Effect Of Coadsorbates Research Articles

A Roadmap for Building Waterborne Virus Traps.

Outbreaks of waterborne viruses pose a massive threat to human health, claiming the lives of hundreds of thousands of people every year. Adsorption-based filtration offers a promising facile and environmentally friendly approach to help provide safe drinking water to a world population of almost 8 billion people, particularly in communities that lack the infrastructure for large-scale facilities. The search for a material that can effectively trap viruses has been mainly driven by a top-down approach, in which old and new materials have been tested for this purpose. Despite substantial advances, finding a material that achieves this crucial goal and meets all associated challenges remains elusive. We suggest that the road forward should strongly rely on a complementary bottom-up approach based on our fundamental understanding of virus interactions at interfaces. We review the state-of-the-art physicochemical knowledge of the forces that drive the adsorption of viruses at solid–water interfaces. Compared to other nanometric colloids, viruses have heterogeneous surface chemistry and diverse morphologies. We advocate that advancing our understanding of virus interactions would require describing their physicochemical properties using novel descriptors that reflect their heterogeneity and diversity. Several other related topics are also addressed, including the effect of coadsorbates on virus adsorption, virus inactivation at interfaces, and experimental considerations to ensure well-grounded research results. We finally conclude with selected examples of materials that made notable advances in the field.

Graphdiyne supported single-atom cobalt catalyst for oxygen reduction reaction: The role of the co-adsorbates

This work investigated the effects of co-adsorbates on the oxygen reduction activity of GDY-supported single-atom catalysts(SACs). We found that the co-adsorbates pull electrons from the metal atom and downshift its d-band center, which weakens the binding of the intermediates. Strong-binding Co/GDY is shifted to the apex of the volcano by co-adsorbed O2 with a low overpotential of 0.16 V. Pd/GDY, Ni/GDY decorated with O2 are also predicted to be promising candidates that are superior to Platinum(111). Our work shows that it is important to consider the effects of the co-adsorbates, and provides a new way of designing GDY-based SACs.

Coadsorption of CO and O over strained metal surfaces

Abstract Coadsorption of CO and O over five metal (1 1 1) surfaces under strain has been computationally investigated, which is relevant to key catalytic processes like CO oxidation. Strain sensitive/insensitive metals with respect to O and CO adsorptions are identified. For strain sensitive metals like Pd and Pt, the effects of strain and coadsorbates can be utilized to tune their catalytic performance, providing a new perspective on solving the problems of CO poisoning. For strain insensitive metals like Rh, Ir, and Cu, both effects are much weaker. Overall, the synergistic effect of coadsorbates and strain should be further investigated for catalyst design.

Dense CO Adlayers as Enablers of CO Hydrogenation Turnovers on Ru Surfaces.

High CO* coverages lead to rates much higher than Langmuirian treatments predict because co-adsorbate interactions destabilize relevant transition states less than their bound precursors. This is shown here by kinetic and spectroscopic data-interpreted by rate equations modified for thermodynamically nonideal surfaces-and by DFT treatments of CO-covered Ru clusters and lattice models that mimic adlayer densification. At conditions (0.01-1 kPa CO; 500-600 K) which create low CO* coverages (0.3-0.8 ML from in situ infrared spectra), turnover rates are accurately described by Langmuirian models. Infrared bands indicate that adlayers nearly saturate and then gradually densify as pressure increases above 1 kPa CO, and rates become increasingly larger than those predicted from Langmuir treatments (15-fold at 25 kPa and 70-fold at 1 MPa CO). These strong rate enhancements are described here by adapting formalisms for reactions in nonideal and nearly incompressible media (liquids, ultrahigh-pressure gases) to handle the strong co-adsorbate interactions within the nearly incompressible CO* adlayer. These approaches show that rates are enhanced by densifying CO* adlayers because CO hydrogenation has a negative activation area (calculated by DFT), analogous to how increasing pressure enhances rates for liquid-phase reactions with negative activation volumes. Without these co-adsorbate effects and the negative activation area of CO activation, Fischer-Tropsch synthesis would not occur at practical rates. These findings and conceptual frameworks accurately treat dense surface adlayers and are relevant in the general treatment of surface catalysis as it is typically practiced at conditions leading to saturation coverages of reactants or products.

Competitive Coadsorption Dynamics of Viruses and Dissolved Organic Matter to Positively Charged Sorbent Surfaces.

