Search

We present a simple and easy-to-scale synthetic method to plug common organic photosensitizers into a cyanide-based network structure for the development of photosensitizer-water oxidation catalyst (PS-WOC) dyad assemblies for the photocatalytic water oxidation process. Three photosensitizers, one of which absorbs red light similar to P680 in photosystem II, were utilized to harvest different regions of the solar spectrum. Photosensitizers are covalently coordinated to CoFe Prussian blue structures to prepare PS-WOC dyads. All dyads exhibit steady water oxidation catalytic activities throughout a 6 h photocatalytic experiment. Our results demonstrate that the covalent coordination between the PS and WOC group not only enhances the photocatalytic activity but also improves the robustness of the organic PS group. The photocatalytic activity of "plug and play" dyads relies on several structural and electronic parameters, including the position of the energy levels of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the PS with respect to the HOMO level of the catalytic site, the intensity and wavelength of the absorption band of the PS, and the number of catalytic sites.

For most semiconductors, especially the visible-light-absorbing ones, the carrier diffusion length is significantly shorter than the light penetration depth, limiting their photoactivities. This limitation could be mitigated through the use of subwavelength semiconductor-based metasurfaces and metamaterials. In this paper, a large-scale compatible metasurface photocathode, made of densely packed disordered p-type chromium oxide (CrOX), is developed to be utilized in photoelectrochemical (PEC) hydrogen generation. For this purpose, first, tightly packed random Cr nanorods are fabricated using an oblique angle deposition technique. Afterward, an annealing step is applied to the sample to transform these metallic units into a semiconducting p-type CrOX-based metasurface. Based on the experimental characterization results and numerical simulations, the proposed design can provide strong light-matter interactions in an ultra-broadband-wavelength range, mainly due to its multidimensional random geometry and ultrasmall gap sizes. Finally, to substantiate the activity of the CrOXnanorods, a core-crown geometry is developed where the NiOXcapping layer catalyzes the hydrogen evolution reaction (HER). The proposed heterostructure metasurface absorber can impose photocurrent values as large as 50 μA cm-2with a photocurrent spectral response extended up to 500 nm. Moreover, the electrode shows outstanding operation under light irradiation for 9 hours. This work demonstrates a simple, scalable design strategy to fabricate low-cost and stable photocathodes for PEC hydrogen evolution. © 2022 American Chemical Society. All rights reserved.

The elucidation of the ideal coordination environment of a catalytic site has been at the heart of catalytic applications. Herein, we show that the water oxidation activities of catalytic cobalt sites in a Prussian blue (PB) structure could be tuned systematically by decorating its coordination sphere with a combination of cyanide and bidentate pyridyl groups. K-0.1[Co(bpy)](2.9)[Fe(CN)(6)](2) ([Cobpy-Fe]), K-0.2[Co(phen)](2.8)[Fe(CN)(6)](2) ([Cophen-Fe]), {[Co(bpy)(2)](3) [Fe(CN)(6)](2) 1[Fe(CN)(6)](1/3) ([Cobpy2-Fe]), and {[Co(phen)(2)](3)[Fe(CN)(6)](2)}[Fe(CN)(6)](1/3) CI0.11 ([Cophen2 - Fe]) were prepared by introducing bidentate pyridyl groups (phen: 1,10-phenanthroline, bpy: 2,2'-bipyridine) to the common synthetic protocol of Co-Fe Prussian blue analogues. Characterization studies indicate that [Cobpy2-Fe] and [Cophen2-Fe] adopt a pentanu- clear molecular structure, while [Cobpy-Fe] and [Cophen-Fe] could be described as cyanide-based coordination polymers with lower-dimensionality and less crystalline nature compared to the regular Co-Fe Prussian blue analogue (PBA), K0.1Co2.9[Fe(CN)(6)](2)([Co-Fe]). Photocatalytic studies reveal that the activities of [Cobpy-Fe] and [Cophen-Fe] are significantly enhanced compared to those of [Co-Fe], while molecular [Cobpy2-Fe] and [Cophen2-Fe] are inactive toward water oxidation. [Cobpy-Fe] and [Cophen-Fe] exhibit upper-bound turnover frequencies (TOFs) of 1.3 and 0.7 s(-1), respectively, which are similar to 50 times higher than that of [Co-Fe] (1.8 X 10(-2) s(-1)). The complete inactivity of [Cobpy2-Fe] and [Cophen2-Fe] confirms the critical role of aqua coordination to the catalytic cobalt sites for oxygen evolution reaction (OER). Computational studies show that bidentate pyridyl groups enhance the susceptibility of the rate-determining Co(IV)-oxo species to the nucleophilic water attack during the critical O-O bond formation. This study opens a new route toward increasing the intrinsic water oxidation activity of the catalytic sites in PB coordination polymers.

