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This study involved the investigation of C₃-hydrocarbon adsorption on a range of metal and supported metal surfaces using FTIR spectroscopy. The initial aim was to use 'model' metal surfaces i.e. single crystal and polycrystalline metals, to determine fingerprint spectra for various adsorption complexes of propene and propyne. These fingerprint spectra were then to be used to help determine the nature of surface species formed on 'real' industrial catalysts. The single crystal study involved adsorption of both propene and propyne on Pt(111) at temperatures of 90 K and >300K. Adsorption of propene on Pt(111) at 90 K yielded the first infrared spectrum of the di-σ propene surface complex. Spectra obtained at higher temperatures for this system provided the signature of the propylidyne species. Upon adsorption of propyne on Pt(111) at 90 K the fingerprint spectrum of a 'Type A' propyne surface complex was recorded. Adsorption of propene on thin polycrystalline films of copper and palladium, at low temperature was investigated using transmission infrared spectroscopy. In this study the first infrared spectra of the π-adsorbed propene complex were recorded. The second half of the study involved investigation of the surface species formed on 'real' industrial catalysts, i.e. Al₂O₃ and Pt/Al₂O₃. Infrared spectra were recorded for a wide range of surface species such as propene complexes, acrolein, acrylate, carboxylates, hydrogencarbonate, and carbonates. These results showed that the main surface chemistry involved on these catalysts was that of the oxide support and not that of the platinum metal.

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Layered metal sulfides MoS2 and WS2 exhibit highly anisotropic surface chemistry. Adsorption of molecules is stronger on the atomic layer edges than on atomic planes. The edges are catalytically active in the petroleum hydrodesulfurization, while the layer planes are inert. Dispersing MoS2 and WS2 on the nanometer scale can also lead to the onset of photocatalytic properties due to the bandgap tuning by quantum confinement. In this work, we aim at determining how the adsorption on surface sites is altered for the nanoparticles compared to the bulk sulfides (micron-sized particles). A comparative study of the MoS2 and WS2 nanoparticles and bulk materials is done by attempting the adsorption of small molecules (N2, CO, acetone, and acetonitrile) to probe the surface sites. MoS2 and WS2 nanoparticles were synthesized by thermal decomposition of the metal hexacarbonyls in presence of sulfur in high-boiling solvents. The size range is 5-30 nm from Transmission Electron Microscopy. Transmission Infrared Spectroscopy was used to monitor the spectra of the probe molecules. A dedicated experimental setup has been constructed that consists of a high-vacuum chamber with a base pressure of 5×10-7 Torr. At the lowest achievable temperature of the sample (-145°C), N2, CO, and acetone were found to not adsorb strongly enough to be retained in vacuum on these materials. Acetonitrile was found to adsorb on these materials at -145°C and to desorb between -90°C and -50°C. The nanomaterial samples adsorbed significantly more acetonitrile than the corresponding bulk sulfides, as judged by the infrared signals intensity. Qualitatively, adsorbed acetonitrile species on nanodispersed and bulk sulfides are the same. It is likely that most of the adsorbed acetonitrile observed is physisorbed as ice or adsorbed on the sulfur-terminated terraces. At the final stages of desorprtion, distinctly different adsorbed species are seen whose CN stretching IR bands are shifted to higher frequencies. It is likely that these minority species are at monolayer or submonolayer coverages. The exact nature of the species requires further studies. / Department of Chemistry