Adsorption onto solid-water interfaces is a key process governing the fate and transport of waterborne viruses. Although negatively charged viruses are known to extensively adsorb onto positively charged adsorbent surfaces, virus adsorption in such systems in the presence of negatively charged dissolved organic matter (DOM) as coadsorbate remains poorly studied and understood. This work provides a systematic assessment of the adsorption dynamics of negatively charged viruses (i.e., bacteriophages MS2, fr, GA, and Qβ) and polystyrene nanospheres onto a positively charged model sorbent surface in the presence of varying DOM concentrations. In all systems studied, DOM competitively suppressed the adsorption of the viruses and nanospheres onto the model surface. Electrostatic repulsion of the highly negatively charged MS2, fr, and the nanospheres impaired their adsorption onto DOM adlayers that formed during the coadsorption process. In contrast, the effect of competition on overall adsorption was attenuated for less-negatively charged GA and Qβ because these viruses also adsorbed onto DOM adlayer surfaces. Competition in MS2-DOM coadsorbate systems were accurately described by a random sequential adsorption model that explicitly accounts for the unfolding of adsorbed DOM. Consistent findings for viruses and nanospheres suggest that the coadsorbate effects described herein generally apply to systems containing negatively charged nanoparticles and DOM.

Synthesis of D–D–A-type small organic molecules with an enlarged linker system towards organic solar cells and the effect of co-adsorbents on cell performance

The synthesis of two D–D–A type novel small molecules and their applications in organic solar cells have been studied.

Thiophene-bithiazole based metal-free dye as DSSC sensitizer: Effect of co-adsorbents on photovoltaic efficiency

A new molecule consisting of a bithiazole chromophore sandwiched between two thiophenes, functionalized with benzothiophene unit at one end and cyanoacrylic acid at the other end (BT1) was synthesized, photophysical properties were studied and employed as a photosensitizer in dye-sensitized solar cells (DSSCs). The molecule exhibited an intense absorption in the UV-visible region with absorption extending up to 500 nm. The ground and excited state potentials of BT1 were calculated to be 1.29 and -0.65 V, respectively vs. NHE using cyclic voltammetry. The ground state energy level is more positive than the triiodide electrolyte and excited state energy level is considerably more negative than the TiO2 satisfying the energetic requirements for a photosensitizer in DSSC. The solar cells fabricated from BT1 exhibited an efficiency of 1.13%. The effect of various co-adsorbents (CDCA,TP1 andTP2) on the DSSC performance was investigated in detail. In the presence of CDCA, the photovoltaic efficiency was enhanced to 1.25%, whereas, in the presence of TP1 and TP2, the efficiency lowered to 0.20% and 0.59%, respectively. The increased efficiency in the presence of CDCA could be attributed to the prevention of the aggregation of dye molecules induced by CDCA. On the other hand, TP1 and TP2 were found to be not as effective as CDCA to prevent aggregation leading to the lowering of photoconversion efficiency.

The effect of coadsorbent and solvent on the photovoltaic performance of 2,9,16,23-Tetrakis(7-coumarinoxy-4-methyl)-phthalocyaninatocopper-sensitized solar cells

The synthesis, characterization and thermal properties of CuPc-Cou were reported and the effects of chenodeoxycholic acid (CHENO) as a coadsorbent and the solvent on the solar cell's performance were investigated. The ground state absorbance of CuPc-Cou showed the molar extinction coefficients as high as 2.90 × 104 dm3 mol−1 cm−1 in DMF and 2.74 × 104 dm3 mol−1 cm−1 in CH2Cl2. The thermal stability studies indicated that CuPc-Cou was stable up to 370 °C. Furthermore, HOMO and LUMO energies made it clear that CuPc-Cou can be used as a sensitizer for DSSC. Adding CHENO onto TiO2 nanoparticles not only reduced the adsorption of phthalocyanine sensitizers but also prevented the aggregation behavior, leading to different photovoltaic performance. The open circuit voltage of the solar cells with CHENO coadsorbent increased due to the enhanced electron lifetime in TiO2 nanoparticles coupled with the band edge shift of TiO2 to negative potentials. The optimal dye adsorption condition of the TiO2 electrode was found to be 3 × 10−4 M CuPc-Cou solution containing 6.0 mM CHENO in dichloromethane, which could contribute to improve the PCE by 69% as compared to the solar cell fabricated with TiO2 electrode sensitized by the CuPc-Cou in absence of CHENO and the optimal condition in DMF. It indicated that CuPc-Cou in DMF was easy to aggregate than in CH2Cl2 for the solvent effect.

