Adsorption and Interface Chemistry Quiz

Surface and Colloid Chemistry

• This presentation covers the properties of solid-liquid interfaces and surfaces, specifically focusing on adsorption.
• Adsorption is defined as an increase in the concentration of surfactant molecules, ions, etc. on the surfaces of minerals, or at interfaces like air-water.
• Adsorbates are the substances adsorbed onto the surface.
• Adsorbent is the material that performs the adsorption process, an example is activated carbon.
• Adsorption occurs at solid/liquid interfaces, depending on the chemical composition of the mineral surface, crystal structure, and charge distribution in the electrical double layer.
• Chemical adsorption happens when a chemical reaction occurs between species in solution and ions that make up the mineral surface.
• Chemical bonds and type of uptake form during chemical adsorption.
• Physical adsorption happens when adsorption occurs via counter ion adsorption in the electrical double layer.

Adsorption

• Adsorption occurs through attraction forces between adsorbents and adsorbates.

• Physical adsorption involves weak van der Waals forces.

• Chemical adsorption involves stronger chemical bonds.

• Adsorption isotherms are graphs of the amount of adsorbate (x) adsorbed on the surface of the adsorbent (m) against concentration, at constant temperature.

• Common adsorption isotherm theories include Freundlich, Langmuir, and BET.

• Adsorption of solutes from solutions is influenced by factors such as solute concentration, temperature, surface area of the adsorbent, pH of the solution, pressure, and time.

• There are several applications of adsorption, including controlling environmental pollution by activated carbon and silica-alumina gels.

Adsorption Experiments

• Adsorption experiments involve adding a specific amount of adsorbent to a liquid solution, mixing, filtering, and analyzing the remaining solute concentration to calculate adsorption density.
• Adsorption density is calculated using the formula: Г = (Ci - Cf). V / m.S.
• Ci is the initial solution concentration
• Cf is the final solution concentration
• V is the solution volume (L)
• m is the adsorbent amount (g)
• S is the surface area of the adsorbent (m²/g)

Preparation of Clay/Chemical Suspension

• Experiments use clay and specific chemical concentrations in suspensions.
• These are then mixed and filtered to obtain the final results.

Transfer to Vacuum Filtration

• The suspension is transferred to a filtration system for further processing.

Chemical Analysis

• Spectrophotometry (UV/Vis) is used to analyze the final solution, determining chemical concentration after adsorption.
• Spectrophotometry works by measuring the amount of light that passes through a solution or sample at a particular wavelength (UV vs. Vis).

Measurement of Surface Area (BET)

• Surface area determination using BET method which stands for Brunauer, Emmett, and Teller.
• This method relates total surface area, including internal surfaces from porous structures, to gas adsorption at a set pressure.

Calculation of Adsorption Density

• Example calculations show how to compute adsorption densities from known experimental data and equations. These involve concentrations (initial and final), volume of solution, mass of the adsorbent, and determined surface area.

Sepiolite-HTAB Adsorption

• Sepiolite is a magnesium silicate characterized by internal channels.
• Hexadecyl trimethyl ammonium bromide (HTAB), a cationic surfactant, was used in the modification process of sepiolite.
• A critical micelle concentration (CMC) occurs in the adsorption process at various stages.
• The process includes regions I, II, and III, where the behavior of the adsorption differs. In Region I, there's ion exchange; in Region II, chain-chain interactions are key; and in Region III, CMC is reached.

Coating Degree Calculations

• Calculations provide degree values to show how much of the surface is covered by the adsorbed surfactant.

Adsorption of HTAB on Sepiolite and Zeolite

• HTAB, an adsorbate molecule with a positive charge, adsorbs onto the negatively charged sepiolite surface.
• Similarly, HTAB adsorbs onto zeolite surfaces through electrostatic interactions.
• In both cases, calculations of coating area and degree were performed showing the degree to which the HTAB covers the surface.