Chemistry and Biochemistry: Research Progress Vol. 11

Surface chemistry examines physicochemical phenomena at interfaces between solid, liquid, and gaseous phases. This chapter provides an integrated account of colloidal systems, adsorption isotherms, and heterogeneous catalysis. It distinguishes true solutions, colloidal dispersions, and suspensions according to particle size and describes the dispersed phase and dispersion medium. The discussion covers the classification, preparation, purification, and principal properties of colloids, including Brownian movement, the Tyndall effect, electrophoresis, electroosmosis, electrical double layers, zeta potential, coagulation, peptisation, protective colloids, and the gold number. Factors affecting colloidal stability are considered alongside the formation and behaviour of micelles, emulsions, emulsifying agents, and surfactants. Adsorption is presented in terms of physisorption, chemisorption, desorption, and the effects of temperature, pressure, adsorbate properties, and adsorbent surface area. The Freundlich, Langmuir, Brunauer–Emmett–Teller, and Gibbs adsorption isotherms are outlined, together with their principal equations and applications to gas- and solution-phase adsorption. The chapter further explains heterogeneous catalysis through adsorption and the Langmuir–Hinshelwood mechanism, including the sequential stages of diffusion, adsorption, surface reaction, desorption, and product diffusion. Quantitative treatments of unimolecular and bimolecular surface reactions are included to relate surface coverage and reactant pressure to reaction rate. Collectively, these topics establish the fundamental relationships between interfacial structure, colloidal behaviour, adsorption, and catalytic processes.