Chlorin e6 sensitized photovoltaic cells: effect of co-adsorbents on cell performance, charge transfer resistance, and charge recombination dynamics

The effect of dye-aggregation-preventing co-adsorbents, cholic acid and deoxycholic acid, on the performance of dye-sensitized solar cells constructed using a metal-free sensitizer, chlorin e6 adsorbed onto TiO2 surface is investigated. Absorption and fluorescence studies of chlorin e6 provided the spectral coverage, whereas electrochemical studies allowed estimation of the free energy of charge injection. B3LYP/6-31G* studies were performed to visualize location of the Frontier orbitals and their contribution to the charge injection when they were surface-modified on TiO2. The concentration of the co-adsorbent and soaking time was optimized for improved cell performance. Better dye regeneration efficiency for co-adsorbed cells compared to the cells with no co-adsorbent was revealed by electrochemical impedance spectroscopy. Femtosecond transient absorption studies were performed to probe the kinetics of charge injection and charge recombination on the TiO2/chlorin e6/co-adsorbent electrodes. Such studies showed slower by an order of magnitude charge recombination rates for electrodes co-adsorbed either with cholic acid or deoxycholic acid while maintaining almost the same charge injection rates, thus rationalizing the importance of co-adsorbents on the overall cell performance.

How Surface Hydroxyls Enhance MgO Reactivity in Basic Catalysis: The Case of Methylbutynol Conversion

This combined experimental and theoretical study aims at understanding why surface hydroxyl groups may enhance catalytic reactivity of MgO surfaces in basic catalysis, whereas hydroxyls are weakly deprotonating groups. We investigated that reactivity enhancement in the catalytic conversion of 2-methyl-but-3-yn-2-ol (MBOH). Reaction kinetics was experimentally determined on partially hydroxylated MgO: active sites were saturated with the reactant and catalyzed its conversion with an activation energy of 85 kJ·mol–1. Reaction pathways were calculated over fully hydroxylated, partially hydroxylated, and dehydroxylated MgO surfaces by means of first-principles simulations. To highlight the effect of reactant coverage, we also calculated the reaction pathway on MgO precovered with MBOH molecules. The results show that the surface OH groups generated by dissociative adsorption of water induce a lowering in the activation energy barriers when they keep a bare Mg2+-O2– pair available in the vicinity for MBOH to adsorb and react. Interestingly, OH groups do not directly interact with MBOH converting on the surface, but they modify the basic properties of the vicinal bare Mg2+-O2– pair on which MBOH adsorbs and converts. A similar effect is predicted when MBOH converts on a bare Mg2+-O2– pair in the vicinity of a second adsorbed MBOH molecule. The beneficial effect of coadsorbates on the reactivity of active sites is analyzed by means of a thermodynamic model and an electronic structure analysis.

Aggregation and Electrolyte Composition Effects on the Efficiency of Dye-Sensitized Solar Cells. A Case of a Near-Infrared Absorbing Dye for Tandem Cells

Time-resolved laser spectroscopy studies of complete solar cells sensitized with a near-infrared absorbing dye (HY103) and filled with different electrolytes are applied to explain their macroscopic parameters (efficiency and short-circuit current). Particular attention is paid to the effect of coadsorbent, size of cations in electrolyte (lithium vs guanidine ones), and addition of tert-butylpyridine. A complete deactivation scheme in the cell is revealed, and the rates of electron injection and all other processes are explored. For the most efficient electrolyte, the electron injection rate constants are 0.21 ps–1 from monomers and 0.07 ps–1 from H-aggregates. Moreover, two important and novel findings are revealed: energy transfer from the excited state of monomers to H-aggregates (with rate constants from 0.04 to 0.25 ps–1) and the decrease of internal conversion rate in HY103 attached to the nanoparticles (0.01 ps–1) with respect to that of free dye in solution (0.06 ps–1). Thus, our study gives more ...