The surface tension of an interface separating two bulk phases is one of the most widely studied properties in surface science research. The importance of surface or interfacial tension is reflected in the diverse number of applications which are influenced by surface tension related effects. This thesis represents a comprehensive experimental and theoretical investigation on molecular adsorption and surface tension from a class of organic compounds in aqueous solutions. The research illustrates the effect of both liquid and vapor phase adsorption on the interfacial properties. Adsorption from both sides of the vapor/liquid interface is considered simultaneously rather than exclusive of one another, which has been the conventional practice. In the experimental study, the surface tension of a number of different volatile organic compounds is measured using the Axisymmetric Drop Shape Analysis-Profile (ADSA-P) method. The experiments were performed in a controlled environment under conditions where the surface tension can be affected by both vapor and liquid phase adsorption. The vapor phase was exerted by the presence of an environment solution containing the same organic component as in the drop solution. The results show that initially the surface tension is influenced by the organic concentration in both the liquid and the vapor phase. At the final steady-state the liquid phase becomes less important and the primary factor influencing the surface tension is the vapor phase concentration. The ADSA-P technique is verified by reproducing a select number of cases using the Wilhelmy plate method. A possible consequence of the surface tension phenomenon is illustrated through time-dependent contact angle experiments. The behavior of the interface at steady-state conditions is investigated by measuring the surface tension response to a change in drop volume. It is concluded that the organic compounds considered in the current study may represent a rather general group of molecules whose surface behavior is unique to that of many conventional surfactants. In the theoretical study an empirical model is proposed to describe the relation between the steady-state surface tension and the concentration of the environment and drop solutions. The results confirm the experimental observation that the final steady-state surface tension is determined primarily by the organic concentration in the vapor phase. In addition, a modified adsorption isotherm is developed to account for simultaneous adsorption from both sides of the vapor/liquid interface at steady-state conditions. The derivation is based upon the classic Langmuir analysis, and the new equation is consistent with the Langmuir isotherm under traditional conditions where adsorption occurs from one side of the interface. The modified isotherm is shown to be consistent with the experimental data and is used to generate the equilibrium parameters for three of the systems studied in this research. The adsorption isotherm is then extended to model the dynamic adsorption process through the creation of a new kinetic transfer equation. As with the adsorption isotherm, the transfer equation is based on Langmuir kinetics and is capable of simulating adsorption from both sides of the interface during surface equilibration. The kinetic transfer equation is validated against experimental data from two systems which exhibit a transfer-controlled adsorption mechanism. The theoretical predictions from the transfer equation fit well with the experimental data for both systems. However, significant variability is observed in the least squares estimates of the kinetic rate constants. The variability is attributed to the limitations of empirical models that utilize adjustable fitting parameters to optimize the model predictions, and the wide range of surfactant concentrations studied. Specific concentration regions are identified where the variability in the rate constants is minimal and thus, where the model is most appropriate.

Desulfurization of liquid and gas phase sulfur compounds has been receiving dramatic attention since sulfur compounds cause environmental damages (especially acid rain) and pose industrial challenges (i.e. corrosion of equipment and deactivation of catalysts). This thesis has focused on the removal of liquid phase aromatic sulfur compounds (i.e. thiophene or dibenzothiophene (DBT)), as well as on the removal of gas phase hydrogen sulfide (H2S) through adsorption method by metal oxide/graphene composites. More specifically, the effects of graphene (or reduced graphite oxide) as a substrate were thoroughly investigated. For liquid phase sulfur removal, graphene which possesses π orbitals can adsorb aromatic sulfur compounds through π-π interactions. In addition, depending on the synthesis methods, higher quality graphene (i.e. thinner or larger graphene) could be obtained; and it improved the amount of DBT adsorption. For gas phase desulfurization (i.e. H2S adsorption), zinc oxide (ZnO) and reduced graphite oxide (rGO) composites have been studied. This study highlights the critical role of rGO as a substrate to enhance the H2S adsorption capacity. The presence of rGO with ZnO increases the surface area compared with pure ZnO since the oxygen functional groups on rGO prevent the aggregation of nano-sized ZnO particles for mid temperature sulfidation processes. The average particle size for pure ZnO was increased from 110 nm to 201 nm during the adsorption process while that for ZnO/rGO was maintained as 95 nm even after adsorption at 300°C. This contributes to explain that the presence of rGO with ZnO can enhance the H2S adsorption capacity from 31.7 mg S/g ads (for pure ZnO) to 172.6 mg S/g ads (for ZnO/rGO), that is more than a 5-fold increase. Morever, the presence of rGO with ZnO considerably improves the stability of the adsorbent; for multiple regeneration cycles at 600°C (in N2 environment), the adsorption capacity for ZnO/rGO stabilized at 93.1 mg S/g ads after the 8th cycle, while that for pure ZnO was nil after 5 cycles. The effects of copper (5, 10, 15, 20 and 25 mol%) with zinc oxide (ZnO) and reduced graphite oxide (rGO) composite on the hydrogen sulfide (H2S) adsorption capacity have also been studied. It was found that depending on the copper loading, the H2S adsorption capacity has been increased by up to 18 times compared to pure ZnO. In order to investigate the oxidation changes on copper and zinc oxides, crystallite analysis by XRD and chemical state analysis by XPS were performed. It was confirmed that the 2D rGO substrate, containing abundant oxygen functional groups, promoted the metal oxide dispersion and increased the H2S adsorption efficiency by providing loosely bonded oxygen ions to the sulfur molecules. In addition, it was determined that the optimum content of copper was 15 mol% relative to ZnO for maximizing the H2S adsorption. The 15% copper with ZnO/rGO led to the highest portion of zinc ions located in the Zn-O lattice; and led to the co-existence of Cu1+ and Cu2+ ions with ZnO. The H2S exposure at 300°C produces metal sulfides (i.e. zinc sulfide and copper sulfide) and sulfate ions.

