Surface Chemistry

A study of a physical and chemical phenomenon that occurs at the interface of two phases including solid-liquid interface, solid-gas interface, liquid-gas interface, and the solid-vacuum interface is surface chemistry. Some of the related practical applications of Surface Chemistry are classified as surface engineering. Surface chemistry encompasses the concept such as semiconductor device fabrication, heterogeneous catalyst, fuel cells, self-assembled monolayers, and adhesives. Surface chemistry is said to be closely related to colloidal science and interface. Physics and interfacial chemistry are common subjects for both, but the methods are different. The colloidal and interface science studies microscopic phenomena that occur in heterogeneous systems due to the particularity of interface. 

What is Surface Chemistry?

[Image to be added Soon]

Roughly if we define the surface chemistry then it can be defined as the study of chemical reactions at interfaces. Surface chemistry is very much related to surface engineering which aims at modifying the chemical composition of the surface by the incorporation of the selected elements or the functional groups that produce various desired effects or improvement in the properties of the interface or the surface. Electrochemistry overlaps with surface chemistry. To the field of the heterogeneous catalyst, surface chemistry is of particular importance.

The addition of gas or liquid molecules to the surface is known as adsorption, this can be either due to chemisorption or by physio absorption. These two are included in surface chemistry. 

History and Chemistry

Heterogeneous catalyst, the field with which the surface chemistry started with pioneered by Paul Sabatier , Fritz Haiber on the Haber process. Irving Langmuir was also known as one of the founders of this field and the scientific generals on the surface of science. The Langmuir adsorption equation is used to model monolayer adsorption where all surface absorption sites have the same affinity for the adsorbing species and do not interact with each other. In 1947, Gerhard Ertl described for the first time the adsorption of hydrogen on the palladium surface by using a novel technique called LEED.

Similar studies are done with nickel, platinum and iron. Most of the recent development in the surface science includes the 2007 Nobel prize winner of Chemistry Gerhard Ertl’s advancements in surface chemistry, especially his interaction or investigation between carbon monoxide molecules and platinum surface.
The study of the phenomenon occurring on the surface of two substances is known as surface chemistry. This is very applicable in the day to day life and industrial use also.

In other words we can say that Surface Chemistry deals with all the other surface phenomena. 

Analysis Techniques

The study of surface analysis techniques involves both physical and chemical analysis techniques. Several methods that are modern probe the topmost that is 1-10 nm of surface exposed to vacuum. These involve X-ray photoelectron spectroscopy (XPS), angle-resolved photoelectron spectroscopy, low energy electron diffraction, thermal desorption spectroscopy, ion scattering spectroscopy, secondary ion mass spectrometry, dual-polarization interferometry, and other surface analysis methods included in the list of material analysis methods.

Vacuum is required for many of these techniques as they rely on the detection of electrons or ions as emitted from the surface under study. Ultra-high vacuum in general, is necessary to reduce surface combination. For the study of the interface, purely optical techniques can be used under a wide range of conditions.

Dual polarization interferometry, reflection-absorption infrared, surface-enhanced Raman spectroscopy, and some of the frequency generation spectroscopy can be used to probe solid-vacuum as well as solid-gas, and liquid-gas surfaces. Surface plasmon resonance which is of multi-parametric surface works in the solid-gas, solid-liquid, liquid-gas surfaces and can even detect the sub nanometric layers. 

Applications

In the era of modern industrialization, Surface Chemistry plays a very important role in various industrial techniques for chemical and energy conservation, information processing, material, environmental protection, health care, etc. The paramount importance of Surface Chemistry is reflected in the tremendous economic impacts made by these technologies. In several major industries, the role of Surface Chemistry is important. Technological development is a further challenge for Surface Chemistry. 

A catalyst’s work is to accelerate a chemical reaction without being consumed in the process. This is the role of a catalyst. For multiple processed products, in the chemical reaction a catalyst may promote the production of a specific product, which is referred to as the selectivity of the catalyst. The heterogeneous chemical reactions occur on the surface of solid catalysts and involve elementary surface chemical processes such as the reaction of adsorbed species and surface diffusion and desorption of the reaction products. The chemical reactions acceleration is due to the higher reactivity of the surface atoms that facilitates bond breaking and bond rearrangement of the adsorbed molecules. In 1800, the large-scale synthesis of important but simple bulk chemicals including ammonia, nitric acid, sulphuric acid, was the first industrial process based on heterogeneous catalysts. 

FAQ (Frequently Asked Questions)

Q1. In Surface Studies Why is it Important to have a Clean Surface?

Ans: It is necessary to have a clean surface as it facilitates the adsorption of the desired gases. If the surface is covered by the film of air then it will not be available for adsorption of the desired gases. Therefore, it is very important to have a clean surface in the surface studies, which is the study in surface chemistry. 

Q2. Why is the Adsorption Reaction always Exothermic?

Ans: The adsorption reaction is always exothermic because when gas is adsorbed on a solid surface, immediately it’s movement is restricted leading to a decrease in the entropy of the gas. For a process to be spontaneous,G should be negative. Here, S is negative, so H has to be negative to make G negative, so adsorption is always exothermic.

Q3. What is the Role of Desorption in the Process of Catalysis?

Ans: The role of desorption in the process of catalysis can be defined as the phenomenon where a substance is released from or through the surface, it is opposite of the sorption process. Desorption helps in the catalyst to make it free for the next reaction.