Heinrich Kayser, a German physicist, coined the term adsorption in 1881. Surface chemistry is concerned with the phenomena that occur at surfaces or interfaces. Solid-gas or solid/gas can be used to represent the interface between a solid and a gas, for example. Because the gases are completely miscible, there is no interface between them. The bulk phases encountered could be pure compounds or solutions a few molecules thick, but their area is determined by the size of the bulk phase particles. Adsorption and absorption are both types of sorption processes.
Adsorption is defined as a surface phenomenon in which particles cling to the top layer of a material. It typically involves molecules, atoms, or even ions of a dissolved gas, liquid, or solid attached to the surface.
Adsorption is caused by surface energy. Surface particles that can be partially exposed tend to attract other particles to their location. Adsorption, which is found in many physical, natural, biological, and chemical systems, is also used in many industrial applications. Two components are required for the adsorption process, they are-
- Adsorbate: A substance that has accumulated on the surface of another substance. For instance, H2, N2, and O2 gases.
- Adsorbent: Adsorbate adsorbs on the surface of a substance. For instance, charcoal, silica gel, and alumina.
Applications of Adsorption
- Production of high vacuum: The last traces of air can be absorbed by charcoal from a vessel evacuated by a vacuum pump to achieve a very high vacuum.
- Gas masks: A gas mask (a device made of activated charcoal or a combination of adsorbents) is commonly used in coal mines to adsorb poisonous gases.
- Control of humidity: Adsorbents such as silica and aluminium gels are used to remove moisture and control humidity.
- Colour removal from solutions: Animal charcoal removes colours from solutions by adsorbing coloured impurities.
- Heterogeneous catalysis: Adsorption of reactants on the solid surfaces of catalysts accelerates the reaction. There are numerous industrially important gaseous reactions that use solid catalysts. The production of ammonia with iron as a catalyst, the production of H2SO4 through a contact process, and the use of finely divided nickel in the hydrogenation of oils are all excellent examples of heterogeneous catalysis.
- Separation of inert gases: Adsorption on coconut charcoal at different temperatures can separate a mixture of noble gases due to the difference in the degree of adsorption of gases by charcoal.
- In curing diseases: Several drugs are used to kill germs by becoming adsorbent on them.
- Froth floatation process: Using pine oil and a frothing agent, a low-grade sulphide ore is concentrated by separating it from silica and other earthy matter.
- Adsorption indicators: Surfaces of certain precipitates, such as silver halides, have the property of adsorbing dyes such as eosin, fluorescein, and others, resulting in a distinct colour at the endpoint.
- Chromatographic analysis: Chromatographic analysis based on the adsorption phenomenon has a variety of applications in analytical and industrial fields.
- Purification of water: Impurities are adsorbed on the alum stone when alum stone is added to water, and the water is purified.
- Separation of noble gases by Dewar’s flask process: In the presence of heated coconut charcoal, a mixture of noble gases (Neon, Argon, and Krypton) is passed through a Dewar’s flask. Argon and Krypton gels have been absorbed, leaving Neon.
Examples of Adsorption
Water Adsorption: Water adsorption at surfaces is critical in these fields. Water adsorption, also known as surface hydration, is the presence of physically or chemically adsorbed water at the surfaces of solids. This is critical in regulating interface properties, chemical reaction pathways, and catalytic performance in a variety of systems. Surface hydration is generally eliminated in the case of physically adsorbed water by the drying process, which occurs at conditions of temperature and pressure and leads to the complete vaporization of water. Hydration of chemically adsorbed water can take the form of either dissociative adsorption or molecular adsorption.
Adsorption in Viruses: Adsorption is the first step in the virus cycle, followed by penetration, uncoating, synthesis, and release. Virus replication cycles are typically similar for different types of viruses.
Polymer Adsorption: Molecule adsorption is observed on polymer surfaces. This feature is important for a variety of use-case applications. Polymers can be adsorbed to surfaces using the process of polyelectrolyte adsorption, which is important in the development of nonstick coatings and several biomedical devices.
Adsorption on catalysts: When molecules adsorb on certain catalytic materials, certain chemical reactions are usually accelerated.
Packets of Silica Gel in New Shoes: Silica gel, a porous form of silica dioxide, is another popular adsorbent. As the beads of silica gel act as a desiccant, or drying agent, the packets are placed with these items. Through adsorption, silica gel removes water from the environment and humidity from the air. Water is the adsorbate in this case.
Occlusion of Hydrogen Gas on Palladium: Adsorption on metals is referred to as occlusion. Occlusion occurs on a variety of metals, including iron, platinum, and palladium, but the only adsorbate is hydrogen gas. When a palladium tube is heated to red hot with hydrogen gas trapped inside, the hydrogen gas is adsorbed onto the surface of the metal, creating a partial vacuum in the tube. Palladium electrodes in a dilute acid solution can also be used to demonstrate adsorption. The cathode will absorb hydrogen until the metal is saturated, at which point it will begin to bubble to the solution’s surface.
Protein Adsorption on Biomaterials: Biomaterials are simply man-made materials that are incorporated into living things, such as medical devices. Proteins adsorb almost instantly onto the surface of biomaterials in living systems. Proteins are the building blocks of the body, and albumin, immunoglobulins, and fibrinogen are among the proteins found in blood and lymph. These proteins have a strong proclivity to accumulate at any interface, and the immune system interacts with the adsorbed proteins to regulate the body’s acceptance or rejection of biomaterial.
Sample Questions
Question 1: Why is the adsorption of a gas on a solid always exothermic explain?
Answer:
Adsorption of a gas on a solid occurs spontaneously. The entropy of gas molecules decreases when a gas adsorbs on a solid due to the molecular interaction process. Adsorption must be exothermic in order for the process to be spontaneous.
Question 2: What are the factors of effective adsorption of gases on solids?
Answer:
- Nature of gases: The easier the liquefication, the more gas is adsorbed.
- Surface area of adsorbent: The greater the surface area, the more gas is adsorbed.
- Temperature: Physisorption increases as temperature decreases, whereas chemisorption increases as temperature rises.
- Pressure: It only affects physisorption if the amount of gas adsorbs increases with pressure.
Question 3: What is the Froth floatation process?
Answer:
Froth flotation is a method of selectively separating hydrophobic materials from hydrophilic materials. This is used in mineral processing, paper recycling, and waste water treatment.
Question 4: What is occlusion?
Answer:
Froth flotation is a technique for selectively separating hydrophobic and hydrophilic materials. This is used in mineral processing, recycling of paper, and waste water treatment.
Question 5: What is an adsorption isotherm?
Answer:
Isotherms are commonly used to describe adsorption. It is due to the fact that temperature plays an important role or has a significant impact on the entire process. In addition, several isotherm models are used to describe the adsorption technique.
Question 6: What is Langmuir Theory?
Answer:
Langmuir proposed the theory of gas adsorption on the surface of a solid to be composed of elementary sites, each of which would adsorb one gas. It is assumed that all adsorption sites are equivalent, and a gas molecule’s ability to bind to any one site is independent of whether or not the neighbouring sites are occupied. Furthermore, it is assumed that there is dynamic equilibrium between adsorbed and non-adsorbed gas molecules.