Discharge of untreated industrial effluents containing heavy metals is hazardous to the environment as they are highly toxic, accumulates in the food chain and persistent in nature. Because of these adverse effects, their removal from wastewater is a substantial step in the protection of the environment and human health. Biosorption is found to be an eco-friendly, economical and lucrative separation technique in the removal of metal ions from effluent. This study explores the seperation potential of a new sorbent, fibroin (constituent of natural silk spun by Bombyx mori) for the removal of lead, chromium, copper and cobalt ions from effluent water. The biosorbent was prepared by the separation of cocoon into its constituents, fibroin and sericin. The removal of sericin from fibroin, called silk degumming, was carried out by water extraction method. Effect of temperature (55-95oC) on the kinetics and quantity of sericin removed was studied. The separation kinetics was approximated by the intraparticle diffusion model and the pseudo-second-order equation. Biosorption characteristics of fibroin for the removal of lead, chromium, copper, and cobalt ions from aqueous solution were investigated through a batch study. The effect of initial solution concentration, contact time and temperature on the sorption process was investigated. The adsorption equilibrium was described by the Langmuir isotherm. The thermodynamic parameters, the change in enthalpy (∆H) and change in entropy (∆S), were calculated by using Van’t Hoff plot. An accurate mathematical expression was used to calculate Gibbs free energy (∆G), for the adsorption of all metals on fibroin. For the kinetic data analysis, pseudo-second-order equation was modified based on the fact that the term qe in the kinetic equation should be the equilibrium uptake corresponding to the instantaneous metal concentration in the solution. In order to evaluate the rate constant k2, sorption kinetic data was fitted to the modified pseudo-second-order equation. The calculated values of rate constant k2, for the adsorption of all metals on fibroin, were used to the modified pseudo-second-order model to predict the kinetic data. A good comparison was observed between the experimental data and model calculations. The kinetic data was also fitted to the intraparticle diffusion model which showed a multi linear trend. The metal ions were desorbed from fibroin up to ten cycles of adsorption and desorption by using 0.05M ethylenediaminetetraacetic acid (EDTA). The removal of metal ions from fibroin was found to be rapid since complete desorption occurred within 15min. The uptake capacity of fibroin and adsorption/desorption kinetics remained almost the same even after ten cycles. The rate constants for both adsorption and desorption were also calculated by fitting the kinetic data to the modified pseudo-second-order model. The dynamic adsorption was studied in a flow-through column packed with fibroin for the removal of all metals. Experiments were performed in order to study the effect of influent concentration (12-75ppm), influent flow rate (0.15-0.24ml/min) and regeneration of fibroin bed (upto 4 cycles). Whereas the bed height, column diameter and amount of adsorbent packed were kept constant during this study. Fibroin bed saturated with metal ions was regenerated effectively by using 0.5M EDTA solution. After four consecutive cycles of adsorption and desorption, no change in the uptake capacity was observed. The bed depth service time model, the Thomas model and the Yoon-Nelson model were used to analyze the breakthrough data. The calculated values of Yoon-Nelson constants were used to predict the breakthrough curves. A good comparison was observed between experimental data and the Yoon-Nelson model calculations. An investigation was conducted to check if the adsorption of metal ions was carried out either by the surface of the fibroin or they were adsorbed deep inside its polymer network, and bulk was used. For this study, silk fibroin was transformed into thin films of three different thicknesses having same surface area. Batch experiments were conducted to study the thickness effect of fibroin films for the adsorption of metal ions. A constant amount of metal uptake for all three fibroin films showed that the adsorption was not a surface phenomenon, but the bulk body of the fibroin was used for this separation. Kinetic data was fitted to the modified pseudo-second-order model. The kinetic rate constant k2 was not significantly affected by the film thickness which abrogated the possibility of simple diffusion mechanism for metal sorption into fibroin. Fibroin films loaded with metal ions were desorbed once dipped in deionized water. The desorption kinetics was again described by the modified pseudo-kinetic-model. The calculated values of desorption rate constant kd were used to predict the kinetics of film desorption. A good comparison was observed between the modified pseudo-second-order model calculations and experimental desorption data of fibroin films.

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No description available.