Kinetic derivation of common isotherm equations for surface and micropore adsorption

t The Langmuir equation is one of the most successful adsorption isotherm equations, being widely used tofit Type I adsorption isotherms. In this article we show thatthe kinetic approach originally used by Langmuir for 2Dmonolayer surface adsorption can also be used to derive a1D analogue of the equation, applicable in ultramicroporeswith single-file diffusion. It is hoped that such a demonstration helps dispel the idea that the Langmuir isothermequation cannot apply to some micropores as more than amathematical correlation. We furthermore seek to extendthe insight provided by the simple kinetic derivation of theLangmuir equation to other isotherm equations capable ofmodelling Type I isotherms. The same kinetic approach isthus also used to derive the Volmer, Fowler-Guggenheimand Hill-de Boer equations, both for surface (2D adsorbedphase) and micropore adsorption (1D and 3D adsorbedphases). It is hoped that this will help make more intuitively clear that these equations can be used as phenomenological models in some instances of adsorption inmicropore

Comparison of Nanosized Gold-Based and Copper-Based Catalysts for the Low-Temperature Water-Gas Shift Reaction

In this paper the catalytic performances for the low-temperature water-gas shift reaction of Au/TiO(2) type A (from World Gold Council), Au/CeO(2) (developed at UPV-CSIC), CuO/Al(2)O(3) (from BASF), and CuO/ZnO/ Al(2)O(3) (from REB Research & Consulting) have been compared. The catalysts were characterized by different techniques such as Raman spectroscopy, BET surface area measurements, temperature-programmed reduction, and high-resolution transmission electron microscopy, which gave additional information on the redox properties and textural and morphological structure of the investigated samples. The performances of these catalysts were evaluated in a wide range of operating conditions in a micro packed-bed reactor. It was observed that the presence of reaction products in the feed (CO(2) and H(2)), as well as CO and H(2)O feed concentrations, have significant effects on the catalytic performances. With a typical reformate feed the Au/CeO(2) catalyst reveals the highest CO conversion at the lowest temperature investigated (150 degrees C). However, while in the long tests performed the CuO/ZnO/Al(2)O(3) catalyst showed a good stability for the entire range of temperatures tested (150-300 degrees C), the Au/CeO(2) sample clearly showed two distinct behaviors: a progressive deactivation at lower temperatures and a good stability at higher ones. The selection of the best catalytic system is therefore clearly dependent upon the range of temperatures used

Impact of the architecture of dye sensitized solar cell-powered electrochromic devices on their photovoltaic performance and the ability to color change

The functional layers arrangement in a dye sensitized solar cell electrochromic device (DSSC-EC) on the energy conversion efficiency and on the ability to change the color is studied. The highest power conversion efficiency of ca. 7% and good color change in closed circuit conditions was observed with electrochromic WO3 deposited on the counter-electrode of the DSSC. When WO3 layer was applied over the photoanode, the DSSC-EC displayed less power conversion efficiency - 3.4%, but a more intense color change was observed under illumination and opened external circuit. Response of the photocurrent vs. applied potential, incident photon-to-current conversion efficiency and optical behavior of the DSSC-EC were assessed and discussed considering optical properties of the components of the device and their energy bands alignment. Smart window and self-powered proof-of-concept pixelated device operating on DSSC-EC are presented

Impact of using cool paints on energy demand and thermal comfort of a residential building

This work studies the impact of using cool paints and/or thermal insulation on the thermal behavior andenergy demand of a residential building. Buildings with thermal characteristics representing both oldand new constructions are considered. The results were obtained using the dynamic computer simulatorESP-r. Recommendations for designers and/or house-owners in terms of deciding the best thermalcomfort solution are withdrawn.For a case-study building in Portugal, in the summer, it was found that an increase in roof and façadevalue of total solar reflectance (TSR) from 50% to 92% reduced the maximum indoor free-float temperature between 2.0 C and 4.7 C in old construction (without thermal insulation), and between 1.2 C and3.0 C in new construction (with thermal insulation). This had as a trade-off effect the decrease of theminimum indoor temperature of up to 1.5 C. The results of annual energy demand for heating showed amaximum penalty of about 30% when using cool paints. However, it was demonstrated that the coolingdemand almost vanishes, eliminating the need to install air-conditioning devices.The analysis of specific real hot weather time periods showed that the maximum altitude of the sun,which is related to the month of the year, determines the solution that originates the highest temperature reduction. As the maximum sun altitude decreases the cool paints show comparatively betterresults

