Salicylic acid as a tridentate anchoring group for azo-bridged zinc porphyrin in dye-sensitized solar cells

Chlorophyll sensitized and salicylic acid functionalized TiO2 nanoparticles as a stable and efficient catalyst for the photocatalytic degradation of ciprofloxacin with visible light

Developing efficient and stable visible light active photocatalyst has significant environmental applications. Though dye sensitization of TiO₂ nanoparticles with natural chlorophyll pigments can potentially impart visible light activity, their long-term stability is a major concern. We investigated the functionalization of TiO₂ with salicylic acid, and subsequent sensitization with chlorophylls to improve the catalyst stability for the photocatalytic degradation of Ciprofloxacin (CPX) under visible light. A significant improvement in the degradation efficiency and catalyst stability was observed for five reuse cycles. Further, an optimum CPX degradation of ∼75% was achieved with 0.75 g L^-1 catalyst dosage of 0.1 chl/0.1 SA-TiO₂, initial pH of 6, and 10 ppm of initial CPX for a visible light exposure of 2 h. The degradation followed the pseudo-second-order kinetics. In addition, the ciprofloxacin degradation was reduced in the wastewater matrix system due to the presence of other scavenging species such as chlorides, sulphates, and alkalinity. Significant reduction in the toxicity of degradation compounds after the photocatalytic degradation was observed in comparison to parent CPX. Further, the degradation pathway and plausible mechanism of degradation of CPX were also proposed.

Binding Modes of Salicylic Acids to Titanium Oxide Molecular Surfaces

A set of titanium oxide clusters (TOCs) comprised of 4 to 16 Ti atoms are synthesized with substituted salicylates (SSAs). The interfacial coordination environment of these SSA/Ti oxide hybrids are surveyed and found to be limited to four binding modes, with the bridging chelate mode being the most common one. The SSA-functionalized TOCs show strong visible light absorption properties. The contribution of the SSAs in the frontier orbitals of the TOCs are analyzed by using TD-DFT calculations based on the molecular geometries determined by X-ray diffraction. For TOCs of relatively high O/Ti ratio, the SSAs narrow the band gap of the TOCs by contributing solely to the HOMOs. Both binding modes and locations of the SSAs are important for the roles of SSAs in changing the HOMOs and thereby the absorption onsets.

Theoretical study on the effect of different π-linker on the performance of sensitizer in carbazole-based dyes

Derived from diarylamine sensitizer diphenyl-(7-pyridin-4-yl-9H-carbazol-2-yl)-amine (N13), a series of novel D[Formula: see text]A carbazole-based organic dye sensitizers with different [Formula: see text]-linkers were designed for searching more effective sensitizers in dye-sensitized solar cells (DSSCs) design. Optimized geometries, electronic structure, and other parameters, which can evaluate the performance of DSSCs effectively and intuitively, were theoretically calculated by density functional theory (DFT) and time-dependent DFT methods at the M06/6-31G(d,p) level. The results indicated that the maximum absorption wavelength of designed dye was red-shifted and the molar absorption coefficient ([Formula: see text]) became higher. This phenomenon can be explained by the modification of the [Formula: see text]-bridge. The simulated Ultraviolet–visible spectroscopy (UV-Vis) absorption spectrum showed that the designed N,N-diphenyl-7-(5-(7-(5-(pyridin-4-yl)thiophen-2-yl)benzo[c][1,2,5]thiadiazol-4-yl)thiophen-2-yl)-9H-carbazol-2-amine (N22) dye presents the largest red-shifted absorption band and the designed (E)-N,N-diphenyl-7-(2-(5[Formula: see text]-(pyridin-4-yl)-[2,2[Formula: see text]-bithiophene]-5-yl)vinyl)-9H-carbazol-2-amine (N21) dye showed the largest [Formula: see text], both of them depicted a high short-circuit photocurrent density ([Formula: see text]. Meanwhile, the charge separation hampered by long [Formula: see text]-linkers was also observed. These results are helpful for designing new sensitizers and providing effective guiding to experimental synthesis.