Highly asymmetric phthalocyanine-sensitized solar cells: The effect of coadsorbent and adsorption temperature of phthalocyanine

Highly asymmetric zinc phthalocyanine derivative (Zn-tri-PcNc) containing tribenzonaphtho-condensed porphyrazine with one carboxyl and three tert-butyl (t-Bu) substituent groups is used as a sensitizer to fabricate dye-sensitized solar cells (DSSCs), and the effects of chenodeoxycholic acid (CDCA) as a coadsorbent and the dye adsorption temperature on the solar cell's performance are investigated. It is found that CDCA coadsorption can hinder the dye aggregation, which is beneficial for improving the electron injection efficiency and retarding the charge recombination, and thus resulting in the enhancement of the short-circuit current density and open-circuit photovoltage. Moreover, the dye adsorption temperature on electrode also shows a significant impact on the photovoltaic performance of the solar cell, and an optimal dye adsorption condition of the TiO2 electrode is found to be 5×10−5M Zn-tri-PcNc ethanol solution containing 7.5mM CDCA at 5°C, which can contribute to the maximum conversion efficiency of 2.89% with short-circuit current density of 9.42mAcm−2 and open-circuit photovoltage of 0.48V, improved by 47% as compared to the solar cell fabricated with TiO2 electrode sensitized by the zinc phthalcoyanine in absence of CDCA.

Surface passivation: The effects of CDCA co-adsorbent and dye bath solvent on the durability of dye-sensitized solar cells

The long-term stability of dye-sensitized solar cells (DSCs) based on an amphiphilic ruthenium sensitizer, CYC-B6L was studied. When the surface of the TiO2 electrode was passivated with a co-adsorbent, chenodeoxycholic acid (CDCA), the resulting DSC reveals very good long-term stability with over 87% of initial performance under a 1000h prolonged light-irradiation and thermal stress (60°C) aging, which is as good as the state-of-the art robust device. The solvent used in dye bath also affects the long-term stability of the DSC devices. The effect of co-adsorbent and the impact of the dye bath solvents on the device durability were investigated using the electrochemical impedance spectroscopy.

Effect of coadsorbents on DSSC sensitized by NIR absorbing poly(ethyl thieno[3,4- b]thiophene-2-carboxylate)

Poly(ethyl thieno[3,4- b]thiophene-2-carboxylate) (PTTEt), showing near infrared (NIR) absorption was employed as a polymer sensitizer in dye-sensitized solar cell (DSSC). The photovoltaic performance of DSSC was investigated with PTTEt of different molecular weights. Low molecular weight aliphatic di-acids were also employed as coadsorbents along with PTTEt. It was revealed that the reduction of polymer molecular weights caused only a slight enhancement in overall power conversion efficiency ( η). The species and concentration of coadsorbents, on the other hand, greatly affects η. The best performance with η of ca. 1.5% was obtained when 3,3′-dithiodipropionic acid was adsorbed along with PTTEt, indicative of significant improvement of η (ca. 50% increase).

Coadsorbate effects on adsorbate vibrational properties

A quantitative analysis of infrared absorption spectra to determine coadsorbate induced relative changes of the vibrational polarizability α v of an adsorbate mode and of the dielectric screening ϵ due to this extra species is presented. Four (ternary) coadsorption systems consisting of the Ru(0 0 0 1)-(2 × 2)-(X + CO + O) layer with additional coadsorbates X = H, NO, CO, or O (all of them occupying the remaining empty fcc site) have been studied with FT-IRAS, TDS, LEED and work function change measurements. On-top CO is thereby used as a probe molecule to monitor coadsorbate effects on the dielectric properties of the layer. The vibrational polarizability α v associated with the internal C–O stretch mode ( ν C–O) of on-top CO is lowered by all coadsorbates. The dielectric screening ϵ within the adsorbate layer is reduced in the presence of the atomic coadsorbates O and H whereas an increase of ϵ is found for the molecular coadsorbates, threefold coordinated CO and NO. The derived changes of α v and dielectric screening ϵ, as well as the involved line shifts of ν C–O and ν Ru–CO can be understood in terms of the standard Blyholder backbonding model, i.e. CO 5 σ charge donation to the metal combined with a backdonation to electronic states with 2π∗ character.