Removal of industrial cutting oil from oil emulsions by polymeric ultra - and microfiltration membranes

The utilization of micro- and ultrafiltration with polymeric membranes for treatment of industrial cutting oil emulsion was investigated. The performance of 14 different membranes with pore sizes in the range of 1-800 nm, representing 8 different materials and varying hydrophobicity, was determined experimentally. Membrane permeances between 1.6 and 939 L m 2h-1bar-1 have been observed for the different samples as well as oil rejections between 3.42% and 99.99%. Membrane pore size and contact angle showed little influence on both values, while an interesting correlation is displayed to the individual membranes capillary pressures. A possible explanation for thisphenomenon is suggested based on the formation of oil films on the membrane surface. From the investigated membranes, the best-suited one for cutting oil treatment was selected and subjected to further experiments. The effect of process temperatures between 22 and 43 °C and of feed oil concentrations between 0 and 20 vol % on the removal performance was determined. The results correspond to the explanation suggested previously

Transparent graphene-based counter-electrodes for iodide/triiodide mediated dye-sensitized solar cells

A new highly transparent and low cost counter-electrode for dye-sensitized solar cells was fabricated, comprised of a structured graphene film over nickel nanoparticles. Annealed nickel particles induced an enhanced restoration of graphene double bonds, which led to cells with energy conversion efficiencies similar to those using a conventional platinum electrode

Transient phenomenological modelling of photoelectrochemical cells for water splitting: application to undoped hematite electrodes

A phenomenological model is proposed for a better understanding of the basic mechanismsof photoelectrochemical (PEC) cells. The main assumptions of the one-dimensionaltransient phenomenological model are: i) bulk recombination of the conduction bandelectrons with holes in the valence band; ii) the mobile charge transport takes place viadiffusion, which arises from the concentration profiles, and migration, caused bya macroscopic electric field; iii) negligible effects of microscopic electric fields in the celland screening effects, as well as negligible Helmholtz and diffuse layers. For modelingpurposes, the photoanode was assumed to be a homogeneous nanocrystalline hematitestructure, with thickness L, porosity 3p and tortuosity s. The TCO/semiconductor interfacewas modeled as an ideal ohmic contact, while the electrolyte/platinized TCO interface wasdescribed by a ButlereVolmer approach. An alkaline electrolyte solution was used,allowing the transport of the ionic species from the counter-electrode to the photoanode.The continuity and transport governing equations are defined for the mobile speciesinvolved: electrons in the conduction band of the semiconductor, holes in the valence bandand hydroxyl ions in the electrolyte. Simulated IeV characteristics were computed and thecorresponding results compared with the experimental values. The simulated results werein straight agreement with the experimental data

Extremely stable bare hematite photoanode for solar water splitting

Photoelectrodes that are efficient, highly stable, made from low cost materials and easily prepared using inexpensive techniques are required for commercially viable solar photoelectrochemical (PEC) water splitting technology. Hematite is one of few materials that is being considered for this application. In this work, bare hematite thin films prepared by spray pyrolysis were systematically optimized following a design of experiments approach. A response surface methodology was applied to factors: (i) sprayed volume of solution; (ii) temperature of the glass substrate during the deposition; and (iii) time gap between sprays and the optimized operating conditions obtained were v = 42 mL, T=425 degrees C and t=35 s. The optimized hematite photoelectrode showed a photocurrent density of ca. 0.94 mA cm(-2) at 1.45 V-RHE, without dopants or co-catalysts, which is remarkable for a thin film of ca. 19 nm. The stability of this photoelectrode was assessed over 1000 h of PEC operation under 1-sun of simulated sunlight. A record breaking result was obtained with no evidences of hematite film degradation neither of current density loss. These results open the door to turn PEC cells into a competitive technology in the solar fuel economy

A review of the techniques to measure the hermeticity of glass frit encapsulated solar cells

Emerging 3rd generation photovoltaic technologies such as perovskite and dye-sensitized solar cells are very attractive for commercialization mainly due to their low-cost materials and fabrication processes. The main drawback of these devices is their poor long-term stability. To increase the long-term stability of these devices, a hermetic encapsulation is required. The hermeticity of encapsulated devices are measured and characterized using hermeticity tests according to standard test procedures. A review of the several techniques to measure the hermeticity is presented, addressing the test methods, limitations and applicability to perovskite and dye-sensitized solar cells glass frit encapsulated devices