Surface Grafting of Ru(II) Diazonium-Based Sensitizers on Metal Oxides Enhances Alkaline Stability for Solar Energy Conversion

The electrografting of [Ru(ttt)(tpy-C₆H₄-N₂⁺)]³⁺, where "ttt" is 4,4',4″-tri-tert-butyl-2,2':6',2″-terpyridine, was investigated on several wide band gap metal oxide surfaces (TiO₂, SnO₂, ZrO₂, ZnO, In₂O₃:Sn) and compared to structurally analogous sensitizers that differed only by the anchoring group, i.e., -PO₃H₂ and -COOH. An optimized procedure for diazonium electrografting to semiconductor metal oxides is presented that allowed surface coverages that ranged between 4.7 × 10^-8 and 10.6 × 10^-8 mol cm^-2 depending on the nature of the metal oxide. FTIR analysis showed the disappearance of the diazonium stretch at 2266 cm^-1 after electrografting. XPS analysis revealed a characteristic peak of Ru 3d at 285 eV as well as a peak at 531.6 eV that was attributed to O 1s in Ti-O-C bonds. Photocurrents were measured to assess electron injection efficiency of these modified surfaces. The electrografted sensitizers exhibited excellent stability across a range of pHs spanning from 1 to 14, where classical binding groups such as carboxylic and phosphonic derivatives were hydrolyzed.

A new class of triphenylamine-based novel sensitizers for DSSCs: a comparative study of three different anchoring groups

Triphenylamine-based dyes with chloro groups suitably placed on their π-linkers affect DSSC efficiency.

Photovoltaic Properties and Long-Term Durability of Porphyrin-Sensitized Solar Cells with Silicon-Based Anchoring Groups

Anchoring groups for dye-sensitized solar cells (DSSCs) play a decisive role in high-power conversion efficiency (η) and long-term cell durability. To date, a carboxylic acid is the most widely used anchoring group for DSSCs. However, the carboxylic acid tends to dissociate from a TiO₂ surface during the cell operation as well as in the presence of water. Considering that the dye dissociation from TiO₂ leads to a decrease in the cell performance, stable anchoring groups are highly desirable to achieve long-term durability of DSSCs toward their practical application. In this study, we designed and synthesized a series of porphyrin dyes with the triethoxysilyl anchoring groups, ZnPSi1, ZnPSi2, and ZnPSi3, to evaluate the effects of the silicon-based anchoring group on cell durability and photovoltaic properties. The DSSCs based on ZnPSi1, ZnPSi2, and ZnPSi3 exhibited moderate η-values of 2.2, 4.7, and 2.3%, respectively. It is noteworthy that the η-value of the DSSC based on ZnPSi2 (4.7%) is the highest among DSSCs based on porphyrin dyes with silicon-based anchoring groups. The moderate η-values are mainly attributed to the low charge collection efficiency originating from the low surface coverage and plausible tilted geometry of the dyes on TiO₂. More importantly, we demonstrated that the DSSC based on ZnPSi2 revealed higher long-term cell durability under illumination than that based on reference porphyrin YD2 -o -C8 having a conventional carboxylic acid anchoring group.

Multilayer Dye Aggregation at Dye/TiO2 Interface via π…π Stacking and Hydrogen Bond and Its Impact on Solar Cell Performance: A DFT Analysis

Multilayer dye aggregation at the dye/TiO₂ interface of dye-sensitized solar cells is probed via first principles calculations, using p-methyl red azo dye as an example. Our calculations suggest that the multilayer dye aggregates at the TiO₂ surface can be stabilized by π…π stacking and hydrogen bond interactions. Compared with previous two-dimensional monolayer dye/TiO₂ model, the multilayer dye aggregation model proposed in this study constructs a three-dimensional multilayer dye/TiO₂ interfacial structure, and provides a better agreement between experimental and computational results in dye coverage and dye adsorption energy. In particular, a dimer forms by π…π stacking interactions between two neighboring azo molecules, while one of them chemisorbs on the TiO₂ surface; a trimer may form by introducing one additional azo molecule on the dimer through a hydrogen bond between two carboxylic acid groups. Different forms of multilayer dye aggregates, either stabilized by π…π stacking or hydrogen bond, exhibit varied optical absorption spectra and electronic properties. Such variations could have a critical impact on the performance of dye sensitized solar cells.