The frequent detection of physiological glucose levels from human blood or sweat requires the development of low-cost electrodes with high sensitivity and selectivity. In this work, we prepared a series of Prussian blue (PB) modified carbon cloth (CC) electrodes with different cyanoferrate groups. We achieved a sensitivity as high as 145.43 μA mm−1cm−2 in a 0.1–6.5 mm concentration range with a response time below 2 s under physiological pH. The electrodes exhibited a superior selectivity of glucose in the presence of interfering agents, including sucrose, lactose, NaCl, ascorbic acid, and uric acid. The electrodes also showed outstanding long-term stability over 15 days. Furthermore, we performed comprehensive electrochemical and characterization studies to elucidate the role of the cyanoferrate group on the morphologic and electronic properties of non-enzymatic glucose sensors.

In this paper, a visible light driven plasmonic based photoelectrochemical water splitting (PEC-WS) cell is designed with an elegant two-step fabrication route. First, titanium dioxide (TiO2) nanowires (NWs) were synthesized using the hydrothermal method. Then, angled deposition was used to selectively coat the tips of the NWs yielding Au-capped TiO2 NWs with multiple sizes and shapes. The provided randomness leads to a multi-resonant system where the superposition of these resonance modes leads to an overall broadband absorption. The excited localized surface resonance (LSPR) modes contribute to the performance enhancement of the cell via near field effects and a hot electron injection mechanism. Moreover, these nanotips can trigger the formation of Fabry-Pérot (FP) cavity modes. The combination of the above-mentioned mechanisms leads to a high performance visible light driven plasmonic cell. At an applied potential of 1.23 V vs RHE, a photocurrent value as high as 82 μA/cm2 is acquired for the plasmonic based photoanode. The proposed design strategy is a large scale compatible route with no material restriction. Therefore, vast variety of semiconductor-metal pairs can be fabricated to obtain highly efficient water splitting cell for hydrogen generation. This work is supported by the Scientific and TechnologicalResearch Council of Turkey (TUBITAK), grant number215Z249. This work is supported by the project DPT-HAMIT aswell as TUBITAK under the project nos. 113E331, 114E374, and115F560

A recently emerging visible light-absorbing semiconductor, brown TiO

A recently emerging visible light-absorbing semiconductor, brown TiO2 (b-TiO2), was coupled with a CoFe Prussian blue (PB) analogue to prepare an entirely earth-abundant semiconductor/water oxidation catalyst hybrid assembly. PB/b-TiO2 exhibits a sevenfold higher photocatalytic water oxidation activity compared to b-TiO2. An elegant band alignment unified with the optical absorption of b-TiO2 and excellent electronic dynamics of PB yield a high-performance photocatalytic system.

Prussian blue (PB) and its analogues (PBAs) have at least a three-century-long history in coordination chemistry. Recently, cobalt-based PBAs have been acknowledged as efficient and robust water oxidation catalysts. Given the flexibility in their synthesis, the structure and morphology of cobalt-based PBAs have been modified for enhanced catalytic activity under electrochemical (EC), photocatalytic (PC), and photoelectrochemical (PEC) conditions. Here, in this review, the work on cobalt-based PBAs is presented in four sections: i) electrocatalytic water oxidation with bare PBAs, ii) photocatalytic processes in the presence of a photosensitizer (PS), iii) photoelectrochemical water oxidation by coupling PBAs to proper semiconductors (SCs), and iv) the utilization of PBA-PS assemblies coated on SCs for the dye-sensitized photoelectrochemical water oxidation. This review will guide readers through the structure and catalytic activity relationship in cobalt-based PBAs by describing the role of each structural component. Furthermore, this review aims to provide insight into common strategies to enhance the catalytic activity of PBAs.

A facial and large-scale compatible fabrication route is established, affording a high-performance heterogeneous plasmonic-based photoelectrode for water oxidation that incorporates a CoFe-Prussian blue analog (PBA) structure as the water oxidation catalytic center. For this purpose, an angled deposition of gold (Au) was used to selectively coat the tips of the bismuth vanadate (BiVO

Herein, we establish a simple synthetic strategy affording a heterogeneous, precious metal-free, dye-sensitized photoelectrode for water oxidation, which incorporates a Prussian blue (PB) structure for the sensitization of TiO2 and water oxidation catalysis. Our approach involves the use of a Fe(CN)(5) bridging group not only as a cyanide precursor for the formation of a PB-type structure but also as an electron shuttle between an organic chromophore and the catalytic center. The resulting hetero-functional PB-modified TiO2 electrode demonstrates a low-cost and easy-to-construct photoanode, which exhibits favorable electron transfers with a remarkable excited state lifetime on the order of nanoseconds and an extended light absorption capacity of up to 500 nm. Our approach paves the way for a new family of precious metal-free robust dye-sensitized photoelectrodes for water oxidation, in which a variety of common organic chromophores can be employed in conjunction with CoFe PB structures.

