Stimuli-responsive materials have garnered significant attention due to their broad application prospects in fields such as optical anti-counterfeiting, sensor technology, and information storage. In this work, two hybrid crystalline materials were successfully synthesized under solvothermal conditions based on Keggin-type polyoxometalates (POMs) and a functionalized isonicotinic acid derivative ligand (L center dot Br = 4-((4-(methylsulfonyl) benzyl)-1-(pyridine-4-carboxylate))pyridinium), namely (L3)center dot[PM12O40]center dot 3H2O (M = Mo in 1, W in 2),which both could present rapid and reversible photochromic performance after photoexcitation, and good electrochemical behavior as well as electrochromic property. Finally, by further assembling them into ionic liquid-enhanced hydrogel matrix, the high-performance ECDs were fabricated and the excellent electrochromic devices performance were presented, which exhibited much faster response speed, higher optical contrast and better cycling stability. Meanwhile, these materials also exhibited promising application potential in the ink-free rewritable printing, and we believe that this work could provide a new material platform and candidate system for the green intelligent display and high-security information encryption technologies.

Electrocatalytic nitrate reduction to ammonia (e-NO3RR) is hindered by competitive adsorption of active hydrogen (*H) and nitrate intermediates on conventional single/heterometallic dual sites. Herein, we construct two novel sandwich-type Co2-GeMo10 and Ni-GeMo10 polyoxometalates (POMs) electrocatalysts with homometallic dual active sites and in-situ formed water-assisted proton channels. Different from previously reported heterometallic tandem catalysts, the single Co or Ni metal species realizes functional differentiation via distinct coordination environments, achieving spatial decoupling of *H generation and nitrate reduction. The intrinsic hydrogen-bond network constructs ordered one-dimensional proton transport pathways, which greatly lowers proton migration barriers and suppresses the competing hydrogen evolution reaction (HER). Benefiting from the above merits, Co2-GeMo10 delivers a superior NH3 yield rate of 22.30 mg h-1 mgcat-1 and a Faradaic efficiency of 86.13%, which is ∼40% higher than our former heterometallic POMs catalysts. Combining in-situ FTIR and DFT calculations, we unambiguously reveal the site-specific catalytic mechanism: ligand-coordinated sites are responsible for water dissociation and *H production, while POM-bonded sites drive the stepwise reduction of nitrate. This work proposes a novel homometallic site engineering strategy, and provides new insights for designing advanced e-NO₃RR electrocatalysts.

Through using a triazole ligand containing a thiophene group, three homopolymolybdate compounds were constructed in traditional hydrothermal and solvothermal environments, namely [Co2(TEP)2(beta-Mo8O26)] (1), [Cu2(TEP)2(beta-Mo8O26)] (2) and [Cu2(TEP)2(H2O)2(beta-Mo8O26)] (3) (TEP = 2-[4-(2-Thiophen-2-yl-ethy1)-4H-[1,2,4]triazol-3-yl]-pyrazine). These three compounds all contain beta-Mo8 anions, in which compounds 1 and 2 have 2D layer structures, and compound 3 exhibits an infinite 1D chain structure. Compounds 1-3 exhibit good electrocatalytic activity and can be used as amperometric sensors for detecting KNO2 and Cr (VI), while also possess good anti-interference ability. In addition, they have a large specific capacitance and can be used as supercapacitor materials. Especially at a current density of 1 A g-1, compound 2 has a specific capacitance of 538.8 F g-1.

