Modulation of photocatalytic properties through counter-ion substitution: tuning the bandgaps of aromatic sulfonium octamolybdates for efficient photo-degradation of rhodamine B

Singh, Mahender; Pradeep, Chullikkattil P.

doi:10.1039/d1dt03609b

Cited by 10 publications

(14 citation statements)

References 64 publications

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“…One of the pathways is N-de-ethylation which involves stepwise de-ethylation of the dye molecule, resulting in a continuous hypsochromic/blue shift in UV–Vis spectra with time. Another pathway is cycloreversion or chromophore destruction, which does not involve any blue shift. , We did not observe any notable blue shift during the degradation reaction, which indicates that the cycloreversion pathway is mainly followed in the present case. To elucidate the reaction pathway, we collected 100 μL of aliquots from the reaction mixture at 0, 60, and 120 min and subjected to ESI-MS analysis.…”

Section: Resultsmentioning

confidence: 43%

Mixed Organic Counterion Strategy Modulates the Self-Assembly of Polyoxometalate Hybrids into Toroids and Affects Their Photochromic and Photocatalytic Properties

Kar

Pradeep

2022

Inorg. Chem.

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A series of five mixed-counterion polyoxometalate (POM) hybrids 1−5 have been developed starting from the [SiW 12 O 40 ] 4− cluster and two different aryl sulfonium counterions (ASCIs), (4-hydroxyphenyl)dimethylsulfonium (HPDS) and (4-formylphenyl)dimethylsulfonium (FPDS), bearing different functional groups −OH and −CHO, respectively. The HPDS/FPDS counterion ratio in hybrids 1−5 varied as 4:0 (1), 3:1 (2), 2:2 (3), 1:3 (4), and 0:4 (5), and it resulted in a morphological transition of the self-assembly of these hybrids. Hybrid 1 exhibited spherical self-assembly, while hybrid 5 exhibited large toroidal self-assembly predominantly. The hybrids 2−4 gave a mixture of spherical, dimpled spherical, and toroidal self-assemblies in varying amounts, indicating a gradual transition of self-assembly from spherical to toroidal as the percentage of FPDS increases in the system. A plausible explanation for the differences in the self-assembly properties of these hybrids has been proposed based on the differences in the H-bonding interactions of the two counterions with the dispersion medium. The HPDS and FPDS counterions exhibited different HOMO− LUMO gaps, and their varying percentages in hybrids 1−5 led to differences in optical band gaps and photochromic activities. Hybrid 2 showed the lowest band gap value and the best photochromic activity (t 1/2 = 0.72 min) in the series. The influence of the mixed-counterion strategy in catalysis has been demonstrated by evaluating the photocatalytic activity of these hybrids toward rhodamine B dye degradation. The hybrid 4, exhibiting stable toroidal self-assembly, showed the best catalytic activity in the series, probably due to a combination of reasons such as the enhanced surface area due to toroid formation and also the presence of Hbonding −OH functionality on the counterion. Therefore, the present study suggests a new method for altering the self-assembly and the materials and catalytic properties of POM hybrids through a mixed-counterion strategy.

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Section: Resultsmentioning

confidence: 43%

Mixed Organic Counterion Strategy Modulates the Self-Assembly of Polyoxometalate Hybrids into Toroids and Affects Their Photochromic and Photocatalytic Properties

Kar

Pradeep

2022

Inorg. Chem.

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“…In general, POMs can be divided into two categories: isopolyoxometalates and heteropolyoxometalates. [85][86] ) are obtained by condensation of different kinds of inorganic oxoacid ions. Now, according to this classification, all the reported articles combining POMs with viologen are described in detail.…”

Section: Polyoxometalates and Viologenmentioning

confidence: 99%

“…Furthermore, the electronic changes (gain or loss) of POMs do not cause changes in their molecular structures. In general, POMs can be divided into two categories: isopolyoxometalates and heteropolyoxometalates [85–86] . Among them, iso‐POMs (such as Mo 8 O 26 4− , W 7 O 24 6− ) are obtained by condensation of the same inorganic oxoacid ions, while hetero‐POMs (such as PW 12 O 40 3− , SiW 12 O 40 4− ) are obtained by condensation of different kinds of inorganic oxoacid ions.…”

Section: Synthesesmentioning

confidence: 99%

Applications of Viologens in Organic and Inorganic Discoloration Materials

Ying

Tian

2022

ChemPlusChem

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Viologen derived from 4,4’‐bipyridine has attracted much attention because of its color changing properties with electron transfer, unique redox stability and structural diversity. These characteristics have led to its successful use in various applications, in particular in color‐changing materials. In the past few years, researchers have been working on the syntheses of viologen‐based color‐changing functional materials, and such materials have been widely used in many fields. In photochromic materials, it is used as anti‐counterfeiting material; in thermochromic, it is used as memory storage material, and in electrochromic, it is used as a battery material. This Review discusses the progress of viologen in organic and inorganic discoloration materials in recent years. The syntheses of viologen and its derivatives are summarized, and its application in the field of discoloration materials is introduced.