A facial and large-scale compatible fabrication route is established, affording a high-performance heterogeneous plasmonic-based photoelectrode for water oxidation that incorporates a CoFe-Prussian blue analog (PBA) structure as the water oxidation catalytic center. For this purpose, an angled deposition of gold (Au) was used to selectively coat the tips of the bismuth vanadate (BiVO4 ) nanostructures, yielding Au-capped BiVO4 (Au-BiVO4 ). The formation of multiple size/dimension Au capping islands provides strong light-matter interactions at nanoscale dimensions. These plasmonic particles not only enhance light absorption in the bulk BiVO4 (through the excitation of Fabry-Perot (FP) modes) but also contribute to photocurrent generation through the injection of sub-band-gap hot electrons. To substantiate the activity of the photoanodes, the interfacial electron dynamics are significantly improved by using a PBA water oxidation catalyst (WOC) resulting in an Au-BiVO4 /PBA assembly. At 1.23 V (vs. RHE), the photocurrent value for a bare BiVO4 photoanode was obtained as 190 μA cm-2 , whereas it was boosted to 295 μA cm-2 and 1800 μA cm-2 for Au-BiVO4 and Au-BiVO4 /PBA, respectively. Our results suggest that this simple and facial synthetic approach paves the way for plasmonic-based solar water splitting, in which a variety of common metals and semiconductors can be employed in conjunction with catalyst designs., Scientific and Technological Research Council of Turkey (TÜBİTAK); DPT-HAMIT; Turkish Academy of Sciences; TÜBA-GEBİP for Young İnvestigator Award; BAGEP for Young Scientist Award

An entirely earth-abundant chromophore-relay water oxidation catalyst triad system, which is robust and efficient at neutral pH, is presented. The synthesis involves the coordination of a porphyrin derivative to a bridging Fe(CN)5 group, which is then reacted with Co ions to prepare a covalently linked chromophore-Prussian blue analogue assembly. Light-driven water oxidation studies in the presence of an electron scavenger indicate that the triad is active and it maintains a steady activity for at least three hours. Transient absorption experiments and computational studies reveal that the Fe(CN)5 group is more than a linker as it takes part in electron-transfer and co-operates with porphyrin in the charge separation process. This work is supported by the Scientific and Technological Research Council of Turkey (TUBITAK), grant number 215Z249. F.K. and Y.D. thank TÜBA-GEBİP for young investigator awards and BAGEP for a young scientist award.

A CoFe Prussian blue analogue (CoFe PB) modified FTO electrode, prepared via a facile electrodeposition method, is investigated as a non-enzymatic glucose sensor under neutral conditions. The electrode exhibits a linear detection of glucose in the 0.1–8.2 mmol/L range with a detection limit of 67 μM, a sensitivity of 18.69 μA/mM.cm2, and a fast response time of less than 7 s under neutral conditions. Its stability is confirmed with both electrochemical experiments and characterization studies performed on the pristine and post-mortem electrode. We also conducted a comprehensive electrochemical analysis to elucidate the identity of the active site and the glucose oxidation mechanism on the Prussian blue surface.

The replacement of traditional ruthenium-based photosensitizers with low-cost and abundant iron analogs is a key step for the advancement of scalable and sustainable dye-sensitized water splitting cells. In this proof-of-concept study, a pyridinium ligand coordinated pentacyanoferrate(II) chromophore is used to construct a cyanide-based CoFe extended bulk framework, in which the iron photosensitizer units are connected to cobalt water oxidation catalytic sites through cyanide linkers. The iron-sensitized photoanode exhibits exceptional stability for at least 5 h at pH 7 and features its photosensitizing ability with an incident photon-to-current conversion capacity up to 500 nm with nanosecond scale excited state lifetime. Ultrafast transient absorption and computational studies reveal that iron and cobalt sites mutually support each other for charge separation via short bridging cyanide groups and for injection to the semiconductor in our proof-of-concept photoelectrochemical device. The reorganization of the excited states due to the mixing of electronic states of metal-based orbitals subsequently tailor the electron transfer cascade during the photoelectrochemical process. This breakthrough in chromophore-catalyst assemblies will spark interest in dye-sensitization with robust bulk systems for photoconversion applications.

Activating agents play significant roles in the preparation of activated carbon (AC) from biomasses and their wastes, which are widely used in AC production. Application methods are also important for the production process. Products give remarkable ideas regarding the method and heat treatment process. The activated carbon was produced from waste tea in accordance with either the conventional method or microwave energy pretreated method using phosphoric acid (H3PO4) as activating agent. The yields of the activated carbons were 51.8% for conventional method and 46.0% for microwave pretreated method. The acid suppressed the formation of tar and promoted the amount of solid and aromatic structure accordance to sp2 hybridisation. Additionally, the waste tea was directly carbonised (without H3PO4) and the yield was 36.3%. Major gas (H2, CH4, C2H6, C2H4, CO2 and CO) products obtained during heat treatment process in a conventional furnace were examined in terms of quantity and quality. The solid products were characterised in terms of surface area, pore size and surface properties. The result of gas analysis showed that phosphoric acid affected formation of activated carbon mechanism and significant reactions occurred during microwave pretreatment process. The authors gratefully acknowledge the support of The Scientific and Technological Research Council of Turkey (TUBITAK), Turkey, for this research (Project No. 109M400 ). We also express our appreciation to Prof. Dr. Ali Sinag, Department of Chemistry, Ankara University, Turkey, for the Micro GC Analysis. Appendix A