Abstract Stimuli-responsive materials have attracted widespread interest due to their broad application prospects in fields such as optical anticounterfeiting, sensor technology, and information storage. In this paper, three Wells–Dawson-type polyoxometalate/lanthanide-based hybrids were hydrothermally synthesized: {[Sm2(L)4(H2O)6][H4P2W18O62]2}·(L)2 (1),{[Dy(L)2(H2O)3] [H2P2W18O62]}·(L)·2H2O (2), and {[La2(L)2(H2O)12][P2W18O62]2}·(L)6·2H2O (3). The three complexes all displayed reversible photochromism under xenon light irradiation. Mechanistic studies (EPR, XPS) reveal that the color change is due to electron transfer from the oxygen atoms of the POM framework to the pyridine nitrogen atoms of the viologen-based ligand. The complexes were incorporated into polyacrylamide/ionic liquid (PAM/PIL) hydrogels, displaying excellent mechanical performance with a distinct lanthanide-dependent trend (La > Sm > Dy), high stretchability (874% strain), conductivity, and reversible photochromism. The hydrogel demonstrates accurate sensing of human motion, such as finger bending, wrist movement, and facial expressions, pointing to potential use in electronic skin. In contrast, the La-based coating on filter paper has been used for inkless printing of patterns, QR codes, and fingerprint-based anticounterfeiting. This combined strategy holds promise for responsive materials in optical and flexible electronics.

In this work, three multi-stimuli-responsive polyoxometalate-viologen-lanthanide (POM-Viologen-Ln) compounds, (Bz2Bipy)1.5[Ln(H2O)3(TeMo6O24)]·DMA·xH2O (x = 1.5, Ln = Sm (1); x = 2, Ln = Eu (2), Tb (3); Bz2Bipy·Cl2 = 1,1'-dibenzyl-[4,4'-bipyridine]-1,1'-diium dichloride) were synthesized via a solvothermal method and characterized structurally using single-crystal X-ray diffraction. These compounds exhibit rapid and reversible photochromism and thermochromism, which are attributed to photo-/thermo-induced electron transfer. This process generates viologen free radicals, as evidenced by UV-Vis, EPR, and XPS analyses. The hydrogels incorporating these compounds exhibit good electrochromic performance, characterized by high optical contrast, fast switching, and high coloration efficiency. Compounds 1-3 exhibit strong lanthanide emissions that are dynamically tunable via light irradiation. Furthermore, the mixed matrix films containing compounds 1-3 demonstrate potential for inkless printing and UV detection. The systematic strategy paves the way for developing multi-stimuli-responsive materials with superior performance and a broader application scope.

The design of electrode materials that combine high efficiency and low cost to effectively reduce environmental pollution and energy consumption represents a core challenge. Herein, a binuclear copper-modified Keggin-type Polyoxometalate (POM) complex based on 1,4-cby ligand (1,4-cby = 1-(4-carboxybenzyl)-4,4'-bipyridine chloride), namely [Cu2(1,4-cby)2(1,4-Hcby)4(H2O)2(GeMo12O40)2]·3H2O (Cu-GeMo12) is synthesized under hydrothermal conditions by utilizing Keggin POMs, renowned as "electron sponges", and binuclear copper complex with excellent catalytic activity. Notably, Cu-GeMo12 achieves an outstanding NH3 yield rate of 14.26 mg h-1 mgcat-1 and a high Faradaic efficiency of 94.06%, significantly surpassing its mononuclear analogue [Cu(1,4-Hcby)4]H3(GeMo12O40)2 (NH3 yield rate of 7.73 mg h-1 mgcat-1 and Faradaic efficiency of 59.83%). Integrated results from in situ Fourier-transform infrared, cyclic voltammetry, and density functional theory calculations reveal that the excellent nitrate-to-ammonia reduction performance of Cu-GeMo12 stems from the continuous electron supply from the POM cluster to the binuclear copper centers, along with the redox-mediating role of the copper sites in promoting the stepwise reduction of nitrogen-containing intermediates. Furthermore, Cu-GeMo12 demonstrates remarkable pseudocapacitive behavior, delivering a high specific capacitance of 1385.09 F·g-1 and retaining 97.27% of its initial capacitance after 5000 cycles. This work provides a novel design strategy for developing POMs functionalized with binuclear metal centers, offering a promising route toward bifunctional materials for applications in electrocatalysis and energy storage.