Fe-tannic acid complex dye as photo sensitizer for different morphological ZnO based DSSCs

In this paper we have synthesized different morphological ZnO nanostructures via microwave hydrothermal methods at low temperature within a short time. We described different morphologies of ZnO at different Zn(NO3)2/KOH mole ratio. The ZnO nanostructures were characterized via X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and UV-vis spectrophotometry. All ZnO structures have hexagonal wurtzite type structures. The FESEM images showed various morphologies of ZnO such as plate, rod and nanoparticles. Dye sensitized solar cells have been assembled by these different morphological structures photo electrode and tannic acid or Fe-tannic acid complex dye as sensitizer. We have achieved at maximum efficiencies of photovoltaic cells prepared with ZnO plate in all dye systems. The conversion efficiencies of dye sensitized solar cells are 0.37% and 1.00% with tannic acid and Fe-tannic acid complex dye, respectively.

Electron-Transfer Kinetics within Supramolecular Assemblies of Donor Tetrapyrrolytic Dyes and an Acceptor Palladium Cluster

9,18,27,36-Tetrakis[meso-(4-carboxyphenyl)]tetrabenzoporphyrinatozinc(II) (TCPBP, as a sodium salt) was prepared in order to compare its photoinduced electron-transfer behavior toward unsaturated cluster Pd3(dppm)3(CO)(2+) ([Pd3(2+)]; dppm = Ph2PCH2PPh2 as a PF6(-) salt) with that of 5,10,15,20-tetrakis[meso-(4-carboxyphenyl)]porphyrinatozinc(II) (TCPP) in nonluminescent assemblies of the type dye···[Pd3(2+)]x (x = 0-4; dye = TCPP and TCPBP) using femtosecond transient absorption spectroscopy. Binding constants extracted from UV-vis titration methods are the same as those extracted from fluorescence quenching measurements (static model), and both indicate that the TCPBP···[Pd3(2+)]x assemblies (K14 = 36000 M(-1)) are slightly more stable than those for TCPP···[Pd3(2+)]x (K14 = 27000 M(-1)). Density functional theory computations (B3LYP) corroborate this finding because the average ionic Pd···O distance is shorter in the TCPBP···[Pd3(2+)] assembly compared to that for TCPP···[Pd3(2+)]. Despite the difference in the binding constants and excited-state driving forces for the photoinduced electron transfer in dye*···[Pd3(2+)] → dye(•+)···[Pd3(•+)], the time scale for this process is ultrafast in both cases (<85 fs). The time scales for the back electron transfers (dye(•+)···[Pd3(•+)] → dye···[Pd3(2+)]) occurring in the various observed species (dye···[Pd3(2+)]x; x = 0-4) are the same for both series of assemblies. It is concluded that the structural modification on going from porphyrin to tetrabenzoporphyrin does not greatly affect the kinetic behavior in these processes.

Molecular engineering of new phenothiazine-based D–A–π–A dyes for dye-sensitized solar cells

We report new D–A–π–A dyes gained by molecular engineering for DSSCs, achieving a highest photoelectric conversion efficiency of 6.35%.

Can nitro groups really anchor onto TiO2? Case study of dye-to-TiO2adsorption using azo dyes with NO2substituents

Molecular rationalization of the photovoltaic performance of dye-sensitized solar cells that employ azo dyes bearing a NO₂anchoring group.

Anchoring groups for dye-sensitized solar cells

The dyes in dye-sensitized solar cells (DSSCs) require one or more chemical substituents that can act as an anchor, enabling their adsorption onto a metal oxide substrate. This adsorption provides a means for electron injection, which is the process that initiates the electrical circuit in a DSSC. Understanding the structure of various DSSC anchors and the search for new anchors are critical factors for the development of improved DSSCs. Traditionally, carboxylic acid and cyanoacrylic acid groups are employed as dye anchors in DSSCs. In recent years, novel anchor groups have emerged, which make a larger pool of materials available for DSSC dyes, and their associated physical and chemical characteristics offer interesting effects at the interface between dye and metal oxide. This review focuses especially on the structural aspects of these novel dye anchors for TiO2-based DSSCs, including pyridine, phosphonic acid, tetracyanate, perylene dicarboxylic acid anhydride, 2-hydroxylbenzonitrile, 8-hydroxylquinoline, pyridine-N-oxide, hydroxylpyridium, catechol, hydroxamate, sulfonic acid, acetylacetanate, boronic acid, nitro, tetrazole, rhodanine, and salicylic acid substituents. We anticipate that further exploration and understanding of these new types of anchoring groups for TiO2 substrates will not only contribute to the development of advanced DSSCs, but also of quantum dot-sensitized solar cells, water splitting systems, and other self-assembled monolayer-based technologies.