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“…These peaks appeared at binding energies of 166.1 and 167.4 eV for hybrid 1; at 166.0 and 167.2 eV for hybrid 2; at 166.0 and 167.1 eV for hybrid 3, and at 166.1 and 167.3 eV for hybrid 4, respectively. 33 In the case of hybrids 1 and 3, the Mo centers showed two doublets due to spin−orbit coupling. 34 The doublet observed for hybrid 1 at higher binding energies, i.e., 232.9 and 236.0 eV, corresponds to Mo 6+ 3d 5/2 and Mo 6+ 3d 3/2 , while the doublet observed at lower binding energies, i.e., 231.8 and 234.9 eV, corresponds to Mo 5+ 3d 5/2 and Mo 5+ 3d 3/2 .…”

Section: ■ Introductionmentioning

confidence: 99%

“…It has been noted that the reaction medium's pH plays an important role in Cr(VI) reduction reactions. 33 Therefore, we performed the reduction experiment under three different pH conditions to study the effect of pH. The natural pH of the dichromate solution used in the experiment was nearly 5.0, and we decided to check the photocatalytic reduction at this pH condition.…”

Section: ■ Introductionmentioning

confidence: 99%

Keggin Cluster Modulated Photocatalytic Activity of Aryl Sulfonium Polyoxometalate Hybrids toward Dichromate Reduction

2022

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Dichromate (Cr2O7 2–) ion having chromium in its +6 oxidation state is a carcinogen and a potential threat to humans and aquatic life. The photocatalytic reduction of toxic Cr(VI) species into less toxic Cr(III) is an important target in heterogeneous catalysis. In this work, the catalytic activities of a series of Keggin cluster-based aryl sulfonium polyoxometalate hybrids, (FPDS)3[PMo12O40] (1), (FPDS)3[PW12O40] (2), (FPDS)4[SiMo12O40] (3), and (FPDS)4[SiW12O40] (4), toward the photocatalytic reduction of Cr(VI) have been analyzed and compared. Here, we used the aryl sulfonium counterions to modulate the POM cluster’s solubility in water and stabilize the photogenerated e––h+ pair on the cluster. All of the hybrids 1–4 catalyzed the reduction of Cr(VI) to Cr(III) under ultraviolet (UV) irradiation, and their photocatalytic efficiencies followed the order hybrid 1 > hybrid 3 > hybrid 2 > hybrid 4, with the rate-constant values of 0.048, 0.0056, 0.0035, and 0.0028 min–1, respectively. Hybrid 1 with [PMo12O40]3– Keggin cluster exhibited the best photocatalytic activity in the series yielding a 99% reduction in 120 min. The reasons behind the best photocatalytic activity of hybrid 1 are identified as its low band gap, less charge recombination, and fast photoresponse. The electron-trapping analyses performed using AgNO3 revealed electrons as the main reactive species responsible for the photocatalytic reduction of Cr(VI). A plausible photocatalytic mechanism has also been proposed based on electron-trapping experiments. The present study shows that aryl sulfonium Keggin hybrids can function as efficient photocatalysts for Cr(VI) reduction, and their catalytic efficiency varies with the nature of the Keggin cluster.

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Modulation of photocatalytic properties through counter-ion substitution: tuning the bandgaps of aromatic sulfonium octamolybdates for efficient photo-degradation of rhodamine B

Abstract: Modulating the photocatalytic properties of polyoxometalate-organic hybrids through counterion substitution is a less explored concept. In this study, a new series of aromatic sulfonium counterions (ASCs) having the general formula...

Cited by 10 publications

References 64 publications

Mixed Organic Counterion Strategy Modulates the Self-Assembly of Polyoxometalate Hybrids into Toroids and Affects Their Photochromic and Photocatalytic Properties

Mixed Organic Counterion Strategy Modulates the Self-Assembly of Polyoxometalate Hybrids into Toroids and Affects Their Photochromic and Photocatalytic Properties

Applications of Viologens in Organic and Inorganic Discoloration Materials

Keggin Cluster Modulated Photocatalytic Activity of Aryl Sulfonium Polyoxometalate Hybrids toward Dichromate Reduction

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