Using 1,3,5-tris ((pyridine-4-carboxylato)methyl) benzene (L) as a ligand, two Keggin-type polyoxometalates (POMs) hybrid inorganic-metalorganic compounds, Ni[(Ni(μ-OH)(μ-ONa))2(L)2(H2O)3][HPMo12O40]·H2O (Ni-PMo) and Ni[(Ni(μ-OH)(μ-OH-Na)(H2O))2(L)2(H2O)3][SiMo12O40]·2H2O (Ni-SiMo), were prepared under hydrothermal conditions and exploited as bifunctional electrode materials for concurrent supercapacitive energy storage and electroanalytical detection. Both compounds exhibit unique three-dimensional molecular structures through interatomic interactions. Benefiting from the synergistic effect of the unique trinickel clusters, the redox-rich POMs, and the three-dimensional framework, the internal ion/electron transport within the compounds is accelerated, leading to significantly enhanced electrochemical performance. In addition, compared with the parent POMs, both compounds demonstrate superior capacitive and sensing behaviors. In particular, Ni-PMo stands out as the optimal candidate, furnishing a specific capacitance value of 496.92 F g⁻1 under 1 A g⁻1 loading conditions, while maintaining 88.24% of its original capacity after prolonged cycling, and offering a wide linear range of 0.5–35 μM and a low detection limit of 0.67 μM for NO2⁻ sensing. These POMs hybrid inorganic-metalorganic compounds provide new insights and guidance for the synthesis of high-performance bifunctional electrode materials.

To address the pollution of hexavalent chromium (Cr(VI)) in wastewater, this work utilizes the “electron sponge” characteristic of polyoxometalates (POMs) to design and synthesize three POM-based complexes: [CoII(Ccbypy)2(OH)4][H3PMo12O40]·2H2O (1); [NiII(Ccbypy)2(OH)4][H3PMo12O40]·2H2O (2) and [AgI(Ccbypy)2][PMo12O40] (3) (Ccbypy = 4-Carboxy-1-(2′-cyano-biphenyl-4-ylmethyl)-pyridinium). Among them, complex 1 exhibits superior photocatalytic performance, achieving 99.80% reduction of 50 ppm Cr(VI) within 20 min under visible light. Complex 2 shows lower activity (88.51%), while complex 3 achieves comparable efficiency (99.50%) but with higher synthetic cost. Complex 1 exhibits reversible photochromism at the end of the reaction, with a color change from yellow to blue, enabling visual indication of reaction completion. Simultaneously, complex 1 exhibits a unique photocharging behavior. After illumination, it can store electrons within the POM framework and continuously release them in the dark to continuously reduce Cr(VI), achieving a removal rate of 7.82% after 1h of dark reaction. Complex 2 showed negligible color change and dark activity, whereas both were weaker for complex 3 than for complex 1. Combined with DRIFTS and other characterization techniques, the photocatalytic mechanism has been revealed of complex 1. The organic ligand captures photogenerated electrons to form a viologen-like radical, while a portion of the electrons can be further delocalized and stored within the POM cluster, enabling the subsequent reduction of Cr(VI). This work provides a new strategy for constructing a multifunctional photocatalytic system that integrates efficient catalysis, smart-response capability, and energy storage.