TiO2-B nanorod based competitive-like non-enzymatic photoelectrochemical sensing platform for noninvasive glucose detection

A new competitive-like non-enzymatic photoelectrochemical biosensor was established for the first time based on a TiO₂-B nanorod platform for noninvasive glucose detection.

Porphyrins as excellent dyes for dye-sensitized solar cells: recent developments and insights

Porphyrin sensitizers have exhibited power conversion efficiencies that are comparable to or even higher than those of well-established highly efficient DSSCs based on ruthenium complexes.

Variation in optoelectronic properties of azo dye-sensitized TiO2 semiconductor interfaces with different adsorption anchors: carboxylate, sulfonate, hydroxyl and pyridyl groups

The optoelectronic properties of four azo dye-sensitized TiO2 interfaces are systematically studied as a function of a changing dye anchoring group: carboxylate, sulfonate, hydroxyl, and pyridyl. The variation in optoelectronic properties of the free dyes and those in dye/TiO2 nanocomposites are studied both experimentally and computationally, in the context of prospective dye-sensitized solar cell (DSSC) applications. Experimental UV/vis absorption spectroscopy, cyclic voltammetry, and DSSC device performance testing reveal a strong dependence on the nature of the anchor of the optoelectronic properties of these dyes, both in solution and as dye/TiO2 nanocomposites. First-principles calculations on both an isolated dye/TiO2 cluster model (using localized basis sets) and each dye modeled onto the surface of a 2D periodic TiO2 nanostructure (using plane wave basis sets) are presented. Detailed examination of these experimental and computational results, in terms of light harvesting, electron conversion and photovoltaic device performance characteristics, indicates that carboxylate is the best anchoring group, and hydroxyl is the worst, whereas sulfonate and pyridyl groups exhibit competing potential. Different sensitization solvents are found to affect critically the extent of dye adsorption achieved in the dye-sensitization of the TiO2 semiconductor, especially where the anchor is a pyridyl group.

Strategy to improve photovoltaic performance of DSSC sensitized by zinc prophyrin using salicylic acid as a tridentate anchoring group

Three new zinc porphyrin dyes attached to ethynyl benzoic acid as an electron transmission and anchoring group have been designed, synthesized, and well-characterized. The performances of their sensitized solar cells have been investigated by optical, photovoltaic, and electrochemical methods. The photoelectric conversion efficiency of the solar cells sensitized by the dye with salicylic acid as an anchoring group demonstrated obvious enhancement when compared with that sensitized by the dye with carboxylic acid as an anchoring group. The density functional theory calculations and the electrochemical impedance spectroscopies revealed that tridentate binding modes could increase the efficiency of electron injection from dyes to the TiO2 nanoparticles by more electron pathways.

Judicious design of indoline chromophores for high-efficiency iodine-free dye-sensitized solar cells

Indoline photosensitizers exhibit impressive short-circuit photocurrent but generally low molar extinction coefficient and rapid charge recombination, which limits their application in thin-film dye-sensitizerd solar cells (DSCs). Here, we incorporate a new dithieno[3,2-b:2',3'-d]pyrrole (DTP) segment (i.e., dihexyloxy-triphenylamine (DHO-TPA) substituted DTP) as the conjugated π-linker to construct a series of high molar absorption coefficient indoline dyes (XW69, XW70, and XW71) for DSCs employing a cobalt(II/III) redox electrolyte. Interestingly, this DTP linker is demonstrated as an efficient building block, not only slowing down the kinetics of charge recombination of titania electrons with tris(1,10-phenanthroline)cobalt(III) ions but also making a great contribution to the light absorption properties in comparison with the dihexylaniline substituted DTP. With respect to the dihexyloxy-triphenylamine dye (XW68), these new indoline dyes exhibit stronger light-harvesting and thus better power conversion efficiency of DSCs made from thin titania films. Benefitting from the bulky rigidity of the donor and π-conjugation unit, the XW70 dye displays a promising conversion efficiency as high as 8.78%, with a short-circuit current density (J(SC)) of 13.3 mA cm(-2), open-circuit voltage (V(OC)) of 943 mV, and fill factor (FF) of 0.70 under AM 1.5 illumination (100 mW cm(-2)). Furthermore, the effect of light irradiation on these dyes adsorbed on nanocrystalline TiO2 films was investigated, proving the photostability of these indoline chromophores. Our work has valued the feasibility of judicious design of indoline chromophores to obtain organic photosensitizers for high-efficiency iodine-free DSCs made from thin titania films.