Cecil A. Coutinho

Photocatalytic degradation of methyl orange using polymer–titania microcomposites

Photodegradation of an organic dye was studied experimentally using novel polymer-titania microcomposites. These microcomposites were prepared from titanium dioxide (TiO(2)) nanoparticles embedded within cross-linked, thermally-responsive microgels of poly(N-isopropylacrylamide) and contained interpenetrating linear chains of poly(acrylic acid) that functionalize the nanoparticles of TiO(2). Because these microcomposites settle more than a hundred times faster than freely suspended TiO(2) nanoparticles, they are extremely useful for simple gravity separation of the photocatalyst in applications that employ titania nanoparticles. Methyl orange (MO) was used as a model contaminant to investigate the degradation kinetics using the microcomposites in aqueous suspensions. Kinetics of the photodegradation were evaluated by monitoring the changes in methyl orange concentration using UV-Vis spectroscopy. The photocatalytic behavior of functional microcomposites containing 65 wt% titania was studied and the influence of the solution pH as well as the total titania concentration in solution was explored. The results indicated that pH of the solution changes the surface interactions between the poly(acrylic acid), titania, and methyl orange and this interplay determined the overall degradation kinetics of the chemical contaminants. Nearly identical reaction rate constants were observed in acidic solutions for the microcomposites when compared to freely suspended titania. The latter showed higher rate constants than the microcomposites at a neutral pH. Release of the titania from the microcomposites was observed under basic conditions. Complete degradation of the microcomposites was observed after prolonged (7-13 h) UV irradiation. However, the microcomposites were easily regenerated by addition of microgels and no loss of photocatalytic activity was observed.

Novel Hybrid Abrasive Particles for Oxide CMP Applications

In the present research, novel abrasive particles are investigated in order to carry out CMP at relatively low down force (low mechanical stress) yet achieve desirable removal rates and superior post CMP surface quality (reduced scratches). Hybrid abrasives are developed where the composition of the polymeric particles formed via colloidal precipitation is modified with inorganic segments to reduce surface damage during CMP. The composition is controlled by changing the time for condensation and hydrolysis of the inorganic oxide. Characterization of these particles is performed by FTIR spectroscopy, dynamic light scattering, and electron microscopy (TEM/SEM). Tribological characteristics during polishing employing these novel particles are studied on a bench-top CMP tester. Surface roughness and defectivity are estimated using Atomic Force Microscopy (AFM).

Chemical Mechanical Polishing: Role of Polymeric Additives and Composite Particles in Slurries

Publisher Summary This chapter highlights the role of polymeric additives in the slurry and the use of novel composite abrasive particles incorporating polymers as promising alternatives to traditional inorganic oxide nanoparticles. Polymeric additives are of fundamental importance to the planarization process as they can control the aggregation, dispersion, surface hardness, and stability of the inorganic oxide nanoparticles. Abrasive composites range from simple inorganic particles surface decorated with organic moieties to compressible polymeric microspheres that incorporate inorganic oxide nanoparticles. Typically, slurries used in mechanical polishing/planarization (CMP) consist of a liquid solvent and a solid dispersant. The liquid phase is generally deionized water with additives like oxidizers, complexing agents inhibitors, and surfactants. The solid phase consists of abrasives, which are typically metal oxides such as alumina (Al2O 3 ), silica (SiO 2 ), and ceria (CeO 2 ). While silica and alumina particles are commonly used for polishing copper and tungsten, silica and ceria are used to polish SiO 2 , poly-Si, and silicon nitride. The stability of the abrasive particles is an important criterion for CMP as particle sedimentation or aggregation often leads to the formation of scratches on the wafer surface after polishing. The CMP process draws upon a broad base of knowledge from the fields of science and engineering, which range across colloidal science, surface and interfacial phenomena, polymer physics and chemistry, tribology, fluid mechanics and dynamics, and surface metrology.

Polymer-Titania Composites for Photocatalysis of Organics in Aqueous Environments

Microcomposites composed of titanium dioxide nanoparticles embedded within cross-linked, thermally responsive microgels of poly( N -isopropylacrylamide) were prepared. These microcomposites showed rapid sedimentation, which is useful for gravity separation of the titania nanoparticles in applications such as environmental remediation. To investigate the degradation kinetics using these microcomposites in aqueous suspensions, methyl orange was employed as a model contaminant. The decline in the methyl orange concentration was monitored using UV-Vis spectroscopy. Degradation of methyl orange was also measured using only nanoparticles TiO 2 (Degussa TM P25) for comparison with the microcomposites. Experiments were performed at different pH conditions that spanned acidic, neutral, and basic conditions to gain insight into the interplay of TiO 2 surface charge, ionization of the polyelctrolyte chains in the microcomposites, and ionization of the methyl orange.