In order to continuously remove Cr(VI) from wastewater, it is very important to develop a photocatalyst with stable performance, especially the synergistic two-component system of photosensitive viologen and redox active polyoxometalate with excellent photocatalytic performance. In this study, three new POM/viologen-based crystalline complexes were successfully constructed by a one-pot hydrothermal method, namely, (Hmimb)2·[SiMo12O40] (1), [Ni(mimb)2(SiMo12O40)]·1.8H2O (2), and {[Ni(mimb)2(H2O)3]2·[Ni4(H2O)2(GeMo9O34)2(MoO2)2]}·9H2O (3) (mimb = 1-((3,5-dimethylisoxazol-4-yl)methyl)-[4,4'-bipyridin]-1-ium). Notably, complex 3 features a rarely reported Mo-capped Finke-type POM structure. These complexes were employed as photocatalysts for Cr(VI) reduction. Complex 3 was demonstrated superior charge separation and visible light absorption capabilities in photoelectrochemical tests, which can also be confirmed by the analysis of the minimum hydrogen bond distances and dihedral angles between adjacent unit cells in the crystal structure. Under the optimized conditions, complex 3 achieved 99.80% Cr(VI) reduction within 30 min under visible light. Moreover, complexes 1-3 exhibited strong resistance to ionic interference (anions/cations), making them highly practical for real water matrices applications. After six consecutive cycles, the Cr(VI) removal efficiency showed only 3% fluctuation. Superoxide radicals (•O2-) and photogenerated electrons (e-) dominate photocatalysis according to radical trapping experiments. This work provides critical insights for designing POM/viologen-based crystalline materials for efficient Cr(VI) reduction.

With the aggravation of water pollution and energy consumption, it is urgent to develop environmentally friendly and high-performance electrode materials and photocatalysts. Herein, three octomolybdates-based viologen complexes, {[(M2(14)4(H2O).4(0-M08O26)1(13-M08O26)}.2H2O, {M = Cu (1), Co (2), Ni (3)} have been synthesized and directly applied as photocatalysts and negative electrode materials for supercapacitors. At the current density of 1 Ag-1, complexes 1 - 3 exhibit good specific capacitances (725.6 F g-,, 491.1 F g-1 and 448.4 F g-1). Furthermore, the asymmetric supercapacitor assembled with 1 and activated carbon (AC) (1//AC ASC) exhibits good energy density (6.16 Wh/kg), power density (3000 W kg-1). Moreover, within 30 min, 1-3 also demonstrate outstanding photocatalytic performance (the degradation efficiencies of Cr(VI) reaching 98.15 %, 96.95 % and 95.24 %, respectively.

In this paper, Anderson-type polyoxometalates (POMs) were combined with a viologen ligand to synthesize four compounds under solvothermal conditions, namely (1,3-bcbby)3 & sdot;(TeMo6O24)& sdot;5H2O (1),(1,3-bcbby)& sdot; [M2(H2O)6TeMo6O24] (2: M = Zn; 3: M = Ni; 4: M = Cu) (1,3-bcbby & sdot;2Cl = 1,1 '-bis(3-carboxybenzyl)-4,4 '- bipyridine dichloride). Compound 1 forms one-dimensional supramolecular chains and two-dimensional supramolecular layers through hydrogen bondings. Isomorphic compounds 24 form one-dimensional inorganic chains through covalent bonds between metal ions and POMs, which were then organized into two-dimensional layered structures through hydrogen bondings. All four compounds can be used as color-changing materials. Among them, compounds 1 and 2 exhibit pronounced reversible photochromic properties under a xenon lamp irradiation, while compounds 3 and 4 show good thermochromic properties. Capitalizing on the prompt response of compounds 1 and 2 to ultraviolet light, they are utilized on filter paper for application in ink-free erasable printing. Additionally, when these four compounds are exposed to atmospheres containing ammonia, ethylenediamine or diethylenetriamine, they exhibit distinct color changes. Based on this character, compound 2 was formulated into a portable amine detection strip, which can detect the freshness of pork in real-time through color changes of the detection strip.

