra of a) [ZN(DCMPPT)(H2O)] and b) [Ag/Zn(DCMPPT)(H2O)(OAc)]
complexes
Fig. 5 Powder XRD pattern of ligand and complexes.
Fig. 6 Tentative structures of [Zn(DCMPPT)(H2O)] and [Ag-Zn(DCMPPT)(H2O)(OAc)]
complexes.
Fig. 7 a) UV-vis and b) UV-vis-DRS spectra of ligand and complexes.
Fig. 8 Cyclic voltagrams of ligand and complexes.
Fig. 9 PL spectra of ligand and complexes.
Fig. 10 Photodegradation of a) AV 7, b) AB 1, and c) RR 120 with [Zn(DCMPPT)(H2O)] and
[Ag-Zn(DCMPPT)(H2O)(OAc)] and d), e) and f) successive absorbance spectral patterns of AV
7, AB 1 and RR 120 with [Ag-Zn(DCMPPT)(H2O)(OAc)].
Fig. 11 UV-visible spectra of in-situ formed Ag NPs.
Fig. 12 a) Photodegradation of IWW in the presence of [Ag-Zn(DCMPPT)(H2O)(OAc)] b)
successive absorbance spectral pattern and c) box chart plot for % of dye degradation under
visible-light-driven.
Fig. 13 Control tests of selective photodegradation of AV 7 with the adding of several radical
foragers: tert-butyl alcohol (TBA, scavenger for hydroxyl radicals), benzoquinone (BQ, forager

for superoxide radicals), K2S2O8 (KSO scavenger for electrons) and Ethylenediaminetetraacetic
acid (EDTA, scavenger for holes) over the optimum [Ag-Zn(DCMPPT)(H2O)(OAc)] under
visible light irradiation.
Fig. 14 Performance of [Ag-Zn(DCMPPT)(H2O)(OAc)]complex upon reusable with 5 cycles of
degradation process of AB 1, AV 7 and RR 120 dyes.
Fig. 15 Powder XRD image of [Ag-Zn(DCMPPT)(H2O)(OAc)] photocatalyst after 5 cycles of
degradation of AV 7 dye.

Fig. 1 EDX images of a) [Zn(DCMPPT)(H2O)] and b) [Ag/Zn(DCMPPT)(H2O)(OAc)]
complexes
Fig. 2 FESEM metaphors of a) DCMPPT, b) [Zn(DCMPPT)(H2O)] and c) [Ag-
Zn(DCMPPT)(H2O)(OAc)]

Fig. 3 Thermograms of both the complexes
Fig.
4
XPS
spectra
of
a)
[ZN(DCMPPT)(H2O)]
and
b)
[Ag/Zn(DCMPPT)(H2O)(OAc)] complexes

DCMPPT
Zn(DCMPPT)(H2O)
[Ag/Zn(DCMPPT)(H2O)](OAc)
10
20
30
40
50
2(Degree)
Fig. 5 powder XRD pattern of ligand and complexes
Fig.6
Tentative
structures
of
[Zn(DCMPPT)(H2O)]
and
[Ag-
Zn(DCMPPT)(H2O)(OAc)] complexes

Fig. 7 a) UV-vis and b) UV-vis-DRS spectra of ligand and complexes
Fig. 8 Cyclic voltagrams of ligand and complexes

Fig. 9 PL spectra of ligand and complexes
Fig. 10 Photodegradation of a) AV 7, b) AB 1, and c) RR 120 with [Zn(DCMPPT)(H2O)]
and [Ag-Zn(DCMPPT)(H2O)(OAc)] and d), e) and f) successive absorbance spectral
patterns of AV 7, AB 1 and RR 120 with [Ag-Zn(DCMPPT)(H2O)(OAc)].

Fig. 11 UV-visible spectra of in-situ formed Ag NPs.
Fig. 12 a) Photodegradation of IWW in the presence of [Ag-Zn(DCMPPT)(H2O)(OAc)] b)
successive absorbance spectral pattern and c) box chart plot for % of dye degradation
under visible-light-driven.