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Point of zero charge

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Lead section
Point of zero charge (pzc) is the pH at which the net charge of total particle surface (i.e. absorbent's surface) is equal to zero, which concept has been introduced in the studies dealt with colloidal flocculation to explain pH affecting the phenomenon. Adsorption depends on pH because different pH leads to different surface charge so that the ions as a sorbate can be affected by pH. Therefore, the pzc value has been examined in many application of adsorption to the environmental science. The pzc value is typically obtained by titrations and several titration method has been developed. Related values associated with the soil characteristics exist along with the pzc value including zero point of charge (zpc), point of zero net charge (pznc), point of zero salt effect (pzse), etc.

Term definition of point of zero charge.
Point of zero charge is the pH for which the net surface charge of adsorbent is equal to zero. This concept has been introduced by an increase of interest in pH of the solution during adsorption. The reason why pH has attracted much attention is that the adsorption of some substances is dependent much on pH. Pzc value is determined by the characteristics of an adsorbent. For example, the surface charge of absorbent is described by the ion that lies on the surface of the particle (adsorbent) structure like image. At the lower pH, protons donating systems, hydrogen ions (protons, H+) would be adsorbed more than other cations (sorbate) so that the other cations would be less adsorbed in the case of the negatively charged particle. On the other hand, if the surface is positively charged and pH is increased, anions will be less adsorbed as hydroxide ions are increased. From the view of the adsorbent, if the pH is below the pzc value, the surface charge of adsorbent would be positive so that the anions can be adsorbed. Conversely, if the pH is above the pzc value, the surface charge would be negative so that the cations can be adsorbed.

Application in environmental geochemistry
In the field of environmental science, adsorption is involved in many parts of technologies that can eliminate pollutants and governs the concentration of chemicals in soils and/or atmosphere. Since adsorption is associated with pH, pzc value has been examined once the application of adsorption to degrade pollutants or explain the geochemical process. For example, in contaminated neutral drainage (CND), minerals in organic matters including wood ash, sawdust, etc. are to be used as an adsorbent by eliminating harmful heavy metals like arsenic, cobalt, mercury ion and so forth. Another example is that the emission of nitrous acid, which controls the atmosphere's oxidative capacity, depends on pH. Raff's group showed that different soil's pH leads to the different surface charges of minerals so the emission of nitrous acid would be varied, further impacting on biological cycle involved in the nitrous acid species.

Lead section
The point of zero charge (pzc) is generally described as the pH at which the net charge of total particle surface (i.e. absorbent's surface) is equal to zero, which concept has been introduced in the studies dealt with colloidal flocculation to explain pH affecting the phenomenon. Adsorption depends on pH because different pH leads to different surface charge so that the ions as an adsorbate can be affected by pH. Therefore, the pzc value has been examined in many application of adsorption to the environmental science. The pzc value is typically obtained by titrations and several titration method has been developed. Related values associated with the soil characteristics exist along with the pzc value including zero point of charge (zpc), point of zero net charge (pznc), etc.

Term definition of point of zero charge.
The point of zero charge is the pH for which the net surface charge of adsorbent is equal to zero. This concept has been introduced by an increase of interest in the pH of the solution during adsorption. The reason why pH has attracted much attention is that the adsorption of some substances is dependent much on pH. The pzc value is determined by the characteristics of an adsorbent. For example, the surface charge of absorbent is described by the ion that lies on the surface of the particle (adsorbent) structure like image. At the lower pH, protons donating systems, hydrogen ions (protons, H+) would be adsorbed more than other cations (adsorbate) so that the other cations would be less adsorbed in the case of the negatively charged particle. On the other hand, if the surface is positively charged and pH is increased, anions will be less adsorbed as hydroxide ions are increased. From the view of the adsorbent, if the pH is below the pzc value, the surface charge of adsorbent would be positive so that the anions can be adsorbed. Conversely, if the pH is above the pzc value, the surface charge would be negative so that the cations can be adsorbed.

Application in environmental geochemistry
In the field of environmental science, adsorption is involved in many parts of technologies that can eliminate pollutants and governs the concentration of chemicals in soils and/or atmosphere. When studying pollutant degradation or the geochemical process, the pzc value related to adsorption has been examined. For example, natural and organic substrates including wood ash, sawdust, etc. are to be used as an adsorbent by eliminating harmful heavy metals like arsenic, cobalt, mercury ion and so forth in contaminated neutral drainage (CND), which is a passive reactor that could possible metal adsorption with low-cost materials. Therefore, the pzc values of the organic substrates were evaluated to optimize the selection of materials in CND. Another example is that the emission of nitrous acid, which controls the atmosphere's oxidative capacity. Different soil pH leads to the different surface charges of minerals so the emission of nitrous acid would be varied, further impacting on the biological cycle involved in the nitrous acid species.