The development of highly sensitive photo-assisted electrochemical (PAEC) sensors for trace detection of heavy metal ions (such as chromium (VI) [Cr(VI)]) is crucial. Herein, three isomorphic compounds, namely {[M(H2O)2]2[M(HTetp)(H2O)2]2[M(P4Mo6O31H6)2]}·nH2O (M = Ni/Co/Fe, n = 5 for Ni-P4Mo6, n = 1 for Co-P4Mo6 and Fe-P4Mo6, Tetp = 4-[4-(2-Thiophen-2-yl-ethyl)-4H-[1,2,4]triazole-3-yl]-pyridine) are synthesized and directly used as electrode materials for PAEC sensors to detect Cr(VI). The excellent photo-electrochemical properties of the M{P4Mo6} based compounds originate from two key factors: (1) the synergistic combination of polyoxometalates (POMs) clusters and transition metal-organic components (TMCs), which promotes interfacial charge transfer. (2) the unique hourglass-shaped structure of the M{P4Mo6} clusters, providing abundant active sites for Cr(VI) adsorption and reduction. In particular, Ni-P4Mo6 exhibits a high sensitivity of 584.81 μA·μM-1 and an ultra-low LOD of 2.34 nM under 40 W white light, surpassing most reported Cr(VI) sensors. The detection of Cr(VI) in real water samples highlights the potential of the sensor in environmental monitoring.

Multi-stimuli-responsive materials have garnered widespread attention due to their exceptional potential in various applications, including optical anti-counterfeiting devices, sensor technology, and information storage materials. In this study, we demonstrate the synthesis of four polyoxometalates/viologens (POMs/Vios)-based compounds featuring remarkable color-changing performance, namely, [Zn6(HL)2(H2O)20(TeMo6O24)3]& sdot;6H2O (1), [Co6(HL)2(H2O)20(TeMo6O24)3]& sdot;4H2O (2), [Zn (TeMo6O24)(H2O)2]& sdot;L2 & sdot;6H2O (3), [Co(TeMo6O24)(H2O)2]& sdot;L2 & sdot;6H2O (4) (L & sdot;Cl2 = 1,1 '-[1,3-phenylenebis(methylene)] bis-(4,4 '-bipyridine) dichloride). Compounds 1, 3, and 4 exhibit rapid and reversible photochromic properties, making them suitable for applications in erasable inkless printing and information storage. Furthermore, hydrogels based on these compounds can act as ultraviolet detectors. An innovative electrochromic (EC) hydrogel can be prepared by incorporating compounds 1-4 into polyacrylamide (PAAm). The integrated electrochromic devices (ECDs) based on EC hydrogel can precisely switch between the coloring and fading states through the precise control of different voltages. They are characterized by simple operation, high sensitivity, and low-voltage drive (ranging from -0.21 to -0.35 V). Additionally, compounds 1-4 act as highly efficient organic amine gas sensors. This work is anticipated to provide inspiration for the systematic design and development of diverse color-changing materials that respond to multiple external stimuli.

Efficient removal of Cr(VI) from water represents one of the hotspots in global environmental protection. The POM-based photocatalysts usually exhibit high reduction efficiency in water for Cr(VI) contamination. Herein, two Anderson polyoxometalate-based complexes, namely [CuI2(HTem)4][AlMo6O18(OH)6]2 (1) and [CuII3O (Tpm)3(SO4)(H2O)3][H2AlMo6O18(OH)6]2 & sdot;H2O (2) (Tem = 4-(2-[1, 2, 4] triazole-4-ethyl) morpholine and Tpm = 4-(2-[1, 2, 4] triazole-4-propyl) morpholine). Different length of spacers in Tem and Tpm induces 1 and 2 POM-based complexes with different dimensions. Through using these two complexes as photocatalysts respectively for the reduction of Cr(VI), the results show that 2 could reduce >= 98.17 % Cr(VI) in 30 min. In Cr (VI)-organic matter mixed solution, the photoreduction efficiency of 2 for Cr(VI) is almost not affected by the interference of other organic pollutants. Moreover, 2 has no effect on the content of organic pollutants. So this indicates that the complexes is also selective for the reduction of Cr(VI). Acting as a catalyst, complex 2 is capable of reducing most of the Cr(VI) present in natural water sources such as tap or river water, and it continues to function efficiently under sunlight exposure. Density Functional Theory (DFT) and experiment of free radical capture shows that e- and center dot O2- produced by photocatalysis play a major role in Cr(VI) reduction. The effect of crystal structure and energy band structure of photocatalyst on Cr(VI) reduction was also explored. This research provides rational data for improving the reductive degradation of Cr(VI) in wastewater.