Effect of coadsorbent on the photovoltaic performance of squaraine sensitizednanocrystalline solar cells

The effect of chenodeoxycholic acid as the coadsorbent with a squaraine sensitizer onTiO2 nanocrystalline solar cells was investigated, and it was found that thecoadsorbent prevents the squaraine sensitizer from aggregating on theTiO2 nanoparticles but reduces dye loading leading to an interdependent photovoltaicperformance. Analysis of the absorption spectra, and incident monochromaticphoton-to-current conversion efficiency data showed that the load of squaraine sensitizer aswell as the appearance of H-aggregates is strongly dependent on the molar concentration ofchenodeoxycholic acid coadsorbent. The open circuit voltage of the solar cellswith chenodeoxycholic acid increases due to the enhanced electron lifetime in theTiO2 nanoparticles coupled with the band edge shift ofTiO2 to negative potentials.

Effect of Coadsorbent on the Photovoltaic Performance of Zinc Pthalocyanine-Sensitized Solar Cells

The effect of chenodeoxycholic acid as a coadsorbent on TiO 2 nanocrystalline solar cells incorporating phthalocyanine sensitizers was studied under various conditions. Adding chenodeoxycholic acid onto TiO 2 nanoparticles not only reduces the adsorption of phthalocyanine sensitizers but also prevents sensitizer aggregation, leading to different photovoltaic performance. The inspection of IPCE and absorption spectra showed that the load of phthalocyanine sensitizers is strongly dependent on the molar concentration of chenodeoxycholic acid coadsorbent. The open circuit voltage of the solar cells with chenodeoxycholic acid coadsorbent increases due to the enhanced electron lifetime in TiO 2 nanoparticles coupled with the band edge shift of TiO 2 to negative potentials.

Modeling the kinetics of large sets of reactions on metal surfaces

We are concerned with constructing and solving kinetic models for large-scale catalytic mechanisms involving hundreds of reactions. We need reliable estimates for hundreds of rate constants for each project we undertake. In order to obtain reliable estimates of activation barriers with co-adsorbate effects, we employ the UBI-QEP method whenever applicable. We also bring quantum mechanical electronic structure methods to bear when necessary. Herein we describe a new model for obtaining reasonable estimates for rate constants for reactions on metal surfaces that yields rate constants and rate constant parameters without large amounts of computer time. The model is based on a novel approach to surface-phase chemistry and a re-thinking regarding the phases from which surface adsorbates react. We will also discuss recent literature regarding trends in Arrhenius pre-exponential factors (prefactors).

Simulation of the life cycle of adsorbate islands on the Pt(1 0 0) surface during the NO + NH 3 reaction

Photoemission electron microscopy (PEEM) of the NO + NH 3 reaction on a Pt(1 0 0) single crystal surface under UHV conditions reveals complicated dynamical behavior. As a rationalization for the observed spatio-temporal evolution of the surface a so-called ‘island growth mechanism’ was proposed. Here, we present the results of 1D simulations with a realistic 7-variable model that takes explicitly into account macroscopic surface defects on the catalyst. Depending on whether or not we consider site-blocking effects of coadsorbates on diffusing species, we obtain different patterns. The experimental PEEM data can be qualitatively reproduced in this way.

Electrochemical Quartz Crystal Microbalance Study on the Kinetics of Nickel Monolayer and Multilayer Electrodeposition on (111)-Oriented Gold Films

The electrodeposition of nickel on (111)-oriented gold films has been studied in electrolytes with different Ni2+ concentrations and/or pH values using the electrochemical quartz crystal microbalance (EQCM). In all solutions, potential step experiments reveal two regimes with different deposition rates, which can be assigned to the deposition of the first Ni layer on the Au substrate and to the growth of subsequent Ni layers, respectively. Deposition of the monolayer is 10−20 times faster than Ni multilayer growth, indicating that the charge-transfer reaction is enhanced on the gold surface as compared to that on the already deposited Ni. For Ni multilayer deposition, we find Tafel slopes of 88−104 mV/decade, in good agreement with previous data, whereas, in the (sub-)monolayer regime, we obtain a slope of ≈40 mV/decade. This indicates a change in the rate-limiting step, which is attributed to the inhibiting effects of coadsorbates on the Ni surface. Furthermore, the studies revealed an increasing current efficiency of the Ni electrodeposition with increasing overpotential. In contrast to the case of Ni deposition, preliminary EQCM results on Co and Fe electrodeposition show a reduced deposition rate in the monolayer range as compared to that at multilayer coverages.