In this paper, two Anderson-type polyoxometalate/viologen-based hybrids were hydrothermally synthesized, {Zn[H(1,4-pmbpy)]2(TeMo6O24)}[H2(1,4-pmbpy)](TeMo6O24)·3H2O (1) and {Co[H(1,4-pmbpy)]2(TeMo6O24)}[H2(1,4-pmbpy)](TeMo6O24)·4H2O (2). Both compounds exhibited rapid, multistimuli-responsive color changes. 1 and 2 showed rapid photochromism under a xenon lamp irradiation, changing from yellow to green within 3 and 5 min, respectively. Meanwhile, compound 2 showed reversible thermochromism. Mechanistic studies (EPR, XPS) reveal that the color change originates from electron transfer from POM oxygen donors to viologen bipyridine nitrogen acceptors, generating viologen radicals. Both compounds selectively detect NH3 and ethylenediamine by size effects. Integration into polyacrylamide/sodium alginate (PAAm/SA) hydrogels yielded gradient photochromism, tunable by crystal concentration, irradiation time, and intensity, along with ultrafast response (2 s), high toughness, and strain-sensitive conductivity. The hydrogel precisely monitors human motions (finger and wrist bending) and facial expressions, demonstrating promise for electronic skin. Moreover, compound 1-based coated filter paper has been successfully utilized in erasable, inkless printing. This synergistic strategy advances stimuli-responsive materials for optical and flexible electronics.

ABSTRACTDesigning efficient photocatalyst has attracted extensive attention for treating polluted wastewater containing Cr (VI). In this work, two viologen/polyoxometalate (POM)‐based compounds were synthesized, [Ni (mimb)2(H2O)4(β‐Mo8O26)]·4H2O (1) and [Zn (mimb)2(H2O)4(β‐Mo8O26)]·4H2O (2) (mimb = 1‐((3,5‐dimethylisoxazol‐4‐yl)methyl)‐[4,4′‐bipyridin]‐1‐ium), through a hydrothermal method and investigated their ability of photocatalytic reduction of Cr (VI). The structures of compounds 1–2 were characterized by single‐crystal X‐ray diffraction, revealing that both possess a zero‐dimensional (0D) structure and can form one‐dimensional (1D) chain structures through hydrogen bondings. Photocatalytic experiments demonstrate that compound 1 has superior photocatalytic performance compared to compound 2. Under optimal conditions (pH = 2, 15 mg catalysts, and 10 mg L−1 Cr (VI) concentration), compound 1 can completely reduce Cr (VI) within 20 min, while compound 2 requires 30 min. Compounds 1–2 also show good stability after photocatalytic reaction, and maintain high photocatalytic activity after five reaction cycles. Additionally, the photocatalytic reaction mechanism of compounds 1–2 was studied, and the free radical scavenging experiments show that its main active species are e−, h+, and ˙O2−. The nitroblue tetrazolium (NBT) experiments further confirm the crucial role of ˙O2− in the photocatalytic process. The good photocatalytic activity, stability, and recyclability of the viologen/POM‐based compounds suggest their potential application in the treatment of wastewater containing Cr (VI).

The remarkable sensitivity of viologen ligands to external stimuli leads to discoloration, which makes them suitable for visual detection. However, the photobleaching of the viologen ligand under prolonged light irradiation has always been a challenging issue. Herein, a novel viologen-polyoxometalate (POM)-based supramolecular compound, [(HMSBP)2(β-SiMo12O40)]·2H2O (V-POM) (MSBP = 1-(4-methanesulfonyl-benzyl)-[4,4']bipyridinyl-1-ium), is synthesized using a hydrothermal method. There are abundant hydrogen bonds in the units of V-POM, which facilitate the formation of a tightly packed two-dimensional (2D) reticular structure through a layer-by-layer assembly process. The 2D V-POM structure is rich in S═O and C═N─H, which makes it possible to detect Ag+ through coordination interaction (LOD = 26.7 nM). Moreover, V-POM exhibits satisfactory recovery rates in detecting Ag+ in various water sources, beverages, and daily necessities. The V-POM-enriched hydrogel is developed, which can quickly and accurately detect Ag+ in beverages and daily necessities by RGB and HSV analysis. Additionally, a fluorescent ink capable of dual information encryption is also created by V-POM. The supramolecular self-assembly of POM and a viologen ligand offers a novel approach to enhance fluorescence stability and visual detection.

Constructing efficient electrode materials and photocatalysts to tackle energy scarcity and water pollution is still extremely challenging. Here, four isomorphic Keggin compounds, namely {[M(Tetp)(6)][H3XMo12O40](2)}center dot 6H(2)O (M=Co/Ni, X=Si/Ge, Co-SiMo12, Ni-SiMo12, Co-GeMo12, Ni-GeMo12, Tetp = 4-[4-(2-Thiophen-2-yl-ethyl)-4H-[1,2,4]triazole-3-yl]-pyridine) were synthesized and directly used as electrode materials for supercapacitors and photocatalysts to reduce Cr (VI). In particular, the combination of polyoxometalates (POMs) that have abundant redox active sites with transition metal-organic compounds (TMCs) improves the internal ion/electron transport efficiency and photocatalytic activity. Specifically, Co-SiMo12 exhibits a higher specific capacitance value (588.46 F g(-1) at 0.5 A g(-1)) and the photocatalytic reduction efficiency (over 90%) of Cr (VI) in 25 min. This work provides a feasible scheme for supercapacitor energy storage and photocatalytic degradation of water pollutants.

To address the challenge of Cr(VI) pollution in wastewater, based on the unique "electronic sponge" properties of polyoxometalates (POMs), we designed and synthesized two redox-active POM-based complexes: [CdⅡ2(dm4bt)4][GeW12O40] (1) and [ZnⅡ2(dm4bt)4][GeW12O40] (2) (dm4bt = 2,2’-dimethyl-4,4’-bithiazole). Complex 1 enables highly sensitive detection of trace Cr(VI) with a detection Limit of 0.21 μM and simultaneously serves as a photocatalyst to reduce Cr(VI) to harmless Cr(III) with 99.85

The development of high-efficiency photocatalytic wastewater treatment technologies depends on designing high-performance photocatalyst. In this work, [TeMo6O24]6- polyoxoanions and viologen ligands were selfassembled to form two dissociated viologen/POM-based compounds containing hydrogen bonding networks, namely (Hmimb)[Co2(H2O)10(TeMo6O24)]center dot 6H2O (1) and [Cd(Hmimb)2(H2O)4](TeMo6O24)center dot 8H2O (2) (mimb = 1-((3,5-dimethylisoxazol-4-yl)methyl)-[4,4 '-bipyridin]-1-ium). These materials could quickly and effectively convert toxic Cr(VI) into less harmful Cr(III) under visible light. After optimizing the reaction conditions, compound 1 exhibited enhanced photocatalytic activity compared with compound 2. It achieved nearly complete removal of Cr(VI) within 30 min under visible light, with a reaction rate constant (k) of 0.2070 min-1. Moreover, compounds 1 - 2 exhibited good anti-interference properties against coexisting anions and cations, demonstrating strong adaptability in real water systems. Even after six consecutive cycles, the Cr(VI) removal efficiency remained approximately 90 %, highlighting their stability and reusability. Compared to our previous research, there were a lot of hydrogen bond interactions in the unit cells of compounds 1 - 2, which could make them have 3D hydrogen bond networks. In addition, compounds 1 - 2 had superior reaction rate constant and cycle stability. Free radical capture experiments confirmed that photogenerated electrons (e-) and superoxide radicals (center dot O2-) were key to the process, and the electron transfer process was indicated by XPS. This study proves the potential of Anderson-type POM/viologen-based materials for removing environmental pollutants.